Showing papers presented at "European Conference on Power Electronics and Applications in 2021"

Proactive SoC Balancing Strategy for Battery Modular Multilevel Management (BM3) Converter Systems and Reconfigurable Batteries

Abstract: The battery modular multilevel management converter topology and different types of reconfigurable battery topologies have been proven to be a viable option for various electric power applications. This paper presents a unique SoC balancing approach for the integrated battery strands/packs of BM3 converter systems or reconfigurable batteries. The suggested approach alternately utilizes different redundant switching state combinations to balance and to keep the battery strands’ SoCs balanced. Furthermore, the suggested algorithm attempts to utilize all converter modules, because the parallel connection of adjacent modules reduces the phase-strand’s battery impedance. Furthermore, the presented approach tries to reduce the number of switching events when changing the switching state combination. Thereby, the ohmic battery losses and switching losses are kept as low as possible. Since no power is dissipated in designated bleeder resistors and no designated active balancing circuitry is required, the suggested approach can be categorized as a proactive balancing approach. Simulations are used to verify the algorithm’s validity.

Charging Strategy for Battery Electric Vehicles with a Battery Modular Multilevel Management (BM3) Converter System using a PR controller

Abstract: Modular Multilevel Converters (MMC) with integrated battery packs have been proven to be a viable option for various electric power applications. In novel applications, fully charged battery packs are used to form flexible output voltage waveforms. Nonetheless, the charging of the batteries after the actual usage has previously not been described for MMC based inverters with integrated battery packs. This paper presents an approach of power grid compliant electric vehicle battery charging for Battery Modular Multilevel Management (BM3) converter systems with three-switch modules using a PR controller when directly connected to the AC grid. By using such a system, the conventional battery electric vehicle’s on-board charger and any additional battery balancing circuitry become obsolete. It is demonstrated, that the analyzed approach is able to charge the battery modules with a current total harmonic distortion of less than 5% at any charging power level without the usage of a dedicated grid filter. Furthermore, the power factor angle can be freely adjusted.

Current Sharing of Parallel SiC MOSFETs under Short Circuit Conditions

Abstract: Device-to-device parametric variations (e.g. threshold voltage V TH , gate resistance R G and junction temperature T J ) can cause variations in the short-circuit currents conducted through parallel-connected devices. In this paper, the impact of variations in V TH , R G and T J on current sharing under short-circuits is investigated using measurements and electrothermal modelling. The results show that V TH is the most critical parameter affecting short-circuit current sharing and directly impacts the peak short circuit current. Variations in gate resistance do not impact the short circuit current sharing unless the variation is over 400% thereby indicating catastrophic failure of the gate wirebond. Variation in the initial junction temperature is also not as critical as variations in V TH since the higher temperature device takes less short circuit current. Electrothermal simulations of parallel connected SiC MOSFETs have been developed to analyze how V TH mismatch impacts short circuit current sharing. These simulations allow for the investigation of the impact of V TH mismatch on the electrothermal stresses of the parallel connected MOSFETs.

Comparative Analysis of High Speed Drive Inverter Designs using different Wide-Band-Gap Power Devices

Abstract: In this paper, a 15 kW drive inverter design with increased switching frequency demand for the high-speed drive of an automotive electrical turbo-compressor unit is described. After comprehensive simulation-based evaluations eight inverter prototypes using different wide-band-gap power semiconductor devices are built and operated. With the aggregated measurement results the simulation models are refined and the inverter design is optimised in terms of efficiency, power density and its thermal characteristics. Finally, a fully functional drive inverter prototype is built.

Fuzzy-based energy management system for isolated microgrids using generation and demand forecast

Abstract: Energy solutions based on sustainable microgrids have been increasing since isolated areas with difficult access can benefit from these feasible solutions. In this context, this paper presents the design of an energy management system based on a fuzzy logic controller for an isolated microgrid composed of a diesel generator, a photovoltaic generator, and a battery energy storage system. The management strategy uses generation and load forecasting to anticipate the future behavior of the microgrid, while considering that the battery state of charge is within safe limits. The main objective is to maintain an average value of the battery state of charge around 75% of its nominal capacity to improve and extend its lifetime. Three different scenarios are performed to provide electric power solutions to an isolated community in Ecuador, and the results are compared with a management strategy without forecasting. The results show that generation and load forecasts help the system to deal with constant load variations, avoiding many times that the battery state of charge reaches the safety limits. At the same time, the proposed strategy reduces the production of wasted diesel power.

