Parallel capacitor bank current equalization protection circuit and system

Abstract

The application discloses a parallel capacitor bank current equalization protection circuit and system, which comprises a positive busbar, a negative busbar, a positive busbar, a negative busbar and a plurality of capacitor branch circuits; the plurality of capacitor branch circuits are arranged in a predetermined direction and are connected between the positive busbar and the negative busbar; the positive busbar is electrically connected with the positive busbar at a first access position, and the negative busbar is electrically connected with the negative busbar at a second access position; a fast-fusing unit is connected in series between each capacitor branch circuit and the corresponding busbar; the fast-fusing unit comprises a first fast-fusing unit and a second fast-fusing unit which are arranged in parallel and reversely. The application improves the current equalization of the multiple branch circuits by the misaligned access of the busbar, improves the single branch circuit rated current bearing capacity by the parallel connection of the fast-fusing units, and reduces the local electromagnetic induction, electromagnetic force influence and electromagnetic interference on the surrounding components by the reverse arrangement of the two fast-fusing units, so that the current equalization capacity and the fault branch isolation capacity of the parallel capacitor bank are improved.

Description

Technical Field

[0001] This invention relates to the field of power electronics and high-power capacitor bank protection technology, specifically to a current balancing protection circuit and system for parallel capacitor banks. Background Technology

[0002] In high-power capacitor bank applications, it is often necessary to connect multiple capacitor banks in parallel to improve the total capacitance, total ripple current withstand capability, and pulse discharge capability. Existing parallel capacitor banks typically employ a single-ended centralized input / output line or a same-side busbar configuration, where the positive and negative terminals are connected from similar locations or the same side, and multiple capacitor branches are sequentially connected in parallel to a common busbar, as exemplified by a marine DC busbar system disclosed in Chinese Patent Publication No. CN216794615U.

[0003] This type of conventional topology has the following problems:

[0004] Firstly, the inconsistent current path lengths from the external busbar to each branch result in variations in path resistance, stray inductance, and contact impedance, leading to an imbalance in the current carried by different capacitor branches. Branches closer to the input end are more likely to withstand larger charging and discharging currents and ripple currents, while branches farther from the input end have relatively smaller currents, causing localized current congestion and inconsistent device utilization.

[0005] Secondly, the local magnetic field superposition between multiple parallel branches arranged in the same direction is obvious. Under the condition of high current rapid charging and discharging, there is strong electromagnetic coupling between adjacent conductors and branches, which can easily cause additional stray inductance, transient overvoltage and unfavorable electrodynamic forces.

[0006] Third, the granularity of fault isolation is insufficient. When a short circuit, breakdown, or severe leakage occurs inside a capacitor branch, if there is a lack of a fast isolation unit for a single branch, the fault current may flow into the fault point from the entire group of capacitors, causing the fault energy to expand and even triggering cascading damage.

[0007] Fourth, when multiple fast fuses are connected in parallel in a single branch to increase the rated current capacity, if the multiple fast fuses are arranged in the same direction laterally, the magnetic field and electrodynamic force generated by their local current paths are easily superimposed in the same direction. This not only increases the electromagnetic force on the fast fuses and adjacent connectors, but may also cause additional electromagnetic interference to the surrounding capacitor connection terminals and busbar structure.

[0008] Therefore, there is an urgent need for a new electrical topology for parallel capacitor banks that can improve the current balance of multiple branches, reduce local electromagnetic coupling, and improve the isolation capability of faulty branches through only the electrical design of the busbar and the bus structure, without relying on complex active control. Summary of the Invention

[0009] The technical problem to be solved by this invention is how to improve the current balance of multiple branches, reduce local electromagnetic coupling, and improve the isolation capability of faulty branches through only the electrical design of the busbar and the bus structure, without relying on complex active control.

[0010] The present invention solves the above-mentioned technical problems through the following technical means: a current balancing protection circuit for a parallel capacitor bank, comprising a positive busbar, a negative busbar, a positive bus, a negative bus, and several sets of capacitor branches; the several sets of capacitor branches are arranged sequentially along a predetermined direction and respectively connected between the positive busbar and the negative busbar; the positive busbar and the positive busbar are electrically connected at a first access position, and the negative busbar and the negative busbar are electrically connected at a second access position, the first access position and the second access position being staggered from each other along a predetermined direction; each set of capacitor branches is connected in series with the positive busbar and the negative busbar; the fast fuse unit includes a first fast fuse and a second fast fuse arranged in parallel, the first fast fuse and the second fast fuse being arranged in opposite directions in space.

