Zero-voltage Switching Operation Research Articles

Multi‐objective optimization of inductive power transfer system with reconfigurable topology for misalignment tolerance

AbstractAt present, most of the analyses or studies about inductive power transfer (IPT) with constant current (CC) output and constant voltage (CV) output are carried out without considering misalignment conditions or different gaps. An IPT system satisfying battery charging demand and anti‐misalignment requirements simultaneously is infrequent. This paper proposes a multi‐objective particle swarm optimization method of IPT reconfigurable topology to realize CC and CV modes at varying resistance conditions and wide coupling ranges. The output characteristics of an inductor–capacitor–capacitor (LCC)–LCC compensation circuit have been explored, and it is found that the secondary‐side compensated capacitors have a greater impact on the output power, which can be used to improve power regulation ability accompanied by coupling varying. Eight optimization compensated parameters of the reconfigurable topology are obtained from the Pareto front to achieve the required CC and CV charging outputs. By switching the compensated capacitors, the selected parameters can make the current and voltage fluctuation less than 9.3% and 7.9%, respectively, during the coupling charging range from 0.3 to 0.22. Moreover, primary zero voltage switching operation is achieved to enable high efficiency. The simulation and the experimental verification are carried out to verify the validity of the proposed method.

An Integrated Double-Sided LCC Compensation Based Dual-Frequency Compatible WPT System with Constant-Current Output and ZVS Operation

This article presents an integrated double-sided inductance and double capacitances (DS-LCC) compensation based dual-frequency compatible wireless power transfer (WPT) system. A cascaded single-phase multi-frequency inverter (CSMI) is constructed to generate the independent dual-frequency power transfer signals. In order to achieve the load-independent constant-current output (CCO) at two frequencies, an integrated DS-LCC compensated topology is reconstructed. By configuring the frequency-selective resonating compensation (FSRC) network in the primary side, the power transfer signals at two frequencies can be superimposed into a single transmitting coil, reducing the cost and volume of the system. Furthermore, to implement zero-voltage switching (ZVS) of the CSMI throughout the entire power range, a general parameter design method of the proposed system is also introduced. A 1.5-kW experimental prototype is built to validate the practicability of the presented dual-frequency compatible WPT System. The system can supply power to different loads at two frequencies simultaneously with CCO and ZVS properties. The peak efficiency reaches 91.75% at a 1.2-kW output power.

Design and development of an LC compensated WPT system with multiple constant voltage outputs function

SummaryWith the increasing demand for the constant voltage (CV) charging of multiple loads, this article proposes an LC compensated wireless power transfer (WPT) system with multiple load‐independent CV outputs function. Each transmission channel consists of a compensation capacitor and a compensation inductor forming a resonant loop. By configuring different combinations of compensation inductor and capacitor for each transmission channel, different CV outputs can be achieved without affecting the output voltages of other transmission channels. In addition, the proposed system can achieve near zero phase angle (ZPA) and zero‐voltage switching (ZVS) operations, thereby improving system efficiency. Firstly, a detailed theoretical derivation of the proposed system with multiple load‐independent CV outputs and ZPA operation is performed, and the detailed parameter design process is provided. Secondly, the implementation method of ZVS operation is introduced and verified through simulation. Finally, an experimental prototype of two transmission channels is taken as an example to verify the correctness and rationality of the proposed system.

Variable Switching Frequency for ZVS over Wide Voltage Range in Dual Active Bridge

The Dual Active Bridge (DAB) converter is known for its advantageous characteristics, including bidirectionality, galvanic isolation, and soft-switching operation. However, achieving Zero Voltage Switching (ZVS) across the complete operation range is not guaranteed, particularly through a wide input–output voltage ratio. This paper explores the integration of the switching frequency as a control variable in the DAB converter to ensure ZVS operation across a wide voltage range, employing Single Phase Shift (SPS) modulation. The study evaluated the RMS and reactive currents under variable switching frequency, presenting the advantages of this approach. Moreover, it includes a design-oriented analysis of the ZVS limits and their relationship with the switching frequency, aiming to ensure ZVS at any operating point. Experimental results validated the theoretical analysis, while presenting the main advantages of variable switching frequency implementation.

