Balancing circuit, charging circuit and on-board charger

Abstract

The application discloses a balancing circuit, a charging circuit and a vehicle-mounted charger. The balancing circuit comprises an energy storage circuit, N switch circuits and a control circuit. The input ends of the N switch circuits are connected with N battery modules one by one, and the output ends of the N switch circuits are all connected with the energy storage circuit. The control circuit is connected with the controlled ends of the N switch circuits respectively, and controls the corresponding switch circuits of two adjacent battery modules to be opened alternately, so as to control the two adjacent battery modules to charge and discharge the energy storage circuit alternately. Therefore, the voltage balancing between the two battery modules is realized, and the voltage balancing between the battery modules is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power supply, in particular to a balancing circuit, a charging circuit and a vehicle-mounted charger. BACKGROUND

[0002] With the rapid development of electric vehicles, the requirements for power batteries of electric vehicles are getting higher and higher, such as safety, reliability and high energy density. The battery pack of an electric vehicle is generally composed of multiple battery modules.

[0003] Due to the difference in characteristics of the whole vehicle battery, the imbalance of the battery will increase with the use time, that is, the imbalance between the battery modules will become larger and larger, thereby not only greatly reducing the capacity of the whole battery pack, but also bringing safety risks. SUMMARY

[0004] The main purpose of the present application is to provide a balancing circuit, which aims to balance the battery modules.

[0005] To achieve the above purpose, the balancing circuit provided by the present application is used to balance N battery modules connected in series, comprising:

[0006] an energy storage circuit;

[0007] N switch circuits having an input end, an output end and a controlled end, the input end of each of the N switch circuits being connected to one of the N battery modules, and the output end of each of the N switch circuits being connected to the energy storage circuit;

[0008] a control circuit connected to the controlled end of each of the N switch circuits, the control circuit being configured to control the switch circuits corresponding to two adjacent battery modules to be alternately turned on, so as to control the two adjacent battery modules to alternately charge and discharge the energy storage circuit;

[0009] wherein N is greater than or equal to 2.

[0010] In an embodiment, the control circuit is configured to control the switch circuits corresponding to two adjacent battery modules to be alternately turned on in sequence, so as to balance the N battery modules connected in series in sequence.

[0011] In an embodiment, the control circuit is an oscillator, and the oscillator is configured to generate at least two PWM signals that are opposite to each other in phase, so as to control the switch circuits corresponding to two adjacent battery modules to be alternately turned on.

[0012] Alternatively, the control circuit is a microcontroller, and the microcontroller is configured to output at least two PWM signals that are opposite to each other in phase, so as to control the switch circuits corresponding to two adjacent battery modules to be alternately turned on.

[0013] In an embodiment, the duty cycle of the PWM signal is 50%.

[0014] The application further provides a charging circuit comprising the above-mentioned equalization circuit.

[0015] In an embodiment, the charging circuit has a charging mode and an equalization mode; two adjacent battery modules are defined as a first battery module and a second battery module, the second electrode of the first battery module is connected to the first electrode of the second battery module; the charging circuit comprises:

[0016] a first switch circuit, an input end of the first switch circuit being connected to the first electrode of the first battery module, and an output end of the first switch circuit being connected to a first end of the energy storage circuit;

[0017] a second switch circuit, an input end of the second switch circuit being connected to a second end of the energy storage circuit, and an output end of the second switch circuit being connected to the second electrode of the second battery module;

[0018] a function switching switch, an input end of the function switching switch being connected to the second end of the energy storage circuit, and an output end of the function switching switch being connected to a common end of the first battery module and the second battery module;

[0019] the function switching switch is used to be turned on when the charging circuit works in the equalization mode, so that the first switch circuit, the second switch circuit and the energy storage circuit form an equalization circuit; and the function switching switch is used to be turned off when the charging circuit works in the charging mode, so that the first switch circuit and the second switch circuit form a secondary side bridge arm of the charging circuit.

