UT Power Engineering Laboratory - "Powering the Future"

Examination of a PHEV Power Conversion System For V2G Reactive Power Compensation


Mithat Can Kisacikoglu
Leon M. Tolbert


The purpose of this study is to examine a PHEV traction drive to utilize it for reactive power support to grid. For this purpose, we are investigating different scenarios to deliver the stored energy from vehicle to grid (V2G) and explaining the effects of this usage on the vehicle traction battery.

Firstly, an initial analysis of supplying reactive power using only the dc-link capacitor of a proposed traction inverter drive system is done. The proposed system is given in Fig. 1. A PHEV battery is connected to the grid via a dc-dc converter and an inverter. According to the analysis, a relation between the dc-link voltage and supplied reactive power is observed as given in the below equation:

where Qs is the reactive power output of the inverter (VAr), Vdc is the dc-link voltage (V), f is the line frequency (Hz), ?Vdc is the voltage ripple magnitude of the dc-link capacitor (V), and C is the dc-link capacitor value (F). Our initial analysis showed that the supplied reactive power is linearly proportional to the dc-link voltage provided that the system is lossless and no battery charging is taking place. On the contrary, Qs is not linearly proportional to the capacitance value itself since the multiplication of (?Vdc.C) is constant with increasing capacitance.

Fig. 1. PHEV charger circuit connected to grid

The first stage of the simulation study is completed and a proposed battery traction drive is used to allow bidirectional power transfer from charger to electric grid and from grid to charger. Initial results show that the system is able to compensate for reactive current demand of the grid as well as charge the PHEV battery. We will proceed with further system analysis to be able to understand the system dynamics.

The described operation resulting (1) is called capacitive operation mode and the following operation modes are now being investigated: inductive operation mode, charging only mode, discharging only mode, charging and capacitive operation mode, charging and inductive operation mode, discharging and capacitive operation mode, and discharging and inductive operation mode. For each mode the corresponding equation will be derived and the system analysis will be completed. After, the simulation study will be developed to verify the system analysis. As a third step, a bench-top experiment will be conducted to compare the simulation results with real data. For this experiment, 6 cells from A123 Systems (LiFePO4 being the cathode material) and a battery charging protector kit from Texas Instruments have been purchased.


1- M. C. Kisacikoglu, B. Ozpineci, L. Tolbert, and Y. Xu "Examination of a PHEV Power Conversion System For V2G Reactive Power Compensation" accepted to be presented at The Applied Power Electronics Conference and Exposition 2010, February 12-25, Palm Springs, CA.

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