Abstract
A modular multilevel matrix converter (MMMxC) has nine arms and each of the arms is composed of H-bridge cells connected in cascade. It can be applied to high voltage ac-ac converters for variable speed wind turbines and motor drives. In this paper, employment of a hierarchical control system for the MMMxC is first considered to distribute computational burden among processors and simplify hardware implementation. The influence of the time delay due to communication of controllers on performance is investigated by numerical simulation. Second, the control scheme for the operation under a cell failure condition is proposed. In the case that a cell breaks down, the operation is continued not only by shorting the faulty cell with an external mechanical switch but by increasing capacitor voltage of the other cells in the same arm. Moreover, a constraint on output voltage of the arm that has the faulty cell is added to avoid occurrence of short circuit of arms. These changes of control schemes are easily implemented because of employing the control system with the hierarchical structure and a space vector modulation control scheme without circulating current control. The proposed control scheme is verified by simulation.
Published Version
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