Leveling circuit for battery pack

Abstract

To provide a leveling circuit that does not require a cell voltage detection part and a control part that controls leveling and autonomously realizes a cell voltage balanced state.SOLUTION: A leveling circuit includes a plurality of transformer circuit parts and switching elements corresponding to a plurality of cells, and each of a transformer circuit part includes a transformer including a first coil, a second coil, and a secondary coil that are magnetically coupled to each other and have the same number of turns, and an output circuit connected to the secondary coil. It is possible to output the leveled charging current from an output end of an output circuit to each corresponding cell, all the first coils of the plurality of transformer circuit parts are connected in series. One end thereof is connectable to a positive electrode terminal of a cell on the highest potential side. The other end thereof is connected to one end of a current path of a switching element. The other end of the current path of the switching element is connectable to a negative electrode terminal of the cell on the lowest potential side, and all the second coils of the plurality of transformer circuit units are connected in parallel.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a leveling circuit for a battery pack in which a plurality of cells are connected in series. [Background technology]

[0002] Batteries with multiple cells connected in series have the advantage of being able to produce high voltage, but as they are repeatedly charged and discharged, the cell voltage balance between each cell is lost and differences appear. If these differences in cell voltage are left unchecked, some cells may become overcharged when the battery is charged, and some may become over-discharged when the battery is discharged, causing the performance of those cells to deteriorate. Because the cells are connected in series, if one cell becomes disconnected, it will affect the entire battery.

[0003] There are known leveling circuits (also called cell balance circuits or averaging circuits) that eliminate differences in the voltages of the cells of a battery pack and make them uniform. For example, a passive system is known in which a cell with a higher voltage discharges into a resistor or the like to equalize the voltage of each cell so that the cell voltage matches the lowest voltage among multiple cells (Patent Documents 1 and 2).

[0004] Another example of a leveling circuit is the active method. One active method uses a charging device such as a DC / DC converter to charge cells with lower voltages to match the highest voltage cell among multiple cells (Patent Document 3). Another active method discharges higher voltage cells first to charge lower voltage cells (Patent Document 4). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-278241 [Patent Document 2] Patent Publication No. 2021-35201 [Patent Document 3] International Publication No. 2019 / 208163 [Patent Document 4] Japanese Patent Publication No. 2020-18085 Summary of the Invention [Problem to be solved by the invention]

[0006] In all conventional voltage leveling circuits, the voltage of each series-connected cell is detected. A control unit is then provided to operate the voltage leveling circuit in response to the detected voltage. Therefore, both systems require a voltage detection unit and a control unit. Furthermore, passive systems perform voltage leveling by discharging voltage from the cells through a resistor, which can result in heat generation and energy loss. Active systems require a charging device and advanced control, resulting in a complex and expensive configuration.

[0007] Note that voltage leveling is not limited to battery packs in which multiple cells are connected in series, but it is also common to level the voltage of each cell pack in a battery pack in which multiple cell packs are connected in series, each cell pack having multiple cells connected in series and / or parallel (however, the rated voltage of each cell pack is the same). In this specification, the smallest unit to be leveled in a battery pack is referred to as a "cell," but this does not only include cases in which the smallest unit is a single cell, but also includes cases in which the smallest unit is a cell pack.

[0008] An object of the present invention is to provide a leveling circuit for a battery pack in which multiple cells are connected in series, which does not require a voltage detection unit that detects the voltage of each cell or a control unit that controls the charging and discharging of each cell for leveling, and which achieves cell balancing autonomously. [Means for solving the problem]

