Soft Commutation Research Articles

Matlab-Based Design Consideration of Series ZVS Single-Ended Resonant DC-DC Converter

The paper presents a model-based design consideration of a series single-ended transistor resonant DC-DC converter with zero voltage switching (ZVS). A characteristic of this converter is that it is highly efficient due to the resonant nature of electromagnetic processes in the power circuit and operation with soft commutations. The manuscript proposes that the determination of some of the circuit elements of the device be carried out with optimization procedures based on the application of artificial intelligence techniques. For this purpose, an objective function is used with additional constraints, such as equalities and inequalities, for both the optimization parameters and the state variables. The use of the proposed method is justified in cases where there is no methodology for the design of the specific power electronic device or there is, but it is too complicated to apply. This is usually due to the increasing complexity of power circuits and their possible modes of operation and the inevitable assumptions and limitations in the analysis and the relevant methodologies based on that analysis. In this way, a natural combination, complement and development of classical design methods with innovative ones based on the application of artificial intelligence techniques is carried out.

High-Efficiency Interleaved Totem-Pole PFC Converter With Voltage Follower Characteristics

High power density, efficiency, control simplification, and robustness are highly demanded for power factor correction (PFC) converters. This paper proposes a totem-pole rectifier based on the switching cell with switching frequency modulation (SC-SFM). The SC-SFM features interleaved operation, soft commutation, and resistive characteristics with continuous conduction in the input inductor. The converter operates without needing sensors and a control loop for the current. Unlike conventional solutions or some sensorless converters, the converter does not require a fast control loop to shape the current since the current naturally follows the input voltage. Only one output voltage sensor and one input half-line cycle detector are required to achieve unitary power factor and regulated DC output voltage. A detailed analysis of the converter operation, including the operating principle, mathematical analysis, a small signal model, and control method, is presented, including the differences in operation from the conventional PFC rectifier with the diode bridge. Experimental results evaluate a 1-kW prototype with different switch technologies (IGBT, SiC, and GaN).

A zero‐current‐transition soft‐switching technique for T‐type NPC three‐level inverter

Based on the commutation property of the T-type neutral point clamped (T-NPC) three-level inverter, a novel zero-current-transition (ZCT) soft-switching topology is proposed. The proposed topology employs only two auxiliary switches and one inductor and capacitor (LC) resonant tank on each phase leg. The commutation process of the soft-switching technique is analyzed. The results show that all switches on main leg and auxiliary leg can achieve soft commutation without changing pulse width modulation (PWM) strategy. The control family of T-NPC three-level ZCT soft-switching topology are analyzed respectively, and then the resonant tank and timing schemes of different modes are given. Using two auxiliary switches in resonance can produce greater resonance current due to the combination of external excitation sources, which is more conducive to realize the soft-switching commutation of the main switch. At last, a half bridge prototype of T-NPC three-level inverter is built. The influence of equivalent internal resistance of power switches, diode reverse recovery and stray inductance for soft commutation is analyzed. The advantages of ZCT soft-switching technology is verified.

An Interleaved PFC Boost Converter With Soft Commutations and Voltage Follower Characteristics

This article presents an interleaved boost rectifier for power factor correction (PFC) that operate in the continuous conduction mode and is grounded on the switching cell with switching frequency modulation. The input current naturally follows the shape of the input voltage, which is a resistive input characteristic (voltage follower). In the proposed converter, only one output voltage control loop is required. Moreover, the proposed topology has a wide range of soft commutation and no reverse recovery when the diodes block. This article presents the operating principle, a mathematical analysis of the converter, and four topological variations. In addition, experimental results of a 1-kW rectifier prototype with four different switch technologies [ <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MOSFET</small> , high voltage superjunction <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MOSFET</small> (CoolMOS), silicon carbide (SiC), and insulated gate bipolar transistor (IGBT)], are discussed and their operational characteristics are demonstrated.

12-Pulse Rectifier with Two DCM Boost-Type Half-Controlled Bridges for Variable- Input-Frequency Applications

This paper presents the analysis of the integration of two three-phase half-controlled boost converters, operating in discontinuous conduction mode (DCM), to the auto-connected 12-pulse rectifier. The proposed structure shows a reduced current harmonic content compared to the traditional 12-pulse rectifiers, being a simpler and effective alternative to using rectifiers with higher pulse numbers. It also presents a greater range of possibilities for regulating the output voltage, without the use of synchronization algorithms or rigorous control techniques, being possible to send to all controlled switches, the same command signal, resulting in a simpler logic. Another advantage of using the proposed technique is the employment of a single-loop voltage control scheme, reducing the computational and financial cost by eliminating some elements such as current sensors. Moreover, the proposed strategy provides soft commutations (Zero-Current-Switching - ZCS). In this work, a small-scale prototype was implemented, aiming to obtain a structure capable to operate in a wide range of line frequencies, without requiring any additional complex techniques. In this regard, the developed structure is capable to work as a Power Factor Correction (PFC) stage in a wide range of input frequencies (30Hz - 120Hz) with a Total Harmonic Distortion of the input current (THDi) of less than 2.19%.

