Inverter Phase Synchronization for Seamless Grid Reconnection
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Solution Overview
Problem
Power conversion systems (PCS) face interruptions when switching from standalone to interconnected operation upon power system restoration, leading to potential power failures and inefficiencies due to phase differences between inverter and system voltages, which can result in overvoltage or overcurrent issues.
Innovation Solution
A power conversion apparatus with a control circuit that detects power system failures, calculates a phase difference between inverter and system voltages, and generates an output frequency pattern to synchronize the inverter frequency with the system frequency, allowing seamless transition from standalone to interconnected operation without interruptions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the PCS is halted when power is restored and then switched to interconnected operation, then phase synchronization can be achieved, but power supply to the electric load is interrupted
Solution Approach 1:
The control circuit performs preliminary actions by detecting power restoration, calculating phase difference, and adjusting inverter frequency before closing the switch to interconnected operation. This ensures phase synchronization is achieved in advance, allowing seamless transition without power interruption to the electric load.
Solution Approach 2:
The inverter frequency is dynamically adjusted based on the calculated phase difference between inverter voltage and system voltage. The control circuit continuously monitors and modifies the frequency during the transition period, enabling smooth phase synchronization while maintaining continuous power supply to the load.
2Speed
If the phase of the output voltage of the inverter is rapidly synchronized with the phase of the system voltage, then transition speed is improved, but adverse effects on electric load occur
Solution Approach 1:
The phase synchronization process is made dynamic by continuously adjusting the inverter frequency based on real-time phase difference calculations. The control circuit modifies the frequency adjustment rate adaptively, enabling fast synchronization while preventing abrupt changes that could harm the electric load.
Solution Approach 2:
The inverter operating parameters (frequency) are changed in a controlled manner during phase synchronization. The control circuit adjusts the frequency parameter dynamically, changing it at an optimized rate that achieves rapid synchronization without creating harmful effects on connected electric loads.
3Object-affected harmful factors
If the synchronization is achieved gently, then adverse effects on electric load are reduced, but energy stored in power storage device is wasted
Solution Approach 1:
The synchronization process uses dynamic frequency adjustment that adapts to the current phase difference and system conditions. This dynamic approach allows the system to achieve gentle synchronization when needed while minimizing energy wastage by optimizing the adjustment rate based on real-time measurements.
Solution Approach 2:
The control circuit optimizes the frequency parameter changes to balance between gentleness and energy efficiency. By carefully controlling the rate and magnitude of frequency adjustments, the system achieves phase synchronization that is gentle enough to protect electric loads while minimizing energy loss from the power storage device.
Data Source
AI summary
An apparatus according to an embodiment includes a control circuit to control operations of an inverter and a switch. The control circuit judges whether or not a power system has a power failure, based on values of the system voltage and a frequency of the power system; and calculates a phase difference between a phase of the output voltage of the inverter and a phase of the system voltage and generate, by means of the phase difference, an output frequency pattern for changing a frequency of the output voltage of the inverter. The control circuit, when it is judged that the power system has recovered from the power failure, controls the inverter to change the frequency of the output voltage of the inverter in line with the output frequency pattern, and closes the switch after the phase difference becomes smaller than or equal to a threshold.