Minimization of EMC Filter for Interconnection
Inverter by High Switching Frequency
Takuya Kataoka, Masakazu Kato

Jun-ichi Itoh

Nagaoka University of Technology
Nagaoka, Niigata,Japan
takuya_kataoka@stn.nagaokaut.ac.jp

Nagaoka University of Technology
Nagaoka, Niigata,Japan
itoh@vos.nagaokaut.ac.jp

Abstract—This paper proposes a design method of a commonmode current feedback type EMC filter in an interconnection
system. First, the relationship between the switching frequency of
the PWM inverter, the common-mode feedback current and thevolume of the filter reactor is theoretically estimated. Moreover,the switching frequency and the current capacity of switching
devices which are necessary in order to estimate the volume of
the EMC filter is determined by this relationship. Second, theinverter loss is calculated based on the experimental result. After
that, the relationship between the cut-off frequency of the EMC
filter and volume of the cooling system is calculated. As a result,the minimum total volume of the EMC filter estimation and thedesign method of the cooling system are clarified. From theexperimental result, the design point of the maximum power
density is clarified. Moreover, the conduction noise of theswitching frequency component suppresses below the prescribedby CISPR11.

problem, the design method for minimization by using Pareto
front curve has been discussed [4].

Keywords—EMC Filter; High-Frequency Switching; Wide
Band-Gap device

I. INTRODUCTION
Recently, attentions are focused on miniaturization of thepower conversion for interconnection system. In particular, itis necessary to reduce volume of an EMC filter because the
EMC filter accounts for a considerable proportion of thepower conversion system. The EMC filter comprised of anormal-mode filter and a common-mode filter. Furthermore,by increasing the switching frequency, passive components inthe normal-mode filter are downsized and consequently thevolume is reduced. Besides, in order to achieve a highfrequency switching operation, the inverter requires fastswitching devices to be used because slow-switching devices
cause a large switching loss and a dead time error. Thereby,
the switching device using a wide band-gap semiconductor
such as gallium nitride (GaN) or silicon carbide (SiC) is used
to the PWM inverter, instead of the silicon based switching
device [1-3]. However, the performance and theminiaturization effect have not been discussed in previous
studies when wide band-gap semiconductors are applied to the
PWM inverter for an interconnection system. Moreover, when
the switching loss is increased by considering a high switchingfrequency, the volume of a cooling system becomes large.
Therefore, there is a trade-off relationship between the EMC
filter volume and cooling system volume. In order to solve thisOn the other hand, when the switching frequency is
increased, electromagnetic noise is also increased. Therefore,
a common-mode filter increases in volume in order to avoid
incorrect operation of peripheral equipment by the conduction
noise [5]. Furthermore, in order to solve this problem, thecommon-mode current feedback type EMC filter has been
proposed [6-7]. In the past work, the normal-mode filter andthe common-mode filter for PWM inverters are discussed [6].
Ref.[6] considers the design method of the normal-mode andcommon-mode filters and the effect of the harmonics
suppression by experiments. Moreover, Ref.[6] clarify adesign method of the common-mode reactor. The commonmode current which flows between the PWM inverter and the
EMC filter becomes small and to be negligible due to increase
the inductance of the filter reactor. When the switchingfrequency is larger than the cut-off frequency, the commonmode current is determined by the inductance of the filter
reactor. In addition, the volume of the filter reactor accounts
for a considerable proportion of the volume of the EMC filter
because the energy density of the filter inductor is lower than
one of the filter capacitor. Thus, it is important to consider the
relationship between the common-mode current and the filter
reactor from a viewpoint of a miniaturization. On the other
hand, detail analyzes of a LC filter and simple design
procedures along with a design example are presented in [7].
Furthermore, Ref.[7] have analyzed a single phase equivalentcircuit of the LC filter. However, common-mode equivalentcircuit and the effect of the power loss of the inverter by thefilter current have not been discussed. Moreover, theminiaturization effect and the effect of reducing conduction
noise have not been discussed in previous studies.
In this paper, a design method for miniaturization of thecommon-mode current feedback type EMC filter with highswitching frequency is proposed. First, the switchingfrequency and the current capacity of switching devices which
are necessary in order to estimate the volume of the EMC
filter are determined. These factors are determined byconsidering 1) the current flowing between the inverter andthe EMC filter, and 2) the relationship between the switchingfrequency and the volume of the filter inductor. Second, theinductance of the filter inductor is varied, and the relationshipbetween the volume of the EMC filter and the cooling system

is considered. Next, the minimum value of the total volume of
the EMC filter and the cooling system is derived due to thetrade-off relationship between the volume of the filter inductor
and the inverter losses. Finally, experiments with a prototypeof the GaN-FET inverter are conducted to verify the validityof the proposed design method. As a result, the design point of
the maximum power density is clarified. Thus the validity ofthe proposed design method is confirmed.

