JP4193786B2 - Signal transmission circuit - Google Patents

Description

  The present invention relates to a signal transmission circuit that operates by receiving power from a battery pack.

  An assembled battery used as a battery of an electric vehicle (EV) or a hybrid electric vehicle (HV) requires a high voltage of about 100V to 400V, and thus has a configuration in which a large number of secondary batteries (cells) are connected in series. ing. For example, in the case of a 300V battery pack, 150 cells are connected in series for a lead battery (about 2V / cell), 250 cells are connected for a nickel metal hydride battery (1.2V / cell), and 80 cells are connected in series for a lithium ion battery (3.6V / cell). Has been. Among these, lithium ion batteries have characteristics superior to lead batteries and nickel metal hydride batteries in terms of volume energy density, weight energy density, and cycle life.

  However, since secondary batteries, particularly lithium ion batteries, are vulnerable to overcharge and overdischarge, there is a risk that the capacity will be remarkably reduced or heat will be generated if they are not used within the specified limit voltage range. Therefore, when using an assembled battery, constant voltage charging control is performed so that the voltage of the assembled battery is within a voltage range determined by a predetermined upper limit voltage and lower limit voltage, and the voltage of the assembled battery is within the above-mentioned limit voltage range. A protection circuit is used so as not to be outside.

Furthermore, there is a problem of variations in cell voltage due to variations in state of charge (SOC) between cells constituting the assembled battery. In an assembled battery, the SOC of each cell and thus the cell voltage varies due to individual differences in capacity and self-discharge characteristics of each cell. In particular, since the overcharge resistance and overdischarge resistance of lithium ion batteries are much weaker than other types of secondary batteries, they cannot be used at all as the SOC variation between the cells progresses. Patent Document 1 discloses an equalization apparatus for solving this problem. In addition, Patent Document 2 discloses an assembled battery voltage adjusting device and an assembled battery voltage adjusting method.
JP 2004-080909 A JP 2000-287370 A

  The inventor of the present application has newly devised a cell voltage equalization apparatus for a battery pack that can perform normalization operation normally even when the cell voltage is highly uneven. This equalization apparatus includes: a discharge circuit connected between terminals of each cell; a reference voltage generation circuit that generates a voltage at each common connection point between cells in a state where all cells are equalized; Comparator for comparing the voltage at the common connection point with the reference voltage corresponding to the common connection point, a signal transmission circuit for transmitting the output signal of the comparator to the discharge control circuit, and a comparator received via the signal transmission circuit The discharge control circuit controls the discharge circuit based on the output signal.

  The comparator of this equalization device operates by receiving supply of power supply voltage from the positive terminal of the cell located on the high potential side and the negative terminal of the cell located on the low potential side with respect to the common connection point between the cells. It has a feature in configuration. The discharge control circuit provided for each cell is based on the output signal of the comparator that compares the voltage of the positive terminal of the cell and the output signal of the comparator that compares the voltage of the negative terminal of the cell. Is generated.

  In this configuration, the ground potential of the comparator and the ground potential of the discharge control circuit may be different. In order to cope with this, the signal transmission circuit includes a level shift circuit. However, when a conventional general-purpose level shift circuit is used, the current flowing through the signal transmission circuit changes according to the magnitude of the cell voltage. This current is supplied from the cells constituting the assembled battery. For this reason, when non-uniformity occurs in the cell voltage, the current flowing through the cell increases or a difference occurs in the current flowing through each cell, resulting in a problem that the non-uniformity cannot be sufficiently eliminated.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to operate by receiving power supply voltage from an assembled battery, and to reduce the influence on the assembled battery due to voltage change of each cell as much as possible. Is to provide.

  According to the means described in claim 1, the first transistor to which the signal is input operates in a state of being grounded with respect to the negative terminal of the second cell constituting the assembled battery. On the other hand, the second transistor that outputs a signal has a connection point between cells located between the positive terminal of the first cell and the negative terminal of the second cell in the assembled battery (hereinafter, cell common connection point). It is operated in a grounded state. Here, the assembled battery is configured by connecting a plurality of secondary battery cells in series, and the second cell is connected to a lower potential side than the first cell.

  When the input signal is at L level, that is, when the input signal voltage is substantially equal to the voltage at the minus terminal of the second cell, the first transistor is turned off. At this time, a current flows from the constant current circuit connected to the positive terminal of the first cell to the cell common connection point via the backflow preventing diode and the resistor. The second transistor is turned on by the voltage drop generated in the resistor, and the output signal becomes L level, that is, approximately equal to the voltage at the cell common connection point.

