Performance Investigation of Active Power Line Conditioner using Simulink

International Journal of Emerging Technology and Advanced Engineering

91

Performance Investigation of Active Power Line Conditioner

using Simulink

Ankita Singh

_{, Sanjiv kumar}

1

_{Research Scholar,}

2

_{Asst. Professor}

,

Abstract— Active power conditioners have been developed over the years to solve the problems to improve power quality. Among which shunt active power conditioners is used to eliminate load current harmonics and reactive power compensation. The controller ensures that the dc-side capacitor voltage is nearly constant with small ripple besides extracting fundamental reference currents. The PLL block assists the active filter to function even under distorted voltage or current conditions. The shunt APLC system is implemented with voltage source inverter and is connected at PCC for compensating the reactive power. The shunt APLC system is modeled and investigated under unbalanced non-linear load conditions using MATLAB simulation. The simulation results reveal that the active power filter line conditioner is effectively compensating the reactive power and improves power factor at point of common coupling.

Keywords—Active power line conditioners (APLC), PWM inverter, PLL, PI, PID, Fuzzy logic controller and Hysteresis current controller (HCC).

I. INTRODUCTION

To cancel the compensate the reactive power APLC is the suitable solution. The APLC concept is to use an inverter to inject currents or voltages harmonic components to cancel the load harmonic components. The more usual configuration is a shunt APLC to inject current harmonics into the point of common coupling (PCC). The APLC can be installed in a low voltage power system to compensate one or more loads; thus, it avoids the propagation of current harmonics in the system. The developments of different control strategies give APLC to a new location. As APLC compensate the reactive power and cancel the harmonics, it is also called as active power line conditioners (APLC). The concept of shunt APLC was first introduced by Gyugyi and strycula in 1976 .

II. BASIC COMPENSATION PRINCIPLE

Figure 1 shows the basic compensation principle of a shunt active power filter.

It is controlled a compensating current ic from the utility, so that it cancels current harmonics on the Ac side, and makes the source current in phase with the source voltage[7,8].

Figure 1 Basic Compensation Principle

The load current waveform, the desired mains current and compensating current injected by the active filter containing all the harmonics, to make mains current sinusoidal [6]. From Figure.1, the instantaneous currents can be written as

Is(t) = il(t) - ic(t) ( 1) Source voltage is given by

Vs (t) = Vm sin wt (2) If a non-linear load is applied, then the load current will have a fundamental component and harmonic components which can be represented as

International Journal of Emerging Technology and Advanced Engineering

92 Pl(t) = Vs(t) * Il(t) (4)

Pl(t) =VmI1 sin2wt *cosΦ1+VmI1 sinwt*coswt* sinΦ1+ Vm sinwt*∑In sin (nwt+Φn)

Pl(t) = P f (t) + Pr (t) + Ph (t) (5) P f (t) =Vm I1 sin2wt*cosΦ1 =Vs (t) * is (t) (6)

From equation (6), the source current supplied by the source, after compensation is

Is (t) =Pf (t)/Vs (t) = I1 cosΦ1 sinwt=Im sinwt (7) Where Ism =I1 cosΦ1

There are also some switching losses in the PWM converter, and hence the utility must supply a small overhead for the capacitor leakage and converter switching losses in addition to the real power of the load. The total peak current supplied by the source is therefore [12] Isp =Ism + Is1 (8)

If the active filter provides the total reactive and harmonic power, then is(t) will be in phase with the utility voltage and purely sinusoidal. At this time, the active filter must provide the following compensation current:

Ic(t)=Il(t)-Is(t) (9) Hence, for accurate and instantaneous compensation of reactive and harmonic power it is necessary to estimate, i.e. the fundamental component of the load current as the reference current [12,13].

