Electric power steering control apparatus and electric power steering control method

1. An electric power steering control apparatus comprising a main controller configured to control motor current for driving an AC motor assisting steering of a steering wheel, based on a d-axis current command value and a q-axis current command value, wherein

the main controller includes, when a dq-converted current command value, which is a root-sum-square of the d-axis current command value and the q-axis current command value, is limited:

a d-axis current limiter configured to calculate a d-axis current limiting value with priority, based on a dq-converted current limiting value, which is a limiting value of the dq-converted current command value, and calculate a limited d-axis current command value by clipping the d-axis current command value to be the d-axis current limiting value or less;

a q-axis current limiter configured to calculate a q-axis current limiting value based on the dq-converted current limiting value and the limited d-axis current command value calculated by the d-axis current limiter, and calculate a limited q-axis current command value by clipping the q-axis current command value to be the q-axis current limiting value or less; and

an inverter controller configured to control the motor current, based on the limited d-axis current command value and the limited q-axis current command value.

2. The electric power steering control apparatus according to claim 1 , wherein

the d-axis current limiter calculates the d-axis current limiting value using the following expression,

Id _ LIM=Id _MAX×( Idq _ LIM/Idq _MAX)

where

Id_MAX denotes a d-axis current rated value,

Idq_MAX denotes a dq-converted current rated value,

Idq_LIM denotes the dq-converted current limiting value, and

Id_LIM denotes the d-axis current limiting value.

3. The electric power steering control apparatus according to claim 2 , wherein

the q-axis current limiter calculates the q-axis current limiting value using the following expression,

Iq _ LIM =√{( Idq _ LIM ) 2 −( Id ′) 2 }

where

Id′ denotes the limited d-axis current command value calculated by the d-axis current limiter,

Idq_LIM denotes the dq-converted current limiting value, and

Iq_LIM denotes the q-axis current limiting value.

4. The electric power steering control apparatus according to claim 3 , wherein

the main controller includes:

a temperature sensor configured to measure an ambient temperature of the main controller; and

a limiting value computing unit configured to determine the dq-converted current limiting value for overheating protection, based on the ambient temperature measured by the temperature sensor.

5. The electric power steering control apparatus according to claim 2 , wherein

the main controller includes:

a temperature sensor configured to measure an ambient temperature of the main controller; and

a limiting value computing unit configured to determine the dq-converted current limiting value for overheating protection, based on the ambient temperature measured by the temperature sensor.

6. The electric power steering control apparatus according to claim 1 , wherein

the q-axis current limiter calculates the q-axis current limiting value using the following expression,

Iq _ LIM =√{( Idq _ LIM ) 2 −( Id ′) 2 }

where

Id′ denotes the limited d-axis current command value calculated by the d-axis current limiter,

Idq_LIM denotes the dq-converted current limiting value, and

Iq_LIM denotes the q-axis current limiting value.

7. The electric power steering control apparatus according to claim 6 , wherein

the main controller includes:

a temperature sensor configured to measure an ambient temperature of the main controller; and

a limiting value computing unit configured to determine the dq-converted current limiting value for overheating protection, based on the ambient temperature measured by the temperature sensor.

8. An electric power steering control apparatus comprising a main controller configured to control motor current for driving an AC motor assisting steering of a steering wheel, based on a d-axis current command value and a q-axis current command value, wherein

the main controller includes:

a temperature sensor configured to measure an ambient temperature of the main controller;

a limiting value computing unit configured to determine a dq-converted current limiting value for overheating protection, based on the ambient temperature measured by the temperature sensor;

a d-axis current limiter configured to calculate a d-axis current limiting value with priority, based on a dq-converted current limiting value, which is a limiting value of the dq-converted current command value, and calculate a limited d-axis current command value by clipping the d-axis current command value to be the d-axis current limiting value or less,

a q-axis current limiter configured to calculate a q-axis current limiting value based on the dq-converted current limiting value and the limited d-axis current command value calculated by the d-axis current limiter, and calculate a limited q-axis current command value by clipping the q-axis current command value to be the q-axis current limiting value or less; and

an inverter controller configured to control the motor current, based on the limited d-axis current command value and the limited q-axis current command value.

9. An electric power steering control method executed by a main controller controlling motor current for driving an AC motor assisting steering of a steering wheel, based on a d-axis current command value and a q-axis current command value, the method comprising: by the main controller, when a dq-converted current command value, which is a root-sum-square of the d-axis current command value and the q-axis current command value, is limited;

a first step of acquiring a dq-converted current limiting value, which is a limiting value of the dq-converted current command value;

a second step of calculating a d-axis current limiting value with priority, based on the dq-converted current limiting value acquired in the first step;

a third step of calculating a limited d-axis current command value by clipping the d-axis current command value to be not more than the d-axis current limiting value, which has been calculated in the second step;

a fourth step of calculating a q-axis current limiting value based on the dq-converted current limiting value acquired in the first step and the limited d-axis current command value calculated in the third step;

a fifth step of calculating a limited q-axis current command value by clipping the q-axis current command value to be not more than the q-axis current limiting value, which has been calculated in the fourth step; and

a sixth step of controlling the motor current, based on the limited d-axis current command value, which has been calculated in the third step, and the limited q-axis current command value, which has been calculated in the fifth step.