Felix Lehfuss

Power hardware in the loop simulation with feedback current filtering for electric systems

Power Hardware-in-the-Loop (PHIL) simulations are suited for electric component tests and electric tests of hardware interacting with complex systems that are simulated. PHIL simulations combine the advantages of a pure software simulation and a hardware system test. At the present time, PHIL simulations unfortunately are not “plug and play”, some important considerations have to be made before a PHIL experiment can be is carried out in a laboratory. This contribution focuses on an improvement on how the hardware part of a PHIL simulation is coupled with the real time computing system by introducing an additional current filter in the feedback path. The filter drastically improves the stability margin of the simulation setup. This method is applied to a use case involving a photovoltaic inverter connected to a low voltage grid with a linear and a nonlinear load. The low voltage grid and the loads are simulated and the photovoltaic inverter connected as real hardware to the simulation environment. The PHIL simulation would not run stably without the introduced feedback filter. With feedback current filtering the PHIL experiment can be stabilized and an insight in the interaction of the nonlinear load and the photovoltaic inverter can be gained. The feedback filter has to be parameterized appropriately; it is a compromise between stability margin and accuracy of the PHIL setup.

Comparison of multiple power amplification types for power Hardware-in-the-Loop applications

This Paper discusses Power Hardware-in-the-Loop simulations from an important point of view: an intrinsic and integral part of PHIL simulation - the power amplification. In various publications PHIL is discussed either in a very theoretical approach or it is briefly featured as the used method. In neither of these publication types the impact of the power amplification to the total PHIL simulation is discussed deeply. This paper extends this discussion into the comparison of three different power amplification units and their usability for PHIL simulations. Finally in the conclusion it is discussed which type of power amplification is best for which type of PHIL experiment.

Online Reconfigurable Control Software for IEDs

The future energy system has to satisfy a continuously growing demand for electricity and to reduce greenhouse gas emissions. Fulfilling such diverse needs requires the integration of renewable energy resources on a large scale. However, the existing information and communication infrastructure controlling the corresponding power grids and components is not directly designed to master the ever increasing complexity. An upcoming requirement is the need for the functional adaption of the control systems during operation. The main aim of this article is to discuss and analyze requirements as well as to introduce a standard-compliant concept for a reconfigurable software architecture used in intelligent electronic devices for distributed and renewable energy resources. A simulation case study shows the applicability of this approach. A secure adaptation of the functional structure and the corresponding algorithms in device controllers can substantially contribute to a more efficient energy system, while at the same time responding to future needs.

The Limitations of Digital Simulation and the Advantages of PHIL Testing in Studying Distributed Generation Provision of Ancillary Services

There is increasing interest in the evaluation of the capability of power-electronic-interfaced distributed generators (DGs) connected to weak medium-voltage (MV) feeders, to provide ancillary services. Classic simulations using simplified DG models have their limitations and may prove insufficient due to the complexity of adequate modeling of power electronic interfaces. Moreover, conventional testing does not allow the investigation of the real generator with the distribution system interactions. Therefore, a scaled-down physical DG (i.e., inverter and dc source) with exactly the same functionalities can be used to evaluate the network integration of the actual DG, by means of power hardware-in-the-loop (PHIL) testing. In this paper, suitable scaling of the power rating and voltage level of the hardware is performed, and an interfacing approach is proposed that achieves stability of simulations without compromising accuracy. The PHIL tests successfully demonstrate potential problems in the coordination of the on-load tap changer controlling the MV feeder with the voltage controller of the DG, such as recurring tap changes, increased reactive power flows, and opposing actions. Moreover, recurring oscillations of the voltage controller of the hardware model are observed at certain system configurations. These inverter control instabilities, which are not visible in purely digital simulations, demonstrate the added value of employing PHIL testing for current and future power system analysis and testing.

Power hardware-in-the-loop implementation and verification of a real time capable battery model

For this contribution a generic and real time capable battery model was implemented within a dedicated Power Hardware-in-the-Loop (PHIL) simulation environment. This was done in order to investigate its implementability and accuracy for PHIL simulations. PHIL simulations offers major benefits to battery inverter tests as reproducibility increases and the preparation time can be reduced significantly. Following a discussion of real time capable battery models, the implemented model is validated with measurement data of a real battery. Finally a PHIL simulation of a battery model is carried out and its applicability is shown.

