A bidirectional charging topology and control method for electric vehicles

Abstract

The application discloses a bidirectional charging topology structure and control method of an electric vehicle, wherein the bidirectional charging topology structure can work in a constant current mode or a constant voltage mode to realize charging of a power battery of the electric vehicle, and can be converted into a power generation state to feed back power battery electric energy to a power grid during a power consumption peak period, so that peak load shifting is realized and stability of the power grid is maintained. Almost all switches in the topology work in a soft switching state, high operation efficiency can be realized, and the interleaved parallel structure in the topology can ensure fault-tolerant operation of the system and greatly reduce high-order harmonics. Furthermore, the control method of the application considers various possible operation modes, so that the converter can work in a constant current mode, a constant voltage mode or a constant power mode, the included soft start control ensures that there is no impact current when the converter starts, and the included energy reversal control ensures that the converter can be smoothly switched between the charging mode and the power generation mode.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronic conversion technology, and particularly relates to a bidirectional charging topology structure and control method for electric vehicles. BACKGROUND

[0002] In the past decade, the penetration rate of electric vehicles has rapidly increased, and the charging of electric vehicle power batteries has become an important issue. At present, the mainstream electric vehicle power battery charging technology includes battery replacement and charging, but the battery replacement technology is limited by enterprise resources and other factors, and it is difficult to popularize at this stage. Fixed charging mainly relies on AC-DC converters to convert alternating current in the power grid into direct current for battery charging. A large number of power battery chargers connected to the network will impact the existing power grid. Reasonable use of power battery characteristics and regulation of battery charging and discharging plans can feed part of the battery energy back to the power grid at appropriate times. Under the current background of implementing peak-valley time-of-use electricity prices, not only can it play a role in peak load shifting and reduce power grid dispatching costs, but also can bring economic benefits to users. In order to realize battery charging and battery energy feedback, a high-power bidirectional isolated AC-DC converter becomes the key to the entire system.

[0003] A high-power bidirectional isolated AC-DC converter can generally be divided into two stages. The front stage is connected to the grid and converts three-phase alternating current into direct current. In order to make the system meet the relevant standards of power grid harmonics, the input current needs to be sinusoidal, that is, the front stage has a PFC function. The rear stage is usually a DC-DC converter with an isolation function, which can adjust the gain in a wide range.

[0004] At present, the commonly used PFC circuit for the front stage is a six-switch two-level voltage source rectifier or a T-type three-level rectifier. The characteristics of this type of converter are that the bus voltage is constant, the input current is sinusoidal and the phase is arbitrarily controllable, but all switches work in a high-frequency switching state, which reduces the operating efficiency of the system. The commonly used topology for the rear stage is usually evolved from traditional isolated unidirectional DC-DC converters. The transformer on both sides can use push-pull, half-bridge, full-bridge, and other structures. However, considering that the high-power bidirectional conversion structure must achieve soft switching, and from the perspective of system power, the number of power devices used by the circuit on both sides of the transformer is basically proportional to the power handled, so the number of bidirectional isolated DC-DC topology structures that can be selected is extremely limited.

[0005] Dual active bridge (DAB) converter is the most representative and most widely used high-power DC-DC converter, and the main control is phase-shift control. The working principle is that two full bridges adopt fixed frequency and duty cycle of 0.5 signal division, and the energy transmission direction and amplitude are controlled by adjusting the phase shift angle of the two full bridge driving signals to adjust the current direction and size of the leakage inductance, thereby controlling the energy transmission direction and amplitude. However, DAB will generate a large circulating current when the input and output voltages are not matched, and the ZVS implementation range becomes smaller as the load decreases, which will increase the loss. In order to solve this problem, various extended phase-shift controls are proposed, although the above problems can be solved, but the control difficulty also increases. SUMMARY

[0006] The problem to be solved by the present application is to provide a bidirectional charging topology structure and control method for electric vehicles, which can realize the functions of charging power batteries of electric vehicles and energy feedback to the power grid, and has higher operation efficiency, and can better handle various complex working conditions such as battery charging and power generation.

