Backflow Commutation Control for Lower Recovery Current Loss

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Solution Overview

Problem

The practical use of novel high-efficiency power conversion devices is hindered by challenges such as high cost and crystal defects in wide band-gap semiconductor elements, making it difficult to achieve efficient power conversion for applications like air-conditioning compressors.

Innovation Solution

A backflow preventing device is introduced, comprising a backflow preventing element, a commutation device, and a controller that performs a commutation operation to redirect current flow, reducing recovery current and energy loss.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If wide band-gap semiconductor elements are used for high efficiency power conversion, then power conversion efficiency is improved, but cost increases and crystal defects occur

Engineering Contradiction:

Improvepower conversion lossVSAvoidcrystal defects

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The patent introduces a backflow preventing device as an intermediary component between the power conversion element and the load. This device includes a backflow preventing element and a commutation device that work together to redirect current flow, preventing direct backflow through the power conversion element and thereby reducing stress and crystal defects while maintaining high efficiency operation

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If backflow preventing element is used to prevent current backflow, then reliability is improved, but recovery current and energy loss increase

Engineering Contradiction:

Improvebackflow preventionVSAvoidrecovery current loss

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The commutation device acts as an intermediary that provides an alternative current path. When backflow occurs, the commutation device activates to redirect current through its own path rather than through the backflow preventing element, thereby eliminating recovery current losses while maintaining reliable backflow prevention

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The controller determines a time period for performing the commutation operation in advance and controls the commutation device to perform commutation based on this predetermined time period. This preliminary timing control ensures that commutation occurs at the optimal moment to prevent recovery current losses while maintaining reliable backflow prevention

Inventive Principle:

Principle #10Preliminary action

3Loss of energy

If commutation operation is performed continuously to reduce recovery current, then energy loss is reduced, but unnecessary energy consumption increases

Engineering Contradiction:

Improverecovery current lossVSAvoidcommutation operation energy

Core Design Contradiction:

Loss of energyVSUse of energy by moving object

Solution Approach 1:

The controller performs commutation operations periodically based on a determined time period rather than continuously. This periodic commutation is triggered only when needed to prevent backflow, eliminating unnecessary energy consumption while still achieving the goal of reducing recovery current losses

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The controller determines the time period for commutation operations in advance and controls the commutation device based on this predetermined timing. This preliminary timing determination ensures that commutation occurs only when necessary to reduce recovery current, avoiding continuous operation and unnecessary energy consumption

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS10003184B2Backflow preventing device, power conversion device, and refrigeration air-conditioning apparatus

Publication Date: 2018.06.19 MITSUBISHI ELECTRIC CORP

AI summary

A backflow preventing device includes a backflow preventing element connected between a power source and a load, for preventing a backflow of a current from the load side to the power source side, a commutation device configured to perform a commutation operation of causing a current to flow through an other path connected in parallel to the backflow preventing element, and a controller configured to change a pulse width of a commutation drive signal for controlling the commutation device to perform the commutation operation based on a current flowing through the backflow preventing element, and transmitting the commutation drive signal having the changed pulse width to the commutation device. The controller transmits the pulse to the commutation device only for a necessary time period so that the commutation device performs the commutation operation, to thereby reduce electric power relating to the commutation operation not contributing to the power conversion.