Line Impedance Variations Research Articles

Robust Power Decoupling Based on Feedforward Decoupling and Extended State Observers for Virtual Synchronous Generator in Weak Grid

Virtual synchronous generator (VSG) can provide inertia support for a more renewable-energy-integrated power system. However, there are power couplings between active power and reactive power in a weak grid. To solve this issue, the dynamic models of active power and reactive power are established first to better reflect the characteristics of power coupling. Then, the feedforward decoupling method using virtual power angle and virtual voltage is designed under the nominal system, which can suppress the power couplings well. Furthermore, considering the variation of line impedance, a power decoupling strategy based on extended state observers (ESOs) is proposed, which can estimate the power couplings as the internal disturbances of the system and output compensations for the feedforward decoupling method. Consequently, the robustness of the proposed strategy is improved greatly, and good decoupling performance can be achieved under different line impedance conditions. Finally, the effectiveness of the proposed method is verified by both simulation and experimental results.

Mismatch in EBG Common-Mode Filters Implemented on PCBs

In this article, impedance mismatch effects on the characteristics of common-mode (CM) electromagnetic bandgap (EBG) filters are studied using three-dimensional (3-D) full-wave numerical simulations. The CM EBG filters considered herein are designed using standard printed circuit board technology and contain either microstrip (MS) differential pairs running above the EBG plane, or stripline (SL) differential pairs running on one of the layers next to the EBG plane. First, the terminations are fixed at 50 Ω, and the effects of the differential line impedance variations on the EBG filter parameters are studied. Overall, the considered variations in the widths of the traces and edge-to-edge separation distances in both the MS and SL structures do not drastically deteriorate the performance of the EBG CM filters. Then impedances of the ports are set different from 50 Ω, and the effects of this mismatch on the baseline SL and MS EBG structures are studied. It is shown that lower port impedances may have significant effect on the characteristics of filters. In addition, baseline EBG filters are cascaded with unmatched four-port load, and this may also deteriorate performance of filters.

The Effect of Kernels in SVM on the Fault Classification Accuracy of a Transmission Line Compensated with TCSC

In a Thyristor Controlled Series Capacitor (TCSC) compensated transmission line the dynamic variation of line impedance during various operating modes of the TCSC affects the performance of the fixed impedance setting-based distance relay. The non linear variation of impedance during fault caused by the operation of the metal oxide varistor (MOV) protecting the TCSC also further affects the performance of the distance relay. This paper presents an improved fault detection and classification approach for TCSC compensated transmission lines by processing the superimposed components of the measured three-phase currents at the relay location through the support vector machine (SVM). The performance of the proposed method is tested for a wide variety of fault cases simulated on a 400 kV TCSC compensated two-machine two-bus system through EMTDC/PSCAD software. Fault classification accuracy is evaluated by considering single end as well as both end current data through SVM classifier with linear, polynomial and Gaussian Kernel functions in RStudio software. The obtained result confirms that with Gaussian Kernel function a fault classification accuracy of 98.94% and 99.60% can be achieved by using single end and both end current data, respectively.

Grid emulator for small scale distributed energy generation laboratory

This paper presents the design of a grid emulator dedicated to test small scale distributed energy generation. laboratory The proposed emulator aims to test its performances under different power quality conditions considering grid codes and standards. The developed emulator can generate common grid faults and line impedance variations. This last point is an additional feature versus common grid emulators. The paper discusses design and implementation aspects. Emulator performance analysis are investigated under special operating conditions. Simulation results are carried out to illustrate theoretical developments and a set of experimental results are provided to demonstrate the effectiveness of the proposed emulator.

Direct power control of grid connected voltage source inverters using port-controlled Hamiltonian system

This paper presents a new direct active and reactive power control (DPC) scheme for a three-phase grid connected voltage source inverter (VSI) based on the passivity viewpoint using the port-controlled Hamiltonian (PCH) system. The proposed controller consists of feedforward and feedback parts. The feedforward part (the reference inputs) is generated through the flatness of the dynamics of the VSI model, which makes the error dynamics in the form of PCH system. The nonlinear feedback part is designed to enhance the damping of the error dynamics by using its Lyapunov function. The proposed control method has an ability of the finite time reaching condition similar to sliding mode control (SMC). Moreover, the exponential stability and uniform performance are guaranteed over all operating points without need for reaching a certain manifold. The proposed method is validated by using an experiment through hardware-in-the-loop system with a digital signal processor. The experimental results for the proposed method are compared with those using SMC-DPC method. The proposed method significantly reduces the total harmonic distortion in the output current without deteriorating the transient response of the active and reactive powers. In addition, it provides robust performance against the line impedance variations and the grid voltage sag.

