Power distribution network voltage and power flow coordination control method and device of multi-port flexible switch

Abstract

The invention provides a power distribution network voltage and power flow coordination control method and device of a multi-port flexible switch. The method comprises the following steps: taking the minimum deviation between the alternating current side node voltage of the second converter and the alternating current side node voltage of the first converter and the minimum deviation between the transformer load rate of the alternating current side feeder line of the second converter and the transformer load rate of the alternating current side feeder line of the first converter as optimization targets; constructing a target function of multi-target coordination control; calculating a power reference value of the second current converter in the current period according to the target function and a coordination controller of the second current converter; and controlling the second converter according to the power reference value of the current period. According to the scheme, under the condition that real-time communication of all node voltages is lacked, power flow distribution between the feeder lines where the converters are located can be achieved, and the voltage out-of-limit condition is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of power grid control, and in particular to a method and device for coordinated control of voltage and power flow in a distribution network of a multi-port flexible switch. Background Art

[0002] With the large-scale access of distributed photovoltaics and the growing demand for electricity from electric vehicles, air conditioners, etc. in the distribution network, the imbalance of distribution network load is becoming increasingly prominent. At the same time, distributed photovoltaics and electric vehicles have significant random characteristics, which can easily cause problems such as voltage over-limit and transformer overload, affecting the safe and reliable operation of the distribution network.

[0003] A multi-terminal soft open point (MTSOP) is usually composed of multiple back-to-back voltage source converters (VSC). Through direct DC interconnection of different converters, power can be transmitted between different AC distribution networks, solving the problem that different transformers in traditional AC distribution networks cannot be directly electrically connected.

[0004] The flexible interconnected distribution network based on MTSOP can effectively optimize the power flow between different distribution networks, improve the voltage level, alleviate the overload of transformers, and improve the acceptance capacity of distributed photovoltaics. It is an important direction for the development of intelligent distribution systems.

[0005] In order to use MTSOP to improve the power distribution of different distribution networks, it is necessary to optimize the transmission power of each port. According to different real-time methods, the control methods of MTSOP include optimization scheduling and real-time control. The MTSOP control method based on master station optimization scheduling optimizes the transmission power of MTSOP by obtaining the status information of the distribution network, and sends it to MTSOP for execution. This method requires the control master station to have strong computing power, but it has high requirements for system communication and measurement conditions. Under weak communication conditions, the distribution network is prone to voltage over-limit. Summary of the invention

[0006] The embodiment of the present invention provides a method and device for coordinated control of distribution network voltage and power flow of a multi-port flexible switch to solve the problem of voltage over-limit caused by a high proportion of distributed power sources connected to the distribution network under weak communication conditions.

[0007] In a first aspect, an embodiment of the present invention provides a method for coordinated control of distribution network voltage and power flow of a multi-port flexible switch, wherein a plurality of distribution networks are connected through a multi-port capacitive switch, and the multi-port flexible switch comprises a first converter and at least one second converter; the first converter is a converter using voltage control, and the second converter is a converter using PQ control; the method is applied to any second converter, and comprises:

[0008] Taking the deviation between the AC side node voltage of the second converter and the AC side node voltage of the first converter as the minimum, and the deviation between the transformer load rate of the AC side feeder of the second converter and the transformer load rate of the AC side feeder of the first converter as the minimum as the optimization objectives, constructing the objective function of multi-objective coordinated control;

[0009] Calculating a power reference value of the second converter in a current cycle according to the objective function and the coordination controller of the second converter;

[0010] The second converter is controlled according to the power reference value of the current cycle.

[0011] In a second aspect, an embodiment of the present invention provides a distribution network voltage and power flow coordination control device of a multi-port flexible switch, wherein a plurality of distribution networks are connected through a multi-port capacitive switch, and the multi-port flexible switch comprises a first converter and at least one second converter; the first converter is a converter using voltage control, and the second converter is a converter using PQ control;

[0012] The device is applied to any second converter, comprising:

[0013] An objective function determination module, used to construct an objective function of multi-objective coordinated control by taking the deviation between the AC side node voltage of the second converter and the AC side node voltage of the first converter and the deviation between the transformer load rate of the AC side feeder of the second converter and the transformer load rate of the AC side feeder of the first converter as optimization objectives;

[0014] A power reference value calculation module, used to calculate the power reference value of the second converter in the current cycle according to the objective function and the coordination controller of the second converter;

[0015] A converter control module is used to control the second converter according to the power reference value of the current cycle.

