Buck-Boost Converter Control for Stable EV Charging Transitions
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Solution Overview
Problem
Conventional buck-boost converters in charging stations experience high ripple and overshoot during transitions between buck, buck-boost, and boost modes, leading to excessive EV charging current and premature termination of charging sessions.
Innovation Solution
Implementing a feed-forward control method in a four-switch buck-boost converter to adjust buck and boost duty cycles instantaneously based on predefined values during transitions between operating modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional control methods are used during transitions between buck, buck-boost, and boost modes, then the converter can operate in all modes, but the controlled current exhibits high ripple and overshoots the controlled current value
Solution Approach 1:
The patent applies preliminary action by detecting the voltage difference between source and target batteries and proactively determining whether to transition between operating modes before the transition occurs. The controller predicts the upcoming mode change and prepares the duty cycle adjustments in advance, specifically using feed-forward control to calculate the required duty cycle changes before the actual transition, thereby preventing current ripple and overshoot that would occur with reactive control methods
Solution Approach 2:
The patent implements feedback control by continuously monitoring the actual charging current and comparing it with the reference current. The controller uses this feedback information to adjust the duty cycles of the buck and boost converters, ensuring that the charging current remains stable during mode transitions. The feedback mechanism allows the system to correct any deviations from the desired current profile in real-time
2Productivity
If the converter operates in buck-boost mode with voltage difference between 20-30, then it can continue charging, but transitions between modes cause high ripple and current overshoot leading to premature termination
Solution Approach 1:
The controller performs preliminary detection of voltage differences and proactively determines the optimal operating mode before transitions occur. By calculating the required duty cycle adjustments in advance using feed-forward control, the system prevents current overshoot that would trigger premature charging termination, thereby ensuring charging continuity and reliability
Solution Approach 2:
The patent implements smooth mode transitions by rapidly adjusting the duty cycles of the buck and boost converters during transitions. The feed-forward control mechanism calculates the exact duty cycle changes needed and applies them immediately, allowing the system to skip through the problematic transition period quickly without sustaining high ripple or overshoot conditions that would cause charging session termination
Data Source
AI summary
A system for controlling a charging current while transferring energy from a source battery to a target battery in an electric vehicle (EV) comprises a four-switch buck-boost converter configured to couple to the source battery and the target battery and configured to operate in (i) a buck mode, in which voltage Vg across the source battery is higher than voltage VEV across the target battery, (ii) a boost mode, in which the voltage Vg is lower than the voltage VEV, and (iii) a buck-boost mode, in which the buck-boost converter operates between the buck mode and the boost mode, and in which the voltages VEV and Vg differ less by a predetermined amount, and a controller configured to, when transitioning to or from the buck-boost mode, instantaneously adjust at least one a buck duty cycle dbuck or a boost duty cycle dboost according to a predefined value.