An Electric Vehicle V2G Energy Storage Charger Circuit and a Direct Power Control Method

Abstract

The present invention relates to an electric vehicle V2G energy storage charger circuit and a direct power control method. Based on a two-stage converter structure cascaded by a three-phase full-bridge AC-DC converter and a Buck / boost DC-DC converter, the AC-DC converter adopts a virtual synchronous machine control method with energy storage power compensation to achieve direct control of the bidirectional power of the energy storage charging and discharging; the DC-DC converter adopts a double closed-loop control method of bus voltage-charging and discharging current to achieve stable control of the bus voltage; the designed direct power control method realizes direct control of the bidirectional power of the energy storage, eliminates the error caused by loss, and ensures the stability of the bus voltage. The invention is applicable to the electric vehicle V2G system, can enable the converter to provide frequency / voltage support for the power grid, helps to improve the power quality of the power grid and ensure the stable operation of the power grid, and enhances the adaptability of the power grid to the large-scale access of electric vehicles.

Description

Technical Field

[0001] The invention relates to an electric vehicle V2G energy storage charger and discharger circuit and a direct power control method, belonging to the technical field of power electronic power conversion. Background Art

[0002] With the emergence of climate change issues and rising energy costs, the number of new energy vehicles, especially electric vehicles, has begun to increase year by year. With this comes the huge energy storage potential of electric vehicle batteries. If it can be applied to active distribution networks, it will be of great benefit to the voltage and frequency stability of the power grid and generate huge economic benefits. Vehicle-to-grid (V2G) automotive smart grid technology has also become a research hotspot. When electric vehicles are not in use, the power of the on-board battery can be sold to the power grid through a converter, and if the on-board battery needs to be charged, the electric vehicle can draw power from the power grid. The research on electric vehicle chargers and dischargers plays an important role in expanding the industrial scale of electric vehicles, application methods, and promoting intelligent management of power grids.

[0003] The charging and discharging device of electric vehicles needs to be able to realize the bidirectional flow of energy, execute the smart grid instructions for rapid adjustment, and control the input and output power quality. In addition, high power density, high efficiency, and high reliability are also key considerations. Since the converter is composed of power electronic devices, although the converter has the ability to respond quickly, it basically does not contain the inertia characteristics of traditional synchronous motors, and cannot be well regulated at the large power grid level. As the core of power generation in the power system, the synchronous generator is also one of the cores of the system. Both in theoretical research and control design, there are already quite mature results. Virtual synchronous machine technology studies the mechanical structure and working characteristics of synchronous generators, improves the control strategy of the inverter, and makes the inverter power supply produce a response similar to that of a synchronous machine during the transient process, so that it produces external characteristics similar to those of a synchronous generator, and improves the virtual inertia of the system.

[0004] Under the control of V2G energy storage in traditional electric vehicles, the front-stage AC-DC converter ensures a stable voltage for the bus through virtual synchronous machine control, while the rear-stage DC-DC converter only controls the charging and discharging current. Under the traditional method, the dynamic response of the bus is poor. At the same time, due to the existence of system losses, there is actually an error between the rear-stage charging power and the power controlled by the virtual synchronous machine. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide an electric vehicle V2G energy storage charger and discharger circuit, which improves working efficiency by using a virtual synchronous machine control with power compensation on the grid side and a double closed-loop control on the energy storage side.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions: The present invention designs an electric vehicle V2G energy storage charger circuit, including phase a u of the three-phase power supply at the grid end a , phase b u b , phase c u c , phase a filter inductor L1 and its internal resistance R1, phase b filter inductor L2 and its internal resistance R2, phase c filter inductor L3 and its internal resistance R3, the first switching tube S1, the second switching tube S2, the third switching tube S3, the fourth switching tube S4, the fifth switching tube S5, the sixth switching tube S6, the seventh switching tube S7, the eighth switching tube S8, the first diode D1, the second diode D2, the third diode D3, the fourth diode D4, the fifth diode D5, the sixth diode D6, the seventh diode D7, the eighth diode D8, the fourth inductor L4, the energy storage, the first bus capacitor C1, and the second bus capacitor C2;

[0007] Among them, one end of phase a u a , one end of phase b u b , and one end of phase c u c are connected to each other. The other end of phase a u a is connected to one end of its internal resistance R1 through phase a filter inductor L1. The other end of phase b u b is connected to one end of its internal resistance R2 through phase b filter inductor L2. The other end of phase c u c is connected to one end of its internal resistance R3 through phase c filter inductor L3; The other end of internal resistance R1, the source electrode of the first switching tube S1, and the drain electrode of the second switching tube S2 are connected to each other. The other end of internal resistance R2, the source electrode of the third switching tube S3, and the drain electrode of the fourth switching tube S4 are connected to each other. The other end of internal resistance R3, the source electrode of the fifth switching tube S5, and the drain electrode of the sixth switching tube S6 are connected to each other; The drain electrodes of the first switching tube S1, the third switching tube S3, the fifth switching tube S5, the seventh switching tube S7, and the positive electrode of the first bus capacitor C1 are connected to each other. The source electrodes of the second switching tube S2, the fourth switching tube S4, the sixth switching tube S6, the eighth switching tube S8, the negative electrode of the first bus capacitor C1, and the negative electrode of the energy storage are connected to each other; One end of the fourth inductor L4, the source electrode of the seventh switching tube S7, and the drain electrode of the eighth switching tube S8 are connected to each other. The other end of the fourth inductor L4 is connected to the positive electrode of the energy storage; The positive electrode of the second capacitor C2 is connected to the positive electrode of the energy storage, and the negative electrode of the second capacitor C2 is connected to the negative electrode of the energy storage;

