阅读说明：本技术 一种电动汽车动力电池soc估算方法及装置 (SOC estimation method and device for power battery of electric vehicle ) 是由 楚金甫 关炀 李毅拓 陈西山 李洪超 冯利平 崔云飞 于 2018-07-03 设计创作，主要内容包括：本发明涉及一种电动汽车动力电池SOC估算方法及装置,在动力电池进行充电或放电时,获取该动力电池初始时刻的荷电状态；计算得到从初始时刻到当前时刻的动力电池的容量变化量；以上次充满电或者放完电情况下计算得到的动力电池的实际最大容量作为该动力电池的最大容量；根据所述该动力电池初始时刻的荷电状态、容量变化量和最大容量,得到该动力电池当前时刻的荷电状态。本发明在计算动力电池SOC时,不再使用标称容量来代替最大容量,而是使用上次充满电或者放完电时计算得到的SOC的实际最大容量来代替该动力电池的最大容量,使用该值将电池老化对电池容量的影响考虑在内,使得对动力电池SOC的估算较为准确。(The invention relates to a method and a device for estimating the SOC of a power battery of an electric automobile, which are used for acquiring the charge state of the power battery at the initial moment when the power battery is charged or discharged; calculating to obtain the capacity variation of the power battery from the initial moment to the current moment; taking the actual maximum capacity of the power battery obtained by calculation under the condition of last full charge or discharge as the maximum capacity of the power battery; and obtaining the current charge state of the power battery according to the charge state, the capacity variation and the maximum capacity of the power battery at the initial moment. When the SOC of the power battery is calculated, the nominal capacity is not used for replacing the maximum capacity, but the actual maximum capacity of the SOC calculated when the power battery is fully charged or discharged last time is used for replacing the maximum capacity of the power battery, and the value is used for considering the influence of battery aging on the battery capacity, so that the estimation of the SOC of the power battery is accurate.)

1. An SOC estimation method for a power battery of an electric automobile is characterized by comprising the following steps:

acquiring the charge state of the power battery at the initial moment when the power battery is charged or discharged;

calculating to obtain the capacity variation of the power battery from the initial moment to the current moment;

taking the actual maximum capacity of the power battery obtained by calculation under the condition of last full charge or discharge as the maximum capacity of the power battery;

obtaining the state of charge of the power battery at the current moment according to the state of charge, the capacity variation and the maximum capacity of the power battery at the initial moment; the state of charge at the current moment is as follows:

SOC_end＝SOC_ini+ΔQ/Q_max

therein, SOC_endIs the state of charge, SOC, of the current moment_iniIs the state of charge at the initial time, Δ Q is the capacity change, Q_maxIs the maximum capacity.

2. The SOC estimation method for the power battery of the electric automobile as claimed in claim 1, wherein when the last working time of the power battery exceeds a set time, the SOC-OCV table is looked up by collecting the terminal voltage of the initial time of the power battery to obtain the SOC of the initial time of the power battery corresponding to the terminal voltage.

3. The SOC estimation method for the power battery of the electric automobile according to claim 1, characterized in that an ampere-hour integration method is adopted to obtain the capacity variation of the power battery from the initial time to the current time:

wherein, the delta Q is the capacity variation of the power battery from the initial time to the current time,as an initial moment of time, the time of day,at the present time, i is a charging current or a discharging current from the initial time to the present time.

4. The SOC estimation method for the power battery of the electric automobile according to claim 1, wherein the actual maximum capacity of the power battery calculated in the last full charge or discharge condition is:

wherein, Q'_maxThe actual maximum capacity of the power cell for the last full charge,the capacity variation during the last full or discharged charge, t_iniIs the initial time t in the last full or discharged state_endI ' is the end time of the last full charge or discharge, and is the charging current during charging at the last full charge or the discharging current, SOC ' during discharging at the last discharge '_endIs the state of charge, SOC ', of the last full charge or after discharge'_iniThe state of charge at the initial time in the case of the last full charge or the last discharge is the state of charge.

