Abstract
This paper studies control strategies for an AC/AC system based on a modular multilevel matrix converter (M3C) when an asymmetric fault occurs in the secondary side ac system. Firstly, the operating principle of M3C is briefly introduced and verified by simulation. Then, based on its mathematical model by double αβ0 transformation, the decoupled control strategies for the primary side and secondary side systems are designed. In view of the asymmetric fault condition of the secondary side system, the positive sequence and negative sequence components of voltages and currents are separated and extracted, and then a proportional resonant controller (PR) is used to regulate the positive and negative sequence currents at the same time to realize decoupled current control in the αβ reference frames. The capacitor voltage balancing control, which consists of an inter-subconverter balancing control and an inner-subconverter balancing control, is realized by adjusting four circulating currents. Finally, the proposed control strategy is validated by simulation in the PSCAD/EMTDC software (Manitoba HVDC Research Center, Canada). The result shows that during the period of the BC-phase short-circuit fault occurring in the secondary side system, the whole system can still operate stably and transmit a certain amount of active power, according to their set values. Furthermore, the capacitor voltages are balanced, with a slight increase during the fault period. The simulation results verify the effectiveness of the proposed control strategy.
Highlights
As a new type of voltage source converter, the modular multilevel converter (MMC) has attracted wide attention and research in both academia and industry since it was proposed by German scholar R.Marquardt in 2001 [1]
An asymmetric fault control strategy for an AC/AC system based on a modular multilevel matrix converter is proposed
A simulation is performed to verify the operational principle of the matrix converter (M3 C) in Figure 1, which the system frequency is 50/3 Hz
Summary
As a new type of voltage source converter, the modular multilevel converter (MMC) has attracted wide attention and research in both academia and industry since it was proposed by German scholar R. Large capacity AC/AC converters are needed in many applications, such as the asynchronous interconnection of different power systems and medium or high voltage motor drives. For these applications, an indirect AC/DC/AC converter with a back-to-back. Whether in motor driving or low frequency AC transmission applications, the power systems often exist in asymmetric operation conditions due to sudden faults, such as single-phase short-circuit faults in the AC system. An asymmetric fault control strategy for an AC/AC system based on a modular multilevel matrix converter is proposed. The simulation results validate that the proposed control strategy can ensure stable of the systems under asymmetric fault conditions
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