Insulation degradation and lifetime of inverter-fed machines with fast switching (high dv/dt) converters

Lead Research Organisation: University of Sheffield
Department Name: Electronic and Electrical Engineering

Abstract

Rapid and transformative advances in power electronic systems are currently taking place following technological breakthroughs in wide-bandgap (WBG) power semiconductor devices. The enhancements in switching speed and operating temperature, and reduction in losses offered by these devices will impact all sectors of low-carbon industry, leading to a new generation of robust, compact, highly efficient and intelligent power conversion solutions. WBG devices are becoming the device of choice in a growing number of power electronic converters used to interface with and control electrical machines in a range of applications including transportation systems (aerospace, automotive, railway and marine propulsion) and renewable energy (e.g. wind power generators). However, the use of WBG devices produces fast-fronted voltage transients with voltage rise-time (dv/dt) in excess of 10~30kV/us which are at least an order of magnitude greater than those seen in conventional Silicon based converters. These voltage transients are expected to significantly reduce the lifetime of the insulation of the connected machines, and hence their reliability or availability. This, in turn, will have serious economic and safety impacts on WBG converter-fed electrical drives in all applications, including safety critical transportation systems.

The project aims to advance our scientific understanding of the impact of WBG devices on machine insulation systems and to make recommendations that will support the design and test of machines with an optimised power density and lifetime when used with a WBG converter. This will be achieved by quantifying the negative impact of fast voltage transients when applied to machine insulation systems, by identifying mitigating strategies that are assessed at the device and systems level and by demonstrating solutions that can support the insulation health monitoring of the WBG converter-fed machine, with support from a range of industrial partners in automotive, aerospace, renewable energy and industrial drives sectors.

Planned Impact

The UK's commitment to creating a low-carbon economy aiming at an ambitious reduction of 80% in CO2 emissions by 2050 will require significant investments in electrical machines and drives technologies underpinned by advances in power electronics both in the generation sector (e.g. wind power) and in consumption. Electrification in automotive, marine, railways and aerospace applications will dominate investments in the transportation industry in the foreseeable future amounting to an economy worth more than £50Bn worldwide and £2Bn in the UK by 2020. The sector is attracting significant investments in R&D and manufacturing in the UK by many global players, including Jaguar Land Rover, Rolls-Royce, United Technologies Corporation, Siemens, and Airbus, etc.

The research conducted in this project will tackle timely the fundamental challenges for applications of wide-bandgap devices in electrical machines and drives, and directly address the EPSRC "Resilient" (Ambitions R1, R4, R5) and "Productive Nation" (Ambition P1) prosperity outcomes and ambitions. It will also directly support the development of the next generation of technologies for the efficient and resilient provision and utilization of clean energy and contribution to low carbon transportation systems. The project will have a significant direct impact on the:
- UK industry by generating knowledge and IPs which will ultimately help the UK maintain and expand its position as a major player in energy conversion technologies, safety critical electric and hybrid-electric propulsion systems, asset management and condition monitoring solutions;
- Society, by developing research that will underpin the development of disruptive advances in the low-carbon technologies, leading to reduced emissions, cleaner transportation (electric/hybrid vehicles, rail, 'more electric' aircraft systems, ship propulsion) and higher efficiency in energy generation and conversion;
- Academia by delivering new scientific breakthroughs on modelling tools, design methods, control and condition monitoring technologies that will enhance UK standing in the international arena;
- UK skilled workforce by training young researchers, PhD students and personnel from industrial partners addressing an area with significant skills shortages.
 
Description There are a number of new findings and knowledge gained during the first 15 months of the project. They include:
1. Reduction of electrical machine lifetime under cyclic load condition has been quantified experimentally under accelerated aging tests. A lifetime model which accounts the effect of thermal cycling has been proposed based on the experimental data.
2. A simple technique has been developed for estimating partial discharge inception voltage of magnet wire commonly used in electrical machine windings and validated by experiments. This provides an effective means for design of machine insulation and for assessing the risk of partial discharge under high dv/dt
3. A technique for modeling high frequency behavior of machine windings under pulse width modulation (PWM) has been developed and the developed model has been experimentally validated. The model has been used to predict voltage stress and distributions in a 60kW traction machine. New understanding of potential excessive voltage in machine winding has been gained.
4. Since a PWM inverter produces both differential mode (DM) and common mode (CM) voltages at its output. It is important to assess both DM and CM voltages in machine windings. The former mainly affects (1) Turn-to-turn voltage, (2) Coil voltage (3) Phase voltage and (4) Phase-to-phase, and their associate insulations, while the latter mainly affects (1) turn-to-ground voltage, (2) coil-to-ground voltage and (3) phase-to-ground voltage and their associated insulations.
5. Excessive voltage oscillations under PWM excitation in electrical machines are governed by two distinctive oscillations modes: the 1st and 2nd anti-resonant modes of combined cable-machine CM impedance. The effect of the cable anti-resonant mode on machine voltage stress has been well-understood, However the effect of machine anti-resonant mode has not. This is because most studies either employ inappropriate models or only consider single phase excitation, and CM voltage is not appropriately represented. With relatively short cable(<10m), the 2nd anti-resonant frequency of the cable-machine system is in a few or a few tens of MHz range while the 1st anti-resonant frequency of the cable-machine system is dominated by the machine anti-resonant frequency and is in a range of few hundreds of kHz. The combined cable-machine HF behaviour is therefore characterised by two oscillation frequencies, the high frequency (HF) oscillation in a few MHz primarily caused by the cable anti-resonance and its interation with the machine and the low frequency (LF) oscillation caused by the machine anti-resonance.
6. The HF oscillation only appears in the first few turns of the 1st coil, and affects both CM voltages, i.e., turn-to-ground volatge, coil-to-ground voltage and phase-to-ground voltage, and DM voltages, i.e., turn-to-turn voltage, coil voltage and phase-to-phase voltage. The LF oscillations can penetrate deep into machine winding, and may give rise to excessive voltage stress across winding conductors and ground, particularly in the turns and coils close to the star-neutral of star-connected windings, or close to middle of a phase in a delta-connected winding. The peak voltage associated with this oscillation may be much greater than that of the HF oscillation. This oscillation mode has not been reported and understood in literature. The voltages associated with this oscillation are of CM nature and hence they only affect turn-to-ground voltage, coil-to-ground voltage and phase-to-ground voltage
7. The presence of the LF oscillation and its potential interaction with the HF oscillation may lead to a number of problems which are not known in literature. For example, massive oscillation can occur if the cable anti-resonant frequency and machine anti-resonant frequency are very close.
8. In the light of the new findings, some of existing concepts and techniques which define and quantify the effect, as well as mitigation measures need to be re-examined/re-considered. For example, since the machine anti-resonant frequency is relatively low, it can be easily excited when the switching frequency approaches to hundred kHz, or the duration of two consecutive pulses is short even if switching frequency is low. The latter can occur when modulation index is close to 1.
9. The influence of environment conditions, such as temperature, pressure, and humidity as well as temporal characteristics of voltage stress on partial discharges and partial discharge inception voltage (PDIV) of magnet wires has been better understood and measured.
10. Mitigation measures to reduce the peak voltage stress in machine insulation have been developed and validated. These include (1) Resonant converter and waveform shaping, PWM control to reduce both CM and DM voltage stresses, and (3) passive filtering.
Exploitation Route The new findings and outcomes of the research have been communicated to 8 industrial partners on the projects regularly. This provides the most efficient and effective means for exploiting our research finding. Three journal papers, IEEE Transactions on Industrial Electronics and Power Electronics, have published and 10 conference papers have been presented to a large number of international audience in ECCE 2019, ECCE 2020, ICEM 2020, and PEMD 2020. Futher three conference papers (ECCE2021) and one journal paper (IEEE Trans. on Industry Applications) have been submitted. We are planning a dedicated tutorial session in ECCE2021 as well as presentations in UK Power Electronic Centre Annual meeting, and APC (Advance propulsion centre) and ATI (Aerospace Technology Institute) conferences, etc., to disseminate our findings. Discussions with interested industrial partners for further collaboration are ongoing. High quality journal papers describing the new findings will be prepared and submitted in the next project period and beyond.
Sectors Aerospace, Defence and Marine,Electronics,Energy,Environment,Manufacturing, including Industrial Biotechology,Transport

