CN117748573A - Dynamic power balance method considering access of electric automobile to regional power grid - Google Patents
Dynamic power balance method considering access of electric automobile to regional power grid Download PDFInfo
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Abstract
The invention relates to a dynamic power balance method considering an electric automobile access regional power grid, which specifically comprises the following steps: according to the existing distribution network structure, a dynamic power balance system structure of the distribution network is established, and a three-phase voltage type pulse width modulation converter is adopted to communicate with each distribution transformer in the distribution network through a direct current line so as to realize reasonable distribution of loads and reduce impact of loads of electric vehicles; two control strategies of a dynamic power balance system of the power distribution network are established, power decoupling outer loop current inner loop control and voltage current double closed loop control are provided, a control instruction reference value calculation value is given, a control instruction is sent to a converter of the dynamic power balance system of the power distribution network, and dynamic self-adaptive adjustment is implemented; the dynamic power balance method effectively solves the problems that the power unbalance of the power distribution network is aggravated by random loads generated when the electric automobile is connected into the power distribution network at present, and the re-planning layout in a short period is not feasible.
Description
Technical Field
The invention belongs to the technical field of power regulation and control of a power electronic power system, and relates to a dynamic power balance method considering access of an electric automobile to a regional power grid.
Background
With the gradual exhaustion of traditional energy sources and the increasing serious problems of environmental pollution, electric automobiles become one of the hot spots for the development of automobile industry. However, the access of a large number of electric vehicles can bring great influence to the distribution network, and particularly, the problem of dynamic power unbalance of the low-voltage distribution network is more remarkable due to the random load. When a large number of electric vehicles are charged simultaneously, the design expectations of the traditional distribution network can be exceeded, and the distribution transformer needs to add more additional power than usual. If a distribution transformer with a larger capacity is replaced, it may still be difficult to meet the requirements and increase unnecessary investment.
At present, a great deal of research has been developed for the influence of electric automobile access on a distribution network in China, and the research is mainly focused on aspects of network loss analysis, electric energy quality analysis, novel intelligent power distribution network coordinated operation and control formed by distributed new energy and electric automobiles, electric automobile load modeling, optimal arrangement of charging piles and the like. But there are few issues on solutions and strategies for the problems of load impact and power imbalance caused by the electric automobile accessing the power distribution network. The charging behavior of an electric car can be seen as a random and dispersed load, which is a large difference from a conventional load. The load characteristics of the electric vehicle are affected by the overall number of electric vehicle charges, the user's usage characteristics, the distribution of charging facilities, and the like.
According to the invention, a dynamic power balance system structure of the distribution network is established on the basis of the existing distribution network structure, and three-phase voltage type pulse width modulation converters are adopted to communicate with all distribution transformers in the distribution network through direct current lines so as to realize reasonable distribution of loads and reduce impact of loads of electric vehicles, a large number of real-time monitoring points are not required to be added, and the dynamic power balance system structure has the characteristics of safety and economy, and can improve the power supply quality of the distribution network and the reliability of system operation to a certain extent. The method effectively solves the problems that the power unbalance of the power distribution network is aggravated by the random load generated by the access of the electric automobile to the power distribution network at present, and the re-planning of the layout in a short period is not feasible.
Disclosure of Invention
In view of the above, the invention provides a dynamic power balancing method considering an electric automobile access regional power grid in order to solve the problems that the power unbalance of the power distribution network is aggravated by the random load generated by the electric automobile access power distribution network and the re-planning layout in a short period is not feasible, and the dynamic power balancing method can better solve the problems of the dynamic power unbalance of the power distribution network accessed by the electric automobile, overload of a distribution transformer and the like, and has the advantages of simple structure, easiness in implementation, easiness in operation and maintenance and the like. The method can be properly adjusted on the basis of the structure and configuration of the existing power distribution network to effectively realize the impact caused by the fact that the charging pile of the electric automobile is connected with the power distribution network, has considerable economical efficiency relative to large-scale power grid transformation, and provides reference for solving a series of problems after the electric automobile is connected with the power distribution network.
