Indranil Bhattacharya

Effects of Gallium-Phosphide and Indium-Gallium-Antimonide semiconductor materials on photon absorption of multijunction solar cells

The main challenge in the photovoltaic industry is making the solar cells more cost effective. Single junction solar cells can only absorb a certain wavelength of the solar spectrum, hence produce less efficiency. In contrary multijunction solar cells direct sunlight towards matched spectral sensitivity by splitting the spectrum into smaller slices. The high efficiency multijunction photovoltaics made up of III-V semiconductor material alloys with high optical sensitivity and ideal combination of band-gaps increase absorption of photons, creates more electron-hole pairs, and hence increase the efficiency of the solar cell. National Renewable Energy Laboratory (NREL), US Department of Energy (DOE) and many leading research organizations all over the world are investing money in the design of III-IV multijunction solar cell projects. In this paper, we introduce a novel multijunction photovoltaic cell based on GaP/InGaAs/InGaSb, and compare it with existing single-junction and multijunction cells. We observe that the inclusion of GaP and InGaSb layers in our design has made a significant improvement in absorption of solar energy in the entire spectral range, thus resulting in higher efficiency.

Regenerative electric power for More Electric Aircraft

The More Electric Aircraft (MEA) emphasizes the utilization of electrical power as opposed to hydraulic, pneumatic, and mechanical power for optimizing aircraft performance and life cycle cost. The main sources of regenerative energy in the more electric aircraft power distribution system are the aircraft actuation systems: ailerons, rudder, flaps, spoilers, horizontal stabilizers and others. Instead of dissipating the energy as heat, the regenerative electric energy from the motor drives can be stored in energy storage elements such as flywheels, ultra-capacitors and batteries. Using the Simcaps toolbox, an aileron model with the electro-mechanical actuator (EMA) is developed in Matlab/Simulink. This regenerative power system consisting of a synchronous generator, three-phase-to dc boost rectifier, EMA including an input filter, ESE and a bidirectional dc-dc converter interfacing with ESE is presented. A single-phase half-bridge bidirectional dc-dc converter is used in this configuration. Two power management control strategies are applied in this simulation study, load-leveling and load-following procedures. In both strategies, ESE compensates for the difference between the electric drive requirements and the power provided by power distribution bus. Considering some important factors, such as weight, size and durability of the ESE, the load-following control strategy appears to be the most suitable for a regenerative power system in the more electric aircraft.

Active filters for harmonics elimination in solar photovoltaic grid-connected and stand-alone systems

Power converters output signal harmonic control is currently becoming immensely important in medium and high power applications due to the development of new grid codes. Advancement in transistor technology has lead to significant changes from large thyristor-equipped grid-connected inverters to smaller and fast switching IGBT (Insulated Gate Bipolar Transistors) equipped converters. These IGBTs increases the power switching frequency in order to extract more energy and fulfill the grid connecting standards. Grid codes usually define a maximum allowed level for each specific harmonic and determine the maximum tolerated THD (Total Harmonic Distortion) of the output signals. Unfortunately, these IGBT-based power drivers generate harmonics that are subsequently transmitted into the power bus. The harmonics are normally eliminated by passive LC or RLC filters. However this passive filtering system has its own limitations. In this paper, we analyze the harmonics created by the IGBT-equipped converter using Fast Fourier Transform (FFT) analysis. The converters are connected to the PV (Photovoltaic) arrays and the utility grid for grid-connected applications and PV arrays & battery modules for stand-alone applications. Using a second-order Butterworth Filter we showed that the THD has been reduced from 32.59% to 1.59%.

Indium phosphide, indium-gallium-arsenide and indium-gallium-antimonide based high efficiency multijunction photovoltaics for solar energy harvesting

Multijunction solar cells direct sunlight towards matched spectral sensitivity by splitting the spectrum into smaller slices. The main challenge in the photovoltaic industry is to make the modules more cost effective. The high efficiency multijunction photovoltaics have played a very significant role in reducing the cost through concentrator photovoltaic systems being implemented around the world. For example National Renewable Energy Laboratory (NREL) and US Department of Energy (DOE) have funded several III–IV multijunction solar cell projects. In this paper we have introduced a new multijunction photovoltaic cell based upon InP/InGaAs/InGaSb, and performed a comparison of solar energy absorption, reflection and transmission with existing single-junction and multijunction cells being deployed around the world. The inclusion of InGaSb layer in the design has made a significant difference in absorption in the spectral range of 598nm-800nm, contributing to a higher efficiency of the solar cell.

