Study On Harmonic Current Detecting And Controlling Of Three- Phase Shunt APF

Compared with the conventional passive power filters, active power filter (APF) has many advantages, so APF technology will be applied widely to improve the quality of distribution systems through compensating the harmonic current and reactive current caused by the nonlinear loads .It is discussed in this paper about the shunt active power filter device based on three-phase PWM voltage-source converter (VSC). The mathematic model of the three-phase PWM VSC is set up based on switching function concept, using coordinate transformation to convert three-phase balance ac variables to two-phase dc variables simplifies the mathematic model, and using state-space averaging method to eliminate the discontinuity of the switching functions, the model is then further simplified. Based on the power balance concept, the fundamental of compensating the harmonic current and reactive current is discussed in the chapter 2. The conventional theory of power is not satisfied to apply in the nonlinear field. Detecting the harmonic current and reactive current (pq method) based on the instantaneous reactive theory is suitable in the APF device. The fundamental and implementation of ip,iq method based on the instantaneous reactive power is presented in the paper. ip,iq method is more accurate under the voltage is deteriorated. id,iq method is a mathematic transformation of ip,iq method. The infinite impulse response (IIR) Butterworth digital low-pass-filter (LPF) is designed to obtain the harmonic current . The phase of voltage and current is needed to use id,iq method ,so three-phase software phase-locked loop implemented by DSP is designed, and the use of lag controller improves its capability of anti-noise. The mathematic model of PWM VSC in synchronous rotating frame is a multi-input/multi-output system, and there exists interaction between d-and q-axis current. The use of complex notation simplifies the model from a multi-input/multi-output system to an equivalent single-input/single-output complex system. Based on generalized zero-pole cancellation method, complex PI controller decouples the interaction between d-and q-axis current. And the performance of the complex system employing the complex PI controller is evaluated using generalized frequency response function and simulation in time-domain. The method to control the DC voltage of capacitor is discussed. A PI controller of compensating current is designed, and effectiveness of the PI and the model of compensating harmonic current are verified by simulation. An APF prototype is constructed, which uses TMS320F240 DSP as the heart of control system. Experimental results demonstrate that the id,iq method based on instantaneous reactive theory can both detect the harmonic current of nonlinear load, and obtain the reactive current rapidly.