Multi-Level Converter Pre-Charging for Energy Storage Reliability
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Solution Overview
Problem
Existing electric energy storage devices, such as battery systems in vehicles and wind turbines, face reliability issues due to potential failures in energy storage modules, which can lead to safety problems and rapid aging of capacitive components when directly connected to intermediate-circuit capacitors, requiring costly and space-intensive pre-charging systems.
Innovation Solution
The implementation of a controllable multiple-voltage level converter within energy storage modules allows for incremental voltage adjustment, enabling gentle and space-saving pre-charging of capacitive components by dividing voltage increments into smaller steps, reducing high current peaks and extending component lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the energy storage device is connected directly to the capacitive component without pre-charging, then the connection is simple and direct, but an extremely high current flows instantaneously causing rapid aging and early failure of components
Solution Approach 1:
The patent divides the voltage adjustment into multiple incremental steps using a multi-level converter with several voltage levels (e.g., Udc, 0.5*Udc, 0.25*Udc). Instead of a single direct connection, the system segments the charging process into discrete voltage stages, each delivering controlled current to the capacitive component. This segmentation prevents instantaneous high current while maintaining a relatively simple overall system structure.
Solution Approach 2:
The patent employs a dynamically controllable multi-level converter that can adjust its output voltage in real-time based on the charging state of the capacitive component. The converter dynamically switches between different voltage levels (Udc, 0.5*Udc, 0.25*Udc) to optimize the charging current at each stage. This dynamic adjustment allows the system to start with lower voltage increments and progressively increase, preventing initial current spikes while maintaining charging efficiency.
2Reliability
If pre-charging contactors and protective resistors are provided, then high current peaks are avoided, but the cost, installation space, and weight increase considerably
Solution Approach 1:
The patent integrates the pre-charging function into the existing multi-level converter that is already part of the energy storage device. The same converter circuitry used for normal operation also performs the pre-charging function by operating in a voltage-increment mode. This eliminates the need for separate pre-charging contactors and protective resistors, as the multi-level converter serves both as the main power conversion device and the pre-charging mechanism.
Solution Approach 2:
The energy storage device performs its own pre-charging operation using its internal multi-level converter without requiring external pre-charging equipment. The system uses its own voltage conversion capability to generate the incremental voltage steps needed for safe capacitive component charging. This self-service approach eliminates additional components and reduces system complexity while maintaining protective functionality.
3Productivity
If voltage increments are large (equal to single storage unit voltage), then the pre-charging process is fast, but high current peaks occur causing rapid aging of capacitive components
Solution Approach 1:
The patent segments the voltage increment into multiple smaller steps by utilizing a multi-level converter with voltage levels at Udc, 0.5*Udc, and 0.25*Udc. Instead of applying the full storage unit voltage in one step, the system divides it into quarter-voltage increments. This segmentation reduces the current peak at each charging stage while still maintaining a relatively fast overall pre-charging process by efficiently transitioning through the voltage levels.
Solution Approach 2:
The patent changes the voltage parameter dynamically during the pre-charging process by switching between different converter output levels. The system starts with smaller voltage increments (0.25*Udc) when the capacitive component voltage is low, then progressively increases to larger increments (0.5*Udc, Udc) as the component charges. This parameter change strategy optimizes both the pre-charging speed and component protection by adapting the voltage increment size to the charging state.
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
This solution effectively prevents rapid aging of capacitive components, enhances reliability, and reduces the cost and space requirements of pre-charging systems, ensuring safer and more efficient operation of electric energy storage devices.
Implementation Method 1
an energy store, for example, a battery, has a low internal resistance and the capacitive component acting as an intermediate-circuit capacitor has a high electrical capacitance
Implementation Method 2
This intermediate circuit is provided with a capacitive component, the intermediate-circuit capacitor, for keeping the DC voltage constant and for suppressing voltage peaks
Data Source
AI summary
An electric energy storage device includes two electrical terminals. The energy storage device further includes at least one first current path configured to electrically connect to the two terminals. The energy storage device further includes at least two energy storage modules configured to be connected to form a series connection of the energy storage modules. The energy storage modules include multiple storage units and a controllable multiple-voltage level converter. The converter is configured to optionally connect the one or more storage units in the first current path for the incremental adjustment of a module voltage, as at least one of a function of a control signal of a control and regulating device of the electric energy storage device.