Noise reduction circuitry, load system and power conversion device

Abstract

[Problem] To suppress the disadvantage that occurs with regard to the flow of a compensation current when a voltage of a power source of a noise canceller is lower than a DC link voltage of a power converter. [Solving means] A noise reduction circuitry includes a noise canceller 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, and 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 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 alternating-current power source side to the first connection point and flowing through the power line on a side closer to the alternating-current power source than the first connection point is Ig(t), when the compensation current whose positive direction is a direction of flow from the alternating-current power source side 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 alternating-current power source than the first connection point and the second connection point is Z2, and when V(t)=2*(Z1*Io(t)−Z2*Ig(t)), the voltage Vcc is set to be a maximum value of a quasi-peak value of V(t) or √2 times or more an effective value of V(t).