Grid-tied Photovoltaic Inverter Research Articles

Comparison Between Hysteresis and Carrier SPWM Current Control Methods of Grid Tied PV Inverter

This paper has been studying two current control techniques for the two stages single-phase grid-tied photovoltaic (PV) inverter. These control techniques are Sinusoidal pulse width modulation (SPWM) and Hysteresis current. The whole structure of the grid-tied PV inverter has been studied in details for each of its parts. For comparison between the two techniques, the designed system has been tested under MATLAB/Simulink environment for different cases such as insolation and load variation. Results found that the Hysteresis current control method has a simple structure where it does not need PWM block, but it produces a higher total harmonic distortion (THD) as compared with the SPWM method

The performance of a multilevel multifunctional solar inverter under various control methods

Photovoltaic (PV) inverters are now supposed to provide additional supporting services with more reliability and efficiency. This paper presents three different control methods for generating reference current in a multifunctional, multilevel grid-tied PV inverter for harmonic, reactive, and unbalance compensation. These methods are the synchronous reference frame (SRF) theory (d-q), the instantaneous reactive power (IRP) theory (p-q), and the conservative power theory (CPT). As a result, the primary goal is to propose a low-cost multifunctional solar invert for distributed generation, with an appropriate prototype developed in the laboratory for experimental validation of various modes of operation. Demonstrated results show that the presented inverter is capable of providing various ancillary services with all three types of control.

Topologies and modulation methods in leakage current suppression for PV grid-tied inverters

Photovoltaic (PV) inverters are widely discussed as solar energy became commonly used as a renewable energy source. Transformerless grid-tied inverters are often chose for their low cost and low energy loss. Since the existence of stray capacitance between PV cells and conducting surface causes a changing common-mode voltage (CMV) which would arise leakage current and thus pollute the output current quality to the grid and endanger human safety, novel topologies and modulation strategies are proposed to save the problem for transformerless inverters. In this paper, different methods to suppress the leakage current will be analysed. The theoretical analysis of CMV and leakage current generation by single-phase inverter is presented. Based on the basic principle of leakage current suppression topologies proposed to eliminate the leakage current are introduced. The effects of some well-known modulation methods on CMV controlling have been compared, and novel methods dealing with three-phase harmonic management are presented.

A Comprehensive Review of Distributed MPPT for Grid-Tied PV Systems at the Sub-Module Level

Energy crises and the growth of the energy demand have increased the interest in utilizing unconventional power sources. Thus, renewable energy sources have become a topic of interest to mitigate rising energy concerns and cope with increased electricity demand. With remarkable merits including cleanness and abundance, photovoltaic (PV) solar energy systems are a key to solving these issues. The employed inverters should effectively utilize the maximum available power from the PV solar system and transfer this power to the utility grid without posing any further limitations. However, the unequal power generation of different PV systems caused by partial shading (PS) and other PV panel degradation factors leads to a reduction in generation capacity. One of the relatively new solutions to mitigate the mismatch concerns between the PV modules and sub-modules is to extract the maximum power of each sub-module individually. The main objective of this paper is to present a comprehensive review of such PV grid-connected inverters topologies associated with sub-module connection and control. It will classify the PV grid-tied inverters in accordance with the level where the maximum power point tracking (MPPT) system is implemented. A special focus has been placed on sub-module microinverters (MI) in terms of circuit topologies, conversion efficiency, and controller design. This paper provides a comprehensive analysis of employing the distributed MPPT (DMPPT) approach to maximize the power generation of PV systems by mitigating the mismatch issues inside the PV module. The circuit topology, PV system configuration, and MPPT algorithms used for applying DMPPT solutions in PV SMs are discussed in detail in this study.

Failures causes analysis of grid-tie photovoltaic inverters based on faults signatures analysis (FCA-B-FSA)

Nowadays, most countries convert conventional electricity power plants to green power generation to limit CO2 emissions and mitigate global warming. Hence, renewable energy sources play a significant role, and Mega-scale Photovoltaic (PV) power plants are widely constructed to use free green solar energy as one of the best practices for using renewable energy sources. The central inverter is considered the most important core equipment in the Mega-scale PV power plant which suffers from several partial and total failures. This paper introduces a new methodology for Failure Causes Analysis (FCA) of grid-connected inverters based on the Faults Signatures Analysis (FSA). Hence, this methodology is called Failure Causes Analysis Based Fault Signature Analysis (FCA-B-FSA). The objective is to link the Fault’s Signatures (FSs) and the correlated Root Causes (RCs). To achieve this objective, this paper discusses many directions starting with reviewing the inverters’ FCA which was investigated in previous publications. As the previous studies of the inverters FCA are limited, this paper focuses on statistical gathering for the FSs of the grid-tie PV inverters and the egalitarian inverters. Then, the investigated work in this paper presents a proposed methodology to link the FSs to the correlated RCs. The investigation outcomes briefly present a proposed validation plan to be considered for FCA-B-FSA of a real incident of a grid-tie PV inverter as a future work.