A Control Strategy for Achieving Constant Voltage Output with an Extensive ZVS Operating Range in Bidirectional Wireless EV Charging Systems

Variations in the coupling coefficient of loosely coupled transformers and dynamic loads have a significant impact on the overall performance of bidirectional inductive power transfer (BIPT) systems. However, a wide range of load and coupling coefficient variations are common in the actual charging process, which may cause the converter on both sides to operate in a hard switching state, resulting in switching noise, reduced efficiency, and potential safety concerns. In this paper, a triple-phase-shift control (TPSC) strategy is proposed to study the zero-voltage switching (ZVS) operating range and constant-voltage output (CVO) characteristics of the double-side-LCC (DS-LCC) topology. To ensure a CVO over the wide range of coupling coefficient variations, a dual-phase-shift control is introduced for AC voltage matching. Based on this, the third phase-shift angle control between the converters on both sides is introduced to ensure the ZVS realization. Meanwhile, the time-domain model is developed to analyze the rationality of the proposed third phase-shift angle and the ZVS operating range. Finally, the effectiveness of the proposed TPSC strategy is validated through a 1.5 kW experimental prototype with an air gap of 100–150 mm.

Research on a soft-start method for LCC-LCC compensated bidirectional wireless power transfer system

The increased popularity of electric vehicles and the pursuit of user convenience makes bidirectional wireless power transfer (BWPT) an attractive technology for charging batteries. To improve the transmission efficiency of BWPT and limit the external radiated magnetic field, it is necessary to ensure the zero-voltage switching (ZVS) operation of the converter on the transmitter-side and limit the transient start-up current of the inverter when the system is working. To solve this problem, this paper proposes a soft-start modulation strategy based on an H-bridge inverter on the transmitter-side. First, the circular characteristics of dual LCC compensation topology are analysed based on an equivalent circuit. Secondly, according to the characteristics of the input impedance angle and current of the transmitter-side, a soft-start control method combining frequency and phase shift control is proposed. Finally, the feasibility of the proposed soft-start modulation strategy is verified on a prototype.

A simple zero-voltage switching technique for a single-phase inverter based on bi-directional inductor current

The majority of soft-switching inverters often use auxiliary semiconductor switches that run for extremely brief periods to provide ZVS conditions for the main switches, potentially raising the inverter system’s cost. This work presented a simple zero-voltage switching (ZVS) approach by employing a bi-directional inductor current for the single-phase inverter, which reduced the cost of auxiliary switches and simplified the soft-switching inverter design. All switches can achieve ZVS operation without additional resonant components. The conventional PWM control strategies are applied in the proposed technique, and thus the problems existing in variable switching frequency converters are removed. This article describes the soft-switching approach and detailed circuit functioning. Different key parameters are optimized to improve efficiency. To confirm the suggested ZVS method, a hardware inverter prototype is created, built, and tested. To validate the inverter’s characteristics and validity, experimental results are presented.

A Hybrid Modulation Strategy for LCC–LCC Compensated Bidirectional Wireless Power Transfer System to Achieve High Efficiency in the Whole Operating Range

A hybrid modulation strategy is proposed for the LCC-LCC compensated bidirectional wireless power transfer system (LCC-BWPT), which aims to boost the efficiencies in the whole operating range. The basic operating modes of LCC-BWPT with the hybrid modulation strategy are analyzed, and the unified discrete-time model is then established based on the full-mode operation, which can accurately describe the state variables under all operating modes. Based on the model, the criteria for optimal operation are put forward in consideration of three working processes of LCC-BWPT, i.e., the constant current (CC) charging process, the constant voltage (CV) charging process, and the CC discharging process. The optimal control variables in three working processes are derived respectively, which realize full zero-voltage switching (ZVS) operation and minimize the reactive current. On this basis, an optimal modulation strategy featuring high efficiency performance is proposed for LCC-BWPT. Besides, a control method independent of the real-time wireless communication is developed for LCC-BWPT with the optimal modulation strategy. Finally, a 1.2kW prototype is applied, and experimental results verify the effectiveness of the proposed optimal modulation strategy, where the efficiencies are improved in the whole operating range.

