Select the type of frequency converter, according to the type of production machinery, speed regulation range, static speed accuracy, starting torque requirements, determine the choice of that control mode of the frequency converter is the most suitable. The so-called suitable is both easy to use and economical to meet the basic conditions and requirements of process and production.
The motor that needs to be controlled and the inverter itself
1) The number of poles of the motor. Generally, the number of motor poles is not more than (extremely appropriate, otherwise the capacity of the inverter should be appropriately increased.
2) Torque characteristics, critical torque, acceleration torque. With the same motor power, the inverter specification can be derated relative to the high overload torque mode. 3) Electromagnetic compatibility. In order to reduce the interference of the main power supply, a reactor can be added to the intermediate circuit or inverter input circuit, or a pre-isolation transformer can be installed. Generally, when the distance between the motor and the inverter exceeds 50m, the reactor, filter or shielded protection cable should be inserted in series between them.
Selection of inverter power
The system efficiency is equal to the product of the efficiency of the inverter and the efficiency of the motor, and the system efficiency is higher only when both are working at higher efficiency. From the perspective of efficiency, when selecting the power of the inverter, pay attention to the following points:
1) The power value of the inverter is most suitable when the power value of the motor is comparable, so as to facilitate the inverter to operate under high efficiency values.
2) When the power rating of the inverter is not the same as the power rating of the motor, the power of the inverter should be as close as possible to the power of the motor, but it should be slightly greater than the power of the motor.
3) When the motor is frequently started, braking or in heavy load starting and working more frequently, a large frequency converter can be selected to use the frequency converter for long-term and safe operation.
4) After testing, the actual power of the motor is indeed surplus, you can consider choosing a frequency converter with less power than the motor power, but pay attention to whether the instantaneous peak current will cause overcurrent protection action.
5) When the power of the inverter and the motor are different, the setting of the energy-saving program must be adjusted accordingly to achieve a higher energy-saving effect.
Selection of inverter box structure
The box structure of the inverter should be adapted to the environmental conditions, that is, temperature, humidity, dust, pH, corrosive gas and other factors must be considered. The following structure types are commonly available for users to choose from:
1) The open type IPOO type itself has no chassis, suitable for installation in the electric control box or the screen, disk, shelf in the electrical room, especially when multiple inverters are used intensively, this type is better, but the environmental conditions are higher;
2) Closed IP20 type is suitable for general use, there can be a small amount of dust or a little temperature, humidity occasions;
3) Sealed IP45 type is suitable for environments with poor industrial site conditions;
4) Closed IP65 type is suitable for occasions with poor environmental conditions, water, dust and certain corrosive gases.
Determination of the capacity of the frequency converter
Reasonable capacity selection is itself an energy-saving measure. Based on the available information and experience, there are three simpler methods:
1) The actual power of the motor is determined. First, the actual power of the motor is determined, and the capacity of the inverter is selected.
2) Formula method. When a frequency converter is used for multiple motors, it should be met: at least consider the influence of the starting current of one motor to avoid the overcurrent trip of the frequency converter.
3) Motor rated current method frequency converter.
The inverter capacity selection process, in fact, is a frequency converter and the motor of the best matching process, the most common, and safer is to make the capacity of the frequency converter greater than or equal to the rated power of the motor, but the actual matching to consider the actual power of the motor and the rated power difference, usually the equipment selection capacity is large, and the actual required capacity is small, so the selection of the frequency converter according to the actual power of the motor is reasonable, to avoid the selection of the frequency converter is too large, so that the investment increases. For light load class, 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 matching the output power rating of the inverter indicated by the manufacturer in the product.
Main power
1) Power supply voltage and fluctuation. Special attention should be paid to adapting to the low voltage protection setting value of the inverter, because in actual use, the possibility of low grid voltage is greater.
2) Main power frequency fluctuation and harmonic interference. This interference increases the heat loss of the inverter system, resulting in increased noise and lower output.
3) 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 taken into account.