Power System Dynamic Simulation Research Articles

Dynamic Simulation of Large-Scale Power Systems Using a Parallel Schur-Complement-Based Decomposition Method

Power system dynamic simulations are crucial for the operation of electric power systems as they provide important information on the dynamic evolution of the system after an occurring disturbance. This paper proposes a robust, accurate and efficient parallel algorithm based on the Schur complement domain decomposition method. The algorithm provides numerical and computational acceleration of the procedure. Based on the shared-memory parallel programming model, a parallel implementation of the proposed algorithm is presented. The implementation is general, portable and scalable on inexpensive, shared-memory, multi-core machines. Two realistic test systems, a medium-scale and a large-scale, are used for performance evaluation of the proposed method.

Dynamic modeling and dynamic responses of grid-connected fuel cell

The active distribution network (ADN) is a new effective approach to facilitate connecting distributed generation (DG) to the network, where the DG is controlled to support the system stability during various kinds of disturbances. Fuel cell is one of the most important DGs, however there are still many issues left to be solved in order to meet the requirements of the ADN, such as dynamic modeling, dynamic responses to power systems, especially during voltage dip, system fault, etc. In the existing grid-connected fuel cell researches, most of the dynamic models did not consider air compressor and its parasitic power consumption. Hence, a dynamic model of grid-connected proton exchange membrane fuel cell (PEMFC) is presented by considering dynamic modeling of the air compressor and its parasitic power consumption. Based on the model, the mutual influences between power system and fuel cell are analyzed when the fuel cell is synchronously grid-connected. The dynamic responses of the fuel cell and its low voltage and fault ride-through capability are studied when the power system fault or voltage dip occurs. Finally, based on the dynamic simulation of the typical power systems with a PEMFC, the theoretical basis and guiding suggestions are presented for grid-connection, dynamic operation, and off-grid of fuel cells.

Modeling of Wind Energy on Isolated Area

In this paper, a model of the wind turbine (WT) with permanent magnet generator (PMSG) and its associated controllers is presented, The increase of wind power penetration in power systems has meant that conventional power plants are gradually being replaced by wind farms. In fact, today wind farms are required to actively participate in power system operation in the same way as conventional power plants. In fact, power system operators have revised the grid connection requirements for wind turbines and wind farms, and now demand that these installations be able to carry out more or less the same control tasks as conventional power plants. For dynamic power system simulations, the PMSG wind turbine model includes an aerodynamic rotor model, a lumped mass representation of the drive train system and generator model. In this paper we propose a model with an implementation in MATLAB / Simulink, each of the system components off-grid small wind turbines. DOI: http://dx.doi.org/10.11591/ijpeds.v4i2.4859

Damping Torques of Multi-Machine Power Systems During Transient Behaviors

A Weierstrass-based numerical method for computing damping torque of a 3-machine power system during transient period is proposed and evaluated. Numerical studies were performed to demonstrate mutual impacts of generators on the damping torque, when one of the generators is presented by a detailed model. The relationship between the averaged self-damping torque coefficient of the detailed model and the damping coefficient of the classical model is numerically studied. One interesting observation from our studies is that the damping torque coefficients tend to become zero at the end of transient stability period if all the generators are represented by the detailed model. This observation can be useful to determine the duration of transient stability period. One application of the proposed Weierstrass-based method is to determine appropriate and accurate damping terms for power system dynamic simulation.

A Comprehensive Evaluation Method on Dynamic Simulation Accuracy of Power System

In order to overcome the shortcomings of the present accuracy assessment methods of power system dynamic simulation, this paper focuses the permanent single phase short-circuit fault which occurs in a large probability in power grids,and selects the typical electrical quantities which is very concerned in engineering after the fault happened. A time-scale based error criteria on simulation validation is proposed, and a comprehensive error criteria according to the average errors between simulation data and actual data is proposed to evaluate objectively the simulation accuracy of the typical electrical quantities. Considering the variation characteristics of the electrical quantities, the simulation accuracy evaluation of a single electrical element is expended to the simulation accuracy evaluation of the entire network, so not only the comprehensive evaluation about the model and its parameters but also the information for model modification and parameter correction can be obtained. The effectiveness of the proposed method is verified by the numerical results on the New England 10 Unit 39 Bus powers system.