[0008] The drain of the first switching transistor S1 is connected to the cathode of the first diode D1, the source of the first switching transistor S1 is connected to the anode of the first diode D1, the drain of the second switching transistor S2 is connected to the cathode of the second diode D2, the source of the second switching transistor S2 is connected to the anode of the second diode D2, the drain of the third switching transistor S3 is connected to the cathode of the third diode D3, the source of the third switching transistor S3 is connected to the anode of the third diode D3, the drain of the fourth switching transistor S4 is connected to the cathode of the fourth diode D4, the source of the fourth switching transistor S4 is connected to the anode of the fourth diode D4, the drain of the fifth switching transistor S5 is connected to the cathode of the fifth diode D5, the source of the fifth switching transistor S5 is connected to the anode of the fifth diode D5, the drain of the sixth switching transistor S6 is connected to the cathode of the sixth diode D6, the source of the sixth switching transistor S6 is connected to the anode of the sixth diode D6, the drain of the seventh switching transistor S7 is connected to the cathode of the seventh diode D7, the source of the seventh switching transistor S7 is connected to the anode of the seventh diode D7, the drain of the eighth switching transistor S8 is connected to the cathode of the eighth diode D8, and the source of the eighth switching transistor S8 is connected to the anode of the eighth diode D8.

[0009] Correspondingly, the technical problem to be solved by the present invention is to provide a direct power control method for an electric vehicle V2G energy storage charger circuit, which improves the working efficiency through the virtual synchronous machine control using power compensation on the grid side and the double closed-loop control on the energy storage side.

[0010] The present invention adopts the following technical solutions to solve the above technical problems: The present invention designs a direct power control method for an electric vehicle V2G energy storage charger circuit, which is executed according to the following steps: the virtual synchronous machine control using power compensation is used on the grid side, and the double closed-loop control is used on the energy storage side;

[0011] Step A. Collect the voltage u a between phase a u b and phase b u ab , the voltage u b between phase b u c and phase c u bc , and calculate to obtain the three-phase voltage u abc . At the same time, collect the current i a of phase a, the current i b of phase b in the three-phase power supply, and calculate to obtain the three-phase inductor current i abc . Then, according to the three-phase voltage u abc and the three-phase inductor current i abc , perform power calculation to obtain the system output active power P and the system output reactive power Q, and enter step B;

[0012] Step B. Simultaneously execute Step B1-1 to Step B1-2, and Step B2-1 to Step B2-3 to obtain the virtual synchronous machine power angle δ and the virtual electromotive force E controlled by the virtual synchronous machine, p , and then enter Step C;

[0013] Step B1-1. According to the charging current I between the fourth inductor L4 and the energy storage source, batt , the voltage U across the energy storage source, batt , and the three-phase voltage u, abc , through active-power regulation and charging power correction, obtain the virtual synchronous machine mechanical torque T, m , and then enter Step B1-2;

[0014] Step B1-2. According to the system output active power P and the virtual synchronous machine mechanical torque T, m , combined with the preset reference angular frequency ω0, the synchronous machine moment of inertia J, and the constant damping coefficient D in the synchronous machine mechanical equation, p , through the synchronous machine mechanical equation, obtain the virtual synchronous machine angular frequency ω, and obtain the virtual synchronous machine power angle δ through the integral link;

[0015] Step B2-1. For the voltage u, ab , obtain the effective value of the grid-side voltage U through effective value calculation, and use the difference between the effective value of the grid-side voltage U and the preset rated effective value of the grid-side voltage U n , multiply by the preset adjustment coefficient k, U , to obtain the voltage regulation electromotive force ΔE, U , and then enter Step B2-2;

[0016] Step B2-2. Use the difference between the system output reactive power Q and the preset reference reactive power Q * , multiply by the preset reactive power adjustment coefficient k, Q , to obtain the power regulation electromotive force ΔE, Q , and then enter Step B2-3;

[0017] Step B2-3. Subtract the power regulation electromotive force ΔE Q and the voltage regulation electromotive force ΔE U from the preset reference no-load electromotive force E0 to obtain the virtual electromotive force E controlled by the virtual synchronous machine, p ;

[0018] Step C. According to the virtual synchronous machine power angle δ and the virtual electromotive force E controlled by the virtual synchronous machine, p , through reference voltage calculation, obtain the voltage e at the grid side of the AC-DC converter, abc , and then enter Step D;

[0019] Step D. According to the voltage e at the grid side of the AC-DC converter,abc , the three-phase voltage u abc , through the electromagnetic equations of the synchronous machine, obtain the reference value i of the three-phase inductance current abcref , and then enter step E;

