One-way series connection type inter-battery-cluster circulation equalization circuit with bypass function

Abstract

The invention discloses a one-way series-connection type inter-battery-cluster circulation equalization circuit with a bypass function, which is characterized in that the circuit topology of the one-way series-connection type inter-battery-cluster circulation equalization circuit comprises a pre-stage circuit and a post-stage circuit. The output side is connected in series with the to-be-compensated cluster, only the circulating current is compensated, and the system loss is small; compared with a bidirectional series compensation circuit, the circuit only needs to work in one direction, and is simple in structure and easy to control; compared with a bidirectional series compensation circuit, positive and negative voltage output can be realized only through post-stage circuit switching, the requirements of different working conditions are met, and the switching process is faster; the post-stage circuit can give consideration to a bypass function, and the fault tolerance is better.

Description

Technical Field

[0001] The invention relates to a unidirectional series-connected inter-cluster battery circulating current balancing circuit, belonging to the technical field of power electronics. Background Art

[0002] With the construction of new power systems, new energy power generation equipment such as wind power and solar power has gradually become the main body of power supply. However, these new energy power generation methods are limited by natural environmental conditions, and their regulation capabilities are relatively weak. It is difficult to respond to changes in load demand in a timely manner, and energy storage needs have emerged. Energy storage plays a vital role in balancing the power on the power generation side and the load side. When the energy supply on the power generation side exceeds the demand on the load side, the excess energy will be stored in the energy storage system; conversely, when the supply on the power generation side is insufficient, the energy storage system releases the stored energy to meet the demand.

[0003] In recent years, electrochemical energy storage technology represented by lithium-ion batteries has become one of the important technical routes for energy storage.

[0004] A typical electrochemical energy storage system includes: battery system, power conversion (PCS=Power Converter System) system and energy management system (EMS=Energy Management System). The battery system consists of a large number of cells and necessary sampling, monitoring, cooling and fire protection components. The power conversion system realizes the bidirectional flow of electric energy between the battery and the grid / load. The energy management system is used to manage the battery and PCS system.

[0005] At present, the voltage and current specifications of a single battery cell are relatively small. Therefore, in order to increase the capacity of the electrochemical energy storage system, the battery system usually requires a large number of battery cells to be connected in series and parallel. The typical series-parallel form is: to facilitate battery cell management, a certain number of battery cells are connected in series to form a battery pack; to increase the voltage of the battery system, a certain number of battery packs are connected in series to form a battery cluster; to increase the capacity of the battery system, a certain number of battery clusters are connected in parallel to form a battery system.

[0006] For example: The typical 5MWH battery system configuration in the industry is as follows:

[0007] (1) Single cell parameters:

[0008] Battery specifications: 314AH; Rated voltage and current: 3.2V; Charge and discharge voltage range: 2.40V~3.60V;

[0009] Rated capacity: 3.2V*314Ah=1KWH.

[0010] (2) The battery pack is composed of 52 cells connected in series, and its typical parameters are:

[0011] Rated voltage: 3.2V*52=166.4V; charge and discharge voltage range: 124.8V~187.2V;

[0012] Rated capacity: 166.4V*314Ah=52.25KWH.

[0013] (3) The battery cluster consists of 8 battery packs connected in series, and its typical parameters are:

[0014] Rated voltage: 8*166.4=1331.2V; charge and discharge voltage range: 998.4V~1497.6V;

[0015] Rated capacity: 52.25*8=418Kwh.

[0016] (4) The battery system consists of 12 battery clusters connected in parallel, and its typical parameters are:

[0017] Rated voltage: 166.4V*8=1331.2V; Charge and discharge voltage range: 998.4V~1497.6V;

[0018] The rated capacity is 418KWH*12=5MWH.

[0019] It can be seen that a typical 5MWH battery system configuration consists of 4992 cells (4992 = 52*8*12) connected in series and parallel. Therefore, the consistency of the factory parameters and the consistency of the operating status of the battery cells are crucial to the performance of the battery system throughout its life cycle.

[0020] With the improvement of industry level, the consistency of battery cells leaving the factory has been greatly improved. The typical parameter differences are: the voltage difference of a single battery cell is less than 5mV, and the internal resistance of the battery cell is less than 0.05mΩ.

[0021] Although the voltage and internal resistance parameter deviations of single cells are small, a cluster of batteries consists of hundreds of cells connected in series. The slight differences between single cells are easily amplified, resulting in differences in voltage or internal resistance between battery clusters. This difference will cause inconsistent currents in each cluster during the charge and discharge process. The inconsistency of charge and discharge currents can easily lead to further discretization of cell parameters, thereby affecting the performance of the battery system.

