A method for local consumption of distributed power sources based on flexible interconnected substations

Abstract

The invention discloses a distributed power local consumption method based on a flexible interconnected substation, which is characterized in that: it comprises a distributed power source, a main transformer, a back-to-back modular multilevel converter, two groups of bus section switches and a 10kV medium-voltage bus equivalent load, and the distributed power source is connected to the 110kV high-voltage bus of the substation through a transmission line; the control capability of the back-to-back modular multilevel converter B2B-MMC is utilized to realize the preferential local consumption of the output of the distributed power source, and the control on the 110kV line is realized, so that the daily active power obtained from the power grid side is minimized; the practical problems such as the uncoordinated development of the power transmission and distribution network and renewable energy, the increased loss and the difficulty in control in cross-regional consumption are solved, which further causes a large number of wind and solar power abandonment phenomena, and the distributed power source is maximized in the local consumption in the substation through the optimization scheduling technology, so that the power absorbed by the main grid system is reduced in the station.

Description

Technical Field

[0001] The present invention belongs to the field of distributed power consumption methods, and in particular relates to a distributed power local consumption method based on a flexible interconnected substation. Background Art

[0002] Renewable energy generation has technical advantages (such as reducing losses and improving voltage distribution), and is resource and environmentally friendly. Therefore, distributed power generation technology has attracted more and more attention. However, with the continuous grid connection of renewable energy, the peak-shaving capacity of the power system and the anti-peak-shaving characteristics of renewable energy are limited, resulting in a large amount of renewable energy waste. The simple decision-making of distributed power planning cannot maximize the benefits.

[0003] The random fluctuation of renewable energy power output leads to poor power supply quality in the distribution network. In order to solve the power quality problem, especially the voltage sag problem, the traditional distribution system must reconfigure the distribution network structure by opening and closing the tie switches between the distribution network feeders. However, due to the limited number of opening and closing times of the tie switches, it is impossible to achieve infinite dynamic adjustment of voltage, and it is easy to cause problems such as impact current when switching. The use of flexible interconnection technology to solve the problem of distributed power consumption has been recognized by many researchers. New power electronic equipment represented by intelligent soft switch (Soft Open Point, SOP) can effectively coordinate the randomness of distributed power supply and load switching through precise active and reactive power flow control, thereby improving the absorption capacity of distributed power supply and system operation reliability. The use of flexible interconnected substations to participate in the local consumption of distributed power is a new method to solve the existing wind and solar power abandonment problems. Summary of the invention

[0004] The technical problem to be solved by the present invention is: to provide a method for on-site consumption of distributed power sources based on flexible interconnected substations, so as to solve the practical problems such as the uncoordinated development of power transmission and distribution networks and renewable energy, increased losses and difficulty in management and control in cross-regional consumption, which in turn cause a large amount of wind and solar power abandonment. Through the optimization scheduling technology, the on-site consumption of distributed power sources in the substation can be maximized, so that the power absorbed by the main grid system is reduced in the station.

[0005] The technical solution of the present invention is:

[0006] A method for consuming distributed power on-site based on a flexible interconnected substation includes a distributed power source, a main transformer, a back-to-back modular multilevel converter, two sets of bus section switches and a 10kV medium-voltage bus equivalent load. The distributed power source is connected to the 110kV high-voltage bus of the substation through a transmission line. The control capability of the back-to-back modular multilevel converter B2B-MMC is utilized to realize the priority consumption of the output of the distributed power source locally, and the control on the 110kV line is realized, so that the daily active power obtained from the power grid side is minimized.

[0007] The method for accommodating distributed power sources on-site based on flexible interconnected substations specifically includes:

[0008] Step 101: Establishing a distributed power supply local consumption operation structure diagram of a flexible interconnected substation;

[0009] Step 102: Obtain the wind / solar day-ahead forecast curve, the load day-ahead forecast curve, and the substation operation mode;

[0010] Step 103: Setting the converter control mode: master-slave, DC voltage droop control;

[0011] Step 104: Establishing an optimal dispatching model for local consumption of distributed power sources of flexible interconnected substations under multiple time scales;

[0012] Step 105: Establishing the objective function and constraints;

[0013] Step 106: Assign a value to the B2B-MMC power according to the power flow optimization calculation result.

[0014] According to the wind / solar day-ahead forecast curve, load day-ahead forecast curve, substation operation mode and B2B-MMC control mode, the optimal power flow calculation based on the substation obtaining the minimum electric energy from the grid side is realized.

[0015] The time scale of the day-ahead forecast curves for wind / solar power and load is one point every 15 minutes, with a total of 96 points of data.

[0016] If the B2B-MMC control mode is master-slave control, the optimal power flow calculation obtains three independent control variables, namely MMC 1 Output reactive power, MMC 2 The output active and reactive power optimization sequence sets the reference input command for B2B-MMC to adjust the B2B-MMC transmission power.

