Western System Coordinating Council Research Articles

Real-time simulation and performance analysis of multimachine power systems using dSPACE simulator

The analysis of the characteristics of multiple machines constituting a power system in real time is of paramount importance. The reported work uses dSPACE, a dynamic simulator, in investigating the characteristics of the said multimachine system. The transient model of the Western System Coordinating Council (WSCC) nine-bus, three-unit system is developed using MATLAB/Simulink. Using real-time interface, the model is executed in the digital signal processor (DSP) of dSPACE hardware. The model is analyzed for its performance against multiple changes in mechanical torque and load variation. The transient behavior of the model upon incidence of a significant network fault and its robustness towards to perturbations in network and system parameters are thoroughly analyzed. The conditions are emulated by usage of the digital signal processor and DS1104 Controller Board.

Wide‐area damping control for inter‐area oscillations using inverse filtering technique

In this study, a non-linear excitation controller using inverse filtering is proposed to damp inter-area oscillations. The proposed controller is based on determining generator flux value for the next sampling time which is obtained by maximising reduction rate of kinetic energy of the system after the fault. The desired flux for the next time interval is obtained using wide-area measurements and the equivalent area rotor angles and velocities are predicted using a non-linear Kalman filter. A supplementary control input for the excitation system, using inverse filtering approach, to track the desired flux is implemented. The inverse filtering approach ensures that the non-linearity introduced because of saturation is well compensated. The efficacy of the proposed controller with and without communication time delay is evaluated on different IEEE benchmark systems including Kundur's two area, Western System Coordinating Council three-area and 16-machine, 68-bus test systems.

Transmission line fault detection and localisation methodology using PMU measurements

Rapid advancements pertaining to measurements and computational technology have brought a paradigm shift for operational architecture of power grids across the globe. Self-healing, a vital operational feature of emerging power grids, necessitates real-time identification and localisation of transmission line faults for the entire power network. This study proposes a novel support vector machine-based fault localisation methodology to precisely identify and localise all types of transmission line faults occurring at any location in the power grid based on phasor measurement unit (PMU) measurements. Detection of fault is achieved through PMU measurements only from a single generator bus for the entire grid. Bus associated with fault, faulty branch and location of fault in faulty branch are calculated using fast Fourier transform analysis of variations pertaining to equivalent voltage phasor angle (EVPA) and equivalent current phasor angle (ECPA). The proposed methodology has been validated through extensive case studies for Western System Coordinating Council (WSCC)-9 and IEEE-14 bus systems. The main contribution of the proposed methodology is that the fault location information can significantly contribute to system protection center for restoration of the line within shortest time span and initiate appropriate wide area control actions to maintain stability.

Impacts of High Penetration of DFIG Wind Turbines on Rotor Angle Stability of Power Systems

With the integration of wind power into power systems continues to increase, the impact of high penetration of wind power on power system stability becomes a very important issue. This paper investigates the impact of doubly fed induction generator (DFIG) control and operation on rotor angle stability. Acontrol strategy for both the rotor-side converter (RSC) and grid-side converter (GSC) of the DFIG is proposed to mitigate DFIGs impacts on the system stability. DFIG-GSC is utilized to be controlled as static synchronous compensator (STATCOM) to provide reactive power support during grid faults. In addition, a power system stabilizer (PSS) is implemented in the reactive power control loop of DFIG-RSC. The proposed approaches are validated on a realistic Western System Coordinating Council (WSCC) power system under both small and large disturbances. The simulation results show the effectiveness and robustness of both DFIG-GSC control strategy and PSS to enhance rotor angle stability of power system.

Probabilistic Allocation of Thyristor-controlled Phase Shifting Transformer for Transient Stability Enhancement of Electric Power System

ABSTRACTDue to the large number of uncertainties in operation and planning of power system, it is appropriate to analyse the transient stability assessment as a stochastic problem. This paper presents the probabilistic approach to determine the optimal location of thyristor-controlled phase shifting transformer (TCPST) for enhancing the transient stability of power system. TCPSTs are the cost-effective means to ensure reliable and efficient power flow control in overloaded transmission lines. This feature leads to reduction of the rotor angle separation of synchronous generators during disturbance occurrence which improves transient stability of the system. To select the optimal location of the TCPSTs, the analysis of angular separation of rotors of generators is calculated by considering the probabilistic factors. The Western-System-Coordinating-Council (WSCC) 9-bus and Institute of Electrical and Electronics Engineers (IEEE) New-England 39 bus test systems were used to demonstrate the feasibility and applicability of the presented method.

