KR101934858B1 - A system for calculating the state of charge of a lfp battery for car and method thereof - Google Patents

Abstract

The present invention relates to a method of calculating a state of charge (SOC) of an LFP battery (LiFePO4 battery) for an automobile, which comprises a) a step of measuring a period in which a change in an open-circuit voltage (OCV) (B), and (c) a step of initializing the accumulated current data in a period in which the change in the open-circuit voltage (OCV) occurs in the step (a) and measuring the charged amount using the accumulated current data in the maintained period And the SOC (STATE OF CHARGE) is calculated with the accumulated current data in the stable section. As a result, an error can be prevented and the accurate state of charge can be measured. As a result, the life of the battery can be extended.

Description

Technical Field [0001] The present invention relates to a system and a method for calculating SOC of an automotive LFP battery,

TECHNICAL FIELD The present invention relates to a method of calculating a state of charge (SOC) of an LFP battery for a vehicle (LiFePO ₄ battery).

As the technology development and demand for mobile devices, electric vehicles and hybrid vehicles increase, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, they exhibit high energy density and operating potential, have a long cycle life, A lithium secondary battery having a low discharge rate is commercialized and widely used.

In recent years, there has been a growing interest in environmental issues, and as a result, electric vehicles (EVs) and hybrid electric vehicles (HEVs), which can replace fossil-fueled vehicles such as gasoline vehicles and diesel vehicles, And the like. Although a nickel metal hydride (Ni-MH) secondary battery is mainly used as a power source for such an electric vehicle (EV) and a hybrid electric vehicle (HEV), a lithium secondary battery having a high energy density, a high discharge voltage, Research is being actively carried out, and some are commercialized.

The lithium secondary battery has a structure in which a non-aqueous electrolyte containing a lithium salt is impregnated in an electrode assembly having a porous separator interposed between a positive electrode and a negative electrode coated with an active material on a current collector.

Lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium composite oxide and the like are used as the positive electrode active material of such a lithium secondary battery. Carbon materials are mainly used as the negative electrode active material, and silicon compounds, Use is also being considered.

In the production of automotive batteries requiring high output characteristics, the necessity of using a cathode material capable of supporting output at a low voltage band has arisen. Recently, a lithium iron phosphate secondary battery using lithium iron phosphate (LiFePO ₄ ) (LiFePO ₄ SECONDARY BATTERY) (hereinafter, generically referred to as an LFP battery).

The LFP battery (LiFePO ₄ BATTERY) has a lower operating voltage range than the conventional cathode active material (LiNiMnCoO ₂ ) or spinel manganese (LiMn ₂ O ₄ ), but has an advantage of stable operation characteristics.

Such an LFP battery (LiFePO ₄ BATTERY), like other lithium secondary batteries, can be charged and discharged by a battery management system (BMS) in order to prevent shortening of lifetime due to chemical change while repeating charge / Close management is required. This will be described with reference to Fig.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing voltage and current measured during charging and discharging of a conventional LFP battery. FIG.

Referring to FIG. 1, a conventional LFP battery (LiFePO ₄ BATTERY) has a voltage measured at the time of charging at 0 °, 25 ° and 50 °, a total current (see A), a voltage measured at the time of discharging, (A, a ') are generated at the beginning and the end of charging, respectively. That is, the LFP battery (LiFePO ₄ BATTERY) has sections t 1 and t 3 during which the voltage changes abruptly at the time of charging or discharging at a low temperature and a normal temperature.

Therefore, the conventional LFP battery (LiFePO ₄ BATTERY) calculates SOC (STATE OF CHARGE) for managing the charging and discharging in the BMS 100, predicts the charge amount and / or the discharge amount based on the SOC The charge / discharge is controlled. However, as described above, there is a period in which the voltage is abruptly changed at the time of charging and discharging, and accumulated error is accumulated.

In other words, since the LFP battery (LiFePO ₄ BATTERY) has a period in which the output voltage varies in a variety of ways, unlike other secondary batteries, when the conventional SOC calculation method is applied, the cumulative error of the accumulated current becomes large, The charging / discharging efficiency is deteriorated, and ultimately the life of the battery is shortened.

