A multi-port ac-dc power distribution network power flow control method based on electric vehicle v2g

Abstract

The application relates to a kind of multi-port AC / DC power distribution network power flow control methods based on electric vehicle V2G, comprising: monitoring the three-phase input voltage and current of transformer AC load side in multi-port AC / DC power distribution network, calculating the AC load of each transformer;Based on the AC load and rated capacity of transformer, the remaining available capacity threshold of transformer is calculated;Based on the remaining available capacity threshold of transformer, the charging and discharging price and charging and discharging power of electric vehicle are updated;The reference value of AC / DC converter DC side current and the reference value of DC / DC converter inductance current are calculated;Based on the current reference value, the control of converter power is realized;Finally, when multiple AC power distribution networks and electric vehicles with V2G function are connected in parallel through DC network, the problem of reasonable allocation of electric vehicle charging and discharging power is solved.Compared with the prior art, the application improves the equipment utilization and operation reliability of power distribution network, is simple to realize, and can avoid transformer overload.

Description

Technical Field

[0001] This invention relates to the field of multi-port AC / DC distribution network control technology, and in particular to a power flow control method for multi-port AC / DC distribution networks based on electric vehicle V2G. Background Technology

[0002] Currently, Vehicle-to-Grid (V2G) technology is receiving widespread attention. Through V2G, the problems of low grid efficiency and renewable energy fluctuations can be significantly alleviated, and benefits can be generated for electric vehicle users. With the development of smart grids and new energy sources, the number of electric vehicles (EVs) has increased significantly, leading to the emergence of new charging and grid technologies. Due to their ability to reduce carbon dioxide emissions, electric vehicles (EVs) have gained widespread support in recent years. Based on this situation, existing technologies have focused on the following: electric vehicles serve as distributed energy sources and provide additional services to the grid; that is, in the V2G model, energy is collected from electric vehicles to provide energy services, including supplementary services from electric vehicles to the grid. Simultaneously, Internet of Things (IoT) technology is growing exponentially, and sensors and devices with corresponding functions are increasingly appearing in transportation systems, providing intelligent services for roads, equipment, and vehicles.

[0003] Renewable energy systems (such as solar and wind power) are being extensively integrated into the power grid. Due to the inherent discontinuity of renewable energy, power generation fluctuates, necessitating the use of alternative energy sources (such as battery energy storage systems) to compensate for this volatility, ensure grid frequency stability, and suppress voltage rises caused by reverse power flow. The concept of Vehicle-to-Grid (V2G) addresses these issues. Its core idea is to utilize the energy storage of numerous electric vehicles as a buffer between the grid and renewable energy sources. When electric vehicles are not in use, the electricity from their batteries is sold to the grid. If the batteries need charging, current flows from the grid to the vehicle. Therefore, effectively planning the charging and discharging of electric vehicles to achieve V2G functionality is crucial. Summary of the Invention

[0004] This invention provides a power flow control method for multi-port AC / DC distribution networks based on electric vehicle V2G. The purpose is to solve the problem of how to rationally allocate the charging and discharging power of electric vehicles when multiple AC distribution networks and electric vehicles with V2G function are interconnected and mutually supportive through DC networks, so as to improve the equipment utilization and operational reliability of the distribution network.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A power flow control method for multi-port AC / DC distribution networks based on electric vehicle V2G includes the following steps:

[0007] 1) Define a multi-port AC / DC distribution network, wherein the multi-port AC / DC distribution network includes multiple AC distribution network input ports and a corresponding number of distribution transformers, each distribution transformer is connected to an AC load and an AC / DC converter on its low-voltage side, and the DC sides of each AC / DC converter are interconnected through a DC bus, and the electric vehicle load is connected to the DC bus through a DC / DC converter;

[0008] 2) Monitor the three-phase input voltage and three-phase input current on the AC load side of each distribution transformer to calculate the AC load of each distribution transformer;

[0009] 3) Obtain the rated capacity of each distribution transformer;

[0010] 4) Based on the AC load and rated capacity of each distribution transformer, calculate the remaining available capacity threshold for each distribution transformer;

[0011] 5) Based on the remaining available capacity threshold of each distribution transformer, update the charging price and discharging price of electric vehicles in real time;

[0012] 6) Based on the charging and discharging prices of the electric vehicles, update the charging and discharging power of the electric vehicles in real time;

[0013] 7) Calculate the AC / DC converter power reference value, and then calculate the AC / DC converter DC side current reference value; based on the charging power and discharging power of the electric vehicle, calculate the DC / DC converter power reference value, and then calculate the DC / DC converter inductor current reference value.

