Abstract: This paper briefly introduces the energy-saving principle of variable frequency speed control technology. Taking a brewery as an example, it analyzes the current status and effects of variable frequency speed control devices in various sections and workshops of the brewery. In addition to energy saving, variable frequency speed control devices can also improve process conditions, which is worthy of manufacturers' attention. Keywords: Load characteristics; Variable frequency speed control; Energy saving; Process introduction According to relevant statistics, the power consumption of pumps and fans accounts for more than half of the total national power generation and about 55% of the total industrial power consumption. AC induction motors used for pumps and fans are the main power loads. In order to meet the various requirements of the production process, many production machines driven by AC motors need to be operated with speed regulation, usually using mechanical or electrical speed regulation methods. Mechanical speed regulation includes speed regulation devices such as mechanical gearboxes, friction drives, hydraulic drives, fluid drives, and fluid couplings. Electrical speed regulation includes speed regulation devices such as voltage regulation, pole changing speed regulation, slip speed regulation, rotor series resistance speed regulation, cascade speed regulation, and variable frequency speed regulation. Compared with mechanical speed regulation, electrical speed regulation is widely used in production equipment due to its superior speed regulation performance, convenient adjustment methods, and high energy utilization rate. In the past decade or so, with the development of power electronics, microelectronics, and power switching devices, AC frequency conversion technology has gradually matured from theory to practice. Frequency conversion speed regulation, with its advantages of high efficiency, wide speed range, high speed accuracy, rigid characteristics, and stepless speed regulation, has gradually become dominant in various AC and DC speed regulation systems. In engineering design or technological transformation across various industries, especially in energy-saving technology transformation, the application of frequency conversion speed regulation technology is constantly expanding, and its application is developing from simple energy saving to a comprehensive direction of improving processes and increasing product quality and output. During the design and implementation process, a common problem encountered is whether using a frequency converter saves energy and whether it can meet production process requirements. This article analyzes the relationship between energy saving and load characteristics of frequency conversion speed regulation technology, specifically using a beer production plant as an example, to illustrate the relationship between energy saving and process, and also provides some quantitative calculation values. Energy saving and consumption reduction are important technical means to reduce product costs and improve product market competitiveness. Taking beer manufacturers as an example, the advanced level in China is around 70 kWh/ton, while the lagging level is around 200 kWh/ton, a difference of 130 kWh/ton. For a 50,000-ton brewery, this translates to a difference of 6,500,000 kWh/ton per year, resulting in a direct economic loss of 3,250,000 yuan! This significant difference has many causes, such as management issues, insufficient operating rates, and excessive non-production electricity consumption. However, outdated equipment, ineffective technological upgrades, and insufficient understanding of new technologies and equipment by manufacturers are also objective problems. A proper understanding of variable frequency drive (VFD) technology and the rational use of VFD devices can help manufacturers effectively solve equipment and technological upgrade problems, achieving the goal of energy conservation and consumption reduction. 1. Energy-Saving Principle and Load Relationship of Variable Frequency Speed ​​Control Technology According to statistics, half of the nation's annual electricity generation is consumed by motors. The vast majority of these motors are simple, convenient, and require minimal maintenance—squirrel-cage motors. Examples include motors for various pumps in breweries, refrigeration compressors, and conveyor belts on bottling lines. Due to technological limitations, speed control of high-power squirrel-cage motors (several kilowatts and above) was a distant dream before the 1980s. In situations requiring speed regulation, DC motors or wound-rotor asynchronous motors were often used, which had high environmental requirements and were unsuitable for humid environments like breweries. In the last two decades, with the development of power electronic devices and advancements in automatic control theory, the price of general-purpose variable frequency drives (VVVF) using variable frequency speed control technology has dropped significantly. Speed ​​control of squirrel-cage motors using VVVF devices has become a reality in most factories. Not all speed control of squirrel-cage motors using variable frequency drives (VFDs) achieves good energy-saving results. This is largely related to the load characteristics of the motor. Through extensive analysis and summarization, the load characteristics of electric equipment are generally divided into three categories (Table 1). Since breweries have almost no constant power loads, the energy-saving characteristics of the other two types of loads (constant torque loads and centrifugal fans/pumps) will be discussed below. 1.1 Energy-saving analysis of constant torque loads For simplicity, it is assumed that the input power of the motor is equal to the shaft power of this type of device, i.e., the effect of device efficiency is not considered. [align=center]Table 1 Classification of motor load characteristics[/align] Since the shaft power of this type of load is proportional to the motor speed, P∝n, theoretically, the energy saved by speed regulation of this type of load is proportional to the speed regulation range. For example, if the speed is reduced to half of the original speed, then 50% of the power consumption will be saved. The main power-consuming device in a brewery—the refrigeration compressor—is this type of load, and its power-speed relationship is shown in Figure 1. [align=center]Figure 1 Ideal Power-Speed ​​Diagram for Two Types of Loads[/align] 1.2 Energy Saving Analysis of Centrifugal Fans and Pumps According to fluid mechanics theory, theoretically, when the speed of a centrifugal pump is changed, the pump characteristics have the following relationship: Where: Q-flow rate, H-head, P-pump shaft power, n-pump speed, subscripts 1 and 2 indicate two different pump speeds. It can be seen from the above formula that when the flow rate changes from 100% to 80%, the power changes from 100% to 51.2%, which can save 48.8% of power consumption. The effect is very significant. Various pipeline pumps in the saccharification workshop and fermentation workshop of breweries, as well as blowers and induced draft fans on boilers, belong to this type of load. The power-speed relationship is shown in the figure. 