Point of Common Coupling Voltage Modulated Direct Power Control of Grid-Tied Photovoltaic Inverter for AC Microgrid Application

A direct power control (DPC) approach is proposed in this study for a grid-tied photovoltaic (PV) voltage source inverter (VSI) to regulate active and reactive power flow directly in between utility grid and microgrid (MG) by controlling point of common coupling (PCC) voltage. The proposed PCC voltage modulated (PVM) theory-based DPC method (PVMT-DPC) is composed of nonlinear PVM, nonlinear damping, conventional feedforward, and feedback PI controllers. For grid synchronization rather than employing phase-locked-loop (PLL) technology, in this study, direct power calculation of the PCC voltage and current is adopted. Subsequently, at PCC, the computed real and reactive powers are compared with reference powers in order to generate the VSI’s control signals using sinusoidal pulse width modulation (SPWM). Because of the absence of the PLL and DPC method adoption, the suggested controller has a faster convergence rate compared to traditional VSI’s power controllers. Additionally, it displays nearly zero steady-state power oscillations, which assure that MG’s power quality is improved significantly. To validate the proposed PVMT-DPC method’s performance, real-time simulations are conducted via real-time digital simulator (RTDS) for a variety of cases. The obtained results demonstrate that using the proposed PVMT-DPC approach, PV VSI can track the reference power within 0.055 s where the output power has low steady-state oscillations and output current has lower total harmonic distortion (THD) of 1.68%.

A Five-Level Switched-Capacitor Based Transformerless Inverter With Boosting Capability for Grid-Tied PV Applications

Transformerless grid-connected inverters have attained a lot of research interest in renewable energy interface applications, due to certain promising properties like greater efficiency, light weight, affordable price, and tolerable power density. Among various types of transformerless grid-tied photovoltaic (PV) inverters, multilevel inverters (MLIs) are mostly popular due to their ability to transmit reactive power, small filter size for reducing total harmonic distortion (THD) and their common-ground (CG) configuration to mitigate the detrimental leakage current due to the parasitic capacitances of the PV array. Again, among different types of MLIs for PV systems, switched-capacitor (SC) based multilevel inverter topologies are the burning topic in current decades due to their single source requirements for producing multilevel output voltage. However, for mostly used single-phase five-level inverters, most of the existing SC based topology requires at least two SCs for power conversion. In this paper, a five-level transformerless inverter based on a single SC is proposed, requiring only seven switches, no diode, a single capacitor, and one dc voltage source. The proposed transformerless MLI also has auto-boosting capability. Notably, the number of power switches operating at high frequency is limited to three, which lowers down the switching losses of the inverter. Rather than a new single SC based five-level transformerless inverter topology, a control scheme is also presented to inject a precisely regulated current into the grid that can govern both the active and reactive power support modes. In-depth comparisons between the proposed and cutting-edge MLIs are also provided. All these claims are validated through MATLAB/Simulink and PLECS computer simulation environments. A laboratory-scaled prototype is also built and tested to support the simulated claims further and validate the effectiveness and feasibility of the proposed five-level transformerless inverter topology.

An Optimized LVRT Control Strategy of Cascaded Modular Medium-Voltage Inverter for Large-Scale PV Power Plant

Active power backflow is an inherent problem of three-phase cascaded H-bridge (CHB) photovoltaic (PV) grid-tied inverters during low-voltage ride through (LVRT), probably resulting in no balanced operating point of the system, and the inverter will be shut down and off-grid due to overvoltage fault. Aiming at this issue, this article first reviews the existing control methods and analyzes their limitations in application, that is, they cannot effectively suppress active power backflow under the scenario of deeper voltage drop and lower output power. On this basis, an optimized LVRT control strategy for cascaded modular medium-voltage PV power generation system is proposed, which adopts different control methods to suppress active power backflow under three types of asymmetric grid drop conditions: single-phase short-circuit fault with ground, two-phase short-circuit fault with ground, and two-phase short-circuit fault without ground, enhancing the adaptability of CHB PV grid-connected inverters to different output powers and different drop depths during grid voltage failure and then improving LVRT capability of the system. Finally, the effectiveness and feasibility of the proposed control strategy are verified by experimental results.

