Grid-connected Solar Inverter Research Articles

Power Factor Analysis of Grid-Connected Solar Inverter under Different Irradiance Levels throughout the Day

The power factor (PF) plays a crucial role in determining the quality of energy produced by grid-connected photovoltaic (PV) systems. When irradiation levels are high, typically during peak sunlight hours, the PV panels generate more electricity. In this scenario, the PF tends to be higher because the real power output closely matches the apparent power drawn from the grid. Whereas, when irradiation levels are low, such as during cloudy weather or nighttime, the PV panels produce less electricity. In these conditions, the power factor may decrease because the real power output diminishes compared to the apparent power drawn from the grid. This could be due to reduced efficiency or increased reactive power flow. PF decreases linearly at solar irradiance values lower than 220 (W/m2). At the same time, it approaches unity at higher solar irradiance values than 220 (W/m2). In this study, the variation of the power coefficient of the grid-connected PV solar system depending on solar irradiation was modeled and analyzed using MATLAB/Simulink 41016490. The analytical expression of the power factor depending on the change in solar irradiation was found using the curve fitting method.

Impact of Multiple Grid-Connected Solar PV Inverters on Harmonics in the High-Frequency Range

In recent years, integration of solar photovoltaic (PV) systems into distribution networks has been increasing rapidly, as it has become the most promising renewable energy source (RES) in the transition of power generation from centralised to decentralised systems. With the power electronic (PE) interfaces that use high-frequency internal switching, all renewable energy sources are considered to be harmonic emitters, especially near switching frequencies, i.e., above 2 kHz. This paper evaluates the behaviour of high-frequency harmonics in the 2–20 kHz range due to the parallel operation of multiple solar PV inverters connected to a low-voltage (LV) network. The circulation current component that flows within the installation due to the low impedance paths at higher frequencies is analysed. Summation of high-frequency harmonic currents is observed with phase diversity analysis. The circulating current component can become 14 times higher than the grid current component at higher frequencies.

Revolutionary building approach for maximal photovoltaic system results to improve maximum power point tracking in solar inverter

Due to the inherent frequency ripple in single-phase photovoltaic (PV) grid-connected solar inverters, the Maximum Power Point Tracking (MPPT) will inevitably be affected. To improve the MPPT performances, a passive LC power decoupling circuit with a Robust Sliding-Mode Control (RSMC) is proposed in this article. The frequency pulsation on the DC link is effectively canceled with the passive LC decoupling path. Thus, the MPPT accuracy is significantly enhanced, and the utilization of a small DC-link capacitor becomes possible. The resonance between the LC circuit and the main DC-link capacitor appears, which can be damped through an active damping method. The proposed RSMC offers good steady-state, dynamic performance (voltage fluctuation and settling time), and the robustness of the DC-link voltage, which is also beneficial to MPPT control in terms of high accuracy and fast dynamics. The systematic design of RSMC is presented, and a detailed parameter optimization design of the LC decoupling circuit is discussed. Experimental tests are performed on a 2.5-kW single-phase grid-connected solar inverter, and the results validate the effectiveness of the proposed strategy.

An improved active islanding detection method for grid-connected solar inverters with a wide range of load conditions and reactive power

An improved active islanding detection method for grid-connected solar inverters with a wide range of load conditions and reactive power

Improved Performance of a Grid-Connected Inverter with Two PV Array Input under Different Environment Conditions using Adaptive Neuro Fis Based Control

Grid-connected inverters based on solar PV cells are becoming increasingly common. At times, the PV can be subjected to a certain environmental situation, such as varying irradiance or temperature. Present developments in gird-connected PV inverters do not have many reliable yields or reliability in this case. In this article, an improved control framework system is intended for two PV that are mismatched in various ways, resulting in a highly effective grid-connected solar inverter with THD under 1% for both voltage and current. The regulator employs a control scheme comprised of an ANFIS-based control system that works in tandem with the incremental conductance technique of MPPT. The outcomes are simulated and validated using MATLAB Simulink.

Fault Ride Through approach for Grid-Connected Photovoltaic System

This paper presents a fault ride-through approach for grid-connected photovoltaic (PV) systems, aimed at improving the system's response during voltage sags and limiting the maximum inverter current during symmetrical faults. A constant active current reactive power injection approach was developed for low-voltage ride-through (LVRT) operation of grid-connected solar PV inverters in low voltage grids. The method manages the active and reactive power references and satisfies grid code requirements while also addressing tripping problems caused by overcurrent. The approach improves the speed response of the power converters during voltage sags, resulting in better dynamic grid support. The authors evaluated the approach using a 2-kW single-phase grid-connected PV system and demonstrated its ability to inject the required reactive power during a fault to improve the voltage profile and achieve dynamic grid support requirements. The accuracy of the proposed methodology is identified to be 98.3%, and the detection time is reduced by a reasonable margin in accordance with the grid standards. Overall, the fault ride-through approach can enhance the performance and reliability of grid-connected PV systems, particularly in low voltage grids.