III. MODELING OF ACTIVE POWER LINE CONDITIONER The proposed shunt Active Power line conditioning diagram shown in figure-2.It has PWM voltage source inverter connected to a Dc capacitor reduction in current harmonics is achieved by injecting equal but opposite current harmonics at the PCC (point of common coupling).This process will cancel the original distortion and improving the power quality of the connected power system. The active filter is based on a PWM voltage source inverter is connected to the PCC through interface filter; the active filter is connected in parallel with the AC/DC converter. This inverter uses dc capacitor as supply and can switch at high frequency to generate the current that will cancel the harmonics from AC/DC converter. The current waveform for canceling harmonics is achieved by using VSI in the current controlled mode and the interface filter[12,13].

Figure 2. Simulink Model of Shunt APLC System with PWM VSI

The model of APLC system contained three subsystems, PLL based reference current generator, PI or PID or Fuzzy logic controller and Hysteresis current controller as shown in Simulation model in fig 3.

Figure 3 Simulink model of Active power line conditioning block

International Journal of Emerging Technology and Advanced Engineering

93 Figure 4 Simulink Model of PLL based Reference Current Generator

The PLL block tracks continuously the fundamental frequency of the system voltages (Vsc,Vsb,Vsa).The PLL based subsystem shown in Fig. 4 determines automatically the system frequency and the outputs of the PLL synchronizing block are Iar, Ibr and Icr the three phase currents.

B Modeling of PI, PID and Fuzzy Logic Controller

This subsystem contained PI or PID or Fuzzy logic controller which on the difference of Vref and Vdc .The PI controller estimates the magnitude of peak reference current Imax and control the dc-side capacitor voltage of voltage source inverter.

Figure 1 Simulink Model of PID controller

Figure 2 Simulink Model of Fuzzy Logic controller

C Modeling of Hysteresis Current Controller

This subsystem Hysteresis Current Controller has been developed for switching of converters by comparing the actual current to the reference current. In the case of positive input current, if the error current e(t) between the desired reference current iref(t) and the actual source current iactual(t) exceeds the upper hysteresis band limit (+h), the upper switch of the inverter arm is become OFF and the lower switch is become ON as shown in the Fig.7. Here the hysteresis band limit h=0.5. The range of the error signal e(t) directly controls the amount of ripple voltage in the output current from the PWM-VSI.

Figure 3 Simulink Model of Hysteresis Current Controller

IV. RESULT ANALYSIS

A. Performance of Proportional Integral controller based APLC system

The simulation of APLC system is done with PI controller. The three phase unbalanced RL load is connected in parallel with diode rectifier load to the three phase ac mains and active power filter is connected in parallel at the PCC for suppressing the harmonics and reactive power.

The Source voltage, source current and load current under unbalanced RL with non linear load without compensation block are shown in Fig 8 (a), (b) and (c) respectively.

Figure 8 Simulation results before compensation under unbalanced RL with non linear load (a) Source voltage (b) source current and

(c) load current

International Journal of Emerging Technology and Advanced Engineering

94 Figure 9 Simulation results after compensation under unbalanced RL

with non linear load (a) Source voltage (b) Dc capacitor side output voltage (c) Source current and (d) load current (e) Compensation

current and (f) Reference current

The dc side capacitance voltage (Vdc) and its settling time are controlled by PI-controller; this controller reduces the ripple and makes settling time less; this is plotted in Fig 9 (b) for non-linear with unbalanced load (t=0.055s).

Figure.10 Power factor after compensation under unbalanced RL with non linear load using PI controller

The power factor is improve after compensation over nonlinear and unbalanced load and reach to unity (0.9998) when simulation of APLC System is done with PI controller.

The active power and reactive power are calculated by averaging the voltage-current product at the fundamental frequency 50 Hz, shown in Figure 11.

