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374 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 29, NO. 1, JANUARY 2014
A Space-Vector Modulation Methodfor Common-Mode Voltage Reduction in
Current-Source ConvertersJian Shang, Student Member, IEEE, and Yun Wei Li, Senior Member, IEEE
AbstractThe common-mode voltage (CMV) produced from aconverter system is a source of many problems, e.g., in the mo-tor drive system, CMV might appear at the neutral point of themotor stator windings with respect to the ground and induce de-structive bearing current. Reduced CMV space-vector modulation(RCMV SVM) methods have been proposed in both voltage-sourceconverter (VSC) and current-source converter (CSC) systems. Theavailable RCMV SVMs reduce the CMV by avoiding using zero-state vectors. However, this will lead to some negative effects, suchas shrink of modulation index range, increase of switching fre-
quencies, bipolar line-to-line voltage pulse patterns in VSCs, andpower quality performance deterioration. In this paper, a RCMVSVM method for CSCs is proposed. By allowing the use of zero-state vectors, the proposed RCMV SVM still produces much lowerCMV. However, its other performance indices, such as switchingfrequency and harmonic performance, are unaffected and com-parable to the conventional SVMs. The effectiveness of the pro-posed RCMV SVM for CSCs is verified in the simulations andexperiments.
Index TermsCurrent-source converter (CSC), power quality,reduced common-mode voltage (CMV) SVM, zero-state vector.
I. INTRODUCTION
ALTHOUGH voltage-source converter (VSC) has been
the preferred solution in many industrial applications,
pulsewidth modulated (PWM) CSCs could be a good alterna-
tive to VSC in the wind energy power generation, superconduc-
tor magnetic energy storage (SEMS), and HVdc transmission
systems. Currently, in the medium-voltage drive systems, trans-
formerless PWM CSCs have already become a very popular in-
dustrial solution [1]. Theconfiguration of such a system is shown
in Fig. 1. The transformerless CSC drive system has advantages
over the conventional drive system, such as higher power den-
sity, lower cost, and higher power efficiency. However, due to
the absence of the input isolation transformer, common-mode
voltage (CMV) at the neutral point of the motor stator windings
Manuscript received December 4, 2012; revised February 10, 2013; acceptedFebruary 11, 2013. Date of current version July 18, 2013. This work was pre-sented at the IEEE Applied Power Electronics Conference and Exposition, LongBeach, CA, USA, March 1721, 2013. Recommended for publication by Asso-ciate Editor B. Wu.
The authors are with the Department of Electrical and Computer Engi-neering, University of Alberta, Edmonton, AB T6G 2V4, Canada (e-mail:
jian.shang@ualberta.ca; yunwei.li@ualberta.ca).Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.Digital Object Identifier 10.1109/TPEL.2013.2248025
with respect to the ground can induce bearing current and lead
to the bearing damage of the motor [2][4].
To mitigate CMV in CSCs, the neutral points of the input and
output capacitors are connected to clamp the CMV to nearly
zero.To limit the large circulatingcommon-mode current caused
by this connection, an integrated dc choke with both differential
and common-mode windings is used [5]. The size of the dc
choke can be reduced if the CMV produced by the rectifier and
inverter is minimized. One of the most effective methods forCMV reduction is to modify the PWM patterns.
Most available RCMV PWM schemes are developed for
VSCs and they reduce CMV by avoiding the use of zero-state
vectors [6]. These RCMV space-vector modulations (SVMs)
can be categorized as active zero-state modulation (AZSM)
[7][9], remote-state modulation (RSM) [10], and near-state
modulation (NSM) [11], [12]. Although those nonzero-state
modulation methods can effectively reduce CMV, they are all
subject to some problems, such as the shrink of modulation in-
dex range, bipolar line-to-line voltage pulse patterns, increased
switching frequencies, higher dc-link ripples, and power qual-
ity performance deterioration. Those drawbacks make RCMV-
PWM for VSCs difficult to be applied in the industry.As for the PWM of CSCs, selective harmonic elimination
(SHE) PWM is popular in the medium-voltage high-power drive
systems due to SHE PWMs excellent harmonic performance
with low switching frequencies. However, SVM, as a kind of
online modulation method, has been used to dampLC resonance
[13], [14], minimize dc-link current [15], control input power
factor [16], [17], etc. In [18], the authors introduce the nonzero-
state modulation concept for VSCs into CSCs. However, the
problems observed in RCMV SVMs for VSCs still exist in
those nonzero-state RCMV SVMs for CSCs.
