Current balance control method based on power electronic transformer

Abstract

The invention discloses a current balance control method based on a power electronic transformer. The current balance control method mainly solves the problems that an existing current balance control method is prone to being affected by parameters of passive devices and low in balance precision. The method comprises the following steps: S1, controlling the voltage conversion proportion of a transformer to a rechargeable battery through a control unit; s2, the control unit receives real-time charging parameters of the rechargeable battery monitored by the battery management unit; s3, the control unit obtains the maximum permissible instantaneous charging current I1 and the maximum permissible continuous charging current I2 of the transformer through the parameters of the transformer; s4, the battery management unit obtains a charging current total reference value I3 of the rechargeable battery under the condition of the maximum allowable continuous charging current I2 according to the parameters of the rechargeable battery, and calculates an average charging current I4 of the rechargeable battery at the same time; and S5, when the average charging current I4 in the real-time charging parameters is greater than the maximum allowable continuous charging current I2, the control unit controls a current balancing module to start, and a delay compensation strategy is adopted to realize current balancing control. According to the method, the current equalization control of the single group of battery cells of the rechargeable battery is realized through the transformer, a better current equalization effect can be achieved more quickly, and the stability of the charging system is enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of current balancing control, and in particular, relates to a current balancing control method based on a power electronic transformer. Background Art

[0002] In recent years, electric vehicles have shown good prospects because of their smaller impact on the environment than traditional vehicles. Since electric vehicles are powered by onboard power and batteries store less energy per unit weight, consumers need to charge them frequently to ensure that they can be used normally. However, current charging technology is gradually unable to meet consumers' requirements for charging speed of electric vehicles.

[0003] Faster charging speed means higher charging power, so the market has higher and higher requirements for the power of the charging module in the charging pile. In existing circuit designs, the series-parallel structure of the circuit topology is generally used to achieve higher power requirements. In the battery management system of electric vehicles, the use of transformers can realize energy transfer between battery cells and perform active balancing control. This solution can not only achieve top balancing, but also bottom balancing, improve the utilization rate of system energy, and have high system efficiency and low loss.

[0004] Existing battery current balancing methods mostly use passive methods for current balancing, and achieve current balancing of any battery parallel branch by using transformers or inductors, capacitors, and passive composites. However, this method is easily affected by the parameters of passive devices and has low balancing accuracy. In recent years, active balancing methods have achieved branch current balancing by connecting DC / DC conversion modules in series in battery parallel branches. The balancing accuracy is high, but the circuit control is complex. Summary of the invention

[0005] The purpose of the present invention is to provide a current balancing control method based on a power electronic transformer, mainly to solve the problem that the existing current balancing control method is easily affected by the parameters of passive components and has low balancing accuracy.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A current balancing control method based on a power electronic transformer includes a transformer, a control unit, a battery management unit and a current balancing module; the current balancing control method includes the following steps:

[0008] S1, controlling the voltage conversion ratio of the transformer to the rechargeable battery through the control unit;

[0009] S2, the control unit receives the real-time charging parameters of the rechargeable battery monitored by the battery management unit;

[0010] S3, the control unit obtains the maximum allowable instantaneous charging current I1 and the maximum allowable continuous charging current I2 of the transformer through the transformer parameters;

[0011] S4, the battery management unit obtains a total reference value I3 of the charging current of the rechargeable battery under the condition of the maximum allowable continuous charging current I2 according to the rechargeable battery parameters, and calculates an average charging current I4 of the rechargeable battery;

[0012] S5, when the average charging current I4 in the real-time charging parameter is greater than the maximum allowable continuous charging current I2, the control unit controls the current balancing module to start, and adopts a delay compensation strategy to achieve current balancing control.

[0013] Furthermore, in step S3, the maximum allowable continuous charging current I2 is calculated as follows:

[0014]

[0015] Among them, soc i It represents the charge capacity of a single group of cells in a rechargeable battery, n means that the rechargeable battery has n groups of cells; let the terminal voltage of a single group of cells at full load be u i , then the average terminal voltage u of the fully loaded rechargeable battery ave for:

[0016]

[0017] According to the maximum allowable continuous charging current I2 and the average terminal voltage u of the fully loaded rechargeable battery ave The balancing current deviation δ of a single group of cells is calculated i :

[0018]

[0019] Among them, k1 and k2 are deviation coefficients, satisfying 0 <k1<1,0<k2<1。

