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Application of Frequency Conversion Technology in Motor Control
Relevant experience shows that introducing frequency conversion technology into motor control can better solve the problems related to the application of asynchronous motors. In particular, the problem of variable frequency speed control of asynchronous motors can be achieved, which can reduce the energy consumption of the motor and improve the efficiency of motor use. In the variable frequency speed control system, DSP is used as the control chip to realize the digital control of the motor. It not only improves the system reliability, but also makes the system's control accuracy, real-time performance, simple hardware and easy software programming. It is a variable frequency speed control system. Among the most promising technologies. Here we discuss the application of frequency conversion technology in motor control.
1, the characteristics and meaning of frequency conversion technology
AC voltage type inverter is the key technical link of frequency conversion technology, which reflects its characteristics and meaning. Mainly by the rectifier unit, filter unit, inverter unit, brake unit, drive unit, detection unit and control unit and other components. The three-phase alternating current that the rectifier unit uses for the power grid becomes direct current. Can be divided into controllable rectifier and uncontrolled rectifier two major categories. Controllable rectification has disadvantages such as the output voltage contains more harmonics, the input power factor is low, the control part is complex, and the pressure regulation inertia caused by the intermediate DC bulk capacitor is relatively slow, and along with the emergence of PWM technology, the controllable rectification in the AC frequency conversion The device has been eliminated. Uncontrollable rectification is currently the mainstream form of AC frequency converters. It has two types of configurations, six rectifier diodes or six thyristors that form a three-phase rectifier bridge. Filtering unit mainly uses large-capacity filter, DC voltage waveform is relatively flat, in the ideal case is a constant voltage source with zero internal impedance, the output AC voltage is a rectangular wave or staircase wave, which is a main voltage-type inverter feature.
2. Frequently Asked Questions in Frequency Conversion Technology
At present, the application of frequency conversion technology in the field of motor control has a wide application prospects. Industrial motors, household motors, and civilian facilities motors all require frequency conversion technology to control, so as to achieve stable operation, energy saving, and reliable and safe operation. As China's true sense of the frequency conversion technology business started late, the development process is relatively slow, despite the rapid development in recent years, it is difficult to make up for the deficiencies left in the early development. Therefore, China's variable frequency technology often appears in this or that problem. In this section, we analyze the common problems of current frequency conversion technology in motor control applications from the factors of frequency conversion technology, human factors, and equipment factors.
2.1 The technology itself
The failure of frequency conversion technology in the application of motor control is mainly caused by the intrinsic factors of frequency conversion technology. The two main problems are the electrical equipment and the electrical system. When the electrical equipment fails, it does not involve the entire motor, but it can affect the motor control, and at the same time, it can also cause relatively large losses to the user. If there is a problem in the electrical system, it will affect the entire motor or even the entire frequency conversion technology in the application of motor control, resulting in great destructive power, so that the motor runs out of stability, resulting in irreversible losses. Most of the problems we see usually belong to the problems that occur to them, and some voltages are suddenly high and extremely low. Extremely unstable conditions are mostly caused by frequency conversion. Therefore, it is important to accurately determine which aspect of the system itself has problems.
2.2 Human Factors
Human factors refer to mistakes made by the staff during the operation, improper operation of the electrical equipment, or negligence. When problems are caused by human factors, it is important to maintain calm and orderly rescue operations and reduce losses. In the event of a personal injury, the first aid must also be done. Faults caused by human factors often include: (1) When the inverter is running, the power supply is suddenly cut off; (2) If the inverter power supply is not turned on, turn on the inverter panel to check and handle defects. (3) Inverter 24V control circuit in the series of AC power often appear. No matter what kind of human factors, as long as there are problems, they need to be handled in a timely manner. To solve the problem before it is expanded, it must not affect the normal operation of the entire motor and electric power safety, and strive to minimize losses. The problems caused by human factors are relatively easy to solve, so be calm when you face relevant issues.
2.3 Equipment Factors
The application of frequency conversion technology caused by equipment factors in motor control mainly refers to the adverse effects of strong magnetic field interference of neighboring electrical equipment or weak signal of variable frequency control. This is mainly manifested in the fact that the inverter controls weak electrical signals from adjacent electrical equipment. The magnetic interference of the AC power supply causes the inverter to control the failure or wrong alarm signal and the condition that the 24V control circuit of the inverter is interfered with by the AC magnetic field of the adjacent operating equipment. For these situations, we mainly use the inverter control signal cable to transform it into an anti-jamming and shielded cable, and perform magnetic field shielding measures on the AC power supply equipment that generates magnetic fields adjacent to each other. These two methods effectively solve the device interference factors on the inverter. The impact of normal operation.
