Methods and systems for distributing load transfers in power supply systems

A power supply system includes an AC power line with an uninterruptible power supply (UPS) device coupled to receive power from the AC power line. The UPS includes control circuitry that couples power conversion circuitry of the UPS to the AC power line when the available AC power is acceptable. The power supply system also includes a second UPS device coupled to receive power from the AC power line. The second UPS includes a timer delay, such that the control circuitry is configured to couple power conversion circuitry to the AC power line when the available AC power is acceptable, and upon expiration of the timer.

BACKGROUND OF INVENTION

1. Field of Invention

Embodiments of the invention relate generally to power management, and more specifically to methods and systems for preventing power failure from large inrush current simultaneously drawn by multiple power loads.

2. Discussion of Related Art

Today's companies and persons rely on having power more than ever before. Without power, companies may be unable to manufacture goods, or to operate at all, such as if the company is in the business of supplying information over the Internet. Without power, businesses and individuals may be completely incapacitated regarding critical activities, such as making goods, providing services, and transacting personal finances (e.g., filing tax returns, and paying bills).

With such a heavy reliance on power, individuals and companies frequently need to be able to have power outages corrected in short order, and/or have backup power supplies so that their affairs and/or businesses are not significantly affected, and/or be notified when power fails. Correcting power outages typically involves calling a local power company to report a power outage and/or troubleshooting a local power supply/conveyance system, e.g., internal to a company or residence, that has gone out. Uninterruptible power supplies (UPSs) are often used to provide backup power in case of a power outage. A UPS provides surge protection and backup battery power for electronic systems. Backup battery power helps prevent loss of data that can occur during a blackout, a brownout (low voltage), or a spike or a surge of electricity through the system. UPSs are commonly used on computing equipment to guard against data being lost due to a power outage before the data are saved. UPSs used with computing equipment also help to guard against a loss in service by providers of information over the Internet, such as by servers, e.g., hosting web pages. UPSs can also help improve availability of network infrastructure in the home during power outages, protect against data loss on personal computers, etc.

SUMMARY OF INVENTION

A facility that has numerous UPS deployed will back up the power for multiple loads, and a number of UPS will connect to a shared line power. During a power outage all the UPS will continue to supply power to their loads. When the power returns, typically all UPS will attempt to connect to the line power simultaneously, this will cause a step load increase on the incoming source as the loads all turn on simultaneously. A large step load increase could potentially cause the input power to fail again. Generally, having a large number of UPS devices instantaneously connect to any power supply source, such as a back up power generator, can create a sudden step load increase, also referred to as inrush current or input surge current, causing failure in the power supply.

At least one embodiment of the invention provides a power supply system that includes an AC power line with a plurality of uninterruptible power supply (UPS) devices coupled to receive power from the AC power line. A first UPS includes control circuitry that couples power conversion circuitry of the UPS to the AC power line when the available AC power is acceptable. The power supply system also includes a second UPS device coupled to receive power from the AC power line. The second UPS includes a timer delay, such that the control circuitry is configured to couple power conversion circuitry to the AC power line when the available AC power is acceptable, and upon expiration of the timer.

DETAILED DESCRIPTION

FIG. 1illustrates a power supply system according to principles of the invention. The system includes an AC power line150that provides power with a first uninterruptible power supply (UPS)110device coupled to a load130. A second UPS device120also provides power from the AC power line150to a load140. The UPS devices110, and120contain control circuitry configured to selectively convert and supply power from the external AC power source110or an internal battery pack (not shown inFIG. 1) to their respective loads130,140with desired voltage characteristics (e.g., voltage) as directed by a control circuit of power circuitry contained within each UPS. The second UPS device120further contains a timer delay120a, that may delay the switching of the power source by the control circuitry.

During a power outage the UPS devices will continue to supply power to their loads by transferring stored power from the internal battery pack, or other energy storage means, such as a flywheel, or capacitor bank. Upon sensing that the available AC power becomes acceptable, the control circuitry of the UPS devices couple power conversion circuitry of the UPS devices110,120to the AC power line150when the available AC power is acceptable. When the power returns, typically all UPS devices will attempt to connect to the line power simultaneously, causing a step load increase on the incoming source as the loads all turn on simultaneously. This step load increase, also referred to as inrush current or input surge current, may cause the input power to fail again. According to principles of the invention, the second UPS includes a timer delay, such that the control circuitry is configured to couple power conversion circuitry to the AC power line when the available AC power is acceptable, and upon expiration of the timer. By staggering the connections of the UPS devices110,120to the AC power line150, a sudden inrush current may be avoided, thus avoiding an overload of the AC power.

On of ordinary skill in the art will understand that multiple UPS devices may connect to a single AC power line, and that several off-line devices may reconnect back to the AC power line simultaneously without causing an overload. With larger numbers of UPS devices, groups of UPS devices may be reconnected in groups, and at different intervals of time. In embodiments of the present invention, the timer delay between the connection of a first UPS (or group of UPS devices) and a second UPS (or group of UPS devices) to the power line may be between 8 and 12 seconds. The delay is short enough so that it is functionally imperceptible to users of the system, but significant enough to prevent a simultaneous inrush. In other embodiments, other delay times may be used.