In order to achieve the above purpose, the present invention provides the following technical solutions:
a dynamic power balance method considering that an electric automobile is connected into a regional power grid comprises the following steps:
s100: parameters such as regional power distribution network topology, the number of feeder lines, a feeder substation transformer and the like are obtained, and a load curve of an electric vehicle accessed by a regional power grid under the charging action is defined through actual measurement data and a Monte Carlo simulation analysis method according to historical statistical data;
s200: the dynamic power balance system structure of the power distribution network is established on the existing distribution network structure, a three-phase voltage type pulse width modulation converter is adopted to communicate with each distribution transformer in the distribution network through a direct current circuit so as to realize reasonable distribution of loads and reduce impact of loads of electric vehicles, and meanwhile, two working state modes of normal operation and high-risk fault operation are adopted in the dynamic power balance system;
s300: establishing two control strategies of a power distribution network dynamic power balance system, namely power decoupling outer loop current inner loop control and voltage and current double closed loop control, wherein the power decoupling control method is generally adopted by the power distribution network dynamic power balance system to directly control the output power of a three-phase voltage type converter, and meanwhile, in order to avoid the instability of direct-current side voltage caused by the uncertainty of the output power of the converter, at least one converter is kept to adopt a current and voltage double closed loop control method, and the switching condition of the two converters is given;
s400: monitoring the active power output by each distribution transformer and the corresponding converter, setting a control target of an operation strategy of a dynamic power balance system of the distribution network, and giving out an active power control instruction reference value calculation value of each converter in the dynamic power balance system of the distribution network;
s500: and a control instruction is sent to a converter of the dynamic power balance system of the power distribution network, so that the self-adaptive adjustment of the power of the regional power grid accessed by the electric automobile is realized.
Further, in step S100, parameters such as a regional distribution network topology, the number of feeder lines, a feeder substation transformer and the like are obtained, according to historical statistical data, a load curve of the regional power grid accessed electric vehicle under the charging action is determined through actual measurement data and a monte carlo simulation analysis method, and the monte carlo simulation analysis method is specifically adopted to determine that the load proportion accessed by the electric vehicle charging station within 24 hours is close to normal distribution, and a fitting probability density function is as follows:
in the formula (1), P x Active power of node x of electric vehicle charging station, S EV The electric vehicle charging node set is an electric vehicle charging node set contained in the whole target object regional power grid; alpha 1 、α 2 、α 3 、β 1 、β 2 、β 3 The distribution coefficients of the fitting probability density function are respectively determined by sample data fitting; f (t) is a probability density function determined after fitting; p (P) x And (t) is a charging load change curve of the distribution network electric automobile within a 24-hour period.
Further, in step S200, a dynamic power balance system structure of the distribution network is established on the existing distribution network structure, and three-phase voltage type pulse width modulation converters are adopted to communicate with each distribution transformer in the distribution network through a direct current line so as to realize reasonable distribution of loads and reduce impact of loads of electric vehicles, wherein n distribution transformers correspond to n voltage type converters; the converter dynamically adjusts the power supply and demand of the power distribution network connected with the electric automobile by controlling the active power reference value and the reactive power reference value output to the alternating-current side power grid; the distribution network dynamic power balance system comprises two working state modes: (1) under the normal operation condition, the connection of the converter and the low-voltage side bus of the distribution transformer is in a long-term working state; when a large-capacity electric automobile is charged in a certain user cell, the corresponding power supply and distribution transformer can be in overload operation, and the converter automatically adjusts the output active power to relieve the deficiency of the power supply capacity of the transformer; when a certain distribution transformer is in light load operation, the corresponding converter regulates the output active power to be negative, and redundant active power is transmitted to other user cells through the converter, so that dynamic power balance is realized, and the distribution transformer is prevented from being in light or heavy load operation; (2) when a user cell fails, the current flowing through the corresponding distribution transformer is rapidly increased, and in order to avoid damaging the converter and increasing the short-circuit capacity of the distribution network, the tie switch is disconnected and the corresponding converter is in a locking state; when the distribution network has serious faults, the power balance system is withdrawn, namely the contact switch is completely opened.
