Dead-time Optimization Research Articles

Investigation of Dead Time Losses in Inverter Switching Leg Operation: GaN FET vs. MOSFET Comparison

This paper investigates the commutation transients of MOSFET and GaN FET devices in motor drive applications during hard-switching and soft-switching commutations at dead time operation. This study compares the switching behaviors of MOSFETs and GaN FETs, focusing on their performance during dead time in inverter legs for voltage source inverters. Experimental tests at various phase current levels reveal distinct switching characteristics and energy dissipation patterns. A validated simulation model estimates the experimental energy exchanged and dissipated during switching transients. The results demonstrate that GaN FETs exhibit lower overall losses at shorter dead times compared to MOSFETs, despite higher reverse conduction voltage drops. The study provides a quantitative framework for selecting optimal dead times to minimize energy losses, enhancing the efficiency of GaN FET-based inverters in low-voltage motor drive applications. Finally, a dead time optimization strategy is proposed and described.

Analysis of Deadtime Effects and Optimum Deadtime Control for Bidirectional Inductive Power Transfer Converters

Analysis of Deadtime Effects and Optimum Deadtime Control for Bidirectional Inductive Power Transfer Converters

A partial soft-switching SiC-based ANPC single-phase inverter with loss model-based dead time optimization for grid-tied PV systems

Single-phase string inverter has been widely applied to grid-tied photovoltaic (PV) rooftop applications for its renewable energy. However, the inherent attribute of intermittency in solar energy may induce instability and unqualified power. To meet the grid-interconnection standards, high demands of efficiency and harmonic distortion need to be imposed on DC/AC inverters. Conventional soft-switching inverters used to sacrificing auxiliary resonant circuits to exchange for soft switching. This requires additional costs as well as sufficient dead time to discharge junction capacitances of all switches, which exacerbates total harmonics distortion (THD) induced by dead-time effect. To improve, this paper proposes a partial soft-switching silicon carbide (SiC) -based active neutral-point-clamped (ANPC) inverter, which possesses high efficiency, eligible dead time, and no auxiliaries. 650-V SiC MOSFET is adopted for its smaller output capacitance compared with Si device. Hybrid PWM modulation is utilized to achieve partial soft switching. Whereas, the soft switching realization range and power losses highly depend on the dead time. To achieve less power loss and improved dead time effect, this paper proposes a loss model-based dead time algorithm through a Power Loss VS. Dead Time mathematical loss model. Moreover, the mechanism of the dead time affected by soft switching is explored. The transition modes, dead time configurable boundaries, and design procedure are also analyzed in detail. A 1-kW prototype is demonstrated with the input of 800 V and the rated output of 220 V/ 4.5 A. Its efficiency could reach 99.6% with THD=0.95% at full power level.

Adaptive Dead-Time and Partial-ZVS Regulation for GaN-Based Active Clamp Flyback Converter With Predictive Hysteresis Current Mode Control

Active clamp flyback (ACF) converter is regarded as a good candidate in high-frequency small-size adapters. With adaptive dead-time optimization method, there is no reverse conduction loss and switching-on loss in power switches, then ACF can realize optimum full-ZVS control at every operating conditions. However, the other losses such as the conduction loss of clamp switch, the primary winding loss of transformer may be increased to counteract this efficiency advantage, but which has not been outlined. Therefore, this paper proposes a higher-efficiency predicted hysteresis current mode (PHCM) control strategy with adaptive dead-time and partial-ZVS regulation for GaN-based ACF converter for the first time. Firstly, the accurate analytical model by considering above losses is derived. Secondly, the optimal valley current is calculated by the minimum loss, to determine the conduction time of clamp switch and the dead time of main switch. Finally, a digital controlled GaN-based ACF converter is designed to verify the method. The computation speed of needed analytical equations and the magnetizing inductance offset are considered in implementation process. The experimental results show the proposed method can improve efficiency by 0.4% than existing method, which also show a fast dynamic response since the cycle-by-cycle variable-frequency control concept.