[0007] The application adopts the following technical scheme: a bidirectional charging topology structure for electric vehicles, comprising:

[0008] Structure S1: input LC filter, comprising filter inductor L f and three filter capacitors C f , one end of the filter inductor L f is connected with a grid-side power supply, and the other end is connected to the bridge arm midpoint of the three-phase bridge rectifier circuit, and the three filter capacitors C f are star-connected, and the input ends are respectively connected with three output ends x, y and z of an input voltage selector of structure S2;

[0009] Structure S2: input voltage selector, comprising a three-phase bridge rectifier circuit and three bidirectional switches, each bidirectional switch being composed of two reverse series full-controlled devices, the three bidirectional switches being star-connected, and the three input ends being respectively connected with the bridge arm midpoints of the three-phase bridge rectifier circuit;

[0010] Structure S3: harmonic current injection circuit, comprising a bridge arm and an inductor, the bridge arm being connected in parallel with the bus of the three-phase bridge rectifier circuit, one end of the inductor being connected with the bridge arm midpoint of the three-phase bridge rectifier circuit, and the other end being connected with the star connection midpoint of the three bidirectional switches;

[0011] Structure S4: interleaved parallel CLLLC resonant converter, comprising three CLLLC submodules, each CLLLC submodule comprising a full-bridge circuit and a resonant cavity, the resonant cavity containing a double-winding transformer, the primary and secondary sides of the double-winding transformer being connected with the midpoints of two bridge arms of the full-bridge circuit through a resonant inductor and a resonant capacitor, and the primary and secondary sides of the three resonant cavities in the three CLLLC submodules being star-connected.

[0012] The technical scheme of the present application also includes a control method of the bidirectional charging topology of an electric vehicle, applied to the bidirectional charging topology of the electric vehicle, comprising the following steps:

[0013] Step 1, control the input voltage selector described in structure S2: sample the three-phase input voltage, control the three-phase bridge rectifier circuit to work in a low-frequency switching state in a synchronous rectification mode, and the switching tube is turned on according to the logic of diode uncontrolled rectification;

[0014] Step 2, control the harmonic current injection circuit described in structure S3, control a bridge arm to work in a high-frequency switching state, and realize the input current sine;

[0015] Step 3, control the interleaved parallel CLLLc resonant converter described in structure S4, determine the working mode of the CLLLc resonant converter according to different working conditions, obtain the driving signal of each CLLLc sub-module, and use the CLLLc resonant converter as a bidirectional converter to realize the charging of the electric vehicle power battery and the energy feedback of the battery to the power grid.

[0016] Specifically, for the input voltage selector described in structure S2, the control strategy includes the following contents:

[0017] Sample the three-phase input voltage, and when the grid voltage harmonics are not considered, the sampled three-phase voltage is:

[0018]

[0019] Wherein, U N represents the input voltage amplitude, and θ represents the input voltage phase angle.

[0020] The switching tube of the three-phase bridge rectifier circuit of the input voltage selector is turned on according to the logic of diode uncontrolled rectification, that is, the three-phase bridge rectifier circuit can be considered to work in a synchronous rectification mode. At this time, the bus of the rectifier circuit obtains the maximum and minimum values of the three-phase voltage. For the phase whose voltage is in the middle, the corresponding bidirectional switch is turned on, and the rest of the bidirectional switches are turned off.

[0021] According to the above principle, the output voltage of the input voltage selector is

[0022]

[0023] The turn-on logic of the bidirectional switch is:

[0024] S b , S a , S c , S b , S a , S c ……

[0025] Specifically, for the harmonic current injection circuit described for structure S3, the control strategy includes the following:

[0026] Step 3.1, obtain the output power P of the CLLLC resonant converter: here the power flowing from the grid side to the power battery side is defined as positive, and the power flowing from the power battery side to the grid side is defined as negative. The power can be obtained by the following method:

[0027] Method 1: obtained by the current sensor and voltage sensor on the battery side;

[0028] Method 2: if the CLLLC resonant converter works in constant power mode, directly take the power command value as the actual power of the system.

