Active battery balancing circuit and control method using flyback transformer correlation

Abstract

The present invention discloses an active battery balancing circuit that utilizes the correlation of the voltage of each winding of a flyback transformer being clamped by a battery, including a control unit, a drive unit, and a charging battery pack; before the battery is balanced and charged, the total voltage is tested to calculate the average voltage of all battery packs; the voltage of each battery pack in the test circuit is tested, the voltage difference between the voltage of all battery packs and the average voltage is calculated, and the battery to be charged is selected according to the relationship between the voltage difference and a preset threshold. The circuit and method enable the battery to be balanced with a large current at any time, so that all single cells in the battery pack can be charged to their highest voltage at the same time, and discharged to their lowest voltage at the same time, fully improving the capacity and utilization of the battery pack, and maintaining the simplicity and high efficiency of the system. The simplicity of the single-ended flyback transformer and the correlation of the voltage of the same transformer winding are utilized to reduce the number of transformers and the sampling points. The balancing is fast.

Description

Technical Field

[0001] The present invention belongs to the field of battery charging circuits, and in particular relates to an active battery balancing circuit utilizing the correlation of a flyback transformer and a control method thereof. Background Art

[0002] At present, in the application of battery-powered equipment, actual work requires multiple batteries to be connected in series, and the capacities of these batteries will always be different. If a single cell is not protected during charging or use, it will cause overcharge or over-discharge of the battery, which will affect the battery life. However, protection will prevent the battery pack capacity from being fully utilized.

[0003] Current battery balancing technologies are classified into active and passive types. Passive energy balancing is generally used, which discharges the overcharged battery after the battery is fully charged. This is inefficient. Active balancing circuits are highly efficient, but the system is complex and balancing can rarely be performed at any time. It is also rare to balance multiple batteries simultaneously. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an active battery balancing circuit and a control method thereof which utilize the correlation of battery voltage clamping of each winding of a flyback transformer, thereby solving the problem of battery power imbalance during the charging and discharging process of a battery pack in the prior art.

[0005] The present invention adopts the following technical solutions to solve the above technical problems:

[0006] An active battery balancing circuit using the correlation of flyback transformers includes a control unit, a drive unit, and a rechargeable battery pack; the control unit includes a drive circuit, a voltage sampling circuit, a current sampling circuit, and a power supply circuit; the drive unit includes more than two groups of branches consisting of drive transistors and flyback transformers, and the output of each branch is connected to a battery pack after flyback rectification to charge the battery pack; the output winding of each flyback transformer includes two output ends, each output end is connected to a battery; one end of the input winding of each flyback transformer is connected to a total power supply, and the other end is connected to the output end of each drive transistor; the input end of the drive transistor is connected to the drive circuit, and the common end of the drive transistor is grounded; the voltage sampling circuit is connected to the positive electrode of each battery pack; the current sampling circuit is connected to the common end of each drive transistor.

[0007] The output winding of each flyback transformer includes two output ends, which are respectively connected to the positive and negative electrodes of two batteries connected in series through diodes; the midpoint of the output winding of the flyback transformer is connected to the midpoint of the two batteries connected in series.

[0008] The power input terminal of the power circuit is connected to the positive electrode of at least one battery.

[0009] The control method of the active battery balancing circuit using the correlation of the flyback transformer comprises the following steps:

[0010] Step 1: Test the total voltage before battery equalization charging and calculate the average voltage of all battery groups;

[0011] Step 2: Test the voltage of each battery pack in the circuit and calculate the voltage difference between the voltage of all battery packs and the average voltage.

[0012] Step 3, determining the relationship between the voltage difference and a preset threshold value, when any set of voltage differences is lower than the preset threshold value, executing step 4, otherwise, executing step 5;

[0013] Step 4, turn on the flyback transformer corresponding to the battery group to charge the battery group. After charging for a preset time, stop charging and return to step 2 and step 3 until the voltages of all battery groups are consistent.

[0014] Step 5: Stop charging all battery packs, wait for a while, and return to step 2.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. Enable the battery to balance a large current at any time, so that all single cells in the battery pack can be charged to their highest voltage and discharged to their lowest voltage at the same time, fully improving the capacity and utilization of the battery pack, and keeping the system simple and efficient.

[0017] 2. Utilize the simplicity of the single-ended flyback transformer and the correlation of the voltages of the same transformer windings to reduce the number of transformers and sampling points.

[0018] 3. Draw current from the overall voltage to supplement weaker batteries and balance quickly.

[0019] 4. The power input terminal of the power circuit is connected to the positive pole of a battery with appropriate voltage, simplifying the system power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 FIG. 4 is a schematic diagram of a battery balancing circuit of the present invention. DETAILED DESCRIPTION

[0021] The structure and working process of the present invention will be further described below in conjunction with the accompanying drawings.

[0022] The present invention proposes a technology for balancing a battery pack by using multiple low-power flyback switching power supplies. It utilizes the correlation of voltages of different windings of the same transformer, greatly simplifies the balancing circuit, and can also perform battery balancing at any time during charging and discharging. This circuit is relatively simple and can perform balancing activities on multiple batteries at any time.

