CN112117792A - Passive equalization system based on model and equalization current estimation method - Google Patents

Passive equalization system based on model and equalization current estimation method Download PDF

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CN112117792A
CN112117792A CN202010760680.2A CN202010760680A CN112117792A CN 112117792 A CN112117792 A CN 112117792A CN 202010760680 A CN202010760680 A CN 202010760680A CN 112117792 A CN112117792 A CN 112117792A
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CN112117792B (en
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徐俊
边嘉豪
王海涛
梅雪松
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Xian Jiaotong University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/0013—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries acting upon several batteries simultaneously or sequentially
    • H02J7/0014—Circuits for equalisation of charge between batteries
    • H02J7/0019—Circuits for equalisation of charge between batteries using switched or multiplexed charge circuits
    • G—PHYSICS
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    • H01M10/4207—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells for several batteries or cells simultaneously or sequentially
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/425—Structural combination with electronic components, e.g. electronic circuits integrated to the outside of the casing
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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    • H02J7/00712—Regulation of charging or discharging current or voltage the cycle being controlled or terminated in response to electric parameters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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    • H02J7/00712—Regulation of charging or discharging current or voltage the cycle being controlled or terminated in response to electric parameters
    • H02J7/00714—Regulation of charging or discharging current or voltage the cycle being controlled or terminated in response to electric parameters in response to battery charging or discharging current
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
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    • H01M10/425—Structural combination with electronic components, e.g. electronic circuits integrated to the outside of the casing
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Abstract

The invention provides a passive equalization system and an equalization current estimation method based on a model, and belongs to the technical field of battery equalization. The invention utilizes the characteristics of the MOSFET, can apply variable and controllable equalizing current to the battery, provides an equalizing current estimation method based on a model for eliminating an equalizing current sensor, and further reduces the system cost. And an experimental platform is built, and the proposed QPBS is experimentally verified. Experimental results show that the maximum equalizing current of QPBS can reach 10a, and the maximum equalizing current of PBM is about 0.1A. Meanwhile, under the condition that the requirement of the balance current is 10A, the cost of the QPBS main circuit is greatly reduced and is greatly lower than that of the PBM.

Description

Passive equalization system based on model and equalization current estimation method
Technical Field
The invention belongs to the technical field of battery equalization, and particularly provides a low-cost quasi-passive equalization system (QPBS) based on a model and an equalization current estimation method.
Background
As a promising solution to the problems of environmental pollution and energy crisis, Electric Vehicles (EV), photovoltaic, wind energy, smart grid, and the like have drawn increasing attention. Batteries are widely used as Energy Storage Systems (ESS) for such applications. However, due to the voltage and capacity limitations of the battery cells, the battery cells should be connected in parallel and/or series to cope with energy and power demands. Unfortunately, inconsistencies are inevitable for series connected cells due to manufacturing and usage factors. In fact, even in the same production lot, the battery cells may be considered to be different from each other. The inconsistency of battery can lead to the biggest available capacity of battery cell to drop, makes the group battery appear in the charging process that low-power monomer is not full of and high-power monomer has overcharged, and high-power monomer still remains and low-power battery monomer has been put when discharging, and the decline of battery energy can be aggravated to the "wooden barrel effect" of production to lead to group battery overall utilization and life to reduce, and then influence electric automobile's life and the continuation of the journey. More seriously, the active components inside the battery react with the electrolyte during overcharge and discharge, which may cause explosion and fire, thereby causing the most concerned safety hazard of the electric vehicle. Balancing, so-called equalization, is considered to be the most effective way to reduce the effects of inconsistencies on the battery string, which may improve the entire battery string. From the viewpoint of energy dissipation, methods of cell balancing may be classified into a Passive Balancing Method (PBM) and an active balancing method. PBM typically dissipates energy through a parallel resistance. The active balancing method charges the other group by using one part of the battery pack, and the active balancing method has good balancing effect, but has high cost and is not suitable for practical application. In contrast to the active balancing approach, PBM typically consumes energy through parallel resistors. PBM is easy to implement and low cost. Therefore, it has been widely used in practical applications.
