Lead-acid battery charging circuit and charging method

Abstract

The present invention discloses a lead-acid battery charging circuit and charging method. The charging circuit includes a battery voltage sampling circuit, a battery charging output circuit, an AC / DC conversion circuit and a control circuit. The input end of the AC / DC conversion circuit is connected to an AC power source, and the output end is connected to the battery charging output circuit. The output end of the battery charging output circuit and the sampling end of the battery voltage sampling circuit are respectively connected to the charging interface of the lead-acid battery. The control circuit includes a microcontroller. The output end of the battery voltage sampling circuit is connected to the battery voltage sampling signal input end of the microcontroller. The control end of the AC / DC conversion circuit and the control end of the battery charging output circuit are respectively connected to the control signal output end of the microcontroller. The module circuits of the charging circuit of the present invention are controlled by the microcontroller, and the accuracy and reliability of the output voltage are good. The charging method of the present invention can identify a variety of voltage specifications, simplify the charging steps of the user, and improve the service life and charging efficiency of the battery.

Description

[Technical field]

[0001] The invention relates to charging of a lead-acid battery for an electric vehicle, and in particular to a charging circuit and a charging method for a lead-acid battery. [Background Technology]

[0002] As electric vehicles are a common means of transportation in small and medium-sized cities, it is inevitable to equip electric vehicles with charging stations. However, during the use of electric vehicle charging stations, it is impossible to determine the voltage specifications of the bicycle batteries used and set the correct charging voltage. As a result, there may be overcharging or undercharging. The overcharging state causes serious heating of the battery, affecting the battery life and even causing serious consequences such as fire, posing a major safety hazard. The battery cannot be charged to full charge in the undervoltage charging state, affecting user use and the charging efficiency of the charging station. In addition, since the charging station needs to manually set the charging voltage, under the premise of correct setting, the charging station will immediately disconnect the output after charging the battery to the set voltage value. At this time, the charged battery capacity has not yet reached the full capacity state. In the long run, it will affect the battery life.

[0003] The utility model with patent number CN201120129232.9 discloses a battery charging circuit for an electric bicycle capable of identifying voltage, including a leakage protector, a fuse, a capacitor, a rectifier bridge, a comparison circuit and a control circuit, characterized in that: the leakage protector is connected to one of the incoming lines of an external AC 220V power supply and then connected to a capacitor connected in parallel with a discharge resistor through a fuse, the capacitor and the other incoming line of the power supply are connected to the input end of the rectifier bridge, the output end of the rectifier bridge is connected to the charged battery through the normally open contact of the relay K and the ammeter, the two ends of the battery are connected in parallel to a detection circuit composed of resistors in series, and the rear end of the fuse takes a 220V AC power supply to connect the capacitor and the rectifier bridge to form an auxiliary power supply circuit. The utility model can automatically detect the rated voltage value of the battery of the charged electric bicycle, and adjust the voltage value of the charged battery after it is fully charged according to the rated value, so as to automatically charge all the qualified electric bicycle batteries on the market, and automatically cut off the battery after it is fully charged, which has good practical value.

[0004] The utility model completely uses analog circuits to adjust the output voltage, which has low accuracy and reliability. In addition, the voltage specifications of commonly used electric vehicle batteries include 36V, 48V, 60V and 72V. The utility model can only identify 36V and 48V voltages, and cannot identify 60V, 72V and other voltages. [Summary of the invention]

[0005] The technical problem to be solved by the present invention is to provide a lead-acid battery charging circuit with good output voltage accuracy and reliability.

[0006] The technical problem to be solved by the present invention is to provide a lead-acid battery charging method which can identify batteries of various voltage specifications and take corresponding charging measures.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is a lead-acid battery charging circuit, including a battery voltage sampling circuit, a battery charging output circuit, an AC-DC conversion circuit and a control circuit, the input end of the AC-DC conversion circuit is connected to an AC power supply, and the output end is connected to the battery charging output circuit; the output end of the battery charging output circuit and the sampling end of the battery voltage sampling circuit are respectively connected to the charging interface of the lead-acid battery, the control circuit includes a microcontroller, the output end of the battery voltage sampling circuit is connected to the battery voltage sampling signal input end of the microcontroller, and the control end of the AC-DC conversion circuit and the control end of the battery charging output circuit are respectively connected to the control signal output end of the microcontroller.

