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Abstract: This paper proposes a hybrid discontinuous control methodology for a voltage source converter (VSC), which is used in an uninterrupted power supply (UPS) application. The UPS controls the voltage at the point of common coupling (PCC). An LC filter is connected at the output of the VSC to bypass switching harmonics. With the help of both filter inductor current and filter capacitor voltage control, the voltage across the filter capacitor is controlled. Based on the voltage error, the control is switched between current and voltage control modes. In this scheme, an extra diode state is used that makes the VSC output current discontinuous. This diode state reduces the switching losses. The UPS controls the active power it supplies to a three-phase, four-wire distribution system. This gives a full flexibility to the grid to buy power from the UPS system depending on its cost and load requirement at any given time. The scheme is validated through simulation using PSCAD. [Copyright &y& Elsevier]

Abstract: The paper discusses the voltage control of a critical load bus using a dynamic voltage restorer (DVR) in a distribution system. The critical load requires a balanced sinusoidal waveform across its terminals preferably at system nominal frequency of 50Hz. It is assumed that the frequency of the supply voltage can vary and is different from the system nominal frequency. The DVR is operated such that it holds the voltage across the critical load bus terminals constant at system nominal frequency irrespective of the frequency of the source voltage. In case of a frequency mismatch, the total real power requirement of the critical load has to be supplied by the DVR. To compensate for frequency variation, the dc link of the DVR is supplied through an uncontrolled rectifier that provides a path for the real power required by the critical load to flow. A simple frequency estimation technique is discussed which uses a moving average process along with zero-crossing detector. Through detailed analysis and simulation studies using PSCAD/EMTDC it is shown that the voltage is completely controlled across the critical load. [Copyright &y& Elsevier]

Abstract: In this paper, the design of a distribution static compensator (DSTATCOM) based on cascaded transformer multilevel inverter is proposed. The topology requires controlling only a common dc storage capacitor. Two-level ramp-comparison current control method is extended for the multilevel inverter using phase-shifted multi-carrier PWM. The method provides equal switching stress and power handling for all the cascaded units. The net switching frequency increases while the ripple magnitude reduces using multilevel topology. These cause the feedforward gain to increase leading to a higher bandwidth of the control loop. An expression of the feedforward gain is derived for fixed switching frequency modulation of the inverter. It is shown that the use of proportional plus resonant controller with proposed multilevel modulation improves the tracking characteristics at fundamental frequency. A seven-level inverter based DSTATCOM is proposed for the application to the three-phase medium voltage distribution system and the results are shown through the PSCAD/EMTDC simulation. The proposed modulation and control scheme is validated through the experimental results that are obtained using the laboratory model of a single-phase, five-level inverter based DSTATCOM. [Copyright &y& Elsevier]

Abstract: This paper discusses the effects of thyristor controlled series compensator (TCSC), a series FACTS controller, on the transient stability of a power system. Trajectory sensitivity analysis (TSA) has been used to measure the transient stability condition of the system. The TCSC is modeled by a variable capacitor, the value of which changes with the firing angle. It is shown that TSA can be used in the design of the controller. The optimal locations of the TCSC-controller for different fault conditions can also be identified with the help of TSA. The paper depicts the advantage of the use of TCSC with a suitable controller over fixed capacitor operation. [Copyright &y& Elsevier]

Abstract: This paper describes a few different topologies of inverters used for realizing a distribution static compensator (DSTATCOM). A brief introduction of the need for shunt compensation as well as the requirements of the shunt compensator has also been given. An algorithm for generating references has been described. Three major topologies of inverters – three-leg inverter with single dc capacitor, three-leg inverter with neutral clamped dc capacitors, four-leg inverter and three single-phase inverters with common dc capacitor – have been described and simulated. DSTATCOM topologies for high voltage distribution systems have also been described. The Voltage Source Converter (VSC) topologies have been compared on the basis of the performance of the inverter for certain chosen system conditions and the number of switch devices and dc capacitors used. All simulations have been performed using PSCAD/EMTDC. [Copyright &y& Elsevier]

