**2. Unified Power Quality Conditioner (UPQC)**

UPQC has composed of two inverters that are connected back to back [2]. One of them is connected to the grid via a parallel transformer and can compensate the current problems (PAF). Another one is connected to the grid via a series transformer and can compensate the voltage problems (SAF). These inverters are controlled for the compensation of the power quality problems instantaneously. Figure 1 shows the general schematic of a UPQC.

**Figure 1.** General schematic of a UPQC

A simple circuit model of the UPQC is shown in Figure 2. Series active filter has been modeled as the voltage source and parallel active filter has been modeled as the current source.

**Figure 2.** Circuit model of UPQC

section 7 concludes the results.

**Figure 1.** General schematic of a UPQC

source.

of introduced active filter with integration of Unified Power Quality Conditioner (UPQC). In this research, voltage problems are compensated by the Series Active Filter (SAF) of the UPQC. On the other hand, issues related to the compensation of current problems are done by the electromechanical active filter and PAF of UPQC. For validation of the proposed theory in power quality compensation, a simulation has been done in MATLAB/SIMULINK

A T-type active power filter for power factor correction is proposed in [4]. In [5], neutral current in three phase four wire systems is compensated by using a four leg PAF for the UPQC. In [6], UPQC is controlled by H∞ approach which needs high calculation demand. In [7], UPQC can be controlled based on phase angle control for share load reactive power between SAF and PAF. In [8] minimum active power injection has been used for SAF in a UPQC-Q, based on its voltage magnitude and phase angle ratings in sag conditions. In [9], UPQC control has been done in parallel and islanding modes in dqo frame use of a high pass filter. In [10-12] two new combinations of SAF and PAF for two independent distribution feeders power quality compensation have been proposed. Section 2 generally introduces UPQC. Section 3 explains connection of the proposed active filter. Section 4 introduces electromechanical active filter. Section 5 explains used algorithm for reference generation of the electromechanical filter in detail. Section 6 simulates the paper. Finally,

UPQC has composed of two inverters that are connected back to back [2]. One of them is connected to the grid via a parallel transformer and can compensate the current problems (PAF). Another one is connected to the grid via a series transformer and can compensate the voltage problems (SAF). These inverters are controlled for the compensation of the power

A simple circuit model of the UPQC is shown in Figure 2. Series active filter has been modeled as the voltage source and parallel active filter has been modeled as the current

quality problems instantaneously. Figure 1 shows the general schematic of a UPQC.

and a number of selected simulation results have been shown.

**2. Unified Power Quality Conditioner (UPQC)** 

#### **3. Connection of Electromechanical Filter**

Figure 3, shows schematic of the proposed compensator system. In this research load current harmonics with higher order than 7, has been determined as PAF of UPQC compensator signal. But, load current harmonics with lower order than 7 and reactive power have been compensated by the proposed electromechanical filter.

**Figure 3.** Proposed compensator system

#### **4. Electromechanical Parallel Active Filter**

Figure 4, shows the simple structure of a synchronous generator. Based on equation (1), a DC field current of *if* produces a constant magnitude flux.

$$F\_f = \mathbf{N}\_f \dot{\mathbf{i}}\_f, \quad \boldsymbol{\varrho}\_f = \prescript{\mathbf{N}\_f \dot{\mathbf{i}}\_f}{\mathbf{R}}\_f, \quad \boldsymbol{\Psi}\_f = \prescript{\mathbf{N}\_f \mathbf{N}\_s \dot{\mathbf{i}}\_f}{\mathbf{R}}\_R \Big/ \mathbf{R} = \mathbf{M} \mathbf{i}\_f \tag{1}$$

As in [13] *N <sup>f</sup>* and *Ns* are effective turns of the field windings and the stator windings, respectively; *Ff* is the magnetomotive force; *R* is the reluctance of the flux line direction and *M* is the mutual induction between rotor and stator windings. Speed of rotor is equal to the synchronous speed ( <sup>120</sup> *<sup>s</sup> <sup>f</sup> <sup>n</sup> <sup>p</sup>* ). Thus, the flux rotates with the angular speed of

2 60 *<sup>s</sup> <sup>s</sup> n* . So, stator windings passing flux has been changed as equation (2). It is assumed that in 0 *t* , direct axis of field and stator first phase windings conform each other.

