Electromagnetic Transient Simulation Tool Research Articles

Dynamic equivalent of inverter-based distributed generations for large voltage disturbances

As the differences among inverter-based distributed generators (DGs) in the active distribution network (ADN), the aggregated dynamic model under large disturbances cannot effectively represent transient characteristics of the ADN. To overcome this issue, in this paper, a generic dynamic equivalent model of DGs is proposed. First, a simulation platform for multiple DGs is built based on electromagnetic transient simulation tool. The simulation results show that the aggregated transient characteristics under large disturbances are mainly determined by the fault ride-through control strategy of each inverter. Based on this, a control strategy is proposed to characterize the differences between inverters, and the equivalent model is derived. To achieve engineering applications, the equivalent structure is simplified, and multiple disturbance curves are used to identify the parameters. The validity and generalization ability of the proposed model is verified by simulation analysis under different disturbance strengths.

Minimum Voltage-Current Characteristic for Calculating Surge Arrester Energy Dissipation in Temporary Overvoltage Conditions

Abstract--A method is described for estimating required energy capability of surge arresters with respect to temporary overvoltages (TOVs). The method makes use of surge arrester catalogue data on thermal energy rating and TOV capability for estimating minimum voltage-current characteristics suitable for energy calculations by electromagnetic transient simulation tools. The need to recalculate composite TOV events for comparison with TOV capability curves is thereby avoided; this makes the method especially useful in conditions of resonant TOVs comprising harmonics, e.g., from energization of transformers in transmission networks with a large share of underground cables.

Transmission-and-Distribution Dynamic Co-Simulation Framework for Distributed Energy Resource Frequency Response

The rapid deployment of distributed energy resources (DERs) in distribution networks has made it challenging to balance the transmission system and stabilize frequency. DERs have the ability to provide frequency regulation services; however, existing frequency dynamic simulation tools—which were developed mainly for the transmission system—lack the capability to simulate distribution network dynamics with high penetrations of DERs. Although electromagnetic transient simulation tools can simulate distribution network dynamics, the computation efficiency limits their use for large-scale transmission-and-distribution (T&D) co-simulation. This paper presents an efficient open-source T&D dynamic co-simulation framework for DER frequency response based on the HELICS platform and off-the-shelf T&D simulators. The challenge of synchronizing the simulation between the transmission network and the DERs in the distribution network is solved through the detailed modeling of DERs in frequency dynamic models while DER power flow models are also preserved in the distribution networks, thereby respecting local voltage constraints when dispatching DER power for frequency response. DER frequency response (primary and secondary) is simulated in case studies to validate the proposed framework. Last, the accuracy of the proposed co-simulation model is benchmarked, and a large T&D system simulation (2k transmission and 1M distribution nodes) is presented to demonstrate the efficiency and effectiveness of the overall framework.

Power Coupling for Transient Stability and Electromagnetic Transient Collaborative Simulation of Power Grids

Co-simulation of heterogeneous systems allows for in-depth analysis of various aspects of power systems’ operation while staying within the environments of the simulation tools that are best fit to represent their respective domains. Equipped with a proprietary co-simulation platform, the paper focuses on the issue of power-conjugate coupling between parts of power grids modeled in transient stability and electromagnetic transient simulation tools. The problems of co-simulation stability and precision in presence of delays are tackled by means of designing a proper coupling interface. It is shown that two established interface methods – the V-I method and the Transmission Line Interface – are special cases of a generalized interface framework proposed in the paper. Moreover, a new interface algorithm is described by parametrizing the generalized framework. Analytical tools are also formulated to aid in the analysis of interface stability and precision via the concepts of passivity and transparency. Simulation results of benchmark systems of various complexity demonstrate the application of the developed power coupling interface.

Practical challenges in hybrid simulation studies interfacing transient stability and electro-magnetic transient simulations

This paper discusses practical challenges of interfacing Transient Stability Analysis and Electro-Magnetic Transient Simulation tools in hybrid simulation studies. Various interfacing approaches are examined and single-port Thevenin equivalent is proposed as a suitable and practical solution to represent the TSA-side system in the EMT simulation. The shortcomings of this representation are discussed and a quantitative measure is proposed to evaluate validity of the interface, which helps capturing the cases where the simulation may run into numerical instability due to simple representation of the external system. The effectiveness of the proposed technique is demonstrated using two practical power systems.

Interpolation for power electronic circuit simulation revisited with matrix exponential and dense outputs

With a high penetration of power electronic equipment, transient simulation for power electronic circuit has been a main challenge for performance improvement of the electromagnetic transient simulation tools. In this paper, two new solvers for the matrix exponential-based simulation method are proposed based on the dense output formula and Padé approximation of different orders. The proposed solvers are implemented with the optimal combination of numerical integration method and interpolation method. Both solvers are L-stable. One has 3rd-order accuracy which is more accurate than existing simulation tools in power electronic simulation. The other solver achieves 1st-order accuracy with a lower precision numerical integration method than the same-order algorithms and is appealing from computation speed perspective. Numerical studies including TCR circuit and two types of VSC-HVDC systems are conducted to demonstrate the effectiveness of the proposed solvers.

