jw_spring08_report.pdf

7/27/2019 jw_spring08_report.pdf

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SuPER Cart DC Motor Model

And

Ultra-Capacitor Addit ion

Joseph Witts


2/28


3/28

Next the motor was turned on with a 1.6 lbs-in load. The steady state battery terminal voltage

and shunt voltage was measured and the batterys internal resistance was calculated as follows.

Open circuit battery voltage = Voc = 11.75 V

Steady state battery terminal voltage = Vss = 10.50 V

Shunt voltage = 15.5 mVShunt Ratio

mV

A

mV

A6.0

50

30==

Shunt current = ( ) AmVmV

AI 3.95.156.0 =

=

Batterys Internal Resistance = =

=

= 129.03.9

5.1075.11

A

VV

I

VssVocRBat

Now that the batterys internal resistance is known. The current supplied by the battery can be

calculated using the following formula:

BatR

tVVoctI

)()(

=

Where V(t) values were taken from the oscilloscope trace of Plot 1. The voltage values and

calculated current values during the motors starting in-rush can be seen in Data Table 1.

Plot 1: Battery terminal voltage trace with DC motor loaded at 8 in-lbs


4/28

Time(ms)

Voltage(V)

Current(A)

230 8.781 23.02

240 8.813 22.77

250 8.844 22.53

260 8.875 22.29

270 8.906 22.05

280 8.938 21.80

290 8.938 21.80

300 8.969 21.56

310 9.000 21.32

320 9.000 21.32

330 9.031 21.08

340 9.031 21.08

350 9.063 20.83360 9.063 20.83

370 9.063 20.83

380 9.094 20.59

390 9.094 20.59

400 9.094 20.59

420 9.125 20.35

450 9.156 20.11

500 9.188 19.86

550 9.188 19.86

1000 9.188 19.86

Time(ms)

Voltage(V)

Current(A)

0 11.750 0.00

10 6.906 37.55

20 6.844 38.03

30 7.094 36.09

40 7.313 34.40

50 7.438 33.43

60 7.531 32.71

70 7.656 31.74

80 7.781 30.77

90 7.875 30.04

100 8.031 28.83

110 8.094 28.34

120 8.156 27.86130 8.250 27.13

140 8.313 26.64

150 8.375 26.16

160 8.469 25.43

170 8.563 24.71

180 8.594 24.47

190 8.625 24.22

200 8.688 23.74

210 8.688 23.74

220 8.719 23.50

Data Table 1: Measured battery terminal voltage obtained from oscilloscope and calculated current

DC Motor Modeling

A PSpice model (Schematic 2) of a permanent magnet DC motor was found athttp://www.ecircuitcenter.com/Circuits/dc_motor_model/DCmotor_model.htm where the author

modeled the mechanical side of the motor with an electrical equivalent. Mechanical torque was

represented by voltage, speed by current, and drag by a resistor.


5/28

Schematic 2: DC motor model found online

After looking at the mechanical side of this model it became apparent that it can only be accuratefor one value of torque. Schematic 3 is a simplified version of the mechanical side of the model.

Once the motor reaches steady state operation the inertia can be ignored, so the speed is

determined by torque and viscous drag (R). If the value of R is determined from the steady state

values of Data Table 1, and the same value of R is used for rated torque the error is large as seenbelow.

R

I ner t i a

Vi scous

Dr agTorque

1 2

Schematic 3: Simplified mechanical side of the DC motor model

Using measured values from Data Table 1 to calculate R:

At steady state inertia does not need to be considered.

( )( DragViscousSpeedTorque _= )

kRPM

inlb

kRPM

inlb

Speed

TorqueR

=

== 944.7

007.1

8


6/28

Using this value of R to calculate speed at rated torque:

( )kRPM

kRPMinlb

inlb

DragViscous

TorqueSpeed 101.1

944.7

75.8

_=

==

Error of the DC motors calculated speed using this value of R for rated speed:

%8.38%100800.1

800.1101.1=

=Error

So this model of a DC motor is missing some component that can yield more reliable results. Icame across a document online for testing and modeling a DC motor at

http://www.mech.utah.edu/~me3200/labs/motorchar.pdf that showed there was another

component of drag that needs to be considered when modeling a motor. Coulomb drag, unlikeviscous drag, is not a function of speed and is constant. So the coulomb drag was modeled as a

DC voltage source opposing the applied torque voltage source of Schematic 4. To solve for theappropriate value of viscous and coulomb drag two equations with two unknowns needed to be

developed. By using the steady state values in Data Table 1 and the motors rated values the twoequations were developed. Below are the calculations used to determine the values of coulomb

drag (X) and viscous drag (R) to be used in Schematic 4.