[0029] Step 3.2, obtain the given value i yref of the harmonic injection current according to the obtained system power and input voltage yref The expression for obtaining the given current i

[0030]

[0031] In the formula, U N The three-phase voltage obtained by sampling the phase angle θ is obtained by coordinate transformation:

[0032]

[0033] Step 3.3, take the obtained i yref as the reference value of the harmonic injection current, take the actual current i y as the feedback value, and subtract the reference value, and obtain the additional voltage u y of the harmonic injection inductance L y through the controller G L :

[0034]

[0035] In the formula, k py , k iy respectively represent the proportional gain coefficient and integral gain coefficient of the harmonic injection current PI regulator, and s is the Laplace operator.

[0036] Step 3.4, superimpose the additional voltage u L of the harmonic injection inductance on the output voltage u yz of the input voltage selector (defined as the voltage difference between the output node y and the output node z), and obtain the duty cycle d of the harmonic current injection circuit through the inverse of the bus voltage u xz ​yp :

[0037]

[0038] Step 3.5, the obtained duty ratio is compared with the carrier intercept to obtain a PWM driving signal of harmonic current injection.

[0039] Specifically, for the CLLL C resonant converter described in structure S4, the control strategy includes the following contents:

[0040] Step 4.1, determine the working mode of the CLLL C resonant circuit according to different working conditions, which can be mainly divided into the following modes, and the equivalent gain M of the CLLL C resonant circuit needs to be obtained in different modes eq .

[0041] Mode 1, constant current mode in charging state: in the initial stage of charging the power battery (less remaining battery capacity), the converter needs to work in constant current mode. At this time, according to the characteristics of the power battery, the given value i of the charging current is given oref . The obtained i oref is taken as the reference value of the charging current, the actual charging current i o is taken as the feedback value, the difference between the obtained reference value and the feedback value is obtained through the proportional integral controller, and the equivalent gain M of the CLLL C resonant converter is obtained eq :

[0042]

[0043] In the formula, k ip , k ii respectively represent the proportional gain coefficient and the integral gain coefficient of the output current PI regulator.

[0044] Mode 2, constant voltage mode in charging state: in the end stage of charging the power battery (more remaining battery capacity). The converter needs to work in constant voltage mode. At this time, according to the characteristics of the power battery, the given value u of the charging voltage is given oref . The obtained u oref is taken as the reference value of the charging voltage, the actual charging voltage u o is taken as the feedback value, the difference between the obtained reference value and the feedback value is obtained through the proportional integral controller, and the equivalent gain M of the CLLL C resonant converter is obtained eq :

[0045]

[0046] In the formula, k up , k ui respectively represent the proportional gain coefficient and the integral gain coefficient of the output voltage PI regulator.

[0047] Mode 3: Constant power mode in energy reversal state. In the energy reversal state, the power P ref injected into the grid is obtained according to the grid side, and the actual power P ref generated is taken as the reference value of the charging current, and the actual power P o generated is taken as the feedback value, and the difference between the two is obtained through a proportional-integral controller to obtain the equivalent gain M eq of the C-LLC resonant converter:

[0048]

[0049] wherein k Pp and k Pi represent the proportional gain coefficient and the integral gain coefficient of the power transmission PI regulator respectively.

[0050] According to the equivalent gain M eq obtained under different modes, the actual gain M is obtained according to the following formula:

[0051]

[0052] wherein θ1 is the value obtained by taking the input voltage phase angle θ modulo π / 3, and after obtaining the actual gain M, the switching frequency of the resonant converter at the current time is obtained through the gain-switching frequency curve of the C-LLC resonant converter.

[0053] Step 4.2: According to different working conditions and the switching frequency of the resonant converter, the driving signal of each sub-module of the resonant converter is obtained, which is specifically divided into the following processes.

[0054] Control logic 1: soft start control: soft start is realized by using the phase shift method. At the start, the duty cycle d r is 0, and then gradually increases until the output voltage u o rises to the given voltage u oref . The curve of the duty cycle changing with time is given according to the following formula:

[0055]

[0056] wherein w represents the soft start coefficient, which is set in the interval (0, 1); k t is a constant, which controls the start rate, and if k t increases, the start rate can be accelerated.

[0057] Control logic 2, energy reversal control: when entering the energy reversal control stage, gradually reduce the input power of the CLLL resonant converter and turn to negative, the energy is transmitted from the power battery side to the network side. This stage needs to maintain the converter voltage smooth, Bang-Bang control is adopted, and the control is carried out through the control of the network side resonant capacitor voltage.

