Analysis of DC reduction motor manufacturers six points of Brushless DC motor control

Consumers' demand for electricity, reliability, functionality and performance is rising, which has promoted the rapid development of electronic equipment (including lawn mowers, refrigerators, vacuum cleaners, automobiles, etc.). The manufacturer hopes to deliver all the goods. Motion control plays an important role in achieving these commitments. Understand the basic principles to achieve this goal.

01. Different sports types

At present, several motor control topologies are available: brushless direct current (BLDC), stepper and inductance. Brushless motor and permanent magnet synchronous motor (PMSM) are two closely related types of brushless motor.

Brushless motors do not need motor brushes, so they are widely used in many applications. These brushless DC topologies use commutation logic to move the rotor, thereby improving the efficiency and reliability of the motor.

The commutation of brush motor is realized through the brush / commutator interface. The interface will generate friction and arc, which will reduce the performance of the brush over time. This friction generates heat and shortens the service life of the motor.

Compared with brush motor, brushless motor has many advantages. They are more energy-saving, smaller, lighter, quieter, more reliable and more durable. In addition, they provide speed control, which is more suitable for variable speed applications.

02. Understand the types of Brushless DC and permanent magnet synchronous motors

The working principle of Brushless DC motor and permanent magnet synchronous motor is the same as that of synchronous motor. Every time the rotor changes direction, it will continue to rotate with the stator, so the motor can continue to run. However, the stator windings of these two types of DC motors use different geometries, so they can produce different back electromotive force (BEMF) responses. The brushless brushless BEFM is trapezoidal. The back EMF of permanent magnet synchronous motor is sinusoidal, so the coil winding is sinusoidal. For better performance, these electrodes are usually commutated with sine waves.

Brushless DC motor and permanent magnet synchronous motor generate electromotive force through their windings during operation. In any motor, the electromotive force generated by movement is called back electromotive force (BEMF), because the electromotive force induced in the motor is opposite to that of the generator.

03. Description of magnetic field direction control

In order to control the sinusoidal waveform of permanent magnet synchronous motor, a field oriented control (FOC) algorithm is needed. FOC usually improves the efficiency of permanent magnet synchronous motors. Compared with brushless DC ladder controller, the sinusoidal controller of permanent magnet synchronous motor is more complex and expensive. However, the increase in cost also brings some advantages, such as reducing the noise and harmonics in the current waveform. The main advantage of Brushless DC motor is easy to control. Select the motor according to the application requirements.

04. brushless DC and PMSM motors with and without sensors

Brushless DC and PMSM motors can be equipped with or without sensors. Motors with sensors are suitable for applications that require starting the motor under load conditions. These motors use Hall sensors, which are embedded in the electrode stator. The sensor is essentially a switch, and its digital output is equivalent to the polarity of the detected magnetic field. Each stage of the motor requires a separate Hall sensor. Therefore, a three-phase motor requires three Hall sensors. Motors without sensors need to use motors as sensors and use an algorithm to run. They depend on the back EMF information. By sampling the back EMF, the position of the rotor can be inferred, eliminating the need for hardware sensors. Regardless of the topology of the motor, controlling these machines requires knowing the position of the rotor so that the motor can effectively reverse.

05. Motor control software algorithm

Now, software algorithms such as computer programs (that is, a set of instructions designed to perform specific tasks) are used to control brushless DC and permanent magnet synchronous motors. These software algorithms improve the efficiency of the motor and reduce the operation cost by monitoring the motor operation. Some main functions of the algorithm include motor initialization, Hall sensor position detection and switch signal check to improve or reduce the current reference.

06. How does the controller handle motor sensor information

Three phase brushless DC motor has six states. As shown in the figure below, the number of operation codes between 1 and 6 can be represented by three digit codes. The sensor is used to provide three digit data output to 68 opcodes (1 - 6). This information is very useful because the controller can determine that when an illegal operation code is issued, the operation code (1 - 6) is executed according to the law, as shown in the figure below. The algorithm obtains the operation code of the hall sensor and decodes it. When the operation code value of Hall sensor changes, the controller will change the transmission scheme to realize commutation. The single chip microcomputer uses the operation code to extract the power transmission information from the look-up table. After using the new sector command to power the three-phase inverter, the magnetic field moves to a new position and pushes the rotor to move in the direction of motion. This process will be repeated continuously when the motor is running.