Special Topics ECEN 2060
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This 8 page Class Notes was uploaded by Mrs. Lacy Schneider on Thursday October 29, 2015. The Class Notes belongs to ECEN 2060 at University of Colorado at Boulder taught by Staff in Fall. Since its upload, it has received 8 views. For similar materials see /class/231804/ecen-2060-university-of-colorado-at-boulder in ELECTRICAL AND COMPUTER ENGINEERING at University of Colorado at Boulder.
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Date Created: 10/29/15
ECEN2060 18 ECEN 2060 Sample Midterm Exam 1 Spring 2008 Instructions Name This is a 50 minute timed closed book test Absolutely no collaboration is allowed You may use a single page one side of one sheet of notes Calculators are allowed No other materials are permitted Work in the space provided or on the back of the pages if you need more space Turn in only these sheets Show all work paitial credit will be given Write your name on page 1 and on page 8 ECEN2060 28 1 30 pts Figure 1a shows a switched mode DC DC converter operating at switching frequency fs 1Ts The switches are in position 1 during DTS and in position 2 during 1 DTs where D is the switch duty ratio Capacitance C is large so that the AC ripple component in the output voltage can be neglected ie you can assume that Vow is a DC voltage DC DC converter L 1 1L 2 y VL 2 1 Vg C R i V Figure 1 Switched mode DC DC converter a 12 pts In this part of the problem converter losses can be neglected Using the inductor volt second balance approach find the DC conversion ratio MD VowVs as a function of the switch duty ratio D ECEN2060 38 b 6 pts An averaged model of the DC DC converter including losses is shown in Fig 1b What are the origins of losses modeled by RL and 1m SW27 DC DC converter averaged model lg 12D RL 1 D 1 1m 7 VV 7 V R r V g out ISM2 Figure 1b Averaged model of the DC DC converter c 12 pts In the model of Fig 1b you can assume that SW1 2 m2 0 Find an expression for the DC conversion ratio M VowVs and the converter efficiency 7 as functions of the switch duty ratio D and the ratio RLR Where R is the load resistance 48 ECEN2060 2 40 pts Figure 2a shows IPVVPV and PPVVPV characteristics of a PV module under standard test conditions full sun insolation S 2 S1 1000 Wmz and for another insolation S 2 S2 The module area is APV 14 m2 Ipv A va V va W 15 20 va V Figure 2a PV module characteristics ECEN2060 3 U V O V 58 6 pts What are the module open circuit voltage Vac short circuit current 15C rated voltage VR rated current IR rated power PR and efficiency an under standard test conditions 2 pts What is S2 8 pts The module is connected directly to a lead acid battery as shown in Fig 2b The battery can be modeled approximately as an ideal voltage source Vim 13 V Find the current but charging the battery for two insolation cases SS1andSS2 but L Battery Figure 2b Direct energy transfer PV module connected directly to the battery d 16 pts The module is connected to the lead acid battery using a DC DC converter the averaged model of which is shown in Fig 2c An MPP tracker adjusts the duty ratio D so that the PV module operates at the maximum power point In the averaged model the converter loss parameter is RL 2 01 2 Find the switch duty cycle D the converter efficiency nDcDC and the battery charging current but for two insolation cases S 2 S1 and S 2 S2 ECEN2060 68 DCDC converter averaged model IPV 1 D RL 1 D 1 bat AA 7 vv 7 VPV Battery D MPPT anal charge controller Figure 2c PV module connected to the battery using a DC DC converter e 8 pts Under the conditions of part d assuming full sun insolation S 2 S1 the battery is charged to 80 SOC state of charge and the DC DC converter switches to constant voltage charging Vim 13 V so that the battery charging current decreases as the battery SOC approaches 100 At the time When the battery charging current drops to 12m 05 A find the duty ratio D the PV voltage m the PV current IPV and the converter efficiency nDcDC ECEN2060 3 78 30 pts Answer the following short questions as precisely and as succinctly as possible a 6 pts What are the major advantages of power transmission using a three phase AC power system compared to a single phase AC power system b 6 pts Draw the equivalent circuit model of a PV cell How does the cell 15C depend on insolation How does the cell Vac depend on temperature c 6 pts Sketch a block diagram of a grid connected PV system including a PV array a DC DC converter and a DC AC inverter The inverter connected to the 60 Hz utility grid at 240 Vrms delivers 2 kW of power What is the RMS value of the AC current State your assumptions d 6 pts You are to design a grid connected PV system for a house in Boulder having a yearly average of 55 hours of full sun per day The system should produce 2500 kWh of electricity per year Assuming DC to AC derating of 60 and PV panel efficiency of 12 find the required peak system DC rating in Wp and the required PV panel area in m2 e 6 pts How do the output voltages of unloaded lead acid batteries differ at 100 state of charge vs 50 state of charge Why ECEN2060 88 Name Exam Scores Problem 1 out of 30 Problem 2 out of 40 Problem 3 out of 30 TOTAL out of 100
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