Comparison of 3D-SVPWM and carrier-based PWM of three-phase four-leg voltage source inverter

This paper deals with design of a new control system for a diesel-electric power supply unit, which output part is composed of a three-phase four-leg voltage source inverter. The main emphasis is given in this paper on employed modulation techniques. We are introducing two modulation strategies: 1) three-dimensional space vector PWM (3D-SVPWM) and 2) improved carrier-based PWM (CBPWM), which employs control of voltage offset via control of the fourth inverter leg. Further, control algorithms enabling operation of the supply unit under arbitrary load conditions (linear, non-linear, symmetrical, unsymmetrical etc.) in any case with sinusoidal voltages at the converter output are described. Behaviour of the designed control system with both 3D-SVPWM and CBPWM strategies has been verified on a laboratory prototype of the power supply unit with rated power of 18kVA.