A Two-Way Direct Power Control Method for Electric Vehicle V2G with Uncontrolled Bus Voltage

Abstract

The present invention relates to a method for V2G bidirectional direct power control of an electric vehicle without controlling the bus voltage. Based on the cascading of a three-phase full-bridge AC-DC converter and a Buck / boost DC-DC converter, the balance between the power of the front and rear stages is achieved through compensation, enabling direct control of the power. There is no need for bus closed-loop control in the control, which simplifies the system control structure. Specifically, it is divided into AC-side compensation and DC-side compensation. Under AC-side compensation, the power of battery charging and discharging is used to correct the power reference value of the virtual synchronous machine on the AC side through a power compensation algorithm, ensuring that the power of the energy storage for charging and discharging is equal to the user-set power. Under DC-side compensation, the power of the virtual synchronous machine is used to correct the reference value of the charging and discharging current on the DC side through a power compensation algorithm, ensuring that the power absorbed from the power grid / delivered to the power grid by the converter is equal to the user-set power. The design helps to improve the power quality of the power grid and ensure the stable operation of the power grid.

Description

Technical Field

[0001] The invention relates to a V2G bidirectional direct power control method for an electric vehicle without controlling bus voltage, and belongs to the technical field of power electronic power conversion control. 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. Along with this comes the huge energy storage potential of electric vehicle batteries. If they 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 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] Electric vehicle charging and discharging devices need to be able to achieve bidirectional energy flow, execute 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. 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 synchronous machine-like response during the transient process, so that it produces external characteristics similar to those of the synchronous generator, thereby improving the virtual inertia of the system. Intelligent control algorithms play an important role in improving the power quality of the power grid and the intelligent management and dispatching of the power grid.

[0004] The two-stage charger and discharger controlled by the traditional virtual synchronous machine needs to perform closed-loop control on the voltage of the busbar, which requires additional detection devices. The control algorithm has a certain complexity and the hardware cost also has certain requirements. Therefore, optimizing the structure and logic of the virtual synchronous machine control and simplifying the traditional methods will greatly promote the large-scale promotion of intelligent control algorithms such as virtual synchronous machine control, help the development of electric vehicle V2G systems, improve the power quality of the power grid, ensure the stable operation of the power grid, and enhance the adaptability of the power grid to large-scale electric vehicle access. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a V2G bidirectional direct power control method for electric vehicles without bus voltage control. The method is based on a two-stage converter structure in which a three-phase full-bridge AC-DC converter and a Buck / boost DC-DC converter are cascaded. The power balance between the front and rear stages is achieved by compensation, and direct power control is achieved. This simplifies the system control structure and improves work efficiency.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions: The present invention designs a V2G bidirectional direct power control method for electric vehicles without bus voltage control, based on the V2G energy storage charger and discharger circuit of the electric vehicle with a three-phase power supply at the grid end and energy storage, and performs the following steps:

[0007] 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;

[0008] Step B. Execute steps B1-1 to B1-2, and steps B2-1 to B2-3 simultaneously to obtain the virtual synchronous machine power angle δ and the virtual potential E controlled by the virtual synchronous machine. p , then go to step C;

[0009] Step B1-1. Three-phase voltage u abc The AC frequency f is obtained through the phase-locked loop module PLL, and the difference between the AC frequency f and the preset reference frequency f0 is multiplied by the preset adjustment coefficient k f , obtain the regulating torque ΔT;

[0010] At the same time, the rated mechanical torque T0 of the virtual synchronous machine is obtained as follows, and the result of adding the adjustment torque ΔT to the rated mechanical torque T0 is obtained, that is, the mechanical torque T of the virtual synchronous machine is obtained. m , then proceed to step B1-2;

[0011] If the electric vehicle V2G bidirectional direct power control method adopts the AC side compensation mode, the charging current I flowing to the energy storage system is first collected. batt , the voltage U across the energy storage batt , after multiplier calculation, the charging power P is obtained batt , then get the charging power P batt With preset power P set The difference between the two passes through the output result of the first PI regulator, and the output result and the preset power P are obtained. setThe addition result is the reference mechanical power P of the virtual synchronous machine obtained. ref Finally, according to the ratio between the reference mechanical power P ref and the angular frequency ω of the virtual synchronous machine, the rated mechanical torque T0 of the virtual synchronous machine is obtained.

