Soft-Switched Bidirectional Buck-Boost Converter Active Snubber
Solution Overview
Problem
High-frequency bidirectional buck-boost converters face significant switching losses due to reverse-recovery-related issues in semiconductor switches, particularly in high-voltage applications, where conventional hard-switching methods are inefficient and costly, and existing solutions like SiC or GaN switches are not economically viable or reliable.
Innovation Solution
The implementation of active snubber methods that achieve soft-switching in all semiconductor switches by controlling the turn-off rate of rectifiers and utilizing zero-voltage switching (ZVS) and zero-current switching (ZCS) techniques, reducing switching losses and enabling the use of slower antiparallel diodes at high frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional hard-switching methods are used in high-voltage bidirectional buck-boost converters, then the converter can operate at high power levels, but switching losses are significant and efficiency is poor
Solution Approach 1:
The active snubber circuit performs preliminary action by controlling the turn-off rate of rectifiers before the main switches operate, and by creating conditions for zero-voltage switching of power switches. This preliminary preparation of switching conditions reduces subsequent switching losses significantly.
Solution Approach 2:
The active snubber circuit acts as an intermediary between the power switches and the rectifiers, mediating the switching transitions. It controls the current turn-off rate of rectifiers and creates zero-voltage conditions for power switches, thereby reducing switching losses without requiring expensive SiC or GaN devices.
2Loss of energy
If SiC or GaN switches are used to reduce reverse-recovery losses, then switching losses are reduced, but cost increases and reliability data is insufficient
Solution Approach 1:
The invention uses conventional, well-tested silicon rectifiers and switches instead of expensive SiC or GaN devices. The active snubber circuit compensates for the limitations of conventional devices, allowing them to operate reliably at high frequencies without requiring costly alternative materials.
Solution Approach 2:
The active snubber circuit changes the operating parameters of the rectifiers by controlling their turn-off rate. This parameter control reduces reverse-recovery losses and enables conventional devices to operate efficiently at high frequencies, eliminating the need for expensive wide-bandgap semiconductors.
3Device complexity
If the current turn-off rate of rectifiers is not controlled, then the circuit is simpler, but reverse-recovery losses increase significantly
Solution Approach 1:
The active snubber circuit serves as an intermediary that controls the current turn-off rate of rectifiers. It introduces controlled complexity through the snubber components and control logic, which in turn eliminates the much larger complexity and cost associated with using expensive SiC or GaN devices.
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 approach significantly reduces switching losses and improves efficiency and EMI performance, allowing for the use of cost-effective semiconductor switches with slower antiparallel diodes at high frequencies, enhancing the overall performance of bidirectional buck-boost converters.
Implementation Method 1
reverse-recovery-related losses in the rectifiers
Implementation Method 2
zero-voltage switching in a power-regulating switch
Implementation Method 3
achieves soft-switching of the snubber switch by turning it off at zero current
Data Source
AI summary
A bidirectional buck-boost converter includes at least one soft-switching cell to reduce switching losses by providing soft-switching of all semiconductor devices. A soft-switching cell comprises an active switch coupled in series with an inductor, a two-winding transformer, and a reset-voltage circuit. The soft-switching cells enable the buck and boost rectifiers to turn off with a controlled turn-off rate of their current to minimize their reverse-recovery losses, the power-controlling buck and boost switch to turn on with zero-voltage switching (ZVS), and the switch of the soft-switching cell to turn off with zero-current switching (ZCS).