Search

Power quality has become a key issue in modern electric power systems due to the increasing number of sensitive loads and disturbing sources. In this scenario, electronic power converters are commonly used to compensate voltage and current disturbances, above all in relation with harmonics. These devices require sophisticated control systems like Proportional Resonant Controllers (PRCs) that must be implemented in Digital Signal Processors (DSPs). However, PRCs are sometimes difficult to design and implement in discrete-time applications. This paper presents a systematic method to design high-performance PRCs. Discrete-time implementation aspects such as frequency adaptability with low computational burden are addressed in detail. The proposed control system improvements are analysed and tested on a 5 kVA prototype of a Series Active Conditioner (SAC) that protects a linear load against voltage sags and harmonics. [ABSTRACT FROM AUTHOR] more...

Series compensators can be used to solve a number of power quality issues in electrical distribution systems. These devices are connected in series between the point of common coupling and a load and they inject a series voltage to compensate voltage sags, swells, unbalances, and many other power quality issues. A series compensator requires a harmonic-tracking algorithm within its controller to eliminate harmonics. However, the uncertainty introduced by linear and non-linear loads connected downstream makes it difficult to guarantee closed-loop stability in every case. To overcome this problem this paper proposes a control algorithm to compensate harmonics that can be adapted in real time avoiding the need for an accurate model of the plant at the design stage. This controller is implemented in a series compensator to eliminate harmonics in two situations: filtering voltage harmonics from the grid voltage and filtering current harmonics generated by a non-linear load. The proposed algorithm was validated on a 5 kVA prototype of a series compensator. [ABSTRACT FROM AUTHOR] more...

Highlights: [•] First implementation of a repetitive controller for a Series Active Conditioner. [•] Voltage sags, harmonics and unbalances in the supply voltage are tackled. [•] The controller deals with small and slow grid frequency variations. [•] An internal instability problem unnoticed in the literature is solved. [•] Experimental results are presented. [Copyright &y& Elsevier] more...

This paper proposes the use of participation factors of complex frequency variables to study the propagation of oscillations in power systems. The method combines the recently proposed concept of complex frequency with modal participation analysis to derive a novel metric that locates the sources of oscillations in the system and tracks their spatial propagation. The proposed approach allows isolating the variables more sensitive to oscillations, bus voltage or frequency, thus facilitating the selection of corrective actions. The validity of the theoretical results and the scalability of the method are supported with extensive simulations performed for test networks of various sizes and with both conventional and inverter-based generation. • The Complex Frequency is employed to study frequency oscillations in power networks. • Complex Frequency Participation Factors are proposed as a novel modal analysis tool. • The proposed tool is suitable for power systems with high penetration of IBRs. [ABSTRACT FROM AUTHOR] more...

To address the reduction of system inertia, transmission system operators are now requesting converter-interfaced generators (CIGs) to participate in frequency support services. Microgrids (MGs) and virtual power plants have been used as a solution for aggregation of small CIGs. It has been recently considered they may use their combined actions to provide frequency services. However, these proposals are not general enough, focusing on specific CIGs controllers and, in many cases, stability and operational limits are not considered. This paper presents an standardised methodology to design MG controllers that are in compliance with the MG transient response specifications (frequency nadir and rate-of-change-of-frequency, ROCOF). The methodology has an iterative nature and can be applied when the network conditions change. In each iteration, the control parameters are adjusted based on the sensitivity of the system eigenvalues against the frequency metrics of interest while stability and operational constraints are respected. Compared to the literature, the use of quantitative parametric sensitivity is performed for the reallocation of several eigenvalues using two sensitivity components, not only one. Moreover, it is suitable for any combination of grid-forming and grid-following devices. The proposed methodology is applied to a benchmark MG and results show that both nadir and ROCOF can be effectively modified and set as required. The methodology was validated by using a real MG comprising four 15 kW converters and one 75 kW converter. • Methodology to adjust grid-forming controllers with frequency response specification. • The methodology can be adapted to any grid-forming strategy. • Small-signal tools are used in the methodology. • Sensitivity analysis is extended to be applied with several eigenvalues. • Theoretical developments validated by simulation and in a laboratory. [ABSTRACT FROM AUTHOR] more...