Position sensor-free control technology for four-phase doubly salient motor

The invention discloses a position sensor-free control method for a four-phase doubly salient motor. During electric running of the four-phase doubly salient motor, counter potential vectors differ from each other by 90 degrees in sequence in a d-q coordinate system. The control method comprises the following steps of: partitioning N (N is a natural number of more than 2) rotating speed ranges for designing wave filters of corresponding cut-off frequencies, only acquiring the terminal voltages of any two adjacent phases, entering a subtractor for removing direct current bias, judging the rotating speed of a motor according to a potential zero crossing point at a certain moment, deciding to enter a wave filter of a certain cut-off frequency through the rotating speed ranges, and acquiring the waveform of potential passing through the wave filter by using a DSP (Digital Signal Processor); establishing a phase shift angle comparison table of a wave filter which corresponds to a certain range specific to different rotating speeds in the range for performing DSP inquiry and corresponding accurate phase shift; and obtaining a practical phase change position through a zero crossing comparator, performing DSP computation, and outputting a driving signal to a switch tube by using an FPGA (Field Programmable Gate Array) to complete phase change. The four-phase doubly salient motor can work in a wide rotating speed range.