Showing papers presented at "European Conference on Power Electronics and Applications in 2018"

Design for Reliability in Power Electronic Systems

Abstract: In recent years, the automotive and aerospace industries have brought stringent reliability constraints on power electronic converters because of safety requirements. Today customers of many power electronic products expect up to 20 years (or even longer) of lifetime and they also want to have a "failure free period" and all with focus on the financials. The renewable energy sectors are also following the same tred, and more and more efforts are being devoted to improving power electronic converters to account for reliability with cost-effective and sustainable solutions. This presentation will introduce the recent progress in the reliability aspect study of power electronic converters for power electronic applications with special focus on renewables. It will cover the following contents: the motivations for highly reliable electric energy conversion in renewables; the reliability requirements of typical power electronic systems; failure mechanisms and lifetime models of key power electronic components (e.g., power semiconductor switches, capacitors, and fans); long-term mission profiles in renewable applications and their components; reliability analysis methods for more complicated systems, tools to be applied, and improvement strategies of power electronic converters in their applications. A few case studies will be given.

MVDC Distribution Grids and Potential Applications: Future Trends and Protection Challenges

Abstract: This paper presents the fundamental system components of medium-voltage direct current (MVDC) grids, including an overview of power electronic converters and protection schemes against DC fault currents. In addition to this, the lack of standardization and the development of efficient and reliable circuit breakers (CBs), which are today considered as showstoppers, are also analyzed in detail. The performances of three DC CBs, namely mechanical breaker with active current injection, solid state CB and hybrid CB are evaluated in terms of clearance times, fault peak current, residual energy dissipation and power losses using simulations. Last but not least, an overview of potential onshore and offshore future applications of MVDC grids is also presented by identifying targeted voltage and power ratings.

Efficiency of Active Three-Level and Five-Level NPC Inverters Compared to a Two-Level Inverter in a Vehicle

Abstract: This paper deals with a comparison of a standard two-level inverter, with a three-level and a five-level active neutral point clamped (ANPC) inverter for vehicle traction applications. The inverter efficiencies during different drive cycles are assessed and an efficiency enhancement of the multilevel inverters for partial loading and different drive cycle scenarios is found.

Hysteresis Losses in the Output Capacitance of Wide Bandgap and Superjunction Transistors

Abstract: This paper deals with switching losses in modern power semiconductors due to a hysteresis in their output capacitance. A modified Sawyer-Tower circuit is presented, which is able to characterize this effect under large signal excitation. Three semiconductor types are analyzed: a Si superjunction MOSFET, a SiC MOSFET and a GaN HEMT. It is revealed that the output capacitance of these devices shows a hysteretic behavior which results in unavoidable losses even under zero voltage turn-on transitions. These losses become a major issue when pushing switching frequencies of power electronics into the megahertz range.

Solar Powered E-Bike Charging Station with AC, DC and Contactless Charging

Abstract: Charging electric vehicles from solar energy provides a sustainable means of transportation. This paper shows the design of solar powered e-bike charging station that provides AC, DC and contactless charging of e-bikes. The DC charger allows direct DC charging of the e-bike from the DC power of the photovoltaic panels (PV) without the need for an external AC charger adapter. In case of the contactless charger, the bike can be charged without the use of any cables providing maximum convenience to the user. Finally, the charging station has an integrated battery that allows for both grid-connected and off-grid operation.

Design and Commissioning of a 10 kV Three-Phase Transformerless Inverter with 15 kV Silicon Carbide MOSFETs

Abstract: A medium voltage inverter based on 15 kV Silicon Carbide (SiC) MOSFETs is presented in this paper. By using a three-level topology it is possible to feed directly into a 10 kVAC distribution grid. Measurement results of the successful operation at full output voltage are shown. A maximum efficiency of over 97% is reached.

Switching SiC MOSFETs Under Conditions of a High Power Module

Abstract: This paper discusses the investigation of SiC MOSFET switching characteristic in high inductive environment. The characteristic product of stray-inductance times nominal current grows with the power rating and is a limiting factor for the speed of current commutation. The reduction of switching speed due to this limit and its impact on switching performance is evaluated. Furthermore this paper proposes a, according to the author's knowledge, novel benchmark for characterisation and comparison of SiC MOSFET switching behaviour.

