Elevator energy feedback suppliers remind you that the use of vertical elevators in high-rise buildings is becoming increasingly popular. To achieve good energy-saving effects in elevators, it can be said that there is a long way to go. In addition to daily management efforts (such as installing automatic sensors on elevators during non peak commuting periods), the most important thing is the technology research and manufacturing process of production enterprises. According to statistical data, the power consumption of the elevator drive host dragging the load accounts for more than 70% of the total power consumption of the elevator. Therefore, the practical operation focus of energy-saving elevators lies in updating and improving the driving and traction systems, elevator speed regulation methods, and control methods.
1. Energy feedback technology
Energy feedback technology is the process of using an inverter to invert the DC side of a frequency converter into AC power and feed it back into the power grid when the motor is in a generating state. From the working characteristics of elevators, it can be seen that half of their operating state is in the power generation state. In theory, the energy-saving effect of energy feedback technology should be very good. According to incomplete statistics, currently over 92% of elevators only waste this energy in the form of regenerative resistance heating. Based on the statistics of nearly 1.3 million elevators in use nationwide at the beginning of 2011, assuming that the average power of each elevator is 15kw and the average power of the regenerative resistor is 5kw, it is equivalent to having an electric furnace of about 7 million kW in China that is heating up without any use. What a waste! Energy feedback technology treats the input power supply of elevators as a controlled object, which has many advantages. At present, this technology has been widely used in several elevator manufacturers, and a power feedback system has been developed, which allows the electricity processed by advanced multiple rectification technology to be fed back to the building power grid for use by other electrical equipment in the building. The PFE series elevator feedback energy-saving device is a dedicated feedback braking unit for elevators. It can effectively convert the regenerated electrical energy stored in the elevator inverter capacitor into AC power and send it back to the grid, turning the elevator into a green "power plant" to supply power to other equipment, and has the effect of saving electricity. In addition, by replacing resistors for energy consumption, the ambient temperature in the machine room is reduced, and the operating temperature of the elevator control system is improved, extending the service life of the elevator. The machine room does not require the use of cooling equipment such as air conditioning, indirectly saving electricity.
2. VVVF (Variable Voltage Variable Frequency Speed Control) technology
VVVF technology has been widely used in modern AC speed regulation elevator drive control systems. The use of mature VVVF technology in elevator drive systems has become the main way to improve elevator drive control performance and enhance elevator operation quality today. VVVF technology has eliminated various types of AC dual speed motor speed control drives and replaced DC gearless drives, which not only improves the operational performance of elevators, but also effectively saves energy and reduces losses. The following analyzes the energy-saving performance of VVVF elevators according to different stages of elevator operation. Elevator operation can be simplified into three stages: starting, steady speed operation, and braking.
(1) Starting stage: VVVF starts under low frequency conditions, resulting in low reactive current and greatly reducing the total starting current and energy consumption.
(2) Steady speed section: The energy consumed by ACVV (voltage and speed regulation) elevators during steady speed operation is similar to that of VVVF controlled elevators under full load and half load upward conditions. During light load up (or heavy load down), due to the reverse pull effect, ACVV elevators need to obtain energy from the power grid to generate braking torque, while VVVF elevators work in a regenerative braking state and do not need to obtain energy from the power grid.
(3) Braking section: ACVV elevators generally use energy consumption braking method in the braking section, which obtains energy consumption braking current from the power grid, and the current is converted into heat energy and consumed in the rotor of the motor. For motors with larger inertia wheels, the energy consumption braking current can reach 60-80A, and the motor's heating is also relatively severe. VVVF elevators do not require any energy from the power grid during the braking phase, and the electric motor operates in a regenerative braking state. The kinetic energy of the elevator system is converted into electrical energy and consumed by the external resistance of the motor, which not only saves energy but also avoids the phenomenon of motor heating caused by braking current.
According to actual operation calculations, elevators controlled by VVVF can save more than 30% energy compared to ACVV speed regulating elevators. The VVVF system can also improve the power factor of the electrical system, reduce the capacity of elevator line equipment and electric motors by more than 30%. Based on the above, it can be seen that VVVF variable frequency speed regulation elevators have obvious energy-saving characteristics, representing the development direction of elevator speed regulation, and have significant economic and social benefits.
