Patent Application
20150171663
The inventive subject matter relates to power supply apparatus and methods and, more particularly, to uninterruptible power supply (UPS) systems and methods.
UPS systems are commonly used in commercial and industrial facilities, such as data centers, telecommunications facilities, factories and hospitals. They are often used to provide reliable, high quality power to critical equipment, such as computer systems.
UPS systems may have any of a number of different types of architectures. For example, AC UPS systems may have an on-line or double conversion architecture including a rectifier configured to be coupled to an AC power source and an inverter coupled to the rectifier by a DC bus and configured to provide AC power to a load. A battery or other DC source may be coupled to the DC source, which may provide backup power in the event of failure of the AC source. Standby AC UPS systems may include an inverter that is configured to be coupled to a load by a transfer switch that switches a load between the inverter and an AC source. AC UPS system may have other architectures, such as line interactive and delta conversion architectures.
48V DC power distribution systems have been traditionally employed in telecommunications applications, such as in telephone switching centers. Such systems may be served by DC UPS systems that provide power from alternative sources. Higher voltage DC power systems are increasingly being introduced in data center applications, as the use of DC power distribution may reduce conversion losses and provide additional benefits in comparison to conventional AC data center power distribution systems.
Some embodiments of the inventive subject matter provide an apparatus including a current source rectifier circuit having an input configured to be coupled to an AC power source and an output configured to be coupled to a load, a coupling circuit configured to couple a DC power source to the current source rectifier, and a control circuit configured to selectively operate the current source rectifier circuit and the coupling circuit to generate a DC output from the AC power source and the DC power source. In some embodiments, the control circuit may be configured to operate the coupling circuit to provide a DC/DC converter circuit that uses an energy storage inductor of the current source rectifier circuit. The apparatus may further include a freewheeling diode shared by the current source rectifier circuit and the DC/DC converter circuit. Such apparatus may be used, for example, in DC UPS applications.
Further embodiments of the inventive subject matter provide an apparatus including a current-source rectifier configured to be coupled to an AC power source and a DC/DC converter configured to be coupled to a DC power source and sharing an energy storage inductor with the current-source rectifier. The apparatus further includes a control circuit configured to selectively operate the current-source rectifier and the DC/DC converter to produce a DC voltage at an output node coupled to the inductor.
In some embodiments, the current-source rectifier may include an active rectifier circuit having an input configured to be coupled to the AC power source. The inductor may couple an output of the active rectifier circuit to an output node. The DC/DC converter may include a coupling circuit configured to couple the inductor to the DC power source. The control circuit may selectively control the active rectifier circuit and the coupling circuit to selectively provide the current-source rectifier and the DC/DC converter, respectively. The apparatus may further include a freewheeling diode shared by the current-source rectifier and the DC/DC converter.
In some embodiments, the coupling circuit may include a switch configured to couple the DC power source to the inductor. The inductor may have a first terminal coupled to the active rectifier circuit and a second terminal coupled to the output node, and the switch may be configured to couple and decouple the DC power source to and from the first terminal of the inductor.
The DC power source may include a battery, and the apparatus may further include a charger circuit configured to charge the battery.
Further embodiments of the inventive subject matter provide a UPS including an input port configured to be coupled to an AC power source, an active rectifier circuit having an input coupled to the input port, an inductor having a terminal coupled to an output of the active rectifier circuit and a switch configured to couple a DC power source to the terminal of the inductor. The UPS may further include a control circuit that operates the active rectifier circuit to provide a current-source rectifier that produces a DC voltage at a second terminal of the inductor from the AC power source and that operates the switch to provide a DC/DC converter that produces a DC voltage at the second terminal of the inductor from the DC power source. The control circuit may be configured to operate the DC/DC converter to produce the DC voltage responsive to a failure of the AC power source.
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.
Some embodiments of the inventive subject matter arise from a realization that current source rectifiers can be advantageously adapted for use in UPS applications. Current source rectifier circuits may be particularly advantageous for UPS applications because they can produce sinusoidal input currents with desirably low harmonic distortion and can effectively limit output current under fault conditions. Some embodiments may use circuit configurations that allow interfacing of a battery or other backup DC power source to the current source rectifier using relatively few components by sharing components between the current source rectifier and battery interface circuitry.
The UPS system 200 further includes a coupling circuit 220 is configured to selectively couple a battery 20 to the inductor Lout. The coupling circuit 220 includes a transistor switch Qd and a blocking diode Dd. The coupling circuit 220, the freewheeling diode Dfw and the inductor Lout may be operated as a DC/DC converter circuit, in particular, a buck converter, that produces the DC output voltage Vout from the battery 20. In particular, the control circuit 230 may control the transistor Qd of the coupling circuit 220 responsive to the inductor current IL and the output voltage Vout. The DC/DC converter may be operated, for example, to maintain the output voltage Vout in the event of failure of the. AC power source 10 and/or the active rectifier circuit 210.
In some embodiments, a separate charger circuit 50 may charge the battery 20. The charging circuit 50 may be powered, for example, by one or more of the phases 10a, 10b, 10c of the AC power source 10. The charger circuit 50 and/or the battery 20 may be integrated with the UPS system 200 in a single assembly, or may be located in one or more separate assemblies electrically coupled to the UPS system 200.
The control circuit 230′ also provides a second pair of nested loops for controlling the coupling circuit 220 when the system 200 is operating as a DC/DC converter for powering an attached load from the battery 20. The loops include an outer voltage control loop that generates a voltage error signal ve2 based on a comparison of the output voltage vout to a reference vref2, which may be the same as the first voltage reference vref1. A third compensation function G3 is applied to the voltage error signal ve2 to generate a command ic2 for an inner current loop. The inner current loop compares the inductor current IL to the command ic2 to generate a current error signal ie2. A fourth compensation function G4 is applied to the current error signal ie2 to generate a control signal (e.g., a PWM waveform) for the coupling circuit 220.
It will be appreciated that the control circuit 230′ may be implemented using any of a variety of different types of electronic circuits, such as microcontroller-based circuits which implement the control architecture illustrated using computer instructions executing on data processor, along with peripheral circuitry for interfacing such digital circuitry to switching and sensing devices of the active rectifier circuit 210 and the coupling circuit 220. It will be further appreciated that the control architectures illustrated may also be implemented using functionally similar analog circuitry.
UPS systems along the lines described above may be advantageously applied in power distribution systems for data centers and other electronic systems. For example, as illustrated in
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.
