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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 performance of inverters strongly depends on the characteristics of the employed semiconductor devices. Bound to a tradeoff between conduction- and switching-optimization, these devices require a decision for the optimal loss balance. In this work, a new medium-voltage semiconductor device consisting of both thyristor-based and transistor-based components is proposed. The goal is reduction of losses in both conduction and switching domain. The circuitry and switching pattern is described and the improvement of overall losses is investigated by finite element method-simulation to give an theoretical outlook on the benefits of the device. A selection of parameters is adapted to analyze the impact on the performance. It is shown that the overall losses can be significantly reduced by combining a gate-commutated thyristor (GCT) with an insulated-gate bipolar transistor (IGBT)  while keeping the silicon area constant, in comparison to a GCT-only device. The work is concluded by characterization results of a constructed prototype, which confirm the simulation results that significant efficiency benefits can be achieved by introducing a turn-off delay between the GCT and IGBT. [ABSTRACT FROM AUTHOR]

The purpose of this study is to present the concept and properties of a dual-active bridge dc–dc converter with a modified auxiliary-resonant commutated (MARC) pole concept, and to discuss preliminary test results of a high-power setup. In this approach, the dual-active bridge based on IGCT is considered. First, the soft-switching boundaries for the converter with lossless snubbers and high switching delays are introduced. Second, the MARC pole is presented to overcome this border to receive full soft-switching capability in the entire operation range of the dc–dc converter. This is of crucial importance since IGCTs will be destroyed in case of a snubber dump. The advantage of the modified circuit is the guaranteed switching under zero-voltage conditions without applying an additional boost current as needed in the classic auxiliary-resonant commutated pole (ARCP) approach. Thus, complexity is reduced and reliability is increased. Measurement results of the MARC are presented from a mega-watt dc–dc converter where the concepts are fully implemented. The results of large-scale systems impressively show how the ARCP reduced the impact of parasitic elements, which would normally affect the switching transitions tremendously. [ABSTRACT FROM AUTHOR]

This paper presents a design concept of a sensorless control for high-speed SRM drives with small DC-link capacitor. In a cost-sensitive application, the expensive large DC-link capacitor should be replaced with a smaller DC-link capacitor for cost reduction. Using a small DC-link capacitor, the DC-link voltage extremely fluctuates during operation. The fluctuating DC-link voltage deteriorates the control stability and performance of the sensorless control. In the literature, the previous work has shown that the workable speed range of the existing sensorless control concept for high speed has been degraded to a smaller range when operating with fluctuating DC-link voltage. The proposed design concept deals with the challenge of improving the control stability of the sensorless control to operate in a wider operating speed range up to 75% (8000-35,000 rpm) under the fluctuating DC-link voltage. The control scheme is developed based on two basis sensorless control techniques, inactive phase method and current gradient method for covering the entire speed range. The proposed solutions work based on the appropriate selection of the detected signals according to the state of DC-link voltage. At the end, the functionality of the proposed technique is validated by experimental results. [ABSTRACT FROM AUTHOR]

The output voltage of power electronic converters is a very important quantity for dynamic control of power electronic systems. In electrical drives without electromechanical position or speed sensor, the terminal reference voltage is used to obtain the rotor position. Dead-time effects and semiconductor voltage drop lead to distortion in the actual output voltage and degrade the control performance when the back electromotive force magnitude is low. Thus, for stable low-speed operation, output voltage sensing becomes necessary. Due to the switching nature of power electronic systems, this is not a trivial task, especially when instantaneous measurement of the terminal voltage is required. In this paper, an instantaneous switching-period average voltage sensing technique is proposed that utilizes a combined approach of oversampling and filtering. Based on the theoretical analysis of the sampling- and filter-induced measurement distortion, a general solution for an optimal filter design is derived. The additional sensing circuit is integrated into the low-side gate driver of the converter outputs. This paper includes details about the hardware implementation and extensive verification measurements. [ABSTRACT FROM AUTHOR]

