Control Strategy Of Active Power Filter Based On Resonant Controller Without Harmonic Calculation

As different kinds of nonlinear load and power electronic converters are connected to the grid, large number of harmonics flow into the power system, which caused a bad impact on power system and electrical equipment. Active power filter can solve the problem of harmonic pollution effectively, which becomes research focus at home and abroad. This paper carries out research on current and voltage control strategy of APF.Firstly, this paper studies current control strategy based on resonant controller, proposes the control structure that harmonic and fundamental current control loop are separate, in which load current can be used directly as harmonic current reference and no harmonic detection calculation unit is needed, then steady compensation accuracy and dynamic response speed can be increased. LCL filter has better filtering effect for switching ripple than single inductor filter, but its phase lag is larger. Resonant controller can ensure high precision tracking of harmonic reference. Conventional resonant controller has small phase margin, and when it is used in APF control, the largest harmonic order which can be compensated is limited. This paper improves the conventional resonant controller, raises system stability margin, so that LCL APF can compensate up to31st harmonic and its compensation performance is increased. What’s more, by choosing corresponding resonant controllers in parallel, selective harmonic compensation can be achieved.Secondly, as performance of resonant controllers get worse when grid frequency shifts, this paper proposes a grid frequency adaptive strategy, tracking the change of grid frequency through phase-locked loop and correct resonant frequency of the resonant controllers, so that APF will have high precision compensation effect even if grid frequency changes. As performance of PLL determines steady compensation precision and dynamic performance of frequency adaptive strategy, PLL design is studied.Thirdly, this paper studies control strategy of DC voltage, analyzes relationship between DC voltage and compensation current active component, adopts a closed-loop control strategy in which square value of DC voltage is controlled, and PI controller is used as DC voltage controller so that DC voltage tracks the reference with zero static error. Then DC side voltage boost mode when APF is started is studied.Finally, APF control system platform is designed. In terms of hardware, sampling board, primary interface board, DSP control board, IGBT driver board and drive adapter board is designed. And in terms of software, DSP and industrial control computer program is designed.