Zero-voltage-switching realized by magnetizing current of transformer in push-pull DC-DC converter

In this paper, a novel soft switching push-pull LC resonant DC-DC converter for energy sources is presented. In a high step-up converter, the input of primary side possesses low voltage and high current, so the losses caused by the current account for most of the total power loss. At the same time, the high-voltage stress of the high-voltage output components on the secondary side is also a major problem. Therefore, a high-gain isolated push-pull converter with a secondary-side resonant circuit is proposed, so that the primary-side switches have zero voltage switching (ZVS) and the secondary-side diodes have zero current switching (ZCS). The push-pull structure can reduce the number of active switches, so that the total power loss on the primary side can be reduced. The converter has a resonant tank circuit arranged between the secondary side of isolation transformer and the high-voltage output rectification module. The high-voltage output rectifier module adopts a full-bridge architecture suitable for high-voltage coupling connection. The low-side power switching module adopts a push-pull architecture suitable for low-voltage and high-current applications. The resonant tank circuit uses an inductor–capacitor (LC) structure to improve the resonant tank circuit, which achieves soft switching during power transfer, increasing the efficiency of the converter and improving the electromagnetic compatibility. The main advantage of this technology is that the secondary-side leakage inductance of transformer and the resonant capacitance are connected in series to achieve ZVS for switches and ZCS for diodes. Finally, a prototype of a high-gain push-pull resonant converter was established. The converter was operated at a fixed switching frequency of 135 kHz and a duty cycle of approximately 0.5. The efficiency of the converter can reach 97.1% under experimental tests at an output voltage of 400 V and a rated output power of 500 W.

Many resonant converters have been proposed previously, and their soft-switching techniques have yielded prominent features of high efficiency and low noise. However, the variable-frequency control is normally used to control the output voltage, and it results in a few problems such as the lowest switching frequency limiting the size reduction of the output filter and noise filter, and the beat phenomenon. In order to eliminate these limitations, we had previously proposed a novel ZVS–PWM controlled current-mode resonant converter with an active-clamp circuit. The purpose of this paper is to clarify the steady-state characteristics of this converter. First, the steady-state characteristics are analyzed, and then an analytical expression for the output voltage is derived through the concept of an equivalent ac resistance. Second, the zero-voltage-switching (ZVS) region is clarified. Finally, these analytical results are confirmed by experiment. Thus, it is possible to realize both ZVS operation and PWM control at a constant switching frequency. © 1999 Scripta Technica, Electron Comm Jpn Pt 2, 83(1): 59–65, 2000

A class E isolated DC/DC power converter for regulating the output voltage at a fixed switching frequency is presented, analyzed and experimentally verified. It consists of class E series-resonant inverter, high-frequency transformer and class E low dv/dt pulse width modulation (PWM) synchronous rectifier. By controlling the conduction time of the controlled switch in the rectifier, high-frequency AC current is rectified and the output voltage can be controlled at the same time. The zero voltage switching (ZVS) condition of all switches can be maintained from full-loaded to open-loaded. The theoretical predictions were in good agreement with the experimental measurements and the maximum efficiency measured at a switching frequency of 1 MHz was 91.2%.

For power supplies of communication system, we propose an active-clamped zero-voltage-switching (ZVS) forward converter with a synchronous rectifier. This converter was designed and fabricated, and the power conversion efficiency was compared with a conventional forward converter having a reset winding with synchronous rectifiers. Here, they were operated on the conditions of input voltage of DC 48 V, output voltage of 5 V, output current of 10 A and switching frequency of 120 kHz. As a measurement result, the conversion efficiency of the proposed converter was 90.6% and it was average 3.1% higher than the conventional forward converter having a reset winding with synchronous rectifiers. If major components of a converter are carefully chosen by considering the switching characteristics and the driving circuit for ZVS is more stabilized, this proposed converter can be used to realize the converter with output voltage lower than 3.3 V, higher conversion efficiency, and higher output current.

This paper introduces a new flyback-current-fed push-pull DC-DC power converter whose significant advantages in comparison with conventional designs are: reduction in the number of output diodes; and unified output characteristics to represent both the buck and the boost operation modes in the continuous conduction mode. Theoretical analysis, design methodology and experimental results taken from a 600 W, 25 kHz laboratory prototype are presented in this paper. The circuit introduced is suitable for switching mode power supply design as well as power factor correction applications.

ZVS(zero voltage switching) PWM(pulse width modulation) inverters have attracted much attention recently. The basic idea is to use ZVS circuit as the main circuit of inverter resonance at the beginning of every carrier period so that each power device can com-mutate when voltage of the main circuit’s DC bus line is zero. To ensure the resonant circuit to operate properly, sawtooth with alternate slope (positive or negative) is used as carrier. But the time of zero voltage vectors with such PWM pattern is greatly different from traditional hard-switching PWM pattern. This paper discusses the locus of flux linkage under soft-switching PWM pattern by using space voltage vector. It is pointed out that, under the hard-switching PWM pattern, speed of flux linkage is adjusted by zero space voltage vector. When soft-switching PWM pattern is used, however, effective time of space voltage vector varies considerably, sometimes even without zero space voltage vector. Therefore non-zero space voltage vector has been used to make the speed of flux linkage locus equal to that of hard-switching PWM pattern. The cause of current distortion in soft-switching PWM inverters is also discussed. Based on the flux linkage locus circle, corresponding compensation methods are proposed. Experimental results show that the described method can effectively improve output current waveform of inverter.

