When using PLC to control the inverter, the following parameters need to be set:
- Inverter parameter setting
Basic parameters
Motor parameters:
Rated power: Set according to the power of the driven motor to ensure that the inverter can provide appropriate power for the motor. For example, if the rated power of the motor is 15kW, set the corresponding rated power parameter in the inverter to 15kW.
Rated voltage: Set to the rated voltage of the motor, common ones are 220V, 380V, etc. If the rated voltage of the motor is 380V, this parameter of the inverter should be set to 380V.
Rated current: Enter the rated current value of the motor so that the inverter can protect the motor from overload. This value can be obtained from the motor nameplate. For example, if the rated current of a motor is 30A, set this parameter in the inverter to 30A.
Rated frequency: The rated frequency of general industrial motors is 50Hz or 60Hz, set according to actual conditions. For example, it is usually set to 50Hz in China.
Motor pole number: set according to the actual number of motor poles, used to determine the synchronous speed of the motor. For example, the synchronous speed of a 4-pole motor is 1500r/min (at 50Hz).
Operation parameters:
Acceleration time: The time required for the motor to accelerate from rest to rated speed. It is set according to the load inertia and production requirements, generally between a few seconds and tens of seconds. For example, for loads with small inertia, the acceleration time can be set to 5s; for loads with large inertia, it may need to be set to 20s.
Deceleration time: The time required for the motor to decelerate from rated speed to rest. The setting principle is similar to the acceleration time. For example, for occasions where rapid parking is required, the deceleration time can be set to 5s; for occasions where high requirements for parking stability are required, it can be set to 10s or longer.
Maximum frequency: The maximum frequency limit of the inverter output to prevent the motor from overspeeding. It can usually be set to about 1.2 times the rated frequency. For example, when the rated frequency is 50Hz, the maximum frequency can be set to 60Hz.
Minimum frequency: The minimum frequency limit of the inverter output to prevent the motor from running unstably at too low a speed. It is set according to actual needs, generally set to 5Hz or higher. For example, for some occasions where low-speed operation is required, the minimum frequency can be set to 10Hz.
Control parameters
Control mode: Select the control mode of the inverter, common ones are V/F control, vector control, etc. Select according to the performance and application requirements of the motor. For example, for general loads such as fans and pumps, V/F control can be selected; for occasions with high requirements for speed control accuracy, such as machine tools and cranes, vector control can be selected.
Start mode: Set the inverter’s starting mode, such as direct start, soft start, etc. Direct start is suitable for small power motors and occasions with low requirements for starting impact; soft start can reduce the impact current when the motor starts, and is suitable for large power motors and occasions with high requirements for starting stability. For example, for motors below 10kW, direct start can be selected; for motors above 10kW, soft start can be selected.
Stop mode: Set the inverter’s stop mode, such as free stop, deceleration stop, etc. Free stop means that after the inverter stops output, the motor relies on inertia to stop freely; deceleration stop means that the inverter controls the motor to gradually decelerate to stop according to the set deceleration time. Select the appropriate stop mode according to actual needs. For example, for situations where a quick stop is required, deceleration stop can be selected; for situations where the stop position requirement is not high, free stop can be selected.
Communication parameters
Communication protocol: Select the protocol for communication with the PLC, common ones are Modbus, Profibus, Profinet, etc. Make sure that both the inverter and the PLC support the selected communication protocol and configure it accordingly. For example, if the PLC supports the Modbus RTU protocol, then the communication protocol of the inverter needs to be set to Modbus RTU, and the correct baud rate, data bit, stop bit, and parity bit parameters need to be set.
Communication address: Assign a unique communication address to the inverter so that the PLC can accurately identify and control the inverter. The communication address is usually configured in the parameter setting of the inverter, and the range is generally an integer between 1 and 255. For example, if there are multiple inverters that need to be controlled by the PLC, different communication addresses can be set for them, such as 1, 2, 3, etc.
- PLC parameter setting
Communication parameters
According to the selected communication protocol, set the communication parameters of the PLC, including baud rate, data bit, stop bit, check bit, etc. These parameters must be consistent with the communication parameters of the inverter to ensure normal communication. For example, if the communication protocol of the inverter is Modbus RTU, the baud rate is 9600bps, the data bit is 8 bits, the stop bit is 1 bit, and there is no check bit, then the same communication parameters need to be set in the PLC.
Set the port for communication between the PLC and the inverter, usually a serial port or an Ethernet port. Select according to the actual hardware connection and make corresponding configurations. For example, if serial communication is used, the serial port port number, communication mode, etc. need to be set; if Ethernet communication is used, the IP address, subnet mask, gateway and other parameters need to be set.
Control parameters
According to the control requirements, write the PLC program and set the variables and parameters for controlling the inverter. For example, you can set an output variable to control the start/stop of the inverter, set an analog output or communication register to control the frequency setting of the inverter, etc.
Set the PLC monitoring parameters for the inverter, such as reading the inverter’s operating status, fault information, current, voltage and other parameters, so as to timely understand the inverter’s operating conditions and perform corresponding processing. These monitoring functions can be realized by reading the inverter’s register or status word through communication.
In short, using PLC to control the inverter requires reasonable settings of the inverter and PLC parameters to ensure normal communication, accurate control, and stable operation. When setting parameters, they should be adjusted according to the actual application requirements and the characteristics of the motor and load to achieve the best control effect.
