Patent ID: 9548685
Date: 2017-01-17
CPC Classifications: H02H,H02P

Claim:
1. An over-voltage prevention device comprising: a first short-circuit device provided between a secondary side of a wound-rotor induction machine and a frequency converter configured to excite the secondary side by a three-phase AC current and having a function of short-circuiting between phases of the three-phase AC current; resistors each connected between the first short-circuit device and the frequency converter for each phase; and second short-circuit devices connected respectively to the resistors in parallel and having a function of short-circuiting between the frequency converter and the secondary side of the wound-rotor induction machine a controller i) configured to, in response to a detection of an over-voltage at the secondary side of the wound-rotor induction machine, activate the first short-circuit device to perform short-circuiting, deactivate the frequency converter, and cancel short-circuiting of the second short-circuit devices, at a first time point ii) configured to restart the frequency converter to set the current flowing through the first short-circuit device to be zero, and cancel short-circuiting of the first short-circuit device, at a second time point after a predetermined time period has elapsed from the first time point and iii) configured to control the second short-circuit devices to perform short-circuiting, at a third time point after a predetermined time has elapsed from the first time point, wherein the third time point comes after the second time point comes, the over-voltage prevention device being controllable such that a short-circuit current flows from the first short-circuit device through the resistors into the frequency converter when short-circuiting of the first short-circuit device is canceled.