Dynamic validated model of a DFIG wind turbine

This paper presents the development and qualitative validation of a doubly-fed induction generator (DFIG) wind turbine model that is represented in terms of behaviour equations of each of the subsystems, mainly the turbine rotor, the drive train, the induction generator, the power converters and associated control systems and a protection system. Simulation results obtained from the models are compared to the field measurement data in a qualitative manner due to rotor wake and lack of ability of a single anemometer for adequate measurement of wind speed acting on the large surface of the rotor. It is concluded that the model is reasonably accurate and can hence be used for representing wind turbines in power system dynamics simulations.

Transient stability enhancement of wind farms connected to a multi-machine power system by using an adaptive ANN-controlled SMES

This paper presents a novel adaptive artificial neural network (ANN)-controlled superconducting magnetic energy storage (SMES) system to enhance the transient stability of wind farms connected to a multi-machine power system during network disturbances. The control strategy of SMES depends mainly on a sinusoidal pulse width modulation (PWM) voltage source converter (VSC) and an adaptive ANN-controlled DC–DC converter using insulated gate bipolar transistors (IGBTs). The effectiveness of the proposed adaptive ANN-controlled SMES is then compared with that of proportional-integral (PI)-controlled SMES optimized by response surface methodology and genetic algorithm (RSM–GA) considering both of symmetrical and unsymmetrical faults. For realistic responses, real wind speed data and two-mass drive train model of wind turbine generator system is considered in the analyses. The validity of the proposed system is verified by the simulation results which are performed using the laboratory standard dynamic power system simulator PSCAD/EMTDC. Notably, the proposed adaptive ANN-controlled SMES enhances the transient stability of wind farms connected to a multi-machine power system.

Improved Power Flow Initialization of Dynamic Studies with Non-linear Composite Load Model

A power flow solution using a static constant MVA load model is a straightforward approach to initialize power system dynamic simulations. Using this model to represent induction motor load, however, may not be suitable due to a natural mismatch between initial bus scheduled powers and actual input powers that are computed afterward using their converged bus voltages. To avoid this mismatch occurrence, the Newton–Raphson power flow algorithm has been newly extended to incorporate non-linear characteristics of a composite load model in order to get an exact operating point of each individual induction motor and static load. The power flow solution of the applied 13-bus industrial power system reveals that the extended algorithm is capable of giving an exact active and reactive power input of the motors in correlation with their converged slips, internal bus voltages, and mechanical load torque characteristics and of voltage-dependent loads in relation to their exponent indices. Moreover, the computational efficiencies of the algorithm have been investigated using IEEE 14-bus and 57-bus networks. The results show that embedding induction motor and static exponent load models directly into the power flow mismatch function and Jacobian can improve computational efficiency since the power flow solution is well converged in a satisfactory quadratic manner.

Accelerated and Localized Newton Schemes for Faster Dynamic Simulation of Large Power Systems

This paper proposes two methods to speed up the demanding time-domain simulations of large power system models. First, the sparse linear system to solve at each Newton iteration is decomposed according to its bordered block diagonal structure in order to solve only those parts that need to be solved and update only submatrices of the Jacobian that need to be updated. This brings computational savings without degradation of accuracy. Next, the Jacobian structure is further exploited to localize the system response, i.e., involve only the components identified as active, with an acceptable and controllable decrease in accuracy. The accuracy and computational savings are assessed on a large-scale test system.

A Novel STATCOM Model for Dynamic Power System Simulations

This paper introduces an advanced model of the STATCOM suitable for steady-state and dynamic simulations of large-scale power systems. It allows for a comprehensive representation of the STATCOM's AC and DC circuits-this is in contrast to current practice where the STATCOM is represented using an equivalent variable voltage source which is not amenable to a proper representation of its DC circuit. The new STATCOM model comprises a voltage source converter (VSC) in series with an LTC transformer. The former is represented by a complex tap-changing transformer whose primary and secondary windings would correspond, in a notional sense, to the VSC's AC and DC buses, respectively. The magnitude and phase angle of the complex tap changer correspond to the amplitude modulation index and the phase shift that would exist in a PWM inverter to enable either reactive power generation or absorption purely by electronic processing of the voltage and current waveforms within the VSC. The numerical technique employed to solve the STATCOM model is the Newton-Raphson method for both operating regimes, the steady-state and the dynamic-state. The latter involves discretization of the STATCOMs and synchronous generators differential equations so that the nonlinear algebraic equations and the discretized differential equations are linearized around a base operating point and assembled together in a unified frame-of-reference for robust iterative solutions.

