Reduction of Input Current Harmonics based onSpace Vector Modulation for Three-phase VSI
with varied Power Factor
Koroku Nishizawa, Jun-ichi Itoh

Akihiro Odaka, Akio Toba, Hidetoshi Umida

Nagaoka University of Technology
Department of Electrical, Electronics and Information
Nagaoka, Niigata, Japan
koroku_nishizawa@stn.nagaokaut.ac.jp,
itoh@vos.nagaokaut.ac.jp

Fuji Electric Co., Ltd.
Tokyo, Japanodaka-akihiro@fujielectric.com,
toba-akio@fujielectric.com,
umida-hidetoshi@fujielectric.com

Abstract—This paper proposes space vector modulation(SVM) which reduces the current harmonics flowing through theDC-link capacitor of three-phase motor drive systems. In a
conventional SVM, the selection of the space vectors results in thelong zero vector period, which increases the inverter input current
harmonics. On the other hand, in the proposed SVM, the space
vectors are selected in order to actively shorten the zero vector
period. Furthermore, by applying the proposed SVM only in theregions where the instantaneous value of the input current is
positive, the input current harmonics are reduced even when theload power factor becomes low. Through the experiment applying
the proposed SVM, it is confirmed that input current harmonics is
reduced by up to 33.9% of that of the conventional method.
Moreover, it is confirmed that the input current harmonics withthe proposed SVM are reduced in all range of the load power
factor compared to that of the conventional SVM.

the modulation methods to reduce the input current harmonics
of the three-phase VSI have also been proposed [8-9]. The input
current harmonics are reduced by minimizing the applied timeof the zero vector as much as possible in each switching period.
However, the input current harmonics cannot be reduced bythese modulation methods when the power factor is low because
the current in the DC-link capacitor is drastically increased byapplying these modulation methods when the power factor islower than 0.866 [9]. Thus, these modulation methods cannot beapplied to the motor drive system, the power factor variation ofwhich is considerably wide.

Keywords—DC link capacitor; input current harmonics; space
vector modulation; two-level, VSI

I. INTRODUCTION
Three-phase AC motors are widely utilized in the industrial
and household applications [1-5]. In recent years, the researches-aiming for long lifetime of the three-phase inverter in the motor
drive system have been actively conducted [6]. The smoothing
capacitor connected to the DC-link of the inverter is required tohave a large capacitance in order to smooth the DC-link voltage.
Generally, an electrolytic capacitor is used as the smoothing
capacitor which absorbs the high harmonics of the DC-linkcurrent. The electrolyte of the electrolytic capacitor deteriorates
by these harmonic components flowing into the electrolytic
capacitor. As a result, the lifetime of the electrolytic capacitor
decreases due to these high harmonics of the DC-link current,
i.e. the input current of the three-phase voltage source inverter(VSI).
In order to extend the lifetime of the smoothing capacitor,
the method to use film capacitors as the smoothing capacitor has
been proposed [7]. However, the motor drive system becomesbulky because the energy density of the film capacitor is muchsmaller than that of the electrolytic capacitor. On the other hand,This paper proposes a new space vector modulation (SVM)
which reduces the input current harmonics of the three-phase
VSI over all range of the power factor. The proposed SVM
achieves the reduction of the input current harmonics byselecting space vectors with the consideration that the zero
vector period is minimized. This paper is organized as follows,
first, the reduction of the input current harmonics by minimizing
the zero vector period is explained, then, the mechanism of the
proposed SVM for the variation of the power factor is proposed.
Finally, the effectiveness of the proposed SVM is confirmed bysimulation and experiment at the time of driving mode withinduction motor.
II. CONVENTIONAL AND PROPOSED SVM
A. Conventional SVM
Fig. 1 shows a three-phase VSI. This inverter consists ofthree half bridges. Switching state of each half bridge isexpressed as following switching functions.

