Sensor-free control system of permanent magnet synchronous motor

The invention discloses a sensor-free control system of a permanent magnet synchronous motor. The control system comprises a multi-way isolated power supply, a controller, a first photoelectric isolation element, an inverter and the permanent magnet synchronous motor, which are sequentially connected, wherein, the multi-way isolated power supply and the inverter are both supplied by the high voltage electricity; and the control system further comprises a protective circuit connected with both the inverter and the controller, a rotor position detection circuit connected with the permanent magnet synchronous motor, and a second photoelectric isolation element connected with both the rotor position detection circuit and the controller. The sensor-free control system utilizes the rotor position detection circuit rather than a traditional speed sensor to detect the current and voltage of a stator and calculate the position and speed of the rotor, thereby realizing controlling and greatly reducing cost.