Variable-step incremental conductance (Inc.Cond.) technique, for photovoltaic (PV) maximum power point tracking, has merits of good tracking accuracy and fast convergence speed. Yet, it lacks simplicity in its implementation due to the mathematical division computations involved in its algorithm structure. Furthermore, the conventional variable step-size, based on the division of the PV module power change by the PV voltage change, encounters steadystate power oscillations and dynamic problems especially under sudden environmental changes. In this study, an enhancement is introduced to Inc.Cond. algorithm in order to entirely eliminate the division calculations involved in its structure. Hence, algorithm implementation complexity is minimised enabling the utilisation of low-cost microcontrollers to cut down system cost. Moreover, the required real processing time is reduced, thus sampling rate can be improved to fasten system response during sudden changes. Regarding the applied step-size, a modified variable-step size, which depends solely on PV power, is proposed. The latter achieves enhanced transient performance with minimal steady-state power oscillations around the MPP even under partial shading. For proposed technique's validation, simulation work is carried out and an experimental set up is implemented in which ARDUINO Uno board, based on low-cost Atmega328 microcontroller, is employed

In this paper, a DC-link voltage sensorless control technique is proposed for single-phase two-stage grid-coupled photovoltaic (PV) converters. Matching conventional control techniques, the proposed scheme assigns the function of PV maximum power point tracking (MPPT) to the chopper stage. However, in the inverter stage, conventional techniques employ two control loops; outer DC-link voltage and inner grid current control loops. Diversely, the proposed technique employs only current control loop and mitigates the voltage control loop thus eliminating the DC-link high-voltage sensor. Hence, system cost and footprint are reduced and control complexity is minimized. Furthermore, removal of the DC-link voltage loop proportional-integral (PI) controller enhances system stability and improves its dynamic response during sudden environmental changes. System simulation is carried out and an experimental rig is implemented to validate the proposed technique effectiveness. In addition, the proposed technique is compared to the conventional one under varying irradiance conditions at different DC-link voltage levels, illustrating the enhanced capabilities of the proposed technique.

Smart grid philosophy recommends a wide spread of residential roof-top installed grid-connected photovoltaic (PV) systems as a benchmark for renewable energy (RE) emphasis to future power generation. These systems must adopt power electronic-based converters to perform grid integration function. On the other side, concerns about voltage fluctuations, which are directly related to power system stability, have arisen from the increasing use of intermittent renewable energy sources (RES) distributed in the grid. Hence, a power electronic-based converter topology, known as Electric Spring (ES), has been developed to be additively connected in series with non-critical residential loads. It has the ability to regulate the mains voltage via reactive power compensation. In this paper, a novel control scheme is proposed for ESs operation. The presented control technique offers conventional ES a decoupled dual functionality. Besides, its inherent ability of feeder voltage regulation, the ES can, under the proposed control technique, simultaneously inject locally available PV power into the grid via the same power electronic converter. The system analysis and mathematical modeling of the proposed control scheme are demonstrated in detail. To verify the proposed technique effectiveness, both simulation and experimental investigation are carried under various bus voltage levels' cases: normal, sag, and swell. Moreover, the system performance is attested under irradiance changes. The results from simulations and experimental setup prove the applicability of the ES dual functionality even under severe disturbances. INDEX TERMS Bus voltage regulation, dual function converter, electric spring, maximum power point tracking, photovoltaic, grid interface, voltage sag, voltage swell.

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Photovoltaic (PV) energy systems rapidly penetrate global renewable energy market recently due to their direct energy conversion, environmental friendly and modularity features. Partial shading and irradiance mismatch create one of the major challenges that face commercial PV converters. Software based maximum power point tracking (MPPT) algorithms show limited performance as only the global peak power of the attached PV string can be captured. On the contrary, modified PV string converters can achieve true MPP acquisition, hence maximizing the system power yield and enhance the overall performance. In this paper, a partial-shading-tolerant PV string system is proposed that feature (i) a multi-input multi-output (MISO) PV string converter and (ii) true MPP seeking event-driven based MPPT technique as well. The presented converter feature a single inductor buck configuration with multi-input ports attached to N number of PV panels offering reduced passive components and extended modularity feature in addition to single digital controller implementation. The presented MPPT technique exhibits decoupled tracking of the true power of each connected PV panel independently irrespective of the other attached panels even under extreme inhomogeneous irradiance distribution. Rigorous simulation results accompanying matched experimental validation assure the proposed system applicability. Dynamic modelling, in addition to various operating conditions assessments, verify the claimed effectiveness of the proposed system.

Stand-alone/grid connected renewable energy systems (RESs) require direct current (DC)/DC converters with continuous-input continuous-output current capabilities as maximum power point tracking (MPPT) converters. The continuous-input current feature minimizes the extracted power ripples while the continuous-output current offers non-pulsating power to the storage batteries/DC-link. CUK, D1 and D2 DC/DC converters are highly competitive candidates for this task especially because they share similar low-component count and functionality. Although these converters are of high resemblance, their performance assessment has not been previously compared. In this paper, a detailed comparison between the previously mentioned converters is carried out as several aspects should be addressed, mainly the converter tracking efficiency, conversion efficiency, inductor loss, system modelling, transient and steady-state performance. First, average model and dynamic analysis of the three converters are derived. Then, D1 and D2 small signal analysis in voltage-fed-mode is originated and compared to that of CUK in order to address the nature of converters’ response to small system changes. Finally, the effect of converters’ inductance variation on their performance is studied using rigorous simulation and experimental implementation under varying operating conditions. The assessment finally revels that D1 converter achieves the best overall efficiency with minimal inductor value.

In this paper, a single-phase single-stage photovoltaic (PV) grid-tied system is investigated. The conventional pulse width modulated (PWM) voltage source inverter (VSI) is replaced by a PWM current source inverter (CSI) for its voltage boosting capabilities, inherent short-circuit proof and higher reliability features. Modeling, design, and analysis of the considered CSI are presented altogether with enhanced proposed control loops aided with a modified PWM technique. DC-link even current harmonics are commonly reflected as low-order odd harmonics in the grid resulting in a poor quality grid current. In order to overcome the latter, a high performance proportional resonant controller, applied in the inverter inner grid current loop, is proposed using cascaded resonant control units tuned at low-order frequencies to eliminate injected grid current harmonics. Hence, with a less-bulky smoothing inductor at the CSI DC-side, grid power quality and system efficiency are simultaneously improved. Simulation and experimental results verify the proposed controller effectiveness.

Low-voltage ride-through (LVRT) and grid support capability are becoming a necessity for grid-tied renewable energy sources to guarantee utility availability, quality and reliability. In this paper, a swap control scheme is proposed for grid-tied permanent magnet synchronous generator (PMSG) MW-level wind turbines. This scheme shifts system operation from maximum power point tracking (MPPT) mode to LVRT mode, during utility voltage sags. In this mode, the rectifier-boost machine-side converter overtakes DC-link voltage regulation independently of the grid-side converter. The latter attains grid synchronization by controlling active power injection into the grid to agree with grid current limits while supporting reactive power injection according to the sag depth. Thus grid code requirements are met and power converters safety is guaranteed. Moreover, the proposed approach uses the turbine-generator rotor inertia to store surplus energy during grid voltage dips; thus, there is no need for extra hardware storage devices. This proposed solution is applied on a converter topology featuring a minimal number of active switches, compared to the popular back-to-back converter topology. This adds to system compatibility, reducing its size, cost and switching losses. Simulation and experimental results are presented to validate the proposed approach during normal and LVRT operation.