Autonomous Charge Balancing in AC Coupled Microgrid Batteries
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Solution Overview
Problem
In droop-controlled microgrids, batteries tend to become unbalanced when communication is interrupted, leading to disparities in charge levels due to small differences in chemistry and manufacturing tolerances, posing a challenge for maintaining equal states of charge without centralized control.
Innovation Solution
Implementing a droop offset proportional to the state of charge in each AC battery's power conditioner, allowing for autonomous charge balancing by adjusting the power flow between batteries to equalize their states of charge without disrupting the stability of droop control, using a droop control module that varies the power term with the state of charge to facilitate energy transfer from fully charged to undercharged batteries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If droop control is used for operating energy storage resources in a microgrid, then power sharing among batteries is achieved, but charge balance drifts apart when communication is interrupted
Solution Approach 1:
The system enables batteries to autonomously balance their own charge levels through local measurements and droop offset adjustments without requiring external communication or centralized control. Each battery independently detects its state of charge relative to others and self-regulates its charging/discharging rate to achieve balance.
Solution Approach 2:
The system implements a feedback mechanism where each battery continuously monitors its state of charge and the states of other batteries, then adjusts its droop offset accordingly. This closed-loop control ensures that charge imbalances are detected and corrected automatically, maintaining reliability without communication infrastructure.
2Device complexity
If conventional droop control is used without communication, then system simplicity is maintained, but batteries drift apart in charge levels
Solution Approach 1:
The system dynamically changes the droop offset parameter based on the state of charge measurements. By adjusting this control parameter in real-time according to actual battery states, the system achieves precise charge equality without requiring complex communication hardware or centralized control architecture.
3Reliability
If communication is used to ensure charge balance, then charge equality is maintained, but system complexity and communication dependency increase
Solution Approach 1:
The system eliminates communication infrastructure by enabling each battery to independently measure and compare its state of charge with others through local sensing. Each battery serves itself by autonomously determining the charge imbalance and adjusting its own operation to correct the imbalance, removing all communication dependencies.
Data Source
AI summary
A method and apparatus for autonomous charge balancing of an energy storage device of the microgrid. In one embodiment the method comprises obtaining, at a droop control module of a power conditioner coupled to an energy storage device in a microgrid, an estimate of a state of charge (SOC) of the energy storage device; introducing a bias, the bias based on (I) the estimate of the SOC and (II) a target SOC value for each energy storage device of a plurality of energy storage devices in the microgrid, to a droop control determination made by the droop control module; and generating, by the power conditioner, an output based on the droop control determination.