Power conversion device
A power converter includes: a conversion circuit for conversion between DC power and N-phase AC power (N 3 3); and a control unit controlling 2N switches. The control unit periodically switches between a first PWM mode in which a high-side or a low-side switch of one phase among the 2N switches is turned on and the switches of the remaining phases are controlled by PWM, and a second PWM mode in which the switches of all phases among the 2N switches are controlled by PWM. The sum of the first period of the first PWM mode and the second period of the second PWM mode is shorter than ½N of one electrical angle cycle of the AC waveform of the AC power. The first period is equal to or longer than one cycle of PWM. The ratio of the first period to the sum of the first and second periods is variable.
1 . A power conversion device comprising:
a power conversion circuit that performs mutual conversion between DC power and N-phase AC power (N is an integer of 3 or more); and
a control unit that controls 2N switches included in the power conversion circuit in a first modulation mode, wherein
in the first modulation mode, the control unit periodically switches between a first PWM mode in which a high-side switch or a low-side switch of one phase among the 2N switches is fixed to be turned on and switches of remaining phases are controlled by pulse width modulation and a second PWM mode in which switches of all phases among the 2N switches are controlled by the pulse width modulation,
a sum of a first period in which the control unit operates in the first PWM mode and a second period in which the control unit operates in the second PWM mode is shorter than ½N of one electrical angle cycle of an AC waveform appearing at a connection terminal of the power conversion circuit,
the first period has a length equal to or longer than one cycle of the pulse width modulation, and
a ratio of the first period to a sum of the first period and the second period is variable.
2 . The power conversion device according to claim 1 , wherein when switching a modulation mode between a second modulation mode in which the ratio is a first ratio and a third modulation mode in which the ratio is a second ratio smaller than the first ratio, the control unit operates in the first modulation mode in a period between a period in which the control unit operates in the second modulation mode and a period in which the control unit operates in the third modulation mode, and changes the ratio continuously or stepwise in a period in which the control unit operates in the first modulation mode.
3 . The power conversion device according to claim 2 , wherein the first ratio in the second modulation mode is 1.
4 . The power conversion device according to claim 2 , wherein the second ratio in the third modulation mode is 0.
5 . The power conversion device according to claim 2 , wherein in the first period, the control unit switches between a third PWM mode in which a high-side switch of one phase among the 2N switches is fixed to be turned on and switches of remaining phases are controlled by the pulse width modulation and a fourth PWM mode in which a low-side switch of one phase among the 2N switches is fixed to be turned on and switches of remaining phases are controlled by the pulse width modulation in a cycle shorter than ½N of one electrical angle cycle.
6 . The power conversion device according to claim 5 , wherein a period in which the control unit operates in the third PWM mode coincides with a period in which the control unit operates in the fourth PWM mode in the first period included in a period in which the control unit operates in the first modulation mode.
7 . The power conversion device according to claim 5 , wherein a period in which the control unit operates in the third PWM mode coincides with a period in which the control unit operates in the fourth PWM mode in the first period included in a period in which the control unit operates in the second modulation mode.
8 . The power conversion device according to claim 1 , wherein in the first period, the control unit switches between a third PWM mode in which a high-side switch of one phase among the 2N switches is fixed to be turned on and switches of remaining phases are controlled by the pulse width modulation and a fourth PWM mode in which a low-side switch of one phase among the 2N switches is fixed to be turned on and switches of remaining phases are controlled by the pulse width modulation in a cycle shorter than ½N of one electrical angle cycle.
9 . The power conversion device according to claim 8 , wherein a period in which the control unit operates in the third PWM mode coincides with a period in which the control unit operates in the fourth PWM mode in the first period.