Limit Cycle Oscillator Synchronization for Power Converters
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Solution Overview
Problem
Conventional synchronization systems for power converters interconnected to the electric grid face challenges in maintaining reliable and efficient synchronization under non-optimal conditions, particularly due to harmonic imbalances and power system disturbances, with Phase-Locked Loop (PLL) techniques being unstable during network failures and requiring complex trigonometric calculations, increasing computational load.
Innovation Solution
A real-time synchronization system comprising a limit cycle oscillator (LCO) operably linked to a Frequency-Locked Loop (FLL) block, which generates pure sinusoidal signals and adapts to frequency and phase changes, providing robustness against harmonics and amplitude variations within the normal operating range of the electrical network, using a feedback signal for synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Phase-Locked Loop (PLL) technique is used for synchronization, then phase angle extraction is achieved, but the system becomes unstable during network failures and requires complex trigonometric calculations
Solution Approach 1:
The patent changes the fundamental parameter being tracked from phase angle (in PLL) to frequency (in FLL). The Frequency-Locked Loop extracts frequency information from the grid voltage signal and uses it to control a voltage-controlled oscillator, avoiding the trigonometric calculations and instability issues of phase-based synchronization during network failures
Solution Approach 2:
The patent extracts only the frequency component from the grid voltage signal using the FLL, discarding the need for phase angle extraction. This selective extraction of the frequency parameter simplifies the synchronization process and eliminates the computational complexity and instability associated with phase-based methods
2Measurement precision
If PLL technique is used for synchronization, then phase angle extraction is achieved, but computational load increases due to complex trigonometric calculations
Solution Approach 1:
The patent changes the synchronization parameter from phase angle to frequency, which eliminates the need for complex trigonometric calculations. The FLL uses frequency discrimination circuits that provide a much simpler computational approach compared to the arctangent and coordinate transformations required by PLL methods
3Reliability
If conventional synchronization methods are used, then synchronization is achieved under optimal conditions, but the system lacks robustness against harmonics and amplitude variations
Solution Approach 1:
The patent implements a dynamic frequency-tracking system where the FLL continuously adapts to frequency changes in the grid. The voltage-controlled oscillator dynamically adjusts its output frequency based on the extracted grid frequency, providing robustness against harmonics and amplitude variations while maintaining synchronization
Solution Approach 2:
The patent employs feedback control in the FLL where the frequency error signal is fed back to adjust the oscillator frequency. This closed-loop feedback mechanism provides automatic adaptation to changing grid conditions, including harmonics and amplitude variations, without requiring complex filtering or compensation algorithms
Data Source
AI summary
The present invention presents a real-time synchronization system for power converters interconnected with the electrical network, whose operation is based on a structurally stable limit cycle oscillator and which develops pure sinusoidal trajectories, creating references free of harmonics and disturbances in network. The proposed invention has the advantage that it has a high degree of immunity and robustness within highly contaminated networks, either due to the presence of harmonics or other types of contamination that may exist in the network, with a better performance than the systems previously reported. Another advantage of the present invention is that regardless of the initial conditions that are established, the system always synchronizes with the signal of the network, guaranteeing a smooth transient from any initial condition to the limit cycle, so it does not require prior tuning. In addition, the proposed scheme does not require Phase-Locked Loop (PLL) or trigonometric functions for synchronization, thus reducing computational time and resources.