Five skills of choosing frequency converter

With the rapid development of industrial automation, as a frequency converter debugging has also been widely used. As an important role of frequency control and energy saving, the main function of frequency converter is to control the power control equipment of AC motor by changing the frequency of working power supply of motor. Its advantages not only improve the process production level for enterprises, but also play an important role in energy saving for enterprises. So how to choose the right frequency converter? Today, the inverter manufacturer will introduce the selection skills of the inverter.
First of all, what should we do to choose frequency converter?
According to the type of production machinery, speed range, static speed accuracy and starting torque requirements, it is determined that the inverter with that control mode is the most appropriate. The so-called appropriateness is not only easy to use, but also economical to meet the basic conditions and requirements of technology and production.
How to judge and choose frequency converter?
1. Motor to be controlled and frequency converter itself
Number of poles of the motor. Generally, the number of motor poles should not be more than 4 poles, otherwise the converter capacity should be increased appropriately. Torque characteristics, critical torque, acceleration torque. In the case of the same motor power, compared with the high overload torque mode, the converter specification can be selected by derating. Electromagnetic compatibility. In order to reduce the interference of the main power supply, reactor can be added to the intermediate circuit or the input circuit of the frequency converter, or pre isolation transformer can be installed. Generally, when the distance between the motor and the frequency converter is more than 50m, the reactor, filter or shielding cable shall be connected in series between them.
2. Selection of converter power
The system efficiency is equal to the product of inverter efficiency and motor efficiency. Only when both of them are working at high efficiency, the system efficiency is high. From the perspective of efficiency, the following points should be paid attention to when selecting converter power:
When the power value of the frequency converter is equal to the power value of the motor, it is most suitable for the operation of the frequency converter under high efficiency value.
When the power classification of the frequency converter is different from that of the motor, the power of the frequency converter shall be close to the power of the motor as much as possible, but slightly greater than the power of the motor.
When the motor is frequently started, braked or in heavy load starting and works more frequently, the inverter of a larger level can be selected to use the inverter for long-term and safe operation.
After testing, the actual power of the motor is indeed surplus. It can be considered to select a frequency converter whose power is less than the motor power, but it should be noted whether the instantaneous peak current will cause overcurrent protection action.
When the power of frequency converter and motor is different, the setting of energy-saving program must be adjusted accordingly to achieve higher energy-saving effect.
3. Selection of inverter box structure
The box structure of the frequency converter should adapt to the environmental conditions, that is, the temperature, humidity, dust, pH, corrosive gas and other factors must be considered. There are several common types of structures for users to choose from:
The open type of ipoo has no case. It is suitable to be installed on the screen, panel and rack in the electric control box or electric room, especially when multiple frequency converters are used in a centralized way. However, the environmental conditions are relatively high. The closed type of IP20 is suitable for general purpose, with a small amount of dust or temperature and humidity. The sealed type of IP45 is suitable for the environment with poor industrial site conditions. The closed type I P65 is suitable for the occasion with poor environmental conditions, water, dust and certain corrosive gas.
4. Determination of converter capacity
Reasonable capacity selection is an energy-saving measure. According to the existing data and experience, there are three simple methods:
Determine the actual power of the motor. First, the actual power of the motor is measured to select the capacity of the frequency converter.
Formula method. When a frequency converter is used for multiple motors, it shall meet the following requirements: at least the influence of starting current of one motor shall be considered to avoid over-current trip of frequency converter.
Motor rated current method frequency converter. The selection of converter capacity is actually the best matching process of converter and motor. The most common and safe thing is to make the converter capacity greater than or equal to the rated power of motor. However, in the actual matching, the difference between the actual power and rated power of motor should be considered. Generally, the selected capacity of equipment is too large, but the actual required capacity is small, so according to the actual situation of motor It is reasonable to choose the frequency converter for the international power, so as to avoid excessive selection of the frequency converter and increase the investment.
For light load type, the converter current shall generally be selected according to 1.1n (n is the rated current of motor), or the maximum motor power matched with the output power rating of the converter indicated by the manufacturer in the product.
5. Main power supply
Power supply voltage and fluctuation. Special attention should be paid to the adaptation to the setting value of the low voltage protection of the frequency converter, because in actual use, the possibility of the low voltage of the power grid is large.
Main power frequency fluctuation and harmonic interference. This kind of interference will increase the heat loss of the converter system, resulting in increased noise and reduced output.
When the frequency converter and motor are working, their own power consumption. When designing the main power supply of the system, the power consumption factors of both should be considered