Effective Energy Management of Hybrid AC-DC Microgrids with Storage Devices

This paper proposes a stochastic framework for the optimal operation and management of hybrid ac–dc microgrids (MGs) in the presence of renewable energy sources (RESs) and storage devices. Hybrid ac–dc MGs can provide benefit over the traditional ac MGs by elimination of inverting equipment and reducing power losses caused by the ac–dc convertors. A stochastic load flow based on an unscented transform is employed to model the uncertainties of active and reactive loads, market power price, wind turbine, and photovoltaic output power. Additionally, a new powerful optimizer based on crow search algorithm (CSA) is devised to search the problem space. The proposed method uses a new two stage modification method to increase the search ability of CSA when avoiding premature convergence. The feasibility and performance assessment of the proposed framework are examined on an IEEE standard test system.

An adaptive step size incremental conductance method for faster maximum power point tracking

Maximum power point (MPP) of a photovoltaic array changes with environmental conditions. To obtain the highest possible amount of power from a solar array it should be operated at MPP in its power-voltage curve. An adaptive step size approach along with the standard incremental conductance method is proposed in this paper. This algorithm includes a fixed step S, an exponential factor M and the incremental conductance in the feedback system. This arrangement dynamically changes the step size to obtain the MPP with lesser number of iterations than that of the conventional incremental conductance method. An optimized set of values for S and M was obtained after inspecting their impacts on the accuracy and speed of convergence. The design and analysis was done using Matlab software. This method can be implemented instead of the standard incremental conductance method for its faster convergence speed while maintaining the same level of accuracy.

A novel GaP/InGaAs/InGaSb triple junction photovoltaic cell with optimized quantum efficiency

The third generation photovoltaic technology mandates high efficiency and low cost. Efficiency will increase when the absorber becomes capable of absorbing more photons, leading to formation of excitons in the absorber. The proposed GaP/InGaAs/InGaSb triple junction solar cell is designed to convert more incident photons to electricity, executing higher internal quantum efficiency (IQE), promoting higher efficiency solar cells. The use of InGaSb (0.54 eV) as a bottom subcell layer empowers the collection of photons deeper in infrared spectrum. This paper presents the result of QE vs. wavelength of each subcell layer. We optimized IQE vs. wavelength by varying different parameters like thicknesses and diffusion lengths to attain higher efficiency and making the solar cells more cost-effective.

MNFIS and other soft computing based MPPT techniques: A comparative analysis

Maximum Power Point Tracking (MPPT) is the process of searching the voltage space for the optimal power generation and tracking the optimum as it changes. This paper presents a performance analysis of soft computing algorithms applied to this endeavor and a deployment recommendation based on performance goals. Specifically, fuzzy logic (FL) and artificial neural networks (ANN) were tested with direct and indirect converter control and compared against multiple metrics for fitness. Along the way a novel algorithm was also developed, deemed the Modified Neuro-Fuzzy Inference System (MNFIS). This algorithm incorporates the strengths of both FL and ANN MPPT while mitigating the weaknesses of either.

Indium Gallium Antimonide a better bottom subcell layer in III–V multijunction solar cells

An approach to modeling of III-V multijunction solar cell utilizing InGaSb as the bottom subcell layer and altering the band gaps of InGaP and InGaAs, a novel triple junction, has been presented which executes the ability to capture photons for wider range of the solar radiation spectrum than state-of-art multijunction designs and projects a theoretical efficiency of 34.33% under one sun concentration. InGaSb with a direct band gap of 0.54eV, internal quantum efficiency of more than 80% and the ability to capture photons in the near and far infrared zone up to 2200 nm has been demonstrated.

Simplified modeling of photovoltaic Maximum Power Point Tracking using MATLAB

In this paper, a simplified approach to modeling Maximum Power Point Tracking (MPPT) for photovoltaic (PV) applications, and a simple procedure for implementing an approximation to MPPT sometimes referenced as the “constant voltage” (CV) method, are presented. To develop these concepts, the photovoltaic source is first modeled. A simplified model of the means for adjusting the photovoltaic source operating point voltage and current is then presented for the case of a DC-DC converter, viewed as a variable load impedance for the PV source. Utilizing this simplified modeling approach, MPPT is then implemented to maximize the available PV output, using the CV procedure as the photovoltaic source irradiance is varied. Results are shown in the form of plots. In summary, it is shown that (1) a simplified modeling approach can yield insight into MPPT without focusing on complexities of system components, and (2) that the CV method can be a very effective alternative to more involved MPPT approaches such as perturb and observe, variable conductance, and other strategies.