A Modified SVM Method for Three-Phase Quasi-Z-Source Rectifier With Fully Soft Switching Operation and Low Conduction Losses

The conventional ZSVM3 (quasi-Z-source space vector modulation) has been used for quasi-Z-source rectifier because it achieves zero voltage switching(ZVS) and zero current switching(ZCS) operation with wide range of output power and without any auxiliary circuits. However, this method can not realize ZVS or ZCS at fully switching period, especially at the sector boundary, leading to low efficiency. To address this problem, in this paper, a modified modulation based on ZSVM3 is proposed. The sequence of active vectors and zero vectors has been modified. Therefore, the ZVS and ZCS operation occurs at any time in one switching cycle, and the conduction losses decrease. Besides, the distribution of Mode 3 duration time is optimized, which increases the range of soft switching conditions. The operating principle of the proposed modified SVM is explained in detail. Then the parameters design is developed. An experimental prototype is constructed to verify the effectiveness of the proposed modulation. Experimental results show that the grid-side THD and conduction losses reduce, all switches and free-wheeling diodes realize ZVS and ZCS operation at full range without any auxiliary circuit, and the highest efficiency is up to 96.87%.

A New Isolated Topology of DC–DC Converter Based on Piezoelectric Resonators

This paper presents a new isolated topology of DC-DC converter based on piezoelectric resonators. Contrary to most existing topologies, the proposed one uses the natural isolation of piezoelectric resonators to isolate the converter's output from the input and vice-versa. Considering the resonators' constraints, our study focuses on the most efficient isolated conversion cycle with zero-voltage switching (ZVS) operations. The case studied is a highly efficient step-down isolated DC-DC converter with a gain ranging from 0 to 1 and an input voltage up to 360 V. The converter uses two piezoelectric resonators working in series. The conversion principle is validated thanks to a prototype operating at a frequency around 95 kHz. Experimental measurements are made on a wide range of input voltage from 12 V to 360 V with a conversion ratio of 0.0165 to 0.95. The output power reaches either 179.1 W with an 89% efficiency at 360 V input voltage and 346 V output voltage, or 4.5 W with a 97.2% peak efficiency for a 48 V to 45.8 V conversion, using a 25 mm piezoelectric disc with a thickness of 2 mm and 1 mm respectively. An efficiency higher than 80% is measured over a wide range of operating points.

Highly Efficient Nonisolated Constant Output Current LCC Resonant Converter With Wide Input Voltage Range

This paper proposes a simple structure highly efficient low-element-count non-isolated constant output current resonant converter for wide input voltage range and high-efficient applications. The converter is developed by combining a basic buck-boost converter with a half-bridge LCC resonant converter to improve the adjustable voltage conversion ratio. In the proposed structure, most of the output power is fed directly, which reduces the conduction power losses and increases efficiency by reduction of the processed power and the switches and rectifier diodes voltage stress is significantly decreased due to cascaded outputs structure. It operates at the resonant frequency to achieve a constant output current feature for applications such as LED drivers and battery chargers and the output current is regulated by the pulse-wide modulation (PWM). The proposed converter can achieve zero-voltage switching (ZVS) operation for all switches and zero-current switching (ZCS) operation for all diodes over a wide range of the input voltage and load conditions. The proposed structure is analyzed in detail. To verify the proposed converter performance, a 21 W laboratory prototype is realized and tested for the wide input voltage range of 12–40 V to provide 350 mA output current. The proposed converter achieves high peak efficiency of 98.15%.

Closed-Form ZVS Boundaries for Three-Phase M-Level-to-N-Level DAB Converters With Different Winding Configurations

One of the essential characteristics of a three-phase dual-active-bridge (DAB) DC-DC converter is its inherent zero-voltage switching (ZVS) capability during the turn-on of the switches. This paper provides closed-form equations that identify the ZVS boundaries for an M-level-to-N-level DAB converter, where M and N can be any natural numbers. It is shown that the derived ZVS boundaries can be used for different converter topologies, including but not limited to: two-level full-bridge converter, three-level neutral-point-clamped converter, T-type converter, transition arm converter, modular multilevel converter, and controlled-transition-bridge converter. The effect of different winding configurations of the medium frequency transformer—YY, Y <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Delta$</tex-math></inline-formula> , and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Delta \Delta$</tex-math></inline-formula> —is also considered in the study. Additionally, easy-to-implement simplified ZVS boundaries are provided, and the effects of the different number of levels, transition times, and dead times on the ZVS operation are quantified. An important result shown is that the converters with the YY and the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Delta \Delta$</tex-math></inline-formula> windings lose ZVS at partial loads as soon as the transition time increases from zero, whereas the ones with the Y <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Delta$</tex-math></inline-formula> configuration retain ZVS at partial loads and DC ratios close to unity, without any advanced modulation techniques. The derived analytical models are validated with MATLAB simulations and experiments.

