Voltage High-power Active Power Filter Design

Active power filter is novel power electronic equipment which is used for harmonic suppression and reactive power compensation.It can compensate harmonic and reactive power without the influence of network impedance when both the magnitude and frequency of the harmonic's and reactive power's change.This dissertation introduces the basic principle of Active power filter and carrier phase-shifted SPWM technology,studies on harmonic measurement method based on instantaneous reactive power theory,analyzes the advantages and disadvantages of multiple converters and cascade H-bridge converter.In the view that the capacity of APF with single PWM converter is limited, the dissertation designs a voltage source high power active power filter by using 9-level cascade H-bridge convertor as main circuit,a improved i_p-i_q measurement method as instruction current calculation strategy and CPS-SPWM technology as current tracking control strategy,aiming at enlarging the capacity up to 1MVA.Sine,cosine signal is generated by PLL circuit and sine,cosine signal occurrence circuit in traditional i_p-i_q measurement method. When the network voltage is distorted the signal has phase difference with positive-sequence voltage of phase A,which leads to inaccuracy of measurement result.To solve this problem,an improved i_p-i_q measurement method without PLL circuit is proposed.The method retrenches PLL circuit,not bound by frequency offset and measures the fundamental current accurately when the network voltage is distorted or asymmetric.A simulation model of voltage source high power active power filter system is found in Matlab/Simulink software.Compared with the APF with single PWM converter,the simulation result shows that the strategy designed in this article could achieve better compensation effect and has better application prospect.