Survey on Photo-Voltaic Powered Interleaved Converter System

Renewable energy is the best solution to meet the growing demand for energy in the country. The solar energy is considered as the most promising energy by the researchers due to its abundant availability, eco-friendly nature, long lasting nature, wide range of application and above all it is a maintenance free system. The energy absorbed by the earth can satisfy 15000 times of today’s total energy demand and its hundred times more than that our conventional energy like coal and other fossil fuels. Though, there are overwhelming advantages in solar energy, It has few drawbacks as well such as its low conversion ratio, inconsistent supply of energy due to variation in the sun light, less efficiency due to ripples in the converter, time dependent and, above all, high capitation cost. These aforementioned flaws have been addressed by the researchers in order to extract maximum energy and attain hundred percentage benefits of this heavenly resource. So, this chapter presents a comprehensive investigation based on photo voltaic (PV) system requirements with the following constraints such as system efficiency, system gain, dynamic response, switching losses are investigated. The overview exhibits and identifies the requirements of a best PV power generation system

A review of grid-tied converter topologies used in photovoltaic systems

This study provides review of grid-tied architectures used in photovoltaic power systems, classified by the granularity level at which maximum power point tracking (MPPT) is applied. Grid-tied PV power systems can be divided into two main groups, namely centralized MPPT (CMPPT) and distributed MPPT (DMPPT). The DMPPT systems are further classified according to the levels at which MPPT can be applied, i.e. string, module, submodule, and cell level. Typical topologies for each category are also introduced, explained and analyzed. The classification is intended to help readers understand the latest developments of grid-tied PV power systems and inform research directions

High-Efficiency Isolated Photovoltaic Microinverter Using Wide-Band Gap Switches for Standalone and Grid-Tied Applications

An isolated photovoltaic micro-inverter for standalone and grid-tied applications is designed and implemented to achieve high efficiency. System configuration and design considerations, including the proposed active-clamp forward-flyback resonant converter for the DC-DC stage and a dual-frequency full-bridge inverter for the DC-AC stage, are analyzed and discussed. A prototype microinverter system is built and tested. Experimental results verify the feasibility of the proposed system, which achieves 95% power conversion efficiency at full load

Interconnected Modular Multilevel Converter (IMMC) Using Wide Band Gap Devices for Multiple Applications

This dissertation proposes a high-power density Interconnected Modular Multilevel Converter (IMMC) with sinusoidal output voltage for multiple applications. The proposed converter utilizes wide band gap devices at a high switching frequency to achieve compact size/weight/volume. The proposed converter is modular in construction, employs high frequency L-C components and can be stacked for voltage sharing. The IMMC is proposed for motor drives applications due to the following advantages: sinusoidal output with adjustable voltage and frequency (v/f), no acoustic noise, low EMI and absence of dv/dt related issues due to long motor leads. Two design examples for low voltage drives using Gallium Nitride (GaN) devices and medium voltage drives using Silicon Carbide (SiC) are discussed in this dissertation. The proposed converter is also evaluated for solar micro-inverter applications due to its compact size and the high-quality output. The proposed system connects the inverter to the PV solar panel through a flyback converter for stepping up the voltage to the grid level, isolation and Maximum Power Point Tracking (MPPT). The proposed inverter eliminates the need for a bulky grid-tie inductor or complex LCL filter. The power can be injected to the grid using a small iron-core inductor due to the sinusoidal nature of the output voltage. A grid-tie control using Fictive Axis Emulation (FAE) is implemented on the converter to optimize the power injected to the grid. Moreover, a DC-AC IMMC to integrate two PV power plants through medium voltage DC collection grid (MVDC) system is proposed. The sinusoidal output of the IMMC facilitates the integration of the solar plants. The inductance required to connect the inverter to the grid is less due to the sinusoidal nature of the output of the IMMC

Low-Complexity Power-Balancing-Point Based Optimization for Photovoltaic Differential Power Processing

