Variable-structure self-energy-storage multi-port soft switch and optimal operation method thereof in power distribution network

Abstract

The invention discloses a variable structure self-energy-storage type multi-port soft switch and an optimal operation method in a power distribution network. The method comprises the following steps: 1, constructing a mathematical model of the variable structure self-energy-storage type multi-port soft switch; 2, power distribution system regulation and control equipment is arranged, and models of all kinds of equipment are established; 3, based on the structure self-energy-storage type multi-port soft switch model and the power distribution system regulation and control equipment model, considering optimal power flow distribution, and establishing a power distribution network optimization operation model containing a variable structure self-energy-storage type multi-port soft switch; and 4, converting the power distribution network optimization operation model based on the power distribution network optimization operation model containing the variable structure self-energy-storage type multi-port soft switch established in the step 3, thereby establishing the mixed integer programming model containing the variable structure self-energy-storage type multi-port soft switch power distribution network optimization operation. According to the TS-SOP model established by the invention, the flexibility of transmission power is further improved, the no-load loss can be reduced by considering the power-off capacity of the converter, and the economical efficiency of system operation is finally enhanced.

Description

Technical Field

[0001] The present invention relates to the field of power distribution system operation optimization, and in particular to a variable structure self-energy storage type multi-port soft switch and an optimal operation method in a power distribution network. Background Art

[0002] In recent years, with the large-scale access of renewable energy to the distribution system and the development of power electronics technology, the distribution system has shown the characteristics of a high proportion of renewable energy access and a high proportion of power electronic equipment application. On the one hand, the output power of renewable energy, mainly wind and solar, has strong uncertainty and is easily affected by the external environment. It is unable to continuously output stable electricity, the problem of renewable energy absorption is becoming more and more serious, and the operating efficiency of the distribution system is reduced; on the other hand, the traditional radial distribution system has gradually evolved into a multi-power system, and the flow direction of the current has also changed from unidirectional flow to bidirectional flow, making the structure and control of the distribution system more complex; in addition, the development of power electronics technology has further promoted the evolution of the distribution system towards a flexible closed-loop structure. How to reasonably use the multi-controllable equipment (such as power electronic equipment) of the distribution system is an urgent challenge to be solved.

[0003] As a new type of power electronic device, the traditional multi-terminal intelligent soft switch has the advantages of precise flow control, fast power transfer, voltage, and frequency active support, etc. It can realize the flexible closed-loop operation of the distribution network, provide active flow control, reactive power compensation and voltage regulation functions, and has a wide range of applications in improving the consumption of new energy and reducing system operation losses. However, the flexibility of the traditional intelligent soft switch in transmitting power is not high, and the converter power-off capability is not considered to reduce the no-load loss; compared with the existing intelligent soft switch SOP model, the variable structure self-storage multi-port soft switch TS-SOP model built by the present invention further improves the flexibility of the transmission power, and considers the converter power-off capability to reduce the no-load loss, and finally enhances the economy of the system operation. Summary of the invention

[0004] The present invention aims to solve the deficiencies of the above-mentioned prior art and proposes a multi-port soft switch based on variable structure self-energy storage and its application in the optimal operation of the distribution network, so as to reasonably utilize the multi-controllable equipment of the distribution system, further improve the flexibility of the soft switch in transmitting power, and consider the power-off capability of the converter to reduce the no-load loss, thereby ultimately enhancing the economy of the system operation.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A variable structure self-energy storage type multi-port soft switch comprises an AC-DC converter, a DC-DC converter and an energy storage ES. The AC-DC converter has multiple parts and is divided into an upper and lower part. Both the upper and lower parts have m AC-DC converters and m feeders. The AC-DC converters correspond to the feeders one by one, and a switch for freely selecting whether the AC-DC converter and the feeder are connected or closed is provided between the AC-DC converter and the feeder. The AC-DC converter is also connected to the energy storage ES through the DC-DC converter. 2m converters are connected to a power distribution system through 2m feeders.

[0007] The optimal operation method of a variable structure self-storage multi-port soft switch in a distribution network includes the following steps:

[0008] Step 1: construct a mathematical model of a variable structure self-storage multi-port soft switch, and consider the topological variability of the structure to determine the control mode of the variable structure self-storage multi-port soft switch, including a dual feeder transmission control mode, a single feeder transmission control mode, and a no-power output mode;

[0009] Step 2: Set the distribution system control equipment, including on-load voltage regulator OLTC, capacitor banks CBs and photovoltaic PV and voltage deviation constraints;

[0010] Step 3: Based on the variable structure self-storage type multi-port soft switch model established in step 1 and the distribution system control equipment model established in step 2, considering the optimal power flow distribution, establish a distribution network optimization operation model containing a variable structure self-storage type multi-port soft switch;

[0011] Step 4: Based on the distribution network optimization operation model containing variable structure self-storage multi-port soft switches established in step 3, the distribution network optimization operation model is transformed to establish a mixed integer programming model for the optimization operation of the distribution network containing variable structure self-storage multi-port soft switches.

[0012] As a further technical solution of the present invention: Step 1 comprises the following steps:

[0013] Step 1.1, construct the loss model of the variable structure self-storage multi-port soft switch TS-SOP subsystem;

[0014] Step 1.2: Construct the operation constraints of the variable structure self-storage multi-port soft switch TS-SOP.

