Abstract:
A method for the alternating operation of power supply units for a device which has at least two power supply units is disclosed. An alternating operation of the at least two power supply units is supplied by a switchover between the two power supply units if the two power supply units are functional. With alternating operation, the power supply unit that is in operation contributes to the power supply for the device, whereas the power supply unit that is not in operation, is cut off from supplying power to the device. In the case of a failure of the power supply unit which is in operation at the moment, an immediate switchover between the at least two power supply units is provided for.

Description:
This application claims priority to German Patent Application 10 2008 010 043.9, which was filed Feb. 20, 2008 and is incorporated herein by reference. 
     TECHNICAL FIELD 
     Embodiments of the invention relate to a method for operating a device with redundant power supply units and a power supply apparatus with redundant power supply units. 
     BACKGROUND 
     With many devices, such as computers, redundant power supplies are provided. A redundant supply is understood to mean the presence of two functionally similar or comparable power supply units that are not simultaneously needed in the normal case. The redundant power supply is designed so that even in the case of a breakdown of one of the two power supply units, an interruption-free operation of the device can be guaranteed. 
     The power supply units are frequently designed so that an individual power supply unit can provide the peak electrical load of the system. 
     The result is that with a simultaneous operation, the two power supply units are operated with an individual output of a maximum 50%. Since power supply units, however, have a specific efficiency, which usually declines with an increasingly smaller electronic load, this mode of operation is very unfavorable for the energy consumption of the overall system. 
     This low efficiency can be avoided by having one of the two power supply units completely turned off during operation of the second power supply unit, that is, keeping one in the so-called “cold stand-by” mode. With a failure of the power supply unit in operation, one must switch over to the replacement power supply unit quickly enough to ensure uninterrupted operation. For this purpose, there must be a suitable electronic switch capable of switching, as quickly as possible, between the switched-off power supply unit and the one in operation. This also requires power supply units that are suitable for an operation of this type and provide for rapid switching. The disadvantage of this mode of operation is that the operating times of the two power supply units will be different. This leads to a different ageing as a result of the dissimilar wear of the two power supply units, and thus to an endangerment of the operating safety of the device. 
     SUMMARY 
     In one aspect, the invention describes a method for operating a device with at least two power supply units whereby interruption-free operation of the device can be ensured, wherein the energy consumption of the apparatus is kept low and a uniform aging of the at least two power supply units is guaranteed. 
     In a particular embodiment a method of the type mentioned above ensures the interruption-free operation of a device which has at least two power supply units, by an alternating operation of the at least two power supply units. By alternating the switchover between the at least two power supply units, as long as they are functional, the malfunction-free operation of the system can be guaranteed. In the alternating operation, the power supply unit in operation contributes to the power supply to the device, whereas the power supply unit not in operation is cut off from supplying power to the device. If the power supply unit which is in operation at the time should suddenly fail, an immediate switchover is initiated, in which it is possible to dispense with a checking of the functionality of the power supply unit to be put into operation. 
     Embodiments thereby utilize a method which, with the planned alternation between the at least two power supply units, provides for a regular checking of the functional readiness of the power supply unit which is not in operation, which counteracts the possible failure of one of the two power supply units due to excessively high wear or aging. After a certain operating time, all power supply units used for the power supply can be successively replaced due to the constant operating alternation and thus, continued smooth operation of the device can be ensured. 
     In another embodiment of the invention, a switchover between at least two power supply units takes place with each startup operation. 
     In another embodiment of the invention, a switchover between the at least two power supply units takes place after a certain time has elapsed, which prevents a failure of one of the at least two power supply units as a result of wear due to excessively long operation. 
     In another embodiment, a power supply apparatus with redundant power supply units is set up for the purpose of carrying out one of the previously described methods. 
     Other details and developments of the invention are described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained, in more detail, in the following with an embodiment and the aid of the drawings. 
       The figures in the drawings show the following: 
         FIG. 1  shows a flow chart for a method for the alternating operation of two power supply units; and 
         FIG. 2  shows a schematic representation of a device with a redundant power supply from two power supply units and an electronic switch. 
     
    
    
     The following list of reference symbols can be used in conjunction with the drawings:
           1  Device     2 ,  3  Power supply unit     4  Switch     5  To the device       

