Grid-connected Photovoltaic Research Articles

Three-Phase Transformerless Inverter for Photovoltaic Grid Connected System with Zero Common Mode Noise

The pervasion of transformerless grid connected photovoltaic (PV) inverters has triggered the concerns of many researchers since it can induce power quality problems. In these types of applications, the generation of common mode (CM) leakage current is one of the major factors that affects the reliability of the overall design. In single-phase systems, the concept of the common ground between the PV negative terminal and the neutral point of the grid is the only topology that “totally” cancels this CM noise. However, none of the existing three-phase inverter techniques is able to totally remove it. Therefore, this paper proposes a three-phase PV inverter based on the concept applied in the single-phase system in order to achieve, for the first time, a zero CM noise in three-phase grid-connected PV applications. The proposed inverter is simulated with a PV array, appropriate modulation technique, corresponding inverter controller, and a three-phase Y-connected alternating current (AC) grid voltage. The simulation of the overall system is done using Matlab/Simulink software. As compared with results of existing three-phase topologies, this is the only three-phase transformerless PV inverter technique that offers generation of multilevel output, total elimination of leakage current flow, simple inverter structure, and uncomplicated modulation technique.

Design and Real-Time Implementation of Cascaded Model Reference Adaptive Controllers for a Three-Phase Grid-Connected PV System

This article proposes the development of a model reference adaptive controller (MRAC) for grid integration of a single-stage three-phase grid-connected photovoltaic system (GCPVS). The performance of a GCPVS is influenced by uncertainties such as measurement noise, solar irradiance, photovoltaic (PV) operating point, aging of the dc-link capacitor, and variation in the filter impedance. In order to achieve the desired tracking performance under both nominal and parametric uncertainties, MRACs are designed for both the outer PV voltage control loop and the inner grid current control loop. The proposed control scheme comprises a reference model and a Lyapunov-based parameter adaptation scheme, which provides the nominal tracking performance despite uncertainties in the GCPVS dynamics. As a result, improved performance of the GCPVS is achieved in terms of low dc-link voltage ripple, superior power extraction, and improved grid power quality. The performance of the proposed adaptive controller is verified by pursuing simulation in MATLAB/Simulink followed by experimentation on a 2.5-kW GCPVS. The control algorithm is implemented in real time on the SPARTAN-6 FPGA scheme. The efficiency of maximum power point tracking (MPPT) is obtained as 99.92%. The total harmonic distortion of grid currents and voltages at the point of common coupling is found to be less than 3%, which is well within the limit specified by the IEEE-1547 standard.

Review of Electricity Distribution Codes and PV Connection Codes

Electricity is the key driver of the global economy. It is the prime energy resource for supplying customers (industry, irrigation, commerce, service, residence, etc.). This paper discusses technical requirements for Electricity Distribution Codes in various countries. The major similarities and differences between Electricity Distribution codes are clarified. Then, a detailed comparison of photovoltaic systems grid connection codes is presented. The comparison includes voltage and frequency deviations, active and reactive power control, power factor control and fault ride through.

Techno-Economic Performance Analysis of a 40.1 kWp Grid-Connected Photovoltaic (GCPV) System after Eight Years of Energy Generation: A Case Study for Tochigi, Japan

In this paper, the grid-connected photovoltaic system in Tochigi prefecture, Japan, is presented, and its technical and economic performance after eight years is evaluated. The system has a peak power of 40.1 kWp and has been in operation since 2012. The entire electricity generated by the system was fed into the state grid. The system is suitably monitored for one year (2019) and analyzed using the parameters developed and defined in the standard IEC 61724-1 by the International Electrotechnical Commission. The system’s different parameters included array yield, final yield, capacity utilization factor, and performance ratio of the system. An analytical model with solar irradiation obtained from Power Data Access Viewer was developed to investigate and evaluate the efficiency of the system monthly and annual energy generation by comparing the simulated and measured energy acquired from the inverter. A positive linear relationship is observed between solar irradiation data obtained from Power Data Access Viewer and the grid-connected photovoltaic system energy injected into the utility grid. While an annual total of 48,521 kWh of energy was expected to be generated, 38,071 kWh was generated and injected into the utility in 2019. This study also introduces and explains the mechanism of the Feed-In-Tariff system in Japan. The performance of the grid-connected photovoltaic system under this study was compared with that of other systems installed across the globe.

