ECE433 –HW4
Due Date : 26th March (Monday)
1) Given the following half-bridge inverter.
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50
Dl
+
50
D2
a)
Determine a switching scheme that provides an ac output voltage vas.
b)
For the switching scheme in a) plot the voltage vas, and the current i as a s s umi ng a
purely inductive load. Label the devices that conduct over the entire period.
60
120
180
240
300
360
60
120
180
240
300
360
c) Describe 2 disadvantages and 1 advantage of the circuit shown to the full h-bridge inverter with
4 switches.
2) Given the circuit shown in Figure 1. All elements are ideal and the following are the
system parameters: The switching scheme is shown in the figure below.
vdc=15v, Lload= 0, rload=20 ohms.
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Figure 1: Inverter circuit
Answer the following questions:
a
Plot vag , vbg , vcg , ias the current through diode 1 (iD1 ), and the current through transistor
1 ( i T1) on the figure below.
3) Given a single-phase inverter. If the output voltage vas is of the form shown below, determine the transistor switching pattern used to achieve the voltage.
b)
True/False: The waveform in a) has a lower 3rd harmonic component than that of a standard
180 degree switching scheme. Support your answer with appropriate mathematics.
c)
If the load is purely inductive, the inverter system is in steady-state, and the phase current ias
has an average value of 0, plot the phase current resulting from the vas shown in a). Label the
devices that conduct over the entire waveform
4) Given the 3-phase inverter shown in Figure 1. The inverter is operated using a sine-triangle
switching scheme. Each phase has a r-l load with r = 1 Ohm, L = 1 mH. Vdc = 250 V
a)
If the phase-a current has a fundamental component Ias = 20cos(377t + 15°), determine the
inverter amplitude modulation Index.
b) Assuming a desired output frequency of 377 rad/sec, what is the maximum amplitude of the
fundamental component of current that can be achieved under the sine-triangle switching
strategy?