[0009] In order to achieve the above object, the present invention provides the following configuration: Note that the reference numerals in parentheses are reference numerals in the drawings to be described later, and are provided for reference. [1] An aspect of the present invention is a leveling circuit (1) for leveling the voltages of each cell of a battery pack (2) including a plurality of cells (C1, Cn...Cn) connected in series, a plurality of transformer circuit units (B1, B2...Bn) corresponding to each of the plurality of cells (C1, Cn...Cn); and at least one switching element (S) that switches between conducting and blocking a current path in response to a control signal; Each of the transformer circuit units (B1, B2...Bn) comprises a transformer (T) having a first coil (N1), a second coil (N2) and at least one secondary coil that are magnetically coupled to each other and have the same number of turns, and an output circuit connected to the secondary coil, and is capable of outputting a leveled charging current from an output terminal (p, n) of the output circuit to each of the corresponding cells (C1, Cn...Cn), the first coils (N1) of each of the plurality of transformer circuit units (B1, B2...Bn) are all connected in series, one end of the series connection is connectable to the positive terminal of the cell (C1) on the highest potential side and the other end is connected to one end of a current path of the switching element (S), and the other end of the current path of the switching element (S) is connectable to the negative terminal of the cell (Cn) on the lowest potential side; The second coils (N2) of each of the plurality of transformer circuit sections (B1, B2, . . . Bn) are all connected in parallel. [2] In the aspect of [1] above, while the switching element (S) is performing a switching operation, a coil voltage equal to an average cell voltage obtained by dividing the voltage across the battery pack (2) by the number of the plurality of cells (C1, Cn...Cn) is generated in each of the first coil (N1), the second coil (N2) and the secondary coil (N3, N4), and a leveled charging current flows through the cells having a cell voltage lower than the coil voltage of the secondary coil via the output circuit, and a leveled discharging current flows through the cells having a cell voltage higher than the coil voltage of the secondary coil. [3] In the aspect [2] above, the secondary coil and the output circuit are configured to output the leveled charging current as a forward current when the switching element (S) is in a conducting state, and to output the leveled charging current as a flyback current when the switching element (S) is in a cut-off state. [4] In the aspect [3] above, the secondary coil through which the forward current flows is loosely coupled to each of the other coils, and the other coils are tightly coupled to each other. [5] In the aspect [1] above, a first connection terminal (J1, J2...) connected to the positive output terminal (p) of the output circuit of each of the transformer circuit units (B1, B2...Bn); and a second connection terminal (J1a, J2a...) connected to the high potential end of the first coil (N1) of each of the transformer circuit units (B1, B2...Bn), Only the first connection terminal and the second connection terminal in the transformer circuit section corresponding to the cell (C1) on the highest potential side are connected to each other. [6] In the above aspect [1], the leveling circuit is capable of operating continuously or intermittently while the battery pack (2) is being charged, discharged, or left unused. [7] An expansion circuit (10) that can be connected in series to the leveling circuit of the battery pack according to any one of the above aspects [1] to [6], The switching element (S) is not included, and one or more transformer circuit units (B1, B2, . . . Bn) are included. [Effects of the Invention]

[0010] According to the present invention, in a leveling circuit for a battery pack in which multiple cells are connected in series, a voltage detection unit that detects the voltage of each cell and a control unit that controls the charging and discharging of each cell for leveling are not required, and cell balancing can be achieved through autonomous operation. [Brief explanation of the drawings]

[0011] [Figure 1]FIG. 1 is a diagram showing an example of the configuration of a series battery leveling circuit according to the present invention. [Figure 2] FIG. 2 shows the operation of the switching element in the conductive state. [Figure 3] FIG. 3 shows the operation of the switching element in the cut-off state. [Figure 4] 4(a) and 4(b) are graphs showing an example of how the leveling circuit of the present invention is used, and a schematic representation of the change over time in the cell voltage of each cell in the battery pack. [Figure 5] FIG. 5 is a schematic diagram showing another example of the transformer circuit section. [Figure 6] FIG. 6 is a diagram showing a schematic diagram of another embodiment of the leveling circuit of the present invention. [Figure 7] FIG. 7 is a diagram showing a schematic diagram of yet another embodiment of the leveling circuit of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a battery pack leveling circuit according to the present invention will be described in detail with reference to the drawings. (1) Circuit configuration Fig. 1 is a schematic diagram showing an example of an embodiment of a leveling circuit 1 according to the present invention together with a battery pack 2. In the example of Fig. 1, the leveling circuit 1 is a device independent of the battery pack 2, and is detachably connected to the battery pack 2 via connection points J1, J2...Jn+1 such as connection terminals. As another example, the leveling circuit 1 may be an internal circuit integrated with the battery pack 2.

