Ghadir Radman

Survey on Smart Grid

Creation of a Smart Grid provides utilities and their customers a significant improvement in power reliability and services. To date, Smart Grid has attracted various researchers from different perspectives. This paper presents a review of Smart Grid technologies and its characteristics. An extensive literature review is introduced. One can see variety of problems and challenges in the field of Smart Grid. Hence, this paper can provide a help to find a new research point in this field.

Effects of STATCOM, SSSC and UPFC on voltage stability

The purpose of this paper is to study the effects of three FACTS controllers: STATCOM, SSSC and UPFC on voltage stability in power systems. Continuation power flow, with accurate model of these controllers, is used for this study. Applying saddle node bifurcation theory with the use of power system analysis toolbox (PSAT), the optimal location of these controllers are determined. Using a 6-bus test system the effects of these controllers on voltage stability are examined. It is found that these controllers significantly increase the loadability margin of power systems.

Contingency selection and static security enhancement in power systems using heuristics-based genetic algorithms

This paper proposes a technique to identify critical double-line outages and enhance static security by optimal placement of FACTS devices using heuristics-based genetic algorithm (GA). Two indices have been used for contingency screening: double-line contingency index (DCI), based on line overflows, and voltage sensitivity index (VSI), based on bus voltage violations. Contingency screening is treated as the primary optimization problem with an objective of finding all double-line outages with maximal DCI and VSI. Security enhancement is treated as a constrained secondary optimization problem. The objective is to reduce transmission losses through the branches of the system and reduce or remove the overflows and voltage violations present. The voltage magnitude at each bus and the line flow through each branch for all the buses and branches have been considered as inequality and equality constraints. The technique is demonstrated using IEEE 14 bus and IEEE 30 bus systems.

Small Signal Analysis of Power Systems With Wind and Energy Storage Units

A study of small signal behavior of power systems including wind generation units and energy capacitor systems (ECSs) is presented in this paper. Modeling of wind units with squirrel-cage induction generators connected to power system through a full-scale AC/AC converter and ECS unit are explained thoroughly. The ECS unit (considered in this paper) consists of electric double-layer capacitors (EDLC) and DC/AC converter. Small signal behavior of three test systems are studied and compared with one another using digital computer simulations. The three systems are: S1) WSCC 9-bus system with three conventional synchronous generators (SGs), S2) the WSCC system with one of the conventional SGs replaced by a wind energy system, and S3) the same as S2) but with the addition of an ECS unit. The study includes comparing of dominant eigenvalues, the participant state variables, and the related participation factors for the three systems. In addition, the effects of loading on the unstable modes of the system with conventional SG, wind and ECS units (system S3) are studied using the trajectory of these modes as loads are increased.

Enhancement of microgrid dynamic voltage stabilty using Microgrid Voltage Stabilizer

The microgrid concept has the potential to solve major problems arising from large penetration of distributed generation in distribution systems. A microgrid is not a robust system when compared to a power system. Therefore, proper control strategies should be implemented for a successful operation of a microgrid. This paper proposes the use of a coordinated control of reactive sources for the improvement of the dynamic voltage stability in a microgrid. The associated controller is termed as a Micro Grid Voltage Stabilizer (MGVS). The MGVS is a secondary level voltage controller which takes the weighted average of the voltage deficiencies at the load Buses and generates a control signal. This control signal is divided among the reactive power sources in the microgrid in proportion to their available capacities; thus each source will be required to generate certain amount of reactive power. The MGVS is implemented in a micro grid test system in MATLAB environment. A dynamic simulation of the test system is carried out for the cases of with and without the MGVS for various disturbances. Both grid-connected and islanded modes of operation are considered. Results show that, with the addition of MGVS, the dynamic voltage profile of the microgrid system, especially at the load Buses, improve drastically.

