Energy Storage MMC Topology for Battery Microcirculation Blocking
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Solution Overview
Problem
Current battery energy storage systems using Modular Multilevel Converters (MMC) face issues with microcirculation, leading to reduced battery life and increased life cycle costs due to unfiltered ripple current, which existing solutions like passive filters and DC-DC converters cannot fully address without increasing complexity and cost.
Innovation Solution
An energy storage MMC topology with six bridge arms in three phases, each comprising two bridge arms with anti-parallel thyristors and energy storage sub-modules, which includes a half-bridge power module and a battery energy storage module, connected via an interface unit to prevent microcirculation by judicious switching control based on operating parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sub-module is connected to battery via passive filter, then microcirculation problem is solved to a certain extent, but larger inductance capacitor is required with high cost and large volume
Solution Approach 1:
The patent extracts and eliminates the harmful ripple current component from the battery current through the thyristor switching mechanism. By selectively blocking the ripple current components while allowing the average current to pass through the battery, the microcirculation problem is solved without requiring large passive filter elements.
Solution Approach 2:
The patent changes the operating parameters of the thyristors (switching timing, conduction angle) to dynamically control the current flow characteristics. By adjusting these parameters, the system can filter out ripple current components while maintaining efficient power transfer, avoiding the need for large fixed passive filters.
2Reliability
If sub-module is connected to battery via DC-DC converter, then ripple current magnitude is suppressed to a certain extent, but microcirculation problem cannot be completely solved and device complexity increases
Solution Approach 1:
The patent introduces thyristors as intermediary switching devices between the sub-module and the battery. These thyristors act as controllable mediators that can selectively pass or block current components based on their instantaneous polarity and magnitude, achieving ripple current suppression without requiring complex DC-DC converter topologies.
Solution Approach 2:
The patent replaces the mechanical/electronic complexity of DC-DC converters with a simpler thyristor-based switching mechanism. The thyristors provide current control through gate triggering signals, substituting the need for complex converter control circuits and multiple power semiconductor devices.
3Device complexity
If no additional measures are taken, then system structure remains simple, but large amount of ripple current flows directly into battery causing microcirculation and life loss
Solution Approach 1:
The patent enables the battery system to protect itself from ripple current damage through the thyristor switching mechanism. The control system monitors battery current and automatically triggers the thyristors to block harmful ripple components, allowing the system to self-regulate and protect the battery without requiring external complex filtering equipment.
Data Source
AI summary
An energy storage MMC topology is proposed to avoid the microcirculation of battery. The topology consists of six bridge arms in three stages and can be connected to DC system and AC system. Each bridge arm is composed of one bridge arm inductance and N energy storage sub-modules with the same structure in series. The energy storage sub-modules include a half-bridge power module, a battery energy storage module and a group of anti-parallel thyristors. The group of anti-parallel thyristors is connected in series over the DC cable between the battery energy storage module and a capacitor of the half-bridge power module. The switching control is performed on the battery in the energy storage MMC according to the systematic operating mode.