AC Subgrid Power Control Using Virtual Voltage Droop Sharing
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Solution Overview
Problem
Controlling power in AC subgrids is complex due to differences in methods compared to DC subgrids, complicating interoperability and frequency management, which is crucial for proper device function.
Innovation Solution
A decentralized power control method using virtual voltages calculated as a weighted average from multiple devices, with a droop current mechanism to adjust frequency, allowing for standardized power control and frequency regulation within a predetermined range, similar to DC subgrids, even in island mode or soft connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If different power control methods are used for AC and DC subgrids, then each grid type can be optimized for its specific characteristics, but interoperability between different power grids becomes complicated
Solution Approach 1:
The patent applies universality by enabling AC subgrid devices to perform both AC power control and DC-like virtual voltage management. The decentralized control mechanism with virtual voltages allows the system to function effectively in both AC and DC modes, making the power control system adaptable to different grid types while maintaining a unified control architecture.
Solution Approach 2:
The patent utilizes parameter changes by introducing virtual voltages as a control parameter that can be adjusted independently of physical AC voltage. This allows the system to maintain DC-like control characteristics (where power flow is determined by voltage differences) while operating in an AC environment, thereby achieving both optimization and interoperability.
2Reliability
If decentralized power control with virtual voltages is implemented in AC subgrids, then frequency stability can be maintained and interoperability improved, but control complexity increases due to multiple devices exchanging virtual voltage information
Solution Approach 1:
The patent applies the intermediary principle by introducing virtual voltages as a mediator between physical AC power flow and control objectives. Instead of directly controlling AC frequency and power, devices exchange virtual voltage information that indirectly regulates power flow and frequency, simplifying the control logic while maintaining stability.
Solution Approach 2:
The decentralized control mechanism implements feedback by having each device continuously measure local frequency, calculate appropriate virtual voltages based on frequency deviations, and exchange this information with neighboring devices. This creates a distributed feedback loop that automatically adjusts power flow to maintain frequency stability without centralized coordination.
3Adaptability or versatility
If AC subgrid operates in island mode disconnected from main grid, then energy independence is achieved, but frequency management becomes more difficult without main grid synchronization
Solution Approach 1:
The patent applies self-service by enabling the AC subgrid to autonomously manage its own frequency and power balance when disconnected from the main grid. Each device independently measures local frequency, calculates virtual voltages based on frequency deviations, and adjusts its power flow accordingly, allowing the islanded subgrid to self-regulate without external synchronization.
Solution Approach 2:
The patent utilizes segmentation by dividing the frequency management task into independent local decisions at each device. Instead of requiring centralized frequency control, each device independently contributes to frequency stabilization through its virtual voltage calculations and power adjustments, making the system adaptable to islanded operation.
Data Source
AI summary
A method and a device for managing power in an AC subgrid is proposed. To do so, virtual voltages from a plurality of other devices in the AC subgrid are received and used to calculate a weighted average virtual voltage. Based on that and a droop curve, a droop current is determined. Furthermore, the frequency in the AC subgrid is measured and used to calculate a set current based on the droop current and the measured frequency. Then, the set current is set in a current control circuit of the device. Finally, an actual virtual voltage based on the droop curve and the set current is determined and sent to other devices in the AC subgrid. In addition, an AC-subgrid is disclosed, comprising a plurality of such devices, which are interconnected in terms of power and data communication.