[0014] 8) Based on the DC-side current reference value, control the power of the AC / DC converter; based on the inductor current reference value, control the power of the DC / DC converter.

[0015] 9) In rectification mode, the AC / DC converter achieves dynamic power distribution of multi-port AC / DC distribution networks through droop control, realizing power flow between the distribution network and electric vehicles; in inverter mode, the AC / DC converter avoids transformer overload through constant power control.

[0016] 10) In Buck mode, the DC / DC converter enables electric vehicles to be charged with constant current through constant power control. In Boost mode, the DC / DC converter enables the discharge power to be distributed according to capacity through droop control.

[0017] Furthermore, the control method is a two-layer control strategy, which includes upper-layer control and lower-layer control. Steps 1) to 6) are completed by the upper-layer control, and steps 7) to 10) are completed by the lower-layer control.

[0018] Furthermore, the expression for calculating the AC load of each distribution transformer is as follows:

[0019]

[0020] Among them, S Load For AC loads, n is the number of AC loads, U i Let I be the effective value of the line voltage on the i-th AC load side. i This represents the effective value of the phase current on the i-th AC load side.

[0021] Furthermore, the expression for calculating the remaining available capacity threshold of each distribution transformer is as follows:

[0022] S T =(S N -S Load )

[0023] Among them, S T S is the threshold of available capacity for distribution transformers. N S represents the rated capacity of the distribution transformer. Load For AC load.

[0024] Furthermore, based on the remaining available capacity threshold of each distribution transformer, the charging and discharging prices of electric vehicles are updated in real time, specifically as follows:

[0025] Increase the charging and discharging prices of electric vehicles when the power grid is in peak demand.

[0026] When the power grid is in a low-demand period, reduce the charging and discharging prices of electric vehicles.

[0027] Furthermore, based on the charging and discharging prices of electric vehicles, the charging and discharging power of electric vehicles are updated in real time. Specifically, a V2G control strategy is adopted to determine the charging and discharging status of electric vehicles based on their charging and discharging prices and SOC status, thereby obtaining real-time updated charging and discharging power.

[0028] Furthermore, the expression for calculating the AC / DC converter power reference value is as follows:

[0029]

[0030] Among them, P ref1 * S is the power reference value for the AC / DC converter. T S is the threshold of available capacity for distribution transformers. T With AC load S Load S changes with the changes LoadIt varies depending on the load conditions, U dc_ref U is the reference value for the DC side voltage of the converter. min U is the minimum output voltage of the converter. max U is the maximum output voltage of the converter. dc This is the measured value of the DC bus voltage. Here, U represents the voltage of both the AC / DC converter and the DC / DC converter. dc_ref U min and U max They are equal in numerical value.

[0031] Furthermore, based on the charging and discharging power of the electric vehicle, the power reference value of the DC / DC converter is calculated, and its expression is as follows:

[0032]

[0033] Among them, P ref2 * I is the power reference value for the DC / DC converter. dc The charging and discharging current for electric vehicles.

[0034] Furthermore, based on the converter power reference value, the converter current reference value I is calculated. ref The calculation formula is as follows:

[0035]

[0036] Among them, P ref * U is the power reference value for the converter. dc This is the measured value of the DC bus voltage;

[0037] Based on the AC / DC converter power reference value, the DC side current reference value I of the AC / DC converter is obtained. ref1 The expression is:

[0038]

[0039] Based on the power reference value of the DC / DC converter, the inductor current reference value I of the DC / DC converter is obtained. ref2 The expression is:

[0040]

[0041] Furthermore, based on the DC-side current reference value, the power control of the AC / DC converter is achieved, including the following steps:

[0042] Obtain the measured value of the DC side current of the AC / DC converter, subtract the measured value from the reference value of the DC side current of the AC / DC converter to obtain the error value, and use the error value to obtain the reference value Id* of the d-axis component of the current through the PI module;

[0043] Obtain the three-phase AC current of the AC / DC converter, convert the three-phase current to the dq coordinate system, obtain the current Id and Iq in the dq coordinate system, calculate the difference between Id* and Id, and apply PI control to the difference.

[0044] Obtain the three-phase voltage on the AC side of the AC / DC converter, convert the three-phase voltage to the dq coordinate system, and obtain the voltages Ud and Uq in the dq coordinate system to decouple the AC side current calculation results of the AC / DC converter.

