Volume Minimization of Current Type ACC with Rogowski Coil
Atsutoshi Okura
Dept. of Electrical, Electronics, andInformation Engineering
Nagaoka University of Technology
Niigata, Japans193118@stn.nagaokaut.ac.jp

Rintaro Kusui
Dept. of Electrical, Electronics, andInformation Engineering
Nagaoka University of Technology
Niigata, Japankusui@stn.nagaokaut.co.jp

Kodai Nishikawa
Dept. of Electrical, Electronics, andInformation Engineering
Nagaoka University of Technology
Niigata, Japanknishikawa@stn.nagaokaut.co.jp

Masamichi Yamaguchi
Dept. of Electrical, Electronics, andInformation Engineering
Nagaoka University of Technology
Niigata, Japanm_yamaguchi@stn.nagaokaut.ac.jp

Hiroki Watanabe
Dept. of Electrical, Electronics, andInformation Engineering
Nagaoka University of Technology
Niigata, Japanhwatanabe@vos.nagaokaut.ac.jp

Jun-ichi Itoh
Dept. of Electrical, Electronics, andInformation Engineering
Nagaoka University of Technology
Niigata, Japan
itoh@vos.nagaokaut.ac.jp

Abstract
This paper proposes a current type active
common-mode noise canceller (ACC) using a Rogowski coil forcommon-mode (CM) noise detection. The proposed method
reduces the volume of a noise filter more than that ofconventional methods. The Rogowski coil is designed based on
CISPR standards for detecting the target noise reduction andthe frequency band. The proposed ACC with the Rogowski coilis evaluated in the experiment. As a result, the conductedemission voltage is reduced by 39dB V.

(a)Keywords
wide-band-gap semiconductor, common-mode
current, passive filter, active common-mode noise canceler

I. INTRODUCTION
In recent years, significant research has been conducted onincreasing power density in power converters using widebandgap devices, such as SiC (silicon carbide) and GaN(gallium nitride)[1-2]. These devices achieve high-speed
switching compared to Si devices, high-frequency drive,
reduced volume of passive components, especially inductors,
and high efficiency. However, high-speed switching leads toa steep potential voltage variation and a pronounced
electromagnetic noise[3]. In addition, it is considered that thenoise regulation frequency for inverters will be expanded to a
low frequency from 150 kHz to 9 kHz. Therefore,
electromagnetic noise suppression technologies will become
increasingly important in the future.
Figure 1 shows conventional electromagnetic noise
suppression methods. Figure 1 (a) is a passive CM filter thatconsists of a common-mode choke and a Y connection
capacitor. The passive CM filters reduce electromagnetic
noise in the frequency band above the cutoff frequency
determined by the inductance and capacitance of the filter
components. However, a low cutoff frequency is required tosignificantly reduce noise over a wide bandwidth. The passive
CM filter with a low cutoff frequency increases the volume ofthe passive components and reduces power density.
On the other hand, active common-mode noise cancellers(ACC) have been extensively researched to reduce the volumeof the CM filter[5-6]. Figure 1 (b) is a voltage type
ACC(Voltage Sensing Voltage Injection: VSVI), and Figure
1 (c) is a current type ACC (Current Sensing Current
Injection: CSCI). The passive CM filters, including commonmode choke inductors and capacitors, are widely used tosuppress electromagnetic noise, especially the CM noise.[4](b)Currenttransformer

