High Frequency ZVS GaN-Inverter with Adaptive Dead Time

A novel current harmonic dead time design method is presented to guarantee zero-volt switching (ZVS) of a resonant LCCL network, regardless of loading condition, accounting for non-linear characteristics of the parasitic output capacitance. Dead time voltage modeling is omitted; an upper bound on necessary dead time to achieve ZVS is instead developed with a charge-based approach to modeling parasitic capacitance. The harmonic dead time design method is shown to conservatively estimate the necessary dead time, using only the harmonics created by all full-bridge inverters. The calculated dead time criterion is shown to be conservative for many loading conditions. Considerations are made for a mistuned systems and parasitic effects. Simulation validation of the design method is presented. A full hardware test also demonstrates the validity of the design technique. The harmonic design method can be applied to nearly any LCCL resonant converter designs to guarantee ZVS at all load conditions.

Aiming at fulfilling the desirable features of compact structure, high efficiency, high reliability, and multifunctionality for the solid state transformers (SSTs), a single-cell matrix-type SST as well as its control method is proposed as the interface between the medium-voltage (MV) and the low-voltage (LV) levels for direct MV AC to LV AC conversion. To achieve zero voltage switching (ZVS) at both the MV and LV sides, a modulation scheme to construct the special resonant currents during the dead time by actively controlling the MV and LV side gate signals is implemented. Furthermore, the ZVS conditions of the MV and LV side bridges are analyzed, and system parameters are properly designed to ensure full range ZVS operation. A 1-kW SST prototype is developed to verify the functionality and effectiveness of the proposed methods. The experiments show that sinusoidal input and output, bidirectional power flow capability, and ZVS at both sides over wide input voltage and load ranges are achieved with the nominal efficiency of 96.1%. The experimental results match the theoretical analysis and the simulation results well.

In modern hybrid electric vehicles, wide-input-range intermediate bus converters (IBCs) are essential in 48V power systems [1]. To increase the power efficiency, e-mode GaN FETs have been adopted in the IBCs [2, 3], as they offer much smaller on-resistance and thus conduction loss than silicon power FETs. However, even with GaN FETs, hard-switching (HS) power converters would still suffer from considerable turn-on V-I overlap loss and dV/dt kickback at high input voltages, degrading the light-load power efficiency, limiting the switching frequency (f SW ) to 100s of kHz, and compromising the converter reliability. To address these issues, different soft switching schemes have been adopted to enable zero-voltage switching (ZVS) in HV power converters [4, 6]. Conventional ZVS scheme [4, 5] can guarantee fixed switching frequency over a wide input range as compared to its resonant-based counterpart [6]. In [4], although a proper gate driver is reported to minimize the reverse conduction loss of the GaN-based ZVS converter, the converter light-load power efficiency is still considerably degraded by the power loss of the ZVS branch. This is because the fixed large continuous inductor current ripple of the ZVS branch for the maximum load case has to be utilized for ensuring full ZVS of GaN FETs for all different load conditions. This large current ripple becomes excessive and results in substantial power loss in high f SW when the load decreases, diminishing the benefit of switching loss removal via the ZVS operation.

For the power management of a wireless power transfer system for implantable mechanical heart pumps, an additional boost DC-DC converter stage is needed in order to control the power delivered to the implant. Particularly, battery powered and implantable medical devices pose special demands on the efficiency and/or power density of the employed converters. Accordingly, soft-switching and/or high switching frequencies must be targeted. Modulation schemes that allow for Zero-Voltage-Switching (ZVS) such as Triangular Current Mode (TCM) offer a highly efficient operation, but suffer from a large operating frequency variation, which is mainly limited by the digital control. Therefore the Clamp-Switch TCM (CL-TCM) converter can be employed which allows also for the control of the switching frequency variation. In this paper, the CL-TCM and the TCM converter are compared regarding the power conversion efficiency and the power density of the converter. Since the CL-TCM converter is not well known in the literature, the converter is analysed in detail and a modulation scheme is explained that allows for ZVS for all switches in the entire range of operation. In addition, the requirements for ZVS and a control scheme (i.e. timing calculations) are provided for the converter in order to limit the maximum switching frequency. The modulation and control scheme are verified with a hardware prototype. Finally, the performance of the CL-TCM converter is measured and compared to the performance of the converter operated in TCM mode. The measurements show that the CL-TCM converter offers similar performance compared to the TCM operation at lower inductor power density, but has the advantage of a significantly reduced switching frequency variation. In applications, where a very high power density is needed, the TCM converter outperforms the CL-TCM converter in terms of efficiency.