However, the main problem with PBM is the balancing capability, and the balancing current of PBM is usually very small, typically about 0.1A. At such small equalization currents, the equalization speed is unsatisfactory. In order to increase the equalizing current, to meet the requirements of low resistance and high power, the cost of the bleeder resistor will increase dramatically. Furthermore, for a certain bleeder resistor, the resistance is constant and the equalizing current is constant and therefore cannot be changed when needed. For practical applications, the speed of equalization, the number of components, the control complexity and the cost of the equalization method should be carefully considered.
Disclosure of Invention
In order to overcome the disadvantages of the prior art, the present invention provides a passive equalization system and an equalization current estimation method based on a model, so as to solve the problems of low equalization speed, high regulation difficulty and high cost in the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:
the invention discloses a passive equalization system based on a model, which comprises an equalization circuit, a battery pack and an equalization control module based on the model;
the battery pack comprises a current sensor and a plurality of battery units which are connected in series;
the equalizing circuit comprises a plurality of MOSFET tubes, each MOSFET tube is connected with one battery unit in parallel and driven by an MOSFET driver;
the model-based equalization control module comprises an equalization current prediction module, an equalization controller and an MOSFET driver, wherein the equalization current prediction module predicts equalization current after acquiring voltage signals from a battery unit and current signals from a current sensor, and the equalization controller generates a control signal PWM to the MOSFET driver so as to control the equalization current.
Preferably, the MOSFET tube is an N-channel MOSFET or a P-channel MOSFET.
Preferably, the MOSFET driver is composed of one resistor and one capacitor CM.
Further preferably, the capacitor CM is large enough to filter the PWM ripple, the gate-source V of the MOSFETGSThe voltage is a DC voltage.
Preferably, the regulation is carried out by setting PWM duty ratio when VGSGreater than a threshold voltage VTHAnd less than a certain voltage, drain currents ID and VGSIs in direct proportion.
Preferably, when one battery cell in the battery pack has higher energy than the other battery cells, the battery cell is equalized to remove the redundant energy, and the MOSFET tube is controlled in an equalization region of the MOSFET transfer characteristic, equivalent to a variable resistor, in parallel to the battery cell.
The invention also discloses an equalization current estimation method based on the passive equalization system based on the model, which comprises the following steps:
introducing a first-order RC model of the battery with balanced current to obtain the electrical relationship of different parameters in the model, and rewriting with V2Is a state space equation of state, said equation being expressed in V2The state space equation for a state is as follows:
Figure BDA0002612997910000031
a, B, C, D is a model correspondence matrix obtained from the battery, and u is the battery current Ic2(ii) a Total current ImComposed of two parts, each of which is a battery current Ic2And an equalizing current Ib2：
Im＝Ic2+Ib2 (7)
For a cell model that considers the equalization current, the state space equation is obtained as follows:
Figure BDA0002612997910000032
wherein, input
Figure BDA0002612997910000033
Is the measured current ImAnd is and
Figure BDA0002612997910000034
in order to obtain the estimated equalization current, the equalization current estimation method is designed as follows:
Figure BDA0002612997910000035
suppose thatError of the measurement
Figure BDA0002612997910000036
And is
Figure BDA0002612997910000037
When K isi2When B, the equation is rewritten as:
Figure BDA0002612997910000038
where E is the identity matrix, according to control theory, as long as all roots AeAll have a negative real part, the system is stable, which means that when t → ∞,
Figure BDA00026129979100000310
estimated equalization current
Figure BDA0002612997910000039
Will converge to a true equilibrium current.
