CN110380493A - A kind of serial lithium battery equalizer circuit - Google Patents

Abstract

The invention discloses a lithium battery voltage equalizing circuit in series, which comprises a battery pack composed of an even number of lithium batteries connected in series in sequence, a high-frequency multi-port transformer, a primary-side half-bridge circuit and several secondary-side half-bridge circuits; The side half-bridge circuit includes an N-type switch S _A , the drain of the N-type switch S _A is respectively connected to the positive pole of the battery pack and one end of the capacitor C1; the source of the N-type switch S _A is respectively connected to the inductor L _P1 One end is connected to the drain of the N-type switch tube S _B ; the source of the N-type switch tube S _B is respectively connected to the negative pole of the battery pack and one end of the capacitor C2; the other end of the capacitor C1 is respectively connected to the primary side coil T _P One end is connected to the other end of the capacitor C2; the other end of the primary coil T _P is connected to the other end of the inductor L _P1 . The circuit structure of the invention is simple, the cost is low, and the minimum voltage of the single battery in the lithium battery pack is avoided from affecting the effective capacity of the battery pack.

Description

A voltage equalizing circuit for lithium batteries in series

technical field

The invention relates to the field of voltage equalization of lithium batteries, in particular to a voltage equalization circuit of series lithium batteries.

Background technique

With the advancement of battery-related technologies, lithium batteries are more and more used in the energy storage link of new energy distributed micro-generation grids, new energy electric vehicle vehicle batteries and other occasions due to their advantages such as high energy density, green environmental protection, and no memory effect. more extensive.

Because the cell voltage of lithium-ion batteries is relatively low, it cannot meet the load requirements of high-power levels in practical applications. A certain number of batteries need to be connected in series to form a battery pack to meet the actual battery voltage requirements. However, limited by the current manufacturing process and the influence of the working temperature and other environments, lithium-ion batteries may have inconsistencies in parameters such as battery capacity and equivalent internal resistance in actual work.

The voltage and remaining capacity of each battery is affected by its battery parameters. Then the inconsistency of the battery parameters in the battery pack will directly cause the inconsistency of the battery voltage and the inconsistency of the remaining capacity in the same battery pack. The effective capacity of the battery pack mainly depends on the lowest voltage single cell in the battery pack, so the excessive voltage difference of the single cell voltage in the same battery pack will affect the service life and efficiency of the battery pack.

Contents of the invention

Aiming at the above-mentioned deficiencies in the prior art, the present invention provides a series lithium battery voltage equalizing circuit to solve the problem that the minimum voltage of the single cells in the lithium battery pack affects the effective capacity of the battery pack.

In order to achieve the above-mentioned purpose of the invention, the technical scheme adopted in the present invention is:

Provided is a voltage equalizing circuit for lithium batteries in series, which includes a battery pack composed of an even number of lithium batteries connected in series in sequence, a high-frequency multi-port transformer, a primary side half-bridge circuit and several secondary side half-bridge circuits; the primary side half-bridge The circuit includes an N-type switch S _A , the drain of the N-type switch S _A is respectively connected to the positive pole of the battery pack and one end of the capacitor C1; the source of the N-type switch S _A is respectively connected to one end of the inductor L _P1 and N The drain of the N-type switch tube S _B is connected; the source of the N-type switch tube S _B is respectively connected to the negative pole of the battery pack and one end of the capacitor C2; the other end of the capacitor C1 is respectively connected to one end of the primary side coil T _P and the capacitor The other end of C2 is connected; the other end of the primary coil T _P is connected to the other end of the inductor L _P1 ;

Every two adjacent lithium batteries form a battery pack and correspond to a secondary side half-bridge circuit. The mth secondary side half-bridge circuit includes an N-type switch tube S _2m-1 , and the N-type switch tube S _2m-1 The drain is connected to the positive pole of the corresponding battery pack; the source of the N-type switch S _2m-1 is respectively connected to the drain of the N-type switch S _2m and one end of the inductance L _sm ; the other end of the inductance L _sm is connected to the two One end of the secondary side coil T _sm is connected; the other end of the secondary side coil T _sm is connected to the positive and negative series lines of the corresponding two lithium batteries; the source of the N-type switch tube S _2m is connected to the corresponding battery pack connected to the negative pole.

Further, the end of the primary side coil T _P connected to the inductor L _P1 is the end of the same name; the end of the secondary coil T _sm connected to the inductor L _sm is the end of the same name.

The beneficial effects of the present invention are: the circuit structure of the present invention is simple, the cost is low, the control mode is convenient, and the battery energy transfer within the battery pack, the energy transfer between the battery packs and the energy transfer between the primary and secondary sides can be realized, and it can control the battery pack with complex voltage distribution. Voltage equalization is carried out to avoid the lowest voltage of the single battery in the lithium battery pack from affecting the effective capacity of the battery pack.

