Quasi Resonant Converter Power Regulation Range Extension
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Solution Overview
Problem
Quasi Resonant converters have a narrow range of adjustable output power in soft-switching mode, leading to increased thermal losses and electromagnetic interferences when power falls below a minimum limit, and irreversible switch damage when exceeding an upper limit, limiting their power regulation range and efficiency.
Innovation Solution
Modulating the activation time of the solid state switch in response to the DC-bus voltage to shape the current profile drawn from the power supply network, increasing the power regulation range without losing soft-switching conditions and without additional hardware, using an inventive modulation technique.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the output power is reduced below the minimum settable power limit, then the power regulation range is extended, but the converter fails to operate in soft-switching mode causing increased thermal losses and electromagnetic interferences
Solution Approach 1:
The patent applies dynamics by making the switching frequency variable rather than fixed. The control unit dynamically adjusts the switching frequency of the solid state switch based on the desired output power level, allowing the converter to maintain soft-switching conditions across a wider power range. This frequency modulation enables the resonant tank to adapt its operating characteristics, preserving ZVS/ZCS conditions even at reduced power levels where fixed-frequency operation would fail.
Solution Approach 2:
The patent changes the operating parameters of the converter by adjusting the switching frequency in response to power regulation requirements. The control unit modifies the frequency parameter to maintain the resonant tank's soft-switching operation across different power levels. This parameter adaptation allows the system to extend its adjustable power range below the traditional minimum limit while avoiding hard switching and associated losses.
2Power
If the output power exceeds the maximum settable power limit, then the power delivery capability is increased, but the resonating voltage exceeds the maximum allowable rating causing irreversible switch damage
Solution Approach 1:
The patent implements feedback control where the control unit continuously monitors the operating conditions and adjusts the switching frequency accordingly. By detecting the relationship between switching frequency, output power, and resonating voltage, the system provides feedback to prevent the resonating voltage from exceeding the switch's maximum rating. This closed-loop control ensures safe operation at high power levels while maintaining reliability.
Solution Approach 2:
The dynamic adjustment of switching frequency allows the converter to operate safely at high power levels by adapting the resonant tank's behavior. When operating near maximum power capacity, the control unit adjusts the frequency to maintain resonating voltage within safe limits, preventing switch damage while maximizing power delivery capability.
3Adaptability or versatility
If the switching frequency is varied to extend power regulation range, then the adaptability is improved, but the harmonic emissions increase
Solution Approach 1:
The patent carefully manages parameter changes by adjusting the switching frequency within a controlled range that extends power regulation capability while considering harmonic emission constraints. The control unit modulates frequency to achieve desired power levels, balancing the need for extended adaptability with the requirement to limit harmonic disturbances to acceptable 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 significantly increases the power regulation range of Quasi Resonant converters by 5% to 40% while maintaining efficiency and reducing thermal losses and electromagnetic interferences, allowing for smoother power delivery to loads like induction coils without food spoilage and within harmonic emission limits.
Implementation Method 1
a resonant tank comprising an inductor L and a capacitor C, the resonant tank being in parallel with the load
Implementation Method 2
converters are typically operated in 'soft-switching' mode which consists in switching the device either when the voltage across it or when the current flowing into it is null (Zero Voltage Switching, ZVS), especially when turning on
Implementation Method 3
the frequency of oscillation of the resonant tank is higher than the frequency of the power supply network
Data Source
Figure 1~2
Figure 3~4
Figure 5A~6
AI summary
A method for improving the power regulation range of a quasi resonant converter supplying an inductive load, particularly an induction heater, in which the activation time of the switch driving the converter is varied along the period of a rectified power supply voltage signal.