Motor drive system control apparatus

1. A motor drive system control apparatus for controlling a motor drive system comprising:

a direct current power supply;

a three-phase alternating current motor; and

a first power converter disposed between the direct current power supply and the three-phase alternating current motor and including switching circuits corresponding to each of three phases of the three-phase alternating current motor and a smoothing condenser disposed electrically in parallel with the switching circuits, said motor drive system control apparatus comprising:

an estimating device for estimating peak generation timing in which a peak is generated in an inter-terminal voltage VH of the smoothing condenser on the basis of at least one of an operating condition of the three-phase alternating current motor including at least one of an electric current corresponding to each of the three phases and a phase of the three-phase alternating current motor and a switching condition of the switching circuits corresponding to each of the three phases; and

a controlling device for controlling a drive condition of the first power converter such that the inter-terminal voltage VH (or a VH peak) in the peak generation timing decreases, for a predetermined period from start timing set in a time domain before the estimated peak generation timing,

wherein said estimating device estimates the peak generation timing on the basis of polarity of an electric current corresponding to each of the three phases and switching timing of the switching circuits corresponding to each of the three phases.

2. The motor drive system control apparatus according to claim 1 , wherein

the switching timing is timing in which a carrier voltage value matches a command voltage value, and

said estimating device estimates (1) first timing in which the electric current is positive and in which the carrier voltage value matches the command voltage value when the command voltage value goes beyond the carrier voltage value and (2) second timing in which the electric current is negative and in which the carrier voltage value matches the command voltage value when the command voltage value falls under the carrier voltage value, as the peak generation timing for each of the three phases.

3. The motor drive system control apparatus according to claim 1 , wherein said estimating device estimates the peak generation timing on the basis of a phase of the three-phase alternating current motor.

4. The motor drive system control apparatus according to claim 1 , wherein

the motor drive system comprises a second power converter, and

said controlling device changes a drive condition of the second power converter as one aspect of controlling the drive condition of the first power converter.

5. The motor drive system control apparatus according to claim 4 , wherein

the second power converter is disposed on a side closer to the direct current power supply than the smoothing condenser and includes a booster circuit capable of boosting a direct current voltage of the direct current power supply and capable of maintaining the inter-terminal voltage VH at a predetermined VH command value, and

said controlling device reduces the VH command value.

6. The motor drive system control apparatus according to claim 1 , wherein

the switching circuits corresponding to each of the three phases are configured to change a switching state in accordance with a magnitude relation between a carrier voltage value and a command voltage value, and

said controlling device reduces the VH peak by changing a frequency of a carrier signal to a high frequency side.

7. The motor drive system control apparatus according to claim 1 , wherein

the switching circuits corresponding to each of the three phases are configured to change a switching state in accordance with a magnitude relation between a carrier voltage value and a command voltage value, and

said controlling device superimposes a predetermined harmonic on the command voltage value.