  On the other hand, when the input signal is at H level, that is, when the input signal voltage is higher than the voltage at the minus terminal of the second cell by the forward voltage Vf, the first transistor is turned on. At this time, the collector of the first transistor becomes substantially equal to the voltage at the negative terminal of the second cell. Since a diode for preventing backflow is connected between the collector of the first transistor and the base of the second transistor, the voltage difference between the voltage at the common connection point and the voltage at the negative terminal of the second cell. Is applied to the diode, and the base-emitter of the second transistor can be protected from overvoltage.

  According to the signal transmission circuit of this means, even if the cell voltage between the plus side terminal of the first cell and the minus side terminal of the second cell changes, or the level of the input signal (L level or H level). ) Changes, the consumption current becomes substantially constant (almost equal to the output current of the constant current circuit). In addition, the current consumption may be a current necessary for performing the level shift operation, and can be minimized. Accordingly, it is possible to reduce the influence on the assembled battery (for example, the promotion of the uneven state of the cell voltage) as much as possible by the consumption current of the signal transmission circuit flowing into the assembled battery.

  According to the means described in claim 2, the first transistor is an output transistor of the comparator. As described in “Background Art” and “Problems to be Solved by the Invention”, the assembled battery is provided with an equalization circuit for equalizing cell voltages. This equalization circuit requires a comparator that performs a comparison operation between the voltage at the common connection point between the cells and the reference voltage corresponding to the common connection point. Therefore, the signal transmission circuit of this means is suitable for an equalizing circuit for an assembled battery.

  According to the means described in claim 3, the comparator receives power supply voltage from the positive side terminal of the first cell and the negative side terminal of the second cell, and the voltage at the cell common connection point and a predetermined reference Compare with voltage. In this way, by supplying the power supply voltage from both terminals of two or more cell groups connected in series across the cell common connection point to be compared to the comparison circuit, the voltage at the cell common connection point and the reference voltage are supplied. Regardless of the magnitude relationship with, the comparator can perform the comparison operation normally.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a main part configuration diagram of an equalization circuit that equalizes the voltages of the cells constituting the assembled battery. The assembled battery 1 is used as a battery for an electric vehicle (EV) or a hybrid electric vehicle (HV), and is composed of, for example, a lithium ion battery. This assembled battery 1 is composed of a plurality of cell groups connected in series, and each cell group is composed of a plurality of (for example, eight) cells BC1, BC2, BC3,. The assembled battery 1 includes a positive terminal T1 of the cell BC1, a positive terminal of the cell BC2 (a negative terminal of the cell BC1) T2, a positive terminal of the cell BC3 (a negative terminal of the cell BC2) T3,. ing.

  The equalization circuit 3 includes cells BC1 and BC2 constituting the assembled battery 1 in a state in which the vehicle IG switch (including a main power switch; the same applies hereinafter) is turned off, that is, in a period when the vehicle is not used such as at night. Is a circuit that equalizes the variation in the state of charge (SOC) of the cells BC1, BC2,... By controlling the discharge so that the voltages of the cells BC1, BC2,. .

  The equalization circuit 3 includes a reference voltage generation circuit 2, comparators CP2, CP3,..., A signal transmission circuit 4, a discharge control circuit unit 5, and a discharge circuit unit 6. However, FIG. 1 completely shows only the circuit related to the discharge of the cell BC2 in the equalization circuit 3, and the other cells BC1, BC3,... Omitted except for the circuits DC1 and DC3. This equalization circuit 3 is integrated into a single chip together with an overcharge / overdischarge detection circuit and the like in a state where the IG switch of the vehicle is turned on. Hereinafter, each circuit configuration will be described in order.

  The reference voltage generation circuit 2 includes resistors R1, R2, R3,... Connected in series. Reference voltages VR2, VR3,... In a state where all the cells BC1, BC2,... Are equalized are generated at the connection node N2 between the resistors R1 and R2, and the connection node N3 between the resistors R2 and R3. It is like that. The cells BC1, BC2,... All have the same standard, and the resistors R1, R2,.

