Abstract

In wind power generation, data exchange between converters and between converters and wind turbine towers involves communication. The control of drive units needs to be connected to the communication network of the entire wind farm, requiring extensive, high-speed, and reliable communication. Therefore, DP plays a crucial role in this process. However, in practice, there is an issue: the controller for controlling the converters only provides a CAN communication interface, and connecting it to the Profibus communication network presents a coexistence problem of two bus protocol standards. The CAN-DP bus bridge product provided by Dingshi Company plays a key role in solving this problem.

Project Overview

Our laboratory collaborated with another company on a wind power generation project, which consists of several parts:

• Grid-side converter and its control DSP board
• Rotor-side converter and its control DSP board
• Communication section, including LCD, local computer, and its control DSP board
• Tower communication section

The communication section is responsible for communicating with the DSP boards of the grid-side and rotor-side converters, coordinating their work, and collecting voltage and current data. The tower communication section needs to communicate via Profibus with the communication section to control the start and stop of converters and monitor their main operating parameters.

Laboratory CAN-Profibus Communication Platform

Since our laboratory does not have PLC equipment, we adopted the WINCC + CP5611 solution to replace the host computer. The specific scheme is shown in the figure below.

WINCC + CP5611 serves as the Profibus master station, and the bus bridge + DSP forms the slave station to simulate Profibus communication. We hope to create a usable interface using WINCC software on the host computer to simulate the communication between converters and the tower in actual wind power systems.

Final Debugging and WINCC Interface

Below is the interface ultimately written for the wind power system.

The WINCC-written interface includes start and stop functions, command sending, and display of some converter operating parameters. The two display areas in the lower right corner show the values of the two registers sent and received by the bus bridge.

Test of the Time Required for One Protocol Conversion by the Bus Bridge

Since the WINCC interface is used as the master station to control communication in the laboratory, and the data update cycle of the WINCC interface is 250ms, which is far from meeting the time requirements of real-time communication. In reality, the time for the host computer to sample the main operating parameters and fault information of the converter is much less than 250ms. Therefore, we need to test the time required for the bus bridge to perform one protocol conversion. The test scheme is shown in the figure below:

• Test Method: Measure the time interval from when the CAN signal is detected by the oscilloscope to when the Profibus signal appears, which is the time the bus bridge takes to process data and perform protocol conversion.
• Test Conditions: CAN baud rate 1Mbps, Profibus baud rate 500Kbps. The DSP sends a message with all “0” data segments and a message with all “F” data segments every 10ms.

Below are the waveforms during the test process.

Finally, the conclusion drawn from the test is that the bus bridge takes about 1.3ms to perform one protocol conversion.

Conclusion

Using Dingshi’s CAN-Profibus bus bridge effectively solves the protocol conversion process between CAN and Profibus communications. Moreover, the test shows that the bus bridge conversion time is approximately 1.3ms, which is quite fast.