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A charging strategy that transitions from constant current (CC) mode to constant voltage (CV) mode is typical for lithium batteries. This presents design challenges for inductive power transfer (IPT) chargers to achieve high efficiency. In this article, a multiband frequency tracking control is proposed to match CC and CV modes and to mitigate misalignment. As in prior work, two load-independent frequencies fCC and fCV are used for respective CC and CV outputs. Unity power factor can be achieved when fully aligned. For misalignment cases, two narrow frequency bands around fCC are selected for control to deliver target output currents and limit reactive power. The duty ratio of the inverter is controlled to set target output voltages. A single-stage IPT system with a series LCC topology is analyzed. The proposed control has advantages of narrow operating frequency ranges, high misalignment tolerance, direct design procedures, and high efficiency in both CC and CV modes. The method is verified on a 4.4 kW prototype with a 150 mm air gap. Experimental results show that the target CC and CV charging profile can be achieved with up to 120 mm of lateral misalignment. When fully aligned, the maximum system conversion efficiency reaches 97.5%. It stays above 95.5% and 93.3% over the entire CC and CV mode ranges. [ABSTRACT FROM AUTHOR]

Three-phase inverters are usually required to output reactive power in electric machine drives, renewable energy generation, static var generators, and other power electronic systems. Therefore, the inverter may operate within wide power factor angle range. However, the traditional zero-voltage-switching space vector modulation (ZVS-SVM) method for three-phase inverters is only applicable when power factor angle is between −π/6 and +π/6. In this article, a general ZVS-SVM method for three-phase inverter with arbitrary output is proposed. The principles for vector selection and vector sequence arrangement are discussed in detail. With only one switching operation of the auxiliary switch in each switching cycle, ZVS of all switches can be achieved. Operation stage analyses and ZVS condition of the inverter with the proposed method are introduced. In addition, the resonant parameters design considerations and loss analyses are investigated. Finally, the proposed ZVS-SVM method is verified by the experiment. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) inverters play important roles in renewable energy integration. Reducing the switching loss is a main challenge in improving the efficiency and power density. This article presents the design, implementation, and field test of a 3-kW two-stage commercial-ready transformerless PV inverter with resonant dc link and zero-voltage-switching pulsewidth modulation (ZVS-PWM) operation. The ZVS-PWM operation periodically resonates the dc-link voltage of the inverter to zero for ZVS of the inverter switches, which enables higher switching frequency and significantly reduced magnetic component size. A 30-kW distributed PV system comprising ten ZVS-PWM PV inverters was built and tested for more than 100 days to evaluate the long-term performance of the PV inverter. The key figure-of-merits for grid-interface operation, such as efficiency, power density, total harmonic distortion, and leakage current, are measured, analyzed, and reported. [ABSTRACT FROM AUTHOR]

Single-phase zero-voltage-switching (ZVS) inverter with wide bandgap devices has higher efficiency and power density. However, the dc-side capacitor of the inverter will suffer double line frequency ripple and reduces the lifetime of the dc bus capacitor. Active power decoupling (APD) is an effective method to replace the short lifetime electrolytic capacitor with a smaller film capacitor. In order to help achieving the ZVS condition for ZVS inverter and the additional APD circuit, this article presents a ZVS topology for single-phase full-bridge inverter with APD circuit by adding an auxiliary branch between the dc source and the bridge legs. The auxiliary branch is composed of a clamping capacitor, an auxiliary switch, and a resonant inductor. A ZVS pulsewidth modulation scheme is proposed for a single-phase inverter with APD. The gate drive pulses are designed to realize the ZVS turn-on for the main switches of both APD circuit and single-phase full-bridge inverter. Circuit operation stages are analyzed and ZVS conditions are given. Finally, the proposed ZVS inverter with APD circuit is verified on a 1.5-kW inverter prototype. [ABSTRACT FROM AUTHOR]

Inductive power transfer (IPT) technology is useful for electric vehicle (EV) charging because of safe, flexible, and convenient features. In this paper, an integrated IPT system design employing variable inductor control is proposed to achieve a target constant current (CC) and constant voltage (CV) battery charging profile with misalignment tolerance. The system is implemented under a fixed switching frequency in both CC and CV modes. Soft switching of the primary inverter can be achieved over the entire charging process and allowed misalignment range without additional switches or dc–dc converters. Theoretical circuit analysis and the system design process are presented. A 3.3-kW prototype is implemented with a 210-mm air gap to demonstrate the validity of the proposed method. Experimental results show that the target CC and CV charging profile can be achieved by adjusting the variable inductor with up to 120 mm of lateral and 300 mm of vertical misalignment. The maximum efficiency of the proposed system is 96.1% at full output power and stays above 95% throughout CC operation. [ABSTRACT FROM AUTHOR]

