Uriel Vargas

Extended Harmonic Domain Model of a Wind Turbine Generator for Harmonic Transient Analysis

This paper presents an extended harmonic domain (EHD) model of a wind turbine generator (WTG) system based on a doubly fed induction generator. The proposed EHD WTG model includes both electrical and mechanical subsystems and permits monitoring step-by-step the harmonics time variation; this allows, among other applications, to detect contingency scenarios, such as resonance problems caused by a specific harmonic. Moreover, control efficiency can be improved by means of the power-quality indices which are instantaneously available by the EHD WTG model. The proposed model is capable of accounting for an arbitrary number of harmonics; however, the more harmonics that are included, the larger the system becomes. This affects the central-processing unit time by the transient simulation. An efficient heuristic remedy is proposed in this paper which consists of accounting for “high-impact” harmonics only, based on the converters frequency spectrum. The EHD WTG model is validated with the power system computer-aided design/electromagnetic transients including dc (PSCAD/EMTDC) software tool via a case study.

Reduced-order extended harmonic domain modeling of switched networks

This paper presents an extended harmonic domain (EHD) reduced-order modeling technique of switched networks based on dominant frequencies. The technique is readily applicable to power electronic converters involved in photovoltaic (PV) and wind generation systems. Generally, the instantaneous product between switching function and voltage/current variable is represented in the EHD as a product of a (theoretically infinite) Toeplitz-type matrix of the former and a harmonic domain (HD) vector of the latter. The proposed approach consists in two simple, yet effective, basic actions. Firstly, the harmonic spectrum of the involved switching function is considered for the harmonic dominancy characterization. Secondly, the commonly used arrangement of the Toeplitz-type matrix is modified in this paper to consider interaction between dominant frequencies only. The obtained reduced-order models provide computational savings while keeping accuracy. Two case studies, involving PV and wind turbine generation systems, are presented to validate the proposed methodology.

Harmonic domain model of a wind turbine generator for steady-state analysis

This paper presents a harmonic domain (HD) [1] model of a wind turbine generator (WTG) system aimed to steady-state analysis. The proposed HD model of the WTG system involves a doubly-fed induction generator (DFIG), a back-to-back (BTB) converter modeled via switching functions, a filter, and a simple AC network. The HD WTG model accounts for high-impact harmonics only, achieving reduced dimensions of harmonic vectors. The steady-state solution of the WTG system can be applied to control scheme efficiency due to the availability of power quality indices. A case study is presented and compared to the results by the PSCAD/EMTDC software [2].

Floquet domain for open-loop transient simulation of switched devices

This paper presents a Floquet-based time-domain (TD) simulation approach of switched devices in open-loop operation. According to the coordinate transformation provided by Floquet theory, a linear time-periodic (LTP) system becomes a system with a constant state matrix via a transformation matrix. The paper primarily shows that Floquet transformation is readily applicable to pulse-width modulation (PWM) schemes employed in modern electrical networks. Furthermore, the paper demonstrates that switched networks modeled in Floquet coordinates exhibits significant computational savings compared to solving the original LTP state-space system by traditional TD techniques. Two switched networks, i.e., an HVDC system and a system equipped with three PV generators, in open-loop operation, are presented as case studies to support the statements above.