Abstract：With the high proportion of wind power connected to the grid, the stable operation capability of full-power wind turbines is facing challenges. The traditional grid-side converter adopts a phase-locked loop (PLL) synchronization strategy. In a high-ratio power electronic system, the PLL is prone to phase-lock instability. The grid-side converter of the grid-forming full-power wind turbine adopts a power synchronization strategy based on the dynamic characteristics of the DC voltage to realize the grid-forming control of the DC voltage synchronization. In the grid-forming control of the full-power wind turbine grid-side converter using DC voltage synchronization, due to the power coupling problem in the grid-forming control, when the grid-side converter needs to transmit reactive power to the grid to provide active voltage support, the reactive power will affect the active power through the coupling channel, which will further affect the stability of the DC voltage and reduce the effective operation capacity of the system. In order to analyze the coupling problem of reactive power and DC voltage in the grid-side converter, this paper first introduces the grid-forming control structure of the DC voltage synchronization of the grid-side converter of the full-power wind turbine and establishes the DC voltage-reactive power coupling model. Through the theory of relative gain, the influence of control parameters on the coupling effect is analyzed in detail. Then, aiming at the grid-side coupling effect, a DC voltage compensation method based on reactive power feedforward is proposed, which reduces the dynamic overshoot of DC voltage fluctuations due to reactive power variations; Finally, the theoretical analysis and the proposed method are verified on the experimental platform of the 5 kW permanent magnet synchronous full-power wind turbine. The following conclusions can be drawn through the theoretical analysis results of the relative gain theory method and the verification of the experimental platform: (1) The influence of DC voltage control loop parameters on the grid-side coupling effect: when parameter T increases, the dynamic response time of the DC voltage will be increased and reduced, but the grid-side coupling degree is not affected. Parameter J has little influence on the dynamic process of the DC voltage: when parameter D increases, the coupling degree of the grid side increases, and the dynamic process of DC voltage becomes worse. (2) The influence of reactive loop control parameters on the grid-side coupling effect: when parameter KQp increases, the dynamic process of DC voltage oscillates, and the oscillation amplitude increases. When parameter KQi increases, the oscillation frequency of the dynamic process of DC voltage increases, but the oscillation amplitude changes little. (3) According to the design of parameter KL and parameter KF in theoretical analysis, after adopting the DC voltage compensation strategy with reactive power feedforward, the oscillation amplitude and overshoot of the DC voltage dynamic process caused by reactive power steps are reduced. In the experiment, if the appropriate parameter KF is selected, the dynamic overshoot amplitude of the DC voltage can be reduced by 81.8%. This method effectively suppresses the coupling effect on the grid side.
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2023, Vol. 38 
