Special frequency converter suppliers remind you that with the rapid development of industrial automation, frequency converters used for frequency conversion debugging have also been widely applied. The frequency converter plays an important role in variable frequency speed regulation and energy conservation. Its main function is to control the power control equipment of AC motors by changing the frequency mode of the motor's working power supply. Its advantages not only improve the production level of enterprises, but also play an important role in energy conservation. So how to choose a suitable frequency converter? Today, the frequency converter manufacturer will introduce the selection techniques for frequency converters.
Firstly, what aspects should be taken into account when choosing a frequency converter?
Choose the type of frequency converter and determine the most suitable control method based on the type of production machinery, speed range, static speed accuracy, and starting torque requirements. The so-called suitability refers to being both easy to use and economical, in order to meet the basic conditions and requirements of technology and production.
How to determine and choose a frequency converter specifically?
1. The motor and frequency converter that need to be controlled themselves
The number of poles of the motor. It is generally recommended that the number of poles in a motor should not exceed 4, otherwise the capacity of the frequency converter should be appropriately increased. Torque characteristics, critical torque, acceleration torque. Under the same motor power conditions, compared to the high overload torque mode, the specifications of the frequency converter can be selected for derating. Electromagnetic compatibility. To reduce interference from the main power supply, reactors can be added to the intermediate circuit or input circuit of the frequency converter, 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 protective cable should be connected in series between them.
2. Selection of frequency converter power
The system efficiency is equal to the product of the efficiency of the frequency converter and the efficiency of the motor. Only when both are operating at a higher efficiency, the system efficiency is higher. From an efficiency perspective, when selecting the power of a frequency converter, the following points should be noted:
When the power value of the frequency converter is equivalent to that of the motor, it is most suitable for the frequency converter to operate at high efficiency values.
When the power classification of the frequency converter is different from that of the motor, the power of the frequency converter should be as close as possible to the power of the motor, but slightly greater than the power of the motor.
When the electric motor is frequently started, braked, or in heavy load starting and frequent operation, a higher-level frequency converter can be selected to ensure long-term and safe operation of the frequency converter.
After testing, it has been found that the actual power of the motor is indeed surplus. It is possible to consider using a frequency converter with a power lower than the motor power, but attention should be paid to whether the instantaneous peak current will cause overcurrent protection action.
When the power of the frequency converter is different from that of the motor, the energy-saving program settings must be adjusted accordingly to achieve higher energy-saving effects.
3. Selection of Inverter Box Structure
The enclosure structure of the frequency converter must be adapted to the environmental conditions, taking into account factors such as temperature, humidity, dust, acidity and alkalinity, and corrosive gases. There are several common structural types available for users to choose from:
The open type IPOO model itself does not have a chassis and is suitable for installation on screens, panels, and racks inside electrical control boxes or electrical rooms. Especially when multiple frequency converters are used together, this type is better, but the environmental conditions require higher requirements; The closed IP20 type is suitable for general use and can be used in situations with a small amount of dust or low temperature and humidity; The sealed IP45 type is suitable for environments with poor industrial site conditions; The sealed IP65 type is suitable for environments with poor environmental conditions, such as water, dust, and certain corrosive gases.
4. Determination of frequency converter capacity
Reasonable capacity selection itself is an energy-saving and consumption reducing measure. Based on existing data and experience, there are three relatively simple methods:
Determine the actual power of the motor. Firstly, measure the actual power of the motor to select the capacity of the frequency converter.
Formula method. When a frequency converter is used for multiple motors, at least one motor's starting current should be considered to avoid overcurrent tripping of the frequency converter.
Motor rated current method frequency converter. The process of selecting the capacity of a frequency converter is actually the best matching process between the frequency converter and the motor. The most common and safe way is to make the capacity of the frequency converter greater than or equal to the rated power of the motor. However, in actual matching, it is necessary to consider how much the actual power of the motor differs from the rated power. Usually, the selected capacity of the equipment is too large, while the actual required capacity is small. Therefore, it is reasonable to choose a frequency converter based on the actual power of the motor to avoid selecting a too large frequency converter and increasing investment.
For light load types, the current of the frequency converter should generally be selected according to 1.1N (N is the rated current of the motor), or according to the maximum motor power specified by the manufacturer in the product that matches the output power rating of the frequency converter.
5. Main power supply
Power supply voltage and fluctuations. Special attention should be paid to adapting to the low voltage protection setting value of the frequency converter, as there is a high possibility of low grid voltage in practical use.
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.
The power consumption of frequency converters and motors during operation. When designing the main power supply for the system, the power consumption factors of both should be taken into account.