Study On Active Power Filter For Electric Locomotives

Most domestic electric locomotives are of rectifier. The electric locomotive gets DC supply to drive traction electromotor through a locomotive's transformer and a set of silicon rectifiers. But rectifier may produce harmonic current and distort the current of contact-grid. Moreover, when the locomotive operates in the regenerative brake mode, it doesn't draw but produce regenerative braking current. If the regenerative energy is utilized well, much of energy is saved. So a device anti–parallel connected with locomotive's silicon rectifier is discussed, which can eliminate harmonic current and inject regenerative energy to the AC grid.Active power filter is the main issue in this paper. Harmonic detection is one of key technologies of active power filter. An adaptive neural network harmonic current detecting method, based on the adaptive noise eliminiting technology and the adaptive linear neural network theory, is discussed. The adaptive linear neural network theory and its core algorithm——LMS algorithm are introduced in detail. On the base of theoretical analysis, a number of simulations are developed. When load currents and the grid voltage change, the detecting method is well adapted. But high detecting precision and rapid dynamic response hardly achieve at the same time, because of the influence of learning speed. So a harmonic current simulation mode is set up. Its learning speed is variable. The results of simulation show that the detecting method is of both high detecting precision and rapid dynamic response.Pulse width modulation (PWM) control method is another key technology of active power filter. Triangle carrier wave PWM control method is adopted in the paper, and the running process of unipolar PWM control method is analyzed. The simulation for active power filter is developed. The results prove that the proposed single-phase active power filter can eliminate harmonic current and purify the supply grid.