The increasing rate of renewable energy penetration in modern power grids has prompted updates to the regulations, standards, and grid codes requiring ancillary services provided by photovoltaic-generating units similar to those applied to conventional generating units. In this work, a comprehensive survey presents a comparison of requirements related to voltage ride through reactive current injection/absorption; active power restoration; frequency stability regulation and active power control; voltage regulation and reactive power control; and the energy quality requisites included in the standards and grid codes of countries around the globe. The survey can be used to observe the differences between the requirements established in the grid codes depending on the power system operating characteristics, development of technology, and renewable energy penetration level. Many of these factors determine the parameters used to establish requisites for different grid codes, making a global standardization of the renewable energy interconnection requirements much harder.

The development of technologies to improve the performance of photovoltaic (PV) module integrated converters (MICs) is fundamental to increase the use of distributed generation systems with photovoltaic power source in large urban centers, mainly for complex residential roofs. For two-stage PV MICs, high step-up DC-DC converters are required to boost the low PV module voltage to a higher voltage, in order to suit the DC bus voltage requirements of grid-tied inverters. Thus, to support researchers interested in developing DC-DC power conversion for PV microinverters, this paper classifies the DC-DC converters according to their operational and constructive characteristics and presents some elementary voltage-boosting techniques to aid in analyzing and understanding more complex topologies. Finally, high step-up DC-DC converters based on magnetic coupling and switched capacitor widely cited by important works related to PV applications are presented, with their principles of operation analysed in a simple and objective way, but sufficient to understand their capability to provide high voltage gain. The approach presented by this paper leads to insight into how to place the energy storage elements to create new topologies of DC-DC converters, so that high voltage gain is achieved, and how to analise the high voltage gain capability of complex topologies

This article proposes a hybrid global maximum power point (MPP) tracking technique, named improved global fractional characteristic curve (IGFCC), which combines the advantages of both the model-based and heuristic techniques. The IGFCC technique aims to achieve high speed and accuracy in tracking the MPP of photovoltaic (PV) modules. The model-based technique employed in the IGFCC technique utilizes a precise single-diode model that considers the effects of irradiance and temperature to estimate the MPP voltage. This model-based approach ensures accurate tracking of the MPP and is particularly suitable for PV series applications with string inverters. One of the advantages of the IGFCC technique is its computational efficiency. It involves solving simple equations derived from the single-diode model, which reduces the computational effort required for MPP tracking. This makes the technique practical and feasible for real-time implementation.

The increasing number of megawatt-scale photovoltaic (PV) power plants and other large inverter-based power stations that are being added to the power system are leading to changes in the way the power grid is operated. In response to these changes, new grid code requirements establish that inverter-based power stations should not only remain connected to the grid during faulty conditions but, also provide dynamic support. This feature is referred in the literature to as momentary cessation operation. The few published studies about momentary cessation operation for PV power plants have not shed much light on the impact of these systems on the overall power system stability problem. As an attempt to address this issue, this paper proposes a control scheme for PV inverters that improves the transient stability of a synchronous generator connected to the grid. It is shown through the paper that the proposed control scheme makes the PV inverter's dc link capacitors absorb some of the kinetic energy stored in the synchronous machine during momentary cessation. Besides that, the proposed solution is also able to improve voltage stability through the injection of reactive power. Experimental and simulation results are presented in order to demonstrate the effectiveness of the proposed control scheme.

This article proposes a current-fed high-gain high-efficiency dc–dc converter for renewable energy applications such as photovoltaic energy. The converter is based on the modified SEPIC, in which the secondary inductor is replaced with a built-in transformer with differentially connected windings (mSEPIC-DBT). The high voltage gain is achieved through a magnetic-coupling-based VMC, in which the built-in transformer is paired to diodes and capacitors. The capacitors, alongside the leakage inductances of the transformer, form a resonant tank, allowing for the zero-current switching of the diodes, while also blocking dc currents from circulating through the transformer windings, which, in turn, allows employing gapless cores for the transformer, reducing its size. The converter operational stages are discussed and steady-state analysis is performed, from which the design guidelines are derived. The theoretical analyses are validated by an experimental 300-W, 50-kHz laboratory prototype. The experimental results show a full-load efficiency of 96.6% and a maximum efficiency of 96.8% at 90% of the full load, which demonstrate that the proposed converter is a strong candidate for applications that require high voltage gains.

In this paper, a generic complex repetitive controller (nk + m RC, k$\times$Z), based on the inverse transfer function of the generalized delayed signal cancelation transformation is proposed. The presented complex controller can be designed for regulating different positive- and negative-sequence harmonic components through a space-vector error signal, with improved response time as compared to traditional repetitive controllers. An evaluation of the proposed control scheme stability, based on phase margin, Nyquist diagram and sensitivity function is presented. The effects of the controller parameters on the system's stability and also on its dynamic response are shown and allow the definition of some control design guidelines. Experimental results are presented to validate the theoretical assumptions through applying the proposed controller for regulating the currents in a three-phase active power filter.