Research On Difficult Points Of Injection Type Hybrid Active Power Filter And Its Engineering Application

Because of large-scale applications of nonlinear and time-varying loads such as high-power power electronic equipments, the harmonic pollution and the lack of reactive power in power grid are getting worse. At the same time, the customers have more and more strict requirement to electric power quality. The problem of voltage quality and harmonic becomes more and more serious. Developing equipment with big capacity for suppressing harmonic and compensating reactive power efficiently and then improving voltage quality and decreasing harmonic content is going necessarily. Passive filter (PF) is a traditional harmonic suppressing device. However, because it can only suppress some specific-order harmonic currents and has the possibility of series parallel resonance with power grid impedance, it will be gradually replaced by new device. The hybride active power filter (HAPF) has the advantages of active power filter (APF) and PF both, so it becomes the main research and development direction of harmonic suppressing and reactive power compensating integrated system.Focusing on some difficulties in the project application of injection type hybrid active power filter (ITHAPF), some factors of ITHAPF were emphatically discussed, such as DC voltage control, current tracking control, and comprehensive design. Base on theoretical research, the realization scheme of harmonic suppressing and reactive power compensating integrated system was presented, and the project application of ITHAPF was carried out.The existence of fundamental series resonance circuit (FSRC) in ITHAPF decides that its DC-voltage can hardly be sustained by controlling the active current of the converter. The common way is using uncontrollable rectifier. However, when Point of Common Coupling (PCC) voltage is not ideal, the energy from AC side will raise the DC-voltage up and then impact the performance and security of the system. This thesis analyzed the reasons of rising of the DC voltage. Based on this, four methods were proposed for solving the DC over-voltage problem including selecting different configurations of APF, optimizing the injection circuit , adding energy releasing circuit and adopting controllable PWM rectifier in DC side. The methods proposed provided precondition for high efficiency, stability and security of whole system. Aiming at the current control of ITHAPF, this thesis analyzed the configuration characteristic of ITHAPF and established its harmonics current control model. Based on this, a new current control algorithm was proposed. Thereinto, recursive integral proportional integral (RIPI) was adopted in this algorithm to eliminate steady error, and precision of controller was improved; fuzzy arithmetic was used to adjust the coefficients of RIPI online for improving the dynamic performance of PI control. A selective harmonic current detection method including time-delay phase angle compensation is proposed for decreasing the influence of system time delay on the stability and control procession of the system. Generation of PWM signal of inverter and compensation of dead-time effect were presented also in this thesis.The main circuit parameters of ITHAPF have a great affect on its performance. Based on theoretical analysis and practical experience, a set of design methods of configuration and parameters for high-power ITHAPF was proposed. In the design of single tuned passive filter, capacity, cost and quality factor should be considered chiefly after tuned frequency was determined according to harmonic current resources. In the design of injection ciruit, the ability of active part harmonic current injection and the voltage which FSRC undertakes should be considered mainly beside the factors proposed in passive filter design. For the design of output filters, suppression of switching harmonic, the abilities of harmonic current output and dynamic tracking should be considered first. The design principle of coupling transformer is that after its capacity was determined, current and voltage of active part should be matched better so as to the capacity of power switching device could be used fully. In the design of DC capacitance, its voltage should have a moderate value considering current tracking ability and cost of active filter. In addition, for diminishing the DC voltage fluctuation, DC capacitance should have adequate capacity. Based on the design principles mentioned above, the realization scheme of an integrated system based on ITHAPF for harmonic current analysis and suppression was proposed in this thesis. Debugging of the integrated system including software and hardware has been finished successfully. The system has been put into use in one substation and application result is very good.