Charging method, charging circuit and vehicle

Abstract

The present invention relates to the field of charging technology and provides a charging method, charging circuit, and vehicle. The method comprises: in a first operating state, rectifying the AC voltage of the power grid via 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 via 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 being greater than the second DC voltage. The present invention can broaden the DC voltage range to meet different battery charging requirements.

Description

Technical Field

[0001] The present invention relates to the field of charging technology, and in particular to a charging method, a charging circuit and a vehicle. Background Art

[0002] Electric vehicles use clean electricity as their power source, improving resource efficiency and balancing transportation resources. A power conversion system (PCS) controls the charging and discharging of electric vehicle batteries, converting AC to DC. For a 400V AC (alternating current) grid, the minimum DC voltage converted by the PCS using existing charging methods is approximately 600V DC (direct current). However, if the battery requires a voltage lower than 600V DC, existing methods, due to their limited voltage range, will not be able to meet power requirements. Summary of the Invention

[0003] The present invention provides a charging method, a charging circuit and a vehicle, which can broaden the voltage range of direct current to meet different battery charging requirements.

[0004] The present invention provides a charging method, which is applied to a charging circuit. The charging circuit includes a first switch, a second switch, a third switch, a fourth switch, and a PCS; a first end of the first switch is connected to a power grid, an end where the second end of the first switch is connected to the first end of the third switch is a first common end, the first common end is connected to the first end of the PCS, an end where the first end of the second switch is connected to the first end of the fourth switch is a second common end, the second common end is connected to the second end of the PCS, the second end of the second switch is connected to a first battery, an end where the second end of the third switch is connected to the second end of the fourth switch is a third common end, and the third common end is connected to the second battery ; 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 working state, after rectifying the AC voltage of the power grid through the PCS, outputting a first DC voltage to charge the first battery; the first working state is to close the first switch and the second switch, and disconnect the third switch and the fourth switch; in a second working 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 working state is to close the second switch and the third switch, and disconnect the first switch and the fourth switch; the first DC voltage is greater than the second DC voltage.

[0005] A charging method provided by the present invention further includes: in a third working state, rectifying the AC voltage of the power grid through the PCS to output the first DC voltage to charge the second battery; the third working state is to close the first switch and the fourth switch, and open the second switch and the third switch.

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

[0007] A charging method provided by the present invention further includes: in the second working state, boosting the second DC voltage of the second battery by the PCS, and then outputting the first DC voltage to charge the first battery.

[0008] According to a charging method provided by the present invention, the charging circuit also includes a power supply transformer arranged between the power grid and the first switch; the neutral point of the power supply transformer is insulated from the ground; and the method further includes: converting the AC voltage of the power grid into a power supply AC voltage through the power supply transformer.

[0009] A charging method provided according to the present invention further includes: feeding back the electric energy of the first battery and / or the second battery to a power grid through the PCS.

[0010] 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 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 to perform 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.

[0011] According to a charging method provided by the present invention, the method further includes: charging the first battery and / or the second battery after converting the voltage of an 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 water power module.

[0012] The present invention also provides a charging circuit, comprising a first switch, a second switch, a third switch, a fourth switch, and a PCS; a first end of the first switch is connected to a power grid, an end where the second end of the first switch is connected to the first end of the third switch is a first common end, the first common end is connected to the first end of the PCS, an end where the first end of the second switch is connected to the first end of the fourth switch is a second common end, the second common end is connected to the second end of the PCS, a second end of the second switch is connected to a first battery, an end where the second end of the third switch is connected to the second end of the fourth switch is a third common end, and the third common end is connected to a second battery; a charging voltage level of the second battery is not higher than a charging voltage level of the first battery; the first battery and / or the second battery is charged using the above-mentioned charging method.

[0013] The present invention also provides a vehicle comprising the above-mentioned charging circuit.

[0014] The present invention provides a charging method, charging circuit, and vehicle. The method includes: in a first operating state, a PCS rectifies the AC voltage of the power grid and outputs a first DC voltage to charge 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, the PCS steps down the first DC voltage of the first battery and outputs a second DC voltage to charge 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. The present invention can broaden the DC voltage range to meet different battery charging requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the present invention or the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 It is a flow chart of the charging method provided by the present invention.

