Patent Application
20140133201
The inventive subject matter relates to power conversion apparatus and methods and, more particularly, to uninterruptible power supply (UPS) apparatus and methods.
UPS systems are commonly used in installations such as data centers, medical centers and industrial facilities. UPS systems may be used in such installations to provide backup power to maintain operation in event of failure of the primary utility supply. These UPS systems often have an “on-line” configuration including a rectifier and inverter coupled by a DC link that is also coupled to an auxiliary power source, such as a battery, fuel cell or other energy storage device. Other configurations, such as standby and line-interactive configurations, may also be used.
UPS systems may have a modular structure including two or more UPS modules, each of which may include, for example, a rectifier, an inverter and a DC/DC converter for interfacing to a battery or other DC power source. The modules commonly are designed to operate in parallel to provide scalable power capacity, e.g., the modules may be coupled in common to an AC source, a DC source (e.g., a battery) and/or a load.
The converter circuits used in such UPS modules are typically switchmode power converter circuits. Paralleled arrangements of such switchmode converters may be vulnerable to the generation of significant high-frequency currents between the modules. In paralleled inverter arrangements, this problem may be addressed by, for example, synchronizing the PWM cycles used by the inverters as described, for example, in U.S. Pat. No. 7,405,494 to Tassitino, Jr. et al. In paralleled DC/DC battery conversion arrangements, large inductors may be connected in the battery connection paths to move resonant frequencies of the battery connection circuitry outside of the PWM frequency range of the DC/DC converters.
Some embodiments of the inventive subject matter provide an uninterruptible power supply (UPS) system including at least two UPS modules having respective switchmode power converter circuits coupled in common to a current source/sink by respective conductors. The system further includes at least one differential mode inductor magnetically coupling the at least two conductors.
In some embodiments, the switchmode power converter circuits may include respective DC/DC converter circuits coupled in common to a terminal of a DC power source by the conductors. The DC/DC converter circuits may operate at variable frequencies and/or may not be synchronized. The at least two UPS modules may further comprise respective inverter circuits having inputs coupled to respective ones of the DC/DC converters and outputs coupled in common to a load.
In some embodiments, the at least one differential mode inductor may include a ferrite core magnetically coupling the conductors. The ferrite core may include, for example, a ferrite ring through which each of the conductors passes at least once.
In further embodiments, the switchmode power converter circuits may include respective inverter circuits coupled in common to a terminal of a load by the conductors. In still further embodiments, the switchmode power converter circuits may include respective rectifier circuits coupled in common to a terminal of an AC power source by the conductors.
According to some embodiments, the at least two UPS modules may include at least three UPS modules having respective switchmode power converter circuits coupled in common to the current source/sink by at least three respective conductors. The at least one differential mode inductor may include a plurality of differential mode inductors, respective ones, of which magnetically couple respective pairs of the at least three conductors. At least one of the at least three conductors may be magnetically coupled to less than all of a remainder of the at least three conductors.
Some embodiments of the inventive subject matter provide a UPS system including at least two UPS modules. Each of the at least two UPS modules includes an inverter circuit having an output configured to be coupled to load and a DC/DC converter circuit coupled to an input of the inverter circuit. The system further includes at least two conductors, respective ones of which couple respective ones of the switchmode DC/DC converter circuits of the UPS modules in common to a terminal of a battery and at least one differential mode inductor magnetically coupling the at least two conductors.
Further embodiments provide methods of operating a UPS system comprising at least two UPS modules and at least two conductors, respective ones of which couple respective switchmode DC/DC converter circuits of the UPS modules in common to a terminal of a battery. The methods include differential mode inductively coupling the at least two conductors.
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 to those skilled in the art. In the drawings, like numbers refer to like elements. It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. 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.
Certain embodiments of the inventive subject matter may be advantageously implemented in modular UPS systems in which DC/DC battery converter circuits of multiple UPS modules are coupled in common to a DC source, such as a battery. In some systems, such DC/DC converters may be unsynchronized and/or may operate at variable PWM frequencies. Consequently, such arrangements may produce significant high frequency currents between the modules. These high frequency currents may stress interconnecting conductors and/or the components of the DC/DC converters, such as filter capacitors. Conventional techniques for mitigating such high-frequency currents, such as PWM synchronization and/or the use of large in-line inductors, may lack robustness and/or may involve undesirable cost, weight and volume.
DC/DC battery converter circuits 216 are coupled to the DC links in the modules 210. Conductors 220 couple the DC/DC converter circuits 216 in common to terminals of a battery 10′. The battery 10′ (which may include one or several cells) and the DC/DC converter circuits 216 may provide auxiliary power to the inverter circuits 214 in the event that the AC power source 10″ degrades or fails. The DC/DC converter circuits 216 may also provide charging current to the battery 10′ from the DC link 215. The DC/DC converter circuits 216 may be unsynchronized and/or may operate at variable PWM frequencies.
Respective differential mode inductors 230 magnetically couple respective pairs of the conductors 220, and may be configured to reduce high-frequency currents passing between the DC/DC converter circuits 216. As illustrated in
According to some embodiments, such differential mode inductors may be implemented using ferrite rings or similar structures. For example, as shown in
In UPS systems including more than two modules, similar functionality may be obtained by using respective differential mode inductors that couple conductors from respective pairs of modules. For example,
According to further embodiments illustrated in
According to further embodiments, a UPS system may similarly use differential mode inductors for the conductors coupling paralleled inverters and/or rectifiers. As shown in
It will be further appreciated that, in some embodiments, differential mode inductors may be used for multiple ones of battery, rectifier and inverter connections. For example, referring to
In the drawings and specification, there have been disclosed exemplary embodiments of the inventive subject matter. 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 inventive subject matter being defined by the following claims.
