Mu-Synthesis Controller for Grid-Connected Inverter Stability
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Solution Overview
Problem
Existing current control methods for grid-connected inverters lack robustness in compensating for disturbances in DC and AC voltages, and do not account for uncertainties in inverter parameters, leading to instability and performance issues under fluctuating conditions.
Innovation Solution
The use of mu-synthesis control design methodology to design a current controller for a grid-connected three-phase inverter, which accounts for uncertainties in DC voltage fluctuations, ensuring robust stability and performance by selecting suitable weighting functions and optimizing the controller to handle structured and unstructured uncertainties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional current control methods are used, then the controller design is simple, but the controller lacks robustness in compensating for disturbances in DC and AC voltages and does not account for uncertainties in inverter parameters
Solution Approach 1:
The patent applies preliminary action by incorporating uncertainty modeling and robustness analysis into the controller design phase itself. Rather than designing for nominal conditions and adding robustness later, the mu-synthesis methodology pre-compensates for expected uncertainties in DC voltage, grid voltage, and filter parameters, ensuring robust performance before the system encounters actual disturbances
Solution Approach 2:
The patent transforms the static controller design into a dynamic robust control system. The mu-synthesis approach creates adaptive controller parameters that automatically adjust to changing operating conditions and uncertainties, making the controller dynamically responsive to disturbances in DC and AC voltages rather than relying on fixed gains designed for nominal conditions
2Reliability
If the inverter operating range is limited to maintain stability, then stability is ensured, but the operating flexibility and range of the inverter is reduced
Solution Approach 1:
The patent makes the inverter operating characteristics dynamic through robust control design. The mu-synthesis methodology enables the controller to adapt its parameters in real-time based on the actual operating conditions and measured uncertainties, allowing the inverter to operate stably across a wider range of DC voltages, grid voltages, and load conditions rather than being constrained to a narrow nominal operating point
Data Source
AI summary
A design method for the current controller of a grid connected inverter is discussed in this disclosure. The repetitive control strategy is used, in tandem with a mu-synthesis based current controller, to attain sinusoidal reference tracking and harmonic rejection. Mu-synthesis based control is chosen to attain reference tracking in the presence of plant uncertainties. The repetitive control strategy is selected since it can reject a large number of harmonics simultaneously, while providing a clean sinusoidal current waveform to the grid, even in the presence of grid load and/or voltage distortions. The repetitive control strategy is implemented via the internal model principle. By applying mu-synthesis principles, a feedback controller that simultaneously achieves stability and tracking performance is obtained.