Abstract
With the increased use of high voltage direct current (HVDC) systems, line commutated converters (LCC-HVDC) and voltage source converters (VSC-HVDC) tend to feed into AC systems over short electrical distances. The flexible power control of VSC-HVDC systems provides an effective approach to suppress the commutation failure of LCC-HVDC systems. A suppression method, based on a controllable operation region, is proposed in this study to reduce the probability of commutation failure in a hybrid dual-infeed HVDC system. First, the quantitative transient reactive power control requirement of VSC-HVDC inverter that could fulfill the suppression control boundary condition of commutation failure was analyzed. Given the maximum current constraint of the VSC-HVDC inverter and the primary frequency modulation constraint of the sending-end grid, a controllable operation region of the hybrid dual-infeed HVDC system was proposed. Furthermore, a commutation failure suppression control method, based on the controllable operation region, was proposed to mitigate continuous commutation failure. Finally, the validity and accuracy of the proposed method was verified by the simulation of PSCAD/EMTDC. The proposed control method can realize reasonable use of the reactive power control capability of the VSC-HVDC system, which effectively improves immunity to commutation failure of the LCC-HVDC system under grid fault.
Highlights
Line commutated converters for high voltage direct currents (LCC-HVDC) have been widely applied due to their large capacity and low construction costs
Voltage source converters for high voltage direct current (VSC-HVDC) power transmission have been rapidly developed because of their advantages decoupling the control of active and reactive power and no risk of commutation failure
With the increase in DC transmission projects, different types of HVDC systems tend to feed into power grids with short electrical distances
Summary
Line commutated converters for high voltage direct currents (LCC-HVDC) have been widely applied due to their large capacity and low construction costs. In a hybrid dual-infeed HVDC system, owing to active and reactive power decoupling control characteristics, VSC-HVDC systems have the ability to support grid voltage and provide an effective way to mitigate continuous commutation failure. Based on the calculation method of the effective short-circuit ratio (SCR) of the hybrid dual-infeed HVDC system, [13] proposed a VSC-HVDC reactive power control strategy to improve the voltage stability of the AC grid. A commutation failure suppression method of a hybrid dual-infeed HVDC system under grid fault was investigated, and the contribution of the reactive power control capacity of VSC-HVDCs to the mitigation of commutation failure was quantitatively analyzed. The simulation results showed that the proposed control method could improve the control capability of the VSC-HVDC system and effectively improve the suppression capability of continuous commutation failure in hybrid dual-infeed HVDC systems
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