A systematic review of grid-connected photovoltaic and photovoltaic/thermal systems: Benefits, challenges and mitigation

Solar energy is the powerhouse where all potential and classified renewable energies lug their sources. The energy transformation from the Sun to electricity requires an adequate control scheme to maximise the generated power and enhance the system efficiency. Besides, more than half of solar irradiation on conventional Photovoltaic (PV) panels is lost. The PV thermal (PV/T) modules have been introduced to convert the lost irradiation to heat. Thus, a systematic review of system components, development, and strategies for grid-connected solar PVs plants is presented. Two solar PVs, traditional PV and PV/T, are evaluated. Each grid-tied PV component is considered a subsystem to analyse the potential improvement of grid-connected PVs. This is from solar resources to grid-tied PV inverter techniques. An intensive assessment of the system improvements is presented to evaluate PV plants’ benefits, challenges, and potential solutions. The improvement trends for the novel generation of grid-connected PV systems consist of applying innovative approaches. It is also found that intelligent strategies optimally ensure the overall efficiency of grid-tied PVs using real-time control and measurement under innovative applications and technologies. These methods effectively assist in enhancing grid-tied diverse solar power approaches. Therefore, this paper would offer a significant foundation for advanced research into the subject of grid-tied PV and PV/T and their innovation and/or technology development.

Robust controller for grid‐tied PV inverters based on continuous non‐linear predictive and integral sliding mode control

This paper proposes a robust continuous nonlinear control method for grid-tied photovoltaic (PV) inverters by combining model predictive control and integral sliding mode control (ISMC). The robustness of the proposed augmented controller is demonstrated mathematically by showing that the equivalent control signal of the ISMC system cancels disturbances to the system. Further, the proposed controller can compensate for system perturbations without knowing their characteristics, thereby simplifying controller design for the PV systems. The robustness of the proposed controller against parameter uncertainties and external disturbances was demonstrated via experimental and simulation verification.

Improving The Controllability of Grid-Tie Inverter for Small-Scale Rooftop Photovoltaic System

This paper aims to apply an Adaptive Network-based Fuzzy Inference System (ANFIS) controller in a DC-link voltage regulator to decrease the power fluctuation for enhancing the performance of the grid-tie inverter for a small-scale rooftop solar Photovoltaic (PV) system. For tracking Maximum Power Point (MPP), a Perturb and Observe (P&O) algorithm was presented. To demonstrate the effectiveness of the proposed controllers for a small-scale 5 kWp rooftop solar PV system, several time-domain simulation results under a three-phase short-circuit fault that happened at a grid-tie inverter system was systematically performed by employing Matlab/ Simulink toolbox. On the basis of the simulation results, it is obvious that the proposed P&O algorithm for MPP tracking and the designed ANFIS controller for DC-link voltage regulator of the grid-tie inverter shows better performance to reduce overshoot and settling time in transient responses of the studied small-scale 5 kW grid-tie rooftop solar PV inverter under the most severe operating condition.

Fast Two-Stage Global Maximum Power Point Tracking for Grid-Tied String PV Inverter Using Characteristics Mapping Principle

In principle, the location of global maximum power point (GMPP) of partially shaded photovoltaic (PV) array highly correlates with the shape of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P - V$ </tex-math></inline-formula> curve, but such correlation is complex and hard to be specified using the traditional mathematic expressions. This article, therefore, first explores the nonlinear characteristics of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P - V$ </tex-math></inline-formula> curve under partial shading conditions (PSCs) using an artificial neural network (ANN), which could help locate the GMPP after scanning several selected characteristic points. Then, the perturb and observe (P&O) algorithm will be further integrated to achieve fast GMPP tracking based on the obtained location of GMPP. Being different from the existing ANN-based GMPPT methods, meteorological information, such as irradiance and temperature, is not mandatory. In implementation, both PV array model construction and ANN training process are performed offline, which will not complicate the online GMPP tracking algorithm. Compared with several GMPPT algorithms in recent references, the proposed method achieves higher tracking speed and meanwhile guarantees a high tracking efficiency. The performance of the proposed method was verified in simulation and experiment, where it achieves an average tracking efficiency of 99.32% and an average tracking time of 0.8 s.

