Electric power conversion systems – Current conversion – Having plural converters for single conversion
Reexamination Certificate
2000-05-23
2002-04-30
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
Having plural converters for single conversion
Reexamination Certificate
active
06381155
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the field of DC to DC power conversion systems and provisions for making optimal use of the system described in conjunction both with the primary DC power sources available and the given loads power consumption demands.
BACKGROUND OF THE INVENTION
The DC power converters which convert power from a primary DC power source into an output DC power draw defined by the load power consumption demands have become widely popular for feeding the electric and electronic circuits of varied devices. A great variety of DC-DC converter designs and circuitry have been invented and are used to address the variety of applications and requirements. Most common DC-DC converter designs were based on a primary power inductor or transformer, at least one switching transistor and an output filter capacitor. However, these prior art designs appear with large number of parts of substantial weight, volume and power losses, and with a limited power conversion density, i.e., the ratio of the number of watts per cubic inch or in regards to the overall cost. Attempts to increase the power conversion density by increasing the operational frequency have been ineffective. Primarily this is because proportional increases in power losses result in heat retention which undermine component reliability.
To overcome these disadvantages, a number of multiple converter topologies have been developed to improve power conversion density and overall power conversion performance. These are power sharing techniques which utilize multiple in-parallel arranged DC power converter units that are relatively small size. Each converter unit delivers only portions of the overall drawn power. Moreover, it is cost effective to design and manufacture standardized individual power converter units that combine into an array to feed a particular load, rather than to design and manufacture specific DC power converters to fit each application.
The power sharing DC-DC power conversion system includes at least one DC primary source, a multi-channel DC-DC power converter and a load. The multi-channel DC-DC power converters may be of any existing topology provided that it contains multiple internal switch-mode power conversion channels. The early prior art designs provide simultaneous operation of paralleled power conversion units. For multi-channel DC-DC power converter this means that each internal channel delivers its portion of power from a DC primary source to a load in a synchronously coincidental mode of operation (syn-phase, provided that all power conversion channels have a common operating frequency to trigger power-on cycles.
In a syn-phase mode of power conversion, all internal channels operate synchronously and simultaneously to each other. This synchronous operation creates large instantaneous power draws and large drops in the voltage of the primary power source. This instantaneous draw creates additional problems by introducing substantial input and output ripple. The ripple is caused by the simultaneous overlay of similar non-linear responses within corresponding circuits due to the non-linearity of any power conversion process.
Different multi channel converter configurations introduce different ripple constituents. In the case of parallel combined inputs and outputs, the input and output currents are summed within respective input and output circuits. The amplitude of the resultant primary source voltage drops increases proportionally to the N number of combined inputs. The resultant consumption and delivery currents have N times multiplied direct and ripple constituents as compared to the single power conversion channel.
In the case of series combined input and/or output power conversion channels circuits, the amplitude of the primary source voltage drop increases proportionally to the number of combined inputs. The resultant delivery voltage has N times multiplied direct and ripple constituents as compared to the same single power conversion channel.
Another disadvantage of the syn-phased power conversion is very slow response to changes in load. The time required responding to a change in load is limited to no less than one switching frequency period. In addition, the feedback circuit (used to control the power-on cycle interval) rate-of-response is severely limited to avoid feedback loops excited by ripple constituents.
Since all converters of the system have a common operating frequency, it was therefore determined reasonable to control the individual converters through staggered timing of their power-on cycles, i.e. in a poly-phase mode. In this way a power demand is also staggered over time eliminating the huge drops in primary power.
In poly-phase mode power, all channels operate with their power-on cycles time-staggered so, that there is a time displacement, &Dgr;t
dspl
, interval between the start-on points of the sequential cycles. Provided that all power conversion channels have the same operating frequency, the resultant summed input and output power draws show substantial improvement from the standpoint of primary power stress and output ripple constituents. Summing the time-staggered portions of converted power produces a filtering effect within the input and output circuits of the combined power conversion channels.
Since all the converters are driven out-of-phase in respect to each other, their non-linear responses are superimposed in a non-simultaneous and non-coincidental order. The result is a staggered inter-related compensation of overlapped portions of non-linear responses. This overlap decreases the non-linearity of the summed power draw.
It is therefore recognized inappropriate to increase the output power draw by increasing the number of parallel syn-phased power conversion channels since it produces proportional increase of input and output ripple constituents. However, increasing the number of poly-phased power conversion channels produces substantial decrease of input and output ripple constituents as compared with a single power conversion channel in the row.
However, the relative advantages of the prior art poly-phase mode power conversion approach do not provide completely satisfactory solutions to DC-DC power conversion.
There are many different applications requiring to deliver high quality DC power to a multiple loads from multiple low quality primary power sources. These varied applications make it desirable to have a modular power conversion system where small conversion units are combined in a single unit where their joint operation produces both a high quality and low loss power transfer from power source load demands.
It is evident that securing the high quality features of poly-phase power sharing DC-DC power conversion within the complex system configurations comprised of multiple primary power sources, DC-DC converters and loads may need more sophisticated control arrangement for operating the technical means. Thus, a better method and apparatus for power sharing techniques is needed.
ADVANTAGES AND SUMMARY OF THE INVENTION
The benefits of the proposed invention may be better disclosed through a comparative appraisal of the syn-phased versus poly-phased multi-channel power conversion systems.
The syn-phased power sharing DC-DC power conversion system, as shown at FIG.
1
(
a
), includes at least one DC primary source
10
, a multi-channel DC-DC power converter
12
and a load
14
. The multi-channel DC-DC power converters
12
may be of any existing topology provided that it contains multiple switch-mode power conversion channels
16
. Each internal channel
16
delivers its portion of power from DC primary source
10
to a load
14
in a synchronously coincidental (syn-phase) mode of operation. Syn-phase operation assumes all power conversion channels have common operating frequency for power-on cycles.
In a syn-phase mode of power conversion, all power conversion channels
16
, as shown at FIG.
3
(
a
), operate synchronously and simultaneously to each other. This coincidental operation creates large instantaneous power draws and
Kadatsky Anatoly F.
Karpov Eugene V.
Volovets Naum I.
Berhane Adolf Deneke
Next Power Corporation
Ray K. Shahani, Esq.
LandOfFree
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