Georg Lauss

Stabilization of Power Hardware-in-the-Loop simulations of electric energy systems

Abstract Power Hardware-in-the-Loop – as a particular simulation technology that includes real hardware with high power rating in the simulation loop – is used more and more in the scientific field. Power Hardware-in-the-Loop simulations may suffer – depending on the attached power hardware and the simulated subsystem – from the drawback of becoming unstable without appropriate countermeasures. This contribution introduces and compares three methods to guarantee stability under unfavorable stability conditions. The three methods behave differently as far as accuracy is concerned. Multi-Rate Partitioning is introduced as a good compromise between effort and performance.

Real-Time Simulation Technologies for Power Systems Design, Testing, and Analysis

This task force paper summarizes the state-of-the-art real-time digital simulation concepts and technologies that are used for the analysis, design, and testing of the electric power system and its apparatus. This paper highlights the main building blocks of the real-time simulator, i.e., hardware, software, input-output systems, modeling, and solution techniques, interfacing capabilities to external hardware and various applications. It covers the most commonly used real-time digital simulators in both industry and academia. A comprehensive list of the real-time simulators is provided in a tabular review. The objective of this paper is to summarize salient features of various real-time simulators, so that the reader can benefit from understanding the relevant technologies and their applications, which will be presented in a separate paper.

Characteristics and Design of Power Hardware-in-the-Loop Simulations for Electrical Power Systems

This paper presents a compendious summary of power hardware-in-the-loop (PHIL) simulations that are used for designing, analyzing, and testing of electrical power system components. PHIL simulations are an advanced application of real-time simulations that represent novel methods, which conjoin software and hardware testing. This contribution outlines necessary requirements for the implementation of PHIL simulations, which are defined by the nature of the digital real-time simulator, the power amplifier, and the power interface (PI). Fundamental characteristics, such as the input/output systems, PI, interface algorithm, and system stability considerations, are discussed for PHIL setups, in order to illustrate both flexibility and complexity of this compound simulation method. The objective of this work is to elaborate an understandable overview of PHIL simulation for electrical power systems and to constitute a contemporary state-of-the-art status of this research area.

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.

Applications of Real-Time Simulation Technologies in Power and Energy Systems

Real-time (RT) simulation is a highly reliable simulation method that is mostly based on electromagnetic transient simulation of complex systems comprising many domains. It is increasingly used in power and energy systems for both academic research and industrial applications. Due to the evolution of the computing power of RT simulators in recent years, new classes of applications and expanded fields of practice could now be addressed with RT simulation. This increase in computation power implies that models can be built more accurately and the whole simulation system gets closer to reality. This Task Force paper summarizes various applications of digital RT simulation technologies in the design, analysis, and testing of power and energy systems.

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.

Lab Tests: Verifying That Smart Grid Power Converters Are Truly Smart

During the last few years, many countries around the world have seen a massive deployment of distributed energy resources (DERs) in their distribution systems. In certain regions, penetration has reached levels that increasingly challenge traditional power system management, affecting the overall stability, reliability, and efficiency of grids. The uncoordinated response of large numbers of DERs may even put overall grid security at risk. This fact was clearly highlighted by the famous 50.2 Hz problem in Europe: it was discovered that the simultaneous tripping of several gigawatts of DERs due to a minor overfrequency event could potentially lead to an undersupply in the European power system so large that it could not be compensated for by using conventional reserve capacities.

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.