Volume 13, Issue 1

This work proposes a new voltage and frequency controller (VFC) for standalone parallel operated self excited induction generators driven by uncontrolled micro hydro turbines. This VFC consists of a current controlled static compensator (STATCOM) for regulating the voltage during different load conditions and a variable frequency induction motor drive driving a water pump operating as an electronic load controller (ELC) for balancing the generated power, which in turn regulates the system frequency. The STATCOM functions as a reactive power compensator for regulating the system voltage and an active filter for harmonics elimination. The control algorithm of STATCOM is based on the synchronous reference frame (SRF) theory.

Power systems usually support disturbances which may initiate a cascading event that could cause total or partial blackouts. Vulnerability assessment is made in order to establish mechanisms that reduce the risk of blackouts. This paper presents a novel approach for assessing vulnerability of an Electric Power System. For this purpose, several indices, that reflect the health of the system, are calculated and the grid is partitioned in electric areas depending on bus electric coherency. The indices allow assessing four different symptoms of system stress such as voltage instability, poorly-damped power oscillations, frequency deviations outside limits, and overloads. The combination of these indices yields a vulnerability index using a fuzzy inference system. The vulnerability index is an indicator of the health of each electric area. The methodology is tested in the 39 bus New England test system via time domain simulations. The results show that vulnerability begins to develop in a specific region of the system, so its assessment and ranking can be used to coordinate and focus control actions that mitigate the consequences of the disturbances and reduce the risk of cascading events and system blackouts.

Quality of power supply has become an important issue with the increasing demand of Distributed Generation (DG) systems either connected to the grid through some power electronics grid-tie inverters or to work in isolated (microgrid) mode towards the development of a smart grid network. In this paper a technical review of Integration of Unified Power Quality Conditioner (UPQC) in Distributed Generation Network has been presented. Though the primary task of UPQC is to minimize the grid voltage and load current disturbance along with the reactive and harmonic power compensation, additional functionalities like compensation of voltage interruption and active power transfer to the load and grid have also been identified. Connection methodologies with their pros and cons are also described. Recent improvements in capacity expansion techniques and future trends for the application of UPQC to cope up with the expanding DG capacity are also reviewed.

A dynamic voltage restorer (DVR) based on an AC-AC converter is presented. It is able to compensate different common disturbances in distribution systems, with the purpose of improving the power quality delivered to the users. A prototype has been assembled to test the feasibility of the proposition. In this paper a modulation strategy based on the well known space vector modulation (SVM) algorithm is presented in order to synthesize controllable voltages in magnitude and waveform for compensation purposes. Unbalanced and harmonic distortion conditions in the supply voltages are taken into account. These results positively confirm the design, simulation, assembling, and expectations about the device.

A pulse amplitude modulation (PAM) control can adjust the DC-link voltage of a motor drive. A bi-directional buck-boost DC-DC converter is required at the primary side of PWM-VSI to implement PAM control. This paper is proposed PAM control technique for a permanent magnet synchronous motor (PMSM) based on fuzzy control system. The PAM coefficient (K_PAM) is a constant value for a conventional PAM control system. It requires online adjustment to improve overall performance of a PAM control system. The proposed fuzzy controller based PAM control regulates the K_PAM according to online commanded load voltage. This paper deals with different operation modes of a bi-directional buck-boost DC-DC cascade converter, motoring (accelerate and steady state) and braking operations of a PMSM at different load conditions and speeds. The total harmonic distortion (THD) and system efficiency are also shown in this paper. Effectiveness of the proposed method is confirmed by simulation results.

This paper has been arisen to show the necessity of the evolution for voltage and reactive power control in distribution systems from conventional to active control techniques. The paper addresses the drawbacks and conflicts that the conventional voltage and reactive power control schemes will face in future distribution systems, especially with high penetration of Distributed Generation (DG). Some of these drawbacks have been verified by carrying out various simulation studies for different IEEE unbalanced radial distribution test systems. The results show that applying the conventional utility voltage regulation control practices in smart grid configuration is intolerable. Therefore, the issue of voltage and reactive power control in smart distribution systems is significant and an evolution of the current control schemes from passive to active is necessary. Using the smart grid technologies, a distributed single layer cooperative control scheme between substation regulators, line regulators and DG units has been proposed. The proposed cooperative scheme is based on the concept of multi-agent systems. Simulation results have been carried out to show the effectiveness of the proposed control scheme.

This paper discusses problems and the possible solutions for protecting series compensated transmission line with distance relays. The paper also takes into consideration the influence of the series compensation on the distance relays installed on the short lines adjacent to the compensated line. Starting from visualising the response of the distance relays, the paper proposes some simple but novel methods to secure and improve the distance relay response. The methods include new impedance and direction determining techniques, placement of CVT and setting considerations. The material presented in this paper is based on the authors experience in protecting series compensated lines with distance relays.