K. C. Sindhu Thampatty

Performance of three phase 11-level inverter with reduced number of switches using different PWM techniques

As compared to conventional inverter topologies like diode clamped and capacitor clamped inverters, the cascaded multilevel inverter has lesser harmonics as well as lower switching stress. The cascaded topology has more number of power switches leading to greater heat losses, larger size, higher cost and more gate drive circuitry. The proposed configuration contains less number of switches and produces lesser harmonics in the output voltage than the cascaded topology. A comparison between four different types of pulse width modulation (PWM) techniques, namely, In-phase disposition (IPD), Anti-phase disposition (APD), Carrier Overlap (CO) and Variable Frequency (VF) PWM methods, has been done. The results have been verified through simulation study in MATLAB/Simulink in order to select the best PWM method that provides minimum THD in the output voltage. An LC filter has been designed to improve the harmonic profile.

Sub-Synchronous Resonance analysis on DFIG based windfarm

The rapidly growing level of wind energy injection into the grid is insisting the modifications in power system. In order to improve power transfer capability, series capacitive compensation in the transmission line is adopted which leads to Sub Synchronous Resonance (SSR) oscillations. The main objective of this paper is to develop a dynamic model of Doubly Fed Induction Generator (DFIG) based wind farm connected into grid through series compensated transmission line for SSR studies. The small signal stability studies are carried out through Eigen value approach. State space representation of the whole system is developed. Different modes of the systems are identified for different wind speeds and for various series compensation levels.

Design and Implementation of RTRL Based Adaptive Controller for TCSC to enhance power system stability

The power system complexity is increasing day by day and the requirement of stable, secure and high quality electrical power is mandatory in present scenario. Flexible AC Transmission System (FACTS) devices such as Thyristor Controlled Series Capacitor (TCSC) are commonly used nowadays to improve the power system performance. This paper presents the design and Implementation of non-linear, Adaptive Real Time Recurrent Learning Algorithm (RTRL) based controller for TCSC to damp power system oscillations and enhance the stability of the system. This control scheme requires two sets of neural networks. The first set is a neuro-identifier and the second set is a neuro-controller which generate the required control signals for the thyristors.

Mathematical modelling of grid connected Doubly Fed Induction Generator based wind farm

The day by day increase in electricity demand and depletion of fossil fuels has made the world to think about the renewable energy sources such as solar, wind etc., This paper focuses on the configuration of large Doubly Fed Induction Generator (DFIG) based wind farm connected into the grid. Nowadays DFIGs are more focused in the wind energy conversion systems due to its own advantages. This paper explains the development of a mathematical model of DFIG driven by wind turbine. The turbine generator set is considered as a two mass model and development of the same is discussed. Mathematical modelling of wind turbine, two mass drive train and grid connected DFIG machines are developed by using the dynamic equations. Dynamics of DFIG Rotor Side Converter (RSC) and Grid Side Converter (GSC) are analyzed for further studies with control. The MATLAB simulation results for a 3730W wind farm is explained in this paper, and analyses of various unbalanced conditions on wind farm has been discussed such as rotor short circuit, grid voltage dip and sudden drop in wind speed. Similarly, different rated DFIG machines can be modeled using different machine specifications with the help of developed model.

Adaptive RTRL based hybrid controller for series connected FACTS devices for damping power system oscillations

This paper presents a novel design of a co-ordinated controller for series connected FACTS devices like Thyristor Controlled Series Capacitor(TCSC) and Thyristor controlled Power Angle Regulator (TCPAR). The scheme can be used for non-linear system control, in which the exact linearized mathematical model of the system is not required, can be used to control many FACTS devices with a single controller. The basis of the proposed design is the Real Time Recurrent Learning (RTRL) algorithm in which the Neural Network (NN) is trained in real time. This requires two sets of neural networks. The first set is a fully connected Recurrent Neural Network (RNN) which acts as a neuro-identifier that provides the dynamic model of the system. The second set of neural network is the neuro-controller, used to generate the required control signals for the thyristors. Simulations results of the system using MATLAB/SIMULINK show that the performance of the system with the proposed controller is better than the conventional PI controllers and GA-based PI controllers.

Output voltage regulation of controlled rectifiers using feedback linearization control algorithm

PWM converters are usually controlled using linear control techniques. As the linear control techniques have a disadvantage of requiring tuning from time-to-time, non-linear control techniques were employed for the control. One such non-linear control technique is feedback linearization control (FBLC). A control strategy for controlling the output voltage of three phase PWM converters through a linearization technique is discussed in this paper. Feedback linearization technique allows a few advantages like the decoupled control of the state variables, wide operating region. The performance analysis of the converter control using FBLC is done for varied conditions of load. The results from simulation of the controller and the analysis made on the thus linearised system shows the effectiveness of the Feedback linearization technique on different operating conditions.

Single stage grid connected solar micro-inverter with two level fuzzy logic MPPT controller

This paper presents a single stage grid connected three phase micro inverter for transfer of power from a solar array to grid controlled by a two level fuzzy logic controller. The system utilizes a line commutated inverter, thus the need for synchronization modules are eliminated. A fuzzy logic controller is designed and developed to track the maximum power from the PV panel and generate an appropriate control variable which is compatible for the switching of thyristorised converter. A two level logic is chosen for faster convergence with variable correction steps for the fuzzy logic controller. The maximum power point voltage window is identified from the PV array characteristics and the rule base for the two levels is developed. The system is tested for two array ratings of 5.8 kW and 8.7 kW to bring out the generic nature of the proposed fuzzy controller for power tracking. The micro inverter system is executed in MATLAB/Simulink for varying ambient conditions of the PV panel and the power balance is verified as proof of theory.

Fuzzy Logic based Rotor Side Converter for constant power control of grid connected DFIG

Technological advancements has made production of electrical energy more efficient and minimized the consumption of non-renewable sources of energy. Wind energy has been harvested for more than a decade and has been considered to be one of the cleaner methods of producing electricity. This paper focuses on wind electric system connected to the grid. There are different types of wind electric generators such as fixed speed generators (synchronous generators) and variable speed generators which are squirrel cage and slip ring induction generators. Variable speed induction generators are widely chosen in wind electric system. In variable speed induction generators, doubly fed induction generators are mostly used because its rotor transfers the slip power when there is high wind speed velocity, and voltage is injected if the wind velocity is less. This paper proposes a method for controlling the stator power output of DFIG at speeds below synchronous speed using a novel fuzzy logic controller for Rotor Side Converter(RSC). The fuzzy logic rule base is formulated based on wind turbine speed and it controls the amount of rotor/slip power to be injected at appropriate slip frequency by varying the reference signal of the PWM generator, hence maintains the constant power flow from stator to grid. The fuzzy based RSC controller is designed and implemented in the laboratory.