A High Current, High Frequency Modular Multiphase Multilevel Converter for Power Hardware-in-the-Loop Emulation

This paper presents a simple Modular Multiphase Multilevel Converter (MMPMC) especially for the usage in Power Hardware-in-the-Loop Emulation systems. Standard half-bridges connected to flux compensated chokes are used to build up an inductive voltage divider to form the multilevel voltage waveform. A modulator with a sorting algorithm is employed to calculate the switching signals of the particular branches. The selection of the switching states is depending on the instantaneous branch currents to ensure a symmetrical distribution of the load current to the branches. A modular and scalable converter system has been engineered, which allows the generation of a six level voltage waveform with a PWM-frequency up to 100 kHz. The prototype is controlled by a specifically designed high-performance signal processing system and offers an output current of more than 100 A. Measurements were performed to evaluate the proper functionality of the converter

Investigation and validation of methods to implement a two-quadrant battery emulator for power Hardware-in-the-Loop Simulation

When new hardware is developed, it is often convenient to test the prototype in a Hardware-in-the-Loop Simulation (HILS). In this technique, the critical parts of the system including the hardware-under-test (HUT) are physically present while the rest of the system is emulated in real time. In this paper, a battery emulator (BE) is implemented to replicate the behaviour of a battery pack in a HILS experiment. For this purpose, a remotely controlled DC power supply is used, combined with external passive elements to allow two-quadrant operation. The emulation fidelity is validated through experimental comparison with a real battery pack under constant and pulsed current loads. These experiments show the importance of the impedance connecting the BE to the HUT and how a poor selection can cause oscillations that would not exist in an experiment with a real battery pack.</p

European White Book on Real-Time Power Hardware in the Loop Testing : DERlab Report No. R- 005.0

The European White Book on Real-Time-Powerhardware-in-the-Loop testing is intended to serve as a reference document on the future of testing of electrical power equipment, with specifi c focus on the emerging hardware-in-the-loop activities and application thereof within testing facilities and procedures. It will provide an outlook of how this powerful tool can be utilised to support the development, testing and validation of specifi cally DER equipment. It aims to report on international experience gained thus far and provides case studies on developments and specifi c technical issues, such as the hardware/software interface. This white book compliments the already existing series of DERlab European white books, covering topics such as grid-inverters and grid-connected storag

A European Platform for Distributed Real Time Modelling & Simulation of Emerging Electricity Systems

This report presents the proposal for the constitution of a European platform consisting of the federation of real-time modelling and simulation facilities applied to the analysis of emerging electricity systems. Such a platform can be understood as a pan-European distributed laboratory aiming at making use of the best available relevant resources and knowledge for the sake of supporting industry and policy makers and conducting advanced scientific research. The report describes the need for such a platform, with reference to the current status of power systems; the state of the art of the relevant technologies; and the character and format that the platform might take. This integrated distributed laboratory will facilitate the modelling, testing and assessment of power systems beyond the capacities of each single entity, enabling remote access to software and equipment anywhere in the EU, by establishing a real-time interconnection to the available facilities and capabilities within the Member States. Such an infrastructure will support the remote testing of devices, enhance simulation capabilities for large multi-scale and multi-layer systems, while also achieving soft-sharing of expertise in a large knowledge-based virtual environment. Furthermore the platform should offer the possibility of keeping confidential all susceptible data/models/algorithms, enabling the participants to determine which specific data will be shared with other actors. This kind of simulation platform will benefit all actors that need to take decisions in the power system area. This includes national and local authorities, regulators, network operators and utilities, manufacturers, consumers/prosumers. The federation of labs is created through real-time remote access to high-performance computing, data infrastructure and hardware and software components (electrical, electronic, ICT) assured by the interconnection of different labs with a server-cloud architecture where the local computers or machines interact with other labs through dedicated VPN (Virtual Private Network) over the GEANT network (the pan-European research and education network that interconnects Europe’s National Research and Education Networks ). The local VPN servers bridge the local simulation platform at each site and the cloud ensuring the security of the data exchange while offering a better coordination of the communication and the multi-point connection. It is then possible the integration of the different sub-systems (distribution grid, transmission grid, generation, market, and consumer behaviour) with a holistic approach

