Double Synchronous Virtual Oscillator Control for Grid Converters
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Solution Overview
Problem
Existing grid-following and grid-forming converters lack effective fault ride-through capabilities, especially under asymmetric AC faults, and require complex PLL structures that can lead to instability, and there is a need for robust synchronization under varying grid conditions without increasing development and maintenance costs.
Innovation Solution
The implementation of a double synchronous unified virtual oscillator controller (DSUVOC) that enables PLL-less grid synchronization and fault ride-through in both grid-following and grid-forming converters, using space vector oscillators and fault detection components to manage faults and maintain synchronization across varying grid conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PLL structures are used for grid synchronization and fault management, then grid-following operation can be achieved, but system complexity increases and stability deteriorates under weak grid conditions
Solution Approach 1:
The patent extracts and removes the PLL component from the control system, replacing it with a virtual oscillator controller that achieves grid synchronization through intrinsic oscillation mechanisms rather than phase-locked feedback. This elimination of PLL simplifies the control architecture while maintaining fault ride-through capability through the VOC's natural synchronization properties.
Solution Approach 2:
The patent substitutes the mechanical/feedback-based PLL system with a virtual oscillator model that uses mathematical oscillation equations to achieve synchronization. This replacement transitions from a feedback-controlled phase-locking mechanism to an open-loop oscillation-based approach, reducing complexity and improving stability under varying grid conditions.
2Reliability
If different control parameters are tuned for different grid impedance conditions, then synchronization performance is optimized, but development and maintenance costs increase
Solution Approach 1:
The virtual oscillator controller is designed with universal parameters that function across all grid impedance conditions without requiring re-tuning. The VOC's oscillation frequency and damping characteristics are inherently adaptive, allowing the same controller parameters to maintain optimal synchronization performance whether the grid is strong or ultra-weak, thereby eliminating the need for condition-specific parameter sets.
Solution Approach 2:
The patent employs parameter-free or minimally-parameterized virtual oscillator models where the oscillation characteristics emerge from the system dynamics rather than fixed parameter settings. This allows the controller to automatically adapt to different grid conditions through intrinsic parameter relationships, avoiding the need for manual parameter tuning across various operating scenarios.
3Reliability
If VOC methods are used for grid-forming operation, then synchronization capability is improved, but harmonic distortion in output voltage increases
Solution Approach 1:
The patent introduces feedback mechanisms within the virtual oscillator control structure that monitor and correct harmonic distortion in the output voltage. By incorporating voltage quality feedback loops, the system maintains the synchronization benefits of VOC while actively compensating for harmonic generation, ensuring both reliable synchronization and acceptable voltage quality.
Solution Approach 2:
The patent adjusts the virtual oscillator parameters (such as damping coefficient and oscillation frequency) to optimize the trade-off between synchronization performance and harmonic distortion. By carefully selecting these parameters, the system achieves robust synchronization while minimizing the generation of harmful harmonics in the output voltage.
Data Source
AI summary
A power electronic converter can utilize exemplary double synchronous unified virtual oscillator control (DSUVOC) logic or circuitry to convert direct current to alternating current that is input into a power grid. An exemplary DSUVOC controller of the present disclosure includes a double synchronous space vector oscillator component, a sequence extraction component, a fault detection component, a pre-synchronization component, a virtual impedance component, a terminal voltage compensation component, and/or an active damping component, wherein the double synchronous unified virtual oscillator controller is capable of controlling a grid following or a grid forming power electronic converter enabling synchronization and fault ride-through under both balanced and unbalanced conditions.