Implementation of a multi-rating interface for Power-Hardware-in-the-Loop simulations

The Power-Hardware-in-the-Loop simulation approach constitutes a complicated integration of a classical, physical system/device test (hardware) in combination with a pure computer simulation (software). This paper presents a new interface topology that takes advantage of modern real-time system capabilities in order to increase stability and accuracy. Basic requirements are stated in a powerful real-time computing system, in a suitable power amplification stage, as well as in an adequate measurement system. In general, the performance of the used devices in the simulation setup is of crucial importance for the quality of simulation results and conclusions based on the executed tests. Furthermore, a first implementation of the proposed new interface topology is discussed. Actual areas of applications for this work can be found in the industrial research and development area as well as for the research of electric energy systems and electric drives and in modern power electronics.

Selection and implementation of a generic battery model for PHIL applications

For this contribution different generic battery models were implemented in a dedicated simulation environment to investigate their usability for Power Hardware-in-the-loop implementations. Following a discussion of various requirements on these models, their validity is determined by comparison with a measured battery test. The applicability of the models to Power Hardware-in-the-loop applications is evaluated on the basis of its execution time and its deviation of the model from the real battery to achieve values representative of embedding the model in a larger simulation.

Simulation-based validation of smart grids - status quo and future research trends

Smart grid systems are characterized by high complexity due to interactions between a traditional passive network and active power electronic components, coupled using communication links. Additionally, automation and information technology plays an important role in order to operate and optimize such cyber-physical energy systems with a high(er) penetration of fluctuating renewable generation and controllable loads. As a result of these developments the validation on the system level becomes much more important during the whole engineering and deployment process, today. In earlier development stages and for larger system configurations laboratory-based testing is not always an option. Due to recent developments, simulation-based approaches are now an appropriate tool to support the development, implementation, and roll-out of smart grid solutions. This paper discusses the current state of simulation-based approaches and outlines the necessary future research and development directions in the domain of power and energy systems.

Examination of LV grid phenomena by means of PHIL testing

This work is giving an approach of comparison between different commonly used methods to evaluate investigations of generation units in electrical grids. State-of-the-art simulation tools are utilized for pure numerical simulation, while physical laboratory tests are conducted as a data reference and validation. Introducing the established Power Hardware in the Loop (PHIL) method, all results are compared one to each other. This composite simulation technique (PHIL) features advantages in terms of setup and simulation flexibility, while its overall validation is up for discussions. This validation is heavily dependent on the quality of the used equipment conjoined with the chosen experiment of interest. Profound know-how in the field of control technique, system theory and measuring method is necessary to obtain clean, useful results out of a valid PHIL simulation. While every method has its advantages in use, time, costs and applicability, it is of importance to know when to use which domain (software or hardware) in order to get the intended answers to arising questions. As a validating case study, a low voltage grid with different grid impedances and two small scale generators connected to two different nodes each is simulated. Thereby, the reactive power control is under examination and the results of the different methods are compared one to each other.

Verbesserung der Genauigkeit und Stabilitatseigenschaften von Power Hardware-in-the-Loop-Simulationen mittels einer Dual-Rate-Schnittstelle

SummaryPower Hardware-in-the Loop Simulation (PHIL) constitutes a complex integration of a classical, physical system test (hardware) in combination with a pure computer simulation (software). This article presents methods to reach applicable characteristics of stability and deals with the closely linked issue of the reachable system accuracy under these given circumstances. Basic requirements are stated in a powerful real time computing system, in a suitable power amplification stage, as well as in an adequate measurement system, whereas the performance of the used devices is of crucial importance for the quality of given conclusions based on PHIL simulations. Current areas of applications can be found in the industrial R&D sector or in the state-of-the-art fields of research of electric energy systems and electric drives as well as in advanced power electronics.ZusammenfassungDie Power Hardware-in-the-Loop-Simulation (PHIL) stellt eine komplexe Integration eines klassischen, physikalischen Systemtests (Hardware) mit einer reinen Simulation (Software) dar. Dieser Beitrag stellt u. a. eine Methode vor, gute Stabilitätseigenschaften einer PHIL-Simulation zu erzielen, und befasst sich mit dem damit gekoppelten Problem der erzielbaren Systemgenauigkeit. Die Basisvoraussetzungen hierfür sind durch ein leistungsfähiges Echtzeitsimulationssystem, einen geeigneten Leistungsverstärker (Linearität und hohe Bandbreite) sowie ein hinreichendes Messsystem definiert, wobei die Güte der verwendeten Geräte bezogen auf die Dynamik eine entscheidende Rolle spielt, um sinnvolle Aussagen mittels PHIL-Simulationen machen zu können. Aktuelle Einsatzgebiete finden sich beispielsweise im industriellen F&E-Bereich, in der modernen elektrischen Energie- und Antriebstechnik und im Bereich der Leistungselektronik.