Model Predictive Control Approach for Distributed Hierarchical Control of VSC-Based Microgrids

Abstract: This paper embeds a high bandwidth distributed hierarchical control structure for a power electronic based ac microgrid. Conventionally, hierarchical linear control loops are applied to control the grid frequency and voltage. However, they suffer slow dynamic response and high sensitivity to parameter variations. In this paper, high bandwidth control approach realized with a finite control set model predictive control (FCS-MPC) scheme to control multiple voltage source converters (VSCs). Furthermore, droop control and virtual impedance are employed to share active and reactive power. At the upper level distributed secondary control can be programmed with much higher bandwidth compare to linearized cascaded control structures. Simulation and experimental results indicate that voltage and frequency have been regulated order of magnitude faster than state of the art.

Design of a Modular Multilevel Converter Prototype for Research Purposes

Abstract: As modular multilevel converters gradually become the preferred topology for many high-voltage and high-power applications, they are widely studied among researchers, who need experimental results to validate their studies. This paper discusses the design of a down-scaled modular multilevel converter prototype for research purposes, equipped with 30 full-bridge submodules and 10 kW rating. The design of this prototype is aimed at safety, flexibility, orderliness, and compactness. The challenges posed by the implementation of the converter prototype are examined, discussing the design of the prototype structure, the communication scheme, the full-bridge submodules, and the control hierarchy. The control system is based on Xilinx Zynq system-on-chip, which integrates programmable logic and processing system, allowing for extensive computational capability as well as simple reconfiguration. Experimental results showing the prototype in operation at nominal ratings are presented along with the devised graphical user interface.

On-board Impedance Diagnostics Method of Li-ion Traction Batteries Using Pseudo-Random Binary Sequences

Abstract: This work deals with the on-board impedance measurements of Li-ion batteries on hybrid electric vehi-cles/electric vehicles by using pseudo-random binary sequences (PRBSs). The impedance of the battery can be related to its state of charge (SOC) and state of health (SOH). However the battery impedance is frequency dependent which makes it difficult to perform the measurement on a pack level in the vehicles. By using an excitation signal like PRBS, it is possible to extract the impedance information of the battery packs. Experiments are performed with different set-ups to verify the PRBS method. A non-parametric method is used to process the data and extract the impedance measurement. Experiments in the laboratory at different state of charge levels and temperatures are made to validate the PRBS method. It is shown that the PRBS method can produce a valid electrochemical impedance spectrum in a limited frequency range, similar to the result from a high accuracy laboratory impedance analyzer. The method is stable at different SOC levels and temperatures. A simulation of the excitation signal in the vehicle is performed where the electric motor is used as the load. It shows that it is possible to some extent to use the driveline in a hybrid electric vehicle/electric vehicle to perform an on-board battery impedance measurement.

A 50 kW Power Hardware-in-the-Loop Test Bench for Permanent Magnet Synchronous Machines based on a Modular Multilevel Converter

Abstract: This paper presents a power hardware-in-the-loop (PHIL) test bench for the emulation of highly utilized permanent magnet synchronous machines based on a square-wave powered Modular Multilevel Converter (SPMMC). Comparisons of the measurement results between an automotive machine and the PHIL during steady state operation and high dynamic current steps are done to show the performance of the PHIL test bench.

AC Grid Forming by Coordinated Control of Offshore Wind Farm connected to Diode Rectifier based HVDC Link - Review and Assessment of Solutions

Abstract: Diode Rectifier (DR) based HVDC transmission can significantly reduce system costs and foot print of an HVDC power station for Offshore Wind Farms (OWFs), but as a consequence, the control of the offshore AC grid becomes challenging. The replacement of the offshore Voltage Source Converter (VSC) by a passive DR leads to major research questions pertaining to the control of the offshore AC grid. To achieve the wind farm operation and seamless power extraction, many grid forming solutions have been devised. This paper reviews a few of the major control solutions for AC grid forming and operation of DR-HVDC based OWFs, following which a comparison is made between them. Then two of these solutions are selected and implemented in a study case OWF model. By using the simulation results and further analysis, the approaches adopted by these two solutions are elaborated further and the various challenges regarding the operation and control of the DR-HVDC based OWF are highlighted.

Medium Voltage Single-Stage Dual Active Bridge Based Solid State Transformer (DABSST)

Abstract: This paper introduces a single-stage medium voltage (MV) solid state transformer (SST) based on dual active bridge topology and recently developed high voltage Super-cascode device. A closed loop control system of the output voltage is designed and verified by simulation results. A fully functional SST based on the proposed concept has been developed and tested with an input voltage of 3.6kV and experimental results show unity power factor operation with zero voltage switching of both primary and secondary devices.