$$\mathbf{w}\_s = \mathbf{i}\_f M \cos(\alpha t) \tag{2}$$

Electromechanical Active Filter as a Novel Custom Power Device (CP) 83

 

(5)

 

> 

*i* . But, if the field current be harmonized as

(4)

(6)

Based on equation (3), if the field current be a DC current, the stator induction voltage will

equation (4) then, the flux and internal induction voltage will be as equations (5) and (6),

sin( ) *<sup>f</sup> dc fn fn n i I I nt*

cos( ) [ sin( )] cos( )

*iM t I I nt M t*

<sup>1</sup> [ sin( ) cos( )] <sup>2</sup>

*o dc f f*

 

two components of the field current. This problem has been shown in Figure 6.

**Figure 6.** Relation of the field current components by the stator voltage components

*e MI t MI t*

*MI t M I n t n t*

*f f dc fn fn n*

<sup>1</sup> cos( ) [sin(( 1) ) sin(( 1) )] <sup>2</sup>

*dc fn fn fn*

 

Equation (6) shows that each component of the generator output voltage has composed of

It seems that a synchronous generator can be assumed as the Current Controlled System (CCS). Thus it can be used for the current harmonic compensation of a nonlinear load ( *hn I* )

From Figure 5, relation between terminal voltage of the generator and *hn I* can be derived as

sin( ) *o pcc n hn n <sup>n</sup> n e V ZI V n t*

 (7)

*MI n n t MI n n t*

2 2

 

1 1 [ cos( ) cos( )] 2 2

*f n f n f n f n*

( 1) ( 1) ( 1) ( 1)

be a sinusoidal voltage by the amplitude of *M <sup>f</sup>*

 

 

2

*n*

as parallel active filter.

equation (7).

**5. Algorithm and method** 

respectively.

The scope of this section is theoretically investigation of a synchronous machine as a rotating active filter. This theory will be investigated in the static state for a circular rotor type synchronous generator that its equivalent circuit has been shown in Figure 5.

**Figure 4.** Simple structure of synchronous generator

**Figure 5.** Equivalent circuit of synchronous generator

Equation (3) shows the relation between magnetic flux and voltage behind synchronous reactance of the generator.

$$e = -\frac{d\boldsymbol{\nu}\_s(t)}{dt}\Big/\_{dt} = -\frac{d(\dot{\boldsymbol{\imath}}\_f M \cos(\alpha t))}{dt}\Big/\_{dt} = -M \Big/ \frac{d(\dot{\boldsymbol{\imath}}\_f \cos(\alpha t))}{dt}\Big/\_{dt}\tag{3}$$

Based on equation (3), if the field current be a DC current, the stator induction voltage will be a sinusoidal voltage by the amplitude of *M <sup>f</sup> i* . But, if the field current be harmonized as equation (4) then, the flux and internal induction voltage will be as equations (5) and (6), respectively.

$$\dot{I}\_f = I\_{dc} + \sum\_{n} I\_{fn} \sin(nwt - \phi\_{fn}) \tag{4}$$

$$\begin{aligned} \, \, \nu \, \, \_f &= i \, \_fM \cos(\alpha t) = [I\_{dc} + \sum\_n I\_{fn} \sin(n\alpha t - \phi\_{fn})]M \cos(\alpha t) = \\ \, \, \, \_{dc}M \, \_{dc}\cos(\alpha t) &+ \frac{1}{2}M \sum I\_{fn} [\sin((n+1)\alpha t - \phi\_{fn}) + \sin((n-1)\alpha t - \phi\_{fn})] \end{aligned} \tag{5}$$

$$\begin{aligned} e\_o^\* &= \left[ -M I\_{dc} \alpha \sin(\alpha t) + \frac{1}{2} M I\_{f/2} \alpha \cos(\alpha t - \phi\_{f2}) \right] + \\ \sum\_{n=2} \left[ \frac{1}{2} M I\_{f(n-1)} \alpha \alpha \cos(\alpha t - \phi\_{f(n-1)}) + \frac{1}{2} M I\_{f(n+1)} \alpha \alpha \cos(\alpha t - \phi\_{f(n+1)}) \right] \end{aligned} \tag{6}$$

Equation (6) shows that each component of the generator output voltage has composed of two components of the field current. This problem has been shown in Figure 6.

**Figure 6.** Relation of the field current components by the stator voltage components

It seems that a synchronous generator can be assumed as the Current Controlled System (CCS). Thus it can be used for the current harmonic compensation of a nonlinear load ( *hn I* ) as parallel active filter.