[0022] Let’s still take the above 5WMH system as an example.

[0023] The rated voltage range of a single battery cell is 3.2V±5mV, and the internal resistance is 0.17mΩ±0.05mΩ.

[0024] The rated voltage range of a single battery cluster is 1331.2V±2.08V, and the internal resistance is 70.72mΩ±20.8mΩ.

[0025] Taking two clusters as an example, one cluster of batteries is equivalent to a battery string resistance model, where the battery voltage is equal to the voltage sum of the series-connected cells in the battery cluster, and the resistance is equal to the internal resistance sum of the series-connected cells in the battery cluster.

[0026] (1) Figure 1 As shown, under ideal working conditions: there is no deviation in the battery cluster voltage and internal resistance.

[0027] The rated voltage of battery cluster R1 is 1331.2V, and the internal resistance is 70.72mΩ.

[0028] The rated voltage of battery cluster R2 is 1331.2V, and the internal resistance is 70.72mΩ.

[0029] Discharging at 314A, the discharge current of battery cluster R1 is 157A, and the discharge current of battery cluster R2 is 157A. The calculation process is as follows:

[0030]

[0031] in:

[0032] V BUS is the voltage of the busbar of the battery cluster in parallel.

[0033] I1 is the discharge current of battery cluster R1, and I2 is the discharge current of battery cluster R2.

[0034] V1 is the series voltage of battery cluster R1, and V2 is the series voltage of battery cluster R2.

[0035] R1 is the series internal resistance of battery cluster R1, and R2 is the series internal resistance of battery cluster R2.

[0036] (2) Figure 2 As shown, non-ideal working condition 1: the battery cluster voltage has deviation, and the internal resistance has no deviation.

[0037] The rated voltage of battery cluster R1 is: 1331.2V+2.08V=1333.28V, and the internal resistance is 70.72mΩ.

[0038] The rated voltage of battery cluster R2 is: 1331.2V-2.08V=1329.12V, and the internal resistance is 70.72mΩ.

[0039] Using the same calculation method as the ideal working condition, we can know that:

[0040] When discharging at 314A, the discharge current of battery cluster R1 is 187.6A, and the charging current of battery cluster R2 is 127.4A.

[0041] Compared with the ideal working condition, a circulation current of 187.6A-157A=30.6A appears between the two clusters.

[0042] (3) Figure 3As shown, non-ideal working condition 2: the battery cluster voltage has no deviation, but the internal resistance has deviation.

[0043] The rated voltage of battery cluster R1 is 1331.2V, and the internal resistance is 70.72mΩ+20.8mΩ=91.52mΩ.

[0044] The rated voltage of battery cluster R2 is 1331.2V, and the internal resistance is 70.72mΩ–20.8mΩ=49.92mΩ.

[0045] Using the same calculation method as the ideal working condition, we can know that:

[0046] When discharging at 314A, the discharge current of battery cluster R1 is 110.8A, and the discharge current of battery cluster R2 is 203.2A.

[0047] Compared with the ideal working condition, a circulation current of 203.2A-157A=46.2A appears between the two clusters.

[0048] Comparing the ideal working condition and the non-ideal working condition 1 and 2, it can be seen that when the battery cluster voltage and internal resistance are the same, there is no circulating current; when there is a slight difference in the battery cluster voltage and internal resistance, in extreme cases, a large circulating current between battery clusters will be generated, affecting the performance of the battery system. Therefore, the circulating current between battery clusters must be controlled. Summary of the invention

[0049] The technical problem to be solved by the present invention is that when there are slight factory differences in the voltage and internal resistance of battery clusters, a large circulating current between battery clusters will be generated, and the circulating current between battery clusters must be controlled.

[0050] In order to solve the above technical problems, the technical solution of the present invention is to provide a unidirectional series type battery cluster inter-circulating current balancing circuit with a bypass function, characterized in that the circuit topology of the unidirectional series type battery cluster inter-circulating current balancing circuit includes a front-stage circuit and a rear-stage circuit, wherein:

[0051] The input side of the front-stage circuit is connected in parallel to the battery system bus or battery cluster, and the front-stage circuit takes power from the input side and outputs a compensation voltage to the rear-stage circuit;

[0052] The output side of the rear-stage circuit is connected in series with the battery cluster to be compensated, and is used to control the direction and bypass of the output side voltage: in the discharge state, it absorbs energy from the input side of the front-stage circuit, and injects a positive voltage into the battery cluster to be compensated through the rear-stage circuit; in the charging state, it absorbs energy from the input side of the front-stage circuit, and injects a negative voltage into the battery cluster to be compensated through the rear-stage circuit.

