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.

This work focuses on the control of instantaneous complex power of a grid-connected VSI. In this work, 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.

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.Index Terms-Grid-tie current-controlled three-phase inverters, power quality, repetitive control (RC), wind energy, wind power generation systems (WPGS). I. INTRODUCTIONW IND power generation systems (WPGS) play a key role in the distributed power generation scenario worldwide [1]. Modern variable-speed WPGS are connected to the grid through a current-controlled three-phase voltagesource inverter (CC-VSI) [2], [3], as shown in Fig. 1. Phase currents injected to the grid must comply with strict power quality standards, such as [4], which demand a total harmonic distortion (THD) of the injected currents below 5%. Given the increasing penetration of WPGS, even more strict limits are expected to be needed in the near future. Moreover, new grid codes are requiring additional features. Known as ancillary functions, they enhance robustness, safety, and reliability of the grid through reactive power injection, fault ride-through capabilities, compensation of harmonic currents generated by nearby nonlinear loads, and mitigation of asymmetrical loads, among others [5]- [7].