| Large-scale exploitation and effective utilization of wind energy has become a urgent need to mitigate the energy crisis and reduce the environmental deterioration. With the advances in power electronics and its deep application in wind generation, variable pitch control and Variable Speed Constant Frequency (VSCF ) have become new trend of wind generation technology development. And Double Fed Induction Generator (DFIG )wind generation and the direct-drive Permanent Magnet Synchronous Generator (PMSG ) wind generation as the representative of new wind technologies have emerged. Among them, the direct-drive PMSG wind generation technology with low noise, high efficiency, high reliability, superior control performance and its technical advantages in grid-friendly wind power system has increasingly become a focus of attention. In a laboratory environment, the establishment of direct-drive PMSG wind generation experimental platform, to research, develop and test the wind technology and related products, will reduce costs and improve the development efficiency and flexibility.In this paper, it gives an overview of key technologies of the direct-drive PMSG wind generation technology and its experimental platform. On this basis, a certain number of key technologies for dual PWM direct-drive PMSG wind generation experimental platform with multi-module parallel are studied, which mainly include wind turbine imitation, multi-module parallel technology and maximum power tracking (MPPT) implementation based on experimental platform.First, the traditional control strategies of wind turbine imitation using DC motor, such as single closed-loop torque control, single closed-loop armature current control and dual-loop speed control, etc. are summarized. Among them, the single closed-loop torque control and armature control inductions calculation large-extent depends on the exact parameters of DC motor; while in the double-loop speed control although the dependence on motor parameters is not strong, but there is a big gap in the operating mechanism compared with the actual wind turbine. Therefore, a novel control strategy of wind turbine imitation by directly controlling DC motor's output power is proposed, which is closer to the actual operating principle of wind turbine.. The actual power calculation only needs the measurement of the motor's terminal voltage and armature current, and is not dependent on motor's exact parameters. Simulation and experimental results effectively validate the feasibility of this control strategy.Then, on the basis of summing up the parallel mode of PWM converters, the carrier phase-shifting line-level parallel way is proposed to heighten the system's equivalent switching frequency, reduce the switch losses and the filter dimension. However, the parallel approach leads into serious zero-sequence circulating current, which increases the switch stress and the wire losses, and can also produce the Electromagnetic Interference (EMI) to the control system. Thus, in view of zero-sequence circulating current of this parallel approach, an analysis of its generating mechanism from the zero-sequence switch states is given. And then ,the corresponding novel restrain strategies using independent DC-bus is proposed, which cuts off the zero-sequence circulating current path and effectively restrains the zero-sequence current, and get an effective simulation and experimental validation.Finally, the paper analyzes the existing wind generation MPPT control schemes, combined with the characteristics of this experimental platform which not needs to measure the wind speed but needs to imitate the conditions under all kinds of wind speeds, chooses the best tip-speed ratio (TSR) to achieve the control of direct-drive PMSG wind generation experiment platform MPPT. The wind field characteristics (including the wind speed, air density, pitch angle, the turbine properties, etc. ), the generator-side converter vector-controls the PMSG to operate at the optimal speed based on the rotor-flux oriented, and gets the optimal TSR corresponding with the present wind speed. And at the same time, the output power of the DC-motor is controlled to imitate the maximum power captured from the wind by the turbine. The grid-side converter is in charge of keeping the DC-link voltage constant and feeding the generator-side power into the grid with a unit power factor, and then the experimental platform MPPT is successfully achieved. Simulation and experimental results effectively verify the correctness of this MPPT control strategy and its feasibility.
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