Operation Control Of Power Converters For Boost-Chopper Direct Driven PMSG-based Wind Energy Conversion System

The direct driven permanent magnet synchronous generator (PMSG)-based wind energy conversion system (WECS), which has the advantages of high efficiency and reliability and high ability to reject the grid disturbances, is a main type of WECS as well as the doubly fed induction generator (DFIG)-based WECS. The boost-chopper converter followed by a three-phase full-wave converter is a common topology of the full-power AC-DC-AC converter in the PMSG-based WECS, whose performance is analyzed in this paper. Then novel control strategies are purposed.The PMSG and the boost-chopper generator side converter form a nonlinear system. Therefore it is difficult for the system to maintain good dynamic performance within normal operating range under control of the ordinary proportional-integral (PI) controller. Besides, the parameters of the PI controller used in the nonlinear system are always difficult to be tuned. Consequently, a piecewise 2nd-order affine nonlinear mathematical model for the whole system including the generator and the generator side converter is built based on certain assumptions, whose input variable and output variable are the duty ratio of the switching signal for the power device and the speed of the generator respectively. Subsequently the nonlinear mathematical model is transformed into a linear one within every single interval by the input-output feedback linearization (IOFL) method based on the differential geometry theory. In addition, a closed loop speed controller is designed on the basis of the optimal control theory. Simulation results verify the good steady and dynamic performance of the system using the proposed controller within normal operating range.A more precise piecewise 3rd-order affine nonlinear mathematical model is built whose state variables are namely the angle of the generator, the speed of the generator and the current of DC-link inductor respectively. Among then, the angle of the generator is selected as the output variable for complete input-output feedback linearization within every single interval. Then a closed loop controller is designed according to the relationship between the output variable and the speed of the generator considering the integral of time multiplied by the absolute error (ITAE). Finally, simulation and experimental results prove that the system has good steady and dynamic performance with the proposed strategy, such as its rapid step response, through which some drawbacks of the ordinary PI controller are overcome. Also, the proposed strategy can be referred to for the generator side controller design of the direct driven PMSG-based WECS with the boost-chopper converter.According to the instantaneous power theory and the mathematical model of the grid side converter, the analytical equations of DC and AC components of the instantaneous power are given under balanced and unbalanced grid voltages respectively. Then two constant switching frequency direct power control (CSF-DPC) strategies are designed using the feedback control theory. One of them contains unbalanced algorithm while the other does not. The two controllers have the advantages of fixed switching frequency and good dynamic performance. At last, simulation and experimental results demonstrate that the two controllers have good steady and dynamic performance under the balanced grid voltages and the controller containing unbalanced algorithm can effectively improve the performance of the system under the unbalanced grid voltages by reducing input current harmonics and the fluctuations of the instantaneous active power.