Microgrid Inverter Startup Sequencing for Stable Frequency Sharing
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Solution Overview
Problem
In independent microgrids without rotating-type generators, frequency and voltage fluctuations can occur during startup due to the absence of rotating-type generators, leading to instability in grid frequency, grid voltage, and converter operations.
Innovation Solution
A startup method for microgrids involving a master and slave inverter power supplies, where the master starts up in Constant Voltage Constant Frequency (CVCF) mode, followed by the slave in grid interconnection mode, and then both switch to droop mode or Virtual Synchronous Generator (VSG) mode when output fluctuations reach a predetermined threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If inverter power supplies start up simultaneously in independent microgrid without rotating-type generators, then quick recovery from power outage is achieved, but frequency and voltage fluctuations occur causing instability
Solution Approach 1:
The startup process is segmented into distinct phases: master inverter starts first in CVCF mode to establish stable frequency and voltage, then slave inverters start subsequently in grid interconnection mode. This temporal segmentation prevents simultaneous startup conflicts and eliminates frequency/voltage fluctuations while maintaining quick recovery.
Solution Approach 2:
The master inverter performs preliminary action by starting first and establishing the grid voltage and frequency before slave inverters connect. This preliminary stabilization creates a stable foundation that prevents fluctuations when slave inverters join the system.
2Adaptability or versatility
If master and slave inverters operate in droop mode or VSG mode from startup, then load sharing is achieved, but frequency and voltage fluctuations occur during startup
Solution Approach 1:
The control mode dynamically transitions from CVCF mode (stable frequency/voltage) during startup to droop mode or VSG mode (load sharing) after stabilization. This dynamic adaptation allows the system to prioritize stability during startup, then transition to load sharing capability once the grid is established.
Solution Approach 2:
The master inverter performs preliminary action by establishing stable frequency and voltage in CVCF mode before slave inverters connect. Only after this preliminary stabilization does the system transition to droop mode or VSG mode for load sharing, preventing startup fluctuations.
3Adaptability or versatility
If slave inverter starts up in grid interconnection mode without master stabilization, then independent operation is achieved, but phase and voltage fluctuations occur
Solution Approach 1:
The master inverter performs preliminary action by establishing stable grid voltage and frequency before slave inverters attempt grid interconnection. This preliminary stabilization ensures that when slave inverters connect, they synchronize with a stable reference, eliminating phase and voltage fluctuations.
Solution Approach 2:
The master inverter acts as an intermediary that provides a stable reference voltage and frequency for slave inverters to synchronize with during grid interconnection. This intermediary role ensures precise phase and voltage alignment when slave inverters join the system.
Data Source
AI summary
A startup method and startup program for microgrid that enable to stably start up the microgrid without producing frequency fluctuation is provided. An embodiment of the present disclosure is a startup method for microgrid configured by a plurality of inverter power supplies independently sharing a load and divided into a master that starts up first and a slave that starts up secondly and later, the startup method comprising: a master initial startup step of initially starting up the master in a CVCF mode; a slave initial startup step of initially starting up the slave in a grid interconnection mode; and a control mode changing step of the master and the slave changing control modes thereof when output fluctuation of the master and the slave becomes a predetermined threshold or less or when the master and the slave or other inverter power supplies become a predetermined operation state while output voltage of said master and said slave becomes a predetermined threshold or less.