Dead-Time Optimization and Magnetizing Current Design for a Current-Fed Dual Active Bridge DC–DC Converter to Secure Full Load Range ZVS in Wide Voltage Range

Current-fed dual active bridge (CF-DAB) converters are widely used because of the small input current ripple and high power density. This paper proposes the dead-time optimization methods and the magnetizing current design for a CF-DAB converter under the pulse-width plus phase-shift (PPS) control to achieve full load range zero-voltage-switching (ZVS) in a wide voltage range. In the ZVS analysis, the influence of junction capacitance and dead time is considered, including the dead-time effect on leakage inductance current, which can effectively explain that the CF-DAB converter under PPS control is difficult to achieve ZVS at light load in practice. Based on the analysis, it is first revealed that the CF-DAB converter under PPS control is not sufficient to achieve ZVS only by adjusting the dead time. Based on the new ZVS model and analysis of the dead-time effect, the magnetizing inductance design and dead-time optimization without adding extra control degrees of freedom and auxiliary components are proposed to achieve the full load range ZVS and improve the overall efficiency of the converter in a wide voltage range. Besides, to obtain the low root-mean-square (RMS) current, the design of DC inductance and leakage inductance are also investigated. Finally, a 1 kW prototype is built to verify the effectiveness of the proposed solution.

A Wide Bandwidth GaN Switching Power Amplifier of Active Magnetic Bearing for a Flywheel Energy Storage System

A switching power amplifier (SPA) provides the driving current for an active magnetic bearing (AMB) to achieve magnetic suspension (MS) control. The performances of the current bandwidth and current ripple should be significantly considered in the SPA of the AMB. The SPA can obtain a wide bandwidth by increasing the dc-link voltage. However, a high dc-link voltage will cause a high current ripple. To achieve a wide bandwidth and low current ripple, a new GaN-device-based SPA for the AMB of a flywheel energy storage system (FESS) is proposed in this article. The GaN SPA can operate at a high switching frequency and high dc-link voltage. Thus, the GaN SPA can improve the performance of the current bandwidth and current ripple compared to the conventional SPA. According to the characteristics of the GaN SPA, a low-loss PWM method and an optimal dead time strategy is proposed to increase the efficiency of the SPA. Furthermore, a high-response control approach of dead-beat model predictive control is proposed to further improve the current bandwidth. The proposed GaN SPA is applied in a 500-kW MS FESS prototype. The effectiveness of the SPA is verified experimentally.

Design and Optimization of a Magnetron DC–DC Isolated Power Supply With High Efficiency

High-efficiency high voltage dc power supply is the core equipment for magnetron in the microwave industry. This article presents an input-parallel output-serial modular high isolated resonant converter for the magnetron. However, the high stray capacitance of the high isolation transformer brings some challenges, such as high turn-<small>off</small> current, longer dead time, increasing gain, and transformer optimization. A simplified model including the stray capacitances is built to deal with these problems, and the minimum turn-<small>off</small> current is derived after the detailed time-domain analysis. The appropriate deadtime and the maximum magnetic inductance needed for the proposed converter are obtained with the minimum turn-<small>off</small> current. Then, a 15 kW, 60 kV isolation multiple-windings output transformer is designed and optimized for the converter. The insulation design, core shape, losses, and parasitic parameters are calculated thoroughly. The Pareto optimization process optimizes the switching frequency and the transformer&#x0027;s turns to obtain higher efficiency and a more stable gain. The finite element method and time-domain simulation verified the optimized design results. Finally, a 0.8&#x002F;2.5 kV, 15 kW all-SiC dc&#x2013;dc converter module is developed to validate the proposed design. The results indicate that the module efficiency is as high as 98.6&#x0025;.

An Optimal Dead Time Compensator Design for Nonsquare Process with Disturbance Rejection

This work aims to establish an optimal design of the Smith dead-time compensator for a nonsquare multivariable system with a transfer function matrix containing first-order dead time elements. The scheme has a set point tracking controller along with disturbance rejection using an optimal estimator. An inverse signal from the estimator eliminates the disturbance. The proposed method significantly improves the disturbance rejection and performance index compared to the other established methods. The common evolutionary algorithms such as the grey wolf optimization technique and teaching learning based algorithm have been used to tune the controllers.

