Increasing Switching Frequency Research Articles

Grid current quality improvement for solid state transformer with an improved current controller

In this paper, the Solid-State Transformer (SST) is performed by integrating an improved harmonic compensator at the Modular Multilevel Converter (MMC) current controller in order to ensure grid current quality regardless the non-linear load or the unbalance position at the SST stages. The proposed MMC current controller is composed of a high-order harmonic compensator based on a fuzzy logic controller, giving the controller an active filtering feature, a low-order harmonic compensator, and a negative sequence harmonic compensator for unbalanced control. This makes the proposed solution a good alternative for solutions based on extra filters or increase switching frequency. Ensuring power quality independent of loads or unbalanced position in the SST while maintaining reduced switching frequency is the main focus. With the proposed current controller, both low order and high order harmonics are effectively attenuated, thereby consistently reducing the total harmonic distortion (THD) of grid current to levels complying with the IEEE-1547 standard, even when non-linear loads are placed at the LV and at the MV stage of the SST. In addition, the controller eliminates negative-sequence harmonics associated with unbalanced loads in the SST, thus preserving the balance of the grid current. Various results of the proposed current controller are presented.

Improved Design of a SiC MOSFET Gate Drive with Crosstalk Suppression Capability

For high-frequency switching applications, silicon carbide (SiC) devices are more suitable than silicon-based devices, which is conducive to improving the efficiency and power density of power electronic equipment. However, as the switching frequency increases, the influence of parasitic parameters on the switching characteristics of devices becomes increasingly apparent. When SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) are applied in bridge circuits, the crosstalk problem easily occurs with the complementary conduction of upper and lower transistors, which seriously limits the promotion of SiC MOSFETs. However, the existing crosstalk suppression drive circuit tends to increase the switching loss, switching delay, and control complexity; therefore, a gate drive with crosstalk suppression capability is proposed. In this paper, the gate drive has two features: a negative voltage to shut down the SiC MOSFET; and an adjustment of the gate-source equivalent impedance. To accomplish this goal, the mechanism of crosstalk voltage generation is analyzed. Furthermore, the operation principle of the gate drive is analyzed, and the parameters of the gate drive are designed. Eventually, the proposed gate drive is verified by an LTspice simulation and experimental platform. The results prove that the gate drive can suppress the crosstalk voltage without affecting the switching speed.

Research on strategy of load-side resonant soft-switching inverter based on interconnection and damping assignment-passivity based control

Soft-switching technologies can effectively solve the problem of switching losses caused by increasing switching frequency of grid-connected inverters. As a branch of soft-switching technologies, load-side resonant soft-switching is a hotspot for applications of high-frequency inverters, because it has the advantage of achieving soft-switching without using additional components. However, the traditional PI control strategy based on the linear model is prone to destabilization and non-robust dynamic performance when large signal perturbation occurs. In this paper, a novel Passivity-Based Control (PBC) method is proposed to improve the dynamic performance of load-side resonant soft-switching grid-connected inverter. Besides, the model based on the Port Controlled Hamiltonian (PCH) model of the soft switching inverter is carried out, and the passivity-based controller is designed based on the established model using the way of interconnection and damping assignmentpassivity based control (IDA-PBC). Both stable performance and dynamic performance of the load-side resonant soft-switching inverter can be improved over the whole operating range. Finally, a 750 W load-side resonant soft-switching inverter simulation model is built and the output performance is compared with the traditional PI control strategy under stable and dynamic conditions. The simulation results show that the proposed control strategy reduces the harmonic distortion rate and improves the quality of the output waveforms.

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.

