Le fournisseur d'unités de freinage à convertisseur de fréquence rappelle qu'avec le développement de l'automatisation industrielle, l'utilisation des convertisseurs de fréquence se généralise. La régulation de vitesse par convertisseur de fréquence est reconnue comme une méthode idéale et prometteuse. L'objectif principal de l'utilisation d'un convertisseur de fréquence universel pour constituer un système de transmission à régulation de vitesse par convertisseur de fréquence est d'améliorer la productivité et la qualité des produits ; l'autre objectif est de réaliser des économies d'énergie et de réduire les coûts de production. Dans ce contexte, la maîtrise des convertisseurs de fréquence est primordiale.
Shielded wires should be used for signal and control lines to prevent interference. When the line is short, such as when the distance jumps by 100 meters, the cross-sectional area of the wire should be enlarged. Signal and control lines should not be placed in the same cable trench or bridge as power lines to avoid mutual interference. It is better to place them in conduit for better suitability.
02 Transmission signals are mainly based on current signals, as current signals are not easily attenuated or interfered with. In practical applications, the signal output by sensors is a voltage signal, which can be converted into a current signal through a converter.
03 Frequency converter closed-loop control is generally positive, meaning that the input signal is large and the output is also large (such as during central air conditioning cooling operation and general pressure, flow, temperature control, etc.). But there is also a reverse effect, that is, when the input signal is large, the output is relatively small (such as when the central air conditioning is working on heating and the heating hot water pump in the heating station).
When using pressure signals in closed-loop control, do not use flow signals. This is because pressure signal sensors have low prices, easy installation, low workload, and convenient debugging. However, if there are flow ratio requirements in the process and precision is required, a flow controller must be selected, and appropriate flow meters (such as electromagnetic, target, vortex, orifice, etc.) must be selected based on actual pressure, flow rate, temperature, medium, velocity, etc.
The built-in PLC and PID functions of the 05 frequency converter are suitable for systems with small and stable signal fluctuations. However, due to the built-in PLC and PID functions only adjusting the time constant during operation, it is difficult to obtain satisfactory transition process requirements, and debugging is time-consuming.
In addition, this type of regulation is not intelligent, so it is generally not used frequently. Instead, an external intelligent PID regulator is selected. When in use, simply set the SV (upper limit value), and there is a PV (operating value) indicator during operation. It is also intelligent, ensuring the best transition process conditions, making it ideal for use. Regarding PLC, various brands of external PLCs can be selected according to the nature, number of points, digital quantity, analog quantity, signal processing and other requirements of the control quantity.
The 06 signal converter is also frequently used in the peripheral circuits of frequency converters, usually consisting of Hall elements and electronic circuits. According to signal transformation and processing methods, it can be divided into various converters such as voltage to current, current to voltage, DC to AC, AC to DC, voltage to frequency, current to frequency, one in multiple out, multiple in one out, signal superposition, signal splitting, etc. For example, the Saint Seil CE-T series electric isolation sensors/transmitters in Shenzhen are very convenient to apply. There are many similar products in China, and users can choose their own applications according to their needs.
When using a 07 frequency converter, it is often necessary to equip it with peripheral circuits, which can be done in the following ways:
(1) A logic functional circuit composed of self-made relays and other control components;
(2) Buy ready-made unit external circuits;
(3) Choose a simple programmable controller logo;
(4) When using different functions of the frequency converter, function cards can be selected;
(5) Select small and medium-sized programmable controllers.
There are two common frequency conversion technology transformation schemes for parallel and constant pressure water supply with multiple water pumps (such as clean water pumps in urban water plants, medium and large water pump stations, hot water supply center stations, etc.):
(1) Save initial investment, but the energy-saving effect is poor. When starting, first start the frequency converter to 50 Hz, then start the power frequency, and then switch to energy-saving control. In the water supply system, only the water pump driven by a frequency converter has slightly lower pressure, and there is turbulence and loss in the system
(2) The investment is relatively large, but it saves 20% more energy than Plan (1). The pressure of the Yuantai pump is consistent, there is no turbulence loss, and the effect is better.
When multiple water pumps are connected in parallel for constant pressure water supply, a signal series connection method is used with only one sensor, which has the following advantages:
(1) Save costs. Just one set of sensors and PID.
