Parallel Inverter Reactive Power Sharing With Dynamic Virtual Impedance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In isolated island mode microgrids, the difference in transmission impedance and load switching leads to uneven reactive power allocation among parallel VSGs, causing inefficiencies in power sharing due to reliance on network communication for power sharing methods.
Innovation Solution
A reactive power sharing method based on virtual impedance and a dynamic droop coefficient, where virtual impedance is constructed through a line impedance observer, and a dynamic droop coefficient is introduced to adjust output voltage, enabling adaptive reactive power sharing according to inverter capacities without requiring communication networks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If network communication is used for reactive power sharing among parallel inverters, then power sharing can be achieved, but communication failure or data delay may occur and system complexity increases
Solution Approach 1:
The patent extracts the communication dependency from the reactive power sharing system by implementing a completely distributed control approach. Each inverter independently calculates its own reactive power output based on local voltage and current measurements, eliminating the need for communication between inverters. This resolves the contradiction by removing the communication system entirely while maintaining power sharing capability through adaptive virtual impedance and droop control.
Solution Approach 2:
Each inverter serves itself by autonomously determining its reactive power contribution without external communication. The inverter uses its own measured voltage and current, combined with droop coefficients and virtual impedance parameters, to self-regulate its output. This self-service mechanism eliminates communication requirements while achieving reliable reactive power sharing.
2Reliability
If conventional virtual impedance strategy is used, then power distribution effect is achieved, but reactive power allocation remains uneven during load switching
Solution Approach 1:
The patent introduces dynamic droop coefficients that adapt in real-time based on system conditions. Instead of fixed impedance values, the virtual impedance and droop parameters are continuously adjusted according to measured voltage and current, enabling the system to maintain precise reactive power allocation during load switching and transient conditions. This dynamic adaptation resolves the precision problem during dynamic operation.
Solution Approach 2:
The patent changes the parameters of virtual impedance and droop coefficients based on operating conditions. By adjusting these parameters dynamically, the system optimizes reactive power sharing accuracy during different load conditions. The parameter changes enable the system to maintain high precision allocation even during load switching, overcoming the limitations of conventional fixed-parameter approaches.
3Ease of operation
If fixed droop coefficient is used, then control simplicity is maintained, but reactive power sharing precision deteriorates during load switching
Solution Approach 1:
The patent transitions from fixed to dynamic droop coefficients that automatically adjust based on real-time measurements. The dynamic coefficients are calculated using local voltage and current data, maintaining control simplicity while significantly improving precision during load switching. This resolves the contradiction by making the coefficients adaptive rather than static.
Solution Approach 2:
The droop coefficient parameters are changed dynamically based on operating conditions. The system calculates appropriate coefficient values in real-time using measured electrical quantities, enabling precise reactive power sharing during transients while maintaining relatively simple control logic. This parameter adaptation resolves the precision-simplicity trade-off.
Data Source
AI summary
The present invention discloses a reactive power sharing method for parallel inverters based on virtual impedance and a dynamic droop coefficient. The virtual impedance is constructed through the parameter design of voltage and current double-closed loop controllers and a line impedance observer, to realize power decoupling. A dynamic droop coefficient is constructed to adjust the output voltage of a virtual synchronous generator adaptively, and the output reactive power of inverters is controlled indirectly to achieve reactive power sharing according to capacities. The present invention does not need a communication network between the inverters, and only needs the local variable information of each inverter, so that a microgrid has the function of “plug and play”.