#### **5. Algorithm and method**

82 An Update on Power Quality

60

**Figure 4.** Simple structure of synchronous generator

**Figure 5.** Equivalent circuit of synchronous generator

reactance of the generator.

 . So, stator windings passing flux has been changed as equation (2). It is assumed that in 0 *t* , direct axis of field and stator first phase windings conform each

cos( ) *s f*

The scope of this section is theoretically investigation of a synchronous machine as a rotating active filter. This theory will be investigated in the static state for a circular rotor

Equation (3) shows the relation between magnetic flux and voltage behind synchronous

( cos( )) ( cos( )) ( ) *f f <sup>s</sup> d t di M t di t e M dt dt dt*

(3)

 

(2)

*iM t*

type synchronous generator that its equivalent circuit has been shown in Figure 5.

2

*<sup>s</sup> <sup>s</sup> n*

other.

From Figure 5, relation between terminal voltage of the generator and *hn I* can be derived as equation (7).

$$e\_o = V\_{pcc} + Z\_n I\_{hn} = \sum\_n V\_n \sin(n\alpha t + \theta\_n) \tag{7}$$

Where, n is the harmonic order; *Z R jnX <sup>n</sup>* is the harmonic impedance of the synchronous generator and connector transformer which are known, *VPCC* is the point of common coupling voltage and *hn I* is the compensator current that has been extracted from the control circuit.

If similar frequency components of voltage signal *<sup>o</sup> e* in equation (6) and *<sup>o</sup> <sup>e</sup>* in equation (7) set equal, the magnitude and phase angle of the related field current components will be extracted as:

For n=1:

$$-M I\_{dc} \alpha \sin(\alpha t) + \frac{1}{2} M I\_{f/2} \alpha \cos(\alpha t - \varphi\_{f2}) = V\_1 \sin(\alpha t + \theta\_1) \tag{8}$$

Electromechanical Active Filter as a Novel Custom Power Device (CP) 85

(17)

(20)

2

*f*

2 2

1 1

 

2 2

*X*

 

*X MI n f n*

*Y MI n f n*

( 1)

( 1)

*f n*

*I*

**Figure 7.** Block diagram of the proposed active filter control

*f n*

tan

For n≥2:

Where, *M* and

2

*f n MI n f n*

*f n MI n f n*

 

 

*f n* (18)

*f n* (19)

( 1) ( 1)

 

*fn fn*

( 1) ( 1)

are the mutual inductance and angular frequency, respectively.

 

( 1)

*f n*

*fn fn*

( 1) ( 1)

 (21)

(22)

*f*

( 1) ( 1) ( 1) ( 1)

( 1) ( 1) ( 1) ( 1)

<sup>2</sup> 1 tan *n*

*X Mn I X Mn I*

*X Mn I*

*Mn*

*V*

cos cos

*n*

*n fn fn*

0.5 sin

tan 0.5 cos

2( 0.5 sin ) sin

 

Obviously for the extraction of required components of filed current from the above equations, first suggestion for DC and first order component of the field current are need. Resulted field current can be injected via a PWM and current inverter to the field windings of the synchronous generator. Figure 7, shows the control circuit of the electromechanical

2( ) sin *dc*

 

1 1 sin sin

*X MI <sup>I</sup> M*

$$\sqrt{\left[-M\mathrm{I}\_{dc}\phi + \frac{1}{2}M\mathrm{I}\_{f2}\phi\sin\varphi\_{f2}\right]^2 + \left[\frac{1}{2}M\mathrm{I}\_{f2}\phi\cos\varphi\_{f2}\right]^2} = V\_1\tag{9}$$

$$\tan^{-1}[\frac{1}{2}\frac{M I\_{f2} \rho \cos \varphi\_{f2}}{-M I\_{dc} \, \alpha + \frac{1}{2} M I\_{f2} \, \rho \sin \varphi\_{f2}}] = \theta\_1 \tag{10}$$

For simplicity equations (9) and (10) can be rewritten as follows:

$$X = -M I\_{dc} \phi + \frac{1}{2} M I\_{f2} \phi \sin \varphi\_{f2} \tag{11}$$

$$Y = \frac{1}{2} M I\_{f2} a \cos \varphi\_{f2} \tag{12}$$

$$X^2 + Y^2 = V\_1^2\tag{13}$$

$$\begin{aligned} \text{X} & \Big\prime\_{\text{Y}} = \theta\_1 \end{aligned} \tag{14}$$

