Battery cluster equalization circuit and control method

Abstract

The invention relates to the technical field of battery protection, and discloses a battery cluster equalization circuit and a control method, a DC / DC converter circuit is improved, an MOSFET field effect transistor and a buffer capacitor are added, when the MOSFET field effect transistor is used for turn-off protection, a follow current loop can be provided through the buffer capacitor, and the overvoltage problem during the turn-off protection of the MOSFET is solved; and meanwhile, the bypass diode is added, and the protection action of the high-voltage box fuse is matched, so that the problem of fault diffusion of short circuit of the direct-current bus when multiple battery clusters are connected in parallel is solved, and the serially connected DC / DC is protected from being damaged.

Description

Technical Field

[0001] The present invention relates to the technical field of battery protection, and in particular to a battery cluster balancing circuit and a control method. Background Art

[0002] As the energy storage market becomes increasingly prosperous, energy storage battery products are developing towards large capacity and high density. Large-capacity batteries and high-energy-density container energy storage systems can effectively reduce integration costs, reduce floor space, and shorten construction periods, thereby improving the economic benefits of energy storage systems. However, this also brings the following problems: Increasing the number of battery clusters in parallel can achieve an increase in power under the same container size, but due to the inconsistency of the internal resistance and temperature of each battery, parallel battery clusters will cause circulation during the charging and discharging process, and the voltages of each cluster will be forced to be balanced. After the battery cluster with a smaller internal resistance is fully charged or discharged, the other battery clusters must stop charging and discharging. The battery system cannot be fully charged or discharged, resulting in battery capacity loss and temperature rise, accelerating battery attenuation, and reducing the available capacity of the battery system. In addition, with the increase in the number of battery clusters in parallel, the circulation problem of energy storage equipment will be aggravated. Improving the balancing ability between battery clusters will become the key to the safe and efficient operation of the energy storage system.

[0003] like Figure 1 As shown, in the series battery cluster balancing system, the capacity mismatch problem and circulating current problem between battery clusters can be eliminated by adjusting the voltage output by the DC / DC converter and compensating for the voltage deviation between different battery clusters. The power capacity and output voltage design range of the series DC / DC converter only need to meet the voltage deviation requirements between battery clusters. Therefore, the cost is lower and the efficiency is higher.

[0004] The input voltage of the series DC / DC converter is the common DC bus voltage of the battery cluster or the battery cluster voltage, and the output voltage is the deviation voltage between the battery clusters. The voltage regulation range is wide, so the existing technology usually adopts isolated DC / DC + bidirectional Buck / boost two-stage conversion. The mainstream isolated DC / DC solutions include dual active bridge solutions and resonant solutions. Taking LLC+Buck / boost circuit as an example, Figure 2 As shown in the figure, when a DC bus short circuit occurs, even if the DC / DC converter circuit is blocked, the battery cluster will form a short circuit loop through the body diode of the switch tube S8 and the inductor L1 on the output side of the DC / DC converter, eventually causing the switch tube S8 to fail due to overcurrent. After the switch tube S8 fails and an open circuit occurs, the output capacitor Cout will also be subjected to reverse pressure, causing the explosion-proof valve to explode. Therefore, it is necessary to provide corresponding protection for the series DC / DC converter to prevent the fault from expanding.

[0005] In the prior art, a high-voltage and high-current IGBT is connected in series in the power loop of the battery cluster and the series DC / DC as a solid-state switch to protect the series DC / DC converter. However, the IGBT is connected in series in the loop, which has large losses and high heat dissipation costs. There is a risk of overvoltage breakdown when the IGBT is turned off, which can easily lead to the continued spread of the DC bus short-circuit fault when multiple battery clusters are connected in parallel, and the reliability is poor. Summary of the invention

[0006] The present invention provides a battery cluster balancing circuit and a control method, which solves the technical problems in the prior art that in a power circuit of a battery cluster and a series DC / DC, an IGBT is connected in series in the circuit, resulting in large losses and high heat dissipation costs, and there is a risk of overvoltage breakdown when the IGBT is turned off, which easily leads to the continued spread of a DC bus short-circuit fault when multiple battery clusters are connected in parallel, and the reliability is poor.

