بهبود پایداری گذرای مبدل متصل به شبکه هنگام افت ولتاژ شدید با تکنیک امپدانس مجازی
محورهای موضوعی : مهندسی برق و کامپیوترامید عبدلی 1 , مهدی قلی‌پور 2 * , رحمت‌الله هوشمند 3
1 - دانشگاه اصفهان
2 - دانشگاه اصفهان
3 - دانشگاه اصفهان
کلید واژه: امپدانس مجازی, PLL, مبدل متصل به شبکه, پایداری گذرا, افت ولتاژ,
چکیده مقاله :
با افزایش نفوذ منابع تولید پراکنده مبتنی بر اینورتر، دستورالعمل‌های شبکه خواستار عدم قطع این مبدل‌ها از شبکه هنگام رخداد خطا می‌باشند. این مبدل‌ها همچنین می‌بایست با تزریق توان راکتیو به رفع خطا کمک کنند. از آنجایی که شبکه‌های برق سلفی خالص نبوده و دارای مقاومت اهمی نیز هستند، این شبکه‌ها هنگام رخداد خطا با مشکل ناپایداری مبدل روبه‌رو می‌شوند. مبدل‌ها که جهت سنکرون‌ماندن با شبکه از حلقه قفل فاز (PLL) استفاده می‌کنند، هنگام رخداد خطای افت ولتاژ سنگین، دیگر قادر به حفظ پایداری با شبکه نیستند. در نتیجه این مبدل‌ها قادر به گذر از خطا نبوده و می‌بایست از شبکه جدا شوند. این مقاله با ارائه روشی جدید مبتنی بر امپدانس مجازی در هنگام رخداد افت ولتاژ سنگین، پایداری سنکرون با شبکه برق را حفظ می‌کند. این روش نیاز به تخمین تقریبی امپدانس شبکه دارد و مبدل را مجازاً با نقطه‌ای که اتصال قوی‌تری دارد سنکرون می‌کند. با استفاده از روش پیشنهادی در هنگام افت ولتاژ، مبدل به شبکه متصل مانده و می‌تواند به شبکه توان راکتیو تزریق کند. نتایج شبیه‌سازی با استفاده از نرم‌افزار Matlab درستی روش پیشنهادی برای بهبود پایداری گذرای مبدل را نشان می‌دهد.
With the rise in the penetration of inverter based distributed energy sources, grid codes say that converters should not be disconnected during the fault. These sources should also help the grid by reactive power injection. Power system grids are resistive inductive and the converter may be unstable during the fault. Converters use phase locked loop (PLL) to synchronize with the grid. PLL is not able to be stable during severe voltage drop, so converters cannot ride through the fault and should be disconnected. In this paper a novel method based on virtual impedance is proposed to maintain the synchronization during severe voltage drop. This method needs grid impedance estimation and virtually connects the converter to a point that has a stronger connection. By this novel method, during voltage drop, the converter stays connected to the grid and injects reactive power. Simulation results in MATLAB verify the ability of proposed method in improving the transient stability of converter.
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