Resonant DC-DC Converter Phase Shift for Wide-Range Soft Switching
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Solution Overview
Problem
Immittance resonant converters face challenges in controlling output power and current across wide voltage and power ranges, particularly at light loads, due to increased conduction and switching losses, making it difficult to maintain zero voltage-switching (ZVS) and near zero-current switching (ZCS) across the entire load range.
Innovation Solution
A phase-shift based modulation strategy is implemented for three-level inverter and rectifier bridges, allowing for simultaneous regulation of output power and current while ensuring ZVS and near ZCS for all semiconductor devices, using a multi-element resonant converter topology with a fixed switching frequency, and capable of operating across a wide range of output voltage and power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If fixed frequency control with phase-shift modulation is used, then output power regulation is achieved, but conduction losses and voltage-current overlap losses increase at light loads
Solution Approach 1:
The patent implements dynamic switching frequency adjustment combined with phase-shift modulation. The switching frequency varies adaptively with load conditions, enabling the converter to maintain optimal efficiency across the entire load range from full load down to 5% of rated power. This dynamic approach replaces fixed frequency operation, allowing the system to optimize its operating point continuously.
Solution Approach 2:
The patent changes multiple operating parameters simultaneously including switching frequency, phase shift angle, and pulse width modulation duty cycle. These parameter variations enable the converter to maintain zero voltage switching (ZVS) conditions while adapting to different load levels, thereby reducing both conduction losses and switching losses across the operating range.
2Productivity
If wide band gap semiconductors are used for high frequency operation, then power density increases, but switching losses increase without soft-switching
Solution Approach 1:
The patent prepares the switching nodes for soft-switching by pre-charging or pre-discharging the parasitic junction capacitors before the actual switching event. This preliminary action ensures that voltage and current do not overlap during switching transitions, eliminating hard charging losses and enabling lossless high-frequency operation with wide band gap semiconductors.
Solution Approach 2:
The patent utilizes resonant oscillations in the LC tank circuit to create natural voltage and current waveforms that facilitate soft-switching. By operating at or near the resonant frequency, the system exploits the inherent oscillatory behavior to achieve zero voltage or zero current switching, thereby maintaining high frequency operation with minimal switching losses.
3Power
If immittance network based resonant converter is used, then fixed voltage to current gain is achieved, but control flexibility for multiple charging modes is limited
Solution Approach 1:
The patent designs the control system to provide multiple operating modes (constant voltage, constant current, constant power) using a unified resonant converter topology. By implementing adaptive control algorithms that can switch between different control strategies, the system achieves multi-functionality, allowing it to serve various battery charging requirements without requiring separate dedicated circuits for each mode.
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 significantly reduces switching and conduction losses, achieving lower converter losses even at light load conditions, ensuring efficient operation across the entire load range with reduced voltage-current overlap losses and balanced current stress on devices.
Implementation Method 1
a resonant network, the circuit electrically connected to the inverter output terminal... a three-element resonant converter... LCL-T resonant converter... resonant frequency
Data Source
AI summary
A novel phase-shift based modulation strategy is disclosed that enables a DC-DC converter to operate with zero voltage-switching (ZVS) across wide voltage and power range. The converter operates at a fixed fundamental frequency, with the output current controlled based on an amount of phase shift of the fundamental component at the output of an inverter portion of the converter. To achieve soft switching a rectifier portion of the converter is controlled to phase shift the fundamental component of the rectifier voltage observed at a rectifier reference terminal. More specifically, by requiring a phase shift of the voltage at the rectifier terminal relative to the output voltage of the inverter, the inverter current is such that ZVS is achieved. A converter and method are provided to implement DC-DC conversion with soft switching.