Active filter operation providing unity power factor supply system for drives and battery charging

PW .EDU.PL GRZESIAK@NOV.ISEP.PW.EDU.PL ABSTRACT 'Ihe paper presents the concept of a parallel adive filter which can operate as a controlled dc source to supply an electric drive.. I

ACTIVE FILTER OPERATION PROVIDING

INSTITUTE OF CONTROL AND INDUSTRIAL ELECTRONICS

TEL +48/22/294992 FAX +48/2/6256633

RUKAT@NOV.ISEP.PW.EDU.PL

TEOFILAK@NOV ISEP PW EDU.PL

GRZESIAK@NOV.ISEP.PW.EDU.PL

ABSTRACT

'Ihe paper presents the concept of a parallel adive filter which can

operate as a controlled dc source to supply an electric drive Such a

system provides sinusoidal shape of input current and operates with

unity power fador Simulation studies and laboratory tests have been

canied out to study the perfonnauce of the filter m two cases In the

first case the filter compensates the non active power in the line

without any dc load connected to the filter and m the second case a

dc load is also linked to it The control diagram of the system is

proposed and tested

INTRODUCTION

A classical dc drive system supplied kom a three phase rectifier,

consisting of diodes (6D), operates with almost unity dqlacement

factor but produw lot of currat harmonics m the ac line Induction

motor drive system built with two series 11l controllable ac/dc and

ddac transiszor convder units 2 * (6T-6D) operates as bi-directional

system which transmits active and readive power with sinusoidal

input current [l], [2], [3] However such a system requires the input

convater trausistors to be loaded by active power co~lsumed by

motor drive and reactive power supplied to utility 'Ihere are Werat

systems with parallel active filters In [5] a hybrid classical resonance

and an active filter current controlled voltage converter is described

whereas in [6] a current controlled current source converter is used

l h e classical diode r e d i e r equipped with parallel compensator for

non active power saves rated power of transistors providing high

quality of input current and sufficient controllability of the input

power for unidirectional drive system In such a system the active

power is uncontrollable and is transmitted by the diode redifer The

produdion of reactive power and adive filter operations* provided by

low power parallel filter, permits the drive to operate with sinusoidal

input current and unity power factor ?he drive is equipped with

parallel filter of non active power The active filtex is designed for

operhon m two modes In the first case the filter is used to improve

the shape of the inpui total curcent and to improve power factor,

whereas m the second case it also supplies an eledric drive or a

battery charger In this mode the filtering abilities depend on power

requirements of this additional load Control idea of the adive filter

and simplified control diagram are presented m the paper

ELECTRIC DRIVE SYSTEM SUPPLLED BY TRANSISTOR

CONVERTER

A transistor convder (6T-6D) may be operated to provide sinusoidal

currat m the supply line, thus operating like au active filter Fig l a

presats a three phase eledric drive system with a controllable input

Converter

Figure la: Eledric drive system with transistor converter

The sydem consistS of an electric drive (an eledric motor supplied through an mvder - not indicated m the figure), dc link capacitance, the input converter and chokes with inductances Lt I h e input

convder transfers power required by the eledric drive Thus, the

input converter switches have to pass current corresponding to eledric drive inslantaneous current It means that power trausistor ratings are

to be calculated according to eledric drive power demand Power losses m converter consist of condudion losses, s w i t b g losses and

off-state losses Condudion losses depend on value of a currat

flowmg through the switches Switching losses become considerable with au maease of a switdhg hquency High s w i t b g kequacy

is required for this system to obtain sinusoidal shape of supply line

current with low contat of harmonics Another important parameter for currmt shaping is input choke mdudaace vdue It should be

designed to provide required currat derivative m the supply h e according to:

u.sin wf + L ~LU, - LL ~ - ~-u,sin(rct k-) = o (1) where ke = -1, +1, depending on configuration of on-state swltches

Figure l b Possible circuit structure while two transistors are swit&edon (ke=+l and%=l)

Fig.2 illustrates 811 example of Sinusoidal current wave obtained in

su& a system with +ase voltage

Figure 2: Supply line current a n d p h e voltage waves

CONCEPT OF AN ELECTRIC DRNE SYSIEM WKff

PARALLEL COMPENSATOR

diode r d e r as is &own m Fig 3 ?he re-ditier current il is not

sinusoidal and its haxmmic amtat is very hi&

=dl

Figure 3: Classical drive systan

me and contat of &er harmoazicS is also s i f l c m t Fig.4 presents

fresuency spedrum of a typical three phase r d e r currat il

16A

"

0.2kl-lz 0.4kI-k 0.6kHz O.8kHz 1.Okl-k

Figure 4: Contat of harmonics m r d e r currat it

An adive Mer cwnected m parallel may be implmented m order to improve the shape of the currrnt m the supply line (Fig.5) The dc

side capacitor keeps at the redifier output voltage with low ripple at

the level U 9 represents the r&er ac side @ut phase

induban= #e p a d e l adive mer is fed %om the same supply line thou& chokes with phase kdudauce 4 The w e n t the q l y