[0017] Figure 2 It is a structural schematic diagram of the charging circuit provided by the present invention.

[0018] Figure 3 It is a schematic diagram of the specific structure of the charging circuit provided by the present invention. DETAILED DESCRIPTION

[0019] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0020] As the global energy crisis continues to deepen, oil resources are becoming increasingly depleted, and the harm of air pollution and global temperature rise is increasing, energy conservation and emission reduction are the main directions for the development of future automotive technology. As a new generation of transportation, electric vehicles have incomparable advantages over traditional vehicles in terms of energy conservation and emission reduction, and reducing human dependence on traditional fossil energy. PCS can convert AC power into DC power to charge the battery, and can also convert battery DC power into AC power and feed it into the power grid. For PCS used in commercial vehicle battery swap stations, it can realize charging, storage and replacement in one, and can charge and discharge the batteries in the battery swap station. Some application manufacturers need to charge batteries outside the station, and need an external charging terminal. By controlling the switching devices, the charging switching between the station and the outside can be realized. In the existing charging method, PCS converts AC power into DC power with a minimum voltage of AC voltage. For an AC400V system, the converted DC voltage is DC565V. Taking voltage fluctuations into account, the minimum voltage is DC600V. However, if the battery of an electric vehicle requires a voltage level lower than 600V, the external charging gun cannot charge vehicles with a voltage platform lower than DC600V.

[0021] Please refer to Figure 1 , Figure 1 This is a schematic flow chart of the charging method provided by the present invention.

[0022] Please refer to Figure 2 , Figure 2 This is a structural diagram of the charging circuit provided by the present invention.

[0023] To solve the technical problems existing in the prior art, the present invention provides a charging method, which is applied to a charging circuit. The charging circuit includes a first switch, a second switch, a third switch, a fourth switch, and a PCS. A first end of the first switch is connected to a power grid, an end where the second end of the first switch is connected to the first end of the third switch serves as a first common end, the first common end is connected to the first end of the PCS, an end where the first end of the second switch is connected to the first end of the fourth switch serves as a second common end, the second common end is connected to the second end of the PCS, a second end of the second switch is connected to a first battery, an end where the second end of the third switch is connected to the second end of the fourth switch serves as a third common end, and the third common end is connected to a second battery. A charging voltage level of the second battery is no higher than a charging voltage level of the first battery.

[0024] Charging methods include:

[0025] 101: In a first working state, the PCS rectifies the AC voltage of the power grid to output a first DC voltage for charging the first battery. The first working state is to close the first switch and the second switch, and to open the third switch and the fourth switch.

[0026] 102: In the second working 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 working 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.

[0027] In the present invention, by closing the first and second switches K1 and K2 and opening the third and fourth switches K3 and K4, AC power from the grid is converted to DC power by the PCS and then charged to the first battery. The grid voltage level is AC400V, and the DC voltage level used to charge the first battery is DC600-900V.

[0028] 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) performs DC / DC step-down conversion through the PCS to charge the second battery (battery 2). 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 requirements and improving charging efficiency.

[0029] It should be noted that the energy storage converter controls the charging and discharging of the battery, converting AC to DC. It also stores electrical energy and can directly power loads in the absence of an external power grid. The PCS consists of a DC / AC bidirectional converter and a control unit. The PCS controller receives control commands from the backend via communication and controls the converter to charge or discharge the battery based on the sign and magnitude of the power command, thereby regulating the active and reactive power of the grid. The PCS controller communicates with the BMS (Battery Management System) via a CAN (Controller Area Network) interface to obtain battery pack status information. This allows for protective charging and discharging of the battery, ensuring safe operation.

[0030] The input power is connected to the DC port of the PCS. The power electronics in the PCS then convert the power to AC. The power electronics in the PCS include thyristors, IGBTs, and MOSFETs. The operating principle of a PCS can be divided into three parts: the input circuit, the power electronics, and the output circuit.

