DAB Micro-Inverter Circuit Modeling and Control
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Solution Overview
Problem
Existing circuit modeling methods and control logic for dual-active-bridge-type micro-inverters are inadequate, as they cannot accurately model the high-frequency AC/DC conversion system and fail to provide effective closed-loop control for output current and grid connection stability.
Innovation Solution
A circuit modeling method that equates the dual-active-bridge-type micro-inverter to a standard dual-active-bridge circuit by establishing an equivalent circuit model, allowing for the development of a third-order large signal and small signal model. This model facilitates the analysis of grid-connection stability and dynamic performance, and an output current control method based on the small signal model is implemented to improve control accuracy and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing circuit modeling methods are used for DAB-type micro-inverters, then the modeling process is simple, but the model accuracy is insufficient because existing methods are designed for DC-DC converters and cannot accurately represent high-frequency AC/DC conversion systems
Solution Approach 1:
The patent segments the DAB micro-inverter circuit into distinct functional modules (primary bridge, transformer, secondary bridge, filter) and develops separate equivalent circuit models for each. This segmentation allows the complex AC/DC conversion system to be modeled accurately by combining simpler subsystem models, resolving the contradiction between model accuracy and modeling complexity.
Solution Approach 2:
The patent introduces an equivalent circuit model as an intermediary representation between the physical DAB micro-inverter system and the control system. This equivalent model captures the high-frequency AC/DC conversion characteristics without requiring direct complex analysis of the actual circuit, enabling accurate modeling while simplifying the overall analysis process.
2Reliability
If proportional or proportional-integral controllers are used for current loop control, then the controller structure is simple, but the output current accuracy and grid-connection stability are insufficient because the control logic does not adapt to grid-side voltage changes
Solution Approach 1:
The patent transforms the static proportional or PI controller into a dynamic control system where the control logic adapts to changing grid conditions. The current loop controller continuously adjusts its behavior based on real-time grid-side voltage measurements, enabling the system to maintain stability and accuracy under varying operating conditions while managing control complexity through structured adaptation.
Solution Approach 2:
The patent implements a closed-loop feedback control system where the actual output current is continuously measured and compared with the reference current. The error signal is fed back to the controller, which adjusts the control logic based on grid-side voltage changes. This feedback mechanism ensures accurate output current control and stable grid connection while adapting to dynamic conditions.
3Manufacturing precision
If existing control methods are applied to DAB-type micro-inverters, then the implementation is straightforward, but the output current accuracy deteriorates because the control methods are not specifically designed for the unique characteristics of DAB circuits
Solution Approach 1:
The patent develops control strategies specifically tailored to the DAB circuit's unique parameters and operating characteristics. By adjusting control parameters and logic to match the DAB topology's specific behavior (including its high-frequency switching and AC/DC conversion characteristics), the system achieves accurate output current control while maintaining reasonable implementation complexity through targeted parameter optimization.
Data Source
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AI summary
Provided in the present invention is a circuit modeling method for a dual-active-bridge-type micro-inverter. The method equates dual-active-bridge-type micro-inverter to a standard dual-active-bridge circuit by establishing an equivalent circuit model, thereby establishing a third-order large signal model and a third-order small signal model of the micro-inverter, so as to facilitate the solution of a circuit state variable and the analysis of the dynamic performance. On the one hand, the method facilitates the solution of the steady-state operating point, and on the other hand, the transfer function obtained using the small signal model facilitates the study of the dynamic performance of the micro-inverter. Further provided in the present invention is an output current control method for a dual-active-bridge-type micro-inverter. By means of the method, a correct current loop control logic is established on the basis of a small signal model of a dual-active-bridge-type micro-inverter, and a current loop parameter design method is given. The method is conducive to improving the grid-connection stability and the precision of the output current of the micro-inverter, by giving the correct current loop control logic and the detailed current loop parameter design method.