3. Principle and Application of DC Bus Elevator Control System
In places where elevators are frequently used, one elevator is not enough, so two or more elevators are often used simultaneously. In this way, it can be considered to feed back the excess energy generated by one or two elevators during power generation to a busbar shared by these elevators, in order to achieve energy-saving goals. The common DC bus elevator control system is generally composed of circuit breakers, contactors, inverters, motors, and fuses. Its characteristic is to connect all elevators on the DC side of the system to a common busbar. In this way, each elevator can convert AC power into DC power through its own inverter during operation and feed it back to the bus. Other elevators on the busbar can fully utilize this energy, reducing the total energy consumption of the system and achieving the goal of energy conservation. When one of the elevators malfunctions, simply turn off the air switch on that elevator. This scheme has the advantages of simple structure, low cost, and safety and reliability.
4. Application of new traction media
The traditional traction medium for elevators is steel wire rope, which consumes a lot of energy due to the weight and friction of the steel wire rope. The application of polyurethane composite steel strip instead of traditional steel wire rope in the elevator industry completely subverts the design concept of traditional elevators, making energy conservation and efficiency possible. Polyurethane steel strips with a thickness of only 3 millimeters are more flexible and durable than traditional steel wire ropes, with a lifespan three times that of traditional steel wire ropes. The high toughness and high drag force of polyurethane steel strip make the design of the main engine tend to be miniaturized. The diameter of the traction wheel of the main engine can be reduced to 100-150 millimeters. Combined with permanent magnet gearless technology, the volume of the traction machine can be reduced by 70% compared to traditional main engines, making it easy to achieve a machine room free design, greatly saving building space and reducing construction costs. At present, both the Otis GEN2 elevator and the Xunda 3300AP elevator have adopted this technology, which has been proven to save up to 50% energy compared to traditional elevators. In addition, Xunda Elevator Company's high-strength coreless synthetic fiber traction rope is currently in the operational verification stage and is believed to enter the Chinese market in the near future.
5. Variable speed technology
Variable speed elevator technology is another new energy-saving and environmentally friendly technology that has emerged in recent years. The research and development of variable speed elevator technology is based on the energy-saving potential of traditional elevator products. During the operation of traditional elevators, the rated speed is only set when the traction machine is at its maximum load, that is, when the output power of the traction machine is at its maximum, under both full and empty load conditions. However, when only about half of the passengers are present, due to the fact that the box is balanced with the counterweight, the load on the traction machine is actually small, and there is still surplus output power. That is to say, only a portion of the power of the traction machine is used. Variable speed elevator technology "is the use of the remaining power when the load is low to increase the speed of the elevator under the same power conditions. The application of this new technology can increase the maximum speed of elevators to 1.6 times the rated speed. The simulation demonstration shows that passenger waiting time has been reduced by about 12%. This not only shortens the elevator waiting time and ride time that passengers are most dissatisfied with, but also improves mobility efficiency and comfort. The improvement of mobility efficiency extends the standby time of elevators, and the lighting of elevators can be turned off, which has a significant energy-saving effect. At the same time, variable speed elevator technology can increase the speed of the elevator by one level without increasing the model of the traction machine, which can play an important role in cost and energy savings.
6. Objective layer selection system
The Xunda M10 control system was the first to apply destination floor selection technology in China. Through continuous improvement and research and development innovation, its usage concept has been accepted by the Chinese people and has led the continuous innovation of followers in the industry. Its new generation system Schindler ID system has been applied to several high-end buildings in China (Nanjing Zifeng Building, PetroChina Building). Simply put, traditional elevators only select the floor after entering the elevator and inform the elevator of the floor they want to go to. During peak hours, they often stop layer by layer, which is inefficient. However, the application of destination floor selection systems allows people going to the same floor to be organized before entering the elevator, which can improve efficiency. By combining relevant software databases, Bluetooth technology, and community management systems, smart card calling and elevator assignment are used to truly integrate elevators into smart buildings. The activity areas for personnel entering the building are pre-set, improving the management efficiency and safety level of the building and community.
7. Update the elevator car lighting system and floor display system
According to relevant information, using LED light-emitting diodes to update the commonly used incandescent lamps, fluorescent lamps, and other lighting fixtures in elevator cars can save about 90% of lighting usage, and the lifespan of the fixtures is 30 to 50 times that of conventional fixtures. LED lamps generally have a power of only 1W, no heat, and can achieve various exterior designs and optical effects, making them beautiful and elegant. The elevator is in standby mode, and the floor display system is always in working mode. Using sleep technology to automatically turn off or reduce brightness by half can also achieve energy-saving goals.
8. Solar powered elevator
Compared with ordinary elevators, elevators powered by solar energy have two obvious characteristics: firstly, the power supply can be automatically switched. The second is the adoption of new technologies for complementary optical networks. It is possible to store solar energy and the electrical energy generated during elevator operation in specific batteries. After reaching certain parameters, the power grid does not need to continue supplying power, but automatically switches to battery powered state, fully utilizing solar energy and recycling electrical energy.