Design of frequency conversion speed regulation monitoring system based on EV3000

With the rapid development of computer technology, power electronics technology and control technology, frequency converters play an important role in improving process quality and production efficiency in industry. EV3000 frequency converter is a high-quality, multi-functional, low-noise vector control general frequency converter produced by Emerson. Through the decoupling control of the motor flux current and torque current, the fast response and accurate control of the torque can be achieved, and a wide range of speed regulation can be performed with high control accuracy. Compared with other speed regulation methods, the speed regulation system composed of variable frequency speed regulation motor and frequency converter has the advantages of high efficiency driving performance, good control characteristics, obvious energy saving effect, good speed regulation performance, wide speed regulation ratio, excellent fast response, wide application range, high cost performance, etc. It is one of the most advanced systems in the current AC speed regulation scheme.

This article introduces the hardware structure, software design, communication principle and communication command of the computer monitoring system of the inverter from the perspective of computer monitoring and control of the inverter, taking the currently widely used Emerson inverter as the control object. The system has been tested and verified on site in actual projects.

1 Hardware structure of the monitoring system

In the overall hardware structure design of the monitoring system, the host computer is the main control unit. In order to enable communication between the computer and the inverter, a conversion interface should be installed between the two. In this way, the computer is connected to the EV3000 inverter through the RS232/RS485 conversion interface, and the inverter drives the variable frequency motor, which drives the turntable to rotate. The encoder feeds back the motor rotation information to the inverter, so that the host computer sends a communication command to control the inverter, and the inverter responds to the command to drive the motor to make the turntable move. The encoder sends the feedback information back to the inverter to complete the control process. The hardware structure of the monitoring system is shown in Figure 1.

According to the actual working environment, the upper PC in this system is Advantech industrial computer, and the EV3000 inverter is used as the core control device of the monitoring system. The use of the inverter can strengthen the protection function of the system and realize overvoltage, overcurrent, undervoltage, open circuit and short circuit protection functions; it realizes stepless speed regulation, wide speed regulation range, good characteristic curve, high control accuracy and good energy saving effect; the variable frequency motor adopts the YVP series variable frequency speed regulation three-phase asynchronous motor produced by Jiaxing Juneng Motor Factory, which has a wide speed regulation range, small vibration, low noise, and can be matched with various SPWM frequency conversion devices. It constitutes an AC variable frequency stepless speed regulation system.

2 Communication method of monitoring system

In order to realize the communication between PC and inverter, we must first understand the communication protocol between them. Hexadecimal numbers are used between the computer and the inverter, and data is automatically transmitted between the computer and the inverter using ASCII code. The PC background is the host and the inverter is the slave. The communication method is "polling" by the host and "response" by the slave.

The data frame structure is: frame header, user data, frame trailer. Frame header: includes start byte, slave address; frame trailer: check data (XOR check); user data: includes parameter data and process data; parameter data: includes function code operation command, response, function code number, function code setting/actual value, there is no parameter data in the short frame; process data: includes host control command/slave status response, host operation main setting/slave operation actual value.

EV3000 can communicate via long and short frames. Short frames are used to independently transmit the control words and status words required by the automatic control system; long frames include both control words and status words as well as content related to operation control, observation, maintenance, and diagnosis (the content is limited by the inverter's own functions). This article uses long frames as an example. The communication transmission frame format from the computer (controller) to the inverter is shown in Figure 2. The communication reception frame format from the inverter to the computer (controller) is shown in Figure 3.

The parameter calibration of EV3000 is as follows:

1) The frequency is calibrated to 1:100. If the inverter is to run at 50 Hz, the main setting should be 1388H (5 000).
2) The time is calibrated to 1:10. If the inverter acceleration time is 30 s, the function code setting should be 012CH (300).
3) The current is calibrated to 1:10. If the inverter feedback current is 012CH, the inverter current is 30 A.

3 Monitoring system software design

The software design is based on the visual integrated development tool Delohi software on the Windows platform. Using the Spcomm control provided by a third party of Delphi, the serial communication of the application can be realized simply and conveniently. The main properties and methods of Spcomm include: 1) CommName: set the serial port; 2) BaudRate: set the baud rate; 3) Paritv: parity bit; 4) ByteSize: set byte length; 5) StopBits: stop bit; 6) Startcomm method, used to open the serial port; 7) StopComm method is used to close the serial port; 8) WriteCommData method is used to send a string to the writing process. The monitoring interface is shown in Figure 4.

The monitoring program interface is mainly used for interaction between the user and the frequency conversion speed regulation system. Through this interface, the user can conveniently control the motor action on the one hand, and on the other hand, can also monitor some important parameters of the frequency conversion speed regulator in real time, such as current, frequency, motor torque and speed, etc., to observe whether its operation is normal. The serial port must be initialized before computer communication, and the parameters must be the same as the inverter parameters, otherwise communication will not be possible. The inverter communication program flow is shown in Figure 5.

In practical applications, the corresponding frequency is set by computer control software to make the turntable run under the matching acceleration. Table 1 lists the corresponding relationship between the frequency converter frequency f, the normal acceleration G of the turntable, the angular velocity ω of the turntable, and the speed N of the turntable.

Figure 6 shows the frequency conversion action of the frequency conversion motor driving the turntable according to the three frequency conversion actions in Table 1, which gradually increases the normal acceleration of the turntable to rotate at 40, 60, and 80 g. By analyzing the experimental data, it can be seen that the host computer monitoring software can stably and accurately control the frequency conversion motor action and complete the operation process.

4 Conclusion

Experiments have proven that the Emerson EV3000 variable frequency speed control monitoring system has successfully achieved normal motor drive and operation status monitoring, simplified the control logic system, and made the operation simple and convenient. The real-time monitoring of the motor by the host computer has greatly improved the running stability of the motor, thus achieving stable and safe operation of the motor.