Investigation of 3D printed polymer-based heat dissipator for GaN transistors

Abstract: GaN transistors are limited in their operational capabilities due to some limitations, of which the thermal management aspects. Until now, most of the existing heat-dissipator systems using additive manufacturing (AM) are based on a metallic finned heat sink, which is heavy and has a relatively high thermal resistance. Heat dissipation based on a phase change as operated in heat pipes is more efficient. Such heat sinks have been experimented with metals or ceramics and not by now with polymers. However, this may be of great interest. The use of polymer may enable reducing weight and cost of the thermal device. It may allow also improving the chemical compatibility of the heat pipe material and fluid, as this is often a severe issue. This work presents a characterization of a 3D-printed polymer-based heat pipe evaporator intended for GaN transistors. The electronic copper circuit on the polymer surface is created using plastronics technology. The metallized circuit presents an adequate electrical conductivity. The thermal characterization performed with the HFE 7000 fluid, shows that it is actually possible to cover the entire heated polymer wall with active nucleation sites once the full developed nucleate boiling regime is reached. The heat conduction through the insulating polymer wall appears as the limiting phenomenon for heat transfer.

Medium Voltage Power Electronic Building Block for Quasi-two-level Operation of a Flying Capacitor Converter

Abstract: Today’s standard medium voltage converters are operated at low switching frequencies and contain bulky line filters. One concept to change this is the Quasi-Two-Level operation of multilevel converters with fast switching semiconductors to minimize passive components. This paper presents the hardware of a full-scale medium voltage SiC-based flying capacitor converter for quasi-two-level operation with up to 10kV DC voltage and 150A line current. This hardware enables studies on the influence of components, modulation principles and control algorithms on the needed filters and the operation of the converter.

Accuracy Study of Calorimetric Switching Loss Energy Measurements for Wide Bandgap Power Transistors

Abstract: Despite soft-switching topologies and modern wide bandgap power semiconductors, switching loss energy is still significant in power electronic application but too small for characterization with electrical measurements. In contrast calorimetric measurements of the soft-switching energy of a commutation cell have been successfully demonstrated for different power classes and semiconductor technologies. In particular, the transient calorimetric measurement method calibrated by thermal impedance (Z th -calibrated) promises an extremely fast and non-invasive loss characterization in a wide power range without modification of the half-bridge. This enables automated determination of the switching behavior and losses over the entire operating point range of different switching voltages and switching currents in a reasonable time frame compared to other thermal measurement methods. Furthermore, it promises to greatly reduce the requirements on the measurement setup in terms of thermal insulation and the integration of temperature sensors.Purpose of this work is to investigate the accuracy of Z th -calibrated calorimetric measurements and to estimate the influence of measurement duration, temperature sensing and thermal insulation, which so far prevent simple application-oriented characterization. Therefore, a gallium nitride (GaN) high-electronmobility transistor (HEMT) half-bridge is used to derive the loss measurement accuracy of different temperature sensors and the modeling of junction temperature dependend on resistance by comparing it to conduction losses that are electrically easy to determine. In addition, the worst-case accuracy of the switching energy calculation based on multiple power dissipation measurements with different switching frequencies is presented.

Design Methodology for Ultra-Compact Rogowski Coils for Current Sensing in Low-Voltage High-Current GaN Based DC/DC-Converters

Abstract: This paper presents a design methodology, verified by measurements, of a differential Rogowski coil based compact, high bandwidth (> 500 MHz) PCB embedded current sensor for minimal invasive sensing (insertion inductance ≈ 200 pH) of transistor and phase currents in 48 V mild-hybrid Gallium Nitride based DC/DC-converters with paralleled transistors for high output currents. Two different sensor concepts with and without a planar shield are described and investigated. More than 30 designs with different winding number, structure and pitch are analyzed in 3D-finite element simulations. Finally, a standalone Rogowski-coil sensor for transistor current and a combination of a magnetoresistance sensor and a Rogowski-coil for phase output current measurements are presented.

