IJE TRANSACTIONS A: Basics Vol. 31, No. 10 (October 2018) 1666-1674   

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M. M. AlyanNezhadi, H. Hassanpour and F. Zare
( Received: May 28, 2018 – Accepted in Revised Form: August 17, 2018 )

Abstract    Grid impedance estimation is used in many power system applications such as grid connected renewable energy systems and power quality analysis of smart grids. The grid impedance estimation techniques based on signal injection uses Ohm’s law for the estimation. In these methods, one or several signal(s) is (are) injected to Point of Common Coupling (PCC). Then the current through and voltage of PCC are measured. Finally, the impedance is assumed as ratio of voltage to current signals in frequency domain. In a noisy system, energy of the injected signal must be sufficient for an accurate approximation. However, power quality issues and regulations limit the energy and the voltage levels of the injected signal. There are three main issues in impedance estimation using signal injection: I) Power quality of grid, II) frequency range of estimation, and finally III) accuracy of estimation. In this paper, the stationary wavelet denoising algorithm is employed instead of increasing the energy of injection signal(s). In the paper, a novel method is proposed for impedance estimation based on selecting several appropriate injection signals and denoising the measured signals. The proposed method is able to impedance estimation in a wide frequency range without any effect on power quality. Finally, simulation results have been carried out to validate the proposed method.


Keywords    Impedance Estimation, Frequency response, Discrete Fourier Transform, Power Quality, smart grids



تخمین امپدانس شبکه‌های قدرت در کاربردهای زیادی مانند شبکه‌های قدرت متصل به انرژی تجدیدپذیر و آنالیز کیفیت توان شبکه‌های هوشمند استفاده می‌شود. روش‌های تخمین امپدانس مبتنی بر تزریق سیگنال از قانون اهم پیروی می‌کنند. در این روش‌ها، یک یا چند سیگنال به نقطه اتصال مشترک (PCC) تزریق می‌شود. سپس سیگنال‌های ولتاژ و جریان عبوری از PCC اندازه‌گیری می‎گردد. در نهایت، امپدانس به صورت نسبت سیگنال ولتاژ به جریان در حوزه فرکانس در نظر گرفته می‌شود. در سیستم‌های نویزی، انرژی سیگنال تزریقی برای تقریب درست امپدانس باید کافی باشد. در هر صورت، مسائل کیفیت توان و قوانین شبکه‌های قدرت باعث محدودیت در انرژی سیگنال تزریقی می‌شود. در تخمین امپدانس شبکه‌های قدرت به کمک روش‌های مبتنی بر تزریق سیگنال سه مسئله اصلی وجود دارد. 1) کیفیت توان شبکه، 2) محدوده تخمین امپدانس و در نهایت 3) دقت تخمین امپدانس. در این مقاله از حذف نویز به کمک تبدیل موجک ایستا به جای افزایش انرژی سیگنال تزریقی استفاده شده است. در این مقاله یک روش جدید برای تخمین امپدانس شبکه بر پایه تزریق چند سیگنال مناسب و حذف نویز سیگنال‌ها ارائه شده است. روش ارائه شده توانایی تخمین امپدانس در یک بازه وسیع فرکانسی بدون تاثیر بر روی کیفیت توان شبکه را دارد. سرانجام، از نتایج شبیه‌سازی‌ها به منظور ارزیابی روش پیشنهادی استفاده شده است.


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