Centralized control method of distributed network-constructing inverter

Abstract

The invention relates to a centralized control method of a distributed network-forming inverter. The centralized control method comprises the following steps: each distributed power supply sends a state power quantity representing the state of the distributed power supply to a central controller; the central controller processes the state power quantity, calculates a scaling coefficient and transmits the scaling coefficient to each distributed power supply; and each distributed power supply sets an active power reference and a reactive power reference according to the received scaling coefficient. According to the invention, the scaling coefficient is obtained through the central controller arranged at the common coupling point of the micro-grid, and the obtained scaling coefficient is used for realizing the control of the distributed power supply, so that the accurate control of the power flow of the power grid is realized; the micro-grid can operate in the grid-connected mode and the island mode, stable switching between the two modes is achieved, and meanwhile critical island detection is not needed; the micro-grid does not need a centralized grid-forming inverter, and the risk of single-point failure is solved.

Description

Technical Field

[0001] The present invention relates to the field of microgrid control technology, and in particular to a centralized control method for a distributed grid-connected inverter. Background Art

[0002] Against the backdrop of rapid growth in electricity demand and increasing shortage of traditional non-renewable energy, my country's electricity production pattern, which is mainly based on thermal power generation, has encountered extremely severe challenges. The use of renewable and clean energy for power generation has become an inevitable trend, and new energy power generation technology will also rise rapidly. Traditional power systems can alleviate the environmental pollution problems caused by the power generation process to a certain extent by improving the utilization rate, quality and power supply efficiency of electricity, while reducing their own power losses. However, the current direct access of new energy equipment to the large power grid will increase the dependence of the receiving power grid on external power, reduce the stability and safety of the power grid operation, and make it difficult to meet the diversification of power supply needs. Therefore, distributed power generation microgrids that can improve energy utilization efficiency and enhance system stability have emerged. They can adapt to decentralized power demand and resource distribution, and have relatively little harm to the environment and human health.

[0003] Advanced microgrids are a possible model to achieve the goal of 100% renewable energy grid. A complete advanced microgrid control method must guide power flow in grid-connected mode, regulate voltage / frequency in island mode, and achieve power sharing between distributed power sources in both modes. Power-based control is a well-known centralized control method that can achieve these three goals. However, a serious disadvantage of the microgrid structure using power-based control methods is that a centralized grid-forming inverter is required to form an island. The centralized grid-forming inverter is a single point of failure, which reduces the scalability of the microgrid and is also an expensive component of the microgrid. Summary of the invention

[0004] In order to solve the problem that the prior art requires a centralized meshing inverter and requires critical island detection, the purpose of the present invention is to provide a centralized control method for distributed meshing inverters that does not require a centralized meshing inverter, has low implementation difficulty, low communication cost, and can achieve precise control of power grid currents.

[0005] To achieve the above object, the present invention adopts the following technical solution: a centralized control method of a distributed grid-type inverter, the method comprising the following steps in order:

[0006] (1) Each distributed power source sends a state power quantity representing its state to the central controller;

[0007] (2) The central controller processes the state power quantity, calculates the scaling factor and transmits it to each distributed power source;

[0008] (3) Each distributed power source sets its active reference and reactive reference according to the received scaling factor, wherein each distributed power source includes a single-phase or balanced three-phase distributed power source, an unbalanced three-phase distributed power source, a distributed power source with reactive power processing constraints, a pure photovoltaic distributed power source, and an active power filter.

[0009] In step (1), the state power quantity is a set of available power generation of a distributed power source, which includes the measured output active power P Dj (k), reactive power Q Dj (k) Maximum active power capacity and reactive power maximum capacity The maximum reactive power capacity The calculation formula is:

[0010]

[0011] Among them, A Dj is the rated apparent power of the jth distributed generation, and k is the period.