R

I ner t i a

Vi scous

Dr agTorque

Coul omb Dr ag

X

1 2

Schematic 4: Variables used to determine both viscous and coulomb drag

At steady state inertia does not need to be considered.

( )(RSpeedXTorque += )

From measured values of Data Table 1

kRPMSpeed

inlbTorque

007.1

8

=

=

)

Equation 1

( ) ( )(RkRPMXinlb 007.18 +=

DC motors rated values

kRPMSpeed

inlbTorque

8.1

75.8

=

=

Equation 2

( ) ( )( )RkRPMXinlb 8.175.8 +=


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Equation 3, solving for X in Equation 2

( ) ( RkRPMinlbX 8.175.8 = )( )

Substitute Equation 3 into Equation 1

( ) ( ) ( )( ) ( )( )RkRPMRkRPMinlbinlb 007.18.175.88 +=

( )kRPM

inlbkRPM

inlbR =

= 9458.0

793.0

75.0

Substitute R into Equation 1 and solve for X

( ) ( )

+=

kRPM

inlbkRPMXinlb 9458.0007.18

inlbX = 048.7

Now that the values of viscous and coulomb drag have been determined, the rest of the DCmotors model parameters can be found. The DC motor model has an electrical side and a

mechanical side represented by electrical components. The electrical side uses an inductor to

represent the motors armature inductance, a resistor for the armature resistance, and a currentcontrolled voltage source to represent the back emf. The mechanical side uses a current

controlled voltage source to represent the applied torque, a DC source for coulomb drag, an

inductor for inertia, and a resistor for viscous drag. All of these parameters, except the twodrags, where solved by trial and error by comparing the simulations output to the data gathered

in Data Table 1. The manufactures supplied values were used for the initial motor parameters

and adjusted until the simulated current waveform Plot 5 represented the actual currentwaveform Plot 4. See Schematic 5 for the final DC motor model circuit and parameters.


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00

0

R_Motor0.16

Viscous_Drag0.9458

L_Motor

0.7m

1

2

Inertia

1.2

1

2

+-

TorqueKt=0.404

V_Battery11.75V

+-

Back_EMFKm=6.1

R_Battery

0.129

Coulomb_Drag7.048

Schematic 5: Final PSpice DC Motor Model

Notice that the magnitude of the armature inductance and resistance is noticeably greater than the

manufacturers values. This is because the testing setup measured the voltage across thebatterys terminals not the direct input to the motor. So the resistance and inductance of the wire

going from the battery to the motors plug, and the 16 foot long cord for plugging in the motor,

are added to the armatures inductance and resistance. To improve this model the voltage needsto be measured at the battery terminal and the input to the 16 foot long plug for the motor. This

way the wire connecting the battery to the plug can be modeled separately, so the final motormodel will represent only the motor and the 16 foot cord connected to the motor.

The following plots below can be used to tell how well the model reflects the actual data bycomparing the actual waveform of the current and voltage during the motors in-rush stage to the

simulation. As you can see by comparing Plot 2 and Plot 3 the voltage sags are reasonably

similar, and the current spike of Plot 4 and Plot 5 are also very similar. There is still room forimproving the model by not lumping the impedance of the wire going from the battery to the

plug and the 16 foot cord with the DC motors armature inductance and resistance. Since this is

just the initial prototype phase of the project, and the wiring will likely change, furtherrefinement of the model was not conducted. Plots 6 and 7 were included to show how the

modeled DC motors applied torque and speed change as a function of time, and how the steady

state values are very close to those in Data Table 1.


