ISG Current Rate Limiting for Hybrid Vehicle Voltage Sag
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Solution Overview
Problem
Hybrid vehicles face challenges in managing current demand during engine starting, leading to potential saturation of the power converter output, which can cause voltage sag on the low-voltage bus, affecting accessory loads and customer experience.
Innovation Solution
A controller is programmed to limit the current increase rate of the integrated starter generator (ISG) electric machine to prevent power converter saturation, ensuring the power converter operates within its capacity and minimizing voltage sag on the low-voltage bus by coordinating with the power converter to manage current demand.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the current increase rate of the integrated starter generator is increased to improve engine starting performance, then the engine starting speed increases, but the power converter output becomes saturated causing voltage sag on the low-voltage bus
Solution Approach 1:
The controller predicts future current demand of the ISG based on engine speed demand and提前 limits the current increase rate before power converter saturation occurs. This preliminary control action prevents voltage sag before it happens, allowing the ISG to reach higher current levels faster while maintaining voltage stability on the low-voltage bus.
2Reliability
If the current increase rate of the integrated starter generator is limited to prevent power converter saturation, then voltage stability on the low-voltage bus is maintained, but the engine starting speed increases more slowly
Solution Approach 1:
The controller dynamically adjusts the current increase rate limit based on real-time operating conditions including engine speed demand, power converter output current, and battery state of charge. This dynamic control allows the system to optimize the balance between voltage stability and engine starting speed under different operating conditions, rather than using a fixed current limit.
Solution Approach 2:
The controller continuously monitors power converter output current and compares it against predicted ISG current demand. Based on this feedback, the controller adjusts the current increase rate limit to prevent saturation while maximizing engine starting performance. The feedback loop ensures voltage stability is maintained while achieving optimal starting speed.
Data Source
AI summary
A vehicle includes a hybrid powertrain with a motor/generator electrically coupled to a high-voltage bus to provide propulsion. The vehicle also includes an integrated starter/generator electrically copulated to a low-voltage bus and configured to start the engine. A vehicle power system includes a power converter electrically coupled between the high-voltage bus and the low-voltage bus. During engine start events, operation of the integrated starter/generator is coordinated with operation of the power converter to reduce voltage sag on the low-voltage bus. An increase rate of current supplied to the integrated starter/generator is limited such that a current output of the power converter does not saturate at a maximum current output for a period of time after initiating the engine start event.