Explain how to coordinate control between inverter and PLC

June 18, 2023

I talked about one of the application modes of PLC control inverter: terminal running command channel + terminal analog channel. The typical application of this mode is to use the remote pressure gauge to detect the pipeline pressure in the constant pressure water supply, convert it into a 0-10V voltage or 4-20MA current analog quantity and feedback it to the PLC, perform PID calculations through the PLC, and then return the calculation results It becomes an analog output, and the frequency of the inverter is controlled through the terminal analog input channel of the inverter to adjust the speed of the water pump, thus forming a closed loop adjustment to achieve constant pressure water supply control, as shown in the following figure:

Let's take Siemens V20 inverter as an example to explain how to coordinate control between inverter and PLC. Since the PLC does not have analog input and output functions as standard, an analog input and output module EMAM06 is selected for expansion. The wiring diagram is as follows:

0+, 0- is the analog input interface, 1M, 1 is the analog output interface, DI1 is the V20 digital input terminal, connected to the output point Q0.0 of the PLC to control the start and stop of the inverter, DIC is the common terminal of digital input , Connect the negative pole of the 24V power supply in the picture.

So how to set the parameters for the inverter?

Before debugging the parameters, restore the factory default value of the inverter, the method is as follows:

parameter Features Set up
P0003 User access level =1 (standard user access level)
P0010 Debug parameters =30 (factory setting)
P0970 Factory reset =21: Reset the parameters to the factory default settings and clear the user default settings (if stored)

V20 sets the parameter access level P0003, you need to change the level to expert to access all application parameters, the method is as follows:

P0003 User access level
0 User-defined parameter list
1 Standard: Allow access to commonly used parameters
2
3 Expert: For expert use only
4 Maintenance: only for authorized maintenance personnel, with password protection

Set the start-stop command source to external terminal control P0700, the method is as follows:

P0700[0...2] Select command source
Select the digital command source.
0 Factory default settings
1 Operation panel (keyboard)
2 Terminal
5 USS/MODBUS on RS485

Set the functions of the external input terminals P0701 to P0704, the method is as follows:

P0701—P0714 Function of digital input terminal
0 Prohibit digital input
1 ON/OFF1
2 ON reverse/OFF1
3 OFF2-Free stop by inertia
4 OFF3-Quick ramp down stop
5 ON/OFF2 command
9 Fault confirmation
10 Forward jog
11 Reverse jog
12 Reverse
13 MOP (electric potentiometer) speed increase (increased frequency)
14 MOP speed reduction (decrease frequency)
15 Fixed frequency selector bit 0
16 Fixed frequency selector bit 1
17 Fixed frequency selector bit 2
18 Fixed frequency selector bit 3
twenty two Fast stop command source 1
twenty three Fast stop command source 2
twenty four Fast stop overriding
25 DC brake enable
27 PID enable
29 External trip
33 Prohibit additional frequency setting value
99 BICO parameter setting enable

Set the control line type P0727, the method is as follows:

Parameter P0727 Features
0 Siemens standard control (start/direction)
1 2-wire control (forward/reverse)
2 3-wire control (forward/reverse)
3 3-wire control (start/direction

To set the frequency setting and select P1000, the method is as follows:

Parameters P1000 Frequency setting selection
0 No main setpoint
1 MOP setting value
2 Analog setting value
3 Fixed frequency
5 USS/MODBUS on RS485
7 Analog setting value 2
10 No main set value + MOP set value
11 MOP set value + MOP set value
12 Analog setting value + MOP setting value
13 Fixed frequency + MOP setting value
15 USS/MODBUS＋MOP setting value on RS485
17 Analog setting value 2+MOP setting value
20 No main set value + analog set value
twenty one MOP setting value + analog setting value
twenty two Analog setting value + analog setting value
twenty three Fixed frequency + analog setting value
25 USS/MODBUS+ analog setting value on RS485
27 Analog setting value 2+analog setting value
30 No main set value + fixed frequency

You can also use the macro function to achieve quick debugging. The system provides several commonly used macros, as shown below. Please refer to the V20 manual for the specific parameter settings of each macro.

Connection macro description
Cn000 Factory default settings. Do not change any parameter settings.
Cn001 BOP panel as the only control source
Cn002 Control by terminal (PNP/NPN)
Cn003 Fixed speed
Cn004 Fixed speed in binary mode
Cn005 Analog input and fixed frequency
Cn006 External button control
Cn007 Combination of external button and analog set value
Cn008 PID control and analog input reference combination
Cn009 PID control and fixed value reference combination
Cn010 USS control
Cn011 MODBUSRTU control

The connection macro method is as follows:

Select and connect the corresponding macro. If individual parameters do not meet the control requirements, you can modify them manually.

Next, write the control program, first configure the hardware system block, the method is as follows:

Then carry on PID wizard configuration, the method is as follows:

After writing the program, you can find the addresses of P loop gain, I integration time, and D differentiation time through the wizard data block, and adjust them by modifying the values. The PID parameters need to be set to the power-off hold type. As shown below:

It can also be adjusted through the PID panel provided by the software to make the adjustment more intuitive, as shown in the figure below:

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