Abstract
Multi-terminal voltage sourced converter (VSC)-based high voltage direct current (HVDC) system composes of a number of VSCs connected to an HVDC grid (or dc grid). The dc grid is often configured by cable interconnections between converter stations, thus imposing resonance issues affecting harmonic interaction in the system. Based on the harmonic transfer characteristics of VSC and HVDC systems, the appearance and the interaction of inter-harmonics in the multi-terminal VSC-based HVDC system are analyzed. Simulation models are built and implemented using SimPowerSystems in MATLAB. The simulation results show that, a series of inter-harmonics are produced and tend to be dominant in low-frequency range. Especially in the dc grid, the inter-harmonic transfer can be magnified due to inter-harmonic resonances. The complex resonance issues in the dc grid are investigated in combination with interaction through the VSC, it is beneficial to harmonic filter designs as well as other harmonic mitigation methods.
Highlights
The voltage sourced converter (VSC)-based high voltage direct current (HVDC) systems have been utilized in power system for many years since the first test in 1997
When the point of common coupling (PCC) of the ac system 1 is subjected to single phase-to-ground fault, the HVDC system will operate under unbalanced conditions, and VSC is quite sensitive to the negative-sequence component in the ac voltage [13]
The inter-harmonics in multi-terminal VSC-based HVDC systems are originated from the characteristic of each converter in asynchronous connection, the distorting in the connected ac systems, and the unsymmetrical fault or unbalance
Summary
The VSC-based HVDC systems have been utilized in power system for many years since the first test in 1997. For emerging applications involving the integration of large scale wind power plants, the multi-terminal VSCbased HVDC systems win over the conventional LCCbased HVDC systems This is due to the VSC-based HVDC has characteristics as independent control of active and reactive power, possibility to supply passive weak networks and black-start capability, no commutation failure, and reverse power transmission without reversing voltage polarity [1,2,3]. A background harmonic in one end ac system will be transferred to produce a series of inter-harmonics in the other end ac systems with different fundamental frequencies. The magnification of these interharmonics strongly depends on the operating configurations of the dc grid. The power contribution of all connected ac systems has certain influence on the harmonic interaction in the entire system
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