[0012] The step (2) specifically comprises the following steps in order:

[0013] (2a) Calculate the total available active power P of the three-phase output of each distributed power source in the kth cycle D3φt (k), single-phase output total available active power P Dmt (k):

[0014]

[0015] Where J represents the total number of distributed power sources, P D3φj (k) represents the available active power of the jth three-phase distributed generation in the kth cycle, P Dmj (k) represents the available active power of the jth single-phase distributed generation in the kth cycle;

[0016] Minimum available active power of three-phase balanced distributed power supply Maximum available active power The calculation formula is as follows:

[0017]

[0018] in, represents the minimum available active power of the jth three-phase distributed generation in the kth cycle, It represents the maximum available active power of the jth three-phase distributed generation in the kth cycle;

[0019] Minimum available active power of single-phase distributed power supply Maximum available active power The calculation formula is as follows:

[0020]

[0021] in, represents the minimum available active power of the jth single-phase distributed generation in the kth cycle, It represents the maximum available active power of the jth single-phase distributed generation in the kth cycle;

[0022] Individual maximum available active power of distributed generation in three-phase voltage control mode The calculation formula is as follows:

[0023]

[0024] in, represents the maximum available active power of the jth three-phase voltage control mode distributed generation in the kth cycle;

[0025] (2b) Calculate the maximum total active power capacity of each distributed generation source that can be used to meet the power demand of the entire microgrid

[0026]

[0027] (2c) Calculate the total active power P required for each phase of the microgrid in the kth cycle MGmt (k):

[0028]

[0029] Among them, P gridm (k) is the active power per phase measured on the grid side of the common coupling point; P VCM3φmj (k) is the active power per phase delivered by the jth three-phase voltage control mode distributed power source as a distributed grid-connected inverter;

[0030] (2d) Calculate the total three-phase active power P processed by the microgrid in the kth cycle MGt (k):

[0031]

[0032] (2e) The central controller obtains the three-phase total active power P MGt (k), calculate the total three-phase active power output of the three-phase balanced distributed power supply in the next cycle, i.e., k+1 cycle Reference values, as well as the total active power per phase of single-phase distributed power and three-phase unbalanced distributed power Reference value:

[0033]

[0034] in, It is the sum of active power reference values ​​of all three-phase voltage control mode distributed power sources; It is the active reference value of each phase of the power flow of the power grid collected by the third-level control layer; M represents the number of phases;

[0035] (2f) Finally, calculate the three-phase active power scaling factor α P3φ and reactive scaling factor α Q3φ , and the single-phase scaling factor α Pm and α Qm , and transmitted to all distributed power sources; α P3φ and α Q3φ Only sent to three-phase balanced devices, and α Pm and α Qm Delivered to single-phase equipment connected to the corresponding m phases, and to three-phase unbalanced distributed power sources; the active power scaling factor is expressed by variable α P Indicates that α P Including α P3φ and α Pm ; The reactive power scaling factor uses variable α Q Indicates that α Q Including α Q3φ and α Qm ; α P and α Q The negative signals of represent the storage of active power and capacitive reactive power, α P and α Q The positive signals represent the transmission of active power and inductive reactive power respectively:

[0036]

[0037] In the formula, It indicates the three-phase available reactive power reference value in k+1 cycle, Represents the single-phase reactive power reference value of k+1 cycle, It indicates the maximum reactive power available in a single phase within k cycles.

[0038] In step (3), the power reference of the single-phase or balanced three-phase distributed power supply is specifically:

[0039]

[0040]

[0041] in, and are the active power reference value and reactive power reference value of the jth distributed generation in k cycles, and Respectively represent the maximum capacity of active power and reactive power, α P is the active power scaling factor, α Q is the reactive power scaling factor.

[0042] In step (3), the power reference of the unbalanced three-phase distributed power supply is specifically:

[0043] The power of three-phase distributed generation is evenly distributed to each phase, and the maximum available phase capacity for reactive power compensation is calculated

[0044]

[0045] In the formula, A D3φmj Represents single-phase apparent power, A D3φj Three-phase apparent power, Indicates the maximum value of single-phase active power, Indicates the maximum value of three-phase active power;

[0046] Active power reference for each phase and reactive power reference for:

[0047]

[0048] In the formula, α Pm and α Qm is the single-phase scaling factor.

[0049] In step (3), the power reference of the distributed power source with reactive power processing constraints is specifically:

[0050] Rated reactive power of distributed generation with reactive power processing constraints and reactive power maximum capacity The calculation formula is as follows:

[0051]

[0052] Where λ represents the percentage of reactive power that a single-phase inverter can handle; A Dmj Indicates the single-phase apparent power of distributed power supply; A Dj (k) represents the measured output active power; A Dj is the rated apparent power of the jth distributed generation;

[0053] if The value is greater than Then Sent to the central controller, otherwise use

[0054] Active power reference value and reactive power reference The calculation formula is as follows:

[0055]

[0056]

[0057] In the formula, Indicates the maximum capacity of active power, Represents the maximum capacity of reactive power, α P is the active power scaling factor, α Q is the reactive power scaling factor.

