Márcio Stefanello

Adaptive Current Control for Grid-Connected Converters With LCL Filter

This paper presents a discrete-time adaptive current controller for grid-connected voltage source PWM converters with LCL-filter. The main attribute of the proposed current controller is that, in steady state, the damping of the LCL resonance does not depend on the grid characteristic since the adaptive feedback gains ensure a predefined behavior for the closed-loop current control. Simulation and experimental results are presented to validate the analysis and to demonstrate the good performance of the proposed controller for grid-connected converters subjected to large grid impedance variation and grid voltage disturbances.

Space vector modulation extended to voltage source converters with multiple legs in parallel

This paper extends the space vector (SV) modulation to Voltage Source Converters (VSC) with multiple legs in parallel. Multiple legs voltage source converters are strong candidates for low voltage high power applications, such as wind power systems where the converter has to handle high currents. The main advantages of the proposed modulation are: (i) minimization of the total harmonic distortion (THD) of the output current or reduction the filter size; (ii) decoupling the output current control loops from the current sharing control loops. In addition the well-known features of the SV modulation such as the full utilization of the DC bus voltage and the possibility of minimization of switching losses can also be achieved. Finally, experimental results from a three phase multiple legs converter are presented to support the analysis carried out as well as to demonstrate the performance of the proposed SV modulation. Furthermore, experimental results are also presented to compare the proposed SV modulation with a conventional PWM with triangular phase-shift.

Design of a Robust Model Reference Adaptive Control for a shunt Active Power Filter

This paper presents a design procedure for a discrete-time robust model reference adaptive control (DRMRAC) applied to a three-phase four-wire shunt active power filter (APF). The first step when designing the controller is to obtain a representative model for the plant. The theoretical basis for the DRMRAC, considers a parametric model which comprises a modeled part of reduced order, whose parameters are allowed to lie in a predefined range, and a multiplicative and/or additive terms describing the unmodeled dynamics. These dynamics pose a level of uncertainty for the plant, and reflect the difficult in describing the plant behavior, usually at high frequencies. The adaptive law is used to compensate the parametric variation of the plant and the control strategy is robust with respect to such unmodeled dynamics. The plant model, design procedures, main constraints and experimental results are presented.

Combined active damping with adaptive current control for converters with LCL filters

This paper proposes a grid side current control technique for Pulse Width Modulated converters connected to the grid through LCL filters. The system is modeled in order to allow the implementation of a multi-loop control strategy. The inner loop is designed for active damping using the classical approach of feeding back the capacitor voltage or current to implement a Proportional plus Derivative or a Proportional controller, respectively. The outer loop is designed for the compensation of parametric uncertainties and disturbances by means of a Model Reference Adaptive Controller. The adaptive behavior allows to easily design the outer controller despite de presence of the inner one.

Controlador repetitivo para inversores PWM com referência de freqüência variável

Repetitive controllers have demonstrated efficacy in the rejection of cyclic disturbances in pulse-width modulated voltage-source inverters. However, the performance of these controllers is compromised if their period are not synchronized with the period of the reference signal. This drawback restrict their use in variable frequency applications. In order to mitigate this problem, it is proposed a modification in these controllers to make them suitable for sinusoidal references with variable frequency. The proposed algorithm is simple given that is only performed a chance in the length of circular buffers and in the pointer used to address them. Experimental results, obtained with two different prototypes, are presented to validate the proposed technique.

Sliding mode control in a multi-loop framework for current control of a grid-tied inverter via LCL-filter

This paper proposes a current controller for grid tied Voltage Source Inverter (VSI) via a LCL filter using discrete-time Sliding Mode Control (SMC) in a multi-loop framework. The inner loop is implemented by the SMC with reference generated by an outer controller for the VSI side current. The tracking of the current entering the distribution network is ensured by a outer controller with a derivative + ressonant structure (for compensation and disturbance rejection with reference tracking). Simulation and experimental results are presented to validate the good performance of the proposed control strategy.

Space vector pulse width modulation for Modular Multilevel Converters

This paper proposes a space vector vector pulse width modulation (SVPWM) stratey for Modular Multilevel Converters (MMCs). The proposed modulation generates multilevel output line-to-line voltages with 4N+1 levels. Furthermore, the virtual vectors are developed for the MMC and it allowed to establish the converter voltage limits and implement a proper inner currents control. Moreover, the voltages across the submodule dc capacitors can be well balanced with closed-loop controllers and a sorting algorithm. Finally, simulation results are presented to support the theoretical analysis demonstrating the good performance of the proposed modulation technique.

Robust control of a grid-connected converter with an LCL-filter using a combined sliding mode and adaptive controller in a multi-loop framework

This paper proposes a multi-loop controller for current control of a grid-connected inverter with an LCL-filter. The inner loop uses the converter current error as the sliding surface in a Sliding Mode Control (SMC) approach. The model obtained allows the application of an outer Model Reference Adaptive Control (MRAC) for the tracking of the grid current in a robust fashion with disturbance rejection. Simulation results are presented to validate the theoretical analysis.

Robust adaptive variable structure controller for shunt active power filters

This paper proposes and analyzes a current control technique applied to the current control of a three-phase shunt Active Power Filter. The technique is based on an adaptive variable structure controller. The adaptive algorithm compensates for the parametric uncertainties and a modification is applied for robustness with respect to the unmodeled dynamics. The variable structure action built in the adaptive controller improves the stability and dynamic performance if compared with a conventional adaptive controller. Theoretical discussions and experimental results are presented to better support the paper.

A Comparison of High Power Multi-Leg Voltage Fed Converters Modulated by Space Vector and Geometric Approach

This paper presents a comparison of space vector modulation (SVM) and geometric approach modulation (GAM) when applied to parallel multi-leg voltage source converters (VSC). Multi-leg VSCs are strong candidates for low voltage high power applications, such as wind power systems where the inverter has to handle high currents. The parameters for comparison are: (i) the Total Harmonic Distortion (THD) of the output current; (iv) Algorithm complexity. Finally, experimental results are presented to support the analysis carried out and to demonstrate the performance.