Innovative Control of Two-Stage Grid-Connected Solar Inverter Based on Genetic Algorithm Optimization

Innovative Control of Two-Stage Grid-Connected Solar Inverter Based on Genetic Algorithm Optimization

Comparison between a Cascaded H-Bridge and a Conventional H-Bridge for a 5-kW Grid-Tied Solar Inverter

This paper compares the cost and efficiency of two inverter topologies for a 5-kW grid-connected solar inverter application: the Conventional H-Bridge Inverter (CHB) and the Cascaded H-Bridge Multilevel Inverter (CHBMLI). Emphasis is put on power switches and passive elements with a detailed study of the losses. Both designs respect the same constraints (cost, efficiency, and junction temperature of the transistors) to ensure a fair comparison between both topologies. The work highlights the important parameters when choosing the components (MOSFETs, capacitors, and magnetic cores for the inductors). The DC-link voltage ripple and the output AC current ripple are the key parameters for the design of the passive elements (capacitors and inductors). On top of that, the transistors MOSFETs are chosen, in both topologies, to limit the conduction losses (by selecting the Rdson) and the switching losses (by selecting the Qrr and dv/dt). Real components are picked in order to make the comparison as complete as possible. Numerical simulations are performed using the MATLAB platform. All equations and parameters are provided. A CHBMLI prototype was built with eight independent H-Bridges to validate the proposed design with thermal and efficiency measurements.

AI/ML and Cybersecurity in Power Electronics

Artificial intelligence and machine learning (AI/ML) have been applied to power electronics and electric drives research for more than 20 years for design, control, estimation, and prediction. With the recent interest in AI/ML for all aspects of smart and connected daily life, the interest in AI/ML applications of power electronics has also increased. With the increase in the number of grid-connected power electronics systems and solar inverters, there is also more interest in cyber physical security of these systems. This opening session of FEPPCON XI looked into the past work and also presented future possibilities for PELS in these areas.

DC/DC Stage Contribution to Bus Voltage in 1000- and 1500-V Grid-Connected Solar Inverters

Modern architectures of transformerless, three-phase-grid-connected photovoltaic (PV) inverter for 1000- and 1500-V commercial/residential applications are analyzed and compared from the point of view of the energy harvested during one year period, system efficiency, and power density. Scenarios for different ac grid voltage levels and inverters topologies are analyzed based on one- and two-stage solutions. The architectures with and without included dc/dc stage are compared from the point of view of the optimized power density. In the case of the two-stage PV inverter architecture, the mini-boost converter concept, presented in previous publications, is extended and the standard boost topology that employs 1200-V rated IGBTs and diodes is replaced by a multilevel, hybrid power converter topology that exhibits high efficiency due to the partial power processing and new classes of 900- and 650-V SiC and GaN devices employed. The inverter’s output filter design space (DS) has been researched from the point of view of the dc bus voltage variation. The cases are analyzed for fully controlled bus voltage at its minimum value and when allowed to vary in the full MPP range. Optimization results of the output filter DSs for the minimum and maximum operating dc bus voltage are compared in terms of the occupied volume in order to investigate whether it is possible to obtain more compact inverter stage by better control of dc bus voltage. The results show that in the case of controlled low dc bus voltage level, it is feasible to design a filter that occupies up to 50% less volume than the filter designed for the full MPP voltage variation. Even more, this can be achieved by maintaining the system efficiency. The simulation and experimental results complement the analysis of the 1000- and 1500-V grid-connected PV inverter systems.

A Novel Topology for Solar PV Inverter Based on an LLC Resonant Converter With Optimal Frequency and Phase-Shift Control

In this article, a new topology for a grid-connected solar photovoltaic inverter for the direct connection to the medium-voltage grid is proposed. This topology employs an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter with a high-frequency (HF) isolation transformer in the dc–dc stage. The output of the dc–dc stage is a rectified sine wave voltage and current at the line frequency. An unfolder inverter interfaces between this dc stage and the grid. A combined phase-shift and frequency control method is used to control the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter. The phase-shift angle and switching frequency values of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter are regulated to track the reference current signal for the whole operation range. The Lagrange multiplier method is applied to find the optimal trajectory to calculate the optimal phase-shift angle and switching frequency pairs for any operation condition by considering power converter and HF transformer losses to achieve the highest efficiency at a varying current. The transformer leakage and magnetization inductances are properly designed to provide a zero-voltage switching (ZVS) for a wide operation area, and additional resonant inductor requirement is removed. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter operates in a ZVS region except in a narrow band around the zero-current crossings of the inverter output. Using an HF transformer in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter, a bulky line frequency transformer requirement is eliminated, and thus, a more compact and efficient design is obtained. The proposed topology is validated by the simulation and experimental results.

