Kartik Prasad Basu

A fuzzy variable structure controller for STATCOM

Abstract Two new variable structure fuzzy control algorithms are presented in this paper for controlling the reactive component of the STATCOM current in a power system. The control signal is obtained from a combination of generator speed deviation and STATCOM bus voltage deviation fed to the variable structure fuzzy controller. The parameters of these fuzzy controllers can be varied widely by a suitable choice of membership functions and parameters in the rule base. Simulation results for typical single-machine and multimachine power systems subject to a wide range of operating condition changes confirm the efficiency of the new controllers.

Stability enhancement of power system by controlling HVDC power flow through the same AC transmission line

HVDC power transmission employing power electronic device provides a wide range of control in power transmission. Remote generators are sometimes used to supply power to infinite bus through a single circuit long ac transmission line. The system may loose stability after the clearance of a fault if the pre-fault power transfer or the fault clearance time is high. Simultaneous ac-dc power transfer through the transmission line may be used for power flow enhancement. It needs conversion of the line for simultaneous ac-dc power flow to keep the system stable with high values of pre fault power and fault clearance time. During the transient period after the clearance of the fault, ac power supply is kept off and the dc power flow is increased to produce a retarding torque to bring back the generator to its normal speed. HVDC current regulator having very fast control facility may be employed for this purpose. AC circuit breakers are then switched on and the ac power flow is resumed at its pre fault value without any oscillation. The power swing is low and the system is optimally damped at the end of first swing. If the augmentation facility of HVDC power controller is limited, proper governor control of remote generators may be used to reduce the total power flow and to maintain the dc power flow only. After the system becomes stable the ac power supply is switched-on and the power oscillation is minimized with HVDC power controller.

Reduction of three-phase transformer magnetizing inrush current by use of point on wave switching

At the time of transformer energization, a high current will be drawn by the transformer. The mentioned current is called transient inrush current and it may rise to ten times the nominal full load current of transformer during operation. Energization transients can produce mechanical stress to the transformer, causes protection system malfunction and it often affect the power system quality and may disrupt the operation of sensitive electrical loads such as computers and medical equipment connected to the system. Reduction and the way to control of energization transients currents have become important concerns to the power industry for engineers. One of the methods to reduce inrush current is use of point on wave switching at the time transformer is initially connected to supply. This paper discusses the simulations and the experimental results on a three-phase transformer for reduction of inrush currents. An electronic three-phase switching controller has been designed and some thyristors were used for switching power to the transformers.

UPFC controller design for power system stabilization with improved genetic algorithm

This paper presents the genetic optimization of the parameters of a fuzzy PI controller for UPFC (unified power flow controller) using an improved genetic algorithm to enhance the transient stability performance of power systems. The function based Takagi-Sugeno-Kang (TSK) fuzzy controller uses minimum number of rules (two rules) and generates the proportional action, which by one-to-two inference mapping gives a variable gain PI controller. This single input function based scheme dispenses the gain dependency of the proportional or integral gains and generates independent control actions. Computer simulation results on a 2-area 4-machine 12-bus power system with an UPFC installed between buses s and r confirm the efficacy of the new approach in damping the local-mode and inter-area mode of oscillations.

A fuzzy variable structure current controller for flexible AC transmission systems

The paper presents the design of function based variable structure fuzzy controllers for flexible AC transmission systems to improve transient stability performance. This controller is tested on a very widely considered FACTS device like static compensator (STATCOM) which is simulated by a current injection model comprising both real and reactive components. The function based fuzzy controller uses the Takagi-Sugeno scheme and generates the proportional action which by one-to-one or one-to-two mapping can produce the variable gain PI controller. Unlike the performance based two input fuzzy controllers considered earlier, the function based one input fuzzy controller dispenses with gain dependency and provides independent tuning for proportional and integral gains. This new fuzzy controller is tested on a single-machine infinite-bus power system operating with a STATCOM for a variety of transient disturbances and variation of operating point to validate its superior performance in comparison to the conventional PI controllers.

Elimination of inrush current in parallel transformers by sequential phase energization

Production of very high inrush currents in transformers during energization may create deep voltage sag causing malfunction to electronic and other loads. In high voltage power system star-delta transformers are generally switched in, one by one, producing inrush currents each time. The inrush current may be reduced by sequential phase energization of each transformer with neutral resistors. This paper suggests that sequential phase energization should be carried out on the first transformer only after paralleling the delta secondary of all the transformers. This procedure eliminates inrush currents in all the remaining transformers without too much increase in the inrush of the first transformer.

Model reference controlled separately excited DC motor

This research article proposes the speed control of a separately excited DC motor (SEDM) in the constant torque region. The novelty of this article lies in the application of artificial neural network-based model reference controller (MRC) for the speed control of SEDM. This paper also discusses and compares the speed control systems of SEDM using PI-controlled and fuzzy logic-controlled chopper circuit with MRC. The entire system has been modeled using MATLAB 7.0/SIMULINK toolbox. It has been observed that chopper-controlled speed control system could be eliminated by the use of MRC and the performance of the proposed system is comparable with speed control system using chopper circuit.

Ride through capabilities of load during voltage sag/swell and power interruption with zigzag transformer

Single-phase voltage sag or swell of a 3-phase system due to one phase to ground fault, capacitor switching or any other reason is to be mitigated immediately for satisfactory operation of all the equipments. A 3-phase zigzag-winding transformer connected across a 3-phase load may mitigate the voltage sag or swell at any one phase of the load. The phase subjected to voltage sag or swell is disconnected from the source first, while the two healthy phases remain connected to the source. The zigzag transformer immediately rebuilds the voltage across the load of the open phase and allows the current to flow to the open phase load. Very low value of zero sequence impedance of the zigzag transformer produces very small voltage drop and the open phase voltage nearly equals the normal voltage. Very short interruption of supply takes place in the affected phase during the transfer of supply to the healthy phases. Proper value of capacitor, connected across the DC load, or the DC link capacitor in a converter system for AC load provides the ride through capability of the highly sensitive load during the period of voltage sag/swell or 1-phase power interruption.

Reduction of magnetizing inrush current in traction transformer

In 25 kV ac main line traction system the traction transformer located in the engine are repeatedly switched off and on during the normal run of the train due to presence of neutral section in the contact wire. The transformer draws inrush current several times the full-load value. Its enegization creates severe power quality problem in each time. The inrush current may be reduced to the full-load value either by using point-on-wave switching device or by connecting an external resistor in series with the primary circuit. The resistor is shorted within a few cycles of energization of the transformer to avoid voltage drop and losses during the steady-state operation of the transformer. Simulation results illustrate the effect of voltage and frequency variation on the production of inrush current. Only one circuit breaker with a delayed contact closing may be used for resistance switching.

MAXIMUM LENGTH TERNARY SIGNAL DESIGN BASED ON NYQUIST POINT MAPPING

Abstract The design of ternary pseudo random maximum length signals suitable for system identification under noisy conditions is considered, where the power content in the specified harmonics should be high. Signal levels conversion for mapping a maximum length sequence in the Galois field into three signal levels is proposed such that the primitive version of the signal has only one nonzero harmonic at the Nyquist frequency. If the primitive signal is subsequently used in the design of a maximum length signal of a larger period, this will result in the latter having high power concentrated at the nonzero harmonics.