Distributed internal fault bypass in a modular...

Details Distributed internal fault bypass in a modular... Distributed internal fault bypass in a modular...

2000-03-29

2001-09-18

Berhane, Adolf Deneke (Department: 2838)

Electric power conversion systems

Current conversion

Having plural converters for single conversion

C307S066000

Reexamination Certificate

active

06292379

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to fault bypass circuitry for power inverters, and more particularly to bypass circuitry for use in modular uninterruptible power supply systems.
BACKGROUND OF THE INVENTION
As more and more segments of the business environment enter the information age, more and more computers and computing power are required. As businesses move from the old to the new economy their reliance on the processing, transference, and storage of digital information is becoming a more and more critical aspect of their overall business strategy. While in the past, computer crashes were seen as a mere nuisance, the loss of computing power and business data may well devastate a business's ability to survive in today's new economy. As such, the need for reliable, uninterruptible electric power to maintain the operational status of the computing equipment and the integrity of the digital data continues to rise.
To meet these requirements, uninterruptible power supplies (UPS) have been developed that utilize a bank of electric storage batteries and solid state conversion equipment. These UPSs operate in association with the utility line voltage to provide continuous electric power to a business's computer systems in the event of a loss or deviation of power from the utility. The number of batteries contained within an UPS is dependent upon the business's length of time that it needs to operate in the event of a utility power system failure. Likewise, the number of power inverters included in an UPS is dependent upon the overall total system load required to be supplied thereby. In the past, uninterruptible power supplies were only available in discrete sizes. However, with the recognition of the various requirements from the multitude of businesses that require UPSs, the development of modular uninterruptible power supplies has provided a flexibility heretofore unknown. Now, a business's UPS power output may grow as its business needs, without requiring the purchase of additional redundant hardware and control boards as in the past.
In addition to the batteries and power inverters, uninterruptible power supplies also have a requirement for the inclusion of fault bypass circuitry that allows the output loads to be supplied directly by the utility line power once activated. Such bypass circuitry is needed to protect the electronic switches of the power inverter in the event that the output load current draw exceeds the maximum rating of the inverter. Additionally, this circuitry may be activated in the event that a failure within the power inverter is detected by the control circuitry such that the output loads may continue to receive electric power. Under the prior paradigm where uninterruptible power supplies were constructed and sold in a given, fixed, maximum output power capacity, these output circuits were properly sized to handle the rated load of the inverter.
However, as modular UPSs
11
were designed, such as illustrated in
FIG. 6
, the output bypass circuitry
17
continued to remain a core circuit element within the UPS chassis. As such, it needed to be sized for the maximum configurable power output capacity of the entire modular UPS, regardless of the actual configuration for a particular customer. This ensured that the modular UPS
11
would be able to handle the bypass current requirement for a maximum output power configured UPS, assuming that a customer had installed the maximum number of power inverters
13
supported. Unfortunately, for customers who do not have this maximum power capacity installed (illustrated by empty slots
15
a-c
), they were still forced to pay the cost for the larger rated circuitry
17
. While such additional cost is acceptable to a business that needs its bypass capacity, the additional cost is hard to justify to a customer who may never utilize such high power output.
Further, prior non-modular UPSs had to coordinate operation only between a single inverter and the output bypass circuitry. Therefore, there was no design concern with respect to differential switching of paralleled inverters as is the case with modular UPSs. That is to say, in prior systems the bypass control circuitry needed to only shut-off one inverter before operating the bypass circuit. In many of these UPSs, the output of the inverter was coupled to the loads through a ferroresonant transformer. As such, there was little concern as to the short period between the turning off of the inverter and the turning on of the bypass circuit because the ferroresonant transformer would not reflect this short break in power during the transition therebetween.
Likewise, many modular UPSs also include ferroresonant transformer coupled outputs which also are not concerned with short breaks in power during the transition from the inverter output to the utility line voltage. Since each of these systems could rely on the output power characteristics of the ferroresonant transformer, these prior systems provided the bypass circuitry function by using a simple mechanical relay to bypass the inverter. Unfortunately, these known methods are inapplicable to modular uninterruptible power supplies that utilize transformerless inverters.
Therefore, there exists a need in the art for a new system of providing UPS bypass functionality without requiring that this circuitry be sized for the total output of the possible configuration of the modular UPS chassis, and that is able to operate with transformerless inverters.
SUMMARY OF THE INVENTION
A method and circuitry for supplying bypass functionality in a multiple module uninterruptible power supply (UPS) is presented. In accordance with a preferred embodiment, this is accomplished by distributing the bypass functionality into each of the power modules in the modular UPS, thereby allowing the bypass capacity to increase as the power rating of the system increases due to the addition of additional power modules. This bypass capacity is therefore proportional to the rating of the installed power modules, unassociated with the potential power rating of the UPS chassis. As such, the circuitry and method of the preferred embodiment reduces the required bypass circuitry's capacity on the system with lower than maximum power requirements, thereby reducing costs on those systems. Additionally, the circuitry of the invention provides redundant bypass circuitry that increases the fault tolerance of the installed system by allowing continued operation in the event of a failure of one of the bypass circuits.
In an embodiment of the invention for a modular uninterruptible power supply, where there is a system failure or the load requires more current than the installed inverters can supply, the UPS transfers the power from the utility source, directly to the load, bypassing the UPS inverters. Further, the circuitry of the invention allows user control to bypass the inverter stages during operation for increased efficiency, servicing, etc.
In a preferred embodiment, an uninterruptible power supply includes a chassis with installable power modules. Each power module added to the system increases the total power rating of the system by the power rating of the individual module. Each power module has circuitry that enables the power module to bypass its inverter circuitry in a controlled manner. This control is provided by circuitry and software for detecting a condition requiring the bypass mode of operation. When one power module detects such a condition, it sends a signal to the other power modules that then, in a coordinated fashion, all switch themselves into bypass mode.
In a preferred embodiment, the module's bypass circuitry is designed to carry bypass current equal to two modules on the UPS. This allows for the continued operation of a system in bypass mode of operation in the event that one of only two installed modules running at maximum capacity is suddenly removed either by the user or due to failure. In the preferred embodiment, the remaining module will be able to sustain the full

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