CN105186590A - Active lithium battery balance control device - Google Patents

Abstract

The invention discloses an active balancing control device for a lithium battery, which relates to the technical field of lithium batteries; it includes a DC/DC power supply module and a main control unit, and the DC/DC power supply module is connected to the main control unit; it is characterized in that: the main control unit The control unit is respectively connected with the lithium battery active balancing module, the voltage detection module, the current detection module and the display module. The invention can solve the problems existing in the existing lithium battery equalization scheme that it is not easy to be modularized, there are many components and the estimation of SOC is inaccurate.

Description

Lithium battery active balance control device

technical field

The invention relates to the technical field of lithium batteries; in particular, an active balancing control device for lithium batteries based on SOC balancing of lithium batteries.

Background technique

With the development of lithium battery technology and more and more attention paid to energy conservation and environmental protection, the application fields of lithium batteries are becoming wider and wider, such as portable electronic products, electric vehicles and solar power generation systems and other new energy fields. Lithium-ion battery is the battery with the highest energy ratio so far. Its specific weight reaches 130 hours per kilogram, and the discharge voltage of a single battery is 3.6 volts, which is three times higher than that of nickel-cadmium batteries. In addition, lithium-ion batteries have small thermal effects, no memory effects, and higher charging efficiency than nickel-cadmium and nickel-hydrogen batteries. However, because its discharge voltage is not high, many sets of batteries need to be used in series in many applications to achieve sufficient output voltage and output power. Due to the inconsistency between the individual cells in the battery pack, after continuous charge and discharge cycles, the state of charge of each individual cell will be seriously unbalanced, which is manifested by the increasing voltage divergence between the individual cells. , which will cause permanent damage to the battery.

At present, lithium battery equalization circuits can be divided into energy dissipation type and energy non-dissipation type according to the energy consumption of the circuit during the equalization process. Dissipative types have the disadvantages of low efficiency and the inability to control the shunted current. For energy non-dissipative equalization schemes, the switched capacitor method and the DC-DC converter method are mostly used in China. The disadvantage of the switched capacitor method is that its reliability is not strong, it can only achieve voltage equalization, it cannot achieve state of charge equalization, and the equalization time is long. There are many topologies for the DC-DC converter scheme, and the currently widely used schemes can be divided into centralized transformer method and distributed equalization method. The centralized transformer method transfers energy to the battery with the lowest voltage through a multi-output transformer. The shortcoming of this structure's equalization method is that it is not easy to be modularized. The distributed structure is to connect an equalization circuit in parallel at both ends of each battery cell, which belongs to the discharge type equalization, that is, the battery with too high energy discharges to the entire battery pack or some other batteries. It is characterized by easy modularization and disadvantages Because there are more devices.

The state of charge of the battery (English: StateofCharge, referred to as SOC) is an important parameter when the electric vehicle is running. Its accurate estimation can provide the necessary data support for the battery management system and the remaining mileage prediction, thereby effectively preventing the battery from overcharging and over-discharging. Extend battery life and reduce operating costs of electric vehicles. However, SOC is not a physical quantity that can be directly measured. The battery itself is a closed electrochemical reaction. When electric vehicles are running, they present strong nonlinearity accompanied by drastic changes in current, which makes it difficult to estimate SOC. Scholars at home and abroad have conducted a lot of research on the SOC estimation of lithium batteries and proposed a variety of scientific methods for SOC estimation. Among them, the discharge test method can obtain a more accurate SOC estimate, but it must interrupt the ongoing work of the battery and cannot be applied to a real vehicle; although the current integration method can estimate the SOC of the battery in real time, it cannot automatically determine the initial value, and the error will increase over time. If it is further increased, the estimation will be inaccurate due to the accumulation of errors; the open circuit voltage method can only be accurately estimated when the battery current is zero, and the battery needs to stand for a long enough time, so it cannot be estimated in real time; the neural network method requires a large amount of training data And suitable training algorithm, and susceptible to interference, not suitable for working conditions with severe current changes.