[0013] The battery pack 2 is composed of cells C1, C2...Cn connected in series. For connection to the leveling circuit 1, the battery pack 2 has a positive terminal J1 of the cell C1 with the highest potential, a negative terminal Jn+1 of the cell Cn with the lowest potential, and connection terminals J2 to Jn between two adjacent cells (the negative terminal of the cell with the highest potential and the positive terminal of the cell with the lowest potential are shared). In the example of FIG. 1, a positive terminal 3 and a negative terminal 4 are separately provided for connecting the battery pack 2 to a charger or a load.

[0014] The cell is a secondary battery, and may be a single cell, a cell pack in which multiple cells are connected in series or parallel, or a cell pack in which multiple cells are connected in both parallel and series. However, the rated voltage of each cell must be the same. Cell types include, for example, lithium-ion cells, nickel-metal hydride cells, lead-acid battery cells, electric double-layer capacitor cells, and lithium-ion capacitor cells. For example, lithium-ion cells have a nominal voltage of 3.6 to 3.7 V.

[0015] The leveling circuit 1 includes a plurality of transformer circuit sections B1, B2, . . . , Bn corresponding to the plurality of cells C1, C2, .

[0016] The following description will be given with reference to one transformer circuit section B1. The transformer circuit section B1 has a transformer T having a core and multiple coils wound around the core. The multiple coils include a first coil N1, a second coil N2, and two secondary coils N3 and N4 that are magnetically coupled to each other. Each coil is indicated by a black dot at its winding start end. In the illustrated example, there are two secondary coils, but this is not limited to this, and there may be at least one secondary coil. All of the coils (four coils in the illustrated example) of the transformer T have the same number of turns. Note that the secondary coil N3 is loosely coupled to the other coils N1, N2, and N4, while the coils N1, N2, and N4 are tightly coupled to each other. This will be explained later.

[0017] An output circuit is connected to the secondary coils N3 and N4. In the illustrated example, the output circuit is composed of a first rectifier element D1 and a second rectifier element D2, which are diodes, and is capable of outputting current to a positive output terminal p and a negative output terminal n. The current output from the transformer circuit section B1 is a charging current for leveling the corresponding cell C1.

[0018] The secondary coils N3 and N4 have opposite polarities, and the winding end of the secondary coil N3 and the winding start of the secondary coil N4 are connected to the negative output terminal n. The anode of the first rectifier element D1 is connected to the winding start of the secondary coil N3, and the cathode is connected to the positive output terminal p. The anode of the second rectifier element D2 is connected to the winding end of the secondary coil N4, and the cathode is connected to the positive output terminal p. The positive output terminal p can be connected to the positive terminal of the corresponding cell C1, here via the connection terminal J1. The negative output terminal n can be connected to the negative terminal of the corresponding cell C1, here via the connection terminal J2.

[0019] Each of the other transformer circuit sections B2 to Bn has the same configuration as the transformer circuit section B1.

[0020] Furthermore, the first coils N1 of each of the multiple transformer circuit units B1, B2...Bn are all connected in series. That is, the winding end and winding start of the two first coils N1 of two adjacent transformer circuit units are connected to each other. One end on the high potential side of the n series-connected first coils N1 is connectable to the positive terminal of the cell C1 on the highest potential side of the battery pack 2, here connected via the connection terminal J1. The other end on the low potential side of the n series-connected first coils N1 is connected to one end of the current path of the switching element S. The other end of the current path of the switching element S is connectable to the negative terminal of the cell Cn on the lowest potential side of the battery pack 2, here connected via the connection terminal Jn+1. Therefore, the current paths of the n first coils N1 and the switching elements S are connected in series, and the voltage across the battery pack 2 can be applied to both ends thereof.

[0021] In the illustrated example, the switching element S is an n-channel MOSFET. The drain of the switching element S is connected to the winding end of the first coil N1 of the transformer circuit section Bn, and the source is connected to the negative terminal of the cell Cn. A pulse voltage, which is a control signal that switches the drain-source current path between conduction and cut-off, is input to the gate, which is the control end. The pulse voltage is a high-frequency pulse of, for example, several tens of kHz, with a duty ratio of, for example, 50%. In the illustrated example, a pulse voltage generation section PG is provided, which generates a control signal using the battery pack 2 as a power source and outputs it to the control end of the switching element S.

[0022] As another example, the switching element S may be a bipolar transistor or an IGBT. As yet another example, the pulse voltage generating unit PG may be installed outside the leveling circuit 1 and may be driven by a power source other than the assembled battery 2.