[0007] In view of this, a first aspect of the present invention provides a battery cluster balancing circuit, comprising a series DC / DC converter and a battery cluster, wherein the series DC / DC converter comprises an LLC circuit and a Buck circuit, wherein the input side of the LLC circuit is coupled to a common DC bus of the battery cluster, and high-voltage box fuses are provided at the coupling points between the two ends of the input side of the LLC circuit and the common DC bus of the battery cluster;

[0008] The output side of the LLC circuit is connected in parallel with the input side of the Buck circuit;

[0009] The output side of the Buck circuit is provided with a freewheeling and filtering inductor branch;

[0010] The freewheeling and filtering inductor branch comprises a filtering inductor L1, a switch tube (S8) and a MOSFET field effect transistor Q1 connected in series;

[0011] An output capacitor Cout and a bypass diode D1 are connected in parallel at the output side of the Buck circuit. The output capacitor Cout and the power diode D1 are connected to the common DC bus of the battery cluster through the battery cluster and the high-voltage box fuse in sequence.

[0012] Optionally, the MOSFET field effect transistor Q1 is further connected in parallel with a capacitor C1.

[0013] Optionally, the MOSFET field effect transistor Q1, the switch tube S8 and the filter inductor L1 are connected in series in sequence.

[0014] Optionally, the switch tube S8, the filter inductor L1 and the MOSFET field effect transistor Q1 are connected in series in sequence.

[0015] Optionally, a thyristor device SCR1 is connected in parallel to the output side of the Buck circuit, the thyristor device SCR1 is connected in parallel to the power diode D1, and the thyristor device SCR1 is connected in series to the battery cluster.

[0016] Optionally, the freewheeling and filtering inductor branch is connected in parallel with an output capacitor Cout, and the output capacitor Cout is a unipolar capacitor.

[0017] Optionally, the filter inductor L1 and the output capacitor Cout are both connected in series with the MOSFET field effect transistor Q1.

[0018] Optionally, a DC / DC input fuse is connected between the high voltage box fuse and the input side of the LLC circuit.

[0019] In a second aspect, the present invention further provides a control method for a battery cluster balancing circuit, which is applied to the battery cluster balancing circuit described in the first aspect, comprising:

[0020] When a short circuit is detected in the common DC bus of the battery cluster, the switch tube of the DC / DC converter is blocked;

[0021] When the output capacitor Cout of the DC / DC converter is discharged through the common DC bus of the battery cluster, when it is detected that the current on the output side of the Buck rises to a preset protection current threshold, the MOSFET field effect transistor Q1 is turned off, so that the current on the output side of the Buck circuit forms a freewheeling loop through the power diode D1 and the battery cluster, and the current flowing through the power diode D1 rises to the preset fuse current of the high-voltage box fuse, and the high-voltage box fuse is blown.

[0022] It can be seen from the above technical solutions that the present invention has the following advantages:

[0023] The present invention improves the DC / DC converter circuit, adds a MOSFET field effect transistor and a buffer capacitor, and provides a freewheeling circuit through the buffer capacitor when the MOSFET field effect transistor is turned off for protection, thereby solving the overvoltage problem when the MOSFET is turned off for protection; at the same time, a bypass diode is added, and the protection action of the high-voltage box fuse is coordinated to solve the fault diffusion problem of the DC bus short circuit when multiple battery clusters are connected in parallel, thereby protecting the series-connected DC / DC from damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of a series battery cluster balancing system in the prior art;

[0025] Figure 2 A circuit diagram of a battery cluster series DC / DC converter of LLC+Buck / boost circuit in the prior art;

[0026] Figure 3 A DC bus short-circuit protection circuit diagram based on a series IGBT switch in the prior art;

[0027] Figure 4 A schematic diagram of a battery cluster balancing circuit provided by the first embodiment of the present invention;

[0028] Figure 5 A schematic diagram of a battery cluster balancing circuit provided by a second embodiment of the present invention;

[0029] Figure 6 A schematic diagram of a battery cluster balancing circuit provided by a third embodiment of the present invention;

[0030] Figure 7 A schematic diagram of a battery cluster balancing circuit provided in accordance with a fourth embodiment of the present invention;

[0031] Figure 8 The present invention provides a flow chart of a control method for a battery cluster balancing circuit. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] It should be noted that the terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or apparatus.