Description of drawings

Fig. 1 is a schematic circuit diagram of the present invention;

Fig. 2 is a working schematic diagram of the present invention carrying out energy transfer in a battery pack;

Fig. 3 is a working schematic diagram of energy transfer between battery packs in the present invention;

Fig. 4 is the working sketch map that the present invention carries out primary and secondary side energy transfer;

Fig. 5 is the working equivalent waveform figure of the present invention;

Fig. 6 is the current mode schematic diagram of working mode 1 of the present invention;

Fig. 7 is the current mode schematic diagram of working mode 2 of the present invention;

Fig. 8 is a schematic diagram of the current mode of working mode 3 of the present invention.

Detailed ways

The specific embodiments of the present invention are described below so that those skilled in the art can understand the present invention, but it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, as long as various changes Within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concept of the present invention are included in the protection list.

As shown in Figure 1, the series lithium battery voltage equalizing circuit includes a battery pack composed of an even number of serially connected lithium batteries, a high-frequency multi-port transformer, a primary side half-bridge circuit and several secondary side half-bridge circuits; The half-bridge circuit includes an N-type switch S _A , the drain of the N-type switch S _A is respectively connected to the positive pole of the battery pack and one end of the capacitor C1; the source of the N-type switch S _A is respectively connected to one end of the inductor L _P1 It is connected to the drain of the N-type switch tube S _B ; the source of the N-type switch tube S _B is respectively connected to the negative pole of the battery pack and one end of the capacitor C2; the other end of the capacitor C1 is respectively connected to one end of the primary side coil T _P It is connected with the other end of the capacitor C2; the other end of the primary side coil T _P is connected with the other end of the inductor L _P1 ;

Every two adjacent lithium batteries form a battery pack and correspond to a secondary side half-bridge circuit. The mth secondary side half-bridge circuit includes an N-type switch tube S _2m-1 , and the N-type switch tube S _2m-1 The drain is connected to the positive pole of the corresponding battery pack; the source of the N-type switch S _2m-1 is respectively connected to the drain of the N-type switch S _2m and one end of the inductance L _sm ; the other end of the inductance L _sm is connected to the two One end of the secondary side coil T _sm is connected; the other end of the secondary side coil T _sm is connected to the positive and negative series lines of the corresponding two lithium batteries; the source of the N-type switch tube S _2m is connected to the corresponding battery pack connected to the negative pole.

The end connected to the primary side coil T _P and the inductor L _P1 is the terminal with the same name; the end connected to the secondary coil T _sm and the inductor L _sm is the terminal with the same name.

In the specific implementation process, the working equivalent waveform diagram of the present invention is shown in Fig. 5, and the voltage equalizing circuit topology of the present invention is essentially a single inductor voltage equalizing and multi-port DC-DC converter for energy transmission. In various working states, there are three different energy transmission modes.

As shown in Figure 2, the first working state is energy transfer in the battery pack, and the voltage of the battery (or capacitor) is detected. If the voltage of the upper battery is higher than the voltage of the lower battery, the switch tube corresponding to the upper battery is turned on during the duty cycle time. At this time, the upper battery is discharged through the inductor, and the inductor accumulates energy. After the duty cycle time is over, the inductor current continues to flow, and the energy is released to the lower battery with low voltage. The battery with the positive pole of the single lithium battery in each battery pack as the positive pole of the battery pack is the upper battery, and the battery with the negative pole of the single lithium battery in each battery pack as the negative pole of the battery pack is the lower battery . Take the secondary side half-bridge circuit (Module 1) completely drawn in Figure 1 as an example, the battery B ₁ in the figure is the upper battery, the corresponding switching tube is the switching tube S ₁ , and the battery B ₂ in the figure is the lower battery, The corresponding switching tube is switching tube S ₂ .

As shown in Figure 3, the second working state is energy transfer between battery packs. The secondary side half-bridge circuit is connected through a high-frequency multi-port transformer to form a multi-port DC-DC with a ratio of 1:1:…:1 converter. At the same time, the battery pack whose battery voltage is higher than the secondary side voltage of the transformer discharges to the transformer, and the transformer charges the battery pack whose battery voltage is lower than the transformer voltage. After several cycles, the cell voltages of each battery pack tend to be equal.

As shown in Figure 4, the third working state is the energy balance of the monomer and the whole. The secondary side half-bridge circuit and the primary side half-bridge circuit are connected together through a high-frequency multi-port transformer, and the composition ratio is n:1:… : 1 multi-port DC-DC converter, which is different from the second way. The current of the secondary-side half-bridge circuit is still determined by the battery voltage of each battery pack and the voltage of the high-frequency multi-port transformer, and the primary-side current is the value converted from the sum of all battery pack currents on the secondary side through the high-frequency multi-port transformer same. The current on the primary side charges and discharges the overall battery pack through the upper and lower busbars, realizing the energy exchange of the overall battery pack.

