Bridgeless PFC Control Circuit Reducing Harmonics With Small Inductors
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Solution Overview
Problem
Existing bridgeless power factor correction (PFC) circuits face challenges in achieving unity power factor and minimizing harmonics due to small inductance values, which result in distorted line currents and limited ability to attain unity power factor in practical applications.
Innovation Solution
A bridgeless PFC circuit with a control circuit that generates a carrier signal to control the switching cycle of switches, determining a duty cycle based on the comparison of the carrier signal and current signals, and extending the pulse duration to ensure the average inductor current is proportional to and in phase with the input voltage waveform, thereby reducing harmonics and improving power factor correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If small inductance values are used in bridgeless PFC circuits, then device size and cost are reduced, but line current distortion increases and unity power factor cannot be achieved
Solution Approach 1:
The patent changes the control parameter from traditional continuous PWM control to discontinuous carrier signal control with duration less than the switching cycle. This parameter change allows the circuit to maintain sinusoidal average inductor current and achieve unity power factor even with small inductance values, resolving the contradiction between small inductor volume and low current distortion
Solution Approach 2:
The patent implements periodic carrier signal generation within each switching cycle, where the carrier signal has a duration that is a fraction of the switching cycle. This periodic action creates discrete control pulses that shape the inductor current to be sinusoidal, enabling unity power factor correction without requiring large inductors
2Device complexity
If traditional PWM control is used in bridgeless PFC circuits, then switching control is simple, but average inductor current cannot be maintained sinusoidal with small inductance
Solution Approach 1:
The patent modifies the control approach by generating a carrier signal with duration less than the switching cycle and using it to create discontinuous control pulses. This parameter change in the control signal timing and duration enables sinusoidal average inductor current maintenance without requiring complex control circuits or large inductors
Solution Approach 2:
The control circuit uses feedback from the inductor current to adjust the carrier signal generation and control pulse timing. This feedback mechanism ensures that the average inductor current remains sinusoidal and in phase with the input voltage, maintaining waveform stability even with simple control circuitry and small inductance values
Data Source
AI summary
This document discusses, among other things, an improved bridgeless power factor correction (PFC) circuit. In an example, the PFC circuit can include a first switch and a control circuit, the control circuit configured to provide a switching cycle, to generate a carrier signal corresponding to the switching cycle, and to generate a control signal for the first switch during the switching cycle. In an example, the control circuit can receive a first signal indicative of current through the first switch and generate a duty cycle for the first switch using a comparison of the first signal and the carrier signal. In an example, the control circuit can initiate the carrier signal at the beginning of the switching cycle and provide a carrier signal duration corresponding to a fraction of a duration of the switching cycle of the PFC circuit (e.g., one-half, one-third, etc.).