Research On Some Key Technologies Of Active Power Filter

The technology of active power filter (APF) is a research field concerning power electronic, detecting technique, control theory, signal processing and computer science. With the increasing of nonlinear loads in power system, serious harmonic current pollution has threathen the running of power system and affected the use of electrical equipments. APF is one of the most prospect methods to suppress harmonic contamination. It contains several theories and technologies, becoming the research hotspot. Today, research on APF mainly concentrates on real time high precision harmonic detectiong and signal processing, current controlling, high power factor conversion technique, main circuit topology structure and nonlinear parameters design.The instantaneous reactive power theory is widely used in harmonic detecting, and its capability is analyzed in this paper. To solve the shortcoming of instantaneous reactive power theory in dynamic performance, a new harmonic detecting method based on lead network compensation is proposed. The method improves the capability of harmonic detecting by correcting its zeros in frequency response. The theoretical analysis and computer simulations show that the method can improve the dynamic performance.Instantanous reactive power theory based harmonic detecting is limited in three-phase circuit and is immune to the electric voltage. Wavelet transform, for its special application value in signal processing, is used in real time harmonic detecting. The principle, wavelet basis, precision and dynamic response of harmonic realtime detecting based on wavelet transform are analyzed. This method has low performance because of boundary extension in wavelet arithmetic. Through analyzing the relationship between amplitude of current and wavelet coefficients, a compensation method is proposed. This compensation method can markedly improve the performance of real time harmonic detecting based on wavelet transform.The accurate mathematics model of active power filter is the theory base for control realization. After establishing the mathematics model, the spectrum of switching function and ac side voltage are analyzed. Studies on main circuit of APF, the calculating methods for main parameters are deduced to meet the performance.Real time and accurate harmonic current control is the key of APF. A harmonic current control, based on predictive control, is presented in this paper. The principle, structure, character and control rule of APF with current predictive control are analyzed. Especially, the stability and dynamic response of control system are discussed and the effects of parameters for performance are analyzed. Predictive control improves the precision and dynamic performance of current control and a useful attempt is made for predictive control to be applied in fast respone system.The APF experimental platform based on TMS320F2812 is presented. Harmonic detecting and current controlling experiments are done on the platform. The results of experiment are analyzed and the conclusions are drawn.