According to the requirements of different industrial and agricultural production machinery, motor drives are divided into three categories: fixed speed drive, speed regulating drive and precision control drive.
1. Fixed-speed drive
In industrial and agricultural production, there are a large number of production machinery that require continuous operation in one direction at a roughly constant speed, such as fans, pumps, compressors, ordinary Machine tools, etc. In the past, most of this type of machinery was driven by three-phase or single-phase asynchronous motors. Asynchronous motors have low cost, simple and reliable structure, and easy maintenance, so they are very suitable for driving this type of machinery. However, asynchronous motors have low efficiency, power factor, and large losses, and this type of motor is widely used in large quantities, so a large amount of electric energy is wasted during use. Secondly, fans and water pumps used extensively in industry and agriculture often need to adjust their flow, which is usually done by adjusting dampers and valves, which wastes a lot of electrical energy. Since the 1970s, people have used frequency converters to adjust the speed of asynchronous motors in fans and water pumps to adjust their flows, achieving considerable energy-saving effects. However, the cost of the frequency converter limits its use, and the low efficiency of the asynchronous motor itself still exists.
For example, household air-conditioning compressors originally used single-phase asynchronous motors, with on-off control of their operation. Noise and high temperature changes were its shortcomings. In the early 1990s, Toshiba Corporation of Japan first adopted variable frequency speed regulation of asynchronous motors in compressor control. The advantages of variable frequency speed regulation promoted the development of variable frequency air conditioners. In recent years, Japanese companies such as Hitachi and Sanyo have begun to use permanent magnet brushless motors to replace the variable frequency speed regulation of asynchronous motors, which has significantly improved efficiency, achieved better energy-saving effects and further reduced noise, at the same rated power and rated speed. Assume that the volume and weight of a single-phase asynchronous motor are 100, then the volume of the permanent magnet brushless DC motor is 38.6, the weight is 34.8, the amount of copper used is 20.9, the amount of iron used is 36.5, the efficiency is increased by more than 10, and the adjustment It is fast and convenient, and the price is comparable to that of asynchronous motors with variable frequency speed regulation. The application of permanent magnet brushless DC motors in air conditioners has promoted the upgrading of air conditioner agents.
Another example is the cooling fan widely used in instruments and other equipment. In the past, it was driven by a single-phase asynchronous motor with an external rotor structure. It is large in size and weight and has low efficiency. In recent years it has been completely replaced by brushless fans driven by permanent magnet brushless DC motors. Brushless fans are used without exception on various computers and other information equipment that are developing rapidly in modern times. Over the years, a complete series of brushless fans has been formed with many varieties and specifications. There are 12 types of outer frame sizes from 15mm to 120mm, 7 types of frame thickness from 6mm to 18mm, and voltage specifications of DC 1.5V. , 3V, 5V, 12V, 24V, 48V, the speed range is from 2100rpm to 14000rpm, divided into 4 types: low speed, medium speed, high speed and ultra-high speed. The life span is more than 30000 hours. The motor is a permanent magnet brushless DC with outer rotor electric motor.
Practice in recent years has shown that in situations where the power is not greater than 10kW and operates continuously, in order to reduce size, save materials, improve efficiency and reduce energy consumption, more and more asynchronous motor drives are being used. It is gradually replaced by permanent magnet brushless DC motor. In high-power applications, due to the high primary cost and investment, in addition to permanent magnet materials, a high-power driver is required, so there are fewer applications.
2. Speed-adjustable drive
There are quite a few working machines whose operating speed needs to be set and adjusted arbitrarily, but the speed control accuracy requirements are not very high. This type of drive system has a large number of applications in packaging machinery, food machinery, printing machinery, material handling machinery, textile machinery and transportation vehicles.
In this type of speed regulation application field, the DC motor speed regulation system was initially used most. After the 1970s, with the development of power electronics technology and control technology, the frequency conversion speed regulation of asynchronous motors quickly penetrated into the original speed regulation system. Application fields of DC speed control system. This is because on the one hand, the performance and price of the asynchronous motor frequency conversion speed control system is completely comparable to that of the DC speed control system. On the other hand, the asynchronous motor has the advantages of large capacity, high reliability, low interference, and long life compared with the DC motor.
Therefore, asynchronous motor frequency conversion speed regulation has quickly replaced the DC speed regulation system in many occasions.
Due to its small size, light weight, high efficiency and energy saving, AC permanent magnet synchronous motor has attracted more and more attention. Its control technology has become increasingly mature, and its controller has been commercialized. The frequency conversion speed regulation of small and medium-power asynchronous motors is gradually being replaced by the permanent magnet synchronous motor speed regulation system. Elevator drives are a typical example. The elevator drive system has certain requirements for the acceleration, steady speed, braking, and positioning of the motor. In the early days, people used DC motor speed control systems, and their shortcomings were self-evident. In the 1970s, frequency conversion technology matured, and the variable frequency speed regulation drive of asynchronous motors quickly replaced the DC speed regulation system in the elevator industry. In recent years, the latest driving technology in the elevator industry is the permanent magnet synchronous motor speed control system. It is small in size, energy-saving, has good control performance, and can be easily made into low-speed direct drive, eliminating the need for gear reduction devices; it has low noise, leveling accuracy and The comfort is better than the previous drive system, and it is suitable for use in machine room-less elevators. The permanent magnet synchronous motor drive system has quickly been favored by major elevator companies, and its supporting special frequency converter series products have been launched in various brands. It is foreseeable that in the case of speed control drive, permanent magnet synchronous motor will dominate. Japan's Fuji Company has launched a series of frequency conversion controllers matching permanent magnet synchronous motor products, with power ranging from 0.4kW to 300kW. The volume is 1 to 2 frame sizes smaller than that of asynchronous motors with the same capacity. The power and energy indicators are significantly higher than those of asynchronous motors. Available Suitable for pumps, transportation machinery, mixers, winches, lifts, cranes and many other places.
3. Precision control drive
① High-precision servo control system
Servo motors play a very important role in operation control in the field of industrial automation. Different application scenarios have different control performance requirements for servo motors. In practical applications, servo motors have various control methods, such as torque control/current control, speed control, position control, etc. The servo motor system has also experienced DC servo system, AC servo system, stepper motor drive system, until the most eye-catching permanent magnet motor AC servo system in recent years. Most of the various types of automation equipment, automatic processing devices and robots imported in recent years use AC servo systems of permanent magnet synchronous motors.
② Permanent magnet synchronous motor in information technology
Today’s information technology is highly developed, and various computer peripherals and office automation equipment are also highly developed. The key components supporting it are micro Motors are in high demand, and precision and performance requirements are getting higher and higher. The requirements for this type of micromotors are miniaturization, thinness, high speed, long life, high reliability, low noise and low vibration, and the accuracy requirements are particularly high. For example, the spindle drive motor of a hard disk drive is a permanent magnet brushless DC motor, which drives the disk to rotate at a high speed of nearly 10,000 rpm. The magnetic head on the disk that performs data reading and writing functions performs suspended motion only 0.1 to 0.3 microns away from the surface of the disk. It can be imagined that the accuracy requirements are very high. The vast majority of drive motors used in various equipment in information technology, such as printers, soft and hard drives, optical disk drives, fax machines, copiers, etc., are permanent magnet brushless DC motors. Due to technical limitations, this type of micromotors cannot be manufactured domestically, and some products are assembled domestically.