Method of Mitsubishi PLC Controlling Mitsubishi Inverter:
Using the PLC’s digital output to control the inverter (i.e., connecting the PLC’s digital output directly to the inverter’s digital input, allowing the PLC to control the inverter’s start, stop, forward, reverse, and multiple speed operation at high, medium, and low speeds through programming).
Using the PLC’s analog signal to control the inverter.
The PLC controls the inverter using the RS-485 Modbus-RTU communication method.
The PLC controls the inverter using fieldbus methods.
The PLC controls the inverter using RS-485 unprotocol communication methods.
Among them, the RS-485 unprotocol communication method for controlling the inverter has been widely used. In the RS-485 unprotocol communication method for controlling the inverter, the PLC is programmed to control via RS serial communication instructions.
1. System Configuration
The hardware configuration of the system includes:
1 FX2N series PLC (product version V3.00 or above);
1 FX2N-485-BD communication board (maximum communication distance 50m) or 1 FXON-485ADP + 1 FX2N-CNV-BD board (maximum communication distance 500m);
Mitsubishi inverters with RS-485 interfaces (F700 series, S500 series, E500 series, F500 series, A500 series), which can be mixed but should not exceed a total of 8 units.
The PLC and the inverter are connected using network cables, specifically connecting the RJ45 plug of the network cable to the PU socket of the inverter.
2. Mitsubishi FR-A500 Series Inverter
1. Terminal Wiring Diagram of FR-A500 Inverter
2. Communication Parameter Settings of FR-A500 Inverter
To establish communication correctly, it is necessary to set the communication-related parameters of the inverter, such as station number, communication rate, stop bit length/word length, parity, etc.
Parameters Pr.117 to Pr.124 in the inverter are used to set communication parameters.
Parameter settings can be done using the operation panel or the inverter setting software FR-SW1-SETUP-WE at the PU port.
FR-A500 Communication Parameter Settings
3. Data Format of FR-A500 Inverter
Using hexadecimal numbers, the data is automatically transmitted in ASCII code between the PLC and the inverter.
1) Communication request data format from PLC to inverter
If the inverter’s communication parameter setting is no LF/CR, then the total number of ASCII characters for the communication data sent from the PLC to the inverter is 12 (format A).
2) Input data format from inverter to PLC
3) Response data format from inverter to PLC when reading data
If the inverter’s communication parameter setting is no LF/CR, then the total number of ASCII characters read from the inverter at one time is 10 (when no errors are found).
4) Sending data format from PLC to inverter when reading data
The above data formats refer to the data transmitted between the PLC and the inverter (such as frequency and parameters).
The waiting time is the specified time between when the inverter receives data from the PLC and when it transmits response data. The waiting time is set between 0 to 150ms based on the PLC’s response time, with a minimum setting unit of 10ms. When the Pr.123 parameter unit of the inverter is not set to 9999, the waiting time is not set by the communication data, and there is no waiting time in the communication data format (missing one character).
The checksum is represented by the lowest byte (8 bits) of the sum (in binary) of the ASCII data being checked, expressed as two ASCII digits (hexadecimal).
4. Control codes and instruction codes of FR-A500 inverter
Explanation of FR-A500 control codes
Instruction codes are sent from the PLC to the inverter to indicate the program requirements (e.g., run, monitor, etc.). Through the corresponding instruction codes, the inverter can perform various modes of operation and monitoring.
Explanation of FR-A500 instruction codes
3. Communication Program Design
1. Special Data Registers
(1) D8120 sets the data communication format
Set the data length to 7 bits, even parity, 2 stop bits, baud rate of 9600b/s, no header and terminator, no added and check code, using unprotocol communication (RS-485). Therefore, the setting of D8120 is: b15～b0＝0000 1100 1000 1110＝0C8EH.
(2) D8122 stores the bytes in the current sent information that have not been sent.
(3) D8123 stores the number of received bytes.
(4) D8124 is the start character (8 bits) initial value STX (02H).
(5) D8125 is the end character (8 bits) initial value EXT (03H).
(6) D8129 sets the data network timeout timer value. Its unit is 10ms.
2. Communication Program
Set the inverter’s station number to 0, data length to 7 bits, even parity, 2 stop bits, baud rate of 9600b/s, no header and terminator, no added and check code, using unprotocol communication (RS-485).
M10 connected controls the inverter to enter forward rotation state, M11 connected controls the inverter to enter stop state, M12 connected controls the inverter to enter reverse state, M13 connected reads the inverter’s operating frequency (D700～D703), M14 connected writes the operating frequency to the inverter (D400～D403).
When any of M10, M11, or M12 is connected, the PLC first sends a running control signal to the inverter, D200～D209 is the address for sending data, where D200 stores the communication request code 05H, D201 and D202 store the inverter’s station number 0, D203 and D204 store the instruction code (run command word FAH), D205 stores the waiting time (0ms), D206～D207 stores the sending data (D206 and D207 store forward rotation 02H/reverse 04H/stop 00H), D208～D209 stores the checksum.
When M14 is connected, the PLC sends the operating frequency to the inverter. Suppose the operating frequency is pre-stored in D400～D403, D200～D211 is the address for sending data, where D200 stores the communication request code 05H, D201 and D202 store the inverter’s station number 0, D203 and D204 store the instruction code (write operating frequency command word EDH), D205 stores the waiting time (0ms), D206～D209 stores the sending data (operating frequency), D210～D211 stores the checksum.
When M13 is connected, the PLC sends a control signal to read the inverter’s operating frequency. D200～D207 is the address for sending data, where D200 stores the communication request code 05H, D201 and D202 store the inverter’s station number 0, D203 and D204 store the instruction code (read operating frequency command word 6DH), D205 stores the waiting time (0ms), D206～D207 stores the checksum.
D500～D509 is the address for receiving data, D600～D609 is the storage address for received data.
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