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The Selection Of Frequency Converter

- Jan 19, 2018 -

Select the type of inverter, according to the type of production machinery, speed range, static speed accuracy, starting torque requirements, the decision to choose the control mode of the frequency converter is the most appropriate. The so-called suitable is not only easy to use, but also the economy to meet the process and production of basic conditions and requirements.

1. Need to control the motor and frequency converter itself

1 The number of poles of the motor. The general number of motor poles to no more than (extremely appropriate, otherwise the frequency converter capacity should be increased appropriately.)

2 torque characteristics, critical torque, accelerated torque. In the same motor power, compared to the high overload torque mode, the frequency converter specification can be reduced.

3 Electromagnetic compatibility. In order to reduce the main power source interference, can be used in the intermediate circuit or inverter input circuit to increase the reactor, or the installation of the front isolation transformer. Generally when the motor and inverter distance of more than 50m, should be in the middle of them into the reactor, filter or shielded protective cable.

2. Frequency Converter Power Selection

System efficiency is equal to the product of frequency converter efficiency and motor efficiency, only if both of them are in high efficiency, the system efficiency is higher. From the efficiency point of view, in the selection of inverter power, we should pay attention to the following points:

1 Frequency converter power value and the motor power value is the most suitable, in order to facilitate the inverter in the high efficiency value of operation.

2 in the frequency converter power grading and motor power grading is not the same, the inverter power to as close to the motor power, but should be slightly larger than the motor power.

3 When the motor is frequent starting, braking work or heavy load starting and more frequent work, can choose a large-level inverter to use the inverter long-term, safe operation.

4 after testing, the actual power of the motor does have surplus, you can consider the use of power less than the motor power inverter, but pay attention to the instantaneous peak current will cause overcurrent protection action.

5 when the inverter and the motor power is not the same, you must adjust the energy-saving program settings, in order to achieve a higher energy-saving effect.

3. Frequency converter Box structure selection

The box structure of inverter should be adapted to the environmental conditions, that is, the temperature, humidity, dust, ph, corrosive gas and other factors must be considered. The following types of structures are common for users to choose from:

1 Open type Ipoo inorganic box, suitable for installation in the electric control box or electrical indoor screen, disk, rack, especially when the use of multiple frequency converter, this type is better, but the environmental requirements are higher; 2 closed IP20 type for general use, can have a small amount of dust or a little temperature, humidity occasions;

3 sealed type IP45 suitable for the environment with poor conditions in industrial field;

4 closed type IP65 suitable for environmental conditions, there is water, dust and a certain corrosive gas occasions.

4. Frequency Converter capacity Determination

The reasonable capacity choice itself is a kind of energy saving and consumption reduction measures. According to the available information and experience, there are three simple methods:

1 The actual power of the motor determines the hair. First, the actual power of the motor is measured to select the capacity of the inverter.

2 Formula method. When a frequency converter is used in many motors, it should be satisfied: at least consider the effect of a motor starting current to avoid the overcurrent tripping of the inverter.

3 Motor rated current method frequency converter. Frequency converter capacity selection process, is actually a frequency converter and the motor of the best matching process, the most common, but also more safe is to make the capacity of the inverter is greater than or equal to the rated power of the motor, but the actual match to consider the actual power of the motor and the rated power difference, is usually the equipment selected capacity is large, and the actual needs of small, Therefore, according to the actual power of the motor to select the frequency converter is reasonable, avoid the selection of the inverter too large, so that investment increases. For light load classes, inverter current should generally be 1.1N (n for the electric machine rated current) to choose, or according to the manufacturer in the product and inverter output power ratings matching the maximum motor power to choose.

5. Main power supply

1 power supply voltage and fluctuation. Special attention should be paid to the low voltage protection setting value of inverter, because in practical use, the probability of low voltage is greater.

2 The main power supply frequency fluctuation and harmonic interference. This interference will increase the heat loss of the inverter system, resulting in increased noise and lower output.

3 Frequency converter and motor when working, its own power consumption. When the system main power supply is designed, both power consumption factors should be considered.