[0034] The input voltage of the series DC / DC converter is the battery cluster voltage, and the output voltage is the deviation voltage between battery clusters. The voltage regulation range is wide, so the existing technology usually adopts isolated DC / DC + bidirectional Buck / boost two-stage conversion. The mainstream isolated DC / DC solutions include dual active bridge solutions and resonant solutions. Take LLC+Buck / boost circuit as an example. Figure 2As shown in the figure, when a DC bus short circuit occurs, even if the DC / DC converter circuit is blocked, the battery cluster will form a short circuit loop through the body diode of the switch tube S8 and the inductor L1 on the output side of the DC / DC converter, eventually causing the switch tube S8 to fail due to overcurrent. After the switch tube S8 fails and an open circuit occurs, the output capacitor Cout will also be subjected to reverse pressure, causing the explosion-proof valve to explode. Therefore, it is necessary to provide corresponding protection for the series DC / DC converter to prevent the fault from expanding.

[0035] The existing technology connects high-voltage and high-current IGBTs in series as solid-state switches in the power circuit of the battery cluster and the series DC / DC converter, which can quickly isolate and clear faults. Figure 3 As shown, Figure 3 The DC bus short-circuit protection circuit based on the series IGBT switch is illustrated. When the DC bus short-circuit occurs, each battery cluster will form a short-circuit loop through the body diode of the output side switch tube S8 of the series DC / DC converter. By turning off the IGBT of the solid-state switch, the fault loop can be cut off to prevent DC / DC from being damaged by overcurrent. The specific process is as follows: 1. When the DC bus short-circuit is detected, the MOSFETs of the primary and secondary sides of the series DC / DC converter are blocked; 2. After blocking, the battery cluster forms a short-circuit loop through the short-circuit point and the body diode of the MOSFETS8 of the DC / DC secondary side Buck circuit, and the current begins to rise; 3. When the overcurrent of the secondary side Buck circuit switch tube S8 is detected, the solid-state switch IGBT is turned off to achieve protection.

[0036] The solid-state switch solution based on high-voltage IGBT has the advantages of fast protection speed and active short-circuit current limitation. However, the IGBT is connected in series in the loop, which has large losses and high heat dissipation costs. There is a risk of overvoltage breakdown when the IGBT is turned off, which can easily lead to the continued spread of DC bus short-circuit faults when multiple battery clusters are connected in parallel, and the reliability is poor.

[0037] In view of this, if Figure 4 As shown, Figure 4 A battery cluster balancing circuit provided by a first embodiment of the present invention is illustrated, comprising a series-connected DC / DC converter and a battery cluster, wherein the series-connected DC / DC converter comprises an LLC circuit and a Buck circuit.

[0038] The LLC circuit includes a parallel-connected DC part, a first switch tube branch, a transformer T1, a second switch tube branch, a third switch tube branch and a DC capacitor. Both ends of the DC part are coupled to the DC bus, the DC part includes two capacitors Cdc1 and Cdc2 connected in series, the first switch tube branch includes two switch tubes S1 and S2 connected in series, the neutral point of the two capacitors Cdc1 and Cdc2 connected in series is connected to the first input end of the primary winding of the transformer T1 through the capacitor Cr, and the two switch tubes S1 and S2 are connected to the second input end of the primary winding of the transformer T1 through the inductor Ls. The second switch tube branch includes two switch tubes S3 and S4 connected in series, the third switch tube branch includes two switch tubes S5 and S6 connected in series, the midpoint of the two switch tubes S3 and S4 connected in series is connected to the midpoint of the two switch tubes S5 and S6 connected in series through the secondary winding of the transformer T1, and both ends of the second and third switch tube branches are connected in parallel with the capacitor Cm1.

[0039] The input side of the LLC circuit is coupled to the common DC bus of the battery cluster, and high-voltage box fuses are provided at the coupling points between the two ends of the input side of the LLC circuit and the common DC bus of the battery cluster;

[0040] The output side of the LLC circuit is connected in parallel with the input side of the Buck circuit;

[0041] The Buck circuit includes a switch tube S7 and a freewheeling and filtering inductor branch. The output side of the Buck circuit is provided with a freewheeling and filtering inductor branch.

[0042] The freewheeling and filtering inductor branch includes a switch tube S8, a filtering inductor L1 and a MOSFET field effect transistor Q1. The MOSFET field effect transistor (Q1), the switch tube (S8) and the filtering inductor (L1) are connected in series in sequence.

