Power conversion device with ripple filtering

1. A power conversion device comprising:

a converter configured to convert first AC power into DC power for output to a power supply node;

an inverter configured to convert said DC power supplied from converter through said power supply node into second AC power;

a capacitor connected between said power supply node and a line of reference voltage, wherein

a capacitance value of said capacitor is set at a smaller value than a capacitance value to smooth a voltage of said power supply node, and

the voltage of said power supply node is a voltage obtained by superimposing, on a DC voltage, a ripple voltage varying sinusoidally at a frequency twice a frequency of an output voltage of said inverter,

a filter configured to receive the voltage of said power supply node and reject said ripple voltage in the received voltage to pass a DC voltage component; and

a control circuit configured to control said converter such that said DC voltage component passed through said filter matches a target voltage,

said filter including:

an extraction circuit configured to extract said ripple voltage from the voltage of said power supply node, and

a subtraction circuit configured to subtract said ripple voltage extracted by said extraction circuit from the voltage of said power supply node to generate said DC voltage component,

said extraction circuit including;

a coordinate transformation circuit configured to transform a coordinate of the voltage of said power supply node from a stationary coordinate to a rotating coordinate rotating at the frequency twice the frequency of the Output voltage of said inverter,

a low order filter configured to reject an AC component in the voltage of said power supply node on said rotating coordinate, and

a coordinate inverse transformation circuit configured to inversely transform the coordinate of an output voltage of said low order filter from said rotating coordinate to said stationary coordinate to generate said ripple voltage, wherein said filter is implemented by a digital signal processor (DSP).

2. The power conversion device according to claim 1 , wherein

the voltage of said power supply node further contains an AC component of a switching frequency of said inverter, and

said filter rejects, in the voltage of said power supply node, said ripple voltage and the AC component of the switching frequency of said inverter to pass said DC voltage component.

3. The power conversion device according to claim 1 , wherein said control circuit controls said converter such that an input voltage and an input current to said converter are in phase and that said DC voltage component matches said target voltage.

4. The power conversion device according to claim 1 , wherein

said first AC power is supplied from a commercial AC power supply,

in a normal state where said first AC power is supplied from said commercial AC power supply, said DC power is supplied to said inverter and is stored in a power storage device, and

in a power interruption state where supply of said first AC power from said commercial AC power supply is interrupted, said converter stops operating, and the DC power is supplied from said power storage device to said inverter.

5. The power conversion device according to claim 1 , wherein the capacitor is connected between said power supply node and ground.

6. The power conversion device according to claim 1 , further comprising:

another capacitor, wherein a first node of the another capacitor is connected between a power supply and the converter, and a second node of the another capacitor is connected to ground.