High-power direct-current charging station for electric vehicle and control optimization method of high-power direct-current charging station

Abstract

The invention discloses an electric vehicle high-power direct current charging station and a control optimization method thereof, and the method comprises the following steps: inputting an external three-phase alternating current into a Vienna rectifier serving as a pre-stage charging circuit, and inputting an output voltage value of the Vienna rectifier into a pre-stage control circuit; after the pre-stage control circuit obtains an output voltage value of the Vienna rectifier, the direction of the voltage is determined, synthesis is carried out by adopting a nearest three-vector method and utilizing three basic voltage vectors closest to a target voltage vector, a three-level SVPWM algorithm based on a two-level theory is adopted in the synthesis process, and finally the action time of the target voltage vector is obtained. And therefore, the Vienna rectifier can be controlled. The operation burden of the control system is reduced, the power grid loss is reduced, and the stability and efficiency of power grid operation are improved.

Description

Technical Field

[0001] The present invention belongs to the field of DC charging piles and relates to a high-power DC charging station for electric vehicles and its control optimization method. Background Art

[0002] With the rapid development of the electric vehicle industry, the popularization of charging facilities has become an important foundation for the promotion of new energy vehicles. As a key infrastructure, the core module of a DC charging station is the power conversion module, which usually adopts a two-stage power conversion structure: the front stage is an AC / DC rectification module, and the rear stage is a DC / DC voltage regulation module. Among them, the Vienna rectifier circuit is widely used because of its advantages of low switching tube loss and high power utilization efficiency. Although the technical solutions of DC charging stations have been developed, there are still deficiencies in actual applications. The traditional three-level space vector pulse width modulation method adopted by the Vienna rectifier circuit has high computational complexity and slow response speed, resulting in poor power factor correction effect and affecting the grid operation efficiency. Summary of the Invention

[0003] The purpose of the present invention is to overcome the above-mentioned disadvantages of the prior art and provide a high-power DC charging station for electric vehicles and its control optimization method, which reduces the computing burden of the control system, helps to reduce grid losses and improve the stability and efficiency of grid operation.

[0004] To achieve the above purpose, the present invention adopts the following technical solutions: A control optimization method for a high-power DC charging station for electric vehicles includes the following processes: External three-phase alternating current is input into the Vienna rectifier as the front-stage charging circuit, and the output voltage value of the Vienna rectifier is input into the front-stage control circuit; after obtaining the output voltage value of the Vienna rectifier, the front-stage control circuit first determines the direction of the voltage, adopts the nearest three-vector method, and uses the three basic voltage vectors closest to the target voltage vector for synthesis. During the synthesis process, a three-level SVPWM algorithm based on two-level theory is adopted to finally obtain the action time of the target voltage vector, thereby controlling the Vienna rectifier.

[0005] Preferably, the process of the three-level SVPWM algorithm based on the two-level theory is as follows: First, the space vectors are divided into six large sectors, each large sector is divided into multiple small sectors, each small sector is a regular hexagon, and they are arranged in a staggered manner. The distances between the vector V0 and the midpoints of each large sector are the vectors corresponding to each small sector. By determining the large sector where the target voltage vector is located, the target voltage vector in the three-level space is converted into the target voltage vector in the small sector. By subtracting the vector corresponding to the small sector, the basic voltage vector is corrected to obtain the corrected basic voltage vector. According to the small sector where it is located, the action times of the three corrected basic voltage vectors are determined, and the action time of the target voltage vector is synthesized.

[0006] Further, each large sector starts from -30° and is divided into one small sector every 60°.

[0007] Preferably, the output of the pre-stage control circuit is defined as Vneutral. When the voltage at the midpoint of the two capacitors at the end of the Vienna rectifier is higher than half of the output voltage, Vneutral is equal to 1; otherwise, it is -1. The inputs of the pre-stage control circuit are: the input voltage and input current vectors of the Vienna rectifier, the voltage value of the output direct current, and Vneutral.

[0008] Preferably, the Vienna rectifier adopts a three-phase three-wire topological structure.

[0009] Preferably, the Vienna rectifier outputs direct current, which is then input to the post-stage charging circuit.

[0010] Further, the post-stage control circuit modulates the post-stage charging circuit through voltage closed-loop feedback control.

