Abstract:
Aspects relate generally to hot swap control in uninterruptible power supply units for systems requiring backup power. A unit may include a pair of MOSFET switches configured as a bidirectional switch for battery charging and discharging current control. This configuration allows the unit to limit inrush current when the unit is connected to a DC power bus of a power system and also allows the unit to eliminate any current flow when it is disconnected. Upon insertion and extraction of the unit, the MOSFET switches are disabled to prevent any disturbances on the DC power bus. Hot swapping in the unit ensures that the overall power system, including the unit and the DC bus, operates reliably.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of the filing date of U.S. Provisional Patent Application No. 61/590,060 filed Jan. 24, 2012, the disclosure of which is hereby incorporated herein by reference. 
    
    
     BACKGROUND 
     Various systems utilize battery backup supply systems, such as uninterruptible power supply (“UPS”) units. The UPS units include batteries that are charged during periods when the system is being powered by an external power source. If the power source is lost, the batteries are used to power the system&#39;s load. A typical system may use two different power supplies, one to run the components (such as devices in a server array) and another to charge the batteries. In addition, when the UPS unit is hot swapped, or connected and disconnected from a live power source (such as a DC distribution bus or DC bus), significant mating and demating current potentially cause mechanical failure in the power connectors of the power supply and the UPS unit. In addition, significant inrush current flowing through the batteries may produce high di/dt and dv/dt, disturb the DC bus, and negatively impact the overall system performance. 
     SUMMARY 
     Aspects of the disclosure provide an uninterruptible power supply unit. The uninterruptible power supply unit includes a battery pack and a pair of MOSFET switches. The pair of MOSFET switches includes a first MOSFET switch and a second MOSFET switch connected in series to the battery pack. The uninterruptible power supply also includes a power connector having three pins. Two pins of the three pins being longer than the third pin. The two longer pins are configured to deliver current from a power source to the uninterruptible power supply unit. The uninterruptible power supply unit also includes a short pin detector in communication with the third pin. The short pin detector is configured to detect whether the third pin is connected to the power source. The uninterruptible power supply unit also includes a protection circuit in communication with the short pin detector such that only when the short pin detector detects that the third pin is connected to the power source does the protection circuit allow the uninterruptible power supply unit to activate first MOSFET switch in order to limit the inrush current from the power source through the first MOSFET switch. 
     In one example, the uninterruptible power supply unit also includes a transistor in communication with the protection circuit and the pair of MOSFET switches, and the protection circuit allows current to be delivered from the power source to the battery pack by sending a signal through the transistor to switch the second MOSFET switch from an off condition to the activated condition. In another example, uninterruptible power supply unit also includes a controller for controlling charging of the battery pack by limiting the charging current through the first MOSFET switch when the first MOSFET switch is operating in a linear region. In this example, the transistor is a NPN transistor. In another example, uninterruptible power supply unit also includes a transistor in communication with the protection circuit and the MOSFET switch, and the protection circuit is configured to allow current to be delivered from the power source to the battery pack by sending a signal through the transistor to activate the first MOSFET switch in order to allow a limited amount current to be delivered from the power source to charge the battery pack. In this example, the protection circuit is configured to send a signal through the transistor to switch the pair of MOSFET switches to the off condition to stop the flow of current from the power source through the two longer pins when the short pin detector detects that the third pin is disconnected from the power source and before the two longer pins are disconnected from the power source. In yet another example, the second MOSFET switch is connected in series with the first MOSFET switch, and the first MOSFET switch and the second MOSFET switch are configured to operate as a bidirectional switch. In this example, the first MOSFET switch and the second MOSFET switch are further configured for charging the battery pack, discharging the battery pack, and disconnecting the battery pack from the power source. 
     Another aspect of the disclosure provides a method of charging a battery pack. The method includes connecting two pins of a power connector having three pins to a power supply. The two pins are longer than the third pin. The two longer pins are configured to deliver current from a power supply to the battery pack. The method also includes detecting, by a short pin detector, whether the third pin is connected to the power source. The method includes, when the third pin is connected to the power source, transmitting a signal through a transistor to a switch in order to switch the switch from an off condition to an activated condition in order to provide the charging current from the power source through the two longer pins to charge the battery pack. The method also includes limiting the charging current through the switch when the switch is in the activated condition. 
