Multi-Phase LLC Converter Balancing With Switch-Controlled Capacitors
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Solution Overview
Problem
Multi-phase LLC power converters face challenges in high-power, high-current applications due to high conduction losses and current unbalance caused by component tolerances, which affect efficiency and power density.
Innovation Solution
A multi-phase LLC power converter system with switch-controlled capacitors (SCCs) is implemented, where a secondary-side controller varies the switching frequency to control output voltage, and a primary-side controller calculates and adjusts the SCC conduction phase angle to equalize resonant frequencies across phases, ensuring balanced output currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If interleaving techniques are used to split output current between multiple phases, then conduction losses are reduced, but current unbalance occurs due to component tolerances
Solution Approach 1:
The patent adjusts the resonant frequency of individual LLC phases by modifying capacitor values to compensate for component tolerances. By changing the resonant frequency parameter of each phase, the system achieves current balance while maintaining the interleaved operation that reduces conduction losses.
2Power
If LLC converter operates at high current, then power density increases, but conduction loss increases
Solution Approach 1:
The patent divides the high-power conversion into multiple interleaved LLC phases. Each phase handles a portion of the total current, and by operating in parallel with proper phase shifting, the system achieves high power density while reducing overall conduction losses through current distribution.
3Stability of the object's composition
If multiple interleaved phases operate at the same switching frequency, then current ripple is reduced, but voltage gains differ due to component tolerances
Solution Approach 1:
The patent modifies the resonant frequency of individual phases by adjusting capacitor values to compensate for component tolerances. This allows each phase to have slightly different operating characteristics that result in equal voltage gains and balanced current distribution, while maintaining the same switching frequency for reduced current ripple.
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 solution achieves high efficiency and power density by reducing conduction losses and current unbalance, with peak efficiency of 96.7% and power density of 3 kW/L, effectively addressing the challenges in high-power applications.
Implementation Method 1
The resonant tank includes a resonant inductor, a resonant capacitor, and a parallel inductance
Implementation Method 2
A primary-side controller is configured to calculate an initial switch-controlled capacitor (SCC) conduction phase angle for each of the LLC phases to cause each of the LLC phases to have equal resonant frequencies; and to operate an SCC switch in accordance with an associated one of the SCC conduction phase angles to adjust the capacitance of the resonant capacitor
Data Source
AI summary
A multi-phase LLC power converter comprises a plurality of LLC phases each including a resonant tank and a switching stage. The resonant tank includes a resonant inductor, a resonant capacitor, and a parallel inductance. The switching stage switches an input power at an operating frequency to apply a switched power to the resonant tank, with the switched power approximating an alternating current (AC) waveform having a switching frequency. A secondary-side controller varies the switching frequency to control an output voltage of the multi-phase LLC power converter. A primary-side controller measures primary-side currents, calculates an initial switch-controlled capacitor (SCC) conduction phase angle for each of the LLC phases, and operates an SCC switch in accordance with an SCC conduction phase angle to adjust the capacitance of the resonant capacitor of an LLC phase to cause each of the LLC phases to have equal resonant frequencies.