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Battery Terminal Voltage During DC Motor In-Rush

Mechanical Load = 8 in-lbs

6

7

8

9

10

11

12

0 100 200 300 400 500 600 700 800 900 1000

Time (ms)

Voltage(V)

Plot 2: Plot of the actual battery terminal voltage from Data Table 1

Ti me

0s 0. 1s 0. 2s 0. 3s 0. 4s 0. 5s 0. 6s 0. 7s 0. 8s 0. 9s 1. 0sV( L_Motor : 1)

6V

8V

10V

12V

Plot 3: Modeled DC motors battery terminal voltage


10/28

DC Motor In-Rush Current

Mechanical Load = 8 in-lbs

0

5

10

15

20

25

30

35

40

0 100 200 300 400 500 600 700 800 900 1000

Time (ms)

Current(A)

Plot 4: Plot of the actual motor in-rush current from Data Table 1

Ti me

0s 0. 1s 0. 2s 0. 3s 0. 4s 0. 5s 0. 6s 0. 7s 0. 8s 0. 9s 1. 0s

I (R_Batt ery)

0A

10A

20A

30A

40A

Plot 5: Modeled DC motors in-rush current draw


11/28

Ti me

0s 0. 1s 0. 2s 0. 3s 0. 4s 0. 5s 0. 6s 0. 7s 0. 8s 0. 9s 1. 0sV( Torque: 3)

0V

4V

8V

12V

16V

Plot 6: Modeled DC motors torque in lb-in

Ti me

0s 0. 1s 0. 2s 0. 3s 0. 4s 0. 5s 0. 6s 0. 7s 0. 8s 0. 9s 1. 0sI ( Coul omb_Dr ag)

0A

0 .5A

1 .0A

Plot 7: Modeled DC motors speed in kRPM

Next the model was used to compare simulated values to actual data found on the wiki (files

dc_motor and dc_motor_solar) and the motors rated values. As you can see from Data Table 2the simulated values are reasonably close to the actual data. One discrepancy is with the

dc_motor file simulation where the simulated speed is 12% less than the actual data. Im not

sure how the data was gathered for the dc_motor file, but if the recorded voltage is actually themotor voltage instead of the battery voltage this could account for the larger error. If this is true

the simulation should have a slightly higher battery voltage, which will increase the simulated

torque and speed slightly and decrease the error. As far as the 20.4% error for the motoroperating at rated values, the error is likely due to the fact that the model has impedance of the

wire going from the battery to the plug and the 16 foot cord, lumped together with the motors

armature inductance and resistance. Even though the battery voltage is 14.45 V the actualvoltage at the input of the motor (manufactures rated voltage location) is lower. So the real


12/28

percent difference is lower than 20%, due to the voltage drop across the wire going from the

battery to the plug and 16 foot cord.

Condi tion Battery Voltage (V) Torque (lb-in) Speed (rpm) Motor Current (A)

Data Table 1 9.188 8.00 1007 19.86

Simulation 9.188 7.98 988 19.76Percent Difference 0.0% -0.2% -1.9% -0.5%

dc_motor_solar 12.2 8.00 1523 20.16

Simulation 12.2 8.42 1453 20.85

Percent Difference 0.0% 5.3% -4.6% 3.4%

dc_motor 8.14 8.00 939 19.80

Simulation 8.14 7.83 826 19.38

Percent Difference 0.0% -2.1% -12.0% -2.1%

Motor Rating 12 8.75 1800 21.00

Simulation 14.45 8.75 1800 21.66

Percent Difference 20.4% 0.0% 0.0% 3.1%

Data Table 2: Comparison of simulated and actual data

Ultra-Capacitor

In an attempt to extend the life of the battery the idea came about to use an ultra-capacitor for

energy storage for short term high energy demands, like the in-rush current associated withstarting the DC motor.

Since the internal resistance of the battery and the batterys open circuit voltage was known, aPSpice simulation was run to determine what would happen if the uncharged ultra-capacitor was

placed across the battery (Schematic 6). It turns out that a large amount of current is drawn for a

significant amount of time due to the large capacitance of the ultra-capacitor (Plot 8).

0

V_Battery12Vdc

R_Battery

0.129

ESR0.019

Ultra_Cap58

Schematic 6: Charging the ultra-capacitor without current limiting resistor


13/28

Ti me

0s 10s 20s 30s 40s 50s 60sI (R_Battery)

0A

50A

100A

Plot 8: High ultra-capacitor charging current due to lack of current limiting resistor

To limit this charging current, a current limiting resistor needs to be added to the circuit. Theparameters that were used to determine the appropriate resistor value were physical resistor size,

power dissipation, and charging time. The larger the resistance, the smaller the resistors became

because they had to dissipate less power, but this also increased the charging time. Likewise, thesmaller the resistance, the larger the resistors become to dissipate a larger amount of power. To

narrow down the options a total charging time of 15 minutes was determined to be an acceptable

charging time, which equals five time constants. The required resistance value to yield this

charging time was calculated as follows:

( )

( )( )=

=== 1.3585

min

sec60min15

min1555F

RRC

Now that knowing a resistance of around 3 was needed to produce a charging time of 15

minutes, the power rating of the resistor could be calculated by using the nominal 12 volts of the

battery.