line & consists of two components: -

where: il represents a current supplied to Eledric Drive 1 and 4

represents the ament m the adive Mer AF

Fittez AF to the grid with dassical ratifier

The aciive tilter dc output voltage u d is greater then ua - load

voltage ua in a static state is equal to d3um, whereas u d is at least

switches So these two voltages are independent and can be adjusted

separately, adequately for drive and filter operation requirements 'Ihe

idea of the adive filter operation is to keep the total input current 4,

as sinusoidal with the required dwplacement fador cp 'Ihe Adive

Filter may also supply an Electric Drive 2 or battery charger

NON AC'ITVE POWER COMPENSATOR OPERATION

Tne electric drive 1 is supplied via rectifier Re (Fig.6) The reference

voltage U& is compared with actual voltage U&

Electric Drive 2

- - ' Battery or Charger

'da

Figure 6: Simplified block diagram for non adive power control

?he dif€erence voltage signal informs whether there was a rise or fall

of the actual voltage U 'Ihe voltage regulator RU converts the

diference voltage signpmto a reference amplitude otinput current

'Ihis amplitude is muhplied by a sinusoidal wave, d e n m

current m the supply line 4, is compared with the reference current

41 Additionally, there is a possibility to preset a reference phase angle

I$ m order to obtain the required displacement angle betwea phase

voltage and phase current m ac line ifthere is such a need

A singlsdup microcontroller SAB 800537 has been implemented to

control the Glter switches Mult~plication

syndxonisation and comparisons U& with U an%% 2::

done m an assembler program The voltage r e a a t o r RUd and current

regulator R j have been realised as digaal regulators Wcroprocessor

control enab es fprotedion of the filter switches

The parallel adive filter AF dc voltage is stabilised by voltage

controller When no load is conneded to its dc side adive power

absorbed by adive filter (for a given period) is zero for a constant dc

voltage Adive Filter can also supply other load (Eledric Drive 2 or

battery charger m Fig.5) That is why two cases can be discussed m its

compasator operation The first one is considered when no load is

connected to its dc side Fig 7a shows a current wave $-taken by the

Adive Filter, rectifier current il and total input current b The filter '

current added to the redifier current iP results in sinusoidal wave 3

table m microprocessor's memory At the end, the actual

input current

108

BA + .+ + +

10At + + +

Figure 7a: Rectifier current iP adive 6lter ament $- (negative) and supply line currat m case when no optional Electric Drive 2 is

working

Negledmg losses m t r d o r convder the Adive Filter does not

traasfer any adive power 'Ihus, to improve power fador m the supply line low rating convder may be used as Adive Filter In second case, Adive Filter supplies Electric Drive 2 Now it plays a role not only of

higher harmonics and displacement compmsator but also of a

supplier It transfers active power required by the Electric Drive 2 Hence, the Adive Filter should be rated to total volt-ampere power of

this load (Electric Drive 2, Battery Charger) In majority of cases Eledric Drive 2 is not MI loaded So the current taken by the Electric Drive 2 is below its nominal value 'Ihe saved power can be generated

to the supply line &om the Adive Filter to improve displacement

fador and power fador Fig 7b presents a situation when an Electric

Drive 2 is connected to Adive Filter

+ .* + +

0.4

-la4 1 , ;

2om

Figure 7b: Rectifier current '1 adive filter current $- (negative) and supply line current b with optional Electric Drive 2 supplied by Adive Filter AF

current il (Fig.7a) 'Ibis is a diEerence between the desired reference

sinusoidal mat aud the r&er current

E ~ p ~ ~ h ~ t a l tests have been carried out to venfy simulation results

Figures 8a, 8b and 8c pr-t respedvely: rectifier phase ament il, aaive filter current 'f and total input current & AU these currents are

shown with supply h e phase voltage ul

221

I

_

I

! _ r : t : - - 1 : - .;,:., , , , < -:- c .-.!.l

I C

Figure Sa: Redifier phase ament il and utility phase voltage u1

l h e re&fier ament il is lagging the voltage wave u1 and the amount

improve the shape of input total ament & (Fig &)

Figure &: Total input phase ament & taka &om the supply line

with phase voltage ul

CONCLUSIONS

I h e papa presents the omazpt of the parallel active filter of non

active power ?his filter is specially designed for drive applications

with classical amveater syjian (ad&) with diode bridge redifier as

an input of an eledric drive ?he total iaput -t is Smusoidal and

system operates with unity power fador The case of unity power fador operation can be provided with low volt-ampere power of the adive filter The control diagram of the Systan is proposed and tested

?his filter cpexates atso as reactive leading and lagging power source

However, au maease of readive power c a w muease of volt- ampere power ofthe adive filter

~

Figure 8b: Adive filter ament +with phase voltage ul

[I] F.Blaabjer& JKPedersen 'An Integrated High Power Fador

one h4ic"txolla' 0-7803-1243-0/93%03.0001.Pages 285-

293

[2] RD Veas, J.W.Dixon, B.0oi 'A Novel Load Current Method for

a Leading Power Fador Voltage Source PWM Reciitier' IEEE

Tnmsadions on Power Eledronics, Vol 9, N0.2 hkr& 1994.Pages:

153-159

[3] G.Blajsznak, ' S p a vedor control of a uni6ed compasator for

non adive power', IEE F'roc-Hec Power Appl Vo1.141, No.4, July

1994 Pages 207-21 1

[4] W.Konara, '"pas& 'm m Demand for Drive Powez' Prw 6th

coaference on Power Eledronics and Mdion Control, PEMC90 VoL2 Budapest, October 1-3,1990, HungW Pages: 354-358

[5] N.BaIbo, D.Sella, R.Penzo, G.Bisia&, D.Cappelini, L.MaleSani,

AZucatto, 'Hybrid Active F a e r For Parallel Hmonic C-d

Roc 5th European Ccmfere~ce on Power Electronics and

AC-DC-AC Cc~lveatm for AC-ma&e~ Implemented

P q e ~ : 133-138

[q S.Fukuda, Tfidoch, 'Control Method aud Charaderistics of

Adive Power Fitteas", Proc of 5th European Conference on Power

EledronicS and Applications, EPE93 VOLS 13-16 Septanber, 1993

[7] P.Bia€oskksIi, W.Konara, W yPower Fador phase

1993, Seattle, USA

222