Novel Auxiliary Resonant Pole Inverter and its Optimal Control Strategy

Conventional inverters operate in hard‐switching mode, and as the switching frequency increases, the switching losses increase dramatically. Increasing the switching frequency helps reduce the size and cost of the inverter, but too high a switching frequency generates greater switching losses, which affects the inverter's transmission efficiency. In response to the problem that conventional hard‐switching inverters cannot be higher in frequency and have high switching losses and low transmission efficiency, an optimized auxiliary resonant commutated inverter and control strategy are proposed to make the inverter work in soft‐switching mode, which helps reduce the switching losses. The auxiliary converters in the bridge arm topology of each phase of the three‐phase inverter are divided into two groups, and the operating auxiliary converters are selected according to the direction of the load current. When the load current direction is positive, the upper bridge arm auxiliary device works and the lower bridge arm auxiliary device turns off, similarly when the load current direction is negative, the lower bridge arm auxiliary device works and the upper bridge arm auxiliary device turns off, this can ensure that only one group of devices works every half cycle, making the control strategy simple and reducing auxiliary circuit losses. Simulation and experimental verification of the effectiveness of the proposed scheme. © 2023 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Design of 3-Level T-type NPC Inverter for EV Applications

In recent years, there has been a significant demand for lightweight converters that provide exceptional control performance while generating minimal acoustic noise. This has resulted in higher switching signals for hard- switched 2-level low voltage 3-phase inverters. However, the increased switching frequencies have a negative impact on the inverters’ efficiency, requiring the use of expensive switch technology to maintain high efficiency. This paper aims to tackle these challenges by introducing the design and implementation of a extremely effective 3-Level T-Type Neutral Point Clamped (NPC) inverter designed for Electric Vehicle (EV) applications. 3-Level T-Type NPC inverter associates the strengths of both NPC and T-Type inverters. Similar towards the NPC, it offers a lower breakdown voltage for the switching devices, thereby reducing switching losses. Additionally, it shares the characteristics of the T-Type inverter, resulting in fewer conduction losses. To validate the feasibility of the converter, simulation is performed using MATLAB software, followed by the development and testing of a lab-scale prototype. The proposed three-level T-type NPC inverter have several merits over traditional 2-level inverters, including reduced distortion, switching losses, and improved efficiency. These benefits contribute to enhanced motor drive performance, reduced electromagnetic interference (EMI), and extended battery life in EVs.

Interruption Tolerance Strategy for LEO Constellation With Optical Inter-Satellite Link

Optical inter-satellite link (ISL) with tens/hundreds Gbps is applied into LEO constellation to overcome the insufficient bandwidth of microwave ISL. Moreover, compared with GEO/MEO constellation, LEO constellation suffers from frequent topology switching because of the lowest orbital-altitude. Topology switching between adjacent topology snapshots is generally done through ISL handover (remove or establish ISL). However, service interruption caused by ISL handover within topology switching is a vital issue to address. After ISL handover occurs, isolated topology and slow route convergence (derived from long ISL delay and forwarding the updated message among hundreds/thousands of satellites) may cause severe service interruption. But considering the fact that time-varying topology is predictable and all the ISL handover could be pre-scheduled for topology management purpose, service interruption problem is investigated from the aspect of ISL handover and routing strategy in this paper. Owing to long establishing time of optical ISL, grouped optical ISL handover scheme is raised to decrease route convergence time during topology switching. Furthermore, predictive-update routing scheme based on Open Shortest Path First (OSPF-PUR) is proposed to minimize route convergence time for each ISL handover. For predictable ISL handover, in OSPF-PUR scheme, forwarding table is refreshed according to locally stored ISL handover information but without flooding. Simulation results illustrate that grouped optical ISL handover scheme reduces route convergence time within topology switching while topology connectivity is guaranteed. The route convergence time of ISL handover is effectively decreased by OSPF-PUR scheme. Besides, for OSPF-PUR scheme, packet loss rate remains unchanged while topology switching frequency increases.

Conditional-Extreme-Point Based Fault-Tolerant Predictive Control of Five-Phase PMSM With Low Switching Frequency

The virtual voltage vector (VVV) based fault-tolerant control has been widely concerned, but suffering from the increased switching frequency and the reduced bus voltage utilization at the faulty operation. Also, the harmonic space is uncontrollable. This paper proposes a conditional-extreme-point based fault-tolerant model predictive control for a five-phase permanent magnet synchronous motor. The conditional extreme point is used to predict the optimal reference voltage vector. Firstly, to suppress the harmonics, dual control sets are established without the sacrifice of bus voltage utilization. Then, the unconditional extreme point and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> -axis voltage are predicted to select the appropriate control set, and two adjacent vectors are pre-selected for generating the optimal reference voltage vector. Subsequently, the conditional extreme point of the cost function is calculated to obtain the optimal reference voltage vector. Due to the unemployment of the null vector, the switching frequency is greatly reduced. Finally, the experimental results are presented to verify the proposed control scheme.

