Switching Frequency Of Power Converters Research Articles

Multirate Modeling and Predictive Control for WBG-Device-Based High-Switching-Frequency Power Converters

With the growth of wide bandgap devices, it is necessary to exploit the high switching frequency benefits to improve the power converter's performance, thus requiring a higher sampling/interrupt frequency in digital signal processors. However, such a short interrupt time duration imposes big computational difficulty in the execution of programming code, especially using the model predictive control (MPC). Thus, most of the existing MPCs are applied with switching frequencies below 20 kilohertz, which cannot exploit the full potential of the wide bandgap device-based power converters. To solve this challenge, this article proposes a multi-rate MPC scheme, where the trigger of interrupt and switching device transition can be performed at different rates. Compared to conventional MPCs, the main uniqueness of the proposed multi-rate MPC is that the high-dimension control sequence is solved and applied within each interrupt interval. Therefore, the increased switching frequency objective can be easily achieved with a low sampling/interrupt frequency configuration, which also significantly relieves the digital execution of the heavy interrupt tasks. The proposed method shows a more optimized control input and higher computational efficiency over the multi-rate finite-control-set MPC counterpart. A silicon carbide inverter-fed AC motor drive system is used to verify the proposed multi-rate MPC. The results show the improved system performance with the combined advantages of both the high switching frequency and MPC strategy.

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.

Latest Advances of Model Predictive Control in Electrical Drives—Part I: Basic Concepts and Advanced Strategies

The application of model predictive control in electrical drives has been studied extensively in the past decade. This article presents what the authors consider the most relevant contributions published in the last years, mainly focusing on three relevant issues: weighting factor calculation when multiple objectives are utilized in the cost function, current/torque harmonic distortion optimization when the power converter switching frequency is reduced, and robustness improvement under parameters uncertainties. Therefore, this article aims to enable readers to have a more precise overview while facilitating their future research work in this exciting area.

Multirate Finite-Control-Set Model Predictive Control for High Switching Frequency Power Converters

Due to the modulator free structure, the finite-control-setmodel predictive control (FCS-MPC) needs a high sampling frequency/interrupt frequency (20–50 kHz) for power converters application, while the typical converter switching frequency is around 20–25% of the sampling frequency. To obtain a high switching frequency, it is not always practical to increase the sampling rate by considering the computational burden in a digital processor. Therefore, increasing the switching frequency without using a high sampling frequency is a critical task for FCS-MPC, particularly applied to silicon carbide and gallium nitride-based high switching frequency power converters. To solve this problem, this article proposes the multirate FCS-MPC (MRFCS-MPC), where the control frequency is allowed to be higher than the sampling frequency. Consequently, the switching frequency can be significantly increased without changing the sampling frequency. The proposed scheme inherits the ability to handle complex control objectives from the traditional FCS-MPC. The lifting model is built to predict the fast rate information of state variables based on the low sampling output. Then, the fast rate control inputs within one sampling interval are solved efficiently with a good tradeoff between computational burden and optimized system performance. The experimental motor drive system tests are carried out to verify the effectiveness of the proposed MRFCS-MPC.

Effect of Semiconductor Parasitic Capacitances on Ground Leakage Current in Three-Phase Current Source Inverters

This paper investigates the influence of power semiconductor parasitic components on the ground leakage current in the three-phase Current Source Inverter topology, in the literature called H7 or CSI7. This topology allows reducing converter conduction losses with respect to the classic CSI, but at the same time makes the topology more susceptible to the parasitic capacitances of the semiconductors devices. In the present work, a grid-connected converter for photovoltaic power systems is considered as a case study, to investigate the equivalent circuit for ground leakage current. The same analysis can be extended to applications regarding electric drives, since the HF model of electric machines is characterized by stray capacitance between windings and the stator slots/motor frame. Simulation results proved the correctness of the proposed simplified common-mode circuit and highlighted the need of an additional common-mode inductor filter in case of resonance frequencies of the common-mode circuit close to harmonics of the power converter switching frequency. Experimental results are in agreement with the theoretical analysis.

