Necmi Altin

Sliding-Mode Control for Single-Phase Grid-Connected

This paper presents a sliding-mode control (SMC) strategy for single-phase grid-connected LCL-filtered voltage source inverters (VSIs) with double-band hysteresis scheme. The proposed SMC is simpler than the existing SMC methods devised for grid-connected VSIs since its sliding-surface function requires the sensing of capacitor voltage and grid current only. In addition, a double-band hysteresis scheme which ensures the switching of a transistor in the VSI during a half cycle while it remains either on or off in the other half cycle of the fundamental period is used to mitigate the switching frequency. Furthermore, the analytical expressions for the instantaneous and average switching frequencies are derived. The theoretical considerations and analytical results are verified through computer simulations and experimental results obtained from a 3.3-kW system. Simulation and experimental results show that the proposed SMC strategy exhibits an excellent performance in achieving the required control objectives such as fast dynamic response, robustness, sinusoidal grid current with low total harmonic distortion, and simplicity in a practical implementation.

\mbox{LCL}

In this study, an extended Lyapunov-function-based control strategy that assures global asymptotic stability is proposed for single-phase UPS inverters. The Lyapunov function is formed from the energy stored in the inductor and capacitor due to the fact that the system states converge to the equilibrium point if the total energy is continuously dissipated. It is shown analytically that the classical Lyapunov-function-based control leads to a globally asymptotically stable system at the expense of steady-state errors in the output voltage, which exist due to the lack of outer voltage loop in the control input. Therefore, an extended Lyapunov-function-based control strategy is proposed, which eliminates the steady-state error without destroying the global stability of the closed-loop system. The steady state and dynamic performance of the proposed control strategy has been tested by simulations and experiments under resistive and diode bridge rectifier loads. The results obtained from a 1-kW inverter demonstrate that the developed control strategy not only offers global stability, but also leads to good quality sinusoidal voltage with a reasonably low THD, almost zero steady-state error in the output voltage, and fast dynamic response under linear and nonlinear loads.

-Filtered VSI With Double-Band Hysteresis Scheme

This paper presents a new control strategy based on Lyapunov-function and proportional-resonant (PR) controller for single-phase grid-connected LCL-filtered voltage-source inverters (VSIs). While Lyapunov-function-based control guarantees the global stability of the system, the PR controller is employed to process the grid current error and determine the inverter current reference. However, it is shown that the conventional Lyapunov-function-based control (CLFBC) together with the PR control cannot damp the inherent resonance of the LCL filter. Therefore, this control approach is modified by adding a capacitor voltage loop so as to achieve the desired resonance damping. In addition, a transfer function from the reference grid current to actual grid current is formulated in terms of the LCL-filter parameters and their possible variations in the proposed control strategy. An important consequence of using the PR controller is that the need for performing first and second derivative operations in the generation of inverter current reference is eliminated. Also, a zero steady-state error in the grid current is guaranteed in the case of variations in the LCL-filter parameters. The computer simulations and experimental results obtained from a 3.3-kW system show that the proposed control strategy exhibits a good performance in achieving the required control objectives such as fast dynamic response, zero steady-state error, global stability, and sinusoidal grid current with low total harmonic distortion (THD).

An Extended Lyapunov-Function-Based Control Strategy for Single-Phase UPS Inverters

In this paper, interval type-2 fuzzy logic controller based maximum power point tracking method is proposed for photovoltaic systems. The proposed interval type-2 fuzzy logic controlle ...

Lyapunov-Function and Proportional-Resonant-Based Control Strategy for Single-Phase Grid-Connected VSI With LCL Filter

Interest of renewable energy sources increases with the increasing world power demand and decreasing of fossil energy sources. Many of the new energy sources like the PV, the fuel cell or the wind, produces direct voltage so it is needed a suitable direct current to alternating current inverter to connect them to an alternating current load or the utility line. In this case utility interactive inverters became more important. In this study, a dSPACE based current controlled utility interactive inverter has been designed and implemented. PI current controller was used for the production of switching pattern and the output of the inverter was filtered by an LCL type filter. A graphical user interface has been designed to monitor the analog and the digital variables. Results of both MATLAB/Simulink simulation and experimental studies show that inverter output current is in phase with line voltage and current harmonics in the limits of international standards (<5%).