[0058] When the resonant capacitor voltage drops to the lower threshold, the power supply charges the resonant capacitor, and the corresponding upper switch tube is turned on. When the resonant capacitor voltage rises to the upper threshold, the corresponding lower switch tube is turned on.

[0059] Control logic 3, interleaved parallel control: for three sub-modules, the carrier of each sub-module is different by 120°, and the carrier frequency of the sub-module is the switching frequency of the CLLL resonant converter obtained in step 1. After the carrier is compared with the duty cycle, the driving signal of each module is obtained.

[0060] Compared with the prior art, the above technical scheme has the following technical effects:

[0061] 1. The bidirectional charging topology structure for electric vehicles provided by the application has almost no switching loss while realizing input current sine, and the circuit rear stage adopts the CLLL resonant converter, which can better realize the functions of electric vehicle power battery charging and energy feedback to the power grid, and has higher efficiency when working in a soft switching state.

[0062] 2. The bidirectional charging topology control method for electric vehicles provided by the application can flexibly control the charging voltage and charging current of the power battery, and can smoothly and quickly switch between charging operation and power generation operation when energy needs to be fed back to the power grid. BRIEF DESCRIPTION OF DRAWINGS

[0063] Figure 1 It is a principle block diagram of the bidirectional charging topology and control method for electric vehicles of the application;

[0064] Figure 2 It is a module control block diagram of the bidirectional charging topology structure for electric vehicles of the application;

[0065] Figure 3 It is a control block diagram of the CLLL resonant converter part of the bidirectional charging topology for electric vehicles of the application. DETAILED DESCRIPTION

[0066] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0067] In an embodiment of the present application, the electric vehicle bidirectional charging topology and control method, as shown in Figure 1 , mainly consists of the following parts:

[0068] Structure S1: input LC filter.

[0069] The filter inductor L f is connected with the grid-side power supply, and the other end is connected to the three-phase bridge rectifier circuit bridge arm midpoint. The filter capacitor C f is star-connected, and the three input ends are respectively connected with the three output ends x, y and z of the input voltage selector.

[0070] Structure S2: input voltage selector.

[0071] It is composed of a three-phase bridge rectifier circuit and three bidirectional switches. Each bidirectional switch is composed of two antiparallel full-controlled devices. The three bidirectional switches are star-connected, and the three input ends are respectively connected with the bridge arm midpoints of the three-phase bridge rectifier circuit.

[0072] Structure S3: harmonic current injection circuit.

[0073] It is composed of a bridge arm and an inductor. The bridge arm is connected in parallel with the bus of the three-phase bridge rectifier circuit, and the inductor is connected with the bridge arm midpoint at one end and connected with the star connection midpoint of the three bidirectional switches at the other end.

[0074] Structure S4: interleaved parallel CLLLc resonant converter.

[0075] It contains three CLLLc sub-modules, and each sub-module is composed of a full-bridge circuit and a resonant cavity. Each resonant cavity contains a double-winding transformer, and the primary and secondary sides of the transformer are connected with the midpoints of two bridge arms of the full-bridge circuit through a resonant inductor and a resonant capacitor.

[0076] The primary and secondary sides of the three resonant cavities in the three CLLLc sub-modules are star-connected, and the primary and secondary sides of the three resonant cavities in the three sub-modules are star-connected.

[0077] In the embodiment, the above-mentioned electric vehicle bidirectional charging topology is controlled, as shown in Figure 2 , including:

[0078] The input voltage selector described in structure S2 is controlled: the three-phase input voltage is sampled, the three-phase bridge rectifier circuit is controlled to work in a low-frequency switching state in a synchronous rectification mode, and the switching tubes are turned on according to the logic of diode uncontrolled rectification;

[0079] The harmonic current injection circuit described in structure S3 is controlled, and one bridge arm is controlled to work in a high-frequency switching state to realize input current sine;

[0080] The interleaved parallel CLLL resonant converter described in structure S4 is controlled, the working mode of the CLLL resonant converter is determined according to different working conditions, the driving signals of each CLLL sub-module are obtained, the CLLL resonant converter is used as a bidirectional converter, and the charging of the electric vehicle power battery and the energy feedback of the battery to the power grid are realized.

