Steady-State Operating Area Analysis and Full Unit-Circle Realization for Current Source Converter

Current source converter (CSC) with dc fault ride-through capability and low-cost advantages, is attracting lots of attention in high-voltage direct current (HVDC) and renewable energy conversion fields. The steady-state operating area (SSOA) of voltage source converter (VSC) should be designed to achieve the full unit-circle in some utility applications. It's based on proper design of main parameters. But in existing studies on CSC, its main parameters are designed mostly based on unit power factor operation, without considering the full unit-circle realization of SSOA. To fill this gap, first the ranges of key parameters are summarized and then used to derive analytical expressions of SSOA constraints in per unit system for CSC. Second, the conditions for main parameters to realize the full unit-circle SSOA are investigated, revealing the L-C filter parameters' effects on the feasible domain of the rated ac voltage. Finally, while the full unit-circle conditions are satisfied, the minimum capacitor voltage is chosen as the optimization objective in the parameters design. Then the optimized parameters in typical HVDC applications are acquired. It's found that the rated ac voltage designed is relatively high for practical applications, indicating further tradeoffs between full unit-circle SSOA and system cost.