Zero Voltage Switching Turn-on Research Articles

A Constant-Frequency High-Voltage Gain Resonant Converter Module With Semiactive Phase-Shifted Voltage Multiplier for MVdc Distribution

A constant-frequency step-up LLC resonant converter module that employs a new phase-shifted semiactive voltage multiplier technique is proposed in this article for a medium-voltage dc distribution grid. In the proposed converter, a wide voltage gain for different loading conditions can be realized by adaptively controlling the phase shift of the auxiliary switch in a voltage quadrupler-based semiactive voltage multiplier. Zero-voltage switching turn-on is always achieved for all the primary side switches with a constant-frequency operation. In the proposed semiactive voltage multiplier, zero-current switching (ZCS) turn-on is achieved for the auxiliary switch with ZCS operations provided for all the output diodes over a wide range of voltage gain and loading conditions. The operating principles of the proposed circuit are discussed in this article. Simulation results on a 120-kW, 10-kV output and experimental results on a modular laboratory-scale silicon carbide (SiC)-based 5-kW (per-module), 240–440-V/5-kV prototype are provided to demonstrate the performance of the proposed converter.

A Hybrid Modulation Featuring Two-Phase Clamped Discontinuous PWM and Zero Voltage Switching for 99% Efficient DC-Type EV Charger

Two-stage AC-DC converters are considered as a prominent solution for DC-type electric vehicle (EV) chargers. However, this kind of architecture suffers from high switching losses with large heatsink and DC-link capacitor volume. To relieve this issue, this paper presents a new hybrid modulation for DC-type EV chargers, where a two-phase clamped discontinuous pulse-width-modulation (DPWM) in the front-end circuit is cooperated with the variable frequency triangular-current-mode (TCM) zero voltage switching (ZVS) or its simplified implementation, i.e., boundary-ZVS (B-ZVS) strategy, in the back-end circuit. The former can stop the switching actions in the front-end stage during two-thirds of the grid period, while the AC currents are at their highest values, which can yield to the best switching loss reduction and deliver high power factor operation. Besides, TCM-ZVS or B-ZVS modulations can achieve ZVS turn-on action for all semiconductors during all operating range in the DC-DC stage to further reduce the power losses on the semiconductors. With such characteristics, the proposed strategies can reduce the switching losses of the system to the best extent, and thus allow an enhancement of the system power density by improving the power conversion efficiency. The proposed strategy is described, analyzed, validated, and benchmarked in a 5 kW SMD SiC MOSFET-based two-stage AC-DC converter. A 99% power efficiency can be achieved with the solution implementing the TCM-ZVS strategy at an output voltage of 400 V and rated power.

A High-Efficiency High-Power-Density On-Board Low-Voltage DC–DC Converter for Electric Vehicles Application

The on-board low-voltage dc-dc converter (LDC) in electric vehicles (EVs) is used to connect the high-voltage battery with the low-voltage auxiliary system. With the advancement of auxiliary equipment in EVs, the output current of the LDC can be hundreds of amperes, which will cause high-conduction loss and severe thermal concern. In this article, a high-efficiency high-power-density on-board LDC is presented. To reduce current stress and improve efficiency, three-phase interleaved LLC dc-dc converters are paralleled to provide 270 A load current. Synchronous rectifier is used to reduce secondary conduction loss. zero-voltage-switching (ZVS) turn-on of primary switches and ZCS turn-off of secondary switches are achieved, thus switching loss can be reduced significantly. Moreover, phase-shedding technology is used to improve light load efficiency. Switch-controlled capacitor (SCC) technology is used to achieve accurate load current sharing among the three phases, which protects the devices against high-current stress, reduces the conduction loss, and improves the reliability of the system. As SCC switches achieve ZVS turn-on and turn-off by its nature, the loss of the SCC circuit is of less concern with regard to the rated output power. In addition, GaN HEMTs are used in the primary side to improve the power density and eventually help achieving light weight. A 3.8-kW (14 V/270 A) LDC prototype is developed and tested. Experimental results show good current balancing among the three phases. A peak efficiency of 96.7% at 140 A load and a full load efficiency of 95.8% are achieved with 3 kW/L power density and 1.5 kg weight.

