Droop frequency controller for maintaining different frequency qualities in a standalone multi-microgrid system and a standalone multi-microgrid system using the same

Multi-grid system for maintaining differential frequency quality per microgrid using droop frequency control

This technology is a multi-microgrid system that connects multiple standalone microgrids via a common DC line and interconnection converters. Each converter's droop frequency controller regulates power flow by converting system frequency deviations into DC link voltage deviations. The controller consists of a droop frequency control unit that calculates normalized frequency deviations, a power control unit that generates reference currents, and a current control unit that outputs modulation signals.

As the adoption of distributed renewable energy sources increases, microgrids face greater frequency and voltage fluctuations, making it difficult to meet power quality requirements. Existing back-to-back converter-based interconnection methods suffer from complex algorithms, a mandatory requirement for communication networks, and significantly higher installation costs as the number of grids increases.

This technology connects each grid to a common DC link using a single AC/DC interconnection converter and regulates active power sharing based solely on local information such as frequency and DC link voltage, allowing for different frequency quality levels per grid without a separate communication network. It can be applied to islanded power grids and renewable energy-integrated campus or industrial microgrids, reducing the number of converters and installation costs while reliably protecting loads that require high-quality power.

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Key Features:

• Standalone multi-microgrid configuration including multiple interconnection converters located between each microgrid and a common DC line to convert AC to DC
• Droop frequency controller that regulates the interconnection converters so that the DC link voltage change of the common DC line is proportional to the system frequency of the corresponding microgrid
• Normalizer and amplifier structure that receives system frequency, calculates normalized frequency deviation, and outputs a DC link voltage deviation multiplied by a proportional constant
• Power and current control unit that performs proportional-integral control on the sum of the DC link voltage deviation and command to generate reference active and reactive currents, outputting modulation signals for terminal current tracking

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This invention was developed with support from the Ministry of Trade, Industry and Energy for the development of resilient hybrid technology for high-quality microgrids.

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