The UPS devices may further contain other circuitry, such as battery monitor units to monitor voltage and temperature of the batteries in the battery pack, and communication units to provide this information to the control circuit via a controller area network (CAN) bus.

FIG. 2Aillustrates a UPS200that may be used in connection with the system ofFIG. 1. UPS200includes an AC input202, a transfer switch204, an output206, a battery208, a controller212, and an inverter214. The UPS200can include a battery charger210, but need not. The AC input202is configured to couple to an AC power source and the output206is configured to couple to a load. The input202provides power received from the AC source to the transfer switch204and to the battery charger210. The transfer switch204receives AC power from the input202or from the inverter214. The inverter214receives DC power from the battery108and converts the DC power to AC power and provides the AC power to the transfer switch204. The controller212determines whether power is to be provided from the AC input202or from the inverter214in accordance with allowable tolerances of the system. The controller212may further include a timer delay212a, for example, a subroutine in an existing software module, a separate programmable software module, a Field Programmable Gate Array (FPGA), or separate hardware device, such that the control circuitry is configured to couple power conversion circuitry to the AC power line when the available AC power is acceptable, and upon expiration of a timer. The timer delay may be programmed as the UPS devices are manufactured, wherein one of several predetermined delay intervals may be selected at the time of manufacture. Alternatively, the UPS devices may be configured such that the timer delay of each UPS device may be manually programmed or re-programmed to one of several predetermined delay intervals.

FIG. 2Billustrates another UPS250configured with a double conversion topology that may be used in connection with the system ofFIG. 1. UPS250includes an AC input252, a AC/DC rectifier254, a switch256, a controller258, a battery260, a DC/AC inverter262, a static bypass switch264and an output266. The AC input252is configured to couple to an AC power source and the output266is configured to couple to a load. The input252provides power received from the AC source to the rectifier254. The rectifier converts the AC power into DC power. In normal operations, the UPS250charges the battery260while supplying the output266with power via the inverter262. If the AC-input supply voltage goes outside any preset tolerance or if it fails, the UPS can enter a stored energy mode wherein the battery260continues to supply power to the output266via the inverter262. The controller258determines whether power is to be provided from the AC input252or the battery260in accordance with allowable tolerances of the system. The controller258may further include a timer delay258a, for example, a subroutine in an existing software module, a separate programmable software module, an Field Programmable Gate Array (FPGA), or separate hardware device, such that the control circuitry is configured to couple power conversion circuitry to the AC power line when available AC power is acceptable, and upon expiration of a timer. Many UPS systems employing a double conversion topology further include a static bypass switch264that allows the AC input to provide power directly to the output under certain conditions, such as internal malfunction of the UPS, or load current transients (inrush or fault clearing). One of ordinary skill in the art will recognize that in some embodiments, the static bypass switch may also be controlled with a timer delay according to principles of the invention.

As with the UPS200ofFIG. 2A, the timer delay of the UPS250inFIG. 2Bmay be programmed as the UPS devices are manufactured, wherein one of several predetermined delay intervals may be selected at the time of manufacture. Alternatively, the UPS devices may be configured such that the timer delay of each UPS device may be manually programmed or re-programmed to one of several predetermined delay intervals.

WhileFIGS. 2A and 2Billustrate UPS devices employing two different power conversion topologies, one of ordinary skill in the art will understand that principles of the present invention are not limited to those topologies, and may be applied to other UPS conversion topologies, or other power conversion topologies.

In yet another power supply system in accordance with principles of the invention, UPS devices may be networked together, wherein a networked interface or controller may set the delay interval between sensing available AC power and reconnecting to the AC power of individual UPS devices.FIG. 3illustrates a computer312and a UPS device300that may be used in such a system.

Referring toFIG. 3, an uninterruptible power supply (UPS) monitoring and control system310comprises a computer312, a communication network314, a UPS300, and UPS-supported equipment including a modem316and a router (or switch or hub)318. The network314is preferably a packet-switched network such as an Ethernet local area network (LAN), although other networks would be acceptable. The UPS300is configured to communicate with the computer312via the network314directly or through the router318. Thus, in the discussion below, reference to communication between a UPS300and a computer312may be through the router318although the router318may not be specifically mentioned.

As shown inFIG. 3, a cable329(e.g., a coaxial cable) for data communication to an external network such as the Internet is connected to the modem316(e.g., a cable modem). An Ethernet line332connects the modem316with the router318, possibly passing through surge protection circuitry in the UPS300. A line333connects the router318and the UPS300for transferring communications, e.g., commands, from the router318to the UPS300. The router318is further coupled to the computer312and the UPS300through Ethernet lines of the network314. The UPS300is configured to provide backup power to the equipment316,318and to provide information regarding use of the backup power via the network314to the computer312. The computer312includes a display screen320for displaying an interface to show the information regarding use of the backup power provided by the UPS300to a user of the computer312.

