Grid-Tie Inverter Synchronization via Common Time Source
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Solution Overview
Problem
In islanded mode, distributed energy resources (DERs) face challenges in maintaining phase alignment due to the lack of a common synchronization source, leading to potential delays in reconnection to the grid when load demand increases, as phase lock loops drift and require synchronization with each other and the macrogrid, and existing methods like sequential inverter connection have limited success.
Innovation Solution
Implementing a common time source, such as a GPS-based timing signal, to synchronize grid-tie inverters across DERs, allowing them to maintain phase alignment and reconnection in parallel, regardless of geographic location, and using DER controllers to determine connection states and adjust synchronization signals based on measured grid values or a common time signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sequential inverter connection is used to synchronize DERs, then phase alignment can be maintained, but reconnection speed and productivity are significantly reduced
Solution Approach 1:
The patent introduces an intermediary synchronization signal derived from the grid voltage that mediates between multiple inverters. This signal acts as a common reference that all inverters can lock onto simultaneously, eliminating the need for sequential connection while maintaining phase alignment. The synchronization signal serves as a mediator that coordinates all inverters to connect in parallel without phase conflicts.
Solution Approach 2:
The patent implements preliminary synchronization by pre-aligning the phase of each inverter output to match the synchronization signal before connection. The control system adjusts the phase angle of each inverter in advance so that when all inverters connect to the grid simultaneously, they are already phase-aligned, eliminating the need for sequential connection and enabling rapid parallel reconnection.
2Adaptability or versatility
If phase lock loops are used without a common synchronization source, then each inverter can operate independently, but phase drift occurs leading to synchronization errors
Solution Approach 1:
The patent merges the independent phase lock loops of multiple inverters by introducing a common synchronization signal that all inverters share. Instead of operating completely independently, the inverters combine their phase control efforts by referencing the same synchronization signal, which is derived from the grid voltage. This merging approach maintains independent operation capability while ensuring consistent phase alignment across all inverters.
3Adaptability or versatility
If multiple DERs are located at different geographic locations, then system coverage and adaptability are improved, but phase shifts and synchronization difficulties increase
Solution Approach 1:
The patent uses the grid voltage as an intermediary synchronization reference that is common to all DERs regardless of their geographic location. Each DER locally derives the synchronization signal from the grid voltage at its location, eliminating the need for direct communication between geographically distributed inverters. This intermediary approach maintains phase synchronization reliability while allowing broad geographic distribution of DERs.
Data Source
AI summary
The present disclosure pertains to systems and methods for selectively synchronizing one or more power conversion units of one or more distributed energy resources with a common time source when in an islanded state and with a measured phase angle of a grid when in a grid-connected state. In various embodiments, detecting whether the distributed energy resource is in a grid-connected state or an islanded state comprises microprocessor based analysis of measurement and monitoring data collected by intelligent electronic devices associated with the grid.