1. Introduction Our company's 2000-ton large hydraulic press has a total induction motor capacity of 225 kW, which operates at a low load of around 25% for extended periods, resulting in significant energy waste. Currently, energy-saving technologies applied to large hydraulic presses are still in the exploratory stage, lacking mature application experience for reference. Therefore, it is necessary to conduct research on the application of applicable energy-saving technologies. Currently, mature technologies for saving energy in induction motors include intelligent energy-saving devices and frequency converters. The working principles of these two energy-saving technologies are introduced below. Intelligent energy-saving devices continuously monitor the motor's operating status, thereby changing the motor's input voltage. When the energy-saving device detects that the motor is under light load or the load is constantly changing, it adjusts the motor's input voltage to match the motor's output power with the real-time load, thereby reducing copper and iron losses, improving the motor's starting and stopping performance, and achieving energy savings. Its advantages are low price and no change in motor speed, but the energy-saving potential is relatively small. Frequency converter energy saving reduces the output power of the hydraulic pump by lowering the motor speed, thus matching the output power of the hydraulic pump with the real-time load, reducing copper and iron losses in the motor, improving the motor's power factor, improving the motor's starting and stopping performance, and reducing pump losses, thereby achieving energy saving. Its advantages are good energy saving effect, reduced noise, and extended hydraulic pump life. Its disadvantages are high investment and impact on the hydraulic press's operating status. [b]2 Experimental Scheme and Objectives 2.1 Experimental Scheme[/b] The following scheme was adopted for this project. A 2000-ton hydraulic press has three 75 kW hydraulic pump motors. Motor #1 is connected to a frequency converter, motor #2 is connected to an energy-saving device, and motor #3 retains its original control circuit. A digital multi-functional power meter was used to measure and test the energy usage of the three motors online throughout the day to obtain actual energy-saving data. A comprehensive technical and economic analysis and evaluation of the two energy-saving technologies were then conducted. 2.2 Experimental Objectives The objectives of this energy-saving technology research experiment are as follows: 1) Comparison of energy-saving rates between induction motor intelligent energy-saving devices and frequency converters in hydraulic press applications. 2) Comparison of the impact of energy-saving devices and frequency converters on the overall system performance in hydraulic press applications. 3) Comparison of the overall cost-effectiveness of energy-saving devices and frequency converters in hydraulic press applications. 3. Experimental Results The electrical control cabinet for the 2000t large hydraulic press energy-saving experiment was commissioned and officially put into operation on July 3, 2006. After one month of operation and testing, the following experimental data (standby power-saving mode) was obtained on August 3, 2006, through the testing power meter (ACR220E). In the experiment, we also tested the mechanical characteristics of the hydraulic pump of the 2000t hydraulic press. The frequency converter driving the #1 hydraulic pump was set to sensorless vector control mode. When the hydraulic pump was working normally, it operated at 50Hz, and the output current of the frequency converter in no-load standby mode was 40.6 A; in standby power-saving mode, it operated at 5Hz, and the output current of the frequency converter was 37.2 A. When the frequency converter is in sensorless vector control mode, the motor operates in constant flux mode, so its output torque is proportional to the output current. Therefore, it can be concluded that the 2000 t hydraulic press is essentially a constant torque load. [b]4 Technical Analysis 4.1 Comparison of Energy Saving Rates of Induction Motor Intelligent Energy Saver and Frequency Converter in Hydraulic Press Applications[/b] Through one month of operational testing, the following conclusions can be drawn from the test data in the table above. 1) After adopting the energy saver, the annual energy savings are: active energy is 3 x 12 x (1714 - 1655) = 2124 kW-h; reactive energy is 3 x 12 x (6746 - 5114) = 58752 kvar-h. The active energy saving rate of the energy saver is 34%, and the reactive energy saving rate is 24.2%. 