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Influence of PWM waveform parameters on the breakdown of harmonic losses in electrical steels
Journal of Magnetism
and Magnetic Materials
160 (I 996) 3 l-32
A ino:Ezll
A A
&&etic materials
ELSEVIER
Influence of PWM waveform parameters on the breakdown of harmonic losses in electrical steels Jean-Paul Swan a3*, Olivier Walti a, Thierry Belgrand b ’ lJnicrr.yit& drs Sciencrs et Technologies de Lillr, L.E.E. P., B& P2, F-59650 Villeneuw d’Ascq, France b Ugine .%A.. Centrr dr Rrcherches
d’lsbrrpes.
B.P. 15, F-62330 Isherpes.
France
Abstract This paper reports on the influence of the number of pulses composing a PWM wave on the harmonic and fundamental losses in grain non-oriented electrical steel. Two different wave shapes have been applied to an Epstein frame. The influence of multiple reversals of dB/dr on harmonic losses is presented. Kcv’wrds:
Soft magnetic
materials;
PWM; Characterization;
Harmonics;
Losses
1. Introduction Today, more and more rotating machines are fed by inverters. The electrical steel constituting the magnetic circuit of the machine is submitted to periodic but nonsinusoidal waves. The behaviour is different to that under sinusoidal conditions. It leads to a different level of losses in the iron and copper [I]. Attempts to represent the behaviour of steel under PWM waveforms have been made by several authors [2,3]. Generally, studies have been performed taking two parameters into account; the peak induction (B,) and the rate of rise of the induction (d B/d?). They seem to give satisfactory results. Nevertheless. from a designer’s point of view [ 11, the fundamental parameters may be interesting to size the machines. In the same way, PWM waves can present a multi-level shape, which is no longer coherent with a single dB/dt. In this work, we use this simple fact to study the behaviour of grain non-oriented steel considering the harmonic components, the fundamental and their impact on the losses. We performed measurements using synchronous modulation on the basis of sine-triangle synthesis. All this work deals with controlled induction at 50 Hz [4]. The fundamental induction (B,) is used as characterization variable. Investigations have been carried out for different numbers of pulses (m) per period of the PWM wave. 2. Experimental
1 f
,_
-1.5
Fig. 1, Typical induction (FB)
(HB). These waves contain harmonics which increase the losses as compared to the sine wave for the same value of B,. One fundamental difference between these two waves is the way the induction varies between the peak values. For FB waves (Fig. I ), d B/dt keeps the same sign between -B, and +B,. For HB waves (Fig. 21, the sign of d B/dt changes during the same half-period.
results
Figs. I and 2 show two typical induction waveforms corresponding to full-bridge (FBI and half-bridge inverters
^ Corresponding author. Now at Universite d’Artois, Laboratoire ‘Systemes Electrotechniques et Environnement’, Technoparc Futura, F-62400 BCthune Cedex, France. Fax: + 33-2 1-6 l-17-80. 0304-8853/96/$15.00 Copyright PII SO304-8853(96)00096-O
-1 5
0 1996 Elsevier Science B.V. All rights reserved.
Fig. 2. Typical induction (HB)
32
J.-P. Swan et al. / Journal oj'Magnetism and Magnetic Materials 160 (1996) 31 32 4.5
1.5
m-20
o~
B{T)
P
3.5
i'l'm =4
1
S i n e 5 0 Hz
3 m increases
2.5 ..
S ne
P o r P1
'
2 (W)
1.5
~m-20
.
,
-
c--
-0~--
~" !1(
H(A,'m) =
30"
200
300
m-~.
~
0.5
200
P1
,A-
1
-300
L- - f
i
s
i
0 0.4
0.6
0.8
1,2
1.4
1.6 -1 I5
B1 { T )
Fig. 6. Magnetization loop (HB).
Fig. 3. Loss characteristics (FB).
fundamental losses are very close to the sine losses and their variation can be neglected. The harmonic part of the losses represents the quasi-whole of the total losses. The magnetization loops in Fig. 5Fig. 6 explain these differences. The increase of the losses for FB conditions mainly arises from the enlargement of the magnetization loop. For HB waves, the magnetization loop contains inner loops which lead to a greater increase in the losses as compared to FB waves. These loops are due to the multiple regressions of the induction. Fast inversion of d B/dt seems to he an important cause of increasing losses [5].
