Showing papers presented at "European Conference on Power Electronics and Applications in 2019"

Inverter and Battery Drive Cycle Efficiency Comparisons of CHB and MMSP Traction Inverters for Electric Vehicles

Abstract: This papers investigates the performance of several inverter types for electric vehicles. A standard two-level and two seven-level multilevel inverters, a cascaded H-bridge (CHB) and a modular multilevel series parallel (MMSP) inverter, are considered. Based on the AC impedance spectra measured on a single battery cell, the battery pack impedances of the multilevel and two-level inverter systems are modeled. The inverter losses are modeled using the semiconductors' datasheets. Based on the loss models, the inverter and battery efficiency during different driving cycles are assessed. In comparison to the two-level inverter system, the multilevel inverter drivetrains show an increased drivetrain efficiency, despite increased battery losses. The MMSP topology showed the best result. In comparison to the CHB topology, the battery losses were reduced by the MMSP inverter system.

Fault-Tolerant DTC Technique for an Inverter-Fed Five-Phase Induction Motor Drive with an Open-Phase Fault

Abstract: The direct torque control (DTC) is one of the powerful, simplest, and fast response technique for highperformance industrial drives application. The conventional and virtual vector (VV) based DTC has been successfully extended for the pre-fault operation of five-phase induction motor (FPIM) drive recently. For the fault-tolerant FPIM, the implementation of DTC is a challenging task to operate the motor with loss of one phase (open-phase fault). To eliminate, the distorted stator currents in FPIM with distributed winding, the third harmonic voltage need to eliminate. For this, the VV concept has been used. In this paper, the DTC technique for a two-level inverter-fed FPIM drive with an open-phase fault has proposed with a modified look-up table. It is based on the VVs concept and its theoretical analysis. The theoretical analysis figured out the VVs impact on change in torque as well as flux response with different speed and loading conditions. From this analysis, the modified look-up table has been constructed. The MATLAB/Simulink results are provided to verify the proposed controller effectiveness under the postfault situation with an open-phase fault.

Power Converters Classification and Characterization in Power Transmission Systems

Abstract: Because of the throng of control strategies based Voltage Source Converters (VSC) recently proposed in the literature; their classification and characterization are becoming a trending topic. The high similarities of the proposed control strategies may lead to confusions and a misunderstanding of vocabulary. Therefore, this paper seeks first to highlight the possible features fulfilled by power converters in a large power system. The combination of these features is used to classify power converters. Furthermore, power converters can be seen by a power transmission system operators as black boxes, and they may have the same inputs and outputs, which makes their characterizations more difficult. This paper looks to show that only the fundamental nature of the source has an influence on the system dynamic behavior, thus, power converter can be characterized from their transient behavior in response to grid disturbances.

Investigation of Ship's Power System with Powerful Electrical Propulsion Drive

Abstract: The power of ship's electric systems grows constantly caused by the growing number of electric consumers. Especially powerful are the ship's power stations on ships with electric propulsion. These are the passenger ships, container vessels, gas and marine vessels. The power of propulsion electric motors of this ships reaches several tens of megawatts. The control of propulsion electric motors is done using electronic converters. In this article, it is proposed mathematical model of ship's power system containing 4 diesel generators and azimuttic propulsion electrical system. With the model are investigated the normal and emergency operating modes of propulsion electric system. Conclusions are drawn for the control and protection of ship's power system.

Analytical Calculation of DC-Link Current for N-Interleaved 3-Phase PWM Inverters Considering AC Current Ripple

Abstract: This paper proposes an analytical computation of the rms current flowing in the input DC capacitor of a PWM inverter. For a chosen PWM control, switching angles are computed in order to estimate the spectrum of the input current, which is the key design parameter of the input capacitor. The calculation takes into account the AC current ripple, as it can be important, especially for interleaved inverters. The impact of the neutral connection between AC and DC side is also studied. The spectral repartition of the current in the DC capacitor is shown and compared to simulation results. The impact of the AC current ripple, of the PWM generation and of the number of interleaved level is discussed.

