JP4378009B2 - Balance correction method and apparatus for secondary batteries connected in series - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a technique for using, as a power source, a plurality of secondary batteries connected in series, such as an electric vehicle or a notebook computer, and in particular, a balance correction method and apparatus for equalizing the voltages of the batteries. About.
[0002]
[Prior art]
As is well known, in the case of a power supply system that uses a secondary battery in series with repeated charging and discharging, it is possible to effectively discharge the battery even in the charging phase in terms of effective use of the battery capacity and the longest battery life. Even in the situation, it is desirable to make the voltage of each battery as uniform as possible. Even if a general battery has the same specifications, it is unavoidable that the characteristics of each battery vary. Therefore, it is necessary to take measures to equalize the voltage of each battery while using a power supply system of series batteries.
[0003]
Therefore, the present inventors have previously developed the following technique disclosed in Japanese Patent Application Laid-Open No. 11-176483. A transformer having a large number of secondary windings with the same number of turns is prepared (this is named a multichannel uniform output type transformer). A series output of a large number of batteries is applied to the series circuit of the primary winding and the switching element of the transformer, and the switching element is turned on and off at a high speed to flow a primary current. The output of each secondary winding of the transformer is rectified and smoothed, and each DC output is applied to each individual battery of the series battery. That is, the on-off converter is driven by the output of the series battery, and each of the series batteries is charged by the multi-channel output of the converter. In this structure, the battery output which shows a higher voltage will charge the battery which shows a lower voltage, and the voltage of each battery is equalized.
[0004]
[Problems to be solved by the invention]
In the converter type balance correction technique using the multi-channel uniform output type transformer described above, a uniform output type transformer having n secondary windings is required for n series batteries. Since n circuits for rectifying and smoothing the output of the next winding are required, there is a problem that the number of component parts is large and the cost is high. For example, an electric vehicle uses a power supply system in which as many as 100 to 200 batteries are connected in series. However, assuming that the above-described conventional technology is applied to this, the above problem is greatly highlighted.
[0005]
The present invention has been made in view of the above-described conventional problems, and its purpose is to highly equalize the voltage of each battery in relation to a power supply system using secondary batteries connected in series. Another object of the present invention is to provide a balance correction method and apparatus that can be realized simply and inexpensively.
[0006]
[Means for Solving the Problems]
In the balance correction method studied prior to this invention, one end of the inductor L is connected to the connection point between the secondary battery B1 and the secondary battery B2 connected in series, and the other end of the inductor L is connected to the other battery B1. A first mode in which current flows in the first closed circuit formed by connecting to the end, and a second mode in which current flows in the second closed circuit formed by connecting the other end of the inductor L to the other end of the battery B2. The operation of repeating the two modes alternately for a short time is executed for an appropriate period to equalize the voltages of the batteries B1 and B2 (see FIG. 1) .
[0007]
The invention of claim 1 is an apparatus for better performing the balance correction method . First, an inductor L whose one end is connected to a connection point between one end of the battery B1 and one end of the battery B2, and an inductor L Is connected to the other end of the battery B1 to form a first closed circuit, and the other end of the inductor L is connected to the other end of the battery B2 to form a second closed circuit. a second switching element S2 to, Ru includes a first switching element S1 and a control circuit for the second switching element S2 to complementarily turn on and off the drive by a short period of time. Each of the first and second switching elements uses a switching element having a body diode that flows a current in the opposite direction to the switching current, such as a MOSFET, and both ends of the first switching element S1 and the second switching element. Capacitors are connected in parallel to both ends of S2 (see FIGS. 4 and 5) .
[0008]
In a more general balance correction method of the present invention, i is an odd number from 1 to (n−1) in a series circuit of four or more even number of secondary batteries B1, B2, B3,. One end of the inductor Li is connected to the connection point between the battery Bi and the battery Bi + 1, and these (n ÷ 2) inductors L1 to Li are all magnetically coupled by a magnetic circuit with the winding poles aligned on the battery side or the switching element side. First, the first mode in which current flows through the odd-numbered closed circuit formed by connecting the other end of the inductor Li to the other end of the battery Bi, and the other end of the inductor Li connected to the other end of the battery Bi + 1. The second mode in which the current is passed through the even-numbered closed circuit formed in the step is alternately repeated for a short period of time to equalize the voltage of each battery (invention of claim 2 ).