Design of Grid-connected and Stand-alone Photovoltaic Systems for Residential Energy Usage: A Technical Analysis

Towards realizing the United Nations sustainable development goals, access to clean, cheap and reliable energy, especially electricity, has been considered as one of the vital indices in any community. Hence, this paper presents the design analysis of both a grid-connected and an offgrid photovoltaic (PV) systems for household users in the highly residential city of Ogbomoso in Nigeria using PVGIS software. For the off-grid design, it is estimated that, given a total daily load of 9.57 kWh, a 3.5 kWp PV array size and a battery capacity of 86 kWh are enough to power the load with 5 days of autonomy and 70% depth of battery discharge. For the grid-connected PV system, the annual energy output for a building-integrated PV system is found to be around 4006 kWh; and a total of eight PV modules (each rated 250 Wp, 30.93 V) are stringed to arrive at the desired capacity of 2 kWp. In terms of performance, the performance ratio (PR) of a building integrated grid-tied PV system at the study location was found to be 71.2% while for a free-standing PV system, the PR was 75%.

Acceptance Ratio Analysis: An Early Fault Indicator for Grid-Connected Photovoltaic System

This paper presents the Acceptance Ratio (AR) analysis for three different grid-connected photovoltaic (GCPV) systems working under the Malaysia tropical climate. AR is a ratio between actual AC power, PAC_actual, and predicted AC power, PAC_predicted. According to Malaysian Standard MS2692:2020,the AR value must ≥ 0.9 to classify as accepted in testing and commissioning test. In contrast, a rate < 0.9 indicates a non-accepted GCPV system. Historical data of the AC power output, solar irradiance, and module temperature from January 1 to December 31, 2019, were used for the analysis. The analysis procedure was carried out using Matlab and Microsoft Excel software. The analysis covers the AC power analysis and the AR analysis based on the threshold of 0.9. The plotted monthly AC power graph shows that all systems have lower than 15 % differences between actual and predicted AC power. On the AR analysis, System 1 was found to show early fault indicator with a monthly cumulative percentage of AR < 0.9 ranges from 34 % to 71 %, meanwhile System 2 and System 3 have a lower cumulative percentage of AR < 0.9 ranges from 5 % to 19 %. This result suggested that only System 2 and 3 are fault-free GCPV systems and working in good condition. The outcome of this study has succeeded in providing preliminary AR analysis results for three GCPV systems located in Malaysia. This study would help to evaluate AR threshold reliability to indicate an early fault of a GCPV system.

Techno-Economic Analysis of Grid-Connected PV System for a Location in Perlis, Malaysia

Hybrid Renewable Energy System (HRES) is a system that comprises of multiple renewable generations with backup generation such as diesel generator or battery system. Currently, most of the remote areas depends on diesel generator for energy. However, diesel releases high amount of CO2. Moreover, diesel prices also are high and fluctuates according to the global market price. Hence, techno-economic analysis of a HRES system of grid-connected photovoltaic (PV) were conducted using Hybrid Optimization of Multiple Energy Resources) software (HOMER. The analyses include inputs such as load demands and renewable resources. The results include Net Present Cost, capital investment, renewable energy fraction, Cost of Energy and CO2 emissions. Multiple configurations will be assessed that suited best for the selected location.

A multi-objective optimization model for sizing decisions of a grid-connected photovoltaic system

Greenhouse gasses are by-products of using fossil fuels to generate energy. It is known that climate change is caused by an increase in greenhouse gasses in the Earth's atmosphere. Solar energy is a renewable energy source that is an environmentally friendly resource for generating power. The photovoltaic (PV) system is a well-established technology for transforming solar energy into electric power. Sizing-decisions of a PV system is a strategic decision-making process that has a long-term impact on the project. This work proposes a multi-objective optimization (MOO) model for sizing-decisions of a grid-connected PV system. The objectives consider the economic aspect in terms of minimizing the project lifespan costs and non-economic aspects, including maximizing system reliability and reducing CO2 emissions. The sizing decisions are the number of PV panels, the amount of energy purchased from the main grid, and the amount of energy supplied to the main grid. In addition to a binary variable for an either-or decision, either purchase or supply from the grid. The model generates Pareto-optima to assist the decision-maker in assessing trade-offs between alternatives. A case study based on monthly demand for the residential area at King Fahd University of Petroleum & Minerals (KFUPM) is provided to clarify the practicality of the model. It is found that 1713 PV modules are required to meet annual demand at an annual cost of M$1.61 over 25 years.

