An adaptive direct power controller for three-phase grid-connected photovoltaic systems with parametric uncertainties

The lack of control in voltage overshoot, transient response, and steady state error are major issues that are frequently encountered in a grid-connected photovoltaic (PV) system, resulting in poor power quality performance and damages to the overall power system. This paper presents the performance of a control strategy for an inverter in a three-phase grid-connected PV system. The system consists of a PV panel, a boost converter, a DC link, an inverter, and a resistor-inductor (RL) filter and is connected to the utility grid through a voltage source inverter. The main objective of the proposed strategy is to improve the power quality performance of the three-phase grid-connected inverter system by optimising the proportional-integral (PI) controller. Such a strategy aims to reduce the DC link input voltage fluctuation, decrease the harmonics, and stabilise the output current, voltage, frequency, and power flow. The particle swarm optimisation (PSO) technique was implemented to tune the PI controller parameters by minimising the error of the voltage regulator and current controller schemes in the inverter system. The system model and control strategies were implemented using MATLAB/Simulink environment (Version 2020A) Simscape-Power system toolbox. Results show that the proposed strategy outperformed other reported research works with total harmonic distortion (THD) at a grid voltage and current of 0.29% and 2.72%, respectively, and a transient response time of 0.1853s. Compared to conventional systems, the PI controller with PSO-based optimization provides less voltage overshoot by 11.1% while reducing the time to reach equilibrium state by 32.6%. The consideration of additional input parameters and the optimization of input parameters were identified to be the two main factors that contribute to the significant improvements in power quality control. Therefore, the proposed strategy effectively enhances the power quality of the utility grid, and such an enhancement contributes to the efficient and smooth integration of the PV system.

This paper presents a three-phase grid-connected photovoltaic generation system with unity power factor for any situation of solar radiation. The model of the PWM inverter and a control strategy using dq0 transformation are proposed the system operates as an active filter capable of compensate harmonic components and reactive power, generated by the other loads connected to the system. A input voltage clamping technique is proposed to control the power between the grid and photovoltaic system, where it is intended to achieve the maximum power point operation. Simulation results and analyses are presented to validate the proposed methodology for grid connected photovoltaic generation system.

Nowadays, due to the high-scale penetration of photovoltaic systems, reliable and efficient grid-connected photovoltaic (PV) systems utilizing the advances of power electronics and control system technology are desirable. Thus, single-stage grid-connected photovoltaic systems, have gained attention, especially in low voltage applications. However, PV systems exhibit nonlinear behavior that could negatively affect the performance of the system if they are not adequately compensated for. In this dissertation, using the general structure for the synchronous dq0 frame, a single-stage three-phase grid-connected photovoltaic system, and a single-stage single-phase grid-connected PV system, both with a nonlinear control strategy, are developed to track the maximum power and to control the active and reactive power, without the necessity of an additional power converter. A novel trajectory of the reference current is obtained online taking into account the dynamics of the DC link capacitor and the switching function of the inverter. Unlike to the three-phase system, the single-phase system includes a novel method to mitigate the double line-frequency current ripple of the PV array, which is the major drawback of the single-phase PV inverter. Moreover, based on the preceded work, the nonlinear controller is combined with adaptive control to estimate the unknown disturbances that physically could appear in the circuit and affect the performance of the system. The stability of the systems and boundedness of signals are demonstrated by Lyapunov stability analysis. Simulation results show the effectiveness and robustness of the proposed controllers to track the maximum power and to control the active and reactive power.

This paper proposed a new linear zero dynamic controller (LZDC) for three-phase grid-connected photovoltaic (PV) systems. To implement the controller, the PV is modeled in dq frame which is obtained from park transformation. In order to analyse the stability, the PV system is linearised about an operating point by using Taylor series expansion method. Here the relative degree is investigated through the concept of Lie derivatives to execute the LZDC. To implement the control theory, the stability of the system is also analysed. Finally the linear control law is obtained and implemented on a three-phase grid-connected PV system to control the current injected into the grid through the inverter of the system. The system has been simulated to demonstrate the effectiveness of the proposed scheme.

