Booster

1. A booster in an electric power steering system having a manual steering input member mechanically connected to apply a manual steering input to at least one road wheel and a motor as a driving source connected for applying assisting force to the power steering system to assist the manual steering input, comprising:

a booster circuit outputting an output voltage to the motor of the electric power steering system, the output voltage being obtained by boosting a power supply voltage; and

a control section controlling the output voltage of the booster circuit through a feedback control based on a deviation of the output voltage from a target voltage,

wherein the control section includes a feedback gain determination section that determines a feedback gain of the feedback control based on the deviation, and

wherein the feedback gain determination section determines the feedback gain such that the feedback gain has a value of a low responsivity in an initial state of the booster circuit based on a start signal or a restart signal, the responsivity increasing from the low responsivity as the deviation of the output voltage from the target voltage decreases.

2. A booster in an electric power steering system having a manual steering input member mechanically connected to apply a manual steering input to at least one road wheel and a motor as a driving source connected for applying assisting force to the power steering system to assist the manual steering input, comprising:

a booster circuit outputting an output voltage to the motor of the electric power steering system, the output voltage being obtained by boosting a power supply voltage; and

a control section controlling the output voltage of the booster circuit through a feedback control based on a deviation of the output voltage from a target voltage,

wherein the control section includes a feedback gain determination section that determines a feedback gain of the feedback control based on the deviation, and

wherein, when the deviation of the output voltage from the target voltage is greater than a predetermined value in an initial state of the booster circuit based on a start signal or a restart signal, the feedback gain determination section determines the feedback gain such that the feedback gain has a value of a lower responsivity than the responsivity of the feedback gain in the case where the deviation of the output voltage from the target voltage is equal to or less than the predetermined value.

3. The booster according to claim 2 , wherein the control section performs, as the feedback control, a proportionality control and an integration control, and wherein, when the deviation of the output voltage from the target voltage is greater than the predetermined value, the feedback gain determination section sets an integration gain of the integration control to zero.

4. A booster in an electric power steering system having a manual steering input member mechanically connected to apply a manual steering input to at least one road wheel and a motor as a driving source connected for applying assisting force to the power steering system to assist the manual steering input, comprising:

a booster circuit outputting an output voltage to the motor of the electric power steering system, the output voltage being obtained by boosting a power supply voltage; and

a control section controlling the output voltage of the booster circuit through a feedback control based on a deviation of the output voltage from a target voltage,

wherein the control section includes:

an initial state determination section that determines whether the booster is in an initial state based on a start signal or a restart signal; and

a feedback gain determination section that determines a feedback gain of the feedback control,

wherein, when the initial state determination section determines that the booster is in the initial state, the feedback gain determination section determines the feedback gain such that the feedback gain has a value of low responsivity, the responsivity increasing as the elapsed time from the start of the initial state increases until a predetermined period elapses from the start of the initial state.

5. A booster in an electric power steering system having a manual steering input member mechanically connected to apply a manual steering input to at least one road wheel and a motor as a driving source connected for applying assisting force to the power steering system to assist the manual steering input, comprising:

a booster circuit outputting an output voltage to the motor of the electric power steering system, the output voltage being obtained by boosting a power supply voltage; and

a control section controlling the output voltage of the booster circuit through a feedback control based on a deviation of the output voltage from a target voltage,

wherein the control section includes:

an initial state determination section that determines whether the booster is in an initial state based on a start signal or a restart signal; and

a feedback gain determination section that determines a feedback gain of the feedback control,

wherein, when the initial state determination section determines that the booster is in the initial state, the feedback gain determination section determines, before a predetermined period elapses from the start of initial state, the feedback gain such that the feedback gain has a value of a lower responsivity than the responsivity of the feedback gain after the predetermined period has elapsed from the start of the initial state.

6. The booster according to claim 5 , wherein the control section performs, as the feedback control, a proportionality control and an integration control, and wherein, when an elapsed time has not elapsed from the start of the initial state, the feedback gain determination section sets an integration gain of the integration control to zero.