Abstract
Conventional position sensorless control methods for a permanent magnet synchronous motor (PMSM) in a low-speed region suffer from some disadvantages such as too much electromagnetic noise, the need for rotor saliency, and so on. On the other hand, a position sensorless method that introduces an induced voltage caused by magnetic saturation (IVMS) has already been reported(14). IVMS can be detected by an open phase of a PMSM using a block commutation drive, and it changes depending on the rotor position. The position sensor-less drive is achieved by detecting the IVMS. This method needs no rotor saliency and or harmonic injection. However, this technique has a disadvantage. Because the IVMS is a very small voltage, it is eliminated by a reversal direction electromotive force (EMF). It is difficult to achieve a reversal rotation drive in a low-speed region. To solve this problem, we introduce a PWM pulse shift to the low-speed region. With this method, both the normal and reversal direction IVMSs can be detected and the bidirectional drive is achieved. We implemented this method by using a 16-bit microcomputer and an FPGA with a 20kHz carrier frequency. Moreover, excellent drive performance in the low-speed region was obtained in the experiments.