5. An SOC estimation device of a power battery of an electric vehicle is characterized by comprising a processor, wherein the processor is used for executing instructions to realize the following method:

acquiring the charge state of the power battery at the initial moment when the power battery is charged or discharged;

calculating to obtain the capacity variation of the power battery from the initial moment to the current moment;

taking the actual maximum capacity of the power battery obtained by calculation under the condition of last full charge or discharge as the maximum capacity of the power battery;

obtaining the state of charge of the power battery at the current moment according to the state of charge, the capacity variation and the maximum capacity of the power battery at the initial moment; the state of charge at the current moment is as follows:

SOC_end＝SOC_ini+ΔQ/Q_max

therein, SOC_endIs the state of charge, SOC, of the current moment_iniIs the state of charge at the initial time, Δ Q is the capacity change, Q_maxIs the maximum capacity.

6. The SOC estimation device for the power battery of the electric automobile as claimed in claim 5, wherein when the last working time of the power battery exceeds a set time, the SOC-OCV table is looked up by collecting the terminal voltage of the initial time of the power battery to obtain the SOC of the initial time of the power battery corresponding to the terminal voltage.

7. The SOC estimation device for the power battery of the electric automobile according to claim 5, characterized in that the capacity variation of the power battery from the initial time to the current time is obtained by adopting an ampere-hour integration method:

wherein, the delta Q is the capacity variation of the power battery from the initial time to the current time,

8. The SOC estimation device for the power battery of the electric automobile according to claim 5, wherein the actual maximum capacity of the power battery calculated in the last full charge or discharge condition is:

wherein, Q'_maxThe actual maximum capacity of the power cell for the last full charge,

Technical Field

The invention belongs to the technical field of electric automobiles, and particularly relates to a method and a device for estimating the SOC of a power battery of an electric automobile.

Background

With the consumption of traditional energy and the continuous development of new energy technology, batteries are increasingly demanded by people as energy storage devices due to high efficiency and safety utilization.

A Battery Management System (BMS) is an important component of an electric vehicle, and State of Charge (SOC) estimation of a Battery is one of key technologies of the Battery management System. If the information such as the battery residual energy and the endurance mileage of the electric automobile can be accurately estimated, great help is provided for the user of the electric automobile, and the battery can be conveniently and reasonably utilized by the user of the electric automobile under the condition of obtaining the useful information, so that the damage to the battery is avoided. Therefore, accurate estimation of the SOC of the power battery of the electric automobile has important significance for ensuring the safety of the battery system, prolonging the service life of the battery system, reducing the maintenance cost of the battery system and the like.

The battery SOC is generally defined as: residual capacity Q_remWith actual capacity Q_NThe percentage of (A) is as follows:however, when estimating the battery SOC, there are the following problems:

1) residual capacity Q_remAnd actual capacity Q_NIs obtained under a certain discharge condition, wherein, when the external voltage of the battery reaches the cut-off voltage, the discharge is finished. However, when the electric vehicle is used, it is impossible to perform discharge at a certain constant current and temperature, and the remaining capacity Q is obtained before the voltage outside the battery reaches the discharge end voltage_remAnd actual capacity Q_NThe SOC of the battery is coupled with the running condition of the battery, and even contradiction occurs;

2) when the electric automobile is actually used, the full charge or the full discharge is not performed according to a certain fixed working condition like a battery cycle test, so that the actual capacity is not easy to obtain. Therefore, when estimating the SOC, the actual capacity is often replaced by the nominal capacity, and this estimation method ignores the problem of the decrease in the actual capacity after the battery ages, which inevitably leads to an increase in the estimation error of the SOC of the battery.

Disclosure of Invention

The invention aims to provide a method and a device for estimating the SOC of a power battery of an electric vehicle, which are used for solving the problem of larger SOC estimation error caused by using a nominal capacity to replace a maximum capacity.

In order to solve the technical problems, the technical scheme of the invention is as follows:

the invention provides an SOC estimation method of a power battery of an electric automobile, which comprises the following steps:

acquiring the charge state of the power battery at the initial moment when the power battery is charged or discharged;

calculating to obtain the capacity variation of the power battery from the initial moment to the current moment;

taking the actual maximum capacity of the power battery obtained by calculation under the condition of last full charge or discharge as the maximum capacity of the power battery;

obtaining the state of charge of the power battery at the current moment according to the state of charge, the capacity variation and the maximum capacity of the power battery at the initial moment; the state of charge at the current moment is as follows:

SOC_end＝SOC_ini+ΔQ/Q_max

therein, SOC_endIs the state of charge, SOC, of the current moment_iniIs the state of charge at the initial time, Δ Q is the capacity change, Q_maxIs the maximum capacity.

