Experimental Verification of Conduction Noise ofThree-level V-connection Rectifier-Inverter System
Jun-ichi Itoh, Huynh Dang Minh, Daisuke Sato
Department of Electrical, Electronics and Information Engineering
Nagaoka University of Technology
Nagaoka, Japan
itoh@vos.nagaokaut.ac.jp
Abstract— This paper discusses the conduction noise
reduction possibility of a transformer-less three-level Vconnection rectifier-inverter system. This circuit is used for themain circuit in an Uninterruptible Power Supply (UPS) system.
The efficiency of this circuit is higher than that of theconventional three-phase rectifier-inverter circuit due to no
isolated transformer in output side. In this paper, to verify the
conduction noise of the V-connection system, a theoreticalanalysis about the common-mode currents which based on thecommon-mode equivalent circuit, is discussed. Based on this, thecomparison of the conduction noise between the three-level Vconnection Back To Back (BTB) system and the conventional
three-level three-phase connection BTB system is assumed. In
addition, the conduction noise of two systems are measured andcompared in order to confirm the assumption. As a result, it isconfirmed that the conduction noise which is generated from thethree-level V-connection rectifier-inverter circuit is higher thanthat of the conventional three-phase rectifier-inverter circuit.
Keywords— Multilevel converter, V-connection
inverter, conducted emission, leakage current

rectifier-I. INTRODUCTION
In recent years, due to the rapid development of theinformation society, the demand of Online Uninterruptible
Power Supply (UPS) has been increasing. UPS which ensures
the stability of the power supply and avoids data loss due topower failure, has been applied in many server system all over
the world [1-2]. However, in this kind of system, the isolationtransformer is required at the output side, which accounts forabout 40% of the UPS total weight. Furthermore, the utility of
the isolation transformer increases the size of UPS. In addition,
the isolation transformer causes the constant loss which lowers
the power conversion efficiency [3].
In order to solve above problems, many methods has been
proposed [2-4]. One of those is the concept of the transformerless two-level V-connection BTB system [3-4]. In this system,by grounding the common phase, it is possible to remove theisolation transformer. As a result, high efficiency andminiaturization of UPS can be achieved. However, the DC link
voltage in the V-connection BTB system becomes two times
higher than that in the three-phase connection BTB system. As
a result, high voltage switching devices are required. In orderto solve this problem, the three-level V-connection BTB
system has been proposed [3]. Compared with the two-levelsystem, the number of the switching devices is increased.
However, due to the characteristic of the multi-level circuit, thevoltage applied across the switching devices become 1/(n-1)

times of the DC link voltage. Here, n is the number of level ofthe circuit. Therefore, low voltage rating devices can be applied.
On the other hand, it is confirmed that the efficiency of thethree-level V-connection BTB system can be improved by
7.9% compared with the three-phase connection BTB system[4]. However, because of the main circuit of UPS, theevaluation of the conduction noise which is generated by thethree-level V-connection BTB system is necessary. Hence, themeasurement and comparison of the conduction noise between
the three-level V-connection BTB system and the conventional
three-level three-phase connection BTB system must be
conducted. In this case, the conduction noise is evaluated by
the conducted emission which transmits in the power line.
Therefore, based on Standard CISPR 22, the conductedemission in frequencies from 150 kHz to 30 MHz is measured
and evaluated.
The V-connection BTB system has many advantages interms of the efficiency improvement and size reduction.
However, it seems that the conducted emission of the Vconnection three-level inverter has not been reported in pastworks. Especially, the behavior of the neutral point voltage ofthe V-connection three-level inverter has not been discussed
compared with three-phase three-level inverter. In addition, theconventional method to evaluate the conducted emission of thepower converter system is measuring the conducted emission
and reproducing it by simulation [5-8]. In this method, thesimulation results can reproduce the experimental results fairly
exactly in the simple systems. However, it does not clarify thereason of the generation of the common-mode voltage.
Therefore, the mechanism of the generation of the commonmode voltage is not clear. Hence, it causes difficulties infinding out the method to reduce the conducted emission of thesystem by suppressing the common-mode voltage.
In this paper, in order to reveal the behavior of the
conducted emission of the V-connection three-level BTB
system, a theoretical analysis about the common-mode currents
which based on the common-mode equivalent circuit, isdiscussed compared with the three-phase three-level BTB
system. The neutral point potential variation of both systems isinvestigated and formulated in order to clarify the generation of
the common-mode voltage. Note that the common-mode
voltage is the source of the common-mode current in thesystem. Moreover, the common-mode current dominates the
conducted emission. Hence, based on this analysis, thecomparison result of the conducted emission between the threephase connection BTB system and the V-connection BTB

system can be assumed. After that, the experimental results ofthe common mode leakage current and the conducted emission
in two systems are demonstrated. Due to the measurement
results, the assumption about the comparison results of the
conducted emission between two systems is confirmed.

