Switching Frequency Of Converter Research Articles

Small-signal modeling comparison of dual active bridge converter

The dual active bridge (DAB) converter is a versatile DC-DC converter, which has AC components in the high-frequency transformer within the converter topology as well as DC components at the input and output sides. These AC components are constructed from infinite sinusoids of multiples of the converter's switching frequency. Different approaches have been proposed to model the DAB converter. The generalized averaging modeling (GAM) includes only the first order harmonic of the inductor current with the DC components of the input and output voltages and currents. For better model accuracy, harmonic-domain models have been employed, where the model includes all the harmonics of all the model state variables up to an arbitrary harmonic index. While the harmonic model provides a systematic approach to include the harmonics, this increases the model complexity. To avoid this complexity, the flexible harmonic model is used where harmonics can be selected per each state variable without needing to be in successive order. The aforementioned modeling approaches have been implemented on the DAB converter. This paper aims to compare between the dynamic performance of GAM and the harmonic modeling approaches under different disturbances, where the GAM approach provided a simple model with acceptable results that can be used for controller design, while the LTP model provided a more complex model with better accuracy that is suitable for harmonic studies. The models have been validated and compared using simulations executed on MATLAB /Simulink environment.

Dead-Time Evaluation With Switching Frequency for GaN-Based Non-Inverting Buck-Boost DC–DC Converter Using FPGA-Based High-Frequency Control

Dead-Time Evaluation With Switching Frequency for GaN-Based Non-Inverting Buck-Boost DC–DC Converter Using FPGA-Based High-Frequency Control

A simple zero-voltage switching technique for a single-phase inverter based on bi-directional inductor current

The majority of soft-switching inverters often use auxiliary semiconductor switches that run for extremely brief periods to provide ZVS conditions for the main switches, potentially raising the inverter system’s cost. This work presented a simple zero-voltage switching (ZVS) approach by employing a bi-directional inductor current for the single-phase inverter, which reduced the cost of auxiliary switches and simplified the soft-switching inverter design. All switches can achieve ZVS operation without additional resonant components. The conventional PWM control strategies are applied in the proposed technique, and thus the problems existing in variable switching frequency converters are removed. This article describes the soft-switching approach and detailed circuit functioning. Different key parameters are optimized to improve efficiency. To confirm the suggested ZVS method, a hardware inverter prototype is created, built, and tested. To validate the inverter’s characteristics and validity, experimental results are presented.

GaN based DC-DC converters for high energy physics applications

This paper introduces a prototype of a GaN-FET based 200 W DC-DC converter. Its design has been carried out to evaluate power density (or power dissipation and volume) and ensure minimal electromagnetic interference (EMI) issues that are commonly associated with the high switching frequency converters. To achieve this ANSYS HFSS-SiWave models have been developed to assess noise emissions based on the parasitic elements of PCB layout. Prototypes performance have been evaluated through extensive testing. This work offers insight into the potential of this technology in future physics detectors.

COMPUTER OPTIMIZATION OF SWITCHING FREQUENCY OF TRANSISTOR PULSE-WIDTH CONVERTERS

The aim of the work is to develop algorithm for determining the optimal switching frequency of a transistor pulse-width converter (PWM) to minimize the total electrical losses in a DC drive. Electrical losses in the armature winding and in PWM transistors are divided into two components: static from the direct current component and dynamic. The latter include losses in the armature winding from the harmonic components of the current and losses in transistors from transient switching currents. Since the dynamic losses in transistors increase with increasing frequency, and in the armature winding from current harmonics they decrease, there is an optimal switching frequency value at which the total dynamic losses in the PWM drive will be minimal. This aim is achieved by solving the problem of determining the analytical dependence of dynamic electrical losses in the armature winding on the PWM switching frequency and computer simulation of a transistor DC drive. As a result of the research, an analytical expression was obtained for calculating the relative dynamic electrical losses in the armature winding with polyharmonic power supply. An algorithm is proposed for determining the optimal switching frequency of the PWM: 1) on computer models of the DC motor and PWM, the dependences of dynamic electrical losses on the switching frequency are determined; 2) build a graph of the dependence of the total dynamic electrical losses, on the which determine the point of minimum losses, which corresponds to the optimal value of the switching frequency. The novelty of the work lies in the fact that the theory of electrical losses in the armature windings with polyharmonic power has been further developed.

