Power Conversion Device Connection Failure Detection

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Solution Overview

Problem

Existing power conversion devices for railway vehicles fail to accurately detect connection failures between inverters and induction motors, particularly in systems with multiple motors connected in parallel, leading to potential overheating and motor burnout due to incorrect wiring or phase disconnections.

Innovation Solution

A power conversion device with a current vector detecting unit, slip frequency calculating unit, speed estimating unit, and connection failure detecting device that uses exciting current detection values to identify connection failures without additional sensors, and employs voltage vector calculation to ensure torque current command adherence, allowing for accurate detection of disconnections and reverse phase errors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If existing detection methods are used in multi-motor systems, then device complexity is reduced, but connection failure detection accuracy deteriorates

Engineering Contradiction:

Improveconnection failure detection accuracyVSAvoiddetection system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The system uses its own existing current detection resources (exciting current detection unit) to detect connection failures, rather than adding separate detection sensors. The control device leverages current data it already collects for motor control purposes to simultaneously detect wiring abnormalities, making the detection system self-sufficient without external additions.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The exciting current detection unit serves dual purposes: it provides exciting current information necessary for vector control of the induction motors, and simultaneously enables connection failure detection by analyzing deviations in exciting current values. This multi-functionality eliminates the need for dedicated detection hardware.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Reliability

If additional sensors are added to detect connection failures, then detection accuracy is improved, but device cost increases

Engineering Contradiction:

Improveconnection failure detection reliabilityVSAvoiddevice cost

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The control device uses its own existing current detection resources (exciting current detection unit) to detect connection failures, rather than adding separate detection sensors. The control device leverages current data it already collects for motor control purposes to simultaneously detect wiring abnormalities, making the detection system self-sufficient without external additions.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The exciting current value serves as an intermediary parameter that links motor control operations with connection failure detection. By monitoring changes in this intermediary current parameter, the system can infer wiring abnormalities without direct physical contact or additional sensing at the connection points.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of operation

If torque-based detection is used, then detection capability is provided, but detection accuracy deteriorates under feedback control

Engineering Contradiction:

Improvedetection capabilityVSAvoiddisconnection detection accuracy

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The invention extracts connection failure detection capability from the torque control loop by using exciting current as the detection parameter. This separates the detection function from torque regulation, allowing connection failures to be detected independently of feedback control actions that mask torque variations.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentEP3200340B1Power conversion device

Publication Date: 2019.01.23 HITACHI LTD

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AI summary

A power conversion device includes: a current vector detecting unit (5) that generates a torque current detection value (Iqf) and an exciting current detection value from a current detection value between the power conversion device and the plurality of induction motors (8A, 8B, 8C, and 8D); a slip frequency calculating unit (3) that generates a slip frequency on the basis of a torque current command value (Iqp) and an exciting current command value (Idp); a speed estimating unit (4) that generates an estimation speed of the induction motor on the basis of a deviation between the torque current detection value (Iqf) and the torque current command value (Iqp); a connection failure detecting device (6) that detects a connection failure of the plurality of induction motors (8A, 8B, 8C, and 8D) on the basis of the exciting current detection value; and a voltage vector calculation unit (1) that generates a voltage command value on the basis of an inverter frequency generated on the basis of the slip frequency and the estimation speed such that the torque current detection value (Iqf) follows the torque current command value (Iqp), the torque current command value (Iqp), and the exciting current command value (Idp).