a novel svm-based hysteresis current controller

8/19/2019 A Novel SVM-Based Hysteresis Current Controller

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IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 13, NO. 2, MARCH 1998 297

A Novel SVM-Based Hysteresis Current ControllerBong-Hwan Kwon, Tae-Woo Kim, and Jang-Hyoun Youm

Abstract— In this paper, a novel space-vector-modulation(SVM)-based hysteresis current controller (HCC) is proposed.This technique utilizes all advantages of the HCC and SVMtechnique. The controller determines a set of space vectors froma region detector and applies a space vector selected accordingto the main HCC. A set of space vectors including the zerovector to reduce the number of switchings is determined fromthe sign of the output frequency and output signals of threecomparators with a little larger hysteresis band than that of themain HCC. A simple hardware implementation is proposed, andexperimental results of the SVM-based HCC are also shown.

Index Terms—Hysteresis current controller, space-vector mod-ulation.

I. INTRODUCTION

CURRENT-CONTROL technique plays the mostimportant role in current-controlled pulse-width-modulated (PWM) inverters, which are widely applied in

high-performance ac drives and reactive power compensation

systems [1][14]. Various techniques for current controller

have been proposed. However, among these techniques,

considering easy implementation, fast dynamic response,

maximum current limit, and insensitivity to load parameter

variations, the hysteresis current controller (HCC) is a rather

popular one. Nevertheless, due to lack of coordination among

individual HCC’s of three phases, high switching frequency

may happen, and the current error is not strictly limited. Somehysteresis current-control techniques applying the zero vector

to reduce the number of switchings were reported recently

[10][12]. However, these techniques require knowledge of

the load counter emf [10] or it does not still show how to

determine a set of space vectors including the zero vector

according to the region to reduce the number of switchings

[11], [12]. On the other hand, the space-vector-modulation

(SVM) technique has two excellent features [13], [14] such

that its maximum output voltage is 15.4% greater and the

number of switchings is about 30% less at the same carrier

frequency than the one obtained by the sinusoidal PWM

method. The SVM technique confines space vectors to be

applied according to the region where the output voltagevector is located. To obtain the zero-output-current error,

the SVM technique requires a measurement of the counter

emf vector which is not practical. On the other hand, the

Manuscript received July 26, 1996; revised May 21, 1997. Recommendedby Associate Editor, D. A. Torrey.

The authors are with the Department of Electronic and Electrical Engineer-ing, Pohang University of Science and Technology, Pohang 790-784, SouthKorea.

Publisher Item Identifier S 0885-8993(98)01949-8.

HCC can be utilized to make the output-current vectortrack the command vector with almost negligible response

time and insensitivity to line voltage and load parameter

variations. However, the HCC generates other vectors

except space vectors required according to the region in the

SVM technique. If the zero vector is applied to reduce the

magnitude of the output-current vector, the line current is

decreased with slow slope and the switching frequency is

decreased. The utilization of nonzero vectors instead of the

zero vector for decreasing the output current increases the

switching frequency. Therefore, a SVM-based HCC utilizing

all features of the HCC and SVM technique needs to be

developed.

In this paper, a novel SVM-based HCC is proposed. Thistechnique utilizes all advantages of the HCC and SVM tech-

nique. This configuration reduces significantly the number of

switchings and at the same time gives the same space vectors

as those obtained from the SVM technique. The proposed

current controller confines space vectors from a region detector

and applies a proper space vector selected according to the

main HCC for better current shape. A set of space vectors

including the zero vector is determined from the sign of

the output frequency and output signals of three comparators

with a little larger hysteresis band than that of the main

HCC. A simple hardware implementation and experimental

results of the SVM-based hysteresis current controller are also

shown.

II. SVM-BASED HCC

Any three functions of time that satisfy

(1)

can be represented in a two-dimensional (2-D) space, where

the coordinates are chosen so that the vector is placed

along the horizontal axis, the vector is by 120 , and

the vector is by additional 120 as shown in Fig. 1.The arbitrary space vector in complex notation is then

given by

(2)

where

(3)

and 2/3 is a scaling factor. From (2) and (3), the coordinate

transformation from the – – axis to – axis is obtained as

08858993/98$10.00 1998 IEEE


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KWON et al.: NOVEL SVM-BASED HYSTERESIS CURRENT CONTROLLER 299

Fig. 2. Voltage-source inverter with the induction motor.

(a) (b)

Fig. 3. Space vectors and voltage components of the VSI: (a) space vectors and (b) voltage components.

(a) (b)

(c)

Fig. 4. Principle of the switching frequency reduction: (a) derivative vectors of the current error in Region I, (b)

and space vectors when the HCC doesnot use the region information, and (c)

and space vectors when the HCC uses the region information.