[0012] If the DC-side compensation mode is adopted for the V2G bidirectional direct power control method of electric vehicles, then according to the ratio between the preset power P set and the angular frequency ω of the virtual synchronous machine, the rated mechanical torque T0 of the virtual synchronous machine is obtained.

[0013] 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.

[0014] 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 U of the grid-side voltage and the preset rated effective value U of the grid-side voltage n is multiplied by the preset adjustment coefficient k U to obtain the voltage regulation potential ΔE U , and then step B2-2 is entered.

[0015] 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 to obtain the power regulation potential ΔE Q , and then step B2-3 is entered.

[0016] Step B2-3. The preset reference no-load potential E0 is subtracted from the power regulation potential ΔE Q and the voltage regulation potential ΔE U to obtain the virtual potential E controlled by the virtual synchronous machine p ;

[0017] Step C. According to the power angle δ of the virtual synchronous machine and the virtual potential E controlled by the virtual synchronous machine p , through reference voltage calculation, the voltage e at the grid side of the AC-DC converter is obtained abc , and then step D is entered.

[0018] 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 step E is entered;

[0019] Step E. Obtain the reference value i of the three-phase inductor current abcref The output result of the difference between the reference value i of the three-phase inductor current and the three-phase inductor current i abc is obtained through the proportional-resonant regulator PR, and then the output result is obtained through the SPWM processing module to output 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, and each switching signal is applied to control the corresponding switch tube respectively, and then step F is entered;

[0020] Step F. According to the preset power P set , the voltage U at both ends of the energy storage source batt , the switching signal S’7 corresponding to the seventh switch tube S7 is obtained, and each switching signal is applied to control the corresponding switch tube respectively.

[0021] As a preferred technical solution of the present invention, the step F includes the following:

[0022] If the V2G bidirectional direct power control method of the electric vehicle adopts the AC side compensation mode, then first according to the preset power P set and the voltage U at both ends of the energy storage source batt , the ratio between them, the reference value I of the charging current is obtained * batt , and then the reference value I of the charging current is obtained * batt The output result of the difference between the reference value I of the charging current and the charging current I flowing into the energy storage source batt is obtained through the second PI regulator, and for this output result, the switching signal S’8 corresponding to the eighth switch tube S8 is obtained through the PWM module, and the switching signal S’8 is inverted to obtain the switching signal S’7 corresponding to the seventh switch tube S7, and each switching signal is applied to control the corresponding switch tube respectively;

[0023] If the V2G bidirectional direct power control method of the electric vehicle adopts the DC side compensation mode, first obtain the output result of the difference between the active power P output by the system and the preset power P set through the second PI regulator, and obtain the ratio between the sum of this output result and the preset power P set and the voltage U at both ends of the energy storage source batt , that is, the reference value I of the charging current is obtained * batt , and then the reference value I of the charging current is obtained * battThe difference between the charging current I flowing into the energy storage and the output result of the third PI regulator. For this output result, through the PWM module, the switching signal S'8 corresponding to the 8th switching transistor S8 is obtained, and by inverting the switching signal S'8, the switching signal S'7 corresponding to the 7th switching transistor S7 is obtained, and each switching signal is applied to control the corresponding switching transistor respectively. batt The difference between the charging current I flowing into the energy storage and the output result of the third PI regulator. For this output result, through the PWM module, the switching signal S'8 corresponding to the 8th switching transistor S8 is obtained, and by inverting the switching signal S'8, the switching signal S'7 corresponding to the 7th switching transistor S7 is obtained, and each switching signal is applied to control the corresponding switching transistor respectively.

[0024] 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 synchronous machine mechanical equation p , through the synchronous machine mechanical equation as follows:

[0025]

[0026] Where:

[0027]

[0028] 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.

[0029] 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:

[0030]

[0031] The voltage e at the grid side of the AC-DC converter is obtained abc .

[0032] 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 synchronous machine electromagnetic equation as follows:

[0033]

[0034] The reference value i of the three-phase inductor current is obtained 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 as follows:

[0035]

[0036] As a preferred technical solution of the present invention: when the preset power P set is greater than zero, the charging and discharging circuit of the electric vehicle V2G energy storage device works 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 works in the power supply mode, and the energy storage device discharges to the power grid.

[0037] As a preferred technical solution of the present invention: the charging and discharging circuit of the electric vehicle V2G energy storage device includes the a-phase u a , b-phase u b , c-phase u c of the three-phase power supply at the grid end, the a-phase filter inductor L1 and its internal resistance R1, the b-phase filter inductor L2 and its internal resistance R2, the 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 device, the first bus capacitor C1, and the second bus capacitor C2;

[0038] Among them, 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 thereof 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; 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;

[0039] 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.

