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The current increase of electric vehicles in Germany requires an adequately developed charging infrastructure. Large numbers of public and semi-public charging stations are necessary to ensure sufficient coverage. To make the installation worthwhile for the mostly private operators as well as public ones, a sufficient utilization is decisive. An essential factor for the degree of utilization is the placement of a charging station. Therefore, the initial site selection plays a critical role in the planning process. This paper proposes a charging station placement procedure based on real-world data on charging station utilization and places of common interest. In the first step, we correlate utilization rates of existing charging infrastructure with places of common interest such as restaurants, shops, bars and sports facilities. This allows us to estimate the untapped potential of unexploited areas across Germany in a second step. In the last step, we employ the resulting geographical extrapolation to derive two optimized expansion strategies based on the attractiveness of locations for electric vehicle charging. [ABSTRACT FROM AUTHOR]

We present a finite-element analysis of the temperature rise of switched reluctance motors (SRM) due to electromagnetic losses. We estimate the various components of electromagnetic losses, including core loss in the lamination as well as copper and eddy-current losses in windings, and then predict the temperature rise within the motor due to these losses. We present simulation results for an 8/6 SRM and discuss various aspects of thermal design of SRMs. To validate the procedure for the estimation of electromagnetic losses, we compare predicted and measured losses. Index Terms--Core loss, finite-element analysis, switched reluctance motor, thermal model.

Currently, gate commutated thyristors (GCTs) are commonly used for high-power voltage-source inverters due to their superior electrical performance as compared to gate-turn-off (GTO) thyristors and high-voltage insulated-gate bipolar transistors (HV-IGBTs). However, the gate driver of GCTs is more complex than an IGBT driver and has to be attached closely to the GCT, which implies several constructional disadvantages. The internally commutated thyristor (ICT), a GCT with integrated turn-off unit, enables the use of a simplified and more reliable gate driver, maintaining the electrical advantages of the GCT. In this paper, the ICT concept is discussed in relation to standard GCTs. Additionally, an optimized gate driver for the ICT is presented. Close attention is paid to improve reliability and easy adaption to different ICT current ratings. Index Terms--Gate drive unit, ICT, IGCT, power semiconductor device, reliability, short-circuit detection.

Electric Vehicles (EVs) are gaining acceptance due to the advantages they offer in the reduction of nitrogen oxide and carbon dioxide emissions. The need for emission reduction and the potential of EVs for these reductions is reflected in the current sustainable mobility policies of the EU as well as the German government. Increasing the penetration of EVs in the grid requires an expansion of EV charging infrastructure, which in turn requires either grid reinforcement or solutions for more efficient use of existing infrastructure to avoid or postpone grid reinforcement. Distribution transformers face increased loading due to EV charging and need to be protected from overloading during peak load periods to ensure continuity of service. Therefore, transformers are one of the components that are upgraded or replaced as a part of grid reinforcement. In this paper, we propose the connection of a Solid-State Transformers (SST) between two buses operating at the same-voltage level as an alternative to replacement or upgrading of conventional transformer as well as to prevent their overloading. We analyse how the proposed topology can be useful to reduce the impact of EV integration on the overloading of distribution transformers and node voltage violations in the distribution grid. [ABSTRACT FROM AUTHOR]

Most power quality problems in distribution systems are related to voltage sags. Therefore, different solutions have been examined to compensate these sags to avoid production losses at sensitive loads. Dynamic Voltage Restorers (DVRs) have been proposed to provide higher power quality. Currently, a system wide integration of DVRs is hampered because of their high cost, in particular, due to the expensive DC-link energy storage devices. The cost of these DC-link capacitors remains high because the DVR requires a minimum DC-link voltage to be able to operate and to compensate a sag. As a result, only a small fraction of the energy stored in the DC-link capacitor is used, which makes it impractical for DVRs to compensate relatively long voltage sags. Present control strategies are only able to minimize the distortions at the load or to allow a better utilization of the storage system by minimizing the needed voltage amplitude. To avoid this drawback, an optimized control strategy is presented in this paper, which is able to reduce the needed injection voltage of the DVR and concurrently to mitigate the transient distortions at the load side. In the following paper, a brief introduction of the basic DVR principle will be given. Next, three standard control strategies will be compared and an optimized control strategy is developed in this paper. Finally, experimental results using a medium-voltage 10-kV DVR setup will be shown to verify and prove the functionality of the presented control strategy in both symmetrical and asymmetrical voltage sag conditions. Index Terms--Asymmetrical voltage sag, dynamic voltage restorer (DVR), in-phase compensation, optimized compensation, pre-sag compensation.