[0020] In an embodiment, the control of the switch circuits corresponding to the adjacent two battery modules to be alternately turned on specifically comprises:

[0021] the frequency of the control of the switch circuits corresponding to the adjacent two battery modules to be alternately turned on is a first preset frequency;

[0022] when the bus voltage reaches a preset voltage value, the frequency of the control of the switch circuits corresponding to the adjacent two battery modules to be alternately turned on is gradually reduced until the frequency of the control of the switch circuits corresponding to the adjacent two battery modules to be alternately turned on is a second preset frequency; the first preset frequency is greater than the second preset frequency.

[0023] In an embodiment, the control of the switch circuits corresponding to the adjacent two battery modules to be alternately turned on specifically comprises:

[0024] The frequency at which the switching circuits corresponding to two adjacent battery modules alternately turn on is controlled to be a first preset frequency, and after a first preset time, the frequency at which the switching circuits corresponding to two adjacent battery modules alternately turn on is gradually reduced until the frequency at which the switching circuits corresponding to two adjacent battery modules alternately turn on is a second preset frequency; the first preset frequency is greater than the second preset frequency.

[0025] In one embodiment, the charging circuit includes a primary bridge arm, a resonant cavity, and a secondary bridge arm connected in sequence;

[0026] The energy storage circuit is the secondary winding of the transformer in the resonant cavity.

[0027] The present invention also proposes an on-board charger, which includes the above-mentioned equalization circuit or charging circuit.

[0028] The technical solution of this invention controls N switching circuits through a control circuit to control the switching circuits corresponding to two adjacent battery modules to turn on alternately, so as to control the two adjacent battery modules to charge and discharge the energy storage circuit alternately, ultimately making the voltage of the two battery modules balanced and effectively improving the service life of the battery module. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0030] Figure 1 This is a circuit block diagram of an embodiment of the equalization circuit of the present invention;

[0031] Figure 2 This is a circuit diagram of an embodiment of the equalization circuit of the present invention;

[0032] Figure 3 This is a circuit diagram of an embodiment of the charging circuit of the present invention;

[0033] Figure 4 This is a waveform diagram of a key node in an embodiment of the charging circuit of the present invention.

[0034] Explanation of icon numbers:

[0035]

[0036]

[0037] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0039] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this invention.

[0040] This invention proposes an equalization circuit for equalizing N battery modules connected in series. It can be applied to full-bridge converters such as LLC, CLLC, CLLLC, and PSFB.

[0041] Reference Figure 1 In one embodiment of the present invention, the equalization circuit includes

[0042] Energy storage circuit 10;

[0043] N switching circuits, each having an input terminal, an output terminal, and a controlled terminal, wherein the input terminals of the N switching circuits are connected one-to-one with the N battery modules, and the output terminals of the N switching circuits are all connected to the energy storage circuit 10.

[0044] The control circuit is connected to the controlled terminals of the N switching circuits respectively. The control circuit is used to control the switching circuits corresponding to two adjacent battery modules to turn on alternately, so as to control the two adjacent battery modules to charge and discharge the energy storage circuit 10 alternately.

[0045] Where N is greater than or equal to 2.

[0046] The energy storage circuit 10 may include an inductor, a capacitor, or other energy storage components.

[0047] Any one or more of the N switching circuits can include one or more combinations of switching devices such as transistors, MOSFETs, or IGBTs.

[0048] The control circuit (not shown in the figure) can be a controller, an oscillator, or other circuit that can generate a PWM signal. There are no restrictions here, as long as the output PWM signal controls the opening and closing of the switching circuit. The duty cycle of the PWM signal is 50%.

[0049] The control of two adjacent battery modules to alternately charge and discharge the energy storage circuit 10 can mean that one of the switching circuits corresponding to the two adjacent battery modules controls the corresponding battery module to discharge the energy storage circuit 10, and the other controls the corresponding battery module to charge the energy storage circuit 10. For example Figure 1 In the example, two adjacent battery modules are the first battery module BT1 and the second battery module BT2, and the initial value of the voltage V_BT1 of the first battery module BT1 is greater than the initial value of the voltage V_BT2 of the second battery module BT2. The first switch K1 controls the first battery module BT1 to periodically discharge the energy storage circuit 1010, and the second switch K2 controls the second battery module BT2 to periodically charge the energy storage circuit 1010.