(2) Since there is only one control signal, the output frequency is consistent, that is, the same frequency, so the pressure is also consistent, and there is no turbulence loss.
(3) When supplying water at constant pressure, the number of pumps in operation is controlled by PLC as the flow rate changes. At least 1 unit is required, 2 units are required for moderate quantities, and 3 units are required for larger quantities. When the frequency converter is not working and stopped, the circuit (current) signal is on the path (there is a signal flowing in, but no output voltage or frequency).
(4) More advantageous is that because the system only has one control signal, even if the three pumps are put into different inputs, the operating frequency is the same (i.e. synchronized) and the pressure is also the same, so the turbulence loss is zero, that is, the loss is minimized, so the energy-saving effect is the best.
Reducing the base frequency is the most effective way to increase the starting torque
This is due to the significant increase in starting torque, so some difficult to start equipment such as extruders, cleaning machines, spin dryers, mixers, coating machines, mixers, large fans, water pumps, Roots blowers, etc. can all be started smoothly. This is more effective than usually increasing the starting frequency for starting. By using this method and combining it with the measures of changing from heavy load to light load, the current protection can be increased to the maximum value, and almost all equipment can be started. Therefore, reducing the base frequency to increase the starting torque is an effective and convenient method.
When applying this condition, the base frequency does not necessarily have to decrease to 30 Hz. It can be gradually decreased every 5 Hz, as long as the frequency reached by the decrease can start the system.
The lower limit of the base frequency should not be lower than 30 Hz. From the perspective of torque, the lower the lower limit, the greater the torque. However, it should also be considered that the IGBT may be damaged when the voltage rises too quickly and the dynamic du/dt is too large. The actual use result is that this torque boosting measure can be safely and confidently used when the frequency drops from 50 Hz to 30 Hz.
Some people are concerned that, for example, when the base frequency is lowered to 30 Hz, the voltage has already reached 380 V. Therefore, when normal operation may require reaching 50 Hz, should the output voltage jump to 380 V so that the motor cannot withstand it? The answer is that such a phenomenon will not occur.
Some people are concerned that if the voltage reaches 380 V when the base frequency drops to 30 Hz, normal operation may require an output frequency of 50 Hz to reach the rated frequency of 50 Hz. The answer is that the output frequency can certainly reach 50 Hz.
The relationship between dynamic pressure, static pressure, and total pressure is as follows:
Static pressure is the pressure (head) required at the outlet of a water pump until the highest point, typically 1 kg of water pressure per 10 meters of water column.
Dynamic pressure is the pressure drop caused by the flow velocity difference between the liquid and the pipe wall, valves (regulating valves, return valves, pressure reducing valves, etc.), and different layers of the same section during the process of water flow. This part is difficult to calculate, and based on actual experience, dynamic pressure is assumed to be 20% (maximum) static pressure value.
Pression totale = (pression statique + pression dynamique) = 1,2 pression statique.
La fréquence limite inférieure de la pompe à eau doit être réglée à environ 30 Hz, faute de quoi l'eau risque de s'évacuer facilement de la conduite fermée. En raison de la grande quantité d'air dissous dans l'eau, une chambre d'air peut se former au démarrage de la pompe, créant ainsi un risque de surpression.
L'introduction des 12 points d'expérience et valeurs économiques est la suivante :
L'utilisation de convertisseurs de fréquence est envisageable pour divers appareils afin de réaliser des économies d'énergie, ce qui a été confirmé par de nombreux cas pratiques concluants.
La valeur d'expérience, relativement prudente et riche en ressources, n'est pas la plus économique et recèle un potentiel inexploité. Son utilisation doit être adaptée aux conditions réelles du site et impliquer certains ajustements des paramètres de fonctionnement, la limite inférieure étant celle qui n'affecte pas l'utilisation normale. Il s'agit d'une condition préalable à la réalisation d'économies d'énergie.
La valeur économique repose sur le principe du respect des conditions limites minimales du système, d'une réduction modérée de la valeur empirique et de l'exploration du potentiel d'économies d'énergie. Comment réaliser des économies d'énergie si les paramètres de fonctionnement restent inchangés ? De plus, le convertisseur de fréquence n'est pas un générateur d'énergie (contrairement aux générateurs, batteries ou panneaux solaires) et, bien que son rendement soit très élevé (de l'ordre de 97 % à 98 %), une perte de 2 % à 3 % subsiste.