[0011] Further, the PI control process is as follows: The output voltage feedback of the post-stage charging circuit and the control voltage are subtracted to calculate the error. The error is output to the PI regulator. The output of the PI regulator and the phase shift angle are summed to obtain the total control quantity, and the phase shift angle in the total control quantity is limited. The total control quantity is generated into two square wave signals, which are respectively output to two gate stages of the DC-DC converter. Both square wave signals are delayed by the phase shift angle and are respectively output to the other two gate stages of the DC-DC converter, and finally the control voltage is output.

[0012] Further, the switching frequency in the post-stage charging circuit is 85 kHz, a feed-forward phase shift of 0.2 is given, and the maximum phase shift angle for each pair of bridge arms is 1 / 2 cycle, and the phase shift angle Vset = 0.2 / 85000 / 2.

[0013] A high-power DC charging station for electric vehicles, comprising a plurality of charging modules connected in parallel to a three-phase AC input. The output end of each charging module is connected to a charging pile, and the output ends of all charging modules are connected in series through switches. Each charging module includes a protection device, a pre-stage charging circuit, and a post-stage charging circuit; the high-power DC charging station for electric vehicles is controlled by the above-mentioned control optimization method for high-power DC charging stations for electric vehicles.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The Vienna rectifier circuit of the present invention adopts a three-level SVPWM algorithm based on the two-level theory. By simplifying the space vector operation, the power factor on the grid side is significantly improved. Compared with the traditional three-level SVPWM method, this algorithm realizes high-efficiency power factor correction while avoiding complex trigonometric function calculations, reducing the operation burden of the control system, and improving the real-time control ability. The power factor is close to 1, which helps to reduce grid losses and improve the stability and efficiency of grid operation. The optimization of the power factor and the realization of high-efficiency energy transmission reduce the power loss of the charging station. At the same time, the charging system operates more efficiently, which helps to reduce carbon dioxide emissions and meets the requirements for energy utilization efficiency and environmental protection under the "dual-carbon" goal.

[0015] The post-stage charging circuit of the present invention realizes fast closed-loop stability adjustment through PI control and feed-forward phase-shift control. The feed-forward phase-shift control predicts the circuit state change in advance and performs pre-regulation, enabling the output voltage to quickly reach a stable state in a dynamic charging scenario, thereby shortening the charging time and improving the charging efficiency. At the same time, through the precise control of the switch conduction time and phase-shift angle, the safety and stability of the system under high-power output are ensured, avoiding overload or instability problems.

[0016] The control strategy of the present invention has good flexibility and can operate efficiently within different battery types and charging voltage ranges. By optimizing the charging circuit and control system design, the voltage output range is wide and continuously adjustable, and it can adapt to the power batteries of different models of electric vehicles. This strong adaptability not only improves the user experience but also significantly enhances the versatility and market competitiveness of the charging station.

[0017] The proposed routing parallel structure of the present invention allows multiple charging modules to operate in parallel. By flexibly expanding the number of modules, it can meet the charging requirements of up to several hundred kilowatts. This modular design can not only significantly increase the total output power of the system to meet the needs of large electric vehicles and multiple vehicles charging simultaneously during peak hours, but also flexibly adjust the module configuration according to specific application scenarios, reduce the initial construction and operation and maintenance costs, and enhance the economy and applicability of the system. The introduction of the routing parallel technology ensures power balance among the charging modules. Even if a certain charging module fails, the intelligent management system can switch to a standby charging module or adjust the operation strategy to ensure the normal operation of the overall system. In addition, the modular design makes expansion and maintenance more convenient, reduces downtime, and improves the reliability and economy of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural diagram of a routing parallel high-power DC charging station according to the present invention; Figure 2 It is a topology diagram of the Vienna rectifier circuit according to the present invention; Figure 3 It is a schematic diagram of the energy flow path under 8 switch combinations of the interval three-time according to the present invention; Figure 4 It is a schematic diagram of the division of small sectors in the first large sector based on the three-level method according to the present invention; Figure 5 It is a topology diagram of the phase-shifted full-bridge circuit according to the present invention; Figure 6 It is a schematic diagram of the switch state and output of the phase-shifted full-bridge circuit according to the present invention; Figure 7 It is a structural diagram of the voltage closed-loop feedback control according to the present invention; Figure 8 It is a schematic diagram of the voltage closed-loop feedback control circuit according to the present invention; Figure 9 It is a charging power curve diagram according to the present invention; Figure 10 It is a dynamic charging output curve diagram according to the present invention; Figure 11 It is a schematic diagram of a high-power DC charging station model according to the present invention; Figure 12 It is a dynamic charging output curve diagram of the high-power DC charging station model according to the present invention; Figure 13 It is a power factor curve diagram according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] Embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where like or similar reference numerals designate like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary only for explaining the present invention and should not be construed as limiting the present invention.

