Photovoltaic Systems (PVS) can be easily integrated in residential buildings hence they will be the main responsible of making low-voltage grid power flow bidirectional. Control issues onboththePVsideandonthegridsidehavereceivedmuchattention from manufacturers, competing for efficiency and low distortion and academia proposing new ideas soon become state-of-theart. This paper aims at reviewing part of these topics (MPPT, current and voltage control) leaving to a future paper to complete the scenario.ImplementationissuesonDigitalSignalProcessor(DSP), the mandatory choice in this market segment, are discussed.

Pulsewidth modulation (PWM) voltage source converters are becoming a popular interface to the power grid for many applications. Hence, issues related to the reduction of PWM harmonics injection in the power grid are becoming more relevant. The use of high-order filters like LCL filters is a standard solution to provide the proper attenuation of PWM carrier and sideband voltage harmonics. However, those grid filters introduce potentially unstable dynamics that should be properly damped either passively or actively. The second solution suffers from control and system complexity (a high number of sensors and a high-order controller), even if it is more attractive due to the absence of losses in the damping resistors and due to its flexibility. An interesting and straightforward active damping solution consists in plugging in, in cascade to the main controller, a filter that should damp the unstable dynamics. No more sensors are needed, but there are open issues such as preserving the bandwidth, robustness, and limited complexity. This paper provides a systematic approach to the design of filter-based active damping methods. The tuning procedures, performance, robustness, and limitations of the different solutions are discussed with theoretical analysis, selected simulation, and experimental results.

This paper describes the design procedure and performance of an LCL grid filter for a medium-voltage neutral-point clamped converter to be adopted for a multimegawatt (multi-MW) wind turbine. The unique filter design challenges in this application are driven by a combination of the medium-voltage converter, a limited allowable switching frequency, component physical size and weight concerns, and the stringent limits for allowable injected current harmonics. Traditional design procedures of grid filters for lower power and higher switching frequency converters are not valid for a multi-MW filter connecting a medium-voltage converter switching at low frequency to the electric grid. This paper demonstrates a frequency-domain-model-based approach to determine the optimum filter parameters that provide the necessary performance under all operating conditions given the necessary design constraints. To achieve this goal, new concepts, such as virtual-harmonic content and virtual filter losses are introduced. Moreover, a new passive-damping technique that provides the necessary damping with low losses and very little degradation of the high-frequency attenuation is proposed.

Multimegawatt wind-turbine systems, often organized in a wind park, are the backbone of the power generation based on renewable-energy systems. This paper reviews the most-adopted wind-turbine systems, the adopted generators, the topologies of the converters, the generator control and grid connection issues, as well as their arrangement in wind parks.

Grid-connected photovoltaic (PV) inverters employ an islanding-detection functionality in order to determine the status of the electrical grid. In fact, the inverter must be stopped once the islanding operating mode is detected according to standards and grid-code limits. Diverse islanding-detection algorithms have been proposed in literature to cope with this safety requirement. Among them, active methods based on the deliberate perturbation of the inverter behavior can minimize the so-called nondetection zone, which is a range of conditions in which the inverter does not recognize that it is operating in an undesired island. In most cases, the performances of these methods have been analyzed considering a highly dispersed generation scheme, where only one distributed-generation power system is connected to the local electrical power system (EPS). However, in some studies, it has been highlighted that if two or more PV inverters are connected to the same local EPS, their anti-islanding algorithms do not behave ideally and can fail in detecting the islanding condition. However, there is no systematic study that has investigated the overall capability of different anti-islanding methods employed on several inverters connected to the same EPS to detect islanding condition. This paper is a first attempt to carry out a systematic study of the performances of the most common active detection methods in a case of two inverters connected to the same EPS. In order to evaluate the global capability of the two systems to detect islanding condition, a new performance index is introduced and applied also to the case when the two inverters employ different anti-islanding algorithms.

Three-phase active rectifiers guarantee sinusoidal input currents and unity power factor at the price of a high switching frequency ripple. To adopt an LCL-filter, instead of an -filter, allows using reduced values for the inductances and so preserving dynamics. However, stability problems can arise in the current control loop if the present resonance is not properly damped. Passive damping simply adds resistors in series with the LCL-filtercapacitors.Thissimplicityisattheexpenseofincreased losses and encumbrances. Active damping modifies the control algorithm to attain stability without using dissipative elements but,sometimes,needingadditionalsensors.Thissolutionhasbeen addressed in many publications. The lead-lag network method is one of the first reported procedures and continues being in use. However, neither there is a direct tuning procedure (without trial anderror)noritsrationalehasbeenexplained.Thus,inthispaper a straightforward procedure is developed to tune the lead-lag network with the help of software tools. The rationale of this procedure,basedonthecapacitorcurrentfeedback,iselucidated. Stability is studied by means of the root locus analysis in -plane. Selecting the lead-lag network for the maximum damping in the closed-loop poles uses a simple optimization algorithm. The robustness against the grid inductance variation is also analyzed. Simulations and experiments confirm the validity of the proposed design flow.