Abstract: Several problems and their solutions for industrial speed regulation applications of four kinds of

commonly used AC- DC-AC voltage source converter were introduced. Aiming at the problems of high dU/dt, shaft

current and power device thermal fatigue related quantitative data were given. Three kinds of rectifier units and common DC bus were demonstrated. Regarding to improvements in cascaded H- bridge (CHB) converters, two four- quadrant control methods and 5-level cascaded H-bridges, which can reduce the number of power units and simplify transformers, were introduced. Finally,a solution of driving 6 kV motor with 3 kV three-level inverters was demonstrated.

    Key words: AC—DC-AC voltage source converter; speed regulation; industrial application