F. Liccardo

Robust and Fast Three-Phase PLL Tracking System

This paper presents a simple, robust, and fast synchronization method to detect the phase angle of the positive sequence of a three-phase ac system. The algorithm was derived from a standard phase-locked-loop (PLL) circuit based on the pq theory, but a feedforward action is implemented to guarantee high dynamic performance in conjunction with a modified feedback action to reduce the phase-angle estimation error to zero. The result is a fast tracking system that improves the start-up stage and rapid input variations. It guarantees accurate phase locking and is robust with respect to ac distortions such as harmonics, subharmonics, and voltage imbalance. The control model for the proposed PLL system was based on the standard qPLL structure. A linear analysis was performed to show the benefits of the proposed solution, and recommendations are given for tuning its parameters. The proposed technique was tested and compared with other algorithms by means of simulations. The experimental and simulation results are shown and compared.

Ancillary Services performed by Distributed Generation in grid integration

In this paper ancillary services performed by distributed generation (DG) sources connected to the grid are discussed. Wind energy is analyzed as case study of renewable DG source. Variable speed wind turbines are connected to the grid by power electronics converters, which are typically controlled in order to transfer to the grid the whole captured active power from the wind. Moreover a proper control of the power converters makes the DG able to perform some ancillary services. In this paper point of common coupling (PCC) voltage amplitude regulation, reactive power compensation and active parallel filtering are analyzed. Converter sizing is discussed to be the limiting factor in performing the considered ancillary services.

Interleaved dc-dc Converters for Photovoltaic Modules

In the present paper, an application of interleaved dc-dc converter in photovoltaic (PV) modular system has been presented. In the multi-string technology, several PV strings are interfaced with their own dc-dc converter to a common dc-ac inverter. Enlargements are easily achieved since a new string with dc-dc converter can be plugged into the existing platform. This paper proposes a simple method to connect various PV modules in order to improve power quality. Thanks to the proposed digital control method, the PV interleaving becomes simple and efficient in terms of dynamic performances, steady-state condition and well regulated output voltage.

Buck-boost DC/DC converter for aeronautical applications

In this document a DC/DC converter for power conversion between +28V/+270V voltage levels is presented, and the main characteristics of the converter are discussed. The topological structure is first introduced, outlining the hardware components used and the modular approach. The step-down (or Buck) and step-up (or Boost) modulations are then discussed, focusing on the switching signals to drive the low-voltage and high-voltage bridges of the single modules. The description of the control phase follows, justifying the controller used to steer the output voltage towards the desired value. The firmware realized for the converter management is equipped also with a supervision and protection logic, realized as a composition of finite state machines. Finally, simulative results and real measurements are provided to evidence the correctness of the overall topological choices and of the control system realized for the bidirectional converter, focusing also on the comparison between the expected results and those obtained.

High Power Three phase four wires Synchronous Active Front-End

In this paper, the authors propose an efficient control technique applied to an innovative three phase four wires active front-end (AFE) topology. It is composed of n parallel-connected two-level three phase AC-DC boost converters, with common DC-link capacitor. In order to improve power quality and performance in high power applications, the n converters are synchronously driven. This proposed system is called SAFE (synchronous active front-end). These converters are used as unitary displacement power factor (DPF) AC-DC PWM rectifiers. A central point technique control by a four-wires AFE is also presented. This solution guarantees the ripple cancellation on the AC side and a higher switching frequency respect to single AFE solution. The overall system can successfully manage the well known trade-off between high power handling and high switching frequency, with regards to utility side effects

Three-phase robust series compensator for voltage disturbances

In this paper the problem of voltage disturbances compensation in a three-phase three-wire electrical industrial system is addressed. A robust synchronous-based control algorithm is proposed for both endogenous and exogenous voltage disturbances compensation. The compensator is made of series transformers fed by a PWM-voltage source inverter (VSI). The control system regulates to zero the d- and q- components of the fundamental negative sequence of the supply voltages and compensates their harmonic content, by means of a feed-forward and of a feedback action. The influence of the passive filter for the switching ripple, on the compensator performances, has been investigated. Numerical simulations validate the effectiveness of the proposed compensation strategy.

Active front-end design criteria

In this paper some design criteria for an active front-end (AFE) are presented. The rules are formulated on the basis of the rated power of the line where the AFE is connected. The proposed AFE is based on the voltage processing and supply current reaction algorithm for power shunt active filters and performs the AC-DC conversion, the line current distortions and the reactive power compensation. A shunt capacitive filter is presented to compensate not only the node voltage disturbances due to the AFE switching, but also the average reactive power. The design criteria and the problems connected to the passive filter are discussed. Numerical simulations validate the proposed criteria.

Interleaved Active Front-Ends Design Criteria for Reliability improvements

This paper describes the advantages that can be obtained in ac/dc conversion, when an innovative four-quadrant converter, named synchronous active front-end (SAFE), is employed. The modular system, which increases the availability of the power delivering, can also be designed in order to obtain an improvement of the mission reliability. The reliability of single-AFE topology and the one of a SAFE are here compared. Based on the classical reliability prediction method, this contribution gives a design criteria of the optimum number of the parallel-connected converters and of their switching frequency, in order to match the reliability constrains.

Three-phase four-wire active front-end feeding a three-level voltage source inverter

A four-wire two-level active front-end (AFE) interlacing a three-level voltage source inverter (VSl) to the utility network is proposed. The AFE consists of a classical three-phase four-wire ac-dc boost rectifier with two split-capacitors. It absorbs almost sinusoidal currents with unity power factor. Moreover it is controlled in order to guarantee the dc-levels balancing. With reference to the control algorithm of the AFE a new robust synchronization mechanism to detect the phase angle of the positive sequence of the node voltages is proposed. Numerical simulations show the effectiveness of the proposed AFE applied to feed an induction motor based adjustable speed drive (ASD) controlled by means of a field oriented control (FOC) technique.

Multilevel harmonics current active compensator for DC feeding line

In this paper a new DC line current compensator is presented. The proposed converter is able to compensate very low amplitude current harmonics and is very useful in railway applications where harmonic pollution can produce interference in the signaling systems over DC lines. The active compensator is modular and composed by multiple cells connected in series and controlled in order to minimize the modulation current ripple. Moreover a design criteria are shown and simulation results demonstrate the effectiveness of the proposed solution.