Closed Loop Control of ZVS Half Bridge DCDC Converter with DCS PWM Control I J E E E S, 4(2) December 2012 121 CLOSED LOOP CONTROL OF ZVS HALF BRIDGE DCDC CONVERTER WITH DCS PWM CONTROL J. SIVAVARA PRASAD 1 , Y.P. OBULESH 2 , AND CH. SAIBABU 3 1 Lakireddy Bali Reddy College of Engineering, Mylavaram, Krishna Dist., A.P. India. 2 Lakireddy Bali Reddy College of Engineering, Mylavaram, Krishna Dist., A.P. India. He is now with the department of Electrical & Electronics Engineering as Professor and Head of the Department. 3 JNTU Kakinada, Kakinada, A.P. India. He is now with the department of Electrical & Electronics Engineering as Professor. Abstract: The main drawback of the conventional symmetric control is that both primary switches in the converter operate at hard switching condition. Moreover, during the off-time period of two switches, the oscillation between the transformer leakage inductance and junction capacitance of the switches results in energy dissipation and electromagnetic interference (EMI) emissions due to reverse recovery of MOSFETs body diodes. The asymmetric (complementary) control was proposed to achieve ZVS operation for HB switches. However, asymmetric stresses distribution on the corresponding components may occur due to the asymmetric duty cycle distribution for the two primary switches. A new control scheme, to be known as duty-cycle shifted PWM (DCS PWM) control, is proposed and applied to the conventional HB dc–dc converters to achieve ZVS for both the switches without adding extra components and without adding asymmetric penalties of the complementary control. The concept of this new control scheme is shifting one of the two symmetric PWM driving signals close to the other, such that ZVS may be achieved for the lagging switch due to the shortened resonant interval. Moreover, based on the DCS PWM control, a new half-bridge topology is proposed to achieve ZVS for both the main switches and auxiliary switch by adding an auxiliary switch and diode in the proposed half bridge. ZVS for the switch is achieved by utilizing the energy trapped in the leakage inductance. There are two control schemes. One is open loop and the other is closed loop. In open loop scheme, the given dc-dc converter is operating under disturbance. This disturbance effect is eliminated in closed loop scheme. Index Terms: Duty-cycle-shifted (DCS), half bridge (HB), metal oxide semiconductor field effect transistors (MOSFETs), pulse-width modulated (PWM), zero-current switching (ZCS), zero-voltage switching (ZVS), Open-loop and Closed-loop. 1 E-mail: janapatisivavaraprasad@gmail.com 2 E-mail: ypobulesh@gmail.com 3 E-mail: chs_eee@yahoo.co.in 1. INTRODUCTION The phase-shifted zero-voltage-switching (ZVS) full bridge is one of the most attractive techniques since it allows all switches to operate at ZVS by utilizing transformer leakage inductance and metal oxide semiconductor field effect transistor’ (MOSFETs) junction capacitance without adding an auxiliary switch. However, the complexity of the full-bridge is almost highest among the conventional topologies due to its large switch count and complicated control and driving. Active- clamp forward topology is another typical example to successfully realize ZVS for the switches by utilizing the leakage inductance, magnetizing inductance and junction capacitance. However, the topology of the converter is asymmetric and