High Switching Frequency Operation Research Articles

A new single modulating and single carrier signal based control technique for symmetrical and asymmetrical multilevel inverter topology

Abstract In literature, to generate gate pulses for any inverter topology, most of the authors are using a single modulating signal with (level-1) or (level-1)/2 carrier-based pulse width modulation (PWM) techniques and single carrier (SC) signal with (level-1)/2 modulating signal based PWM techniques. Then, while going to higher-level inverter topologies, the complexity of the PWM control approach in both cases can increase. To reduce the control complexity, few authors have reported a single modulating signal with single carrier-based PWM techniques. However, these techniques need more mathematical equations and if-else loops. This article proposes a new single-modulating and single-carrier signal-based generalized PWM control approach using floor function (FF). This technique has been verified by considering one of the single-phase conventional symmetrical and asymmetrical multilevel inverter (MLI) topologies. Generally, FF rounds the value to the nearest integer towards the negative infinity. The proposed PWM control implementation process is very simple and suitable for both high switching frequency (HSF) and low switching frequency (LSF) operations. The proposed control technique (PCT) has been experimentally verified with different steady-state and transient-state studies of results under standalone operation.

A Comprehensive Investigation into Bidirectional DC-DC Converters with Soft Switching for Electric Vehicles

Electric vehicles (EVs) are one of the the promising solutions for the environmental issues such as carbon emission and global warming. The high voltage traction battery in EVs is charged from utility grid by an EV charger. The Society of Automotive Engineers (SAE) standardize EV charges into two categories on-board chargers and off-board chargers. Usually, the on-board chargers are located inside the vehicle whereas, off-board chargers are not mounted on the vehicle. For onboard chargers, size and power density of charger become a prior matter of concern. The only way to reduce the size of a converter and thereby increase the power density is to operate power electronic conversion system (PECS) at very high switching frequency (HSF) resulting in reduced size of magnetic component in the charger configuration. However, HSF operation may lead to a high electromagnetic interference (EMI), loss in switch and switch duty. The work in this paper is focused on the development of high frequency bi-directional DC-DC converter (BD2C) stage priory used in on-board chargers due to distributed sources of energy as well as to manage the power distribution in the configuration. The power electronic BDCs are derived from boost and buck unit. The boost derived converter are current fed converters and offers advantages in terms of inherent voltage gain, short circuit protection and lower input current ripple. The voltage spikes across switches, high rated device selection, hard switching, snubber and auxiliary circuit requirements are some of the undesirable factors. This occurrence happened due to unbalance power transfer by the power electronics converter. Similarly, voltage fed converter offers good voltage control during power transfer.

Comprehensive Conducted Emission Analysis of the Three-Phase and Single-Phase LLC Resonant Converters for EV Application

Resonant <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter is a preferred candidate for emerging electric vehicle (EV) applications, thanks to its high efficiency and high power density characteristics, which are achieved due to high switching frequency and soft-switching operation. On the other hand, planar transformers (PTs) for EVs offer power density in a small package and withstand vibrations. However, large parasitic capacitance is a characteristic of PT, which along with the large <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv/dt</i> of the converter leads to severe conducted emission problems. Therefore, multifold complicated and bulky electromagnetic interference (EMI) filters are required to suppress conducted noise and meet the requirements of the relevant standards. In this article, a comprehensive analysis has been conducted to model and study both single-phase and three-phase <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converters from a conducted noise perspective. With this study, a better understanding of the EMI behavior of these converters can be obtained. Owing to the symmetrical design of the three-phase converter, several harmonics cancel out each other, resulting in lower common-mode (CM) emissions. It is also shown that differential-mode (DM) current generated from the three-phase converter contains lower peak amplitude at high frequency. For comparison purposes, two prototype converters based on the conventional single-phase and the three-phase configuration are fabricated and their conducted emissions are measured and compared experimentally. Simulation and experimental results verify that the three-phase converter effectively suppresses CM and DM noise by a considerable amount.

