Charging method, charging circuit, and vehicle

Abstract

The present invention relates to the technical field of charging, and provides a charging method, a charging circuit, and a vehicle. The method comprises: in a first working state, after an alternating current voltage of a power grid is rectified by means of a PCS, outputting a first direct current voltage to charge a first battery, the first working state being a first switch and a second switch being closed, and a third switch and a fourth switch being open; in a second working state, after the first direct current voltage of the first battery is stepped down by means of the PCS, outputting a second direct current voltage to charge a second battery, the second working state being the second switch and the third switch being closed, and the first switch and the fourth switch being open. The first direct current voltage is greater than the second direct current voltage. The present invention can widen a direct current voltage range, thereby satisfying different battery charging requirements.

Description

A charging method, a charging circuit, and a vehicle

[0001] This application claims priority to Chinese Patent Application No. 202411177761.4, filed on August 26, 2024, entitled “A charging method, charging circuit and vehicle”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to the field of charging technology, and more particularly to a charging method, a charging circuit, and a vehicle. Background Technology

[0003] Electric vehicles use electricity, a clean energy source, as their power source, improving the resource utilization efficiency of transportation. A PCS (Power Conversion System) controls the charging and discharging process of an electric vehicle's battery, performing AC / DC conversion. For a 400V AC (Alternating Current) grid, the lowest DC voltage that a PCS can convert using existing charging methods is approximately 600V DC (Direct Current). However, if the battery requires a voltage level lower than DC 600V, existing methods, due to their limited voltage range, cannot meet the electricity demand. Summary of the Invention

[0004] This invention provides a charging method, a charging circuit, and a vehicle that can broaden the voltage range of direct current, thereby meeting different battery charging needs.

[0005] This invention provides a charging method applied to a charging circuit, the charging circuit including a first switch, a second switch, a third switch, a fourth switch, and an energy storage converter (PCS); a first terminal of the first switch is connected to the power grid; a first common terminal is formed by connecting the second terminal of the first switch and the first terminal of the third switch, and this first common terminal is connected to the first terminal of the PCS; a second common terminal is formed by connecting the first terminal of the second switch and the first terminal of the fourth switch, and this second common terminal is connected to the second terminal of the PCS; a second terminal of the second switch is connected to a first battery; and a third common terminal is formed by connecting the second terminal of the third switch and the second terminal of the fourth switch, and this third common terminal is connected to the second battery... The battery is connected; the charging voltage level of the second battery is not higher than the charging voltage level of the first battery; the charging method includes: in a first operating state, rectifying the AC voltage of the power grid through the PCS and outputting a first DC voltage to charge the first battery; the first operating state is to close the first switch and the second switch, and open the third switch and the fourth switch; in a second operating state, after stepping down the first DC voltage of the first battery through the PCS, outputting a second DC voltage to charge the second battery; the second operating state is to close the second switch and the third switch, and open the first switch and the fourth switch; the first DC voltage is greater than the second DC voltage.

[0006] According to a charging method provided by the present invention, the method further includes: in a third operating state, rectifying the AC voltage of the power grid through the PCS and outputting the first DC voltage to charge the second battery; the third operating state is to close the first switch and the fourth switch, and open the second switch and the third switch.

[0007] According to a charging method provided by the present invention, the method further includes: in a fourth operating state, rectifying the AC voltage of the power grid through the PCS and outputting the first DC voltage to charge the first battery and the second battery simultaneously; the fourth operating state is to close the first switch, the second switch and the fourth switch, and open the third switch.

[0008] According to a charging method provided by the present invention, the method further includes: in the second operating state, after boosting the second DC voltage of the second battery through the PCS, outputting the first DC voltage to charge the first battery.

[0009] According to a charging method provided by the present invention, the charging circuit further includes a power supply transformer disposed between the power grid and the first switch; the neutral point of the power supply transformer is insulated from ground; the method further includes: converting the AC voltage of the power grid into a power supply AC voltage through the power supply transformer.

[0010] According to a charging method provided by the present invention, the method further includes: feeding back the electrical energy of the first battery and / or the second battery to the power grid through the PCS.

