Reconfigurable Battery Voltage for Electric Propulsion Losses
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Solution Overview
Problem
Electric propulsion systems for vehicles face limitations in torque band operation due to limited battery voltage, leading to increased electrical losses and performance penalties, especially when using permanent magnet-type electric traction motors, as they require aggressive flux-weakening operations at lower machine speeds.
Innovation Solution
A reconfigurable energy storage system (RESS) with multiple battery modules that can be connected in series or parallel, controlled by a controller to optimize voltage levels between low (250V-350V) and high (500V-700V) settings based on power losses, torque, and speed requirements, minimizing drive cycle losses and adapting to platform-specific needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If battery voltage is limited to low levels (250V-350V), then system safety and component stress are reduced, but torque band operation efficiency deteriorates due to increased electrical losses
Solution Approach 1:
The battery pack configuration is made dynamic by enabling real-time switching between series and parallel connections. The controller monitors operating conditions (torque demand, speed, temperature) and reconfigures the battery modules accordingly, transitioning from parallel (low voltage, high current) to series (high voltage, low current) configuration as needed to optimize efficiency while maintaining safety
Solution Approach 2:
The system changes the electrical parameters (voltage and current) by reconfiguring the battery modules. At low speeds and high torque demands, the system operates in parallel configuration with lower voltage and higher current. At higher speeds and lower torque demands, it switches to series configuration with higher voltage and lower current, thereby optimizing the torque band operation and reducing electrical losses
2Productivity
If battery voltage is increased to high levels (500V-700V), then propulsion performance and efficiency are improved, but stress on electric machine components increases
Solution Approach 1:
The system dynamically adjusts voltage levels by reconfiguring battery modules between series and parallel connections based on real-time operating conditions. High voltage (series configuration) is applied only when propulsion efficiency benefits are achieved, while low voltage (parallel configuration) is used when component stress becomes excessive, thereby optimizing the trade-off between performance and component durability
Solution Approach 2:
The system changes the operating voltage parameter by switching battery configurations. The controller monitors component stress indicators and adjusts the voltage level accordingly, transitioning from high voltage (series) to low voltage (parallel) configuration when component stress thresholds are approached, thereby protecting components while maintaining optimal propulsion efficiency
3Force
If aggressive flux-weakening operations are performed at lower machine speeds, then torque requirements are met, but electrical losses and performance penalties increase
Solution Approach 1:
The system changes the voltage parameter by switching to parallel configuration at lower machine speeds where flux-weakening operations would otherwise be required. This maintains adequate torque while avoiding the electrical losses associated with aggressive flux-weakening, as the lower voltage, higher current operation in parallel configuration is more efficient in this operating regime
Data Source
AI summary
An electric propulsion system includes a polyphase rotary electric machine that imparts motor torque to a load, a traction power inverter module (“TPIM”) connected to the electric machine, a reconfigurable energy storage system (“RESS”) connected to the TPIM, and a controller. The RESS has multiple battery modules and a switching circuit. The battery modules are connectable in a series-connected (“P-connected”) configuration at a first/low battery voltage level, and a series-connected (“S-connected”) configuration at a second/high battery voltage level that exceeds the first voltage. The controller determines power losses of the electric propulsion system at the first and second battery voltage levels, receives a commanded output torque and output speed of the electric machine, and selects the S-connected or P-connected configuration based on the predetermined power loss and commanded output torque and speed.