Two most importantperformanceindices forPWM patterns in
the medium-voltage drives and grid-tied converters are switch-ing frequency [19][21] and harmonic performance [22][24],
which are also two important considerations in the design of
RCMV SVM for CSCs. A novel RCMV SVM method for CSR
and CSI is proposed in this paper to reduce the CMV by se-
lecting proper zero-state vectors instead of completely avoiding
using them. To better illustrate the working principles of the pro-
posed RCMV SVM for CSCs, Section II presents the definition
of CMV in a CSC drive system and the CMV values associated
with all the space vectors. Section III describesthe working prin-
ciples of the proposed RCMV SVM in detail, including zero-
state vectors selection, sequences selection for switching fre-
quency minimization, and single-sequence rule for harmonic
0885-8993/$31.00 2013 IEEE
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Fig. 1. Configuration of transformerless current-source drive system.
performance optimization. To verify the effectiveness of the
proposed RCMV SVM for CSCs, Sections IV and V present
the simulation and experimental results for the RCMV SVM
and the comparison results with conventional three-segment and
five-segment SVMs. The results show that the CMV can be re-duced up to 50% compared to the conventional SVM methods.
The switching frequency and harmonic performance of the pro-
posed RCMV SVM are comparable to the conventional SVMs.
II. CMVIN CURRENT-SOURCECONVERTERS
A. CMV in Current-Source Converters
The CMV produced in the CSC system, as shown in Fig. 1,
consists of CMVin the current-source rectifier (CSR) side vcm rand CMV in the current-source inverter (CSI) sidevcm i , whichcan be defined, respectively, by
vcm r = vp1g +vn1g2
(1)
vcm i =vp2o + vn 2o
2 (2)
where vp1g and vn1g are the voltages at points p1 and n1,respectively, with respect to the ground, and vp2o andvn 2oare the voltages at points p2 andn2, respectively, with respectto the neutral of the induction motor.
If the differential inductance in the positive dc rail is equal to
that in the negative dc rail, the CMV in the whole drive system
vog can be given by
vog =vcm r vcm i = vp1g +vn 1g2
vp2o+ vn2o2
.
(3)
When PWM control is applied to the CSC drive systems,
vcm r , vcm i , andvog can be expressed as
vcm r = [ S1 + S4 S3 + S6 S5 + S2].
0.5va
0.5vb
0.5vc
(4)
vcm i = [ S1 + S
4 S
3 + S
6 S
5 + S
2].
0.5vu
0.5vv
0.5vw
(5)
Fig. 2. Operating principle of SVM for CSCs and space vectors definition.
vog = [ S1 + S4 S3 + S6 S5 + S2].
0.5va
0.5vb
0.5vc
[ S1 + S
4 S
3 + S
6 S
5 + S
2].
0.5vu
0.5vv
0.5vw
(6)
whereS1S6 are the switching states of CSRs switching de-vices,S1S
6 the switching states of CSIs switching devices,
va , vb andvc the phase voltages of the grid, andvu , vv , andvware the phase voltages of the motor stator [25], [26].
B. CMV Associated With Space Vectors
Fig. 2 illustrates the operating principle of SVM for CSCs
and the space vectors definition. According to (4) and (5), the
instantaneous value of CMV associated with the space vectors
can be obtained and summarized in Table I using CSR as an
example. The CMV peak value is determined by many factors,
such as delay angle for CSR (in a current-source drive, the dc-
link current is usually regulated by the delay angle control in the
CSR side [1]),LC filter capacitance, dc-link current, modulation
index, and CSI load power factor. In the conventional SVMs,
the maximum CMV peak value produced by zero-state vectors
in the SVM for CSR or CSI can be as high as the peak value of
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376 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 29, NO. 1, JANUARY 2014
TABLE ICMV ASSOCIATED WITHSPACEVECTORS INSVM FOR CSCS
phase voltage of grid side|Vg |or that of motor stator side|Vm |,while the maximum CMV peak value produced by active-state
vectors is equal to |Vg | /2or |Vm | /2. Thus, the maximum CMVpeak value in the drive system|Vog |is|Vg |+|Vm |.
