Soft-switching Mode Research Articles

APPLICATION OF SOFT SWITCHING IN THREE-PHASE VOLTAGE INVERTERS OF TRACTIONAL ROLLING STOCK

Autonomous voltage inverters with PWM, which are used in electric drive systems with brushless motors, occupy an important place in the complex of electrical equipment of modern traction rolling stock of railways. The article presents the results of the research of the traction three-phase bridge voltage inverter with soft switching of power switches. Using the soft switching mode allows you to reduce the switching losses in the power transistors of the keys, increase the PWM frequency and improve other performance indicators of the converter. It is advisable to implement soft switching in the key transistors of the three-phase voltage inverter using soft switching nodes with fast-acting four-quadrant switches based on IGBT. It is proposed to consider the possibility of using transistor switches of a voltage inverter with capacitive non-dissipative snubbers at high PWM frequencies. For this purpose, a synthesis of the scheme and algorithm for the implementation of soft switching in a three-phase bridge voltage inverter with bipolar sinusoidal PWM with soft switching nodes with high-speed four-quadrant switches based on IGBT was performed. An analysis of the characteristics of the three-phase voltage inverter was carried out when using high-speed switches in the soft switching nodes to implement soft switching in the power transistors of the inverter switches.On the basis of the study, it is proposed to modernize the scheme of the soft switching unit in order to provide better preparation for the switching of the power transistors of the keys at large load currents. The improved soft switching unit includes low-voltage sources of constant voltage, which will compensate for energy losses in the recharging circuit of the snubber capacitors and contribute to the soft switching on of the power transistors of the voltage inverter keys. The performance test was carried out and the characteristics of the converter were analyzed when using a modernized soft switching node using simulation modeling in the MATLAB package.

Control Design for Soft Transition for Landing Preparation of Light Compound-Wing Unmanned Aerial Vehicles Based on Incremental Nonlinear Dynamic Inversion

This paper proposes a soft switching mode for electric vertical takeoff and landing (eVTOL) compound-wing unmanned aerial vehicles (UAVs) to achieve a smooth transition between modes. The proposed mode pre-compensates the lift loss with the rotary wing during the deceleration stage before UAV landing. The control law adopted in this paper consists of implicit nonlinear dynamic inversion (NDI) and incremental nonlinear dynamic inversion (INDI). The outer loop (attitude angle loop) control law is based on implicit NDI, while the inner loop (attitude angle rate loop) controller is based on INDI. An extended state observer (ESO) is employed to estimate the angular acceleration. This paper innovates by proposing a soft switching strategy that improves the robustness, safety, and smoothness of the transition for the compound-wing UAV, and applying advanced control law to mode transition design. For the future application of eVTOL aircraft in UAM scenarios, this paper evaluates the smoothness of transition and passenger comfort using normal overload as a physical quantity. The Monte Carlo (MC) simulation results demonstrate that the proposed mode can reduce the peak normal overload by about 89%.

An Innovative Design Approach for Resonant DC/AC Converters, Based on Symmetry in Their Operating Modes

The manuscript presents an innovative approach for the engineering design of resonant DC/AC converters used as sources of high-frequency electricity for a variety of needs: industrial and domestic applications, wireless power transmission, high-performance lighting, and more. The methodology is based on the generalized consideration of electromagnetic processes in a series resonant RLC circuit fed by a square-wave voltage source. Due to the symmetry in the form of the current in the AC circuit of the DC/AC converter, it is possible to generalize all their possible operating modes. This was realized by applying the quasi-boundary method to the analysis of resonant DC/AC converters with and without reverse diodes operating in soft and hard switching modes. On this basis, the transfer functions of the devices, which give the relationship between their output and input voltages, are defined and analytically determined. Additionally considered are cases of resonant DC/AC converters with complex output circuits, which are applied to match the load needs and the capabilities of the power electronic device. In this sense, the basic dependencies for designing the main types of resonant DC/AC converters using series and parallel load compensation are given. The effectiveness of the proposed methods is demonstrated through several examples, and their verification and validation is achieved with simulations and prototypes. The proposed innovative design approach is applicable not only in power electronics education, but also in the design and prototyping of a whole class of power electronic devices. The unification of design methodologies formalizes and algorithmizes the design process, which is an important step for its automation and for applying various optimization procedures to achieve certain goals.

