Study Of Inverter Control Strategy To Improve The Stability Of HVDC/AC System Connected To Weak AC System

A notable advantage of DC transmission systems is that it is highly controllable. This is very helpful for improving the stability of systems. HVDC system connected to weak AC system is vulnerable to numerous operating difficulties, such as the high-magnitude AC voltage oscillations and the difficulties in recovery from disturbances. The traditional method is to equip reactive power compensators such as SC or SVC at the inverter side, which will increase the operating cost greatly. Moreover, the adjusting performance of reactive compensators is not so satisfactory under transient conditions.Based on the conventional control scheme, this paper applies a new supplementary b controller, with its feedback signals reflecting the abnormal system conditions, to modulate the inverter reactive consumption and improve the stability of weak AC/DC system. H section of the additional controller makes its operation more robust. This paper considers two controllers with different feedback signals ?the AC current phase angle of converter transformer and the AC voltage magnitude of inverter bus, respectively.PSCAD/EMTDC simulation software is used for the controller testing. The test models used for the analysis are the CIGRE HVDC benchmark systems with different SCR at the inverter side. Through the testing, the parameters of the two controllers are determined. The simulating results under faulty conditions show that the proposed controllers are effective forimproving system transient stability and they make the HVDC system can operate with very weak receiving end AC system .