Korean Registered Patent No. 10-0669476 (2007.01.09) Korean Patent Laid-Open No. 10-2013-0074048 (Feb.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to solve the above-mentioned problems of the related art. It is an object of the present invention to reduce the cumulative error of an LFP battery (LiFePO ₄ BATTERY) mounted on an electric vehicle (EV), a hybrid vehicle And a method for calculating the SOC of an LFP battery for an automobile.

The present invention can achieve the following objects in order to achieve the above object.

The present invention includes an LFP battery pack (LiFePO ₄ BATTERY PACK) having a plurality of LFP battery cells (LiFePO ₄ BATTERY CELL) and a battery management system (BMS) for controlling charge and discharge of the LFP battery pack , non-LMS (BMS) is LFP battery pack and (LiFePO ₄ bATTERY PACK) voltage, sensors to detect current, at least one of the temperature and the resistance portion of, LFP battery pack (LiFePO ₄ bATTERY PACK) and the load, or LFP battery pack (LiFePO ₄ bATTERY PACK) and reception by measuring the SOC of the switching unit and the sensor unit detects signals for energizing or cut off the power line between the charger and, actuating the switch by using the measured SOC to LFP battery pack (LiFePO ₄ bATTERY PACK) And the control unit controls the charging and discharging of the battery. The control unit controls the charging unit such that the voltage sensed by the sensor unit is lowered in the first period t1, the second period in which the voltage is leveled and the second period t2, A third section t3 which is detected by the sensor section, And a current accumulation module for accumulating the voltage value and the current value accumulated in the storage unit when the first period t1 and the third period t3 are detected by the period detection module, And a calculation module for calculating an SOC (STATE OF CHARGE) by integrating a current value measured at a second section (t2) sensed by the section detection module with respect to time, 1 section t1 is a section up to the inflection point a where the open-circuit voltage OCV measured in the section of the calculated SOC 30% or less is maintained within the reference range, and the second section t2 is a section from the first section the open-circuit voltage of the SOC 80% or less is maintained within the reference range after the first period t1 and the third period t3 is the period during which the change of the open-circuit voltage OCV starts at the SOC 80% (A ') after the inflection point, and the number of sensor modules is the number of LFP battery packs 200 (LiFePO ₄ BATTERY PACK) The calculation module measures the total resistance of the LFP battery pack and the resistance value of each LFP battery cell through the resistance value of the resistance sensor to calculate the lifetime of the LFP battery pack. And an SOC calculation system for an LFP battery for an automobile.

delete

Therefore, the present invention resets this data in a section where the output voltage changes significantly in an LFP battery (LiFePO ₄ BATTERY) mounted on an electric car or a hybrid vehicle, and outputs SOC (STATE OF CHARGE) as the accumulated current data in the stable section It is possible to prevent an error and calculate a precise state of charge, thereby prolonging the service life of the battery.

1 is a graph showing SOC of a conventional LFP battery.
2 is a block diagram showing an SOC calculation system of an LFP battery for a vehicle according to the present invention.
3 is a block diagram showing the control unit of FIG.
4 is a flowchart showing a method of calculating the SOC of an LFP battery for a vehicle according to the present invention.
5 is a graph showing an embodiment of the present invention.

Hereinafter, embodiments and examples of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention.

However, the present invention may be embodied in many different forms and is not limited to the embodiments and examples described herein, and the terms and words used in the specification and claims are not to be construed in a conventional or dictionary sense, It should be construed as meaning and concept consistent with the technical idea of.

Throughout the specification, when an element is referred to as "comprising ", it means that it can include other elements as well, without excluding other elements unless specifically stated otherwise.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of an SOC calculation system and method of an LFP battery for a vehicle according to the present invention will be described in detail with reference to the accompanying drawings.

2 is a block diagram showing an SOC calculation system of an LFP battery for a vehicle according to the present invention.

2, the present invention relates to an LFP battery pack 200 (LiFePO ₄ BATTERY PACK) in which a plurality of LFP secondary battery cells (LiFePO ₄ SECONDARY BATTERY CELL, hereinafter collectively referred to as LFP battery cells) are combined, And a battery management system (BMS) 100 for controlling the charging and discharging of the pack 200.

