Research On Harmonic Detection And Control Strategy Of Four-leg Active Power Filter

In recent years,new electrical equipment such as new energy electric vehicles are gradually getting into our lives,which will bring a great impact on the power grid.Especially,the charging facilities composed of uncontrolled rectifiers and choppers put a lot of harmonics into the power grid.Active Power Filter(APF)is a popular solution to deal with harmonics.This thesis studies the harmonic current detection,the compensating current control strategy and the three-level 3D-SVPWM control strategy of three-level four-leg APF.In the four-leg APF system,the phase locked loop is of great significance for the harmonic detection.This thesis proposes a phase locked loop(CFESOGI-PLL)combining the complex filter and the enhanced second-order generalized integrator.The complex filter is utilized to extract the components of positive sequence fundamental voltage,combined with the enhanced second-order generalized integrator to filter out the DC components.So that it can still have a great performance when the grid voltage is asymmetric,even has harmonics and DC components.The simulation compares the performance of the phase locked loop based on the traditional second-order generalized integrator and the phase locked loop based on the enhanced second-order generalized integrator when the grid voltage contains different DC components,and simulates the performance of CFESOGI-PLL under a bad grid voltage condition.The current control strategy is of great significance for the current compensation.The traditional deadbeat control strategy is actually with a delay.So this thesis will study this current control strategy to improve the current tracking performance of APF,and get it combined with the repetitive controller to improve its robustness.This thesis designs the main parameters of the repetitive controller,so that it can track the reference current stably in combination with the enhanced deadbeat control strategy.The simulation verifies the current tracking performance of the proposed control strategy when the load is unbalanced and mutative.3D-SVPWM will output the pulse signals.The traditional three-level3D-SVPWM control strategy of APF is complicated,this thesis proposes a simplified control strategy to make it more effective.The three-level voltage vectors can be decomposed into two-level structures.Then,a simplified two-level pulse width modulation control strategy can be utilized to improve the calculation efficiency of APF.The simulation verifies the output performance of the proposed control strategy when the reference voltage is asymmetric and mutative,and verifies the overall scheme.At last,the effectiveness of all the proposed control strategies are verified in a three-level four-leg APF experimental platform.This thesis has 93 figures,13 tables and 85 references.