[0020] Step E. Obtain the reference value i of the three-phase inductance current abcref and the difference between the three-phase inductance current i abc , the output result of the proportional-resonant regulator PR, and then obtain the switching signals S’1, S’2, S’3, S’4, S’5, S’6 corresponding to the first switch tube S1, the second switch tube S2, the third switch tube S3, the fourth switch tube S4, the fifth switch tube S5, and the sixth switch tube S6 respectively output by the SPWM processing module for the output result, and apply each switching signal to control the corresponding switch tube respectively, and then enter step F;

[0021] Step F. Obtain the bus voltage U across the first bus capacitor C1 dc , and obtain the bus voltage U dc and the difference between the preset bus reference voltage U * dc , the inversion of the output result of the second PI regulator, that is, obtain the reference value I of the charging current * batt , and then enter step G;

[0022] Step G. Obtain the charging current I batt and the difference between the charging current I * batt , the output result of the third PI regulator, and for this output result, obtain the switching signal S’8 corresponding to the eighth switch tube S8 through the PWM module, and invert the switching signal S’8 to obtain the switching signal S’7 corresponding to the seventh switch tube S7, and apply each switching signal to control the corresponding switch tube respectively.

[0023] As a preferred technical solution of the present invention: the step B1-1 includes the following:

[0024] Execute charging power correction. First, collect the charging current I between the fourth inductor L4 and the energy storage source batt , and the voltage U across the energy storage source batt , calculate through a multiplier to obtain the charging power P batt , and then obtain the difference between the charging power P batt and the preset power P set , the output result of the first PI regulator, and obtain the sum of this output result and the preset power P set , that is, obtain the reference mechanical power P of the virtual synchronous machine ref , and finally according to the reference mechanical power Pref The ratio with the angular frequency ω of the virtual synchronous machine is used to obtain the rated mechanical torque T0 of the virtual synchronous machine;

[0025] At the same time, active-power regulation is performed, and the three-phase voltage u abc Passes through the phase-locked loop module PLL to obtain the AC frequency f, and multiplies the difference between the AC frequency f and the preset reference frequency f0 by the preset adjustment coefficient k f to obtain the adjustment torque ΔT;

[0026] The result of adding the adjustment torque ΔT and the rated mechanical torque T0 is obtained, that is, the mechanical torque T of the virtual synchronous machine is obtained m .

[0027] As a preferred technical solution of the present invention: in the step B1-2, according to the active power P output by the system and the mechanical torque T of the virtual synchronous machine m , combined with the preset reference angular frequency ω0, the moment of inertia J of the synchronous machine, and the constant damping coefficient D in the mechanical equation of the synchronous machine p , through the mechanical equation of the synchronous machine as follows:

[0028]

[0029] Where:

[0030]

[0031] The power angle δ of the virtual synchronous machine is obtained, where T e , T d are the electromagnetic torque and damping torque of the virtual synchronous machine respectively; ω is the angular frequency of the virtual synchronous machine, and δ is the power angle of the synchronous machine.

[0032] As a preferred technical solution of the present invention: in the step C, according to the power angle δ of the virtual synchronous machine and the virtual electromotive force E controlled by the virtual synchronous machine p , through the following reference voltage calculation:

[0033]

[0034] The voltage e at the grid side of the AC-DC converter is obtained abc .

[0035] As a preferred technical solution of the present invention: in the step D, according to the voltage e at the grid side of the AC-DC converter abc , the three-phase voltage u abc , through the electromagnetic equation of the synchronous machine as follows:

[0036]

[0037] The reference value i of the three-phase inductor current is obtainedabcref , where i abc represents the three-phase inductor current, and L and R are the grid-side inductor and parasitic resistance respectively, and are equal to the stator inductor and resistance of the virtual synchronous machine as follows:

[0038]

[0039] As a preferred technical solution of the present invention: when the preset power P set is greater than zero, the electric vehicle V2G energy storage charger circuit operates in the charging state, and the energy storage is charged by the energy provided by the grid; when the preset power P set is less than zero, the electric vehicle V2G energy storage charger circuit operates in the power supply mode, and the energy storage discharges to the grid.

[0040] For the electric vehicle V2G energy storage charger circuit and the direct power control method of the present invention, compared with the prior art by adopting the above technical solutions, the following technical effects are achieved:

[0041] (1) The electric vehicle V2G energy storage charger circuit and the direct power control method designed by the present invention have the characteristics of traditional virtual synchronous machine control. While ensuring low harmonic distortion of the grid-connected current, it can also respond to grid voltage / frequency abnormal events, enabling the power converter to exhibit mechanical inertia and damping power oscillation capabilities during grid voltage / frequency disturbances and load switching processes, and can improve the stability of the grid to a certain extent. This method can reduce the impact of electric vehicle charging on the grid and improve the adaptability of the grid to large-scale electric vehicle access;

[0042] (2) The electric vehicle V2G energy storage charger circuit and the direct power control method designed by the present invention eliminate the power control error caused by system error in traditional virtual synchronous machine control through power compensation, and can directly control the energy storage power to ensure the accuracy of energy storage charge and discharge power control;

