Hybrid EV DC Link Switching for High-Speed Motor Power
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Solution Overview
Problem
In hybrid electric vehicles, the traction motor's power output is limited by the voltage on the DC link at high speeds, restricting its performance due to a constant torque to constant power ratio, where power is constant below a certain speed and torque decreases above it.
Innovation Solution
A system that includes a controllable switch allowing the DC link to operate independently of the energy storage system, enabling voltage boosting by coupling the generator to the engine when needed, thereby increasing the available power to the traction motor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the DC link is connected to the energy storage system, then the system provides stable voltage and power, but the traction motor power output is limited at high speeds
Solution Approach 1:
The system segments the power supply architecture by introducing a controllable switch that divides the DC link into two operational modes: connected to energy storage system for stable operation, and disconnected for high-speed power boosting. This segmentation allows the traction motor to access higher power from the generator without compromising the stability provided by the energy storage system during normal operation.
Solution Approach 2:
The system dynamically switches between different power supply configurations using a controllable switch. When high-speed operation is required, the switch disconnects the energy storage system and connects the generator to the DC link, allowing voltage and power to increase. This dynamic reconfiguration enables the system to adapt its power delivery characteristics to match operational demands.
2Speed
If the DC link voltage is increased to boost motor power, then high speed performance improves, but the energy storage system may be degraded
Solution Approach 1:
The system extracts the energy storage system from the DC link connection during high-speed operation by opening the controllable switch. This isolation protects the energy storage system from the high voltage and current stresses that would occur during voltage boosting, while still allowing the generator to provide the necessary power for high-speed motor operation.
Solution Approach 2:
The controllable switch acts as an intermediary element that mediates between the energy storage system and the DC link. It selectively connects or disconnects the energy storage system based on operational requirements, allowing the system to achieve high-speed performance while protecting the energy storage system from damaging conditions.
3Power
If the constant torque to constant power ratio is increased, then high speed power capability improves, but the voltage on the DC link must be increased
Solution Approach 1:
The system performs preliminary action by pre-charging the capacitor bank before high-speed operation. This allows the DC link voltage to be boosted to the required level for high-power operation without immediately stressing the energy storage system. The capacitor bank serves as a buffer that can be charged in advance and then discharge during high-speed demands.
Solution Approach 2:
The system changes the voltage parameter of the DC link dynamically based on operational requirements. During high-speed operation, the DC link voltage is increased to enable higher power output from the traction motor. The controllable switch enables this parameter change by isolating the energy storage system while allowing the generator to boost the voltage.
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 enhances the traction motor's performance by increasing the constant torque to constant power ratio, allowing higher power output at high speeds without degrading the energy storage system, thus overcoming the voltage limitations.
Implementation Method 1
The first inverter, when the generator is coupled to the engine, is configured to receive AC power from the generator and provide DC power for the DC link
Implementation Method 2
The second inverter configured to receive the DC power from the first inverter and the energy storage system when coupled and provide AC power to the motor
Data Source
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AI summary
A hybrid electric vehicle having a controllable switch that enables a DC link to be operated independent from an energy storage system (ESS) is provided. The ESS is selectively couplable to the DC link via the controllable switch. A processor is configured to control the switch to open and close under certain conditions. When the switch is opened, the processor is configured to instruct an engine controller to cause an engine which is coupled to a generator to boost engine output. The generator is coupled to a generator inverter which is also coupled to the DC link. A motor inverter is also coupled to the DC link and is configured to provide AC power to the motor.