[0023] Furthermore, the second coils N2 of each of the multiple transformer circuit units B1, B2, . . . Bn are all connected in parallel, i.e., the winding start ends of all the second coils N2 are connected to each other, and the winding end ends of all the second coils N2 are connected to each other.

[0024] (2) Leveling operation The operation of the leveling circuit of Figure 1 will be described with reference to Figures 2 and 3. Figure 2 shows the operation of the switching element S in the conductive state, and Figure 3 shows the operation of the switching element S in the cut-off state. For simplicity, the leveling circuit 1 is shown with only two transformer circuit sections B1 and B2, the battery pack 2 is shown with only two cells C1 and C2, and the switching element S is shown simply as a switch. The leveling circuit 1 of the present invention can operate during charging of the battery pack 2 by the charger 5, during discharging from the battery pack 2 to the load 6, and when the battery pack 2 is left unused (disconnected from both the charger 5 and the load 6). Figures 2 and 3 show the battery pack 2 being charged, and a charging current is actually flowing, but the charging current is not shown to simplify the explanation of the leveling operation. Figures 2 and 3 only show the current related to the leveling operation.

[0025] The voltage across the battery pack 2 varies with the charge and discharge of the battery pack 2. The voltage obtained by dividing the voltage across the battery pack 2 at the time points shown in FIGS. 2 and 3 by the number of cells n is defined as the average cell voltage Vx. Also, at this time point, it is assumed that the cell voltage Va of cell C1 and the cell voltage Vb of cell C2 are unbalanced, with Va < Vx and Vb > Vx.

[0026] When the switching element S is in the conducting state (on), as shown in FIG. 2, the voltage across the battery pack 2 is applied across both ends of the n first coils N1 connected in series. As a result, a current i1 flows through the current paths of the n first coils N1 and the switching element S, a coil voltage is induced in each first coil N1, and coil voltages are also induced in the second coil N2 and the secondary coils N3 and N4 magnetically coupled thereto. Here, since all the second coils N2 are connected in parallel, the voltages induced in each second coil N2 are forced to be equal. Therefore, in any of the transformers T, the coil voltages of the other coils N1, N3, and N4 having the same number of turns magnetically coupled to the second coil N2 are equal to the coil voltage of the second coil N2. As a result, the coil voltages induced in the first coil N1, the second coil N2, and the secondary coils N3 and N4 are equal to the average cell voltage Vx.

[0027] In the output circuits of each of the transformer circuit sections B1 and B2, the coil voltage Vx generated in the secondary coil N3 is in the forward direction with respect to the first rectifying element D1, and the coil voltage Vx generated in the secondary coil N4 is in the reverse direction with respect to the second rectifying element D2. On the other hand, the cell voltages Va and Vb of the respective cells C1 and C2 of the battery pack 2 are applied between the output terminals p and n of the output circuits of each of the transformer circuit sections B1 and B2.

[0028] In the transformer circuit section B1, since the cell voltage Va of the corresponding cell C1 is smaller than the average cell voltage Vx (Va < Vx), a leveling charging current ic (so called to distinguish it from the charging current by the charger 5) is output through the path of the secondary coil N3 → the first rectifying element D1 → the cell C1. The current ic at this time is a forward current. Since the forward current flowing when the switching element S is on may become a short-circuit excessive current, the secondary coil N3 is loosely coupled with other coils. For example, by providing a gap in the core so as to generate leakage magnetic flux or separating it from other coils, the magnetic resistance of the magnetic circuit is increased, and the excessive current during on can be suppressed.

[0029] On the other hand, in the transformer circuit section B2, since the cell voltage Vb of the corresponding cell C2 is larger than the average cell voltage Vx (Vb > Vx), no current flows through the output circuit. Instead, a leveling discharge current id (so called to distinguish it from the discharge current to the load 6) flows through the cell C2. The current i1 flowing through the switching element S and the leveling discharge current id flowing through the battery pack 2 flow in the same loop, so they are the same. Note that a combined current of the leveling charging current ic and the leveling discharge current id flows through the cell C1.

