POWER ELECTRONICS (BPB23204)
TUTORIAL 4
S JANUARY 2021
Question 1
a) With reference to the circuit diagram shown in Figure 1 and the switching pattern in
Table 1, sketch and label clearly the equivalent circuits for all intervals (0-60, 60120, 120-180, 180-240, 240-300, 300-360) ̊.
b) For the interval 180 – 240 in a), If E = 600V and R = 50Ω (Balance load), evaluate:
i.
Phase voltages; VAN, VBN and VCN
ii.
Line voltages; VAB, VBC and VCA
iii.
Determine power to the load.
Table 1
Interval
S1
S2
S3
S4
S5
S6
0º to 60º
ON
OFF
OFF
OFF
ON
ON
60º to 120º
ON
ON
OFF
OFF
OFF
ON
120º to
ON
ON
ON
OFF
OFF
OFF
OFF
ON
ON
ON
OFF
OFF
OFF
OFF
ON
ON
ON
OFF
OFF
OFF
OFF
ON
ON
ON
180º
180º to
240º
240º to
300º
300º to
360º
c). The operation of the circuit in Figure 1 is change to 120˚ conduction mode with the
switching operation as shown in Table 2.
i.
Draw an equivalent circuit for an interval 180˚ to 240˚
ii. Evaluate the phase voltage VAN, VBN, and VCN for the equivalent circuit in part (i)
iii. From the value of phase voltages in (ii), calculate the line voltage, VAB, VBC, and
VCA
iv. Determine the power delivered to the load in each phase.
Figure 1
Table 2
Interval
S1
S2
S3
S4
S5
S6
0˚ to 60˚
ON
OFF
OFF
OFF
OFF
ON
60˚ to 120˚
ON
ON
OFF
OFF
OFF
OFF
120˚ to
OFF
ON
ON
OFF
OFF
OFF
OFF
OFF
ON
ON
OFF
OFF
OFF
OFF
OFF
ON
ON
OFF
OFF
OFF
OFF
OFF
ON
ON
180˚
180˚ to
240˚
240˚ to
300˚
300˚ to
360˚