14 p
.
_
12 ~10 -
m=7~ •
i 8 P
or
4," *
m decreases
"
"
• /
m=18
' "
4
P1
(W)
6 ~
.... Sine
] 4 I~
2
/
II~
'
0.4
0.6
0.8
1
~*
1.2
_
P1
,I
1.4
1.6
3. Conclusion
B1 ( T )
Fig. 4. Loss characteristics (HB).
Figs. 3 and 4 show the variation of the losses and the part attributed to harmonics. Sine induction characteristics are also presented to demonstrate the influence of the harmonics on the fundamental losses ( P i ) . The increase of losses is very different in these two examples. For FB waves, the harmonics increase the total losses, but they reduce the fundamental losses. This effect is not negligible compared to the gap ( P - P~i,e). In the case of HB waves, the increase of losses is higher than for FB waves. The
We have tried to quantify the losses generated in a grain non-oriented steel using harmonic formalism. This treatment constitutes an approach that throws some light on the differences which can exist between the behaviour of a material under sine waves and PWM waves. For the studied waves, we demonstrate that, for a given B~, fundamental losses are lower than (FB), or of the same order of magnitude as (HB), sine losses. The actual excitation in the stator of a machine is more complex than reported here and should be taken into account in the future. Acknowledgement: This work was supported by the regional council Nord-Pas de Calais, the regional delegation of Research and Technology and Electricit6 de France.
References B(T) 2
ks_ -
~
~
...........
~
H(A/rn)
-2
1
Fig. 5. Magnetization loop (FB).
[1] S. Wahsh and M. E1-Bakry, ETEP 1 (1991) 189. [2] G. Bertotti, P. Mazzetti and G.P. Soardo, J. Magn. Magn. Mater. 26 (1982) 225. [3] A. Boglietti et al., IEEE Trans. Ind. Appl. 36 (1994) 1580. [4] O. Walti, J.-P. Swan and T. Belgrand, Measurement bench for fine characterization of soft magnetic materials under arbitrary waveform excitations, SMM 12. Cracow, 1995. [5] J.D. Lavers. P.P. Biringer and H. Hollitscher, IEEE Trans. Magn. 14 (1978) 386.
and Magnetic Materials
160 (I 996) 3 l-32
A ino:Ezll
A A
&&etic materials
ELSEVIER
Influence of PWM waveform parameters on the breakdown of harmonic losses in electrical steels Jean-Paul Swan a3*, Olivier Walti a, Thierry Belgrand b ’ lJnicrr.yit& drs Sciencrs et Technologies de Lillr, L.E.E. P., B& P2, F-59650 Villeneuw d’Ascq, France b Ugine .%A.. Centrr dr Rrcherches
d’lsbrrpes.
B.P. 15, F-62330 Isherpes.
France
Abstract This paper reports on the influence of the number of pulses composing a PWM wave on the harmonic and fundamental losses in grain non-oriented electrical steel. Two different wave shapes have been applied to an Epstein frame. The influence of multiple reversals of dB/dr on harmonic losses is presented. Kcv’wrds:
Soft magnetic
materials;
PWM; Characterization;
Harmonics;
Losses
1. Introduction Today, more and more rotating machines are fed by inverters. The electrical steel constituting the magnetic circuit of the machine is submitted to periodic but nonsinusoidal waves. The behaviour is different to that under sinusoidal conditions. It leads to a different level of losses in the iron and copper [I]. Attempts to represent the behaviour of steel under PWM waveforms have been made by several authors [2,3]. Generally, studies have been performed taking two parameters into account; the peak induction (B,) and the rate of rise of the induction (d B/d?). They seem to give satisfactory results. Nevertheless. from a designer’s point of view [ 11, the fundamental parameters may be interesting to size the machines. In the same way, PWM waves can present a multi-level shape, which is no longer coherent with a single dB/dt. In this work, we use this simple fact to study the behaviour of grain non-oriented steel considering the harmonic components, the fundamental and their impact on the losses. We performed measurements using synchronous modulation on the basis of sine-triangle synthesis. All this work deals with controlled induction at 50 Hz [4]. The fundamental induction (B,) is used as characterization variable. Investigations have been carried out for different numbers of pulses (m) per period of the PWM wave. 2. Experimental
1 f
,_
-1.5
Fig. 1, Typical induction (FB)
(HB). These waves contain harmonics which increase the losses as compared to the sine wave for the same value of B,. One fundamental difference between these two waves is the way the induction varies between the peak values. For FB waves (Fig. I ), d B/dt keeps the same sign between -B, and +B,. For HB waves (Fig. 21, the sign of d B/dt changes during the same half-period.
