grid-side converter control strategy
The general grid-side converter control system requires an AC voltage sensor, an AC current sensor, and a DC voltage sensor to detect the control amount and protect the system, increasing the system cost, making the rectifier device bulky, and both the sensor signal loss and the noise interference. May degrade system performance. It is necessary to omit the sensor control strategy for this study. Based on the traditional svpwm method, this paper uses the virtual flux linkage to calculate the angle, eliminating the need to detect the AC voltage signal, eliminating the AC voltage sensor, reducing the system cost, reducing the device size, and simplifying the circuit structure. Moreover, it has a strong inhibitory effect on grid interference, and the distortion of the input current of the grid is small, and the system has better dynamic and static control characteristics.
4.1 The concept of virtual flux linkage
The concept of virtual flux linkage is derived from a virtual motor. The grid-side power supply (dashed line in Figure 3) can be viewed as a virtual AC "motor" where the resistance and inductance can be considered as virtual motor stator resistance and stator leakage inductance, respectively.
In this paper, the dual pwm converter is used as the grid-connected circuit of the direct-drive permanent magnet synchronous wind turbine. A control strategy for the separate control of the motor-side converter and the grid-side converter is proposed. The simulation results verify the correctness of the proposed control strategy: the motor side can track the best tip speed ratio to obtain the maximum wind energy and stabilize the DC side voltage when the motor side is below the rated wind speed; the grid side can maintain the grid side power factor. It runs and eliminates the AC voltage sensor and has good dynamic and static performance. The motor side and the grid side perform their duties, making the control method simple and effective.
