MMC Control System Communication Delay Reduction
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Solution Overview
Problem
The communication transmission delay between the central control device and cell control devices in Modular Multilevel Converters (MMC) is significant, leading to reduced control response due to lengthy communication frames and increased control periods.
Innovation Solution
The implementation of a power conversion apparatus with a daisy-chain connected central control device, intermediate control devices, and cell control devices using optical fiber cables, where the communication frame is optimized to include only common command information and minimal cell-specific data, such as capacitor voltage information and failure diagnosis, to reduce the frame length and transmission time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the central control device transmits and receives information to and from all cell control devices using a daisy-chain connection through optical fiber cables, then the control system can monitor and control all cells, but the communication frame becomes long and the communication period increases causing transmission delay
Solution Approach 1:
The patent divides the communication system into multiple independent communication paths. Instead of using a single long communication frame that visits all cell control devices sequentially, the system segments the communication into shorter frames that are transmitted to multiple cells simultaneously through different paths in the daisy-chain network, reducing overall transmission delay
Solution Approach 2:
The patent transforms the traditional sequential one-dimensional communication approach into a multi-dimensional communication structure. By utilizing the daisy-chain topology to create parallel communication paths, information can be transmitted to multiple cell control devices simultaneously rather than sequentially, effectively reducing communication time
2Reliability
If the communication frame includes comprehensive information for all cells, then complete control and monitoring is achieved, but the frame length increases and transmission time increases
Solution Approach 1:
The patent extracts only the essential control information needed for each cell into the communication frame, rather than including all possible data. By taking out only the critical parameters required for control and monitoring, the frame length is reduced while maintaining complete control functionality
Solution Approach 2:
The patent applies local quality by tailoring the communication frame content to the specific needs of each cell or group of cells. Different communication frames can be transmitted to different cells with customized information sets, optimizing the frame length for each local requirement rather than using a uniform comprehensive frame for all cells
Data Source
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AI summary
A power conversion apparatus (116a) includes a cell (105) which includes an energy storage element (204) and a switching device (202, 203) and which outputs either of a positive or negative voltage and a zero voltage relying on a voltage of the energy storage element by on or off of the switching device; an arm (104) in which one or a plurality of the cells (105) are serially connected; a power conversion circuit (103) which includes the arm (104) in plurality and which is capable of converting an alternating current to a direct current or converting a direct current to an alternating current; a central control device (107) which collectively controls each of the cells (105); a plurality of intermediate control devices (113) which are daisy-chain connected to the central control device (107) through an optical fiber cable (111); and a cell control device (213) which is connected to the intermediate control device (113) and which controls each of the cells (105). To AC terminals U, V, and W of each phase, one end of each serial circuit is connected. To DC terminals P and N, the other end of each of the serial circuits is connected in parallel.