Power Losses of Advanced MMC Submodule Topologies Using Si- and SiC-Semiconductors

Abstract: High power Modular Multilevel Converters (MMC) have become key components for many future application fields, particularly, the efficient use of solar [1]–[5] and wind power resources [6]–[10] and improvement of grid infrastructure (i.e.: multi-terminal HVDC- and MVDC-networks). Further reduction of power losses, capacitor size and footprint of the converters are important issues. Fully electronic failure management and protection are additional important requirements. Main drivers of progress are improved semiconductors (Si and SiC) combined with advanced submodule topologies. The most promising combinations of submodule and semiconductors are investigated and compared by analytical methods – providing general insight. The results clearly show, that essential reduction of power losses and capacitor size are achievable – in addition to fully electronic protection and failure management.

Fully ZVS, Minimum RMS Current Operation of Isolated Dual Active Bridge DC-DC Converter Employing Dual Phase-Shift Control

Abstract: This paper proposes the least possible transformer rms current control strategy to operate an isolated dual active bridge (DAB) dc-dc converter using dual phase-shift (DPS) control. Close-form expressions of converter parameters e.g. average and rms current, active and apparent power are derived for four possible operating modes under DPS control. The Lagrangian objective function is formulated such that apparent power and hence reactive power are truly minimized for the desired active power transfer. As the output power is varied, optimal phase-shift ratios are deduced numerically, which constitute the minimum rms current trajectory. Using the optimal trajectory, a closed-loop controller is devised which employs feedforward control. It obviates the use of a lookup-table-based approach, requiring off-line precomputation of optimal duty ratios. In addition, necessary boundary conditions are also derived to ensures fully zero-voltage switching (ZVS) operation in both active H-bridges of DAB converter. A 4.0 kW, 400/400 V, 25 kHz, isolated DAB converter is simulated in MATLAB/Simulink. At rated output, a maximum reactive to active power ratio (Q/P) of 1.158 and a minimum efficiency of 98.77% are observed, which validates the performance of proposed minimum rms current control strategy.

A Comparative Study on Damping Methods of Virtual Synchronous Generator Control

Abstract: Grid-tied inverters adopting virtual synchronous generator (VSG) control can provide frequency support for the power grid in a similar way to conventional synchronous generators. However, virtual inertia emulation also introduces an oscillatory mode. Various damping methods capable to assign closed-loop poles are proposed in the literature. In this paper, theoretical analyses and experimental results are presented to compare these methods, in respect of dynamic response and ripple attenuation ability.

Classification and review of MTPA algorithms for synchronous reluctance and interior permanent magnet motor drives

Abstract: The MTPA algorithms are attractive solutions for reaching very high energy efficient drives. The paper presents a general formulation of the MTPA problem statement, including also the magnetic saturation in the formulation. A classification and a review of the MTPA techniques is proposed in this paper. A distinctive feature of the proposed classification is the highlighting of the most important characteristics (e.g. needs of motor parameters, signal injection, self-commissioning tests, etc.) of each technique. Also, offline and online techniques are thoroughly discussed. All synchronous motors, with or without permanent magnets, are considered.

RC Snubber Design Procedure for Enhanced Oscillation Damping in Wide-Bandgap Switching Cells

Abstract: This paper introduces an effortless design procedure for resistive-capacitive (RC) snubbers, aiming to damp the oscillations caused by wide-bandgap (WBG) power semiconductor devices in power electronic switching cells. Not only do overvoltages stress the semiconductor devices, the oscillations may also raise electromagnetic compatibility (EMC) issues. Although RC snubbers are popular as damping elements, most existing design strategies are very complex. In this paper, a simple analytical design approach is derived. The resulting closed-form expressions for the snubber parameters ensure maximum damping and enable a well-founded design in very little time. To validate the approach, double-pulse measurements are conducted on a printed circuit board (PCB) with an RC-snubbered WBG switching cell. The experimental results are in good agreement with the theoretical findings.