3, to explore the solution to the problem
Although there are many problems in the application of motor control in our country's frequency conversion technology, these problems cannot be avoided. Therefore, these problems can be solved by people taking appropriate and appropriate measures. Based on the survey results, we conducted repeated analysis and research, and actively communicated with some experts and scholars, and initially proposed a corresponding solution. Of course, the solution to the problem needs to be timely and fundamental. Here we discuss the current problems, to help the application of national frequency conversion technology in motor control.
3.1 improve the performance of the frequency conversion system
To solve this problem, we must first encourage innovation and we must have more and more technological breakthroughs. Encouraging innovation should not only stay on top of the slogan, but require the country or the company to invest heavily in technology innovation as a long-term main task. Second, we can set up relevant awards to encourage more employees to devote more enthusiasm to technological innovation. Finally, we should strengthen the communication between the government and companies in the frequency conversion technology in the motor control hardware devices, and more in-depth work of technological innovation. Increasing the performance of frequency conversion technology is not a single one, and it needs to work together with other related technologies. The application of frequency conversion technology in motor control is quite complicated, and every link of hardware equipment has strict technical inspection. To improve the performance of the frequency conversion system can solve most of the problems, and it is of great significance to the development and innovation of frequency conversion technology.
3.2 Strengthen the construction of personnel
We all know that the continuous development of an industry requires excellent teams to provide power. In fact, the application of frequency conversion technology in motor control is most indispensable to the professional team. Therefore, the problems existing in the frequency conversion technology in the motor control application team are very worth our attention and are also urgent to be solved. We can increase our efforts in personnel training and strive to enhance the overall quality of personnel. Secondly, we can also improve the relevant systems, use the system to restrain some people with low quality, and reduce the unqualified personnel of frequency conversion technology in motor control applications. In the end, we should strengthen the overall construction of the team, proceed from the overall situation, and comprehensively improve the overall level of motor frequency conversion equipment operation. Therefore, it is an effective way to solve the many problems that currently exist in our company.
3.3 Introduce credits
The reference of the integral link is to eliminate the system steady-state error and improve the system's no-difference, so as to ensure that the actual value does not track the set value. However, the introduction of the integral link will make the dynamic response of the system slower. In practice, the integral action is often combined with two other regulation laws to form a PI controller or a PID controller. The introduction of the differential link role is mainly to improve the response speed and stability of the control system. The differential action can reflect the variation law of the system deviation and predict the trend of deviation change, so it can produce advanced control. The strength of differential action depends on the size of the differential time. The greater the time, the stronger the differential action, and the weaker the opposite.
However, in fact, in the design process of the device, the designer has designed the cooling system of the rectifier device in accordance with the aforementioned principle of ensuring the reliability of the device. The cooling system already has a redundant standby function and an automatic monitoring function, and its reliability is already quite high. According to the large number of devices that our company has put into operation at present, it has not occurred that the device has stopped or exited due to the wind turbine being stopped.
(2) Disadvantages of stopping wind operation: 1 The basic requirements for forced air cooling are violated; forced air cooling of high-power silicon controlled rectifier devices is inseparable from the cooling fan. 2 The requirements for the environment are more stringent; in order to facilitate the operation of stopping the wind, the ventilation requirements for the ambient temperature, dust, and devices are quite strict. 3 The rectifier device selects the situation of large horse-drawn carts; the choice of SCR parameters needs to exceed the rated operation requirements greatly, resulting in great waste. 4 The reliability and safety of the entire device are greatly reduced; if the thyristor elements in the rectifier device are operated in a high temperature environment for a long time, the life of the device will be greatly affected. 5 The external dimensions of the device are increased; because there is no fan forced air cooling, it can only be achieved by increasing the space or automatically cooling the area.
5 Instructions for setting the switch on the AC-DC side of the rectifier
At present, in the domestic excitation system, it is generally required to provide a breaker or a breaker on the AC-DC side of the rectifier cabinet. The purpose is to solve the problem of isolation when the rectifier device fails and the isolation during overhaul.