[0030] Subsequently, as shown in FIG. 3, when the switching element S is in the cut-off state (off), in each of the transformer circuit sections B1 and B2, reverse coil voltages Vx are generated in the secondary coils N3 and N4, respectively. The coil voltage Vx generated in the secondary coil N3 becomes reverse to the first rectifying element D1, and the voltage Vx generated in the secondary coil N4 becomes forward to the second rectifying element D2. In the transformer circuit section B1, since the cell voltage Va of the corresponding cell C1 is smaller than the average cell voltage Vx (Va < Vx), a leveling charging current ic is output from the secondary coil N4 → the second rectifying element D2 → the cell C1. The current ic at this time is a flyback current.

[0031] On the other hand, in the transformer circuit section B2, since the cell voltage Vb of the corresponding cell C2 is larger than the average cell voltage Vx (Vb > Vx), no current flows through the output circuit either.

[0032] To summarize the above, as the switching element S switches, a leveling charging current ic flows through cells whose cell voltage is lower than the average cell voltage Vx, causing their cell voltages to rise, while a leveling discharging current id flows through cells whose cell voltage is higher than the average cell voltage Vx, causing their cell voltages to drop. This operation continues until the cell voltages of all cells in the battery pack 2 are leveled, that is, until the average cell voltage Vx is reached.

[0033] Once the voltage leveling state is reached, it will be maintained as long as the voltage leveling circuit 1 continues to operate. This is because the above operation is performed autonomously immediately if the cell voltages of the individual cells become unbalanced. As a result, the cell voltage imbalance can be prevented from continuing for a long period of time, which also has the effect of suppressing the progression of cell degradation. In contrast, conventional voltage leveling circuits constantly monitor the cell voltage of each cell and begin leveling operation when a predetermined voltage is reached. Therefore, the imbalance continues until the predetermined voltage is reached, which accelerates cell degradation.

[0034] The battery pack leveling circuit of the present invention does not require a voltage detection unit for each cell, nor does it require a control unit that determines which cells require leveling and controls discharging or charging for leveling. The leveling circuit of the present invention can autonomously achieve cell balancing by simply continuing the switching operation of one switching element S.

[0035] Furthermore, in the leveling circuit of the present invention, power is simply exchanged between the cells charged by the leveled charging current and the cells discharged by the leveled discharging current, so there is no power loss due to discharge outside the battery pack.

[0036] Furthermore, in the leveling circuit of the present invention, the leveling charge current and leveling discharge current flow from the battery pack itself, which contains the cells, and therefore the overcharging and over-discharging that can occur when charging and discharging from an external source do not occur, which also means that an external power source or external load is not required for the leveling charge current and leveling discharge current.

[0037] 4(a) and 4(b) are graphs showing the cell voltage of each cell of a battery pack over time, illustrating an example of how the leveling circuit of the present invention can be used. Here, the battery pack includes three cells C1, C2, and C3.

[0038] Figure 4(a) shows the change in the cell voltages of cells C1, C2, and C3 when the leveling circuit starts operating continuously from a discharging state where the cell voltages of cells C1, C2, and C3 are unbalanced, and the cells are then charged (connected to a charger), left alone (disconnected), and discharged (connected to a load) in that order. When the leveling circuit starts operating, the uneven cell voltages converge to the average cell voltage and are leveled out. Since the leveling circuit continues to operate continuously after that, the leveled state is maintained.

[0039] Figure 4(b) shows the change in cell voltage of each cell when a battery consisting of three cells C1, C2, and C3 is charged, left standing, and discharged in sequence, as in (a). However, in this case, the voltage leveling circuit is operated intermittently. Such intermittent operation can be achieved, for example, by incorporating a timer into the pulse voltage generator PG in Figure 1, which alternates between control signal output periods (operation) and stop periods (non-operation). During the non-operational periods of the voltage leveling circuit, the variation in the cell voltages gradually increases. When the voltage leveling circuit is activated, the cell voltages converge to the average cell voltage and are leveled, and this leveled state is maintained during the operation period.

[0040] FIG. 5 is a schematic diagram showing another example of a transformer circuit section. Only one transformer circuit section B2 is shown here. In this example, a first coil N1, a second coil N2, and one secondary coil N3 are wound around the transformer T, and all coils have the same number of turns. The secondary coil N3 is loosely coupled to the first coil N1 and the second coil N2, and the first coil N1 and the second coil N2 are tightly coupled.