Experimental Study of Radiated Emission Due to Secondary Common-Mode Current in Buck Converters

High switching frequency and fast switching speed of wide bandgap power semiconductor device-based power converters may increase radiated emissions more than conventional silicon-power device-based power converters. Based on the background, this article experimentally investigates radiated emission sources in buck converters. The experimental system constructed in this article has two common-mode noise paths, the primary common-mode and the secondary common-mode. First, this article outlines that a secondary common-mode voltage source is caused by a primary common-mode current and an imbalance of power supply side impedances, and the secondary common-mode current path acts as a monopole antenna. The common-mode currents and the radiated emissions are measured in an anechoic chamber when the common-mode inductor for each mode is connected. The measurement results show that the primary common-mode current generates the secondary common-mode noise, and the secondary common-mode noise is the dominant source of radiated emission in the experimental system.

Optimized Voltage Equalization Algorithm for Modular Multilevel Converters

The switching frequency of modular multilevel converters increases with the number of bridge arm submodules. Therefore, an improved voltage equalization technology based on fast sorting algorithm is proposed, which introduces the maximum voltage deviation between sub-modules and reduces the unnecessary switching operations caused by small changes in the capacitor voltage of factor modules. With the help of Matlab/Simulink, a modular multilevel converter with optimized control was simulated to verify the downscaling effect of the voltage-sharing optimization method.

Improved Triple-Phase-Shift Modulation for Bidirectional CLLC Converters

CLLC resonant converters are an attractive option for battery charging applications due to their bidirectional power flow and high efficiency. Pulse frequency modulation (PFM) is the simple method to drive CLLC converters. However, PFM cannot regulate the output voltage under the light-load condition properly, which leads to high switching and core losses. Phase shift modulation techniques like dual-phase shift (DPS) modulation can overcome this challenge. However, more improvements are demanded due to high circulating currents in phase shift modulations. In this paper, an improved modulation technique based on triple-phase shift (TPS) has been applied in CLLC converters to improve the light-load efficiency. TPS modulation like any other phase-shift modulation, keeps the switching frequency of CLLC converters fixed at the resonant frequency under the light-load condition and regulates the output voltage by its three phase shift parameters. The improved TPS modulation has lower circulating current at the same average output current compared to DPS modulation. Therefore, higher efficiency, smaller peak, and RMS current values can be achieved under the light-load condition. In addition, the proposed TPS modulation has a better flexibility in regulating the output voltage under the light-load condition due to an extra phase shift parameter compared to DPS modulation. The proposed TPS modulation has been analyzed thoroughly in this paper and a proper selection of phase shift values has been explained to improve the efficiency of the converter. Finally, advantages of the improved TPS modulation have been validated by simulation and a 1 kW experimental setup.

Voltage-Controlled Variable Inductor for Fixed-Frequency Critical Conduction Mode Operation

This study proposes a novel voltage-controlled variable inductor (VI) for fixing the switching frequency of DC-DC converters in the critical conduction mode (CRM). It overcomes the limitations of conventional current-controlled VIs such as complex winding structures, difficulties in control, and high sensitivity to temperature. In the proposed voltage-controlled VI, the primary-side inductance of a coupled inductor is regulated by an auxiliary voltage source on the secondary side. The auxiliary voltage source is implemented by an auxiliary DC-DC converter, which delivers power to the load in parallel with the main converter. The operating principle of the converter system for employing the proposed VI is presented, and a control loop is designed to fix the switching frequency, considering the small-signal model of the auxiliary converter. The validity of the proposed VI is experimentally verified using a prototype CRM boost converter with an output voltage of 400 V and a maximum power of 400 W. The switching frequency is fixed at 100 kHz and the soft switching of the main converter is maintained regardless of the input voltage and output power.

