Electric power steering apparatus

An electric power steering apparatus of a vector control system that converts dq-axes current command values calculated based on at least a steering torque into 3-phase voltage command values, converts said 3-phase voltage command values into duty command values, driving-controls a 3-phase brushless motor by an inverter of a pulse width modulation (PWM) control, and applies an assist torque to a steering system of a vehicle, comprising:

• a spatial vector modulating section to spatial-vector-modulate said dq-axes current command values and obtain said 3-phase voltage command values;
• a midpoint voltage estimating section to estimate midpoint voltages based on 3-phase motor terminal voltages, a motor rotational angle, a motor rotational number and an inverter-applying voltage;
• a 3-phase detection voltage calculating section to calculate 3-phase detection voltages from said midpoint voltages and said 3-phase motor terminal voltages;
• a 3-phase command voltage calculating section to calculate 3-phase command voltages based on said duty command values and said inverter-applying voltage;
• a 3-phase loss voltage calculating section to estimate loss voltages due to a dead time of said inverter from differences between said 3-phase detection voltages and said 3-phase command voltages;
• and
• a compensation value limiting section to limit said dead time compensation values by making 3-phase loss voltages calculated at said 3-phase loss voltage calculating section be sensitive to said inverter-applying voltage,
• wherein a dead time compensation of said inverter is performed by adding said limited dead time compensation values to said 3-phase voltage command values.

An electric power steering apparatus of a vector control system that converts dq-axes current command values calculated based on at least a steering torque into 3-phase duty command values, driving-controls a 3-phase brushless motor by an inverter of a pulse width modulation (PWM) control, and applies an assist torque to a steering system of a vehicle,

• wherein 3-phase detection voltages are estimated based on 3-phase motor terminal voltages,
• wherein loss voltages due to a dead time of said inverter are estimated from differences between 3-phase command voltages calculated from said duty command values and said 3-phase detection voltages,
• wherein said calculated loss voltages are set as a basic compensation amount,
• wherein voltage differences between ideal dead time compensation values and said loss voltages, which are a shortage compensation amount, are corrected, and
• wherein a dead time compensation of said inverter is performed by feeding-back corrected 3-phase values as dead time compensation values to said 3-phase voltage command values.

An electric power steering apparatus of a vector control system that converts a d-axis current command value and a q-axis current command value calculated based on at least a steering torque into 3-phase voltage command values, driving-controls a 3-phase brushless motor by an inverter of a pulse width modulation (PWM) control using calculated 3-phase duty command values, and applies an assist torque to a steering system of a vehicle, comprising:

• a midpoint voltage estimating section to estimate midpoint voltages based on 3-phase motor terminal voltages, a motor rotational angle, a motor rotational number and an inverter-applying voltage;
• a 3-phase detection voltage calculating section to calculate 3-phase detection voltages from said midpoint voltages and said 3-phase motor terminal voltages;
• a 3-phase command voltage calculating section to calculate 3-phase command voltages based on said 3-phase duty command values and said inverter-applying voltage;
• a loss voltage calculating section to estimate 3-phase loss voltages due to a dead time of said inverter from differences between said 3-phase detection voltages and said 3-phase command voltages;
• an ideal dead time compensation model to obtain 3-phase ideal dead time compensation values based on said motor rotational angle, said motor rotational number and said inverter-applying voltage;
• a correcting section to correct voltage differences between said 3-phase loss voltages and said 3-phase ideal dead time compensation values based on said q-axis current command value;
• and
• an outputting section to output 3-phase dead time compensation values by processing compensation values from said correcting section based on said inverter-applying voltage,
• wherein a dead time compensation of said inverter is performed by feeding-back said 3-phase dead time compensation values to said 3-phase voltage command values.