     In one example, the method also includes, after transmitting the signal, limiting the charging current by operating the switch in a linear region. In another example, the method also includes, when third pin is disconnected from the power source, transmitting a second signal through the transistor to switch the switch to the off condition thereby stopping the flow of current from the power source through the two longer pins to the battery pack before the two longer pins are disconnected from the power source. In another example, the switch is a MOSFET switch. 
     A further aspect of the disclosure provides a system. The system includes a power source for providing current and an uninterruptible power supply unit. The uninterruptible power supply unit includes a battery pack, a MOSFET switch connected in series to the battery pack, and a power connector having three pins. Two pins of the three pins being longer than the third pin. The two longer pins are configured to deliver current from a power source to the uninterruptible power supply unit. The uninterruptible power supply unit also includes a short pin detector in communication with the third pin. The short pin detector is configured to detect whether the third pin is connected to the power source. The uninterruptible power supply unit also includes a protection circuit in communication with the short pin detector such that only after the short pin detector detects that the third pin is connected to the power source does the protection circuit allow the uninterruptible power supply unit switch the MOSFET to an activated condition and to limit the charging current from the power source through the MOSFET in order to charge the battery pack. 
     In one example, the uninterruptible power supply unit also includes a transistor in communication with the protection circuit and the MOSFET switch, and the protection circuit allows current to be delivered from the power supply to the battery by sending a signal through the transistor to switch the MOSFET switch from an off condition to the activated condition. In this example, the uninterruptible power supply unit also includes a controller for limiting the charging current through the MOSFET switch when the MOSFET switch is operating in a linear region. In addition or alternatively, the transistor is a NPN transistor. In another example, the uninterruptible power supply unit further comprises a transistor in communication with the protection circuit and the MOSFET switch transistor. In this example, the protection circuit is also configured to allow current to be delivered from the power supply to the battery by sending a signal through the transistor to switch the MOSFET switch from an off condition to an activated condition in order to allow current to be delivered from the DC bus to charge the two or more batteries, and, when the short pin detector detects that the third pin is disconnected from the power source, the protection circuit is also configured to send a signal through the transistor to switch the MOSFET switches to the off condition stopping the flow of current from the power bus through the two longer pins before the two longer pins are disconnected from the power source. In another example, power supply includes a DC power bus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an example diagram of power architecture in accordance with implementations of the disclosure. 
         FIG. 2  is a diagram of a UPS unit in accordance with implementations of the disclosure. 
         FIG. 3  is an example diagram of circuits of UPS units in accordance with implementations of the disclosure. 
         FIGS. 4A-4C  are example diagrams of connectors in accordance with an implementation of the disclosure. 
         FIG. 5  is an example flow diagram in accordance with implementations of the disclosure. 
         FIG. 6A  is an example of a server architecture in accordance with implementations of the disclosure. 
         FIG. 6B  is an example of a network system architecture in accordance with implementations of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The configurations described herein disclose a UPS unit that supports hot swapping without disturbing the DC distribution bus, thus providing a reliable back up power system. For example, by utilizing two metal-oxide semiconductor field effect transistors (“MOSFET”) switches in series as a bi-directional switch, the MOSFET switches may act as a disconnect device when disconnecting the battery pack of the UPS unit from the DC bus. The UPS unit may have a three pin blind mating connector. Two of the pins may include power pins, the third pin may be somewhat shorter than the power pins. Upon connection of a UPS unit with a DC bus, a short pin detector senses when the short pin is connected to the DC bus. Before the short pin is completely connected, but after the power pins establish contacts, the MOSFET switches remain turned off so that current from the DC bus does not flow to the battery pack. When the short pin is completely connected to the DC bus, the MOSFET switches are activated under charging conditions and begin limiting the charging current at a predetermined level to prevent very high inrush current during the insertion (and extraction) of the UPS unit. If the battery voltage is higher than the DC bus voltage, the discharging MOSFET may be immediately turned off by the protection circuit. 
     Upon extraction of UPS unit from the DC bus, the short pin disengages from the DC bus before the power pins are disconnected. When the short pin loses the contact, the MOSFET switches are immediately turned off so that no charging and discharging current (i.e., demating current) flow is allowed at the time of the power pin removal. This allows for safe removal and connection of the UPS unit from the DC bus. Thus, the MOSFET switches may allow for hot swapping, charging and discharging in a single circuit configuration. In this configuration, neither a separate battery charger (or backup converter) nor a separate hot swapping circuit are needed. 