[0031] The input circuit is the DC port of the PCS, which receives DC power from the power system. It typically consists of a DC power supply, filter capacitors, and protection circuits. The DC power supply can be a battery, photovoltaic cell, wind turbine, or other source. The filter capacitor removes high-frequency noise from the input power supply, while the protection circuit protects the PCS power electronics from overvoltage or overcurrent.

[0032] Power electronic devices are core components of PCSs, 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, thereby achieving power conversion. The choice of power electronic device 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.

[0033] The output circuit is the AC port of the PCS, which outputs the converted power to the power system. It typically consists of filter capacitors, filter inductors, and protection circuits. The filter capacitors and inductors remove high-frequency noise from the output power supply, while the protection circuits protect the PCS power electronics from overvoltage or overcurrent.

[0034] The BMS accurately estimates the power battery pack's state of charge (SOC), or the remaining charge in the battery, ensuring the SOC remains within a reasonable range to prevent damage to the battery due to overcharging or over-discharging. It also displays the remaining energy in the electric vehicle's energy storage battery, or the battery's SOC, at all times. During the battery charging and discharging process, the BMS collects the terminal voltage and temperature, charge and discharge current, and total battery pack voltage of each cell in the electric vehicle's battery pack in real time to prevent overcharging or over-discharging. It also provides timely battery status information, identifying problematic cells and maintaining the reliability and efficiency of the entire battery pack, making it possible to implement a remaining charge estimation model. The BMS also enables balanced charging of individual cells, ensuring that each cell in the battery pack reaches a consistent and balanced state.

[0035] Battery power consumption periods are specifically divided into: valley electricity price period, flat electricity price period and peak electricity price period. Different electricity price periods can be divided by the local power supply department based on local electricity consumption data statistics.

[0036] The battery can be selected from one or more 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.

[0037] As a preferred embodiment, it also includes: in a third working 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 working state is to close the first switch and the fourth switch, and open the second switch and the third switch.

[0038] In this embodiment, the first and fourth switches K1 and K4 are closed, and the second and third switches K2 and K3 are opened. The grid AC power is converted to DC power by the PCS to charge the second battery. The grid voltage level is AC400V, and the output DC voltage level is DC600-900V.

[0039] As a preferred embodiment, it also includes: in a fourth working state, after rectifying the AC voltage of the power grid through the PCS, outputting a first DC voltage to simultaneously charge the first battery and the second battery; the fourth working state is to close the first switch, the second switch and the fourth switch, and open the third switch.

[0040] 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 of the grid is converted into DC power by the PCS to charge the first battery and the second battery simultaneously.

[0041] As a preferred embodiment, the method further includes: in the second working state, boosting the second DC voltage of the second battery by the PCS, and outputting the first DC voltage to charge the first battery.

[0042] 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 performs DC / DC boost conversion through the PCS to charge the first battery. The voltage level of the second battery is DC200-600V, and the DC voltage level for charging the first battery is DC600-900V.

[0043] As a preferred embodiment, the charging circuit further includes a power supply transformer arranged between the power grid and the first switch; the neutral point of the power supply transformer is insulated from the ground; and the method further includes: converting the AC voltage of the power grid into a power supply AC voltage through the power supply transformer.

[0044] In this embodiment, a power transformer is provided between the power grid and the first switch. The power transformer converts the AC voltage of the power grid into a power supply AC voltage. The power supply AC voltage undergoes PCS AC / DC conversion to charge the first battery and / or the second battery. The neutral point of the power transformer is insulated from the ground, i.e., a neutral point ungrounded system is employed. This makes short-distance power supply safer, thereby improving the safety and reliability of electric vehicles.

[0045] As a preferred embodiment, the method further includes: feeding back the electric energy of the first battery and / or the second battery to the power grid via the PCS.

[0046] The power grid can charge electric vehicles; conversely, when the grid's power supply is low, the electricity in the electric vehicle is fed back to the grid, achieving a two-way flow of energy. Specifically, during peak hours, the PCS converts the battery's DC power into AC power to power the charging pile. During off-peak hours, the PCS converts the grid's AC power into DC power to charge the battery, storing the energy and shaving peak loads for the charging pile, improving power quality, increasing reliability, and reducing costs.