[0043] An output capacitor Cout and a bypass diode D1 are connected in parallel at the output side of the Buck circuit. The output capacitor Cout and the power diode D1 are connected to the common DC bus of the battery cluster through the battery cluster and the high-voltage box fuse in sequence.

[0044] The MOSFET field effect transistor Q1 is also connected in parallel with a capacitor C1.

[0045] The cathode of the power diode D1 is connected to the negative electrode of the battery cluster, and the positive electrode of the battery cluster is connected to the input side of the LLC circuit and the high-voltage box fuse F1.

[0046] Among them, the MOSFET field effect transistor Q1, the switch tube S8 and the filter inductor L1 are connected in series in sequence.

[0047] In some embodiments, the filter inductor branch is connected in parallel with an output capacitor Cout, and the output capacitor Cout is a bipolar capacitor.

[0048] A DC / DC input fuse is connected between the high voltage box fuse and the input side of the LLC circuit.

[0049] The control principle of a battery cluster balancing circuit provided by the first embodiment of the present invention is:

[0050] During normal operation, the MOSFET field effect transistor Q1 is always on.

[0051] When a short circuit is detected in the common DC bus of the battery cluster, the switch tube of the DC / DC converter is blocked;

[0052] When the output capacitor Cout of the DC / DC converter is discharged through the common DC bus of the battery cluster, when the current on the output side of the Buck circuit is detected to rise to the preset protection current threshold, the MOSFET field effect transistor Q1 is turned off to achieve overcurrent protection. After the MOSFET field effect transistor Q1 is turned off, the current of the inductor L1 forms a freewheeling loop through the output capacitor Cout, the capacitor C1 connected in parallel at both ends of Q1, and the body diode of S8, thereby preventing Q1 from overvoltage failure; at the same time, the current flowing through the power diode D1 gradually rises to the preset fuse current of the high-voltage box fuse, and the high-voltage box fuse is blown to achieve protection.

[0053] Among them, after the capacitor Cout on the output side of the series DC / DC converter is discharged through the DC bus, the positive electrode BAT+ of the battery cluster will return to the negative electrode BAT- of the battery through the short-circuit point of the DC bus and the diode D1 in parallel on the DC / DC output side in sequence; on the other hand, the positive electrode BAT+ of the battery cluster will also return to the negative electrode BAT- of the battery through the short-circuit point of the DC bus, the MOSFET field effect transistor Q1 on the output side of the series DC / DC converter, the body diode of the switch tube S8, and the filter inductor L1 of the LLC circuit.

[0054] like Figure 5 As shown, Figure 5 A battery cluster balancing circuit provided by a second embodiment of the present invention is illustrated, comprising a series-connected DC / DC converter and a battery cluster, wherein the series-connected DC / DC converter comprises an LLC circuit and a Buck circuit.

[0055] The LLC circuit includes a parallel-connected DC part, a first switch tube branch, a transformer T1, a second switch tube branch, a third switch tube branch and a DC capacitor. Both ends of the DC part are coupled to the DC bus, the DC part includes two capacitors Cdc1 and Cdc2 connected in series, the first switch tube branch includes two switch tubes S1 and S2 connected in series, the neutral point of the two capacitors Cdc1 and Cdc2 connected in series is connected to the first input end of the primary winding of the transformer T1 through the capacitor Cr, and the two switch tubes S1 and S2 are connected to the second input end of the primary winding of the transformer T1 through the inductor Ls. The second switch tube branch includes two switch tubes S3 and S4 connected in series, the third switch tube branch includes two switch tubes S5 and S6 connected in series, the midpoint of the two switch tubes S3 and S4 connected in series is connected to the midpoint of the two switch tubes S5 and S6 connected in series through the secondary winding of the transformer T1, and both ends of the second and third switch tube branches are connected in parallel with the capacitor Cm1.

[0056] The input side of the LLC circuit is coupled to the common DC bus of the battery cluster, and high-voltage box fuses are provided at the coupling points between the two ends of the input side of the LLC circuit and the DC bus;

[0057] The output side of the LLC circuit is connected in parallel with the input side of the Buck circuit;

[0058] The Buck circuit includes a switch tube S7 and a freewheeling and filtering inductor branch. The output side of the Buck circuit is provided with a freewheeling and filtering inductor branch.