Analytical eddy current loss model for foil conductors in gapped cores

Abstract: For modelling and optimizing gapped high-frequency inductors, the calculation of eddy current losses in foil windings due to the two-dimensional fringing field caused by air gaps in the core is important. The winding loss models must offer a high accuracy when calculating the 2D field distribution and must be computationally efficient in order to enable several thousand calculations required during the optimization. This article proposes an analytical model based on the magnetic vector potential formulation that can predict the eddy current losses in foil windings due to the fringing field of an arbitrary number of air gaps. The analytical model is combined into a closed-form loss formula and verified by FEA simulations.

FEM-based Parameter Estimation for a Variable Phase-Pole Induction Machine

Abstract: In this paper, lumped parameters for a variable phase-pole induction machine with wound independently controlled stator coils are computed using finite-element simulations. Differently from finite-element simulations of conventional electrical machines, this solution uses a per-solenoid approach.

Reliability analysis of the bus-bar systems in multiterminal HVDC systems

Abstract: In this paper, novel scrutiny of different types of bus-bar configurations is carried out to support the design of the system taking into account reliability aspects. The selection process of proper bus-bar configuration is dependent on several aspects which are: the degree of reliability, degree of security, cost, maintenance, operational flexibility, and safety as well as the selected fault DC grid protection strategy. The evaluation is carried out by evaluating the impact of different bus-bar topologies and DC fault clearing strategies on system overall reliability by considering equipment failures. In this assessment, switching and reconfiguration events are reflected to reveal realistic numerical results. At the end, a comprehensive comparison amongst different bus-bars is carried out from system point of view that highlights the level of reliability of various bas-bar configurations.

Dead Time Management in GaN Based Three-Phase Motor Drives

Abstract: This paper deals with the dead time selection in Gallium Nitride (GaN) FET based three-phase brushless DC motor drives. The GaN wide-bandgap (WBG) technology enables the increase of the switching frequency compared with silicon MOSFET. In inverter applications, it is necessary to insert a dead time in the switching signals, to avoid cross conduction in the inverter leg. The dead time selection is a compromise between the switching time and the quality of the inverter output waveforms. GaN FETs can operate with dead times in the range of tens of ns. In this paper the advantages of the GaN technology in the reduction of dead time in terms of output waveforms distortion and speed ripple compared with silicon MOSFET are carried out. Furthermore, an evaluation on the dead time compensation technique compared with the hardware technology reduction is investigated demonstrating the effectiveness and the saving of software and hardware resources obtained by GaN FET devices.

Design and Analysis of a Fully-integrated Planar Transformer for LCLC Resonant Converters

Abstract: The isolated LCLC resonant converter needs five discrete passive components including two capacitors, two inductors and a transformer. In this paper, to cut down the number of components of this converter, a new design for a high-frequency transformer is proposed which integrates all the five magnetic and capacitive components in only a single magnetic device. The series capacitor and inductor are integrated into the primary winding and the parallel capacitor and inductor are integrated into the secondary winding. The design guideline for this transformer is presented in detail and theoretical analysis is confirmed by simulation results.

Lifetime Extension of Power Semiconductor Devices by Closed-Loop Junction Temperature Control

Abstract: The lifetime of power semiconductor devices is mainly affected by the thermal stress they are exposed to. Especially temperature swings damage these devices due to different coefficients of thermal expansion of the material layers inside the device. This leads to mechanical strain between these layers. This paper proposes a closed loop junction temperature control system, which is able to reduce occurring temperature swings in order to reduce the damage and to extend the expected lifetime. An online junction temperature measurement is required in order to obtain information about the real-time temperature. This is realized by measuring the temperature sensitive on-resistance of the used MOSFET. Then, the junction temperature is estimated with a calibration curve. Another requirement is the possibility to influence the junction temperature during operation. Therefore, the switching frequency is varied to affect the switching losses. This influences the junction temperature. In addition, a set-value generator is presented, which generates suitable set values to reduce temperature swings.

