In the industrial automation control system, the most common combination of PLC and frequency converter, and the production of a variety of PLC control inverter methods, which use RS-485 communication method to achieve control is widely used: because It has strong anti-interference ability, high transmission rate, long transmission distance and low cost. However, RS-485 communication must solve a series of technical problems such as data coding, checksum, framing, transmit data, parity of received data, timeout processing and error retransmission, a simple inverter operation instruction. Sometimes it is necessary to write dozens of PLC ladder instructions to achieve, the programming workload is large and cumbersome, which makes the designer daunting.
This article introduces a very simple Mitsubishi FX series PLC communication mode to control the inverter: it only needs to install an RS-485 communication board or attach an RS-485 communication module on the PLC host; embed a piece under the PLC panel The "function expansion storage box" with a cost of only a few hundred yuan can be used to write four extremely simple PLC ladder commands, which can realize the reading, writing and monitoring and control of the parameters of 8 inverters. Up to 50m or 500m. This method is very simple and convenient, and easy to master. This article takes Mitsubishi products as an example to give a brief introduction to this simple method of using an extended memory communication control inverter.
2. Mitsubishi PLC adopts extended memory communication to control the system configuration of the inverter
2.1 system hardware components
One FX2N series PLC (product version V 3.00 or higher) (software adopts FX-PCS/WIN-C V 3.00 version);
1 block of FX2N-485-BD communication template (maximum communication distance 50m);
Or 1 block of FX0N-485ADP communication module + 1 block of FX2N-CNV-BD board (the longest communication distance is 500m);
FX2N-ROM-E1 function expansion storage box 1 (installed in the PLC body);
8 sets of Mitsubishi inverters with RS485 communication port (S500 series, E500 series, F500 series, F700 series, A500 series, V500 series, etc., can be mixed with each other, the total number does not exceed 8 units; the communication parameter number of all series of Mitsubishi inverters , the command code and the data code are the same.);
RJ45 cable (5 core with shielding);
Terminal resistor (terminal resistance) 100Ω;
Option: 1 set of human-machine interface (such as small touch screen such as F930GOT).
2.2 Hardware Installation Method
(1) Use one of the cable crimping pliers to crimp one end of the cable to the RJ45 crystal head; the other end to connect the FX2N-485-BD communication template according to the method of Figure 1 to Figure 3. The two unused P5S ends are not Pick up.
(2) Uncover the panel cover on the left side of the PLC main unit, and install the FX2N-485-BD communication template and FX2N-ROM-E1 function expansion memory to cover the upper panel.
(3) Connect the RJ45 cable to the PU port of the inverter separately, and connect a 100Ω terminating resistor between the receiving signal terminals RDA and RDB of the inverter at the end of the network to eliminate the possibility of reflection due to signal transmission speed, transmission distance, etc. The communication barrier caused by the impact.
2.3 Inverter communication parameter setting
In order to establish communication correctly, parameters related to communication such as "station number", "communication rate", "stop bit length/word length", "parity", etc. must be set in the inverter. The Pr.117~Pr.124 parameters in the inverter are used to set the communication parameters. The parameter setting is performed on the PU port using the operation panel or the inverter setting software FR-SW1-SETUP-WE.
2.4 Inverter setting items and instruction code examples
2.5 Inverter data code table example
2.6 PLC programming method and example
(1) Communication method
The master-slave mode is used for communication between the PLC and the inverter. The PLC is the master and the inverter is the slave. There is only one host in one network, and the host distinguishes different slaves by station number. They use half-duplex two-way communication, and the slave sends data only after receiving the host's read and write commands.
(2) PLC command specifications controlled by the inverter
(3) PLC statement table program example and comment of inverter operation monitoring
LD M8000 operation monitoring;
EXTR K10 K0 H6F D0 EXTR K10: Operation monitor command; K0: station number 0; H6F: frequency code (see Table 1); D0: PLC read address (data register).
Explanation of the command: The PLC always monitors the speed (frequency) of the inverter with station number 0.
(4) PLC statement table program example and comment of inverter operation control
The LD X0 run command is input by X0;
SET M0 sets the M0 auxiliary relay;
LD M0 EXTR K11 K0 HFA H02 EXTR K11: Operation control command; K0: Station number 0; HFA: Operation command H02: Forward command.
The execution of the AND M8029 instruction ends;
RST M0 resets the M0 auxiliary relay.
Explanation of the instruction: The PLC issues a forward rotation command to the inverter with station number 0.
(5) PLC statement table program example and comment for inverter parameter reading
The LD X3 parameter read command is input by X3;
SET M2 sets the M2 auxiliary relay;
LD M2 EXTR K12 K3 K2 D2 EXTR K10: Inverter parameter read command; K3: station number 3; K2: parameter 2 - lower limit frequency; D2: PLC read address (data register).
OR RST M2 resets the M2 auxiliary relay.
