Abstract:
A telecommunications power system includes a power bus and a battery module with a plurality of batteries. A contactor connects the batteries to the power bus. A distribution module and a plurality of rectifier modules are connected to the power bus. A plurality of loads are connected by the distribution module to the power bus. A controller disconnects the batteries using the contactor when a voltage of the batteries falls below a low voltage disconnect threshold when AC power is lost and/or the rectifier modules fail. The controller minimizes current surge and high voltage transients when the rectifier modules begin providing power and the contactor closes to reconnect the batteries to the power bus. To minimize current surge and high voltage transients, the controller lowers a voltage of the rectifier modules to the voltage of the batteries before the contactor reconnects the batteries to the power bus. After reconnection, the controller gradually increases the voltage of the rectifier modules to the float voltage. The controller employs a serial communications protocol over a communications bus.

Description:
TECHNICAL FIELD OF THE INVENTION 
   This invention relates to telecommunications power systems. More particularly, this invention relates to the reconnection of backup batteries to the telecommunications power system after the backup batteries are disconnected to prevent excessive battery discharge. 
   BACKGROUND AND SUMMARY OF THE INVENTION 
   Telecommunications power systems generally employ rectifiers that generate a direct current (DC) voltage from an alternating current (AC) power source. Distribution modules include circuit breakers that connect the rectifiers to loads and that distribute current to the loads. The loads in a telecommunications power system typically include telephone switches, cellular equipment, routers and other associated equipment. In the event that AC power is lost, the telecommunications power systems generally rely on backup batteries to provide power and to prevent costly down time. Telephone switches, cellular equipment and routers normally carry thousands of calls and/or data streams that will be interrupted if power is lost causing a significant loss of revenue. 
   The backup batteries provide power for a predetermined backup period which varies depending on the number and size of the loads. The backup batteries should provide a sufficient time to allow skilled technicians to troubleshoot and to fix the problem or to connect a backup generator. Sometimes, however, the technicians are unable to solve the problem quickly and/or backup generators are not readily available. If the backup batteries continue to provide power beyond the predetermined backup period, the backup batteries discharge excessively which will shorten the useful life of the backup batteries. Since backup batteries often constitute approximately 50% of the cost of the telecommunications power system, operators often disconnect the backup batteries and accept the loss of service to prevent damage to the backup batteries. 
   During normal operation, the rectifiers operate at a float voltage of the backup batteries. When the rectifiers operate at the float voltage, the backup batteries provide little or no power and remain in a charged state. When the AC power is lost or the rectifiers fail, the output voltage of the rectifiers decreases below the float voltage and the batteries begin providing power to the loads through the distribution module. As the backup batteries discharge, they reach an output voltage below which damage to the backup batteries generally occurs. 
   To prevent damage to the backup batteries, operators generally disconnect the batteries in one of two ways. A contactor disconnects either the loads or the backup batteries. Since the contactor is a single point of failure, customers increasingly request battery disconnection rather than load disconnection. When the former method is employed, the telecommunications power system remains operational if the contactor fails during normal operation. When the latter method is employed, service is lost if the contactor fails during normal operation. 
   Once AC power returns after a failure that results in the backup batteries being disconnected due to excessive discharge, the rectifiers begin providing power to the loads. If the backup batteries are reconnected by closing the contactor, sharp voltage transients and high in-rush current occurs which may damage the batteries and the contactor and disrupt the operation of the loads. 
   The battery reconnect system according to the present invention eliminates the problems that may occur when batteries are reconnected in a telecommunications power system. The battery reconnect system senses whether the contactor is open. If the contactor is open and if the rectifier voltage is higher than a reconnect threshold, a reconnect procedure begins. The rectifier voltage is gradually decreased until the rectifier voltage approximately equals the disconnected battery voltage. The battery reconnect system closes the contactor. Subsequently, the reconnect system gradually increases the voltage of the rectifier to the float voltage while controlling current in a current limiting mode such that the batteries are optimally recharged. 
