Les fournisseurs d'équipements d'ascenseurs à économie d'énergie rappellent que les convertisseurs de fréquence sont désormais largement utilisés dans divers secteurs, tels que la climatisation, les ascenseurs et l'industrie lourde. Vous trouverez ci-dessous les principes de base de l'utilisation des convertisseurs de fréquence dans les ascenseurs :
1. Qu'est-ce qu'un convertisseur de fréquence ?
Un convertisseur de fréquence est un dispositif de contrôle de l'énergie électrique qui utilise la fonction marche/arrêt des dispositifs semi-conducteurs de puissance pour convertir les sources de fréquence électrique en une autre fréquence.
2. Quelles sont les différences entre PWM et PAM ?
PWM est l'abréviation de « modulation de largeur d'impulsion », une technique de modulation qui ajuste la forme d'onde et le signal de sortie en modifiant la largeur d'une série d'impulsions selon un schéma précis. PAM signifie « modulation d'amplitude d'impulsion » ; il s'agit d'une méthode de modulation qui ajuste la valeur et la forme d'onde de sortie en modifiant l'amplitude d'une série d'impulsions selon une règle définie.
3. Quelle est la différence entre un type de tension et un type de courant ?
Le circuit principal d'un convertisseur de fréquence peut être grossièrement divisé en deux catégories : le convertisseur de tension est un convertisseur de fréquence qui convertit le courant continu d'une source de tension en courant alternatif, et le filtrage du circuit continu est assuré par un condensateur ; le convertisseur de courant est un convertisseur de fréquence qui convertit le courant continu d'une source de courant en courant alternatif, avec un filtre de circuit continu et une inductance.
4. Pourquoi la tension et le courant d'un convertisseur de fréquence varient-ils proportionnellement ?
The torque of an asynchronous motor is generated by the interaction between the magnetic flux of the motor and the current flowing through the rotor. At the rated frequency, if the voltage is constant and only the frequency is reduced, the magnetic flux will be too large, the magnetic circuit will saturate, and in severe cases, the motor will be burned out. Therefore, the frequency and voltage should be changed proportionally, that is, while changing the frequency, the output voltage of the frequency converter should be controlled to maintain a certain magnetic flux of the motor and avoid the occurrence of weak magnetism and magnetic saturation phenomena. This control method is commonly used for energy-saving frequency converters in fans and pumps.
5. When the electric motor is driven by a power frequency source, the current increases when the voltage drops; For frequency converter drive, if the voltage also decreases when the frequency decreases, does the current increase?
When the frequency decreases (at low speed), if the same power is output, the current increases, but under the condition of constant torque, the current remains almost unchanged.
6. What are the starting current and starting torque of the motor when using a frequency converter for operation?
Using a frequency converter for operation, the frequency and voltage increase correspondingly with the acceleration of the motor, and the starting current is limited to below 150% of the rated current (125%~200% depending on the model). When starting directly with a mains power supply, the starting current is 6-7 times, resulting in mechanical and electrical shocks. Using a frequency converter drive can smoothly start (with longer starting time). The starting current is 1.2~1.5 times the rated current, and the starting torque is 70%~120% of the rated torque; For frequency converters with automatic torque enhancement function, the starting torque is above 100% and can start with full load.
7. What does V/f mode mean?
When the frequency decreases, the voltage V also decreases proportionally, as explained in answer 4. The proportional relationship between V and f is predetermined taking into account the characteristics of the motor, and usually there are several characteristics stored in the storage device (ROM) of the controller, which can be selected using switches or dials.
8. How does the torque of the motor change when V and f are proportionally changed?
When the frequency decreases and the voltage decreases proportionally, the decrease in AC impedance while the DC resistance remains unchanged will result in a tendency to reduce the ground torque generated at low speeds. Therefore, given V/f at low frequencies, it is necessary to increase the output voltage slightly in order to obtain a certain starting torque. This compensation is called enhanced starting. Various methods can be used to achieve this, including automatic operation, selecting V/f mode, or adjusting potentiometer.
9. Is there no output power below 6Hz, as the manual states a speed range of 60~6Hz, which is 10:1?
Power can still be output below 6Hz, but based on the temperature rise and starting torque of the motor, the minimum operating frequency is around 6Hz. At this time, the motor can output rated torque without causing serious heating problems. The actual output frequency (starting frequency) of the frequency converter varies from 0.5 to 3Hz depending on the model.
10. Is it possible to require a constant torque for general motor combinations above 60Hz?
Usually it is not possible. When the voltage remains constant above 60Hz (and there are also modes above 50Hz), it is generally a constant power characteristic. When the same torque is required at high speeds, attention must be paid to the selection of motor and inverter capacity.
11. What does' open-loop 'mean?
A speed detector (PG) is installed on the motor device used to feed back the actual speed to the control device for control, which is called a "closed loop". If it does not operate with PG, it is called an "open loop". Universal frequency converters are mostly open-loop, and some models can also use options for PG feedback.
12. What should be done when the actual speed deviates from the given speed?
When open-loop, even if the frequency converter outputs a given frequency, the motor's speed varies within the range of rated slip rate (1%~5%) when running with load. For situations where high speed regulation accuracy is required and even load changes require operation close to a given speed, a frequency converter with PG feedback function (optional) can be used.
13. If a motor with PG is used for feedback, can the speed accuracy be improved?
The frequency converter with PG feedback function has improved accuracy. But the accuracy of speed depends on the precision of PG itself and the resolution of the output frequency of the frequency converter.
14. What does stall prevention function mean?
If the given acceleration time is too short and the output frequency of the frequency converter changes much more than the speed (electrical angular frequency), the frequency converter will trip and stop running due to overcurrent, which is called stall. To prevent the motor from continuing to operate due to stall, it is necessary to detect the magnitude of the current for frequency control. When the acceleration current is too high, slow down the acceleration rate appropriately. The same applies when decelerating. The combination of the two is the stall function.
15. What is the significance of models with separately given acceleration time and deceleration time, and models with jointly given acceleration and deceleration time?
L'accélération et la décélération peuvent être spécifiées séparément pour différents types de machines, ce qui convient aux accélérations brèves, aux décélérations lentes ou aux situations où un temps de cycle de production strict est requis pour les petites machines-outils. Cependant, dans des cas comme celui de la transmission par ventilateur, les temps d'accélération et de décélération sont relativement longs ; il est alors possible de les spécifier simultanément.
16. Qu'est-ce que le freinage régénératif ?
Si la fréquence de commande est réduite pendant le fonctionnement du moteur électrique, celui-ci deviendra un générateur asynchrone et fonctionnera comme un frein, ce que l'on appelle le freinage régénératif (électrique).
17. Qu'est-ce que le retour d'énergie d'un ascenseur ?
Convertir le courant continu inutilisé de l'ascenseur en courant alternatif exploitable. Ce courant alternatif converti est simultanément réinjecté dans le réseau local autour de l'ascenseur pour être réutilisé.