[0011] Furthermore, the first access position is located in the front half of the area formed by the arrangement of the plurality of capacitor branches, and the second access position is located in the rear half of the area formed by the arrangement of the plurality of capacitor branches.

[0012] Furthermore, the first access position is located in the first quarter to the first half of the area formed by the arrangement of the plurality of capacitor branches, and the second access position is located in the last half to the end of the area formed by the arrangement of the plurality of capacitor branches.

[0013] Furthermore, the capacitor branch has twelve circuits, with the positive busbar connected to the positive busbar near the fourth capacitor branch and the negative busbar connected to the negative busbar near the seventh capacitor branch.

[0014] Furthermore, the fast-fusing unit is disposed between the capacitor branch and the positive busbar.

[0015] Furthermore, the fast-fuse unit is disposed between the capacitor branch and the negative busbar.

[0016] Furthermore, fast-melting units are installed on both the positive and negative sides of the same branch.

[0017] Furthermore, the reverse arrangement means that the first fast fuse and the second fast fuse are electrically connected in parallel, and the positive electrode connection terminals of the first fast fuse and the second fast fuse are located on opposite sides of the fast fuse unit, and the negative electrode connection terminals of the first fast fuse and the second fast fuse are located on opposite sides of the fast fuse unit.

[0018] Furthermore, the first fast fuse is connected between the positive electrode side connection terminal and the negative electrode side connection terminal of the first fast fuse, and the second fast fuse is connected between the negative electrode side connection terminal and the positive electrode side connection terminal of the second fast fuse.

[0019] The present invention also provides a parallel capacitor bank system, including an external power supply or a DC port of a converter, and the aforementioned parallel capacitor bank current balancing protection circuit. The positive and negative terminals of the external power supply or the DC port of the converter are respectively connected to the positive busbar and the negative busbar. When any capacitor branch experiences a short circuit or abnormal overcurrent, the fast fuse unit corresponding to that capacitor branch operates to isolate the faulty branch from the parallel capacitor bank, while the remaining unfaulty branches continue to operate in parallel.

[0020] The advantages of this invention are: (1) This invention uses a staggered connection method between the positive and negative busbars to compensate for the path impedance experienced by different capacitor branches on both the positive and negative sides. Although the positive path of the branch closer to the positive connection point is shorter, its negative path is relatively longer; the opposite is true for the branch closer to the negative connection point; the branch in the middle region has a more balanced path on both sides. Thus, topologically, this helps to reduce the dispersion of the total equivalent path impedance of each branch and improve the current sharing effect of multiple branches. This invention does not concentrate the positive and negative poles at the same end for feeding, but uses a double-sided staggered busbar, so that the positive and negative busbars are connected at different branch positions, which reduces the excessive current concentration at one end of the busbar, reduces the risk of local current congestion and hot spots, and helps to reduce the voltage distribution deviation along the length of the busbar. Each capacitor branch is equipped with an independent fast-blow fuse unit. When a faulty capacitor branch experiences a short circuit, breakdown, or serious abnormality, its corresponding fast-blow fuse will be used to cut off the fault first, thereby localizing the fault energy and preventing the entire capacitor group from continuously flowing into the fault point, thus improving the continuity of system operation and the controllability of faults.

[0021] (2) The fast-fuse unit of the present invention includes a first fast-fuse and a second fast-fuse arranged in parallel. The two fast-fuses are electrically connected in parallel to improve the rated current carrying capacity of a single branch, and are arranged in opposite directions in space to reduce local electromagnetic induction. Compared with the two fast-fuses being placed horizontally in the same direction, the reverse arrangement can reduce the tendency of local magnetic fields to be superimposed in the same direction, reduce the electromagnetic force on the fast-fuse and connectors, and reduce electromagnetic interference to the surrounding capacitor terminals, busbars and other components.

