Raghav Khanna

Maximum Power Point Tracking Using Model Reference Adaptive Control

This paper proposes an adaptive control architecture for maximum power point tracking (MPPT) in photovoltaic systems. MPPT technologies have been used in photovoltaic systems to deliver the maximum available power to the load under changes of the solar insolation and ambient temperature. To improve the performance of MPPT, this paper develops a two-level adaptive control architecture that can reduce complexity in system control and effectively handle the uncertainties and perturbations in the photovoltaic systems and the environment. The first level of control is ripple correlation control (RCC), and the second level is model reference adaptive control (MRAC). By decoupling these two control algorithms, the system achieves MPPT with overall system stability. This paper focuses mostly on the design of the MRAC algorithm, which compensates the underdamped characteristics of the power conversion system. The original transfer function of the power conversion system has time-varying parameters, and its step response contains oscillatory transients that vanish slowly. Using the Lyapunov approach, an adaption law of the controller is derived for the MRAC system to eliminate the underdamped modes in power conversion. It is shown that the proposed control algorithm enables the system to converge to the maximum power point in milliseconds.

An analytical model for evaluating the influence of device parasitics on Cdv/dt induced false turn-on in SiC MOSFETs

Reported here is an analytical methodology for modeling the Cdv/dt induced false turn-on in SiC MOSFETs. A Cdv/dt test circuit is utilized to assess the influence of the parasitic device parameters on the magnitude of the induced gate-source voltage during false turn-on. The effect that each parasitic parameter has on the damping of the SiC MOSFETs drain-source voltage is also evaluated. Experimental results are provided to validate the analytical model. The methods presented here will enable design engineers to project the performance of next generation SiC MOSFETs in high dv/dt circuits like the synchronous buck converter.

Optimized carrier based multilevel generated modified dual three-phase open-winding inverter for medium power application

This paper presents a novel carrier based multilevel modulation for modified dual three-phase open-winding inverter applicable for low-voltage/high-current applications. A standard three-phase voltage source inverter (VSI) is connected across the open-winding of both ends of the motor. Each VSI incorporates an additional bi-directional switching device (MOSFET/IGBT) per phase and all three legs link to the neutral of two capacitors in the power circuit. An original optimal double carrier zero-shifted five-level modulation (DCZ SFM) algorithm is also presented and is used to modulate each VSI in a similar way to a 5-level multilevel inverter. The complete model based system is simulated in Matlab/PLECS softwares and set of results are presented which shows good conformity with the theoretical analysis.

Effects of parasitic capacitances on gallium nitride heterostructure power transistors

The parasitic capacitances of GaN have been evaluated in order to assess the impact that each capacitance has on the switching losses of GaN devices. This required developing and validating equivalent GaN HFET device models in SaberRD and implementing the models in a switching test circuit under variable parasitic capacitance conditions. The data presented here can facilitate optimizing the area and hence capacitance of GaN devices for future generation power electronics.

Characterization and Modeling of 10-kV Silicon Carbide Modules for Naval Applications

This paper presents a detailed characterization and modeling effort applied to a set of 10-kV SiC MOSFET modules, which have not been exhaustively described in the literature to date. This paper builds on a previous effort by the authors, in which an empirical performance evaluation was performed using a reduced-scale variant of the medium-voltage direct current (MVDC)-rated SiC MOSFET module. In this paper, full-scale module samples are used, which are capable of continuous operation at 120 A. Thus, the evaluation provided here offers improved relevance to the category of full-scale MVDC applications of which future naval shipboard power systems are expected to be a part. The evaluation effort described here considers both the static and dynamic performances of the considered 10-kV SiC MOSFET module, along with the identification of integration considerations that will be of use to designers of future applications based on this technology. Specific contributions of this paper that belong to this category include the presentation of a custom gate-drive circuit designed to operate the modules under consideration and the presentation of a detailed behavioral simulation model created to predict the performance of the same. The output of this model is compared with experimental waveforms captured during pulsed switching experiments at a bus voltage of 2 kV and a load current of 100 A. The simulation output is demonstrated to offer good agreement with the experimental waveforms during both turn-on and turn-off transitions. The availability of such a model is important because it makes possible the execution of a wide range of feasibility and trade studies for future applications by researchers without physical access to this technology.

Modeling and characterization of a 300 V GaN based boost converter with 96% efficiency at 1 MHz

Presented here is experimental and simulated demonstration of a 96% efficient GaN based synchronous boost converter switching at 1 MHz. First, experimental implementation of the GaN based boost converter with 96% efficiency is established. A behavioral model of the GaN transistor is then developed in Saber, by reproducing five experimentally measured DC characteristics. The GaN device model is subsequently implemented in the same synchronous boost converter topology as in experimentation. It will be shown that the simulated converter topology, which consists of the GaN device models, is also capable of delivering power at an efficiency of at least 96%. Thus, the validated device model presented here will be utilized in the future to project the performance of the GaN transistors in larger more complex power conversion circuits, such as those often implemented in automotive and renewable energy applications.

Analytical and experimental optimization of external gate resistance for safe rapid turn on of normally off GaN HFETs

This paper presents an analytical framework, supplemented with experimental validation, for optimizing the value of the external gate resistance employed in power conversion circuits using EPC enhancement-mode GaN transistors. A second order analytical model of the GaN device is utilized to determine a function that relates the external gate resistance to the peak gate voltage during turn-on. The results obtained from the analytical model were experimentally validated in a double pulse-test. The derived model allows for optimal selection of gate resistances such that GaN HFETs can be switched as rapidly as possible while keeping them in their safe operating region.

Comparison of GaN and Si-based photovoltaic power conversion circuits using various maximum power point tracking algorithms

In this paper, several maximum power point tracking algorithms are implemented in both GaN-based and Si-based photovoltaic power conversion systems. Due to their simplicity and versatility, the algorithms chosen for this study include the constant voltage method (CVM), perturb and observe (P&O), and incremental conductance (INC). Each of these algorithms is implemented in GaN-based and Si-based boost converters to extract maximum power from a PV panel. When irradiance on the panel is increased from zero to its maximum level, each converter utilizes the algorithms to track this change and reach the maximum power point. It is noted that the improved efficiency of the GaN device over the Si device is not algorithm dependent and thus algorithms implementable on a Si-based converter are anticipated to be implementable on a GaN-based converter with increased efficiency and enhanced convergence.

An inexpensive, battery powered and portable instrument for the optical detection of pathogens

In order to satisfy an emergent demand in point of care (POC) diagnostics as well as low resource settings such as in developing countries, we have integrated optical and bio-medical engineering to implement a device, which detects pathogens and displays test results using cell phones. The device employs DNA amplification and off-the-shelf components to obtain the diagnosis.

Low Cost, Battery Powered Optical Detection of Pathogens

To satisfy an emergent demand in developing countries, we integrated optical and bio-medical engineering to implement a device which detects pathogens. The device employs DNA amplification and off the shelf components to obtain the diagnosis.