From the above equations, magnitude and phase of the second component of filed current can result in:

$$X = \frac{V\_1}{\sqrt{1 + \tan^2 \theta\_1}}\tag{15}$$

$$\tan \phi\_{f2} = \frac{X + MI\_{dc}o}{X \tan \theta\_1} \tag{16}$$

Electromechanical Active Filter as a Novel Custom Power Device (CP) 85

$$I\_{f2} = \frac{2(X + MI\_{dc}o)}{Mos\sin\varphi\_{f2}}\tag{17}$$

For n≥2:

84 An Update on Power Quality

control circuit.

extracted as:

can result in:

For n=1:

If similar frequency components of voltage signal *<sup>o</sup> e*

 For simplicity equations (9) and (10) can be rewritten as follows:

Where, n is the harmonic order; *Z R jnX <sup>n</sup>* is the harmonic impedance of the synchronous generator and connector transformer which are known, *VPCC* is the point of common coupling voltage and *hn I* is the compensator current that has been extracted from the

set equal, the magnitude and phase angle of the related field current components will be

*MI t MI t V t dc*

 

2 2

2 2 <sup>1</sup>

*MI*

*MI MI*

*X MI MI dc*

1

2 *Y MIf*

> *X Y*

*<sup>V</sup> <sup>X</sup>*

2

*f*

tan

<sup>2</sup> tan [ ] <sup>1</sup> sin 2

 

1

1 1 [ sin ] [ cos ] 2 2 *MI MI dc*

<sup>1</sup> sin( ) cos( ) sin( ) <sup>2</sup>

 

cos

*f f*

 

2

*dc f f*

 

<sup>1</sup> sin

 *f f* 

2 2

cos

1

1 2 <sup>1</sup> 1 tan

1

tan *dc*

*X MI X*

From the above equations, magnitude and phase of the second component of filed current

*<sup>f</sup>*

2 21 1

*<sup>f</sup> <sup>f</sup>* (8)

2 2 2 21

2 2

2 2

 *f f MIf <sup>f</sup> V* (9)

 

1

22 2 *XYV*<sup>1</sup> (13)

in equation (6) and *<sup>o</sup> <sup>e</sup>* in equation (7)

(10)

(11)

(12)

(14)

(15)

(16)

$$X = \frac{1}{2} M I\_{f(n-1)} n o \sin \varphi\_{f(n-1)} + \frac{1}{2} M I\_{f(n+1)} n o \sin \varphi\_{f(n+1)} \tag{18}$$

$$Y = \frac{1}{2} M I\_{f(n-1)} n o \cos \phi\_{f(n-1)} + \frac{1}{2} M I\_{f(n+1)} n o \cos \phi\_{f(n+1)} \tag{19}$$

$$X = \frac{V\_n}{\sqrt{1 + \tan^2 \theta\_n}} \tag{20}$$

$$
\tan \phi\_{f(n+1)} = \frac{X - 0.5MnoI\_{f(n-1)} \sin \phi\_{f(n-1)}}{X \tan \theta\_n - 0.5MnoI\_{f(n-1)} \cos \phi\_{f(n-1)}} \tag{21}
$$

$$I\_{f(n+1)} = \frac{2(X - 0.5MuoI\_{f(n-1)}\sin\varphi\_{f(n-1)})}{Mno\sin\varphi\_{f(n-1)}}\tag{22}$$

Where, *M* and are the mutual inductance and angular frequency, respectively. Obviously for the extraction of required components of filed current from the above equations, first suggestion for DC and first order component of the field current are need. Resulted field current can be injected via a PWM and current inverter to the field windings of the synchronous generator. Figure 7, shows the control circuit of the electromechanical

**Figure 7.** Block diagram of the proposed active filter control

active filter. *hI* and *<sup>f</sup> <sup>I</sup>* are desired compensator current and calculated field current signal. Detail of the proposed control circuit can be found in the equations (11) to (22). In the present research controlled voltage source of MATLAB has been used instead of required PWM and inverter. Constant and integrator coefficients in the PI controller have been chosen 1000 and 200, respectively. As mentioned earlier first order load active and reactive powers can be easily attended in the electromechanically compensated share of load current for decrease of SAF and PAF power range of UPQC. This problem can control power flow as well as power quality. In other word it can be possible to use a synchronous generator not only for first order voltage generation but, also for the harmonic compensation too.

