Stability analysis of grid-connected photovoltaic systems using a linear zero dynamic controller

In this paper, a direct power control (DPC) approach is used to control the active and reactive power injection into the grid from a photovoltaic (PV) unit. The dynamics of active and reactive power are used to develop the dynamical model of the three-phase grid-connected PV (GCPV) system while a nonlinear adaptive technique is employed to design the proposed controller. The parametric uncertainties are incorporated within the dynamical model of three-phase GCPV systems by considering the parameters as totally unknown. The unknown parameters are estimated through adaptation laws and control Lyapunov functions (CLFs) are formulated during the different stages of the controller design process to ensure the overall stability of the GCPV system. The theoretical stability of the three-phase GCPV, with the proposed control scheme, is analyzed through the negative semi-definiteness of the derivatives of CLFs. Simulations are carried out to further validate the performance of the proposed control scheme on a three-phase GCPV system in terms of injecting power (both active and reactive) into the grid along with the power quality. Simulation results demonstrate effectiveness of the proposed controller as compared to an existing sliding mode controller (SMC).

For utility-scale photovoltaic (PV) systems, the control objectives, such as maximum power point tracking, synchronization with grid, current control, and harmonic reduction in output current, are realized in single stage for high efficiency and simple power converter topology. This paper considers a high-power three-phase single-stage PV system, which is connected to a distribution network, with a modified control strategy, which includes compensation for grid voltage dip and reactive power injection capability. To regulate the dc-link voltage, a modified voltage controller using feedback linearization scheme with feedforward PV current signal is presented. The real and reactive powers are controlled by using $dq$ components of the grid current. A small-signal stability/eigenvalue analysis of a grid-connected PV system with the complete linearized model is performed to assess the robustness of the controller and the decoupling character of the grid-connected PV system. The dynamic performance is evaluated on a real-time digital simulator.

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.

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 novel multi-input multi-output (MIMO) linear zero dynamic controller (LZDC) for a three-phase grid-connected photovoltaic (PV) system. The relative degree is investigated through the concept of Lie derivative to execute the LZDC for three phase grid connected PV system. To implement the control theory, system stability is checked by the LZDC scheme. The linear zero dynamic control law is obtained to control the injected power into the grid through the system's inverter. Finally, the simulation results are presented to show the performance of MIMO LZDC scheme with weather disturbances such as 10%, 20%, and 30% sunshade on the PV strings and also proved that the system operated at the unity power factor.

Problems with voltage and stability have arisen as a result of the dramatic development in renewable energy generating units, notably solar energy systems linked to low and medium voltage networks, and the influence of active loads that vary rapidly from time to time during the day. Because reactive power is directly proportional to voltage, its use to renewable energy producing units can only improve their efficiency. Better performance for these controllers is possible via the usage of several controller types. In this paper, we use a salp swarm optimization algorithm (SSA) to design fractional order proportional-integral (FO-PI) controllers, whose job it is to regulate the active and reactive power of solar inverters by compensating for the overvoltage and undervoltage presented by the inverters' ability to absorb and produce reactive power. After that, we compared the FO-PI controller's results to those of the standard PI controller. Grid-connected photovoltaic (PV) system modeling and simulation were performed using the MATLAB/ Simulink modeling and simulation tools. After that, the full PV system was simulated in the most likely situations across a range of grid and weather conditions. We may infer from the simulation results that this model is credible, reliable, and applicable to the analysis of grid-connected PV systems.

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.

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

Assesment of grid-connected photovoltaic systems in the Kuwaiti climate

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.

Grid-connected photovoltaic (PV) systems with relatively high capacity effectively reduce peak load, but because of their reverse power flow, they can cause overvoltage along a feeder that can exceed five percent of the rated voltage. Modern PV systems with the capability of Volt/Var control can mitigate overvoltage by either injecting or absorbing reactive power. Thus, the objectives of this study are to (1) model a distribution network (feeder J1 located in the northeastern United States and enhanced by thirteen PV systems) using OpenDSS; (2) use actual collected load profile data as input data to the simulation model and PV generation output data at 15-minute intervals; and (3) calculate the time-series steady-state power flow of the distribution network when PV systems generate or absorb reactive power. Finally, it addresses overvoltage resulting from the deployment of high-capacity grid-connected renewable PV systems and mitigation techniques for such overvoltage issues, particularly Volt/Var management and control.

Grid-connected photovoltaic (PV) systems are currently developed by merging a PV array and a DC/AC inverter which are designed separately, without considering the impact of the PV array operational characteristics on the power losses of the DC/AC inverter. In this paper, a co-design technique is presented, where the optimal design parameters of the PV array and DC/AC inverter in a grid-connected PV system are calculated concurrently through a unified design process. The proposed technique enables to optimally match the PV array configuration and the DC/AC inverter structure. A study has been performed, where the PV systems synthesized by applying the proposed co-design technique are compared with the PV system configurations comprising PV arrays and DC/AC inverters that have been designed separately, through distinct optimization processes based on various alternative optimization objectives. The design results for two installation sites, with different meteorological conditions during a year, demonstrated that only the proposed co-design optimization technique is capable of ensuring the maximization of the annual energy production of the overall grid-connected PV system.

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

Performance results and analysis of 3 kW grid-connected PV systems

The performance of grid-connected Photovoltaic (PV) power generation system operating in the field is inevitably affected by environmental parameters (solar irradiance, temperature, humidity, wind speed, spectrum, cloud cover, dust, etc.), of which the main factors are solar irradiance and temperature. Based on the data of 100kW PV system of ShangYi PV Plant captured form June 1, 2012 to May 31, 2013 (1 min resolution) and the data of Qinghai Delingha 20MW PV Plant in China captured in 2012., the influence of solar irradiance and temperature on PV system is analyzed. The results show hourly PV array DC power has highly significant positive correlation with hourly total solar radiation, also PV system AC power output and solar irradiance have good consistency. Both of them show irradiance is the main environment factor to the PV system. Then using the captured data, the relationship between maximum load and PV panels surface temperature is also analyzed, the surface temperature is higher, the maximum load is lower.