Zero-voltage Switching Performance Research Articles

Phase-Shifting Adaptive LLC Resonant Converter with Reduced Turn-Off Loss in Wide Voltage Application

In this paper, a hybrid control method with adaptive phase-shifting modulation (PSM) and pulse-frequency modulation (PFM) is proposed to optimize the steady-state performance of an LLC resonant converter in wide voltage-gain range application. For the primary-side switches under the hybrid control method, zero-voltage switching (ZVS) performance is maintained over wide voltage-gain range and the turn-off loss is reduced; therefore, the converter reconciles wide voltage-gain range and high efficiency. Mode characteristics under different phase-shifting-angle-θ and switching-frequency-fs combinations is analyzed, and then the soft-switching characteristic is revealed. By introducing time domain analysis, the turn-on current of the primary-side switches is calculated, and thus the ZVS boundary of different θ and fs combinations is inferred. In addition, to acquire the optimum steady-state operation of the converter, the turn-off current is calculated; by making the converter work near to the minimum turn-off current operating point, the turn-off loss can be reduced greatly. With the principles of achieving ZVS performance and minimizing turn-off current, the phase-shifting angle θ of PSM is designed to be adaptive to the reference output voltage, no additional circuits are needed, and the two control degrees (θ and fs) are simplified to one (fs). The simulation and experiment are developed to verify the feasibility and effectiveness of the hybrid control method; the results show that ZVS performance is maintained at wide voltage-gain range and the turn-off current of the hybrid control method is reduced to that of the single PFM, and thus the turn-off loss is reduced. The efficiency comparison validates the fact that the hybrid control method has less power loss than single PSM and single PFM.

A Class-E-Based Multichannel Auxiliary Power Supply With Individual Hysteresis Control

A high performance auxiliary power supply (APS) with multiple isolated outputs plays a crucial role in ensuring the effective operation of power converter systems. An isolated resonant current source converter is usually adopted as the APS in medium-voltage (MV) applications with the advantages of low coupling capacitance and high insulation strength. In this paper, a Class E-based multichannel APS, featuring a low component count, modular circuit structure and ease of scalability to multiple output channels, is proposed. The operation principle of the proposed circuit is presented in detail. To overcome the cross-regulation problem in multiple outputs, an individual hysteresis control approach is introduced to regulate each output separately and decouple the multiple outputs. The converter performance under open/short-circuit fault conditions is also explored with the proposed control scheme. Design considerations, including the zero-voltage-switching (ZVS) realization and the output power capabilities, are presented, together with a step-by-step parameter design approach. Finally, an 8 output APS experimental prototype (with different output voltage levels) is presented. The experimental results demonstrate the output voltage decoupled regulation and load independent ZVS performance of the prototype.

Performance improvement of a zero‐voltage switching interleaved high step‐up DC–DC converter with low‐voltage stresses

AbstractThis paper proposes a novel interleaved ultra‐large gain zero‐voltage switching (ZVS) DC–DC converter for renewable energy systems. By using coupled inductor (CI) and built‐in transformer (BIT), a high‐voltage gain is achieved. The secondary windings of the CIs are connected in series with the primary winding of the BIT and the secondary winding of the BIT is inserted in voltage multiplier cell (VMC). In such a case, the voltage gain is proportional to the multiplication of the turn's ratios of the CI and BIT. To increase the devices’ utilization, the active clamp circuit not only provide ZVS performance for the metal‐oxide‐semiconductor field‐effect transistor (MOSFETs) and recycles the leakage energy, but also participates in voltage gain enhancement. The voltage stress across the switches is considerably decreased and the low duty cycle reduces the conduction and switching losses. Low input current ripple, equal current sharing without a dedicated controller and common ground are the other merits of the proposed converter. Steady‐state analyses are presented and through a fair comparison, the superiority of the proposed converter over the state‐of‐the‐art is guaranteed. Finally, a 500‐W laboratory prototype with 20‐ to 400‐V voltage conversion is built to demonstrate the effectiveness of the proposed converter.

