Onboard Charger DC-DC Control for Low-Oscillation Battery Charging
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Solution Overview
Problem
Existing DC-DC converters in electric and hybrid vehicles generate oscillating currents that can prematurely age lithium-ion batteries, and existing control methods struggle to maintain these oscillations below a predefined threshold, especially in resonant converters with pulse frequency modulation control, leading to resonance issues and slow response times.
Innovation Solution
A control device comprising a low-pass filter, corrective controller, harmonic compensator, control unit, and drive unit forms a control loop that rapidly sets initial operating limits and gradually increases them to stabilize the output current, using PFM or PWM signals to minimize oscillations and ensure quick regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a resonant DC-DC converter with pulse frequency modulation is used, then conversion efficiency is improved, but output current oscillations increase causing battery aging
Solution Approach 1:
The patent implements a feedback control mechanism where the output current is continuously monitored and fed back to the control unit. The control unit compares the actual output current with the reference current and adjusts the switching frequency of the resonant converter accordingly, enabling automatic compensation for current oscillations while maintaining high conversion efficiency
Solution Approach 2:
The patent dynamically changes the operating parameters of the resonant converter, specifically the switching frequency, to optimize performance. By adjusting the switching frequency based on load conditions and output current feedback, the system maintains high efficiency while suppressing harmful current oscillations that would otherwise cause battery aging
2Speed
If the switching frequency is increased to improve regulation response, then regulation speed is improved, but oscillations are amplified
Solution Approach 1:
The patent employs dynamic switching frequency adjustment rather than fixed frequency operation. The control unit continuously adapts the switching frequency based on real-time feedback from the output current, enabling fast regulation response when needed while automatically reducing frequency to suppress oscillations, thus resolving the contradiction between speed and stability
Solution Approach 2:
The patent utilizes periodic switching action with variable period (frequency). By controlling the switching frequency dynamically and using resonant circuits that operate at specific resonant frequencies, the system achieves fast regulation through periodic control while avoiding frequency ranges that would amplify oscillations
3Device complexity
If conventional controllers are used, then device complexity is reduced, but ability to control high-frequency oscillations deteriorates
Solution Approach 1:
The patent introduces resonant circuits as intermediary elements between the conventional controller and the power conversion process. These resonant circuits naturally filter high-frequency oscillations through their frequency-selective properties, allowing simple controllers to achieve reliable oscillation control without requiring complex control algorithms or additional filtering components
Data Source
AI summary
A control device for controlling a DC-DC converter of an electric charger for an electric or hybrid motor vehicle, including in particular a corrective controller, a harmonic compensator and a control unit configured so as, when the control device starts, to periodically send to the corrective controller and to the harmonic compensator a lower operating limit and an upper operating limit, each having an initial value imposing an output current of the DC-DC converter whose intensity is close to zero and less than 500 mA, and a ramp increase to control the oscillations of the control signal supplied by the control device to the DC-DC converter.