Active Islanding Detection Using High-Frequency Signal Injection

Abstract

Islanding detection is of great importance for reliable operation of smart grids. Islanding-detection methods can be classified into three different groups, i.e., active, passive, and communication-based methods. Active methods inject a disturbing signal (typically a voltage) and analyze the system response (typically in the current). These techniques have a low nondetection zone (NDZ) but present the inconvenience inherent to injecting a disturbing signal. Passive methods monitor the grid condition from the grid variables. These techniques are easy to implement but present a large NDZ. Communication methods have the inconvenience of relying on communications, currently being of limited use. This paper proposes a new active islanding-detection method, based on the measurement of the grid high-frequency impedance by means of the injection of a high-frequency voltage. The advantages of the method are almost negligible adverse effects due to the injected high-frequency voltage and accurate and fast islanding detection, i.e., in the range of a few milliseconds. Furthermore, the estimated high-frequency impedance can be used for the adaptive control of the power converter.Index Terms-Active islanding detection, grid impedance measurement, high-frequency signal injection, power system monitoring.

Observer-Based Pulsed Signal Injection for Grid Impedance Estimation in Three-Phase Systems

“…The existing literature approaches, as discussed before, rely on the injection of a voltage/current signal and measuring the resulting current/voltage [18], [28]; the use of the closed-loop current response for implementing a MRAS strategy [12]; or the use of observers or estimators [27]. In this paper, the estimation of the system parameters is carried out by using an RLS approach [24], [44].…”

“…The least squares problem is formulated in recursive form using the equations (15)- (18). The system equations are represented by defining the variables and coefficients vectors, X…”

“…For the excitation signal, several approaches have been proposed: 1) Pulsed Signal Injection (PSI) [9], [23]- [25]; 2) High Frequency Signal Injection (HFSI) at constant high frequency [18], [19], [26]- [28]; 3) current regulator reaction [19]; 4) Low Frequency Signal Injection (LFSI) [20], [29], [30]; 5) Binary Sequence Signal Injection (BSSI) [21], [31], [32].…”

Low frequency signal injection for grid impedance estimation in three phase systems

“…In the literature there are mainly two approaches. To calculate the impedance as the quotient of the injected voltage and the resulting current [10] or to use an observer or an estimator [13]. In this paper, the estimation of the system parameters is done by using a RLS approach [26].…”

“…For the signal excitation, several approaches can be followed. 1) High Frequency Signal Injection (HFSI) [10]- [13], 2) current regulator reaction [11], 3) Low Frequency Signal Injection (LFSI) [14], [15]. 1) and 2) are based on the same physical explanation.…”