Study on fitting equations of HVDC recovery P-Q characteristics after faults

The large demand of dynamic reactive power for MIDC recovery is a big challenge to voltage stability of the receiving system. Thus, the research on active power (P) and reactive power (Q) characteristics of inverter station in the recovery process of multi-infeed HVDC (MIDC) attracts more and more attention. With the CIGRE HVDC benchmark, this paper studies the P and Q responses under various faults through the electromagnetic transient simulation platform PSCAD/EMTDC. The major factors dominating P-Q behaviors are analyzed. Then, in order to obtain a relative simple and analytical relation between P (or Q) and HVDC control means in recovery for future theoretical stability analysis method, numerical analysis technique is used to establish reasonable fitting equations of V=f(V) and Q=f(P). When considering voltage dependant current order limiter (VDCOL) of HVDC, the VDCOL control equation and P-Q coupling equation is combined into a simplified model of DC recovery. It helps transient stability mechanism analysis of MIDC system in whole, only utilizing the external characteristic of HVDC and avoiding HVDC complex structure and control schemes. The obtained model of power recovery of HVDC is tested with good engineering accuracy shown.