DC/AC Converter Control Law for Grid Disappearance

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Solution Overview

Problem

DC/AC converters face instability and safety risks during switching from current source mode to virtual synchronous generator mode, particularly when the electrical network disappears, leading to voltage and frequency instabilities and operational hazards.

Innovation Solution

A control law is implemented that defaults to current source mode but switches to virtual synchronous generator mode upon network disappearance, monitoring frequency and phase to emulate the synchronous generator mode without interrupting power, using a control law with routines for current source and synchronous generator operations, and a switching management module to manage the transition.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the converter switches from current source mode to virtual synchronous generator mode upon network disappearance, then the converter can maintain network stability and continue supplying power, but voltage and frequency instabilities occur during the switching transition

Engineering Contradiction:

Improvenetwork stabilityVSAvoidvoltage and frequency stability

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The control law pre-prepares the converter for mode switching by continuously monitoring network frequency and phase while in current source mode. This preliminary monitoring and preparation enables a smoother transition to virtual synchronous generator mode, reducing voltage and frequency instabilities during the switching event.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The converter dynamically adapts its control mode based on network conditions. The control law automatically transitions from current source mode to virtual synchronous generator mode when network disappearance is detected, allowing the system to maintain stability under varying operational conditions while continuing to supply power.

Inventive Principle:

Principle #15Dynamics

2Stability of the object's composition

If the converter operates in current source mode by default, then the converter affords relative stability to the electrical distribution network, but the converter cannot respond to network insufficiency or disappearance

Engineering Contradiction:

Improvenetwork stabilityVSAvoidresponse to network disappearance

Core Design Contradiction:

Stability of the object's compositionVSAdaptability or versatility

Solution Approach 1:

The converter is designed with dynamic mode-switching capability that allows it to operate in current source mode during normal network conditions (providing stability) and automatically transition to virtual synchronous generator mode when network insufficiency or disappearance occurs (providing adaptability). This dynamic adaptation resolves the contradiction between default stability and emergency response capability.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The converter is equipped with multi-functionality through the control law that enables it to perform both current source operation (for normal stable network conditions) and virtual synchronous generator operation (for network insufficiency or disappearance). This universal capability allows the single converter to handle multiple operational scenarios, resolving the contradiction between default mode stability and adaptability to network failures.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Adaptability or versatility

If the converter operates in virtual synchronous generator mode, then the converter can respond to network disappearance and distribute loads, but the mode presents danger to operators and requires particular precautions during maintenance

Engineering Contradiction:

Improveresponse to network disappearanceVSAvoidsafety risk to operators

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The converter dynamically switches between operational modes based on network conditions. It operates in the safer current source mode during normal conditions and only transitions to virtual synchronous generator mode when network disappearance is detected. This dynamic approach minimizes the time the converter spends in the potentially hazardous mode, reducing exposure to safety risks for operators while maintaining the necessary adaptability to respond to network failures.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS11394314B2Control method of a DC/AC converter

Publication Date: 2022.07.19 SCHNEIDER ELECTRIC IND SAS

AI summary

A method for controlling a DC/AC converter connected to an electrical network, the converter being controlled by a control law that is configured to require the converter to operate, by default, in a current source mode, and in case of disappearance of the electrical network, to control the switching of said converter from the current source mode to a virtual synchronous generator mode, the control law being also configured to, as long as the converter is running in the current source mode, monitor the electrical network frequency and phase allowing the initialization of the emulation of the virtual synchronous generator mode, by said control law, at the time of detection of the disappearance of the electrical network.