• Energy Research

Traction systems are single-phase, nonlinear loads, which can unbalance and pollute supply voltages. To reduce voltage unbalance, reactances are usually connected in delta configuration with traction systems. This setup is called the Steinmetz circuit. Parallel and series resonances can occur between the Steinmetz capacitor and system inductors, increasing voltage distortion. Thus, it is important to analyze the parallel resonance “observed” from the traction system to avoid harmonic problems due to its injected harmonic currents. This paper studies this resonance analytically and presents simple expressions to locate it. Experimental measurements are also provided to validate the obtained analytical results. These expressions are also used to analyze resonance in several power systems in the literature.

© 2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting /republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works Multi-terminal high voltage direct current (HVDC) systems, together with AC transmission systems and voltage source converters (VSCs), form hybrid AC/DC grids with complex dynamic and transient interactions. VSCs characterization taking into account DC- and AC-side dynamics in order to study these interactions is not yet well solved. This paper presents a three-port transfer admittance-based matrix model of VSCs that can be applied for such purpose. It is derived from dq-complex space vectors and characterizes both AC- and DC-side dynamics by relating AC- and DC-side current and voltages in a three-dimensional admittance transfer matrix which considers the VSC outer control loops. The paper also proposes a systematical procedure for studying multi-terminal HVDC hybrid AC/DC transmission grids by the Norton admittance method, where the proposed VSC model can be easily included in the Norton admittance matrix. This procedure allows the study of grid dynamics using impedance-based stability criteria. The proposed model and procedure are applied to a stability study in a multi-terminal HVDC hybrid AC/DC transmission grid. PSCAD/EMTDC simulations are used to validate the application. Peer Reviewed

Aeronautical ground lighting (AGL) systems provide a visual reference for aircraft during airport operations. Fast detection and location of failed luminaires is an important safety concern in AGL systems. In the event of luminaire failure, AGL transformers introduce harmonic currents. Resonances can increase harmonics, worsening the problem. This paper presents analytical expressions for determining resonance frequencies in AGL systems, as well as a simple procedure based on these expressions for locating failed luminaires from measurements.

Converters are the key for increasing the development of renewable energy generation but their dynamic interaction with the grid has an important impact on stability. Oscillatory instabilities in different grid‐connected converter systems at several frequency ranges are reported. In particular, sub and supersynchronous oscillatory instabilities in AC power systems with type‐3 and type‐4 wind turbine generators (WTGs) were recently registered at several wind farm areas. A number of works based on eigenvalue analysis and frequency domain approaches are carried out to analyse this new stability issue and more research is going on to analyse in detail the electric and control parameters that may affect this phenomenon. This study contributes analysing in detail the influence of system parameters on the subsynchronous oscillations (SSOs) in AC power systems with type‐4 WTGs. This study is based on a new approach for subsynchronous stability assessment which could also be used for analysing other types of SSOs (e.g. subsynchronous control interactions between doubly‐fed induction generators and series‐compensated networks) as well as supersynchronous oscillations. A representative example of weak AC grids with type‐4 WTGs is used to illustrate the contributions of the study. Results are validated with PSCAD/EMTDC time‐domain simulations.

High-voltage direct current (HVDC) systems linked to AC grids with converters are promising energy transmission systems. These systems present complex AC- and DC-side dynamic interactions. Impedance-based stability studies have recently been proposed to assess DC-side dynamics from DC-side characterization of voltage source converters (VSCs) considering AC-side dynamics. However, the existing approaches used for stability studies in VSC-HVDC systems do not completely model VSCs because they do not consider together the VSC delay, the grid voltage feedforward filter, and all the d- and q-reference current controls. Moreover, these approaches are analytically characterized from dq-real space vectors (less related to circuit theory than dq-complex space vectors), and some work with simple AC grids. The main contribution of this paper is a detailed and complete DC admittance model of VSCs from dq-complex space vectors, which considers the VSC delay, feedforward filter, and d- and q-reference current controls, and also a general AC grid. The proposed model can be used for DC-side stability studies in VSC-HVDC systems considering AC grid dynamics. The capabilities and drawbacks of impedance-based stability methods for DC-side stability assessment were analyzed, and the positive-net-damping criterion was validated as a robust approach. The model was validated by PSCAD/EMTDC simulations and applied to a stability study in a VSC-HVDC system.

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. Resonance instabilities in power systems can be assessed with the positive-net-damping stability criterion. This criterion is a review of the complex torque coefficients method, but it does not provide the frequency of the closed-loop oscillatory modes. This paper presents an alternative approach of the positive-net-damping stability criterion to analyze electrical resonance instability. In this approach, resonance instabilities are identified in feedback systems derived from impedance-based equivalent circuits. The proposed approach is used to characterize the frequency of closed-loop oscillatory modes and identify the physical and control parameters of the system that increase or reduce the damping of these modes. The extension of the proposed approach to study the stability of single-input single-output and multiple-input multiple-output feedback systems is analyzed, and the approach is also compared with other stability methods in the literature. An example of an offshore wind power plant illustrates the theoretical study and compares the proposed approach with different methods to evaluate stability. Time-domain simulations in Power System Computer Aided Design/Electro Magnetic Transient Design and Control (PSCAD/EMTDC) are shown to validate the stability study.