A novel direct power control strategy of double hysteresis and multiple switching tables for rectifiers

In order to alleviate the problems, such as the periodic fluctuations of reactive power, the poor quality of ac current and the long steady-state response time, caused by the traditional direct power control(DPC) in three-phase voltage source (Pulse Width Modulation)PWM rectifier, a novel DPC strategy of double hysteresis comparator bands and multiple switching tables (DM-DPC) is put forward in this paper. According to the instantaneous errors between the commanded and estimated active and reactive power, the different switching table and hysteresis comparator band are selected in the new strategy. The effect intensity table, which is used to increase/decrease active and reactive powers through switching state vectors in different sector, is summarized. Based on the effect intensity table, four switching tables are provided. The simulation model is constructed to compare the results obtained from both the proposed and the traditional direct power control strategy. The simulation results show that, by using the novel scheme, not only the reactive power becomes more stable, but the ac current harmonic total distortion rate (THD) and the time that the system takes to reach the steady-state are also reduced to 33.5%, 62.5% of the classical one respectively.