Typically, single-phase asynchronous motors are most commonly used in household appliances, relying on capacitors or resistors for phase splitting. These motors often operate in a short-term, repetitive on/off cycle, such as in air conditioners and refrigerators. This inevitably leads to frequent starting, high noise levels, shorter motor lifespan, poor temperature stability, and high energy consumption. The application of variable frequency speed control technology not only brings increased functionality and improved performance to these appliances, but also offers significant energy savings and noise reduction, while simultaneously extending the overall lifespan compared to traditional appliances.
There are many methods for controlling the speed of asynchronous motors, such as pole-changing speed control, slip-ratio speed control, and variable frequency speed control. The first two methods have high slip losses and low efficiency, and have certain limitations in terms of motor characteristics. Variable frequency speed control achieves motor speed control by changing the frequency of the stator power supply to alter the synchronous frequency. Throughout the entire speed control process, a limited slip ratio can be maintained from high speed to low speed, resulting in high efficiency, a wide speed range (10-100%), and high precision, with energy savings of 20-30%.
There are two methods of variable frequency speed control: one is AC-DC-AC conversion, suitable for high-speed, low-capacity motors; the other is AC-AC conversion, suitable for low-speed, high-capacity drive systems.
Variable frequency air conditioners can be classified into 3A and 3D variable frequency air conditioners based on the type of their indoor fan motor, outdoor fan, and compressor. Variable frequency air conditioners where the indoor and outdoor fans and the variable frequency compressor are all AC (alternating current) are generally called 3A variable frequency air conditioners; while those where the indoor and outdoor fans and the variable frequency compressor are all three-phase brushless DC motors (DCBLM) are generally called 3D variable frequency air conditioners. The latter is significantly more expensive than the former; the material cost alone is nearly 300 yuan higher than a 3A variable frequency air conditioner of the same power, and the development is more difficult, with higher complexity in the coordination of the air conditioning system and the controller.