M51971 Ver la hoja de datos (PDF) - MITSUBISHI ELECTRIC
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M51971 Datasheet PDF : 13 Pages
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MITSUBISHI <CONTROL / DRIVER IC>
M51971L/FP
MOTOR SPEED CONTROL
Hint for designing a stabilized speed control
system
(Method for determining the filter constants (CF1, CF2 and RF) at
pin 8 )
The filter constants at pin 8 must be determined to satisfy the
system stability.
1. Transfer Function of the Motor Speed Control
System
Control circuit
- GC (S)
Motor
GM (S)
Motor speed control system
The motor speed control system is a negative feedback system
including a control circuit and a motor.
As the condition necessary for stable negative feedback, the phase
must be generally 180˚ or less in the frequency area where the
gain of open-loop transfer function (GC(S) • GM(S)) is 1 or more.
2. Transfer Function of Motor
If the motor armature current and angular velocity are assumed to
be la and ωv, respectively, the following equation is established.
∆Tg = KT • ∆la = (SJ+D) • ∆ωv (1) • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
Where: Tg : Torque generated in the motor
KT : Proportional constant between the torque genera-
ted in the motor and the armature current
J : Inertia moment of Motor and load
D : Coefficient of viscosity friction
If the number of poles in the tacho-generator is assumed to be P,
the relation of ω = P • ωv exists between tacho-generator angular
frequency ω and motor angular velocity ωv and, therefore, the
motor transfer function (transfer function including motor and
tacho-generator) GM(S) takes a single-pole transfer function as
follows:
GM(S) =
∆ω
∆la
=
P • KT
D • (1+S •
J
)
D
(2) • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
= KM
1
+
S
ωM
(3) • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
Where: KM = P • KT (4) • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
D
ωM = D
J
(5) • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
ωM
log ω
Approximate motor transfer function
3. Transfer Function of Control Circuit Using the
M51971
If input information is assumed to be given continuously (the tacho-
generator frequency is assumed to be infinitely high), the transfer
function from the input at pin 4 to the output at pin 9 is as follows:
GC(M51971)(S)
≡
∆
∆
(output voltage at pin 9
(input frequency at pin
)
4
)
= Tτ ( I 8 C + I 8 d ) x 1 + S/ωF1 • • • • • • • • • • • (6)
CF1 + CF2
S(1 + S/ωF2)
Where : Tτ : Timer pulse width ~~ 1.10 x Rτ x Cτ
l 8 C : Charging current at pin 8
l 8 d : Discharging current at pin 8
ωF1
≡
1
RF • CF2
ωF2 ≡ CF1 + CF2
RF • CF1 • CF2
If the gain of the circuit connected to the back of pin 9 of the
M51971 is assumed to be KCP, transfer function GC(S) for the
entire circuit is as follows:
GC(S) = KCP x Tτ ( I 8 C + I 8 d ) x 1 + S/ωF1 • • • • • • • • • • • • • (7)
CF1 + CF2
S(1 + S/ωF2)
ωF1
ωF2
log ω
Approximate transfer function of control circuit
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