[0043] (3) The electric vehicle V2G energy storage charger circuit and the direct power control method designed by the present invention are applicable to the electric vehicle V2G system, can enable the converter to provide frequency / voltage support for the grid, contribute to improving the power quality of the grid and ensuring the stable operation of the grid, and improve the adaptability of the grid to large-scale electric vehicle access. The present invention adopts a new control method, which can reduce the cost at the hardware level and improve the operation efficiency of the system. Description of the Drawings

[0044] Figure 1 is a schematic diagram of the electric vehicle V2G energy storage charger circuit designed by the invention;

[0045] Figure 2It is a schematic diagram of the direct power control method for the V2G energy storage charger circuit of the electric vehicle designed by the invention. Specific embodiments

[0046] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings of the specification.

[0047] The present invention designs an electric vehicle V2G energy storage charger circuit, as Figure 1 shown, including the a-phase u of the three-phase power supply at the grid end a , b-phase u b , c-phase u c , a-phase filter inductor L1 and its internal resistance R1, b-phase filter inductor L2 and its internal resistance R2, c-phase filter inductor L3 and its internal resistance R3, the first switching tube S1, the second switching tube S2, the third switching tube S3, the fourth switching tube S4, the fifth switching tube S5, the sixth switching tube S6, the seventh switching tube S7, the eighth switching tube S8, the first diode D1, the second diode D2, the third diode D3, the fourth diode D4, the fifth diode D5, the sixth diode D6, the seventh diode D7, the eighth diode D8, the fourth inductor L4, the energy storage, the first bus capacitor C1, and the second bus capacitor C2.

[0048] As Figure 1 shown, one end of the a-phase u a , one end of the b-phase u b , and one end of the c-phase u c are connected to each other. The other end of the a-phase u a is connected to one end of its internal resistance R1 through the a-phase filter inductor L1. The other end of the b-phase u b is connected to one end of its internal resistance R2 through the b-phase filter inductor L2. The other end of the c-phase u cThe other end of it is connected to one end of its internal resistance R3 through the c-phase filter inductor L3; the other end of the internal resistance R1, the source electrode of the first switching tube S1, and the drain electrode of the second switching tube S2 are connected to each other; the other end of the internal resistance R2, the source electrode of the third switching tube S3, and the drain electrode of the fourth switching tube S4 are connected to each other; the other end of the internal resistance R3, the source electrode of the fifth switching tube S5, and the drain electrode of the sixth switching tube S6 are connected to each other; the drain electrodes of the first switching tube S1, the third switching tube S3, the fifth switching tube S5, the seventh switching tube S7, and the positive electrode of the bus first capacitor C1 are connected to each other; the source electrodes of the second switching tube S2, the fourth switching tube S4, the sixth switching tube S6, the eighth switching tube S8, the negative electrode of the bus first capacitor C1, and the negative electrode of the energy storage source are connected to each other; one end of the fourth inductor L4, the source electrode of the seventh switching tube S7, and the drain electrode of the eighth switching tube S8 are connected to each other, and the other end of the fourth inductor L4 is connected to the positive electrode of the energy storage source; the positive electrode of the second capacitor C2 is connected to the positive electrode of the energy storage source, and the negative electrode of the second capacitor C2 is connected to the negative electrode of the energy storage source;

[0049] As Figure 1 shown, the drain electrode of the first switching tube S1 is docked with the cathode of the first diode D1, the source electrode of the first switching tube S1 is docked with the anode of the first diode D1, the drain electrode of the second switching tube S2 is docked with the cathode of the second diode D2, the source electrode of the second switching tube S2 is docked with the anode of the second diode D2, the drain electrode of the third switching tube S3 is docked with the cathode of the third diode D3, the source electrode of the third switching tube S3 is docked with the anode of the third diode D3, the drain electrode of the fourth switching tube S4 is docked with the cathode of the fourth diode D4, the source electrode of the fourth switching tube S4 is docked with the anode of the fourth diode D4, the drain electrode of the fifth switching tube S5 is docked with the cathode of the fifth diode D5, the source electrode of the fifth switching tube S5 is docked with the anode of the fifth diode D5, the drain electrode of the sixth switching tube S6 is docked with the cathode of the sixth diode D6, the source electrode of the sixth switching tube S6 is docked with the anode of the sixth diode D6, the drain electrode of the seventh switching tube S7 is docked with the cathode of the seventh diode D7, the source electrode of the seventh switching tube S7 is docked with the anode of the seventh diode D7, the drain electrode of the eighth switching tube S8 is docked with the cathode of the eighth diode D8, and the source electrode of the eighth switching tube S8 is docked with the anode of the eighth diode D8.

[0050] Furthermore, the present invention designs a direct power control method for the charging and discharging circuit of the V2G energy storage source of an electric vehicle. As Figure 2 shown, it is executed according to the following steps. The virtual synchronous machine control with power compensation is used on the grid side, and the double closed-loop control is used on the energy storage source side.

[0051] Step A. Collect the voltage u a between phase a u b and phase b u ab, phase-b voltage u b and phase-c voltage u c to obtain the voltage u bc between them, and calculate the three-phase voltage u abc . Meanwhile, collect the phase-a current i a and phase-b current i b in the three-phase power supply, and calculate the three-phase inductor current i abc . Then, based on the three-phase voltage u abc and the three-phase inductor current i abc , perform power calculation to obtain the active power P output by the system and the reactive power Q output by the system, and enter step B.

[0052] Step B. Simultaneously execute steps B1-1 to B1-2, and steps B2-1 to B2-3 to obtain the virtual synchronous machine power angle δ and the virtual electromotive force E controlled by the virtual synchronous machine p , and then enter step C.

[0053] Step B1-1. Based on the charging current I batt between the fourth inductor L4 and the energy storage source, the voltage U batt across the energy storage source, and the three-phase voltage u abc , through active-power regulation and charging power correction, obtain the virtual synchronous machine mechanical torque T m , and then enter step B1-2.

[0054] In practical applications, step B1-1 is specifically executed as follows:

[0055] Execute charging power correction. First, collect the charging current I batt between the fourth inductor L4 and the energy storage source, and the voltage U batt across the energy storage source. Through the calculation of a multiplier, obtain the charging power P batt . Then, obtain the difference between the charging power P batt and the preset power P set . The output result of the first PI regulator for this difference is, that is , and obtain the sum of this output result and the preset power P set , that is, P ref =P set +ΔP, to obtain the reference mechanical power P ref of the virtual synchronous machine. In this way, by using the power correction algorithm, ensure the accuracy of the energy storage source charging power. Finally, according to the ratio between the reference mechanical power P ref and the virtual synchronous machine angular frequency ω, obtain the rated mechanical torque T0 of the virtual synchronous machine, where K P and K I are the proportional coefficient and integral coefficient of the first PI regulator

[0056] At the same time, active-power regulation is performed, and the three-phase voltage u abc passes through the phase-locked loop module PLL to obtain the AC frequency f, and multiplies the difference between the AC frequency f and the preset reference frequency f0 by the preset regulation coefficient k f to obtain the regulation torque ΔT.

[0057] The result of adding the regulation torque ΔT and the rated mechanical torque T0 is obtained, that is, the mechanical torque T of the virtual synchronous machine is obtained m .

[0058] Step B1-2. According to the active power P output by the system and the mechanical torque T of the virtual synchronous machine m , combined with the preset reference angular frequency ω0, the synchronous machine moment of inertia J, and the constant damping coefficient D in the synchronous machine mechanical equation p , through the synchronous machine mechanical equation, the angular frequency ω of the virtual synchronous machine is obtained, and the power angle δ of the virtual synchronous machine is obtained through the integral link.

[0059] In practical applications, the above step B1-2 is based on the active power P output by the system and the mechanical torque T of the virtual synchronous machine m , combined with the preset reference angular frequency ω0, the synchronous machine moment of inertia J, and the constant damping coefficient D in the synchronous machine mechanical equation p , through the synchronous machine mechanical equation as follows:

[0060]

[0061] Among them:

[0062]

[0063] The power angle δ of the virtual synchronous machine is obtained, where T e , T d are the electromagnetic torque and damping torque of the virtual synchronous machine respectively; ω is the angular frequency of the virtual synchronous machine, and δ is the power angle of the synchronous machine.

[0064] The electromagnetic torque T e can be obtained from the system power P:

[0065] T e = P / ω

[0066] In practical applications, in the active power regulation part, the power-frequency characteristic of the synchronous machine can be expressed as follows:

[0067] T m = T0 + ΔT = P ref / ω + k f (f - f0)

[0068] Among them: T mIt consists of two parts: the rated torque command T0 and the frequency deviation feedback command ΔT. P ref is the reference power of the virtual synchronous machine; T0 is the rated torque, and ΔT is the angular velocity deviation feedback; the regulation of the frequency response can be achieved through a virtual frequency modulation unit, which is taken as a proportional link here, k f is the frequency response coefficient; f is the grid frequency, and f0 is the rated grid frequency.

[0069] Step B2-1. For the voltage u ab , the effective value of the grid-side voltage U is obtained through effective value calculation, and the difference between the effective value of the grid-side voltage U and the preset rated grid-side voltage effective value U n is multiplied by the preset adjustment coefficient k U , that is, ΔE U = k U (U n - U) to obtain the voltage regulation potential ΔE U , and then enter Step B2-2.

[0070] Step B2-2. The difference between the reactive power Q output by the system and the preset reference reactive power Q * is multiplied by the preset reactive power adjustment coefficient k Q , that is, ΔE Q = k q (Q * - Q) to obtain the power regulation potential ΔE Q , and then enter Step B2-3.

[0071] Step B2-3. Subtract the power regulation potential ΔE Q and the voltage regulation potential ΔE U from the preset reference no-load potential E0, that is, E p = E0 - ΔE Q - ΔE U to obtain the virtual potential E p for virtual synchronous machine control.

[0072] Step C. According to the power angle δ of the virtual synchronous machine and the virtual potential E p for virtual synchronous machine control, calculate through the following reference voltage:

[0073]

[0074] to obtain the voltage e abc at the grid side of the AC-DC converter, and then enter Step D.