AC/DC converters are widely used in various fields. To address the issues of large volume and limited power density associated with conventional two-stage converters, the Dual-Active-Bridge (DAB) based quasi-single-stage AC/DC converters (QSSDAB) have garnered significant attention. Benefiting from the wide voltage gain range of DAB converters, the QSSDAB topology requires only film capacitors to maintain the sinusoidal half-wave rectified by synchronous rectification. This configuration eliminates the need for electrolytic capacitors, thereby enabling volume reduction for enhanced power density. To further enhance the efficiency of QSSDAB, a wide range of Zero Voltage Switching (ZVS) is needed. However, when the AC voltage is low, the ZVS is hard to guarantee solely by the control strategy. In this paper, a wide range ZVS strategy that utilizes split inductors and magnetizing current compensation to broaden the ZVS range is proposed. First, in this paper, the topology and model of the converter are analyzed. Then, the operation modes of the DAB are explained together with the ZVS- required current. Herein, ZVS is realized through a combination of control strategy, and magnetizing current compensation, where the control strategy ensures that each switch achieves at least Zero Current Switching (ZCS), and the ZVS current is realized through magnetizing current compensation. Finally, a comprehensive simulation are performed to validate the proposed strategy.

This paper proposes a predictive zero-voltage-switching (ZVS) control with improved ZVS time margin and limited variable switching frequency range for a 99% efficient megahertz (MHz) GaN totem-pole power-factor-correction (PFC) rectifier. The conventional ZVS control methods for totem-pole PFC may lead to zero ZVS time margin and ultra-wide switching frequency range. This paper proposes that the synchronous rectifier (SR) turn- off current is a new degree of freedom for the ZVS control. Thus, the proposed cycle-by-cycle predictive ZVS control method controls the SR turn- off currents to extend the ZVS time margin and to reduce the maximum switching frequency. With the proposed ZVS control, the minimum ZVS time margin and a limited maximum switching frequency can be realized in a MHz GaN-based totem-pole PFC. With the improved ZVS time margin, the reliability for realizing ZVS is significantly improved. With the limited maximum frequency and the limited frequency range, the difficulty in high-speed current sensing and digital control is reduced, and the frequency-related loss is also reduced, which is important for improving the light-load efficiency. To accurately extract the current and timing parameters for the proposed ZVS control, an analytical model for the ZVS totem-pole PFC is proposed. The proposed ZVS control and analytical model are applicable over the full input and output voltage range, and over the full load range. In addition, a hybrid current control is proposed and implemented based on the proposed ZVS control. Finally, a 3.2-kW MHz GaN totem-pole PFC prototype is developed and tested with full-range ZVS, minimum ZVS time margin, limited switching frequency range, 99% peak efficiency, and 130-W/in3 power density based on the proposed ZVS control and system control strategy. The realized efficiency, power level, and power density are among the best ever reported for the GaN-based totem-pole PFC.

Derived from the class-E resonant converters, the isolated class- $\Phi _{2}$ resonant converters have much reduced voltage stress of the control FET owing to a shunt branch paralleled with the switch to provide low pass path for the second harmonic voltage. With the increase of the input voltage, the reverse conduction time of the power FETs varies seriously and the gate drive voltage can hardly match efficiently with the drain voltage of the synchronous rectifier (SR) FET. This causes the earlier turn-on of the SR FET before zero voltage switching (ZVS) is achieved, which results in high turn-on loss at multi-MHz. Moreover, with the enhancement mode gallium nitride (eGaN) HEMTs, the mismatch between the drive voltage and drain voltage results in high reverse conduction mechanism loss after the SR FET turns off in the switching period of hundreds of nanoseconds. The reverse conduction mechanism of the control eGaN HEMT can be triggered before ZVS turn-on, which causes high reverse conduction loss. It is interesting to find that when the output voltage is controlled to follow the input voltage proportionally, the drive voltage can match well with the drain voltage of the power FETs over a wide input voltage range, which is proved mathematically by the state-space analysis. Then, a voltage following control is proposed to control the isolated resonant converters as dc transformers (DCXs). The turn-on loss of the SR FET and reverse conduction loss of the SR and control FETs can be minimized. An 18–24 V input, 18 W/2 A output, 10-MHz eGaN DCX was implemented to verify the advantages. With the proposed control, the efficiency is improved from 79.9% to 85.5% at 18 W output and 24 V input.