[0050] As the first battery module BT1 and the second battery module BT2 charge and discharge the energy storage circuit 1010, the voltage V_BT1 of the first battery module BT1 gradually decreases, while the voltage V_BT2 of the second battery module BT2 gradually increases, ultimately achieving voltage balance between the first battery module BT1 and the second battery module BT2. It is easy to understand that when N is greater than 2, that is, when the number of battery modules exceeds two, after balancing the voltage between the first battery module BT1 and the second battery module BT2, the voltage between the other two battery modules, such as the second battery module BT2 and the third electronic module BT3 (not shown in the figure), can be balanced, ultimately achieving voltage balance between each pair of N battery modules, thus achieving voltage balance among all N battery modules.

[0051] The technical solution of this invention controls N switching circuits through a control circuit to control the switching circuits corresponding to two adjacent battery modules to turn on alternately, thereby controlling the two adjacent battery modules to alternately charge and discharge the energy storage circuit 10, ultimately making the voltage of the two battery modules balanced and effectively improving the service life of the battery module.

[0052] For example, refer to Figure 2The following explanation focuses on two adjacent first battery modules BT1 and BT2, and their corresponding first and second switching circuits K1 and K2. The energy storage circuit 10 includes a first inductor L1, the first switching circuit K1 includes a first switching transistor Q1, and the second switching circuit K2 includes a second switching transistor Q2. The control signals for the first and second switching transistors Q1 and Q2 are two mutually opposite PWM signals with a 50% duty cycle. For example, refer to... Figure 4 PWM1 and PWM2. The explanation will still take the example where the initial value of the voltage V_BT1 of the first battery module BT1 is greater than the initial value of the voltage V_BT2 of the second battery module BT2.

[0053] When the first switch Q1 is turned on, the second switch Q2 is turned off, and the first battery module BT1 charges the first inductor L1; when the second switch Q2 is turned on, the first switch Q1 is turned off, and the first inductor L1 discharges the battery module BT2. By controlling the first switch Q1 and the second switch Q2 to be turned on and off alternately multiple times, the first inductor is charged and discharged alternately, and finally the voltage V_BT1 of the first battery module BT1 and the voltage V_BT2 of the second battery module BT2 are balanced.

[0054] In one embodiment, the control circuit is used to sequentially control the switching circuits corresponding to two adjacent battery modules to alternately turn on, so as to balance the N battery modules connected in series in sequence.

[0055] Reference Figure 1 The first battery module BT1 to the nth battery module BTn are connected in series. After the voltage balance between the first battery module BT1 and the second battery module BT2 is achieved, the voltage balance between the second battery module BT2 and the third battery module BT3 is achieved, until the voltage balance between the (n-1)th battery module BTn-1 and the nth battery module BTn is achieved. By continuously balancing the voltage between adjacent battery modules among the N battery modules, the balance of the N battery modules is achieved.

[0056] In one embodiment, the control circuit is an oscillator, which is used to generate at least two mutually opposite PWM signals to control the switching circuits corresponding to two adjacent battery modules to turn on alternately;

[0057] Reference Figure 1 In this embodiment, an oscillator control circuit is used to generate control signals for the first switching circuit K1 and the second switching circuit K2, which are two mutually inverse PWM signals, for example... Figure 4The PWM1 and PWM2 shown are examples of this. The control logic is simple, so when the equalization circuit of this embodiment is applied to the charging circuit or other circuits, it does not need to occupy the controller resources of the charging circuit or other circuits that use this equalization circuit. Therefore, it is not necessary to adjust the control circuit of the charging circuit or other circuits that use this equalization circuit. Thus, the equalization circuit of this embodiment can be directly applied to the already debugged and designed charging circuit or other circuits, and modified to add equalization function, effectively reducing design costs.

[0058] In one embodiment, the control circuit is a microcontroller, which outputs at least two mutually opposite PWM signals to control the switching circuits corresponding to the two adjacent battery modules to turn on alternately.

[0059] In this embodiment, the microcontroller can be an independently configured microcontroller, which can then be directly applied to a charging circuit or other circuit that has been debugged and designed.