Event-Driven Approach With Time-Scale Hierarchical Automaton for Switching Transient Simulation of SiC-Based High-Frequency Converter

On the emerging development of SiC MOSFET, the switching frequency of power converters has been pushed to the order of hundreds of kilohertz or even megahertz to improve power density. However, the state-of-the-art simulations for such high-frequency power electronics circuits are usually time-consuming, blocking the studies of long dynamics such as several seconds. What’s worse, adopting physical models to simulate the turn-on and turn-off transients leads to high stiffness and therefore convergence problems. In this paper, an event-driven approach is proposed to improve the solving speed and simulation stability of SiC based high-frequency converters. A time-scale hierarchical automaton is proposed to model the system, where piecewise analytical transient model for SiC MOSFET is established as the second layer in the automaton to simulate the switching transients with improved numerical stability. Simulation of the system is driven by discrete events in the automaton. A 3.3 kW 79.1 kHz wireless power transfer system for the wireless charging of electric vehicle is studied. Compared with ideal switch model in Simulink and physical switch model in LTspice, 60-fold and 400-fold increases in terms of simulation speed with same level of accuracy are achieved respectively. The simulated results are also attested to by experimental verifications.

Digital Pulsewidth Modulation (DPWM) Using Direct Digital Synthesis

Wide-bandgap semiconductor power devices are being adopted to increase efficiency and switching frequency for power converters. This requires a demand for higher resolution digital pulsewidth modulation (DPWM) in digitally controlled power converters. This is because, in a digitally controlled dc–dc converter, steady-state limit-cycle oscillations can exist if the resolution of DPWM is less than the ADC resolution. This article proposes a cost-competitive, high-performance, functionally integrated with a small package-sized, a complete direct digital synthesis-based DPWM architecture to achieve a high resolution, linear, monotonic behavior, and extremely fast frequency hopping ability. This article presents a detailed analysis of the new DPWM architecture. Simulation and experimental results are presented to verify the analysis. This article also discusses the various advantages and numerous applications addressed by the proposed method.

Estimation of Power Losses Caused by Supraharmonics

Nowadays increases the number of power electronic devices in distribution electrical networks rapidly. Modern generation and consumption units use high switching frequency power converters for the network connection and therefore cause the voltage and current distortion in the frequency range over 2 kHz (so-called “supraharmonics”) in addition to conventional harmonics. Supraharmonics cause additional power losses in electrical equipment. The goal of the offered paper is the estimation of power losses caused by supraharmonics. The method of the supraharmonic power losses estimation combining the analytic determination of AC cable resistances at the supraharmonic frequencies with the use of measurement results of supraharmonic currents in a real MV/LV cable network is considered in the paper. In the paper is shown that supraharmonic power losses in a MV cable under study can reach the values of several percent with respect to the power losses at the fundamental frequency and can exceed 10% regarding the power losses caused by conventional current harmonics. &nbsp

Stability Study and Nonlinear Analysis of DC–DC Power Converters With Constant Power Loads at the Fast Timescale

Rapidly growing distributed renewable networks make an increasing demand for various types of power converters to feed different loads. Power converters with constant power load (CPL) are one typical configuration that can degrade the stability of the power conversion system due to the negative impedance characteristic. This article presents a nonlinear analysis method using the developed complete-cycle solution matrix method by transforming the original linear time-variant system into a summation of segmented linear time-invariant systems. Thus, the stability of the nonlinear system can be studied using a series of the corresponding state transition matrix and saltation matrix. As this derived matrix contains all the comprehensive information relating to the system’s stability, the influence of the CPL to system’s fast-timescale stability in both continuous conduction mode and the discontinuous conduction mode can be fully investigated and analyzed. The phenomena of the fast-timescale instability around switching frequency for power converters with a CPL are observed and investigated numerically. Finally, experimental results have proven the analysis and verified the effectiveness of the developed method.

Estimation of Power Losses Caused by Supraharmonics

Nowadays increases the number of power electronic devices in distribution electrical networks rapidly. Modern generation and consumption units use high switching frequency power converters for the network connection and therefore cause the voltage and current distortion in the frequency range over 2 kHz (so-called “supraharmonics”) in addition to conventional harmonics. Supraharmonics cause additional power losses in electrical equipment. The goal of the offered paper is the estimation of power losses caused by supraharmonics. The estimation is based on the measurement results obtained in a real MV/LV network in Germany.

