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 gure 10.12 is 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 lter 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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ECE_320_Homework9_Soln - Operation of a buck boost chopper...

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