Hysteretic Power Factor Control for Single-Stage Converters
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Solution Overview
Problem
Current single-phase active power factor control techniques, particularly two-stage approaches, suffer from lower efficiency and increased complexity and cost due to the need for separate stages for power factor correction and DC/DC conversion, making single-stage approaches more desirable for low-power applications.
Innovation Solution
A switching power converter with a hysteretic control loop that adjusts a threshold value to operate in either constant on-time or constant power modes based on input voltage conditions, ensuring high power factor and low total harmonic distortion by maintaining a product of switch on-time and input voltage amplitude as constant, thereby achieving a power factor close to 1.0.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a two-stage power factor control approach is used, then input current shaping and power factor correction are achieved, but efficiency decreases and device complexity increases
Solution Approach 1:
The patent combines the power factor correction stage and DC/DC conversion stage into a single integrated stage, eliminating the need for separate front-end PFC circuitry. This single-stage architecture processes power through one conversion path rather than two, reducing energy losses while maintaining effective input current shaping and power factor correction performance through unified control of the switch node.
Solution Approach 2:
The single switch node in the patent performs multiple functions simultaneously: it enables both power factor correction and DC/DC voltage conversion. By designing the circuit topology and control strategy to achieve dual functionality in one stage, the system avoids the efficiency penalties of sequential two-stage processing while maintaining comprehensive power management capability.
2Reliability
If a two-stage power factor control approach is used, then input current shaping is achieved, but device complexity and cost increase
Solution Approach 1:
The patent merges the PFC functionality and DC/DC conversion functionality into a single integrated stage with one switch node, eliminating the separate front-end PFC stage required in two-stage architectures. This reduction in the number of stages directly decreases device complexity and component count while preserving effective input current shaping through the unified control mechanism.
Solution Approach 2:
The single switch node is designed to perform multiple functions: power factor correction, input current shaping, and DC/DC voltage conversion. This multi-functional design eliminates the need for dedicated PFC circuitry, reducing overall device complexity and cost while maintaining high-quality input current shaping and power factor correction performance.
3Device complexity
If constant on-time mode is used, then circuit simplicity is maintained, but power factor and total harmonic distortion performance deteriorate
Solution Approach 1:
The patent implements a dynamic control mechanism that adjusts the switch node on-time based on real-time operating conditions. Rather than using a fixed constant on-time approach, the controller dynamically modifies the on-time duration to maintain optimal power factor and minimize total harmonic distortion across varying input voltages and load conditions, while still retaining the fundamental simplicity of on-time control architecture.
Solution Approach 2:
The patent incorporates feedback control that monitors the operating state and adjusts the switch node on-time accordingly. This feedback mechanism enables the system to maintain high power factor and low total harmonic distortion by continuously optimizing the on-time parameter based on actual performance, rather than relying on a static constant on-time setting that degrades under varying conditions.
4Reliability
If constant power mode is used, then power factor is improved, but control complexity increases
Solution Approach 1:
The patent uses dynamic adjustment of the switch node on-time to achieve constant power operation. By continuously adapting the on-time parameter in response to changing operating conditions, the system maintains high power factor performance without requiring the complex control mechanisms of traditional constant power approaches. The dynamic control is implemented through straightforward timing adjustments rather than complex computational algorithms.
Data Source
AI summary
In one aspect, a switching power converter is described that includes a transformer, a switch, and a controller that generates a control signal to turn on and turn off the switch. For each alternating current (AC) half-cycle of an input voltage, the controller determines a minimum value of a signal representing an on-time of the power converter, compares the determined minimum value with a threshold value that is used to determine whether the switching power converter operates in a constant on-time mode or in a constant power mode, and adjusts the threshold value based on a result of the comparison. The controller further generates the control signal to operate the switching power converter in a constant power mode during a first time period of the AC half-cycle, the first time period representing a duration where the threshold value is larger than an instantaneous value of the first signal.