Space vector based analysis of the variation and control of the neutral point potential of hysteresis current controlled three-phase/switch/level PWM rectifier systems

This paper treats the control of the the capacitive output voltage center point of a unidirectional three-phase three-level PWM rectifier system. It is shown that, for hysteresis control of the input phase currents and resistive fundamental mains behavior, the center point potential can be controlled by an offset of the phase current reference values. Based on the results of a digital simulation, the transfer function is determined which describes the dynamic behavior of the system part to be controlled. Furthermore, the dimensioning of the center point voltage control is discussed. There, the considerations are related to an application of the PWM rectifier system for supplying the DC link of an uninterruptible power supply (8 kW rated power). Finally, the control behavior for stationary operation and for a step change of the load of the output voltage center point is examined for verifying the controller dimensioning