M. A. Mahmud

Investigation of the Impacts of Large-Scale Wind Power Penetration on the Angle and Voltage Stability of Power Systems

The complexity of power systems has increased in recent years due to the operation of existing transmission lines closer to their limits, using flexible AC transmission system (FACTS) devices, and also due to the increased penetration of new types of generators that have more intermittent characteristics and lower inertial response, such as wind generators. This changing nature of a power system has considerable effect on its dynamic behaviors resulting in power swings, dynamic interactions between different power system devices, and less synchronized coupling. This paper presents some analyses of this changing nature of power systems and their dynamic behaviors to identify critical issues that limit the large-scale integration of wind generators and FACTS devices. In addition, this paper addresses some general concerns toward high compensations in different grid topologies. The studies in this paper are conducted on the New England and New York power system model under both small and large disturbances. From the analyses, it can be concluded that high compensation can reduce the security limits under certain operating conditions, and the modes related to operating slip and shaft stiffness are critical as they may limit the large-scale integration of wind generation.

Dynamic Stability of Three-Phase Grid-Connected Photovoltaic System Using Zero Dynamic Design Approach

This paper presents a new approach to control the grid current and dc-link voltage for maximum power point tracking and improvement of the dynamic response of a three-phase grid-connected photovoltaic (PV) system. To control the grid current and dc-link voltage, the zero dynamic design approach of feedback linearization is used, which linearizes the system partially and enables controller design for reduced-order PV system. This paper also describes the zero dynamic stability of the three-phase grid-connected PV system, which is a key requirement for the implementation of such controllers. Simulation results on a large-scale grid-connected PV system show the effectiveness of the proposed control scheme in terms of delivering maximum power into the grid.

Partial Feedback Linearizing Excitation Controller for Multimachine Power Systems to Improve Transient Stability

In this paper a new nonlinear excitation controller design to enhance transient stability of multimachine power systems is presented. Partial feedback linearization is first used to transform the nonlinear power system model into a partially linear system comprising a reduced-order linear part and a nonlinear dynamic autonomous part. Then a linear state feedback stabilizing controller is designed for the reduced-order linear part using optimal control theory to enhance the stability of the whole system. In this way, the performance of the stabilizing controller would be independent of the operating points of the power system and therefore is superior to those designed for completely linearized systems. It is shown that the controller design method ensures the stability of the nonlinear dynamic autonomous part. The design method is applicable to multimachine power systems but tested on a 3-machine 11-bus two-area test system. The performance of the proposed control scheme to large disturbances is evaluated, through computer simulation, and compared with a conventional power system stabilizer and an exact feedback linearizing controller.

Nonlinear Current Control Scheme for a Single-Phase Grid-Connected Photovoltaic System

This paper presents a new nonlinear current control scheme for a single-phase grid-connected photovoltaic (PV) system. The controller is designed using partial feedback linearization which linearizes the system partially and enables the controller design scheme for reduced-order PV systems. The reference current is calculated from the maximum power point tracking system. The proposed current control approach introduces the internal dynamics and the stability of the internal dynamics is a key requirement for the implementation of the controller. In this paper, an energy-based Lyapunov function is used to analyze the stability of internal dynamics of a PV system. The performance of the controller is evaluated based on the tracking of grid current to the reference current by considering the changes in atmospheric conditions. To ensure the suitability of the proposed controller in a real system, a large system similar to a practical system is simulated under different operating conditions such as changes in atmospheric conditions and faults on various parts of the system and compared with conventional controllers. The experimental validation of the proposed control scheme is also presented in this paper.

Voltage control of distribution networks with distributed generation using reactive power compensation

Voltage profile of distribution networks with distributed generation are affected significantly due to the integration of distributed generation (DG) on it. This paper presents a way to control voltage of distribution networks with DG using reactive power compensation approach. In this paper, the voltage control approach is shown based on the worst case scenario of the network. To keep the voltage profile within the specified limits, it is essential to regulate the reactive power of the compensators. Finally, based on this concept, a static analysis is done on a 15- bus Japanese distribution system, called Kumumoto system where the system is modified with the inclusion of distributed wind generators, photovoltaics, and synchronous generators.

