Downwind starting method for permanent magnet synchronous motor without back electromotive force sampling circuit

A downwind starting method for a permanent magnet synchronous motor without a back electromotive force sampling circuit, a permanent magnet synchronous motor comprising a microprocessor, an inverter circuit, a permanent magnet rotor, and a stator assembly, the stator assembly comprising a stator core and a plurality of phase windings, the inverter circuit comprising a plurality of bridge arms, each bridge arm comprising an upper switch transistor and a lower switch transistor, a connection between the upper switch transistor and the lower switch transistor being connected to one end of one of the phase windings, the other ends of the plurality of phase windings being connected, the microprocessor outputting drive signals to control the upper switch transistor and the lower switch transistor of each bridge arm, and the downwind starting method comprising:

• (I) obtaining a starting position of the permanent magnet rotor:
• utilizing a back electromotive force generated by a rotating magnetic field that is generated through downwind rotation of the permanent magnet rotor before starting the permanent magnet synchronous motor cutting the plurality of phase windings of the stator assembly to control a lower switch transistor of one of the phase windings to be turned on while turning off lower switch transistors of the remaining phase windings, detecting whether a current is generated, and recording time when the current is generated;
• repeating the above operations until time when a current is generated for each phase winding is obtained;
• summing the time when the current is generated for each phase winding to obtain an electrical cycle, and calculating an electrical frequency of the motor by using the electrical cycle;
• and utilizing the electrical frequency and the time when the current is generated for each phase winding to calculate a corresponding position angle of the permanent magnet rotor respectively as a starting position of the motor;
• and
• (II) starting the motor in a certain control manner.