Direct current charging circuit and direct current charging pile

Abstract

The invention relates to a direct current charging circuit and a direct current charging pile. The direct current charging circuit comprises a rectification circuit, a conversion circuit and a control circuit. The rectification circuit is connected with the conversion circuit and the control circuit, and the conversion circuit is also connected with a target load; the rectifying circuit is used for accessing alternating current; the control circuit is used for determining a bus voltage reference value of the rectifying circuit according to an output voltage reference value required for charging the target load and controlling the rectifying circuit to rectify the alternating current into direct current of the bus voltage reference value; and the conversion circuit is used for regulating the direct current of the bus voltage reference value into an output voltage reference value and transmitting the output voltage reference value to a target load for charging. The rectification circuit carries out rectification according to the bus voltage reference value corresponding to the output voltage reference value required by the target load, so that compared with the prior art, the rectification circuit of a preceding stage can be associated with the output voltage reference value, a large-capacity electrolytic capacitor is not needed in the rectification circuit, and the size of the circuit is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of direct current charging, in particular to a direct current charging circuit and a direct current charging pile. BACKGROUND

[0002] At present, as a device for obtaining electric energy of electric vehicles, charging piles play a key role in the electric vehicle industry chain. Charging piles are generally divided into two types: alternating current charging piles and direct current charging piles. The alternating current charging pile is also known as a slow charging pile, which needs to rely on the vehicle-mounted charger to charge the vehicle battery. The direct current charging pile is generally referred to as a fast charging pile, which usually integrates a two-stage architecture conversion circuit inside, has high power and fast charging speed.

[0003] The two-stage architecture in the direct current charging pile includes a front-stage Vienna rectifier circuit and a rear-stage DC / DC conversion circuit. However, when charging through the direct current charging pile, the control circuit first controls the front-stage Vienna rectifier circuit to lock the received alternating current into direct current of a certain fixed bus voltage value, and then controls the rear-stage DC / DC conversion circuit to independently regulate the direct current to the output voltage reference value required for charging. Since the front-stage and the rear-stage are controlled independently, the fixed bus voltage value generated by the front-stage Vienna rectifier circuit is not directly feedback related to the output voltage reference value required by the rear-stage in real time, so that the bus capacitor in the front-stage Vienna rectifier circuit needs a large-capacity electrolytic capacitor to buffer energy (for example, in the case that the fixed bus voltage value and the output voltage reference value are greatly different), thereby resulting in a large circuit volume. SUMMARY

[0004] The main purpose of the present application is to provide a direct current charging circuit and a direct current charging pile, aiming to solve the technical problem that in the prior art, the fixed bus voltage value generated by the front-stage Vienna rectifier circuit is not directly feedback related to the output voltage reference value required by the rear-stage DC / DC conversion circuit in real time, so that the bus capacitor in the front-stage Vienna rectifier circuit needs a large-capacity electrolytic capacitor to buffer energy, thereby resulting in a large circuit volume.

[0005] To achieve the above-mentioned purpose, the present application provides a direct current charging circuit, which comprises a rectifier circuit, a conversion circuit and a control circuit.

[0006] The rectifier circuit is connected with the conversion circuit and the control circuit, and the conversion circuit is further connected with a target load.

[0007] The rectifier circuit is configured to access alternating current.

[0008] The control circuit is configured to determine a bus voltage reference value of the rectifier circuit according to an output voltage reference value required for charging the target load, and control the rectifier circuit to rectify the alternating current into direct current of the bus voltage reference value.

[0009] The conversion circuit is configured to convert the DC voltage of the bus voltage reference value into the output voltage reference value and transmit the output voltage reference value to the target load for charging.

[0010] In an embodiment, the control circuit comprises a three-phase voltage reference value generation module, a bus voltage reference value generation module, and a pulse width modulation control module.

[0011] The bus voltage reference value generation module is connected to the three-phase voltage reference value generation module and the pulse width modulation module, and the pulse width modulation module is further connected to the rectifier circuit.

[0012] The three-phase voltage reference value generation module is configured to determine the three-phase voltage reference value of the alternating current according to the output voltage reference value and an output voltage sampling value of the conversion circuit.

[0013] The bus voltage reference value generation module is configured to generate the bus voltage reference value according to the three-phase voltage reference value.

[0014] The pulse width modulation control module is configured to generate a first driving signal according to the three-phase voltage reference value, and control the rectifier circuit to rectify the alternating current into the DC voltage of the bus voltage reference value through the first driving signal.

[0015] In an embodiment, the three-phase voltage reference value generation module comprises an output voltage control submodule and a grid current control submodule.

[0016] The grid current control submodule is connected to the output voltage control submodule, the bus voltage reference value generation module, and the pulse width modulation module.

[0017] The output voltage control submodule is configured to determine an output current reference value of the conversion circuit according to the output voltage reference value and the output voltage sampling value.

[0018] The grid current control submodule is configured to obtain a three-phase voltage sampling value of the alternating current and a three-phase current sampling value of the alternating current, and determine the three-phase voltage reference value according to the output current reference value, the three-phase voltage sampling value, and the three-phase current sampling value.

[0019] In an embodiment, the output voltage control submodule is further configured to determine a voltage error between the output voltage reference value and the output voltage sampling value.

[0020] The output voltage control submodule is further configured to perform proportional-integral operation on the voltage error to obtain an active current compensation amount.

[0021] The output voltage control submodule is further configured to superimpose the active current compensation quantity on an output current sample value of the conversion circuit to obtain the output current reference value.

[0022] In an embodiment, the grid current control submodule comprises a phase-locked loop unit and a grid current control unit.

[0023] The grid current control unit is connected with the phase-locked loop unit, the output voltage control submodule and the bus voltage reference value generation module respectively.

[0024] The phase-locked loop unit is configured to determine a grid phase angle according to the three-phase voltage sample value.

[0025] The grid current control unit is configured to determine the three-phase voltage reference value according to the grid phase angle, the three-phase voltage sample value, the three-phase current sample value and the output current reference value.

[0026] In an embodiment, the phase-locked loop unit comprises a first converter, an integrator, a second converter and a phase calculation submodule.

[0027] The integrator is connected with the first converter and the second converter respectively, and the phase calculation submodule is connected with the second converter and the grid current control unit respectively.

[0028] The first converter is configured to determine a first voltage vector on an α axis and a second voltage vector on a β axis according to the three-phase voltage sample value.

[0029] The integrator is configured to extract a positive sequence component of the first voltage vector to obtain a first positive sequence voltage and extract a positive sequence component of the second voltage vector to obtain a second positive sequence voltage.

[0030] The second converter is configured to determine a third voltage vector on a q axis according to the first positive sequence voltage and the second positive sequence voltage.

[0031] The phase calculation submodule is configured to determine the grid phase angle according to the third voltage vector and an angular frequency of the alternating current.

[0032] In an embodiment, the grid current control unit comprises a third converter, a grid current control submodule and a fourth converter.

[0033] The third converter is connected with the phase-locked loop unit and the grid current control submodule respectively, the grid current control submodule is further connected with the output voltage control submodule and the fourth converter respectively, and the fourth converter is further connected with the bus voltage reference value generation module.

[0034] the third transformer, configured to determine a third voltage vector and a first current vector on a q-axis, and a fourth voltage vector and a second current vector on a d-axis, according to the phase angle, the three-phase voltage sample values, the three-phase current sample values, and an angular frequency of the alternating current;

[0035] the grid current control subunit, configured to acquire a grid voltage effective value of the alternating current, and determine a first voltage reference vector on the q-axis and a second voltage reference vector on the d-axis according to the output current reference value, the third voltage vector, the first current vector, the fourth voltage vector, the second current vector, and the grid voltage effective value;

[0036] the fourth transformer, configured to determine the three-phase voltage reference values according to the first voltage reference vector and the second voltage reference vector.

[0037] In an embodiment, the grid current control subunit is further configured to determine a power reference value according to the output current reference value and the output voltage reference value;

[0038] the grid current control subunit is further configured to determine an equivalent conductance according to the power reference value and the grid voltage effective value;

[0039] the grid current control subunit is further configured to determine a first current reference vector on the q-axis according to the equivalent conductance and the third voltage vector, and determine the first voltage reference vector according to the first current reference vector, the first current vector, and the third voltage vector;

[0040] the grid current control subunit is further configured to determine a second current reference vector on the d-axis according to the equivalent conductance and the fourth voltage vector, and determine the second voltage reference vector according to the second current reference vector, the second current vector, and the fourth voltage vector.

[0041] In an embodiment, the bus voltage reference value generation module is further configured to determine a maximum voltage reference value and a minimum voltage reference value in the three-phase voltage reference values;

[0042] the bus voltage reference value generation module is further configured to determine a voltage reference difference value of the maximum voltage reference value and the minimum voltage reference value, and take the voltage reference difference value as the bus voltage reference value.

[0043] In an embodiment, the rectifier circuit includes a three-phase switching circuit;

[0044] Each phase of the switching circuit is connected with the transformation circuit and the pulse width modulation control module.

[0045] The pulse width modulation control module is further configured to control the switching operation of the switching circuit of one phase and control the switching circuit of the remaining two phases not to perform the switching operation when the rectifier circuit performs the rectification through the first driving signal.

[0046] In an embodiment, the pulse width modulation control module is further configured to obtain a bus voltage sampling value, and determine a target zero sequence component according to the three-phase voltage reference value;

[0047] The pulse width modulation control module is further configured to superimpose the three-phase voltage reference value according to the target zero sequence component;

[0048] The pulse width modulation control module is further configured to generate the first driving signal according to the bus voltage sampling value and the superimposed three-phase voltage reference value.

