Power Converter Dead Time Control for Zero Crossing Detection Accuracy
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Solution Overview
Problem
Power converting apparatuses face malfunctions due to incorrect zero crossing detection caused by noise in alternating-current power, leading to increased losses and harmonic components in the power-supply current, especially when using low-pass filters that introduce signal transmission delays.
Innovation Solution
A power converting apparatus with a bridge circuit, current detecting unit, zero crossing detecting unit, and control unit that sets longer dead times for switching based on voltage polarity changes, allowing precise control of switching elements to prevent malfunctions and reduce noise-related errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a low-pass filter is used to remove noise from alternating-current power, then noise removal is improved, but signal transmission delay increases causing zero crossing detection delay
Solution Approach 1:
The control unit predicts the zero crossing timing by extrapolating from the detected voltage polarity and signal characteristics, performing the zero crossing detection in advance rather than waiting for the actual zero crossing point. This preliminary action compensates for the delay introduced by the low-pass filter.
Solution Approach 2:
The control unit acts as an intermediary between the low-pass filter output and the switching element control, introducing a predictive calculation layer that translates the delayed filter output into accurate zero crossing timing information for switching control.
2Ease of operation
If zero crossing detection is performed based on voltage polarity changes, then switching control is simplified, but malfunctions occur due to noise-induced false zero crossing detection
Solution Approach 1:
The control unit continuously monitors the voltage polarity and compares it with the predicted zero crossing timing, using feedback from the actual signal characteristics to validate and adjust the predicted timing, thereby preventing false detection caused by noise.
Solution Approach 2:
The control unit applies preliminary anti-action by predicting the true zero crossing timing in advance and using this prediction to prevent false switching operations that would result from noise-induced false zero crossing detection.
3Reliability
If dead time is set for switching elements, then switching malfunctions are prevented, but switching response speed decreases
Solution Approach 1:
The control unit determines the optimal dead time duration in advance based on the predicted zero crossing timing and system characteristics, setting the dead time before the actual switching operation occurs. This preliminary determination allows for optimized dead time that maintains reliability without excessive response delay.
Data Source
AI summary
A power converting apparatus includes: a bridge circuit that includes at least two legs each including switching elements connected in series, and converts an alternating-current voltage output from an alternating-current power supply into a direct-current voltage; a power-supply current detecting unit that detects a current from the alternating-current power supply; a zero crossing detecting unit that detects a voltage polarity of the alternating-current power supply; and a control unit that controls ON and OFF of the switching elements depending on outputs of the power-supply current detecting unit and the zero crossing detecting unit, in which a dead time that is set for switching and includes a change in the voltage polarity of the alternating-current power supply is longer than a dead time that is set for switching and does not include a change in the polarity.