Neutral Line Detection Circuit Using EMI Capacitors in Three-Phase Loads

Solution Overview

Problem

Existing methods for detecting the neutral line in three-phase power electronic converters are inefficient, costly, and alter the circuit structure, leading to additional losses and increased design costs.

Innovation Solution

A neutral line detection circuit and method using capacitors connected in series with phase branches of a three-phase circuit, allowing for reliable detection by transitioning load conditions and comparing load characteristic quantities to determine the presence or absence of a neutral line without additional equipment or power loss.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If additional resistors are used to detect the neutral line, then the detection function is achieved, but the circuit structure is changed and normal operation is affected

Engineering Contradiction:

Improveneutral line detection accuracyVSAvoidcircuit structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The existing EMI filter capacitors in the three-phase power electronic converter are made to serve dual purposes: their original EMI filtering function and the additional function of neutral line detection. By utilizing the capacitors already present in the circuit, the patent eliminates the need for separate detection equipment, thereby maintaining circuit structure simplicity while achieving reliable neutral line detection.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The system uses its own existing components (EMI filter capacitors) to perform the detection function rather than relying on external additional equipment. The capacitors inherently present in the circuit are leveraged to detect the neutral line, making the system self-sufficient and avoiding structural modifications.

Inventive Principle:

Principle #25Self-service

2Reliability

If additional resistors are used to detect the neutral line, then the detection function is achieved, but additional power loss is produced and efficiency is reduced

Engineering Contradiction:

Improveneutral line detection accuracyVSAvoidpower loss

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The existing EMI filter capacitors in the three-phase power electronic converter are made to serve dual purposes: their original EMI filtering function and the additional function of neutral line detection. By utilizing the capacitors already present in the circuit, the patent eliminates the need for separate detection equipment, thereby maintaining circuit structure simplicity while achieving reliable neutral line detection.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The system uses its own existing components (EMI filter capacitors) to perform the detection function rather than relying on external additional equipment. The capacitors inherently present in the circuit are leveraged to detect the neutral line, making the system self-sufficient and avoiding structural modifications.

Inventive Principle:

Principle #25Self-service

3Reliability

If additional resistors are used to detect the neutral line, then the detection function is achieved, but design cost is increased

Engineering Contradiction:

Improveneutral line detection accuracyVSAvoiddesign cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The existing EMI filter capacitors in the three-phase power electronic converter are made to serve dual purposes: their original EMI filtering function and the additional function of neutral line detection. By utilizing the capacitors already present in the circuit, the patent eliminates the need for separate detection equipment, thereby maintaining circuit structure simplicity while achieving reliable neutral line detection.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The system uses its own existing components (EMI filter capacitors) to perform the detection function rather than relying on external additional equipment. The capacitors inherently present in the circuit are leveraged to detect the neutral line, making the system self-sufficient and avoiding structural modifications.

Inventive Principle:

Principle #25Self-service

Data Source

PatentEP4679706A1Neutral line detection circuit and method

Publication Date: 2026.01.14 DELTA ELECTRONICS (SHANGHAI) CO LTD

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Figure 3A~3B

AI summary

The present disclosure discloses a neutral line detection circuit (100) and method (200). The neutral line detection circuit (100) configured for a three-phase circuit (10)comprises three switches (20: S1, S2, S3) connected in series with respective phase branches (11) of the three-phase circuit (10); three first capacitors (30: C1, C2, C3) connected between a load neutral point (N) of the three-phase circuit (10) and first side nodes (A, B, C) of the respective switches(20: S1, S2, S3); three second capacitors (40: C4, C5, C6) connected between the load neutral point (N) and second side nodes (A', B', C') of the respective switches (20: S1, S2, S3); a controller configured to execute: changing a state of the at least one switch to establish different load conditions; detecting parameter values of at least one load characteristic quantity under different load conditions; calculating a comparison value of the parameter values of the load characteristic quantity under different load conditions; determining whether the comparison value is within a specified threshold, if yes, determining presence of a neutral line; if no, determining absence of the neutral line.