[0049] In an embodiment, the rectifier circuit further comprises a first thin film capacitor and a second thin film capacitor.

[0050] The upper bus, the neutral point and the lower bus of the rectifier circuit are connected with the conversion circuit.

[0051] The first end of the first thin film capacitor is connected with the upper bus, the second end of the first thin film capacitor and the first end of the second thin film capacitor are connected with the neutral point, and the second end of the second thin film capacitor is connected with the lower bus.

[0052] In an embodiment, the conversion circuit comprises a switching module, a first conversion module and a second conversion module.

[0053] The first conversion module is connected with the upper bus of the rectifier circuit, the second conversion circuit is connected with the lower bus of the rectifier circuit, the first conversion module and the second conversion module are both connected with the switching module, the control circuit, the target load and the neutral point of the rectifier circuit, and the switching module is further connected with the control circuit.

[0054] The switching module is configured to switch the first conversion module and the second conversion module in series and in parallel according to the output voltage reference value.

[0055] The control module is configured to generate a second driving signal according to the bus voltage reference value, and control the first conversion module and the second conversion module to step down the direct current of the bus voltage reference value to the output voltage reference value and transmit to the target load for charging through the second driving signal.

[0056] In an embodiment, the control circuit comprises a feedforward gain module and a bus voltage control module.

[0057] The bus voltage control module is connected with the feedforward gain module, the first conversion module and the second conversion module respectively.

[0058] The feedforward gain module is configured to acquire a quality factor and a current voltage gain of the conversion circuit, and determine a feedforward frequency according to the quality factor and the current voltage gain.

[0059] The bus voltage control module is configured to determine a first working frequency and a second working frequency according to the bus voltage reference value and the feedforward frequency, and generate the second driving signal according to the first working frequency and the second working frequency.

[0060] In an embodiment, the bus voltage control module is further configured to determine a half bus voltage reference value according to the bus voltage reference value, and acquire an upper bus voltage sampling value and a lower bus voltage sampling value.

[0061] The bus voltage control module is further configured to determine an upper bus error value between the half bus voltage reference value and the upper bus voltage sampling value, and determine a lower bus error value between the half bus voltage reference value and the lower bus voltage sampling value.

[0062] The bus voltage control module is further configured to perform proportional-integral operation on the upper bus error and the lower bus error respectively, and obtain the first working frequency by superimposing the feedforward frequency on the operated upper bus error, and obtain the second working frequency by superimposing the feedforward frequency on the operated lower bus error.

[0063] In addition, to achieve the above-mentioned purpose, the application further provides a direct current charging pile, which comprises the direct current charging circuit as described above.

[0064] The application provides a direct current charging circuit and a direct current charging pile. The direct current charging circuit comprises a rectifier circuit, a conversion circuit and a control circuit. The rectifier circuit is connected with the conversion circuit and the control circuit. The conversion circuit is further connected with a target load. The rectifier circuit is configured to access alternating current. The control circuit is configured to determine a bus voltage reference value of the rectifier circuit according to an output voltage reference value required by the target load for charging, and control the rectifier circuit to rectify the alternating current into direct current with the bus voltage reference value. The conversion circuit is configured to step down the direct current with the bus voltage reference value to the output voltage reference value, and transmit the direct current to the target load for charging.

[0065] The direct current charging circuit in the application can obtain the output voltage reference value required by the target load in working, and then determine the bus voltage reference value that the rectifier circuit can output according to the output voltage reference value, control the rectifier circuit to rectify the input alternating current into direct current of the bus voltage reference value, and then control the conversion circuit to regulate the direct current of the bus voltage reference value to the output voltage reference value, and finally the conversion circuit transmits the direct current of the output voltage reference value to the target load for power supply. Compared with the prior art, the rectifier circuit in the application is rectified according to the bus voltage reference value corresponding to the output voltage reference value required by the target load, so that the rectifier circuit of the previous stage is associated with the output voltage reference value, and thus the large-capacity electrolytic capacitor is not required in the rectifier circuit, thereby reducing the circuit size. BRIEF DESCRIPTION OF DRAWINGS

[0066] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor based on the drawings shown.

[0067] Figure 1 It is a circuit principle diagram of the traditional direct current charging circuit;

[0068] Figure 2 It is a structure block diagram of the first embodiment of the direct current charging circuit proposed by the embodiments of the present application;

[0069] Figure 3 It is a circuit principle diagram of the first conversion circuit or the second conversion circuit in the first embodiment of the direct current charging circuit proposed by the embodiments of the present application;

[0070] Figure 4 It is an architecture diagram of the control circuit in the second embodiment of the direct current charging circuit proposed by the embodiments of the present application;

[0071] Figure 5 It is a control strategy schematic diagram of the control circuit in the second embodiment of the direct current charging circuit proposed by the embodiments of the present application;

[0072] Figure 6 It is a control strategy schematic diagram of the phase-locked loop unit in the second embodiment of the direct current charging circuit proposed by the embodiments of the present application;

[0073] Figure 7 It is a control strategy schematic diagram of the pulse width modulation control module in the second embodiment of the direct current charging circuit proposed by the embodiments of the present application.

[0074] EXPLANATION OF DRAWINGS:

[0075] Rectifier circuit 1, conversion circuit 2, switching module 21, first conversion module 22, second conversion module 23, control circuit 3, three-phase voltage reference value generation module 31, output voltage control sub-module 311, grid current control sub-module 312, phase-locked loop unit 3121, grid current control unit 3122, bus voltage reference value generation module 32, pulse width modulation control module 33, feedforward gain module 34, bus voltage control module 35, first converter 41, integrator 42, second converter 43, phase calculation sub-unit 44, third converter 45, grid current control sub-unit 46, fourth converter 47, A-phase AC power supply Ua, B-phase AC power supply Ub, C-phase AC power supply Uc, A-phase inductor LA, B-phase inductor LB, C-phase inductor LC, first bus capacitor to second bus capacitor Cm1-Cm2, first rectifier tube to twelfth rectifier tube D1-D12, first switch tube to sixth switch tube Q1-Q6, first thin film capacitor to second thin film capacitor Cb1-Cb2, first transistor to sixth transistor T1-T6, first DC capacitor to third DC capacitor Cr1-Cr3, first resonance inductor to third resonance inductor Lr1-Lr3, first filter inductor to third filter inductor Lm1-Lm3, first transformer to third transformer Tn1-Tn3, output capacitor Co.

[0076] The implementation, functional features and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0077] It should be understood that the specific embodiments described herein merely exemplify the application and do not limit the application.

[0078] The technical solutions in the embodiments of the present application will be described clearly and completely in the embodiments of the present application with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0079] It should be noted that all the directionality indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present application are only used to explain the relative position relationship, movement condition, etc. between the components in a certain posture (as shown in the drawings). If the certain posture changes, the directionality indications also change accordingly.

[0080] In addition, the descriptions involving "first", "second", etc. in the present application are only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first", "second" can explicitly or implicitly include at least one of the features. In addition, the technical solutions of various embodiments can be combined with each other, but it must be based on the fact that a person skilled in the art can realize it, and when the combination of technical solutions contradicts each other or cannot be realized, it should be considered that the combination of technical solutions does not exist and is not within the protection scope required by the present application.

[0081] It should be noted that at present, as a device for electric vehicles to obtain electric energy, charging piles play a key role in the electric vehicle industry chain. Charging piles are generally divided into two types: AC charging piles and DC charging piles. AC charging piles are also known as slow charging piles, which need to rely on on-board chargers to charge the battery of the vehicle. DC charging piles are generally referred to as fast charging piles, which usually integrate a two-stage architecture conversion circuit inside, with high power and fast charging speed.

[0082] The two-stage architecture in the DC charging pile includes a front-stage Vienna rectifier circuit and a rear-stage DC / DC conversion circuit. However, when charging through the DC charging pile, the control circuit 3 first controls the front-stage Vienna rectifier circuit to lock the received AC power into a certain fixed bus voltage value of DC power, and then controls the rear-stage DC / DC conversion circuit to independently regulate the DC power to the required output voltage reference value. Since the front-stage and rear-stage are controlled independently, the fixed bus voltage value generated by the front-stage has no direct feedback connection with the real-time required output voltage reference value of the rear-stage, thus resulting in the need for large-capacity electrolytic capacitors for the bus capacitor in the front-stage Vienna rectifier circuit to buffer energy (for example, in the case where the fixed bus voltage value and the output voltage reference value differ greatly), thereby resulting in a large circuit volume.

[0083] For ease of understanding, reference is made to Figure 1 , Figure 1 is a circuit schematic diagram of a conventional DC charging circuit. As shown in Figure 1 , the conventional DC charging circuit can include a Vienna rectifier circuit and a DC / DC conversion circuit, wherein the input end of the Vienna rectifier circuit can be connected with an AC power grid for accessing AC power.

[0084] As shown in Figure 1 , the three phases of AC power can be denoted as A-phase AC power supply Ua, B-phase AC power supply Ub, and C-phase AC power supply Uc, and the A-phase AC power supply Ua, B-phase AC power supply Ub, and C-phase AC power supply Uc are connected with corresponding rectifier bridge arms, respectively.

[0085] Continuing as Figure 1As shown, the Vienna rectifier circuit may include: A-phase inductor LA, B-phase inductor LB, C-phase inductor LC, A-phase rectifier bridge arm, B-phase rectifier bridge arm, C-phase rectifier bridge arm, A-phase switching switch, B-phase switching switch, C-phase switching switch, first bus capacitor Cm1 and second bus capacitor Cm2.

