Nested redundant uninterruptible power supply apparatus and methods

An uninterruptible power supply (UPS) system includes at least three UPSs configured to be connected in parallel to a common load. The system further includes control circuitry configured to support at least two redundant groups among the UPSs and to support at least two redundant subgroups among at least one of the redundant groups of UPSs. In this manner, a nested redundancy may be provided.

BACKGROUND OF THE INVENTION

The present invention relates to uninterruptible power supply (UPS) apparatus and methods and, more particularly, to parallel redundant UPS apparatus and methods.

A variety of different techniques have been used to improve reliability of uninterruptible power supply systems. The techniques include standby redundant, serial redundant, and parallel redundant approaches. A typical standby redundant UPS configuration includes one or more UPS units operating on a stand-by basis, with no load or only a partial load, which can immediately back up a faulty UPS unit by a transfer of the load. A typical serial redundant arrangement involves first and second UPSs connected in a serial fashion wherein, in a first mode of operation, the first UPS is bypassed while the second UPS is serving the load and, in a second mode of operation, the second UPS is bypassed while the first UPS serves the load, such that the first and second UPSs may serve as standby backups for one another.

In a typical parallel redundant arrangement, multiple uninterruptible power supplies (UPSs) are coupled in parallel to a load to provide redundancy and, often, increased load capability. Parallel redundant arrangements of AC power supplies (e.g., UPSs) are described, for example, in U.S. Pat. No. 5,745,357 to Tassitino, Jr. et al., U.S. Pat. No. 6,549,440 to Tassitino, Jr. et al., U.S. Pat. No. 6,803,679 to Luo et al., U.S. Pat. No. 6,118,680 to Wallace et al., U.S. Pat. No. 4,104,539 to Hase, United States Patent Publication No. 2005/0162792 to Wang et al., and United States Patent Publication No. 2005/0073783 to Luo et al.

SUMMARY OF THE INVENTION

In some embodiments of the present invention, an uninterruptible power supply (UPS) system includes at least three UPSs configured to be connected in parallel to a common load. The system further includes control circuitry configured to support at least two redundant groups among the UPSs and to support at least two redundant subgroups among at least one of the redundant groups of UPSs. In this manner, a “nested” redundancy may be provided.

In some embodiments, the control circuitry is configured to provide the at least two redundant subgroups when a loading of the at least one redundant group is less than a predetermined level. The control circuitry may be configured to allow selective enabling and disabling of the UPSs within the redundant group when the loading of the redundant group is less than the predetermined level and to require collective enabling and disabling of the UPSs in the redundant group when the loading of the redundant group is greater than the predetermined level.

In further embodiments of the present invention, respective ones of the redundant groups of UPSs include respective UPS assemblies. Each UPS assembly includes a plurality of UPS modules and a control circuit configured to communicate with the plurality of UPS modules over a first digital communications bus and to communicate with a control circuit of another UPS assembly over a second digital communications bus. The control circuit may include a network bridge between the first and second digital communications busses. Each UPS assembly may further include a bypass circuit, and the control circuit in the UPS assembly may be configured to control the bypass circuit to bypass the UPS modules in the UPS assembly. The UPS modules and control circuit of a UPS assembly may be mounted in and/or on a common frame.

Further embodiments of the present invention provide a UPS assembly including a frame, a plurality of UPS modules mounted in and/or on the frame, a first digital communications bus coupled to each of the UPS modules, and a control circuit mounted in and/or on the frame, coupled to the first digital communications bus and configured to be coupled to a second digital communications bus. The control circuit is operative to communicate AC waveform synchronization information to the UPS modules over the first digital communications bus and to another UPS assembly over the second digital communications bus. The AC waveform synchronization information may include frequency and phase error information. The control circuit may be configured, when the UPS assembly is connected in parallel to a load with the other UPS assembly, to operate the UPS assembly as a redundant backup for the other UPS assembly and to provide at least two redundant subgroups within its plurality of UPS modules.