This paper presents a control scheme that allows minimization of dc-link capacitance in switched reluctance drives (SRDs). In switched reluctance motors (SRMs), the demagnetization energy of the outgoing phase causes a voltage increase in the dc-link. Therefore, large dc-link capacitors are required in conventional drives to absorb this energy to avoid overvoltages. The proposed control scheme balances the power flow between phases in such a way that the demagnetization energy of the outgoing phase does not flow back into the dc-link but directly into the incoming phase. Using this scheme, electrolytic capacitors can be replaced by film or ceramic capacitors leading to higher power density, longer lifetime, and higher reliability. Index Terms--Capacitance minimization, control, dc-link capacitance, switched reluctance drives (SRDs).

The market of converters connected to transmission lines continues to require insulated gate bipolar transistors (IGBTs) with higher blocking voltages to reduce the number of IGBTs connected in series in high-voltage converters. To cope with these demands, semiconductor manufactures have developed several technologies. Nowadays, IGBTs up to 6.5-kV blocking voltage and IEGTs up to 4.5-kV blocking voltage are on the market. However, these IGBTs and injection-enhanced gate transistors (IEGTs) still have very high switching losses compared to low-voltage devices, leading to a realistic switching frequency of up to 1 kHz. To reduce switching losses in high-power applications, the auxiliary resonant commutated pole inverter (ARCPI) is a possible alternative. In this paper, switching losses and on-state voltages of NPT-IGBT (3.3 kV-1200 A), FS-IGBT (6.5 kV--600 A), SPT-IGBT (2.5 kV-1200 A, 3.3 kV-1200 A and 6.5 kV-600 A) and IEGT (3.3 kV-1200 A) are measured under hard-switching and zero-voltage switching (ZVS) conditions. The aim of this selection is to evaluate the impact of ZVS on various devices of the same voltage ranges. In addition, the difference in ZVS effects among the devices with various blocking voltage levels is evaluated. Index Terms--Auxiliary resonant commutated pole (ARCP), insulated gate bipolar transistors, soft-switching.

Recently, the interest in offshore wind farms has been increased significantly. Besides the huge amount of space available, they have the advantage of an increased and more constant wind speed, leading to a higher and more constant production of power. Although, a lot of mechanical problems for constructing these farms have been solved during the past decade, the electrification is still a major issue in research. For large wind farms situated more than 60 km from the shore, an HVdc connection is favorable. Consequently, a pure dc system could be an interesting and cost-effective solution for offshore wind farms. In this paper, a control structure for such a dc grid is presented and analyzed. Furthermore, different configurations are compared and the developed simulation models are presented. Index Terms--DC power systems, HVdc, power distribution, power systems, power transmission, wind, wind energy, wind power generation.

Due to the increasing importance of power electronic components in automobiles, it becomes necessary to consider their reliability. This applies especially to hybrid electrical vehicles (HEV) where a malfunction of the power electronics may prevent the vehicle to operate. Of paramount importance for the reliability of power electronics is the component operating temperature and temperature cycling. This paper deals with the development of an advanced simulation tool which is capable of determining the component temperature of a three-phase converter over long mission profiles. In addition, the expected converter reliability is calculated. To accomplish this, losses in the semiconductors and dc-link capacitors are determined first. Next, this loss data is fed into a thermal model to compute the component temperatures, for the whole mission profile. As basis for the reliability computation, failure-rate catalogs, such as Military Handbook 217F or RDF 2000, are used. Also an approach using simple formulas for lifetime prediction is presented. According to failure-rate catalogs, temperature cycles are of particular importance for the reliability of power semiconductors. A novel algorithm, detecting all relevant temperature cycles within the computed temperature curve is developed. Finally, the applicability and significance of the presented reliability prediction methods is assessed. Index Terms--Failure-rate catalogs, hybrid electrical vehicles (HEV), reliability, temperature cycles.

