Fan Drive Starting into Naturally Rotating Load by Sinusoidal Sensorless Permanent Magnet Motor Control

Abstract

A permanent magnet (PM) motor is a primary motor of choice for small fan motor drive applications. A traditional fan drive based on a permanent magnet motor uses position feedback sensors such as Hall effect sensors. Recently PM motor drive with sinusoidal current and no position sensor has been demanded for many applications including air conditioner outdoor unit fan control. The elimination of sensors is required due to the increased reliability demand and low cost requirement for a drive. Some fan and pump applications require that the drive has to start into naturally forward rotating load without stopping the load first. A fan used in the air conditioner outdoor unit, for example, is one of these applications. A fan needs to be started at any naturally rotating forward speed or from standstill and brought to the desired speed. When it naturally rotates in reverse direction, the drive must transition from reverse to forward rotation in a drive system without regeneration capability. With the traditional fan drive, which includes a Hall sensor to detect the rotor position of PM motor, this is a relatively simple task since excitation angle and speed of the controller at startup can be synchronized to the angle and speed at which the fan naturally rotates. In case of the drive without the position sensor, this task is more elaborate due to the fact that speed reversal is required without position sensing.