In some embodiments, the control circuit may be configured to provide the at least two redundant subgroups when a loading of the UPS assembly is less than predetermined level. The control circuit may be configured to allow selective enabling and disabling of the UPS modules when the loading of the UPS assembly is less than the predetermined level and to require collective enabling and disabling of the UPS modules when the loading of the UPS assembly is greater than the predetermined level. The UPS assembly may further include a bypass circuit mounted in and/or on the frame, and the control circuit may be configured to control the bypass circuit to bypass the plurality of UPS modules. The control circuit may include a network bridge between the first and second digital communications busses.

Additional embodiments of the present invention provide methods of operating an uninterruptible power supply (UPS) system. At least three UPSs are connected in parallel to a common load. The at least three UPSs are controlled to support at least two redundant groups among the UPSs and to further support at least two redundant subgroups among at least one of the redundant groups of UPSs. Controlling the at least three UPSs to support at least two redundant groups among the UPSs and to further support at least two redundant subgroups among at least one of the redundant groups of UPSs may include providing the at least two redundant subgroups when a loading of the at least one redundant group is less than a predetermined level. For example, selective enabling and disabling of the UPSs within the at least one redundant group may be allowed when the loading of the at least one redundant group is less than the predetermined level and collective enabling and disabling of the UPSs in the at least one redundant group may be required when the loading of the at least one redundant group is greater than the predetermined level. Respective ones of the redundant groups of UPSs may include respective UPS assemblies, each UPS assembly including a plurality of UPS modules and a control circuit configured to communicate with the UPS modules of the UPS assembly and with a control circuit of another UPS assembly.

DETAILED DESCRIPTION

Some embodiments of the present invention arise from a realization that improved reliability in UPS systems may be achieved by using a nested redundant arrangement of UPSs. In some embodiments, a plurality of parallel-connected UPSs is controlled such that at least two redundant groups of the UPSs are provided and, within, at least one of these redundant groups, at least two redundant subgroups of the UPSs are provided. Such an approach may be particularly advantageous in modular UPS configurations. A nested redundant structure may be implemented, for example, using modular UPS assemblies that include respective pluralities of UPS modules and respective control circuits that control the UPS modules and communicate with one another to support nested redundancy.

FIG. 1illustrates a UPS system100according to some embodiments of the present invention. The system100includes a plurality of UPSs112a,112b,112c,112dconnected in parallel to a load20. As shown, the UPSs112a,112b,112c,112dare “on-line” UPSs, but it will be understood that, in some embodiments of the present invention, “standby,” “line interactive” or other configurations may be used. The UPSs112a,112b,112c,112dare controlled to provide first and second redundant groups110a,110b, e.g., the second group110bmay serve as a backup to the first group110a(and/or vice versa) such that one of the groups110a,110bmay continue to serve the load20in the event of failure of the other of the groups110a,110b. It will be appreciated that this redundant operation may be limited to a certain operational envelope, e.g., the redundancy may be limited to cases in which the load20is less than a capacity of an individual one of the UPS groups110a,110b, and that, when such capacity is exceeded, the UPS groups110a,110bmay, for example, be collectively disabled and/or bypassed.

Within at least one group110athere are further defined redundant subgroups111a,111b, the first subgroup111aincluding two UPSs112a,112band the second subgroup111bincluding two UPSs112c,112d.Within the group110a, for example, the first subgroup111amay serve to backup operation of the second subgroup111band/or vice versa.

It will be understood that the groups110a,110band subgroups111a,111bare provided for purposes of illustration, and that other redundant groupings and subgroupings may be used in other embodiments of the present invention. For example, in some embodiments, redundant subgroups may be provided in all redundant groups or only in a subset of the redundant groups. In some embodiments, additional redundant groups may be provided to backup the groups110a,110b, and these may or may not include redundant subgroups therein. According to further embodiments, an even higher level of nested redundancy may be provided, e.g., some or all of the UPSs112a,112b,112c,112dmay actually include multiple parallel-connected UPSs that are arranged to provide redundant subgroups therein. Other redundancy may also be provided, e.g., some or all of the UPSs112a,112b,112c,112dmay include redundant components, such as redundant rectifiers or inverters. In still further embodiments, redundant groups and/or subgroups may be dynamically redefined depending, for example, on loading and/or disposition (e.g., availability due to maintenance or other events) of particular UPSs.

