Microgrid Synchronization via Synchrophasor Phase Angle Control

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Solution Overview

Problem

Microgrids face challenges in synchronizing with the main grid after islanding, leading to potential equipment damage due to voltage phase angle differences, which can cause inrush currents and system oscillations during reconnection.

Innovation Solution

A method and system utilizing synchrophasor measurements and a digital controller to calculate phase angle differences and adjust the frequency of diesel generators, ensuring synchronization by eliminating voltage phase angle mismatches across the circuit breaker, thereby facilitating seamless reconnection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the microgrid is disconnected from the main grid during emergency islanding, then the microgrid can operate autonomously and maintain local power supply reliability, but the microgrid loses synchronization with the main grid leading to voltage phase angle differences that cause inrush currents and system oscillations during reconnection

Engineering Contradiction:

Improvelocal power supply reliabilityVSAvoidinrush current and system oscillation

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The control system continuously monitors voltage phase angles and frequency differences before reconnection occurs. By performing preliminary synchronization checks and adjusting generator output in advance, the system eliminates voltage phase angle differences before the circuit breaker closes, preventing inrush currents and oscillations during the actual reconnection event

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system uses real-time feedback from phase angle sensors and frequency monitors to continuously adjust the diesel generator's output frequency and phase. This closed-loop control ensures that the microgrid remains synchronized with the main grid during the reconnection process, eliminating the harmful effects of phase mismatches

Inventive Principle:

Principle #23Feedback

2Speed

If the circuit breaker attempts to reconnect the microgrid without synchronization control, then reconnection speed is fast, but voltage phase angle differences reach up to 60 degrees causing huge inrush currents that can damage equipment

Engineering Contradiction:

Improvereconnection speedVSAvoidequipment durability

Core Design Contradiction:

SpeedVSStrength

Solution Approach 1:

The control system performs preliminary synchronization adjustments by modifying the diesel generator's frequency and phase output before the reconnection moment. This preliminary action eliminates voltage phase angle differences in advance, allowing fast reconnection without equipment damage

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system dynamically changes the frequency and phase angle parameters of the diesel generator output to match the main grid parameters. By adjusting these parameters in real-time before reconnection, the system achieves both fast reconnection speed and protection against inrush currents

Inventive Principle:

Principle #35Parameter changes

3Reliability

If synchrophasor measurements and digital control are used to calculate phase angle differences and adjust generator frequency, then seamless reconnection is achieved without shutting down generators, but the system complexity increases

Engineering Contradiction:

Improveseamless reconnection capabilityVSAvoidcontrol system complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The system replaces mechanical synchronization methods with digital synchrophasor measurements and computational control algorithms. Digital processors calculate phase angle differences and automatically adjust generator frequency, achieving seamless reconnection while managing complexity through software-based control rather than complex mechanical synchronization devices

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS9720395B2Synchronization control for reconnecting microgrid to main grid after islanding

Publication Date: 2017.08.01 NEC CORP

AI summary

A method and system are provided. The method includes synchronously reconnecting a microgrid to a main grid after islanding of the microgrid. The synchronously reconnecting step includes calculating a phase angle difference between synchrophasor measurements collected from a common coupling on the main grid and synchrophasor measurements collected from a common coupling on the microgrid. The synchronously reconnecting step further includes calculating, by a controller, a frequency reference deviation based on the phase angle difference. The synchronously reconnecting step also includes adjusting a frequency of the diesel generator based on the frequency reference deviation.