Further, two control strategies of the dynamic power balance system of the power distribution network are established in step S300, the dynamic power balance system of the power distribution network generally adopts a power decoupling control method to directly control the output power of the three-phase voltage type converter, and the power decoupling outer loop current inner loop control equation of the converter is as follows:
in the formulas (2) and (3), the parameter of superscript indicates the reference value of control; k (k) gp 、k gi Proportional-integral coefficient, v of the current inner loop controller respectively d * 、v q * The reference values of d and q axis components of the alternating-current side voltage of the converter are respectively obtained; i.e d * 、i q * The reference values of d and q axis components of the current transformer are respectively; u (u) d -ωLi q U q +ωLi d A feedforward compensation term for the introduction; k (k) lp 、k li Proportional integral coefficients of the power outer loop controller are respectively; p (P) * 、Q * The reference values are respectively the active power reference value and the reactive power reference value of the converter; the power reference value can be set according to different targets, and the current reference value of the current inner loop controller can be determined through the power outer loop controller; meanwhile, in order to avoid the instability of direct-current side voltage caused by uncertainty of output power of the current transformer, at least one current transformer is kept to adopt a current-voltage double closed-loop control method to changeThe control equation of the current transformer voltage outer loop controller is:
i d * ＝k vp (U dc * -U dc )+k vi ∫(U dc * -U dc )dt (4)
in the formula (4), k vp 、k vi Respectively the proportional integral coefficients of the voltage outer loop controller, U dc * Is a direct current side voltage reference value; determining switching conditions of the two control strategies: if the current transformer for stabilizing the direct current side voltage in the dynamic power balance system of the distribution network is out of operation due to faults or other reasons, the current transformer with the smallest capacity among the rest current transformers is selected as a standby stable direct current side voltage current transformer, and the control strategy of the current transformer is switched from the power decoupling outer loop current inner loop control to the voltage current double closed loop control.
Further, in step S400, the active power output by each distribution transformer and the corresponding converter is monitored, a control target of the operation strategy of the dynamic power balance system of the power distribution network is set, and a calculation formula of the active power control command reference value of each converter in the dynamic power balance system of the power distribution network is given, which is specifically as follows:
in the formulas (5) and (6),the active power and reactive power control instruction reference values of an ith converter of the dynamic power balance system of the distribution network are respectively represented, and under the condition of steady-state operation, the output reactive power reference value of the converter is 0 so as to realize unit power operation, so that the setting of the active power reference value is mainly discussed; p (P) gmax·i Maximum allowable output power of the ith converter; s is S i The capacity of the distribution transformer is the ith distribution transformer in the transformer area; s is S o The total capacity of n distribution transformers contained for the whole research object regional power grid; p (P) gi The active power output by the ith converter to the alternating-current side power grid is represented; p (P) ei Representing the active power output by the ith distribution transformer to a user; active power control of the current transformer is in a piecewise function control mode as a whole.
Further, in step S500, in combination with the actual regional power grid situation, a result is obtained according to the control command reference value calculation, and the result is sent to the converter of the dynamic power balance system of the power distribution network, so as to realize the adaptive adjustment of the regional power grid power accessed by the electric automobile; the method can be properly adjusted on the basis of the structure and configuration of the existing power distribution network, so that the impact caused by the fact that the charging pile of the electric automobile is connected into the power distribution network can be effectively realized.
The invention has the beneficial effects that:
1. the dynamic power balance method considering the electric automobile access regional power grid disclosed by the invention can realize reasonable distribution of the distribution transformer load, avoid insufficient transformer capacity and improve the power supply reliability; the influence of large fluctuation generated when the electric automobile is connected into the power distribution network on the operation of a single distribution transformer is reduced, and the functions of improving the power supply quality and the like are achieved; the problem that the power unbalance of the power distribution network is aggravated by the random load generated by the access of the electric automobile to the power distribution network and the problem that the re-planning layout in a short period is not feasible is effectively solved, and a reference can be provided for solving a series of problems after the access of the electric automobile to the power distribution network.
2. The dynamic power balance method considering the electric automobile access regional power grid disclosed by the invention can be effectively realized by properly adjusting the structure and configuration of the existing power distribution network, the overall parameter setting architecture is simple and rapid, the utilized basic data is easy to obtain in an engineering site, the calculated amount is small, the operation and maintenance are easy, and the dynamic power balance method is an effective supplement of the traditional dynamic power balance technology.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and other advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the specification.