Improved Control Strategy of Triple-Voltage Three-Phase DAB (T2-DAB) Converter for Current Stress and Zero-Voltage-Switching Optimization

Three-phase triple-voltage dual-active-bridge (T <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> -DAB) converter possesses high input voltage and large output current capacity, which can be adopted to constitute a high-power-density dc transformer. However, when employing conventional phase-shifted (PS) control strategy, zero-voltage switching (ZVS) turn-on is easily lost under light-load and voltage-mismatching situations. Hence, this article presents an optimized asymmetrical duty-cycle modulation strategy for T <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> -DAB converter, ensuring ZVS for switches and reducing the current stress over wide power and voltage ranges. The detailed model is established with a time-domain analysis method, and ZVS constraints are given with the particular consideration of dead time and parasitic capacitances of switches. Then, the MATLAB optimization toolbox is adopted to calculate the optimum duty cycle and PS angle, and the specific control scheme is introduced. Finally, a 2-kW prototype is built to verify the theoretical analysis, whose input voltage ranges from 480 to 720 V and output voltage is 200 V. The experimental results show that the proposed optimized control scheme can realize ZVS turn-on for all switches over wide voltage and power ranges, and the efficiency is improved, especially under light-load and voltage-mismatching situation.

Auto-Resonant Detection Method for Optimized ZVS Operation in IPT Systems With Wide Variation of Magnetic Coupling and Load

In wireless charging systems, the H-bridge converter's switching frequency is set close to the system's natural resonance for achieving optimized zero voltage switching (ZVS). Variations to the system's natural resonance are commonly tracked by following the changes in the resonant current's polarity, i.e., current zero-crossings. The main implementation challenge is accounting for the time delay between the real monitored current and the final resulting switches’ commutations. This becomes critical at high switching frequencies, particularly when the magnetic coupling and loading vary widely. This paper proposes an auto-resonant detection method that continuously ensures optimized ZVS turn-on with the minimal circulating current over the operable range of magnetic coupling and load. The suggested implementation provides two split variable references for the resonant frequency detection, which adaptatively compensate for the propagation delay based on the resonant current slope. The auto-resonant scheme is benchmarked against the commonly employed method with fixed current detection references. The results highlight the auto-resonant strategy's advantages, namely extended operable range, wider ZVS turn-on region, ease start-up, and improved DC-to-DC efficiency. The auto-resonant features and functionality are verified experimentally with a 200 W low-voltage e-bike wireless charger. Finally, the benefits of the presented method are analytically explored for high-power applications by considering the H-bridge semiconductor losses of a state-of-art 50 kW wireless charging system.

A 2-MHz 9–45-V Input High-Efficiency Three-Switch ZVS Step-Up/-Down Hybrid Converter

This article presents a three-switch zero-voltage switching (ZVS) step-up/-down hybrid dc–dc converter with e-mode GaN transistors for wide-input-range applications. With a flying capacitor, the proposed hybrid converter saves one auxiliary branch for establishing ZVS and one power FET compared with the conventional buck–boost counterpart, thereby reducing the converter volume and power loss. The capability of having ZVS turn-ON of all power FETs enables the proposed converter to operate in the MHz range under high input voltages by removing the switching power loss. The flying capacitor in the proposed converter further lowers the main inductor current in the step-down mode, significantly decreasing the conduction loss of the inductor. The proposed converter was validated using three 100-V e-mode GaN HEMTs with the on-chip gate drivers implemented in a high-voltage 0.5- $\mu \text{m}$ process. The proposed converter supports a wide input range from 9 to 45 V with a maximum 48-W output power, operates at 2 MHz, and achieves peak power efficiencies of 97.6% and 96% in step-down and -up modes, respectively. The volume of the external components in the proposed converter is also reduced by at least three times compared with the prior art.

High step‐up DC–DC converter based on coupled‐inductor for renewable energy systems

The present study introduced a novel soft-switched high step-up DC–DC converter based on coupled inductors. The higher boost-factor is achieved relying on previous topologies by adjusting the turns ratio of the coupled inductors. Thus, the proposed converter provides a higher voltage gain with lower duty ratios. Two active clamp circuits are employed to clamp the voltage spikes resulted from parasitic inductances. This active clamp circuit provides zero-voltage switching turn-on operations and zero-current switching turn on/off operations for active switches and power diodes, respectively. In addition, the equivalent leakage inductance of the coupled inductors is placed in series with the power diodes, which significantly alleviates the reverse-recovery problem of diodes. The other features of the proposed topology include fewer components, low cost, small input current ripple, and the low voltage stress on power switches. Low voltage stress allows choosing a lower voltage rating metal–oxide–semiconductor field-effect transistor, which directly reduces the cost. The experimental results evaluated the performance of the proposed topology. For this purpose, a 48 V/380 V/500 W laboratory prototype was built and tested, and the results confirmed the performance of the presented converter.