[0045] The decoupled AC side current result is subjected to dq / abc inverse transformation and input into the PWM waveform generator to generate 6 PWM signals to control the on and off of the IGBTs in the AC / DC converter, thereby realizing the control of the AC / DC converter power.

[0046] Furthermore, based on the inductor current reference value, the power control of the DC / DC converter is achieved, including the following steps:

[0047] The measured value of the inductor current of the DC / DC converter is obtained. The difference between the measured value and the reference value of the inductor current of the DC / DC converter is calculated to obtain the error value. The error value is then input into the PWM waveform generator through the PI module to generate two PWM signals to control the conduction and cutoff of the IGBT in the DC / DC converter, thereby realizing the control of the power of the DC / DC converter.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] 1. This invention adopts a two-layer control strategy, which includes upper-layer control and lower-layer control. In the upper-layer control, a V2G control strategy based on time-of-use pricing is proposed to control the power flow of the distribution network, taking into account the interests of the power grid and users. In the lower-layer control, the transformer capacity overload is avoided by using the real-time calculated transformer remaining available capacity threshold, and the DC voltage is kept stable by using PI control of DC current, thereby realizing the rational distribution of power among converters and improving the equipment utilization and operational reliability of the distribution network.

[0050] 2. In the prior art, the control strategy between some V2G technologies and multiple distribution transformers requires knowledge of all relevant parameters of the entire system, such as transformers and converters. The present invention only needs to calculate the remaining capacity parameters of the distribution transformers in the line where the converter is located and the battery status of the electric vehicle to realize the dynamic allocation between the charging and discharging power of the electric vehicle and the capacity of the distribution transformer using V2G technology. The implementation method is simple and easy to operate.

[0051] 3. In the existing technology, the traditional droop control method is to fix the droop coefficient, which can only achieve power distribution and cannot adapt to power changes, making it easy to overload the transformer. This method can control the output power of the AC device by calculating the remaining available capacity threshold of the distribution transformer, thereby avoiding the occurrence of transformer overload problems. Attached Figure Description

[0052] Figure 1 This is a flowchart illustrating the implementation of the present invention;

[0053] Figure 2 This is a schematic diagram of the topology of a multi-port AC / DC distribution network.

[0054] Figure 3 This is a logical diagram of a two-layer control strategy;

[0055] Figure 4 This is a control block diagram of an AC / DC converter when it is in rectification mode.

[0056] Figure 5 This is a block diagram of a DC / DC converter control.

[0057] Figure 6 This is a schematic diagram of a time-of-use pricing strategy;

[0058] Figure 7 A schematic diagram of the V2G control strategy when both grid A and grid B are under medium load.

[0059] Figure 8 A schematic diagram of the V2G control strategy when grid A is under light load or overload and grid B is under medium load.

[0060] Figure 9 A schematic diagram of the V2G control strategy when both power grids A and B are under light load or overload conditions;

[0061] Figure 10 The simulation analysis results show the output power of the converter and electric vehicle under light and medium load conditions.

[0062] Figure 11 The simulation analysis results show the output power of the transformer under light and medium load conditions.

[0063] Figure 12The simulation analysis results show the output power of the converter and electric vehicle under medium load and overload conditions.

[0064] Figure 13 The results are simulation analysis of the transformer's output power under medium load and overload conditions. Detailed Implementation

[0065] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0066] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0067] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0068] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0069] This invention is described in detail with reference to the schematic diagrams. When detailing the embodiments of this invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not adhering to the usual scale. Furthermore, the schematic diagrams are merely examples and should not be construed as limiting the scope of protection of this invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0070] Furthermore, in the description of this invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used solely for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In addition, the terms "first," "second," or "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0071] Unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" in this invention should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; similarly, they can refer to mechanical connections, electrical connections, or direct connections, or indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0072] Example:

[0073] like Figure 1 As shown, a power flow control method for a multi-port AC / DC distribution network based on electric vehicle V2G includes the following steps:

[0074] 1) Define a multi-port AC / DC distribution network. The multi-port AC / DC distribution network includes multiple AC distribution network input ports and a corresponding number of distribution transformers. Each distribution transformer is connected to an AC load and an AC / DC converter on its low-voltage side. The DC sides of each AC / DC converter are interconnected through a DC bus. Electric vehicle loads are connected to the DC bus through DC / DC converters.