Abstract: The paper discusses the operation and control algorithms of shunt and series active filters. Performance of each of these filters is studied separately when it is connected to protect sensitive loads in a power distribution system. It is assumed that the distribution system is polluted due to the presence of the loads that may be unbalanced and draw interharmonic currents from the feeder. Separate algorithms have been proposed for the shunt and the series active filters. These are operated such that the voltage waveform at the sensitive load bus terminal is a clean balanced sinusoid. The proposed algorithms are verified through the computer simulation studies using PSCAD/EMTDC software package. [Copyright &y& Elsevier]

Various load compensation schemes proposed in literature assume that voltage source at point of common coupling (PCC) is stiff. In practice, however, the load is remote from a distribution substation and is supplied by a feeder. In the presence of feeder impedance, the PWM inverter switchings distort both the PCC voltage and the source currents. In this paper load compensation with such a non-stiff source is considered. A switching control of the voltage source inverter (VSI) based on state feedback is used for load compensation with non-stiff source. The design of the state feedback controller requires careful considerations in choosing a gain matrix and in the generation of reference quantities. These aspects are considered in this paper. Detailed simulation and experimental results are given to support the control design. [Copyright &y& Elsevier]

Single-phase distributed energy resources (DERs), such as rooftop photovoltaic arrays, are usually installed based on the need and affordability of clients without any regard to the power demand of the connected phase of a three-phase system. It might so happen that the power generation in a particular phase is more than its load demand. This may cause a reverse power flow in a particular phase, especially in a three-phase, four-wire distribution system. If now the load demand in the other two phases is more than their respective generations, then these two phases will see a forward power flow, while there will be a reverse power flow in the third phase. This will create severe unbalance in the upstream network. In this paper, a distribution static compensator (DSTATCOM) is used to circulate the excess generation from one phase to the others such that a set of balanced currents flow from or into the upstream network. Two different topologies of DSTATCOM are proposed in this paper for the low and medium voltage feeders. Two different power circulation strategies are developed for this purpose. Furthermore, a suitable feedback scheme is developed for each topology for power converter control. The performance of the proposed topologies and the control schemes for the DSTATCOM is evaluated through computer simulation studies using PSCAD/EMTDC. [ABSTRACT FROM AUTHOR]

Abstract: A new technique for optimal planning of MV and LV segments of a distribution system is presented in this paper. The main goal is to find optimally distribution transformer and substation locations and ratings, as well as, the route and type of Medium Voltage (MV) and Low Voltage (LV) feeders. The proposed technique is applicable to both uniform and non-uniform load densities areas. In this method, the planning area is divided into regions with relatively uniform load density such as urban, semi-urban, sub-urban. Each of regions is divided into zones, called LV zone. Each LV zone is supplied by an MV/LV transformer. The dimensions of LV zones are found based on the average load of each region. The placement and rating of MV/LV transformers, the type and route of LV conductors in an LV zone all depend on its loads’ location and power. Regarding the placement and rating of MV/LV transformers in planning area and the space of regions, the dimensions of a zone which is supplied by a HV/MV transformer, called MV zone, is determined. Additionally, the location and rating of HV/MV transformers as well as the feeder''s routes and types are calculated. Since the dimensions of an LV zone influence the associated length of MV feeder, the MV feeder cost needs to be included in the total cost associated with the LV zone. This requires the MV feeder type to be known to calculate the corresponding cost. However, the MV feeder type is determined as an output from MV zone planning. As a result, an iterative based method is proposed to consider this common element in computations to develop integrated planning of both LV and MV zones. It is observed that the iterative technique quickly converges to the same results as the exhaustive search method. Discrete particle swarm optimization (DPSO) method is employed for solving the planning problem. The results are compared with nonlinear programming, genetic algorithm and exhaustive search methods. It is observed that DPSO is as accurate as the exhaustive search method for integrated planning of MV–LV distribution systems while its computation time is significantly lower. [Copyright &y& Elsevier]