Inverter
Motor

LISN
Tr1
C0

Tr2

(c) Inverter circuit with CSCI
Fig.1. Conventional CM Filter
The ACC cancels the CM voltage or current with CM
transformers or injecting amplifiers. Therefore, the ACC can
reduce the circuit volume compared with the passive CM
filters in the wide bandwidth design. There are two types ofACC: voltage and current. The voltage type ACC adds theinverted waveform of the CM voltage to the output voltage ofthe inverter with a CM transformer. In contrast, the current
type ACC injects the inverted waveform of the CM current,
which is detected by a current transformer, to the grand wireof the load. The current type ACC has the advantage over thevoltage type ACC in terms of high-power density because thecurrent transformers are only required to detect the highfrequency component of the CM current.
The combination of an active EMI filter (AEF) and amodified LCL-LC harmonic suppression filter is proposed toreplace the traditional EMI filter that has been proposed tosolve the EMI issue without introducing additional systemcosts [11]. The final harmonic distortion analysis results ofthe grid-side current show the satisfactory harmonic
attenuation performance of the modified LCL-LC filter, andthe conducted EMI measurement results verify the superiorityof the combination of the AEF and the modified LCL-LC filter.
However, a transformer is used for CM current detection [11].
The transformer occupies a large portion of the circuit volume.
The transformer increases the circuit volume.
A balanced feedforward current-sense currentcompensation common-mode active electromagnetic
interference filter has been proposed [12]. The proposed filter
is applied to an L-C-L EMI filter for a 2.2 kW resonant
inverter, and the CM noises are further reduced by 3 to 18 dB
from 150 kHz to 10 MHz. The problem of the CM-todifferential mode noise transformation due to an unbalanced
filter structure is also investigated by the measurements using
a vector network analyzer. However, [12] uses transformers
and transistors in the filter, which reduces the noise reduction
effect at high frequencies.
This paper proposes the current type ACC with Rogowski
coils, which is used as the CM current detection in order tominimize the volume of the current transformer. The
advantage of the Rogowski coil is that the primary winding
becomes just one turn. Moreover, the Rogowski coil caneasily increase the number of turns on the secondary side.
Consequently, the Rogowski coil is smaller than that of thenormal current transformer for CM current detection. The
target frequency range of the CM current reduction is from150 kHz to 30 MHz based on the guidelines of the CISPR
standard. The new contribution of this paper is that the
proposed design method reveals the number of turns and thedetection resistance of the Rogowski coil to respect the CISPR
standard.
The paper is organized as follows: firstly, The circuit
configuration of the current type ACC is described. Secondly,
the design method of a current type ACC according to the
reduction gain of the conducted emission voltage. Finally, theproposed design method is evaluated by the experiment anddiscussed in terms of the noise reduction effect of the
proposed circuit.
II. CIRCUIT CONFIGURATION
Figure 2 shows the circuit diagram of the proposed current
type ACC. The current type ACC includes the CM current
detection using a Rogowski coil, a non-inverting amplifier
circuit, a voltage regulator for the amplifier, and a coupling
capacitor C0. The CM current is detected by the Rogowski coil.
The detected current is converted to a voltage by a resistor on
the secondary side of the Rogowski coil. The non-inverting

Fig.3. Equivalent block diagram of ACC in common mode
circuit.
amplifier circuit amplifies the voltage value and injects acompensation current between the motor and the grand wire
via the coupling capacitor.
Figure 3 shows a block diagram of the current type ACC
in a common-mode equivalent circuit. The current type ACC
is configured as a feedback control system for the CM current
flowing into the power supply side. It suppresses the CM
current by proportional control with a command value of 0 A.
The noise reduction effect depends on the proportional gain,
determined by the detection current-detection voltage ratio
and amplifier gain.
The conducted emission voltage suppression will beinsufficient when the frequency range for each of the circuits(current detection section using Rogowski coils, amplification
section using operational amplifiers, and compensation
current injection section) that make up the current type ACC
is low compared to the compensation frequency band. The
devices and other components that have a significant influenceon the respective frequency bands are described below.
A. Amplifier part
The amplifier section in the conventional ACC often uses
a push-pull voltage follower circuit, limiting the bandwidth [710]. However, high-voltage transistors connected directly to
the DC bus have a low-frequency response. Therefore it isdifficult to achieve high bandwidth ACC. This paper applies
a non-inverting amplifier circuit using a high-performancecurrent feedback operational amplifier to increase the ACC
bandwidth. The power supply part of the amplifier is suppliedwith a DC bus voltage divided by a capacitor and stepped
down to 15 V by a series regulator.

