Energy transfer circuit and power storage system

1. An energy transfer circuit comprising:

an inductor;

a cell selection circuit provided between the inductor and n cells connected in series, where n is an integer of two or more, the cell selection circuit being configured to electrically connect both ends of any cell of the n cells to both ends of the inductor;

a clamp switch for forming a closed loop including the inductor in a state where the cell selection circuit does not select any cell; and

a controller that controls the cell selection circuit and the clamp switch,

wherein the controller is configured to:

cause the cell selection circuit to electrically connect both ends of a cell to be discharged among the n cells to both ends of the inductor for a predetermined time,

cause the cell selection circuit to electrically disconnect the n cells from the inductor, and turn on the clamp switch, and

turn off the clamp switch, and cause the cell selection circuit to electrically connect both ends of a cell to be charged among the n cells to both ends of the inductor for a predetermined time, and

the cell selection circuit includes:

a first wiring connected to one end of the inductor;

a second wiring connected to another end of the inductor;

(n+1) first wiring side switches each connected between the first wiring and a corresponding one of nodes of the n cells connected in series; and

(n+1) second wiring side switches connected each between the second wiring and a corresponding one of nodes of the n cells connected in series.

2. The energy transfer circuit according to claim 1 , wherein n is an integer of five or more.

3. The energy transfer circuit according to claim 1 , further comprising a voltage detector that detects a voltage of each of the n cells,

wherein the controller is configured to execute equalization processing among the n cells based on the voltages of the n cells detected by the voltage detector.

4. The energy transfer circuit according to claim 3 , wherein the controller is configured to determine a target voltage or a target capacity of the n cells based on the voltages of the n cells detected by the voltage detector, determine a cell having a voltage or a capacity higher than the target voltage or the target capacity as a cell to be discharged, and determine a cell having a voltage or a capacity lower than the target voltage or the target capacity as a cell to be charged.

5. A power storage system, comprising:

the energy transfer circuit according to claim 1 ; and

the n cells, where n is an integer of two or more, connected in series.

6. An energy transfer circuit comprising:

an energy holding circuit including:

an inductor; and

four clamp switches that are fully bridge-connected;

a cell selection circuit provided between the energy holding circuit and n cells connected in series, where n is an integer of two or more, the cell selection circuit being configured to electrically connecting both ends of any cell of the n cells to both ends of the energy holding circuit;

and

a controller configured to cause the cell selection circuit and the four clamp switches, wherein:

the four clamp switches form a closed loop including the inductor in a state where the cell selection circuit does not select any cell,

the cell selection circuit includes:

a first wiring connected to one end of the energy holding circuit,

a second wiring connected to another end of the energy holding circuit,

(n+1) first wiring side switches each connected between the first wiring and a corresponding one of nodes of the n cells connected in series, and

(n+1) second wiring side switches each connected between the second wiring and a corresponding one of nodes of the n cells connected in series,

among the four clamp switches, a first arm having a first clamp switch and a second clamp switch connected in series and a second arm having a third clamp switch and a fourth clamp switch connected in series are connected in parallel between the first wiring and the second wiring, and

the inductor is connected between a node between the first clamp switch and the second clamp switch and a node between the third clamp switch and the fourth clamp switch.

7. The energy transfer circuit according to claim 6 , wherein

the controller is configured to control, in this order,

a first state for controlling a corresponding one of the first wiring side switches and a corresponding one of the at least one second wiring side switch connected to the nodes on both sides of a discharge cell to be discharged among the n cells to an on state, and the first clamp switch and the fourth clamp switch or the second clamp switch and the third clamp switch to an on state,

a second state for controlling the corresponding one of the first wiring side switch and the corresponding one of the at least one second wiring side switch connected to the nodes on both sides of the discharge cell to an off state, and the second clamp switch and the fourth clamp switch or the first clamp switch and the third clamp switch to an on state, and

a third state for controlling the corresponding one of the first wiring side switch and the corresponding one of the at least one second wiring side switch connected to the nodes on both sides of a charging cell to be charged among the n cells to an on state, and the first clamp switch and the fourth clamp switch, or the second clamp switch and the third clamp switch to an on state to allow a current to flow through the charging cell.

8. The energy transfer circuit according to claim 6 , wherein

each of the plurality of first wiring side switches includes two switching elements each having a body diode connected in series in opposite directions, and

each of the at least one second wiring side switch includes two switching elements each having a body diode connected in series in opposite directions.

9. The energy transfer circuit according to claim 6 , wherein each of the four clamp switches includes two switching elements each having a body diode connected in series in opposite directions.