Wireless Secondary Control for Parallel Inverter Frequency Stability
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Solution Overview
Problem
Existing micro grid systems with parallel inverters face instability and inefficiencies due to droop control-induced frequency and voltage amplitude deviations, which are exacerbated by the need for communication lines and complex central or distributed controllers, and are not suitable for rapid load changes.
Innovation Solution
A wireless secondary control method that dynamically adjusts the droop bias of inverters by extracting AC signal values and regulating output voltage based on droop control principles, allowing inverters to automatically adjust their output power and synchronize frequency and voltage amplitude without communication lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If droop control technology is used to regulate active power and reactive power without communication lines, then the system complexity is reduced and geographical dispersion is enabled, but frequency and voltage amplitude deviation occurs compromising power sharing and frequency adjustment
Solution Approach 1:
Each inverter independently extracts AC signal values from its own output and performs secondary control calculations locally without requiring communication with other inverters. The inverter serves itself by using its own output voltage and current to generate compensation instructions, eliminating the need for interconnection lines while maintaining frequency and voltage stability.
Solution Approach 2:
The patent extracts AC signal values (frequency and voltage amplitude information) directly from the inverter's own output current and voltage signals. By extracting only the necessary control information from the full output signals and using only local resources, the system achieves secondary control without communication infrastructure.
2Reliability
If a central controller is used to send compensation instructions synchronically to parallel inverters, then frequency and voltage amplitude deviation is eliminated, but system complexity increases and system reliability decreases
Solution Approach 1:
The centralized secondary control function is segmented and distributed to each individual inverter. Each inverter independently performs the secondary control calculations that were previously centralized, dividing the control task into autonomous units that operate without coordination through communication lines.
Solution Approach 2:
Each inverter independently extracts AC signal values from its own output and performs secondary control calculations locally without requiring communication with other inverters. The inverter serves itself by using its own output voltage and current to generate compensation instructions, eliminating the need for interconnection lines while maintaining frequency and voltage stability.
3Reliability
If distributed controllers replace the central controller for secondary control, then system reliability is improved, but communication lines are still required increasing costs and reducing anti-interference performance
Solution Approach 1:
The patent extracts AC signal values (frequency and voltage amplitude information) directly from the inverter's own output current and voltage signals. By extracting only the necessary control information from the full output signals and using only local resources, the system achieves secondary control without communication infrastructure.
Solution Approach 2:
Each inverter independently extracts AC signal values from its own output and performs secondary control calculations locally without requiring communication with other inverters. The inverter serves itself by using its own output voltage and current to generate compensation instructions, eliminating the need for interconnection lines while maintaining frequency and voltage stability.
4Reliability
If integrator is used in the controller of parallel inverters for secondary control, then frequency and voltage amplitude deviation is compensated, but differences in controller parameters result in different stable operating points affecting power sharing characteristics
Solution Approach 1:
The patent changes the control approach from using an integrator that accumulates errors to using AC signal extraction and droop-based compensation. By extracting AC signal values and using them to generate compensation instructions through droop control relationships, the system maintains frequency and voltage stability while ensuring consistent power sharing characteristics across all inverters regardless of parameter variations.
Data Source
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AI summary
The present invention discloses a secondary control method and apparatus of parallel inverters in a micro grid, comprising: generating frequency and amplitude of fundamental voltage in the voltage instruction of inverter by droop control according to output voltage and output current of inverter to obtain a fundamental voltage instruction value; extracting voltage values and current values of a first and second AC signals from output voltage and output current of inverter, generating frequency instruction values of the first and second AC signals by droop control to obtain voltage instruction values of the first and second AC signals; regulating the output voltage of inverter according to the voltage instruction value of the first AC signal, the voltage instruction value of the second AC signal and the fundamental voltage instruction value.