Study On Detecting Method And Control Strategy Of Harmonic And Reactive Current In Unified Power Quality Controller

Along with the rapid development of science technology and national economy, the demand of electric power increases; moreover with the increase of nonlinear loads and striking loads in the distributed power system, such as electrified railway, arc furnace and large rectifying equipments, power quality is deteriorated increasingly; Unified power quality controller as an advanced power electronic equipment can improve the power quality effectively.Thus, load harmonic current, reactive and negative-sequence current compensation are selected as controlling objects, the combination of shunt and series active power filter, i.e., the unified power quality controller is deeply studied in this dissertation to lay a theoretical and technical foundation for the development and application of unified power quality conditioner, which is part of the project of Flexible Alterative Current Distribution System which is belongs to School Fifteenth Special Science and Technology Fund.The shunt active power filter unit of unified power quality controller is decided as the major object of study from the analysis of the system total topology and compensating characteristic and the establishment of mathematical model for union control. As a result, the operating performance depends on the accurate and real time diction of harmonic, reactive and negative sequence current of load current to a great extent. And it is required that the compensating current reference should rapidly adapt to load current changes. Thus, two harmonic and reactive current detecting method based on different reactive power theory are presented in this dissertation, according to the load harmonic and reactive current detecting principle of unified power quality controller. Then, the detailed analysis is made in accordance with the detecting methods. Simulations are developed and the results show that the proposed methods can detect harmonic, reactive and negative sequence currents validly and precisely.After the compensating current reference is determined according to the harmonic and reactive current detection method, the control system will become the next key link for the performance and efficiency of active power filter. An improved current control method based on voltage space vector is presented from the analysis of mathematical model and basic current control law for active power filter. Because of the adoption of voltage space vector, the closed loop way control enhanced the utilization of DC-link voltage and reduces the power rating of system.This dissertation also designs the parameters of shunt APF main circuit and combination with simulation to optimize the parameters. These unit circuits conclude the selection of power switching device, the realization of a certain functional module, the choice of control chips and isolation circuits and the computations of filter capacitors and inductances which play an important role for device's dynamic performance. A full digital control system based on DSP is built with TMS320F2812 and the hardware circuit of shunt converter control system have been designed and tested. The control program is written by C language. Finally this dissertation does the experiments of shunt APF, the excellent performance of unified power quality controller verifies the validity of theoretical analysis and effectiveness of the proposed method in this dissertation.