[0020] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the described features. In the description of the present invention, "a plurality" means two or more unless otherwise specifically defined.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs. The terms "mounted", "connected", "coupled" should be construed broadly, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection or can communicate with each other; it can be directly connected, or indirectly connected through an intermediate medium, and can be the internal communication of two elements or the interaction relationship between two elements. The term "and / or" used herein includes any and all combinations of one or more of the related listed items. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. The terms used in the description of the present invention in this specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0022] In the present invention, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature may include the direct contact between the first and second features, or may include the situation where the first and second features are not in direct contact but in contact through additional features therebetween. Moreover, the first feature being "above", "over" and "on top of" the second feature includes that the first feature is directly above and obliquely above the second feature, or merely indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature being "under", "beneath" and "underneath" the second feature includes that the first feature is directly below and obliquely below the second feature, or merely indicates that the horizontal height of the first feature is less than that of the second feature.

[0023] The following disclosure provides many different embodiments or examples for implementing different structures of the present invention. To simplify the disclosure of the present invention, the components and settings of specific examples are described hereinafter. Of course, they are merely examples and are not intended to limit the present invention. In addition, the present invention may repeat reference numerals and / or reference letters in different examples. Such repetition is for the purpose of simplification and clarity, and does not itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides examples of various specific processes and materials, but those of ordinary skill in the art may be aware of the application of other processes and / or the use of other materials.

[0024] As Figure 1 As shown, the high-power DC charging station for electric vehicles described in the present invention adopts a routing parallel structure of a high-power DC charging station, which includes a plurality of charging modules connected in parallel to a three-phase AC input. A charging pile is connected to the output end of each charging module, and all the output ends of the charging modules are connected in series through switches. Each charging module includes a protection device, a pre-stage charging circuit and a post-stage charging circuit. The Vienna rectifier is used as the pre-stage charging circuit of the charging module. The pre-stage charging circuit is connected to a pre-stage control circuit. The post-stage charging circuit adopts a phase-shifted full-bridge circuit, and the post-stage charging circuit is connected to a post-stage control circuit.

[0025] The routing parallel technology connects a plurality of charging modules in parallel through switches to form a high-power charging station. The DC charging station realizes unified power scheduling by adopting an intelligent management system and a power distribution device, which can not only greatly improve the charging power of ordinary vehicles, but also solve the problem of insufficient power of traditional single DC charging modules. The parallel charging modules can achieve efficient energy transfer and power control, and realize power balance and optimized distribution through an intelligent control system. This structure can effectively improve the charging efficiency and charging speed, and meet the requirements of different vehicle models and charging needs.

[0026] Pre-stage charging circuit: There are two types of Vienna rectifiers, namely three-phase three-wire and three-phase four-wire. In the three-phase three-wire system, the midpoint of the capacitor is not connected to the neutral point of the power grid; while in the three-phase four-wire system, the midpoint of the capacitor is connected to the neutral point of the power grid. For the three-phase four-wire topology, there is a neutral wire connecting the midpoint of the grid side and the midpoint of the output bus, and the application scenario is limited. The present invention adopts the main circuit topology based on the three-phase three-wire system, such as Figure 2 as shown.

[0027] Each phase of the three phases of the Vienna rectifier is provided with a reverse series switch tube, S a , S b , S c respectively represent three reverse series switch tubes, and each phase has the same working process. A power grid cycle can be divided into 6 small intervals. Each time the interval is switched, the polarity of one phase of the abc phases of the rectifier will change.

[0028] 1 indicates that the reverse series switch tube is on, 0 indicates that the reverse series switch tube is off, and there are 23 states of the reverse series switch tube, that is, 8 combination modes.

