3.22EjemploDRM007 Co..

Software Design Considerations
Controller Design
5.3 Controller Design
The motor system to be controlled was considered as a first order
system, with a time constant of 10 milliseconds. For a robust operation
of the washing machine, a PI controller was implemented with a
controller period of 1 millisecond. The actual motor speed is calculated
from input capture channels, and the desired speed is generated in the
microcontroller depending on the washing machine process being
executed.
The system has the following transfer function in the continuous time
domain.
1
G(
s)
= τ
s + 1
τ
Taking the Z transformation and considering the zero-order-hold of the
PWM module, the system’s transfer function becomes:
⎛
⎜1
− e
G(
z)
=
⎝
−
1−e
−T
τ
⎞
⎟z
⎠
⋅ z
The PI controller transfer function in the Z domain is:
C
T
τ
( Kp + Ki )
( z)
=
−1
−1
−1
− Kp ⋅ z
1−
z
−1
BLDC Motor Control Board for Industrial and Appliance Applications
DRM007
MOTOROLA Software Design Considerations 73