Abstract
MMC-HVdc transmission system has become the mainstream of power construction and plays an increasingly important role in the power system. However, the dc line fault results in shutting down of the converters, which can greatly endanger the security of the power grid. So it is essential to find a fast fault identification strategy for dc line protection technology. Besides, the existing backup protection scheme has the problems of long delay and strict communication synchronization requirements. Therefore, this paper proposes a novel protection scheme for mmc-HVdc transmission lines based on the Cross-Entropy of charge. The fault current oscillation phenomenon and fault current frequency characteristics of mmc-HVdc transmission lines are analyzed first. Secondly, this paper proposes a method to filter out distributed capacitance current by charge and eliminate the current oscillation. Finally, the difference of the charge during different faults (internal fault and external fault) is analyzed, and the Cross-Entropy is introduced to express this difference. Hence, this paper proposes a new principle of identifying faults using the Cross-Entropy of the charge. Simulation results show that the protection principle is not affected by the distributed capacitive current and does not require strict communication synchronization. It has excellent performance in intolerance to fault resistance and noise interference and can be used as backup protection for the mmc-HVdc transmission system.
Highlights
MMC-HVdc has great advantages in solving new energy grid connections, central load power supply, and regional grid interconnection
This paper proposes a protection principle based on the time domain, which completely solves the problem of distributed capacitive current, and uses the full current signal to ensure the reliability of the protection
In this paper, a novel protection scheme based on the CrossEntropy of charge is proposed to meet both the speed and selectivity requirement of mmc-HVdc line protection
Summary
MMC-HVdc has great advantages in solving new energy grid connections, central load power supply, and regional grid interconnection. 3) The protection principle based on the frequency domain relies on extracting the information on a single frequency to solve the distributed capacitance current, but at the same time, it brings the problem of low reliability. This paper proposes a protection principle based on the time domain, which completely solves the problem of distributed capacitive current, and uses the full current signal to ensure the reliability of the protection. FAULT IDENTIFICATION PRINCIPLE BASED ON CURRENT INTEGRAL CROSS-ENTROPY This section first introduces the theoretical derivation of charge filtering distributed capacitor current. The charge is referred to as ‘current integral’ in the following
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