Abstract:
A processor controlled DC pump system charges back-up batteries using utility supplied AC power. In the absence of AC the batteries energize a DC load. When AC is restored, the processor regulates total output current to charge the batteries and energize the load without exceeding the maximum allowable total output current.

Description:
FIELD OF THE INVENTION 
     The invention pertains to uninterruptable power supplies. More particularly, the invention pertains to such supplies that can be used to charge a battery alone or in combination with energizing a DC pump motor. 
     BACKGROUND OF THE INVENTION 
     Uninterruptable power supplies to provide backup in the absence of utility power are known. One such supply is disclosed and claimed in Reichard U.S. Pat. No. 5,508,905, entitled Low Distortion Variable Output Power Supply and assigned to the assignee hereof. The system of Reichard charges a DC battery or batteries, and, in normal operation provides utility supplied AC to a load such as an AC sump pump. In the absence of utility AC Reichard&#39;s system generates an AC output which can be used to energize that pump. 
     Reichard&#39;s system is AC-to-AC. A market exists for DC sump pumps which are installed to backup a primary AC pump. DC pumps are often small enough that they can be installed into a sump along with a physically larger AC pump. When so installed they provide an additional degree of redundancy. 
     AC-to-DC backup supplies must address previously unmet challenges. Such supplies store energy in wet cells, for example deep discharge marine batteries. Such batteries must be kept fully charged for long time intervals between utility power failures. When a utility failure occurs, the battery or batteries must be able to immediately start to supply energy to drive the pump. 
     One known approach to battery charging is to periodically charge the battery or batteries for a predetermined period of time irrespective of their condition. While easy to implement, this approach fails to adequately address fully charged batteries and substantially discharged batteries. 
     Over-charging is potentially dangerous. Under-charging may result in a battery having inadequate energy in an emergency. 
     In addition, where a pump is demanding current and the battery or batteries need to be charged, output voltage from the supply can be substantially reduced. Conservation of energy principles require that in such instances, output current from the supply increase significantly and as a result may exceed the ratings of the supply. 
     Thus there continues to be a need for an uninterruptable power supply for driving DC pumps. Preferably such a supply could not only maintain the battery or batteries in a fully charged condition, without over-charging the battery or batteries, but it will also limit output current so as to protect the integrity of the respective supply. Finally, it would be preferable if such supplies were price competitive with existing supplies. 
     SUMMARY OF THE INVENTION 
     A high current capacity direct current supply incorporates a programmed processor and executable instructions to monitor changing output load conditions as well as changing utility line input conditions. In one embodiment, energy can be stored in rechargeable, deep discharge marine batteries. 
     Power conversion in one embodiment can be implemented by one or more transformers in combination with a switching regulator. A variable control signal can be used to vary regulator output. In another embodiment, a transformer can be combined with a linear regulator. 
     In another aspect, a total output current sensor, coupled to the processor, can be used to monitor output power and to limit maximum output current to a predetermined value. A separate load current sensor, also coupled to the processor, can be used to monitor the load. 
     Executable instructions, in response to detecting an over current condition, adjust the power conversion circuitry to limit that current. Other instructions maintain charge on the battery or batteries and reduce current thereto so as to avoid an overcharged condition which can damage the battery or batteries. 
     Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an over-all block diagram of a DC pump control system in accordance with the present invention; 
     FIG. 2 is an interconnect diagram illustrating additional details of the system of FIG. 1; 
     FIG. 3 is a more detailed block diagram of the control system of FIG. 1; 
     FIG. 4 is a graph illustrating AC line voltage when the system of FIG. 3 is in a stand-by mode; 
     FIG. 5 is a graph illustrating AC line voltage superimposed with an input current waveform; 
     FIG. 6 illustrates AC line voltage and an input current waveform while the system is energizing a pump motor; and, 
     FIG. 7 is a graph illustrating switching characteristics of the power transformer during pump operation. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     While this invention is susceptible of embodiment in many different forms, there are shown in the drawing and will be described herein in detail specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated. 
     A system  10  includes an AC line plug  12  which can be coupled to an AC utility receptacle. The receptacle functions as a source of utility AC power under normal operating conditions. A control system power supply  14  is coupled to plug  12  and receives utility AC power therethrough. 
     The supply  14  converts AC input energy to DC output energy at line  14   a . This energy can be used for two different purposes as discussed below. Output line  14   a  from supply  14  includes a total output current sensor  16   a.    
     A rechargeable storage battery, such as a deep discharge marine battery,  20  and a DC load, such as a DC pump,  22  are coupled in parallel via lines  14   b,c  across the output line  14   a . Additional current sensors  16   b,c  can be incorporated so as to monitor battery and load currents. 
     System  10  includes programmed processor  30  and pre-stored executable instructions  32 . Processor  30  can monitor currents from sensors  16   a,b,c.  It can also control the operation of supply  14  via control line  30   a.    
     FIG. 2 illustrates one way in which supply  14  can be coupled to battery  20  and pump  22 . In another configuration, sensor  16   b  can be incorporated in series with battery  20 . 
     FIG. 3 illustrates system  10  in greater detail. Supply  14  includes an input filter and transformer section  14 - 1 . A full bridge rectifier and filter section  14 - 2  is coupled thereto. Solid state switching elements and a second transformer configurated as a switching regulator  14 - 3  are coupled thereto. Supply  14  also includes an output filter section  14 - 4  and overcurrent protection circuitry  14 - 5 . 
     In addition to the sensors noted above, processor  30  can receive inputs from a thermal sensor  40   a,  a battery voltage sensing input  40   b,  motor switch contacts  40   c,  and an AC line status input  40   d.  Human discenable feedback can be provided via an alphanumeric display  40   e  which receives inputs from processor  30 . 
     In a preferred embodiment, utility power is converted down by means of a step-down (buck) transformer configured in the full-bridge topology, ( 14 - 3 .) Typical regulated power supplies are generally intended to supply an output current at some voltage into some load, whether it be resistive or inductive. The fact that the power supply is regulated infers that the output voltage is constant over some variable input voltage range and changing load condition. 
     This design utilizes a full-bridge/transformer combination for the power conversion process. An output LC filter (inductor-capacitor) filter further reduces the output ripple voltage. As is known: 
     
       
         Power In=Power Out+Losses. 
       
