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Basics: - Thyristor Units - IGBT-Power Converter (IPC)

Manfred Schleicher

Why Power Units?

Basics Thyristor Units + IGBT-Power Converter (IPC)

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Why Power Units?


Thyristor power switches are actuators with a low price: 24 V

Basics Thyristor Units + IGBT-Power Converter (IPC)

230 V

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Why Power Units?


Some processes need electrical power in a range of 0…100 %
A Thyristor unit can chance the power continuously in a range from 0…100 %

0…100%

Basics Thyristor Units + IGBT-Power Converter (IPC)

0…5 kW

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Difference Thyristor Unit/ Power Converter IPC


The considerable difference between thyristor units and power converters are the operating modes…

Basics Thyristor Units + IGBT-Power Converter (IPC)

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Thyristor Units Burst-firing operation
In Burst-firing operation, the thyristor unit switches the supply voltage (for the percentage rate of the output level) on the load voltage: 0…100%


Example output level 60%: the thyristor unit switches the supply voltage - 3 full-waves - on the load voltage while 2 full-waves are locked:

Basics Thyristor Units + IGBT-Power Converter (IPC)

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Thyristor Units Burst-firing operation
Factory-made the thyristor unit switches as often as possible
At 50 Hz the frequency duration of a full wave is 20 ms
With an output level of 60 % the thyristor unit switches 3 full waves on (3 x 20 mS) and 2 full waves off (2 x 20 ms) → In our example the cycle time is 100 ms
If requested, operation can be done as well with a firm cycle time of 500 ms (change of configuration)

Basics Thyristor Units + IGBT-Power Converter (IPC)

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Thyristor Units Phase - angle control
In phase – angle control the thyristor switches only a part of the supply voltage half-waves on the load voltage: 0…100%


Example: Control with a phase angle of α=45°

Basics Thyristor Units + IGBT-Power Converter (IPC)

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Thyristor Units Comparsion of the operating modes
Burst-firing operation


Phase – angel control

 For fast applications

 For very fast applications (e.g. control of candlepower)

 Low EMC- interferences, because of switching at zero point  No reactive power

 Large interference sensitivity EMC (harmonic wave)

 fluctuations in the supply voltage (voltage flicker)

 no voltage flicker

Basics Thyristor Units + IGBT-Power Converter (IPC)

 High percentage of reactive power - especially with a big control angle

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Thyristor Units Comparsion of the operating modes
Burst-firing operation When connecting the load voltage to heating elements with less mass, the temperature at the element rises. If the load voltage is switched off, the temperature falls.


Phase – angel control Very short turn on and turn off times, thus less stress for the heating elements

=> large temperature change => higher max. temperatures => Stress for the heating elements => shorter durability of heating elements

Basics Thyristor Units + IGBT-Power Converter (IPC)

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IGBT-Power Converter IPC With amplitude control
The power converter - a device with amplitude control:

To operate the IPC, an inductor (choke) is indispensable

Inductivity

0…100%

Basics Thyristor Units + IGBT-Power Converter (IPC)

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IGBT-Power Converter IPC With amplitude control
The power converter varies the amplitude of the load voltage in proportion to the control signal:


The load voltage has the same frequency as the supply voltage – but positive half-waves only

Basics Thyristor Units + IGBT-Power Converter (IPC)

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IGBT-Power Converter IPC With amplitude control
The shape of the supply current is as well sinusoidal; phasing is identical with the voltage supply phasing:

As phasing of currentand voltage supply are identical, only active power is taken from mains !

Basics Thyristor Units + IGBT-Power Converter (IPC)

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IGBT-Power Converter IPC Functional principle


The switch drawn in corresponds to the IGBT component. By switch on and off the IGBT with high frequency, a sinus voltage at the load is generated.

Basics Thyristor Units + IGBT-Power Converter (IPC)

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IGBT-Power Converter IPC Advantage - constant power output Basicly thyristor units provide the heating elements either with full power or none power. With the operating mode amplitude control the IPC provides the elements with a constant power output. This fact is the basis of the following advantages:
If the control signal remains the same, the temperature of the heating elements is stable and the max. temperature is lower (less stress for the elements and mostly longer durability)
No voltage flicker as with burst-firing operation
Lower connected wattage through stable power consumption (less payments to the power supply company)
Considerably less EMC-interferences than with phase – angel control
No essential reactive power (please refer to phase – angel control) Basics Thyristor Units + IGBT-Power Converter (IPC)

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IGBT-Power Converter IPC Operation of low voltage heaters without transformer Up to now the classic operation of low voltage heaters required a transformer L1

Prime current

Second. current

furnace

60 VAC

230 VAC N

With the operating mode amplitude control the transformer is not required anymore: L1

furnace

choke

60 VAC

230 VAC N

Basics Thyristor Units + IGBT-Power Converter (IPC)

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Subordinate Control Action U2- Control action Factory - made the power units control the square of the load voltage (UL) in proportion to the control signal

Even if the Supply voltage is not stable, U2 is adjusted. With a stable resistive load RL the power is controlled and adjusted: U2 P= RL

Basics Thyristor Units + IGBT-Power Converter (IPC)

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Subordinate Control Action U2- Control action
The U2 – control is suitable for heating elements with a positive or constant temperature coefficient (TC)
In cold condition the ohmic resistance of heating elements with positive TC is low; it increases with rising temperature:

Due to the low resistance in cold condition, some heating elements show an impermissible high current. In such cases the option current limiting is used.

