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So why is the inverter going so quickly and deeply into all aspects of human life?
First of all, let's take a look at the final execution unit of our modern industrial base, the electric motor, and we will know that the movement or control of any object must be achieved by the motor, the most basic electric energy-mechanical energy conversion device, and the main control of the inverter. The object is an asynchronous motor with wide adaptability, high reliability, robustness, and almost zero maintenance. The AC motor has advantages in terms of its simple structure, small moment of inertia, low cost, etc., and its application in the field of electrical transmission has been indisputable. The control characteristic is no less than the cumbersome maintenance of a large amount of DC speed control equipment. It can be said that as long as the motor is used, we can add an inverter to replace or improve the original control characteristics and functions. The standard industrial control interface and communication function provided by the intelligent frequency converter can be compatible with the DCS distributed control system, and can also send controlled object parameters to all levels of digital terminal equipment, thereby realizing the automation of the entire system. In Western developed countries, in the field of speed regulation, the application of AC speed control is over 80%, and in the AC motor speed control, frequency control has occupied a large proportion. The speed control application already exceeds 80%, and in its AC motor speed control, frequency conversion speed control has occupied a large proportion.
Second, the most important role of the inverter is to achieve stepless speed regulation of the motor. Inverter through the power module voltage variable frequency output, in the same speed to ensure that the motor output torque to adjust the speed of the motor, the characteristics of hard, the maximum can provide 150-200% of the rated torque, the speed changes in the external load is almost no Landing and speed regulation are important execution units for adjustment of various production and living parameters. For example, after the application of electric locomotive traction, elevators, machine tool processing, paper making, steel production lines, power station air supply, water supply, coal feeding, and tobacco machinery, the degree of comfort, processing technology, product quality, and productivity can be greatly improved.
Third, the inverter has an energy saving feature that is not equal to any other speed controller. Ordinary mechanical speed control, variable voltage speed control, slip motor and other speed control methods all greatly waste precious energy. However, the frequency converter has the principle of how much energy is drawn from the power grid and uses energy efficiently. Especially used in the fan, pump control, generally saving about 30%. Judging from the current electricity price and variable-frequency investment, it will be able to recover all the investment within one to two years. For the power station, it can greatly reduce the cost of power generation and increase the efficiency of power generation. Under the current environment in which the electricity market is gradually implementing competitive bidding, the investment in frequency conversion technology will undoubtedly have the most realistic significance.
It is because of these valuable advantages of the frequency converter that the inverter has been widely and deeply applied.
Second, the frequency changer structure and the control principle are as follows, is the common voltage type frequency changer structural drawing for the market. The frequency converter is divided into three parts: the main circuit, the control and the protection circuit. The main circuit rectifies and filters the input voltage, and the output voltage and frequency are adjustable. The control loop is mainly based on the external operating instructions to operate and issue control instructions to control the inverter power module. For applications that require more accurate speed or fast response, it is often necessary to perform detection operations on the DC part of the main loop and the AC output section. The protection circuit is used to prevent damage to the device caused by overvoltage and overcurrent in the main circuit of the inverter, and it also protects asynchronous motors and transmission equipment.
The main loop is composed of three parts, that is, the AC voltage of the industrial frequency is converted into the rectification part of the DC; the capacitive filtering part of the voltage and current ripple generated during the rectification or the inverter is absorbed; and the inverter part of the DC/AC voltage conversion output is absorbed. . In addition, when the asynchronous motor needs to be braked, the braking unit can be added to the four-quadrant operation of the motor in the DC capacitor filtering section. 
We know that the speed of the asynchronous motor is determined by the power frequency and the number of poles, so changing the speed of the motor can change the speed, but when the frequency changes, the internal impedance of the motor also changes, so changing only the frequency will cause the weak field of the motor. Insufficient torque, over-excitation saturation, while the inverter changes the output frequency, by adjusting the control waveform to change the output voltage, so as to ensure that the motor air gap flux is rated, so that the motor torque, speed can be very Good control.
Today's most advanced speed-sensing vector control inverter principle is based on the same torque generation mechanism of asynchronous motor and DC motor. The stator current supplied to the asynchronous machine is divided into two current vectors perpendicular to each other: generating excitation magnetic field The current components and the current component of the generated output torque are individually controlled, and the resultant stator current is supplied to the motor. In this way, the same speed and torque control effects as the control of the DC motor can be obtained. It has the characteristics of starting current without pulsation, small current, large torque and hard characteristics.
