Switching Power Source Device Pulse Width Control for Harmonic Noise Reduction

Solution Overview

Problem

In switching power source devices with PFC circuits, the rapid switching of the switching element based on PWM signals leads to significant harmonic noise, reducing power conversion efficiency, especially as the handled power increases.

Innovation Solution

The implementation of a switching power source device that controls the switching element using a pulse signal with a shorter cycle and gradually increasing pulse width during the initial and final periods of the PWM ON period, and adjusts the pulse width based on the detected noise levels to minimize harmonic noise generation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the switching element is rapidly switched based on PWM signals to achieve precise control, then the control precision is improved, but harmonic noise increases and power conversion efficiency decreases

Engineering Contradiction:

Improvecontrol precisionVSAvoidharmonic noise

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The patent applies preliminary action by gradually increasing the pulse width in the initial period before the main PWM switching begins. This gradual transition prepares the circuit for the upcoming rapid switching, reducing the shock and harmonic noise generated by abrupt current changes. The pulse width modulation signal starts with a small duty cycle and gradually increases to the target duty cycle, smoothing the current waveform at the beginning of the switching cycle.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements periodic action by dividing the PWM cycle into multiple periods: an initial period with gradually increasing pulse width, a main period with standard PWM switching, and a final period with gradually decreasing pulse width. This periodic structure applies different switching strategies at different stages of the cycle, reducing harmonic noise at the critical transition points while maintaining efficient power conversion during the main period.

Inventive Principle:

Principle #19Periodic action

2Measurement precision

If the switching element is rapidly switched based on PWM signals to achieve desired DC voltage, then the voltage control accuracy is improved, but power conversion efficiency decreases due to harmonic noise

Engineering Contradiction:

Improvevoltage control accuracyVSAvoidpower conversion efficiency

Core Design Contradiction:

Measurement precisionVSLoss of energy

Solution Approach 1:

The patent applies preliminary action by gradually increasing the pulse width in the initial period before the main PWM switching begins. This gradual transition prepares the circuit for the upcoming rapid switching, reducing the shock and harmonic noise generated by abrupt current changes. The pulse width modulation signal starts with a small duty cycle and gradually increases to the target duty cycle, smoothing the current waveform at the beginning of the switching cycle.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements periodic action by dividing the PWM cycle into multiple periods: an initial period with gradually increasing pulse width, a main period with standard PWM switching, and a final period with gradually decreasing pulse width. This periodic structure applies different switching strategies at different stages of the cycle, reducing harmonic noise at the critical transition points while maintaining efficient power conversion during the main period.

Inventive Principle:

Principle #19Periodic action

3Object-generated harmful factors

If the pulse width is gradually increased in the initial period, then harmonic noise is reduced, but the control response time increases

Engineering Contradiction:

Improveharmonic noiseVSAvoidcontrol response time

Core Design Contradiction:

Object-generated harmful factorsVSLoss of time

Solution Approach 1:

The patent applies partial action by implementing gradual pulse width increase only in the initial period, which is a small fraction of the total PWM cycle. The majority of the cycle (the main period) uses standard rapid PWM switching for efficient power conversion. This partial application of gradual modulation minimizes the time penalty while still achieving noise reduction at the critical transition point.

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The patent implements periodic action by dividing the PWM cycle into multiple periods: an initial period with gradually increasing pulse width, a main period with standard PWM switching, and a final period with gradually decreasing pulse width. This periodic structure applies different switching strategies at different stages of the cycle, reducing harmonic noise at the critical transition points while maintaining efficient power conversion during the main period.

Inventive Principle:

Principle #19Periodic action

Data Source

PatentUS10199938B2Switching power source device, semiconductor device, and AC/DC converter including a switching control

Publication Date: 2019.02.05 RENESAS ELECTRONICS CORP

AI summary

A switching power source device for controlling a current flowing through a coil by turning on/off a switching element by a PWM control to obtain a desired DC voltage, includes in a PWM ON period to turn on the switching element by the PWM control, a switching control of the switching element is enabled by a first pulse signal whose cycle is shorter than a PWM cycle based on the PWM control and whose pulse width is gradually increased, in a first period just after the PWM ON period is started, and the switching control of the switching element is enabled by the PWM signal based on the PWM control after the first period has elapsed.