A New Predictive Current Control With Reduced Current Tracking Error and Switching Frequency for Multilevel Inverters

The forward Euler's integration method is widely used to compute the trajectories of the control variables in conventional predictive current control (PCC) techniques. However, the computational error caused by the forward Euler's method proportionally increases with the sampling time. Hence, the current tracking ability of conventional PCC techniques deteriorates when operating with a large sampling time. Furthermore, the conventional PCC methods produce more switching transitions to reduce the current tracking error, thereby leading to a high switching frequency operation. To overcome these problems, Heun's integration method is proposed for the PCC in this article. The proposed method has predictor and corrector stages to minimize the computational error caused by the large sampling time during the prediction process of the control variables. Thereby, the proposed Heun's method-based PCC techniques produce fewer switching transitions to minimize the current tracking error. Consequently, this results in a decrease in switching frequency. The proposed PCC method is applied to a four-level multilevel inverter (4L-MLI). The discrete-time system models are developed using Heun's integration method to implement the proposed PCC. The working philosophy of the proposed method is demonstrated through the dSPACE/DS1103 controlled 4L-MLI laboratory prototype. The experimental performance of the proposed PCC is compared with that of the conventional PCC in terms of average switching frequency, current tracking error, current harmonic distortion, and transient response time.

A new single modulating and single carrier‐based predictive current control technique for single‐phase quadruple boost multilevel inverter topology

SummaryA new floor function single carrier‐based modulated model predictive current control (F2‐SCM2PC2) technique has been proposed in this paper by considering traditional single‐phase quadruple boost switched capacitor‐based multilevel inverter (QB‐SCMLI) topology. Conventionally, the implementation process of single modulating and single carrier‐based pulse width modulation (PWM) techniques are very much complex and finite control set‐based model predictive control (FCS‐MPC) technique inherently operates with variable switching frequency (VSF) operation, which is not suitable for industrial applications. To alleviate the aforementioned issues, a new generalized closed‐loop F2‐SCM2PC2 technique has been proposed. It consists of a simple PWM implementation process and can easily be integrated with a predictive algorithm, thereby providing a constant switching frequency (CSF) of operation. The particular single modulating and single carrier‐based PWM technique with floor function is also suitable for low and high switching frequency (LSF‐HSF) operations. The validation of floor function‐based PWM technique in open‐loop and closed‐loop F2‐SCM2PC2 techniques has been effectively verified through experimentation on QB‐SCMLI topology with consideration of resistive–inductive load.

A PWM Method for Reducing dv/dt and Switching Losses in Two-Stage Power Converters

Today's semiconductor devices are accompanied by high switching frequencies (> kilo-hertz) and small transition times (< micro-seconds). Such fast transition times are accompanied by undesirable effects such as voltage overshoots at the load terminals, ground leakage currents, wide-band electromagnetic noise, etc. With the advent of wide band-gap devices, several applications are moving towards higher switching frequency operation with at-least an order of magnitude reduction in transition times. While these characteristics are considered necessary to break the next-generation barriers in power density, efficiency and applicability, the undesirable effects due to faster transitions are expected to present obstacles. This work proposes a PWM approach to modify the shape of the switching voltages to overcome the disadvantages of the fast transition times without any increase in switching losses. In fact, several of the switching transitions feature ZVS operation, resulting in reduced switching losses. The paper discusses the analytical details of the approach using a simple DC-DC boost-buck converter and extends it to a DC to three-phase AC converter using the principles of space vector modulation. The paper presents detailed simulation and comparative results in terms of voltage over-shoots over long cables, loss calculations and electromagnetic noise. Results from a laboratory-scale working prototype confirm the benefits of the proposed approach in terms of EMI and loss reduction.