[0009]
Invention of Claim 3 is an apparatus for performing the balance correction method of Claim 2 , Comprising: Inductor Li by which one end is connected to the connection point of battery Bi and battery Bi + 1, and these (n / 2) A magnetic circuit for magnetically coupling the inductors L1 to Li, an odd-numbered switching element Si for connecting the other end of the inductor Li to the other end of the battery Bi to form an odd-numbered closed circuit, and the other end of the inductor Li Is connected to the other end of the battery Bi + 1, and the even-numbered switching element Si + 1 for forming the even-numbered closed circuit, and the odd-numbered switching element Si and the even-numbered switching element Si + 1 are complementarily turned on and off for a short time. And a control circuit for this purpose. In this device, it is desirable to connect a capacitor in parallel to each of the odd-numbered switching element Si and the even-numbered switching element Si + 1 (invention of claim 4 ).
[0010]
DETAILED DESCRIPTION OF THE INVENTION
=== Correcting the balance of two series batteries ===
FIG. 1 shows a reference circuit for explaining a technique studied prior to the present invention. In this reference circuit, secondary batteries B1 and B2 are connected in series, and one end of an inductor L is connected to the midpoint of both batteries B1 and B2. Switching element S1 is connected between the other end (plus terminal) of battery B1 and the other end of inductor L, and switching element S2 is connected between the other end (minus terminal) of battery B2 and the other end of inductor L. Has been.
[0011]
The switching elements S1 and S2 are MOSFETs, and are driven by gate drivers D1 and D2 that operate in a complementary manner so that when one switching element is on, the other is off. The controller 10 generates a pulse train having a predetermined cycle with a duty ratio of 50% and inputs it to the gate drivers D1 and D2 during the period of executing the balance correction of the batteries B1 and B2. Thereby, as shown in the timing chart of FIG. 2, the switching elements S1 and S2 are repeatedly turned on and off in a complementary manner. On time and off time are equal.
[0012]
When the switching element S1 is on and the switching element S2 is off, the battery B1, the switching element S1, and the inductor L form a closed circuit (this closed circuit is called a B1 loop), and the switching element S1 is off and the switching element S2 Is on, battery B2, inductor L, and switching element S2 form a closed circuit (this closed circuit is called a B2 loop).
[0013]
It is assumed that a loop current flows in the forward direction due to the electromotive force of the battery B1 during the B1 loop period. When the voltage of the battery B1 is e1 and the inductance value of the inductor L is L, the forward current during the B1 loop period increases with time at a change rate of (e1 / L).
[0014]
It is assumed that the switching elements S1 and S2 are inverted from the state in which the forward current flows during the B1 loop period and switched to the B2 loop period. At this time, the current flowing through the inductor L is in the opposite direction to the electromotive force of the battery B2. That is, the current in the forward direction with respect to the electromotive force of the battery B1 during the B1 loop period is a current in the reverse direction with respect to the electromotive force of the battery B2 during the B2 loop period. This reverse current gradually decreases due to the electromotive force of the battery B2. The rate of change is (e2 / L), where e2 is the voltage of battery B2.
[0015]
In the waveform diagram illustrated in FIG. 2, in the B2 loop period (A), a current in the reverse direction initially flows with respect to the electromotive force of the battery B2 (this period is referred to as the previous charge mode time), and the reverse direction thereof. The current gradually decreases at the rate of change of (e2 / L) and finally becomes zero, and further becomes a forward current with respect to the electromotive force of the battery B2, and the forward current has the same rate of change (e2 / L). Gradually increases (this period is set as the late discharge mode time), and when a certain time comes, the switching elements S1 and S2 are inverted and switched to the B1 loop period (c).
[0016]
In the B1 loop period (c), a current in the reverse direction initially flows with respect to the electromotive force of the battery B1 (which is the previous charge mode time), and the reverse current decreases at a rate of change of (e1 / L). Eventually it becomes zero, and further becomes a forward current with respect to the electromotive force of the battery B1, and the forward current gradually increases at the same rate of change (e1 / L) (the late discharge mode time) When a certain time comes, the switching elements S1 and S2 are inverted and switched to the B2 loop period (D).
[0017]
Typically, the above operations are repeated. Here, it is assumed that the voltage e1 of the battery B1 is considerably higher than the voltage e2 of the battery B2. In this case, the change rate (e1 / L) of the B1 loop current is larger than the change rate (e2 / L) of the B2 loop current. Therefore, during the B1 loop period, the first charge mode time is short and the late discharge mode time is long, and conversely, during the B2 loop period, the first charge mode time is long and the late discharge mode time is short.
[0018]
The reason for naming it as the first charge mode time and the latter discharge mode time is as follows.
At the beginning of switching to the B1 loop period, a current in the reverse direction flows in the electromotive force of the battery B1, and the battery B1 is charged by this current. Therefore, this period is referred to as the first charge mode time. Subsequently, a forward current flows in the electromotive force of the battery B1, and this is because the battery B1 is discharged and current is flowing, and this period is called a late discharge mode time.