In this paper, a hybrid switch with the combination of large-current silicon (Si) insulated gate bipolar transistor (IGBT) and small-current silicon carbide (SiC) metal-oxide semiconductor field-effect transistor (mosfet) is utilized in a three-phase T-type three-level grid inverter. The hybrid switch can optimize the cost of the system while achieving high efficiency. The relationship between efficiency improvement and cost of the hybrid switch is investigated. Several switching patterns, which can decrease the loss of the small-current SiC mosfet for the hybrid switch, are studied. Different switching patterns for the hybrid switch of the grid inverter are compared based on the inverter efficiency. Finally, a 20 kW three-phase T-type three-level grid inverter prototype with the hybrid switch of large-current Si IGBT and small-current SiC mosfet (1:2.4 SiC/Si current ratio) is built to verify the main results. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Although SiC-mosfet has significant advantages on switching performance over traditional Si-IGBT, the switching loss of SiC-mosfet devices at hard switching rises quickly with the increment in the switching frequency. This has narrowed down further possibilities of improving efficiency and power density of the grid inverter. Zero-voltage-switching (ZVS) space-vector-modulation (SVM) technique is introduced to further push the power density of SiC-mosfet inverter. This paper focuses on the impact of applying the ZVS-SVM to three-phase two-level SiC-mosfet inverter. With the same efficiency requirement the ZVS-SVM SiC inverter can operate at a much higher switching frequency, which gives the opportunity to further reduce the size of passive components. The loss distributions, conversion efficiencies, and volumes of passive components of both a 20-kW SiC-mosfet hard-switching inverter and a 20-kW SiC-mosfet ZVS-SVM inverter have been compared under switching-frequency range from 50 to 300 kHz. Meanwhile, a new metric called “efficiency stiffness” is proposed to compare different inverters with respect to the efficiency performance against switching-frequency characteristics. In addition, high voltage overshoot of SiC-mosfet and high thermal stress of resonant inductor are the two critical issues in the SiC-mosfet ZVS-SVM inverter with high switching frequency. A power module including seven SiC-mosfet bare dies with low stray inductance is designed for ZVS-SVM inverter instead of the existing seven discrete TO-247 package SiC-mosfets to reduce the voltage overshoots on the switches. Besides, to reduce the power loss of the resonant inductor caused by large amplitude of current at hundreds of kHz excitation frequency, design of the inductor with distributed air gap and optimal winding thickness are studied. A 20-kW SiC-mosfet ZVS-SVM grid inverter prototype is built to verify the proposed design. [ABSTRACT FROM AUTHOR]

In a zero-voltage switching (ZVS) inverter, high conversion efficiency and miniaturization are expected since switching loss can be dramatically reduced with proper design. In order to realize ZVS condition, auxiliary components such as inductors, capacitors, and switches are embedded in the inverter to implement the function. Since the design of auxiliary components is critical to the ZVS inverter, it is impossible to realize maximum efficiency or minimum size by following the conventional design procedure. This paper introduces an optimized design methodology for a three-phase ZVS inverter with objectives of both high efficiency and miniaturization. Based on the loss models of different commercial IGBT modules under different ZVS conditions, as well as the loss models of auxiliary components and filter inductors, the issue of pursuing highest efficiency and power density is transformed into solving a constrained nonlinear multivariable problem. According to the proposed design methodology, all parameters that influence the efficiency and physical dimensions are considered simultaneously. Thus, the optimized selection of the IGBT module, the parameters of the auxiliary components and the filter inductors would be obtained. A 30-kW three-phase ZVS inverter prototype is built to verify the proposed design method. With proposed design method, the improved prototype has achieved both smaller passive components volume and higher efficiency compared to the former prototype. [ABSTRACT FROM AUTHOR]

A zero-voltage switching (ZVS) grid-connected full-bridge inverter and its modulation schemes are investigated. A novel sinusoidal pulse width modulation scheme for the ZVS full-bridge inverter (ZVS SPWM) is proposed in this paper. The ZVS SPWM is evolved from the double-frequency SPWM by adding gate drive to the auxiliary switch. The ZVS condition is analyzed and the circulation loss of the resonant branch is optimized by adjusting the energy storage in the resonant inductor. The reverse recovery of the body-diode of MOSFET is relieved and ZVS is realized for both main and auxiliary switches. The filter inductors are significantly reduced with higher switching frequency. The design guideline of resonant parameters and the implementation of ZVS SPWM in DSP controller are introduced. The ZVS SPWM scheme is verified on a 3-kW inverter prototype. According to the experimental result, peak efficiency as 98.8% is achieved. [ABSTRACT FROM AUTHOR]

Due to the long cold start time and slow dynamics of proton exchange membrane (PEM) fuel cell (FC) stack, operating modes transfer control strategy for fuel cell uninterruptible power supply (FC-UPS) is different from the traditional uninterruptible power supply (UPS) system. In this paper, a seamless transfer control strategy, which is suitable for FC-UPS, is proposed. The power conversion architecture of FC-UPS is presented with the characteristic analysis of PEMFC and the requirements of UPS. Then, the scheme of the seamless transfer control strategy is investigated. The proposed seamless transfer control strategy is not only capable of guaranteeing the uninterruptible load voltage, but also protecting FC against the power demands beyond its allowable bandwidth during the transition for long lifespan and safety. Finally, the control scheme has been verified on a 10-kW FC-UPS prototype. [ABSTRACT FROM AUTHOR]