[0008] The lead-acid battery charging circuit described above, the battery voltage sampling circuit includes a resistor voltage divider circuit, a voltage follower and a first RC filter circuit, the input end of the resistor voltage divider circuit is connected to the charging interface of the lead-acid battery as the sampling end of the battery voltage sampling circuit, the output end of the resistor voltage divider circuit is connected to the input end of the voltage follower, and the output end of the voltage follower is connected to the battery voltage sampling signal input end of the microcontroller through the first RC filter circuit.

[0009] In the lead-acid battery charging circuit described above, the negative terminal of the lead-acid battery charging interface is grounded, and the battery voltage sampling circuit includes a first diode and a second diode, the cathode of the first diode and the anode of the second diode are connected to the battery voltage sampling signal input terminal of the microcontroller, the anode of the first diode is grounded, and the cathode of the second diode is connected to the positive electrode of the chip power supply.

[0010] The lead-acid battery charging circuit described above, the battery charging output circuit includes an electronic switch, a second RC filter circuit, a fuse, an isolation drive module and the charging interface, the input end of the electronic switch is connected to the positive electrode of the output end of the AC-DC conversion circuit, and the negative electrode of the output end of the AC-DC conversion circuit is grounded; the output end of the electronic switch is connected to the positive electrode of the charging interface through the second RC filter circuit and the fuse in sequence, and the negative electrode of the charging interface is grounded; the control signal output end of the microcontroller is connected to the control end of the electronic switch through the isolation drive module.

[0011] In the lead-acid battery charging circuit described above, the electronic switch includes two MOS tubes connected in reverse series, the isolation drive module includes a photocoupler and a transistor, the two MOS tubes connected in reverse series are connected between the positive electrode of the output end of the AC / DC conversion circuit and the second RC filter circuit, the anode of the light-emitting diode of the photocoupler is connected to the positive electrode of the power supply, the cathode of the light-emitting diode is connected to the collector of the transistor, the emitter of the transistor is grounded, and the base of the transistor is connected to the control signal output end of the microcontroller; the output end of the photosensitive transistor of the photocoupler is connected to the gates of the two MOS tubes.

[0012] The lead-acid battery charging circuit described above, the AC / DC conversion circuit includes an AC / DC conversion circuit, a DC / DC conversion circuit and a drive circuit; the input end of the AC / DC conversion circuit is connected to an AC power supply, the input end of the DC / DC conversion circuit is connected to the output end of the AC / DC conversion circuit, and the output end of the DC / DC conversion circuit is connected to a battery charging output circuit; the AC / DC conversion circuit and / or the DC / DC conversion circuit includes a plurality of switch tubes, the control end of the switch tube is connected to the output end of the drive circuit, and the input end of the drive circuit is connected to the drive signal output end of the microcontroller.

[0013] A method for charging a lead-acid battery, using the lead-acid battery charging circuit, comprises the following steps:

[0014] 701) When the voltage of the connected battery is within the voltage overlap region of the two voltage specifications of the battery, the battery is charged with the upper limit voltage of the overlap region, and the voltage specification of the connected battery is determined according to the charging rate;

[0015] 702) Charging is performed using corresponding charging specifications according to the voltage specifications of the connected battery.

[0016] The above-mentioned charging method comprises the following steps:

[0017] 801) In step 701, the battery is charged with a constant current at the upper limit voltage of the overlap region, and the voltage specification of the connected battery is determined by the charging rate;

[0018] 802) In step 702, constant current charging is performed with the voltage upper limit value of the identified battery voltage specification as the charging voltage upper limit, and when the connected battery is charged to the set voltage upper limit value, it is switched to constant voltage charging.

[0019] In the charging method described above, in step 802, when it is detected that the charging current of the constant voltage charging is less than the set value, floating charging is performed until the charging is completed.

[0020] Each module circuit of the lead-acid battery charging circuit of the present invention is controlled by a microcontroller, and the accuracy and reliability of the output voltage are good.