Direct Power Control Based on Point of Common Coupling Voltage Modulation for Grid-Tied AC Microgrid PV Inverter

In this paper, a direct power control (DPC) approach is proposed for grid-tied AC MG’s photovoltaic (PV) voltage source inverter (VSI) to regulate directly active and reactive powers by modulating microgrid’s (MG) point of common coupling (PCC) voltage. The proposed PCC voltage modulated (PVM) theory-based DPC method (PVMT-DPC) is composed of nonlinear PVM, nonlinear damping, conventional feedforward and feedback PI controllers. For grid synchronization rather than employing phase-locked-loop (PLL) technology, in this study, direct power calculation of the PCC voltage and current is adopted. Subsequently, at PCC, the computed real and reactive powers are compared with reference powers in order to generate the VSI’s control signals using sinusoidal pulse width modulation (SPWM). Because of the absence of the PLL and DPC method adoption, the suggested controller has a faster convergence rate compared to traditional VSI’s power controllers. Additionally, it displays nearly zero steady-state power oscillations, which assures that MG’s power quality is improved significantly. To validate the proposed PVMT-DPC method’s performance real-time simulations are conducted via real-time digital simulator (RTDS) for a variety of cases. The results demonstrate that PV VSI using the suggested PVMT-DPC approach can track the reference power quicker (0.055 s) along with very low steady-state power oscillations, and lower total harmonic distortion (THD) of 1.697% at VSI output current.

Three-Level T-Type Quasi-Z Source PV Grid-Tied Inverter With Active Power Filter Functionality Under Distorted Grid Voltage

Distributed energy resources (DER) such as solar photovoltaic (PV) interfaces with the utility grid by high-efficiency power electronic converters. This equipment is sometimes underutilized in terms of its power capacity; thus, the remaining capacity can be used to provide support to the distribution system. In this sense, this work assesses the performance of the three-level T-type quasi-impedance source inverter (3L-T-type qZSI) injecting not only active power to the grid, but also providing support to it by injecting reactive power and acting as an active power filter (APF) simultaneously. The global control strategy of the grid-connected inverter is derived from the instantaneous <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$i_{d}$ </tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$i_{q}$ </tex-math></inline-formula> power theory. The combination of an improved deadbeat current controller and a level-shifted carrier-based pulse-width-modulation (PWM) technique, using both the upper shoot-through (UST) and the lower shoot-through (LST) alternating states, allows a successful tracking of the current references. Both the dc-link voltage control and the neutral-point balancing are properly achieved by taking the advantage of the shoot-through (ST) states and the redundant states simultaneously. These control actions are implemented by simple proportional-integral (PI) controllers. The simulation and experimental results demonstrate the above-mentioned functionalities and verify the stability and good dynamic response of the grid-connected 3L-T-type qZSI.

Equivalent Input Disturbance-Based Control Design for Three Phase Dual-Stage Grid-Tied Photovoltaic System Considering Dead Time Effect

Grid-tied inverter is the prominent component of the three-phase dual-stage photovoltaic (PV) grid-tied power generation system. However, the disturbances caused by dead time effect will pose the reduction of grid-tied current quality and even cause the imbalance of inverter itself or other circuit devices. In this paper, a current control strategy is proposed to damp dead time effect for the three-phase dual-stage PV grid-tied inverter system, and its design, stability analysis, and implementation are carried out. First, the inverter model is modified by regarding the dq reference frame coupling terms, uncertainties, and external and internal disturbances as an unknown lumped disturbance. Then, a current control scheme based on compensation of equivalent input disturbance is introduced, and it estimates and compensates the unknown lumped disturbance, which effectively realizes the inverter model decoupling and comprehensive disturbance rejection. Last, simulation results demonstrate the effectiveness and superiority of the proposed current controller.

Analysis and Simulation of Current-source Flyback Inverter with Efficient BCM Control Strategy

The Flyback inverter is a single-stage power inverter which represent an attractive solution for photovoltaic (PV) grid-tied inverter application. The main advantages of a current-source flyback inverter are high power density and high efficiency due to its small, as well as low total harmonic distortion (THD) operation. However, a flyback topology works with Discontinuous Conduction Mode (DCM) control strategy has lower efficiency and poor THD values. In this paper, an efficient current-source flyback inverter topology works with Boundary Conduction Mode (BCM) control strategy is presented. Besides, an efficient incremental conductance (IC) maximum power point tracking (MPPT) is used to extract the maximum power from the PV module. To verify the proposed control a power simulator (PSIM) software is used. As a result, the simulation results indicates that the BCM control is more efficient than the DCM method for various weather conditions. Finally, the proposed BCM strategy is compared with DCM control in terms of THD and thus it is achieved lower THD contain in the injection current of grid.