[0011] According to a charging method provided by the present invention, the PCS includes an AC input unit, a power conversion unit, and a DC output unit connected in sequence; the AC input unit is used to input the AC voltage of the power grid; the power conversion unit is a three-phase fully controlled rectifier / inverter bridge; the three-phase fully controlled rectifier / inverter bridge is used to perform controllable rectification / inversion under SVPWM modulation; and the DC output unit is used to output DC voltage to charge the first battery and / or the second battery.

[0012] According to a charging method provided by the present invention, the method further includes: charging the first battery and / or the second battery by converting the voltage of the external new energy power supply module through the PCS; the external new energy power supply module includes a solar panel, a wind power module, or a hydropower module.

[0013] The present invention also provides a charging circuit, including a first switch, a second switch, a third switch, a fourth switch, and a PCS; a first terminal of the first switch is connected to the power grid; a first common terminal is formed by connecting the second terminal of the first switch and the first terminal of the third switch, and the first common terminal is connected to the first terminal of the PCS; a second common terminal is formed by connecting the first terminal of the second switch and the first terminal of the fourth switch, and the second common terminal is connected to the second terminal of the PCS; a second terminal of the second switch is connected to a first battery; a third common terminal is formed by connecting the second terminal of the third switch and the second terminal of the fourth switch, and the third common terminal is connected to a second battery; the charging voltage level of the second battery is not higher than the charging voltage level of the first battery; the first battery and / or the second battery are charged by the above-described charging method.

[0014] The present invention also provides a vehicle including the above-described charging circuit.

[0015] This invention provides a charging method, charging circuit, and vehicle. The method includes: in a first operating state, rectifying the AC voltage from the power grid using a PCS to output a first DC voltage for charging a first battery; the first operating state involves closing a first switch and a second switch, and opening a third switch and a fourth switch; in a second operating state, stepping down the first DC voltage of the first battery using the PCS to output a second DC voltage for charging a second battery; the second operating state involves closing the second switch and the third switch, and opening the first switch and the fourth switch; the first DC voltage is greater than the second DC voltage. This invention can broaden the voltage range of DC power, thereby meeting different battery charging needs. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in this 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 some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 is a schematic flowchart of the charging method provided by the present invention.

[0018] Figure 2 is a schematic diagram of the charging circuit provided by the present invention.

[0019] Figure 3 is a schematic diagram of the specific structure of the charging circuit provided by the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0021] With the deepening global energy crisis, the depletion of oil resources, and the increasing harm of air pollution and rising global temperatures, energy conservation and emission reduction are the main directions for future automotive technology development. Electric vehicles, as a new generation of transportation, possess unparalleled advantages over traditional vehicles in terms of energy conservation, emission reduction, and reducing human dependence on traditional fossil fuels. A battery charging system (PCS) can convert AC to DC to charge batteries, and can also convert DC from batteries back to AC for grid connection. For commercial vehicle battery swapping stations, PCS integrates charging, storage, and swapping, enabling charging and discharging of batteries within the station. Some manufacturers require charging batteries outside the station, necessitating external charging terminals and switching between in-station and out-of-station charging via switching devices. Among existing charging methods, the minimum voltage required for PCS to convert AC to DC is [not specified in the original text]. For an AC400V system, the converted DC voltage is DC565V. Considering voltage fluctuations, the minimum voltage is DC600V. However, if an electric vehicle's battery requires a voltage level below 600V, the external charging gun cannot charge vehicles with a voltage platform below DC600V.

[0022] Please refer to Figure 1, which is a schematic flowchart of the charging method provided by the present invention.

[0023] Please refer to Figure 2, which is a schematic diagram of the charging circuit provided by the present invention.

[0024] To address the technical problems existing in the prior art, the present invention provides a charging method applied to a charging circuit, which includes a first switch, a second switch, a third switch, a fourth switch, and a PCS; the first terminal of the first switch is connected to the power grid; the second terminal of the first switch and the first terminal of the third switch are connected to form a first common terminal, which is connected to the first terminal of the PCS; the first terminal of the second switch and the first terminal of the fourth switch are connected to form a second common terminal, which is connected to the second terminal of the PCS; the second terminal of the second switch is connected to a first battery; the second terminal of the third switch and the second terminal of the fourth switch are connected to form a third common terminal, which is connected to a second battery; the charging voltage level of the second battery is not higher than the charging voltage level of the first battery.

