Inverter technology, if we want to find theoretical basis from textbooks, can be attributed to the power electronics technology discipline. Power electronics technology is the use of semiconductor power devices (such as IGBT) to convert, control and optimize the use of technology. For sales or for the company, it can be called a mechatronic product.
The popularity of frequency converters can be understood as a type of power supply. What is the power supply? We know that the role of the transformer is to perform the voltage conversion process. For example, step-up transformers, step-down transformers, auto-transformers, etc., and even reactors, the input voltage and output voltage may be increased or decreased, or they may be constant, all of which realize energy transfer. Universal transmission is a device that realizes energy transfer by changing the voltage and frequency of the power grid, so it can be understood as a power supply. Most of the power requirements in the industry are three-phase 380 volts and 50 hertz. The universal transmission inverter modulates this power supply to 0-380 volts, 0-50 hertz.
From the point of view of the drag system, a process flow includes control, drive, execution, and load. Control refers to the operation part, such as the host computer, the general operation box, the control cabinet, the programmable logic controller, etc.; the drive is our product, including the ordinary transmission frequency converter, the servo power supply, etc.; the execution part is the motor or the servo motor; The load is what we say about fans, pumps, air compressors and so on.
The promotion on the mine can be understood as follows:
Applying High Technology to Transform Traditional Coal Industry.
Electric power technology was first used in mines and it was on mine hoists. Developed countries are also used for belt conveyors, fans and pumps.
Belt conveyors:
The application of universal transmission frequency converters in domestic coal mines is mainly concentrated on belt conveyors. As we all know, the belt is an elastic body, and a large amount of energy is stored in the belt when it is stationary or in operation. If the soft starter is not added during the start-up of the belt conveyor, the energy stored in the belt will be quickly released and released on the belt. Form tension waves and quickly travel along the belt. Excessive tension waves can easily cause the belt to be torn. Therefore, the "Coal Mine Safety Regulations" stipulates that a soft starter must be added to the belt conveyor. At present, most of the soft starters used in coal mines are hydraulic couplings. Although the hydrodynamic coupling can partially solve the soft start problem of the belt conveyor, it still has obvious disadvantages compared with the drive of the universal transmission. First, when the fluid coupling is used, the motor must be started with no load first. When the frequency is started, the initial current is very large, which is 4-7 times the rated current of the motor. A large starting momentary current may cause a shock during the starting process, causing changes in the mechanical and thermal stresses inside the motor, causing serious wear or even damage to the mechanical parts. At the same time, it will also cause the grid voltage to drop, which will affect the normal operation of other equipment in the grid. Therefore, large-capacity belt conveyors must also be equipped with motor soft-start equipment. Secondly, when the fluid coupling is operated for a long time, the liquid temperature rises, the alloy plug is melted, leakage is caused, the maintenance workload is increased, and the environment is polluted. Thirdly, when the fluid coupling is used, the loading time of the belt conveyor is short and the tension of the belt is easily changed. Therefore, the requirements for belt strength are higher. Fourth, the general belt conveyors are long-distance and large-capacity. They are usually driven by multiple motors and are driven by hydraulic couplings. It is difficult to solve the problem of power balance when driving multiple motors. With the development of power electronics technology. Frequency conversion technology has developed rapidly in the last two decades and has been widely used in some coal mining enterprises, such as Jincheng Coal Mining Group, Luan Coal Mining Bureau, and Huaibei Mining Bureau.
The use of universal transmission converters to transform the drive of the belt conveyor will bring great social and economic benefits to the user:
First, the soft start of the belt conveyor system was truly realized. The use of universal frequency converter to drive the belt conveyor, using the soft start function of the ordinary transmission frequency converter, the soft start of the motor and the soft start of the belt conveyor combined into one, through the slow start of the motor, drive the belt slowly When starting, the energy stored inside the belt is slowly released, so that the tension wave formed by the belt conveyor during the starting process is extremely small, and almost no damage is caused to the belt.