Analysis, Design, and Investigation of a Soft-Switched Buck Converter With High Efficiency

In this article, a new simple buck converter with zero voltage switching (ZVS) performance and almost zero output current ripple is proposed. The proposed structure's auxiliary circuit contains a capacitor and an inductor without any switches, which makes it possible to minimize the switching losses and eliminate other additional losses. The main power diode also turns <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> under zero current switching condition and the reverse recovery losses of the power diode is minimized. Eliminating the switching losses and the reverse recovery losses allows the converter to operate with high power efficiency, which makes it a good option for high power efficiency-required applications. In this article, five operational modes are explained. The design section includes the designing criteria of the components. Also, the efficiency analysis, control system for stabilizing the output voltage, and applying a variable inductor to ensure the soft-switching operation are analyzed. The comparison results are also discussed. Moreover, an experimental prototype of the proposed structure at 200 W output power and 75 kHz frequency is built to prove the above-mentioned advantages. Finally, the soft-switching waveforms are obtained for different output powers with various duty cycles and equal switching frequency to verify the ZVS performance of the converter at different loads and changes in input voltage and duty cycle.

Modeling and Analysis of DC Microgrids as Stochastic Hybrid Systems

This article proposes a method of predicting the influence of random load behavior on the dynamics of dc microgrids and distribution systems. This is accomplished by combining stochastic load models and deterministic microgrid models. Together, these elements constitute a stochastic hybrid system. The resulting model enables straightforward calculation of dynamic state moments, which are used to assess the probability of desirable operating conditions. Specific consideration is given to systems based on the dual active bridge (DAB) topology. Bounds are derived for the probability of zero voltage switching (ZVS) in DAB converters. A simple example is presented to demonstrate how these bounds may be used to improve ZVS performance as an optimization problem. Predictions of state moment dynamics and ZVS probability assessments are verified through comparisons to Monte Carlo simulations.

Zero-Voltage-Switching Asymmetrical PWM Full-Bridge DC–DC Converter With Reduced Circulating Current

In the article, an asymmetrical pulsewidth modulation (PWM) full-bridge converter with zero-voltage-switching (ZVS) and reduced circulating current is proposed. For the conventional phase-shift full-bridge converters, the circulating current in the primary side of the transformer degrades the efficiency. The converter cannot meet a high efficiency in the wide input or output voltage range. In order to reduce the circulating current, the modified full-bridge dc-dc converter with the split capacitors and improved rectifier stage is controlled by the asymmetrical PWM. The two transformers in the proposed converter share the output power equally, so the volume of the transformers is easy to optimize. Furthermore, all the switches can still achieve the ZVS performance. Besides, the proposed converter can reduce the current ripple of the filter inductor, leading to a reduction in output filter inductance. Finally, a 1-kW prototype is built to verify the proposed converter. The performance is compared with the other full-bridge dc-dc converters.

Analysis of Diode Reverse Recovery Effect on ZVS Condition for GaN-Based LLC Resonant Converter

LLC resonant converter can achieve zero voltage switching (ZVS) for primary-side devices and zero current switching (ZCS) for secondary-side rectifiers. However, the reverse recovery and junction capacitance ( Cj ) of secondary-side diode critically affect the ZVS condition of primary-side switches. The effect of Cj has been discussed in literature, but not the reverse recovery. In this paper, the reverse recovery charge ( Q rr) is converted to an equivalent capacitance $(C_{{\rm rr}\_{\rm eq}})$ for the study of primary-side ZVS performance. An accurate model during deadtime is derived and further applied to characterize ZVS performance with different reverse recovery charges in different regions. The concept of establishing parameter C total to consider both Cj and $C_{{\rm rr}\_{\rm eq}}$ is proposed to evaluate the effect of the secondary-side rectifiers. This concept provides the guideline for diode and synchronous rectification mosfet selection to ensure ZVS condition for LLC converters. To verify the concept and the derived model, a 200/400 V 400 W LLC resonant converter prototype operating from 200 to 700 kHz is built and its ZVS performances with different diodes are compared. Two issues caused by Q rr effect, including $V_{\rm ds}$ reverse charging and asymmetrical waveform during deadtime, are explained thoroughly as well.