Compared with the prior art, the invention has the following beneficial effects:
the passive equalization system based on the model disclosed by the invention can apply variable and controllable equalization current to a battery by utilizing the characteristics of the MOSFET, the MOSFET is used for replacing a parallel resistor and equivalently regarded as an adjustable resistor, the equalization current can be controlled according to the requirement by controlling the MOSFET in an equalization area, and the equalization current can be greatly increased so as to improve the equalization speed.
The model-based equilibrium current estimation method provided by the invention reduces the current sensors to reduce the cost, controls the equilibrium current by utilizing the characteristics of the MOSFET, realizes the technical effects of high efficiency and low cost of the QPBS, and reduces the system cost because the current sensors for balancing the current are not needed. A prototype of the QPBS is constructed, the superiorities of high equalizing current and high equalizing speed of the QPBS are verified through experiments, and experimental results show that the cost of the QPBS main circuit is greatly reduced and is only 11.8% of PBM with the equalizing current of 10A. The maximum equalization current may be as high as 10A. In the case of the 19% SOC difference, the inconsistency of the battery cells can be compensated for in a short time (about 10 minutes). Therefore, the QPBS provided by the invention has the advantages of low cost and high equalization speed.
Drawings
FIG. 1 is a schematic diagram of a model-based passive equalization system according to the present invention;
FIG. 2 is a schematic diagram of an equalizing current prediction module according to the present invention;
FIG. 3a is a block diagram of an equalizer driver of the present invention;
FIG. 3b is a diagram of an equalizing equivalent circuit according to the present invention;
FIG. 3c is a graph of the transmission characteristics of a MOSFET of the present invention;
FIG. 4 is a graph of experimental results during cell equalization according to an embodiment of the present invention; wherein (a) a QPBS with a 10A equalization current; (b) a model-based current estimation; (c) SOC results for QPBS with 10A equalization current in UDDS; (d) SOC results for PBM using 33 Ω balancing resistance in UDDS; (e) QPBS results for different initial SOCs in UDDS; (f) the result of QPBS on charging.
Detailed Description
In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
The invention is described in further detail below with reference to the accompanying drawings:
referring to fig. 1, a model-based equalization system is composed of three parts, namely, an equalization circuit, a battery pack and a model-based equalization control module.
The equalizing circuit is composed of a MOSFET SnIs implemented in parallel connection with each battery cell and is driven by a MOSFET driver.
Further, MOSFET SnEither an N-channel MOSFET or a P-channel MOSFET.
Referring to fig. 2, the equalizing current prediction module of the present invention compares the measured voltage with the calculated voltage, and feeds back the measured voltage to the battery model through the PIO to correct the predicted current.
Referring to fig. 3a, the MOSFET driver is composed of one resistor and one capacitor CM.
Further, the PWM generated by the balancing controller is used to control the MOSFETs and thus the balancing current. The capacitor CM is large enough to filter the PWM ripple, and therefore, the gate-source (GS) V of the MOSFETGSThe voltage is a DC voltage.
Referring to fig. 3b, by setting the PWM duty, control can be performed as needed. According to the MOSFET transmission characteristics, when VGSGreater than a threshold voltage VTHAnd less than a certain voltage, drain current IDAlmost with VGSIs in direct proportion. Since the drain current is a balanced current, V can pass through the MOSFETGSTo control the equalization current. That is, the MOSFET and its driver may be regarded as a variable resistor controlled by PWM in consideration of the characteristics of the circuit.
Referring to fig. 3c, when one cell in the battery pack has higher energy than the other cells, the battery pack should cope with the sameThe cell is equalized and excess energy is removed therefrom. In this case, the MOSFET S is controlled in the equalizing region of the MOSFET transfer characteristicnEquivalent to a variable resistor connected in parallel to the battery cell. Thus, the battery cells are discharged through the parallel equivalent variable resistors. In a certain time, the excess energy is removed and the cells are in equilibrium. The equalization process can be performed in parallel and the equalization speed can be increased.
The battery pack is composed of n batteries connected in series.
