CLAIMS 1. A power converter comprising:
a power converting unit including a switching element, the power converting unit converting DC power into AC power; and
a control unit including a modulated-wave generating unit to generate a modulated wave synchronized with an output voltage command of the power converting unit and a carrier-wave generating unit to output a carrier wave having a freguency higher than a frequency of the modulated wave, the control unit controlling the power converting unit by comparing the modulated wave and the carrier wave to output a switching signal for driving the switching element, wherein
when a modulation factor in converting the DC power into the AC power is equal to or higher than a mode switching modulation factor and is lower than Tt/4, the power converting unit converts the DC power into the AC power in an over-modulation mode, in which switching of the switching element is stopped for a period longer than one cycle of the carrier wave, in a first period in which an output voltage command is positive and timing of a positive peak value of the output voltage command is included.
2. A power converter comprising:
a power converting unit including a switching element, the power converting unit converting DC power into AC power; and
a control unit including a modulated-wave generating unit to generate a modulated wave synchronized with an output voltage command of the power converting unit and a carrier-wave generating unit to output a carrier wave having a frequency higher than a frequency of the modulated

wave, the control unit controlling the power converting unit by comparing the modulated wave and the carrier wave to output a switching signal for driving the switching element, wherein
5 when a modulation factor in converting the DC power
into the AC power is lower than a mode switching modulation factor and is lower than TI/V(12}, the power converting unit outputs an AC voltage superimposed with 3n-th fn is a positive integer) order harmonics, and
0 when the modulation factor is equal to or higher than the mode switching modulation factor, the power converting unit converts the DC power into the AC power in an over-modulation mode, in which switching of the switching element is stopped for a period longer than one cycle of
5 the carrier wave, in a first period in which an output
voltage command is positive and timing of a positive peak value of the output voltage command is included.
3. The power converter according to claim 1 or 2, wherein,
0 in the over-modulation mode, the power converting unit
causes the switching of the switching element to be stopped for a period longer than one cycle of the carrier wave in a second period in which the output voltage command is negative and timing of a negative peak value of the output 5 voltage command is included.
4. The power converter according to claim 3, wherein, in
a third period, which is a period other than the first
period and the second period, the modulated-wave generating
0 unit corrects a value of the modulated wave to reduce an
absolute value of an output voltage of the power converting unit .

5. The power converter according to claim 1 or 2, wherein
the power converting unit increases a ratio of the first
period in one cycle of an AC output voltage stepwise as the
modulation factor increases in the over-modulation mode.
6. The power converter according to claim 5, wherein the
power converting unit reduces a number of times of
switching of the switching element included in one cycle of
the AC voltage by a multiple of four at a time as the
modulation factor increases in the over-modulation mode.
7. The power converter according to claim 3, wherein the
modulated-wave generating unit increases or reduces, as the
modulation factor increases or decreases, a correction
amount for correcting a value of the modulated wave to
increase a decrease amount of an absolute value of an
output voltage of the power converting unit.
8. The power converter according to claim 1 or 2, wherein
the modulated-wave generating unit includes:
a mode selecting unit to generate a mode selection code for identifying a PWM mode on the basis of the modulation factor; and
a correction-coefficient selecting unit to store a correction coefficient corresponding to the PWM mode, and select a correction coefficient corresponding to the mode selection code, and
the modulated-wave generating unit corrects the modulation factor according to the correction coefficient selected by the correction-coefficient selecting unit to correct a value of the modulated wave.
9. The power converter according to claim 1 or 2, wherein

the modulated-wave generating unit includes:
a mode selecting unit to generate a mode selection code for identifying a PWM mode on the basis of the modulation factor; and
a specific-phase selecting unit to store a specific phase corresponding to the PWM mode therein and select a specific phase corresponding to the mode selection code, and
the modulated-wave generating unit generates the modulated wave according to the specific phase selected by the specific-phase selecting unit.
10. The power converter according to claim 1 or 2, wherein
the carrier wave is synchronized with the modulated wave.
11. The power converter according to claim 10/ wherein,
when a pulse of a first carrier wave at a time when the
output voltage command is positive is negative, a number of
maximum value points of a carrier wave included in the
first period is an odd number and, when the pulse of the
first carrier wave at the time when the output voltage
command is positive is positive, the number of the maximum
value points of the carrier wave included in the first
period is an even number.
12. The power converter according to claim 1 or 2, wherein
a modulated wave generated by the modulated wave and the
carrier wave is a three-phase modulated wave.
13. The power converter according to claim 1 or 2, wherein
the mode switching modulation factor is equal to or higher
than a lower limit modulation factor determined by a
minimum pulse width of the switching element and a

frequency of the carrier wave.
14. The power converter according to claim 1 or 2, wherein
the switching element included in the power converter is
5 formed by a wide-band gap semiconductor.
15. The power converter according to claim 14, wherein the
wide-band gap semiconductor is a semiconductor in which
silicon carbide, a gallium nitride material, or diamond is
3 used.
16. A vehicle driving system comprising:
the power converter according to claim 1 or 2; an input circuit to generate input power to the power 5 converter; and
an electric motor driven by the power converter.