[0023] This active battery balancing circuit using the correlation of flyback transformers includes a control unit, a drive unit, and a rechargeable battery pack; the control unit includes a drive circuit, a voltage sampling circuit, a current sampling circuit, and a power supply circuit; the drive unit includes more than two groups of branches consisting of drive transistors and flyback transformers, and the output of each branch is connected to the battery pack after flyback rectification to charge the battery pack; the output winding of each flyback transformer includes two output ends, each output end is connected to a battery; one end of the input winding of the flyback transformer is connected to the power supply, and the other end is connected to the output end of the drive transistor; the input end of the drive transistor is connected to the drive circuit, and the common end of the drive transistor is grounded; the voltage sampling circuit is connected to the positive pole of each battery pack; the current sampling circuit is connected to the common end of each drive transistor.

[0024] The output winding of each flyback transformer includes two output ends, which are respectively connected to the positive and negative electrodes of two batteries connected in series through diodes; the midpoint of the output winding of the flyback transformer is connected to the midpoint of the two batteries connected in series.

[0025] The power input terminal of the power circuit is connected to the positive electrode of at least one battery.

[0026] The control method of the active battery balancing circuit using the correlation of the flyback transformer comprises the following steps:

[0027] Step 1: Test the total voltage before battery equalization charging and calculate the average voltage of all battery groups;

[0028] Step 2: Test the voltage of each battery pack in the circuit and calculate the voltage difference between the voltage of all battery packs and the average voltage.

[0029] Step 3, determining the relationship between the voltage difference and a preset threshold value, when any set of voltage differences is lower than the preset threshold value, executing step 4, otherwise, executing step 5;

[0030] Step 4, turn on the flyback transformer corresponding to the battery group to charge the battery group. After charging for a preset time, stop charging and return to step 2 and step 3 until the voltages of all battery groups are consistent.

[0031] Step 5: Stop charging all battery packs, wait for a while, and return to step 2.

[0032] Specific embodiments, such as Figure 1 As shown:

[0033] An active battery balancing circuit using the correlation of a flyback transformer comprises a control unit, a drive unit and a charging battery pack; the specific circuit structure is as follows: the control unit comprises a control single chip microcomputer and a drive circuit, a voltage sampling circuit, a current sampling circuit and a power supply circuit connected thereto; the drive unit comprises four flyback circuit branches composed of drive MOS tubes MA, MB, MC and MD and flyback transformers TA, TB, TC and TD; the transformer outputs two sets of voltages which are flyback rectified to charge battery packs A, B, C and D; the battery pack A comprises batteries A1 and A2 connected in series; similarly, the battery packs B, C and D are respectively composed of batteries B1, B2, C1, C2, D1 and D2; the current sampling circuit comprises sampling resistors RA, RB, RC and RD. The following takes the flyback circuit branch corresponding to battery pack A as an example to introduce the circuit topology in detail. The output winding of the flyback transformer TA includes two output terminals, which are respectively connected to batteries A1 and A2; one end of the input winding of the flyback transformer TA is connected to the power supply, and the other end is connected to the drain of the driving MOS tube; the gate of the driving MOS tube is connected to the driving circuit, and the source of the driving MOS tube is grounded after passing through the sampling resistor RA; the voltage sampling circuit is connected to the positive electrode of the battery A2.

[0034] The output winding of the flyback transformer TA includes two output terminals, the first output terminal is connected to the positive pole of the battery A2 through the diode DA2, and the second output terminal is connected to the negative pole of the battery A1 through the reverse diode DA1; the midpoint of the output winding of the flyback transformer TA is connected to the midpoint of the series-connected batteries A1 and A2. This circuit is used to reduce the battery voltage sampling by half.

[0035] The control system is powered by partially balanced batteries of appropriate voltage.

[0036] The power input terminal of the power supply circuit is connected to the positive electrode of a battery with a suitable voltage. In this embodiment, it is connected to the positive electrode of battery B2. If the voltage is suitable, it can also be connected to the positive electrode of battery A2, or the positive electrode of other batteries with suitable voltages.

[0037] The working process of the equalization circuit is as follows:

[0038] When the system control microcontroller detects that the voltage of battery pack A is lower than the average value, it will send pulses to the MOS tube MA through the drive circuit to control the two symmetrical windings of the transformer TA to charge the batteries A1 and A2. Since the two windings of the transformer are symmetrical, when the voltages of batteries A1 and A2 are asymmetrical, the transformer will give priority to charging the battery with lower voltage. In this way, after a period of time, the voltages of the two batteries will automatically approach each other. When the voltages of the two batteries are close, the current will be automatically distributed according to the internal resistance of the batteries. When the voltages of the two batteries reach the set voltage, the control circuit will turn off the pulses of the power tube MA through the drive circuit and control TA to turn off the charging circuit.

[0039] The control method of the equalization circuit comprises the following steps:

[0040] Step 1: Test the total voltage before battery equalization charging and calculate the average voltage of all battery groups;

[0041] Step 2: Test the voltage of each battery pack in the circuit and calculate the voltage difference between the voltage of all battery packs and the average voltage.

