Patent ID: 7091690

Claim:
A power conversion device comprising: a power converter that converts an AC of an AC power source to an AC with an arbitrary frequency so as to drive an AC motor; a control section that controls an inverter section of said power converter; a voltage detection section that detects a voltage of said AC power source; a current detection section that detects an input current of said AC motor; and a speed detection section that detects directly or indirectly a rotational speed of said AC motor, wherein said control section comprises a vector control section that converts a current detected by said current detection section into a torque current component and an exciting current component orthogonal thereto and respectively independently controls said torque current component and exciting current component, when an electrical quantity found from said voltage detected by said voltage detection section drops below a first predetermined value, said control section reduces an instruction value or limiting value of said torque current component in a predetermined ratio in response to a lowered electrical quantity and, when said electrical quantity drops below a second prescribed value smaller than said first predetermined value, said control section reduces said instruction value or limiting value of said torque current component to zero.