Novel ZCS PWM Methods for Industrial Applications
Abstract
Pulse width modulation (PWM) converters that consist of two or more interleaved boost/buck converter modules are used widely in industry. Soft-switching approaches for these converters can either be zero-voltage switching (ZVS) if implemented with MOSFETs or zero-current switching (ZCS) if implemented with IGBTs. The main idea of this thesis is to implement ZCS for IGBT turn-on and turn-off. Most converters use an auxiliary circuit that is activated whenever a main converter switch is about to be turned off, gradually diverting current away from the switch so that it can turn off with ZCS.
ZCS-PWM converters that use an auxiliary circuit to help the main converter switch turn-on with ZCS are generally less efficient than hard-switching converters at light loads. The main reason for this is that the auxiliary circuit losses dominate when the converter is operating under these conditions. Auxiliary circuit losses include the turning on and off of the auxiliary switch and additional conduction losses. ZCS-PWM converters achieve their improved efficiency over hard-switching converters at heavier loads when the switching losses of the main switch are eliminated. These switching losses - especially the IGBT current tail losses - are greater than the auxiliary circuit losses.
Ideally, the auxiliary circuit used to achieve ZCS operation in a ZCS-PWM converter should be activated only when the converter is operating with heavier loads and not used when the converter is operating with lighter loads. The proposed converters operate in such a manner and would ensure the optimal efficiency profile over the entire load range. Also, they operate for a short period of time which leads to reduction of the conduction losses and the ability to operate with higher power.
The operation of novel interleaved ZCS-PWM boost, buck, and multiport converters that cab be used in industrial applications is discussed. Afterwards, based on a mathematical analysis of the proposed converters under steady-stage conditions, a procedure for the proper design of each converter is presented and is then used to design a proof-of-concept prototype. The feasibility of the converters proposed in this thesis is confirmed by computer simulation and by experimental results obtained from a proof-of-concept prototype. Finally, after a summary of the contents of this thesis, the conclusions and the contributions of this thesis are stated and suggestions for future work are made.