Junction temperature monitoring for cascode GaN devices using the Si MOSFET's body diode voltage drop

In this paper, a new online junction temperature monitoring method is proposed for cascode GaN devices using the body diode of Si MOSFET. The reverse current during soft-switching mode is utilized to extract the voltage drop of the Si MOSFET's body diode. It is pointed out that, to accurately obtain the voltage drop of Si MOSFET's body diode, the VDS voltage of cascode GaN device should be measured when the reverse current is small during the dead-time period. An experimental platform has been designed to validate the proposed method. The proposed method exhibits an accuracy within 0.6 °C and a R2 = 0.99 goodness of linear fit on a test Buck converter, showing that this method is practical for real applications.

A Novel Hybrid Multilevel DC–DC Converter Employing Trapezoidal Modulation

This paper presents a new hybrid multilevel converter for medium voltage dc-dc interconnection. The structure of the topology is a hybrid of two level converter and the modular multilevel converter (MMC). The proposed converter provides three-phase trapezoidal output voltages with a controlled slope while using only a single MMC leg. Therefore, using fewer SMs and sensors, and with its feature of low energy storage requirement (ESR), the overall size of the converter reduces. The front-to-front configuration of the proposed converter provides the desired voltage matching, grounding flexibility and dc fault blocking capability. Moreover, the phase leg switches and the bidirectional switches (BSs) of the converter are operated in the soft switching mode reducing the converter losses. A detailed mathematical analysis is presented to substantiate the low ESR and losses of the proposed converter. The performance evaluation of the proposed dc-dc converter is carried out in PSCAD/EMTDC and analyzed in detail. The operation of the converter is also verified on a developed scaled-down laboratory prototype. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup>

Topology and control strategy optimization of an auxiliary resonant commutated pole-based, soft-switching grid-connected inverter

With the development of new energy industries such as photovoltaics, microgrids, or distributed energy sources require many DC-AC grid-connected interfaces. Reducing the switching loss of the inverter is important to improve the transmission efficiency of the inverter, reduce the heat generation of the inverter, promote the high frequency and miniaturization of the inverter, and efficiently use the distributed energy. Therefore, considering the wide application of DC-AC power electronic interfaces in microgrid and distributed energy, and to make up for existing deficiencies in traditional hard-switching inverters, an optimal control strategy and topology for an optimal-auxiliary resonant commutated pole (O-ARCP) inverter is proposed in this article. Firstly, this paper introduces the proposed inverter topology and analyzes the operation mode of the circuit with the control strategy. Then simulation experiments in islanding mode are carried out to verify the rationality of the content, and finally simplified experimental verification is carried out based on the simulation results. Simulation and experimental testing reveal that all switches of the proposed topology are in soft-switching mode, which proves the effectiveness of the proposed control strategy and analysis. The analysis and validation of this paper provide assistance in the development of control strategies and structures for soft-switching inverters.

Reverse Current Stress Induced Dynamic Ron of GaN HEMTs in Soft-Switching Mode

Reverse Current Stress Induced Dynamic R_on of GaN HEMTs in Soft-Switching Mode

Энергоэффективный конденсаторный DC-DC преобразователь для автономной системы электроснабжения