Three-Phase Power Converter Based Real-Time Synchronous Generator Emulation

To bridge the gap between power system research and their real application in power grids, a Hardware Test-Bed (HTB) with modular three-phase power converters has been developed at the CURENT center, the University of Tennessee, Knoxville, to emulate transmission level power systems with actual power flowing. This dissertation focuses on the development and verification of a real-time synchronous generator (SG) emulator in the HTB. The research involved in this dissertation aims at designing a proper control to achieve emulator performance goal and investigating the sources of error and its influence on interconnected SG-emulator networks. First, different interface algorithms (IAs) are compared and the voltage type ideal transformer model (ITM) is selected considering the accuracy and stability. At the same time, closed-loop voltage control with current feed-forward is proposed to decrease the error caused by the non-ideality of the power amplifier. The emulation is then verified through two different ways. First, the output waveforms of the emulator in experiment are compared with the simulation under the same condition. Second, a transfer function perturbation (TFP) based error model is obtained and redefined as the relative error for the amplitude and phase between the emulated and the target system over the frequency range of interest. The major cause of the error is investigated through a quantitative analysis of the error with varying parameters. Third, the stability issue associated with the interconnection of two SG emulators is studied. The small signal models of the two-generation system with constant current and constant impedance load are developed, and the main reasons that cause instability are researched and verified. The developed SG emulator is also verified in the two-area system by comparing the system dynamics visually. At last, the 6th-order SG model including transformer voltages and saturation effect is applied in the three-phase symmetrical fault scenario. Control parameters are designed based on the TFP error evaluation of the fault condition. The developed SG emulator is then tested and verified in line-to-line fault condition. In addition, the stability of the new SG emulator is studied again and compared with the previous emulation

Verkkoimpedanssin mallinnus ja sähköinen emulointi vaihtosuuntaajien stabiiliustarkasteluun

The access to reliable and affordable energy is vital for a modern society. The climate change and increased consciousness of the environment has shifted the global energy production towards new, renewable alternatives. The rapid growth of renewable energy production increases the amount of grid-connected converters in the power system. However, the dynamics and grid requirements for converters are very different than for conventional rotating generators. The interface between the converter and grid is prone to stability issues. The stability can be assessed based on the ratio of the inverter output impedance and the grid impedance. However, the grid impedance is often an unknown parameter and modeled based on simplified assumptions. The most common model for the grid impedance is a series connected inductor and resistor. Grid impedance measurements have shown the grid impedance to have more complex, resonant and time-variant characteristics, which are neglected in the conventional modeling approach. This thesis presents grid impedance models, in which the complex nature of the grid impedance is accurately considered. The enhanced models are based on aggregation of grid elements into sub-models, where the resonant and time-variant behavior is clearly shown. In addition, this work introduces a power hardware-in-the-loop setup for testing a grid-connected inverter in various grid conditions. The derived grid models are applied in a real-time grid simulator, which in turn provides references for a linear amplifier operating as a grid emulator. Thus, a real inverter can be connected to a simulated grid conditions. The versatility and desired behavior of the setup are verified with grid impedance measurements from the grid emulator

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Department of Electrical EngineeringA resonant converter has been widely used in various industrial applications, since it has high power conversion efficiency. The increase of the power density is necessary to obtain high cost-effectiveness and design freedom on the electric products. A high switching frequency operation can be an effective method to obtain the high power density of power converters. In this dissertation, three topic will be discussed to obtain the high power conversion efficiency and the high power density for the resonant converter, as follows: First, the power stage and feedback loop are designed for the high switching frequency operation. The power stage is designed to obtain the high power conversion efficiency at the high switching frequency operation. In addition, the feedback loop is designed to guarantee the stability. Second, the control algorithm is proposed to obtain the tight output voltage regulation at the high switching frequency operation. The operational principle and design of control algorithm are analyzed to obtain the tight output voltage regulation. Third, the spread spectrum technique (SST) will be applied to the resonant converter to reduce the electromagnetic interference (EMI), which can improve the power density with small EMI filter size. In this research, the design constraint to implement the SST on the resonant converter is analyzed to obtain the dual functionality properly. In addition, the control algorithms are proposed to achieve tight output voltage regulation and EMI reduction, simultaneously. All the proposed design considerations and control algorithms are verified with the simulation and experimental results.clos