Voltage Command Correction for DC Bus Current Detection
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Solution Overview
Problem
Conventional power conversion devices face challenges in precise phase current detection on a DC bus conductor due to voltage command limits, especially during high-speed motor operation and high carrier frequencies, leading to reduced motor control precision and detection errors.
Innovation Solution
A power conversion device with a voltage command correcting mechanism that adjusts voltage commands for all three phases, ensuring line voltages between phases are equal to or greater than a predetermined value, and uses a half-cycle of a triangular wave carrier as a unit cycle to maintain current detection precision, even under adverse conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage command correction is applied to extend pulsed current flow time for detection, then phase current detection precision is improved, but voltage command limits are exceeded causing detection failure
Solution Approach 1:
The patent changes the parameter of voltage command correction by introducing a phase-specific correction amount calculation that considers the triangular wave carrier phase. Instead of uniform correction, the correction amount is dynamically adjusted based on the relationship between the voltage command phase and the triangular wave carrier phase, ensuring detection precision without exceeding voltage limits.
Solution Approach 2:
The patent implements dynamic correction amount determination that adapts to real-time operating conditions. The correction amount is calculated based on the instantaneous phase relationship between voltage commands and the triangular wave carrier, making the system responsive to changing motor speed and carrier frequency conditions while maintaining reliable detection.
2Measurement precision
If carrier frequency is increased to improve motor control precision, then motor control precision is improved, but pulsed current flow time is reduced causing detection failure
Solution Approach 1:
The patent addresses the carrier frequency effect by dynamically calculating correction amounts that compensate for the reduced pulse width at higher frequencies. The correction magnitude is adjusted based on the carrier phase relationship, effectively extending the detectable current flow duration without reducing the carrier frequency, thus maintaining both detection capability and motor control precision.
3Stability of the object's composition
If voltage command limits are enforced to maintain system stability, then system stability is maintained, but phase current detection becomes impossible under certain conditions
Solution Approach 1:
The patent resolves this contradiction by implementing a dynamic correction strategy that operates within voltage limits. The correction amount is calculated based on the phase relationship between voltage commands and the triangular wave carrier, allowing the system to adaptively extend current detection windows without violating voltage command limits, thus maintaining both stability and detection capability.
Data Source
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AI summary
In a power conversion device that includes a PWM converting means for generating a PWM pulse by comparing three-phase voltage commands with a triangular wave carrier signal, a power converter for converting between a DC voltage and a three-phase AC voltage by driving a switching element according to the PWM pulse, a current detecting means for detecting a pulsed current flowing through a DC bus conductor of a main circuit, and a voltage command correcting means for correcting three-phase voltage commands, which corrects the three-phase voltage commands so that a line voltage value between the maximum phase and an intermediate phase and a line voltage value between the intermediate phase and the minimum phase are each equal to or larger than a predetermined value, the maximum phase, intermediate phase, and minimum phase being determined in correspondence to momentary values of the three-phase voltage commands arranged in descending order, if the voltage command is outside an allowable upper limit or lower limit, not only the voltage command for the maximum phase and/or the minimum phase but also the voltage command for the intermediate phase are corrected. Accordingly, the inability to detect a current due to a restriction imposed by an upper limit or a lower limit for an output voltage is eliminated, and highly precise control of the power conversion device is achieved independently of the situation.