• Energy Research

This paper studies the DFT-based algorithm for the phasor measurement application and investigates its performance for off-nominal frequency conditions, harmonics, inter-harmonics, and out-of-band interfering signals. It is mathematically shown that the DFT technique can provide accurate estimation of the phasors in off-nominal frequency conditions when a three-phase balanced system is concerned. The negative-sequence component causes errors to the DFT estimates though. It is also rigorously shown why the DFT cannot accomplish this task in a single-phase system. Moreover, the DFT method is highly robust to the presence of harmonics but it fails to effectively reject inter-harmonics and/or out-of-band interference signals.

Abstract The optimal, resilient and flexible operation of the power system is one of the most important challenges of the power grid. Fast resources as a backup capacity to provide power are one of the ways the power system to be more flexible and resilient. In this paper, a new joint power and reserve scheduling is done considering scheduling based on power instead of scheduling based on energy, the correct management of the thermal units’ ramp, the use of responsive loads includes a collection of commercial customers and plug-in electric vehicles (PEVs) in the secondary (15-minute) and tertiary (30-minute) reserves and discharge management of PEVs. A part of the power demand of these responsive loads is provided as free by renewable resources in times when there are no bad weather conditions. The use of responsive loads, correct management of the ramp of thermal units and a part of the discharge of PEVs can help restore the network quickly. The mixed-integer linear programming (MILP) method has been used to solve the joint power and reserve scheduling problem. The results show that the proposed model can lead to more flexibility and resiliency of the system and reduce the cost of the system.

Abstract The first part of this article reviews the concepts of apparent power and power factor in single-phase circuits with non-negligible line impedances. The study is based on the well-known definition that the apparent power is the maximum load power subject to constant line losses and constant load voltage. In reality, however, all transmission/distribution lines have some finite impedance, and thus, the constant voltage condition cannot be maintained at the load terminals. In this article, the constant load voltage condition is relaxed and allowed to change, as long as it remains within acceptable range of application. This is a scenario that better reflects the realistic situations. Modified expressions for the apparent power and power factor are derived and discussed. The second part of the article presents a new concept called the current factor as the ratio of the minimal current to the actual current while keeping the load power constant. The current factor coincides with the power factor when...

This paper presents a phasor measurement algorithm for three-phase systems based on a modified phase-locked loop (PLL) system and presents the results of numerical simulations that show its performance with respect to different signal scenarios. The modified PLL system is first designed to estimate the phasors of the individual phases, frequency, and rate of change of frequency of the input signal. The positive-sequence phasor is then calculated based on the information provided by the PLL. Various simulations show that the proposed method exceeds most of the requirements stated in the IEEE Standard for Synchrophasor Measurements for Power Systems for a phasor measurement unit (PMU) of Class P.

Abstract Nowadays, Energy Efficiency as a strategic energy policy has been extended to handle the power system either in demand-side or supply-side affecting the proficiency of the grid. On the other hand, the penetration rates of green resources as PhotoVoltaic (PV) system and Vehicle to Grid (V2G) technologies and; Demand Response (DR) resources as virtual resources have been extremely expanded in the smart power system. Accordingly, in this paper, a novel concept of energy efficiency form economic aspect in presence of Green Virtual Resources (GVRs) will be presented while an economic model for Energy Efficiency Programs (EEPs) is nominated. Therefore, an economic efficiency maximization model of energy management in a Micro Grid (MG) is suggested based upon the difference of revenues and financial burden; whereas the optimal sitting and sizing of GVRs are determined. Furthermore, three multifarious techno economic coefficients including Economic Efficiency Index (EEI), Technical Efficiency Index (TEI) and Total Technical Efficiency Index (TTEI) are nominated to evaluate the impact of GVRs in efficiency improvement of the MG. To evaluate the capability of GVRs, the standard 33-bus IEEE distribution system is conducted. Results indicate that by selecting proper location and size of GVRs, significant improvement is obtained.

This paper presents a method to design a control system for a three-phase voltage source converter (VSC) that connects a renewable energy source to the utility grid through an output L-type or LCL-type filter. The well-known abc/dq transformation method creates coupling terms that are visible and can readily be canceled in the L-type filter. Such terms, however, are very complicated when an LCL filter is used. This paper, first revisits the derivation of the decoupling control method for an L-ype output filter and then, for the first time, derives the decoupling terms for an LCL-type filter. Having successfully decoupled the real and reactive power loops, feedback controllers are presented and designed to achieve desirable performance. The proposed controller provides active damping of the LCL resonance mode, robustness with respect to grid frequency, and impedance uncertainty. Moreover, a new controller is designed to improve the startup transient of the system. The methodology used in this paper is inspired from the feedback linearization theory and it provides a clear design method for the nonlinear systems. Simulation results are presented to confirm the analytical results.

