US 12,413,156 B2
Capacitor balancing control in an HVDC MMC
Shuhei Fujiwara, Tokyo (JP); Yoshiyuki Kono, Tokyo (JP); Ryosuke Uda, Tokyo (JP); Takuya Kajiyama, Tokyo (JP); Toshiyuki Fujii, Tokyo (JP); and Shigeo Hayashi, Tokyo (JP)
Assigned to Mitsubishi Electric Corporation, Tokyo (JP)
Appl. No. 17/919,917
Filed by Mitsubishi Electric Corporation, Tokyo (JP)
PCT Filed Jun. 17, 2020, PCT No. PCT/JP2020/023806
§ 371(c)(1), (2) Date Oct. 19, 2022,
PCT Pub. No. WO2021/255865, PCT Pub. Date Dec. 23, 2021.
Prior Publication US 2023/0163694 A1, May 25, 2023
Int. Cl. H02M 7/483 (2007.01)
CPC H02M 7/4835 (2021.05) [H02M 7/4833 (2021.05)] 11 Claims
OG exemplary drawing
 
1. A power conversion device comprising:
a power converter including at least one arm having a plurality of converter cells connected to each other in cascade,
each of the converter cells including:
a first input/output terminal on a high potential side;
a second input/output terminal on a low potential side;
a plurality of switching elements;
a power storage element having a positive electrode terminal and a negative electrode terminal, holding a positive voltage between the positive and negative electrode terminals, and electrically connected to the first input/output terminal and the second input/output terminal through the switching elements; and
a voltage detector to detect a voltage of the power storage element; and
a control device to perform phase shift pulse width control for the converter cells included in the at least one arm, wherein
the control device calculates an evaluation value representing a degree of variations in positive voltage of the power storage elements in the converter cells included in the at least one arm, and when the evaluation value exceeds a threshold value, performs phase shift pulse width control for at least one of the converter cells such that at least one of the following is implemented:
(i) when current in a first direction that is a direction from the first input/output terminal to the second input/output terminal flows through at least one first converter cell with a positive voltage of the power storage element greater than a mean value, reducing a time for a positive voltage output caused by a first switching state of the switching elements in which the positive electrode terminal of the power storage element is connected to the first input/output terminal and the negative electrode terminal of the power storage element is connected to the second input/output terminal;
(ii) when current in a second direction opposite to the first direction flows through the first converter cell, increasing a time for the positive voltage output caused by the first switching state;
(iii) when current in the first direction flows through at least one second converter cell with a positive voltage of the power storage element smaller than a mean value, increasing a time for the positive voltage output caused by the first switching state; or
(iv) when current in the second direction flows through the second converter cell, reducing a time for the positive voltage output caused by the first switching state.