 
Description (IMITAES) - Insulation monitoring for IT Aerospace Electrical Systems
Amount € 848,258 (EUR)
Funding ID 101008082 
Organisation European Commission 
Sector Public
Country European Union (EU)
Start 07/2021 
End 06/2023
 
Description Collaboration Partners 
Organisation Control Techniques Dynamics Limited
Country United Kingdom 
Sector Private 
PI Contribution The main advances made to date by the academic consortium members are summarised as follows. 1. Since a PWM inverter produces both differential mode (DM) and common mode (CM) voltages at its output. It is important to assess both DM and CM voltages in machine windings. The former mainly affects (1) Turn-to-turn voltage, (2) Coil voltage (3) Phase voltage and (4) Phase-to-phase, and their associate insulations, while the latter mainly affects (1) turn-to-ground voltage, (2) coil-to-ground voltage and (3) phase-to-ground voltage and their associated insulations. 2. Excessive voltage oscillations under PWM excitation in electrical machines are governed by two distinctive oscillations modes: the 1st and 2nd anti-resonant modes of combined cable-machine CM impedance. The effect of the cable anti-resonant mode on machine voltage stress has been well-understood, However the effect of machine anti-resonant mode has not. This is because most studies either employ inappropriate models or only consider single phase excitation, and CM voltage is not appropriately represented. With relatively short cable(<10m), the 2nd anti-resonant frequency of the cable-machine system is in a few or a few tens of MHz range while the 1st anti-resonant frequency of the cable-machine system is dominated by the machine anti-resonant frequency and is in a range of few hundreds of kHz. The combined cable-machine HF behaviour is therefore characterised by two oscillation frequencies, the high frequency (HF) oscillation in a few MHz primarily caused by the cable anti-resonance and its interation with the machine and the low frequency (LF) oscillation caused by the machine anti-resonance. 3. The HF oscillation only appears in the first few turns of the 1st coil, and affects both CM voltages, i.e., turn-to-ground volatge, coil-to-ground voltage and phase-to-ground voltage, and DM voltages, i.e., turn-to-turn voltage, coil voltage and phase-to-phase voltage. The LF oscillations can penetrate deep into machine winding, and may give rise to excessive voltage stress across winding conductors and ground, particularly in the turns and coils close to the star-neutral of star-connected windings, or close to middle of a phase in a delta-connected winding. The peak voltage associated with this oscillation may be much greater than that of the HF oscillation. This oscillation mode has not been reported and understood in literature. The voltages associated with this oscillation are of CM nature and hence they only affect turn-to-ground voltage, coil-to-ground voltage and phase-to-ground voltage 4. The presence of the LF oscillation and its potential interaction with the HF oscillation may lead to a number of problems which are not known in literature. For example, massive oscillation can occur if the cable anti-resonant frequency and machine anti-resonant frequency are very close. 5. In the light of the new findings, some of existing concepts and techniques which define and quantify the effect, as well as mitigation measures need to be re-examined/re-considered. For example, since the machine anti-resonant frequency is relatively low, it can be easily excited when the switching frequency approaches to hundred kHz, or the duration of two consecutive pulses is short even if switching frequency is low. The latter can occur when modulation index is close to 1. 6. The influence of environment conditions, such as temperature, pressure, and humidity as well as temporal characteristics of voltage stress on partial discharges and partial discharge inception voltage (PDIV) of magnet wires has been better understood and measured. 7. Mitigation measures to reduce the peak voltage stress in machine insulation have been developed and validated. These include (1) Resonant converter and waveform shaping, PWM control to reduce both CM and DM voltage stresses, and (3) passive filtering. The latest findings are disseminated to the industrial collaborators in various forms: 1. Presentations and discussions of the latest development and findings in project review meetings 2. Seminars and web meeetings between academic and industrial partners on issues of their interests 3. Industrial visits
Collaborator Contribution The industrial partners have contributed their expertise in power electronics, machine insulation and design, and drive system integrations in aerospace, automotive, wind power generation and industrial automation to the project, as well as provided guidance on relevant standards and manufacturing. They also provided additional resources to the project, including 1. Control Techniques Dynamics Ltd provides 20 customer made motor winding samples for lifetime testing 2. Rolls-Royce provided additional in-case support of ca. £50k to the project.
Impact Confidential reports to Rolls-Royce plc.
Start Year 2019
 
