Ramesh Kumar Tripathi

Voltage stability improvement in power systems using facts controllers: State-of-the-art review

Flexible AC Transmission Systems (FACTS) devices have been used in power systems since the 1970s for the improvement of its dynamic performance. This paper presents a review on the research and developments in the voltage stability improvement by using FACTS controllers. In this paper several technical issues related to FACTS installations have been highlighted and performance comparison of different FACTS controllers have been discussed. In addition, real-world installations and semiconductor technology development have been reviewed and summarized. This paper also includes the main causes of voltage instability and power scenario in India. In order to deal with the voltage stability problem, the solutions with FACTS-controllers provide voltage support and/or appropriately co-ordinated control actions. Authors strongly believe that this survey article will be very much useful to the researchers for finding out the relevant references in the field of voltage stability improvement by using FACTS controllers in power system environments.

Low voltage ride through (LVRT) ability of DFIG based wind energy conversion system II

Doubly Fed Induction Generators (DFIGs) are nowadays extensively used in variable speed wind power plants. Doubly fed induction generators (DFIG) offer many advantages such as reduced converter rating, low cost and reduced losses with an improved efficiency, easy implementation of power factor correction schemes, variable speed operation and four quadrants active and reactive power control capabilities. Due to variable speed operation total energy output is much more in case of DFIG based WECS so capacity utilization factor is improved and cost of per unit energy is reduced. But the main disadvantage of DFIG is that it is very sensitive to grid disturbance/fault, especially for the voltage dip. Since the doubly-fed induction generator (DFIG) has been widely used in wind energy conversion, the low voltage ride through (LVRT) technology of the DFIG has been investigated extensively in recent times. This paper focuses on the fault ride-through capability of doubly fed induction generator (DFIG) based WECSs Under three phase symmetrical fault. The paper also provides an overview on the interaction between variable-speed DFIG based WECSs and the power system subjected to three phase symmetrical fault. The Steady state behaviour under normal condition and dynamic behaviour of DFIG wind turbines during grid faults is simulated and assessed.

Power quality control of unregulated non-linear loads

Increasing non-linear loads cause various undesirable effects and power quality problems on utility supply, like low system efficiency, poor power factor, derating of power supply equipments, disturbance to other consumers and interference in nearby communications networks etc. This work proposes a parallel power processing scheme to improve the power quality of uncontrolled diode bridge rectifier nonlinear loads. In this scheme a single phase synchronous link converter (SLC) is used as an auxiliary converter, in parallel to the diode bridge rectifier having DC capacitor supplying a resistive load, as main converter. Bulk amount of active power flows through the main converter; whereas the auxiliary converter takes care of the harmonics and reactive power requirement of main converter. A power transformer with 2:1 turn ratio is used at the input of the auxiliary converter in order to match the DC output voltages of two converters. The source current reference is derived using a PI controller which uses the output DC voltage feedback. The regulated output voltage is achieved using inner current control loop. The auxiliary converter current is controlled using HCC such as the summation of main and auxiliary converter input currents are sinusoidal and in phase with source voltage. A laboratory prototype experimental set-up with dedicated LabVIEW based controller is developed and tested in laboratory for experimentation. The simulation and experimental results obtained are in agreement.

Power electronics applications in wind energy conversion system: A review

This paper gives a review on the power electronic applications for wind energy conversion systems. Different types of wind energy conversion system (WECS) with different generators and power electronic converters are described, and different technical features are compared. The electrical topologies of WECS with different wind turbines are summarized and the possible uses of power electronic converters with wind farms are given. In conclusion, the possible methods of using the power electronic technology for improving wind turbine performance in power systems to meet the main grid connection requirements are discussed.

An LQR and pole placement controller for CSC based STATCOM

Flexible AC Transmission Systems (FACTS) devices have been used for the solving power quality problems in the transmission system. In FACTs devices, Static Synchronous Compensator (STATCOM) is a shunt FACTS device, which is able to provide the reactive power compensation to the transmission line. STATCOM is the many input and many output system (MIMO). In this paper, the CSC based STATCOM is controlled by pole placement and LQR methods. These methods are tested in MATLAB, and their results are obtained. The simulation results show an improvement in input-output response of CSC based STATCOM.

Transient energy dissipation and damping improvement using STATCOM & SSSC

In large power systems the generators are of generally synchronous type, so it is necessary to maintain synchronism with the grid in order to provide standard service to consumer. The disturbance in power system is mainly due to sudden change of heavy load, faults, and loss of excitation. In this paper, the rate of change of transient energy of the system is taken into account i.e. the dissipation of kinetic energy (K.E.) of the power system due to disturbances as a measure of system damping. To provide additional damping in the power system without additional cost, the output power of the FACTS devices like STATCOM and SSSC already connected in the power system for compensation is used. They modulate the system output, so as to reduce the system oscillation and hence stability improves.

Minimization of torque ripples in SRM drive using DITC for electrical vehicle application

This paper presents Direct Instantaneous Torque Control (DITC) technique for minimization of torque ripple in Switched Reluctance Motor drive. SRM is a unique choice as a drive system for EV application due to its robustness, high starting torque and wide speed range operation. But high torque ripple is a major drawback in SRM which is due to its double salient structure. In DITC torque is taken as a direct control variable on an instantaneous basis. In this paper hysteresis controller is used for controlling the torque in which torque is used as a reference variable. Look up table is used for estimation of phase torque with phase current and flux linkage as input parameter. In DITC torque is maintain within the hysteresis band by changing the switching states of phases. The dynamic performances of machine are discussed in terms of torque ripple with DITC in MATLAB/SIMULINK software.

Simulation of variable incremental conductance method with direct control method using boost converter

This paper presents simulation of variable incremental conductance (IncCond) maximum power point tracking (MPPT) used in solar array power systems with direct control method [1]. The main difference of the proposed method to existing MPPT methods is the elimination of proportional-integral control loop and investigating the results. The incremental conductance (INC) algorithm is widely used due to the high tracking accuracy at steady state and good adaptability to the rapidly changing atmospheric conditions. A variable step size INC MPPT algorithm is proposed, which automatically adjusts the step size to track the PV array maximum power point. The proposed method was tested in MATLAB/SIMULINK environment. Results indicate the feasibility and improved functionality of the system.

Study of a three level converter interfaced vector controlled DFIG system under fault

There is a steady increase in penetration of wind turbine generation units to power systems. A large proportion of these units are based on Double- Fed Induction Generators (DFIG) with increased interest towards vector control. This paper discusses operation and performance of a vector controlled DFIG wind turbine system tied to grid using three level converters. The performance of DFIG with variable speed wind turbine under faulty condition has been studied using systems developed in MATLAB/SIMULINK. The controller performance is demonstrated using simulation results obtained under fault condition and after the clearance of the fault. A critical assessment of the transient behavior of the double fed induction generator has been performed for grid side faults.

MPPT scheme for small/large time partially shaded condition of a PV cell, array

In the recent years various algorithms have been proposed by researchers to extract the maximum power out of the solar cell/array, called maximum power point tracking (MPPT) algorithms. Out of these incremental conductance (INC) algorithm is most widely used due to its easy implementation and high accuracy. These algorithms also work for non ideal conditions such as long time partial shading condition (PSC). In this paper, a modified INC MPPT algorithm has been proposed, which also works to solve the problem of small time partial shading by comparing the previous and present duty ratios (D) of boost converter.