[0041] The output circuit is composed of a first rectifier element D1, a second rectifier element D2, a third rectifier element D3, and a fourth rectifier element D4, which are diodes in the illustrated example, and is capable of outputting current to a positive output terminal p and a negative output terminal n. The anode of the first rectifier element D1 and the cathode of the third rectifier element D3 are connected to the winding start end of the secondary coil N3. The anode of the second rectifier element D2 and the cathode of the fourth rectifier element D4 are connected to the winding end of the secondary coil N3. The cathodes of the first rectifier element D1 and the second rectifier element D2 are connected to the positive output terminal p. The anodes of the third rectifier element D3 and the fourth rectifier element D4 are connected to the negative output terminal n. The positive output terminal p is connected to the positive terminal of the corresponding cell C2, and the negative output terminal n is connected to the negative terminal of the corresponding cell C2. The operation of the leveling circuit including the transformer circuit unit of FIG. 5 is substantially the same as that described with reference to FIGS. 2 and 3, and therefore will not be described here.

[0042] 6 is a diagram schematically illustrating another embodiment of the leveling circuit of the present invention. The leveling circuit 1 of this embodiment is configured to be connectable to a battery pack 2 in which cells C1 to C4 are connected in series, the number of which (for example, four) is smaller than the number (for example, eight) of transformer circuit sections B1 to B8 (illustration simplified) provided in the leveling circuit 1.

[0043] The leveling circuit 1 is a device independent of the battery pack 2, and has first connection terminals J1, J2, . . . Jn+1 for connection to the battery pack 2, similar to the embodiment shown in FIG. In this embodiment, the transformer circuit sections B1 to B7 further include second connection terminals J1a, J2a, . . . Ja7 connected to the high potential ends of the first coils N1, respectively. The transformer circuit B8 does not have a second connection terminal because leveling is not necessary if there is only one cell. It is assumed that there are two or more cells in the battery pack 2 and two or more transformer circuit units in the leveling device 1.

[0044] When connecting a leveling circuit 1 having eight transformer circuit sections B1 to B8 to a battery pack 2 having four cells C1 to C4 connected in series, the first connection terminal J5 and the second connection terminal J5a of the fourth transformer circuit section B5 from the bottom in the leveling circuit 1 are connected by a connection wire L. This makes it possible to apply the voltage across the battery pack 2 to both ends of the bottom four first coils N1 in the leveling circuit 1.

[0045] The leveling circuit 1 shown in FIG. 6 can be connected to a battery pack 2 consisting of 2 to 8 cells using a connection line L to perform leveling.

[0046] 7 is a diagram schematically illustrating yet another embodiment of the leveling circuit of the present invention. This embodiment includes a leveling circuit 1 having four transformer circuit sections B1 to B4 and a switching element S, and an expansion circuit 10 having four transformer circuit sections B11 to B14 but no switching element S.

[0047] The leveling circuit 1 and the expansion circuit 10 can be connected in series by a connection terminal unit J21. The connection terminal unit J21 electrically connects the first coil N1, the second coil N2, and the output circuit of the transformer circuit B1 on the highest potential side of the leveling circuit 1 and the transformer circuit B14 on the lowest potential side of the expansion circuit 10. The expansion circuit 10 has one or more transformer circuit units, and the expansion circuit 10 with the required number of transformer circuit units is selected based on the number of cells in the battery pack. This results in a leveling circuit with the same functionality as one having eight transformer circuit units.

[0048] As in the embodiment shown in FIG. 6, the leveling circuit 1 and the extension circuit 10 include second connection terminals J1a to J3a and J11a to J14a respectively connected to the high potential end of the first coil N1.

[0049] In the illustrated example, the leveling circuit 1 and the expansion circuit 10 are connected to two battery packs 2 connected in series at a connection point J22. Instead of two battery packs 2, a single battery pack with eight cells connected in series may be used. As in the embodiment of FIG. 6, the first connection terminal J11 and the second connection terminal J11a of the transformer circuit section B11 on the highest potential side are connected by a connection line L. This makes it possible to apply the voltage across the two battery packs 2 to both ends of the eight first coils N1 connected in series.

