Patent ID: 7035123

Claim:
A method of controlling a voltage controlled PWM (Pulse Width Modulated) frequency converter comprising a single phase rectifier bridge ( 10 ) connectable to a sinusoidal single phase supply, a DC intermediate circuit ( 11 ) and a controlled inverter bridge ( 12 ) for generating an AC output voltage (U out ) with varying amplitude and frequency to a load, said inverter bridge ( 12 ) having PWM controlled semiconductor switches (V 11 –V 16 ) and flywheel diodes (D 11 –D 16 ) connected in inverse-parallel with the semiconductor switches, the method comprising the steps of: controlling the frequency converter so that the supply line current (I in ) is substantially sinusoidal and in phase with the supply line voltage (U in ), controlling the inverter bridge so that a curve of filtered average current (I dc ) in the DC intermediate circuit substantially follows a curve of a rectified AC supply voltage (U dc ), and directly connecting the rectifier bridge is ( 10 ) to the inverter bridge ( 12 ), wherein a curve of the power fed to a load is formed substantially as sin 2 (2πft) (f=line frequency t=time).