PWM Converter And Control Strategies For Wind Power Generation

Wind power generation is one of the most successful solutions to global energy crisis and environmental pollution in terms of widespread takeup and commercial development. A PWM converter applied to grid connection of wind turbine systems (WTS) and its current control strategies are researched through theoretical investigation, simulation and experimental verification. Additionally harmonic cancellation for multiple configuration is also analyzed.This dissertation summarizes the art-of-the-state of WTS, comparing predominant technologies including doubly fed induction machines (DFIM) and the direct-drive topology. In the 1.2MW direct-drive system adopted, a dual PWM converter is employed as grid interface. Following introduction of the topology characteristics and control requirements of the system, the grid-side converter is emphasized. Not only are mathematical models at low and high frequency and in rotating (d-q) frame given for general circuits, bur they are established for the real system with neutral line. In duplication, control for harmonic cancellation is studied from current ripple amplitude and SPWM harmonic analysis. Simultaneously a novel harmonic cancellation method of SVPWM symmetrical space vector synthesis is represented based on the SPWM carrier shifting technique.For models of the main circuits, three current control strategies are discussed subsequently. Parameters in vector control are devised by employing dc steady-state and dynamic investigation. The principle and process of instantaneous current control are described in detail. Further via transformation to a rotating frame and small-signal linearization, continuous time-invariant linear equations for predicted current control (PCFF) are attained, according to which the steady-state solutions and transfer function matrix could be calculated. Moreover the general dc voltage controller and particular compensator for the system with neutral line are also designed. The simulation verification is made using MatLab for the large-scale system.Three control schemes for the PWM converter are testified experimentally, following designing the hardware circuits and DSP programmes of the control system. The results and analysis for steady-state waveforms, dynamic performances and harmonic cancellation of duplication are provided demonstrating the feasibility in wind power generation and validating the theory presented before.