Multi-Stage Switching Converter Control for Low-Power Soft Switching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing full-bridge inverters for induction cooktops face challenges in delivering very low output power without resorting to hard-switching or discontinuous operation modes, especially when multiple heating coils are involved, leading to inefficiency and audible noise.
Innovation Solution
A method of controlling a full-bridge inverter by adjusting the switching frequency and phase displacement of PWM control signals, maintaining soft-switching conditions, and using a multi-stage inverter architecture with master and slave half-bridge stages to manage power delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If full-bridge inverter is used to improve efficiency by decreasing circulating current, then conversion 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 inverters, each capable of operating autonomously. This segmentation allows the system to achieve full-bridge performance when needed while simplifying to half-bridge operation for low-power applications, reducing the effective complexity at different operating points.
Solution Approach 2:
The inverter topology is made dynamic by enabling switching between full-bridge and half-bridge configurations based on power level requirements. The control system dynamically selects which half-bridge stage is active, allowing the device to adapt its complexity to the actual operating conditions.
2Adaptability or versatility
If phase displacement control is used to regulate output power, then power control range is improved, but hard-switching conditions occur at low power levels
Solution Approach 1:
The system dynamically switches between full-bridge and half-bridge topologies based on the required power level. At low power levels, it transitions to half-bridge mode with continuous soft-switching, avoiding the hard-switching conditions that would otherwise occur with excessive phase displacement in full-bridge mode.
Solution Approach 2:
The control method changes the operating parameters by adjusting the phase displacement between half-bridge stages to maintain soft-switching conditions. When phase displacement would cause hard-switching, the system changes topology rather than pushing the phase displacement to extreme values.
3Measurement precision
If switching frequency is increased to improve power regulation precision, then output power control precision is improved, but acoustic noise increases
Solution Approach 1:
The system dynamically adjusts the switching frequency based on the required power level. At low power levels, it operates at lower frequencies to minimize audible noise, while maintaining precise control through the half-bridge topology and phase displacement control mechanism.
Solution Approach 2:
The control method changes the switching frequency parameter adaptively, lowering it at low power levels to avoid the audible frequency range while maintaining sufficient resolution for precise power control through the half-bridge operation 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
Enables efficient power regulation over a wide range, including very low power levels, without hard-switching or discontinuous operation, reducing acoustic noise and maintaining high conversion efficiency.
Implementation Method 1
the load is a series resonant circuit composed of a resonant capacitor and an inductor, and the inductor represents the induction coil and the pot placed on the cooktop surface above it
Implementation Method 2
induction heating elements with a regulated supply power generated from a main energy supply
Data Source
Figure 1~2c
Figure 3
Figure 4
AI summary
According to the method of controlling a switching converter of this disclosure, the following operations are carried out: : regulation of the output power to be delivered to the at least one resonant load is obtained adjusting the common switching frequency of all said PWM control signals and the phase displacement of all said PWM control signals, wherein said step of adjusting the phase displacement is carried out by adjusting a time delay between the 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 wherein when said hard switching working conditions are met the method further comprises the step of adjusting the common switching frequency of all said PWM control signals to thereby prevent hard-switching working conditions. The control method of this disclosure is particularly suitable for being used in multi-stage inverters according to this disclosure, comprising more than three half-bridge switching stages.