A new topology of resonant inverter including a piezoelectric component

Abstract: This document introduces a new resonant inverter topology based on the Φ2 inverter. This new topology uses multiple resonance to pass fundamental and third harmonic at the switch terminals by filtering second harmonic with a piezoelectric component. This helps to reduce the voltage stress on the switch. Adding a piezoelectric resonator allows a better frequency stability and a better performance than a classic LC circuit. The structure and the design of the topology are described. Experimental results demonstrating the feasibility of the topology and a comparison with simulation results are done. The prototype works at 1.4MHz for an input voltage of 20V, an AC output voltage of 20V and an output power of 15W.

Battery electric vehicle (BEV) powertrain modelling and testing for real-time control prototyping platform integration

Abstract: This paper presents a method to virtually evaluate the performances and energy consumption of a battery electric vehicle (BEV) powertrain, whose propulsion is assured by a wound rotor synchronous machine. For that, the powertrain’s subsystems are modeled using Energetic Macroscopic Representation (EMR) concept and adapted for later implementation in a real-time control prototyping platform. Two levels of complexity are developed for the propulsion motor, resulting in two BEV powertrain models. The resulting powertrain models are validated by comparing the simulation results with the experimental measurements obtained from a real Renault ZOE Q90 car. In order to evaluate the accuracy of the models under study, two driving cycles profiles, a mixed urban and extra-urban profile and a highway one, are chosen to characterise the system behaviour under normal and maximum vehicle speed conditions. Furthermore, as the developed powertrain is dedicated to real-time applications, the simulation time of the two proposed models are compared in order to choose the one that computes results with desired accuracy in a reduced amount of time.

A Fast Short-Circuit Detection and Protection Method for Wide Band-gap Devices based on Current Derivative Sensing

Abstract: Over the years, robust Short-Circuit (SC) detection and protection methods have been developed for silicon (Si) devices, such as Si Insulated Gate Bipolar Transistors (IGBT) or Si Metal Oxide Field Effect Transistors (MOSFET). The emergence of Wide Band-Gap (WBG) devices as Silicon Carbide (SiC) MOSFETs and Gallium Nitride (GaN) High Electron Mobility Transistors (HEMT) brought the need of new protection methods. Indeed, the SC ruggedness of WBG devices is much lower than their Si counterparts. Moreover, the high switching speed of SiC and GaN devices requires special care regarding switching cell design. Indeed, reduction of parasitic inductance is a key parameter to fully take advantage of such components. However, low switching loop inductance can lead to very short transient before reaching the peak current during short-circuit (several hundred of Amps in few nano-seconds), making some usual SC detection methods inappropriate. On one hand, the most common method being the DeSat, may not be used as it stands for GaN. Indeed, the inherent delay time of these methods are inadequate. On the other hand, methods that are using direct current measurements, such as shunt, are also inappropriate due the degradation of the switching cell, being a key point with GaN devices. This paper proposes a fast analogue short-circuit detection and protection method for WBG devices, in particular GaN devices. The proposed circuit relies on current derivative sensing method. In fact, the current derivative pattern varies in case of short-circuit. The signal coming from the current derivative sensors is used to trigger the protection circuit placed as close as possible to the power device, shortening the protection delay time.

An Analytical Switching Loss Model for a SiC MOSFET and Schottky Diode Half-Bridge Based on Nonlinear Differential Equations

Abstract: An accurate analytical switching loss model for a SiC MOSFET and Schottky diode half-bridge for a wide operating range is proposed in this paper, which is based on nonlinear differential circuit equations including parasitics. In the model, nonlinear device characteristics are used, including the dynamic gate-drain capacitance and the transfer characteristics measured under real switching conditions. With the proposed model, the accuracy improvement by using measured characteristics instead of device data sheet information is analyzed. In addition, the impact of making different common assumptions/simplifications on the accuracy of switching loss models is evaluated.

