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Parallel inverters are commonly adopted in high power applications, for instance wind energy system, smart transformer, and power conditioners. Meanwhile, interleaved PWM is usually considered as an optimal approach to reduce the current ripple and harmonics of the parallel inverters. However, in case of a common dc-link, the problem of circulating current emerges and leads to performance degradation...
The massive integration of decentralized energy resources (DERs) poses a big challenge on the grid management. The resulting problems often require advanced power electronics based solutions like active filters or STATCOMs or even more futuristic system level solutions like smart transformers. The interaction of all the mentioned systems through grid connected converters originate stability problems...
In this paper the design and measurement results of a grid analysis and grid impedance measurement system are presented. The system is provided to measüre the freqüency dependent grid impedance in different PoCs to detect resonances and improve the power quality especially of grids with high amount of DERs. Moreover Active Filtering (AF) and reactive power feed-in are possible. It comprises also measurement...
The most stressful operation point for the inverter of an electric vehicle drive is at low speed. In this operation point, one power semiconductor is mainly stressed because of a high loss concentration. The possibilities of distributing the losses among the power semiconductors through a new modulation is studied for the three-level NPC and the T-Type inverter. The effect of the proposed modulation...
Due to an increasing number of distributed energy generation systems connected to low voltage grids, further investigations are required to ensure high power quality and power system stability. One important power system parameter is the frequency depending grid impedance at the points of connection referred to as grid impedance. This impedance considerably affects power quality and system stability...
More and more energy is fed especially by decentralized converters from renewable energy sources into the grid. Therefore, it is important to know the grid behavior at a wide frequency range from the fundamental frequency up to the kHz-range. This paper presents an advanced impedance medium-voltage measurement system with a high frequency range for an electrical medium-voltage grid. A sinusoidal current...
Development and research for power converters is focused on high power density, high modularity, low costs as well as high reliability and efficiency. The use of multilevel converters, like Neutral Point Clamped (NPC) Converters, in high power applications in the range of 1.5 MW up to 6MW can be favorable because of the filter size reduction and therefore reduction of weight and total volume of the...
Digital current control of three-phase voltage-source power electronic converters is analyzed. Special attention is paid to the exact discrete time-domain modeling of inductive-resistive current dynamics in the rotating reference frame whereas three different regular sampling strategies are incorporated to the analysis. The exact system model motivates the development of a new current control structure...
Power semiconductor losses of hysteresis current controlled grid connected 2-level and 3-level ANPC inverters will be presented in this paper. A special focus will be on the calculations for currents consisting of two components, one current with the frequency of the grid and one with a harmonic frequency. These currents are typical for inverters in grid impedance measurement and inverters with active...
The system resonance frequency of a grid connected inverter with LCL filter depends on the filter parameters and the time varying grid impedance. To obtain stability and to preserve good dynamic behavior of the system, grid impedance adaptation of the current controller is proposed. The design of the current controller is described and the adaptation strategy to prevent the excitation of the system...
In this contribution the concept of a multi-tap transformer topology for SS-compensated Inductive Power Transfer (IPT) systems is proposed. The objective is an improvement in terms of overall efficiency and maximum tolerable misalignment of the secondary transformer coil that is assumed to be mounted underneath an electric vehicle (EV). In a first step mathematical expressions are derived to describe...
This paper presents a method for the calculation of the power semiconductor rating based on data sheet parameters of the three-level Neutral-Point-Clamped (NPC) inverter. Beside the basic equations for calculating the turn-on and turn-off losses for Insulated Gate Bipolar Transistors (IGBT) and diodes, the electrical inverter topology, the different current paths for the commutations and the critical...
A neutral point (NP) balancing modulation for a three-level inverter with cosϕ > 0.9 is presented. In the low modulation range, standard space vector modulation (SVM) is applied using the redundancy of the small space vectors (SV) for the NP balancing. In the high modulation range, the switching sequence is adapted so that the neutral-point voltage can be also balanced. The proposed method is compared...
A comparison of the two-level voltage-source inverter, the three-level Neutral-Point-Clamped inverter and the T-Type inverter based on the power semiconductor rating is presented for drive inverters of electric vehicles. The comparison of the power semiconductor design rating is done for four different drive train configurations: normal operation with a constant DC-link voltage, an overload capability,...
Knowledge of the frequency depending grid impedance is necessary for adequate grid integration, including setting of standards, of renewable energy sources. It is also essential for the design of power converters for renewable energy sources. In this paper wide frequency range measurements of the positive sequence grid impedance in public low voltage grids with high proportion of renewable energy...
In this contribution the optimal power electronics topology in SS-compensated IPT systems for Electric Vehicles (EVs) is investigated in terms of required rated semiconductor power and efficiency. The novelty of this paper is the focus on high power (> 1 kW) and low output voltage (<100 V) applications. It is shown that the required semiconductor power which can be assumed to be proportional...
Due to the changing structure of the electric power system, stability analysis in the distribution grid are increasingly important. In this paper an impedance based method to determine the stability and the robustness of a grid connected converter under various grid conditions is presented. Therefore, the inverter output impedance is modeled in a modular way based on state space systems. Additionally,...
The measurement of the grid impedance is important for filter and control design, for active filter functionality of grid connected inverters and also for distribution network operators. It supports knowledge of the grid and design of decentralized energy generator power flow. Not only the impedance at fundamental frequency but also the impedance at harmonic and interharmonic frequencies is of common...
Small wind turbines are used for local energy production or in island networks. They are usually installed at places, where the wind speed is relatively low and considerable fluctuation occurs, resulting in a challenge to offer a high energy production especially at low and gusty wind speeds. For these conditions an optimal drive train has to be selected. In this paper the focus is on typical rectifier...
The 3-level NPC is investigated for the application in electric vehicles for inverter operation. Two different optimisation approaches for the NPC will be investigated to increase the efficiency. For the first method, the DC link input voltage is controlled variable, fed by a DC/DC converter. The effect of the varied DC link voltage on the loss distribution and on the efficiency is presented. Secondly,...
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