Electromechanical Active Filter as a Novel Custom Power Device (CP) 87

voltage harmonic condition, utility voltages have harmonic and negative sequence components between 0.05 s and 0.2 s. Also, for the investigation of the proposed control strategy in unbalance condition, magnitude of the first phase voltage is increased to the 1.25 pu between 0.05 s and 0.1 s and decreased to the 0.75 pu between 0.15 s to 0.2 s. Table 1, shows the utility voltage harmonic and sequence parameters data and Table 2, shows the load power and voltage parameters. A number of selected simulation results will be showed further.

> Voltage Order Sequence Magnitude (pu) Phase Angle (deg) 5 1 0.12 -45 3 2 0.1 0

Load Nominal Power (kVA) Nominal Voltage (RMS, L-L)

Figure 9, shows the source side voltage of phase 1. Figure 10, shows the compensator voltage of phase 1. Figure 11, shows load side voltage of phase 1. Figure 12, shows the load side current of phase 1. Figure 13, shows the CCS current of phase 1 that has been supplied by the proposed active filter. Figure 14, shows the PAF of UPQC current of phase 1. Figure 15, shows the source side current of phase 1. Figure 16, shows the field current of the proposed harmonic filter. Figure 17 and 18 show source voltage and load voltage frequency spectrum, respectively. Figure 19 and 20 show load current and source current frequency spectrum, respectively. Figure 21 and 22 show CCS and PAF frequency spectrum, respectively. Table 3 shows THDs of source and load voltages and currents. Load voltage

**Figure 9.** Source side voltage of phase 1 (swell has been occurred between 0.05 and 0.1 sec and sag has been occurred between 0.15 and 0.2 sec. Also, harmonics of positive and negative sequences have been

<sup>0</sup> 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 -400

Time (Sec)

Linear 10 380V Non linear 5 380V

and source current harmonics have been compensated satisfactory.

**Table 1.** Utility voltage harmonic and sequence parameters data

**Table 2.** Load power and voltage parameters data

concluded between 0.05 to 0.2 sec)

Voltage (V)

#### **6. Results**

For the investigation of the validity of the mentioned control strategy for power quality compensation of a distribution system, simulation of the test circuit of Figure 8, has been done in MATLAB software. Source current and load voltage, have been measured and analyzed in the proposed control system for the determination of the compensator signals of SAF, PAF and filed current of the electromechanical active filter. Related equations of the controlled system and proposed model of the electromechanical active filter as a current controlled source have been compiled in MATLAB software via M-file. In mentioned control strategy, voltage harmonics have been compensated by SAF of the UPQC and current harmonics with higher order than 7, have been compensated by PAF of UPQC. But, the total of load reactive power, 25 percent of load active power and load current harmonics with lower order than 7 have been compensated by the proposed CCS. This power system consists of a harmonized and unbalanced three phase 380V (RMS, L-L), 50 Hz utility, a three phase balanced R-L load and a three phase rectifier as a nonlinear load. For the investigation of the

**Figure 8.** General test system circuit

voltage harmonic condition, utility voltages have harmonic and negative sequence components between 0.05 s and 0.2 s. Also, for the investigation of the proposed control strategy in unbalance condition, magnitude of the first phase voltage is increased to the 1.25 pu between 0.05 s and 0.1 s and decreased to the 0.75 pu between 0.15 s to 0.2 s. Table 1, shows the utility voltage harmonic and sequence parameters data and Table 2, shows the load power and voltage parameters. A number of selected simulation results will be showed further.


**Table 1.** Utility voltage harmonic and sequence parameters data


86 An Update on Power Quality

and *<sup>f</sup> <sup>I</sup>*

**Figure 8.** General test system circuit

are desired compensator current and calculated field current signal.

