Jorge Rodrigo Massing

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.

Adaptive current control for grid-connected converters with LCL-filter

This paper presents a discrete-time adaptive current controller for grid-connected pulse width modulation voltage source 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. An overview of model reference adaptive state feedback theory is presented aiming to give the reader the required background for the adaptive current control design. The digital implementation delay is included in the model, and the stability concerning the variation of the grid parameters is analyzed in detail. Furthermore, current distortions due to the grid background voltage are rejected without using the conventional stationary resonant controllers or the synchronous proportional-plus-integral controllers. 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.

LMI-Based Control for Grid-Connected Converters With LCL Filters Under Uncertain Parameters

This paper presents a linear matrix inequality-based procedure for the design of state feedback current controllers that are robust to uncertainties on grid inductance for grid-connected converters with LCL filters. The state feedback control law includes the filter state variables, the states of resonant controllers, and considers also the delay from digital control implementation. As the main contribution here, the proposed strategy allows to deal with resonant controllers of arbitrary dimension, and provides results complying with IEEE Standard 1547 requirements. The control synthesis condition takes into account the assignment of the closed-loop eigenvalues in a circular region with radius r, located inside the unit circle, and the control design relies only on the choice of the value of the radius in the interval 0 <; r ≤ 1, providing all the state feedback gains in a simple and efficient procedure.

Stability analysis of grid-connected voltage source inverters with LCL-filters using partial state feedback

This paper addresses the stability of discrete controlled grid connected voltage source inverters with LCL-filter usually found in wind power generation systems. First a theorem that relates the controllability of the discrete dynamic equation with the LCL-filter parameters and the sampling frequency is derived. Then, a robust partial state feedback design on the linear matrix inequalities framework guarantee the stability damping the LCL-filter resonance for a large set of grid conditions without requiring tuning procedures. Finally, an internal model controller is added to ensure asymptotic reference tracking and disturbance rejection, therefore reducing significantly the impact of grid background voltage distortion on the line currents. Simulation and experimental results are presented to support the theoretical analysis carried out and to demonstrate the system performance.

Robust ℌ ∞ control for grid connected PWM inverters with LCL filters

This paper provides a robust control design based on linear matrix inequalities applied to PWM inverters with LCL filters connected to the grid under uncertain parameters. The proposed controller ensures: i) closed-loop robust stability against parameter uncertainty; ii) robust pole location with a prescribed ℌ∞ guaranteed cost; iii) tracking of sinusoidal reference and rejection of disturbances. Simulation and experimental results show good transient and frequency responses for the closed-loop system, as well as limits of robust stability.

Design and control of doubly-fed induction generators with series grid-side converter

This paper proposes and describes the controllers for doubly-fed induction generators (DFIG) with series grid side converter. It is demonstrated that with series grid side converter instead of a conventional shunt grid side converter the DFIG stator voltage can be kept balanced even under heavy unbalance grid voltages. Therefore, in this way it is avoided the undesired effects such as torque oscillations and high stator and rotor currents presents under unbalance voltages. In addition, it is demonstrated that it is possible with a conventional back-to-back three phase PWM converter to satisfy the grid code active and reactive power requirements. The design and control of the series grid-side converter with a LC-filter will also be presented. An Hinfin controller is designed to achieve robustness as well as good tracking and disturbance rejection performance for the series voltage converter. Furthermore, the DC-link, rotor currents and active and reactive power controllers are as well described, where the controllers transfer functions are selected to ensure good performance even in the presence of grid voltage unbalance. Finally, simulation results of a 2.27 MVA wind turbine generator are presented to demonstrate the good performance of the DFIG with the proposed controllers.

Robust current control of grid-connected converters with LCL-filter

This paper presents a robust current controller for grid-connected converters with LCL-filter. The design of the controller considers uncertainty on the grid impedance parameter and includes an internal model structure that ensures asymptotic tracking of the sinusoidal current reference as well as disturbance rejection of the background voltage. A state feedback control law, which depends on the states of the converter and of the internal model controller, is considered here. Then, a robust design is developed on linear matrix inequalities framework. Results that verify the robust stability and good performance of the proposed current controller are presented for different cases of grid impedance at the point of common coupling.

Adaptive current control of grid-connected VSC with LCL-filters using parallel feedforward compensation

This paper deals with the design of a discrete-time adaptive current controller for grid connected voltage source converters with LCL-filter. A mandatory condition to allow the use of discrete-time model reference adaptive control (MRAC) is that the plant must be minimum phase. Even if the system is minimum phase but it has poorly damped zeros, undesired oscillatory modes may appear in some systems variables. This paper proposes the use of parallel feedforward compensation to change the location of the zeros of current controlled grid connected converters with LCL-filter. Then, a discrete-time adaptive state feedback for the augmented system is applied to ensure stability and performance for a wide set of grid conditions. The theoretical background on parallel feedforward compensation as well as on discrete-time adaptive state feedback is briefly presented. Finally, the effectiveness of the proposed controller is confirmed by results that demonstrate the good system performance.

Small signal stability of DFIG with series grid-side converter

This paper develops the full order models of doubly-fed induction generator (DFIG) with series grid-side converter aiming to derive its stability region on the PQ-plane. The stability region on the PQ-plane is given and reveals that the DFIG with series grid-side converter is a feasible solution for wind turbines connected to unbalanced voltage grids. The configuration of DFIGs with series grid side converter instead of a conventional shunt grid side converter can keep the DFIG stator voltage balanced even under heavy unbalance grid voltages, avoiding the undesired effects such as torque oscillations and high stator and rotor currents under unbalance voltages. The linearized model for different operation setpoints is obtained for this configuration, including the rotor-side and grid-side converters. Furthermore, the stability of the complete nonlinear system is derived based on the eigenvalue analysis of the linearized model. Simulation results validate the previous analysis.

A robust PI current controller for grid-connected renewable energy systems

This paper presents a robust PI current controller for three-phase grid-connected converters with LCL-filter for renewable energy systems. The controller is designed in synchronous reference frame and the grid impedance uncertainty is considered in the design. The controller consists of a PI current controller and state-feedback, where the gains of the PI controller and the gains of the state-feedback are designed together in a one-step procedure. The robustness of the current controller is ensured by an LMI approach, which guarantees closed-loop stability in the whole range for the considered grid impedance uncertainty.