[0075] Step D. According to the voltage e abc at the grid side of the AC-DC converter and the three-phase voltage u abc , through the synchronous machine electromagnetic equation as follows:

[0076]

[0077] Obtain the reference value \(i\) of the three-phase inductor current abcref , where \(i\) abc represents the three-phase inductor current, and \(L\) and \(R\) are the grid-side inductor and parasitic resistance respectively, and are equal to the stator inductor and resistance of the virtual synchronous machine respectively as follows:

[0078]

[0079] Then enter step E.

[0080] Step E. Obtain the reference value \(i\) of the three-phase inductor current abcref and the output result of the proportional-resonant regulator PR for the difference between the three-phase inductor current \(i\) abc . Then obtain the switching signals \(S'_1\), \(S'_2\), \(S'_3\), \(S'_4\), \(S'_5\), \(S'_6\) corresponding to the first switch tube \(S_1\), the second switch tube \(S_2\), the third switch tube \(S_3\), the fourth switch tube \(S_4\), the fifth switch tube \(S_5\), and the sixth switch tube \(S_6\) respectively output by the SPWM processing module, and apply each switching signal to control the corresponding switch tube respectively, and then enter step F.

[0081] Step F. Obtain the bus voltage \(U\) across the first bus capacitor \(C_1\) dc , and obtain the bus voltage \(U\) dc and the inverted output result of the second PI regulator for the difference between the preset bus reference voltage \(U\) * dc , that is, obtain the reference value \(I\) of the charging current * batt , and then enter step G.

[0082] Step G. Obtain the charging current \(I\) batt and the output result of the third PI regulator for the difference between the charging current \(I\) * batt . And for this output result, obtain the switching signal \(S'_8\) corresponding to the eighth switch tube \(S_8\) through the PWM module, and invert the switching signal \(S'_8\) to obtain the switching signal \(S'_7\) corresponding to the seventh switch tube \(S_7\), and apply each switching signal to control the corresponding switch tube respectively.

[0083] The direct power control method designed by the present invention, in practical applications, the front-stage AC-DC converter realizes the direct control of the charging and discharging power of the energy storage through compensation on the grid side, ensures the accuracy of the charging and discharging power of the energy storage, eliminates the charging power error caused by system losses, can accurately control the charging and discharging of current, and at the same time, the compensation algorithm is simple and the requirement for the controller is low. The rear-stage DC-DC converter realizes the stable control of the bus voltage through double closed-loop control, can obtain better dynamic response effects, and ensures stable charging and discharging current.

[0084] And in the application, when the preset power P set is greater than zero, the charging and discharging circuit of the electric vehicle V2G energy storage works in the charging state, and the energy storage is charged by the energy provided by the grid; when the preset power P set is less than zero, the charging and discharging circuit of the electric vehicle V2G energy storage works in the power supply mode, and the energy storage discharges to the grid.

[0085] Compared with the traditional virtual synchronous machine control, the present invention directly controls the charging and discharging power at the energy storage end through grid-side compensation, eliminating the error caused by losses; the rear-stage DC-DC converter can obtain better dynamic response effects of the bus voltage through double closed-loop control.

[0086] The charging and discharging circuit of the electric vehicle V2G energy storage and the direct power control method designed by the above technical solution have the characteristics of the traditional virtual synchronous machine control. While ensuring low harmonic distortion of the grid-connected current, it can also respond to abnormal grid voltage / frequency events, enabling the power converter to exhibit mechanical inertia and damping power oscillation capabilities during grid voltage / frequency disturbances and load switching processes, and can improve the stability of the grid to a certain extent. This method can reduce the impact of electric vehicle charging on the grid and improve the adaptability of the grid to the access of a large number of electric vehicles.

[0087] And it is designed to eliminate the power control error caused by system errors in the traditional virtual synchronous machine control through power compensation, can directly control the energy storage power, and ensure the accuracy of the charging and discharging power control of the energy storage;

[0088] The entire solution design is applicable to the electric vehicle V2G system, can enable the converter to provide frequency / voltage support for the grid, helps improve the power quality of the grid and ensure the stable operation of the grid, and improves the adaptability of the grid to the access of a large number of electric vehicles. The present invention adopts a new control method, can reduce the cost at the hardware level, and improve the operation efficiency of the system.

[0089] The embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the scope of knowledge possessed by those of ordinary skill in the art.