1, (Sxp : ON, Sxn: : OFF)sx  
, ( x  u, v, w) 
0, (Sxp : OFF, Sxn: : ON)

Output currents of inverter at steady state are expressed as iu  I m cos    

 



 iv  I m cos    
3 


 


iw  I m cos     3 

iDC.in
Sup



iu
iv vuv
iw vvw

+
Cdc

Edc

Svn

Sun

where, Im is the maximum value of output current, θ is phaseangle and φ is load power factor angle, respectively.
Fig. 2 shows the definitions of the conventional SVM. Fig.
2(a) and 2(b) are the space vectors of the inverter in  plane
and the sector definition of the conventional SVM, respectively.
In particular, there are eight fundamental vectors (six active
vectors and two zero vectors) and each fundamental vector canbe expressed by using switching functions as V(su sv sw). The plane area where three-phase VSI can output is divided into six
sectors (sector 1 ~ 6) in every 60 degrees of the voltage reference
vector’s phase angle. The voltage reference vector can be
expressed with modulation index (m) and phase angle as below.

Swp

Svp

Fig. 1.

V*  m 

SwnThree-phase VSI with motor load.
V2 (1 1 0)

V3 (0 1 0)

SectorV*②③
V4 (0 1 1)

Sector ①

V7 (1 1 1)

V0 (0 0 0) V (1 0 0)
1
⑥

④



The voltage reference vector sampled in each control period(Ts) is generated by synthesizing three time-averaged
fundamental vectors Va, Vb, Vc as following equations.

V5 (0 0 1)

Fig. 2.

t0Ts60° <  ≤ 120°③120° <  ≤ 180°④

180° <  ≤ 240°⑤240° <  ≤ 300°⑥

300° <  ≤ 360°(b) Sector definition.

V0 

t1
t
V1  2 V2
Ts
Ts

t2
V2
Ts

Ts  ta  tb  tc

iDC.in-iw
iu

iDC.iniv

V2 (1 1 0)



V*

iu+iv

0

Ts

where, ta, tb, tc are on duty of each selected fundamental vectors
and a, b, c mean the number of selected fundamental vector.

B. Evaluation for Input Current Harmonics
An Instantaneous value of the inverter input current can becalculated from switching functions and output current asfollowing [11].

0° <  ≤ 60°②

Definitions of conventional SVM.



Fig. 3 shows the conventional SVM. Fig. 3(a) and 3(b) are
the conventional generation of the voltage reference vector andthe input current waveform with the conventional SVM,
respectively. In the conventional SVM, the voltage reference
vector (V*) is generated by using two adjacent active vectors, i.e.
V1 and V2 as shown in Fig. 3(a), and one zero vector (V0) at eachcontrol period when the voltage reference vector is in the sector
1 [10]. In other words, three fundamental vectors which are theclosest to the voltage reference vector (V*) are used in order togenerate the voltage reference vector in the conventional SVM.
Consequently, the applied time of the zero vector (t0 or t7)
becomes maximum. During the zero vector period, the input
current of the inverter becomes zero, which results in the highstep change of the input current waveform. This leads to theincrease in the input current harmonics. Therefore, in order toreduce the input current harmonics, the period of the zero vector
is required to be minimized.

Phase angle①

V6 (1 0 1)(a) Space vectors in  plane.

V* 

t
t
t
V *  a Va  b Vb  c Vc
Ts
Ts
Ts 

IM

MVK8115A-R
Pn = 3.7 [kW]Nn = 1500 [rpm]Vn = 188 [Vrms]
In = 18 [Arms]
Poles = 4

⑤



vwu



V0 (0 0 0)

t0
Ts

t1
V1 (1 0 0)
V1
Ts
Ts : Switching period
tx : Applying time of Vx



iw

V0

V0 V1

V2

V1 V0

(a) Generation of voltage reference vector. (b) Waveform of input current.
Fig. 3.

Conventional SVM.

iDC .in   c x  ix  x u , v , w

Since the input side of three-phase VSI operates at six-foldfundamental frequency, calculating the rms value of the inverter
input current over a sixth of the fundamental period.



iDC .in.RMS 

3





tk

 
i
  
T
30k a ,b ,cs

2
DC .in,k


d 





where, tk is the on duty of selected fundamental vector and iDC.in,kis the instantaneous value of the inverter input current whenselected fundamental vector is applied.

