一、Application introduction

Common large and medium-sized air compressors are screw or piston compressors. When working, a motor drives the screw or piston to inflate the gas tank, when the pressure of the gas tank rises to the set maximum pressure, the clutch plate acts, the motor is automatically unloaded, the motor is idling, the screw or piston stops the compressed air, and the main motor of the air compressor runs in a star-shaped to triangular buck start-up and then runs at full pressure. The control mode of adding and unloading the air supply is the inlet valve switch control mode, that is, the valve is closed when the pressure reaches the upper limit, and the compressor runs without load; When the pressure reaches the lower limit, the valve is opened and the compressor is loaded and run. If the system pressure rises to the upper pressure value, the controller closes the intake valve and runs the compressor without load until the system pressure drops to the lower pressure limit, the controller makes the intake valve reopen, the exhaust valve closes, the compressor opens, the compressor runs at full load, and the above process is repeated. The exhaust volume and pressure of the air compressor are not unchanged in operation, and the air consumption often changes due to changes in working conditions, so the air compressor is always repeating the full load-unloading working mode when working. The working current at full load is close to the rated current of the motor, and the idling current when unloading is about 30-50% of the rated current of the motor, which is not useful work, but the idle loss of the machinery at the rated speed.

二、System design

Meixin MR500 series inverter adopts leading open-loop vector control algorithm, strong overload output capacity, excellent performance, high reliability, built-in PID regulator, various parameters can be flexibly set, can well meet the control requirements.

The air compressor adopts Meixin MR500 frequency converter and PLC controller to form the air compressor control system. The pressure value is set by the PLC controller, the pressure sensor detects the pressure of the gas supply pipeline network in real time, and converts it through the transmitter, outputs the standard 4-20mA signal, sends it to the PLC controller for feedback, and gives a 4-20mA signal to the analog input control frequency of the inverter after the PLC controller calculation. According to the requirements of the system air consumption, the output of the inverter is adjusted in real time, so as to adjust the speed of the compressor motor in real time to ensure the constant pressure of the pipe network. The inverter fault signal is sent to the system controller through the relay output; The system controller uses RS485 bus to read the status value of the inverter (output frequency, output voltage, output current, output power and fault code, etc.) through the MODBUS-RTU method.

Principle of constant pressure air supply:

Wiring diagram:

2.1 Advantages after the implementation of the project

三、Apply effects