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 (CMV) 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 paper, we propose a zero common-mode voltage (ZCMV) modulation and control strategy combined with an active neutral-point (NP) 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 (NPC) topology, which is used to control a single-plane, two-degree-of-freedom AMB and can be readily extended to multi-DOF magnetic bearing systems. The ZCMV modulation strategy significantly suppresses common-mode 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.