Current supply installation with voltage-controlled current supply devices connected in parallel on the output side

A current supply installation is disclosed which comprises at least two voltage-controlled current supply devices connected in parallel at an output side without decoupling. In each of the current supply devices, a compound voltage value is formed by a first voltage proportional to a no-load voltage and a voltage proportional to an output voltage of the respective current supply device. This compound voltage value is used a the basis for an actul value for voltage control in each of the current supply devices.

BACKGROUND OF THE INVENTION 
The invention relates to a current supply installation consisting of at 
least two voltage-controlled current supply devices connected in parallel 
without decoupling means on the output side. 
Such a circuit arrangement is already known (U.S. Pat. No. 3,515,974). 
This current supply installation relates to a plurality of DC blocking 
converters working to a common output, and whose power circuits consisting 
of a switching transistor, a transformer and a filter network are 
connected in parallel. A control voltage for the switching transistors is 
generated in dependence on the output voltage in an oscillator circuit 
common to all blocking converters. Connection techniques for uniform load 
division between the individual blocking converters are not provided, 
because, due to the intermediate storage of the energy to be transformed 
in the transformer, a rigid coupling between the individual switching 
transistors and the common output is lacking. 
SUMMARY OF THE INVENTION 
An object of the invention is, with minimum circuit complexity, to make 
possible a secure redundant operation of a plurality of current supply 
devices connected in parallel without decoupling means and to make 
possible operational monitoring, whereby, in addition to constant 
readiness for service, a nearly uniform load division is obtained. 
In connecting current supply devices in parallel, slight differences of the 
rated output voltage are produced because of tolerances that are caused by 
the component parts. In voltage-controlled current supply devices, as a 
result of these differences in the output voltage, a totally unequal 
loading of the individual current supply devices arises, since only the 
current supply device with the highest output voltage can assume the 
entire load, whereas all other current supply devices, for which an actual 
value that is too high is simulated, are nearly disengaged. In this state, 
it cannot be determined by means of monitoring the output voltage whether 
a current supply device is carrying under-voltage because of a defect and 
which of the current supply devices, for example, is responsible for an 
over-voltage. 
According to the invention, these disadvantages can be avoided with minimal 
circuit complexity in that a compound voltage value formed out of a 
voltage proportional to the no-load voltage and a voltage proportional to 
the output voltage of the current supply devices, is taken as the basis 
for each current supply device as the actual value of the voltage control. 
The voltage proportional to the no-load voltage is evaluated for 
monitoring purposes. 
By means of these techniques, all current supply devices that are not 
conducting current are regulated to a voltage in the magnitude of the 
rated output voltage. 
In accord with an advantageous embodiment of the invention, this solution 
can be realized circuit-wise in such manner that all current supply 
devices exhibit an auxiliary circuit separated from the main circuit with 
a similar frequency response as that of the main circuit, which is 
terminated with an actual value divider, and that a partial resistance or 
impedance of the actual value divider is connected in parallel with a 
partial resistance or impedance of a second actual value divider connected 
in the main circuit for the formation of the compound voltage value. This 
compound voltage can represent the average value of the two actual values. 
The monitoring of the individual current supply devices can now ensue by 
means of a voltage monitoring circuit connected in each case to the output 
of the auxiliary circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Two voltage-controlled current supply devices Stvl and Stv2 (FIG. 1) are 
connected in parallel on the output side without decoupling diodes and 
deliver an output voltage U.sub.A. Both current supply devices are 
operated with a voltage U.sub.E which can be subject to fluctuations. Of 
the two current supply devices, only the output circuit with a part of the 
regulation loop is illustrated. Each respective actual value divider, 
consisting of the resistances R1, R2 and R1', R2', delivers the actual 
value U.sub.Ist1 and U.sub.Ist2 and each respective reference voltage 
circuit with the series resistance Rv and a Zener diode Z1 or Rv' and Z2, 
respectively, is connected with each respective control circuit Rg1 and 
Rg2 for the formation of a deviation signal. Although both current supply 
devices are designed alike and their output voltage U.sub.A is equally 
rated, slight differences in the output voltage induced by the component 
parts can exist, which lead to the fact that, in any given case, the 
device with the higher output voltage assumes the entire load, whereas the 
other current supply device carries a voltage at its output which is too 
high with reference to its nominal rated output voltage and therefore is 
regulated down to a very small voltage. In this state, neither a load 
division to the two current supply devices is possible nor can the 
current-carrying device be determined by monitoring the output voltage 
U.sub.A and the readiness for service of the current supply device not 
carrying current at that time be determined. This disadvantage could be 
partially eliminated in that the parallel connection of the two current 
supply devices ensues via decoupling diodes. Particularly in the case of 
low output voltages, however, the diodes would have the disadvantage that 
they would severely deteriorate the resulting efficiency of the current 
supply installation. 
