Pn2-11 Filtro Activo Monofasico

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Single-Phase Active Power Filter Design

Using EMTP Simulation

Byung-Moon Han, Ji-Heon Lee, and Hye-Yeon Lee

Department of Electrical Engineering, Myongji University, San 38-2 Namdong, Cheoin-gu, Yongin-si, Gyeonggido,

449-728, Korea

Abstract

This paper describes a low cost single-phase active power filter for the digital load, such as computers, communication devices,and automation devices. The developed active power filter consists of a half-bridge IGBT inverter and a simple controller with

analog circuit to reduce the system cost. The operation of developed active power filter was verified through computer

simulations with EMTP. The feasibility of hardware implementation was confirmed building and testing a prototype. Thedeveloped active power filter can offer reduction of power loss and improvement of power quality.

Keywords: active power filter, half-bridge inverter, source voltage detection method

1. INTRODUCTION

Recently, many digital loads, such as computers, andcommunication devices, and automation devices come intowide use. These devices have a rectifier for AC-DC power conversion, which generates harmonic current and consumes

reactive power. The rectifier can be represented by anon-linear load when it is looked into from the source side.

A single-phase active power filter is very effective toremove the harmonics generated from the non-linear load[1,2].

Basically there are two methods to generate thecompensating current of active power filter, the sourcevoltage detection method and the load current detectionmethod [3]. The load current detection method generates thecompensating current directly from the measured loadcurrent. In the early days a notch filter or a band-pass filter was used to extract the reference signal from the load current.However, the phase delay of harmonic components brings

about the performance degradation of active power filter.The source voltage detection method generates the

compensating current indirectly to make the source currentsinusoidal and in phase with the source voltage [4,5]. The performance of PLL is very important to determine the performance of whole system. Also, the control stability is akey issue in the controller design [6].

In this research a low cost design of single-phase active power filter was investigated because many digital loadscome into wide use in office and even at home. So, costreduction is key point in design considering installation atoffice or home. In this system the active power filter was

designed using one dual IGBT for inverter and an analogcontroller with operational amplifiers. Also, source voltagedetection method is selected which requires one currentsensor and two voltage sensors.

This paper describes a single-phase active power filter withlow cost configuration using source voltage detectionmethod. The operation of proposed system was verifiedthrough computer simulations with EMTP software, inwhich the controller is modeled using TACS. The

performance of active power filter was confirmed by building and testing a prototype of 2kVA system.

2. SINGLE-PHASE ACTIVE FILTER

The digital loads, such as computers, communicationdevices, and automation devices include a rectifier toconvert the single-phase AC power to the DC power. Therectifier can be simply represented by the circuit shown inFigure 1.

Figure 1. Simplified circuit of rectifier for digital load

First page Template

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The International Conference on Electrical Engineering 2008

Panel Discussion 2: Power System Transients SimulationPart 3 Applications to power electronics and power systems



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The waveforms of DC voltage and AC current are shown inFigure 2. The DC filter capacitor is very effective to obtain aconstant voltage at the DC side. However, it makes the inputAC current distorted, in which many low order harmonicsare involved. Therefore, the rectifier shows a characteristic

of non-linear load.

The input AC current has frequency spectra shown in Figure3, using Fourier transform. The magnitude of 3 rd, 5th, 7th, and9

thharmonics is respectively about 68%, 28%, 9%, and 7%

to that of the fundamental component, which is very highcompared with the level of higher order harmonics. So, inorder to make the input AC current sinusoidal, these loworder harmonics should be effectively removed. In this paper it is assumed that the active power filter removes theharmonics of 3rd to 19th order.

Figure 4 shows the operational principle of active power

filter which makes the source current sinusoidal bysupplying a harmonic current to the non-linear load.

The input current through non-linear load can be expressed by equation (1).

1

( ) ( ) L nn

sin n t i t I Z T

f

¦ (1)

In order to make the source current sinusoidal, the harmoniccomponents with higher order than the fundamental

Figure 2. DC voltage, AC input current

Figure 3. Frequency characteristic of input AC current

component should be removed by injecting samecomponents from the active power filter.

