Soft Switching Converter via Leakage and Magnetizing Inductance Control
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Solution Overview
Problem
Existing converter technologies face challenges in achieving zero voltage switching across all switching elements, particularly at varying load conditions, due to insufficient energy from leakage inductance to fully discharge parasitic capacitances, leading to increased conduction losses and inefficiencies.
Innovation Solution
The proposed solution involves a design and control method for converters that utilize a combination of resonant discharge from leakage inductance and magnetizing inductance, along with current injection, to ensure zero voltage switching. This method includes tailoring the switching frequency and current pulses to ensure the current through synchronous rectifiers reaches zero or slightly negative before turn-off, allowing the difference between magnetizing current and output choke current to discharge parasitic capacitances effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If only leakage inductance energy is used to discharge parasitic capacitances, then the discharge capability is sufficient at higher loads, but it becomes insufficient at middle range and light load conditions
Solution Approach 1:
The patent combines leakage inductance energy and magnetizing inductance energy to work together in discharging parasitic capacitances. The control circuit is designed to first utilize leakage inductance energy, then supplement with magnetizing inductance energy when the leakage energy is insufficient, creating a hybrid energy utilization system that adapts to different load conditions.
Solution Approach 2:
The patent implements dynamic switching between different energy sources based on real-time load conditions. The control circuit dynamically determines whether to use leakage inductance energy alone or to supplement with magnetizing inductance energy, adapting the energy discharge strategy to match the current operating conditions.
2Productivity
If switching frequency is increased to improve power density, then conversion efficiency improves, but achieving zero voltage switching becomes more difficult across all load conditions
Solution Approach 1:
The patent applies preliminary action by proactively discharging parasitic capacitances before the switching elements are turned on. The control circuit initiates the discharge process using leakage and magnetizing inductance energies during the dead time period, ensuring that voltage is reduced to zero before the next switching action, thereby enabling reliable zero voltage switching at high frequencies.
3Speed
If conventional switching methods are used, then the converter operates at higher frequencies, but conduction losses increase due to incomplete parasitic capacitance discharge
Solution Approach 1:
The patent employs feedback control to monitor the voltage across parasitic capacitances and adjust the discharge process accordingly. The control circuit detects when parasitic capacitances are fully discharged and coordinates the switching actions to minimize conduction losses, creating a closed-loop system that optimizes both switching frequency and loss reduction.
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 enables zero voltage switching across all switching elements, reducing conduction losses and improving efficiency by effectively utilizing energy from both leakage and magnetizing inductances, and allowing for tailored current injection to fully discharge parasitic capacitances.
Implementation Method 1
the resonant discharge produced by the energy contained in the leakage inductance
Implementation Method 2
the leakage inductance energy is 'stored' during the dead time of the primary switchers
Implementation Method 3
we will use the energy contained in the magnetizing inductance in the event the magnetizing inductance reflected in the secondary it is larger than the current flowing through the output choke
Data Source
AI summary
A method is shown to create soft transition in selected topologies by preserving the leakage inductance energy during the dead time and using several techniques to supplement the energy require to discharge the parasitic capacitance of the primary switchers and obtain zero voltage switching. One technique consists in a current pulse injection across the synchronous rectifiers during the dead time and prior the turn off of the synchronous rectifiers. A second technique consist in tailoring the magnetizing current through frequency modulation to increase the energy in the leakage inductance and use that energy to discharge the parasitic capacitance of the primary switchers and at lighter load to have a magnetizing current which exceeds the current through the output inductor at the end of the dead time. The third technique is interleaving two converters and sharing a couple inductance in a way to lower the current through each output inductor under the level of the magnetizing current at its lowest amplitude. The fourth technique is controlling the turn off timing of the primary switchers and turn on timing for the secondary synchronous rectifier and in this way to control the energy in the leakage inductance during the dead time in order to build enough energy in the leakage inductance to discharge the parasitic capacitances of the primary switchers to zero. In a given application we may use one or several of these technique function of the operating conditions.