PSpice Application Notes

APPLICATION NOTE 3 Translating to the specified model units, you get: I(SHAFTSPEED) = 2ߨ(B · V)(SHAFTSPEED) This is just the equation for a resistor attached to node SHAFT_SPEED and ground, with a value of 1/(2ߨB). .PARAM B=.36;Damping and eddy current losses (g*cm*sec/rad) Reddy shaft_speed 0 {1/(B*twopi)} Another mechanical loss is the frictional loss. This loss is a fixed torque which opposes the direction of rotation. To model this loss, use a table to specify the shape of the loss curve, and an Analog Behavioral Modeling current source to multiply the loss curve by the loss factor F (g·cm). .PARAM F = .72 ; Friction losses (constant torque loss) (g*cm) Gdrag shaft_speed ld1 VALUE = {F * V(drag)} nonlinear drag Ldummy1 ld1 0 100mH ; force timestep control Edrag2 drag 0 TABLE {V(shaft_speed)}=(-.001, -1) (.001, 1) Rdummy1 drag 0 1 The Ldummy1 inductor is inserted in series with the Gdrag current source to help PSpice do timestep size control. Since inductor is in series with the current source it has no effect on the current (torque) produced by Gdrag. But the voltage across it reflects the derivative of the current and allows PSpice to do timestep size control on that derivative. When using the Analog Behavioral Models, it is often a good idea to place an inductor in series with a controlled current source, or a capacitor in parallel with a controlled voltage source, to help PSpice with timestep control. Another torque is the magnetic detent torque which tends to align the rotor magnetic poles with the stator poles. This torque is periodic, and is described by the equation: Tdetent = D · sin(Nd · A · θ) Where, D is the magnetic detent torque (g·cm) A is the number of north poles on the rotor Nd is an integer determined by the number of stator slots and the structure of the rotor You can translate this directly into a behavioral modeling current source: .PARAM D = 2.9 ; Magnetic detent torque (g*cm) .PARAM A = 2 ; number of north poles on the rotor .PARAM P = 3 ; number of stator phases Gdetent shaft_speed ld2 VALUE={D *sin(2*A*P*V(shaft_angle))} All of these together give you the following model for the mechanical part of the motor: .subckt motor_mech shaft_speed shaft_angle + params: + J= .30 ; moment of inertia of rotor (g*cm*sec*sec) + B= .36 ; Damping and eddy current losses ; (linear torque with speed) (g*cm*sec/rad) + F= .72 ; Friction/drag losses (constant torque losses) ; +(g*cm) + D= 2.9 Magnetic detent torque (g*cm) + A= 2 ; Number of north poles on the rotor

• Cover