Practical Current Derivation Method for a Highly Accurate Variable Switching Frequency ZVS regulation in TCM operated Bidirectional Buck/Boost Converters

Abstract

Triangular conduction mode (TCM) is a technique to operate non-isolated buck/boost converters under zero voltage switching (ZVS) turn-on. In TCM, a negative current is required for the active device to turn on under ZVS condition. The magnitude of this current is well-known and established. However, the derivation of the variable switching frequency according to the operating condition is usually simplified with the linear character of the magnetization and demagnetization of the inductors in the converter. The utilization of this simplification can increase the peak-to-peak current ripple in the inductor and burden the duty cycle loss in the controller. Additionally, it can increase the turn-off loss in the devices. This paper presents a highly accurate computation for the variable switching frequency to reduce the negative effects of the simplified method. Derivations are presented for charging and discharging modes, and they were tested in a 15-kW rated bidirectional dual-phase buck-boost converter.