Hardware Reference
In-Depth Information
Figure 4.89: Gate signals for the three-phase inverter in twelve-step starting.
An alternative to the above mentioned method, the twelve-step starting [131],
improves the starting performance. In the twelve-step pattern, the inverter
gate is switched over every 30
◦
, and hence the power electronics devices in
the converter circuit conduct for 150
◦
, instead of 120
◦
in the six-step start-
ing. The corresponding gate signals are shown in Figure 4.89 and the phase
voltages with step amplitudes V
DC
/3, V
DC
/2and2V
DC
/3 are illustrated in
Figure 4.90.
To realize the twelve-step pattern, an additional switching state is inserted
between every two successive states of the six-step sequence, making it twelve
states in the starting sequence. The switching sequences of both the six-step
and twelve-step are listed in Table 4.4.
Table 4.4: Switching sequence for six-step and twelve-step starting method
Starting
Method
Switching Sequence
Six-step
(AH, BL) (AH, CL) (BH, CL)
(BH, AL) (CH, AL) (CH, BL)
Twelve-step
(AH, BL) (AH, BL, CL) (AH, CL) (AH, BH, CL)
(BH,CL)(AL,BH,CL)(BH,AL)(AL,BH,CH)
(CH, AL) (AL, BL, CH) (CH, BL) (AH, BL, CH)