Second, realize the power balance when driving multiple belt motors. When using a universal inverter to drive a belt conveyor, one-to-one control is generally used. When multiple motors are driven, master-slave control is used to achieve power balance. In the Jincheng Coal Group Wangtai No. 2 wells, the slot-slot belt is driven by a 2×200KW/660V motor. After master-slave control is adopted, the master-slave motor current differs by about 5A at light load, and is about 2A at full load.
Third, reduce the belt strength. After being driven by universal transmission, the starting time of the universal transmission can be adjusted from 1S to 3600S. Usually, the starting time of the belt is within 60S~200S. According to the field setting, the starting time of the belt conveyor is extended, and the belt is greatly reduced. With strong requirements, reduce the initial investment in equipment.
Fourth, reduce the amount of equipment maintenance. Universal transmission is an integration of electronic devices. It converts the life of a machine into the life of an electronic device. The service life is very long, which greatly reduces the amount of equipment maintenance. At the same time, the soft start of the frequency converter is used to realize the soft start of the belt conveyor. During the start-up process, there is basically no impact on the machine, which also greatly reduces the maintenance of the mechanical part of the belt conveyor system. If Jincheng Coal Industry Group Wangtai No.2 well-slotted belt is driven by a universal transmission, only one year of belt deduction will save more than 10,000 yuan.
Fifth, energy conservation. The energy-saving effect of variable frequency drive on the belt conveyor is mainly reflected in the system power factor and system efficiency. 1. Increase the power factor of the system Under normal circumstances, the surplus of the motor used in the coal mine during the design process is relatively large. Most of the work cannot be fully loaded during operation. The motor works at full voltage and full speed and the load is often very small. There are also some times. No-load operation. From the motor design and operating characteristics, it is known that the motor has the highest efficiency and the best power factor only when it is near full load, and decreases when the load is light, causing unnecessary power loss. This is because when the light load, the stator current active component is very small, mainly the reactive component of the excitation, so the power factor is very low. After being driven by universal transmission, the power factor reaches 0.9 or more in the whole process, which greatly saves reactive power. 2. After the system efficiency is improved, the motor and the speed reducer are directly connected with each other, and the fluid coupling is reduced in the middle. The transmission efficiency of the fluid coupling itself is not high, and the fluid coupling is mainly driven by the liquid, and the transmission efficiency of the liquid is much lower than the transmission efficiency of the direct hard connection, so the drive is driven by the universal transmission. The total transmission efficiency of the system is 5% to 10% higher than that of the hydrodynamic coupling. In addition, the mine is usually far away from the substation, voltage fluctuations at different times, the use of the automatic voltage regulator function, there are also some energy-saving effect. In summary, the adoption of the universal transmission technology to transform the traditional belt conveyor drive system is not only significant in terms of advanced technology, but also brings great social and economic benefits. With the development of society, Ultimately, the use of frequency converters in the drive of belt conveyors will replace the dominant position of hydraulic couplings. This has been proven in a large number of application cases in Jincheng Coal Group, Luan, and Huaibei Mining Group.
At present, there are two successful companies, Chengdu Jialing and Germany Siemens.
II. Mine hoisting Mine hoisting equipment is a large-scale mechanical equipment that lifts coal, ore, lifters and equipment, and decentralized materials along the wellbore. It is the hub connecting the underground production system of the mine and the ground industrial plaza. It is the throat of the mine transportation. Therefore, the mine lifting equipment occupies an extremely important position in the whole process of mine production, and its safety and reliability are particularly prominent. In the mine production process, if the lifting equipment fails, it will inevitably result in production suspension. The lighter ones will affect the coal production, while the heaviest ones will endanger personal safety. In addition, the mine hoisting equipment is a large-scale integrated mechanical-electrical equipment, and its cost and power consumption are relatively high. Therefore, in the design of the new mine and the reconstruction design of the old mine, when a reasonable lifting system is determined, it must go through many The technical and economical aspects of the comparison, combined with the specific conditions of the mine, ensure that the lifting equipment is reasonable in terms of both type selection and operation, that is, the mine lifting equipment is required to be economical. In the traditional hoisting system, the speed regulation method of the motor is the speed regulation of the motor rotor series resistance. With the development of power electronics technology, the drawbacks of the motor rotor series resistance method are increasingly obvious:
First, the control accuracy is poor. Adopting motor rotor series resistance speed regulation belongs to stepped speed regulation. There is a speed jump in the switching of different speed segments. The control is rough and the positioning is inaccurate.
