Summary:...
1. Different types of exercise
Several motor control topologies are currently available: brushes, brushless direct current (BLDC), steppers, and inductors. Brushless motors and permanent magnet synchronous motors (PMSM) are two types of brushless motors that are closely related.
Brushless motors do not require 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 the brush motor is realized through the brush/commutator interface. The interface will generate friction and arcing, which will reduce the performance of the brush over time. This friction generates heat and shortens the life of the motor.
Compared with brush motors, brushless motors have many advantages. They are more energy efficient, smaller, lighter, quieter, more reliable, and more durable. In addition, they provide speed control and are more suitable for variable speed applications.
2. Understand the types of brushless DC and permanent magnet synchronous motors
The working principle of
brushless DC gear 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 two types of DC motor stator windings use different geometries, so they can generate different back electromotive force (BEMF) responses. The brushless BEFM is trapezoidal. The back electromotive force of the permanent magnet synchronous motor is sinusoidal, so the coil winding is sinusoidal. In order to achieve greater performance, these electrodes are usually commutated with sine waves.
Brushless DC motors and permanent magnet synchronous motors generate electromotive force through their windings during operation. In any motor, the electromotive force generated due to movement is called back electromotive force (BEMF), because the electromotive force induced in the motor is opposite to the electromotive force of the generator.
3. Description of magnetic field direction control
In order to control the sinusoidal waveform of a permanent magnet synchronous motor, a field-oriented control (FOC) algorithm is required. FOC generally improves the efficiency of permanent magnet synchronous motors. Compared with the brushless DC trapezoidal controller, the sinusoidal controller of the permanent magnet synchronous motor is more complicated 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 motors is that they are easy to control. Choose the motor according to the application requirements.
4. 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 need to start 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. A motor without a sensor needs to use the motor as a sensor and use an algorithm to run. They rely on 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 commutate effectively.
5. 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 operating cost by monitoring the operation of the motor. Some of the main functions in the algorithm include motor initialization, Hall sensor position detection, and switching signal inspection to increase or decrease the current reference.
6. How does the controller process motor sensor information
Three-phase brushless DC motors have 6 states. As shown in the figure below, a three-digit code can be used to indicate the number of operational codes between 1 and 6. The sensor is used to provide three-bit 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 operation code (1-6) is executed according to the law. As shown in the figure below, the algorithm obtains the Hall sensor's operation code and decodes it. When the operational code value of the Hall sensor changes, the controller will change the power transmission scheme to achieve commutation. The single-chip microcomputer uses the opcode to extract the power transmission information from the look-up table. After using the new sector command to supply power to the three-phase inverter, the magnetic field moves to a new position while pushing the rotor to move in the direction of movement. This process will be repeated continuously while the motor is running.
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