Power Electronic Converters for Single-Phase Grid Connected Photovoltaic System: An Overview

The Solar photovoltaic (PV) power system have achieved meteoric rise through the years. The uptake is not difficult to explain – a drop in cost of PV systems and spiraling electricity cost, have  encouraged the end-user to lessen their bills by producing cheaper electricity and can generate revenue  by feeding excess power back to the grid. The solar PV is intermittent in nature so it dependent on irradiance and ambient temperature. Power electronics technologies plays an important part for optimizing the energy harvesting from PV system. In order to get maximum extracted power and ensure the load is supplied with a good quality voltage, different dc-dc converters topologies and inverters configurations are used. This paper provides an overview of PV inverter configurations and DC-DC topologies to offer a useful insight and reference point for the researchers working in the field of photovoltaic system

Control Design of a Single-Phase DC/AC Inverter for PV Applications

This thesis presents controller designs of a 2 kVA single-phase inverter for photovoltaic (PV) applications. The demand for better controller designs is constantly rising as the renewable energy market continues to rapidly grow. Some background research has been done on solar energy, PV inverter configurations, inverter control design, and hardware component selection. Controllers are designed both for stand-alone and grid-connected modes of operation. For stand-alone inverter control, the outer control loop regulates the filter capacitor voltage. Combining the synchronous frame outer control loop with the capacitor current feedback inner control loop, the system can achieve both zero steady-state error and better step load performance. For grid-tied inverter control, proportional capacitor current feedback is used. This achieves the active damping needed to suppress the LCL filter resonance problem. The outer loop regulates the inverter output current flowing into the grid with a proportional resonant controller and harmonic compensators. With a revised grid synchronization unit, the active power and reactive power can be decoupled and controlled separately through a serial communication based user interface. To validate the designed controllers, a scaled down prototype is constructed and tested with a digital signal processor (DSP) TMS320F28335

Design and implementation of a dual-input single-output photovoltaic converter

In many solar inverters, a dc/dc converter is mainly located between the solar arrays and the inverter. This study presents an enhanced maximum power point tracking (MPPT) algorithm for photovoltaic (PV) systems that drives solar array voltages to track a reference value and decreases fluctuations and oscillations in PV voltage. Different from the previously presented methods, a novel MPPT method is proposed that ensures tracking accuracy by considering output voltage in addition to input voltage and currents. The proposed method detects dI/dV variations, compares the output voltage with the desired reference to shift operation mode and refreshes step size. The digital filtering, enhanced PI, and perturb-and-observe (P&O) tracking features of the proposed MPPT method make it robust to mitigate source fluctuations and sensitivity to partial shading based oscillations. In order to validate the success of the proposed method, a test rig has been installed with dual boost converters. The performance improvements have been verified by both simulation and experimental results that are compared to InCon and P&O MPPT methods. It is also confirmed by experimental results that the proposed MPPT method provides robust control capability in terms of tracking the reference voltage and rejecting the effects of various shading situations on solar arrays

Application of Modular Multilevel Converter for Interfacing Grid-Connected Photovoltaic Conversion Plants

This thesis investigates the applicability of the Modular Multilevel Converter (MMC) for interfacing grid connected photovoltaic conversion plants. A detailed three-phase 9-level simulation model is implemented in Simulink. Two control objectives are identified as distinctive for the MMC: Capacitor voltage balancing and suppression of circulating currents, both of which are included in the model. The MMC is controlled by a modified Level-Shifted Pulse Width Modulator. The model is verified by comparing its behaviour to that of the mathematical model of the MMC. The nature of photovoltaic power generation makes Maximum Power Point Tracking (MPPT) important to maximize the power yield from a pv module. All the pv modules connected to the same MPP tracker should have the same operating conditions. For largescale pv farms this is only feasible with multiple MPP trackers. Two pv inverter configurations are identified as suitable for grid connection of large-scale pv farms using the MMC: Cascaded dc-dc converters and multi-string inverter. With the former, the three phase legs share the same dc link voltage. With a multi-string topology, each submodule is fed by a separate pv string. Thus, power imbalance between the submodules are inevitable. This can be remedied by power imbalance compensation. For grid side control Synchronous Reference Frame Control (SRFC) and Model Predictive Control (MPC) is considered. MPC has the advantage of handling non-linear constraints on both states and variables. In addition it is reported to perform better than SRFC during dynamic conditions, which are likely to occur with power generation from pv modules. SRFC is implemented in the MMC simulation model. It synchronizes with the grid and delivers power at unity power factor