Then, the average value of the inverter input current over asixth of the fundamental period can be calculated as following.

V* 



iDC .in 




3


3
0



tk

 
i
  Tk  a ,b , c

DC .in, ks3m  I m cos 
4


d

 

V3 (0 1 0)







1 Ts 2iDC .in dt
Ts 0



t 2
  k iDC
.in, kTk  a ,b , c s

0

Ts




V1 (1 0 0)

iw
V1

V2

V3

V2

V1

(a) Generation of voltage reference vector. (b) Waveform of input current.
Fig. 4.
Optimized vector pattern for a minimum minimum rms value of
inverter input current when iu and iv are positive and iw is negativein the case of high modulation index.

From (6), it is understood that the rms value of the inverter input
current changes according to the choice of fundamental vectors.
On the other hand, from (7), it is understood that the averagevalue of the inverter input current dose not depend on the choiceof fundamental vectors, but the modulation index and the load
power factor. In other words, the average value of the inverter
input current is constant regardless of the choice of fundamental
vectors. Therefore, by selecting fundamental vectors in order tominimize the rms value of the inverter input current, the rms
value of the smoothing capacitor current is also minimized. To
analyze the optimized vector patterns for a minimum rms valueof the inverter input current, the rms value of the inverter input
current over a control period, derived from (6), is used for the
analysis [12].

iu

iDC.in
iv

V*

t1
V1
Ts

2
2
iC.RMS  iDC.in. RMS  iDC .in 

iDC .in.RMS Ts  

t3
V3
Ts

iDC.in-iwiu

V2 (1 1 0)
t2
V2
Ts

The rms value of the current flowing into the smoothing
capacitor can be calculated by using (6) and (7) as following.


t
t1
t
V1  2 V2  3 V3
Ts
Ts
Ts







Note that the smaller the difference between the instantaneous
value and average value of input current (shown by the coloredarea in Fig. 3(b)) is, the smaller the value of (9) becomes.
Additionally, the value of (9) is independent from the switching
period. Therefore, the rms value of the inverter input current is
independent from the switching frequency.
C. Reduction Method for Input Current Harmonics
Fig. 4 shows an optimized vector pattern for the minimum
rms value of the inverter input current when iu and iv are positiveand iw is negative in the case of the high modulation index. As
shown in Fig. 4(a), three consecutive active vectors (V1, V2 andV3) are used to generate the voltage reference vector, which
results in the elimination of the zero vector [8]. Note that, theelimination of the zero vector is achieved only when the tip ofvoltage reference vector belongs to the triangle formed by thetips of three consecutive fundamental vectors (V1, V2 and V3) asshown by the colored area in Fig. 4(a), i.e. in the case of highmodulation index. Besides, the area that can be output by using
three consecutive fundamental vectors is same as the

V* 



t0
Ts

V0 

t
t1
V1  3 V3Ts
Ts

iDC.iniu
iDC.iniv

V3 (0 1 0)

iu

0

t3
V3
Ts

Ts

V*

V0 (0 0 0)
t0

Ts


V0

t1
V1
Ts


V1 (1 0 0)

iw
V0

V3

V1

V3

V0

(a) Generation of voltage reference vector. (b) Waveform of input current.
Fig. 5.
Optimized vector pattern for a minimum minimum rms value of
inverter input current when iu and iv are positive and iw is negativein the case of low modulation index.