Description Collaboration Partners 
Organisation High Voltage Partial Discharge
Country United Kingdom 
Sector Private 
PI Contribution The main advances made to date by the academic consortium members are summarised as follows. 1. Since a PWM inverter produces both differential mode (DM) and common mode (CM) voltages at its output. It is important to assess both DM and CM voltages in machine windings. The former mainly affects (1) Turn-to-turn voltage, (2) Coil voltage (3) Phase voltage and (4) Phase-to-phase, and their associate insulations, while the latter mainly affects (1) turn-to-ground voltage, (2) coil-to-ground voltage and (3) phase-to-ground voltage and their associated insulations. 2. Excessive voltage oscillations under PWM excitation in electrical machines are governed by two distinctive oscillations modes: the 1st and 2nd anti-resonant modes of combined cable-machine CM impedance. The effect of the cable anti-resonant mode on machine voltage stress has been well-understood, However the effect of machine anti-resonant mode has not. This is because most studies either employ inappropriate models or only consider single phase excitation, and CM voltage is not appropriately represented. With relatively short cable(<10m), the 2nd anti-resonant frequency of the cable-machine system is in a few or a few tens of MHz range while the 1st anti-resonant frequency of the cable-machine system is dominated by the machine anti-resonant frequency and is in a range of few hundreds of kHz. The combined cable-machine HF behaviour is therefore characterised by two oscillation frequencies, the high frequency (HF) oscillation in a few MHz primarily caused by the cable anti-resonance and its interation with the machine and the low frequency (LF) oscillation caused by the machine anti-resonance. 3. The HF oscillation only appears in the first few turns of the 1st coil, and affects both CM voltages, i.e., turn-to-ground volatge, coil-to-ground voltage and phase-to-ground voltage, and DM voltages, i.e., turn-to-turn voltage, coil voltage and phase-to-phase voltage. The LF oscillations can penetrate deep into machine winding, and may give rise to excessive voltage stress across winding conductors and ground, particularly in the turns and coils close to the star-neutral of star-connected windings, or close to middle of a phase in a delta-connected winding. The peak voltage associated with this oscillation may be much greater than that of the HF oscillation. This oscillation mode has not been reported and understood in literature. The voltages associated with this oscillation are of CM nature and hence they only affect turn-to-ground voltage, coil-to-ground voltage and phase-to-ground voltage 4. The presence of the LF oscillation and its potential interaction with the HF oscillation may lead to a number of problems which are not known in literature. For example, massive oscillation can occur if the cable anti-resonant frequency and machine anti-resonant frequency are very close. 5. In the light of the new findings, some of existing concepts and techniques which define and quantify the effect, as well as mitigation measures need to be re-examined/re-considered. For example, since the machine anti-resonant frequency is relatively low, it can be easily excited when the switching frequency approaches to hundred kHz, or the duration of two consecutive pulses is short even if switching frequency is low. The latter can occur when modulation index is close to 1. 6. The influence of environment conditions, such as temperature, pressure, and humidity as well as temporal characteristics of voltage stress on partial discharges and partial discharge inception voltage (PDIV) of magnet wires has been better understood and measured. 7. Mitigation measures to reduce the peak voltage stress in machine insulation have been developed and validated. These include (1) Resonant converter and waveform shaping, PWM control to reduce both CM and DM voltage stresses, and (3) passive filtering. The latest findings are disseminated to the industrial collaborators in various forms: 1. Presentations and discussions of the latest development and findings in project review meetings 2. Seminars and web meeetings between academic and industrial partners on issues of their interests 3. Industrial visits
Collaborator Contribution The industrial partners have contributed their expertise in power electronics, machine insulation and design, and drive system integrations in aerospace, automotive, wind power generation and industrial automation to the project, as well as provided guidance on relevant standards and manufacturing. They also provided additional resources to the project, including 1. Control Techniques Dynamics Ltd provides 20 customer made motor winding samples for lifetime testing 2. Rolls-Royce provided additional in-case support of ca. £50k to the project.
Impact Confidential reports to Rolls-Royce plc.
Start Year 2019
 
Description Collaboration Partners 
Organisation Jaguar Land Rover Automotive PLC
Department Jaguar Land Rover
Country United Kingdom 
Sector Private 
PI Contribution The main advances made to date by the academic consortium members are summarised as follows. 1. Since a PWM inverter produces both differential mode (DM) and common mode (CM) voltages at its output. It is important to assess both DM and CM voltages in machine windings. The former mainly affects (1) Turn-to-turn voltage, (2) Coil voltage (3) Phase voltage and (4) Phase-to-phase, and their associate insulations, while the latter mainly affects (1) turn-to-ground voltage, (2) coil-to-ground voltage and (3) phase-to-ground voltage and their associated insulations. 2. Excessive voltage oscillations under PWM excitation in electrical machines are governed by two distinctive oscillations modes: the 1st and 2nd anti-resonant modes of combined cable-machine CM impedance. The effect of the cable anti-resonant mode on machine voltage stress has been well-understood, However the effect of machine anti-resonant mode has not. This is because most studies either employ inappropriate models or only consider single phase excitation, and CM voltage is not appropriately represented. With relatively short cable(<10m), the 2nd anti-resonant frequency of the cable-machine system is in a few or a few tens of MHz range while the 1st anti-resonant frequency of the cable-machine system is dominated by the machine anti-resonant frequency and is in a range of few hundreds of kHz. The combined cable-machine HF behaviour is therefore characterised by two oscillation frequencies, the high frequency (HF) oscillation in a few MHz primarily caused by the cable anti-resonance and its interation with the machine and the low frequency (LF) oscillation caused by the machine anti-resonance. 3. The HF oscillation only appears in the first few turns of the 1st coil, and affects both CM voltages, i.e., turn-to-ground volatge, coil-to-ground voltage and phase-to-ground voltage, and DM voltages, i.e., turn-to-turn voltage, coil voltage and phase-to-phase voltage. The LF oscillations can penetrate deep into machine winding, and may give rise to excessive voltage stress across winding conductors and ground, particularly in the turns and coils close to the star-neutral of star-connected windings, or close to middle of a phase in a delta-connected winding. The peak voltage associated with this oscillation may be much greater than that of the HF oscillation. This oscillation mode has not been reported and understood in literature. The voltages associated with this oscillation are of CM nature and hence they only affect turn-to-ground voltage, coil-to-ground voltage and phase-to-ground voltage 4. The presence of the LF oscillation and its potential interaction with the HF oscillation may lead to a number of problems which are not known in literature. For example, massive oscillation can occur if the cable anti-resonant frequency and machine anti-resonant frequency are very close. 5. In the light of the new findings, some of existing concepts and techniques which define and quantify the effect, as well as mitigation measures need to be re-examined/re-considered. For example, since the machine anti-resonant frequency is relatively low, it can be easily excited when the switching frequency approaches to hundred kHz, or the duration of two consecutive pulses is short even if switching frequency is low. The latter can occur when modulation index is close to 1. 6. The influence of environment conditions, such as temperature, pressure, and humidity as well as temporal characteristics of voltage stress on partial discharges and partial discharge inception voltage (PDIV) of magnet wires has been better understood and measured. 7. Mitigation measures to reduce the peak voltage stress in machine insulation have been developed and validated. These include (1) Resonant converter and waveform shaping, PWM control to reduce both CM and DM voltage stresses, and (3) passive filtering. The latest findings are disseminated to the industrial collaborators in various forms: 1. Presentations and discussions of the latest development and findings in project review meetings 2. Seminars and web meeetings between academic and industrial partners on issues of their interests 3. Industrial visits
Collaborator Contribution The industrial partners have contributed their expertise in power electronics, machine insulation and design, and drive system integrations in aerospace, automotive, wind power generation and industrial automation to the project, as well as provided guidance on relevant standards and manufacturing. They also provided additional resources to the project, including 1. Control Techniques Dynamics Ltd provides 20 customer made motor winding samples for lifetime testing 2. Rolls-Royce provided additional in-case support of ca. £50k to the project.
Impact Confidential reports to Rolls-Royce plc.
Start Year 2019
 