This paper deals with a key solution for power outages problem experienced by many African countries and this through grid-connected photovoltaic (PV) systems with batteries storage. African grids are characterized by an insufficient power supply and frequent interruptions. Due to this fact, users who especially use classical grid-connected photovoltaic systems are unable to profit from their installation even if there is sun. In this study, we suggest the using of a grid-connected photovoltaic system with batteries storage as a solution to these problems. This photovoltaic system works by injecting the surplus of electricity production into grid and can also deliver electricity as a stand-alone system with all security needed. To achieve our study objectives, firstly we conducted a survey of a real situation of one African electrical grid, the case of Burkina Faso (SONABEL: National Electricity Company of Burkina). Secondly, as study case, we undertake a sizing, a modeling and a simulation of a grid-connected PV system with batteries storage for the LAME laboratory at the University of Ouagadougou. The simulation shows that the proposed grid-connected system allows users to profit from their photovoltaic installation at any time even if the public electrical grid has some failures either during the day or at night.

Recently, the demand for small grid-connected photovoltaic (PV) systems has been rapidly increasing; this is due to the reduction in the costs of grid-connected storage systems as compared to those of the stand-alone ones. Notably, the performance of the solar tracking system is not only depending on the types but also the region that they are set up and used. To understand how solar tracking systems work globally, we need to know their performance in each country and even the different parts of a country. In this study, two grid-connected PV systems with 250 W solar modules were used to investigate the efficient improvement of a single-axis sun tracking system in Central Vietnam. First, a mechanical tracking device with a linear actuator and a controller was designed and then its performance was comprehensively investigated with a grid-connected PV system. In addition to evaluating the energy gain by the tracking system, this study also considered the energy consumption of the linear actuator with its controller and a small grid-connected PV system; this has generally been omitted in previous works. Experimental results indicate that the total energy consumption of the tracking system was approximately 2–8% of the energy generated by the grid-connected PV system. The maximum overall energy generation was confirmed to have increased by up to 30.3% on a sunny day upon using the proposed tracking system; further, the net energy gain by using the sun tracker was ascertained to be 15.2% in average weather conditions. Based on the success of this work, we will keep experimenting with other parts of Vietnam. Also, we will collaborate with colleagues in other countries to create a guideline for understanding and using the solar tracker regionally and globally.

The main objective of this paper is to propose a variable step size Perturb and Observe (P&O) maximum power point tracking (MPPT) algorithm for two-stage three-phase grid-connected photovoltaic (PV) systems. The previous-stage Boost circuit achieves the maximum power point tracking control. The inverter side of the rear-stage realizes the stability of the DC bus voltage and the control of the grid-connected current. By adopting a novel variable-step size P&O algorithm, a fixed step size is adopted when the distance is far from the maximum power point, and the step size is reduced by half every time the working point crosses the peak point, until the final step is smaller than the set threshold and the operating point is stable at the maximum power point. The proposed method effectively solves the problem of slow tracking speed and voltage disturbance near the power point in the conventional fixed-step P&O. In the inverter side, the use of double closed-loop control can ensure the stability of the DC bus voltage and achieve unit power factor grid-connected control. Finally, the proposed algorithm is applied to the two-phase three-phase grid-connected simulation model established in MATLAB. The simulation results show that the proposed method shortens the tracking time by 0.08s and eliminates the power oscillation phenomenon near the maximum power point compared to the fixed step P&O.

This paper considers a three-phase grid-connected photovoltaic (GCPV) system, which comprises a 120kW PV farm connected to the grid through a step-up transformer. GCPV is considered as a distributed generation (DG) serving a variable local load (LL) connected to the low voltage side of the transformer. A power conditioning unit (PCU) consisting of a two-stage energy conversion device is used to (i) maximize the extracted PV farm output power, and (ii) control power exchange with the grid. The PCU regulates the LL voltage level by means of reactive power compensation (RPC). The proposed system is equipped with an intelligent energy harvesting method based on particle swarm optimization-subgradient algorithm (PSO-SG). It is shown that the system operates efficiently using the proposed PCU. Validation of the model has been carried out by using MATLAB/Simulink.