conventional SVM. Thus, the optimized vector patterns for theminimum rms value of the inverter input current allows to obtainthe same output voltage limits as the conventional SVM. Fig.
4(b) shows the waveform of the input current with the optimized
vector pattern when iu and iv are positive and iw is negative in thecase of the high modulation index. The difference between the
instantaneous value and average value of the input current asshown by the colored area in Fig. 4(b) is smaller than that in Fig.
3(b). Thus, the input current harmonics are reduced at most withthis optimized selection of the fundamental vectors [13].
Fig. 5 shows the optimized vector pattern for the minimum
rms value of the inverter input current when iu and iv are positiveand iw is negative in the case of the low modulation index. As
shown in Fig. 5(a), one active vector (V1), one non-adjacentactive vector (V3) and one zero vector (V0) are used in order togenerate the voltage reference vector in the proposed SVM [9].
When the tip of voltage reference vector belongs to the triangle
formed by the tips of these three fundamental vectors (V1, V3
and V0), i.e. the case of the low modulation index, theelimination of the zero vector cannot be achieved. However, theperiod of the zero vector can be reduced by selecting a nonadjacent active vector (V3) instead of the adjacent active vector(V2). Consequently, the difference between the instantaneous
value and average value of input current as shown by the coloredarea in Fig. 5(b) becomes small. This reduces the input current
harmonics compared with that of the conventional SVM evenwhen modulation index is low.

D. Approach to deal with variation of Load Power Factor
As discussed in the previous section, the fundamental
vectors are selected so that the zero vector periods are minimized
for reducing the rms value of the inverter input current. However,when the power factor becomes low, the minimization of thezero vector period no longer reduces the input current harmonics.
Table 1 shows sector definitions of the proposed SVM. The
sectors of the proposed SVM (A ~ F) are determined by the
combination of the inverter three-phase output current’s
polarities, i.e. iu, iv and iw. When load power factor changes andthe magnitude relations of the output currents also changes, it isnecessary to select the fundamental vectors so that the zero
vector periods are minimized according to these changes. The
vector patterns in Fig. 4 and Fig. 5 are effective to minimize therms value of the inverter input current only when iu and iv are
positive and iw is negative, i.e. at sector B. Thus, by determining
the sector from the magnitude relations of the output currents as
Table 1, the vector patterns whose the rms value of the theinverter input current is minimum at that moment can be appliedcorresponding to the load power factor change without detecting
the load power factor (cosφ). In particular, the sector of the
proposed SVM is shifted corresponding to the phase angle of theoutput currents.
Table 2 shows the switching table of modulation method.
When the power factor is lower than 0.866, i.e. the power factor
angle (φ) is larger than 30 degrees, the areas which cannot be
modulated by the optimized vector patterns occur. Therefore, theconventional SVM is selected in these periods. In order to solve
this problem, first, these periods where the optimized vector
patterns cannot be applied are determined by the sector
information of the conventional and proposed SVM, then theconventional SVM is applied in these periods.
Fig. 6 shows the waveforms of the output voltage references,
the output currents and the input current with the proposed SVM(Left hand) and space vector map of proposed SVM (Righthand) at different load power factors. Fig. 6(a) and 6(b) shows
the cases of φ = 0° and φ = 60°, respectively. The sectors ofproposed SVM (A ~ F) are determined from the combination ofpolarities of the output currents based on Table 1. In the case ofunity power factor, it is found that the optimized vector patterns
are effective to minimize the rms value of the inverter input
current at all times from Table 2. Thus, the optimized vector
patterns is applied at all times in the case of unity power factor.
In the case of low power factor (cos φ = 0.5), there are areas
which cannot be modulated by the optimized vector patterns
expressed as shaded area in right hand of Fig. 6(b). Hence, theconventional SVM is applied in these areas and the optimized
vector pattern is applied in other areas in the case of the low
power factor.
Table 3 shows the selected vectors at each sector in theconventional SVM and optimized vector patterns for theminimum rms value of the inverter input current. Note that thezero vector (V0 or V7) is selected with the consideration that the
number of switching at each switching period is minimized.

TABLE I.

SECTOR DEFINITION OF PROPOSED SVM
Current polarity

Sector

iu
iv
iw
P
N
N
P
P
N
N
P
N
N
P
P
N
N
P
P
N
P
P : Positive,
N : Negative

A
B
C
D
E
F

TABLE II.