  The comparator CP2 is supplied with a voltage for two cells as a power supply voltage from the plus side terminal T1 of the cell BC1 located on the high potential side and the minus side terminal T3 of the cell BC2 located on the low potential side with respect to the terminal T2. In operation, the voltage V2 at the terminal T2 is compared with the reference voltage VR2 at the node N2. Similarly, the comparator CP3 supplies a voltage for two cells as a power supply voltage from the plus side terminal T2 of the cell BC2 located on the high potential side and the minus side terminal T4 of the cell BC3 located on the low potential side with respect to the terminal T3. In response to this, the voltage V3 at the terminal T3 is compared with the reference voltage VR3 at the node N3. The output portions of the comparators CP2 and CP3 include open collector type transistors Q1 and Q2, respectively.

  The discharge circuit unit 6 includes a discharge circuit DC1 connected between both terminals of the cell BC1, a discharge circuit DC2,... Connected between both terminals of the cell BC2. The discharge control circuit unit 5 outputs a discharge control signal to the discharge circuit unit 6 based on the output signals of the comparators CP2, CP3,... Input via the signal transmission circuit 4, and includes the discharge control circuit LG1, It is composed of control circuits LG2,.

  The signal transmission circuit 4 related to the discharge control of the cell BC2 is a circuit that transmits the output signals of the comparators CP2 and CP3 to the discharge control circuit LG2. The ground potentials of the comparator CP2 and the discharge control circuit LG2 are both the voltage V3 of the terminal T3, but the ground potential of the comparator CP3 is the voltage V4 of the terminal T4. Therefore, the output signal of the comparator CP3 needs to be level-shifted and transmitted to the discharge control circuit LG2. In the signal transmission circuit 4 related to the discharge control of the cell BC2, the cell BC2 corresponds to the first cell, and the cell BC3 corresponds to the second cell.

  The output transistor Q1 of the comparator CP2 is grounded with respect to the terminal T3, and its collector is connected to the terminal T1 via the constant current circuit 7. Between the terminal T2 and the terminal T3, the resistor R11 and the collector and emitter of the transistor Q3 are connected in series, and the resistor R12 is connected between the base and emitter of the transistor Q3. The collector of the transistor Q1 is connected to the base of the transistor Q3. A transmission signal of the output signal of the comparator CP2 is output from the collector of the transistor Q3.

On the other hand, the output transistor Q2 (corresponding to the first transistor) of the comparator CP3 is grounded with respect to the terminal T4 (corresponding to the negative terminal of the second cell), and its collector is connected via the constant current circuit 8. It is connected to a terminal T2 (corresponding to the positive terminal of the first cell). A resistor R13 (corresponding to a load circuit) and a transistor Q4 (corresponding to a second transistor) are connected in series between a terminal T2 and a terminal T3 (corresponding to a connection point between cells), and the transistor Q4 A resistor R14 is connected between the base and emitter. A backflow prevention diode D1 is connected between the collector of the transistor Q2 and the base of the transistor Q4. A transmission signal of the output signal of the comparator CP3 is output from the collector of the transistor Q4.
The “signal transmission circuit” referred to in the present invention includes the signal transmission circuit 4 and the output transistor Q1 of the comparator CP2.

Next, the operation of this embodiment will be described.
The assembled battery 1 is repeatedly charged and discharged in use. When charging / discharging is repeated, the state of charge (SOC) of the cells BC1, BC2,... Varies due to individual differences in capacity of the cells BC1, BC2,. . Therefore, the equalization circuit 3 equalizes the cell voltages as follows in a state where the IG switch of the vehicle is turned off.

  The comparator CP2 compares the voltage V2 with the reference voltage VR2. When V2 <VR2, the transistor Q1 is turned off. In the signal transmission circuit 4, a constant current flows from the constant current circuit 7 to the resistor R12, and the transistor Q3 is turned on. As a result, the transmission signal to the discharge control circuit LG2 becomes L level. On the other hand, when V2> VR2, the transistor Q1 is turned on, and the output current of the constant current circuit 7 flows through the transistor Q1. As a result, the transistor Q3 is turned off, and the transmission signal to the discharge control circuit LG2 becomes H level.

  The comparator CP3 compares the voltage V3 with the reference voltage VR3. When V3 <VR3, the transistor Q2 is turned off. In the signal transmission circuit 4, a constant current flows from the constant current circuit 8 to the resistor R14 via the diode D1, and the transistor Q4 is turned on. As a result, the transmission signal to the discharge control circuit LG2 becomes L level.

