Zero-voltage Switching Operation Research Articles

Variable Frequency Average Current Mode Control for ZVS Symmetrical Dual-Buck H-Bridge All-GaN Inverter

The quasi-square-wave (QSW) zero-voltage-switching (ZVS) symmetrical dual-buck H-bridge (DBHB) all-GaN inverter has been proven to have high efficiency and high density in Google's Little Box Challenge. This variable frequency QSW ZVS inverter is drawing more and more interest in the industry and academia. However, the ac current control with cycle-by-cycle variable frequency ZVS operation is a basic challenge for this inverter. The conventional control methods for this QSW ZVS inverter, such as the hysteresis current mode control and the variable on-time control, require high-speed current sensing or zero-crossing detection (ZCD) circuits, which are very sensitive to noises. In this article, achieving variable frequency average current mode control with variable frequency pulsewidth modulation (VFPWM) is discussed and implemented for this QSW ZVS inverter to eliminate high-speed current sensing or ZCD circuits. For any synchronous half-bridge type converter, the voltage conversion ratio is dependent only on the duty-cycle in either continuous conduction mode (CCM) or QSW ZVS mode. The frequency of the PWM triangular carrier is another degree of freedom. In this control method, the averaged inductor current is sensed and regulated by the average current mode feedback controller and the duty-cycle is generated by the average current controller. The frequency of the PWM carrier is variable and directly calculated based on the duty-cycle signal and the sensed and filtered voltage and current signals. Since all the sensed signals for this current controller are low speed and filtered signals, this current control is highly immune to noises. The reliability of ZVS for this inverter is improved. The complexity of the controller is also reduced. A detailed analysis of the QSW ZVS conditions for the full range operation of the symmetrical DBHB inverter is done in this article. More negative currents can be introduced to reduce the switching frequency and increase the reliability of ZVS. A frequency limiter helps limit the frequency when the current is close to zero or under light load conditions. A frequency updating method with a constant and low interrupt frequency in a digital controller is also discussed. Finally, to verify this control method, a 1-kW all-GaN DBHB inverter prototype is developed and tested in this article.

General Closed-Form ZVS Analysis of Dual-Bridge Series Resonant DC–DC Converters

Switching behavior analysis is an indispensable step for evaluating the steady-state performance of a bidirectional dc–dc converter and a prerequisite for soft-switching modulation design. For dual-bridge series resonant dc–dc converters (DBSRCs), the commonly used fundamental harmonic approximation (FHA) does not usually provide predictions accurate enough for reliable analysis and design. This paper discloses the exact closed-form solution for the zero-voltage switching (ZVS) operation conditions of DBSRCs for the most general case, in which all modulation quantities—i.e., phase shift, duty cycles, and switching frequency—are included. The proposed approach relies on a geometrical analysis of the converter state-plane trajectory, and allows us to analytically predict the ZVS or hard-switching state of any switch and for any given converter operating point. By inherently capturing the effects of all tank harmonics, the model disclosed in this paper shows higher accuracy than the conventional FHA-based approach, and translates into a practical tool for ZVS prediction and optimization at the converter design stage. Based on the derived analytical results, switching behavior of DBSRCs with minimum rms current trajectory (MCT) modulation is investigated, and an effective design choice of resonant-to-switching frequency ratio is presented, which contributes to reduced switching losses and enhanced efficiency. Furthermore, a variable frequency modulation scheme is formulated, achieving ZVS operation of all transistors over a wide input/output voltage range and efficiency improvement versus MCT technique. The analysis and conclusions are validated via extensive experimental tests on a 700 W DBSRC prototype.

Soft-switching SiC power electronic conversion for distributed energy resources and storage applications

Power electronic conversion plays an important role in flexible AC or DC transmission and distribution systems, integration of renewable energy resources, and energy storage systems to enhance efficiency, controllability, stability, and reliability of the grid. The efficiency and reliability of power electronic conversion are critical to power system applications. One way to enhance the efficiency and reliability of power electronic conversion is soft-switching technology. This paper introduces a generic zero-voltage-switching (ZVS) technique based on silicon carbide (SiC) power device. Using the proposed ZVS technique, all semiconductor switching devices in a power converter can realize ZVS operations. Next, the applications of the ZVS technique in different power electronic conversion systems such as photovoltaic inverters, wind power systems, energy storage systems and flexible AC transmission system devices are discussed. Finally, as an example, the operation performance and efficiency improvement of a SiC metal-oxide-semiconductor field-effect transistor (MOSFET) ZVS back-to-back converter are discussed.

