The type of frequency converter should be selected based on the type of production machinery, speed control range, static speed accuracy, and starting torque requirements. The most suitable frequency converter is one that is both easy to use and economical, meeting the basic conditions and requirements of the process and production.
Considerations for the motor and the frequency converter itself
Motor pole number: Generally, the motor pole number should not be too high (preferably 2 or 4 poles), otherwise the frequency converter capacity will need to be increased accordingly.
Torque characteristics, critical torque, and acceleration torque: Under the same motor power, the frequency converter specifications can be derated compared to high overload torque modes. Electromagnetic compatibility: To reduce interference from the main power supply, a reactor can be added to the intermediate circuit or the frequency converter input circuit, or a pre-isolation transformer can be installed. Generally, when the distance between the motor and the frequency converter exceeds 50m, a reactor, filter, or shielded cable should be used between them.
Selection of Frequency Converter Power
The system efficiency is equal to the product of the frequency converter efficiency and the motor efficiency. High system efficiency is achieved only when both operate at high efficiency. From an efficiency perspective, the following points should be considered when selecting the frequency converter power:
The most suitable situation is when the frequency converter power is equivalent to the motor power, allowing the frequency converter to operate at high efficiency.
If the power ratings of the frequency converter and the motor do not match, the frequency converter power should be as close as possible to the motor power, but slightly larger.
When the motor is frequently started and braked, or operates under heavy load starting conditions, a larger frequency converter can be selected to ensure long-term, safe operation.
If testing shows that the motor has sufficient power margin, a frequency converter with a power rating less than the motor power can be considered, but attention should be paid to whether the instantaneous peak current will trigger overcurrent protection.
When the frequency converter and motor power ratings do not match, the energy-saving program settings must be adjusted accordingly to achieve higher energy-saving effects.
Selection of Inverter Enclosure Structure
The inverter enclosure structure must be adapted to the environmental conditions, considering factors such as temperature, humidity, dust, acidity, and corrosive gases. The following structural types are commonly available for users:
Open type IP00: This type has no enclosure and is suitable for installation in control cabinets or on panels and racks in electrical rooms, especially when multiple inverters are used together. However, it requires stricter environmental conditions;
Enclosed type IP20: Suitable for general use, in environments with small amounts of dust or slight variations in temperature and humidity;
Sealed type IP45: Suitable for harsh industrial environments;
Hermetically sealed type IP65: Suitable for environments with poor conditions, including water, dust, and certain corrosive gases.
Determination of Inverter Capacity
Choosing the right capacity is itself an energy-saving measure. Based on existing data and experience, there are three relatively simple methods:
Determination based on actual motor power: First, measure the actual power of the motor and use this to select the inverter capacity.
Formula method: When one inverter is used for multiple motors, it should satisfy the condition that at least the starting current of one motor is considered to avoid inverter overcurrent tripping.
Motor rated current method
The process of selecting the inverter capacity is actually a process of optimally matching the inverter and the motor. The most common and safest approach is to make the inverter capacity greater than or equal to the motor's rated power. However, in actual matching, the difference between the motor's actual power and rated power should be considered. Usually, the selected equipment capacity is larger than the actual required capacity. Therefore, selecting the inverter based on the motor's actual power is reasonable, avoiding oversized inverters and increased investment. For light loads, the inverter current should generally be selected at 1.1N (N is the motor's rated current), or according to the maximum motor power specified by the manufacturer that matches the inverter's output power rating.
Main Power Supply
Power supply voltage and fluctuations. Special attention should be paid to matching the low-voltage protection setting of the frequency converter, as the possibility of low grid voltage is relatively high in practical use.
Main power supply frequency fluctuations and harmonic interference. This type of interference will increase the heat loss of the frequency converter system, leading to increased noise and reduced output.
The power consumption of the frequency converter and the motor during operation. Both power consumption factors should be considered when designing the main power supply for the system.