[0022] (3) The staggered bus, grouped fast fuse, and fast fuse reverse parallel scheme adopted in this invention are pure topology-level electrical optimizations, which do not rely on complex control algorithms or additional current sharing drives. They are suitable for high-power, high-pulse, and high-ripple current applications and have good engineering feasibility. The topology of this invention also has good modular expansion characteristics. When the number of parallel branches increases, the connection position is proportionally extended while maintaining the staggered bus principle, thereby maintaining a good current balance design idea under different capacity levels. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall structure of a parallel capacitor bank current balancing protection circuit disclosed in Embodiment 1 of the present invention; Figure 2 This is a top view of the busbar position relationship of a parallel capacitor bank current balancing protection circuit disclosed in Embodiment 1 of the present invention. Figure 3 This is a schematic diagram of the busbar side view of the current balancing protection circuit for a parallel capacitor bank disclosed in Embodiment 1 of the present invention. Figure 4 This is a partial structural diagram of the fast-fuse unit of the parallel capacitor bank current balancing protection circuit disclosed in Embodiment 1 of the present invention, arranged in reverse parallel. Wherein: 1—positive busbar; 2—negative busbar; 3—positive busbar; 4—negative busbar; 511—positive side connection terminal of the first fast fuse; 512—negative side connection terminal of the first fast fuse; 521—negative side connection terminal of the second fast fuse; 522—positive side connection terminal of the second fast fuse; 61—positive electrode access hole; 62—negative electrode access hole. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1 like Figures 1 to 4As shown, Embodiment 1 of the present invention provides a current balancing protection circuit for a parallel capacitor bank, including a positive busbar 1, a negative busbar 2, a positive busbar 3, a negative busbar 4, multiple fast-blow fuse units, and multiple capacitor branches. The fast-blow fuse units include a first fast-blow fuse and a second fast-blow fuse arranged in parallel, with the first and second fast-blow fuses spatially opposite. The figure shows the positive side connection terminal 511, the negative side connection terminal 512, the negative side connection terminal 521, and the positive side connection terminal 522 of the first fast-blow fuse. The figure also shows the capacitor connection points 6 of the capacitor branches, where 61 is the positive connection hole and 62 is the negative connection hole. In this embodiment, both the positive busbar 1 and the positive busbar 3 belong to the positive electrical connection path, and both the negative busbar 2 and the negative busbar 4 belong to the negative electrical connection path. The positive busbar 3 and the negative busbar 4 are the capacitor bank busbars for each capacitor branch to connect to.

[0026] Multiple capacitor branches are arranged sequentially along the length. Each capacitor branch is connected between the positive busbar 3 and the negative busbar 4, thus realizing the parallel connection of multiple sets of capacitor branches. The three-way connection in the figure is the connection point for the capacitors to be connected to the busbar.

[0027] The positive busbar 3 is not connected to the positive busbar 1 at the very end, but rather at a position slightly forward, though not at the very front. Similarly, the negative busbar 4 is not connected to the negative busbar 2 at the same position as the positive busbar, but rather at a relatively rearward position. This dual-sided busbar structure allows the external positive and negative busbars to connect to the capacitor bank busbars from different branches. Taking twelve capacitor branches as an example, the positive busbar 3 connects to the positive busbar 1 near the fourth capacitor branch, and the negative busbar 4 connects to the negative busbar 2 near the seventh capacitor branch. In other embodiments, the number of capacitor branches is not limited to twelve, and the connection points of the positive busbar 3 and the negative busbar 4 are not limited to the fourth and seventh branches. In principle, as long as the positive and negative connection positions are staggered along the branch arrangement direction and the dispersion of the total path impedance on both sides of different branches is reduced, they fall within the scope of protection of this invention.

[0028] As a further improvement, the positive and negative connection positions can be selected based on the total number of branches, the rated current of the branches, the target current sharing accuracy, and the simulation results of parasitic parameters. For systems with a large number of branches, the positive connection position can be set in the first quarter to the first half of the area formed by several groups of capacitor branches, and the negative connection position can be set in the last half to the end of the area formed by the same groups of capacitor branches, thus taking into account both current sharing effect and fault energy distribution.