SiC-Based 4 MHz 10 kW ZVS Inverter With Fast Resonance Frequency Tracking Control for High-Density Plasma Generators

A high-efficiency power conversion system to drive high-density plasma is proposed for plasma CO2 reforming (PCR). For high durability, the system is designed for inductively coupled plasma (ICP) without performance degradation. The proposed system consists of a novel control method and a 10 kW 4 MHz switching inverter to obtain a high-induced electromotive force that is necessary to generate and maintain ICP. The proposed control method quickly tracks the resonance frequency of plasma impedance with high-frequency resolution, which guarantees zero-voltage switching operation and power supply under highly variable plasma impedance. Moreover, the inverter is designed to be suitable for high-power high-frequency switching operation, consisting of SiC- mosfet s and gate driver circuits with a negative turn- off voltage. Owing to the proposed system, plasma with much higher density than that of conventional plasma generators can be safely driven. A prototype system is presented to demonstrate the proposed operation, and the technical feasibility of PCR is verified. The proposed control can also be widely utilized for various high-frequency switching inverters that operate in variable load impedance.

A Control Strategy for Efficiency Optimization and Wide ZVS Operation Range in Bidirectional Inductive Power Transfer System

The efficiency of bidirectional inductive power transfer (BIPT) systems is strongly dependent on the load. Besides, the soft-switching operation of power switches is critical to high-frequency converter in the BIPT systems. In this paper, a triple-phase-shift (TPS) control strategy is proposed to achieve load matching while realizing zero voltage switching (ZVS) for all power switches within the entire power range. The load matching condition of the BIPT system with double-sided LCC compensation network is analyzed. And a dual side phase shift control is proposed to adjust power flow while realizing load matching. To realize ZVS operation, the third phase shift between primary and secondary side is introduced as an extra control variable. A time domain model of double-sided LCC compensation network is established to analyze the ZVS range. With the proposed TPS control, wide ZVS operation range of the system can be achieved while maintaining load matching. At last, a scale down prototype of 1 kW BIPT system is developed. The experimental results show good agreement with theoretical analysis, all switches realize ZVS within the entire power range and a peak efficiency of 94.83% is achieved.

Optimized Parameters Design and Adaptive Duty-Cycle Adjustment for Class E DC–DC Converter With on‐off Control

The Class E dc–dc converter, with a simple topology and zero-voltage-switching (ZVS) for the power switch, can operate at a switching frequency of up to megahertz. In this paper, an optimized ZVS operation condition for minimizing the switch voltage stress, switch rms current, and switch voltage harmonic components is derived for the on ‐ off controlled Class E dc–dc converter by optimizing the time instant at which the switch voltage resonates back to zero. Based on this result, a step-by-step parameter design approach is proposed for a Class E dc–dc converter with a large input inductor, which avoids time-consuming simulations or complex numerical calculations. Then, a capacitance compensation approach is further proposed to extend the design results to a Class E dc–dc converter with a resonant input inductor. Furthermore, an adaptive duty-cycle adjustment scheme is proposed for reducing the reverse conduction loss of the power switch, thereby improving the conversion efficiency over the entire input voltage range. Finally, a prototype of a 20-MHz 10-W Class E dc–dc converter is built and tested in the laboratory, and experimental results are presented to verify the effectiveness of the proposed optimized parameter design approach and the adaptive duty-cycle adjustment scheme.

Zero-Voltage-Switching Sinusoidal Pulsewidth Modulation Method for Three-Phase Four-Wire Inverter

A zero-voltage-switching (ZVS) sinusoidal pulsewidth modulation (SPWM) method for a three-phase four-wire inverter is proposed in order to achieve higher efficiency and power density. With the proposed modulation scheme, the ZVS operation of all switches, including the main switches and the auxiliary switch, can be realized. Besides, all seven switches operate at a fixed frequency. The ZVS SPWM scheme is introduced by considering the various combinations of the polarities in three-phase filter inductor currents and the analysis of operating stages is presented. ZVS condition of the ZVS SPWM scheme is derived and discussions of ZVS condition for typical three-phase loads are also provided. In addition, the resonant parameters design and loss analysis are briefly investigated. Finally, the proposed ZVS SPWM scheme is verified on a 10-kW inverter prototype with SiC mosfet devices.

