A. Del Pizzo

A high performance control technique of power electronic transformers in medium voltage grid-connected PV plants

With reference to medium-voltage grid-connection of large photovoltaic (PV) plants, the paper proposes and analyses a high performance solution based on a power electronic transformer (PET). It Includes dc-links and multilevel converters either in low-voltage or in high-voltage side, and a medium-frequency (MF) transformer. Together with the very reduced sizes of the whole conversion apparatus, an important feature of the proposed topology is the permitted presence of unbalanced voltages on the different dc-links corresponding to the partitions of the PV plant. This is enabled by the multilevel cascaded H-bridge configuration of the low-voltage side converter, in order to take into account the nonuniform distribution either of temperature or (mainly) of solar radiation on the different cells arrays, together with eventual different kind or age of used cells. another advantageous feature is the good level of power quality indexes on grid quantities, ensured by a multilevel NPC front-end: mainly low values of either harmonic distortion, or voltage and current dissymmetry. this occurs even if the commutation frequency of the switching devices of this converter is not high (1÷2 kHz). However, the paper is mainly focused on the control technique of the multilevel converters connected to the primary and secondary windings of the MF transformer, imposing multistep- or square-wave voltages. Some simple control algorithms are presented in order to maximize the power generated by every partition of the plant (also in unbalanced operations) together with the minimization of the joule losses of the central conversion unit in quasi-stationary operating conditions.

An efficient architecture of a PV plant for ancillary service supplying

The use of Distributed Generation (DG) units for grid ancillary services, in particular for smart grid applications, has been deeply considered in the last few years. It has been demonstrated that DG units can produce not only active power, which is obviously the principal role, but also they can provide ancillary services such as: voltage control, spinning reserve, backup supply, harmonic compensation, peak shaving and others. Recently, the use of Photovoltaic (PV) DG units has been proposed for reactive power ancillary service production; the concept has been fully demonstrated, highlighting the potentiality of PV DG units as ancillary service provider. In this paper, some improvements are proposed for a PV DG unit as provider of ancillary services in terms of single components modeling and global optimization of the system. The capability of a PV plant of generating both active and reactive power is demonstrated.

High performance control technique for unbalanced operations of single-vsi dual-PM brushles motor drives

The paper deals with isotropic PM-brushless drives in configuration “single-inverter, dual-motor” operating with unbalanced load-torques. After a short review of some control techniques based on the classical control methodologies of single-motor PM drives, an innovative control algorithm is presented. It is suitable to minimize the resultant armature current needed to obtain an assigned resultant motor torque, whatever is the load unbalance. Simplified analytical expressions are given in order to quickly evaluate optimized reference currents with good approximation. From these reference values, a predictive feeding algorithm evaluates the reference voltage space-vector for the inverter supplying the two motors in parallel. Current and torque oscillation, torque/current ratio, dynamic response and stability are the mainly observed quantities. Effectiveness of proposed control technique is highlighted.

A power traction converter based on Modular Multilevel architecture integrated with energy storage devices

In this paper a power converter based on a modular multilevel topology integrated with energy storage devices for directly supplying of traction motors is discussed. The Modular Multilevel Converter (MMC) is one of the emerging technology for high- or medium- voltage transformerless power conversion. The possibility to directly control the traction motors by means of a dc/ac MMC topology, using also integrated energy storage systems (ESS) for recovering the kinetic energy, is exploited. Furthermore, a simplified mathematical model of the MMC with integrated ESS has been developed in order to evaluate the behavior of the traction unit during a typical load-cycle. The control law of the traction motor, integrated with energy storage flow management, has been introduced. The numerical results reported in the paper permit to confirm the feasibility of the proposed design and control strategy for light travel vehicle.

A PV AC-module based on coupled-inductors boost DC/AC converter

In this paper the design and the control of a PV (Photovoltaic) AC-module based on a double coupled-inductors boost topology are discussed. This circuital configuration allows obtaining of the high voltage amplification needed in individual panel applications. The operation principle of the proposed circuit is analyzed and a proper calibration of the PV panel simulation model is performed. The adopted control strategy is based upon sliding control technique in order to exploit its well-known properties of robustness. Furthermore, a Maximum Power Point Tracking (MPPT) approach based on a Incremental Conductance (IC) algorithm is used to track the actual maximum power point. Finally, the numerical results reported in the paper permit to confirm the feasibility of the proposed design and control strategy.

Optimized control technique of single inverter dual motor AC-brushless drives

The paper deals with controlled PM-brushless drives in configuration ldquosingle-inverter, dual-motorrdquo operating with unbalanced loads at the shafts of the two motors. Some control techniques are analyzed and their relevant features are compared. Starting from some simple control circuits which refer to an equivalent ldquosingle-inverter, single-motorrdquo configuration, some compensation blocks are added in order to improve steady-state and transient performances. Current and torque distortion, total efficiency, dynamic response and stability are the main quantities observed. Their values are compared in order to evidence the advantages of the different examined control techniques.

Performance analysis on a power architecture for EV ultra-fast charging stations

This paper is focused on the design criteria of the power conversion systems operating within ultra-fast charging stations for electric vehicles. The proposed architecture is based on a DC bus, which features the integration of renewable energy sources and buffered storage systems, performing the new concept of smart grid system. Simulations of the power converters and storage systems, working as power devices of recharging station architecture, are implemented in the Matlab-Simulink environment with models of each subcomponent provided by the Sim-Power-System tool. The reported simulations are mainly devoted to verify the design criteria of the architecture scheme and the control strategies of the power fluxes related to power converters. The advantages and convenience in terms of power quality and requirements from the main grid are shown, also during the EV fast-charging operations. Finally, the resulted recharging times are evaluated as comparable to the fuelling times generally taken by traditional oil based vehicles.

A low cost microcogeneration system for domestic and industrial applications

The paper deals with design and manufacturing aspects of a small cogeneration unit suitable for domestic and low power industrial applications. It is conceived to meet high global and electric efficiency, high power factor, low pollution emissions, low maintenance and easy use, low industrial cost. These requirements led to select a modern low-cost small utility engine as prime mover base for the development of the cogeneration plant, and to provide it with an electronic fuel feeding apparatus. A three-phase induction machine has been used in the electric generator unit in order to reduce installation and maintenance costs and to improve reliability; if grid-isolated operations are required the electrical machine has to be equipped with a suitable electronic control unit. The performance of the generation unit is analysed by means of a model and the numerical results are compared with the experimental ones, obtained by an investigation on a laboratory cogenerator prototype.

Efficiency evaluation of a micro-generation system for energy recovery in water distribution networks

The paper deals with the efficiency evaluation of a micro-generation unit for energy recovery in water distribution networks. The analyzed system includes an electric motor-driven pump working as turbine/generator, connected to the electrical grid through a bi-directional power converter. The micro-generation unit is implemented in an experimental setup which simulates a real water network in a reduced scale. The unit was tested and analyzed in order to monitor some critical electrical quantities as well as to evaluate its generating efficiency. In the measurements campaign, various operating conditions were analyzed. The corresponding results are reported and discussed.

An analysis of modular multilevel converter for full frequency range operations

In this paper an analysis of a power converter based on a modular multilevel topology is discussed. A mathematical model of the MMC is developed in order to evaluate its dynamic behavior and to better understand the incidence of the circulating current phenomenon which could compromise converter performance in variable speed drive applications. In fact, if such problem is not properly addressed reliability problems arise.