For practical application we are interested only for significant harmonics. Therefore we neglect the harmonics with amplitude less then5V.
IV. MATHEMATICAL MODEL OF A TWO-PHASE INDUCTION MOTOR For the system which is associated with the rotating
magnetic field, following equation of a two-phase asynchronous machine are valid [14].
1
2
1
2
ds s s ds s qs
qs s s qs s ds
dr r r dr s m qr
qr r r qr s m dr
d u R i dt d u R i dt d u R i dt d u R i dt !
"!
!
"!
!
" " !
!
" " !
(13)
Since homopolar components of the system are zero, the equation of the machine can be
transformed into single axis.
ds qs
r dr qr
s ds qs
r dr qr
s ds qs
r dr qr
u ju
u ju
j
j
i ji
i ji
!! !!
su u
i
i
Equations (11) take a form.
s s s s s s
r r r r s m r
d Rj dt d Rj dt " "" ui ui
(14)
With the flux linking components defined as.
s s s m r
r m s r r
LL LL (15) After the solving (12) and (13), we obtain for stator and rotor current phasors.
22
22
/ ./
./
s r r
s
s s r r m
m
r
s s r r m
R s j L R j L R s j L L
jL R j L R s j L L
" " " " " " " "
u
i
i
(16)
The phase currents 1212 ;;; ssrr iiiiare obtained on the base of current phasors by Fortescou transformation used e.g. in [14]. For the electromagnetic torque the following relation is valid. 2 1 1 2 em m s r s r M pL i i i i ## (17)
Fig. 7. Calculated waveforms of supply voltages. V. EXAMPLES OF SIMULATIONS USING FOURIER METHOD The following pictures show waveforms of stator currents and electromagnetic torque and in a steady state. The parameters of a prototype of a two-pole induction motor were used in a model. The motor has the parameters:
12
31 ; 51 ; 1.181 ; 0.15 ; SR m RR L H L L H $$ % % # The stator and rotor inductance are defined:
1
2
1,331 1,331
sm
rm
L L L H L L L H $ $ # The stator and rotor voltages and currents were calculated for each of harmonic. For the waveforms the following equations are valid. 9 9 9 9
1 1 2 2 1 1 2 2 1 1 1 1 ; ; ; ; k k k k s s s s s s s s k k k k u u u u i i i i Fig. 7 shows of the stator voltages waveform, calculated on the base of 9 harmonics. Similarly we can write for the torque waveform. 9
1
k em em k MM Fig. 8 shows the waveforms of the stator current for no loaded motor. In the Fig. 10 is the calculated waveform of the electromagnetic torque for no loaded machine.
Fig. 8. Stator current waveform for no-loaded motor.
0 2 4 6 8 10 12 14 16 18
-400
-200
0
200
400
u1S (V)
t (ms)
0 2 4 6 8 10 12 14 16 18
-400
-200
0
200
400
u2S (V)
t (ms)
0 2 4 6 8 10 12 14 16 18 20
-0.4
-0.2
0
0.2
0.4
0.6
i1s (A)
t (ms)
734