A Very High Frequency Self-Oscillating Inverter Based on a Novel Free-Running Oscillator

This letter introduces a self-oscillating very high-frequency (VHF) class $\phi$ 2 inverter based on a free-running oscillator. The class $\phi$ 2 is a low-voltage semiconductor stress, fast-transient, single-transistor inverter topology suitable for VHF applications. With new advancements in GaN technology, the tendency to increase the switching frequency in power converters is on the rise. Switching at VHF (VHF: 30–300 MHz) allows for smaller passive components and more compact power converters. However, although GaN components are able to switch at 100 MHz and beyond, gate drivers available in the market struggle to provide the adequate switching signal at VHF. Hence, there is a need for an alternative to VHF converters using those gate drivers—self-oscillating topologies. To that end, a self-oscillating class $\phi$ 2 inverter switching at 30 MHz is presented and a design methodology is provided. A 30 MHz prototype with 30 V input voltage using a GaN Systems GS61004B is also built and tested, showing good matching between the simulation and experimental results.

Power Electronic Converter Based Flexible Transmission Line Emulation

A power electronic converter based transmission line emulator (TLE) is presented in this paper. The TLE can emulate medium and long lines in steady-state and symmetrical faults occurring at any point in the line. A traveling wave based numerical scheme for the emulation of the line is identified and then implemented on a novel digital architecture in the field-programmable gate array part of a system on chip platform. The proposed architecture meets the real-time computation constraints through parallel processing and optimal use of hardware resources (DSP slices, block RAMs, etc.). A comprehensive analysis to determine the two important parameters of the TLE-the power converter switching frequency and observer update period while satisfying a number of constraints coming from the numerical scheme, power, and embedded hardware-has been presented. Finally, relevant simulation and experimental results on a developed 400-V 15-kVA TLE prototype have been presented for validation.

High-Frequency PCB Winding Transformer With Integrated Inductors for a Bi-Directional Resonant Converter

The momentum toward high power density high-efficiency power converters continues unabated. The key to reducing the size of power converters is high-frequency operation and the bottleneck is the magnetic components. With the emerging widebandgap devices, the switching frequency of power converters increases significantly, to hundreds of kilohertz, which provides us the opportunity to adopt printed circuit board (PCB) winding planar magnetics. Compared with the conventional litz-wire-based magnetics, planar magnetics can not only effectively reduce the converter size, but also offer improved reliability through automated manufacturing process with repeatable parasitics. Another way to reduce the number of magnetic components and shrink the size of power converters is through the magnetic integration. In this paper, a novel PCB winding based magnetic structure is proposed to integrate both inductor and transformer into one component. In this structure, the inductor value can be easily controlled by changing the cross-sectional area of the core or the length of the air gap. A 6.6-kW 500-kHz CLLC resonant converter prototype with 98% efficiency and 130-W/in3 (8 kW/L) power density is built to verify the feasibility of the proposed PCB winding based magnetic structure.

FPGA Implementation of a Novel Oversampling Deadbeat Controller for PMSM Drives

This paper presents a novel oversampling deadbeat current control approach for permanent magnet synchronous motor drives capable of operating at a controller sampling frequency multiple of the power converter switching frequency. Model-based controllers suffer from heavy computational demand and performance degradation due to parameter uncertainties. The proposed controller concurrently with field-programmable gate array implementation permits to achieve a constant switching frequency and an optimal current ripple along with a high current-loop bandwidth and robust behavior to parameter variation. A disturbance observer has been added to the proposed controller in order to compensate for the converter voltage distortions. The proposed control strategy is tested through both simulations and experiments.

Soft-switched quasi-Z-source inverter-fed permanent magnet synchronous machine for hybrid/electric vehicle applications

The switching frequency of power converters is increasingly high to reduce the size of passive elements and improve the dynamic performance of electric power-train in hybrid/electric vehicle applications. Thus, the development of soft-switching technology devices has taken an accelerated pace. This paper introduces a novel soft switching bidirectional quasi-Z-source inverter (QZSI). By using a resonant capacitor and coupled inductors, the proposed QZSI topology provides a solution to hard-switching problems for variable speed electric drives for hybrid/electric vehicle applications. A soft switching topology is presented, which aims at reducing active devices switching stresses as well as mastering the slew rate dv/dt that have an adverse effect over the motor/generator windings. The effectiveness of the proposed topology has been analytically studied and simulated in Matlab/Simulink and the results have been validated by experiment for both propulsion (motoring) and braking (generating) modes on the laboratory test bench.