Analysis and Suppression of Common Mode Interference in Flyback Switching Power Supplies

In the flyback power supply, with the increase of switching frequency, the electromagnetic interference caused by the power switch becomes more and more serious. In order to control the interference problem, the common mode (CM) interference noise source and transmission path of the flyback power supply are analyzed, the equivalent model of the transmission path is established, and the parameters affecting the common mode noise magnitude are deduced. On this basis, an active gate driver (AGD) circuit is proposed to suppress the noise generated by interference sources. The AGD circuit reduces the du/dt of the power switching tube by reducing the driving current during the turn-off dynamic period and thus achieves the reduction of the common-mode noise. Compared with traditional drive mode, the AGD can increase switching losses less at the same target. Finally, the feasibility of the AGD method is verified by experiments on the test platform.

An improved maximum boost control technique for CDBC-based three-level ZSI

ABSTRACT This study presents an improved maximum boost control (MBC) method for three-level impedance source inverter. This technique offers removal of sixth frequency component from the inductor current present in the existing MBC technique of ZSI (Impedance Source Inverter). In addition, the proposed technique reduces the common mode voltage to 1/6th of dc bus voltage. The conventional zero vectors of three-level switching diagram are suitably modified and implemented for the case of 3L-CDBCZSI (three level controlled diode bridge clamped based impedance source inverter). It offers increased switching frequency of impedance network and reduces the size of passive components. On the basis of the proposed technique, the merits offered by 3L-CDBCZSI are highlighted and compared with T-type and diode clamped based ZSI. Simulation and experimental results are presented to verify the correctness of the proposed method.

High-Frequency Characteristics Analysis of Transformer-Based Voltage Multiplier in Lightweight Process of Unidirectional High Step-up Converters for Offshore Wind Farms

To realize the lightweight of unidirectional high step-up converters for offshore wind farms, it is necessary to increase the switching frequency. However, there is a gap in the analysis of the switching frequency effect, the frequency characteristics of the converter are not clear enough to provide theoretical guidance for the high-frequency design. To address this problem, the effect of switching frequency on the voltage conversion ratio (VCR) and maximum output power (MOP) of the widely used transformer-based voltage multiplier (TBVM) in unidirectional high step-up converters is discussed in this paper. More accurate mathematical models for two types of TBVMs, pulse-width-modulation TBVM (PTBVM) and resonant TBVM (RTBVM) are established. The effect of frequency on VCR, MOP, stresses together with losses is analyzed in detail accordingly. Theoretical analysis and comparison show that, in PTBVM, the increase in switching frequency decreases MOP and enlarges the VCR sensitivity to the load, and power switches suffer from large current stresses due to circulating power. In contrast, RTBVM is more suitable for high-frequency applications for the following advantages: duty cycle independent characteristics, higher maximum output power, higher efficiency, and load-insensitive VCR. Finally, experiments at 100 kHz switching frequency verified the theoretical analysis.

Reducing heat generation in a boost inductor using a magnetic tape

Increasing the switching frequency of direct current–direct current converters is effective in reducing the size of magnetic components used in converters. However, as the switching frequency increases, the loss and heat generated by the magnetic components increase. Therefore, in this study, a magnetic tape that bypasses the magnetic flux in the windings of magnetic components is proposed to reduce the loss and heat generation of these components. The effect of suppressing the temperature rise of magnetic components with a magnetic tape during the converter drive was investigated. The temperature rise of a 1-MHz 100-V/200-V 800-W boost inductor was reduced by 16.8 K by applying the magnetic tape. Additionally, applying the magnetic tape to the inductor reduced the heat generation.