Referring to fig. 1, the model-based equalization control module estimates an accurate equalization current, and feedback signals are voltages and currents of a battery cell and a battery pack, respectively. And realizing feedback control on the balance current by using a balance current estimation method based on a model, and controlling the balance current according to the requirement.
Further, when inconsistency is detected, different balancing strategies are adopted to generate balancing current requirements of each battery. This equalization current requirement is applied as a command to the equalization controller, which generates a control signal to the MOSFET driver.
Further, to form a closed loop control of the equalization, the actual equalization current should be fed back and compared with the equalization current command. To reduce the cost of the entire balancing system and eliminate the balancing current sensors, a model-based approach is used to estimate the accurate balancing current. Thus, the feedback signals are the voltage and current of the battery cell and the battery pack, respectively. And realizing feedback control on the equalizing current by using an equalizing current estimation method based on a model, and controlling the equalizing current according to the requirement.
A balanced current estimation method based on a model introduces a first-order RC model of a battery with balanced current to obtain the electrical relation of different parameters in the model, and rewrites the electrical relation by V2Is a state space equation for a state.
The state space equation with the V2 as the state is as follows:
Figure BDA0002612997910000071
wherein x ═ V2,
Figure BDA0002612997910000072
C＝1,D＝R1,y＝Vo-Voc(z),u＝Ic2.
Further, the total current ImComposed of two parts, each of which is a battery current Ic2And an equalizing current Ib2：
Im＝Ic2+Ib2 (2)
Further, for a battery model that considers the equalization current, the state space equation can be obtained as follows:
Figure BDA0002612997910000073
wherein the input is
Figure BDA0002612997910000074
Is the measured current ImAnd is
Figure BDA0002612997910000075
And a, B, C and D are known coefficient matrices as described above.
Further, in order to obtain an estimated equilibrium current, a PIO equilibrium current estimation method is proposed and designed as follows:
Figure BDA0002612997910000076
further, assume error
Figure BDA0002612997910000077
And is
Figure BDA0002612997910000078
When K isi2When B, the equation can be rewritten as:
Figure BDA0002612997910000079
where E is the identity matrix. According to the control theory, as long as all roots AeAll have negative real parts and the system is stable. This means that when t → ∞,
Figure BDA00026129979100000711
estimated equalization current
Figure BDA00026129979100000710
Will converge to a true equilibrium current.
Fig. 4 is a graph of experimental results of the battery equalization process in this embodiment, which respectively shows: (a) QPBS with 10A equalization current; (b) a model-based current estimation; (c) SOC results for QPBS with 10A equalization current in UDDS; (d) SOC results for PBM using 33 Ω balancing resistance in UDDS; (e) QPBS results for different initial SOCs in UDDS; (f) the result of QPBS on charging.
As shown in fig. 4 (a), the equalizing current command is set to 10A at about 10s and continues for about 30s, the measured actual equalizing current quickly reaches 10A, and the current value is maintained at 10A with little fluctuation. When no equalization is required, the actual equalization current immediately becomes 0A. The experimental result proves the working principle of the balancing circuit.
As shown in fig. 4 (b), the measured true equalization current plots the estimated equalization current comparison. It can be seen that the estimated equalization current converges to the reference equalization current in a short time. Meanwhile, the estimated equilibrium current curve is overlapped with the reference current curve, the error is small, and the accuracy of the equilibrium current estimation method is shown.
As shown in fig. 4 (c), the proposed method reaches equilibrium in the cell at about 600s (10 minutes). In contrast, as shown in fig. 4 (d), the SOC variation of PBM changed from 19% to about 16% even after 6000 s.
To further verify the proposed QPBS, a different initial SOC is applied to the proposed QPBS, as shown in figure 4 (e). In fig. 4, (f) represents the QPBS when the battery is charged at a rate of 0.5C. In both cases, it is necessary to equalize two cells, namely cells 1 and 4. Also, the equilibration rate is still very fast, almost the same as in (c) of FIG. 4, and the inconsistency problem can be resolved in less than 10 minutes.