Fig.4. Noninverting amplifier circuit.

Fig.6. Mesurment circuit configulation of ACC frequency
charcteristics.

Table 1. Operational Amplifier Resistance.

Fig.7. Gin characteristics of ACC circuit only.
amplifier is the common mode circuit of the motor andinverter. However, the load is connected to the reference point(DC bus mid-point) of the operational amplifier power
generation circuit, which is composed of a capacitor voltage
divider and regulator.
Fig.5. Gain characteristics of amplifier only.
Figure 4 shows a non-inverting amplifier circuit using thecurrent feedback operational amplifier. The amplifier in the
ACC requires a very wide frequency range and a large output
current. As a result, an output current feedback type amplifier(THS3491 (Texas Instruments)), which operates with amaximum bandwidth of 900 MHz in ideal state operation, isselected. Table 1 shows the amplifier circuit listed in thedatasheet, showing the optimum combination of resistors to
obtain the desired gain. The amplifier circuit for each gain was
created using the resistor values in this table.
Figure 5 shows the frequency characteristics of the noninverting amplifier circuit when the resistors described in thedata sheet are used. The figure shows that all gains areconstant up to 30 MHz in the amplifier circuit alone.
Figure 6 shows the circuit configuration in which thefrequency-gain characteristics of the amplifier of the current
type ACC are measured. The voltage applied to the load wasmeasured when a sinusoidal voltage from 100 kHz to 30 MHz
was input to the amplifier by a function generator. The load
was connected in series with a 50
resistor and a 1 F
capacitor. In actual operation as ACC, the return line of the

Figure 7 shows the measured frequency-gain
characteristics of the ACC circuit. At high-frequency regions,the effect of the wiring inductance increases. The connection
to the circuit increases the wiring inductance and reduces thegain characteristics of the amplifier. However, the amplifier
operates with the designed gain up to 14 MHz at two times
gain, 20 MHz at five times gain, 15 MHz at ten times gain,
and 12 MHz at 20 times gain.
B. Compensation current injection section
The compensation current output by the operational
amplifier is injected into the grand wire via the coupling
capacitor C0. The electromagnetic noise must be reduced tothe specified value determined by the CISPR for 150 kHz to
30 MHz. Thus the capacitance of the coupling capacitor
should be selected so that the impedance of the capacitor at
150 kHz is sufficiently low. In this paper, the value is set to 1
F, approximately 1 at 150 kHz
C. CM current detection section
Current transformers (CT) are widely used in the currenttype ACCs to detect CM currents, as CT uses a magnetic coreand detects CM currents according to the ratio of primary andsecondary windings, making it easy to design a high detection

Fig.8. Rogowski coil conceptual diagram.
gain. However, the number of primary windings and magnetic
cores used limit the frequency band that is detected. For thisreason, this paper applies the Rogowski coil to broaden the
bandwidth of the detection unit of the ACC and expand the
reduction range of the conducted emission voltage. The
detailed design of the Rogowski coil is described in the next
chapter.
III. DESIGN OF ROGOWSKI COILS
Figure 8 shows the principle diagram of a Rogowski coil.
The coupling between the primary winding (the winding
through which the CM current flows) and the secondary
winding (the Rogowski coil) does not necessarily have to behigh when applying a Rogowski coil. The CISPR defines theallowable conducted emission voltage in the band between
150 kHz and 30 MHz; the evaluation of the characteristics ofthe voltage output to the detected current at the detection unit
is carried out in the band between 150 kHz and 30 MHz. The
evaluation of the characteristics of the output voltage
concerning the detected current of the detection unit is carriedout in the 150 kHz to 30 MHz band.
Figure 9 shows the design flow of the Rogowski coil. In
the design of the Rogowski coil, the cutoff frequency must be
designed sufficiently low compared to 150 kHz for the ACC
to have a sufficient reduction effect in all conducted noise
measurement frequency bands. In addition, the detection
current-to-detection voltage ratio should be designed to behigh to increase the noise reduction effect of the ACC. The
average flux density B at the cross-section of the Rogowski
coil is expressed as

Fig.9. Design flow of ACC
relationship between the power V at both ends of the
Rogowski coil and the secondary side current i2 is expressedby the following equation.
....................................................................