[0029] Taking the third interval as an example, when U a >0, U b >0, U c <0. The energy flow paths of the eight switch states of S a , S b , S c are as shown in Figure 3 as shown, and the thick red part in the figure is the current path.

[0030] At the third interval, the magnitudes of U ao , U bo , U co in the eight switch states are shown in Table 1.

[0031] Table 1 Magnitudes of the output voltage of each phase in 8 switch combinations at the third interval

[0032] Build a Vienna rectifier circuit in Simulink, with a three-phase three-wire system and a reverse series switch structure as the topology of the main circuit. IabcMess is the input three-phase alternating current phase current, VabcMess is the input phase voltage, and VDcBus is the output voltage. Vne is the output of the front-end control loop of the output direct current, which is defined as Vneutral. When the voltage at the midpoint of the two capacitors at the end is higher than half of the output voltage, Vneutral is equal to 1, otherwise it is -1. SA, SB, and SC are the switching signals of the reverse series switches, with two values: 0 and 1. When SA (SB, SC) = 0, the reverse series switch conducts to the left; when SA (SB, SC) = 1, the reverse series switch conducts to the right.

[0033] Front-end control circuit: In order for the Vienna rectifier circuit to operate properly, appropriate control signals are needed to control its operation. There are mainly three control signal modulation methods for the Vienna rectifier circuit, namely sinusoidal pulse width modulation (SPWM), selective harmonic elimination PWM (SHEPWM), and space vector pulse width modulation method (SVPWM). When the switching frequency of SVPWM modulation is low, the degree of sinusoidality is low, the voltage utilization rate is low, and the THD is large. Therefore, this invention adopts the SVPWM modulation method and applies the PWM Generator (Vienna Rectifier) module. This module uses a simplified space vector modulation method (SVPWM) based on the equivalence between two-level and three-level converters to generate control pulses. Compared with the traditional three-level SVPWM method, this modulation method avoids a large number of trigonometric function operations and is more simple and effective in calculation.

[0034] Based on SVPWM in the two-level mode, the space vector is first divided into six large sectors. Each large sector starts at -30° and is divided into a small sector every 60°. Each small sector is a regular hexagon and is arranged alternately. The distance from vector V0 to the midpoint of each large sector is the vector V1 - V6 corresponding to each small sector. By determining the large sector where the target voltage vector is located, the target voltage vector in the three-level space is converted into the target voltage vector in the small sector, that is (1) Among them, U'ref is the synthesized target voltage vector, Uref is the original target voltage vector.

[0035] Similarly, by subtracting the corresponding vector of the small sector, the basic voltage vector is corrected to obtain the corrected basic voltage vector, realizing the vector synthesis from the three-level to the two-level space, as Figure 4 shown.

[0036] Determine the corrected target voltage vector U'ref Determine the small sector where it is located. The small sector judgment rules are shown in Table 2.

[0037] Table 2 Small sector judgment rules based on two-level mode

[0038] After determining the large and small sectors, determine the action time of the basic voltage vector according to the small sector where it is located. Taking the No. I small sector in the first sector as an example, the basic vectors in this small sector are .

[0039] (2) Solve to get: (3) In summary, the whole process of the pre-stage control circuit outputting the control signal is as follows: The input line voltage of the Vienna rectifier is 380V three-phase alternating current, and the output is direct current. First, define the output of the pre-stage control circuit of the output direct current as Vneutral. When the voltage at the midpoint of the two capacitors at the end is higher than half of the output voltage, Vneutral is equal to 1, otherwise it is -1. The charging pile inputs the measured vectors of the three-phase input voltage and input current, the voltage value of the output direct current, and Vneutral to the pre-stage control circuit of the Vienna rectifier circuit. After obtaining the signal, the pre-stage control circuit first determines the direction of the voltage. To make the current direction as close as possible to the voltage direction (the power factor is close to 1), the Nearest Three-Vector method is used, and the three basic voltage vectors closest to the target voltage vector in the sector where it is located are used for synthesis. In this synthesis process, the method based on two-level space vector modulation is applied, and finally the action time of the target voltage vector is obtained, so as to determine the states of each switch.

