Drive circuit for a permanent magnet motor

A drive circuit for an electric motor adapted to be connected in series with an AC power source between a first node and a second node, the drive circuit comprising:

• a controllable bidirectional AC switch;
• an AC-DC conversion circuit connected in parallel with the controllable bidirectional AC switch between the first node and the second node, wherein the first node and second node are short circuited when the controllable bidirectional AC switch is conductive and there is no current flowing through the AC-DC conversion circuit when the controllable bidirectional AC switch is conductive;
• a position sensor configured to detect a position of a rotor of the motor;
• and a switch control circuit configured to control the controllable bidirectional AC switch to be conductive or non-conductive in a preset way based on the position of the rotor and a polarity of the AC power source.

A drive circuit for a synchronous motor comprising a stator and a rotor rotatable relative to the stator, the stator comprising a stator core and a stator winding wound on the stator core and adapted to be connected in series with an AC power source between a first node and a second node, the rotor comprising at least one permanent magnet and operating at a constant rotational speed of 60 f/p during a steady state phase of the motor, where f is a frequency of the AC power supply and p is the number of pole pairs of the rotor, wherein the drive circuit comprises:

• a controllable bidirectional AC switch;
• an AC-DC conversion circuit connected in parallel with the controllable bidirectional AC switch between the first node and the second node, wherein the first node and second node are short circuited when the controllable bidirectional AC switch is conductive and there is no current flowing through the AC-DC conversion circuit in the case the controllable bidirectional AC switch is conductive;
• a position sensor configured to detect a position of the rotor;
• and a switch control circuit configured to control the controllable bidirectional AC switch to be conductive or non-conductive in a preset way based on the position of the rotor and a polarity of the AC power source such that the stator winding drives the rotor to rotate only in a predetermined direction during a starting phase of the motor.