Contents of the invention

The purpose of the present invention is to provide an active balancing control device for lithium batteries, which can solve the problems existing in the existing lithium battery balancing schemes that it is not easy to be modularized, there are many components, and the estimation of SOC is inaccurate.

In order to solve the above problems, the technical solution adopted by the present invention is: the lithium battery active balance control device includes a DC/DC power supply module and a main control unit, and the DC/DC power supply module is connected to the main control unit; The main control unit is respectively connected with the lithium battery active balancing module, the voltage detection module, the current detection module and the display module.

Among the above technical solutions, a more specific solution may also be: the lithium battery active equalization module includes a voltage stabilization processing circuit and an isolated DC/DC circuit; the input terminal of the voltage stabilization processing circuit receives The voltage signal, its first output terminal is connected to the input terminal of the isolated DC/DC circuit, and its second output terminal is connected to the second input terminal of the inverter; the output terminal of the isolated DC/DC circuit is connected to the high-speed The second input end of the optocoupler isolation circuit is connected, the output end of the high-speed optocoupler isolation circuit is connected to the first input end of the inverter, and the output end of the inverter is connected to the input end of the switch circuit, The output end of the switch circuit is connected to the input end of the energy storage inductance circuit, and the output end of the energy storage inductance circuit is connected to the series lithium battery pack; the first input end of the high-speed optocoupler isolation circuit receives the main control unit control signal.

Further: the main control unit is a TMS320F28335 digital signal processor; the voltage stabilization processing circuit is a 12-volt voltage stabilization processing circuit; the isolated DC/DC circuit is a 12-volt to 5-volt isolated DC/DC circuit.

Further: the inverter is a 74HC04 inverter.

Due to the adoption of the above technical solution, compared with the prior art, the present invention has the following beneficial effects: since the present invention is provided with a lithium battery active equalization module, a buck-boost energy storage circuit is provided in the lithium battery active equalization module, As a carrier of energy transmission, it can transfer energy from a battery with a high state of charge to an inductor, and then from the inductor to a battery with a low state of charge to achieve energy flow.

The present invention applies Uncented Kalman Filter (UKF) to lithium battery SOC estimation, so that the estimation can achieve higher accuracy.

Description of drawings

Figure 1 is a schematic block diagram of the present invention.

Fig. 2 is a schematic block diagram of a lithium battery active balancing module.

Figure 3 is a Thevenin model diagram.

Detailed ways

Below in conjunction with accompanying drawing and embodiment the present invention is described in further detail:

The lithium battery active balancing control device shown in Figure 1 and Figure 2 includes a DC/DC power supply module 1 and a main control unit 2, and the DC/DC power supply module 1 is connected to the main control unit 2; the main control unit 2 is respectively connected to the lithium battery active The balance module 3, the voltage detection module 5, the current detection module 6 and the display module 4 are connected.

Among them, the detection of the voltage and current of the lithium battery is carried out by the main control unit 2 controlling the voltage detection module 5 and the current detection module 6; the operation of the Uncented Kalman Filter (UKF for short) algorithm is completed by the main control unit 2; The control of the lithium battery is completed by the main control unit 2 controlling the active balancing module 3 of the lithium battery;

The lithium battery active equalization module 3 includes a voltage stabilization processing circuit 3-1 and an isolated DC/DC circuit 3-2; the input terminal of the voltage stabilization processing circuit 3-1 receives the voltage signal transmitted from the series lithium battery pack, and its first output end is connected with the input end of the isolated DC/DC circuit 3-2, and its second output end is connected with the second input end of the inverter 3-4; the output end of the isolated DC/DC circuit 3-2 is isolated from the high-speed optocoupler The second input terminal of the circuit 3-3 is connected, the output terminal of the high-speed optocoupler isolation circuit 3-3 is connected with the first input terminal of the inverter 3-4, and the output terminal of the inverter 3-4 is connected with the switch circuit 3-4. The input terminal of 5 is connected, the output terminal of the switch circuit 3-5 is connected with the input terminal of the energy storage inductance circuit 3-6, and the output terminal of the energy storage inductance circuit 3-6 is connected with the lithium battery pack in series; the high-speed optocoupler isolation circuit 3 The first input end of -3 receives the control signal of the main control unit 2 .