SWITCHING TABLE OF MODULATION METHOD
Sector of proposed SVM

①
②
③
④
⑤
⑥

Sectorofconventional
SVM

Sector
[-]
1.154

A

B C

vu*

vv*

D

E

A
B
C
D
E
F
O
O
C
O
O
C
C
O
O
C
O
O
O
C
O
O
C
O
O
O
C
O
O
C
C
O
O
C
O
O
O
C
O
O
C
O
O : Optimized vector pattern
C : Conventional SVM

F

Optimized
vector pattern



vw*

V3

V2
C

B

-1.154[p.u.]
1.0

iu

iv

②

iw

V4

0

③

D

④

-1.0
[p.u.]
1.0

1 [p.u.] = 10 [A]iDC.in

⑥

F
V6

V5

0
0.00

0.01

A

⑤

E

0.5

V1 

①

0

[s]

0.02

(a) φ = 0° (cosφ = 1.0).
Sector
[-]
1.154

A
vu*

B C

D

vv*

vw*

E

F

 vector pattern

V30-1.154[p.u.]
1.00-1.0[p.u.] iDC.in
1.0
0.5
0
-0.5
0.00

Optimized

Conventional SVM

V2
A

B
iu

iv

②

iw

V4
1 [p.u.] = 10 [A]

③

C

D

0.02

V1 

①

④ 0

V5
0.01



F

⑥
⑤

E
V6

[s]

(b) φ = 60° (cosφ = 0.5).
Fig. 6.
Waveforms of output voltage references and output currents andinput current with proposed SVM (Left hand),space vector map of proposed SVM (Right hand).

III. SIMULATION AND EXPERIMENTAL RESULTS
Table 4 shows the simulation and experimental conditions.
In the experiment, a three-phase induction motor (MVK8115AR, Fuji Electric Co., Ltd.), the rated power of which is 3.7 kW isused as the test motor, whereas the load power factor is varied
from 0.258 to 0.866 by controlling the torque reference of theload motor (GRK2371A, Fuji Electric Co., Ltd.). In this paper,
the input current harmonics of three-phase VSI are evaluated as
IDC.in(p.u.) expressed asI DC .in( p.u.) 

I DC .in( RMS )
Im

1

Im

Conventional SVM

2

 1


iDC .in,n  2
n 1 m

TABLE III.
SELECTED VECTORS AT EACH SECTOR IN
CONVENTIONAL SVM AND OPTIMIZED VECTOR PATTERNSFOR MINIMUM RMS VALUE OF INVERTER INPUT CURRENT



Selected vectors
High mod.
Low mod.
index
index

①

V1, V2, V0

A

V6, V1, V2

V6, V2, V7②

V2, V3, V7

B

V1, V2, V3

V1, V3, V0③

V3, V4, V0C

V2, V3, V4

V2, V4, V7④

V4, V5, V7

D

V3, V4, V5

V3, V5, V0⑤

V5, V6, V0

E

V4, V5, V6

V4, V6, V7⑥

V6, V1, V7

F

V5, V6, V1

V5, V1, V0

SIMULATION AND EXPERIMENTAL CONDITIONSParameters
DC link voltage
Maximum output
current
Switching frequency
Modulation index
Load power factor
Input current harmonics iDC.in(p.u.) [p.u.]

Fig. 8 shows the waveforms of the driving test for the threephase induction motor with each SVM at the power factor of
0.866, i.e. the load power factor is high, and the modulationindex of 0.7. Fig. 8(a) and 8(b) are the waveforms with theconventional SVM and proposed SVM, respectively. When theload power factor is high, the applying ratio of the optimized
vector patterns is also high. In particular, the optimized vector
patterns are applied at all time at the load power factor of 0.866.
It is confirmed from Fig. 8 that the width of the step change in
the input current is reduced by applying the optimized vector
patterns.

Sectorvectors

TABLE IV.