[0040] Compared with the prior art by adopting the above technical solution, the V2G bidirectional direct power control method for an electric vehicle with uncontrolled bus voltage according to the present invention has the following technical effects:

[0041] (1) The present invention designs a V2G bidirectional direct power control method for electric vehicles with uncontrolled bus voltage, which has the characteristics of 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 power grid to a certain extent. This method can reduce the impact of electric vehicle charging on the power grid and enhance the adaptability of the power grid to the access of a large number of electric vehicles;

[0042] (2) The present invention designs a V2G bidirectional direct power control method for electric vehicles with uncontrolled bus voltage. In terms of control, the balance between the front-stage and rear-stage powers is achieved through compensation to directly control the charging and discharging power of the energy storage on the DC side or the interactive power with the AC-side power grid, eliminating the power control error caused by system losses; in terms of hardware, a bus voltage sensor is not required, reducing the hardware cost;

[0043] (3) The present invention designs a V2G bidirectional direct power control method for electric vehicles with uncontrolled bus voltage, which involves large-scale electric vehicle batteries participating in the regulation of the power grid, contributing to improving the power quality of the power grid and ensuring the stable operation of the power grid. The overall solution can reduce the cost at the hardware level and improve the operating efficiency of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is a schematic diagram of the AC-side compensation mode in the V2G bidirectional direct power control method for electric vehicles with uncontrolled bus voltage designed by the present invention;

[0045] Figure 2 is a schematic diagram of the DC-side compensation mode in the V2G bidirectional direct power control method for electric vehicles with uncontrolled bus voltage designed by the present invention;

[0046] Figure 3 is a schematic diagram of the circuit of the V2G energy storage charger for electric vehicles designed by the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0047] The following further describes in detail the specific embodiments of the present invention with reference to the accompanying drawings of the specification.

[0048] The present invention designs a V2G bidirectional direct power control method for electric vehicles with uncontrolled bus voltage, based on the V2G energy storage charger circuit of the three-phase power supply at the grid end and the energy storage of the electric vehicle, as Figure 3 shown. The circuit includes phase a u a of the three-phase power supply at the grid end, phase b u b and phase c u c, the a-phase filter inductor L1 and its internal resistance R1, the b-phase filter inductor L2 and its internal resistance R2, the c-phase filter inductor L3 and its internal resistance R3, the first switching transistor S1, the second switching transistor S2, the third switching transistor S3, the fourth switching transistor S4, the fifth switching transistor S5, the sixth switching transistor S6, the seventh switching transistor S7, the eighth switching transistor 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, and the second bus capacitor C2.

[0049] Among them, 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 together. 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 c 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 transistor S1, and the drain electrode of the second switching transistor S2 are connected together. The other end of the internal resistance R2, the source electrode of the third switching transistor S3, and the drain electrode of the fourth switching transistor S4 are connected together. The other end of the internal resistance R3, the source electrode of the fifth switching transistor S5, and the drain electrode of the sixth switching transistor S6 are connected together; the drain electrodes of the first switching transistor S1, the third switching transistor S3, the fifth switching transistor S5, the seventh switching transistor S7, and the positive electrode of the first bus capacitor C1 are connected together. The source electrodes of the second switching transistor S2, the fourth switching transistor S4, the sixth switching transistor S6, the eighth switching transistor 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 transistor S7, and the drain electrode of the eighth switching transistor 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.

[0050] 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.

[0051] Based on the above electric vehicle V2G energy storage charger circuit, the present invention designs a method for bidirectional direct power control of an electric vehicle V2G with uncontrolled bus voltage. In practical applications, as Figure 1 and Figure 2 shown, the following steps A to F are executed.

[0052] Step A. Collect the voltage u a between phase a u b and phase b u ab of the three-phase power supply, 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 and 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, based on 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.

[0053] 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 p controlled by the virtual synchronous machine, and then enter step C.

[0054] Step B1-1. The three-phase voltage u abcThrough the phase-locked loop module PLL, the alternating current frequency f is obtained, and the difference between the alternating current frequency f and the preset reference frequency f0 is multiplied by the preset adjustment coefficient k f , and the adjustment torque ΔT is obtained;

[0055] Meanwhile, the rated mechanical torque T0 of the virtual synchronous machine is obtained in the following manner, and the sum of the adjustment torque ΔT and the rated mechanical torque T0 is obtained, that is, T m = T0 + ΔT = P ref / ω + k f (f - f0), and the mechanical torque T of the virtual synchronous machine is obtained m , and then step B1-2 is entered.

