CN115986878A - Balance system for local energy transfer and control method thereof - Google Patents

Abstract

The present invention relates to the technical field of battery equalization, in particular to a local energy transfer equalization system and a control method thereof. The system includes at least one battery cluster, and the battery cluster includes a plurality of battery cells connected in series. For any current battery cell, there is also It includes a first switch loop and a second switch loop, the first switch loop includes the current cell connected in series, a first switch and an inductance, the second switch loop includes the current cell connected in series, the second switch and another inductance, the first switching loop of the adjacent cell shares the inductance, the second switching loop of the adjacent cell shares the other inductance, the inductance in the first switching loop and the second switching loop The inductance in the loop is on a different pole of the current cell. By using the shared inductance, electric energy can be transferred between adjacent cells to achieve partial balance of battery electric energy, reduce the total cost of the system, and effectively improve the reliability of the system.

Description

A balance system for local energy transfer and its control method

technical field

The invention relates to the technical field of battery balancing, in particular to a balancing system for local energy transfer and a control method thereof.

Background technique

The traditional BMS uses passive equalization, which is not efficient, and the capacity of the energy storage system is large, and the equalization time is long; therefore, the BMS active equalization scheme is gradually proposed. At present, the flyback topology is commonly used, and the cell terminal is selected through the channel, which will require Active balancing cells are connected to the power supply voltage to achieve active balancing. In this method, MOS tubes are usually used as switches to control channel selection. Therefore, more MOS tubes are used, the circuit is huge and complex, and the price of the bill of materials is relatively high. , In addition, the active balanced power supply of each cell depends on the power supply voltage, which has high requirements on the power supply capacity of the power supply voltage, and is prone to failure due to voltage fluctuations.

Contents of the invention

In view of the fact that the above active equalization circuit uses many MOS tubes, the price of the bill of materials is relatively high, and there are high requirements for the power supply capacity of the power supply voltage, and it is easy to cause failure due to the influence of voltage fluctuations. The present invention is based on the principle of buck-boost control circuit , combined with the idea of energy transfer between cells and group control, a balance system for local energy transfer and its control method are proposed.

In order to realize the above-mentioned purpose of the invention, the present invention provides the following technical solutions:

A balancing system for local energy transfer, comprising at least one battery cluster, the battery cluster includes a plurality of battery cells connected in series, and for any current battery cell, it also includes a first switching circuit and a second switching circuit, the first The switching loop includes a current cell connected in series, a first switching switch, and an inductor, the second switching loop includes a current cell connected in series, a second switching switch, and another inductor, and the first switching of an adjacent cell The loops share the inductance, the second switching loops of adjacent cells share the other inductance, and the inductance in the first switching loop and the inductance in the second switching loop are located at different electrodes of the current cell.

As a preferred solution, it also includes an isolation transformer. Among the plurality of cells connected in series, the last cell in the battery cluster forms a series circuit with the first port of the isolation transformer and the second switch, and the second switch of the isolation transformer The ports are connected in parallel to both ends of the first cell.

As a preferred solution, it also includes a pre-charging switch, a pre-charging resistor and a main circuit switch. The pre-charging resistor and the pre-charging switch are connected in series between the positive pole of the battery cluster and the positive pole of the DC bus, and the main circuit switch is connected in parallel to the positive pole of the DC bus. and the positive electrode of the battery cluster.

As a preferred solution, it also includes a discharge switch and a discharge resistor, the discharge switch and the discharge resistor are connected in series to form a discharge branch, and the two ends of the discharge branch are connected in parallel to the two ends of the battery cluster.

As a preferred solution, it also includes a processor and an isolated driver,

The processor is connected to the first switch and the second switch through an isolated drive, and is used to control the opening and closing of the first switch and the second switch respectively.

Based on the same idea, a control method for a balanced system of local energy transfer is also proposed, and a balanced system for local energy transfer as described in any one of the foregoing is constructed, and the control method includes the following steps:

Mark the cell with the highest voltage as the current cell, and then compare the voltage of the current cell, the voltage of the previous cell adjacent to the current cell, and the voltage of the next cell; the voltage of the current cell is greater than the voltage of the next cell The voltage of the battery cell, then close the first switching switch corresponding to the current battery cell, charge the inductance shared by the current battery cell and the previous battery cell, then disconnect the first switching switch corresponding to the current battery cell and close the previous battery cell at the same time The corresponding first switching switch supplies power to the previous battery until the voltage difference between the current battery and the previous battery is less than the voltage difference threshold; the voltage of the current battery is lower than the voltage of the next battery, and the current battery is closed The corresponding second switching switch charges the inductance shared by the current battery cell and the next battery cell, and then turns off the second switching switch corresponding to the current battery cell and simultaneously closes the second switching switch corresponding to the next battery cell to charge the next battery cell. The cell is recharged until the voltage difference between the current cell and the next cell is less than the voltage difference threshold.

