Method for controlling power converter
One or both of a duty for conducting a switch for intermittently applying a first voltage boosted from a booster to a direct-current link and the first voltage are controlled. When an alternating-current power output from an inverter is equal to or more than a second threshold less than a first threshold, an equivalent direct-current voltage is controlled to be higher than a peak value of a rectified voltage that is rectified by a converter and equal to or less than a first voltage; and when the alternating-current power has a first value more than the first threshold, the equivalent direct-current voltage is higher than the equivalent direct-current voltage when the alternating-current power has a second value more than the second threshold and less than the first threshold.
1 . A method for controlling a power converter, the power converter including:
a direct-current link;
a converter that rectifies a single-phase alternating-current voltage, converts a first alternating-current power based on the alternating-current voltage into a direct-current power, and output a first instantaneous power;
an active buffer that exchanges power with the direct-current link and buffers the power at a second instantaneous power; and
an inverter that converts a third instantaneous power input from the direct-current link into a second alternating-current power and outputs the second alternating-current power,
the active buffer includes
a booster that boosts a rectified voltage obtained by rectifying the alternating-current voltage to generate a first voltage; and
a switch that intermittently applies the first voltage from the booster to the direct-current link,
the method comprising:
bringing the switch into conduction with a first duty;
by controlling one or both of the first duty and the first voltage:
controlling an equivalent direct-current voltage to be more than a peak value of the rectified voltage and equal to or less than the first voltage when the second alternating-current power is equal to or more than a second threshold less than a first threshold; and
setting the equivalent direct-current voltage when the second alternating-current power has a first value more than the first threshold to be higher than the equivalent direct-current voltage when the second alternating-current power has a second value more than the second threshold and less than the first threshold,
wherein the equivalent direct-current voltage is a direct-current voltage applied to the direct-current link and obtained by dividing the third instantaneous power by a direct current which is an average value of a current flowing through the inverter.
2 . The method for controlling the power converter according to claim 1 , comprising, by the active buffer, receiving a fourth instantaneous power that is a part of the first instantaneous power from the direct-current link, outputting a fifth instantaneous power to the direct-current link, and buffering the second instantaneous power,
wherein the third instantaneous power is a sum of the fifth instantaneous power and a sixth instantaneous power obtained by subtracting the fourth instantaneous power from the first instantaneous power,
wherein a power ratio is a ratio of the sixth instantaneous power to the first instantaneous power, and
the method comprising setting the power ratio when the second alternating-current power has the first value to be less than the power ratio when the second alternating-current power has the second value.
3 . The method for controlling the power converter according to claim 1 , wherein when the second alternating-current power is more than the second threshold, a maximum value of a second duty, which is a value obtained by subtracting the first duty from 1, is more than 0 and less than 1/√3, or more than 1/√3 and equal to or less than 1.
4 . The method for controlling the power converter according to claim 3 , wherein when the second alternating-current power is more than the second threshold, a maximum value of the second duty is more than 0 and less than 1/√3.
5 . The method for controlling the power converter according to claim 4 , wherein
a boost ratio is a value obtained by dividing the first voltage by the peak value,
a voltage utilization ratio is a value obtained by dividing the equivalent direct-current voltage by the peak value,
the boost ratio is able to have any of a third value and a fourth value more than the third value,
in a case where the second alternating-current power is more than the second threshold:
when the boost ratio has the third value, an amplitude of a harmonic for the alternating-current voltage due to switching of the switch is equal to or more than a predetermined threshold with respect to the voltage utilization ratio within a first range more than 1, and the amplitude of the harmonic is less than the predetermined threshold with respect to the voltage utilization ratio outside the first range;
when the boost ratio has the fourth value, the amplitude of the harmonic is equal to or more than the predetermined threshold with respect to the voltage utilization ratios within a second range more than 1, and the amplitude of the harmonic is less than the predetermined threshold with respect to the voltage utilization ratio outside the second range; and
the fourth value is adopted as the boost ratio when the voltage utilization ratio is more than an upper limit of the second range.
6 . The method for controlling the power converter according to claim 4 , wherein
a boost ratio is a value obtained by dividing the first voltage by the peak value,
a voltage utilization ratio is a value obtained by dividing the equivalent direct-current voltage by the peak value,
the boost ratio is able to have any of a third value and a fourth value more than the third value,
in a case where the second alternating-current power is more than the second threshold:
when the boost ratio has the third value, an amplitude of a harmonic for the alternating-current voltage due to switching of the switch is equal to or more than a predetermined threshold with respect to the voltage utilization ratio within a first range more than 1, and the amplitude of the harmonic is less than the predetermined threshold with respect to the voltage utilization ratio outside the first range;
when the boost ratio has the fourth value, the amplitude of the harmonic is equal to or more than the predetermined threshold with respect to the voltage utilization ratio within a second range more than 1, and the amplitude of the harmonic is less than the predetermined threshold with respect to the voltage utilization ratio outside the second range; and
the third value is adopted as the boost ratio when the voltage utilization ratio is more than an upper limit of the first range and equal to or less than an upper limit of the second range.
