Hysteresis Current Control in Three-Phase Voltage Source Inverter

The current control methods play an important role in power electronic circuits, particulary in current regulated PWM inverters which are widely applied in ac motor drives and continuous ac power supplies where the objective is to produce a sinusoidal ac output. The main task of the control systems in current regulated inverters is to force the current vector in the three phase load according to a reference trajectory. In this paper, two hysteresis current control methods (hexagon and square hysteresis based controls) of three-phase voltage source inverter (VSI) have been implemented. Both controllers work with current components represented in stationary (α, β) coordinate system. Introduction Three major classes of regulators have been developed over last few decades: hysteresis regulators, linear PI regulators and predictive dead-beat regulators [1]. A short review of the available current control techniques for the threephase systems is presented in [2]. Among the various PWM technique, the hysteresis band current control is used very often because of its simplicity of implementation. Also, besides fast response current loop, the method does not need any knowledge of load parameters. However, the current control with a fixed hysteresis band has the disadvantage that the PWM frequency varies within a band because peak-topeak current ripple is required to be controlled at all points of the fundamental frequency wave. The method of adaptive hysteresis-band current control PWM technique where the band can be programmed as a function of load to optimize the PWM performance is described in [3]. The basic implementation of hysteresis current control is based on deriving the switching signals from the comparison of the current error with a fixed tolerance band. This control is based on the comparison of the actual phase current with the tolerance band around the reference current associated with that phase. On the other hand, this type of band control is negatively affected by the phase current interactions which is typical in three-phase systems. This is mainly due to the interference between the commutations of the three phases, since each phase current not only depends on the corresponding phase voltage but is also affected by the voltage of the other two phases. Depending on load conditions switching frequency may vary during the the fundamental period, resulting in irregular inverter operation. In [4] the authors proposed a new method that 1 minimize the effect of interference between phases while maintaining the advantages of the hysteresis methods by using phase-locked loop (PLL) technique to constrain the inverter switching at a fixed predetermined frequency. In this paper, the current control of PWM-VSI has been implemented in the stationary (α, β) reference frame. One method is based on space vector control using multilevel hysteresis comparators where the hysteresis band appear as a hysteresis square. The second method is based on predictive current control where the three hysteresis bands form a hysteresis hexagon. Model of the Three-Phase VSI The power circuit of a three-phase VSI is shown in figure 1. The load model is consisting of a sinusoidal inner voltage e and an inductance (L).