DC motor
Generally, DC motors have the same working principle and application characteristics, but their composition is different. In addition to the motor itself, the former also has a commutation circuit, which is closely combined with the motor itself. The motor itself of many small power motors is integrated with the commutation circuit. From the appearance, the DC brushless motor is exactly the same as the DC motor.
The motor of brushless DC motor is an electromechanical energy conversion part, which is equipped with sensors in addition to motor armature and permanent magnet excitation. The motor itself is the core of the DC brushless motor, which is not only related to performance indicators, noise and vibration, reliability and service life, but also involves manufacturing costs and product costs. Because of the use of permanent magnetic field, the brushless DC motor gets rid of the traditional design and structure of ordinary DC motor, meets the requirements of various application markets, and develops towards the direction of copper saving and material saving and simple manufacturing. The development of permanent magnetic field is closely related to the application of permanent magnetic materials. The application of the third generation of permanent magnetic materials promotes the DC brushless motor to move towards high efficiency, miniaturization and energy conservation.
In order to realize electronic commutation, there must be a position signal to control the circuit. In the early days, electromechanical position sensors were used to obtain position signals. Now, electronic position sensors or other methods are gradually used to obtain position signals. The simplest method is to use the potential signal of the armature winding as the position signal.
To realize the control of motor speed, there must be a speed signal. The simplest speed sensor is the combination of frequency measuring tachogenerator and electronic circuit.
The commutation circuit of DC brushless motor is composed of drive and control parts, which are not easy to be separated, especially the small power circuit often integrates the two parts into a single ASIC. In the motor with large power, the drive circuit and control circuit can be integrated separately. The driving circuit outputs electric power, drives the armature winding of the motor, and is controlled by the control circuit. The driving circuit has changed from a linear amplification state to a PWM switching state, and the corresponding circuit composition has also changed from a transistor discrete circuit to a modular integrated circuit. Modular integrated circuits are composed of power bipolar transistors, power field effect transistors and isolated gate field effect bipolar transistors. Although the isolated gate field-effect bipolar transistor is expensive, it is more appropriate to select it from the perspective of reliability, safety and performance.
The control circuit is used to control the speed, steering, current (or torque) of the motor and protect the motor from overcurrent, overvoltage, overheating, etc. The above parameters can easily be converted into analog signals, which is relatively simple to control. However, from the perspective of development, the motor parameters should be converted into digital quantities, and the motor should be controlled through digital control circuits. At present, the control circuit consists of ASIC, microprocessor and digital signal processor. It is a simple and practical way to compose control circuit with ASIC in the occasion of low requirements for motor control. The control circuit composed of digital signal processor is the future development direction. The digital signal processor will be introduced in the following AC synchronous servo motor.
Brushless DC motor is a new type of motor with rapid development in the field of micro power. Because each application field needs its own unique DC brushless motor, there are many types of DC brushless motor. Generally, there are external computer memory and flat coreless motor structure for VCD, DVD and CD spindle drive, external rotor motor structure for small ventilators, multipole magnetic field structure and built-in structure for household appliances, multipole and external rotor structure for electric bicycles, etc. The motor and the circuit of the DC brushless motor are integrated, which is very convenient to use and has a large output. In order to meet the market demand of large quantities and low cost, the production of DC brushless motor must form economies of scale. Therefore, DC brushless motor is a high input and high output industry. At the same time, we should take into account that the market is also constantly developing. For example, the motor for household air conditioner is changing from 3A to 3D, which requires a large number of small and medium power DC brushless DC motors. Therefore, it is urgent to research and develop small and medium power DC brushless DC motors.
Brushless motor
BLDCM is developed on the basis of brushless DC motor, but its driving current is absolutely AC; Brushless DC motor can be divided into brushless speed motor and brushless torque motor. Generally, there are two kinds of drive current of brushless motor, one is trapezoidal wave (generally "square wave"), and the other is sine wave. Sometimes the former is called DC brushless motor, and the latter is called AC servo motor. To be exact, it is a kind of AC servo motor.
In order to reduce the moment of inertia, brushless DC motor usually adopts a "slender" structure. The brushless DC motor is much smaller in weight and volume than the brushless DC motor, and the corresponding moment of inertia can be reduced by 40% - 50%. Due to the processing problem of permanent magnet materials, the capacity of brushless DC motor is generally below 100kW.
This kind of motor has good linearity of mechanical characteristics and regulation characteristics, wide speed range, long service life, convenient maintenance and low noise, and does not have a series of problems caused by brushes. Therefore, this kind of motor has great application potential in the control system.
The stator winding of motor is usually made into three-phase symmetrical star connection, which is very similar to three-phase asynchronous motor. The rotor of the motor is attached with a magnetized permanent magnet. In order to detect the polarity of the motor rotor, a position sensor is installed in the motor. The driver is composed of power electronic devices and integrated circuits. Its functions are: to receive the starting, stopping and braking signals of the motor to control the starting, stopping and braking of the motor; Receive the position sensor signal and the forward and reverse signals, which are used to control the on-off of each power tube of the inverter bridge to generate continuous torque; Receive speed command and speed feedback signal to control and adjust speed; Provide protection, display, etc.
Since brushless DC motor operates in automatic control mode, it will not add starting winding on the rotor as synchronous motor with heavy load starting under variable frequency speed regulation, nor will it generate oscillation and out of step when the load changes suddenly. The permanent magnet of small and medium capacity brushless DC motor mostly adopts rare earth Nd-Fe-B material with high magnetic energy product. Therefore, the volume of rare earth permanent magnet brushless motor is one frame size smaller than that of three-phase asynchronous motor with the same capacity.
In the last three decades, the research on variable frequency speed regulation of asynchronous motor is to find a way to control the torque of asynchronous motor in the final analysis. Rare earth permanent magnet brushless DC motor will show its advantages in the speed regulation field with its wide speed regulation, small size, high efficiency and small steady-state speed error.
Brushless DC motor is also called DC frequency conversion because it has the characteristics of DC brushless motor and is also a device for frequency change. The international term is BLDC The operation efficiency, low speed torque, speed accuracy, etc. of brushless DC motor are better than any frequency converter with any control technology, so it deserves the attention of the industry This product has been produced more than 55kW and can be designed to 400kW, which can meet the demand of industry for power saving and high-performance drive.