7 . The method for controlling the power converter according to claim 4 , wherein
a boost ratio is a value obtained by dividing the first voltage by the peak value,
a voltage utilization ratio is a value obtained by dividing the equivalent direct-current voltage by the peak value,
the boost ratio is able to have any of a third value and a fourth value more than the third value,
in a case where the second alternating-current power is more than the second threshold:
when the boost ratio has the third value, an amplitude of a harmonic for the alternating-current voltage due to switching of the switch is equal to or more than a predetermined threshold with respect to the voltage utilization ratio equal to or less than a first lower limit value more than 1, and the amplitude of the harmonic is less than the predetermined threshold with respect to the voltage utilization ratio more than the first lower limit value;
when the boost ratio has the fourth value, the amplitude of the harmonic is equal to or more than the predetermined threshold with respect to the voltage utilization ratio equal to or less than a second lower limit value higher than the first lower limit value, and the amplitude of the harmonic is less than the predetermined threshold with respect to the voltage utilization ratio more than the second lower limit value;
when the third value is equal to or more than the second lower limit value, the third value is adopted as the boost ratio when the voltage utilization ratio is more than the first lower limit value and less than the second lower limit value; and
when the third value is less than the second lower limit value, the third value is adopted as the boost ratio when the voltage utilization ratio is more than the first lower limit value and less than the third value.
8 . The method for controlling the power converter according to claim 7 , wherein when the third value is equal to or more than the second lower limit value, the fourth value is adopted as the boost ratio when the voltage utilization ratio is more than the second lower limit value.
9 . The method for controlling the power converter according to claim 3 , wherein when the second alternating-current power is more than the second threshold, a maximum value of the second duty is more than 1/√3 and equal to or less than 1.
10 . The method for controlling the power converter according to claim 9 , wherein
a boost ratio is a value obtained by dividing the first voltage by the peak value,
a voltage utilization ratio is a value obtained by dividing the equivalent direct-current voltage by the peak value,
the boost ratio is able to have any of a third value and a fourth value more than the third value,
in a case where the second alternating-current power is more than the second threshold:
when the boost ratio has the third value, an amplitude of a harmonic for the alternating-current voltage due to switching of the switch is equal to or more than a predetermined threshold with respect to the voltage utilization ratio within a first range more than 1, and the amplitude of the harmonic is less than the predetermined threshold with respect to the voltage utilization ratio outside the first range;
when the boost ratio has the fourth value, the amplitude of the harmonic is equal to or more than the predetermined threshold with respect to the voltage utilization ratio within a second range more than 1, and the amplitude of the harmonic is less than the predetermined threshold with respect to the voltage utilization ratio outside the second range; and
the fourth value is adopted as the boost ratio when the voltage utilization ratio is equal to or more than a lower limit of the first range and is less than a lower limit of the second range.
11 . The method for controlling the power converter according to claim 9 , wherein
a boost ratio is a value obtained by dividing the first voltage by the peak value,
a voltage utilization ratio is a value obtained by dividing the equivalent direct-current voltage by the peak value,
the boost ratio is able to have any of a third value and a fourth value more than the third value,
in a case where the second alternating-current power is more than the second threshold:
when the boost ratio has the third value, an amplitude of a harmonic for the alternating-current voltage due to switching of the switch is equal to or more than a predetermined threshold with respect to the voltage utilization ratio within a first range more than 1, and the amplitude of the harmonic is less than the predetermined threshold with respect to the voltage utilization ratio outside the first range;
when the boost ratio has the fourth value, the amplitude of the harmonic is equal to or more than the predetermined threshold with respect to the voltage utilization ratio within a second range more than 1, and the amplitude of the harmonic is less than the predetermined threshold with respect to the voltage utilization ratio outside the second range;
when the first duty has a fifth value and the boost ratio has the fourth value, the voltage utilization ratio has a lower limit of the first range, and
when the voltage utilization ratio is less than a lower limit of the first range, a value less than the fifth value is adopted as the first duty, and the third value is adopted as the boost ratio.
12 . The method for controlling the power converter according to claim 1 ,
wherein the booster includes a boost chopper, and
the method comprising causing the boost chopper to execute chopping of a current to be input to the boost chopper by using a frequency higher than a frequency of a carrier used for switching of the inverter.
13 . The method for controlling the power converter according to claim 12 ,
wherein the power converter further includes a filter having a cutoff frequency lower than the frequency of the carrier,
the method comprising inputting the alternating-current voltage to the converter via the filter.
14 . The method for controlling the power converter according to claim 12 ,
wherein the power converter further includes a filter having a cutoff frequency lower than the frequency of the carrier, and
the method comprising outputting the first instantaneous power from the converter via the filter.
15 . The method for controlling the power converter according to claim 1 ,
wherein the booster includes a boost chopper,
the method comprising causing the boost chopper to execute chopping of a current to be input to the boost chopper by using a frequency higher than a frequency at which the switch performs switching.
16 . The method for controlling the power converter according to claim 15 ,
wherein the power converter further includes a filter having a cutoff frequency lower than the frequency at which the switch performs switching,
the method comprising inputting the alternating-current voltage to the converter via the filter.
17 . The method for controlling the power converter according to claim 15 ,
wherein the power converter further includes a filter having a cutoff frequency lower than the frequency at which the switch performs switching,
the method comprising outputting the first instantaneous power from the converter via the filter.
18 . The method for controlling the power converter according to claim 1 , the method comprising,
by controlling the first duty, when the second alternating-current power is less than the second threshold:
adopting any one of;
performing control to alternately provide a non-conduction period in which the first duty is 0 and a conduction period in which the first duty is positive; and
performing another control in which a length of the non-conduction period is substantially 0.