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.
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机译:在由脉宽调制(PWM)开关功率放大器驱动的自感应主动磁轴承(AMB)系统中,可以通过特定的信号解调过程从线圈电流和电压信号中提取转子位置信息。在本研究中,为降低硬件的复杂性,未对线圈电压信号进行滤波,而是通过DSP的eCAP端口(TMS320F28335)以占空比的形式对其进行了测量。建立了数学模型以提供转子位置,电流纹波和占空比之间的关系。利用傅里叶级数,雅可比-安杰(Jacobi-Anger)恒等式和贝塞尔函数,对开关频率下线圈电流的幅频特性进行了理论分析。实验结果表明,时变占空比会在开关频率附近产生无限的边沿频率。旁侧频率间隔取决于占空比的变化频率。可以通过测量占空比并解调线圈电流纹波来计算转子位置。通过这种自感应策略,AMB支持的转子系统可以以3000 r / min的速度稳定旋转。
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