[0056] Among them, when the V2G bidirectional direct power control method of the electric vehicle adopts the AC side compensation mode, as Figure 1 shown, the charging current I flowing into the energy storage is first collected batt , the voltage U across the energy storage batt , and through the calculation of the multiplier, the charging power P is obtained batt , and then the charging power P batt and the preset power P set The output result of the difference between them through the first PI regulator is, that is and the sum of this output result and the preset power P set is obtained, that is, P ref = P set + ΔP, and the reference mechanical power P of the virtual synchronous machine is obtained ref , and finally, according to the ratio of the reference mechanical power P ref to the angular frequency ω of the virtual synchronous machine, the rated mechanical torque T0 of the virtual synchronous machine is obtained; where, K P and K I are the proportional coefficient and integral coefficient of the first PI regulator.

[0057] If the V2G bidirectional direct power control method of the electric vehicle adopts the DC side compensation mode, as Figure 2 shown, then according to the ratio of the preset power P set to the angular frequency ω of the virtual synchronous machine, the rated mechanical torque T0 of the virtual synchronous machine is obtained.

[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 the actual application of the above step B1-2, the mechanical equation of the synchronous motor is as follows:

[0060]

[0061] Where:

[0062]

[0063] The virtual synchronous machine power angle δ 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] 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 regulation 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.

[0065] 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 regulation 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.

[0066] Step B2-3. The preset reference no-load potential E0 is subtracted from the power regulation potential ΔE Q and the voltage regulation potential ΔE U , that is, E p = E0 - ΔE Q - ΔE U to obtain the virtual potential E p controlled by the virtual synchronous machine.

[0067] Step C. According to the virtual synchronous machine power angle δ and the virtual potential E p controlled by the virtual synchronous machine, the following reference voltage calculation is carried out:

[0068]

[0069] The voltage e abc at the grid side of the AC-DC converter is obtained, and then enter step D.

[0070] 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 motor as follows:

[0071]

[0072] Obtain the reference value i of the three-phase inductor current abcref , and then enter Step E; 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:

[0073]

[0074] Step E. Obtain the output result of the difference between the reference value i of the three-phase inductor current abcref and the three-phase inductor current i abc through 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 output by the SPWM processing module, and apply each switching signal to control the corresponding switch tube respectively, and then enter Step F.

[0075] Step F. According to the preset power P set , the voltage U at both ends of the energy storage batt , 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.

[0076] In practical applications, the above Step F includes the following:

[0077] When the V2G bidirectional direct power control method of the electric vehicle adopts the AC-side compensation mode, as Figure 1 shown, then first according to the ratio between the preset power P set and the voltage U at both ends of the energy storage batt , that is obtain the reference value I of the charging current * batt , and then obtain the reference value I of the charging current * batt and the charging current I flowing into the energy storage battThe difference between them is the output result of the second PI regulator. For this output result, the switching signal S'8 corresponding to the 8th switching transistor S8 is obtained through the PWM module, and the switching signal S'7 corresponding to the 7th switching transistor S7 is obtained by inverting the switching signal S'8. Each switching signal is applied to control the corresponding switching transistor respectively.

[0078] When the V2G bidirectional direct power control method for electric vehicles adopts the DC side compensation mode, as Figure 2 shown, first, the difference between the active power P output by the system and the preset power P set is the output result of passing through the second PI regulator, that is, and the sum of this output result and the preset power P set is obtained, and the ratio of this sum to the voltage U across the energy storage source is obtained, that is, batt the reference charging current I is obtained, where K * batt , and K P and K I are the proportional coefficient and integral coefficient of the second PI regulator respectively; then the difference between the reference charging current I * batt and the charging current I batt flowing into the energy storage source is the output result of passing through the third PI regulator. For this output result, the switching signal S'8 corresponding to the 8th switching transistor S8 is obtained through the PWM module, and the switching signal S'7 corresponding to the 7th switching transistor S7 is obtained by inverting the switching signal S'8. Each switching signal is applied to control the corresponding switching transistor respectively.

