Motor Control Device Feedback Switching for High Duty Ratio Accuracy
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Solution Overview
Problem
In motor control devices using PWM control, the increased duty ratio of pulse waves leads to shortened current detection time by shunt resistors, resulting in lower current detection accuracy and limited motor output due to inadequate control of three-phase currents.
Innovation Solution
A motor control device and method that employs a controller to execute first and second feedback controls, switching between control current values calculated from different phase currents to improve detection accuracy and increase duty ratios, using a three-phase two-axis conversion unit to adjust the control current values based on equations that account for variations in phase currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the duty ratio of pulse waves is increased to improve motor output, then motor output is improved, but current detection time is shortened resulting in lower current detection accuracy
Solution Approach 1:
The patent introduces an intermediary calculation method that uses the relationship between three-phase currents and the fact that their sum is zero. Instead of directly detecting current during the shortened detection window, the system calculates the control current value using detected phase currents and mathematical relationships, acting as an intermediary that preserves accuracy without requiring extended detection time.
Solution Approach 2:
The patent changes the parameter being measured from direct current magnitude to a calculated value based on phase relationships. By detecting phase currents and using the relationship that the sum of three-phase currents equals zero, the system calculates the control current value, transforming the measurement approach to work effectively within shortened detection windows at high duty ratios.
2Power
If the duty ratio is increased beyond a certain extent, then motor output should be improved, but control current value cannot be suitably controlled due to insufficient current detection accuracy
Solution Approach 1:
The patent implements a feedback mechanism where the calculated control current value is used to adjust PWM control signals. The system continuously monitors phase currents, calculates control values using the intermediary method, and feeds this information back to maintain accurate control even at high duty ratios where direct detection would fail.
Solution Approach 2:
The calculation based on phase current relationships serves as an intermediary that bridges the gap between shortened detection time and required control accuracy. This intermediary approach allows the system to maintain reliable control current values without being constrained by detection time limitations at high duty ratios.
3Ease of operation
If shunt resistor detection is used to monitor phase current, then current control is achieved, but detection accuracy deteriorates when duty ratio increases
Solution Approach 1:
The patent replaces direct mechanical/electrical detection reliance with a computational approach. Instead of depending solely on shunt resistor detection during limited time windows, the system substitutes direct measurement with calculation based on phase relationships, eliminating the detection accuracy limitation while preserving control capability.
Solution Approach 2:
The patent changes from direct current magnitude measurement to calculation based on phase current relationships. By using the relationship that the sum of three-phase currents equals zero, the system transforms the measurement parameter from direct detection to derived calculation, maintaining accuracy independent of duty ratio.
Data Source
AI summary
A motor control device includes a controller to control a three-phase current by feeding back a control current value obtained based on the three-phase current. The controller is configured or programmed to execute first feedback control of feeding back any one of a first control current value calculated based on a second phase current and the third phase current, a second control current value calculated based on the third phase current and a first phase current, and a third control current value calculated based on the first phase current and the second phase current as a control current value and second feedback control in which the first control current value, the second control current value, and the third control current value are switched and fed back as the control current value.