Inverter control for restraining current flowing into DC capacitor
A power conversion apparatus includes a rectification and boost unit that rectifies a first alternating-current power supplied from a commercial power supply and boosts voltage of the first alternating-current power; a capacitor connected to output terminals of the rectification and boost unit; an inverter that is connected across the capacitor, converts power output from the rectification and boost unit and the capacitor into a second alternating-current power, and outputs the second alternating-current power to a load including a motor; and a control unit that performs operation control on the rectification and boost unit, and performs operation control on the inverter to cause the second alternating-current power that includes a pulsation based on a pulsation of power that flows into the capacitor from the rectification and boost unit to be output from the inverter to the load, to restrain a current that flows into the capacitor.
1 . A power conversion apparatus comprising:
a rectification and boost unit rectifying a first alternating-current power supplied from a commercial power supply and boosting a voltage of the first alternating-current power;
a capacitor connected to output terminals of the rectification and boost unit;
an inverter that is connected across the capacitor, converts power output from the rectification and boost unit and the capacitor into a second alternating-current power, and outputs the second alternating-current power to a load including a motor;
a voltage and current detection unit provided between the commercial power supply and the rectification and boost unit, and detecting a voltage value and a current value of the first alternating-current power supplied from the commercial power supply;
a voltage detection unit provided between the rectification and boost unit and the capacitor, and detecting a voltage value of power output from the rectification and boost unit;
a current detection unit provided between the inverter and the load, and detecting a current value of the second alternating-current power output from the inverter; and
a control unit configured to obtain, as detection values, the voltage value and the current value of the first alternating-current power from the voltage and current detection unit, the voltage value of the power output from the rectification and boost unit from the voltage detection unit, and the current value of the second alternating-current power from the current detection unit, perform operation control on the rectification and boost unit on the basis of the detection values, and perform operation control only on the inverter on the basis of the detection values to cause the second alternating-current power that includes a pulsation to be output from the inverter to the load such that a current on which pulsating current whose main component is a frequency component of a current flowing from the rectification and boost unit is superimposed flows into the inverter, to restrain a current that flows into the capacitor, the pulsation being based on a pulsation of power flowing into the capacitor from the rectification and boost unit,
wherein a maximum value of voltage ripple generated across the capacitor is less than twice a minimum value of the voltage ripple.
2 . The power conversion apparatus according to claim 1 , wherein
the control unit performs power factor improvement control on the first alternating-current power supplied from the commercial power supply and average voltage control for the capacitor through operation control of the rectification and boost unit.
3 . The power conversion apparatus according to claim 1 , wherein
the control unit performs operation control on the inverter to cause a pulsation included in the second alternating-current power that is output from the inverter to become smaller than a pulsation of power that is output from the rectification and boost unit.
4 . The power conversion apparatus according to claim 1 , wherein
the control unit performs amplitude and phase control on a pulsation included in the second alternating-current power that is output from the inverter to cause voltage ripple generated across the capacitor to be smaller than voltage ripple that is generated across the capacitor if the second alternating-current power that is output from the inverter does not include a pulsation based on a pulsation of power that flows into the capacitor.
5 . The power conversion apparatus according to claim 1 , wherein
the control unit performs amplitude and phase control on a pulsation included in the second alternating-current power that is output from the inverter to cause current ripple that flows into and out of the capacitor to be smaller than current ripple that is generated through the capacitor if the second alternating-current power that is output from the inverter does not include a pulsation based on a pulsation of power that flows into the capacitor.
6 . The power conversion apparatus according to claim 1 , wherein
the rectification and boost unit includes
a rectification unit including a plurality of rectifier elements, and
a boost unit including a rectifier element and a switching element that is turned on and off under control of the control unit, and
the rectification unit and the boost unit are connected in series or parallel.
7 . The power conversion apparatus according to claim 1 , wherein
the rectification and boost unit includes
a plurality of switching elements that are turned on and off under control of the control unit, and
a plurality of rectifier elements connected in parallel with the plurality of switching elements, respectively.
8 . The power conversion apparatus according to claim 1 , wherein
the control unit performs operation control further on the rectification and boost unit to cause power including a variable frequency component among pulsations included in the second alternating-current power to be output from the rectification and boost unit, the variable frequency component being other than a frequency component that is double a frequency of the first alternating-current power if the first alternating-current power is single-phase or six times a frequency of the first alternating-current power if the first alternating-current power is three-phase.
9 . The power conversion apparatus according to claim 8 , wherein
the control unit controls the variable frequency component with a command value for the commercial power supply.
10 . The power conversion apparatus according to claim 8 , wherein
the variable frequency component is controlled by the control unit to be prevented from being up to a 40th order component that is an integer multiple of a frequency of the first alternating-current power or to be less than or equal to a specified value.
11 . The power conversion apparatus according to claim 1 , wherein
the capacitor is an electrolytic capacitor or a film capacitor.
12 . The power conversion apparatus according to claim 1 , wherein
the rectification and boost unit performs full-wave rectification, and a voltage generated across the capacitor assumes a shape that is not a full-wave rectified waveform of the commercial power supply.
13 . A motor drive apparatus comprising the power conversion apparatus according to claim 1 .
14 . A refrigeration cycle apparatus comprising the power conversion apparatus according to claim 1 .