Power converter controlling apparatus and method providing ride through capability during power interruption in a motor drive system

A power converter controlling apparatus for controlling a power converter of a motor drive system, said controlling apparatus comprising:

• a current controller, which outputs gating signals to said power converter as a function of a torque current reference and a flux current reference;
• and
• a torque current reference generator, which generates the torque current reference used by said current controller, wherein
• said current controller controls said power converter during a first operating mode to create torque current flowing from said power converter to the motor to achieve desired motor speed;
• controls the power converter in a second operating mode, initiated when power to said power converter is interrupted, so that negative torque current between said power converter and said motor draws mechanical energy from said motor and charges an element on a power supply side of said power converter;
• and
• controls the torque current between said power converter and said motor to limit maximum transient bus voltage;
• wherein said torque current reference generator:
• monitors DC bus voltage between said power converter and the power supply;
• compares the monitored DC bus voltage to a reference value;
• and
• controls a torque current reference based on the result of said comparing step to limit a maximum DC bus voltage during transition between the first and second operating modes.