Backup power supply

Abstract

The present invention reduces the capacity of the AC-DC converter for the peak load and realizes low price and reduction in the volume of the power unit. The apparatus built-in backup power supply has the peak cut function for sharing a part of the load current at the time of peak load from the secondary battery. The two-way DC-DC converter 5 and the secondary battery 4 are installed on the DC output side of the AC-DC converter 3 and a current larger than a predetermined peak cut level is discharged from the secondary battery 4 at the time of peak load. Further, when the load is less than the predetermined cut level, the secondary battery 4 is charged from the AC-DC converter 3 via the two-way DC-DC converter 5. Furthermore, a most suitable peak cut level according to the SOC of the secondary battery and load pattern is automatically set and dynamically changed.

What is claimed is:  
     
         1 . A backup power supply built in a power supply circuit for converting an alternating current received from a commercial AC power supply to a direct current and a load operated by said current generated by said power supply circuit, comprising: 
 at least one AC-DC converter connected to said commercial alternating current, a load connected to a DC output side of said AC-DC converter, at least one two-way DC-DC converter with one side thereof connected to said DC output side, and a secondary battery connected to another side of said two-way DC-DC converter, wherein:    when a load current is a predetermined peak cut current or larger, said backup power supply supplies a differential current between said load current and said predetermined peak cut current to said load from said secondary battery via said two-way DC-DC converter.    
     
     
         2 . A backup power supply according to  claim 1 , wherein 
 when said load current is smaller than said predetermined peak cut current, said backup power supply supplies said load current from said AC-DC converter, charges said secondary battery using said two-way DC-DC converter by a charging current having an upper limit of a predetermined current, takes in only a current equivalent to a differential current between said predetermined peak cut current and said load current from said two-way DC-DC converter.    
     
     
         3 . A backup power supply built in a power supply circuit for converting an alternating current received from a commercial AC power supply to a direct current and a load operated by said current generated by said power supply circuit, comprising: 
 at least one AC-DC converter connected to said commercial alternating current, a load connected to a DC output side of said AC-DC converter, at least one two-way DC-DC converter with one side thereof connected to said DC output side, and a secondary battery connected to another side of said two-way DC-DC converter, wherein:    when a load current is a predetermined peak cut current or larger, said backup power supply supplies a differential current between said load current and said predetermined peak cut current to said load from said secondary battery via said two-way DC-DC converter and performs a peak cut operation and when said load current is smaller than said predetermined peak cut current, said backup power supply supplies said load current from said AC-DC converter and charges said secondary battery via said two-way DC-DC converter.    
     
     
         4 . A backup power supply according to  claim 3 , 
 wherein said charging current for charging said secondary battery has an upper limit of a predetermined current and said backup power supply takes in only a current equivalent to a differential current between said predetermined peak cut current and said load current from said two-way DC-DC converter and charges said secondary battery.    
     
     
         5 . A backup power supply according to claims  1  or  3 , wherein 
 said backup power supply has detection means for detecting said charging and discharging currents of said secondary battery, means for detecting a voltage of said secondary battery, and a circuit for calculating a residual capacity of said secondary battery and changes said predetermined peak cut current according to said residual capacity of said secondary battery.  
 
     
     
         6 . A backup power supply according to  claim 5 , wherein 
 when said residual capacity of said secondary battery is reduced lower than a predetermined capacity, said peak cut operation is stopped.    
     
     
         7 . A backup power supply according to  claim 5 , wherein 
 when said residual capacity of said secondary battery is reduced lower than said predetermined capacity at a time of service interruption or at a time of occurrence of a fault of said AC-DC converter, a discharge operation is performed.    
     
     
         8 . A backup power supply according to any one of  claims 1  to  3 , wherein 
 from said residual capacity of said secondary battery and said load current, said backup power supply has a function for calculating and displaying a service interruption holding time at said point of time.  
 
     
     
         9 . A backup power supply according to any one of  claims 1  to  3 , wherein 
 from said residual capacity of said secondary battery and said load current, said backup power supply calculates said residual capacity of said secondary battery necessary to ensure a predetermined service interruption holding time at said point of time and performs said peak cut operation within a range having said calculated residual capacity.  
 
     
     
         10 . A backup power supply according to any one of  claims 1  to  3 , wherein a voltage at a connection point of said AC-DC converter and said two-way DC-DC converter is higher than a voltage of said secondary battery, and when said two-way DC-DC converter is discharged from a side of said secondary battery, said converter is operated as a booster chopper circuit, and when said secondary battery is charged, said converter is operated as a voltage reduction chopper circuit.  
     
     
         11 . A backup power supply according to any one of  claims 1  to  3 , wherein 
 said backup power supply has n storage means for dividing a preset time period into n parts by a sampling time sufficiently shorter than said period and corresponding to said divisions, means for detecting said load current, and means for calculating a mean value of load currents from said detected load current and a last value stored in corresponding storage means, overwriting in said corresponding means, and changing said predetermined peak cut current from said calculated new mean value of load currents.  
 
     
     
         12 . A backup power supply according to  claim 11 , wherein 
 said preset time period is  24  hours.    
     
     
         13 . A backup power supply according to  claim 11 , wherein 
 said preset time period is one week.    
     
     
         14 . A backup power supply comprising an AC-DC converter connected to a commercial alternating current, a load connected to a DC output side of said AC-DC converter, a DC-DC converter with one side thereof connected to said DC output side, and a secondary battery connected to one side of said DC-DC converter, wherein 
 said DC-DC converter has means for alternately switching a short-circuit mode for short-circuiting said secondary battery and an inductance by a switching element and a booster mode for ejecting energy stored in said inductance in said short-circuit mode to said load, means for detecting an inductance current in said booster mode, and mean for averaging said inductance current in said booster mode, and only when a result obtained by subtracting a predetermined peak cut current level from said load current is positive, sets said value as a peak cut current command value, compares said value with said averaged current, and controls a ratio of said short-circuit mode to said booster mode.    
     
     
         15 . A backup power supply built in a power supply circuit for converting an alternating current received from a commercial AC power supply to a direct current and a load operated by said current generated by said power supply circuit, comprising: 
 at least one AC-DC converter connected to said commercial alternating current, a load connected to a DC output side of said AC-DC converter, at least one two-way DC-DC converter with one side thereof connected to said DC output side, a secondary battery connected to another side of said two-way DC-DC converter, a service interruption fault detection circuit portion connected to said commercial alternating current, a two-way operation mode changeover circuit portion, a drive signal change-over means for changing over a drive signal of said two-way DC-DC converter by receiving a signal which is output by said two-way operation mode change-over circuit, a discharge control circuit portion for outputting a discharge control signal to said two-way DC-DC converter through a drive signal change-over means, and a SOC calculation portion for calculating a residual capacity of said secondary battery, wherein    an output of said SOC calculation portion is received by said charge control circuit portion.