Detail of the proposed control circuit can be found in the equations (11) to (22). In the present research controlled voltage source of MATLAB has been used instead of required PWM and inverter. Constant and integrator coefficients in the PI controller have been chosen 1000 and 200, respectively. As mentioned earlier first order load active and reactive powers can be easily attended in the electromechanically compensated share of load current for decrease of SAF and PAF power range of UPQC. This problem can control power flow as well as power quality. In other word it can be possible to use a synchronous generator not

For the investigation of the validity of the mentioned control strategy for power quality compensation of a distribution system, simulation of the test circuit of Figure 8, has been done in MATLAB software. Source current and load voltage, have been measured and analyzed in the proposed control system for the determination of the compensator signals of SAF, PAF and filed current of the electromechanical active filter. Related equations of the controlled system and proposed model of the electromechanical active filter as a current controlled source have been compiled in MATLAB software via M-file. In mentioned control strategy, voltage harmonics have been compensated by SAF of the UPQC and current harmonics with higher order than 7, have been compensated by PAF of UPQC. But, the total of load reactive power, 25 percent of load active power and load current harmonics with lower order than 7 have been compensated by the proposed CCS. This power system consists of a harmonized and unbalanced three phase 380V (RMS, L-L), 50 Hz utility, a three phase balanced R-L load and a three phase rectifier as a nonlinear load. For the investigation of the

only for first order voltage generation but, also for the harmonic compensation too.

active filter. *hI*

**6. Results** 

Figure 9, shows the source side voltage of phase 1. Figure 10, shows the compensator voltage of phase 1. Figure 11, shows load side voltage of phase 1. Figure 12, shows the load side current of phase 1. Figure 13, shows the CCS current of phase 1 that has been supplied by the proposed active filter. Figure 14, shows the PAF of UPQC current of phase 1. Figure 15, shows the source side current of phase 1. Figure 16, shows the field current of the proposed harmonic filter. Figure 17 and 18 show source voltage and load voltage frequency spectrum, respectively. Figure 19 and 20 show load current and source current frequency spectrum, respectively. Figure 21 and 22 show CCS and PAF frequency spectrum, respectively. Table 3 shows THDs of source and load voltages and currents. Load voltage and source current harmonics have been compensated satisfactory.

**Figure 9.** Source side voltage of phase 1 (swell has been occurred between 0.05 and 0.1 sec and sag has been occurred between 0.15 and 0.2 sec. Also, harmonics of positive and negative sequences have been concluded between 0.05 to 0.2 sec)

Electromechanical Active Filter as a Novel Custom Power Device (CP) 89

**Figure 13.** Proposed CCS current of phase 1 (this current has been injected to the grid by the electromechanical active filter. The solid line shows output current of filter and dotted line shows

<sup>0</sup> 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 -20

Time (Sec)

**Figure 14.** PAF of UPQC current of phase 1 (this current has been injected to the grid by the parallel

<sup>0</sup> 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 -30

Time (Sec)

**Figure 15.** Source side current of phase 1 (harmonics and reactive components of load current have

<sup>0</sup> 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 -40

Time (Sec)

desired current of filter)

Current (A)

Current (A)

Current (A)

active filter of UPQC)

been canceled)

**Figure 10.** Compensator voltage of phase 1 (compensator voltage has been determined for the sag, swell, negative sequence and harmonics improvement)

**Figure 11.** Load side voltage of phase 1 (sag, swell, harmonics, positive and negative sequences have been canceled)

**Figure 12.** Load side current of phase 1 (it is harmonized. It should be noticed that this current has been calculated after the voltage compensation and thus voltage unbalance has not been transmitted to the current)

been canceled)

current)

**Figure 10.** Compensator voltage of phase 1 (compensator voltage has been determined for the sag,

<sup>0</sup> 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 -150

Time (Sec)

**Figure 11.** Load side voltage of phase 1 (sag, swell, harmonics, positive and negative sequences have

<sup>0</sup> 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 -400

Time (Sec)

**Figure 12.** Load side current of phase 1 (it is harmonized. It should be noticed that this current has been calculated after the voltage compensation and thus voltage unbalance has not been transmitted to the

<sup>0</sup> 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 -40

Time (Sec)

swell, negative sequence and harmonics improvement)

Current (A)

Voltage (V)



0

Voltage (V)

50

100

150

**Figure 13.** Proposed CCS current of phase 1 (this current has been injected to the grid by the electromechanical active filter. The solid line shows output current of filter and dotted line shows desired current of filter)

**Figure 14.** PAF of UPQC current of phase 1 (this current has been injected to the grid by the parallel active filter of UPQC)

**Figure 15.** Source side current of phase 1 (harmonics and reactive components of load current have been canceled)

Electromechanical Active Filter as a Novel Custom Power Device (CP) 91

**Figure 19.** Load side current frequency spectrum

Amplitude (A)