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300 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 13, NO. 2, MARCH 1998

(a)

(b)

Fig. 5. SVM-based HCC: (a) block diagram of the proposed current controller and (b) relation of voltage vectors and line-current errors.

(a) (b)

Fig. 6. Operation of the region detector: (a) waveforms of the line current and (b) region determined by the region detector.

However, the calculation is not practical since it requires ameasurement of the counter emf vector. On the other hand,

the HCC can be utilized to make the output-current vector

track the command vector with almost negligible response time

and insensitivity to line voltage and load parameter variations.

However, due to lack of coordination among three individ-

ual HCC’s, high switching frequency may happen and the

current error is not strictly limited. This problem in the HCC

can be solved using the space-vector concept. When the

desired output space vector is in Region I, the derivative

vectors of the current error corresponding to the PWM phase

voltage are shown in Fig. 4(a). The proper discrete space

vectors giving small derivative value of the current error forthe space voltage vector in Region I are , , and .

However, the conventional HCC generates other state-space

vectors including these vectors in Fig. 4(b). To reduce the

number of switchings, is the most important variable.

In order to reduce the number of switchings, it is necessary

to choose a voltage vector so that the corresponding

is small. If the zero vector is only applied to reduce

the magnitude of the current error vector except and

in Region I, the line current varies with slow slope and the

number of switchings is decreased as shown in Fig. 4(c). In the

simulation of Fig. 4(c), the region was predetermined from the


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Fig. 7. Control circuit for the proposed current controller.

voltage vector . The utilization of nonzero vectors instead

of the zero vector gives steep slope for the current error due to

large voltage difference . Thus, a set of space vectors

to be applied according to the sector depends on the position

of the desired space voltage vector in (16).

A region detector is proposed to detect the position of the

output space vector . A region is detected from output

signals ( and ) of three comparators with a little

larger hysteresis band than that of the main HCC and the sign

of the output frequency . The proposed SVM HCC is

TABLE ISWITCHING TABLE FOR THE P ROPOSED CURRENT CONTROLLER

shown in Fig. 5(a), where a region detector is utilized without

information of the back emf, and it confines the same space

voltage vectors as the SVM technique generates.

denotes the positive frequency of the output and

the negative frequency. denotes a status of the inner bound

of the -axis current error, and denotes a status of the

outer bound of the -axis current error with a wider band than

that of the inner bound. A set of space voltage vectors to be

applied is determined according to the region. If a voltage

vector is properly applied at a correct instant, the current error

will remain inside the band. On the other side, if a voltage

vector which is not correct is applied, the current gets out of

the hysteresis band. From this appearance, the region of thedesired output voltage vector can be detected using the

outer hysteresis comparator with wider band than that of the

inner one. The relation of space vectors and outer band signals

is shown in Fig. 5(b), where two regions are determined by the

outer band signals. Recently recorded outer band information

becomes the region of the desired voltage vector . Thus, the

region of the desired voltage vector is determined between

two regions according to the sign as shown in Table I.

When the sign of the output frequency varies, Fig. 6

shows that the region of the desired output voltage vector

is uniquely determined by the region detector. Therefore, the

region detector determines a set of space vectors to be applied

according to the outer band signals and the sign of the outputfrequency. For an example, , , and

indicate Region I for and Region VI for .

The inner three hysteresis comparators with narrow band are

used to track the reference current and limit the current error

within the specified bound. Fig. 5(b) shows Region I, where

the space vectors , , and are utilized like the SVM

technique. When the current error of the axis hits the inner

upper bound of the hysteresis comparator and the current error

of the axis hits the inner lower bound, and .

The voltage vector is applied to decrease the -axis current

and -axis current simultaneously when and


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(a) (b)

(c)

Fig. 8. Space vectors and region generated by current controllers: (a) space vectors by the HCC, (b) space vectors by the SVM HCC, and (c) regiongenerated by the SVM HCC.

(a) (b)

(c)

Fig. 9. Waveforms of the line currents by the HCC and SVM HCC: (a)

by the HCC with the outer band, (b)

by the HCC with the innerband, and (c)

by the SVM HCC.

. On the other hand, is applied to increase and

simultaneously when and . In the other

cases, the zero vector is applied. Whenever the outer

hysteresis bound is hit due to incorrect regions, a proper

nonzero space vector is always triggered to reduce the current

error magnitude, and the correct region is then recorded.

