Voltage Sharing in Series Battery Modules via Droop Control
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Solution Overview
Problem
In plug-and-play DC microgrids, existing voltage regulation approaches for series-connected battery modules are not well-suited for modular and hot-swappable operations, leading to challenges in voltage sharing and state-of-charge balancing, especially with varying capacities and chemistries of battery packs.
Innovation Solution
A battery management system and controller that generate a droop current based on converter voltage errors, using a non-linear droop multiplier to control switching of DC/DC converters, ensuring voltage sharing and state-of-charge balancing across series-connected modules by regulating input currents and adjusting current references according to the average state-of-charge and bus voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing voltage regulation approaches are used for series-connected battery modules, then voltage control is achieved, but voltage sharing and state-of-charge balancing deteriorate with varying capacities and chemistries
Solution Approach 1:
The patent implements a non-linear droop multiplier that dynamically adjusts the droop coefficient based on operating conditions, allowing the system to adapt to different battery capacities and chemistries while maintaining proper voltage sharing. This parameter change enables the controller to optimize performance for varying module characteristics without requiring fundamental changes to the regulation approach.
Solution Approach 2:
The system employs feedback mechanisms where the controller continuously monitors converter output voltages and state-of-charge levels, then adjusts droop currents and switching control accordingly. This closed-loop feedback ensures that voltage sharing is maintained across series-connected modules with different capacities and chemistries, resolving the contradiction between reliable voltage sharing and adaptability.
2Ease of operation
If modular and hot-swappable operations are implemented, then ease of operation and adaptability improve, but voltage regulation and voltage sharing deteriorate
Solution Approach 1:
The patent enables modules to self-regulate their voltage contribution through the droop control mechanism, where each module automatically adjusts its output based on local measurements and the non-linear droop multiplier. This self-service capability allows hot-swappable operations without disrupting overall voltage regulation, as newly connected modules seamlessly integrate and self-adjust to the existing system conditions.
Solution Approach 2:
The system dynamically adapts to changing configurations by continuously adjusting droop currents and control parameters based on real-time operating conditions. This dynamic control ensures that voltage regulation is maintained even as modules are added or removed, resolving the contradiction between operational flexibility and regulation stability.
3Reliability
If droop control with non-linear droop multiplier is used, then voltage sharing improves, but device complexity increases
Solution Approach 1:
The non-linear droop multiplier is implemented as a computationally efficient function that adjusts the droop coefficient based on measurable operating parameters. By using parameter changes rather than complex control algorithms, the system achieves improved voltage sharing while minimizing the increase in device complexity. The controller leverages existing sensor data to compute the droop multiplier without requiring additional hardware or complex processing.
Data Source
AI summary
An apparatus for voltage sharing of series connected battery modules in a DC microgrid includes a battery management system and a battery module controller that generates, for an mth of N converters connected together to a DC microbus, a droop current ĩd,m that includes a converter voltage error signal {tilde over (v)}err,m multiplied by a droop multiplier gd(i). Each converter is a DC/DC converter connected between a battery module, with one or more battery cells, and the DC microbus. The mth converter uses the droop current ĩd,m, a common current reference ĩall of a battery pack that includes the battery modules and an input current ĩm to the mth converter to control switching of the mth converter. The common current reference ĩall is from the battery management system. The voltage error signal {tilde over (v)}err,m is based on an output voltage {tilde over (v)}o,m of the mth converter and an average converter output voltage {tilde over (v)}avgeodcmastereodcmastereodcmaster.