[0040] Post-stage charging circuit: The direct current output by the Vienna rectifier is input to the post-stage charging circuit, and the post-stage charging circuit adopts a phase-shifting full-bridge circuit.

[0041] The topological structure of the Phase-Shifting Full-Bridge Converter (PSFB) circuit is as Figure 5 shown. The phase-shifting full-bridge circuit consists of two parts: the primary inverter side and the secondary rectifier side. Four MOSFETs are used on the primary side to form a full bridge, which are composed of two half bridges respectively. The two switching nodes of the half bridge are respectively connected to both ends of the transformer. The secondary side of the transformer adopts a center-tapped structure, which is an uncontrollable diode full-wave rectifier circuit. The structure is simple and does not participate in the voltage regulation process. The existence of the transformer is due to the consideration of system safety and relevant regulations. This topology is called an isolated converter topology.

[0042] Primary-side voltage of the phase-shifted full-bridge circuit transformer v AB , current i p , output voltage v out as Figure 6 shown

[0043] t 0 -t 1 In the stage, the primary side S 1 and S 4 conduct simultaneously, and the secondary side D 5 conducts, and the current i p is in the rising state of the positive half-cycle

[0044] t 1 -t 2 In the stage, S 4 receives the trigger signal and conducts. At the same time S 1 turns off S 1 The parasitic capacitance of S 3 is charged, and the parasitic capacitance of S3 is discharged to prepare for the ZVS turn-on of

[0045] t 2 -t 3 In the stage S 3 turns on at zero voltage and continues to flow through L the freewheeling

[0046] t 3 -t 4 In the stage S 4 turns off S 4 The parasitic capacitance of S 2 is charged, and the parasitic capacitance of S 2 is discharged to prepare for the ZVS turn-on of D 5 and D 6During the commutation stage, the primary current is not sufficient to support the load current.

[0047] t 4 -t 5 stage, S 2 The switch ZVS turns on. The current drops to 0 at t 5 moment and starts to increase in the opposite direction at the next moment. The secondary D 5 and D 6 is still in the circulating current stage, and the primary current is not sufficient to support the load current.

[0048] t 5 -t 6 stage, the primary S 2 and S 3 conduct simultaneously. The secondary D 5 conducts. The current i p rises on the negative half-axis.

[0049] So far, one cycle ends, enters the next cycle, and repeats the above process.

[0050] Post-stage control circuit: Digital PID control adjusts the output voltage discretely and comparatively in each sampling period, enabling the output voltage of the system to be stably and reliably output. However, the way of obtaining the differential signal in PID control will cause the amplification of interference signals and affect the system stability. Therefore, the present invention uses a post-stage control circuit to modulate the post-stage charging circuit using voltage closed-loop feedback control (closed-loop PI control).

[0051] Figure 7 The system structure diagram of the voltage control mode is shown, which is a classic closed-loop feedback control mode. The feedback loop of this mode can effectively eliminate the influence of external interference and internal disturbance on the system performance and achieve precise control of the output voltage.

[0052] The specific implementation process of the closed-loop PI control is as follows.

[0053] (1) Feedback the output voltage of the post-stage charging circuit and the control voltage to find the difference and calculate the error.

[0054] (2) Output the error to the PI regulator (compensator). The compensator formula is , the parameters of PI control can be obtained by the method of trial parameters, P = 0.1, I = 0.003.

[0055] (3) The output of the compensator is added to to obtain the total control amount. The switching frequency is 85 kHz, and the feedforward phase shift control is preset to accelerate the calculation to reach the stable speed. The present invention gives a feedforward phase shift of 0.2, and the maximum phase shift angle of each pair of bridge arms is 1 / 2 cycle, so there is Vset = 0.2 / 85000 / 2. The switching frequency is 85 kHz.

[0056] (4) The phase shift angle is limited by the Saturation module. The upper limit is 0.98 / 85000 / 2, and the lower limit is 0.02 / 85000 / 2.

[0057] (5) Use a square wave generator to generate two square wave signals, both with a period of 1 / 85000 seconds and a pulse width of 49 (percentage of the period) to prevent short circuits due to simultaneous conduction. The phase delay of one generator is 0 seconds, and the other generator is 1 / 85000 / 2 seconds.

