Mario Gonzalez

A load identification method for residential building applications

In this paper, the topic of electric load identification in household applications is addressed. The identification of load powers and of duty cycles is performed in a nonintrusive way from the signals flowing throughout the meter panel of electricity consumption of the building. The identification of loads is based on the detection of the on-off transitions in the active power, from which the power level, the start time, the end time, the duty cycle, and the power consumption can all be computed.

Fault diagnosis in a grid-connected photovoltaic system by applying a signal approach

An analysis of fault diagnosis in the power conversion stage of a grid-connected photovoltaic system is developed in this work. The system under study, based on the classical dc-dc boost converter and the voltage-source full-bridge inverter, is a widely installed circuit in photovoltaic applications, which is convenient for such study. The objective is to provide methods to diagnose faults in the components of the converter, in order to achieve faster preventive or corrective maintenances. The analyses, based on the frequency spectrum of the signals, are performed under different scenarios, using different control schemes and different solar irradiances received by the photovoltaic array.

Advantages of the passivity based control in dynamic voltage restorers for power quality improvement

Abstract A better and feasible control strategy for dynamic voltage restorers (DVR) is presented in this paper: the passivity based control (PBC) allows a better compensation performance under transient and steady state operating conditions, and provides tracking with zero error of any reference for linear and nonlinear loads. The closed-loop source-DVR-PBC-load system is asymptotically stable at all operating points, with practically very slight constraints; its transient response is faster than with classical controllers, and does not present overshoots. These characteristics do not depend on source voltage disturbances, the kind of load, or parameter variations. The PBC uses less digital operations than the PI, and does not require dq transformations.

An Optimal Selection of the References Generation Scheme for the DQ Theory to Compensate Unbalance, Reactive Power, Harmonic Distortion and Non Characteristic Harmonics

An optimal selection of parameters of a references generation scheme for the DQ theory is presented in this paper. With this selection, an active filter is theoretically able to perform an adequate compensation of all the most common polluting perturbations of electrical systems, such as unbalances, harmonic distortion, non characteristic harmonics, reactive power and power factor. This approach is only valid at steady state or for slow transient events, because the settling time of the active filter reaches a high value, almost three 60 Hz cycles. However, this is very useful for active filters as it will keep the system free of pollutions permanently

Large scale Photovoltaic structures with medium-frequency isolation

Energy generation via Photovoltaic (PV) technologies has increased in the last years. Large scale PV generation have attracted interest among countries due to low operation cost and wide PV resource disposition. However, some operative challenges in large scale PV plants had been detected: power imbalance, low power quality in terms of total harmonic distortion (THD), power factor and conversion efficiency, can be mentioned. This paper is focused on topologies featuring medium-frequency (MF) isolation and presents a review of different approaches to solve those operative issues. Medium-frequency isolation reduces current and improves efficiency, reliability, and provides isolated DC sources for power electronics converters, and can replace bulky low-frequency transformers, thus reducing PV system volume. Simulations of three-phase 10 kW PV systems are presented: MF link PV system, Delta inverter and a PV system based on a matrix converter.

Nonexistent harmonics generation phenomenon caused by the processing of DQ transformation in power quality applications

A phenomenon that occurs when using the DQ Transformation to obtain the compensation references in active filter applications is presented in this paper, in which new harmonics that had not existed originally in the system, are injected to it. Although these new injected harmonics have very low magnitude, they do exist and correct processing must be assured in order not to increase their magnitudes. The phenomenon is generated by the filtering action at the dq reference frame; the filter does not have an ideal behavior, it inserts a gain or attenuation and a phase-shift, different for each frequency component. The phenomenon takes place if only the d signal is filtered out to separate the dc component. But, if both d and q components are filtered, the phenomenon disappears. However, in fact the THD of the compensated variables are lower using the scheme that injects new harmonics than using the one that does not. This phenomenon is formally analyzed under general three-phase unbalanced conditions.