Research On The Theory And Engineering Application Of High-capacity Active Power Filter With Single Injection Circuit

The target of electricity market's reform around the world is to improve the efficiency of electric power production and operation, provide better auxiliary services, improve security and stability, strengthen the reliability of power systems, as well as ensure better power quality. The application of new power electronic equipment in power grid makes the power transformation and application more convenient; on the other hand, it brings serious power quality problems such as harmonic pollution, reactive power problems, voltage fluctuations, imbalances and etc. As a traditional means of harmonic control, Passive Filter (PF) will be gradually replaced by new devices, due to the disadvantage that it can only filter some specific orders of harmonic and may lead to series-parallel resonant with power grid. Active Power Filter (APF) has been recognized as the most effective means of harmonic control, reactive pollution control and power quality improving. Now it has become a new research focus in application of the power electronics technology. Parallel APF is the most basic, practical and beneficial to industrialization. In this paper, a research on parallel APF is made systematically and deeply both in theory and application, which lays a good foundation for its application in factories and mines.Based on the actual situation of a high voltage distribution network's harmonic elimination in factories and mines, as well as general consideration on command of harmonic control and reactive power compensation, a high active power filter with single injection circuit (HAPFSIC) is proposed in this paper. Its injection branch provides a low impedance channel for harmonic which insulates network voltage and compensates certain reactive power. The fundamental currents that flow through the injection branch will flow into the series LC network resonating in fundamental frequency, so that the inverter of HAPFSIC with smaller capacity is needed and it also has certain ability of static reactive compensation. Based on the structural features of HAPFSIC, a control system equation is then set up. Deep research and simulation are made on its topology, compensation and output characteristics. Conclusions are that the active part of device undertakes little grid fundamental voltage, there is no fundamental current flowing, the inverter capacity is small and the initial investment is small. To detect the distorted current in grid accurately and in real-time, and then to provide reference signal for active power filter control system's accurate compensation is the key to determine the compensation performance of active power filter. In this paper, problems as slow changes in voltage frequency and fundamental current's mutation in actual operation are considered. By the premise of meeting the demands of real-time performance and accuracy of active power filter harmonic detection, an adaptive frequency tracking current frequency division detection method based on extended Prony spectrum estimation is proposed. This method uses N index Portfolio combinations with amplitude, phase and frequency to approach a sampling data sequence with equal interval L, and adopts LMS algorithm of adaptive adjustment algorithm to optimize the frequency of conductance matrix in extended Prony spectrum estimation. The method is of low computational complexity with the only need to solve amplitude, and to a certain degree it realizes tracking load change in the time shorter than a fundamental cycle.The control method of active power filter will directly affect the system's response speed and harmonic elimination effect, moreover, HAPFSIC is a converter of power electronic switching devices with natural changing structure system, using sliding mode variable structure control has very obvious advantage. But in traditional sliding mode variable structure control, controller's structure can only switch on both sides of surface, and it can't track reference input signal without static difference. So according to the characteristics of slow current changing (oppose to power fundamental cycle) and periodicity for a most loads (such as rectifiers, motor, computer and other electrical equipments), this paper proposes an advanced sliding mode variable structure control algorithm based on repetitive control. It combines fast response speed of the sliding mode variable structure control algorithm and non-steady-state error of repetitive control algorithm. It unifies the dynamic performance and the control accuracy, and will not make obvious high-frequency switch burr, thus it is very suitable for HAPFSIC control and can fully meet the requirements of distribution network harmonic elimination in factories and mines.Finally, on the basis of theory analysis, practical experience and the application of active power filter in some factories in Jiangxi, and in order to minimize the costs of system energy and investment of filter device, a HAPFSIC structure and parameter design method suiting for harmonic suppression are proposed which provide useful references for promotion application of shunt active power filter. It makes a detailed exposition on parameter optimization design, device's practical engineering application in various components of HAPFSIC's main circuit. It is combined with computer simulation results, which proves the feasibility and effectiveness of HAPFSIC in operation. It has been put into operation in some factories and shows good effect.