Power conversion device and electric motor drive system

1. A power conversion device comprising:

an inverter configured to convert direct current (DC) power into alternating current (AC) power by causing a switching element to perform a switching operation and supply the AC power to an electric motor;

a current detector configured to detect a load current that flows from the inverter to a winding of the electric motor;

a frequency analysis processing unit configured to calculate an odd-order harmonic frequency component of a fundamental frequency, which is a frequency of fundamental waves corresponding to a reference rotational rate of the electric motor, as a frequency component of the load current on the basis of a result of detecting the load current, the fundamental frequency being a fundamental frequency of the load current;

a storage unit configured to store restriction information for excluding a reference rotational rate related to a specific rotational rate of the electric motor from among a plurality of reference rotational rates for designating rotational rates of the electric motor;

a determination unit configured to determine a frequency at which a signal component having a magnitude exceeding a prescribed value has been detected among frequency components of the load current, generate restriction information for excluding a reference rotational rate related to the rotational rate corresponding to the frequency at which the signal component has been detected on the basis of a determination result after the determination, and cause the storage unit to store the generated restriction information;

a reference rotational rate change unit configured to change the reference rotational rate of the electric motor so that mechanical resonance of the frequency at which the signal component has been detected is avoided on the basis of the stored restriction information; and

a rate control unit configured to control a rotational rate of the inverter using the changed reference rotational rate and cause the electric motor to be driven at the controlled rotational rate.

2. The power conversion device according to claim 1 , wherein the frequency analysis processing unit calculates a frequency component defined on the basis of fundamental waves of an AC of the load current using a high-rate Fourier transform process.

3. The power conversion device according to claim 1 , further comprising an extraction unit configured to extract integer-order harmonic components of values of a reference rotational rate ω_ref from a spectrum using the values of the reference rotational rate ω_ref,

wherein the frequency analysis processing unit generates a spectrum of the load current, and

wherein the extraction unit calculates frequency components of the load current corresponding to a frequency of an integer-order harmonic component of a fundamental frequency and outputs the frequency components of the load current corresponding to the frequency of the integer-order harmonic component.

4. The power conversion device according to claim 1 , further comprising an extraction unit configured to extract integer-order harmonic components of values of a reference rotational rate ω_ref from a spectrum using the values of the reference rotational rate ω_ref,

wherein the frequency analysis processing unit generates a spectrum of the load current, and

wherein the extraction unit calculates frequency components of the load current corresponding to a frequency of an odd-order harmonic component of a fundamental frequency and outputs the frequency components of the load current corresponding to the frequency of the odd-order harmonic component.

5. The power conversion device according to claim 1 ,

wherein the storage unit stores the restriction information for defining whether or not the rotational rate required to be restricted is within a range thereof in a table associated with the plurality of reference rotational rates, the restriction information being restriction information for excluding the reference rotational rate related to the specific rotational speed of the electric motor from among the plurality of reference rotational rates whose values are defined different from each other,

wherein the determination unit causes the generated restriction information to be stored in the table of the storage unit, and

wherein, when a first rotational rate for the frequency at which the signal component has been detected has been designated as the rotational rate of the electric motor, the reference rotational rate change unit changes the reference rotational rate of the electric motor from the first rotational rate to a second rotational rate for the frequency at which the signal component has not been detected among rotational rates relatively near the first rotational rate on the basis of the stored restriction information included in the table.

6. The power conversion device according to claim 5 , wherein, when the first rotational rate for the frequency at which the signal component has been detected has been designated as the rotational rate of the electric motor, the reference rotational rate change unit changes the reference rotational rate of the electric motor from the first rotational rate to one of a lower limit value and an upper limit value of a second rotational rate for the frequency at which the signal component has not been detected among rotational rates relatively near the first rotational rate on the basis of the stored restriction information included in the table.

7. The power conversion device according to claim 6 , wherein the reference rotational rate change unit switches the reference rotational rate of the electric motor to one of the lower limit value and the upper limit value using a value between the lower limit value and the upper limit value of the range defined in the table.

8. An electric motor drive system comprising:

an electric motor;

an inverter configured to convert direct current (DC) power into alternating current (AC) power by causing a switching element to perform a switching operation and supply the AC power to the electric motor;

a current detector configured to detect a load current that flows from the inverter to a winding of the electric motor;

a frequency analysis processing unit configured to calculate an odd-order harmonic frequency component of a fundamental frequency, which is a frequency of fundamental waves corresponding to a reference rotational rate of the electric motor, as a frequency component of the load current on the basis of a result of detecting the load current, the fundamental frequency being a fundamental frequency of the load current;

a storage unit configured to store restriction information for excluding a reference rotational rate related to a specific rotational rate of the electric motor from among a plurality of reference rotational rates for designating rotational rates of the electric motor;

a determination unit configured to determine a frequency at which a signal component having a magnitude exceeding a prescribed value has been detected among frequency components of the load current, generate restriction information for excluding a reference rotational rate related to the rotational rate corresponding to the frequency at which the signal component has been detected on the basis of a determination result after the determination, and cause the storage unit to store the generated restriction information;

a reference rotational rate change unit configured to change the reference rotational rate of the electric motor so that mechanical resonance of the frequency at which the signal component has been detected is avoided on the basis of the stored restriction information; and

a controller configured to control the inverter using the changed reference rotational rate so that the electric motor is driven at the rotational rate based on the reference rotational rate.