05-03-2013, 11:30 AM
CUSTOM POWER DEVICES FOR POWER QUALITY IMPROVEMENT: A REVIEW
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ABSTRACT
During Last decade power quality problems has become more complex at all level of power system. Recently, the Power electronics controllers are gaining concern to provide the quality of power for both power suppliers and consumers. Various power filtering technology i.e. passive filters, active power filters, hybrid filters have applied from time to time for giving the solution of power quality problems to users, But could not fully satisfied them. Now day’s a new concept of custom power is used for customers’ satisfaction. This paper present a comprehensive survey of custom power devises in distribution level. Classified references are also presented, would be very useful for researchers dealing with power quality problems.
INTRODUCTION
Recently, Power quality problems have become an important issues for electricity consumers at all the level of usage. The deregulation of electric power energy has boosted the public awareness toward power quality among the different categories of users. The subject power quality and its problems related to electric power network has discussed in publications [1]-[10].
To provide an active & flexible solution for power quality problems, various efforts have done from time to time. Among these power quality solution lossless passive filters [11-13] consists of L-C tuned component have been widely used to suppress harmonic. Passive filters are advantageous as its initial cost is low and high efficiency. on the other hand it have various drawbacks of instability, fixed compensation , resonance with supply as well as loads and utility impedance. To overcome these limitations active power filters [14-16] have been used .active power filter has various configurations: shunt, series and hybrid. Hybrid is the combination of series and shunt types.
CUSTOM POWER DEVICES
Custom power is a strategy, which is intended principally to convene the requirement of industrial and commercial consumers. The concept of the custom power is tools of application of power electronics controller devices into power distribution system to supply a quality of power, demanded by the sensitive users. These power electronics controller devices are also called custom power devices because through these valuable powers is applied to the customers. They have good performance at medium distribution levels and most are available as commercial products. For the generation of custom power devices VSI is generally used, due to self-supporting of dc bus voltage with a large dc capacitor. The custom power devices are mainly divided into two groups: network reconfiguring type and compensating type. The complete classification of custom power devices is shown in the Fig 2.
Solid State Breaker
The solid state breaker is based on the GTO or thyristor switching technology. It is a highspeed
switching device, applied to reduces the electrical fault and protect from large current
in distribution system. It can be used in a single switch, static transfer switch, hybrid switch
or a low level fault interrupter. The voltage and current rating of the breaker describes the
requirement of no. of switching devices, cost and the losses of the breaker. It perform autoreclosing
function [25].
COMPENSATING POWER DEVICES
The compensating custom power devices are used for active filtering, load balancing, power
factor improvement voltage regulating (sag/ swell) [33]. These devices are mainly three
types: static shunt compensator, series and hybrid compensator. These are also called as
DSTATCOM, DVR and UPQC respectively.
Distribution Static Compensator (DSTATCOM)
DSTATCOM is a Voltage source inverter (VSI) based static compensator device
(STATCOM, FACTS controller ) applied to maintain bus voltage sags at the required level
by supplying or receiving of reactive power in the distribution system [33]-[34]. It is
connected in shunt with distribution feeder with the help of coupling transformer. The single
line diag. of DSTATCOM is shown in shown fig.5. The DSTATCOM consists of a VSI, dc
energy storage device, an ac filter and coupling transformer.
Static Series Compensator
Commercially, static series compensator is known as Dynamic Voltage Restorer (DVR). It is
a high-speed switching power electronic controlling device. The world’s first DVR has been
installed in the Dukey power distribution system to protect a sensitive textile customer from
voltage dips on August 26, 1996 [42]. DVR is a series connected custom power device,
designed to inject a dynamically controlled voltage in magnitude and phase in to distribution
line via coupling transformer to correct load voltage. The generalized block diag. of DVR is
shown in the Fig 9.
Unified Power Quality Compensator (UPQC)
It is the combination of back to back connected shunt and series compensators through a
common dc bus voltage. In this dc link storage capacitor is connected between two voltage
source inverters for operating as combination of shunt and series compensator. The single
line diagram of unified power quality compensator is shown in Fig 12.
It is a most flexible device, can suppress current in shunt and voltage in series
simultaneously. It can balance the terminal voltage and eliminate negative sequence current
components at the same time. Two type of are UPQC are suggested in literature surveys. One
is called Left- Shunt UPQC [48] and another is known as Right-Shunt UPQC [25]. The
overall performance of right-shunt UPQC is better than left-shunt UPQC. When UPQC is
connected between two feeders then, called Interline Unified Power Quality Compensator
(IUPQC) [49].
CONCLUSIONS
This paper provides a literature review of custom power devices which has been proposed/installed in power distribution system to eliminate various power quality problems; voltage sag/swells, flicker, dip, current harmonics, power factor reduction. These devices can be used by the customers at practical cast for high quality power. The DSTATCOM, which is connected in shunt can provide good power quality in both transmission and distribution level. UPQC is the key of custom power devices, can compensate both voltage and current related problems at the same time