[0081] It is particularly necessary to point out that, Figure 1 In each control module, the number of driving signals output by the control logic is indicated by the number beside the arrow pointing to the corresponding structure. The number of driving signals output by the control logic of the input voltage selector of structure S2 is 12, the number of driving signals output by the control logic of the harmonic current injection circuit of structure S3 is 2, and the number of driving signals output by the control logic of the interleaved parallel CLLL resonant converter of structure S4 is 6.

[0082] Specifically, for the input voltage selector described in structure S2, the control strategy includes the following contents:

[0083] The three-phase input voltage is sampled, and when the grid voltage harmonics are not considered, the sampled three-phase voltage is:

[0084]

[0085] The switching tubes of the three-phase bridge rectifier circuit of the input voltage selector are turned on according to the logic of diode uncontrolled rectification, that is, the three-phase bridge rectifier circuit is considered to work in a synchronous rectification mode. At this time, the bus of the rectifier circuit obtains the maximum and minimum values of the three-phase voltage. For the phase whose voltage is in the middle, the corresponding bidirectional switch is turned on, and the remaining bidirectional switches are turned off. According to the above principle, the output voltage of the input voltage selector is:

[0086]

[0087] According to the above principle, a complete cycle can be divided into 6 sectors, as shown in (a) of Figure 2 .

[0088] The turn-on logic of the bidirectional switch is:

[0089] S b , S a , S c, S b , S a , S c …

[0090] In particular, for the harmonic current injection circuit described in structure S3, its control strategy includes the following:

[0091] Step 1, obtain the output power of the converter.

[0092] Here, the power flowing from the grid side to the battery side is defined as a positive value, and the power flowing from the battery side to the grid side is defined as a negative value. The power can be obtained by the following method:

[0093] Method 1: obtained by the current sensor and voltage sensor on the battery side;

[0094] Method 2: if the CLLLc resonant converter works in constant power mode, directly take the power instruction value as the actual power of the system.

[0095] Step 2, obtain the given value of the harmonic injection current i yref according to the obtained system power and input voltage.

[0096] The acquisition of the given current is related to the phase corresponding to the instantaneous value of the intermediate phase of the three-phase voltage, and the specific expression of the current given i yref is:

[0097]

[0098] In the formula, U N and the phase angle θ are obtained by coordinate transformation through sampling of the three-phase voltage:

[0099]

[0100] The waveform of i yref is shown in (b) of FIG. 8. Figure 2

[0101] Step 3, take i yref obtained in step 2 as the reference value of the harmonic injection current, take the actual current i y as the feedback value, and subtract the reference value obtained in step 2, and obtain the additional voltage u L of the harmonic injection inductance L y through the controller G y (s):

[0102]

[0103] Step 4, superimpose the additional voltage u L of the harmonic injection inductance obtained in step 3 on the output voltage u​yz (Defined as the voltage difference between output node y and output node z), and transmitted through the bus voltage u. xz The reciprocal of the equation yields the duty cycle d of the harmonic current injection circuit. yp :

[0104]

[0105] Step 5: Compare the duty cycle obtained in Step 4 with the carrier intersection to obtain the PWM drive signal for harmonic current injection.

[0106] Specifically, for the CLLLC resonant converter described by structure S4, its control strategy is as follows: Figure 3 As shown, it mainly includes the following:

[0107] Step 1: Determine the operating mode of the CLLLC resonant circuit according to different operating conditions. These modes can be mainly divided into the following categories. Under each mode, the equivalent gain M of the CLLLC must ultimately be obtained. eq .

[0108] Mode 1: Constant current mode during charging.

[0109] During the initial stage of battery charging (when the battery has low remaining charge), the converter needs to operate in constant current mode. At this time, a charging current setpoint i needs to be provided based on the characteristics of the battery. oref , will obtain i oref As a reference value for the charging current, the actual charging current i o The difference between the feedback value and the acquired reference value is used to obtain the equivalent gain M of the CLLLC resonant converter through a proportional-integral controller. eq :

[0110]

[0111] Mode 2: Constant voltage mode during charging.

