Phase commutation soft switching system for treating current imbalance of power distribution network and evaluation method

Abstract

The application provides a commutation soft switching system for treating current imbalance of a power distribution network and an evaluation method. The commutation soft switching system combines a low-voltage commutation device and an intelligent soft switching device, realizes current flow transfer between different phases, flexibly adjusts the current flow transfer and current distribution between phases, is beneficial to balancing the current difference between three phases of the power distribution network, thereby improving the output efficiency of the power distribution transformer and reducing network loss. The application builds an optimization model based on network flow constraints, solves the optimization model with the minimum current imbalance degree as the target, obtains outgoing currents of each phase and outgoing average currents of three phases, and obtains an index for evaluating the commutation soft switching system for treating the current imbalance problem in the power distribution network through the size of the outgoing currents of each phase and the outgoing average currents of three phases.

Description

Technical Field

[0001] This invention relates to the field of power distribution network technology, and more specifically, to a commutation soft-switching system and evaluation method for mitigating current imbalance in power distribution networks. Background Technology

[0002] Currently, my country is accelerating the construction of a new power system based on new energy sources, vigorously developing new energy, and gradually phasing out traditional energy sources on the basis of safe and reliable replacement by new energy, thus accelerating the decarbonization of the power industry and promoting a clean energy transition. However, with the introduction of high-proportion clean energy units, such as wind power and hydropower, the randomness and volatility of distribution network operation have become more significant, and the power output imbalance between the three phases has also increased. At the same time, the distribution of single-phase loads at the terminal of the distribution network is often unbalanced, which exacerbates the current imbalance in the distribution network, leading to problems such as reduced output efficiency of distribution transformers and increased network line losses. Intelligent soft switching, as a new type of power electronic device, can actively control the transfer of power flow between different nodes. Compared with traditional tie lines, it has advantages such as real-time control, no switching action, and rapid response. However, current intelligent soft switching devices can only achieve power flow transfer between the same phase, and it is difficult to achieve current balance between different phases. The improvement effect on the current imbalance problem is limited, and there is a lack of an evaluation method for intelligent soft switching devices with commutation to address the current imbalance problem. Summary of the Invention

[0003] To address the aforementioned shortcomings in the existing technology, this invention provides a commutation soft-switching system and evaluation method for mitigating current imbalance in power distribution networks, solving the following technical problems:

[0004] 1. Currently, intelligent soft-switching devices can only achieve power flow transfer between the same phase, and it is difficult to achieve current balance between different phases;

[0005] 2. There is a lack of an evaluation method for addressing current imbalance problems with intelligent soft-switching devices with phase commutation.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows: a commutation soft-switching system for addressing current imbalance in power distribution networks, comprising: an inverter, a rectifier, a common capacitor, three low-voltage commutation devices, and an intelligent soft-switching device;

[0007] The inverter and rectifier are set on the three-phase transmission line, and a common capacitor is set between the inverter and rectifier as a common DC terminal;

[0008] One side of each low-voltage commutation device is connected to a three-phase node at one end, and the three terminals on the other side are respectively connected to the three terminals of the inverter.

[0009] The intelligent soft-switching device is installed on the inverter and rectifier.

[0010] Furthermore, the system satisfies the three-phase power flow transfer equation, which is:

[0011]

[0012]

[0013]

[0014]

[0015]

[0016]

[0017] in, The common active power of the intelligent soft-switching device at connection node i. This refers to the common active power of the intelligent soft-switching device at connection node i1. M represents the common active power of the intelligent soft-switching device at connection node i2, where i1 is the first node connecting the intelligent soft-switching device to the three-phase transmission line, i2 is the second node connecting the intelligent soft-switching device to the three-phase transmission line, and M... k Let k be the k-th commutation matrix, where k = 1, 2, 3. It can be 0 or 1. When (0, 1, 0), it indicates that the three phases A, B, and C of the rectifier side are connected to the three phases A, B, and C of the inverter side respectively; (0, 1, 0) indicates that the three phases A, B, and C of the rectifier side are connected to the three phases CA and B of the inverter side; and (0, 0, 1) indicates that the three phases A, B, and C of the rectifier side are connected to the three phases B, C, and B of the inverter side. The active power of the intelligent soft-switching device at connection node i. This refers to the power loss of the intelligent soft-switching device at connection node i. The reactive power of the intelligent soft-switching device at connection node i. The capacity of the intelligent soft-switching device at connection node i. Let i be the power loss coefficient of the intelligent soft-switching device at connection node i. In the same equation, i can take either i1 or i2, and diag is a diagonal matrix function.