The BMS 100 includes a sensor unit 120 for sensing the temperature and voltage / current of the battery pack 200, a switching unit 130 for shutting off or energizing the power line connected to the load in the LFP battery pack 200, A controller 110 for receiving the sensing signal of the sensor unit 120 and controlling the charging and discharging by selectively controlling the switching unit 130 and a storage unit for accumulating and storing the accumulated current data of the LFP battery pack 200. [ (140).

Sensor unit 120 is, for example, LFP battery pack 200 voltage for sensing the voltage of the (LiFePO ₄ BATTERY PACK) temperature sensor and, LFP battery pack 200 (LiFePO ₄ BATTERY PACK) for sensing a temperature of a sensor and, LFP battery (LiFePO ₄ bATTERY PACK) at least one of a resistance sensor for sensing the resistance of the current sensor and the LFP cells (LiFePO ₄ bATTERY PACK) for sensing the current of the. Therefore, the sensor unit 120 senses the temperature, voltage, current, and / or resistance of the LFP battery (LiFePO ₄ battery pack) and outputs the sensed temperature to the controller 110.

Here, the voltage is, for example, an open-circuit voltage (OCV) measured in a state in which the starter is turned off in the case of, for example, a mild hybrid secondary battery pack 200 mounted on a hybrid vehicle (HEV) Or a discharge voltage.

The control unit 110 receives the sensing signal of the sensor unit 120 and cumulatively stores the accumulated current data of the LFP battery pack 200 (LiFePO ₄ BATTERY PACK) in the storage unit 140, The charged amount is measured by the voltage. The STATE OF CHARGE of the LFP battery pack 200 (LiFePO ₄ battery pack) is calculated and the LFP battery pack 200 calculates the charging rate and the discharge rate to control the switching unit 130. The detailed configuration of the control unit 110 will be described with reference to FIG.

3 is a block diagram showing the detailed configuration of the control unit 110. As shown in FIG.

3, the control unit 110 includes an interval detection module 111 for detecting a change interval of the open-circuit voltage OCV, a current integration module 112 for cumulatively integrating the current values per unit time sensed by the sensor unit 120, A reset module 113 for resetting accumulated current data accumulated in a period in which a change in the open-circuit voltage OCV sensed by the section detection module 111 exceeds a set reference range? V, And a calculation module 114 for measuring the charge amount and / or the charge state (STATE OF CHARGE) by summing the current data and the open-circuit voltage (OCV).

The interval detection module 111 detects a change in the open-circuit voltage (OCV) of the LFP battery pack 200 according to the interval. For example, the open-circuit voltage (OCV) is upward and / or downward at 30% and 80% of SOC, respectively, and remains flat within a certain range. Accordingly, the section detection module 111 detects a point where the open-circuit voltage (OCV) is upward or downward and a flattening section, respectively.

The current integration module 112 accumulates the accumulated current data, which is the current value per unit time of the LFP battery pack 200, and stores the accumulated current data in the storage unit 140. In addition, the current integrating module 112 may store the voltage value (open-circuit voltage (OCV)) sensed by the sensor unit 120.

The reset module 113 initializes the accumulated current data accumulated during the corresponding period (time) when detecting the upward or downward sections t1 and t3 (see FIG. 5) in the section detection module 111. FIG. That is, the reset module 113 initializes the integrated current data measured in the section where the voltage change is large, so that only the integrated current data sensed in the flattening section is stored in the storage section 140.

The calculation module 114 checks the accumulated current data and the open-circuit voltage (OCV) stored in the storage unit 140 and measures the charge amount and / or the SOC. For example, the computing module 114 sets the voltage of the battery to the open-circuit voltage (OCV) in a known voltage measuring method, and compares it with the integrated current data and the temperature. Such a method of calculating the SOC using the integrated current data and the open-circuit voltage (OCV) is a well-known technique, and a description thereof will be omitted.

Alternatively, the calculation module 114 may apply a current integration method that measures the current of the LFP battery pack 200 and integrates the current with respect to time to calculate the SOC.

Here, the calculation module 114 can calculate the service life through the resistance of the LFP battery pack 200 sensed by the sensor unit 120 (for example, a resistance sensor).

More preferably, the resistance sensor is connected to each of the LFP battery cells of the LFP battery pack 200 (LiFePO ₄ battery pack), and the resistance is measured to determine the total resistance of the entire LFP battery (LiFePO ₄ battery pack) So that the resistance value of each battery cell can be measured. Therefore, the calculation module 114 can predict both the lifetime of the LFP battery pack (LiFePO ₄ battery pack) and the lifetime of each battery cell.