[0016] The embodiment of the present invention provides a method and device for coordinated control of voltage and power flow of a distribution network of a multi-port flexible switch. The method takes the deviation between the AC side node voltage of the second converter and the AC side node voltage of the first converter and the deviation between the transformer load rate of the AC side feeder of the second converter and the transformer load rate of the AC side feeder of the first converter as optimization targets, constructs an objective function of multi-objective coordinated control; calculates the power reference value of the second converter in the current cycle according to the objective function and the coordinated controller of the second converter; and controls the second converter according to the power reference value of the current cycle. In the absence of real-time communication of all node voltages, the above scheme senses the node voltage change caused by the random change of photovoltaic output through the change of the AC side node voltage of each converter port. Through the objective function of multi-objective coordinated control, not only can the power flow distribution of each second converter and the wiring where the first converter is located be realized, but also the power coupling relationship between each converter can be used to realize the power flow distribution between the feeders where each converter is located, so as to avoid voltage over-limit. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0018] Figure 1 This is an application scenario diagram of the distribution network voltage and power flow coordinated control method of the multi-port flexible switch provided in an embodiment of the present invention;

[0019] Figure 2 It is a flow chart for implementing a method for coordinated control of voltage and power flow in a distribution network of a multi-port flexible switch provided by an embodiment of the present invention;

[0020] Figure 3 is a signal flow diagram of a coordination controller provided by an embodiment of the present invention;

[0021] Figure 4 Schematic diagram of transmission power of each port of MTSOP during adjustment in the first simulation scenario provided by an embodiment of the present invention;

[0022] Figure 5 is a schematic diagram of comparing node voltages of each feeder in a distribution network under a first simulation scenario provided by an embodiment of the present invention;

[0023] Figure 6 1 is a schematic diagram of power transmission of each port of MTSOP during the adjustment process under the second simulation scenario provided by an embodiment of the present invention;

[0024] Figure 7 is a schematic diagram of node voltage changes of each feeder in the distribution network before and after adjustment in the second simulation situation provided by an embodiment of the present invention;

[0025] Figure 8 It is a structural schematic diagram of a distribution network voltage and power flow coordination control device of a multi-port flexible switch provided in an embodiment of the present invention;

[0026] Fig. 9 is a schematic diagram of a terminal provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0027] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clear, specific embodiments will be described below in conjunction with the accompanying drawings.

[0029] Figure 1 A schematic diagram of the connection of a distribution network of a multi-port flexible switch provided by an embodiment of the present invention. Figure 1 As shown, multiple distribution networks are connected through a multi-port capacitive switch, and the multi-port flexible switch includes a first converter and at least one second converter; the first converter is a converter using voltage control, and the second converter is a converter using PQ control; in the multi-port capacitive switch, the AC end of each converter is connected to the corresponding distribution network feeder, and the DC end is connected to the DC end of other converters.

[0030] Specifically, MTSOP connects different distribution feeders through multiple VSCs to achieve power transmission between different feeders. In MTSOP, usually one VSC uses a constant DC voltage control (V dc Control), the rest of the VSCs use constant DC power control (PQ control); all VSCs use constant reactive power control on the AC side. When the transmission power loss of the VSC is not considered, the power balance relationship in the MTSOP can be expressed as:

[0031]

[0032] Among them, P i It represents the power injected into the AC grid by the i-th VSC, and N represents the number of VSCs in the MTSOP.

[0033] The voltage amplitude level of the distribution network is affected by the photovoltaic output and load power. When the photovoltaic output is large and the load power is small, the distribution network voltage is higher than the upper limit, and the transformer transmits power in reverse to the upper grid; when there is no photovoltaic or the photovoltaic output is small and the load power is large, the distribution network voltage is lower than the lower limit, and the transformer is heavily overloaded. MTSOP exchanges power between different feeders and transfers the power of the heavy-loaded feeder to the light-loaded feeder, thereby improving the voltage level and balancing the transformer load rate.

[0034] by Figure 1 Taking the flexible interconnected distribution network shown in the figure as an example, it is assumed that VSC1 is the first converter, using Vdc control, and VSC2 and VSC3 are the second converters, using PQ control. Since the voltage control command of the VSC controlled by Vdc is only used to maintain the stability of the DC voltage inside the MTSOP and does not affect its transmission power, its transmission power is determined by the power control command of the remaining VSCs. When the power injected into the AC distribution network by VSC2 and VSC3 is P2 and P3 respectively, according to the power balance relationship in the MTSOP, the power P1 injected into the AC distribution network by VSC1 is: P1 = -P2-P3.

[0035] Assuming that the substation voltage is approximately unchanged, the linear power flow model of the distribution network is used to analyze the impact of the active power regulation of each port of the MTSOP on the voltage of each node of the distribution network. In the radial distribution network, the system rated voltage is used to approximately replace the actual voltage of each node. When the power change ΔP of a certain node i i When the voltage at node j changes ΔU j ,and

[0036]

[0037] Where: Ω ij represents the set of common lines on the path from nodes i and j to the transformer bus, R l Indicates the resistance of branch l; U N Indicates the rated voltage of the system.