Hence, due to automatic updating of the region, an initial

region can be arbitrary assigned. The switching table for all

regions is shown in Table I. Fig. 7 shows a control circuit for

the proposed current controller. Therefore, the gate logic of


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(a) (b)

Fig. 10. Number of switchings for

,

, and

: (a) HCC and (b) SVM HCC.

the programmable array logic (PAL) device is given by

where is the logical NOT operator.

III. SIMULATION AND EXPERIMENTAL RESULTS

To verify the validity of the proposed current controllers,

simulation and experiment are made for an induction motor.

The nameplate data and parameter values of the inductionmotor used in the experiment are given as follows:

Nameplate data:

squirrel-cage induction motor

[hp] [V] [A]

[rpm] [Hz] three-phase, four poles

Parameter values:

stator resistance

rotor resistance

stator leakage inductance [mH]

rotor leakage inductance [mH]

magnetizing inductance [mH]

The dc-link voltage of the VSI is 280 V. The computer

simulation was done for the induction motor as shown in


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(a) (b)

(c) (d)

Fig. 11. Number of switchings when the peak output current is 30 A: (a) for the peak emf voltage 10 V, (b) peak emf voltage 50 V, (c) peak emf voltage 100 V, and (d) peak emf voltage 150 V.

(a) (b)

(c) (d)

Fig. 12. Dynamic characteristics of the SVM HCC: (a) step response of the current

at

Hz, (b) waveform of the current command

at

Hz, (c) step response of the current

at

Hz, and (d) waveform of the current command

at

Hz.

Fig. 1. The current command is 30 A, and the inner and outer

bands are 0.8 and 1.2 A, respectively. The proposed SVM-

based HCC (SVM HCC) gives less changes of space vectors

and more regular pattern compared with the conventional

HCC as shown in Fig. 8(a) and (b). The proposed algorithm

has switchings between adjacent space vectors and the zero

vector. Thus, PWM pulses have similar waveform to those of

the SVM scheme. In the proposed current controller, the zero

vector is more used than in the HCC. Signals

and give six different regions. According to the region,

a set of space vectors to be applied to the induction motor

is determined as shown in Table I. Fig. 8(c) shows the


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(a) (b)

(c) (d)

Fig. 13. Gate signals and waveform of the line current by the HCC: (a)

, (b)

, (c)

, and (d)

.

(a)

(b)

(c)

(d)

(e)

(f)

(g)

Fig. 14. Waveforms by the SVM HCC in the case of

: (a)

,(b)

, (c)

, (d)

, (e)

, (f)

, and (g)

.

region changes determined from the outer hysteresis band.

Each state remains for 60 and the outer vector varies six

times every period, i.e., the outer band plays as a region

(a)

(b)

(c)

(d)

(e)

(f)

(g)

Fig. 15. Waveforms by the SVM HCC in the case of

: (a)

,(b)

, (c)

, (d)

, (e)

, (f)

, and (g)

.

detector of the output voltage vector. The case that the line

current hits the outer band occurs only two times every period

per phase. Except this case, the line current remains always


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(a)

(b)

(c)

(d)

Fig. 16. Waveforms by the HCC in pulse-dropping region: (a)

, (b)

,(c)

, and (d)

.

in the inner band. In the case of the HCC with the outer

band, the line current as shown in Fig. 9(a) has a largerripple than that of the SVM HCC. Fig. 9(b) and (c) shows

the line-current waveforms generated by the HCC and the

proposed current controller with the same inner hysteresis

band, respectively. In simulation results of Figs. 8 and 9, an

external three-phase inductance of 5 mH is included to show

detail current waveforms and switchings of space vectors. The

switchings of and by the HCC are happened on

all regions as shown in Fig. 10(a). However, the switchings

of and by the SVM HCC are similar to those

of the SVM technique as shown in Fig. 10(b). Fig. 11 shows

the number of switchings for the SVM HCC and HCC with

the same inner band. The number of switchings or switching

frequency generated from the SVM HCC is significantlyreduced compared to the HCC in various kinds of emf voltage.

The test results of the presented SVM HCC are shown

in Figs. 1217. Fig. 12 shows good step responses of the

proposed current controller. Fig. 12(a) and (b) shows the

waveforms of the line current and current command with 60-

Hz output frequency and Fig. 12(c) and (d) shows the current

waveforms in case of 0.033-Hz output frequency. Figs. 1315

show gate signals and the line-current waveform generated

from the HCC and SVM HCC with the same inner hysteresis

band, respectively. One can see that the proposed algorithm

reduces dramatically the number of switchings compared with

(a)

(b)

(c)

(d)

(e)

(f)

(g)

Fig. 17. Waveforms by the SVM HCC in pulse-dropping region: (a)

,(b)

, (c)

, (d)

, (e)

, (f)

, and (g)

.

the HCC. Figs. 14 and 15 show switching patterns by the SVMHCC in cases of and , respectively. The

SVM HCC works good in the pulse-dropping region compared

with the HCC as shown in Figs. 16 and 17.

