UNINTERRUPTIBLE POWER SYSTEMS USING CURRENT SOURCE RECTIFIERS AND METHODS OF OPERATING THE SAME

An apparatus includes 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.

BACKGROUND

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.

SUMMARY

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.

DETAILED DESCRIPTION

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.

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.

FIG. 1illustrates an uninterruptible power supply apparatus100according to some embodiments of the inventive subject matter. The apparatus100includes an active rectifier circuit130, which is configured to be coupled to an AC power source10, such as a utility power source and/or local generator. The apparatus100further includes a coupling circuit140configured to be coupled to a DC power source20, such as a battery, fuel cell, flywheel power source or the like. The active rectifier circuit130and the coupling circuit140are configured to implement a current source rectifier110and a DC/DC converter120using a shared energy storage inductor150. The current source rectifier110is configured to provide DC power to a load30from the AC power source10. The DC/DC converter120is configured to provide DC power to the load30from the DC power source20. In some embodiments, the DC/DC converter120may be used to provide power to the load30from the DC power source20in the event of a failure of the AC power source10and/or the active rectifier circuit130.

FIG. 2illustrates an exemplary implementation of the architecture illustrated inFIG. 1according to further embodiments. A UPS system200includes a three-phase active rectifier circuit210including three bridge circuits coupled to respective phases10a,10b,10cof an AC source10. The bridge circuits include upper transistor switches Qa1, Qb1, Qc1and lower transistor switches Qa2, Qb2, Qc2(here shown as power MOSFETs), which are configured to selectively couple the phases10a,10b,10cto first and second DC busses215a,215bat an output of the active rectifier circuit210. Upper and lower diodes Da1, Db1, Dc1, Da2, Db2, Dc2are configured to prevent backfeed through the transistors Qa1, Qb1, Qc1, Qa2, Qb2, Qc2from the buses215a,215b.The output of the active rectifier circuit210is coupled to an inductor Loutand a capacitor Cout, and a freewheeling diode Dfwis coupled across the output of the active rectifier circuit210. The active rectifier circuit210, freewheeling diode Dfw, and inductor Lout may be operated as a current source rectifier that produces a DC output voltage Voutacross the capacitor Cout from the AC power source10. In particular, a control circuit230may control the transistors Qa1, Qb1, Qc1, Qa2, Qb2, Qc2responsive to the output voltage Voutand a current iLthrough the inductor Loutto regulate the output voltage Vout. It will be understood that the capacitor Coutmay be included in the UPS system220as shown inFIG. 2and/or may be provided by a capacitance included in a load coupled to the UPS system220.

The UPS system200further includes a coupling circuit220is configured to selectively couple a battery20to the inductor Lout. The coupling circuit220includes a transistor switch Qdand a blocking diode Dd. The coupling circuit220, the freewheeling diode Dfwand the inductor Loutmay be operated as a DC/DC converter circuit, in particular, a buck converter, that produces the DC output voltage Voutfrom the battery20. In particular, the control circuit230may control the transistor Qdof the coupling circuit220responsive to the inductor current ILand the output voltage Vout. The DC/DC converter may be operated, for example, to maintain the output voltage Voutin the event of failure of the. AC power source10and/or the active rectifier circuit210.

In some embodiments, a separate charger circuit50may charge the battery20. The charging circuit50may be powered, for example, by one or more of the phases10a,10b,10cof the AC power source10. The charger circuit50and/or the battery20may be integrated with the UPS system200in a single assembly, or may be located in one or more separate assemblies electrically coupled to the UPS system200.

FIG. 3illustrates an example of a control architecture that may be implemented by the control circuit230to support the two modes of operation described above. As shown, a control circuit230′ may provide a first pair of nested control loops for controlling the active rectifier circuit230when operating the system200as a current source rectifier to provide power to a load from the AC source. The loops include an outer voltage control loop that generates a voltage error signal ve1based on a comparison of the output voltage voutto a reference vref1, and applies a first compensation function G1to the error to generate a command ic1for an inner current loop. The inner current loop compares the inductor current iLto the command ic1to generate a current error signal1e1. A second compensation function is applied to the current error signal ie1to generate a control signal (e.g., a pulse width modulated (PWM) signal) for the active rectifier circuit210.

The control circuit230′ also provides a second pair of nested loops for controlling the coupling circuit220when the system200is operating as a DC/DC converter for powering an attached load from the battery20. The loops include an outer voltage control loop that generates a voltage error signal ve2based on a comparison of the output voltage voutto a reference vref2, which may be the same as the first voltage reference vref1. A third compensation function G3is applied to the voltage error signal ve2to generate a command ic2for an inner current loop. The inner current loop compares the inductor current ILto the command ic2to generate a current error signal ie2. A fourth compensation function G4is applied to the current error signal ie2to generate a control signal (e.g., a PWM waveform) for the coupling circuit220.

It will be appreciated that the control circuit230′ 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 circuit210and the coupling circuit220. 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 inFIG. 4, UPS systems such as those illustrated inFIGS. 1-3may be used in a DC UPS420configured to be installed in an equipment rack400that houses one or more devices410, such as servers, routers, hubs and/or other data processing or network devices. The DC UPS420may provide DC power to the devices410to directly or indirectly power motherboards and/or other systems in the devices410. Referring toFIG. 5, a DC UPS520may be similarly used to provide DC power to multiple racks510in a data center or similar facility, each rack510housing multiple devices512powered by the DC UPS520.

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.