07-08-2012, 09:47 AM
VOLTAGE STABILITY ENHANCEMENT USING D-STATCOM
CONTROL ALGORITHMS FOR c.pptx (Size: 753.39 KB / Downloads: 51)
INTRODUCTION
VOLTAGE INSTABILITY:
The inability of power system to maintain stable voltage in all the buses after being subjected to disturbances.
Mainly the causes for voltage instability are
1.voltage swell
2.voltage sag
3.reactive power imbalance
4.electro magnetic and radio frequency interference.
DISADVANTAGES OF CONVENTIONALCONTROLLER
Their installations have to be supplemented with filters as they inject harmonic currents in the network.
They exhibit poor dynamic performance, under voltage variations.
They do not support the system under low voltage conditions
PROPOSED DEVICES
The DSTATCOM falls into the category of the custom power devices which provide protection for commercial and industrial customers from power quality problem.
Basically there are 3 categories of custom power devices
Dynamic voltage regulator(DVR)
Distribution static compensator(DSTATCOM)
Unified power quality compensator(UPQC) The DSTATCOM is widely preferred over the other two because of its advantages and reliability which we shall discuss further .
DSTATCOM
Distribution Static Compensator is a fast-compensating reactive power source that’s applied on the transmission or distribution system to reduce voltage variations such as sags, surges, and flicker, along with instability caused by rapidly varying reactive power demand. DSTATCOM can also help provide quick recovery for the transmission system after contingency events such as loss of part of the system or individual equipment
WORKING OF DSTATCOM
DSTATCOM generates a variable voltage, Vd, that is very nearly in phase with the source voltage, Vs. The inductance in this simplified circuit, L, consists of the inductance of the coupling transformer and filter. The voltage across the inductance, VL, equals Vs-Vd and is small in per-unit terms . . . on the order of 5-20%.
LITERATURE REVIEW
The voltage deviation during load change and power transfer limitation which arise due to reactive power imbalances can be overcome by employing custom power devices such as DSTATCOM which make use of FACTS devices
There are various control algorithms for DSTATCOM based on different theories such as phase shift control, instantaneous pq theory, synchronous reference frame theory.
Among these control schemes instantaneous reactive power theory and synchronous rotating reference frame theory are most widely used. The conventional reactive power in ac circuits has been defined on the basis of phasor values of sinusoidal voltages and currents in steady states.
The instantaneous reactive power and real power have been defined in various papers based on instantaneous values of voltages and currents. A new instantaneous reactive power compensator comprising switching devices is proposed which requires practically no energy storage components.