       FIG. 1  is an example of a distributed power architecture  100  for a server system having a load and a plurality of UPS units  140 . In this example, the architecture includes an AC power source  110  that supplies power to AC-DC power supplies  120 . The AC-DC power supplies  120  provide power to a load  130 . In this example, the load  130  may include a plurality of computing components. 
     The AC-DC power supplies  120  are also connected to the plurality of UPS units  140 . As shown in  FIG. 1 , the UPS units  140  are arranged on a common DC distribution bus in parallel with the AC-DC power supplies  120  and the load  130 . The UPS units  140  are used to ensure continued operation of the load  130  in the event of a failure of the AC power source  110  and/or AC-DC power supplies  120 . The number of UPS units (N) used in the system may be determined based on the amount of backup power required to power the load for some pre-determined period of time. 
       FIG. 2  is an example of a UPS unit  140 . In this example, the UPS unit  140  includes a housing  210 , a connector  240  having power terminals  220 ,  222 ,  224  to receive power from the AC-DC power supplies  120 , as well as driving circuitry  230 . Terminals  220  and  222  may include power pins that provide power from the DC bus to the UPS unit. Terminal  224  may include a third pin, shorter than the power pins. 
       FIG. 3  is an example of driving circuitry that may be used with the UPS unit  140 . In this examples, the driving circuitry includes a controller  310 , a battery pack  320  having one or more batteries, switches  340  and  342 , a feedback device  350 , and a short pin detector  370 . In addition, these circuits may also include a protection circuit  380  and a transistor  390  for fast off switching of the switches  340  and  342  based on temperature, voltage and current information associated with the batteries. As shown in these examples, the battery pack  320 , the switches  340  and  342 , and the feedback device  350  are arranged in series with one another. 
     The switches  340 ,  342  desirably comprise MOSFET switches. MOSFET switches are used to supply current for battery charging and discharging. The MOSFET SWITCHES have different modes of operation. For example, a MOSFET have a switched mode of operation, including a “fully off” condition and a “fully on” condition. Another mode of operation is a linear region of operation where the drain-to-source voltage and the drain current can be regulated by adjusting gate-to-source voltage. In this example, when operating in the linear region, the MOSFET allows a gate-to-source voltage of between 0 and 12 volts to pass through the MOSFET&#39;s gate. Whether a MOSFET are used as switches or in operated in their linear mode depends on whether the batteries are being charged (linear operation), discharged (on), or disconnected (off) from the load and the AC power supply. 
     The pair of MOSFET switches may be used for both the charging and discharging of the batteries. For example, MOSFET switch  340  can be used to control the charging of the batteries while MOSFET switch  342  can be used for discharging of the batteries. This combination of a charging MOSFET and a discharging MOSFET allows operation as a bidirectional switch. 
     The protection circuit  380  may be configured to turn off and on both MOSFET switches  340  and  342  in order to disconnect or connect the battery pack  320  from the DC bus. The protection circuit  380  may include a microcontroller, CPU, or any type of circuit that can sense the condition of the current, temperature or voltage of the battery. If one or more of these conditions is outside of a predetermined normal operating range (for example, operating at an abnormal voltage, current, and/or temperature), the protection circuit  380  may automatically switch the MOSFET switches  340  and  342  to the off condition disconnecting the UPS from the AC-DC power supply and the load. The protection circuit may operate much faster to shut off the MOSFET switches than the controller. 
     In addition to monitoring the current, temperature, and voltage of the batteries of the battery pack, the protection circuit  380  may also receive information from a short pin detector  370 . The short pin detector may include a circuit that produces a high or low signal (for example, 0 or 1) to the protection circuit when the short pin is engaged with the DC bus. Based on this information, the protection circuit may switch on or off the MOSFET switches through the transistor  390 . 
     For example, the UPS unit may be placed on a battery shelf in the rack. The connector  240  of the UPS unit is lined up with the blind mating connector  360  of the DC bus (or some other connection to the DC bus). As shown in  FIG. 4A , as the connectors  240  and  360  approach one another, the two long power pins  220 ,  222  may reach connector  422  first. As shown in  FIG. 4B , as the connectors are moved closer together, the two long power pins  220 ,  222  make contact with connector  360  (as indicated by their placement past reference line  424  in  FIG. 4B ) before the short pin  224 . Thus, even though the two long power pins are connected to the DC bus connector, the charging and discharging MOSFET switches may remain in the deactivated condition so that no current flows through the MOSFET switches. 