[0017] If the B2B-MMC control mode is DC voltage droop control, the converters at both ends are responsible for DC voltage stability and power transmission at the same time. The independent control obtained by the optimal power flow calculation includes MMC 1 、MMC2 The output reactive power, DC voltage and droop coefficient optimization sequence are used as reference input commands for the converters on both sides of the B2B-MMC to adjust the B2B-MMC transmission power.

[0018] The optimal dispatching model for local consumption of distributed power sources of flexible interconnected substations under multiple time scales is based on the principle that the substation obtains the minimum amount of power from the grid, i.e., min∑P S1 +P S2 To optimize the target, the constraints include equality constraints and inequality constraints, where the equality constraints include AC system power flow constraints, DC system power flow constraints, and converter power transfer characteristics.

[0019] The inequality constraints include converter capacity constraints and node voltage constraints. To prevent the converter output power plus the load power from exceeding the main transformer carrying capacity, the maximum load of the main transformer capacity is selected as the upper limit.

[0020] The beneficial effects of the present invention are:

[0021] The flexible interconnected substation established by the present invention participates in the local consumption method of distributed power sources, which has the following advantages:

[0022] 1) The present invention establishes a distributed power on-site consumption scheduling model for flexible interconnected substations, which fully considers the distributed power day-ahead forecast data, load day-ahead forecast data and various related influencing factors of substation operation mode, making the optimization scheduling results of the distributed power on-site consumption method of flexible interconnected substations more comprehensive.

[0023] 2) An optimization model is established based on the predicted data to realize the dynamic adjustment of the B2B-MMC power output command value, which solves the problem of local consumption of distributed power sources and optimal control of absorbing the minimum power of the main grid, making the optimized scheduling results closer to the actual operating conditions.

[0024] It solves the current practical problems such as the lack of coordination between the transmission and distribution network and the development of renewable energy, increased losses in cross-regional consumption, and difficulties in management and control, which have led to a large amount of wind and solar power abandonment. Through this optimized scheduling technology, the local consumption of distributed power sources in the substation can be maximized, reducing the power absorbed by the main grid system in the station. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a flow chart for optimizing the local consumption of distributed power sources in a specific implementation method;

[0026] Figure 2 It is a diagram of the distributed power on-site consumption system including flexible interconnected substations in a specific implementation method. DETAILED DESCRIPTION

[0027] A distributed power local consumption method based on a flexible interconnected substation includes a distributed power source, a main transformer, a back-to-back modular multilevel converter, two sets of bus section switches and a 10kV medium voltage bus equivalent load. The distributed power source is connected to the 110kV high voltage bus of the substation through a transmission line. The control capability of B2B-MMC is used to realize the priority of local consumption of the distributed power source output, and the control on the 110kV line is realized, so that the daily active power obtained from the grid side is minimized.

[0028] The present invention will be further described below with reference to the accompanying drawings and examples.

[0029] Embodiment 1:

[0030] The present invention proposes a method for local consumption of distributed power sources based on flexible interconnected substations, the implementation flow chart of which is as follows: Figure 1 As shown, the specific steps include:

[0031] Step 101: Establishing a distributed power supply local consumption operation structure diagram of a flexible interconnected substation;

[0032] Step 102: Obtain the wind / solar day-ahead forecast curve, the load day-ahead forecast curve, and the substation operation mode;

[0033] Step 103: Setting the converter control mode: master-slave, DC voltage droop control;

[0034] Step 104: Establishing an optimal dispatching model for local consumption of distributed power sources of flexible interconnected substations under multiple time scales;

[0035] Step 105: Establishing the objective function and constraints;

[0036] Step 106: Assign a value to the B2B-MMC power according to the power flow optimization calculation result.

[0037] The distributed power supply on-site consumption operation structure diagram of the flexible interconnected substation in step 101 is as follows: Figure 2 shown.

[0038] The different operation modes of the power station described in step 102 determine the optimal result of the entire system optimization, and also affect the local absorption capacity of distributed power sources, which depends on the selection of the optimal operation mode of the substation. The substation operation mode specifically includes: 1. Tie switch QF 1 In closed state, QF 2 In disconnected state; 2. Contact switch QF 1 In disconnected state, QF 2 In disconnected state.