Hereinafter, an SOC calculation method of an LFP battery for an automobile including the above-described configuration will be described with reference to the accompanying drawings.

FIG. 4 is a flowchart showing a charging state calculation method of an LFP battery according to the present invention, and FIG. 5 is a graph showing an embodiment of the present invention.

Referring to FIG. 4, the present invention includes a step S110 of calculating an SOC by measuring an open-circuit voltage (OCV), and a step S120 of determining whether a range where the open-circuit voltage OCV rises or falls corresponds to a set reference range? And a step S30 of initializing the integrated current data of the section in which the reference range? V set in the open-circuit voltage OCV is exceeded, and a step S130 of initializing the integrated current data in the flattened section not exceeding the reference range? V set in the open- Accumulating accumulated current data, accumulating and storing the accumulated current data, correcting the SOC using the cumulative integrated current data and the open-circuit voltage (OCV), and controlling the charging or discharging through the corrected SOC .

In step S110, the controller 110 senses, accumulates, and stores the open-circuit voltage (OCV) and the current per unit time through the sensing signal of the sensor unit 120. [ Here, the current integrating module 112 of the control unit 110 stores the open-circuit voltage (OCV) and the accumulated current data in the storage unit 140. The interval detection module 111 of the control unit 110 receives the open-circuit voltage (OCV) detection signal of the sensor unit 120 in real time and confirms the inflection point (a, a ') of the upward or downward section. At this time, the calculation module 114 calculates the SOC through the open-circuit voltage (OCV) received in real time.

In step S120, the interval detection module 111 checks whether the change of the open-circuit voltage OCV exceeds the set reference range? V. For example, as shown in the graph of FIG. 5, the open-circuit voltage (OCV) of the LFP battery pack 200 is set to a value higher than the reference range set in the first section t1 from the point where the SOC is 0 to 30% And is outputted as a curve of the third section t3 which is raised from the inflection point a 'corresponding to 80% while maintaining the second section t2 flattened from the inflection point a.

Here, the reference range [Delta] V defines the range of the voltage change level and can be set to, for example, ± 0.1 to 0.3V.

Therefore, the section detection module 111 detects the first section t1 and the third section t3 as shown in the above graph, and detects the second section t2 between the inflection points a and a 'within the reference range V And outputs a detection signal for each section to the reset module 113 and the arithmetic module 114.

The step S 130 is a step of initializing the integrated current data of the corresponding interval when the detection module 113 receives a detection signal having a larger variation than the reference range V. The reset module 113 compares the accumulated current I3 of the first section t1 before the inflection point a and the third section t3 after the inflection point a 'except for the second section t2 detected by the section detection module 111, Initialize the data.

The step S140 accumulates the accumulated current data of the second section t2 in which the open-circuit voltage OCV is kept constant in the current accumulation module 112 in the storage section 140 and stores the accumulated current data. The integrated current data of the second section t2 is sensed by the sensor section 120 and output to the control section 110. The control section 110 stores the accumulated current data in the storage section 140 in the current integration module 112. [

In step S150, the calculation module 114 corrects the SOC (STATE OF CHARGE) using the accumulated current data accumulated in step S140 and the open-circuit voltage (OCV). The calculated SOC includes the first interval t1 and / or the third interval t3 in which the change of the open-circuit voltage OCV is large, so that the error can be accumulated. Therefore, the present invention measures the SOC by using the integrated current data and the open-circuit voltage (OCV) of the second section t2 in which the open-circuit voltage (OCV) is maintained within the constant reference range? V and corrects the SOC in step S110 do.

In step S160, charge / discharge of the LFP battery pack 200 is controlled using the SOC corrected in step S150. That is, the control unit 110 controls the switching unit 130 to selectively energize or cut off the power line connected to the LFP battery pack 200 and the load (not shown) and the charger (not shown).

As described above, the present invention can accurately measure the SOC because the accumulated error can be initialized by measuring the SOC in a stable section in which the voltage is not changed in consideration of the electrical characteristics of the LFP battery.