The recently proposed RCMV SVMs for CSCs in [18] re-
duce CMV by avoiding the use of zero-state vectors, resultingin a maximum CMV peak value as high as |Vg | /2or |Vm | /2.However, instead of completely avoiding the use of zero-state
vectors, another effective method for CMV reduction is to se-
lect the zero-state vector producing the lowest CMV from the
three ones in each SVM sample. In this way, the maximum
CMV peak value produced by the proposed RCMV SVM can
be lower than|Vg | /2or|Vm | /2as well, but it will not cause theaforementioned negative effects in those nonzero-state RCMV
SVMs.
III. PROPOSEDRCMV SVM FORCSCS
The design of the proposed RCMV SVM is discussed in
this section. The zero-state vectors selection rule is proposed to
reduce CMV and a sequence selection rule is then applied to
minimize switching frequencies. The single-sequence rule is
also applied in some cases to realize the harmonic performance
optimization.
A. Zero-State Vectors Selection Rule for CMV Reduction
The zero-state vectors selection rule is that the zero-state vec-
tor producing the lowest CMV among the three zero-state vec-tors at any sampling period would be selected. For example, in
Fig. 3, the absolute value of phase B voltage is the lowest among
the three phase voltages during Ta , so the CMV produced byI0b (S3 , S6 )would be the lowest among the three zero-state vec-
tors. Therefore,I0b (S3 , S6 )should be used to minimize CMV
during Ta . According to this zero-state vectors selection rule,the selected zero-state vectors and the corresponding phase volt-
ages in one fundamental period are shown in Fig. 3. Using this
zero-state vectors selection method, the maximum CMV peak
value produced by zero-state vectors would be half of the peak
value of ac-side phase voltages, which is same as that produced
by active-state vectors.
Fig. 3. Selected zero-state vectors in RCMV SVM in each instant of onefundamental period.
Fig. 4. Conventional SVM sequences for CSCs: (a) three-segment sequenceand (b) five-segment sequence.
B. Sequence Selection Rule for Switching Frequency
Minimization
Six types of SVM sequences for CSCs have been compared
in [27], where it shows the five-segment SVM sequence hasthe best harmonic performance in high modulation index range,
while the three-segment SVM sequence has the best in low
modulation index range. The conventional three-segment and
five-segment SVM sequences are shown in Fig. 4. According
to the analysis in [27], the sampling frequencies for SVM of
CSCs have to be set as an integral multiple of 6 f1 (wheref1 isthe fundamental frequency) in order to synchronize the PWM
waveform with the fundamental frequency and eliminate even
and triplen harmonics. In order to obtain low switching frequen-
cies fit for high-power application, the sampling frequencies for
conventional three-segment and five-segment SVMs are 18f1and 24f1 , respectively.
To avoid the increase of switching frequencies compared tothe conventional SVMs, the sequence for RCMV SVM should
be redesigned since the zero-state vectors selection rule has
changed as compared to the conventional SVMs. For instance,
bothI0b and
I0c (instead of
I0a ) could be possibly selected in
sector I according to the zero-state vectors selection rule for
CMV reduction. In this case, there will be extra switching if the
three-segment sequence is applied in RCMV SVM. To avoid
the increase of switching frequency, two types of five-segment
sequences, as shown in Fig. 5, should be applied according to
the selected zero-state vectors. Specifically, ifI0 has one com-
mon on-state switch withIn+ 1 , sequence (a) should be selected.
Otherwise, sequence (b) should be selected. In some cases,
I0
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Fig. 5. Two sequences for RCMV SVM. Sequence (a)applied whenI0 has
one common on-state switch withIn + 1 . Sequence (b)applied when
I0 has
one common on-state switch withIn .
Fig. 6. Selected zero-state vectors and sequences in RCMV SVM for CSR
(= 0
).
may have one common on-state switch with both active-state
vectors in that sector (such asI0a in sector I), so both sequences
(a) and (b) are eligible in terms of switching frequency mini-
mization. To optimize the harmonic performance, the sequence
selection for this type of zero-state vector should abide by the
single-sequence rule (only one type of sequence is applied
during one fundamental period), which would be explained in
detail later. Note that the five-segment sequence with the active-
state vector positioned in the center, as shown in Fig. 4(b), can
be also applied in RCMV SVM. It has a similar performance
with those sequences in Fig. 5, where the zero-state vector ispositioned in the center.
C. Selected Zero-State Vectors and Sequences for SVM in CSR
Control
According to the aforementioned zero-state vectors and se-
quence selection rules, the selected zero-state vectors and se-
quences in RCMV SVM in CSR control are shown in Figs. 68
when the delay angle is 0, 30, and 60, respectively.Fig. 6 shows the selected zero-state vectors and sequences
in all the sectors when the delay angle is 0. The phase A
voltage is around the peak value in sector I when the delay
angle is 0
, so the peak value of CMV produced by
I0a in the
Fig. 7. Selected zero-state vectors and sequences in RCMV SVM for CSR(= 30).
