María-Isabel Milanés-Montero

Novel method for synchronization to disturbed three-phase and single-phase systems

An autoadjustable synchronous reference frame for extracting the positive-sequence fundamental component of the voltage in the point of common coupling is proposed in this paper. It operates suitably under unbalanced and distorted input voltages, with no steady state error in amplitude, phase and frequency tracking. The dynamic response of the method in case of frequency or amplitude variations is good, achieving the steady state in only two cycles of the fundamental period. The method allows a simple adaptation for being used in single-phase systems too. Simulation and experimental results are presented to test the novel method.

Three-phase bidirectional battery charger for smart electric vehicles

A three-phase battery charger for electric vehicles is proposed in this paper. The charger is bidirectional, allowing the Charging and Vehicle to Grid operation modes. A novel Balanced Sinusoidal Source Current control strategy is proposed so that the charger demands or injects into the grid a perfect sinusoidal and balanced source current in phase with the positive sequence fundamental component of the phase-to-neutral grid voltage, achieving a unity displacement power factor. In this way, the charger turns the car into a smart vehicle, reducing the existing problem of harmonic current demand by electric and hybrid vehicles and improving the power quality of the electric power system. The topology and control stage of the charger are shown. Simulation tests are conducted to validate the proper operation of the charger under sinusoidal, distorted and unbalanced source voltages.

A new criterion for selecting the inductors of an Active Power Line Conditioner

This paper analyzes the inductances used at the terminals of an Active Power Line Conditioner (APLC) based on a voltage source inverter (VSI) in some current correction topologies. The criteria to select the optimal inductances values are determined and a novel design criterion, named “control criterion”, is proposed. This novel method is applied to situations where there are sharp current variations as the case of a three phase rectifier feeding a resistive load. A parametrical analysis of the expressions obtained for the inductors is performed, obtaining the intervals of possible values of inductance that can meet the initial specifications. Finally a simulation is carried out to verify how the method presented reaches these specifications.

Cooperative converters in power electronic systems

The specifications of power electronic systems are becoming ever more exigent - better performance (dynamic and steady state), increased efficiency, reliability, and quality, and decreased power rating, size (volume and weight), and cost. One strategy for the overall improvement of these systems is to use various cooperating converters with the system functions being shared among them, optimizing each converter for the functions assigned it. The result will be a converter with better characteristics than a conventional design based on a single converter (or on a simple parallel association of converters) responsible for all the functions assigned to the system. This paper analyzes the possibilities of such cooperative converters, considering the filtering inductor size, and the efficiency, reliability, and power rating.

Simulation study of the grid-connected single-phase impedance-sourced NPC inverter with different control methods

Focus is on three operation strategies for a grid-connected three-level neutral-poi n t-clamped quasi impedance source inverter in a single-ph as e application. Each control scheme wa s implemented in the PS CAD/EMTDC simulation tool a n d underwent different tests, which involved some steps in the reference values and in the perturbations applied to the system. A comparison according to their responses was based on different criteria, such as rise time, settle time, overshoot a n d steady state error, in order to determine which would be more suitable for such application.

Three-phase regenerative electronic load to test shunt power conditioners

A 3-phase regenerative electronic load to test shunt equipments such as active power filters and power conditioners at high power levels is presented in this paper. The electronic load is composed by two inverters with a common DC-bus. One inverter draws from the grid a configurable load current with the harmonic and imbalance desired levels, and the other one is used to inject the energy into the grid trying to minimize the losses, while the active filter performance is being tested. The control strategies and the current controller for both inverters are explained. Simulations and experimental results showing the proper operation of the electronic load to test shunt power conditioners are presented.

Three-phase three-level neutral-point-clamped qZ source inverter with active filtering capabilities

In our effort to take advantage of a distributed location of a grid-connected photovoltaic inverter, focus is on active filtering capabilities for a grid-connected three-phase three-branch three-level neutral-point-clamped quasi impedance source inverter. An operation strategy derived from the classical p-q theory and a tracking technique for such topology are detailed. Different scenarios are considered with non-linear loads, to validate the proposed ideas and control systems. Our results from the PSCAD/EMTDC simulation tool show that the whole system performs well.

Active power injection control of a photovoltaic system through ultracapacitor storage

This document presents a three-phase grid-connected power injection system for a photovoltaic power source with control of the injected active power through an energy storage system based on ultracapacitors. The ultracapacitor technology offers high power density that matches properly in a Smart-Grid scenario with the need of active power regulation for quasi-manageable energy ability. A voltage source inverter injects the power into the grid, while a bidirectional direct current converter regulates the charge of the ultracapacitor. In this way, the ultracapacitor could be charged when the active power needed in the grid is below the photovoltaic power, it could be discharged in the opposite case, and, if the ultracapacitor is saturated the power point tracked depends on the reference, injecting the desired active power in every assumption. The system has been implemented in a prototype through a FPGA/processor controller, so the hardware/software co-design is detailed. Finally, the performance of the configuration is exposed via experimental tests.

PSCAD/EMTDC model for photovoltaic modules with MPPT based on manufacturer specifications

Commonly used simulation models for photovoltaic arrays often require the knowledge of unavailable parameters and the calculation of equivalent resistances to be used. Those resistances are not provided by manufacturers and their calculation makes the application of the designed models difficult. This paper proposes a photovoltaic panel or array model based on the specifications provided by manufacturers in datasheets. The model emulates the characteristic curves declared by the panel manufacturer and an integrated MPPT (Maximum Power Point Tracking) technique. The well-known PSCAD/EMTDC software has been selected to develop the proposed model and commercial panels have been used for validation.

Analysis and optimization of sinusoidal Voltage Source Inverter losses for variable output power applications

In this paper, a general analysis of converter losses is done. The aim of this analysis is to determine the parameters that have great influence in these losses. The losses study presented in this paper is focused in a Two-level Three-branch Voltage Source Inverter (VSI) and it is particularized for the case in which this inverter has to generate sinusoidal currents, showing the losses and efficiencies of the converter for different output power. Finally, the opportunities of using a topology based in a DC/DC converter connected in cascade with the VSI for decreasing the losses and achieving greater converter efficiencies are shown.