How to choose the corresponding inverter according to the demand?
Select the type of frequency converter, according to the type of production machine, speed regulation range, static speed accuracy, starting torque requirements, determine the frequency converter control mode the most appropriate. The so-called suitable is not only easy to use, but also economical, in order to meet the basic conditions and requirements of process and production.
In order to choose the inverter that meets our needs, we first briefly understand the classification of the inverter,Classified by 1 conversion link:
It can be split into AC inverter. That is, it converts the power frequency AC directly to AC at an adjustable frequency and voltage. This is also known as a direct frequency converter. The AC-DC-AC frequency converter first converts the power frequency AC to. DC through a rectifier and then convert DC to AC at an adjustable frequency and voltage. It is also called an indirect frequency converter, which is a universal frequency converter that is widely used today.
According to the nature of DC power supply:
(1) Current type inverter
A feature of current inverters is that the intermediate DC link uses a large inductance as an energy storage link to buffer reactive power, that is, to control changes in current.
It is called a current source type inverter (current type) because the voltage is close to a sine wave and the DC internal anode is relatively large. Features (merits) of current inverters
You can control frequent and rapid changes in load current. It is often selected when the load current changes significantly.
(2) Voltage type inverter
A feature of voltage inverters is that the energy storage element of the intermediate DC link uses a large capacitor, which buffers the reactive power of the load. Since the DC voltage is relatively stable and the DC internal cathode is a small power source and a very dry voltage source, we often choose to have large changes in the dry load voltage.
In addition, frequency converters can be categorized according to output voltage adjustment mode, control mode, main switch components, and input voltage level.
1. The motor to be controlled and the drive itself
1) The number of poles of the motor. As a rule, the number of poles of the motor should not be extremely high, otherwise the capacity of the inverter should be increased appropriately.
2) Torque characteristics, critical torque, acceleration torque. In the case of the same motor power, compared to the high overload torque mode, the drive specifications can be selected by derating.
3) Electromagnetic compatibility. In order to reduce interference from the main power supply, an inductor can be added to the intermediate circuit or the input circuit of the inverter, or a front-end isolation transformer can be installed. In general, when the distance between the motor and the drive exceeds 50 meters, the reactors, filters or shielded protection cables should be connected in series with each other.
2. How to choose the power of the inverter?
The efficiency of the system is equal to the product of the efficiency of the frequency converter and the efficiency of the motor, and the efficiency of the system is only higher when both are running at higher efficiency. From the point of view of efficiency, when selecting the power of the inverter, pay attention to the following points:
1) It is more suitable when the inverter power value is equal to the motor power value, so that the inverter can work at high efficiency value.
2) When the power classification of the frequency converter is different from the power classification of the motor, the power of the frequency converter should be as close as possible to the power of the motor, but should be slightly higher than the power of the motor.
3) When the motor is frequently started, braked or under heavy load, starts and runs more frequently, a higher level frequency converter can be selected to use the frequency converter for long term and safe operation.
4) After test, the actual motor power is actually excess, you can consider using a frequency converter with lower power than the motor power, but pay attention to whether the instantaneous peak current will cause overload protection. overcurrents.
5) When the power of frequency converter and motor are not the same, the parameters of energy saving program should be adjusted accordingly in order to achieve higher energy saving effect.
3. How to choose the structure of the inverter housing?
The structure of the inverter cabinet must be suitable for the environmental conditions, i.e. factors such as temperature, humidity, dust, pH and corrosive gases must be taken into account . Usually, users can choose from the following types of structures:
1) The open type IPOO type does not have a chassis itself and is suitable for installation in the electrical control box or on the display, panel and rack of the electrical room, especially when multiple inverters are used centrally. better to choose, but the environmental conditions are more demanding.
2) The closed IP20 type is suitable for general use, where there is a small amount of dust or a small amount of temperature and humidity.
3) IP45 waterproof type is suitable for environments with poor industrial site conditions.
4) The included IP65 type is suitable for occasions with bad environmental condition, water, dust and some corrosive gas.
4. How to determine the capacity of the inverter?
Reasonable capacity selection in itself is a measure of energy saving and consumption reduction. According to the existing information and experience, there are three simpler methods:
1) The actual engine power is determined. First determine the actual motor power to select the inverter capacity.
2) Formula method. When a frequency converter is used for several motors, it must be satisfied: at least the influence of the starting current of a motor must be taken into account to prevent the frequency converter from tripping in the event of an overcurrent.
5. Precautions for main power supply
1) Power supply voltage and fluctuation. In actual use, the grid voltage is likely to be low, so special care must be taken to match the inverter's low voltage protection settings.
2) Fluctuations in mains frequency and harmonic interference. This interference increases the heat loss of the inverter system, increases noise and reduces output.
3) When the inverters and motors are operating, their own power consumption. Both power factors must be taken into account when designing the mains for the system.
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