Three-Level LLC Converter for 800 V Input Voltage Stress
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Solution Overview
Problem
Conventional switch-mode power supplies with three-phase inputs face challenges in designing downstream DC-DC converters due to high output voltages from Vienna rectifier topologies, leading to inefficiencies in high-frequency operations with 1200 V rated Si devices.
Innovation Solution
A three-level LLC circuit topology with 600-650 V rated devices and asymmetrical control is used, coupled with a voltage doubler power factor correction (PFC) circuit and a control circuit for zero-voltage switching (ZVS) to reduce conduction losses and optimize transformer design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a conventional high efficiency half-bridge or full-bridge LLC converter is used with 1200 V rated Si devices, then the converter can handle high input voltages, but the efficiency decreases at medium and high switching frequencies
Solution Approach 1:
The patent divides the single high-voltage switching stage into two lower-voltage switching stages using a three-level topology. The input voltage is split across two series-connected capacitors, allowing each switch to operate at approximately half the input voltage (600-650 V rated devices instead of 1200 V), which reduces conduction losses and enables efficient operation at medium and high switching frequencies.
Solution Approach 2:
The patent introduces a third voltage level by adding a midpoint connection between two series capacitors, transforming the conventional two-level switching into a three-level switching architecture. This dimensional change in voltage levels allows for lower voltage stress on individual switches while maintaining the ability to handle high input voltages.
2Power
If asymmetrical control is used in three-level LLC topology, then a high step-down ratio is achieved with lower transformer ratio, but the control complexity increases
Solution Approach 1:
The patent implements asymmetrical control where the two half-bridges operate with different duty cycles. One half-bridge operates with a duty cycle greater than 50% while the other operates with a duty cycle less than 50%, allowing the converter to achieve high step-down ratios with lower transformer turns ratios. This asymmetrical operation enables flexible voltage conversion ratios while maintaining continuous current flow through the resonant tank.
3Use of energy by moving object
If Vienna rectifier topology is used for power factor correction, then efficient PFC is achieved, but the output voltage becomes around 800 Volts which makes downstream DC-DC converter design difficult
Solution Approach 1:
The patent changes the operating parameters of the downstream DC-DC converter to accommodate the 800 V input from the Vienna rectifier. By using three-level LLC topology with split capacitors, the converter is designed to operate with capacitors rated at approximately 400-450 V each, allowing the high-voltage input to be divided into manageable voltage levels that simplify the design of downstream 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
This configuration achieves high efficiency and reduced conduction losses, allowing for efficient operation at medium and high switching frequencies with lower transformer ratios, suitable for 800 V inputs, and adaptable for both low and high line voltage ranges.
Implementation Method 1
a voltage doubler power factor correction (PFC) circuit coupled between the pair of input terminals and the three-level LLC circuit
Implementation Method 2
a control circuit coupled to operate the at least four switches to supply the DC voltage output to the load
Data Source
AI summary
A switch-mode power supply includes a pair of input terminals for receiving an alternating current (AC) or direct current (DC) voltage input from an input power source, a pair of output terminals for supplying a direct current (DC) voltage output to a load, 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. The power supply also includes a voltage doubler power factor correction (PFC) circuit coupled between the pair of input terminals and the three-level LLC circuit, and a control circuit coupled to operate the at least four switches to supply the DC voltage output to the load.