Aerospace power systems, including satellites in low earth orbit (LEO) and geostationary earth orbit (GEO), face stringent thermal constraints to minimize size, weight, and power (SWaP). Gallium nitride (GaN) devices offer superior radiation hardness—critical for the harsh space environment—and MHz-level switching capabilities. This high-frequency operation minimizes passive components, particularly magnetics, thereby reducing the overall volume. However, above 10 MHz, magnetic cores become impractical due to material limitations. To address these issues, this article proposes a design methodology for a GaN-based quasi-square-wave (QSW) buck converter integrated with a PCB air-core inductor. First, the impact of the switching frequency and dead time on the zero-voltage switching (ZVS) condition is elaborated. Then, a power loss model accounting for various loss mechanisms is presented. To overcome high GaN body diode reverse conduction loss, an auxiliary diode is employed. Based on the model, a design procedure is developed to optimize the inductor for 10 MHz operation while maximizing efficiency. To validate the design, a 28 V/12 V, 18 W prototype was built and tested. Experimental results demonstrate a peak efficiency of 86.5% at 10 MHz. The auxiliary diode improves efficiency by 4%, verifying reverse conduction loss mitigation. Thermal analysis confirms a full-load case temperature of 62.2 °C, providing a 47.8 °C safety margin compliant with aerospace derating standards. These findings validate the solution for high-frequency, space-constrained aerospace applications.

An algorithm for providing adaptive control and dead time compensation of single input-single output systems with unknown or varying dead time is presented. The algorithm is designed by pole-zero placement and is unique in that an explicit estimate of the dead time is not required, thus avoiding a difficult estimation problem. Parameter estimation for the adaptive controller/dead time compensator is performed with a recursive least squares algorithm. Simulation studies and experimental application on a heat exchange loop on a pilot scale distillation column verify the performance of the algorithm. In each example, the performance of the adaptive controller/dead time compensator is compared to that of a proportional plus integral controller, illustrating the improvement in performance obtainable with the adaptive algortihm.

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.

This paper proposes a new pulse-width modulation scheme for a Zero-Voltage-Switching (ZVS) single-phase inverter to operate in rectifier mode. The ZVS single-phase inverter and its ZVS-SPWM modulation scheme is reviewed. The commutation in rectifier mode is analyzed to design the proper modulation scheme. ZVS turn-on of switching devices is achieved as well as the reverse recovery of body-diode is relieved with the new modulation in rectifier mode. The principle of ZVS rectifier operation is explained in detail and verified on a 100kHz ZVS single-phase inverter prototype. The modulation scheme of rectifier operation makes the ZVS single-phase inverter suitable for bidirectional power conversion applications such as energy storage system and vehicle-to-grid (V2G) chargers.

A comprehensive procedure for the derivation of optimal, full-operating-range zero voltage switching (ZVS) modulation schemes for single-phase, single-stage, bidirectional and isolated dual active bridge (DAB) ac-dc converters is presented. The converter topology consists of a DAB dc-dc converter, receiving a rectified ac line voltage via a synchronous rectifier. The DAB comprises primary and secondary side full bridges, linked by a high-frequency isolation transformer and a series inductor. ZVS modulation schemes previously proposed in the literature are either based on current-based or energy-based ZVS analyses. The procedure outlined in this paper for the calculation of optimal DAB modulation schemes (i.e., combined phase-shift, duty-cycle, and switching frequency modulation) relies on a novel, more accurate, current-dependent charge-based ZVS analysis, taking into account the amount of charge that is required to charge the nonlinear parasitic output capacitances of the switches during commutation. Thereby, the concept of “commutation inductance(s)” is shown to be an essential element in achieving full-operating-range ZVS. The proposed methods are applied to a 3.7 kW, bidirectional, and unity power factor electric vehicle battery charger which interfaces a 400 V dc-bus with the 230 Vac, 50-Hz utility grid. Experimental results obtained from a high-power-density, high-efficiency converter prototype are given to validate the theoretical analysis and practical feasibility of the proposed strategy.

Many power distribution architectures, including the now-popular “isolated bus” architecture, call for a small and efficient unregulated dc transformer stage. Typical isolated converters can be both small and efficient through high-frequency operation and soft switching, but timing and control can be challenging as switching frequencies increase. We present an isolated bus converter that achieves zero-voltage switching (ZVS) for both inverter and rectifier switches with equal and constant dead times regardless of load, greatly simplifying control. It accomplishes this by using additional capacitors to aid the magnetizing current in commutating switch voltages during the dead time. The converter’s operation and advantages are verified with a 1.4-MHz prototype. The converter operates from 36 to 12 $\text{V}_{\mathrm{ dc}}{}_{out}$ at up to 36-W rating and achieves $>94.5$ % peak efficiency with 300-W/in3 power density.