These experimental results further demonstrate that the proposed QPBS has a larger equalizing current and equalizing speed much faster than PBM. In addition, the proposed QPBS has a function of equalizing the battery cells in the battery pack simultaneously in the case of charging and discharging, and further improves the equalization speed.
The invention provides a model-based low-cost quasi-passive equalization system (QPBS). By using the characteristics of the MOSFETs, a variable, controllable equalization current can be applied to the battery. In order to eliminate the equalizing current sensor, an equalizing current estimation method based on a model is provided, and the system cost is further reduced. And an experimental platform is built, and the proposed QPBS is experimentally verified. Experimental results show that the maximum equalizing current of QPBS can reach 10a, and the maximum equalizing current of PBM is about 0.1A. Meanwhile, under the condition that the requirement of the balance current is 10A, the cost of the QPBS main circuit is greatly reduced and is greatly lower than that of the PBM.
The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.

Claims (7)

1. A passive equalization system based on a model is characterized by comprising an equalization circuit, a battery pack and an equalization control module based on the model;
the battery pack comprises a current sensor and a plurality of battery units which are connected in series;
the equalizing circuit comprises a plurality of MOSFET tubes, each MOSFET tube is connected with one battery unit in parallel and driven by an MOSFET driver;
the model-based equalization control module comprises an equalization current prediction module, an equalization controller and an MOSFET driver, wherein the equalization current prediction module predicts equalization current after acquiring voltage signals from a battery unit and current signals from a current sensor, and the equalization controller generates a control signal PWM to the MOSFET driver so as to control the equalization current.
2. The model-based passive equalization system of claim 1, wherein the MOSFET transistor is an N-channel MOSFET or a P-channel MOSFET.
3. The model-based passive equalization system of claim 1 wherein the MOSFET driver is comprised of a resistor and a capacitor CM.
4. The model-based passive equalization system of claim 3, wherein the capacitor CM is large enough to filter PWM ripple, the gate-source V of the MOSFETGSThe voltage is a DC voltage.
5. The model-based passive equalization system of claim 1, wherein regulation is performed by setting a PWM duty cycle when V isGSGreater than a threshold voltage VTHAnd less than a certain voltage, drain currents ID and VGSIs in direct proportion.
6. The model-based passive equalization system of claim 1, wherein when one cell in the battery pack has higher energy than the other cells, the cell is equalized to remove excess energy, and the MOSFET tubes are controlled in the equalization region of the MOSFET transfer characteristic, equivalent to variable resistors, in parallel to the cells.
7. An equalization current estimation method based on the model-based passive equalization system according to any one of claims 1 to 6, comprising:
introducing a first-order RC model of the battery with balanced current to obtain different parameters in the modelElectrical relationship of number, rewritten by V2Is a state space equation of state, said equation being expressed in V2The state space equation for a state is as follows:
Figure FDA0002612997900000021
a, B, C, D is a model correspondence matrix obtained from the battery, and u is the battery current Ic2；
Total current ImComposed of two parts, each of which is a battery current Ic2And an equalizing current Ib2：
Im＝Ic2+Ib2 (2)
For a cell model that considers the equalization current, the state space equation is obtained as follows:
Figure FDA0002612997900000022
wherein, input
Figure FDA0002612997900000023
Is the measured current ImAnd is and
Figure FDA0002612997900000024
in order to obtain the estimated equalization current, the equalization current estimation method is designed as follows:
Figure FDA0002612997900000025
assumed error
Figure FDA0002612997900000026
And is
Figure FDA0002612997900000027
When K isi2When B, the equation is rewritten as:
Figure FDA0002612997900000028
where E is the identity matrix, all roots AeAll have negative real parts, the system is stable, and when t → ∞,
Figure FDA0002612997900000029
estimated equalization current
Figure FDA00026129979000000210
Will converge to a true equilibrium current.
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