Modeling and Coordinated Control Strategy of Large Scale Grid-Connected Wind/Photovoltaic/Energy Storage Hybrid Energy Conversion System

An AC-linked large scale wind/photovoltaic (PV)/energy storage (ES) hybrid energy conversion system for grid-connected application was proposed in this paper. Wind energy conversion system (WECS) and PV generation system are the primary power sources of the hybrid system. The ES system, including battery and fuel cell (FC), is used as a backup and a power regulation unit to ensure continuous power supply and to take care of the intermittent nature of wind and photovoltaic resources. Static synchronous compensator (STATCOM) is employed to support the AC-linked bus voltage and improve low voltage ride through (LVRT) capability of the proposed system. An overall power coordinated control strategy is designed to manage real-power and reactive-power flows among the different energy sources, the storage unit, and the STATCOM system in the hybrid system. A simulation case study carried out on Western System Coordinating Council (WSCC) 3-machine 9-bus test system for the large scale hybrid energy conversion system has been developed using the DIgSILENT/Power Factory software platform. The hybrid system performance under different scenarios has been verified by simulation studies using practical load demand profiles and real weather data.

A Novel Method for Generation Rescheduling to Alleviate Line Overloads

This paper presents a method for real-time transmission congestion management. Congestion can be alleviated by incorporating line capacity constraints in the dispatch and scheduling process. The objective of this paper is to alleviate the overload and minimize the cost of operation. Here, two objectives congestion and cost are simultaneously minimized. Generation rescheduling of participating generators is done to overcome the congestion. Particle Swarm Optimization (PSO) technique, aims in finding the global optimum of the real-valued function (fitness function) defined in the given space (search space). The technique has been tested on Western System Coordinating Council (WSCC) 3-Machine 9-Bus system and the results are discussed.

Shuffled frog leaping algorithm optimization for AC--DC optimal power flow dispatch

In this paper, a simple-implemented and reliable AC{DC optimal power ow (OPF) is proposed. Although high-voltage direct current (HVDC) transmission lines are being increasingly used in power systems, new optimization algorithms such as evolutionary and memetic algorithms, which never stick in local minimum, so far have not been implemented in the AC{DC OPF problem. An evolutionary algorithm known as the shued frog leaping algorithm (SFLA) is proposed in this paper to solve the OPF dispatch in an AC{DC power system (including both high-voltage alternating current and HVDC transmission lines). The implementation of the AC{DC OPF with these kinds of methods is much simpler than that of traditional (numerical) algorithms. In order to prove the quality of the SFLA, the proposed method is applied to 2 case studies, including the Western System Coordinating Council 9-bus and IEEE 30-bus power systems, and compared with the conventional particle swarm optimization (PSO) algorithm and 3 of its modied versions, while the constraints are all satised. The results of comparison indicate that the SFLA is a reliable and fast optimization

Damping Inter-Area Oscillations Based on a Model Predictive Control (MPC) HVDC Supplementary Controller

This paper introduces, formulates and evaluates an approach for damping inter-area oscillations of power systems based on supplementary current control of a line-commutated HVDC link. The proposed control is based on the model predictive control (MPC) strategy. The salient feature of the MPC as compared with other optimal control strategies, e.g., the linear quadratic Gaussian (LQG) control, is that it adjusts the control signal to achieve the objectives while explicitly respecting the plant constraints. This paper also compares the performance of the MPC with that of the LQG control. The two approaches are tested on the Western System Coordinating Council (WSCC) 9-bus system and the IEEE 14-bus system. Small-signal disturbance and large-signal disturbance stability studies are performed to demonstrate and compare the performances of the LQG and MPC methodologies. The study results show the effective and superior performance of the MPC for damping poorly damped oscillatory modes of the test systems.

