SPWM DC Offset Harmonic Noise Reduction

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Solution Overview

Problem

Existing sinusoidal pulse width modulation (SPWM) techniques in PWM inverters and rectifiers face limitations in reducing harmonic and electromagnetic interference (EMI) noise, particularly due to high dv/dt and di/dt, which cause leakage current and motor bearing damage, and are restricted in application to three-phase systems, with advanced modulation techniques introducing extra harmonics and being costly to implement.

Innovation Solution

A closed-form expression for total harmonic energy is derived for a single bridge, enabling a SPWM technique with DC offset that reduces total harmonic and EMI noise by adjusting the modulation index and duty cycle, applicable to half-bridge, H-bridge, and three-phase bridge circuits, without requiring additional hardware.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If conventional SPWM techniques are used in PWM inverters and rectifiers, then the system can operate with standard modulation, but high dv/dt and di/dt cause large leakage current, electromagnetic interference (EMI) and motor bearing damage

Engineering Contradiction:

Improveleakage current, EMI and motor bearing damageVSAvoidharmonic energy

Core Design Contradiction:

Object-affected harmful factorsVSLoss of energy

Solution Approach 1:

The patent applies parameter changes by modifying the carrier wave parameters (introducing DC offset to the carrier wave) to reduce harmonic content and dv/dt di/dt effects. This changes the waveform characteristics to minimize harmful effects while maintaining functional performance

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the harmful high dv/dt and di/dt characteristics into beneficial low dv/dt and di/dt waveforms by using optimized carrier waves with DC offset, thereby reducing leakage current and EMI while maintaining the power conversion function

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Object-affected harmful factors

If advanced modulation techniques are used to suppress harmonic noise and EMI noise, then harmonic and EMI noise can be reduced, but extra harmonics are introduced and hardware requirements increase

Engineering Contradiction:

Improveharmonic noise and EMI noiseVSAvoidhardware requirements

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent uses self-service by implementing harmonic suppression through software-based modulation techniques only, without requiring any additional hardware components. The carrier wave with DC offset inherently suppresses harmonics while the system serves its own noise reduction needs

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent extracts only the essential modulation function needed for noise suppression by using a simplified carrier wave approach with DC offset, eliminating the need for complex additional hardware while achieving the desired harmonic and EMI noise reduction

Inventive Principle:

Principle #2Taking out (Extraction)

3Object-affected harmful factors

If SPWM techniques are applied to reduce harmonic and EMI noise, then noise suppression can be achieved, but the techniques are restricted to three-phase systems

Engineering Contradiction:

Improveharmonic and EMI noiseVSAvoidapplication scope

Core Design Contradiction:

Object-affected harmful factorsVSAdaptability or versatility

Solution Approach 1:

The patent achieves universality by developing a carrier wave modulation technique with DC offset that can be applied to any bridge configuration (half-bridge, H-bridge, three-phase bridge), making the noise suppression method universally applicable across different system topologies and phases

Inventive Principle:

Principle #6Universality (Multi-functionality)

4Object-affected harmful factors

If the modulation index and duty cycle are adjusted to reduce total harmonic energy, then harmonic and EMI noise can be suppressed, but the optimization becomes complex

Engineering Contradiction:

Improvetotal harmonic energyVSAvoidmodulation control complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent uses parameter changes by systematically adjusting the carrier wave DC offset and modulation index based on derived closed-form expressions, transforming the complex optimization problem into a structured parameter adjustment process that reduces total harmonic energy effectively

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS10541602B2SPWM with DC offset based on total energy reduction

Publication Date: 2020.01.21 UNIV OF FLORIDA RESEARCH FOUNDATION INC

AI summary

Various examples related to sinusoidal pulse width modulation (SPWM) techniques for harmonic and electromagnetic interference (EMI) noise suppression are provided. In one example, a method includes applying a DC offset to a sinusoidal modulation waveform to change an average duty cycle of a switching circuit; and controlling switching of an array of switches of the switching circuit based at least in part upon the offset sinusoidal modulation waveform and a carrier waveform, thereby reducing total energy. In another example, a system includes a switching circuit with an array of semiconductor switches that control application of a voltage source to a load; and controller circuitry that can control switching of the array of semiconductor switches by applying a DC offset to a sinusoidal modulation waveform to change an average duty cycle of the switching circuit.