Voltage Stability Impact of Grid-tied Photovoltaic Systems Utilizing Dynamic Reactive Power Control


Book Description

ABSTRACT: Photovoltaic (PV) DGs can be optimized to provide reactive power support to the grid, although this feature is currently rarely utilized as most DG systems are designed to operate with unity power factor and supply real power only to the grid. In this work, the voltage stability of a power system embedded with PV DG is examined in the context of the high reactive power requirement after a voltage sag or fault. A real-time dynamic multi-function power controller that enables renewable source PV DGs to provide the reactive power support necessary to maintain the voltage stability of the microgrid, and consequently, the wider power system is proposed. The loadability limit necessary to maintain the voltage stability of an interconnected microgrid is determined by using bifurcation analysis to test for the singularity of the network Jacobian and load differential equations with and without the contribution of the DG. The maximum and minimum real and reactive power support permissible from the DG is obtained from the loadability limit and used as the limiting factors in controlling the real and reactive power contribution from the PV source. The designed controller regulates the voltage output based on instantaneous power theory at the point-of-common coupling (PCC) while the reactive power supply is controlled by means of the power factor and reactive current droop method. The control method is implemented in a modified IEEE 13-bus test feeder system using PSCAD® power system analysis software and is applied to the model of a Tampa Electric PV installation at Lowry Park Zoo in Tampa, FL. This dissertation accomplishes the systematic analysis of the voltage impact of a PV DG-embedded power distribution system. The method employed in this work bases the contribution of the PV resource on the voltage stability margins of the microgrid rather than the commonly used loss-of-load probability (LOLP) and effective load-carrying capability (ELCC) measures. The results of the proposed method show good improvement in the before-, during-, and post-start voltage levels at the motor terminals. The voltage stability margin approach provides the utility a more useful measure in sizing and locating PV resources to support the overall power system stability in an emerging smart grid.




Modelling, Control and Stability Analysis of Photovoltaic Systems in Power System Dynamic Studies


Book Description

This thesis investigates the impact of: i) the low voltage ride-through and dynamic voltage support capability; ii) the active current recovery rate; iii) the local voltage control; and iv) the plant-level voltage control of large-scale photovoltaic systems on short-term voltage stability and fault-induced delayed voltage recovery as well as transient and frequency stability. The power system dynamic performance is analysed using state-of-the-art methods, such as phasor mode time-domain simulations and the calculation of the critical clearing time that determines the stability margin. Moreover, the recently developed Kullback-Leibler divergence measure is applied to assess the quality of the voltage recovery. Drawbacks of this metric are outlined and a novel metric, the so-called voltage recovery index, is defined that quantifies the delayed voltage recovery more systematically. The studies are performed with a generic photovoltaic system model and typical model parameters are used that were determined in collaboration with a manufacturer. The stability analysis is performed in DIgSILENT PowerFactory using: i) a one-load infinite-bus system; and ii) an IEEE multi-machine voltage stability test system, namely the Nordic test system. The results show that with the adequate control of photovoltaic systems, power system dynamic performance can be significantly improved.




Robust Control for Grid Voltage Stability: High Penetration of Renewable Energy


Book Description

This book makes the area of integration of renewable energy into the existing electricity grid accessible to engineers and researchers. This is a self-contained text which has models of power system devices and control theory necessary to understand and tune controllers in use currently. The new research in renewable energy integration is put into perspective by comparing the change in the system dynamics as compared to the traditional electricity grid. The emergence of the voltage stability problem is motivated by extensive examples. Various methods to mitigate this problem are discussed bringing out their merits clearly. As a solution to the voltage stability problem, the book covers the use of FACTS devices and basic control methods. An important contribution of this book is to introduce advanced control methods for voltage stability. It covers the application of output feedback methods with a special emphasis on how to bound modelling uncertainties and the use of robust control theory to design controllers for practical power systems. Special emphasis is given to designing controllers for FACTS devices to improve low-voltage ride-through capability of induction generators. As generally PV is connected in low voltage distribution area, this book also provides a systematic control design for the PV unit in distribution systems. The theory is amply illustrated with large IEEE Test systems with multiple generators and dynamic load. Controllers are designed using Matlab and tested using full system models in PSSE.




Reactive Power Support Using Photovoltaic Systems


Book Description

With the widespread adoption of photovoltaic (PV) systems across the world, many researchers, industry players, and regulators have been exploring the use of reactive power from PV to support the grid. This thesis is the first to comprehensively quantify and analyse the techno-economic cost and benefits of reactive power support using PV. On top of formulating the cost of PV reactive power and identifying the feasible range of its monetary incentives, this thesis has also proposed practical methods to implement the reactive power dispatch effectively and efficiently, with and without communication infrastructure. The findings and approaches in this work can therefore help power system planners and operators towards better integration of PV into the electrical grid, both in terms of regulation and implementation.