Battery Charger with Bidirectional Power Transmission

The gradual reduction in price of electric batteries contributes to their wider use in autonomous and centralized power supply systems as a backup source of electricity and increase the share of electric vehicles. In the paper the conditions for increasing the efficiency of electric vehicle batteries, in particular in the framework of the concept of V2G (Vehicle to Grid) as a drive for the organization of autonomous power supply systems are analyzed. It is shown that this is possible only with the simple integration of batteries into the system, flexibility, and a wide range of modes that have to be provided by unified charge-discharge devices. Such charging devices have to have such features: a wide range of input and output voltage parameters; correction of the input power factor; the ability to take the maximum power from renewable energy sources; high energy efficiency. A review of possible topologies for a charger with bidirectional power transmission and a bridge converter with soft switching of transistors at zero voltage, which has a high efficiency, galvanic isolation and the ability to correct the shape of the current. The modes of operation of the converter are analyzed and conditions of soft switching is obtained. It is shown that soft switching is valid for current that is not less than minimal one. Efficiency of the converter with soft commutation is compared with a similar converter with rigid commutation of transistors. It is shown that static losses in converter with soft commutation it higher than in the rigid one. So, the proposed converter should be used if the increase in static losses is compensated by the lack of dynamic losses. Additional feature of the converter is that the regulation of the output voltage of the converter with soft switching is carried out according to the law of frequency-pulse modulation with a constant pause duration, where the pause duration is determined by the period of resonant processes of the converter. The model of the converter in Matlab Simulink is built and it is shown that the efficiency of the proposed converter topology is 10-15% higher, which together with the possibility of sinusoidal current with THD ≈ 20% and two-way transmission energy indicates the feasibility of its use as a charger for electric vehicles under the concept of V2G. However, it should be noted that the use of LCL filter creates a phase shift between voltage and current and degrades the THD value. To improve the shape, it is possible to use specialized laws of modulation [or to use modular converters, which allow to obtain a continuous current shape and reduce the volume of the filter.

Switching Cell With Frequency Modulation for CCM Voltage-Follower Converters

This letter proposes a new switching cell with switching frequency modulation (SFM) and resistive characteristic (voltage follower) for converters that are current-fed. Soft commutation and current null (when the diode blocks) are achieved with SFM and a fixed duty cycle for converters based on this switching cell. The operating principle, a mathematical analysis of the cell, and two topological variations are presented. In addition, the basic characteristics of the main topologies are shown, and the experimental results of a 1-kW boost continuous conduction mode converter prototype are discussed to demonstrate the operating characteristics.

A Class of Single-Phase Z-Source AC–AC Converters With Magnetic Coupling and Safe-Commutation Strategy

This article proposes a family of single-phase transformer based Z-source ac-ac converters (ZSACs). The proposed converters inherit all the benefits associated with the classical single-phase ZSAC, which are providing the buck-boost operation, maintaining or reversing the phase angle, and improving reliability. The proposed converters also have the improved input profile, continuous input current, and shared ground between input and output. Moreover, they use the turns ratio of transformers to produce the required voltage gain, which can be tuned by either increasing or decreasing the turns ratio of transformer depending on the configuration of Z-source structure. A safe-commutation strategy is also presented to achieve the soft commutation, which eliminates the voltage and current spikes without any additional snubber circuits. The features of proposed converters are comprehensively discussed with the detailed theoretical analysis. Thereafter, its performances are evaluated by both simulation and experimental tests.

Single-Phase ZAC-Source AC–AC Converter With High Buck and Boost Voltage Conversion Capability

In this article, a novel ZAC-source single-phase ac-ac converter with high buck and boost voltage conversion capability is introduced. The proposed topology utilizes the ZAC-source network to regulate the frequency and magnitude of the output voltage. The proposed converter operates in buck mode when the duty cycle lies between 0 and 0.33, and boost mode when the duty cycle lies between 0.33 and 1. The switching control strategy is discussed and the proposed converter provides a feature to control the magnitude and frequency of the output voltage independently. Employment of capacitors in the outer closed loop results in a highly consistent operation characterized by inherent soft commutation capability, removal of the source shoot-through risk, and enhanced input current waveform quality. Due to these advantages, it can be applied to the adjustable speed drives and traction systems. The control code is executed in dSPACE 1006 embedded with field-programmable gate array (FPGA) dS5203 board and the performance of the proposed converter is tested experimentally. The obtained experimental results are provided which validates the theoretical analysis and performance of the proposed converter.