Second, the work reliability is not high. Because there are many resistors connected in series on the rotor side of the motor, and the contactor is used to short-circuit the upper resistor in the step-by-step speed regulation process, the life of the contactor is mainly reflected in the life of its mechanical part. The life of the mechanical part is well known. The life of the electronic type is much shorter than that of the electronic type. Sometimes the current is too large, resulting in a contactor.
The contacts are stuck together and cannot be switched. This can cause accidents such as speeding and seriously affect the reliability of the system. Third, maintenance workload is large. Since the contactor is used to switch the resistance in sections, the contactor must be maintained frequently, which greatly increases the working strength of the maintenance personnel.
Fourth, energy consumption. The motor rotor series resistor speed regulation is a slip power consumption type speed regulation method. In the entire speed regulation process, a large amount of electric energy is consumed in the resistor, which is very uneconomical.
Fifth, the stability is poor. Rotor series resistance of the motor speed, when running in the low speed, poor stability. Because the lower the rotational speed, the softer the characteristics, and the larger the rotational speed change caused by the fluctuation of the load torque, the poorer the running stability. With the development of power electronics technology and the maturity of frequency conversion technology, the state expressly stipulates that in the promotion of more vehicle systems, it is recommended to use AC frequency converters. The use of an AC variable speed governor to drive the hoist winch has the following advantages: First, the control accuracy is high. Normally, the frequency converter uses magnetic flux vector control, which makes the speed control performance of the AC motor almost equal to the DC motor, and the control accuracy is very high. Second, work reliability is high. Pure frequency converter uses electronic devices, has a long service life, and has a perfect protection function. When used to control the winch, its reliability is high. Third, there is basically no maintenance workload, which reduces the workload of maintenance personnel. Fourth, the speed range is wide, belonging to stepless speed regulation, and good stability at low speed. Fifth, energy conservation. Pu-Transformer is a speed-regulation method with a constant slip power. In the entire speed regulation process, its energy-saving method is shown in two aspects: 1. Energy-saving in the hoisting state When the hoisting hoist is in the upward-lifting state, the motor works in the electric state. Due to the fact that the hoist winch is a constant torque load, the proportion of energy saved is a percentage of the speed reduction. 2. Decentralized state When the hoisting hoist is in the decentralized state, the motor works in the power generation state and converts the potential energy into electric energy. If the universal transmission adopts the energy feedback type universal transmission, the universal transmission will return this energy back to the grid. Xishan Coking Coal Group Ximing Mine An endless rope winch using frequency conversion, the energy-saving effect of about 30%. This universal transmission frequency converter is energy-conservation braking type. If energy feedback type is adopted, its energy-saving effect will be better. There are many hoisting winches in coal mining enterprises. After adopting frequency conversion, the energy saving effect will be very obvious. Nowadays, many new winch systems have been driven by variable frequency drives. Third, the emulsion pump station emulsion pump station is mainly for the hydraulic support to provide a constant liquid pressure. Usually, the hydraulic support does not move, but the emulsion pump still works for a long time and consumes a lot of energy. If variable frequency drive is used, a pressure sensor is used to form a closed loop constant pressure control. When the hydraulic support is moved, the emulsion pump increases the liquid flow and maintains the variable force. When the hydraulic support is not moved, the emulsion pump provides a small flow of liquid to maintain the pressure. Change to achieve constant pressure control. The use of universal transmission drive emulsion pump, energy-saving effect is obvious. Shandong Zibo Mining Bureau Yucun coal mine next a 55KW/660V universal transmission inverter for emulsion pumps, after calculation, its energy-saving effect of about 50%. In addition, after adopting the universal transmission frequency converter, the rotation speed of the motor and the pump is reduced, the wear of the mechanical part will be reduced much, and the equipment maintenance period is prolonged. In addition, in some coal mines, the main fan has also adopted frequency conversion technology, such as the Ningxia Coal Group, but at present, the application of universal transmission frequency converters in coal mines is mainly concentrated on belt conveyors and winches.