Research On The Quasi-Z-Source Inverter Based On A Direct-drive Wind Generation System

A growing problem as the earth’s energy crisis, all kinds of renewable energy, including wind power connected grid technology is becoming a hot spot of current research. A variety of new topology power converter topology is applied to wind power generation system, one of which is prominent quasi-Z-Source inverter. Quasi-Z-Source inverter has the ability of boost/buck which could be done in the single-stage topology. It overcomes the limitations of the traditional VSI, thus can get higher reliability, higher efficiency and better economic. It has a lot of advantages applied to wind power generation system. This paper mainly research quasi-Z-Source inverter in direct drive permanent magnet (DDPMSM)wind power generation system of the traditional linear control method and the application of model predictive control(MPC) of quasi-Z-Source inverter with resistor and inductor load.At first, the paper introduces the quasi Z source inverter topology structure and the working principle of the quasi-Z-Source. Utilizing its working principle and the mathematical relationship got its mathematical modeling, and obtain the simplified version of the small signal model block diagram of the system, derived its small signal model. It is also could be got that the transfer function between the DC voltage of VSI and the shoot-through duty ratio D, the transfer function between the inductor current of quasi Z impedance network and the shoot-through duty ratio D. For direct-drive permanent magnet wind power generation system, wind turbine and permanent magnet synchronous generator are modeling and simulated. Introduced the working principle of PLL and verified by the simulation system, and obtained the conditions of VSCF wind power generation system in maximum wind energy utilization.Studied the quasi Z source inverter grid connected technology in the wind power generation system. Using HCS method realize MPPT in system. The traditional linear control in grid side is the same with traditional three-phase VSI control methods. Using the grid voltage oriented control and feed-forward decoupling control, set the grid reactive power is 0, makes the quasi-Z-Source running in the state of the unit power factor. The double closed loop control, composed by the quasi-Z-Source inverse inductance current inner loop and the capacitor voltage outer loop, adjust rapidly the output of the shoot-through duty ratio D, combined with the grid side inverter voltage component under two-phase static coordinate system. Introducing some kinds of SVPWM modulation methods in the quasi-Z-Source inverse and the basic principle of model predictive control. Established equivalent model and discretization mathematical model in active state, null state, and shoot-through state of quasi-Z-Source inverter. Using Matlab/Simulink to realize MPC of quasi-Z-Source inverter with resistor and inductor load, the system output can accurately track the given reference value and has high precision output. It has a good application prospect.Finally, using quasi-Z-Source inverter sectional shoot-through SVPWM technology, and maintain the stability of the dc side voltage inverter. The simulation research of the system has carried on in the condition of variable wind. The correctness and effectiveness of the method was demonstrated by the conclusion.