SymbolEdc

Simulation
200 V

Experiment
200 V

Im

10.0 A

5.5 ~ 12.5 A

fsw
m
cos φ

10 kHz0 ~ 1.15
0.0 ~ 1.0

10 kHz0.256 ~ 1.15
0.259 ~ 0.866

0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00

φ＝90
(cosφ = 0)
φ＝75
φ＝60
φ＝45
φ＝30
φ＝15

0

0.2

0.4

0.6

0.8

1

1.2

φ＝0
(cosφ = 1)

Modulation index m [-](a) Conventional SVM.
Input current harmonics iDC.in(p.u.) [p.u.]

Fig. 7 shows the simulation results of the analysis of the
input current harmonics with the conventional and proposed
SVM. When the conventional SVM is applied, the maximum
value of IDC.in(p.u.) is 0.450 p.u. at the unity power factor and themodulation index of 0.6. By applying the optimized vector
patterns, the maximum value of IDC.in(p.u.) at this point is reduced
by 0.313 p.u.. Furthermore, it is confirmed that compared to theconventional SVM, the input current harmonics are reduced inany case of the modulation index and the power factor. Besides,
the higher the load power factor is, the greater the reduction
effect of the input current harmonics is obtained. This is because
the applying ratio of the optimized vector patterns becomes
higher as the load power factor becomes higher.

Selected

Sectorwhere, IDC.in(RMS) is the RMS value of the input current
harmonics, Im is the maximum value of the output current, n isharmonic order and iDC.in,n is n-order component of the input
current harmonics. The fundamental component of the input
current harmonics is 75 Hz at rated load. Harmonic componentsof the input current up to 20-order of the switching frequency(up to m-order component of the input current harmonics) areconsidered in this calculation.

Optimized vector patterns

0.50
0.45

φ＝90
(cosφ = 0)
φ＝75

0.40

Fig. 9 shows the frequency analysis measurement results ofinverter input current with each SVM at the load power factor of
0.866 and the modulation index of 0.7 (under the same
conditions as Fig. 8). Fig. 9(a) and 9(b) are the results with theconventional SVM and proposed SVM, respectively. 100% of
vertical axis implies the maximum value of output current Im.
When the conventional SVM is applied, the inverter input
current includes large switching frequency-order harmonic, thevalue of which is 31.0%. By applying the optimized vector
patterns for the minimum rms value of the inverter input current,
the switching frequency-order harmonic is reduced by 6.60%.

Fig. 7.

Fig. 10 shows the simulation and experimental results of theanalysis of the input current harmonics with the conventional
and proposed SVM. At the power factor of 0.866, i.e. when theload power factor is high, the value of IDC.in(p.u.) with theconventional SVM is reduced by 33.9% at most by applying the
proposed SVM. Besides, at the power factor of 0.259, i.e. when

the load power factor is low, the value of IDC.in(p.u.) with theconventional SVM is reduced by 6.19% at most by applying the
proposed SVM. It is confirmed that as the load power factor
becomes smaller, the input current harmonics-reduction effectdiminishes from this results. Furthermore, the experimental

0.35
0.30

φ＝60

0.25

φ＝45

0.20

φ＝30

0.15
0.10

φ＝15

0.05

φ＝0
(cosφ = 1)

0.00
0

0.2

0.4
0.6
0.8
Modulation index m [-]1

1.2(b) Proposed SVM.
Simulation results of input current harmonics.

Sector
①

③

②

④

⑤

⑥

Sector
Sectorvuv[200V/div.]

0

B

A
0

0

C

D

vuv[200V/div.]0iDC.in[10A/div.]

iDC.in[10A/div.]00iu[20A/div.]0iu[20A/div.]

0[5 ms/div.][5 ms/div.](a) Conventional SVM.
Fig. 8.

F

E(b) Proposed SVM.

Experimental waveforms at cosφ = 0.866, m = 0.7 : Sector, output line voltage, input current and U-phase output current.
100
IDC.in(p.u.) = 0.432 [p.u.]

100

31.0 %

IDC.in(p.u.) = 0.286 [p.u.]

6.60 %

10
Input current [%]Input current [%]

10
1
0.1

0.01
0.001
10

100

1000
10000
Frequency [Hz]

1
0.1

0.01

0.001
10

100000100(a) Conventional SVM.

