C. Picardi

A Power Electrical Signal Tracking Strategy Based on the Modulating Functions Method

The number of pieces of equipment based on static converters such as uninterrupted power systems, series or shunt compensators, and distributed generation systems is increasing in the actual power distribution systems. For correct operation in grid-connected condition, these equipment need the information about amplitude, phase angle, and frequency of the grid fundamental voltages and currents. Since noise, harmonic pollution, and frequency variations are common problems in the utility grid, then it is necessary to have systems able to extract information about the fundamental values from highly distorted signals. For these reasons, robust and accurate estimation and synchronization methods are necessary to obtain the aforementioned information also in noise environmental. This paper presents a power electrical signal tracking strategy consisting in the combined use of a simple and robust frequency estimation method based on modulating functions and an orthogonal system generator including the second-order generalized integrator. The proposed strategy has the advantages of a fast and accurate signal tracking capability and a good rejection to noise due to the low-pass filter properties of the modulating functions. The effectiveness of the proposed method is validated through comparisons with existing methods performing simulated and laboratory experiments.

Power management by grid-connected inverters using a voltage and current control strategy for Microgrid applications

This paper presents the application of a suitable control strategy for multibus microgrid applications. The control strategy, used with each distributed generation system in the microgrid is developed so as to combine the advantages of the current control and the voltage control strategies. The performance of the proposed application in terms of power management has been verified in simulation on a microgrid test.

Sliding-Mode Observer with Resistances or Speed Adaptation for Field-Oriented Induction Motor Drives

A sliding-mode observer working in parallel with a particular adaptive scheme is proposed for field-oriented control of induction motor. The observer detects the rotor flux components in the two-phase stationary reference frame. The adaptive scheme is able to on-line estimate either the motor resistive parameters or the rotor speed. In the former case, the adaptive scheme allows to have continuously the exact values of the stator and rotor resistances, parameters usually subjected to variations from their nominal values. In the second one, the scheme can be used to realize an induction motor sensorless speed control. The analytical development of the sliding mode observer and the adaptive scheme is fully explained. Simulation results, based on a Matlab/Simulink/real-time-workshop model designed on purpose, are presented to verify the validity of the proposed adaptive observer structure

A simple and low-cost PLL structure for single-phase grid-connected inverters

This paper presents a new PLL structure for single-phase grid-connected systems. Its peculiarity consists in the presence of an orthogonal signal generator, not dependent on the frequency of the input grid voltage and realized by simple and low-cost analog and digital devices. The paper gives a detailed description of the proposed PLL structure, also dealing with the appropriate design of the analog section that includes integrator and derivator circuits. The effectiveness of the proposal is validated by laboratory experiments on a prototypical realization of the proposed PLL structure.

Grid-connected inverters for alternative energy sources with a combined voltage and current control strategy

Renewable energy sources are considered as important generation alternatives in electric power systems due to their no exhausted nature and benign environmental effects. In order to utilize the infrastructure of the actual distribution network, grid-connected inverters are needed. In this paper a new control strategy for a pulse width modulation (PWM) three-phase voltage source inverter (VSI) connected to the grid and able to support bi-directional power flow is presented. In particular, the proposed strategy is developed so as to combine the advantages of the current control and the voltage control. The effectiveness of this combined control strategy is proved by some numerical results compared with those obtained applying only the conventional current control strategy.

Grid-connected inverter power flow control based on a new modeling approach of electrical signals

The authors have recently presented a new modeling approach for electrical signals in power systems. A significant advantage lies in the possibility to define quantities typically considered in sinusoidal steady-state conditions also during the transients. This paper presents a power flow control strategy, based on the aforesaid approach, for a PWM inverter able to support bidirectional power flow and so to operate as efficient interface between a DC power source (for example a photovoltaic source) and the power distribution grid.

Reactive power and voltage harmonics compensation applied of a shunt power active filter

This paper proposes a particular shunt power active filter including a conventional three-leg voltage source-inverter connected to the point of common coupling (PCC) between the distribution network and the load. The paper describes the structure of the power filter and then it gives a detailed explanation of the adopted strategy to control the reactive and active power flows and to compensate the voltage harmonics. Simulation results are presented to verify the performance of the proposed power active filter

A novel integrated configuration of Grid-connected photovoltaic plant with UPS: reliability estimation

This paper proposes a novel configuration of an electrical system, in which a photovoltaic plant (PV), used as support and integration, is interconnected to the DC-side of a conventional uninterruptible power system (UPS). The proposed configuration introduces important advantages compared to the configuration, in which no direct PV-UPS interconnection exists. In the paper, the attention is focused on the estimation of the reliability improvement as regards the supply of the critical loads. In particular, the reliability estimation is performed in terms of the number of the critical loads interruptions over a certain period of time by using the Monte Carlo simulation method.

A new modeling approach of electrical signals for power systems

This paper presents a new approach to model the electrical signals in power systems. The approach is based on the concept, derived from differential geometry, of contact between a signal and an osculating sinusoid. A direct application leads to a synchronization algorithm performing tasks comparable to those of single-phase PLL as verified by some different simulation results. Moreover, a significant advantage of the approach is the possibility to define quantities typically considered in sinusoidal steady state conditions also during the transients.

A new active filtering technique for grid-connected inverters

This paper presents a new active filtering technique, that is an attractive interfacing for single-phase grid-connected inverter in power distribution systems using renewable energy. The active filtering is obtained by a “filter” full-bridge inverter, characterized by low power and high switching frequency. It is suitably connected by a high frequency transformer and a light passive filter to the main power full-bridge, so as to greatly reduce the harmonic content of the grid current. The implementation of the proposed technique is realized by a single inverter with four legs and two proportional-resonant current controllers.