[0075] 2) Monitor the three-phase input voltage and three-phase input current on the AC load side of each distribution transformer to calculate the AC load of each distribution transformer;

[0076] 3) Obtain the rated capacity of each distribution transformer;

[0077] 4) Based on the AC load and rated capacity of each distribution transformer, calculate the remaining available capacity threshold for each distribution transformer;

[0078] 5) Based on the remaining available capacity threshold of each distribution transformer, update the charging price and discharging price of electric vehicles in real time;

[0079] 6) Based on the charging and discharging prices of electric vehicles, update the charging and discharging power of electric vehicles in real time;

[0080] 7) Calculate the AC / DC converter power reference value, and then calculate the DC side current reference value of the AC / DC converter; based on the charging power and discharging power of the electric vehicle, calculate the DC / DC converter power reference value, and then calculate the inductor current reference value of the DC / DC converter.

[0081] 8) Power control of the AC / DC converter is achieved based on the DC-side current reference value; power control of the DC / DC converter is achieved based on the inductor current reference value.

[0082] 9) In rectification mode, the AC / DC converter achieves dynamic power distribution of the DC distribution network in a multi-port AC / DC distribution network through droop control, realizing power flow between the AC distribution network and electric vehicles; in inverter mode, the AC / DC converter avoids transformer overload through constant power control.

[0083] 10) In Buck mode, the DC / DC converter enables electric vehicles to be charged with constant current through constant power control. In Boost mode, the DC / DC converter enables the discharge power to be distributed according to capacity through droop control.

[0084] The control method is a two-layer control strategy, which includes upper-layer control and lower-layer control. Steps 1) to 6) are completed by the upper-layer control, and steps 7) to 10) are completed by the lower-layer control.

[0085] Reference Figures 1-7 This invention provides a preferred embodiment of a multi-port AC / DC power flow control method based on electric vehicle V2G, comprising the following steps:

[0086] S1: Determine a multi-port AC / DC distribution network, obtain the three-phase input voltage and three-phase input current on the AC load side, and calculate the AC load in real time;

[0087] In this embodiment, a multi-port AC / DC distribution network model is established, which includes: n AC distribution networks and m electric vehicles, where n>0 and m>0; wherein the AC distribution networks are connected to the AC loads via distribution transformers from the grid, and then connected to the DC bus via AC / DC converters. The electric vehicles are connected to the DC bus via DC / DC converters and coupled to the AC distribution networks via a common DC bus.

[0088] It should be noted that the purpose of establishing a multi-terminal AC / DC distribution network model is to simulate the operating state of the distribution network in real-world scenarios.

[0089] Furthermore, the three-phase input voltage and three-phase input current on the AC load side are obtained, and the AC load size is calculated in real time. The calculation formula is as follows:

[0090]

[0091] Among them, S Load For AC loads, n is the number of AC loads, U i Let I be the effective value of the line voltage on the i-th AC load side. i This represents the effective value of the phase current on the i-th AC load side.

[0092] S2: Based on the AC load and the rated capacity of the transformer, calculate the remaining available capacity threshold of each distribution transformer in real time;

[0093] Furthermore, it is first necessary to obtain the rated capacity of each distribution transformer within the distribution area;

[0094] It should be noted that all of the above data can be directly obtained through the established multi-terminal AC / DC distribution network model;

[0095] Furthermore, based on the AC load and the rated capacity of the transformers, the remaining available capacity threshold for each distribution transformer is calculated. The calculation formula is as follows:

[0096] S T =(S N -S Load )

[0097] Among them, S T S is the threshold of available capacity for distribution transformers. N S represents the rated capacity of the distribution transformer. Load For AC load.

[0098] It should be noted that traditional droop control uses a fixed droop coefficient, which can only achieve power distribution and cannot adapt to power changes, making it prone to transformer overload. This method, by calculating the remaining available capacity threshold, can control the output power of the AC unit, thereby avoiding transformer overload problems.

[0099] S3: Based on the remaining available capacity threshold of the distribution transformer, update the charging and discharging price of electric vehicles in real time;

[0100] In the upper-level control, the charging and discharging prices of multiple distribution networks are dynamically adjusted according to their real-time status.

[0101] During peak electricity demand periods, the charging and discharging prices for electric vehicles are increased, and electric vehicle users supply power to the distribution network.

[0102] When the power grid is in a low-demand period, reduce the charging and discharging prices of electric vehicles to encourage electric vehicle users to charge.

[0103] S4: Based on the charging and discharging price of electric vehicles, the charging and discharging power of electric vehicles is updated in real time in the upper-level control. Specifically, a V2G control strategy is adopted to determine the charging and discharging status of electric vehicles based on the charging and discharging price and SOC status, thereby obtaining the real-time updated charging and discharging power of electric vehicles.