케이블 임피던스 측정 및 검증 방법

This paper present detail description on determining cable parameters of an electrical power cable. A method known as short-open method is employed in this work where the series parameters of a two wire cable are determined by shorting the end of the cable while the shunt parameters are extracted by opening the end terminal of the cable. Network analyzer and LCR meter are utilized in carrying out the short-open method. The measured parameters from both network analyzer and the LCR meter are compared and verified by finding the propagation delay of the cable through an experiment. The propagation delay value from the experiment is compared to a propagation delay value computed from the primary parameters to check for accuracy. The experimental setup constituted of a DSP board, 30kHz buck converter, 150V DC power supply and a 16m power cable. The 16m cable was selected because it was much easier to manage in the laboratory. The cable parameters were extracted at 30kHz frequency which is the same as the buck converter switching frequency. At 30kHz a propagation delay of 84ns was obtained for LCR meter while network analyzer had 83ns. Propagation delay from using the buck converter gave a propagation delay of 84ns which is the same as computed propagation delay value from LCR meter.

Termination Design Optimization of High-Current PCB-Winding Matrix Transformers

Due to their high power densities and efficiencies, high-frequency resonant converters using printed circuit board (PCB)-based transformers are gaining popularity in applications, such as datacenters and automotive. However, in such high-frequency, high-current applications, the PCB transformer's termination losses may become significant if not designed properly. This article aims to highlight multiple design considerations to minimize the termination losses while designing a PCB-based matrix transformer. Various termination techniques for full-bridge and center-tap secondary-rectifiers are studied, and it is shown that placing the devices and output filter capacitors directly on the secondary windings results in the lowest termination loss. However, this results in the output filter capacitors being split between the two secondary PCB layers, resulting in a long paralleling loop between them. It is demonstrated that the parasitic inductance of this loop undergoes parallel resonance with the filter capacitors, resulting in high circulating currents and, hence, high termination losses. Methods to mitigate this effect at the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter's switching frequency are discussed. Improvements of the proposed terminations are demonstrated by modeling and measuring the transformer's ac resistance. Furthermore, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converters' efficiency improvements are also showcased with the improved terminations.

Voltage-Mode Variable-Frequency Controlled LLC Resonant Power Factor Correction Converter and Its Accurate Numerical Calculation Analysis

LLC resonant converter is a good candidate for single-stage ac–dc converter, which can realize both functions of power factor correction (PFC) and output voltage regulation, and contribute to the improvement of conversion efficiency and power density. However, voltage mode (VM) controlled single-stage half-bridge LLC PFC converter has the disadvantages of large dead-zone of input current and hard-switching operation, since there is no current control. Besides, the voltage ripple of input filter brings asymmetrical operation of the converter between the positive and the negative half-switching cycle. In order to solve these problems, this article presents a modified numerical calculation method, which can realize accurate characterization of the asymmetrical behavior of resonant current and voltage. Based on that, the switching frequency of LLC resonant converter for unity power factor (PF) is derived. A method of fitting the switching frequency is proposed to simplify the circuit implementation. A 250-W/48-V prototype has been built to verify the analysis results. Experimental results show that the proposed voltage-mode variable-frequency (VM-VF) controlled LLC resonant PFC converter can achieve high efficiency of up to 94.08% and power factor of 0.95 over the input voltage range of 180–260 VAC.

Grid Current Control for Active-Front-End Electric Propulsion Systems in AC Ship Microgrids

This article proposes a finite control set (FCS) current controller for grid-tied converters, specifically tailored to meet the characteristics of ac ship microgrids in all-electric ships (AESs). Contrary to a pulsewidth modulator (PWM)-based design, which often employs an LCL filter, the proposal is able to meet applicable harmonic regulations using an L filter with the same total inductance as the LCL filter and the same switching frequency required by PWM-based solutions. Moreover, the proposed design provides a low sensitivity in a wide frequency range from dc to the switching frequency of the power converter. This low sensitivity permits to quickly attenuate low-order disturbances and it is particularly convenient in marine applications with a weak grid, where the frequent connection and disconnection of high power nonlinear loads can significantly affect the voltage waveform quality.

