Hybrid Vehicle Electric Machine Control for Post-Failure Bus Voltage
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Solution Overview
Problem
In hybrid vehicle electrical systems, battery pack disconnection limits post-failure vehicle range due to insufficient reserve power, as conventional methods discharge bus capacitors and rely solely on auxiliary batteries, which can only sustain essential loads for a limited time.
Innovation Solution
The electric machine is controlled to operate as a generator, first reducing battery pack current to zero and then maintaining bus voltage, using synchronous vector current commands to ensure continued vehicle operation after battery pack disconnection, bypassing traditional torque-based control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the battery pack is disconnected from the electrical system during a failure mode, then safety is improved by isolating the fault source, but the vehicle range is reduced due to insufficient reserve power in bus capacitors and auxiliary battery
Solution Approach 1:
The electric machine serves as an intermediary power source between the disconnected battery pack and the electrical loads. When the battery pack is disconnected, the electric machine generates electricity to power essential loads (ignition system, fuel pump, sensors) that the auxiliary battery alone cannot sustain, thereby extending vehicle range while maintaining safety isolation.
Solution Approach 2:
The control system changes the operating parameters of the electric machine from motor mode to generator mode. By detecting battery pack disconnection and switching the electric machine's function, the system transforms the vehicle from relying solely on auxiliary battery power to utilizing generated electrical power, thus extending operational duration without compromising safety.
2Device complexity
If conventional control methods are used after battery disconnection, then system simplicity is maintained, but the vehicle enters a 'walk-home' condition with limited operational capability
Solution Approach 1:
The control system dynamically adapts its behavior based on the operational state. When battery disconnection is detected, the system automatically switches from conventional control to failure-mode control, where the electric machine transitions to generating mode. This dynamic adaptation extends post-failure operational capability while adding minimal complexity, as the same control unit manages both normal and failure modes.
3Device complexity
If the electric machine is controlled using traditional torque-based control after battery disconnection, then control simplicity is maintained, but response time is insufficient to maintain bus voltage and enable continued operation
Solution Approach 1:
The control method changes from torque-based control to synchronous vector current control. This parameter change in the control strategy enables direct control of the electric machine's current vectors, providing faster response time to maintain bus voltage after battery disconnection. The synchronous vector control directly regulates d-axis and q-axis currents, allowing rapid adjustment of electrical output to match load demands.
Solution Approach 2:
The patent replaces traditional mechanical torque-based control with an electrical field-based synchronous vector control approach. By controlling the electrical current vectors directly rather than relying on mechanical torque feedback, the system achieves faster response time for maintaining bus voltage, enabling continued vehicle operation without the delays inherent in traditional control methods.
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 approach enables continued operation of the vehicle by utilizing the electric machine's generating capability, preventing a 'walk-home' condition and maintaining engine and electrical load operation until the engine is turned off, thereby extending vehicle range.
Implementation Method 1
an AC electric machine selectively operable in generating and motoring modes
Implementation Method 2
one or more bus capacitors for maintaining the bus voltage
Data Source
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AI summary
A control methodology for an engine-driven electric machine (18) of a hybrid vehicle electrical system (22) for enabling continued operation of the vehicle electrical system (22) under failure mode conditions that require or result in disconnection of the battery pack (20) from the electrical system (22). At the onset of a fault condition requiring battery disconnection (102), the electric machine (18) is controlled to drive the battery pack current toward zero (118, 96, 98) before disconnecting the battery pack (20). Once the battery pack (20) is disconnected, whether by relay or fuse, the electric machine (18) is controlled to maintain the bus voltage of the electrical system (22) at a specified value (94-98). In both operating modes, the electric machine (20) is controlled based on a synchronous vector current command (94, 118) that is determined directly as a function of the control objective (zero battery pack current or maintaining bus voltage) for improved response time compared to a traditional torque-based control.