Research On Control Strategy Of Grid-side Converter For Wind Power Generation

The wind power generation is a kind of effective renewable energy source, which is received more and more attention in recent years. The grid-side converter plays a very important role in the wind power generation. This thesis does some research on control strategy of the grid-side converter, taking three-phase voltage source PWM converter with LCL filter (LCL-VSC) as the object of study. Firstly, under the balanced voltage condition, LCL-VSC mathematical model is established in the three-phase static and two-phase rotate coordinates, to provide the theory for the control strategy analysis and the control system design.Then a multiloop control scheme is proposed for LCL-VSC. Within this scheme, 3 cascaded inner current loops along with an outer voltage loop are used to achieve stable dc-link voltage, currents decoupling and feedforward, as well as the unity power factor control. With this scheme, the capacitor voltage estimation is performed with complex power theory resulting the omission of the transducers for the capacitor voltage measurement.To control the LCL-VSC effectively under unbalanced grid condition, the positive and negative sequence phase should be calculated. This thesis proposed a novel phase locked loop (PLL) based on the unbalanced grid condition, which may calculate the positive sequence phase angle and the negative sequence phase angle, used for LCL-VSC unbalanced control. The main idea of this method is first to draw the posive and negative sequence components under the unbalanced grid condition, then to get the phases of positive and negative sequence with the SFR-SPLL separately.The LCL-VSC mathematical model for unbalanced control is established under unbalanced grid condition. The reference current algorithm is given based on the LCL-VSC. For different purposes, it can be realized either symmetrical grid-side current or constant DC-side voltage without twice order ripple.Finally, a 15kVA LCL-VSC experimental system is established. The simulation and the experimental result verify the theoretical analysis and the design.