[0038] Therefore, when the power injected into the AC distribution network by VSC2 and VSC3 in MTSOP is P2 and P3 respectively, the voltage change of the AC side node of each port in MTSOP is:

[0039]

[0040] Among them, ΔU VSC1 , ΔU VSC2 , ΔU VSC3 The voltage changes of the AC side nodes of VSC1, VSC2 and VSC3 respectively; Ω VSC1 ,Ω VSC2 ,Ω VSC3They are the line sets on the path from the AC side nodes of VSC1, VSC2, and VSC3 to the transformer busbar.

[0041] For ease of description, the voltage sensitivity coefficient S is defined as the quotient of the sum of the resistances of the line on the path from the i-th VSC AC side node to the transformer bus and the rated voltage. i ,Right now:

[0042]

[0043] Among them, Ω VSCi It represents the set of lines from the AC side node of the i-th VSC to the transformer bus path. When the power injected into the AC distribution network by VSC2 and VSC3 in MTSOP is P2 and P3 respectively, the change in active load of each transformer is:

[0044] ΔP T1 =P2+P3;

[0045] ΔP T2 =-P2;

[0046] ΔP T3 =-P3;

[0047] Among them, ΔP T1 , ΔP T2 and ΔP T3 They are the active power changes of transformers T1, T2 and T3 respectively.

[0048] Generally, the purpose of MTSOP to optimize the power flow distribution of distribution network includes improving voltage level and balancing transformer load. Figure 1 As shown in Figure 1, the load information of the transformer can be obtained by means of the communication between the MTSOP and the transformer. For the MTSOP interconnected at the end of the feeder, the MTSOP can obtain the node voltage at the end of the feeder, but due to the certain distance between the SOP and other load nodes, the communication cost of the MTSOP to obtain the voltage information of each load node is high.

[0049] In the case that MTSOP cannot obtain the voltage of each load node in real time, the correlation between the voltage on the SOP AC side and the voltage on each load node is analyzed. In the distribution network where the feeder end is flexibly interconnected through SOP, the change of photovoltaic output in the feeder will cause the change of the voltage on the SOP AC side node. Figure 1 As shown in the figure, feeder 2 is taken as an example for analysis. When the power injected into a node i changes ΔP Ti When, according to the formula It can be seen that the voltage change between the AC side node of VSC2 and any node j is:

[0050]

[0051] When node j is not on the branch line The voltage change trend of node j is the same as that of the AC side node of VSC2, and the voltage change range of the latter is larger. It can be seen that in the absence of real-time communication of all node voltages, SOP can sense the system node voltage changes caused by random changes in photovoltaic output based on the changes in the AC side node voltage of each port, and adjust the voltage based on this.

[0052] Based on this, this embodiment provides a method for coordinated control of voltage and power flow in a distribution network of a multi-port flexible switch, see Figure 2 , which shows a flow chart of the implementation of the method for coordinated control of distribution network voltage and power flow of a multi-port flexible switch provided in an embodiment of the present invention. The execution subject of the method is the control of any second converter, which is described in detail as follows:

[0053] S101: Taking minimizing the deviation between the AC side node voltage of the second converter and the AC side node voltage of the first converter and minimizing the deviation between the transformer load rate of the AC side feeder of the second converter and the transformer load rate of the AC side feeder of the first converter as optimization objectives, constructing an objective function of multi-objective coordinated control.

[0054] In one possible implementation, the objective function is:

[0055]

[0056] Among them, P Ti represents the transformer power on the AC side feeder of the i-th second converter, P T1 represents the transformer power on the AC side feeder of the first converter; S Ti represents the rated capacity of the transformer on the AC side feeder of the i-th second converter, S T1 represents the rated capacity of the transformer on the AC side feeder of the first converter; U devi represents the deviation between the AC side node voltage of the i-th second converter and the AC side node voltage of the first converter; U VSCi represents the AC side node voltage of the i-th second converter; U VSC1 represents the AC side node voltage of the first converter; T devi represents the deviation between the transformer load rate of the AC side feeder of the i-th second converter and the transformer load rate of the AC side feeder of the first converter; α and β represent weights respectively.

[0057] In this embodiment, in order to achieve power flow distribution between different feeders and improve system voltage, the AC side node voltage of each PQ control VSC is connected to V dcThe voltage deviation of the VSC AC side is minimized as the target function of voltage control. Assuming that VSC1 in MTSOP adopts V dc Control, define the voltage deviation between the AC side of the VSC controlled by the ith PQ and VSC1 as U devi , then U devi =U VSCi -U VSC1 .

[0058] For the ith PQ-controlled VSC, the objective function of voltage coordination control is: minf Vi =U devi .

[0059] To further achieve load balancing of each feeder transformer, the transformer load rate of the feeder where the PQ control VSC is located is compared with the V dc The transformer load rate of the feeder where the VSC is located is controlled to minimize the deviation as the objective function of transformer load balancing control. Define the transformer load rate of the feeder where the VSC controlled by the i-th PQ is located and V dc The deviation of the transformer load rate of the feeder where the VSC is located is T devi , then T devi =P Ti / S Ti -P T1 / S T1 .