[0060] The microcontroller can also be a controller in a charging circuit or other circuit using this equalization circuit. Therefore, equalization can be achieved simply by adjusting the software control program of the controller in the charging circuit or other circuit using this equalization circuit, reducing the need for additional components. Furthermore, in this embodiment, the controller in the charging circuit or other circuit using this equalization circuit outputs at least two mutually opposite PWM signals. No feedback signal is required; simply outputting the PWM signals in an open loop is sufficient. This allows for direct application to a pre-designed and debugged charging circuit or other circuit, reducing the resource consumption of the controller in the charging circuit or other circuit using this equalization circuit.

[0061] In one embodiment, the present invention further includes a charging circuit, which includes the equalization circuit described above. The specific structure of the charging circuit is as described in the above embodiments. Since the charging circuit adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be described in detail here.

[0062] It's worth noting that the battery pack of an electric vehicle typically consists of multiple battery modules, each composed of individual cells connected in series and parallel. The balancing of cells within a battery module is usually handled by the onboard BMS (Battery Management System), and the balancing power is relatively small, typically ranging from a few watts to tens of watts. However, balancing between battery modules requires significantly more power, generally from several hundred watts to tens of kilowatts. This necessitates the design of more powerful energy conversion equipment and better heat dissipation components, which undoubtedly increases the size of the BMS and its heat dissipation requirements.

[0063] This embodiment incorporates an equalization circuit into the charging circuit. This equalization circuit can balance the voltage of the battery modules during periods when the charging circuit is not charging the battery modules. It makes full use of the charging circuit's own heat dissipation components, thereby achieving voltage equalization between battery modules without increasing the size of the BMS or its heat dissipation requirements. This has significant practical value.

[0064] Reference Figure 3 In one embodiment, the charging circuit includes a charging mode and an equalization mode; two adjacent battery modules are defined as a first battery module BT1 and a second battery module BT2, with the second electrode of the first battery module BT1 connected to the first electrode of the second battery module BT2; the charging circuit includes:

[0065] A first switching circuit K1, the input terminal of the first switching circuit K1 is connected to the first electrode of the first battery module BT1, and the output terminal of the first switching circuit K1 is connected to the first terminal of the energy storage circuit 10.

[0066] The second switching circuit K2 has its input terminal connected to the second terminal of the energy storage circuit 10, and its output terminal connected to the second electrode of the second battery module BT2.

[0067] A function switch 20, the input terminal of which is connected to the second terminal of the energy storage circuit 10, and the output terminal of which is connected to the common terminal of the first battery module BT1 and the second battery module BT2;

[0068] The function switch 20 is turned on when the charging circuit is in equalization mode, so that the first switch circuit K1, the second switch circuit K2 and the energy storage circuit 10 form an equalization circuit; and turned off when the charging circuit is in charging mode, so that the first switch circuit K1 and the second switch circuit K2 form the secondary side arm of the charging circuit.

[0069] In this embodiment, the first electrode of the battery module can be a positive electrode, and the second electrode can be a negative electrode. Of course, the first electrode can also be a negative electrode, and the second electrode can be a positive electrode. The charging circuit includes a primary side bridge arm, a resonant cavity, and a secondary side bridge arm connected in sequence.

[0070] The primary bridge arm may include the third switch Q3, the fourth switch Q4, the fifth switch Q5, and the sixth switch Q6. The resonant cavity may consist of a secondary resonant capacitor Cs, a primary resonant capacitor Cr, and a primary resonant inductor Lr. The secondary bridge arm may include the seventh switch Q7, the eighth switch Q8, the ninth switch Q9, and the tenth switch Q10. The specific connection relationships of the primary bridge arm, the resonant cavity, and the secondary bridge arm are shown in the appendix. Figure 3 This will not be elaborated upon here. In addition, the input terminal of the primary side bridge arm is connected to the bus capacitor C1, and the output terminal of the secondary side bridge arm is connected to the output capacitor C2.

[0071] Specifically, the first switching circuit K1 and the second switching circuit K2 can correspond to the seventh switching transistor Q7 and the eighth switching transistor Q8 in the secondary bridge arm, or the first switching circuit K1 and the second switching circuit K2 can correspond to the ninth switching transistor Q9 and the tenth switching transistor Q10 in the secondary bridge arm. The function switching switch 20 can be one or more of the following: transistor, MOSFET, IGBT, or relay.

[0072] When the battery modules need to be charged, the controller of the charging circuit can control the function switching switch 20 to be turned off. The charging circuit will convert the energy in the DC bus Vbus and output it to charge N battery modules connected in series.