[0059] The freewheeling and filtering inductor branch includes a switch tube S8, a filtering inductor L1 and a MOSFET field effect transistor Q1, and the switch tube S8, the filtering inductor L1 and the MOSFET field effect transistor Q1 are connected in series in sequence.

[0060] An output capacitor Cout and a bypass diode D1 are connected in parallel at the output side of the Buck circuit. The output capacitor Cout and the power diode D1 are connected to the common DC bus of the battery cluster through the battery cluster and the high-voltage box fuse in sequence.

[0061] The MOSFET field effect transistor Q1 is also connected in parallel with a capacitor C1.

[0062] The cathode of the power diode D1 is connected to the negative electrode of the battery cluster, and the positive electrode of the battery cluster is connected to the input side of the LLC circuit and the high-voltage box fuse F1.

[0063] Among them, the switch tube S8, the filter inductor L1 and the MOSFET field effect transistor Q1 are connected in series in sequence.

[0064] The filter inductor branch is connected in parallel with an output capacitor Cout, and the output capacitor Cout is a bipolar capacitor.

[0065] A DC / DC input fuse is connected between the high voltage box fuse and the input side of the LLC circuit.

[0066] The control principle of a battery cluster balancing circuit provided by the second embodiment of the present invention is:

[0067] During normal operation, the MOSFET field effect transistor Q1 is always on.

[0068] When a short circuit is detected in the common DC bus of the battery cluster, the switch tube of the DC / DC converter is blocked;

[0069] When the output capacitor Cout of the DC / DC converter is discharged through the common DC bus of the battery cluster, when the current on the output side of the Buck circuit is detected to rise to the preset protection current threshold, the MOSFET field effect transistor Q1 is turned off to achieve overcurrent protection. After the MOSFET field effect transistor Q1 is turned off, the current of the inductor L1 forms a freewheeling loop through the capacitor C1, the output capacitor Cout, and the body diode of S8 connected in parallel at both ends of Q1, thereby preventing Q1 from overvoltage failure. At the same time, the current flowing through the power diode D1 gradually rises to the preset fuse current of the high-voltage box fuse, and the high-voltage box fuse is blown to achieve protection.

[0070] Among them, after the capacitor Cout on the output side of the series DC / DC converter is discharged through the DC bus, the positive electrode BAT+ of the battery cluster will return to the negative electrode BAT- of the battery through the short-circuit point of the DC bus and the diode D1 connected in parallel on the DC / DC output side in sequence; on the other hand, the positive electrode BAT+ of the battery cluster will also return to the negative electrode BAT- of the battery through the short-circuit point of the DC bus, the body diode of the switch tube S8 on the output side of the series DC / DC converter, the filter inductor L1 of the LLC circuit, and the MOSFET field effect transistor Q1.

[0071] like Figure 6 As shown, Figure 6 A battery cluster balancing circuit provided by a third embodiment of the present invention is illustrated, comprising a series-connected DC / DC converter and a battery cluster, wherein the series-connected DC / DC converter comprises an LLC circuit and a Buck circuit.

[0072] The LLC circuit includes a parallel-connected DC part, a first switch tube branch, a transformer T1, a second switch tube branch, a third switch tube branch and a DC capacitor. Both ends of the DC part are coupled to the DC bus, the DC part includes two capacitors Cdc1 and Cdc2 connected in series, the first switch tube branch includes two switch tubes S1 and S2 connected in series, the neutral point of the two capacitors Cdc1 and Cdc2 connected in series is connected to the first input end of the primary winding of the transformer T1 through the capacitor Cr, and the two switch tubes S1 and S2 are connected to the second input end of the primary winding of the transformer T1 through the inductor Ls. The second switch tube branch includes two switch tubes S3 and S4 connected in series, the third switch tube branch includes two switch tubes S5 and S6 connected in series, the midpoint of the two switch tubes S3 and S4 connected in series is connected to the midpoint of the two switch tubes S5 and S6 connected in series through the secondary winding of the transformer T1, and both ends of the second and third switch tube branches are connected in parallel with the capacitor Cm1.