[0112] At the final stage of battery charging (when the battery has a significant remaining charge), the converter needs to operate in constant voltage mode. At this time, based on the characteristics of the battery, a charging voltage setpoint u is provided. oref , will obtain u oref As a reference value for the charging voltage, the actual charging voltage u is used. o The difference between the feedback value and the acquired reference value is used to obtain the equivalent gain M of the CLLLC resonant converter through a proportional-integral controller. eq :

[0113]

[0114] Mode 3: Constant power mode under energy reversal conditions.

[0115] In the energy reversal state, the power P injected into the grid needs to be obtained from the grid side. ref , will obtain P ref As a reference value for the charging current, the actual power generation P is used. o The difference between the feedback value and the acquired reference value is used to obtain the equivalent gain M of the CLLLC resonant converter through a proportional-integral controller. eq :

[0116]

[0117] The equivalent gain M obtained under different modes eq The actual gain M is obtained by finding the following formula:

[0118]

[0119] Where θ1 is the value of the input voltage phase angle θ modulo π / 3. After obtaining the actual gain M, the switching frequency of the resonant converter at the current moment is obtained by looking up the gain-switching frequency curve of the CLLLC resonant converter in a table.

[0120] Step 2: Based on different operating conditions and the switching frequency of the resonant converter, obtain the drive signal for each sub-module of the resonant converter. The specific process is as follows.

[0121] Control Logic 1: Soft start control.

[0122] Soft starting is achieved using a phase-shifting method, such as... Figure 2 As shown in (d) in the diagram, the duty cycle d at startup is... r It starts at 0, then gradually increases until the output voltage u... o Rise to a given voltage u oref The duty cycle as a function of time is given by the following formula:

[0123]

[0124] Where, k t The constant k controls the startup rate. t Increasing the number of entries can speed up the startup process.

[0125] Control Logic 2: Energy Reversal Control.

[0126] When entering the energy reversal control phase, the input power of the converter is gradually reduced and turns negative, and energy is transferred from the power battery side to the grid side. During this phase, it is necessary to maintain a stable converter voltage, which is achieved using Bang-Bang control. Figure 2 As shown in (c), the control is achieved by controlling the voltage of the resonant capacitor on the grid side.

[0127] When the resonant capacitor voltage drops to the lower threshold, the power supply charges the resonant capacitor, and the corresponding upper switch is turned on. When the resonant capacitor voltage rises to the upper threshold, the corresponding lower switch is turned on.

[0128] Control logic 3: staggered parallel control.

[0129] For three CLLLC sub-modules, as shown in (e) in the figure, the carrier of each sub-module is 120° apart, and the carrier frequency of the sub-module is the switching frequency of the CLLLC resonant converter obtained in step 1. After comparing the carrier and the duty cycle, the driving signal of each module is obtained. Figure 2

[0130] In summary, the bidirectional charging topology and control method for electric vehicles provided by the application has the following advantages: on the one hand, the front stage adopts a three-phase bridge rectifier circuit, the conduction logic is the same as that of uncontrolled rectification, and the input current is sinusoidal through the harmonic injection circuit. The three-phase bridge rectifier circuit for power transmission works in a low-frequency switching state, almost no switching loss is generated, and at the same time, only one bridge arm of the harmonic injection circuit works in a high-frequency switching state, which makes the system have very high efficiency. On the other hand, the circuit rear stage adopts a CLLLC resonant converter, which is evolved from the traditional LLC resonant converter. Whether it is forward or reverse operation, it can be approximated to the traditional LLC resonant converter. CLLLC has a highly symmetrical topology, and its advantages as a bidirectional converter are obvious. Therefore, the application can better realize the functions of charging the power battery of an electric vehicle and feeding energy back to the power grid, and at the same time has higher efficiency.