A Hybrid PV-Battery System for ON-Grid and OFF-Grid Applications—Controller-In-Loop Simulation Validation

In remote locations such as villages, islands and hilly areas, there is a possibility of frequent power failures, voltage drops or power fluctuations due to grid-side faults. Grid-connected renewable energy systems or micro-grid systems are preferable for such remote locations to meet the local critical load requirements during grid-side failures. In renewable energy systems, solar photovoltaic (PV) power systems are accessible and hybrid PV-battery systems or energy storage systems (ESS) are more capable of providing uninterruptible power to the local critical loads during grid-side faults. This energy storage system also improves the system dynamics during power fluctuations. In present work, a PV-battery hybrid system with DC-side coupling is considered, and a power balancing control (PBC) is proposed to transfer the power to grid/load and the battery. In this system, a solar power conditioning system (PCS) acts as an interface across PV source, battery and the load/central grid. With the proposed PBC technique, the system can operate in following operational modes: (a) PCS can be able to work in grid-connected mode during regular operation; (b) PCS can be able to charge the batteries and (c) PCS can be able to operate in standalone mode during grid side faults and deliver power to the local loads. The proposed controls are explained, and the system response during transient and steady-state conditions is described. With the help of controller-in-loop simulation results, the proposed power balancing controls are validated, for both off-grid and on-grid conditions

Modeling, Analysis, and Design of a PV-Based Grid-Tied Plug-In Hybrid Electric Vehicle Battery Pack Charger

Ever-increasing fossil fuels consumption in recent decades has emitted tremendous amounts of greenhouse gases, a big part of which cannot be absorbed by natural processes happening in nature. These gases have increased earth temperature by absorbing extra radiations from sunlight and turning them into heat. Global warming has had terrible effects for all creatures around the world and can threat life on Earth in future. Utilization of green or renewable energies during the recent years is getting more popular and can be a solution to this serious problem. A big source of these pollutants is transportation sector. Electrification of transportation can noticeably reduce greenhouse gasses if the electricity is obtained using renewable energy sources. Otherwise, it will just shift the problem from streets to fossil fuel power plants. Electric vehicles (EVs) were introduced around one century ago; however, they were replaced by internal combustion engine cars over time. Nevertheless, recently they are getting more interest because of their superior performance and clean operation. Solar electricity which can be obtained using photovoltaic panels is one of the easiest ways as long as sun is available. They can be easily mounted on the roofs of buildings or roof tops of parking slots generating electric power to charge the battery pack of the EVs while providing shade for the cars. Since solar energy is intermittent and variable, power grid should be involved to ensure enough power is available. Conventional solar chargers inject power to the grid and use grid as the main source because of its reliability and being infinite. Hence, they use grid as a kind of energy storage system. This approach can lead to problems for grid stability if solar panels are utilized in large scales and comparable to the grid. In this work, a solar powered grid-tied EV/PHEV charger is introduced which uses all the available power from PV panels as the main energy source and drains only the remaining required power from the grid. The proposed configuration provides great flexibility and supports all the possible power flows. To design an efficient system the load should be known well enough first. A comprehensive study has been done about behavior, characteristics and different models of different chemistries of batteries. Specific phenomena happening in battery packs are outlined. A novel maximum power point tracking (MPPT) technique has been proposed specifically for battery charging applications. A specific configuration involving DC link coupling technique has been proposed to connect different parts of the system. Different possible topologies for different parts of the proposed configuration have been considered and the suitable ones have been selected. Dual active bridge topology is the heart of this configuration which acts as the bidirectional charger. A detailed state space modeling process has been followed for the power converters and various small signal transfer functions have been derived. Controllers have been designed for different power converters using SISO design tool of Matlab/Simulink. Different modes of operation for the charger including constant current mode (CCM) and constant voltage mode (CVM) have been analyzed and appropriate cascade controllers have been designed based on required time domain and frequency domain characteristics. Finally, simulation tests have been conducted and test results have been graphed and analyzed for different modes of operation, all possible power flows and various voltage and current set points