This application note describes how to tune the embedded control loops on the IRMCF3xx series
of control IC’s. This covers the IRMCF312, IRMCF311 and IRMCF343 digital control IC’s for air-
conditioning systems and the IRMCF341 IC for washing machine applications. The control loops
include the ID and IQ current control loops, the velocity control loop, the field weakening loop,
IPM control and bus voltage protection. The note describes the equations used to derive the
control loop constants and experimental methods to tune control constants.
There are 3 main control loops associated with IRMCK3xx series products. These control loops
are current control loop, speed control loop and Field-weakening control loop. The following table
summarizes the parameter dependence of each control loop.
Voltage constant (Ke)
Motor parameters are required (Parameter Configurator) for drive setup. These parameters are
normally obtained from motor data sheet. IR Sensorless motor controller can tolerate +/-10 %
motor parameter error without noticeable performance degradation.
Increased parameter mismatch between motor and controller will result in degradation of torque
per Amp capability. The degree of degradation is dependent on the operating conditions (speed,
load) and motor characteristics (motor parameters and saturation).
The iMotion current controller utilizes Field-Oriented synchronously rotating reference frame type
regulators. Field-Orientation provides significant simplification to the control dynamics of the
current loop. There are two current regulators (one for d-channel and one for q-channel)
employed for current regulation. The q-channel (torque) control structure is identical to d-channel
(flux). The current control dynamics of d-channel is depicted in Figure 1. The motor can be
represented by a first order lag with time constant T = L/R. This time constant involves motor
inductance and equivalent resistance (R: cable + winding). For a surface mounted permanent
magnet motor, the d and q channel inductances are almost equal. In the case of Interior
permanent magnet motor, the q-channel inductance is normally higher than the d-channel
In the current control dynamic diagram Figure 1, forward gain A translates digital controller output
to voltage (include inverter gain) and feedback gain B translates current feedback (Ampere) to
internal digital counts via A/D converter. The calculation of the controller gains (KxIreg, KpIreg_D)
is done by using pole-zero cancellation technique as illustrated in Figure 2 where the current
controller is rearranged to give transfer function block C(S). Setting KpIreg_D/KxIreg of C(S) to
the time constant of the motor (T), the controller zero will cancel off the motor pole (pole-zero
cancellation). Therefore, the controller dynamics can be further simplified as shown in Figure 3.
The equivalent transfer function of Figure 3 is a first order lag with time constant Tc. By selecting
appropriate current regulator response (typically 0.5 to 1 msec, entry of parameter configurator,
Current Reg BW = 1/Tc) for a particular application, the current regulator gains can be readily
obtained. It may be noticed that using pole zero cancellation technique, motor inductance enters
into proportional gain calculation and resistance enters into integral gain calculation.
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