Possibilities of Conventional PD Measurements with Non-Sinusoidal Waveforms for Electric Vehicles

Electrical traction machines in electric vehicles are normally fed by converters with DC link voltages up to 800 V. The resulting voltage pulses place particular stress on the insulating system of the drivetrain. In order to be able to investigate insulating material samples, e.g. twisted pair enameled wire, with voltages of different shapes and high frequency, a shielded experimental setup for the investigation of partial discharges (PD) at low voltages and high frequencies is presented. A medium frequency transformer with a frequency range up to 2500 Hz is used for this purpose, fed by a linear power amplifier on the primary side. The amplifier has a slew rate of 52 V/μs and is capable of sourcing various voltage waveforms such as sinusiodal, triangular or rectangular, with a maximum frequency of 30 kHz. Electrical PD measuring methods according to IEC 60270 as well as acoustic and optical measurement methods are applied for PD diagnosis. The experimental setup is intended to demonstrate the possibilities and limitations of conventional PD diagnostics for nonsinusoidal voltages. Focus is placed on the application of filters, the damping behavior of the step-up transformer and the rise times of the voltages

Emulation of grid-forming inverters using real-time PC and 4-quadrant voltage amplifier = Emulation netzbildender Wechselrichter mittels Echtzeit-PC und 4-Quadranten-Spannungsverstärker

Vorgestellt wird ein Versuchsstand zur Evaluierung neuartiger Regelungsverfahren für Wechselrichter zur regenerativen Stromerzeugung. Das Verhalten von netzgeführter und netzbildender Regelung wird in einem Testszenario untersucht und verglichen. Unter Verwendung einer echtzeitfähigen Regelungsplattform mit einer Zykluszeit von 50 μs können mit Matlab/Simulink entwickelte Regelungsverfahren implementiert werden. Der Einfachheit halber wird anstelle eines Wechselrichters ein dreiphasiger 4-Quadranten-Spannungsverstärker verwendet. Somit kann auf den Einsatz von Modulation und geschalteten Leistungshalbleitern verzichtet werden. Um ein realistisches Verhalten eines netzseitigen Filters zu zeigen, können passive Komponenten automatisiert als L-, LC- oder LCL-Filter zugeschaltet werden. Der Versuchsstand hat eine Nennwirkleistung von 43,6 kW und eine Nennspannung von 400 V. Als modernes netzfolgendes Regelverfahren ist im Versuchsstand eine Stromregelung im d/q-System implementiert. Als netzbildendes Regelverfahren wird eine virtuelle Synchronmaschine, der Synchronverter, eingesetzt. In Kombination mit einer frequenzvariablen Netznachbildung wird das Verhalten beider Regelverfahren im Falle einer Lastzuschaltung in einer Inselnetzumgebung untersucht

Partial discharge diagnostics on inverter-fed drives of electric vehicles = Teilentladungsdiagnostik an umrichtergespeisten Antrieben der Elektromobilität

In this paper, the possibilities of partial discharge measurement at square-wave voltages are discussed. The focus is on low-voltage machines, such as those used in electric vehicles. An insight into common measurement methods is given. In this work, high-frequency current transformers and near-field probes are used as sensors. The generation of a realistic steep-edged test voltage according to IEC/TS 61934 is also discussed and demonstrated on an inverter with silicon carbide semiconductors. Experiments are conducted to compare the sensors used. A direct comparison between cable-based sensors (HFCT) and antennas (near-field probes) is provided. Resonance points to open motor windings according to IEC/TS 60034-27‑5 and their significance for partial discharge measurement are also investigated. The results show that the high-frequency current transformers and the ball probe are able to detect PD even at steep voltage edges. Excitation with a fast voltage edge results in non-negligible overshoots in the overall system due to resonances. It can be shown that the partial discharges occur during these overvoltages

Fault discrimination and protection coordination for a bipolar full-bridge MMC-HVDC scheme

