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In this article, a subharmonics switching technique named bifrequency pulse train (BF-PT) control for wireless battery charging system with tapped transmitter (Tx) winding is proposed to regulate the output power against the variation of load and coupling coefficient. The tapped Tx winding is spilt into two subwindings: subwinding I is connected to the inverter while subwinding II is in open circuit. The charging current and charging voltage can be acquired by measuring the induced current of subwinding I and the induced voltage of subwinding II, respectively, without dual-side communication. BF-PT control, which contains high- and low-frequency pulse trains, can achieve zero voltage switching over a wide operating range. The high- and low-frequency pulse trains are uniformly distributed to suppress the winding current oscillation and to minimize the output voltage ripple. When the coupling becomes weaker and/or light-load conditions, the switches are operated at the subharmonics frequency to further reduce the average switching frequency of the system. To verify the validity of the proposed method, a wireless charging system with 72 V/3 A output is fabricated. The experimental results confirmed that the proposed method is able to maintain constant current and constant voltage output regardless of the load and coupling variations. [ABSTRACT FROM AUTHOR]

In this article, a half-bridge class-D audio amplifier (HB-CDAA) system with embedded bidirectional buck–boost converter is proposed. The proposed HB-CDAA system consists of a front-end symmetric bipolar output converter, a bidirectional buck–boost converter, and an HB-CDAA. With the help of the embedded bidirectional buck–boost converter, bus voltage pumping on the output of the front-end symmetric bipolar output converter of HB-CDAA can be suppressed. Thus, small ceramic capacitors can be used as bus capacitors to increase power density and to improve audio output quality. Furthermore, ZVS of the embedded bidirectional buck–boost converter can be achieved. The operating principle of the proposed circuit is analyzed and an experimental prototype is built. Experimental results show that ZVS of the embedded bidirectional buck–boost converter is achieved, and bus voltage pumping is successfully suppressed with small bus capacitors. [ABSTRACT FROM AUTHOR]

Inductive power transfer (IPT) systems with multiple output voltages are potential to supply a variety of loads simultaneously. This article proposes an IPT system with multiple semiactive rectifier cells (SARCs) connected in series at the receiver (Rx) side. These SARCs are independent of each other and their output voltages can be regulated individually with single receiver coil, which reduces the cost and volume. The proposed IPT configuration has the advantages of high flexibility, simple control, and no cross regulation. Considering that the SARC may cause additional reactance and lead to detuning of the Rx side, variable inductor is introduced to ensure the full tuning condition. Thus, the proposed IPT system can maintain zero phase angle operation with unity power factor in the whole load range, minimizing the reactive power losses. In addition, both primary inverter and the SARCs can achieve zero voltage switching. To verify the feasibility and validity of the proposed IPT system, an experimental prototype with two outputs of 640 W/150 V and 400 W/120 V is built. [ABSTRACT FROM AUTHOR]

Based on the current-mode switching cell (CMSC), an inductive power transfer (IPT) system with dual-output is proposed in this letter. In the proposed IPT system, two CMSCs are inversely connected in series at the Rx side. Two CMSCs operate in the positive half-cycle and in the negative half-cycle of the Rx coil current, respectively. The dual output voltages can be regulated independently. The circuit structure of the CMSC is quite simple and helps to make the Rx side more compact. The control scheme is based on Rx-side real-time regulation and thereby wireless communication links are not required. Additionally, zero voltage switching is ensured for all switches. In order to verify the theoretical analysis, an experimental prototype with 20 V/3.3 A and 5 V/3 A outputs is fabricated, and the maximum efficiency can reach 92.8%. [ABSTRACT FROM AUTHOR]

