Delta-Connected MMC Control for Scalable Cell Voltage Balancing
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Solution Overview
Problem
The capacity of modular multilevel converters (MMCs) is limited by the number of connectable cells due to the constraints of control device connectors and computing capability, which hinders the ability to control current components and balance DC capacitor voltages in delta-connected configurations.
Innovation Solution
A power conversion device with a delta-connected MMC configuration that utilizes multiple control devices to communicate and control cell sets, generating voltage command values to manage currents and balance capacitor voltages across a larger number of cells, allowing for increased capacity without being limited by connector or computing constraints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the number of cells in an MMC is increased to enhance capacity, then the power conversion capability is improved, but the control device's connector availability and computing capability become insufficient
Solution Approach 1:
The control device is segmented into a master control device and multiple slave control devices. Each slave control device manages a specific subset of cells, while the master control device coordinates overall control. This segmentation allows the system to control a larger number of cells by distributing the control burden across multiple independent control units, thereby enhancing power conversion capability without overwhelming a single control device's connectors and computing resources.
2Quantity of substance
If multiple control devices are introduced to manage more cells, then the capacity is increased, but the control system complexity increases
Solution Approach 1:
Multiple slave control devices are merged under the coordination of a single master control device. The master control device integrates information from all slave control devices and generates centralized control commands. This merging approach allows the system to manage a larger number of cells through multiple control devices while maintaining a unified control architecture, thereby increasing capacity without proportionally increasing overall system complexity.
3Device complexity
If a single control device manages all cells, then the control system is simple, but the maximum number of controllable cells is limited
Solution Approach 1:
The control architecture transitions from a single-dimension hierarchical structure to a multi-dimensional distributed structure. Instead of one control device managing all cells directly, the system introduces an intermediate dimension with multiple slave control devices, each managing specific cell groups. This dimensional expansion allows the system to scale to control thousands of cells while maintaining manageable complexity through modular organization.
Data Source
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AI summary
A power conversion device (200) includes a first control device to an m-th control device (Cc, to Ccm) that are capable of communicating with each other. A k-th control device (Cck) transmits specific information to control devices other than the k-th control device (Cck) among the first control device to the m-th control device (Ccl to Cc.). The specific information includes voltage values of a plurality of unit converters included in a k-th cell set (Suk, Svk, Swk) in each of a first arm to a third arm (A1 to A3). From each control device other than the k-th control device (Cck) among the first control device to the m-th control device (Ccl to Ccm), the k-th control device (Cck) receives specific information including the voltage values of the plurality of unit converters included in a cell set controlled by the each control device other than the k-th control device (Cck). The k-th control device (Cck) calculates a phase representative value of the voltage values of the plurality of unit converters included in each of the first arm to the third arm (A1 to A3).