The main requirement for autonomous power supply systems is improved weight-size and energy parameters. A promising way to solve this problem is to use DC-DC converters based on resonant structures with switched capacitors. Improvement of energy indicators of the converter is achieved due to soft-switching mode of semiconductor elements providing reduction of dynamic power losses and increasing the level of the primary source. Improvement of weight-size parameters of the converter is provided due to the following: multi-cycle principle of the design providing a significant increase of frequency conversion up to several hundred kHz due to multiple reduction of installed capacity of semiconductor elements; high specific energy indicators of modern multilayer ceramic capacitors, more than two orders of magnitude higher than similar indicators of reactors and transformers; optimization of parameters of semiconductor and reactive elements, which also contributes to significant reduction of weight and volume of power supply systems. The authors have conducted the analysis of weight-size parameters of the step-up DC-DC converter and the value of its efficiency under the assumption of proportionality of weight and volume of reactive converter elements to the maximum accumulated energy and proportionality of weight and volume of semiconductor elements to their installed capacity. The authors have proposed and studied the circuit of multipolar DC-DC converter based on structures with switched capacitors, which has the space symmetry. The space symmetry provides a significant improvement of weight-size parameters due to two-fold reduction of the total installed capacity of semiconductor elements. The volume and energy indicators of the converter under study as a part of power supply system have been evaluated. A method to design a power circuit of a capacitor converter with improved energy and weight-size parameters as a part of an autonomous power supply system is proposed. The authors have established the most effective ways to improve the weight-size and energy indicators of DC voltage converters. The improvement of weight-size parameters is achieved due to a twofold reduction of the installed capacity of semiconductor elements and optimization of the parameters of reactive elements. Improvement of energy indicators is achieved due to increasing the input voltage level of the converter and soft switching of its semiconductor elements.

Perturbation Observation Method-Based Optimization Seeking Control of Soft-Switching and No Backflow Power for LCL Resonant-Type Dual Active Bridge DC–DC Converters

LCL-type resonant dual active bridge (LCL-DAB) DC-DC converters feature high gain, high power density, and low reactive current. To further improve the efficiency, based on the dual-phase shift (DPS) modulation method, the operating characteristics are firstly derived and the design regions of soft-switching and no backflow power are established, and then a perturbation observation method based optimization seeking control of soft-switching and no backflow power is proposed in this paper. In the starting process, the system firstly tracks the reference voltage according to the relationship between the inner and outer phase shift ratio obtained by the first harmonic approximation. Then, the outer phase shift ratio is perturbed based on the characteristics of soft-switching and backflow power, approaching the target phase shift ratio stepwise, while the inner phase shift ratio is calibrated to hold the output voltage. Both H bridges can operate in soft-switching mode, and on this basis, the backflow power was eliminated to the maximum extent. Finally, the simulation and experimental results verified the feasibility and effectiveness of the proposed method.

A Single-Stage AC–DC Converter Based on Semi Dual-Active-Bridge With Decoupled Inductor Current Modulation Strategy

In this article, a novel decoupled inductor current modulation strategy for a single-stage AC-DC converter based on semi-dual-active-bridge (semi-DAB) is proposed, which helps to minimize the total harmonics distortion (THD) and improve the conversion efficiency. The transformer turns ratio is designed in an optimized method for higher conversion efficiency. Only two control variables are used. And the converter could achieve wider output voltage range and high power factor without mandatory current tracking loop and look-up tables. In addition, losses, THD and backflow power comparisons between the decoupled inductor current and the optimal peak current modulation are presented. The power transfer capability, mode transition mechanism, soft switching range and mode operation region and parameter design are analyzed. Switches can achieve zero-voltage-switching (ZVS) within wide operating rang and rectifier diodes can achieve zero-current-switching (ZCS) off in all operation situations. Besides, a 1kW experimental prototype was built to verify the effectiveness of the proposed control strategy.

A Reconfigurable AC Power Cycling Test Setup for Comprehensive Reliability Evaluation of GaN HEMTs

To address the challenges in long-term reliability testing of GaN power devices, this paper proposes a reconfigurable AC power cycling test setup. While addressing the limitations of existing aging tests, the proposed setup enables accelerated aging of GaN devices under a wide range of realistic stress conditions. Specifically, various hard and soft switching modes can be tested to realistically emulate different application scenarios. In addition to the ability to control test temperature, the setup also features adjustable power loop inductance that enables precise control over voltage overshoot during hard switching transients. Further, an on-state resistance based junction temperature estimation technique is used for closed loop junction temperature control. For this, a fast drain-source voltage measurement circuit along with an algorithm for closed-loop control of the mean junction temperature is presented in detail. Furthermore, the magnitudes of the temperature swing under different operation conditions are discussed in depth which provides a good insight to control temperature swings. Finally, a prototype is built to validate the proposed test design.

