Coordinated Control Strategy of PMSG and Cascaded H-Bridge STATCOM in Dispersed Wind Farm for Suppressing Unbalanced Grid Voltage

This article proposes an unbalanced voltage compensation method for a dispersed wind farm (DWF) by cooperating permanent magnetic synchronous generators (PMSGs) with a star-connected cascaded H-bridges (CHB) static synchronous compensator (STATCOM). The topology of a typical DWF is given and the mathematical models of CHB-STATCOM and PMSG inverter are established to show that the unbalanced grid voltage can be suppressed by controlling their virtual negative-sequence output admittance (NSOA). The relationship between maximum phase voltage and dc voltage corresponding to zero-sequence voltage injection is obtained to quantitatively analyze the negative-sequence current injection ability of the CHB-STATCOM. Moreover, the phase current limit is introduced to address the over-current problem, and a virtual NSOA method for sharing unbalanced voltage is proposed. An allocation coefficient calculation method is also proposed in consideration of both remaining capacity and voltage unbalanced factor (VUF) for different PMSGs. Furthermore, a coordinated control strategy of PMSGs and CHB-STATCOM for unbalanced voltage suppression is proposed. The effectiveness of the proposed coordinated control strategy is verified by simulation on a 50 MW DWF with a +/- 5 MVar star-connected CHB-STATCOM.