[0021] The charging method of the present invention can identify a variety of voltage specifications, simplify the charging steps for users, and improve the service life and charging efficiency of the battery. [Drawings]

[0022] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0023] Figure 1 It is a structural block diagram of a lead-acid battery charging circuit according to an embodiment of the present invention.

[0024] Figure 2 It is a schematic structural diagram of an AC-DC conversion circuit according to an embodiment of the present invention.

[0025] Figure 3 It is a circuit diagram of the main circuit of the lead-acid battery charging circuit according to an embodiment of the present invention.

[0026] Figure 4 4 is a circuit diagram of an isolation driving module according to an embodiment of the present invention.

[0027] Figure 5 1 is a voltage specification diagram of 36V, 48V, 60V and 72V batteries according to an embodiment of the present invention.

[0028] Figure 6 It is a charging characteristic curve diagram of a 48V battery and a 60V battery voltage overlap region tested at a 59V charging voltage according to an embodiment of the present invention.

[0029] Figure 7 It is a charging characteristic curve diagram of a 60V battery and a 72V battery voltage overlap region tested at a charging voltage of 73.7V according to an embodiment of the present invention. [Specific implementation method]

[0030] The lead-acid battery charging circuit of the embodiment of the present invention is as follows Figures 1 to 4 As shown, it includes a battery voltage sampling circuit, a battery charging output circuit, an AC / DC conversion circuit and a control circuit. The input end of the AC / DC conversion circuit is connected to an AC power supply, and the output end is connected to the battery charging output circuit. The output end of the battery charging output circuit and the sampling end of the battery voltage sampling circuit are respectively connected to the charging interface J1 of the lead-acid battery. The control circuit includes a microcontroller (single-chip microcomputer STM32). The output end of the battery voltage sampling circuit is connected to the battery voltage sampling signal input end of the microcontroller. The control end of the AC / DC conversion circuit and the control end of the battery charging output circuit are respectively connected to the control signal output end of the microcontroller.

[0031] like Figure 3As shown, the battery voltage sampling circuit includes a resistor divider circuit composed of resistors R1 and R2 connected in series, a voltage follower U1-A, a voltage stabilizing resistor R3, a first RC filter circuit composed of R4 and C2, and a bidirectional conducting diode D8. The resistance of R1 is 200K, the resistance of R2 is 6.8K, and the resistance of R3 is 1K. The resistor R2 is connected in parallel to the filter capacitor C1.

[0032] The input end of the resistor divider circuit is connected to the positive pole (OUT1+) of the lead-acid battery charging interface J1 as the sampling end of the battery voltage sampling circuit. The negative terminal of the lead-acid battery charging interface J1 is connected to the analog ground AGND, and the other end of the resistor divider circuit is also connected to the analog ground AGND. The output end of the resistor divider circuit (the connection point of resistors R1 and R2) is connected to the positive input terminal PIN3 of the operational amplifier U1-A. The sampling result is a voltage value less than 3.3V, which is the pin3 pin voltage value. The inverting input terminal PIN2 of the operational amplifier U1-A is connected to the output terminal PIN1 of the operational amplifier U1-A, and the operational amplifier U1-A forms a voltage follower.

[0033] The output end of the voltage follower U1-A is connected to the battery voltage sampling signal input end PIN8 of the microcontroller through PIN1, a voltage-stabilizing resistor and a first RC filter circuit.

[0034] The cathode of the first diode and the anode of the second diode of the overvoltage protection bidirectional conduction diode D8 are connected to the battery voltage sampling signal input terminal of the microcontroller, the anode of the first diode is grounded, and the cathode of the second diode is connected to the positive electrode of the chip power supply (+3.3V). The output value of the voltage follower is the sampling value of the voltage divider sampling resistor. When the output voltage of the voltage follower exceeds 3.3V, the second diode of the bidirectional conduction diode D8 is forward-conducted, pulling down the overvoltage and protecting the microcontroller.