Optimal Coordination of G2V and V2G to Support Power Grids With High Penetration of Renewable Energy

Electric vehicles (EVs) have recently gained much popularity as a green alternative to fossil-fuel cars and a feasible solution to reduce air pollution in big cities. The use of EVs can also be extended as a demand response tool to support high penetration of renewable energy (RE) sources in future smart grid. Based on the certainty equivalent adaptive control (CECA) principle and a customer participation program, this paper presents a novel control strategy using optimization technique to coordinate not only the charging but also the discharging of EV batteries to deal with the intermittency in RE production. In addition, customer charging requirements and schedules are incorporated into the optimization algorithm to ensure customer satisfaction, and further improve the control performance. The merits of this scheme are its simplicity, efficiency, robustness and readiness for practical applications. The effectiveness of the proposed control algorithm is demonstrated by computer simulations of a power system with high level of wind energy integration.

Robust nonlinear distributed controller design for active and reactive power sharing in islanded microgrids

This paper presents a robust nonlinear distributed controller design for islanded operation of microgrids in order to maintain active and reactive power balance. In this paper, microgrids are considered as inverter-dominated networks integrated with renewable energy sources (RESs) and battery energy storage systems (BESSs), where solar photovoltaic generators act as RESs and plug-in hybrid electric vehicles as BESSs to supply power into the grid. The proposed controller is designed by using partial feedback linearization and the robustness of this control scheme is ensured by considering structured uncertainties within the RESs and BESSs. An approach for modeling the uncertainties through the satisfaction of matching conditions is also provided in this paper. The proposed distributed control scheme requires information from local and neighboring generators to communicate with each other and the communication among RESs, BESSs, and control centers is developed by using the concept of the graph theory. Finally, the performance of the proposed robust controller is demonstrated on a test microgrid and simulation results indicate the superiority of the proposed scheme under different operating conditions as compared to a linear-quadratic-regulator-based controller.

Robust Partial Feedback Linearizing Stabilization Scheme for Three-Phase Grid-Connected Photovoltaic Systems

This paper presents a robust stabilization scheme for a three-phase grid-connected photovoltaic system to control the current injected into the grid and dc-link voltage to extract maximum power from photovoltaic (PV) units. The scheme is mainly based on the design of a robust controller using a partial feedback linearizing approach of feedback linearization, where the robustness of the proposed scheme is ensured by considering uncertainties within the PV system model. In this paper, the uncertainties are modeled as structured uncertainties based on the satisfaction of matching conditions. The performance of the proposed stabilization scheme is evaluated on a three-phase grid-connected PV system in terms of delivering maximum power under changes in atmospheric conditions.

Robust Nonlinear Controller Design for Three-Phase Grid-Connected Photovoltaic Systems Under Structured Uncertainties

This paper presents a robust nonlinear controller design for a three-phase grid-connected photovoltaic (PV) system to control the current injected into the grid and the dc-link voltage for extracting maximum power from PV units. The controller is designed based on the partial feedback linearization approach, and the robustness of the proposed control scheme is ensured by considering structured uncertainties within the PV system model. An approach for modeling the uncertainties through the satisfaction of matching conditions is provided. The superiority of the proposed robust controller is demonstrated on a test system through simulation results under different system contingencies along with changes in atmospheric conditions. From the simulation results, it is evident that the robust controller provides excellent performance under various operating conditions.

Voltage Variation on Distribution Networks With Distributed Generation: Worst Case Scenario

This paper presents an analytical approach to establish a relationship between the voltage variation and distributed generation (DG) integration for the planning and operation of distribution networks with DG. The proposed approach is mainly based on the derivation of a voltage variation formula for distribution networks with DG and the consideration of the worst case scenario, which establishes a relationship between the amount of voltage variation and maximum permissible DG. Some recommendations are presented based on the worst case voltage variation formula and DG integration to counteract the voltage variation effect. The relationship between the connection cost and voltage level is also presented in this paper. The feasibility of the proposed approach is validated by comparing the voltage profile obtained from the derived formula to that with the existing power system simulation software.