Matthias Luther

Dynamic Study Model for the interconnected power system of Continental Europe in different simulation tools

This paper describes the development process of the Dynamic Study Model (DSM) for the synchronously interconnected power system of Continental Europe in different simulation tools1. The model was developed by the European Network of Transmission System Operators for Electricity (ENTSO-E) working group System Protection and Dynamics2 and the University of Erlangen-Nuremberg within a collaboration. The paper describes the DSM scope, input and necessary steps towards an adequate basis for the novel dynamic data enhancement process by means of standard dynamic models for generation units and allocation criteria. Through a parameter variation process the DSM has been successively tuned to match a frequency measurement of a system event with respect to system inertia, frequency containment reserve and one of the typical oscillation modes within Continental Europe. Finally, the DSM behavior has been verified by means of previous experience from operation.

Generic modeling of a line commutated HVDC system for power system stability studies

This paper will reveal a novel comprehensive approach for generic modeling and control design of line commutated HVDC systems. The model will be developed based on the essential HVDC equations and transfer functions. Due to comparing the generic model with an EMT (Electro-Magnetic Transient) HVDC model the consistence of the dynamic behavior will be shown. Furthermore modeling of additional HVDC system facilities like transformer tap-changers and AC filters will be annotated. Control design schemes for line commutated HVDC systems will be derived and the interactions of the controllers applied to the developed model will be investigated.

Generic modeling of a self-commutated multilevel VSC HVDC system for power system stability studies

This paper provides a generic stability model of a self-commutated multilevel VSC (Voltage Source Converter) HVDC (High Voltage Direct Current) and its appropriate control. At first the approach of modeling depicts the independence of the AC and DC quantities and therefore two separate models - one for the AC and one for the DC side - can be figured out. The AC side model is developed in the dq frame out of the according differential equations. For the DC side no further transformation is required. Regarding the fact of balanced energy terms the two models can be merged. The consolidation of both models reveals a comprehensive large signal model of a multilevel based HVDC system which can be used for detailed analyses in power system stability studies. Due to the comparison of the generic stability model with an EMT (Electro-Magnetic Transient) HVDC model the consistence of the dynamic behavior is shown.

Disturbance localization in power systems using wide area measurement systems

There are different innovative concepts to localize disturbances with an electromechanical impact in power systems using synchronized frequency measurements from Wide Area Measurement Systems. This paper investigates five approaches, of which four are mainly discussed and one is novel: Gradient Search, Triangulation, Parzen Windows, Probability Circles and Time Distance Ratios. The similarities and differences of the methods are described and analyzed within a case study using publicly available frequency measurements and a dynamic study model. The cases are selected with the aim to point out the limits of the methods and to derive recommendations for improvements to be further developed. The study explicitly shows the challenges of the application and provides suggestions how to meet them.

An innovative method to develop power system equivalents with focus on inter-area oscillations and primary control representation

An innovative method to develop power system equivalents is presented in this paper. The purpose is the representation of system inertia, inter-area oscillations and primary control of large interconnected power systems by means of publicly available information. The approach to reach this target is based on a systematically developed load-flow model and the representation of system dynamics by means of standard dynamic models for generation units, their appropriate control and loads. The initial parameters of the standard dynamic models are tuned with regard to frequency measurements and published power system characteristics. The developed method allows general analysis of extensive influences on the dynamic behavior of a particular power system. Conceivable applications of the developed method are proposed for further system analysis. Finally an employment of the method is shown for the Continental Europe synchronous area (CESA).

A novel approach for analytical modeling of line commutated converter based HVDC systems for electromagnetic transient analysis

A novel approach is used to derive a completely analytical model of a six pulse line commutated converter based HVDC system. The system is split into two subsystems and is then solved individually. Therefore each period of a subsystem is divided into six intervals. Hence it is only necessary to solve one period analytically for the state of commutation as well as for the state of two-valve conduction. All other solutions are then deduced from the original solution with a simple rotation. Afterwards the subsystems are connected and the dependencies of each other are taken into consideration. The space vector transformation is used to split the system into independent subsystems (two for the state of commutation and one for the state of two-valve conduction), which allows to obtain a closed form solution. Accuracy of the model is approved by comparison with electromagnetic transient models.

