A transformer-based battery voltage equalization circuit and control method

Abstract

A transformer-based battery voltage equalization circuit comprises a first DC controller module and a second DC controller module, the DC ports of the two DC controller modules are connected with a first bus and a second bus respectively, two sub-lines of the first bus are connected with the positive and negative poles of the J1th battery in a battery string through switches, J1 is an odd number, two sub-lines of the second bus are connected with the positive and negative poles of the J2th battery in the battery string through switches, J2 is an even number, the AC ports of the two DC controllers are connected with the primary side and the secondary side of a transformer respectively, the battery voltage equalization circuit further comprises a switch control module connected with each switch control, the DC controller module has full-bridge rectification function and can realize bidirectional charging and discharging between the DC port and the AC port. The application can select specific batteries to charge specific batteries through a switch network, cooperate with a voltage detection circuit, reduce the charging and discharging times of the batteries while realizing voltage equalization, and prolong the service life of the batteries.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of integrated circuits, and relates to a battery voltage equalization technology, in particular to a transformer-based battery voltage equalization circuit and a control method. BACKGROUND

[0002] In the application of battery series, the voltage uniformity of each battery in the battery series has a high requirement. The non-uniformity of the battery voltage in the battery series causes the battery to be frequently reversed charged, which causes the battery life to be rapidly shortened, and even causes the battery to explode in an extreme case. The biggest disadvantage of the current scheme of realizing that any battery string in a plurality of lithium battery groups charges the entire battery group by using a transformer is that the charging and discharging between any two battery strings cannot be realized. Once the voltage of the lithium battery group is equalized, the battery string with a high voltage will be charged and discharged for many times, which reduces the service life of the battery.

[0003] This mode has the following disadvantages: for example, the voltage of the No. 1 battery is the highest, and after the battery string is discharged, the voltage is reduced. Among the batteries being charged, the voltage of the No. 2 battery becomes the new highest voltage battery, and the No. 2 battery charges other batteries including the No. 1 battery, which actually causes the No. 1 battery to be repeatedly charged and discharged, and seriously affects the service life of the battery. SUMMARY

[0004] In view of the defects in the prior art, the application discloses a transformer-based battery voltage equalization circuit.

[0005] The transformer-based battery voltage equalization circuit disclosed by the application comprises a first direct current controller module and a second direct current controller module, the direct current ports of the two direct current controller modules are connected with a first bus and a second bus respectively, two sub-lines of the first bus are connected with the positive and negative poles of the first, third, J1th batteries in the battery string through battery switches respectively, J1 is an odd number, two sub-lines of the second bus are connected with the positive and negative poles of the second, fourth, J2th batteries in the battery string through battery switches respectively, J2 is an even number, the alternating current ports of the two direct current controllers are connected with the primary side and the secondary side of the transformer respectively, the battery voltage equalization circuit further comprises a switch control module connected with each battery switch control, the direct current controller module has a full-bridge rectification function and can realize bidirectional charging and discharging between the direct current port and the alternating current port.

[0006] Preferably, the battery voltage equalization circuit further comprises a battery voltage detection circuit, which is used for detecting the voltage of each battery in the battery string.

[0007] Preferably, the direct current controller module comprises a first control switch and a second control switch connected with the first direct current port, a third control switch and a fourth control switch connected with the second direct current port, the first control switch and the fourth control switch are connected with the first alternating current port at the other end not connected with the direct current port, the second control switch and the third control switch are connected with the second alternating current port through the current detection circuit and the fifth control switch at the other end not connected with the direct current port.

[0008] The current detection circuit comprises a detection resistor connected with the fifth control switch in series, and further comprises a comparator with two input ends connected with two ends of the detection resistor, and an output end of the comparator connected with the direct current control circuit.

[0009] Preferably, the direct current control circuit is connected with the switch control module.

[0010] Preferably, the switch is a transmission gate, a triode or a MOS tube.