In the embodiment according to FIG. 2, the invention is shown with the 
example of two flow converters connected in parallel on the output side. 
Each of the two flow converters essentially consists of a transformer U 
whose primary winding w is periodically connected to an input voltage 
U.sub.E via a controlled switching transistor Ts. The output voltage 
U.sub.A is obtained at a secondary winding w1 via a diode and a LC-filter 
member L1, C1. The control of the switching transistor Ts ensues via a 
pulse generator T delivering a rectangular control voltage. The 
controlling AC voltage is influenced in its duty cycle as a function of 
the amplified deviation. Such a control circuit is described, for example, 
in U.S. Pat. No. 3,226,630 incorporated herein by reference. The output of 
the secondary circuit with the winding w1 exhibits an actual value divider 
Z1, Z2, which delivers a measuring value for a rated-value--actual-value 
comparison in a control circuit. 
Beyond this main circuit, the flow converter exhibits an auxiliary circuit 
of similar construction which consists of a further secondary winding w2, 
a diode rectifier, and a LC-filter circuit L2, C2. The auxiliary circuit 
is terminated by means of an actual value divider Z3, Z4 and does not 
serve for power output. The divider elements Z1 through Z4 can, in 
general, be impedances which, for example, are formed out of parallel 
connections of resistors and capacitors. This, for example, can be 
necessary for the actual value filtering. The special design of this 
circuit consists in that one respective actual value proportional to the 
output voltage U1 or U2, respectively, is tapped for a mix from the actual 
value dividers of the main and auxiliary circuit. To this end, the 
resistors Z2 and Z4 of the actual value divider are connected in parallel. 
The interrelationships can be most simply illustrated in the average or 
mean value formation of the actual values. The prerequisite for the mean 
value formation is that equally large voltages are dropped across the 
resistors Z2 and Z4 in the no-load operation of the flow converter. This 
condition can be met most simply in that the main and auxiliary circuit 
are equally rated, i.e. that the secondary winding is designed such that 
w1=w2 and the resistors of the actual value divider are made Z1=Z3 and 
Z2=Z4. By means of a comparison of the mean actual value thus gained with 
a rated value, the deviation is developed which determines the duty cycle 
of the controlling AC voltage at the switching transistor Ts. When, for 
example, the current supply device Stv2 has a rated value which lies 2% 
below that of the current supply device Stv1, then the current supply 
device Stv1 regulates to the corresponding value U.sub.A, whereas the 
current supply device Stv2 would like to force an output voltage that is 
2% lower, i.e. would like to switch itself off. By means of the specific 
auxiliary circuit, however, the actual value of the current supply device 
Stv2 is brought up to the value of the rated value. The voltage U2 on the 
auxiliary circuit would then lie about 4% below the voltage U.sub.A at the 
outputs of the current supply devices connected in parallel. 
In a static load of the devices, the auxiliary voltage can be directly 
evaluated for monitoring purposes in a monitoring circuit UW. With a 
dynamic load, however, U.sub.2 can fluctuate significantly. In order to 
also be able to work with narrow monitoring limits in this case, according 
to FIG. 3, a compound voltage of U.sub.A and U.sub.2 is also formed for 
monitoring. This compound voltage is supplied to the monitoring circuit 
UW. The circuit required for this is different from the arrangement 
according to FIG. 2 in that by means of a voltage divider Z5, Z6 a 
monitoring voltage U.sub.3 is formed from the difference of the output 
voltage U.sub.A and the auxiliary voltage U.sub.2. Therefore, it must be 
observed that Z5/Z6=Z1/Z3 must be selected. In an operation free of 
interference, U.sub.3 is always proportional to the voltage that the 
device in question would output in individual operation. 
The specified basic circuit diagram is also applicable for parallel 
connection of more than two current supply devices as well as for all 
other controlled types of current supply devices, for example, 
continuously operating control devices. 
The control circuit Rg employed in this invention is well known in the art 
and may be easily constructed by one skilled in this art. The same is true 
of the monitoring circuit UW. 
Although various minor modifications may be suggested by those versed in 
the art, it should be understood that I wish to embody within the scope of 
the patent warranted hereon, all such embodiments as reasonably and 
properly come within the scope of my contribution to the art.