[0058] (6) Output the two square wave signals generated in (5) to the gate levels of the DC-DC converters S1 and S2 respectively.

[0059] (7) Use the Variable Time Delay module to delay the two square wave signals generated in (5) by the phase shift angle generated in (3), and output them to the gate levels of the DC-DC converters S4 and S3 respectively.

[0060] So far, the closed-loop PI control ends, and the control circuit is as Figure 8 shown.

[0061] Through innovations in circuit design and control methods, the present invention has achieved an overall improvement in charging efficiency, power factor, dynamic response, adaptability, and system reliability. It can not only significantly improve the technical bottlenecks of existing high-power DC charging stations but also provide important technical support and reference value for the development of future new energy vehicle charging infrastructure.

[0062] Simulation of the single charging module control method: The single charging module model implemented by the present invention connects the front-stage charging circuit and the rear-stage charging circuit in series. On this basis, we successively set the output voltages to 342V, 344V, 344.25V, and 344.4V, and obtained the charging power curves as Figure 9 shown. The results of multiple experiments show that the maximum charging power of the model is slightly higher than 20 kW, and the charging voltage is 344.25V at this time. When the output is too high, the charging power curve will show a phenomenon of temporarily losing stability.

[0063] To verify the adjustability of the simulation power control and its response speed, the Manual Switch module in Simulink is used to adjust Vref. First, set Vref to 344.25V. After the output enters the steady state for a period of time, change Vref to 342V, and then set Vref to 344.25 after a period of time. The waveform is as Figure 10 shown.

[0064] As can be seen from the above dynamic waveform of the power control simulation, this model has the adjustability of power control, a relatively fast response speed, and has reference value for the further experiment and optimization of the power battery charging control.

[0065] Simulation of the control method for high-power DC charging stations: In Simulink, a single module is encapsulated into a subsystem, and 6 modules are connected in parallel, as Figure 11 shown.

[0066] To verify the adjustability of the simulation of the power control of the parallel high-power charging station and its response speed, repeat the methods of the pre-stage control circuit and the post-stage control circuit. Use the Manual Switch module in Simulink to adjust the Vref of the 6 modules. First, set Vref to 350V. After the output enters the steady state for a period of time, change Vref to 362V. The waveform is as Figure 12 shown.

[0067] From the above dynamic waveform of the power control simulation, this model has the adjustability of power control and a relatively fast response speed, and can provide reference for the further experiment of the power control of high-power charging stations for electric vehicles.

[0068] Power factor on the grid side To maintain the stable operation of the grid and the efficient use of electric energy, the power factor of the DC charging pile of the present invention should be as close to 1 as possible. Measure the change of the power factor with time on the grid side of a single module. The power factor on the grid side at an output voltage of 342V is as Figure 13 shown, and the power factor on the grid side at an output voltage of 344V is as Figure 13 shown.

[0069] It can be seen that since the phase of the control voltage and current of the pre-stage Vienna rectifier circuit is as equal as possible, the power factor on the grid side of the power control simulation model of the DC charging pile designed by the present invention is close to 1. At the same time, as the output increases, the overall power factor will decrease.

[0070] The serial numbers of the embodiments of the present application above are only for description and do not represent the advantages and disadvantages of the embodiments.

[0071] In the above embodiments of the present application, the descriptions of the respective embodiments have their own emphases. For parts not detailed in a certain embodiment, reference may be made to the relevant descriptions of other embodiments.

[0072] In several embodiments provided by the present application, it should be understood that the disclosed technical content can be implemented in other ways. Among them, the device embodiments described above are merely illustrative. For example, the division of the units can be a logical function division. In actual implementation, there can be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed couplings or direct couplings or communication connections with each other can be through some interfaces. The indirect couplings or communication connections of the units or modules can be in an electrical or other form.

[0073] The units described as separate components may or may not be physically separated. The components displayed as units may or may not be physical units, that is, they can be located in one place or distributed to multiple units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0074] The above is only the preferred embodiment of the present application. It should be noted that for those of ordinary skill in the art in the technical field, without departing from the principle of the present application, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present application.