[0086] Phase A rectifier bridge arm may include: first rectifier tube D1 and second rectifier tube D2; Phase B rectifier bridge arm may include: third rectifier tube D3 and fourth rectifier tube D4; Phase C rectifier bridge arm may include: fifth rectifier tube D5 and sixth rectifier tube D6.

[0087] A-phase switching switch may include: a first switch Q1 and a second switch Q2; B-phase switching switch may include: a third switch Q3 and a fourth switch Q4; C-phase switching switch may include: a fifth switch Q5 and a sixth switch Q6;

[0088] like Figure 1 As shown, the point connecting the second terminal of the first capacitor and the first terminal of the second capacitor can be taken as the neutral point. The first terminal of the A-phase inductor LA can be connected to the A-phase AC power supply Ua. The second terminal of the A-phase inductor LA can be connected to the anode of the first rectifier diode D1, the cathode of the second rectifier diode D2, and the first terminal of the first switch diode Q1. The second terminal of the first switch diode Q1 is connected to the first terminal of the second switch diode Q2. The second terminal of the second switch diode Q2 is connected to the neutral point of rectifier circuit 1. The first terminal of the B-phase inductor LB can be connected to the B-phase AC power supply Ub. The second terminal of the B-phase inductor LB can be connected to the third rectifier diode D3. The anode of the first rectifier, the cathode of the fourth rectifier diode D4, and the first terminal of the third switch diode Q3 are connected. The second terminal of the third switch diode Q3 is connected to the first terminal of the fourth switch diode Q4. The second terminal of the fourth switch diode Q4 is connected to the neutral point of the rectifier circuit 1. The first terminal of the C-phase inductor LC can be connected to the C-phase AC power supply Uc. The second terminal of the C-phase inductor LC can be connected to the anode of the fifth rectifier diode D5, the cathode of the sixth rectifier diode D6, and the first terminal of the fifth switch diode Q5. The second terminal of the fifth switch diode Q5 is connected to the first terminal of the sixth switch diode Q6. The second terminal of the sixth switch diode Q6 is connected to the neutral point of the rectifier circuit 1.

[0089] The cathodes of the first rectifier diode D1, the third rectifier diode D3, and the fifth rectifier diode D5, as well as the first terminal of the first bus capacitor Cm1, are connected to the upper bus. The upper bus is also connected to the DC / DC converter circuit. The second terminal of the first bus capacitor Cm1 and the first terminal of the second bus capacitor Cm2 are both connected to the neutral point and then connected to the DC / DC converter circuit. The anodes of the second rectifier diode D2, the fourth rectifier diode D4, and the sixth rectifier diode D6, as well as the second terminal of the second bus capacitor Cm2, are connected to the lower bus. The lower bus is also connected to the DC / DC converter circuit, which is also connected to the target load.

[0090] It is emphasized that the control end of the first switch tube Q1 to the control end of the sixth switch tube Q6 can also be connected with the control circuit 3. When charging the target load, the Vienna rectifier circuit can receive three-phase alternating current provided by the alternating current power grid, and then the control circuit 3 can first output a driving signal to the first switch tube Q1 to the sixth switch tube Q6, so as to control the Vienna rectifier circuit to lock the voltage value of the alternating current as a certain fixed bus voltage value, and then transmit the direct current of the bus voltage value to the DC / DC conversion circuit, and the control circuit 3 outputs another driving signal to the DC / DC conversion circuit, so that the DC / DC conversion circuit can regulate the direct current of the bus voltage value to the output voltage reference value required for charging the target load.

[0091] Obviously, since the traditional front and rear stages are independently controlled, the fixed bus voltage value generated by the front-stage Vienna rectifier circuit has no direct feedback connection with the output voltage reference value required by the rear stage in real time, so that the first bus capacitor Cm1 and the second bus capacitor Cm2 in the front-stage Vienna rectifier circuit need large-capacity electrolytic capacitors to buffer energy, thereby resulting in a large circuit volume.

[0092] To solve the above technical problems, the embodiment provides a direct current charging circuit. When the direct current charging circuit works, the control circuit 3 can first obtain the output voltage reference value required for charging the target load, then determine the bus voltage reference value that the rectifier circuit 1 can output according to the output voltage reference value, control the rectifier circuit 1 to rectify the alternating current accessed into direct current of the bus voltage reference value, and then control the conversion circuit 2 to regulate the direct current of the bus voltage reference value to the output voltage reference value, and finally the conversion circuit 2 transmits the direct current of the output voltage reference value to the target load for power supply. Since the rectifier circuit 1 in the embodiment rectifies the bus voltage reference value corresponding to the output voltage reference value required by the target load, compared with the prior art, the embodiment can associate the rectifier circuit 1 of the front stage with the output voltage reference value, so that the rectifier circuit 1 does not need large-capacity electrolytic capacitors, thereby reducing the circuit volume.

[0093] For the convenience of understanding, the following will be combined with Figures 2 to 7 The direct current charging circuit provided by the embodiment of the application will be specifically introduced.

[0094] Referring to Figure 2 , Figure 2 The structure block diagram of the first embodiment of the direct current charging circuit provided by the embodiment of the application.

[0095] As Figure 2 shown, in the embodiment, the direct current charging circuit can include a rectifier circuit 1, a conversion circuit 2 and a control circuit 3.

[0096] The rectifier circuit 1 is connected with the conversion circuit 2 and the control circuit 3, and the conversion circuit 2 is further connected with a target load.

[0097] It should be noted that the above-mentioned can be applied in the direct current charging pile in the embodiment, and of course can also be applied in other devices which need to charge the target load with direct current, and the direct current charging pile is used for illustration in the embodiment. The above-mentioned target load can be any load which needs to be charged with direct current, and the power battery of the automobile is used for illustration in the embodiment.

[0098] It should be further noted that the above-mentioned rectifier circuit 1 in the embodiment can be any circuit with rectification function, and the Vienna rectifier circuit is still used for illustration in the embodiment consistent with the tradition, as shown in Figure 2 The specific components and connection relationship in the rectifier circuit 1 in the embodiment can be referred to the related description in Figure 1 , and the embodiment does not add redundant description.

[0099] It can be understood that the above-mentioned conversion circuit 2 in the embodiment can be a circuit for DC / DC conversion, for example, an Inductor-Inductor-Capacitor (LLC) converter, and of course other converters can also be used, and the embodiment does not limit this.

[0100] It can also be understood that the above-mentioned control circuit 3 in the embodiment can be any circuit for driving the switch tube in the rectifier circuit 1 and the switch tube in the conversion circuit 2, so as to complete the direct current charging, for example, a controller and the like, and the embodiment does not limit this. The control circuit 3 in the embodiment can output a driving signal to drive the rectifier circuit 1 and the conversion circuit 2 to work, and the driving signal can be a Pulse Width Modulation (PWM) signal.

[0101] As shown in Figure 1 , in the embodiment, in order to reduce the volume of the first bus capacitor Cm1 and the second bus capacitor Cm2, the rectifier circuit 1 is used for connecting the alternating current.

[0102] The control circuit 3 is used for determining the bus voltage reference value of the rectifier circuit 1 according to the output voltage reference value required by the target load charging, and controlling the rectifier circuit 1 to rectify the alternating current into direct current with the bus voltage reference value.

[0103] The conversion circuit 2 is used for regulating the direct current with the bus voltage reference value to the output voltage reference value, and transmitting to the target load for charging.

[0104] It should be understood that the aforementioned alternating current can be any three-phase alternating current used for DC charging, such as... Figure 2 As shown, in this embodiment, the input terminal of the rectifier circuit 1 can be connected to the AC power grid (i.e., Figure 2 (Ua, Ub, and Uc) are used to receive three-phase alternating current.

[0105] It should also be understood that the aforementioned output voltage reference value can be the voltage reference value required when the target load is charging. In this embodiment, the control circuit 3 can also be communicatively connected to the target load (not shown in the figure). For example, when charging a car, after the user plugs in the charging gun, the car's charging management system can communicate with the control circuit 3, thereby informing the control circuit 3 of the voltage required for charging the power battery at this time. This voltage can be used as the aforementioned output voltage reference value. For ease of subsequent explanation, in this embodiment and the following embodiments, the aforementioned output voltage reference value is denoted as u. o * .

[0106] It should be noted that the aforementioned bus voltage reference value can be the voltage value between the upper and lower buses of rectifier circuit 1 that matches the output voltage reference value required for charging the target load, that is, the theoretical output voltage value of rectifier circuit 1 that matches the output voltage reference value required for charging the target load. Figure 2 As shown, in this embodiment, point p can be taken as a point on the upper bus of rectifier circuit 1, and point n can be taken as a point on the lower bus of rectifier circuit 1. Therefore, the aforementioned bus voltage reference value can be the voltage reference value between point p and point n. For ease of subsequent explanation, in this embodiment and the following embodiments, the aforementioned bus voltage reference value is denoted as u. pn * .

[0107] It should be emphasized that, in this embodiment, when the control circuit 3 determines the bus voltage reference value based on the output voltage reference value, it can directly use the output voltage reference value as the bus voltage reference value. Of course, other determination methods can also be used, and this embodiment does not limit this.

[0108] In practical use, when charging the target load, the control circuit 3 first receives the output voltage reference value required for charging the target load, and determines the bus voltage reference value output by the rectifier circuit 1 based on the output voltage reference value. Then, it controls the rectifier circuit 1 to rectify the AC power into DC power of the bus voltage reference value and transmits this DC power to the conversion circuit 2. Since the target load requires a wide range and isolation of DC power during charging, in this embodiment, the conversion circuit 2 can be controlled to adjust the DC power of the bus voltage reference value to the output voltage reference value, and finally output it to the target load for charging.

