Electric Motor High Loss Mode Charge Rate Management
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Solution Overview
Problem
In electrified vehicles, regenerative braking during full battery state of charge or high charge rates leads to inefficiencies and undesirable noise, vibration, and harshness due to the need for friction brakes or compression braking, and existing control systems fail to optimize energy dissipation effectively.
Innovation Solution
The system operates the electric motor and inverter in a high loss mode by injecting direct axis current and changing PWM strategies to dissipate energy, reducing charge rates through internal short circuits and increased switching losses, and using existing energy dissipation methods or friction brakes when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If regenerative braking is used to charge the battery during braking, then energy recovery is improved, but when the battery is full or charge rate is high, friction brakes must be used which reduces efficiency and increases wear
Solution Approach 1:
The controller changes the operating parameters of the electric machine by injecting direct axis current to create high loss mode operation. This intentionally increases electrical losses to reduce the charge rate to acceptable levels, allowing regenerative braking to continue without requiring friction brakes when the battery is full or charge rate is high.
Solution Approach 2:
The system converts the harmful effect of excessive charge rate or full battery state into a beneficial outcome by intentionally creating high loss mode operation. The electrical losses generated during high loss mode serve to dissipate excess energy and reduce charge rate, transforming what would be a problem (inability to charge) into a solution (active charge rate management).
2Reliability
If friction brakes are used to limit charge rate during regenerative braking, then battery protection is improved, but energy dissipation efficiency deteriorates and brake wear increases
Solution Approach 1:
The system replaces the mechanical friction braking system with an electrical control solution. Instead of using friction brakes to dissipate energy and limit charge rate, the controller injects direct axis current into the electric machine to create high loss mode operation, converting mechanical energy dissipation into electrical loss management.
Solution Approach 2:
The controller changes the electrical operating parameters of the machine by injecting direct axis current, transforming the operating mode to high loss mode. This parameter change allows the system to manage charge rate through electrical losses rather than mechanical friction, improving energy efficiency and reducing brake wear.
3Loss of energy
If the electric machine operates efficiently during regenerative braking, then energy recovery is maximized, but charge rate may exceed battery acceptance limits causing thermal issues
Solution Approach 1:
The system dynamically adjusts the operating mode of the electric machine based on real-time battery state. The controller monitors charge rate and battery state of charge, and dynamically switches between normal efficient operation and high loss mode by injecting direct axis current, allowing adaptive management of energy recovery and thermal conditions.
Solution Approach 2:
The controller changes the electrical parameters of the machine operation by injecting direct axis current to create high loss mode. This parameter change reduces the charge rate to match battery acceptance limits, preventing thermal issues while maintaining energy recovery where possible.
4Reliability
If direct axis current is injected to create high loss mode, then charge rate is reduced to acceptable levels, but energy dissipation efficiency decreases
Solution Approach 1:
The system converts the inefficiency of direct axis current injection into a beneficial control mechanism. The energy losses created by high loss mode operation are intentionally used to manage charge rate and prevent battery overload, transforming what appears to be wasted energy into a useful control tool for maintaining system reliability.
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 reduces the frequency of friction brake application, enhances energy dissipation during regenerative braking, and improves NVH performance by intentionally operating inefficiently to manage battery charge rates and thermal limitations.
Implementation Method 1
operates switches of the inverter according to a first method of commutation
Implementation Method 2
The electric machine may transform electrical energy from the traction battery to mechanical energy to move wheels of the vehicle
Implementation Method 3
The electric machine may also transform mechanical energy from the wheels to electrical energy for storge in the traction battery
Implementation Method 4
operates the inverter to inject direct axis current into the electric machine
Implementation Method 5
operates the switches according to a first method of commutation responsive to a negative wheel torque request
Data Source
AI summary
A drivetrain includes an electric machine, an inverter, and a controller. The controller, for a given operating point of the electric machine, may schedule a method of commutation for switches of the inverter during presence of a negative wheel torque request according to a charge rate corresponding to the negative wheel torque request, temperatures of the electric machine and/or inverter, and/or a battery state of charge.