Analytical modelling of high‐frequency losses in toroidal inductors

AbstractToroidal inductors are widely used in power electronic systems. With the increasing switching frequency of power devices, the AC losses of high‐frequency inductor windings have become an issue that cannot be ignored in design. A method with low computational time cost and high accuracy is urgently needed by designers. This paper proposes a modified analytical method for winding loss calculation of toroidal inductors based on the one‐dimensional Dowell method and the two‐dimensional Ferreira method, and proposes a compensated analytical model considering the proximity effect of inter‐turn conductors of toroidal windings. The analytical method calculates the non‐linear porosity of toroidal windings, and can accurately solve the AC losses of toroidal inductors with arbitrary porosity winding encapsulation. The analytical results are in good agreement with the finite element method (FEM) and experimental data. The experimental measurement data verifies the validity of the proposed model within 1‐MHz frequency, the calculation error of the modified analytical method is less than 25%, and the calculation error of the compensated analytical model is reduced to 10%.

Design of a 7.5 kW Dual Active Bridge Converter in 650 V GaN Technology for Charging Applications

High-voltage GaN switches offer low conduction and commutation losses compared with their Si counterparts, enabling the development of high-efficiency switching-mode DC–DC converters with increased switching frequency, faster dynamics, and more compact dimensions. Nonetheless, the potential of GaN switches can be fully exploited only by means of accurate simulations, optimal switch driving, suitable converter topology, accurate component selection, PCB layout optimization, and fast digital converter control. This paper describes the detailed design, simulation, and implementation of an air-cooled, 7.5 kW, dual active bridge converter exploiting commercial 650 V GaN switches, a compact planar transformer, and low ESL/ESR metal film capacitors. The isolated bidirectional converter operates at a 200 kHz switching frequency, with an output voltage range of 200–500 V at nominal 400 V input voltage, and a maximum output current of 28 A, with a wide full-power ZVS region. The overall efficiency at full power is 98.2%. This converter was developed in particular for battery charging applications, when bidirectional power flow is required.

Decomposed Nearest Level PWM Method With Reduced Switching Frequency for MMC

For modular multilevel converters in medium-voltage applications, the nearest level pulse width modulation (NL-PWM), which combines the nearest level modulation (NLM) with pulse width modulation (PWM), has the advantage of better harmonic characteristics over conventional NLM. However, the introduction of high-frequency PWM also results in a significant increase in switching frequency. To solve this issue, a decomposed NL-PWM method is proposed in this article. By properly allocating the rising edge and falling edge of PWM to two different SMs, the capacitor voltage differences can be decreased more efficiently. On this basis, the allocation priority of different switching transitions is quantitatively analyzed, and then a new voltage-balancing strategy involving five switching modes is proposed. Moreover, to achieve a good tradeoff between voltage-balancing effect and switching loss, the relationship between voltage threshold and switching frequency under the proposed method is also derived. Finally, the comparative simulation and experimental results demonstrate the superiority of the proposed method in different aspects of performance.

Research on the Switching Characteristics Based on the SiC MOSFET Model

With the continuous development of power electronics technology, the third-generation semiconductor materials represented by SiC and GaN have significant advantages in the band gap width, breakdown electric field, thermal conductivity, electron saturation rate and other key parameters, which meet the needs of modern industry for high power, high voltage and high frequency. When the SiC MOSFET plays its high frequency advantage, with the increase of switching frequency, the voltage change rate and current change rate of the device will be larger in the process of turning on and off. This paper mainly analyzes the characteristics of SiC MOSFET devices, and modifies the model based on the model provided by the manufacturer. By establishing static and dynamic test circuits, the static characteristic curves of the model were observed, and the drain voltage and current waveforms of the original model and the optimized model were compared during the switching process. The results show that the switching time of the optimized model is improved, and the oscillation waveform is greatly improved. Then, the accuracy of the optimized model is verified by the double-pulse circuit, and the drain source voltage and the drain source current are studied and observed under different temperature and drive resistance conditions. This paper provides data support for improving the switching characteristics of SiC MOSFET in practical applications.

