Current estimating device

1. A current estimating device included in a power converter and estimating a power source current which is a current upstream of a capacitor, the power converter including: a rectifying circuit rectifying an AC power output from an AC power source; an inverter circuit supplied with power from the rectifying circuit; the capacitor connected between the rectifying circuit and the inverter circuit in parallel with the rectifying circuit; and a reactor connected between the AC power source and the capacitor, the current estimating device comprising:

a voltage detection circuit which is a voltage divider circuit including a plurality of resistances, the voltage detection circuit detecting voltages correlating with a power source voltage of the AC power source; and

a calculation unit obtaining an across voltage of the reactor based on detection results detected by the voltage detection circuit, and estimating the power source current based on the across voltage, wherein

the calculation unit:

corrects gains of the detection results of the voltage detection circuit so that a value correlating with an average value per predetermined time period of the estimated power source current matches a value correlating with an average value per the predetermined time period of a current downstream of the capacitor; and

obtains the across voltage of the reactor based on the detection results, of the voltage detection circuit, with the gains corrected.

2. The current estimating device of claim 1 , wherein

the capacitor absorbs voltage fluctuation caused by switching of the inverter circuit without absorbing voltage fluctuation from the rectifying circuit.

3. The current estimating device of claim 1 , wherein

the calculation unit further obtains the across voltage of the reactor based on a voltage drop of the reactor.

4. The current estimating device of claim 1 , wherein

the rectifying circuit is configured as a diode bridge circuit including a plurality of diodes connected in a bridge configuration, and

the calculation unit further obtains the across voltage of the reactor based on a voltage drop generated in the diodes.

5. The current estimating device of claim 4 , wherein

the voltage detection circuit detects voltages correlating with a power source voltage of the AC power source between the AC power source and the rectifying circuit.

6. The current estimating device of claim 1 , wherein

the voltage detection circuit includes: a first voltage detection unit corresponding to a positive side output of the AC power source; and a second voltage detection unit corresponding to a negative side output of the AC power source, and

the calculation unit:

corrects the gains each for one of the first detection result of the first voltage detection unit and of the second detection result of the second voltage detection unit so that the value correlating with the average value per the predetermined time period of the estimated power source current matches the value correlating with the average value per the predetermined time period of the current downstream of the capacitor; and

obtains the across voltage of the reactor based on a difference between the first detection result with the gain corrected and the second detection result with the gain corrected.

7. The current estimating device of claim 1 , wherein

the calculation unit:

calculates, as a first value, a value correlating with an average value per the predetermined time period of an integrated value of the across voltage of the reactor;

calculates, as a second value, a value correlating with an average value per the predetermined time period of a sum of a derivative value of the across voltage of the capacitor and the current downstream of the capacitor; and

corrects the gains of the detection results of the voltage detection circuit so that, when the first value matches the second value, the value correlating with the average value per the predetermined time period of the estimated power source current matches the value correlating with the average value per the predetermined time period of the current downstream of the capacitor.

8. The current estimating device of claim 7 , wherein

the predetermined time period is set to a half period of the AC power source.

9. The current estimating device of claim 1 , wherein

the calculation unit:

calculates, as a third value, the power source current based the integrated value of the across voltage of the reactor;

calculates, as a fourth value, the power source current based on the derivative value of the across voltage of the capacitor;

corrects offsets of the detection results of the voltage detection circuit so that a phase of the third value matches a phase of the fourth value; and

obtains the across voltage of the reactor based on the detection results, of the voltage detection circuit, with the offsets corrected.

10. The current estimating device of claim 9 , wherein

the calculation unit:

calculates amplitudes each for one of the third value and the fourth value with predetermined-high frequency waves of a power source frequency,

when the amplitudes are larger than a predetermined value, corrects the offsets of the detection results of the voltage detection circuit; and

when the amplitudes are smaller than the predetermined value, keeps from correcting the offsets of the detection results of the voltage detection circuit.

11. The current estimating device of claim 9 , wherein

the calculation unit corrects the gains of the detection results of the voltage detection circuit, and then corrects the offsets of the detection results of the voltage detection circuit.

12. The current estimating device of claim 9 , wherein

the reactor is connected between the AC power source and the rectifying circuit.

13. The current estimating device of claim 1 , wherein

the calculation unit:

obtains an average value of the detection results in a section, of one period of the AC power source, in which the detection results of the voltage detection circuit are not dominant, and, using the average value, corrects the offsets of the detection results of the voltage detection circuit; and

obtains the across voltage of the reactor based on the detection results, of the voltage detection circuit, with the offsets corrected.

14. The current estimating device of claim 1 , wherein

the calculation unit:

calculates a power source voltage of the AC power source based on the detection results of the voltage detection circuit;

corrects the offsets of the detection results of the voltage detection circuit, using a voltage value of the power source voltage near a zero cross of the AC power source, and

obtains the across voltage of the reactor based on the detection results, of the voltage detection circuit, with the offsets corrected.

15. A power converter comprising the current estimating device of claim 1 .

16. A current estimation method to be used for a power converter and for estimating a power source current which is a current upstream of a capacitor, the power converter including: a rectifying circuit rectifying an AC power output from an AC power source; an inverter circuit supplied with power from the rectifying circuit; the capacitor connected between the rectifying circuit and the inverter circuit in parallel with the rectifying circuit; and a reactor connected between the AC power source and the capacitor, the current estimation method comprising:

detecting, by a voltage divider circuit including a plurality of resistances, voltages correlating with a power source voltage of the AC power source;

first estimating including: obtaining an across voltage of the reactor based on the voltages correlating with the power source voltage of the AC power source; and estimating the power source current based on the across voltage;

correcting gains of the voltages correlating with the detected power source voltage of the AC power source so that a value correlating with an average value per predetermined time period of the estimated power source current matches a value correlating with an average value per the predetermined time period of a current downstream of the capacitor; and

second estimating including: obtaining the across voltage of the reactor based on the voltages, with the gains corrected, correlating with the power source voltage of the AC power source; and estimating the power source current based on the obtained across voltage of the reactor.