DC Power Line Comunication

8/13/2019 DC Power Line Comunication

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experimental and model results. Note that, in Figure 9, there is close correlation between

the experimental and model performance for the load resistance values of 500, 1000,

and 200Q.

800

700 -

600

7ii'

.E500

Q.

~400c

co

-g300a.

E

-200 -

100

, , , '" I

R, = 200 Ohm Exp

R, = 200 Ohm Mod

o R, = 100 Ohm Exp

_ R, = 100 Ohm Mod

R, = 50 Ohm Exp

R, = 50 Ohm Mod

I

I I I

. -, , . i '"1 I I

(2)

Fig. 9. Impedance of transmission line transformer with terminating resistor

2.4. System Performance

Having verified the TLT model, the next step is to evaluate the system performance

when a number of nodes are connected to the CPS line through the Guanella TLT (See

Figure 10). Note that the Guanella TLT is arranged in symmetric form for the sender and

the receivers. Specifically, we are interested in broadcasting data to many receiver nodes,

as illustrated in the figure. Gain and impedance must be evaluated as the number of nodes

n becomes large. The impedance seen from the sender-side terminals is given by:

ZOw) = Vin~W)

linOw)

The frequency transfer function from the input voltage of the sender to the output

voltage of a receiver is given by:

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the two are not directly linked. Therefore, the gain dip frequency and the peak impedance

frequency can be separated.

2500

2000 -1= ~:~ I. - L-5e-5 .

1500-----------

1000 --------------------- --

0.8 I L=5


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Fig. 15.

Central Control

Unit

Prototype DC powerlinc communication system with 30 nodes

Figure 16 shows the modem used to interface each node with the system.

PIC16F84

(A)

Transmission Line

Transformer

D/A Converter AM Modulator

Schmitt-Trigger

Amplifier

(B)

Fig. 16. Top and bottom views of prototype modem

It consists of a transmission line transformer, a coupling capacitor, a microprocessor

(PIC 16F84), a signal modulation chipset, and a DC/DC converter. A DC servomotor

equipped with a 12V PWM amplifier was connected to each node. The microprocessor is

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-30

-35 muu

Freq [Hz]

Fig. 18. Noise spectrum of operating motor and noise induced by randomly turning the

motors on and off

The desired transmission frequency depends not only on the line impedance and noise

characteristics described above but also on the required transmission rate and the gain

and peak impedance conditions discussed in the previous sections. Sending command

information at and above 100 kbps determines the carrier frequency for modulation.

Frequency shift keying (FSK) modulation chipsets using carrier frequencies between 3

and 10 MHz meet this requirement. The required amplitude modulation (AM) carrier

frequency is on the order of mega-Hertz2

. The exact carrier frequency was determined

based on the modem's coupling circuit design.

3.2.2. Selection of Coupling Circuit Component Values

We design the coupling circuitry based on the analysis described in the preViOUS

section. In turn, experimental data is recorded and compared to the model to verify the

design procedure. In addition to the bandwidth restrictions imposed by the power supply

2 Carrier frequency values of AM chip sets have much more variability than their FSK

counterparts. We chose to use AM in order to evaluate the transmission characteristics for a range

of carrier frequencies from 2 - 10 MHz.

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600

500 -------i----t-_.LrtlliI~:I-t---,--!-i-i[r!-----, ~----[---i--i--!-!-!i!---------i----!-----i-1-i-!!

100 --.m..~----LtU.UU. ..------l---.tLl-1~j-lmm--.~m.J..-i~~.~~: 1 111111 ' 1.1

: : : : : : ::: :::. :::: :::: : : ::: "" I . . . . . . .. " . . . . . .. . o.o

I , I

"' I "' . . . . . .... . . . ,.... . . . .. .. , "'"..... , , .- ",..; ..- , .

106

Freq [Hz]

Fig. 20. Signal transmission impedance viewed from sender for n = 1

3000

2500 uum+ - ---+ --+ --~-+-H H --------or - - - -+ -- -rn1-+-1-~~-1- u _m r n;._u~ --1-+-~-~+~---------r_m -rn -;--H - ;-r :........ , , . I . . . , .. "" "" .. . . . , .. . . . . . . . . . ...: ~ l::::::: :::: : :::: :::: : :::

f:::l]:~ftjw~mItI:IJllli ltj::IlIIJIII::::I::::I:I!Irll: : : : : : : : : :::: : : : : : : ~ : : : : : : : : : :::: : : : :: : : : : : ::: :::: : :::::: : : : : : : ::: :::: : :::1 i 1 ill 111 j i j i j j j 1 ~) j j i j i j ill j j j j i j ij

50: mu-l:--t--tHl[tlu---I--turlJ~iu\::tUl-ttt!u-u!uLlJliJl104 105 106 107 108

Freq[Hz]

Fig. 21. Signal transmission impedance viewed from sender for n = 30

The question may arise as to how well our model predicts the limiting case as n

becomes large. To address this issue, it is helpful to look at the model and experimental

results as a function of n. Specifically we can look at the magnitude of the impedance

peak, and the frequency at which it occurs. We showed earlier that the peak magnitude

and frequency reach a maximum and minimum value (respectively) well before n reaches

infinity. We now try to calculate the error in the predicted and actual steady-state values.

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Figure 22(A) shows how the peak magnitude varies as a function of n according to the

model and experimental results. There is 'final' error of soon (20%). For the frequency

plot given in Figure 22(B), there is an error of 50 kHz (5%). Thus, while the limiting

value of impedance magnitude shows significant error, the frequency at which it occurs

can be predicted quite closely_ In our design procedure, this frequency is critical because

it is used to help determine the parameter values of Table 1. However, the magnitude is

not as important. Thus, the utility of the model is verified once again in terms of its

ability to predict the limiting behavior as a function of n.

2------ Experimental

- Model

30252015# Receivers n

i

1_5 \ ..: I.N I I

~ - -r -- -- -- -- -- -j --- -- -- ------j---- --- ----1- __m_

g 1 --- -r---t---j- -1--~ I I i I~ ! I ! !

! I I0.5 --t I !

I I II I 'I I 1

302510 15 20# Receivers n

5

(A) (B)

Fig. 22. Resonant behavior; peak magnitude and peak frequency as a function of the

number of receivers

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Fig. 23. Mobility aids for disabled children and elderly persons

The mechanized walker and standing aid shown here both use some standard servo-

system design. With the apparatus presented in this work, such machines can be

simplified. The central controller and power supply (a battery, in this case) can be kept to

a small size. Actuators can then be placed directly at the wheels, leaving the rest of the

apparatus aesthetically appealing and easily maneuverable. A simple schematic

illustrating this idea is pictured in Figure 24.

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DC Power Line Comunication

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