[0018] An evaluation method for a commutation soft-switching system for mitigating current imbalance in a power distribution network includes:

[0019] An optimization model based on network power flow constraints is established with the goal of minimizing current imbalance.

[0020] The optimization model based on network power flow constraints is solved to obtain the outgoing current of each phase and the average outgoing current of the three phases.

[0021] Based on the outgoing current of each phase and the average outgoing current of the three phases, the evaluation index for the commutation soft switching system to address the current imbalance problem in the power distribution network is calculated.

[0022] Furthermore, the optimization model based on network power flow constraints is as follows:

[0023]

[0024] in, For the secondary side of the transformer in the power distribution network Phase output current, I A,0 I is the outgoing current of phase A on the secondary side of the transformer in the power distribution network. B,0 I is the outgoing current of phase B on the secondary side of the transformer in the power distribution network. C,0 Let || be the outgoing current of phase C on the secondary side of the transformer in the power distribution network, || is the absolute value operation, and min is the minimum value.

[0025] Furthermore, the network flow constraint is as follows:

[0026] s t =diag(S tj )-diag(S lt -z lt L lt )

[0027] or

[0028]

[0029]

[0030]

[0031]

[0032]

[0033]

[0034] Where t, j, and l are three-phase nodes at different positions, and s t Let S be the injected power at the t-th three-phase node. tj Let be the apparent power of the branch connecting the t-th three-phase node and the j-th three-phase node. S represents the maximum apparent power of the branch connecting the t-th three-phase node and the j-th three-phase node. ltz is the apparent power of the branch connecting the l-th three-phase node and the t-th three-phase node. lt Let L be the impedance of the branch connecting the l-th three-phase node and the t-th three-phase node. lt Let L be the square term of the current in the branch connecting the l-th three-phase node and the t-th three-phase node. tj Let be the square term of the current in the branch connecting the t-th three-phase node and the j-th three-phase node. This refers to the active power of the intelligent soft-switching device at the three-phase node t. This refers to the reactive power of the intelligent soft-switching device at the three-phase node t. Let be the active load of the t-th three-phase node. Let v be the reactive load of the t-th three-phase node. j Let v be the squared voltage term of the j-th three-phase node. t Let be the squared voltage term of the t-th three-phase node. v t Let be the minimum value of the squared voltage term at the t-th three-phase node. z is the maximum value of the squared voltage term at the t-th three-phase node. tj Let H be the impedance of the branch connecting the t-th three-phase node and the j-th three-phase node, H be the conjugate transpose, rank[] be the matrix rank operation, and V be the impedance of the branch connecting the t-th three-phase node and the j-th three-phase node. t Let I be the node voltage of the t-th three-phase node. tj Let be the current in the branch connecting the t-th three-phase node and the j-th three-phase node. Let be a Hermitian matrix, diag be a diagonal matrix function, and g be the imaginary unit.

[0035] Furthermore, the formula for calculating the evaluation index of the commutation soft-switching system for addressing current imbalance in the distribution network is as follows:

[0036]

[0037] Among them, R I Evaluation indicators for addressing current imbalance issues in power distribution networks using commutation soft-switching systems. To obtain the maximum value of the sequence, For the secondary side of the transformer in the power distribution network Phase output current, This represents the average outgoing current of phases A, B, and C on the secondary side of the transformer in the power distribution network. A represents phase A, B represents phase B, and C represents phase C.

[0038] The technical solutions of the embodiments of the present invention have at least the following advantages and beneficial effects:

[0039] 1. The commutation soft switching system of the present invention combines a low-voltage commutation device and an intelligent soft switching device to realize the power flow transfer between different phases, flexibly adjust the power flow transfer and current distribution between phases, which is beneficial to balancing the current difference between the three phases of the distribution network, thereby improving the output efficiency of the distribution transformer and reducing network losses.

