Fault-tolerant control of modular multilevel converter using cold-reserve scheme and hot-reserve scheme
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Date
2019-06
Authors
Oi, Ching Xien
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Abstract
Modular multilevel converter (MMC) has become the most attractive topology in the high-voltage and high-power application. Presence of the large number of sub-modules (SMs) in the MMC increases the likelihood of the fault occurrence. A faulty SM can essentially lead to expensive downtime. In order to cope with the SM fault of MMC, a faulttolerant control with redundancy backup is used. In this thesis, two different types of faulttolerant control strategies are studied, which are cold-reserve scheme and hot-reserve scheme. A single-phase MMC model is constructed in MATLAB Simulink. The MMC model is integrated with cold-reserve scheme and hot-reserve scheme. A situation that one SM fault due to short circuit is set at a fixed time, t = 0.021s. Simulation is carried out to observe the performances of both fault-tolerant controls. The simulation shows that hotreserve scheme has better performance compared to cold-reserve scheme as there is no surge present in the output current and output voltage. Besides that, hot-reserve scheme has shorter response time (t=0.669ms) compared to cold-reserve scheme (t=1ms). The transient waveform quality is better in hot-reserve scheme compared to cold-reserve scheme. Therefore, it is concluded that hot-reserve scheme possesses better performance compared to cold-reserve scheme.