Tài liệu Bài giảng động cơ điện một chiều doc

The machine is required to operate with rated load torque at one third of the rated speed.. Determine necessary resistance that has to be added in series with the armature.. a The machin

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Vv

Vv

Vv

—

B

Vv

v

v

M

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Vv

Vv

Vv

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Te

Ww

<— base speed region —» 7 <— field weakening —»

Dac tinh co

Te

wo

o>

Ti

forward motoring

2S

ch)

@ +

forward braking

T +

oO + N

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T 4

reverse motoring

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reverse braking

WO 1

Pout < 0 Pout > 0

Forward braking Forward motoring

II | T,

Il IV

Pout > 0 Pout < 0

Reverse motoring Reverse braking

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T, =ko

T, A : \ | ° he

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(Electric vehicle type) (Crane type) Dac tinh tai

5.3 Speed Control of DC Machines

5.3.1 Separately Excited DC Motor

Ve =E+ R, i

0; = ely

E =c;©® ,@=Kkl -@

T, = 0,0 1, =k yl,

T, = T,

V, = E+ Ryly = klp@ + Ryly = 1, = (Vy — Mo) /R,

T„ = KI,l„ = KH r (V„ — kIy@Ì (R,

V, R

O= a — a T

Tin =Vin [Ry

_— an _ a

KE, (kL jy

e

_ Ven _ (R, + Ridded |

Rik

L_—

R¿ Vr= Re Ip

+4—————

V, T.=klrl,

Van, reducing Vr

¬ a v

® =(V_—Ra Ia) /k Ip= Va/k Ip — Ra Te / (k 1p)?

Thém Ryaa nOi tiép cudn dây phần ứng

Example 1:

A separately excited DC motor has data 40 kW, 220 V, 1500 rpm, 200 A and armature resistance is 0.1 Q Voltage supply of both windings is constant and rated The machine

is required to operate with rated load torque at one third of the rated speed Determine necessary resistance that has to be added in series with the armature Evaluate efficiency in this operating point, assuming that power loss in the excitation winding is

1 kW

Example 2:

A separately excited DC motor has data 40 kW, 220 V, 1500 rpm, 200 A and armature resistance is 0.1 Q Voltage supply for both windings 1s provided from power electronic converters

a) The machine is required to operate with rated load torque at one third of the rated

speed Determine required armature voltage value for operation at this speed

b) The machine is required to operate with half of the rated torque at twice the rated speed Determine necessary percentage reduction in the excitation winding voltage for such an operation

Example 3:

Separately excited DC motor, with constant rated excitation flux, drives a load whose

load torque is 7, = 0.000S@*+15 [Nm] Calculate operating speed and electromagnetic

torque when armature voltage is 100%, 50% and 25% of the rated value Motor rated data are 5 kW, 230 V, 26.1 A, 150 rad/s, and armature resistance is 1.1 Q

3.3.2 Series Excited DC Motor

V =E+(R,+R,)I

lạ=lr=l

E = klr@ = kl@

T, = KIL, = KI?

[, = Tì

V =(R,+R,)\[+E =(R,+R,)1+klo = 1 = !

(R, +R,)+ ko

kV?

(Re + R,] + ke]

For rated voltage supply

kV,

T=

(R, + R;) + ka|

1:

reducing voltage

V

Đặc tính cơ của động cơ DC kích từ nối tiếp Example 4:

A series DC motor operates under rated conditions with 161.2 Nm torque, 1000 rpm

speed, 41 A current and 420 V voltage Resistance of excitation and armature winding

is 0.2 Q Find the speed and current of the motor if the torque is now 87 Nm

Example 5:

Series DC motor operates under rated conditions at 380 V with speed of 400 rpm and

current of 33.3 A Sum of excitation and armature winding resistances is | Q Load

torque is proportional to the speed squared Determine the voltage that needs to be

supplied to the motor if the motor is required to operate at 300 rpm

5.4 Rectifiers and Rectifier Control of Separately Excited DC Motors

_ 2N2W/

7 7

_ 22,

V diode bridge rectifier

¬ O ¬

Single-phase bridge rectifier

Three-phase bridge rectifier

` ⁄

v 41,4 2,3 1,4 v4 1,4 2,3

180 360 eC |

FT v

Lid

+

3 phase

380V

50 Hz

armature excitation

Smri6

3[—cos(Ø— z/ 6)| „„

7

27m

27 0 2

xi2

231;

y= 3/2 V31/ _ 212 Vir-1

V = 5-6 [2431 sin(Ø— z/ 6) = oe 3|cos(Zz/ 3+ ø) — cos(2Z / 3+ ø\|

mi2+a

lạ

Rectifier output voltage

a

Reference and carrier waves

|

Switch driving signals

4 pf

† Voltage across motor

nnfTn

Switch

ti

J

aan

FDA

J

Speed

controller

(PI)

Voltage

reference

Actual

speed

Firing

circuit

or chopper

arma- ture

Tachogenerator

Speed

| Pl

speed c

Current

control

Firing

circuit

Rectifier /

chopper

Measured armature current

Measured speed of rotation