This paper presents a detailed comparison between the conventional ac collector-grid configuration and two proposed dc collector-grid configurations for large photovoltaic (PV) parks. One complete year of measured weather data at two different locations, one very sunny and the other with relatively less sun, is used for the evaluation. An already validated PV performance model is used to estimate the expected energy yield of the PV park for the given environmental and connection conditions. Loss mechanisms in different grid components in the three configurations are discussed based on the developed models. These components include the inverters, transformers, cables, and dc–dc converters. A comparison of the total losses in these components helps to identify the configuration that has the potential to operate at higher efficiency and, hence, generate maximum revenue. The economic viability metrics are calculated and a sensitivity analysis is carried out using the Monte Carlo method with a \pm \mathbf 5\% uncertainty in the considered cost and energy yield parameters. [ABSTRACT FROM PUBLISHER]

Zero-volt loop (ZVL) algorithms are known to be able to reduce peak flux linkages and resulting iron losses while keeping the same average torque in average torque control (ATC) of switched reluctance motors (SRMs). However, exploiting ZVLs to minimize the losses has been challenging due to the strongly nonlinear correlations between the torque and the control parameters of ATC caused by extensive magnetic saturation. In this paper, a fast optimization method for loss minimization is proposed, which can utilize all control parameters of ATC while operating with ZVL control. The proposed optimization method quickly calculates the current reference, which is one of the control parameters, so as to satisfy a torque reference, and consequently removes the time-consuming nonlinear constraint on the torque from conventional optimization methods. Using the proposed optimization method, the impact of ZVL control in loss minimization of SRMs is investigated with detailed simulations and experiments. The results verified that the utilization of ZVLs reduces iron losses without significantly increasing copper losses. It was found that the loss reduction was especially large (more than 15%) at medium speed and partial load. The loss reduction in the Japanese JC08 driving cycle for automotive propulsion for city driving was investigated and was as large as 15%. Furthermore, the vibrations that cause acoustic noise were also reduced. [ABSTRACT FROM AUTHOR]

In this study, a 3-kW inductive power transfer system is investigated, specifically intended for contactless vehicle charging. A series-series-compensated topology with dual-side power control and a corresponding control strategy is proposed to significantly increase the overall efficiency, especially for systems with large coupling factor variations and in partial load mode. The topology, which is closely related to the dual-active bridge converter, enables the dual-side power control without adding additional dc/dc converters to the system, and thus keeping the additional hardware effort minimal. A detailed analysis of the proposed topology is provided, and the benefits of the dual-side control are demonstrated both theoretically and experimentally. A hardware prototype is built and a peak dc-to-dc efficiency of 95.8% at 100 mm air gap and a minimal efficiency of 92.1% at 170 mm air gap is measured, including the power electronic components. The partial load efficiency at 500 W output power is still as high as 90.6% at 135 mm air gap. Overall, the proposed topology provides a practical method to overcome the main drawback of most single-side controlled inductive power transfer systems, which is a significant efficiency drop outside the nominal operating point. [ABSTRACT FROM AUTHOR]

A new discrete-time state feedback controller is presented, which allows high-bandwidth voltage control of a buck converter for any load condition, whether it operates in discontinuous conduction mode (DCM), continuous conduction mode (CCM), or at the boundary of these regions. This makes the buck converter applicable for a wide range of applications. For the control design process, two large-signal models, which represent the buck converter's discrete time dynamics in CCM and DCM, are developed. A simple proportional-integral regulator is used for the voltage control of the converter. The operation mode is detected and the voltage controller is connected in cascade to a current controller in CCM or to a nonlinear state feedback decoupling structure in DCM. In this paper, the modeling and design of the proposed control topology are introduced and its performance is demonstrated in simulation and experiment. [ABSTRACT FROM PUBLISHER]

A comprehensive vibration synthesis process for synthesizing the electromagnetically excited acoustic vibrations in electric drives is explored in this paper. The study is performed on a traction drive for a hybrid electric vehicle. The work derives and highlights several key aspects for modeling and assessing the acoustic characteristics of electric drives. The influence of different force excitation shapes on the resulting overall vibration is shown, and the importance of including tangential forces in the synthesis process is highlighted. The resulting operational deflections at selected operating points are analyzed and compared to measurements. The load level dependence of the noise components is investigated. Finally, acoustic maps are introduced as a means to display and compare predicted and measured acoustic characteristics of variable-speed drives. The synthesized acoustic maps are validated by comparison against their measured counterparts. [ABSTRACT FROM AUTHOR]