[0035] When the charging interface J1 is connected to the lead-acid battery to be charged, the battery voltage sampling circuit detects the battery voltage value, and transmits the voltage sampling value to the PIN8 pin of the microcontroller through the voltage-dividing sampling resistors R1 and R2. The PIN8 pin is used as the battery voltage detection pin of the single-chip microcomputer to obtain the voltage sampling value [R2 / (R1+R2)]*OUT1+ (OUT1+ is the positive voltage of the battery) of the voltage-dividing circuit. After the microcontroller receives and processes the signal, the corresponding PWM driving square wave is sent out from the PIN44 pin to drive the switch tube of the AC / DC conversion circuit and the output rectifier module to output the corresponding charging voltage value VOUT, which is a constant voltage value slightly higher than the battery voltage. At the same time, the high-level signal module sends out instructions from the PIN39 (BATON1) pin of the microcontroller, and the electronic switches Q1 and Q2 are driven by the isolation drive module to charge the battery until the battery is fully charged, and then the drive is disconnected.

[0036] like Figure 2 As shown, the AC / DC conversion circuit includes an AC / DC conversion circuit, a DC / DC conversion circuit and a drive circuit. The input end of the AC / DC conversion circuit is connected to an AC power source, the input end of the DC / DC conversion circuit is connected to the output end of the AC / DC conversion circuit, and the output end of the DC / DC conversion circuit is connected to a battery charging output circuit. The AC / DC conversion circuit and the DC / DC conversion circuit each include a plurality of switch tubes, the control end of the switch tubes of the AC / DC conversion circuit and the DC / DC conversion circuit are connected to the output end of the drive circuit, and the input end of the drive circuit is connected to the drive signal output end of the microcontroller.

[0037] The battery charging output circuit includes an electronic switch composed of MOS tubes Q1 and Q2, a second RC filter circuit composed of resistors R7, R8, R9, R10 and C4, a fuse, an isolation drive module and a charging interface J1. The input end of the electronic switch is connected to the positive electrode VOUT of the output end of the AC / DC conversion circuit, and the negative electrode of the output end of the AC / DC conversion circuit is connected to the analog ground AGND. The output end of the electronic switch is connected to the positive electrode OUT1+ of the charging interface J1 through the second RC filter circuit and the fuse, and the negative electrode of the charging interface J1 is connected to the analog ground AGND. The control signal output end PIN39 (BATON1) of the microcontroller is connected to the control end of the electronic switch through the isolation drive module.

[0038] The two MOS tubes Q1 and Q2 of the electronic switch are connected in reverse series, that is, the output terminal VOUT of the AC / DC conversion circuit is connected to the D pole of the MOS tube Q1, the PIN39 pin of the microcontroller is connected to the G poles of the MOS tubes Q1 and Q2 through the isolation drive module, the MOS tube Q1 is connected to the S pole of the MOS tube Q2, the G pole of the MOS tube Q1 is connected to the discharge resistor to the S pole, the G pole of the MOS tube Q2 is connected to the discharge resistor to the S pole, and the resistance of the discharge resistors R5 and R6 is 10K. The D pole of the MOS tube Q2 is connected to the first end of the output fuse, and the other end of the output fuse is connected to OUT1+, that is, the positive pole of the charging interface J1 of the acid battery.

[0039] The isolation drive module includes a photocoupler U2 and a transistor. Two MOS transistors connected in reverse series are connected between the positive electrode of the output end of the AC / DC conversion circuit and the second RC filter circuit. The anode of the light-emitting diode of the photocoupler U2 is connected to the positive electrode of the power supply, the cathode of the light-emitting diode is connected to the collector of the transistor Q5, the emitter of the transistor Q5 is grounded, and the base of the transistor Q5 is connected to the control signal output terminal PIN39 (BATON1) of the microcontroller. The output end of the photosensitive transistor of the photocoupler U2 is connected to the gates of the two MOS tubes Q1 and Q2.

[0040] When the PIN8 pin of the microcontroller (single-chip microcomputer STM32) detects the voltage of the lead-acid battery to be charged, the PWM driving square wave with the corresponding duty cycle is sent out by the pin44 pin, and the switch tubes of the AC / DC conversion circuit and the DC / DC conversion circuit are driven through the driving circuit of the AC / DC conversion circuit. The AC / DC conversion circuit outputs the charging voltage VOUT for charging the battery. At the same time, the pin39 pin of the microcontroller sends a high level, and drives the MOS tubes Q1 and Q2 to turn on through the isolation drive module circuit, and outputs the battery charging voltage VOUT until the microcontroller detects that the battery is fully charged. The PIN44 pin of the microcontroller stops sending the PWM wave, the pin39 pin potential is pulled low, the MOS tubes Q1 and Q2 are turned off, and the charging is completed.

