Integrated Power Quality Control Of Electrified Railway Based On Magnetically Conrtolled Reactor And Hybrid Filter

Electrified railway has high speed, large volume, outstanding comprehensive benefits and other advantages. So it is the inevitable trend of railway development, however, it also bring higher requirements to the grid along the road which take the task of supplying power. As electrified railway has adopt the way of single-phase supply, and has used nonlinear high-power single-phase multi-stage full-wave or bridge rectifier electric locomotive, as a result, there are still exist many problems in electrified railway power supply system of electric traction. Such as idle work, harmonic wave, negative sequence, and so on. Above factors not only affect the safe operation of electrified railways, but also adversely affect the local power grid.Against the growing problems of power quality, railway departments have adopted relevant measures and related compensation equipments to control the electrified railway power quality, and have achieved gratifying successes. However, as various compensation equipments have certain defects, there do still existing problems of idle work, harmonic wave, the negative sequence in electrified railway power supply system of electric traction. Magnetically Controlled Reactor and the Hybrid Filter System are the effective ways to improve the electrified railway power quality. As a result, research on magnetically controlled reactor and the hybrid filter system is of great importance to improve the electrified railway power quality. Besides, the magnetically controlled reactor should own reasonable structure of magnetic valve, fast dynamic response, and low harmonic. The hybrid filter system aims to be high performance and good stability.This thesis targeted power quality problems in the electrified railway, and conducted a detailed study on magnetic valve structure harmonic optimization, fast response feature of new type magnetically controlled reactor and the hybrid filter system with high performance and good stability.(1) At first, the structure and working principle of the magnetically controlled reactor was introduced, and magnetization curve model of its core material was discussed. According to its equivalent circuit, this paper established the basic equations and analyzed three basic working conditions of the magnetically controlled reactor. On the basis of its basic model, and adopted ATP-EMTP simulation software, analyzed its voltammeter and control characteristics. Simulation results showed that the voltammeter characteristic curve was obvious nonlinear, and it showed constant current characteristic in a certain range of AC voltage. Control characteristic curve was also nonlinear. It was possible to change the DC control voltage according to its control characteristic curve in order to adjust its output capacity.(2) From the equivalent circuit of the magnetically controlled reactor, electromagnetic transient under three basic working conditions which were no-load, half saturation limit and limit saturated was analyzed. It also made a detailed derivation of the general expression about the electromagnetic parameters. Based on the basic theory of electromagnetic fields, this essay established a physics simulation model of a single-stage magnetron reactor and made use of the Ansoft Maxwell simulation software to analyze the single magnetic valve reactor’ field distribution and eddy current loss. At the same time, optimization was made to analysis of structures in the various magnetic valves.Optimization results showed that magnetic field of multi-level magnetic valves’ structures are evenly distributed; magnetic lines of force were well-regulated and smooth. Effect in inhibitory the edge effect was obvious, magnetic core loss ratio reduced 47.6% compared to the single-stage valve-type reactor; winding eddy current loss ratio decreased 62.9% compared to the former. The optimal area ratio was 3:2:1 to the two-stage magnetic valve reactor, the total loss was 10.9348W. Slightly lower than the single-stage magnetic valve reactor that total loss was 11.36W.(3) Based on the harmonic characteristics of the single-stage magnetron reactor, and aimed at the equivalent model of four-stage reactor core, the thesis equivalent magnetization curve of the four-stage magnetic valve reactors’ cores was detected. According to its reactor equivalent circuit equation, its harmonic current expression was obtained. The relationship between reactors under different working conditions and different degrees of saturation was detailed analyzed, and the harmonic was optimized. In the mean while, causes of the transition process of the reactor was analyzed and conventional approach of improving the response speed was put forward. According to quick response mechanism of the reactors, the use of PWM reversible converter technology was proposed in order to improve quick response of the magnetically controlled reactor.The results showed that:①The four-stage reactor had better harmonic characteristics than single-level and bipolar-level magnetron reactor, it also greatly reduced the remaining harmonics and total harmonic content, the maximum of total harmonic content is less than 3.7%,3rd,5th and 7th harmonic current amplitude does not exceed the maximum rating 3.6%,1%,0.88%.②The adoption of PWM reversible converter greatly increased the magnetron reactor response time. The response speed was only two waves, when the reactor changed from no load state to rated state, or rated state to empty state.(4) This thesis used Yingtan substation and Yingtan South traction substations as the test points and made a detailed analysis of their harmonic voltage, harmonic current, power factor, active power, reactive power and three phase imbalance of power quality conditions. Analysis showed that:①3rd,5th,7th, and 11th harmonic voltage rate and total harmonic distortion rate exceeded the national standard.②Current harmonic content is very large, according to the most lenient standard, 3rd,5th,9th,15th,17th,19th, and 21st harmonic currents also exceeded the national standard.③Power factor changed greatly by time, fluctuations were obvious. Minimum power factor was only 0.037, and during the long period of time, power factor was very low and is only about 0.1. Phenomenon of sending back to the system reactive power was very serious. It caused the time of system voltage exceeded the rated voltage accounting for about 80% of the total time.④The maximum degree of three-phase voltage unbalance in Yingtan South traction substation was 4.83%, a maximum of 95% probability was 2.89%, greatly exceeded the national standard value of 2%. And time of exceeding the national standard accounting for about 16% of the total time.(5) Based on the instantaneous reactive power theory, this thesis discussed the improved single-phase harmonic current detection and specified harmonic current detection method. It also established the average active power filter model, and made robustness analysis and calculation of the active power filter based on control theory. Proposed and analyzed in detail to the hybrid power filter harmonic suppression scheme used in electrified railways. The experiments showed that:①Harmonic suppression works well based on the control of electric railway, when parameter pretreated, THD was relatively little changed, the system can accurately followed the load change, the system had strong robustness.②Injective hybrid filter can significantly improved the filtering effect of passive filter. The total waveform distortion filter downs to 11%, respectively, compared with no filtering device and only install 3 times,5 times passive filter waveform, the total distortion rate declines 73% and 62%. In addition, the injective hybrid power filter guaranteed the effect of guaranteeing at the same time, and also greatly reduced the capacity of active power filter.(6) Based on Hilbert transform theory, this thesis analysis basic principle of detecting active and reactive power in electrified railway. Used the load balancing method, and derived on the capacity allocation formula of magnetron SVC used in the electric railway to compensate reactive power and balance the capacity of the negative sequence.It also explained the control strategy of the SVC in compensating reactive power and the negative sequence, and analyzed the hardware and software implementation of the control system. The results showed that:①Based on Hilbert Digital Phase Filter, reactive power measurement method can effectively and rapidly detected the rapidly changing active and reactive current in the electric traction load, magnetron SVC can quickly and accurately issued real-time calculated compensation capacity, and it can made the system’s power factor to a level close to 1, the three-phase current was basic symmetrical, magnetic SVC dynamic compensation effect was obvious.②Active filter and magnetron SVC comprehensive compensation scheme was feasible and effective in inhibiting electrified railway harmonics, compensating reactive power and balancing the negative sequence. Active filters can not only eliminated the harmonics generated by load, but also eliminated the harmonics generated by the magnetron SVC.