In this embodiment, the main control unit 2 is a TMS320F28335 digital signal processor; the voltage stabilization processing circuit 3-1 is a 12-volt voltage stabilization processing circuit; the isolated DC/DC circuit 3-2 is a 12-volt to 5-volt isolated DC/DC circuit ; Inverter 3-4 is a 74HC04 inverter.

The 12V voltage stabilization processing circuit 3-1 is to stabilize the terminal voltage of the lithium battery pack in series to provide power for the 74HC04 inverter 3-4; the 12V to 5V isolated DC/DC circuit 3-2 is to use 12V voltage stabilization processing The voltage output by the circuit 3-1 is converted to provide an isolated output voltage to provide power to the high-speed optocoupler isolation circuit 3-3, and to provide a reference potential for the S terminal of the MOSFET in the switch circuit 3-5; the high-speed optocoupler isolation Circuit 3-3 isolates and outputs the duty cycle of PWM output by main control unit 2, provides driving voltage for MOSFET, and plays the role of isolating and protecting main control unit 2 at the same time; the function of 74HC04 inverter 3-4 is: because The output of the high-speed optocoupler isolation circuit 3-3 and the output of the PWM duty cycle of the main control unit 2 are reversed, and the positive output can be obtained through the 74HC04 inverter 4, so that the PWM duty cycle of the main control unit 2 It is synchronous with the opening of the MOSFET; the switching circuit 3-5 is composed of MOSFET and diode, and the flow direction and magnitude of the current can be controlled by controlling the switch of the MOSFET, wherein the diode acts as a reverse cut-off to avoid energy reverse flow; The function of the energy storage sensing circuit 3-6 is: the energy storage sensing circuit 3-6 is used as a carrier for energy transmission, transferring energy from a battery with a high state of charge to an inductor, and then from the inductor to a battery with a low state of charge. In order to realize the flow of energy, the energy storage inductor is connected in series with the transient bidirectional suppression diode to avoid the impact of the instantaneous pulse on the circuit.

The present invention is applicable to the balanced control of series lithium battery packs. When the present invention is connected to series lithium battery packs, the voltage and current of each battery in the series series lithium battery packs can be collected, and the SOC of each battery pack can be estimated in real time. Based on the SOC, the energy transfer active equalization is carried out. When the difference between the SOC of a battery cell in the series lithium battery pack and the average SOC of the series lithium battery pack reaches 2%, the equalization system is started, and the SOC in the series lithium battery pack The energy of the high battery is transferred to the battery with low SOC, until the SOC difference of each battery in the series lithium battery pack is within 2%, the average SOC of the series lithium battery pack and the maximum voltage difference of the single cells of the series lithium battery pack pass The display module 4 displays.

The accuracy of the battery model is a prerequisite for battery SOC estimation. Thevenin model is the most representative equivalent circuit model, which considers the polarization phenomenon in the internal chemical reaction of the battery, and can better reflect the dynamic and static characteristics of the battery; at the same time, it considers the internal resistance affected by temperature, current and charge and discharge state. It can accurately simulate the charging and discharging behavior of the battery, and the structure is relatively simple, which is more suitable for the modeling and simulation of power batteries. The model is shown in Figure 3.

Uoc in Figure 3 is the open circuit voltage; is the ohmic internal resistance of the battery; and are the polarization internal resistance and polarization capacitance respectively, and U is the terminal voltage of the battery.

will SOC and voltage on As the state variable of the system, the battery operating current For system input, battery operating voltage For the system output, a discrete state-space model is built.

The state equation of the model is:

(1)

In the formula, T is the sampling period, is the SOC value at sampling point k, is the sampling point of The voltage estimate on the, is the time constant, is the rated capacity of the battery, is the discharge efficiency, is Gaussian white noise.