Magnetic energy stored in the inductor L as a source of discharge of the battery B1 during the latter discharge mode time of the B1 loop period is released during the first charge mode time of the immediately following B2 loop period and is a source of energy for charging the battery B2. It becomes. Similarly, the magnetic energy stored in the inductor L as a source of discharge of the battery B2 during the latter discharge mode time of the B2 loop period is released during the first charge mode time of the immediately following B1 loop period to charge the battery B1. It becomes a source of energy.
[0019]
As described above, when the voltage e1 of the battery B1 is higher than the voltage e2 of the battery B2, the first charge mode time is short and the second discharge mode time is long during the B1 loop period, and conversely, the first charge mode time is long during the B2 loop period. Is longer and the late discharge mode time is shorter. Therefore, the battery B1 on the higher voltage side is discharged in total, and the battery B2 on the lower voltage side is charged in total. That is, the battery B2 is charged with the output of the battery B1. As a result, the voltage e1 of the battery B1 gradually decreases, the voltage e2 of the battery B2 increases gradually, and the voltage e1 and the voltage e2 are equalized.
[0020]
=== More series battery balance correction ===
FIG. 3 shows an embodiment of the present invention. In the circuit of the embodiment shown in the figure, six batteries B1 to B6 are connected in series. As for the pair of the battery B1 and the battery B2, the inductor L1 and the two switching elements S1 and S2 are connected as in the reference circuit of FIG. The inductor L3 and the two switching elements S3 and S4 are connected to the pair of the battery B3 and the battery B4 so as to have the same connection relationship as these. Similarly, an inductor L5 and two switching elements S5 and S6 are connected to a pair of the battery B5 and the battery B6.
[0021]
The odd-numbered three switching elements S1, S3, and S5 are simultaneously turned on and off by the gate driver D1, and the even-numbered three switching elements S2, S4, and S6 are simultaneously turned on and off by the gate driver D2. The gate drivers D1 and D2 receive a pulse train having a predetermined cycle with a duty ratio of 50% from the controller 10 and perform complementary operations, thereby setting the odd-numbered switching elements S1, S3, and S5 and the even-numbered switching elements S2, S4, and S6. The other set is driven on and off in a complementary manner, and when one set is on, the other set is off. The on period and the off period are equal.
[0022]
As is apparent from FIG. 3, when the odd-numbered switching elements S1, S3, and S5 are turned on, a loop around the battery B1, the switching element S1, and the inductor L1, and a loop around the battery B3, the switching element S3, and the inductor L3. In addition, current flows through the loop around battery B5, switching element S5, and inductor L5. When the set of the even-numbered switching elements S2, S4, and S6 is turned on, the loop around the battery B2, the inductor L1, and the switching element S2, the loop around the battery B4, the inductor L3, and the switching element S4, the battery B6, the inductor L5, A current flows through each loop around the switching element S6.
[0023]
In this embodiment, it is a very important technical element that the inductors L1, L3, and L5 are wound around the common core 20 and are closely magnetically coupled. The polarity of these magnetically coupled inductors L1, L3, L5 and the connection relationship between each battery pair are equal (the number of turns is also the same), and when current flows in the same direction of each inductor L1, L3, L5, A magnetic flux in the same direction is induced in the core 20 by the current.
[0024]
If this magnetic coupling is not considered, the two batteries described in detail in the embodiment of FIG. 1 in each of the pair of the battery B1 and the battery B2, the pair of the battery B3 and the battery B4, and the pair of the battery B5 and the battery B6 Voltage equalization occurs. This can be easily understood. In addition to this, an action of equalizing all voltages of the six batteries B <b> 1 to B <b> 6 occurs by an energy transfer action by magnetic coupling of the inductors L <b> 1, L <b> 3, and L <b> 5.
[0025]
That is, the inductors L1, L3, and L5 are wound around the common core 20 and have the same number of turns. Therefore, when a magnetic flux is generated in the core 20, a voltage determined by the magnetic flux and the number of turns is set to each inductor L1. It occurs equal to L3 · L5. Therefore, the circuit operates in a state where the voltages across the inductors L1, L3, and L5 are equal. This means that the magnetic energy originating from the current flowing in the inductor connected to one battery pair is transferred to the inductor connected to another battery pair and released from that inductor as electrical output. ing. As a result, the battery energy on the higher voltage side among the six batteries B1 to B6 is once changed into magnetic energy and transferred, and supplied as charging energy for the battery having a lower voltage. With the above operation, all the voltages of the six batteries B1 to B6 are gradually equalized.
