DC Microgrid Voltage Compensation for SoC-Balanced Power Sharing
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Solution Overview
Problem
Conventional droop-based control methods in DC microgrids struggle with unbalanced current distribution, voltage deviation, and state-of-charge (SoC) drift among distributed battery units, particularly in scenarios with fluctuating loads and dynamic SoC conditions, leading to inefficiencies and reliability issues.
Innovation Solution
A state-of-charge (SoC)-based double-loop control approach combined with a fractional-order proportional-integral (FOPI) voltage compensation mechanism, where an inner loop regulates charging and discharging rates based on SOC, and an outer FOPI loop enhances dynamic response and stability, using a small-signal model and optimized controller parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional droop-based control methods are used, then decentralized current sharing is achieved, but unbalanced current distribution and voltage deviation occur under fluctuating loads and dynamic SoC conditions
Solution Approach 1:
The patent implements a feedback mechanism where the state of charge (SoC) of each battery unit is continuously monitored and fed back to the control system. This feedback enables dynamic adjustment of droop coefficients, allowing the system to compensate for SoC variations and maintain balanced current distribution among parallel-connected converters without requiring centralized control or communication links.
Solution Approach 2:
The patent introduces dynamic droop coefficients that adapt in real-time based on the state of charge conditions of battery units. Instead of using fixed droop parameters, the system dynamically adjusts the droop characteristics to match changing operating conditions, thereby maintaining stable current sharing and voltage regulation under fluctuating loads and varying SoC levels.
2Extent of automation
If droop parameters are mismatched or SoC conditions are dynamic, then autonomous control is maintained, but voltage deviation and SoC drift among distributed battery units increase
Solution Approach 1:
The patent changes the droop parameters dynamically based on the state of charge of each battery unit. By adjusting the droop coefficients in real-time according to SoC levels, the system maintains voltage stability and prevents voltage deviation even when operating conditions change, all while preserving autonomous control without centralized coordination.
Solution Approach 2:
The patent incorporates preliminary compensation actions by pre-calculating and applying SoC-based droop coefficient adjustments before significant voltage deviations occur. This proactive approach allows the system to anticipate and counteract potential voltage instability caused by dynamic SoC conditions, maintaining stable operation before problems arise.
3Reliability
If centralized control architectures with high-bandwidth communication are implemented, then improved power sharing and SoC management are achieved, but reliability decreases due to single points of failure and communication dependency
Solution Approach 1:
The patent enables each battery unit to autonomously determine its own droop coefficients based on its local state of charge measurements. This self-service approach eliminates the need for centralized control or high-bandwidth communication infrastructure, as each unit independently adjusts its parameters to achieve balanced power sharing and SoC management, thereby maintaining high reliability without communication dependency.
Solution Approach 2:
The patent segments the control function so that each parallel-connected converter operates independently with its own localized control logic. By dividing the overall control system into autonomous segments that each manage their own droop parameters based on local conditions, the system achieves coordinated power sharing without requiring centralized coordination or communication links between units.
Data Source
AI summary
A control system for a direct current (DC) microgrid is described. The control system includes a DC bus with a positive bus line and a negative bus line, DC battery circuits with a positive coupler connected to the positive bus line and a negative coupler connected to the negative bus line, switches including a control input terminal located in each DC battery circuit, a distributed generator circuit connected to the DC bus, a constant load power circuit connected to the DC bus, a computing device connected to each control input terminal, the DC bus, the distributed generator circuit and the constant load power circuit. The computing device includes an electric circuitry, a memory, and at least one processor to determine a DC bus voltage, determine the SoC of the DC battery circuits, generate PWM signals that control the DC bus voltage, and balance the SoC of the DC battery circuits.