Abstract: The installation of domestic rooftop photovoltaic cells (PVs) are on the rise due to feed-in tariff and changes driven by environmental concerns. Even though the increase in the PV installation is gradual, their locations and ratings are often random. Therefore, such single-phase bi-directional power flow can have adverse effect on the voltage imbalance of a three-phase distribution network. In this paper, a voltage imbalance sensitivity analysis and stochastic evaluation based on the ratings and locations of single-phase grid-connected rooftop PVs in a residential low voltage distribution network are presented. The stochastic evaluation, based on Monte Carlo method, predicts a failure index of non-standard voltage imbalance in the network in presence of PVs. Some improvement methods are discussed and a new improvement method based on PV converter control is proposed. [Copyright &y& Elsevier]

Abstract: This paper discusses the control and protection of a microgrid that is connected to utility through back-to-back converters. The back-to-back converter connection facilitates bidirectional power flow between the utility and the microgrid. These converters can operate in two different modes–one in which a fixed amount of power is drawn from the utility and the other in which the microgrid power shortfall is supplied by the utility. In the case of a fault in the utility or microgrid side, the protection system should act not only to clear the fault but also to block the back-to-back converters such that its dc bus voltage does not fall during fault. Furthermore, a converter internal mechanism prevents it from supplying high current during a fault and this complicates the operation of a protection system. To overcome this, an admittance based relay scheme is proposed, which has an inverse time characteristic based on measured admittance of the line. The proposed protection and control schemes are able to ensure reliable operation of the microgrid. [Copyright &y& Elsevier]

Abstract: This paper shows how the power quality can be improved in a microgrid that is supplying a nonlinear and unbalanced load. The microgrid contains a hybrid combination of inertial and converter interfaced distributed generation units where a decentralized power sharing algorithm is used to control its power management. One of the distributed generators in the microgrid is used as a power quality compensator for the unbalanced and harmonic load. The current reference generation for power quality improvement takes into account the active and reactive power to be supplied by the micro-source which is connected to the compensator. Depending on the power requirement of the nonlinear load, the proposed control scheme can change modes of operation without any external communication interfaces. The compensator can operate in two modes depending on the entire power demand of the unbalanced nonlinear load. The proposed control scheme can even compensate system unbalance caused by the single-phase micro-sources and load changes. The efficacy of the proposed power quality improvement control and method in such a microgrid is validated through extensive simulation studies using PSCAD/EMTDC software with detailed dynamic models of the micro-sources and power electronic converters. [Copyright &y& Elsevier]

Abstract: This paper proposes a new approach for state estimation of angles and frequencies of equivalent areas in large power systems with synchronized phasor measurement units. Defining coherent generators and their correspondent areas, generators are aggregated and system reduction is performed in each area of inter-connected power systems. The structure of the reduced system is obtained based on the characteristics of the reduced linear model and measurement data to form the nonlinear model of the reduced system. Then a Kalman estimator is designed for the reduced system to provide an equivalent dynamic system state estimation using the synchronized phasor measurement data. The method is simulated on two test systems to evaluate the feasibility of the proposed method. [Copyright &y& Elsevier]

• Cooperative game technique used to make a clustered microgrid, and each microgrid has generation resources and batteries. • All possible coalitions are discussed to find the optimum results, and an algorithm is developed to find most feasible solution. • Capacity is allocated to each player, and maximized the profit for clustered system, and sensitivity analysis is performed. • Player's careful selection is important for a game formation to get maximum profit. In this paper a cooperative type of game theoretical technique is proposed at the planning stage to model a grid-connected clustered microgrid. In order to make it more applicable, the selected microgrid consists of different combinations of generation resources like wind turbines, solar cells, and batteries. In the game model, generation resources are considered as players and their profit as the payoff. The technique of the Nash bargaining solution is adopted in this study for capacity allocation of generation resources and batteries, and also to maximize the annual profit of individual microgrids and its cluster. As a cooperative game model, all possible coalitions are discussed between the players to find their optimum sizes, and most the suitable one is selected based upon the game theory technique and maximum payoff value. For this purpose, a particle swarm optimization (PSO) algorithm is developed to find the most feasible Nash bargaining solution using MATLAB software. In the simulations and for the system analysis, the realistic electrical load data and weather forecast is taken for a remote town Mount Magnet in Western Australia. Finally, a sensitivity analysis is performed to validate and show the reasonability of the optimized results concerning the proposed clustered system. [ABSTRACT FROM AUTHOR]