Parallel Inverter Adaptive Impedance Control for Balanced Power Sharing
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Solution Overview
Problem
In micro-grid systems with multiple inverters in parallel, achieving accurate power distribution and reducing excessive circulating current is challenging due to uncertainties in inverter and line impedance, leading to unbalanced power distribution.
Innovation Solution
An adaptive control method that acquires state information from master and slave inverter units, calculates active power, adjusts reference voltages, and adaptively adjusts virtual impedance to match output impedance, ensuring equal power distribution and reducing circulating current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If droop control is used for parallel inverters, then power distribution is achieved, but distribution accuracy deteriorates due to impedance uncertainties
Solution Approach 1:
The patent changes the control parameters by introducing adaptive virtual impedance that dynamically adjusts based on detected impedance variations. This allows the system to compensate for impedance uncertainties without requiring complex centralized control, thereby improving power distribution accuracy while maintaining relatively simple device architecture.
Solution Approach 2:
The patent implements a feedback mechanism where the system detects actual impedance values and uses this information to adjust the virtual impedance parameters in real-time. This closed-loop feedback enables the system to adapt to impedance changes and maintain accurate power distribution despite uncertainties in the physical parameters.
2Power
If parallel inverter connection is used, then power capacity and system redundancy are improved, but circulating current increases due to unbalanced power distribution
Solution Approach 1:
The patent modifies the impedance parameters by introducing adaptive virtual impedance that matches the output impedance of the master inverter. This parameter adjustment equalizes the total impedance (physical + virtual) of parallel inverters, thereby eliminating the cause of circulating current while preserving the power capacity benefits of parallel connection.
3Measurement precision
If adaptive virtual impedance adjustment is used, then power distribution accuracy is improved, but control complexity increases
Solution Approach 1:
The patent enables the system to self-adjust by automatically detecting impedance values and computing appropriate virtual impedance parameters without requiring external intervention or complex centralized coordination. Each inverter unit independently adapts its control parameters based on system conditions, simplifying the overall control architecture while achieving accurate power distribution.
Data Source
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Figure 5B
AI summary
An adaptive control method for multiple inverters in parallel and a system with multiple inverters in parallel. The method average distribute the active power of each inverter unit by means of acquiring state information of inverter units, adjusting a reference voltage output by each of the inverter units based on a deviation between the output active power and the average active power, which is calculated by the state information, re-acquiring the state information and calculating a voltage component difference and a current component difference between the inverter units based on the adjusted reference voltage, and then adaptively adjusting the virtual impedance of the slave inverter unit according to the voltage component difference and the current component difference so that the output impedance of the slave inverter unit and master inverter unit is matched.