Amir Moghadasi

Enhancing LVRT capability of FSIG wind turbine using current source UPQC based on resistive SFCL

This paper presents a current-source converter based unified power quality conditioner (UPQC) is used for a fixed-speed induction generator (FSIG) wind turbines in order to enhance the low voltage ride through (LVRT) capability. When voltage sag occurs due to grid side fault, the series compensator of the UPQC injects required voltage to prevent disconnecting of FSIG wind turbine. On the other hand, faults produced by wind turbine generator systems will impact not only the wind farms but also the interconnected system including the grid if proper protection is not ensured. Therefore, the resistive SFCL incorporated in series with the dc-link inductance of UPQC is proposed to limit excessive current in the event of the generator side fault. Detailed simulation studies implemented in PSCAD/EMTDC confirm that both of resistive SFCL and large dc-link inductance are effective in decreasing the fault current thereby reducing the voltage dip at the generator terminal.

Defending mechanisms for protecting power systems against intelligent attacks

The power system forms the backbone of a modern society, and its security is of paramount importance to nations economy. However, the power system is vulnerable to intelligent attacks by attackers who have enough knowledge of how the power system is operated, monitored and controlled. This paper proposes a game theoretic approach to explore and evaluate strategies for the defender to protect the power systems against such intelligent attacks. First, a risk assessment is presented to quantify the physical impacts inflicted by attacks. Based upon the results of the risk assessment, this paper represents the interactions between the attacker and the defender by extending the current zero-sum game model to more generalized game models for diverse assumptions concerning the attackers motivation. The attacker and defenders equilibrium strategies are attained by solving these game models. In addition, a numerical illustration is demonstrated to warrant the theoretical outcomes.

LVRT capability assessment of FSIG-based wind turbine utilizing UPQC and SFCL

This paper investigates a fixed-speed induction generator (FSIG)-based wind turbines in effective combination with unified power quality conditioner (UPQC) and resistive superconducting fault current limiter (RSFCL). The UPQC control scheme is introduced to ensure the maximum low voltage ride-through (LVRT) enhancement of the FSIG-based wind turbine by compensating the voltage sag at the point of common coupling (PCC). Additionally, a realistic estimation of the voltampere rating requirements of UPQC for this type of application is carried out. In this paper the utilization of RSFCL is proposed to limit excessive current in the event of the fault. For this purpose, the electro-thermal model of the SFCL is implemented in PSCAD/EMTDC software as a component to verify SFCL damping performance. The obtained results confirm that the SFCL can not only reduce the volt-ampere rating of the UPQC, thereby reducing the installation cost but also aid to the LVRT capability improvement of the wind turbine as well as dynamic performance of the induction generator.

Pareto optimization of circular power pads for contactless electric vehicle battery charger

Design optimization of circular power pads for inductive power transfer (IPT) systems with applications in electric vehicle battery charger is proposed. A multi-objective optimization coupled with 2D finite element analysis (FEA) is used to find the Pareto-optimal solutions for circular magnetic structures considering different objective functions, such as power transfer efficiency, material cost, and horizontal misalignment tolerance of the IPT system. 2D FEA is used to calculate self and mutual inductances between primary and secondary pads, ohmic loss in coils, core loss in ferrites, stray loss in aluminum shields and electromagnetic field (EMF) emissions of the system. Practical limitations of the power electronic converters such as frequency, VA rating, operating quality factor, and EMF emissions are all considered in the proposed optimization. A 10 kW electric vehicle battery charger IPT system with circular power pads is investigated as the case study and Pareto-optimal solutions for this system are presented. Experimental test results on one of the Pareto-optimal solutions are in good agreement with the calculations using the proposed method. The proposed design optimization method provides a tool for finding highly efficient, flexible and cost-effective solutions for contactless electric vehicle battery charger.

A single-stage three-phase AC-AC converter for inductive power transfer systems

A three-phase ac-ac matrix converter for inductive power transfer (IPT) systems with soft-switching operation and bidirectional power flow is introduced. The proposed converter can generate high-frequency current directly from a three-phase ac power source without a dc link. Unlike conventional ac-dc-ac converters, the proposed converter can provide a high frequency current without any current sag around ac source zero-crossings for IPT systems. The proposed topology is expected to have high reliability and extended lifetime due to the soft-switching operation and elimination of short life electrolytic capacitors. Soft-switching operation will also reduce switching stress, switching losses, and electromagnetic interference (EMI) of the converter. A simple control strategy based on energy injection and free oscillation technique is used as the control method. The proposed converter is comprised only seven switches, which in turn increase the reliability, efficiency and reduce cost. The converter operates in eight modes, which are described in detail. Theoretical analysis and simulation results on a 2kW IPT system, show that the current control method can fully regulate the output current with low ripple which is suitable waveforms for IPT applications.