Low Voltage Power Supply in Modular Multilevel Converter based Split Battery Systems for Electrical Vehicles

Abstract: Usually the low voltage power supply in electric vehicles is generated out of the high voltage DC-BUS by a dedicated DC/DC converter. When substituting the conventional drive train/motor converter by a modular multilevel converter with split batteries, this DC-BUS is obliterated. In this paper we introduce an approach to generate this low voltage supply efficiently based on the modular concept. By adding just, a single capacitor based module to each converter arm, a solution for an efficient bidirectional energy exchange between the low voltage power supply and the traction battery can be realized. The comparison to state-of-the art solutions shows that the new approach enables an efficient integration not only of the low voltage power supply, but of any energy consumer and producer into split Battery Storage Systems. It will be shown by simulations and measurements on a first prototype, that an implementation based on that technology enables a power exchange in any operation point of the electrical vehicle.

High efficiency 20kW SiC based Isolated DC-DC Converter for Battery Charger Applications

Abstract: The paper presents the design, and demonstration of a high efficiency 20 kW SiC based isolated de-de converter for battery charger application that can be used for fast charging or vehicle to grid charging. The paper discusses the design considerations and analysis of various losses in the converter. The de-de converter has an input voltage of 700V and the output is connected to a 700V battery bank. The de-de converter uses 1200V SiC MOSFET at the primary side and 1200V SiC diodes at the secondary side of the converter. The hardware prototype of the converter is developed and the efficiency of the converter is measured. The proposed converter has achieved a maximum measured conversion efficiency of 97.8%,98.7% and 98.9%, at output voltages of 350 V, 560V and 686V respectively.

Direct Multivariable Control of Modular Multilevel Converters

Abstract: While Modular Multilevel Converters (MMC) have become state of the art in many high power/high voltage applications like HVDC, other important future applications (i.e. multiterminal-DC-grids, wind parks, electric ships, …) are still under development. The increased number of variables available for essentially improved control of MMC has to be made accessible and fully used by improved control concepts. Future progress in hardware, especially smaller submodule capacitors, is tightly interrelated to progress of control performance. The same applies to fully electronic fault management and protection at system level, which will be very valuable and important in future. A novel multivariable control concept for MMC, according to these requirements, is presented and explained. Its performance is investigated by extensive simulation results.

Analysis of Battery Fault Tolerance in Modular Multilevel Converter with Integrated Battery Energy Storage System

Abstract: Integrating batteries into modular multilevel converter (MMC) in a distributed manner improves the system reliability. For further reliability, MMC should also work normally in battery fault condition, which can cause serious unbalance of submodule power. In this paper, submodule voltage redistribution based method is proposed to balance submodule power. On the basis, a graphic method is proposed to study the system fault tolerance, which is mainly affected by the percentage of battery power, power factor and capacitor voltage balancing control method. Then an optimized control strategy with high fault tolerance is proposed. Finally, the analysis and control strategy is verified through MATLAB simulation.

Gate Driver Architectures Impacts on Voltage Balancing of SiC MOSFETs in Series Connection

Abstract: In power converter configurations like multi-cell, multi-level, series connection of power devices etc. under very high switching speeds, several dv/dt sources generated at different floating points produce conducted EMI perturbations from the power part to the control part through the many gate driver circuitries. The modifications of the parasitic capacitive propagation paths between the power and the control sides have impacts on the circulating current produced by high dv/dt, which, in turns, affects the voltages distributions (static and transient) among the power devices. This paper presents news architectures for gate drivers power supplies implementations in series connection to minimize parasitic currents, especially reducing the common mode currents and to minimize the unbalance voltages of SiC-MOSFET devices in series connections. Simulations and experiments validate the advantages of the gate driver power supplies proposed architectures on the common mode currents and drain-to-source voltages of series-connected devices.

Advanced Test Circuit for DC Circuit Breakers

Abstract: In future HVDC systems, many DC circuit breakers (DCCBs) will be required. In this paper, an advanced test circuit for DCCBs is described. A DC source is combined with a capacitor bank. In contrast to other test circuits, the proposed test circuit allows to replicate constant DC and temporary faults. In addition to conventional faults, this enables testing of auto-reclosing, proactive commutation, and complex test sequences combining all of these modes. The test circuit is easy to setup and also suitable for smaller research facilities. Experimental results from a down-scaled mock-up are included to demonstrate the capabilities of the test circuit.