Demonstration of a Compact Hard-Switched 3.5 kW DC/DC Converter utilizing Planar Magnetics optimized for low Capacitive Loss

Abstract: It is necessary to accurately determine the power losses in a converter to obtain a high efficient design. This paper presents an in-depth analysis of all the power losses in a converter. The capacitive loss of the transformer and switches is investigated. A highly efficient 7:1 planar transformer is presented and the design is carefully interleaved to provide a small differential-mode capacitance and AC-resistance. Very accurate finite element simulations of the transformer equivalent circuit parameters are performed using Ansys Maxwell. A compact 3.5kW hard-switched isolated full-bridge forward converter is constructed with a power density of 9.9kW/L when the heatsink is excluded and 6.4kW/L when the heatsink is included. The calculated and measured peak efficiency of the converter is in close agreement with 98.0% and 97.7% respectively, thereby proving the accuracy of the power loss calculations.

Deadbeat Flux Vector Control with Continuous Transition from Linear to Overmodulation including Six-Step Operation Considering the Voltage and Current Limits by Applying One Single Control Law

Abstract: Six-step operation of interior permanent magnet synchronous machines (IPMSMs) has many advantages such as the full utilization of the DC-link voltage and the minimization of the switching losses. Deadbeat Flux Control (DBFC) is a control strategy designed to achieve overmodulation and six-step operation with competent dynamic performance. This paper presents an upgraded implementation of the DBFC controller. One unique control law can operate in the entire torque-speed plane with a simple methodology for continuous and smooth transition between the four different operating regions (i.e., linear, overmodulation I, overmodulation II, and six-step), and under voltage and current limitations. Combining multiple controllers and switching between different control laws is completely avoided. This paper presents an approach for closed-loop torque regulation that has high dynamic performance, high accuracy, and is robust against parameter variations. The proposed controller is evaluated in simulation and experimentally. It is implemented on an automotive microcontroller for a 300 kW IPMSM traction drive.

Cooperative Power Conditioners for Microgrids in Mining

Abstract: This paper proposes a cooperative control scheme for power quality compensation, exploiting the remaining capacity of power electronics converters typically used in microgrids for active power supply. Consensus terms are proposed to mitigate imbalances and harmonics in a mining-industry microgrid. In contrast to the classical approach, cooperative power compensation uses not only information from local loads, but also information from neighboring compensators and power sources. Simulations show that the proposed cooperative scheme reduces the unwanted power components similarly than the classical approach, but also turns the system robust to communication network changes and converters saturation.

Comparison of Reverse Conducting IGBT Concepts regarding Reverse-Recovery Behavior and Gate Drive Requirements

Abstract: Reverse Conducting IGBT use n-shorts at the backside emitter to allow conduction of the body diode of the MOS structure. The p-well of the MOS cell acts as an anode of the diode. The anode efficiency strongly depends on the gate-emitter voltage. There are different concepts on how to deal with this behavior. This paper describes the influence on the static and dynamic diode behavior and the consequences for the gate drive.

Battery Management System Evaluation within a Complete Electric Vehicle Model with Software-in-the-Loop and Hardware-in-the-Loop Approaches

Abstract: A detailed battery pack model has been developed within Simcenter Amesim by Siemens Industry Software. The model illustrates the Battery Management System (BMS) control development process from Model in the Loop (MiL), Software in the Loop (SiL) to Hardware in the Loop (HiL). The battery pack model has been integrated in a validated vehicle model, which corresponds to an existing vehicle developed by Voltia, named the Voltia eVan. This originally diesel engine powered light duty trucks have been electrified. The electrified version has been tested on the roller bench at the Eindhoven University of Technology.The interest of detailing the battery pack model is to have access to a multiple virtual temperature and voltage sensors, which allows validating the balancing methodologies that could be integrated in a BMS. A real-time analysis of the model has been conducted to ensure the model is compatible with the control constraint of the BMS.Finally, the complete model has been connected to a functional BMS in order to validate the approach. For that purpose, several BMS functions have been implemented in the control model developed with MATLAB/Simulink, such as the state of charge (SOC) estimation, the cell balancing, the charge/discharging and the thermal management. Once the cosimulation in SiL environment has been validated, a test on HiL platform has been done in real-time condition in order to reproduce realistic cell balancing and to study charging strategies, which are key functions to ensure better lifetime of the battery.