   As can be appreciated, the reconnect system according to the invention provides a very reliable solution for reconnecting backup batteries to the telecommunications power system after AC power is lost and the backup batteries are disconnected to prevent low voltage discharge. The need for intervention by a highly skilled technician is eliminated. The reconnect system reduces the cost of operation and increases up time of the telecommunications power system. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of a telecommunications power system that includes a frame that is connected to a plurality of loads and a battery pallet with a plurality of batteries according to the invention; 
       FIG. 2  is a functional block diagram of the telecommunications power system of  FIG. 1 ; 
       FIG. 3  is a simplified circuit that illustrates rectifiers that are connected to an AC source, loads, a contactor, and a battery; 
       FIG. 4  is a functional block diagram of the distribution module of  FIG. 1  in further detail; 
       FIG. 5  is a functional block diagram of the rectifier module of  FIG. 1  in further detail; 
       FIG. 6  is a functional block diagram of the battery connection module of  FIG. 1  in further detail; 
       FIG. 7  is a flow chart illustrating steps for reconnecting the backup batteries after AC power is lost and the backup batteries are disconnected to prevent excessive battery discharge; 
       FIG. 8A  illustrates an output voltage of a rectifier when AC voltage is restored after the backup batteries are disconnected; 
       FIG. 8B  illustrates the rectifier voltage exceeding a reconnect voltage threshold which initiates the reconnect procedure; 
       FIG. 8C  illustrates the rectifier voltage gradually decreasing to the battery voltage according to the reconnect procedure; 
       FIG. 8D  illustrates the rectifier voltage equal to the battery voltage when the contactor is closed according to the reconnect procedure; and 
       FIG. 8E  illustrates the rectifier voltage and battery voltage gradually increasing while current is provided by the rectifiers to the batteries. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to  FIG. 1 , a telecommunications power system  10  is illustrated and includes one or more frames  12 , each including a rack  16 . A direct current (DC) bus  30  includes first and second conductors  32  and  34  that extend along the rack  16  in a vertical direction and that are separated by an insulating layer (not shown). A communications bus  40  is located adjacent to the DC bus  30  and likewise includes a layer (not shown) that insulates the communications bus  40  from the first and second conductors  32  and  34 . 
   The design of the telecommunications power system  10  is modular such that the capacity of the telecommunications power system  10  can be changed by adding or removing modules from the telecommunications power system  10 . The design of the telecommunications power system  10  has been optimized through the use of modular connectors (not shown) to facilitate the connection and disconnection of the modules from the frame  12 . 
   The telecommunications power system  10  includes one or more battery connection modules  44  that are connected to the DC bus  30  and the communications bus  40 . The battery connection module  44  is connected to a pallet of backup batteries  48  that includes a plurality of battery cells  50 . In a preferred embodiment, each of the battery cells provides a two-volt output and a relatively high current output. The battery cells  50  are typically connected into battery strings that contain from 24 to 26 battery cells. Each battery string provides 48 VDC for telephone switch and router applications. Depending upon the length of time desired for the battery backup and the size of load to be supplied, the size and/or number of batteries may be varied. Skilled artisans can appreciate that other voltages, string sizes and packaging arrangements can be employed if desired. 
   One or more distribution modules  56  are connected to the DC bus  30  and the communications bus  40 . The distribution modules  56  distribute power to one or more loads  60  such as telecommunications switches, cellular equipment and routers. For example in  FIG. 1 , the distribution module  56 - 1  delivers power to loads  66 ,  68  and  70 . The distribution module  56 - 2  delivers power to loads  72 ,  74 ,  76 ,  78 . The number of distribution modules depends on the size and number of the loads that are associated with the telecommunications power system  10 . Connections between the loads and the backup batteries have been omitted for purposes of clarity. 
   A master controller  86  is connected to the DC power bus  30  and to the communications bus  40 . The master controller  86  includes a display  90  and an input device  94  that preferably includes a touch pad  96  and buttons  98  and  100 . The alternative display can be a computer monitor. The input device  94  and the display  90  can be combined in a touch screen display. A keyboard and/or a mouse may also be employed. The master controller  86  preferably provides an internet browser-like interface that is navigated using the touchpad  96  in a conventional point-and-click manner or using the touchpad  96  and the buttons  98  and  100 . Alternately, a text-based, menu-driven interface can be employed. 
   Referring now to  FIG. 2 , the telecommunications power system  10  further includes one or more rectifier modules  104  that are connected to the DC bus  30  and the communications bus  40 . The rectifier modules  104  are connected to an AC power ource  105  such as that provided by utilities or other power generating systems. Preferably, circuit breakers  107  are provided between the AC source  105  and the rectifier modules  104 . Alternately, an AC power bus may be employed. 
