Inverter connected battery technology with advanced fault ride through capability on LV grid system to help offset the need for standby generation

There are significant changes within both the transport and electricity industries that mean that significant work needs to happen to ensure that the components that will make up the new smart grid concept are available in a timely manner. At present dynamic voltage restorers and UPS systems are available to assist the consumer with power quality issues. However, it is now appropriate timing to consider using modified battery/inverter power conditioning systems (PCS) to provide much more in the way of grid support (even though this is not necessarily an option currently supported by standards). The aim of the project is to model, prototype and test a power electronic inverter system which interfaces used car batteries (or vehicles with EV batteries) to an electricity grid system, which is designed to meet the following key requirements; low cost, reliable, easily reproducible, single phase operation (leading to three phase operation), able to charge and discharge batteries safely and to provide enhanced DER (Distributed Energy Resource) functionality to support smart grid functionality.The research will focus on the more advanced features of the enhanced DER functionality:1. Advanced condition monitoring of the batteries to ensure that they are optimally utilised to end of life. At present there are several techniques available which look at battery SOC (state of charge). EIS (Electrochemical Impedance Spectroscopy) measurements are widely used with relation to determining battery health. However, EIS has traditionally been slow to commute. New techniques published over the last few years show that there is now the possibility of including the EIS measurement within the power electronics and choosing to undertake the processing within the power electronic DSP. This will save on hardware costs and give a very accurate indication as to the health of the battery.2. Fault ride through and voltage support to help with stability issues.Standards in the UK and the USA request that connected generation drop out on island detection and under voltage detection. This has led to the blackouts that have been seen over the past ten years in Europe and USA. Within the EU there are a number of countries all of which have slightly different fault ride through capability. To ensure that power electronics can assist with voltage support the power conditioning systems needs to be able to meet all these requirements rather than the less onerous ones that are in the current standards. This leads to the need to develop the control strategy to deal with this.3. Fast response spinning reserve support. Battery systems are capable of reacting quickly to changes in frequency and responding over a sufficient time scale to assume the role of a spinning generator. Lumped systems could represent a big load reduction at a substation acting in the same way as an increase in generation at a substation. There is scope to modify the control system to determine when primary responce spinning load is needed and react appropriately.4. Communication to a smart grid system Any future system that will integrate with a smart grid system will need to be able to communicate with a controller whether this be a residential power controller or an industrial power controller. The PCS will be required to pass information that assists with the collation of data at the operations centre such as the battery availability, condition monitoring information (eg temperatures) or fault information. 5. Power Quality correctionThere is much published literature on power quality problems and UPS and DVR systems have been developed to deal with these. The battery/inverter system suggested is capable of assuming this responsibility for active power quality management.

This research has important and far reaching consequences and forms part of a much bigger platform of research relating to the changing face of the electricity supply industry around the smart grid concept. The idea of the research is to develop the prototype systems needed to take old electric vehicle batteries and use them to support the grid system through peaks and fault scenarios. The key to this work is the integration of techniques which combine fault ride through with voltage, frequency and power quality support to aid grid stability. Additional key work is to look at advanced adaptive EIS measurement techniques to assess the condition of the battery and at its ability to respond to faults. This information would then be available to a smart controller at either a residential or industrial property to feed back to into the smart grid system. There are four main beneficiaries 1, The Electrical Utilities 2. Electric vehicle/battery manufacturers 3. The general public 4. Industrial establishments The most immediate of these benefits is a cost related. The Utilities will be able to offset some of the spinning reserve generation in favour of meeting their supply requirements via battery backup systems. Other key benefits could include reduced distribution losses at peak load, improved power factor correction, network upgrade savings, retirement of old, expensive, inefficient diesel generation designed to meet peak load requirements, greater reliability and reduced outage times Benefits to industrial/residential consumers include possible reduced harmonics and network imbalance with improved power quality and reduced power losses. It should be possible to use the inverter technology with other distributed generation platforms such as solar or fuel cells to help embedded generation penetration. Being able to use old electric vehicle batteries as a source of power feeding back into a grid system ensures that electric vehicle batteries have an end of life usage which will aid their penetration into the general market place. This helps to offset the recycling costs and the planned monitoring system ensures that the maximum benefit can be obtained from the batteries. This will help electric vehicle and battery manufactures to realise the full potential of their products. Realistically the benefits will take around 10-20 years to materialise in any quantifiable way. This is because the research is linked to electric/hybrid vehicle market penetration. It will also be dependent on the need for significant fault testing and field trials on a distribution network to properly understand all the implications both cost and technical around this form of electricity support. Short term this work will benefit policy makers including those that sit on the G83/G59 standards and grid code boards. This is because the ramifications of this work could affect the way that voltage is controlled in the grid in the future. Changes as profound as those being suggested need careful study on a practical level to ensure all possible fault and failure mode scenarios are considered at an early stage in the design process. It will enable Utilities to better understand the likely implications both cost and technical of what significant embedded generation at residential level will mean to them. Long term the result of undertaking this type of work is to reduce CO2 emissions and help to ensure security of supply in a potentially fast changing electricity grid network. The work is designed to benefit the general public by helping with integration issues into the smart grid and encouraging distributed storage/generation.