Optimal design of a matrix converter with a LC active buffer for onboard vehicle battery charger in single phase grid structure

This paper discusses a design approach of an isolated type of single phase power converter that uses a matrix converter (MC) with a LC active buffer for the on-board vehicle battery charger in PHEV/EV. The MC is advantaged in terms of size due to the lack of DC bus, where the electrolytic capacitor is not required as direct conversion of AC/AC is possible. However, in the case of single phase, the 50/60 Hz grid power will cause power fluctuation in the battery current due to the lack of smoothing capacitor in the matrix converter stage. In order to compensate the power fluctuation, a LC buffer that utilizes the center-tapped of transformer in the inverter (INV) stage has been discussed. As a result, the circuit features small size because a low volume of capacitor is achieved. Furthermore, switching loss in MC stage is greatly reduced because the switching devices can achieve ZVS (zero voltage switching) behavior by using a synchronize control. In this paper, first the tradeoff relationship between the capacitor volume and efficiency which is subjected to the voltage conditions is discussed. Then, a design flow chart that considers between the capacitor volume, isolated transformer and device losses are discussed accordingly. Finally, based on the design flow chart, an ultraslim thickness of prototype (203mm × 113mm × 10mm) was constructed and the results show a conversion efficiency of 92% at a power density of 4.36W/cc.