GaN-FET
Inverter

Ld
Cy

II. SYSTEM CONFIGURATION

III. ESTIMATION OF VOLUME AND POWER LOSS
A. Volume of reactor
In this paper, the reactor volume is focused because theenergy density of the filter inductor is lower than one of thefilter capacitor. In addition, the reactor of the EMC filter isdesigned by the Area product concept using a window area
and a cross-sectional area [8]. Then volume of the reactor isgiven by (1).

 2W 
volL  K v 
 K u Bm J (1)where Kv is the constant value depending on the shape of aused reactor core. W is the maximum power of the reactor. Ku
is the occupancy of the window area of core. Bm is the
maximum flux density of the core. J is the current density of
the wire which is used to the reactor. From (1), the volume ofreactor is proportional to the power of 3/4 of maximum energyof the reactor.
B. Power loss of Inverter and Volume of Cooling system
A power loss of the inverter is separated into the
conduction loss and the switching loss of the switching
devices. Generally, the conduction loss of the switching
devices is calculated by the on-state resistance Ron and theswitching loss is calculated by turn-on loss Pon and turn-off
loss Poff according to the datasheet. In this paper, loss analysis
is based on the experimental results of the simplify estimationof volume of the cooling system.
Table 1 shows the circuit parameters on experiment. The
GaN-FETs (VDSmax = 600 V, ID_max = 10 A) are used for thePWM inverter in order to achieve the 300-kHz switchingic
Fig. 1. Three-phase inverter system with the commonmode current feedback type EMC filter.
Table 1. Conditions of Experimental for measurement thepower loss of GaN-FET inverter with RL load.
Input voltage Vin
141 V
1Modulation ratio Output frequency fout
20 Hz
Load impedance Zload
51 
0.99
Power factor cosAmbient temperature Ta
25 ℃
Dead time Td
100 ns14

Total loss Ptotal [W]Fig.1 shows the circuit configuration of an Three-phase
inverter with the common-mode current feedback type EMC
filter. The natural point of a Y-type capacitor in the commonmode current feedback-type EMC filter is connected to thenatural point of the DC link bus because it is possible toincrease the allowable current ic in comparison withconnecting to the ground case. In this paper, the current ic
flowing between the inverter and the EMC filter is called as
the filter current. Furthermore, the volume of the filter
inductor accounts for the majority of the EMC filter volume
because the energy density of the filter inductor is lower than
one of the filter capacitor. Hence, the filter inductor volume isdiscussed with a special emphasis in this paper.

3
4

grid

LC filter
Vin

Ptotal=1.47×10-5fsw+4.67

12
10
8
6
150

300
450
Carrier frequency fsw [kHz]600

Fig. 2. Measurement result of relationship between
switching frequency and power loss of GaN-FET inverter.

frequency. The PWM signals are generated by comparing theoutput voltage command with the triangle wave.
Fig.2 shows the measured power loss of the GaN-FET
inverter in Fig.1. The conduction loss is given byy-intercept of approximation formula b because it is not
related to the switching frequency. On the other hand, theswitching loss of PWM inverter is given by slope of theapproximation formula. As a result, the conduction loss andthe switching loss on arbitrary output power are calculated by(2) and (3).

PSW  afsw

VDC _ calc I out _ calc
VDC _ test I out _ test(2) I out _ calc PCON  b   I out _ test 



2

(3)

where Iout_calc is the output current on arbitrary output power,
Iout_test is the output current when the power loss is measured inexperiment, VDC_calc is the DC link voltage on arbitrary output
power, and VDC_test is the DC link voltage when the power loss
is measured in experiment. Thus, the power loss is given by
the following equation.

