Suppliers of frequency converter energy feedback devices remind you that in modern industrial automation production, the application scope of pumps, fans and other equipment is becoming more and more extensive. Their consumption of electrical energy, throttling losses of baffles, valves and other equipment, as well as daily maintenance and repair costs, account for almost 20% of the cost. This is a considerable production expense. With the development of the economy, the deepening of reforms, and the intensification of market competition, energy conservation and consumption reduction have gradually become an important means to improve product quality and reduce production costs.
1. Basic Theory of Variable Frequency Energy saving Technology
The basic principle of frequency conversion technology is that for a long period of time, the frequency of the alternating current used by electrical equipment is maintained in a fixed state. The application of frequency conversion technology is to make the frequency a resource that can be adjusted and utilized freely. Nowadays, the most active and rapidly developing variable frequency technology is the speed regulation technology of variable frequency.
Frequency conversion technology includes computer technology, power electronics technology, and click transmission technology. It is a comprehensive technology that combines mechanical equipment and strong and weak electricity. It refers to the conversion of the signal of the power frequency current into other frequencies, which is mainly achieved through semiconductor components. Then, the alternating current is converted into direct current, and the inverter regulates the current and voltage while achieving stepless speed regulation of the electromechanical equipment. In summary, frequency conversion technology is to control the speed of a motor by changing the frequency of the current, thereby effectively controlling the motor equipment. These are all achieved on the basis of the year-on-year increase in current frequency and motor speed. The characteristic of frequency conversion technology is that it can ensure the smooth operation of the motor, automatically control acceleration and deceleration, and reduce energy consumption while improving work efficiency.
In the daily use of frequency converters, direct torque control and vector control are mainly used. In the future development of frequency converters, artificial neural networks and fuzzy self optimization control methods will be used. Moreover, as frequency converters continue to develop, their comprehensiveness will become increasingly high. In addition to completing basic speed regulation functions, they also have communication, programmable, and parameter identification functions set internally.
2. Energy saving principle of frequency converter
2.1 Variable frequency energy-saving methods
According to fluid mechanics, power=pressure * flow rate. Flow rate and speed to the power of one are proportional, pressure is proportional to the square of speed, and power is proportional to the cube of speed. If the efficiency of the water pump is fixed, when the flow rate decreases, the speed will decrease proportionally, and the output power will also decrease in a cubic relationship. Therefore, the speed of the water pump is approximately proportional to the power consumption of the motor. For example, when a 55kW water pump motor is turned to 80% of its original speed, its power consumption is 28kW/h, with a power saving rate of 48%. But if the speed is adjusted to 50% of the original, the power consumption becomes 6 kilowatts per hour, and the power saving rate reaches 87%.
2.2 Adopting power factor compensation for energy conservation
The reactive power not only causes equipment to heat up and increases wire wear, but most importantly, the decrease in power factor leads to a decrease in the active power of the power grid. As a result, a large amount of reactive energy is consumed in the power lines, leading to a decrease in equipment efficiency and serious waste. After using a variable frequency speed regulation device, the reactive power loss is further reduced due to the filtering capacitor inside the frequency converter, which increases the active power of the power grid.
2.3 Using soft start method for energy conservation
Due to the fact that the motor is started through Y/D or direct starting, the starting current is four to seven times the rated current, which can cause serious impact on the power grid and electromechanical equipment. Moreover, this requires a very high capacity of the power grid, generating a relatively large current during starting, and causing significant damage to valves and baffles during vibration, which is also very detrimental to the service life of pipelines and equipment. The use of frequency converters utilizes the soft start function of the frequency converter to start the current from zero, and the maximum value will not exceed the rated current. Therefore, the impact on the power grid and the requirements for power supply capacity are greatly reduced, and the service life of valves and equipment is greatly extended.
3. Application examples of variable frequency energy-saving technology
We used the installation of a variable frequency speed controller on a 160kW circulating water pump as an example to retrofit the variable frequency energy-saving equipment. We tested the electricity consumption before and after the retrofit and achieved very satisfactory results.
3.1 Control mode before frequency conversion transformation
Lors du fonctionnement d'une pompe de circulation d'eau, lorsque le débit varie en fonction des exigences du procédé, il est nécessaire d'ajuster l'ouverture des vannes d'entrée et de sortie afin de modifier le débit réel. Cette méthode d'ajustement est appelée régulation par étranglement. Dans cet exemple, l'ouverture des vannes d'entrée et de sortie est d'environ 60 %. Du point de vue de la consommation d'énergie, cette méthode d'ajustement est très énergivore.
3.2 Mode de contrôle après transformation de fréquence
Lors du fonctionnement d'une pompe de circulation d'eau, lorsque le débit varie en fonction des besoins du procédé, les vannes d'entrée et de sortie sont complètement ouvertes. En ajustant la vitesse du moteur, on peut trouver un point de fonctionnement optimal pour obtenir le débit souhaité. Selon la situation et les besoins du site, une commande manuelle ou automatique peut être mise en œuvre. Dans cet exemple, le débit n'ayant pas besoin d'être ajusté fréquemment, la fréquence de fonctionnement du moteur est fixée à 40 Hz, et la commande manuelle est privilégiée afin d'économiser la consommation d'énergie.
4. Modifications du fonctionnement après utilisation d'un système de régulation de vitesse à fréquence variable
Le démarrage progressif est désormais parfaitement maîtrisé. Au démarrage du moteur, la vitesse du rotor augmente graduellement à la fréquence du courant d'entrée, assurant ainsi une montée en vitesse en douceur. Le temps de démarrage de l'ensemble du système est d'environ 20 secondes, ce qui n'a aucun impact sur son fonctionnement et offre une transition plus fluide que la méthode de démarrage précédente.
La consommation électrique du réseau a été considérablement réduite, ce qui améliore la sécurité d'utilisation des équipements électriques. Parallèlement, la diminution de la fréquence entraîne une réduction de la vitesse du moteur, limitant ainsi l'usure mécanique et diminuant fortement les risques de panne et les coûts de maintenance. Le transformateur alimentant la pompe à eau a permis de réaliser d'importantes économies de puissance. La simple réduction de la charge active a permis d'économiser environ 50 kilowatts, optimisant ainsi l'efficacité énergétique de l'équipement. Le facteur de puissance du moteur s'en trouve également amélioré, ce qui rend son fonctionnement plus économique.
L'utilisation de la technologie de conversion de fréquence a permis d'améliorer la qualité des produits, de réduire la consommation d'énergie et de réaliser des économies, tout en renforçant la rentabilité des entreprises. L'application de la technologie de régulation de vitesse par conversion de fréquence nécessite la modernisation de ces équipements afin de réaliser des économies d'énergie.