[0053] Preferably, the front-stage circuit is composed of a unidirectional DC / DC converter.

[0054] Preferably, the unidirectional DC / DC converter is a single-stage DCDC converter or a derivative structure thereof, or a multi-stage DCDC converter or a derivative structure thereof.

[0055] Preferably, the subsequent circuit includes a commutation bypass circuit consisting of a switch device 1, a switch device 2, a switch device 3 and a switch device 4, wherein:

[0056] One end of switch device one is connected to an output end of the preceding stage circuit and one end of switch device three, the other end of switch device one is connected to one end of switch device two and one end of a unidirectional series battery cluster, the other end of switch device two is connected to another output end of the preceding stage circuit and the other end of switch device four, and the other end of switch device three is connected to one end of switch device four and the other end of the unidirectional series battery cluster.

[0057] Preferably, the switch device 1, the switch device 2, the switch device 3 and the switch device 4 are power devices or mechanical switches.

[0058] Compared with the prior art solutions, the present invention has the following beneficial effects:

[0059] 1. The output side of the present invention is connected in series to the cluster to be compensated, and only the circulating current is compensated, resulting in small system loss.

[0060] 2. Compared with the bidirectional series compensation circuit, the present invention only needs to work in one direction, has a simple circuit structure, and is easy to control.

[0061] 3. Compared with the bidirectional series compensation circuit, the present invention can achieve positive and negative voltage output only by switching the subsequent circuit, meet the requirements of different working conditions, and the switching process is faster.

[0062] 4. The back-end circuit of the present invention can also take into account the bypass function and has better fault tolerance. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 The ideal working condition is shown;

[0064] Figure 2 It shows the non-ideal working condition 1;

[0065] Figure 3 The second non-ideal working condition is shown;

[0066] Figure 4 The circuit topology of the present invention is illustrated;

[0067] Figure 5 The comparison diagram of discharge condition 1 is shown, in which the left side is without compensation and the right side is with compensation;

[0068] Figure 6The comparison diagram of discharge condition 2 is shown. In the diagram, the left side is without compensation and the right side is with compensation.

[0069] Figure 7 The comparison diagram of charging condition 1 is shown, in which the left side is without compensation and the right side is with compensation;

[0070] Figure 8 A comparison diagram of charging condition 2 is shown, in which the left side is without compensation and the right side is with compensation. DETAILED DESCRIPTION

[0071] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0072] The embodiment of the present invention discloses a unidirectional series type battery cluster inter-circulation current balancing circuit with bypass function, and its circuit topology is as follows: Figure 4 As shown, it includes two stages of circuits. The front stage circuit is composed of a unidirectional DC / DC converter. The DCDC converter takes power from the input side and outputs a compensation voltage. The input side is connected in parallel to the battery system bus or battery cluster. The rear stage circuit is composed of a commutation bypass circuit composed of switches SW1 to SW4, which is used to control the direction and bypass of the output side voltage. The output side is connected in series to the battery cluster to be compensated. When a positive voltage needs to be output, switches SW1 and SW4 are closed; when a negative voltage needs to be output, switches SW2 and SW3 are closed; when compensation or bypass is not required, switches SW1 and SW3 are closed or switches SW2 and SW4 are closed.

[0073] Specific:

[0074] like Figure 5 As shown, discharge condition 1: the battery clusters have different voltages and the same internal resistance. The balancing topology draws power from the parallel bus and injects a positive voltage into the battery cluster R2, which equivalently increases the voltage of the battery cluster R2 to achieve current sharing.

[0075] like Figure 6 As shown, discharge condition 2: the battery clusters have the same voltage but different internal resistances. The balancing topology draws power from the parallel bus and injects a positive voltage into the battery cluster R1, which equivalently reduces the resistance of the battery cluster R1 and realizes current sharing.

[0076] like Figure 7 As shown, charging condition 1: the battery clusters have different voltages and the same internal resistance. The cluster balancer draws power from the parallel bus and injects a negative voltage into the battery cluster R1, which equivalently reduces the voltage of the battery cluster R1 and realizes current sharing.