Quasi-Two-Level Operation of a Five-Level Flying-Capacitor Converter

Abstract: This paper deals with the quasi-two-level operation of a five-level Flying-Capacitor converter. The combination of the quasi-two-level operation and multilevel converters enables several opportunities. The series connection of low-voltage devices allows higher switching frequencies even at high DC-link voltages. The use of intermediate levels decreases the $\mathrm{d}v/\mathrm{d}t$ of the output voltage during the switching transients and improves the voltage spectrum. Furthermore, regarding the flying capacitors, the installed capacitance required can be significantly reduced. The redundant switching states are usually used to balance the capacitor voltages. However, this can be associated with enormous complexity, especially with a high number of levels. This paper considers two methods of voltage balancing for the quasi-two-level operation, which do without the redundant switching states and are based solely on the adaptation of the dwell times of the individual intermediate levels. The first considers the flying capacitors separated so that the change of the dwell time happens independently. However, this leads to a variable $\mathrm{d}v/\mathrm{d}t$ of the output voltage. The second method considers all flying capacitors of a phase together and assigns the dwell time according to the capacitor voltages. This results in an approximately constant $\mathrm{d}v/\mathrm{d}t$ of the output voltage. The functionality of the quasi-two-level operation and the two balancing methods are explained and confirmed by simulation.

Estimation-based Consensus Approach for Decentralized Frequency Control of AC Microgrids

Abstract: In this paper, a decentralized frequency control of ac microgrid (MG) governed by $P-\omega$ droop characteristics is presented. This approach is realized by applying an active power estimation to eliminate the required communication infrastructure in the secondary control layer. The proposed decentralized frequency control is achieved by employing the unique feature of the frequency as a global variable in autonomous ac MGs. By utilizing a consensus protocol, the proposed method restores the MG frequency to the nominal value while maintaining accurate power sharing of the droop mechanism. The consensus protocol is an estimation-based approach and does not require communication infrastructure. Experimental results verified accurate power-sharing and the frequency restoration to the nominal value without any communication requirement.

Exponential Modular Multilevel Converter for Low Voltage Applications

Abstract: This paper presents the structure and control of a single phase Exponential Modular Multilevel Converter (EMMC), which works as a bidirectional AC/DC converter. In addition to the main H-bridge converter, it uses series connected H-bridges with DC link capacitors. The nominal voltage rating of the capacitors is increased with each module by factor of two. In this manner, the number of output voltage levels exponentially increases with the number of series connected H-bridges. By using low-voltage MOSFETs it is possible to achieve a very high efficiency, especially at partial loading. The high number of voltage levels reduces the output voltage THD, while using a low switching frequency. Thus, the required grid filter size can be substantially reduced. Furthermore, the additional capacitor modules increase the nominal output voltage at the AC side, so that the flow of the active and reactive power can be dynamically adjusted. Therefore, the EMMC could be used, for instance, as a vehicle charger directly connected to the grid.

Power cycling results of high power IGBT modules close to 50 Hz heating process

Abstract: The dominating heating time of power semiconductor devices in 50 Hz grid connected converters in applications such as renewable energies (wind or photovoltaic) or high voltage direct current transmission is 10 ms, since the conduction losses created by the 50 Hz AC component are dominating. In the power cycling test, a heating time of several seconds is however usually used, which may trigger different failure mode and deduce a wrong lifetime. For a precise lifetime prediction of power semiconductor devices in such applications, power cycling test with heating time and temperature swing closed to the application condition is necessary. Experimental results for 10 ms heating time at small temperature swing with more than 500 million cycles to failure are presented in this paper for the first time.

Online Parameter Identification of Permanent Magnet Synchronous Machines with Nonlinear Magnetics based on the Inverter Induced Current Slopes and the dq-System Equations

Abstract: This paper shows a fast online parameter identification method for permanent magnet synchronous machines (PSMs), which uses the PWM (pulse width modulation) excitations and no additional test signals. Based on the inverter induced current slopes, the corresponding applied voltages, the rotor angle and a precise machine model, the model's parameters are calculated. Thereby the machine model consists of the dq-system equations, linearized within one PWM period. For stable and precise identification of the PSM machine parameters, the machine model has to be modified with a regularization approach. The identified parameters enable self-commissioning, tuning of the control parameters, condition monitoring or inner fault detection. In this paper the theoretical approach of the suggested method and simulation results of an equivalent test-bench system are presented.