Microcontroller-Based Trapezoidal Slope Compensation Technique for Peak Current Mode Control at MHz Frequencies

Slope compensation is necessary for the peak cur-rent mode control technique to ensure the stability of the power converter. Micro-controllers (μCs) existing in the market implement the slope compensation using built-in digital to analog converters (DACs). DACs exhibit finite transient times, which can be negligible when the μCs are used to control the power converters at switching frequencies in the order of a few hundreds of kHz. However, for high device switching frequency (HDSF) operation ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\geq 1\, \rm{MHz}$</tex-math></inline-formula> ), the DAC transient time becomes significant and can make it difficult, if not impossible, to achieve the conventional ramp slope compensation. Hence, in this paper, a novel concept of ‘trapezoidal’ slope compensation is proposed by considering the transient time of the μC. A detailed analysis is performed to understand the effect of the transient period on the converter stability. The proposed technique is validated with an experimental prototype of 400 W at 1 MHz switching frequency and it is shown to ensure stability of the converter at all operating points within the specification.

SiC switch‐based isolated DC‐DC converter for simultaneous charging of Li‐ion batteries of different voltage ratings for low‐ and medium‐power electric vehicle battery charging application

SummaryThe use of electric vehicles (EVs) has gained traction in recent years. With the widespread use of EVs in the future, the waiting time before charging will be high due to the use of slow chargers in developing countries. This work proposes a novel DC‐DC converter based on an isolated single‐ended primary inductor converter (SEPIC) and isolated Ćuk converter to enable simultaneous charging of batteries of low‐ and medium‐power EVs. The proposed converter operates without spikes in input and output currents, even during a sudden source disturbance. It can charge one battery at the output voltage level and simultaneously charge two batteries at half the output voltage. Simulation results for open‐loop and closed‐loop operations are provided to validate the converter operation and the simplicity of control. The proposed converter operation has been experimentally validated using a scaled‐down prototype by charging one 48 V lithium‐ion battery and then simultaneously charging two 24 V lithium‐ion batteries. The converter's response is provided to present the novelty and advantages of the proposed converter. The proposed converter uses fewer switches, diodes, inductors, and capacitors. The size of the system is reduced due to the high switching frequency operation of SiC devices. A low‐side gate driver is sufficient for driving the MOSFET, and the control is simple. The proposed converter offers a new and simple converter to charge multiple low‐ and medium‐power EV batteries of different ratings simultaneously with a low component count.

A Highly Efficient Si-/SiC-Based Hybrid Active NPC Converter With a Novel Modulation Scheme

With the increasing demand for high-performance power electronic systems, the semiconductor device utilization has gained significant importance. This article proposes the Si/SiC devices based active neutral-point-clamped converter comprising SiC-based H-bridge structure. A novel pulsewidth modulation (PWM) scheme is also proposed that results in an effective utilization of the switching devices. In the proposed converter, the Si devices are soft-switched for all power-factor loading conditions. Therefore, high efficiency can be obtained even at high switching frequency operation with wide range of power factor values. Further, the conduction losses of the SiC <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> s are minimized by strategically selecting the switching states in such a way that the SiC <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> s conduct in parallel conduction paths during the null state operation. This leads to further enhanced efficiency. This article presents the detailed operating principle of the proposed topology operated with the presented PWM scheme. Moreover, a device loss analysis is presented to evaluate the conduction and switching losses of the proposed topology. The presented experimental results validate the performance parameters of the proposed topology with the proposed PWM scheme. Finally, the proposed PWM scheme is compared with the existing PWM schemes using efficiency values of the proposed and some of the prominent existing converter configurations.