( )W

V

R

VP 48

3

1222

=

==

Using the calculated resistance and power rating, an Ohmite 270 series 3 50W resistor was

determined to be a good choice. Ideally the PV array should charge the ultra-capacitor instead of

the battery. The problem with this is that the output of the DC-DC converter is usually between13V and 14V. So the resistor needs to be able to handle the higher power dissipation due to the

higher output voltage of the converter. The resistors datasheet states the resistor can take an

overload of 10 times rated power for 5 seconds without damaging the resistor. A simulation wasconducted using a 14V source simulating the DC-DC convert (Schematic 7), plotting the

charging current and resistor power dissipation as a function of time (Plot 9). From the

simulation one can conclude that the resistor can handle the increased power dissipation, since


14/28

the maximum power is only 1.3 times the rated value and decays to the rated value in about 20

seconds.

0

V_Converter14Vdc

ESR0.019

Ultra_Cap58

R_Charging

3

Schematic 7: Charging the ultra-capacitor with PV array using current limiting resistor

Ti me

0s 50s 100s 150s 200s 250s 300s 350s 400s 450s 500sW(R_Cha rgi ng) I ( R_Cha rgi ng)

0

20

40

60

80

Plot 9: Charging current and power dissipated by the 3 current limiting resistor

Operating Mode PCB

Once the ultra-capacitor is charged to the same voltage as the battery, there is no need for the

current limiting resistor. So a circuit needed to be developed that could switch a current limitingresistor in and out of the system. Since we are still in the prototype phase of the project we

might have to remove the ultra-capacitor at some point, so there should be a provision to safely

discharge the capacitor. So the circuit will have three different modes of operation callednormal, charging, and discharging, and will be known as the operating mode PCB (Schematic 8).

In normal mode power will come from the battery and pass through the board to the charged

capacitor and the load bus (Schematic 9). During the charging mode a 3 resistor will be placedin series with the battery and capacitor to limit the initial charging current of the uncharged ultra-

capacitor (Schematic 10). When in the discharge mode the ultra-capacitor will be isolated from

the battery and connect to ground through a 3 resistor (Schematic 11). Power MOSFETs willbe used to act as the switches on the operating mode PCB. The switching of the circuit will be

controlled by the computer, so the board must be able to interface with the NiDAQs.


15/28

S2

S1Char gi ng Resi st or

Di schargi ng

Resi st or

Bat t er y DC t o DC

Convert er

0

To Load Bus

Ul t ra

Capaci t or

S0

S3

Schematic 8: Simplified version of the operating mode PCB

S2


Di schargi ng

Resi st or


Convert er

0

To Load Bus

Ul t ra

Capaci t or

S0

S3

Schematic 9: Operating mode PCB in normal mode


16/28

S2


Di schargi ng

Resi st or


Convert er

0

To Load Bus

Ul t ra

Capaci t or

S0

S3

Schematic 10: Operating mode PCB in charging mode

S2


Di schargi ngResi st or


Convert er

0

To Load Bus

Ul t ra

Capaci t or

S0

S3

Schematic 11: Operating mode PCB in discharge mode

The actual circuit is obviously more complicated than the simplified versions above, and was

constructed on a six by eight inch board. Schematics 12 and 13 show the componentconnections on the PCB, while the rest of this section explains how components were selected.


