Motor drive device and refrigeration equipment

A motor drive device having an alternating power supply connected on an input side and a motor connected on an output side, the motor drive device comprising:

• a rectifier circuit configured to convert an alternating current voltage supplied from the alternating power supply into a direct current voltage;
• a smoothing capacitor configured to smooth a direct current voltage outputted from the rectifier circuit, the smoothing capacitor being formed of a film capacitor or a capacitor having a capacity of 200 microfarad or less;
• voltage detecting means configured to detect a voltage across the smoothing capacitor and output a direct current voltage signal;
• an inverter circuit configured to convert a direct current voltage outputted from the smoothing capacitor into an alternating current voltage;
• current sensing means configured to detect a direct current or an alternating current of the inverter circuit and output a current signal;
• and
• a controller configured to control the inverter circuit based on the direct current voltage signal and the current signal,
• wherein the controller includes:
• a voltage controller configured to generate a voltage command value used for controlling the motor,
• a ripple frequency arithmetic unit configured to operate a ripple frequency included in the direct current voltage signal, and
• a harmonic suppressor configured to process a signal based on the current signal using an S controller having a gain near the ripple frequency and output a corrected amount;
• and
• the inverter circuit is controlled based on a signal that the voltage command value is corrected using the corrected amount,
• wherein the ripple frequency arithmetic unit calculates a ripple frequency of the direct current voltage signal by extracting a ripple component of the direct current voltage signal, generating a signal having a different frequency component through a multiplication process of a sine wave and a cosine wave of a fixed frequency, and operating a phase through arctangent operation on a difference frequency component between a frequency of the ripple component and the fixed frequency.