<sup>0</sup> <sup>100</sup> <sup>200</sup> <sup>300</sup> <sup>400</sup> <sup>500</sup> <sup>600</sup> <sup>700</sup> <sup>800</sup> <sup>900</sup> <sup>1000</sup> <sup>1100</sup> <sup>1200</sup> <sup>1300</sup> <sup>1400</sup>

Frequency (Hz)

<sup>0</sup> <sup>100</sup> <sup>200</sup> <sup>300</sup> <sup>400</sup> <sup>500</sup> <sup>600</sup> <sup>700</sup> <sup>800</sup> <sup>900</sup> <sup>1000</sup> <sup>1100</sup> <sup>1200</sup> <sup>1300</sup> <sup>1400</sup>

Frequency (Hz)

<sup>0</sup> <sup>100</sup> <sup>200</sup> <sup>300</sup> <sup>400</sup> <sup>500</sup> <sup>600</sup> <sup>700</sup> <sup>800</sup> <sup>900</sup> <sup>1000</sup> <sup>1100</sup> <sup>1200</sup> <sup>1300</sup> <sup>1400</sup>

Frequency (Hz)

**Figure 20.** Source side current frequency spectrum

Amplitude (A)

Amplitude (A)

**Figure 21.** Proposed current controlled system frequency spectrum

**Figure 16.** Field current of proposed harmonic filter (field current is controlled for the load active, reactive and harmonic current compensation)

**Figure 17.** Source side voltage frequency spectrum

**Figure 18.** Load side voltage frequency spectrum

**Figure 19.** Load side current frequency spectrum

reactive and harmonic current compensation)

Amplitude (V)

Current (A)

**Figure 17.** Source side voltage frequency spectrum

**Figure 18.** Load side voltage frequency spectrum

Amplitude (V)

**Figure 16.** Field current of proposed harmonic filter (field current is controlled for the load active,

<sup>0</sup> 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

Time (Sec)

<sup>0</sup> <sup>100</sup> <sup>200</sup> <sup>300</sup> <sup>400</sup> <sup>500</sup> <sup>600</sup> <sup>700</sup> <sup>800</sup> <sup>900</sup> 1,0001,100 1,200 1,3001,400

Frequency (Hz)

<sup>0</sup> <sup>100</sup> <sup>200</sup> <sup>300</sup> <sup>400</sup> <sup>500</sup> <sup>600</sup> <sup>700</sup> <sup>800</sup> <sup>900</sup> <sup>1000</sup> <sup>1100</sup> <sup>1200</sup> <sup>1300</sup> <sup>1400</sup>

Frequency (Hz)

**Figure 20.** Source side current frequency spectrum

**Figure 21.** Proposed current controlled system frequency spectrum

Electromechanical Active Filter as a Novel Custom Power Device (CP) 93

**Author details** 

**8. References** 

315-322.

2005; 20(2) 1650-1656.

Industry Applications 2009; 45(5) 1897-1902.

Transactions on Power Delivery 2007; 22(1) 364-372.

Delivery 2010; 25(2) 1068-1076.

21(1) 330-338.

1679-1686.

152.

1238.

*Iran* 

Ahad Mokhtarpour, Heidarali Shayanfar and Mitra Sarhangzadeh

*Department of Electrical Engineering, Tabriz Branch, Islamic Azad University, Tabriz,* 

[1] Fujita H., Akagi H. The Unified Power Quality Conditioner: The Integration of Series and Shunt Active Filters. IEEE Transaction on Power Electronics 1998; 13(2)

[2] Shayanfar H. A., Mokhtarpour A. Management, Control and Automation of Power Quality Improvement. In: Eberhard A. (ed.) Power Quality. Austria: InTech; 2010. p127-

[3] Hannan M. A., Mohamed A. PSCAD/EMTDC Simulation of Unified Series-Shunt Compensator for Power Quality Improvement. IEEE Transaction on Power Delivery

[4] Han Y., Khan M.M., Yao G., Zhou L.D., Chen C. A novel harmonic-free power factor corrector based on T-type APF with adaptive linear neural network (ADALINE) control. Simulation Modeling Practice and Theory 2008; 16 (9) 1215–

[5] Khadkikar V., Chandra A. A Novel Structure for Three Phase Four Wire Distribution System Utilizing Unified Power Quality Conditioner (UPQC). IEEE Transactions on

[6] Kwan K. H., Chu Y.C., So P.L. Model-Based H∞ Control of a Unied Power Quality Conditioner. IEEE Transactions on Industrial Electronics 2009; 56 (7) 2493-2504. [7] 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] 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

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

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

[11] Jindal A.K., Ghosh A., Joshi A. Interline Unified Power Quality Conditioner. IEEE

Series Inverters. IEEE Transactions on Power Delivery 2008; 23 (4) 2522-2534.