LOW THD GRID-CONNECTED INVERTER FOR TWO PV ARRAY

Grid-connected inverters based on solar PV cells are becoming increasingly common. The PV can sometimes be subjected to a certain environmental situation, such as varying irradiance or temperature. In this case, present developments in grid-connected PV inverters do not have many reliable yields or reliability. In this article, an improved control framework system is intended for two PVs that are mismatched in various ways, resulting in a highly effective grid-connected solar inverter with THD under 1% for both voltage and current. The regulator employs a control scheme comprised of an ANFIS-based control system that works in tandem with the incremental conductance technique of MPPT. The outcomes are simulated and validated using MATLAB Simulink

A New Six-Level Transformer-Less Grid-Connected Solar Photovoltaic Inverter With Less Leakage Current

This paper presents a novel structure of the transformer-less grid-connected inverters. The proposed inverter is combined with six power switches and two power diodes which can generate six voltage levels at the output. Furthermore, the proposed inverter can overcome the leakage current issue in the photovoltaic (PV) system, which is the major problem in grid-tied PV applications. Additional significant features include-reduced filter size, lower total harmonic distortion (THD) of the injected current to the grid, and voltage boosting ability. Moreover, the proposed topology provides full reactive power support to the grid. A control strategy is designed and implemented to provide a voltage boost ability without using any additional dc-dc boost converter. Finally, the performance of the proposed inverter is validated by the 770 <i>W</i> laboratory prototype.

Design and Control of A Novel Dual Function Grid-Connected Solar Inverter

In this paper, a novel dual-function grid-connected solar inverter is developed for better utility interaction applications. The proposed topology is able to inject active power, reactive power, and mitigate harmonic problems caused by non-linear loads. The proposed configuration consists of switched LC-connected inverter (SLC-CI) in parallel with static VAR compensator (SVC) to achieve the design requirements. The system description, mathematical model, control algorithm, and parameter design of the proposed system is systematically developed to ensure acceptable performance. The system performance is evaluated with both linear and non-linear loads and compared to two conventional topologies; inductive and capacitive grid connected inverters. The results demonstrate that the proposed topology have better performance, comparing to other topologies, in terms of using lower DC-bus voltage (25% less) and using around half the power rating of inverter. Moreover, the proposed double switched LC filter-connected inverter (DSLC-CI) shows its ability to work as active power filter and mitigate harmonics to acceptable level.

A novel technique for online resonance frequencies monitoring based on wavelet transform for grid-connected solar inverters

Photovoltaic systems are often connected to the main grid through multiple paralleled inverters to support and to reinforce the power generation into the grid. This interconnection can be affected by resonance phenomena that may be introduced by the excitation of passive filters and lead either to small oscillations that can deteriorate the power quality or large oscillations that can affect the whole system reliability. Therefore, early detection of such oscillations is essential to keep a resilient operation. This paper proposes a novel algorithm for an online resonance frequency monitoring based on wavelet transform (RFM-WT) that can perform fast detection of undesired resonance frequencies. The RFM-WT is performed through two steps. The first step consists in decomposing each inverter output current into different signals using the wavelet transform. This allows separating the different frequencies that exist in the inverter output current. The second step allows estimating the frequencies from the signals obtained in the first step. Accordingly, a comprehensive approach describing the design of the proposed monitoring algorithm is presented. Its effectiveness is compared to the classical PLL algorithm. Unlike the PLL algorithm, the proposed technique is easy to implement and doesn't require regulators’ parameters design and configuration. The simulations and experiments proved that the algorithm can accurately locate the resonance frequencies in inverters output currents. Thus, its robustness was validated through load variation and transition from grid- connected to islanded mode.

Conducted Emission Suppression Using an EMI Filter for Grid-Tied Three-Phase/Level T-Type Solar Inverter

Electromagnetic interference in power converters is a crucial problem for circuit designers. Electromagnetically compliant converter design is required for the safety of an operation. A novel filter design approach considering ground leakage current, different winding styles for common mode choke, tolerance of filter capacitor is proposed in this study to solve the electromagnetic interference problem. In the study, electromagnetic compatibility issue is investigated for a 25 kW, 15 kHz switching frequency, three-phase/level T-type grid-connected solar inverter. The test setup is installed based on EN55011 standard, and the interferences emitted by the inverter to the grid through conduction are measured. Then, a filter design is made to prevent these interferences from being transmitted to the grid. After the filter is designed and engaged, the measurements are repeated. So, the noise attenuation of the EMI filter is verified experimentally. Experiences obtained from the hardware modification in the EMI filter, which is designed for an industrial solar inverter, have been discussed. It is observed that the result of conducted emission measurement is within the limits of the EN55011 Class B standard.

