Aug 18, 2020
Five tips for choosing inverter
With the rapid development of the process of industrial automation, the frequency converter as a frequency conversion debugging has also been widely used. As an important role of variable frequency speed regulation and energy saving, the main function of the frequency converter is to control the power control equipment of the AC motor by changing the working power frequency of the motor. Its advantages not only improve the production level of enterprises, but also play an important role in energy conservation for enterprises. So how to choose the right inverter? Today, the inverter manufacturer will introduce the purchasing skills of the inverter.
First of all, what aspects should we start with when choosing an inverter?
Choose the type of frequency converter, according to the type of production machinery, speed regulation range, static speed accuracy, starting torque requirements, decide which control mode frequency converter is most suitable. The so-called suitable is not only easy to use, but also economical to meet the basic conditions and requirements of technology and production.
How to judge the selection of inverter specifically?
1. The motor to be controlled and the inverter itself
The number of poles of the motor. Generally, the number of poles of the motor should not be more than 4, otherwise the capacity of the inverter must be appropriately increased. Torque characteristics, critical torque, acceleration torque. In the case of the same motor power, relative to the high overload torque mode, the inverter specifications can be selected by derating. Electromagnetic compatibility. In order to reduce the main power interference, a reactor can be added to the intermediate circuit or the input circuit of the frequency converter, or a front isolation transformer can be installed. Generally, when the distance between the motor and the inverter exceeds 50m, reactors, filters or shielded protective cables should be connected in series between them.
2. Selection of inverter power
The efficiency of the system is equal to the product of the efficiency of the frequency converter and the efficiency of the motor, and the system efficiency is higher only when both work at higher efficiency. From the perspective of efficiency, when selecting inverter power, pay attention to the following points:
When the power value of the frequency converter is equivalent to the power value of the motor, it is most appropriate to facilitate the frequency converter to operate at a high efficiency value.
When the power classification of the frequency converter is different from the power classification of the motor, the power of the frequency converter should be as close as possible to the power of the motor, but should be slightly larger than the power of the motor.
When the motor is frequently started, braked, or under heavy load starting and working more frequently, a higher-level frequency converter can be selected to use the frequency converter for long-term and safe operation.
After testing, the actual power of the motor does have a surplus. You can consider using a frequency converter with a power lower than the power of the motor, but pay attention to whether the instantaneous peak current will cause overcurrent protection.
When the power of the frequency converter and the motor are not the same, the settings of the energy saving program must be adjusted accordingly in order to achieve higher energy saving effects.
3. Selection of inverter box structure
The cabinet structure of the inverter must be adapted to the environmental conditions, that is, factors such as temperature, humidity, dust, pH, and corrosive gas must be considered. There are commonly the following structure types for users to choose:
The open type IPOO type itself has no chassis, and is suitable for installation in the electric control box or on the screen, panel, and rack in the electric room, especially when multiple inverters are used in a centralized manner. This type is better to choose, but the environmental conditions are higher; The enclosed type IP20 is suitable for general use, where there may be a small amount of dust or a little temperature and humidity; the sealed type IP45 is suitable for environments with poor industrial site conditions; the enclosed type IP65 is suitable for poor environmental conditions, with water, dust and certain corrosiveness Gas occasions.
4. Determination of inverter capacity
Reasonable capacity selection is itself a measure of energy saving and consumption reduction. According to existing information and experience, there are three simpler methods:
The actual power of the motor is determined. First determine the actual power of the motor to select the capacity of the inverter.
Formula method. When a frequency converter is used for multiple motors, it should be satisfied: at least the influence of the starting current of one motor must be considered to avoid the frequency converter from over-current tripping.
Motor rated current method inverter. The process of selecting the inverter capacity is actually the best matching process between the inverter and the motor. The most common and safer is to make the capacity of the inverter greater than or equal to the rated power of the motor, but the actual matching must consider the motor’s What is the difference between the actual power and the rated power? Usually, the selected capacity of the equipment is too large, but the actual required capacity is small. Therefore, it is reasonable to choose the inverter according to the actual power of the motor. Avoid using an excessively large inverter and increase the investment. .
For light loads, the inverter current should generally be selected according to 1.1N (N is the rated current of the motor), or according to the maximum motor power indicated by the manufacturer in the product that matches the output power rating of the inverter.
5. Main power
Power supply voltage and fluctuations. Special attention should be paid to adapt to the setting value of the inverter's low-voltage protection, because in actual use, the grid voltage is more likely to be low.
Main power frequency fluctuation and harmonic interference. This interference will increase the heat loss of the inverter system, resulting in increased noise and decreased output.
When the inverter 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 taken into consideration.