Development Of The Shunt Active Power Filter

Being used widely in the industrial domain and normal life, non-linear loads and current convertors bring some big problems into the power system as well as convenience. Thyristor rectifiers, diode rectifier circuits with capacitor on the DC side, arc furnaces and static var compensators are the main harmonic source, a mass of fluorescent lamps, color televisions and personal computers also inject harmonics into the gird. Harmonics can contaminate the power system and communications system, consequently, it is important to remove the harmonic currents from power system.Active Power Filter (APF) is an ideal harmonic and reactive currents generator. Compared with passive power filter, it can remove the harmonic and reactive component from the power system undepending on power system impedance and cause no resonance. APF's circuit topology, work principle and characteristics are analysed thoroughly in this paper.Presently in active power filter technology, the instantaneous reactive power (IRP) theory-based methodologies for harmonics and reactive power currents detection are predominantly utilized, i.e. the p-q and i_p-i_q methods. However, detailed analysis shows that the applied condition and scope of these methods are quite limited. The prevailing current detection algorithms available for harmonics and reactive power compensation are no longer suitable for the intensively non-linear loads like arc furnaces with both the voltages and currents varying quasi-stochastically. Based on orthogonal mathematic transforms and with combination of both the ip-iq and p-q methods, the paper presents an effective algorithm to accurately extract the instantaneous positive-sequence active currents of base-frequency, without using PLL. The methodology is in a generalized style and can be applied to three-phase circuits of any possible working conditions, including three-phase three-wire systems, three-phase four-wire systems, asymmetric or harmonic voltage and current waveforms, etc., and hence gives a feasible solution to instantaneous reactive power and harmonic currents detection for quasi-stochastic loads especially with supply voltages in severely distorted waveforms.The capacitor on the DC side of APF can provide a steady voltage to transmit harmonic power into AC side, the inductor between APF and power system can transform the voltage signal to current signal. Through the design of APF, both of the value of capacitor and inductor are vital to the effect and cost of APF. The selection algorithms of capacitor and inductor at present are compared in chapter 4.A design scheme for active power filter based on TMS320F2810 is presented in chapter 5. The DSP controls the intelligence power module (IPM) and the inductors to produce the current reversed in phase with the detected current, which is penetrated into the power system. The mixed wave of the produced current and the load current will be sine wave which is in the same phase with the grid voltage. Therefore, the harmful influence brought by the harmonic and reactive currents will be eliminated.