Description Collaboration Partners 
Organisation Motor Design Ltd
Country United Kingdom 
Sector Private 
PI Contribution The main advances made to date by the academic consortium members are summarised as follows. 1. Since a PWM inverter produces both differential mode (DM) and common mode (CM) voltages at its output. It is important to assess both DM and CM voltages in machine windings. The former mainly affects (1) Turn-to-turn voltage, (2) Coil voltage (3) Phase voltage and (4) Phase-to-phase, and their associate insulations, while the latter mainly affects (1) turn-to-ground voltage, (2) coil-to-ground voltage and (3) phase-to-ground voltage and their associated insulations. 2. Excessive voltage oscillations under PWM excitation in electrical machines are governed by two distinctive oscillations modes: the 1st and 2nd anti-resonant modes of combined cable-machine CM impedance. The effect of the cable anti-resonant mode on machine voltage stress has been well-understood, However the effect of machine anti-resonant mode has not. This is because most studies either employ inappropriate models or only consider single phase excitation, and CM voltage is not appropriately represented. With relatively short cable(<10m), the 2nd anti-resonant frequency of the cable-machine system is in a few or a few tens of MHz range while the 1st anti-resonant frequency of the cable-machine system is dominated by the machine anti-resonant frequency and is in a range of few hundreds of kHz. The combined cable-machine HF behaviour is therefore characterised by two oscillation frequencies, the high frequency (HF) oscillation in a few MHz primarily caused by the cable anti-resonance and its interation with the machine and the low frequency (LF) oscillation caused by the machine anti-resonance. 3. The HF oscillation only appears in the first few turns of the 1st coil, and affects both CM voltages, i.e., turn-to-ground volatge, coil-to-ground voltage and phase-to-ground voltage, and DM voltages, i.e., turn-to-turn voltage, coil voltage and phase-to-phase voltage. The LF oscillations can penetrate deep into machine winding, and may give rise to excessive voltage stress across winding conductors and ground, particularly in the turns and coils close to the star-neutral of star-connected windings, or close to middle of a phase in a delta-connected winding. The peak voltage associated with this oscillation may be much greater than that of the HF oscillation. This oscillation mode has not been reported and understood in literature. The voltages associated with this oscillation are of CM nature and hence they only affect turn-to-ground voltage, coil-to-ground voltage and phase-to-ground voltage 4. The presence of the LF oscillation and its potential interaction with the HF oscillation may lead to a number of problems which are not known in literature. For example, massive oscillation can occur if the cable anti-resonant frequency and machine anti-resonant frequency are very close. 5. In the light of the new findings, some of existing concepts and techniques which define and quantify the effect, as well as mitigation measures need to be re-examined/re-considered. For example, since the machine anti-resonant frequency is relatively low, it can be easily excited when the switching frequency approaches to hundred kHz, or the duration of two consecutive pulses is short even if switching frequency is low. The latter can occur when modulation index is close to 1. 6. The influence of environment conditions, such as temperature, pressure, and humidity as well as temporal characteristics of voltage stress on partial discharges and partial discharge inception voltage (PDIV) of magnet wires has been better understood and measured. 7. Mitigation measures to reduce the peak voltage stress in machine insulation have been developed and validated. These include (1) Resonant converter and waveform shaping, PWM control to reduce both CM and DM voltage stresses, and (3) passive filtering. The latest findings are disseminated to the industrial collaborators in various forms: 1. Presentations and discussions of the latest development and findings in project review meetings 2. Seminars and web meeetings between academic and industrial partners on issues of their interests 3. Industrial visits
Collaborator Contribution The industrial partners have contributed their expertise in power electronics, machine insulation and design, and drive system integrations in aerospace, automotive, wind power generation and industrial automation to the project, as well as provided guidance on relevant standards and manufacturing. They also provided additional resources to the project, including 1. Control Techniques Dynamics Ltd provides 20 customer made motor winding samples for lifetime testing 2. Rolls-Royce provided additional in-case support of ca. £50k to the project.
Impact Confidential reports to Rolls-Royce plc.
Start Year 2019
 