Fig. 8. Selected zero-state vectors and sequences in RCMV SVM for CSR(= 60).
conventional SVMs would be as high as the peak value of phase
voltages. According to the proposed zero-state vectors selection
method for CMV reduction,I0b and
I0c (instead of
I0a in the
conventional SVMs) should be applied successively to reduce
the CMV in sector I. Both types of five-segment sequence inFig. 5 are used according to the sequence selection rule for
switching frequency minimization.
Fig. 7 shows the selected zero-state vectors and sequences in
all the sectors when the delay angle is 30. According to the
zero-state vector and sequence selection rules discussed previ-
ously, the sequence (b) of RCMV SVM is always used in one
fundamental period.
Fig. 8 shows the selected zero-state vectors and sequences in
all the sectors when the delay angle is 60. Different from the
two previous cases, here one of the desired zero-state vectors
in one sector has one common on-state switch with both two
active-state vectors in the same sector. For example,
Ioa (S1 , S4 )
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Fig. 9. 5th and 7th harmonics comparison of the switching current Iw and THD comparison of line currentIs when Sequence (a) and (b) and Single-sequence(b) is applied, respectively (= 60): (a) 5th harmonics ofIw, (b) 7th harmonics ofIw, and (c) THD ofIs .
TABLE IISELECTEDSEQUENCES FOR ALL THEPOSSIBLEDELAYANGLESUNDER THESEQUENCESELECTIONRULE FORSWITCHINGFREQUENCYMINIMIZATION
selected in sector I has the common on-state switch S1 withboth of the active-state vectors,
I1 (S1 , S6 )and
I2 (S1 , S2 ). A s a
result, this zero-state vector can be used to build either sequence(a) or sequence (b). On the other hand, the other selected zero-
state vectorIob (S2 , S5 ) in sector I will require sequence (b)
to avoid additional switching. Therefore, there are two possible
sequence combinations in this case: 1) only sequence (b) is used
and 2) both sequences (a) and (b) are used. Here, we name these
two possibilities as Single-sequence (b) and Sequence (a)
and (b), respectively.
Fig. 9(a) and (b) shows the 5th and 7th harmonics of the
switching current Iw , when Sequence (a) and (b) and Single-sequence (b) are used, respectively. Fig. 9(c) shows the THD
of line currents Is with an LC cutoff frequency of 3.33 p.u.(This cutoff frequency of CSRs LC filter is selected to avoid
amplification of the 5th harmonic current [27].) As shown, 5thand 7th harmonics ofIw are lower and THD ofIs is better ifSingle-sequence (b) is applied. It means that rotational use of
sequences (a) and (b) in one fundamental period will deteriorate
the harmonic performance. Moreover, the switching frequency
is lower if Single-sequence (b)is applied, because switching
between sequences (a) and (b) involves more devices. As a
consequence, Single-sequence (b) will be a better option in
this case. Here, the rule that only one type of sequence in one
fundamental period is selected to maintain a better harmonic
performance is named as single-sequence rule.
Table II shows the selected sequences for all the possible
delay angles under this sequence selection rule.
D. Single-Sequence Rule for Harmonic Performance
Optimization
As discussed in the previous section, the use of sequences(a) and (b) in combination would deteriorate the harmonic per-
formance. From Table II, we can find that the single-sequence
rule is violated in the delay angle ranges of30
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Fig. 10. Selected zero-state vectors and sequences based on the single-
sequence rule (= 15
).
TABLE IIISELECTEDSEQUENCES FOR ALL THEPOSSIBLEDELAYANGLES INRCMV
SVM USINGSINGLE-SEQUENCERULE
sequence is applied in one fundamental period, when the delay
angle is in those two ranges. With this method, the switching fre-
quency would increase, but CMV would be kept lower than half
the peak value of ac-side phase voltage and harmonic perfor-
mance would not be deteriorated. Since the increased switching
frequency is not favorable in high power CSC drives, this alter-
native method will not be discussed in detail.
Table III shows the selected sequences for all possible delay
angles in RCMV SVM using single-sequence rule.