Explanation of the instruction: The PLC always reads the parameter No. 2 of the inverter of station number 3 - the lower limit frequency.
(6) PLC statement table program example and comment written by inverter parameters
The LD X1 parameter change command is input by X3;
SET M1 sets the M1 auxiliary relay
LD M1 EXTR K13 K3 K7 K10 EXTR K13: Inverter parameter write command; K3: station number 3; K7: parameter 7 - acceleration time; K10: value written.
EXTR K13 K3 K8 K10 EXTR K13: Inverter parameter write command; K3: station number 3; K8: parameter 8 - deceleration time; K10: value written.
The execution of the AND M8029 instruction ends;
RST M1 resets the M1 auxiliary relay.
Explanation of the command: The PLC changes the parameter No. 7 of the inverter of station No. 3 - acceleration time, parameter No. 8 - deceleration time to 10.
3. Comprehensive review and comparison of various methods of Mitsubishi PLC control inverter
3.1 PLC switching signal control inverter
The output point and COM point of the PLC (MR type or MT type) are directly connected to the STF (forward rotation start), RH (high speed), RM (medium speed), RL (low speed), and input SG ports of the inverter. The PLC can control the start, stop and reset of the inverter through the program; it can also control the different combinations of high-speed, medium-speed and low-speed terminals of the inverter to realize multi-speed operation. However, because it is controlled by the amount of switching, its speed regulation curve is not a continuous smooth curve, nor can it achieve fine speed adjustment. This kind of switching quantity control method can not compare the speed regulation accuracy with the extended memory communication control.
3.2 PLC analog signal control inverter
Hardware: FX1N type, FX2N type PLC host, configure 1 channel simple FX1N-1DA-BD extended analog output board; or analog input/output hybrid module FX0N-3A; or two output FX2N-2DA; or four way Output FX2N-4DA module, etc.
Advantages: PLC programming is simple and convenient, the speed regulation curve is smooth and continuous, and the work is stable.
Disadvantages: In large-scale production lines, the control cable is long, especially when the DA module uses voltage signal output, the line has a large voltage drop, which affects the stability and reliability of the system. In addition, from an economic point of view, if you control 8 inverters, you need 2 FX2N-4DA modules, and the cost is 5 to 7 times that of extended memory communication control.
3.3 PLC uses RS-485 non-protocol communication method to control the inverter
This is the most commonly used method, PLC is programmed with RS serial communication instructions.
Advantages: The hardware is simple, the cost is the lowest, and 32 inverters can be controlled.
Disadvantages: The programming workload is large. From the second chapter of this paper, the programming with extended memory communication control is extremely simple. The technicians who have worked on PLC programming only need to know how to check the table, only a few hours can be mastered, and the added hardware cost is also very low. The ease of programming in this method is incomparable with the RS-485 protocol-free communication control method.
3.4 PLC uses RS-485 Modbus-RTU communication method to control the inverter
Mitsubishi's new F700 series inverters use the RS-485 terminal to communicate with the PLC using the Modbus-RTU protocol.
Advantages: PLC programming of Modbus communication mode is simpler and more convenient than RS-485 non-protocol mode.
Disadvantages: PLC programming workload is still large.
3.5 PLC uses fieldbus mode to control the inverter
Mitsubishi inverters can be equipped with various types of communication options, such as the FR-A5NC option for CC-Link fieldbus; FR-A5AP(A) option for Profibus DP fieldbus; for DeviceNet fieldbus FR-A5ND options and more. The Mitsubishi FX series PLC has a corresponding communication interface module to interface with it.
Advantages: Fast speed, long distance, high efficiency, stable operation, simple programming, and a large number of connected inverters.
Disadvantages: The cost is higher, much higher than the cost of using extended memory communication control.
In summary, PLC's method of using extended memory communication to control the inverter has the advantages of low cost, easy to learn and use, and reliable performance. If the man-machine interface is configured, the inverter parameter setting and monitoring will become more convenient.
An AC variable frequency drive system consisting of 1 PLC and no more than 8 inverters is a common small industrial automation system, widely used in small paper production lines, single-face corrugated board machinery, plastic film production lines, printing and dyeing and bleaching machinery, and loopers. Metal wire drawing machines and other industrial fields. The simple control method can make the engineering scheme have many advantages of communication control, and can save many complicated calculations in RS-485 data communication, so that the engineering quality and work efficiency are greatly improved. However, this simple method also has its drawbacks: it can only control the frequency converter and cannot control other devices; in addition, the number of control inverters is also limited.
4 Conclusion
This paper introduces in detail the simple method of PLC using extended memory communication to control the inverter, and comprehensively reviews the various methods of Mitsubishi PLC control inverter. A deep understanding of these methods will help to improve the scientific, advanced and economical design of the AC variable frequency drive control system. Readers can choose the right solution according to the specific conditions of the system. The simple method highlighted in this paper, despite its shortcomings, is still a good method of promoting value.
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