Optimized Nonlinear High-Frequency Injection for Sensorless PMSM in Low-Speed Industrial Servo Systems

The paper describes an improved nonlinear high frequency injection (HFI) sensorless permanent magnet synchronous motor (PMSM) control technique in low speed industrial servo applications. The solutions to these underlying issues of the company-proposed technique include reducing position estimation errors and signal-to-noise ratio degradation at low speeds due to adaptive signal processing and computationally more efficient demodulation algorithms. This is formulated into a non-linear injection strategy with amplitude modulation with respect to the operating conditions in an attempt to reduce torque-ripple without compromising it robust position tracking. A PMSM is test-verified to show improved results, with position estimation error cut down to ±0.8 at 10 rpm or a 65 percent improvement as compared to traditional HFI techniques. The intended design has a stable operation even at 2 rpm with torque ripple of less than 3%.