Minimization Electric Losses in Transistor DC Drives

Abstract

This work is devoted to develop the algorithm for determining the optimal switching frequency of a transistor pulse-width converter (PWM) to minimize the total electric losses in a DC drive. Electric losses in the armature winding and in the PWM transistors are divided into two compo-nents: static, from the direct current component, and dynamic. The latter include losses in the armature winding from the harmonic components of the current and losses in transistors from transient switching currents. Since the dynamic losses in transistors increase with increasing frequency, and in the armature winding they decrease from current harmonics, there is an optimal switching frequency value at which the total dynamic losses in the PWM drive will be minimal. This aim is achieved by solving the problem of determining the analytical dependence of dynamic electric losses in the armature winding on the PWM switching frequency and computer simulation of a transistor DC drive. As a result of the research, an analytical expression was obtained for calculating the relative dynamic electric losses in the armature winding with polyharmonic power supply. An algorithm was proposed for determining the optimal switching frequency of the PWM: 1) on computer models of the DC motor and PWM, the dependences of dynamic electrical losses on the switching frequency were determined; 2) the graph was built showing the dependence of the total dynamic electric losses, on which the point was determined of minimum losses, which corresponds to the optimal value of the switching frequency. The novelty of the work was that the theory of electric losses in the armature windings with polyharmonic power was further developed.