[0029] With the above layout, for any capacitor branch, the total path from the external power supply to that branch is no longer entirely determined by one side, but by the combined length of the positive and negative paths. Although the path lengths on one side of capacitor branches located in different positions differ, the total path impedance on both sides is more likely to form a complementary relationship. Therefore, compared with the conventional structure where both positive and negative terminals are fed from the same side, this embodiment helps to reduce the differences in the total equivalent resistance and total equivalent stray inductance of different branches, making the distribution of charging / discharging current and ripple current in each branch more balanced.

[0030] In this embodiment, each capacitor branch is connected in series with its corresponding busbar. The fast-fuse unit includes a first fast-fuse and a second fast-fuse connected in parallel, arranged in opposite directions. The first and second fast-fuse are electrically connected in parallel to improve the rated current carrying capacity and protection coordination margin of the branch. The opposite arrangement means that the first and second fast-fuse are electrically connected in parallel, with the positive terminal 511 and the positive terminal 522 of the first and second fast-fuse located on opposite sides of the fast-fuse unit, and the negative terminal 512 and the negative terminal 521 of the first and second fast-fuse located on opposite sides of the fast-fuse unit. The first fast-fuse is connected between the positive terminal 511 and the negative terminal 512 of the first fast-fuse, and the second fast-fuse is connected between the negative terminal 521 and the positive terminal 522 of the second fast-fuse. In this way, when a short circuit, insulation breakdown, or severe overcurrent occurs inside a capacitor branch, the fault current will preferentially flow through that set of fast-blow fuses. The fast-blow fuses will melt and blow after meeting the operating conditions, thereby disconnecting the faulty branch from the entire parallel capacitor bank. The remaining unfaulty branches will remain connected to the positive busbar 3 and the negative busbar 4, reducing the overall probability of downtime.

[0031] By adopting the above-mentioned reverse arrangement, while saving installation space by placing it horizontally, the local current paths around the two parallel fast fuses form a magnetic field distribution trend that cancels each other out, thereby reducing local electromagnetic induction, reducing the electromagnetic force on the structure, and reducing electromagnetic interference to other surrounding components.

[0032] It should be noted that the capacitor units in the capacitor branch are all connected with the same polarity, not in reverse. The reverse arrangement structure in this embodiment is mainly for the fast fuse unit, not for the capacitor unit.

[0033] Under normal operating conditions, the external power supply is input through the positive busbar 1 and distributed to each capacitor branch through the positive busbar 3. Each capacitor branch then forms a complete parallel circuit through the negative busbar 4 and the negative busbar 2. Because the positive and negative sides are staggered, the electrical distance between each branch in the entire circuit tends to be balanced, so the overall current sharing performance is better than that of a single-ended centralized feed structure.

[0034] Under fault conditions, assuming an internal short circuit occurs in a capacitor branch, the fault current flows from positive busbar 1 through positive busbar 3 to the corresponding fast-blow fuse unit, then into the faulty capacitor branch, and finally through negative busbar 4 and negative busbar 2 to form a fault loop. As the fault current rises rapidly, the fast-blow fuse unit corresponding to that branch activates first and blows, thus isolating the faulty capacitor branch from the positive side and blocking subsequent fault energy injection. Because each branch has an independent fast-blow fuse, the fault isolation granularity reaches the branch level, rather than the entire group level.

[0035] In other embodiments, the fast-blow fuse unit can also be set on the negative side, or fast-blow fuse units can be set on both the positive and negative sides of the same branch to meet different rated voltages, fault energy and protection coordination requirements.

[0036] In this embodiment, the capacitor is arranged between the positive terminal access hole 61 and the negative terminal access hole 62. A complete current path is: positive busbar 1 or positive busbar 3 — fast fuse positive interface (positive side connection terminal 511 of the first fast fuse or positive side connection terminal 522 of the second fast fuse) — fast fuse unit — fast fuse negative interface (negative side connection terminal 512 of the first fast fuse or negative side connection terminal 521 of the second fast fuse) — positive terminal access hole 61 — capacitor — negative terminal access hole 62 — negative busbar 4 or negative busbar. The capacitor and fast fuse device models are not shown in the figure, only the connection holes are shown.