[0041] like Figure 5 As shown, the overlapping voltage of 36V and 48V lead-acid batteries is 42V-44.2V, the overlapping voltage of 48V and 60V lead-acid batteries is 52.5V-59V, and the overlapping voltage of 60V and 72V lead-acid batteries is 63V-73.7V.

[0042] like Figure 6 As shown, according to the charging characteristic curves of the 48V battery and the 60V battery tested at a charging voltage of 59V in the voltage overlap area, it can be seen that the charging rate of the 60V battery is significantly faster than the charging rate of the 48V lead-acid battery.

[0043] like Figure 7 As shown in the figure, the charging characteristic curves of the 72V battery and the 60V battery tested at a charging voltage of 73.7V in the voltage overlap area. It can be seen that the charging rate of the 72V battery is significantly faster than that of the 60V lead-acid battery.

[0044] Therefore, it can be determined that, in the voltage overlap region, when batteries of different voltage specifications are charged at the upper limit voltage of the overlap region, the charging rate of the battery with a higher voltage specification is significantly higher than the charging rate of the battery with a lower voltage specification.

[0045] When the connected battery voltage is in the overlapping area of ​​the two voltage specifications, the battery is charged with constant current at the upper limit voltage of the overlapping area, and the voltage specification of the connected lead-acid battery is determined according to the charging rate. The upper limit value of the identified battery voltage specification is used as the charging voltage upper limit, and constant current charging is performed to the upper limit value set by the voltage. When the battery is charged to the upper limit value set by the voltage, it is switched from constant current charging to constant voltage charging. At this time, the charging current will gradually decrease. When the charging current is detected to be at a very small value (0.3A), the microcontroller issues a command to float charge at a voltage value slightly lower than the upper limit value of the voltage specification to maintain the battery voltage stable.

[0046] During the floating charge process, the detection is continued for 30 minutes. If the charging current is always less than 0.3A during the detection time, the floating charge mode is exited and the battery charging output circuit is shut down.

[0047] For example, if the detected connected battery voltage is 55V, the system can determine that the battery voltage is between 52.5-59V, the overlapping area of ​​48V and 60V battery voltages, and adjust the output voltage through the microcontroller to charge the battery with an output voltage of 59V. Figure 6 As shown in the figure, the charging rate of a 60V battery is significantly faster than that of a 48V lead-acid battery. Based on the charging rate, it can be determined whether the connected battery voltage specification is a 60V lead-acid battery or a 48V lead-acid battery. If the charging rate of the connected battery is detected to be a high charging rate, it can be determined that the connected battery is a 60V lead-acid battery. The voltage range of a 60V lead-acid battery is 52.5V-73.7V, and the battery is charged to a full charge state at an output voltage of 73.7V.

[0048] Each module circuit of the charging circuit in the above embodiment of the present invention is controlled by a microcontroller, and has good output voltage accuracy, strong working reliability and practicality, good recognition effect, and high control precision.

[0049] The control method of the above embodiment of the present invention can accurately determine the voltage of lead-acid batteries of various specifications such as 36V, 48V, 60V, 72V on the market and charge them to full charge and full capacity. It can solve the problems of different charging equipment parameters and high cost investment that are common in charging stations. It can also simplify the user's charging steps, avoid safety hazards caused by operational errors, improve the safety performance of the charging station, and increase the battery life and charging efficiency.