[0011] The application further discloses a transformer-based battery voltage equalization control method based on the battery voltage equalization circuit, comprising the following steps:

[0012] Step 1. selecting a battery to be charged and a discharge battery for discharging the battery to be charged;

[0013] Step 2. adjusting the battery switch so that the battery to be charged and the discharge battery are connected with the first bus or the second bus respectively;

[0014] Step 3. adjusting the direct current controller module to adjust the voltage signal input from the bus by using the full-bridge rectification function so that the voltage polarity connected with the transformer is fixed;

[0015] Step 4. the discharge battery starts to charge the primary coil of the transformer until the charging current reaches a first set threshold;

[0016] Step 5. disconnecting the transformer from the discharge battery, connecting the battery to be charged to the secondary coil of the transformer, charging the battery to be charged by using the direct current controller module until the current on the secondary coil of the transformer is less than a second set threshold, and disconnecting the transformer from the battery to be charged;

[0017] Step 6. repeating steps 4 to 5 until the battery to be charged and the discharge battery need to be replaced;

[0018] Step 7. selecting a battery to be charged and a discharge battery for discharging the battery to be charged again, and repeating steps 1 to 6 again.

[0019] The transformer-based battery voltage equalization circuit and control method can select a specific battery to charge a specific battery through a switch network, and can easily realize an optimal charging scheme such as charging the lowest voltage battery by the highest voltage battery, while reducing the number of battery charging and discharging times and prolonging the battery life. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A specific embodiment structure schematic diagram of the transformer-based battery voltage equalization circuit is provided.

[0021] Figure 2 A specific embodiment schematic diagram of the DC controller module is provided.

[0022] Figure 3 A typical current timing schematic diagram of the DC controller module in operation is provided.

[0023] Figure 4 A simulation waveform schematic diagram of the DC controller module in operation is provided.

[0024] The figure legend names are: U1-first DC controller module, U2-second DC controller module, S1-first battery switch, S2-second battery switch, S3-third battery switch, S4-fourth battery switch, S5-fifth battery switch, S6-sixth battery switch, S7-seventh battery switch, S8-eighth battery switch, B1-first battery, B2-second battery, B3-third battery, B4-fourth battery, T-transformer, SD1-first control switch, SD2-second control switch, SD3-third control switch, SD4-fourth control switch, SD5-fifth control switch, R-detection resistor, COMP-comparator, CTRL-DC control circuit, P1-first DC port, P2-second DC port, P3-first AC port, P4-second AC port. DETAILED DESCRIPTION

[0025] To more clearly describe the technical solutions of the present application, the following will be described in detail in combination with specific examples and example drawings.

[0026] To make the purpose, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described in combination with the specific embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0027] The transformer-based battery voltage equalization circuit according to the present application, as shown in Figure 1 A specific embodiment is shown in Figure 1 The two sub-lines of the first bus are connected to the positive and negative poles of the 1st, 3rd,..., and J1th batteries in the battery string through switches, J1 is an odd number, and the two sub-lines of the second bus are connected to the positive and negative poles of the 2nd, 4th,..., and J2th batteries in the battery string through switches, J2 is an even number. The AC ports of the two DC controllers are connected to the primary side and secondary side of the transformer, respectively. The battery voltage equalization circuit further comprises a switch control module connected to each switch control. The DC controller module has full-bridge rectification function and can realize bidirectional charging and discharging between the DC port and the AC port.

[0028] In specific use, a specific application mode of four battery strings in series is shown in Figure 1 When the fourth battery voltage is found to be the highest and the first battery voltage is the lowest, the fourth battery B4 is needed to charge the first battery B1. Then, the first battery switch S1, the second battery switch S2, the seventh battery switch S7, and the eighth battery switch S8 are closed, and the remaining switches are opened. The fourth battery B4 is connected to the second bus, and the first battery B1 is connected to the first bus. The voltage difference of the fourth battery is high, and the second DC controller module U2 is input through the second bus. The second DC controller module converts the DC voltage input from the DC port into an AC signal and outputs from the AC port to the primary side of the transformer. The secondary side of the transformer receives energy and inputs to the first DC controller module U1. The first DC controller module converts the AC signal received from the AC port into a DC signal through full-bridge rectification and outputs from the DC port to the first battery for charging. After conversion by the transformer, the absolute values of the DC voltages of the two batteries are no longer considered, and only the voltage difference between the positive and negative poles of the two batteries is considered to achieve reasonable charging and discharging direction.

[0029] For example, when the second battery is needed to charge the third battery, the third battery switch S3, the fourth battery switch S4, the fifth battery switch S5, and the sixth battery switch S6 are closed, and the remaining switches are opened. The second battery B2 is connected to the second bus, and the third battery B1 is connected to the first bus, realizing the charging of the third battery by the second battery. For those skilled in the art, through the above description, two batteries can be arbitrarily selected as the charging battery and the discharging battery, and the charging process between the two batteries can be completed by controlling the switch state.