[0073] The input side of the LLC circuit is coupled to the common DC bus of the battery cluster, and high-voltage box fuses are provided at the coupling points between the two ends of the input side of the LLC circuit and the common DC bus of the battery cluster;

[0074] The output side of the LLC circuit is connected in parallel with the input side of the Buck circuit;

[0075] The Buck circuit includes a switch tube S7 and a freewheeling and filtering inductor branch. The output side of the Buck circuit is provided with a freewheeling and filtering inductor branch.

[0076] The freewheeling and filtering inductor branch includes a switch tube S8, a filtering inductor L1 and a MOSFET field effect transistor Q1. The MOSFET field effect transistor Q1, the switch tube S8 and the filtering inductor L1 are connected in series in sequence.

[0077] An output capacitor Cout and a bypass diode D1 are connected in parallel at the output side of the Buck circuit. The output capacitor Cout and the power diode D1 are connected to the common DC bus of the battery cluster through the battery cluster and the high-voltage box fuse in sequence.

[0078] The MOSFET field effect transistor Q1 is also connected in parallel with a capacitor C1.

[0079] The cathode of the power diode D1 is connected to the negative electrode of the battery cluster, and the positive electrode of the battery cluster is connected to the input side of the LLC circuit and the high voltage box fuse.

[0080] Among them, the MOSFET field effect transistor Q1, the switch tube S8 and the filter inductor L1 are connected in series in sequence.

[0081] The freewheeling and filtering inductor branch is connected in parallel with an output capacitor Cout, which is a bipolar capacitor.

[0082] A thyristor device SCR1 is connected in parallel to the output side of the Buck circuit, the thyristor device SCR1 is connected in parallel to the power diode D1, and the thyristor device SCR1 is connected in series to the battery cluster.

[0083] A DC / DC input fuse is connected between the high voltage box fuse and the input side of the LLC circuit.

[0084] The control principle of a battery cluster balancing circuit provided by the third embodiment of the present invention is:

[0085] During normal operation, the MOSFET field effect transistor Q1 is always on.

[0086] When a short circuit is detected in the battery cluster, the switch tube of the DC / DC converter is blocked.

[0087] After the switch tube is turned off, the positive electrodes PCS+ of other battery clusters on the common DC bus of the battery cluster will pass through the short-circuit point of the faulty battery cluster and the capacitor C on the output side of the series DC / DC converter. OUT Back to the negative pole PCS- of the DC bus, it is equivalent to the DC bus quickly charging the series DC / DC output side capacitor of the faulty battery cluster. Since the series DC / DC converter only needs to adjust the potential difference between different battery clusters when it is working normally, and the working voltage is lower than 100V, therefore, when a fault occurs, the DC bus voltage is above 1000V to charge the output capacitor of the series DC / DC converter, which will cause the low-voltage side device to fail due to overvoltage, and even serious consequences such as insulation breakdown.

[0088] When the output capacitor Cout of the DC / DC converter of the faulty battery cluster is charged at the common DC bus of the battery cluster, when the capacitor voltage at the output side of the Buck circuit is detected to exceed the set threshold, the parallel thyristor device SCR1 is turned on, and the positive electrode PCS+ of other battery clusters on the DC bus will return to the negative electrode PCS- of the DC bus through the short-circuit point of the battery in this cluster and the thyristor device SCR1. The energy of the output capacitor can also be discharged through SCR1, thereby solving the problem of overvoltage on the output side; when the short-circuit current flowing through the thyristor device SCR1 increases to a certain extent, the input fuses F1 and F2 of the high-voltage box of the battery cluster are blown to achieve protection, thereby protecting the low-voltage side of the series DC / DC converter from overvoltage failure and insulation breakdown.

[0089] like Figure 7 As shown, Figure 7 A battery cluster balancing circuit provided by a fourth embodiment of the present invention is illustrated, comprising a series DC / DC converter and a battery cluster, wherein the series DC / DC converter comprises an LLC circuit and a Buck circuit.

