Isolated BESS Topology for HVDC Grids
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Solution Overview
Problem
Current Battery Energy Storage Systems (BESS) are not suitable for Medium Voltage Direct Current (MVDC) or High Voltage Direct Current (HVDC) applications due to power rating and voltage rating limitations, and they require complex and costly battery management systems for high voltage AC grid applications.
Innovation Solution
A family of isolated BESS topologies with multiple functions, including energy storage, active filtering, low voltage fault ride through, and current limiting, using an AC transformer with cascade connected voltage source converter sub-modules and energy storage battery units, allowing for modular design with low voltage rated components suitable for high voltage and high power DC grid applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If hundreds of battery cells are connected in series to build a high voltage battery bank, then the battery bank voltage is increased, but the complexity, failure rate and cost of the battery management system increase
Solution Approach 1:
The battery bank is divided into multiple series battery branches, each containing a manageable number of battery cells (e.g., 32 cells per branch). This segmentation allows the BMS to monitor and manage each branch independently, reducing the complexity and cost of the BMS while achieving high voltage through the series connection of multiple branches.
2Power
If hundreds of battery cells are connected in series to build a high voltage battery bank, then the battery bank voltage is increased, but the failure rate of the battery management system increases
Solution Approach 1:
By segmenting the battery bank into multiple series branches with fewer cells each, the BMS manages smaller groups of cells independently. This reduces the failure rate because each branch is easier to monitor and control, and the failure of one branch does not necessarily compromise the entire system.
3Device complexity
If traditional BESS topology is used, then the system is simple, but the power rating and voltage rating are not suitable for MVDC or HVDC applications
Solution Approach 1:
The converter is segmented into multiple voltage source converter sub-modules connected in cascade. Each sub-module operates at a lower voltage level, but their series connection achieves the required high voltage and power rating for MVDC/HVDC applications. This modular segmentation maintains relative simplicity while enabling high power operation.
Solution Approach 2:
The system transitions from a single-stage DC-DC converter to a multi-stage DC-AC-DC conversion path. By adding the AC dimension with transformer isolation, the system achieves high voltage and power ratings suitable for MVDC/HVDC applications while maintaining flexibility and control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables efficient energy storage and active filtering in high voltage DC grids with reduced system loss and cost, supporting hybrid energy storage systems and various modulation methods, such as square wave and sinusoidal wave modulation, while ensuring precise control of DC grid side current.
Implementation Method 1
an AC transformer having a primary side and a secondary side
Implementation Method 2
a plurality of cascade connected voltage source converter sub-modules
Implementation Method 3
a plurality of energy storage battery units
Data Source
AI summary
This invention presents a family of isolated BESS topologies with multiple functions, which are suitable for high voltage and high power DC grid application. A battery energy storage system (BESS) for direct current (DC) grid applications is provided, including an alternating current (AC) transformer having a primary side and a secondary side, at least one primary side arm coupled to the primary side of the AC transformer, the at least one primary side arm comprising a plurality of cascade connected voltage source converter sub-modules and a plurality of energy storage battery units and at least one secondary side arm coupled between the secondary side of the AC transformer and a DC grid voltage bus, the at least one secondary side arm comprising a plurality of cascade connected voltage source converter sub-modules. Modulation and control strategies for the various topologies are also provided.