Review of Nonisolated High-Step-Up DC/DC Converters in Photovoltaic Grid-Connected Applications

The photovoltaic (PV) grid-connected power system in the residential applications is becoming a fast growing segment due to the shortage of the fossil fuel energy and the great environmental pollution. A new research trend in the residential generation system is to employ the PV parallel connected configuration rather than the series-connected configuration to satisfy the safety requirements and to make full use of the PV generated power. This paper mainly investigates and compares four dc-dc converters i.e. Conventional Boost Converter (CBC), Quadratic Boost Converter (QBC), Flying Capacitor Boost Converter (FCBC) and a new high step-up dc-dc converter in wide range power conversion from the aspects of silicon devices, passive components requirements, efficiency and cost. In the proposed topology a high voltage gain is achieved at relatively low duty ratio. Moreover, the stress on the power switches and the inductor size is reduced, which means the cost and the losses is minimized.

The objective of this paper is to establish the performance of 8 kWp grid-connected photovoltaic (PV) power systems based on different PV module technologies in Nanjing, China. Nanjing has a hot summer and a cold winter which are considered based on monthly average solar irradiation and ambient temperature specifically for the deployment of grid-connected PV systems. The study focuses on performance assessment of grid-connected PV systems using typical PV modules made of monocrystalline silicon (m-Si), polycrystalline silicon (p-Si), edge-defined film-fed growth silicon (EFG-Si), cadmium telluride (CdTe) thin film, copper indium selenide (CIS) thin film, heterojunction with intrinsic thin layer (HIT), and hydrogenated amorphous silicon single-junction (a-Si:H single-PV) installed on location. The yearly average energy output, PV module and system efficiency, array yield, final yield, reference yield, performance ratio, monthly average array capture losses, and system losses of seven PV module technologies are all analyzed. The results show that grid-connected PV power system performance depends on geographical location, PV module types, and climate conditions such as solar radiation and ambient temperature. In addition, based on energy output and efficiency, the HIT PV power technology can be considered as the best option and CdTe and p-Si as the least suitable options for this area. The monthly average performance ratio of the CdTe technology was higher than those of other technologies over the monitoring period in Nanjing.

Model of quasi-Z-source inverter-based PV power systems for stability studies of multi-terminal AC grid-connected PV power systems

A grid-connected photovoltaic (PV) power system with the high step-up ZVT interleaved boost converter is presented in this paper. For a typical PV module, the output voltage is relatively low. So the high voltage gain is obligatory to realize the grid-connected function. The proposed PV system employs a ZVT interleaved boost converter with an active-clamp circuit as the first power processing stage, which can boost a low voltage of PV array up to the high DC bus. And a full bridge inverter with bidirectional power flow is used as the second power processing stage, which can stabilize the DC bus voltage and shape the output current. Two compensation units are added to perform in system control loops and low THD of the current is achieved. In addition a simple sensor-less MPPT method is applied in the PV system and represents a good performance. At last, a 1.5-kW prototype was built and tested to verify the theoretical analysis of the paper.

As the energy crisis and the pollution are serious, the exploitation of solar has received more and more attentions. The configuration and principle of photovoltaic grid-connected power system are analyzed in detail. The method of maximum power point tracking is designed and the control principle of voltage and current double closed-loop is analyzed in this paper. At the same time an improved phase locked tracking method combined with software and hardware is presented. The experimental results show that the current waveform of grid-connected inverter has the same frequency and phase angle with the grid voltage, the power factor of grid-connected inverter is 0.999, which meets the design requirement entirely.

With the increasing of the capacity of grid-connected photovoltaic (PV) power system, islanding detection becomes more prominent and significant. At present, islanding detection methods used in grid-connected photovoltaic system can be divided into passive detection methods and active detection methods these two categories, which can also be divided into a variety of methods. This paper shows a comprehensive review of islanding detection methods, classifies the methods of islanding detection, analyzes the principles and characteristics of various islanding detection methods, indicates their appropriate situations, and pointes out the prospect of islanding detection methods. In practical applications, according to the actual situation, selects one or more islanding detection methods can attain better detection effect.

