Shagufta Khan

Small signal stability improvement of a single machine infinite bus system using SVC

FACTS (Flexible AC Transmission Systems) controllers are used to enhance power transmission capability of existing transmission corridors. Shunt FACTS controllers achieve this by improving the bus voltage profile of the system. The Static Var Compensator (SVC) is a shunt FACTS controller which is used to improve the system bus voltage profile by providing reactive power compensation. In addition, SVC firing angle modulation using a damping controller can achieve the additional objective of power oscillation damping. It is observed that SVC with only voltage controller increases the small signal stability marginally. However, when a damping controller is added, a marked increase in the system small signal stability is achieved. A damping controller can use a variety of auxiliary or supplementary signals to improve the power oscillation damping. Usually, at the SVC location, electrical power, synthesized frequency, line current etc. are used as auxiliary signals. This paper presents the small signal stability improvement of a single machine infinite bus (SMIB) system with a SVC connected at the mid-point of the transmission line. Line current signal is used as a supplementary signal for the SVC damping controller. Multiple case studies are carried out to validate the results.

Modelling of neutral point clamped based VSC-HVDC system

This work shows the performance of Voltage Source Converter (VSC) based High Voltage DC (HVDC) transmission system. A 200 MVA, ±100 kV link is modeled between two identical asynchronous AC systems. The system studies are based on three level neutral point clamped (NPC) converters. Current controlled scheme is used for active and reactive power control. One converter is operated in DC voltage control mode, while the other operated in Active and Reactive power (PQ) control mode. The results are carried out in MATLAB software. The smoothness of DC voltages shows the feasibility of the work.

A novel sequential power-flow model for hybrid AC-DC systems

This paper represents the study of integrated AC-DC Newton Raphson power flow modelling of Multi-terminal HVDC (M-HVDC) systems. Some electrical parameters are specified to control the HVDC system in Power Flow Modelling. A set of specified parameters is known as the control strategy. The number of control strategies increases with the increase in the number of DC terminals. It is observed that the power flow convergence is affected by the control strategy. In this paper, sequential method is used for integrated AC-MTDC power flow analysis. Numerous case studies are conducted with the IEEE-30 bus test system in MATLAB software.

A Fuzzy TCSC Controller for transient stability improvement

This paper discusses a Fuzzy Logic Controller for a Thyristor Controlled Series Compensator (TCSC) to improve power system transient stability. A TCSC is a series FACTS controller which is used to improve the power transmission capability of a line. It is also used for power system transient and small signal stability improvement along with mitigation of SSR. Conventional TCSC damping controllers are not robust as their parameters have to be changed as per the operating condition. In this respect, Fuzzy Logic based damping controllers adjust themselves automatically. In this paper, a Fuzzy Logic based TCSC damping controller is used in a Single Machine Infinite Bus (SMIB) system to enhance the power system transient stability improvement.

Effect of DC Link Control Strategies on Multiterminal AC-DC Power Flow

For power-flow solution of power systems incorporating multiterminal DC (MTDC) network(s), five quantities are required to be solved per converter. On the other hand, only three independent equations comprising two basic converter equations and one DC network equation exist per converter. Thus, for solution, two additional equations are required. These two equations are derived from the control specifications adopted for the DC links. Depending on the application, several combinations of valid control specifications are possible. Each combination of a set of valid control specifications is known as a control strategy. The number of control strategies increases with an increase in the number of the DC terminals or converters. It is observed that the power-flow convergence of integrated AC-MTDC power systems is strongly affected by the control strategy adopted for the DC links. This work investigates the mechanism by which different control strategies affect the power-flow convergence pattern of AC-MTDC power systems. To solve the DC variables in the Newton-Raphson (NR) power-flow model, sequential method is considered in this paper. Numerous case studies carried out on a three-terminal DC network incorporated in the IEEE-300 bus test system validate this.

A novel power flow model of a Static Synchronous Series Compensator (SSSC)

This paper presents a novel Newton Raphson Power Flow model of a Static Synchronous Series Compensator (SSSC). The SSSC is a voltage sourced converter (VSC) based series FACTS device. This model includes multiple control modes of the SSSC. The SSSC is operated on following control modes: 1) the active power flow on the transmission line; 2) the reactive power flow on the transmission line; 3) the voltage at the sending or receiving end bus. In this model, the impedance of coupling transformer is included with the transmission line impedance. Numerous case studies carried out with multiple SSSCs incorporated in the IEEE-30 bus test system validates the proposed model.

A study of Static Synchronous Compensator in two power flow models

This paper demonstrate the modeling and control of the Static Synchronous Compensator (STATCOM) using Newton Raphson Load Flow (NRLF) and Fast Decoupled Load Flow (FDLF) algorithm in MATLAB environment. To reduce the complexity of the program, decoupling method is used. The STATCOM is a shunt FACTS (Flexible AC Transmission System) controller which is used to improve the bus voltage profile. Both models are used in multiple control modes. A fictitious bus is created in both models to connect the STATCOM and to reduce the complexity of the program. The STATCOM is connected via coupling transformer impedance. The switching losses and losses in the coupling transformer are also incorporated in this model. The various case studies are carried out in IEEE 30-bus test network with and without the STATCOM. The results justify the enhancement of power quality for multiple case studies.