[0050] The embodiments shown in FIGS. 6 and 7 can be applied as a solution when the number of transformer circuit units in the leveling circuit does not match the number of cells in the assembled battery. The leveling circuit of the present invention does not have a voltage detection unit that detects the voltage of each cell in the battery pack or a control unit that controls the leveling of each cell, so it can relatively easily accommodate changes in the number of cells to be leveled.

[0051] Although the embodiments of the present invention have been described with reference to exemplary configurations, the embodiments of the present invention are not limited to these examples, and various modifications are also within the scope of the present invention as long as they comply with the principles of the present invention. [Explanation of symbols]

[0052] 1. Equalization circuit 10 Expansion circuit B1, B2...Bn transformer circuit section N1 First coil N2 Second coil N3 secondary coil N4 secondary coil D1 First rectifier element D2 Second rectifier D3 Third rectifier element D4 Fourth rectifier element PG pulse voltage generator S Switching element J1, J2, ..Jn, Jn+1 connection terminals (connection points) J1a, J2a,... connection terminals J21 connection unit J22 connection terminal L connecting wire 2 battery packs 3 Positive terminal 4 Negative terminal 5 charger 6 Load C1, C2..Cn cells Vx average cell voltage Va, Vb Cell voltage

Claims

1. A leveling circuit (1) for leveling the cell voltages of a battery pack (2) including a plurality of cells (C1, Cn, Cn) connected in series, a plurality of transformer circuit units (B1, B2...Bn) corresponding to each of the plurality of cells (C1, Cn...Cn); and at least one switching element (S) that switches between conducting and blocking a current path in response to a control signal; Each of the transformer circuit units (B1, B2...Bn) includes a transformer (T) having a first coil (N1), a second coil (N2) and at least one secondary coil that are magnetically coupled to each other and have the same number of turns, and an output circuit connected to the secondary coil, and is capable of outputting a leveled charging current from an output terminal (p, n) of the output circuit to each of the corresponding cells (C1, Cn...Cn), the first coils (N1) of each of the plurality of transformer circuit units (B1, B2, . . . Bn) are all connected in series, one end of the series connection is connectable to the positive terminal of the cell (C1) on the highest potential side and the other end is connected to one end of a current path of the switching element (S), and the other end of the current path of the switching element (S) is connectable to the negative terminal of the cell (Cn) on the lowest potential side; The battery pack leveling circuit is characterized in that the second coils (N2) of the plurality of transformer circuit sections (B1, B2, Bn) are all connected in parallel.

2. 2. The battery pack leveling circuit according to claim 1, wherein, while the switching element (S) performs a switching operation, a coil voltage equal to an average cell voltage obtained by dividing the voltage across the battery pack (2) by the number of the plurality of cells (C1, Cn, Cn) is generated in each of the first coil (N1), the second coil (N2), and the secondary coil (N3, N4), and a leveling charging current flows via the output circuit to cells whose cell voltages are lower than the coil voltage of the secondary coil, and a leveling discharging current flows to cells whose cell voltages are higher than the coil voltage of the secondary coil.

3. 3. The battery pack leveling circuit according to claim 2, wherein the secondary coil and the output circuit are configured to output the leveled charging current as a forward current when the switching element (S) is in a conducting state, and to output the leveled charging current as a flyback current when the switching element (S) is in a cut-off state.

4. 4. The battery pack leveling circuit according to claim 3, wherein the secondary coil through which the forward current flows is loosely coupled to each of the other coils, and the other coils are tightly coupled to each other.

5. a first connection terminal (J1, J2...) connected to the positive output terminal (p) of the output circuit of each of the transformer circuit units (B1, B2...Bn); and a second connection terminal (J1a, J2a...) connected to a high potential end of the first coil (N1) of each of the transformer circuit units (B1, B2...Bn), 2. The battery pack leveling circuit according to claim 1, wherein only the first connection terminal and the second connection terminal of the transformer circuit section corresponding to the cell (C1) on the highest potential side are connected to each other.

6. 2. The battery pack leveling circuit according to claim 1, wherein the leveling circuit (1) can operate continuously or intermittently while the battery pack (2) is being charged, discharged, or left unused.

7. An expansion circuit (10) that can be connected in series to the battery pack leveling circuit according to any one of claims 1 to 6, An expansion circuit characterized by having one or more of the transformer circuit sections (B1, B2, . . . Bn) without the switching element (S).

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