Sub-synchronous oscillations (SSOs) in doubly-fed induction generator (DFIG)-based series compensated power systems are mainly caused by sub-synchronous control interaction (SSCI). SSCI is the most recently found type of sub-synchronous resonances. In this article, SSCI is elaborated and investigated by performing eigenvalue analysis on a mathematically modeled DFIG system. The occurrence of SSCI is observed and the results of eigenvalue analysis are validated through a down-scaled 7.5-kW experimental setup of a grid-connected DFIG. Based on the analysis, the proportional control parameters of the rotor-side converter (RSC) are found to be very sensitive towards the sub-synchronous modes of the system. The results obtained from both the simulation and the experimental analysis show that if the sensitive proportional parameters of the RSC are tuned properly, then the DFIG system can become immune to the SSCI for any level of series compensation.

The modern power system is moving towards the high integration of renewable energy sources at a fast pace. The integration of wind power in the power system raises many challenges along with the benefits. One of the recent challenges is the sub-synchronous oscillation (SSO) that occurs in doubly-fed induction generator (DFIG) based wind farms. This oscillation is caused by sub-synchronous control interaction (SSCI). The SSCI condition occurs when the DFIG-based wind farm is radially connected to a series compensated transmission line. The aim of this thesis is to investigate and study the circumstances and causes of SSCI, and to develop the techniques that could mitigate this condition from the system. A mathematical model of DFIG-based power system is designed and an eigenvalue analysis is performed. The eigenvalue analysis shows that out of many factors, the level of series compensation play major role in inflicting SSCI in the system. The eigenvalue sensitivity analysis is performed on all the controller parameters of DFIG converters. It is shown that the proportional parameter of the rotor-side converter (RSC) is the most sensitive parameters and the stability of the system is highly dependent on its value. Moreover, the participation factors of the system are also computed to understand the phenomenon better. SSCI is also explained through the internal impedance of induction generator, as seen from the stator terminal. It is shown that the presence of RSC controller enables the occurrence of SSCI, by increasing the negative resistance of the rotor, and its proportional parameters adds up to the negative resistance.

Two mitigation techniques are presented in this thesis. In the first technique a power oscillation damper (POD) is designed and tuned. The proper placement of a tuned POD in the DFIG converter can eliminate the SSCI from the system using a local signal. In the second technique, the boomerang effect of the most sensitive control parameter is presented and it is proposed that the proper selection of control parameters can eliminate the risk of SSCI from the system, even for higher series compensation levels. Along with linearized and non-linear simulations, the sensitivity analysis and the mitigation of SSCI through proper selection of control parameters is validated experimentally using an actual 7.5 kW DFIG system. The analysis of SSCI is also carried out in a multi-machine two-area system and the mitigation techniques are successfully implemented. The influence of synchronous generator on SSCI is also studied, and the mitigation of SSCI using PSS in the synchronous generator is presented. It is shown that by implementing all the mitigation techniques simultaneously, the multi-machine systems can be made immune to SSCI for any realistic level of series compensation.

The phenomenon of sub-synchronous control interaction (SSCI) in doubly-fed induction generators (DFIGs) is investigated and the optimal tuning and placement of a power oscillation damper (POD) for its mitigation is proposed in this paper. The effect of the POD on the DFIG system is studied by placing it at all the summation junctions of rotor-side converter (RSC) and grid-side converter (GSC) controllers, turn by turn. Five local signals are examined as different input signals to the POD out of which three local signals gave promising results. These signals include the DFIG's active power, the magnitude of the DFIG's apparent power, and the magnitude of the current through the transmission line. Residues are calculated for each POD placement and for each input to the POD. The calculated residues are studied along with the root-locus plots to see the effect of the POD on the mitigation of SSCI and the stability of the DFIG-based system.

The aim of this research work is to analyse subsynchronous control interaction (SSCI) in doubly-fed induction generators (DFIGs) and to design a supplementary control technique for the mitigation of SSCI. A mathematical model of the DFIG is derived and linearized in order to perform an eigenvalue analysis. This analysis pinpoints the parameters of the system which are sensitive in making sub-synchronous modes unstable and hence are responsible for causing SSCI. A power oscillation damper (POD) is designed using a residue method to make the DFIG system immune to the SSCI. The POD control signal acts as a supplementary control, which is fed to the controller of the grid-side converter (GSC). The POD signal is applied to different summation junctions of the GSC controller in order to determine the best placement of the POD for effective mitigation of SSCI and for the increased damping of the system.

Inaccurate line loss predictions leads to additional regulation costs for Transmission System Operators (TSOs) that place energy bids at the day-ahead market to account for these losses. This paper presents a line loss prediction model design, applicable with the TSOs forecast conditions, that can reduce additional expenditure due to inaccurate predictions. The model predicts line losses for the next day per bidding area in relation to prognosis data on electrical demand, supply, renewable energy generation and regional exchange flows. Linear regression analysis can extract these relation factors, known as line loss rates, and derive a line loss prediction with increased accuracy and precision. Required input data is available at the power exchange markets apart from future exchange flows, which instead have been modelled as an optimisation problem and predicted by linear programming. Simulations performed on the Swedish National Grid for 2015 demonstrate the models performance and adequacy for TSO application.

This research work deals with the analysis of sub-synchronous control interaction (SSCI) in doubly-fed induction generators (DFIGs). The time-invariant model of the DFIG is linearized to perform eigenvalue analysis and to obtain the participation factor of each state variable for unstable modes. The sensitivity of system eigenvalues related to sub-synchronous modes is analyzed with respect to all the proportional and integral parameters of the controllers in the rotor-side-converters and grid-side-converters. The major contribution of this research work is the outcomes based on eigenvalue analysis that clearly point out the control parameters to which sub-synchronous modes are highly sensitive. The effect of series compensation level on DFIG system and on the sensitivity of converter control parameters is also studied.

This paper presents a novel design of a wireless power transmission system which transfers an appreciable amount of electrical power wirelessly using low resonant frequency, with an excellent efficiency, and has a very low cost implementation. The designs of induction coils at both source and receiver sides are also presented in this paper. The mechanism for power transmission is through electro-magnetic induction. Also an immense knowledge of electronics was applied in order to design the source and receiver between which this transfer took place. In order to realize this method an AC-AC converter, and AC-DC rectifier were used at source and receiver sides respectively along with the resonant circuits. The work was carried out by the experimental setup and results demonstrate that proposed system design can successfully transfer the amount of power that can be used in many practical applications.