[0020] Furthermore, in step S4, the calculation of the average charging current I4 of the rechargeable battery is shown as follows:

[0021]

[0022] Furthermore, the delay compensation strategy is as follows:

[0023] S41, the control unit converts the balancing command signal into a switching signal through modulation and applies it to the transformer, and makes the actual current of the battery management unit track the command current after a sampling period;

[0024] S42, obtaining a balancing current control model according to the balancing current deviation and the average charging current I4 of the rechargeable battery;

[0025] S43, using the command current of the t+2th sampling period to compensate the output current of the t+1th sampling period, and inputting the compensated current into the balanced current control model;

[0026] S44, feeding back the command current output by the balanced current control model to the current balancing module;

[0027] S45, the current balancing module outputs a balancing control voltage according to the command current, and the control unit converts the balancing control voltage into a control signal and outputs it to the transformer, and the transformer adjusts the voltage conversion ratio to achieve current balancing control.

[0028] Furthermore, the expression of the balanced current control model is:

[0029]

[0030] Wherein, t represents the tth sampling period, and λ represents the voltage conversion proportional coefficient of the transformer at the current sampling moment.

[0031] Furthermore, the parameters of each group of single battery cells are the same.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The current balancing control method of the present invention uses the maximum allowable instantaneous charging current I1 and the maximum allowable continuous charging current I2 of the transformer to calculate the average charging current during the battery charging process, and according to the relationship between the average charging current and the maximum allowable continuous charging current of the transformer, uses the current balancing module to adjust the voltage conversion ratio of the transformer by adopting a delay compensation strategy. Thus, the current balancing control of a single group of cells of the rechargeable battery can be achieved through the transformer, and a better current balancing effect can be achieved faster, thereby enhancing the stability of the charging system. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the process of the present invention.

[0035] Figure 2 It is a flow chart of the delay compensation strategy in the method of the present invention. DETAILED DESCRIPTION

[0036] The present invention is further described below in conjunction with the accompanying drawings and embodiments. The embodiments of the present invention include but are not limited to the following embodiments.

[0037] Example

[0038] The present invention discloses a current balancing control method based on a power electronic transformer, comprising a transformer, a control unit, a battery management unit and a current balancing module; Figure 1 As shown, the method uses a control unit to control the voltage conversion ratio of the transformer to the rechargeable battery. At the same time, the control unit receives the real-time charging parameters monitored by the battery management unit on the rechargeable battery.

[0039] Subsequently, the control unit obtains the maximum allowable instantaneous charging current I1 and the maximum allowable continuous charging current I2 of the transformer through the transformer parameters; wherein the transformer parameters are the rated parameter information of the transformer itself, and the control unit directly obtains them through the transformer product information. The maximum allowable continuous charging current is related to the rear-end load of the transformer. In the present invention, the maximum allowable continuous charging current I2 is calculated as follows:

[0040]

[0041] Among them, soc i It represents the charge capacity of a single group of cells in a rechargeable battery, and n represents that the rechargeable battery has n groups of cells; assuming that the parameters of each group of cells are the same, the terminal voltage of a single group of cells at full load is u i , then the average terminal voltage u of the fully loaded rechargeable battery ave for:

[0042]

[0043] According to the maximum allowable continuous charging current I2 and the average terminal voltage u of the fully loaded rechargeable battery ave The balancing current deviation δ of a single group of cells is calculated i :

[0044]

[0045] Among them, k1 and k2 are deviation coefficients, satisfying 0 <k1<1,0<k2<1。

[0046] The battery management unit obtains the total reference value I3 of the charging current of the rechargeable battery under the condition of the maximum allowable continuous charging current I2 according to the rechargeable battery parameters, and calculates the average charging current I4 of the rechargeable battery at the same time; the calculation of the average charging current I4 of the rechargeable battery is shown as follows:

[0047]

[0048] Finally, when the average charging current I4 in the real-time charging parameter is greater than the maximum allowable continuous charging current I2, the control unit controls the current balancing module to start, and adopts the delay compensation strategy to achieve current balancing control. Figure 2As shown, the delay compensation strategy is as follows: the control unit converts the balancing command signal into a switching signal through modulation and applies it to the transformer, and makes the actual current of the battery management unit track the command current after a sampling cycle; the balancing current control model is obtained according to the balancing current deviation and the average charging current I4 of the rechargeable battery:

[0049]

[0050] Among them, t represents the tth sampling period, and λ represents the voltage conversion ratio coefficient of the transformer at the current sampling moment. The command current of the t+2th sampling period is used to compensate the output current of the t+1 sampling period, and the compensated circuit is input into the balanced current control model; the command current output by the balanced current control model is fed back to the current balancing module; the current balancing module outputs the balanced control voltage according to the command current, and the control unit converts the balanced control voltage into a control signal and outputs it to the transformer, and the transformer adjusts the voltage conversion ratio to achieve current balanced control.

