ECE_320_Homework9_Soln

# ECE_320_Homework9_Soln - Operation of a buck boost chopper...

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120 DC-DC CONVERSION Fig. 10.8 Calculating the output voltage ripple for a boost inverter 10.3 BUCK-BOOST CONVERTER This converter, the topology of which is shown in ﬁgure 10.9, can provide output voltage that can be lower or higher than that of the input. Fig. 10.9 Basic buck-boost converter Again the operation of the converter can be analyzed using the two topologies resulting from operation of the switch, shown in ﬁgure 10.10. By equating the integral of the inductor voltage to zero we can get: V d DT s + ( - V o )(1 - D ) T s = 0 (10.17) V o V d = D 1 - D (10.18) At the boundary between continuous and discontinuous conduction we can use ﬁgure 10.11 to ﬁnd that I o = T s V o 2 L (1 - D ) 2 (10.19)

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BUCK-BOOST CONVERTER 121 Fig. 10.10 Operation of a buck boost chopper Fig. 10.11
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Unformatted text preview: Operation of a buck boost chopper The output voltage ripple, as calculated based on ﬁgure 10.12 is Δ V o V o = D T s RC (10.20) 10.3.1 Example The input of a step down converter varies from 30 V to 40 V and the output voltage is to be constant 20 V , with output power varying between 100 W and 200 W . The switch is operating at 20 kHz . What is the inductor needed to keep the inductor current continuous? What is then the ﬁlter capacitor needed to keep the output ripple below 2% . The duty cycle will vary between D 1 = 20 / 30 = 0 . 667 and D 2 = 20 / 40 = 0 . 5 . The load current will range between I o 1 = 100 / 20 = 5 A and I o 2 = 200 / 20 = 10 A ....
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## This note was uploaded on 09/21/2010 for the course ECE 320 taught by Professor Jurkovic during the Spring '08 term at Michigan State University.

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ECE_320_Homework9_Soln - Operation of a buck boost chopper...

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