An Intelligent Diagnostic Method for Permanent Magnet Synchronous Motors (PMSM) in the Electric Drive of Autonomous Vehicles

Abstract: In highly automated electric vehicles, the reliability of electrical powertrain system is very important. A critical failure in the powertrain system, e.g. electric machine, would lead to breakdown of the vehicle. To avoid this dangerous situation, the critical faults should be detected at an early stage. This paper focuses on three common faults in the stator of a permanent magnet synchronous machine (PMSM). Based on analytical models, the physical behaviors of the electrical machine within these three faults are analyzed. Then, a data-driven diagnostic method, artificial neural network(ANN), to detect and classify these faults is presented. Simulation data of electric machine under healthy and faulty conditions as well as at different operating points are used to train the ANN model. The three phase currents of PMSM and the inverter input current are selected as input signals of model. Various features in time domain(e.g. average, maximum,…) and frequency domain(e.g. 2nd, 3rd harmonics) are extracted from the selected signals. The result shows that the fault diagnostic model is capable of classifying the faults with near perfect accuracy over 98%, even in case of slight fault. Finally, a driving cycle simulation is used to validate the robustness of the ANN model in dynamic driving situations.

A low-cost, high-power-density DC-DC converter for hybrid and electric vehicle applications

Abstract: A 400 V to 12 V soft-switching DC-DC converter is designed to supply power to the low-voltage system of the hybrid and electric vehicle from the high-voltage battery. The use of soft-switching topology, SiC MOSFET and an optimised design of the transformer and filter inductors enables a low profile layout for the converter. Optimised layouts of the components increased its volumetric and specific power density over the commercial state-of-the-arts and ensured a simple construction process. The 3.5 kW converter achieved a volumetric power density of 2 kW / litre and a specific power density of 1.2 kW / kg. The prototype converter operated at 3.6 kW, 150 kHz, 425 – 13 V and achieved 87% efficiency. Experimental results from 100 W to 3.6 kW operations verified the superiority of the soft-switching topology over hard-switching operations.

Analytical design considerations for MVDC solid-state circuit breakers

Abstract: This paper investigates the design principles of a solid-state circuit breaker (SS CB) for medium voltage direct current (MVDC) grids. The emphasis is given on the design of the required active and passive components that employed in a SS DCCB based on analytic methodology. Several cases related to the characteristics of the current technology of power semiconductor devices have been investigated and evaluated in terms of maximum short-circuit current, maximum switch current, maximum switch voltage, clearance time, as well as, passive elements requirements. It has been shown that potential improvements of the current power semiconductor technology could lead to improved performance of SS DCCB with lower requirements for passive elements. In particular, the most significant characteristic that improves the overall SS breaker performance was found to be a potential reduce of the falling time (or increase of power dissipation) of the switches used in SS breaker.

Aging Effects of Twice Line Frequency Ripple on Lithium Iron Phosphate (LiFePO 4 ) Batteries

Abstract: The charge/discharge current profile is one of the most important factors that affects the behavior of lithium-ion batteries (LIBs). Most of previous studies evaluate the behavior of LIBs under pure constant current conditions, when in reality battery packs in arguably the most important applications experience alternating currents (AC), superimposed on DC components. So-called ‘ripple currents’ commonly present at twice line frequency (i.e., 100/120 Hz) and their presence forces designers of single-phase AC-DC converters to incorporate a large DC-link capacitor into these devices. And yet, all this effort presupposes that AC ripple constitutes a serious problem, when it is still unclear to what extent the LIB lifetime may be reduced by the presence of 100 Hz ripple current. While many studies claim that AC harmonics accelerate the degradation of LIBs, there are others that refute this. Different chemistries of LIBs have been included in these studies, however, a systematic study on cells with LiFePO 4 (LFP) as the cathode material, considered as one of the most promising chemistries in many different applications, has not been done yet. This paper presents the results of a detailed and systematic experimental study on aging impacts of 100 Hz-ripple currents on 13 fresh LFP cells. The degradation of the cells is characterized based on capacity fade and impedance rise. The results show that the superimposed 100 Hz ripple currents do not cause a significant amount of degradation on LFP cells. This means that in many inverters, the size of the DC-link capacitor is probably excessive, thereby allowing a marked reduction in size of this expensive system component.

