Rotary Electric Machine Control Device for Torque Ripple Reduction
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Solution Overview
Problem
Existing rotary electric machine control devices cannot effectively specify a short-circuited location in a rotating state, leading to torque ripple issues due to the inability to identify short-circuits during motor operation.
Innovation Solution
A rotary electric machine control device with an inverter, power source relay, terminal voltage detector, and controller that cuts off power supply to abnormal systems, allowing for the determination of short-circuited locations based on terminal voltages generated by counter electromotive force, and adjusts command values to reduce torque ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the motor is operated in a rotating state, then the electric power steering system can provide assistance torque, but it becomes impossible to specify the short-circuited location due to the inability to detect terminal voltage accurately during rotation
Solution Approach 1:
The system performs preliminary detection of terminal voltages during periods when the motor is not rotating (e.g., when the steering wheel is not being operated). This advance detection stores diagnostic information that can be used later when the motor is operating, resolving the contradiction by preparing the diagnostic data in advance rather than attempting real-time detection during rotation.
Solution Approach 2:
The system uses the motor's own counter electromotive force (back-EMF) generated during rotation as the signal source for detecting terminal voltages. By utilizing the motor's inherent electrical characteristics during operation, the system can specify short-circuited locations even while rotating, eliminating the need to stop the motor for diagnosis.
2Measurement precision
If PWM control is stopped to detect switching element failures, then short-circuit locations can be identified, but the motor must be stopped and assistance torque cannot be provided
Solution Approach 1:
The system utilizes the counter electromotive force naturally generated by the motor during rotation as the excitation source for voltage detection. This eliminates the need to stop PWM control or the motor itself, allowing continuous operation while performing diagnostic measurements using the motor's own operational characteristics.
Solution Approach 2:
The system changes the detection approach from requiring motor stoppage to using terminal voltage measurements during rotation. By monitoring voltage parameters while the motor operates and comparing them against expected values, the system can identify switching element failures without interrupting assistance torque provision.
3Productivity
If terminal voltage detection is performed during motor rotation, then continuous operation can be maintained, but torque ripple increases due to uncorrected short-circuit effects
Solution Approach 1:
The system continuously monitors terminal voltages during motor operation and uses this feedback information to identify short-circuited phases. Once detected, the control strategy is adjusted to compensate for the identified faults, allowing continuous operation while minimizing torque ripple through active correction based on real-time voltage measurements.
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
Enables accurate specification of short-circuited locations and reduction of torque ripple during motor operation, ensuring stable and efficient operation of electric power steering systems.
Implementation Method 1
a short-circuited location is determined based on a terminal voltage generated by counter electromotive force of the rotary electric machine
Data Source
AI summary
A rotary electric machine control device for a rotary electric machine having winding sets with coils includes: an inverter for each winding set; a power source relay for each inverter; a terminal voltage detector detecting a terminal voltage of each coil; and a controller including an inverter controller, a relay controller and an abnormality determination unit. Each winding set and a corresponding inverter provides a system. When the rotary electric machine is driven using a normal system: the relay controller controls the power source relay to cut off power supply from a power source to the inverter in an abnormal system; the abnormality determination unit specifies a short-circuited location based on the terminal voltage in the abnormal system; and the inverter controller corrects a command value related to control of the inverter in the normal system according to a specified short-circuited location.