Les fournisseurs de convertisseurs de fréquence spéciaux pour ascenseurs rappellent qu'avec le développement continu du secteur de la construction en Chine et l'amélioration constante du niveau de mécanisation des chantiers, les exigences en matière de qualité de fabrication et de niveau technique global des ascenseurs de chantier augmentent également. Les ascenseurs classiques utilisent généralement une commande par relais de contacteur, qui démarre directement et freine mécaniquement en cas de freinage forcé. L'impact du démarrage et du freinage est important, ce qui endommage considérablement la structure et le mécanisme, et les composants électriques sont également susceptibles d'être endommagés. De plus, le risque de chute de matériaux dans la cabine est élevé, ce qui affecte non seulement la vitesse de chantier, mais aussi la productivité de l'entreprise. Les ascenseurs de chantier à double usage (personnes et marchandises) présentent des risques importants pour la sécurité. Face aux exigences croissantes des utilisateurs en matière de performance et de sécurité des ascenseurs de chantier, les méthodes de commande traditionnelles sont de plus en plus inadaptées.
In view of the above reasons, professional manufacturers at home and abroad have made many new acceleration application attempts in the lifting speed regulation of elevators, such as using multi-stage electric motors for voltage regulation and speed regulation, and introducing variable frequency speed regulation. Gradually, with the continuous development of frequency conversion technology, it has surpassed any other speed control scheme with absolute advantages and occupies a dominant position. The use of variable frequency speed regulation in elevators has many advantages, such as zero speed holding brakes, which have no wear on the brakes; Any low positioning speed, high leveling accuracy; The smooth transition of speed has no impact on the mechanism and structural components, improving the safety of the elevator; The almost arbitrary wide speed range improves the working efficiency of the elevator; The energy-saving speed regulation method reduces the energy consumption of the system operation. It is precisely because of these obvious characteristics and advantages that frequency converters have been widely used in elevators, which will have important significance for the safe operation of elevators and the reduction of operating energy consumption.
Structure and Control of Elevators:
A construction elevator is a construction machinery that uses a cage (or platform, hopper) to transport people and goods up and down along a guide rail frame or guide rail. It is widely used in construction and other fields, such as industrial and civil buildings, bridge construction, underground construction, large chimney construction, etc. It is an ideal equipment for transporting materials and personnel. As a permanent or semi permanent construction elevator, it can also be used in different occasions such as warehouses and high towers. Vertical transportation is the busiest type of machinery in high-rise building construction and has been recognized as one of the essential key equipment for high-rise building construction.
The main components of the construction elevator are as follows: guide rail frame, lifting cage, transmission system, wall frame, chassis guardrail, electrical system, safety protection device, cable power supply device, etc.
Design of Variable Frequency Speed Control System for Elevators
1. Introduction to the Structure of Variable Frequency Speed Control System
The elevator variable frequency speed regulation system consists of the following parts: disc brake three-phase asynchronous motor, variable frequency speed controller, variable frequency brake unit and brake resistor, linkage platform, electrical protection device, etc. The control process is to operate the speed conversion switch on the linkage platform, select the speed gear, and then output a signal to the frequency converter to change the frequency value, ultimately achieving the purpose of speed regulation.
2. Design points of electronic control system
⑴ Selection of electric motor
After the basic parameters of the transmission system (such as maximum lifting capacity, maximum working speed, etc.) are given, the number of stages and power of the electric motor can be determined and calculated. The lifting mechanism of the construction elevator should choose a variable frequency motor suitable for frequent starting, low moment of inertia, and high starting torque. The selection of motor power should be based on the size of the driving mechanical load, and its calculation formula is:
P=WV/(η×10-3)(1)
In the formula, W represents the weight of the rated load plus the weight of the cage and rope
V - Operating speed, m/s;
η - Mechanical efficiency (the product of the transmission efficiency of each part of the transmission system).
Due to the constant torque characteristic of the elevator load torque, the torque remains basically unchanged at low frequencies, requiring the motor and frequency converter to operate at low speeds. Therefore, it is necessary to increase the power of the motor or install an external fan for cooling.
⑵ Selection of frequency converter
Once the motor of the system is determined, the design of the control system can begin. Firstly, the selection of frequency converters. Currently, there are many brands of frequency converters both domestically and internationally, with significant differences in control level and reliability. For the transmission system of elevators, it is best to choose a frequency converter with vector control or direct torque control, stable operation, and high reliability. Due to different brands of frequency converters, the overload capacity and rated current value of frequency converters are not completely consistent under the same power. Therefore, when choosing the capacity of a frequency converter, it is not only necessary to consider the rated power, but also to verify whether the rated working current is greater than the rated current of the motor. The general experience is to choose a frequency converter with a capacity one level larger than that of the motor.
⑶ Selection of braking resistor
As a frequency conversion system used for lifting, the focus of its design is on the reliability of the system when the motor is in feedback braking state, because such system failures often occur during the working conditions when the cage descends, such as overvoltage, overspeed, and rolling. The frequency conversion system keeps the motor in a generating state throughout the entire process of heavy object descent. Regenerated electrical energy is returned to the DC bus of the frequency converter, and energy consuming devices such as braking units and braking resistors are usually connected to the DC side. It is difficult to determine the exact values of parameters in the early stages of system design. Before the product is completed, it is impossible to accurately measure and calculate the transmission inertia of each component; In practical use, the deceleration characteristics of the system will change according to the needs of the site. So in most cases, the value of experience is generally between 40% and 70% of the motor power. The resistance value R of the braking resistor is calculated within the following range.
3. Debugging of Variable Frequency Speed Control System
After ensuring the correct wiring of the main circuit and control circuit, the system begins power on debugging. Set the parameters of the motor through the operation panel on the frequency converter, and select the static self-learning method to identify the motor. After identification is completed, set the control mode, output frequency, acceleration and deceleration time, relay RO1 output mode, detection frequency for brake release and locking, and other corresponding parameters (see the user manual of each frequency converter for specific setting parameters). After parameter setting is completed, according to the national standard experimental rules for construction elevators, several stages of no-load debugging, rated load debugging, and 125% rated load debugging will be carried out. During debugging, if there is a slipping phenomenon, the frequency of the brake can be adjusted appropriately, but it should not be set too high, otherwise the frequency converter is prone to reporting faults. Generally, it is set within 0.3~2Hz.
4. Safety debugging of elevators
La sécurité est primordiale pour les ascenseurs de chantier, et des essais de sécurité doivent être réalisés conformément aux normes nationales lors de la mise en service du système. Lors de la mise en service à vide, il est possible de vérifier le bon fonctionnement des interrupteurs de fin de course haut et bas de la cabine, ainsi que des portes de celle-ci. Après une mise en service à 125 % de la charge nominale, le protecteur de surcharge est réglé à 110 % et un essai de surcharge est effectué. Les essais antichute impliquent généralement l'installation de dispositifs de sécurité antichute sur les ascenseurs de chantier. Ces dispositifs, éléments essentiels, permettent d'éviter les chutes de cabine. Les ascenseurs utilisés sur les chantiers doivent subir un essai de chute tous les trois mois. Cet essai consiste à augmenter la fréquence de sortie du variateur de fréquence du moteur afin de simuler une chute et de vérifier l'activation du dispositif antichute.