The Research And Development On Excitation Control System Of Variable-Speed Constant-Frequency Wind Power Conversion Using Doubly Fed Generator

Now, energy sources consume is increasing daily and environment pollution become more serious gradually. Because of its stand out merits, wind power is paid great attention in the exploitation of renewable energy source. This dissertation chose the most attractive and booming approach—Doubly-fed induction generator (DFIG) as research object, the approach of this system reduced the capacity of inverter, the generator has a very wide speed range which can be adjusted from sub synchronous speed to super synchronous speed. The stator voltage and its frequency keep constant, so the active power and reactive power can be controlled freely. Besides, the DFIG can be equipment for reactive power compensation of the Power Network, improve its stability.Firstly, the research status of wind power generation technology and VSCF technology are summarized in this paper. All kinds of excitation control strategies for VSCF generator and future trends are reviewed. After studying the mathematical model in static three-phase coordinate and in rotary two-phase coordinate, the stator field-oriented vector control strategy is issued. Based on the analysis of the dynamic mathematical model of DFIG and its stator-flux-oriented vector control, a dual-closed-loop control scheme is developed and realizes decoupled control of the active and reactive power. Simulation study is carried out on the platform of MATLAB/SIMULINK and validates the proposed strategy, which will guide designing and debugging the practical software and hardware systems.PWM converter which is the key equipment to realize the control of DFIG has a decisive influence to the control characteristics and the power quality. By using the operating characteristics of AC-excited VSCF wind power generator, this dissertation designed a dual PWM converter which can let the power flow to the two direction, and also discussed the function and control difference of the two converter. The grid-side PWM converter can realize unity power factor and keep dc-bus voltage constant by using grid voltage vector orientation control method and load current fed-forward control method based on power balance between the two PWM converters. In order to realize decoupled control of DFIG active & reactive power and to capture the maxim wind power, field oriented vector control technique was applied to DFIG control. A general control strategy based on stator flux oriented vector control was proposed as well. According to the different operation conditions below and above the synchronous speed, the two converter can shift automatically at rectifier/ inverter (or inverter/ rectifier) state, and then bi-directional power flow is realized.Finally, simulating system of variable speed constant frequency wind generating is designed based on DSP and simulating. It is composed of a 7.5kW DFIG and grid-side and rotor-side converter which controlled by dual DSP controllers. The design of signal processing circuit, communications interface circuit, quadrature encoder pulse circuit and protection circuit has been detailed.