Switching Converter Control Unit Pre-Distortion for THD Reduction
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Solution Overview
Problem
Existing control solutions for power factor correction (PFC) converters operating in discontinuous-conduction mode (DCM) fail to maintain a high power factor and low total harmonic distortion (THD) due to non-sinusoidal input current trends, requiring complex implementations and additional pins, leading to compromises in distortion characteristics and implementation costs.
Innovation Solution
A control unit with a pre-distortion stage that adjusts the reference voltage to compensate for input current distortions, ensuring the input current becomes sinusoidal and in phase with the input voltage, thereby optimizing converter performance by using a pre-distortion factor that inversely corrects the distortion caused by the switching operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a PFC converter operates in discontinuous-conduction mode with conventional control, then the converter can handle varying load conditions, but the input current becomes non-sinusoidal causing high THD and degraded power factor
Solution Approach 1:
The control unit applies a pre-distortion factor to the reference voltage before the switching operation, anticipating and compensating for the distortion that will occur during discontinuous conduction mode. This preliminary adjustment ensures that the input current remains sinusoidal despite the non-continuous conduction, thereby maintaining low THD and high power factor across varying load conditions
2Object-generated harmful factors
If complex control implementations are used to correct input current distortion, then THD can be reduced, but the device complexity and implementation cost increase
Solution Approach 1:
The invention changes the parameter of the reference voltage by applying a pre-distortion factor that compensates for the expected current distortion. This parameter modification is achieved through straightforward mathematical adjustment in the control unit, avoiding the need for complex additional circuits or multiple pins, thus maintaining simplicity while effectively reducing THD
Data Source
AI summary
A control unit for a switching converter has an inductor element coupled to an input and a switch element coupled to the inductor element. The control unit generates a command signal with a switching period to control the switching of the switch element and to determine a first time period where an inductor current is flowing in the inductor element for storing energy and a second time period where energy is transferred to a load. The second time period has an end portion where the inductor current drops to zero. The control unit determines the duration of the first time period based on a comparison between a sensing voltage, indicative of the peak value of the inductor current, and a reference voltage. A pre-distortion stage pre-distorts the reference voltage in order to compensate for a corresponding distortion on an input current of the converter compared to a desired sinusoidal characteristic.