To regulate the output voltage of inductor–capacitor–capacitor-series (LCC-S) compensated wireless power transfer (WPT) system, a hybrid control strategy of phase shift modulation (PSM) and a switch-controlled capacitor is presented in this article. In the proposed hybrid control strategy, LCC-S compensated WPT system can realize wide output voltage regulation with zero voltage switching (ZVS), and the reactive current in a resonant tank can be minimized in the whole voltage range. Besides, the current in the primary coil of LCC-S compensated WPT system can be regulated with PSM, which helps to reduce the power loss of the primary coil at light load. Compared with conventional dual-loop hybrid control, the proposed hybrid control can regulate two control variables with one feedback loop simultaneously. To verify the theoretical analysis, a 500-W prototype with 400-V input voltage, 100−250-V output voltage is built. The experimental results show that the inverter can realize ZVS within the whole voltage range and a peak efficiency of 94.7% can be obtained. [ABSTRACT FROM AUTHOR]

Single-stage boost-LLC ac–dc converters have been a popular soft-switched topology because of the high-efficiency and being cost-effective. However, low power capacity is its main disadvantage. In this article, a novel single-stage interleaved boost-LLC ac–dc converter with higher power capacity is presented while achieving the low input current ripple. However, it still suffers from the wide and high bus voltage for universal operation, as a result of the conventional pulse frequency modulation (PFM) with the duty cycle of 0.5. Furthermore, this wide bus voltage will bring the difficulties in designing the LLC resonant cell. To solve these issues, a dual-loop feedback control strategy based on PFM/interleaved asymmetric pulsewidth modulation hybrid modulation and power balance based optimal design are proposed. With the proposed control strategy and optimal design, the bus voltage of the studied converter is not only significantly reduced, but also zero voltage switching for the primary switches and zero current switching for the secondary diodes are still maintained. Thus, the higher efficiency can be achieved. Operation principles and control scheme for the studied converter are fully addressed. The optimal design based on power balance principle is also discussed in this article. A 300 W prototype is fabricated to validate the theoretical analysis and optimal design. The experimental results demonstrate the prototype can simultaneously obtain the universal operation with high power factor above 0.98 and the quasi-constant bus voltage below 500 V. The measured peak efficiency is 92.7% under 115 Vac input voltage at full load. [ABSTRACT FROM AUTHOR]

In this article, a zero-voltage switching (ZVS) series–series compensated wireless power transfer (WPT) converter with phase shift modulation is proposed, which can realize output current regulation over wide range. In the proposed WPT converter, an auxiliary LCL resonant network is connected between two midpoints of the H-bridge legs of inverter to provide the peak current for ZVS operation during the dead time, with low rms current to decrease the conduction losses. To reduce the volume of the auxiliary network, an integrated coil structure is applied and the magnetic saturation is avoided due to the orthogonal coil currents. Time-domain analysis and ZVS operation of the proposed WPT converter are performed. Design and optimization of the LCL network are performed. Experimental results of a prototype with 8−20 A adjustable output current confirm the feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

Two-stage power conversion of class-D amplifier with front-end switching mode power supply affects the power conversion efficiency of audio amplifier system. Single-stage inverter (SSI) developed from cycloconverter can be used as audio amplifier to improve efficiency. However, current commutation of cycloconverter switches challenges for high efficiency and low total harmonic distortion (THD). In this article, a bipolar phase shift modulation (BPSM) SSI is proposed for high efficiency low distortion audio amplification. Full bridge active clamp (FBAC) circuit is used to clamp the voltage across cycloconverter switches and recycle the energy of filter inductor and leakage inductance. By using active clamp, utilization of magnetizing inductance current and optimization of driving sequence of clamp switches, zero voltage switching of the proposed BPSM FBAC-SSI is achieved over wide range. With BPSM and voltage clamp across cycloconverter switches, low THD of output voltage is also achieved. A 200 kHz prototype with 250 W output power is presented to verify the analysis results of the proposed BPSM FBAC-SSI. [ABSTRACT FROM AUTHOR]