Description Collaboration Partners 
Organisation Ricardo UK Ltd
Country United Kingdom 
Sector Private 
PI Contribution The main advances made to date by the academic consortium members are summarised as follows. 1. Since a PWM inverter produces both differential mode (DM) and common mode (CM) voltages at its output. It is important to assess both DM and CM voltages in machine windings. The former mainly affects (1) Turn-to-turn voltage, (2) Coil voltage (3) Phase voltage and (4) Phase-to-phase, and their associate insulations, while the latter mainly affects (1) turn-to-ground voltage, (2) coil-to-ground voltage and (3) phase-to-ground voltage and their associated insulations. 2. Excessive voltage oscillations under PWM excitation in electrical machines are governed by two distinctive oscillations modes: the 1st and 2nd anti-resonant modes of combined cable-machine CM impedance. The effect of the cable anti-resonant mode on machine voltage stress has been well-understood, However the effect of machine anti-resonant mode has not. This is because most studies either employ inappropriate models or only consider single phase excitation, and CM voltage is not appropriately represented. With relatively short cable(<10m), the 2nd anti-resonant frequency of the cable-machine system is in a few or a few tens of MHz range while the 1st anti-resonant frequency of the cable-machine system is dominated by the machine anti-resonant frequency and is in a range of few hundreds of kHz. The combined cable-machine HF behaviour is therefore characterised by two oscillation frequencies, the high frequency (HF) oscillation in a few MHz primarily caused by the cable anti-resonance and its interation with the machine and the low frequency (LF) oscillation caused by the machine anti-resonance. 3. The HF oscillation only appears in the first few turns of the 1st coil, and affects both CM voltages, i.e., turn-to-ground volatge, coil-to-ground voltage and phase-to-ground voltage, and DM voltages, i.e., turn-to-turn voltage, coil voltage and phase-to-phase voltage. The LF oscillations can penetrate deep into machine winding, and may give rise to excessive voltage stress across winding conductors and ground, particularly in the turns and coils close to the star-neutral of star-connected windings, or close to middle of a phase in a delta-connected winding. The peak voltage associated with this oscillation may be much greater than that of the HF oscillation. This oscillation mode has not been reported and understood in literature. The voltages associated with this oscillation are of CM nature and hence they only affect turn-to-ground voltage, coil-to-ground voltage and phase-to-ground voltage 4. The presence of the LF oscillation and its potential interaction with the HF oscillation may lead to a number of problems which are not known in literature. For example, massive oscillation can occur if the cable anti-resonant frequency and machine anti-resonant frequency are very close. 5. In the light of the new findings, some of existing concepts and techniques which define and quantify the effect, as well as mitigation measures need to be re-examined/re-considered. For example, since the machine anti-resonant frequency is relatively low, it can be easily excited when the switching frequency approaches to hundred kHz, or the duration of two consecutive pulses is short even if switching frequency is low. The latter can occur when modulation index is close to 1. 6. The influence of environment conditions, such as temperature, pressure, and humidity as well as temporal characteristics of voltage stress on partial discharges and partial discharge inception voltage (PDIV) of magnet wires has been better understood and measured. 7. Mitigation measures to reduce the peak voltage stress in machine insulation have been developed and validated. These include (1) Resonant converter and waveform shaping, PWM control to reduce both CM and DM voltage stresses, and (3) passive filtering. The latest findings are disseminated to the industrial collaborators in various forms: 1. Presentations and discussions of the latest development and findings in project review meetings 2. Seminars and web meeetings between academic and industrial partners on issues of their interests 3. Industrial visits
Collaborator Contribution The industrial partners have contributed their expertise in power electronics, machine insulation and design, and drive system integrations in aerospace, automotive, wind power generation and industrial automation to the project, as well as provided guidance on relevant standards and manufacturing. They also provided additional resources to the project, including 1. Control Techniques Dynamics Ltd provides 20 customer made motor winding samples for lifetime testing 2. Rolls-Royce provided additional in-case support of ca. £50k to the project.
Impact Confidential reports to Rolls-Royce plc.
Start Year 2019
 
Description Collaboration Partners 
Organisation Rolls Royce Group Plc
Country United Kingdom 
Sector Private 
PI Contribution The main advances made to date by the academic consortium members are summarised as follows. 1. Since a PWM inverter produces both differential mode (DM) and common mode (CM) voltages at its output. It is important to assess both DM and CM voltages in machine windings. The former mainly affects (1) Turn-to-turn voltage, (2) Coil voltage (3) Phase voltage and (4) Phase-to-phase, and their associate insulations, while the latter mainly affects (1) turn-to-ground voltage, (2) coil-to-ground voltage and (3) phase-to-ground voltage and their associated insulations. 2. Excessive voltage oscillations under PWM excitation in electrical machines are governed by two distinctive oscillations modes: the 1st and 2nd anti-resonant modes of combined cable-machine CM impedance. The effect of the cable anti-resonant mode on machine voltage stress has been well-understood, However the effect of machine anti-resonant mode has not. This is because most studies either employ inappropriate models or only consider single phase excitation, and CM voltage is not appropriately represented. With relatively short cable(<10m), the 2nd anti-resonant frequency of the cable-machine system is in a few or a few tens of MHz range while the 1st anti-resonant frequency of the cable-machine system is dominated by the machine anti-resonant frequency and is in a range of few hundreds of kHz. The combined cable-machine HF behaviour is therefore characterised by two oscillation frequencies, the high frequency (HF) oscillation in a few MHz primarily caused by the cable anti-resonance and its interation with the machine and the low frequency (LF) oscillation caused by the machine anti-resonance. 3. The HF oscillation only appears in the first few turns of the 1st coil, and affects both CM voltages, i.e., turn-to-ground volatge, coil-to-ground voltage and phase-to-ground voltage, and DM voltages, i.e., turn-to-turn voltage, coil voltage and phase-to-phase voltage. The LF oscillations can penetrate deep into machine winding, and may give rise to excessive voltage stress across winding conductors and ground, particularly in the turns and coils close to the star-neutral of star-connected windings, or close to middle of a phase in a delta-connected winding. The peak voltage associated with this oscillation may be much greater than that of the HF oscillation. This oscillation mode has not been reported and understood in literature. The voltages associated with this oscillation are of CM nature and hence they only affect turn-to-ground voltage, coil-to-ground voltage and phase-to-ground voltage 4. The presence of the LF oscillation and its potential interaction with the HF oscillation may lead to a number of problems which are not known in literature. For example, massive oscillation can occur if the cable anti-resonant frequency and machine anti-resonant frequency are very close. 5. In the light of the new findings, some of existing concepts and techniques which define and quantify the effect, as well as mitigation measures need to be re-examined/re-considered. For example, since the machine anti-resonant frequency is relatively low, it can be easily excited when the switching frequency approaches to hundred kHz, or the duration of two consecutive pulses is short even if switching frequency is low. The latter can occur when modulation index is close to 1. 6. The influence of environment conditions, such as temperature, pressure, and humidity as well as temporal characteristics of voltage stress on partial discharges and partial discharge inception voltage (PDIV) of magnet wires has been better understood and measured. 7. Mitigation measures to reduce the peak voltage stress in machine insulation have been developed and validated. These include (1) Resonant converter and waveform shaping, PWM control to reduce both CM and DM voltage stresses, and (3) passive filtering. The latest findings are disseminated to the industrial collaborators in various forms: 1. Presentations and discussions of the latest development and findings in project review meetings 2. Seminars and web meeetings between academic and industrial partners on issues of their interests 3. Industrial visits
Collaborator Contribution The industrial partners have contributed their expertise in power electronics, machine insulation and design, and drive system integrations in aerospace, automotive, wind power generation and industrial automation to the project, as well as provided guidance on relevant standards and manufacturing. They also provided additional resources to the project, including 1. Control Techniques Dynamics Ltd provides 20 customer made motor winding samples for lifetime testing 2. Rolls-Royce provided additional in-case support of ca. £50k to the project.
Impact Confidential reports to Rolls-Royce plc.
Start Year 2019
 