[0025] Charging methods include:

[0026] 101: In the first operating state, the AC voltage of the power grid is rectified by the PCS and a first DC voltage is output to charge the first battery; the first operating state is to close the first switch and the second switch, and open the third switch and the fourth switch.

[0027] 102: In the second operating state, after the first DC voltage of the first battery is stepped down by the PCS, the second DC voltage is output to charge the second battery; the second operating state is to close the second switch and the third switch, and open the first switch and the fourth switch; the first DC voltage is greater than the second DC voltage.

[0028] This invention charges the first battery by closing the first switch K1 and the second switch K2, and opening the third switch K3 and the fourth switch K4, allowing the AC power from the mains grid to be converted to DC power by the PCS. The mains voltage level is AC 400V, and the DC voltage level for charging the first battery is DC 600-900V.

[0029] Then, the second switch K2 and the third switch K3 are closed, and the first switch K1 and the fourth switch K4 are opened. The first battery (battery 1) charges the second battery (battery 2) through the DC / DC step-down conversion of the PCS. The voltage level of the first battery is DC600-900V, and the DC voltage level for charging the second battery is DC200-600V. This can broaden the DC voltage range, thereby meeting different battery charging needs and achieving higher charging efficiency.

[0030] It should be noted that the energy storage converter can control the charging and discharging process of the battery, perform AC / DC conversion, and store electrical energy, directly supplying power to the load when there is no external power grid. The PCS consists of a DC / AC bidirectional converter, a control unit, etc. The PCS controller receives control commands from the background via communication and controls the converter to charge or discharge the battery according to the sign and magnitude of the power command, thereby regulating the active and reactive power of the power grid. The PCS controller communicates with the BMS (Battery Management System) through a CAN (Controller Area Network) interface to obtain battery status information, enabling protective charging and discharging of the battery to ensure safe battery operation.

[0031] The input power supply is connected to the DC port of the PCS, and then the power is converted by the power electronic devices of the PCS, finally outputting the converted power to the AC port. The power electronic devices of the PCS include thyristors, IGBTs, MOSFETs, etc. The working principle of the PCS can be divided into three parts: input circuit, power electronic devices, and output circuit.

[0032] The input circuit is the DC port of the PCS, which accepts DC power from the power system. The input circuit typically consists of a DC power supply, filter capacitors, and protection circuitry. The DC power supply can be a battery, photovoltaic cell, wind turbine, etc. The filter capacitors remove high-frequency noise from the input power supply, and the protection circuitry protects the PCS power electronic devices from overvoltage or overcurrent from the input power supply.

[0033] Power electronic devices are the core components of a power control system (PCS), primarily used to convert input power into output power. These devices typically consist of thyristors, IGBTs (Insulated Gate Bipolar Transistors), and MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors). These devices control current and voltage to achieve power conversion. The choice of power electronic devices depends on the current and voltage requirements and the application scenario. For example, high-voltage and high-current applications require IGBTs, while low-voltage and low-current applications can use MOSFETs.

[0034] The output circuit is the AC port of the PCS, which outputs the converted power to the power system. The output circuit typically consists of filter capacitors, filter inductors, and protection circuitry. The filter capacitors and inductors remove high-frequency noise from the output power supply, while the protection circuitry protects the PCS power electronic devices from overvoltage or overcurrent in the output power supply.

[0035] Battery Management System (BMS) can accurately estimate the State of Charge (SOC) of a power battery pack, i.e., the remaining battery capacity, ensuring that the SOC is maintained within a reasonable range to prevent damage to the battery due to overcharging or over-discharging. It also displays the remaining energy of the electric vehicle's energy storage battery in real time, i.e., the SOC of the energy storage battery. During battery charging and discharging, the BMS collects real-time data on the terminal voltage and temperature of each battery in the electric vehicle's battery pack, the charging and discharging current, and the total voltage of the battery pack to prevent overcharging or over-discharging. Simultaneously, it can promptly provide battery status information, identify problematic batteries, maintain the reliability and efficiency of the entire battery pack operation, and make the implementation of the remaining capacity estimation model possible. The BMS can achieve equalization charging of individual batteries, ensuring that each battery in the battery pack reaches a balanced and consistent state.

