Three-Level LLC Converter with Fifth Switch for High Voltage
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Solution Overview
Problem
Conventional switch-mode power supplies with three-level LLC circuits face challenges in efficiently handling high output voltages, such as 800 V, due to high conduction losses in switches and inefficiencies in medium to high switching frequencies, especially with 1200 V rated Si devices.
Innovation Solution
A switch-mode power supply design incorporating a three-level LLC circuit with a fifth switch to short circuit switches Q3 and Q4, and a control circuit with a voltage-controlled oscillator (VCO) and logic gates for zero-voltage switching (ZVS), reducing conduction losses and optimizing transformer design for efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a conventional half-bridge or full-bridge LLC converter is used with 1200 V rated Si devices, then the power supply can handle high output voltages, but conduction losses increase and efficiency decreases at medium and high switching frequencies
Solution Approach 1:
The power supply circuit is divided into two independent half-bridges (first half-bridge with switches Q1-Q2, second half-bridge with switches Q3-Q4), each handling a portion of the power conversion. This segmentation allows each switch to operate at lower voltage stress while maintaining the ability to handle high output voltages through the combined action of both half-bridges, thereby reducing conduction losses.
Solution Approach 2:
The patent combines two half-bridge circuits into a unified three-level LLC converter architecture. By merging the functionality of both half-bridges and coordinating their operation through the control circuit, the system achieves high voltage handling capability while utilizing lower voltage-rated switches (600-650 V) that exhibit lower conduction losses compared to 1200 V switches.
2Temperature
If 1200 V rated Si devices are used for switching, then the power supply can operate at high output voltages, but switching efficiency decreases at medium and high switching frequencies
Solution Approach 1:
The patent changes the voltage rating parameter of the switching devices from 1200 V to 600-650 V, which fundamentally alters the conduction characteristics and reduces on-resistance. This parameter change enables the use of switches with lower conduction losses while the three-level topology maintains the required voltage handling capability through its circuit architecture, thereby improving switching efficiency at medium and high frequencies.
3Power
If asymmetrical control is used in three-level LLC topology, then a high step-down ratio can be achieved with lower transformer ratio, but RMS current through certain switches increases
Solution Approach 1:
The patent employs asymmetrical control where the two half-bridges operate with different duty cycles and timing. The first half-bridge and second half-bridge are controlled independently to optimize current distribution. This asymmetrical operation allows achievement of high step-down ratios with lower transformer ratios while managing switch current stresses through coordinated unequal duty cycles.
Solution Approach 2:
The control circuit dynamically adjusts the switching patterns and duty cycles of the two half-bridges based on operating conditions. By making the control parameters dynamic rather than fixed, the system can optimize the trade-off between step-down ratio and RMS current losses in real-time, adapting to different load and input 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 reduces conduction losses and improves efficiency by allowing reduced transformer ratios and ZVS operation for all primary switches, enhancing the power supply's performance with high voltage inputs like 800 V.
Implementation Method 1
a control circuit. The control circuit includes a voltage-controlled oscillator (VCO) and multiple logic gates and flip-flops coupled to operate the at least four switches with zero-voltage switching (ZVS)
Data Source
AI summary
A switch-mode power supply includes a pair of input terminals, a pair of output terminals, and at least four switches coupled in a three-level LLC circuit arrangement between the pair of input terminals and the pair of output terminals. First and second ones of the at least four switches define a first half-bridge and third and fourth ones of the at least four switches define a second half-bridge. The power supply also includes a fifth switch coupled across the second switch and the third switch to short circuit the second switch and the third switch when the fifth switch is closed, and a control circuit. The control circuit includes a voltage-controlled oscillator (VCO) and multiple logic gates and flip-flops coupled to operate the at least four switches with zero-voltage switching (ZVS).