Variable-Frequency Microgrid Control for Grid Outage Islanding
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Solution Overview
Problem
Grid-tied renewable energy systems shut down during grid outages, violating safety codes and preventing power generation from secondary sources, and existing systems lack flexibility in frequency adjustment to match varying load demands.
Innovation Solution
A microgrid system with an adapter and power controller that disconnects from the grid during outages, allowing independent operation and frequency adjustment to match load demands using variable frequency electronics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If grid-tied inverter systems are used to connect renewable energy sources to the electrical grid, then power can be distributed to the grid, but the system must shut down during grid outages to prevent backfeeding, resulting in loss of power supply continuity
Solution Approach 1:
The system is divided into two independent operational modes: grid-tied mode for normal operation and islanded mode for grid outages. The transfer switch mechanism segments the electrical connection, allowing the renewable energy system to operate independently from the grid when needed, thus maintaining power supply continuity while adhering to safety requirements.
Solution Approach 2:
The system dynamically transitions between grid-tied and islanded operational modes based on grid status. The transfer switch automatically detects grid failures and switches the system configuration, enabling continuous operation without manual intervention. This dynamic adaptability resolves the contradiction by making the shutdown requirement conditional rather than absolute.
2Adaptability or versatility
If fixed frequency power supply is used to match grid standards, then grid synchronization is achieved, but flexibility to match varying load demands is lost
Solution Approach 1:
The system employs dynamic frequency adjustment capability in islanded mode, allowing the inverter to vary output frequency based on load requirements. During grid-tied operation, frequency is fixed to match grid standards. This dynamic behavior enables the system to adapt to varying load demands while maintaining grid synchronization when connected, thus resolving the contradiction between adaptability and reliability.
Solution Approach 2:
The system changes the frequency parameter conditionally: maintaining fixed grid frequency (e.g., 60Hz) when connected to the grid, and allowing variable frequency adjustment when operating in islanded mode. This parameter change strategy enables the system to achieve both grid synchronization and load adaptability at different operational stages.
3Reliability
If grid-tied operation is maintained during outages to preserve connection, then grid synchronization is maintained, but safety violations occur due to backfeeding risks
Solution Approach 1:
The transfer switch acts as an intermediary device that physically disconnects the renewable energy system from the grid during outages. This intermediary mechanism eliminates backfeeding risks by creating an electrical isolation barrier, while simultaneously enabling continuous power supply to critical loads through the islanded operational mode.
Solution Approach 2:
The system extracts the connection to the grid during outage conditions, separating the renewable energy system from the grid infrastructure. This extraction eliminates the backfeeding hazard while preserving the core function of power generation and distribution to essential loads, thus maintaining reliability without compromising safety.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Ensures continuous power supply from secondary sources and optimizes energy use by adjusting frequency to match load requirements, extending resource longevity and improving efficiency.
Implementation Method 1
an inverter to which the local secondary energy source is connected
Data Source
AI summary
A micro grid system comprises a secondary energy source and a power controller. The secondary energy source is associated with a micro grid that includes a fixed or mobile facility, and the secondary energy source is configured to generate first DC power signal. The power controller is in communication with the secondary energy source and an electric grid, and configured to receive first AC power signal from the electric grid and the first DC power signal from the secondary energy source and output a second AC power signal to loads in communication with the power controller. The power controller comprises an AC to DC frequency converter configured to change frequency and/or voltage of the second AC power signal, a processor, and a memory configured to store instructions that, when executed, cause the processor to control the frequency converter to change the frequency and/or voltage of the second AC power signal.