Cell balance control device that prevents temperature increase of bypass circuit substrate

1. A cell balance control device comprising:

a plurality of bypass circuits, the bypass circuit comprising a direct circuit with a bypass resistance and a switching element, the plurality of bypass circuits being connected in parallel to each of a plurality of cells comprised in a battery;

a cell voltage detection unit detecting a cell voltage of each of the plurality of cells;

a temperature detection unit detecting a temperature of a substrate on which the bypass circuit is mounted; and

a control unit controlling and computing a duty ratio of the switching element based on a value detected by the temperature detection unit and a cell voltage of a discharge-needed cell obtained by the cell voltage detection unit.

2. The cell balance control device according to claim 1 , wherein the control unit comprises a discharge predetermined electric power calculation unit, a discharge-needed cell discharge electric power calculation unit, and a duty control unit, wherein:

based on the value detected by the temperature detection unit, the discharge predetermined electric power calculation unit computes a discharge predetermined electric power necessary for increasing the temperature of the substrate to a maximum allowable temperature;

based on the cell voltage of the discharge-needed cell, the discharge-needed cell discharge electric power calculation unit computes a discharge-needed cell discharge electric power consumed by a bypass circuit connected to the discharge-needed cell; and

the duty control unit computes a duty ratio based on the discharge predetermined electric power and the discharge-needed cell discharge electric power, and uses this duty ratio to perform a duty control of the switching element of the bypass circuit connected to the discharge-needed cell.

3. The cell balance control device according to claim 2 , wherein the discharge predetermined electric power calculation unit computes the discharge predetermined electric power based on a following equation (1)

W 1=( T max− Ta )/ Rth   (1), wherein

W 1 represents the discharge predetermined electric power, Tmax represents the maximum allowable temperature, Ta represents the temperature of the substrate, and Rth represents a thermal resistance of the substrate.

4. The cell balance control device according to claim 2 , wherein the discharge-needed cell discharge electric power calculation unit computes the discharge-needed cell discharge electric power W 2 based on a following equation (2)

W 2=Σ( Vi 2 /r )  (2), wherein

W 2 represents the discharge-needed cell discharge electric power, Vi represents the cell voltage of the discharge-needed cell, i represents an identification number of the discharge-needed cell, and r represents a sum of the resistances of the plurality of bypass circuits.

5. The cell balance control device according to claim 2 , wherein the duty control unit computes the duty ratio based on a following equation (3)

Dy =( W 1 /W 2)×100  (3), wherein

Dy represents the duty ratio, W 1 represents the discharge predetermined electric power, and W 2 represents the discharge-needed cell discharge electric power.

6. The cell balance control device according to claim 1 , wherein the control unit transmits to an upper level control device, each of the cell voltage of the plurality of cells obtained by the cell voltage detection unit, and receives from the upper level control device, an identification result of the discharge-needed cell.