[0104] Furthermore, obtain the DC bus voltage U dc Compare it with the reference DC voltage U dc_ref Make a comparison.

[0105] Furthermore, based on the calculation formula for the converter power reference value, the power reference values ​​for AC / DC converters and DC / DC converters are obtained. The calculation formula for the AC / DC converter power reference value is expressed as follows:

[0106]

[0107] Among them, P ref1 * S is the power reference value for the AC / DC converter. T S is the threshold of available capacity for distribution transformers. T With AC load S Load S changes with the changes Load U varies depending on the load conditions. dc_ref U is the reference value for the DC side voltage. dc U is the measured value of the DC side voltage. min U is the minimum output voltage of the converter. max This represents the maximum output voltage of the converter. Here, U represents the voltage output of both the AC / DC converter and the DC / DC converter. dc_ref U min and U max They are equal in numerical value.

[0108] It is worth noting that when U dc_ref <U dc <U max At this time, the AC / DC converter is used to distribute the charging and discharging power of the electric vehicle. The sum of the power reference values ​​of all AC / DC converters at this point equals the charging power of the electric vehicle. The formula for calculating the power reference value of the DC / DC converter is expressed as:

[0109]

[0110] Among them, P ref2 * I is the power reference value for the DC / DC converter. dc The charging and discharging current for electric vehicles.

[0111] It is worth noting that when U dc_ref <U dc <U max At that time, U dc ·I dc This refers to the charging and discharging power of an electric vehicle.

[0112] Furthermore, based on the converter power reference value P ref * Obtain the converter current reference value I ref The formula for calculating the reference current value is expressed as follows:

[0113]

[0114] Among them, P ref * U is the power reference value for the converter. dc This is the actual voltage of the DC bus.

[0115] Specifically, the DC side current reference value I of the AC / DC converter ref1 The expression is:

[0116]

[0117] DC / DC converter inductor current reference value I ref2 The expression is:

[0118]

[0119] S5: Control the power of the AC / DC converter and the DC / DC converter based on the current reference value;

[0120] Based on the DC-side current reference value, the power control of the AC / DC converter is achieved, including the following steps:

[0121] Obtain the measured value of the DC side current of the AC / DC converter, subtract the measured value from the reference value of the DC side current of the AC / DC converter to obtain the error value, and use the error value to obtain the reference value Id* of the d-axis component of the current through the PI module;

[0122] Obtain the three-phase AC current of the AC / DC converter, convert the three-phase current to the dq coordinate system, obtain the current Id and Iq in the dq coordinate system, calculate the difference between Id* and Id, and apply PI control to the difference.

[0123] Obtain the three-phase voltage on the AC side of the AC / DC converter, convert the three-phase voltage to the dq coordinate system, and obtain the voltages Ud and Uq in the dq coordinate system to decouple the AC side current calculation results of the AC / DC converter.

[0124] It is important to know that the d and q variables in the expression obtained by the three-phase PWM converter through the rotating coordinate transformation are coupled together and need to be decoupled.

[0125] Furthermore, the decoupled AC side current result is subjected to dq / abc inverse transformation and input into the PWM waveform generator to generate a PWM signal to control the IGBTs in the AC / DC converter to turn on and off, thereby realizing the control of the AC / DC converter power.

[0126] Controlling the power of a DC / DC converter based on an inductor current reference value includes the following steps:

[0127] The measured value of the inductor current of the DC / DC converter is obtained. The difference between the measured value and the reference value of the inductor current of the DC / DC converter is calculated to obtain the error value. The error value is then input into the PWM waveform generator through the PI module to generate two PWM signals to control the conduction and cutoff of the IGBT in the DC / DC converter, thereby realizing the control of the power of the DC / DC converter.

[0128] It's important to know that the PWM signal controls the IGBT's on / off state through modules in the Simulink simulation.

[0129] It should be noted that some V2G technologies and control strategies between multiple distribution transformers require knowledge of all transformers, converters, and other relevant parameters of the entire system to complete. This invention only requires knowledge of the remaining capacity parameters of the distribution transformers in the line where the converter is located and the battery status of the electric vehicle to realize the dynamic allocation between the charging and discharging power of the electric vehicle and the capacity of the distribution transformer using V2G technology. The implementation method is simple and easy to operate.

[0130] Reference Figures 2 to 13 This embodiment is the result of scientific demonstration through simulation experiments to verify the beneficial effects of the present invention.