Aiming at the reduction of the influence of the dead time setting on power level and efficiency of the inverter of double-sided LCC resonant wireless power transfer (WPT) system, a dead time soft switching optimization method for metal–oxide–semiconductor field-effect transistor (MOSFET) is proposed. At first, the mathematic description of double-sided LCC resonant wireless charging system is established, and the operating mode is analyzed as well, deducing the quantitative characteristic that the secondary side compensation capacitor C2 can be adjusted to ensure that the circuit is inductive. A dead time optimization design method is proposed, contributing to achieving zero-voltage switching (ZVS) of the inverter, which is closely related to the performance of the WPT system. In the end, a prototype is built. The experimental results verify that dead time calculated by this optimized method can ensure the soft switching of the inverter MOSFET and promote the power and efficiency of the WPT.

Hard switching specifies the stressful switching behavior of the controlled switches. During the turn-off and turn-on processes, the power electronic device has to withstand high current and voltage simultaneously, resulting in high stress and switching losses. The switching loss is directly proportional to the switch frequency, thus reducing the maximum switch frequency of the power electronic converter. The concept was to incorporate resonant tanks in the converters to create oscillatory (usually sinusoidal) voltage and/or current waveforms, so the zero current switching (ZCS) or zero voltage switching (ZVS) conditions can be achieved for the power control switches. The Soft-switched power converters are generally utilizing the resonance condition. Resonance condition is generally occurred just during the turn-off and turn-on processes, so as to create ZCS and ZVS across each switch. The Regulated three and five multiple-output dc-dc converter under zero-voltage switching (ZVS) condition is proposed. The converter is consists of three outputs altogether. With the help of two asymmetric half bridge converters, the first and second outputs are controlled. Based on the phase shift between two asymmetric half bridge converters, the third output is controlled. At high switching frequency, these multiple-output dc–dc converters can give higher efficiency. The various stages of operation, soft switching condition and controlling schemes are also explained. A closed loop and open loop control techniques of the three multiple output converter is explained.

SummaryIn battery energy storage system (BESS) applications, the life of the battery depends on the quality of the charging/discharging current. However, the dual active bridge (DAB) converter, which interfaces BESS with the DC link, suffers from a backflow current in all modulation schemes, degrading the battery's performance. Hence, this paper proposes a particle swarm optimization (PSO) based universal phase shift (UPS) modulation scheme to improve the battery's life. In the proposed modulation scheme, the phase shift ratio of DAB to eliminate the backflow power is estimated using PSO. Also, it is observed that there is an improvement in the zero voltage switching (ZVS) range of the DAB. Hence, the overall efficiency of the DAB converter is increased over a wide operating region. The operating principle of the proposed modulation scheme, steady state analysis of power transmission, and backflow power are reported in this paper. The theoretical performance of the proposed modulation scheme is validated in a 2 kW experimental setup.

This paper presents a phase shifted series resonant converter with step up high frequency transformer to achieve the functions of high output voltage, high power density and wide range of Zero Voltage Switching (ZVS). In this approach, the output voltage is controlled by varying the switching frequency. The controller has been designed to achieve a good stability under different load conditions. The converter will react to the load variation by varying its switching frequency to satisfy the output voltage requirements. Therefore in order to maintain constant output voltage, for light load (50% of the load), the switching frequency will be decreased to meet the desired output, while for the full load (100%) conditions, the switching frequency will be increased. Since the controlled switching frequency is limited by the range between the higher and lower resonant frequencies , the switches can be turned on under ZVS. In this study, a laboratory experiment has been conducted to verify the effectiveness of the system performance.

The performances of various 1200 V insulated gate bipolar transistor (IGBT) structures for hard- and soft-switching (both the zero-voltage and the zero-current switching) at high temperature and under various test conditions are investigated in detail. A comparison is made between a conventional planar punchthrough IGBT (P-IGBT) using global lifetime control, a trench punchthrough IGBT (T-IGBT) using local lifetime control and a enhanced planar punchthrough IGBT (N-IGBT) also using the local lifetime control process. A simple and effective specific test circuit allows hard- and soft-switching operating modes, and provides also an independent control on the test parameters (load current, clamping voltage, gate resistance, temperature, dead times). It is highlighted that the local lifetime control is very efficient at high temperature reducing especially the turn-off losses. Furthermore, the T-IGBT exhibits very good performances during hard- and soft-switching turn-off, but this is not the case during hard-switching and zero-voltage switching turn-on. Due to its high input capacitance, the hard-switching turn-on losses are relatively high. Regarding the N-IGBT, it presents good performances under hard-switching and also zero-voltage switching. However, like the T-IGBT, its structure has a strong inductance behavior during zero-voltage turn-on increasing the conductivity modulation lag and also the voltage spike leading to high losses. All these data allow to provide useful information for the devices modeling, design, and optimization.