ISM-Band Frequency Transformer Modeling for Isolated High-Power Conversions

In the last few years, the switching frequency of power electronic converters is extended to the several MHz range. ISM frequency bands are specified in this range for power electronic applications. Most converter circuits, such as resonance and soft-switching circuits require an accurate modeling of the circuit components, such as the high frequency inductors and transformers. This paper focuses on the evaluation of a practically simple but accurate high frequency transformer model. In first, a three-capacitor lumped model is chosen due to its simplicity as well as to the physics-oriented concept. Furthermore, the extraction of the parameters is straightforward. It is found that splitting the leakage inductances in two halves based on the winding capacitance would make the model more accurate for modeling high frequency characteristics. The paper analyzes the model and provides a closed form transfer function for the input impedance and the voltage gain. To verify the model, different kinds of transformer hardware are fabricated, and their input impedances are measured from 1 MHz to 30 MHz, which includes three ISM bands. The measurements are then compared with the impedance function developed from the model. The model shows well-matching with the measurement as compared to the conventional models. Finally, the model is validated experimentally by designing an isolated 13.56 MHz Class-E power conversion circuit, which includes a transformer with soft-switching. The soft-switching is designed based on the conventional, three-capacitor and the proposed model, respectively. The proposed model provides more accurate design for the inverter assuring soft-switching and optimum performance of the circuit.

AC Resistance and Leakage Inductance Estimation for Planar Transformers With Parallel-Connected Windings

Regarding the ever-increasing switching frequency of power converters, there is a lack of tools to perform a quick and effective optimization of the high-frequency transformers embedded in isolated power converters. Indeed, at high operating frequency, the geometry of the core and windings deeply impacts the overall transformer performance. Specifically, assessing accurately the current distribution in parallel-connected windings is a challenging and key issue. Winding parallelization, frequently implemented in low-voltage and high-current applications so as to decrease Joule losses, may be an ineffective solution because of skin and proximity effects. They create an unbalanced current distribution in the parallel-connected windings, which greatly impacts the ac resistance and leakage inductance of the transformer. This article proposes an innovative frequency analytical model permitting to simply and accurately compute the current distribution in the transformer windings, the ac resistance, and the leakage inductance. The proposed approach is comprehensively presented, validated using both measurements and two-dimensional finite element analysis and analyzed giving guidelines to engineers designing high-frequency transformers.

Comprehensive Review of Power Electronic Converters in Electric Vehicle Applications

Emerging electric vehicle (EV) technology requires high-voltage energy storage systems, efficient electric motors, electrified power trains, and power converters. If we consider forecasts for EV demand and driving applications, this article comprehensively reviewed power converter topologies, control schemes, output power, reliability, losses, switching frequency, operations, charging systems, advantages, and disadvantages. This article is intended to help engineers and researchers forecast typical recharging/discharging durations, the lifetime of energy storage with the help of control systems and machine learning, and the performance probability of using AlGaN/GaN heterojunction-based high-electron-mobility transistors (HEMTs) in EV systems. The analysis of this extensive review paper suggests that the Vienna rectifier provides significant performance among all AC–DC rectifier converters. Moreover, the multi-device interleaved DC–DC boost converter is best suited for the DC–DC conversion stage. Among DC–AC converters, the third harmonic injected seven-level inverter is found to be one of the best in EV driving. Furthermore, the utilization of multi-level inverters can terminate the requirement of the intermediate DC–DC converter. In addition, the current status, opportunities, challenges, and applications of wireless power transfer in hybrid and all-electric vehicles were also discussed in this paper. Moreover, the adoption of wide bandgap semiconductors was considered. Because of their higher power density, breakdown voltage, and switching frequency characteristics, a light yet efficient power converter design can be achieved for EVs. Finally, the article’s intent was to provide a reference for engineers and researchers in the automobile industry for forecasting calculations.

