Bidirectional Inverter Control in DC Microgrids With Energy Storage
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Solution Overview
Problem
Microgrids face challenges in efficiently managing the integration of renewable energy sources and energy storage with the national grid, requiring advanced control systems to ensure stable and secure electricity supply while minimizing reliance on 'dirty' AC power sources.
Innovation Solution
A DC distribution network with a bi-directional AC grid interface and a multi-tiered controller that adjusts power flow between renewable energy sources, energy storage units, and the national grid, using an inverter to manage voltage differences and optimize energy distribution between consumer units, including low-power and high-power appliances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a microgrid uses renewable energy sources and energy storage units to reduce reliance on the national grid, then environmental friendliness and energy independence are improved, but system complexity and control difficulty increase
Solution Approach 1:
The control system is segmented into multiple independent controllers: a first controller manages the inverter and AC grid interface, while a second controller manages DC/DC converters and energy storage units. This segmentation allows each controller to specialize in specific functions, reducing overall control complexity while maintaining environmental benefits.
Solution Approach 2:
The patent introduces a bi-directional inverter as an intermediary device between the DC distribution network and AC grid. This intermediary handles voltage conversion and power flow management, simplifying the control architecture by centralizing AC-DC interface functions in a single device rather than distributing complexity across multiple control points.
2Object-affected harmful factors
If the microgrid prioritizes local renewable energy generation, then environmental sustainability is improved, but reliability and security of supply may worsen due to intermittent nature of renewable sources
Solution Approach 1:
Energy storage units are charged in advance during periods of high renewable generation or low demand, storing energy before it is needed. This preliminary action ensures that energy is available when renewable sources are intermittent, maintaining supply reliability while prioritizing green energy usage.
Solution Approach 2:
The system dynamically changes operational parameters by adjusting the bi-directional inverter's power flow based on real-time conditions. When renewable generation is sufficient, the inverter operates in one direction; when storage is depleted or demand exceeds generation, it switches to draw from the AC grid, thus adapting to maintain reliability while minimizing carbon footprint.
3Adaptability or versatility
If the microgrid interface is designed to be bi-directional for flexibility, then adaptability and versatility are improved, but device complexity and control difficulty increase
Solution Approach 1:
The bi-directional inverter is designed as a universal interface that can perform multiple functions: exporting excess DC power to the AC grid, importing AC power when DC generation is insufficient, and providing voltage support. By consolidating these multiple functions into a single device, the patent achieves high adaptability without proportionally increasing complexity.
Solution Approach 2:
The inverter incorporates feedback mechanisms that continuously monitor DC bus voltage, AC grid conditions, and power flow directions. This feedback enables the inverter to automatically adjust its operation mode based on real-time system state, reducing the need for complex external control while maintaining bi-directional flexibility and adaptability.
4Reliability
If energy storage units are integrated into the DC distribution network, then energy security and supply stability are improved, but system complexity and cost increase
Solution Approach 1:
The control functionality for energy storage units is extracted and separated from the main DC distribution network control. A dedicated second controller manages DC/DC converters and energy storage units independently, simplifying the overall system architecture by isolating storage management functions from the primary distribution control.
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
The system ensures stable and efficient operation of microgrids by prioritizing renewable energy use, maintaining energy storage levels, and minimizing AC grid dependency, while ensuring secure and environmentally friendly energy supply to consumer units.
Implementation Method 1
an inverter (15i) having an output voltage that is controlled by the controller (70) to vary between above and below that of the grid voltage selectively to cause current to be drawn from the DC distribution network (10) through the inverter (15i) when the inverter output voltage is greater than the grid voltage and to cause current to be drawn from the external AC grid when the inverter output voltage is less than the grid voltage
Data Source
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AI summary
A DC distribution network (10) including DC energy storage units (20) charged from and discharge into the DC distribution network, low-power and high-power consumer units (40, 50) and renewable energy source units (60). The DC distribution network (10) further includes an interface (30) to an external AC grid (2) for taking and optionally also supplying electrical power from and to the AC grid respectively. The AC grid interface (30) has an inverter (15i) with an output voltage that is controlled by a controller (70) to vary between above and below that of the AC grid voltage selectively to cause current to be drawn from the DC distribution network (10) through the inverter (15i) when the inverter output voltage is greater than the grid voltage and to cause current to be drawn from the external AC grid when the inverter output voltage is less than the grid voltage.