Ploss  PSW  PCON(4)

The switching devices that used for the PWM inverter isheated by the loss of the conduction loss and the switchingloss. The rising in temperature causes a breaking the switching
device. Hence, the PWM inverter requires a cooling systemsuch as heatsinks and fans. In this paper, consideration of thecooling system is the heatsinks only. Generally, a thermal
resistance is used in order to evaluate the cooling system
performance. However, it is not enough because theevaluation based on thermal resistance does not consider thevolume of the cooling system. In this paper, CSPI (Cooling
System Performance Index), which is a reciprocal of the
product of the volume and the thermal resistance, is introduce
for the volume of the cooling system estimation. The CSPI
indicates the cooling performance per unit volume of thecooling system. Thereby, it means that a high CSPI shows ahigh performance cooling system. Therefore, in order todownsize a cooling system, PWM inverter needs a coolingsystem which has high CSPI. The volume of the coolingsystem is given by the relationship between the power loss andthe rise in temperature by the following equation [9].

volcooling 

Ploss
1

Rth  CSPI T j  Ta  CSPI

(2)

where Rth is the thermal resistance of the cooling system, Tj isthe junction temperature of switching devices, Ta is theambient temperature, Ploss is the power loss of the switching
devices that used for PWM inverter.
IV. DESIGN CONSIDERATION OF EMC FILTER
Fig. 3 shows the part of common-mode equivalent circuitof GaN-FET inverter and the EMC filter in Fig.1. The filter
current ic flows between the GaN-FET inverter and the EMC
filter. The filter current ic and cut-off frequency of the EMC
filter are given by the following equations.

ic j 3C y 

1   Ld / 33C y 

c 

2

1
Ld C yvinv(   2 c )(Ld / 3)
2

(5)

(6)

where is the switching angular frequency, c is the
cut-off angular frequency of the EMC filter, Ld is the

Table 2. Simulation and calculation parameters.
Input voltage Vin
282 V
Output voltage vout
200 V
Output frequency fout
50 Hz
Load resister Rload
26.67 Load reactor Lload
1 mH
Switching frequency fsw
600 kHz1
Modulation Ratio 
CSPI
3
Ambient temperature Ta
20 ˚C
Junction temperature Tj
100 ˚C
Slope in Fig.2 a
1.47  10-5
y-intercept in Fig.2 b
4.67

vinv

To input

Ld/3
ic

To output
3Cy

Fig. 3. Interconnection system with the common-mode
current feedback type EMC filter. The filter current iscalculated by use of the filter reactor Ld, the filter
capacitor Cy and the common-mode voltage vinv.
inductance of the filter reactor and vinv is the common-mode
voltage of the inverter.
When the switching frequency is much larger than the cutoff frequency of the EMC filter, ( 2   2 c ) can beapproximated to  2 . Therefore, the changes of the filter
current due to the effect of resonant is negligibly small.
Hence, the approximation formula of the film current ic isgiven by the following equation.

ic 

1

v

 ( Ld / 3) inv(7)

Fig. 4 shows the relationship between the filter current andthe volume of the filter inductor from (7), when the switchingfrequency is varied. Table 2 shows the calculation condition
for the designed EMC filter. In order to eliminate the effect ofresonant of the EMC filter, the cut-off frequency is set as 1/10of the switching frequency. As a result, when the switchingfrequency is high, the volume of the filter inductor is small.
Moreover, the relationship between the filter current and thefilter reactor volume is a trade-off relationship. Therefore, theswitching frequency and power loss of the switching devices
are necessary in order to estimate the volume of the EMC
filter and it is determined by this relationship.

Fig. 7 shows the relationship between the cut-off
frequency of the EMC filter and total volume at 300-kHz
switching frequency. In the simulation, the EMC filter isdesigned based on switching frequency of 600-kHz. However,switching frequency is 300-kHz in experiment. Therefore, theEMC filter needs to be redesigned. As a result, the relationshipbetween the cut-off frequency and total volume is established
as a downward convex function and similar to Fig. 6.
Therefore, the minimum value of total volume is clarified. At
this point, total volume can be estimated at minimum point
when the percentage ofan impedance of the filter
inductor %Z is 0.8% as the cut-off frequency is 50-kHz.

Table 3 shows the experimental condition. In theexperiment, the GaN-FET inverter is operated at 300-kHz
switching frequency. The inverter is controlled by an openloop control system. The conduction noise which be generated
by control circuit is deducted to evaluate the conduction noiseby main circuit.
Fig. 9 shows output waveforms of the inverter. The load
current has low distorted sinusoidal waveform. The reactor
current has large ripple current comparing to the load current
because the reactor current is composed from the load current
and the filter current. When the filter current is large, thereactor current ripple become large; thereby, the inverter loss
and conduction loss of the filter reactor is increased. The
maximum value of the filter current is 3.32A in the experiment.
However, in the simulation, the maximum value of the filter

50kHz
100kHz1.01

300kHz600kHz0.8
0.8

Smaller andLower loss

0.6
0.6
0.4
0.4
0.2
0.2

00

0

0.1
0.1

0.2

0.3
0.3

0.4
0.4

0.5
0.5

0.6

Common-mode filter current ic [p.u.]
Fig. 4. Relationship between the filter current ic and thevolume of the filter inductor, when the switching frequency
is varied.
ic=1.42 p.u.

