A Load Adaptive Control Approach for a Zero-Voltage-Switching DC/DC Converter Used for Electric Vehicles

Abstract

This paper presents a load adaptive control approach to optimally control the amount of reactive current required to guarantee zero-voltage switching (ZVS) of the converter switches. The proposed dc/dc converter is used as a battery charger for an electric vehicle (EV). Since this application demands a wide range of load variations, the converter should be able to sustain ZVS from full-load to no-load condition. The converter employs an asymmetric auxiliary circuit to provide the reactive current for the full-bridge semiconductor switches, which guarantees ZVS at turn-on times. The proposed control scheme is able to determine the optimum value of the reactive current injected by the auxiliary circuit in order to minimize extra conduction losses in the power MOSFETs, as well as the losses in the auxiliary circuit. In the proposed approach, the peak value of the reactive current is controlled by controlling the switching frequency to make sure that there is enough current to charge and discharge the snubber capacitors during the deadtime. In addition, some practical issues of this application (battery charger for an EV) are discussed in this paper. Experimental results for a 2-kW dc/dc converter are presented. The results show an improvement in efficiency and better performance of the converter.Index Terms-DC/DC converter, full-bridge converter, lagging leg, leading leg, shoot-through, snubber capacitor, zero-voltage switching (ZVS).

An Overview of Power Electronics Techniques in Electric Systems for Transport Applications

“…In [74], a load adaptive control approach was proposed for a zero-voltage-switching (ZVS) DC-DC converter for EV application. The converter should have the ability to sustain ZVS from full-load to no-load owing to the demand of a wide range of load variations.…”

Controller Design for a Quick Charger System Suitable for Electric Vehicles

“…The phase-shifting fullbridge DC-DC converter performs the zero voltage switching and the output voltage regulation. By means of the high frequency transformer, the reliability of the system is excellent [10,11].…”

Simple High Efficiency Full-Bridge DC-DC Converter using a Series Resonant Capacitor

“…Therefore, many methods of overcoming these drawbacks have been proposed [6][7][8][9][10][11]. In one such method, passive auxiliary circuits of parallel type are connected to both legs of the conventional full-bridge converter to achieve the ZVS of the primary switches over the entire load range [6].…”

“…However, the current flowing through the auxiliary circuits increases the conduction loss and decreases the power conversion efficiency under heavy loads. To solve this problem, adaptive auxiliary circuits and their associated control techniques are introduced to reduce the conduction loss and large turn-on duty loss under heavy load conditions [7][8][9]. This provides a partial solution to the problem of [6], but results in an expensive and bulky system.…”

“…However, this technique is difficult for the design optimization of the magnetic components, due to the variation in the switching frequency resulting from the PFM operation of the converter [9,11]. In [12], an auxiliary circuit with an active switch in the converter secondary side is added, and another auxiliary circuit with a third auxiliary winding of the main transformer is suggested in [13] and [14] for the zero current switching (ZCS) of the lagging leg.…”