**9. References**


[6] Khadkikar V., Chandra A. A New Control Philosophy for a Unified Power Quality Conditioner (UPQC) to Coordinate Load-Reactive Power Demand Between Shunt and Series Inverters. IEEE Transactions on Power Delivery 2008; 23 (4) 2522-2534.

**Section 3** 

**Power Quality Improvement in End Users Stage** 


**Power Quality Improvement in End Users Stage** 

118 An Update on Power Quality

21(1) 330-338.

1679-1686.

Delivery 2010; 25(2) 1068-1076.

Engineering 2011; 3(4) 115-119.

Physical Problems of Engineering 2011; 3(4) 120-126.

[6] Khadkikar V., Chandra A. A New Control Philosophy for a Unified Power Quality Conditioner (UPQC) to Coordinate Load-Reactive Power Demand Between Shunt and

[8] Han B., Bae B., Kim H., Baek S. Combined Operation of Unified Power-Quality Conditioner with Distributed Generation. IEEE Transaction on Power Delivery 2006;

[9] Mohammadi H.R., Varjani A.Y., Mokhtari H. Multiconverter Unified Power-Quality Conditioning System: MC-UPQC. IEEE Transactions on Power Delivery 2009; 24(3)

[10] Mokhtarpour A., Shayanfar H.A., Bathaee. S.M.T Extension of Fourier Transform for Very Fast Reference Generation of UPQC. International Journal on Technical and

[11] Mokhtarpour A., Shayanfar H.A., Bathaee. S.M.T UPQC Control Based on MO-ADALINE Approach. International Journal on Technical and Physical Problems of

Series Inverters. IEEE Transactions on Power Delivery 2008; 23 (4) 2522-2534. [7] Lee W.C., Lee D.M., Lee T.K. New Control Scheme for a Unified Power Quality Compensator-Q with Minimum Active Power Injection. IEEE Transactions on Power

**Chapter 7** 

© 2013 Ahmed and Alam, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,

**Power Quality Improvement Using** 

Power quality describes the quality of voltage and current. It is an important consideration in industries and commercial applications. Power quality problems commonly faced are transients, sags, swells, surges, outages, harmonics and impulses [1]. Among these voltage sags and extended under voltages have large negative impact on industrial productivity, and could be the most important type of power quality variation for many industrial and

Voltage sags is mainly due to the fault occurring in the transmission and distribution system, loads like welding and operation of building construction equipment, switching of the loaded feeders or equipments. Both momentary and continuous voltage sags are undesirable in complex process controls and household appliances as they use precision

Major problems associated with the unregulated long term voltage sags include equipment failure, overheating and complete shutdown. Tap changing transformers with siliconcontrolled rectifiers (SCR) are usually used as a solution of continuous voltage sags [6]. They require large transformer with many SCRs to control the voltage at the load which lacks the facility of adjusting to momentary changes. Some solutions have been suggested in the past to encounter the problems of voltage sag [7-11]. But these proposals have not been realized

Now a day's various power semiconductor devices are used to raise power quality levels to meet the requirements [12]. Several AC voltage regulators have been studied as a solution of voltage sags [13-18]. In [13] the input current was not sinusoidal, in [14-16] the efficiency of the regulator was not analyzed and in [17-18] the input power factor was very low and the efficiency is also found poor. Compact and fully electronic voltage regulators are still

and reproduction in any medium, provided the original work is properly cited.

**Switch Mode Regulator** 

Raju Ahmed and Mohammad Jahangir Alam

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/53234

commercial customers [1-5].

unavailable practically.

electronic and computerized control.

practically to replace conventional tap changing transformers.

**1. Introduction** 

**Chapter 7** 