[0073] When voltage balancing of the battery modules is required, the controller of the charging circuit can turn on the function switching switch 20, using the secondary winding of the transformer T1 in the resonant cavity as the energy storage circuit 10. At this time, simply outputting two opposing PWM signals to the first switching circuit K1 and the second switching circuit K2 is sufficient to achieve voltage balancing between the first battery module BT1 and the second battery module BT2. This embodiment reuses the secondary bridge arm in the charging circuit, thus requiring only the addition of the function switching switch 20, for example, by adding a relay, to add a balancing circuit to the charging circuit.

[0074] Furthermore, it is easy to understand that the battery pack of an electric vehicle generally consists of two battery modules. By directly reusing the two switching transistors of a secondary bridge arm, the voltage of the two battery modules can be balanced. When the battery pack of an electric vehicle includes more than two battery modules, only the corresponding number of switching transistors need to be added, which will not be elaborated here.

[0075] The principle of the charging circuit in this embodiment will be explained below.

[0076] Assume that the initial value of the voltage V_BT1 of the first battery module BT1 is greater than the initial value of the voltage V_BT2 of the second battery module BT2; the first switching circuit K1 and the second switching circuit K2 can correspond to the ninth switch Q9 and the tenth switch Q10 in the secondary bridge arm. The control signals of the first switching circuit K1 and the second switching circuit K2 are two PWM signals PWM1 and PWM2 with a duty cycle D = 50% and a frequency f = 150kHz, where PWM1 is the control signal of the first switching circuit K1 and PWM is the control signal of the second switching current.

[0077] During the first half-cycle of the PWM signal, the ninth switch Q9 is turned on, and the tenth switches Q10 and Q8 are turned off. The first battery module BT1 charges the secondary winding of the transformer T1. During the second half-cycle of the PWM signal, the ninth switch Q9 and Q7 are turned off, and the tenth switch Q10 is turned on. The secondary winding of the transformer T1 charges the second battery module BT2.

[0078] During the charging process of the secondary winding of transformer T1 by the first battery module BT1, energy is simultaneously transferred to the primary winding of transformer T1 via coupling between the primary and secondary windings, and the bus capacitor C1 is also charged. Simultaneously, due to the unequal charging and discharging voltages of the secondary winding (V_BT1>V_BT2), the charging currents of the primary winding during the positive and negative half-cycles are also unequal, generating a DC bias voltage Vcr on the primary resonant capacitor. This DC bias voltage Vcr, after conversion using the turns ratio of the primary and secondary windings of transformer T1, ensures that the positive and negative half-cycle voltages superimposed on the secondary winding of transformer T1 are equal. Furthermore, because the positive and negative half-cycle times are equal, the secondary winding maintains volt-second balance during the positive and negative half-cycles. Figure 4 Let iL be the current in the secondary winding of transformer T1. Therefore, by using the secondary winding of transformer T1 as the energy storage circuit 10, the technical effect of preventing the core of transformer T1 from saturating even if the balancing circuit operates for a long time can be achieved. This effectively solves the problem of core saturation in energy storage circuit 10 caused by the charging voltage being greater than the discharging voltage.

[0079] Specifically, the steady-state expression of the equalization circuit is as follows:

[0080] Vcr / N=V_BT1-(V_BT1+V_BT2) / 2

[0081] Or: Vcr / N=(V_BT1+V_BT2) / 2-V_BT2

[0082] Where Vcr is the DC bias voltage across the primary resonant capacitor Cr, and N is the turns ratio of the primary and secondary sides of transformer T1. (See details...) Figure 4As the balancing process continues, the voltage V_BT1 of the first battery module BT1 gradually decreases, while the voltage V_BT2 of the second battery module BT1 gradually increases. The difference between the voltages V_BT1 and V_BT2 of the first and second battery modules BT1 becomes smaller and smaller. Consequently, the second DC bias voltage Vcr also gradually decreases until the voltage V_BT1 of the first battery module BT1 equals the voltage V_BT2 of the second battery module BT1. Simultaneously, the DC bias voltage Vcr becomes zero, and only the periodically varying AC voltage remains across Cr.