E. Switching Frequency Analysis of the Proposed RCMV SVMfor CSCs
According to the previous analysis, the proposed RCMV
SVM, compared with the conventional five-segment SVM, has
no extra switching during switching states transitions in one
sector if their sampling frequencies are the same. The extra
switching can only happen during the sector crossing. Fig. 11
illustrates the possible device switching of the proposed RCMV
SVM in the sector crossing from sector I to sector II. If the
sampling frequency of RCMV SVM is an even multiple of 6 f1(just like conventional five-segment SVM), there are three pos-
sible cases during the sector crossing as shown in Fig. 11(a)(c),
respectively, depending on the selected zero-state vectors in the
Fig. 11. Possible device switching of the proposed RCMV SVM in the sectorcrossing from sector I to sector II.
sector crossing and the moment of the sector crossing. The sec-
tor crossing in Fig. 11(a) and (b) happens in the center of the
sequence, while that in Fig. 11(c) happens in the end of the
sequence.
Fig. 11(a) shows that the selected zero-state vectors for the
last sample in sector I and the first sample in sector II are bothI0c . This zero-state vector selection method, which has beenapplied in the conventional five-segment SVMs in [27], leads
to minimum device switching. This scenario in Fig. 11(a) couldpossibly happen in the proposed RCMV SVM ifI0c is thezero-state vector needed for CMV reduction during the sector
crossing. The switching frequency in this case is 8f1 if thesampling frequency is 24f1 .
Since the freedom of the zero-state vectors selection has been
used for CMV minimization in RCMV SVM, the device switch-
ing minimization, like in the case shown in Fig 11(a), cannot
be guaranteed all the time. However, the increase of switching
frequency, which is one fundamental frequency, is not signifi-
cant. Other zero-state vectors, likeI0a in Fig. 11(b), could be
selected to reduce CMV during the sector crossing. Compared
to the case in Fig. 11(a), one extra device switching could hap-
pen in Fig. 11(b) between I0 and In+ 1 in the first sample ofsector II. As a result, the switching frequency in this case is 9f1if the sampling frequency is 24f1 .
As shown in Fig. 11(c), the sector crossing can also happen in
the end of the sequence. There is one switching during the sector
crossing under this scenario (which is similar to the situation that
conventional five-segment SVM in Fig. 4(b) with sector crossing
at the center of the sequence). The switching frequency in this
case is also 9f1 if the sampling frequency is 24f1 . Furthermore,if two types of sequences in RCMV SVM are used in one
fundamental period, this extra switching would happen in the
moment of sequences (a) and (b) transition instead of sector
crossings.
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TABLE IVMAINCIRCUITPARAMETERS OFCSR SYSTEM IN THE
SIMULATION ANDEXPERIMENT
Therefore, the switching frequency of RCMV SVM is 8f1or 9f1 depending on the selected zero-state vectors in the sectorcrossing and the moment of sector crossing if the sampling fre-
quency is 24f1 . Thus, under the same sampling frequencies, theswitching frequency of RCMV SVM is equal to or f1 different
from conventional five-segment SVM.
F. Implementation of RCMC SVM in the CSR and CSI control
Similar to the conventional five-segment SVM, each five-
segment sequence of the proposed RCMV SVM needs two
samples to complete. The sectors and active-state vectors are
updated every sample, whereas the zero-state vectors are up-
dated before the beginning of the sequence (two samples) and
kept unchanged during the two samples. In this way, good con-
trol accuracy could be obtained and the switching frequency
would not increase.
In the CSI application, the number of samples in one cycle of
SVM (or the sampling frequency) is changing with the funda-mentalfrequency, which is related to themotor speed.Moreover,
there is no delay angle control in the CSI control. However, these
two differences from CSR control would not affect the RCMV
SVMs application in the CSI side. In the application in the CSI
side, phase voltages of the motor stator or CSI output capacitor
Vm can be detected to determine which zero-state vector andsequence should be applied.
To determine whether the single-sequence rule for har-
monic performance optimization should be applied, the equiv-
alent delay angle (or voltage current displacement angle) in the
CSI control should be known. It depends on the CSI output ca-
pacitance, motor parameters, and motor operating conditions.This equivalent delay angle in CSI control should be defined as
the phase displacement angle ofVm (jw)/Im w (jw), whereVmis the phase voltage of motor stator andIm w is the CSI outputswitching current.
IV. SIMULATIONVERIFICATIONS
The proposed RCM SVM method is first tested in MATLAB/
Simulink simulations. The CSR testing system parameters in
the simulation are shown in Table IV.