     Eventually, after a few milliseconds, the UPS unit connector and the DC bus connector will be fully engaged. For example, as shown in  FIG. 4C  the short pin  224  may pass reference line  424  and mate with the connector  360 . In response to this connection, the short pin connector may send a signal to second protection circuit, indicating that the short pin is connected. For example, once the short pin detector  370  detects that the short pin  224  is connected to the DC bus connector  360 , a signal is sent to the protection circuit  380 . 
     The protection circuit may respond by detecting the status of the batteries and the DC bus via the feedback device  350 . For example, protection circuit  380  may monitor the battery and DC bus voltages to determine whether these voltages are acceptable to charge and discharge the battery. The protection circuit  380  also receives information about the battery temperatures and currents to determine if they are acceptable. 
     If no fault or conditions outside of the predetermined normal operating range are detected, the UPS unit is ready for operation and the protection circuit activates the MOSFET switches through transistor  390  under charging conditions in order to begin the charging of the battery pack  320 . In this regard, the UPS unit may allow charging current to flow through the batteries only when the connectors between the UPS unit and the DC bus are fully engaged. For example, rather than switching the MOSFET switches to a fully on condition, the MOSFET switches are activated so that they operate in the linear region in order to provide charging current to the battery pack. This prevents significant inrush current from flowing through the battery pack and prevents damage to the UPS unit and the DC bus. When the MOSFET switches are operated in the linear region, the charging current may be limited by the MOSFET switches to a very low level, as described below, in order to not disturb the DC bus. 
     The controller  310  controls the charging of the battery pack. The controller  310  may be, in one example, an amplifier configured to receive information from the feedback device. Based on the received information, the controller is able to automatically transition the UPS unit from using an outside power source to charge the battery to supplying power to a load. The feedback device  350  can include a shunt or current sense resistor that senses current from one of the power pins  220  and sends it to the negative terminal of the controller  310 . 
     The controller automatically detects the state of the bus voltage based on current feedback received from the feedback device  350 . For example, when the DC bus voltage is greater than the battery voltage, the controller is in charging mode. In the charging mode, the controller regulates or limits the charging current through the charging MOSFET, MOSFET switch  340 , by adjusting the gate-to-source voltage of the MOSFET switch  340  based on current received from the feedback device  350 . In one example, the controller  310  is desirably associated with a reference current value. This value can be set through a pulse-width modulation (PWM) signal  360  at the positive terminal of the controller  310 . In some examples, the reference charging current value is set very low in comparison to the discharging current needed to power the load. By using a relatively low charging current, the thermal stress on the charging MOSFET operating in the linear region is low as well. If the current through the charging MOSFET is too high, the MOSFET can heat up and fail. This can also reduce the power drain on the AC-DC power supplies  120 . 
     The controller compares the reference current value and the information from the feedback device, and adjusts the current through the MOSFET  340  in order to control the charging of the battery pack  320 . The charging current feedback at the negative terminal, received from the feedback device  350 , follows the current defined at the positive terminal in voltage. 
     When the charging current becomes a bit lower than the reference current value, the DC bus voltage will be very close to or the same as the battery voltage. At this point, the battery may be almost fully charged. In response to current feedback from the current sense device, the output of the controller may be saturated at the maximum gate voltage and the battery is float charged to keep the battery close to or at its fully charged level. 
     As noted above, the control circuitry  230  can also be used for discharging. If the power source  110  and/or AC-DC power supplies  120  fail, the power received at the terminals  220 ,  222  of the UPS unit will drop off. The DC bus voltage will be less than the battery voltage. This causes the charging current feedback to be significantly lower than the reference current value. The difference between the charging current feedback and the reference current value causes the controller&#39;s output to go into saturation and causes the MOSFET switches to go into the fully on condition. In other words, the MOSFET switches are no longer operating in the linear region. At this point, the controller is no longer controlling the charging of the battery pack  320 , and the current from the battery pack can discharge and flow through the terminals  220  to power the load  130 . Having the MOSFET switches in the fully on condition when the battery pack is discharging can also reduce conduction loss. 