[0058] In step (3), the power reference of the pure photovoltaic distributed power source is specifically:

[0059] Pure photovoltaic distributed power source active power reference is its maximum available active power

[0060]

[0061] In the case of unrestricted reactive power processing, pure photovoltaic distributed power reactive power reference The calculation formula is as follows:

[0062]

[0063] in, represents the maximum available reactive power provided by pure photovoltaic distributed generation in cycle k;

[0064] If the pure photovoltaic distributed power source has reactive power limit, the reactive power reference of the pure photovoltaic distributed power source is The calculation formula is as follows:

[0065]

[0066] in, Represents the rated reactive power of pure photovoltaic distributed power source; α Q is the reactive power scaling factor;

[0067] If the pure photovoltaic distributed generation operates at unity power factor, its reactive power reference is zero.

[0068] In step (3), the power reference of the active power filter is specifically:

[0069] The active power reference of the active power filter is zero, and the reactive power reference of the active power filter is Defined as:

[0070]

[0071] in, represents the maximum available reactive power of the active power filter, α Qm is the single-phase scaling factor.

[0072] It can be seen from the above technical scheme that the beneficial effects of the present invention are: first, compared with previous implementation methods, the implementation difficulty of the present invention is lower; second, the present invention obtains the scaling factor by the central controller set at the common coupling point of the microgrid, and uses the obtained scaling factor to realize the control of the distributed power source, thereby realizing the precise control of the power grid flow; third, the present invention has lower requirements on the communication infrastructure than the previous methods, and the communication cost is reduced; fourth, the microgrid of the present invention can achieve proportional power sharing between distributed power sources without understanding the grid parameters, and can achieve plug-and-play of new distributed power sources; fifth, the microgrid of the present invention can operate in both grid-connected and island modes, realizing smooth switching between the two modes, and no critical island detection is required; sixth, the microgrid of the present invention does not require a centralized grid-connected inverter, which solves the risk of single-point failure. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 is a flow chart of the method of the present invention;

[0074] Figure 2 It is a maximum reactive power evaluation flow chart of a distributed power source with reactive power processing constraints according to the present invention. DETAILED DESCRIPTION

[0075] like Figure 1 As shown, a centralized control method for a distributed grid-type inverter comprises the following steps in sequence:

[0076] (1) Each distributed power source sends a state power quantity representing its state to the central controller;

[0077] (2) The central controller processes the state power quantity, calculates the scaling factor and transmits it to each distributed power source;

[0078] (3) Each distributed power source sets its active reference and reactive reference according to the received scaling factor, wherein each distributed power source includes a single-phase or balanced three-phase distributed power source, an unbalanced three-phase distributed power source, a distributed power source with reactive power processing constraints, a pure photovoltaic distributed power source, and an active power filter.

[0079] In step (1), the state power quantity is a set of available power generation of a distributed power source, which includes the measured output active power P Dj (k), reactive power Q Dj(k) Maximum active power capacity and reactive power maximum capacity The maximum reactive power capacity The calculation formula is:

[0080]

[0081] Among them, A Dj is the rated apparent power of the jth distributed generation, and k is the period.

[0082] The step (2) specifically comprises the following steps in order:

[0083] (2a) Calculate the total available active power P of the three-phase output of each distributed power source in the kth cycle D3φt (k), single-phase output total available active power P Dmt (k):

[0084]

[0085] Where J represents the total number of distributed power sources, P D3φj (k) represents the available active power of the jth three-phase distributed generation in the kth cycle, P Dmj (k) represents the available active power of the jth single-phase distributed generation in the kth cycle;

[0086] Minimum available active power of three-phase balanced distributed power supply Maximum available active power The calculation formula is as follows:

[0087]

[0088] in, represents the minimum available active power of the jth three-phase distributed generation in the kth cycle, It represents the maximum available active power of the jth three-phase distributed generation in the kth cycle;

