3–32

“B” Group: Fine Tuning Functions

Configuring

Drive Parameters

 

 

B_91/B_88: 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 B_91 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 B_88 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 B_91=00. However, applications such as HVAC fan control will often use a free-run stop (B_91=01). This practice decreases dynamic stress on system components, prolonging system life. In this case, you will typically set B_88=01 in order to resume from the current speed after a free-run stop (see diagram below, right). Note that using the default setting, B_88=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 3–24), 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 B_03, Retry Wait Time Before Motor Restart, sets the minimum time the inverter will free-run. For example, if B_03 = 4 seconds (and B_91=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.

 

B_91 = 01

Stop Mode = free-run stop

 

B_91 = 01

Stop Mode = free-run stop

 

 

 

Resume from 0Hz

 

 

 

Resume from current speed

 

B_88 = 00

 

B_88 = 01

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Zero-frequency start

 

 

 

 

 

 

 

 

 

 

 

B 03

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Motor

 

 

 

 

 

 

 

 

 

Motor

 

 

 

 

 

 

 

 

 

Wait time

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

speed

 

 

 

 

 

 

 

 

 

speed

 

 

 

 

 

 

 

 

 

 

 

 

[FW, RV]

 

 

 

 

 

 

 

 

[FW, RV]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

t

 

 

 

 

 

 

 

 

 

 

 

 

 

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