ECEN 45171Lecture 3ECEN 4517/5517DC-DC converterBattery charge controllerPeak power trackerExperiment 3ECEN 45172Due datesThis week in lab:Experiment 1 report (one from every group)Next week in lecture:Exp. 3 prelab assignment (one from every student)Next week in lab:Exp. 2 scoresheet (you should be able to submit in lab this week, but beginning of lab next week at the latest) (one from every group)Late assignments will not be accepted. Assignments are due within five minutes of beginning of period.ECEN 45173Lab reports• One report per group. Include names of every group member on first page of report.• Report all data from every step of procedure and calculations. Adequately document each step.• Discuss every step of procedure and calculations– Interpret the data– It is your job to convince the grader that you understand what is going on with every step– Regurgitating the data, with no discussion or interpretation, will not yield very many points– Concise is goodECEN 45174Experiment 2: this weekOrientation to MSP430F2616 and Code Composer Suite tools• No prelab or report• Instead: get TA to initial sheet at end of experiment procedure• See Lecture 2 slides and Exp. 2 procedureMaterials needed for this lab:• MSP430F2616 boardIn power lab kitYou will need to solder JTAG header and power supply leads• MOSFET, gate driver, etc.In power lab kit• Oscilloscope probeIn undergraduate circuits kit, or available at E storeECEN 45175Goals in upcoming weeksExp. 3: A three-part experimentExp. 3 Part 1:Demonstrate dc-dc converter power stage operating open loop, driven by MSP430 PWM outputInside, with input power supply and resistive loadOutside, between PV panel and batteryDC system simulationExp. 3 Parts 2 and 3:Demonstrate working sensor circuitry, interfaced to microprocessorDemonstrate peak power tracker and battery charge controller algorithms, outside with converter connected between PV panel and batteryECEN 45176Exp. 3, Part 1Demonstrate dc-dc power stage insideECEN 45177Converter Power StageSome choicesBuck converter• Steps down voltage• Industry workhorse• High efficiencySEPIC• Can step voltage up or down, to peak power track over wider voltage range• More complex• Good efficiencyECEN 45178Gate drive circuitwith transformer isolation• Gate driver output vd(t) has a dc component when d 0.5• Transformer will saturate if we apply dc• Primary blocking capacitor removes dc component• Secondary capacitor and diodes form a diode clamp circuit that restores the dc componentECEN 45179Gate driver transformer• Use ferrite toroid in your kit• Leakage inductance is minimized if bifilar winding is used• Need enough turns so that applied volt-seconds do not saturate core:B = V1DTs /n1AcECEN 451710Alternate smaller version of gate driver• Uses only one gate driver instead of two, to produce half the voltage swing on primary• Transformer turns ratio is 1:1• Produces half as much gate current• Suitable for smaller MOSFETsECEN 451711Exp. 3, Part 1Test open-loop converter, outsideBasic control characteristics:How does the duty cycle control the PV and battery voltages and currents?ECEN 451712Prelab assignmentExp. 3, Part 1Design your buck converter power stage1. Work out the current waveforms of each component: MOSFET, diode, inductor, capacitors2. Design your inductor• Use Kg method explained in ECEN 4797/5797• You decide how much ripple to allow, how much power loss to allow, etc.• Use one of the ferrite cores in your kit3. Check the voltage and current stresses on each power component and make sure the components operate within their datasheet ratingsContents of parts kit, with links to datasheets, is on web athttp://ecee.colorado.edu/~ecen4517/components/kit.htmlECEN 451713Core Material 7070TSC Ferrite InternationalSee parts kit web page for complete datasheetsKit includes ferrite cores made of this material, in three geometries:PQ 32/20PQ 26/2513-07-06 toroidECEN 451714Converter modeling and simulationConduction modes– Continuous conduction mode (CCM)– Discontinuous conduction mode (DCM)Equivalent circuit modeling– The dc transformer model: CCM– DCM modelSimulation– Averaged switch model in CCM– Averaged switch model in DCM– A combined automatic model for PSPICE (or Simulink, optional)ECEN 451715Averaged switch modelingBasic approach (CCM)D1Q1R+V–+–CLVgGiven a switching converter operating in CCMBuck converter exampleSeparate the switching elements from the remainder of the converterDefine the terminal voltages and currents of the two-port switch networkR+V–+–CLVgD1Q1+v1–+v2–Switchnetworki1i2ECEN 451716Terminal waveforms of the switch networkRelationship between average terminal waveforms:ECEN 451717Averaged model of switch networkv1d=v2d= vgi2d=i1d= iLSov1=ddv2i2=ddi1+–+ v2(t)Ts– i1(t)TsAveraged switch network+ v1(t)Ts– i2(t)Tsd(t)d(t)v2(t)Tsd(t)d(t)i1(t)TsModeling the switch network viaaveraged dependent sourcesECEN 451718PSPICE simulationExp. 3 Part 1: open loopBuck converter modelPV+–i2(t)Tsv2(t)Tsv1(t)Tsi1(t)Tsd+–+–12345CCM-DCM1PV modelBatterymodel• Use your PV model from Exp. 1• Replace buck converter switches with averaged switch model• CCM-DCM1 and other PSPICE model library elements are linked on course web page• You may optionally develop a Simulink model insteadECEN 451719Sensing the battery current and voltageExp. 3 Part 2ECEN 451720Exp. 3 Part 3• Implement maximum power point tracking algorithm• Demonstrate on PV cart
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