[0083] In one embodiment, controlling the switching circuits corresponding to two adjacent battery modules to alternately turn on specifically involves:

[0084] The frequency at which the switching circuits corresponding to two adjacent battery modules are alternately turned on is a first preset frequency;

[0085] When the bus voltage reaches a preset voltage value, the frequency at which the switching circuits corresponding to two adjacent battery modules alternately turn on is gradually reduced until the frequency at which the switching circuits corresponding to two adjacent battery modules alternately turn on is a second preset frequency; the first preset frequency is greater than the second preset frequency.

[0086] The preset voltage value can be the stable voltage value of the bus voltage. The specific setting depends on the application scenario of the charging circuit; for example, when used in an on-board charger, the preset voltage value can be set to 150 volts. The second preset frequency can be the operating frequency of the equalization circuit, selected based on the operating power of the equalization circuit, for example, 150 Hz. The first preset frequency can be two to three times the operating frequency of the equalization circuit, for example, 400 Hz.

[0087] It is understood that by controlling the frequency at which the switching circuits corresponding to two adjacent battery modules alternately turn on to a first preset frequency, this embodiment can avoid the problem of excessive bus current causing transformer T1 core saturation when the equalization circuit starts.

[0088] Specifically, at the instant the equalization circuit starts, the equalization circuit, primary winding, primary resonant inductor Lr, primary resonant capacitor, and bus capacitor C1 form a loop, and at this time the voltage of bus capacitor C1 is zero, which is equivalent to a short circuit. Therefore, when the equalization circuit starts, the charging current coupled to bus capacitor C1 through transformer T1 will be relatively large, which will lead to core saturation of transformer T1.

[0089] The specific formula is as follows: L*di / dt=Vbat

[0090] That is: L*Imax / DT=Vbat

[0091] That is: Imax = Vbat * DT / L

[0092] Where L is the inductance of the secondary winding of transformer T1, Vbat is the charging voltage of the battery module charging the secondary winding of the transformer, D and T are the duty cycle and period of the control signal of the first switching circuit K1, respectively, Imax is the maximum current value of the secondary winding of transformer T1, and i is the current of the secondary winding of transformer T1. It is easy to understand that D = 0.5 is a fixed value, and Vbat can be the average voltage of the first and second battery modules, which is also a fixed value. Therefore, Imax is proportional to T. Thus, in this embodiment, increasing the frequency (the reciprocal of the period T) when the equalization circuit starts can reduce Imax when the equalization circuit starts, solving the problem that because the voltage of the bus capacitor C1 is zero, equivalent to a short circuit, the charging current coupled from transformer T1 to the bus capacitor C1 will be relatively large, leading to core saturation of transformer T1.

[0093] Furthermore, by selecting a suitable second preset frequency in this embodiment, the magnitude of the equalization power of the equalization circuit can be effectively adjusted, as detailed below:

[0094] L*di / dt=Vbat; Vbat=(V_BT1+V_BT2) / 2; di=Vbat*dt / L

[0095] Where L is the inductance of the secondary winding of transformer T1, and V_BT1 and V_BT2 are the voltage values ​​of the first battery module and the second battery module, respectively. Integrate both sides of the above equation with respect to time 0 to T / 2.

[0096] The following formula is obtained: Imax = Vbat * DT / L;

[0097] At this point, the equalization power of the equalization circuit is:

[0098] P_balance = Vbat * Imax * 1 / 2 = Vbat * Vbat * DT / L * 1 / 2;

[0099] As can be seen from the above, the equalization power can be controlled by controlling T, which is equivalent to controlling the operating frequency f. Therefore, in this embodiment, the equalization power of the equalization circuit can be effectively adjusted by regulating the operating frequency of the equalization circuit.

[0100] Reference Figure 3 In one embodiment, controlling the switching circuits corresponding to two adjacent battery modules to alternately turn on specifically involves:

[0101] The frequency at which the switching circuits corresponding to two adjacent battery modules alternately turn on is controlled to be a first preset frequency, and after a first preset time, the frequency at which the switching circuits corresponding to two adjacent battery modules alternately turn on is gradually reduced until the frequency at which the switching circuits corresponding to two adjacent battery modules alternately turn on is a second preset frequency; the first preset frequency is greater than the second preset frequency.