When the inverter is used for speed regulation or energy saving applications, the connection and installation of its equipment is very convenient. It only changes the power input to the motor's mains power supply to the inverter, and then connects the inverter output to the motor. This is particularly convenient and feasible for the transformation of old equipment.
When the frequency converter drives the motor to start, since the frequency and voltage increase progressively over time according to need, the starting current is generally below twice the rated current, and no other starting device is required, nor does it cause current shock, which is in the tens of kilowatts. Applications above the motor are particularly suitable.
The inverter's control loop provides industrial standard control digital input and output, analog input and output, pulse interface and communication interface. It can receive and feedback all kinds of real-time status parameters controlled by the omnibearing and can be added to DCS and each Digital analog control system.
Third, the inverter energy-saving analysis Fan pump load torque is proportional to the square of the speed, the shaft power and speed is proportional to the cube, so the motor will run at a constant speed, the baffle valve to adjust the amount of feng shui, change According to the amount of feng shui required, a large amount of power-saving effect can be obtained by adjusting the rotation speed with the inverter.
1) Fan air flow control The motor runs at constant speed. The typical method of adjusting the air flow of the fan is to use baffle control. According to the installation position of the baffle in the air duct, it can be divided into outlet baffle control and inlet baffle control. When using the baffle control, the wind resistance is increased when the baffle is closed, and the air volume cannot be adjusted in a wide range. Compared with the baffle control, the power saving effect of the speed control is large. See below 
If there are 235KW inverters applied to a 235KW fan, if the required average air volume is 60% and the annual operating time is calculated in 6000 hours, then the annual power saving is compared with the frequency inverter control of one fan and the population baffle control. It can reach 235KW*0.3*6000H=423000 degrees, with a calculation of 0.9 yuan per degree.
The annual electricity fee is 380,000 yuan. Less than one year to recover investment.
2) Pump flow control When the pump speed changes within a certain range, the flow rate, total head, and shaft power have a linear, squared, and cubic relationship in sequence. However, for the actual pump load, there is usually an actual head related to the height difference. The smaller the head, the closer the shaft power is to the steady characteristic of the same speed setting, and the greater the power saving effect caused by the speed control.
If the head factor is ignored, the power saving effect of the inverter can be considered in the figure above as the difference between the output power of the outlet baffle control and the inverter. If the total export volume is 60% and the annual operation time is calculated as 6000 hours, compared with the frequency converter and valve control (outbound baffle control) for one fan, the annual energy saving can reach 235KW*0.6*6000h. In the year of 846000, each degree is calculated at 0.9 yuan, and the annual electricity bill is 760,000 yuan. Less than the production year to recover investment.
3) constant torque load and speed control For compressors, conveyors, roller and other loads, the relationship between the load torque and speed is not too large, but this constant torque load can also save energy by using the inverter speed control. The output power P expression of the motor is PâˆTXN (load X speed)
That is, when the inverter reduces the speed of the motor, the output power of the motor will decrease. Compared with the step-down speed regulation of the stator used in the slippery electromagnetic speed-regulating motor and squirrel-cage motor of the drive unit for the coal coal machine, the low-speed efficiency of the inverter is much greater. Therefore, inverter drives are used to replace these former ones. Speed-adjusting motor can fully save energy. The electricity saving rate is about 10%.
IV. Example of Inverter Application 1) Blower Application Boiler blower includes blower (FD) and induced draft fan (ID), etc. Generally, when the power station is designed, the air supply of the selected blower can meet 80% of the rated air flow of the blower and can be satisfied. Generator maximum output. In addition, thermal power plants often perform load adjustments. Most of them operate at 80% (upper limit) during the day and most of them operate at very low speeds during the night. The longer the small air flow rate of the frequency converter fan is, the greater the benefit will be.
For the combustion control of small-capacity boilers, some use thorium oxide to measure the oxygen content of the flue, and control the fan to minimize the oxygen content to reduce the heat released to the flue. This will not only save energy, but also save fuel.
When the frequency converter is used in a boiler blower, it should be noted that when the frequency converter has a fault or an overload, it must be able to switch to the power frequency power supply, not to stop the boiler from operating, and vice versa. Also consider the effect of higher harmonics on the motor and the bus.