[0109] Since the rectifier circuit 1 in the embodiment rectifies the bus voltage reference value corresponding to the output voltage reference value required by the target load, compared with the prior art, the rectifier circuit 1 in the embodiment is associated with the output voltage reference value, and thus the electrolytic capacitor with large capacity is not required in the rectifier circuit 1, and the circuit volume is reduced.

[0110] Further, since it has been described above that the electrolytic capacitor with large capacity is not required, but considering that if the capacitor is not directly arranged, the voltage fluctuation will affect the circuit, in order to absorb the small energy fluctuation, the bus capacitor in the embodiment is replaced by the electrolytic capacitor, as shown in the following figure, in the embodiment, the rectifier circuit 1 further comprises a first thin film capacitor Cb1 and a second thin film capacitor Cb2. Figure 2

[0111] The upper bus, the neutral point and the lower bus of the rectifier circuit 1 are connected with the conversion circuit 2.

[0112] The first end of the first thin film capacitor Cb1 is connected with the upper bus, the second end of the first thin film capacitor Cb1 and the first end of the second thin film capacitor Cb2 are connected with the neutral point, and the second end of the second thin film capacitor Cb2 is connected with the lower bus.

[0113] As shown in the following figure, in the embodiment, the first end of the first electrolytic capacitor is connected with the p point on the upper bus, and the second end of the second electrolytic capacitor is connected with the n point on the lower bus. Figure 2

[0114] Further, the electrolytic capacitor with small volume is used to replace the bus capacitor in the embodiment, so that the volume of the circuit is reduced. It also needs to be emphasized that, compared with the prior art that the front stage adopts fixed power output and the rear stage adopts fixed voltage output, since the rectifier circuit 1 in the front stage outputs according to the bus voltage reference value, and the bus voltage reference value is determined according to the output voltage reference value of the target load, compared with the above-mentioned way, the capacitance value of the electrolytic capacitor in the embodiment can be smaller.

[0115] Further, in order to make the charging circuit compatible with a wide range of output voltage requirements, for example, compatible with 200V to 1000V, in the embodiment, as shown in the following figure, the conversion circuit 2 comprises a switching module 21, a first conversion module 22 and a second conversion module 23. Figure 2

[0116] ​​​The first conversion module 22 is connected with the upper bus of the rectifier circuit 1, the second conversion circuit 2 is connected with the lower bus of the rectifier circuit 1, the first conversion module 22 and the second conversion module 23 are both connected with the switching module 21, the control circuit 3, the target load and the neutral point of the rectifier circuit 1, and the switching module 21 is also connected with the control circuit 3;

[0117] The switching module 21 is configured to switch the first conversion module 22 and the second conversion module 23 in series and in parallel according to the output voltage reference value.

[0118] The control module is configured to generate a second driving signal according to the bus voltage reference value, and control the first conversion module 22 and the second conversion module 23 to regulate the direct current of the bus voltage reference value to the output voltage reference value and transmit to the target load for charging through the second driving signal.

[0119] It should be noted that the first conversion circuit 2 and the second conversion circuit 2 in the embodiment can be a circuit for DC / DC conversion, such as a single-phase LLC converter. However, considering that the single-phase LLC converter needs to be connected in parallel in multiple ways at high power and is difficult to realize current sharing, the first conversion module 22 and the second conversion module 23 in the embodiment can adopt a three-phase LLC converter.

[0120] Referring to Figure 3 , Figure 3 The circuit principle diagram of the first conversion circuit 2 or the second conversion circuit 2 in the first embodiment of the DC charging circuit proposed by the embodiment of the application is shown in FIG. 1. Figure 3 As shown in the figure, in the embodiment, since the architectures of the first conversion circuit 2 and the second conversion circuit 2 are consistent, any one of them is used for illustration. Specifically, the first conversion circuit 2 is used for illustration, that is, the first conversion circuit 2 includes: first to sixth transistors T1-T6, first to third direct current capacitors Cr1-Cr3, first to third resonant inductors Lr1-Lr3, first to third filter inductors Lm1-Lm3, first to third transformers Tn1-Tn3, seventh to twelfth rectifier tubes D7-D12 and an output capacitor Co.

[0121] The first end of the first transistor T1 is connected with the output end of the rectifier circuit 1, the first end of the third transistor T3 and the first end of the fifth transistor T5, the second end of the first transistor T1 is connected with the first end of the first direct current capacitor Cr1 and the first end of the second transistor T2 respectively, the second end of the third transistor T3 is connected with the first end of the second direct current capacitor Cr2 and the first end of the fourth transistor T4 respectively, the second end of the fifth transistor T5 is connected with the first end of the third direct current capacitor Cr3 and the first end of the sixth transistor T6 respectively, the second end of the second transistor T2 is connected with the output end of the rectifier circuit 1, the second end of the fourth transistor T4 and the second end of the sixth transistor T6 respectively.

[0122] The second end of the first direct current capacitor Cr1 is connected with the first end of the first resonant inductor Lr1, the second end of the second direct current capacitor Cr2 is connected with the first end of the second resonant inductor Lr2, and the second end of the third direct current capacitor Cr3 is connected with the first end of the third resonant inductor Lr3.

[0123] The second end of the first resonant inductor Lr1 is connected with the first end of the first filter inductor Lm1 and the first end of the primary side of the first transformer Tn1, the second end of the primary side of the first transformer Tn1 is connected with the second end of the first filter inductor Lm1, the second end of the second filter inductor Lm2 and the second end of the third filter inductor Lm3, the first end of the secondary side of the first transformer Tn1 is connected with the anode of the seventh rectifier D7 and the cathode of the eighth rectifier D8, and the second end of the secondary side of the first transformer Tn1 is connected with the second end of the secondary side of the second transformer Tn2 and the second end of the secondary side of the third transformer Tn3.

[0124] The second end of the second resonant inductor Lr2 is connected with the first end of the second filter inductor Lm2 and the first end of the primary side of the second transformer Tn2, the second end of the primary side of the second transformer Tn2 is connected with the second end of the second filter inductor Lm2, and the first end of the secondary side of the second transformer Tn2 is connected with the anode of the ninth rectifier D9 and the cathode of the tenth rectifier D10.

[0125] The second end of the third resonant inductor Lr3 is connected with the first end of the third filter inductor Lm3 and the first end of the primary side of the third transformer Tn3, the second end of the primary side of the third transformer Tn3 is connected with the second end of the third filter inductor Lm3, and the first end of the secondary side of the third transformer Tn3 is connected with the anode of the eleventh rectifier D11 and the cathode of the twelfth rectifier D12.

[0126] The cathode of the seventh rectifier D7 is connected with the cathode of the ninth rectifier D9, the cathode of the eleventh rectifier D11 and the first end of the output capacitor Co, and the anode of the eighth rectifier D8 is connected with the anode of the tenth rectifier D10, the anode of the twelfth rectifier D12 and the second end of the output capacitor Co.

[0127] It should be noted that the turns ratio of the first transformer Tn1 to the third transformer Tn3 can be set according to actual conditions, and the present embodiment does not limit this.

[0128] It should also be noted that, as shown in Figure 2 , the input end (i.e. Figure 3 V i ) of the LLC converter can be connected with the output end of the rectifier circuit 1. Specifically, when it is the first conversion module 22, the positive pole of the input end can be connected with the upper bus, and the negative pole can be connected with the neutral point. The positive pole of the output end (i.e. Figure 3 V o ) can be connected with the positive pole of the target load, and the negative pole of the output end can be connected with the negative pole of the target load.

[0129] Similarly, when it is the second converter 43, the positive pole of the input end can be connected with the neutral point, and the negative pole can be connected with the lower bus. The positive pole of the output end (i.e. Figure 3 V o ) can be connected with the positive pole of the target load, and the negative pole of the output end can be connected with the negative pole of the target load.

[0130] It should be emphasized that the first conversion module 22 and the second conversion module 23 in the present embodiment can adopt a series-parallel switching connection mode, which can be implemented through Figure 3 the switching module 21. The switching module 21 can be a module for realizing series-parallel switching, for example, composed of a plurality of switching tubes according to a certain connection relationship. The specific mode can be set according to actual conditions, and the present embodiment does not limit this.

[0131] It should also be emphasized that the control ends of the first transistor T1 to the sixth transistor T6 in the first conversion module 22 and the second conversion module 23 in the present embodiment are connected with the control circuit 3, so that the control circuit 3 can output the second driving signal to the first conversion module 22 and the second conversion module 23 under its action, realizing the direct current voltage regulation of the bus voltage reference value to the output voltage reference value. Moreover, the control circuit 3 can also be connected with the switching module 21 to realize series-parallel switching through the switching module 21.

[0132] Specifically, when determining whether to adopt a series connection mode or a parallel connection mode, the control circuit 3 in the present embodiment can be used to compare the output voltage reference value with a preset voltage threshold value. When the output voltage reference value is higher than the preset voltage threshold value, the first conversion module 22 and the second conversion module 23 are connected in series through the switching module 21. When the output voltage reference value is lower than the preset voltage threshold value, the first converter 41 and the second converter 43 are connected in parallel through the switching module 21.

[0133] It should be noted that the above-mentioned preset voltage threshold can be set by the actual situation, and the embodiment does not limit it. Exemplarily, if the preset voltage threshold is 400V, when the output voltage reference value is higher than 400V, the control circuit 3 can control the switching module 21 to perform series voltage boosting between the first conversion module 22 and the second conversion module 23, and when the output voltage reference value is lower than 400V, the control circuit 3 can control the switching module 21 to perform parallel output between the first conversion module 22 and the second conversion module 23, so that the direct current charging circuit can adapt to different voltage requirements.

