Training Principle

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ACS6000ccycloconverter

Phase

current

Principiul CYCLOCONVERTORULUI

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Cycloconverter

Convertor de frecven de turaie joas i putere mare

n Funcioneaz numai cu motor sincron (synchronous motor AC motor with DC excitation)

n Putere pn la (Power up to) 27MW

n Tensiune nominal (Motor nominal voltage) 1350V... 1570V

n Curent continuu maxim (Maximum continuous current up to) :4500A(rcire cu ap-water cooled)

n Turaie nominal (Nominal speed of delivered motors ):30220rpm

n Turaie maxim (Maximum speed):720rpm


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Cycloconverter n metalurgie (in metals)Linoare (Rolling mills)n Nominal power 0,5...15 MW

n Suprasarcin maxim (Max. Load) : 115...300 %

n Cupluri mari (High torques) : >1000 kNm

n Performance and availability are most important


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Cycloconverter in Marine with AzipodMain propellern Nominal power up to 20 MW

n Speed 100..300rpm

n In cruise vessel normally 2 or 3 main propellers

n Siguran i redundan (Safety and redundancy are really important)


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Operation of synchronous motor

n The magnetic field of the stator attracts the rotor magnet

n The rotor rotates until the rotor N-pole meets the S-pole of stator

n Continuous rotation is not possible with permanent magnet

N

S


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Operation of synchronous motorStator magnetic field

n Battery voltage makes current

n Current induce field

n Attracts rotor magnet

Battery voltage polarity reversingn Schimbarea polaritii (Stator

magnetic polarity swap)

n Rotor turns 180

Right timing of U swapsn Rotaia continu a rotorului e

ngreunat n anumite poziii

n Apar distorsiuni de cuplu (Jumpy torque)

+

_

S

N

N

S

_

+

CurentCuplu


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Operation of synchronous motorStator

n Pentru a permite pornirea n orice poziie se folosete o n furare statoric trifazat (In order to allow starting in any position a stator with 3 phase winding is used)

n Fiecare faz este divizat n dou seciuni dispuse diametral opus fa de axul rotoric (A phase winding is divided in two parts opposite side of stator)

Excitation Magnetul permanent este nlocuit cu o nfurare de c.c.(Rotor permanent magnet is also replaced with winding)


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Operation of synchronous motor

DC pulse control (simple method)n Cuplul nu este neted,prezint

distorsiuni (Torque is not smooth)

n Funcionarea se aseamn cu cea a motorului pas cu pas (Step operation-stepper motor)

AC sinusoidal supplyn Cuplu neted(Smooth torque)

n Dac e posibil controlul tensiunii i frecvenei atunci este posibil i controlul turaiei (If frequency and voltage can be controlled also motor speed can be controlled)

CurentCuplu

CurentCuplu


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97.

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03Dependena turaie frecven la motorul sincron- SM frequency vs. speed

oprire

Uor nainte Repede nainte

Reversare rapid


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Sursa de alimentare (Motor power supply)

Cerine principale (Main requirements for the power supply of motor):

n Cureni sinusoidali (Sinusoidal phase currents)

n Tensiune i frecven variabile (Variable frequency and voltage)

n Pierderi reduse (Low losses -cyclo >99,5 % at rated load)

n Uurina conectrii la reeaua de consumatori (Can be easily connected to utilitys power network)

n Control rapid al cuplului i curenilor (Fast control of currents for fast torque control)


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CICLOCONVERTORUL-Cycloconverter

n Input frequency 50 or 60 Hz + 5 %

n Input voltage 1000V(1000V or 1200V in marine)

n Output voltage controllable 01500V(01570 in marine)

n Output frequency controllable 0...20 / 24 Hz

n Auxiliary voltage 220..690VAC

CONSTANT FREQUENCY ACNETWORK 50 / 60 HZ

M

3 -PHASEVARIABLE FREQUENCY0...20 / 24 HZ


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Supply network

timeu r

u s

u t

Three phase constant frequency (50 Hz or 60 Hz) constant voltage system

20 ms (for 50 Hz) 16.7 ms (for 60 Hz)