This paper presents the design and an encoder-based starting strategy for a low-cost single-phase switched reluctance machine (SRM). The single-phase SRM cannot produce a continuous torque over one revolution. Therefore, applications that do not require a continuous torque, e.g., pumps and fans, are especially suitable. Another issue of single-phase machines is start up. The starting direction is affected by the initial rotor position. Due to the functional concept of SRM the machine produces no torque at aligned and unaligned position of the rotor and consequently, cannot be started from these positions. To start up from every rotor position a saturation-based starting method is used. The design of the rotor with the saturable area is shown and the principles of an encoder-based starting strategy for a fast start-up under 0.5 s are introduced. Finally, the build prototype and experimental results of the starting strategy are shown. [ABSTRACT FROM AUTHOR]

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. [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. [ABSTRACT FROM AUTHOR]

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 µs. [ABSTRACT FROM AUTHOR]

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 μs. 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. [ABSTRACT FROM AUTHOR]

Presents an online instantaneous torque control technique for switched reluctance machines called direct instantaneous torque control (DITC). Estimation of instantaneous torque; Theoretical and practical operating range of DITC; Results of simulation and experimental tests.

Presents a study which developed a technique to estimate online average torque of switched reluctance machines. Estimation of the average torque; Simulation of the operating principle of the torque estimator under dynamic conditions; Control variables for direct average torque controller.

Focuses on a study which implemented physically based models of high power semiconductors. Description of the modeling method; Verification of the models; Conclusion.

Presents a study which developed four-leg inverters to power unbalanced/nonlinear three-phase loads. Circuit topology, modeling and transforms; Synchronous-frame controller; Conclusions.

Compares the properties of several soft-switching converter topologies when used to achieve dc-dc conversion of high-power and high-voltage levels. High-frequency magnetic core materials; Turnoff energy; Series/parallel resonant; Simulation results.

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]

This article presents a method for designing converter systems embedding power modules for a specified degradation monitoring performance in real-time applications. It builds upon prior work which identified specific variations in three-dimensional transient heat transfer with interface and interconnect state-of-health. This article contributes a joint, module-converter concurrent design method to quantify opportunities and limits in using chip-based temperature sensing to integrate electrothermal impedance spectroscopy in situ. Challenges intrinsic to modules, such as many, closely packed heat sources, are quantified. This article also examines spatial degrees-of-freedom for placing additional degradation sensing temperature detectors. Experimental measurements of transient thermal frequency response show trends that can be exploited to push temperature sensors against their signal-to-noise ratio limits. Overall, the design method relies on circuit topology and modulation details; it is directed toward early-stage converter development. To that end, an included harmonic loss modeling step immediately provides a designer with feedback about the feasibility of a degradation sensing concept. [ABSTRACT FROM AUTHOR]

To effectively find an optimal solution in the development process of electrical machines, it is essential to predict machine iron loss and thermal behavior in the predesign stage. Most existing publications only consider thermal behavior by roughly limiting the maximum current density. However, especially for high-speed application, iron loss can also be an essential part in thermal-behavior estimation. This paper proposes a simplified model to efficiently calculate iron loss and thermal behavior in the design procedure of switched reluctance machines. For this purpose, a maximum coenergy loop control method is implemented to facilitate the estimation of flux waveform and machine torque. Three different iron loss calculation methods are compared in terms of accuracy and time. Besides, a simplified lumped parameter thermal network is applied for machine sizing. Furthermore, the impact of number of turns and peak magnetomotive force on the losses and machine sizing is discussed. The efficiency and power density of various machine geometries are comparatively analyzed. Finally, the accuracy of the simplified model is verified by comparison with finite element simulations and experiment results. [ABSTRACT FROM AUTHOR]

