A T-Type DC-DC Converter With Reduced Middle-Leg Switch Current Stress and Improved Light-Load Efficiency

Abstract

The ZVS T-type converter can be used as an alternative to the conventional ZVS-PWM full-bridge (FB) converter for applications where improved light-load operation is required. In this converter, two of the switches conduct only the current that flows during a freewheeling mode of operation and two of the switches conduct only the current that flows in the converter when it is in an energy-transfer mode. This is unlike the switches in the ZVS-PWM-FB converter that must conduct both currents. Although the ZVS T-type converter needs less inductive energy to achieve ZVS in its switches, it has a higher primary current during its freewheeling modes than the ZVS-PWM-FB converter because it is basically a half-bridge converter. In this paper, the use of ZVZCS methods to reduce the RMS value of the current in switches that are used in the freewheeling current path is investigated. The operation of the ZVS-PWM T-type converter and a T-type converter operating with ZVZCS are reviewed and compared analytically. Experimental results obtained from prototypes of the two converters along with results from prototypes of the standard ZVS-PWM-FB converter and a ZVZCS-PWM-FB converter are presented. It is demonstrated that a T-type converter with ZVZCS has a better light-load efficiency than the ZVS-PWM-FB and the ZVS T-type converters and that the current stress in its middle-leg switches is much smaller; thus, it can be implemented with much smaller and inexpensive middle-leg switches.

Keywords

• DC-DC power conversion
• Zero voltage switching (ZVS)
• Zero-voltage-zero-current switching (ZVZCS)
• ZVS T-Type converter