FIG. 2illustrates a UPS system200with a modular architecture according to further embodiments of the present invention. First and second redundant groups of UPSs are provided in the form of respective UPS assemblies210a,210b. The UPS assemblies210a,210binclude respective pluralities of UPS modules214that are connected in parallel to a load20and that communicate with respective control circuits212. The control circuits212are also configured to communicate with one another. According to embodiments of the present invention, the control circuits212and the UPS modules214support redundant operation of the UPS assemblies210a,210bsuch that the pluralities of UPS modules214therein serve as respective redundant groups of UPSs, e.g., the group of UPS modules214of the UPS assembly210bmay act as a group to back up the group of UPS modules214of the UPS assembly210a. Within one or both of the UPS assemblies210a,210b, an inner redundancy is provided among the UPS modules214thereof. For example, as shown, the modules214and control circuit212within a UPS assembly may be configured to provide redundant subgroups211a,211bwithin the UPS assembly.

Such nested redundancy may be achieved using communications among the control circuits212and the UPS modules214. For example, in some embodiments, each UPS module214within the first UPS assembly210amay communicate status information to the associated control circuit212. Such status information may indicate, for example, whether a failure is imminent in the UPS module214and information pertaining the load currently being served by the UPS module214. In response to such information, the control circuit212may determine whether a selective disabling of the UPS module214may be allowed such that other UPS modules214within the UPS assembly210amay continue to serve the load20. For example, as explained in detail with reference toFIG. 7below, if loading of the UPS assembly210ais below a certain threshold, it may be possible to let other UPS modules214in the UPS assembly210ato continue to supply power to the load20. If, however, the loading on the UPS assembly210ais so high that the remaining operational UPS modules214do not have sufficient capacity to serve the load20, the control law of the control circuit212may require collective disabling of all of the UPS modules214in the UPS assembly210a.

The control circuit210may further communicate this information to other UPS assemblies, so that they may take coordinated action. For example, in response to receipt of such information from the first UPS assembly210a, if the control circuit212of the second UPS assembly210bdetermines that it will not be able to serve the load20once the first UPS assembly210agoes completely off-line, the control law of the control circuit212of the second UPS assembly210bmay require collective disabling of all of its currently operational UPS modules214as well. This election may be further communicated to the control circuit212of the first UPS assembly212and/or to other UPS assemblies (not shown) that may be connected to the load20, so that they may take further actions. For example, if a sufficient number of UPS assemblies are not capable of serving the load20, they may be collectively bypassed, such that an AC utility or other power source is directly connected to the load20.

FIG. 3illustrates exemplary configurations for a UPS assembly300according to some embodiments of the present invention that may be used in a UPS system along the lines described above with reference toFIG. 2. UPS modules310include a rectifier312configured to receive an AC input via a first switch (e.g., a contactor or relay)316. An inverter313is coupled by a DC bus315to the rectifier312. An output of the inverter313may be connected and disconnected from a load (not shown inFIG. 3) via a second switch317. A DC-DC converter314is also coupled to the DC bus315and is configured to be connected to a battery (not shown). The DC-DC converter314may allow the battery to provide DC power to the DC bus315in the absence of AC power at the input of the rectifier312. The DC-DC converter314may also allow charging of the battery from the DC bus315. A control circuit311is configured to control the rectifier312, inverter313, DC-DC converter314and the switches316,316. The control circuit311includes a digital communications interface, here shown as a controller area network (CAN) interface311a, coupled to a digital communications bus330.

