Sergio A. Gonzalez

A Robust Predictive Current Control for Three-Phase Grid-Connected Inverters

This paper presents a new predictive control algorithm for grid-connected current-controlled inverters. The control combines a two-sample deadbeat control law with a Luenberger observer to estimate the future value of the grid currents. The resulting control offers robustness against the computational delay inherent in the digital implementation and considerably enhances the gain and phase margins of the previous predictive controls while maintaining the high-speed response typical of the deadbeat controllers.

Adaptive Dead-Time Compensation for Grid-Connected PWM Inverters of Single-Stage PV Systems

This study presents a new software-based plug-in dead-time compensator for grid-connected pulsewidth modulated voltage-source inverters of single-stage photovoltaic (PV) systems using predictive current controllers (PCCs) to regulate phase currents. First, a nonlinear dead-time disturbance model is reviewed, which is then used for the generation of a feed-forward compensation signal that eliminates the current distortion associated with current clamping effects around zero-current crossing points. A novel closed-loop adaptive adjustment scheme is proposed for fine tuning in real time the compensation model parameters, thereby ensuring accurate results even under the highly varying operating conditions typically found in PV systems due to insolation, temperature, and shadowing effects, among others. The algorithm implementation is straightforward and computationally efficient, and can be easily attached to an existent PCC to enhance its dead-time rejection capability without modifying its internal structure. Experimental results with a 5-kW PV system prototype are presented.

Harmonic Computation Technique Suitable for Active Power Filters

The design and implementation of a novel method for reference generation that is applied to active power Alters (APFs) is introduced in this paper. The proposed reference generation performs harmonic detection based on the Goertzel algorithm. The method computes both the module I1 and the phase phi of the signal, with minimum computation overhead. This makes the method suitable for APFs or other applications that require harmonic detection. A comparison analysis between the discrete Fourier transform and the proposed method is carried out. The proposed reference generator is implemented using a digital signal processor and tested with waveforms from typical load currents. Experimental results are obtained under both stationary and transient states.

Novel stepper motor controller based on FPGA hardware implementation

This paper proposes a novel stepper motor controller based on field programable gate arrays, showing a remarkable performance. The system provides a combination between a novel algorithm and programmable logic to achieve both high speed and high precision on a compact hardware.

Calculation-Delay Tolerant Predictive Current Controller for Three-Phase Inverters

This work presents an improved deadbeat predictive current controller for grid-tie inverters that addresses issues related to implementation delays. The total delay is composed of the integer computational delay and a fractional delay, which is taken into account in the design of the controller algorithm, to improve its performance and robustness. The control strategy, based on a model that includes these delays, employs state feedback and a prediction observer in order to obtain a true two-sample ripple-free deadbeat response. System robustness can be adjusted with an appropriate selection of the location of the observer poles, at the expense of reducing control bandwidth. The proposed control scheme is both simple and computationally efficient since only few operations are required to include the delay in the algorithm. Experimental results show an improvement of the dynamic response even when mismatch in the load-inductance value estimation occurs.

Robust Predictive Control of Grid-Tied Converters Based on Direct Power Control

This study focuses on the control of instantaneous complex power of a grid-connected voltage-source inverter (VSI). In this study, a new space-vector-modulation-based direct power control approach is proposed: the robust predictive direct power control (RP-DPC). The proposed predictive control algorithm ensures that both, instantaneous real and imaginary powers, track the reference with high speed and accuracy reducing steady-state errors. In order to reduce the total harmonic distortion (THD) in the output currents, a fundamental frequency positive sequence detector is used in conjunction with a prediction grid voltage observer. Comparative simulations and experimental results of a 10-kW three-phase grid-connected VSI showing the steady-state and transient performance of the proposed RP-DPC are given. A low THD and balanced output currents are maintained even under severe voltage unbalance conditions.

Analysis of a Cascade Asymmetric Topology for Multilevel Converters

In this paper a complete analysis of a cascaded asymmetric topology for multilevel converters is presented. This topology allows to synthesize five voltage levels with a reduced number of switches and capacitors when compared to the generalized topology or the most common symmetric topologies. The converter behaves like an hybrid converter with the advantage of working with only one DC bus. It appears as a very good and simple alternative to build five level converters with minimum number of switches and only one flying capacitor per phase. The proposal is tested with Pspice simulations in a STATCOM application.

Repetitive Control With Adaptive Sampling Frequency for Wind Power Generation Systems

This paper presents a novel repetitive control (RC) for wind power generation systems (WPGS), which achieves optimal performance in steady-state conditions due to a variable sampling/switching period technique (VSPT). The main objective of VSPT is to obtain an integer number of samples per grid period, which solves the main problem of RC, i.e., the loss of rejection to periodic disturbances due to grid frequency drift. The sampling/switching frequency is adjusted with a variable sampling period filter phase-locked loop, which also adds robustness to the system due to its inherent tolerance to grid voltage distortion and unbalances, and events such as frequency steps and faults. The control and synchronism subsystems are described, designed, and verified experimentally in a 10-kW WPGS. The results obtained prove the accuracy of the proposed control even under severe disturbances, typical in grids with high WPGS penetration, providing ancillary functions to enhance reliability and reduce operational costs.

Generalized Predictive Current Control (GPCC) for Grid-Tie Three-Phase Inverters

This work proposes a linear generalized predictive current control (GPCC) for grid-connected voltage-source inverters, which presents a fast response to current reference step changes, parameter variation robustness, and low distortion at the output currents, with reduced computational effort. Experimental results on a 10-kW converter connected to a real grid are shown, and the proposed controller is compared against a classical proportional resonant controller.

Implementation of a novel synchronization method using Sliding Goertzel DFT

This work presents a synchronization method based on the implementation of a sliding-window digital-filter that uses the Goertzel algorithm. The proposed method filters the incoming power grid signal and specifies the input frequency by measuring the period of the output phase. The sampling frequency is adjusted to correct the phase errors introduced by the filter whenever variations in the frequency occur. Regardless of the magnitude of the input frequency variations, this method determines the input frequency with high accuracy.