results
Figs. I and 2 show two typical induction waveforms corresponding to full-bridge (FBI and half-bridge inverters
^ Corresponding author. Now at Universite d’Artois, Laboratoire ‘Systemes Electrotechniques et Environnement’, Technoparc Futura, F-62400 BCthune Cedex, France. Fax: + 33-2 1-6 l-17-80. 0304-8853/96/$15.00 Copyright PII SO304-8853(96)00096-O
-1 5
0 1996 Elsevier Science B.V. All rights reserved.
Fig. 2. Typical induction (HB)
32
J.-P. Swan et al. / Journal oj'Magnetism and Magnetic Materials 160 (1996) 31 32 4.5
1.5
m-20
o~
B{T)
P
3.5
i'l'm =4
1
S i n e 5 0 Hz
3 m increases
2.5 ..
S ne
P o r P1
'
2 (W)
1.5
~m-20
.
,
-
c--
-0~--
~" !1(
H(A,'m) =
30"
200
300
m-~.
~
0.5
200
P1
,A-
1
-300
L- - f
i
s
i
0 0.4
0.6
0.8
1,2
1.4
1.6 -1 I5
B1 { T )
Fig. 6. Magnetization loop (HB).
Fig. 3. Loss characteristics (FB).
fundamental losses are very close to the sine losses and their variation can be neglected. The harmonic part of the losses represents the quasi-whole of the total losses. The magnetization loops in Fig. 5Fig. 6 explain these differences. The increase of the losses for FB conditions mainly arises from the enlargement of the magnetization loop. For HB waves, the magnetization loop contains inner loops which lead to a greater increase in the losses as compared to FB waves. These loops are due to the multiple regressions of the induction. Fast inversion of d B/dt seems to he an important cause of increasing losses [5].
14 p
.
_
12 ~10 -
m=7~ •
i 8 P
or
4," *
m decreases
"
"
• /
m=18
' "
4
P1
(W)
6 ~
.... Sine
] 4 I~
2
/
II~
'
0.4
0.6
0.8
1
~*
1.2
_
P1
,I
1.4
1.6
3. Conclusion
B1 ( T )
Fig. 4. Loss characteristics (HB).
Figs. 3 and 4 show the variation of the losses and the part attributed to harmonics. Sine induction characteristics are also presented to demonstrate the influence of the harmonics on the fundamental losses ( P i ) . The increase of losses is very different in these two examples. For FB waves, the harmonics increase the total losses, but they reduce the fundamental losses. This effect is not negligible compared to the gap ( P - P~i,e). In the case of HB waves, the increase of losses is higher than for FB waves. The
We have tried to quantify the losses generated in a grain non-oriented steel using harmonic formalism. This treatment constitutes an approach that throws some light on the differences which can exist between the behaviour of a material under sine waves and PWM waves. For the studied waves, we demonstrate that, for a given B~, fundamental losses are lower than (FB), or of the same order of magnitude as (HB), sine losses. The actual excitation in the stator of a machine is more complex than reported here and should be taken into account in the future. Acknowledgement: This work was supported by the regional council Nord-Pas de Calais, the regional delegation of Research and Technology and Electricit6 de France.
References B(T) 2
ks_ -
~
~
...........
~
H(A/rn)
-2
1
Fig. 5. Magnetization loop (FB).
[1] S. Wahsh and M. E1-Bakry, ETEP 1 (1991) 189. [2] G. Bertotti, P. Mazzetti and G.P. Soardo, J. Magn. Magn. Mater. 26 (1982) 225. [3] A. Boglietti et al., IEEE Trans. Ind. Appl. 36 (1994) 1580. [4] O. Walti, J.-P. Swan and T. Belgrand, Measurement bench for fine characterization of soft magnetic materials under arbitrary waveform excitations, SMM 12. Cracow, 1995. [5] J.D. Lavers. P.P. Biringer and H. Hollitscher, IEEE Trans. Magn. 14 (1978) 386.