Description Collaboration Partners 
Organisation Safran Power UK
Country United Kingdom 
Sector Private 
PI Contribution The main advances made to date by the academic consortium members are summarised as follows. 1. Since a PWM inverter produces both differential mode (DM) and common mode (CM) voltages at its output. It is important to assess both DM and CM voltages in machine windings. The former mainly affects (1) Turn-to-turn voltage, (2) Coil voltage (3) Phase voltage and (4) Phase-to-phase, and their associate insulations, while the latter mainly affects (1) turn-to-ground voltage, (2) coil-to-ground voltage and (3) phase-to-ground voltage and their associated insulations. 2. Excessive voltage oscillations under PWM excitation in electrical machines are governed by two distinctive oscillations modes: the 1st and 2nd anti-resonant modes of combined cable-machine CM impedance. The effect of the cable anti-resonant mode on machine voltage stress has been well-understood, However the effect of machine anti-resonant mode has not. This is because most studies either employ inappropriate models or only consider single phase excitation, and CM voltage is not appropriately represented. With relatively short cable(<10m), the 2nd anti-resonant frequency of the cable-machine system is in a few or a few tens of MHz range while the 1st anti-resonant frequency of the cable-machine system is dominated by the machine anti-resonant frequency and is in a range of few hundreds of kHz. The combined cable-machine HF behaviour is therefore characterised by two oscillation frequencies, the high frequency (HF) oscillation in a few MHz primarily caused by the cable anti-resonance and its interation with the machine and the low frequency (LF) oscillation caused by the machine anti-resonance. 3. The HF oscillation only appears in the first few turns of the 1st coil, and affects both CM voltages, i.e., turn-to-ground volatge, coil-to-ground voltage and phase-to-ground voltage, and DM voltages, i.e., turn-to-turn voltage, coil voltage and phase-to-phase voltage. The LF oscillations can penetrate deep into machine winding, and may give rise to excessive voltage stress across winding conductors and ground, particularly in the turns and coils close to the star-neutral of star-connected windings, or close to middle of a phase in a delta-connected winding. The peak voltage associated with this oscillation may be much greater than that of the HF oscillation. This oscillation mode has not been reported and understood in literature. The voltages associated with this oscillation are of CM nature and hence they only affect turn-to-ground voltage, coil-to-ground voltage and phase-to-ground voltage 4. The presence of the LF oscillation and its potential interaction with the HF oscillation may lead to a number of problems which are not known in literature. For example, massive oscillation can occur if the cable anti-resonant frequency and machine anti-resonant frequency are very close. 5. In the light of the new findings, some of existing concepts and techniques which define and quantify the effect, as well as mitigation measures need to be re-examined/re-considered. For example, since the machine anti-resonant frequency is relatively low, it can be easily excited when the switching frequency approaches to hundred kHz, or the duration of two consecutive pulses is short even if switching frequency is low. The latter can occur when modulation index is close to 1. 6. The influence of environment conditions, such as temperature, pressure, and humidity as well as temporal characteristics of voltage stress on partial discharges and partial discharge inception voltage (PDIV) of magnet wires has been better understood and measured. 7. Mitigation measures to reduce the peak voltage stress in machine insulation have been developed and validated. These include (1) Resonant converter and waveform shaping, PWM control to reduce both CM and DM voltage stresses, and (3) passive filtering. The latest findings are disseminated to the industrial collaborators in various forms: 1. Presentations and discussions of the latest development and findings in project review meetings 2. Seminars and web meeetings between academic and industrial partners on issues of their interests 3. Industrial visits
Collaborator Contribution The industrial partners have contributed their expertise in power electronics, machine insulation and design, and drive system integrations in aerospace, automotive, wind power generation and industrial automation to the project, as well as provided guidance on relevant standards and manufacturing. They also provided additional resources to the project, including 1. Control Techniques Dynamics Ltd provides 20 customer made motor winding samples for lifetime testing 2. Rolls-Royce provided additional in-case support of ca. £50k to the project.
Impact Confidential reports to Rolls-Royce plc.
Start Year 2019
 
Description Collaboration Partners 
Organisation Siemens AG
Department Siemens plc, Keele
Country United Kingdom 
Sector Private 
PI Contribution The main advances made to date by the academic consortium members are summarised as follows. 1. Since a PWM inverter produces both differential mode (DM) and common mode (CM) voltages at its output. It is important to assess both DM and CM voltages in machine windings. The former mainly affects (1) Turn-to-turn voltage, (2) Coil voltage (3) Phase voltage and (4) Phase-to-phase, and their associate insulations, while the latter mainly affects (1) turn-to-ground voltage, (2) coil-to-ground voltage and (3) phase-to-ground voltage and their associated insulations. 2. Excessive voltage oscillations under PWM excitation in electrical machines are governed by two distinctive oscillations modes: the 1st and 2nd anti-resonant modes of combined cable-machine CM impedance. The effect of the cable anti-resonant mode on machine voltage stress has been well-understood, However the effect of machine anti-resonant mode has not. This is because most studies either employ inappropriate models or only consider single phase excitation, and CM voltage is not appropriately represented. With relatively short cable(<10m), the 2nd anti-resonant frequency of the cable-machine system is in a few or a few tens of MHz range while the 1st anti-resonant frequency of the cable-machine system is dominated by the machine anti-resonant frequency and is in a range of few hundreds of kHz. The combined cable-machine HF behaviour is therefore characterised by two oscillation frequencies, the high frequency (HF) oscillation in a few MHz primarily caused by the cable anti-resonance and its interation with the machine and the low frequency (LF) oscillation caused by the machine anti-resonance. 3. The HF oscillation only appears in the first few turns of the 1st coil, and affects both CM voltages, i.e., turn-to-ground volatge, coil-to-ground voltage and phase-to-ground voltage, and DM voltages, i.e., turn-to-turn voltage, coil voltage and phase-to-phase voltage. The LF oscillations can penetrate deep into machine winding, and may give rise to excessive voltage stress across winding conductors and ground, particularly in the turns and coils close to the star-neutral of star-connected windings, or close to middle of a phase in a delta-connected winding. The peak voltage associated with this oscillation may be much greater than that of the HF oscillation. This oscillation mode has not been reported and understood in literature. The voltages associated with this oscillation are of CM nature and hence they only affect turn-to-ground voltage, coil-to-ground voltage and phase-to-ground voltage 4. The presence of the LF oscillation and its potential interaction with the HF oscillation may lead to a number of problems which are not known in literature. For example, massive oscillation can occur if the cable anti-resonant frequency and machine anti-resonant frequency are very close. 5. In the light of the new findings, some of existing concepts and techniques which define and quantify the effect, as well as mitigation measures need to be re-examined/re-considered. For example, since the machine anti-resonant frequency is relatively low, it can be easily excited when the switching frequency approaches to hundred kHz, or the duration of two consecutive pulses is short even if switching frequency is low. The latter can occur when modulation index is close to 1. 6. The influence of environment conditions, such as temperature, pressure, and humidity as well as temporal characteristics of voltage stress on partial discharges and partial discharge inception voltage (PDIV) of magnet wires has been better understood and measured. 7. Mitigation measures to reduce the peak voltage stress in machine insulation have been developed and validated. These include (1) Resonant converter and waveform shaping, PWM control to reduce both CM and DM voltage stresses, and (3) passive filtering. The latest findings are disseminated to the industrial collaborators in various forms: 1. Presentations and discussions of the latest development and findings in project review meetings 2. Seminars and web meeetings between academic and industrial partners on issues of their interests 3. Industrial visits
Collaborator Contribution The industrial partners have contributed their expertise in power electronics, machine insulation and design, and drive system integrations in aerospace, automotive, wind power generation and industrial automation to the project, as well as provided guidance on relevant standards and manufacturing. They also provided additional resources to the project, including 1. Control Techniques Dynamics Ltd provides 20 customer made motor winding samples for lifetime testing 2. Rolls-Royce provided additional in-case support of ca. £50k to the project.
Impact Confidential reports to Rolls-Royce plc.
Start Year 2019
 
