Thyristor Rectifiers

Overview – Main Functionality

The thyristor converters accomplish the AC to controlled DC conversion. On the AC side the

line-frequency voltages are present and, for given AC line voltages, the average DC-side voltage

can be controlled from a positive maximum to a negative minimum value in a continuous manner.

The converter’s average DC output current is only positive and cannot change direction. Therefore,

a converter of this type can operate in only two quadrants where positive values of voltage and

current imply rectification in which the power flow is from the AC to the DC side. The power flow

changes direction when the output voltage becomes negative. Nevertheless, when the 4-quadrant

operation is necessary an anti-parallel configuration of two thyristor converters can offer this



The high current capability of the thyristors makes thyristor converters suitable for applications

where high DC current is required. Such high DC current demands can be found in applications

where the production of magnetic field is essential and consequently also the high current feeding

the magnets and the coils.


The thyristor bridge(s) are connected through a three-phase transformer with one or more

secondaries and a circuit breaker to the AC supply system as is shown in the figure above. The

thyristor converter rectifies the AC line voltages and injects current to the load through a filter only

if this is necessary according to the customer’s needs. With a reference signal the output current

and voltage are regulated through an in-house built digital controller with high precision.



The operating ratings that define the thyristor converter are depending of course on the needs of

the application. However, the numbers, in the table below, cover a range of ratings where the

design of thyristors converters is feasible based on the knowledge and former experience of

Ampulz but also the current technological boundaries.

Mode of operation : Continuous mode, Pulsed mode

Supply : Grid or Generator

Max output current : from 1 kA to 100 kA

Output voltage : from 10 V to 5 kV

Thyristor rectifier line voltage : from 10 V to 1700 V

Precision : up to 1 ppm

Cooling : Water-cooled or air-cooled


Our thyristor converters can operate in continuous mode or pulsed mode which is the operational

need for current injection into coils. The power source is the grid 400 V, 10 kV, 20, 33 kV at 50/60

Hz or a generator with special combination of voltage and frequency. The output current, the

output voltage and the accuracy are specified by the customer and define the design decisions for the converter.