     DETAILED DESCRIPTION 
       FIG. 1  shows a flow chart for a method for the alternating operation of two power supply units, wherein the functionality of the power supply units is checked before each switchover. A block diagram of a device  1  with two mains power supplies  2 ,  3  is shown in  FIG. 2 . 
     Proceeding from a device  1  with two power supply units  2 ,  3 , step S 1  provides for the operation of one of the two power supply units  2  or  3 , while the second one does not contribute to the power supply of device  1 . 
     In step S 2 , a check is performed to determine whether a criterion for the switchover between the two power supply units  2 ,  3  is met. Possible switchover criteria here are switching device  1  at start-up, or reaching a certain temperature or operating time of the power supply unit  2  or  3  in operation. 
     If one of the provided-for switchover criteria is met, the operation of the two power supply units  2 ,  3  is provided, for a short time, in step S 3 , to ensure that both power supply units  2 ,  3  function properly. 
     Subsequently, step S 4  provides for testing the two power supply units  2 ,  3 . This can be done, for example, by measuring an output voltage of the power supply units  2 ,  3 . 
     In step S 5 , a query is made as to whether both power supply units  2 ,  3  are functional. 
     If the functionality of the two power supply units  2 ,  3  is ensured, step S 6  provides for the switchover between the two power supply units  2 ,  3 . If the query in step S 5  is answered negatively and the second power supply unit  2  or  3 , which was not previously in operation, is not functional, then a switchover between the two power supply units  2 ,  3  does not take place, which is given by step S 7 . In this case, exclusive operation of the power supply unit  2  or  3  that was previously in operation is provided for. The defective second power supply unit  2  or  3  is again separated from its voltage supply, and can be repaired or replaced. Thus, an interruption-free operation of the apparatus can be ensured. 
     In addition, in case of the functional incapacity of one of the two power supply units  2 ,  3 , issuance of a warning signal is provided for, as is shown in step S 8 . 
     This procedure guarantees that the functionality of the power supply units  2 ,  3  can remain easy to check. 
     If the currently operating power supply unit  2 ,  3  fails suddenly (as shown in step S 0 ), then a switchover between the two power supply units  2 ,  3  takes place immediately with the omission of steps S 2 -S 5 , as shown in step S 6 . Immediately here means that the switchover is undertaken as rapidly as possible, preferably so rapidly that the power supply of device  1  is not impaired, and interruption-free operation continues. In this case, one dispenses completely with both the short-term parallel operation of the power supply units  2 ,  3  (step S 3 ) and the function check in step S 5  of the power supply unit  2  or  3  to be put in operation, so as to ensure the interruption-free operation of the system. The failed power supply unit  2  or  3  can be subsequently replaced or repaired, after which the alternating operation of the two power supply units  2 ,  3  can again be started up. 
     An arrangement that includes a device  1  that has a redundant power supply apparatus from two power supply units  2 ,  3  is shown in  FIG. 2 . The redundant supply is indicated in the Figure by the broken-line box around the two power supply units  2 ,  3 . An electronic switch  4  is provided to enable switching between the two power supply units  2 ,  3 . 
     The device  1 , can be a computer system, such as an ordinary personal computer (PC) or a server, as an example. The device  1  can alternately be a medical device or a other device that desires a high availability. As a redundant power supply apparatus, it is possible to provide not just two but rather several power supply units  2 ,  3 . Likewise, two power supply units can be used in a single housing, in which all essential components are doubled. 
     Switch  4  is provided for switching between the power supply units  2 ,  3  and to ensure an alternating operation of the power supply units  2 ,  3 . Switch  4  also makes possible a short-term parallel operation of the power supply units  2 ,  3 , to enable testing the functionality of both power supply units  2 ,  3 . Moreover, switch  4  is preferably set up for the purpose of isolating the power supply unit  2  or  3  that is not currently in operation from its voltage supply so that no power is consumed. 
     A triac arrangement consisting of thyristors, for example, is possible for the electronic switch  4  provided for switching between the at least two power supply units  2 ,  3 . 
     A possible implementation of the switch  4  would also be, however, an arrangement of transistors as the switching element. 
     An electromechanical apparatus with a relay as the switching element is another possibility. 
     Checking the functionality of the power supply units  2 ,  3  can be performed by measurement of an output voltage, which is compared with a prespecified reference value. 
     As indicated in  FIG. 2 , diodes can be used to prevent the power supply units  2 ,  3  from short-circuiting each other. 
     The switchover between the at least two power supply units  2 ,  3  can take place according to various criteria, such as with each startup operation of the device  1 , or after a certain operation time of the power supply unit  2  or  3  has elapsed. Certain operating conditions of the two power supply units  2 ,  3  can also be provided as the switchover criterion, such as the reaching of a certain temperature in the power supply unit  2  or  3  in operation. The temperature can be determined with the aid of measurement sensors (not shown). Other possible operating conditions would involve falling below a predetermined minimum fan speed, or the voltage stability of the power supply unit  2  or  3  in operation at the moment. Monitoring the temperature and the fan speed of the power supply units  2 ,  3  serves, for example, to recognize a possible overheating of the power supply units  2 ,  3  and thus their potential premature breakdown, and enable taking timely countermeasures (such as an immediate switchover between the two power supply units  2 ,  3  and a subsequent replacement of the affected fan or power supply unit  2 ,  3 ). 
     The respective switchover criteria are not mutually exclusive. A combination of various criteria, such as a switchover after a certain operation time has elapsed and even with each boot routine, as could be used, for example, in the operation of servers, is thus also conceivable. 
     Also, a switchover of the operation that is necessary for maintenance and repair purposes, for example, by manual actuation of a control button that can be provided in switch  4 , or by a programming of switch  4  effected via an interface, is guaranteed at any time. 
     The regular switchover between the at least two power supply units  2 ,  3  guarantees the same operating duration for the power supply units  2 ,  3 , wherein their uniform usage and wear are achieved and thus the reliability of device  1  is guaranteed. 
     By operating only one of the at least two power supply units  2 ,  3  at a time, a good utilization of the power supply unit  2  or  3  in operation can also be ensured, and thus the energy consumption of device  1  can be lowered.