Back-EMF DC-Link Voltage Regulation for EV Accessory Power
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Solution Overview
Problem
In electric vehicles, the disconnection of the battery pack during operation can lead to the accessory devices becoming inoperable due to loss of power supply, causing the vehicle to slow down and eventually halt, as existing systems fail to maintain a stable DC supply voltage when the battery pack is disconnected.
Innovation Solution
A system that utilizes back EMF generated by the electric motor to maintain a minimum DC supply voltage on the DC power bus, employing a controller with torque, voltage, and field weakening controllers to regulate the motor and inverter, ensuring the DC-link voltage remains within a safe operating range, thereby keeping the accessory devices operational even when the battery pack is disconnected.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the battery pack is disconnected during operation, then the vehicle can recover from overvoltage conditions, but the accessory devices become inoperable due to loss of power supply
Solution Approach 1:
The patent introduces a DC-DC converter as an intermediary device between the motor generator and accessory devices. When the battery pack is disconnected, the DC-DC converter acts as a mediator to transfer power from the motor generator to the accessory devices, maintaining their operability while allowing the battery to be disconnected for overvoltage recovery.
Solution Approach 2:
The system dynamically changes operating parameters by switching between battery-powered mode and back-EMF powered mode. The controller monitors DC bus voltage and motor speed to determine when to activate the back-EMF harvesting mode, adjusting the system's power source parameters based on real-time conditions.
2Ease of operation
If the battery pack remains connected to supply accessory devices, then accessory devices remain operational, but the vehicle cannot recover from overvoltage conditions
Solution Approach 1:
The system implements dynamic operation by enabling the battery pack to be disconnected and reconnected based on operating conditions. The DC-DC converter enables flexible power routing, allowing the system to adapt between different power supply configurations to optimize both reliability and operability.
3Ease of operation
If back EMF is used to maintain DC supply voltage after battery disconnection, then accessory devices remain operational, but the system complexity increases
Solution Approach 1:
The motor generator serves multiple functions: it acts as a propulsion motor during acceleration, as a DC source for back-EMF harvesting during deceleration/coasting, and as a means to recharge the battery during regenerative braking. The DC-DC converter also provides multiple functions including voltage regulation and power routing between different sources and loads.
4Ease of operation
If the vehicle slows down to maintain minimum DC supply voltage, then accessory devices remain operational, but vehicle productivity decreases
Solution Approach 1:
The system changes the power source parameter from battery-only to a combination of battery and back-EMF harvesting. This allows the vehicle to maintain accessory power supply at higher speeds than would be possible with battery disconnection alone, effectively changing the operating speed parameter while maintaining voltage levels.
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 ensures that accessory devices remain operational as long as the vehicle is moving, by using the back EMF to maintain the DC supply voltage above a minimum threshold, preventing the accessory devices from becoming disabled due to voltage fluctuations, thus maintaining vehicle functionality.
Implementation Method 1
During operation of the electric vehicle, the electric motor generates a counter-electromotive force or a back electromotive force ('back EMF').
Data Source
AI summary
A controller generates a target motor torque and target accessory power information during operation of an electric vehicle. The target motor torque and target accessory power information maintain a DC-link of the electric vehicle powertrain within a safe DC-link operating range. The DC-link has a DC-link voltage that is used to supply an accessory device and a motor. The accessory device is disposed on the electric vehicle and includes vehicle indictors, hydraulics, or any other accessory involved in the operation of the vehicle. The motor drives the vehicle. The controller receives the DC-link voltage, motor speed, desired output torque information, desired accessory power information, and the safe DC-link operating range and generates therefrom the target motor torque and the target accessory power information.