[0089] Minimum available active power of single-phase distributed power supply Maximum available active power The calculation formula is as follows:

[0090]

[0091] in, represents the minimum available active power of the jth single-phase distributed generation in the kth cycle, It represents the maximum available active power of the jth single-phase distributed generation in the kth cycle;

[0092] Individual maximum available active power of distributed generation in three-phase voltage control mode The calculation formula is as follows:

[0093]

[0094] in, represents the maximum available active power of the jth three-phase voltage control mode distributed generation in the kth cycle;

[0095] (2b) Calculate the maximum total active power capacity of each distributed generation source that can be used to meet the power demand of the entire microgrid

[0096]

[0097] (2c) Calculate the total active power P required for each phase of the microgrid in the kth cycle MGmt (k):

[0098]

[0099] Among them, P gridm (k) is the active power per phase measured on the grid side of the common coupling point; P VCM3φmj (k) is the active power per phase delivered by the jth three-phase voltage control mode distributed power source as a distributed grid-connected inverter;

[0100] (2d) Calculate the total three-phase active power P processed by the microgrid in the kth cycle MGt (k):

[0101]

[0102] (2e) The central controller obtains the three-phase total active power P MGt (k), calculate the total three-phase active power output of the three-phase balanced distributed power supply in the next cycle, i.e., k+1 cycle Reference values, as well as the total active power per phase of single-phase distributed power and three-phase unbalanced distributed power Reference value:

[0103]

[0104] in, It is the sum of active power reference values ​​of all three-phase voltage control mode distributed power sources; It is the active reference value of each phase of the power flow of the power grid collected by the third-level control layer; M represents the number of phases;

[0105] (2f) Finally, calculate the three-phase active power scaling factor α P3δ and reactive scaling factor α Q3φ, and the single-phase scaling factor α Pm and α Qm , and transmitted to all distributed power sources; α P3φ and α Q3φ Only sent to three-phase balanced devices, and α Pm and α Qm Delivered to single-phase equipment connected to the corresponding m phases, and to three-phase unbalanced distributed power sources; the active power scaling factor is expressed by variable α P Indicates that α P Including α P3φ and α Pm ; The reactive power scaling factor uses variable α Q Indicates that α Q Including α Q3φ and α Qm ; α P and α Q The negative signals of represent the storage of active power and capacitive reactive power, α P and α Q The positive signals represent the transmission of active power and inductive reactive power respectively:

[0106]

[0107] In the formula, It indicates the three-phase available reactive power reference value in k+1 cycle, Represents the single-phase reactive power reference value of k+1 cycle, It indicates the maximum reactive power available in a single phase within k cycles.

[0108] In step (3), the power reference of the single-phase or balanced three-phase distributed power supply is specifically:

[0109]

[0110]

[0111] in, and are the active power reference value and reactive power reference value of the jth distributed generation in k cycles, and Respectively represent the maximum capacity of active power and reactive power, α P is the active power scaling factor, α Q is the reactive power scaling factor.

[0112] In step (3), the power reference of the unbalanced three-phase distributed power supply is specifically:

[0113] The power of three-phase distributed generation is evenly distributed to each phase, and the maximum available phase capacity for reactive power compensation is calculated

[0114]

[0115] In the formula, A D3φmj Represents single-phase apparent power, A D3φj Three-phase apparent power, Indicates the maximum value of single-phase active power, Indicates the maximum value of three-phase active power;

[0116] Active power reference for each phase and reactive power reference for:

[0117]

[0118] In the formula, α Pm and α Qm is the single-phase scaling factor.

[0119] In step (3), if Figure 2 As shown, the power reference of the distributed power source with reactive power processing constraints is specifically:

[0120] Rated reactive power of distributed generation with reactive power processing constraints and reactive power maximum capacity The calculation formula is as follows:

[0121]

[0122] Where λ represents the percentage of reactive power that a single-phase inverter can handle; A Dmj Represents the single-phase apparent power of distributed power source; P Dj (k) represents the measured output active power; A Dj is the rated apparent power of the jth distributed generation;

[0123] if The value is greater than Then Sent to the central controller, otherwise use

[0124] Active power reference value and reactive power reference The calculation formula is as follows:

[0125]

[0126]

[0127] In the formula, Indicates the maximum capacity of active power, Represents the maximum capacity of reactive power, α P is the active power scaling factor, α Q is the reactive power scaling factor.