[0051] Through the above design, the current balancing control method of the present invention uses the maximum allowable instantaneous charging current I1 and the maximum allowable continuous charging current I2 of the transformer to calculate the average charging current during the battery charging process, and according to the relationship between the average charging current and the maximum allowable continuous charging current of the transformer, the current balancing module uses a delay compensation strategy to adjust the voltage conversion ratio of the transformer. Thus, the current balancing control of a single group of cells of the rechargeable battery can be achieved through the transformer, and a better current balancing effect can be achieved faster, thereby enhancing the stability of the charging system.

[0052] The above embodiment is only one of the preferred implementation modes of the present invention and should not be used to limit the protection scope of the present invention. Any changes or modifications that are made to the main design concept and spirit of the present invention and have no substantive significance, and the technical problems they solve are still consistent with the present invention, should be included in the protection scope of the present invention.

Claims

1. A current balancing control method based on a power electronic transformer, comprising a transformer, a control unit, a battery management unit and a current balancing module; characterized in that: The current balancing control method comprises the following steps: S1, controlling the voltage conversion ratio of the transformer to the rechargeable battery through the control unit; S2, the control unit receives the real-time charging parameters of the rechargeable battery monitored by the battery management unit; S3, the control unit obtains the maximum allowable instantaneous charging current I1 and the maximum allowable continuous charging current I2 of the transformer through the transformer parameters; S4, the battery management unit obtains a total reference value I3 of the charging current of the rechargeable battery under the condition of the maximum allowable continuous charging current I2 according to the rechargeable battery parameters, and calculates an average charging current I4 of the rechargeable battery; S5, when the average charging current I4 in the real-time charging parameter is greater than the maximum allowable continuous charging current I2, the control unit controls the current balancing module to start, and adopts a delay compensation strategy to achieve current balancing control.

2. A current balancing control method based on a power electronic transformer according to claim 1, characterized in that: In step S3, the maximum allowable continuous charging current I2 is calculated as follows: Among them, soc i It represents the charge capacity of a single group of cells in a rechargeable battery, n means that the rechargeable battery has n groups of cells; let the terminal voltage of a single group of cells at full load be u i , then the average terminal voltage u of the fully loaded rechargeable battery ave for: According to the maximum allowable continuous charging current I2 and the average terminal voltage u of the fully loaded rechargeable battery ave The balancing current deviation δ of a single group of cells is calculated i : Among them, k1 and k2 are deviation coefficients, satisfying 0 <k1<1,0<k2<1。 3. A current balancing control method based on a power electronic transformer according to claim 2, characterized in that: In step S4, the calculation of the average charging current I4 of the rechargeable battery is shown as follows:

4. The current balancing control method based on a power electronic transformer according to claim 3 is characterized in that: The delay compensation strategy is as follows: S41, the control unit converts the balancing command signal into a switching signal through modulation and applies it to the transformer, and makes the actual current of the battery management unit track the command current after a sampling period; S42, obtaining a balancing current control model according to the balancing current deviation and the average charging current I4 of the rechargeable battery; S43, using the command current of the t+2th sampling period to compensate the output current of the t+1th sampling period, and inputting the compensated current into the balanced current control model; S44, feeding back the command current output by the balanced current control model to the current balancing module; S45, the current balancing module outputs a balancing control voltage according to the command current, and the control unit converts the balancing control voltage into a control signal and outputs it to the transformer, and the transformer adjusts the voltage conversion ratio to achieve current balancing control.

5. A current balancing control method based on a power electronic transformer according to claim 4, characterized in that: The expression of the balanced current control model is: Wherein, t represents the tth sampling period, and λ represents the voltage conversion proportional coefficient of the transformer at the current sampling moment.

6. The current balancing control method based on a power electronic transformer according to claim 5, characterized in that: The parameters of the single battery cells in each group are the same.

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