Guide for type selection of frequency converter
Publish：Shenzhen Hong Jia Wei Technology Co., Ltd. Time：2018-01-03
Guide for type selection of frequency converter
The main indicators to measure the performance of universal inverter include control mode, starting torque, torque control accuracy, speed control accuracy, control signal type, speed control mode, multi stage speed setting, carrier frequency, frequency hopping function, communication interface and so on. The correct selection of the frequency converter is very important to the normal operation of the electronic control system of the mechanical equipment. When selecting frequency converters, we first identify the field requirements of mechanical equipment, load torque characteristics, speed regulation range, static speed accuracy, starting torque and application environment requirements, and then decide which control mode and frequency converter to protect structure are most suitable. The so-called suitable is to meet the actual process of mechanical equipment production requirements and use the premise, the realization of the best cost performance of the frequency converter.
The principle of type selection of frequency converter
In order to ensure the reliable realization of the process requirements of the frequency converter, the following technical parameters should be paid close attention to when the frequency converter is selected.
1. Select the frequency converter according to the actual working current of the motor
The actual working current of the motor is the most critical factor for the selection of the frequency converter. When the inverter works for a long time, it must meet the output current of the inverter and the actual working current of the motor. The rated power of the motor can only be used as a reference! Remember!!!
The actual working current of the motor is not the rated current marked on the nameplate of the motor. When the frequency converter is selected, it should first be familiar with the working condition and estimate the relationship between the working current and the time, so as to determine the type of the inverter.
1.1 in general, the frequency converter dragged the constant torque load motor, and selected the frequency converter on the basis of the rated current of the motor.
1.2 in general, the frequency converter dragged the motor of the fan and the load of the pump, and chose the frequency converter on the basis of the rated current of the motor.
1.3 the overloading cycle and overload current need to be calculated. The inverter drives the motor of this type of load. The maximum output current Imax of the inverter is greater than the peak current of the motor, and the I2t of the converter can enlarge one or several files to meet the needs of the field within the scope of its own permission. Now, 10kW and 20A rated current motor example: if the motor works intermittently, the peak current will be 40A (rated current 2 times) in one second, then stop for 20 seconds. This selection will be used in inverter overload: first motor current curve versus time curves, followed by the output current of inverter motor current curve coverage curve (i.e., the output current of converter motor is more than when the working current, motor) converter type only the inverter output current curve covering motor current curve is suitable for heavy load the. Some experience data can be used for the selection of heavy load frequency converter.
2. The influence of the environment on the frequency converter should be fully considered.
2.1 temperature transducer effects of inverter use environment temperature from -10 to 40 DEG C, if the ambient temperature is higher than 40 degrees Celsius, every increase of 1 degrees, the inverter should drop 5% per liter; ambient temperature of 10 DEG C, half frequency converter life, so the surrounding environment and the inverter cooling problems must be solved.
The influence of 2.2 humidity on the frequency converter works in the environment of less than 90% humidity, the relative humidity of the air is less than or equal to 90%, and the air is not exposed. When the humidity is too high and the humidity varies greatly, the condensation phenomenon is easy to appear in the converter, and its insulation performance will be greatly reduced and even may lead to short circuit. When necessary, a desiccant or heater must be added to the box. The influence of 2.3 altitude on the frequency converter is installed at the altitude of less than 1000m, which can output the rated power. At an altitude of more than 1000m, the output power will decrease.
2.4 the impact of dust on the frequency converter in the case of metal conductive dust, it is not suitable for installation of frequency converter. Conductive dust intruded into the frequency converter, the frequency converter will be short circuit, when serious will burn down the frequency converter.
3. The selection of the power supply for the converter
The common voltage is single phase 220VAC, three-phase 220VAC, three phase 380VAC and three phase 690VAC. The power supply of the incoming line is determined by the voltage level of the existing upstream transformer, and it should be clear in the early stage of the type selection of the inverter.
The voltage level also determines the connection mode of the motor junction box. Star connection has higher voltage resistance and smaller working current than trigonometric connection.
The frequency of the power supply is generally in 50Hz, and the frequency converter has a high ability to withstand the fluctuation of the line frequency. The frequency converter diode rectifier bridge is not sensitive to the frequency.
4. Correct selection of the cooling mode of frequency converter
Common 1000VAC low voltage inverter, mostly internal air cooling. When the high power frequency converter is set in group transmission, the noise of the fan is very noisy. In the case of necessary, water cooled series inverter can be used.
5. A long distance between the frequency converter and the motor
If the frequency converter wants to run long cable, we should take measures to restrain the influence of the long cable to the earth coupling capacitance at this time, so as to avoid the influence of the inverter on the insulation of the motor, so we should install the output reactor at the output end of the converter. Generally, when the electric cable is greater than 50m, the reactor should be added to the output end of the inverter.
6, a frequency converter controls multiple motors
When the frequency converter is used to control several parallel motors, the capacity of the inverter = (1.2-1.5) * (motor 1+ motor 2+ motor 3+... ). In addition, in this case, the control mode of frequency converter can only be controlled by V/F, and the inverter can not realize the overcurrent and overload protection of motors.
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