GFigure 4. Principle of active power filter

3. PROPOSED ACTIVE POWER FILTER

Normally, single-phase active power filter has low power rating and it is installed at the place close to the load. So,

system reliability and low cost are key point in asingle-phase active power filter.

Figure 5 shows the configuration of a single-phase active power filter with a controller which uses a source voltagedetection method. The active power filter is designed as ahalf-bridge inverter using one dual IGBT. The controller hasone current sensor for measuring the source current and twovoltage sensors for measuring the source voltage and the DCvoltage of active power filter.

The source voltage is detected and sent to the unit sine wave

generator for building the phase angle of reference sourcecurrent. The DC voltage of active power filter is measuredand compared with the reference value. The error is sent to

the PI control for calculating the magnitude of referencesource current.The reference source current is compared with the measuredsource current to generate an error signal. The error signal is

Figure 5. Configuration of single-phase active power filter

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July 6-10, 2008, OKINAWA, JAPAN



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sent to the error amplifier for generating the referencevoltage of inverter. The reference voltage is compared withthe triangular carrier wave to generate the PWM gate pulsefor inverter.

4. COMPUTER SIMULATIONz

Many simulations have been carried out to verify the

operation and performance of proposed active power filter using EMTP software. Figure 6 shows a simulation modelfor the proposed active power filter and the non-linear load.The power circuit is modeled with voltage-controlledswitches and passive circuit elements. Major circuit parameters for the single-phase active power filter aredescribed in Table 1.

Table 1. Circuit parameters for simulation model

Parameter Values

Source voltage 110V, 60Hz

Non-linear Load C=6880ȝF, R=10, 35ȍ

DC capacitor C=2000ȝF

Filter reactor 5mH

Switching freq. 6120Hz

Figure 6 Power circuit for EMTP simulation

Figure 7 Controller configuration for EMTP simulation

Table 2. Parameters for simulation controller

Reference

Parameter Values

DC voltage 420V

Kp 70Ki 876

K1 1/120

K2 -25

Figure7 shows the configuration of proposed controller which is designed using TACS program. This controller hassame structure and operation sequence as described at thecontrol blocks shown in Figure 5. Major control parametersthe single-phase active power filter are described in Table 2.

Figure 8 shows the simulation results based on thedeveloped simulation model. Figure 8(a) shows the source

voltage, source current, and load current waveforms. Thesource current is very close to the sine wave because theactive power filter compensates the harmonics which are

generated in the load. Figure 8(b) shows the measured valueof compensating current which follows the reference valueaccurately. It is confirmed that the current control isoperated accurately. Figure 8(c) shows the source currentwhen the load changes from 10 to 35 ȍ. The active power filter starts to operate at 120ms. The load resistance ischanged at 250ms and returned at 380ms. Figure 8(d) showsthe variation of DC voltage. It is confirmed that the DCvoltage is maintained with constant value during loadchange.

(a) Source voltage VS, Source current IS, Load current IL

(b) Compensating current Ic




4

(c) Source current IS in load change

(d) DC voltage Vdc in load changeFigure 8 Simulation results

5. HARDWARE PROTOTYPE

A 2kVA hardware prototype shown in Figure 9 was builtand tested to confirm the simulation results and to verify the

feasibility of hardware implementation. The prototype isconnected with a mid point between the 110V power sourceand the diode rectifier with RC load. The switching elementused in inverter has a rating of 600V/50A dual IGBT and theswitching frequency is 8 KHz.

Figure 10 shows analog controller that was developed usingOP Amp and digital logic circuit. This circuit consists of asine generator, DC control, current control, triangular wave

generator, and dead-time generator. Sine generator is usedfor generating the reference value of source current, which is

in phase with the source voltage.

Figure 9 Prototype single-phase active power filter

The sine generator makes the inverter output current in

phase with the source voltage, which offers power factor correction without separate control of power factor. It cangenerate a unit sine wave without regard to the magnitude

change of source voltage.