Very Fast Short Circuit Protection for Gallium-Nitride Power Transistors Based on Printed Circuit Board Integrated Current Sensor

Abstract: Gallium-Nitride power transistors have a limited short-circuit withstand time, which can be as low as 200 ns. Typical short-circuit detection methods such as the desaturation detection method and current based methods present difficulties when they are applied to Gallium Nitride devices. The former requires a blanking time and therefore can detect a short-circuit at a relatively late stage, this method also reacts slowly under high-inductive short circuits. Current based methods require either a special transistor with a current mirror or a special package with a Kelvin connection. This work presents the use of a current sensor integrated into a printed circuit board to perform a very fast short-circuit detection. Two detection methods using the integrated current sensor were implemented, which neither use a blanking time nor require a special transistor package. The functioning under both Hard Switch Fault and Fault Under Load types of short circuit was experimentally tested and a resulting short circuit detection time as low as 30 ns is demonstrated.

Design of Droop Controllers for Converters in DC Microgrids Towards Reducing Bus Capacitance

Abstract: DC microgrids based on droop-controlled Distributed Energy Resources (DERs) converters tend to have large bus capacitance in order to guarantee stiff bus voltage. Large bus capacitance leads to the increase of weight, size, and cost. Indeed, since the droop control inherently allows the bus voltage to vary in a certain range, there is no need to restrict the dynamic bus voltage fluctuation to such a low level. Thus, as long as the bus voltage is maintained in the acceptable range, smaller bus capacitance can be chosen. This paper firstly gives the design criterion of the output capacitance for DERs converters. Then, the design of droop controllers are presented, so that the output capacitance can be reduced while the bus voltage is still kept in the allowable range during any transient. Since voltage-current ( $V-I$ ) and current-voltage ( $I-V$ ) droop control methods show different characteristics, separate design procedures are introduced for them. Finally, the proposed design methods are validated by means of experimental results performed on a dc microgrid prototype composed of two 3kW converters.

Equivalent Circuit Analysis of an Ultra-Lightweight Motor Designed with Magnetic Resonance Coupling

Abstract: Electric aircraft may reduce the environmental impact of next-generation transportation technologies. In order to put electric aircraft into practical use, the weight of electric motors must be reduced dramatically. To produce an ultra-lightweight motor, we propose a novel motor that eschews the magnetic cores typically used in induction-motor designs. This article studies a motor design that exploits magnetic resonance coupling to transmit power from coil to coil across an air gap efficiently. This article describes the design concept for such a novel motor and formalizes its equivalent circuit. Then finite-element analysis is used to validate that the equivalent circuit represents the behavior of a realistic magnetic resonance coupling motor. The results indicate that the proposed motor can efficiently achieve high-power density, and the equivalent circuit formalized in this article can be used for further analysis in the design of such a motor.

Hybrid Converter With Alternate Common Arm and Director Thyristors for High-Power Capability

Abstract: This paper presents the basic operating principles of a new hybrid converter that combines thyristors and full-bridge (FB) arms for achieving high active-power capability. This converter consists of a modular multilevel converter (MMC) equipped with additional common arms, which alternate between the upper and lower dc poles. This alternation is achieved by the thyristors that are utilized as director switches and allow the parallel connection of the common arms and the arms of the MMC. The main contributions of this paper are the analysis of the operating principles, the simulation verification of the functionality of the proposed converter, and the comparison of the latter with the full-bridge modular multilevel converter (FB-MMC).

Analysis of Device and Circuit Parameters Variability in SiC MOSFETs-Based Multichip Power Module

Abstract: In this contribution, a previously developed temperature-dependent SPICE model for SiC power MOSFETs is calibrated on experimental data of commercially available devices. Thereafter, its features are exploited for dynamic ET simulations of paralleled devices for multichip power module application. Finally, Monte Carlo ET simulations of paralleled devices during switching condition are used to evaluate the expected impact of statistical variation of device and circuit parameters on current sharing and on dissipated switching energy unbalance.