Claims

1. A V2G energy storage charger circuit for electric vehicles, characterized in that: Including phase a u of the three-phase power supply at the grid end a , phase b u b , phase c u c , phase a filter inductor L1 and its internal resistance R1, phase b filter inductor L2 and its internal resistance R2, phase c filter inductor L3 and its internal resistance R3, the first switching tube S1, the second switching tube S2, the third switching tube S3, the fourth switching tube S4, the fifth switching tube S5, the sixth switching tube S6, the seventh switching tube S7, the eighth switching tube S8, the first diode D1, the second diode D2, the third diode D3, the fourth diode D4, the fifth diode D5, the sixth diode D6, the seventh diode D7, the eighth diode D8, the fourth inductor L4, the energy storage source, the first bus capacitor C1, the second bus capacitor C2; Among them, one end of the u-phase of phase a a is connected to one end of the u-phase of phase b b and one end of the u-phase of phase c c are connected together. The other end of the u-phase of phase a a is connected to one end of its internal resistance R1 through the filter inductor L1 of phase a. The other end of the u-phase of phase b b is connected to one end of its internal resistance R2 through the filter inductor L2 of phase b. The other end of the u-phase of phase c c is connected to one end of its internal resistance R3 through the filter inductor L3 of phase c; the other end of the internal resistance R1, the source electrode of the first switching tube S1, and the drain electrode of the second switching tube S2 are connected together. The other end of the internal resistance R2, the source electrode of the third switching tube S3, and the drain electrode of the fourth switching tube S4 are connected together. The other end of the internal resistance R3, the source electrode of the fifth switching tube S5, and the drain electrode of the sixth switching tube S6 are connected together; the drain electrodes of the first switching tube S1, the third switching tube S3, the fifth switching tube S5, the seventh switching tube S7, and the positive electrode of the first bus capacitor C1 are connected together. The source electrodes of the second switching tube S2, the fourth switching tube S4, the sixth switching tube S6, the eighth switching tube S8, the negative electrode of the first bus capacitor C1, and the negative electrode of the energy storage source are connected together; one end of the fourth inductor L4, the source electrode of the seventh switching tube S7, and the drain electrode of the eighth switching tube S8 are connected together. The other end of the fourth inductor L4 is connected to the positive electrode of the energy storage source; the positive electrode of the second capacitor C2 is connected to the positive electrode of the energy storage source, and the negative electrode of the second capacitor C2 is connected to the negative electrode of the energy storage source; The drain of the first switching transistor S1 is connected to the cathode of the first diode D1, and the source of the first switching transistor S1 is connected to the anode of the first diode D1. The drain of the second switching transistor S2 is connected to the cathode of the second diode D2, and the source of the second switching transistor S2 is connected to the anode of the second diode D2. The drain of the third switching transistor S3 is connected to the cathode of the third diode D3, and the source of the third switching transistor S3 is connected to the anode of the third diode D3. The drain of the fourth switching transistor S4 is connected to the cathode of the fourth diode D4, and the source of the fourth switching transistor S4 is connected to the anode of the fourth diode D4. The drain of the fifth switching transistor S5 is connected to the cathode of the fifth diode D5, and the source of the fifth switching transistor S5 is connected to the anode of the fifth diode D5. The drain of the sixth switching transistor S6 is connected to the cathode of the sixth diode D6, and the source of the sixth switching transistor S6 is connected to the anode of the sixth diode D6. The drain of the seventh switching transistor S7 is connected to the cathode of the seventh diode D7, and the source of the seventh switching transistor S7 is connected to the anode of the seventh diode D7. The drain of the eighth switching transistor S8 is connected to the cathode of the eighth diode D8, and the source of the eighth switching transistor S8 is connected to the anode of the eighth diode D8.

2. The direct power control method for the charging and discharging circuit of an energy storage device of an electric vehicle V2G according to claim 1, characterized in that: Execute according to the following steps. The virtual synchronous machine control with power compensation is used on the grid side, and the double closed-loop control is used on the energy storage side. Step A. Collect the a phase u of the three-phase power supply a With b b Voltage u ab , b phase u b With c c Voltage u bc , and calculate the three-phase voltage u abc At the same time, the a-phase current i in the three-phase power supply is collected a , b-phase current i b , and calculate the three-phase inductor current i abc , then according to the three-phase voltage u abc , three-phase inductor current i abc , perform power calculation, obtain the system output active power P and the system output reactive power Q, and enter step B; Step B. Simultaneously execute Step B1-1 to Step B1-2, and Step B2-1 to Step B2-3 to obtain the virtual synchronous machine power angle δ and the virtual electromotive force E controlled by the virtual synchronous machine, and then proceed to Step C; p , and then enter Step C; Step B1-1. According to the charging current I between the fourth inductor L4 and the energy storage source batt , the voltage U across the energy storage source batt , and the three-phase voltage u abc , through active-power regulation and charging power correction, obtain the mechanical torque T of the virtual synchronous machine m , and then proceed to Step B1-2; Step B1-2. According to the active power P output by the system and the mechanical torque T of the virtual synchronous machine m , combined with the preset reference angular frequency ω0, the moment of inertia J of the synchronous machine, and the constant damping coefficient D in the mechanical equation of the synchronous machine p , through the mechanical equation of the synchronous machine, the angular frequency ω of the virtual synchronous machine is obtained, and the power angle δ of the virtual synchronous machine is obtained through the integral link; Step B2-1. For voltage u ab , obtain the effective value U of the grid-side voltage through effective value calculation, and use the difference between the effective value U of the grid-side voltage and the preset rated effective value U of the grid-side voltage n , multiply it by the preset adjustment coefficient k U , to obtain the voltage regulation potential ΔE U , and then proceed to Step B2-2; Step B2-2. Multiply the difference between the reactive power Q output by the system and the preset reference reactive power Q * by a preset reactive power regulation coefficient k Q to obtain a power regulation electromotive force ΔE Q , and then proceed to Step B2-3; Step B2-3. Obtain the virtual electromotive force E for virtual synchronous machine control by subtracting the preset reference no-load electromotive force E0 from the power regulation electromotive force ΔE Q and the voltage regulation electromotive force ΔE U ; p ​ Step C. Based on the virtual synchronous machine power angle δ and the virtual electromotive force E controlled by the virtual synchronous machine p , through reference voltage calculation, obtain the voltage e at the grid side of the AC-DC converter abc , and then proceed to Step D; Step D. According to the voltage e at the grid side of the AC-DC converter abc and the three-phase voltage u abc , the reference value i of the three-phase inductor current is obtained through the electromagnetic equation of the synchronous motor abcref , and then proceed to Step E; Step E. Obtain the three-phase inductor current reference value i abcref The difference between the three-phase inductor current i abc and the output result of the proportional-resonant regulator PR, and then obtain the switching signals S’1, S’2, S’3, S’4, S’5, S’6 corresponding to the first switch tube S1, the second switch tube S2, the third switch tube S3, the fourth switch tube S4, the fifth switch tube S5, and the sixth switch tube S6 respectively output by the SPWM processing module for the output result, and apply each switching signal to control the corresponding switch tube respectively, and then enter Step F; Step F. Obtain the bus voltage U across the first bus capacitor C1 dc and obtain the bus voltage U dc and the inverse of the output result of the difference between the preset bus reference voltage U * dc through the second PI regulator, that is, obtain the reference charging current I * batt , and then enter Step G; Step G. Obtain the charging current I batt The difference between the charging current and the charging current reference value I * batt The output result of the third PI regulator, and for this output result, obtain the switching signal S'8 corresponding to the 8th switching transistor S8 through the PWM module, and invert the switching signal S'8 to obtain the switching signal S'7 corresponding to the 7th switching transistor S7, and apply each switching signal to control the corresponding switching transistor respectively.

