u U c e ; for k
c for k
(6) Similarly for the output voltage of the second transistor branch: 01 01 01
01 01 1
01 01
01
1 2
0
0
2
nnjk jk
n
m
jk en kn
nn
n
c e e jk u U c e ; for k
c for k
(7) So does for third transistor branch. 02 02 02
02 02 1
02 02
02
1 2
0
0
2
nnjk jk
n
m
jk en kn
nn
n
c e e jk u U c e ; for k
c for k
(8) The phase voltages are given by a difference between branch voltages as following.
1 0 01 0 01 1
2 0 02 0 02 1
m
jk S e n n kn
m
jk S e n n kn
u u u U c c e ;
u u u U c c e ;
(9)
Where e U -DC inverter input voltage In the Fig. 5 are shown the phase voltages waveforms, which were calculated on the base on equations (9).
Fig. 5. Waveforms of the phase voltages.
The waveforms were calculated for modulation frequency of 2 kHz ( ).
III. HARMONIC ANALYSIS OF THE SUPPLY VOLTAGES On the base of Fourier series formulas of the phase supply voltages, can be made a harmonic analysis of the supply waveforms. Phasor of each of voltage harmonics is given by a product of sum of complex Fourier’s coefficient and DC input voltage 10 0 1 1 20 0 2 1 2 2 m k k k s e n n n m k k k s e n n n U c c U c c U U (10)
Fig. 6. Harmonic analysis of the PWM controlled output voltage.
With amplitude and phase k k k k A abs ; P angle ; UU (11) The Fig.6 depicts a harmonic analysis of the PWM controlled output voltage for desired frequency of 50 Hz and modulation frequency of 2 kHz ( 40 m ).