Patent Description:
Data centers, industrial facilities, medical facilities and the like often have AC power distribution systems that are protected by UPS systems. UPS systems may be used in such applications to provide backup power to maintain operation in event of failure of the primary utility supply. UPS systems commonly have an "on-line" configuration including a rectifier and inverter coupled by a DC link that is also coupled to an auxiliary source, such as a battery, flywheel converter or other energy storage device. In some UPS applications, a renewable source, such as a photovoltaic source, may be coupled to the DC link of an on-line UPS to provide supplemental power, as described, for example, in <CIT> to Parmley and an article entitled "<NPL>). Further, attention is drawn to <CIT>, which relates to an electronic interface that couples a combination of generation and storage devices with a power grid and/or a load. The interface comprises a DC bus; a DC storage device coupled to the DC bus; a first DC-to-AC inverter having a DC port operatively coupled to the DC bus, and an AC port; a second DC-to-AC inverter having a DC port operatively coupled to the DC bus, and an AC port; a switch for electrically coupling the AC port of the second DC-to-AC inverter to a first generator or an AC storage device; a first rectifier for coupling an AC output of the first generator to the DC bus; and a second rectifier for coupling an AC output of the AC storage device to the DC bus. Document <CIT> is another example of prior art document.

In accordance with the present invention, a UPS system and a method as set forth in claims <NUM> and <NUM> are provided. Further embodiments are inter alia disclosed in the dependent claims. Embodiments of the inventive subject matter provide uninterruptible power supply (UPS) systems. Such systems inter alia include an AC input configured to be coupled to an AC power source, an AC output configured to be coupled to a load a first power conversion circuit including a first converter circuit coupled to the AC input, a second converter circuit coupled to the AC output and a first DC bus coupling the first converter circuit to the second converter circuit. The system further includes a second power conversion circuit having a third converter circuit having an output coupled to the AC output, a fourth converter circuit coupled and a second DC bus coupling the third converter circuit to the fourth converter circuit, the second DC bus being configured to receive power from a photovoltaic power source. The system further has a control circuit operatively associated with the first and second power conversion modules and configured to cooperatively control the first to third converter circuits to concurrently transfer power to the load from the AC power source via the first and second converter circuits and from the photovoltaic power source via the third converter circuit. The first DC bus may be coupled to an auxiliary power source, while the second DC bus is connected to the photovoltaic power source , such that the first DC bus and the second DC bus are not connected in common to the auxiliary power source. In this manner, the photovoltaic power source may be relatively isolated from the first DC bus.

In some embodiments, the first power conversion module may be configured to provide a rectifier coupled to the AC input and an inverter coupled to the AC output. The second power conversion module may be configured to provide an inverter as the third power conversion module coupled to the AC output with the DC bus of the second power conversion module coupled to the photovoltaic power source.

In some embodiments, the fourth converter unit is inactive. Each of the power conversion modules may include a DC bus interface unit, and the DC bus interface unit of the second power conversion module may be configured to couple the DC bus to the photovoltaic power source. In further embodiments, the fourth converter unit may have an input coupled to the photovoltaic power source and the DC bus of the second power conversion module may be additionally coupled to an auxiliary power source, such as a battery.

Additional embodiments of the inventive subject matter provide methods including populating a UPS system with a plurality of power conversion modules as claimed.

Specific exemplary embodiments of the inventive subject matter now will be described with reference to the accompanying drawings. This inventive subject matter may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive subject matter as defined by the appended claims to those skilled in the art. As used herein the term "and/or" includes any and all combinations of one or more of the associated listed items.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the inventive subject matter. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms "includes," "comprises," "including" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this inventive subject matter belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

As will be appreciated by one of skill in the art, the inventive subject matter may be embodied as systems, methods and computer program products. Some embodiments of the inventive subject matter may include hardware and/or combinations of hardware and software. Some embodiments of the inventive subject matter include circuitry configured to provide functions described herein. It will be appreciated that such circuitry may include analog circuits, digital circuits, and combinations of analog and digital circuits.

Embodiments of the inventive subject matter are described below with reference to block diagrams and/or operational illustrations of systems and methods according to various embodiments of the inventive subject matter. It will be understood that each block of the block diagrams and/or operational illustrations, and combinations of blocks in the block diagrams and/or operational illustrations, can be implemented by analog and/or digital hardware, and/or computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, ASIC, and/or other programmable data processing apparatus, such that the instructions, which execute via the processor of the computer and/or other programmable data processing apparatus, create means for implementing the functions/acts specified in the block diagrams and/or operational illustrations. In some implementations, the functions/acts noted in the figures may occur out of the order noted in the block diagrams and/or operational illustrations. For example, two operations shown as occurring in succession may, in fact, be executed substantially concurrently or the operations may sometimes be executed in the reverse order, depending upon the functionality/acts involved.