[0128] In step (3), the power reference of the pure photovoltaic distributed power source is specifically:

[0129] Pure photovoltaic distributed power source active power reference is its maximum available active power

[0130]

[0131] In the case of unrestricted reactive power processing, pure photovoltaic distributed power reactive power reference The calculation formula is as follows:

[0132]

[0133] in, represents the maximum available reactive power provided by pure photovoltaic distributed generation in cycle k;

[0134] If the pure photovoltaic distributed power source has reactive power limit, the reactive power reference of the pure photovoltaic distributed power source is The calculation formula is as follows:

[0135]

[0136] in, Represents the rated reactive power of pure photovoltaic distributed power source; α Q is the reactive power scaling factor;

[0137] If the pure photovoltaic distributed generation operates at unity power factor, its reactive power reference is zero.

[0138] In step (3), the power reference of the active power filter is specifically:

[0139] The active power reference of the active power filter is zero, and the reactive power reference of the active power filter is Defined as:

[0140]

[0141] in, represents the maximum available reactive power of the active power filter, α Qm is the single-phase scaling factor.

[0142] In summary, the present invention obtains the scaling factor by a central controller set at the common coupling point of the microgrid, and uses the obtained scaling factor to control the distributed power source, thereby achieving precise control of the power grid flow; the microgrid of the present invention can operate in both grid-connected and island modes, achieving smooth switching between the two modes, and does not require critical island detection; the microgrid of the present invention does not require a centralized grid-connected inverter, thereby solving the risk of single-point failure.

Claims

1. A centralized control method for distributed grid-connected inverters, characterized in that: The method comprises the following steps in order: (1) Each distributed power source sends a state power quantity representing its state to the central controller; (2) The central controller processes the state power quantity, calculates the scaling factor and transmits it to each distributed power source; (3) Each distributed power source sets its active reference and reactive reference according to the received scaling factor, wherein each distributed power source includes a single-phase or balanced three-phase distributed power source, an unbalanced three-phase distributed power source, a distributed power source with reactive power processing constraints, a pure photovoltaic distributed power source, and an active power filter.

2. The centralized control method of distributed grid-connected inverter according to claim 1, characterized in that: In step (1), the state power quantity is a set of available power generation of a distributed power source, which includes the measured output active power P Dj (k), reactive power Q Dj (k) Maximum active power capacity and reactive power maximum capacity The maximum reactive power capacity The calculation formula is: Among them, A Dj is the rated apparent power of the jth distributed generation, and k is the period.

3. The centralized control method of distributed grid-connected inverter according to claim 1, characterized in that: The step (2) specifically comprises the following steps in order: (2a) Calculate the total available active power P of the three-phase output of each distributed power source in the kth cycle D3φt (k), single-phase output total available active power P Dmt (k): Where J represents the total number of distributed power sources, P D3φj (k) represents the available active power of the jth three-phase distributed generation in the kth cycle, P Dmj (k) represents the available active power of the jth single-phase distributed generation in the kth cycle; Minimum available active power of three-phase balanced distributed power supply Maximum available active power The calculation formula is as follows: in, represents the minimum available active power of the jth three-phase distributed generation in the kth cycle, It represents the maximum available active power of the jth three-phase distributed generation in the kth cycle; Minimum available active power of single-phase distributed power supply Maximum available active power The calculation formula is as follows: in, represents the minimum available active power of the jth single-phase distributed generation in the kth cycle, It represents the maximum available active power of the jth single-phase distributed generation in the kth cycle; The maximum available active power of distributed power generation in three-phase voltage control mode The calculation formula is as follows: in, represents the maximum available active power of the jth three-phase voltage control mode distributed generation in the kth cycle; (2b) Calculate the maximum total active power capacity of each distributed generation source that can be used to meet the power demand of the entire microgrid (2c) Calculate the total active power P required for each phase of the microgrid in the kth cycle MGmt (k): Among them, P gridm (k) is the active power per phase measured on the grid side of the common coupling point; P VCM3φmj (k) is the active power per phase delivered by the jth three-phase voltage control mode distributed power source as a distributed grid-connected inverter; (2d) Calculate the total three-phase active power P processed by the microgrid in the kth cycle MGt (k): (2e) The central controller obtains the three-phase total active power P MGt (k), calculate the total three-phase active power output of the three-phase balanced distributed power supply in the next cycle, i.e., k+1 cycle Reference values, as well as the total active power per phase of single-phase distributed power and three-phase unbalanced distributed power Reference value: in, It is the sum of active power reference values ​​of all three-phase voltage control mode distributed power sources; It is the active reference value of each phase of the power flow of the power grid collected by the third-level control layer; M represents the number of phases; (2f) Finally, calculate the three-phase active power scaling factor α P3φ and reactive scaling factor α Q3φ , and the single-phase scaling factor α Pm and α Qm , and transmitted to all distributed power sources; α P3φ and α Q3φ Only sent to three-phase balanced devices, and α Pm and α Qm Delivered to single-phase equipment connected to the corresponding m phases, and to three-phase unbalanced distributed power sources; the active power scaling factor is expressed by variable α P Indicates that α P Including α P3φ and α Pm ; The reactive power scaling factor uses variable α Q Indicates that α Q Including α Q3φ and α Qm ; α P and α Q The negative signals of represent the storage of active power and capacitive reactive power, α P and α Q The positive signals represent the transmission of active power and inductive reactive power respectively: In the formula, It indicates the three-phase available reactive power reference value in k+1 cycle. Represents the single-phase reactive power reference value of k+1 cycle, It indicates the maximum reactive power available in a single phase within k cycles.