[0036] Battery power consumption periods are specifically divided into: off-peak electricity price periods, flat electricity price periods, and peak electricity price periods. These different electricity price periods can be divided by the local power supply department based on local electricity consumption data statistics.

[0037] The choice of storage battery can be one or a combination of lead-acid batteries, lead-carbon batteries, flow batteries, sodium-sulfur batteries, lithium iron phosphate batteries, ternary lithium-ion batteries, lithium titanate batteries, and supercapacitors.

[0038] As a preferred embodiment, it further includes: in the third operating state, after rectifying the AC voltage of the power grid through the PCS, outputting a first DC voltage to charge the second battery; the third operating state is to close the first switch and the fourth switch, and open the second switch and the third switch.

[0039] In this embodiment, the first switch K1 and the fourth switch K4 are closed, while the second switch K2 and the third switch K3 are opened. The AC power from the mains is converted to AC / DC by the PCS to charge the second battery. The mains voltage is AC 400V, and the output DC voltage is DC 600-900V.

[0040] As a preferred embodiment, it further includes: in the fourth operating state, after rectifying the AC voltage of the power grid through the PCS, the first DC voltage is output to charge the first battery and the second battery simultaneously; the fourth operating state is to close the first switch, the second switch and the fourth switch, and open the third switch.

[0041] In this embodiment, the first switch K1, the second switch K2, and the fourth switch K4 are closed, and the third switch K3 is opened. The AC power from the mains is converted to AC / DC by the PCS to charge the first battery and the second battery simultaneously.

[0042] In a preferred embodiment, the method further includes: in the second operating state, after boosting the second DC voltage of the second battery through the PCS, outputting a first DC voltage to charge the first battery.

[0043] In this embodiment, the second switch K2 and the third switch K3 are closed, and the first switch K1 and the fourth switch K4 are opened. The second battery charges the first battery through DC / DC boost conversion via the PCS. The voltage level of the second battery is DC200-600V, and the DC voltage level for charging the first battery is DC600-900V.

[0044] In a preferred embodiment, the charging circuit further includes a power supply transformer disposed between the power grid and the first switch; the neutral point of the power supply transformer is insulated from ground; the method further includes converting the AC voltage of the power grid into the AC voltage of the power supply through the power supply transformer.

[0045] In this embodiment, a power supply transformer is installed between the power grid and the first switch. The power supply transformer converts the AC voltage of the power grid into a power supply AC voltage. This power supply AC voltage is then converted by a PCSAC / DC converter to charge the first battery and / or the second battery. The neutral point of the power supply transformer is insulated from the ground, i.e., a neutral point ungrounded system is adopted, making short-distance power supply safer, thereby improving the safety and reliability of electric vehicle use.

[0046] As a preferred embodiment, it further includes: feeding the electrical energy of the first battery and / or the second battery back to the power grid via the PCS.

[0047] The power grid can charge electric vehicles; conversely, when the power supply from the grid is low, the electricity in the electric vehicle will be fed back to the grid, realizing bidirectional energy flow. Specifically, during peak electricity demand periods, the power supply system (PCS) converts the direct current (DC) from the battery into alternating current (AC) to supply power to the charging stations. During off-peak electricity demand periods, the PCS converts the alternating current from the grid into DC to charge the battery, storing electrical energy. This achieves peak shaving and valley filling for charging stations, improves power quality, increases reliability, and reduces costs.

[0048] Please refer to Figure 3, which is a schematic diagram of the specific structure of the charging circuit provided by the present invention.

[0049] In a preferred embodiment, the PCS includes an AC input unit, a power conversion unit, and a DC output unit connected in sequence; the AC input unit is used to input the AC voltage from the power grid; the power conversion unit is a three-phase fully controlled rectifier / inverter bridge; the three-phase fully controlled rectifier / inverter bridge is used for controllable rectification / inversion under SVPWM modulation; the DC output unit is used to output DC voltage to charge the first battery and / or the second battery.

