ECEN 4517 1

Lecture 9ECEN 4517/5517

Buck converter

Battery charge controller

Peak power tracker

Experiment 5

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Due dates

This week in lab:Experiment 3 report (one from every group)

Due within five minutes of beginning of your lab section

Next week in lecture:Midterm exam

March 31 in lecture:Exp. 5 prelab assignment

Late assignments will not be accepted.

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Lab reports

• One report per group. Include names of every groupmember on first page of report.

• Report all data from every step of procedure andcalculations. Adequately document each step.

• Discuss every step of procedure and calculations– Interpret the data

– It is your job to convince the grader that you understandwhat is going on with every step

– Regurgitating the data, with no discussion or interpretation,will not yield very many points

– Concise is good

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Goals in upcoming weeksExp. 5: A three-part experiment

Exp. 5 Part 1:Demonstrate buck

converter power stageoperating open loop

Inside, with input powersupply and resistive load

Outside, between PV paneland battery

DC system simulation

Exp. 5 Part 2:Demonstrate open-loop control of converter from microprocessor

Demonstrate working sensor circuitry, interfaced to microprocessorDemonstrate peak power tracker and battery charge controller algorithms,outside with converter connected between PV panel and battery

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Exp. 5, Part 1Demonstrate buck power stage inside

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Gate drive circuitwith transformer isolation

• Gate driver output vd(t) has a dc componentwhen d 0.5

• Transformer will saturate if we apply dc

• Primary blocking capacitor removes dccomponent

• Secondary capacitor and diodes form adiode clamp circuit that restores the dccomponent

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Gate driver transformer

• Use ferrite toroid in your kit

• Leakage inductance is minimized if bifilarwinding is used

• Need enough turns so that applied volt-seconds do not saturate core:

B = V1DTs /n1Ac

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Alternate smaller version of gate driver

• Uses only one gate driver instead of two, toproduce half the voltage swing on primary

• Transformer turns ratio is 1:1

• Produces half as much gate current

• Suitable for smaller MOSFETs

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Exp. 5, Part 1Test open-loop converter, outside

Basic control characteristics:

How does the duty cyclecontrol the PV and batteryvoltages and currents?

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Converter modeling and simulation

Conduction modes– Continuous conduction mode (CCM)

– Discontinuous conduction mode (DCM)

Equivalent circuit modeling– The dc transformer model: CCM– DCM model

Simulation– Averaged switch model in CCM

– Averaged switch model in DCM

– A combined automatic model for PSPICE

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Averaged switch modelingBasic approach (CCM)

D1

Q1

R

+

V

–

+– C

L

Vg

Given a switching converteroperating in CCM

Buck converter example

Separate the switchingelements from theremainder of the converter

Define the terminalvoltages and currents ofthe two-port switchnetwork

R

+

V

–

+– C

L

Vg

D1Q1

+

v1

–

+

v2

–

Switchnetwork

i1 i2

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Terminal waveforms of the switch network

⟨ ⟩

⟨ ⟩

⟨ ⟩

⟨ ⟩

v1(t) T =d′(t)nd(t)

v2(t) T

i2(t) T =d′(t)nd(t)

i1(t) T

Relationship between averageterminal waveforms:

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Averaged model of switch network

v1

d′=

v2

d= vg

i2

d′=

i1

d= iL

So

v1 = d′d

v2

i2 = d′d

i1

+–

+

⟨v2(t)⟩Ts

–

⟨i1(t)⟩Ts

Averaged switch network

+

⟨v1(t)⟩Ts

–

⟨i2(t)⟩Ts

d′(t)d(t)

v2(t) Ts

d′(t)d(t)

i1(t) Ts

Modeling the switch network viaaveraged dependent sources

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PSPICE simulationExp. 5 Part 1: open loop

Buck converter model

PV

+

–

i2(t) Ts

v2(t) Tsv1(t) Ts

i1(t) Ts

d

+

–

+

–

1

2

3

45

CCM-DCM1

PV 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 oncourse web page

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Sensing the battery current and voltageExp. 5 Part 2

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ZXCT 1009 High-side current sense IC

Basic circuit for sensing current in a load

Vout = Iload Rsense Rout / 100

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About the ZXCT1009

Power is supplied through the Vsense+ and Iout pinsThe IC is sensitive to negative-going signals or noise on the Vsense+

and Vsense- pins

Filtering the waveforms:ibatt

Rsense

A/DZXCT1009

MicrocontrollerMSP 430

Power board ground

Rout

Vsense+ -

Iout

Microprocessor board ground

Twisted pair

Filter

Filter

{

{

If necessary, a differential amplifier can be addedto the microprocessor board, to obtain additionalfiltering and noise immunity

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Exp. 5 Part 3

• Implement maximum power point tracking algorithm

• Demonstrate on PV cart outside