[0079] A V2G bidirectional direct power control method for electric vehicles with uncontrolled bus voltage designed by the present invention, in practical applications, when the preset power P set is greater than zero, the energy storage charger circuit of the electric vehicle V2G works in the charging state, and the energy storage source is charged by the energy provided by the power grid; when the preset power P set is less than zero, the energy storage charger circuit of the electric vehicle V2G works in the power supply mode, and the energy storage source discharges to the power grid.

[0080] In practical applications, when adopting the AC side compensation power composite control, the set power of the system is equal to the charge and discharge power of the battery, and the actual power on the AC side is the value after compensation and correction. By adopting this method, accurate control of the battery charge and discharge power can be achieved, the stability and accuracy of the battery current can be ensured, and it is applicable to the applicable occasions that require battery charge and discharge control, such as those that require strict control of charge and discharge current, power, etc.

[0081] When adopting DC-side compensated power composite control, the set power of the system is equal to the power absorbed from the power grid by the system / delivered to the power grid by the system, while the actual DC-side battery charge and discharge power is the value after compensation and correction; adopting this method can achieve accurate control of the grid interaction power, and can ensure the stability and accuracy of the power transmitted between the system and the power grid. It is applicable to occasions where grid interaction power control is required, such as calculating the overall energy consumption of the system and the power generated to the power grid, etc.

[0082] The above technical solution designs a V2G bidirectional direct power control method for electric vehicles with uncontrolled bus voltage, which has 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 power grid to a certain extent. This method can reduce the impact of electric vehicle charging on the power grid and improve the adaptability of the power grid to the access of large-scale electric vehicles.

[0083] And in terms of control, the balance between the front-stage and rear-stage powers is achieved through compensation, realizing the direct control of the DC-side energy storage charge and discharge power or the AC-side grid interaction power, and eliminating the power control error caused by system losses; in terms of hardware, a bus voltage sensor is not required, reducing the hardware cost; the entire design scheme involves large-scale electric vehicle batteries participating in the regulation of the power grid, which helps to improve the power quality of the power grid and ensure the stable operation of the power grid. The overall scheme can reduce the cost at the hardware level and improve the operation efficiency of the system.

[0084] The above technical solution designs a V2G bidirectional direct power control method for electric vehicles with uncontrolled bus voltage, 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 balance between the front-stage and rear-stage powers is achieved through compensation, realizing the direct control of power. In terms of control, bus closed-loop control is not required, simplifying the system control structure; in terms of hardware, a bus voltage sensor is not required, reducing the hardware cost; it is specifically divided into AC-side compensation and DC-side compensation. Under AC-side compensation, the power of battery charge and discharge is used to correct the power reference value of the AC-side virtual synchronous machine through a power compensation algorithm, ensuring that the charge and discharge power of the energy storage is equal to the user-set power; under DC-side compensation, the power of the virtual synchronous machine is used to correct the reference value of the DC-side charge and discharge current through a power compensation algorithm, ensuring that the power absorbed from the power grid by the converter / delivered to the power grid by the converter is equal to the user-set power; the design can enable the converter to provide frequency / voltage support for the power grid, which helps to improve the power quality of the power grid and ensure the stable operation of the power grid, and improve the adaptability of the power grid to the access of large-scale electric vehicles.

[0085] 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 bidirectional direct power control method for electric vehicles with uncontrolled bus voltage, characterized in that: For the electric vehicle V2G energy storage charger circuit based on the three-phase power supply at the grid end and the energy storage source, the following steps are executed: 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. Three-phase voltage u abc Pass through the phase-locked loop module PLL to obtain the alternating current frequency f, and multiply the difference between the alternating current frequency f and the preset reference frequency f0 by the preset adjustment coefficient k f , to obtain the adjustment torque ΔT; Meanwhile, the rated mechanical torque T0 of the virtual synchronous machine is obtained in the following manner, and the result of adding the regulating torque ΔT to the rated mechanical torque T0 is obtained, that is, the mechanical torque T of the virtual synchronous machine is obtained m , and then step B1-2 is entered; When the V2G bidirectional direct power control method for electric vehicles adopts the AC side compensation mode, the charging current I flowing into the energy storage is first collected batt , the voltage U across the energy storage batt , and through the calculation of a multiplier, the charging power P batt is obtained. Then, the difference between the charging power P batt and the preset power P set is passed through the output result of the first PI regulator, and the sum of this output result and the preset power P set is obtained, that is, the reference mechanical power P ref of the virtual synchronous machine is obtained. Finally, according to the ratio between the reference mechanical power P ref and the angular frequency ω of the virtual synchronous machine, the rated mechanical torque T0 of the virtual synchronous machine is obtained; When the V2G bidirectional direct power control method of an electric vehicle adopts the DC-side compensation mode, the rated mechanical torque T0 of the virtual synchronous machine is obtained according to the ratio between the preset power P set and the angular frequency ω of the virtual synchronous machine; 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 the 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 n of the grid side, multiply it by the preset adjustment coefficient k U to obtain the voltage regulation potential ΔE U , and then enter 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 the preset reactive power regulation coefficient k Q to obtain the 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. Apply each switching signal to control the corresponding switch tube respectively, and then enter Step F; Step F. According to the preset power P set and the voltage U across the energy storage source batt , obtain the switching signal S'7 corresponding to the seventh switching transistor S7, and apply each switching signal to control the corresponding switching transistor respectively.

