Series Compensated Transmission Network Research Articles

Equivalent Modeling of Dfig-Based Wind Farms for Sub-Synchronous Resonance Analysis

The order of the detailed model of doubly-fed induction generator (DFIG) wind farms are too high and the simulation is difficult. Most of the existing research has used a single-machine equivalent model and clustering aggregation model for equivalence and few papers have explored the principles and equivalent conditions of the single-machine equivalent model under sub-synchronous resonance (SSR). Due to this reason, this paper equates DFIG wind farms connected with series compensated transmission network to two separate units based on the principle of matrix similarity transformation and the mathematical model and physical model of each unit has been studied. Then, the DFIG wind farm equivalent model’s validity is analyzed in number difference and collecting line difference based on linearization analysis. Finally, the system model is built in EMTDC/PSCAD, the damping analysis method is used to test the equivalent model’s validity and further reveal the mechanism of the system’s unstable operation. The results show that: the equivalent model can effectively reduce the system dimension and accurately reflect the dominant oscillation characteristics of DFIG wind farm under SSR; when SSR occurs, the damping coefficient of DFIG wind farm is negative under the oscillation frequency.

Subsynchronous oscillation mitigation strategy based on adaptive band-stop filter in DFIG-based wind farms

Subsynchronous Oscillation (SSO) may exist in doubly-fed induction generator (DFIG)-based wind farms connected with a series compensated transmission network, also called subsynchronous control interaction (SSCI). Different from thermal power units, the SSO frequency of wind farm varies with the change of system operating conditions, and has the characteristic of time-varying. When the operating conditions change, the existing mitigation strategies may lose the effect. To address this issue, a SSO mitigation strategy based on adaptive band-stop filter (ABSF) is proposed in this paper: When SSO occurs in the system, the ABSF parameter is adjusted according to the oscillation frequency measured by PASTd algorithm to filter out the subsynchronous component in the RSC loop effectively, so as to break the generation path of SSO and suppress SSO. Compared with the existing mitigation strategies, the proposed strategy doesn’t need the mathematical model of the system, and can ensure strong robustness under various operating conditions. Finally, the effectiveness and robustness of the proposed strategy are verified on the Matlab/Simulink.

Reactive power control strategy of DFIG‐based wind farm to mitigate SSO

Wind farms connected with series compensated transmission network suffer from the risk of sub-synchronous oscillation (SSO). Moreover, the strong active and reactive power control ability of doubly fed induction generator (DFIG) exerts non-negligible influence on SSO. In this study, the impacts of adjustable parameters on SSO are studied based on eigenvalue analysis. The results indicate that increasing inductive reactive power produced by DFIG can provide positive damping to the system; furthermore, the universality of this rule is verified in the whole operating region of DFIG. According to the rule, a reactive power control strategy of DFIG is proposed for SSO suppression. The reactive power is suggested to increase gradually once the SSO is detected and stop until SSO is suppressed or the reactive power limit is reached. The proposed control method is a low-cost method, which only need to adjust the reactive power reference value of DFIG to damp SSO. Finally, the time-domain simulation results illustrate the validity and adaptability of the proposed SSO reactive power control strategy.

Mitigating SSR Using DFIG-Based Wind Generation

Subsynchronous resonance (SSR) phenomenon in wind farms connected with series compensated transmission network has been researched in recent literature. Mitigating SSR using FACTS devices such as TCSC, SVC, and STATCOM has also been explored in the literature. The ability of the power converters in doubly-fed induction generator (DFIG) wind farms in mitigating SSR has rarely been investigated. In this paper, the DFIG converters will be explored for SSR mitigation. The investigation in this paper includes the design of auxiliary SSR damping controller and selection of control signals. Residue-based analysis, root locus diagrams, and time-domain simulation in Matlab/Simulink will be carried out. The major contributions of the paper are 1) investigation of the potential of wind farm converters for SSR mitigation and 2) identification of an effective control signal for SSR damping controller to simultaneously enhance both subsynchronous and supersynchronous resonance modes.

Technical considerations concerning the use of magnetic potential transformers on MOV series-compensated transmission network

This paper discusses technical considerations concerning the use of magnetic-type potential transformers (PT) on a series-compensated transmission system. Particularly when series capacitors equipped with metal oxide varistors (MOV) are used, magnetic-type PTs will be subject to special conditions, one being the presence of very low subsynchronous voltages due to fault clearing. Other aspects of MOV series compensation are also discussed. Solutions for obtaining an accurate PT despite these phenomena are proposed, and the problem of PT characteristics verification is discussed. These PTs will be used in a shunt-reactor switching scheme for overall voltage control along the Hydro-Quebec transmission network. >

A Digital Computer Method to Evaluate Load Rejection Overvoltages on a Series Compensated Line with Static Shunt Compensator

A method of analysis for computing dynamic overvoltages following load rejection on a series compensated line with static compensator is presented in this paper. The method incorporates detailed models of a synchronous machine, excitation systems, a series compensated transmission network and a static shunt compensator. The problem has been simulated on an ICL 2960 computer system. The receiving-end voltage envelopes following load rejection were evaluated for a typical 400 kV system having different levels of series compensation with a static compensator. These studies are useful for choosing the kind and quantum of compensation required for a particular power system.

Subsynchronous oscillations part 1 ߞ comprehensive system stability analysis

This paper describes a frequency response method for analyzing the stability of subsynchronous oscillations in power systems, as modeled by a number of synchronous machines and an extensive series compensated transmission network. This method allows the simultaneous detailed modeling of all machine shafts and control loops, and hence permits investigation of possible interaction in the subsynchronous oscillation frequency band between machines in different plants. An example application of the method indicates that such interactions may, indeed, occur.