Hybrid Power System Optimization for Microgrids

Abstract: The paper deals with design of hybrid optimization based on cyber physical power system (CPPS) for microgrids. An adjustable multilevel inverter is developed. From only one power converter circuit, the developed topology allows working in five levels or in four levels according to the applied control strategy. The main interest of this system is the use of power optimization system based on genetic algorithm approach for medium and high voltage applications in the target to have an excellent power quality and less electromagnetic perturbations with hybrid offline/online optimization.

Verification of the Analytical Torque Calculation and Active Weight Optimization for a Scalable Axial Flux Motor

Abstract: A novel motor concept of a scalable axial flux motor with U-core plates (AxMDM) and a GRP (glass fiber reinforced plastic) disk rotor was developed. In this paper, the verification of the analytically calculated torque for the AxMDM is shown. It is also shown that a miniaturization of the U-core lamination improves the ratio of torque per active weight.

Online identification of semiconductor switching times in inverters with inductive load using field programmable gate arrays

Abstract: The nonlinear behavior of inverters is mainly influenced by the interlocking and switching times of the semiconductors. In the following work, a method is presented that enables the possibility of an online identification of the switching times of the semiconductors. This information allows a compensation of the non-linear behavior, a reduction of the locking time and can be used for diagnostic purposes. First, a theoretical derivation of the method is made by considering different cases when switching of the inverter and deriving identification possibilities. The method is then extended so that the entire module is taken into account. Furthermore, a possible theoretical implementation is shown. After the methodology has been investigated with possible limitations, boundary conditions and with respect to real hardware, an implementation in the FPGA is performed. Finally, the results are presented, discussed and further improvements are presented in an outlook.

Modelling and Control of a Power Flow Controller for DC Microgrids

Abstract: This paper presents a state feedback control method for a power flow controller for meshed DC micro-grids. A modular generic dynamic model of the system is proposed. This model is augmented with integrators and linearised, and a state feedback control law is proposed to define the duty cycles for the PWM switching of the IGBTs. The power in each line and the voltage of a reservoir capacitor in the converter are directly controlled. The validity of the proposed model and control law are assessed on an experimental setup.

Reliability and Cost Assessment of Fault-Tolerant Inverter Topologies for Multi-Motor Drive Systems

Abstract: Automotive x-by-wire (XBW) systems require the development of cost-effective, compact, and reliable motor drive solutions. With the multiport inverter architecture, it is possible to improve on these aspects. In this paper inverter fault tolerance strategies are first reviewed, and proper ones are selected. The strategies are then applied to single-input multi-output (SIMO) inverter topologies and 2, 3 and 4 motor systems are considered. Next, the cost and reliability of the resulting topologies are assessed and compared. Finally, the suitability of these topologies considering automotive applications requirements is discussed. It was found that the leg redundant strategy is the most suitable one and that the cost and reliability are both improved when that strategy is applied to SIMO topologies. The improvements are also more significant for a higher number of motors. The conventional combined topology was found to be the best for general XBW systems but in special applications the shared-leg topology can be a better solution.

Reduction of Common Mode EMI Emissions by Optimizing the Planar Transformer of Phase-Shifted Full-Bridge DC/DC Converters

Abstract: An increasing number of isolated converters are designed with planar transformers to reduce the size of the converters. These highly integrated transformers usually have flat windings with a large surface which results in high parasitic capacitances in the transformers. One of the main common mode EMI paths in isolated DC/DC converters are the inter-winding capacitances of transformers. This paper focuses on an optimized design of planar transformers for the reduction of EMI emissions to decrease the filter effort. Therefore, different transformer structures are investigated and an optimized setup with a minimized inter-winding capacitance is analyzed and built up in a prototype. The proposed optimized design is verified by simulations and measurements.