[0060] For the i-th PQ-controlled VSC, the objective function of the transformer load factor coordinated control is:

[0061] minf Ti =T devi .

[0062] In order to achieve the goals of improving the voltage level and balancing the transformer load rate at the same time, the objective function of multi-objective coordinated control is constructed by setting weights for different objective functions: minf i =αU devi +βT devi .

[0063] The above comprehensive control objectives can not only achieve PQ control of the feeder where the VSC is located and the V dc The power flow distribution of the feeder where the VSC is located can be controlled, and the power coupling relationship between the VSCs can be used to realize the power flow distribution between the feeders where the PQ control VSCs are located.

[0064] S102: Calculate a power reference value of the second converter in a current cycle according to the objective function and the coordination controller of the second converter.

[0065] In one possible implementation, the specific implementation process of S102 includes:

[0066] S201: Determine, based on the objective function, a deviation of an AC side node voltage and a deviation of a transformer load rate of the second converter in a previous cycle;

[0067] S202: Input the power reference value of the second converter in the previous cycle, the deviation of the AC side node voltage, and the deviation of the transformer load rate into the coordination controller to calculate the power reference value of the second converter in the current cycle.

[0068] In one possible implementation, the formula of the coordination controller is:

[0069]

[0070] Among them, P i (k+1) represents the power reference value of the i-th second converter in the k+1-th cycle; K i represents the feedback control gain, represents a deviation between an AC side node voltage of the i-th second converter in the k-th cycle and an AC side node voltage of the first converter; represents the deviation between the transformer load rate of the AC side feeder of the i-th second converter in the k-th cycle and the transformer load rate of the AC side feeder of the first converter; α and β represent weights respectively; P i (k) represents the power reference value of the i-th second converter in the k-th cycle.

[0071] In this embodiment, the coordinated controller of each VSC is designed according to the objective function. For the VSC under the ith PQ control, the power reference value in the k+1th control is:

[0072]

[0073] Accordingly, for the i-th PQ-controlled VSC, the designed coordinated controller is as follows: Figure 3 shown.

[0074] S103: Control the second converter according to the power reference value of the current cycle.

[0075] In a possible implementation manner, before S202, the method provided in this embodiment further includes:

[0076] S301: Determine a voltage sensitivity coefficient based on the resistance of a line on a path from the AC side node of the second converter to the transformer bus and a system rated voltage;

[0077] S302: Determine a voltage feedback control gain according to a voltage sensitivity coefficient of the second converter.

[0078] In one possible implementation, the specific implementation process of S301 includes:

[0079] Based on the formula Determine the voltage sensitivity coefficient;

[0080] Among them, S i represents the voltage sensitivity coefficient of the i-th second converter, R l represents the resistance of the lth line on the path from the AC side node of the i-th second converter to the transformer bus, U N Indicates the system rated voltage, Ω VSCi represents the set of lines on the path from the AC side node of the i-th second converter to the transformer bus.

[0081] In one possible implementation, the specific implementation process of S302 includes:

[0082] Based on the formula determining a voltage feedback control gain of the second converter;

[0083] Among them, S i represents the voltage sensitivity coefficient of the i-th second converter, K i represents the voltage feedback control gain of the i-th second converter, S1 represents the voltage sensitivity coefficient of the first converter, and ε represents the control step coefficient.

[0084] In this embodiment, in order to improve the voltage control speed, a voltage feedback control gain KU design method based on a gradient algorithm is proposed. For the control objective function: minf = x; its feedback controller can be designed as: Among them, u(k) represents the k-th control instruction; ε represents the control step coefficient, which is usually 0.1; x(k) represents the state parameter of the k-th control.

[0085] For the ith PQ-controlled VSC, the voltage deviation variable U devi The gradient of VSC power can be expressed as:

[0086]

[0087] According to the power balance relationship between PQ controlled VSC and Vdc controlled VSC, the above formula is further expressed as:

[0088]

[0089] Combining formulas We can get:

[0090] Therefore, for the i-th PQ-controlled VSC, its voltage feedback control gain is:

[0091] In a possible implementation manner, the specific implementation process of S103 includes:

[0092] Based on the PQ control algorithm and the power reference value of the current cycle, a PWM signal for controlling the second converter is generated.

[0093] In order to further verify the accuracy of the distribution network voltage and power flow coordinated control method of the multi-port flexible switch provided in this embodiment, this embodiment performs a simulation test, as follows:

[0094] use Figure 1 The three-terminal flexible interconnected distribution network shown in the figure has a voltage level of 10kV. Node 1 in each feeder is a transformer bus node, and its voltage is set to 1.0pu. The impedance parameters of each line are shown in Table 1. The transformer capacity is 5MW, and α and β are set to 1 and 0.1 respectively.