**Figure 22.** Parallel active filter frequency spectrum


**Table 3.** Total Harmonic Distortion (THD)

#### **7. Conclusions**

It is known that use of small synchronous generators in distributed generated networks can reduce transmitted active and reactive powers from the main source and consequently line losses. In this research power quality compensation was done by composition of UPQC and synchronous generators as electromechanical active filter. In other word, by proper determination and control of synchronous generator field current it could be used as controlled current source for power quality compensation. This was for reduction of UPQC power rating in the distributed generated networks. Also, an algorithm was investigated for the determination of the reference field current. Proposed CCS modeling was implemented based on the mentioned related algorithm in MATLAB software. Control strategy had three instantaneously stages. Voltage harmonics were compensated by SAF of the UPQC. Current harmonics with higher order than 7 were compensated by PAF of the UPQC. Lower order current harmonics, load reactive power and a part of load active power were compensated by the proposed controlled current source. Total harmonic distortion of load voltage before compensation was 0.15 which was reduced to almost zero after compensation. Also, total harmonic distortion of the source current before compensation was 0.12 which was reduced to almost zero after compensation.

### **Author details**

92 An Update on Power Quality

**Figure 22.** Parallel active filter frequency spectrum

0.2 0.4 0.6 0.8 1 1.2 1.4

Amplitude (A)

**Table 3.** Total Harmonic Distortion (THD)

to almost zero after compensation.

**7. Conclusions** 

VS THD IL THD VL THD IS THD

<sup>0</sup> <sup>100</sup> <sup>200</sup> <sup>300</sup> <sup>400</sup> <sup>500</sup> <sup>600</sup> <sup>700</sup> <sup>800</sup> <sup>900</sup> <sup>1000</sup> <sup>1100</sup> <sup>1200</sup> <sup>1300</sup> <sup>1400</sup> <sup>0</sup>

Frequency (Hz)

0.1561 0.1179 .001 .0012

It is known that use of small synchronous generators in distributed generated networks can reduce transmitted active and reactive powers from the main source and consequently line losses. In this research power quality compensation was done by composition of UPQC and synchronous generators as electromechanical active filter. In other word, by proper determination and control of synchronous generator field current it could be used as controlled current source for power quality compensation. This was for reduction of UPQC power rating in the distributed generated networks. Also, an algorithm was investigated for the determination of the reference field current. Proposed CCS modeling was implemented based on the mentioned related algorithm in MATLAB software. Control strategy had three instantaneously stages. Voltage harmonics were compensated by SAF of the UPQC. Current harmonics with higher order than 7 were compensated by PAF of the UPQC. Lower order current harmonics, load reactive power and a part of load active power were compensated by the proposed controlled current source. Total harmonic distortion of load voltage before compensation was 0.15 which was reduced to almost zero after compensation. Also, total harmonic distortion of the source current before compensation was 0.12 which was reduced Ahad Mokhtarpour, Heidarali Shayanfar and Mitra Sarhangzadeh *Department of Electrical Engineering, Tabriz Branch, Islamic Azad University, Tabriz, Iran* 

#### **8. References**


[12] Mokhtarpour A., Shayanfar H.A., Tabatabaei N.M. Power Quality Compensation in two Independent Distribution Feeders. International Journal for Knowledge, Science and Technology 2009; 1 (1) 98-105.

**Chapter 6** 

© 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,

**Reference Generation** 

Ahad Mokhtarpour, Heidarali Shayanfar and Seiied Mohammad Taghi Bathaee

Additional information is available at the end of the chapter

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

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

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

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

http://dx.doi.org/10.5772/54680

quality problems of utility.

circuit for extraction of the reference signals.

**1. Introduction** 

themselves.

**of Custom Power Devices (CPs)** 

[13] Machowski J., Bialek J., Bumby J.R. Power System Dynamics and Stability, United Kingdom: John Wiley and Sons; 1997.

**Chapter 6** 
