Abstract：The power amplifier constitutes the critical actuating element in active magnetic bearings (AMBs). While elevating input voltage enhances dynamic response characteristics, this approach introduces significant operational challenges. High-voltage operation induces excessive voltage stress on power switching devices, escalates switching losses, and generates substantial electromagnetic interference (EMI) during circuit operation. A fundamental constraint of conventional three-level configurations is their fixed input voltage maintenance, regardless of tracking error magnitude, which leads to aggravated circuit stress conditions. Furthermore, the power switching devices exhibit particular vulnerability under combined high-voltage, high-current, and high-frequency switching conditions, potentially compromising AMBs' operational safety. Switching device failures generally manifest as either open-circuit or short-circuit modes. Compared to open-circuit failures, short-circuit faults present more severe consequences. Effective fault-tolerant strategies must therefore integrate rapid detection mechanisms with responsive protection measures to mitigate overcurrent risks in load coils during short-circuit events. Firstly, this paper introduces the operational principle of a five-level power amplifier topology, guided by the design philosophy of “high voltage for large errors, low voltage for small errors”. The analysis demonstrates that under high dynamic response requirements, the five-level switching power amplifier circuit operates at a high voltage level while maintaining dynamic response capabilities equivalent to those of three-level ones. Conversely, under low dynamic response requirements, the five-level switching power amplifier circuit switches to a low-voltage level, where its input voltage is reduced to half that of conventional amplifiers. This voltage reduction halves the voltage stress on power electronic devices. Accordingly, voltage breakdown risks are mitigated, and the switching loss and electromagnetic noise in the circuit are reduced. Furthermore, a control strategy is presented for five-level operation, defining three distinct operational modes: low-voltage, transitional, and high-voltage. Through analytical derivation, we establish the critical current frequency governing inter-mode transitions and map the operating modes of five-level switching amplifiers across different AMBs speed ranges. This paper then presents a fault-tolerant strategy for switch device short-circuit conditions in respective bridge arms of a five-level switching power amplifier topology. Furthermore, a diagnostic method is proposed through real-time monitoring of current flow in bridge arm freewheeling diodes and verification against predefined logical relationships with switching states. The implemented fault-tolerant strategy allows for a seamless transition between normal and fault-tolerant operation modes through controller parameter adjustments, completing mode switching within a single switching cycle. Finally, the experimental results verify that the five-level switching power amplifier successfully tracks reference currents at different frequencies and maintains preset operational states. Compared with three-level switching power amplifiers, the five-level configuration demonstrates superior operational performance. When short-circuit faults occur in switching devices, the five-level switching power amplifier rapidly transitions to fault-tolerant states while maintaining continuous operation.
刘紫怡, 李翁衡, 祝长生. 具有短路容错能力的五电平主动电磁轴承开关功率放大器[J]. 电工技术学报, 2026, 41(4): 1195-1209.
Liu Ziyi, Li Wengheng, Zhu Changsheng. Five-Level Switching Power Amplifier for Active Magnetic Bearings with Short-Circuit Fault-Tolerance. Transactions of China Electrotechnical Society, 2026, 41(4): 1195-1209.
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