Research On LCL Three-level Active Power Filter

With the rapid development of power electronic technology,the application of nonlinear electronic device used more and more extensive,harmonic pollution in power grid also along with the increasingly serious.Governance of harmonic pollution and improved the quality of power has become the current research hotspot.Active power filter on the elimination of harmonic pollution in the grid,has excellent performance,so favored,the application of Active Power Filter prospect is very broad.This paper focuses on the three-level active power filter.Firstly,the basic working principle of three-level active power filter was introduced and analyzed the three-level continuous space vector pulse modulation(CSVPWM).In detail analyzed of the three-level continuous space vector modulation(CSVPWM),at the same time,the discontinuous space vector modulation(DSVPWM)and the clamp level methods were analyzed,and three different methods of level clamp were obtained.This paper studies the problem of the neutral point voltage of the three-level neutral point clamp(NPC),the control method of the three-level midpoint voltage under SVPWM modulation was summarized,then the equivalent relationship between SVPWM and sine pulse width modulation(SPWM)was established by used zero sequence voltage component as bridge.Under the SPWM modulation,the expression between the neutral point voltage and the neutral point current was obtained by using the average switching model,using of the expression as a breakout point to get the relationship between the zero sequence voltage and the neutral point voltage deviation,thus a neutral point voltage controller(NPVC)was designed,and on the injection of zero sequence voltage to optimize with the maximum current does not switch.Secondly,in view of the LCL filter resonance problem,this paper analyzed typical passive damping and active damping method of restraint LCL resonance and put forward an active damping method of introducing the grid side current loop,which was based on the feedback control quantity of inverter side current.Due to the active power filter need to compensate the harmonic current,so in this research,the inverter side current loop is designed as complex control strategy of proportional integral and repeated control parallel to increase the compensation effect on the harmonic current.Finally,a prototype of three-level active power filter with rated capacity of 30 KVA was set up,and the relevant experiments of this paper proposed method on the experimental prototype was carried out.The experimental results show that the method proposed in this paper can effectively control the three-level topological midpoint voltage and suppress LCL resonance.