Control Concept for Parallel Interleaved Three-Phase Converters with Decoupled Balancing Control

Abstract: The parallel operation of multiple switches, modules or complete converters allows the realization of power electronic systems with high output currents. However, an equal distribution of the total current between the parallel modules has to be ensured to avoid excessive losses and the saturation of individual inductors. In this paper, a novel current balancing control approach is presented that is decoupled from the output voltage and current controllers and combines the benefits of an intuitive operation principle, simple controller design and low implementation effort. The analysis, discussion as well as the simulative verification of the concept are exemplarily performed for a three-phase four-wire grid connected 10 kVA converter for smart grid applications.

Fixed Frequency Predictive MPPT for Phase-Shift Modulated LLC Resonant Micro-Inverter

Abstract: The variability of the environmental conditions tuned the Maximum Power Point Tracking (MPPT) control to be a fundamental technique for Photovoltaic (PV) systems. The majority of the well-known MPPT techniques are good fitting to conventional (PWM) converters; but they are not suitable for resonant converters applications, as its output gain is frequency dependent. In this paper, a fixed frequency predictive phase shift MPPT technique for the LLC resonant converter. A two-stage Micro-inverter is presented, for grid tied PV applications, employing the LLC resonant converter as the first DC/DC stage, due to it's high power density, high efficiency and the possibility to operate at Zero-Voltage Switching (ZVS) or Zero-Current Switching (ZCS). The second stage is formed from traditional H-bridge Inverter. The proposed control is a fixed frequency predictive phase shift MPPT technique for the LLC converter stage with both fixed and variable steps. To demonstrate the proper operation of the proposed MPPT methodology, a 300 W simulation model for the converter is tested. Hardware prototype is being built in the lab and samples of the experimental results are presented that proves the advantage of the proposed control.

Paralleling of High Power Dual Modules: Standard Building Block Design for Evaluation of Module Related Current Mismatch

Abstract: 3 Abstract This paper discusses the challenges of paralleling dual modules with special focus on the currently introduced half bridge modules with 100 mm * 140 mm footprint like LinPak, ${}_{\mathrm{n}}\mathrm{HPD}^{2}$ , XHP2/3, LV/HV100, etc. Compared to conventional high power converters build up using single switches (e.g. 190 mm * 140 mm footprint) a higher number of paralleled dual modules (by a factor of 3 to 4) is required to achieve equivalent output power, needed e.g. for traction applications. This paper picks up known design features [1], required to avoid design related current imbalance and suggests a reference setup for the paralleling of high power dual modules to focus on current imbalances that are generated by semiconductor device characteristics. This reference setup is based on the uniform basic design idea by the device manufacturers, to put the parallel modules in a row and to design the converter, corresponding to the semiconductor module, as a strip line [2]. Remaining design options are discussed with regard to gate control to conclude with a standardized reference design.

Characterization of Ferroelectric Ceramic Capacitors

Abstract: The fundamental role of the $Q=f(v)$ function in the characterization of ferroelectric ceramic capacitors is delineated and analyzed. Guidelines for reconstructing the $Q=f{v}$ data from manufacturers' data are developed and shown to yield additional information on the capacitors. The analytical derivations were backed by simulation and experimental results. Application of the voltage dependent ferroelectric capacitors as a control element for a fixed frequency series resonant converter was tested by simulation. The results suggest that this proposed approach is viable and that the expected performance is comparable to that of a variable frequency series resonant converter.

A Proposal for Wireless Control of Submodules in Modular Multilevel Converters

Abstract: The modular multilevel converter is one of the most preferred converters for high-power conversion applications. Wireless control of the submodules can contribute to its evolution by lowering the material and labor costs of cabling. However, wireless control leads to many challenges for the control and modulation of the converter as well as for proper low-latency high-reliability communication. This paper investigates the tolerable asynchronism between phase-shifted carriers used in modulation from a wireless control point of view and proposes a control method along with communication protocol for wireless control. The functionality of the proposed method is validated by computer simulations in steady state.

Experimental Comparison and 3D FEM Based Optimization of Current Measurement Methods for GaN Switching Characterization

Abstract: Three high bandwidth current measurement methods to acquire fast switching transients with GaN HEMTs are compared. A 3D FEM (finite element method) simulation is used for analysis and optimization of a very low inductive SMD shunt. The focus is on the use of an FEM simulation in order to adapt the current measurement method to the requirements for GaN HEMTs characterization. The simulation results and optimizations are verified with experimental results. In conclusion, the optimized SMD shunt achieves a high bandwidth (> 500 MHz) with a very small additional inductance in the power loop.