+
vrv
Input vst

Edc/2

ir
is
it

Fig. 2 shows the control block diagram of the rectifier unit
in three-level V-connection BTB system. The rectifier unit iscontrolled by the Automatic Current Regulator (ACR) and theAutomatic Voltage Regulator (AVR) to obtain the sinusoidal
input current and to regulate the DC link voltage. In order toobtain the high input power factor, the phase references of thecurrent command value of the ACR are calculated from the
input voltage phases. On the other hand, the inverter unit iscontrolled by open-loop, and the modulation scheme isunipolar PWM modulation, which has the carrier changes
between 0 and a positive peak, while the reference is always
positive [3]. In the three-phase connection BTB system, thecontrol strategy of the rectifier unit is the same as the Vconnection BTB system. However, the current command valueof the S phase is derived from the current command value of R
phase and T phase by (1).
is*  (ir*  it* ) .......................................................... (1)where ir*, is*, it* are the input current commands.
When carrying out the experiment, in order to change fromthe three-phase connection BTB system to V-connection BTB
system, the PWM signal which control the ON / OFF state of
the switch of S phase and V phase module in the three-phaseconnection BTB system, will be set to OFF state.
III. EVALUATION SYSTEMS
A. Configuration of evaluation system
Fig. 3 shows system configuration to evaluate theconducted emission and the places to observe the commonmode leakage current. These systems are built for simulating
the circuit of the UPS. Therefore, there are two EMC filters at
the input and output to restrain the EMI noise which is
generated from the switching of the main circuit. In addition,an output Low-pass Filter (LPF) is put in order to obtain thesinusoidal waveform. The leakage inductance of the output
transformer is used as the filter L in the LPF.
Fig. 3(b) shows the V-connection BTB system. It also has
two EMC filters at the input and output, and a LPF at theoutput. However, in the V-connection system, an inductor

vu
vv
iv

+

II. MAIN CIRCUIT CONFIGURATION AND CONTROL STRATEGY
Fig. 1 shows the circuit diagrams of a three-level threephase connection BTB system, and a three-level V-connection
BTB system, respectively. In order to obtain the same output
voltage, the DC voltage of the three-level V-connection BTB
system is set to two times higher than that of the three-phaseconnection BTB system. Therefore, in the three-level Vconnection BTB system, high voltage switching devices are
required. However, in this paper, the same voltage rating
switching devices are applied in both systems in terms of thecomparison of the conducted emission performance dependingon the circuit topology. In addition, the same switchingfrequency is applied regardless of the connection method.

iu
iw

Outputvw

Edc/2(a)Three-level three-phase-connection BTB system

Edc/2 +
vr
vs
vt

Input

iu

ir
is
it

vu
vv
vw

iv

Outputiw

Edc/2 +(b)Three-level V-connection BTB system
Fig.1. Main circuit configuration, which has the PWM rectifier
unit at the input and the PWM inverter unit at the output (BTB
system)Edcref

+

AVR
-

x

Ir_ref * +

-1

x

ACR

vrref

-

Ir_ref0

EdcdetEdcrate

Irpu

1
EdcdetIt_ref *x+-

It_ref0

-1

ACR

x

vtref

Itpu
sin

qin

tan1

vα,vβ

3Φ/αβ

vr
vt

Fig.2. Control block diagram for three-level V-connection
rectifier-inverter. It consists of AVR (to control the DC link
voltage) and ACR (to control the input current)

