Suitability Analysis of Inverter Topologies and Their Modulation Strategies for Two-Phase Bearingless Motors

Different from the traditional three-phase form of the bearingless motor (BM), the two-phase form of BM has unique advantages in sensor assembly and signal interpretation. As the current link directly determines the torque/levitation characteristics, the selection of the inverter topology and the design of the modulation scheme are the keys to determining the current control performance of BM. The available inverter topologies (full bridge topology, staggered parallel topology and split capacitor topology) and their corresponding modulation schemes for two-phase BM, which are sinusoidal pulse width modulation (SPWM) and space vector pulse width modulation (SVPWM), are compared and analyzed in detail from the perspective of four dimensions, i.e., system cost, control performance, voltage utilization, and algorithm complexity. The staggered parallel topology is selected as the inverter topology for two-phase BM in this paper for its low system cost and high control performance, and an improved SPWM scheme, which increases the voltage utilization from 50% to 71%, is proposed. It is worth mentioning that the idea of carrier phase shifting is applied to the two-phase BM drive system in this paper to improve the system efficiency further. Finally, based on a set of 4000rpm/100W two-phase BM prototype platform, the inverter topology and its modulation scheme explored in this paper are given a complete comparison of simulation and experimental quantitative data to demonstrate the effectiveness and superiority of the proposed improved two-phase BM SPWM drive scheme based on the staggered parallel topology.