[0047] Please refer to Figure 3 , Figure 3 This is a schematic diagram of the specific structure of the charging circuit provided by the present invention.

[0048] As 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 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; the DC output unit is used to output a DC voltage to charge the first battery and / or the second battery.

[0049] In this embodiment, the AC input unit inputs the AC voltage of the grid, the grid voltage passes through a three-phase fully controlled rectifier / inverter bridge, performs controllable rectification under SVPWM modulation, and charges the first battery and / or the second battery through the DC output unit.

[0050] In addition, the first battery and / or the second battery are discharged to the grid through a three-phase fully controlled rectifier / inverter bridge and inverter under SVPWM modulation.

[0051] The first battery is charged by the three-phase full-controlled rectifier / inverter bridge and the second battery is charged by the step-down rectifier under SVPWM modulation; the second battery is charged by the three-phase full-controlled rectifier / inverter bridge and the first battery is charged by the step-up rectifier under SVPWM modulation.

[0052] Space vector pulse width modulation (SVPWM) is a control method for permanent magnet synchronous motors. The principle of SVPWM is to use different combinations of switching control signals from the inverter's bridge arms to make the trajectory of the inverter's output voltage vector as close to a circle as possible. Specifically, when a three-phase AC symmetrical sinusoidal voltage charges the motor, it generates a circular rotating magnetic field in space, thereby producing a constant electromagnetic torque. If the ideal flux linkage circle in the AC motor is used as a reference circle, the effective vectors generated by different inverter switching patterns are used to approximate the reference circle. In other words, regular polygonal magnetic links are used to approximate the circular flux linkage, forming a rotating magnetic field, thus achieving the purpose of motor control.

[0053] The PCS may further include an auxiliary control unit for assisting in controlling the closing or opening of the switching element, which is not particularly limited in the present invention.

[0054] KA1 is the AC soft start switch. When power is turned on, KA1 needs to be closed first to charge the bus capacitor. KA1 should be disconnected after the soft start is completed.

[0055] KA2 is the capacitor switching switch. When a capacitor is switched on, an inrush current is generated. The magnitude of this current is related to the line impedance and the voltage difference between the capacitor and the power supply when the capacitor is switched on. 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, so it is desirable to minimize the inrush current. To reduce the inrush current when the capacitor is switched on, KA2 is closed. A current-limiting resistor is first connected to the circuit to pre-charge the capacitor, thereby reducing the voltage difference between the power supply and the capacitor. The main contacts then short-circuit the current-limiting resistor, reducing the inrush current to less than five times the rated current. However, arcing is inevitable when the capacitor is switched off, so high requirements are placed on the contact to ensure a sufficient service life.

[0056] As a preferred embodiment, it also includes: charging the first battery and / or the second battery after converting the voltage of the external new energy power supply module through PCS; the external new energy power supply module includes a solar panel, a wind power module or a water power module.

[0057] In this embodiment, the new energy power supply module can be a solar panel, or a wind power module or a hydropower module, which can output the electricity generated by light energy, wind energy or hydropower to the electric vehicle or the power grid, thereby improving the power supply efficiency and economic efficiency of the electric vehicle charging system.

[0058] The charging circuit provided by the present invention is described below. The charging circuit described below and the charging method described above can be referenced to each other.

[0059] The present invention also provides a charging circuit, comprising a first switch, a second switch, a third switch, a fourth switch and a PCS; a first end of the first switch is connected to a power grid, an end where the second end of the first switch is connected to the first end of the third switch is a first common end, the first common end is connected to the first end of the PCS, an end where the first end of the second switch is connected to the first end of the fourth switch is a second common end, the second common end is connected to the second end of the PCS, the second end of the second switch is connected to the first battery, an end where the second end of the third switch is connected to the second end of the fourth switch is a third common end, and the third common end is connected to the second battery; a charging voltage level of the second battery is not higher than a charging voltage level of the first battery; the first battery and / or the second battery are charged using the above-mentioned charging method.

[0060] The vehicle provided by the present invention is described below. The vehicle described below and the charging method described above can be referenced to each other.

[0061] The present invention also provides a vehicle comprising the above-mentioned charging circuit.