Accuracy Improvement Method of Energy Storage Utilization with DC Voltage Estimation in Large-Scale Photovoltaic Power Plants

In regard to electric devices, currently designed large-scale distributed generation systems require a precise prediction strategy based on the composition of internal component owing to an environmental fluctuating condition and forecasted power variation. A number of renewable resources, such as solar or marine based energies, are made up of a low voltage direct current (DC) network. In addition to actively considering a power compensation plan, these generation systems have negative effects, which can be induced to a connected power system. When a storage is connected to a DC-based generation system on an inner network along with other generators, a precise state analysis plan should back the utilization process. This paper presents a cooperative operating condition, consisting of the shared DC section, which includes photovoltaic (PVs) and energy storage devices. An active storage management plan with voltage-expectation is introduced and compared via a commercialized electro-magnetic transient simulation tool with designed environmental conditions. Owing to their complexity, the case studies were sequentially advanced by dividing state analysis verification and storage device operation.

Exponential integration algorithm for large-scale wind farm simulation with Krylov subspace acceleration

Facing the increasingly complex power system transient characteristics, the electromagnetic transient simulation tools are gaining popularity, thanks to their detailed modeling of power system equipment and high fidelity simulation results. Consequently, the Electro-Magnetic Transient Programs are increasingly used in simulation studies of higher dimensions and wider range of scales, which challenges the circuit-based algorithmic design of these programs. This paper proposes to use explicit integration formulas based on the matrix exponential function in the transient simulations of large-scale wind farms, which possess both high efficiency of explicit methods and numerical stability of implicit methods. A Krylov subspace-based order reduction technique embedded into the integration formulas was developed to specifically address the simulation needs of high dimensional EMT model of detailed wind farms. Numerical studies are conducted based on a realistic large-scale wind farm, where the proposed state space modeling framework is established, and the matrix exponential-based algorithm is implemented and compared against a set of classical stiff ODE solvers. Simulation tests with different fault types and fault locations are presented, showing a superior computation speed for studies with both equivalent and detailed wind farm modeling. On the other hand, numerical errors of the new algorithm are shown to be at least one order of magnitude smaller than other solvers in the range of typical step sizes, under the same simulation setting. These properties ensure an efficient, reliable and highly scalable simulation capability for the computation challenges in the studies of large-scale wind farms.

Efficient approach for commutation failure immunity level assessment in hybrid multi‐infeed HVDC systems

Commutation failure (CF) of hybrid multi-infeed high voltage-direct current (HMIDC) systems, comprising line commutated converter-based high-voltage direct current (LCC-HVDC) and voltage source converter-based high-voltage direct current (VSC-HVDC) links, has been mainly analysed by electromagnetic transient simulation tools, resulting in heavy workload and long computational time. This study proposes an efficient approach for CF immunity level assessment based on CF immunity index in HMIDC systems. Thus, an equivalent dual-bus analytical model of the HMIDC systems is first established, which then provides a theoretical basis for defining an equivalent voltage stability indicator (EVSI). It is then shown that such an EVSI index can be employed in the proposed approach. Moreover, the proposed approach is validated by a hybrid dual-infeed HVDC system. In particular, an unexpected phenomenon is observed that the CF characteristic of the LCC-HVDC link is somewhat deteriorated, due to the incorporation of the VSC-HVDC link when the VSC-HVDC link feeds into the alternating current system with both active and reactive power transferred in relatively high levels close to their limits.

Efficient Computation of Feedback-Based Control System Equations for Electromagnetic Transients

This paper contributes to the accurate and efficient computation of control system equations in electromagnetic-transient simulation tools. The proposed approach is based on the formulation of a reduced rank Jacobian matrix in a fully iterative Newton method. In addition, this paper compares the accuracy and efficiency for the proposed method's variants, including a hybrid approach with a fixed-point solution.

Modeling and Simulation about Long Term Dynamics Using Real Time Digital Simulator

RTDS (Real Time Digital Simulator) has several benefits. First, current power system simulation tool dose not simulate electromagnetic transient phenomenon, but it is possible using RTDS. Second, off-line electromagnetic transient simulation tools (EMTDC, PS-CAD, etc.) do not simulate real-time analysis, but RTDS is able to do real-time analysis. Third, RTDS is able to simulate related external devices those are protection relays, new developed control devices and power system devices. So many engineers use RTDS in power industry using these advantages of RTDS. KEPCO (Korea Electric Power Corporation) also use RTDS for developing new special protection scheme that is a new developed protection scheme for maintaining voltage stability in metropolitan area using real time synchro phasor data. Voltage stability phenomena of power system are divided three parts by time period. Those are transient, short term and long term voltage stability phenomena. Almost critical voltage stability problems happen in long term time period. Because power system devices and loads those influence voltage stability have long term dynamic characteristic. So if we want correct results of voltage stability analysis, then we have to analyze long term dynamic about voltage stability. Long term dynamic characteristic of voltage stability that is influenced by under voltage tap changer, over excite limiter, dynamic loads and so on. Unfortunately, we had not an analysis environment about long term dynamics for validating new control system. So this paper discusses about modeling and simulation of long term dynamics using RTDS. First, we build well known test system that consists of 2 generators and 11 buses using RTDS. Second, we model dynamic controllers and devices those are under load tap changer, over exciting limiter and dynamic load and we validate those dynamic characteristics. Those influence to long term voltage stability. Lastly, we simulate voltage collapse phenomena during long term time period using test-system include built long term dynamic models when occurring line fault.