A Comprehensive Analysis of Voltage to Ground of Floating Submodule for MMC

Abstract: Modular multilevel converter (MMC), which are widely used in VSC-HVDC transmission systems, is usually composed of numerous submodules (SMs) whose voltage are floating in respect to ground. During the commutation transient, high dv/dt for SMs will cause common-mode current to flow into the ground through parasitic capacitors, resulting in conducted EMI. Due to the large number of SMs for MMC, the SMs at different positions have different voltage to the ground, and the voltage jump to the ground of the SMs are also affected by the operating conditions. Therefore, this paper comprehensively analysis the change rules of voltage to ground for SMs under different operating conditions and identify the sensitive SMs with respect to dv/dt. The relevant simulation results can verify the analysis results for the position of the sensitive SMs and the voltage jump rules for SMs under different operating conditions. Furthermore, a double-pulse test of SM is implemented to verify that the common-mode current is conducted when the SM is switching.

System-Level Motor Drive Modelling for Optimization-based Designs

Abstract: To achieve optimal system weight and efficiency, the design of main components in an AC motor drive (electric machine and power converter) have to be optimized together. This is challenging considering the multiphysics and complex nature of its operation and interactions between the components. There are few papers that address a formal approach towards this design optimization for motor drives at a system-level. This paper aims to fill this gap by presenting a fast and accurate system-level motor drive model, for use in an optimization-based design approach. At a system-level, the presented model is able to consider several aspects of machine-converter interactions. The model is fully analytical, making it very computationally efficient, and its accuracy is validated using a back-to-back motor-drive test setup.

Measuring and Modeling of Dynamic On-State Resistance of GaN-HEMTs

Abstract: GaN-HEMTs as switching devices impress with their very good properties and gain therefore a lot of attention from the power electronics community. However, some GaN devices may exhibit increased resistance during on-state due to charge trapping effects. As for designers of switch mode power supplies the internal structure of devices is concealed, measurements are the only way to gain information. This paper shows the measurement of the static on-state resistance of a GaN-HEMT. Furthermore, it quantifies the dynamic on-state resistance by measurement with a novel clamping circuit using a digitizer card with high resolution. Based on these results, it presents an easy to implement method for calculating conduction losses in the presence of dynamic on-state resistance.

Economic Dispatch by Secondary Distributed Control in Microgrids

Abstract: This paper proposes a distributed controller in order to achieve the economic dispatch (ED) of a microgrid, which complies with the Karush-Kuhn-Tucker optimality conditions for a linear optimal power flow formulation. The consensus over the Lagrange multipliers allows an optimal dispatch without considering an electrical microgrid model, preserving the frequency and voltage restoration into the secondary control level for isolated microgrids.

650 V SiC Trench MOSFET for high-efficiency power supplies

Abstract: This work introduces a new SiC Trench MOSFET technology with 650 V nominal blocking voltage. The technology is tailored to address the needs of power supplies in the power range from several hundred watts to some tens of kilowatts including server and telecom switch-mode power supply (SMPS), solar inverters and electric-vehicle charging. These applications benefit strongly from power semiconductors that serve high switching frequencies, enable fast switching under hard-switching conditions, and provide low conduction losses as well as a small output and reverse-recovery charge. The MOSFET technology introduced enables new, highly efficient topologies such as the full-bridge totem-pole in the power-factor correction (PFC) stage. The paper further presents long-term reliability data and performance evaluations indicating a possible absolute PFC stage efficiency of 99%. Such an efficiency is essential to gain an overall system efficiency of 98%.

