Inverter Voltage Control to Eliminate EV Brake Torque in Limp Mode
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Solution Overview
Problem
Hybrid and electric vehicles face challenges when an electric motor encounters issues, such as overcurrent or faulted rotor position, leading to a limp mode where some vehicle functions are unavailable, and unwanted charging current can flow to the traction battery.
Innovation Solution
A system that includes a controller which, upon detecting a predefined condition, turns off the inverter, deactivates the motor, and enables the engine for propulsion, while commanding the variable voltage control circuitry to generate a target input voltage for the inverter based on a speed limit, ensuring no charging current flow to the traction battery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the motor is deactivated and inverter is turned off during a fault condition, then the vehicle can continue propulsion using the engine, but the motor rotating at speed may generate unwanted charging current to the traction battery
Solution Approach 1:
The system dynamically adjusts the DC bus voltage parameter to prevent unwanted charging current. By commanding the variable voltage control circuitry to generate a target DC bus voltage that corresponds to the motor's current speed, the system changes the voltage parameter to match the motor's operational state, thereby preventing current flow to the battery while maintaining safe propulsion speeds
Solution Approach 2:
The controller continuously monitors motor speed and uses this feedback to dynamically adjust the DC bus voltage setpoint. The speed-limiting mechanism receives feedback from the motor speed sensor and adjusts the voltage command accordingly, creating a closed-loop control system that prevents charging current by maintaining the appropriate voltage-speed relationship
2Reliability
If the vehicle operates in limp mode with limited speed, then safe propulsion is maintained during motor faults, but the vehicle functionality is reduced
Solution Approach 1:
The system applies partial action by enabling the engine to provide only the necessary propulsion power required in limp mode, rather than full vehicle performance. The speed limiting mechanism intentionally restricts the vehicle to a subset of its full speed range, providing just enough propulsion capability to reach safe locations while preventing harmful charging current
Solution Approach 2:
The system extracts and isolates the propulsion function from other vehicle functions during fault conditions. By separating the engine-driven propulsion system from the faulty electric motor system, the vehicle can maintain essential movement capability while excluding the malfunctioning motor from operation, thereby preserving critical productivity
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 allows the vehicle to operate in a limp mode with limited speed, preventing unwanted charging current and ensuring safe propulsion, thereby maintaining vehicle functionality during electric motor faults.
Implementation Method 1
variable voltage control circuitry that boosts an input voltage to the inverter
Data Source
AI summary
A controller, while a motor is deactivated and a corresponding inverter is disabled, enables an engine for propulsion of a vehicle such that the motor rotates at a speed due to the propulsion, and commands variable voltage control circuitry to generate a target input voltage for the inverter that is based on a speed limit for the vehicle such that the speed of the motor corresponding to the vehicle travelling results in zero braking torque from the motor and zero charging current flow to a traction battery.