[0134] It should be emphasized that the embodiment adopts a single controller to uniformly control all the switching tubes of the front and rear stages, replacing the original two controllers of the front and rear stages, and eliminating the complexity and instability factors caused by communication between the two stages.

[0135] In the working process of the direct current charging circuit, the control circuit 3 can first obtain the output voltage reference value required by the target load charging, then determine the bus voltage reference value that can be output by the rectifier circuit 1 according to the output voltage reference value, control the rectifier circuit 1 to rectify the input alternating current into direct current with the bus voltage reference value, and then control the conversion circuit 2 to step down the direct current with the bus voltage reference value to the output voltage reference value, and finally the conversion circuit 2 transmits the direct current with the output voltage reference value to the target load for power supply. Compared with the prior art, in the embodiment, the rectifier circuit 1 is rectified according to the bus voltage reference value corresponding to the output voltage reference value required by the target load, so that the rectifier circuit 1 of the front stage is associated with the output voltage reference value, and thus a large-capacity electrolytic capacitor is not needed in the rectifier circuit 1, reducing the circuit size. The integrated design helps to reduce the size of the direct current charging pile, improve the efficiency and reliability.

[0136] Referring to Figure 4 , Figure 4 The architecture diagram of the control circuit 3 in the second embodiment of the direct current charging circuit proposed by the embodiment.

[0137] Based on the above-mentioned first embodiment, the second embodiment of the direct current charging circuit of the application is proposed, as shown in Figure 4 In order to determine the bus voltage reference value according to the output voltage reference value, so as to drive the rectifier circuit 1 to output direct current with the bus voltage reference value. In the embodiment, the control circuit 3 comprises: a three-phase voltage reference value generation module 31, a bus voltage reference value generation module 32, and a pulse width modulation control module 33;

[0138] The bus voltage reference value generation module 32 is connected with the three-phase voltage reference value generation module 31 and the pulse width modulation module, respectively, and the pulse width modulation module is also connected with the rectifier circuit 1;

[0139] The three-phase voltage reference value generation module 31 is used to determine the three-phase voltage reference value of the AC power based on the output voltage reference value and the output voltage sampling value of the conversion circuit 2.

[0140] The bus voltage reference value generation module 32 is used to generate the bus voltage reference value based on the three-phase voltage reference value;

[0141] The pulse width modulation control module 33 is used to generate a first drive signal based on the three-phase voltage reference value, and control the rectifier circuit 1 to rectify the AC power into DC power based on the bus voltage reference value through the first drive signal.

[0142] It should be noted that the above three-phase voltage reference values ​​can be the voltage reference values ​​corresponding to phases A, B, and C in AC power, respectively. For ease of explanation later, in this embodiment, the phase A voltage reference value is denoted as u. a * ,Right now Figure 2 The reference voltage value at point a between the phase A AC power supply Ua and the phase A inductor LA is denoted as the phase B voltage reference value among the three-phase voltage reference values. b * ,Right now Figure 2 The reference voltage value at point b between the phase B AC power supply Ub and the phase B inductor LB is denoted as the phase C voltage reference value among the three-phase voltage reference values. c * ,Right now Figure 2 The reference voltage value at point c between the C-phase AC power supply Uc and the C-phase inductor LC.

[0143] It should also be noted that the above-mentioned output voltage sampling value can be the real-time voltage value received by the target load when the DC charging circuit is charging the target load. Specifically, it can be... Figure 2 The voltage value at the connection point between the intermediate conversion circuit 2 and the target load can be obtained by sampling. For ease of subsequent explanation, the output voltage sample value is denoted as u in this embodiment. o .

[0144] It is understood that the first driving signal mentioned above can be used to drive the rectifier circuit 1 to rectify the AC power into DC power of the bus voltage reference value.

[0145] In practical use, the three-phase voltage reference value can first obtain the output voltage reference value and the output voltage sample value, and then calculate and determine the voltage reference value of each phase voltage in the AC power based on the output voltage reference value and the output voltage sample value, which is used as the three-phase voltage reference value, and then transmit the three-phase voltage reference value to the bus voltage reference value generation module 32.

[0146] The bus voltage reference value generating module 32 further generates a bus voltage reference value according to the three-phase voltage reference value, and transmits the bus voltage reference value to the pulse width modulation control module 33. The pulse width modulation control module 33 generates a PWM signal as the first driving signal according to the bus voltage reference value, and transmits the PWM signal to the switch tube in the rectifier circuit 1, so that the rectifier circuit 1 realizes rectification of the alternating current into the bus voltage reference value direct current.

[0147] Specifically, in order to generate the three-phase voltage reference value, as shown in the following figure, in the embodiment, the three-phase voltage reference value generating module 31 comprises an output voltage control submodule 311 and a power grid current control submodule 312. Figure 4

[0148] The power grid current control submodule 312 is connected with the output voltage control submodule 311, the bus voltage reference value generating module 32 and the pulse width modulation module respectively.

[0149] The output voltage control submodule 311 is configured to determine an output current reference value of the conversion circuit 2 according to the output voltage reference value and the output voltage sampling value.

[0150] The power grid current control submodule 312 is configured to obtain three-phase voltage sampling values and three-phase current sampling values of the alternating current, and determine the three-phase voltage reference value according to the output current reference value, the three-phase voltage sampling values and the three-phase current sampling values.

[0151] It can be understood that the above-mentioned output current reference value can be a current reference value required when the target load is charged, and the output current reference value can be obtained by calculation.

[0152] The above-mentioned three-phase voltage sampling values can be voltage values of each phase of the three-phase power output by the alternating current in real time during actual use. In order to facilitate subsequent description, the A-phase voltage sampling value (i.e. a in the following figure) is denoted as u a in the embodiment. Figure 2 a The B-phase voltage sampling value (i.e. b in the following figure) is denoted as u b. Figure 2 b The C-phase voltage sampling value (i.e. c in the following figure) is denoted as u c. Figure 2 c .

[0153] The above-mentioned three-phase current sampling values can be current values of each phase of the three-phase power output by the alternating current in real time during actual use. In order to facilitate subsequent description, the A-phase current sampling value (i.e. a in the following figure) is denoted as i a in the embodiment. Figure 2 a The B-phase current sampling value (i.e. b in the following figure) is denoted as i b. Figure 2 b ​​​​​​​The C-phase current sampling value (i.e. Figure 2 (at point c) is denoted as i c .

[0154] In practical use, the output voltage control submodule 311 can first obtain the output voltage reference value and the output voltage sample value, calculate the output current reference value based on the output voltage reference value and the output voltage sample value, and transmit the output current reference value to the grid current control submodule 312. The grid current control submodule 312 can first obtain the three-phase voltage sample value and the three-phase current sample value, and then calculate the three-phase voltage reference value by combining the output current reference value, the three-phase voltage sample value and the three-phase current sample value.

[0155] Furthermore, in order to obtain the output current reference value, refer to Figure 5 , Figure 5 This is a schematic diagram of the control strategy of control circuit 3 in the second embodiment of the DC charging circuit proposed in this application. Figure 5 As shown, in this embodiment, the output voltage control submodule 311 is further used to determine the voltage error between the output voltage reference value and the output voltage sample value;

[0156] The output voltage control submodule 311 is also used to perform proportional-integral calculation on the voltage error to obtain the active current compensation amount.

[0157] The output voltage control submodule 311 is also used to superimpose the active current compensation amount with the output current sampling value of the conversion circuit 2 to obtain the output current reference value.

[0158] It should be noted that the above-mentioned active current compensation amount can be the equivalent current compensation amount under this voltage error, which can be denoted as i for ease of subsequent explanation. Co * .

[0159] It should also be noted that the above-mentioned output current sampling value can be the real-time current value obtained by the target load, that is, the current value received by the target load in real time. For ease of explanation later, it can be denoted as i. o .

[0160] like Figure 5 As shown, the output voltage control submodule 311 can first obtain the output voltage reference value u. o * and the output voltage sample value u o And the difference between the output voltage reference value and the output voltage sample value (i.e. Figure 3 The voltage error is obtained by using the "-" sign in the output voltage control submodule 311; then, a proportional-integral operation can be performed on this voltage error (i.e., ...). Figure 3The PI in the output voltage control submodule 311 is used to obtain the active current compensation amount i. Co * Then, the active power compensation is superimposed on the obtained output current sampling value i. o (Right now Figure 3 The "+" sign in the output voltage control submodule 311 can be used to obtain the output current reference value. Figure 3 The output result of the output voltage module is the reference value of the output current.

[0161] Furthermore, in order to obtain the three-phase voltage reference value, continue as follows: Figure 4 As shown, in this embodiment, the grid current control submodule 312 includes: a phase-locked loop unit 3121 and a grid current control unit 3122;

[0162] The grid current control unit 3122 is connected to the phase-locked loop unit 3121, the output voltage control submodule 311, and the bus voltage reference value generation module 32, respectively.

[0163] The phase-locked loop unit 3121 is used to determine the grid phase angle based on the three-phase voltage sampling values;

[0164] The grid current control unit 3122 is used to determine the three-phase voltage reference value based on the grid phase angle, the three-phase voltage sample value, the three-phase current sample value, and the output current reference value.

[0165] It is understandable that the above-mentioned grid phase angle can be the phase position of a certain phase voltage or current in the three-phase AC power relative to a reference point (such as the zero crossing point of phase A). For ease of explanation later, it can be denoted as θ.