17/28

C151u

R7

1k

BATTERY

MAIN LINE

GND

LOAD VOLTAGE

S0

S1

S2

U6LM2937ET-5.0

IN1

OUT3

GND

2

U5 LM2937ET-8.0

BATTERY IN1

OUT3

GND

2

Switch S3IRF2804

C8

0.1u

U7

MAX1822

C1+1

C1-7

C2+6

C2-2

Vcc

8

GND

4

Vout5

U8 SN7406N Inve ter

Input1

Input3

Output4

Output2

Input5

Input9

Input11

Output6

Output8

Output10

Vcc

14

GND

7

Input13

Output12

R4

51k

C910u

C101u

C111u

C12

1u

GND

Header f rom NiDAQ

1 2 3 4 5 6

C13

0.1u C1410u

Schematic 12: First half of the operating mode PCB

ULTRA-CAPACITOR AND LOAD BUS

U2LM2937ET-3.3

IN1

OUT3

GND

2

U1 LM2937ET-8.0

IN1

OUT3

GND

2

C161u

R8

1k

C171u

R9

1k

MAIN LINE

S2

Switch S2IRF2804

S1

C181u

S0

R10

1k

Switch S1IRF540

Switch S0IRF540

MAIN LINE

U3

MAX622

C1+1

C1-7

C2+6

C2-2

Vcc

8

GND

4

Vout5

U4MM74C90X Buff er

Output1

Output3

Input4

Input2

Output5

Output9

Output11

Input6

Input8

Input10

Vcc

14

GND

7

Output13

Output12

R1

51k

R2

51k

R3

51k

C2

10u

C51u

C61u

C7

1u

C1

0.1u

C30.1u

GND

Charging

3

Discharge

3

LOAD VOLTAGE

R6

51k

R5

51k

C4

10u

U17

LM741

V+

7

+3

OS25

OUT6

-2

V-

4

OS11

Schematic 13: Second half of the operating mode PCB


18/28

MOSFET Selection

An IRF2804S power MOSFET was selected for switches S2 and S3, which are connected to the

high current traces of the operating mode PCB. These MOSFET need to be rated for at least

30A continuous, with low on resistance to make the voltage drop across the MOSFETs as small

as possible. The MOSFETs have a continuous drain current rating of 75A, and an on resistanceof 2.5m, so the voltage drop across each MOSFET will be 70mV at 30A. A D2pak package

was used in order to increase the surface area that will carry the high current. The drain terminalon this package has a large flat surface that gets soldered directly to the board, which should also

help to dissipate heat.

The selection of switches S0 an S1 was not as critical as switches S2 and S3, since the will nothave high current flowing through them. They also do not need a low on resistance, since they

are only being used to charge and discharge the ultra-capacitor. An IRF540PBF power

MOSFET rated for 28A and an on resistance of 77m was selected. Since only a small amountof current will flow through these MOSFETs, a TO-220 was used to save board space.

Gate Driver Selection

Since the source terminal of the MOSFETs used for switches S1, S2, and S3 will be around 12 V

when the switches are on, the gate voltage must be higher than 12V to turn the MOSFETs on. AMaxim MAX622 high-side power supply was selected to generate a gate voltage above 12V.

The output voltage of the MAX622 is 11V higher than MAX622 supply voltage.

Voltage Regulators

The maximum gate to source voltage of the MOSFETs is 20V. If the MAX622 was supplied by

the battery the output voltage would be the battery voltage plus 11V, which could be as high as25V if the battery is being charged and the DC-DC converter is outputting 14V. This would

cause the gate to source junction to breakdown if the source of the MOSFETs were ever

grounded during a fault, or in the case of switch S0 connected to ground through the dischargingresistor to discharge the ultra-capacitor. So an 8V regulator was selected for the MAX622s Vcc

to limit the voltage output to 19V.

It turns out that even though the NiDAQs are supposed to output 5V for a high signal, theyrealistically can output as low as 2V according to Eran Tals thesis. So a 3.3V regulator was

used for the buffers Vcc, to work with the NiDAQs low VOH. However the inverter has a 5V

regulator for Vcc, which has a VIH minimum of 2V, so it is compatible with the NiDAQs.

Buffer/Inverter Selection

The control signals will comes out of the NiDAQs and to the inputs of either a buffer or inverter.

A MM74C906 open drain buffer was used, so that when the input is high the output is floating.


19/28

And a SN7406 open collector inverter was used, so that when the input is low the output is

floating. The outputs are connect to the MAX622s output by a 51k resistor. When theinverter or buffers output is low the MOSFETs are turned off, and when the outputs are floating

the MOSFETs gate voltage will be 19V turning them on.

In an effort to make the PCB more reliable it needed to be determined if there are any conditionsthat could cause the NiDAQs to function strangely, and turn on a switch that should be off. It

turns out there are two conditions. When the computer is initially turned on the NiDAQs outputa high signal, which remains high until the program controlling the circuit switching is executed.

If all the gates are driven by buffers connected to the NiDAQ, then all the MOSFETS turn on.