In recent years, power electronic energy storage systems using super capacitor bank have been widely studied and developed for the electronic vehicles. In this paper, a full-bridge/centertapped push-pull circuit-based bidirectional DC-DC converter and its control method are proposed and discussed. From the results of detailed experimental demonstration, the proposed system is able to perform adequate charging and discharging operation between low-voltage high-current super capacitor side and high-voltage low-current side with drive train and main battery. Furthermore, conduction losses and voltage/current surge are drastically reduced by ZVS operation with lossless snubber capacitor in high-voltage side as well as the synchronous rectification in low-voltage high-current super capacitor side.

This paper proposes a novel and simple direct power control of three-phase PWM rectifiers with constant switching frequency using space vector modulation (DPC-SVM). The active and reactive power is used as the pulse width modulated (PWM) control variables instead of the three-phase line currents usually used. Moreover, line voltage sensors are replaced by a virtual flux (VF) estimator. The theoretical principle of this method is discussed. The steady state and dynamic results of DPC-SVM that illustrate the operation and performance of the proposed system are presented. It is shown that DPC-SVM exhibits several features as: simple algorithm, good dynamic response, constant switching frequency and particularly provide sinusoidal line current when supply voltage is not ideal. Results have proven excellent performances and verify the validity of the proposed system.

SummaryThis paper proposes an advanced power converter setup to charge an electric vehicle battery from a renewable energy source, such as solar photovoltaic. An improved Z‐source DC–DC boost converter (IZSBC) is utilized in the first stage. A synchronous rectifier (SR) of a phase‐shifted full‐bridge converter (PSFBC) with continuous conduction mode (CCM) is employed in the second stage using the zero voltage switching (ZVS) technique to provide isolation between the source and the load. To address the disadvantage of undesirable dynamic characteristics of the PSFBC‐SR, an advanced voltage control using the advanced model predictive controller (AMPC) is suggested to improve the dynamic characteristic of the PSFBC‐SR converter and prevent output voltage overshoot. An AMPC‐based new control method is preferred to eliminate body‐diode conduction for improved efficiency at any load conditions. Simulation and experimental designs of 0.5 kW with a 25 V DC input from the SPV, a boosted output of 100 V for a 60 V, 16 Ah battery bank and switching frequencies of 100 and 250 kHz for IZSBC and PSFBC‐SR, respectively, are produced and evaluated. Results show an efficiency of 93.7% with 31.44 W loss in simulations and 93.94% with 30.25 W loss in hardware tests. The preferred system has fast dynamics and is robust to sudden load impedance changes, thereby improving current tracking and reducing converter losses. The AMPC strategy proposed in this paper can increase conversion efficiency and control the output voltage without additional gain tuning.

A novel carrier-based unipolar-sinusoidal pulse width modulation (SPWM)-oriented modulation technique with synchronous rectification for isolated bidirectional single-stage high-frequency-ac link dc–ac converters using SiC MOSFET is presented in this paper. The dc–ac converter is composed of a full-bridge (FB) inverter cascaded with a cycloconverter through a high-frequency transformer. A carrier-based unipolar-SPWM-oriented modulation technique with synchronous rectification is proposed to realize zero-voltage-switching (ZVS) for the FB inverter and zero-current or zero-voltage-switching (ZVS/ZCS) for the cycloconverter in all load ranges, and to suppress the voltage spikes introduced by the transformer leakage inductance as well. In order to increase the switching frequency, efficiency, and power density, this paper proposes to utilize SiC MOSFETs for the converter. Synchronous rectification is implemented to further increase the converter efficiency. With the novel modulation technique, there are two switches in the cycloconverter that are continuously on at each interval, which eliminates on-fourth of the switching loss. A simulation model and a 400 VDC–240 VAC, 1.2=kW prototype have been developed to validate the effectiveness and performance of the proposed unipolar soft-switching modulation technique and SiC converter.

Pulse-width modulated (PWM) full-bridge boost converters are used in applications where the output voltage is considerably higher than the input voltage. Zero-voltage-switching (ZVS) is typically implemented in these converters. A new ZVS-PWM full-bridge converter is proposed in this paper. The proposed converter does not have any of the disadvantages associated with other converters of this type, including a complicated auxiliary circuit, increased current stresses in the main power switches, and load-dependent ZVS operation. The operation of the proposed converter, its steady-state characteristics, and its design are explained and examined. The feasibility of the converter is confirmed with results obtained from an experimental prototype.

Full-bridge phase-shifting zero voltage switching (ZVS) pulse width modulation (PWM) circuit adopts phase control and by resonance, the circuit can realize zero voltage conduct of switch device, eliminate conduct loss. However, the lagging legs of full-bridge circuit is difficult to realize ZVS in a little current. The main circuit topological structure of full-bridge phase-shifting ZVS high frequency power supply based on adaptive delay control technology is applied in this paper. By adaptive delay control technology, it can detect voltage of power grid and bridge arm midpoint in real time, and expand the ZVS operating range by adjusting the triggered time of switch devices. The main transformer and resonance inductance parameters are designed in this paper. The experimental results proved that adaptive delay control technology can expand the ZVS operating range, and improve the efficiency of the power supply.