FOC control technology that simplifies BLDC motor design

From small vibration motors in mobile phones to more complex motors used in domestic washing machines and air conditioners, motors have become everyday devices in the consumer sector. The motor is also an important part of the industrial field and is widely used in many applications, such as driving fans, pumps and Other mechanical equipment. The energy consumption of these motors is very large: research shows that in China alone, motors consume 60% to 70% of total industrial energy, and fans and pumps consume nearly four percent of China's overall power consumption. One of the points. Although this number may not be as high in other countries, reducing the energy consumption of motors in electronic systems has become a priority in the world.

Traditional AC (AC) motors have been widely used for more than a century. AC motors are the simplest induction motors, but they waste a lot of energy. This is because the AC motor only outputs a constant speed and cannot be adapted to changes in operating conditions. There are now some simple ways to adjust the speed of an AC motor (for example, a standard home fan that offers three speed options), but these methods have a limited range of applications and are difficult to transfer to more complex systems.

But for a direct current (DC) motor, you can change and control the speed by changing the voltage to speed up or slow down the work according to your application needs. This saves a lot of energy because the motor can be operated according to the required conditions. In general, DC motors are more efficient than AC motors.

Figure 1: Replacing a traditional AC motor with a smaller, more efficient BLDC motor saves energy and reduces costs, but the algorithms required for BLDC control are so complex that many designers are reluctant to convert. A dedicated IC specifically designed for BLDC motor control makes this job easier.

Advantages of BLDC motors

The DC motor can be designed as a brush motor or a brushless motor. Brushless DC (BLDC) motors are often the best choice for most applications. Such motors are more reliable and quieter, produce less electromagnetic radiation, and are safer because they eliminate sparks caused by brushes and commutators. BLDC motors are smaller and more efficient, which means they need less energy.

The BLDC motor operates at a lower temperature than the AC motor, and its more efficient design results in less heat generated by its internal components. This not only increases the service life of the bearing system, but also increases the reliability of the electrical system and the fan.

In addition, the BLDC motor has a higher power density than the AC motor. For the same energy output, the DC motor is smaller in size and weight than the AC motor. This makes the transport and installation of BLDC motors easier and less expensive.

However, the trouble with using a BLDC motor is that the system requires more sophisticated electronics to manage the motor. Motor control has always been a focus area for electronics engineers, and many developers cannot easily design the necessary control circuits due to lack of experience or expertise. The development of BLDC motors requires additional time and technical support, which means longer development cycles and higher system costs, making it more difficult for system manufacturers to transition from familiar AC motors to BLDC motors.

However, for more and more manufacturers, the complexity of using BLDC motors will not be offset by the increased demand for more energy efficient appliances. According to the 2011 IMS survey, approximately 40% of air conditioners in China use variable frequency control BLDC motors. This situation is on the rise and, to a certain extent, thanks to dedicated circuits designed for BLDC motor control.

Sensorless magnetic field steering control technology

The conventional method for controlling a BLDC motor employs a six-step process of driving the stator, thereby generating pulsations in the generated torque. The so-called "six-step square wave" process uses a Hall effect sensor to detect the permanent magnet position in the BLDC motor.

The six-step process is relatively simple, but is prone to noise and is not sufficiently responsive for more advanced applications that need to quickly change the motor speed based on changes in conditions. In the case of a washing machine, the load varies depending on the selected washing cycle and also varies throughout the cycle. In drum type washing machines, this situation is more complicated, and gravity affects the motor when the clothes are rotated to the top of the drum.

In these cases, a more advanced algorithm is needed. Magnetic Field Oriented Control (FOC) provides the response time required for fast speed changes and has become the motor control method of choice for today's more advanced energy-efficient home appliances.

There are several ways to implement FOC. One method is to use a sensor (similar to the six-step square wave process method), but the sensor is more difficult to install and maintain, especially if the application involves complex harnesses or when the motor is exposed to water. A simpler, more cost-effective way to achieve FOC is to cancel the sensor. Sensorless FOC involves a constant rotor magnetic field generated by a permanent magnet on the rotor and is a very effective control method.

The FOC method allows the motor to run smoothly over the full speed range, producing maximum torque at zero speed and rapid acceleration and deceleration. In fact, due to the small size, low cost, and low power consumption of the motor, the many advantages of sensorless FOC make it a popular choice for applications that require less performance.

Battery charging stations may be installed anywhere within the system where the production process allows the AGV to stop (staging areas, turn arounds, loading stops etc.).

A battery charging contact consists of a base plate, which is installed on the floor or laterally at a bracket adjacent of the AGV runway, and a current collector which is installed on the vehicle.

A Battery Charger supplies current to the base plate. Once the AGV is in charging position and the collector has made contact with the base plate, the AGV computer turns on the current.

The base plate has chamfered entry/exit ramps to facilitate smooth drive-on/drive-off of the spring loaded collector. 

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