[0030] In the application, two switches are connected between the nodes of adjacent batteries, and the DC controller module can realize bidirectional charge and discharge between the DC port and the AC port, when the second battery needs to charge the third battery, the second battery switch S2, the fourth battery switch S4, the fifth battery switch S5 and the seventh battery switch S7 can be closed, and the remaining switches are opened, at this time, the second battery is connected with the first bus through the second battery switch and the fifth battery switch, and the third battery is connected with the second bus through the fourth battery switch and the seventh battery switch, and the DC controller module in the application can realize bidirectional charge and discharge between the DC port and the AC port, and can also realize the charging of the second battery to the third battery.

[0031] Figure 1 The specific embodiments of the application give a typical embodiment of four batteries, and those skilled in the art can easily obtain more specific circuit forms and charging and discharging methods when more batteries are connected in series through the above specific embodiments, and the specific embodiments of more batteries are not described here.

[0032] In use, the application is usually also connected with a battery voltage detection circuit for detecting the voltage of each battery in the battery string, and the typical way of the battery voltage detection circuit is that two input ends are connected with the voltage amplifier of the positive and negative electrodes of each battery, and the voltage of the battery is obtained by detecting the voltage difference between the positive and negative electrodes, and the battery voltage detection circuit can also be a multi-input analog-to-digital converter, and the positive electrodes of each battery in the battery string are connected with the multiple input ends, since the batteries are connected in series, the positive electrode of a certain battery is the negative electrode of the adjacent battery, and the voltage difference of each battery can be obtained by detection and calculation, and the application does not involve the improvement of the battery voltage detection circuit. Through the battery voltage detection circuit, the battery with the highest voltage and the battery with the lowest voltage can be found, so that the decision of which battery to charge which battery can be made.

[0033] In use, the application can adopt the following method for voltage balancing of the battery string, comprising the following steps:

[0034] Step 1. Selecting a battery to be charged and a discharge battery for discharging the battery to be charged;

[0035] Usually, the battery to be charged is the battery with the lowest voltage in the battery string, and the discharge battery is the battery with the highest voltage in the battery string.

[0036] Step 2. Adjusting the battery switch to connect the battery to be charged and the discharge battery to the first bus or the second bus respectively;

[0037] Step 3. Adjusting the DC controller module to adjust the voltage signal input from the bus by using the full-bridge rectification function, so that the voltage polarity connected to the transformer is fixed; the polarity fixing makes the transformer can normally obtain energy from the discharge battery and provide energy to the battery to be charged.

[0038] Step 4. The discharge battery starts to charge the primary coil of the transformer until the charging current reaches a first set threshold;

[0039] Step 5. Disconnect the transformer from the discharge battery, connect the battery to be charged to the secondary coil of the transformer, and use the DC controller module to charge the battery to be charged until the current on the secondary coil of the transformer is less than a second set threshold, and disconnect the transformer from the battery to be charged;

[0040] Step 6. Re-select the battery to be charged and the discharge battery that discharges the battery to be charged, and repeat steps 1 to 5.

[0041] The DC controller module is used to store energy in the transformer using DC voltage, and then output energy externally after storage. The DC controller module can be built using existing AC / DC converters and DC / DC converter chipsets to realize bidirectional AC / DC conversion. For cost and power consumption reduction, as shown in Figure 2 a specific embodiment of the DC controller module in the present application is given.

[0042] As shown in Figure 2 the DC controller module includes a first control switch SD1 and a second control switch SD2 connected to a first DC port P1, a third control switch SD3 and a fourth control switch SD4 connected to a second DC port P2, the other end of the first control switch and the fourth control switch not connected to the DC port is connected to a first AC port, the other end of the second control switch and the third control switch not connected to the DC port is connected to a second AC port through a current detection circuit and a fifth control switch SD5, the current detection circuit includes a detection resistor connected in series with the fifth control switch, and further includes a comparator COMP with two input ends connected to both ends of the detection resistor, the output end of the comparator is connected to a DC control circuit CTRL, and the DC control circuit is connected to each switch control in the DC controller module.

[0043] By detecting the battery voltage, it can be determined which battery needs to be charged by which battery. By the action of the external battery switches, it can be determined whether the voltage input to the two DC ports of the DC controller module is positive or negative, and which bus is input energy and which bus is responsible for accepting energy.

[0044] For example, the first battery switch selection state described earlier, in which the second battery B2 is used to charge the third battery B3, the third battery switch S3, the fourth battery switch S4, the fifth battery switch S5 and the sixth battery switch S6 are closed, and the remaining switches are open. At this time, for the two DC controller modules, the voltage of the first DC port P1 is higher than that of the second DC port P2, and the energy flows from the second bus to the first bus.

[0045] In the second switch selection state, the second battery switch S2, the fourth battery switch S4, the fifth battery switch S5 and the seventh battery switch S7 are closed, and the rest of the switches are open. At this time, for both DC controller modules, the first DC port P1 voltage is lower than the second DC port P2, and energy flows from the first bus to the second bus.

[0046] The working principle of the DC controller module is described below by taking the second switch selection state as an example, in which energy needs to be transmitted from the first bus to the second bus, i.e., the second battery B2 charges the third battery B3. It is defined that Figure 2 The lower half of the transformer connected with the first DC controller module U1 is the primary coil, and the upper half of the transformer connected with the second DC controller module U2 is the secondary coil.

[0047] First, the state of each battery switch is determined. If the first DC port P1 voltage is higher than the second DC port P2, the first control switch SD1 and the third control switch SD3 are closed, and the second control switch SD2 and the fourth control switch SD4 are open. Otherwise, the second control switch SD2 and the fourth control switch SD4 are closed, and the first control switch SD1 and the third control switch SD3 are open. This makes the voltage at point A1 connected with the first AC port higher than the voltage at point A2 connected with the detection resistor R. At the same time, the fifth control switch SD5 of the first DC controller module U1 connected with the first bus is closed, so that the first DC controller module is connected with the transformer primary coil. The battery connected with the first bus, i.e., the second battery, starts to charge, and the current rises.

[0048] The detection resistor R can be an external physical resistor or the parasitic resistance of a switching device such as a MOS tube. In this case, no physical resistor is needed, and the connection point of the switching tube can be directly detected.

[0049] At the same time when the fifth control switch SD5 of the first DC controller module U1 is closed, the fifth control switch SD5 of the second DC controller module U2 remains open.

[0050] The primary coil current of the transformer is detected by the comparator COMP of the first DC controller module U1. When the current rises to a first set threshold, the fifth control switch SD5 of the first DC controller module U1 is opened, and the fifth control switch SD5 of the second DC controller module U2 is closed. Energy is transmitted from the transformer primary coil to the secondary coil.

[0051] The fifth control switch SD5 of the first DC controller module U1 is disconnected, the current on the primary coil is maximum, the magnetic field is strongest, the current on the secondary coil jumps from zero to maximum, and then gradually decreases. During the gradually decreasing process, the second DC controller module U2 charges the third battery, the second control switch SD2 and the fourth control switch SD4 of the second DC controller module U2 are closed, and the first control switch SD1 and the third control switch SD3 are disconnected. A negative voltage difference is formed between the two DC ports of the second DC controller module U2, and the third battery connected to the second bus is charged.

[0052] With the charging process, the current on the secondary coil of the transformer gradually decreases. When the current on the secondary coil decreases to the second set threshold, the fifth control switch SD5 of the second DC controller module U2 is disconnected, and the current charging process ends. The next cycle can be entered. When the fifth switch is NMOS, a simulation waveform is as shown in Figure 4 .

[0053] The first set threshold is greater than the second set threshold. The first set threshold and the second set threshold are generally set according to the equalization current and the transformer power.

[0054] The switching state of the fifth control switch SD5 of the two DC controller modules in the current cycle and a typical time sequence waveform of the primary and secondary coil currents are as shown in Figure 3 . In the figure, the horizontal coordinate is time, the vertical coordinate represents the switching state and the current value, and the vertical dotted line represents the time starting end point of the adjacent charge and discharge cycle.

[0055] At this time, the fifth control switch SD5 of the two DC controller modules is disconnected, and the transformer is not connected with the two DC controller modules. The DC control circuit of the two DC controller modules can also be connected with the switch control module, so that the switch control module judges the current charging state.

[0056] In the next cycle, the battery voltage detection circuit of the battery string detects the voltage of each battery again, selects a suitable battery, and connects the battery to the two DC controller modules through the selection and switching of the battery switch. The similar charge and discharge operation is performed again.