Research on full-bridge LCL resonant converter as constant current source in the ZVS condition

A LCL-based resonant converter is shown to behave as a constant-current source when operated at resonant frequency in this paper. This paper focuses on the realization of zero voltage switching (ZVS) in the case of constant-current in LCL resonant converter and how to reduce the influence of high harmonics on the output current. First, the principle of LCL resonant converter as a constant-current source is described. Second, when the switching frequency of the converter deviates from the resonant frequency point, the current gain curves corresponding to different quality factor Q and the boundary curves realizing ZVS turn-on are analyzed. Third, the influence of the ratio (m) of resonant inductors on the output current of the converter and ZVS turn-on is analyzed, and the value of m is determined. Finally, Pexprt software was used to design the magnetic component model, and combined with Simplorer software for combined-simulation. A simulation circuit model with output 80W/0.32A was designed and experimental results are presented. The correctness of the theoretical analysis has been verified.

Zero-Voltage-Switching Single-Phase Full-Bridge Inverter With Active Power Decoupling

Single-phase zero-voltage-switching (ZVS) inverter with wide bandgap devices has higher efficiency and power density. However, the dc-side capacitor of the inverter will suffer double line frequency ripple and reduces the lifetime of the dc bus capacitor. Active power decoupling (APD) is an effective method to replace the short lifetime electrolytic capacitor with a smaller film capacitor. In order to help achieving the ZVS condition for ZVS inverter and the additional APD circuit, this article presents a ZVS topology for single-phase full-bridge inverter with APD circuit by adding an auxiliary branch between the dc source and the bridge legs. The auxiliary branch is composed of a clamping capacitor, an auxiliary switch, and a resonant inductor. A ZVS pulsewidth modulation scheme is proposed for a single-phase inverter with APD. The gate drive pulses are designed to realize the ZVS turn-on for the main switches of both APD circuit and single-phase full-bridge inverter. Circuit operation stages are analyzed and ZVS conditions are given. Finally, the proposed ZVS inverter with APD circuit is verified on a 1.5-kW inverter prototype.

Achieving Zero Switching Loss in Silicon Carbide MOSFET

Due to the unipolar conduction mechanism, the switching loss of silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (mosfet) is reduced significantly when compared with silicon insulated gate bipolar transistor (IGBT). This enables the use of SiC mosfet in high-frequency application. However, the switching loss could still thermally limit the upper limit of the switching frequency. Further reduction of switching loss of SiC mosfet, therefore, remains an open challenge for higher frequency applications. Based on the in-depth revelation of device physics of the switching process, accurate switching loss model is established which highlights the dependence of the switching loss on the gate driving condition. With extreme fast gate driving condition, several loss limitations can be established. The minimum turn-on loss is the energy stored in the output capacitance and the minimum turn-off loss can approach zero or the so-called zero turn-off loss (ZTL). Furthermore, zero switching loss (ZSL) is achieved when utilizing zero-voltage switching turn-on and ZTL turn-off condition. With ZSL, the upper limit of the switching frequency is no long thermally limited which is verified by co-package experimental demonstration. We believe the trailblazing concepts of SiC mosfet switching loss will provide guiding principles for device innovation, package optimization, gate driver improvement, and current possible solutions toward higher frequency applications.

Analysis and Design of Current-Fed Three-Phase-Isolated LCC-T Resonant Converter for Low-Voltage High-Current Applications

A three-phase-isolated current-fed dc–dc converter with LCC-T resonant tank to achieve an efficient and compact design is proposed. Traditional dc–dc converters require an external parallel inductor to increase the transformer magnetizing current to realize soft switching under light-load conditions. The proposed LCC-T configuration eliminates this requirement and realizes light-load soft switching with reduced circulating current. In addition, the proposed topology maintains zero-voltage switching (ZVS) turn-ON of primary switches, ZVS turn-ON and zero-voltage-zero-current switching turn-OFF of secondary diodes for all load conditions. Steady-state operation, analysis, and design of the proposed converter are reported. Experimental results of 1-kW hardware prototype to verify the claims of the proposed analysis and design are presented.