[0015] As a further technical solution of the present invention: the step 1.1 comprises the following steps:

[0016] Step 1.1.1: Construct the loss constraint of the converter using equations (1)-(2):

[0017]

[0018] In formula (1)-formula (2), and are the losses generated by the mth converter AC-DC connected to node i and node j at time t respectively; and are the apparent power of the mth converter AC-DC connected to node i and node j at time t; b 1,t,m and b 2,t,m are the switch state variables of the mth converter connected to node i and node j at time t, respectively. When 1 is taken, it means the switch is on, and when 0 is taken, it means the switch is off; c a0 、c a1 and c a2 They are the no-load loss, voltage regulation loss coefficient and ohmic loss coefficient of the AC-DC converter respectively;

[0019] Step 1.1.2: Construct the loss of the DC-DC converter from equation (3):

[0020]

[0021] In formula (3), and is the loss and active power of the DC-DC converter at time t; b 3,t is the state variable of the DC-DC converter power-on control switch at time t. When it is 1, it means the switch is on, and when it is 0, it means the switch is off; c d0 、c d1 and c d2 They represent the no-load loss, voltage regulation loss coefficient and ohmic loss coefficient of the DC-DC converter respectively;

[0022] Step 1.1.3: Construct the loss constraint of energy storage ES by formula (4):

[0023]

[0024] In formula (4), and are the energy storage ES loss and output active power at time t; c aux is the auxiliary system loss; c ES It is the internal resistance loss of energy storage.

[0025] As a further technical solution of the present invention: the step 1.2 comprises the following steps:

[0026] Step 1.2.1, construct the active power balance constraint of TS-SOP by equation (5)-(6);

[0027]

[0028] In formula (5)-formula (6), are the active power output of the mth converter connected to node i and node j at time t; N m is the AC-DC converter set, N m ={1,2,…,m};

[0029] Step 1.2.2: Construct the capacity constraints of the AC-DC converter and the DC-DC converter using equations (7) to (9):

[0030]

[0031]

[0032] In formula (7) to formula (9), and are the reactive power output by the mth AC-DC converter connected to the node i and the node j at time t respectively; and The capacity of the AC-DC converter connected to node i and node j respectively; is the upper limit of the capacity of the DC-DC converter;

[0033] Step 1.2.3, the time continuity constraint of the energy storage system state of charge SOC is constructed by formula (10), the variation range constraint of the energy storage charging and discharging power and the energy storage system state of charge SOC is constructed by formula (11)-(12), and the final energy of the energy storage system state of charge SOC is equal to the initial storage energy constraint is constructed by formula (13):

[0034]

[0035] SoC min ≤SoC t ≤SoC max (12)

[0036] SoC1=SoC T (13)

[0037] In formula (10)-(13), SoC t is the charge state of the energy storage ES at time t; and They are the upper and lower limits of the charging and discharging power of the energy storage ES; SoC max and SoC min They are the upper and lower limits of the energy storage state of charge SOC; SoC1 and SoC T They are the initial and final values ​​of the energy storage state of charge SOC in a day;

[0038] Step 1.2.4: To ensure that the converter AC-DC is connected to at most one feeder at time t and that the connected feeder complies with the TS-SOP topology change, the converter selection constraint is constructed by (14) to (16):

[0039]

[0040]

[0041] In formula (14) to formula (16), b 1,t,p , b 2,t,q They are the switch state variables of the pth and qth AC-DC converters connected to the nodes i and j at time t, respectively. When 1 is taken, it indicates that the switch is turned on, and when 0 is taken, it indicates that the switch is turned off.

[0042] As a further technical solution of the present invention: Step 2 comprises the following steps:

[0043] Step 2.1: Construct the OLTC operation constraints from (17) to (19):

[0044] V2=(kij,0+Kt,ijΔkij)V1 (17)

[0045]

[0046] In equations (17) to (19), V2 is the voltage on the secondary side of the OLTC: ij，0 is the initial voltage transformation ratio of OLTC; K t,ij is the adjustable gear position of OLTC on branch ij at time t; Δk ij is the change in the unit-gear voltage transformation ratio of the OLTC on branch ij; The maximum number of OLTC operations allowed in one day; is the maximum adjustable gear position of OLTC at branch ij;

[0047] Step 2.2: Construct the operating constraints of the on-load tap-changing transformer CBs from (20) to (22):

[0048]

[0049]

[0050] In formula (20)-formula (22): is the number of capacitor banks put into operation at node i at time t; is the capacity of each group of capacitors at node i; The maximum allowable switching times of the capacitor bank in one day; The maximum number of capacitor banks allowed to be put into use;

[0051] Step 2.3: Construct the photovoltaic PV operation constraints from (23) to (25):

[0052]

[0053] At the same time, each PV should meet its capacity constraints:

[0054]

[0055] In formula (23) to formula (25), and are the available active power and active reduction of photovoltaic power at node i at time t, respectively; is the rated capacity of the photovoltaic at node i;

[0056] Step 2.4: Construct the voltage deviation constraint from (26):

[0057]

[0058] In formula (26), f v,t is the system voltage deviation at time t, V t,i is the voltage on node i at time t, is the upper limit of system voltage, V thr The lower limit of system voltage.