A novel dynamic model for Multiterminal HVDC systems based on self-commutated full- and half-bridge Multilevel Voltage Sourced Converters

This paper discusses a novel model for stability studies of a Multiterminal High Voltage Direct Current system (MT HVDC) as part of an overlay grid in a hybrid AC system. The dynamic model is set up for Multilevel Voltage Sourced Converter (VSC) technology. The new model provides the opportunity to analyse the impact of full- and half-bridge modules during AC and DC faults. In the present paper a radial DC system with four converter stations was built up and simulated in PSS®NETOMAC. In principle the model can be expanded to a multiterminal HVDC system with a higher number of converter stations. Generally the structure of the DC grid does not subject to any restrictions. For steady state control of a MT HVDC system the Voltage Margin Method (VMM) was implemented. The main focus of the presented model is placed on dynamic stability studies in case of DC faults and their effects on the AC grid. But due to the possibility of VSC converters to provide general system services, e.g. to supply reactive power, the effects and advantages of VSC converters during AC faults can also be analysed. In principle Insulated Gate Bipolar Transistor (IGBT) technology offers the possibility of clearing DC faults on the DC side. Depending on the type of modules (full- or half-bridge modules) used in a Multilevel VSC converter the fault clearing strategy and therefore the effects to the AC grid differ enormously. It is essential for the transient stability of a highly stressed AC grid to ensure a very low fault clearance time to keep the system stable. The proposed control design was designed as a two partition macro in PSS®NETOMAC and can be used for planning a Multiterminal DC system in any AC grid. It was applied to a small test grid in order to prove its performance. For more realistic results the model was implemented and applied in a dynamic model of the Continental Europe high voltage power transmission grid.

Analytical derivation of controller parameters for series connected LCC multiterminal HVDC systems through the use of a decoupling filter

This paper demonstrates the design process of a decoupled control for any series connected Line-Commutated Converter (LCC) Multiterminal (MT) High-Voltage Direct Current (HVDC) system. After the introduction of a modular average model, devoid of the typical current converter switching behavior, a structured mathematical description as a Multiple-Input-Multiple-Output-system (MIMO) is presented. This facilitates the calculation of a decoupling filter and enables the analytical derivation of Pi-controller parameters. For that purpose, an approach using Amplitude Optimum was chosen. Compared to a conventional control design, the sophisticated method clearly shows improvement of operational behavior and stability of an Electro-Magnetic-Transient (EMT) model.

Modeling and control design of hybrid - LCC and VSC based - HVDC systems

This paper reveals an approach for dynamic modeling and control design of hybrid High-Voltage Direct Current (HVDC) systems. In this case a hybrid system is supposed to be a connection of different converter topologies as Line Commutated (LCC) and Voltage Source Converters (VSC). Modeling will be based on the mathematical correlations of the respective topologies and therefore a model for each converter type is carried out. These models can be merged regarding the fact of balanced energy terms. A control strategy for the hybrid HVDC system is presented, where the LCC Converter controls the voltage of the DC link and the VSC Converter is in P/Q control mode and hence is responsible for DC current regulation. Due to the comparison of the generic stability model with an EMT (Electro-Magnetic Transient) HVDC model the consistence of the dynamic behavior is shown and a comprehensive large signal model of a hybrid HVDC system which can be used for power system stability studies is revealed.

Analysis of a disturbance localization method for incidents in continental Europe

To localize incidents such as generator trips or load shedding, which cause transients in power systems, a technique from seismology is used in this paper: triangulation by means of information from Phasor Measurement Units (PMU). The synchronized observation of frequency change arrival times, which represent an electromechanical disturbance propagation, allows to approximate the disturbance location and thereby to support a reliable power system operation. For the verification and further development of this method a post analysis of three incidents of last years in the Continental Europe synchronous area (CESA) power system is done using two different numerical methods to solve the set of triangulation equations. The calculated deviations of estimated to real locations show on the one hand a relative good approximation to the real incident locations, but also a high dependency on the assumed electromechanical disturbance propagation speed and the chosen parameters of signal processing. Nevertheless, the method seems to be promising for future applications and is worth to be further developed.