Referring toFIG. 4, with further reference toFIG. 3, a UPS400, that may be used as UPS300inFIG. 3includes an AC input402, a transfer switch404, an output406, a battery408, a controller412, and an inverter414. The UPS400can include a battery charger410, but need not. The AC input402is configured to couple to an AC power source and the output406is configured to couple to a load. The input402provides power received from the AC source to the transfer switch404and to the battery charger410. The transfer switch404receives AC power from the input402or from the inverter414. The inverter414receives DC power from the battery408and converts the DC power to AC power and provides the AC power to the transfer switch404. The controller412determines whether power is to be provided from the AC input402or from the inverter414in accordance with allowable tolerances of the system400. Depending on the capacity of the battery408and the power requirements of the load, the UPS400can provide power to the load during brief AC power source “dropouts” or for extended power outages. The UPS400is exemplary only and not limiting as other UPS configurations can be used with embodiments of the invention.

The UPS400further includes a processor416and a network interface418. The processor416may be referred to as a slave processor, or simply a slave, and the controller412, that includes a processor, may be referred to as a master processor, or simply a master. The master412is configured to monitor data regarding status parameters of the UPS400and to implement control commands to control operation of the UPS400. The slave416is configured to relay information between the network interface418and the master processor412. The master412and the slave416preferably operate without software, instead executing instructions in firmware. The slave416preferably can communicate with the master412at a rapid rate such as 9600 baud.

Similarly, a UPS employing a double conversion topology as illustrated in connection withFIG. 2B, or other conversion topologies (not shown) may be configured with a network interface and used in place of UPS400.

The slave processor416includes embedded Ethernet capability. Using embedded Ethernet circuitry may help control the cost of the UPS400, e.g., to make the UPS400desirable for home or small business use.

The master microprocessor412is configured to control various aspects of the UPS400independently or in accordance with instructions received from the slave416from the computer312. The controller412is configured to determine when battery power is needed and to control the transfer switch404to provide power to the output406from either the AC input402and/or the battery408, via the inverter414, as appropriate. A processor in controller412is configured to perform its various functions by reading and executing computer-readable, computer-executable software instructions stored in a memory. The master412can further receive commands/instructions from the computer312via the network414, the interface418, and the slave416and control portions of the UPS400to implement the commands. For example, the timer delay412aof the master412can be set through the computer312via the network414, the interface418, and the slave416such that the delay interval is programmed to one of several preprogrammed delay intervals.

Because the UPS devices may be networked with a centralized intelligent controller (such as computer312), the centralized controller may keep track of the delay intervals of each of the UPS devices within the networked power supply system, and take into account those delays when setting assigning or reassigning timer delays for individual UPS devices within the system, such that the devices powering on the AC line at certain times are evenly distributed.

The storage systems used in connection with the controllers, processors, or timer delays may typically include a computer readable and writeable nonvolatile recording medium in which signals are stored that define a program to be executed by the processor or information stored on or in the medium to be processed by the program to perform one or more functions associated with embodiments described herein. The medium may, for example, be a disk or flash memory. Typically, in operation, the processor causes data to be read from the nonvolatile recording medium into another memory that allows for faster access to the information by the processor than does the medium. The invention is not limited to a particular memory system or storage system.

Although computer system312is shown by way of example as one type of computer system upon which various aspects of the invention may be practiced, it should be appreciated that aspects of the invention are not limited to being implemented on the computer system as shown inFIG. 3. Computer system312may be a general-purpose computer system that is programmable using a high-level computer programming language. Computer system312may be also implemented using specially programmed, special purpose hardware.

The processor and operating system together define a computer platform for which application programs in high-level programming languages are written. It should be understood that embodiments of the invention are not limited to a particular computer system platform, processor, operating system, or network. Also, it should be apparent to those skilled in the art that the present invention is not limited to a specific programming language or computer system. Further, it should be appreciated that other appropriate programming languages and other appropriate computer systems could also be used.

One or more portions of the computer system may be distributed across one or more computer systems coupled to a communications network. For example, a computer system that determines available power capacity may be located remotely from a system manager. These computer systems also may be general-purpose computer systems. For example, various aspects of the invention may be distributed among one or more computer systems configured to provide a service (e.g., servers) to one or more client computers, or to perform an overall task as part of a distributed system. For example, various aspects of the invention may be performed on a client-server or multi-tier system that includes components distributed among one or more server systems that perform various functions according to various embodiments of the invention. These components may be executable, intermediate (e.g., IL) or interpreted (e.g., Java) code which communicate over a communication network (e.g., the Internet) using a communication protocol (e.g., TCP/IP). For example, one or more database servers may be used to store device data, such as expected power draw, that is used in designing layouts associated with embodiments of the present invention.

It should be appreciated that the invention is not limited to executing on any particular system or group of systems. Also, it should be appreciated that the invention is not limited to any particular distributed architecture, network, or communication protocol.