Which means the battery will be connected to ground through a 3 resistor. So the idea of usinginverters instead of a buffer to control the switching came up, but this yield a new problem. If

the NiDAQs loose power their output is low, which will cause the inverters (powered by the

battery) to output high turning all the switches on. So an extra switch (S3) was added to theboard to eliminate the problem of turning on switches when they should be off. The board is set

up so that the gate on switch S3 is connected to the NiDAQs through an inverter, and the control

circuitry is powered directly by the battery. Whereas the gate on switch S0, S1, and S2 isconnected to the NiDAQs through a buffer and the control circuitry is powered up only when

switch S3 is on. This way when the NiDAQs are initially turned on and all outputs are high

switch S3 is turned off, which de-energizes the control circuitry of switch S0, S1, and S2 turningthem off. If the NiDAQs loose power and all outputs go low switch S0, S1, and S2 turn off,

while switch S3 turns on.

The best solution for this problem would be to purchase new NiDAQs that output low when

initially energized, which means the board can function properly by only using buffers tointerface with the NiDAQs. This way the cost and size of the board can be reduced byeliminating a number of components that will no longer be needed, such as switch S3 and all of

its control circuitry.

Operating Mode PCB Testing

Once the operating mode PCB was constructed it needed to be tested before being installed on

the SuPER cart. Since there are no power supplies that can supply 30A, the DC source from theAC machines lab was used. Data Table 3 shows voltage drop across switches S2 and S3 and the

calculated MOSFET on resistance at different current values.

I (A) S2 (mV) S3 (mV) Rds on S3 (m) Rds on S2 (m)

5 13.3 8.3 1.7 2.710 22.6 19.1 1.9 2.3

15 32.5 25.0 1.7 2.2

20 49.5 41.2 2.1 2.5

22 53.7 45.9 2.1 2.4

25 59.6 50.6 2.0 2.4

28 66.7 55.9 2.0 2.4

30 72.4 59.9 2.0 2.4


20/28

Data Table 3: MOSFET on resistance of switch S2 and S3

Plot 10 shows the voltage drop across each as a function of current. The slope of the trend line

represents the average on resistance, and this value could be used to describe the MOSFETs

resistance for simulation purposes.

Voltage Drop Across MOSFETS

y = 2.4199x - 0.5978

y = 2.1147x - 2.7353

0

10

20

30

40

50

60

70

80

0 5 10 15 20 25 30 35

Current (A)

VoltageDrop(mV)

S3

S2

Plot 10: Voltage drop across switch S2 and S3

DC Motor Model with Ultra-Capacitor Simulation

Although there is no data to prove how well the simulation compares to actual results, the circuit(Schematic 14) was simulated to get an idea of how the circuit might behave when the DC motor

is started with the ultra-capacitor connected. The in-rush DC motor current peaks at about 62A,

with the battery suppling about 8A and the ultra-capacitor supplying about 54A. By looking at

Plot 13 the DC motors torque reaches steady state in about 0.5 seconds. However, according toPlot 15 the speed doesnt reach steady state until 35 seconds after start up which seems rather

long. If the circuit does behave like the simulation, then the battery is definitely not suppling alarge amount of current during motor start up. The bulk of the current is coming from the ultra-

capacitor.


21/28

00

0

R_Motor

0.16

Viscous_Drag

0.9458

L_Motor

0.7m

1

2

Inertia

1.2

1

2

+-

TorqueKt=0.404

V_Battery11.75

+-

Back_EMFKm=6.1

ESR

0.019

Ultra-Cap

58

R_Battery

0.129

Coulomb_Drag7.048

Schematic 14: DC motor simulation with ultra-capacitor

Ti me

0s 5s 10s 15s 20s 25s 30s 35s 40s 45s 50s 55s 60sI ( R_Bat t er y) I ( ESR) I ( L _Mot or ) V( Ul t r a- Cap: +)

0

20

40

60

80

Plot 11: Ultra-capacitor voltage and battery, ultra-capacitor, and DC motor current at steady state


22/28

Ti me

0s 0. 1s 0. 2s 0. 3s 0. 4s 0. 5s 0. 6s 0. 7s 0. 8s 0. 9s 1. 0sI ( R_Bat t er y) I ( ESR) I ( L_Mot or )