ZVS Soft Switching Operation Region Analysis of Modular Multi Active Bridge Converter Under Single Phase Shift Control

Modular multi active bridge (MMAB) converter can provide multiple dc ports using modular H-bridge. When voltage conversion ratios of each port are not equally balanced, zero-voltage-switching (ZVS) turn-on of power semiconductors in the MMAB converter cannot be secured under single phase shift (SPS) control, increasing power loss and leading to lower efficiency. To estimate the efficiency of the converter in various conditions, ZVS operation region of MMAB converters under SPS is comprehensively derived based on steady-state time domain with superposition theorem. Voltage conversion ratios are taken as main variables for ZVS region analysis and influences of them are comprehensively analyzed. Full ZVS regions and constrained ZVS regions are obtained by ZVS discriminants. Simulation and experimental results for a three-port MMAB prototype are given to verify the theoretical analysis of ZVS operation region.

Dual-Phase-Shift Control Strategy With Switch-Controlled Capacitor for Overall Efficiency Optimization in Wireless Power Transfer System

In this paper, a dual-phase-shift control strategy combining with a switch-controlled capacitor (SCC) is proposed to realize efficiency maximization while realizing zero voltage switching (ZVS) for a LCC-LCC compensated wireless power transfer (WPT) system. The dual-phase-shift control is employed with a semi-active rectifier (SAR) to reduce the current stress in the resonant network. To realize accurate ZVS operation, both the SCC control angle and the SAR phase-shift angle are used as the control variables. First, the conditions of ZVS operation and circulating reactive power minimization are derived based on the time-domain model. Then, the power losses in the resonant network, inverter and semi-active rectifier are analyzed and optimized under the constant voltage output. An optimal control strategy is further proposed to maintain the constant voltage output while maximizing overall system efficiency. It is worth mentioning that the proposed control strategy allows the decoupling of the ZVS control and the power regulation. Finally, the performance of the proposed control strategy is examined based on a 6.6-kW WPT prototype. The results show that all switches realize ZVS operation within the entire power range with a peak system efficiency of 95.1%, which exhibits a good agreement with the theoretical analysis.

Comprehensive Analysis of ZVS Operation Range and Deadband Conditions of a Dual H-Bridge Bidirectional DC-DC Converter with Phase Shift Control

This study offers a thorough examination of the zero voltage switching (ZVS) operation range and deadband conditions for a bidirectional DC-DC converter with phase shift control, featuring dual H-bridge. The analysis considers the soft switching range of the DAB converter, accounting for the impact of the headband and the ZVS capacitor. By applying the differential equation of the circuit during deadband time, a sufficient constraint for the input and output bridges can be calculated. The findings indicate that as the output voltage increases, the minimum phase shift value required to achieve ZVS decreases, and expanding the phase shift value will expand the ZVS range and reduce switching losses. The study provides simulation results for various operating conditions, validating the theoretical analysis of the proposed system. In addition, the results furnish information about the circuit behavior during the deadband and waveforms. Finally, MATLAB/SIMULINK verifies the simulation results for different operating stages.

Robust Class E2 Wireless Power Transfer System Based on Parity–Time Symmetry

Thanks to the superiority of zero-voltage switching (ZVS), the Class E <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> topology has become a promising candidate in wireless power transfer (WPT) at medium and small power levels. However, in practical applications, it is a challenging and significant issue to maintain robust WPT under varying transfer distances, especially for the highly sensitive Class E power amplifier (PA). To solve this issue, the parity–time (PT) theory is initially developed into the Class E <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> WPT system. A general design procedure for the PT-symmetry-based Class E <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> WPT system is proposed, including the parameters of the Class E PA, resonant tank, and Class E rectifier. The power losses and efficiencies of the above-mentioned components are analytically derived as well. The ZVS operation is quantitatively described for the PT-symmetry-based Class E <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> WPT system, demonstrating that the maximum phase variation with coupling coefficient is rather small and independent of the natural resonant frequency, thereby achieving robust and highly efficient power transfer. Finally, the prototype with current feedback control to guarantee the PT mechanism and ZVS is built. The experimental results illustrate that under various coupling coefficients, robust and efficient power transfer is realized by a 165-W prototype with about 92.6% efficiency.