[0102] The first preset time can be set according to the actual test results, for example, it can be set to 300 milliseconds.

[0103] In this embodiment, the frequency at which the switching circuits corresponding to two adjacent battery modules alternately turn on is a first preset frequency, and after a first preset time, the default bus voltage reaches a preset voltage value. In this way, the control circuit of the balancing circuit does not need to monitor the bus voltage; it only needs to adjust the frequency of the two mutually opposite PWM signals output in an open-loop manner when the timer reaches the first preset time, effectively reducing the resource consumption of the charging circuit controller.

[0104] The present invention also proposes an on-board charger, which includes the above-mentioned equalization circuit or charging circuit; the specific structure of the equalization circuit or charging circuit is as described in the above embodiments. Since this charging circuit adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, and will not be described in detail here.

[0105] The above description is merely an optional embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A charging circuit comprising N battery modules connected in series, characterized in that, The charging circuit also includes: An equalization circuit, wherein the equalization circuit is used to equalize N battery modules connected in series, the equalization circuit comprising: Energy storage circuit; N switching circuits, each having an input terminal, an output terminal, and a controlled terminal, wherein the input terminals of the N switching circuits are connected one-to-one with the N battery modules, and the output terminals of the N switching circuits are all connected to the energy storage circuit. A control circuit is connected to the controlled terminals of N switching circuits respectively. The control circuit is used to control the switching circuits corresponding to two adjacent battery modules to turn on alternately, so as to control the two adjacent battery modules to charge and discharge the energy storage circuit alternately. Where N is greater than or equal to 2; The specific method of controlling the switching circuits corresponding to two adjacent battery modules to alternately turn on is as follows: The frequency at which the switching circuits corresponding to two adjacent battery modules are alternately turned on is a first preset frequency; When the bus voltage reaches a preset voltage value, the frequency at which the switching circuits corresponding to two adjacent battery modules alternately turn on decreases step by step until the frequency at which the switching circuits corresponding to two adjacent battery modules alternately turn on is a second preset frequency; the first preset frequency is greater than the second preset frequency.

2. The charging circuit as described in claim 1, characterized in that, The control circuit is used to sequentially control the switching circuits corresponding to two adjacent battery modules to turn on alternately, so as to balance the N battery modules connected in series in sequence.

3. The charging circuit as described in claim 1, characterized in that, The control circuit is an oscillator, which is used to generate at least two mutually opposite PWM signals to control the switching circuits corresponding to two adjacent battery modules to turn on alternately. Alternatively, the control circuit is a microcontroller, which outputs at least two mutually opposite PWM signals to control the switching circuits corresponding to the two adjacent battery modules to turn on alternately.

4. The charging circuit as described in claim 3, characterized in that, The duty cycle of the PWM signal is 50%.

5. The charging circuit as described in claim 1, characterized in that, The charging circuit has a charging mode and an equalization mode; two adjacent battery modules are defined as a first battery module and a second battery module, and the second electrode of the first battery module is connected to the first electrode of the second battery module; the charging circuit includes: A first switching circuit, wherein the input terminal of the first switching circuit is connected to the first electrode of the first battery module, and the output terminal of the first switching circuit is connected to the first terminal of the energy storage circuit; The second switching circuit has its input terminal connected to the second terminal of the energy storage circuit and its output terminal connected to the second electrode of the second battery module. A function switch, wherein the input terminal of the function switch is connected to the second terminal of the energy storage circuit, and the output terminal of the function switch is connected to the common terminal of the first battery module and the second battery module; The function switch is used to turn on when the charging circuit is operating in equalization mode, so that the first switch circuit, the second switch circuit, and the energy storage circuit form an equalization circuit; and to turn off when the charging circuit is operating in charging mode, so that the first switch circuit and the second switch circuit form the secondary bridge arm of the charging circuit.

6. The charging circuit as described in claim 1, characterized in that, The charging circuit includes a primary side bridge arm, a resonant cavity, and a secondary side bridge arm connected in sequence. The energy storage circuit is the secondary winding of the transformer in the resonant cavity.

7. An on-board charger, characterized in that, The on-board charger includes the charging circuit as described in any one of claims 1 to 6.

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