Investigation of Zero Voltage Switching Capability for Bidirectional Series Resonant Converter Using Phase-Shift Modulation

A series resonant converter (SRC) using a phase-shift modulation (PSM) was invented to implement the bidirectional power flow. However, it has a narrow zero voltage switching (ZVS) range, which reduces the power conversion efficiency for the light load condition. In this paper, the ZVS condition of the SRC is analyzed according to the power flow directions. From this analysis, the SRC using an extended PSM and single PSM is proposed to obtain the soft switching for the entire load range. The analysis of ZVS condition and performance of proposed control algorithm are verified using simulation and experimental results with a 500-W prototype converter.

Dual-Active-Bridge Converter With Parallel-Connected Full Bridges in Low-Voltage Side for ZVS by Using Auxiliary Coupling Inductor

A dual-active-bridge (DAB) converter with parallel-connected full bridges in low-voltage side is proposed in this paper. A coupling inductor is integrated into the two low-voltage-side full bridges for zero-voltage-switching (ZVS) operation throughout full-load range. By analyzing the working modes of the converter, the ZVS range of the converter is derived. To compromise the ZVS and the conduction loss caused by the coupling inductor, the modulation trajectory is designed in terms of the boundary conditions of the ZVS range. The conduction loss of the proposed converter is compared with the conventional parallel-connected DAB converter, which illustrates that the conduction loss of the proposed converter is only increased under light loads. Finally, a 1.2-kW experimental prototype is built to verify the proposed converter and the modulation scheme, which demonstrates the remarkable ZVS performance and efficiency improvement.

Output-Series Connected Dual Active Bridge Converters for Zero-Voltage Switching Throughout Full Load Range by Employing Auxiliary LC Networks

This paper presents an output-series connected dual active bridge (DAB) converter for efficient zero-voltage switching (ZVS) by employing dual auxiliary LC networks in high-output voltage applications. The dual auxiliary LC networks are integrated into the converter for ZVS throughout full load range. The gate signals of the output side switches can control the current in the LC networks. By analyzing the working modes of the converter, the modulation trajectory is designed in terms of the boundaries of the ZVS range. The conduction loss caused by the auxiliary LC networks is adjusted according to the voltage and load power. The modulation scheme can achieve seamless transition between the adjacent working modes. The conduction loss of the proposed converter is compared with the conventional output-series DAB converter. Although the conduction loss is increased under light loads, all the switches can achieve ZVS. The reduced switching loss can improve the overall efficiency. Finally, a 1.3 kW experimental prototype was built to verify the effectiveness of the proposed converter and the modulation scheme, which demonstrates the ZVS performance and efficiency improvement.

Three-Level Bidirectional DC–DC Converter With an Auxiliary Inductor in Adaptive Working Mode for Full-Operation Zero-Voltage Switching

This paper proposes a three-level bidirectional dc–dc converter with an auxiliary inductor for full-operation zero-voltage switching (ZVS) in high-output voltage applications. The auxiliary inductor is connected across the middle node of the split flying capacitors and the center tap of the secondary winding in the transformer. In this topology, the outer and inner switches in the three-level stage can generate two independent 50% duty-cycle square waveforms, which are used to control the current in the auxiliary inductor to extend the ZVS from no loads to full loads. Considering the phase-shift angle in three-level stage, the ZVS range of the converter is analyzed, and the modulation trajectory to maintain the full-operation ZVS range with low condition loss is proposed. A flowchart implementation can guarantee the seamless transfer in different working modes. Then, the conduction loss in the proposed converter is compared with the previous three-level bidirectional solution, which illustrates that the conduction loss in the proposed converter only increases in light loads. Finally, the experimental results verify the theoretical analyses and ZVS performance across the whole power and voltage range, and the efficiency curves demonstrate the efficiency improvement.