In modern high-power medium voltage drives, multilevel converters are increasingly used. Employing slight topological modifications, soft-switching technology can be applied to multilevel converters to reduce the switching losses. As a result, the switching frequency can be increased, thereby reducing the output filter size. However, common converter controls have to be modified. In this paper, a flexible control platform is presented that allows rapid prototyping of soft-switching topologies. An analysis of different auxiliary resonant commutated pole (ARCP) topologies shows that all switching commands can be synthesized with synchronized signals of two-level ARCP converters. Therefore, a flexible state-machine for two-level converters was developed first, which can also be used to build controls for multilevel topologies. It supports drivers with built-in intelligence as well as the control of additional switches that are required in some ARCP neutral-point-clamped (NPC) topologies. The switching commands for the state machines can be generated by standard multilevel modulation methods. Illegal switching states are filtered and multiple simultaneous commutations per phase are prevented for ARCP NPC converters. To verify the functionality, the control scheme was realized in a field programmable gate array and a completely modular test converter was developed. This test converter can be used to quickly implement all common multilevel topologies and test different modulation strategies. Experimental results are presented in this paper. Index Terms--Auxiliary resonant commutated pole (ARCP) topologies, diode-clamped-multilevel (DCML) inverter, field programmable gate array (FPGA), neutral-point-clamped (NPC) topologies, pulsewidth modulation (PWM) inverter.

The increasing usage of distributed power generation, leads to an increased short-circuit power in medium voltage grids. As a consequence, new concepts for limiting short-circuit currents are required. One possible solution is based on resonant circuits. These circuits are able to limit short-circuit currents fast, at preset levels. Four different circuits will be presented and compared with regard to technical aspects. In order to integrate new technologies into present power systems, costs are a decisive factor. In this paper, a complete Life Cycle Cost (LCC) analysis is carried out. It will be shown that, the design of resonant circuits offers some degree of freedom, which gives the opportunity to design circuits at minimal costs. The optimized solution strongly depends on the economical life time, which is assumed to be 10 or 20 years in present power systems. Finally, these costs are compared with solid-state circuit breakers, which are able to turn-off a short-circuit within a few 100 [micro]s. Index Terms--Circuit breakers, costs, current limiters, fault current limiters, life cycle costing, power distribution, power quality, protection.

Solid-state circuit breakers (SCBs), based on modern high-power semiconductors, offer considerable advantages when compared to mechanical circuit breakers with respect to speed and life. For instance, voltage quality of a power grid can be improved during a short circuit because the fault current is reduced. The interval over which voltage distortions occur, caused by a three-phase short circuit, can be limited to a few 100 [micro]s. In contrast to this, present circuit breaker technology requires at least 100 ms to clear a fault. Major drawbacks of all SCB solutions presented so far are material costs and on-state losses. Primarily because of these disadvantages, SCB systems have not been widely used yet. Consequently, new solutions should be developed which are more cost effective and offer reduced on-state losses. This paper presents a conceptual approach based on active thyristor circuits. It is proven that these topologies can lead to a wider integration of SCBs in existing grids due to the economical advantages of silicon-controlled rectifiers compared to turn-off semiconductors. After a brief introduction and a presentation of the fundamentals, different topologies are described and assessed in this paper. Index Terms--Silicon controlled rectifiers (SCRs), solid-state circuit breakers (SCB).

This paper presents the development of a four-quadrant switched reluctance machine (SRM) drive for high dynamic applications. Comprehensive fundamentals and analysis for operating switched reluctance machines in four quadrants are presented. The drive is designed based on a high dynamic control strategy called Direct Instantaneous Torque Control (DITC). The functionality of DITC is discussed in detail for both motoring and generating operation. A methodology to generate switching functions directly by the hysteresis torque controllers for SRMs is proposed. The proposed controller was prototyped and tested on a digital signal processor/field-programmable gate array development platform. High dynamic operation in both motoring and generating mode and the transition between these modes are validated by experimental results presented at the end of this paper. Index Terms--Four quadrant, switched reluctance machine (SRM), torque controller.

