Xiaohui Qu

Bio: Xiaohui Qu is an academic researcher from Southeast University. The author has contributed to research in topics: LED lamp & Constant current. The author has an hindex of 17, co-authored 51 publications receiving 1212 citations. Previous affiliations of Xiaohui Qu include Hong Kong Polytechnic University & Nanjing University.

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.

Higher Order Compensation for Inductive-Power-Transfer Converters With Constant-Voltage or Constant-Current Output Combating Transformer Parameter Constraints

Abstract: Compensation is crucial for improving performance of inductive-power-transfer (IPT) converters. With proper compensation at some specific frequencies, an IPT converter can achieve load-independent constant output voltage or current, near zero reactive power, and soft switching of power switches simultaneously, resulting in simplified control circuitry, reduced component ratings, and improved power conversion efficiency. However, constant output voltage or current depends significantly on parameters of the transformer, which is often space constrained, making the converter design hard to optimize. To free the design from the constraints imposed by the transformer parameters, this paper proposes a family of higher order compensation circuits for IPT converters that achieves any desired constant-voltage or constant-current (CC) output with near zero reactive power and soft switching. Detailed derivation of the compensation method is given for the desired transfer function not constrained by transformer parameters. Prototypes of CC IPT configurations based on a single transformer are constructed to verify the analysis with three different output specifications.

Resonance-Assisted Buck Converter for Offline Driving of Power LED Replacement Lamps

Abstract: LEDs are potential successors of incandescent lamps with high luminous efficacy and long lifetime. To improve the overall luminair efficacy and lifetime, the power efficiency and lifetime of LED ballasts become important factors. Efficiency gain in transformerless power converters appears attractive for applications without isolation. Driving solid-state LED bulbs in an existing lighting fixture such as PAR30 style housing from universal mains necessitates a high-voltage step-down ratio in order to produce an output voltage of about 10-20 V, which is very common in LED lighting applications. Traditional nonisolated step-down pulse width modulation buck converters may suffer from poor efficiency due to the long diode freewheeling time at small duty cycles. In this paper, we propose a resonance-assisted buck converter to achieve a high-voltage step-down ratio and high converter efficiency, whilst maintaining durability and compatibility with existing incandescent dimmers. The performance of the proposed LED driver is verified experimentally..

Noncascading Structure for Electronic Ballast Design for Multiple LED Lamps With Independent Brightness Control

Abstract: LED light sources, which are more compact, capable to change color in real time, less dissipative, and more durable are finding more applications than conventional light bulbs in domestic, commercial, and industrial environments However, requirements such as high-power factor, long lifetime, accurate current control, and high-efficiency pose challenges to the design of LED ballast circuits This paper proposes an LED ballast with a dual noncascading structure The first-stage noncascading structure is an isolated current-fed power factor correction (PFC) preregulator In the proposed design, the short-lifetime high-voltage storage capacitor at the primary is replaced by a long-lifetime low-voltage capacitor at the secondary, thus extending the overall system lifetime The PFC is programmed by the conventional averaged current-mode control for high-power-factor applications Furthermore, the high-voltage stress on the main switch, which is typical in current-fed converters, is reduced substantially by appropriately exploiting the transformer leakage inductance The design uses two secondary transformer windings and an LED current driver to form a second noncascading structure to improve efficiency Multiple noncascading structures can be used for LED lamps for instant independent brightness control Analysis, design example, and prototype verification are given for the LED ballast

An IPT Battery Charger With Near Unity Power Factor and Load-Independent Constant Output Combating Design Constraints of Input Voltage and Transformer Parameters

Abstract: Inductive power transfer (IPT) techniques are becoming popular in battery charging applications due to some unique advantages compared to the conventional plug-in systems. A high-performance IPT charger should provide the battery with an efficient charging profile consisting of constant charging current and constant charging voltage. However, with a wide load range, it is hard to realize the initial load-independent constant current (CC) and the subsequent load-independent constant voltage (CV) using a single IPT converter while maintaining nearly unity power factor and soft switching of power switches simultaneously. This paper systematically analyzed the characteristics of an LCC – LCC compensated IPT converter and proposed a design method to realize the required load-independent CC and CV outputs at two zero-phase angle frequencies. The design also combats the constraints of an IPT transformer and input voltage, thus facilitating the use of a simple duty cycle control operating at two fixed frequencies for both CC and CV operations. The design criteria, control logic, and sensitivities of compensation parameters to the input impedance and load-independent output are discussed. Finally, an IPT battery charger prototype with 1 A charging current and 24 V battery voltage is built to verify the analysis.

Compensation Topologies of High-Power Wireless Power Transfer Systems

Abstract: Wireless power transfer (WPT) is an emerging technology that can realize electric power transmission over certain distances without physical contact, offering significant benefits to modern automation systems, medical applications, consumer electronics, etc. This paper provides a comprehensive review of existing compensation topologies for the loosely coupled transformer. Compensation topologies are reviewed and evaluated based on their basic and advanced functions. Individual passive resonant networks used to achieve constant (load-independent) voltage or current output are analyzed and summarized. Popular WPT compensation topologies are given as application examples, which can be regarded as the combination of multiple blocks of resonant networks. Analyses of the input zero phase angle and soft switching are conducted as well. This paper also discusses the compensation requirements for achieving the maximum efficiency according to different WPT application areas.

Virtual-Impedance-Based Control for Voltage-Source and Current-Source Converters

Abstract: The virtual impedance concept is increasingly used for the control of power electronic systems. Generally, the virtual impedance loop can either be embedded as an additional degree of freedom for active stabilization and disturbance rejection, or be employed as a command reference generator for the converters to provide ancillary services. This paper presents an overview of the virtual-impedance-based control strategies for voltage-source and current-source converters. The control output impedance shaping attained by the virtual impedances is generalized first using the impedance-based models. Different virtual impedances and their implementation issues are then discussed. A number of practical examples are demonstrated to illustrate the feasibility of virtual impedances. Emerging applications and future trends of virtual impedances in power electronic systems conclude this paper.

A High-Efficiency Dimmable LED Driver for Low-Power Lighting Applications

Abstract: This paper presents a dimmable light-emitting diode (LED) driver with adaptive feedback control for low-power lighting applications. An improved pulsewidth modulation dimming technique is studied for regulating the LED current and brightness. Under universal input voltage operation, high efficiency and high power factor can be achieved by a coupled inductor single-ended primary inductance converter power factor correction (PFC) converter with a simple commercial transition-mode PFC controller. The operation principles and design considerations of the studied LED driver are analyzed and discussed. A laboratory prototype is also designed and tested to verify the feasibility.

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.

Analysis and Design of the Integrated Double Buck–Boost Converter as a High-Power-Factor Driver for Power-LED Lamps

Abstract: In this paper, an integrated double buck-boost (IDBB) converter is proposed as a high-power-factor offline power supply for power-LED lamps. The IDBB converter features just one controlled switch and two inductors and is able to supply a solid-state lamp from the mains, providing high power factor and good efficiency. In this paper, the IDBB converter is analyzed, and a design methodology is proposed. It is demonstrated that, with a careful design of the converter, the filter capacitances can be made small enough so that film capacitors may be used. In this way, the converter mean time between failures can be made as high as that of the solid-state lamp. A design example for a 70-W converter supplied from a 230 V/50 Hz mains for street lighting applications is shown. Finally, experimental results from a laboratory prototype are also presented.