Abstract This paper presents a new available efficiency index (AEI) and then optimizes it in order to increase the number of hours the load is supplied while decrease the losses as well as expected energy not supplied in a smart grid. The effectiveness of the presence of energy storage system (ESS) along with renewable energy sources (RESs) that are associated with uncertainty is investigated on the availability of the smart grid. The combination of the ARIMA model with K-Means scenario reduction method is used to model the uncertainty of load. The feed-in tariff of all generations is considered to calculate the total profit of the system; also, the costs of carbon emissions and opportunity costs from non-production of carbon emission and non-payment of fossil fuel costs due to the use of renewable resources are considered. Also, the energy storage system and the pumped-storage hydropower are considered. In this paper, an improved multi-objective crow search algorithm (IMCSA) is used to find the optimal operation of a smart grid in order to increase the AEI and profit of the system. The proposed method not only can minimize the power losses of the smart grid but also can improve the availability, reliability and total profit of smart grid.

Abstract One of the main challenges and essentials of the power system is the flexibility of generation scheduling. The flexibility of a system can be enhanced by using a smart grid comprising demand response, hybrid/diesel generation units and energy storage system. In this paper, an improved flexibility index is defined with the concept of fast reserve supply. The uncertainties of wind/solar power plants and required reserve of thermal units are considered using Latin Hypercube Sampling (LHS). The smart grid supplies a part of load profile of commercial consumers and a part of charge profile of plug-in hybrid electric vehicles (PHEVs) through wind and solar virtual power plants (VPPs), responsive loads, distributed generators (DGs) and the energy storage system. Moreover, the PHEVs considered in this paper provide a system with more flexibility. This paper has solved the unit commitment problem in a single-node system that has no transmission constraints. The mixed integer linear programming (MILP) and the mixed integer non-linear programming (MINLP) methods have been used in order to solve the unit commitment problem and the smart grid scheduling, respectively. The results show that the presented model can optimize the costs of the system and causes the system to become more flexible.

Traditional proportional integral (PI) control has been extensively used for power control of voltage source converters in microgrid systems. Previous studies show that fixed-gain PI controllers cannot easily adapt to power changes, disturbances, and parameters variation, especially in large microgrids; hence the need for continuous algorithms to adjust the controller gains over the transients cannot be neglected. In this paper, a novel online tuning algorithm for PI controllers is proposed and implemented in a microgrid system. In this algorithm, which is based on the neuro-dynamic programming concept, a fuzzy critic is employed to evaluate the credibility of the control system performance and provide an evaluation signal, which is then used in the gain-tuning process. The PI controller gains are updated in an optimization process based on steepest decent rule so that the evaluation signal produced by the critic is minimized. The developed control structure, which is named critic-based self-tuning PI controller, is tested in a microgrid system with different penetrations of distributed generators and operational scenarios. The simulation results verify that implementation of a heuristic gain-tuning algorithm results in a model-independent controller with increased adaptivity compared with conventional PI control. Furthermore, due to simple learning rules, the convergence time is significantly reduced and the transient response is improved. The proposed gain-tuning algorithm can also be applied to PI controllers in other applications of controllable systems.

Nowadays, the energy hub as one of the most interesting aspects of smart grid power system concept has been emerged. The heat energy market is a novel concept in the energy hub scheduling problem. Furthermore, the demand side Energy Efficiency Programs (EEPs) and Demand Response Programs (DRPs) as energy democracy policy plays important role in the smart grid power system. It is should be noted that although the EEPs are mid-term programs but, effects of EEPs on the short term programs such as energy hub scheduling programs are impressive. Therefore, in this paper a new model of the energy hub scheduling is provided associated with EEPs and DRPs. Also, the heat energy market has been considered to increase the efficiency of the proposed energy hub framework. In this regard, the various type of demand such as electrical, thermal and gas is considered in the provided structure. The proposed Mixed Integer Linear Programing (MILP) Model is implemented with CPLEX solver in GAMS Environment. The results of the study shows that the EEPs and DRPs has a significant impact of the operation cost on the energy hub system.