The CAN bus330is also coupled to a CAN interface322aof a control circuit322of an I/O and bypass module320of the UPS assembly300. The I/O and bypass module320further includes a bypass switch326that is configured to bypass the UPS modules310responsive to a control signal from the control circuit322. The I/O and bypass module320further includes a CAN bridge324that provides communications between the internal communications bus330and an external bus340. Via the CAN bridge324and the external bus340, information may be exchanged with other UPS assemblies.

FIG. 4illustrates an exemplary implementation of a modular UPS assembly300′ having an architecture along the lines of the UPS assembly300illustrated inFIG. 3. In the illustrated embodiments, three UPS modules310′ and an I/O and bypass module320′ are mounted in and/or on a common frame, here shown as a cabinet410. It will be understood that the configuration illustrated inFIG. 4may be appropriate, for example, to a relatively high capacity UPS system, and that other form factors, including greater or lesser numbers of UPS modules, may be used in other embodiments of the present invention.

FIGS. 5 and 6illustrate exemplary signaling that may be used in the modular UPS assembly300ofFIG. 3. The control circuit322of the I/O and bypass module320may transmit waveform synchronization information and enable/disable commands to the UPS modules310over the internal CAN bus330. This information may also be transmitted to another UPS assembly external to the UPS assembly300via the CAN bridge324. Referring toFIG. 6, the UPS modules310may transmit waveform synchronization information and status information to the control circuit322over the internal CAN bus330. In other embodiments of the present invention, synchronization may be achieved without such explicit signaling, for example, by using techniques along lined described in U.S. Pat. No. 5,745,355 to Tracy et al. and U.S. Pat. No. 5,745,356 to Tassitino, Jr. et al, the contents of each of which is incorporated by reference herein in their entireties.

According to some embodiments of the present invention, the waveform synchronization information may include frequency and phase error information that may be used by the modules310to synchronize operation of their inverters313. For example, referring toFIG. 7, synchronization information transmitted to a control circuit of a UPS module, such as the UPS modules310ofFIG. 3, may include a target frequency and phase error that are passed to a phase locked loop controller710that generates a reference signal for an inverter driver730of the module. As shown, for purposes of balancing load share among modules, the phase lock loop compensation may be augmented by a load share controller720that operates responsive to a measure of power output of the module, along lines, for example, described in U.S. Pat. No. 6,549,440 to Tassitino et al., the disclosure of which is hereby incorporated by reference herein in its entirety. As shown inFIG. 8, in some embodiments, the phase locked loop and load share control functions shown inFIG. 7may be implemented in an AC waveform reference generator810that generates an AC waveform reference signal for an inverter driver820.

FIG. 9illustrates exemplary UPS operations for nested redundant operation of a UPS assembly according to further embodiments of the present invention. A load is powered by at least two parallel UPS assemblies, e.g., modular UPS assemblies such as the assemblies300,300′ ofFIGS. 3 and 4(block910). Upon detection of a failure of a UPS module in a first one of the UPS assemblies (block920), the control circuit of the first UPS assembly determines whether the level of loading allows for intra-assembly redundancy, i.e., will allow remaining operative UPS modules in the assembly to continue supplying the load (block930). If the load is sufficiently low, the control circuit may disable the failed module, and allow the remaining modules to continue to drive the load (block940), thus providing intra-assembly redundancy. It will be understood that a second module mail fail in a second one of the UPS assemblies, which may lead to disabling of that second module without requiring changes to the operation of the first UPS assembly. If insufficient capacity exists, however, the control circuit collectively disables all of the modules in the assembly and signals another assembly to inform it of the collective shutdown (block950). In further embodiments of the present invention, other operations may be performed. For example, in some embodiments, dynamic redefinition of redundant groups and/or subgroups may occur in response to shutdown or other unavailability of particular modules.

In the drawings and specification, there have been disclosed exemplary embodiments of the invention. Although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being defined by the following claims.