DC/DC Converter Phase Shift Control for Switching Loss Reduction
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Solution Overview
Problem
DC/DC converters, particularly dual active bridge types, face significant switching losses due to the lack of zero voltage switching (ZVS) in light load conditions, leading to inefficiencies and increased temperature rises.
Innovation Solution
A DC/DC converter design incorporating a primary and secondary side converter with full bridge circuits, capacitors, and a control unit that adjusts switching control phases and ON-duty cycles to minimize switching losses by matching turning ON periods and phases of semiconductor switching elements, even when ZVS is not achieved, utilizing leakage inductance and capacitors to reduce voltage applied to switching elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional switching control is used in light load conditions, then the converter can operate, but switching loss becomes large due to lack of zero voltage switching
Solution Approach 1:
The invention changes the switching control parameters by introducing phase shift control between primary and secondary sides. By adjusting the phase difference θ between the switching signals of the primary full-bridge circuit and secondary full-bridge circuit, the converter achieves soft switching conditions even in light load cases, thereby reducing switching loss and improving conversion efficiency
Solution Approach 2:
The invention implements dynamic switching control where the ON-duty ratios and phase shifts of switching elements are continuously adjusted based on load conditions. The control unit dynamically modifies the switching timing and duration to maintain zero voltage switching conditions across varying load levels, preventing large switching losses in light load scenarios
2Reliability
If flyback period is lengthened to achieve soft start, then startup is smoother, but zero voltage switching cannot be achieved in all switching elements
Solution Approach 1:
The invention uses dynamic phase shift control to adapt the switching timing to different operational states. During soft start, the phase difference is adjusted to achieve gradual power transfer, while in steady-state operation, the phase shift is optimized to ensure zero voltage switching for all elements, thus eliminating switching loss without compromising soft start performance
3Loss of energy
If magnetic excitation energy is increased to ensure ZVS, then switching elements achieve zero voltage switching, but converter size and complexity increase
Solution Approach 1:
Instead of increasing magnetic excitation energy by adding larger reactors or capacitors, the invention changes the control parameters (phase shift θ and ON-duty ratios) to achieve zero voltage switching. This parameter-based approach reduces switching loss without increasing the physical size or structural complexity of the converter components
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 effectively reduces switching losses by half, improving efficiency and suppressing local temperature rises, while maintaining seamless power transmission direction switching and minimizing output power fluctuations.
Implementation Method 1
the magnetic excitation energy accumulated in a reactor connected with a switching element to be turned ON becomes low
Implementation Method 2
a primary side converter that has a primary side reactor, plural primary side semiconductor switching elements, and plural primary side capacitors which are respectively connected in parallel with the plural primary side semiconductor switching elements
Data Source
AI summary
A control unit 10 performs switching control of IGBTs 5a to 5d, 8b, and 8d, makes IGBTs 8a and 8c an OFF state, changes ON-duty of the IGBTs 5a to 5d, 8b, and 8d, and thereby adjusts first output power output from a secondary side converter 200. The IGBTs 5b, 5c, and 8b are synchronized together and switched in a prescribed cycle, and the IGBTs 5d and 8d are switched in a state where a phase is shifted by half a cycle with respect to the IGBTs 5b, 5c, and 8b (in a state where the phase is shifted by 180 degrees).