Multilevel Inverter Neutral-Phase Control for DC Midpoint Voltage Ripple

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Solution Overview

Problem

Conventional multilevel inverters experience DC midpoint voltage ripple and imbalance due to large single-phase loads or short circuits, potentially damaging capacitors and active components.

Innovation Solution

A method and system for generating neutral-phase reference and compensation waveforms to create switch command signals that control the inverter switches, reducing DC midpoint voltage ripple and imbalance by ensuring equivalent connection times to the midpoint rail during switching cycles.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If conventional multilevel inverter switching is used to handle large single-phase loads, then the inverter can accommodate unbalanced load conditions, but DC midpoint voltage ripple and imbalance occur that can damage capacitors and active components

Engineering Contradiction:

Improveability to handle unbalanced load conditionsVSAvoidDC midpoint voltage stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The control system continuously monitors the DC midpoint voltage and uses this feedback information to dynamically adjust the neutral-phase switch command signals. This closed-loop control ensures that the neutral phase connects to the midpoint rail for equivalent periods, actively compensating for voltage ripple and maintaining DC midpoint voltage stability under unbalanced load conditions

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The invention implements periodic switching of the neutral-phase switches at the fundamental frequency and its harmonics. By connecting the neutral phase to the midpoint rail for equivalent periods during switching cycles, the system creates a periodic balancing action that eliminates DC midpoint voltage ripple while maintaining the ability to handle unbalanced loads

Inventive Principle:

Principle #19Periodic action

2Power

If active components are cycled to regulate voltages in the inverter, then voltage regulation is achieved, but ripple is induced in the DC midpoint voltage causing voltage stress on capacitors and active components

Engineering Contradiction:

Improvevoltage regulation capabilityVSAvoidDC midpoint voltage ripple and voltage stress

Core Design Contradiction:

PowerVSObject-affected harmful factors

Solution Approach 1:

The neutral-phase switches act as an intermediary element between the neutral wire and the DC midpoint rail. By controlling these switches to connect the neutral phase to the midpoint rail for equivalent periods, the system mediates the voltage imbalance caused by active component cycling, reducing DC midpoint voltage ripple and protecting capacitors and active components from excessive voltage stress

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentEP3694097A1Multilevel active inverters and methods of controlling multilevel active inverters

Publication Date: 2020.08.12 HAMILTON SUNDSTRAND CORP

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AI summary

A method of controlling an inverter includes generating a neutral-phase reference waveform, generating a neutral-phase midpoint compensation waveform using the neutral-phase reference waveform, and generating a neutral-phase compensated duty cycle waveform using the neutral-phase midpoint compensation waveform. Neutral-phase switch command signals are generated for switches of a neutral-phase of the inverter using the neutral-phase compensated duty cycle waveform. Inverters and computer program products are also described.