[0059] As a further technical solution of the present invention: the specific process of step 3 is as follows:

[0060] The power flow model constraints of the distribution system containing variable structure self-storage multi-port soft switch TS-SOP are constructed by (27)-(33):

[0061]

[0062] In formula (27)-(31), P t,ij and Q t,ij are the active power and reactive power flowing through branch ij at time t, and the direction is from node i to node j; P t,jk and Q t,jk P is the active power and reactive power flowing through branch jk at time t, and the direction is from node j to node k; t,i and Q t,i are the active power and reactive power injected into node i at time t; V t,i is the voltage of node i at time t; Ω b is the set of all branches; r ij and x ij are the resistance and reactance of branch ij respectively; is the photovoltaic active output at node i at time t; and They are the photovoltaic PV reactive output and the capacitor CB reactive output at node i at time t respectively; and are the active power and reactive power of the load at node i at time t respectively; and are respectively the active power and reactive power output when the mth converter switch connected to node i is turned on at time t;

[0063] The voltage security constraint of the distribution network is:

[0064]

[0065] In addition, the power loss of each branch is calculated using formula (33):

[0066]

[0067] Where: V t,i is the voltage on node i at time t; and V are the upper and lower limits of the node voltage respectively; V1 is the substation bus voltage 1.0pu;

[0068] The objective function f with the minimum system loss and voltage deviation is constructed by equation (34)-(35):

[0069]

[0070] In formula (34)-(35), f is the objective function of minimizing the comprehensive system loss and voltage deviation, f loss,t is the system active power loss cost at time t; C loss is the cost coefficient of system active power loss; is the active power loss of branch ij at time t; K t,ij is the OLTC tap position of branch ij at time t; is the number of capacitor banks at node i at time t; Δt is the discrete time interval; Ω T ,Ω S They are the set of optimization time and the set of nodes respectively.

[0071] As a further technical solution of the present invention: Step 4 is to convert the optimal operation constraints of the distribution network containing the variable structure self-storage type multi-port soft switch into mixed integer second-order cone programming constraints and then solve them to obtain an operation plan of the distribution system including the variable structure self-storage type multi-port soft switch action, the on-load tap-changing transformer action, the switchable capacitor action, the energy storage system action, etc., which specifically includes the following steps:

[0072] Step 4.1: Use auxiliary variable k 11,t,m ,k 12,t,m ,k 21,t,m ,k 22,t,m replace After that, formula (1)-(2) can be linearly expressed as:

[0073]

[0074] The auxiliary variables are specifically expressed as follows:

[0075]

[0076] The above formulas (39)-(41) are relaxed and can be transformed into a second-order cone. The transformed formulas are as follows:

[0077]

[0078]

[0079] In order to ensure that the AC-DC converter loss is zero when the feeder switch is disconnected, the following

[0080] The following constraints:

[0081]

[0082] In addition, in order to ensure that at time t, each AC-DC converter has at most one feeder connected and the connected feeder complies with the TS-SOP topology change, the following feeder selection constraints are considered:

[0083]

[0084] Step 4.2: Use auxiliary variables k 3,t After substitution, formula (3) can be linearized as:

[0085]

[0086] The auxiliary variables are specifically expressed as follows:

[0087]

[0088]

[0089] For the absolute value in formula (23), it can be linearized as:

[0090]

[0091] The above formula (24) is relaxed and can be transformed into a second-order cone. The transformed formula is as follows:

[0092]

[0093] To ensure that the loss of the DC-DC converter is zero when the feeder switch is turned off, the following constraints are considered:

[0094]

[0095] Step 4.3: Use auxiliary variable k 4,t After substitution, formula (4) can be linearized as:

[0096]

[0097] The auxiliary variables are specifically expressed as follows:

[0098]

[0099] The above formula (60) is relaxed and can be transformed into a second-order cone. The transformed formula is as follows:

[0100]

[0101] In formula (59), c aux is the auxiliary system loss; c ES is the internal resistance loss of energy storage;

[0102] Step 4.4, formula (7)-(8) is relaxed, and the second-order cone transformation is obtained:

[0103]

[0104]

[0105] Step 4.5: Introduce auxiliary variable Aux for the absolute value term in formula (26): t,i To express the voltage deviation degree constraint, formula (26) can be linearized as:

[0106]

[0107] Aux t,i ≥-V t,i +( V thr ) 2 (66)

[0108] Aux t,i ≥0 (67)

[0109] Step 4.6: For the quadratic nonlinear constraints (25), (33), they can be transformed into rotational quadratic cone constraints:

[0110]

[0111] Through the above linearization and cone relaxation methods, the distribution network optimization operation model containing variable structure self-energy storage multi-port soft switches has been converted into a mathematical model that meets the requirements of second-order cone programming solution.

[0112] An electronic device includes a memory and a processor, wherein the memory is used to store a program that supports the processor to execute the above method, and the processor is configured to execute the program stored in the memory.

[0113] A computer-readable storage medium stores a computer program, which executes the steps of the above method when executed by a processor.

[0114] Compared with the prior art, the present invention has the following beneficial effects:

[0115] 1. The present invention adopts a variable structure self-energy storage type multi-port soft switch converter which is not directly connected to the feeder but dynamically connected to the converter and the feeder, which greatly improves the flexibility of power transmission; and considers the power-off capability of the converter to reduce no-load loss and enhance the economy of system operation.