7

ic=0.12 p.u.

6

ic=0.38 p.u.

Conduction
loss

5

Switching
loss

4
3

1[p.u.]=4.33Arms,Cy=100nF

2

Rated power of inverter:1.5kW=100%

1

Ld:small

0
0

50

100
150
Cut-off frequency [kHz]200

Fig. 5. Relationship between the cut-off frequency of the
EMC filter and a power loss of the inverter.
0.8

0.5

Total volume
0.7

0.4

volume of reactor[dm3]Fig. 8 shows the circuit diagram for conducting experiment.
From the experiment setup, in order to simplify experiment,
the load resister is used, instead of the grid. Furthermore, inorder to reduce the conduction noise, the EMC filter isconnected to the earth via grounded capacitor Cyg. Moreover,the RL load is connected to the earth via capacitor Cs. The
capacitor Cs imitates stray capacitance.

10kHz

1.2
1.2

Power Loss[%]

V. EXPERIMENTAL RESULTS

Volume of filter reactor[p.u.]

Fig. 6 shows the relationship between the cut-off
frequency of the EMC filter and total volume of the filter
inductor and the cooling system, when the switchingfrequency is 600 kHz. In this paper, the total volume is sumof the volume of the heatsink and the filter reactor. When the
cut-off frequency decreases, the inductance of the filter
inductor becomes large, and the volume of the filter inductor
also becomes large. On the other hand, when the cut-off
frequency increases, the filter current becomes small, whereas
the volume of the cooling system becomes large due to theincreasing of the inverter losses. As a result, the relationshipbetween the cut-off frequency and total volume is established
as a downward convex function. Therefore, the minimum
value of total volume is clarified.

1[p.u.]= 0.337dm3(50kHz,ic=0.05p.u.)
4.3A(rated current)
1.4
1.4

Total volume andHeatsink volume [dm3]Fig. 5 shows the relationship between the cut-off
frequency of the EMC filter and the power loss of the GaNinverter, when the filter capacitor is 100 nF, and the switchingfrequency is 600 kHz. Fig. 5 is based on the simulation resultsby referring to (3) and (4). When the cut-off frequency
increases, the filter current becomes large due to thedecreasing of the inductance of the filter reactor; therefore, thepower loss of the inverter becomes large.

0.6

0.3

Volume of heatsink
0.5

0.2

0.4

0.1

Volume of reactor

0.3

0
0

50

100

150

Cut-off frequency [kHz]200

Fig. 6. Relationship among the cut-off frequency of the
EMC filter and volume of reactor, heatsink and total.
The relationship is established as a downward convex.
Therefore, the minimum value of total volume is clarified.
current is 2.91A. The difference between experiment andsimulation has occurred. The possible cause of the differenceis the effect of the grounded capacitor. However, this paper
does not consider this matter in details.
Fig. 10 shows the measurement result of the relationshipbetween the cut-off frequency and the efficiency. In this case,Fig.11 shows the Pareto front curve of the relationshipbetween power density and efficiency. The total volume iscalculated as sum of volumes of the EMC filter and thecooling system. In particular, the volume of the inverter iscalculated from the measurement results of inverter losses byusing CSPI. The volume of the filter reactor is calculated fromthe inductance of the filter reactor which using is experimentby (1). From these results, the maximum point of power
density of the interconnection system with the common-mode
current feedback-type EMC filter is clarified. At this point, thepower density can be clarified at the maximum point when the
inductance of the filter inductor is 150-H as the cut-off
frequency is 49-kHz.
Fig. 12 shows the measurement result of the conduction
noise of the prototype circuit of the inverter with the commonmode current feedback-type EMC filter. As a result, theconduction noise of the fundamental component of theswitching frequency and the high-frequency components areless than 2MHz is generated by the main circuit and it mostly
suppressed according to the regulation value of CISPR11. Inorder to suppress fully according to the regulation, the revisingof cut-off frequency is needed. However, the conduction noisein the range of more than 2MHz has exceeded the limit of
CISPR11. This problem occurs due to the device mounting
such as a stray capacitor. However, this problem is notconsidered in this paper. Based on these results, the validity ofthe proposed design method for the common-mode current
feedback-type EMC filter is confirmed.
VI. CONCLUSION
This paper proposes a design method of the common-mode
current feedback type EMC filter in an interconnection system.
In this paper, the relationship between the cut-off frequency of
the EMC filter and the total volume of the GaN-FET inverter
and the EMC filter is discussed based on a simulation and an
experiment results. As a result, the design point of theminimum volume of the sum of the EMC filter and the coolingsystem is clarified. In the experiment, the designed point of
the maximum power density is clarified. In addition, the load
current has low distorted sinusoidal waveform. Furthermore,
the conduction noise of the fundamental component of theswitching frequency and the high-frequency components areless than 2MHz is generated by the main circuit and it
suppressed according to the regulation value of CISPR11 bydesigned EMC filter. These results, the proposed design

