Nonlinear Control for Micro-Grid Inverter Anti-Disturbance
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Solution Overview
Problem
Micro-grid inverters face challenges in maintaining accurate power transmission and stability due to poor grid voltage quality, harmonics, voltage amplitude fluctuations, and frequency changes, which affect energy transfer efficiency and system stability, especially in medium- and low-voltage grids.
Innovation Solution
A nonlinear control method for LCL type grid-connected inverters is introduced, using a two-phase stationary coordinate system, which collects filter capacitor voltage and grid-side inductance current, generates a reference signal based on instantaneous reactive power theory, and employs a nonlinear control model with Lyapunov function to stabilize the system and track power commands accurately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional PI control is used in synchronous rotating coordinate system, then steady-state error can be eliminated, but control complexity increases and performance degrades under non-ideal grid voltage conditions
Solution Approach 1:
The patent transforms the control variables from time-domain to frequency-domain by applying Fourier transform to the tracking error signal. This parameter transformation enables the PR controller to achieve high gain at fundamental frequency without requiring complex coordinate transformations, thereby maintaining steady-state accuracy while simplifying the control structure.
Solution Approach 2:
The patent replaces the mechanical coordinate transformation system (synchronous rotating coordinate system requiring phase-locked loop) with a frequency-domain filtering approach. By using a band-pass filter tuned to the fundamental frequency, the system eliminates the need for complex coordinate transformations and phase-locking mechanisms while maintaining effective error tracking.
2Device complexity
If PR controller is used in two-phase static coordinate system, then control complexity is reduced, but ability to eliminate harmonic components decreases
Solution Approach 1:
The patent introduces a band-pass filter as an intermediary component between the error signal and the PR controller. This filter acts as a mediator that selectively passes the fundamental frequency component while blocking harmonic components, thereby enabling the simple two-phase static coordinate system to achieve both low complexity and effective harmonic rejection.
Solution Approach 2:
The patent applies frequency-selective filtering at specific stages of the control system where harmonic content needs to be suppressed. By placing the band-pass filter in the feedback path and using resonant controllers tuned to specific harmonic frequencies, the system achieves local quality improvement by targeting specific frequency components without affecting the overall simple structure.
3Adaptability or versatility
If three-phase natural coordinate system control is used, then each phase can be controlled independently, but controller structure becomes complicated
Solution Approach 1:
The patent employs a unified PR controller structure in the two-phase static coordinate system that inherently handles all three phases through mathematical transformation. This universal controller structure performs multiple functions including active power control, reactive power control, and harmonic suppression simultaneously, eliminating the need for separate control structures for each phase while maintaining independent control capability.
4Device complexity
If conventional control methods are used, then system structure is simple, but anti-disturbance ability deteriorates under poor grid voltage quality
Solution Approach 1:
The patent implements dynamic adaptive control by continuously adjusting the resonant frequencies of the PR controllers based on the detected grid frequency. This dynamic adjustment enables the system to maintain high gain at the fundamental frequency and effectively suppress harmonics even when grid conditions change, thereby achieving strong anti-disturbance ability while keeping the control structure relatively simple.
Solution Approach 2:
The patent employs multiple feedback mechanisms including the band-pass filter feedback for fundamental frequency tracking, PR controller feedback for harmonic suppression, and the overall power control feedback. These nested feedback loops work together to enhance anti-disturbance ability by continuously correcting deviations caused by grid voltage fluctuations and harmonics without significantly increasing structural complexity.
Data Source
AI summary
Nonlinear control method for the micro-grid inverter with anti-disturbance. By generating reference currents that satisfy specific active and reactive power command under various working conditions, and introducing a nonlinear control method based on Lyapunov function to control the inverter, fast and accurate tracking of the generated reference signals is realized. The method realizes effective decoupling control of active power and reactive power. The system has high dynamic response and good robustness. Besides, the control structure of the method is simple and easy to implement, and the synchronous control link and the additional voltage and current regulator are omitted. The method realizes fast and accurate power exchange and stable power transmission between the inverter and the grid in the micro-grid under various working conditions, and provides a guarantee for improving the energy management efficiency within the micro-grid.