As a preferred solution, the last battery cell in the battery cluster supplies electricity to the first battery cell in the battery cluster through an isolation transformer.

As a preferred solution, the steps further include: when the system is powered on, detecting the voltage of the battery cluster, and if the voltage difference of the battery cluster is greater than or equal to the discharge threshold, the voltage in the battery cluster is passed through a discharge resistor connected in parallel to the battery cluster for passive charging. Balanced discharge.

As a preferred solution, if the voltage difference of the battery clusters is less than the discharge threshold when the system is powered on, inter-cluster equalization is performed among multiple battery clusters.

As a preferred solution, if the voltage difference between the battery clusters is less than the inter-cluster voltage difference threshold, each battery cluster discharges the AC grid through the positive pole of the DC bus and the negative pole of the DC bus, or charges from the AC grid.

Compared with prior art, the beneficial effect of the present invention:

The present invention proposes a balance system for local energy transfer. In the circuit structure, each battery core shares inductance with the adjacent battery core through two switching circuits, and the electric energy of the adjacent battery core can be transferred from the shared inductance by switching the switch. The inductance is transmitted to form a local battery cell balance. And based on this circuit, local traversal and group equalization of cells can be realized. During active equalization, the number of switches controlled at the same time is greatly reduced, and the amount of switch data used for active equalization is also greatly reduced, which simplifies the circuit and reduces the material cost. price. At the same time, even if the power supply capacity of the power supply voltage used for active equalization is low, the effect of equalization will not be affected.

Description of drawings

Fig. 1 is a kind of balanced system topological diagram of partial energy transfer in embodiment 1;

Fig. 2 is a topological diagram of a local energy transfer equalization system with an isolation transformer and a passive equalization circuit in Embodiment 1;

Fig. 3 is a kind of local energy transfer equalization system diagram with precharging circuit and isolated drive in embodiment 1;

Fig. 4 is a kind of balanced system diagram of specific local energy transfer in embodiment 2;

Figure 5 is a schematic diagram of the discharge path when the cluster voltage is higher than 20V in Example 2;

Fig. 6 is a schematic diagram of equalization of battery cell 2 to battery cell 1 in embodiment 2;

Fig. 7 is a schematic diagram of equalization of battery cell 2 to battery cell 3 in embodiment 2;

FIG. 8 is a flow chart of a specific balancing strategy method in Embodiment 2.

Detailed ways

The present invention will be further described in detail below in conjunction with test examples and specific embodiments. However, it should not be understood that the scope of the above subject matter of the present invention is limited to the following embodiments, and all technologies realized based on the content of the present invention belong to the scope of the present invention.

Example 1

A balanced system for local energy transfer, the topological diagram is shown in Figure 1, including at least one battery cluster, and the battery cluster includes a plurality of battery cells connected in series, in Figure 1, battery cluster 1, battery cluster 2 ... battery cluster As an example, each battery cluster includes several battery cells connected in series, as shown in Figure 1, battery cell 1, battery cell 2, battery cell 3, battery cell 4... cell n-1, cell n, In addition, both ends of the battery cluster are respectively connected to the positive pole P+ of the DC bus and the negative pole P- of the DC bus for supplying power to the DC bus or obtaining electric energy from the DC bus. It also includes several inductors (for example, L1, L2, L3...Ln, Ln-1 in Figure 1), several first changeover switches (for example, D1, D2, D3...Dn in Figure 1) and several second Toggle switches (for example, D1b, D2b, D3b...Dnb in Figure 1).

