DC-DC Converter Voltage Control for Zero Current Fluctuation
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Solution Overview
Problem
In power supply devices with multiple power storage units and voltage conversion units, variations in output voltage occur due to dead time deviations in boost/buck DC-DC converters, especially when request power approaches zero, leading to significant voltage fluctuations when currents in multiple converters become close to zero.
Innovation Solution
A control method that generates commands to prevent simultaneous zero current passage in voltage conversion units by actively managing electric power flow between power storage units, using a command generation unit to control voltage conversion units and estimate state of charge, ensuring different current passages and directing power flow based on state of charge differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple voltage conversion units are used to increase power supply capacity, then the power supply capacity is improved, but output voltage variation increases when current passage approaches zero
Solution Approach 1:
The control device proactively manages current passage in voltage conversion units before output voltage variation occurs. By monitoring and controlling the current passage amounts, the system prevents the condition where multiple converters simultaneously operate near zero current, thereby preventing output voltage variation before it happens.
Solution Approach 2:
The control device continuously monitors the current passage amounts in each voltage conversion unit and adjusts their operation based on this feedback. When detecting that current passage is approaching zero in multiple units, the control device modifies the duty ratios or switching patterns to maintain minimum current flow, thus stabilizing the output voltage.
2Reliability
If dead time is provided in boost/buck DC-DC converter to prevent short circuit, then switching safety is improved, but duty cycle deviation occurs causing voltage variation
Solution Approach 1:
The control device monitors the actual current passage through the converter and compares it with the commanded duty cycle. It detects deviations caused by dead time effects and applies compensatory adjustments to the duty ratio commands, thereby maintaining accurate voltage control despite the presence of dead time for switching safety.
3Manufacturing precision
If feedback control is used to correct duty deviation, then voltage control accuracy is improved, but response delay occurs when current direction reverses
Solution Approach 1:
The control device anticipates current direction reversals by monitoring the operating state of the converters. Before the reversal occurs, it pre-adjusts the duty ratios or switching patterns to account for the upcoming change in current flow direction. This proactive adjustment eliminates the delay that would otherwise occur while the feedback control adapts to the new operating condition.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively suppresses output voltage variations by preventing simultaneous zero current passage in voltage conversion units, thereby stabilizing the output voltage and maintaining efficient power distribution across power storage units.
Implementation Method 1
each of the voltage conversion units includes a DC chopper circuit capable of performing bidirectional voltage conversion between a corresponding one of the power storage units and the electric power line
Data Source
AI summary
When request power required of a power supply device (1) by a driving force generation unit (3) is close to zero, a converter ECU (2) controls first and second converters (8-1, 8-2) to prohibit respective amounts of current passage in the first and second converters (8-1, 8-2) from simultaneously becoming close to zero. That is, when the request power is close to zero, the converter ECU (2) performs voltage control of the first converter (8-1) and sets an electric power control value for the second converter (8-2) subjected to current control (electric power control) to a nonzero value, such that electric power is supplied and received between the first and second converters (8-1, 8-2).