Interval Type-2 Fuzzy Logic Controller Based Maximum Power Point Tracking in Photovoltaic Systems

This paper presents a novel photovoltaic (PV) based three-phase three-level grid-interactive inverter. The proposed system consist of a DC/DC converter, and a three-phase three-level inverter. In order to ensure maximum power point tracking, incremental conductance (IC) technique is used. In addition, to meet international standards for all operating modes, three-phase three-level inverter has been designed and controlled by PI plus grid voltage feed-forward control technique. The proposed system can also operate in various modes to meet smart grids requirements: (1) active power mode in a day time, (2) active and reactive power mode in a day time, (3) reactive power mode at night. To support grid voltage regulation during the day, Mode 1 and Mode 2 are used. These three operation modes bring some benefits such as efficient operation, and reactive power support capability. The proposed system is designed and simulated in Matlab&Simulink software. The simulation results show that the proposed system has an excellent performance under different operating modes.

dSPACE based control of voltage source utility interactive inverter

In this study, a single stage, three-phase, three-level neutral point clamped inverter is designed for grid connected renewable energy systems. The proposed voltage source inverter is operated in current controlled mode and a PI current controller is used for the production of switching pattern. Also the proposed inverter is operated in parallel with public grid by using phase locked loop method. Maximum power point tracking process which is aimed to obtain maximum energy from the supply is performed via the proposed inverter without using any additional DC-DC converter. Maximum power point tracking algorithm generates the current reference for the current controller. Results of experimental studies show that inverter output current is in phase with line and unity power factor operation is obtained. Also inverter output current total harmonic distortion is measured as 3.95%. This value is in the limits of international standards (5%).

Three-phase multilevel grid interactive inverter for PV systems with reactive power support capability

Interleaved DC-DC buck converters are used in medium to high power applications with their advantages such as low electromagnetic interference and output voltage ripples. Although, discrete core inductors can be used, coupled inductors which use the same magnetic core can be used to obtain optimum design such as volume, cost and efficiency in interleaved converters. Also, in coupled inductor applications, duty ratio, saturation effect and interactions of the windings should be analyzed carefully. In this study, selection of core structure with different types of coupled inductors is investigated for whole operation range. Simulations are performed with co-simulations of Ansoft-Maxwel 3D and Simplorer software. Inductors that are designed in Maxwell by using Kool Mu E cores are used with buck converter, which was modeled in Simplorer. Results obtained from simulation studies are reported and compared with each other.

Single stage three-level MPPT inverter for solar supplied systems

In this study, simulation of the single phase grid interactive photovoltaic system is proposed. The proposed system consists of a maximum power point tracking boost converter and a grid interactive voltage source inverter. Interval type-2 fuzzy logic controller is used to track the maximum power point of photovoltaic arrays. Photovoltaic supplied DC electric energy is inverted to AC and imported to the grid via voltage source grid interactive inverter. PI current controller was used for the production of switching pattern of the grid interactive inverter. LCL type filter is used at the output of the inverter to filter switching noise. Simulation studies are carried out by MATLAB/Simulink. The simulation results show that, proposed maximum power point tracking algorithm has fast transient response and it is especially suitable for fast changing environmental conditions. Also inverter output current is in phase with line voltage and current harmonics of the inverter is in the limits of international standards (>5%).

Comprehensive analysis of inductors for an interleaved buck converter

In this study, power factor correction rectifier is proposed for wind turbines with three phase permanent magnet synchronous generators to provide maximum energy conversion efficiency. Reference values for the rectifier are controlled by a fuzzy logic based algorithm to track maximum power point of the wind turbine which varies with turbine characteristics, wind speed, temperature, etc. The proposed maximum power point tracking algorithm removes the requirement of knowledge about the wind generator optimal power characteristics, or measurement of the wind speed, and provides variable speed operation of wind turbine. Therefore, wind energy conversion system with higher reliability, lower complexity and cost, and less mechanical stress are obtained. Maximum power point tracking algorithm and phase locked loop circuit determining the current reference values are determined, and PI regulators are used to control of the DC voltage and line currents of the rectifier. Three level neutral point clamped rectifier topology is used as main converter. Because this topology does not require isolated DC sources and power switch modules for a leg of the rectifier are commercially available, design and implementation of the neutral point clamped rectifier is simple. Simulation results show that proposed rectifier tracks the maximum power point of the wind turbine either in variable frequency and power levels. Also line currents of the rectifiers are in same phase and frequency with permanent magnet synchronous generator voltage. In addition, THD levels of the rectifier input currents and power factor are obtained as <;5% and 0.99, respectively.