[0166] In practical use, such as Figure 5 As shown, firstly, the phase-locked loop unit 3121 (i.e. Figure 5 The PLL can first be based on the three-phase voltage sampling value u a u b u c (Right now Figure 5 middle u abc The phase angle θ of the alternating current grid is determined and transmitted to the grid current control unit 3122 (i.e., Figure 5 The mains current control submodule 312 (excluding the PLL) contains the following components: After receiving the grid phase angle, the grid current control unit 3122 can determine the grid current control unit based on the grid phase angle and the sampled three-phase voltage value u. a u b u c Three-phase current sampling value i a i b i c(Right now Figure 5 in i abc The three-phase voltage reference value u is determined by the output current reference value. a * u b * u c * .

[0167] The bus voltage reference value generation module 32 can then generate a bus voltage reference value u based on the three-phase voltage reference values. pn * (Right now Figure 5 The intermediate bus voltage reference value generation module 32 receives u a * u b * u c * And output u pn * The pulse width modulation control module 33 generates a first drive signal based on the three-phase voltage reference value to control the rectifier circuit 1 to rectify the AC power into DC power of the bus voltage reference value (i.e., DC power). Figure 5 The bus voltage reference value generation module 32 will generate u a * u b * u c * Output to S 1-6 S 1-6 (This refers to the switching transistor in rectifier circuit 1).

[0168] Furthermore, in order to reduce the interference of negative sequence components on the accuracy of the phase-locked loop and ensure the accuracy of phase-locking, refer to Figure 6 , Figure 6 This is a schematic diagram of the control strategy of the phase-locked loop unit 3121 in the second embodiment of the DC charging circuit proposed in this application. Figure 6 As shown, in this embodiment, the phase-locked loop unit 3121 includes: a first converter 41, an integrator 42, a second converter 43, and a phase calculation subunit 44;

[0169] The integrator 42 is connected to the first converter 41 and the second converter 43 respectively, and the phase calculation subunit 44 is connected to the second converter 43 and the grid current control unit 3122 respectively.

[0170] The first converter 41 is used to determine a first voltage vector on the α axis and a second voltage vector on the β axis based on the three-phase voltage sample values;

[0171] The integrator 42 is configured to extract positive sequence components from the first voltage vector to obtain a first positive sequence voltage, and extract positive sequence components from the second voltage vector to obtain a second positive sequence voltage.

[0172] The second transformer 43 is configured to determine a third voltage vector on a q-axis according to the first positive sequence voltage and the second positive sequence voltage.

[0173] The phase calculation subunit 44 is configured to determine the grid phase angle according to the third voltage vector and an angular frequency of the alternating current.

[0174] It should be noted that the first transformer 41 can be a Clark transformer, the integrator 42 can be a second-order generalized integrator 42, and the second transformer 43 can be a Park transformer.

[0175] In actual use, first, the first transformer 41 can receive three-phase voltage sampling values u a , u b , and u c , convert the three-phase voltage sampling values into voltage vectors in a two-phase stationary coordinate system (i.e., αβ) through Clark transformation (abc→αβ), and obtain a first voltage vector u α on an α-axis and a second voltage vector u β on a β-axis.

[0176] Then, the integrator 42 obtains the first voltage vector on the α-axis and the second voltage vector on the β-axis, and filters out negative sequence and harmonic components from the first voltage vector and the second voltage vector through the second-order generalized integrator 42 (SOGI) to extract positive sequence voltage components. Specifically, a 90° phase shift of the grid voltage signal can be first realized to generate two mutually orthogonal signals u α ' and qu α ' and u β ' and qu β '. The first positive sequence voltage u α + is obtained by subtracting the signals u β ' and u α ', and the second positive sequence voltage uβ+ is obtained by subtracting the signals qu α ' and qu β '.

[0177] Then, the first positive sequence voltage and the second positive sequence voltage are transmitted to the second transformer 43, and the positive sequence voltage vector is converted into a q-axis voltage vector in a synchronous rotating coordinate system through Park transformation (αβ to dq), i.e., the third voltage vector u q . Finally, the q-axis third voltage vector is subjected to proportional-integral operation through a PI controller, and the grid phase angle θ is obtained in combination with the angular frequency ω of the alternating current.

[0178] Since the positive sequence component of the power grid can be extracted through the SOGI link in the embodiment, the interference of the negative sequence component on the precision of the phase-locked loop is reduced, and the phase-locked accuracy is ensured.

[0179] Further, in order to determine the three-phase voltage reference value, the power grid current control unit 3122 includes a third transformer 45, a power grid current control subunit 46, and a fourth transformer 47, as shown in Figure 5

[0180] The third transformer 45 is connected with the phase-locked loop unit 3121 and the power grid current control subunit 46 respectively, the power grid current control subunit 46 is further connected with the output voltage control sub-module 311 and the fourth transformer 47 respectively, and the fourth transformer 47 is further connected with the bus voltage reference value generation module 32.

[0181] It should be noted that the third transformer 45 and the fourth transformer 47 described above can be inverse Park transformers.

[0182] The third transformer 45 is configured to determine a third voltage vector and a first current vector on a q-axis, and a fourth voltage vector and a second current vector on a d-axis, according to the phase angle, the three-phase voltage sampling value, the three-phase current sampling value, and the angular frequency of the alternating current.

[0183] It can be understood that, as shown in Figure 5 The third transformer 45 can first obtain the phase angle θ, the three-phase voltage sampling value u a , u b , u c , the three-phase current sampling value i a , i b , i c , and the angular frequency ω, and convert the three-phase voltage sampling value and the three-phase current sampling value to the synchronous rotating coordinate system (i.e., the dq coordinate system) according to these parameters, so as to obtain the third voltage vector u q on the q-axis and the first current vector i q on the q-axis, and the fourth voltage vector u d on the d-axis and the second current vector i d on the d-axis. Converting the voltage and current in the three-phase static coordinate system into the vector in the synchronous rotating coordinate system facilitates subsequent control processing.

[0184] ​The grid current control subunit 46 is configured to obtain a grid voltage effective value of the alternating current, and determine a first voltage reference vector on a q-axis and a second voltage reference vector on a d-axis according to the output current reference value, the third voltage vector, the first current vector, the fourth voltage vector, the second current vector, and the grid voltage effective value.

[0185] It should be understood that the grid voltage effective value (i.e. Figure 5 3 / 2U Φ 2 may be an effective value of the alternating current.

[0186] In actual use, the grid current control subunit 46 can obtain the grid current effective value after receiving the output current reference value, and receive the third voltage vector, the first current vector, the fourth voltage vector, and the second current vector output by the third converter 45, and obtain the first voltage reference vector u q * on the q-axis and the second voltage reference vector u d * on the d-axis according to these parameters. The first voltage reference vector can be used as a voltage reference value for controlling the q-axis current, and the second voltage reference vector can be used as a voltage reference value for controlling the d-axis current.

[0187] The fourth converter 47 is configured to determine the three-phase voltage reference value according to the first voltage reference vector and the second voltage reference vector.

[0188] In actual use, when the fourth converter 47 receives the first voltage reference vector and the second voltage reference vector, the voltage reference value in the three-phase stationary coordinate system can be obtained by inverse Park conversion, that is, the three-phase voltage reference value u a * , u b * , u c * .

[0189] Specifically, in order to enable the grid current control subunit 46 to determine the first voltage reference vector and the second voltage reference vector, as shown in Figure 5 , in the embodiment, the grid current control subunit 46 is further configured to determine a power reference value according to the output current reference value and the output voltage reference value.

[0190] It should be noted that the power reference value can be an expected active power. As shown in Figure 5 , the grid current control subunit 46 can combine the output voltage reference value uo * Multiplying them together yields the power reference value P. * .

[0191] The grid current control subunit 46 is also used to determine the equivalent conductance based on the power reference value and the effective value of the grid voltage.

[0192] Understandably, the equivalent conductance described above can be a parameter used to calculate the desired input current. For example... Figure 5 As shown, after obtaining the power reference value, based on the power reference value P... * and the effective value of the grid voltage 3 / 2U Φ 2 The equivalent conductance G is calculated by division. * .

[0193] The grid current control subunit 46 is further configured to determine a first current reference vector on the q-axis based on the equivalent conductance and the third voltage vector, and to determine the first voltage reference vector based on the first current reference vector, the first current vector and the third voltage vector.

[0194] It should be understood that the aforementioned first current reference vector can be the desired current value on the q-axis, the aforementioned third voltage vector can be the actual voltage vector on the q-axis, and the aforementioned first voltage reference vector can be the desired voltage value on the q-axis. For example... Figure 5 As shown, in obtaining the equivalent conductance G * Then, the equivalent conductance can be compared with the third voltage vector u. q Multiply to obtain the first current reference vector i on the q-axis. q * Then, the first current reference vector i q * With the first current vector i q The difference is calculated, and the result is then subjected to a proportional-integral operation. The result is then compared with the third voltage vector u. q Summing is performed to obtain the first voltage reference vector u. q * .

[0195] The grid current control subunit 46 is further configured to determine a second current reference vector on the d-axis based on the equivalent conductance and the fourth voltage vector, and to determine the second voltage reference vector based on the second current reference vector, the second current vector and the fourth voltage vector.

[0196] It should be understood that the aforementioned second current reference vector can be the desired current value on the d-axis, the aforementioned fourth voltage vector can be the actual voltage vector on the d-axis, and the aforementioned second voltage reference vector can be the desired voltage value on the d-axis. Similarly, the equivalent conductance G is obtained. * Then, the equivalent conductance can be compared with the fourth voltage vector u. d Multiplying them together yields the second current reference vector i on the d-axis. d * Then, the second current reference vector i d * With the second current vector i d The difference is calculated, and the result is then subjected to a proportional-integral operation. The result is then compared with the fourth voltage vector u. d Summing is performed to obtain the second voltage reference vector u. d * .

