Zero Common-Mode Voltage Modulation Strategy for Three-Level Half-Bridge Neutral-Point-Clamped Topology Applied to Active Magnetic Bearings

Active magnetic bearing (AMB) systems serve as a key enabling technology for high-speed rotating machinery. As power ratings continue to rise, the dc-link voltage, phase current, and physical dimensions of the power converter and cabling also increase, which results in larger common-mode voltage swings and parasitic capacitive currents. Consequently, power–signal coupling issues, especially common-mode electromagnetic interference (CM EMI), become more severe and have attracted growing research attention in practical applications. In this article, we propose a zero common-mode voltage (ZCMV) modulation and control strategy combined with an active neutral-point voltage balancing scheme for the power electronic converter of a high-power AMB system. The proposed solution is implemented on a four-leg three-level half-bridge neutral-point-clamped topology, which is used to control a single-plane, two-degree-of-freedom AMB and can be readily extended to multi-degree-of-freedom magnetic bearing systems. The ZCMV modulation strategy significantly suppresses CM EMI and reduces interference with position sensors in the AMB control loop, thereby enhancing position control accuracy. Experimental results from a high-load-capacity AMB motor testbed demonstrate the effectiveness of the proposed approach.