Description Collaboration Partners 
Organisation UTC Aerospace Systems
Country United States 
Sector Private 
PI Contribution The main advances made to date by the academic consortium members are summarised as follows. 1. Since a PWM inverter produces both differential mode (DM) and common mode (CM) voltages at its output. It is important to assess both DM and CM voltages in machine windings. The former mainly affects (1) Turn-to-turn voltage, (2) Coil voltage (3) Phase voltage and (4) Phase-to-phase, and their associate insulations, while the latter mainly affects (1) turn-to-ground voltage, (2) coil-to-ground voltage and (3) phase-to-ground voltage and their associated insulations. 2. Excessive voltage oscillations under PWM excitation in electrical machines are governed by two distinctive oscillations modes: the 1st and 2nd anti-resonant modes of combined cable-machine CM impedance. The effect of the cable anti-resonant mode on machine voltage stress has been well-understood, However the effect of machine anti-resonant mode has not. This is because most studies either employ inappropriate models or only consider single phase excitation, and CM voltage is not appropriately represented. With relatively short cable(<10m), the 2nd anti-resonant frequency of the cable-machine system is in a few or a few tens of MHz range while the 1st anti-resonant frequency of the cable-machine system is dominated by the machine anti-resonant frequency and is in a range of few hundreds of kHz. The combined cable-machine HF behaviour is therefore characterised by two oscillation frequencies, the high frequency (HF) oscillation in a few MHz primarily caused by the cable anti-resonance and its interation with the machine and the low frequency (LF) oscillation caused by the machine anti-resonance. 3. The HF oscillation only appears in the first few turns of the 1st coil, and affects both CM voltages, i.e., turn-to-ground volatge, coil-to-ground voltage and phase-to-ground voltage, and DM voltages, i.e., turn-to-turn voltage, coil voltage and phase-to-phase voltage. The LF oscillations can penetrate deep into machine winding, and may give rise to excessive voltage stress across winding conductors and ground, particularly in the turns and coils close to the star-neutral of star-connected windings, or close to middle of a phase in a delta-connected winding. The peak voltage associated with this oscillation may be much greater than that of the HF oscillation. This oscillation mode has not been reported and understood in literature. The voltages associated with this oscillation are of CM nature and hence they only affect turn-to-ground voltage, coil-to-ground voltage and phase-to-ground voltage 4. The presence of the LF oscillation and its potential interaction with the HF oscillation may lead to a number of problems which are not known in literature. For example, massive oscillation can occur if the cable anti-resonant frequency and machine anti-resonant frequency are very close. 5. In the light of the new findings, some of existing concepts and techniques which define and quantify the effect, as well as mitigation measures need to be re-examined/re-considered. For example, since the machine anti-resonant frequency is relatively low, it can be easily excited when the switching frequency approaches to hundred kHz, or the duration of two consecutive pulses is short even if switching frequency is low. The latter can occur when modulation index is close to 1. 6. The influence of environment conditions, such as temperature, pressure, and humidity as well as temporal characteristics of voltage stress on partial discharges and partial discharge inception voltage (PDIV) of magnet wires has been better understood and measured. 7. Mitigation measures to reduce the peak voltage stress in machine insulation have been developed and validated. These include (1) Resonant converter and waveform shaping, PWM control to reduce both CM and DM voltage stresses, and (3) passive filtering. The latest findings are disseminated to the industrial collaborators in various forms: 1. Presentations and discussions of the latest development and findings in project review meetings 2. Seminars and web meeetings between academic and industrial partners on issues of their interests 3. Industrial visits
Collaborator Contribution The industrial partners have contributed their expertise in power electronics, machine insulation and design, and drive system integrations in aerospace, automotive, wind power generation and industrial automation to the project, as well as provided guidance on relevant standards and manufacturing. They also provided additional resources to the project, including 1. Control Techniques Dynamics Ltd provides 20 customer made motor winding samples for lifetime testing 2. Rolls-Royce provided additional in-case support of ca. £50k to the project.
Impact Confidential reports to Rolls-Royce plc.
Start Year 2019
 