A Review of Passive Power Filters for Three-Phase Grid-Connected Voltage-Source Converters

In order to reduce size and cost, high-order passive filters are generally preferred in power converters to cancel out high-frequency harmonics caused by pulsewidth modulation. However, the filter resonance peaks may require the use of passive dampers to stabilize the interactions between the load and source impedances. Furthermore, the stabilizing effect is more difficult to be guaranteed for cost-optimized filters, which are characterized by low-inductance and high-capacitance passive components. In this paper, several passive filter topologies used to interface voltage-source converters with the utility grid are reviewed and evaluated in terms of damping capability, stored energy in the passive components, and power loss in the damping circuit. In addition, the influences of different switching frequencies of power converters on the passive filter design are discussed in the range 1–15 kHz. Illustrative design examples of the passive filters and experimental data are also provided.

Resonant gate driver with efficient gate energy recovery and switching loss reduction

This article describes a novel resonant gate driver for charging the gate capacitor of power metal-oxide semiconductor field-effect-transistors (MOSFETs) that operate at a high switching frequency in power converters. The proposed resonant gate driver is designed with three small MOSFETs to build up the inductor current in addition to an inductor for temporary energy storage. The proposed resonant gate driver recovers the CV2 gate loss, which is the largest loss dissipated in the gate resistance in conventional gate drivers. In addition, the switching loss is reduced at the instants of turn on and turn off in the power MOSFETs of power converters by using the proposed gate driver. Mathematical analyses of the total loss appearing in the gate driver circuit and the switching loss reduction in the power switch of power converters are discussed. Finally, the proposed resonant gate driver is verified with experimental results at a switching frequency of 1 MHz.

PMSM Drive Position Estimation: Contribution to the High-Frequency Injection Voltage Selection Issue

High-frequency injection (HFI) is an alternative method to estimate permanent magnet synchronous motor (PMSM) rotor position using magnetic saliency. Once the maximum fundamental electrical frequency and the power converter switching frequency are set, the HFI voltage amplitude tuning is generally based on trial and error. This paper proposes a methodology to select the appropriate high-frequency signal injection voltage amplitude for rotor position estimation. The technique is based on an analytical model taking into account the noise in the voltage supply to derive the resulting currents containing the information on the rotor position. This model allows setting the injection voltage amplitude that leads to the maximum acceptable position error for a given signal-to-noise ratio and a speed range. The approach is validated with the analytical and the global drive models through extensive simulations. Experimental results on a 1-kW PMSM drive confirm the interest of the proposed solution.

Iron Loss Calculation of AC Filter Inductor for Three‐Phase PWM Inverters

SUMMARYIn recent years, remarkable advancement of new power semiconductor devices, such as SiC and GaN, enables the increase of switching frequency of power converters, and hence the volume of passive components, such as ac filters and transformers, can be reduced. However, temperature rise caused by the inductor loss is increasing, and hence iron loss evaluation of the inductor is one of the most important issues to realize high power density converters. Conventionally, an improved generalized Steinmetz equation (iGSE) has proposed in order to calculate the iron loss under a pulse voltage magnetizing condition. However, accurate iron loss calculation of the ac filter inductor used in a PWM inverter cannot be realized. The authors have proposed two methods of iron loss evaluation of ac filter inductors. The first one is a loss map method which can calculate the iron loss without using a real PWM inverter. Another one is an ILA (Inductor Loss Analyzer) which can measure the iron loss in every switching period in a real PWM inverter. In this paper, comparisons of the iron loss between the ILA and the loss map method on both the single‐phase and three‐phase inverters are studied. It is found that iron loss of the ac filter inductor in the three‐phase PWM inverter which is calculated by the loss map method cause a large error on a specific condition. In order to prevent the calculation error, the authors proposed a revised loss map method and proved the effectiveness of the method.

Evolution of Very High Frequency Power Supplies

The ongoing demand for smaller and lighter power supplies is driving the motivation to increase the switching frequencies of power converters. Drastic increases however, come along with new challenges, namely the increase of switching losses in all components. The application of power circuits used in radio frequency transmission equipment helps to overcome those. However, those circuits were not designed to meet the same requirements as power converters. This paper summarizes the contributions in the recent years in the application of very high frequency (VHF) technologies in power electronics, which show the results of the recent advances and describes the remaining challenges. The presented results include a self-oscillating gate drive, air-core inductor optimizations, an offline LED driver with a power density of 8.9 W/cm 3 , and a 120-MHz, 9-W dc powered LED driver with 89% efficiency as well as a bidirectional VHF converter. The challenges to be solved before VHF converters can be used effectively in industrial products are within those three categories: 1) components; 2) circuit architectures; and 3) reliability testing.