A PWM ZVS High-Frequency-Link Three-Phase Inverter With T-Type NPC Unfolder

In this article, a pulsewidth modulated single-stage high frequency link three-phase dc–ac converter is proposed for grid integration of solar and fuel cell-based energy sources. On the dc side, the converter has three half-bridge legs which are zero-voltage switched over the entire line cycle without using any additional snubber circuit. On the ac side, two diode bridge rectifiers and one neutral point clamped (NPC) T-type three-level inverter are employed. The active switches in NPC inverter are switched either at line frequency or twice of it, incurring negligible switching loss. Modulation ensures soft commutation in the diode bridges. The intermediate three-level dc bus is pulsating and does not require any dc-filter capacitor and thus reduces overall filtering requirements. The high frequency galvanic isolation provides high power density, low-cost converter solution. The converter operation is analyzed in detail and verified on a 2-kW hardware prototype.

Full-Bridge Converter with Soft Commutation in All Load Range

The development of converters with soft commutation improves issues of radiation interference and electromagnetic compatibility, reduce weight and size parameters by increasing efficiency and conversion frequency. A significant reduction in commutation losses allows the use of high-power IGBT modules at higher frequencies which they are not able to withstand in traditional converters with pulse-width commutation.

Single-Inductor Dual-Output DC–DC Converter With Capability of Feeding a Constant Power Load in Open-Loop Manner

In this paper, a single-inductor dual-output (SIDO) dc-dc converter is proposed. The significant feature of the proposed converter is feeding a constant power load in low-voltage side (LVS) port, where even feeding a variable load at LVS does not have any cross regulation to high-voltage side port with the desired approximation. Magnificently, both merits are obtained in open-loop manner, which is an outstanding characteristic in comparison with that of the existed converters. In this paper, soft commutation and soft switching of switches and diodes are investigated along with the aforementioned main novelty. Moreover, detailed theoretical analyses of the proposed SIDO dc-dc converter in continuous conduction mode are presented besides the comparisons with some other structures. Finally, theoretical analyses are verified through a 1500 W experimental prototype results.

Research on characteristics of bidirectional CLLC DC–DC transformer used in DC microgrid

In the DC microgrid system, the energy storage system must have both high power density and high energy density, and it is difficult for a single type of energy storage device to meet this requirement. The battery and the super capacitor are highly complementary in performance. Here, the battery and the super capacitor are, respectively, connected to the DC bus through a bidirectional DC–DC converter to form a hybrid energy storage system. For a 380V DC microgrid system, a new type of symmetrical circuit topology structure with two inductors and two capacitors (CLLC) resonant network is proposed. Since the symmetrical CLLC resonant network has the zero voltage switching capability of the main power switch and the soft commutation capability of the output rectifier, the converter can operate at high power conversion efficiency. Finally, the effectiveness of the system control strategy is verified through simulation and experiments.

Dual-Buck AC–AC Converter With Inverting and Non-Inverting Operations

In this paper, a novel buck–boost ac–ac converter is proposed. The basic switching unit of the proposed converter is a unidirectional buck circuit; therefore, it has no shoot-through worries. It can achieve safe commutation without using RC snubbers or soft commutation strategies. It can be implemented with power MOSFETs without their body diodes conducting and, for current freewheeling external diodes, can be used to minimize the reverse recovery issues and related loss. It has a bipolar voltage gain with both inverting and non-inverting operations. The non-inverting operation can be used to compensate voltage sag, and inverting operation can be used to compensate voltage swell. Therefore, the proposed converter as a dynamic voltage restorer is capable of compensating for both voltage sag and swell in a wide range. The detailed theoretical analysis followed by detailed experimental results of a 300-W prototype converter is provided.

A Single-Stage Three-Phase Bidirectional AC/DC Converter With High-Frequency Isolation and PFC

This paper presents a novel single-stage ac/dc rectifier with high-frequency isolation and bidirectional power flow capability, which is feasible to connect dc grids to ac ones. A thorough analysis is performed based on the development of an actual model as well as a fundamental one using the double-sideband amplitude modulation equations. The derived models allow the determination of the active and reactive power flow through the transformer as well as defining the operating regions for which soft commutation is achieved. Besides, the current stresses of the semiconductors devices are analyzed in detail. Experimental results obtained from a 5 kW prototype are presented and discussed in order to validate the proposed model as well as demonstrate the converter's performance and claimed advantages. The proposed concept can also be extended to dc/dc, ac/ac, and multilevel topologies.