Assesment of grid-connected photovoltaic systems in the Kuwaiti climate

Installations of grid-connected photovoltaic (PV) systems in the United States have increased dramatically in recent years, growing from less than 20 MW in 2000 to nearly 500 MW at the end of 2007, a compound average annual growth rate of 59%. Of particular note is the increasing contribution of 'non-residential' grid-connected PV systems--defined here as those systems installed on the customer (rather than utility) side of the meter at commercial, institutional, non-profit, or governmental properties--to the overall growth trend. Although there is some uncertainty in the numbers, non-residential PV capacity grew from less than half of aggregate annual capacity installations in 2000-2002 to nearly two-thirds in 2007. This relative growth trend is expected to have continued through 2008. The non-residential sector's commanding lead in terms of installed capacity in recent years primarily reflects two important differences between the non-residential and residential markets: (1) the greater federal 'Tax Benefits'--including the 30% investment tax credit (ITC) and accelerated tax depreciation--provided to commercial (relative to residential) PV systems, at least historically (this relative tax advantage has largely disappeared starting in 2009) and (2) larger non-residential project size. These two attributes have attracted to the market a number of institutional investors (referred to in this report as 'Tax Investors') seeking to invest in PV projects primarily to capture their Tax Benefits. The presence of these Tax Investors, in turn, has fostered a variety of innovative approaches to financing non-residential PV systems. This financial innovation--which is the topic of this report--has helped to overcome some of the largest barriers to the adoption of non-residential PV, and is therefore partly responsible (along with the policy changes that have driven this innovation) for the rapid growth in the market seen in recent years.ii Specifically, due to financial innovation, non-residential entities interested in PV no longer face prohibitively high up-front costs, no longer need to be able to absorb Tax Benefits in order to make the economics pencil out, no longer need to be able to operate and maintain the system, and no longer need to accept the risk that the system does not perform as expected.

Grid-connected photovoltaic (PV) systems require a power converter to extract maximum power and deliver high-quality electricity to the grid. Traditional control methods, such as proportional-integral (PI) control for DC-link voltage regulation, often struggle under abnormal operating conditions, resulting in voltage fluctuations and instability in the maximum power point tracker (MPPT). This paper proposes a synergistic control strategy that combines a musical chairs algorithm (MCA) MPPT with sliding mode control (SMC) together for the boost converter DC-link control. This approach enhances DC-link voltage stability by switching the MPPT to SMC of the boost converter when the DC-link voltage exceeds the predefined limit. This strategy enhances the stability of the DC-link voltage and allows for a smaller DC-link capacitor, thereby reducing system cost and improving the power quality of PV systems. A phase-locked loop (PLL) further ensures effective grid synchronization. The reduction in DC-link voltage overshoot (from 570 V to 522 V) improved stability under varying irradiance conditions. Moreover, a 48 V reduction in overshoot voltage and a 66% decrease in DC-link voltage ripple (standard deviation from 17.93 V to 5.92 V) occurred. Simulation and experimental results demonstrate the superiority of the proposed strategy compared to the case without coordination between the DC-DC converter and inverter controllers, particularly under challenging conditions.

Optimal sizing of grid-connected photovoltaic system for a large commercial load in Saudi Arabia

Control of multi-functional grid-connected PV systems with load compensation under distorted and unbalanced grid voltages

Lifetime estimation of modular cascaded H-bridge MLPVI for grid-connected PV systems considering mission profile

To address the issue of energy scarcity and to use solar photovoltaic energy as a renewable source, a three-phase grid-connected photovoltaic inverter system with uncertain system model parameters is investigated, which converts DC power into AC power, feeds it into the grid, and maintains the grid-connected part’s quality. An enhanced back-stepping approach is proposed to explore the control strategy of three-phase solar grid-connected inverter, which includes adaptive control, dissipative theory, sliding mode control, and rapid terminal sliding mode control, respectively. It is verified that the system is subjected to external interference F = 5 during 0.5 s–0.8 s. As per the simulation results, the improved adaptive terminal sliding mode control method can suppress the interference to a certain extent and has strong robustness to the external interference. When compared with the adaptive sliding mode control approach, the anti-interference ability is better, and the system stability is improved. Then, to improve the above approach, a high speed terminal sliding mode control method is proposed, which can swiftly converge in finite time and the estimated value of uncertain parameters is closer to the actual value, thereby boosting the system’s robustness.