Variable Frequency Drive Multi-Pump Control System Design and Implementation: A Complete Engineering Application Solution

The variable frequency drive multi-pump control system is widely used in the industrial field and can achieve intelligent scheduling and energy-saving operation of water pumps. This article details a multi-pump control system solution based on the S7-1200 PLC.

1. Hardware Configuration

PLC and Expansion Selection

• • Master Station: SIMATIC S7-1200 CPU1215C DC/DC/DC

• • Analog Expansion: SM1234 4AI/2AO

• • Digital Expansion: SM1222 16DO

I/O Point Allocation

Input Points:

%I0.0 - System Start Button

%I0.1 - System Stop Button

%I0.2~I0.5 - Pump 1~4 Running Feedback

%IW64 - System Pressure Measurement (AI0)

%IW66 - System Flow Measurement (AI1)


Output Points:

%Q0.0~Q0.3 - Pump 1~4 Start Signals

%QW80 - Main Pump VFD Speed Control (AO0)

Peripheral Device Selection

• • Variable Frequency Drive: SINAMICS V20 2.2kW

• • Pressure Sensor: 4-20mA Output

• • Flow Meter: 4-20mA Output

• • Touch Screen: SIMATIC KTP700 Basic

2. Control Program Design

Global Variable Definition

DB_SYSTEM_PARA

    r_PressureSetPoint : Real    // Pressure Setpoint

    r_FlowSetPoint : Real        // Flow Setpoint

    r_PumpStartDelay : Time      // Pump Start Delay

    r_PIDKp : Real              // PID Proportional Coefficient

    r_PIDTi : Real              // PID Integral Time

    r_PIDTd : Real              // PID Derivative Time

Program Architecture

1. 1. OB1 Main Loop Program

• • System Status Monitoring

• • Operating Mode Switching

• • Pump Group Scheduling Control

• • Data Collection and Recording

• • PID Control Calculation

• • Variable Frequency Drive Output Control

• • Real-time Data Update

Core Function Block Design

FB_PUMP_GROUP_CONTROL

VAR_INPUT

    i_bSystemStart : Bool;       // System Start Command

    i_rPressureValue : Real;     // Actual Pressure Value

    i_rPressureSetPoint : Real;  // Pressure Setpoint

END_VAR


VAR_OUTPUT

    o_bPumpRun[1..4] : Bool;    // Pump Run Command

    o_rSpeedOutput : Real;       // Variable Frequency Drive Speed Output

END_VAR


VAR

    PID : FB_PID;               // PID Controller Instance

    TON_PumpDelay : TON;        // Pump Start Delay Timer

END_VAR

Pump Group Control Logic

1. 1. Calculate PID Output based on Pressure Deviation

2. 2. Delay Start of Auxiliary Pumps when VFD Speed reaches 90%

3. 3. Delay Stop of Auxiliary Pumps when VFD Speed drops below 40%

4. 4. Implement Alternating Operation of Pumps to Ensure Balanced Running Time

3. User Interface Design

Main Screen Layout

• • System Operating Status Display

• • Real-time Pressure and Flow Curves

• • Pump Operating Status Indicator

• • Fault Alarm Information

Parameter Setting Screen

• • PID Parameter Tuning

• • Pressure Setpoint Adjustment

• • Pump Start Delay Setting

• • Alternating Time Setting

4. System Debugging Methods

Single Pump Debugging

1. 1. Check Variable Frequency Drive Communication

2. 2. Adjust PID Parameters

3. 3. Verify Pressure Control Accuracy

Group Control Debugging

1. 1. Set Pump Start/Stop Thresholds

2. 2. Verify Alternating Function

3. 3. Test Fault Switching Function

5. Experience Summary

System Optimization Suggestions

1. 1. The minimum operating frequency of the VFD should not be lower than 20Hz

2. 2. PID Integral Time is recommended to be set between 3-5 seconds

3. 3. Pump Start Delay is recommended to be set above 5 seconds

Maintenance Key Points

1. 1. Regularly check the accuracy of the pressure sensor

2. 2. Monitor the balance of pump operating time

3. 3. Backup system parameters and programs

The above is a complete solution for the variable frequency drive multi-pump control. If you have any questions, feel free to discuss and if you encounter specific issues during project implementation, we can also discuss solutions at any time.