which has a same inductance of the leakage inductance of thetransformer in the three-phase connection BTB system isneeded as the filter L. Note that iCM_heatsink is the leakage
current from the heat sink, iCM_output is the leakage current of
the output EMC filter, iCM_input is the leakage current of the
input EMC filter, and iCM_LISN is the leakage current whichflows into Line Impedance Stabilization Network (LISN).
In addition, it is important to achieve the same stray
capacitances between the heat sink and switching devices
regardless of the connection method. Therefore, whenchanging the connection method from three-phase connection
to V-connection, the common phase (S phase and V phase) isconnected to the neutral point of electrolytic capacitor, andswitching devices of the common phase (S phase and V phase)are always turned off.
Fig. 4 shows the circuit configuration of the EMC filter.
The EMC filter has three parts: X capacitor, Common Mode
Choke (CMC) and Y capacitor. The X capacitor is used tosuppress the Differential Mode (DM) current, while CMC andY capacitor is used to suppress the Common Mode (CM)current. In addition, the design of EMC filter is based on
Ref.[12]. Here, the X capacitor’s capacity is designed based on

an allowable lead angle of current φ because it reduces thepower factor at the light load [12]. In addition, the Y
capacitor’s capacity is designed based on the acceptableleakage current [12].
B. Common-Mode equivalent circuit
Fig. 5 shows the equivalent circuit for the common-mode
voltage and current of both systems. Note that the polarity of
the rectifier common-mode voltage vrec is opposite to that of
the inverter common-mode voltage vinv [11]. Next, LL1 and RL1
are the CM inductance and resistance values of the boost
reactor on the input side of the three-phase connection inverter,
while LL2 and RL2 are the CM inductance and resistance valuesof the V-connection inverter. Note that there is unbalance
between the values of LL1, RL1 and LL2, RL2. It is because in thethree-phase connection BTB system, there are three boost
reactors on the input, while there are just two boost reactors inthe V-connection BTB system. In addition, Rload and Lload are
the CM inductance and resistance values of the RL load. Here,it can be considered LISN as the parallel circuit of L1, C1 andR1. In addition, the voltage which appears across R1 is the
conducted emission voltage. Furthermore, CGH1, CGH2 and CGH3
are the parasitic capacitances between the IGBT modules andthe heat sink [8]. They are measured between three output
terminals of the IGBT modules and the heat sink. Moreover,
LEMC1, REMC1 are the inductance and resistance of the input
CMC, while LEMC2, REMC2 are the inductance and resistancevalues of the output CMC. Finally, LGH, LGF1, LGF2 are the strayinductances of the grounded lines, while CGL, CGTrans are thestray capacitances of the load and the isolation transformer.
From Fig. 5, it can be known that there are many CM
current loops which flow around in the systems. However, forsimplicity, only the CM currents which flow through the LISN
are considered, because the voltage of this resistance is used toanalyze the conducted emission of the system. Therefore, there
are three CM leakage currents which are considered in thiscase:
 Loop 1 : Generated from inverter → Output filter L →stray capacitance of transformer Ctrans (or not in Vconnection) // Output EMC filter // Load → Output
EMC filter grounded line → input EMC filter // LISN
→ rectifier → inverter Loop 2 : Generated from rectifier → Boot reactor →input EMC filer // LISN → Heat sink grounded line →Stray capacitance between IGBT modules and heat sink
CGH2 // 2CGH3 // CGH1 → rectifier
 Loop 3 : Generated from inverter → Stray capacitance
between IGBT modules and heat sink CGH2 → Heat sinkgrounded line → input EMC filter // LISN → Boost
reactor → rectifier → inverter
From 3 loops above, it can be considered that the input
EMC filter plays an important role in bypassing the CM current
which flows out the power supply, while the output EMC filter
only bypasses the CM current which flows to the load. In
addition, it can be known that the stray capacitor of the IGBT
modules CGH1, CGH2, CGH3 and the stray inductance of thegrounded line of heat sink LGH play an important role in thegeneration of many CM leakage currents. It is because if notr
LISN s
t G
t

r
s

Boost
reactor Rectifier

Inverter Transformer
Filter C

EMC
filteriCM_LISN

Heat sinkiCM_input

EMC
filter

Load

iCM_output

iCM_heatsink(a)Three-level three-phase-connection BTB system
Boost
Inverterreactor Rectifier
r
EMC
s
LISN
t G
t filterHeat sinkiCM_input
iCM_LISNiCM_heatsinkrsFilter L Filter C

EMC
filter

Load

iCM_output(b)Three-level V-connection BTB system
Fig.3. Circuit diagram when measuring conducted emission, which
use common main circuit for both systems
CMC
Input

