Inverter Torque Control via Voltage and Slip Frequency Commands
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Solution Overview
Problem
Current electric motor drive systems in vehicles face challenges in accurately controlling torque production when a current sensor error occurs, leading to insufficient, excessive, or oscillating torque, which adversely affects vehicle performance.
Innovation Solution
The system operates the inverter based on a voltage command and a slip frequency command corresponding to minimal motor current, allowing the electric motor to produce a commanded torque even in the absence of accurate current sensor feedback, by using pre-characterized voltage and slip frequency values for each torque and speed combination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a closed-loop control system uses current sensors to measure motor current for torque control, then torque control precision is improved, but system reliability deteriorates when current sensor errors occur
Solution Approach 1:
The patent introduces an intermediary control approach by using voltage commands and slip frequency commands as intermediate control variables instead of directly controlling current through faulty sensors. The voltage command serves as a mediator that indirectly influences motor current and torque production without requiring accurate current sensor feedback, thereby maintaining torque control reliability despite sensor errors
Solution Approach 2:
The patent segments the torque control process into two independent control dimensions: voltage control and slip frequency control. By separating current control into these two components, the system can control torque production through voltage magnitude while using slip frequency to optimize current minimization, eliminating dependence on faulty current sensor feedback for overall control stability
2Reliability
If the control system ceases or drastically reduces current provision in response to current sensor error, then system safety is improved, but vehicle functionality deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-characterizing the motor to establish the relationship between voltage commands, slip frequency commands, and resulting current/torque output. This pre-characterization data allows the control system to immediately switch to an alternative control mode using voltage and slip frequency commands when sensor errors are detected, without requiring system shutdown or drastic current reduction, thereby maintaining vehicle functionality while ensuring safety
Solution Approach 2:
The patent changes the control parameters from current-based control to voltage-based control with slip frequency optimization. By transitioning from controlling motor current directly (which requires accurate sensor feedback) to controlling voltage magnitude and slip frequency (which do not require current sensor feedback), the system maintains both safety and continuous vehicle operation despite current sensor errors
3Reliability
If voltage command and slip frequency command are used to control torque without current sensor feedback, then system reliability is improved, but torque response speed deteriorates
Solution Approach 1:
The patent applies dynamics by making the slip frequency command variable and adaptive rather than fixed. The slip frequency command is dynamically adjusted based on the instantaneous motor speed and voltage command to optimize the motor's current characteristics in real-time. This dynamic adjustment allows the system to maintain reliable torque control without current sensor feedback while improving torque response speed by adapting to changing operating conditions
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 controlled torque production that is close to the commanded value while minimizing input current, providing redundancy and maintaining vehicle functionality despite current sensor errors, although with potentially slower torque response.
Implementation Method 1
many electric motors are operated using pulse-width modulation (PWM) techniques in combination with an inverter (or another switched-mode power supply) to control the voltage across the motor windings
Implementation Method 2
alternating current (AC) motor drives are used to provide a requested torque to the motor shaft
Data Source
AI summary
Methods and systems are provided for producing a commanded torque in an electric motor in a vehicle. A method comprises obtaining a torque command, obtaining a speed of the electric motor, and operating the inverter based at least in part on a voltage command that corresponds to minimal current through the electric motor for producing the commanded torque at the instantaneous speed of the electric motor.