Frequency converter supporting equipment supplier: With the rapid development of power electronics technology and microelectronics technology, the manufacturing process of high-power rectifier devices has been further developed. The development of frequency converters is changing rapidly, and they are widely used in industrial and mining enterprises. The application of frequency converters in enterprises is becoming more and more widespread, and the problems they bring are also increasingly attracting people's attention.
1、 Characteristics of frequency converter
With the rapid development of power electronics technology and microelectronics technology, the manufacturing process of high-power rectifier devices has been further developed, and the development of frequency converters is changing rapidly. Frequency converters are widely used in industrial and mining enterprises and have four major advantages:
The first one can meet the process requirements for speed regulation, and the speed regulation range of the frequency converter is above 10:11.
The second is to facilitate automation control, as the frequency converter itself is controlled by a 16 (or 32) bit microprocessor with RS485 or 422, A/D input, and D/A output interfaces, creating sufficient conditions for automatic control.
The third is to achieve significant energy-saving effects, especially in the application of high-power (above 15KW) fans and pumps, which can save more than 20% of energy.
The fourth is to reduce the labor intensity of maintenance workers. Due to the high overall reliability, low failure rate, and long maintenance cycle of the speed control system, it can reduce the workload of relevant maintenance personnel.
2、 Selection of frequency converter
The selection of frequency converters should be considered according to the type of controlled object, speed range, static speed accuracy, starting torque, etc., so as to meet the requirements of process and production while being both user-friendly and economical.
1. The number of poles of the frequency converter and the controlled motor should generally not exceed 4 poles, otherwise the speed regulation is not meaningful; Torque characteristics, critical torque, acceleration torque. Under the same motor power, the specifications of the frequency converter can be downgraded compared to the high overload torque mode. Electromagnetic compatibility. To reduce interference from the main power supply, reactors should be added to the intermediate circuit or input circuit of the frequency converter, or pre isolation transformers should be installed. Generally, when the distance between the motor and the frequency converter exceeds 50 meters, reactors, filters, or shielded protective cables should be connected in series between them.
2. The selection of inverter enclosure structure: The enclosure structure of the inverter must be adapted to the conditions, and factors such as temperature, humidity, dust, acidity, and corrosive gases must be considered. There are several common structures:
Open type: It does not have a chassis and can be installed on the screen rack inside the electrical control box or electrical room. It is especially suitable for use when multiple frequency converters are used together, but the environmental conditions require high standards.
Closed type: suitable for general use, may have a small amount of dust or humidity.
Sealed type: suitable for environments with poor industrial site conditions.
Sealed type: suitable for environments with poor conditions, water, dust, and certain corrosive gases.
3. The selection of frequency converter power must pay attention to the relationship between frequency converter load rate and efficiency. System efficiency is equal to the product of frequency converter efficiency and motor efficiency. From the perspective of efficiency, when selecting frequency converter power, the following points should be noted: it is appropriate when the frequency converter power is equivalent to the motor power, in order to facilitate the operation of the frequency converter in a high-efficiency state. When the power classification of the frequency converter is different from that of the motor, the power of the frequency converter should be as close as possible to the power of the motor and slightly greater than the power of the motor. When the electric motor is frequently started, braking is in operation, or when it is under heavy load and started frequently, a one level larger frequency converter can be selected to facilitate the long-term safe operation of the frequency converter. After testing, it has been found that the actual power of the motor is indeed surplus. Therefore, it is possible to consider using a frequency converter with a power lower than the motor power, but attention should be paid to whether the instantaneous peak current will cause overcurrent protection action. When the power of the frequency converter is different from that of the motor, the parameters of the frequency converter must be adjusted accordingly to achieve a higher energy-saving effect.
3、 Anti interference measures in frequency converter applications
The anti-interference of frequency converters in applications mainly manifests in issues such as high-order harmonics, noise and vibration, load matching, and heat generation. These interferences are inevitable because the input part of the frequency converter is a rectifier circuit and the output part is an inverter circuit, both of which are composed of nonlinear components that act as switches. During the process of opening and closing the circuit, high-order harmonics are generated, causing distortion of the input power supply and output voltage and current waveforms. The following analysis and corresponding measures are proposed for harmonic problems. The harm of high-order harmonics is significant, and the interference of high-order harmonics can affect equipment and detection components, which may cause misoperation in severe cases. According to relevant literature reports, the sensitivity of various objects to high-order harmonics is as follows: electric motors are below 10-20%. No impact, Instrument voltage distortion is 10%, current distortion is 10% The error is below 1%; Electronic switches exceeding 10% will cause misoperation, while computers exceeding 5% will cause errors. In the industrial field, measures must be taken to reduce interference and suppress it within the allowable range.
1. Cutting off the propagation path of interference is often achieved through the use of grounding wires. Separating the grounding of power lines from the grounding of control lines is the fundamental method to cut off this path. When the signal line is close to a wire with interference, the interference will be induced to interfere with the signal on the signal line. Wiring separation is effective in eliminating this interference. In actual cable laying, high-voltage cables, power cables, and control cables are often separated from instrument cables and computer cables and routed through different cable trays. The control line of the frequency converter is routed vertically with the main circuit line.
2. L'installation de réactances de ligne en amont du convertisseur de fréquence permet de supprimer les harmoniques d'ordre élevé, de limiter les surtensions côté alimentation et de réduire la distorsion du courant générée par le convertisseur, évitant ainsi des perturbations importantes sur l'alimentation principale. L'installation d'un filtre passif LC en amont du convertisseur de fréquence permet d'éliminer les harmoniques d'ordre élevé, généralement les harmoniques 5 et 7. Cette méthode dépend entièrement de l'alimentation et de la charge, et présente une faible flexibilité. Lorsque l'environnement de l'appareil est soumis à des interférences électromagnétiques, un filtre anti-parasites radiofréquences doit être installé afin de réduire les émissions de conduction de l'alimentation principale, et des mesures doivent être prises pour blinder l'alimentation du moteur. Lorsque la longueur du câble entre le moteur et le convertisseur de fréquence est supérieure à 50 mètres ou 80 mètres (non blindé), une réactance est installée entre le convertisseur de fréquence et le moteur afin de prévenir les surtensions instantanées au démarrage du moteur, de réduire les courants de fuite et les parasites du moteur vers la terre, et de protéger le moteur. En utilisant un fonctionnement multiphasé des transformateurs, le convertisseur de fréquence universel emploie un redresseur à six impulsions, ce qui génère d'importantes harmoniques. Dans ce cas, le déphasage entre les transformateurs est de 30°. Par exemple, une combinaison de transformateurs Y-△ et △-△ permet d'obtenir un effet à 12 impulsions, réduisant ainsi les courants harmoniques de bas rang et supprimant efficacement les harmoniques.