A Capacity Optimized LC-Filter CHB STATCOM and Its Control Method for the Unbalanced Compensation

Cascaded H-bridge static synchronous compensator (STATCOM) with delta-connected configuration is an effective solution to compensate reactive current and negative-sequence current. In this paper, a capacity optimized LC-filter CHB STATCOM and its comprehensive control method are proposed. Firstly, operating principle of CHB STATCOM for unbalanced compensation is introduced. On this basis, the working modes of L-filter STATCOM and LC-filter STATCOMs are derived according to the vector analysis. At the same time, the mathematical models of three kinds of STATCOMs are carried out to quantitatively analyze the voltage stress. Comparison results demonstrate that proposed LC-filer CHB STATCOM has advantages of lower DC-link voltage and rated power. In order to eliminate the DC component of phase-cluster power in unbalanced compensation stage, two methods of circulating current injection are proposed and the analytical expressions of circulating currents are derived. Moreover, the comprehensive control methods for LC-filter CHB STATCOM are proposed, where AC or DC circulating current can be adopted and controlled for cluster voltage balance for negative-sequence compensation. Finally, the results of experiment effectively verify the proposed structure and control method.