Control law design for full-bridge converter with soft commutation based on frequency variation of transistors switching

A method of pulse-width control of the high power full-bridge converter with widely varied supply voltage is proposed. The method is based on the carrier frequency variation and is implemented as proportional-integral controller with adjustable parameters. The proposed method allows improving dynamic characteristics of the system and limiting of maximum current commuted by transistors. The proposed control law allows receiving desired load voltage.

Bipolar-type Dynamic Voltage Conditioner Using P-Leg and N-Leg Structured AC-AC Converter

The voltage fluctuation caused by the high proportion of residential photovoltaic (PV) grid-connected not only restricts the capacity of network to absorb renewable energy, but also seriously affects the normal operation of electrical equipment. Voltage problems in the low voltage distribution network with high proportion of residential PV are described and a novel bipolar-type dynamic voltage conditioner (B-DVC) is introduced to solve the voltage problem in this paper. The topology of the B-DVC adopts the positive current leg (P-Leg) and the negative current leg (N-Leg). By combining two separation inductors together, the voltage distortion caused by the traditional full-bridge two-way switch converter is overcome. Due to the use of the P-Leg and N-Leg structure, the B-DVC can be short- and open-circuited without damaging the switching devices. Neither lossy RC snubber nor a dedicated soft commutation strategy is required in the proposed B-DVC. Furthermore, B-DVC can not only output the voltage with the same polarity as the grid voltage, but also output the voltage opposite the polarity, which can ensure the stability of the power grid voltage and improve the capacity of grid to absorb renewable energy. A 10-kW prototype of single-phase B-DVC is developed, and its performance is experimentally verified.

A New Reliable Three-Phase Buck-Boost AC–AC Converter

This paper proposes a new bidirectional direct pulse width modulation (PWM) three-phase buck-boost ac–ac converter. It requires six switches and three inductors and can provide wide range buck-boost voltage operation. It has high reliability due to no short-circuit and open-circuit risks in the converter. Therefore, it solves the commutation problem without using lossy snubber circuits, soft commutation strategies, and coupled inductors. It can be designed with metal–oxide–semiconductor field-effect transistors (MOSFETs) without their body diodes conducting, which eliminate reverse recovery issues and losses of body diodes. In addition, to reduce the ripples in input and output voltages and currents, the proposed converter can be operated with a PWM strategy-II. The PWM strategy-II is a type of interleaved PWM strategy with dead- and overlap-times operating modes. To validate the effectiveness of the proposed converter extensive analysis followed by detailed experimental results are provided.

Dynamic Voltage Restorer Using Switching Cell Structured Multilevel AC–AC Converter

Dynamic voltage restorer (DVR) technology has become a mature power quality product. In high-power applications, DVR using a multilevel converter is commonly used. However, DVR using a multilevel direct pulse width modulation (PWM) ac–ac converter has not been well studied. This paper presents a new DVR topology using a cascaded multilevel direct PWM ac–ac converter. In the proposed scheme, the unit cell of the multilevel converter consists of a single-phase PWM ac-ac converter using switching cell structure with coupled inductors. Therefore, the multilevel converter can be short- and open-circuited without damaging the switching devices. Neither lossy RC snubber nor a dedicated soft commutation strategy is required in the proposed DVR. This improves the reliability of the DVR system. The output voltage levels of the multilevel converter increase with the number of cascaded unit cells, and a high ac output voltage is obtained by using low-voltage-rating switching devices. Furthermore, a phase-shifted PWM technique is applied to significantly reduce the size of the output filter inductor. A 1-kW prototype of single-phase DVR is developed, and its performance is experimentally verified. Finally, the simulation results are shown for a three-phase DVR system.

A Family of True Zero Voltage Zero Current Switching (ZVZCS) Nonisolated Bidirectional DC–DC Converter With Wide Soft Switching Range

This paper proposes a true zero voltage zero current switching (ZVZCS) nonisolated bidirectional dc–dc converter with reduced component count. An auxiliary resonant network—which comprises of an inductor, capacitor, diode, and two switches—provides the zero voltage switching transitions of the main switches at turn on and turn off instants. In addition, a pair of auxiliary inductors, which act as inductive snubbers, aids the zero current switching transitions. The proposed configuration is able to provide soft commutation for the main switches for a wide range of input voltage, switching frequency, and load current variations—thus significantly improving the efficiency profile over a wide operating window. Besides, the auxiliary switches are also soft commutated, while the reverse recovery loss induced by the high side diode is eliminated. The ZVZCS soft switching operation is demonstrated by a 150 W prototype converter; it is proven consistent with the waveforms derived from the theoretical analysis. Its performance is evaluated against the standard hard-switched boost, buck, and several other leading soft switching converters published in the recent literature. The maximum full load efficiency at 100 kHz is recorded at 98.2% and 97.5% in the boost and buck modes, respectively.