An evaluation of frequency methods for creating a system to control semiconductor converters

Abstract

I explore the possibility of increasing the response speed of the semiconductor converters that operate in the pulse mode by increasing the carrier frequency or rejecting pulse-width modulation (PWM) in favor of frequency PWM. The relation between the PWM carrier frequency and the limit response speed of the current loop achievable in closed control systems using classical frequency methods for creation of linear systems has been established. A model of mathematical simulation of a semiconductor device is proposed. The model is approximated by ideal elements without considering the voltage drop on the semiconductor keys and the dead-time interval. Using the simulation model, the frequency characteristics of of the frequency converters are compared with one converter operating in the linear mode and the other in the pulse mode. The limiting value of the frequency starting from which the frequency characteristics of the linear and pulse systems diverge has been determined for different kinds of the transfer functions of the “unchangeable” part. It has been established that this frequency approaches the Nyquist frequency most closely at resonance-peak amplitude A_m > 1.