Hybrid intelligent system for a synchronous rectifier converter control and soft switching ensurement

This research implements an intelligent control strategy in a synchronous rectifier buck converter to assure that the converter operates in soft-switching mode. The converter is analysed and the two different switching modes are presented: Hard-switching and Soft-Switching. Afterwards, an intelligent model is implemented with the aim of identifying and classifying the switching mode of the power converter. The model implementation is based on classification methods through intelligent algorithms that differentiate between the two modes of operation. Satisfactory results have been obtained with the implemented classification method, achieving high accuracy and allowing the implementation of the model into the control strategy of the converter; assuring that the converter operates in the desired operating mode: Soft-Switching mode.

Импульсные частотно-фазовый и частотно-широтный способы регулирования выходной мощности резонансного инвертора напряжения для индукционного нагрева

The article considers the issue of the use of a combined pulse together with a frequency phase or latitude control method, with the mandatory fulfillment of the conditions of the soft switching mode. The limits of the application of the combined method are considered, under which the conditions of the mode are met, its effectiveness in terms of narrowing the frequency range, as well as the question of implementing the combined method due to the relationship established in the work of the frequency detuning of the inverter from the latitude and phase parameters of the power key control pulses.

Mixed Inverter Regulation Method for Induction Heating

One of the commonly used methods of voltage source inverter regulation for induction heating is a frequency method of regulating the output power of the inverter, based on the frequency selectivity of the resonance load circuit. With frequency regulation at low values of the Q-factor of the resonance circuit, deep regulation of the output power is impossible. As a result, other methods of regulation are desirable. The article discusses the issue of using a mixed pulse and frequency phase or latitude regulation method under the obligatory conditions of the soft switching mode.

Medium Voltage Soft-Switching DC/DC Converter With Series-Connected SiC MOSFETs

Nowadays, due to the growing demands of data centers, the traditional line frequency transformer based data center power distribution system (DC-PDS) is becoming bulky and inefficient. Although SST-based DC-PDS dramatically improves the system efficiency, the traditional multicell SST with input-series output-parallel architectures has limitations. Using high-voltage devices to develop single-cell SST improves system performance, however, its application is limited by high-voltage power devices. As an alternative solution, achieving high blocking voltage through the series connection of low-voltage devices brings several advantages. Nevertheless, the series connection brings about two main problems, namely the voltage imbalance among devices and the increment of switching loss. This article proposes a medium voltage series resonant converter (MVSRC) with series-connected SiC MOSFETs. By adding snubber capacitor to each SiC MOSFET and working at LLC resonant soft-switching mode, the voltage imbalance is reduced and switching loss is decreased. Due to snubber capacitors, there are differences between MVSRC and traditional LLC converter, hence the analytical model of MVSRC is established. Moreover, the voltage imbalance model is established and the voltage imbalance sensitivity is defined to guide the snubber parameter selections. Then, a design example of the 99% efficient 5-kV/400-V prototype is presented. Last, the experimental results show that the voltage imbalance is reduced effectively and the switching loss is decreased dramatically, verifying the validity of proposed methods and the accuracy of analysis.

Design and Implementation of Series Resonant DC-DC Converter

The resonant DC-DC converter is known as advantageous over conventional DC-DC converter in terms of efficiency. This is primarily because the resonant converter operates at soft switching mode. In this paper, we report our work on the design and implementation of a series resonant DC-DC converter with full-bridge switching. The developed converter consisted of two main parts, namely the PWM signal-generating circuit as the driver for MOSFET and converter primary circuit. The first part was implemented by using Arduino UNO R3, whose output was amplified with IR2110 optocoupler. The latter was made up of full-bridge inverter, which employs MOSFET as the electronic switches, resonance circuit, and full-bridge uncontrolled rectifier. Performance of the developed converter was tested by supplying input voltage ranging from 20 to 30 V. It was shown that the converter functioned as a step-down “DC” transformer, i.e. voltage reducer. The maximum output voltage level obtained was half of the input, which was achieved at switching frequency of 40 kHz and efficiency of 50%. The converter was also tested to supply practical electrical load. In this case, a 12-V electric drill was put in place. The drill worked well, and a converter efficiency of 43% could be calculated during this operation.Keywords : DC-DC Converter, Series Resonance and Switching

Large Power Hybrid Soft Switching Mode PWM Full Bridge DC–DC Converter With Minimized Turn-on and Turn-off Switching Loss