   In use, the AC power provided to the telecommunications power system  10  has a voltage that is typically between 80 and 300 VAC at a frequency between 45 and 65 Hz. The rectifier modules  104  rectify the AC voltage. The rectifier modules  104  provide a controllable output voltage and current and are rated at 48 volts nominal and 50 or 200 amps. Skilled artisans can appreciate that other voltages and currents may be provided by the rectifier modules  104  for systems having different current and voltage requirements. 
   Depending upon the type of backup batteries employed, the output voltage of the rectifier modules  104  will be set higher than 48 volts. Typically, the rectifier modules  104  operate at a float voltage of the backup batteries during normal operation so that the backup batteries do not discharge current. The float voltage is typically between 52 and 54 VDC depending on the battery construction details. The backup batteries are connected as battery strings  106 . The rectifier modules  104  preferably include a shunt and an analog to digital (A/D) converter for sensing rectifier voltage and current. The rectifier module  104  transmits digital signals representing the rectifier voltage and current (in addition to other digital control and communications signals) to the controller  86  via the communications bus  40 . Preferably, the controller  86  employs a serial communications protocol that is insensitive to noise. In a preferred embodiment, the communications system employs serial communications using a CAN protocol such as CAN version 2.0B. 
   The distribution modules  56  include one or more circuit breakers (not shown) which are preferably modular plug-in type circuit breakers to facilitate connection and disconnection of the loads  60 . The distribution module connects the loads  60  to the power bus  30 . 
   Referring now to  FIG. 3 , the operation of the battery reconnect system according to the invention is illustrated by an equivalent circuit that is identified at  120 . During use, the AC power source  122  generates an AC voltage that is input (through circuit breakers that are not shown) to the rectifiers  124 . The rectifiers  124  generate a DC voltage from the AC voltage. The loads  128  are connected in parallel to the rectifiers  124 . During normal operation, the voltage output of the rectifiers  124  is preferably at the float voltage of backup batteries  132  to prevent current discharge. A battery contactor  136  connects and disconnects the backup batteries  132  and is generally closed during operation. When the AC source  122  is interrupted, the output current of the rectifiers decreases to zero. The backup batteries  132  begin discharging and provide power to the loads  128 . 
   To prevent damage to the backup batteries  132 , the battery reconnect system according to the invention disconnects the battery contactor  136  when the voltage provided by the backup batteries  132  falls below a low voltage disconnect threshold to prevent damage to the batteries due to excessive discharge. If no other power source is present, the telecommunications power system  10  is in a failure mode—no power is supplied to the loads  128  and service is lost. 
   When the AC source  122  is re-established, the rectifiers  124  begin increasing output voltage and current provided to the loads  128 . The battery contactor,  136  remains in an open state. When the rectifiers  124  reach a reconnection threshold voltage, the reconnect procedure begins. The reconnect procedure decreases the voltage of the rectifiers  124  until the rectifier output voltage equals the backup battery output voltage. Then, the battery reconnect system closes the battery contactor  136 . 
   Since the voltage mismatch between the DC output voltage of rectifiers  124  and the output voltage of the backup batteries is minimized, the battery reconnect procedure reduces or eliminates high transient voltages and in-rush currents that would otherwise occur. The battery reconnect system controls the current in a current limit mode to optimize charging of the backup batteries  132  without damaging the backup batteries. After closing the battery contactor  136 , the rectifier voltage is gradually increased. The battery reconnection system completes the reconnection procedure when the backup batteries are charged and the rectifier voltage again reaches the float voltage of the backup batteries. 
   Referring now to  FIG. 4 , the distribution module  56  is illustrated in further detail. The distribution module  56  includes one or more circuit breakers (not shown) that are located between the loads  60  and the DC bus  30 . The distribution module  56  includes a contactor  150 , a shunt  154 , an A/D converter  158 , an input/output (I/O) interface  162 , and a neuron  166 . The contactor  150  is controlled by the neuron  166  through the I/O interface  162 . The contactor  150  connects and disconnects the loads  60  and is provided if the telecommunications system operator desires load disconnection. Because contactors are a single point of failure, some system operators opt for battery disconnection instead of load disconnection. When the contactor  150  fails, power to the loads is interrupted. When battery disconnection is used, the load is not interrupted when the contactor fails. Both types of disconnection may be employed if desired. 