4. The centralized control method of distributed grid-connected inverter according to claim 1, characterized in that: In step (3), the power reference of the single-phase or balanced three-phase distributed power supply is specifically: in, and are the active power reference value and reactive power reference value of the jth distributed generation in k cycles, and Respectively represent the maximum capacity of active power and reactive power, α P is the active power scaling factor, α Q is the reactive power scaling factor.

5. The centralized control method of distributed grid-connected inverter according to claim 1, characterized in that: In step (3), the power reference of the unbalanced three-phase distributed power supply is specifically: The power of three-phase distributed generation is evenly distributed to each phase, and the maximum available phase capacity for reactive power compensation is calculated In the formula, A D3φmj Represents single-phase apparent power, A D3φj Three-phase apparent power, Indicates the maximum value of single-phase active power, Indicates the maximum value of three-phase active power; Active power reference for each phase and reactive power reference for: In the formula, α Pm and α Qm is the single-phase scaling factor.

6. The centralized control method of distributed grid-connected inverter according to claim 1, characterized in that: In step (3), the power reference of the distributed power source with reactive power processing constraints is specifically: Rated reactive power of distributed generation with reactive power processing constraints and reactive power maximum capacity The calculation formula is as follows: Where λ represents the percentage of reactive power that a single-phase inverter can handle; A Dmj Represents the single-phase apparent power of distributed power source; P Dj (k) represents the measured output active power; A Dj is the rated apparent power of the jth distributed generation; if The value is greater than Then Sent to the central controller, otherwise use Active power reference value and reactive power reference The calculation formula is as follows: In the formula, Indicates the maximum capacity of active power, Represents the maximum capacity of reactive power, α P is the active power scaling factor, α Q is the reactive power scaling factor.

7. The centralized control method of distributed grid-connected inverter according to claim 1, characterized in that: In step (3), the power reference of the pure photovoltaic distributed power source is specifically: Pure photovoltaic distributed power source active power reference is its maximum available active power In the case of unrestricted reactive power processing, pure photovoltaic distributed power reactive power reference The calculation formula is as follows: in, It represents the maximum available reactive power provided by pure photovoltaic distributed generation in cycle k; If the pure photovoltaic distributed power source has reactive power limit, the reactive power reference of the pure photovoltaic distributed power source is The calculation formula is as follows: in, Represents the rated reactive power of pure photovoltaic distributed power source; α Q is the reactive power scaling factor; If the pure photovoltaic distributed generation operates at unity power factor, its reactive power reference is zero.

8. The centralized control method of distributed grid-connected inverter according to claim 1, characterized in that: In step (3), the power reference of the active power filter is specifically: The active power reference of the active power filter is zero, and the reactive power reference of the active power filter is Defined as: in, represents the maximum available reactive power of the active power filter, α Qm is the single-phase scaling factor.

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