Micro-grid power coordination optimization control method based on power electronic transformer

Abstract

The invention discloses a micro-grid power coordination optimization control method based on a power electronic transformer. The micro-grid power coordination optimization control method mainly solves the problems that an existing micro-grid control method is poor in control effect and the like. The control method comprises the following steps: S1, establishing a transformer power distribution constraint of a micro-grid composed of a plurality of energy power generation systems; the method comprises the following specific steps: S2, establishing a transformer power safety constraint under the full-load power of the micro-grid; and S3, establishing a power optimization model considering micro-grid power balance and transformer operation cost, and solving the power optimization model. According to the method, a microgrid transformer power distribution model is constructed through the short-circuit ratio of microgrid grid-connected points, so that a power optimization model considering microgrid power balance and transformer operation cost is established, and the model is solved in combination with transformer power distribution constraints and transformer power safety constraints; therefore, the safety of the transformer in micro-grid power coordination control is improved, the operation control cost of the micro-grid is reduced, and the reliability of the system is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of power grid power control, and in particular, relates to a microgrid power coordination optimization control method based on power electronic transformers. Background Art

[0002] As the carrier of distributed power generation system, microgrid can effectively transform and utilize new energy and renewable energy, and bear the responsibility and mission of connecting distributed energy with large power grid. Its stable operation is of great significance. However, when microgrid is in an isolated operation state, the randomness and volatility of output power of distributed renewable energy itself affected by meteorological conditions, as well as the variability and uncontrollability of load, make the real-time power balance of microgrid face huge challenges.

[0003] Existing microgrid control methods often only focus on one aspect, such as voltage, frequency, and operating economy, and have problems such as single control method and poor control effect. Summary of the invention

[0004] The purpose of the present invention is to provide a microgrid power coordinated optimization control method based on power electronic transformers, mainly to solve the problems of poor control effect of existing microgrid control methods.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A power coordinated optimization control method for a microgrid based on a power electronic transformer comprises the following steps:

[0007] S1, establish the transformer power allocation constraints of the microgrid composed of multiple energy generation systems; the specific steps are as follows:

[0008] S11, based on the installed capacity of the microgrid and the grid-connected capacity of the microgrid, determine the short-circuit ratio of the microgrid grid-connected point, and control the short-circuit ratio of the microgrid grid-connected point to be greater than or equal to the minimum short-circuit ratio of the microgrid grid-connected point, so as to provide transformer voltage support when the microgrid is connected to the grid to ensure safe operation of the transformer;

[0009] S12, based on different grid-connected capacity states of the microgrid, a microgrid transformer power distribution model is constructed through the short-circuit ratio of the microgrid grid-connected point;

[0010] S13, the voltage support strength requirement for safe operation of transformers when the microgrid is connected to the grid is expressed as the allocation constraint of the transformer power allocation model under the microgrid grid-connected state, and its expression is:

[0011] V i (t) = {P i (t)|P i (t)→λi (t)},i=1,2,…,m

[0012] Where t is the time when the microgrid is connected to the grid, i is the transformer number, m is the total number of transformers, λ is the Lagrange multiplier, V i (t) is the voltage support strength requirement of a transformer in the microgrid; P i (t) is the real-time power of the transformer;

[0013] S2, establish transformer power safety constraints under full load power of the microgrid;

[0014] S3, establish and solve the power optimization model considering the power balance of the microgrid and the operating cost of the transformer.

[0015] Furthermore, in the present invention, the power generation system includes a wind-solar power generation system, a thermal power generation system and a nuclear power generation system.

[0016] Furthermore, in the present invention, the expression of the microgrid transformer power distribution model is as follows:

[0017]

[0018] Where j is the number of the microgrid grid connection point, n is the total number of microgrid grid connection points; l ij It represents the short-circuit ratio of transformer i at microgrid connection point j.

[0019] Furthermore, in the present invention, the transformer power safety constraint expression is as follows:

[0020]

[0021] Where E(t) represents the active power of the microgrid at full load power, B capacity is the rated power of the transformer; P i (t) min and P i (t) max They are the minimum and maximum values ​​of transformer power under full grid load power.