For any current cell, it also includes a first switch loop and a second switch loop, the first switch loop includes the current cell connected in series, the first switch and the inductor, and the second switch loop includes the current cell connected in series The core, the second switching switch and another inductance, the inductance in the first switching loop and the inductance in the second switching loop are located at different electrodes of the current cell. Taking cell 2 as an example, when cell 2 is the current cell, there are two switching circuits corresponding to cell 2: the first switching circuit and the second switching circuit. In the first switching loop, the battery cell 2, the first switching switch D2 and the inductor L1 are connected in series; in the second switching loop, the battery cell 2, the second switching switch D2b and the inductor L2 are connected in series, and the inductor L1 is connected to the positive pole of the battery cell 2, and the inductor L2 is connected to the negative pole of the cell 2, and the inductors L1 and L2 are not at the same end of the cell 2. Each cell has a corresponding first switching loop and a second switching loop, and the first switching loops of adjacent cells share an inductance, and the second switching loops of adjacent cells share another inductance. 2, there are two cells adjacent to it, cell 1 with the serial number at the front and cell 3 with the sequence number at the rear. Since the inductance L1 and L2 are not at the same end of the cell 2, the cell 1 The first switching circuit of the battery cell 2 shares the inductance L1 with the first switching circuit of the battery cell 2. The inductance L1 in the first switching circuit of the battery cell 1 is also the inductance L1 in the first switching circuit of the battery cell 2, and the second switching circuit of the battery cell 3 The switching circuit and the second switching circuit of the cell 2 share the inductance L2, and the inductance L2 in the second switching circuit of the cell 3 is also the inductance L2 in the second switching circuit of the cell 2, forming inductances in the first switching circuit and A staggered arrangement in the second switching loop.

A topological diagram of a partial energy transfer equalization system with an isolation transformer and a passive equalization circuit is shown in Figure 2. Taking the cell cluster 1 as an example, the connection relationship between the above-mentioned cells, the first switching switch, the second switching switch, and the inductor is analyzed. Note that there is a one-to-one correspondence between the serial numbers of the first switch, the second switch, and the battery cells. The first switch D2 is connected in parallel to the right side of the battery cell 2 in the cell cluster 1, and the second switch D2b is connected in parallel to the left side; For example, an inductor L1 is connected between the anode of the cell 2 and the first switch D2, and an inductor L2 is connected between the cathode of the cell 2 and the second switch D2b. The inductor L1 is connected between the switch D2, and the inductor L2 is connected between the anode of the cell 2 and the second switch D2b; the inductor L1 is shared between the cell 2 and the previous cell (cell 1), and the cell 2 and the second switch D2b share the inductor L1. The latter cell (cell 3) shares the inductance L2.

Further, as shown in Figure 2, the last battery cell in each battery cluster forms a series loop with the first port of the isolation transformer and the second switch, and the second port of the isolation transformer is connected in parallel to the first battery cell in the battery cluster. both ends of the core. Take cell cluster 1 in Figure 2 as an example to explain: the negative pole of the last cell (cell n) in cell cluster 1 is connected to pin 1 of the first port of the isolation transformer Ln, and the first port of the isolation transformer Ln After the No. 2 pin of the port is connected to the second switching switch Dnb, the second switching switch Dnb is connected back to the positive pole of the cell n to form a series circuit. Pins 3 and 4 of the second port of the isolation transformer Ln are connected in parallel to the cell 1 of the cell cluster 1 .

In addition to local active equalization, the system can also achieve passive equalization. Each battery cluster also has a corresponding passive equalization circuit. As shown in Figure 2, the passive equalization circuit includes discharge switches (K1b, K2b, K3b...Knb) and Discharge resistors (R1a, R2a, R3a...Rna), the discharge switch and the discharge resistor are connected in series to form a discharge branch, and the two ends of the discharge branch are connected in parallel to the two ends of the battery cluster. Figure 2 shows the passive battery cluster 1 Equalization circuit, when the discharge switch Knb is closed, the cells connected in series in the battery cluster are discharged through the discharge resistor Rna to achieve passive equalization.

A partial energy transfer equalization system diagram with pre-charging circuit and isolated drive is shown in Figure 3. The system also includes pre-charging switches (K1, K2, K3...Kn), pre-charging resistors (R1, R2, R3... Rn) and the main circuit switch (K1a, K2a, K3a...Kna), the pre-charging resistor and the pre-charging switch are connected in series between the positive pole of the battery cluster and the positive pole of the DC bus, and the main circuit switch is connected in parallel between the positive pole of the DC bus and the positive pole of the DC bus. Between the positive poles of the battery clusters, a pre-charging circuit is formed. Each battery cluster has a corresponding pre-charging circuit, and the number of each device in the pre-charging circuit is distinguished by a natural number of 1, 2, 3...n.