Dynamic Stability Enhancement of a DC-Segmented AC Power System Via HVDC Operating-Point Adjustment

Hopf bifurcation phenomenon of a power system results in oscillatory dynamics which can lead to instabilities in the system. Therefore, it is desirable to operate the system such that a sufficient margin to Hopf bifurcation is ensured. This paper presents a methodology based on the adjustment of the setpoint values of the HVDC link controllers, to prevent instability or increase the stability margin of the system subject to Hopf bifurcation. In this paper, the first-order sensitivities of the Hopf stability margin to the setpoint values of the HVDC links are presented. These sensitivities identify the optimum direction to change the HVDC setpoints to steer the system away from instability, increase the stability margin, and improve the damping of oscillatory modes. The proposed method is evaluated on various system configurations subject to Hopf bifurcation phenomena caused by a variety of events, such as load and line impedance variations. Simulation results show that at the optimum operating point, for a variety of Hopf bifurcations, the stability margin and damping of the oscillatory modes improve.

A new capability to detect and locate insulation defects in complex wiring systems

Pulse arrested spark discharge (PASD) is an effective means to detect and locate a variety of insulation defects in complex wiring geometries such as breached insulation, chafing, and physically small insulation cracks. It is highly immune to line impedance variations, an important property in aircraft wiring systems, and has been shown to be nondestructive to electrical insulation materials. Because of the simplicity of the PASD concept, the low energy PASD pulser and diagnostics can be readily implemented into a portable, briefcase-sized diagnostic system. Although this patented technique will likely evolve as it enters into field applications, it is capable of making a near-term impact on the ability of inspection and maintenance organizations to detect and locate potentially hazardous insulation defects.

Modern approaches for protection of series compensated transmission lines

Series compensation has been employed to improve power transfer in long-distance transmission systems worldwide. However, this in turn introduces problems in conventional distance protection. The complex variation of line impedance is accentuated, as the capacitor's own protection equipment operates randomly under fault conditions. This paper proposes two approaches based on travelling waves and artificial neural networks (ANN) for fault type classification and faulted phase selection of series compensated transmission lines. A modal transformation technique, which decomposes the three-phase line into three single-phase lines, is used for this purpose. Algorithms based on two different modal transformations are developed for phase selection and fault classification. Each algorithm is derived from a corresponding truth table. The truth tables are constructed for different types of faults with different faulted phases and different transformation bases. The proposed ANN topology is composed of two levels of neural networks: In level-1, a neural network (ANN F) is used to detect the fault. In level-2, four neural networks (ANN A, ANN B, ANN C and ANN G) are used to identify faulted phase(s), and activated by the output of ANN F if there is a fault. System simulation and test results, which are presented and analyzed in this paper indicate the feasibility of using travelling waves and ANN in the protection of series compensated transmission lines.

A 3.3-V CMOS adaptive analog video line driver with low distortion performance

An analog line driver for video applications is presented. Utilizing a class-AB error amplifier structure, the design achieved 1.2-V peak-to-peak output swing with better than 42-dB linearity for frequencies up to 5 MHz. An adaptive tuning scheme for output impedance matching using peak detection is used to provide uniform performance across line impedance variations. The circuit is designed in AMI 0.5-μm CMOS technology and has a tuning range of 70-180 /spl Omega/ with a power consumption of about 26.4 mW at 75-/spl Omega/ load.

PROTECTION SCHEME FOR EHV TRANSMISSION SYSTEMS WITH THYRISTOR CONTROLLED SERIES COMPENSATION USING RADIAL BASIS FUNCTION NEURAL NETWORKS

ABSTRACT Since die complex variation of line impedance measured is controlled by thyristors and is accentuated as the capacitor's own protection equipment operates randomly under fault conditions in controllable series compensated transmission systems (CSC), conventional distance protection schemes are limited to certain applications. The authors have extensively addressed the development of new protection techniques for such systems using multilayer percetrons. The basic idea of the method is to design a protection scheme using a neural network approach by catching die feature signals in a certain frequency range under fault conditions. This is different from conventional schemes that are based on deriving implicit mathematical equations based on the infoimation obtained by complex filtering techniques. This paper presents some recent results of employing radial basis function neural networks (RBFN) for this particular application. The use of RBFN is because it has a number of advantages over multilayer percetrons. The study shows that die RBFN based protection works well in CSC systems under a number of system and fault conditions.

Performance of an adaptive protection scheme for series compensated EHV transmission systems using neural networks

Since the complex variation of line impedance is accentuated as the capacitor's own protection equipment operates randomly under fault conditions in series compensated transmission systems, conventional distance protection schemes are limited to certain applications. This paper proposes an adaptive protection scheme based on neural networks with special emphasis on analysis of the first-zone performance. The paper describes in detail the feature extraction, sampling rate, data window and structures of the neural networks. The basic idea of the method is to design a protection scheme using a neural network approach by catching the feature signals in a certain frequency range under fault conditions. This is different from conventional schemes that are based on deriving implicit mathematical equations based on the information obtained by complex filtering techniques. System simulation and test results presented and analysed in the paper demonstrate the feasibility of the proposed scheme.