The invention also provides an SOC estimation device of the power battery of the electric automobile, which comprises a processor, wherein the processor is used for executing instructions to realize the following method:

acquiring the charge state of the power battery at the initial moment when the power battery is charged or discharged;

calculating to obtain the capacity variation of the power battery from the initial moment to the current moment;

taking the actual maximum capacity of the power battery obtained by calculation under the condition of last full charge or discharge as the maximum capacity of the power battery;

obtaining the state of charge of the power battery at the current moment according to the state of charge, the capacity variation and the maximum capacity of the power battery at the initial moment; the state of charge at the current moment is as follows:

SOC_end＝SOC_ini+ΔQ/Q_max

therein, SOC_endIs the state of charge, SOC, of the current moment_iniIs the state of charge at the initial time, Δ Q is the capacity change, Q_maxIs the maximum capacity.

The invention has the beneficial effects that:

when the SOC of the power battery is calculated, the nominal capacity is not used for replacing the maximum capacity, but a value which is close to the maximum capacity of the power battery is used, namely the actual maximum capacity of the SOC calculated when the power battery is fully charged or discharged last time is used for replacing the maximum capacity of the power battery, and the value is used for considering the influence of battery aging on the battery capacity, so that the estimation of the SOC of the power battery is accurate.

As a further improvement of the method, in order to obtain the state of charge of the power battery at the accurate initial time, when the distance between the power battery and the last working time exceeds the set time, the state of charge of the power battery at the initial time corresponding to the terminal voltage is obtained by acquiring the terminal voltage of the power battery at the initial time and checking an SOC-OCV table.

Under the condition that the last working time of the power battery exceeds the set time, the voltage of the power battery is stable, so that the state of charge of the power battery at the initial moment obtained by a table look-up method is accurate.

As a further improvement of the method, an ampere-hour integration method is adopted to obtain the capacity variation of the power battery from the initial time to the current time:

wherein, the delta Q is the capacity variation of the power battery from the initial time to the current time,

as an initial moment of time, the time of day,

at the present time, i is a charging current or a discharging current from the initial time to the present time.

As a further improvement of the method, in order to obtain the actual maximum capacity of the power battery, the actual maximum capacity of the power battery calculated in the last full charge or discharge condition is:

wherein, Q'_maxThe actual maximum capacity of the power cell for the last full charge,

the capacity variation during the last full or discharged charge, t_iniIs the initial time t in the last full or discharged state_endI ' is the end time of the last full charge or discharge, and is the charging current during charging at the last full charge or the discharging current, SOC ' during discharging at the last discharge '_endIs the state of charge, SOC ', of the last full charge or after discharge'_iniThe state of charge at the initial time in the case of the last full charge or the last discharge is the state of charge.

As a further improvement of the device, in order to obtain the charging device of the power battery at the accurate initial time, when the distance between the power battery and the last working time exceeds the set time, the SOC-OCV table is checked by acquiring the terminal voltage of the power battery at the initial time to obtain the charging state of the power battery at the initial time corresponding to the terminal voltage.

Under the condition that the last working time of the power battery exceeds the set time, the voltage of the power battery is stable, so that the state of charge of the power battery at the initial moment obtained by a table look-up method is accurate.

As a further improvement of the device, an ampere-hour integration method is adopted to obtain the capacity change amount of the power battery from the initial time to the current time:

wherein, the delta Q is the capacity variation of the power battery from the initial time to the current time,

as an initial moment of time, the time of day,

at the present time, i is a charging current or a discharging current from the initial time to the present time.

As a further improvement of the device, in order to obtain the actual maximum capacity of the power battery, the actual maximum capacity of the power battery calculated in the last full charge or discharge condition is:

wherein, Q'_maxThe actual maximum capacity of the power cell for the last full charge,

the capacity variation during the last full or discharged charge, t_iniIs the initial time t in the last full or discharged state_endI ' is the end time of the last full charge or discharge, and is the charging current during charging at the last full charge or the discharging current, SOC ' during discharging at the last discharge '_endFor the last time charged orThe state of charge after discharge, SOC'_iniThe state of charge at the initial time in the case of the last full charge or the last discharge is the state of charge.