A novel PWM full bridge (FB) dc–dc converter for large power industrial applications is proposed in this paper. The soft switching mode of the primary switches can be varied under different input and output conditions to achieve optimum system efficiency. In the zero-voltage and zero-current switching (ZVZCS) mode, the turn- on and turn- off switching loss can be optimized because the soft switching conditions of the turn- on and turn- off instants are well decoupled. In the zero-voltage switching (ZVS) mode, the turn- off switching loss can also be optimized because there is no requirement for light load operation in this mode. Four mosfet s with ultra-low on-state resistance are used, thus, the added conduction loss is small. The auxiliary mosfet s with high switching frequency are turned on with zero-current and off with zero-voltage, hence, the added switching loss can also be neglected. Furthermore, some drawbacks of the conventional ZVS and ZVZCS converters, e.g., narrow ZVS load range, high primary circulating current, incomplete reset of the primary current, and unreasonable VA rating of the added components, have been well solved. The operation principles and soft switching characteristics are discussed. Experimental results from an 18-kW prototype are provided to verify the proposed converter.

Wide Load Range Capacitor Clamped ZVZCS Half Bridge Three-Level DC-DC Converter with Two Unsymmetrical Bi-directional Switches

This paper presents a zero-voltage and zero-current switching (ZVZCS) capacitor-clamped half bridge (HB) three-level dc-dc converter (TLDC), which is well fit for high input voltage dc-dc industrial applications. The maximum voltage stress of the primary switches is limited by the flying capacitor and input capacitors, which is very close to Vin/2. Two unsymmetrical bidirectional switches are used to replace two of the primary switches in a conventional capacitor-clamped HB TLDC, which ensure ZVZCS of the main switches in wide load range. The reverse direction MOSFETs in the unsymmetrical bidirectional switches have low on-state resistance and are controlled with soft-switching mode irrelevant to the load current. Therefore, the additional power loss can be omitted. The current of the flying capacitor is greatly reduced due to ZVZCS operation, which would result in a smaller volume flying capacitor and high system reliability. Furthermore, the current imbalance problem of the power devices is also well solved. The circuit, basic operation principles and some important technical analyses are discussed in this paper, and experimental results from a 1-kW prototype are provided to evaluate the proposed converter.

A 20 MHz Low-Profile DC–DC Converter With Magnetic-Free Characteristics

This paper proposes a 20 MHz low-profile dc–dc converter with magnetic-free characteristics based on aircore planar inductors. The switch and diode of the proposed converter operate in soft-switching modes, which significantly reduces the switching loss. Furthermore, the parasitic capacitances are taken as part of corresponding resonant capacitors. A high-performance aircore inductor with a variable width and an optimal connecting angle is analyzed. The optimal parameters design method to achieve minimum winding resistance is derived in detail. The resonant driving method is adopted to reduce driving loss in a high-frequency condition. A 20 MHz prototype is built to verify the feasibility of the proposed converter.

Efficient solution of the DC-link hard switching inverter of the PV system

Soft switching inverter alleviate and treat the negative impacts resulted from hard switching inverter. It provides many advantages such as low power losses, high efficiency, stress reduction during switching instants, and high reliability and lowering EMI generation. Soft switching is achieved in this paper by adding the LC resonant circuit to the voltage source inverters (VSI). This is the first time to achieve soft switching with the photovoltaic (PV) system. To demonstrate the effectiveness of this technique, the simulation of the PV system is using both switching techniques; the resonant dc-link soft switching inverter and the conventional hard switching inverter; is introduced, analyzed and compared. The total resonant dc-link soft switching losses are reduced dramatically to the half of the total hard switching losses in case of not using soft switching. To validate our work, the detailed comparisons between the proposed topology with another famous one is introduced, analyzed and evaluated. In addition, the resonant dc-link soft switching losses and the hard switching losses of the inverter are estimated. The total resonant dc-link soft switching losses and the total hard switching losses are calculated under similar operating conditions and the conduction losses are kept constant in both switching modes. The simulation results prove the superiority performance of the PV system based on the proposed resonant dc-link soft switching mode compared to the other ones based on the conventional hard switching mode and single transistor resonant dc-link soft switching inverter.