[0040] 2. This invention constructs an optimization model based on network power flow constraints and solves the optimization model with the goal of minimizing current imbalance. The outgoing current of each phase and the average outgoing current of the three phases are obtained. By measuring the magnitude of the outgoing current of each phase and the average outgoing current of the three phases, an index for evaluating the current imbalance problem in the distribution network caused by the commutation soft switching system is obtained. Attached Figure Description

[0041] Figure 1 A schematic diagram of a commutation soft-switching system for mitigating current imbalance in a power distribution network;

[0042] Figure 2 This is a flowchart of an evaluation method for a commutation soft-switching system to address current imbalance in a power distribution network. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0044] like Figure 1 As shown, a commutation soft-switching system for mitigating current imbalance in a power distribution network includes: an inverter, a rectifier, a common capacitor, three low-voltage commutation devices, and an intelligent soft-switching device.

[0045] The inverter and rectifier are set on the three-phase transmission line, and a common capacitor is set between the inverter and rectifier as a common DC terminal;

[0046] One side of each low-voltage commutation device is connected to a three-phase node at one end, and the three terminals on the other side are respectively connected to the three terminals of the inverter.

[0047] The intelligent soft-switching device is installed on the inverter and rectifier.

[0048] The system satisfies the three-phase power flow transfer equation, which is as follows:

[0049]

[0050]

[0051]

[0052]

[0053]

[0054]

[0055] in, The common active power of the intelligent soft-switching device at connection node i. This refers to the common active power of the intelligent soft-switching device at connection node i1. M represents the common active power of the intelligent soft-switching device at connection node i2, where i1 is the first node connecting the intelligent soft-switching device to the three-phase transmission line, i2 is the second node connecting the intelligent soft-switching device to the three-phase transmission line, and M... k Let k be the k-th commutation matrix, where k = 1, 2, 3. It can be 0 or 1. When (0, 1, 0), it indicates that the three phases A, B, and C of the rectifier side are connected to the three phases A, B, and C of the inverter side respectively; (0, 1, 0) indicates that the three phases A, B, and C of the rectifier side are connected to the three phases CA and B of the inverter side; and (0, 0, 1) indicates that the three phases A, B, and C of the rectifier side are connected to the three phases B, C, and B of the inverter side. The active power of the intelligent soft-switching device at connection node i. This refers to the power loss of the intelligent soft-switching device at connection node i. The reactive power of the intelligent soft-switching device at connection node i. The capacity of the intelligent soft-switching device at connection node i. Let i be the power loss coefficient of the intelligent soft-switching device at connection node i. In the same equation, i can take either i1 or i2, and diag is a diagonal matrix function.

[0056] The three phases A, B, and C of the rectifier side are connected to the three phases A, B, C, and D of the inverter side, respectively. (0, 1, 0) indicates that the three phases A, B, and C of the rectifier side are connected to the three phases CA and B of the inverter side, and (0, 0, 1) indicates that the three phases A, B, and C of the rectifier side are connected to the three phases BCA of the inverter side. Specifically:

[0057] (1, 0, 0) indicates that rectifier phase A is connected to inverter phase A, rectifier phase B is connected to inverter phase B, and rectifier phase C is connected to inverter phase C; (0, 1, 0) indicates that rectifier phase A is connected to inverter phase C, rectifier phase B is connected to inverter phase A, and rectifier phase C is connected to inverter phase B; (0, 0, 1) indicates that rectifier phase A is connected to inverter phase B, rectifier phase B is connected to inverter phase C, and rectifier phase C is connected to inverter phase A.

[0058] like Figure 2 As shown, an evaluation method for a commutation soft-switching system for mitigating current imbalance in a power distribution network includes the following steps:

[0059] S1. Establish an optimization model based on network power flow constraints with the goal of minimizing current imbalance.

[0060] In step S1, the optimization model based on network power flow constraints is as follows:

[0061]

[0062] in, For the secondary side of the transformer in the power distribution network Phase output current, I A,0 I is the outgoing current of phase A on the secondary side of the transformer in the power distribution network. B,0 I is the outgoing current of phase B on the secondary side of the transformer in the power distribution network. C,0 Let || be the outgoing current of phase C on the secondary side of the transformer in the power distribution network, || is the absolute value operation, and min is the minimum value.