1 second = 1000 milliseconds = 1000 ms


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CathodeAnode

A KGGate

SCR thyristorSemiconductor switch

n Switches in the rectifiers have to be fast, in 50 Hz network they have to close and open 50 times every second

n Thus mechanical switches are unsuitable and a semiconductor switch is used instead

n A high power thyristor is a 0.5 mm thick and 50 - 150 mm diameter disk of silicon packed in a housing made of metal and ceramics

n A thyristor can withstand a voltage of over 5000 volts and conduct a current of several thousand amperes(4200 or 5200 Volts SCRs used in cycloconverter)

n Thyristor is controlled by a short gate current pulse of few amperes (the firing pulse)


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Controlled bridge

timeu r

u s

u t

u + Average voltage

DC voltage can be varied a = 0 a 0

n Output voltage can be controller by controlling firing angle

n Motor current can be controlled by controlling drive output voltage

U output


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Firing angle


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Sinusoidal output

U output

I output

Supply voltage


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Positive and negative thyristor bridge

-1

-0,5

0

0,5

1

0 90 180 270 360I

Thyristor bridge change time


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Phase currentsPhase currents of a rolling mill cycloconverter drive, f = 8 Hz (simulation)

-1.5

-1

-0.5

0

0.5

1

1.5

600 620 640 660 680 700 720 740 760 780 800per u

nit

Time (ms)

Phase a current Phase b current Phase c current


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Phase voltagesPhase voltages of a rolling mill cycloconverter drive, f = 8 Hz (simulation)

-1.5

-1

-0.5

0

0.5

1

1.5

600 620 640 660 680 700 720 740 760 780 800per u

nit

Time (ms)

Phase a voltage Phase b voltage Phase c voltage


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Cycloconverter drive

Excitation current (DC current)

Phase

current

Positive bridge Negative bridge


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Operation curves, VOLTAGE and FLUX

0 Base speed Speed

Flux

Voltage

All electrical motors have a so called base speed or nominal speed. On AC motors it is related to frequency.

at this speed the motor voltage is nominal(100%) below this speed excitation current is kept constant if speed is increased above this speed motor flux has to be reduced to prevent motor over voltage .

Stator voltage formula is Us = Y * wY = flux, controlled by excitation currentw = speed

This means that faster the motor is running the higher is the voltage provided that flux is kept constant

At zero speed flux is nominal 100% and speed 0%, thus Us=100% * 0% = 0%

At nominal speed both flux and speed are nominal, thenUs=100% * 100% =100%=Nominal voltage

If speed is increased over the base speed then flux(i.e.. excitation current) has to be reduced. For example 2 * base speed.Us= Y * w = 50% * 200% = 100%

Nominalflux

Nominalvoltage

Constant flux/torque range Field weakening/constant power range


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Operation curves, TORQUE

0 Base speed Speed

Torque

Flux

Stator current

Motor torque is the product of flux and torque.

Motor torque formula is T = Y * Is

Y = flux, controlled by excitation currentIs = stator current

Normally all drives can produce full current through the whole speed range. Same applies also to cycloconverter.

Because flux is reduced in field weakening area the absolute torque(Nm) is reduced.



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Operation curves, POWER

0 Base speed Speed

Torque

Power

Speed

Flux

Power


Motor shaft power is product of torque and speed.

Motor power formula is P = T * w

T = Torquew = motor speed

This means that full power could be reached only at base speed.


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Operation curves, propeller and fan

0 125rpm Speed

145rpm

Motor torque

Maximum power

Power

Propeller load curve

Constant flux/torque range Field weakeningconstant power range

Load curve of propeller or fan is quadratic.

For example in cruise liner main propulsion field weakening point could be 125rpm and maximum speed 145rpm.


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Operation curves, rolling mill

0 125rpm Speed

Torque

Power

Constant flux/torque range Field weakeningconstant power range

Rolling mills and extrudes are constant load machines. The load depends on the rolling schedule and material. In Extruder load depends mainly on material.

On the example there are roughing mill passes 15. First passes are at low speed and high torque

1

2 3

45


Date post:	17-Dec-2015
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