People who know the frequency conversion speed regulation have become quite common, but most people can always hook up with energy saving when they mention the frequency conversion speed regulation. In recent years, although China has made rapid progress in energy development, it has not kept up with the growth of demand, and the issue of energy conservation has always been in a prominent position. After many theoretical researches and the application of the No.5 and No.6 converters, the Xuanhua Steelmaking Plant used a large number of frequency converters in the 150T converter dust removal fan, water pump and vibration feeding, which contributed to China's energy conservation cause.
1 working principle of the inverter
The inverter is mainly composed of a module, a CPU control board, and a power drive board set.
We know that the synchronous motor speed expression of the AC motor is: n=60f(1-s)/p(1) where n is the speed of the asynchronous motor; f is the frequency of the asynchronous motor; s is the motor slip; p is The number of poles of the motor. It can be seen from equation (1) that the rotational speed n is proportional to the frequency f, and the rotational speed of the motor can be changed by changing the frequency f. When the frequency f is varied within the range of 0 to 50 Hz, the motor rotational speed adjustment range is very wide. The inverter is to adjust the speed of the motor by changing the frequency of the motor. It is an ideal high-efficiency, high-performance speed control method. If you think that the motor can save energy by using the inverter, it is too far-fetched.
The frequency converter is a concrete embodiment of power electronics science. It is an electronic circuit device that utilizes the on-off function of power electronic semiconductor devices to realize the conversion and control of high-power electric power, that is, the power circuit is electronically realized, and can be intuitively controlled and displayed. Due to the superiority of the frequency converter, the application field is becoming wider and wider, the technology used is also expanding, and at the same time, in pursuit of miniaturization of the frequency converter, people have been constantly fighting the heat of the components. Since the new generation of IGBTs adopts a new drain-control technology, the collector-emitter simple saturation voltage (Ucesat) is greatly reduced, so that the new device has low loss and has the effect of reducing heat generation and eliminating loss.
The 380V small-capacity general-purpose inverter is widely used at present, but the power consumption is relatively large, and the most significant energy-saving effect is the high-voltage large-capacity inverter. With the development of frequency conversion speed regulation technology, the high-voltage frequency conversion speed regulation technology as a large-capacity transmission has been widely used, and its application scope basically covers all major industries in China, such as electric power, metallurgy, petroleum, chemical industry and papermaking. The product voltage grade includes 3kV, 6kV and 10kV and 1,600V-2,400V products used in oilfield dedicated submersible electric pumps, and basic draggable fans, pumps, compressors and other loads.
The high-voltage motor can realize stepless speed regulation by using high-voltage frequency converter, which can meet the requirements of the motor speed control of the production process, and can save energy and reduce production cost. With the development of self-shutdown devices represented by GTO, IGBT, IGCT, etc., the research on various main circuit topologies suitable for high-voltage frequency conversion has been further deepened, and the rapid popularization of intelligent control chips represented by DSP is The application research of high-voltage variable frequency speed control technology has also laid a solid foundation. As a resource-saving product, high-voltage inverters, with the continuous development of power electronics technology, continuous improvement of products, deep concept, and market expansion, will show huge technological development prospects and market demand. Accordingly, The energy-saving requirements for the inverter have also increased accordingly.
2 frequency converter energy saving principle
2.1 frequency conversion energy saving
The energy saving of the inverter is mainly reflected in the application of fans and pumps. Xuanhua Steelmaking Plant has a large number of fan-type pump loads. This type of load is known from fluid mechanics. p (power) = Q (flow) × H (pressure), flow Q is proportional to the primary of rotational speed N, pressure H It is proportional to the square of the rotational speed N. The power P is proportional to the cube of the rotational speed N. If the efficiency of the water pump is constant, when the required flow rate is required to decrease, the rotational speed N can be proportionally decreased, and at this time, the shaft output power P is reduced. . That is, the relationship between the power consumption of the pump motor and the rotational speed is approximately proportional.