A Novel Interleaved Nonisolated Ultrahigh-Step-Up DC–DC Converter With ZVS Performance

This paper presents an interleaved nonisolated dc-dc converter with high-voltage gain and zero-voltage switching (ZVS) performance. Both coupled inductor and voltage multiplier cell techniques are used to increase the voltage gain. The ZVS circuit is composed of an active clamp which is in series with the output filter capacitors. This will give rise to further extension of the voltage gain. Applying the interleaving technique at the input of the converter, the ripple of the input current is reduced. Due to the leakage inductances of coupled inductors, the diodes are turned-off under zero-current switching condition. Hence, the reverse current recovery problem is alleviated. The steady-state analysis of the proposed converter is also presented. Finally, a 900-V to 415-W laboratory prototype is implemented to validate the performance of the proposed converter.

High step‐up isolated resonant converter with voltage quadrupler rectifier and dual‐phase‐shift control

An isolated resonant converter with voltage-quadrupler rectifier (VQR) and dual-phase-shift (DPS) control strategy is proposed for high step-up and wide voltage range applications. The VQR is composed of a resonant-type voltage doubler and a conventional voltage doubler. The output voltage is improved and the voltage stresses of the secondary-side devices are reduced significantly. Hence, low voltage-rated switches and diodes with better switching and conduction performances can be applied to improve the efficiency. The DPS modulation strategy is adopted to implement the boost and buck modes operation, and to achieve wide voltage gain range. With the DPS control strategy, zero-voltage switching performance is achieved for both the primary and secondary sides power devices, and zero-current switching is achieved for all of the diodes within the entire voltage and load ranges. The operational principles and characteristics of the proposed converter are presented in detail. The analysis and performance have been fully validated experimentally on a 400 V/400 W output hardware prototype.

Charge-Equalization Circuit for Series-Connected Batteries with Quasi-Resonant Flyback Converters

A charge equalization circuit for balance discharging in a series-connected battery bank is proposed in this paper. The circuit comprises several parallel-connected flyback converters which connect each unit battery in the bank to supply the electric load. The transformer leakage inductance and capacitances of MOSFETs are applied to fulfill the quasi-resonant zero voltage switching (ZVS), which consequently eliminates the voltage spikes and enhance the conversion efficiency. Design equations are derived and numerical analysis results are applied to evaluate the required values of the inductance and capacitance to realize ZVS performance. A battery bank with four series-connected lead-acid batteries is used to verify the proposed charge equalization circuit. The experimental results advocate the applicability of the proposal.

High-Efficiency Active-Clamp Forward Converter With Transient Current Build-Up (TCB) ZVS Technique

In this paper, an active-clamp forward converter with transient current build-up zero-voltage switching (ZVS) technique is proposed. The proposed converter is suitable for the low-voltage and high-current applications. The structure of the proposed converter is the same as that of the conventional active-clamp forward converter. However, since it controls the secondary synchronous switch to build up the primary current during the very short period of time, the ZVS operation is easily achieved without any additional conduction losses of magnetizing current in the transformer and clamp circuit. Furthermore, there are no additional circuits required for the ZVS operation of power switches. Therefore, the proposed converter can achieve the high efficiency and low electromagnetic-interference noise resulting from the soft switching without any additional conduction losses and shows the high power density resulting from the high efficiency and no additional components added. The operational principle and design example are presented. Experimental results demonstrate that the proposed converter can achieve an excellent ZVS performance throughout all load conditions and a significant improvement in the efficiency for the 100-W (5 V, 20 A) prototype converter