A Novel Transformerless Single-Stage Grid-Connected Solar Inverter

A novel tranformerless single-stage grid-connected solar inverter with a combination of a bidirectional dc/dc boost converter followed by a flyback inductor inverter is proposed. The inverter shares a common ground with the photovoltaic (PV) panel and the grid, which realizes a zero leakage current and it is the most desired feature in transformerless inverters. Further, the proposed inverter provides the boost voltage operation, hence it does not require a second stage which decreases the system cost and increases the system reliability. The other advantage of the proposed inverter is that it provides both the symmetrical positive voltage gain and negative voltage gain, which allows to use simple sinusoidal pulsewidth modulation technique for realizing the ac sinusoidal output voltage. The proposed inverter steady-state operation and the design equations are presented in detail. The converter dynamic model is developed using state-space averaging approach, and a proportional resonant current controller is designed for inverter closed-loop operation with the grid. The presented analysis and the design are verified with both the simulation and experimental results.

A random carrier frequency PWM technique with a narrowband for a grid-connected solar inverter

The quality of power is always a concern for the high penetration of a grid-connected solar photovoltaic (PV) system due to the variation in solar irradiation and the temperature change of solar output, which in turn varies the fundamental component of power delivered to the grid. A solar source requires an inverter interface to supply the AC load as well as for the grid interconnection. Any reduction in the fundamental component generated by solar PV at a lower irradiation level or at high- temperature results in increasing %THD at the output of inverter for a given fixed switching frequency since harmonics due to PWM technique is comparable with the fundamental component. The selection of high-fixed-switching-frequency PWM reduces harmonics but increases the stress on switches and switching losses. It also suffers from issues of harmonics at carrier frequency and its sideband at multiples of switching frequency that causes acoustic noise and EMI. The random frequency PWM (Random PWM) method overcomes these issues presented by the fixed-frequency PWM method. However, a wide band of Random PWM makes the inverter filter design difficult and causes resonance in the distribution system. In addition, asymmetry in the carrier wave introduces even-order harmonics in the line current. Hence, this paper proposes a narrowband random frequency PWM method to reduce sideband harmonics, lower-order harmonics, even-order harmonics and a total harmonic distortion (THD) for a solar-based grid-connected inverter. Simulation results present a satisfactory performance of the proposed control technique for a steady-state and transient results. Experimental validation of the same is carried out on the OPAL-RT OP4500-based laboratory prototype of a 2-kVA inverter which depicts reduction in harmonics and hence improvement in power quality.

Droop Control Based Grid-Connected Solar Photovoltaic Inverters for Distributed Generation

In day to day the demand of electrical energy has been increasing in worldwide, as well the share of solar photovoltaic power generation has increased extremely because of population growth, urbanization, etc. Although the power generated from solar photovoltaic is erratically, and it makes the stability and reliability problems in a utility grid. This paper projects a P/Q droop control strategy for a grid-tied PWM inverter. This paper introduces an entire model of grid-connected solar photovoltaic array; inverter with droop control, and loads are developed for this operation. The locus points of the both power sharing of the DG system is developed by the proposed control operation. PI controllers were used in this droop control was espoused to adjust the constraints of PI controller. The results of the proposed droop control inject positive and reactive power into a variation of loads and improving the quality of power as compared to the conventional PID controllers.

Harmonic Analysis and Control of Grid-Connected Solar PV Inverter under Normal and LVRT Operating Modes

Environmental factors and active involvement in grid-connected solar PV inverter ancillary operations may impact the quality of the current injected into the grid. The future grid-connected solar PV system with ancillary facilities (e.g., low voltage ride-through (LVRT)) will be more active and intelligent, which will degrade grid current reliability. The grid current distortions are specifically caused by the dc-link voltage variations and the modulation of pulse width (PWM) control applied to the PV inverter. This article analyzes the current harmonic distortion under the two-stage grid-connected PV system's regular (MPPT) and fault (LVRT) condition. Furthermore, a dc-link voltage variation control system for the two-stage photovoltaic (PV) inverter is presented during low voltage ride-through (LVRT) operation mode..The dc-link voltage differences are regulated under the fault condition to preserve the high modulation ratio in order to considerably mitigate the distortion rate of the grid current. Besides, the proposed system of control is designed to protect the PV inverter from the overcurrent failure under the faults to meet the modern LVRT grid codes. The conducted simulation tests have confirmed that the proposed control scheme leads to reduce a grid currents harmonics level by controlling the dc-link voltage variations.