Variable-Frequency Microgrid Isolation for Grid Outage Power Continuity
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Solution Overview
Problem
Grid-tied renewable energy systems shut down during electrical grid outages, preventing power generation and distribution due to the requirement for grid reference voltage and frequency, as defined by National Electric Code, ANSI/UL 1741, California Rule 21, and IEEE 1547, leading to power disruptions and inefficiencies.
Innovation Solution
A microgrid system with an adapter and power controller that disconnects from the grid when abnormal conditions are detected, allowing a secondary energy source to supply power to loads independently, using a connection switch, safety switch, and sensor to manage frequency and prevent backfeeding, and employing variable frequency electronics to optimize energy usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If grid-tied inverter is used to connect secondary energy source to electrical grid, then power can be distributed to electrical grid, but system shuts down during grid outages due to safety requirements
Solution Approach 1:
The system segments the power distribution network into grid-tied mode and islanded mode through the microgrid adapter. The adapter contains internal switches that can isolate the secondary energy source from the electrical grid, allowing independent operation during outages while maintaining grid connection during normal operation. This segmentation resolves the contradiction by enabling the system to switch between two operational states.
Solution Approach 2:
The microgrid adapter dynamically changes the system's operational state based on grid conditions. It monitors grid voltage and frequency, and automatically transitions between grid-tied and islanded modes. This dynamic adaptability allows the system to maintain reliability during outages while preserving productivity during normal grid operation.
2Object-affected harmful factors
If inverter shuts down during grid outages to prevent backfeeding, then safety requirements are met, but power supply to facility is interrupted
Solution Approach 1:
The microgrid adapter acts as an intermediary device between the secondary energy source and the electrical grid. It contains safety switches and monitoring circuitry that prevent backfeeding into the de-energized grid while simultaneously enabling continuous power supply to the facility during outages. This intermediary function resolves the contradiction by providing both safety and reliability.
3Stability of the object's composition
If fixed frequency power is supplied from grid, then grid stability is maintained, but appliances cannot operate at optimized frequency for energy efficiency
Solution Approach 1:
The variable frequency drive changes the electrical frequency parameter from the fixed grid frequency to optimized frequencies for specific motor loads. When operating in islanded mode, the system can supply power at frequencies that maximize appliance efficiency (e.g., 40-60 Hz for motors). This parameter change resolves the contradiction by allowing energy optimization without compromising grid stability during grid-tied operation.
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
Enables continuous power supply from secondary energy sources during grid outages, enhances energy efficiency by adjusting frequency to match load demands, and prevents power backfeeding into the grid, thereby extending the lifespan of energy storage systems like batteries.
Implementation Method 1
The inverter is configured to receive DC power from the secondary energy source, convert the DC power to AC power, and supply the AC power to the loads
Implementation Method 2
The adapter is in communication with an electric grid and configured to connect and disconnect a connection between the electric grid and a micro grid
Implementation Method 3
The power controller is configured to obtain grid information and determine whether the electric grid is abnormal based on the grid information
Implementation Method 4
employing variable frequency electronics to optimize energy usage
Data Source
AI summary
A microgrid comprises an electric vehicle battery storage system that supplies a first DC signal, a bus bar that receives the first DC signal and provides a combined DC signal, a frequency variable and/or voltage variable inverter that receives the combined DC signal, converts, responsive to one or more control signals, the combined DC signal into a first AC signal having variable frequency and/or variable voltage, and provides the first AC signal having the variable frequency and/or voltage to the electrical loads of the facility, and a DC to AC that receives, responsive to the one or more control signals, the combined DC signal from the bus bar, and converts the combined DC signal to a second AC signal.