Abstract
This paper proposes a generic analysis framework for a grid supporting modular multilevel converter (MMC)-high voltage DC (HVDC) in a multi-infeed of line commutated converter (LCC) and MMC (MILM) system. MMC-HVDC can support the grid by compensating for the exact reactive power consumptions within the MMC-HVDC system and the varying power system conditions in the MILM system. Maximum active/reactive power capability (MPQC) curve and PQ loading curve comparison process is introduced to properly design a grid supporting MMC-HVDC. While the MPQC curve presents the maximum PQ range of the MMC-HVDC system based on the submodule capacitance value and the modulation index, the PQ loading curve presents the reactive power requirement from the power system that MMC-HVDC needs to compensate. Finally, the comparison of these two curves yields the proper value of submodule capacitance and the modulation index for sufficiently supporting the MILM system. The proposed framework is validated with detailed PSCAD/EMTDC simulation; it demonstrated that it could be applied to various power system conditions.
Highlights
The line-commutated converter (LCC)-high voltage DC (HVDC) has long been adopted in the power grids and demonstrated to be the preferred solution for several different applications [1,2,3,4,5]
The modular multilevel converter (MMC)-HVDC is considered to be adequately designed with sufficient energy to deliver QMMC to fully support the AC/DC interaction in LCC-HVDC, reactive power consumptions within MMC-HVDC, and power system if the MPQC curve is larger than the PQ loading curve at the point of required active power
Loading curve conveniently indicates the proper value of submodule capacitance and modulation index of MMC-HVDC system, allowing MMC-HVDC to support sufficient reactive power to the MILM system to compensate for reactive power consumptions
Summary
The line-commutated converter (LCC)-high voltage DC (HVDC) has long been adopted in the power grids and demonstrated to be the preferred solution for several different applications [1,2,3,4,5]. The MMC-HVDC should be designed based on the actual reactive power requirements, i.e., reactive power consumptions within the MMC-HVDC system for a set of component selections and the feasible grid operating conditions as follows: (1) different values of arm inductance (Larm ) and transformer leakage impedance (xtr ) determined by manufacturers, (2) variation in system strength or short circuit capacity (SCC), (3) variation in angle spread between MILM terminal and power system, (4) power variation in LCC-HVDC, and (5) maintaining voltage at point of common coupling (PCC) (VPCC ) to 1 per unit (pu). This paper suggests a generic analysis framework to determine the exact maximum active/reactive power capability (MPQC) of MMC-HVDC by accurately calculating exact reactive power consumptions within the MILM system through PQ loading analysis. The proposed framework determines the required submodule capacitance (Csm ) and modulation index (m) of MMC-HVDC by a simple comparison of the MPQC and PQ loading curves
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