The classic top to down structure of electrical infrastructure is changing due to the extensive spread of renewable energy sources which are connected to medium-voltage and low-voltage grids. Especially for medium-voltage direct-current grids, the three-phase dual-active bridge (DAB) dc–dc converter is one of the most promising converter topologies, as it features bidirectional power flow and galvanic isolation at highest efficiency. Unwanted saturation of the transformer of this converter can occur, particularly for multimegawatt converters with highly efficient, low-loss transformers. The saturation leads to additional core losses, elevated voltage stress at the windings, and increased magnetostriction of the transformer core, which can result in undesired acoustic emissions. The following article presents a feedback control and modulation method that controls the DAB converter such that saturation of the transformer is avoided. The chosen approach evaluates the star-point voltage of the transformer to determine the dc component of the magnetizing current, thereby avoiding the need for expensive high-precision current sensors. The control method is analytically derived and verified by simulation. Experiments carried out using a 5 MW medium-voltage three-phase DAB converter prototype verify the presented modulation method. [ABSTRACT FROM AUTHOR]

An isolated bidirectional dc–dc converter, which combines parallel-connected two-level converters (TLCs) on the medium-voltage side and a modular multilevel converter (MMC) on the high-voltage side, namely a TLC-MMC converter, is a promising candidate for the interconnection of medium-voltage direct current (MVDC) and HVdc grids. Different from typical phase-shift controlled isolated bidirectional dc–dc converters, transformer currents of a TLC-MMC converter are regulated by the MMC in a closed-loop manner in order to achieve extremely low switching losses and low total device rating of power-semiconductor devices in TLCs. This paper addresses the dedicated operation technique and the voltage-balancing control of the TLC-MMC converter. The MMC in the TLC-MMC converter operates with six-step phase voltages and sinusoidal phase currents. Such an operation makes the MMC present remarkable differences to ac–dc applications. The direct-modulation technique, which is the most-used technique performed to MMCs in line-frequency ac–dc power conversion, has been concluded not applicable to the MMC in a TLC-MMC converter due to the significant sixth-order oscillation resulted in the dc-link voltage. Thus, the indirect-modulation technique is employed, and consequently a closed-loop voltage-balancing control is mandatory for the MMC. Possible measures for voltage balancing have been explored, and effective voltage-balancing control with a simplified implementation is proposed. Validity and effectiveness of the proposed control strategy have been verified by both simulations and experiment using a downscale prototype. [ABSTRACT FROM AUTHOR]

Electrical drive systems without dedicated speed transducer require precise information about the terminal phase voltage to achieve an acceptable low-speed performance. Recently, voltage-sensing techniques have gained in importance as they improve stability at low-speeds compared to the conventional estimation based on reference values. However, the additional sensors increase the sensitivity to sensor offset drift, which can cause self-sensing control algorithms to fail at very low speeds. In this article, a novel offset adaption method is introduced that compensates sensor offsets during operation while being fully decoupled from the control algorithm. Using a pair of phase current and voltage sensors per phase, the dead-time-related inverter voltage-distortion curve is monitored continuously. Its point-symmetrical nature is utilized for the sensor offset detection. This way, both sensor offsets can be calibrated continuously during operation and for each phase individually. This article gives a step-by-step description of the calibration algorithm and addresses implementation aspects to ensure deterministic calibration dynamics. The method is evaluated through measurements performed on a test bench for an electric-vehicle traction drive. [ABSTRACT FROM AUTHOR]

This paper presents a methodology for real-time monitoring of 3-D temperature distributions and device losses within power electronic modules. It allows precise thermal management, empirical lifetime prognosis, and detection of critical degradation of the power module. By effective combination of thermal 3-D finite difference modeling, parametric loss models, and model truncation techniques, a compact thermal real-time model is derived. It enables the computation of device losses and temperatures at critical locations within a power module, e.g., at the devices, solder interfaces or the base plate, on a conventional digital signal processor. The real-time model as well as real-time junction temperature information are combined in a new Luenberger-style observer structure. Applying bandwidth partitioning, the observer estimates the temperatures throughout the power module every switching period and averaged over one excitation period with nearly zero lag, even if the junction temperature measurement exhibits delays and has noisy signals. Furthermore, it estimates errors in the loss prediction process that can be tracked over the lifetime of the power module to detect degradation of the devices or the power module. The observer and its features are experimentally evaluated under realistic operating conditions on a load emulator using a state-of-the-art automotive power module. [ABSTRACT FROM AUTHOR]