Optimizing cache energy efficiency in multicore power system simulations

Due to recent trends in computer chip design and architecture, the power consumption of computing systems is increasing. Further, with increasing number of cores on a single chip, the size of cache is also increasing and hence, their contribution in overall processor power consumption has become significant. As computing systems become ubiquitous, their excessive power consumption is likely to increase the demands of electricity, thus increasing the level of stress on power systems. In this paper, we propose an approach for reducing cache energy consumption in power system dynamic simulations which are computationally intensive. Our approach is based on the observation that there exists large intra- and inter-program variation in cache resource demand in simulation of different contingencies. Thus, using decay cache technique, we dynamically turn off the cache blocks to save cache energy. In multicore systems, the requirements of meeting worst-case cache demand leads to over-provisioning of resources and hence, saving cache energy is even more important in multicore systems. Hence, we evaluate energy savings in the context of both dual-core and quad-core processors. We simulate several contingencies of different power systems using time domain simulation. Further, we explore the opportunity of dynamically saving cache energy by using a computer architecture simulator and simulate dual-core and quad-core processor configurations. The results show that our technique is effective in saving cache energy and also keeps the loss in performance minimal.

Initializing Dynamic Power System Simulations Using Eigenvalue Formulations of the Induction Machine and Power Flow Models

Initializing internal variables in dynamic power system simulations is a two-stage process. First, a power flow model is used to find the steady state bus variables. Second, values for the internal variables associated with bus connected components are determined such that the components' terminal values match the bus variables calculated from the power flow model. Initializing most components' variables is a straightforward, direct process. However, initializing induction machine variables traditionally uses an indirect, iterative process. In this paper, eigenvalue formulations are detailed for both the induction machine initialization and power flow models, which provide a direct method for determining all possible sets of induction machine initializations and offer a novel model for the power flow equations.

Design, dynamic simulation and construction of a hybrid HTS SMES (high-temperature superconducting magnetic energy storage systems) for Chinese power grid

High-temperature superconducting magnetic energy storage systems (HTS SMES) are an emerging technology with fast response and large power capacities which can address the challenges of growing power systems and ensure a reliable power supply. China Electric Power Research Institute (CEPRI) has developed a kJ-range, 20 kW SMES using two state of art HTS conductors, BSCCO and YBCO tapes. This SMES system is used to compensate a power drop and a fluctuation in order to damp low frequency oscillations to increase stability of a power system. This paper presents an optimized design of the SMES system to achieve a maximum energy capacity. A voltage source converter using IGBTs is built and can be used to control the power flow between the SMES system and external circuits. A control system using a digital signal processor (DSP) and micro-programmed control unit (MCU) is constructed. SVPWM pulse modulation is used as a control strategy. The whole system was experimentally tested for compensation of power fluctuation within milliseconds in a dynamic power system simulation laboratory. The result validates the design and control circuit, and more importantly, the application capability of SMES systems in a power grid.

Making use of BDF-GMRES methods for solving short and long-term dynamics in power systems

This paper applies the BDF-GMRES methods for solving the Differential Algebraic Equations (DAEs) associated to the simulation of short and long-term dynamics in power systems. The investigations are concentrated on the construction of a fine ILU-GMRES preconditioner for solving efficiently not only the well-conditioned coefficient matrices but specially the ill-ones. It is shown that, if the image matrix (preconditioner origin) is firstly preprocessed (scaled, normalized and reordered), a high quality ILU preconditioner is achieved. Numerical experiments considering different test-systems and different operation conditions illustrate how tricky can be the simulation of power system dynamics if the Jacobian matrix (coefficient matrix) is ill-conditioned, normally associated to an adverse operation condition. It is shown that a traditional implicit integration method may fail in this case, whereas the combination BDF-GMRES presents an outstanding performance.

Dynamic Load Modeling Based on Extreme Learning Machine

The dynamic load characteristics have significant impact on the power flow, transient stability computation, voltage stability calculation of the power system, and so on. Noticing that traditional mechanism loads model has difficulty in precisely describing the dynamic characteristics of synthetic load, this paper presents a non-mechanism dynamic load model based on Extreme Learning Machine (ELM). The Power Fault Recorder and Measurement System (PFRMS) is used to obtain data for load modeling. Take voltage and real/reactive power with different time delay as inputs, and take real/reactive power as output, train the ELM using the samples formed by fault data, the real power model and reactive power model are established respectively. The number of hidden layer nodes which has impact on the ELM model is also discussed. Dynamic simulation experiment is conducted at power system dynamic simulation laboratory. The simulation result shows that the ELM load model is simple and flexible, its parameters are easy to be identified. The ELM load model can describe the dynamic load characteristics accurately.

