Simplified design of communication between VFD (Variable-frequency Drive) and Mitsubishi PLC

I. Introduction

In the industrial automation control system, the most common is the combined application of PLC and VFD (Variable-frequency Drive), and has produced a variety of methods for PLC to control VFD (Variable-frequency Drive), among which RS-485 communication mode is adopted The scheme of implementing control is widely used: because of its 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 encoding, checksum calculation, framing, sending data, receiving data parity, timeout processing and error retransmission. A simple VFD (Variable- Frequency Drive) operation instructions, sometimes it is necessary to write dozens of PLC ladder diagram instructions to achieve, the programming workload is heavy and cumbersome, which makes the designer daunting.

This article introduces a very simple method of controlling VFD (Variable-frequency Drive) by Mitsubishi FX series PLC communication mode: it only needs to install an RS-485 communication board or connect an RS-485 communication module on the PLC host; A "function expansion storage box" with a cost of only a few hundred yuan is embedded under the panel, and four extremely simple PLC ladder diagram instructions can be written to realize reading, writing, and various parameters of eight VFDs (Variable-frequency Drive). Monitoring and control of this kind of operation, the communication distance can reach 50m or 500m. This method is very simple and convenient, easy to master. This article takes Mitsubishi products as an example, and briefly introduces this convenient method of "using extended memory communication to control VFD (Variable-frequency Drive)".

2. Mitsubishi PLC uses extended memory communication to control VFD (Variable-frequency Drive) system configuration

1. System hardware composition

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Figure 1 Mitsubishi PLC uses extended memory communication to control VFD (Variable-frequency Drive) system configuration

Figure 2 Outline drawing of FX2N-485-BD communication board

Figure 3 Mitsubishi VFD (Variable-frequency Drive) PU socket shape and pin number

One FX2N series PLC (product version V 3.00 and above) (the software adopts FX-PCS/WIN-C V 3.00); one FX2N-485-BD communication module (the longest communication distance is 50m); or FX0N-485ADP communication module 1 piece + 1 piece of FX2N-CNV-BD board (the longest communication distance is 500m); 1 piece of FX2N-ROM-E1 function expansion storage box (installed in the PLC body) Mitsubishi VFD (Variable-frequency Drive) with RS485 communication port 8 units (S500 series, E500 series, F500 series, F700 series, A500 series, V500 series, etc., can be mixed with each other, and the total number does not exceed 8 units; the communication parameter numbers and command codes of all Mitsubishi VFD (Variable-frequency Drive) series The same as the data code.); RJ45 cable (5 cores with shielding); terminal impedance (terminal resistance) 100Ω; option: man-machine interface (such as F930GOT and other small touch screen) 1 set.

2. Hardware installation method

(1) Use special crimping pliers for network cables to crimp one end of the cable with the RJ45 crystal head; catch.

(2) Uncover the panel cover on the left side of the PLC host, install the FX2N-485-BD communication module and the FX2N-ROM-E1 function expansion memory, and cover the panel.

(3) Connect the RJ45 cables to the PU ports of the VFD (Variable-frequency Drive) respectively, and connect a 100Ω terminal resistor between the receiving signal terminals RDA and RDB of the VFD (Variable-frequency Drive) at the end of the network to eliminate the signal transmission speed , transmission distance and other reasons, there may be communication obstacles caused by the influence of reflection.

3. VFD (Variable-frequency Drive) 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 check" and so on must be set in the VFD (Variable-frequency Drive). Parameters Pr.117~Pr.124 in VFD (Variable-frequency Drive) are used to set communication parameters. Parameter setting is carried out at the PU port using the operation panel or VFD (Variable-frequency Drive) setting software FR-SW1-SETUP-WE.

4. Examples of VFD (Variable-frequency Drive) setting items and command codes

?As shown in Table 1. After the parameter setting is completed, set the instruction code, data and start communication through the PLC program, allowing various types of operation and monitoring.

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5. Example of VFD (Variable-frequency Drive) data code table

?As shown in table 2.

6. PLC programming methods and examples

(1) Communication method

The communication between PLC and VFD (Variable-frequency Drive) adopts the master-slave mode, PLC is the master, and VFD (Variable-frequency Drive) is the slave. There is only one master in a network, and the master distinguishes different slaves by the station number. They use half-duplex two-way communication, and the slave only sends data after receiving the read and write commands from the master.

(2) PLC instruction specification controlled by VFD (Variable-frequency Drive)

(3) PLC statement list program example and notes for VFD (Variable-frequency Drive) operation monitoring

LD M8000 Running monitoring; EXTR K10 K0 H6F D0 EXTR K10: Running monitoring command; K0: Station number 0; H6F: Frequency code (see Table 1); D0: PLC read address (data register). Command explanation: PLC always monitors the speed (frequency) of VFD (Variable-frequency Drive) whose station number is 0.

(4) PLC statement list program example and notes for VFD (Variable-frequency Drive) operation control

LD X0 The running command is input by X0;

SET M0 Set M0 auxiliary relay;

LD M0

EXTR K11 K0 HFA H02 EXTR K11: running control command; K0: station number 0; HFA: running command (see table 1); H02: forward rotation command (see table 1).

AND M8029 instruction execution ends; string 9

RST M0 Reset M0 auxiliary relay.

Command explanation: PLC sends forward rotation command to VFD (Variable-frequency Drive) whose station number is 0.

(5) PLC statement list program example and notes for reading VFD (Variable-frequency Drive) parameters

LD X3 parameter read instruction is input by X3;

SET M2 Set M2 auxiliary relay;

LD M2

EXTR K12 K3 K2 D2 EXTR K10: VFD (Variable-frequency Drive) parameter read command; K3: station number 3; K2: parameter 2-lower limit frequency (see Table 2); D2: PLC read address (data register).

OR RST M2 Reset M2 auxiliary relay.

Command explanation: PLC always reads the No. 2 parameter of the VFD (Variable-frequency Drive) of station No. 3 - the lower limit frequency.

(6) PLC statement list program example and notes written by VFD (Variable-frequency Drive) parameters

LD X1 parameter change command is input by X3;

SET M1 Set M1 auxiliary relay;

LD M1

EXTR K13 K3 K7 K10 EXTR K13: VFD (Variable-frequency Drive) parameter write command; K3: station