Noise reduction circuitry, load system and power conversion device

Noise reduction circuitry comprising:

• noise canceller circuitry that injects a compensation current into a power line or an earth to reduce a common mode noise current flowing to an alternating-current power source from a power converter including a switching element connected to the alternating-current power source through the power line and the earth;
• and
• a direct-current power source that supplies power to the noise canceller circuitry, wherein
• a voltage Vcc of the direct-current power source is less than ⅔ of a peak value of a DC link voltage of the power converter, and
• when a connection point between the power line and a path connecting the power line and the earth via the noise canceller circuitry is a first connection point, and a connection point between the path and the earth is a second connection point,
• when the compensated common mode noise current whose positive direction is a direction of flow from the first connection point to the power converter side and flowing through the power line on a side closer to the power converter than the first connection point is Ic′(t),
• when the compensation current whose positive direction is a direction of flow from the second connection point to the first connection point and flowing through the path is Io(t),
• when an impedance of the path is Z1,
• when an impedance on a side closer to the power converter than the first connection point and the second connection point is Z3, and
• when V(t)=2*(Z1*Io(t)+Z3*Ic′(t)),
• the voltage Vcc is set to be a maximum value of a quasi-peak value of the V(t) or √2 times or more an effective value of the V(t).

A power conversion device comprising:

• noise canceller circuitry that injects a compensation current into a power line or an earth to reduce a common mode noise current flowing to an alternating-current power source from a power converter including a switching element connected to the alternating-current power source through the power line and the earth;
• and
• a direct-current power source that supplies power to the noise canceller circuitry, wherein
• the direct-current power source is connected to the power line via a coupling capacitor on a side closer to the alternating-current power source than the power converter,
• a voltage Vcc of the direct-current power source is less than ⅔ of a peak value of a DC link voltage of the power converter,
• a noise filter including a common mode choke coil or a Y capacitor is provided between the alternating-current power source and the power converter, and
• a noise detector and the coupling capacitor are connected to the power line on a side closer to the alternating-current power source than the noise filter.