I. Introduction
In the field of industrial automation, PLC (Programmable Logic Controller) and frequency converter are indispensable key equipment.PLC is widely used in various automation systems with its powerful logic control ability and stability; while frequency converter realizes the precise control of AC motor by changing the frequency of the motor working power supply. This article will introduce in detail how to control the AC motor through PLC. In this paper, we will introduce in detail how to control the frequency converter through PLC, including the control principle, control methods, application scenarios and precautions, aiming at providing reference for the design, application and maintenance of industrial automation system.
II. The principle of PLC control inverter
The principle of PLC control of inverters is mainly based on the communication and collaboration between the two. PLC as the control body, responsible for receiving external input signals (such as sensor signals, operating instructions, etc.), and according to the preset program logic for arithmetic processing, and then output control signals to the inverter. The inverter then adjusts its output frequency and voltage according to the received control signals, thus realizing precise control of the motor.
Specifically, the communication between PLC and inverter can be realized in various ways, including analog control, switching control and communication control. Among them, analog control means that PLC outputs an analog signal (e.g., 0-10V, 4-20mA, etc.) through the analog output module, which is converted into the corresponding frequency command after being received by the inverter; switching control is to control the start-stop, forward and reverse of the inverter through the PLC's switching output module; and communication control is to make use of the PLC's communication function through a specific communication protocol ( Such as Modbus, Profibus, etc.) and the frequency converter for data transmission and instructions issued.
III. PLC control inverter method
Terminal running command channel + terminal analog channel
This is one of the most commonly used methods of PLC control of inverters. Through the PLC switching output module to control the start and stop of the inverter, forward and reverse, etc., and at the same time, use the analog output module to output an analog signal to the frequency setting terminal of the inverter, so as to realize the precise control of the inverter output frequency.
Terminal running command channel + communication frequency setting
In this method, PLC controls the start/stop, forward/reverse rotation, etc. of the frequency converter through the switching output module, while the frequency setting of the frequency converter is realized through communication.PLC establishes a communication connection with the frequency converter by using the communication module and realizes the precise control of the output frequency of the frequency converter by sending the frequency setting instruction to the frequency converter.
Communication running channel + communication frequency setting
This method completely relies on communication to realize PLC control of frequency converter, PLC establishes communication connection with frequency converter through communication module, sends running command and frequency setting command to frequency converter, and frequency converter executes corresponding operation according to the received command. This method has the advantages of simple wiring, easy maintenance, etc., and is suitable for remote control or centralized monitoring occasions.
IV. Application Scenarios of PLC Controlled Inverter
PLC control frequency converter is widely used in various industrial automation systems, such as machinery manufacturing, petrochemical, power transmission, air conditioning and refrigeration and other fields. In these systems, PLC control of inverters to achieve precise control of the motor, thereby realizing the automatic operation of equipment and energy saving.
For example, in the field of machinery manufacturing, PLC control frequency converter can realize the accurate speed regulation and positioning of machine tool spindle; in the field of petrochemical industry, PLC control frequency converter can control the running speed and flow of pumps and fans, etc.; in the field of electric power transmission, PLC control frequency converter can realize the reactive power compensation of the power grid and voltage stabilization; in the field of air conditioning and refrigeration, PLC control frequency converter can realize the energy-saving operation and intelligent control of air conditioning system. In the field of air conditioning and refrigeration, PLC controlled inverter can realize the energy-saving operation and intelligent control of air conditioning system.
V. Precautions
When carrying out PLC control of inverters, it is necessary to ensure that the communication protocols between PLC and inverters are compatible and the communication parameters are set correctly.
In the selection of PLC and inverter, need to be based on the actual demand and system size for reasonable selection, to avoid waste of resources and inadequate performance.
When programming the PLC, it is necessary to give full consideration to the safety and stability of the system to avoid program errors or misoperation leading to equipment damage or safety accidents.
In the commissioning and operation of the system, it is necessary to pay close attention to the operating status and performance indicators of the equipment, and find and solve problems in a timely manner.
VI. Conclusion
PLC control inverter is one of the important means to realize industrial automation control. By reasonably selecting and configuring PLC and frequency converter, and adopting appropriate control methods and technical means, it can realize the precise control and efficient operation of the motor. With the continuous development and progress of industrial automation technology, PLC control inverter will be widely used and promoted in more fields.