Motor controller and electronic power steering apparatus

A motor controller capable of applying a field-weakening control to drive a brushless motor, comprising:

• a command current setting section that decides d-axis and q-axis current command values indicating a current that is to be supplied to the brushless motor;
• a control operating section that calculates d-axis and q-axis voltage command values indicating a voltage that is to be applied to the brushless motor, based on the d-axis and q-axis current command values decided by the command current setting section;
• and
• a driving section that drives the brushless motor based on the d-axis and q-axis voltage command values calculated by the control operating section,
• wherein the command current setting section decides the d-axis and q-axis current command values within a predetermined voltage limit value and a predetermined current limit value so that the d-axis and q-axis voltage command values and the d-axis and q-axis current command values satisfy both inequalities given as follows,
• √{square root over ( )}(vd2+vq2)≦Vlim,
• √{square root over ( )}(id2+iq2)≦Ilim,
• where vd is the d-axis voltage command value, vq is the q-axis voltage command value, Vlim is the voltage limit value, id is the d-axis current command value, iq is the q-axis current command value, and Ilim is the current limit value.