Some embodiments of the inventive subject matter relate to interfacing of variably available power sources with UPSs. As referred to herein, "variably available power sources" include power sources, such as solar, wind, tidal and similar renewable energy sources, having an availability (e.g., presence and capacity) that fluctuates with environmental conditions (e.g., availability of wind, sun or tidal change) and that are not, as a general rule, available on demand. Such power sources may also be referred to as "variable", "intermittent" or "non-dispatchable" and, for purposes of the present application, such sources shall be referred to as "variably available power sources.

Some embodiments of the inventive subject matter arise from a realization that the DC link bus can be a critical point in the UPS architecture. Failure of a variably available power source, such as a photovoltaic array, coupled to the DC link can potentially impact the output of the UPS and/or reduce system robustness and reliability. Some embodiments of the inventive subject matter may address such issues by using a variably available power source interface circuit comprising a converter having an output coupled to the AC output and an input configured to receive power from a variably available power source. In some UPS system embodiments, for example, generic power conversion modules may be configured to include one or more modules configured to provide online-UPS functions, output-paralleled with one or more modules configured to provide a variably available power source interface for the UPS system. In this manner, isolation between the variably available power source and DC bus of the UPS module(s) may be provided. In addition, modules may be selectively configured for use as UPS modules or variably available power source interfaces depending on the relative capacities and requirements of the system.

<FIG> illustrates a UPS system <NUM> useful in understanding the inventive subject matter but not covered by the claim. The UPS system <NUM> includes a UPS circuit <NUM> including a first converter circuit, e.g., a rectifier <NUM>, and a second converter circuit, e.g., an inverter <NUM>, coupled by a DC link <NUM>. An auxiliary power source <NUM>, e.g., one or more batteries, may be coupled to the DC link <NUM>. The input of the rectifier <NUM> is coupled to an AC input <NUM> of the UPS system, and the output of the inverter <NUM> is coupled to an AC output <NUM> of the UPS system <NUM>. The UPS circuit <NUM> is configured to provide uninterruptible power to a load <NUM> coupled to the AC output <NUM> from an AC power source <NUM> (e.g., a utility source and/or local generator) coupled to the AC input <NUM> and from the auxiliary power source <NUM>, which may provide power in the event of a failure of the AC source <NUM>. The UPS system <NUM> may also include a bypass circuit <NUM> (e.g., a static switch), which may be used to bypass the UPS circuit <NUM> to provide power directly from the AC power source <NUM> to the load <NUM>, which may support maintenance and high-efficiency modes of operation. It will be appreciated that the UPS system <NUM> may be a single-phase or multiphase (e.g., three-phase) system.

The UPS system <NUM> further comprises a third converter circuit <NUM>, coupled between the AC output <NUM> and a variably available power source <NUM>, such as a solar or wind power source. A control circuit <NUM> is operatively associated with the UPS circuit <NUM> and the converter circuit <NUM> (and, optionally, the bypass circuit <NUM>) and is configured to cooperatively control the UPS circuit <NUM> and the converter circuit <NUM> to selectively transfer power to the load <NUM> from the AC power source <NUM> and the variably available power source <NUM>.

For example, as illustrated in <FIG>, when the AC power source <NUM> is producing power in manner meeting predetermined criteria, power may be provided to the load <NUM> from the AC power source <NUM> through the rectifier <NUM> and inverter <NUM> (and/or via the bypass circuit <NUM>), while power is concurrently transferred to the load <NUM> from the variably available power source <NUM> via the converter <NUM>. As shown in <FIG>, upon failure of the AC power source <NUM>, the control circuit <NUM> may operate the inverter <NUM> of the UPS circuit <NUM> and the converter <NUM> such that power is concurrently delivered to the load <NUM> from the variably available power source <NUM> and the auxiliary power source <NUM>.

It will be appreciated that the above-described components of the UPS system <NUM> may be integrated in one assembly or may implemented using multiple interoperating assemblies with connecting power and control links.

<FIG> illustrates a modular UPS system <NUM> with a variably available power source interface capability according to embodiments of the inventive subject matter. The UPS system <NUM> includes an AC input <NUM> configured to be coupled to an AC power source <NUM> and an AC output <NUM> configured to be coupled to a load <NUM>. The UPS system <NUM> further includes first and second power conversion modules <NUM>, <NUM> having a common architecture, including a first converter unit <NUM> and a second converter unit <NUM> coupled by a DC bus <NUM>, a DC bus interface unit <NUM> and a module control circuit <NUM> configured to control the first converter unit <NUM>, the second converter unit <NUM> and/or the DC bus interface unit <NUM>. A system control circuit <NUM> controls interoperation of the first and second power conversion modules <NUM>, <NUM> and a bypass circuit <NUM>.

The first power conversion module <NUM> is configured to provide a UPS function. In particular, the first module <NUM> is configured to operate the first converter unit <NUM> as a rectifier to produce a DC voltage on the DC bus <NUM> from the AC power source <NUM>. In some embodiments, the first converter units <NUM> may comprise passive rectifiers while, in other embodiments, the first converter units <NUM> may be active circuits that may be used to implement a rectifier function, but that are selectively reconfigurable to provide other conversion operations, such as DC/DC conversion, by, for example, changing the manner in which the active circuits are controlled. The first module <NUM> is further configured to operate the second converter unit <NUM> as an inverter to produce an AC voltage at the AC output <NUM>. The DC bus interface unit <NUM> of the first module <NUM> provides an interface to one or more batteries <NUM>, which may be used to provide auxiliary power in the event of a failure of the AC power source <NUM>.