.............................................................

where i1 is the CM current to be measured, i2 is the current
flowing in the Rogowski coil, N is the number of coil turns,
and rR is the radius of the circle formed by the Rogowski coil.
The electromotive force V induced at both ends of the
Rogowski coil is expressed as...................................

where SR is the cross-sectional area of the Rogowski coil. If
the output resistance connected to the secondary side is R andthe parasitic resistance of the Rogowski coil is r, theThe self-inductance L of the Rogowski coil is expressed by
the following equation............................................................... (4)Substituting (3) and (4) into (2), the differential equation
concerning voltage is obtained from the following differential
equation concerning voltage.......................................( )..................................................... (6)where (R + r)/L is the dimension of angular frequency, so thecutoff frequency is expressed by the following equation.......................................................................

..................................................

Fig.10. Rogowski coil.
First, the window area of the core is determined by thecurrent flowing in the main circuit. The cross-sectional area of
the wiring, Aw, is expressed by the following equation,
assuming a DC idc and winding current density J.
............................................................................

The load motor is 200 V, 750 W. The DC side current at
rating is assumed to be 3.5 A, and the winding current density
is designed to be 4 A/mm2. Since a maximum current of 3.5 A
flows in the circuit, the cross-sectional area of the wiringneeds to be at least 0.875 mm2 according to formula (9), taking
into account the fact that two wires pass through to detect theCM current, the wiring covering, etc. Furthermore, a core withan inner diameter of 33.2 mm2 was selected to allow a margin,
taking into account the ease of winding the secondary winding
and the availability of cores.
Next, the number of turns of the Rogowski coil isdetermined. To detect CM currents from the low-frequency
range, the bandwidth of the Rogowski coil must be low, andthe number of turns must be increased to increase theinductance from equation (7). Therefore, the magnetic path
length of the core selected this time was 56 mm, and 120 turnsof 0.4 mm enameled wire were used. For the core material, aferrite core with a magnetic permeability r of 450 at 950 kHz
was selected because of the need to design a high selfinductance.
Finally, the detection resistor R is designed. The detection
resistor was set to 2400
so that the cutoff frequency
calculated by equation (7) is sufficiently low relative to themeasurement range of 150 kHz, and the detection gain
calculated by equation (8) is larger. The design with theparameters determined above resulted in a cutoff frequency of
17 kHz and a detection current-to-detection voltage ratio of 20
times, which were sufficiently low compared to the cutoff
frequency of 150 kHz so that the designed Rogowski coil isused as a CM current detection unit. The designed Rogowski
coil is used above the CISPR standard of 150 kHz.
Figure 10 shows the photo of the created Rogowski coil.
Table 2 shows the parameters of the Rogowski coil. The outershape of the Rogowski coil, including the windings, is 26 mm,
and its weight is 28.6 g. The Rogowski coil in the detection
section detects the CM current flowing in the main circuit,
converts the current voltage on the secondary side, and outputs
it to the amplifier.
Figure 11 shows the characteristics of the detected currentdetected voltage ratio of the Rogowski coil as a function of
frequency change. The measurement results show that a
detection gain of 25dB was obtained for the Rogowski coil.