When designing the system, it is considered that a large number of switches are used, and the switching of the switches is likely to interfere with the circuit. Therefore, the system also includes a processor and an isolated driver. The processor (MCU) communicates with the first switch (such as , D1, D2, D3...Dn in Figure 3) and the second switch (for example, D1b, D2b, D3b...Dnb in Figure 3) are connected to control the first switch and the second switch respectively on and off.

Based on the same idea, a control method for a balanced system of local energy transfer is also proposed, including the following steps:

The cell with the highest marked voltage is the current cell, and then compare the voltage of the previous cell and the next cell of the current cell;

The voltage of the current battery cell is greater than the voltage of the next battery cell, then close the first switching switch corresponding to the current battery cell, charge the inductance shared by the current battery cell and the previous battery cell, and disconnect the first switch corresponding to the current battery cell While switching the switch, close the first switching switch corresponding to the previous battery cell, and supply power to the previous battery cell until the voltage difference between the current battery cell and the previous battery cell is less than the voltage difference threshold. Take the battery cell 2 in the battery cluster 1 in Figure 3 as an example for illustration. If the voltage of the battery cell 3 is greater than the voltage of the battery cell 1, the first switching switch D2 corresponding to the battery cell 2 is closed, and the battery cell 2 supplies the battery cell 2 Charge the inductance L1 shared with the battery cell 1, and then close the first switch D1 of the battery cell 1 while turning off the first switch D2 corresponding to the battery cell 2, the inductance L1 discharges, and the power released by the inductance L1 is used for power supply Cell 1 is powered, so that the power on cell 3 is transferred to cell 1 through inductance L1, and this conversion can continue until the voltage difference between cell 1 and cell 3 is less than the voltage difference threshold, complete local energy balance.

The voltage of the current cell is lower than the voltage of the next cell, close the second switch corresponding to the current cell, charge the inductance shared by the current cell and the next cell, and then disconnect the second switch corresponding to the current cell switch and at the same time close the second switch corresponding to the latter battery cell to replenish power to the latter battery cell until the voltage difference between the current battery cell and the next battery cell is less than the voltage difference threshold. Take the battery cell 2 in the battery cluster 1 in Figure 3 as an example for illustration. If the voltage of the battery cell 3 is lower than the voltage of the battery cell 1, the second switching switch D2b corresponding to the battery cell 2 is closed, and the battery cell 2 supplies power. The inductance L2 shared by the cell 2 and the cell 1 is charged, and then the second switch D3b of the cell 3 is closed while the second switch D2b corresponding to the cell 2 is turned off, the inductance L2 is discharged, and the power released by the inductance L2 is given to Cell 3 is charged, so that the power on cell 1 is transferred to cell 3 through inductance L2, and this conversion can continue until the voltage difference between cell 1 and cell 3 is less than the threshold value of the voltage difference. Complete local energy balance.

In the system, the cells connected in series are all discharged or recharged through the adjacent cells, but the first cell in the battery cluster - cell 1 and the last cell - cell n, are only An adjacent battery cell cannot realize the balanced discharge or balanced power supply of other batteries through the adjacent battery cells. The improvement is to use the isolation transformer to connect the first battery cell in the battery cluster-cell 1 and the last battery pack. A cell-cell n is connected in parallel. After this connection, the cells adjacent to cell 1 are cell 2 and cell n, and the cells adjacent to cell n are cell n-1 and cell 1. The last battery cell in the cluster supplies power to the first battery cell in the battery cluster through an isolation transformer.

As a preferred solution, the steps also include: when the system is powered on, detecting the voltage of the battery cluster, if the voltage difference of a certain battery cluster is greater than or equal to the discharge threshold (for example, 20V), then the voltage in the battery cluster is connected in parallel to the battery cluster The discharge resistors (R1a, R2a, R3a...Rna) perform passive equalization discharge. That is, before the energy balance between the clusters, the passive equalization discharge of the battery clusters is performed first, and the balance between the battery clusters is performed after the voltage difference is less than the discharge threshold.

If the voltage of the battery cluster is less than the discharge threshold (for example, 20V) and greater than or equal to the inter-cluster voltage difference threshold (for example, 5V), the inter-cluster equalization among multiple battery clusters can be directly performed. If the voltage difference between the battery clusters is greater than or less than the inter-cluster voltage difference threshold, it means that the energy between the clusters is balanced, and each battery cluster discharges the AC grid through the positive pole of the DC bus and the negative pole of the DC bus, or charges from the AC grid. By setting the discharge threshold and the inter-cluster voltage difference threshold, the phase division of the power balance is made finer, which facilitates accurate monitoring and avoids unnecessary time or capacity consumption.

