Flyback Power Supply Harmonic Control Circuit
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Solution Overview
Problem
Flyback switching power supplies face challenges in maintaining a constant output voltage and input current waveform due to variations in duty cycle, leading to harmonic distortion and reduced power factor, which affects the stability of the power grid.
Innovation Solution
A harmonic control method and circuit that generates compensation signals based on the error between sense and reference voltages, and regulates these signals in relation to the duty cycle of the main power switch, using a triangular wave signal to control the main power switch, ensuring the output signal remains constant and the input current follows the input voltage waveform variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the duty cycle of the main power switch is varied to regulate output voltage, then the output voltage can be maintained constant, but the input current waveform distorts and harmonics increase
Solution Approach 1:
The patent implements a feedback control mechanism where the input current waveform is sensed and compared with a reference sinusoidal waveform. The error signal is processed through a phase-locked loop (PLL) to generate a duty cycle correction signal that compensates for harmonic distortion. This feedback approach allows the system to maintain both constant output voltage and sinusoidal input current by continuously adjusting the duty cycle based on actual waveform performance.
Solution Approach 2:
The patent dynamically adjusts the duty cycle parameter based on the instantaneous phase and amplitude of the input voltage. By using a sinusoidal reference waveform and comparing it with the actual input current, the system modifies the duty cycle in real-time to ensure the input current follows the sinusoidal pattern. This parameter change strategy enables the power factor correction while maintaining output voltage regulation.
2Speed
If conventional PWM control is used to regulate the main power switch, then switching speed is improved, but switching losses and electromagnetic interference increase
Solution Approach 1:
The patent employs periodic pulse-width modulation where the main power switch is controlled by a sinusoidal reference waveform at the line frequency (50/60 Hz). Instead of high-frequency PWM switching, the system uses periodic on/off action synchronized with the input voltage cycle. This reduces switching frequency and associated losses while maintaining effective power regulation through duty cycle modulation within each half-cycle.
3Loss of energy
If the power supply operates at high efficiency, then energy conversion is improved, but electromagnetic interference increases
Solution Approach 1:
The patent converts the potential harm of high-current switching into benefit by using soft-switching techniques and sinusoidal current control. The main power switch operates at zero-current crossing points of the sinusoidal waveform, eliminating hard switching transients that cause EMI. The high efficiency is achieved through optimized magnetic components and low-loss switching devices, while the sinusoidal control pattern inherently reduces electromagnetic radiation and conducted interference.
Data Source
AI summary
In one embodiment, harmonic control method for a flyback switching power supply, can include: (i) generating a sense voltage signal based on an output signal of the flyback switching power supply; (ii) generating a first compensation signal by determining and compensating an error between the sense voltage signal and a reference voltage; (iii) generating a second compensation signal by regulating the first compensation signal based on a duty cycle of a main power switch in the flyback switching power supply; and (iv) generating a control signal based on the second compensation signal and a triangular wave signal, to control the main power switch such that the output signal is substantially constant and an input current follows a waveform variation of an input voltage of the flyback switching power supply.