Drawings
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings, in which:
FIG. 1 is a flow chart of a dynamic power balancing method considering that an electric automobile is connected to a regional power grid;
FIG. 2 is a block diagram of a dynamic power balancing system of the present invention;
fig. 3 is a schematic switching diagram of two control strategies of the current transformer in the dynamic power balance system according to the present invention;
fig. 4 is a schematic structural diagram of an electric vehicle access area network according to an embodiment of the present invention;
fig. 5 is a comparison of simulation results of the two cases in which the dynamic power balancing is implemented by the method and no measures are taken in the embodiment of the present invention, fig. 5 (a) is a load distribution case of 3 transformers in the case where no power balancing measures are taken, and fig. 5 (b) is a load distribution case of 3 transformers in the case where the dynamic power balancing measures are implemented by the method.
Detailed Description
Other advantages and effects of the present invention will become apparent to those skilled in the art from the following disclosure, which describes the embodiments of the present invention with reference to specific examples. The invention may be practiced or carried out in other embodiments that depart from the specific details, and the details of the present description may be modified or varied from the spirit and scope of the present invention. It should be noted that the illustrations provided in the following embodiments merely illustrate the basic idea of the present invention by way of illustration, and the following embodiments and features in the embodiments may be combined with each other without conflict.
Wherein the drawings are for illustrative purposes only and are shown in schematic, non-physical, and not intended to limit the invention; for the purpose of better illustrating embodiments of the invention, certain elements of the drawings may be omitted, enlarged or reduced and do not represent the size of the actual product; it will be appreciated by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
The dynamic power balance method considering the electric automobile access area power grid as shown in fig. 1 comprises the following steps:
s100: parameters such as regional power distribution network topology, the number of feeder lines, a feeder substation transformer and the like are obtained, and a load curve of an electric vehicle accessed by a regional power grid under the charging action is defined through actual measurement data and a Monte Carlo simulation analysis method according to historical statistical data;
specifically, a Monte Carlo simulation analysis method is adopted to calculate the load proportion of the electric vehicle charging station access within 24 hours to be close to normal distribution, and the fitting probability density function is as follows:
in the formula (1), P x Active power of node x of electric vehicle charging station, S EV The electric vehicle charging node set is an electric vehicle charging node set contained in the whole target object regional power grid; alpha 1 、α 2 、α 3 、β 1 、β 2 、β 3 The distribution coefficients of the fitting probability density function are respectively determined by sample data fitting; f (t) is a probability density function determined after fitting; p (P) x And (t) is a charging load change curve of the distribution network electric automobile within a 24-hour period.
S200: the dynamic power balance system structure of the power distribution network is established on the existing distribution network structure, a three-phase voltage type pulse width modulation converter is adopted to communicate with each distribution transformer in the distribution network through a direct current line so as to realize reasonable distribution of loads and reduce impact of loads of electric vehicles, and n distribution transformers correspond to n voltage type converters; the converter dynamically adjusts the power supply and demand of the power distribution network connected with the electric automobile by controlling the active power reference value and the reactive power reference value output to the alternating-current side power grid; the distribution network dynamic power balance system comprises two working state modes: (1) under the normal operation condition, the connection of the converter and the low-voltage side bus of the distribution transformer is in a long-term working state; when a large-capacity electric automobile is charged in a certain user cell, the corresponding power supply and distribution transformer can be in overload operation, and the converter automatically adjusts the output active power to relieve the deficiency of the power supply capacity of the transformer; when a certain distribution transformer is in light load operation, the corresponding converter regulates the output active power to be negative, and redundant active power is transmitted to other user cells through the converter, so that dynamic power balance is realized, and the distribution transformer is prevented from being in light or heavy load operation; (2) when a user cell fails, the current flowing through the corresponding distribution transformer is rapidly increased, and in order to avoid damaging the converter and increasing the short-circuit capacity of the distribution network, the tie switch is disconnected and the corresponding converter is in a locking state; when the distribution network has serious faults, the power balance system is withdrawn, namely the contact switch is completely opened.