[0050] In this embodiment, the AC input unit receives the AC voltage from the power grid. The power grid voltage is rectified under SVPWM modulation by a three-phase fully controlled rectifier / inverter bridge and then used to charge the first battery and / or the second battery via the DC output unit.

[0051] In addition, the first battery and / or the second battery are discharged to the grid via a three-phase fully controlled rectifier / inverter bridge under SVPWM modulation.

[0052] The first battery charges the second battery by stepping down and rectifying under SVPWM modulation via a three-phase fully controlled rectifier / inverter bridge; the second battery charges the first battery by stepping up and rectifying under SVPWM modulation via a three-phase fully controlled rectifier / inverter bridge.

[0053] Space Vector Pulse Width Modulation (SVPWM) is a control method for permanent magnet synchronous motors. The principle of SVPWM is to utilize different combinations of control signals from the inverter's bridge arms to make the inverter's output voltage vector trajectory as close to a circle as possible. Specifically, when a three-phase AC symmetrical sinusoidal voltage charges the motor, the AC motor generates a circular rotating magnetic field in space, thus producing a constant electromagnetic torque. If the ideal flux linkage circle in the AC motor is used as a reference circle, and the effective vectors generated by different switching modes of the inverter are used to approximate the reference circle—that is, using regular polygonal flux linkages to approximate the circular flux linkage—to form a rotating magnetic field, the purpose of controlling the motor can be achieved.

[0054] The PCS may also include an auxiliary control unit for assisting in controlling the closing or opening of the switching elements; however, this invention does not impose any particular limitation on this.

[0055] KA1 is an AC soft start switch. When powering on, KA1 needs to be closed first to charge the bus capacitor. After the soft start is completed, KA1 should be opened.

[0056] KA2 is a capacitor switching switch. When a capacitor is switched on, an inrush current occurs. The magnitude of this inrush current is related to the line impedance and the voltage difference between the capacitor and the power supply at the time of switching. In extreme cases, the inrush current can exceed 100 times the capacitor's rated current. Such a large inrush current can significantly impact the capacitor's lifespan and interfere with the power grid; therefore, minimizing the inrush current is desirable. To reduce the inrush current when switching on a capacitor, closing KA2 allows a current-limiting resistor to pre-charge the capacitor, reducing the voltage difference between the power supply and the capacitor. Then, the main contacts short-circuit the current-limiting resistor, reducing the inrush current to below 5 times the rated current. However, arcing during capacitor disconnection is unavoidable; therefore, the connection points require high precision to ensure sufficient lifespan.

[0057] As a preferred embodiment, the method further includes: using a PCS to convert the voltage of an external new energy power supply module to charge the first battery and / or the second battery; the external new energy power supply module includes a solar panel, a wind power module, or a hydropower module.

[0058] In this embodiment, the new energy power supply module can be a solar panel, a wind power module, or a hydropower module, which can output the electrical energy generated by solar energy, wind energy, or hydropower to electric vehicles or the power grid, thereby improving the power supply efficiency and economic efficiency of the electric vehicle charging system.

[0059] The charging circuit provided by the present invention is described below. The charging circuit described below and the charging method described above can be referred to in correspondence.

[0060] The present invention also provides a charging circuit, including a first switch, a second switch, a third switch, a fourth switch, and a PCS; a first terminal of the first switch is connected to the power grid; a first common terminal is formed by connecting the second terminal of the first switch and the first terminal of the third switch, and the first common terminal is connected to the first terminal of the PCS; a second common terminal is formed by connecting the first terminal of the second switch and the first terminal of the fourth switch, and the second common terminal is connected to the second terminal of the PCS; a second terminal of the second switch is connected to a first battery; a third common terminal is formed by connecting the second terminal of the third switch and the second terminal of the fourth switch, and the third common terminal is connected to a second battery; the charging voltage level of the second battery is not higher than the charging voltage level of the first battery; the first battery and / or the second battery are charged by the above-described charging method.

[0061] The vehicle provided by the present invention will be described below. The vehicle described below and the charging method described above can be referred to in correspondence.

