at least two capacitors, and

at least one power unit group, wherein,

the at least one power unit group each comprises one or more power units;

the capacitors are connected in series and parallel to form a capacitor head terminal, a capacitor end terminal and a capacitor midpoint, wherein capacitance between the capacitor midpoint and the capacitor head terminal is the same as capacitance between the capacitor midpoint and the capacitor end terminal; and

positive poles of direct current (DC) sides of the power units are equidistantly connected with the capacitor head terminal, negative poles of the DC sides of the power units are equidistantly connected with the capacitor end terminal, and midpoints of the DC sides of the power units are equidistantly connected with the capacitor midpoint.