[0131] The above shows and describes the basic principles, main features and advantages of the method of the application. Those skilled in the art should understand that the application is not limited to the above embodiments, and the above embodiments and descriptions in the specification are only to illustrate the principles of the application. Without departing from the spirit and scope of the application, various changes and improvements can be made to the application, and these changes and improvements all fall within the scope of the claimed application.​

Claims

1. A bidirectional charging topology for electric vehicles, characterized in that, Comprise: Structure S1: input LC filter, including filter inductor L f and three filter capacitors C f , the filter inductor L f one end is connected with the network side power supply, and the other end is connected to the three-phase bridge rectifier circuit bridge arm midpoint, three filter capacitors C f star connection, the input end is connected with three output ends x, y, z of structure S2 input voltage selector respectively; Structure S2: input voltage selector, comprising a three-phase bridge rectifier circuit and three bidirectional switches, each bidirectional switch is composed of two fully controlled devices in reverse series, the three bidirectional switches are star-connected, and three input ends are connected with the bridge arm midpoints of the three-phase bridge rectifier circuit respectively; Structure S3: harmonic current injection circuit, comprising a bridge arm and an inductor, the bridge arm is connected in parallel with the bus of the three-phase bridge rectifier circuit, one end of the inductor is connected with the bridge arm midpoint of the three-phase bridge rectifier circuit, and the other end is connected with the star connection midpoint of the three bidirectional switches; Structure S4: interleaved parallel CLLLc resonant converter, comprising three CLLLc sub-modules, each CLLLc sub-module comprises a full-bridge circuit and a resonant cavity, the resonant cavity contains a double-winding transformer, the primary and secondary sides of the double-winding transformer are connected with the midpoints of two bridge arms of the full-bridge circuit through a resonant inductor and a resonant capacitor, and the primary and secondary sides of the three resonant cavities in the three CLLLc sub-modules are star-connected; The control method of the bidirectional charging topology of the electric vehicle comprises the following steps: Step 1: control the input voltage selector described in structure S2: sample the three-phase input voltage, control the three-phase bridge rectifier circuit to work in a low-frequency switching state in a synchronous rectification mode, and the switching tube is turned on according to the logic of diode uncontrolled rectification; Step 2: control the harmonic current injection circuit described in structure S3, control a bridge arm to work in a high-frequency switching state, and realize input current sine; Step 3: control the interleaved parallel CLLLc resonant converter described in structure S4, determine the working mode of the CLLLc resonant converter according to different working conditions, obtain the driving signal of each CLLLc sub-module, and take the CLLLc resonant converter as a bidirectional converter to realize electric vehicle power battery charging and battery energy feedback to the grid; Determine the working mode of the CLLLc resonant converter according to different working conditions, comprising: Mode 1, constant current mode in charging state: in the initial stage of charging the power battery, make the CLLLL resonant converter work in constant current mode, according to the characteristics of the power battery, give the charging current given value , the actual charging current is taken as the charging current reference value, and the actual charging current is taken as the feedback value, and the reference value is obtained by the proportional integral controller, and the equivalent gain of the CLLLL resonant converter is obtained : ； In the formula, , respectively represent the proportional gain coefficient and the integral gain coefficient of the output current PI regulator, is the Laplace operator; Mode 2, constant voltage mode in charging state: in the end stage of power battery charging, make the CLLLLC resonant converter work in constant voltage mode, according to the characteristics of power battery, give the given value of charging voltage , the actual charging voltage is taken as the reference value of charging voltage , the difference between the obtained reference value and the feedback value is obtained through the proportional integral controller to obtain the equivalent gain of the CLLLLC resonant converter : ； wherein , respectively represent the proportional gain coefficient and the integral gain coefficient of the output voltage PI regulator; Mode 3, constant power mode in energy reversal state: in energy reversal state, the power injected into the grid is obtained according to the grid side , the obtained actual power generation is taken as the charging current reference value , the obtained reference value is subtracted from the feedback value, and the equivalent gain of the CLLL C resonant converter is obtained through a proportional integral controller : ； wherein , respectively represent the proportional gain coefficient and the integral gain coefficient of the power transfer PI regulator; In step 3, the interleaved parallel CLLLc resonant converter described in structure S4 is controlled, and the strategy is as follows: Step 3.1, determining the working mode of the CLLL C resonance circuit according to different working conditions, obtaining the equivalent gain of the CLLL C resonance circuit under different modes , obtaining the actual gain according to the equivalent gain under different modes , : ； wherein the input voltage phase angle the value modulo π / 3; Step 3.2, obtaining actual gain After that, the switching frequency of the resonant converter at the current moment is obtained by looking up the gain-switching frequency curve of the CLLL C resonant converter. Step 3.3: according to different working conditions and the switching frequency of the CLLLc resonant converter, the driving signal of each CLLLc sub-module is obtained, and the electric vehicle power battery charging and the battery energy feedback to the grid are realized.