Supercapacitors, also known as ultracapacitors or electric double-layer capacitors (ELDCs), are electrical energy storage devices, which offer high power density, extremely high cycling capability, and mechanical robustness. Due to their electrical performance, supercapacitors have a high potential to be used in industrial applications. To improve the performance, reliability, and lifetime of these capacitors, charge-balancing circuits are employed. In this paper, different equalization concepts are analyzed and evaluated. In addition, a simulation approach for the design of supercapacitor systems is proposed. As an example, results from an automotive application are presented. Index Terms--Charge-balancing circuits, electric double-layer capacitor (ELDC), supercapacitor, ultracapacitor.

Torque control of a spherical machine combining three degrees of freedom in motion is presented. This drive can be used for machine tools and robots to replace conventional rotating or linear machines which are connected in series or parallel. The proposed motor consists of a rotor sphere with permanent magnets and an outer stator core casing with 96 stator poles and windings. The currents of the stator coils have to be controlled individually because the pole pitch can vary continuously during operation. A unique solution to calculate all 96 current commands to produce the desired torque does not exist. Different control algorithms are presented on how to choose the individual phase currents to reach the required torque vector. Simulations show satisfying results which are confirmed by experiments. In addition, the controllability of three-dimensional motion is demonstrated. Index Terms--Linear machines, permanent magnets, phase currents, rotor sphere, stator coils, stator core, torque control.

State-of-the-art mechanical circuit breakers in medium-voltage systems allow a safe handling of short-circuits if the short circuit power of the grid is limited. Using delayed turn-off times, the circuit breakers can be coordinated with lower level protection gear. Hence, a high availability of the grid can be guaranteed. However, during a short-circuit a significant voltage sag can be noticed locally in the medium-voltage grid. Sensitive loads such as computers will fail even if the voltage returns within a few seconds. A semiconductor circuit breaker, however, is able to switch fast enough to keep voltage disturbance within acceptable limits. The optimization and selection of power electronic switch topologies is critical. In this paper, different semiconductors are briefly compared considering the requirements of a solid-state switch integrated into a 20-kV medium-voltage grid. Based on these semiconductor characteristics, various switch topologies are developed, which are compared under technical and economical aspects. It is shown that solid-state circuit breakers offer significant advantages when compared to present solutions and can be used in today's medium-voltage power systems. Index Terms--Current limiters, semiconductors, solid-state circuit breakers.

This paper presents three new rapid prototyping tools to develop power electronic systems. The effectiveness of these tools is demonstrated by designing and building a shunt active power filter. First, a digital signal processor (DSP) model to embed complex control algorithms has been created for detailed offline simulations with PSpice. This DSP model emulates the discrete behavior of digital control circuits. The control algorithms in the DSP model are implemented in C-code. Secondly, the control C-code can be downloaded to the ISEADSP for real-time execution. The ISEADSP is a universal DSP control board based on two 80 SHARC processors which execute control algorithms of various nature and highest complexity at 80 MFLOP per second. Thirdly, power electronic building blocks (PEBBs) based on IGBT devices were developed to build and analyze quickly different converter topologies. Combining these three rapid prototyping tools led to a significant reduction of development time of power electronic applications. Index Terms--DSP, IGBT, ISEADSP, PEBBs.

A new method is developed to embed DSP control algorithms into PSpice providing accurate time stamped simulation of real-time applications. The proposed method allows to build new PSpice models with an arbitrary number of external nodes using PSpice's Device Equation option. Sampled systems can be simulated including the effects of discrete sampling times as well as propagation delays caused by processors. Control code developed in C-language can be embedded into this PSpice control model prior to downloading into the real-time DSP environment. To verify the simulation approach, simulation results and experimntal results of a shunt active filter for harmonic current compensation in a three-phase system are presented. Index Terms--Device equation, PSpice, real-time DSP, shunt active filter, simulation.

Circuit simulation is a powerful tool for the design of high power converters, if suitable device models exist. Unfortunately, the commercially available circuit simulators do not have accurate models for high power semiconductors. Therefore, new device models are developed for power diodes and thyristor based devices, such as GTO, IGCT, and MTO. These models are based on semiconductor physics, which guarantees a wide range of validity. Electrical and thermal behavior is implemented, which allows transient temperature simulation. The models are programmed in the C++ language and are implemented in the widely used circuit simulator PSpice using the Device Equation Option. Simulation results are compared with measurements. Index Terms--Circuit simulation, GTO, high-power semiconductor, IGCT, MTO, physical model, PSpice, thermal model.

