Frequency has been applied in the industrial field as the main means of AC motor speed control is very extensive, it has a wide speed range, speed and high accuracy, fast dynamic response, suitable for a wide range of technical performance and reliable operation, has been gradually replace the DC motor speed control system. There are three ways of controlling the variable frequency governor.
(1) through the frequency converter panel operation, that is, through the operation panel to change the output of frequency and other operating parameters;
(2) the input 0-10V or 4-20mA signals are input at the input analog input of the inverter, and the output frequency of the inverter is controlled by changing the size of the input analog.
(3) control through the communication port of the frequency converter
The first method is generally used for manual adjustment and parameter setting in the field, and the latter two ways are used for automatic adjustment and remote control. PLC, DCS and other control systems commonly used in industrial control area have control modules suitable for inverter interface conditions, which can facilitate the realization of closed loop automatic empty boxes of frequency converter, which is widely used in large and medium-sized control systems. The control device for some smallexperimental device and embedded processor in VVVF control, generally also need to deal with the keyboard input, display, data acquisition and other work such as process control, this control is more suitable for single-chip control system as the core, and the PLC operation panel, although the function but the cost is too high, should not be used.
The use of single machine control variable frequency governor can choose the latter two ways. The use of communication port control, the advantage is that the control function is comprehensive. The corresponding level conversion circuit is suitable for the communication of inverters, and it can communicate with the frequency converter. The hardware is simple, and the number of connections between the two is less, and the connection is convenient. The disadvantage is that it is necessary to understand and master the communication protocol of the variable frequency governor to control programming, and the design of software is complex. Due to the different communication interfaces and communication protocols of different brands, there is no uniform standard at present. It can only be developed for a frequency converter, narrowing the selection range of variable-frequency governor, and the adaptability is limited. For analog input control mode, it can be supported in almost all frequency converters, although it can meet the requirements of most occasions, but it is relatively simple in function, and the mode control mode is very backward.
To realize the control of the variable frequency speed control system by single chip microcomputer, and to the frequency converter in different situations, only the developer can be programmed again according to the communication protocol.