Power Converter Zero Cross Voltage Error Correction
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Solution Overview
Problem
Conventional methods for correcting voltage errors caused by dead time in electric power converters struggle to accurately switch polarity at the zero cross point of output phase current, leading to rotational irregularities and degraded performance, especially at low frequency AC outputs and low-speed rotary machine operations.
Innovation Solution
An electric power converter with a voltage-command correction unit that calculates and applies a correction voltage to the AC voltage command based on the zero cross timing of the output current, ensuring the correction voltage has the same polarity as the output current around the zero cross point, thereby reducing voltage errors and improving rotational stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dead time is introduced to prevent simultaneous conduction of upper and lower arm power devices, then short circuit prevention is improved, but voltage error between command and actual output increases
Solution Approach 1:
The patent implements feedback control by detecting the output phase current polarity and using it to dynamically adjust the voltage command polarity. The current detection unit monitors the actual current flow direction, and this information is fed back to the control unit which then corrects the voltage command to compensate for dead-time effects, ensuring accurate voltage output while maintaining short circuit protection.
Solution Approach 2:
The patent changes the parameter being controlled from fixed voltage command to dynamic voltage command with polarity adjustment. By detecting current polarity and adjusting the voltage command polarity accordingly, the system adapts to varying operating conditions and compensates for dead-time induced errors, transforming a static control approach into a dynamic one that maintains accuracy across different load conditions.
2Manufacturing precision
If voltage correction is applied near current zero cross point, then voltage error correction is improved, but polarity detection accuracy deteriorates due to chattering and small current magnitude
Solution Approach 1:
The patent applies preliminary action by proactively adjusting the voltage command polarity before the actual polarity switch occurs at the zero cross point. By detecting when current magnitude falls below a threshold (indicating approach to zero cross), the system preemptively switches the correction voltage polarity, avoiding the chattering problem that would occur if waiting for exact zero crossing detection.
Solution Approach 2:
The patent introduces an intermediary threshold value as a mediator between the current detection and polarity switching. Instead of directly responding to the noisy zero-crossing point, the system uses a current magnitude threshold as an intermediary signal that indicates when to switch polarity, filtering out the chattering effects and providing a stable control signal.
3Ease of operation
If conventional polarity detection methods are used near zero cross point, then detection simplicity is maintained, but rotational stability deteriorates due to polarity switching errors
Solution Approach 1:
The patent replaces the mechanical/physical approach of direct current polarity sensing with an electrical/control-based approach using threshold comparison and command voltage adjustment. Instead of relying on precise mechanical switching or complex sensing circuits, the system uses simple threshold-based detection and electrical signal processing to achieve stable polarity control, substituting physical complexity with control intelligence.
Data Source
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AI summary
For providing an electric power converter capable of outputting an AC power just as an AC power command from an electric-power conversion unit by accurately correcting a voltage error caused by a dead time near a zero cross point of an output current, a voltage-command correction unit provided between the electric-power conversion unit and a voltage-command calculation unit provides a predetermined current range including the zero level for the detected output current, and, at a first clock time when the output current enters from outside to inside of the current range, sets a clock time for switching the polarity of the correction voltage that corrects the AC voltage command calculated and output by the voltage-command calculation unit to the zero cross timing of the output current based on the first clock time and the frequency f (and furthermore, the output current), that is, switches the polarity of the correction voltage to correct the voltage error caused by the dead time at the zero cross point of the output current, thereby making a configuration capable of correcting the AC voltage command with the correction voltage with the same polarity as the polarity of the output current around the zero cross point of the output current.