Three-Phase Machine Control Device for Torque Ripple Mitigation
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Solution Overview
Problem
Existing control devices for three-phase rotating machines with two three-phase winding sets face issues with torque ripples and heat characteristics, particularly during low-speed rotation, due to current differences between units, and fail to restrict overcurrent when one unit is faulty.
Innovation Solution
A control device that includes a first and second power converter, current sensing sections, and a current feedback computing section with a current sum controller and difference controller, which adjusts the phase angle of alternating currents between units by 30°±60° to control current sum and difference, and varies responsiveness based on reference frequency to mitigate torque ripples and overcurrent.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If only the sum of currents from two power converters is controlled, then the control structure is simple, but current difference arises between units causing torque ripples and worsened heat characteristic
Solution Approach 1:
The patent segments the current control into two independent control loops: a sum control loop that controls the sum of currents from both power converters, and a difference control loop that controls the current difference between the two units. This segmentation allows independent optimization of each control objective, eliminating torque ripples and improving heat characteristic while maintaining reasonable control complexity.
Solution Approach 2:
The patent introduces a phase shift parameter (30°±60°×n) between the alternating currents from the two power converters. By changing the phase relationship parameter, the patent achieves better current distribution between units, reducing current difference and its harmful effects while maintaining system simplicity.
2Reliability
If one unit is accidentally opened, then the system has fault tolerance, but excessive current equivalent to twice the normal current flows in the other unit
Solution Approach 1:
The patent implements feedback control for both current sum and current difference. The difference control loop continuously monitors and adjusts the current distribution between units, providing feedback that prevents excessive current in the healthy unit when one unit fails. This feedback mechanism maintains reliability while preventing overcurrent damage.
3Device complexity
If the gain ratio between sum gain and difference gain is fixed, then the control is simple, but the responsiveness cannot be optimized for different operating conditions
Solution Approach 1:
The patent makes the gain ratio dynamic rather than fixed. The difference gain is adjusted based on the reference frequency (rotational speed) of the motor. At low speeds where torque ripples are more problematic, the difference gain is increased for better current balancing. At high speeds where vibrations are more concerning, the gain ratio is optimized accordingly. This dynamic adjustment reduces harmful effects across all 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
The solution effectively reduces torque ripples, improves heat characteristics, and restricts overcurrent in faulty units, while suppressing vibrations and sounds during high-speed rotation by phase-shifting currents and adjusting responsiveness.
Implementation Method 1
While being supplied with power, the first and second three-phase winding sets are coupled magnetically to each other, producing a mutual inductance
Data Source
AI summary
In a control device for a three-phase rotating machine with first and second winding sets, a current feedback computing section includes a current sum controller and a current difference controller. The current sum controller multiplies, by a sum gain, an error between a sum of current command values for alternating currents output from first and second inverters and a sum of sensed current values and computes a sum of voltage command values. The current difference controller multiplies, by a difference gain, an error between a difference of the current command values and a difference between the sensed current values, and computes a difference of voltage command values. In a variable-responsiveness mode, a gain ratio between the sum gain and the difference gain is varied according to a reference frequency such that the current sum controller and the current different controller are different in responsiveness.