MMC 기반 STATCOM 밸브의 성능시험을 위한 토폴로지

Abstract

This paper proposes a new topology for the performance test of a valve consisting MMC based STATCOM. The conventional valve performance test equipment requires high voltage AC source of several kV rating. However, the DC power source voltage of the proposed test circuit is only several∼tens of volts. Therefore, the size and cost for the performance test equipment can be reduced considerably. The proposed scheme satisfies the requirement of IEC 62927 standard. IEC62927 requires several major tests such as over-load operating duty test, minimum start voltage test, overcurrent turn-off test, and short-circuit current test. Usually, the number of submodules in each arm of a STATCOM is dozens of. In order to test the dozens of submodules at the same time huge power supply is necessary. Fortunately, IEC62927 describes that the minimum number of submodules to be tested should be at least three, which makes the power rating of the power supply for the test small. Therefore, the proposed power supply is designed for the test of three series connected submodules. To obtain a proper voltage and current pattern of the submodule operating characteristics of a 50[MVA] rated MMC-STATCOM is analysed through simulation. The current and voltage waveforms of the proposed topology are almost the same with those of real MMC-STATCOM system. Operating principle including test current control, voltage drop compensation, and capacitor voltage control is described carefully. Design procedure is also described. Simulations are carried out for a valve of 50[MVA] MMC based STATCOM. Experimental results with a scaled-down set up shows the validity of the proposed performance test topology. The major features of the proposed topology is as follows. The current and voltage waveforms resemble those of real MMC-STATCOM. The power rating of the topology can be minimized because the required power is to compensate the loss component of IGBTs and inductor. Cost-effective test circuit can be implemented with reduced size and volume, and low DC voltage. It is expected that the proposed topology can be used in the field of MMC-based high power high voltage system.