Real Power and Reactive Power Control of a Three-Phase Single-Stage-PV System and PV Voltage Stability


Book Description

Grid-connected photovoltaic (PV) systems with power electronic interfaces can provide both real and reactive power to meet power system needs with appropriate control algorithms. This paper presents the control algorithm design for a three-phase single-stage grid-connected PV inverter to achieve either maximum power point tracking (MPPT) or a certain amount of real power injection, as well as the voltage/var control. The switching between MPPT control mode and a certain amount of real power control mode is automatic and seamless. Without the DC-to-DC booster stage, PV DC voltage stability is an important issue in the control design especially when the PV inverter is operating at maximum power point (MPP) with voltage/var control. The PV DC voltage collapse phenomenon and its reason are discussed. The method based on dynamic correction of the PV inverter output is proposed to ensure PV DC voltage stability. Simulation results of the single-stage PV system during system disturbances and fast solar irradiation changes confirm that the proposed control algorithm for single-stage PV inverters can provide appropriate real and reactive power services and ensure PV DC voltage stability during dynamic system operation and atmospheric conditions.




Grid Converters for Photovoltaic and Wind Power Systems


Book Description

Grid converters are the key player in renewable energy integration. The high penetration of renewable energy systems is calling for new more stringent grid requirements. As a consequence, the grid converters should be able to exhibit advanced functions like: dynamic control of active and reactive power, operation within a wide range of voltage and frequency, voltage ride-through capability, reactive current injection during faults, grid services support. This book explains the topologies, modulation and control of grid converters for both photovoltaic and wind power applications. In addition to power electronics, this book focuses on the specific applications in photovoltaic wind power systems where grid condition is an essential factor. With a review of the most recent grid requirements for photovoltaic and wind power systems, the book discusses these other relevant issues: modern grid inverter topologies for photovoltaic and wind turbines islanding detection methods for photovoltaic systems synchronization techniques based on second order generalized integrators (SOGI) advanced synchronization techniques with robust operation under grid unbalance condition grid filter design and active damping techniques power control under grid fault conditions, considering both positive and negative sequences Grid Converters for Photovoltaic and Wind Power Systems is intended as a coursebook for graduated students with a background in electrical engineering and also for professionals in the evolving renewable energy industry. For people from academia interested in adopting the course, a set of slides is available for download from the website. www.wiley.com/go/grid_converters







Design and Power Quality Improvement of Photovoltaic Power System


Book Description

This book presents a case study on a new approach for the optimum design of rooftop, grid-connected photovoltaic-system installation. The study includes two scenarios using different brands of commercially available PV modules and inverters. It investigates and compares several different rooftop grid-connected PV-system configurations taking into account PV modules and inverter specifications. The book also discusses the detailed dynamic MATLAB/Simulink model of the proposed rooftop grid-connected PV system, and uses this model to estimate the energy production capabilities, cost of energy (COE), simple payback time (SPBT) and greenhouse gas (GHG) emissions for each configuration. The book then presents a comprehensive small signal MATLAB/Simulink model for the DC-DC converter operated under continuous conduction mode (CCM). First, the buck converter is modeled using state-space average model and dynamic equations, depicting the converter, are derived. Then a detailed MATLAB/Simulink model utilizing SimElectronics® Toolbox is developed. Lastly, the robustness of the converter model is verified against input voltage variations and step load changes.




Autonomous Voltage Control Strategies in Distribution Grids with Photovoltaic Systems


Book Description

This thesis analyzes the technical and economic potential of autonomous voltage control strategies for improving distribution grid operation with high shares of photovoltaic (PV) generation. Key issues include: The simultaneity of local photovoltaic generation and local consumption as well as its influence on reverse power flows.The theoretical potential of autonomous voltage control strategies to increase a grid’s hosting capacity for additional photovoltaic generation.Stability analyses of a voltage-dependent combined active and reactive power control strategy for photovoltaic inverters.The cost savings potential (CAPEX & OPEX) of autonomous voltage control strategies, compared to traditional grid reinforcement measures. The results suggest that autonomous voltage control strategies can be used to improve the technical and economic distribution grid integration of PV systems. If applied appropriately, these strategies are capable of deferring grid reinforcement measures and hence shifting investment costs to future points in time. Of all investigated autonomous voltage control strategies, the on-load tap changer voltage control and a combined Q(V)/P(V) PV inverter control strategy showed the most promising results, from a technical and an economic perspective.




Enhancement of Grid-Connected Photovoltaic Systems Using Artificial Intelligence


Book Description

​Enhancement of Grid-Connected Photovoltaic Systems Using Artificial Intelligence presents methods for monitoring transmission systems and enhancing distribution system performance using modern optimization techniques considering different multi-objective functions such as voltage loss sensitivity indexes, reducing total annual cost, and voltage deviation. The authors offer a comprehensive survey of distributed energy resources (DERs), explain the backward/forward sweep (BFS) power flow algorithm, and present simulation results on the optimal integration of photovoltaic-based distributed generators (PV-DG) and distribution static synchronous compensators (DSTATCOM) in different transmission and distribution systems. This book will be a valuable academic and industry resource for electrical engineers, students, and researchers working on optimization techniques, photovoltaic systems, energy engineering, and artificial intelligence.