Photovoltaic (PV) energy has grown at an average annual rate of 60% in the last five years, surpassing one third of the cumulative wind energy installed capacity, and is quickly becoming an important part of the energy mix in some regions and power systems. This has been driven by a reduction in the cost of PV modules. This growth has also triggered the evolution of classic PV power converters from conventional singlephase grid-tied inverters to more complex topologies to increase efficiency, power extraction from the modules, and reliability without impacting the cost. This article presents an overview of the existing PV energy conversion systems, addressing the system configuration of different PV plants and the PV converter topologies that have found practical applications for grid-connected systems. In addition, the recent research and emerging PV converter technology are discussed, highlighting their possible advantages compared with the present technology. Solar PV energy conversion systems have had a huge growth from an accumulative total power equal to approximately 1.2 GW in 1992 to 136 GW in 2013 (36 GW during 2013) [1]. This phenomenon has been possible because of several factors all working together to push the PV energy to cope with one important position today (and potentially a fundamental position in the near future). Among these factors are the cost reduction and increase in efficiency of the PV modules, the search for alternative clean energy sources (not based on fossil fuels), increased environmental awareness, and favorable political regulations from local governments (establishing feed-in tariffs designed to accelerate investment in renewable energy technologies). It has become usual to see PV systems installed on the roofs of houses or PV farms next to the roads in the countryside. Grid-connected PV systems account for more than 99% of the PV installed capacity compared to

An Overview of Recent Research and Emerging PV Converter Technology

Photovoltaic (PV) energy has grown at an average annual rate of 60% in the last five years, surpassing one third of the cumulative wind energy installed capacity, and is quickly becoming an important part of the energy mix in some regions and power systems. This has been driven by a reduction in the cost of PV modules. This growth has also triggered the evolution of classic PV power converters from conventional single-phase grid-tied inverters to more complex topologies to increase efficiency, power extraction from the modules, and reliability without impacting the cost. This article presents an overview of the existing PV energy conversion systems, addressing the system configuration of different PV plants and the PV converter topologies that have found practical applications for grid-connected systems. In addition, the recent research and emerging PV converter technology are discussed, highlighting their possible advantages compared with the present technology.

Grid-Connected Photovoltaic Systems: An Overview of Recent Research and Emerging PV Converter Technology

Global warming is the main driving force behind worldwide interest for the generation of bulk electrical energy from renewable sources. As a consequence of advancements in solar cell fabrication and converter technology, solar PV has emerged as one of the most promising renewable sources for bulk power generation. If the current commissioning rate continues, PV power would lead to the modification of several aspects of power system and could influence the stability of the system. This paper extensively reviews the technical challenges, on particular, the stability issues associated with the integration of large-scale PV into the power system. In addition, the paper also reviews the dynamic model of large-scale PV for stability studies as well as the grid codes for large-scale PV integration into the system. Finally, this paper summarizes the research findings about the technical solutions to overcome the power system stability challenges regarding the large-scale PV integration into the transmission and sub-transmission or medium voltage distribution system.

A review of key power system stability challenges for large-scale PV integration

Optimal placement of DG in radial distribution systems based on new voltage stability index under load growth

The installed capacity of photovoltaic (PV) systems globally reached 177 GW at the end of 2014 The annual rate of installations, 387 GW in 2014, continues to increase A large part of this is installed as residential systems connected to low voltage (LV) networks The majority of the LV distribution networks are radial, unbalanced with respect to loads and feeder structures and have high R/X ratios The large scale deployment of PV within the LV distribution networks is limited by voltage quality problems, particularly over voltages and unbalance Development of proper mitigation techniques is essential to effectively and efficiently manage high penetration of PV within the LV distribution networks A number of techniques have already been developed and implemented in LV distribution networks to alleviate those problems This paper provides an extensive review of the present status, impacts and technical challenges of PV penetration in LV distribution networks In addition, the review comprehensively examines the commercially available and emerging mitigation methods and provides a framework that systematically explores the full range of technical methods and limitations for PV impact mitigation These will provide a useful framework and strong point of reference for the researchers working further in this field

A review of high PV penetrations in LV distribution networks: Present status, impacts and mitigation measures

This paper introduces the domestic and foreign standards for interconnecting distributed resources with electric power systems, and compares the contents of power quality, response to abnormal conditions, power control, voltage regulation and the ability of fault ride-through in some typical standards. Some items in wind power generation and photovoltaic power generation standards are concretely introduced. The cause of the difference between the standards is analyzed, and the development trend of the future standards for interconnecting distributed resources with electric power systems is discussed. This paper provides reference for the further improvement of the standards for grid-integration of distributed resources.

Study and comparison on standard for interconnecting distributed resources with electric power systems

In the case of unbalanced power grid, the grid-connected inverter with traditional control strategies will produce a large amount of harmonics at both the dc side and ac side, and then lead to fluctuations in power and performance deterioration. Therefore, more effective control is needed to improve the capability and functionality of grid-connected inverter interfaced distribute generator (IIDG). To overcome the problem, this paper analyzes the impacts of different control objectives on the inverter output power and grid current, presents a unified reference current vector expression, and proposes a control method that combines the dual current control loop for positive and negative sequence and linear reactive power control. The control strategy can effectively adjust the voltage at the point of common coupling, reduce the imbalance of the system, and the ability of the inverter is enhanced. The simulation results validated the effectiveness of the proposed method.

Research on control strategy of grid-connected inverter under unbalanced voltage conditions

Mechanism analysis and unified calculation model of exergy flow distribution in regional integrated energy system

With the increasing installed capacity of renewable energy in the energy system, the uncertainty of renewable energy has an increasingly prominent impact on power system planning and operation. Renewable energy such as wind and solar energy is greatly affected by the external weather. How to use a reasonable method to describe the relationship between weather and renewable energy output, so as to measure the uncertainty of renewable energy more accurately, is an important problem. To solve this problem, this paper proposes a renewable energy scenario generation method based on a conditional generation countermeasure network and combination weighting method (CWM-CGAN). In this method, the combination of AHP and the entropy weight method is used to analyze the meteorological factors, the weather classification is defined as the condition label in the conditional generation countermeasure network, and the energy scenario is generated by the conditional generation confrontation network. In this paper, the proposed method is tested with actual PV data, and the results show that the proposed model can describe the uncertainty of PV more accurately.

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CWM-CGAN Method for Renewable Energy Scenario Generation Based on Weather Label Multi-Factor Definition

Integrated energy systems are one of the main technologies to address the issue of renewable energy consumption. Existing studies have discussed the impact of renewable energy on integrated energy systems from an energy perspective, but not from an energy quality perspective. Firstly, this paper summarizes the exergy flow mechanism model of the integrated energy system. Then, the exergy flow calculation method is proposed for wind turbines, distributed ground source heat pumps, and distributed hydrogen injection. Finally, a sensitivity analysis of distributed renewables in a typical case study. The impact of three types of distributed renewable energy on the energy quality of an integrated energy system is described.

Jiaxi Li

Papers

Study and comparison on standard for interconnecting distributed resources with electric power systems

Research on control strategy of grid-connected inverter under unbalanced voltage conditions

Mechanism analysis and unified calculation model of exergy flow distribution in regional integrated energy system

CWM-CGAN Method for Renewable Energy Scenario Generation Based on Weather Label Multi-Factor Definition

Calculation and Analysis of the Exergy Flow of an Integrated Energy System with Distributed Renewable Energy