Frequency converter and its control method

Abstract

Method of controlling a voltage controlled PWM (Pulse Width Modulated) frequency converter comprising a single phase rectifier bridge () connectable to a sinusoidal single phase supply, a DC intermediate circuit () and a controlled inverter bridge () for generating an AC output voltage with varying amplitude and frequency to a load, said inverter bridge () having PWM controlled semiconductor switches (VV) and flywheel diodes (DD) connected in inverse-parallel with the semiconductor switches, wherein the DC intermediate circuit () is provided with a DC capacitor unit, and wherein the frequency converter is controlled so that the supply line current (I) is essentially sinusoidal and in phase with the supply line voltage (U). The inverter bridge is controlled so that the curve of filtered average current (I) in the DC intermediate circuit follows essentially the curve of the rectified AC supply voltage (U), the rectifier bridge is () connected to the inverter bridge () directly without a DC capacitor unit acting as an intermediate energy storage, and the curve of the power fed to the load has essentially the form sin(2πft) (f=line frequency t=time).