[0062] The vehicle may be an electric car or an electric excavator, and the present invention does not impose any particular limitation thereto.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A charging method, characterized in that: A charging circuit for an electric excavator includes a first switch, a second switch, a third switch, a fourth switch, and a PCS; a first end of the first switch is connected to a power grid, a second end of the first switch is connected to a first end of the third switch as a first common end, the first common end is connected to a first end of the PCS, a first end of the second switch is connected to a first end of the fourth switch as a second common end, the second common end is connected to a second end of the PCS, a second end of the second switch is connected to a first battery, a second end of the third switch is connected to a second end of the fourth switch as a third common end, and the third common end is connected to a second battery; a charging voltage level of the second battery is not higher than a charging voltage level of the first battery; a charging voltage level of the first battery is DC600-900V, and a charging voltage level of the second battery is DC200-600V; the PCS communicates with a BMS to obtain a battery state of charge; The charging method includes: In a first working state, the PCS rectifies the AC voltage of the power grid to output a first DC voltage for charging the first battery. The first working state is to close the first switch and the second switch, and open the third switch and the fourth switch. In a second working state, the PCS steps down the first DC voltage of the first battery and outputs a second DC voltage to charge the second battery. The second working state is such that the second switch and the third switch are closed and the first switch and the fourth switch are open. The first DC voltage is greater than the second DC voltage. Also includes: Feeding back the electric energy of the first battery and / or the second battery to the power grid through the PCS; The charging circuit further includes a power supply transformer disposed between the power grid and the first switch; a neutral point of the power supply transformer is insulated from the ground; The method further comprises: converting the AC voltage of the power grid into a power supply AC voltage through the power supply transformer; The charging circuit also includes an AC soft start switch and a capacitor switching switch; The method further comprises: When powering on, it is necessary to first close the AC soft start switch to charge the bus capacitor, and then disconnect the AC soft start switch after the soft start is completed; Closing the capacitor switching switch to reduce the inrush current when the capacitor is put into operation; 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; The DC output unit is used to output a DC voltage to charge the first battery and / or the second battery.

2. The charging method according to claim 1, wherein: Also includes: In the third working state, after the AC voltage of the power grid is rectified by the PCS, the first DC voltage is output to charge the second battery; the third working 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, wherein: Also includes: In a fourth working state, after the AC voltage of the power grid is rectified by the PCS, the first DC voltage is output to simultaneously charge the first battery and the second battery. The fourth working 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, wherein: Also includes: In the second working state, the second DC voltage of the second battery is boosted by the PCS, and the first DC voltage is output to charge the first battery.

5. The charging method according to any one of claims 1 to 4, characterized in that: Also includes: The PCS converts the voltage of the external new energy power supply module into a voltage 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 water power module.

6. A charging circuit for an electric excavator, characterized in that: The invention comprises a first switch, a second switch, a third switch, a fourth switch and a PCS; a first end of the first switch is connected to the grid, a second end of the first switch is connected to the first end of the third switch as a first common end, the first common end is connected to the first end of the PCS, a first end of the second switch is connected to the first end of the fourth switch as a second common end, the second common end is connected to the second end of the PCS, a second end of the second switch is connected to the first battery, a second end of the third switch is connected to the second end of the fourth switch as a third common end, and the third common end is connected to the second battery; a charging voltage level of the second battery is not higher than a charging voltage level of the first battery; a charging voltage level of the first battery is DC600-900V, and a charging voltage level of the second battery is DC200-600V; the PCS communicates with a BMS to obtain a battery state of charge; the first battery and / or the second battery are charged by the charging method according to any one of claims 1 to 5; The charging circuit further includes a power supply transformer disposed between the power grid and the first switch; a neutral point of the power supply transformer is insulated from the ground; and the power supply transformer is configured to convert an AC voltage of the power grid into a power supply AC voltage; The charging circuit also includes an AC soft start switch and a capacitor switching switch; 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; The DC output unit is used to output a DC voltage to charge the first battery and / or the second battery.

7. An electric excavator, characterized in that: A charging circuit for an electric excavator comprising the method of claim 6.

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