Reactive Power Control of Hybrid Multi-Terminal HVDC Systems Considering the Interaction Between the AC Network and Multiple LCCs

A strategy was developed for reactive power control of the line-commutated converters (LCCs) of hybrid multi-terminal high-voltage direct current (MT-HVDC) systems. In the conventional method, the reactive power outputs of hybrid MT-HVDC systems are regulated discontinuously by only using switched shunt devices (SSDs). If continuous reactive power compensation is required, additional devices, including a static compensator (STATCOM), are essential, but these are costly solution. However, in the proposed method, the reactive power outputs of hybrid MT-HVDC systems can be continuously regulated without any additional compensating device by adjusting DC voltage and using SSDs. Therefore, with the proposed method, an HVDC operator can control reactive power outputs and reduce costs, simultaneously. To achieve our objectives, we first describe how to determine the DC voltage set points that regulate the reactive power outputs of multiple grid-connected LCCs, and then realize coordinated control using SSDs. The utility of the method is demonstrated by case studies simulated using PSCAD and MATLAB.