Model predictive power control approach for three-phase single-stage grid-tied PV module-integrated converter

This paper presents the concept of the three-phase module-integrated converters (MICs) incorporated in grid-tied large-scale photovoltaic (PV) systems. The current-source converter (CSC) with dc voltage boost capability, namely single-stage power conversion system, is proposed for three-phase PV MIC system. A model predictive scheme with low switching frequency is designed to control the proposed topology in such a way that provides a certain amount of active and reactive power in steady-state operation and also provides a proper ratio of reactive power under transient conditions to meet the low voltage ride through (LVRT) regulations. To predict the future behavior of current control values and switching states, a discrete-time model of the MIC is developed in synchronous reference frame. It is demonstrated that the injected active and reactive power can be controlled using minimizing the cost function introduced in the predictive switching algorithm. The proposed structure is simulated in MATLAB/SIMULINK software. The results verify the desired performance of the proposed control scheme for exchanging of both active and reactive powers between the PV MIC and the grid within different operating conditions.

Toward a Smart City of Interdependent Critical Infrastructure Networks

A smart city requires synergistic interaction between several functionally interdependent networks like energy, transportation, water, oil, gas, and emergency services to provide on-demand, reliable services to prosumers. The sustainability of smart city can be guaranteed only through ubiquitous communication and decentralized information exchange between optimization and computational models for the operation, visibility, and control of each constituent network. With the city spanning different societies and jurisdictions, the models must also account for challenges like interoperability, security, latency, resiliency, policymaking, and social behavior. Solutions in the current literature address these challenges in each network exclusively, but the interdependency between them is not properly emphasized. The chapter addresses this gap in research by considering smart city networks with special emphasis on energy, communication, data analytics, and transportation. It introduces each of these networks, identifies state of the art in them and explores open challenges for future research. As its key contribution to the literature, the chapter brings out the interdependencies between these networks through realistic examples and scenarios, identifying the critical need to design, develop, and implement solutions that value such dependencies. Thus, the chapter aims to serve as a starting point for researchers entering the domain of smart city and is interested in conducting cross-functional research across its different interdependent networks.

Power quality and voltage profile analyses of high penetration grid-tied photovoltaics: A case study

Installed Photovoltaic (PV) capacity across the smart distribution grid has been on the rise in order to reduce greenhouse gas emissions. However, under high penetration of PV, there could be potential impacts on the operation and planning of distribution networks. In order to evaluate the impacts of grid-tied PV, a case study on power quality and voltage profile analyses is conducted using a 1.1 MW AC grid-tied PV power plant located at Florida International University. As part of the power quality analysis, study explores Total Harmonic Distortion (THD) and high power and high energy ramp rate analysis. Current THD is posed to trigger problems when generation is highly intermittent wherein Voltage THD does not have a tight relationship with power output. For voltage profile analysis, the case study considers peak and minimum daytime load scenarios under different levels of penetration, including the existing level, and appraises the plants current and potential impacts in steady-state and time-series scenarios. The effect of using smart inverters with grid-support functions is also simulated. Results show that some major problems like voltage deviations and feeder losses can be expected at 60% PV penetration in minimum daytime load. The number of switching operations for voltage regulators also increase when smart inverters operate at Volt/VAr control mode. Results of the case study are discussed to highlight the significance of these issues in high penetration scenarios.

Prioritized coordinated reactive power control of wind turbin involving STATCOM using multi-objective optimization

This paper presents a computational intelligence technique for optimal coordinated reactive power control between a wind turbine (WT) equipped with doubly fed induction generator (DFIG) and a static synchronous compensator (STATCOM), during faults. The proposed control model is formulated as a multi-objective optimization problem (MOP) in order to simultaneously minimize two conflicting objectives: 1) voltage deviations at the WT terminal during and after grid faults and 2) low-frequency oscillations of the active power after clearing the faults. For this purpose, it is necessary to achieve the optimal values of control variables, such as the reactive power references for both DFIG and STATCOM controllers. The aforementioned problem is solved by using the stochastic normalized simulated annealing (NSA) algorithm. Since the proposed problem is a MOP incorporating several solutions, the NSA algorithm finds the Pareto-optimal solutions for the proposed control system, based on the assigned priorities (weights) for each objective. For online applications, where the control system needs to act very fast, a fuzzy logic controller (FLC) is used, so that tuning the fuzzy model and fuzzy rules are accomplished offline by the NSA algorithm. To validate the effectiveness of the proposed control strategy, a case study including a 1.5-MW DFIG and a 1.5-MVar STATCOM were carried out with MATLAB/Simulink.

A simplified power control approach with reliable axis decoupling capability for three-phase current source inverter

This paper discusses the integration of a three-phase Distributed generation (DG) into a grid-tied Photovoltaic (PV) system. A single-stage power conversion system comprising a Current Source Inverter (CSI) capable of dc voltage boost is proposed for this PV MIC system, to control which, a multivariable-proportional-integral (PI) regulator-based power control strategy is designed. It will control the proposed CSI-based MIC system through structural simplicity and fast dynamic response. When contrasted with the conventional PI methods, the proposed control scheme grants a fully decoupled axes in terms of step jumps and falls in the active and reactive power commands. By controlling the modulation index and the angle introduced by the Phasor PWM (PPWM) switching patterns, the active and reactive powers are demonstrated to be obtained and exchanged between the PV MIC and the grid. An experimental verification is provided to justify the performance of the proposed control method through a 300-VA laboratory prototype, and the results are compared with that of the conventional PI regulation approaches.