Realization of High-Efficiency Dual-Active-Bridge Converter With Reconfigurable Multilevel Modulation Scheme

Efficiency optimization of dual-active-bridge (DAB) converters involves the minimization of both conduction and switching losses. However, it is challenging to achieve these two objectives simultaneously due to their conflicting nature, i.e., circulating current is required to realize zero-voltage switching (ZVS) but the presence of an excessive amount of the circulating current is the main cause of conduction loss and low efficiency. This dilemma has been common to conventional DAB converter topologies and modulation schemes which cannot provide sufficient degrees of freedom (DoFs) to the design of their operation modes. This paper is an illustration of the merits of utilizing reconfigurability of the operation mode as a new DoF in designing the operation of DAB converters to minimize both conduction and switching losses. The proposed DAB converter is designed to switch between two operation modes. For 25%-100% of the rated output power, a new modulation scheme based on the four-level ac voltages is proposed to achieve zero circulating current, zero backflow power, and full-range ZVS. Below 25% of the rated output power, the new modulation scheme transitions smoothly to the enhanced dual-phase-shift (EDPS) modulation scheme that continues to achieve zero backflow power and full-range ZVS while the incurred circulating current is moderated by operating the ac voltages at half-amplitude. The experimental results obtained from a 2-kW prototype show that, in comparison to conventional modulation schemes, the proposed modulation scheme is capable of maintaining the highest efficiency over the full output power range and greatly improves the reliability of switches due to full-range ZVS operation.

Analysis, Design, and Implementation of WPT System for EV's Battery Charging Based on Optimal Operation Frequency Range

Charging electric vehicles wirelessly is promising because of its convenience as well as saving of charging cables. However, the existing wireless power transfer systems suffer from high resonant peaks and poor efficiency. Therefore, zero voltage switching (ZVS) operation of inverter should be achieved especially in high transfer power. Based on the variable frequency phase shift control strategy (VFPSC), this paper presents an optimal operation frequency range (OOFR) where the wireless power transfer (WPT) system can realize the required output and ZVS operation of inverter simultaneously without extra dc–dc converters. Meanwhile, based on OOFR, an optimized electrical parameter design method based on VFPSC is proposed with the multiple boundary conditions. Moreover, a novel three-loop control strategy (TLCS) is proposed to make the system operate at any points of OOFR. Especially, an implementation method of the TLCS is proposed, which can dynamically adjust frequency and phase shift to make the system always operate at the preset ZVS angle and realize the required output simultaneously. Finally, a 500-W WPT system is built to verify the correctness of theoretical analysis. The experimental results show that a very high overall efficiency is achieved in the whole charging process and the maximum efficiency can achieve 94.9% with $k$ = 0.2.

A Constant Frequency ZVS Control System for the Four-Switch Buck–Boost DC–DC Converter With Reduced Inductor Current

A constant frequency zero-voltage-switching (ZVS) control strategy with a minimum root mean square (rms) value of inductor current is proposed in this letter for the four-switch buck-boost (FSBB) dc-dc converter that is used as a 48 V intermediate bus pre-regulator in distributed power systems. The quadrilateral inductor current modulation is adopted to achieve ZVS operation. The four control time intervals are optimally selected such that the inductor current rms value is minimized, thus reducing the conduction loss. The proposed closed-loop ZVS control scheme can be implemented without sensing the load current, although the rms minimum current algorithm needs the input and output voltages and load current at given a steady-state condition. The control scheme is verified in a 300 W dc-dc prototype of the ZVS FSBB converter. The input voltage and load transition tests are provided to verify the closed-loop characteristics without sensing load current.

Automated design tools for piezoelectric transformer‐based power supplies

This paper proposed a design approach for piezoelectric-transformer-based power supplies. Initially, an analytical approach is used to derive the Mason equivalent circuit parameters of a PT. This is coupled with a semi-automated procedure to decide the appropriate physical dimensions of the PT. The procedure is applied to a typical low-power power supply specification, whereupon a specific transformer is design, verified using COMSOL and used as a simulated converter in SPICE. Results show that the design can be successfully implemented while maintaining efficient zero-voltage switching operation.

