DC-DC Converter with Capacitive Coupling for Light Load Efficiency
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Solution Overview
Problem
Existing DC-DC converters for electric vehicle on-board chargers, such as LLC and ZVS SRC, face inefficiencies at light loads due to high primary winding currents and magnetizing currents, leading to poor light-load efficiency and increased conduction losses.
Innovation Solution
A DC-DC converter with a series resonant topology that uses capacitive coupling between transformers and a control unit to manage phase-shifted alternating voltages, allowing for constant switching frequency operation and reduced RMS currents, thereby improving efficiency across a wide range of power and voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If LLC topology operates at variable frequency, then voltage adaption is achieved across battery voltage range, but EMI filter design complexity and transformer design complexity increase
Solution Approach 1:
The patent uses dynamic frequency adjustment to maintain resonant operation across the entire battery voltage range. By continuously adapting the switching frequency to match the resonant frequency at each operating point, the system achieves wide voltage adaption while maintaining simple filter design, as the resonant topology naturally suppresses EMI at the operating frequency
Solution Approach 2:
The patent employs periodic resonant oscillations at the tuned frequency to transfer power efficiently across different voltage levels. The periodic nature of the resonant operation allows for predictable EMI characteristics that can be filtered with simpler circuits compared to variable frequency PWM schemes
2Adaptability or versatility
If magnetizing current is increased to cover required battery voltage range in LLC, then voltage adaption is achieved, but conduction losses increase at light load
Solution Approach 1:
The patent dynamically adjusts the resonant frequency to maintain optimal magnetizing current levels across different load conditions. At light load, the frequency is adjusted to reduce magnetizing current, thereby reducing conduction losses while still maintaining the ability to cover the required battery voltage range when needed. The control unit manages this by adapting the frequency based on the detected load and voltage conditions
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
The solution achieves lower primary winding RMS currents and improved efficiency at light loads, reducing conduction losses and simplifying EMC filter requirements, while maintaining high efficiency throughout the operating range.
Implementation Method 1
a transformer, arranged to supply a current to a primary winding of the transformer and to supply a current to a secondary winding of the transformer
Implementation Method 2
one of the output terminals of the first inductive element being capacitively coupled to one of the output terminals of the second inductive element
Implementation Method 3
A DC-DC converter with a series resonant topology that uses capacitive coupling between transformers and a control unit to manage phase-shifted alternating voltages, allowing for constant switching frequency operation and reduced RMS currents
Data Source
AI summary
A DC-DC converter comprises at least a first and a second inductive element. Each inductive element comprises a transformer (312, 322), input terminals (314, 324, 315, 325) and output terminals (316,326, 317, 327). A switching circuit (2) is arranged to supply a first alternating voltage to input terminals (314, 315) of the first inductive element, and a second alternating voltage to input terminals of the second inductive element (31, 32). A rectification circuit (4) is arranged to rectify a first and a second output voltage arising at output terminals (316, 317) of the first and second inductive elements (31, 32), respectively. One of the output terminals of the first inductive element (31) is capacitively coupled to one of the output terminals of the second inductive element (32).