Elevator energy-saving equipment suppliers remind you that with the continuous enhancement of environmental awareness, energy conservation and environmental protection have become a fundamental national policy with practical significance advocated by China. In today's increasingly competitive elevator industry, the adoption of new technologies, faster speeds, and heavier loads are the most prominent aspects that highlight product advantages. However, it cannot be denied that the economic and environmental benefits of elevators after they are put into use are also factors that must be considered when purchasing elevators.
1、 Basic Structure and Operating Status of Elevators
1. Basic structure of elevator
Nowadays, elevators are mainly composed of traction machine systems, guidance systems, car systems, and door systems. Composed of weight balance system, electric drive system, electrical control system, safety protection system, etc. These parts are installed in the shaft and machine room of the building respectively. Usually, steel wire rope transmission is used, with the steel wire rope winding around the traction wheel and connecting the car and counterweight at both ends. The traction machine drives the traction wheel to lift and lower the car.
2. Analysis of elevator operation status:
When the elevator runs upwards, it consumes energy, and when the elevator descends from a high place, it releases energy. The load dragged by the traction machine in the elevator is composed of the passenger car and the counterweight. In order to balance the drag load, the two are only balanced when the car load is added to 50% of the rated load of the car (for example, a passenger elevator with a load of 1050kg has about 7 passengers). Although this move changes the peak point of energy consumption, it cannot change the average energy consumption. In actual use, the frequency of occurrence of the weight of the counterweight is relatively low, as the weight of the car plus the weight of the passengers is exactly equal to the weight of the counterweight. So the operating state of elevators is basically in an unbalanced state, and it is also very likely that the car will descend when there are many passengers, and rise again when there are few or no passengers. If the first situation occurs when the gravitational potential energy of passengers is released, and the second situation occurs when the gravitational potential energy of the counterweight is released, due to the effect of the potential load, the speed is higher than the synchronous speed, that is, when n>no, the slip rate s=(no - n)/no<0, the rotor induced electromotive force is reversed, the stator winding feeds back electrical energy to the grid, and the T direction is opposite to the speed direction. The motor not only feeds back electrical energy, but also generates mechanical braking torque on the shaft. The sentence is:. However, due to the irreversibility of the AC/DC rectification circuit of the elevator's frequency converter, the generated electricity cannot be fed back to the grid, resulting in an increase in the voltage at both ends of the main circuit capacitor and the generation of "pump up voltage". Generally, variable frequency elevators use resistors to consume stored electrical energy in capacitors to prevent capacitor overvoltage. During elevator operation, these resistors emit a large amount of heat (with a surface temperature of over 100 ℃), and this wasted energy accounts for 25% to 45% of the total electricity consumption of the elevator. The energy consumption of resistors not only reduces the efficiency of the system, but also generates a large amount of heat that accelerates the flow of dust in the air of the machine room, adsorbs static electricity, and greatly affects the environment around the elevator control cabinet. At the same time, the increase in temperature will significantly shorten the service life of the original components of the elevator, and the aging and failure of the components will continue. In order to lower the temperature of the computer room to room temperature and prevent elevator malfunctions caused by high temperatures, users need to install air conditioners or fans with large exhaust volumes; In machine rooms with high elevator power, multiple air conditioners and fans often need to be started simultaneously. Make elevators and air conditioning the most energy consuming "electric tigers".
2、 Operating principle of elevator energy feedback device
To save energy in elevators, the key is to utilize the electrical energy generated by the traction machine during power generation. The energy generated by the braking resistor is then converted back into AC power through inversion, supplied to other electrical equipment, or fed back to the power grid. The general energy inversion efficiency is around 85%, and the energy consumption of the braking resistor mentioned above accounts for 25% to 45% of the total electricity consumption of the elevator. If the floor is higher or the elevator speed is faster, the feedback effect of electrical energy will be more obvious. The main circuit structure of the energy feedback system is mainly composed of filtering capacitors, three IGBT full bridges, series inductors, and peripheral circuits. The input end of the elevator energy feedback system is connected to the DC bus side of the elevator frequency converter, and the output end is connected to the grid side. When the elevator traction machine is operating in electric mode, all switches of the energy feedback system are in the off state. When the traction machine is operating in power generation mode, the pump voltage on the DC bus side of the frequency converter increases and meets other inversion conditions. After that, the energy feedback system starts to operate. As the current energy on the DC is fed back to the grid, the DC bus voltage decreases until it falls back to the set value, and the system stops working.
The active inverter that converts DC electrical energy into AC electrical energy is the essence of elevator energy feedback. The purpose is to feedback the electrical energy generated by the traction machine during power generation through the inverter, achieving energy conservation and avoiding pollution to the power grid caused by the inverter output. So in the process of energy feedback generated by traction machine power generation, four control conditions must be met in terms of phase, voltage, and current:
a) The system cannot be started casually. The inverter device will only start and provide energy feedback when the DC bus voltage exceeds the set value;
b) The inverter current must meet the demand for feedback power and cannot exceed the maximum current allowed by the inverter circuit;
c) The inverter process needs to be synchronized with the phase of the power grid, and the energy feedback to the power grid should be at the high voltage end of the power grid;
d) Minimize the pollution of the power grid caused by the inverter process as much as possible.