0.7

Switching frequency : 300 kHz
Output power : 1.5 kW
Cy : 100 nF(%Y = 0.16%)

0.65
Total volume [dm3]the capacitance of the filter capacitor is kept at a constantvalue. Therefore, the cut-off frequency is varies by changing
the inductance of the filter inductor. The efficiency includes
total efficiencies of both the inverter and the EMC filter and it
measured by the power meter of Yokogawa, WT1800. Whenthe filter inductor is small, the loss of the inverter becomeslarge due to the increasing of the filter current ic. In contrast,
when the filter inductor is large, the core loss of the filter
inductor becomes large. As a result, the efficiency can be
represented into an upward convex function in experiment.
Therefore, the maximum point of efficiency is clarified. Hence,the efficiency is clarified at the maximum point when the
inductance of the filter inductor is 150-H as the cut-off
frequency is 49-kHz.

Ld = 100 H (%Z = 0.8%)
fc = 50 kHz

0.6
0.55
0.5
0.45
0.4
0

20

40

60

80

100

Cut-off frequency fc [kHz]Fig.7. Relationship between the cut-off frequency of the
EMC filter and total volume.
Carirrer
300kHz
Vref

200V
50Hz

Controll
circuit
6

LISN

Diode
rectifierLC filter

RL load

GaN-FET
inverterheatsink

ic

Cy=110nF
Cyg=4.7nF

Cs=1nF

Fig. 8. Circuit diagram for the conduction noise
evaluation.
Table 3. Experimental conditions.
Input voltage vin
200 V
Input frequency
50 Hz
0.866
Modulation Ratio 
Load resister Rload
75 
Load reactor Lload
1 mH
Switching frequency fsw
300 kHz1
Modulation Ratio 
Dead time Td
100 nsInverter output voltage(line to line) [V]
500[V/div]0

2[A/div]
0U-phase Load current (Green) [A]U-phase filter reactor current (blue)[A]
3.32[A]
0
Filter current [A]2[A/div]
4[ms/div]

Fig. 9. Output waveform of the GaN-FET inverter at 300kHz switching frequency. The load current obtains low
distorted sinusoidal waveform.

[4]

[5]

[6]

[7]
[8]
[9]

Filter loss
large

Inverter losslarge

Efficiency [%]fc = 30 kHz
Ld = 260 H

91
91

90
90

fc = 39 kHz
Ld = 150 H

fc = 46 kHz
Ld = 110 H

Carrier frequency : 300 kHz
Output power : 220 W
20
20

30
30

40
40

50
50

Cut-off frequency fc [kHz]Fig. 10. Measurement result of the relationship between
the cut-off frequency and the efficiency. In condition, thefilter capacitor is kept at constant value, whereas the filter
inductor is varied. The efficiency is represented into an
upward convex function. Therefore, a maximum point ofefficiency is clarified.
Carrier frequency : 300 kHz
Output power : 220 W
Cy : 110 nF

93.0
93.0

Efficiency [%]

[3]

92
92

89
89

92.0
92.0

High power density

fc = 30 kHz
Ld = 260 H(0.104 dm3)

fc = 39 kHz
Ld = 150 H(0.104 dm3)

91.0
91.0

fc = 46 kHz
Ld = 110 H(0.124 dm3)

90.0
90.0

89.0
89.0
1.5
1.5

1.7
1.7

1.9
1.9

2.1
2.1

2.3
2.3

2.5
2.5

Power density[kW/dm3]

Fig. 11. Calculation result of the Pareto front curve of the relationship between the power
density and the efficiency.
CISPR11Class.A(QP)

100

Conduction noise[dBV][2]

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ic:large
Ld :small

93
93

method achieves minimization of interconnection system
which include the EMC filter. In future work, the effect ofsuppression of conduction noise will be improvement.

[1]

ic:small
Ld :large

80

60

40

20
0.15

0.3
(fsw)

1

10

30

frequency[MHz]Fig. 12. Measurement result of the conduction noise of the
prototype circuit with proposed EMC filter.