Research On The Power Filter Used In The Electrified Railway Supply System

As power system's supply quality problems generated by thyristor converters become serious as they are widely used in electrified railway, eliminating power system's harmonic and improving power factor are more and more important.Active Power Filter (APF) has good dynamic compensating performance and can compensate reactive power continuously, while Passive Power Filter (PPF) can endure higher voltage level and reach bulkier capacity, so power system's supply quality can be improved well by integrating APF and PPF into Parallel Hybrid Power Filter (PHPF).The thesis analyzes and compares several currents detecting methods used in single-phase APF, and discusses the methods based on Instantaneous Reactive Power Theory (IRPT) and on Active Current Separate Method (ACSM) in detail. In comparison to two methods by MATLAB simulation, it can be concluded that the former detecting result is more accurate than the latter, but which is at the cost of longer delay and slower dynamic response.Hysteresis Current Control (HCC) is applied in single-phase circuit extensively by virtue of its many merits, such as simpler hardware circuit, faster dynamic response and better stability etc. Therefore, HCC is applied for compensating currents controlling in the thesis.In PHPF, on the basis of PPF's function being effectively implemented, APF exists in the circuit as controlled voltage source for diminishing influence of harmonic voltage to supply grid, and ensuring more load harmonic currents into PPF. APF voltage can be controlled by supply current solely, or by load current solely, or by supply current and load current together, or by supply current, load current and junction voltage simultaneously, and or by load current and junction voltage. It is elicited that the 4th and 5th methods above can realize ideal filtering.To validate control effect of APF applied in the thesis, APF is simulated with SimPowerSystems Blockset in MATLAB. The simulation results show thatvoltage loop control makes DC voltage of inverter reach its referenced value after half a period of simulation, and current loop control strategy ensures APF favorable compensation characteristic except that hysteresis widths influence response speed and accuracy.