Figs. 12 and 13 show the comparison of the CMV, switch-
ing current, and line current under the operating conditions
of ma = 0.7 and = 0
and ma = 0.3 and = 0
, re-
spectively. According to previous analysis, the sampling fre-
quency for the conventional three-segment SVM is 1080 Hz,
while that for the conventional five-segment and RCMV SVM
is 1440 Hz. In the figures, 3Seg (such as CMV_3Seg)
and 5Seg (such as CMV_5Seg) represent conven-
tional three-segment and five-segment SVMs, respectively,
while RCMV (such as CMV_RCMV) and RCMV_TF
(such as CMV_RCMV_TF) represent the proposed RCMV
SVM without and with the single-sequence rule applied,
respectively.
Table V summarizes the simulation results. In Table V,
Iw 5/Iw 1 and Iw 7/Iw 1 represent the 5th and 7th harmon-ics over the fundamental current in the switching current. fs represents the switching frequency and CMV_pk represents
the peak value of CMV. It should be noted that the CMV pro-
duced by conventional SVMs is a bit higher than the peak value
of the grid side phase voltage. This is due to the voltage distor-
tion in the CSRs connection point with the LC filter, which is
caused by harmonic current flowing through the line inductor.
From the simulation results, we can find that the CMV producedby the proposed RCMV SVM is almost half of that produced
by conventional SVMs.
As expected, the switching frequency of RCMV SVM is
60 Hz higher than the conventional five-segment SVM andequal
to the conventional three-segment SVM. Since the delay angle
of 0 is in the range where single-sequence rule can be applied
to avoid harmonic performance deterioration, the performance
of the RCMV SVM with and without using single-sequence
rule is also compared. The RCMV SVM using the single-
sequence rule produces less low-order harmonic currents but
a bit higher CMV than that without using the single-sequence
rule.Fig. 14 is the comparison results of THD ofIs versus mawhen is 0, 30, and 60, respectively, which is tested basedon the simulation parameters in Table IV. This comprehensive
harmonic performance comparsion verifies that the proposed
RCMV SVM has a simialr harmonic performance with the con-
ventional five-segment SVM.
V. EXPERIMENTALVERIFICATIONS
The proposed RCMV SVM for CSC is verified in a 10 kVA
CSR prototype system in the lab. The CSR control plat-
form is designed based on a dSPACE (DS1103)-CPLD (Xilinx
XCR3064XL) system. The DS1103 PPC controller generatesthe control signals and the CPLD is used to convert the electrical
signals from the DS1103 to the optic signals for driving inte-
grated gate-commutated thyristors (IGCTs). The experimental
system parameters in the main circuit are shown in Table IV.
The effectiveness of RCMV SVM in the CSR is verified un-
der three operating conditions, i.e., ma = 0.7 and = 0,
ma = 0.7 and = 30, and ma = 0.7 and = 60, re-spectively. Its performance is compared with the conventional
three-segment and five-segment SVM. The sampling frequen-
cies of the conventional three-segment and five-segment SVMs
and RCMV SVM are same as those in the simulation. When
the delay angle is 0
, single-sequence rule can be applied to
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Fig. 12. Simulation results comparison of conventional three-segment SVM, conventional five-segment SVM, RCMV SVM using Sequence (a) and (b) andRCMV SVM using Single-sequence (b) under the operating condition ofma =0.7 and = 0
: (a) CMV, (b) switching current, and (c) line current.
Fig. 13. Simulation results comparison of conventional three-segment SVM, conventional five-segment SVM, RCMV SVM using Sequence (a) and (b) andRCMV SVM using Single-sequence (b) under the operating condition ofma =0.3 and = 0
: (a) CMV, (b) switching current, and (c) line current.
maintain good harmonic performance. As for the 30 and 60
delay angle, the single-sequence rule is already satisfied ac-
cording to the sequence selection rule for switching frequency
minimization.
A. Operating Condition ofma =0.7 and=0
Figs. 15 and 16 present the CMV, switching current, and line
current waveforms comparison under the operating condition of
ma = 0.7 and = 0. Table VI summarizes the experimen-
tal results of the four types of SVMs. The experimental results
show that the peak value of CMV produced from conventional
three- and five-segment SVMs [as shown in Fig. 15(a) and (b)] is
approximately equal to the peak value of the line phase voltage,
while that produced from RCMV SVM using Sequence (a) and
(b) [as shown in Fig. 15(c)] is approximately half of the peak
value of the line phase voltage. From Table VI, it can be seen that
the RCMV SVMusing Sequence(a) and(b) canproduce more
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TABLE VSIMULATION RESULTSCOMPARISON OFFOURTYPES OFSVM UNDER THEOPERATINGCONDITIONS OFm a = 0.7 AND = 0
ANDm a = 0.3 AND = 0
Fig. 14. THD of line current versusma comparison: (a) = 0, (b) = 30, and (c) = 60.