An Improved High-Resistance Fault Detection Method in DC Microgrid Based on Orthogonal Wavelet Decomposition

High-resistance faults in direct current (DC) microgrids are small and thus difficult to detect. Such faults may be “invisible” in that grid operation continues for a considerable time, which damages the grid. It is essential to detect and remove high-resistance faults; we present a detection method herein. First, the transient DC current during the fault is subjected to hierarchical wavelet decomposition to identify high-resistance faults accurately and sensitively; the wavelet coefficients are detected using the singular value decomposition (SVD) method. The SVD valve can denoise the dc microgrid fault current, which eliminates the influence of converter switching frequency and background noise effectively. Power system computer-aided design (PSCAD)/electromagnetic transients including direct current (EMTDC)-based simulations showed that our method successfully identified high-resistance faults.

High Bandwidth Series-Form Switch-Linear Hybrid Envelope Tracking Power Supply With Reduced Bandwidth Envelope and Step-Wave Edge Adjustment Methods

The series-form switch-linear hybrid envelope tracking (ET) power supply is constituted by a multilevel converter and a linear amplifier connected in series, featuring high efficiency and wide tracking bandwidth. With the development of wireless communication, the envelope bandwidth of the radio-frequency signal reaches tens of megahertz and even hundreds of megahertz, leading to a high switching loss in the multilevel converter and thus degraded overall efficiency of the ET power supply. To reduce the switching loss and ensure high tracking bandwidth, this article proposes to let the multilevel converter track the reduced bandwidth envelope signal and the linear amplifier track the original one. Then, a step-wave edge adjustment method is proposed to adjust or eliminate the rising and falling edges of the step-wave voltage for further reducing the equivalent switching frequency of the multilevel converter and the voltage across the power device of the linear amplifier. As a result, the switching loss in the multilevel converter and the power loss in the linear amplifier could be reduced, leading to a notably higher overall efficiency. A prototype with 40 MHz tracking bandwidth, 7–27 V output voltage, and 15 W average output power is fabricated and tested in the lab, and the experimental results are provided to verify the effectiveness of the proposed method.

Minimization Electric Losses in Transistor DC Drives

This work is devoted to develop the algorithm for determining the optimal switching frequency of a transistor pulse-width converter (PWM) to minimize the total electric losses in a DC drive. Electric losses in the armature winding and in the PWM transistors are divided into two compo-nents: static, from the direct current component, and dynamic. The latter include losses in the armature winding from the harmonic components of the current and losses in transistors from transient switching currents. Since the dynamic losses in transistors increase with increasing frequency, and in the armature winding they decrease from current harmonics, there is an optimal switching frequency value at which the total dynamic losses in the PWM drive will be minimal. This aim is achieved by solving the problem of determining the analytical dependence of dynamic electric losses in the armature winding on the PWM switching frequency and computer simulation of a transistor DC drive. As a result of the research, an analytical expression was obtained for calculating the relative dynamic electric losses in the armature winding with polyharmonic power supply. An algorithm was proposed for determining the optimal switching frequency of the PWM: 1) on computer models of the DC motor and PWM, the dependences of dynamic electrical losses on the switching frequency were determined; 2) the graph was built showing the dependence of the total dynamic electric losses, on which the point was determined of minimum losses, which corresponds to the optimal value of the switching frequency. The novelty of the work was that the theory of electric losses in the armature windings with polyharmonic power was further developed.

Passivity-Based Multisampled Converter-Side Current Control of LCL-Filtered VSCs

With the gradually decreasing cost of high-performance digital processors, multisampling current control is a potential method to reduce the control delay and improve the stability in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> -filtered grid-connected converters. In the practical implementation, an antialiasing filter is required to remove the sampled switching harmonics and suppress the low-order aliasing. However, due to the phase lag from the antialiasing filter, the dissipative region of converter output admittance still cannot be lifted to switching frequency, which leads to a risk of system instability under wide grid admittance variation. In order to tackle this challenge, a filter capacitor voltage feedforward scheme using multisampling is proposed in this article. Consequently, the dissipation below the switching frequency is harvested for a three-phase converter. Furthermore, by doubling the multisampling rate, the proposed method can extend the dissipative region to the apparent switching frequency for a single-phase converter using unipolar modulation. The experimental results validate the effectiveness of the proposed method on a down-scaled single/three-phase converter.