[0116] 2. The present invention provides a power scheduling and adaptive feeder selection and multi-port implementation method of a variable structure self-energy storage type multi-port soft switch, and can realize the coordinated scheduling of the variable structure self-energy storage type multi-port soft switch and a variety of controllable devices; the variable structure self-energy storage type multi-port soft switch cooperates with the load-controlled tap-changing transformer and the switchable capacitor group in the distribution system to jointly optimize the power flow distribution of the distribution system; thereby significantly improving the energy utilization efficiency, enhancing the system stability, reducing the operation and maintenance costs, and providing strong support for the intelligent upgrade of the distribution system.

[0117] 3. The present invention realizes the optimal distribution of power flow through the adaptive feeder selection of variable structure self-energy storage multi-port soft switch and the coordination with the distribution system, effectively reduces the operating loss of the distribution system, and improves the operating efficiency of the distribution system.

[0118] 4. The present invention can realize dynamic interconnection between multiple feeders in the distribution system, make full use of controllable resources between different distribution areas, and allow the converter of variable structure self-energy storage type multi-port soft switch to be connected to any feeder, thereby realizing flexible linkage of power between feeders and improving the distribution system's ability to absorb renewable energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0119] Figure 1 It is a topology diagram of a variable structure self-storage multi-port soft switch;

[0120] Figure 2It is a schematic diagram of the variable structure self-energy storage type multi-port soft switch dual feeder transmission control mode (energy storage ES is turned on);

[0121] Figure 3 It is a schematic diagram of the variable structure self-energy storage type multi-port soft switch dual feeder transmission control mode (energy storage ES removal);

[0122] Figure 4 It is a schematic diagram of a single feeder transmission control mode of a variable structure self-storage multi-port soft switch;

[0123] Figure 5 It is a schematic diagram of a variable structure self-energy storage type multi-port soft switch with no power output mode;

[0124] Figure 6 It is a flow chart of a variable structure self-storage multi-port soft switch and its application in the optimal operation of a distribution network. DETAILED DESCRIPTION

[0125] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0126] Embodiment 1, as Figure 1-6 As shown, the present invention discloses a variable structure self-storage multi-port soft switch, referred to as TS-SO. The TS-SOP is composed of subsystems such as a converter AC-DC, a converter DC-DC, an energy storage ES, and a switch-based topology transformation module. The topology structure of the variable structure self-storage multi-port soft switch TS-SOP is shown in FIG. Figure 1 As shown, there are m AC-DC converters and m feeders on both the upper and lower sides. The converters are not directly connected to the feeders, but can be freely selected to be connected or closed to the feeders. This greatly improves the flexibility of power transmission, and considering the converter power-off capability can reduce no-load losses and enhance the economy of system operation; the variable structure self-energy storage multi-port soft switch TS-SOP is connected to the distribution system through 2m feeders, and it has three working modes (for the sake of simplicity, m is 2 at this time). Mode 1-TS-SOP dual feeder transmission: both AC-DC1 and AC-DC2 converters are turned on, and ES can be turned on or off; Mode 2-TS-SOP single feeder transmission: only one of the AC-DC1 and AC-DC2 converters is turned on, and ES is turned on. Mode 3-TS-SOP does not transmit power: both AC-DC1 and AC-DC2 converters are cut off. By Figure 2 , Figure 3As shown in Figure 1, when TS-SOP works in mode 1, its function is to transmit active power between two feeders and provide reactive power support. However, unlike the existing SOP, TS-SOP can select feeders, which enhances the flexibility of power transmission. Figure 3 As shown in Figure 2, when TS-SOP works in mode 2, its function is to charge and discharge ES through a single feeder. Both modes 2 and 3 usually occur when the actual power transmission is too small to overcome the no-load loss of the device. This converter power-off behavior can increase the utilization of the converter and thus reduce system losses.

[0127] Embodiment 2, based on embodiment 1, the present invention further discloses an optimal operation method of a variable structure self-storage type multi-port soft switch in a distribution network, comprising the following steps:

[0128] Step 1: Construct a mathematical model of a variable structure self-storage multi-port soft switch, and consider the topological variability of the structure to determine the control mode of the variable structure self-storage multi-port soft switch, including a dual feeder transmission control mode, a single feeder transmission control mode, and a power-free output mode; specifically:

[0129] Step 1.1, construct the loss model of the variable structure self-storage multi-port soft switch TS-SOP subsystem;

[0130] Step 1.1.1: Construct the loss constraint of the converter using equations (1)-(2):

[0131]

[0132] In formula (1)-formula (2), and are the losses generated by the mth converter AC-DC connected to node i and node j at time t respectively; and are the apparent power of the mth converter AC-DC connected to node i and node j at time t; b 1,t,m and b 2,t,m are the switch state variables of the mth converter connected to node i and node j at time t, respectively. When 1 is taken, it means the switch is on, and when 0 is taken, it means the switch is off; c a0 、c a1 and c a2 They are the no-load loss, voltage regulation loss coefficient and ohmic loss coefficient of the AC-DC converter respectively;

[0133] Step 1.1.2: Construct the loss of the DC-DC converter from equation (3):

[0134]

[0135] In formula (3), and is the loss and active power of the DC-DC converter at time t; b 3,t is the state variable of the DC-DC converter power-on control switch at time t. When it is 1, it means the switch is on, and when it is 0, it means the switch is off; c d0 、c d1 and c d2 They represent the no-load loss, voltage regulation loss coefficient and ohmic loss coefficient of the DC-DC converter respectively;

[0136] Step 1.1.3: Construct the loss constraint of energy storage ES by formula (4):

[0137]

[0138] In formula (4), and are the energy storage ES loss and output active power at time t; c aux is the auxiliary system loss; c ES It is the internal resistance loss of energy storage.