Example 2

The present invention designs a specific balance system diagram of local energy transfer as shown in Figure 4, including isolation drive optocoupler, switch tube, inductor, MCU, isolation transformer and resistors, etc., the aforementioned components are combined into an active and passive equalization circuit . This circuit has the advantages of high equalization efficiency, high reliability, small size, and low BOM cost. The switch can be a switching device such as a MOS or a triode.

The detailed working principle of the system is as follows:

1) When the system is powered on, first check the voltage of each cluster. If the voltage difference of each cluster is greater than the discharge threshold of 20V, close the discharge switch Knb of the battery cluster with a higher voltage difference, so that it can discharge through the discharge resistor Rna until the voltage difference is lowered. Until the discharge threshold is less than 20V (see the path marked by the arrow line on the right in Figure 5 for the discharge path).

If the voltage difference of each cluster is less than 20V and the voltage difference of each cluster is greater than or equal to 5V, the pre-charge switches K1~Kn are directly closed, and the inter-cluster equalization is performed through the pre-charge resistor Rn. When the voltage difference of each cluster is less than 5V, it means that the energy between the clusters is balanced, and then the battery clusters are connected in parallel to the DC bus P+ and P-.

As an optimal solution, instead of directly connecting the battery clusters in parallel to the DC busbars P+ and P-, the main circuit switches K1a~Kna are closed, and the pre-charging switches K1~Kn are turned off after 1s, so that each cluster is connected in parallel to the DC busbars P+ and P-. P-on.

2) After the high voltage is applied, the BMS periodically detects the voltage of all cells, marks the highest cell voltage position n, and then compares the voltage of n-1 and n+1 cells. If cell n-1 is greater than cell n+1, then Close the switch Dn (D ₁ , D ₂ D ₃ ... D _n is the first switch), and then close D1 to supply power to the cell n-1 until the voltage difference is less than 10mV, if the cell n-1 is smaller than the cell n +1, close switch Dnb, and then close Dn+1b to supply power to cell n+1 until the voltage difference is less than 10mV.

Example: Suppose the highest voltage is cell 2 at this time, if the voltage of cell 1 is > cell 3, the MCU closes D2 to charge L1 (see the arrow path where cell 2 is located in Figure 6), then disconnects D2, and closes the adjacent D1 , then the energy stored in L1 charges battery cell 1 (see the arrow path where battery cell 1 is located in Figure 6); see Figure 5 for the detailed current path;

If the voltage of cell 1 is less than that of cell 3, the MCU closes D2b (D1b, D2b, D3b...Dnb is the second switch) to charge L2 (see the arrow path where cell 2 is located in Figure 7), then disconnects D2b, and closes D3b, then the energy stored in L2 charges the battery cell 3 (see the arrow path where the battery cell 3 is located in Figure 7).

3) Then continue to detect the voltage to find the highest cell voltage, and use the same method to turn off and on the corresponding switch tube to supply the adjacent cells with equal power. If this continues, the voltage of each cluster of cells will tend to be consistent .

4) Since the last cell n is electrically non-adjacent to the first cell, an isolation transformer is used to form a closed loop of energy transfer. If the voltage of cell n is too high, it is enough to control the corresponding MOS or BJT switch Charge battery 1.

Based on the above principles, the flow chart of the specific balancing strategy method is shown in Figure 8, which specifically includes the following steps:

S1, the BMS power-on self-test is completed;

S2, detect whether the voltage difference of each cluster is greater than 20V; if it is greater, mark the highest cluster voltage, close the switch Knb of the highest cluster voltage, and discharge it until the voltage difference is less than 20V; otherwise, execute step S3;

S3, closing switches K1-Kn;

S4, detect whether the voltage difference of each cluster is greater than 5V, if so, return to step S3, otherwise, close the switches K1a~Kna, and turn off the switches K1~Kn after 1S;

S5, periodically detect the voltage of each cluster of cells;

S6, mark the cell position n with the highest voltage;

S7, judging whether the voltage of cell n-1 is greater than that of cell n+1, if so, execute step S8, otherwise execute step S10;

S8, close the switch Dn, and then close D1 to supply power to the battery cell n-1;

S9, judging whether the voltage of cell n and cell n-1 is less than 10mV, if yes, return to step S5, otherwise return to step S8.

S10, close switch Dnb, then close Dn+1b to supply power to cell n+1;

S11, if the voltage of battery cell n and battery cell n+1 is less than 10mV, if yes, return to step S10, otherwise return to step S11.

