A Direct Frequency Changer with Control of Input Reactive Power

Abstract For a direct frequency changer using forced commutation of the electronic switches a new control method is proposed, which contains, in wide ranges, input reactive power adjustment independent of the load power factor and the desired output voltage. The method is based on the combination of two conversion modes, which differ in their effects on the input dispiacement angle . The proper sequences of switching states of the converter are determined by a so-called transfer vector which consists of two components according to the two modes combined. A control scheme computes, according to the wanted reactive input power and to the wanted output voltage waves, the amplitudes and phase angles of these two components as functions of the output current. The generation of the switching pattern by means of pulse width modulation and digital signal processing is described. Experimental results taken from an analog simulation of the power circuit demonstrate the operation of the control device.