ELECTRIC STORAGE SYSTEM

• US 20160254683A1
• Filed: 10/08/2014
• Published: 09/01/2016
• Est. Priority Date: 10/16/2013
• Status: Active Grant

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: MATSUMOTO, Junichi, OGURA, Takashi
• Granted Patent: US 10,044,199 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B60L 2240/547 Voltage
• CPC Class Codes: B60L 2240/549 Current
• CPC Class Codes: B60L 58/13 Maintaining the SoC within a determined range
• CPC Class Codes: B60L 58/15 Preventing overcharging
• CPC Class Codes: B60L 58/22 Balancing the charge of battery modules
• CPC Class Codes: H02J 2310/48 for electric vehicles [EV] or hybrid vehicles [HEV]
• CPC Class Codes: H02J 7/0014 Circuits for equalisation of charge between batteries
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits
• CPC Class Codes: H02J 7/007184 in response to battery voltage gradient
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries

Abstract

An electric storage system includes plural electric storage elements, a voltage detection circuit, a discharging circuit, and a controller. The controller is configured to: (a) control an operation of the discharging circuit on the basis of the voltage values detected by the voltage detecting circuit, (b) determine a first reference voltage value indicating a lowest voltage value from the voltage values of the plurality of electric storage elements, (c) discharge the electric storage element indicating the voltage value of which a voltage difference from the first reference voltage value is greater than a first threshold value, and (d) set the first threshold value to a smaller value as the first reference voltage value becomes lower.

Claims

1. An electric storage system comprising:

a plurality of electric storage elements that are connected in series, a slope of a voltage curve of the electric storage element at a lower-limit voltage value being greater than a slope of the voltage curve at another voltage value in a range of an upper-limit voltage value and the lower-limit voltage value in which charging and discharging of the electric storage element are allowed, the voltage curve being a curve indicating a relationship between a charging quantity and a voltage value in the electric storage element;

a voltage detecting circuit configured to detect the voltage values of each of the plurality of electric storage elements;

a discharging circuit configured to discharge each of the plurality of electric storage elements; and

a controller configured to;

(a) control an operation of the discharging circuit on the basis of the voltage values detected by the voltage detecting circuit;

(b) determine a first reference voltage value indicating a lowest voltage value from the voltage values of the plurality of electric storage elements;

(c) discharge the electric storage element indicating the voltage value of which a voltage difference from the first reference voltage value is greater than a first threshold value; and

(d) set the first threshold value to a smaller value as the first reference voltage value becomes lower.

2. The electric storage system according to claim 1, wherein

the controller sets the first threshold value to a smallest value when the first reference voltage value is the lower-limit voltage value, and the controller sets the first threshold value to a largest value when the first reference voltage value is the upper-limit voltage value.

3. The electric storage system according to claim 1, wherein

the controller is configured to:

(e) determine the first reference voltage value for each of a plurality of electric storage element groups, the electric storage element group including the plurality of electric storage elements connected in series, the plurality of electric storage element groups are connected in series;

(f) determine the electric storage element to be subjected to discharging control using the first reference voltage value and the first threshold value for each of the electric storage element groups;

(g) determine a non-discharge electric storage group including no electric storage element to be subjected to the discharging control;

(h) determine the electric storage element group including the electric storage element indicating a lowest voltage value and the other electric storage element groups on the basis of the voltage values of the electric storage elements included in the non-discharge electric storage groups when two or more non-discharge electric storage element groups are present;

(i) determine a second reference voltage value indicating a lowest voltage value from the voltage values of the electric storage elements included in the non-discharge electric storage groups when two or more non-discharge electric storage element groups are present;

(j) discharge the electric storage elements included in the other electric storage element groups when the voltage differences between the second reference voltage value and the voltage value of the electric storage elements included in the other electric storage element groups are greater than a second threshold value; and

(k) set the second threshold value to a smaller value as the second reference voltage value becomes higher.

4. The electric storage system according to claim 3, wherein

the controller is configured to:

(l) set the second threshold value to a largest value when the second reference voltage value is the lower-limit voltage value; and

(m) set the second threshold value to a smallest value when the second reference voltage value is the upper-limit voltage value.

5. The electric storage system according to claim 14, wherein

the controller is configured to:

(n) determine the first reference voltage value for each of a plurality of electric storage element groups including the plurality of electric storage elements connected in series, the plurality of electric storage element groups are connected in series;

(o) determine the electric storage element to be subjected to discharging control using the first reference voltage value and the first threshold value for each electric storage element group;

(p) determine a non-discharge electric storage group including no electric storage element to be subjected to the discharging control;

(q) estimate, when two or more non-discharge electric storage element groups are present, SOCs of the electric storage elements in the non-discharge electric storage element groups after the electric storage elements in the non-discharge electric storage element groups are charged on the basis of full charging capacities and current SOCs of the electric storage elements; and

(r) discharge the electric storage element in which a difference between the minimum value of the estimated SOCs of the electric storage elements and the estimated SOCs of the electric storage elements is greater than a third threshold value.

6. The electric storage system according to claim 1, further comprising:

a zener diode of which a cathode is connected to a positive electrode terminal of each electric storage element and an anode is connected to a negative electrode terminal of each electric storage element via a line connecting the corresponding electric storage element and the voltage detecting circuit, wherein

the controller is configured to determine whether a leakage current flows in the zener diode corresponding to one of the electric storage elements, when the voltage value of the one of the electric storage elements becomes lower than a lower limit value of a predetermined range and the voltage value of the electric storage element connected in series to the one of the electric storage elements indicating becomes higher than an upper limit value of the predetermined range, after the voltage values of the plurality of electric storage elements are adjusted to the predetermined range through the discharging control of the electric storage elements based on the first threshold value.