Fig. 15. CMV waveforms under the operating condition ofm a = 0.7 and = 0. (a) Conventional three-segment SVM. (b) Conventional five-segmentSVM. (c) RCMV SVM using Sequence (a) and (b). (d) RCMV SVM usingSingle-sequence (b).
low-order harmonics and deteriorate the harmonic performance
compared with the conventional five-segment SVM. However,single-sequence rule can be applied to improve its harmonic
performance by sacrificing the CMV reduction capability a lit-
tle. The peak value of CMV produced from RCMV SVM using
Single-sequence (b) [as shown in Fig. 15(d)] is a bit higher
than RCMV SVM using Sequence (a) and (b) but still much
lower than the conventional SVMs. As for the harmonic perfor-
mance,the low-order,i.e., 5th and7th, harmonics produced from
RCMV SVM using Single-sequence (b) are almost the same
as those produced from the conventional five-segment SVM.
This verifies the effectiveness of the single-sequence rule for
harmonic performance optimization.
The experimental waveforms comparison of switching cur-
rent verifies once again that switching frequencies of theconven-
Fig. 16. Switching current Iw and the line current Is under the operatingcondition ofma = 0.7 and = 0
. (a) Conventional three-segment SVM.
(b) Conventional five-segment SVM. (c) RCMV SVM using Sequence (a) and(b). (d) RCMV SVM using Single-sequence (b).
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SHANGANDLI:SPACE-VECTORMODULATIONMETHODFORCOMMON-MODEVOLTAGEREDUCTIONIN CURRENT-SOURCE CONVERTERS 383
TABLE VIEXPERIMENTALRESULTSCOMPARISON OFFOURTYPES OFSVM UNDER THEOPERATINGCONDITIONS OFma =0.7 AND = 0
,ma =0.7 AND = 30,AND
ma =0.7 AND = 60
Fig. 17. CMV waveforms under the operating condition ofm a = 0.7 and= 30. (a) Conventional three-segment SVM. (b) Conventional five-segment
SVM. (c) RCMV SVM.
tional three-segment SVM, the RCMV SVM using Sequence
(a) and (b), and the RCMV SVM using Single-sequence (b)
are all equal and only 60 Hz higher than conventional five-
segment SVM.
B. Operating Condition ofma =0.7 and=30
Figs. 17 and 18 present the CMV, switching current, and line
current waveforms comparison under the operating condition of
ma =0.7 and= 30. Table VI summarizes the experimentalresults of the three types of SVM. The proposed RCMV SVMs
CMV reduction capability is also verified in this case. The CMV
produced by RCMV SVM is around 50% of that produced
by conventional SVMs. Moreover, RCMV SVMs switching
frequency is still 540 Hz. The harmonic performance of the
RCMV SVM is also similar with the conventional five-segment
SVM.
C. Operating Condition ofma =0.7 and= 60
Figs. 19 and 20 present the CMV, switching current, and line
current waveforms comparison under the operating condition
ofma = 0.7 and = 60. Table VI summarizes the experi-
mental results of the three types of SVM. The effiectiveness of
Fig. 18. Switching current Iw and the line current Is under the operatingcondition ofm a = 0.7 and = 30
. (a) Conventional three-segment SVM.(b) Conventional five-segment SVM. (c) RCMV SVM.
the RCMV SVM is also verified in this case. The CMV pro-
duced by RCMV SVM is also around half of the peak value of
ac-side phase voltage. Note that CMV produced from conven-
tional three-segment SVM is as low as the CMV produced from
the RCMV SVM. It is because the zero-state vectors utilized
in the conventional three-segment SVM are just the ones pro-
ducing low CMV in this case. Likewise, neither the switching
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384 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 29, NO. 1, JANUARY 2014
Fig. 19. CMV waveforms under the operating condition ofm a = 0.7 and= 60. (a) Conventional three-segment SVM. (b) Conventional five-segmentSVM. (c) RCMV SVM.