Design and Performance Analysis of Grid Connected Photovoltaic (GCPV) based DSTATCOM for Power Quality Improvements

Solar energy has become the most prominent renewable energy for electrical power generation of the sustainable development agenda. This project focuses on power quality improvement in the low voltage distribution network by using a three-phase three-wire Distributed Static compensator (DSTATCOM) supplied by a single-stage grid-connected solar photovoltaic (GCPV) system. The instantaneous reactive power theory (IRPT) or P-Q theory will be used as the control algorithm of the PV based DSTATCOM to eliminate the harmonic current caused by the non-linear loads in the distribution system. This control method has great impact on the accuracy of the harmonic current and reactive power compensation for harmonic current elimination according to the requirement of THD limit set by IEEE 519-2014. Sizing of the grid-connected solar PV system based DSTATCOM will be presented and capable to deliver the active power demand to the utility grid under variation of solar irradiances. This system is modelled and simulated in the MATLAB/Simulink environment.

Control of Transformerless Inverter-Based Two-Stage Grid-Connected Photovoltaic System Using Adaptive-PI and Adaptive Sliding Mode Controllers

To enhance the move towards a sustainable society, the solar Photovoltaic (PV) industry and its applications are progressing at a rapid rate. However, the associated issues need to be addressed when connecting PV to the grid. Advanced and efficient controllers are required for the DC link to control the second harmonic ripple and current controllers to inject quality active and reactive power to the grid in the grid-connected PV system. In this paper, DC-link voltage, active power, and reactive power are successfully controlled in stationary reference using Adaptive-PI (A-PI) and Adaptive-Sliding Mode Controller (A-SMC) for a 3 kW single-phase two-stage transformerless grid-connected inverter. A Resonant Harmonic Compensator (RHC)-based Proportional Resonant (PR) controller is employed in the current-controlled loop. The magnitude, phase, and frequency information of the grid voltage are provided by Second-Order General Integral (SOGI)-based PLL that has harmonic immunity, fast-tracking accuracy, and a rapid-dynamic response. MATLAB®/Simulink®/Simscape R2017b were used for the test bench implementation. Two scenarios were considered: in the first case, the input PV power feedforward loop was avoided, while in second case, it was included. The feedforward loop of input PV power improved the overall system dynamics. The results show that the designed controller improves both the steady-state and dynamic performance as compared with a proper-regulated PI-controller. The proposed controllers are insensitive to active and reactive power variations, and are robust, stable, faster, and fault tolerant, as compared to controllers from prior studies.

An energy balancing strategy for modular multilevel converter based grid‐connected photovoltaic systems

Modular multilevel converters (MMC)s are promising candidates for large-scale grid-connected photovoltaic (PV) systems. Due to their modular structure, MMCs provide a direct connection of the PV arrays to the converter submodules. They also offer scalability, independent maximum power point tracking, and enhanced power quality with internal power flow capabilities. However, the intermittent nature of PV arrays introduces a power unbalance inside the converter, which affects its operation. This paper addresses the issue and proposes an energy balancing strategy for the grid-connected MMC-based PV system. It uses the internally generated leg currents to control the power flow inside the converter and inject a three-phase balanced current to the grid with low total harmonic distortion. Compared to the existing strategies, the proposed strategy can overcome any condition of the power unbalance with minimal submodule voltage fluctuations. A 162-kW, 9-kV PV grid-connected system is modelled and simulated in MATLAB Simulink environment. The corresponding results are presented to demonstrate the effectiveness of the proposed control strategy for grid-connected PV systems.

Evaluation and Analysis of Soft Computing Techniques for Grid Connected Photo Voltaic System to Enhance Power Quality Issues

The major problem in grid connected transmission and distribution networks are the power quality issues due to the unbalance loads. The power quality issues relate to the current and voltage based issues generated at the point of common coupling. Some of the current based power quality issues relate to reactive power extraction, poor zero voltage regulation, harmonics in the load currents undesired neutral current and power factor and. Several DSTATCOM compensation techniques has been introduced for compensation of reactive power and power quality issues in the three phase, four wire system. The proposed system focus on DSTATCOM soft computing techniques such as: Widrow–Hoff least mean square, vectorial filter, discrete adaptive filter and quasi Newton control algorithms. The proposed algorithms controlled the switches pulses to drive the voltage source converter section in the DSTATCOM network thereby mitigating power quality issues and reactive power generation in the grid connected photovoltaic system. The soft computing techniques has maintained constant DC bus capacitor voltage and common coupling voltage along with unity power factor, zero voltage regulation under linear and non-linear load conditions, eliminating the harmonics in the load currents. The proportional integral controller is used for error correction between the reference and capacitor voltage. The novel drift-free maximum power point technique has shown better results under varying temperature and irradiances conditions. The DSTATCOM soft computing techniques has been implemented and simulated in MATLAB/SIMULINK.

