Kumar Modepalli

A direct AC LED driver with high power factor without the use of passive components

In this paper, a novel driver for high brightness LED applications that can directly run from AC voltage is presented. Conventional LED drivers for such applications consist of switching-type converters which require passive components like high value inductors and electrolytic capacitors for their operation. The use of such components increases the size and cost of the LED system while decreasing the overall life time. The proposed circuit only needs active devices like MOSFETs and op-amps for power processing. The input current is selectively controlled to follow a sinusoidal waveform to achieve low harmonic distortion and high power factor. A simple start-up circuit is also designed for self-sufficient operation with a more efficient set-up under development. The efficiency of the proposed system is around 82% for a 1.5W converter with 9% total harmonic distortion. Such an implementation is also more suitable for IC design. Both simulation and experimental results have been presented to validate the operation of the proposed set-up.

Dual-Purpose Offline LED Driver for Illumination and Visible Light Communication

This paper presents a dual-purpose offline LED driver with illumination control and visible light communications (VLC). LEDs, due to their nonlinear I-V characteristics, are driven by constant current sources. The proposed dual-purpose offline LED driver realizes a constant current source by a buck converter without a capacitor using average current mode control. VLC is implemented through variable pulse position modulation scheme using a shunt switch in parallel to LED string. Conventional LED drivers are typically designed to perform illumination control with pulsewidth modulation (PWM) dimming at low frequencies (<; 20 kHz), which results in audible noise due to the mechanical vibrations of inductors and piezoelectric properties of ceramic capacitors. The proposed converter presents an illumination control with PWM dimming frequencies above the audible range. The detailed control and modeling of the proposed dual-purpose LED driver using high-frequency model of LED string is discussed. The effects of the phosphor on phosphor-based white LEDs for VLC are reported. The proposed driver is experimentally evaluated on 110/120 ac mains with 450-lm output. The linear characteristics of PWM dimming for data transfer of 2 Mb/s are demonstrated. Detailed simulation and experimental results to validate the operation of the proposed converter are presented.

A New Optimum Power Control Scheme for Low-Power Energy Harvesting Systems

Energy harvesting has become a popular source for low-power electronic systems such as wireless sensors and biomedical implants. Energy can be extracted from a number of ambient conditions such as vibration, solar, and thermal gradient. Just like renewable sources, the associated switching power converters can be controlled to harvest maximum power from these miniature systems. However, conventional schemes, such as a conventional maximum power point tracking (MPPT) controller for solar cells, are complex and cannot be utilized in low-power energy systems due to their cost and power requirements. In this paper, a novel optimum energy harvesting scheme is proposed, which controls the duty cycle of the converter to maximize the output power of the system. The control system employs only simple mixed-signal components and can be applied to low-power systems. The proposed scheme does not depend on the characteristics of a specific source and is applicable for different energy systems. In this paper, it is utilized to achieve optimized energy harvesting for two completely different fixed excitation systems, namely, a low-voltage vibration-based electromagnetic microgenerator and a miniature solar cell array. Both simulation and experimental results are provided to validate the proposed scheme.

A Scalable N -Color LED Driver Using Single Inductor Multiple Current Output Topology

Constant current sources are required to drive multiple color LED strings and the LED drivers that drive these LED lighting systems should provide multiple constant currents from a single dc source. In this paper, a single inductor multiple current output (SIMCO) converter that can provide N- independently controllable constant current outputs is reported. The average current in each color LED string is controlled independently by using hybrid average current mode control (HACMC). The HACMC combines the advantage of both average current mode control and charge control method. Traditional dimming approaches such as pulse width modulation and analog dimming can be incorporated in the proposed topology for color tunability and correlated color temperature control. The proposed approach uses a simple control logic, which is modular and can be scalable to N color LED lighting systems. The operation of the SIMCO converter with the HACMC is explained in detail. Simulation and experimental results with 48 V input and 12 W for N = 3 (RGB) color systems are presented.

Dual purpose HB-LED driver for illumination and visible light communication

The recent improvements in luminous efficacy, lifetime of the LEDs and energy savings resulted in the increased usage of solid state lighting. The major advantage of LED lighting is that they can be used for Visible Light Communications. To achieve Visible Light Communication High Brightness-LEDs used for illumination has to be switched fast in Multi Megahertz range to transmit the data. In this paper, average current mode controlled buck converter with illumination control and data transfer using Variable Pulse Position Modulation scheme is presented. Illumination control is achieved through PWM dimming. Simulations and experimental results demonstrating visible light communications and illumination control for the proposed dual purpose buck converter are presented.

