BESS Secondary Control for State-of-Charge Balancing
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Solution Overview
Problem
Grid-scale Battery Energy Storage Systems (BESSs) face issues with state-of-charge (SoC) unbalance among units, leading to reduced utilization time and reliability due to differences in charge and discharge, which existing communication and hardware adaptations struggle to address effectively.
Innovation Solution
A method involving a first and second controller unit that adjusts active power setpoints based on state-of-charge (SoC) and capacity, ensuring balanced operation by distributing power demands among BESS units, incorporating a secondary controller to manage power setpoints and account for varying capacities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If communication among BESS units is established to address state of charge unbalance, then state of charge balancing is improved, but response time and reliability deteriorate due to communication delays and failures
Solution Approach 1:
The patent extracts the communication function from the control system and replaces it with a communication-free control mechanism. The secondary controller directly measures state of charge values from each battery energy storage unit and uses these measurements to generate differentiated power setpoints, eliminating the need for inter-unit communication while maintaining balancing capability.
Solution Approach 2:
The patent introduces a secondary controller as an intermediary that receives power setpoints from the primary controller and translates them into unit-specific power setpoints based on measured state of charge values. This intermediary enables centralized balancing control without requiring direct communication between distributed BESS units.
2Reliability
If hardware adaptations in power-electronics converter are implemented for state of charge balancing, then state of charge balancing is improved, but device complexity and cost increase
Solution Approach 1:
The patent makes the secondary controller a universal component that can interface with any type of power converter (VSC, CSC, or hybrid) without requiring hardware modifications. The controller universally measures state of charge from different converter types and applies a unified balancing algorithm, eliminating the need for type-specific hardware adaptations.
Solution Approach 2:
The patent replaces hardware-based balancing mechanisms with a software/control-based approach. Instead of modifying power-electronics converters with additional hardware circuits for balancing, the solution uses a secondary controller that processes state of charge measurements and generates adjusted power setpoints through computational algorithms.
3Reliability
If adaptive power and frequency droop control is used for state of charge balancing, then state of charge balancing is improved, but ease of operation deteriorates due to difficulty in implementation with different converter types
Solution Approach 1:
The patent segments the control function into two independent parts: a primary controller that handles overall power and frequency control, and a secondary controller that handles state of charge balancing. This segmentation allows each controller to specialize in its function, making the overall system easier to implement with different converter types since the secondary controller operates independently of converter-specific characteristics.
Solution Approach 2:
The patent changes the control parameter from converter-specific adaptive droop characteristics to a universal state of charge measurement parameter. By basing the balancing control on directly measurable state of charge values rather than on converter type-specific parameters, the system becomes easier to implement across different power converter technologies without requiring type-specific tuning or complex adaptive algorithms.
Data Source
Figure 1
AI summary
The invention relates to a battery energy storage system comprising at least two batteries, which are connectable to a grid by means of a converter and transformer, and a first controller unit (1a) and a second controller unit (1b) for controlling to either charge the batteries with electric energy from the grid or discharge electric energy from the batteries into the grid, characterized in that the second controller unit (1b) are provided for monitoring the actual state-of-charge and the capacity of the batteries.