S300: as shown in fig. 3, two control strategies of a dynamic power balance system of a power distribution network are established, namely power decoupling outer loop current inner loop control and voltage current double closed loop control, the dynamic power balance system of the power distribution network generally adopts a power decoupling control method to directly control the output power of a three-phase voltage type converter, and a converter power decoupling outer loop current inner loop control equation is as follows:
in the formulas (2) and (3), the parameter of superscript indicates the reference value of control; k (k) gp 、k gi Proportional-integral coefficient, v of the current inner loop controller respectively d * 、v q * The reference values of d and q axis components of the alternating-current side voltage of the converter are respectively obtained; i.e d * 、i q * The reference values of d and q axis components of the current transformer are respectively; u (u) d -ωLi q U q +ωLi d A feedforward compensation term for the introduction; k (k) lp 、k li Proportional integral coefficients of the power outer loop controller are respectively; p (P) * 、Q * The reference values are respectively the active power reference value and the reactive power reference value of the converter; the power reference value can be set according to different targets, and the current reference value of the current inner loop controller can be determined through the power outer loop controller; meanwhile, in order to avoid the instability of direct-current side voltage caused by uncertainty of output power of the current transformer, at least one current transformer is kept to adopt a current-voltage double closed-loop control method, and a control equation of a voltage outer loop controller of the current transformer is as follows:
i d * ＝k vp (U dc * -U dc )+k vi ∫(U dc * -U dc )dt (4)
in the formula (4), k vp 、k vi Respectively the proportional integral coefficients of the voltage outer loop controller, U dc * Is a direct current side voltage reference value; determining switching conditions of the two control strategies: if the current transformer for stabilizing the direct current side voltage in the dynamic power balance system of the distribution network is out of operation due to faults or other reasons, the current transformer with the smallest capacity among the rest current transformers is selected as a standby stable direct current side voltage current transformer, and the control strategy of the current transformer is switched from the power decoupling outer loop current inner loop control to the voltage current double closed loop control.
S400: the method comprises the steps of monitoring active power output by each distribution transformer and corresponding converter, setting a control target of an operation strategy of a dynamic power balance system of a power distribution network, and giving out an active power control instruction reference value calculation formula of each converter in the dynamic power balance system of the power distribution network, wherein the calculation formula is specifically as follows:
in the formulas (5) and (6),the active power and reactive power control instruction reference values of an ith converter of the dynamic power balance system of the distribution network are respectively represented, and under the condition of steady-state operation, the output reactive power reference value of the converter is 0 so as to realize unit power operation, so that the setting of the active power reference value is mainly discussed; p (P) gmax·i Maximum allowable output power of the ith converter; s is S i The capacity of the distribution transformer is the ith distribution transformer in the transformer area; s is S o The total capacity of n distribution transformers contained for the whole research object regional power grid; p (P) gi The active power output by the ith converter to the alternating-current side power grid is represented; p (P) ei Representing the active power output by the ith distribution transformer to a user; active power control of the current transformer is in a piecewise function control mode as a whole.
S500: combining the actual regional power grid situation, obtaining a result according to the control instruction reference value calculation, and sending the result to a converter of a dynamic power balance system of the power distribution network to realize the self-adaptive adjustment of the regional power grid power accessed by the electric automobile; the method can be properly adjusted on the basis of the structure and configuration of the existing power distribution network, so that the impact caused by the fact that the charging pile of the electric automobile is connected into the power distribution network can be effectively realized.
Examples
The process of the above method is described in detail below by way of specific examples, as shown in fig. 4, comprising 3 feeders, 3 distribution transformers, 10kV connected from a distribution master station, and the parameters of the system and equipment during normal operation of the specific test system are shown in table 1 below. According to the method, a distribution network dynamic power balance system consisting of 3 converters sharing a direct current bus is designed, and the rated direct current voltage of a direct current line of the distribution network dynamic power balance system is 800V and T 2 The corresponding converter of the distribution transformer adopts a voltage-current double closed-loop control strategy, and the control parameter instruction of the method is executed to implement dynamic power balance.