[0057] In actual operation, the battery voltage is not detected every cycle. In application, the battery voltage is detected again after continuous work of 1 second / 5 seconds / 10 seconds / 20 seconds.

[0058] When energy needs to be transmitted from the second bus to the first bus, i.e. the second battery B2 charges the third battery B3, the process of transferring energy is similar to the above-mentioned mode. When the voltage of the first DC port P1 is higher than that of the second DC port P2, the first control switch SD1 and the third control switch SD3 are selected to be closed, and the second control switch SD2 and the fourth control switch SD4 are selected to be opened, so that the voltage of the A1 point connected to the first AC port is higher than the voltage of the A2 point connected to the detection resistor R, i.e. the above-mentioned detection mode can be realized.

[0059] The foregoing is merely the various preferred embodiments of the present application, and the preferred embodiments in the various preferred embodiments can be arbitrarily combined and used if not obviously contradictory or with a certain preferred embodiment as a prerequisite. The embodiments and specific parameters in the embodiments are merely for clearly describing the inventor's verification process, and are not intended to limit the patent protection scope of the present application. The patent protection scope of the present application is still subject to its claims, and any equivalent structural changes made by using the content of the present application should also be included in the protection scope of the present application.

Claims

1. A transformer-based battery voltage equalization circuit, comprising: The battery voltage equalization circuit comprises a first DC controller module and a second DC controller module, DC ports of the two DC controller modules are connected with a first bus and a second bus respectively, two sub-lines of the first bus are connected with positive and negative poles of the 1st, 3rd,..., J1th batteries in a battery string through battery switches, J1 is an odd number, two sub-lines of the second bus are connected with positive and negative poles of the 2nd, 4th,..., J2th batteries in the battery string through battery switches, J2 is an even number, AC ports of the two DC controllers are connected with a primary side and a secondary side of a transformer respectively, the battery voltage equalization circuit further comprises a switch control module connected with each battery switch, the DC controller module has full-bridge rectification function and can realize bidirectional charge and discharge between the DC port and the AC port; The DC controller module comprises a first control switch (SD1) and a second control switch (SD2) connected with a first DC port (P1), a third control switch (SD3) and a fourth control switch (SD4) connected with a second DC port (P2), the other end of the first control switch (SD1) and the fourth control switch (SD4) not connected with the DC port is connected with a first AC port (P3), the other end of the second control switch (SD2) and the third control switch (SD3) not connected with the DC port is connected with a second AC port (P4) through a current detection circuit and a fifth control switch (SD5); The current detection circuit comprises a detection resistor (R) connected with the fifth control switch (SD5) in series, and further comprises a comparator (COMP) with two input ends connected with both ends of the detection resistor, and an output end of the comparator (COMP) connected with a DC control circuit (CTRL).

2. The transformer-based battery voltage balancing circuit of claim 1, wherein, The battery voltage detection circuit is further comprised for detecting the voltage of each battery in the battery string.

3. The transformer-based battery voltage balancing circuit of claim 1, wherein, The DC control circuit is connected with the switch control module.

4. The transformer-based battery voltage balancing circuit of claim 1, wherein, The switch is a transmission gate, a transistor or a MOS tube.

5. A transformer-based battery voltage equalization control method, characterized by, Based on the battery voltage equalization circuit according to any one of claims 1 to 4, comprising the following steps: Step 1. selecting a battery to be charged and a discharge battery for discharging the battery to be charged; Step 2. adjusting the battery switch so that the battery to be charged and the discharge battery are connected with the first bus or the second bus respectively; Step 3. adjusting the DC controller module to adjust the voltage signal input from the bus by using the full-bridge rectification function so that the voltage polarity connected to the transformer is fixed; Step 4. the discharge battery starts to charge the primary coil of the transformer until the charging current reaches a first set threshold; Step 5. disconnecting the transformer from the discharge battery, connecting the battery to be charged to the secondary coil of the transformer, and charging the battery to be charged by using the DC controller module until the current on the secondary coil of the transformer is less than a second set threshold, and disconnecting the transformer from the battery to be charged; Step 6. repeating steps 4 to 5 until the battery to be charged and the discharge battery need to be replaced; Step 7. reselecting a battery to be charged and a discharge battery for discharging the battery to be charged, and repeating steps 1 to 6 again.

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