AN2388 Datasheet, PDF (36/54 Pages) STMicroelectronics – Sensor field oriented control

Software design
X, Y, Z
SVPWM variables
Low_Limit_Flux, Up_Limit_Flux Flux range in PI regulator
Low_Limit_Torque, Up_Limit_TorqueTorque range in PI regulator
AN2388
4.4
4.4.1
Base values and PU model
Since the ST10F276 is a fixed point microcontroller with DSP features, a Per Unit (PU)
model of the motor has been used. In this model all quantities are referred to base values.
The base values are determined from the nominal values by using the following equations,
where I_n, V_n, f_n are respectively the phase nominal current, the phase to neutral nominal
voltage and the nominal frequency in a star-connected induction motor:
I_b = 2I_n
V_b = 2V_n
ω_b = 2πf _n
ϕ_b
=
V_b
ω_b
and where I_b, V_b are the nominal values of the phase nominal current and voltage; ω_b is the
electrical nominal rotor flux speed; φ_b is the base flux.
The base values of the motor used in this asynchronous drive are stated below:
I_b = 2I _n = 2 *1 = 1.41A
V_b = 2V_n = 2 * 220 = 310V
ω_b
=
2πf _n
=
314.15 ^rad
sec
ϕ_b =
V_b
ω_b
= 0.98Wb
Magnetizing current
In the normal speed range (where speed is lower or equal to the nominal speed) the IFOC
structure requires the magnetizing current as input to estimate the rotor flux component.
Thanks to the following motor equivalent circuit, valid only in stationary steady state, the
magnetizing current may be first estimated.
Figure 32. Equivalent electrical circuit
36/54