A carrier modulation method for minimizing the dc link capacitor current ripple of the HEV DC-DC converter and inverter systems

Minimization of the dc capacitor is an essential step towards developing and manufacturing compact low-cost hybrid electric vehicle (HEV) converter/inverter systems for high temperature operation, long life and high reliability. Previously, most papers have been focused on the AC-DC-AC pulse-width modulation (PWM) converters with relatively complicated close-loop control methods, while few papers have analyzed the DC-DC-AC PWM converters that also commonly exist in HEV systems. The so-called DC-DC-AC PWM converter consists of a bidirectional dc-dc converter and an inverter cascaded together. This paper proposes a carrier modulation method for the previously mentioned dc-dc converter, which connects the battery or any energy storage system to the dc link, in order to match the converter output current with the inverter input current so as to minimize the current ripple going through the dc link capacitor. Compared with the conventional triangle carrier, the proposed carrier is able to shift the converter output current pulses left and right, so they match with the inverter input current, and finally minimize the current ripple flowing through the dc link capacitor at unity power factor by a simple and easy implementation. Simulation and experimental results are provided to validate the effectiveness of the proposed method.