[0197] Referring again to the figures above and based on the embodiments described above, a third embodiment of the DC charging circuit of this application is proposed. In this embodiment, in order to obtain a bus voltage reference value, such as... Figure 5 As shown, the bus voltage reference value generation module 32 is also used to determine the maximum voltage reference value and the minimum voltage reference value among the three-phase voltage reference values;

[0198] The bus voltage reference value generation module 32 is further configured to determine the voltage reference difference between the maximum voltage reference value and the minimum voltage reference value, and use the voltage reference difference as the bus voltage reference value.

[0199] It should be noted that the above maximum voltage reference value can be the largest voltage reference value among the three-phase voltage reference values, and the minimum voltage reference value can be the smallest voltage reference value among the three-phase voltage reference values.

[0200] In this embodiment, as Figure 5 As shown in the diagram of the bus voltage reference value generation module 32, the three-phase voltage reference value u is obtained in the bus voltage reference value generation module 32. a * u b * u c * Then, phase selection can be performed to determine the maximum reference voltage u. max * and minimum reference voltage u min * Next, the maximum reference voltage u max * and minimum reference voltage u min *The difference is made, a voltage reference difference is obtained, and the voltage reference difference is used as the bus voltage reference value u pn * .

[0201] Further, in order to reduce the switching loss while clamping the voltage to the bus voltage reference value, in the embodiment, the rectifier circuit 1 comprises a three-phase switching circuit;

[0202] Each phase of the switching circuit is connected with the conversion circuit 2 and the pulse width modulation control module 33.

[0203] The pulse width modulation control module 33 is further configured to control the switching circuit of one phase to perform switching action and control the switching circuits of the other two phases not to perform switching action when the rectifier circuit 1 performs rectification through the first driving signal.

[0204] As shown in Figure 1 , in the embodiment, the first switch Q1 to the sixth switch Q6 in Figure 1 can be used as the three-phase switching circuit, wherein the first switch Q1 and the second switch Q2 are used as one phase, the third switch Q3 and the fourth switch Q4 are used as one phase, and the fifth switch Q5 and the sixth switch Q6 are used as one phase.

[0205] When the control circuit 3 controls the rectifier circuit 1 to rectify the alternating current into the bus voltage reference value, the control circuit 3 in the embodiment can output a first driving signal to the first switch Q1 to the sixth switch Q6, and the first driving signal can control the switching circuit of one phase to perform switching action and control the switching circuits of the other two phases not to perform switching action. That is, only one phase of the switching circuit performs switching action at a time, which reduces the switching loss of the Vienna rectifier and cooperates with the subsequent stage to control the output voltage, the grid current and the bus voltage. At the same time, the generated bus voltage sampling value can be clamped at the maximum line voltage at all times.

[0206] Further, in order to make the pulse width modulation control module 33 control only one phase of the switching circuit to perform switching action at a time, refer to Figure 7 , Figure 7 The control strategy diagram of the pulse width modulation control module 33 in the second embodiment of the direct current charging circuit proposed by the embodiment of the application is shown in Figure 7 . The pulse width modulation control module 33 is further configured to obtain a bus voltage sampling value and determine a target zero sequence component according to the three-phase voltage reference value.

[0207] The pulse width modulation control module 33 is further configured to superimpose the three-phase voltage reference value according to the target zero sequence component.

[0208] The pulse width modulation control module 33 is also used to generate the first driving signal based on the bus voltage sample value and the superimposed three-phase voltage reference value.

[0209] It should be noted that the aforementioned target zero-sequence component can be the zero-sequence component used to eliminate voltage imbalance. The aforementioned bus voltage sample value can be the real-time voltage value acquired between the upper and lower buses of rectifier circuit 1, denoted as u. pn .

[0210] like Figure 7 As shown, when the pulse width modulation control module 33 receives the three-phase voltage reference value u a * u b * u c * Next, the maximum reference voltage u can be selected based on the three-phase voltage reference values. max * Intermediate reference voltage u mid * and minimum reference voltage u min * , where u max * =max{u a * u b * u c *}, u mid * =mid{u a * u b * u c *}, u mid * =min{u a * u b * u c *};

[0211] To obtain the maximum reference voltage u max * Intermediate reference voltage u mid * and minimum reference voltage u min * Then, based on the maximum reference voltage u max * Intermediate reference voltage u mid * and minimum reference voltage umin * The target zero-sequence component u0 is obtained, specifically, by the following zero-sequence component calculation formula:

[0212] u0 = -min{u a * , u b * , u c *}-1 / 2u pn = -1 / 2(max{u a * , u b * , u c *}+min{u a * , u b * , u c *}) = 1 / 2mid{u a * , u b * , u c *};

[0213] After the target zero-sequence component u0 is obtained, the voltage reference values in the middle are superimposed by the target zero-sequence component respectively, and the maximum and minimum are not operated. If the superimposed A-phase voltage reference value is denoted as u a ** , the superimposed B-phase voltage reference value is denoted as u b ** , and the superimposed C-phase voltage reference value is denoted as u c ** , then u a ** = u a * + u0, u b ** = u b * + u0, and u c ** = u c * + u0.

[0214] After the superimposed three-phase voltage reference values u a ** , u b ** , and u c **After that, the bus voltage reference value is multiplied by 1 / 2 and then divided by the superimposed three-phase voltage reference value respectively, and compared with the triangular carrier, and the driving signal of the switching circuit for each phase can be obtained by the carrier comparison method (i.e. Figure 7 S a , S b and S c ) as the first driving signal. Therefore, in this embodiment, the switching circuit in the rectifier circuit 1 can be switched only once in one phase (i.e. in the middle phase) by the first driving signal, thereby reducing the loss.

[0215] As shown in Figure 4 , in this embodiment, in order to generate the second driving signal, the control circuit 3 further comprises a feedforward gain module 34 and a bus voltage control module 35.

[0216] The bus voltage control module 35 is connected with the feedforward gain module 34, the first conversion module 22 and the second conversion module 23 respectively.

[0217] The feedforward gain module 34 is configured to obtain the quality factor and the current voltage gain of the conversion circuit 2, and determine the feedforward frequency according to the quality factor and the current voltage gain.

[0218] The bus voltage control module 35 is configured to determine the first working frequency and the second working frequency according to the bus voltage reference value and the feedforward frequency, and generate the second driving signal according to the first working frequency and the second power frequency.

[0219] Specifically, the bus voltage reference value generation module 32 can be further connected with the bus voltage control module 35, so as to transmit the generated bus voltage reference value to the bus voltage control module 35.

[0220] It should be noted that the quality factor Q * may be a parameter of energy loss in the circuit, which can be obtained by real-time measurement of the circuit. The current voltage gain M * may be the ratio of the output voltage to the input voltage of the LLC converter, which can also be obtained by real-time measurement.

[0221] It can be understood that the first working frequency can be the frequency for controlling the working of the first conversion module 22, and the second working frequency can be the frequency for controlling the working of the second conversion module 23.

[0222] As shown in Figure 5 , in this embodiment, the feedforward gain module 34 can first obtain the quality factor Q * and the current voltage gain M *And query the preset mapping table ( Figure 5 Middle 2

[0223] D-LUT), thereby obtaining the feedforward frequency f for controlling the LLC converter. feedforward The feedforward frequency can then be transmitted to the bus voltage control module 35, which in turn controls the frequency according to the bus voltage reference value u. pn The first operating frequency and the second operating frequency can be obtained by the feedforward frequency. The corresponding second driving signal can be generated based on the first operating frequency and the second operating frequency to control the operation of the conversion circuit 2.

[0224] Specifically, in order to obtain the first operating frequency and the second operating frequency, such as Figure 5 As shown, in this embodiment, the bus voltage control module 35 is further configured to determine the half bus voltage reference value based on the bus voltage reference value, and to obtain the upper bus voltage sample value and the lower bus voltage sample value.

[0225] It should be understood that the above-mentioned half bus voltage reference value can be half of the bus voltage reference value, denoted as u. po * The aforementioned upper bus voltage sampling value can be the real-time voltage value collected from the upper bus, i.e., the voltage value between point p and the neutral point, denoted as u. po The aforementioned busbar voltage sampling value can be the real-time voltage value collected from the busbar, i.e., the voltage value between point n and the neutral point, denoted as u. on .

[0226] like Figure 5 As shown, the bus voltage reference value u is obtained in the bus voltage control module 35. pn * Then, multiply by 0.5 to obtain the half-bus voltage reference value u. po * Next, the sampled value u of the upper bus voltage is obtained. po and the lower bus voltage sampling value u on .

[0227] The bus voltage control module 35 is further configured to determine the upper bus error value between the half bus voltage reference value and the upper bus voltage sample value, and to determine the lower bus error value between the half bus voltage reference value and the lower bus voltage sample value.

[0228] like Figure 5 As shown, the bus voltage control module 35 can control the half bus voltage reference value u. po * With the upper bus voltage sampling value u po The difference is taken as the upper busbar error value; the half busbar voltage reference value u po* The lower bus voltage sampling value u on The difference is taken as the lower bus error value.

[0229] The bus voltage control module 35 is further configured to perform proportional-integral operation on the upper bus error and the lower bus error respectively, and add the feedforward frequency to the upper bus error after operation to obtain the first working frequency, and add the feedforward frequency to the lower bus error after operation to obtain the second working frequency.

[0230] After the difference is taken, proportional-integral operation is performed on the upper bus error value, and the upper bus error value after operation is added to the feedforward frequency f feedforward , so as to obtain the first working frequency f s1 ; proportional-integral operation is performed on the lower bus error value, and the lower bus error value after operation is added to the feedforward frequency f feedforward , so as to obtain the second working frequency f s2 .