This paper proposes a generalized design procedure for repetitive current controllers in distorted distribution grids to obtain good disturbance rejection properties and well behaved and robust system dynamics. Different implementation options for repetitive controllers (RCs) are discussed based on an accurate discrete time model. A simple control design is derived, which allows any desirable dynamics to be adjusted by one single parameter. Even a deadbeat design is possible. The impact of model inaccuracies and numerical errors on the dynamic and stability of the system is investigated. It is shown that the RC leads to low damping or even instability at high switching frequencies caused by modeling errors or numerical inaccuracies. Based on the stability analysis, it is discussed how to handle these design challenges, which exist especially for RCs of high order. The proposed control structure and control design concept is verified by simulations and experiments. [ABSTRACT FROM AUTHOR]

A method for in situ high-bandwidth junction temperature estimation of insulated-gate bipolar transistors is introduced in this paper. The method is based on the acquisition of the gate voltage plateau during turn-on. It can be related to the junction temperature at any known device current, that can be effectively approximated using existing phase current measurements. This allows fast overtemperature protection of the power device or even active thermal cycle reduction via thermal control. This paper discusses, first, the physical mechanisms leading to the temperature sensitivity of the gate voltage plateau. Second, a rigorous sensitivity analysis of the gate voltage plateau is conducted. It allows to determine the maximal estimation error and provides information about the suitability of this method for various devices and applications. Finally, a sensing circuitry is presented, which allows accurate gate voltage plateau sensing every switching period as well as an easy integration into the gate driver. The performance of the proposed method is experimentally demonstrated with the sensing circuitry on a double pulse test bench over a wide operation range. [ABSTRACT FROM AUTHOR]

DC grid technology is regarded as a promising solution for future electric networks integrating a great amount of renewable energies. It calls for high-efficiency dc–dc converters with high voltage step-up ratio to interconnect medium-voltage (MV) dc distribution grids and high-voltage (HV) dc transmission grids. This paper presents an isolated bidirectional soft-switching dc–dc converter combining two-level converters in parallel on the MV side and a modular multilevel converter (MMC) on the HV side. A dedicated control method of the proposed converter is presented. By the proposed method, a certain reactive current is injected into the MV side by the MMC to ensure soft-switching on the MV side. The proposed converter presents low power-semiconductor total device rating and low semiconductor losses over a wide power range at variable input and output voltages. Simulation of a 50 kV/400 kV, 400 MW converter is conducted to evaluate semiconductor losses and verify the validity of this work. [ABSTRACT FROM PUBLISHER]

Switched-reluctance technology is appealing to the automotive industry due to its low cost. Conventional research focuses on the two main issues, namely torque ripple and acoustic noise. However, control schemes usually only address one of these two issues at a time. This study unifies the approaches of direct instantaneous torque control and direct instantaneous force control to simultaneously eliminate two central drawbacks of switched reluctance machines (SRMs). A search algorithm was used to predict appropriate reference values for each phase to keep torque and overall radial force smooth at any time. Simulation and measurement results confirmed that the control objectives were met so that torque ripple was reduced and the acoustic behaviour of the investigated automotive traction drive was simultaneously improved. A comparison with conventional control methods investigating vibrations and efficiency is provided. The proposed control approach thus provides future engineers with a powerful tool for adapting SRMs to the requirements of the automotive sector. [ABSTRACT FROM AUTHOR]

Switched‐reluctance technology is appealing to the automotive industry due to its low cost. Conventional research focuses on the two main issues, namely torque ripple and acoustic noise. However, control schemes usually only address one of these two issues at a time. This study unifies the approaches of direct instantaneous torque control and direct instantaneous force control to simultaneously eliminate two central drawbacks of switched reluctance machines (SRMs). A search algorithm was used to predict appropriate reference values for each phase to keep torque and overall radial force smooth at any time. Simulation and measurement results confirmed that the control objectives were met so that torque ripple was reduced and the acoustic behaviour of the investigated automotive traction drive was simultaneously improved. A comparison with conventional control methods investigating vibrations and efficiency is provided. The proposed control approach thus provides future engineers with a powerful tool for adapting SRMs to the requirements of the automotive sector. [ABSTRACT FROM AUTHOR]