TABLE 1 testing System State parameters
To improve efficiency, the simulation cycle simulates the variation of the electric vehicle load and the conventional load of each user cell within 24 hours a day with 24 s. The dynamic power balance is implemented by adopting the method, and no measures are taken, and the simulation results of the two cases are compared with each other, as shown in fig. 5. Fig. 5 (a) shows the load distribution of 3 transformers without power balancing measures, and fig. 5 (b) shows the load distribution of 3 transformers with dynamic power balancing measures implemented by the method. The comparison result shows that: if the dynamic power balance system of the distribution network is not adopted, the load distribution of 3 transformers is seriously uneven, T 3 Distribution transformer load is even greater than large capacity T 1 The load of the distribution transformer and overload behavior occurs within 15s to 20 s. The method not only increases the distribution network loss and reduces the power supply reliability, but also brings hidden danger to the operation safety of the power grid.
When the dynamic power balance system is adopted, when the load of the electric vehicle charging station is continuously increased, the increased load is distributed to each distribution transformer according to a certain proportion under the action of the dynamic power balance system, and the partial load is prevented from being totally formed by T 3 Distribution transformers bear, therefore T 3 The distribution transformer is not overloaded. Because each distribution transformer is connected with each other through a direct current circuit, the load of different transformers can be increased or decreased at the same time to realize balance. The comparison result shows that the method of the invention realizes the aim of carrying out load balance between different distribution transformers of the distribution network containing the electric automobile access, and avoids the difficult operation problem caused by dynamic power unbalance of the distribution network.
Finally, it is noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications and equivalents may be made thereto without departing from the spirit and scope of the present invention, which is intended to be covered by the claims of the present invention.
Claims (8)
1. The dynamic power balance method considering the electric automobile to access the regional power grid is characterized by comprising the following steps of:
s100: acquiring regional distribution network topology, the number of feeder lines and feeder substation transformer parameters, and determining a load curve of an electric vehicle accessed by a regional power grid under the charging action of the electric vehicle according to historical statistical data by using actual measurement data and a Monte Carlo simulation analysis method;
s200: the method comprises the steps that a dynamic power balance system structure of a power distribution network is established on the existing distribution network structure in the step S100, three-phase voltage type pulse width modulation converters are adopted to communicate with all distribution transformers in the distribution network through direct current lines so as to realize reasonable distribution of loads and reduce impact of loads of electric vehicles, and meanwhile, two working state modes of normal operation and high-risk fault operation are adopted for the balance system;
s300: in the different working state modes of step S200, two control strategies of a dynamic power balance system of the power distribution network are established, the power decoupling outer loop current inner loop control and the voltage and current double closed loop control are adopted, the dynamic power balance system of the power distribution network generally adopts a power decoupling control method to directly control the output power of a three-phase voltage type converter, and meanwhile, in order to avoid the instability of direct-current side voltage caused by the uncertainty of the output power of the converter, at least one converter is reserved to adopt a current and voltage double closed loop control method, and the switching condition of the two converters is given;
s400: monitoring the active power output by each distribution transformer and the corresponding converter, setting a control target of an operation strategy of a dynamic power balance system of the distribution network, and giving out an active power control instruction reference value calculation value of each converter in the dynamic power balance system of the distribution network;
s500: and according to the result obtained by the calculation formula of the control instruction reference value in the step S400, a control instruction is sent to a converter of a dynamic power balance system of the power distribution network, so that the self-adaptive adjustment of the power of the electric automobile access region power grid is realized, and the impact caused by the electric automobile charging pile access to the power distribution network is reduced.
2. The method according to claim 1, wherein the load ratio of the electric vehicle charging station to the regional power grid is normally distributed within 24 hours in step S100.
3. The method for dynamic power balance considering access of electric vehicles to regional power grids as claimed in claim 2, wherein the step S100 of obtaining the load curve under the charging behavior of the electric vehicles is specifically as follows: the Monte Carlo simulation analysis method is adopted to calculate the load proportion of the electric vehicle charging station in 24 hours, and the fitting probability density function is as follows:
in the formula (1), P x Active power of node x of electric vehicle charging station, S EV The electric vehicle charging node set is an electric vehicle charging node set contained in the whole target object regional power grid; alpha 1 、α 2 、α 3 、β 1 、β 2 、β 3 The distribution coefficients of the fitting probability density function are respectively determined by sample data fitting; f (t) is a probability density function determined after fitting; p (P) x And (t) is a charging load change curve of the distribution network electric automobile within a 24-hour period.