OutputCX

CY

Fig.4. EMC filter

grounding the heat sink, there is only one loop of the CMleakage current which exists in the CM equivalent circuit.
Compared Fig. 5(a) to Fig. 5(b), it can be seen that there isunbalance between three-phase connection BTB system and Vconnection BTB system: in the three-phase BTB connection
system, there is a stray capacitor of isolation transformer
CGTrans on the output side while there is not a similar
component in the V-connection BTB system. However, thisunbalance is negligible because the impedance of CGTrans isalways much larger than the impedance of the output EMC
filter connected in parallel to the load.
IV. NEUTRAL POINT POTENTIAL VARIATION
From the CM equivalent circuit, it can be considered that
the CM voltage current paths and stray components are similar
in both systems. Therefore, the difference in the magnitude of
the CM leakage currents between two systems will be causedby the difference in the magnitude of the CM voltage source
vrec and vinv. Note that vrec is the CM voltage between theneutral point of the power supply and the neutral point, while
vinv is the CM voltage between the neutral point of the load andthe neutral point. Based on this, the analysis of the neutral point
potential variation in both systems is necessary. Because of thesymmetric of the BTB system, only the analysis of thegeneration of vinv is needed for discussion. The analysis of thegeneration of vrec is similar.
Only two of the four switches of one phase are turned on,
and connect the output terminal to one of three switchingstates: Positive (output voltage = +Edc/2), Zero (output voltage= 0), Negative (output voltage = -Edc/2). Using switching
function Su, Sv, Sw to represent the switching state of each phase
U, V, W. In this case, Su, Sv, Sw can only have one of threevalues {1, 0, -1} at any time. Here, the switching statevariables Su, Sv, Sw =1 when the output terminal of thecorresponding phase is connected to swiching state Positive; Su,
Sv, Sw =0 when connected to switching state Zero and Su, Sv, Sw

Input
EMC filter
LEMC1 REMC1

LISN

Output
EMC filter

Main circuit
LC1

RC1

Neutral point

vrec

+

vinv
+

Lfilter

REMC2
LEMC2

L1
C1

CY1/3

CGH3

Rload/3

CY2/3

CGH3
CGH2

CGH2

LGF1

R1

CGH1

CGH1

Lload/3

CGL

LGF2

LGH
Loop 1Loop 2Loop 3(a). Three-phase connection BTB system
Input
EMC filter
LEMC1 REMC1

LISN

Output
EMC filter

Main circuit
LC2

RC2

+

Neutral point

vrec

vinv
+

Lfilter

REMC2
LEMC2

L1
C1

CY1/3

CGH1

Rload/3

CY2/3

CGH3
CGH2

CGH2

LGF1

R1

CGH1
CGH3

Lload/3

LGF2

CGL

LGH
Loop 1Loop 2Loop 3(b). V-connection BTB system
Fig.5. Common-mode equivalent circuit in both systems, the leakage inductance of the isolation transformer
in the three-phase connection is replaced by filter L in the V-connection= -1 when connected to switching state Negative. Thus, theneutral point potential variation vnOUT_MP of the three-phaseconnection can be caculated by
vnOUT _ MP 

Edc _ threecon
6( Su  Sv  S w ) …………..….…….(2)where Edc_threecon is the DC link voltage of the three phaseconnection inverter.
Similarly, in the V-connection inverter, it can be consideredthat the switching state variable of V phase is always equal
zero i.e. Sv =0, and the DC link voltage Edc_Vcon = 2Edc_threecon.
Hence, (2) can be rewritten as
vnOUT _ MP 

Edc _ Vcon
6

( Su  S w ) ………………….….…….(3)Based on (2), it can be considered that in the three-phaseconnection inverter, the maximum value of the neutral point
potential variation vnOUT_MP = Edc_threecon/2 when the switchingstate of all three phases is Positive. In addition, based on (3), inthe V-connection inverter, it can be considered that the
maximum value of the neutral point potential variation vnOUT_MP= Edc_Vcon/3 when the switching state of all two phases is
Positive. Because the DC link voltage of the V-connection
inverter is two times higher than that of the three-phaseconnection inverter Edc_Vcon = 2Edc_threecon, it can be concluded
that the maximum value of the neutral point potential variation
vnOUT_MP of the V-connection inverter is higher than that of thethree-phase connection inverter. On the other hand, the CM
voltage sources vrec and vinv dominate the magnitude of the CM

