Motor drive system and method capable of suppressing heat generation during low speed operation

A motor drive system capable of suppressing heat generation during a low speed operation, the motor drive system comprising:

• an inverter including a plurality of switching elements to convert direct current power to alternating current power having a plurality of phases;
• a motor driven with the alternating current power converted in the inverter;
• and
• a controller configured to determine an operating point of the motor based on a torque command of the motor and generate a d-axis current command and a q-axis current command corresponding to the operating point,
• wherein when a switching element of the plurality of switching elements is overheated, the controller is configured to change the d-axis current command and the q-axis current command by changing the operating point to a different operating point corresponding to a torque of the same magnitude as the torque command, and
• wherein when the switching element is overheated, the controller is configured to:
• convert three phase currents based on the d-axis current command and the q-axis current command by using the following Equations:
• ρ
• =
• θ
• +
• 270
• -
• β
• x
• ,
• ⁢
• I
• U
• =
• Im
• x
• ·
• sin
• ⁢
• ⁢
• ρ
• ,
• ⁢
• I
• V
• =
• Im
• xx
• ·
• sin
• ⁡
• (
• ρ
• +
• 2
• 3
• ⁢
• π
• )
• ,
• and
• I
• W
• =
• Im
• x
• ·
• sin
• ⁡
• (
• p
• -
• 2
• 3
• ⁢
• π
• )
• ,
• where, Imx is a peak value of each of the three phase currents, and βX is a phase angle of the d-axis current command and the q-axis current command, and
• change the operating point of the motor by searching for the phase angle of the d-axis current command and the q-axis current command so as to change an angle section to which a variable ρ belongs in a plurality of angle sections divided at preset intervals.