Motor Inverter Current Detection Using Low-Pass Filtering
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Solution Overview
Problem
Conventional motor drive devices face issues with large detection errors in the effective value of motor drive current due to the dependency on high-speed ADC performance, leading to inaccurate current detection.
Innovation Solution
A control device and method that utilizes a low-pass filter and averaging processing to detect current through an electric resistance unit, reducing dependency on ADC performance by using a low-pass filter with a specific frequency characteristic and executing averaging processing on multiple current detections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-speed ADC is used to accurately detect current, then detection accuracy of effective value of motor drive current is improved, but device complexity and cost increase
Solution Approach 1:
The patent introduces a low-pass filter as an intermediary component between the current detection unit and the ADC. This filter removes high-frequency PWM components from the current detection signal before it reaches the ADC, allowing accurate effective value detection with a lower-performance ADC. The low-pass filter acts as a mediator that prepares the signal for processing by a less complex detection unit.
Solution Approach 2:
The patent performs preliminary filtering of the current detection signal using a low-pass filter before the ADC processes it. By removing PWM frequency components in advance, the system enables accurate effective value detection without requiring a high-speed ADC, thus reducing device complexity while maintaining measurement precision.
2Measurement precision
If a high-speed ADC is used to detect current accurately, then detection precision is improved, but dependency on current detection unit performance increases
Solution Approach 1:
The low-pass filter serves as a protective intermediary that decouples the detection accuracy from the ADC performance requirements. By filtering out PWM components before detection, the system reduces its dependency on the current detection unit's performance, making the effective value detection more reliable and less sensitive to variations in ADC quality.
Solution Approach 2:
The patent creates a filtered version of the current signal that contains only the relevant low-frequency components for effective value calculation. This copied and processed signal can be accurately measured by a lower-performance ADC, reducing the system's dependency on high-performance detection units while maintaining measurement reliability.
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
Accurately detects the effective value of power supply current while minimizing reliance on current detection unit performance, improving stability and followability in current detection.
Implementation Method 1
a low-pass filter 4 having a frequency characteristic corresponding to a time constant τ
Implementation Method 2
an averaging processing unit 25 that executes averaging processing on a current value of a current Ia detected by the current detection unit 24 at a plurality of current detection times
Implementation Method 3
current flowing through an electric resistance unit connected between a DC power supply unit and the N-phase inverter
Data Source
AI summary
A control device controls an N-phase inverter when N is an integer of three or more. The control device includes a low-pass filter, a current detection unit, and an averaging processing unit. The low-pass filter has a frequency characteristic corresponding to a time constant. The current detection unit detects current flowing through an electric resistance unit connected between a DC power supply unit and the N-phase inverter via the low-pass filter. The averaging processing unit executes averaging processing on a current value of the current detected by the current detection unit at a plurality of current detection times.