currents of each system. Therefore, it can be assumed that themagnitude of the CM currents in the V-connection BTB system
is higher than that in the three-phase BTB connection system.
Moreover, the CM currents dominate the generation of the
conducted emission. Based on this, it can also be assumed thatthe conducted emission of the V-connection BTB system ishigher than that of the three-phase connection BTB system.
Table 1 shows the output voltage states of the neutral point
potential variation vnOUT_MP of the three-phase connection
inverter. From table 1, it can be confirmed that there are sevenoutput voltage states in the three-connection inverter. Table 2
shows the output voltage states of the neutral point potential
variation vnOUT_MP of the V-connection inverter. From table 2, it
can be confirmed that the number of the output voltages statesof the V-connection inverter is less than that of the three-phaseconnection inverter. Note that in table 1, the DC link voltage ofthe three phase connection inverter Edc_threecon = Edc, while intable 2, the DC link voltage of the V-connection inverter
Edc_Vcon = 2Edc.
Fig. 6 shows the distribution of the output voltage state of
the neutral point potential variation vnOUT_MP with response to
the output voltage vector in both systems. Note that there is anindividual mark which is used to represent for each output
voltage state. Comparing Fig. 6(a) to Fig. 6(b), it can be
confirmed that the number of the switching states of the threephase connection inverter is more than that of the V-connection
inverter. Based on this, it can be concluded that the degree ofTable 1．Ouput voltage states of the neutral point potential
variation vnOUT_MP of the three-phase connection inverter.
In this case, the DC link voltage Edc_threecon = Edc
U phase
1
1
1
-1
-1
-1
0

V phase
1
0
0
-1
0
0
0

W phase
1
0
1
-1
-1
0
0

vnOUT_MP
Edc/2
Edc/6
Edc/3
-Edc/2-Edc/3-Edc/60

V21

V phase00000W phase
1
0
-1
1
0

V19
V20

V12
V3

V11

V24 V23 V10V2

V27 V1 V26
V13
V14

V15

V6

Table 2．Ouput voltage states of the neutral point potential
variation vnOUT_MP of the V-connection inverter. In this case,
the DC link voltage Edc_Vcon = 2Edc
U phase
1
1
-1
-1
0

b

Vv

V18 V5

V17 V

V9

V8

Fig. 8 shows the harmonic analysis results of the CMleakage currents of both systems. From Fig. 8, it can be
confirmed that the CM leakage currents from heat sink, the CMleakage currents of input and output EMC filter of the threephase connection BTB system is lower than those of the Vconnection BTB system. It is because that the neutral point
potential variation of the V-connection BTB systems is higher
than that of the three-phase connection BTB system. The
neutral point potential variation dominates the magnitude of theCM voltage. Hence, the CM voltage source of the Vconnection BTB system also becomes higher than that of thethree-phase connection BTB system. In addition, the leakage
current which flows into LISN iCM_LISN is the smallest among
the CM leakage currents. From this, the effect of bypassing the
CM leakage current of the input EMC filter is confirmed.
Moreover, it can be known that the CM leakage current of theheat sink is dominant in both systems. It is because this CM
leakage current is generated from the resonance of the stray
capacitance of the IGBT modules CGH1, CGH2, CGH3 and thestray inductance of the grounded line of heat sink LGH. From
Fig. 5, it can be seen that the CM leakage current of the heatsink has a synthetic CM voltage source vrec + vinv. Therefore, it
becomes a dominant CM leakage current.
Fig. 9 shows the measurement result of the conductedemission of both systems. From Fig. 9, in all frequencies from150 kHz to 30 MHz, it is confirmed that the conducted

V16

4

V7

V9
b
Vvw
V6
V8

V3
a

V4

V2

Vwu

Fig. 7 shows the measurement results of the neutral point
potential variation. From Fig. 9, it can be confirmed that theneutral point potential variation of the V-connection BTB
system is higher than that of the three-phase connection BTB
system.

Edc/2
Edc/3
Edc/6
0
-Edc/6-Edc/3-Edc/2a(a). Three-phase connection inverter

freedom of switching in the three-phase connection inverter ishigher than that of the V-connection inverter.

Table 3 shows the experimental conditions. Whenmeasuring the conducted emission, a combination between aspectrum analyzer R3131A (Advantest Corporation) and a
LISN is applied, and the noise measurement is carried out in ashielded room.