Agent-based modeling for trading wind power with uncertainty in the day-ahead wholesale electricity markets of single-sided auctions

This paper, for the first time, adopts agent-based simulation approach to investigate the bidding optimization of a wind generation company in the deregulated day-ahead electricity wholesale markets, by considering the effect of short-term forecasting accuracy of wind power generation. Two different wind penetration levels (12% and 24%) are investigated and compared. Based on MATPOWER 4.0 software package and the 9-bus 3-generator power system defined by Western System Coordinating Council, the agent-based models are built and run under the uniform price auction rule and locational marginal pricing mechanism. Each generation company could learn from its past experience and improves its day-ahead strategic offers by using Variant Roth–Erev reinforcement learning algorithm. The results clearly demonstrate that improving wind forecasting accuracy helps increase the net earnings of the wind generation company. Also, the wind generation company can further increase its net earnings with the adoption of learning algorithm. Besides, it is verified that increasing wind penetration level within the investigation range can help reduce the market clearing price. Furthermore, it is also demonstrated that agent-based simulation is a viable modeling tool which can provide realistic insights for the complex interactions among different market participants and various market factors.

Rescheduling of power systems constrained with transient stability limits in restructured power systems

This paper investigates various approaches to relieve the transient stability constraint in restructured power systems. The approaches adopted fall into two broad categories: those based on eliminating the constraint in the least-cost way and those based on eliminating with the least possible rescheduling. The latter group can, on the other hand, emerge in the form of a pool-protected policy in which the bilateral contracts are rescheduled to maintain the stability or in the form of a contract-protected policy in which the realizable bilateral contracts are maximized while minimizing the rescheduling in pool market. Transient energy function (TEF) method is used as a tool to calculate the sensitivity of energy margin to the variations in the magnitude of generation and load. The effectiveness of the method is illustrated by case studies on Western System Coordinating Council (WSCC) 3-machine 9-bus power system and on the 10-machine 39-bus New England test system and the results are compared. The results are also verified by time domain simulations.

Bifurcation Analysis on a Multimachine Power System Model

In this article bifurcation analysis of the 9 bus power system model corresponding to the Western Systems Coordinating Council is performed. In order to use standard continuation packages like MATCONT, a full ordinary differential equations model, including the corresponding dynamics of the control loops and the transmission lines, is derived. Different loading conditions are studied by using the load demands as bifurcation parameters. For variations of one of the loads, it is shown that the equilibrium point undergoes Hopf and saddle-node bifurcations. Furthermore, the bifurcation analysis varying two loads simultaneously reveals the existence of a pair of double Hopf and a zero-Hopf bifurcations, acting as organizing centers of the dynamics. Finally, a power system stabilizer has been added in order to modify the location of a Hopf bifurcation curve.

Decentralized sliding mode block control of multimachine power systems

A decentralized sliding mode stabilizing excitation controller for multimachine Electric Power Systems (EPS) is designed. The block control approach is used in order to derive a nonlinear sliding manifold, on which the inherent plant model nonlinearities are compensated and the mechanical dynamics are linearized. A local Sliding Mode Speed Stabilizer (SMSS) and Sliding Mode Voltage Regulator (SMVR) control is designed to achieve attractiveness of the derived manifold, regulate the terminal voltage and stabilize the speed of each generation unit in spite of high level external disturbances. The simulation of the Western System Coordinating Council (WSCC) system exhibits the comparison between the traditional Automatic Voltage Regulator/Power System Stabilizer (AVR/PSS) and proposed SMSS/SMVR control schemes.

Multimachine Power-System Control: Integral-SM Approach

In this paper, a robust nonlinear control scheme based on the combination of the block-control linearization and integral sliding modes is proposed. This control technique is applied to multimachine electric-power systems. The plant model takes into account the interactions in power systems between the electrical and mechanical dynamics and load constraints. A nonlinear observer is designed to estimate the synchronous generators' rotor fluxes. The proposed control scheme requires only local information of each generator. The considered controller was tested and compared with a classical one through simulation on the Western System Coordinating Council system.