However, an error of 3.8% occurred due to changes inmagnetic permeability and differences in wiring impedancecompared to the design value. The cutoff frequency was 20
kHz, which is sufficiently small compared to 150 kHz. The
detection gain is constant up to 30 MHz, indicating that theCM current detection unit is used in the noise measurement
range from 150 kHz to 30 MHz with the designed detectiongain.
IV. EXPERIMENTAL RESULTS
Figure 12 shows the measurement layout of a conductedemission voltage. As the layout for measuring conductedemission voltages that are defined by CISPR 16, comparative
measurements were carried out under conditions close to thedefined measurement method. The inverter and the induction
motor were placed 40 cm from the ground surface on support.
A spectrum analyzer measures an electromagnetic conductedemission voltage reaching the LISN as the conducted emission
voltage.
Figure 13 shows the CM current waveforms under theexperimental measurements. Figure 13 (a) shows the CM
current waveform without ACC. Figure 13 (b) shows the
waveforms of the measured results of the CM current between
inverter and motor, between ACC and inverter, and between
ACC and power supply when the amplifier gain is multipliedby 20. The CM current resonating at 3.3 MHz flows to the
grand wire at a maximum of 400 mA without the ACC. On
the other hand, CM current flows through the motor, amplifier,amplifier power supply, and inverter paths, reducing the CM
current flowing to the LISN side with ACC.
Figure 14 shows the comparison of the measured
conducted emission voltage with and without ACC. The
conducted emission voltage was measured under four
conditions of the amplifier gain with ACC: the amplifier gain
is two times, five times, ten times, and 20 times. The
conducted emission voltage of 90.7dB is measured at 2.7 MHz
without ACC. The conducted emission voltage decreased inall bands from 150 kHz to 30 MHz with ACC. From this, thecurrent type ACC with the designed Rogowski coil is effective
for noise reduction in all frequency bands of the measurement

Fig.12. EMI evaluation layout.
(a) Design value.

(a) Without ACC.
(b) Measured value.
range. Also, when the ACC was operated, a reduction of
17.9dB was obtained at 2.7 MHz when the amplifier gain was
two times, 24.4dB at five times, 27.0dB at ten times, and35.9dB at 20 times, confirming that the noise reduction effectis improved by increasing the amplifier gain and designing ahigher gain of the ACC. Figure 12 (d) shows the conductedemission voltage when the amplifier gain is increased by 20
times and the conducted emission voltage limits specified in
CISPR12. The figure shows that the conducted emission
voltage reduced by ACC exceeds the specified value definedby CISPR at around 3 MHz.
To further improve the noise reduction effect of ACC, theresistance value of the non-inverting amplifier circuit waschanged, as shown in Table 3.
Figure 15 shows the results of the frequency response
measured at 30 times the gain with the circuit configuration
shown in Fig. 6. The figure shows that the gain is lower at 10
MHz and above. However, the gain is higher than 20 times inall frequency bands, indicating that the noise reduction of
ACC is expected to be higher.
Figure 16 shows the measured conducted emission voltage
when the amplifier gain is increased to 30 times. The figure
shows that the amount of noise reduction increased in all
frequency ranges compared to when the amplifier gain wasincreased to 20 times and that the CISPR-specified values,
which were exceeded when the amplifier gain was increased
to 20 times, were satisfied.
V. CONCLUSION
This paper proposed a Rogowski coil design for use in thedetection section of a current type ACC. The cutoff frequency(b) With ACC.
Fig.13. CM current waveforms.
was designed to be sufficiently low compared to 150 kHz. It
was confirmed that the noise reduction effect of ACC was
expanded by designing a wider frequency band. The
experimental results demonstrated a maximum noise
reduction of 39.0dB V in the frequency range of 150 kHz to
30 MHz, which is the frequency band specified by CISPR. In
addition, the conducted emission voltage was reduced moreby increasing the ACC gain, which is calculated by the ratioof the detected current to the voltage of the Rogowski coil andthe amplifier gain. The experimental results show that thenoise reduction effect was confirmed in all frequency bands
between 150 kHz and 30 MHz, the frequency band specified
in the CISPR, and that the Rogowski coil designed in thisstudy is sufficiently effective in reducing conducted noise.
In the future, the current-type ACC will be designed toachieve arbitrary noise reduction through a more detailed
design.

Table 3. Operational Amplifier Resistance. (Gain:30 times)(a)Fig.15. Amplifier gain characteristics. (Gain: 30 times)(b)

Fig.16. Conducted emission voltage. (Gain: 30 times)
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