[0063] The network flow constraint is:

[0064] s t =diag(S tj )-diag(S lt -z lt L lt )

[0065] or

[0066]

[0067]

[0068]

[0069]

[0070]

[0071]

[0072] Where t, j, and l are three-phase nodes at different positions, and s t Let S be the injected power at the t-th three-phase node. tj Let be the apparent power of the branch connecting the t-th three-phase node and the j-th three-phase node. S represents the maximum apparent power of the branch connecting the t-th three-phase node and the j-th three-phase node.lt z is the apparent power of the branch connecting the l-th three-phase node and the t-th three-phase node. lt Let L be the impedance of the branch connecting the l-th three-phase node and the t-th three-phase node. lt Let L be the square term of the current in the branch connecting the l-th three-phase node and the t-th three-phase node. tj Let be the square term of the current in the branch connecting the t-th three-phase node and the j-th three-phase node. This refers to the active power of the intelligent soft-switching device at the three-phase node t. This refers to the reactive power of the intelligent soft-switching device at the three-phase node t. Let be the active load of the t-th three-phase node. Let v be the reactive load of the t-th three-phase node. j Let v be the squared voltage term of the j-th three-phase node. t Let be the squared voltage term of the t-th three-phase node. v t Let be the minimum value of the squared voltage term at the t-th three-phase node. z is the maximum value of the squared voltage term at the t-th three-phase node. tj Let H be the impedance of the branch connecting the t-th three-phase node and the j-th three-phase node, H be the conjugate transpose, rank[] be the matrix rank operation, and V be the impedance of the branch connecting the t-th three-phase node and the j-th three-phase node. t Let I be the node voltage of the t-th three-phase node. tj Let be the current in the branch connecting the t-th three-phase node and the j-th three-phase node. Let be a Hermitian matrix, diag be a diagonal matrix function, and g be the imaginary unit.

[0073] S2. Solve the optimization model based on network power flow constraints to obtain the outgoing current of each phase and the average outgoing current of the three phases.

[0074] S3. Based on the outgoing current of each phase and the average outgoing current of the three phases, calculate the evaluation index for the commutation soft switching system to address the current imbalance problem in the power distribution network.

[0075] In step S3, the formula for calculating the evaluation index of the commutation soft-switching system for addressing current imbalance in the distribution network is as follows:

[0076]

[0077] Among them, R I Evaluation indicators for addressing current imbalance issues in power distribution networks using commutation soft-switching systems. To obtain the maximum value of the sequence, For the secondary side of the transformer in the power distribution network Phase output current, This represents the average outgoing current of phases A, B, and C on the secondary side of the transformer in the power distribution network. A represents phase A, B represents phase B, and C represents phase C.

[0078] The technical solutions of the embodiments of the present invention have at least the following advantages and beneficial effects:

[0079] 1. The commutation soft switching system of the present invention combines a low-voltage commutation device and an intelligent soft switching device to realize the power flow transfer between different phases, flexibly adjust the power flow transfer and current distribution between phases, which is beneficial to balancing the current difference between the three phases of the distribution network, thereby improving the output efficiency of the distribution transformer and reducing network losses.

[0080] 2. This invention constructs an optimization model based on network power flow constraints and solves the optimization model with the goal of minimizing current imbalance. The outgoing current of each phase and the average outgoing current of the three phases are obtained. By measuring the magnitude of the outgoing current of each phase and the average outgoing current of the three phases, an index for evaluating the current imbalance problem in the distribution network caused by the commutation soft switching system is obtained.

