Single-Shunt Motor Current Measurement Without PWM Voltage Distortion
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Solution Overview
Problem
Conventional single-shunt current measurement techniques for three-phase motor controllers face challenges in forming current measurement windows without distorting phase voltage, leading to insufficient measurement duration and subsequent voltage distortion, which affects motor control accuracy.
Innovation Solution
The method involves adjusting the duration of current measurement windows within a pulse width modulation (PWM) period by a time delta value to ensure a minimum time for accurate motor current measurement, allowing for measurement of only two phases during the first PWM period and compensating in subsequent periods to maintain motor control accuracy without voltage distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current measurement windows are extended to ensure accurate motor current measurement, then measurement precision is improved, but phase voltage distortion occurs
Solution Approach 1:
The patent pre-calculates and stores optimal current measurement window durations in lookup tables during system initialization or calibration phases. These pre-determined values represent the maximum measurement duration achievable without causing voltage distortion under various operating conditions. During real-time motor control, the controller directly retrieves these pre-computed values based on current operating parameters, eliminating the need for real-time optimization calculations and ensuring measurement windows never exceed distortion-free limits.
Solution Approach 2:
The patent dynamically adjusts current measurement window duration as a variable parameter based on real-time motor operating conditions such as speed, load, and PWM duty cycle. By changing the measurement window duration parameter adaptively rather than using fixed values, the system optimizes measurement accuracy for each operating point while staying within distortion-free boundaries. The controller selects from multiple pre-calculated duration values corresponding to different operating ranges.
2Object-generated harmful factors
If current measurement windows are shortened to avoid phase voltage distortion, then voltage distortion is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent pre-calculates and stores optimal current measurement window durations in lookup tables during system initialization or calibration phases. These pre-determined values represent the maximum measurement duration achievable without causing voltage distortion under various operating conditions. During real-time motor control, the controller directly retrieves these pre-computed values based on current operating parameters, eliminating the need for real-time optimization calculations and ensuring measurement windows never exceed distortion-free limits.
Solution Approach 2:
The patent dynamically adjusts current measurement window duration as a variable parameter based on real-time motor operating conditions such as speed, load, and PWM duty cycle. By changing the measurement window duration parameter adaptively rather than using fixed values, the system optimizes measurement accuracy for each operating point while staying within distortion-free boundaries. The controller selects from multiple pre-calculated duration values corresponding to different operating ranges.
3Measurement precision
If measurement time is increased to improve current measurement accuracy, then measurement precision is improved, but control response time is reduced
Solution Approach 1:
The patent pre-calculates and stores optimal current measurement window durations in lookup tables during system initialization or calibration phases. These pre-determined values represent the maximum measurement duration achievable without causing voltage distortion under various operating conditions. During real-time motor control, the controller directly retrieves these pre-computed values based on current operating parameters, eliminating the need for real-time optimization calculations and ensuring measurement windows never exceed distortion-free limits.
Solution Approach 2:
The patent dynamically adjusts current measurement window duration as a variable parameter based on real-time motor operating conditions such as speed, load, and PWM duty cycle. By changing the measurement window duration parameter adaptively rather than using fixed values, the system optimizes measurement accuracy for each operating point while staying within distortion-free boundaries. The controller selects from multiple pre-calculated duration values corresponding to different operating ranges.
Data Source
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AI summary
Methods and apparatus for controlling a three-phase electric motor by determining a duration of current measurement windows within a first pulse width modulation period for measuring motor current using a single shunt coupled to the motor. A duration of a first one of the current measurement windows can be adjusted by a time delta value to meet a minimum time to measure the motor current. A next PWM period can include compensation for the time delta value. In embodiments window adjustments are made by modifying the high state of a middle phase signal for phase signals to switches that energize the motor.