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The R12 Power Converter is used in North experimental area to power mainly a serie of quadrupole magnets, for DC application.
This power converter is composed of 3 main parts:
The Power part contains the transformer,the Main Circuit Breaker, the thyristors bridge, the DCCT, the polarity reversal switch and auxiliary circuitry.
The Power Supply Crate is integrated directly in the Power Converter enclosure. Its function is to provide the local interface between the Power Converter and the Converter Crate.
The Converter Crate is remotely located from the rest of the power converter components, in a temperature controlled area, to enhance the stability of the analog circuitry. Its function is to achieve with two loops the regulation of the output current and voltage and interface to a common data bus which is daisy chained externally to other Power Converters and to the VME front end with the Data Bus.
North Area power converter architecture
The transformer has two primary delta windings connected in parallel and the two transformer secondary windings are a zig-zag star connection with star point brought out. Each secondary phase consists of two windings which can be connected in parallel or series, depending of the output voltage requirement.
The secondaries each feeds a 3 phases thyristor bridge assembly A and B connected in parallel via a inductor. An external voltage booster module called "Diode Module" can be added in series with the thyristor bridge to increase the output voltage.
The secondary circuits are protected against negative voltage with two Free Wheeling diodes connected to the transformer star point.The DC output is connected to a polarity reversal switch, allowing the output voltage to be connected normally, inverted or disconnected from the load.
Power Part simplified Architecture / Topology .pdf
Power Part simplified Architecture / Topology with Diode Module
Control: The new VME crate is in operation since 2006 and replaced the old junction crate. It's the heart of the control system, there is one crate installed per building.
Control system simplified schematic
Software architecture simplified schematic
Software used to control North power converters:
Regulation: Regulation of the output current and voltage is achieved with two loops, one for the voltage and one for the current. The voltage loop ensures fast correction of the output for perturbations on the incoming mains supply. The current loop ensures stabilisation for low frequency perturbations and has a variable integration time constant selection possibility. The voltage loop feedback is from a resistor potential divider network connected across the final output. The current loop is driven by a remote controlled precision reference source (DAC). A precision current transducer (DCCT) measures the output current and produces a voltage developed across high precision and stability resistors (burden). A precision comparator amplifier with very high gain, compares the DAC and DCCT signals and produces a voltage to drive the voltage loop of the regulator. The regulator circuit develops a control voltage (-5 to +7V) from the above two loops, to control the firing of the thyristor bridges. The firing of the thyristors in the bridge, which is synchronised with the 50 Hz incoming supply, occurs at a 300 Hz frequency. During operation such as Polarity Switch change and under fault circumstances, the Blocking signal acts directly on the Thyristor trigger drivers to inhibit the output firing circuits.
Regulation Control simplified schematic .pdf
Each magnet connected to a North Area Power Converter can have a number of bits of feedback data for monitoring its status.
These can be as follows depending on the magnet involved:
Activation of any of the above signals automatically causes the “Stop” signal to be generated, causing the Reference Current value to go to zero, followed 30 seconds later with the switch off of the MCB, if the Polarity switch is not in the Stop position. This is initiated by the MCB Release signal.
In North area, there are two ways to connect a power converter to a magnet:
Magnet connection simplified schematic
Line selector mattrix
R12 power converters supplies the following loads:
Number of R12 power converters installed in North area: