CN105703434A - Battery management system with active equalization function - Google Patents

Abstract

The disclosure of the present invention relates to a battery management system with an active balancing function, and specifically describes the battery management system with the active balancing function. The system includes a low-voltage MOSFET and associated drive circuit for each cell, a multi-winding transformer and a microcontroller (MCU) for the battery pack. The role of the microcontroller (MCU) is to control the on and off of each MOSFET, detect the battery voltage and balance the battery cells with different voltages in each battery pack. Through modularity, the system can achieve equalization of any number of battery cells.

Description

A battery management system with active balancing function

technical field

The invention relates to a battery management system, in particular to a battery management system with an active balancing function, which is mainly used for the control and management of high-voltage and high-power serial battery packs in electric vehicles.

Background technique

In recent years, hybrid, plug-in hybrid and pure electric vehicles have been commercialized. High-voltage and high-power series battery packs play an important role in electric vehicles, and lithium-ion batteries are the best choice because of their high energy storage and high energy density. However, lithium-ion batteries also have deficiencies, especially that they cannot be overcharged, and their safety in terms of overcharge, overdischarge and improper use is also the most concerned issue for people. When a large number of lithium-ion batteries are connected in series for high-power and high-energy applications, it is necessary to have a battery management system with balancing function. In order to make the battery cells connected in series healthier and safer, and to improve the usable capacity and battery life, a battery management system is required to detect and equalize the voltage of the battery. Sensing and balancing are two important parts in a battery management system.

In existing designs like patents US7939965B2 and US005659237A, the detection circuit is directly connected to the battery unit. For a battery pack in series, the potential on the battery terminals may be high, so the detection circuit is subjected to high voltage. This can significantly increase the cost of the circuit. US Patent No. US6538414 proposes a method in which the detection circuit is connected to the battery unit through a multi-winding transformer, thereby isolating the detection circuit from the battery unit. Therefore, low power devices can be used. At the same time, the transformer is also part of the equalization circuit. In this way, overall costs can be reduced. However in US6538414 the number of transformer windings is very large and each MOSFET needs a transformer to drive. Too many windings and transformers add to the cost of the circuit.

Contents of the invention

The technical problem to be solved by the invention is to provide a multi-winding transformer to isolate the detection circuit from the battery unit, so that low-power devices can be used. More importantly, the present disclosure reduces the number of transformer windings and eliminates the drive transformer, thereby reducing substantial circuit costs.

In order to solve the above technical problems, the present invention provides a battery management system with an active equalization function, which includes: N single batteries connected in series, and these batteries are divided into M pairs of battery cell pairs, where N is an even number greater than zero;

A multi-winding transformer with M windings, each of the M windings has one end connected to the midpoint of the battery cell pair, and the M windings are respectively connected to the midpoint of the M battery cell pairs;

N low-voltage switching devices are associated with N battery cells. The N low-voltage switching devices are also divided into M pairs. The midpoint of each switch pair is connected to the other end of the M transformer windings. Each switch is selectively operation;

Wherein, the driving circuit controls the on-off of the low-voltage switching device, wherein the driving circuit selectively operates the low-voltage switching device to transfer energy from one of the N batteries to another;

The multi-winding transformer with M windings also includes an additional winding, through which the isolated measurement of the battery cell voltage is realized.

Preferably, a micro-control unit is also included, the voltage on the additional winding is output to the micro-control unit for sampling through a low-pass filter and a signal conditioning circuit, and the micro-controller is based on the sampling voltage and the battery pack The current calculates the remaining battery capacity; the micro-control unit sends a driving signal and controls the low-voltage switching device through the driving circuit to transfer energy from a battery with a high remaining capacity to a battery with a low remaining capacity.

Preferably, each low-voltage switching device corresponds to a coupling diode connected in parallel.

Preferably, the low-voltage switching device is a transistor.

Preferably, corresponding to each pair of low-voltage switching devices, the first low-voltage switching device is a P-channel MOSFET, and the second low-voltage switching device is an N-channel MOSFET.

Preferably, the drive circuit includes a drive chip, the drive chip is TC4428, the reverse output OUTA of the drive chip is electrically connected to the P-communication metal oxide semiconductor field effect transistor, and the positive output OUTB of the drive chip is The terminal is electrically connected to the N-communication metal-oxide-semiconductor field effect transistor.

Preferably, an isolation circuit is provided between the micro control unit and the driving circuit.

Preferably, the isolation circuit is an optocoupler isolation circuit; or a resistor, a diode and a capacitor of the isolation circuit.

Preferably, the micro control unit outputs the driving signal according to the driving signal generating circuit, the driving signal generating circuit includes two multiplexers, the micro control unit outputs the PWM signal and the address signal to the multiplexer, wherein One multiplexer outputs drive signals to odd-numbered low-voltage switching device drive circuits, and the other multiplexer outputs drive signals to even-numbered low-voltage switch device drive circuits.

A modular battery system, including P groups of battery management units, each group of battery management units is a battery management unit group composed of a multi-winding transformer with active balancing function, and each group of battery management units is equipped with a bidirectional DC /DC converter, the DC/DC converter is used for energy exchange between different groups of battery management units, the input end of the DC/DC converter is connected to the positive and negative poles of the corresponding group of battery management units, and the DC The output terminal of the /DC converter is connected to a common bus, and the micro control unit sends and receives the information of each battery management unit group through the common bus, and controls the DC/DC converter to transfer energy from the battery management unit with high remaining power The group transfers to the battery management unit group with a low remaining battery capacity.

The proposed system consists of a low-voltage switch (M1~M2n) and a multi-winding transformer T(T1~Tn,Tm). A low-voltage switch (M1~M2n) is used for each battery cell (B1~B2n), and a multi-winding transformer T (T1~Tn,Tm) is used for each battery pack. Two adjacent battery cells share one winding (T1~Tn), and the winding Tm is used to detect the battery voltage. The proposed circuit has two working phases, detection phase and equalization phase. In the detection phase, all switches are turned on in sequence, and the induced voltage on Tm is sampled to detect the battery cell voltage. Through the measurement of battery cell voltage, and statistics of other signals such as battery current and historical data, the micro control unit (MCU) can calculate the battery cells that need to be charged or discharged, select the path of energy transfer and start at a certain time balancing process. The detection and equalization phases are then repeated. Due to the limitation of the number of transformer T windings, it is difficult for a multi-winding transformer to meet the situation of a large number of batteries. A theory of modularity is therefore proposed, which can easily support any number of battery cells. The proposed system uses a multi-winding transformer to isolate the detection circuit from the battery cell, thus enabling the use of low-voltage power devices and reducing device cost. Compared with the prior art, when the number of battery cells is the same, the system uses less transformer windings and saves the driving transformer, so the circuit cost can be greatly reduced.

Description of drawings

Below in conjunction with accompanying drawing and specific embodiment the present invention will be described in further detail:

FIG. 1 is a schematic diagram of Embodiment 1 of the battery management system with active balancing function of the present invention.

FIG. 2 is a drive signal for detection operation of the system of FIG. 1. FIG.

FIG. 3 is a drive signal for the equalization operation of the system of FIG. 1. FIG.

FIG. 4 is a partial specific circuit diagram of Embodiment 2 of the battery management system with active balancing function of the present invention.

FIG. 5 is an alternative circuit to the drive circuit in FIG. 4 .

FIG. 6 is a partial specific circuit diagram of Embodiment 3 of the battery management system with active balancing function of the present invention.

Fig. 7 is a schematic diagram of an embodiment of a modular battery system of the present invention.

detailed description

Example 1:

A battery management system with an active equalization function in the present invention includes: N single cells connected in series, and these batteries are divided into M pairs of battery cells, where N is an even number greater than zero; a multi-cell battery with M windings Winding transformer, each of the M windings has one end connected to the midpoint of the battery cell pair, and the M windings are respectively connected to the midpoint of the M battery cell pairs; N low-voltage switching devices are related to the N battery cells The N low-voltage switch devices are also divided into M pairs, the midpoint of each switch pair is connected to the other end of the M transformer windings, and each switch is selectively operated; wherein, the drive circuit controls the low-voltage switch On and off of the device, wherein the drive circuit selectively operates the low-voltage switching device to transfer energy from one of the N batteries to the other; an additional winding is included on the multi-winding transformer with M windings, through This winding enables isolated measurement of battery cell voltage. It also includes a micro control unit, the voltage on the additional winding is output to the micro control unit for sampling through the low pass filter and the signal conditioning circuit, and the micro controller calculates based on the sampling voltage and the battery pack current The remaining power of the battery: the micro control unit sends a driving signal and controls the low-voltage switching device through the driving circuit to transfer energy from a battery with a high remaining power to a battery with a low remaining power.

The circuit structure is shown in Figure 1. In this embodiment, B1~B2n are battery cells connected in series, T1~Tn are the windings of a multi-winding transformer T, which are connected in parallel with the battery cells, and M1~M2n are with anti-parallel diodes. switch, Tm is another winding of the multi-winding transformer for voltage detection. The voltage across Tm is processed through a low-pass filter and signal conditioning circuit. The processed signal is sampled by an analog-to-digital converter controlled by a microcontroller unit (MCU). The MCU calculates the remaining battery capacity (SOC) based on the battery voltage and battery pack current. According to the calculation result, the MCU will send a driving signal to control the switch to transfer energy from the battery with high remaining power to the battery with low remaining power. Each low-voltage switching device corresponds to a coupling diode connected in parallel. The specific circuit principle is shown in the figure, and will not be repeated here.

Figure 2 shows the drive signals used for detection. All switches are turned on sequentially. When the switch is closed, the voltage on the corresponding battery is applied to one winding of the transformer T. This voltage will be coupled to the detection winding Tm. As long as the MCU controls the A/D converter to sample at the correct time, the voltage of all single cells in the battery pack can be measured.

Figure 3 shows the principle of energy transfer from one battery to another. For example, to transfer energy from B1 to B4, first close M1, and the energy will flow out from B1 and be stored in transformer T. After opening M1 and closing M4, the energy stored in the transformer T will flow into B4. Repeating this process for a definite amount of time will transfer more energy.

Example 2:

The difference between this embodiment and the foregoing embodiments lies in that the low-voltage switching device is a transistor. Corresponding to each pair of low-voltage switching devices, wherein the first low-voltage switching device is a P-channel MOSFET, and the second low-voltage switching device is an N-channel MOSFET. The drive circuit includes a drive chip, the drive chip is TC4428, the reverse output OUTA of the drive chip is electrically connected to the P-communication metal oxide semiconductor field effect transistor, and the positive output OUTB terminal of the drive chip is electrically connected to The N-communication MOSFET.

As shown in Fig. 4, this circuit does not include generating G1 to G2n. M1, M3...M2n-1 selects a P-channel metal oxide semiconductor field effect transistor P-MOS. M2, M4...M2n selects an N-channel metal oxide semiconductor field effect transistor N-MOS. In the design, the TC4428A driver chip is used, and the reverse output OUTA is connected to the P-MOS, and the positive phase output OUTB is connected to the N-MOS. In order to ensure the safety of the circuit, the control signal from the MCU is isolated through an optocoupler. When there is no control signal, OUTA is high and OUTB is low. This means that all MOSFETS are off. When there is input current on G1, G2, ... G2n, the corresponding MOSFETS will be turned on.

Of course, Fig. 5 is an alternative circuit of the driving circuit in Fig. 4, and the optocoupler is replaced by resistors, diodes and capacitors to reduce the cost. Although this design is not isolated, the capacitor can easily withstand a voltage of more than 1000V to ensure safety.

Example 3:

The difference between this embodiment and the above embodiment is that the micro-control unit outputs the drive signal according to the drive signal generation circuit, the drive signal generation circuit includes two multiplexers, and the micro-control unit outputs the PWM signal and the address Signals are sent to multiplexers, one of the multiplexers outputs drive signals to odd-numbered low-voltage switching device drive circuits, and the other multiplexer outputs drive signals to even-numbered low-voltage switch device drive circuits. As shown in FIG. 6 , this circuit is used to generate G1 to G2n in FIG. 1 . The MCU outputs PWM1 and PWM2, and also outputs an address indicating which switch should follow the PWM signal. PWM signals and address signals are sent to two multiplexers. One multiplexer (MUX1) is connected to the odd switch drive circuit and the other multiplexer (MUX2) is connected to the even switch drive circuit. PWM1 is connected to the enable pin of MUX2 and PWM2 is connected to the enable pin of MUX1. In this way, it is possible to prevent both switches from being turned on at the same time.

Examples of modular battery systems:

A modular battery system, including P groups of battery management units, each group of battery management units is a battery management unit group composed of a multi-winding transformer with active balancing function, and each group of battery management units is equipped with a bidirectional DC /DC converter, the DC/DC converter is used for energy exchange between different groups of battery management units, the input end of the DC/DC converter is connected to the positive and negative poles of the corresponding group of battery management units, and the DC The output terminal of the /DC converter is connected to a common bus, and the micro control unit sends and receives the information of each battery management unit group through the common bus, and controls the DC/DC converter to transfer energy from the battery management unit with high remaining power The group transfers to the battery management unit group with a low remaining battery capacity.

Figure 7 shows the schematic diagram of the modular approach. The battery cells are divided into groups, and the construction of each group is the same. A bidirectional DC/DC converter is added to each group. The DC/DC converter is used to exchange energy between groups. The input of the DC/DC converter is connected to the +/- poles of the battery pack, and the output is connected to a common bus through which all the battery packs can exchange energy. The MCU sends and receives battery information through the CAN bus, and controls the DC/DC converter to transfer energy from the battery pack with high remaining power to the battery pack with low remaining power.

The proposed system consists of a low-voltage switch (M1~M2n) and a multi-winding transformer T(T1~Tn,Tm). A low-voltage switch (M1~M2n) is used for each battery cell (B1~B2n), and a multi-winding transformer T (T1~Tn,Tm) is used for each battery pack. Two adjacent battery cells share one winding (T1~Tn), and the winding Tm is used to detect the battery voltage. The proposed circuit has two working phases, detection phase and equalization phase. In the detection phase, all switches are turned on in sequence, and the induced voltage on Tm is sampled to detect the battery cell voltage. Through the measurement of battery cell voltage, and statistics of other signals such as battery current and historical data, the micro control unit (MCU) can calculate the battery cells that need to be charged or discharged, select the path of energy transfer and start at a certain time balancing process. The detection and equalization phases are then repeated. Due to the limitation of the number of transformer T windings, it is difficult for a multi-winding transformer to meet the situation of a large number of batteries. A theory of modularity is therefore proposed, which can easily support any number of battery cells. The proposed system uses a multi-winding transformer to isolate the detection circuit from the battery cell, thus enabling the use of low-voltage power devices and reducing device cost. Compared with the prior art, when the number of battery cells is the same, the system uses less transformer windings and saves the driving transformer, so the circuit cost can be greatly reduced.

The foregoing description has been provided for purposes of illustration and description only, and it is not intended to be exhaustive or to limit the present disclosure. A single factor or a specific feature is generally not limiting to a specific embodiment, but is applicable where applicable, and can be used in a selected embodiment, even if not specifically stated. It can also be varied in many ways as well. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

Claims (10)

1. A battery management system with active balancing function, comprising: N cells connected in series, divide these batteries into M pairs of cell pairs, where N is an even number greater than zero; A multi-winding transformer with M windings, each of the M windings has one end connected to the midpoint of the battery cell pair, and the M windings are respectively connected to the midpoint of the M battery cell pairs; N low-voltage switching devices are associated with N battery cells. The N low-voltage switching devices are also divided into M pairs. The midpoint of each switch pair is connected to the other end of the M transformer windings. Each switch is selectively operation; It is characterized in that the driving circuit controls the on-off of the low-voltage switching device, wherein the driving circuit selectively operates the low-voltage switching device to transfer energy from one of the N batteries to another; The multi-winding transformer with M windings also includes an additional winding, through which the isolated measurement of the battery cell voltage is realized. 2. The battery management system with active equalization according to claim 1, further comprising a micro control unit, the voltage on the additional winding outputs a signal to the micro through a low-pass filter and a signal conditioning circuit Sampling is controlled by the control unit, and the micro-controller calculates the remaining battery power based on the sampling voltage and the battery pack current; the micro-control unit sends a driving signal and controls the low-voltage switching device through the driving circuit so that the energy is transferred from the battery with a high remaining power The battery shifts to a battery with a low remaining charge. 3. The battery management system with active equalization according to claim 2, wherein each low-voltage switching device is connected in parallel with a coupling diode. 4. The battery management system with active equalization according to claim 2, wherein the low-voltage switching device is a transistor. 5. The battery management system with active equalization according to claim 4, characterized in that, corresponding to each pair of low-voltage switching devices, wherein the first low-voltage switching device is a P-channel metal-oxide-semiconductor field-effect transistor, and the second The two low-voltage switching devices are N-channel MOSFETs. 6. The battery management system with active equalization according to claim 5, wherein the drive circuit includes a drive chip, the drive chip is TC4428, and the reverse output OUTA of the drive chip is electrically connected to the P A communication metal oxide semiconductor field effect transistor, the positive output OUTB terminal of the driving chip is electrically connected to the N communication metal oxide semiconductor field effect transistor. 7. The battery management system with active equalization according to claim 2, wherein an isolation circuit is provided between the micro control unit and the driving circuit. 8. The battery management system with active equalization according to claim 7, wherein the isolation circuit is an optocoupler isolation circuit; or the isolation circuit is a resistor, a diode and a capacitor. 9. The battery management system with active equalization according to claim 2, wherein the micro control unit outputs a driving signal according to a driving signal generating circuit, and the driving signal generating circuit includes two multiplexers, The micro control unit outputs PWM signals and address signals to multiplexers, one of the multiplexers outputs drive signals to odd-numbered low-voltage switching device drive circuits, and the other multiplexer outputs drive signals to even-numbered low-voltage switch devices Drive circuit. 10. A modular battery system, characterized in that it includes P groups of battery management units, each group of battery management units is a group of battery management units with an active balancing function composed of a multi-winding transformer, and each group of battery management units is equipped with A bidirectional DC/DC converter, the DC/DC converter is used for energy exchange between different groups of battery management units, and the input end of the DC/DC converter is connected to the positive and negative poles of the corresponding group of battery management units , the output end of the DC/DC converter is connected to a common bus, and the micro-control unit sends and receives the information of each battery management unit group through the common bus, and controls the DC/DC converter to convert the energy from the remaining power to the high The battery management unit group of the battery is transferred to the battery management unit group of the battery with low remaining power.