2 Application of Variable Frequency Drives in Breweries 2.1 Main Applications of Variable Frequency Drives in Breweries Variable frequency drives are currently used in breweries for two main purposes: (1) energy saving, which is well known to most manufacturers; (2) improvement of process conditions. Currently, variable frequency drives (VFDs) are mainly used in the following locations in breweries (Table 2): ① Application in wort filtration pumps in the saccharification workshop. In wort filtration, to facilitate the formation of the mash layer, it is necessary to adjust the wort flow rate. Traditionally, flow rate is controlled by regulating valves, but this cannot control the suction at the pump inlet, which is detrimental to the formation of the mash layer. Some manufacturers use VFDs to control the pump speed, which not only changes the pump flow rate but also effectively alters the suction at the pump inlet, thereby controlling the speed and tightness of the mash layer formation, thus improving process conditions. Practical experience has shown that this method is very effective. Furthermore, using VFDs to control the pump flow rate saves energy compared to using valves. For example, the following calculations were performed at a brewery: Conditions: ① Motor power 7.5KW ② Filtration time 3 hours per batch ③ 1200 batches produced annually ④ Speed ​​range 10-50Hz, randomly distributed. Results: Conservative calculation: 7.5 * 1200 * 3 * 50% = 13500 (kWh), at 0.5 yuan per kWh, it can save 6750 yuan/year. ② Fermentation tank refrigerant circulation supply pump. This is a typical constant pressure liquid supply system [1]. Due to the large power of the pump and the long working time, the energy saving effect is very significant. Taking a brewery as an example, the calculation is as follows: Conditions: ① Motor power 22KW ② Working 24 hours a day, 360 days a year ③ Speed ​​range 30～50Hz, randomly distributed. Results: It can save 22 * ​​24 * 360 * 33.73% = 64114 (kWh), at 0.5 yuan per kWh, it can save 32057 yuan/year. In addition to saving energy, this constant pressure liquid supply system also has the following advantages: stabilize the liquid supply pressure and prevent pipe burst accidents that may be caused by the increase in pipeline pressure when fewer fermentation tanks are working. The above two cases are comparisons of energy-saving analysis when adjusting the pump outlet valve and adjusting the pump speed. This is related to the resistance characteristic curve of the pipeline, the flow state of the liquid in the pipe (laminar flow and turbulent flow), and the degree of matching between the selected pump power and the actual required power. For detailed analysis, please refer to reference [1]. ③ Conveyor motor on the bottling line in the bottling workshop. This part of the device is generally matched with the bottling line. The power is small, the energy-saving significance is not significant, and it cannot improve the beer production process conditions. It mainly facilitates the flexible operation of the bottling line. 2.2 The next step prospect of the application of variable frequency speed control device in brewery [align=center]Table 2 Application and effect of variable frequency speed controller[/align] The main power consumer in brewery is the refrigeration compressor. It has a large power (several hundred KW) and a large number of units. It is generally operated in parallel. The cooling capacity is adjusted by adjusting the number of units in operation. The fluctuation is large. Manufacturers often have this feeling in actual use: the cooling capacity is not enough when all units are turned on during the peak production season, and the cooling capacity is still excessive when only one unit is turned on during the off-season. Adjustment is made by manual detection or feeling. This easily causes large fluctuations in the working conditions and wastes energy. Currently, there is virtually no domestic manufacturer using variable frequency drives (VFDs) to control refrigeration compressors. The main reasons are: ① Manufacturers are unaware of the energy-saving effects of using VFDs in this part; ② The initial investment is large, and they believe there are technical risks involved. In fact, it is common for multiple water pumps to operate in parallel in water supply systems, sometimes as many as dozens. Therefore, there is no technical problem with operating multiple compressors in parallel. However, in order to maximize energy efficiency and ensure stable process operation, it is necessary to establish necessary predictive models and control strategies based on the relationships between the number of saccharification workshops, the yield per batch of wort, the number and volume of fermentation tanks, the number and power of compressors, and the actual and required cooling capacity. These models should be coordinated with the fermentation automation system. According to rough estimates, there is an energy saving capacity of about 15% to 20%. Based on an annual production of 50,000 tons of beer and an electricity consumption of 120 kWh per ton of beer, this could save 900,000 to 1,200,000 kWh of electricity per year. At 0.5 yuan per kWh, this could save 450,000 to 600,000 yuan, allowing the entire investment to be recovered within one year. In addition to the direct benefits, it can also make the refrigerant temperature more stable and improve the fermentation process conditions, which is worth the attention of manufacturers with economic strength. 3 Conclusion Energy saving and consumption reduction are important means to reduce production costs. Reducing production costs and improving the market competitiveness of products are the hard truths for manufacturers to seek development. How to use new products and technologies to carry out technical transformation of equipment is something that manufacturers should always pay attention to and understand. Variable frequency speed controller is such a new technology and new product. Using it to transform certain electric equipment in breweries can achieve significant energy saving effects and improve beer production process conditions, which is worthy of manufacturers' attention. References: [1] Wang Nianchun. Energy saving analysis of variable frequency speed control technology in water supply system[J]. Journal of Electrical Engineering, 2001, (6): 38-40.