Drawings

FIG. 1 is a system block diagram;

FIG. 2-1 is a circuit diagram of a current splitting module in the current sensing module circuit;

2-2 is a current amplifying circuit, an A/D sampling circuit and a signal isolating circuit in the current detection module circuit;

FIG. 3-1 is a circuit diagram of twelve battery inputs in the cell voltage detection circuit;

FIG. 3-2 is a diagram of a cell voltage acquisition circuit and a signal isolation circuit in the cell voltage detection circuit;

fig. 4 is a flow chart of a method of the present invention.

Detailed Description

In order to realize accurate estimation of the SOC of the power battery of the electric automobile, the invention provides an SOC estimation device of the power battery of the electric automobile, which comprises a processor, wherein the processor is used for executing instructions to realize the SOC estimation method of the power battery of the electric automobile. The method is further described in detail below with reference to the drawings and examples.

The principle of the method is explained and illustrated in detail below, with the following steps:

1. definition of the State of Charge of a Battery

SOC_end＝Q_rem/Q_max＝SOC_ini+ΔQ/Q_max(1)

Therein, SOC_iniIs the state of charge, SOC, at the initial moment_endΔ Q is the change of the capacity of the power battery from the initial time to the current time, Q_maxThe maximum capacity of the power battery.

From equation (1), it can be seen that the SOC for the current time is realized_endThe parameters to be determined comprise the capacity change quantity delta Q of the power battery from the initial moment to the current moment, and the state of charge SOC at the initial moment_iniAnd maximum capacity Q of power battery_max。

2. Calculation of capacity variation Δ Q of power battery from initial time to current time

Because the power battery has high charge-discharge capacity efficiency, the delta Q can be obtained by an ampere-hour integration method, namely, the delta Q is obtained by integrating current with time:

wherein the content of the first and second substances,

as an initial moment of time, the time of day,

at the present time, i is a charging current or a discharging current from the initial time to the present time.

3. State of charge SOC at initial time_iniIs estimated by

When the battery is kept still for more than 2 hours (the time can be set according to the actual situation), the voltage of the single battery is stable, and the terminal voltage U of each single battery is collected_ocvObtaining the SOC of the initial moment of the power battery corresponding to the terminal voltage by looking up the SOC-OCV table_ini：

1) When the vehicle is parked for a while, e.g. at night, the polarization voltage U of the battery_pCan be sufficiently reduced, and the SOC of the power battery at the initial moment can be controlled_iniCorrecting;

2) when the power battery is fully charged, on one hand, the influence of open-circuit voltage on the change rate of the state of charge of the battery is large, on the other hand, the charging current is small, the ohmic drop and the polarization voltage can be ignored, and the SOC of the power battery at the initial moment is directly realized according to the voltage outside the battery_iniAnd (4) correcting.

4. Maximum capacity Q of power battery_maxIs calculated by

Combining the definition of the state of charge of the battery and the above calculation, the maximum capacity of the power battery can be calculated by the following formula:

according to the above description, Δ Q of the power battery during actual charging or discharging can be accumulated on-line, as long as SOC can be effectively obtained during the process_iniAnd SOC_endCan realize the pair Q'_maxAnd (4) estimating. For better estimation, SOC is needed_ini～SOC_endAs large as possible, the maximum available capacity of the battery can be corrected at two moments before and after charging. Therefore, the actual maximum capacity Q 'obtained in the last full charge or discharge state can be used'_maxThe maximum capacity Q of the power battery in the charge or discharge as the power battery_max。

In order to implement the above method, a system as shown in fig. 1 is adopted to implement the current and terminal voltage acquisition, and the specific current acquisition circuit and the specific voltage acquisition circuit are respectively shown in fig. 2-1, 2-2, 3-1 and 3-2.

As shown in FIG. 1, the system comprises an MCU module, a current detection module connected through an IIC interface, and a single battery voltage detection module connected through an SPI interface. The MCU module is a core processing module of the system, CAN read current data acquired by the current detection module and voltage data acquired by the single battery voltage detection module so as to realize the estimation of the power battery SOC, and sends the information to the vehicle control unit through the CAN1 interface.

The MCU module CAN adopt a singlechip MPC5744P chip, the chip is provided with three CAN interfaces, the CAN1 interface is externally connected with a whole vehicle controller, the CAN2 interface is externally connected with a charger, and the CAN3 interface is a reserved interface.

As shown in fig. 2-1 and 2-2, the current detection module includes a shunt circuit, a current amplification circuit, an a/D sampling circuit, and a signal isolation circuit.