     
     The input power to the power supply is equivalent to the output power of the supply PLUS any related efficiency losses (ie, switching losses, transformer core losses, etc.). As the output current increases due to load demands the input current too increases (provided the input voltage is constant or falling). By monitoring the current on the primary of the transformer winding one could get a fair assessment of the magnitude of the current on the secondary of the transformer, provided the output voltage of the supply is always constant. 
     A constant output voltage is not the case with the system  10 . Though the power supply  14  is a regulated power supply, the load to which the power supply is coupled is extremely capacitive. Capacitors do not permit fast changes or fluctuations in voltage across their terminals. The noted load is the deep-cycle marine battery  20  which supplies current to the sump pump  22  as needed. 
     In one operating scenario, the AC line voltage has been lost. Since there is no available utility power, the DC sump pump  22  must run entirely off the reserve energy provided by the battery  20 . Assuming that the utility power has been out for some lengthy duration and that the sump pump has been utilized extensively during this time, it is very likely that the voltage of the battery  20  will have fallen from some initial value (fully charged condition) to some lower value. 
     When the AC line is restored, the power supply  14  will now be expected to provide power to charge the battery  20  and run the sump pump  22  if it is still called for. This is an extremely stressful condition. Since the battery voltage has fallen to some unknown value, the power supply output voltage (which is in parallel with the battery) is clamped to this voltage. Since: 
     
       
         ( V in* I in)=( V out* I out)+losses 
       
     
     then 
     
       
           I out=(( V in* I in)−losses)/ V out 
       
     
     Hence, if constant input power is maintained (and constant losses) and the voltage on the output of the supply suddenly decreases (i.e., the application of the used deep cycle battery), then the output current will increase to balance the power equation. This again assumes monitoring only the transformer primary current (which is generally the case in most current-mode control designs). This might not be a problem if the output components of supply  14  are rated with large current capacities. However, high current ratings are directly proportional to higher component costs. 
     System  10  incorporates a separate current monitoring element  14 - 5 . This element is intended to limit the maximum output current to some specified level regardless of changing output voltage levels. As the output current rises to that maximum level a signal is sent to a PWM controller in element  14 - 3  which interrupts the gating cycle. This decreases the current to a safer value. 
     Below is a list of representative scenarios which may occur during system operation: 
     Scenario #1 
     If: 
     (AC line is valid) and 
     (sump Pm is called for) and 
     (motor current&gt;=motor running current) 
     Then: 
     (system is operating properly). 
     Scenario #2 
     If: 
     (AC line is valid) and 
     (sump pump is called for) and 
     (Motor current&lt;motor running current) 
     Then: 
     (motor fuse may be blown) or 
     (motor winding may have opened). 
     Scenario #3 
     If: 
     (AC line is valid) and 
     (sump pump is called for) and 
     (motor current&gt;=motor running current) and 
     (over-current monitor&lt;minimum current threshold) 
     Then 
     (charger fuse is blown open). 
     Scenario #4 
     If: 
     (AC line is invalid) and 
     (sump pump is called for) and 
     (motor current&gt;=motor running current) 
     Then: 
     (system is running properly). 
     Scenario #5 
     If: 
     (AC line is invalid) and 
     (sump pump is called for) and 
     (motor current &lt;motor running current) 
     Then: 
     (motor fuse may be blown) or 
     (motor winding may have opened). 
     The system  10  further includes circuitry and software to sound an alarm indicative of motor failure using a third motor lead. The system  10  can also incorporate a secondary switch which would act as a high water alarm and a redundant motor run switch. The system  10  can also incorporate a display, such as one implementing using light emitting diodes which would allow the user to check in system operation. 
     FIG. 4 shows the AC line voltage while the system  10  is in STANDBY mode. The RMS voltage is approximately 120 VAC. No distortion to the sinusoidal waveform is observable during this mode of operation. 
     FIG. 5 shows the AC line voltage waveform superimposed on the input current waveform. During STANDBY mode, the system  10  draws very little current from the utility. The input current is drawn in pulses through the bridge rectifier and into the input capacitor and power supply. 
     FIG. 6 shows the AC line voltage along with input current waveform while the DC pump controller is operating the pump motor. Notice the change in input current amplitude between the waveforms in FIGS. 2 and 3. The AC line voltage waveform remains fairly distortionless during this mode of operation which allows for very little harmonic distortion to the utility line. This can be attributed to the input filter (see block diagram) in the power supply. 
     FIG. 7 is a waveform illustrating the switching characteristics of the power transformer during pump operation. Notice that the switching frequency of the unit is 100 kHz. This allows for very efficient power conversion and a reduction in component size. 
     During an output over-current event, this switching waveform would disappear. It would appear as a horizontal line on the graph which would imply that no switching activity was occurring. This lack of operation would cause the output of the power supply to suddenly drop output voltage and consequently output current. After a minimum reset time determined by the PWM gating controller, the switching would resume. (Similar to the graph illustrated in FIG. 7.) This would allow the output voltage to rise along with the output current. 
     If the output current rises beyond the maximum allowable threshold, the switching activity would again be terminated and the cycle would repeat. This is known as foldback current limiting. 
     From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.