Frequency converters used in industry are divided into single-phase and three-phase. This is distinguished by the voltage of the main circuit power supply. Three-phase means that the main circuit must be connected to the RST three-phase 380 volt AC power single-phase main circuit is connected to the single-phase 220 volt LN AC power, and the output is also connected to the UVW three-phase line to the motor. The inverter input between the main circuit and the power grid needs to be connected in series with the power supply through an air switch to form protection . Do not use a leakage protection switch, otherwise it will not work properly because the leakage current of the frequency converter is very large. The output end of the inverter needs to be directly connected to the motor. Do not use devices such as contactors in series, otherwise the voltage drop caused by the contacts may cause unbalanced operation of the motor.
The control loop of the frequency converter seems to have a lot of lines. In fact, it can be understood as two major logics. One is start-stop logic control, which is used to meet the start and stop requirements of the frequency converter. This can be done through the external I/O terminals . To control, simply put, one or two switch contacts are input to the inverter, which can be accomplished using self-locking buttons, PLC output points or self-protecting relay contacts. Of course, this start-stop logic can also be completed through the RUN and STOP buttons on the panel, or controlled through a host computer such as a touch-screen industrial computer using communication formats. For most inverters currently on the market, the factory-set parameters are controlled by the RUN and STOP buttons on the panel to achieve this startup logic control.
The other is frequency signal given logic, which is a continuous analog quantity. Of course, it can also be understood as a string of logical data. Factory parameters are often operated through the ↑↓ buttons on the surface. The common method is to connect an external 1-10K potentiometer. The two ends of the potentiometer are connected to the 10-volt positive electrode and the ground wire, and the middle tap is taken. In this way, the potentiometer can be rotated to output 0-10K. 10VDC voltage is given to the frequency converter, and the frequency converter will be given a frequency command of 0-50HZ. Of course, this analog quantity can also be given in communication format through a potentiometer on the inverter operation panel or a host computer such as a touch screen. There is also a multi-speed mode setting. For example, there are three ports H1H2H3 on the terminal. The combination can have 8 different frequency values for speed regulation of the inverter.
Therefore, as long as the start-stop source and frequency source of the inverter are set, the inverter can operate normally. The corresponding parameters in the manual of each inverter will be slightly different, but the principle is the same. Finally, you can also set some overload and overcurrent protection parameters, acceleration and deceleration time, frequency upper limit parameters, torque boost parameters, starting frequency and other speed signal output ranges, etc. The selection depends on the actual equipment and working conditions requirements. |
