Wide Speed Range Sensorless AC Motor Drives, including Operation at Zero-Frequency, without using Test Signals

Lead Research Organisation: University of Nottingham
Department Name: Sch of Electrical and Electronic Eng


A sensorless electric motor drive is the popular term for drives which do not use shaft mounted speed or position sensors. Sensorless operation is highly desirable for reasons of cost, simplicity and system integrity. However, it is well known that there are serious problems with sensorless motor drive control at zero and low speeds and this has been one of the main research topics in this field for many years. The conventional method for sensorless control, used in commercial products, is to estimate the machine flux and speed using a mathematical model of the motor. Below 1 to 2% base speed however, position and speed estimation using such a model deteriorates and speed and torque control is lost. There has been a recent impetus for zero speed sensorless drives for more-electric aircraft and vehicular applications. For the former, there is a requirement for direct electromechanical (EM) actuation of critical actuators in which locking of the mechanical transmission is not permissible. In the vehicular field direct EM drives will be required for the main drive train, and for power steering, active suspension and braking actuation. One approach to the solution of the zero speed problem, which does not require a machine model, has been to exploit the natural asymmetries or saliencies in AC machines. These saliencies are cause by magnetic flux saturation and the geometry of the construction of the motor itself. Flux or rotor position can then be tracked by processing the current response to a test voltage signal injection overlaid on the supplied motor voltage. These signal injection methods are now quite well understood, but do contribute to increased accoustic noise, reduced efficiency, the requirement for additional sensors, and an increase in bearing wear and electrical stress within the machine windings.The current proposal aims to overcome the above disadvantages by developing methodologies by which:1) No signal injection is required, the method being integrated with the fundamental voltage applied to the drive via the power converter. This eliminates the problems of extra noise, losses, bearing wear and electrical stresses.2) The requirements for sensors is substantially reduced (depending on the application). For bespoke applications (e.g. aerospace, automotive), the aim will be for one current sensor and one low cost di/dt sensor. For industrial standard drives the target aim is to use only the existing line current sensors. These aims are quite challenging. Mathematical feasibility of a non-signal injection method has been shown at Nottingham and the technique is currently subject to patent at the University. Practical investigation is now possible owing to advances in high-accuracy timing and sampling available in low-cost digital control systems.


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Description Variable AC electric motor drives are now found in many applications ranging from industrial systems through to electric transportation. The work undertaken in this research project has developed novel control strategies which mean that the drive no-longer needs an expensive, fragile shaft mounted position encoder. Instead, the natural switching actions used by the power converter can be expoited: the current responses to these switching actions can be analysed to extract information concerning rotor position. This approach uses increased processing available in most modern motor drive systems and significantly reduces the hardware and installation requirements of the drive.
Exploitation Route This can result in significant speed up of the assembly process of these motor drives in the factory (the encoder is the biggest source of production line faults) and it also makes the system more robust to physical and electromagnetic disturbances. as such it makes them an excellent choice for safety critical applications such as automotive and aerospace based motor drive systems.
Sectors Aerospace, Defence and Marine,Energy,Manufacturing, including Industrial Biotechology,Transport

Description Research continues to develop this technique as a practical method for encoderless control. For example the technique has been used as part of other PhD projects ( in collaboration with TRW, Control Techniques) and is currently being investigated for Actuation 2015. It also formed part of the investigation for the Cummins KPT project.
First Year Of Impact 2006
Sector Aerospace, Defence and Marine,Energy,Manufacturing, including Industrial Biotechology,Transport
Description Follow on Funding
Amount £87,900 (GBP)
Funding ID EP/H007873/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 01/2010 
End 02/2011
Description KTP, Baldwin and Francis
Amount £138,572 (GBP)
Funding ID KTP8479 
Organisation Baldwin and Francis 
Sector Private
Country United Kingdom
Start 03/2011 
End 07/2013
Description KTS, Baldwin and Francis
Amount £92,843 (GBP)
Funding ID KTP008479 
Organisation Baldwin and Francis 
Sector Private
Country United Kingdom
Start 11/2007 
End 01/2011
Description Baldwin and Francis 
Organisation Baldwin and Francis
Country United Kingdom 
Sector Private 
PI Contribution New control algorithms
Collaborator Contribution test machines
Impact Control algorithms
Start Year 2010
Description Control Techniques Drives Ltd 
Organisation Control Techniques Drives Ltd
Country United Kingdom 
Sector Private 
PI Contribution New control and fault location algorithms
Collaborator Contribution Applications information, test motors
Impact Knowledge associated with control algorithms and motor design
Start Year 2006
Description Power Electronic Measurements Ltd 
Organisation Power Electronic Measurements Ltd
Country United Kingdom 
Sector Private 
PI Contribution Knowledge on sensor less motor control
Collaborator Contribution knowledge on sensor design and bespoke could for our research
Impact confidential reports
Start Year 2006
Description TRW Automotive Technical Centre 
Organisation TRW Automotive
Department TRW Automotive Technical Centre
Country United Kingdom 
Sector Private 
PI Contribution Investigating new control and fault detection algorithms for power steering systems.
Collaborator Contribution Provision of test drive system and applications experience
Impact PhD thesis and report providing evaluation of control algorithms
Start Year 2006
Description PEMC Group Annual Conference 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Conference provided by the research group to disseminate findings to wider industrial network

Collaborations with Cummins, and Baldwin and Francis
Year(s) Of Engagement Activity 2010,2011,2012,2013,2014