Dec 01, 2020
What are the key knowledge points of inverter energy saving and emission reduction?
Recently, a netizen posted a message on the Internet that energy-saving and emission reduction of inverters is pseudo-science, and they have a certain discussion on this point of view. The following is a partial discussion.
"More than 70% of the articles I have seen use very specific examples to illustrate the energy-saving effects, and most of them are focused on water supply from water plants. The article does not give various parameters as you require in the post. But from the perspective of energy conservation, it is the same for one year (assuming that the water characteristics are the same). The energy-saving effect does appear before and after the frequency conversion speed regulation is adopted, and it is generally around 20%. I don't know what you have about it. view?
Whether it is harmonic loss, efficiency reduction, or energy changes in other intermediate links, the frequency conversion has an energy-saving effect on the whole. At the same time, in practice, many methods can be used to achieve effective harmonic loss. The use of reactors is a common one. The copper loss of the motor can be reduced by the optimization algorithm of current control. Of course, there may be a prerequisite for this. Because the original water supply system of the water plant considered a larger desire for water supply, the selected motors and pumps were larger than the actual ones, but I think this choice The type is still reasonable. The overall trend of urban water supply is upward development. When the population increases and the overall demand for water supply becomes greater, this selection can reflect its rationality.
It is mentioned that the energy loss of the frequency converter in the ordinary constant pressure water supply is generally more than 30%; the energy loss in the constant pressure water supply of the water plant is generally more than 20%. It can be considered that under normal conditions, the frequency converter constant pressure water supply In theory, it is 100% negative energy saving.
What we understand is whether this argument believes that motors and water pumps that have not been reasonably selected consume a lot of energy. After the use of inverters, the energy loss caused by incorrect selection is relatively reduced, but it is relatively reasonable after selection. In other words, electricity is still wasted. If not, then I would like to know the object of the energy loss mentioned in it, and whether there is theoretical or actual data basis for such loss. If so, I think it is feasible to use frequency conversion to reduce loss. The frequency converter can mainly realize the smooth speed regulation of the water pump and eliminate the water hammer effect. At the same time, the harmonic loss of most high-end frequency converters is relatively small compared with the low-end parameters, basically within 5%.
As for high-rise water supply and other occasions with higher water pressure requirements, it is unrealistic for me to artificially save energy with frequency conversion. "
It can be seen that the opinions of netizens on it are a bit one-sided, and the following is the explanation of relevant experts.
1. Frequency conversion energy saving
Inverter energy saving is mainly manifested in the application of fans and water pumps. In order to ensure the reliability of production, various production machines have a certain margin when they are designed and equipped with power drives. When the motor cannot run under full load, in addition to meeting the power drive requirements, the excess torque increases the active power consumption and causes a waste of electrical energy. The traditional speed regulation method of fans, pumps and other equipment is to adjust the air supply and water supply by adjusting the inlet or outlet baffle and valve opening. Its input power is large, and a large amount of energy consumption baffle, In the process of valve closure. When using frequency conversion speed regulation, if the flow requirement is reduced, the requirement can be met by reducing the speed of the pump or fan.
According to fluid mechanics, P (power) = Q (flow) × H (pressure), flow Q is proportional to the first power of speed N, pressure H is proportional to the square of speed N, and power P is proportional to the cube of speed N If the efficiency of the water pump is constant, the speed N can be reduced proportionally when the required adjustment flow drops, and the shaft output power P decreases in a square relationship at this time. That is, the power consumption of the water pump motor and the speed are approximately in a square ratio relationship. When the required flow rate Q decreases, the output frequency of the inverter can be adjusted to reduce the motor speed n proportionally. The power P of the motor will be greatly reduced according to the cubic relationship, which is 40%-50% more energy-saving than regulating baffles and valves, so as to achieve the purpose of saving electricity.
For example: a centrifugal pump motor has a power of 55 kilowatts. When the speed drops to 4/5 of the original speed, the power consumption is 28.16 kilowatts, which saves 48.8% of electricity. When the speed drops to 1/2 of the original speed At the time, its power consumption was 6.875 kilowatts, saving 87.5% of electricity.
2, power factor compensation energy saving
Reactive power increases line loss and heat generation of equipment, and more importantly, the reduction of power factor leads to the reduction of active power of the grid. Among a large number of reactive power consumption lines, equipment use efficiency is low and waste is serious. After using frequency conversion speed control device, frequency conversion The filter capacitor functions inside the device, thereby reducing reactive power loss and increasing the active power of the grid.
3, soft start energy saving
The hard start of the motor will cause a serious impact on the power grid, and it will also require too much power grid capacity. When a large current and vibration are generated during startup, the baffle and valves will be greatly damaged, and the service life of the equipment and pipelines is extremely unfavorable. After using the frequency conversion energy-saving device, the use of the soft start function of the frequency converter will make the starting current start from zero, and the maximum value will exceed the rated current, which reduces the impact on the grid and the requirements for power supply capacity, and extends the service life of equipment and valves. Save the maintenance of equipment. However, Weierkai Electric Shanghai Co., Ltd. CEO Chen Jianyi explained the energy-saving effect of the inverter: "The main working principle of the inverter is: through the use of microelectronics, power electronics and control technology, it will provide The power frequency AC power of the motor stator is rectified into DC by diodes, and then converted into AC power with adjustable frequency and voltage by IGBTs and other inverters. This power then drives the motor and the load. Frequency conversion speed regulation developed in the early 1980s The technology conforms to the requirements of the development of industrial production automation and creates a new era of intelligent motors. It changes the old mode that ordinary motors can only run at a fixed speed, so that the motor and its drag load can be used without any changes. The speed output can be adjusted according to the requirements of the production process, thereby reducing the power consumption of the motor and achieving the purpose of efficient operation of the system. At present, it has been practically applied in the motor transmission equipment of various industries such as electric power, metallurgy, petroleum, steel, chemical, water supply and drainage , Has become a main development direction of modern electric drive technology. The power-saving measures of AC asynchronous motors can adopt different ways of speed regulation and energy saving. Generally, the more commonly used speed regulation methods include fluid coupling speed regulation, cascade speed regulation, There are four types of electromagnetic speed regulation and frequency conversion speed regulation. In comparison, frequency conversion speed regulation has significant power saving effects, especially on fans and water pumps. According to the principle that the power consumed by fans and water pumps is proportional to the third power of the speed. If necessary If the air volume is reduced by 20%, the corresponding motor speed should be reduced by 20%. The actual speed is 80%, then (0.8)3≈51%, and the fan can save energy up to 50%. If the speed is reduced by half, then (0.5)3≈13 %, it is expected to save 87% of electricity. Based on this principle, the use of frequency converter speed control method to adjust the air volume or flow rate is an effective method for saving electricity."