[Abstract] In line with the national policy of energy conservation and emission reduction, Delta Electronics, adhering to the environmental protection, energy-saving, and Earth-loving philosophy, has developed the AFE2000 active energy regeneration unit based on its own R&D capabilities. The AFE2000 employs advanced SVPWM control methods, which not only feed the energy regenerated by the drive system back to the grid, saving electricity, but also improve the power factor of the grid and effectively reduce grid harmonics. Its effectiveness has been well verified through practical applications in elevators.
【Abstract】Comply with the national policy of energy conservation and emissions reduction, Delta uphold the concept of environmental protection, energy-saving, loving the earth, relying on its own research and development strength, develop the active energy unit retrogradation AFE2000, AFE2000 advanced SVPWM control method, not only can drive system anabiosis energy back to power grid, saving power, but also can improve the power factor of power grid and effectively reduce the power grid harmonic. Through practical application in the elevator, it has been well validated.
[Keywords] AFE2000; energy feedback; elevator
【Keywords】AFE2000; energy feedback; elevator
According to statistics from the China Elevator Industry Association, there are currently approximately 2.5 million elevators in China, with new elevator sales increasing by more than 500,000 units annually. China has become a global elevator superpower. With the rapid increase in the number of elevators in China, an average elevator consumes approximately 50-150 kilowatt-hours of electricity per day. Assuming an average daily consumption of 80 kilowatt-hours per elevator and a conservative estimate of 2.5 million elevators nationwide, this translates to a daily energy consumption of approximately 200 million kilowatt-hours, or an annual consumption of 72 billion kilowatt-hours. This is close to the annual power generation of the Three Gorges Dam, demonstrating the enormous energy consumption of elevators. Therefore, energy-saving elevators are an urgent necessity and an inevitable trend in future elevator development.
In the past decade, gearless traction machines have gradually replaced geared traction machines, saving about 40% more energy than traditional geared traction machines. This represents a significant step forward in elevator energy conservation. However, elevators still consume a large amount of energy, ranking alongside air conditioners as two major "energy hogs," and the need for energy conservation remains urgent. In recent years, elevator energy feedback devices have emerged on the market, marking another significant step towards elevator energy conservation.
Currently, most variable frequency speed control elevators in China use resistors to dissipate the energy stored in capacitors to prevent capacitor overvoltage. Because the heat generated by the resistors during elevator operation is extremely high, with localized resistor temperatures typically exceeding 100℃, users need to install high-volume air conditioners or fans to lower the machine room temperature and prevent elevator malfunctions due to overheating. In machine rooms with high elevator power, air conditioners and fans often need to be used simultaneously, or multiple air conditioners and fans need to be running at the same time. In some places, the power consumption of cooling equipment is often higher than the power consumption of the elevator itself. Users are aware of the serious energy consumption but are powerless to address it.
1. Elevator operating characteristics and current energy-saving solutions
As we all know, elevators move in a reciprocating motion. When the elevator is heavily loaded and going up, or lightly loaded and going down, the traction machine is in electric mode, driving the car to move. When the elevator is heavily loaded and going down, or lightly loaded and going up, the traction machine is in generator mode. The electricity generated by the traction machine will increase the DC voltage of the drive. In order to ensure the normal operation of the drive, the generated electricity must be disposed of. The traditional approach is to add a braking unit and a braking resistor to the drive, and dissipate the electricity generated by the traction machine through the braking resistor in the form of heat loss.
Figure 1 Traction machine electrical dynamics Figure 2 Traction machine power generation status
Since the electricity generated by the traction machine is consumed as heat by the braking resistor and is not effectively utilized, there are currently some solutions to utilize this energy consumption. These mainly include the following:
(1) Using a large capacitor for energy storage, when the elevator traction machine is in the power generation state, the large capacitor is charged through the circuit, and the electrical energy of the large capacitor is used to provide power to the control circuit of the driver.