Five-Level Hybrid Active-NPC H-Bridge Converter With Novel Space-Vector-Modulation Scheme

This article presents a five-level hybrid active-neutral-point-clamped H-bridge (HANPC H-bridge) converter topology for a single-phase system. The proposed HANPC H-bridge topology utilizes a combination of silicon (Si) and silicon carbide (SiC) switches to enable high switching frequency operation. Furthermore, a novel space-vector-modulation (SVM) scheme is proposed to switch the two legs of the proposed converter at different switching frequencies. For this, a generalized approach to control relative difference in the switching frequencies of the two converter legs based on converter switching losses is proposed. Using the proposed modulation scheme, HANPC H-bridge converter features reduced switching losses, improved harmonic performance of output voltage and current, and optimal device utilization to achieve low cost at high efficiency. Moreover, a closed-loop control to balance the dc-link capacitors is presented, which provides the capacitor voltage balancing even under dynamic loading conditions without affecting its output voltage. The performance of the proposed converter is analyzed using the analytical and simulation results. Finally, experimental results are presented using the scaled-down prototype to validate the operating principles and performance of HANPC H-bridge converter using the proposed SVM scheme and capacitor voltage balancing control.

Behavior, Switching Losses, and Efficiency Enhancement Potentials of 1200 V SiC Power Devices for Hard-Switched Power Converters

Semiconductor power devices are the major constituents of any power conversion system. These systems are faced by many circumscriptions due to the operating constraints of silicon (Si) based semiconductors under certain conditions. The emergence and persistence evolution of wide bandgap technology pledge to transcend the restrictions imposed by Si based semiconductors. This paper presents a thorough experimental study and assessment of the performance of three power devices: 1200 V SiC cascode, 1200 V SiC MOSFET, and 1200 V Si IGBT under the same hardware setup. The study aims to capture the major attributes for each power device toward determining their realistic potential applications. The switching performance of each power device is studied and reported. As the gate resistance is a crucial factor in a power device characterization, an extensive analysis of hard-switching losses under different separated turn-on and turn-off gate resistances is also performed and discussed. To appraise the fast switching capability, the switching dv/dts and di/dts are measured and analyzed for each power device. Furthermore, insights are provided about the dependency of switching energy losses on the power device current and blocking voltage. This paper also focuses on evaluating the operations and the performances of these power devices in a hard-switched dc-dc converter topology. While using of 1200 V SiC Schottky diode in the converter design with each power device, the high switching frequency operations and efficiency of the converter are reported and thoroughly explored. The SiC cascode exhibited superior performance when compared to the other two power devices. The results and analyses represent guidelines and prospects for designing advanced power conversion systems.

Investigation of Full SiC Power Modules for More Electric Aircraft With Focus on FIT Rate and High-Frequency Switching

The development of more electric aircraft (MEA) has accelerated in recent years. Power converter systems for MEA require higher reliability compared with the conventional power converter systems as well as higher energy efficiency. A power device at high altitude might break down at a certain rate because of cosmic rays. Thus, it is necessary to carefully consider the reliability of single event burnout together with the converter design. This study examines a failure in time (FIT) rate comparison among three different inverter configurations using 3.3-kV and 6.5-kV full SiC power modules (FSPMs) under several operating conditions. It presents module and inverter configuration selection criteria in consideration of the FIT rate. In addition, the transitions of FIT rates during the flight are calculated using actual flight data to help the power converter system designers understand how the FIT rate should be considered. Furthermore, this study verifies a high-frequency switching operation at various bus voltages for a 6.5-kV FSPM and the power loss calculation for MEA applications.

DAB Converter for EV Onboard Chargers Using Bare-Die SiC MOSFETs and Leakage-Integrated Planar Transformer

This article discusses electrical design optimization of a 3.3 kW, 380 V to 250–380 V, 500 kHz, dual-active-bridge dc–dc converter for onboard chargers, operated with constant-power (CP) charging. In order to operate the converter at 500 kHz without concerns on switching performance and efficiency while also improving power density, a low-parasitics, PCB-based, wire-bondless full-bridge module featuring bare-die SiC MOSFETs and compact, electrothermally multifunctional coolers is employed. High switching frequency operation also felicitates the realization of the DAB inductor using the transformer’s leakage inductance, thereby enhancing the power density by eliminating the need for a discrete inductor. Design strategy for such magnetic integration in a planar transformer is discussed, followed by a systematic design optimization of the transformer, including the selection of leakage inductance value, the core geometry, and the number of turns for achieving zero-voltage switching (ZVS) and maximum average efficiency over the entire charging profile. Experimental validation was performed using a proof-of-concept prototype, which is operated up to 3.3 kW and has a final projected power density of 5.44 kW/L. Results demonstrate the operation with ZVS over the entire charging profile with satisfactory high-frequency waveforms and a peak efficiency of 98%.