Analysis and Design Considerations of Efficiency Enhanced Hierarchical Battery Equalizer Based on Bipolar CCM Buck–Boost Units

Compared with the conventional hard switching battery equalizers, hierarchical battery equalizer based on the bipolar continuous-conduction mode buck-boost units could effectively reduce the switching loss and improve the conversion efficiency. This paper mainly addresses the key technical challenges associated with the optimal design of this battery equalizer. The inductor current is controlled to enter into the negative region. Thus, the mosfet body diode provides a freewheeling path for the inductor current during the dead band. This ensures zero-voltage switching turn-on of both power mosfets in each buck-boost unit without auxiliary snubbers. Therefore, the switching losses are significantly reduced. Meanwhile, the integral of the inductor negative current is precisely controlled to minimize the circulating current. This guarantees both minimized conduction losses and suitable equalization speed. Furthermore, an equalization algorithm, which compensates the battery internal resistance induced state-of-charge error, is proposed to improve the equalization accuracy. The operating principles and design considerations are analyzed in detail. An experimental prototype to balance four series-connected lithium-ion battery cells is implemented. The experimental results validate the design of the equalizer and demonstrate obvious efficiency enhancement over the conventional method.

Parallel current‐fed resonant converter with balance current sharing and no input ripple current

This studies a parallel current-fed resonant converter with the advantages of the balance current sharing and no input ripple current. The basic structure of the developed circuit includes a boost converter and half-bridge resonant converter with the same power switches to reduce switch counts. Two boost-type converters with an interleaved pulse with modulation are used in the front stage to eliminate input ripple current and reduce the size of boost inductor. Parallel resonant converter with magnetic coupling current balancing cell is adopted in the rear stage to automatically balance two resonant circuits and realise the zero-voltage turn-on switching for power devices. The voltage doubler circuit is employed on the secondary-side to achieve high-voltage output. The developed converter can be used for current-type input source and voltage-type output. Finally, experiments with 1 kW laboratory prototype are provided to confirm the feasibility of the proposed converter.

A ZVS Bidirectional Inverting Buck-Boost Converter Using Coupled Inductors

The bidirectional inverting buck-boost converter (BIBBC) has a simple structure and a wide voltage ratio. It can be used in the battery supercapacitor hybrid energy storage system (BSHESS) and the motor drive system. However, the traditional continuous conduction mode (CCM) BIBBC will have severe switching loss. The triangular current mode (TCM) BIBBC can reduce the switching loss, but it will increase core loss and filter capacitance. To solve these problems, this paper proposes a new zero voltage switching (ZVS) BIBBC using a coupled inductor. This ZVS BIBBC will provide ZVS conditions for both transistors whether in positive operation or negative operation. Meanwhile, this ZVS BIBBC has small core losses and filter capacitance, and can be used simply. Finally, experimental results obtained from these BIBBC experimental prototypes are presented to validate the soft-switching achieving and the efficiency improvement performance. Experimental results show that both transistors of the ZVS BIBBC achieve ZVS turn-on conditions. The efficiency of the ZVS BIBBC increased by up to 10 percent compared to the traditional CCM BIBBC at heave load, and by up to 1.5 percent compared to the TCM BIBBC at a light load.

Improved Modulation Strategy Using Dual Phase Shift Modulation for Active Commutated Current-Fed Dual Active Bridge

This paper proposes dual phase shift modulation (DPSM) for active commutated current-fed dual active bridge for low-voltage (LV) high-power application to improve the performance of the converter at light loads. The proposed DPSM uses an additional control variable to actively control the peak current in the converter that helps to improve the performance as compared to simpler single variable but unregulated peak current control, phase shift modulation (PSM). The control variables are chosen such that the excess current is just enough to achieve zero current switching (ZCS) turn-off of the LV devices. In the reverse direction, the converter is a full-bridge converter with LC filter. The implementation of the conventional PSM to the full bridge, popularly known as phase-shift full bridge is simple but restricted by the zero voltage switching (ZVS) range. The proposed DPSM is implemented in the reverse direction to maintain the ZVS turn-on of the high-voltage (HV) devices even at very light loads by utilizing the LV devices instead of using them only for synchronous rectification. At higher loads where achieving ZVS is relatively easy, the modulation shifts to conventional PSM to reduce the circulating current and the associated duty cycle loss. The improvement in the performance is validated experimentally with a 1-kW prototype developed for a 30 $\%$ variation in the LV voltage (42–56 V) for both directions of operation. The control of the peak current improved the efficiency by 12 $\%$ from the conventional PSM at 10 $\%$ load at the highest current (42 V) in the forward operation. In the reverse direction, the ZVS turn-on for the HV devices is achieved even at 6 $\%$ load by the proposed modulation at the highest voltage (56 V). Thus, the proposed DPSM is a software-only solution that does not require any additional active or passive components, offering an improved performance while maintaining a low component count and simplicity of the power electronics circuit.

