Analyzing and Reducing Current Harmonics of AC and DC sides of Cascaded H-Bridge Converters for Electric Vehicle Charging Stations

In this paper, average modeling is derived for both AC and DC sides of grid-tied cascaded H-bridge converter (CHB). The proposed technique uses the AC current harmonics to control and reduce the current harmonic ripples on the DC sides of the CHB converter. By using the proposed modeling technique, the DC current harmonics of all cells of the CHB can be balanced including the zero- and the second-order current harmonics. This balancing technique has several advantages. First, due to balancing and regulating the even order current harmonics of all cells, the DC side current harmonics of batteries of electric vehicle are equal. So, the lifetimes of all batteries are kept the same due to dealing with the similar current harmonic spectrums. Next, as will be derived in the equations, controlling the odd-order AC side current harmonics of the grid-tied converter can reduce the even-order harmonics of the DC sides of the converter. This can increase the lifespans of batteries. Finally, the low-frequency selective harmonic current mitigation-pulse width modulation (SHCM-PWM) technique is used in this paper which meets the requirements of IEEE-519 for AC side harmonics. The simulation and experimental results in this paper validate the advantages of the proposed current harmonic balancing technique.