**1. Introduction**

94 An Update on Power Quality

Technology 2009; 1 (1) 98-105.

Kingdom: John Wiley and Sons; 1997.

[12] Mokhtarpour A., Shayanfar H.A., Tabatabaei N.M. Power Quality Compensation in two Independent Distribution Feeders. International Journal for Knowledge, Science and

[13] Machowski J., Bialek J., Bumby J.R. Power System Dynamics and Stability, United

One of the serious problems in electrical power systems is the increase of electronic devices which are used by the industry. These devices, which need high-quality energy to work properly, at the same time, are the most responsible ones for decreasing of power quality by themselves.

Custom power devices (CP) used in distribution systems can control power quality. One of the most efficient CPs is Unified Power Quality Conditioner (UPQC). It consists of a Parallel-Active Filter (PAF) and a Series-Active Filter (SAF) together with a common dc link [1-3]. This combination allows a simultaneous compensation for source side currents and delivered voltage to the load. In this way, operation of the UPQC isolates the utility from current quality problems of the load and at the same time isolates the load from the voltage quality problems of utility.

Reference generation of UPQC is an important problem. One of the scopes of this research is extending of Fourier transform for increasing of its responsibility speed twelve times as the main control part of reference generation of the UPQC. Proposed approach named Very Fast Fourier Transform (VFFT) can be used in balanced three phase systems for extraction of reference voltage and current signals. Proposed approach has fast responsibility as well as good steady state response. As it is known, Fourier transform response needs at least one cycle data for the settling down which results in slow responsibility and week capability in dynamic condition. In the proposed approach there are two different data window lengths. In the sag or swell condition, control system switches to T/12 data window length but, in the steady state condition it is switched to T/2 data window length. It causes fast responsibility as well as good steady state response. This approach will be used for the UPQC control circuit for extraction of the reference signals.

© 2013 Shayanfar et al., 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, and reproduction in any medium, provided the original work is properly cited.

Second scope of this research is to use Multy Output ADAptive LINEar (MOADALINE) approach for the reference generation of UPQC. Simplicity and flexibility in extraction of different reference signals can be advantage of the proposed algorithm. Third scope of this research is reference generation of UPQC with the scope of power flow control as well as power quality compensation. In this stage, SAF is controlled by dqo approach for voltage sag, swell, unbalance, interruption, harmonic compensation and power flow control. Also, PAF is controlled by composition of dqo and Fourier theories for current harmonic and reactive power compensation.

Reference Generation of Custom Power Devices (CPs) 97

Fourier transform has the capability of different order components extraction of distorted periodic voltage and current. It is possible to use voltage and current first order components for determining the compensator signals. Based on the related equations of Fourier transform, there is a need for at least one cycle data for settling down the response. This problem can cause week responsibility in dynamic condition. Proposed extended Fourier transform will be responsible for improving this problem. First order Fourier coefficients of

> 2 4 ( )cos( ) ( )cos( ) 2 2 *a v t td t v t td t*

> 2 4 ( )sin( ) ( )sin( ) 2 2 *b v t td t v t td t*

Based on equations (1) and (2) it is possible to reduce settling time of the Fourier transform responsibility to T/2; where, T is the main period of the signal. In this condition the responsibility speed will be increased twice but, it is not reasonable speed in dynamic condition yet. Equation (5) can be resulted from equations (3) and (4), for a sinusoidal signal

> <sup>4</sup> sin( )cos( ) sin <sup>2</sup> *t td t*

 

3

*t td t t td t*

6

 

6

*t td t t td t*

 

6

*t td t t td t*

 

 

*t td t t td t*

 

 

 

> 

 

*t td t t td t*

8 8 sin( )cos( ) sin( )cos( ) sin 2 2

 

8 8 sin( )sin( ) sin( )sin( ) cos 2 2

 

 

     

8 8 sin( )cos( ) sin( )cos( ) 2 2

 

 

 

   

 

(2)

(1)

 

 

 

(3)

 

 

> 

   

 

 

(4)

(5)

(6)

**3. VFFT problem statement** 

a sinusoidal signal can be written as equations (1) and (2).

2

2

with phase angle *Φ*. Equation (6) can be resulted similarly.

 

> 

 

 

> 

 0

<sup>8</sup> sin( )cos( ) sin <sup>2</sup>

0 0 3 5 6 6 2 4 6 6

0 0 3 5 6 6 2 4 6 6

 

> 

 

> 

6 6 2 0

 

*t td t*

 

4 8 sin( )cos( ) sin( )cos( ) 2 2

4 8 sin( )sin( ) sin( )sin( ) 2 2

Equations (7) and (8) can be rewritten from equations (5) and (6) respectively.

1 0 0

1 0 0

Also for the validity of the proposed approaches, power quality compensation has been done in a test circuit via simulation. Voltage sag, swell and harmonics will be compensated by SAF of UPQC. Also, current harmonics and reactive power will be compensated by PAF of UPQC. Section 2 generally introduces UPQC and its equivalent circuit. Section 3 explains the proposed VFFT and related equations. Section 4 introduces UPQC reference generation system based on the proposed VFFT approach. Section 5 explains proposed MOADALINE algorithm for reference generation. Section 6 explains reference generation based on power flow control. Section 7 simulates the research. Finally, section 8 concludes the results.