3、 Hardware Design of Elevator Energy Feedback System
1. Power inverter circuit
In the power inverter circuit, the direct current stored on the DC bus side of the elevator frequency converter during the operation of the elevator traction machine in the power generation state is converted into alternating current by controlling the on/off of the switch. It is the main circuit of the elevator energy feedback system, which has different structures according to different classifications of inverter circuits. By controlling the on/off of the switch, the DC power stored on the DC bus side of the elevator frequency converter during the operation of the traction machine in the power generation state is converted into AC power. In a circuit, the upper and lower switches on the same bridge arm cannot conduct simultaneously, and the conduction time and duration of each item are controlled according to the inverter control algorithm.
2. Grid synchronization circuit
The phase synchronization control plays a key role in whether the elevator can effectively feedback the energy on the DC bus to the power grid. The grid synchronization circuit adopts grid line voltage synchronization, and in order to avoid dead zone effects during commutation, switches are operated at 120 degrees on the same bridge arm. The logical relationship between the grid synchronization signal and the zero crossing signal of the power grid is obtained through a comparator, and the relationship between the grid synchronization signal of each switching device and the power grid voltage is obtained through Multisim simulation. Each switch has a working angle of 120 degrees and is spaced 60 degrees in sequence. At any time, only two switch tubes in the inverter bridge are conductive, ensuring safe and reliable operation. Additionally, each two switches operate in the highest voltage range of the power grid line, resulting in high inverter efficiency.
3. Voltage detection control circuit
Due to the high voltage on the DC bus side of the elevator frequency converter, it is necessary to first use resistors for voltage division, and then isolate and reduce the bus voltage through Hall voltage sensors, and convert it into a low voltage signal. In the voltage detection control circuit, hysteresis tracking comparison control method is adopted, which adds positive feedback on the basis of the comparator and provides two comparison values for the comparator, namely the upper and lower threshold values. Implemented by hardware circuits, control is both fast and accurate. The voltage detection control circuit can not only avoid the instantaneous superposition of interference signals on the voltage signal, causing the output state of the comparator to shake, but also prevent the energy feedback system from starting and closing too frequently.
4. Current detection control circuit
Lors du processus de récupération d'énergie, le courant doit satisfaire les besoins en puissance, et la puissance réinjectée sur le réseau doit être supérieure ou égale à la puissance maximale lorsque la machine de traction fonctionne en mode générateur. Dans le cas contraire, la chute de tension sur le bus CC continuera d'augmenter. Lorsque la tension du réseau est constante, la puissance de récupération d'énergie du système est déterminée par le courant de récupération. De plus, ce courant doit être limité à la plage nominale du dispositif de commutation de puissance de l'onduleur. Par ailleurs, la bobine d'arrêt réactante entre le réseau et l'onduleur permet le passage de courants importants tout en minimisant le volume de la réactance. Par conséquent, l'inductance de la réactance doit être faible pour garantir une récupération d'énergie efficace. La vitesse de variation du courant est très rapide. L'utilisation simultanée d'une commande à hystérésis de courant permet de contrôler efficacement le courant de récupération et de prévenir les surintensités.
5. Circuit de commande principal
L'unité centrale de traitement du système de récupération d'énergie de l'ascenseur est le circuit de commande principal, qui gère le fonctionnement de l'ensemble du système. Ce circuit est composé d'un microcontrôleur et de circuits périphériques qui génèrent des signaux PWM de haute précision selon des algorithmes de contrôle. Par ailleurs, grâce au signal de synchronisation avec le réseau, la gestion des défauts IPM garantit le bon déroulement et la sécurité de l'ensemble du processus de récupération d'énergie.
6. Circuit de commande de protection logique
Le signal de synchronisation pour le raccordement au réseau, les signaux de commande de tension et de courant, le signal de défaut IPM et le signal de commande provenant du circuit de commande principal doivent tous transiter par le circuit de protection logique pour un fonctionnement optimal, avant d'être transmis au circuit de l'onduleur afin de contrôler le processus de rétroaction. De cette manière, on garantit la synchronisation de la puissance alternative produite par l'onduleur avec le réseau et on bloque le signal de commande en cas de surintensité, de surtension, de sous-tension ou de défaut IPM dans le circuit, interrompant ainsi le processus de rétroaction d'énergie.
Le système de récupération d'énergie de l'ascenseur ne se déclenche que lorsque la machine de traction est en fonctionnement, ce qui lui confère une durée de vie supérieure à celle de l'ascenseur lui-même. Il apparaît donc que, compte tenu de ses principes, de ses effets bénéfiques sur l'énergie et de ses performances, l'application de tels systèmes mérite d'être activement encouragée dans un contexte de raréfaction croissante des ressources énergétiques. Elle contribue ainsi à un environnement plus sain et plus économe en énergie, répond aux objectifs nationaux et gouvernementaux de conservation et de réduction de la consommation d'énergie, et participe à la construction d'une société plus durable, contribuant ainsi aux efforts du pays en matière d'économie d'énergie et de réduction des émissions.