Stability norms control using the virtual impedance concept for power frequency applications

In small-signal stability studies, various stability criteria have been proposed based on impedance or admittance norms to assess the stability of power systems. Controlling these norms can drag a system from a stable to an unstable operating condition. Therefore, finding a control variable that has a direct linear relation with these norms will facilitate the utilisation of data-driven control principles to build a control system based on small-signal impedance. For a STATCOM connected to a power network, the control system parameters of the STATCOM are tested to identify their relationships with the stability norms. Different types of virtual impedance are tested, and the suitability of each virtual impedance type and connection is examined and presented

Transient analysis of interline dynamic voltage restorer using dynamic phasor representation

Computer planning and simulation of power systems require system components to be represented mathematically. A method for building a dynamic phasor model of an Interline Dynamic Voltage Restorer (IDVR) is presented, and the resulting model is tested in a simple radial distribution system. Mathematical analysis is carried out for each individual component of the IDVR as modular models, which are then aggregated to generate the final model. The proposed technique has the advantage of simplifying the modelling of any flexible AC transmission system (FACTS) device in dynamic phasor mode when compared to other modelling techniques reported in the literature. The IDVR, including the series injection transformer, is analysed in both ABC and DQ dynamic phasor modes, and IDVR power management is also presented. The ensure compatibility with transient stability programs, the analysis is performed for the fundamental frequency only, with other frequency components being truncated and without considering harmonics. Results produced by the IDVR dynamic phasor model are validated by comparison with results gained from a detailed MATLAB/Simulink IDVR model

Dynamic phasor modelling of VSC FACTS devices for small signal stability studies

The existence of harmonics and oscillations represent major problems for reliable operation of power system components. Therefore, investigating their response requires finding an appropriate model which reflects their response including these variations. The mathematical derivation of the state space models and impedance models of some of voltage source converters in flexible ac transmission systems (VSC-FACTS) systems is presented using synchronous dq and dq-dynamic phasor approach.;Two types of the VSC-FACTS devices are studied in this thesis; the static synchronous compensator (STATCOM) due to its popularity in the power system network and static synchronous series compensator (SSSC) due to its effective on damping system oscillations. The effect of mechanical section of the synchronous machine and turbine sections on the machine impedance is analysed. A generalised state space and impedance modelling is proposed by converting the synchronous dq models to dq-dynamic phasor models;A development of harmonic stability criteria for the proposed modelling is presented. The proposed modelling is employed to present the harmonics effect on the STATCOM and SSSC response and to identify their unbalanced operation in frequency domain. The main features of the proposed modelling technique are compared comprehensively with the conventional modelling techniques for stability studies assessment. It shows the advantages of proposed method and the importance of including the harmonics in the stability studies.;A comparison between different control modes of the SSSC is discussed in the frequency domain. The effectiveness of these control modes on damping system oscillations is investigated using the impedance concept. It presented the effectiveness of impedance control mode on damping system oscillations over the other control modes. A fast impedance measurement unit (IMU) is proposed to monitor the small signal stability.;The proposed IMU can measure accurately the system impedance within a very short time without any filtering requirements. The effect of changing the STATCOM control gains on the impedance norm is investigated. Also, the effect of shunt and series virtual impedances on the infinite norm of the STATCOM impedance which can be used by network operators to retain the stability is discussed.The existence of harmonics and oscillations represent major problems for reliable operation of power system components. Therefore, investigating their response requires finding an appropriate model which reflects their response including these variations. The mathematical derivation of the state space models and impedance models of some of voltage source converters in flexible ac transmission systems (VSC-FACTS) systems is presented using synchronous dq and dq-dynamic phasor approach.;Two types of the VSC-FACTS devices are studied in this thesis; the static synchronous compensator (STATCOM) due to its popularity in the power system network and static synchronous series compensator (SSSC) due to its effective on damping system oscillations. The effect of mechanical section of the synchronous machine and turbine sections on the machine impedance is analysed. A generalised state space and impedance modelling is proposed by converting the synchronous dq models to dq-dynamic phasor models;A development of harmonic stability criteria for the proposed modelling is presented. The proposed modelling is employed to present the harmonics effect on the STATCOM and SSSC response and to identify their unbalanced operation in frequency domain. The main features of the proposed modelling technique are compared comprehensively with the conventional modelling techniques for stability studies assessment. It shows the advantages of proposed method and the importance of including the harmonics in the stability studies.;A comparison between different control modes of the SSSC is discussed in the frequency domain. The effectiveness of these control modes on damping system oscillations is investigated using the impedance concept. It presented the effectiveness of impedance control mode on damping system oscillations over the other control modes. A fast impedance measurement unit (IMU) is proposed to monitor the small signal stability.;The proposed IMU can measure accurately the system impedance within a very short time without any filtering requirements. The effect of changing the STATCOM control gains on the impedance norm is investigated. Also, the effect of shunt and series virtual impedances on the infinite norm of the STATCOM impedance which can be used by network operators to retain the stability is discussed