2. The bidirectional charging topology for electric vehicles of claim 1, wherein, In step 1, the input voltage selector described in structure S2 is controlled, and the strategy is as follows: sampled three-phase input voltage, representing the input voltage amplitude, without considering grid voltage harmonics, the sampled three-phase input voltage , , is: ； The three-phase bridge rectifier circuit in the input voltage selector works in a synchronous rectification mode, and the switch tubes are turned on according to the logic of diode uncontrolled rectification. The maximum value and the minimum value of the three-phase voltage are obtained through the bus of the three-phase bridge rectifier circuit, wherein one phase corresponding to the maximum value and the minimum value of the voltage is turned on, and the rest two phases are turned off. The output voltage of the input voltage selector is: , , : ； Three bidirectional switches S a , S b , S c The on logic is: S b , S a , S c , S b , S a , S c …… 3. The bidirectional charging topology for electric vehicles of claim 2, wherein, In step 2, the harmonic current injection circuit described in structure S3 is controlled, and the strategy is as follows: Step 2.1: obtain the output power P of the CLLLc resonant converter; Step 2.

2. Obtaining a given value of the harmonic injection current as a function of the output power and the input voltage The obtaining of the given current is related to the phase corresponding to the intermediate phase of the three-phase voltage instantaneous values, obtaining the given value of the current The formula is as follows: ； In the formula, The three-phase voltage with the input voltage phase angle θ is obtained by coordinate transformation through sampling: ； ； Step 2.3, the acquired The actual current As a feedback value, the difference between the reference value and the actual current The additional voltage of the harmonic injection inductance : ； In the formula, , respectively represent the proportional gain coefficient and the integral gain coefficient of the harmonic injection current PI regulator; Step 2.4: Inject the acquired harmonics into the inductor with an additional voltage u. L The output voltage of the input voltage selector is superimposed. and through bus voltage The reciprocal of the product yields the duty cycle of the harmonic current injection circuit. : ； wherein the output voltage is defined as the difference between the voltage at the input voltage selector output node y and the voltage at the output node z; Step 2.5, the duty cycle d yp After the carrier interception comparison, the PWM driving signal with harmonic current injection is obtained.

4. The bidirectional charging topology for electric vehicles of claim 3, wherein, Step 2.1: obtain the output power of the CLLLc resonant converter, define the power flowing from the grid side to the power battery side as positive, define the power flowing from the power battery side to the grid side as negative, and obtain the output power by the following method: Method 1: obtained through the current sensor and voltage sensor on the electric vehicle battery side; Method 2: if the CLLLc resonant converter works in constant power mode, the power instruction value is considered as the actual output power of the system.

5. The bidirectional charging topology for electric vehicles of claim 3, wherein, The control logic of the driving signal of each CLLLc sub-module is as follows: Control Logic 1: Soft Start Control: Soft start is achieved using a phase-shifting method. During startup, the duty cycle... It starts at 0, then gradually increases until the output voltage u... o Rise to a given voltage The curve of duty cycle changing with time t is given by the following formula: ； wherein, represents a soft start coefficient, which is set in the interval (0, 1); is a constant for controlling the start rate, and if is increased, the start rate can be accelerated; Control logic 2, energy reversal control: when entering the energy reversal control stage, gradually reduce the input power of the CLLL resonant converter and turn to negative value, the energy is transmitted from the power battery side to the network side, the energy reversal control stage needs to maintain the voltage of the CLLL resonant converter stable, Bang-Bang control is adopted, and the control is carried out through the control of the resonant capacitor voltage of the network side; When the resonant capacitor voltage drops to the lower limit threshold, the power supply charges the resonant capacitor, and the corresponding upper switch tube is turned on; when the resonant capacitor voltage rises to the upper limit threshold, the corresponding lower switch tube is turned on. Control logic 3, interleaved parallel control: for three CLLL sub-modules, the carrier waves of each sub-module are different by 120°, and the carrier wave frequency of each sub-module is the switching frequency of the CLLL resonant converter. After comparing the carrier wave and the duty cycle, the driving signal of each sub-module is obtained.

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