Patent ID: 11881785
Assignee: MITSUBISHI ELECTRIC CORPORATION
Field: Electrical machinery, apparatus, energy (Electrical engineering)
Classification: CPC H  Y | IPC H

Claim 12:
13. A power conversion device including a first DC terminal and a second DC terminal, the power conversion device comprising:
a transformer including a first winding and a second winding that are magnetically coupled;
a first bridge circuit connected between the first DC terminal and a first AC terminal connected to the first winding, the first bridge circuit executing power conversion between a first DC voltage of the first DC terminal and a first AC voltage of the first AC terminal;
a second bridge circuit connected between the second DC terminal and a second AC terminal connected to the second winding, the second bridge circuit executing power conversion between a second DC voltage of the second DC terminal and a second AC voltage of the second AC terminal,
each of the first and second bridge circuits including a plurality of switching legs connected in parallel,
each of the plurality of switching legs including:
a positive-side switching element and a negative-side switching element connected in series; and
a snubber capacitor connected in parallel to each of the positive-side switching element and the negative-side switching element; and
a control circuit to control on and off of each of the positive-side switching elements and each of the negative-side switching elements in the first and second bridge circuits, wherein

the control circuit alternately turns on and off the positive-side switching element and the negative-side switching element after a dead time having a predetermined length is provided in each of the switching legs,
the power conversion device has a first operation mode in which power transmission is executed between the first DC terminal and the second DC terminal,
in the first operation mode, the control circuit controls on and off of each of the positive-side switching elements and each of the negative-side switching elements of the first and second bridge circuits so that
a first phase difference between switching phases of the first bridge circuit and the second bridge circuit is provided in order to control transmission power,
a zero voltage period is provided in one of the first AC voltage and the second AC voltage, while the zero voltage period is not provided in the other of the first AC voltage and the second AC voltage,

in the first operation mode, a length of the zero voltage period is determined such that charging and discharging of the snubber capacitor are completed during the dead time in each of the switching legs of one of the first and second bridge circuits that outputs the other of the first AC voltage and the second AC voltage, and
wherein, in the first operation mode, the control circuit obtains a second current value completing the charging and discharging of the snubber capacitor during the dead time as a zero volt switching current value, using the dead time, a capacitance value of the snubber capacitor, and a converted value of the second DC voltage on the side of the first winding or the first DC voltage, and sets the length of the zero voltage period in accordance with a predetermined first arithmetic expression including the zero volt switching current value, switching frequency of the positive-side switching element and the negative-side switching element, the first DC voltage, a converted value of the second DC voltage on the side of the first winding, and an inductance value of an inductance element between the transformer and the first bridge circuit or the second bridge circuit.