[0037] In summary, this invention achieves current balancing, improved rated current capability of fast fuses, and optimized fault isolation for parallel capacitor banks under high-power conditions through a combination design of positive and negative staggered current merging, grouped fast fuses, and reverse parallel arrangement of fast fuses. It is especially suitable for application scenarios with high requirements for current consistency, transient response, and branch reliability.

[0038] Example 2 Embodiment 2 of the present invention provides a parallel capacitor bank system, including an external power supply or a DC port of a converter, and a current balancing protection circuit for the parallel capacitor bank as described in Embodiment 1. The positive and negative terminals of the external power supply or the DC port of the converter are connected to the positive busbar 1 and the negative busbar 2, respectively. When any capacitor branch experiences a short circuit or abnormal overcurrent, the fast fuse unit corresponding to that capacitor branch operates to isolate the faulty branch from the parallel capacitor bank, while the remaining unfaulty branches continue to operate in parallel.

[0039] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A current balancing protection circuit for a parallel capacitor bank, characterized in that, It includes a positive busbar, a negative busbar, a positive bus, a negative bus, and several sets of capacitor branches; the several sets of capacitor branches are arranged sequentially along a predetermined direction and are respectively connected between the positive bus and the negative bus; the positive bus and the positive busbar are electrically connected at a first access position, and the negative bus and the negative busbar are electrically connected at a second access position, the first access position and the second access position are staggered from each other along the predetermined direction; each set of capacitor branches is connected in series with the positive bus and the negative busbar; the fast fuse unit includes a first fast fuse and a second fast fuse arranged in parallel, the first fast fuse and the second fast fuse are arranged in opposite directions in space.

2. The current balancing protection circuit for a parallel capacitor bank according to claim 1, characterized in that, The first access position is located in the front half of the area formed by the arrangement of the plurality of capacitor branches, and the second access position is located in the rear half of the area formed by the arrangement of the plurality of capacitor branches.

3. The current balancing protection circuit for a parallel capacitor bank according to claim 2, characterized in that, The first access position is located in the first 1 / 4 to the first 1 / 2 of the area formed by the arrangement of the plurality of capacitor branches, and the second access position is located in the last 1 / 2 to the end of the area formed by the arrangement of the plurality of capacitor branches.

4. The current balancing protection circuit for a parallel capacitor bank according to claim 2, characterized in that, The capacitor branch has twelve circuits. The positive busbar is connected to the positive busbar near the fourth capacitor branch, and the negative busbar is connected to the negative busbar near the seventh capacitor branch.

5. The current balancing protection circuit for a parallel capacitor bank according to claim 1, characterized in that, The fast-melting unit is located between the capacitor branch and the positive busbar.

6. The current balancing protection circuit for a parallel capacitor bank according to claim 1, characterized in that, The fast-fuse unit is located between the capacitor branch and the negative busbar.

7. The current balancing protection circuit for a parallel capacitor bank according to claim 1, characterized in that, Fast-melting units are installed on both the positive and negative sides of the same branch.

8. The current balancing protection circuit for a parallel capacitor bank according to claim 1, characterized in that, The reverse arrangement means that the first fast fuse and the second fast fuse are electrically connected in parallel, and the positive electrode connection terminals of the first fast fuse and the second fast fuse are located on opposite sides of the fast fuse unit, and the negative electrode connection terminals of the first fast fuse and the second fast fuse are located on opposite sides of the fast fuse unit.

9. A current balancing protection circuit for a parallel capacitor bank according to claim 8, characterized in that, The first fast fuse is connected between the positive electrode side connection terminal and the negative electrode side connection terminal of the first fast fuse, and the second fast fuse is connected between the negative electrode side connection terminal and the positive electrode side connection terminal of the second fast fuse.

10. A parallel capacitor bank system, characterized in that, It includes an external power supply or a converter DC port, and a parallel capacitor bank current balancing protection circuit as described in any one of claims 1 to 9, wherein the positive and negative terminals of the external power supply or converter DC port are respectively connected to the positive busbar and the negative busbar; when any capacitor branch experiences a short circuit or abnormal overcurrent, the fast fuse unit corresponding to that capacitor branch operates to isolate the faulty branch from the parallel capacitor bank, while the remaining non-faulty branches continue to operate in parallel.

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