[0077] like Figure 8As shown, charging condition 2: the battery clusters have the same voltage and internal resistance, and the balancing topology draws power from the parallel bus and injects a reverse voltage into the battery cluster R1, which is equivalent to reducing the resistance of the battery cluster R1 and achieving current sharing.

[0078] From the above analysis, it can be seen that the input side of the balancing circuit proposed by the present invention is connected in parallel to the battery bus or both ends of the battery cluster, and the low-voltage side is connected in series to the battery cluster to be compensated. In the discharge state, the balancing circuit absorbs energy from the input side and injects a positive voltage into the battery cluster to be compensated. In the charging state, the balancing circuit absorbs energy from the input side and injects a negative voltage into the battery cluster to be compensated. Under different working conditions, the battery cluster equalizer only requires unidirectional energy flow, and different compensation targets can be met by controlling the positive direction of the output voltage.

[0079] In this solution, the front-stage circuit can be composed of a common single-stage DCDC converter or its derivative structure, such as a Buck circuit or its derivative circuit, an LLC circuit and its derivative circuit, a DAB circuit and its derivative circuit, etc. The front-stage circuit can also be composed of a multi-stage DCDC converter or its derivative structure, such as a two-stage circuit composed of an LLC circuit and a Buck circuit connected in series.

[0080] The subsequent circuit can be implemented using power devices or mechanical switches.

Claims

1. A unidirectional series battery cluster inter-cluster circulating current balancing circuit with bypass function, characterized in that: The circuit topology of the unidirectional series type inter-cluster circulating current balancing circuit includes a front-stage circuit and a rear-stage circuit, wherein: The input side of the front-stage circuit is connected in parallel to the battery system bus or battery cluster, and the front-stage circuit takes power from the input side and outputs a compensation voltage to the rear-stage circuit; The output side of the rear-stage circuit is connected in series with the battery cluster to be compensated, and is used to control the direction and bypass of the output side voltage: in the discharge state, it absorbs energy from the input side of the front-stage circuit, and injects a positive voltage into the battery cluster to be compensated through the rear-stage circuit; in the charging state, it absorbs energy from the input side of the front-stage circuit, and injects a negative voltage into the battery cluster to be compensated through the rear-stage circuit.

2. A unidirectional series type battery cluster circulating current balancing circuit with bypass function as claimed in claim 1, characterized in that: The front stage circuit is composed of a unidirectional DC / DC converter, the DCDC converter takes power from the input side and outputs a compensation voltage. The input side is connected in parallel to the battery system bus or battery cluster.

3. A unidirectional series type battery cluster circulating current balancing circuit with bypass function as claimed in claim 2, characterized in that: The unidirectional DC / DC converter is a single-stage DCDC converter or a derivative structure thereof, or a multi-stage DCDC converter or a derivative structure thereof.

4. The unidirectional series type battery cluster circulating current balancing circuit with bypass function as claimed in claim 1, characterized in that: The latter circuit is composed of a commutation bypass circuit composed of switch devices SW1 to SW4, which is used to control the direction and bypass of the output side voltage, and the output side is connected in series with the battery cluster to be compensated. When a positive voltage needs to be output, the switch device SW1 and the switch device SW4 are closed; when a negative voltage needs to be output, the switch device SW2 and the switch device SW3 are closed; when no compensation or bypass is required, the switch device SW1 and the switch device SW3 are closed or the switch device SW2 and the switch device SW4 are closed.

5. The unidirectional series-connected battery cluster circulating current balancing circuit with bypass function as claimed in claim 4, characterized in that: The latter circuit includes a commutation bypass circuit composed of a switch device SW1, a switch device SW2, a switch device SW3 and a switch device SW4, wherein: One end of the switch device SW1 is connected to an output end of the preceding stage circuit and one end of the switch device SW3, the other end of the switch device SW1 is connected to one end of the switch device SW2 and one end of the unidirectional series battery cluster, the other end of the switch device SW2 is connected to another output end of the preceding stage circuit and the other end of the switch device 4, and the other end of the switch device SW3 is connected to one end of the switch device SW4 and the other end of the unidirectional series battery cluster.

6. The unidirectional series-connected battery cluster circulating current balancing circuit with bypass function as claimed in claim 1, characterized in that: The switch device SW1 , the switch device SW2 , the switch device SW3 , and the switch device SW4 are power devices or mechanical switches.

7. The unidirectional series-connected battery cluster circulating current balancing circuit with bypass function as claimed in claim 1, characterized in that: The front stage circuit is composed of a unidirectional DC / DC converter.

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