Flying restart circuit

The flying restart function makes it possible to restart a coasting motor on the fly during operation without speed feedback. Synchronicity between the inverter and the motor is coordinated so that the transition to the rotating drive is effected without jerk at the time of connection.

Preconditions

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Drive systems with speed feedback do not need a flying restart circuit because there is always a jerk-free synchronisation to the feedback speed.

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The flying restart circuit operates safely and reliably in case of drives with high centrifugal masses. If several motors with different centrifugal masses are connected to the inverter, the flying restart circuit must not be used.

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The flying restart circuit serves to identify rotating field frequencies of up to maximally ±200 Hz.

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Especially at high power, very high mass inertias and mains voltages higher than 440 V, a temporary overvoltage in the DC bus may occur. The use of a brake resistor can prevent this behaviour.

Use of a brake resistor

Required settings before the flying restart circuit is used:

1.

The motor data must be set correctly.

Motor data

2.

The settings for the current controller and the flying restart controller must be adapted to the motor. The settings are made automatically if one of the following optimisations is carried out:

Select motor from motor catalog

Automatic motor identification (energized)

Automatic motor calibration (non-energized)

Details

The inverter determines synchronicity by identifying the synchronous rotating field frequency. The "search" starts in the positive direction.

Duration:

–

The flying restart process is determined within approx. 0.5 ... 1.5 seconds.

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The duration is influenced by the start frequency 0x2BA1:001 (P718.01).

Setting the function:

1.

As start behavior, set the selection "Flying restart circuit [2]" in 0x2838:001 (P203.01).

–

Thus, every inverter enable causes a synchronisation to the rotating or standing
motor.

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After the inverter has been enabled, the motor can temporarily start or reverse if drives with low friction and low mass inertia are used.

–

If the inverter is operated with the default settings, no further settings are required for most applications.

2.

If required, adapt the current 0x2BA1:001 (P718.01) and the start frequency 0x2BA1:002 (P718.02) for the flying restart circuit.

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Setting notes can be found in the "Info" column for the respective parameter.

For diagnostic purposes, the frequency detected when the motor has been restarted on the fly is displayed in 0x2BA1:008 (P718.08).

Parameter

Address	Name / setting range / [default setting]	Information
0x2BA1:001 (P718.01)	Flying restart circuit: Current (Flying restart: Current) 0 ... [30] ... 100 %	The current set here is injected into the motor during the flying restart process for the identification of the rotating field frequency. – 100 % = Rated motor current 0x6075 (P323.00) – Reducing the current causes a reduction of the motor torque during the flying restart process. A short-time starting action or reversing of the motor is prevented with low flying restart currents. – If the current is set too low, the rotating field frequency cannot be identified correctly. – If the current is increased, this improves the robustness of the flying restart circuit. – In case of high mass inertias and high speeds, the flying restart circuit may cause an overvoltage in the DC bus if no brake resistor is connected. In this case, the current must be reduced.
0x2BA1:002 (P718.02)	Flying restart circuit: Start frequency (Flying restart: Start frequency) -599.0 ... [20.0] ... 599.0 Hz	The frequency set here defines the starting point for the flying restart process. – The search starts in positive direction. – The default setting is adjusted to standard asynchronous motors. – In case of systems with a known search speed (e.g. torque-controlled drive systems that are to synchronise to a defined speed), the start frequency can be adapted for reducing the flying restart time.
0x2BA1:008 (P718.08)	Flying restart circuit: Flying restart frequency (Flying restart: Fl.res.frequency) – Read only: x.x Hz	Display of the found frequency at which the motor has been successfully restarted on the fly.