Inverter Protection and Ride-Through: Today's Photovoltaic and Energy Storage Inverters

Modern grid-tied photovoltaic (PV) and energy storage inverters are designed with control capabilities that can support and/or enhance the existing global grid infrastructure. Inverter-based generation is growing today in the residential, commercial, and utility segments. This article will explore how modern inverter controls can have a positive effect on today's evolving electrical grids in the utility sector. I will examine the inverter protection mechanisms used to keep dc-side and ac-side faults from causing damage to the inverter. Inverter grid supporting functions, along with voltage and frequency ride-through, provide key behaviors that both support and enhance grid reliability. Today's PV and energy storage inverters can be deployed individually and in a mixed design, affording plant designers options for energy capture and grid support. The following topics are as general as possible with some unavoidable linkage to SMA inverters.

System efficiency prediction of a 1kW capacity grid-tied photovoltaic inverter

&lt;p&gt;This article presents the system design and prediction performance of a 1kW capacity grid-tied photovoltaic inverter applicable for low or medium-voltage electrical distri-bution networks. System parameters, for instance, the longitude and latitude of the solar plant location, panel orientation, tilt and azimuth angle calculation, feasibility testing, optimal sizing of installment are analyzed in the model and the utility is sim-ulated precisely to construct an efficient solar power plant for residential applications. In this paper, meteorological data are computed to discuss the impact of environmen-tal variables. As regards ensuring reliability and sustenance, a simulation model of the system of interest is tested in the PVsyst software package. Simulation results yield that the optimum energy injected to the national grid from the solar plant, specific pro-duction, and performance ratio are 1676kWh/year, 1552kWh/kWp/year, and 79.29% respectively. Moreover, the predicted carbon footprint reduction is 23.467 tons during the 30 years lifetime of the system. Therefore, the performance assessments affirm the effectiveness of the proposed research.&lt;/p&gt;

A Novel Per Unit (P.U.) Integer Format Applied to the Control of a Grid-Tied Solar PV Inverter

In advanced power electronic applications such as a grid-tied solar photovoltaic (PV) inverter, control algorithms demand high-level computational support, typically provided by an expensive 32-bit digital-signal-processor (DSP) or microcontroller. In cost-sensitive markets, this may prove to be a significant component of the overall cost of the system. Using a low-cost 16-bit microcontroller is, therefore, highly desirable. However, it poses certain challenges such as fewer bits for the mathematical and logical operations, computations in the fixed-point environment, and lower speeds. In this article, a novel per-unit integer system is proposed towards using a low-cost microcontroller for complex computations, which overcomes the above limitations while maintaining the core functionality in a fixed-point environment. An improved hybrid phase locked loop implementation scheme, that uses the p.u. integer system has also been presented, which significantly reduces the execution time for grid-synchronization. To demonstrate the performance of the proposed concepts, control of a grid-tied PV inverter has been implemented on a low-cost fixed-point microcontroller (dsPIC33FJ16GS402) as well as on an advanced DSP microcontroller (TMS320F28069). Timing analysis and experimental results for a 1 kW grid-tied PV system confirm that the performance of the system using a low-cost microcontroller is comparable to that of the advanced microcontroller.

A grid-tied photovoltaic transformer-less inverter with reduced leakage current

The importance of transformer-less inverters has been increased since these are highly efficient, less costly, reduced in weight compared to conventional inverters for PV systems connected to grid. This fact led researchers to propose various topologies of transformer-less inverters, which have been validated for only injection of real power towards grid. However, recently new regulation has been imposed by all international power regulatory agency is that these PV inverters integrated with grid should have the capability of handling flow of a certain quantity of reactive power. By considering this point, a noble topology of transformer-less inverter has been developed for grid integrated PV system. Unlike previous topologies during reactive power injection, the new topology does not face reverse recovery issues, which helps to enhance the efficiency of the proposed inverter by exploiting MOSFET switches. Moreover, leakage current becomes low by keeping the common mode (CM) voltage at input DC voltage’s midpoint.