Inverter Current Detection During Overmodulation
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Solution Overview
Problem
Existing inverter control methods fail to achieve stable current detection during overmodulation control using a single current sensor, leading to instability in inverter control.
Innovation Solution
An inverter apparatus with a current detection unit that calculates γ-axis and δ-axis currents using advanced arithmetic expressions, allowing for stable current detection even during overmodulation control, by employing a first current calculation section for γ-axis current and a second current calculation section for δ-axis current, and optimizing processing during varying duty cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If overmodulation control is performed with switching elements kept on/off over one control cycle, then voltage utilization rate is improved, but current detection accuracy deteriorates
Solution Approach 1:
The patent pre-calculates and stores γ-axis current arithmetic expressions that account for overmodulation conditions. By preparing these expressions in advance, the system can accurately detect current even when switching elements remain on/off for extended periods during overmodulation control, thus resolving the contradiction between maintaining high voltage utilization and preserving current detection accuracy.
2Device complexity
If one current sensor is used to detect three phase currents, then device complexity is reduced, but measurement precision deteriorates during overmodulation control
Solution Approach 1:
The patent introduces γ-axis current arithmetic expressions as an intermediary computational mechanism. These expressions enable a single current sensor to accurately derive three-phase current information during overmodulation control by mathematically compensating for the limitations of single-sensor detection, thus maintaining measurement precision while reducing device complexity.
3Measurement precision
If complex arithmetic processing is performed for current detection, then measurement precision is improved, but use of energy increases
Solution Approach 1:
The patent pre-calculates and stores γ-axis current arithmetic expressions during system initialization or offline preparation. By performing the computationally intensive work in advance and storing the results, the system reduces real-time processing requirements during operation, thereby maintaining high measurement precision while minimizing energy consumption during actual motor control operations.
Data Source
AI summary
An object of the present invention is to achieve stable inverter control by means of current detection using one current sensor in all of periods in which overmodulation control is performed. An inverter controller includes a γ-axis current calculation section that holds, in advance, a γ-axis current arithmetic expression including a direct current as a parameter, and calculates a γ-axis current using a direct current detected by a current sensor for the γ-axis current arithmetic expression.