Vu
V25

Vw

vnOUT_MP
2Edc/3
Edc/3-2Edc/3-Edc/30

V. EXPERIMENTAL RESULTS

V22

Vuv

V7
V5

2Edc/3Edc/3
0-Edc/3-2Edc/3

Vwv
V1(b). V-connection inverter
Fig.6. Distribution of the output voltage state of the neutral point
potential variation in both systems

emission of the V-connection BTB system is higher than thatof the three-phase connection BTB system. In addition, from
Fig. 9(a), in the three-phase connection BTB system, there are
the peaks at 550 kHz, 1.6 MHz and 5 MHz. Compared with Fig.
8(a), these peaks of the conducted emission almost matchedwith the peak’s frequencies of the CM leakage current
measurement result. Moreover, in the frequencies below 10
MHz, the tendency of the leakage current waveforms,
especially the waveform of the leakage current which flows
into LISN iCM_LISN, match with the conducted emission
measurement result. In the frequencies from 10 MHz to 30
MHz, the conducted emission from gate drive power supplies
become considerable [9], [10]. Therefore, in the frequencies
from 10 MHz to 30 MHz, the tendency of the conductedemission becomes different from the tendency of the CMleakage currents. From these analyses above, it can beconcluded that the CM leakage current dominates thegeneration of the conducted emission, especially in thefrequencies below 10 MHz. In the V-connection BTB system,
it can also be confirmed that the CM leakage current dominates
the generation of the conducted emission, in similar.
VI. CONCLUSION
In this paper, the neutral point potential variation of thethree-level three-phase connection BTB system and the threelevel V-connection BTB system was discussed. As a result, it isconfirmed that the neutral point potential variation of the Vconnection BTB system is higher than that of the three-phaseconnection BTB system. It causes the CM leakage currents of
the V-connection BTB system become higher. Hence, it can beconcluded that since higher neutral point potential variation,

Table 3. Experimental conditions
V-connection
Three-phase

Leakage current [dBmA]

Input AC Voltage(line -to-line)
DC-link voltage
Output AC Voltage (line -toline) & phase current
Output power
Power supply frequency
Output frequency
Switching frequency
Load
IGBT module

70

200 V
600 V

300 V
145 V, 6.4 A

1.6 kW
50 Hz
60 Hz
16 kHzRL load (13 Ω, 5 mH)
SK150MLI066T (Semikron)

Neutral point potential variation VMP_nOUT [V]Output
EMC filter
1.8 MHzHeatsink

30

5 MHz
9 MHz

550 kHzInput
EMC filter

-10
0.15

0.3

LISN current
1
3Frequency [MHz]

0.5

5

10

30

(a) Three-level three-phase-connection BTB system

100[V/div]

Leakage current [dBmA]

70

05[ms/div](a). Three-phase connection inverter
Neutral point potential variation VMP_nOUT [V]

1.6 MHz

1.4 MHz
2.1 MHz
6.7 MHz

9.5 MHz

30 Heatsink

Output
EMC filter

-10
0.15

100[V/div]

Input
EMC filter

0.3

0.5

LISN
1
3
Frequency [MHz]

5

10

30

(b) Three-level V-connection BTB system
Fig.8. Harmonic analysis of CM leakage current
Conducted emission [dBmV]

100

05[ms/div](b). V-connection inverter
Fig.7. Neutral point potential variation, it can be confirmed that theneutral point potential variation of the V-connection BTB system ishigher than that of the three-phase connection BTB system

the conducted emission of the V-connection BTB system
become higher than that of the three-phase connection BTB
system. In the future, in order to reduce the conducted emissionof the V-connection BTB system, the switching patterns will beanalyzed. Based on this, a new control method which can
reduce the conducted emission by suppressing the commonmode voltage in the V-connection BTB system will be derived.
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[1]

[2]
[3]

[4]

[5]

E. Demirkutlu, et al., “Output Voltage Control of A Four-Leg Inverter
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V-connection

1.4 MHz
1.6 MHz

550 kHz

60 Three-phaseconnection

20
0.15

0.3

0.5

5 MHz

1
3
Frequency [MHz]6.7 MHz5

1030

Fig.9. Measurement results of conducted emission in both
systems, conducted emission of the V-connection is higher thanthat of the three-phase connection in all frequencies
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