Current signal generator and method of implementing such a generator
A generator for providing regulated current signals, to terminals of a load includes: a plurality of secondary stages, including a direct voltage source insulated from those of other stages, connected in series between the midpoint of the second half-bridge of each secondary stage and the midpoint of the first half-bridge of the next secondary stage, the load terminals being respectively connected to the midpoint of the first half-bridge of a first secondary stage, and to the midpoint of the second half-bridge of a last secondary stage; and a control circuit capable of: selecting a group of secondary active stages, and at least one regulating stage; simultaneously controlling each active stage, except the regulating stage, at the frequency of the current slots; controlling the regulating stage according to a frequency higher than the previous one; and controlling the switches of the non-selected secondary stages to insulate their voltage source.
1. A generator of current signals, suitable to gating pulses of regulated current of alternating polarity under high voltage to the terminals of a load, said generator comprising:
a plurality of circuits, so-called secondary stages,
each secondary stage including at least one source of DC voltage isolated from the voltage sources of the other secondary stages, and a switching circuit comprising four switches arranged in first and second half-bridges each formed of two switches connected in series between the positive pole and the negative pole of the voltage source,
the secondary stages being interconnected in such a way that the midpoint of the second half-bridge of each secondary stage is linked to the midpoint of the first half-bridge of the following secondary stage, the terminals of the load being respectively linked to the midpoint of the first half-bridge of a first secondary stage and to the midpoint of the second half-bridge of a last secondary stage, and
a control circuit,
select a group of secondary stages, so-called active stages, depending on a set point of a current flowing in the load,
select from said active stages at least one stage, the so-called regulation stage,
control simultaneously the switches of each active stage, with the exception of the regulation stage, at the frequency of, and synchronously with, the gating pulses of current, so as to place the voltage sources of these stages in series,
control the switches of said regulation stage in accordance with a frequency higher than the preceding frequency, with a control duty cycle that is suitable to regulate the current flowing in the load to the set point,
control the switches of the non-selected secondary stages, in order to isolate their voltage source,
wherein
the voltage source of each secondary stage includes a secondary winding of a three-phases transformer fed by a primary stage, a diode rectifier bridge including six diodes and a filter capacitor.
2. The generator as claimed in claim 1 , wherein the transformer is directly coupled to a three-phase current source.
3. The generator as claimed in claim 2 , wherein the three-phase current source is a generating set.
4. The generator as claimed in claim 1 , wherein the voltage sources of the secondary stages exhibit a staging of their output voltage in an open circuit, enabling an adjustment of the output voltage of the generator.
5. The generator as claimed in claim 1 , wherein the switches are insulated-gate bipolar transistors.
6. The generator as claimed in claim 5 , wherein said transistors are mounted on oil radiators.
7. The generator as claimed in claim 1 , wherein the control circuit is linked to the switches by an optical-fiber link.
8. A process for generation of current signals, suitable to provide gating pulses of regulated current of alternating polarity under high voltage to the terminals of a load, in which:
a generator including a plurality of secondary stages each including a source of DC voltage isolated from the voltage sources of the other secondary stages, said voltage source including a secondary winding of a three-phase transformer and a six-diodes rectifier bridge, and a switching circuit comprising four switches arranged in first and second half-bridges each formed of two switches connected in series between the positive pole and the negative pole of the voltage source are used, the secondary stages being interconnected in such a way that the midpoint of the second half-bridge of each secondary stage is linked to the midpoint of the first half-bridge of the following secondary stage, the terminals of the load being respectively linked to the midpoint of the first half-bridge of a first secondary stage and to the midpoint of the second half-bridge of a last secondary stage, wherein:
current signals in the form of gating pulses are voluntarily generated,
a group of secondary stages, so-called active stages, is selected, depending on a set point of a current flowing in the load,
from said active stages at least one stage, the so-called regulation stage, is selected,
simultaneously the switches of each active stage, with the exception of the regulation stage, are controlled at the frequency of, and synchronously with, the gating pulses of current, so as to place the voltage sources of these stages in series,
the switches of said regulation stage are controlled in accordance with a frequency higher than the preceding frequency, with a control duty cycle that is suitable to regulate the current flowing in the load to the set point,
the switches of the non-selected secondary stages are controlled, in order to isolate their voltage source.