A phase-shift pulse-frequency modulation (PS-PFM) for a full-bridge LCC resonant converter is proposed in this paper to reduce both switching frequency variation range and reactive power of a traditional PFM LCC resonant converter. Like the PFM LCC resonant converter, a PS-PFM LCC resonant converter has a wider zero voltage switching operation range than a phase-shift modulated LCC resonant converter. By integrating a voltage-controlled carrier generator, the proposed PS-PFM modulator can adjust phase-shift angle and switching frequency simultaneously, resulting in one more degree of control freedom to optimize the steady-state performance of an LCC resonant converter. A detailed analysis of the proposed PS-PFM LCC resonant converter is performed and a step-by-step parameter design procedure is given. A 500-W/48-V prototype with 100–200 V input voltage is built to verify the theoretical analysis. The maximum efficiency of the prototype reaches 95.3%. [ABSTRACT FROM AUTHOR]

A dual-carrier modulation technique is proposed to improve the performance of the half-bridge resonant converter in this paper. By alternately using two different sawtooth waveforms as a carrier, the dual-carrier modulation combines the characteristics of both variable frequency modulation and fixed-frequency modulation. According to the structure of modulator, there are two kinds of dual-carrier modulation: type A and type B. Type A dual-carrier modulation is suitable for resonant converters operating in inductive region to achieve a wide zero voltage switching (ZVS) range, while type B dual-carrier modulation is preferred for resonant converters operating in capacitive region to obtain a wide zero current switching range. By utilizing both switching frequency modulation and duty ratio modulation, the proposed dual-carrier modulation not only extends soft-switching range of the resonant converter, but also reduces switching frequency variation range. In order to verify the benefits of the proposed modulation, a 500-W dual-carrier modulated LCC resonant converter operating in inductive region is designed and built. Simulation and experimental results show the prototype achieves ZVS soft-switching operation for 200–400 V input voltage and 100–500 W output power, with only about 10 kHz switching frequency variation. [ABSTRACT FROM AUTHOR]

Compared with traditional two-stage class-D audio amplifier, audio amplifier based on cycloconverter-type single-stage inverter (CSSI) has advantages of high efficiency and no bus voltage pumping (BVP). However, CSSI requires complex active clamp circuits for the current commutation of cycloconverter, especially for multichannel amplification. In this letter, a 2.1-channel switching amplifier with dc/high-frequency-ac (HFAC) mixed power supply is proposed, where CSSI is used as low-frequency audio channel amplifier and two class-D amplifiers are used as high-frequency audio channel amplifiers. With dc/HFAC mixed power supply, the proposed 2.1-channel switching amplifier does not require additional active clamp circuits for current commutation of cycloconverter. Besides, wide range soft switching of cycloconverter switches can be achieved. Benefiting from single-stage power conversion of low-frequency audio channel and wide range soft switching of cycloconverter switches, high efficiency of the proposed 2.1-channel amplifier is achieved. Without BVP, low voltage stress of switches and low distortion of low-frequency audio signal are realized in the proposed 2.1-channel amplifier. A 200-W prototype is presented to verify the analysis results. [ABSTRACT FROM AUTHOR]

A two‐switch equaliser for series‐connected battery stack using zeta type converter and symmetrical capacitor–diode circuit is proposed. The proposed equaliser consists of a zeta type front‐end dc–dc converter and symmetrical capacitor–diode circuit, uses only two active switches and two magnetic components, thus it benefits from small circuit volume and flexible for extension. Meanwhile, it can work under open loop, which makes its control simple. Furthermore, high efficiency is achieved by zero voltage switching of all switches. Finally, experimental results of a prototype of the proposed equaliser are presented to verify the analysis results. [ABSTRACT FROM AUTHOR]

An asymmetrical hybrid‐controlled half‐bridge LCC resonant converter which integrated a buck–boost converter and a half‐bridge LCC resonant converter is proposed. It benefits with wide soft switching range, low conduction loss and high power density. By utilising an asymmetrical hybrid control strategy, its switching frequency and duty ratio can be adjusted simultaneously. The proposed LCC resonant converter maintains output voltage regulation and zero‐voltage switching of switches in wide input voltage and load variation range. Experiment results of a 500 W prototype are provided to verify the theoretical analysis results. [ABSTRACT FROM AUTHOR]