[0131] Figure 2 This is a multi-port AC / DC distribution network topology, consisting of n AC distribution networks and m electric vehicles, where n>0 and m>0. The AC distribution networks are connected to the AC loads via transformers and then to the DC bus via AC / DC converters. The electric vehicles are connected to the DC bus via DC / DC converters and coupled to the AC distribution networks via a common DC bus. In this simulation experiment, a simulation model is built using an AC distribution network with two transformers each having a capacity of 250kVA.

[0132] Figure 3 This is the logic diagram for a two-layer control strategy. The upper-layer control is a V2G control strategy based on time-of-use pricing. It exchanges information with the AC distribution network and EVs, proposing charging and discharging strategies for EVs by monitoring the remaining capacity of the AC distribution transformer, the SOC status of the EVs, and the charging and discharging prices of the AC distribution network, thus realizing power flow control of the AC / DC distribution network. The lower-layer control consists of the rectification and inversion strategies of the AC / DC converter and the charging and discharging strategies of the DC / DC converter. The control block diagram when the AC / DC converter is in rectification mode is shown below. Figure 4As shown, adaptive droop control distributes power between the AC distribution network and the EV by changing the droop coefficient based on the remaining capacity of the AC distribution network transformer. When the AC / DC converter is in inverter mode, it uses constant power control to compensate for transformer overload. In buck mode, the DC / DC converter uses constant power control to charge the EV, and in boost mode, it uses droop control to distribute discharge power according to capacity. The DC / DC converter control block diagram is shown below. Figure 5 As shown. Among them, Figure 4 Formula (1) in the text refers to the formula for calculating the power reference value of the AC / DC converter. Figure 5 Formula (2) in the formula refers to the formula for calculating the power reference value of the DC / DC converter.

[0133] Figure 6 The diagram illustrates a time-of-use (TOU) pricing strategy. Based on the remaining available capacity threshold of the distribution transformers, the charging and discharging prices for each distribution network are dynamically adjusted. During peak electricity demand periods, the charging and discharging prices for electric vehicles (EVs) are increased, encouraging EV users to supply power to the distribution network. During off-peak electricity demand periods, the charging and discharging prices for EVs are reduced to incentivize EV users to charge.

[0134] When the number of AC distribution networks in a multi-terminal AC / DC distribution network is 2, Figure 7 , 8 Figure 9 shows the corresponding V2G control strategy. Based on the charging and discharging price of electric vehicles and their State of Charge (SOC), the charging and discharging mode of each electric vehicle is adjusted to obtain the charging and discharging power of the electric vehicle at that time. This strategy considers the interests of both DSO (Discharge-Oriented System) and EV users. The discharge capacity of the electric vehicle is determined by the SOC (State of Charge) of the electric vehicle battery.

[0135] 1. When the SOC of an electric vehicle battery is greater than 70%, the battery has sufficient charge and is allowed to discharge.

[0136] 2. When the SOC of an electric vehicle battery is less than 30%, the battery power is relatively scarce and can only meet the driving needs, so the user tends to charge the battery.

[0137] 3. In the discharge working state, in order to prevent over-discharge from damaging the battery, a limiting circuit is added. When the battery SOC is detected to be below 5%, the discharge will automatically stop.

[0138] 4. In charging mode, to prevent damage to the battery from high-current charging, when the battery SOC>90%, the charging station automatically switches to low-current trickle charging, at which time the rated charging current I=5A.

[0139] Depend on Figure 7 Assuming both grid A and grid B are under medium load, the charging and discharging of electric vehicles depends on the grid electricity price and discharge capacity. When the discharge capacity is sufficient, the vehicle will discharge if the discharge price is higher than the user's set value, and charge if the price is lower than the set value. When the discharge capacity is insufficient, the vehicle will charge.

[0140] Assuming grid A is under light or overload conditions, and grid B is under medium load conditions, it is necessary to determine whether grid A is under light or overload conditions, and the control strategy is as follows: Figure 8 As shown. If grid A is overloaded, according to the time-of-use pricing strategy, the discharge price is lower. If the discharge price set by the user is not reached, grid B, which has remaining capacity, will prioritize providing power to grid A. If grid A is lightly loaded, the charging price is lower, electric vehicles will be charged first, and the charging power will be primarily provided by grid A. The same applies when grid A is under medium load and grid B is under light or overload.

