Bi-Directional AC/DC Converter ZVT Cell for Soft Switching
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Solution Overview
Problem
Existing AC/DC converters lack bi-directional power delivery capability and do not have a blocking diode to prevent circulation current, leading to inefficiencies and switching losses.
Innovation Solution
Integration of a Zero Voltage Transient (ZVT) cell into bi-directional AC/DC converters, utilizing high and low switching frequency MOSFETs or IGBTs, diodes, capacitors, and inductors, with modified totem-pole modulation techniques to achieve soft switching and prevent short circuits, enabling bi-directional power flow without duty cycle jumping or switching loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional AC/DC converters use standard switching circuits, then the circuit structure is simple, but switching loss occurs and bi-directional power delivery is not achieved
Solution Approach 1:
The converter circuit is divided into functional modules including a bridge circuit with four arms, a ZVT cell with specific components (capacitor C1, inductor L1, diodes D1-D4, switches S1-S4), and control circuitry. This segmentation allows each module to perform its specific function optimally while reducing overall switching loss through coordinated operation.
Solution Approach 2:
The ZVT cell acts as an intermediary between the bridge circuit and the load, providing zero-voltage switching conditions for the main switches. The capacitor C1 and inductor L1 in the ZVT cell create resonant conditions that enable soft switching, eliminating switching loss without requiring complete redesign of the power conversion topology.
2Stability of the object's composition
If conventional modulation methods are used, then the control is simple, but duty cycle jumping occurs at zero-crossing points
Solution Approach 1:
The modulation method dynamically adjusts the switching patterns of different arms based on the AC line cycle phase. During positive half-cycles, arms A and B are activated with specific duty cycles, while during negative half-cycles, arms C and D are activated. This dynamic switching strategy eliminates duty cycle jumping at zero-crossing points by ensuring continuous, smooth transitions between half-cycles.
Solution Approach 2:
The control circuit implements periodic switching patterns synchronized with the AC line frequency. Each arm is activated for specific durations during each half-cycle, with the switching patterns repeating periodically. This periodic action ensures stable duty cycles throughout the AC cycle, including at zero-crossing transitions, by maintaining consistent timing relationships.
3Reliability
If blocking diodes are not used, then the circuit is simpler, but circulation current cannot be prevented
Solution Approach 1:
The circuit uses synchronous rectification where the body diodes of the MOSFETs in the bridge circuit perform the blocking function that would otherwise require separate blocking diodes. The controlled switching of the MOSFETs ensures that current flows in the correct direction during each half-cycle, and the body diodes naturally block reverse current, eliminating the need for additional blocking diode 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 provides soft switching for all switches, eliminating switching loss and enabling bi-directional power delivery with no duty cycle jumping, enhancing converter efficiency and preventing short circuits.
Implementation Method 1
one capacitor (Cs)
Implementation Method 2
one inductor (Ls)
Data Source
AI summary
A zero voltage transient cell comprising (i) one high switching frequency mosfet, (ii) two low switching frequency mosfet or two insulated-gate bipolar transistors, (iii) four diodes, (iv) one capacitor; and (v) one inductor or one additional diode in series with the inductor, which zero voltage transient cell can be used in a bi-directional AC/DC converter with switches and in a method of modulation that causes no switching loss in the conversion of AC to DC or DC to AC. The bi-directional AC/DC converter with the zero voltage transient cell can be used in a vehicle onboard charger.