Full-Bridge Inverter Phase Control for Low-Power Soft Switching
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Solution Overview
Problem
Existing switching converters for induction cooktops, particularly full-bridge inverters, face challenges in efficiently regulating output power to low values without resorting to hard-switching or ON/OFF modes, which leads to inefficiencies and audible noise when powering multiple coils at the same frequency.
Innovation Solution
The method involves adjusting the switching frequency and phase displacement of PWM control signals for full-bridge inverters, ensuring soft-switching conditions by optimizing the time delay between the turning-on instants of diagonal switches, and adjusting the common switching frequency to prevent hard-switching when necessary, allowing for continuous power regulation down to very low values without discontinuous operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If full-bridge inverters are used to improve efficiency by decreasing circulating current, then efficiency is improved, but device complexity increases due to doubled number of switching devices
Solution Approach 1:
The full-bridge inverter is segmented into two independent half-bridge legs, each capable of operating autonomously. This segmentation allows the system to achieve full-bridge performance (reduced circulating current) while maintaining simpler control structures similar to half-bridge converters, thereby improving efficiency without proportionally increasing control complexity.
Solution Approach 2:
Each half-bridge leg is designed to be multi-functional, capable of operating in both full-bridge mode (with diagonal switching) and half-bridge mode (with common rail switching). This universality allows the same hardware architecture to deliver full-bridge efficiency benefits while retaining the simpler control characteristics of half-bridge operation when needed.
2Adaptability or versatility
If phase displacement control is used to regulate output power, then power regulation capability is improved, but hard-switching conditions occur at low power values leading to inefficiency and audible noise
Solution Approach 1:
The switching frequency is made dynamic and adaptable based on the operating power level. At low power values, the system automatically adjusts the switching frequency to maintain soft-switching conditions, preventing hard-switching losses and audible noise while preserving wide power regulation capability through phase displacement control.
Solution Approach 2:
The system changes the switching frequency parameter in response to power level changes. By dynamically adjusting this parameter, the converter maintains optimal soft-switching operation across the entire power range, especially preventing hard-switching at low power values where phase displacement control would otherwise cause efficiency degradation and audible noise.
3Power
If switching frequency is increased to improve power delivery, then power output is improved, but audible noise increases due to hard-switching
Solution Approach 1:
The control system incorporates feedback mechanisms that monitor operating conditions and automatically adjust the switching frequency to maintain soft-switching. This feedback ensures that power output requirements are met while preventing the generation of audible noise by avoiding hard-switching conditions, even at elevated power levels.
Solution Approach 2:
The switching frequency parameter is dynamically changed based on power delivery requirements and acoustic considerations. The system adjusts this parameter to achieve the necessary power output while maintaining soft-switching operation, thereby eliminating audible noise generation even when operating at high power levels.
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 efficient power regulation across a wide range, maintaining soft-switching conditions and preventing audible noise, even at low output powers, by modulating the phase displacement and switching frequency, thus enhancing the controllability and efficiency of the power delivery to resonant loads.
Implementation Method 1
At least a first L-C resonant pair is connected between two intermediate current terminals of two half-bridge switching stages of the plurality of half-bridge switching stages, the first L-C resonant pair being configured to be magnetically coupled with a respective load, thereby defining at least a first equivalent resonant load (R-L-C)
Implementation Method 2
the inductor represents the induction coil and the pot placed on the cooktop surface above it
Data Source
AI summary
A method of controlling a switching includes a regulating the output power to be delivered to the at least one resonant load, adjusting a common switching frequency of all PWM control signals sent to a plurality of switches and the phase displacement of all said PWM control signals by adjusting a time delay between turning-on of diagonal switches of said two half-bridge switching stages connecting said resonant load within the same switching period. The phase displacement is carried out until hard-switching working conditions for said half-bridge switching stages are met, and when said hard switching working conditions are met, the common switching frequency of all said PWM control signals are adjusted to prevent hard-switching working conditions.