2) Annual energy savings after adopting frequency converters for the entire machine: Active energy savings are 3 x 12 x (1,714 x 1,029) = 24,660 kW-h; reactive energy savings are 3 x 12 x (6,746 x 179) = 236,412 kvar-h. The active energy saving rate of the frequency converter is 40%, and the reactive energy saving rate is 97.3%. The significance of active energy saving lies in directly saving electricity expenses and reducing production costs. The significance of reactive energy saving lies in reducing the line loss of the workshop power supply bus and reducing the secondary current of the workshop distribution transformer. The saved reactive current can be transferred to newly installed equipment in the power grid, thereby solving the problem of increasing the capacity of the workshop distribution transformer after the addition of new equipment. From the above energy saving data, it can be seen that regardless of whether it is the energy-saving device scheme or the frequency converter scheme, the reactive energy saved is much greater than the active energy saved. The indirect benefits of reactive energy saving to the workshop power grid are very obvious. 4.2 Comparison of the Impact of Energy Savers and Frequency Converters on the Overall System Performance of Hydraulic Presses Intelligent energy savers continuously monitor the operating status of the motor, thereby changing the motor's input voltage. When the energy saver detects that the motor is under light load or the load is constantly changing, it adjusts the motor's input voltage to match the motor's output power with the real-time load, thereby reducing copper and iron losses, improving the motor's starting and stopping performance, and achieving energy saving. Its advantages are low price and no change in motor speed, but the energy saving potential is relatively small. Frequency converter energy saving reduces the output power of the hydraulic pump by reducing the motor speed, matching the hydraulic pump's output power with the real-time load, reducing copper and iron losses, improving the motor's power factor, improving the motor's starting and stopping performance, and reducing pump losses, thereby achieving energy saving, noise reduction, and extended hydraulic pump life. Test results show that the hydraulic pump of a 2000-ton hydraulic press is essentially a constant torque load. Under no-load conditions, when the hydraulic pump speed is reduced to 1/10 of its rated speed, the active power consumed is also proportionally reduced to 1/10 of the original power consumption, thus significantly saving electricity. Its advantages are good energy saving effect, extended hydraulic pump life, and reduced noise. The disadvantages are high investment and impact on the hydraulic press's operating status. 4.3 Comparison of the Overall Cost-Effectiveness of Energy Savers and Frequency Converters in Hydraulic Press Applications As the above analysis shows, in the energy-saving test of a 2000t large hydraulic press, the frequency converter demonstrated superior performance that energy savers could not match. Specifically, after using frequency converter energy-saving control, the overall energy saving rate reached 85.7%, reducing machine noise and extending the hydraulic pump's life. Its disadvantage is that since it achieves energy saving by reducing the hydraulic pump speed, it affects the hydraulic press's operating status. However, this disadvantage can be addressed through electrical control. While energy savers do not change the motor speed and have no impact on the hydraulic press's operating status, their energy-saving potential is smaller. This analysis considers the overall cost-effectiveness of energy savers and frequency converters. A 75 kW domestic Senlan frequency converter costs 33,000 yuan, while a 75 kW domestic Qilida energy-saving device costs 13,000 yuan. The frequency converter's overall energy-saving rate is 4.285 times that of the energy-saving device, while its price is only 2.538 times that of the energy-saving device. Furthermore, the frequency converter energy-saving solution has two significant advantages that the energy-saving device solution lacks: reduced machine tool noise and extended hydraulic pump life. Extending the hydraulic pump life means saving on equipment maintenance costs, and reducing machine tool noise improves the working environment for workers, thus contributing to environmental noise pollution control. In conclusion , in the energy-saving test of the 2000t large hydraulic press, the frequency converter energy-saving solution demonstrated superior performance that the energy-saving device solution cannot match, achieving an overall energy-saving rate of up to 85.7%, while also showing significant effects in reducing machine tool noise and extending hydraulic pump life. Therefore, the overall cost-effectiveness of the frequency converter energy-saving solution is superior to that of the energy-saving device solution.