[0022] Furthermore, in the present invention, the power optimization model is:

[0023] minR=min(R 1 +R 2 +R 3 )

[0024] Among them, R 1 The power generation cost of the microgrid grid-connected unit is:

[0025]

[0026] In the formula, a I , b I and c I is the power generation cost coefficient, G I is the generator output power, s is the number of grid-connected units;

[0027] R 2 is the operating cost of the transformer in the microgrid:

[0028]

[0029] Where, d J 、e J and f J is the transformer operation cost coefficient, P J Output power for transformer;

[0030] R 3 The power balance adjustment cost of the grid-connected units in the microgrid is:

[0031]

[0032] In the formula, is the regulation cost of a single grid-connected unit, n is the total number of microgrid grid-connected points, and K is the total number of grid-connected units for power balance regulation.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The power distribution of transformers is taken into consideration in the coordinated power control of the microgrid of the present invention. A microgrid transformer power distribution model is constructed according to the short-circuit ratio of the microgrid grid-connected point based on the installed capacity of the microgrid and the grid-connected capacity of the microgrid, thereby establishing a power optimization model that takes into account the power balance of the microgrid and the operating cost of the transformer. The model is solved in combination with the transformer power distribution constraint and the transformer power safety constraint, thereby improving the safety of the transformer in the coordinated power control of the microgrid, reducing the operating control cost of the microgrid, and improving the reliability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic diagram of the process of the present invention.

[0036] Figure 2 This is a simulation experiment waveform diagram in an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The present invention is further described below in conjunction with the accompanying drawings and embodiments. The embodiments of the present invention include but are not limited to the following embodiments.

[0038] Example

[0039] like Figure 1As shown, the present invention discloses a microgrid power coordination optimization control method based on a power electronic transformer, comprising the following steps:

[0040] First, establish the transformer power allocation constraints of the microgrid composed of multiple energy generation systems; wherein the generation systems include wind and solar power generation systems, thermal power generation systems and nuclear power generation systems. The specific steps are as follows:

[0041] (1) Based on the installed capacity of the microgrid and the grid-connected capacity of the microgrid, the short-circuit ratio of the microgrid grid-connected point is determined, and the short-circuit ratio of the microgrid grid-connected point is controlled to be greater than or equal to the minimum short-circuit ratio of the microgrid grid-connected point, so as to provide transformer voltage support when the microgrid is connected to the grid to ensure the safe operation of the transformer.

[0042] (2) Based on the different grid-connected capacity states of the microgrid, a microgrid transformer power distribution model is constructed through the short-circuit ratio of the microgrid grid-connected point. The expression of the microgrid transformer power distribution model is as follows:

[0043]

[0044] Where j is the number of the microgrid grid connection point, n is the total number of microgrid grid connection points; l ij It represents the short-circuit ratio of transformer i at microgrid connection point j.

[0045] (3) The voltage support strength requirement for safe operation of transformers when the microgrid is connected to the grid is expressed as the allocation constraint of the transformer power allocation model when the microgrid is connected to the grid, and its expression is:

[0046] V i (t) = {P i (t)|P i (t)→λ i (t)},i=1,2,…,m

[0047] Where t is the time when the microgrid is connected to the grid, i is the transformer number, m is the total number of transformers, λ is the Lagrange multiplier, V i (t) is the voltage support strength requirement of a transformer in the microgrid; P i (t) is the real-time power of the transformer.

[0048] Then, the transformer power safety constraint under the full load power of the microgrid is established; the transformer power safety constraint expression is as follows:

[0049]

[0050] Where E(t) represents the active power of the microgrid at full load power, B capacity is the rated power of the transformer; P i (t)min and P i (t) max They are the minimum and maximum values ​​of transformer power under full grid load power.

[0051] Finally, a power optimization model considering the power balance of the microgrid and the operating cost of the transformer is established and solved. The power optimization model is:

[0052] minR=min(R 1 +R 2 +R 3 )

[0053] Among them, R 1 The power generation cost of the microgrid grid-connected unit is:

[0054]

[0055] In the formula, a I 、b I and c I is the power generation cost coefficient, G I is the generator output power, s is the number of grid-connected units;

[0056] R 2 is the operating cost of the transformer in the microgrid:

[0057]

[0058] Where, d J 、e J and f J is the transformer operation cost coefficient, P J Output power for transformer;

[0059] R 3 The power balance adjustment cost of the grid-connected units in the microgrid is:

[0060]

[0061] In the formula, is the regulation cost of a single grid-connected unit, n is the total number of microgrid grid-connected points, and K is the total number of grid-connected units for power balance regulation.