In one embodiment of the invention, when the transformer voltage is lower than all battery cell voltages, all secondary half-bridge circuits discharge to the high-frequency multiport transformer, so that the primary half-bridge current is all secondary The sum of the half-bridge circuit currents. In this mode, the current flow direction of the entire topology is single and fixed, which is convenient for analysis. Therefore, this mode is taken as an example here, and the voltage and current waveforms and circuit modal diagrams are used for analysis. In this mode, in order to make all the batteries equal to the average voltage, only the switch tubes corresponding to the batteries with higher than the average voltage are turned on.

As shown in Figure 6, working mode 1: detect the upper battery in each battery pack on the secondary side, and at time t ₀ , turn on the secondary switch tubes in the first j battery packs whose upper battery voltage is higher than the average voltage. At this time, the corresponding switching tube S _A of the primary side is turned on, and the energy flows out from all the upper batteries in the first j battery packs, and charges the inductance L _s1 ... L _sj through the respective switching tubes, and i _ls1 ... i _lsj rises linearly, At the same time, the energy is transferred to the primary side through the high-frequency multi-port transformer, _{i Lp} rises linearly, and the energy is transferred to the overall battery pack through the switch tube SA. There is also an induced voltage V _TS on the last k windings of the secondary side of the high-frequency multi-port transformer. However, due to the setting of the transformer ratio, V _TS <V _Bk1 +V _D , the body diode of S _k1 will not be turned on. So there is no current path. This stage realizes the transmission of energy from a single battery to the overall battery pack.

As shown in Figure 7, working mode 2: At time _t1 , the first j odd-numbered switches S ₁ ... S _2j-1 and the switch S _A are turned off at the same time, and the energy stored in the inductance of the high-frequency multi-port transformer passes through S _A and the anti-parallel diodes of the first j odd-numbered switch tubes S ₁ ... S _2j-1 freewheel, the primary side is released to the overall battery pack through the diode of the switch tube S _A , and the secondary side is passed through the first j even-numbered switch tubes The diodes of S ₁ ... S _2j-1 are released to the lower battery in the group corresponding to the upper battery discharged in the last cycle. At this stage, the secondary side realizes the voltage sharing of the single inductor in the secondary side half-bridge circuit, and the primary side realizes the transfer of inductive energy to the whole. Although each secondary-side half-bridge circuit has different discharge speeds due to different battery voltages, as time progresses, each secondary-side half-bridge circuit will slowly complete freewheeling within the dead time. At ₂ , all the secondary side half-bridge circuits complete freewheeling, and only the excitation current still exists in the circuit. In this stage, the energy stored in the inductor is released to the low-voltage battery, which is actually the second half of the single-inductor voltage equalization stage.

As shown in Figure 8, working mode 3: This stage is the freewheeling stage of the excitation current. Since the high-frequency multi-port transformer has quit working, the excitation current can only pass through the capacitor C2, the body diode of the switch tube S _B and the primary inductance L _P1 freewheeling. The voltage of the switching tube S _B is clamped to zero, and the soft switching of the switching tube S _B is realized at time t3. Start the energy release of the high-voltage battery to the whole battery pack and the low-voltage battery in the second half cycle.

To sum up, the circuit structure of the present invention is simple, low in cost, and convenient in control mode, and can realize battery energy transfer within a battery pack, energy transfer between battery packs, and primary and secondary side energy transfer, and it can balance battery packs with complex voltage distributions. Voltage, to avoid the lowest voltage of the single cell in the lithium battery pack from affecting the effective capacity of the battery pack.

Claims (2)

1. a kind of serial lithium battery equalizer circuit, which is characterized in that including the lithium battery group that is sequentially connected in series by even number at electricity Chi Bao, high frequency multiport transformer, primary side half-bridge circuit and several secondary side half-bridge circuits；The primary side half-bridge circuit Including N type switch tube S_A, the N type switch tube S_ADrain electrode be connected respectively with the anode of battery pack and one end of capacitor C1；Institute State N type switch tube S_ASource electrode respectively with inductance L_P1One end and N type switch tube S_BDrain electrode be connected；The N type switch tube S_B Source electrode be connected respectively with one end of the cathode of battery pack and capacitor C2；The other end of the capacitor C1 respectively with a side line Enclose T_POne end be connected with the other end of capacitor C2；The first siding ring T_PThe other end and inductance L_P1The other end be connected It connects；

Every two adjacent lithium battery forms a battery pack and a corresponding secondary side half-bridge circuit, m-th of secondary side half-bridge Circuit includes N type switch tube S_2m-1, the N type switch tube S_2m-1Drain electrode be connected with the anode of corresponding battery pack；Institute State N type switch tube S_2m-1Source electrode be separately connected N type switch tube S_2mDrain electrode and inductance L_smOne end；The inductance L_smIt is another One end and second siding ring T_smOne end be connected；The second siding ring T_smThe other end be connected to corresponding two The positive and negative anodes series line of lithium battery；The N type switch tube S_2mSource electrode be connected with the cathode of corresponding battery pack.

2. serial lithium battery equalizer circuit according to claim 1, which is characterized in that the first siding ring T_PWith inductance L_P1The one end being connected is Same Name of Ends；The second siding ring T_smWith inductance L_smThe one end being connected is Same Name of Ends.