To explore the PLC to control frequency converter -

For beginners who just contact with PLC controller and frequency converter, often don't know how to cooperate with PLC and frequency converter to use, frequency converter parameters how to debug. Specially finishing this article today, hope for your help.

PLC as the logic controller in the initiative; Inverter is as actuators in a passive position. PLC usually need to control frequency converter start-stop, positive &negative operation and operation frequency, etc. To understand the PLC to control frequency converter, the first to know what frequency converter input channel and output channel. Frequency converter are usually provides a digital input terminals ( Multi-function terminal) , analog output channel ( AI） And digital output terminals ( A transistor and a relay) , analog output terminals ( AO） 。 PLC controller control signals is through digital input and analog input into the inverter, the inverter can be run again information through digital output and analog output feedback to the PLC, it cooperate to make the system stable operation.

understand the control input and output channels, there are three kinds of frequency converter operation channel: button operation command channel, terminal operation command channel, communication channels to run commands. Had multiple frequency channels: digital Settings for the keyboard, the keyboard analog channel, terminal analog channel, multistage speed frequency setting, the PID control setting, communication frequency setting, we should design reasonable control scheme according to system requirements, usually by PLC control scheme has the following kinds:

1. Channel + terminals analog channel terminal operation instruction. ( The most commonly used)

2。 Terminal operation instruction + communication channel frequency setting.

3。 Communication channel + communication frequency set operation.

4。 Terminal operation channel + multistage speed frequency setting.

below we specific to a Siemens S7 - 200 the smart and the British witten GD10 series inverter as an example, the use of the following four solutions.

scheme a channel + terminals, terminal operation instructions analog channel.

this scheme using the multi-function input terminal control operation, the frequency is given by the terminals analog input channel, typical applications for constant pressure water supply to the community.

parameter Settings are as follows:

run command channel should be set to terminal operation instruction, as shown in figure 1 1. Figure 1

- 1

multi-function terminal function defined as shown in figure 1 2. Figure 1

- 2

Settings as shown in figure 1 - control mode 3, the most commonly used models for two line 1. Figure 1

- 3

frequency source channel should be set to terminal simulation set, as shown in figure 1 4, usually there will be two frequency source A and B, can through setting different parameters combination, as shown in figure 1 5. Figure 1

- 4

figure 1 - 5

frequency converter and PLC connection diagram as shown in figure 1 6. Figure 1

- 6

2 + communication channel frequency setting, terminal operation instruction.

run command channel should be set to terminal operation instruction and plan a, the same frequency source channel should be set to the MODBUS communication set, as shown in figure 2 1.

FIG. 2 1

in addition to set the frequency source channel for communication mode, to set up communication related parameters, as shown in figure 2 2. Baud rate and data check Settings should be in line with PLC communication mouth parameters, instructions for SMART defaults in figure.

FIG. 2 2

connection as shown in figure 2 - frequency converter and PLC 3.

FIG. 2 3

written communication program control the inverter frequency address must know the inverter frequency, learned address as shown in figure 2 - refer to instructions 4.

FIG. 2 4

3, communication channel operation + communication frequency setting.

run the program and the frequency are given by the communication, PLC and frequency converter need only a two core ( Twisted-pair shielded wire) Communication lines to connect. Run the command channel communication should be set to a given, as shown in figure 3 - 1.

figure 3 - 1

frequency source channel should be set to the MODBUS communication set, same as the second scheme.

frequency converter and PLC connection as shown in figure 3 - 2.

figure 3 - 2

solution more than four, terminal channel + running period of speed frequency setting ( Application is less) 。

the external terminal by the frequency converter based on PLC control, operation frequency, external terminal combination multiple stage by the frequency converter, and given the scheme applied to the inverter needs at different times in different speed Settings, such as ball mill. Some ball mill special inverter without PLC can automatic switching speed.

run command channel should be set to terminal operation instruction, and the same. Frequency source set up multi-segment speed operation set, as shown in figure 4 1.

figure 4 - 1

need to external multi-function terminal S definition to multistage speed, defining methods as shown in figure 4 2.

figure 4 - 2

how much needed period of speed should be set in advance, can set up to 16 segment. Set the method as shown in figure 4 3.

figure 4 - 3

after the set period of speed combined with external multi-function terminal to call period of speed, more than four period of terminal velocity function according to the permutation and combination into 0 - in a binary form 15 a total of 16 segment, as shown in figure 4 4. Only need to use the PLC controller output terminal combination according to the picture through multistage speed terminal, can be called a scale of 0 - 15 period of speed, such as the need to use 4 period of speed, speed to define at least two more sections terminal, through the combination of S1 and S2 call 0,1,2,3 period of speed.

figure 4 - 4

frequency converter and PLC connection as shown in figure 4 5.

figure 4 - 5

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