High precision scalable power converter for accelerator magnets

The lower conduction power losses and the positive temperature coefficient that favours parallel connections, make Silicon Carbide (SiC) Metal Oxide Semiconductor Field-Effect Transistors (MOSFETs) to be an excellent replacement of existing Silicon Insulated Gate Bipolar Transistors (IGBTs) technology. These characteristics combined with high switching frequency operation, enables the design of high-accuracy DC-DC converters with minimised filtering requirements. This paper investigates the design for a converter with high-accuracy current (0.9 ppm) supplying a 0.05 H electromagnetic load, aiming to achieve the accuracy without the use of active filters, by using SiC MOSFETs and a scalable module-based converter design.

A low-profile, high-performance, GaN converter design for a portable SPV charger

ABSTRACT The technology requirements for portable gadgets are challenging as they demand miniaturization with smaller footprint power converters, with high performance. A high-frequency switching operation is essential to achieve the above requirements. Further, the converter design needs to be optimum with an effective control loop and component sizing. An attempt is been made to develop a portable charger with high performance using Gallium Nitride (GaN) devices. A 2.5 W, 500 kHz synchronous buck converter suitable for the handy portable application with USB standardization is realized based on an effective design strategy in compensation is discussed. Analog control of the converter with optimized inductance and capacitance for the low-profile design is realized with good stability and transient response. An accurate loss estimation method, with the proposed loop compensation technique, is incorporated leading to a reduction in output capacitance with the needed transient response. The application needs of a Solar Photo Voltaic (SPV) charger that demands low-profile design is met with choices of inductor along with operating switching frequency of the GaN device for its high-performance. A low-profile, 4.7 mm height, GaN-based converter with 97.04% efficiency, is evaluated for various conditions of the hand-held SPV module to charge the gadget with USB normalization.

Comparisons on Different Innovative Cascode GaN HEMT E-Mode Power Modules and Their Efficiencies on the Flyback Converter

The conventional cascode structure for driving depletion-mode (D-mode) gallium nitride (GaN) high electron mobility transistors (HEMTs) raises reliability concerns. This is because of the possibility of the gate to source voltage of the GaN HEMT surging to a negative voltage during the turn off transition. The existing solutions for this problem in the literature produce additional drawbacks such as reducing the switching frequency or introducing many additional components. These drawbacks may outweigh the advantages of using a GaN HEMT over its silicon (Si) alternative. This paper proposes two innovative gate drive circuits for D-mode GaN HEMTs—namely the GaN-switching based cascode GaN HEMT and the modified GaN-switching based cascode GaN HEMT. In these schemes, the Si MOSFET in series with the D-mode GaN HEMT is always turned on during regular operation. The GaN HEMT is then switched on and off by using a charge pump based circuit and a conventional gate driver. Since the GaN HEMT is driven independently, the highly negative gate-to-source voltage surge during turn off is avoided, and in addition, high switching frequency operation is made possible. Only two diodes and one capacitor are used in each of the schemes. The application of the proposed circuits is experimentally demonstrated in a high voltage flyback converter, where more than 96% efficiency is obtained for 60 W output load.