Therefore, the LFP battery pack to which the present invention is applied can accurately control the charge / discharge of the SOC, which can prolong the lifetime of the LFP battery.

It will be apparent to those skilled in the art that various modifications and equivalent arrangements may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

It is therefore to be understood that the invention is not limited to the form set forth in the foregoing description. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims. It is also to be understood that the invention includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

100: BMS 110: Control unit
111: interval detection module 112: current integration module
113: reset module 114: operation module
120: Sensor unit 130:
140: storage unit 200: LFP battery pack

Claims (6)

An LFP battery pack (LiFePO ₄ BATTERY PACK) having a plurality of LFP battery cells (LiFePO ₄ BATTERY CELL);
And a battery management system (BMS) for controlling charging and discharging of the LFP battery pack,
BMS (BMS)
A sensor unit for sensing at least one of voltage, current, temperature and resistance of the LFP battery pack (LiFePO ₄ battery pack);
A switching unit for energizing or shutting off the power supply line between the LFP battery pack (LiFePO ₄ BATTERY PACK) and the load or between the LFP battery pack (LiFePO ₄ BATTERY PACK) and the charger; And
And a controller for controlling the charge / discharge of the LFP battery pack (LiFePO ₄ BATTERY PACK) by measuring the SOC by receiving the sensing signal of the sensor unit and driving the switching unit using the measured SOC,
The control unit
A period sensing module for sensing a first section t1 in which the voltage sensed by the sensor section is downward, a second section in which the voltage is flattened, and a third section t3 in which the voltage is raised after the second section t2, ;
A current integrating module for cumulatively storing the voltage value and the current value sensed by the sensor unit in a storage unit;
A reset module for initializing a voltage value and a current value of a corresponding section stored in the storage section when at least one of the first section t1 and the third section t3 is sensed by the section detection module;
And a calculation module for calculating an SOC (STATE OF CHARGE) by integrating the current value measured in the second section (t2) detected by the section detection module with respect to time,
The first section t1 is a section up to the inflection point (a) at which the open-circuit voltage (OCV) measured in the section of the calculated SOC 30% or less is maintained within the reference range,
The second section t2 is a section in which the open-circuit voltage of SOC 80% or less is maintained within the reference range from the first section t1,
The third period t3 is a period after the inflection point a 'at which the change of the open-circuit voltage OCV starts at SOC 80% or more after the second period t2,
The sensor module further includes a resistance sensor that is connected to each of the LFP battery cells of the LFP battery pack 200 (LiFePO ₄ battery pack) to measure resistance,
Wherein the calculation module measures the total resistance of the LFP battery pack and the resistance value of each LFP battery cell through the resistance value of the resistance sensor to calculate the lifetime of the LFP battery pack.
The SOC calculation system for an automotive LFP battery according to claim 1, wherein the current value is integrated current data that is a current value accumulated per hour.

delete A method of calculating the SOC of an LFP battery for automobiles of BMS (Battery Management System), which controls charge / discharge of an LFP battery pack (LiFePO ₄ BATTERY PACK) having a plurality of LFP battery cells (LiFePO ₄ battery cells)
a) calculating an SOC (STATE OF CHARGE) using open-circuit voltage (OCV) and accumulated current data;
b) detecting whether the change in the open-circuit voltage (OCV) is within a set range;
c) calculating the SOC (STATE OF CHARGE) using the accumulated current data and the open-circuit voltage (OCV) measured in the interval in which the open-circuit voltage (OCV) is maintained within the reference range, and correcting the SOC calculated in the step a) Comprising:
b) The step
the first section t1 from the first section t1 to the inflection point a where the open-circuit voltage OCV measured in the section of SOC 30% or less calculated in step a) starts to be maintained within the reference range, A second period t2 during which the open-circuit voltage of SOC 80% or less is maintained within the reference range and an inflection point a 'at which the change of the OCV starts at SOC 80% or more after the second period t2, And detects the third period t3 from then on,
The step c) initializes the accumulated current data measured in the first period t1 and the third period t3, corrects the SOC as the cubic current data in the second period t2,
The method according to any one of the above a) to c)
Calculating the total resistance value of the LFP battery pack and the resistance value of the individual LFP battery cell to calculate the lifetime of the LFP battery pack and the life of the individual LFP battery cell.




delete delete

Images