Fault discrimination and protection design for bipolar high-voltage direct current transmission solutions based on modular multilevel converters (MMC-HVDC) links are of significant importance for a reliable and resilient power transmission. If full-bridge submodules are utilised, fault-dependent handling concepts considering the location of an event are enabled. This study presents a comprehensive approach to differentiate and deal with internal converter and dc side faults. While a multitude of measurements inside and at the clamps of each converter is usually only used for simple threshold-based hardware-related protection, additional differential and derivative criteria may further improve selectivity. However, this requires careful configuration to avoid improper reactions. To highlight the coordinated manner of the proposed concept, various faults are analysed and selected examples are explicitly investigated and visualised using the PSCAD EMTDC software

Machine-learning-based Bayesian state estimation in electrical energy systems

In many algorithmic applications in electrical power grids, state estimation (SE) represents the first step of a process chain. In SE, sensor measurements are processed to infer the most probable grid state. Classical methods such as weighted least squares (WLSs) based approaches use statistical methods that can be based on sensor noise and erroneous measurements. With these methods, only point estimates are made, which results in a lack of knowledge about prediction uncertainties. In this study, machine-learning-based methods for determining the actual state of the grid are proposed. Bayesian optimisation is applied to find the optimal hyperparameter configurations for neural networks (NNs) for SE tasks. The application of Bayesian inference using Bayesian NNs is proposed, which allows the prediction of point estimates as well as uncertainty intervals for the system states. The advantages of using Bayesian approaches in comparison to classical SE methods like WLS are shown

An Optimal Power Flow Algorithm for the Simulation of Energy Storage Systems in Unbalanced Three-Phase Distribution Grids

An optimal power flow algorithm for unbalanced three-phase distribution grids is pre-sented in this paper as a new tool for grid planning on low voltage level. As additional equipmentlike electric vehicles, heat pumps or solar power systems can sometimes cause unbalanced powerflows, existing algorithms have to be adapted. In comparison to algorithms considering balancedpower flows, the presented algorithm uses a complete model of a three-phase four-wire low voltagegrid. Additionally, a constraint for the voltage unbalance in the grid is introduced. The algorithm canbe used to optimize the operation of energy storage systems in unbalanced systems. The used gridmodel, constraints, objective function and solver are explained in detail. A validation of the algorithmusing a commercial tool is done. Additionally, three exemplary optimizations are performed to showpossible applications for this tool

Time-Dependent Flexibility Potential of Heat Pump Systems for Smart Energy System Operation

The integration of multiple energy sectors, such as electricity, heating, and mobility, into an overall smart energy system is a key part of the journey towards a fossil-free energy system. Exploiting the operational flexibility of these sectors will lead to the efficient operation of the integrated smart energy system. The use of heat pumps for the heating supply based on renewable energy resources is reasonable in many cases. Combining heat pumps with thermal storages, these systems can offer flexibility to an energy system based on fluctuating power generation. Flexibility can be defined as the capability to adapt an initial schedule in order to support the energy system in terms of the provision of power reserve. In this paper, an approach to determine the time-dependent flexibility potential of a heat pump system is presented. The optimization-based approach considers all the constraints resulting from the system topology, including the required heating demand of the connected building. As a result, constraints for the integration of the available flexibility in a modified Optimal Power Flow (OPF) calculation are given. These lead to the ensured feasibility of the flexibility provision without considering the system boundaries of the heat pump site within the OPF

Operation of Battery Storage as a Temporary Equipment During Grid Reinforcement Caused by Electric Vehicles

Electric vehicle charging stresses distribution grids significantly with high penetrations of electric vehicles. This will lead to grid reinforcement works in several distribution grids. Battery storage is a possible solution to bypass times of grid reinforcement due to electric vehicle charging. In this paper, different operation strategies for such a battery storage are tested at first in simulations. The main difference between the strategies is the necessary input data. Following the simulations, selected strategies are tested in reality in the project ”Netzlabor E-Mobility-Allee”. It is proved that battery storage is a functioning possibility to bypass times of grid reinforcement