An adaptive neuro fuzzy power system stabilizer for damping inter-area oscillations in power systems

An adaptive neuro-fuzzy inference system (ANFIS) based PSS is proposed in this paper. The controller is essentially divided into two sub-systems, a recursive least square identifier for the generator and an adaptive neuro fuzzy PSS to damp the oscillations. The PSS is coupled to a single machine in every area and the parameters of this PSS are tuned online in order to minimize a cost function. The cost function consists of a summation of terms, in which each term is made up of the square of the difference in speed between the machine to which the PSS is connected and another machine in that same area (the number of terms equal the number of machines in that area excluding the machine installed with a PSS). The PSS is trained to reduce the speed difference between machines in every area while helping to reduce inter area oscillations. The proposed technique is illustrated on a 2 area 4-machine 13 bus system. This ANFIS PSS showed satisfactory performance under severe faulting conditions, where a three-phase fault applied to a line, was cleared after a extended period of time. The conventional PSS and the ANFIS using the original cost function (consisting of just the square of the speed difference of the generator installed with the PSS) failed to perform under such conditions.

Performance evaluation of PID power system stabilizer for synchronous generator

The excitation control of a synchronous generator using proportional, integral, and derivative (PID) control is considered. The proposed PID power system stabilizer uses the generator frequency and voltage deviations to provide a supplementary signal for the excitation control. The gains of the PIC controller are calculated for complete pole placement. Digital simulation of synchronous machine subject to a disturbance is performed to demonstrate the effectiveness of the proposed controller. It is found that the proposed PID stabilizer outperforms the traditional power system stabilizer currently used by most power plants.<<ETX>>

Investigating effect of voltage changes on static ZIP load model in a microgrid environment

This paper presents effects of voltage changes on static polynomial (ZIP) load under three phase fault in a microgrid environment. The objective of the paper is investigating the behavior of the ZIP load model under a faulty condition. Load representation is a crucial factor on approaching power system realistically. The static characteristics of the load can be classified into constant power, constant current and constant impedance load, depending on the power relation to the voltage. For a constant impedance load (Z), the power dependence on voltage is quadratic, for a constant current (I) it is linear, and for a constant power (P) the power it is independent of changes in voltage. The ZIP model is a polynomial model that represents the sum of these three categories. Behavior of the ZIP loads connected to the Microgrid test system will be investigated and overall changes will be discussed.

Initialization for Dynamic Simulation of Stressed Power Systems Considering Induction Motor Components of Loads

Power flow solution is used for the initialization of power system dynamic simulation. Available production grade software packages (PSS/E in case of this paper) assume PQ-model for induction motor components of the loads during initialization process but consider accurate dynamic model for the dynamic simulation phase. Since the reactive power consumed by the motor is not known prior to power flow solution, a fictitious shunt reactance is added to the system bus to account for the difference between the assumed and the actual reactive power consumption of the motor. With the added fictitious reactance to different buses, the simulation system no longer represents the actual power system. The objective of this paper is to show that, although the existing method of initialization used by available software packages (PSS/E in case of this paper) produces satisfactory results for lightly loaded systems, it gives erroneous results in the case of stressed systems. The IEEE 14-bus test system is used to prove this claim. The system is simulated for stressed and unstressed situations applying commonly used initialization method and other method that considers the actual induction motor model during the initialization process which does not require the fictitious added reactance. It was seen that the commonly used initialization method could result in inaccurate assessment for power system stability in case of stressed system. Also in this paper, an iterative procedure is proposed that shows how to obtain the correct initial values using PSS/E without the need for the fictitious added reactance that causes erroneous simulation results.

A study of interaction between dynamic load and STATCOM

This paper presents the improvement obtained in voltage profile of power systems with dynamic loads using STATCOM, under various transient conditions. A composite dynamic load model, consisting of three-phase induction motors and impedance loads, is used to capture the actual load characteristics. The voltage source inverter-based STATCOM is modeled using the dynamics of the dc link and incorporating the widely used PI control scheme, operating in voltage control mode. Simulation of a modified four-bus Heffron-Phillips test system shows the interaction of the STATCOM with dynamic load in an effort to improve the system dynamics under various transient conditions