Variable frequency controlled LCC resonant converter suffers from wide variation of switching frequency. Although fixed frequency controlled LCC resonant converter benefits from constant switching frequency, it suffers from narrow zero voltage switching (ZVS) range of power switch and high circulating energy. A pulse width modulation – pulse frequency modulation (PWM‐PFM) hybrid controlled LCC resonant converter is proposed to achieve wide ZVS range of power switch with narrow variation of switching frequency. Experiment results of a 500 W prototype are provided to verify theoretical analysis of the proposed converter. [ABSTRACT FROM AUTHOR]

A two‐channel single‐stage switching amplifier (SSA) based on high‐frequency link inverter is proposed. The audio input signals are modulated by phase shift between primary‐side switches and secondary‐side switches, thus independent amplifications of two channels can be obtained. Benefiting from multiplexing of primary‐side power switches for two channels, only a half bridge inverter is utilised at primary side. Clamp circuits at the secondary side of transformer eliminate spike voltages across the secondary‐side switches during the current commutation of the cycloconverters. Zero voltage switching of primary‐side switches and clamp switches are achieved by utilising magnetising inductor current. A 320 V/250W prototype is presented to verify the analysis results of the proposed two‐channel SSA. [ABSTRACT FROM AUTHOR]

A novel soft‐switching step‐up/down DC–DC converter is proposed, which generates symmetric bipolar outputs while maintaining the grounded capability. The proposed converter consists of a zeta converter cell and a buck–boost converter cell, sharing an inductor and a power switch. High efficiency is achieved by zero voltage switching for all switches. Meanwhile, by connecting one load between positive and negative output terminals, high voltage gain can be achieved. Experimental results of a 3.7 V battery input and ±10 VDC/10 W outputs prototype are presented to verify the analysis results of the proposed converter. [ABSTRACT FROM AUTHOR]

Based on soft‐switched continuous conduction mode boost converter, a zero‐voltage zero‐current switching DC/DC converter is proposed by introducing a flyback‐unit and a voltage‐double‐unit. The proposed converter can achieve high voltage gain without operating at extreme high duty cycle. Moreover, by replacing the output diode of conventional boost converter with an active switch, zero‐voltage‐switched turn‐on of switches and zero‐current‐switched turn‐off of diodes can be achieved, which reduce switching loss and alleviate reverse‐recovery problem of diodes. Furthermore, the energy in leakage inductor can be transferred into the output of the converter to improve the efficiency. The operating characteristics and the voltage gain of the proposed converter are analysed. Experimental results of a 100 W prototype are provided to verify the theoretical analysis results. [ABSTRACT FROM AUTHOR]

Compared with conventional forward converters, active clamp forward (ACF) converters have many advantages, including lower voltage stress on the primary power devices, the ability to switch at zero voltage, reduced EMI and duty cycle operation above 50%. Thus, it has been the most popular solution for the low bus voltage applications, such as 48 V and 28 V. However, because of the poor performance of Si MOSFETs, the efficiency of active clamp forward converters is difficult to further improved. Focusing on the bus voltage of 28 V with 18~36 V voltage range application, the Gallium Nitride high electron-mobility transistors (GaN HEMT) with ultralow on-resistance, low parasitic capacitances, and no reverse recovery, is incorporated into active clamp forward converters for achieving higher efficiency and power density, in this paper. Meanwhile, the comparative analysis is performed for Si MOSFET and GaN HEMT. In order to demonstrate the feasibility and validity of the proposed solution and comparative analysis, two 18~36 V input, 120 W/12 V output, synchronous rectification prototype with different power devices are built and compared in the lab. The experimental results show the GaN version can achieve the efficiency of 95.45%, which is around 1% higher than its counterpart under the whole load condition and the same power density of 2.2 W/cm3. [ABSTRACT FROM AUTHOR]