4. The method according to claim 1, wherein the converter in step S200 dynamically adjusts the power supply and demand of the distribution network including the electric vehicle access by controlling the active and reactive power reference values output to the ac side power network.
5. The method for dynamic power balance considering electric vehicle access to regional power grid as set forth in claim 4, wherein the distribution network dynamic power balance system in step S200 comprises two operation state modes: (1) under the normal operation condition, the connection of the converter and the low-voltage side bus of the distribution transformer is in a long-term working state; when a large-capacity electric automobile is charged in a certain user cell, the corresponding power supply and distribution transformer is in overload operation, and the converter automatically adjusts the output active power to relieve the deficiency of the power supply capacity of the transformer; when a certain distribution transformer is in light load operation, the corresponding converter regulates the output active power to be negative, and redundant active power is transmitted to other user cells through the converter, so that dynamic power balance is realized, and the distribution transformer is prevented from being in light or heavy load operation; (2) when a user cell fails, the current flowing through the corresponding distribution transformer is rapidly increased, and in order to avoid damaging the converter and increasing the short-circuit capacity of the distribution network, the tie switch is disconnected and the corresponding converter is in a locking state; when the distribution network has serious faults, the power balance system is withdrawn, namely the contact switch is completely opened.
6. The method for dynamic power balance considering electric vehicle access to regional power grid as set forth in claim 1, wherein two control strategy switching conditions of the dynamic power balance system of the power distribution network in step S300 are: if the current transformer for stabilizing the direct current side voltage in the distribution network dynamic power balance system is out of operation due to faults or other reasons, the current transformer with the smallest capacity among the rest current transformers is selected as a standby stable direct current side voltage current transformer, and the control strategy of the current transformer is switched from the power decoupling outer loop current inner loop control to the voltage current double closed loop control.
7. The method for dynamic power balance considering electric automobile access regional power grid as claimed in claim 6, wherein in step S300, the output power of the three-phase voltage type converter is directly controlled by adopting a power decoupling control method, and the converter power decoupling outer loop current inner loop control equation is as follows:
in the formulas (2) and (3), the parameter of superscript indicates the reference value of control; k (k) gp 、k gi Proportional-integral coefficient, v of the current inner loop controller respectively d * 、v q * The reference values of d and q axis components of the alternating-current side voltage of the converter are respectively obtained; i.e d * 、i q * The reference values of d and q axis components of the current transformer are respectively; u (u) d -ωLi q U q +ωLi d A feedforward compensation term for the introduction; k (k) lp 、k li Proportional integral coefficients of the power outer loop controller are respectively; p (P) * 、Q * The reference values are respectively the active power reference value and the reactive power reference value of the converter; setting power reference values according to different targets, and determining current reference values of a current inner loop controller through a power outer loop controller;
in order to avoid instability of direct-current side voltage caused by uncertainty of output power of the current transformer, at least one current transformer is kept to adopt a current-voltage double closed-loop control method, wherein a control equation of a voltage outer loop controller of the current transformer is as follows:
i d * ＝k vp (U dc * -U dc )+k vi ∫(U dc * -U dc )dt (4)
in the formula (4), k vp 、k vi Respectively the proportional integral coefficients of the voltage outer loop controller, U dc * Is a direct current side voltage reference value; and determining the switching conditions of the two control strategies.
8. The method of claim 1, wherein the calculation formula of the reference value of the active power control command of each converter in step S400 is as follows:
in the formulas (5) and (6),the active power and reactive power control instruction reference values of an ith converter of the dynamic power balance system of the distribution network are respectively represented, and under the condition of steady-state operation, the output reactive power reference value of the converter is 0 so as to realize unit power operation, so that the setting of the active power reference value is mainly discussed; p (P) gmax·i Maximum allowable output power of the ith converter; s is S i The capacity of the distribution transformer is the ith distribution transformer in the transformer area; s is S o The total capacity of n distribution transformers contained for the whole research object regional power grid; p (P) gi The active power output by the ith converter to the alternating-current side power grid is represented; p (P) ei Representing the active power output by the ith distribution transformer to a user; active power control of the current transformer is in a piecewise function control mode as a whole. />
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