Journal of Zhejiang University SCIENCE C

, Volume 14, Issue 8, pp 600–611 | Cite as

Self-sensing active magnetic bearing using real-time duty cycle

  • Ming Tang
  • Chang-sheng Zhu
  • Jie Yu


In a self-sensing active magnetic bearing (AMB) system driven by pulse width modulation (PWM) switching power amplifiers, the rotor position information can be extracted from coil current and voltage signals by a specific signal demodulation process. In this study, to reduce the complexity of hardware, the coil voltage signal was not filtered but measured in the form of a duty cycle by the eCAP port of DSP (TMS320F28335). A mathematical model was established to provide the relationship between rotor position, current ripple, and duty cycle. Theoretical analysis of the amplitude-frequency characteristic of the coil current at the switching frequency was presented using Fourier series, Jacobi-Anger identity, and Bessel function. Experimental results showed that the time-varying duty cycle causes infinite side frequencies around the switching frequency. The side frequency interval depends on the varying frequency of the duty cycle. Rotor position can be calculated by measuring the duty cycle and demodulating the coil current ripple. With this self-sensing strategy, the rotor system supported by AMBs can steadily rotate at a speed of 3000 r/min.

Key words

Self-sensing Active magnetic bearing (AMB) Frequency spectrum characteristic 

CLC number



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Copyright information

© Journal of Zhejiang University Science Editorial Office and Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  1. 1.State Grid Sichuan Electric Power Research InstituteChengduChina
  2. 2.College of Electrical EngineeringZhejiang UniversityHangzhouChina

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