The shunt circuit comprises a shunt FL1 arranged on the bus and used for collecting the bus current signal of the power battery. The current signal collected by the shunt FL1 is input to a current amplification circuit to amplify the collected signal.

The current amplifying circuit comprises a filtering module and an operational amplifier chip U1, wherein the filtering module is used for filtering a current signal collected by the shunt FL1, the input end of the filtering module is connected with the output end of the shunt FL1, and the output end of the filtering module is connected to the input end IN-/IN + of the operational amplifier chip U1 and is used for amplifying the filtered signal through the operational amplifier chip U1. The filtering module is composed of a first pi-type filter, a second pi-type filter, a resistor R1 and a resistor R2. The operational amplifier chip U1 selects AD620AN, and the output end DUTPUT of the operational amplifier chip U1 is connected with the input end of the A/D sampling circuit through a resistor R4; meanwhile, the first pin of the operational amplifier chip U1 is connected to the eighth pin of the operational amplifier chip U1 through an operational amplifier gain coefficient resistor R3.

The A/D sampling circuit comprises an A/D chip U2, wherein an input end AIN0 of the A/D chip U2 is connected with an output end of an operational amplifier chip U1 through a resistor R4 and is grounded through a capacitor C1; the output end of the A/D chip U2 is connected with the input end of the signal isolation circuit. The ADS1115 is used as the A/D chip U2.

The signal isolation circuit comprises a digital isolation chip U3, wherein the SCL1 end of the digital isolation chip U3 is connected with the SCL end of the A/D chip U2, and is also connected with +5VS through a pull-up resistor R5; the SDA1 end is connected with the SDA end of the A/D chip, and is also connected with +5VS through a pull-up resistor R6. The bus current acquisition value is sent to the MCU module by the output end SCL2 and the SDA2 of the digital isolation chip U3; the SCL2 terminal is also connected with +5VS through a pull-up resistor R7, and the SDA2 terminal is also connected with +5VS through a pull-up resistor R8.

The single battery voltage detection circuit comprises twelve battery input circuits, as shown in fig. 3-1, a filtering module consisting of resistors R11-R23, capacitors C10-C22, an inductor L4 and zener diodes D1-D13, and the filtered signals are input to a battery monitoring chip U4 for voltage acquisition. The battery monitoring chip U4 is selected from LTC6803HG-4 (i.e. A/D chip) for voltage collection. Then, as shown in fig. 3-2, the acquired voltage signal is transmitted to the MCU module via the digital isolation chip U5. The digital isolation chip can be selected from ADuM1401 ARZ.

Based on the circuit, the method of the invention can be applied to the estimation of the SOC of the power battery of the electric vehicle, and the specific control process is shown in fig. 4:

1. the system is powered on by two modes of switching gears through an ignition key switch or inserting a charger plug, and the MCU module is started.

2. And the MCU performs software initialization work, including hardware initialization and system variable quantity initialization. The hardware initialization comprises the initialization of a current detection module, the initialization of a single battery voltage detection module and the like; system variable initialization includes SOC_iniAnd Q_maxAssigned value (SOC)_iniAnd Q_maxRead from EEPROM).

3. At the moment, the electric automobile is not started, the output current of the power battery is small, the ohmic voltage drop and the polarization voltage can be ignored, and the MCU module starts the single battery voltage detection module to obtain the voltage data of the single battery.

4. The MCU module acquires the SOC of the battery corresponding to the voltage data of the single battery by inquiring the SOC-OCV table_ini. If the starting time interval of the MCU module at the current time and the last time is more than 2 hours, updating the system variable SOC_iniAnd updating the SOC in the EEPROM_ini(ii) a Otherwise, the SOC obtained by the table lookup is lost_ini。

5. The MCU module reads the current data of the current detection module every 100ms, and the discharge/charge change capacity delta Q is obtained through the integration of the current to the time.

6. In the running process of the electric automobile, the MCU module can be used for controlling the driving according to the SOC_iniΔ Q and Q_maxAnd estimating the state of charge of the battery in real time according to the formula (1).

7. When the electric automobile is fully charged, the MCU module corrects Q according to the formula (3)_maxAnd updating Q in EEPROM_max。

8. When the ignition lock is powered off, the MCU module updates the SOC in the EEPROM_end。

While the present invention has been described in detail with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be determined from the following claims.