The second power conversion module <NUM> is configured differently to provide an interface to a variably available power source <NUM> (e.g., wind, solar, tidal, etc.). The second converter unit <NUM> of the second module <NUM> is operated as an inverter. The first converter unit <NUM>, however, is inactive. The variably available power source <NUM> is coupled to the DC bus <NUM> using the DC bus interface unit <NUM>. Depending on the nature of the variably available power source <NUM>, the DC bus interface unit <NUM> may simply connect the variably available power source <NUM> to the DC bus <NUM> without a voltage conversion, or the DC bus interface unit <NUM> may provide, for example, a DC/DC or AC/DC conversion function.

<FIG> illustrates a combination of power conversion modules 510a, 510b, 510c configured to provide a system such as the system <NUM> of <FIG>. The modules 501a, 510b, 510c each comprise a first converter unit <NUM> and a second converter unit <NUM> coupled by DC busses <NUM>, as well as a DC bus interface unit <NUM> that may be used for coupling to a battery or other power source. The first converter units <NUM>, the second converter units <NUM> and the DC bus interface units <NUM> each include circuitry wherein active switching units <NUM> may be installed to realize half-bridge circuits. The modules 510a, 510b, 510c may also include inductors, capacitors, current sensors, contactors and fuses.

The first and second modules 510a, 510b are configured to operate as paralleled UPSs, with the first converter units <NUM> configured to operate as rectifiers coupled to an AC input bus <NUM> and the second converter units <NUM> configured to operate as inverters coupled to an AC output bus <NUM>. The DC bus interface units <NUM> of the first and second modules 510a, 510b are configured to provide DC/DC converters coupled to battery busses <NUM>.

A third module 510c is configured to provide an interface for connection of a photovoltaic (PV) power source via a PV bus <NUM>. The second converter unit <NUM> of the third module 510c is configured to operate as an inverter, output-paralleled with the first and second modules 510a, 510b at the AC output bus <NUM>. The first converter unit <NUM> of the third module is inactive, e.g., it may be operationally deactivated or active devices and passive components thereof may be depopulated. As shown, active components may be depopulated from the DC bus interface unit <NUM> of the third module 510c to allow a direct connection of the DC busses <NUM> thereof to the PV bus <NUM>.

A bypass circuit including a static switch <NUM> is also provided. The static switch <NUM> is coupled to a bypass bus <NUM>, which may be connected to the same AC source as the AC input bus <NUM>. The modular configuration illustrated in <FIG> provides for use of common power conversion modules while supporting a degree of isolation of the PV source from the DC busses <NUM> of the first and second modules 510a, <NUM>0c, which are operated as UPSs.

<FIG> illustrates a modular UPS system <NUM> according to further embodiments of the inventive subject matter. The system <NUM> uses first and second modules <NUM>, <NUM> as shown in <FIG>, except that the module <NUM> is configured to provide power from a variably available power source <NUM> via a first converter unit <NUM> of the second module <NUM>, rather than via the DC bus interface unit <NUM>. Depending on the nature of the variably available power source <NUM>, the first converter unit <NUM> of the second module <NUM> may be operated as a rectifier or as a DC/DC converter. The bus interface unit <NUM> may be used for connection of one or more additional batteries <NUM>.

Claim 1:
An uninterruptible power supply, in short UPS, system (<NUM>; <NUM>), comprising:
an AC input (<NUM>) configured to be coupled to an AC power source (<NUM>);
an AC output (<NUM>) configured to be coupled to a load (<NUM>);
a first power conversion module (<NUM>) comprising a first converter circuit (<NUM>) coupled to the AC input (<NUM>), a second converter circuit (<NUM>) coupled to the AC output (<NUM>) and a first DC bus (<NUM>) coupling the first converter circuit (<NUM>) to the second converter circuit (<NUM>);
the UPS system (<NUM>; <NUM>) characterised by further comprising:
a second power conversion module (<NUM>) comprising a third converter circuit (<NUM>) having an output coupled to the AC output (<NUM>), a fourth converter circuit (<NUM>) coupled to the third converter circuit (<NUM>), and a second DC bus (<NUM>) coupling the third converter circuit to the fourth converter circuit and configured to receive power from a photovoltaic power source (<NUM>); and
a control circuit (<NUM>) operatively associated with the first power conversion module (<NUM>) and the second power conversion module (<NUM>) and configured to control the first converter circuit (<NUM>), the second converter circuit (<NUM>) and the third converter circuit (<NUM>) to concurrently transfer power to the load from the AC power source (<NUM>) via the first converter circuit (<NUM>) and the second converter circuit (<NUM>) and from the photovoltaic power source (<NUM>) to the load via the third converter circuit (<NUM>).