AC-AC converter system for AC drives

This paper deals with a three-phase quasidirect AC-AC converter system by means of pulse width modulation (PWM). The control of the source converter is based on the minor current loop in a synchronous rotating-frame with a feed-forward load current component added in the reference, completed with the DC voltage control loop in a cascaded manner. The synchronous rotor based reference frame was used for the field-oriented controllers involved in the load side. Two control boards, based on the dSMC (digital smart motion controller) 30 MIPS 32-bit fixed-point digital signal processor (DSP), were involved in the AC-AC system driving. The power stage of the 37-kW prototype unit is based on two 1200 V IGBTs three-phase voltage power modules followed by SKHI drive types from Semikron. By a proper control sinusoidal input current, a nearly unity power factor (0,998), bidirectional power flow, small (up to 5%) ripple in the DC link voltage in any operated conditions, disturbance compensation capability, fast control response and high quality balanced three-phase output voltages were obtained. The performances of the AC-AC converter system were shown through the experimental results.