Stabilizing multi-rotation periodic trajectories by the time-varying switching extended time-delay feedback control

Control parameters are frequently subjected to certain restrictions in the engineering practice of chaos control. It is difficult to stabilize multi-rotation unstable periodic trajectory when the stability range is too small and outside the restrictions of control parameters. Thus, it is fundamentally important to expand the stability range of the controlled multi-rotation unstable periodic trajectory by using an applicable method. In this work, the original extended time-delay feedback control is improved based on the time-varying switching strategy, which leads to the time-varying switching extended time-delay feedback control. The time-varying switching extended time-delay feedback control only applies the control to the controlled system in a specific period, and does not apply the control to it in other periods, this is different from the continuous control of the original extended time-delay feedback control. The specific performance of the time-varying switching extended time-delay feedback control in stabilizing unstable multi-rotation periodic trajectories is investigated by case studies. The maximum Floquet multiplier of the controlled periodic trajectory is calculated, and the relationship between the stability region of the controlled multi-rotation periodic trajectory and the switching frequency is obtained. The results show that with the increase of switching frequency, the stability region of the controlled multi-rotation periodic trajectory presents a non-smooth change. In particular, the stability region of the time-varying switching extended time-delay feedback control is significantly larger than that of the original extended time-delay feedback control when an appropriate switching frequency is selected.

Novel Common Mode Voltage Elimination Methods in Three-Phase Four-Wire Grid-Connected Inverters

This paper presents two current control methods to attenuate the common mode (CM) conducted emissions in three-phase four-wire four-pole inverters connected to an AC distribution bus and operating in grid-following mode. Delta modulation and model predictive control both achieve elimination of the common mode voltage at the output of the three-phase four-pole inverter and meet the requirements of the military standard 461G without a full-size CM choke. The differential mode performance is comparable to that achieved with the benchmark three-dimensional space vector modulation, which does not cancel the CM voltage. A physics-based model of the system was developed to simulate the conducted emissions and DM performance of the two proposed methods. As the CM voltage cancellation methods result in increased switching frequency, wide bandgap devices were used to build a laboratory prototype, on which the simulated results were successfully validated.

Evaluation and Performance of Three-Phase Inverter Using Multiple Bidirectional Choppers Intended for 1.5-kVdc PV Systems

This article focuses on the chopper-cell number of a novel three-phase inverter for utility-scale photovoltaic (PV) systems where multiple cascaded bidirectional chopper cells and a three-phase line-frequency transformer with a three-legged core are used. The inverter per phase is composed of a main converter, which is equivalent to the conventional bidirectional chopper, and an auxiliary converter, which is composed of multiple cascaded chopper cells. Although the inverter performance can be improved by increasing the chopper-cell number because of increased switching frequency and reduced voltage steps, the increased cell number may result in increased converter loss and cost. However, no paper has evaluated the chopper-cell number of the inverter to the best of the authors’ knowledge. Further, no paper has carried out experimental verification of the inverter during the power faults. This article evaluates the inverter using two cells per phase (two-cell inverter) with the one using three cells per phase (three-cell inverter) under the same equivalent switching frequency in terms of converter loss, efficiency, and steady/transient state performance. The numerical analysis shows that the two-cell inverter shows superiority over the three-cell inverter in converter efficiency. Further, the experiments using a 1.5-kW downscaled model verify the inverter performance under the normal and fault conditions.

Ultrafast Current Shunt (UFCS): A Gigahertz Bandwidth Ultra-Low-Inductance Current Sensor

In an effort to reduce switching loss, increase switching frequencies, and shrink passive component sizes, power device switching times are being pushed into nanosecond and subnanosecond intervals. However, these fast switching times require high rates of change of current making the power devices susceptible to overvoltage damage from parasitic inductance in the power loop. This presents challenges in measuring the device switching current accurately and, in turn, makes accurate measurements of device switching energy and stored charge difficult. Traditional current measurement methods either do not have the required frequency response to view the switching edge accurately or have a high parasitic inductance that can significantly alter switching performance and cause damage to the power device. In this article, an active current measurement system is developed. This circuit achieves up to 1.6-GHz bandwidth with zero overshoot. By utilizing mutual inductance cancellation, an insertion inductance down to 20 pH has been achieved. The research performed in this article thereby allows for an accurate measurement of device switching loss with minimal power circuit disturbance. The performance of this current measurement is experimentally verified in the frequency domain using a vector network analyzer, and time-domain switching measurements are compared with state-of-the-art current measurement.