1000
10000
Frequency [Hz]100000(b) Proposed SVM.

Fig. 9.
Frequency analysis measurement results of inverter input current at cosφ = 0.866, m = 0.7 (under the same conditions as Fig. 8).
Fundamental frequency is 45 Hz.

IDC.in(p.u.) [p.u.]

0.40

0.30

0.50

cos φ = 0.866(φ = 30 deg.)Lines : Sim. results
Plots : Exp. results

0.40

IDC.in(p.u.) [p.u.]

0.50

cos φ = 0.259(φ = 75 deg.)

0.20

cos φ = 0.707(φ = 45 deg.)

0.10

cos φ = 0.866(φ = 30 deg.)

0.30
0.20

cos φ = 0.259(φ = 75 deg.)cos φ = 0.707(φ = 45 deg.)

0.10
0.00

0.00
0.0

0.2

0.4
0.6
0.8
Modulation index m [-]

1.0

0.0

1.2

(a) Conventional SVM.
Fig. 10.

Lines : Sim. results
Plots : Exp. results

0.2

0.4
0.6
0.8
Modulation index m [-]

1.0

1.2

(b) Proposed SVM.

Simulation and experimental results of input current harmonics.

results of IDC.in(p.u.) almost agree with the simulation results.
These results confirm that the proposed SVM can reduce theinverter input current harmonics at any load power factor byboth simulation and experiments.
Fig. 11 shows the total harmonic distortion (THD) of the Uphase output line current at the load power factor of 0.866. THDof the output line current is calculated as i  
40



THD 

n2

2
n



i1

where, in is n-order component of the output line current
harmonics. In this case, the rated fundamental component of theIV. CONCLUSION
In this paper, the new SVM to reduce the input current
harmonics of the three-phase VSI in case that the power factor
varies was proposed. This method contributed to the long
lifetime of the smoothing capacitor in the motor drive system.
The inverter input current harmonics was reduced by optimizing
vector patterns in order to minimize the rms value of the inverter
input current. In particular, three consecutive active vectors wereselected in the case of the high modulation index, whereas two
non-adjacent active vectors and one zero vector were selected in
the case of the low modulation index. These optimized vector
patterns were effective to reduce the rms value of the inverter
input current under certain conditions of the output line currents.
By determining sectors of the proposed SVM from three-phase
output line currents magnitude relations, the input current
harmonics are reduced over wide range of the load power factor.
The effectiveness of the proposed SVM was confirmed byboth simulations and experiments with the motor. The
experimental results confirmed that the input current harmonics
was reduced by 33.9% by applying the proposed SVM.
Moreover, it was also confirmed that the input current harmonics
was reduced over all range of the power factor. On the other
hand, THD of output line current deteriorated by applying the
proposed SVM. However, the increase of the output line current
THD with the proposed SVM can be suppressed by increasing
the switching frequency because the increase in the switchingfrequnecy have no influences on the inverter input current
harmonics.
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10
THD of iu [%]output line current harmonics i1 is 75 Hz. At all modulationindex, the THD of the U-phase output line current increases byapplying the proposed SVM. In particular, THD of the output
line current increases in two times at the maximum by applying
the proposed SVM. In the conventional SVM, three fundamental
vectors, the tips of which are the closest to the tip of the voltage
reference vector, are selected to modulate. Thus, theconventional SVM is the modulation scheme which achieves theminimum output harmonic [14]. In the proposed SVM, thereduction of the input current harmonics is achieved by actively
selecting the fundamental vectors which is located far from thevoltage reference vector in order to minimize the zero vector
period. Furthermore, the line current ripple in the inverter-fed
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current harmonics because the rms value of inverter input
curretn is independent from the switching period.

cos φ = 0.866(φ = 30 deg.)

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Proposed SVM

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Conventional SVM

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Modulation index m [-]Fig. 11. Total harmonic distortion of output line current with each SVM
at power factor of 0.866.

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