0A

20A

40A

60A

80A

Plot 12: Battery, ultra-capacitor, and DC motor current during in-rush

Ti me

0s 0. 1s 0. 2s 0. 3s 0. 4s 0. 5s 0. 6s 0. 7s 0. 8s 0. 9s 1. 0sV( Torque: 3)

0V

10V

20V

30V

Plot 13: Modeled DC motors torque in lb-in with ultra-capacitor


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Ti me

0s 0. 1s 0. 2s 0. 3s 0. 4s 0. 5s 0. 6s 0. 7s 0. 8s 0. 9s 1. 0sI ( Coul omb_Dr ag)

0A

0.5A

1.0A

1.5A

Plot 14: Modeled DC motors peak speed in kRPM with ultra-capacitor

Ti me

0s 10s 20s 30s 40s 50s 60sI ( Coul omb_Dr ag)

0A

0.5A

1.0A

1.5A

Plot 15: Modeled DC motors steady state speed in kRPM with ultra-capacitor


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Parts List

Description Part # Newark Part # Price

R1 51k MCRC1/4G513JT-RH 73K0336 0.128

R2 51k MCRC1/4G513JT-RH 73K0336 0.128

R3 51k MCRC1/4G513JT-RH 73K0336 0.128R4 51k MCRC1/4G513JT-RH 73K0336 0.128

R5 51k MCRC1/4G513JT-RH 73K0336 0.128

R6 51k MCRC1/4G513JT-RH 73K0336 0.128

R7 1k MCRC1/4G102JT-RH 72K6178 0.128

R8 1k MCRC1/4G102JT-RH 72K6178 0.128

R9 1k MCRC1/4G102JT-RH 72K6178 0.128

R10 1k MCRC1/4G102JT-RH 72K6178 0.128

Total 1.28


C1 0.1F KME50VBR10M5X11LL 91F3293 0.143

C2 10 F 106CKH100M 69K7898 0.106

C3 0.1 F KME50VBR10M5X11LL 91F3293 0.143

C4 10 F 106CKH100M 69K7898 0.106

C5 1 F 105CKH050M 69K7895 0.038

C6 1 F 105CKH050M 69K7895 0.038

C7 1 F 105CKH050M 69K7895 0.038

C8 0.1 F KME50VBR10M5X11LL 91F3293 0.143

C9 10 F 106CKH100M 69K7898 0.106

C10 1 F 105CKH050M 69K7895 0.038

C11 1 F 105CKH050M 69K7895 0.038

C12 1 F 105CKH050M 69K7895 0.038C13 0.1 F KME50VBR10M5X11LL 91F3293 0.143

C14 10 F 106CKH100M 69K7898 0.106

C15 1 F 105CKH050M 69K7895 0.038

C16 1 F 105CKH050M 69K7895 0.038

C17 1 F 105CKH050M 69K7895 0.038

C18 1 F 105CKH050M 69K7895 0.038

Total 1.38

Description Part # Mouser Part # Price

X1 15 amp terminal 7690 534-7690 0.46

X2 15 amp terminal 7690 534-7690 0.46

X3 15 amp terminal 7690 534-7690 0.46

X4 15 amp terminal 7690 534-7690 0.46

X5 30 amp terminal 8196 534-8196 1.24

X6 30 amp terminal 8196 534-8196 1.24

X7 30 amp terminal 8196 534-8196 1.24

Total 5.56


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U1 8V Regulator LM2937ET-8.0 07B6337 2.62

U2 3.3V Regulator LM2937ET-3.3 41K4552 2.49

U3 High-Side Power Supply MAX622 0

U4 Buffer MM74C906N 58K1928 2.58

U5 8V Regulator LM2937ET-8.0 07B6337 2.62

U6 5V Regulator LM2937ET-5.0 41K4553 2.62

U7 High-Side Power Supply MAX1822 0

U8 Inverter SN7406N 08F7825 1.05

U9 MOSFET IRF540PBF 63J7322 1.00

U10 MOSFET IRF540PBF 63J7322 1.00

U15 MOSFET IRF2804SPBF 73K8240 3.55

U16 MOSFET IRF2804SPBF 73K8240 3.55

U17 Op Amp LM741 78K6012 0.296

Total 23.38

Description Part # Newark Part # Mouser Part # Quantity Price Total3 ohm 50W L50J3R0E 64K5014 2 8.61 17.22

Crimp Connector 3-350980-1 52K4327 6 0.061 0.366

6 terminal housing 640250-6 571-6402506 1 0.17 0.17

6 terminal header 640445-6 571-6404456 1 0.18 0.18

Total 17.94

How to Operate the SuPER Cart

SuPER Prototype OperationModified 6/11/07 J. Witts

1) Ensure that all breakers are open.2) Insert the hub cables into the laptop USB ports, followed by the NI DAQ device cables.