[0062] The simulation experiment of the above method is as follows: the grid power command is set to be updated every 5 minutes, the microgrid grid connection requirement is that the 1-minute power fluctuation is less than 10% of the installed capacity, and if the transformer power exceeds the transformer voltage support strength limit for 3 consecutive minutes, the microgrid will perform power coordination. Figure 2 It is the active power waveform of the microgrid under the coordinated control strategy of the present invention.

[0063] The present invention aims at the installed capacity of the microgrid and the grid-connected capacity of the microgrid, constructs a microgrid transformer power distribution model through the short-circuit ratio of the microgrid grid-connected point, thereby establishing a power optimization model that considers the microgrid power balance and transformer operating cost, and solves the model in combination with the transformer power distribution constraint and the transformer power safety constraint, thereby improving the safety of the transformer in the microgrid power coordinated control, reducing the microgrid operation control cost, and improving the reliability of the system.

[0064] The above embodiment is only one of the preferred implementation modes of the present invention and should not be used to limit the protection scope of the present invention. Any changes or modifications that are made to the main design concept and spirit of the present invention and have no substantive significance, and the technical problems they solve are still consistent with the present invention, should be included in the protection scope of the present invention.

Claims

1. A microgrid power coordination optimization control method based on power electronic transformer, characterized in that: The following steps are involved: S1, establish the transformer power allocation constraints of the microgrid composed of multiple energy generation systems; the specific steps are as follows: S11, based on the installed capacity of the microgrid and the grid-connected capacity of the microgrid, determine the short-circuit ratio of the microgrid grid-connected point, and control the short-circuit ratio of the microgrid grid-connected point to be greater than or equal to the minimum short-circuit ratio of the microgrid grid-connected point, so as to provide transformer voltage support when the microgrid is connected to the grid to ensure safe operation of the transformer; S12, based on different grid-connected capacity states of the microgrid, a microgrid transformer power distribution model is constructed through the short-circuit ratio of the microgrid grid-connected point; S13, the voltage support strength requirement for safe operation of transformers when the microgrid is connected to the grid is expressed as the allocation constraint of the transformer power allocation model under the microgrid grid-connected state, and its expression is: V i (t)={P i (t)|P i (t)→λ i (t)},i=1,2,…,m Where t is the time when the microgrid is connected to the grid, i is the transformer number, m is the total number of transformers, λ is the Lagrange multiplier, V i (t) is the voltage support strength requirement of a transformer in the microgrid; P i (t) is the real-time power of the transformer; S2, establish transformer power safety constraints under full load power of the microgrid; S3, establish and solve the power optimization model considering the power balance of the microgrid and the operating cost of the transformer.

2. According to claim 1, a microgrid power coordination optimization control method based on power electronic transformer is characterized in that: The power generation system includes a wind and solar power generation system, a thermal power generation system and a nuclear power generation system.

3. The power coordination optimization control method of a microgrid based on a power electronic transformer according to claim 2 is characterized in that: The expression of the microgrid transformer power distribution model is as follows: Where j is the number of the microgrid grid connection point, n is the total number of microgrid grid connection points; l ij It represents the short-circuit ratio of transformer i at microgrid connection point j.

4. The power coordination optimization control method of a microgrid based on a power electronic transformer according to claim 3 is characterized in that: The transformer power safety constraint expression is as follows: Where E(t) represents the active power of the microgrid at full load power, B capacity is the rated power of the transformer; P i (t) min and P i (t) max They are the minimum and maximum values ​​of transformer power under full grid load power.

5. The power coordination optimization control method of a microgrid based on a power electronic transformer according to claim 4 is characterized in that: The power optimization model is: minR=min(R1+R2+R3) Among them, R1 is the power generation cost of the microgrid grid-connected unit: In the formula, a I 、b I and c I is the power generation cost coefficient, G I is the generator output power, s is the number of grid-connected units; R2 is the operating cost of the transformer in the microgrid: Where, d J 、e J and f J is the transformer operation cost coefficient, P J Output power for transformer; R3 is the power balance adjustment cost of the grid-connected units in the microgrid: In the formula, is the regulation cost of a single grid-connected unit, n is the total number of microgrid grid-connected points, and K is the total number of grid-connected units for power balance regulation.

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