Effect of rectifier alpha min limiter on dynamic response of HVDC transmission system

Rectifier Alpha Min Limiter (RAML) is a standard configuration in the control system of modern HVDC systems. Considering the fact that RAML could be a double-edged sword to the satisfying operation of the AC/DC hybrid power system, this paper makes a detailed assessment of RAML. First, the RAML control logic is introduced. Secondly, an HVDC system model which has the same control logic as that used in a real HVDC system is built in PSCAD/EMTDC, based on this model, the effect of RAML on the dynamic responses of the rectifier side is studied. Finally, the sensitivity of the dynamic responses of the rectifier side to the parameters of RAML is investigated. The analysis results indicate that theoretically, by increasing RAML_MAX or U
set
, or by decreasing RAML_DEC, the restoring speed of the DC voltage, DC current and the active power transferred by the HVDC system will be slowed down.