Thermal Characteristics and Simulation of an Integrated GaN eHEMT Power Module

Abstract: Compact power modules are emerging which combine both direct bonded copper (DBC) and printed circuit boards (PCB) in integrated structures to achieve fast switching of wide bandgap semiconductors. The literature presenting the new integrated structures only include the DBC in their thermal analysis, and thus the influence of the PCB is often disregarded. In this paper the thermal characteristics of a new integrated GaN eHEMT power module are obtained experimentally. A simulation workflow to extract the thermal characteristics of the integrated module structure using finite element method software is presented and verified. The results predict an error of up to 13% in thermal impedance if the PCB board is not included in the simulation model.

A new, universal Series Hybrid Cascaded H-Bridge Converter for Power-Hardware in the Loop Emulation

Abstract: This paper presents a new Series-Hybrid Cascaded H-Bridge (SH-CHB) Converter for Power-Hardware in the Loop (PHIL) systems. The converter combines the benefits of CHB-Cells, high power density and high system efficiency, with the advantages of Linear Power Amplifiers (LPA), high bandwidth and high fidelity. The introduced system is used to emulate different AC-grids as well as DC-grids with simultaneous supply of sinusoidal test signals for impedance spectroscopy of converters. The system provides sinusoidal test signals up to 105 kHz with a three-phase output AC voltage of 400 V or a DC voltage of 1000 V. The maximum output power of the system is 60 kVA.

Model Predictive Pulse Pattern Control with Integrated Balancing of the Neutral Point Potential

Abstract: A neutral-point-clamped inverter operated with optimized pulse patterns is considered with an induction machine. For this setup, a control method is proposed that achieves high-bandwidth control of the electromagnetic torque and machine magnetization through stator flux trajectory tracking while balancing the inverter's neutral point (NP) potential. More specifically, a model predictive pulse pattern control problem is formulated and solved that addresses stator flux control and balancing of the NP potential in one single control loop. The proposed controller achieves minimal current distortions per switching frequency and is thus well-suited to medium-voltage power converters operating at low pulse numbers.

Comparison between a bearingless PM motor with separated and combined winding for torque and lateral force generation

Abstract: This work compares two geometrically identical bearingless permanent magnet synchronous machines in a slotted cylindrical design, one equipped with two separated torque and suspension windings and one equipped with a single combined winding. It is found that the combined winding is superior in terms of thermal utilization and manufacturing effort.

Expansion of the Junction Temperature Measurement via the Internal Gate Resistance to a wide range of Power Semiconductors

Abstract: The temperature dependent internal gate resistance R gi of MOS devices is suitable for online $T$ j acquisition in operating application circuits. Recent publications have shown various measurement approaches and tested them for specific DUTs. In this work the issues arising when applying the Rgi-method to DUTs with a low Rgi and to SiC MOSFETs are described. If a device exhibits a low Rgi the measurement error due to parasitic resistance becomes relevant. For SiC MOSFETs frequency dependent effects, which can presumably be attributed to charge trapping at the gate oxide, have a significant influence on the measured data.

Performance Evaluation of Wideband Binary Identification of Grid Impedance Using Grid-connected Inverters

Abstract: The application of the pseudo random binary sequence (PRBS) estimation technique for wideband grid impedance estimation using grid-connected inverters has gained more attention recently because of its several advantages. This includes its simple implementation in the control loop of the inverters and the small disturbance amplitude produced. In this context, this paper aims to evaluate the performance influences of the PRBS design parameters bit length, frequency resolution, and disturbance amplitude. This goal is achieved by exploring their effects on the grid impedance estimation accuracy and the produced total distortion (THD%+PRBS noise) of the inverter output current. A 3-phase balanced inverter system is simulated and investigated using MATLAB/Simulink based on a discrete-time model to show the trade-off of a real implementation such as the PRBS disturbance amplitude and the sampling frequency of the analog-to-digital converters. Simulation results show the trade-off between the investigated PRBS parameters and the accuracy and frequency range of the estimated grid impedance as well as the total distortion.