     The battery pack can continue to discharge until the battery pack is fully discharged or until the power source  110  and/or AC-DC power supplies  120  have been restored. When the power source has been restored, the UPS unit can automatically transition from discharging to charging via the controller. 
     Returning to the example of  FIG. 3 , when the power from the AC-DC power supplies  120  is restored, the charging current feedback causes the controller  310  to immediately limit the charging current to the battery pack as described above. 
     When the UPS unit is extracted from the rack, the short pin may disengage from the DC bus connector before the two long power pins. After a gap of a few milliseconds, the two long power pins may also disengage from the DC bus connector. During this few millisecond gap, the short pin detector  370  may send a signal to the protection circuit  380 . In response, the protection circuit may immediately turn off the charging and discharging MOSFET switches through transistor  390 . Thus, the MOSFET switches are turned off before the two long power pins are disengaged from the DC bus connector. 
     The currents that flow through the batteries during the mating and demating of the connectors may be reduced or eliminated by the detection of the status of the short pin, the battery pack, and the DC bus voltage. Significant current during the mating and demating may cause mechanical failure at the connectors. The short pin, short pin detector, protection circuit, and charging MOSFET may simplify the hot swap control of the batteries. This configuration may eliminate the need for separate hot swapping circuitry as the hot swapping control is integrated into the UPS unit&#39;s connection to the DC bus. This may also allow for efficient switching of the charging and discharging MOSFET switches, whereas the controller  310  may not be fast enough to deactivate the MOSFET switches. Accordingly, the UPS unit may be hot swapped without risking damage to the UPS unit or other features of the system  100 . 
     Flow diagram  500  of  FIG. 5  depicts an example of the hot swapping and short pin detection process described above. For example, at block  502 , the two long power pins of a connector are connected to a power supply. The short pin detector detects when the short pin has been connected to the power source at block  504 . In response, a signal is transmitted through a transistor  390  in order to switch a MOSFET switch to an activated condition at block  506 . Power from the power source is then delivered through the two long power pins in order to charge the batteries at block  508 . Next, at block  510 , the charging current of the batteries is then limited through the MOSFET as described above. As the UPS unit is removed from the rack, the short pin detector detects when the short pin has been disconnected from the power supply at block  512 . In response, a signal is transmitted through the transistor  390  in order to switch the MOSFET to the deactivated condition at block  514 . This stops the current flow through the MOSFET to the batteries and ends the charging and the discharging of the two or more batteries. 
     The UPS units described herein can be used in conjunction with various backup power systems. For example, these devices may be useful in telecom systems or server architectures.  FIG. 6A  is an example of a server architecture including a plurality of the UPS units described herein. In this example, the server  610  includes a rack  620 , having a set of shelves  630 , for housing the load  130  as well as the UPS units  140 . The AC-DC power supplies  120  can be incorporated into the rack  610  (as shown in  FIG. 6A ) or can be at a different location, for example, as the AC power source  110  is shown in  FIG. 6A . 
     The load  130  can include a variety of devices. For example, the load  130  can include a dedicated storage device, for example, including any type of memory capable of storing information accessible by a processor, such as a hard-drive, memory card, ROM, RAM, DVD, CD-ROM, or solid state memory. The load may include a preprogrammed load which draws power from the AC-DC power supplies  120  in order to test the operation of the server  610 . The load  130  may also include a computer including a processor, memory, instructions, and other components typically present in server computers. 
       FIG. 6B  is an example of a network system including the server architecture of  FIG. 6A . For example, server  610  may be at one node of a network  640  and capable of directly and indirectly communicating with other nodes of the network. For example, these computers may exchange information with different nodes of a network for the purpose of receiving, processing and transmitting data to one or more client devices  660 - 62  via network  640 . In this regard, server  610  may transmit information for display to user  660  on display of client device  660 . In the event of a failure of the AC power source  110 , the UPS units may allow the server  610  to continue communications with the other nodes without interruption. 
     As these and other variations and combinations of the features discussed above can be utilized without departing from the subject matter defined by the claims, the foregoing description of the embodiments should be taken by way of illustration rather than by way of limitation of the subject matter defined by the claims. It will also be understood that the provision of the examples disclosed herein (as well as clauses phrased as “such as,” “including” and the like) should not be interpreted as limiting the claimed subject matter to the specific examples; rather, the examples are intended to illustrate only one of many possible embodiments. Further, the same reference numbers in different drawings may identify the same or similar elements.