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

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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.