Differential power processing (DPP) is regarded as a promising architecture in solving mismatching issues among photovoltaic (PV) submodules. Although conventional total-minimum-power-point (TMPP)-based real-time optimization algorithm by using the distributed submodule-level maximum power point tracking and simultaneously the centralized total-minimum-power tracking shows effectiveness in maximizing the power yield. However, uneven power stress among DPP converters, large oscillations, high additional cost for communication among DPP converters, and complicated implementation hinder the practical application. This article proposed a low-complexity power balancing point-based optimization algorithm to reduce the system cost and size, improve the system efficiency, and realize the standardized modular design for DPP converters. Furthermore, simple submodule-level voltage equalization control is implemented to eliminate expensive communication and relieve the control complexity while guaranteeing high maximum-power-point efficiency. The proposed algorithm can reduce the power rating of DPP converters compared with conventional TMPP-based control, which is beneficial to the improvement of system cost, reliability, and lifetime. Both simulation and experimental results under various scenarios are provided to validate the advantages of the proposed algorithm

Investigation of a GaN-Based Power Supply Topology Utilizing Solid State Transformer for Low Power Applications

Gallium nitride (GaN) power devices exhibit a much lower gate capacitance for a similar on-resistance than its silicon counterparts, making it highly desirable for high-frequency operation in switching converters, which leads to their significant benefits on power density, cost, and system volume. High-density switching converters are being realized with GaN power devices due to their high switching speeds that reduce the size of energy-storage circuit components. The purpose of this dissertation research is to investigate a new isolated GaN AC/DC switching converter based on solid-state transformer configuration with a totem-pole power factor corrector (PFC) front-end, a half-bridge series-resonant converter (SRC) for power conversion, and a current-doubler rectifier (CDR) at its output. A new equivalent circuit model for the converter is constructed consisting of a loss-free resistor model for the PFC rectifier with first harmonic approximation model for the SRC and the CDR. Then, state-space analysis is performed to derive the converter transfer function in order to design the controllers to yield sufficient phase margins. The converter offers the advantages of voltage regulation feature of the solid-state transformer, low harmonics and close-to-unity power factor of the PFC rectifier, soft-switching of the half-bridge SRC, reduced size of the high-frequency transformer, and smaller leakage inductance of the CDR which is used for low-voltage high-current applications as the CDR draws half of the load current in the transformer secondary side yielding less copper losses. A high-frequency nanocrystalline toroid transformer, based on a modified equation to determine its leakage inductance, is designed and fabricated to satisfy the performance specifications of the converter. A meticulously planned gate driving strategy together with a Kelvin-source return circuitry is used to mitigate Miller effects, minimize gate ringing, and minimize the parasitics of the pull-down and pull-up loops of the converter. A new programming method that combines MATLAB Simulink embedded coder with code composer studio for the TMS320F28335 digital signal processor (DSP) controller is developed and demonstrated. Finally, the GaN-based AC/DC converter is experimentally verified for a 120Vac to 48Vdc/60Vdc conversion operating at 100 kHz for various loadings

Asynchronous differential power processing for true maximum power point tracking of photovoltaic sub-modules

This thesis examines maximum power point tracking (MPPT) at the photovoltaic (PV) sub-module level, but in the context of large arrays. Central communication carries large overheads, and neighbor-to-neighbor communication can have long propagation times in large arrays, so a communication-less solution was explored. An MPPT algorithm that could be run asynchronously was developed, and simulations confirmed its viability. Simulated tracking efficiencies of 99.977% and above were attained at steady-state. Next, a power electronics hardware prototype was designed to implement the MPPT algorithm. A differential power processing (DPP) architecture was used to achieve high system efficiencies. The efficiency of a single DPP converter reached a peak of 94.0%. In the laboratory tests performed, an increase in PV module power of up to 29.7% was observed using the proposed method when compared to no sub-module MPPT. Additionally, a long-term measurement system for a 12-module PV array was constructed. The system provided a safe, durable, and weatherproof mounting scheme for the power electronics and related circuitry. Furthermore, the setup allowed communication with the power electronics, so sub-module data could be collected and analyzed to determine the performance of the MPPT. Possible future work includes gathering more results, revising the circuit board, and simplifying the measurement system