Therefore, when the required flow rate Q is reduced, the output frequency of the inverter can be adjusted to reduce the motor speed n proportionally, and the speed control mode can still operate the pump with high efficiency at low speed and small flow rate. At this time, the power p of the motor will be greatly reduced in a cubic relationship, which is 40% to 50% more energy-efficient than the regulating baffle and the valve, thereby achieving the purpose of power saving. In order to ensure the reliability of production, all kinds of production machinery have a certain margin when designing with power drive. When the motor can't run under full load, in addition to meeting the power drive requirements, the excess torque increases the consumption of active power, resulting in wasted power. Fans, pumps and other equipment traditional speed control method is to adjust the air volume and water supply by adjusting the baffle and valve opening of the inlet or outlet. The input power is large, and a large amount of energy is consumed in the interception process of the baffle and the valve. in. When using variable frequency speed regulation, if the flow demand is reduced, the speed can be met by reducing the speed of the pump or fan.
For example, a centrifugal pump motor has a power of 55 kW. When the speed drops to 4/5 of the original speed, its power consumption is 28.16 kW, saving 48.8%. When the speed drops to l/2 of the original speed, The power consumption is 6.875 kW, saving 87.5%.
2.2 Power factor compensation energy saving
Reactive power not only increases the line loss and heat of the equipment, but also the power factor decreases, which leads to the reduction of the active power of the power grid. In the large amount of reactive power consumption lines, the equipment is inefficient and wasteful. After using the variable frequency speed control device Due to the internal filter capacitor of the inverter, the reactive power loss is reduced, and the active power of the power grid is increased.
2.3 soft start energy saving
The hard start of the motor has a serious impact on the power grid, and it also requires too much power grid capacity. The large current and vibration generated during startup have great damage to the baffle and the valve, which is extremely detrimental to the service life of the equipment and pipeline. After using the variable frequency energy-saving device, the soft start function of the inverter will start the starting current from zero, and the maximum value will not exceed the rated current, which will reduce the impact on the power grid and the power supply capacity, and prolong the use of equipment and valves. life. Saves on equipment maintenance costs.
3 conclusions
The reason why the frequency conversion speed regulation is energy-saving is mainly to save the wasted electric energy in the full-speed operation. In particular, the closed-loop speed control system, such as the constant pressure water supply system, achieves the on-demand drag, which almost completely eliminates the waste of the drag system during operation. This is energy saving from a big perspective, but it does not mean that the energy saving potential has been tapped clean. In fact, on many occasions, there are still big horse-drawn cars, and in this respect, there is still great potential.
The inverter can save power. This is an indelible fact. In some cases, it can save more than 40% of electricity. However, in some cases, it will be wasted than not being connected to the inverter! The inverter is energy-saving by light load step-down. The dynamic torque load does not change much because of the speed. Even if the voltage is reduced, it will not be much, so the energy saving is very weak, but it is different in the fan environment. When a small air volume is needed, the motor will reduce the speed. We know the fan. The energy consumption is proportional to the 1.7th power of the speed, so the torque of the motor will drop sharply and the energy saving effect will be obvious.
Of course, if the environmental requirements must be adjusted, the energy-saving effect of the inverter is still obvious. In the case of no speed regulation, the inverter will not save power and can only improve the power factor. In fact, the specific effects achieved by the inverter and even the power electronics industry are as follows: 1) Further improve the efficiency of power conversion and reduce standby loss. 2) Avoid power pollution, minimize current harmonics, and improve power factor. 3) Improve the electromagnetic compatibility of the power supply unit and system. 4) Reduce electrical noise. 5) Achieve high performance controllability. The dust removal fan, water system and feeding system of Xuanhua Steelmaking Plant are also adapted to this characteristic of the frequency converter. After many theoretical researches, the frequency converter has been adopted to make certain contributions to China's energy conservation cause.