Multi-parameter Uncertainty Analysis in Power System Dynamic Simulation: A New Solution Based on the Stochastic Response Surface Method and Trajectory Sensitivity Method

Power system simulations are greatly affected by uncertainties arising from models and parameters. The conventional methods of uncertainty analysis involve many thousand rounds of computation, which are both time and effort demanding. Based on the stochastic response surface method and the trajectory sensitivity method, this article proposes a new solution to reduce the number of uncertain inputs and to expedite the calculation of uncertainty. The trajectory sensitivity method is first applied to narrow down a set of parameters with high sensitivity, and the stochastic response surface method is then applied on this set to analyze the uncertainties, which can greatly speed up the computation process. The uncertainties estimated this way are close to those by 105 Monte Carlo simulations in case studies of the NE power grid of China.

Design and Development of Embedded Turbine Supervisory Instruments Based on ARM and Linux

Aiming at issues of the modern embedded turbine supervisory instruments such as simplistic function, weak process power, low efficiency and so on, the technique of double CPUs with the cores of Intel PXA270 and Cyclone II EP2C20 microprocessors is employed in the present design. With embedded linux operating system and the developing platform of Qt software implemented, important functions such as data acquisition, data transfer based on TCP/IP protocols, display of data waveform, local storage of data, data analysis, elementary fault diagnosis and so forth can be achieved all together in a single facility. After tested on the Rotor Kit 4 of Bently Nevada and applied on 300MW turbine of the Power System Dynamic Simulation Laboratory in North China Electric Power University, the newly designed embedded turbine supervisory instruments show that the technique of double CPUs is effective, and the portable system can overcome the deficiencies of the modern embedded turbine supervisory instruments as mentioned above.

Dynamic Simulation of Large-Scale Power Systems Using a Two-Level Computation Tree Model

A new tree structure called the two-level computation tree model is proposed for real time dynamic simulation of large-scale power systems. The features of the computation tree method are that the root node of the tree corresponds to a disconnected linear network, which is easy to be dealt with, and the tree leaf-nodes represent the partitioned subsystems. In the process of trajectory simulation, the correction factors of Newton type iteration are computed through a tree traversal procedure. One advantage of the new method is that the computation tasks for all subsystems can be carried out simultaneously using any parallel computation facilities. Case studies on the 10-generator New England test power system and on a representation of Northeast China power system verify the accuracy and validate the potential application of the proposed method in the real time contingency simulation for realistic large-scale power system.

A Class of New Preconditioners for Linear Solvers Used in Power System Time-Domain Simulation

In this paper, a new class of preconditioners for iterative methods is proposed for the solution of linear equations that arise in the time-domain simulation of the power system. The system of linear equations results from an attempt to solve the differential algebraic equations (DAE) encountered in the power system dynamic simulation. The preconditioners are based on the multifrontal direct methods. The proposed method is compared to the incomplete LU factorization (ILU) based preconditioned iterative methods and other conventional direct linear sparse solvers. The comparison shows the proposed method achieves great computational efficiency relative to these other methods.

Optimum generation capacities of micro combined heat and power systems in apartment complexes with varying numbers of apartment units

Abstract A dynamic simulation of micro combined heat and power (micro-CHP) systems that includes the transient behavior of the system was developed by modeling the generation of electricity and recovery of heat separately. Residential load profiles were calculated based on statistical reports from a Korean government agency, and were used as input data to select the optimum capacities of micro-CHP systems based on the number of apartment units being served, focusing on both economic and energetic criteria. The capacity of internal combustion engine (ICE) based micro-CHP was assumed to be in the range 1–500 kW, and the dependence of the efficiency of the generator unit on the capacity was included. It was found that the configuration (i.e., the capacity and number of generator units) that maximized the annual savings also had favorable energetic performance. Additionally, the statistical mode calculated from the annual electrical load distribution was verified as a suitable indicator when deciding the optimum capacity of a micro-CHP system.