3. The direct power control method of the V2G energy storage charger circuit for an electric vehicle according to claim 2, characterized in that: The step B1-1 includes the following: Execute charging power correction. First, collect the charging current I between the fourth inductor L4 and the energy storage source batt , and the voltage U across the energy storage source batt . Through the calculation of a multiplier, obtain the charging power P batt . Then obtain the charging power P batt and the difference between the preset power P set . The output result of the first PI regulator is obtained, and the sum of this output result and the preset power P set is obtained, that is, the reference mechanical power P of the virtual synchronous machine is obtained ref . Finally, according to the ratio between the reference mechanical power P ref and the angular frequency ω of the virtual synchronous machine, obtain the rated mechanical torque T0 of the virtual synchronous machine; Simultaneously perform active-power regulation, and for three-phase voltage u abc Through the phase-locked loop module PLL, obtain the AC frequency f, and multiply the difference between the AC frequency f and the preset reference frequency f0 by the preset adjustment coefficient k f , to obtain the adjustment torque ΔT; Obtain the result of adding the regulated torque ΔT to the rated mechanical torque T0, that is, obtain the mechanical torque T of the virtual synchronous machine m .

4. The direct power control method for the charger circuit of the V2G energy storage of an electric vehicle according to claim 2, characterized in that: In the step B1-2, according to the active power P output by the system and the mechanical torque T of the virtual synchronous machine m , combined with the preset reference angular frequency ω0, the moment of inertia J of the synchronous machine, and the constant damping coefficient D in the mechanical equation of the synchronous machine p , the mechanical equation of the synchronous machine is as follows: Wherein: Obtain the power angle δ of the virtual synchronous machine, where T e and T d are the electromagnetic torque and damping torque of the virtual synchronous machine respectively; ω is the angular frequency of the virtual synchronous machine, and δ is the power angle of the synchronous machine.

5. The direct power control method for the V2G energy storage charger circuit of an electric vehicle according to claim 2, characterized in that: In the step C, according to the power angle δ of the virtual synchronous machine and the virtual electromotive force E controlled by the virtual synchronous machine p , the following reference voltage is calculated: Obtain the voltage e at the grid side of the AC-DC converter abc .

6. The direct power control method of the charging and discharging circuit of an electric vehicle V2G energy storage charger according to claim 2, characterized in that: In the step D, according to the voltage e at the grid side of the AC-DC converter abc and the three-phase voltage u abc , the electromagnetic equation of the synchronous motor is as follows: Obtain the three-phase inductor current reference value \(i\) abcref , where \(i\) abc represents the three-phase inductor current, and \(L\) and \(R\) are the grid-side inductor and parasitic resistance respectively, and are respectively equal to the stator inductor and resistance of the virtual synchronous machine as follows:

7. The direct power control method of an electric vehicle V2G energy storage charger circuit according to claim 2, characterized in that: When the preset power P set is greater than zero, the charging and discharging circuit of the electric vehicle V2G energy storage device operates in the charging state, and the energy storage device is charged by the energy provided by the power grid; when the preset power P set is less than zero, the charging and discharging circuit of the electric vehicle V2G energy storage device operates in the power supply mode, and the energy storage device discharges to the power grid.

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