Resonant converter with wide input voltage range and input current ripple‐free

A current fed resonant converter is presented and developed to have the advantages of wide input voltage operation range and less ripple current. The developed circuit includes two boost inverters in the front stage and one resonant converter in the rear stage. Two boost converters are operated using interleave pulse-width modulation in order to reduce the input ripple current. The resonant converter with voltage doubler circuit topology is adopted to obtain high-voltage output and realise zero-voltage turn-on switching for all power switches over all load ranges. The active switches of two boost converters and the resonant converter share the same power switches so that the switch counts in the studied circuit are reduced. In order to extend the input voltage operation range, an additional boost converter is active when the input voltage is lower than the defined voltage level. Therefore, a wide input voltage range operation, 24–76 V, of the developed circuit can be realised to apply in the fuel cells or solar cells input applications. The feasibility and practicality of the developed circuit are confirmed by the test results with an 800 W prototype circuit.

Parallel soft switching converter with fewer switch counts

A parallel direct current (DC) to DC converter is presented for medium power applications. The studied converter includes three half-bridge circuits with sharing two power switches at high-voltage side to reduce switch counts. Three half-bridge circuits are connected by primary-parallel and secondary-parallel to reduce the current stress of power devices at low-voltage side. Each half-bridge circuit supplies one-third of the total power to the output load. Asymmetric pulse-width modulation is employed to generate the gated signals of the switches and regulate the output voltage. Based on the resonant behaviour of the output capacitance of power switches and the leakage inductance of the transformer, the zero-voltage switching turn-on of power switches can be achieved. Current doubler rectifier topology is adopted at the low-voltage side to have the advantage of low ripple current at output capacitor. A laboratory prototype with 1440 W power is built to verify theory analysis and effectiveness of the studied converter.

New Parallel Loaded Resonant Converter With Wide Output Voltage Range

This paper proposes a new parallel loaded resonant converter operating in a narrow switching frequency under wide output voltage range. The proposed converter is capable of operating under zero-voltage switching turn-on of switches and zero-current switching turn-off of diodes. Also, the resonant capacitor with feasible capacitance and current rating can be selected by adjusting the turn ratio of the transformer, making the proposed converter more realizable in high power application. Further, the proposed converter has zero voltage gain at notch resonant frequency, and therefore there are no current and voltage stress in the resonant tank during start-up. Experimental results from a 3-kW prototype are provided to validate the proposed concept.

Soft-Switched High Voltage Gain Boost-Integrated Flyback Converter Interfaced Single-Phase Grid-Tied Inverter for SPV Integration

A two-stage grid-tied efficient solar photovoltaic (SPV) system with zero voltage switching (ZVS) and zero current switching (ZCS) at the dc–dc converter stage and adaptive synchronization at the inverter stage is proposed. In the first stage, an improved high step-up boost-integrated flyback converter with quasi resonant voltage multiplier cell is proposed. ZVS turn-on of all mosfet s and ZCS turn-off of all diodes of resonant voltage multiplier cell results in high efficient power conversion compared with the conventional boost-integrated flyback converters. Small-sized coupled inductor enhances magnetic utilization in this converter. Second stage consists of a single-phase H-bridge grid interfaced inverter with variable band hysteresis current control technique. Amplitude adaptive notch filter is used to extract fundamental unit voltage vector of grid voltage required for estimation of synchronized reference current for hysteresis controller. A 250 W laboratory prototype is developed and experimentally evaluated. Experimental results demonstrate efficient renewable energy conversion at dc–dc converter stage and quality power injection at dc–ac inverter stage of the proposed grid-tied SPV system under changing solar insulation levels.

Bidirectional active clamp DC–DC converter with high conversion ratio

A bidirectional DC/DC converter is presented with the advantages of high conversion ratio in boost and buck mode, low conduction loss, recycling the energy of leakage inductor, and zero-voltage switching (ZVS) in some switches. This new topology can realise a higher step-up voltage gain by the using of a coupled inductor. Then an active clamp circuit was applied to reduce conduction loss and recycle the energy of the leakage inductor. The soft-switching technique is applied to achieve ZVS turn-on. The main circuit of the DC–DC converter is analysed in detail and the performance of the proposed converter is verified by the experimental verifications with a 200 W prototype.