Volume 9, Issue 6

A new topology of DSTATCOM (distribution static compensator) is proposed for power quality improvement in three-phase four-wire distribution systems. A three-leg VSC (Voltage Source Converter) is integrated with a star/hexagon transformer for the compensation of reactive power for voltage regulation or for power factor correction along with load balancing, elimination of harmonics currents and neutral current compensation. The star/hexagon connected transformer provides a path to the zero sequence current in a three-phase four-wire distribution system. In order to optimize the voltage rating of the VSC, the star/hexagon transformer is designed to have a suitable voltage rating for the secondary windings for integrating the three-leg VSC. This transformer connection provides the selection of 'off the shelf' VSC for this application and it also provides isolation for the VSC system. The performance of the proposed DSTATCOM system is validated through simulations using MATLAB software with its Simulink and Power System Block set (PSB) toolboxes.

The paper presents an energy approach based on controllability and observability gramians for the optimal location of controllers/sensors in large-scale power systems. This approach consists of solving a stochastic optimization problem based on scenarios reflecting various operational situations (load changes, line tripping…). This approach could be regarded as part of a structural optimization procedure aiming at defining some new control systems in the context of security improvements of large-scale power systems. Application to the "Two-area power system" gives very promising results.

The connection of distributed generation (DG) essentially changes the distribution network operation and creates a range of well-documented effects varying the voltage levels and short circuit currents. Among others, DG can alter protection system operations in distribution networks, leading to the failure of reclosing, the disconnection of the healthy feeder or the prevention of a protection operation. This paper proposes a procedure, based on Petri nets and supported by a centralized monitoring architecture, for monitoring failures of the protection systems in radial distribution networks. Some case studies applied to a real Italian distribution network proved the effectiveness of the proposed procedure that can therefore represent an effective solution to improve distribution systems reliability in the presence of DG.

This paper proposes a new method to identify the real and reactive power transfer between generators and load using modified nodal equations. Based on available load flow results, the method partitions the Y-bus matrix to decompose the current of the load buses as a function of the generators' current and load voltages. Then, it uses the modified admittance matrix to decompose the load voltage-dependent term into components of generator dependent terms. By using these two decompositions of current and voltage terms, the real and reactive power transfer between loads and generators are obtained. The effectiveness of the proposed method is demonstrated by using a simple 5-bus system and the modified IEEE 30-bus system. The proposed methodology provides reasonable and acceptable results to real and reactive power transfer allocation.

This paper proposes a control strategy for important transients of a single-stage, three-phase, PV system that is connected to a distribution network. The proposed control strategy adopts an inner current-control loop and an outer DC-link voltage control loop. The current-control mechanism renders the PV system protected against external faults, enables control of the DC-link voltage and, therefore, controls/maximizes the PV system power output. The paper also proposes a feed-forward compensation strategy for the DC-link voltage control loop to mitigate the impact of the nonlinear characteristic of the PV array on the closed-loop stability, and to permit design and optimization of the DC-link voltage controller for a wide range of operating conditions. A mathematical model and a control design methodology are presented for the PV system, and it is shown that under the proposed control, the PV system fulfills the operational requirements of a grid-connected PV system. The effectiveness of the proposed control strategy and the most important transients of the PV system are evaluated through simulation studies conducted on a detailed switched model of the PV system in the PSCAD/EMTDC software environment.