Stella Morris

Energy Storage System for Mitigating Voltage Unbalance on Low-Voltage Networks With Photovoltaic Systems

The growth of building integrated photovoltaic (BIPV) systems in low-voltage (LV) networks has the potential to raise several technical issues, including voltage unbalance and distribution system efficiency. This paper proposes an energy storage system (ESS) for mitigating voltage unbalance as well as improving the efficiency of the network. In the study, a power system simulation tool, namely PSCAD, is used to model two generic LV networks, BIPV systems and an ESS in order to simulate the performance of the networks with various levels of BIPV penetrations. A control algorithm is developed and implemented in the energy storage model in order to study the ability of the ESS to mitigate network voltage unbalance and reduce losses. Experimental studies are carried out in the experimental small-scale energy zone to investigate the effectiveness of the energy storage system under various levels of PV penetration and load conditions. The simulation and experimental studies carried out clearly show the effectiveness of the ESS in reducing the voltage unbalance factor and improving the efficiency of the two networks considered.

A fuzzy variable structure controller for STATCOM

Abstract Two new variable structure fuzzy control algorithms are presented in this paper for controlling the reactive component of the STATCOM current in a power system. The control signal is obtained from a combination of generator speed deviation and STATCOM bus voltage deviation fed to the variable structure fuzzy controller. The parameters of these fuzzy controllers can be varied widely by a suitable choice of membership functions and parameters in the rule base. Simulation results for typical single-machine and multimachine power systems subject to a wide range of operating condition changes confirm the efficiency of the new controllers.

Design of a nonlinear variable-gain fuzzy controller for FACTS devices

The paper presents the design of a nonlinear variable-gain fuzzy controller for a flexible ac transmission systems (FACTS) device like the unified power flow controller (UPFC) to enhance the transient stability performance of power systems. The fuzzy controller uses a numerical consequent rule base of the Takagi-Sugeno type, which can be either linear- or nonlinear-producing control-gain variation over a very wide range. This type of fuzzy control is expected to be more robust and effective in damping electromechanical oscillations of the power systems in comparison with the conventional PI regulators used for UPFC control. Computer simulation results validate the superior performance of this controller.

A Neuro-Sliding Mode Controller for STATCOM

The paper presents a new controller design for STATCOM for damping electromechanical oscillations in a power system. The STATCOM is modeled as a reactive current source and the magnitude of this current is obtained by using a sliding mode control strategy. The parameters of the sliding mode controller (SMC) are obtained using linearised model of single-machine infinite-bus power system and a pole placement technique. In order to avoid repeated computation of the sliding mode control gains at different operating conditions, a single neuron controller is used to adapt the parameters of the SMC. Several simulation results are presented to show the marked improvement in transient stability enhancement of the single-machine infinite-bus and multimachine power systems over a wide range of operating conditions.

A fuzzy variable structure current controller for flexible AC transmission systems

The paper presents the design of function based variable structure fuzzy controllers for flexible AC transmission systems to improve transient stability performance. This controller is tested on a very widely considered FACTS device like static compensator (STATCOM) which is simulated by a current injection model comprising both real and reactive components. The function based fuzzy controller uses the Takagi-Sugeno scheme and generates the proportional action which by one-to-one or one-to-two mapping can produce the variable gain PI controller. Unlike the performance based two input fuzzy controllers considered earlier, the function based one input fuzzy controller dispenses with gain dependency and provides independent tuning for proportional and integral gains. This new fuzzy controller is tested on a single-machine infinite-bus power system operating with a STATCOM for a variety of transient disturbances and variation of operating point to validate its superior performance in comparison to the conventional PI controllers.

Elimination of inrush current in parallel transformers by sequential phase energization

Production of very high inrush currents in transformers during energization may create deep voltage sag causing malfunction to electronic and other loads. In high voltage power system star-delta transformers are generally switched in, one by one, producing inrush currents each time. The inrush current may be reduced by sequential phase energization of each transformer with neutral resistors. This paper suggests that sequential phase energization should be carried out on the first transformer only after paralleling the delta secondary of all the transformers. This procedure eliminates inrush currents in all the remaining transformers without too much increase in the inrush of the first transformer.

Reduction of magnetizing inrush current in traction transformer

In 25 kV ac main line traction system the traction transformer located in the engine are repeatedly switched off and on during the normal run of the train due to presence of neutral section in the contact wire. The transformer draws inrush current several times the full-load value. Its enegization creates severe power quality problem in each time. The inrush current may be reduced to the full-load value either by using point-on-wave switching device or by connecting an external resistor in series with the primary circuit. The resistor is shorted within a few cycles of energization of the transformer to avoid voltage drop and losses during the steady-state operation of the transformer. Simulation results illustrate the effect of voltage and frequency variation on the production of inrush current. Only one circuit breaker with a delayed contact closing may be used for resistance switching.

A feedback linearization based fuzzy-neuro controller for current source inverter-based STATCOM

This paper presents a nonlinear control approach to the MIMO system of a current source inverter (CSI) based static synchronous compensator (STATCOM). Nonlinear control approach based on feedback linearizing scheme for FACTS devices has been proved in previous literature to have superior performance In damping the electromechanical oscillations of the power system. In this proposed control scheme, the artificial neural network (ANN) will be trained based on feedback linearization control scheme. Radial basis function neural networks (RBFNN) are used as online approximators to learn the unknown dynamics of the system. However, steady state error after the disturbances occurs in conventional feedback linearizing controller. Thus, training of RBFNN as conventional feedback linearizing controller became unrealizable. Consequently, fuzzy controller based on TSK IV control scheme has been used to filtered out the steady state error. This proposed controller is expected to approximate and replace complex mathematical equations of feedback linearization control scheme. To demonstrate the application of the proposed controller, case studies are done with a single-machine infinite-bus power system with current source inverter (CSI)-based STATCOM installed at certain bus. The efficacy of the control strategy is evaluated by digital computer simulation studies using MATLAB under various transient disturbances and a wide range of operating conditions. The approximated control signals are compared with that of targeted control signals to exhibit the elegance of the proposed control scheme.

Methodology for optimizing geographical distribution and capacities of biomass power plants in Sabah, East Malaysia

Purpose – Biomass waste can be used as fuel in biomass power plants to generate electricity. It is a type of renewable energy widely available in Malaysia because 12 million tons of the biomass waste is produced every year. At present, only 5 per cent of the total biomass waste in Sabah, one of the states in Malaysia, is used to generate electricity for on-site consumption. The remaining 95 per cent of the biomass waste has not been utilized because the transportation cost for shifting the waste from the plantations to the power plants is substantial, hence making the cost of the biomass generated electricity to be high. Therefore, a methodology is developed and presented in this paper to determine the optimum geographic distribution and capacities of the biomass power plants around a region so that the cost of biomass generated electricity can be minimized. The paper aims to discuss these issues. Design/methodology/approach – The methodology is able to identify the potential locations of biomass power pl...

Effect of Sequential Phase Energization on the Inrush Current of a Delta Connected Transformer

Magnetizing inrush current in power transformer creates severe power quality problems. Energization of the transformer from the delta side of a delta-star transformer does not allow the control of neutral resistor at the time of switching the supply for reducing the inrush current. Controlled switching at peak value of the voltage may reduce inrush current in one winding of the transformer, but the line currents are not reduced. Delayed and controlled energization of the third phase may reduce inrush winding currents in two windings and only one line current is reduced, but the inrush currents in the other two lines become very high. Simulation studies of delta side energization of a delta-star transformer depict the results under various switching conditions.