Resonant Converter Startup Mode Reduces Hard Commutation
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Solution Overview
Problem
Bi-directional and uni-directional power converters face challenges with high current levels and hard commutation issues, particularly with MOSFETs, leading to high voltage spikes and inefficiencies in component selection and operation.
Innovation Solution
A controller is configured to operate in a startup mode with three phases, using peak detection, zero-crossing detection, and discontinuous-current mode to control bridge circuits, reducing hard commutation and inrush currents, and transitioning to soft switching in steady-state mode for efficient power conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If hard commutation is used with MOSFETs as rectifiers, then the converter can operate in discharge mode, but high voltage spikes are induced on the switches
Solution Approach 1:
The patent applies preliminary action by implementing a soft-start sequence that gradually transitions the converter through three phases (Phase 1: rectifier mode with body diodes, Phase 2: synchronous rectification with zero-crossing detection, Phase 3: full bridge operation) before reaching steady-state discharge mode. This preliminary progression prevents direct hard commutation by preparing the circuit conditions in advance, thereby avoiding voltage spikes while enabling discharge mode operation.
Solution Approach 2:
The patent applies dynamics by making the switching strategy adaptive based on the operating phase. The control circuit dynamically adjusts its behavior: in Phase 1, body diodes conduct naturally; in Phase 2, zero-crossing detection triggers synchronous rectification; in Phase 3, full bridge operation with controlled commutation is enabled. This dynamic adaptation allows the system to operate in discharge mode while managing voltage spikes through phase-appropriate control methods.
2Power
If high current levels are handled in the LC tank and bridge switches, then high power application is achieved, but cost and efficiency are compromised due to component selection
Solution Approach 1:
The patent applies parameter changes by modifying the operating characteristics of the MOSFETs throughout the startup sequence. In Phase 1, the body diodes conduct at their natural parameters. In Phase 2, zero-crossing detection changes the switching parameters to enable synchronous rectification. In Phase 3, the full bridge operation with controlled commutation changes the current and voltage stress parameters on the switches. These parameter transitions allow high power capability while using more economical components by avoiding sustained hard commutation conditions.
3Reliability
If a three-phase startup mode is implemented, then hard commutation and inrush currents are reduced, but device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the startup process into three distinct phases with specific control strategies for each. Phase 1 uses simple rectifier mode control, Phase 2 introduces zero-crossing detection for synchronous rectification, and Phase 3 enables full bridge operation. This segmentation allows the control circuit to manage complexity by handling one phase at a time with appropriate control methods, reducing hard commutation while keeping each phase's control logic relatively simple.
Solution Approach 2:
The patent applies feedback through zero-crossing detection in Phase 2, where the control circuit monitors the current waveform and triggers synchronous rectification at the appropriate moment. This feedback mechanism enables the system to automatically adjust its operation to reduce hard commutation without requiring complex predictive control, thereby improving reliability while managing device complexity through responsive rather than purely open-loop control.
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 hard commutation and inrush currents, allowing for the use of less expensive components and improving efficiency in power converters, particularly in high-power applications with bi-directional and uni-directional converters.
Implementation Method 1
The startup generation circuit is configured to operate in a first phase of the startup mode using peak detection
Implementation Method 2
The startup generation circuit is configured to operate in a first phase of the startup mode using peak detection and zero-crossing detection of a signal indicating an electrical current in the power converter
Implementation Method 3
The steady-state generation circuit is configured to control the bridge circuit using soft switching while operating in a steady-state mode after the third phase of the startup mode
Implementation Method 4
A bi-directional resonant converter can charge or discharge a storage battery from/to high voltage bus
Data Source
AI summary
In some examples, a controller includes a startup generation circuit configured to control, while operating in a first phase of a startup mode, a bridge circuit using peak detection and using zero-crossing detection of an electrical current through a tank circuit coupled to the bridge circuit. The startup generation circuit is also configured to control the bridge circuit using the zero-crossing detection while operating in a second phase of the startup mode after the first phase. The startup generation circuit is further configured to control the bridge circuit using a discontinuous-current mode for the electrical current while operating in a third phase of the startup mode after the second phase. The controller also includes a steady-state generation circuit configured to control the bridge circuit using soft switching while operating in a steady-state mode after the third phase of the startup mode.