   The neuron  166  is preferably a controller that includes a processor and memory (not shown). The neuron  166  performs local processing for the distribution module  56  and I/O communications between the distribution module  56 , the master controller  86 , and other modules in the telecommunications power system  10 . The I/O module  162  is connected to the neuron  156  and to the A/D converter  158 . The A/D converter  158  includes sensing leads  170  and  172  that sense a voltage across the contactor  150 . The sensing lead  170  and sensing lead  174  sense a voltage across the shunt  154 . The sensing leads  174  and  176  sense a voltage across the loads  60 . 
   Referring now to  FIG. 5 , the rectifier modules  104  are illustrated in further detail and include a rectifier  180 , a shunt  182 , an A/D converter  184 , an I/O interface  186 , and a neuron  188 . The neuron  188  performs local processing functions for the rectifier module  104  and controls I/O communications between the rectifier module  104 , the master controller  86  and other modules in the telecommunications power system  10 . The A/D converter  184  includes sensing leads  190 ,  192 , and  194 . The A/D converter  184  senses the rectifier voltage using the sensing leads  192  and  194  and the rectifier current by sensing voltage across the shunt  182  using leads  190  and  192 . 
   Referring now to  FIG. 6 , the battery connection module  44  is illustrated and includes a neuron  200 , an I/O interface  202 , an A/D converter  204 , a shunt  206  and a contactor  208 . The neuron  200  performs local processing functions and I/O communications between the battery connection module  44 , the master controller  86  and other modules in the telecommunications power system  10 . The contactor  208  is controlled by the neuron  200  through the I/O interface  202 . The A/D converter  204  includes sensing leas  210 ,  212 ,  214 , and  216 . The A/D converter  204  senses battery voltage using the leads  214  and  216 . The A/D converter  204  senses battery current by sensing a voltage drop across the shunt  206  using the leads  212  and  214 . The A/D converter  204  senses the voltage across the contactor  208  using the leads  210  and  212 . The voltages of the battery connection module  44  and the rectifier modules  104  can be sensed using the leads  214  and  216  and the leads  192  and  194 , respectively. Alternately, the voltage across the contactor  208  can be sensed using the leads  210  and  212 . When the voltage across the contactor  208  is approximately zero, the contactor  208  can be closed. 
   Referring now to FIGS.  7  and  8 A- 8 E, steps for operating the battery reconnect system are illustrated. Control begins at step  300 . At step  301 , the master controller and/or the neurons determine whether AC power is interrupted and the batteries are discharging. If not, control loops to step  301 . Otherwise, control continues with step  302  where the master controller  86  determines if the voltage of the backup batteries is less than a low voltage disconnect threshold. If not, control loops to step  302 . Otherwise, control continues with step  304  where the master controller and/or the neuron opens the contactor  208  to disconnect the backup batteries from the telecommunications power system  10 . 
   Later, the AC source returns, the rectifiers begin to provide power (see  FIG. 8A ) and the rectifier voltage (V1) increases. In step  306 , the master controller  86  determines whether the rectifier voltage (V1) is greater than a reconnect voltage threshold (V3) (see FIG.  8 B). If not, control loops and continues with step  306 . Otherwise, control continues with step  308  where the master controller  86  determines whether the rectifier voltage (V1) equals the battery voltage (V2) within a predetermined tolerance. If not, control continues with step  310  where control reduces the rectifier voltage (see  FIG. 8C ) and continues with step  308 . When the rectifier voltage V1 equals the battery voltage V2, the contactor is closed in step  316  (see FIG.  8 D). Control continues with step  318  where the master controller  86  determines whether the battery is charged. If not, control continues with step  320  where control gradually charges the battery by operating in a current limit mode (see  FIG. 8E ) and allowing rectifier voltage output to gradually increase. Control continues with step  318  until the backup battery is fully charged. When the battery is charged, control continues with step  301 . 
   While the preferred embodiment performs control using the master controller  86 , control can be distributed amongst various combinations of neurons, shared by the master controller and one or more neurons, or performed by a neuron. 
   As can be appreciated, the battery reconnect system prevents high transient voltages and in-rush currents when reconnecting batteries that are disconnected to prevent excessive discharge. The battery reconnect system is automated and does not require skilled technicians to perform manual battery reconnection which reduces owning and operating costs and increases up time. Other advantages will be readily apparent to skilled artisans. 
   Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.