2) The application of power plant boiler load to the feed pump often changes, of course, will cause changes in the water supply and drum pressure level, but only by adjusting the outlet valve will cause a lot of pressure loss, so that efficiency becomes low. If you control the speed of the feed pump to maintain the optimal pressure, you can eliminate pressure loss and achieve energy savings. If there are multiple pairs of feed pumps, a set of constant pressure water supply automatic cycle switching system can be established to keep the steam drum working in the best condition. In this type of system, the smaller the actual head to full head ratio, the greater the energy saving effect.
3) Application of Coal Feeder In the past, a slip electromagnetic speed control motor was used to control the speed of the coal feeder to achieve the control of the combustion of the furnace. The frequency conversion governor and the fully-closed governor and the fully enclosed external fan-type squirrel cage induction motor were used. In comparison, after the application of the inverter, the speed range can be increased from 20% to 100% of the slip motor to 2% to 200% (maximum). Especially when the amount of coal is small, the operating frequency is increased to 60Hz. And then increase the output. While saving electricity, it is also possible to avoid the use of slip-adjustable speed-regulating motors that are prone to frequent burnout due to clogging of coal powder, which seriously affects production.
Since the load torque of the powdered coal feed system during starting is larger than that during normal operation, the load characteristics must be taken into consideration when selecting the frequency converter, and a frequency converter with a larger primary capacity than the original motor must be selected, and the working mode of the frequency converter should be set. In vector mode to provide strong torque at low frequencies.
Due to the influence of the powder or its humidity in the hopper or the quality of coal, clogging may occur, resulting in an abnormally high starting torque and failure to start. In this case, there should be a design that starts directly with the power frequency to ensure that in any case, Coal machines can work reliably and reliably.
4) For the same application to the powder machine, due to the shortcomings of the slip speed regulation, replacing the inverter with the inverter can prevent the rotor blockage of the slip motor and realize synchronous and accurate proportional operation under the DCS. The powder amount can be precisely adjusted and the combustion can be controlled.
In order to prevent the influence of other faults, in the inverter, the minimum operating speed should be set to prevent complete interruption of powder feeding.
5) Loading, unloading, and transporting Automatic warehouses for power stations In order to increase productivity, achieve energy savings and save space, it is imperative to achieve high-speed and miniaturization of tower cranes. Tower cranes have been using DC motors or pole-electrode motors or series resistors to control the movement of the goods when they are walking and loading and unloading. However, in order to miniaturize and simplify the transmission and improve the positioning accuracy, inverters are increasingly used. .
With the use of frequency converters, the space and weight of the transmission can be reduced, using a standard gear motor or a disk motor. With a frequency converter you can also switch between walking and loading and unloading. The speed can be arbitrarily set to improve the parking accuracy.
When using, it should be noted that in order to speed up the working time, the motor capacity may be increased due to insufficient acceleration torque of the motor. Therefore, attention should be paid to the motor capacity and acceleration/deceleration characteristics. When the motor is running at a speed of 60HZ or more, the standard reducer may not be used, so the 6-pole motor and reducer can be selected to work at 90Hz or above.
V. Conclusion The development and application of the frequency converter benefits from this era, thanks to its intrinsic ability to achieve automation, stepless speed regulation and significant energy savings. Today, the extensive application of frequency converters has become a significant feature of modern power plants. This article lists several examples of inverter applications in power stations. Actually, there are many other aspects that are not detailed here. Afterwards, detailed topics such as the harmonics of the inverter technology, motor cooling, braking, and instantaneous stop and start can be discussed.
Application of frequency converter in power station
First, the development and characteristics of the inverter The inverter benefits from the rapid development of modern power electronic technology, automatic control technology and computer technology. The frequency changer has moved from the primary practical stage of the 1980s to the mature commercial stage of the 1990s. With the development of large-scale transistor switching modules GTO, GTR, and IGBTIPM, their voltage levels have increased from low voltage to high voltages of 6000 years, and the current has increased from several amps to several thousand amps. The cost has been greatly reduced, the volume has decreased, and the reliability has increased. mature. With the increase of computer E-PLD, CPU speed, and integration, new vector-type inverters with communication functions, intelligent high-performance field-oriented control technology, and direct torque control technology have adopted frequency conversion technology from simple industrial applications. The occasions brought people to various areas around them, such as household appliances, automobile manufacturing, building control, water supply, and agricultural irrigation. Becomes relevant to everyone. The huge economic and social benefits brought about by the application of power plants in particular are staggering.