Figure.11 Active Power and Reactive Power without Active Power Line Conditioner

Figure .12 Active Power and Reactive Power with Active Power Line Conditioner

B. Performance of Proportional Integral derivative controller based APLC system

International Journal of Emerging Technology and Advanced Engineering

95 Figure .13 Simulation results after compensation under

unbalanced RL with non linear load” (a) Source voltage, (b) Source

current, (c) load current, (d) Dc capacitor side outputvoltage, (e)

Compensation current and (f) Reference current

The dc side capacitance voltage (Vdc) and its settling time are controlled by PID-controller; this controller reduces the ripple and makes settling time less; this is plotted in Fig 13 (d) for non-linear with unbalanced load (t=0.053s)

Figure .14Power factor after compensation under unbalanced RL with non linear load

The power factor is improve after compensation over nonlinear and unbalanced load and reach to unity (0.9999) when simulation of APLC System is done with PI controller. The active power and reactive power of PID based APLC system are calculated by averaging the voltage-current product at the fundamental frequency 50 Hz, shown in Figure 15.

Figure. 15 Active Power and Reactive Power with Active Power Line Conditioner

C. Performance of Fuzzy Logic controller based APLC system

The Simulation results for Fuzzy logic controller based APLC system under unbalanced RL with non linear load with compensation are shown in Fig 16.

Figure.16 Simulation results after compensation under unbalanced RL with non linear load” (a) Source voltage, (b) Dc capacitor side

output voltage, (c) Source current, (d) load current, (e) Compensation current and (f) Reference current

International Journal of Emerging Technology and Advanced Engineering

96 Figure. 17 Power factor after compensation under unbalanced RL

with non linear load

The power factor is reach to unity when fuzzy logic controller is used in the place of PI and PID controller. This is the best power factor for APLC system.

Figure.18 Active Power and Reactive Power with Active Power Line Conditioner

The active power and reactive power of FLC based active power line Conditioning are calculated by averaging the voltage-current product at the fundamental frequency 50 Hz, shown in Figure 18.

D. Comparison of Performance of PI, PID And Fuzzy Logic Controllers

The settling time of the DC-side capacitor voltage of the inverter using PI, PID and fuzzy logic controller for non linear and unbalance load conditions; these are presented in Table 1.

Table 1 :Comparison of PI, PID and FLC for DC voltage settling time and power factor

Types of Controller

VDC settling time in seconds

Power Factor

PI 0.55 0.9998

PID 0.53 0.9999

FLC 0.50 1

The simulation is done for various non-linear unbalanced load conditions. PI, PID and fuzzy logic controller with PLL synchronizing control based compensator filter makes the source current balanced and sinusoidal after compensation. . The PI or PID or FLC ensures that the dc-side capacitor voltage is nearly constant with small ripple besides extracting fundamental reference currents. The performance of a PI, PID and fuzzy logic controlled APLC system is verified and compared under non-linear and unbalanced loads with various parameters that are presented graphically.

This simulation model of APLC system improves power factor on non-linear unbalanced load conditions.

Real power in watts (W) and reactive power in volt-amperes (VAR) are measured under non-linear with unbalanced load condition and are presented in table 2.

Table 2

Comparison of PI, PID and FLC for real Power and reactive Power

Compe nsation conditio

ns

Types of Controller

PI PID FLC

Without APLC P=14.68KW Q=0.85VAR P=14.68KW Q=0.85VAR P=14.68KW Q=0.85VAR With APLC

P = 34.50KW Q = 0.68VAR

P=34.80KW Q=0.45VAR

P= 19.1KW Q= 0.21VAR

The phase locked loop with Fuzzy logic controller based APLC system effectively compensates the reactive power and improves power factor.

V. CONCLUSIONS

International Journal of Emerging Technology and Advanced Engineering

97 APLC system is verified and compared under non-linear and unbalanced loads with various parameters that are presented graphically. This active power line conditioner system is tested and verified using MATLAB. The synchronous reference frame controller is used to extract the reference current from the distorted line current. This facilitates to improve the power quality parameters such as reactive power and power factor due to nonlinear load. The obtained results indicate that DC-capacitor voltage and the reactive power control can be adapted easily under non-linear load conditions.

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