Bi-capacitor design for fast state of charge equalization

A state of charge (SOC) balancing system, comprising:

• a first battery;
• a second battery;
• a first capacitor;
• a second capacitor;
• a state of charge module configured to determine first and second states of charge of the first and second batteries, respectively;
• and
• a switching module configured to selectively, when the first SOC of the first battery is greater than the second SOC of the second battery:
• (i) electrically connect the first and second capacitors in parallel;
• (ii) after (i), electrically connect the first battery to the first and second capacitors while the first and second capacitors are electrically connected in parallel;
• (iii) after (ii), electrically disconnect the first battery from the first and second capacitors;
• (iv) after (iii), electrically connect the first and second capacitors in series;
• (v) after (iv), electrically connect the second battery to the first and second capacitors while the first and second capacitors are electrically connected in series;
• and
• (vi) after (v), electrically disconnect the second battery from the first and second capacitors.

A state of charge (SOC) balancing method, comprising:

• determining first and second states of charge of first and second batteries, respectively,
• the first battery having a first positive terminal and a first negative terminal;
• the second battery having a second positive terminal and a second negative terminal and connected in series with the first battery;
• selectively, when the first SOC of the first battery is greater than the second SOC of the second battery:
• (i) close fifth and seventh switches, close first and third switches, and open second, fourth, and sixth switches,
• where:
• the first switch is configured to connect and disconnect the first positive terminal to and from a first node;
• the second switch is configured to connect and disconnect the second positive terminal to and from the first node;
• the third switch is configured to connect and disconnect the first negative terminal to and from a second node;
• the fourth switch is configured to connect and disconnect the second negative terminal to and from the second node;
• a first capacitor includes a first end connected to the first node and a second end connected to a third node;
• the fifth switch is configured to connect and disconnect the first node to and from a fourth node;
• the sixth switch is configured to connect and disconnect the fourth node to and from the third node;
• the seventh switch is configured to connect and disconnect the third node to and from the second node;
• and
• a second capacitor includes a first end connected the fourth node and a second end connected to the second node;
• (ii) after (i), open the fifth, seventh, first, and third switches;
• (iii) after (ii), close the sixth switch, close the second and fourth switches, and open the first, third, fifth, and seventh switches;
• and
• (iv) after (iii), open the first, second, third, fourth, fifth, sixth, and seventh switches.