Motor Control Apparatus Current Estimation High Duty Ratio
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The accuracy of motor control and abnormality detection in three-phase AC motors is compromised due to measurement errors caused by high duty ratios in PWM signals, leading to incorrect current value measurements.
Innovation Solution
The motor control apparatus replaces erroneous current measurements with estimated values based on rotor rotation angle information and coefficient values, improving the accuracy of current values used in processing, and includes a failure detection unit to identify motor abnormalities using highly accurate current values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current values are measured using a current sense resistor in the inverter, then current measurement is achieved, but measurement accuracy deteriorates when the duty ratio of the PWM driving signal is high
Solution Approach 1:
The patent stores coefficient values in advance during periods when the duty ratio is low (when measurements are accurate). These pre-stored coefficients are then used to estimate current values during periods when the duty ratio is high (when measurements would be inaccurate), thus avoiding the measurement error without real-time adjustment
Solution Approach 2:
The patent uses feedback by continuously monitoring the duty ratio and switching between measured current values (when duty ratio is low) and estimated current values based on stored coefficients (when duty ratio is high). This feedback mechanism ensures accurate current information is always available for motor control
2Productivity
If measured current values are used directly for motor control processing, then processing speed is maintained, but control accuracy deteriorates due to measurement errors at high duty ratios
Solution Approach 1:
Coefficient values are calculated and stored in advance during low duty ratio periods when measurements are reliable. This preliminary action allows the system to quickly retrieve and use these coefficients during high duty ratio periods without performing complex real-time calculations, thus maintaining processing speed while ensuring accuracy
Solution Approach 2:
The patent changes the parameter used for current information based on the duty ratio condition. When duty ratio is low, it uses directly measured current values. When duty ratio is high, it switches to using estimated current values calculated from stored coefficient values and rotor position information, thus adapting to maintain accuracy across different operating conditions
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A motor control apparatus includes a current estimation unit configured to output a detected current value corresponding to each of the three-phase AC currents based on the measured current value and rotor rotation angle information of the motor. The current estimation unit defines a phase whose duty ratio of a driving pulse supplied to an inverter circuit, which generates the three-phase AC currents, becomes more than or equal to an operation switching threshold as an estimation target phase, calculates, for the estimation target phase, an estimated current value based on a coefficient value, which is calculated from the measured current value by the current measurement unit in a period in which the duty ratio of the driving pulse is lower than the operation switching threshold, and the rotor rotation angle information, and outputs the calculated estimated current value as the detected current value of the estimation target phase.