[0095] Table 1 Line impedance parameters

[0096]

[0097] The first simulation scenario:

[0098] The simulation scenario provided in this embodiment analyzes the control effect of the proposed MTSOP voltage coordination control method when the photovoltaic output is high during the day. At this time, the net injected power of each node is shown in Table 2.

[0099] Table 2 Node power table

[0100]

[0101] Assuming that the power of each port is 0 before MTSOP participates in regulation, the AC side voltage of VSC and the load rate of the transformer are shown in Table 3. It can be seen that due to the large photovoltaic output power of feeder 1, the node voltage increases and the transformer is reversely overloaded; the load power of feeder 2 is large, the node voltage is low, and the transformer is overloaded. There is potential for power flow optimization between different feeders.

[0102] Table 3 Node voltage and transformer load table

[0103]

[0104] Specifically, MTSOP starts power adjustment at 0.5s, and the sampling period is 10ms. During the adjustment process, the transmission power of each port of MTSOP is as follows: Figure 4 As shown. Figure 4 It can be seen that the power injected by VSC2 into feeder 2 increases, and the power absorbed by VSC1 from feeder 1 increases, achieving optimal control of power between feeder 1 and feeder 2.

[0105] The node voltage comparison of each feeder before and after MTSOP coordinated control is as follows: Figure 5 After regulation, the voltage of feeder 1 dropped from 1.0440pu to 0.9710pu, and the voltage of feeder 2 increased from 0.9384pu to 0.9966pu, which effectively improved the voltage level of the distribution network.

[0106] The comparison of transformer loads of each feeder before and after the implementation of MTSOP coordinated control is shown in Table 4. Through MTSOP coordinated control, the transformer load rates of feeder 1 and feeder 2 were reduced from 53.6% and 69.58% to 20.42% and 30.78%, respectively, effectively avoiding transformer overload. The simulation results show that the proposed MTSOP coordinated control strategy can effectively improve the voltage level and balance the transformer load during the period of photovoltaic power generation.

[0107] Table 4 Transformer load changes before and after regulation

[0108]

[0109] The second simulation scenario

[0110] The simulation scenario provided in this embodiment analyzes the control effect of the proposed MTSOP voltage coordination control method when there is no photovoltaic output at night and the distribution network load is heavy. At this time, the net injected power of each load node is shown in Table 5.

[0111] Table 5 Node power table in case 2

[0112]

[0113] Assume that before MTSOP participates in regulation, the power of each port is 0. The AC side voltage of each VSC and the load rate of the transformer are shown in Table 6. It can be seen that the AC side voltages of VSC1 and VSC2 are 0.9274pu and 0.9384pu respectively, and the transformer load rates of feeder 1 and feeder 2 are 73.46% and 69.58% respectively. Transformer 1 and transformer 2 are both overloaded.

[0114] Table 6 Node voltage and transformer load table before regulation

[0115]

[0116] During the MTSOP adjustment process, the MTSOP power of each port is as follows: Figure 6 As shown in the figure, the voltage changes before and after adjustment are as follows Figure 7 As shown in the figure, the power absorbed by VSC1 and VSC2 from feeder 1 and feeder 2 increases, and the power injected into feeder 3 by VSC3 increases, thereby achieving optimal control of power between different feeders. Figure 7It can be seen that after the control is completed, the AC side voltage of VSC1 and VSC2 increases from 0.9274pu and 0.9384pu to 0.9550pu and 0.9549pu. The simulation results show that when multiple interconnected feeders are overloaded, the MTSOP coordinated control method proposed in this embodiment can still effectively improve the system voltage.

[0117] The comparison of transformer loads before and after the implementation of MTSOP voltage coordination control is shown in Table 7. Through MTSOP voltage coordination control, the load rates of transformer 1 and transformer 2 were reduced from 73.46% and 69.58% to 58.82% and 58.52%, respectively, effectively reducing the degree of transformer overload.

[0118] Table 7 Transformer load before and after regulation

[0119]

[0120] This embodiment can also set two single-objective control methods, namely control strategy 1: pure voltage control strategy (minf Vi =U devi ) and control strategy 2: pure transformer load balancing control strategy (minf Ti =T devi ), the multi-objective control method proposed in this embodiment is compared with the single-objective control method, and the control effect comparison results of different control strategies are shown in Table 8. It can be seen that in situation 1, control strategy 2 causes the voltage of feeder 1 to exceed the limit. It can be seen that the control strategy with the transformer load rate balance as the goal cannot effectively improve the system voltage level during the photovoltaic power generation period. In situation 2 where multiple transformers are overloaded, control strategy 1 with the goal of improving voltage cannot effectively balance the transformer load rate. Compared with control strategy 1 and control strategy 2, the voltage and transformer load coordination control strategy proposed in this embodiment can effectively avoid node voltage exceeding the limit and transformer overloading at the same time, and has a good control effect.