Fig. 20. Switching current Iw and the line current Is under the operatingcondition ofm a = 0.7 and = 60
. (a) Conventional three-segment SVM.(b) Conventional five-segment SVM. (c) RCMV SVM.
frequency nor harmonics performance of RCMV SVM becomes
worse in this case.
From Table VI, we can see that the CMV produced from
RCMV SVM has been reduced significantly under all the
cases. This CMV reduction will result in the loss reduction
on common-mode inductors, which are integrated in the dc-
link choke. However, the switching frequency is equal to or
60 Hz higher than conventional ones (depending on whether it is
three-segment or five-segment seqeunce). Thus, we can approx-
imately assume that the switching loss of RCMV SVM will not
increase. Moreover, the harmonic perfromance of RCMV SVM
is also similar with the conventional ones. Note that Iw 5/Iw 1increases with the increase of delay anlge . Its because thedc-link current is not ideally constant. The voltage harmonics in
the CSRs connection point with theLCfilter, which are caused
by harmonic current flowing through the line inductor, can, in
turn, produce harmonic current in the dc-link [28]. This dc-link
harmonic current has more obvious effect on ac-side harmonic
current, when the dc-link current is lower (i.e., when the delay
angle is larger).
VI. CONCLUSION
This paper proposes a reduced CMV SVM for CSCs. The
proposed method significantly reduces the CMV without avoid-
ing the use of the zero-state vectors, so that it has superior
performance over the traditional nonzero-state RCMV SVMs.
Unlike the traditional ones, it is not subject to problems suchas the shrink of modulation index range, the increased switch-
ing frequency, lower harmonic performance, etc. Moreover, the
proposed RCMV SVM can be easily implemented in the digi-
tal controller. Although RCMV CMV in some delay angle (or
equivalent delay angle in CSI) ranges needs both sequences (a)
and (b) in one fundamental period, the single-sequence rule
can be applied to improve the harmonic performance by slightly
sacrificing the CMV reduction capability. Note that the RCMV
SVM can be applied in the CSI side as well. In the RCMV
SVMs application in CSI side, the detected voltages used for
zero-state vectors selection are the motor stator voltages instead
of the grid voltages in the CSR application.
The simulation and experimental results show that the RCMVSVM works well under various operating conditions. The peak
value of CMV produced by the proposed RCMV SVM can be
50% lower than that produced from the conventional methods.
Its harmonic performance is very similar to the conventional
five-segment SVM. As for the switching frequency, depending
on the selected zero-state vectors in sector crossing and the mo-
ment of sector crossing, the proposed RCMV SVMs switching
frequency is equal to or a fundamental frequency different from
the conventional five-segment SVM if their sampling frequen-
cies are the same. In comparison with the conventional three-
segment SVM, the proposed RCMV SVM produces a lower
CMV. It also has a better harmonic performance in the highmodulation range when the same switching frequency is used.
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Jian Shang (S12) was born in Shandong, China.He received the B.Eng. degree in electrical engineer-ing from Shandong University, Shandong, China, in2010. He is currently working toward the M.Sc. de-gree in electrical power engineering in the Depart-ment of Electrical and Computer Engineering, Uni-versity of Alberta, Edmonton, Canada.
His current research interests include electricdrives,common-mode voltage mitigation techniques,and renewable energy power generation.
Yun Wei Li(S04M05SM11) received the B.Sc.degree in electrical engineering from Tianjin Univer-sity, Tianjin, China, in 2002, and the Ph.D. degreefrom Nanyang Technological University, Singapore,Singapore, in 2006.
In 2005, he was a Visiting Scholar with theAalborg University, Denmark, where he was in-volved in the medium-voltage dynamic voltage re-storer (DVR) system. From 2006 to 2007, he was aPostdoctoral Research Fellow at Ryerson University,Canada, working on the high-power converter and
electric drives. In 2007, he was also at Rockwell Automation Canada, wherewas engaged in the development of power factor compensation strategies forinduction motor drives. Since 2007, he has been with the Department of Elec-
trical and Computer Engineering, University of Alberta, Edmonton, Canada,where he was initially as an Assistant Professor and then became an AssociateProfessor from 2013. His current research interests include distributed gener-ation, microgrid, renewable energy, power quality, high-power converters, andelectric motor drives.
Dr. Li is currently an Associate Editor for IEEE TRANSACTIONS ONINDUSTRIAL ELECTRONICS and a Guest Editor for the IEEE TRANSACTIONSON INDUSTRIALELECTRONICSSpecial Session on Distributed Generation andMicrogrids.