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“B” Group: Fine Tuning Functions
Configuring
Drive Parameters
3–40
B091/B088: Stop Mode / Restart Mode Configuration – You can configure how the
inverter performs a standard stop (each time Run FWD and REV signals turn OFF).
Setting B091 determines whether the inverter will control the deceleration, or whether it
will perform a free-run stop (coast to a stop). When using the free-run stop selection, it is
imperative to also configure how you want the inverter to resume control of motor speed.
Setting B088 determines whether the inverter will ensure the motor always resumes at
0 Hz, or whether the motor resumes from its current coasting speed (also called
frequency matching). The Run command may turn OFF briefly, allowing the motor to
coast to a slower speed from which normal operation can resume.
In most applications a controlled deceleration is desirable, corresponding to B091=00.
However, applications such as HVAC fan control will often use a free-run stop
(B091=01). This practice decreases dynamic stress on system components, prolonging
system life. In this case, you will typically set B088=01 in order to resume from the
current speed after a free-run stop (see diagram below, right). Note that using the default
setting, B088=00, can cause trip events when the inverter attempts to force the load
quickly to zero speed.
NOTE: Other events can cause (or be configured to cause) a free-run stop, such as
power loss (see “
Automatic Restart Mode” on page 3–31), or an intelligent input
terminal [FRS] signal. If all free-run stop behavior is important to your application (such
as HVAC), be sure to configure each event accordingly.
An additional parameter further configures all instances of a free-run stop. Parameter
B003, Retry Wait Time Before Motor Restart, sets the minimum time the inverter will
free-run. For example, if B003 = 4 seconds (and B091=01) and the cause of the free-run-
stop lasts 10 seconds, the inverter will free-run (coast) for a total of 14 seconds before
driving the motor again.
Stop Mode = free-run stop
B091
=
01 B091
=
01
B088
=
00 B088
=
01
[FW, RV]
Motor
speed
t
Resume from 0Hz
Zero-frequency start
t
Stop Mode = free-run stop
Resume from current speed
[FW, RV]
Motor
speed
Wait time
B003