  On the other hand, when V3> VR3, the transistor Q2 is turned on, and the output current of the constant current circuit 8 flows to the terminal T4 through the transistor Q2. At this time, the collector potential of the transistor Q2 drops to near the voltage V4 at the terminal T4, but the backflow prevention diode D1 is connected between the collector of the transistor Q2 and the base of the transistor Q4, so that the terminal T3 The voltage difference between the voltage V3 and the voltage V4 at the terminal T4 is applied to the diode D1, and is not applied between the base and emitter of the transistor Q4. Thereby, it is possible to prevent the occurrence of a Zener break between the base and emitter of the transistor Q4.

  The discharge control circuit LG2 is connected to the discharge circuit DC2 when the transmission signal from the comparator CP2 obtained through the signal transmission circuit 4 is at the H level and the transmission signal from the comparator CP3 obtained through the signal transmission circuit 4 is at the L level. A discharge control signal for instructing discharge is output. In other cases, a discharge control signal for instructing the discharge circuit DC2 to stop discharging is output. The control of the discharge circuit DC2 of the cell BC2 is the same as the control of the discharge circuits DC3,... Of the other cells BC3,. Control of the discharge circuit DC1 of the cell BC1 is performed based on the output signal of the comparator CP2.

  As described above, the equalization circuit 3 of the assembled battery 1 requires the signal transmission circuit 4 having a level shift function in order to transmit the output signals of the comparators CP2, CP3,... To the discharge control circuit unit 5. In the signal transmission circuit 4 used in the present embodiment, even when the cell voltage between the plus side terminal of the cell BC2 and the minus side terminal of the cell BC3 changes, or the output transistor Q2 of the comparator CP3 is turned on or off. Even if it changes, the current consumption of the signal transmission circuit 4 becomes substantially constant (if the resistance values of the resistors R11 and R13 are large, it is substantially equal to the sum of the output currents of the constant current circuits 7 and 8). In addition, since this current consumption may be a current necessary for performing the signal transmission operation, it can be minimized.

  Since the consumption current of the signal transmission circuit 4 is supplied from the assembled battery 1, the current flowing through each cell BC1, BC2, BC3,... Current) can be reduced as much as possible, and uneven generation of current between cells can be prevented. As a result, it is possible to suppress the discharge from the cell having a low cell voltage and to prevent the generation of an uneven discharge current that hinders the discharge control for equalization by the equalization circuit 3.

  The comparator CP3 receives power supply voltage from both terminals of the two cells BC3 and BC4 connected in series across the terminal T3 to be compared. Therefore, the comparison operation can be performed normally. The same applies to the comparator CP2.

The present invention is not limited to the embodiment described above and shown in the drawings. For example, the present invention can be modified or expanded as follows.
The first transistor constituting the signal transmission circuit according to the present invention is not limited to the output transistor of the comparator. Further, the signal transmitted by the signal transmission circuit is not limited to the output signal of the comparator.

  The comparator CP3 only needs to operate with power supplied from the positive terminal of the cell located on the high potential side and the negative terminal of the cell located on the low potential side with respect to the terminal T3. For example, the cell BC1 The power supply may be received from the plus side terminal of the cell and the minus side terminal of the cell BC4 (not shown).

The principal part block diagram of the equalization circuit which shows one Embodiment of this invention

Explanation of symbols

  1 is an assembled battery, 4 is a signal transmission circuit, 8 is a constant current circuit, BC2 is a cell (first cell), BC3 is a cell (second cell), CP2 and CP3 are comparators, Q2 is a transistor (first transistor) Transistors), Q4 are transistors (second transistors), D1 is a diode (diode for backflow prevention), R13 is a resistor (load circuit), R14 is a resistor, and T1, T2, T3, T4,.

Claims (3)

In a signal transmission circuit that operates by receiving power from an assembled battery,
A constant current circuit connected in series between a plus side terminal of a first cell constituting the assembled battery and a minus side terminal of a second cell connected to a lower potential side than the first cell; One transistor,
Between the plus side terminal of the first cell and the connection point between cells located between the plus side terminal of the first cell and the minus side terminal of the second cell in the assembled battery, A load circuit and a second transistor connected in series;
A backflow preventing diode connected between the collector of the first transistor and the base of the second transistor;
A resistor connected between a base and an emitter of the second transistor;
A signal transmission circuit configured to output an output signal corresponding to an input signal applied to a base of the first transistor from a collector of the second transistor.   The signal transmission circuit according to claim 1, wherein the first transistor is an output transistor of a comparator. The comparator receives power from the positive terminal of the first cell and the negative terminal of the second cell, and compares the voltage at the connection point between the cells with a predetermined reference voltage. The signal transmission circuit according to claim 2, wherein the signal transmission circuit is configured as described above.

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