[0090] The LLC circuit includes a parallel-connected DC part, a first switch tube branch, a transformer T1, a second switch tube branch, a third switch tube branch and a DC capacitor. Both ends of the DC part are coupled to the DC bus, the DC part includes two capacitors Cdc1 and Cdc2 connected in series, the first switch tube branch includes two switch tubes S1 and S2 connected in series, the neutral point of the two capacitors Cdc1 and Cdc2 connected in series is connected to the first input end of the primary winding of the transformer T1 through the capacitor Cr, and the two switch tubes S1 and S2 are connected to the second input end of the primary winding of the transformer T1 through the inductor Ls. The second switch tube branch includes two switch tubes S3 and S4 connected in series, the third switch tube branch includes two switch tubes S5 and S6 connected in series, the midpoint of the two switch tubes S3 and S4 connected in series is connected to the midpoint of the two switch tubes S5 and S6 connected in series through the secondary winding of the transformer T1, and both ends of the second and third switch tube branches are connected in parallel with the capacitor Cm1.

[0091] The input side of the LLC circuit is coupled to the common DC bus of the battery cluster, and high-voltage box fuses are provided at the coupling points between the two ends of the input side of the LLC circuit and the common DC bus of the battery cluster;

[0092] The output side of the LLC circuit is connected in parallel with the input side of the Buck circuit;

[0093] The Buck circuit includes a switch tube S7 and a freewheeling and filtering inductor branch. The output side of the Buck circuit is provided with a freewheeling and filtering inductor branch.

[0094] The freewheeling and filtering inductor branch includes a switch tube S8 and a filtering inductor L1.

[0095] An output capacitor Cout is connected in parallel to the output side of the Buck circuit.

[0096] The filter inductor L1 and the output capacitor Cout are both connected in series with the MOSFET field effect transistor Q1.

[0097] The MOSFET field effect transistor Q1 is also connected in parallel with a capacitor C1.

[0098] The cathode of the power diode D1 is connected to the negative electrode of the battery cluster, and the positive electrode of the battery cluster is connected to the common DC bus of the battery cluster through a high-voltage box fuse.

[0099] Output capacitor C out A unipolar capacitor.

[0100] The filter inductor L1 and the output capacitor Cout are both connected in series with the MOSFET field effect transistor Q1.

[0101] The thyristor device SCR1 is connected in parallel with the power diode D1, and the thyristor device SCR1 is connected in series with the battery cluster.

[0102] A DC / DC input fuse is connected between the high voltage box fuse and the input side of the LLC circuit.

[0103] To further solve the problem of output capacitor Cout being subjected to reverse voltage when the DC bus is short-circuited, Figure 7 As shown, the fault protection MOSFET field effect transistor Q1 can be connected in series to the branch at the rear end of the output capacitor Cout. When the MOSFET field effect transistor Q1 is turned off and the power diode D1 is turned on, the output capacitor Cout will not be subjected to the conduction voltage drop of the power diode D1, so that a lower-cost unipolar electrolytic capacitor can be used.

[0104] Specifically, the control principle of a battery cluster balancing circuit provided by the fourth embodiment of the present invention is:

[0105] During normal operation, the MOSFET field effect transistor Q1 is always on.

[0106] When a short circuit is detected in the common DC bus of the battery cluster, the switch tube of the DC / DC converter is blocked.

[0107] The capacitor Cout on the output side of the series DC / DC converter discharges to the DC bus through the MOSFET field effect transistor Q1. When the output current of the DC / DC converter flowing through the MOSFET field effect transistor Q1 rises to the protection threshold, the MOSFET field effect transistor Q1 is turned off to achieve overcurrent protection.

[0108] After the MOSFET field effect transistor Q1 is turned off, the power diode D1 is naturally turned on. When the short-circuit current flowing through the power diode D1 gradually increases to the fusing current, the input fuses F1 and F2 of the high-voltage box of the battery cluster are finally blown to achieve protection.

[0109] It should be noted that the present invention improves the DC / DC converter circuit, adds MOSFET field effect transistors and buffer capacitors, and provides a freewheeling circuit through the buffer capacitor when the MOSFET field effect transistor is turned off for protection, thereby solving the overvoltage problem when the MOSFET is turned off for protection; at the same time, a bypass diode is added, and the protection action of the high-voltage box fuse is coordinated, and the fault propagation problem of DC bus short circuit when multiple battery clusters are connected in parallel is solved, thereby protecting the series-connected DC / DC from damage.

[0110] like Figure 8 As shown, the present invention also provides a control method for the battery cluster balancing circuit using the above embodiment, including:

[0111] Step S1: When a short circuit of the common DC bus of the battery cluster is detected, the switch tube of the DC / DC converter is blocked.