[0231] In addition, to achieve the above object, the embodiment further provides a direct current charging pile, which comprises the direct current charging circuit as described above.

[0232] The specific structure of the direct current charging circuit can refer to the above embodiments. Since the direct current charging pile adopts all the technical solutions of the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, which will not be repeated here.

[0233] The above is only the preferred embodiment of the application, and does not limit the application range of the application, and any equivalent structure or equivalent process transformation using the content of the specification and drawings, or direct or indirect application in other related technical fields, are also included in the application protection range of the application.

Claims

1. A DC charging circuit, characterized in that, The DC charging circuit includes: a rectifier circuit, a converter circuit, and a control circuit; The rectifier circuit is connected to the converter circuit and the control circuit, and the converter circuit is also connected to the target load; The rectifier circuit is used to connect to AC power; The control circuit is used to determine the bus voltage reference value of the rectifier circuit based on the output voltage reference value required for charging the target load, and to control the rectifier circuit to rectify the AC power into DC power of the bus voltage reference value. The conversion circuit is used to adjust the DC voltage of the bus voltage reference value to the output voltage reference value and transmit it to the target load for charging.

2. The DC charging circuit as described in claim 1, characterized in that, The control circuit includes: a three-phase voltage reference value generation module, a bus voltage reference value generation module, and a pulse width modulation control module; The bus voltage reference value generation module is connected to the three-phase voltage reference value generation module and the pulse width modulation module, respectively. The pulse width modulation module is also connected to the rectifier circuit. The three-phase voltage reference value generation module is used to determine the three-phase voltage reference value of the AC power based on the output voltage reference value and the output voltage sampling value of the conversion circuit; The bus voltage reference value generation module is used to generate the bus voltage reference value based on the three-phase voltage reference value; The pulse width modulation control module is used to generate a first drive signal based on the three-phase voltage reference value, and control the rectifier circuit to rectify the AC power into DC power based on the bus voltage reference value through the first drive signal.

3. The DC charging circuit as described in claim 2, characterized in that, The three-phase voltage reference value generation module includes: an output voltage control submodule and a grid current control submodule; The power grid current control submodule is connected to the output voltage control submodule, the bus voltage reference value generation module, and the pulse width modulation module, respectively. The output voltage control submodule is used to determine the output current reference value of the conversion circuit based on the output voltage reference value and the output voltage sample value. The power grid current control submodule is used to acquire the three-phase voltage sampling value and the three-phase current sampling value of the AC power, and to determine the three-phase voltage reference value based on the output current reference value, the three-phase voltage sampling value and the three-phase current sampling value.

4. The DC charging circuit as described in claim 3, characterized in that, The output voltage control submodule is also used to determine the voltage error between the output voltage reference value and the output voltage sample value; The output voltage control submodule is also used to perform proportional-integral calculation on the voltage error to obtain the active current compensation amount. The output voltage control submodule is also used to superimpose the active current compensation amount with the output current sampling value of the conversion circuit to obtain the output current reference value.

5. The DC charging circuit as described in claim 3, characterized in that, The grid current control submodule includes: a phase-locked loop unit and a grid current control unit; The grid current control unit is connected to the phase-locked loop unit, the output voltage control submodule, and the bus voltage reference value generation module, respectively. The phase-locked loop unit is used to determine the grid phase angle based on the three-phase voltage sampling values; The power grid current control unit is used to determine the three-phase voltage reference value based on the power grid phase angle, the three-phase voltage sample value, the three-phase current sample value, and the output current reference value.

6. The DC charging circuit as described in claim 5, characterized in that, The phase-locked loop unit includes: a first converter, an integrator, a second converter, and a phase calculation subunit; The integrator is connected to the first converter and the second converter respectively, and the phase calculation subunit is connected to the second converter and the grid current control unit respectively; The first converter is configured to determine a first voltage vector on the α-axis and a second voltage vector on the β-axis based on the three-phase voltage sample values; The integrator is used to extract the positive-sequence component of the first voltage vector to obtain a first positive-sequence voltage, and to extract the positive-sequence component of the second voltage vector to obtain a second positive-sequence voltage. The second converter is configured to determine a third voltage vector on the q-axis based on the first positive-sequence voltage and the second positive-sequence voltage; The phase calculation subunit is used to determine the power grid phase angle based on the third voltage vector and the angular frequency of the alternating current.

7. The DC charging circuit as described in claim 5, characterized in that, The grid current control unit includes: a third converter, a grid current control subunit, and a fourth converter; The third converter is connected to the phase-locked loop unit and the grid current control subunit respectively. The grid current control subunit is also connected to the output voltage control submodule and the fourth converter respectively. The fourth converter is also connected to the bus voltage reference value generation module. The third converter is used to determine a third voltage vector and a first current vector on the q-axis, and a fourth voltage vector and a second current vector on the d-axis, based on the phase angle, the three-phase voltage sample value, the three-phase current sample value, and the angular frequency of the alternating current. The grid current control subunit is used to obtain the effective value of the grid voltage of the AC power, and determine the first voltage reference vector on the q axis and the second voltage reference vector on the d axis based on the output current reference value, the third voltage vector, the first current vector, the fourth voltage vector, the second current vector and the effective value of the grid voltage. The fourth converter is used to determine the three-phase voltage reference value based on the first voltage reference vector and the second voltage reference vector.

8. The DC charging circuit as described in claim 7, characterized in that, The grid current control subunit is also used to determine the power reference value based on the output current reference value and the output voltage reference value; The grid current control subunit is also used to determine the equivalent conductance based on the power reference value and the effective value of the grid voltage; The grid current control subunit is further configured to determine a first current reference vector on the q-axis based on the equivalent conductance and the third voltage vector, and to determine the first voltage reference vector based on the first current reference vector, the first current vector and the third voltage vector; The grid current control subunit is further configured to determine a second current reference vector on the d-axis based on the equivalent conductance and the fourth voltage vector, and to determine the second voltage reference vector based on the second current reference vector, the second current vector and the fourth voltage vector.

9. The DC charging circuit as described in claim 2, characterized in that, The bus voltage reference value generation module is also used to determine the maximum voltage reference value and the minimum voltage reference value among the three-phase voltage reference values; The bus voltage reference value generation module is further configured to determine the voltage reference difference between the maximum voltage reference value and the minimum voltage reference value, and use the voltage reference difference as the bus voltage reference value.

10. The DC charging circuit as described in claim 2, characterized in that, The rectifier circuit includes a three-phase switching circuit; The switching circuits of each phase are all connected to the conversion circuit and the pulse width modulation control module; The pulse width modulation control module is further configured to control one phase of the switching circuit to perform a switching action when the rectifier circuit is performing rectification, and to control the other two phases of the switching circuit not to perform a switching action, by using the first driving signal.

11. The DC charging circuit as described in claim 10, characterized in that, The pulse width modulation control module is also used to acquire the bus voltage sampling value and determine the target zero-sequence component based on the three-phase voltage reference value; The pulse width modulation control module is also used to superimpose the three-phase voltage reference value according to the target zero-sequence component; The pulse width modulation control module is further configured to generate the first drive signal based on the bus voltage sample value and the superimposed three-phase voltage reference value.

12. The DC charging circuit as described in claim 1, characterized in that, The rectifier circuit further includes: a first thin-film capacitor and a second thin-film capacitor; The upper bus, neutral point, and lower bus of the rectifier circuit are all connected to the converter circuit. The first end of the first film capacitor is connected to the upper busbar, the second end of the first film capacitor is connected to the neutral point and the first end of the second film capacitor, and the second end of the second film capacitor is connected to the lower busbar.

13. The DC charging circuit as described in claim 1, characterized in that, The conversion circuit includes: a switching module, a first conversion module, and a second conversion module; The first conversion module is connected to the upper bus of the rectifier circuit, and the second conversion circuit is connected to the lower bus of the rectifier circuit. Both the first conversion module and the second conversion module are also connected to the switching module, the control circuit, the target load, and the neutral point of the rectifier circuit. The switching module is also connected to the control circuit. The switching module is used to switch between the first conversion module and the second conversion module in series or parallel according to the output voltage reference value; The control module is used to generate a second drive signal based on the bus voltage reference value, and control the first conversion module and the second conversion module to adjust the DC voltage of the bus voltage reference value to the output voltage reference value through the second drive signal, and transmit it to the target load for charging.

14. The DC charging circuit as described in claim 13, characterized in that, The control circuit includes: a feedforward gain module and a bus voltage control module; The bus voltage control module is connected to the feedforward gain module, the first conversion module and the second conversion module respectively; The feedforward gain module is used to obtain the quality factor and current voltage gain of the conversion circuit, and determine the feedforward frequency based on the quality factor and the current voltage gain. The bus voltage control module is used to determine a first operating frequency and a second operating frequency based on the bus voltage reference value and the feedforward frequency, and to generate the second drive signal based on the first operating frequency and the second power frequency.

15. The DC charging circuit as described in claim 14, characterized in that, The bus voltage control module is also used to determine the half bus voltage reference value based on the bus voltage reference value, and to obtain the upper bus voltage sample value and the lower bus voltage sample value. The bus voltage control module is further configured to determine the upper bus error value between the half bus voltage reference value and the upper bus voltage sample value, and to determine the lower bus error value between the half bus voltage reference value and the lower bus voltage sample value; The bus voltage control module is further configured to perform proportional-integral calculations on the upper bus error and the lower bus error respectively, and to obtain the first operating frequency by superimposing the calculated upper bus error with the feedforward frequency, and to obtain the second operating frequency by superimposing the calculated lower bus error with the feedforward frequency.

16. A DC charging pile, characterized in that, The DC charging pile includes a DC charging circuit as described in any one of claims 1 to 15.

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