[0081] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A commutation soft-switching system for mitigating current imbalance in power distribution networks, characterized in that, include: Inverter, rectifier, common capacitor, three low-voltage commutation devices and intelligent soft switching equipment; The inverter and rectifier are set on the three-phase transmission line, and a common capacitor is set between the inverter and rectifier as a common DC terminal; One side of each low-voltage commutation device is connected to a three-phase node at one end, and the three terminals on the other side are respectively connected to the three terminals of the inverter. The intelligent soft-switching device is installed on the inverter and rectifier; The system satisfies the three-phase power flow transfer equation, which is: in, For intelligent soft switching devices at connection nodes Public active power at the location For intelligent soft switching devices at connection nodes Public active power at the location For intelligent soft switching devices at connection nodes Public active power at the location This is the first node connecting the intelligent soft-switching device to the three-phase transmission line. This is the second node connecting the intelligent soft-switching device to the three-phase transmission line. For the first A commutation matrix, , It can be 0 or 1. When (0, 1, 0), it indicates that the three phases ABC on the rectifier side are connected to the three phases ABC on the inverter side respectively; (0, 1, 0) indicates that the three phases ABC on the rectifier side are connected to the three phases CAB on the inverter side; and (0, 0, 1) indicates that the three phases ABC on the rectifier side are connected to the three phases BCA on the inverter side. For intelligent soft switching devices at connection nodes Active power at the location, For intelligent soft switching devices at connection nodes Power loss at the point, For intelligent soft switching devices at connection nodes reactive power at the location, For intelligent soft switching devices at connection nodes Capacity at the location, For intelligent soft switching devices at connection nodes The power loss coefficient at the same point, in the same equation Pick or , It is a diagonal matrix function.

2. An evaluation method for a commutation soft-switching system for mitigating current imbalance in a power distribution network according to claim 1, characterized in that, include: An optimization model based on network power flow constraints is established with the goal of minimizing current imbalance. The optimization model based on network power flow constraints is solved to obtain the outgoing current of each phase and the average outgoing current of the three phases. Based on the outgoing current of each phase and the average outgoing current of the three phases, the evaluation index for the commutation soft switching system to address the current imbalance problem in the power distribution network is calculated.

3. The evaluation method for a commutation soft-switching system for mitigating current imbalance in a power distribution network according to claim 2, characterized in that, The optimization model based on network power flow constraints is as follows: in, For the secondary side of the transformer in the power distribution network Phase output current, For the secondary side of the transformer in the power distribution network Phase output current, For the secondary side of the transformer in the power distribution network Phase output current, For the secondary side of the transformer in the power distribution network Phase output current, For absolute value operations, To find the minimum value.

4. The evaluation method for a commutation soft-switching system for mitigating current imbalance in power distribution networks according to claim 3, characterized in that, The network flow constraint is: or in, , , For three-phase nodes at different locations, For the first The injected power of each three-phase node, For the first The three-phase node and the first Apparent power of a branch connected by a three-phase node For the first The three-phase node and the first The maximum apparent power of the branch connected by each three-phase node. For the first The three-phase node and the first Apparent power of a branch connected by a three-phase node For the first The three-phase node and the first The impedance of a branch connected by a three-phase node For the first The three-phase node and the first The square term of the current in the branch connected by a three-phase node For the first The three-phase node and the first The square term of the current in the branch connected by a three-phase node For intelligent soft switching equipment in connection with three-phase nodes Active power at the location, For intelligent soft switching equipment in connection with three-phase nodes reactive power at the location, For the first Active load of a three-phase node For the first Reactive load of three-phase nodes, For the first The square term of the voltage at each three-phase node, For the first The square term of the voltage at each three-phase node, For the first The minimum value of the squared voltage term at each three-phase node. For the first The maximum value of the squared voltage term at each three-phase node For the first The three-phase node and the first The impedance of a branch connected by a three-phase node It is the conjugate transpose. The rank-finding operation for a matrix, For the first The node voltage of a three-phase node, For the first The three-phase node and the first The current in the branch connected by a three-phase node It is a Hermitian matrix. For diagonal matrix functions, It is the imaginary unit.

5. The evaluation method for a commutation soft-switching system for mitigating current imbalance in a power distribution network according to claim 2, characterized in that, The formula for calculating the evaluation index of the commutation soft-switching system for addressing current imbalance in the power distribution network is as follows: in, Evaluation indicators for addressing current imbalance issues in power distribution networks using commutation soft-switching systems. To obtain the maximum value of the sequence, For the secondary side of the transformer in the power distribution network Phase output current, This represents the average outgoing current of phases A, B, and C on the secondary side of the transformer in the power distribution network. express Mutually, express Mutually, express Mutually.

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