Power conversion apparatus, power conversion method, and motor system

A power conversion apparatus which converts an input voltage which is a single-phase AC voltage into output voltages forming a two-phase AC voltage, the power conversion apparatus comprising:

• a pair of input terminals to which the input voltage is applied;
• a pair of first output terminals which output one of the output voltages as a first-phase output voltage;
• a pair of second output terminals which output the other of the output voltages as a second-phase output voltage;
• four first bidirectional switches each corresponding to a different combination of one of the paired input terminals and one of the paired first output terminals to switch connection and disconnection between the corresponding input terminal and first output terminal according to a corresponding one of first control signals;
• four second bidirectional switches each corresponding to a different combination of one of the paired input terminals and one of the paired second output terminals to switch connection and disconnection between the corresponding input terminal and second output terminal according to a corresponding one of second control signals;
• a target voltage designating unit configured to designate a first target voltage representing, using one of AC voltages forming a two-phase AC voltage, consecutive target values of the first-phase output voltage and a second target voltage representing, using the other of the AC voltages forming the two-phase AC voltage, consecutive target values of the second-phase output voltage;
• a target frequency designating unit configured to designate a frequency of the first target voltage and the second target voltage;
• a control signal generating unit configured to (i) generate the first control signals to cyclically connect and disconnect the pair of the input terminals and the pair of the first output terminals via the first bidirectional switches at a duty cycle corresponding to a ratio of an instantaneous absolute value of the first target voltage to an instantaneous absolute value of the input voltage during a time period in which the instantaneous absolute value of the input voltage is greater than the instantaneous absolute value of the first target voltage, and (ii) generate the second control signals to cyclically connect and disconnect the pair of the input terminals and the pair of the second output terminals via the second bidirectional switches at a duty cycle corresponding to a ratio of an instantaneous absolute value of the second target voltage to the instantaneous absolute value of the input voltage during a time period in which the instantaneous absolute value of the input voltage is greater than the instantaneous absolute value of the second target voltage;
• and
• a driver which supplies the generated first control signals to the first bidirectional switches and the generated second control signals to the second bidirectional switches,
• wherein the target voltage designating unit is configured to designate AC voltages as the first target voltage and the second target voltage, the AC voltages forming a two-phase AC voltage and having (i) an amplitude 1/√2 times smaller than an amplitude of the input voltage, and (ii) phase differences of +45 degrees and −45 degrees relative to the input voltage, and
• the target frequency designating unit is configured to designate, as the frequency of the first target voltage and the second target voltage, a frequency other than a frequency twice a frequency of the input voltage.