Multilevel Converter Cell Capacitor Charging Circuit

Solution Overview

Problem

Existing multilevel power converter systems face complexity in charging cell capacitors, often requiring complicated circuitry with current-limiting resistors and switching circuits, which can be inefficient and costly.

Innovation Solution

The method involves applying an auxiliary DC voltage across the converter's DC bus terminals, alternately switching selected cells between a state to bypass them and a state to charge the capacitors using a charging current from an auxiliary source, eliminating the need for precharging resistors and associated circuitry by employing the existing cell switching circuitry with precharge logic.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional charging circuitry with current-limiting resistors and switching circuits is used, then capacitor charging can be achieved, but device complexity and cost increase

Engineering Contradiction:

Improvecapacitor charging reliabilityVSAvoidcharging circuit complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The existing cell switching circuitry is made to serve dual purposes: normal converter operation and capacitor precharging. The switching circuitry automatically performs both functions without requiring separate dedicated precharging components, as the same switches and control logic are reused for both operational modes.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The cell switching circuitry is designed to perform multiple functions: it handles normal power conversion operations during converter operation, and simultaneously serves as the charging circuitry for precharging cell capacitors during startup. This multi-functionality eliminates the need for separate precharging resistors and dedicated switching circuits.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Reliability

If separate precharging circuitry is implemented, then capacitor charging is ensured, but manufacturing cost increases

Engineering Contradiction:

Improvecapacitor charging reliabilityVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The existing cell switching circuitry is made to serve dual purposes: normal converter operation and capacitor precharging. The switching circuitry automatically performs both functions without requiring separate dedicated precharging components, as the same switches and control logic are reused for both operational modes.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The precharging function is merged with the existing cell switching circuitry rather than being implemented as a separate system. The same physical components (switches, control logic) are combined to perform both normal operation and precharging functions, reducing total component count and manufacturing cost.

Inventive Principle:

Principle #5Merging (Combining)

3Ease of operation

If current-limiting resistors are used in charging circuitry, then capacitor charging is controlled, but component quantity and complexity increase

Engineering Contradiction:

Improvecharging controlVSAvoidnumber of components

Core Design Contradiction:

Ease of operationVSQuantity of substance

Solution Approach 1:

The existing cell switching circuitry is made to serve dual purposes: normal converter operation and capacitor precharging. The switching circuitry automatically performs both functions without requiring separate dedicated precharging components, as the same switches and control logic are reused for both operational modes.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

Physical current-limiting resistors are replaced with electronic control of the switching circuitry. Instead of using passive resistive elements to limit current, the patent uses active switching control to regulate charging current, eliminating the need for separate current-limiting components.

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 approach simplifies the charging process, reduces component needs, and enhances efficiency by using the output inductors for charging, allowing for sequential or concurrent charging of capacitors without the need for precharging resistors, thus improving operational reliability and reducing costs.

Implementation Method 1

charging current from the auxiliary charging source... charge the capacitor or capacitors of the selected cell

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS9559541B2Modular multilevel converter and charging circuit therefor

Publication Date: 2017.01.31 ROCKWELL AUTOMATION TECH INC

AI summary

Methods and charging apparatus are presented for charging cell capacitors of a multilevel power conversion system, in which an auxiliary charging source is selectively applied across DC bus terminals while one or more selected multilevel converter cells are alternately switched between a first state to bypass the selected cell or cells and a second state to charge the cell capacitor or capacitors of the selected cell via charging current from the auxiliary charging source.