IV. CONCLUDING REMARKS

In this paper, a novel SVM-based HCC has been presented.

This technique utilizes all advantages of the HCC and SVMtechnique. This configuration reduces significantly the number

of switchings than the conventional HCC and at the same

time gives the same space vectors as those obtained from

the SVM technique. The proposed current controller gives

the same maximum output voltage as the SVM technique,

almost negligible response time of the current error, and

insensitivity to line voltage and load parameter variations. The

current controller confines state-space vectors from the region

detector and applies a proper space vector selected according

to the main HCC for better current shape. A simple hardware

implementation of the SVM-based HCC has been presented.


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It has been also shown via simulation and experimental results

that the presented current controller gives the excellent features

of the HCC and SVM techniques.

REFERENCES

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[2] B. K. Bose, “Recent advances in power electronics,” IEEE Trans. Power

Electron., vol. 7, no. 1, pp. 216, 1992.[3] D. M. Brod and D. W. Novotny, “Current control of VSI-PWM

inverters,” IEEE Trans. Ind. Applicat., vol. IA-21, no. 4, pp. 562569,1985.

[4] B. K. Bose, “An adaptive hysteresis-band current controller techniqueof a voltage-fed PWM inverter for machine drive system,” IEEE Trans.

Ind. Electron., vol. 37, no. 5, pp. 402408, 1990.[5] L. Malesani and P. Tenti, “A novel hysteresis control method for current

controlled VSI PWM inverters with constant modulation frequency,” IEEE Trans. Ind. Applicat., vol. 26, no. 1, pp. 8892, 1990.

[6] A. B. Plunkett, “A current controlled PWM transistor inverter drive,”in IEEE-IAS, Annu. Meet. Conf. Rec., 1979, pp. 785792.

[7] J. Holtz and E. Bube, “Field-oriented asynchronous pulse-width mod-ulation for high-performance ac machine operating at low switchingfrequency,” IEEE Trans. Ind. Applicat., vol. 27, no. 3, pp. 574581,1991.

[8] A. Nabae, S. O. Wara, and Y. Iwagi, “A novel current scheme for current

controlled PWM inverters,” IEEE Trans. Ind. Applicat., vol. IA-22, no.4, pp. 697701, 1986.

[9] M. P. Kazmierkowski and W. Sulkowski, “A novel vector controlscheme for transistor PWM inverter-fed induction motor drive,” IEEE Trans. Ind. Electron., vol. 38, no. 1, pp. 4147, 1991.

[10] G. Pffaf, A. Weschta, and A. Wick, “Design and experimental resultsof a brushless AC servo-drive,” in IEEE-IAS, Annu. Meet. Conf. Rec.,1982, pp. 692697.

[11] M. P. Kazmierkowski, M. A. Dzieniakowski, and W. Sulkowski, “Novelspace vector based current controller for PWM-inverters,” IEEE Trans.Power Electron., vol. 6, no. 1, pp. 158166, 1991.

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Bong-Hwan Kwon was born in Pohang, Korea,on March 15, 1958. He received the B.S. degreefrom Kyungbuk National University, Taegu, Korea,in 1982 and the M.S. and Ph.D. degrees in electricalengineering from the Korea Advanced Institute of Science and Technology (KAIST), Seoul, Korea, in1984 and 1987, respectively.

He has been with the Department of Electronicand Electrical Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Ko-

rea, since 1987, where he is now an AssociateProfessor. His research interests are system control theory, microproces-sor/computer control, motor drives, and high-frequency converters.

Tae-Woo Kim was born in Pusan, Korea, on Feb-ruary 8, 1972. He received the B.S. degree from thePusan National University, Pusan, Korea, in 1995and the M.S. degree in electronic and electricalengineering from the Pohang University of Scienceand Technology (POSTECH), Pohang, Korea, in1997. He is currently working toward the Ph.D.degree at POSTECH.

His current research interests include motor drivesand microprocessor applications.

Jang-Hyoun Youm was born in Pusan, Korea, onOctober 7, 1969. He received the B.S. degree fromthe Hanyang University, Seoul, Korea, in 1993and the M.S. degree in electronic and electricalengineering from the Pohang University of Scienceand Technology (POSTECH), Pohang, Korea, in1995. He is currently working toward the Ph.D.degree at POSTECH.

His current research interests include motordrives, ac choppers, and microprocessor applica-tions.

a novel svm-based hysteresis current controller

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