Description Collaboration with GKN Automotive 
Organisation GKN
Department GKN Automotive
Country United Kingdom 
Sector Private 
PI Contribution The main advances made to date by the academic consortium members are summarised as follows. 1. Since a PWM inverter produces both differential mode (DM) and common mode (CM) voltages at its output. It is important to assess both DM and CM voltages in machine windings. The former mainly affects (1) Turn-to-turn voltage, (2) Coil voltage (3) Phase voltage and (4) Phase-to-phase, and their associate insulations, while the latter mainly affects (1) turn-to-ground voltage, (2) coil-to-ground voltage and (3) phase-to-ground voltage and their associated insulations. 2. Excessive voltage oscillations under PWM excitation in electrical machines are governed by two distinctive oscillations modes: the 1st and 2nd anti-resonant modes of combined cable-machine CM impedance. The effect of the cable anti-resonant mode on machine voltage stress has been well-understood, However the effect of machine anti-resonant mode has not. This is because most studies either employ inappropriate models or only consider single phase excitation, and CM voltage is not appropriately represented. With relatively short cable(<10m), the 2nd anti-resonant frequency of the cable-machine system is in a few or a few tens of MHz range while the 1st anti-resonant frequency of the cable-machine system is dominated by the machine anti-resonant frequency and is in a range of few hundreds of kHz. The combined cable-machine HF behaviour is therefore characterised by two oscillation frequencies, the high frequency (HF) oscillation in a few MHz primarily caused by the cable anti-resonance and its interation with the machine and the low frequency (LF) oscillation caused by the machine anti-resonance. 3. The HF oscillation only appears in the first few turns of the 1st coil, and affects both CM voltages, i.e., turn-to-ground volatge, coil-to-ground voltage and phase-to-ground voltage, and DM voltages, i.e., turn-to-turn voltage, coil voltage and phase-to-phase voltage. The LF oscillations can penetrate deep into machine winding, and may give rise to excessive voltage stress across winding conductors and ground, particularly in the turns and coils close to the star-neutral of star-connected windings, or close to middle of a phase in a delta-connected winding. The peak voltage associated with this oscillation may be much greater than that of the HF oscillation. This oscillation mode has not been reported and understood in literature. The voltages associated with this oscillation are of CM nature and hence they only affect turn-to-ground voltage, coil-to-ground voltage and phase-to-ground voltage 4. The presence of the LF oscillation and its potential interaction with the HF oscillation may lead to a number of problems which are not known in literature. For example, massive oscillation can occur if the cable anti-resonant frequency and machine anti-resonant frequency are very close. 5. In the light of the new findings, some of existing concepts and techniques which define and quantify the effect, as well as mitigation measures need to be re-examined/re-considered. For example, since the machine anti-resonant frequency is relatively low, it can be easily excited when the switching frequency approaches to hundred kHz, or the duration of two consecutive pulses is short even if switching frequency is low. The latter can occur when modulation index is close to 1. 6. The influence of environment conditions, such as temperature, pressure, and humidity as well as temporal characteristics of voltage stress on partial discharges and partial discharge inception voltage (PDIV) of magnet wires has been better understood and measured. 7. Mitigation measures to reduce the peak voltage stress in machine insulation have been developed and validated. These include (1) Resonant converter and waveform shaping, PWM control to reduce both CM and DM voltage stresses, and (3) passive filtering. The latest findings are disseminated to GKN automotive in various forms: 1. Presentations and discussions of the latest development and findings in project review meetings 2. Two Seminars (web meeetings) between University of Sheffield and GKN Automotive
Collaborator Contribution GKN Automotive Ltd has joined the consortium as an industrial partner since May 2020. The company has contributed their expertise in design and manufacturing of next-generation electric drive technologies for electric and hybrid-electric vehicles, and has agreed to provide in-kind support of £450,000 in 3 years.
Impact Two deliverable reports.
Start Year 2020
 
Company Name aerospaceHV Ltd 
Description aerospaceHV was jointly founded in 2018 by Ian Cotton (Technical Director) and David Chambers (Managing Director) in order to service the aerospace sector with highly bespoke training, design and testing services to meet the increasing demands of operating aircraft at increasingly high voltages. Since the creation of the company aerospaceHV have provided high voltage engineering and test services to companies working across a range of technical areas included aerospace, electric vehicle and renewable energy applications. 
Year Established 2018 
Impact aerospaceHV has conducted significant testing for the aerospace and automotive sector -- details of most projects cannot be released owing to non-disclosure agreements. The part-time role held by Ian Cotton at The University of Manchester and aerospaceHV has allowed the named projects to develop his network and has resulted in an increased commercial test income for aerospaceHV.
Website http://www.aerospacehv.com
 
Description High frequency modelling workshop with GKN automotive 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact A dedicated workshop on modelling high frequency behaviour of cable and electrical machine systems and predicting peak voltage stresses in machine windings fed by power electronic converter was given to technical staff in GKN Automotive Innovation Centre on 16 and 18 Nov 2020. Technical discussions were followed on issues pertinent to the insulation design of electric traction motor fed by SiC converters.
Year(s) Of Engagement Activity 2020
 
Description Project review meetings with industrial partners 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact 9 industrial partners representing automotive, aerospace, renewable and industrial drives sectors are invited to project review meetings and discussions of interim results, in every 6-months. Four such meetings were organised on 14 May, 5 Dec 2019, 14 May and 25 Nov 2020. Relevant knowledge and new findings have been disseminated to the industrial partners, and likewise, the feedback from the industrial partners on essential and pertinent issues to be addressed is used to influence the future planning. For example, a dedicated session on multi-stress reliability model for electrical machines was held on 14 May, and a presentation for estimating partial discharge inception voltage of magnet wires commonly used in electrical machine winding was given on 5 Dec.

Issues raised by specific industrial partners were also followed up, and separate meetings were taken place. For example, a teleconference call was held on 8 January 2012 between the University of Sheffield and Motor Design Limited on possible knowledge transfer of high frequency modelling technique for predicting voltage stress in machine windings under high dv/dt. University of Sheffield visited UTAS on 21 January to discuss the issued of their concerns on potential risks of inverter-fed drives in aerospace actuation and power generation. Siemens GAMESA visited Manchester in September 2019 to discuss estimation of partial discharge inception voltage of their products and partial discharge detection techniques.
Year(s) Of Engagement Activity 2019,2020
 
Description Technical engagements with Rolls-Royce 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Dedicated work and investigations have been undertaken as a part of the in-cash support given by Rolls-Royce plc on the issues pertinent to the insulation design of aerospace electrical machines fed by power electronic converters. Monthly meetings with working group staff specialising insulation materials and design, power electronics and electric drives with Rolls-Royce Electrical Systems were taken place in 2020. Four dedicated presentations on the outcomes of the research were given on 14 July, 28 July, 27 Oct and 8 Dec 2020.
Year(s) Of Engagement Activity 2020
 
Description Workshop on the impacts of modern power electronic converters on machine insulations 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact The workshop is given to academic and industrial partners of the Future Electrical Machine Manufacturing Research Hub funded by UKRI-EPSRC (EP/S018034/1) as well as members of industry and scientific advisory boards (IAB and SAB).

Power electronic converter-fed machines and drives are increasingly being used in a variety of applications ranging from electrification of transport and renewable energy generations to industrial automation and household appliances. Converters or inverters operating in pulse width modulation (PWM) provide effective and efficient control of energy conversion and machine operation. However, the PWM voltage pulses at a high frequency and high voltage slew rate (dv/dt) can result in excessive voltage at the machine terminal and non-uniform voltage distribution within the winding. These voltage transients are expected to significantly reduce the lifetime of the insulation of the connected machine/generator owing to increased voltage overshoot, increased voltage across turns, phases and phase-to-ground, and higher frequencies.

In this training course, insulation structures and designs of typical electrical machines over a wide range of power, speed and torque rating are outlined, the effects of impulse and high frequency PWM voltage produced by power electronic converters on voltage distributions in machine winding and insulation systems are analyses and characterised, and measures to mitigate these effects discussed. The potentials for advanced manufacturing processes that may improve insulation systems are also highlighted.
Year(s) Of Engagement Activity 2021