The use of large capacitors for energy storage represents an advancement in the reuse of generated electricity. However, the control circuit of the driver has very low power, resulting in a small amount of energy consumption. Therefore, not all the electrical energy generated by the traction machine can be stored in the large capacitor, and the unstored portion still needs to be dissipated as heat through the braking resistor.
(2) Using batteries for energy storage is actually the same principle as using large capacitors.
(3) A simpler way to save energy is to cut off the power supply to the drive and lighting when the elevator is idle. However, this method does not actually reflect the true energy consumption of the elevator.
The above-mentioned elevator energy-saving solutions all fail to truly achieve the goal of energy saving, or can only utilize a small portion of the electricity generated by the traction machine, while the majority is still consumed as heat energy through the braking resistor, thus failing to fundamentally achieve energy saving in elevators.
2 Delta AFE2000 Energy Feedback Unit
Delta Electronics, leveraging its R&D capabilities, developed and designed the AFE2000 energy feedback unit to meet the needs of four-quadrant operation. When combined with a frequency converter, the AFE2000 can achieve four-quadrant operation of the frequency converter.
The AFE2000 is applied to elevators, fundamentally solving the energy-saving problem of elevators. When the elevator is in motor mode, the AFE2000 supplies power to the elevator drive, improves the power factor, and reduces harmonics. When the elevator traction machine is in generator mode, the AFE2000 can invert the electricity generated by the traction machine into AC power with the same frequency, phase, and amplitude as the power grid, and then feed it back into the power grid to power other surrounding equipment, thus fundamentally and effectively utilizing the electrical energy generated by the traction machine.
Figure 3 System Diagram and Test Architecture
3. AFE200 Circuit Principle
The AFE2000 uses IGBT rectification and SVPWM control. The high-performance central controller MCU controls the motor feedback state, rectifying the AC voltage of the grid into DC voltage to supply the frequency converter of the elevator drive unit. When the elevator is in motor output mode, the AFE2000 provides energy to the frequency converter. When the elevator is in regenerative braking mode, the AFE2000 converts the electricity generated by the traction machine into AC electricity with the same phase and amplitude as the grid and feeds it back into the grid.
Figure 4 Original block diagram of AFE2000
4 AFE2000 Elevator Application Test
An AFE2000 was installed on an elevator on the 6th floor of Building 2 at Delta Electronics' Wujiang plant. After more than a year of testing and actual operation, the energy feedback effect has met expectations.
Figure 5 System Diagram and Test Architecture
In actual use, the three-phase AC elevator is connected to the AFE2000 through a reactor. The AFE2000 and Delta's integrated elevator IED are connected through DCbus. When the traction machine is in the power generation state, the IED transmits the power generated by the traction machine to the AFE2000 through DCbus, and the AFE2000 inverts the DC power into three-phase AC power and feeds it back into the power grid.
Figure 6. Without AFE2000 installed. Figure 7. After AFE2000 installed.
By conducting actual operational tests with and without AFE2000 installed, the effects of energy feedback and power factor improvement were monitored.
Average power factor comparison (including PF value when AFE is not working):
Before installing AFE2000: Power factor = WK/VA = (345/395) × 100% = 87%
After adding AFE2000: Power factor = WK/VA = (261/280) × 100% = 93%
5. Summary Delta's AFE2000 series active power regeneration unit can directly feed regenerated braking energy back to the mains power grid, eliminating the need to convert it into heat energy from the braking resistor. In other words, it enables four-quadrant operation of the inverter and further reduces energy consumption. If the system has high braking power and operates during frequent braking processes, the regenerated energy can be fed back to the mains power grid via the AFE2000 to improve power quality, resulting in more significant green energy-saving benefits and truly achieving "environmental protection, energy saving, and love for the Earth."
About the author:
Shao Shifeng, male, born in 1980, graduated from Henan Polytechnic University with a major in Electronic Information Engineering. He is currently a project engineer at Delta Electronics Application Technology Center. He has been engaged in the research and development and application of inverter hardware and is now engaged in the application solutions and industry development of power quality products.
