Grid-Disconnect Inverter Control for Local Load Priority
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Solution Overview
Problem
Smart inverters, certified under UL1741 SA, are capacity limited and prioritized for supporting electric utility grid stability, leading to unpredictable energy delivery from local renewable sources to the grid, limiting real power supply to local loads and causing lost production due to grid interactive mode operations.
Innovation Solution
A power system with a user-selectable switch and local controller that allows the system to operate in both 'on grid' and 'off grid' modes, enabling disconnection from the electric utility grid when grid demands limit real or reactive power supply, allowing the local bus to prioritize local load needs and maintain flexibility in energy usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the smart inverter operates in grid interactive mode to support electric utility grid stability, then the electric utility grid stability is improved, but the amount of real power the inverter can provide to local loads is reduced
Solution Approach 1:
The inverter dynamically switches between grid interactive mode and standalone mode based on real-time grid conditions and local load requirements. The controller monitors grid status and automatically transitions operating modes to optimize both grid support and local power supply, making the system adaptive rather than static.
Solution Approach 2:
The system segments the inverter's operational capacity by creating distinct operating modes (grid interactive and standalone) that can be selectively activated. This segmentation allows the inverter to dedicate full capacity to either grid support or local load supply depending on conditions, avoiding the capacity sharing constraints of continuous grid-interactive operation.
2Reliability
If the smart inverter supplies reactive power to meet electric utility grid demand, then the electric utility grid stability is improved, but the amount of real power the inverter can provide is reduced
Solution Approach 1:
The inverter dynamically adjusts its power factor and reactive power output based on operating mode. In standalone mode, it operates at unity power factor to maximize real power delivery to local loads, while in grid interactive mode it can provide reactive power support. This dynamic adjustment eliminates the fixed capacity limitation imposed by grid-interactive requirements.
Solution Approach 2:
The system changes key operating parameters (power factor, reactive power output, operating mode) based on grid conditions and local needs. By transitioning from grid-interactive mode with fixed power factor requirements to standalone mode with flexible parameter control, the inverter can optimize real power delivery when operating independently.
3Reliability
If the local energy producer is tied to the grid through a smart inverter, then the electric utility grid stability is improved, but the control and predictability of power delivery to the electric utility grid is reduced
Solution Approach 1:
The system dynamically transitions between being grid-dependent and grid-independent based on operational requirements. When full control is needed, the inverter switches to standalone mode, eliminating grid constraints. When grid support is desired, it transitions to grid interactive mode. This dynamic capability provides both grid stability benefits and operational flexibility.
Solution Approach 2:
Instead of the conventional approach where the inverter is permanently tied to the grid and must follow grid rules, this system inverts the relationship by allowing the local system to operate independently when needed. The inverter can choose to connect to or disconnect from the grid based on local priorities, reversing the traditional hierarchy of control.
4Quantity of substance
If more renewable energy is deployed to the electric utility grid, then the renewable energy penetration is increased, but the electric utility grid stability becomes more challenging to maintain
Solution Approach 1:
The system segments renewable energy deployment into grid-connected and standalone portions. Local systems can operate independently when grid stability is concerns, allowing high renewable penetration without compromising overall grid reliability. Each local system acts as an independent island that can connect or disconnect based on grid conditions.
Solution Approach 2:
The system provides a cushioning effect on grid stability by allowing local systems to disconnect during periods of grid stress. This prevents renewable energy fluctuations from directly impacting grid stability, as local systems can isolate themselves when needed, protecting the broader grid from instability.
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
This solution optimizes energy production and usage by allowing the local grid operator to control energy flow, reducing curtailment of renewable energy generation, and maintaining grid stability by dynamically managing power distribution between the local load and the electric utility grid.
Implementation Method 1
an inverter that receives energy in the form of DC electrical energy and converts it into available AC electrical energy
Data Source
AI summary
A power system connectable to an electric utility grid includes a local bus connected to at least one source of electrical energy; a connection to an electric utility grid; an inverter electrically interposed between the electric utility grid and the local bus, the inverter having an AC side and a DC side; a user-selectable switch electrically connected between the electric utility grid and the inverter, the switch having an open position and a closed position; and a local controller in communication with the inverter and the switch, the local controller configured to selectively open the switch to disconnect the power system from the electric utility grid and to selectively close the switch to reconnect the power system to the electric utility grid.