Dead Time Optimization in a GaN-Based Buck Converter

A gallium nitride (GaN) field effect transistor can provide superior performance over a Si- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> due to its low <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -state resistance and low junction capacitances. However, a GaN-based converter exhibits higher dead time loss during reverse conduction. Thus, to improve the efficiency, dead time optimization is required. This article proposes simple models for dead time optimization in a GaN-based buck converter under different load conditions. The proposed models are analytical in nature compared to the conventional models available for Si-based converters. A buck converter prototype is designed using a 100 V GaN device (GS61008P from GaN Systems) and the proposed analytical model-based dead time optimization techniques are validated experimentally. The proposed modeling techniques can be extended for other GaN-based dc–dc converters.

Efficiency Boost of a Quasi-Z-Source Inverter: A Novel Shoot-Through Injection Method with Dead-Time

A quasi-Z-source inverter (qZSI) is a single-stage inverter that enables a boost of the input dc voltage through the utilization of a so-called shoot-through state (STS). Generally, the efficiency of the qZSI depends on the utilized STS injection method to a significant extent. This paper presents a novel method of STS injection, called the zero-sync method, in which the STS occurrence is synchronized with the beginning of the zero switching states (ZSSs) of the three-phase sinusoidal pulse width modulation (SPWM). In this way, compared to the conventional STS injection method, the total number of switchings per transistor is reduced. The ZSSs are detected by utilizing the SPWM pulses and the logic OR gates. The desired duration of the STS is implemented by utilizing the LM555CN timer. The laboratory setup of the three-phase qZSI in the stand-alone operation mode was built to compare the proposed zero-sync method with the conventional STS injection method. The comparison was carried out for different values of the switching frequency, input voltage, duty ratio, and load power. As a result of the implementation of the zero-sync method, the qZSI efficiency was increased by up to 4%. In addition, the unintended STSs, caused by the non-ideal switching dynamics of the involved transistors, were successfully eliminated by introducing the optimal dead-time as part of the modified zero-sync method. As a result, the efficiency was increased by up to 12% with regard to the conventional method.

An Accurate Datasheet-Based Full-Characteristics Analytical Model of GaN HEMTs for Deadtime Optimization

The gallium nitride high electron mobility transistors (GaN HEMTs) are a superior candidate for the new-generation power electronics systems with higher efficiency and power density. However, due to the unique reverse characteristics, the reverse voltage drop of GaN HEMTs is much higher than that of diode. The deadtime loss in GaN-based bridge converters will be comparable to switching losses if the deadtime is not optimized. To optimize the deadtime for higher efficiency, this article proposes an accurate analytical model of GaN HEMTs, including circuit's parasitic inductances, the nonlinear capacitances, the unique reverse characteristics, etc. Taking a GaN-based synchronous buck converter as the example, the proposed model is realized, which fully uses the datasheet to avoid additional experiments. In order to accurately measure the switching current for validation, a novel parasitics-based current measurement method is proposed. The proposed model is verified by simulation in LTspice and experiment, and good agreement is shown. Based on the accurate analytical model, the deadtime is optimized for different load currents to improve the efficiency within the full load range. Compared with the fixed deadtime of 15 ns, the increase of efficiency can be up to 8%. This work will promote the high-frequency application of GaN HEMTs.