[0121] It can be seen from the above embodiments that in order to solve the voltage over-limit and transformer overload problems caused by the access of a high proportion of distributed power sources, this embodiment proposes a voltage and power flow coordination control strategy for a flexible interconnected distribution network based on MTSOP. The MTSOP coordination control strategy does not rely on the system master station, and can quickly and effectively optimize the power flow distribution of the flexible interconnected distribution network, improve the voltage level and balance the transformer load; and the MTSOP coordination control strategy can be effectively applied to different situations such as large photovoltaic power generation during the day and multiple transformer overloads at night, and has good applicability.

[0122] Table 8 Node voltage and transformer load before regulation

[0123]

[0124]

[0125] It should be understood that the order of execution of the steps in the above embodiment does not necessarily mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention.

[0126] The following is an embodiment of the device of the present invention. For details not described in detail, reference may be made to the corresponding method embodiments described above.

[0127] Figure 8 The schematic diagram of the structure of the voltage and power flow coordination control device of the distribution network of the multi-port flexible switch provided by the embodiment of the present invention is shown. For the convenience of explanation, only the part related to the embodiment of the present invention is shown, which is described in detail as follows:

[0128] like Figure 8 As shown, the distribution network voltage and power flow coordination control device 100 of the multi-port flexible switch includes:

[0129] An objective function determination module 110 is used to construct an objective function of multi-objective coordinated control by taking the deviation between the AC side node voltage of the second converter and the AC side node voltage of the first converter and the deviation between the transformer load rate of the AC side feeder of the second converter and the transformer load rate of the AC side feeder of the first converter as optimization objectives;

[0130] A power reference value calculation module 120, configured to calculate a power reference value of the second converter in a current cycle according to the objective function and the coordination controller of the second converter;

[0131] The converter control module 130 is used to control the second converter according to the power reference value of the current cycle.

[0132] In one possible implementation, the objective function is:

[0133]

[0134] Among them, P Ti represents the transformer power on the AC side feeder of the i-th second converter, P T1 represents the transformer power on the AC side feeder of the first converter; S Ti represents the rated capacity of the transformer on the AC side feeder of the i-th second converter, S T1 represents the rated capacity of the transformer on the AC side feeder of the first converter; U devi represents the deviation between the AC side node voltage of the i-th second converter and the AC side node voltage of the first converter; U VSCirepresents the AC side node voltage of the i-th second converter; U VSC1 represents the AC side node voltage of the first converter; T devi represents the deviation between the transformer load rate of the AC side feeder of the i-th second converter and the transformer load rate of the AC side feeder of the first converter; α and β represent weights respectively.

[0135] In one possible implementation, the power reference value calculation module 120 includes:

[0136] A previous cycle data acquisition unit, used to determine the deviation of the AC side node voltage and the transformer load rate of the second converter in the previous cycle based on the objective function;

[0137] The coordination control unit is used to input the power reference value of the second converter in the previous cycle, the deviation of the AC side node voltage and the deviation of the transformer load rate into the coordination controller to calculate the power reference value of the second converter in the current cycle.

[0138] In one possible implementation, the formula of the coordination controller is:

[0139]

[0140] Among them, P i (k+1) represents the power reference value of the i-th second converter in the k+1-th cycle; K i represents the feedback control gain, represents a deviation between an AC side node voltage of the i-th second converter in the k-th cycle and an AC side node voltage of the first converter; represents the deviation between the transformer load rate of the AC side feeder of the i-th second converter in the k-th cycle and the transformer load rate of the AC side feeder of the first converter; α and β represent weights respectively; P i (k) represents the power reference value of the i-th second converter in the k-th cycle.

[0141] In a possible implementation manner, the distribution network voltage and power flow coordination control device 100 with a multi-port flexible switch further includes:

[0142] A sensitivity determination module, configured to determine a voltage sensitivity coefficient based on the resistance of a line on a path from the AC side node of the second converter to the transformer bus and a system rated voltage;

[0143] A voltage feedback control gain calculation module is used to determine the voltage feedback control gain according to the voltage sensitivity coefficient of the second converter.

[0144] In one possible implementation, the sensitivity determination module includes:

[0145] Based on the formula Determine the voltage sensitivity coefficient;

[0146] Among them, S i represents the voltage sensitivity coefficient of the i-th second converter, R l represents the resistance of the lth line on the path from the AC side node of the i-th second converter to the transformer bus, U N Indicates the system rated voltage, Ω VSCi represents the set of lines on the path from the AC side node of the i-th second converter to the transformer bus.

[0147] In one possible implementation, the voltage feedback control gain calculation module includes:

[0148] Based on the formula determining a voltage feedback control gain of the second converter;

[0149] Among them, S i represents the voltage sensitivity coefficient of the i-th second converter, K i represents the voltage feedback control gain of the i-th second converter, S1 represents the voltage sensitivity coefficient of the first converter, and ε represents the control step coefficient.

