Three-Level Chopper Protection Circuit for Switch Failure

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Solution Overview

Problem

Conventional three-level chopper apparatuses face issues with capacitor overvoltage when a switch fails, leading to potential damage and inefficiency due to uncontrolled charging voltages.

Innovation Solution

Incorporation of a bidirectional protection switch circuit that can dynamically reroute current pathways to prevent overvoltage on capacitors during switch failures, using silicon diodes or a combination of silicon and silicon carbide diodes to minimize power loss and noise, and incorporating resistances and protection capacitors to dampen resonant currents.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional protection methods are used (turning off switches or inverter), then the speed controller is protected from failure, but capacitor overvoltage occurs due to uncontrolled resonant current charging

Engineering Contradiction:

Improveprotection against switch failureVSAvoidcapacitor overvoltage

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent introduces a protection switch circuit as an intermediary component between the resonant current path and the capacitor. This protection switch acts as a mediator that selectively blocks the harmful resonant current while allowing normal operation current to pass through, thereby protecting the capacitor from overvoltage without affecting the overall system protection mechanism

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent segments the protection function into two independent parts: (1) the main protection mechanism that turns off switches or inverter for overall system protection, and (2) the additional protection switch circuit that specifically protects against capacitor overvoltage. This segmentation allows each protection mechanism to address its specific function without interfering with the other, solving the contradiction between system protection and capacitor voltage control

Inventive Principle:

Principle #1Segmentation

2Reliability

If the other switch is turned off to protect against failure, then the speed controller is protected, but a series resonant current charges the capacitor to overvoltage

Engineering Contradiction:

Improveprotection against switch failureVSAvoidenergy loss due to overvoltage

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The protection switch circuit serves as an intermediary that specifically targets and blocks the harmful resonant current path while leaving the main power conversion function intact. This allows the system to maintain normal energy conversion efficiency during operation and only activates protection when needed, minimizing unnecessary energy loss

Inventive Principle:

Principle #24Intermediary (Mediator)

3Object-affected harmful factors

If bidirectional protection switch circuit is added to prevent overvoltage, then capacitor protection is improved, but device complexity increases

Engineering Contradiction:

Improvecapacitor overvoltage protectionVSAvoidcircuit complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent merges the protection switch circuit with the existing chopper circuit architecture, integrating the protection function into the current pathway structure. The protection switch is strategically placed within the existing circuit topology, allowing it to share structural elements and control mechanisms with the main circuit, thereby reducing the overall complexity increase that would result from a completely separate protection system

Inventive Principle:

Principle #5Merging (Combining)

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

Effectively inhibits capacitor overvoltage, reduces power loss, and enhances the reliability of the three-level chopper apparatus by ensuring safe and efficient operation even during switch failures.

Implementation Method 1

the protection switch circuit is controllable to change a current pathway through which an overvoltage is applied to the second capacitor or the first capacitor to a current pathway through which no overvoltage is applied to the second capacitor or the first capacitor

Methodology Applied

Scientific EffectElectrical conduction and current pathway control: Conduction (electrical)

Implementation Method 2

using silicon diodes or a combination of silicon and silicon carbide diodes to minimize power loss and noise

Methodology Applied

Scientific EffectDiode rectification and electrical conduction: Diode

Implementation Method 3

incorporating resistances and protection capacitors to dampen resonant currents

Methodology Applied

Scientific EffectElectrical resistance and energy dissipation: Electrical Resistance

Implementation Method 4

incorporating resistances and protection capacitors to dampen resonant currents

Methodology Applied

Scientific EffectResonance damping: Damping

Implementation Method 5

a first capacitor and a second capacitor connected in series to each other

Methodology Applied

Scientific EffectElectrical capacitance and energy storage: Capacitance

Data Source

PatentUS9893606B1Three-level chopper apparatus

Publication Date: 2018.02.13 FUJI ELECTRIC CO LTD

AI summary

A three-level chopper apparatus includes a protection switch circuit that changes a current pathway through which an overvoltage is applied to a second capacitor or a first capacitor to a current pathway through which no overvoltage is applied to the second capacitor or the first capacitor when a first switch or a second switch has a failure.