Use of Optical Fiber in Motor Control

At the PWM generator, connect an infrared LED (6 in a 3Ph system) attach an optical fiber to each of them and a photransistor to the other end. Supply an isolated source to the collectors and connect the emitters to each IGBT gate.

Some VFD use optical links between the main control board and the gate driver module (which is part of the motor-side inverter and, where applicable, respectively the IGBT supply unit), especially with some larger drives the control module can be mounted separately from the inverter module(s) which can be some sort of draw-out chassis assembly type (not hot-swappable).

Typically an IGBT supply unit has its own control module and the drive-side unit its own control module and those control modules can also be interconnected by optical fiber. Depending on the drive the interface for the PC is also with optical fiber, which is very convenient as there are no PC-link-related EMC nor ground loop and other potential-related issues.

In case of parallel modules or multdrive configuration control modules can also be linked optically in order to handle load sharing as well as special functions like e.g. master/slave synchronization.

Of course diode and thyristor supply units are more common than IGBT supply units (basically the drive side inverter power module can (but must not necessarily) be identical to the IGBT supply unit but the control firmware are different.

By timing the light signals with the motor and power supply phases.

We're talking about two different things:

Optical fiber bus communication between various control boards within a drive and IGBT gate modulation pulses transmitted by optical fiber between the gate controller and the IGBT gate drivers. The latter are only pulses for PWM while the former is some sort of serial communication, mostly with an non-disclosed proprietary protocol.

Not that not all VFD include optical fiber links.

So your not asking about optical signals going to the gate of an IGBT, as the fractured sentence structure implied. You want to know how optics communicate with a proprietary protocol to a proprietary controller that then controls an IGBT for motor control.

I recommend that you study the provided definition of proprietary.

optical fibers are basically used where there is high bandwidth, and I could not figure out the necessity for it here.

it appears to me that optical fiber is used in induction motor control for precise thyristor triggering through gate triggering, so that accurate ac signals at desired frequency and voltage can be produced towards the load side of the IGBT.

I was more interested in applicationwise (functionalwise) rather than technical details.

Regs,

I understand that the optical fibre connection can be categorized at two geographical parts:

1. between control boards i.e. station control panels and local control panels

2. between local control panels and IGBT controllers.

- what efficiency or economy does it bring apart from the fact that o.f. are prone to electromagnetic interference?

- at both of the stages, transmitter, optical fiber cables and receivers are required. For thyristor triggering also, optical fibers should be converted to electrical signals in my opinion.

Regs,

Come on guys... for all we know... the OP is asking how to control a motor some where in his vessel from the "bridge".

http://www.youtube.com/watch?v=FV2CCIiPnVQ SubCooledHeatPump IGBT noise & fiber optic drive isolation.

Fiber optic isolation begins at 4:00.

1) Galvanic Separation (like a giant optocoupler)

In IGBT-based drives high insulation voltages are required because of voltage peaks in the motor supply lines.

2) Immune to Electromagnetic Interferences

EMC (Electromagnetic Compatibility) is important in drive design because the drive electronics must obviously be immune to the perturbations created by the drive itself. Also cheap plastic fiber can be used for links up to a couple of meters while using shielded cables would not ensure 100% immunity and depending on how a panel builder routes the cables and respects more or less well the recommended cabling and cabinet assembling rules cables it could work or not while with fiber no one has to worry about EMC, it's more about the maximum length, correct handling and mechanical installation (like bending radii, pull forces and other mechanical details as even plastic fiber is much less forgiving than copper strands).

Here referring to large drives based on separate power and control modules where the panel builder installs some fiber links himself; in small drives links are already installed in the factory as those drives are delivered ready-to-use.

The typically used plastic fiber senders and receivers are inexpensive off-the-shelf components, also cable confection is straightforward (much simpler than with glass fiber) but usually the fiber cables are provided ready-to-plug by the drive manufacturer (in some cases there are different types for longer or shorter links as well as color codings to help preventing some plugging in errors but connectors are not necessarily mechanically coded).

For a duplex data link there are two plastic fibers, each fiber connects a sender to a receiver. For the "discrete" gate driving control signals only simplex links are needed.