Study On Single Phase Active Power Filter For The Electrified Railway Supply System

With the application of power electronics more and more widely, it lead to the capacitance of nonlinear load increase correspondingly. At the same time, power system is polluted with harmonic current seriously. As a high voltage single phase nonlinear load, the electrified railway load has become one of the harmonic sources of power system. So, the research on harmonic suppression scheme for electrified railway load is becoming a hot subject in recent years.A single phase parallel active power filter is proposed based on suppressing the electrified railway supply system harmomc current. The two keys of harmonic current detecting and compensating current control have a great impact on the performance of it. Exact and real-time detecting of the instantaneous variable harmonic current in load is the premise for compensating of active power filter. This paper discusses several harmonic current detecting methods. The simple arithmetic and realization, little delay and quick response velocity of the harmonic current detecting method based on the phase distinguishing technology are improved by theoretical analysis and simulative research. This detecting method is on fit for the electrified railway supply system.Compensating current control is the key tache to accomplish the various functions of active power filter. In the text, the improved triangle-wave modulation current control method and the one cycle control for double-direction compensating control scheme of active power filter compensate harmonic current of the electrified railway supply system effectively, and compare to traditional methods, its show more superiority. The simulative result shows that the range of current error with the improved current control method is smaller than that with the traditional method, and the former method can heighten the control precision. The double-direction compensating control scheme need not detect harmonic current as well as bring referenced current signal, while display excellent compensating performance and simple control circuit.To verify the feasibility of the harmonic current detecting method and compensating current control method, this paper simulates single phase active power filter used in the electrified railway supply system in MATLAB6.5. The simulative result shows that the phase distinguishing technology combined current control method above can filter a majority of the electric locomotive harmonic current and lower THD of the source current. Furthermore the active power filter possesses good dynamic capability and synthetical compensation.