Multiphase LLC Resonant Converter Current Sharing
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Solution Overview
Problem
Conventional LLC series resonant converters face limitations due to large circulation currents, which increase conduction losses and stress on components, reducing efficiency and requiring higher tolerance components.
Innovation Solution
A multiphase resonant converter design with N unit converters connected in parallel, where inverters are driven by phase-shifted signals, sharing current among units to reduce conduction losses and stress on components, while maintaining zero voltage switching and wide load range capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional LLC series resonant converter topology is used, then zero voltage switching and wide load range are achieved, but large circulation currents increase conduction losses and component stress
Solution Approach 1:
The patent divides the single resonant converter into N parallel unit converters, each handling a portion of the total load current. This segmentation reduces the circulation current in each individual unit, thereby reducing conduction losses and stress on components while maintaining the overall converter functionality and zero voltage switching characteristics
2Reliability
If higher tolerance components are used to handle circulation currents, then component reliability improves, but device complexity and cost increase
Solution Approach 1:
By segmenting the converter into N parallel units, the current through each component is reduced proportionally. This allows the use of standard tolerance components in each unit, as the reduced current stress eliminates the need for high-tolerance, high-cost components that would be required in a single-unit design handling the full current
3Productivity
If current sharing control circuitry is added, then current distribution among phases is optimized, but device complexity increases
Solution Approach 1:
The patent employs passive current sharing where the phase-shifted PWM control automatically distributes current among the N parallel units based on their instantaneous impedance and voltage conditions. No active current sensing or complex control circuitry is required, as the system self-regulates current distribution through the inherent characteristics of the resonant tanks and phase-shifted driving signals
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 multiphase resonant converter achieves higher efficiency, reduced component stress, and automatic current sharing without additional control circuitry, preserving desirable features like zero voltage switching and fast transient response.
Implementation Method 1
The resonant tank comprises an inductor Ls, a series capacitor Cs, and an inductor Lp connected in series to realize resonance
Implementation Method 2
The inverter is realized by a half-bridge inverter with switches Mp and Mn that are driven complementary to generate a square wave at the input of the resonant tank
Implementation Method 3
The rectifier comprises a center-tapped transformer, a filter capacitor CF, and two rectifier diodes DP and DN. The rectifier rectifies the ac waveform from the resonant network into a dc output
Implementation Method 4
In low output voltage high current applications, the two rectifier diodes must be replaced with synchronized rectifiers (SR) to reduce the voltage drop (conduction losses) across each semiconductor rectifier
Data Source
AI summary
The various embodiments and example provided herein are generally directed to novel multiphase resonant converters. In an embodiment, a multiphase resonant converter comprises N unit resonant converters having inputs and outputs connected in parallel, respectively. Each unit converter comprises an inverter, a LLC series resonant tank, and a rectifier. In a preferred embodiment, the inverters of the N unit converters are driven by N drive signals phase-shifted 2π/N degrees apart. During operation, the current of the multiphase converter is shared among the unit converters, resulting in a smaller current in each unit converter. The smaller current in each unit converter reduces conduction losses, thereby increasing the efficiency of the multiphase converter. In addition, the smaller current in each unit converter reduces the amount of stress placed on individual components of the converter allowing for the use of lower tolerance components. Further, the multiphase converter has automatic current sharing ability.