Chapter: Special Electrical Machines : Permanent Magnet Brushless D.C. Motors
Torque Equation of BLPM Square Wave Motor
TORQUE EQUATION OF BLPM SQUARE
WAVE MOTOR
Power
input = VI
=[ 2 eph + 2 I Rph + 2 Vdd] I …………………….(4.22)
VI=[ 2 eph + 2 I Rph + 2 Vdd] I ……………………..(4.23)
VI=
electrical power input
2 eph I =
power converted as mechanical
2 I2 Rph
= power loss in the armature winding
2 Vdd I =
power loss in the device
Mechanical power developed= 2 eph I …………………..….(4.24)
eph=
2(2BgrlTphωm)I
eph= 4BgrlTphωm ……………….(4.25)
Mechanical power = (2πN/60)T ………………..…(4.26)
= ωmT ……………………..(4.27)
Where
N=Speed in rpm
T=Torque
in N-m
ωm=Speed
in rad/sec
Therefore T=4BgrlTphI ……………………….…(4.28)
=KtT ……………………..…..(4.29)
Where Kt = 4BgrlTph=Ke …………………………....(4.30)
(a) Case1: Starting Torque
ωm=0
Istg=(V/2Rph) ……………………….…(4.31)
Tstg=4BgrlTph(V/2Rph) ………………………....(4.32)
Tstg=Kt(V/2Rph) ………………………...(4.33)
Starting
torque or stalling torque depends upon V.
To vary
the starting torque the supply voltage is to be varied.
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