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Chapter: Special Electrical Machines - Permanent Magnet Brushless D.C. Motors

Torque Equation of BLPM Square Wave Motor

Special Electrical Machines - Permanent Magnet Brushless D.C. Motors

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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