[0139] Step 1.2, construct the operation constraints of the variable structure self-storage multi-port soft switch TS-SOP;

[0140] Step 1.2.1, construct the active power balance constraint of TS-SOP by equation (5)-(6);

[0141]

[0142] In formula (5)-formula (6), are the active power output of the mth converter connected to node i and node j at time t; N m is the AC-DC converter set, N m ={1,2,…,m};

[0143] Step 1.2.2: Construct the capacity constraints of the AC-DC converter and the DC-DC converter using equations (7) to (9):

[0144]

[0145] In formula (7) to formula (9), and are the reactive power output by the mth AC-DC converter connected to the node i and the node j at time t respectively; and The capacity of the AC-DC converter connected to node i and node j respectively; is the upper limit of the capacity of the DC-DC converter;

[0146] Step 1.2.3, the time continuity constraint of the energy storage system state of charge SOC is constructed by formula (10), the variation range constraint of the energy storage charging and discharging power and the energy storage system state of charge SOC is constructed by formula (11)-(12), and the final energy of the energy storage system state of charge SOC is equal to the initial storage energy constraint is constructed by formula (13):

[0147]

[0148] SoC min ≤SoC t ≤SoC max (12)

[0149] SoC1=SoC T (13)

[0150] In formula (10)-(13), SoC t is the charge state of the energy storage ES at time t; and They are the upper and lower limits of the charging and discharging power of the energy storage ES; SoC max and SoC min They are the upper and lower limits of the energy storage state of charge SOC; SoC1 and SoC T They are the initial and final values ​​of the energy storage state of charge SOC in a day;

[0151] Step 1.2.4: To ensure that the converter AC-DC is connected to at most one feeder at time t and that the connected feeder complies with the TS-SOP topology change, the converter selection constraint is constructed by (14) to (16):

[0152]

[0153] In formula (14) to formula (16), b 1,t,p 、b 2,t,q They are the switch state variables of the pth and qth AC-DC converters connected to the nodes i and j at time t, respectively. When 1 is taken, it indicates that the switch is turned on, and when 0 is taken, it indicates that the switch is turned off.

[0154] Step 2: Set the distribution system control equipment, including on-load tap changer OLTC, capacitor banks CBs and photovoltaic PV and voltage deviation constraints; specifically include:

[0155] Step 2.1: Construct the OLTC operation constraints from (17) to (19):

[0156] V2=(kij,0+Kt,ijΔkij)V1 (17)

[0157]

[0158] In equations (17) to (19), V2 is the voltage on the secondary side of the OLTC: ij，0 is the initial voltage transformation ratio of OLTC; K t,ij is the adjustable gear position of OLTC on branch ij at time t; Δk ij is the change in the unit-gear voltage transformation ratio of the OLTC on branch ij; The maximum number of OLTC operations allowed in one day; is the maximum adjustable gear position of OLTC at branch ij;

[0159] Step 2.2: Construct the operating constraints of the on-load tap-changing transformer CBs from (20) to (22):

[0160]

[0161] In formula (20)-formula (22): is the number of capacitor banks put into operation at node i at time t; is the capacity of each group of capacitors at node i; The maximum allowable switching times of the capacitor bank in one day; The maximum number of capacitors allowed to be put into use;

[0162] Step 2.3: Construct the photovoltaic PV operation constraints from (23) to (25):

[0163]

[0164] At the same time, each PV should meet its capacity constraints:

[0165]

[0166] In formula (23) to formula (25), and are the available active power and active reduction of photovoltaic power at node i at time t, respectively; is the rated capacity of the photovoltaic at node i;

[0167] Step 2.4: Construct the voltage deviation constraint from (26):

[0168]

[0169] In formula (26), f v,t is the system voltage deviation at time t, V t,i is the voltage on node i at time t, is the upper limit of system voltage, V thr The lower limit of system voltage.