Three-Phase Current-Fed Isolated DC–DC Converter With Zero-Current Switching

A new current-fed zero-current switching (ZCS) three-phase dc–dc converter topology is proposed in this paper. The converter architecture consists of a current-fed three-phase three-leg IGBT bridge, three single-phase high-frequency transformers with star-connected primary, and three single-phase rectifier bridges. Each secondary winding of the high-frequency transformer forms the input for single-phase rectifier bridges at the output. The parallel-connected outputs of these bridges supply the desired load. The three-leg IGBT-based primary bridge is modulated with constant frequency phase-shift pulse width modulation technique. ZCS for all the primary IGBTs is achieved with the aid of transformer leakage inductance, small auxiliary ac capacitors connected in parallel to secondary side of single-phase transformers and modulation scheme. Detailed operation with converter design and analysis are discussed. Digital simulation and experimental test results on a laboratory prototype are presented to investigate the converter design and operation.

Lighting Up with a Dual-Purpose Driver: A Viable Option for a Light-Emitting Diode Driver for Visible Light Communication

This article presents a dual-purpose offline light-emitt ing diode (LED) driver using a single-stage buck?boost?buck (S2-B3) converter. The proposed (S2-B3) converter provides combined illumination control and visible light communication (VLC) along with power factor correction (PFC) and is designed to operate the buck?boost section in discontinuous conduction mode (DCM) with constant duty ratio to provide PFC. The buck section of the converter is operated in continuous conduction mode (CCM) with average current mode control (ACMC) to realize a constant current source for a high-brightness LED (HB-LED) load. The HBLED load connected to the converter is switched on and off at 2 MHz to facilitate both illumination and VLC . Data transfer and illumination control are achieved through variable pulse position modulation (VPPM) and high-frequency pulsewidth modulation (PWM) dimming, respectively. The modeling and design of the proposed (S2-B3) converter with a VPPM modulation scheme are detailed. Simulation and experimental results of the proposed converter with 500-lm output and 2-Mb/s data transfer of phosphor-converted (PC)-white LEDs for 110/120-V ac input are demonstrated.

Offshore wind energy systems using high frequency isolated current-fed modular converters

In this paper a new offshore wind energy power conversion architecture with grid integration using HVDC link is presented. Multi-MW multiple three-phase winding Permanent Magnetic Synchronous Generators (PMSG) captures the offshore wind energy. Each of the three-phase winding of PMSG are connected to Current Source Converters (CSC) that are controlled by MPPT. The outputs of these CSCs are series connected to from an intermediate medium voltage bus. Modular Input Series Output Parallel (ISOP) Current-Fed High Frequency (CF-HF) DC-DC converter provides galvanic isolation to the outputs of series connected CSCs and isolates them from High Voltage Direct Current (HVDC) link. The outputs of CF-HF DC-DC converters from different Multi-MW PMSGs are series connected to form HVDC link. At the grid interface, ISOP connection of CF-HF DC-DC converter modules are employed to provide isolation and to maintain a constant HVDC-link current. Voltage source converters (VSC) connected to the output of the DC-DC converters provides grid interface. Control and modeling of the proposed system are detailed. Simulation results demonstrate the proposed power conversion architecture control and operation.

A scalable HB-LED driver for multi-color Adaptive lighting systems

In this paper a HB- LED driver that can drive multi-color HB-LED strings using Single Inductor Multiple Current Output (SIMCO) buck converter topology is presented. Constant current sources are required to drive LED strings due to their non-linear I-V characteristics. In the proposed topology the average current in multi-color LED strings are controlled independently by using a combination of non-linear charge control and traditional Average Current Mode Control (ACMC) from a single DC voltage source. The SIMCO buck converter is operated in Continuous Conduction Mode (CCM) with ACMC to realize a constant source feeding multi-color LED strings. Simulation and experimental results of a high color rendering index (CRI) multi-color LED lighting system with 48V DC input and 500lm output are presented.

Single stage dual purpose offline HB-LED driver with power factor correction for illumination and visible light communication

In this paper a dual purpose offline LED driver using Single Stage Buck-Boost Buck (S2-B3) converter for illumination control and Visible Light Communications (VLC) with Power Factor Correction (PFC) is presented. The (S2-B3) converter is designed to operate buck-boost section in Discontinuous Conduction Mode (DCM) with constant duty ratio to provide inherent power factor correction (PFC). The buck section of the converter is operated in Continuous Conduction Mode (CCM) with Average Current Mode Control (ACMC) to realize a constant current source for LED loads. LEDs when switched ON and OFF with megahertz frequencies will facilitate VLC along with illumination. Data transfer and illumination control are achieved through Variable Pulse Position Modulation (VPPM) and high frequency dimming respectively. Simulation and experimental results of the proposed dual purpose converter with PFC for a 500 lm output with 110/120V AC input are presented.