[0039] The setting of the converter control mode in step 103 includes the selection of two modes. If the B2B-MMC control mode is master-slave control, the optimal power flow calculation obtains three independent control variables, namely, MMC 1 Output reactive power, MMC 2 The output active and reactive power optimization sequence is then used to set the reference input command for B2B-MMC to adjust the B2B-MMC transmission power; if the B2B-MMC control mode is DC voltage droop control, the converters at both ends are responsible for DC voltage stability and power transmission at the same time, and the independent control obtained by the optimal power flow calculation includes MMC 1 、MMC 2 The output reactive power, DC voltage and droop coefficient optimization sequence are used as reference input commands for converters on both sides of the B2B-MMC to adjust the B2B-MMC transmission power;

[0040] The optimization dispatching model for local consumption of distributed power sources in the flexible interconnected substation under multiple time scales described in step 104 is specifically as follows: the time scale of the day-ahead forecast curve of wind / solar and load is one point every 15 minutes, with a total of 96 point data. The optimization dispatching model for local consumption of distributed power sources is pre-established for the forecast data of the regional power grid connected to the flexible interconnected substation;

[0041] The objective function and constraint conditions established in step 105 are as follows: the power obtained by the substation from the grid is minimized, that is, min∑P S1 +P S2 To optimize the target, the constraints include equality constraints and inequality constraints, where equality constraints include constraints such as AC system power flow constraints, DC system power flow constraints, and converter power transmission characteristics, and inequality constraints include converter capacity constraints and node voltage constraints. The above constraints have been given in the literature or patents, and the present invention will not repeat them. However, in order to prevent the converter output power plus the load power from exceeding the main transformer carrying capacity, the maximum load of the main transformer capacity is selected as the upper limit. Therefore, there is also an inequality constraint relationship between the converter, the main transformer and the load. The specific constraints are as follows:

[0042]

[0043] In formula (1): P MMC and Q MMC Respectively represent the active and reactive power output of the converter; P Di and Q Di Respectively represent the active and reactive power at the connection point with the converter; S T Indicates the main transformer capacity.

[0044] The step 106 of assigning a value to the B2B-MMC power according to the power flow optimization calculation result specifically includes assigning a value to the active type and reactive type of the converter, which depends on the specific control strategy of the B2B-MMC.

Claims

1. A method for accommodating distributed power sources on-site based on flexible interconnected substations, characterized in that: It includes distributed power sources, main transformers, back-to-back modular multilevel converters, two sets of bus sectionalizers and 10kV medium-voltage bus equivalent loads. The distributed power sources are connected to the 110kV high-voltage bus of the substation through transmission lines. The control capability of the back-to-back modular multilevel converter B2B-MMC is used to achieve the priority of local consumption of the output of the distributed power sources, and to achieve the control on the 110kV line, so that the daily active power obtained from the power grid side is minimized. The local consumption method of the distributed power sources specifically includes: Step 101: Establishing a distributed power supply local consumption operation structure diagram of a flexible interconnected substation; Step 102: Obtain the wind / solar day-ahead forecast curve, the load day-ahead forecast curve, and the substation operation mode; the substation operation mode specifically includes:

1. The tie switch QF1 is in a closed state, and QF2 is in an open state; 2. The tie switch QF1 is in an open state, and QF2 is in an open state; Step 103: Setting the converter control mode: master-slave, DC voltage droop control; Step 104: Establishing an optimal dispatching model for local consumption of distributed power sources of flexible interconnected substations under multiple time scales; Step 105: Establishing the objective function and constraints; Step 106: According to the wind / solar day-ahead forecast curve, the load day-ahead forecast curve, the substation operation mode and the B2B-MMC control mode, the optimal power flow calculation based on the substation obtaining the minimum electric energy from the grid side is realized, and the B2B-MMC power is assigned according to the power flow optimization calculation result; If the B2B-MMC control mode is master-slave control, the optimal power flow calculation obtains three independent control variables, namely the reactive power output by MMC1, the active and reactive optimization sequences output by MMC2, and then sets a reference input command for B2B-MMC to adjust the B2B-MMC transmission power; If the B2B-MMC control mode is DC voltage droop control, the converters at both ends are responsible for DC voltage stability and power transmission at the same time. The independent control obtained by the optimal power flow calculation includes the reactive power, DC voltage and droop coefficient optimization sequence output by MMC1 and MMC2, which is then used as the reference input command for the converters on both sides of the B2B-MMC to adjust the B2B-MMC transmission power. The optimal dispatching model for local consumption of distributed power sources of flexible interconnected substations under multiple time scales is based on the principle that the substation obtains the minimum amount of power from the grid, i.e., min∑P S1 +P S2 To optimize the target, the constraints include equality constraints and inequality constraints, where the equality constraints include AC system power flow constraints, DC system power flow constraints, and converter power transfer characteristics. The inequality constraints include converter capacity constraints and node voltage constraints. To prevent the converter output power plus the load power from exceeding the main transformer carrying capacity, the maximum load of the main transformer capacity is selected as the upper limit. Therefore, there are also inequality constraints between the converter, the main transformer and the load. The specific constraints are as follows: In formula (1): P MMC and Q MMC Respectively represent the active and reactive power output of the converter; P Di and Q Di Respectively represent the active and reactive power at the connection point with the converter; S T Indicates the main transformer capacity.

2. According to claim 1, a method for accommodating distributed power sources on-site based on flexible interconnected substations is characterized in that: The time scale of the day-ahead forecast curves for wind / solar power and load is one point every 15 minutes, with a total of 96 points of data.

Images