[0150] In one possible implementation, the converter control module 130 includes:

[0151] Based on the PQ control algorithm and the power reference value of the current cycle, a PWM signal for controlling the second converter is generated.

[0152] Fig. 9 is a schematic diagram of a terminal provided by an embodiment of the present invention. Fig. 9 As shown, the terminal 9 of this embodiment includes: a processor 90 and a memory 91. The memory 91 is used to store a computer program 92, and the processor 90 is used to call and run the computer program 92 stored in the memory 91 to execute the steps in the above-mentioned embodiments of the coordinated control method of the voltage and power flow of the distribution network of each multi-port flexible switch, for example Figure 2 Alternatively, the processor 90 is used to call and run the computer program 92 stored in the memory 91 to implement the functions of each module / unit in the above-mentioned device embodiments, for example Figure 8 The functions of the modules 110 to 130 are shown.

[0153] Exemplarily, the computer program 92 may be divided into one or more modules / units, which are stored in the memory 91 and executed by the processor 90 to implement the present invention. The one or more modules / units may be a series of computer program instruction segments capable of implementing specific functions, which are used to describe the execution process of the computer program 92 in the terminal 9. For example, the computer program 92 may be divided into Figure 8 Modules 110 to 130 are shown.

[0154] The terminal 9 may be a computing device such as a desktop computer, a notebook, a PDA, or a cloud server. The terminal 9 may include, but is not limited to, a processor 90 and a memory 91. Those skilled in the art will appreciate that Fig. 9 It is only an example of terminal 9 and does not constitute a limitation on terminal 9. It may include more or fewer components than shown in the figure, or a combination of certain components, or different components. For example, the terminal may also include input and output devices, network access devices, buses, etc.

[0155] The processor 90 may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor, etc.

[0156] The memory 91 may be an internal storage unit of the terminal 9, such as a hard disk or memory of the terminal 9. The memory 91 may also be an external storage device of the terminal 9, such as a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, etc. equipped on the terminal 9. Further, the memory 91 may also include both an internal storage unit of the terminal 9 and an external storage device. The memory 91 is used to store the computer program and other programs and data required by the terminal. The memory 91 may also be used to temporarily store data that has been output or is to be output.

[0157] The technicians in the relevant field can clearly understand that for the convenience and simplicity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In practical applications, the above-mentioned function allocation can be completed by different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiment can be integrated in a processing unit, or each unit can exist physically separately, or two or more units can be integrated in one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of this application. The specific working process of the units and modules in the above-mentioned system can refer to the corresponding process in the aforementioned method embodiment, which will not be repeated here.

[0158] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0159] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0160] In the embodiments provided by the present invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are only schematic. For example, the division of the modules or units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0161] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0162] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0163] If the integrated module / unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by the processor, the steps of the above-mentioned distribution network voltage and power flow coordinated control method embodiments of each multi-port flexible switch can be implemented. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device that can carry the computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electric carrier signal, telecommunication signal and software distribution medium. It should be noted that the content contained in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practices in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practices, computer-readable media does not include electrical carrier signals and telecommunication signals.

[0164] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A method for coordinated control of voltage and power flow in a distribution network of a multi-port flexible switch, characterized in that: A plurality of distribution networks are connected via a multi-port capacitive switch, and the multi-port flexible switch comprises a first converter and at least one second converter; the first converter is a converter using voltage control, and the second converter is a converter using PQ control; The method is applied to any second converter, comprising: Taking the deviation between the AC side node voltage of the second converter and the AC side node voltage of the first converter as the minimum, and the deviation between the transformer load rate of the AC side feeder of the second converter and the transformer load rate of the AC side feeder of the first converter as the minimum as the optimization objectives, constructing the objective function of multi-objective coordinated control; Calculating a power reference value of the second converter in a current cycle according to the objective function and the coordination controller of the second converter; The second converter is controlled according to the power reference value of the current cycle.

2. The method for coordinated control of voltage and power flow in a distribution network of a multi-port flexible switch according to claim 1, characterized in that: The objective function is: Among them, P Ti represents the transformer power on the AC side feeder of the i-th second converter, P T1 represents the transformer power on the AC side feeder of the first converter; S Ti represents the rated capacity of the transformer on the AC side feeder of the i-th second converter, S T1 represents the rated capacity of the transformer on the AC side feeder of the first converter; U devi represents the deviation between the AC side node voltage of the i-th second converter and the AC side node voltage of the first converter; U VSCi represents the AC side node voltage of the i-th second converter; U VSC1 represents the AC side node voltage of the first converter; T devi represents the deviation between the transformer load rate of the AC side feeder of the i-th second converter and the transformer load rate of the AC side feeder of the first converter; α and β represent weights respectively.