DC voltage control is required to determine the magnitudeof source current. The DC voltage is normally measured bya commercial device AD210AN, which is rather expensive.In this research, a new DC voltage measuring circuit wasdeveloped to reduce the system cost. The developed circuitconsists of a cheap DC voltage sensor and a differentialamplifier using OP Amp.

The current control is to make the source current follows thereference value. So, it measures the source current using CT

(current transformer) and compares it with the reference

current obtained from the source voltage and the sinegenerator. The triangular waveform generator makes thecarrier wave for PWM pulse generation. It is designed usingSchmitt trigger circuit and Integration circuit. The switchingfrequency is determined by adjusting the value of resistance.

20

1

1( )

4

R f

RC R

(2)

The dead-time compensator is needed to remove the shortcircuit state during inverter switching operation, which isvery important in the voltage source inerter. In order togenerate the dead-time signal, a square wave is processed to

get RC time constant. In this experiment the dead time is set by 4ȝsec.

Figure 11 shows the experimental results using the prototypeactive power filter. Figure 11(a) shows measured value of source voltage, source current and load current. Asexplained in the simulation results, the waveform of sourcecurrent is close to sinusoidal by compensation of active power filter. Also, the phase of source current is almost in

Figure 10 Circuit diagram for analog controller




5

(a) Source voltage VS, source current IS, load current IL

(b) Compensating current IC

(c) Load current harmonic analysis

(d) Source current harmonic analysis

(e) Source current IS

Figure 11 Experimentation results with prototype

phase with the source voltage, which means that power factor is corrected. Figure 11(b) shows the waveform of compensating current, which is injected by the active power filter.

Figure 11(c) shows the expanded waveform of load currentand its harmonic analysis results. The load current has loworder harmonics which has rather high magnitude. Figure11(d) shows the expanded waveform of source current andits harmonic analysis results. It is confirmed that theharmonics generated by non-linear load can be removed bythe active power filter. Figure 11(e) shows the variation of source current during the load change from 35 to 10. It isconfirmed that the developed controller operates in stablemanner without regard to the load variation.

6. CONCLUSIONS

This paper proposes a low cost single-phase active power filter for digital load, such as computers, communicationdevices, and automation equipment used at office and home.The active power filter proposed in this paper was designedusing one dual IGBT for inverter and an analog controller with operational amplifiers.

The developed active power filter consists of a half-bridgeIGBT inverter and a simple controller with analog circuit toreduce the system cost. The operation of developed active power filter was verified through computer simulations with

EMTP. The feasibility of hardware implementation wasconfirmed building and testing a prototype.

The developed active power filter can offer reduction of power loss and improvement of power quality. It can beeasily produced using commercially available components.

REFERENCES

[1] H. Akagi, Y. Kanazawa and A. Nabae, "GeneralizedTheory of the Instantaneous Reactive Power inThree-Phase Circuits" Int. Conf. Power Electronics,

Tokyo, 1983, pp. 1375ൄ1386.

[2] L. Malesani, L. Rossetto, and P. Tenti, "Active Filter for reactive power and harmonics compensation", IEEE

Power Electron. Spec. Conf. Rec., pp. 321ൄ330, 1986.

[3] H. Jou, J. Wu, and H. Chu, "New single-phase active

power filter", IEE Proceeding Electric Power Application, vol. 141, no. 3, pp. 129-134, May 1994.

[4] C. Y. Hsu and H. Y. Wu, "A new single-phase active power filter with reduced energy storage", IEE Proc. onElectric Power Application, Vol. 143, No. 1, pp. 25-30,January 1996.

[5] J. C. Wu and H. L. Jou, "Simplified control method for the single-phase active power filter", IEE Proc. onElectric Power Application, Vol. 143, No. 3, pp.219-234, May 1996.

[6] F. Harashima, H. Inaba, and K. Tsubio, "A colsed-loopcontrol system for the reduction of reactive power




6

required by electronic converters", IEEE Trans.,

IECI-23, (2), pp. 162ൄ166, 1976.

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Pn2-11 Filtro Activo Monofasico