Microinverter SoC Averaging for Distributed Battery Storage
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Solution Overview
Problem
Conventional AC storage systems require high accuracy in state-of-charge (SoC) estimation, which adds significant cost and complexity due to the need for expensive sensors and high-frequency communications for current measurements, making them impractical for distributed battery management.
Innovation Solution
A distributed SoC estimation technique using microinverters that calculate and communicate their own state-of-charge estimates to an average, eliminating the need for high-frequency communications by broadcasting and averaging these estimates within the battery management unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If single voltage/current measurement is implemented in conventional AC storage systems, then SoC estimation accuracy is improved, but system cost and complexity increase significantly
Solution Approach 1:
The patent divides the SoC estimation function into multiple segments, with each microinverter independently calculating its own SoC estimate based on local measurements. These distributed estimates are then aggregated to form the final SoC value, eliminating the need for a single complex measurement system in the BMU.
Solution Approach 2:
The patent introduces communication between microinverters as an intermediary mechanism. Each microinverter shares its local SoC estimate with others through communication interfaces, allowing the system to achieve accurate aggregate SoC measurement without requiring expensive sensors or high-frequency communication infrastructure in the traditional sense.
2Measurement precision
If expensive sensors and high-frequency communications are used for current measurements, then SoC estimation accuracy is improved, but system cost increases
Solution Approach 1:
Each microinverter serves itself by independently calculating its own SoC estimate using locally available measurements. This self-service approach eliminates the need for centralized expensive sensing infrastructure, as each unit contributes to the overall system accuracy using its own resources.
Solution Approach 2:
Instead of using expensive physical sensors for current measurement, the system creates virtual copies of current information through communication. Each microinverter communicates its local current measurement data to others, allowing the aggregation of multiple lower-cost measurements to achieve the accuracy of a single expensive measurement.
3Device complexity
If distributed SoC estimation without high-frequency communications is implemented, then system complexity is reduced, but maintaining measurement precision becomes challenging
Solution Approach 1:
The patent merges multiple independent SoC estimates from different microinverters into a single aggregate SoC value. By combining the results from multiple distributed sources, the system achieves measurement precision comparable to centralized systems while maintaining the simplicity of distributed architecture.
Solution Approach 2:
The system implements feedback mechanisms where each microinverter receives and processes SoC estimates from other microinverters. This feedback loop allows each unit to refine its local estimate based on information from others, collectively achieving high precision without requiring high-frequency communication infrastructure.
Data Source
AI summary
A storage system configured for use with an energy management system is provided herein and comprises a battery, a battery management unit coupled to the battery and a power converter comprising plurality of microinverters operably coupled to the battery and the battery management unit, each microinverter of the plurality of microinverters configured to calculate an estimate of state-of-charge of the battery and periodically communicate a calculated estimate of state-of-charge to the other microinverters, such that each microinverter of the plurality of microinverters calculates an average state-of-charge of the battery and communicates the calculated average state-of-charge to the battery management unit for controlling charging/discharging of the battery.