[0170] Step 3: Based on the variable structure self-storage type multi-port soft switch model established in step 1 and the distribution system control equipment model established in step 2, considering the optimal power flow distribution, establish a distribution network optimization operation model containing a variable structure self-storage type multi-port soft switch; specifically including:

[0171] The power flow model constraints of the distribution system containing variable structure self-storage multi-port soft switch TS-SOP are constructed by (27)-(33):

[0172]

[0173] In formula (27)-(31), P t,ij and Q t,ij are the active power and reactive power flowing through branch ij at time t, and the direction is from node i to node j; P t,jk and Q t,jk P is the active power and reactive power flowing through branch jk at time t, and the direction is from node j to node k; t,i and Q t,i are the active power and reactive power injected into node i at time t; V t,i is the voltage of node i at time t; Ω b is the set of all branches; r ij and x ij are the resistance and reactance of branch ij respectively; is the photovoltaic active output at node i at time t; and They are the photovoltaic PV reactive output and the capacitor CB reactive output at node i at time t respectively; and are the active power and reactive power of the load at node i at time t respectively; and are respectively the active power and reactive power output when the mth converter switch connected to node i is turned on at time t;

[0174] The voltage security constraint of the distribution network is:

[0175]

[0176] In addition, the power loss of each branch is calculated using formula (33):

[0177]

[0178] Where: V t,i is the voltage on node i at time t; and V are the upper and lower limits of the node voltage respectively; V1 is the substation bus voltage 1.0pu;

[0179] The objective function f with the minimum system loss and voltage deviation is constructed by equation (34)-(35):

[0180]

[0181]

[0182] In formula (34)-(35), f is the objective function of minimizing the comprehensive system loss and voltage deviation, f loss,t is the system active power loss cost at time t; C loss is the cost coefficient of system active power loss; is the active power loss of branch ij at time t; K t,ij is the OLTC tap position of branch ij at time t; is the number of capacitor banks at node i at time t; Δt is the discrete time interval; Ω T ,Ω S They are the set of optimization time and the set of nodes respectively.

[0183] Step 4: Based on the distribution network optimization operation model with variable structure self-storage type multi-port soft switch established in step 3, the distribution network optimization operation model is transformed to establish a mixed integer programming model for the distribution network optimization operation with variable structure self-storage type multi-port soft switch; specifically including:

[0184] Step 4.1: Use auxiliary variable k 11,t,m ,k 12,t,m ,k 21,t,m ,k 22,t,m replace After that, formula (1)-(2) can be linearly expressed as:

[0185]

[0186] The auxiliary variables are specifically expressed as follows:

[0187]

[0188]

[0189] The above formulas (39)-(41) are relaxed and can be transformed into a second-order cone. The transformed formulas are as follows:

[0190]

[0191] In order to ensure that the AC-DC converter loss is zero when the feeder switch is disconnected, the following

[0192] Lower beam:

[0193]

[0194] In addition, in order to ensure that at time t, each AC-DC converter has at most one feeder connected and the connected feeder complies with the TS-SOP topology change, the following feeder selection constraints are considered:

[0195]

[0196] Step 4.2: Use auxiliary variables k 3,t After substitution, formula (3) can be linearized as:

[0197]

[0198] The auxiliary variables are specifically expressed as follows:

[0199]

[0200] For the absolute value in formula (23), it can be linearized as:

[0201]

[0202] The above formula (24) is relaxed and can be transformed into a second-order cone. The transformed formula is as follows:

[0203]

[0204] To ensure that the loss of the DC-DC converter is zero when the feeder switch is turned off, the following constraints are considered:

[0205]

[0206] Step 4.3: Use auxiliary variable k 4,t After substitution, formula (4) can be linearized as:

[0207]

[0208] The auxiliary variables are specifically expressed as follows:

[0209]

[0210] The above formula (60) is relaxed and can be transformed into a second-order cone. The transformed formula is as follows:

[0211]

[0212] In formula (59), c aux is the auxiliary system loss; c ES is the internal resistance loss of energy storage;

[0213] Step 4.4, formula (7)-(8) is relaxed, and the second-order cone transformation is obtained:

[0214]

[0215] Step 4.5: Introduce auxiliary variable Aux for the absolute value term in formula (26): t,i To express the voltage deviation degree constraint, formula (26) can be linearized as:

[0216]

[0217] Aux t,i ≥-V t,i +( V thr ) 2 (66)

[0218] Aux t,i ≥0 (67)

[0219] Step 4.6: For the quadratic nonlinear constraints (25), (33), they can be transformed into rotational quadratic cone constraints:

[0220]

[0221]

[0222] Through the above linearization and cone relaxation methods, the distribution network optimization operation model containing variable structure self-energy storage multi-port soft switches has been converted into a mathematical model that meets the requirements of second-order cone programming solution.

[0223] Embodiment 3, based on embodiment 2, the present invention further discloses an electronic device, including a memory and a processor, wherein the memory is used to store a program that supports the processor to execute the above method, and the processor is configured to execute the program stored in the memory.

[0224] Embodiment 4, based on embodiment 2, the present invention further discloses a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the steps of the above method are executed.

[0225] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0226] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode includes only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. Variable structure self-storage multi-port soft switch, characterized by: It includes an AC-DC converter, a DC-DC converter and an energy storage ES. There are multiple AC-DC converters, which are divided into two paths, an upper path and an lower path. Both the upper path and the lower path have m AC-DC converters and m feeders. The AC-DC converters correspond to the feeders one by one, and a switch for freely selecting the connection or disconnection of the AC-DC converter and the feeder is provided between the AC-DC converter and the feeder. The AC-DC converter is also connected to the energy storage ES through the DC-DC converter. 2m converters are connected to the power distribution system through 2m feeders.