Modeling and Implementation of Optimal Asymmetric Variable Dead-Time Setting for SiC MOSFET-Based Three-Phase Two-Level Inverters

Efficiency, power quality, and reliability of SiC MOSFET-based voltage-source converters are significantly affected by the dead-time settings. The conventional fixed dead-time setting can induce large output voltage loss and additional energy loss due to the output capacitance of the SiC MOSFETs and the SiC Schottky barrier diodes or the freewheeling of the diodes, which will be more serious under high switching frequencies. This paper analyzes and models the detailed switching process of the SiC MOSFET half-bridge circuit when various dead-time settings are adopted. Based on the models, an optimal asymmetric variable dead-time (OAVDT) setting is proposed, which can avoid the discharging loss of the output capacitance and redundant freewheeling loss of the diode. The OAVDT setting is realized by adjusting the optimal dead-time in real time after the active device is turned off , which does not require any additional hardware circuits. The OAVDT setting can also reduce the output voltage loss to a certain level compared to the fixed dead-time setting. A three-phase two-level SiC MOSFET inverter has been built in the lab to verify the proposed OAVDT setting. Experimental results show a decrease of power loss by 22.5% with reduced output voltage loss compared to the fixed dead-time setting of 0.28 μs when the output power is 8 kW and the switching frequency is 40 kHz. The proposed OAVDT setting shows clear advantages over that of fixed dead-time setting, especially at light load and high switching frequencies.

A High Efficiency Model-Based Adaptive Dead-Time Control Method for GaN HEMTs Considering Nonlinear Junction Capacitors in Triangular Current Mode Operation

Gallium nitride (GaN) high-electron-mobility transistor (HEMT) has the advantages of high switching speed and low ON-resistance, which make it widely used in high-frequency applications to realize high power density. Triangular current mode (TCM) modulation has been used in GaN-based converters to simultaneously achieve high power density and high efficiency through full-range zero voltage switching (ZVS). However, as switching frequency increases, the effect of dead time becomes more significant. Meanwhile, because of the junction capacitors of GaN HEMTs, the optimum dead time changes greatly with the turn-off current. Inappropriate dead time will induce extra loss that goes against the further improvement of power density. In order to minimize the dead-time loss in GaN HEMT-based TCM converter, this article proposes a strategy of adaptive dead-time control. An accurate turn-off transient model is proposed to calculate optimal dead time with consideration of the nonlinear capacitors. Based on this model, a loss model is established to evaluate the effect of dead time involving the short circuit in dead time. A new method of drive signal generation in TCM is proposed to increase the accuracy of dead-time control and reduce the current ripple. By reusing the detection signal in TCM, the adaptive dead-time control is realized without extra sensors. The proposed model is verified by a dual-pulse test, which shows the maximum error between the calculated and the experimental turn-off time is below 3 ns. The proposed adaptive dead-time control is implemented in a GaN HEMT-based boost converter. The experimental results show that the adaptive dead-time control can improve the efficiency over all operation conditions compared with using the fixed dead time, and the total loss is reduced by 26.7% at 800-W load and 70.8% at 50-W load.

Predictive auto‐reclosure approach to enhance transient stability of grid‐connected DGs

This study introduces a predictive auto-reclosure scheme based on faster-than-real-time (FTRT) analysis for synchronous generator type of distributed generation (DG) units to decrease DG oscillations after successful reclosure and also enhance transient stability margin of the unit after unsuccessful reclosure. The FTRT analysis, as a new concept for the protective relaying, represents a powerful predictive auto-reclosure scheme which is based on a state-space model of the DG unit. After a fault scenario and the first operation of the associated breaker, the FTRT analysis predicts energy level of the DG unit and determines an optimum dead-time corresponding to the minimum energy level of the DG unit for reclosure that can provide an appropriate margin for transient stability. The effectiveness and accuracy of the proposed method are verified based on a test system. The results confirm that the proposed approach can effectively enhance transient stability for unsuccessful reclosure and reduce the corresponding oscillations after reclosure.

Optimized gate driver for high-frequency buck converter

With the increasing system complexity in the automotive business sector the integration of efficient and low electromagnetic emission (EME) switch mode power supplies (SMPS) is crucial. The main methods to bring down EME and keep high efficiency are to introduce external filters on the input and output sides, to use spread spectrum techniques on the switching frequency and to control the switching activity of output driver in the desired range. This paper presents the concept of output driver implementation with adaptive driver strength control and dead time optimization for high frequency buck converters with external power MOSFETs. The proposed concept allows the following characteristics to be achieved: improved control of switching activity in a closely defined range, efficiency optimization by minimization the body diode forward conduction, reduction of the reverse recovery losses and zero voltage switching. All these can be realized despite the unknown MOSFET technological parameter distribution (propagation on/off delay, gate resistance of the package, Miller gate charge) and the external parameters (temperature, input voltage, load current). The proposed concept was implemented for a 1.2 V output voltage and a 1.8 MHz switching frequency buck converter.

