A Study On Improving The Power Quality Of The Railway's Power Supply System Based On The Hybrid Power Active Filter

In recent years, electric locomotives are more and more employed in modern railway, for electric locomotives have such merits as having large tractive power, large overload capacity, low running cost & operating cost, putting into effect automation easily and producing no environmental pollution damage. In our country, we usually employ the AC converting DC electric locomotives whose converters are step winding full-wave or bridge rectifiers which convert the AC energy to the DC energy to drive the DC pulling motor in the electric locomotive, and the step winding full-wave or bridge rectifiers will produce relative large harmonic current, fundamental wave negative- sequence current and reactive current which severely pollute the power supply system. Electrified railway's traction load is usually the big consumer for the electric power system, so electrified railway's traction load is the main power quality pollution source. The electric power system's transmission network & transmission equipments, distribution equipments and power equipments will come to superheat, produce vibration and worsen the insulator of the equipments when the electric power system's power quality is deteriorative, what's more it will make the equipments spoiled if the power quality deteriorate to some extend. Therefore, in order to improve the whole power supply system in our country, to improve the power quality of the traction power supply system is very vital.There are three technologies to improve the power quality of the power supply system, which are the passive power filter, the active power filter and the hybrid active power filter technique. Comparing with the passive power filter technique, the active power filter technique has such merits as it little be affected by the impedance of the power supply system transmission network, and it also can dynamically track and synthetically compensate the power quality of the power supply system. Hence, the active power filter technique is the main technique to improve the power quality of the power supply system. To employ the active power filter solely to improve the power quality of the traction power supply system is not economical because it needs corresponding large power active power filter to improve the power quality of the traction power supply system, for the traction locomotives generally are very large power rectifier loads, and they are the main loads of the traction power supply system, and the invest of the power filter directly proportions with the active power filter's power. Therefore, a hybrid active power filter is studied which is to take advantages of the passive compensating units' merits, those are low invest, can improve large reactive current, harmonic current and fundamental negative-sequence current, and it also can take advantage of the active power filter's merits, those are dynamically tracking and synthetically compensating the power quality of the power supply system. Hence, this kind of hybrid active power filter can not only well improve the power quality of the power supply system and also reduce investment outlay.To make the hybrid active power filter dynamically track and synthetically compensate the power quality of the power supply system well, the detection mode which can detect the distortion currents of the power supply system real-time and accurately is very vital. In this thesis, a method that structure two phase equivalence power system from the single phase power system is studied, and it make the three instantaneous reactive power theory can be used correctly in the single phase traction power supply system to detect the distortion currents real-time and accurately in this system, and to offer the current command signal to the hybrid active power filter. The signal and data operational speed of the control system is the key to real-time and accurately detect the distorted currents of the power supply system for the application the three phase instantaneous reactive power theory must employ many multipliers. Therefore, in ord...