2. The optimal operation method of the variable structure self-storage multi-port soft switch in the distribution network is characterized by: The following steps are involved: Step 1: construct a mathematical model of a variable structure self-storage multi-port soft switch, and consider the topological variability of the structure to determine the control mode of the variable structure self-storage multi-port soft switch, including a dual feeder transmission control mode, a single feeder transmission control mode, and a no-power output mode; Step 2: Set the distribution system control equipment, including on-load voltage regulator OLTC, capacitor banks CBs and photovoltaic PV and voltage deviation constraints; Step 3: Based on the variable structure self-storage type multi-port soft switch model established in step 1 and the distribution system control equipment model established in step 2, considering the optimal power flow distribution, establish a distribution network optimization operation model containing a variable structure self-storage type multi-port soft switch; Step 4: Based on the distribution network optimization operation model containing variable structure self-storage multi-port soft switches established in step 3, the distribution network optimization operation model is transformed to establish a mixed integer programming model for the optimization operation of the distribution network containing variable structure self-storage multi-port soft switches.

3. The optimal operation method of the variable structure self-storage type multi-port soft switch in the distribution network according to claim 2 is characterized in that: The step 1 comprises the following steps: Step 1.1, construct the loss model of the variable structure self-storage multi-port soft switch TS-SOP subsystem; Step 1.2: Construct the operation constraints of the variable structure self-storage multi-port soft switch TS-SOP.

4. The optimal operation method of the variable structure self-storage type multi-port soft switch in the distribution network according to claim 3 is characterized in that: The step 1.1 comprises the following steps: Step 1.1.1: Construct the loss constraint of the converter using equations (1)-(2): In formula (1)-formula (2), and are the losses generated by the mth converter AC-DC connected to node i and node j at time t respectively; and are the apparent power of the mth converter AC-DC connected to node i and node j at time t; b 1,t,m and b 2,t,m are the switch state variables of the mth converter connected to node i and node j at time t, respectively. When 1 is taken, it means the switch is on, and when 0 is taken, it means the switch is off; c a0 、c a1 and c a2 They are the no-load loss, voltage regulation loss coefficient and ohmic loss coefficient of the AC-DC converter respectively; Step 1.1.2: Construct the loss of the DC-DC converter from equation (3): In formula (3), and is the loss and active power of the DC-DC converter at time t; b 3,t is the state variable of the DC-DC converter power-on control switch at time t. When it is 1, it means the switch is on, and when it is 0, it means the switch is off; c d0 、c d1 and c d2 They represent the no-load loss, voltage regulation loss coefficient and ohmic loss coefficient of the DC-DC converter respectively; Step 1.1.3: Construct the loss constraint of energy storage ES by formula (4): In formula (4), and are the energy storage ES loss and output active power at time t; c aux is the auxiliary system loss; c ES It is the internal resistance loss of energy storage.

5. The optimal operation method of the variable structure self-storage type multi-port soft switch in the distribution network according to claim 4 is characterized in that: The step 1.2 comprises the following steps: Step 1.2.1, construct the active power balance constraint of TS-SOP by equation (5)-(6); In formula (5)-formula (6), are the active power output of the mth converter connected to node i and node j at time t; N m is the AC-DC converter set, N m ={1,2,…,m}; Step 1.2.2: Construct the capacity constraints of the AC-DC converter and the DC-DC converter using equations (7) to (9): In formula (7) to formula (9), and are the reactive power output by the mth AC-DC converter connected to the node i and the node j at time t respectively; and The capacity of the AC-DC converter connected to node i and node j respectively; is the upper limit of the capacity of the DC-DC converter; Step 1.2.3, the time continuity constraint of the energy storage system state of charge SOC is constructed by formula (10), the variation range constraint of the energy storage charging and discharging power and the energy storage system state of charge SOC is constructed by formula (11)-(12), and the final energy of the energy storage system state of charge SOC is equal to the initial storage energy constraint is constructed by formula (13): In formula (10)-(13), SoC t is the charge state of the energy storage ES at time t; and They are the upper and lower limits of the charging and discharging power of the energy storage ES; SoC max and SoC min They are the upper and lower limits of the energy storage state of charge SOC; SoC1 and SoC T They are the initial and final values ​​of the energy storage state of charge SOC in a day; Step 1.2.4: To ensure that the converter AC-DC is connected to at most one feeder at time t and that the connected feeder complies with the TS-SOP topology change, the converter selection constraint is constructed by (14) to (16): In formula (14) to formula (16), b 1,t,p 、b 2,t,q They are the switch state variables of the pth and qth AC-DC converters connected to the nodes i and j at time t, respectively. When 1 is taken, it indicates that the switch is turned on, and when 0 is taken, it indicates that the switch is turned off.

6. The optimal operation method of the variable structure self-storage type multi-port soft switch in the distribution network according to claim 5 is characterized in that: Step 2 includes the following steps: Step 2.1: Construct the OLTC operation constraints from (17) to (19): V2=(kij,0+Kt,ijΔkij)V1 (17) In equations (17) to (19), V2 is the voltage on the secondary side of the OLTC: ij，0 is the initial voltage transformation ratio of OLTC; K t,ij is the adjustable gear position of OLTC on branch ij at time t; Δk ij is the change in the unit-gear voltage transformation ratio of the OLTC on branch ij; The maximum number of OLTC operations allowed in one day; is the maximum adjustable gear position of OLTC at branch ij; Step 2.2: Construct the operating constraints of the on-load tap-changing transformer CBs from (20) to (22): In formula (20)-formula (22): is the number of capacitor banks put into operation at node i at time t; is the capacity of each group of capacitors at node i; The maximum allowable switching times of the capacitor bank in one day; The maximum number of capacitor banks allowed to be put into use; Step 2.3: Construct the photovoltaic PV operation constraints from (23) to (25): At the same time, each PV should meet its capacity constraints: In formula (23) to formula (25), and are the available active power and active reduction of photovoltaic power at node i at time t, respectively; is the rated capacity of the photovoltaic at node i; Step 2.4: Construct the voltage deviation constraint from (26): In formula (26), f v,t is the system voltage deviation at time t, V t,i is the voltage on node i at time t, is the upper limit of system voltage, V thr The lower limit of system voltage.