Research on Optimal Strategy of Peak-shaving of Photovoltaic Grid-connected System Based on Simulated Annealing-Q Learning Algorithm

In order to alleviate the problem of large-scale grid-connected photovoltaics and increase the pressure of grid peak regulation, this paper proposes a dynamic economic dispatch method considering the system peak regulation margin. The system peak shaving margin is proposed to deal with the flexibility problem in economic dispatch and improve the enthusiasm of thermal power unit peak shaving. The economic dispatch model is transformed into a dynamic programming model and solved by the simulated annealing-Q learning algorithm. The analysis of the results shows that the proposed dynamic programming strategy can effectively improve the operating economy of the system and increase the flexibility of peak shaving of thermal power units.

Grid-Connected PV Systems Controlled by Sliding via Wireless Communication

Grid-connected photovoltaic (PV) systems are designed to provide energy to the grid. This energy transfer must fulfil some requirements such as system stability, power quality and reliability. Thus, the aim of this work is to design and control a grid-connected PV system via wireless to guarantee the correct operation of the system. It is crucial to monitor and supervise the system to control and/or detect faults in real time and in a remote way. To do that, the DC/DC converter and the DC/AC converter of the grid-connected PV system are controlled wirelessly, reducing costs in cabling installations. The used control methods are the sliding for the DC/DC converter and the Proportional-Integral (PI) for the inverter. The sliding control is robust, ensures system stability under perturbations, and is proven to work well via wireless. The PI control is simple and effective, proving its validity through wireless too. In addition, the effect of the communications is analysed in both controllers. An experimental platform has been built to conduct the experiments to verify the operation of the grid-connected PV system remotely. The results show that the system operates well, achieving the desired values for the maximum power point tracker (MPPT) sliding control and the energy transfer from the inverter to the grid.

Monitoring, measured and simulated performance analysis of a 2.4 kWp grid-connected PV system installed on the Mulhouse campus, France

This paper presents the performance analysis of a 2.4 kWp grid-connected photovoltaic (PV) system installed in August 2018 at the Institute University of Technology (IUT) in Mulhouse, France. The analysis covers the results obtained from system monitoring from August 2018 to May 2020. Various performance parameters in accordance with the International Energy Agency IEC 61724 standard were calculated from the measured results, including the PV energy output and yield factor (YF), capacity utilization factor (CUF) and the avoided CO2 emissions. Then, the 2.4 kWp PV grid connected system is simulated using three widely used PV simulation software (PVGIS, PV Watts, and HOMER). The results obtained in terms of YF and CUF were compared with the results of PV systems installed on different continents (Europe, Asia and, Africa). The energy produced is estimated at 968.43 kWh, 3246.47 kWh and 1382.75 kWh for the 2018, 2019 and 2020 operating periods, respectively. For the year 2019, the PV system produces a YF of 3.75 kWh/kWp and a CUF of 15.65%. The total energy over the lifetime of the system and the amount of CO2 emissions avoided are 5597.65 kWh and 4.17 tons, respectively. Finally, the simulation results obtained by the three software are compared to the actual performance of the system. Regarding the measured values, the results of PV Watts and HOMER are close and both give underestimated values with an annual YF average of 1250.33–1250.83 kWh/kWp and a CUF of 14.36–14.27%, respectively. However, the results predicted by the PVGIS software are overestimated compared to the measured performance.

Optimal power reallocation of large-scale grid-connected photovoltaic power station integrated with hydrogen production