The output observation equation is:

(2)

In the formula, there is a one-to-one correspondence between the open circuit voltage Uoc and the SOC, using represents the relationship, which can be obtained experimentally, is Gaussian white noise, and r0 is the ohmic internal resistance of the battery.

The experiment selects a single lithium iron phosphate battery. Through the HPPC test, the lithium battery is discharged with a short-term constant current pulse, and the recovery process of the battery terminal voltage is recorded. According to this curve, it is determined and , and determine the time constant of the circuit by recording the time, and finally determine the value of the capacitance. The parameter values of Thevenin circuit model can be obtained by using nonlinear least squares, as shown in Table 1.

Table 1 RC parameter table R ₀ R ₁ C ₁ 0.032 0.004 580.1316

Based on the Unscented Transform (UT), UKF realizes the approximation of the state distribution through UT. This method avoids the analytical derivation of nonlinear functions, and considers the problem of probability propagation. The approximation accuracy is improved to at least second order, improving the accuracy of SOC estimation. Combined with the battery model (1) (2), the UKF is applied to the SOC estimation process as follows:

(1) System initialization

Filter initial value: (3)

in, is the matrix formed by the initial value of SOC and the initial value of polarization voltage, is the initial value of the state covariance.

(2) Generate sigma points

(4)

(5)

(6)

(7)

in, is a small positive number, usually taken as =1; n is the number of system state variables, for a single battery, , is a proportionality coefficient, is the state variable of the corresponding sigma point.

(3) Determine the weighting coefficient

(8)

,(9)

(10)

in, is the second-order proportionality coefficient, usually taken as =1; Used to combine prior information, for a Gaussian white noise system, take =2, is the weighting coefficient of the corresponding sigma point.

(4) Time update (UT)

(11)

(12)

(13)

in is the ith column of the square root of the matrix, is the weight, is the process noise variance, is the state update value obtained by unscented transformation, The state covariance update value obtained for the unscented transformation.

(5) Measurement update

(14)

(15)

(16)

(17)

(18)

in is the measured system output, , is the state covariance, is the system output matrix, For the measurement noise variance, is the updated state covariance of the measure.

UKF generates Sigma points, performs UT on Sigma points, uses nonlinear state equations and observation equations, avoids linear errors, improves estimation accuracy, and avoids calculating partial derivatives of the matrix, reducing the amount of calculation.

Claims (5)

1. A lithium battery active balance control device, comprising a DC/DC power module and a main control unit, the DC/DC power module is connected to the main control unit; it is characterized in that: the main control unit is connected to the lithium battery respectively The active equalization module, the voltage detection module, the current detection module and the display module are connected. 2. The lithium battery active equalization control device according to claim 1, characterized in that: the lithium battery active equalization module includes a voltage stabilization processing circuit and an isolated DC/DC circuit; The first output terminal of the voltage signal delivered by the series lithium battery pack is connected to the input terminal of the isolated DC/DC circuit, and the second output terminal is connected to the second input terminal of the inverter; the isolated DC/DC The output end of the circuit is connected to the second input end of the high-speed optocoupler isolation circuit, the output end of the high-speed optocoupler isolation circuit is connected to the first input end of the inverter, and the output end of the inverter is connected to the switch The input end of the circuit is connected, the output end of the switch circuit is connected to the input end of the energy storage inductance circuit, and the output end of the energy storage inductance circuit is connected to the series lithium battery pack; the first high-speed optocoupler isolation circuit An input terminal receives a control signal of the main control unit. 3. The lithium battery active equalization control device according to claim 1 or 2, characterized in that: the main control unit is a TMS320F28335 digital signal processor; the voltage stabilization processing circuit is a 12 volt voltage stabilization processing circuit; The isolated DC/DC circuit is a 12 volt to 5 volt isolated DC/DC circuit. 4. The lithium battery active balancing control device according to claim 1 or 2, wherein the inverter is a 74HC04 inverter. 5. The lithium battery active balancing control device according to claim 3, wherein the inverter is a 74HC04 inverter.