Power quality optimization using a novel backstepping control of a three-phase grid-connected photovoltaic systems

A novel nonlinear backstepping controller based on direct current (DC) link voltage control is proposed in three-phase grid-connected solar photovoltaic (PV) systems to control the active and reactive power flow between the PV system and the grid with improved power quality in terms of pure sinusoidal current injection with lower total harmonic distortion (THD), as well as to ensure unity power factor, or to compensate for reactive power required by the load, i.e., the electrical grid. The output power of the PV array is supplied to the grid through a boost converter with maximum power point tracking (MPPT) control and an inverter. Simulation results of the proposed controller show good robustness under nominal conditions, parameter variations, and load disturbances, which presents the main advantage of this controller as compared to an existing controller. The performance of this work was evaluated using a MATLAB/Simulink environment

Backstepping based power control of a three-phase Single-stage Grid-connected PV system

In order to reduce costs while maintaining superior performance, this paper presents a new control methodology of a three-phase grid connected photovoltaic system without using the intermediary DC/DC converter. Based on the synchronized nonlinear model of the whole photovoltaic system, two controllers have been proposed for the three-phase inverter in order to ensure the operation of the PV system at the maximum power point with unity power factor and minimum grid disturbance. Grid synchronization has been ensured by a three-phase 2nd order PLL (Phase-Locked Loop). The stability of each controller is demonstrated by means of Lyapunov analysis and evaluated under changing atmospheric conditions using the Matlab/Simulink environment, the simulation results clearly demonstrate the performance provided by each controller

Grid-connected photovoltaic systems based on nonlinear control.

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

Nonlinear control of two-stage single-phase standalone photovoltaic system

This paper presents a single-phase Photovoltaic (PV) inverter with its superior and robust control in a standalone mode. Initially, modeling and layout of the Buck-Boost DC-DC converter by adopting a non-linear Robust Integral Back-stepping controller (RIBSC) is provided. The controller makes use of a reference voltage generated through the regression plane so that the operating point corresponding to the maximum power point (MPP) could be achieved through the converter under changing climatic conditions. The other main purpose of the Buck-Boost converter is to act like a transformer and produce an increased voltage at the inverter input whenever desired. By not using a transformer makes the circuit size more compact and cost-effective. The proposed RIBSC is applied to an H-bridge inverter with an LC filter to produce the sinusoidal wave in the presence of variations in the output to minimize the difference between the output voltage and the reference voltage. Lyapunov stability criterion has been used to verify the stability and finite-time convergence of the overall system. The overall system is simulated in MATLAB/Simulink to test the system performance with different loads, varying climatic conditions and inverter reference voltages. The proposed methodology is compared with a back-stepping controller and Proportional Integral Derivative (PID) controller under rapidly varying climatic conditions. Results demonstrated that the proposed technique yielded a tracking time of 0.01s, a total harmonic distortion of 9.71% and a root means square error of 0.3998 in the case of resistive load thus showing superior control performance compared to the state-of-the-art control techniques

Design and PIL Test of High Performance MPPT Controller Based on P&O-Backstepping Applied to DC-DC Converter

This paper presents the design, test and validation process of the maximum power point tracking (MPPT) based on the Perturb and Observe backstepping controller. The design of this robust controller follows a sequence of two tests of the validated model-based design (MBD) approach. Our contribution is to give a roadmap for designing, testing and validating embedded software for MPPT algorithms. Perturb and observe algorithm is used to generate the reference voltage which is used by the backstepping controller to generate the maximum power. Then, after simulation of all these techniques, generated optimized C code for the STM32F4 microcontroller is necessary to test the controller on embedded platform. Therefore, the algorithm of MPPT is simulated by Model in the Loop (MIL) and Processor in the Loop (PIL) techniques. The results show that the proposed system has full control over reference power, for different atmospheric changes, by backstepping and integrating into a 32-bit ARM microcontroller. In all of the various tests, the embedded software developed demonstrates high compliance and high performance with MPPT requirements