Inverter Current Detection Correction for Zero-Phase Noise
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Solution Overview
Problem
Conventional three-phase voltage-type inverters struggle with accurate current detection and control due to zero-phase noise components, leading to torque ripple, vibration, and noise in AC rotating electric machines, especially when voltage command amplitudes are high.
Innovation Solution
The electric-power conversion apparatus employs a three-phase inverter configuration where current detection values are corrected based on effective voltage vectors, shifting voltage commands to align with PWM carrier signals, allowing accurate detection and control without zero-phase noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current detection is performed in all three phases simultaneously, then measurement precision is improved, but zero-phase noise components interfere with control accuracy
Solution Approach 1:
The patent extracts and eliminates zero-phase noise components from current detection values through coordinate transformation. By transforming three-phase current values into two-axis coordinate systems (stationary or rotating), the method separates and removes the zero-phase component that causes noise, while preserving the useful current information for control.
Solution Approach 2:
The patent changes the dimensional representation of current values by performing coordinate transformation from three-phase coordinates to two-axis coordinates. This dimensional reduction eliminates the zero-phase noise component while maintaining the essential current information needed for precise control.
2Power
If voltage command amplitude is increased, then power output is improved, but current detection accuracy deteriorates due to insufficient lower arm on-time
Solution Approach 1:
The patent performs preliminary coordinate transformation on current detection values before using them for control. By pre-processing the current values through transformation to two-axis coordinates, the system eliminates zero-phase noise that would otherwise deteriorate detection accuracy at high voltage command amplitudes.
Solution Approach 2:
The patent implements feedback control using transformed current values. The coordinate-transformed current detection values, free from zero-phase noise, are fed back to the control system to generate accurate voltage commands, enabling precise control even at high power output levels.
3Ease of operation
If PWM control is applied to all three phases, then voltage control is improved, but switching device on-time becomes insufficient for accurate current detection
Solution Approach 1:
The patent extracts useful current information from phases with insufficient on-time by transforming to two-axis coordinates. This transformation allows the system to derive accurate current values even when direct detection in certain phases is limited by PWM switching constraints.
Solution Approach 2:
The patent makes the control system universally applicable to all three phases through coordinate transformation. Instead of treating each phase independently with limited on-time, the transformation creates a unified current representation that maintains accuracy across all phases regardless of individual switching constraints.
Data Source
Figure 1
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Figure 4A~4C
AI summary
Voltage commands of respective phases are substantially equally shifted in such a way that a maximum-phase voltage command coincides with the maximum value of a PWM carrier signal and are compared with the PWM carrier signal, so that a voltage is controlled; in addition to that, a current detection value corresponding to the phase where the lower-arm switching device is turned on is corrected based on a current detection value corresponding to the phase where the upper-arm switching device is turned on.