Then insert the PIC cable into the open laptop port. The mouse cable should be insertedinto the hub.

3) Power on the laptop (at this point running on its internal battery) and at the GRUBwindow choose the latest version of Red Hat.

4) Login using root:super1.5) Open a shell and change directories (cd) to/home/super1/pvpro/src to control the PV

and main switch board.6) Close PV, converter and battery circuits by flipping the breakers marked PV, BATT

and BUS. The PV array will start charging the battery even though no programs are

running, because the NiDAQs default output is high (turning MOSFET switches on).

7) Execute the software with the command ./contAcquireNChan .8) Open a new shell and change directories (cd) to/home/super1/cap/src to control the

ultra-capacitor board.

9) Execute the software with the command ./cap .


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10) If the ultra-capacitor is not needed leave the breaker labeled CAP open, enter n tooperate the capacitor board in normal operation, and skip to step 14. If the capacitor isneeded proceed to step 11.

11) Check the capacitor voltage with a voltmeter. If the capacitor voltage is within 2 V ofthe battery terminal voltage, run the capacitor board in normal mode. If the capacitor

voltage is not, run the capacitor board in charging mode. Once the capacitor voltage iswithin 2 V of the battery terminal voltage, change the operating mode from charging to

normal. Follow prompt and enter correct mode of operation.

c to charge the capacitor (used if capacitor is not at battery voltage)n for normal operation (used to operate the cart without any resistors)

12) Once the capacitor board is operating in the correct mode determined from step 11,close the breaker labeled CAP. Once the capacitor is at the same voltage as the batterynode and the operating mode is set to normal, the SuPER cart is ready to operate

13) Close the breakers as desired to power indicated loads.14) To turn the system off, open all circuit breakers connected to the load bus.15) While in the shell for the ultra-capacitor board type

o to turn all switches off (used to turn all capacitor board switches off) thenq to quit (used to exit program)16) Now go to the shell running the PV software and use q to quit.17) Shut everything down by opening all circuits at the breakers.

Note: If the ultra-capacitor has to be physically taken off the cart it must be discharged first.

Follow the instructions below to safely disconnect the ultra-capacitor.

1) Follow steps 1 through 4 listed above.2) Close the breaker labeled BATT.3) Follow steps 8 through 9 to run the ultra-capacitor board software. Set the board to run in

discharge mode by entering d.

4) Close the breaker labeled CAP.5) When capacitor is fully discharged (use voltmeter to ensure 0 V) turn off the system

following step 15 listed above. The capacitor can now be safely removed.

Circuit Breaker Rearrangement

In order to connect the capacitor to the SuPER cart, some of the circuit breakers needed to bemoved. The 2 amp circuit breaker labeled BUS, that powers the sensors and control elements,

had to be removed from the load bus. When the ultra-capacitor is charging it pulls the busvoltage down to zero volts, then slowly rises to the batterys voltage. When the voltage is pulleddown to zero, none of the control circuitry can be used. This means the PV array cannot be used

to charge the ultra-capacitor, only the battery will be able to charge the ultra-capacitor. So by

moving the BUS circuit breaker off the load bus and powering it off the battery, the PV array cannow be used to charge the ultra-capacitor.


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A 6 amp circuit breaker was selected to protect the capacitor. The breaker size was selected

based on looking at the simulated capacitor current during start up (plot 12), and compared to thecircuit breaker curve of plot 16. Since the circuit breaker curve is based on constant current

during a fault, the breaker should not operate for the decaying transient of the DC motors in-

rush current. The ultra-capacitors circuit breaker could not be directly connected to the load bus,

since the circuit breakers can only interrupt faults in one direction. The construction of thecircuit breaker only allows mounting in one direction, so it had to be installed adjacent to the

load bus. See Schematic 15 for actual breaker locations. The circuit breaker was connected thisway to interrupt fault current supplied by the ultra-capacitor if the load bus, or any point

connected to the load bus, was faulted to ground.

Plot 16: CBI circuit breaker curve


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Schematic 15: Gavin Baskins SuPER schematic

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