Isolated Bidirectional DC–DC Converter With Quasi-Resonant Zero-Voltage Switching for Battery Charge Equalization

Charge equalization for a series-connected battery string is necessary to enhance usage life and performance of cells. In this paper, an isolated bidirectional dc-dc converter with quasi-resonant zero-voltage switching (ZVS) is proposed for centralized charge equalization system. Through the quasi-resonant operation, the proposed converter can achieve ZVS operations in both boost and buck modes, which decreases switching losses and improves the efficiency. The energy in leakage inductance is released to output side in the boost mode and recycled to the input side in the buck mode, which eliminates the voltage spike. Moreover, the proposed converter has fewer components than existing converters used in the centralized charge equalization system. The operating principle and theoretical derivation of the proposed converter are presented. The ZVS implementations and conditions are analyzed and illustrated in detail. Finally, the experiments using a 7.2 Ah battery string of 13 cells are conducted. The results verify the validity of the proposed converter and show that the equalizer achieves good performance in terms of equalizing speed and efficiency.

Development and Evaluation of an Isolated Resonant Converter for Auxiliary Power Supply in DC Traction

This paper presents the implementation and evaluation of an isolated resonant converter and also compares the efficiencies of hard and soft switching isolated converter topologies using high-frequency transformer for auxiliary power supplies in DC traction. The half-bridge DC-DC converter with resonant network has been tested under zero voltage switching (ZVS), zero current switching (ZCS) operations, and also dead time variation of the power switches improving the overall system efficiency. This paper provides guidelines for a cost effective DC-DC converter design based on discrete 1200V/40A IGBTs driven with high switching frequency. That would allow optimization of passive elements by reducing their mass making the converter suitable for traction application. Simulations and test results of an experimental setup with output power up to 3kW are presented. The overall system efficiency of the ZVS and ZCS operations of half-bridge LLC DC-DC converter were compared with a classic hard switching topology.

A Novel Soft-Switching Secondary-Side Modulated Multioutput DC–DC Converter With Extended ZVS Range

In this paper, a novel soft-switching secondary-side modulated dc–dc structure with extended zero voltage switching (ZVS) range is proposed. In a simple manner, this structure can be extended to provide isolated multioutputs with independent voltage regulation capability. Besides, the secondary side can be bidirectional to interface with energy storage elements such as batteries and ultracapacitors. The proposed topology is suitable for high voltage gain or high output dc-link voltage, low-power, and multioutput applications. The primary-side full-bridge switches operate complementarily to generate a two-level square wave. Therefore, the circulating energy is significantly smaller than conventional phase-modulated full-bridge converters. The output voltage is regulated by controlling the duty cycle of the auxiliary mosfet on the active/semiactive rectifier, which offers a simple control. Moreover, the ZVS operation range of full-bridge mosfet s is enhanced due to the volt-second balance of magnetizing inductance and the secondary-side control. All the secondary-side rectifying diodes turn off with limited di / dt. A 1-kW prototype generating two 390 V, 330–400 V outputs from a 130–180 V dc link is designed to serve as a proof of concept. The full-load efficiency is 95.6% at 100 kHz switching frequency.

Maintaining Continuous ZVS Operation of a Dual Active Bridge by Reduced Coupling Transformers

A major advantage of the dual active bridge (DAB) dc–dc converter is its ability to operate under zero voltage switching (ZVS) conditions to reduce switching losses. However, when the ac link coupling transformer is conventionally designed to minimize its magnetizing current, nonideal switching conditions almost invariably lead to hard switching operation at particular power transfer levels and dc–dc voltage ratios. This paper presents a mathematically based design approach for a coupling transformer with a reduced magnetizing inductance that creates just sufficient ac link circulating current to maintain continuous ZVS operation over the converter's entire specified operating range without incurring significant additional losses. The required magnetizing inductance reduction is found to be a function of the inherent transformer leakage inductances, switching dead-time, and device parasitic capacitances. The analysis approach is validated by matching experimental results.

Capacitive Coupling Wireless Power Transfer Circuit with a Compensated L for High Voltage Gain and Soft Switching

A Capacitive coupling wireless power transfer (WPT) circuit with a compensated L is proposed. Two pairs of small area metal electrodes are used to produce two coupling capacitors and a resonant inductor is employed for the capacitive coupling wireless power transfer. By adding one parallel inductor to the series resonant circuit, an output voltage gain greater than 1 can be achieved. In addition, zero voltage switching (ZVS), zero current switching (ZCS), and higher output voltage can be obtained using the compensated inductor even at high frequency operation. A 6.3W Capacitive coupling WPT system is implemented with an approximately 700pF coupling capacitance by two 108cm2 copper plates and 6.78MHz operation for charging a small power electric device. The experimental results confirm the ZVS and ZCS operation, higher efficiency, and larger output voltage.