In this letter, a transformed unsaturated inductance characteristic-based method is proposed for the rotor position of the switched reluctance machine. Due to the magnetic saturation effect, the phase inductance characteristics have a narrow linear region, which increases the difficulty of their analytical expression. To reduce the complexity of the analytical expression, the unsaturated inductance characteristic is transformed from the phase inductance characteristics. Then, a linear model is presented to explicitly describe the relationship between the rotor position and unsaturated phase inductance. Experimental verification is carried out to verify the effectiveness and accuracy of the proposed method. The proposed method can serve as a low-effort way to provide the accurate rotor position for the industry application at medium and high-speed ranges. [ABSTRACT FROM AUTHOR]

This work proposes an active thermal management technology that operates ac drive inverters safely at thermal limits to maximize their current and torque capability. For that purpose, the technology exploits two fundamental opportunities: First, it monitors the coolant and junction temperature to adaptively determine the maximal peak current capability that increases at low coolant temperature. Second, it takes advantage of the thermal impedance frequency response function $Z_{\mathrm{th}}(\text {j}\omega)$ that decays with higher frequencies. Thus, larger currents are feasible at higher excitation frequencies without increasing peak junction temperature, because the associated transient losses are absorbed by the thermal capacitance of the power module. This article presents a unique active thermal management algorithm that addresses the two identified opportunities. It utilizes primarily a reduced-order electrothermal real-time model as well as negative temperature coefficient thermistor temperature information. Thus, it can be applied on most drive systems with small software modifications to adaptively maximize its current capability. To make this technology applicable in ac drives, this article also proposes torque control strategies that utilize variable current limits and discusses essential design limitation. With the introduced technology, state-of-the-art drive inverters can operate safely at up to 200% overload current and torque across a wide speed range. This supports the development of highly reliable drives with increased base speed range and power density that save space, cost, and resources. [ABSTRACT FROM AUTHOR]

The very high switching speed of wide bandgap semiconductor devices enables higher switching frequencies at lower losses. However, it can also cause negative effects on the insulation material. For investigating the effect of steep voltage slopes on interwinding insulation systems, a gallium nitride based full-bridge converter with digitally adjustable voltage slopes is developed and presented within this article. [ABSTRACT FROM AUTHOR]

This letter proposes a closed-loop black start-up control for the dual-active-bridge (DAB) converter. With a simple combination of the extended phase-shift and triple phase-shift modulation schemes, the DAB converter can start up with the maximum allowable precharge current while realizing soft-switching operation in the trapezoidal current mode simultaneously. Compared to the conventional start-up procedure that usually requires multiple steps of operation and parameter fine-tuning, the proposed start-up method can be implemented simply into the existing closed-loop controller and can shorten the start-up transients of the DAB converter significantly. The presented methods are validated experimentally on a downscaled DAB converter prototype. [ABSTRACT FROM AUTHOR]

Compared with integrated gate commutated thyristors (GCTs), an integrated emitter turn-off thyristor (IETO) has a potential of higher turn-off current capability and requires lower power consumption for gate driver units, which is more suitable for high-power applications. Thus, in this article, an advanced design of 4-in IETO was presented. To reduce the gate commutation impedance and enhance the turn-off current, the turn-off circuit with low impedance DirectFETs was integrated into the housing. And the housing structure was carefully designed to provide a compact current commutation path. Then, a 4-in IETO prototype based on a 4.5 kV/5 kA GCT wafer was developed. Experimental results show that its maximum turn-off current was over 8.1 kA with an extremely short commutation time of 130 ns. And the total commutation inductance was only 0.38 nH. Additionally, the thermal and mechanical characteristics of the housing were also taken into consideration during design and verified by the thermal simulation and mechanical stress test. Consequently, according to this article, IETO has the potential to be a competitive device in high-power applications in the near future. [ABSTRACT FROM AUTHOR]