2. A two-way direct power control method for an electric vehicle V2G with uncontrolled bus voltage according to claim 1, characterized in that, The said step F includes the following: When the V2G bidirectional direct power control method of an electric vehicle adopts the AC side compensation mode, first, according to the ratio between the preset power P set and the voltage U batt across the energy storage, the reference charging current value I * batt is obtained. Then, the output result of the difference between the reference charging current value I * batt and the charging current I batt flowing into the energy storage through the second PI regulator is obtained. For this output result, the switching signal S’8 corresponding to the 8th switching tube S8 is obtained through the PWM module, and the switching signal S’7 corresponding to the 7th switching tube S7 is obtained by inverting the switching signal S’8. Each switching signal is applied to control the corresponding switching tube respectively; When the V2G bidirectional direct power control method for electric vehicles adopts the DC side compensation mode, first obtain the output active power P of the system and the difference between the preset power P set The output result of the second PI regulator for the difference between them, and obtain the sum of this output result and the preset power P set The ratio between the sum and the voltage U across the energy storage batt That is, obtain the reference charging current I * batt , and then obtain the reference charging current I * batt The output result of the third PI regulator for the difference between the reference charging current I batt and the charging current I flowing into the energy storage. 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 two-way direct power control method for V2G of an electric vehicle with uncontrolled bus voltage according to claim 1, 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.

4. A method for bidirectional direct power control of an electric vehicle V2G with uncontrolled bus voltage according to claim 1, characterized in that: In the step C, according to the virtual synchronous machine power angle δ and the virtual electromotive force E controlled by the virtual synchronous machine p , the following reference voltage calculation is performed: Obtain the voltage e at the grid side of the AC-DC converter abc .

5. A two-way direct power control method for an electric vehicle V2G with uncontrolled bus voltage according to claim 1, 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:

6. The V2G bidirectional direct power control method for an electric vehicle with uncontrolled bus voltage according to claim 1, 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.

7. A two-way direct power control method for electric vehicle V2G with uncontrolled bus voltage according to claim 1, characterized in that: The V2G energy storage charger circuit of the electric vehicle includes 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; 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 is connected to one end of the u-phase of phase c c ; the other end of the u-phase of phase a a is connected to one end of its internal resistance R1 through the filtering 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 filtering inductor L2 of phase b, and the other end of the u-phase of phase c c is connected to one end of its internal resistance R3 through the filtering 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 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, and 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 first bus capacitor C1 are connected to each other, and 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 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; The drain of the first switch tube S1 is connected to the cathode of the first diode D1, the source of the first switch tube S1 is connected to the anode of the first diode D1, the drain of the second switch tube S2 is connected to the cathode of the second diode D2, the source of the second switch tube S2 is connected to the anode of the second diode D2, the drain of the third switch tube S3 is connected to the cathode of the third diode D3, the source of the third switch tube S3 is connected to the anode of the third diode D3, the drain of the fourth switch tube S4 is connected to the cathode of the fourth diode D4, the source of the fourth switch tube S4 is connected to the anode of the fourth diode D4, the drain of the fifth switch tube S5 is connected to the cathode of the fifth diode D5, the source of the fifth switch tube S5 is connected to the anode of the fifth diode D5, the drain of the sixth switch tube S6 is connected to the cathode of the sixth diode D6, the source of the sixth switch tube S6 is connected to the anode of the sixth diode D6, the drain of the seventh switch tube S7 is connected to the cathode of the seventh diode D7, the source of the seventh switch tube S7 is connected to the anode of the seventh diode D7, the drain of the eighth switch tube S8 is connected to the cathode of the eighth diode D8, and the source of the eighth switch tube S8 is connected to the anode of the eighth diode D8.

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