How to design your refrigerator motor drive

Motors are everywhere in our daily lives. If you look inside the ordinary home appliances, such as refrigerators, you'll find advanced applications such as stepper and brushless DC (BLDC) motors, throttles and BLDC fans. These applications play an important role in the efficient operation of the refrigerator.

Throttle valve

The throttle valve is a small throttle that controls the air flow from the refrigerator to the refrigerator. It is usually located on the top of the refrigerator or near the top of the rear panel. The throttle valve is controlled by a thermostat that triggers its opening or closing according to the temperature of the air in the refrigerator. Inside the throttle valve is a permanent magnet (PM) stepper motor and gearbox. Let's take a look at a throttle valve (as an engineer, this is my favorite part!).

As you can see, the small PM stepper motor drives the gearbox and opens or closes the throttle. This stepper motor has a drive voltage of 12V and usually does not require current regulation. So, how do you distinguish whether the stepper motor is driven by voltage or current? Just measure the DC resistance of the motor phase. If the resistance is about 30 ohms to hundreds of ohms, it should be voltage driven. If the resistance is below 20 ohms, in most cases below 10 ohms, it is most likely driven by current. Typically, voltage-driven motors are common in small-power PM stepper motors and unipolar stepper motors with very low drive currents. In this case, the resistance loss of I2 x R is not too great. The current drive type can be found in most medium and high power hybrid stepper motors.

Ok, let's go back to the throttle. The throttle valve I disassembled has a PM voltage driven stepper motor with a resistance of approximately 400 ohms. Let's find the most suitable drive for it. The DRV8848 is very suitable. The 4V to 18V drive voltage range, dual H-bridge integration, pulse width modulation (PWM) control interface, up to 2A operating current, and full protection make it an ideal choice for driving throttles. If you want to learn more about driving logic, look at the reference design for the complete solution, and you can choose the hardware and software for it.

As you can see in the picture below, the refrigerator fan module circulates the cold air in the refrigerator and evenly distributes it in every corner of the refrigerator to prevent frosting, which greatly improves the performance of the refrigerator.

This fan module includes a single or three phase brushless motor. At present, we are more common in three-phase BLDC because these motors are smaller, work quieter, and operate efficiently for long periods of time. In this application, you will see a Hall sensor or sensorless control. Thanks to TI's three-phase sensorless sinusoidal motor driver, the DRV10983, we can achieve state-of-the-art 180° brushless BLDC control without entanglement with control algorithms.

We classify the DRV10983 as a fan drive for efficient and super quiet operation in the reference design. Since most refrigerator manufacturers now use PWM power to power the fan module and change its speed, we use FG feedback and PWM power regulation to apply closed-loop speed control, which minimizes hardware changes to existing solutions. With closed loop speed control, we can maintain the required speed value regardless of motor parameter changes, power supply variations, mechanical wear or service life. In this video, learn how machine operation benefits from speed control.

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