The advantages of the circuit and equalization strategy of the present invention are: (1) the invention uses circuit components equivalent to traditional passive equalization to achieve the effect of active equalization; (2) the circuit is simple, low in cost and good in reliability; (3) the matching Appropriate equalization strategy can make the equalization effect very good; (4) This scheme has strong compatibility and is suitable for all inter-cluster and intra-cluster battery module equalization schemes. This solution is not limited to energy storage battery systems, and can be extended to battery systems of any voltage platform.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (10)

1. A balanced system for local energy transfer, characterized in that it includes at least one battery cluster, the battery cluster includes a plurality of battery cells connected in series, and for any current battery cell, it also includes a first switching circuit and a second switching circuit loop, the first switching loop includes a current cell connected in series, a first switch and an inductor, the second switching loop includes a current cell connected in series, a second switch and another inductor, and the adjacent cell The first switching loop of the shared inductance, the second switching loop of the adjacent cell shares the other inductance, the inductance in the first switching loop and the inductance in the second switching loop are located in the current cell different electrodes. 2. The equalization system of a kind of local energy transmission as claimed in claim 1, it is characterized in that, also comprises isolation transformer, among the plurality of batteries connected in series, the last battery core and the first of described isolation transformer The port and the second switch form a series loop, and the second port of the isolation transformer is connected in parallel to both ends of the first cell. 3. The equalization system of a kind of local energy transfer as claimed in claim 1, is characterized in that, also comprises precharge switch, precharge resistance and main circuit switch, and precharge resistance and precharge switch are connected in series in battery cluster Between the positive pole and the positive pole of the DC bus, the main circuit switch is connected in parallel between the positive pole of the DC bus and the positive pole of the battery cluster. 4. The equalization system of a kind of local energy transmission as claimed in claim 1, is characterized in that, also comprises discharge switch and discharge resistance, after described discharge switch and discharge resistance are connected in series, form discharge branch, discharge branch two ends connected in parallel at both ends of the battery cluster. 5. The equalization system of a kind of local energy transfer as described in any one of claims 1 to 4, further comprising a processor and an isolation drive, The processor is connected to the first switch and the second switch through an isolated drive, and is used to control the opening and closing of the first switch and the second switch respectively. 6. A control method of a balanced system of local energy transmission, characterized in that, constructing a balanced system of a kind of local energy transmission as claimed in any one of claims 1-5, the control method may further comprise the steps: Mark the cell with the highest voltage as the current cell, and then compare the voltage of the current cell, the voltage of the previous cell adjacent to the current cell, and the voltage of the next cell; The voltage of the current battery cell is greater than the voltage of the next battery cell, then close the first switching switch corresponding to the current battery cell, charge the inductance shared by the current battery cell and the previous battery cell, and then disconnect the first switching switch corresponding to the current battery cell Switching the switch and simultaneously closing the first switching switch corresponding to the previous battery cell, supplying electricity to the previous battery cell until the voltage difference between the current battery cell and the previous battery cell is less than the voltage difference threshold; The voltage of the current cell is lower than the voltage of the next cell, close the second switch corresponding to the current cell, charge the inductance shared by the current cell and the next cell, and then disconnect the second switch corresponding to the current cell switch and at the same time close the second switch corresponding to the latter battery cell to replenish power to the latter battery cell until the voltage difference between the current battery cell and the next battery cell is less than the voltage difference threshold. 7. The control method of a local energy transfer equalization system according to claim 6, wherein the last battery cell in the battery cluster supplies power to the first battery cell in the battery cluster through an isolation transformer. 8. The control method of a balance system of local energy transfer as claimed in claim 6 or 7, wherein the step further comprises: when the system is powered on, detecting the voltage of the battery cluster, if the voltage difference of the battery cluster is greater than or equal to the discharge threshold, the voltage in the battery cluster is passed through the discharge resistor connected in parallel to the battery cluster for passive equalization discharge. 9. The control method of a balance system of local energy transfer as claimed in claim 8, wherein if the voltage difference of the battery cluster is less than the discharge threshold when the system is powered on, the battery clusters are clustered. balance between. 10. The control method of a balanced system of local energy transfer as claimed in claim 9, wherein if the voltage difference between battery clusters is less than the inter-cluster voltage difference threshold, each battery cluster passes through the positive pole of the DC bus and The negative pole of the DC bus discharges the AC grid or charges it from the AC grid.

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