Multilevel Inverter Drive Unit with Modular Battery Coupling
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Solution Overview
Problem
High voltage and current requirements in battery systems for electric vehicles and stationary applications lead to issues with compensation currents, voltage stabilization, and reliability due to series-connected battery cells, which can result in system failure if a single cell fails, and pose safety risks and high costs for components like contactors and capacitors.
Innovation Solution
A drive unit comprising a multilevel inverter and battery module strings with coupling units that allow for adjustable connection of battery cells between terminals in response to control signals, using center taps to divide the battery module string and a control unit to output signals for adjusting potential at the multilevel inverter outputs, enabling sinusoidal potential adjustment with variable frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If battery cells are connected in series to achieve high voltage, then the output voltage increases, but the system reliability decreases because a single cell failure causes entire battery failure
Solution Approach 1:
The battery system is divided into multiple independent battery modules, each with its own coupling unit. This segmentation allows the system to maintain high voltage through series connection while improving reliability, as a failure in one module does not necessarily cause entire system failure due to the independent modular architecture and ability to reconfigure connections.
Solution Approach 2:
The coupling units enable dynamic reconfiguration of battery module connections. The system can switch between series and parallel connections of battery modules based on operational requirements and cell status, allowing adaptive maintenance of high voltage output while managing reliability risks through flexible topology changes.
2Power
If battery cells are connected in parallel to increase maximum current, then the available power increases, but compensation currents occur due to cell capacitances and voltage differences
Solution Approach 1:
The battery system is divided into multiple independent battery modules with separate coupling units. This segmentation isolates the parallel connection operations to individual modules, limiting the propagation of compensation currents to local modules rather than affecting the entire battery system, thereby reducing overall energy losses.
Solution Approach 2:
The coupling units act as intermediary devices between battery modules, providing controlled connection and disconnection capabilities. These intermediaries enable selective parallel connection of modules for power enhancement while managing voltage and current balancing, reducing unwanted compensation currents through controlled switching operations.
3Stability of the object's composition
If a large capacitor is used to stabilize DC voltage intermediate circuit, then the voltage stabilization improves, but the cost and space requirement increase significantly
Solution Approach 1:
The voltage stabilization function is distributed across multiple battery modules rather than requiring a single large capacitor. Each module contributes to overall voltage stability through its coupling unit and controlled connection to the DC intermediate circuit, enabling reduced capacitor sizing while maintaining stabilization performance.
Solution Approach 2:
The system dynamically changes the effective capacitance of the DC intermediate circuit by controlling the connection state of battery modules through coupling units. This allows the circuit to exhibit high capacitance characteristics when needed for stabilization while maintaining lower physical capacitor requirements through active management of energy storage distribution.
4Object-affected harmful factors
If contactors are used to disconnect battery cells for safety, then the safety improves, but the device complexity and cost increase considerably
Solution Approach 1:
The disconnection function is distributed to individual coupling units in each battery module rather than requiring centralized contactor systems. This segmentation reduces the complexity and cost of safety devices while maintaining comprehensive safety coverage, as each module can be independently disconnected through its own coupling unit.
Solution Approach 2:
The coupling units serve multiple functions including voltage regulation, current management, and safety disconnection. This multi-functionality eliminates the need for separate dedicated contactors for each battery module, reducing overall device complexity and cost while maintaining safety capabilities.
Data Source
AI summary
A drive unit for an electric motor comprises a multilevel inverter and a battery. The battery comprises at least one battery module train comprising a plurality of battery modules connected in series, each module having at least one battery cell and one coupling unit. The at least one battery cell is connected between a first input and a second input of the coupling unit. The coupling unit is designed to connect the at least one battery cell between two terminals of the battery module in response to on a first control signal and to connect the two terminals in response to a second control signal. Several center taps are arranged on the battery module train, by means of which a potential can be tapped at a connection between two battery modules respectively. Inputs of the multilevel inverter are connected to the taps.