[0112] Step S2: When the output capacitor Cout of the DC / DC converter is discharged through the common DC bus of the battery cluster, when it is detected that the current on the output side of the Buck circuit rises to a preset protection current threshold, the MOSFET field effect transistor Q1 is turned off, so that the current on the output side of the Buck circuit forms a freewheeling loop through the power diode D1 and the battery cluster, and the current flowing through the power diode D1 rises to a preset fuse current of the high-voltage box fuse, and the high-voltage box fuse is blown.

[0113] It can be understood that the control method of the battery cluster balancing circuit provided by the present invention using the above-mentioned embodiment can provide a freewheeling circuit through a buffer capacitor when using the MOSFET field effect transistor shutdown protection, thereby solving the fault diffusion problem of DC bus short circuit when multiple battery clusters are connected in parallel, thereby protecting the series DC / DC from damage. At the same time, the MOSFET field effect transistor has low loss and low heat dissipation risk when working normally, avoiding the overvoltage problem of high-voltage IGBT shutdown.

[0114] In several embodiments provided by the present invention, it is understood that each box in the flow chart or block diagram can represent a module, a program segment or a part of a code, and a part of a module, a program segment or a code includes one or more executable instructions for realizing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box can also occur in a different order from that marked in the accompanying drawings. For example, two consecutive boxes can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved.

[0115] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery cluster balancing circuit, comprising a series DC / DC converter and a battery cluster, wherein the series DC / DC converter comprises an LLC circuit and a Buck circuit, characterized in that: The input side of the LLC circuit is coupled to a common DC bus of the battery cluster, and high-voltage box fuses are provided at the coupling points between the two ends of the input side of the LLC circuit and the common DC bus of the battery cluster; The output side of the LLC circuit is connected in parallel with the input side of the Buck circuit; The output side of the Buck circuit is provided with a freewheeling and filtering inductor branch; The freewheeling and filtering inductor branch comprises a filtering inductor (L1), a switch tube (S8) and a MOSFET field effect transistor (Q1) connected in series; An output capacitor (Cout) and a bypass diode (D1) are connected in parallel on the output side of the Buck circuit, and the output capacitor (Cout) and the power diode (D1) are connected to a common DC bus of the battery cluster through the battery cluster and the high-voltage box fuse in sequence.

2. The battery cluster balancing circuit according to claim 1, characterized in that: The MOSFET field effect transistor (Q1) is also connected in parallel with a capacitor (C1).

3. The battery cluster balancing circuit according to claim 1, characterized in that: The MOSFET field effect transistor (Q1), the switch tube (S8) and the filter inductor (L1) are sequentially connected in series.

4. The battery cluster balancing circuit according to claim 1, characterized in that: The switch tube (S8), the filter inductor (L1) and the MOSFET field effect transistor (Q1) are connected in series in sequence.

5. The battery cluster balancing circuit according to claim 1, characterized in that: A thyristor device (SCR1) is connected in parallel to the output side of the Buck circuit, the thyristor device (SCR1) is connected in parallel to the power diode (D1), and the thyristor device (SCR1) is connected in series to the battery cluster.

6. The battery cluster balancing circuit according to claim 1, characterized in that: The output capacitor (Cout) is a unipolar capacitor.

7. The battery cluster balancing circuit according to claim 6, characterized in that: The filter inductor (L1) and the output capacitor (Cout) are both connected in series with the MOSFET field effect transistor (Q1).

8. The battery cluster balancing circuit according to claim 1, characterized in that: A DC / DC input fuse is connected between the high voltage box fuse and the input side of the LLC circuit.

9. A control method for a battery cluster balancing circuit, applied to the battery cluster balancing circuit according to any one of claims 1 to 8, characterized in that: include: When a short circuit is detected in the common DC bus of the battery cluster, the switch tube of the DC / DC converter is blocked; When the output capacitor (Cout) of the DC / DC converter is discharged through the common DC bus of the battery cluster, when it is detected that the current on the output side of the Buck rises to a preset protection current threshold, the MOSFET field effect transistor (Q1) is turned off, so that the current on the output side of the Buck circuit forms a freewheeling loop through the power diode (D1) and the battery cluster, and the current flowing through the power diode (D1) rises to a preset fuse current of a high-voltage box fuse, and the high-voltage box fuse is blown.

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