This work presents a flexible thermal modeling methodology for power semiconductor modules. It allows time efficient simulation of temperature cycling for different module designs and operation profiles. To keep the model compact and flexible as well as accurate, the solid state heat conduction paths of the power modules are modeled by a 3D finite difference model. It is combined with an analytical heat sink model describing convective cooling. The temperature gradient of the cooling fluid is captured by a mass transportation model. The resulting linear state space model can be easily formulated in discrete time domain to allow a fast and detailed simulation of thermal load transients. With the balanced truncation based model reduction technique, the thermal state space model is efficiently reduced to allow fast analysis of thermal cycling and reliability issues. Finally, the thermal model is validated with measurements and data from the manufacture. [ABSTRACT FROM AUTHOR]

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]

Three-phase dual active bridge (3p-DAB) dc-to-dc converters are typically avoided in low-power applications especially for wide voltage and power ranges. Even so, the 3p-DAB do offer a means to reduce filter costs and volume. The aim of this study is to propose the triangular and trapezoidal modulation for the 3p-DAB to address the problem of poor partial load efficiency. The proposed modulation schemes were compared with two conventional DAB concepts. It was found that the efficiency of the 3p-DAB increased substantially. Moreover, the 3p-DAB showed a considerably lower filter volume than that of the single-phase dual active bridge converter (1p-DAB). In conclusion, a modulation strategy combining the two proposed modulation schemes with the phase-shift modulation is ideal, because they boost efficiency and take most benefit from the inherent low filter volume. Ultimately, the three-phase dual active bridge may offer a promising solution to miniaturize galvanically isolated dc-to-dc converters for electric vehicles. [ABSTRACT FROM AUTHOR]

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]

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 paper presents a method to calculate the harmonic content of stator vibrations and acoustic noise resulting from radial force excitations in switched reluctance machines (SRM). The method is based on a thin cylinder approximation of the stator. The eigen modes are represented by their transmission impedance. The spectral composition of the vibrations can be calculated using superposition of the eigen modes and vibrations caused by all phases of the SRM. [ABSTRACT FROM AUTHOR]

During the last several years, increasing effort has been spent to advance offshore wind power. So far, only small test fields have been realized, and the electrification of offshore wind farms still remains a research topic. Currently, offshore wind farms are equipped with three-phase ac grids, some of them will be connected to the transmission grid via a high-voltage direct-current (dc) link. Consequently, a dc system encompassing the whole wind farm might constitute an alternative to a conventional ac grid. In this paper, the transient stability of such a dc grid is analyzed. Based on traveling wave theory, critical frequencies and cable lengths are calculated analytically. Furthermore, a large dc grid for an offshore wind farm is simulated. The goal is to provide guidelines that support stable operation of an offshore dc grid. [ABSTRACT FROM AUTHOR]

This paper introduces a novel phase-interleaving algorithm for asymmetric multiterminal power converters. Using a variable phase interleaving (VI), the first harmonic of the dc-link current and voltage can be thoroughly eliminated even under the situation where the input voltage and current of each converter differ. This means that the cost and size of the dc-link capacitor can be significantly reduced compared to when the standard (symmetric) interleaving algorithm is used. The VI-algorithm does not require any additional hardware and has only slight influence on the control loop of the converters when compared to the standard solution, which simplifies the integration of this algorithm. As a concrete application, the VI-algorithm is integrated into a photovoltaic inverter with three independent input converters. This paper also provides a method for determining the required dclink capacitance through a worst-case analysis. Furthermore, a performance comparison between edge-aligned fixed interleaving, center-aligned fixed interleaving and VI and is given. [ABSTRACT FROM AUTHOR]

This paper presents a control scheme that allows minimization of dc-link capacitance in switched reluctance drives (SRDs). In switched reluctance motors (SRM5), 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 over-voltages. 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. [ABSTRACT FROM AUTHOR]

