1, select the low-voltage inverter steps
It is mainly divided into seven steps: (1) the equipment is determined in terms of working mode, volume and load type; (2) the equipment is determined in terms of technology, functional standards and control requirements; (3) (4) Summarize all performance standards and requirements; (5) Make direct bidding or technical consultation according to the conclusion drawn from the summary; (6) Comprehensively compare the service life, the price , Performance and service, etc .; (7) the inverter models, specifications, brands and suppliers to be clear.
2, select the method of low-voltage inverter
On the transmission control system in terms of routine operation, the wise choice of general-purpose inverter is essential, first, we should determine the ultimate goal of universal inverter to use, according to the production machinery in the speed range, the speed response , Type and starting torque, control accuracy and other requirements, a comprehensive analysis of the inverter drive load characteristics, and then decide on the choice of general-purpose inverter to choose what function constitutes a control system, and then determine the optimal selection of control forms. Determined universal inverter not only to meet the needs of the production process, but also in line with technical and economic standards. At the same time, we must also pay attention to whether the inverter has any problems in terms of technical standards, efficiency, harmonics, life span, power factor and sales service. At the same time, the general inverter keeps running. The inverter has the following features: output interface, In the DC braking unit and the inverter accessories such as matching accessories is also crucial.
The choice of general-purpose inverters includes two aspects of type selection and capacity selection of general-purpose inverters. The choice should be followed: First, the main performance of the inverters ensures the effective meeting of the needs of the process. Second, the price / performance ratio should be ideal. In the choice of general-purpose inverter type should start from the load characteristics. In the balance of fan and pump torque, when the speed is low, with a smaller load torque, the general should choose ordinary or special-purpose function of universal inverter. The constant torque load or static speed accuracy demanding machinery in the choice should have a torque control performance of high-performance general-purpose inverter, the universal inverter torque lower, harder static mechanical properties, Load impact will not be affected, there are excavator performance. To be able to carry out relatively large speed constant torque control, the general size of the general inverter to be increased. The high precision requirements, better dynamic performance, faster speed response of the production machinery, such as injection molding machines, paper machinery or rolling mills, etc., to choose directly to the torque control or vector control type of general-purpose inverter.
From a volume point of view, under normal circumstances, general frequency converter has been equipped with the motor power, rated current and rated capacity and other aspects of the parameters marked, and can be equipped with the motor power and rated capacity, responsible for the production of universal inverter People generally according to the company or the motor produced by the specifications of the country is given, there is no clear expression inverter shows load performance, only the rated current as a general inverter load performance can be expressed as an important parameter. Therefore, according to the rated current of the motor is less than the rated current of the general inverter for the inverter capacity selection is the most important principle, only the motor rated power reference selection.
Moreover, before using a certain drive capacity, you should first know the specific parameters of the motor and the operation flow, and must consider the motor operating characteristics and models, to retain certain limits. For example, generally speaking, the maximum current of the motor in the submersible pump is larger than the maximum current of the ordinary motor. For the metallurgical enterprises, the maximum current of the professional motor used in the submersible pump is not only larger than normal, but also short- Current can also be normal operation, the general use of multiple motors operating equipment, but should ensure that the operation of the total current can not exceed the maximum limit of the motor current limit. In addition, if the use of ordinary motor, and no gear box, should consider to some extent, increase the motor current storage capacity to ensure that the motor can operate normally. At the same time should consider the output of ordinary inverter is very unstable, may cause different degrees of damage to the motor. Therefore, using the inverter to power the motor increases the current flow of the motor compared to the normal grid output current, causing the motor temperature to rise. Therefore, in the use of inverter power supply, should consider leaving a certain flow limit, to prevent the temperature rising, damage to the motor.
3, the inverter to choose the full attention to environmental factors
(1) Inverter affected by humidity: When the inverter humidity is below 90%, the relative humidity in the air is ≤90%, and there is no condensation. When the humidity is too high and the humidity has a large change range, the inverter may not only dew, but also reduce the insulation performance, and may also cause a short circuit accident. Conditions permit, must be in the box with heaters and desiccant.
(2) Inverter affected by temperature: Under normal circumstances, the temperature of inverter environment should be between -10 ℃ ~ + 40 ℃. If the ambient temperature is above 40 ℃, each time there is 1 ℃ rise, the inverter The amount of power will be reduced by 5%. Each time the ambient temperature rises by 10 ° C, it will reduce the life of the inverter in half, so be sure to properly handle the surrounding ambient temperature and inverter cooling.
(3) Inverter affected by dust: If metal conductive dust is used in the occasion, it is not recommended to install the inverter. When the conductive dust intrudes into the inverter, the internal wiring of the inverter will be short-circuited. If the situation is serious, the inverter will be burned. Although the non-conductive dust, however, it will greatly affect the inverter, because the inverter in the change of power, it will have its own heat, usually when the general inverter cooling with forced air, if the radiator is more More dust, will interfere with the heat, resulting in reducing the output capacity of the inverter or failure.
(4) Inverter affected by altitude: If the location of inverter is less than 1km above sea level, it can output rated power. If the altitude above 1km in the case, will reduce the output power.
4, concluded
In today’s age of widespread use of frequency inverters, there is a great challenge to the application and choice of most engineers and technicians, especially in large equipment drive systems, where the frequency converter is very complicated in terms of selection , We must fully consider all the details, parameters and the main performance, so as to be able to provide an orderly and reliable operation of the system to provide protection.
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