Multi-Level Inverter Resonant Converter for Low Gain Efficiency
Solution Overview
Problem
Conventional LLC resonant converters experience a significant drop in conversion efficiency and load capacity when output voltage gains are low, due to increased switching losses and inability to maintain zero current switching for secondary-side rectifier diodes.
Innovation Solution
A resonant converter circuit with a multi-level inverter circuit and a controller that adjusts the input voltage to the resonant unit, allowing the circuit to operate near its resonant frequency even at low output voltages, reducing semiconductor switching losses and improving efficiency and load capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the working frequency is increased to achieve low output voltage gain, then the output voltage requirement is met, but the switching loss increases greatly and conversion efficiency drops
Solution Approach 1:
A multi-level inverter circuit is introduced as an intermediary between the input power supply and the resonant converter. This inverter circuit divides the input voltage into multiple levels (e.g., ±E/2, 0), allowing the resonant converter to receive a reduced voltage input. Consequently, the resonant converter can operate at its resonant frequency with lower switching losses while still achieving the required output voltage through the transformer turns ratio.
Solution Approach 2:
The invention changes the voltage parameter at the input of the resonant converter by using a multi-level inverter to reduce the input voltage from E to E/2 or other divided levels. This parameter change allows the resonant converter to operate at its resonant frequency rather than at a higher frequency, thereby reducing switching losses and improving conversion efficiency while maintaining the required output voltage gain.
2Power
If the working frequency is increased to achieve low output voltage gain, then the output voltage requirement is met, but the load capacity drops
Solution Approach 1:
The multi-level inverter circuit serves as an intermediary that reduces the input voltage to the resonant converter, enabling operation at resonant frequency. This maintains optimal loading conditions for the transformer and resonant components, thereby preserving load capacity while achieving the required low output voltage gain.
Solution Approach 2:
By changing the input voltage parameter to the resonant converter through the multi-level inverter, the system can operate at its resonant frequency where the impedance matching is optimal. This maintains maximum power transfer capability and load capacity, avoiding the degraded performance that occurs when operating at frequencies far from resonance.
3Loss of energy
If the amplitude of square wave voltage signal is reduced to maintain resonant frequency operation, then switching losses are reduced, but the output voltage gain decreases
Solution Approach 1:
The voltage conversion function is segmented between two stages: the multi-level inverter circuit performs the first stage by dividing the input voltage into multiple levels (reducing amplitude), and the resonant converter with transformer performs the second stage to achieve the final output voltage. This segmentation allows each stage to operate optimally - the inverter at reduced voltage with low switching losses, and the transformer to provide the necessary voltage multiplication.
Solution Approach 2:
The multi-level inverter circuit acts as an intermediary that reduces the voltage amplitude before it enters the resonant converter. This intermediary stage enables the resonant converter to operate at its resonant frequency with reduced switching losses, while the transformer subsequently compensates for the reduced input amplitude to achieve the required output voltage gain.
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 maintains high conversion efficiency and load capacity by adjusting the input voltage to the resonant unit, ensuring the resonant converter operates near its resonant frequency even at low output voltages, thereby reducing semiconductor switching losses.
Implementation Method 1
The LLC resonant unit includes a resonant inductor Lr, a resonant capacitor Cr, where Lr may be a physical inductor device or leakage inductance of a transformer, and an Lm that may be a physical inductor device or an excitation inductance of a transformer. A switching frequency of the switching network is controlled to regulate an output voltage.
Implementation Method 2
three primary-side windings of the three-phase transformer are connected to output terminals of the three resonant units respectively in a one-to-one mode, where the three-phase transformer is configured to perform voltage conversion on voltage signals output by the three resonant units
Data Source
AI summary
A resonant converter circuit comprises a multi-level inverter circuit placed before a resonant unit, and the multi-level inverter circuit can reduce a voltage to be input to the resonant unit. The reduced input voltage of the resonant unit results in a drop in an output voltage of the entire resonant converter circuit. In this process, the final output voltage is adjusted by adjusting the input voltage of the resonant unit, with no need to substantially adjust a switching frequency of the resonant converter circuit.