Repetitive Control With Adaptive Sampling Frequency for Wind Power Generation Systems

Abstract

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].

A Review on Impacts of Power Quality, Control and Optimization Strategies of Integration of Renewable Energy Based Microgrid Operation

“…In [34,35] repetitive controller is a simple learning control method which maintains low total harmonic distortion (THD) in load voltage and grid current. Also, it reaches smooth and continuous transfer of operation mode.…”

Virtual Variable Sampling Repetitive Control of Single-Phase DC/AC PWM Converters

“…However, it's difficult or even impossible to have a constant integral ratio T r /T s especially when the reference fundamental frequency f r is varying or under certain disturbance. A generic way to address this problem is to use a varying sampling frequency scheme [23], [24]. However, the limitations of these varying frequency schemes are their high requirement of CPU processing capacity and the influence on overall system stability.…”

“…Variable sampling/switching period techniques were developed to maintain fixed integer samples per reference period for wind and aircraft power systems [23], [24]. However, it requires that the digital control system has the capability of the variable sampling frequency.…”

A Fractional Delay Variable Frequency Repetitive Control for Torque Ripple Reduction in PMSMs

“…So every time the speed is changed, the periodic compensating current reference stored in the controller memory must be cleared and a new learning process must be initiated or alternatively the memory content must be processed in order to adapt it to the new operating speed. In order to solve this variable frequency issue, the variable sampling frequency RC is presented in [19,20] for converters. For PMSM drive, since the torque ripple is in fact periodic with respect to rotor position, [11] presents an angle-based RC which works effectively within a limited variable speed range of 50rpm to 70rpm.…”