Improved Control Strategies for Totem-Pole PFC With True Full Range ZVS Operation

Zero voltage switching (ZVS) of power semiconductor devices is an effective way to improve the efficiency and power density of the power electronic converters with extremely high switching frequency. This article aims to analyze and realize the true full-range ZVS operation of a totem-pole power factor correction circuit. The available ZVS control strategies are investigated, and the conditions for the realization of full-range ZVS operation are analyzed. It is revealed that the existed control strategies did not consider the influence of the dead-time, resulting in the failure of ZVS operation in some input voltage ranges. To address this issue, two feasible retrofitted control strategies, namely the turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> current optimization control and the adaptive dead-time control, are proposed. The merits and drawbacks of the two control strategies are carefully analyzed and compared. It is found that the adaptive dead-time control can not only achieve the true full range ZVS but also significantly reduce the loss of the freewheeling diodes. The design consideration of key parameters is discussed. Finally, the feasibility of the proposed control and the correctness of the theoretical analyses are verified by simulation and experiment.

A Load Adaptive Hybrid DPS Control for DAB to Secure Minimum Current Stress and Full ZVS Operation Over Wide Load and Voltage Conversion Ratio

Wide variations in voltage conversion ratio and loading are the most important parameters to consider when designing off-board EV chargers to achieve high power density and efficiency. Dual phase shift (DPS) modulation provides a better way for dual active bridge (DAB) DC-DC converter operation when load side parameter variation is utmost important. To accomplish this, conventional DPS control is modified to ensure zero voltage switching (ZVS) across the entire load range despite wide variations in voltage conversion ratio. The designed control provides ZVS of all FETs as compared to the conventional DPS control over full loading range. For this, magnetizing inductance of HF isolation transformer is utilized and designed to shape the secondary side current for getting ZVS for both active legs. The light loading performance of the converter is improved with the bidirectional conduction angle control. The hybrid utilization of DPS control is incorporated with minimum peak current stress considerations. A Karush-Kuhn-Tucker (KKT) method based on Lagrange's multipliers is used for mathematical derivation of optimized solution of both control parameters. Performance of designed control is verified using experimental results for wide variation in battery terminal voltage. For validation, a 1250 W laboratory prototype is developed. A comparison of ZVS regions among the conventional and designed modulation technique, shows the effectiveness under wide voltage and loading scenarios.

A ZVS-PWM Scheme for Three-Phase Active-Clamping T-Type Inverters

For increasing power density and other performance of T-type three-level inverters, the soft-switching technique is studied. This article proposes a novel zero-voltage switching (ZVS) PWM scheme for active clamping three-phase T-type inverters, which can realize the ZVS operation of all switches and reduce the switching loss. The proposed ZVS PWM scheme is evolved from discontinuous PWM and modified for the requirements of T-type inverter. It enables all switches, including main switches and auxiliary switches, operate at a fixed frequency. However, a larger current on the power semiconductor devices occurs at 60° zone transition. To suppress this current surge, the carriers used in the ZVS PWM scheme are phase shifted. Finally, the novel ZVS PWM scheme is verified on a 10 kW/150 kHz SiC-based ZVS T-type inverter prototype.

A Modulation Map for a Family of Phase-Shift-Modulated Resonant Switched-Capacitor Converters

In this article, a modulation map for a family of phase-shift-modulated resonant switched-capacitor converters (RSCs) which reflects the relationship between the control variables and converter characteristics is proposed to guide the converter operation and design in the expected voltage gain range, low component stress region, and zero-voltage-switching (ZVS) operation region. A hybrid modulation strategy combing phase-shift and variable frequency is applied to extend the voltage gain range and ZVS region. On the basis, the modulation map with the favorable operation region is obtained to assist the converter operation and design in the expected conversion ratio range, low component stress region, and ZVS operation region. Similar analyzing methods and modulation maps can be extended to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> -mode RSCs and other phase-shift-modulated RSCs, providing operation and design reference for such converter families. A 43–60 to 150 V prototype of a triple-mode RSC with power level 225 W and peak efficiency 96.2% was designed and tested to verify the converter operation and validity of the proposed modulation map.