Rohan Dayal

Design and Implementation of a Direct AC–DC Boost Converter for Low-Voltage Energy Harvesting

In this paper, a direct ac-dc power electronic converter topology is proposed for efficient and optimum energy harvesting from low-voltage microgenerators. The converter utilizes the bidirectional current-conduction capability of MOSFETs to avoid the use of a front-end bridge rectifier. It is operated in discontinuous conduction mode and offers a resistive load to the microgenerator. Detailed analysis and modeling of the converter is presented. In such low-power applications, the power consumption of gate drive and control circuits should be minimal. In this paper, they are specifically designed to consume very low power. A suitable startup circuit and auxiliary dc supply circuit is proposed for the implementation of the converter. A low-voltage microgenerator is used to verify the performance and operation of the converter and the gate drive circuits.

A New Design for Vibration-Based Electromagnetic Energy Harvesting Systems Using Coil Inductance of Microgenerator

In this paper, a new design methodology for low-voltage electromagnetic energy harvesting systems consisting of a microgenerator and power processing circuit is introduced. In the first section of this paper, a simple topology for a resonance-based electromagnetic generator is presented. The microgenerator is capable of producing a voltage of a few hundred millivolts. Since traditional two-stage power conversion schemes cannot be used for such a low ac voltage, a suitable single-stage ac-dc converter is utilized for power processing. The converter boosts the low ac voltage to a nominal dc voltage required by electronic devices. As a part of integrated design, the coil of the microgenerator is fabricated such that it can be utilized both for electromagnetic induction and power processing. Such an arrangement improves efficiency and makes the system compact. The converter is controlled to regulate the output voltage under varying input or load conditions. Simulation and experimental results are presented to validate the operation of the proposed converter with a low-voltage microgenerator.

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.

Efficient direct ac-to-dc converters for vibration-based low voltage energy harvesting

In this paper two direct ac-to-dc power electronics converter topologies are proposed for efficient and optimum energy harvesting from low voltage microgenerators. The conventional power electronics converters used for such applications have two stages, a diode bridge rectifier at the front end followed by a dc-dc boost converter. However, the extremely low output voltage of electromagnetic microgenerators does not allow diode bridge rectification. Even if possible, the losses in the front end diode bridge make the conventional power electronic interfaces quite inefficient. The proposed single stage converters directly boost the microgenerator low ac voltage to usable dc voltage level, and hence, achieve higher efficiency. The single stage ac-to-dc power conversion is achieved by utilizing the bidirectional current conduction capability of MOSFETs. Moreover, for optimum energy harvesting the power converter should be able to control the load resistance as seen by a microgenerator. The conventional converters are not conducive for such control. With the proposed converter topologies the optimal energy harvesting can be successfully realized.

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 Novel direct AC/DC converter for efficient low voltage energy harvesting

In this paper, a direct ac-to-dc power converter is proposed for efficient energy harvesting from the low voltage inertial microgenerators. The conventional power converters use diode bridge rectifiers and condition the microgenerator outputs in two stages. Hence, they are inefficient and may not be a feasible option for very low voltage microgenerators. Moreover, they are not conducive for optimum energy harvesting. The proposed converter avoids the use of bridge rectifiers, and directly converts the ac input to the required dc output. This converter uses a boost converter and a buck-boost converter to process the positive and negative half cycles of the ac input voltage, respectively. Furthermore, using this converter, maximum energy harvesting can be implemented effectively. Analysis of the converter is carried out. Based on the analysis, two schemes are proposed to control the converter. Simulation results are presented to validate the proposed converter topology and control scheme. Experimental results are also presented for verification.

High voltage normally-off GaN MOSC-HEMTs on silicon substrates for power switching applications

We report our experimental results on high voltage normally-off GaN MOS channel HEMTs (MOSC-HEMT) on silicon substrates with best specific on-resistance (Ron,sp) of 4 mΩ-cm2 and breakdown voltage (BV) of 840V. The switching performance of the device was evaluated by SPICE simulations of a buck-boost converter and showed a system efficiency of 10% higher than that using a commercial GaN HEMT. A bidirectional switch consisted two GaN MOSC-HEMTs were also demonstrated.

A new single stage AC-DC converter for low voltage electromagnetic energy harvesting

In this paper, a direct AC-DC converter for electromagnetic microgenerators is presented. In recent years, researchers have developed a number of microgenerator configurations that are capable of producing an AC voltage of a few hundred millivolts. However, little work has been reported on conversion of such low voltages to a steady DC voltage required by most devices. The authors present a new converter topology that can be used for such low voltage, low power energy harvesting. It utilizes the bidirectional current capability of MOSFETs to avoid the use of front-end bridge rectifier. The converter offers a resistive load to the microgenerator making it suitable for optimum energy harvesting. Simulation and experimental results are depicted to verify the operation of the converter.

Non-isolated topologies for high step-down offline LED driver applications

In this paper, two non-isolated DC-DC converter topologies suitable for offline Light-emitting Diode (LED) driver applications are presented. The output voltage for such applications is generally less than 42 V DC to satisfy LED lighting system requirements. Isolated converters are normally used for this higher step-down (170V-42V/15V DC) operation. However, an isolation transformer introduces increased complexities in the implementation of feedback and control. Dedicated passive or active circuitry is also required to mitigate the energy in the leakage inductance. The proposed topologies are non-isolated and hence are much simpler in implementation. The converters are suited for two nominal step-down conversions - (1) 170V-42V DC, (2) 170V-15V DC operation while maintaining a reasonable duty cycle and efficiency. Their operation is described in detail. Both the converters can be controlled to achieve active power factor correction. Simulation results with relevant parasitic are presented to verify the claimed step-down conversions.

Hybrid start-up strategy for low voltage electromagnetic energy harvesting systems

In this paper, a new strategy to provide start-up energy for low voltage energy harvesting systems is presented. There has been a lot of interest in electromagnetic microgenerators due to their high energy density for low power harvesting. However, they exhibit extremely low voltages of the order of few hundred millivolts AC. In recent years, a number of converters have been presented that can boost such low voltages to satisfy the load end requirements (1.8-3.3V DC). A key limiting factor has been a lack of proper start-up strategy for such systems. The present work involves the use of a hybrid set-up consisting of a piezo-strip to provide sufficient voltage for the start-up operation of the converter. An auxiliary DC supply is designed for the boost converter. The operation of this circuit is verified first using a battery and then, using the hybrid set-up. Simulation and experimental results are presented to verify the proposed system.