Direct 12V/24V-to-1V Tri-State Double Step-Down Power Converter With Online V CF Rebalancing and In-Situ Precharge Rate Regulation

In response to fast-growing high-voltage (HV) power IC market demands, this article presents a tri-state double step-down (DSD) power converter to achieve direct 12V/24V- to-1V dc-dc power delivery with high efficiency and high power density. By taking advantage of the benefits from both three-level and DSD converter topologies, the converter allows the use of lower voltage rating power devices and thus facilitates high switching frequency operation with smaller power passives. An online flying capacitor voltage ( V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CF</sub> ) rebalancing scheme is introduced to optimize switching nodes voltages and minimize power path mismatch for improved reliability and efficiency. During startup transients, an in-situ precharge rate regulation technique manages the charging process on flying capacitors precisely in avoidance of potential device breakdown. An IC prototype of this design was fabricated using a 180 nm HV bipolar-CMOS-DMOS (BCD) process with an active area die of 6.3 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . At 3-W output power, a chip power density of 476 mW/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is accomplished. The online V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CF</sub> rebalancing reduces voltage mismatch between the flying capacitors by 16.7%. The converter achieves peak efficiencies of 88.3% and 92.1% for 24V/1V and 12V/1V conversion, respectively.

Improved Modeling of a Multi-Level Inverter for TACS to Reduce Computational Time and Improve Accuracy

A modeling of a turbo air compressor system (TACS), with a multi-level inverter for driving variable speed, combining an electrical model of an electric motor drive system (EMDS) and a mechanical model of a turbo air compressor, is essential to accurately analyze dynamics characteristics. Compared to the mechanical model, the electrical model has a short sampling time due to the high frequency switching operation of the numerous power semiconductors inside the multi-level inverter. This causes the problem of increased computational time for dynamic characteristics analysis of TACS. To solve this problem, the conventional model of the multi-level inverter has been proposed to simplify the switching operation of the power semiconductors, however it has low accuracy because it does not consider pulse width modulation (PWM) operation. Therefore, this paper proposes an improved modeling of the multi-level inverter for TACS to reduce computational time and improve the accuracy of electrical and mechanical responses. In order to verify the reduced computational time of the proposed model, the conventional model using the simplified model is compared and analyzed using an electronic circuit simulation software PSIM. Then, the improved accuracy of the proposed model is verified by comparison with the experimental results.

Design of a Portable Photovoltaic I–V Curve Tracer Based on the DC–DC Converter Method

The I–V curve tracer is an instrument that captures the current–voltage characteristics of photovoltaic (PV) generators under real operating conditions. Such device can be used to evaluate their performance and identify faults or aging effects, but its high costs have prevented it from being widely used in the industry. This article thus proposes the design of a low-cost, portable I–V curve tracer based on the classic dc–dc Cuk converter for PV modules of up to 300 W. In order to obtain a compact device, some design techniques are proposed, including circuit reduction, high switching frequency operation, specification of the optimum load resistor power rating, and improved measurement distribution because of a nonlinear duty cycle variation. Experimental curves were compared with those acquired from commercial PV tracers to demonstrate its accuracy. In addition, the physical parameters of the well-known single-diode model have been extracted and compared with data provided by manufacturers to identify aging effects and module performance.

Experimental Assessment of High Frequency Bearing Currents in an Induction Motor Driven by a SiC Inverter

Compared with silicon (Si) IGBTs, silicon carbide (SiC) MOSFETs have much faster switching speeds and high switching frequency operation capability, enabling compact and high-efficiency motor drive systems. However, the increased switching speed and frequency also cause increased-level of common-mode (CM) voltage with higher slew rates ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dt</i> ). The CM voltage leads to machine leakage currents as well as bearing currents such as electric discharge machining (EDM) type current and capacitive-type ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dt</i> ) current. These bearing currents can cause degradation or failure of motor bearings. In order to investigate the impact of SiC motor drives on the motor bearing currents, in this paper, the mechanism and modelling of bearing currents are analyzed first. Then, a direct measurement method is used to assess the bearing currents in the induction motor driven by the SiC converter. In the experiment, the number of EDM current events is counted and the amplitude of the capacitive-type of current is also examined under various switching speeds and frequencies of SiC devices. Furthermore, the bearing currents are also extensively tested under various bearing temperatures, motor speeds and dc-link voltages. The correlations between the bearing currents and various factors have been revealed in this paper.