Achieving Efficiencies Exceeding 99% in a Super-Junction 5-kW DC–DC Converter Power Stage Through the Use of an Energy Recovery Snubber and Dead-Time Optimization

A highly efficient 5-kW bidirectional dc–dc converter power stage operating from a 400-V supply implementing super-junction (SJ) metal–oxide–semiconductor field-effect transistor (MOSFETs) is presented. SJ MOSFETs have low on-state resistances and low switching losses. However, their application in voltage-source converters can be compromised by the reverse recovery behavior of their intrinsic diodes and their highly nonlinear output capacitances. A series switching-aid circuit is used to control the output capacitance charging current. The dead times between switching transitions are assessed and optimized in order to deactivate the intrinsic diodes. The combination of these techniques enables very high efficiencies to be attained. Calorimetric measurements indicate a full-load efficiency of 99.1% for the prototype 5-kW dc–dc converter power stage. A loss reduction of approximately 50% is achieved with the prototype converter power stage when compared to an equivalent insulated-gate bipolar transistor (IGBT)-based power stage. Lastly, a loss versus duty cycle function is experimentally determined, which can be used to inform the design of a maximum efficiency point tracking system.

Switching Device Dead Time Optimization of Resonant Double-Sided LCC Wireless Charging System for Electric Vehicles

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.

Dynamic Optimum Dead Time in Piezoelectric Transformer-Based Switch-Mode Power Supplies

Soft switching is required to attain high efficiency in high-frequency power converters. Piezoelectric-transformer-based converters can benefit from soft switching in terms of significantly diminished switching losses and stresses. Adequate dead time is needed in order to deliver sufficient energy to charge and discharge the input capacitance of piezoelectric transformers in order to achieve zero-voltage switching. This paper proposes a method for detecting the optimum dead time in piezoelectric transformer-based switch-mode power supplies. The provision of sufficient dead time in every cycle of the switching period results in the quick start-up of resonant current inside the transformer. The new method is implemented by dynamically detecting the optimum dead time for each resonant cycle and results in reduced energy loss and, consequently, increased efficiency in the converter during initialization time and steady-state operation. The theory of optimum dead time operation is also discussed in this paper. Experimental results and simulation are provided to show the implementation of the concept.

Dynamic Dead-Time Optimization and Phase Skipping Control Techniques for Three-Phase Microinverter Applications

This paper introduces a combination of two proposed efficiency improvement techniques for a microinverter with current mode control zero-voltage switching output stages. The first technique is dynamic dead-time optimization wherein pulse width modulation dead times are dynamically adjusted as a function of load current. The second method is advanced phase skipping control which maximizes inverter efficiency by controlling power on individual phases depending on the available input power from the photovoltaic source. Neither of the techniques requires any additional circuit components and both can be easily implemented in digital controller firmware. The two techniques were designed and implemented in a 400-W three-phase microinverter prototype. The experimental results validate the theoretical analysis of these techniques and demonstrate that a significant efficiency improvement can be achieved by combining the two proposed control techniques.

High-Temperature GaN Active-Clamp Flyback Converter With Resonant Operation Mode

An isolated active-clamp flyback power supply with a new resonant operation mode is designed and experimentally tested. A full soft-switching design based on dead-time optimization new approach is implemented. Each topology phase is detailed. An experimental board is presented for high ambient temperature (200 °C) operation. The power supply is dedicated to provide the driver power of wide bandgap power components in a phase-leg configuration. The constraint for galvanic isolation is high and guides the design of the transformer. The power-supply capabilities are 15 V input voltage, 6 V output voltage, 2 W output power, 75% peak efficiency, 11 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> footprint, and nominal operation at 200 °C ambient temperature.