Xiaoyong Ren

Bio: Xiaoyong Ren is an academic researcher from Nanjing University. The author has contributed to research in topics: Boost converter & Inductor. The author has an hindex of 12, co-authored 21 publications receiving 401 citations.

Three-Mode Dual-Frequency Two-Edge Modulation Scheme for Four-Switch Buck–Boost Converter

Abstract: Four-switch buck-boost (FSBB) converter features low-voltage stress across the power switches and positive output voltage. They have two active power switches and two synchronous rectifiers, so two freedoms, i.e., the duty cycles of the two active switches, are available to regulate the output voltage. This paper proposes a two-edge modulation (TEM), in which the two active switches are trailing-edge and leading-edge modulated, respectively. Thus, the inductor current ripple can be reduced. Furthermore, a 3-mode TEM is derived to reduce the root-mean-square value of the inductor current to reduce the conduction loss. The line range is divided into three regions, and FSBB operates at boost, buck-boost, and buck modes in the lower, medium, and higher input voltage regions, respectively. At buck and boost modes, only two switches are high-frequency switched, so that the total switching loss is reduced. In the buck-boost mode, the inductor current ripple is very low compared with other two modes. Hence, the switching frequency is lowered to reduce the switching loss. The 3-mode TEM can achieve high efficiency over the line range, which is verified by a 48-V (36-75 V) input, 48-V @ 6.25-A output prototype. The measured efficiency is higher than 96.5% over the line range and the efficiency at the nominal input voltage is 97.8%.

A Bandpass Filter Incorporated Into the Inductor Current Feedback Path for Improving Dynamic Performance of the Front-End DC–DC Converter in Two-Stage Inverter

Abstract: The instantaneous output power of a two-stage single-phase inverter pulsates at twice the output voltage frequency, generating second harmonic current (SHC) in the front-end dc-dc converter. To reduce the SHC, this paper proposes a virtual impedance based control strategy. For the case of adopting a resistor as the virtual impedance, a closed-loop parameter design method is presented, revealing that the voltage loop crossover frequency is relatively low under such circumstance. To overcome this problem, a control strategy incorporating a bandpass filter (BPF) into the inductor current feedback path is put forward and a damping resistor is further added into the BPF for the purpose of improving the system stability margin. Hence, the proposed control scheme can not only reduce the SHC significantly, but also improve the dynamic performance of the front-end dc-dc converter effectively while guaranteeing the stability of the converter. Finally, a 1-kVA prototype is built and tested in the laboratory, and the experimental results are presented to verify the effectiveness of the proposed control strategy.

Four Switch Buck-Boost Converter for Telecom DC-DC power supply applications

Abstract: Converters for telecom DC/DC power supply applications often require an output voltage somewhere within a wide range of input voltages. While the design of traditional converters will come with a heavy penalty in terms of component stresses and losses, and with the restrictions on the output voltage. Besides that, the high efficiency around the nominal input is another restriction for traditional converters. A controlling scheme for the four switch buck-boost converter is proposed to achieve high efficiency within the line range and the highest efficiency around the nominal input. A 48 V(36-75 V) input 12 V@25 A output two-stage prototype composed of the proposed converter and a full bridge converter is built in the lab. The experimental results verified the analysis.

Self-Oscillating Contactless Resonant Converter With Phase Detection Contactless Current Transformer

Abstract: In this paper, a self-oscillating control strategy is proposed for a series-series type contactless resonant converter (CRC). By detecting the secondary current phase of a CRC to control the inverter, better output controllability, dynamic response, and self-adaptability can be achieved. While the realization of self-oscillating control strategy depends on phase detection of secondary current. To provide a passive solution, a current transformer with shorted secondary, called phase detection contactless current transformer (PDCCT) is proposed. The proposed PDCCT can detect the current phase from the secondary side of a CRC and feedback to the primary side rapidly and accurately despite the changes in air gap. To guarantee the accuracy of self-oscillating control strategy, the time delay in control circuitry is studied and compensated. A 60-W self-oscillating CRC with PDCCT is then fabricated to demonstrate the validity of both PDCCT and self-oscillating control strategy. Besides, a testing circuit is designed to emulate the changes in converter parameters, and the dynamic performance shows that self-oscillating control strategy can respond to parameter changes in a switching period.

Analysis and control of S/SP compensation contactless resonant converter with constant voltage gain

Abstract: A novel S/SP type compensation contactless resonant converter is proposed in this paper, which features the advantage of constant gain intersection point with zero phase angle of input impedance. Different from S/P compensation, the constant gain value is not only independent of load change but also independent of transformer's coupling coefficient change causing by the change of gap or misalignment. The characteristic analysis of the proposed resonant converter is performed in this paper. It is also found that with the proposed S/SP compensation the output voltage gain is not sensitive to the parameter change around the gain intersection point. Therefore, both phase locking control and fixed-frequency control can be employed for the proposed converter. A 60W prototype with PLL control and a 1.5kW prototype with constant frequency control are built to verify the analysis. Experimental results testify the theoretical analysis very well. The efficiency of the fabricated prototype reaches 95.2% with 1.5kW output at 10 cm gap.

