Application of PLC controlled VFD (Variable-frequency Drive) in LAN

Abstract: Connecting the VFD (Variable-frequency Drive) with the PLC in the local area network enables the VFD (Variable-frequency Drive) to achieve intelligent remote control, which provides convenience for maintenance personnel to quickly find faults.

Keywords: LAN; VFD (Variable-frequency Drive); PLC; application

0 Preface

After decades of development, the current VFD (Variable-frequency Drive) speed regulation has become the mainstream of electrical speed regulation. VFD (Variable-frequency Drive) speed regulation has been originally only used for fans and pumps. Speed regulation transitions to high-performance speed regulation control for various types of high precision and fast response.

With the development and popularization of intelligence, the use of PLC combined with VFD (Variable-frequency Drive) to realize remote control of VFD (Variable-frequency Drive) is currently the mainstream in electric drive remote control.

1 PLC control of VFD (Variable-frequency Drive)

1.1 Connection between VFD (Variable-frequency Drive) and PLC

In May 2005, Anyang Steel's 380m3 blast furnace coal injection entered the electrical commissioning stage. The key equipment for coal injection is the separator installed on the top of the medium-speed mill. The main control unit is ABB's ACS400 VFD (Variable-frequency Drive). The control mode of the VFD (Variable-frequency Drive) is set to remote control, and Siemens' S7-300 PLC is used to control it. For communication between VFD (Variable-frequency Drive) and PLC, first create a project in the Step7 software and configure the hardware equipment of the project. And establish the Profibus DP network, configure the ACS400 VFD (Variable-frequency Drive) in the Profibus DP=>Simovert folder, and set the communication address range.

ABB VFD (Variable-frequency Drive) can communicate with external control systems through the serial channel ACS 400 standard Modbus (RS-485). ACS400 has 2 serial channels, channel 0 and channel 1. Channel 1 is standard Modbus. To communicate with PLC, it must be set to be controlled by channel 1. The settings are shown in Table 1.

1.2 Control method

To realize Modbus control, the start and stop commands and frequency of ACS400 must be set, and the ACS400 must be under remote control.

1.3 Define the output signal

The analog output and 2 relays can be controlled by channel 1.

1.4 Register map

ACS400 maps all drive parameters, control and status information to 4×××× register areas, which can be read and written by external devices. The transmission parameters are mapped to the 4 ×××× area:

(1) 40001~40009 are used for transmission control registers;

(2) 40101~40199 is used for the actual value of group D1;

(3) 40201~40299 are used for parameter group D2;

(4) 40301~40399 are used for fault and alarm information;

(5)?Other parameter groups;

(6) 49901~49999 are used for starting data.

2 Comparison of various methods of PLC control VFD (Variable-frequency Drive)

2.1 Switch signal control VFD (Variable-frequency Drive)

The output point and COM point of the PLC are directly connected to the STF (forward start), RH (high speed), RM (medium speed), RL (low speed), input terminal SG and other ports of the VFD (Variable-frequency Drive). PLC can control the start, stop, and reset of VFD (Variable-frequency Drive) through programs; it can also control different combinations of high-speed, medium-speed, and low-speed terminals of VFD (Variable-frequency Drive) to achieve multi-speed operation. However, because it uses switching values to implement control, its speed regulation curve is not a continuous and smooth curve, and it cannot achieve fine speed regulation.

2.2 Analog signal control VFD (Variable-frequency Drive)

Hardware: PLC host, equipped with 1 simple expansion analog output board; other types of analog input and output hybrid modules can also be used.

Advantages: PLC programming is simple and convenient, the speed control curve is smooth and continuous, and the work is stable.

Disadvantages: In large-scale production lines, the control cables are long, especially for DA modules.