Unbalanced control of grid-side converter based on DSOGI-PLL

Due to the nonlinear load and transient power grid failure (such as phase jumps, voltage sags and swells, frequency changes, harmonic pollutions), three-phase voltage is asymmetry and in distortion state. In this case, grid-side converter control system will lose control of the power signal, causing protection system tripping or damaged. Thus, we need to design a control strategy to ensure reliable and safe operation under abnormal power grid condition, which can help to low voltage ride through and grid voltage frequency support. This paper designed the current control system containing unbalanced algorithm. On the basis of the traditional dq control, this paper added the negative sequence current compensation part and solved the oscillation problem of injected active power and reactive power. This paper also presented a design method of PI regulator in current control loop. The new controller needs to deal with positive and negative sequence components respectively, so we designed the double second-order generalized integrator phase-locked loop (DSOGI-SPLL). The small signal model of phase-locked loop and the parameter setting method were given. In the end, we compared the old and new methods on the performance in balanced and imbalanced power grid. It was proved that the new control strategy can meet the target.