Active Compensation Circuit for Zero-Sequence Current Limiting

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Solution Overview

Problem

Existing systems using voltage inverters in electrotechnical systems struggle to effectively eliminate various types of zero-sequence currents, particularly when inverters are connected in parallel, leading to inter-inverter and parasitic currents that cause overvoltages and electromagnetic compatibility issues.

Innovation Solution

An active compensation circuit using a magnetic component with a voltage source is introduced to generate a zero-sequence magnetic flux that opposes the zero-sequence currents, canceling or limiting them through a coil wound around a magnetic core connected to the converters, allowing for serial active compensation of zero-sequence components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If voltage inverters are connected in parallel to handle higher currents with reduced size, then the current handling capacity and power density are improved, but inter-inverter zero-sequence currents and electromagnetic compatibility issues worsen

Engineering Contradiction:

Improvecurrent handling capacityVSAvoidzero-sequence currents

Core Design Contradiction:

PowerVSObject-affected harmful factors

Solution Approach 1:

A tertiary winding is introduced as an intermediary element between the primary and secondary windings of the transformer. This tertiary winding is specifically designed to counterbalance zero-sequence currents by generating opposing magnetic flux, thereby eliminating the harmful effects of parallel inverter operation while maintaining the power handling benefits

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention converts the harmful zero-sequence currents into a useful function by using them to generate magnetic flux in the tertiary winding. This flux is then used to create counterbalancing effects that actively cancel the harmful currents, transforming a problematic phenomenon into a control mechanism

Inventive Principle:

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

2Object-affected harmful factors

If common-mode current limiting circuits are used to eliminate zero-sequence currents, then electromagnetic compatibility is improved, but the circuit complexity and device size increase

Engineering Contradiction:

Improvezero-sequence currentsVSAvoidcircuit structure

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The zero-sequence current limiting function is merged into the existing transformer structure by adding a tertiary winding to the magnetic core. This integrates the compensation function into the power transformation process itself, eliminating the need for separate common-mode filtering circuits and reducing overall system complexity

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The transformer is designed with multi-functionality: the primary windings handle power transformation, the secondary windings provide isolation and voltage transformation, and the tertiary windings provide zero-sequence current compensation. This single device performs multiple functions that would otherwise require separate components

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Object-affected harmful factors

If certain switching states are prohibited to limit zero-sequence currents, then zero-sequence current reduction is achieved, but the converter control flexibility and power handling capability are reduced

Engineering Contradiction:

Improvezero-sequence currentsVSAvoidconverter control flexibility

Core Design Contradiction:

Object-affected harmful factorsVSAdaptability or versatility

Solution Approach 1:

The invention replaces the mechanical/control-based approach of prohibiting switching states with a magnetic field-based approach using the tertiary winding. This substitution allows full switching flexibility to be maintained while achieving zero-sequence current compensation through magnetic flux interactions rather than control restrictions

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This solution effectively eliminates all types of zero-sequence currents, including those between inverters and ground, reduces magnetic component saturation, and optimizes the design by reducing the necessary impedance and weight of magnetic components, while maintaining the benefits of parallel inverter operation and voltage interleaving.

Implementation Method 1

an active compensation circuit comprising a magnetic component and a voltage source connected to the magnetic component, the voltage source and the magnetic component being adapted to serially inject an active compensation voltage of the zero-sequence voltages generated by the converter

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS10790697B2System for converting electrical energy supplied by a network and a conversion method implemented by means of such a conversion system

Publication Date: 2020.09.29 GE ENERGY POWER CONVERSION TECHNOLOGY LTD(GB)

AI summary

This system for converting the electrical energy delivered by a supply network comprises of: a converter and at least one zero-sequence current limiting stage flowing in the converter. The or each limiting stage comprises an active compensation circuit comprising a magnetic component and a voltage source connected to the magnetic component, the voltage source and the magnetic component being adapted to serially inject with the converter an active compensation voltage of the zero-sequence voltages generated by the converter.