Basics Thyristor Units + IGBT-Power Converter (IPC)

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Current Limiting Thyristor unit and IPC
If the option „current limiting“ is available, the current is reduced to the requested value, if e.g. the heating elements are in cold condition:

Poti to be turned left … …until the diode lights

Remark: The thyristor unit offers the option „current limiting“ with operating mode phase control only. Basics Thyristor Units + IGBT-Power Converter (IPC)

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U2-Control Supporting effect on the control loop
As already mentioned, the resistance of heating elements with positive TC increases with rising temperature:


At the output thyristor units control the effective value of voltage (U2) in proportion to the input signal
Temperature and resistance rise
With rising temperature (resistance) the power is reduced (P=U2/R); exceeding the setpoint is now more unlikely Basics Thyristor Units + IGBT-Power Converter (IPC)

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I2-Control
If the thyristor unit is configured for I2 control, they control the effective value of the current (I2) in proportion to the input signal:

Basics Thyristor Units + IGBT-Power Converter (IPC)

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I2-Control Supporting effect on the control loop
I2-control is recommended for heating elements with negative TC
With rising temperature they reduce their resistance


P=I2 x R shows that the power is automatically reduced with rising temperatures
With falling temperature the power is increased automatically Basics Thyristor Units + IGBT-Power Converter (IPC)

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P-Control Ageing process compensation
During lifetime some heaters change their nominal resistance considerably (SIC-heating elements):

Ageing Nominal resistance (RN)


For such kind of heaters the P-Control applies

Basics Thyristor Units + IGBT-Power Converter (IPC)

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Load / Part Load Failure Supervision Load fail – Example: Thyristor units
Available with extra codes TR or TO
If the load resistance is too low, load fail is activated
This function applies for heaters with constant TC


Adjustment of switching threshold:
to connect load
to adjust full output
to adjust trimmer load fail in a way that the yellow diode barely turns off
the binary output is available as output for messages

Basics Thyristor Units + IGBT-Power Converter (IPC)

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Load / Part Load Failure Supervision Low current monitoring
Part load failure supervision (low current monitoring) is used in applications with heaters in parallel circuit


If a heating element fails, the load current decreases


A partial load failure is recognized and signalized

Basics Thyristor Units + IGBT-Power Converter (IPC)

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Load / Part Load Failure Supervision Over-current supervision
The function can be used as over-current monitoring as well (after modification of the configuration)
It applies for heaters with series connection:
A short circuit of a heater causes rising load current


A partial load failure is recognized and signalized

Basics Thyristor Units + IGBT-Power Converter (IPC)

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Firing Pulse Inhibit Inhibit – Example: Thyristor units
The power of the heaters can be shut off with an external contact

Even if firing - pulse inhibit is active, the load is not strainless! Disconnect the voltage supply! Basics Thyristor Units + IGBT-Power Converter (IPC)

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Start-up - Thyristor Units Rating

Basics Thyristor Units + IGBT-Power Converter (IPC)

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Start-up – Thyristor Units Electrical connection UN

Controller

IL

Dimensioning - thyristor unit: UThy=UN IThy=P/UN IThy=IL

Fuse

ITh Load

Control circuit

Basics Thyristor Units + IGBT-Power Converter (IPC)

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Start-up - IPC Dimensioning

Loadcurren t =

Mains _ current =

Capacity _ Heatingele ments Loadvoltag e

capacity _ Heatingele ments + 2 A(losses ) Voltage _ Supply _ Power _ Section

Basics Thyristor Units + IGBT-Power Converter (IPC)

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Start-up - IPC Details

Basics Thyristor Units + IGBT-Power Converter (IPC)

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Start-up - IPC Electrical connection

0…20 mA + -

Load voltage

Supply for control section

Basics Thyristor Units + IGBT-Power Converter (IPC)

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Start-up - IPC Electrical connection
The previous drawing did not show the mains filter which must be connected as well:

Basics Thyristor Units + IGBT-Power Converter (IPC)

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Auf Wiedersehen Au revoir Good Bye

JUMO GmbH & Co. KG MANFRED SCHLEICHER Dipl. Ing. (FH) Head of Training Tel.: +49 661 6003-396 E-Mail:[email protected]