Characterizing and Modeling Transient Behavior in Power Electronic Circuits with Wide Bandgap Semiconductors and in Maximum Power Point Tracking for Photovoltaic Systems

This dissertation examines the transient characteristics in next generation power electronic circuits at both the device-level and the systems-level. At the device-level, the effect of the parasitic capacitances on the switching performance of emerging wide bandgap semiconductors (WBG) is evaluated. Equivalent device models based on gallium nitride (GaN) and silicon carbide (SiC) are implemented in SaberRD and MATLAB, and transient switching characteristics are analyzed in great detail. The effects of the parasitic capacitances on detrimental circuit behavior such as “overshoot,” “ringing,” and “false turn-on” are investigated. The modeled results are supplemented and validated with experimental characterization of the devices in various power conversion circuits. The models can be used to aid in the design of next generation WBG devices so that the undesirable transient effects displayed by contemporary versions of these devices can be mitigated. At the systems-level, the transient overshoot demonstrated by conventional maximum power point tracking algorithms for photovoltaic power conversion systems is investigated. An adaptive controller is implemented so that the operating point can converge to the optimal power point rapidly with minimal overshoot. This new controller overcomes the parasitic components inherent to the power converter which limit its ability to deliver maximum power rapidly. It will be shown that with the new controller, the maximum power point is attainable in 4 milliseconds. The work accomplished in this dissertation lays a foundation for power electronic engineers to integrate semiconductor device theory with control theory to optimize the performance of next generation power conversion systems

Efficient, High Power Density, Modular Wide Band-gap Based Converters for Medium Voltage Application

Recent advances in semiconductor technology have accelerated developments in medium-voltage direct-current (MVDC) power system transmission and distribution. A DC-DC converter is widely considered to be the most important technology for future DC networks. Wide band-gap (WBG) power devices (i.e. Silicon Carbide (SiC) and Gallium Nitride (GaN) devices) have paved the way for improving the efficiency and power density of power converters by means of higher switching frequencies with lower conduction and switching losses compared to their Silicon (Si) counterparts. However, due to rapid variation of the voltage and current, di/dt and dv/dt, to fully utilize the advantages of the Wide-bandgap semiconductors, more focus is needed to design the printed circuit boards (PCB) in terms of minimizing the parasitic components, which impacts efficiency. The aim of this dissertation is to study the technical challenges associated with the implementation of WBG devices and propose different power converter topologies for MVDC applications. Ship power system with MVDC distribution is attracting widespread interest due to higher reliability and reduced fuel consumption. Also, since the charging time is a barrier for adopting the electric vehicles, increasing the voltage level of the dc bus to achieve the fast charging is considered to be the most important solution to address this concern. Moreover, raising the voltage level reduces the size and cost of cables in the car. Employing MVDC system in the power grid offers secure, flexible and efficient power flow. It is shown that to reach optimal performance in terms of low package inductance and high slew rate of switches, designing a PCB with low common source inductance, power loop inductance, and gate-driver loop are essential. Compared with traditional power converters, the proposed circuits can reduce the voltage stress on switches and diodes, as well as the input current ripple. A lower voltage stress allows the designer to employ the switches and diodes with lower on-resistance RDS(ON) and forward voltage drop, respectively. Consequently, more efficient power conversion system can be achieved. Moreover, the proposed converters offer a high voltage gain that helps the power switches with smaller duty-cycle, which leads to lower current and voltage stress across them. To verify the proposed concept and prove the correctness of the theoretical analysis, the laboratory prototype of the converters using WBG devices were implemented. The proposed converters can provide energy conversion with an efficiency of 97% feeding the nominal load, which is 2% more than the efficiency of the-state-of-the-art converters. Besides the efficiency, shrinking the current ripple leads to 50% size reduction of the input filter inductors