With the consumption of fossil fuels and the aggravation of environmental pollution, the use of photovoltaic (PV) power to produce hydrogen is of great significance to improve power utilization and promote cleaner production. Determining the optimal power and capacity allocation is an urgent problem in the planning and construction stages of hybrid systems. This study focused on exploring a universal method for determining the power reallocation and capacity configuration for a grid-connected PV power station integrated hydrogen production system. First, considering the PV output characteristics and electricity transmission requirements, a model for determining the grid connection dispatch with the objective of minimizing PV curtailment was constructed. The operational control strategies of the hydrogen system considering the hydrogen production process under different storage configurations were proposed. Then, an optimal capacity decision method considering grid connection modes, hydrogen storage, and transportation modes, and hydrogen transportation distance was formed. Finally, a case study on the 100 MW PV demonstration base in the Qinghai province of China was used to confirm their feasibility. The results indicated that: (1) the liquid hydrogen is more suitable for long-distance transportation, and the 5-segment mode is best for grid connection; (2) the optimal capacity configurations for the hydrogen production system under the 5-segment grid connection mode were three sets of 800 Nm3/hr electrolyzers and 3 MW of the liquefier; and (3) when the transportation distance is 3000 km, the net present value (NPV) of the entire life cycle is $15.85 million, which is about four times that of the PV demonstration base only for grid connection ($3.83 million), and the annual hydrogen output is 7.01 million Nm3, which can reduce CO2 emissions by 7.72 thousand tons. Thus, the method has important guiding significance for reducing carbon dioxide emissions and realizing cleaner production.

Performance analysis and investigation of a 6 MW grid-connected ground-based PV plant installed in hot desert climate conditions

This paper experimentally analyzed and investigated 12-months of a 6 MW grid-connected photovoltaic (PV) plant mounted on a ground-base in Zaouiet Kounta (27°13′00" N, 0°12′00" W), southern Algeria. According to the Koppen-Geiger climate classification, the Adrar region is a hot desert climate. The performance ratio and several main normalized parameters (system efficiency, capacity factor, and system and total losses) were calculated according to IEC 61,724 standards. Additionally, the assessment and analysis of the degradation rate were limited to a one-year data. The results can be used to improve the prediction of future large-scale photovoltaic plants mounted in hot desert climates and could help in designing, operating and maintaining new grid-connected systems.

Inverter Performance in Grid-Connected Photovoltaic System

Inverter, as one of photovoltaic (PV) system’s component coordinates various operating states such as supplying power to the grid, purchasing electricity from the grid and self-supply with solar power. Since we notice that PV power supply is a one-way process, where current only flows from PV generator in one direction directly into the grid and gradually coming to an end. In its place, self-supply with solar power is gaining important. In medium voltage range, particularly inverters are also increasingly undertaking tasks to stabilize the grid during voltage fluctuations.This paper reviews the inverter performance in a PV system that is integrated with a power distribution network (i.e., medium to low voltage), or we called it grid-connected PV system. Since the PV system is connected to the public grid, then the inverter eventually called “grid-tie inverter” (GTI). In general, the inverter used is a centralized inverter with settings based on the multiple power point tracker (MPPT) algorithm. The MPPT control is installed on both DC and AC sides which requires a voltage setting that is in accordance with the PV system.

Reliability Analysis and Repair Activity for the Components of 350 kW Inverters in a Large Scale Grid-Connected Photovoltaic System

The reliability of photovoltaic (PV) generators is strongly affected by the performance of Direct Current/Alternating Current (DC/AC) converters, being the major source of PV underperformance. However, generally, their reliability is not investigated at component level: thus, the present work presents a reliability analysis and the repair activity for the components of full bridge DC/AC converters. In the first part of the paper, a reliability analysis using failure rates from literature is carried out for 132 inverters (AC rated power of 350 kW each) with global AC power of 46 MW in a large scale grid-connected PV plant. Then, in the second part of the work, results from literature are compared with data obtained by analyzing industrial maintenance reports in the years 2015–2017. In conclusion, the yearly energy losses involved in the downtime are quantified, as well as their availability.

Electromagnetic interference‐based comparative study between transformerless H5 and optimised H5 grid‐connected photovoltaic inverters

In this study, a comparative study between two single-phase transformerless grid-connected photovoltaic (PV) inverters, namely H5 and optimised H5 (oH5), is carried out based on conducted electromagnetic interference (EMI) performance. For this purpose, a high-frequency (HF) model of the grid-connected inverters is proposed and simulated using Simulation Program with Integrated Circuit Emphasis (SPICE)-based circuit simulation software. Moreover, an experimental setup is developed to measure the conducted emissions. The obtained results show an EMI advantage of the oH5 inverter at low frequencies but not at HF frequencies. Therefore, a mitigation method is proposed to optimise the oH5 topology in the HF range. It consists in using only one Resistor–Capacitor (RC) snubber circuit connected in parallel with the inverter's extra switch. The obtained results show that the oH5 inverter with only one RC snubber circuit provides lower conducted EMI than the H5 in a wider frequency range without worsening the efficiency. The proposed EMI mitigation method can therefore be considered as an adequate and preferred solution for the transformerless grid-connected oH5 PV inverter.