Hybrid IPT Topologies With Constant Current or Constant Voltage Output for Battery Charging Applications

Abstract: The inductive power transfer (IPT) technique in battery charging applications has many advantages compared to conventional plug-in systems. Due to the dependencies on transformer characteristics, loading profile, and operating frequency of an IPT system, it is not a trivial design task to provide the battery the required constant charging current (CC) or constant battery charging voltage (CV) efficiently under the condition of a wide load range possibly defined by the charging profile. This paper analyzes four basic IPT circuits with series–series (SS), series–parallel (SP), parallel–series (PS), and parallel–parallel (PP) compensations systematically to identify conditions for realizing load-independent output current or voltage, as well as resistive input impedance. Specifically, one load-independent current output circuit and one load-independent voltage output circuit having the same transformer, compensating capacitors, and operating frequency can be readily combined into a hybrid topology with fewest additional switches to facilitate the transition from CC to CV. Finally, hybrid topologies using either SS and PS compensation or SP and PP compensation are proposed for battery charging. Fixed-frequency duty cycle control can be easily implemented for the converters.

A current and future study on non-isolated DC–DC converters for photovoltaic applications

Abstract: Photovoltaic (PV) is a fast growing segment among renewable energy (RE) systems, whose development is owed to depleting fossil fuel and climate-changing environmental pollution. PV power output capacity, however, is still low and the associated costs still high, so efforts continue to develop PV converter and its controller, aiming for higher power-extracting efficiency and cost effectiveness. Different algorithms have been proposed for Maximum Power Point Tracking (MPPT). Since the choice of right converter for different application has an important influence in the optimum performance of the photovoltaic system, this paper reviews the state-of-the-art in research works on non-isolated DC–DC buck, boost, buck–boost, Cuk and SEPIC converters and their characteristics, to find a solution best suiting an application with Maximum Power Point Tracking. Review shows that there is a limitation in the system's performance according to the type of converter used. In can be concluded that the best selection of DC–DC converter which is really suitable and applicable in the PV system is the buck–boost DC–DC converter since it is capable of achieving optimal operation regardless of the load value with negotiable performance efficiency and price issue.

Recent progress and development on power DC-DC converter topology, control, design and applications: A review

Abstract: Over the last few decennia, power DC/DC converters have been the subject of great interest due to its extensive increment of utilization in different applications. A thorough review on recent developed power DC/DC converters is presented in this paper. The study is focused on the topologies in different applications such as renewable energy, automobile, high-voltage and medium-voltage DC power systems, telecommunication, etc. In addition, an overview of the modulation techniques, the state-of-the-art of control strategies of well-established converters are discussed. Photovoltaic (PV) systems as the noticeable renewable energy resources generally suffer from poor conversion efficiency with instability and intermittent characteristics. Therefore, DC/DC converter with Maximum Power Point Tracking (MPPT) algorithm is essential to ensure maximum available power harnessed from the PV. Important features of DC/DC converters with MPPT are also figured with various performances. Furthermore, the design and optimization of different parameters are addressed systematically. Finally, the researcher’s future challenges and focusing trends are briefly described. For the next-generation converters design and applications, these are considered in details, and will provide useful framework and point of references.

Variable Frequency Controller for Inductive Power Transfer in Dynamic Conditions

Abstract: Inductive power transfer is a highly attractive option for powering unmanned aerial or underwater vehicles, in harsh environments and while in continuous motion. This study presents a variable frequency controller for series–series compensated contactless chargers operating in dynamic conditions. The controller tracks, in real time, the frequency for which the output voltage is load independent. The criterion for that is the zeroing of the phase difference between the secondary current and the primary-side inverter output voltage. Control is performed by a phase-locked loop with optical communication between the two sides. Experimental results on a 1-kW prototype, for power transfer while in motion, show fast frequency response, along with steady output voltage, despite load variations. Comparison is performed with two other fixed frequencies of operation; the natural frequency of the primary resonant circuit and the maximum output power frequency at nominal gap. The proposed control is proven superior in terms of output power level and stability, as well as safety to highly misaligned conditions.

Ripple Eliminator to Smooth DC-Bus Voltage and Reduce the Total Capacitance Required

Abstract: Bulky electrolytic capacitors, which are often needed in dc systems to filter out voltage ripples, considerably reduce power density and system reliability. In this paper, a ripple eliminator, which is a bidirectional buck–boost converter terminated with an auxiliary capacitor, is adopted to replace bulky capacitors in dc systems. The voltage ripples on the terminals (i.e., the dc bus) can be transferred to the auxiliary capacitor, and the ripples on the auxiliary capacitor can vary in a wide range. Moreover, the average voltage of the auxiliary capacitor can be controlled either lower or higher than the dc-bus voltage, which offers a wide operational range for the ripple eliminator and also the possibility of further reducing the auxiliary capacitance. Hence, the total capacitance required can be much smaller than the originally needed. After proposing a control strategy to transfer the voltage ripples to the auxiliary capacitor, three control strategies are proposed to regulate the auxiliary-capacitor voltage to maintain proper operation. Intensive experimental results are presented to demonstrate the performance.