Chapter 9 - Grid-connected solar PV power systems

Techno-economic comparative study of grid-connected PV power systems in five climate zones, China

Until now, there is a great development in photovoltaic grid-connected power system. In addition, there is an ongoing research on the problems existed in the system. Islanding of photovoltaic grid-connected power system have adverse impact on power quality and utility equipments, affecting the performance of the utility even worse, it may damage people's lives. Islanding detection is a key consideration for grid-connected DG. The effects of islanding detection are not only subject to the strategy it employed, but also subject to the parameter setting. Non-detection zone (NDZ) is an important index to evaluate the performance of islanding detection. In this paper, the NDZs of active frequency drift and active frequency drift with positive feedback (AFDPF) are mapped into two different load space, i.e. L×C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">norm</inf> space and Q <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f0</inf> × C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">norm</inf> space. Based on it, theoretical deductions are given and simulations are developed to validate the discussions.

Photovoltaic (PV) power generation systems are one of the most promising renewable power sources to reduce carbon footprint. Grid-connected PV power systems do not generally have a battery to store the excess charge. However, due to severe imbalance between the peak PV power generation and peak load demand, battery-less Grid-connected PV systems are much less effective for the purpose of power generation and demand mismatch mitigation. Grid-connected PV systems equipped with a battery indeed require elaborate management. This is the first paper that introduces a systematic battery management optimization that accommodates arbitrary electricity billing policies. We formulate an optimization framework to determine the battery charging current from the Grid and PV array taking into account the limited battery capacity, power converter efficiency, battery's internal resistance and rate capacity effect, and maximum power tracking of the PV array. Experimental results show that the proposed algorithm effectively reduces the electricity bill by as much as 28% when compared with previous state-of-the-art battery management policies.

The connection of grid-connected photovoltaic (PV) power system brings to the consumer the benefit of having their demand partially supplied by solar energy, reducing the dependency of the utility and, consequently, obtaining some economy related with electricity costs. However, in a new reality, where there is the growth of grid-connected PV power system, the power flow undergoes changes related to the power quality of the grid, as imbalances between phases, overvoltage and power factor variation in the bar voltage. It was considering this current scenario that this work was established, in which was developed a program for load flow studies applied to an electric power radial distribution systems. The results show the voltage in the bars, the power flow, the power factor and the variation of the energy consumption in three distinct scenarios.

Nowadays, grid-connected photovoltaic (PV) power system is quite popular in many countries. For grid-connected PV power system, to achieve maximum power and good power quality of the system are considered as big challenges. In order to achieve this, artificial intelligent (AI) controller-based maximum power point tracking (MPPT) algorithm has been investigated for PV system as well as a new cascade multilevel inverter (MLI) is proposed for grid integration of PV system. The proposed cascade MLI has been designed with a smaller number of power electronic switches and it can be operated at asynchronous voltage sources, which is most adaptable for PV system. This proposed inverter can reduce the total harmonic distortion (THD) at output side by means of increasing the output voltage level with this power quality of the system has been improved. The microgrid integration of proposed inverter has been controlled by using AI-based voltage source controller and this proposed system is designed and simulated in MATLAB environment at various weather conditions and loading conditions. Finally, prototype model has been developed in laboratory and evaluating its performance. The simulation results and prototype results were verified with IEEE 1547 standard that proves the proposed system effectiveness.

Grid-connected photovoltaic power system is not only related to solar battery and grid inverter technology, but also involves the system control and optimization problem. The research and improvement about control technology play a vital role in improving the efficiency of the system and Realizing optimization grid. On the basis of considering about control requirements in grid-connected photovoltaic power system, the paper analyzes comprehensively the control technology about MPPT, grid of inverter and island detection. At last, the paper points out the research hotspots and development trend in each part.

This study presents a systematic way to evaluate reliability performance of large grid-connected photovoltaic (PV) power systems considering variation of input power and ambient-condition-dependent failure rates of critical components including PV modules, inverters, and capacitors. State enumeration is used to analyze real-life grid-connected PV systems. Ambient-condition-dependent failure rates of major components in PV systems are formulated and incorporated in reliability analysis. A series of reliability indices are defined to quantify PV systems' reliability performance. In addition, sensitivity analyses are extensively conducted to investigate the impact of different factors on the performances of PV power systems. Test results on a practical 20-kW PV project are presented to demonstrate the effectiveness of the proposed method.

In order to realize the solar photovoltaic (PV) system connecting with grid friendly, a PV system with voltage-controlled inverter based on virtual synchronous generator (SG) is presented. This kind of system has features of SG, which supply the virtual moment of inertia to grid. The mathematical model of PV and virtual SG is built, and the control strategy of the maximum power point tracking (MPPT) is also studied in the paper. Simulation model of the grid-connected PV power system is built on Matlab/Simulink. Finally, correctness and feasibility of this system are verified by simulation results.