Volume 7, Issue 3

Since the development of the first control strategy for the active power filters (APF) introduced by H. Akagi [H. Akagi, Y. Kanazawa,A. Nabae, Generalized theory of the instantaneous reactive power in three-phase circuits, in: Proceedings of International Power Electronics Conference, Tokyo, Japan (1983) 1375–1386.], many efforts have been concentrated to improve their performances. However, when electrical networks supplies high current non-linear loads, a single inverter-based APF has limited power capability. In this paper, we studied parallel operation achieving high power level. More particularly, we examined a modular APF based on two three-phase inverters. This structure allows zero-sequence current circulating through the inverters, as demonstrated by using averaged modelling of the APF. To solve this problem and based on previous averaged model, we proposed a new optimal control strategy, suppressing the zero-sequence circulating current. Simulation results validate the proposed control.

The aging of insulators often results in corona discharge, and the measurement of the ultraviolet light (UV-light) can be used to detect insulator defects. This paper introduces a new tester, the ultraviolet detector, which can detect defective insulators by measuring the UV-light from the discharging insulators. Some tests were carried out. The results indicated that the detector can identify the existence of corona discharge with good performance. And it can be used for discharge detection of power system and transformer substation.

Electrostatic and electrodynamic field analyses of 33kV line insulators were introduced to compare the electric-field and the current density profiles of commonly used line insulators in Oman; namely, silicone rubber (SiR) and porcelain line post insulators, and porcelain cap and pin insulator string. SLIM software package was used for such simulation, which is a fully integrated collection of software modules that provides facilities for the generation and solution of electromagnetic finite element models. The simulation results reveal that for the electrostatic simulation under pollution conditions, SiR and porcelain line-post insulators give maximum values of the electric field of 360kV/m and 1700kV/m, respectively. The latter value exceeds the recommended electric field level of 500kV/m. For the electrodynamic simulation under pollution conditions, the electric field and the current density are much higher for porcelain insulator compared to those of SiR insulator. The simulation of four cap-pin standard insulator string reveals that there is high electric field (1250kV/m) at the cap-insulator gap which can cause high current density for polluted case. Finally, the trend of the simulation results has been verified by experimental tests, which has been conducted on different 33kV line insulators having different designs and materials.

Three algorithms for reactive power optimization are proposed in this paper with three different objective functions. The objectives in the proposed algorithm are to minimize the sum of the squares of the voltage deviations of the load buses, minimization of sum of squares of voltage stability L-indices of load buses (?L2) algorithm, and also the objective of system real power loss (Ploss) minimization. The approach adopted is an iterative scheme with successive power flow analysis using decoupled technique and solution of the linear programming problem using upper bound optimization technique. Results obtained with all these objectives are compared. The analysis of these objective functions are presented to illustrate their advantages. It is observed comparing different objective functions it is possible to identify critical On Load Tap Changers (OLTCs) that should be made manual to avoid possible voltage instability due to their operation based on voltage improvement criteria under heavy load conditions. These algorithms have been tested under simulated conditions on few test systems. The results obtained on practical systems of 24-node equivalent EHV Indian power network, and for a 205 bus EHV system are presented for illustration purposes.

This paper presents Three novel error driven dynamic controllers for the Static Synchronous Compensator (STATCOM) Facts device to stabilize both Wind Energy Conversion stand alone systems (SWECS) as well as hybrid scheme of wind plus small hydro with employing self excited induction generator. The unified AC system of standalone wind energy conversion scheme and hybrid wind/small hydro scheme are connected to a hybrid electric load. Three novel error driven dynamic controllers are validated for the STATCOM as a voltage stabilization scheme. Two novel controller are error driven dynamic controllers with auxiliary tracking control loop. The first controller is tri loop dynamic error driven controller using the RMS Load bus voltage, RMS-Load Current and the instantaneous AC load power. The second controller is DC voltage dynamic tracking controller using the dc link capacitor voltage. The third dynamic controller is based on the decoupled (d-q) current control strategy, namely the direct and quadrature current component for the STATCOM current. The dynamic response results demonstrated the effectiveness of the STATCOM-Facts device in stabilizing both AC wind energy system and the hybrid wind/hydro scheme by ensuring effective generator/load bus voltage regulation and dynamic reactive power compensation under load, wind and other prime mover excursions.

In a deregulated electric service environment, an effective electric transmission and distribution networks are vital to the competitive environment of reliable electric service. Power quality (PQ) is an item of steadily increasing concern in power transmission and distribution. The traditional approach to overcoming capacity and quality limitations in power transmission and distribution in many cases is the addition of new transmission and/or generating capacity. This, however, may not be practicable or desirable in the real case, for many of reasons. From technical, economical and environmental points of view, there are two important - and most of the time combined - alternatives for building new transmission or distribution networks to enhance the transmission system capacity, and power quality: the Flexible alternating current transmission devices and controllers, and the distributed generation resources near the load centers. The connection of distributed generation to the distribution grid may influence the stability of the power system, i.e. angle, frequency and voltage stability. It might also have an impact on the protection selectivity, and the frequency and voltage control in the system. This paper presents a low cost FACTS based Dynamic Distribution System Compensator (DDSC) scheme for voltage stabilization and power transfer and quality enhancement of the distribution feeders connected to a dispersed wind generator, using MATLAB/ SimPower System simulation tool.

With more emphasis being laid on clean and renewable sources of energy, engineers look for the best possible ways to harness the wind energy to the maximum extent. FACTs controllers that were earlier being used at the transmission level find their use at generation level when it comes to extracting reliable and quality power from Wind Energy Conversion Systems (WECS). This article presents a review of the important modeling techniques employed for developing FACTs controllers and examines the role of HVDC-Light transmission in exploiting the Off-shore wind energy resources.