Voltage fluctuation compensating apparatus

Abstract

Voltage compensating circuits are connected serially to a power system, including capacitors each having different charging voltages (in relationship of approximately 2 k (K=0, 1, 2, . . . ) times the smallest charging voltage value). The voltage compensating circuits convert DC voltages in the capacitors into AC voltages and output the AC voltages, respectively. The voltages of the capacitors are detected as detected values V 1 to V 3. The detected values V 1 to V 3 are used as bit signals for a reference value to check a voltage dip amount of the power system with the reference value and to convert the voltage dip amount into a binary signal. A combination is selected from the voltage compensating circuits in accordance with the binary signal so that the sum of output voltages of the selected voltage compensating circuits compensates the voltage dip of the power system.

1. A voltage fluctuation compensating apparatus for suppressing fluctuation of a voltage supplied to a load, comprising:  A power output apparatus which outputs power to a load, comprising:
 a detection/control portion for detecting a voltage dip in a power system, and controlling power feeding in accordance with detection of a voltage dip; and  
 a plurality of voltage compensating circuits connected to the power system in series, each of the voltage compensating circuits including a plurality of energy storage units respectively having charging voltages different from one another, the voltage compensating circuits converting DC voltages of the respective energy storage units into AC voltages and outputting the AC voltages, wherein 
 the charging voltages of the energy storage units in the voltage compensating circuits are used as bit signals for a reference value to check a voltage dip amount of the power system with the reference value and to convert the voltage dip amount into a binary signal, and  
 a combination of the voltage compensating circuits is selected from the plurality of voltage compensating circuits in accordance with the binary signal so that a sum of output voltages of the voltage compensating circuits selected compensates for the voltage dip of the power system.  
 
 a series connection of a plurality of power output circuits each connected to a power storage unit storing power; and  
   a control circuit which controls the power output circuits so that voltage having repeated predetermined peak values is output from the series connected power output circuits to the load,    
   wherein the control circuit controls the power output circuits to transfer power from a higher voltage power storage unit of one power output circuit to a lower voltage power storage unit of another series connected power output circuit while outputting the voltage having the repeated predetermined peak values.   
 
     
     
       2. The voltage fluctuation compensating apparatus according to  claim 1 , wherein the energy storage units in the voltage compensating circuits respectively have charging voltages of approximately 2 k  (where K=0, 1, 2, . . . ) times a smallest charging voltage of the charging voltages.  The power output apparatus according to  claim 1 , further comprising:
   a voltage level detecting circuit that detects a voltage level of each of the power storage units and provides an output indicating the detected voltage level of each of the power storage units to the control circuit,    
   wherein the control circuit controls the power output circuits to provide the voltage of the repeated predetermined peak values to the load based on the output indicating the detected voltage level of each of the power storage units from the voltage level detecting circuit.   
 
     
     
       3. The voltage fluctuation compensating apparatus according to  claim 1 , wherein respective the energy storage units are a plurality of capacitors.  A power output apparatus which outputs power to a load, comprising:
   a series connection of a plurality of power output circuits, and at least one of the power output circuits connected to a power storage unit storing power; and    
   a control circuit which controls the power output circuits so that voltage having repeated predetermined peak values is output from the series connected power output circuits to the load,    
   wherein the control circuit controls the power circuits to transfer power from a higher voltage power output circuit to a power storage unit of a lower voltage power output circuit of another series connected power output circuit while outputting the voltage having the repeated predetermined peak values.   
 
     
     
       4. The voltage fluctuation compensating apparatus according to  claim 3 , wherein the charging voltages of the capacitors used as a reference value for converting the voltage dip amount into a binary signal are detected voltages obtained by detecting voltages of the respective capacitors at any time.  The power output apparatus according to  claim 3 , wherein the voltage of the repeated predetermined peak values output from the series connected power output circuits to the load has a first polarity and a second polarity opposite to the first polarity. 
     