[0042] Step 3, determining the relationship between the voltage difference and a preset threshold value, when any set of voltage differences is lower than the preset threshold value, executing step 4, otherwise, executing step 5;

[0043] Step 4, turn on the flyback transformer corresponding to the battery group to charge the battery group. After charging for a preset time, stop charging and return to step 2 and step 3 until the voltages of all battery groups are consistent.

[0044] Step 5: Stop charging all battery packs, wait for a short while, and return to step 2.

[0045] In step 3 of this embodiment, the preset threshold is 1% of the average voltage, and in step 4, the preset charging time is one minute.

[0046] The short period of time in step 5 can be set as required. Those skilled in the art can understand the specific meaning of a short period of time, and no specific time is required and can be set as required.

[0047] For example: In the figure, when the voltage of batteries in groups A and C is lower than the average value, the charging circuits of A and C are turned on to charge A and C. After charging, the voltages of A and C increase, while the voltages of B and D decrease. If A reaches the average voltage, only C will be charged in the next cycle, and this cycle will repeat until all voltages are within the error range.

[0048] The equalization circuit has a charging protection function, as follows:

[0049] This charging process can be performed at any time during charging and discharging to ensure that the battery can be fully utilized. However, when the voltage of a battery is too low, the transformer charging it will not be able to reset, causing a surge in the transformer input current. At this time, the pulse width should be reduced. If the voltage still cannot be increased after a period of charging, the battery is damaged and the system will prompt to repair or replace the battery.

[0050] All power circuits of the balancing circuit are provided by the battery of the system: The control power supply of this system is powered by a battery, which is connected to the connection of four batteries, about 12 volts, which will cause battery imbalance under normal circumstances, but because the balancing of this system occurs all the time, the balancing circuit will automatically increase the current to supply power without affecting the balanced use of the battery, and can also simplify the control power supply.

[0051] The working principle and working process of the sampling circuit of the equalization circuit are as follows:

[0052] The sampling circuit of the balancing circuit is divided into voltage sampling and current sampling. The voltage sampling corresponds to the current sampling one by one, and measures the battery voltage and charging current of every two groups. The voltage sampling is formed by resistor voltage division. When the battery voltage is the same, the voltage divided to the AD sampling chip is the same. The current sampling is amplified by the amplifier and then sent to the AD sampling chip.

[0053] Take the average value from the highest voltage sample to automatically balance the battery voltage under the same transformer.

[0054] The control method of sampling pulse sampling improves the sampling accuracy of voltage, that is, setting a short charging cycle, not sampling during charging, and not charging during sampling, to avoid the influence of charging on sampling.

[0055] The preferred embodiments of the present invention are described above. It should be understood that the present invention is not limited to the above-mentioned specific embodiments, and the circuits, devices and structures not described in detail should be understood to be implemented in a common manner in the art; any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the above-disclosed methods and technical contents without departing from the scope of the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes, which does not affect the essential content of the present invention. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of protection of the technical solution of the present invention.

Claims

1. A control method for an active battery balancing circuit using the association of a flyback transformer, wherein the active battery balancing circuit comprises a control unit, a driving unit, and a rechargeable battery pack; the control unit comprises a driving circuit, a voltage sampling circuit, a current sampling circuit, and a power supply circuit; the driving unit comprises two or more branches consisting of driving transistors and flyback transformers, and the output of each branch is connected to a battery pack after flyback rectification to charge the battery pack; the output winding of each flyback transformer comprises two output terminals, each of which is connected to a battery; one end of the input winding of each flyback transformer is connected to a total power supply, and the other end is connected to the output terminal of each driving transistor; the input terminal of the driving transistor is connected to the driving circuit, and the common terminal of the driving transistor is grounded; the voltage sampling circuit is connected to the positive electrode of each battery pack; the current sampling circuit is connected to the common terminal of each driving transistor; the characteristics are: The steps include: Step 1: Test the total voltage before battery equalization charging and calculate the average voltage of all battery groups; Step 2: Test the voltage of each battery pack in the circuit and calculate the voltage difference between the voltage of all battery packs and the average voltage. Step 3, determining the relationship between the voltage difference and a preset threshold value, when any set of voltage differences is lower than the preset threshold value, executing step 4, otherwise, executing step 5; Step 4, turn on the flyback transformer corresponding to the battery group to charge the battery group. After charging for a preset time, stop charging and return to step 2 and step 3 until the voltages of all battery groups are consistent. Step 5: Stop charging all battery packs, wait for a while, and return to step 2.

2. The control method of the active battery balancing circuit using the flyback transformer correlation according to claim 1, characterized in that: The output winding of each flyback transformer includes two output ends, which are respectively connected to the positive and negative electrodes of two batteries connected in series through diodes; the midpoint of the output winding of the flyback transformer is connected to the midpoint of the two batteries connected in series.

3. The control method of the active battery balancing circuit using the flyback transformer correlation according to claim 1, characterized in that: The power input terminal of the power circuit is connected to the positive electrode of at least one battery.

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