[0075] It should be understood that the above description is for illustrative purposes and not for limitation. By reading the above description, many embodiments and many applications other than the provided examples will be obvious to those skilled in the art. Therefore, the scope of this patent should not be determined with reference to the above description, but should be determined with reference to the full scope of the foregoing claims and the equivalents of these claims. For the sake of comprehensiveness, all articles and references including patent applications and published announcements are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein in the foregoing claims is not intended to abandon such subject matter, nor should it be considered that the applicant has not considered such subject matter as part of the disclosed inventive subject matter.

Claims

1. A control optimization method for a high-power DC charging station for electric vehicles, characterized in that: The process includes: The external three-phase AC power is input into the Vienna rectifier as the front-stage charging circuit, and the output voltage value of the Vienna rectifier is input into the front-stage control circuit. After the front-stage control circuit obtains the output voltage value of the Vienna rectifier, it first determines the direction of the voltage, and adopts the nearest three-vector method to synthesize the three basic voltage vectors closest to the target voltage vector. During the synthesis process, a three-level SVPWM algorithm based on the two-level theory is adopted, and finally the action time of the target voltage vector is obtained, thereby controlling the Vienna rectifier.

2. The electric vehicle high-power DC charging station control optimization method according to claim 1 is characterized in that: The process of the three-level SVPWM algorithm based on the two-level theory is as follows: first, the space vector is divided into six large sectors, each large sector is divided into multiple small sectors, each small sector is a regular hexagon, and is staggered. The distance between the vector V0 and the midpoint of each large sector is the vector corresponding to each small sector; by determining the large sector where the target voltage vector is located, the target voltage vector in the three-level space is converted into the target voltage vector in the small sector, and the basic voltage vector is corrected by subtracting the vector corresponding to the small sector to obtain the corrected basic voltage vector. The action time of the three corrected basic voltage vectors is determined according to the small sector where they are located, and the action time of the target voltage vector is synthesized.

3. The electric vehicle high-power DC charging station control optimization method according to claim 2 is characterized in that: Each large sector starts at -30° and every 60° zone is divided into a small sector.

4. The electric vehicle high-power DC charging station control optimization method according to claim 1 is characterized in that: The output of the front-stage control circuit is defined as Vneutral. When the midpoint voltage of the two capacitors at the end of the Vienna rectifier is higher than half of the output voltage, Vneutral is equal to 1, otherwise it is -1. The input of the front-stage control circuit is: the vector of the input voltage and input current of the Vienna rectifier, the voltage value of the output DC power and Vneutral.

5. The electric vehicle high-power DC charging station control optimization method according to claim 1, characterized in that: Vienna rectifier adopts three-phase three-wire topology.

6. The electric vehicle high-power DC charging station control optimization method according to claim 1 is characterized in that: The Vienna rectifier outputs direct current, which is then input into the subsequent charging circuit.

7. The electric vehicle high-power DC charging station control optimization method according to claim 6 is characterized in that: A post-stage control circuit is used to modulate the post-stage charging circuit through voltage closed-loop feedback control.

8. The electric vehicle high-power DC charging station control optimization method according to claim 7 is characterized in that: The PI control process is: The output voltage feedback of the subsequent charging circuit and the control voltage are subtracted to calculate the error; Output the error to the PI regulator; The total control quantity is obtained by summing the output of the PI regulator and the phase shift angle, and the phase shift angle in the total control quantity is limited; The total control quantity is generated into two square wave signals, which are respectively output to two gate levels of the DC-DC converter; Both square wave signals are delayed and shifted to the angle, and are output to the other two gate stages of the DC-DC converter respectively, and finally output the control voltage.

9. The electric vehicle high-power DC charging station control optimization method according to claim 8, characterized in that: The switching frequency in the post-stage charging circuit is 85kHz, and a feedforward phase shift of 0.2 is given. The maximum phase shift angle of each pair of bridge arms is 1 / 2 cycle. Vset =0.2 / 85000 / 2.

10. A high-power DC charging station for electric vehicles, characterized in that: It comprises a plurality of charging modules connected in parallel to a three-phase AC input, each charging module output end is connected to a charging pile, and the output ends of all the charging modules are connected in series through switches, and each charging module comprises a protection device, a front-stage charging circuit and a rear-stage charging circuit; the electric vehicle high-power DC charging station is controlled by the electric vehicle high-power DC charging station control optimization method described in any one of claims 1-9.

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