To select a frequency conversion control cabinet suitable for the automation system, the following factors need to be considered comprehensively:
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Load type
Constant torque load: such as conveyor belts, cranes, etc. For this type of load, a frequency converter with good torque characteristics should be selected, which can output stable torque in the entire range from low speed to high speed to ensure stable operation of the load.
Square torque load: For loads such as fans and water pumps, the torque is proportional to the square of the speed. When selecting a frequency conversion control cabinet, attention should be paid to the matching of the capacity of the frequency converter and the load characteristics, and the energy-saving function of the frequency converter should be used to adjust the motor speed according to the actual working conditions to achieve energy saving.
Constant power load: For example, when selecting a control cabinet for a winding machine, the frequency converter needs to be able to maintain constant power within a certain speed range to meet the working requirements of the load.
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Motor parameters
Motor power: The rated power of the frequency converter should match the motor power. In general, the power of the frequency converter should be greater than or equal to the motor power, and a certain margin (usually 10% – 20%) should be considered to cope with motor overload or other special working conditions.
Motor voltage and frequency: Ensure that the output voltage and frequency range of the frequency converter cabinet can meet the requirements of the motor. For example, the rated voltage of common motors is 380V, 660V, etc., and the rated frequency is 50Hz or 60Hz. The frequency converter must be able to provide compatible output.
Number of motor poles: The number of motor poles affects the speed and torque characteristics of the motor. When selecting a frequency converter for motors with different pole numbers, it is necessary to consider whether the output frequency range of the frequency converter can enable the motor to reach the appropriate speed, and ensure that the control method of the frequency converter is suitable for the number of poles of the motor.
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Control function requirements
Speed control accuracy: If the automation system has high requirements for motor speed control accuracy, such as in CNC machine tools, textile machinery and other equipment, it is necessary to select a frequency converter cabinet with high-precision speed control function, such as a frequency converter using vector control technology, whose speed control accuracy can reach ±0.01%.
Multi-speed control: For equipment that requires multiple operating speeds, such as elevators, material conveying systems, etc., a control cabinet with multi-speed control function should be selected. And the required number of speed segments and speed adjustment range should be determined according to actual needs.
Remote control and communication function: In a system with a high degree of automation, the frequency conversion control cabinet needs to be able to communicate with the host computer, PLC or other control systems to achieve remote monitoring, parameter setting and centralized management. Therefore, a frequency conversion control cabinet that supports standard communication protocols (such as Modbus, Profibus, etc.) should be selected.
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Environmental factors
Temperature and humidity: If the frequency conversion control cabinet is installed in an environment with high temperature, high humidity or large temperature changes, the protection level and heat dissipation measures of the control cabinet need to be considered. For example, in a high temperature environment, a control cabinet with a good heat dissipation device (such as a fan, a radiator) should be selected, and its electronic components should be able to work stably at high temperatures; in a humid environment, the control cabinet is required to have a higher protection level (such as IP54 or above) to prevent moisture from entering and causing a short circuit.
Dust and corrosive gases: In places with a lot of dust or corrosive gases, such as cement plants and chemical plants, a frequency conversion control cabinet with good sealing performance should be selected, and its shell and internal components should have a certain degree of corrosion resistance to extend the service life.
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Reliability and stability
Brand and quality: Choose a well-known brand of variable frequency control cabinet, which usually has a strict quality control system and mature technology, and the product reliability is high. You can check the product’s certification, user reviews and other information to evaluate its quality.
Redundant design and backup function: For some automation systems with extremely high continuity requirements, such as chemical production, sewage treatment, etc., you can consider choosing a control cabinet with redundant design (such as dual inverter backup) to reduce the risk of fault downtime.
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Cost factors
Initial purchase cost: Compare the prices of variable frequency control cabinets of different brands and different functional configurations, and choose cost-effective products according to the project budget and performance requirements. However, it should be noted that price cannot be used as the only criterion. Low-priced products may have deficiencies in quality and performance.
Operation cost: Consider factors such as the energy consumption and maintenance cost of the inverter. Although some energy-efficient inverters may have a high initial purchase cost, they can save a lot of electricity bills in the long run; at the same time, easy-to-maintain control cabinets can reduce maintenance costs and downtime.