     
       5. The voltage fluctuation compensating apparatus according to  claim 3 , wherein  The power output apparatus according to  claim 3 , wherein the voltage of the repeated predetermined peak values output from the series connected power output circuits has a value of approximately  2   K  ( where K is an integer of  0  or larger )  times a value of a voltage output from a minimum power output circuit producing a smallest absolute value of voltage compared to a level of voltage output from the other series connected power output circuits. 
 a system current of the power system is monitored; and  
 the charging voltages of the capacitors used as a reference value for converting the voltage dip amount into a binary signal are voltages calculated at any time by predicting voltage dip amounts of the capacitors based on the system current monitored.  
 
     
     
       6. The voltage fluctuation compensating apparatus according to  claim 3 , wherein charging voltages of the respective capacitors in the voltage compensating circuits are set so that an available maximum output voltage of a total compensating circuit constituting by all of the voltage compensating circuits connected in series exceeds a maximum voltage dip amount in the power system. 
     
     
       7. The voltage fluctuation compensating apparatus according to  claim 3 , wherein respective capacitances of the capacitors in the voltage compensating circuits become lower as the charging voltages of the capacitors increase. 
     
     
       8. The voltage fluctuation compensating apparatus according to  claim 7 , wherein respective capacitances of the capacitors in the voltage compensating circuits are, at least, approximately equal 2 k    (where K=0, 1, 2, . . . ) times the smallest of the capacitances.    
     
     
       9. The voltage fluctuation compensating apparatus according to  claim 3 , wherein, when the voltage dip amount is converted into the binary signal, 1 is added to the binary signal so that a smallest charging voltage of the capacitors is added to a total sum of the output voltages from the voltage compensating circuits determined in accordance with the binary signal, if the sum of the output voltages is not higher than a voltage value obtained by subtracting a pre-determined voltage amount from the voltage dip amount. 
     
     
       10. The voltage fluctuation compensating apparatus according to  claim 7 , further comprising a sag voltage compensating circuit connected to the power system in series, together with the voltage compensating circuits, the sag voltage compensating circuit converting a DC voltage of a capacitor into an AC voltage and outputting the AC voltage, wherein, when it is detected that voltages of the respective capacitors in the voltage compensating circuits dip and are not higher than a predetermined value, the sag voltage compensating circuit is operated in accordance with operations of the voltage compensating circuits so that a sum of output voltages of the voltage compensating circuits and an output voltage of the sag voltage compensating circuit compensates for the voltage dip of the power system. 
     
     
       11. The voltage fluctuation compensating apparatus according to  claim 3 , wherein
 the voltage compensating circuits selected in accordance with the binary signal include voltage compensation circuits having output voltages with a polarity reverse to voltage polarity of the power system; and    the respective capacitors in the voltage compensating circuits having output voltages with the same polarity as the power system are discharged, in operation, while the respective capacitors in the voltage compensating circuits having output voltages in reverse polarity to the power system are charged, in operation.    
     
     
       12. The voltage fluctuation compensating apparatus according to  claim 11 , wherein
 a logic table is created for selecting a combination of the voltage compensating circuits;    the logic table converts the binary signal into a binary value in which each bit value is set to 1 when a capacitor is discharged and −1 when a capacitor is charged; and    when a voltage dip is detected in one of the capacitors in the voltage compensating circuits, a binary value indicating a mode in which the detected capacitor can be charged is chosen from the logic table in accordance with the detected state so that each capacitor in the voltage compensating circuits selected in accordance with respective bit values of the binary value is charged when the bit value corresponding to the capacitor is 1 and discharged when the bit value corresponding to the capacitor is 4.    
     
     
       13. The voltage fluctuation-compensating apparatus according to  claim 11 , wherein
 an output voltage of one of the voltage compensating circuits has a first polarity while output voltages of other voltage compensating circuits have a second polarity reverse to the first polarity;    absolute value of a charging voltage of the capacitor having the first polarity is approximately equal to an absolute value of a sum of charging voltages of the capacitors having the second-polarity;    a combination of the voltage compensation circuits having the second-polarity and the voltage compensation circuits having the first-polarity are selectively operated when the voltage of the power system has the first polarity; and    a combination of only the voltage compensation circuits having the second-polarity voltage compensating circuits is selectively operated when the voltage of the power system has the second polarity.