Inverter Control Reducing Harmonic Distortion

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Solution Overview

Problem

DC to AC inverters face challenges in reducing total harmonic distortion and voltage unbalance due to unregulated negative sequence and zero sequence components, particularly when powering single phase loads, as existing control schemes do not provide infinite gain at relevant frequencies, leading to increased harmonics and unbalanced output voltages.

Innovation Solution

A control system employing multiple synchronous reference frame control structures with voltage controllers providing infinite gain at specific frequencies, along with a shared current controller and a neutral control structure, to regulate negative sequence and zero sequence components, ensuring wideband control and reduced harmonic distortion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If natural frame control scheme is used, then control structure is simple and identical for each phase, but controller does not provide infinite gain at harmonic frequencies leading to increased total harmonic distortion and voltage unbalance

Engineering Contradiction:

Improvecontrol structure complexityVSAvoidoutput voltage quality

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The control system is segmented into multiple synchronous reference frame control structures, each dedicated to controlling a specific frequency component (fundamental, negative sequence, zero sequence, harmonics). This segmentation allows each controller to provide infinite gain at its target frequency while maintaining manageable individual controller complexity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent transitions from natural frame control to synchronous reference frame control, changing the dimensional approach by introducing rotating reference frames that rotate at different speeds and directions. This allows controllers to operate at DC in their respective reference frames, achieving infinite gain at specific frequencies.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Manufacturing precision

If synchronous reference frame control scheme is used, then infinite gain is provided at fundamental frequency, but controller bandwidth is limited causing gaps in control action and insufficient negative sequence attenuation

Engineering Contradiction:

Improvefundamental frequency control precisionVSAvoidcontrol coverage continuity

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

Multiple synchronous reference frame control structures are used, each with a voltage controller operating at a specific frequency. This segmentation ensures that each controller maintains infinite gain at its designated frequency without bandwidth limitations, eliminating control gaps.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The shared current controller serves multiple functions by acting as an inner control loop for all voltage controllers simultaneously. It processes current references from different frequency controllers and generates unified voltage commands, ensuring continuous and comprehensive control coverage.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Adaptability or versatility

If single phase loads are powered from multiphase inverter, then inverter versatility is improved, but unbalanced loading creates negative sequence and zero sequence currents increasing total harmonic distortion

Engineering Contradiction:

Improveload compatibilityVSAvoidharmonic distortion and voltage unbalance

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

The control system uses feedback from voltage and current measurements to continuously regulate negative sequence and zero sequence components. Voltage controllers compare actual voltages with reference values and adjust current references accordingly, while the shared current controller implements these adjustments through voltage commands to bridge circuits.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent converts the harmful effect of unbalanced loading into a controllable parameter. Instead of treating negative sequence and zero sequence currents as unwanted byproducts, the control system actively regulates them using dedicated synchronous reference frame controllers, transforming the problem into a controlled adjustment mechanism.

Inventive Principle:

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

Data Source

PatentUS10326352B2Control of AC source inverter to reduce total harmonic distortation and output voltage unbalance

Publication Date: 2019.06.18 GE AVIATION SYSTEMS LLC

AI summary

Systems and methods for controlling a DC to AC inverter providing a multiphase output at a fundamental frequency are provided. More particularly, a synchronous reference frame control scheme can be employed to regulate a DC to AC inverter to attenuate error at various frequencies of interest for the DC to AC inverter. According to particular example aspects of the present disclosure, the synchronous reference frame control scheme can include control structures to provide for attenuation of the negative sequence and zero sequence currents, leading to reduced total harmonic distortion and voltage unbalance in the output voltage of the inverter.