[0141] When both power grids A and B are under light load or overload, the situation needs to be discussed separately, and the logical strategy is as follows: Figure 9 As shown in the diagram. When both grid A and grid B are overloaded, according to the time-of-use pricing strategy, the charging and discharging price for electric vehicles (EVs) is the highest, and it is recommended that EVs discharge to the grid. When one grid is overloaded and the other is lightly loaded, the grid still has a lot of spare capacity. At this time, the charging and discharging price for EVs is moderate, with the charging price lower than the discharging price. It is recommended that EVs charge, with the lightly loaded grid supplying power to the overloaded grid. When both grids A and B are lightly loaded, the charging and discharging price is the lowest, and all idle EVs should charge.

[0142] In the simulation model of the multi-terminal AC / DC distribution network, the AC side consists of two distribution networks, No. 1 and No. 2. Let the transformer of network No. 1 be T1 and the AC-DC converter be VSC1, and the transformer of network No. 2 be T2 and the AC-DC converter be VSC2. Figure 10 , Figure 11 The simulation results show the transformer under light and medium load conditions. The initial simulation conditions are: the rated power of each transformer is 250kW, the total charging and discharging power of the electric vehicle on the DC side is 40kW, and the AC side loads PL1 and PL2 are set to 20kW and 100kW respectively. At this time, T1 is under light load and T2 is under medium load. At t = 0.3s, the AC side load PL1 increases to 150kW, at which point both transformers are under medium load. At t = 0s, transformer T1 is under light load, according to... Figure 4 It can be seen that the electric vehicle is in a charging state at this time, and the charging power is provided by T1. At t = 0.3s, both transformers T1 and T2 are under medium load. Figure 4As can be seen, the electric vehicle is still in the charging state. At this time, both transformers use adaptive droop control to distribute the charging power of the electric vehicle according to the remaining capacity of the transformers. VSC1 provides 16kW of power, T1 outputs 166kW of power, VSC2 provides 24kW of power, and T2 outputs 124kW of power. The simulation results are shown in the figure below. Figure 10 , 11 As shown.

[0143] Figure 12 , Figure 13 The simulation results show the transformer under medium and overload conditions. The initial simulation conditions are: a rated power of 250kW for each transformer, a total charging and discharging power of 60kW for the DC-side electric vehicle, and AC-side loads PL1 and PL2 set to 300kW and 100kW respectively. At this point, T1 is under overload and T2 is under medium load. At t = 0.3s, the AC-side load PL2 increases to 260kW, at which point both transformers are under overload. At t = 0s, according to... Figure 4 Electric vehicles are given priority for charging. At t = 0.3s, according to... Figure 4 Transformer T1 is overloaded by 50kW, and transformer T2 is overloaded by 10kW. At this point, the electric vehicle should be in a discharging state. VSC1 absorbs 50kW of power, VSC2 absorbs 10kW of power, the EV outputs 60kW, and both T1 and T2 ultimately output 250kW. The simulation results are shown in the figure below. Figure 12 , 13 As shown.

[0144] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A power flow control method for multi-port AC / DC distribution networks based on electric vehicle V2G, characterized in that, Includes the following steps: A multi-port AC / DC distribution network is defined, which includes multiple AC distribution network input ports and a corresponding number of distribution transformers. Each distribution transformer is connected to an AC load and an AC / DC converter on its low-voltage side. The DC sides of each AC / DC converter are interconnected through a DC bus. Electric vehicle loads are connected to the DC bus through DC / DC converters. Monitor the three-phase input voltage and three-phase input current on the AC load side of each distribution transformer to calculate the AC load of each distribution transformer; Obtain the rated capacity of each distribution transformer; Based on the AC load and rated capacity of each distribution transformer, calculate the remaining available capacity threshold of each distribution transformer; Based on the remaining available capacity threshold of each distribution transformer, the charging price and discharging price of electric vehicles are updated in real time. Based on the charging and discharging prices of the electric vehicles, the charging power and discharging power of the electric vehicles are updated in real time. Calculate the power reference value of the AC / DC converter, and then calculate the DC side current reference value of the AC / DC converter; Based on the charging and discharging power of the electric vehicle, the reference value of the DC / DC converter power is calculated, and then the reference value of the DC / DC converter inductor current is calculated. Based on the DC-side current reference value, the power of the AC / DC converter can be controlled. Based on the inductor current reference value, the power of the DC / DC converter can be controlled. In rectification mode, the AC / DC converter achieves dynamic power distribution of multi-port AC / DC distribution networks through droop control, enabling power flow between the distribution network and electric vehicles; in inverter mode, the AC / DC converter avoids transformer overload through constant power control. In Buck mode, the DC / DC converter enables electric vehicles to be charged with a constant current through constant power control. In Boost mode, the DC / DC converter enables the discharge power to be distributed according to capacity through droop control. The expression for calculating the AC / DC converter power reference value is as follows: in, This is the power reference value for the AC / DC converter. This represents the threshold for the available capacity of distribution transformers. This is the reference value for the DC side voltage of the converter. This is the minimum output voltage of the converter. This is the maximum output voltage of the converter. This is the measured value of the DC bus voltage; Based on the charging and discharging power of the electric vehicle, the power reference value of the DC / DC converter is calculated, and its expression is as follows: in, This is the power reference value for the DC / DC converter. The charging and discharging current for electric vehicles.