Claims

1. A method for charging a lead-acid battery, characterized in that: The invention comprises a lead-acid battery charging circuit, which comprises a battery voltage sampling circuit, a battery charging output circuit, an AC / DC conversion circuit and a control circuit. The input end of the AC / DC conversion circuit is connected to an AC power supply, and the output end is connected to the battery charging output circuit. The output end of the battery charging output circuit and the sampling end of the battery voltage sampling circuit are respectively connected to the charging interface of the lead-acid battery. The invention is characterized in that the control circuit comprises a microcontroller, the output end of the battery voltage sampling circuit is connected to the battery voltage sampling signal input end of the microcontroller, and the control end of the AC / DC conversion circuit and the control end of the battery charging output circuit are respectively connected to the control signal output end of the microcontroller. When the lead-acid battery charging circuit is working, the invention comprises the following steps: 101) When the voltage of the connected battery is within the voltage overlap region of the two voltage specifications of the battery, the battery is charged with the upper limit voltage of the overlap region, and the voltage specification of the connected battery is determined according to the charging rate, a high charging rate is determined as a high voltage specification, and a low charging rate is determined as a low voltage specification; 102) Charging is performed using corresponding charging specifications according to the voltage specifications of the connected battery.

2. The method for charging a lead-acid battery according to claim 1, characterized in that: The battery voltage sampling circuit includes a resistor voltage divider circuit, a voltage follower and a first RC filter circuit. The input end of the resistor voltage divider circuit is connected to the charging interface of the lead-acid battery as the sampling end of the battery voltage sampling circuit, the output end of the resistor voltage divider circuit is connected to the input end of the voltage follower, and the output end of the voltage follower is connected to the battery voltage sampling signal input end of the microcontroller through the first RC filter circuit.

3. The method for charging a lead-acid battery according to claim 2, characterized in that: The negative terminal of the lead-acid battery charging interface is grounded, and the battery voltage sampling circuit includes a first diode and a second diode. The cathode of the first diode and the anode of the second diode are connected to the battery voltage sampling signal input terminal of the microcontroller, the anode of the first diode is grounded, and the cathode of the second diode is connected to the positive electrode of the chip power supply.

4. The method for charging a lead-acid battery according to claim 1, characterized in that: The battery charging output circuit comprises an electronic switch, a second RC filter circuit, a fuse, an isolation drive module and the charging interface. The input end of the electronic switch is connected to the positive electrode of the output end of the AC / DC conversion circuit, and the negative electrode of the output end of the AC / DC conversion circuit is grounded; the output end of the electronic switch is connected to the positive electrode of the charging interface through the second RC filter circuit and the fuse in sequence, and the negative electrode of the charging interface is grounded; the control signal output end of the microcontroller is connected to the control end of the electronic switch through the isolation drive module.

5. The method for charging a lead-acid battery according to claim 4, characterized in that: The electronic switch comprises two MOS tubes connected in reverse series, the isolation driving module comprises a photoelectric coupler and a triode, the two MOS tubes connected in reverse series are connected between the positive electrode of the output end of the AC / DC conversion circuit and the second RC filter circuit, the anode of the light emitting diode of the photoelectric coupler is connected to the positive electrode of the power supply, the cathode of the light emitting diode is connected to the collector of the triode, the emitter of the triode is grounded, and the base of the triode is connected to the control signal output end of the microcontroller; the output end of the photosensitive triode of the photoelectric coupler is connected to the gates of the two MOS tubes.

6. The method for charging a lead-acid battery according to claim 1, characterized in that: The AC / DC conversion circuit includes an AC / DC conversion circuit, a DC / DC conversion circuit and a drive circuit; the input end of the AC / DC conversion circuit is connected to an AC power supply, the input end of the DC / DC conversion circuit is connected to the output end of the AC / DC conversion circuit, and the output end of the DC / DC conversion circuit is connected to a battery charging output circuit; the AC / DC conversion circuit and / or the DC / DC conversion circuit includes a plurality of switch tubes, the control end of the switch tube is connected to the output end of the drive circuit, and the input end of the drive circuit is connected to the drive signal output end of the microcontroller.

7. The charging method according to claim 1, characterized in that: The following steps are involved: 701) In step 101, the battery is charged with a constant current at the upper limit voltage of the overlap region, and the voltage specification of the connected battery is determined by the charging rate; 702) In step 102, constant current charging is performed with the voltage upper limit value of the identified battery voltage specification as the charging voltage upper limit, and when the connected battery is charged to the set voltage upper limit value, it is switched to constant voltage charging.

8. The charging method according to claim 7, characterized in that: In step 702, when it is detected that the charging current of the constant voltage charging is less than the set value, floating charging is performed until the charging is completed.

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