7. The optimal operation method of the variable structure self-storage type multi-port soft switch in the distribution network according to claim 6 is characterized in that: The specific process of step 3 is as follows: The power flow model constraints of the distribution system containing variable structure self-storage multi-port soft switch TS-SOP are constructed by (27)-(33): In formula (27)-(31), P t,ij and Q t,ij are the active power and reactive power flowing through branch ij at time t, and the direction is from node i to node j; P t,jk and Q t,jk P is the active power and reactive power flowing through branch jk at time t, and the direction is from node j to node k; t,i and Q t,i are the active power and reactive power injected into node i at time t; V t,i is the voltage of node i at time t; Ω b is the set of all branches; r ij and x ij are the resistance and reactance of branch ij respectively; is the photovoltaic active output at node i at time t; and They are the photovoltaic PV reactive output and the capacitor CB reactive output at node i at time t respectively; and are the active power and reactive power of the load at node i at time t respectively; and are respectively the active power and reactive power output when the mth converter switch connected to node i is turned on at time t; The voltage security constraint of the distribution network is: In addition, the power loss of each branch is calculated using formula (33): Where: V t,i is the voltage on node i at time t; and V are the upper and lower limits of the node voltage respectively; V1 is the substation bus voltage 1.0pu; The objective function f with the minimum system loss and voltage deviation is constructed by equation (34)-(35): In formula (34)-(35), f is the objective function of minimizing the comprehensive system loss and voltage deviation, f loss,t is the system active power loss cost at time t; C loss is the cost coefficient of system active power loss; is the active power loss of branch ij at time t; K t,ij is the OLTC tap position of branch ij at time t; is the number of capacitor banks at node i at time t; Δt is the discrete time interval; Ω T ,Ω S They are the set of optimization time and the set of nodes respectively.

8. The optimal operation method of the variable structure self-storage type multi-port soft switch in the distribution network according to claim 7 is characterized in that: The step 4 is to convert the optimal operation constraints of the distribution network containing the variable structure self-storage multi-port soft switch into mixed integer second-order cone programming constraints and then solve them to obtain the operation plan of the distribution system including the action of the variable structure self-storage multi-port soft switch, the action of the on-load tap-changing transformer, the action of the switchable capacitor, the action of the energy storage system, etc., which specifically includes the following steps: Step 4.1: Use auxiliary variable k 11,t,m ,k 12,t,m ,k 21,t,m ,k 22,t,m replace After that, formula (1)-(2) can be linearly expressed as: The auxiliary variables are specifically expressed as follows: The above formulas (39)-(41) are relaxed and can be transformed into a second-order cone. The transformed formulas are as follows: To ensure zero loss in the AC-DC converter when the feeder switch is turned off, the following constraints are considered: In addition, in order to ensure that at time t, each AC-DC converter has at most one feeder connected and the connected feeder complies with the TS-SOP topology change, the following feeder selection constraints are considered: Step 4.2: Use auxiliary variables k 3,t After substitution, formula (3) can be linearized as: The auxiliary variables are specifically expressed as follows: For the absolute value in formula (23), it can be linearized as: The above formula (24) is relaxed and can be transformed into a second-order cone. The transformed formula is as follows: To ensure that the loss of the DC-DC converter is zero when the feeder switch is turned off, the following constraints are considered: Step 4.3: Use auxiliary variable k 4,t After substitution, formula (4) can be linearized as: The auxiliary variables are specifically expressed as follows: The above formula (60) is relaxed and can be transformed into a second-order cone. The transformed formula is as follows: In formula (59), c aux is the auxiliary system loss; c ES is the internal resistance loss of energy storage; Step 4.4, formula (7)-(8) is relaxed, and the second-order cone transformation is obtained: Step 4.5: Introduce auxiliary variable Aux for the absolute value term in formula (26): t,i To express the voltage deviation degree constraint, formula (26) can be linearized as: Step 4.6: For the quadratic nonlinear constraints (25), (33), they can be transformed into rotational quadratic cone constraints: Through the above linearization and cone relaxation methods, the distribution network optimization operation model containing variable structure self-energy storage multi-port soft switches has been converted into a mathematical model that meets the requirements of second-order cone programming solution.

9. An electronic device, comprising a memory and a processor, wherein the memory is used to store a program that supports the processor to execute the method according to any one of claims 2 to 8, and the processor is configured to execute the program stored in the memory.

10. A computer-readable storage medium having a computer program stored thereon, wherein the computer program executes the steps of the method according to any one of claims 2 to 8 when executed by a processor.

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