2. The power flow control method for a multi-port AC / DC distribution network based on electric vehicle V2G according to claim 1, characterized in that, The expression for calculating the AC load of each distribution transformer is as follows: in, For AC loads, n is the number of AC loads, U i Let I be the effective value of the line voltage on the i-th AC load side. i This represents the effective value of the phase current on the i-th AC load side.

3. The power flow control method for a multi-port AC / DC distribution network based on electric vehicle V2G according to claim 2, characterized in that, The expression for calculating the remaining available capacity threshold of each distribution transformer is as follows: in, This represents the threshold for the available capacity of distribution transformers. The rated capacity of the distribution transformer For AC load.

4. The power flow control method for a multi-port AC / DC distribution network based on electric vehicle V2G according to claim 1, characterized in that, Based on the remaining available capacity threshold of each distribution transformer, the charging and discharging prices of electric vehicles are updated in real time, specifically as follows: Increase the charging and discharging prices of electric vehicles when the power grid is in peak demand. When the power grid is in a low-demand period, reduce the charging and discharging prices of electric vehicles.

5. The power flow control method for a multi-port AC / DC distribution network based on electric vehicle V2G according to claim 1, characterized in that, Based on the charging and discharging prices of electric vehicles, the charging and discharging power of electric vehicles is updated in real time. Specifically, a V2G control strategy is adopted to determine the charging and discharging status of electric vehicles based on their charging and discharging prices and SOC status, thereby obtaining the real-time updated charging and discharging power of electric vehicles.

6. The power flow control method for a multi-port AC / DC distribution network based on electric vehicle V2G according to claim 1, characterized in that, Calculate the converter current reference value based on the converter power reference value. The calculation formula is as follows: in, This is the power reference value for the converter. This is the measured value of the DC bus voltage; Based on the AC / DC converter power reference value, the DC side current reference value of the AC / DC converter is obtained. The expression is: Based on the power reference value of the DC / DC converter, the inductor current reference value of the DC / DC converter is obtained. The expression is: 。 7. The power flow control method for a multi-port AC / DC distribution network based on electric vehicle V2G according to claim 1, characterized in that, Based on the DC-side current reference value, the power control of the AC / DC converter is achieved, including the following steps: Obtain the measured value of the DC-side current of the AC / DC converter, and subtract this measured value from the reference value of the DC-side current of the AC / DC converter to obtain the error value. Then, process this error value through a PI module to obtain the reference value Id for the d-axis component of the current. ; Obtain the three-phase AC current of the AC / DC converter, convert the three-phase current to the dq coordinate system, and obtain the currents Id and Iq in the dq coordinate system. The difference between the value and the Id value is calculated, and this difference is then subjected to PI control. Obtain the three-phase voltage on the AC side of the AC / DC converter, convert the three-phase voltage to the dq coordinate system, and obtain the voltages Ud and Uq in the dq coordinate system to decouple the AC side current calculation results of the AC / DC converter. The decoupled AC side current result is subjected to dq / abc inverse transformation and input into the PWM waveform generator to generate 6 PWM signals to control the on and off of the IGBTs in the AC / DC converter, thereby realizing the control of the AC / DC converter power.

8. The power flow control method for a multi-port AC / DC distribution network based on electric vehicle V2G according to claim 1, characterized in that, Based on the inductor current reference value, the power control of the DC / DC converter is achieved, including the following steps: The measured value of the inductor current of the DC / DC converter is obtained. The difference between the measured value and the reference value of the inductor current of the DC / DC converter is calculated to obtain the error value. The error value is then input into the PWM waveform generator through the PI module to generate two PWM signals to control the conduction and cutoff of the IGBT in the DC / DC converter, thereby realizing the control of the power of the DC / DC converter.

Images