Research On Delayless Harmonic Detection And PI-repetitive Control Of Three-phase Four Wire APF

With the rapid growing use of nonlinear load and power electronic switching devices, the harmonic currents into the power grid is increasing seriously, which is harmful to transfer efficiency of power grid and safe operation of other equipments. Most of the loads in power system obtain power through the three-phase four-wire system, in which all the harmonics of the positive sequence component and negative sequence component can be offset by each other in the neutral line, but all the harmonics of the zero sequence component in the neutral line are of superposition, which may bring instability to the system. Since the power quality of three-phase four-wire systems is closely related with people’s daily lives, any quality problems in this system are drawing more and more attention.Firstly, the basic working principle of the shunt APF(Active Power Filter) is introduced. Through analyzing the compensate ability of two typical three-phase four-wire active power filter topologies, the main circuit topology of the simulation was ultimately determined, and the mathematical model of this topology was established in abc coordinate and dqO coordinate respectively. Secondly, based on the theory of instantaneous reactive power, the traditional ip-iq testing method is improved to satisfy the using conditions for three-phase four-wire APF. Also, this thesis analyzed the causes of time-delay in calculation of the harmonic current and the following influence on compensation performance, and used a simple and feasible phase compensation method to reduce the effect of time-delay. Thirdly, in order to improve the performance of dynamic tracking timeliness and compensation stability of the active power filter effectively, PI-repetitive control system is proposed, providing a complete derivation process.Finally, the designed time-delay compensation method and PI-repetitive control system were verified in three-phase three-wire APF devices. Experimental results show that the compensation effect has improved significantly. Especially when a siltation or a new steady state happens to the nonlinear loads, the designed APF still has a good tracking control effect.