Basic principle of the hottest motor control

Basic principle of motor control

many applications will use small motors with power less than 300 W, such as cars, printers, copiers, paper processors, factory automation, space and military vehicles, test equipment and robots. On the whole, the output of motor is about inversely proportional to its power, which means that the output of small motor is much higher than that of large motor. The most widely used small motors include DC motor, brushless DC motor and stepping motor

the main difference between stepping motor, DC motor and brushless DC motor lies in their driving mode. Stepper motor moves in steps, while DC motor and brushless DC motor usually adopt continuous moving analog control mode. Because the stepping motor adopts step-by-step movement, the adjustment method and precautions are suitable for absolute addressing applications. At present, the stepping motor commonly used in the market can provide accurate movement ability of 1.8 ° or 0.9 ° per step. The stepping motor adopts direct control mode, and its main command and control variables are step position; In contrast, DC motor takes motor voltage as control variable and position or speed as command variable. The DC motor needs a feedback control system, which will indirectly control the motor position, and the stepper motor system is mostly operated in an "open-loop" manner

stepper motors

stepper motors can be classified according to motor structure, driving structure and stepping mode. There are several structures of stepper motors, including variable reluctance, permanent magnet and hybrid permanent magnet. The cost of permanent magnet stepper motors is very low, and most of them are used in low-cost consumer products. Hybrid stepping motor "the price of the relevant leaders of the foreign cooperation center project 5 of the Ministry of environmental protection is slightly higher, and it is the most common motor in industrial mobile control applications.". Variable reluctance motors usually have 3 or 5 phases and need different drive circuit architectures

unipolar and bipolar are the two most commonly used driving architectures for stepper motors. The unipolar driving circuit uses four transistors to drive two groups of phases of the stepping motor. The motor structure is shown in Figure 1, including two groups of coils with intermediate taps. The whole motor has a total of six lines connected to the outside world. This kind of motor is sometimes called four phase motor, but this name is easy to confuse and incorrect, because it actually has only two phases. To be precise, it should be a two-phase six wire stepping motor. Although six wire stepping motor is also called unipolar stepping motor, it can use unipolar or bipolar driving circuit at the same time

Figure 1: unipolar stepping motor drive circuit

the drive circuit of bipolar stepping motor is shown in Figure 2. It will use eight transistors of Jinan Shijin to drive two groups of phases due to the large number of customers. Bipolar drive circuit can drive four wire or six wire stepping motor at the same time. Although four wire motor can only use bipolar drive circuit, it can greatly reduce the cost of mass production applications. The number of transistors in the bipolar stepping motor drive circuit is twice that of the unipolar drive circuit. Four lower end transistors are usually directly driven by the microcontroller, while the upper end transistors require a higher cost upper end drive circuit. The transistor of bipolar drive circuit only needs to bear the motor voltage, so it does not need a clamping circuit like unipolar drive circuit

Figure 2: Bipolar stepping motor drive circuit

DC and brushless DC motors

DC motors are the most common and cost-effective small motors, but with the continuous development of high molecular materials and plastic products, they are widely used in various applications. Brushless DC motor claims to provide higher reliability, lower noise and cost, but so far, it can only replace traditional DC motor in a few mass production applications such as disk or computer fan. In some applications, brushless DC motor has many advantages over traditional brush motor. For example, it replaces the brush with electronic components and sensors, which not only prolongs the service life of the motor and reduces the maintenance cost, but also has no noise generated by the brush. The characteristics of DC motor make it the easiest motor to use in speed regulation system. (end)