Virtual Synchronizer Grid-Connection Control for Inverter Voltage and Frequency
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Solution Overview
Problem
Conventional grid-connected control methods for energy-storage inverters based on virtual synchronizers fail to ensure seamless and impact-free connection to the grid, as they do not adequately synchronize voltage and frequency, leading to potential disruptions during grid-connected operations.
Innovation Solution
A grid-connected control method that synchronizes the output voltage and frequency of the inverter with the grid by adjusting the set output voltage and frequency within predefined thresholds, ensuring that the inverter is only connected when synchronous, thereby minimizing grid impact and enabling smooth power transfer between microgrids and external grids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the inverter is connected to the grid without adequate voltage and frequency synchronization checks, then the grid-connected operation can be initiated quickly, but it causes impact and disruptions to the grid during the connection process
Solution Approach 1:
The control device performs preliminary voltage and frequency synchronization checks before allowing grid connection. The synchronous determination unit evaluates whether the inverter's output voltage and frequency match the grid parameters within preset thresholds before enabling the connection switch, preventing premature connection that would cause grid disruptions.
Solution Approach 2:
The control device prevents grid connection when synchronization conditions are not met by blocking the connection switch. This preliminary protective action avoids the harmful effect of asynchronous connection, which would cause voltage shocks and frequency disruptions to the grid system.
2Reliability
If strict voltage and frequency synchronization thresholds are enforced before grid connection, then grid impact is minimized, but the complexity of the control system increases
Solution Approach 1:
The control device uses adjustable preset thresholds for voltage and frequency synchronization. These parameters can be configured according to specific application requirements, allowing flexibility in balancing connection reliability and system complexity. The synchronous determination unit compares actual parameters against these configurable thresholds to make connection decisions.
Solution Approach 2:
The control system is divided into distinct functional modules: a detection unit for monitoring voltage and frequency, a synchronous determination unit for evaluating synchronization conditions, and a control unit for executing connection decisions. This modular segmentation simplifies the overall control architecture while maintaining comprehensive synchronization checks.
3Measurement precision
If the inverter output voltage and frequency are continuously adjusted to match grid parameters, then synchronization accuracy is improved, but the adjustment time and control complexity increase
Solution Approach 1:
The control device adjusts the inverter's output voltage and frequency to match grid parameters only to the extent necessary for successful synchronization. Rather than continuous fine-tuning, the system makes sufficient adjustments to meet the preset thresholds, then proceeds with connection, reducing adjustment time while maintaining adequate synchronization accuracy.
Data Source
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AI summary
A grid-connected control method based on a virtual synchronizer is provided. The method includes: detecting whether a first deviation between an output voltage of an inverter and a voltage of a grid exceeds a first set voltage threshold, and adjusting a set output voltage of the inverter if the first deviation exceeds the first set voltage threshold, so that the first deviation falls within the first set voltage threshold; detecting whether a second deviation between an output frequency of the inverter and a frequency of the grid exceeds a first set frequency threshold, and adjusting a set output frequency of the inverter if the second deviation exceeds the first set frequency threshold, so that the second deviation falls within the first set frequency threshold; and controlling the inverter to connect to the grid. A grid-connected control device based on a virtual synchronizer is further provided.