The market of converters connected to transmission lines continues to require insulated gate bipolar transistors (IGHTs) 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-ky blocking voltage and IEGTs up to 4.5-ky 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. [ABSTRACT FROM AUTHOR]

To predict performance of modern power electronic systems, simulation-based design methods are used. This work employs the method of electrochemical impedance spectroscopy to. find new equivalent-circuit models for supercapacitors and Lithiumion batteries. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper reports on laboratory studies into the ac impedance spectra of nickel–metal hydride and nickel–cadmium batteries, aiming at finding out possible correlation between electrical parameters, extracted directly from the high frequency region, and the battery state-of-charge (SoC). Impedance diagrams were recorded immediately after interrupting the dc charge, or discharge, current. The study revealed that the series resonance frequency, at which the dynamic cell behavior switches from an inductive character (Z″>0) to a capacitive one (Z″<0), varied monotonously as a function of state-of-charge. This behavior was reproducible after intermittent charge and discharge. Half-cell measurements were also conducted to associate the cell impedance with either processes occurring at the positive or negative plates. [Copyright &y& Elsevier]

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]

The three-phase dual-active-bridge (DAB) converter is a promising topology for high-power dc–dc conversion in dc grids and industrial applications. However, the conventional single-phase-shift modulation shows a limited soft-switching range and large reactive currents under light-load operation especially with large voltage variations. This article proposes an asymmetrical duty-cycle control method for the three-phase DAB to extend the soft-switching range and reduce reactive currents by realizing three-phase triangular- and trapezoidal-current-mode operation. Closed-form solutions of the proposed modulation schemes are derived that enable a simple online calculation of the control parameters. The proposed modulation schemes can substantially reduce losses of both power semiconductor devices and the medium-frequency transformer. Thus, the three-phase DAB converter can realize high efficiency over a wide operation range, especially under light-load conditions. Considering the practical implementation, a compensation method is presented to correct the distorted current waveforms caused by the dead time and ensure the desired soft-switching operation. Besides, the power loss imbalance between top and bottom switches induced by the asymmetrical duty cycle is addressed by an active thermal balancing strategy. The effectiveness of the proposed method is validated by simulation results and experiments on a downscaled converter prototype. [ABSTRACT FROM AUTHOR]

New device models for circuit simulation are developed for high-power thyristor-type devices, such as gate-turn-off thyristors, integrated gate-commutated thyristors, and MOS turn-off thyristors. These models are based on semiconductor physics, which guarantees a wide range of validity. In particular, the proposed models are based on the lumped charge approach. Coupled electrical and thermal behavior is implemented to allow transient thermal simulations. To account for the nonuniform current distribution during turn-off, several of these single-cell models are connected in parallel to simulate a complete device. Simulation results are compared with measurements. [ABSTRACT FROM AUTHOR]

Proposes a method to embed digital signal processor (DSP) control algorithms into PSpice computer software providing time stamped simulation of real-time applications. Results of a shunt active filter for active filter for harmonic current compensation in a three-phase system; Effects of propagation delays caused by the processor; Overview of the time discrete behavior of most DSP algorithm.

Electrochemical impedance spectroscopy can be used to obtain simulation models for the non-linear, non-stationary dynamic behavior of electrochemical power sources. Some extensions of porous-electrode theory are necessary for this purpose, which are not provided by standard EIS data evaluation software. This paper presents experimental data and consistent equivalent-circuit models for different dc conditions, regarding three electrochemical systems: supercapacitors as almost ideally blocking porous electrodes, lead/acid batteries under overcharge (water electrolysis) operation, and the same battery type under discharge/charge operation. The series inductance which masks the electrochemical behavior for frequencies as low as 100 Hz for a 100 Ah cell can be attributed mainly to the macroscopic cell geometry. The dependence of impedance parameters on direct current (non-linearity), temperature, state-of-charge, and previous discharge/charge regime is investigated. It is shown that model parameters extracted from the impedance spectra are closely linked with the charge-transfer kinetics, double-layer capacitance, transport limitation, and porous structure of the electrodes. Consequences for impedance-based determination of the battery''s state-of-charge or state-of-health are discussed. [Copyright &y& Elsevier]