An Improved Autonomous Current-Fed Push-Pull Parallel-Resonant Inverter for Inductive Power Transfer System

In the inductive power transfer (IPT) system, it is recommended to drive the resonant inverter in zero-voltage switching (ZVS) or zero-current switching (ZCS) operation to reduce switching losses, especially in dynamic applications with variable couplings. This paper proposes an improved autonomous current-fed push-pull parallel-resonant inverter, which not only realizes the ZVS operation by tracking the zero phase angle (ZPA) frequency, but also improves the output power and overall efficiency in a wide range by reducing gate losses and switching losses. The ZPA frequencies characteristic of the parallel-parallel resonant circuit in both bifurcation and bifurcation-free regions is derived and verified by theory and experiments, and the comparative experimental results demonstrate that the improved inverter can significantly increase the output power from 7.68 W to 8.74 W and has an overall efficiency ranging from 63.5% to 72.5% compared with the traditional inverter at a 2 cm coil distance. Furthermore, with a 2-fold input voltage (24 V), the improved inverter can achieve an approximate 4-fold output power of 38.9 W and overall efficiency of 83.6% at a 2 cm coil distance.

A High-Gain, High-Efficiency Nonisolated Bidirectional DC–DC Converter With Sustained ZVS Operation

This paper proposes a high-gain, highly efficient nonisolated bidirectional dc–dc converter with soft-switching capabilities. An intermediate energy storage cell enables the converter to generate high gain in the continuous current mode. Two auxiliary resonant networks, each consisting of a low-power switch, a capacitor, and an inductor, are integrated to provide the soft switching [zero-voltage switching (ZVS)] for the main switches. The dedicated resonant networks ensure the ZVS is sustained over a wide operating range of duty cycle and power. The auxiliary switches are also soft switched to boost the efficiency further. Additionally, the reverse recovery loss is eliminated by optimizing the resonant capacitors. The validity of the design is verified by a 200 W prototype converter. A maximum gain of 17.8 is observed at a duty cycle ratio of 0.8. At 30 kHz, a full load efficiency of 97.5% and 95.5% is recorded in the boost and buck modes, respectively. On the other hand, at 100 kHz, these efficiencies are 97.0% and 94.5%, respectively. Consequently, the experimental results validate the proposed concept and design procedures. This performance exceeds that of high gain topologies published in the recent literature.

Analysis and Design of a Family of Two-Level PWM Plus Phase-Shift-Modulated DC–DC Converters

A comprehensive analysis for a family of two-level pulsewidth modulation plus phase-shift (PPS)-modulated-isolated-bidirectional dc–dc converters is presented in this paper. Compared with the traditional phase-shift control, the PPS control features reduced current stresses, reduced conduction losses, guaranteed zero-voltage switching (ZVS) operation, and wide conversion-ratio variation range. In this paper, all eight operation modes are revealed, and then the unified solution of the power transmission capability for each mode is proposed, applicable for any two-level PPS converters. Based on the unified solution, component stresses and ZVS operation are analyzed to assist component selection. Most importantly, the control maps for three different combinations of the two-level PPS converters are proposed, to assist converter operation and design in the low-circulating-current region. In the control map, a circuit parameter k is proposed and its upper limit is found, providing a design limit to select switching frequency, leakage inductance, turns ratio, and power level. A 29–67 V/380 V prototype—the combination of group C plus group A—rated at 100–1000 W was built. The analysis is verified by both simulation and experimental results.

ZVS Modulation Scheme for Reduced Complexity Clamp-Switch TCM DC–DC Boost Converter

DC–DC boost converter zero-voltage-switching (ZVS) modulation schemes such as triangular current mode (TCM) offer a highly efficient operation but suffer from large switching frequency variations, which are complicating the EMI filter design and the digital control. As a solution, a tri-state boost converter operated in ZVS mode, referred to as clamp-switch TCM (CL-TCM) operation can be introduced, which allows to limit the switching frequency variation significantly. This paper presents two variations of the CL-TCM boost converter with reduced number of active switches in the circuit, which are suitable for high input-to-output voltage conversion ratios. In addition, the ZVS modulation schemes, its limitations, the converter design and the controller implementation are presented and analyzed in detail for both converter topologies. The timing calculations for the switching signals are provided for two operating modes, either offering a minimized switching frequency variation and minimized RMS inductor current or a constant switching frequency operation, which in turn comes at the expense of an increased RMS inductor current. The ZVS operation and the operating modes are experimentally verified using a hardware prototype.