[0026]
=== Soft switching ===
As shown in FIG. 4 and FIG. 5, a change in switching operation can be moderated appropriately by connecting a capacitor in parallel with each switching element in the reference example and the embodiment described above, thereby reducing noise. There are effects such as.
For example, in FIG. 4, when the switching element S2 of the MOSFET is switched from on to off and S2 is switched from off to on, the inductor current flowing in the path B2-L-S2 is regenerated in the direction of charging B1 through C1. To do. At this time, the terminal voltage of C1 becomes -0.6V (the body diode forward voltage of the switching element S1 of the MOSFET) having a polarity opposite to that of the voltage E1 of B1, and in this state, S1 is turned off. By turning it on, a so-called zero volt switch (soft switching) is realized. Thereby, the switching loss and noise accompanying the discontinuous change of the inductor current can be effectively reduced.
[0027]
=== Other Embodiments ===
In the above embodiments, MOSFETs are used as switching elements, but other switching elements such as bipolar transistors may of course be used. In that case, it is preferable to add a diode corresponding to the body diode of the MOSFET so that a reverse current can flow.
[0028]
In the above description of the embodiment, it is described that the switching element Si and the switching element Si + 1 are reversed at the same time (with no dead time), but generally speaking, the switching element Si and the switching element Si + 1. It is preferable to set a slight time (dead time) during which both are turned off simultaneously.
[0029]
【The invention's effect】
According to the present invention, with respect to a power supply system in which n secondary batteries are connected in series, the voltage of each battery can be increased by a simple and inexpensive means using half n / 2 inductors. Can be equalized.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a first reference example studied prior to the present invention.
FIG. 2 is a timing chart for explaining the operation of the circuit of FIG . 1 ;
FIG. 3 is a circuit diagram showing a first embodiment of the present invention.
FIG. 4 is a circuit diagram showing a second embodiment of the present invention.
FIG. 5 is a circuit diagram showing a third embodiment of the present invention.
[Explanation of symbols]
B1-B6 Secondary batteries L, L1, L3, L5 Inductors S1-S6 Switching elements

Claims (4)

One end of the inductor L is connected to a connection point between one end of the secondary battery B1 and one end of the secondary battery B2 connected in series, and the other end of the inductor L is connected to the other end of the battery B1. A first mode in which current flows through the first closed circuit and a second mode in which current flows through the second closed circuit formed by connecting the other end of the inductor L to the other end of the battery B2. A balance correction device that performs an alternating operation for an appropriate period and equalizes the voltages of the battery B1 and the battery B2,
A first switching element S1 for forming the first closed circuit by connecting the other end of the inductor L to the other end of the battery B1, and a second closed circuit by connecting the other end of the inductor L to the other end of the battery B2. And a control circuit for driving the first switching element S1 and the second switching element S2 in a complementary manner on and off for a short time,
Each of the first and second switching elements uses a switching element having a body diode that flows a current in a direction opposite to the switching current,
A balance correction apparatus, wherein a capacitor is connected in parallel to each of the first switching element S1 and the second switching element S2.   In a series circuit of four or more even number of secondary batteries B1, B2, B3,..., Bn, i is an odd number from 1 to (n−1), and the inductor Li is connected to the connection point between the battery Bi and the battery Bi + 1. The odd-numbered side formed by connecting one end and magnetically coupling all the (n ÷ 2) inductors L1 to Li by a magnetic circuit and connecting the other end of the inductor Li to the other end of the battery Bi. An operation of alternately repeating a first mode in which current flows in a closed circuit and a second mode in which current flows in an even-numbered closed circuit formed by connecting the other end of the inductor Li to the other end of the battery Bi + 1. Is executed for an appropriate period, and the voltage of each battery is equalized. An apparatus for executing the balance correction method according to claim 2 , wherein an inductor Li having one end connected to a connection point between the battery Bi and the battery Bi + 1 and the (n ÷ 2) inductors L1 to Li are provided. A magnetic circuit to be magnetically coupled, an odd-side switching element Si for forming an odd-side closed circuit by connecting the other end of the inductor Li to the other end of the battery Bi, and the other end of the inductor Li to the other end of the battery Bi + 1 An even-numbered switching element Si + 1 for connecting and forming an even-numbered closed circuit; and a control circuit for complementarily driving the odd-numbered switching element Si and the even-numbered switching element Si + 1 on and off for a short time. A balance correction device characterized by that. 4. The balance correction apparatus according to claim 3, wherein a capacitor is connected in parallel to each of the odd-numbered switching element Si and the even-numbered switching element Si + 1.

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