DG-IRMCK203 Datasheet, PDF (25/67 Pages) International Rectifier – Application Developer’s Guide

IRMCK203 Application Developer’s Guide
2) Open-loop – Immediately after Parking stage, the rotor angle is estimated in an open-loop fashion, which
utilizes a simple motor-load mechanical model to estimate the rotor angle (estimate load characteristics). If
the mismatch between the external load characteristics and the internal motor-load model is exceedingly
large, start-up performance will suffer.
3) Closed-loop – motor speed increases during start-up; the motor voltage also builds up due to the increase in
speed. Useful information for rotor angle estimation can be then be extracted from the motor voltage
(estimated by using motor current and DC bus voltage). The drive will enter Closed-loop control mode as
shown in Figure 11.
3.1.3 Diagnostic Mode Functions
Diagnostic mode functions are provided in the ServoDesigner tool to fine tune drive performance. It is recommended
to go through diagnostic mode in the proper order (Parking Diagnostic then Start-up Diagnostic).
Figure 12. Parking Diagnostic Function
Parking Diagnostic
With the Parking diagnostic (shown in Figure 12), the optimal Parking current (ParkI) and the Parking time duration
(ParkTm) can be readily determined. In addition, current controller and current feedback can also be verified.
When the Parking Diagnostic function is executed, the drive is forced to stay in Parking state for five seconds,
followed by a stop. The diagnostic can be stopped anytime by executing the Stop Motor function. The characteristic
of parking depends on the amount of dc current injection.
It is possible to verify current control by observing the actual current flowing through the motor windings using
current sensing instrumentation (current probe). The amount of parking current injected to the motor is controlled by
parameter ParkI as shown in Figure 12. The full scale of ParkI is 255 digital counts, which represents 86.7% rated
motor current (in peak Amps). During motor parking, dc current is injected (by inverter) into W-phase and V-phase
of the motor; the current in U-phase is regulated to zero. For instance, if motor rated current is 2.7Arms, a value of
77 digital counts in ParkI will produce 1 Amp dc current in W-phase (- 1 Amp) and V-phase (+ 1Amp).
In practice, it is much more than sufficient to park a motor with rated motor current. If an exceedingly large value of
ParkI is used, the motor shaft will hunt during parking. This will increase the time for the rotor shaft to settle and
hence increase parking time. Systems with a higher inertia to friction ratio will tend to hunt more. Therefore, it is
recommended to start with a lower value (say 4% ParkI = 12).
The user can experience the effect of using different ParkI values. It may be noticed that the parking characteristics
will also depend on the initial rotor angle (when drive is off). Therefore, the shaft should be rotated (manually,
while the drive is off) to a different position before each parking evaluation. It is recommend to use the highest
possible value (not to cause excessive motor hunting) of ParkI such that the duration of parking can be minimized.
Once the optimal parking current (ParkI) is determined, please note the time required for the motor shaft to settle
This document is the property of International Rectifier and may not be copied or distributed without expressed consent.
25