Nonlinear Passivity Robust Decentralized Controller for Large Scale Power System

A nonlinear passivity based decentralized excitation controller for multimachine power system is designed to stabilize the speed and regulate the terminal generator voltages. To design a control sliding function the passivity technique is used. Then, with this function a sliding mode integral controller is proposed. This combination enables to reject internal and/or external perturbations and take advantage of the energy properties of the power systems. The designed controller was tested through simulation on an equivalent of WSCC (Western System Coordinating Council) under small and large perturbations. The presented simulations confirm effectiveness of the proposed controller.

Security assessment of the electricity infrastructure under terrorism

The electrical network is a critical infrastructure which is highly interconnected and strongly interdependent on other basic infrastructures on which basic human activities depend. As a result, this network is often targeted by terrorist attacks. The occurrence of events (that may affect the system) due to terrorism must be considered in power system security assessment. In this way, proper decisions in the planning and operation of the power system can be taken so that an appropriate balance between operative cost and robustness in the case that a terrorist act affects the system can be reached. In this paper we present a methodology that enables us to assess the power system security with regard to the possibility of terrorist acts, considering also the uncertainties associated with load and generation. The method is a validated Western System Coordinating Council (WSCC) nine-bus test system, taking as an example the terrorism conditions of the Colombian electricity infrastructure.

Price discovery in restructured electricity markets

We empirically investigate the degree of integration that existed prior to the cost increases that caused emergency conditions in the Western Systems Coordinating Council (WSCC), particularly California, during the summer of 2000. Evidence from Granger causality tests and common features analysis over the period from December 1994 to September 1999 indicates a moderate degree of integration among these markets. However, price effects throughout the region were often only unidirectional, did not exhibit the characteristics of perfect substitutability, and were significantly influenced by institutional changes in the California market. Most importantly, our research suggests that these markets were not as highly integrated as earlier research had indicated.

Dynamic model for power systems with multiple FACTS controllers

Computer simulation and analysis of power systems are necessary for both planning and operation. This requires an appropriate mathematical model of the system that includes many inter-related linear/nonlinear differential and algebraic equations. Such mathematical model is also needed for the design of globally coordinated controllers to improve power system dynamic performance and stability. This paper presents a procedure for finding comprehensive dynamic models of power systems fitted with shunt and/or series connected FACTS controllers such as STATCOM, SSSC, and UPFC. In this procedure, individual components of a power system are modeled using appropriate frame of references. Then all related equations are transformed to a common network frame of reference and tied to each other through the Y-matrix of the transmission network. The procedure is tested on the Western System Coordinating Council (WSCC) test system including FACTS controllers by performing computer simulations of the system for three-phase short circuit faults. MATLAB/Simulink software package is used for the simulations.

New approach for strategic bidding of Gencos in energy and spinning reserve markets

In restructured and de-regulated power systems, generating companies (Gencos) are responsible for supplying electricity for both energy and reserve markets, which usually operate simultaneously. In this condition, the question is how much and for what price must each Genco generate for each market to maximize its profit, so this paper intends to answer to this question. In this paper, first, the combined energy and reserve markets are considered, and the Nash equilibrium points are determined. Then, the bidding strategies for each Genco at these points will be presented. The bids for the energy and 10 min spinning reserve (TMSR) markets are separated in the second stage, and again, the bidding strategies for each Genco for the two separated markets will be demonstrated. Comparison of the results shows that the separated bidding strategies, while being simplified with the algebraic optimization model and reducing the time consumed, give the same results as the combined ones. The Western System Coordinating Council (WSCC) nine bus test system is employed to illustrate and verify the results of the proposed method.

Social impact based contingency screening and ranking

This paper develops a new index to rank the contingencies in different partitioned areas of networks. The new index considers the social and economic impacts of the contingencies and ranks them by using an overall index that combines these effects with technical factors. This overall index is implemented in the Western Systems Coordinating Council (WSCC) system. Load flow is run in different scenarios; and real power losses, Available Transmission Capability (ATC), and Expected Socially Unserved Energy (ESUE) are compared.