[0062] The present invention also provides a vehicle including the above-described charging circuit.

[0063] The vehicle can be an electric car or an electric excavator; this invention does not impose any particular limitation.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A charging method, characterized in that, This invention is applied to a charging circuit, which includes a first switch, a second switch, a third switch, a fourth switch, and an energy storage converter (PCS). The first terminal of the first switch is connected to the power grid. A first common terminal is formed by connecting the second terminal of the first switch to the first terminal of the third switch, and this first common terminal is connected to the first terminal of the PCS. A second common terminal is formed by connecting the first terminal of the second switch to the first terminal of the fourth switch, and this second common terminal is connected to the second terminal of the PCS. The second terminal of the second switch is connected to a first battery. A third common terminal is formed by connecting the second terminal of the third switch to the second terminal of the fourth switch, and this third common terminal is connected to a second battery. The charging voltage level of the second battery is not higher than that of the first battery. The charging method includes: In the first operating state, the PCS rectifies the AC voltage of the power grid and outputs a first DC voltage to charge the first battery; the first operating state is to close the first switch and the second switch, and open the third switch and the fourth switch; In the second operating state, after the first DC voltage of the first battery is stepped down by the PCS, a second DC voltage is output to charge the second battery; the second operating state is to close the second switch and the third switch, and open the first switch and the fourth switch; the first DC voltage is greater than the second DC voltage.

2. The charging method according to claim 1, characterized in that, Also includes: In the third operating state, the AC voltage of the power grid is rectified by the PCS and the first DC voltage is output to charge the second battery; the third operating state is to close the first switch and the fourth switch, and open the second switch and the third switch.

3. The charging method according to claim 1, characterized in that, Also includes: In the fourth operating state, the AC voltage of the power grid is rectified by the PCS and the first DC voltage is output to charge the first battery and the second battery simultaneously; the fourth operating state is to close the first switch, the second switch and the fourth switch, and open the third switch.

4. The charging method according to claim 1, characterized in that, Also includes: In the second operating state, the second DC voltage of the second battery is boosted by the PCS, and then the first DC voltage is output to charge the first battery.

5. The charging method according to claim 1, characterized in that, The charging circuit also includes a power supply transformer disposed between the power grid and the first switch; The neutral point of the power supply transformer is insulated from ground; The method further includes: The power supply transformer converts the AC voltage of the power grid into the AC voltage for power supply.

6. The charging method according to claim 1, characterized in that, Also includes: The PCS feeds the electrical energy of the first battery and / or the second battery back to the power grid.

7. The charging method according to claim 1, characterized in that, The PCS includes an AC input unit, a power conversion unit, and a DC output unit connected in sequence. The AC input unit is used to input the AC voltage from the power grid; The power conversion unit is a three-phase fully controlled rectifier / inverter bridge; the three-phase fully controlled rectifier / inverter bridge is used for controllable rectification / inversion under SVPWM modulation; The DC output unit is used to output DC voltage to charge the first battery and / or the second battery.

8. The charging method according to any one of claims 1 to 7, characterized in that, Also includes: The PCS converts the voltage of the external new energy power supply module to charge the first battery and / or the second battery. The external new energy power supply module includes solar panels, wind power modules, or hydropower modules.

9. A charging circuit, characterized in that, The device includes a first switch, a second switch, a third switch, a fourth switch, and an energy storage converter (PCS). A first terminal of the first switch is connected to the power grid. A first common terminal is formed by connecting the second terminal of the first switch to the first terminal of the third switch. This first common terminal is connected to the first terminal of the PCS. A second common terminal is formed by connecting the first terminal of the second switch to the first terminal of the fourth switch. This second common terminal is connected to the second terminal of the PCS. A second terminal of the second switch is connected to a first battery. A third common terminal is formed by connecting the second terminal of the third switch to the second terminal of the fourth switch. This third common terminal is connected to a second battery. The charging voltage level of the second battery is not higher than the charging voltage level of the first battery. The first battery and / or the second battery are charged using the charging method described in any one of claims 1 to 8.

10. A vehicle, characterized in that, Includes the charging circuit as described in claim 9.

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