3. The method for coordinated control of voltage and power flow in a distribution network of a multi-port flexible switch according to claim 1, characterized in that: The calculating, according to the objective function and the coordinated controller of the second converter, the power reference value of the second converter in the current cycle includes: Based on the objective function, determining a deviation of an AC side node voltage and a deviation of a transformer load rate of the second converter in a previous cycle; The power reference value of the second converter in the previous cycle, the deviation of the AC side node voltage and the deviation of the transformer load rate are input into the coordination controller to calculate the power reference value of the second converter in the current cycle.

4. The method for coordinated control of voltage and power flow in a distribution network of a multi-port flexible switch according to claim 1, characterized in that: The formula of the coordinated controller is: Among them, P i (k+1) represents the power reference value of the i-th second converter in the k+1-th cycle; K i represents the feedback control gain, represents a deviation between an AC side node voltage of the i-th second converter in the k-th cycle and an AC side node voltage of the first converter; represents the deviation between the transformer load rate of the AC side feeder of the i-th second converter in the k-th cycle and the transformer load rate of the AC side feeder of the first converter; α and β represent weights respectively; P i (k) represents the power reference value of the i-th second converter in the k-th cycle.

5. The method for coordinated control of voltage and power flow in a distribution network of a multi-port flexible switch according to claim 4, characterized in that: Before inputting the power reference value of the second converter in the previous cycle, the deviation of the AC side node voltage, and the deviation of the transformer load rate into the coordination controller to calculate the power reference value of the second converter in the current cycle, the method further includes: Determining a voltage sensitivity coefficient based on the resistance of a line on a path from the AC side node of the second converter to the transformer bus and the rated voltage of the system; A voltage feedback control gain is determined according to a voltage sensitivity coefficient of the second converter.

6. The method for coordinated control of voltage and power flow in a distribution network of a multi-port flexible switch according to claim 5, characterized in that: The determining of the voltage sensitivity coefficient based on the resistance of the line on the path from the AC side node of the second converter to the transformer bus and the system rated voltage comprises: Based on the formula Determine the voltage sensitivity coefficient; Among them, S i represents the voltage sensitivity coefficient of the i-th second converter, R l represents the resistance of the lth line on the path from the AC side node of the i-th second converter to the transformer bus, U N Indicates the system rated voltage, Ω VSCi represents the set of lines on the path from the AC side node of the i-th second converter to the transformer bus.

7. The method for coordinated control of voltage and power flow in a distribution network of a multi-port flexible switch according to claim 5, characterized in that: The step of determining a voltage feedback control gain according to a voltage sensitivity coefficient of the second converter comprises: Based on the formula determining a voltage feedback control gain of the second converter; Among them, S i represents the voltage sensitivity coefficient of the i-th second converter, K i represents the voltage feedback control gain of the i-th second converter, S1 represents the voltage sensitivity coefficient of the first converter, and ε represents the control step coefficient.

8. The method for coordinated control of voltage and power flow in a distribution network of a multi-port flexible switch according to any one of claims 1 to 7, characterized in that: The controlling the second converter according to the power reference value of the current cycle includes: Based on the PQ control algorithm and the power reference value of the current cycle, a PWM signal for controlling the second converter is generated.

9. A distribution network voltage and power flow coordination control device with a multi-port flexible switch, characterized in that: A plurality of distribution networks are connected via a multi-port capacitive switch, and the multi-port flexible switch comprises a first converter and at least one second converter; the first converter is a converter using voltage control, and the second converter is a converter using PQ control; The device is applied to any second converter, comprising: An objective function determination module, used to construct an objective function of multi-objective coordinated control by taking the deviation between the AC side node voltage of the second converter and the AC side node voltage of the first converter and the deviation between the transformer load rate of the AC side feeder of the second converter and the transformer load rate of the AC side feeder of the first converter as optimization objectives; A power reference value calculation module, used to calculate the power reference value of the second converter in the current cycle according to the objective function and the coordination controller of the second converter; A converter control module is used to control the second converter according to the power reference value of the current cycle.

10. The distribution network voltage and power flow coordination control device of a multi-port flexible switch according to claim 9, characterized in that: The objective function is: Among them, P Ti represents the transformer power on the AC side feeder of the i-th second converter, P T1 represents the transformer power on the AC side feeder of the first converter; S Ti represents the rated capacity of the transformer on the AC side feeder of the i-th second converter, S T1 represents the rated capacity of the transformer on the AC side feeder of the first converter; U devi represents the deviation between the AC side node voltage of the i-th second converter and the AC side node voltage of the first converter; U VSCi represents the AC side node voltage of the i-th second converter; U VSC1 represents the AC side node voltage of the first converter; T devi represents the deviation between the transformer load rate of the AC side feeder of the i-th second converter and the transformer load rate of the AC side feeder of the first converter; α and β represent weights respectively.

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