Operation control method and system of photovoltaic distribution network, and medium

Abstract

The invention discloses an operation control method and system of a photovoltaic distribution network and a medium. According to the scheme, the operation control of the photovoltaic distribution network is divided into first-stage control, second-stage control and third-stage control; the first-stage control is used for adjusting the output voltage and frequency of an inverter according to reference voltage values calculated by a current inner loop and a voltage outer loop so as to realize flexible operation of photovoltaic power generation under a non-communication condition; the second-stage control is used for compensating voltage and frequency deviations caused by the primary control and is also responsible for ensuring seamless access or exit of the photovoltaic power generation equipment in the micro-grid; the third-stage control is used for optimizing power flow distribution between the micro-grid and the power distribution network and performing overall energy management on the micro-grid from the system level; the energy of the micro-grid is managed through multi-stage control cooperation, the energy efficiency and economy of the system are improved, and the effectiveness and rationality of overall energy scheduling are ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic distribution network, and in particular to an operation control method, system and medium of a photovoltaic distribution network. Background Art

[0002] With the continuous growth of global energy demand and the increasing prominence of environmental problems, the development and utilization of clean energy has become an important direction for global sustainable development. Among them, photovoltaic power generation, as a kind of renewable energy, has been widely used around the world due to its clean, pollution-free and inexhaustible characteristics. In recent years, photovoltaic power generation technology has continued to advance, installed capacity has steadily increased, and it has gradually shifted from centralized power generation to distributed power generation. Distributed photovoltaic power generation systems can not only alleviate the pressure on traditional centralized power grids, but also improve energy utilization efficiency and reduce transmission losses. However, the widespread application of distributed photovoltaic power generation systems has also put forward higher requirements for the operation and control of distribution networks.

[0003] The intermittency and volatility of photovoltaic power generation is one of the key factors affecting the stable operation of the distribution network. Since photovoltaic power generation relies on solar energy and is affected by natural factors such as weather and day and night changes, the output power of photovoltaic power generation is random and uncertain. This instability causes fluctuations in grid voltage and frequency, resulting in poor power supply quality and stability. Summary of the invention

[0004] The technical problem to be solved by the present invention is that the intermittent and volatile nature of photovoltaic power generation affects the stable operation of the distribution network. The purpose of the present invention is to provide an operation control method, system and medium for a photovoltaic distribution network, and to divide the operation control of the photovoltaic distribution network into first-level control, second-level control and third-level control; the first-level control adjusts the output voltage and frequency of the inverter according to the reference voltage value calculated by the current inner loop and the voltage outer loop to achieve flexible operation of photovoltaic power generation under non-communication conditions; the second-level control is used to compensate for the voltage and frequency deviations caused by the primary control, and is also responsible for ensuring the seamless access or exit of photovoltaic power generation equipment in the microgrid; the third-level control is used to optimize the power flow distribution between the microgrid and the distribution network, and to perform overall energy management of the microgrid from the system level; multi-level control cooperates to manage the energy of the microgrid, improves the system energy efficiency and economy, and ensures the effectiveness and rationality of the overall energy scheduling.

[0005] The present invention is achieved through the following technical solutions: This solution provides an operation control method for a photovoltaic distribution network, including: The operation control of the photovoltaic distribution network is divided into first-level control, second-level control and third-level control; The first level control is used to adjust the output power of each inverter based on the reference voltage value calculated by the current inner loop and the voltage outer loop; The second level control is used to compensate for the voltage deviation and frequency deviation caused by the first level control, and is responsible for ensuring the seamless access or exit of the photovoltaic power generation equipment in the microgrid; The third level control is used to optimize the power flow distribution between the microgrid and the photovoltaic distribution network.

[0006] A further optimization scheme is that, in the first level of control, when several inverters are connected in parallel to the microgrid, the active power output by the photovoltaic power generation equipment is adjusted by changing the frequency of the inverter output voltage; The adjustment relationship includes: f=f * -m(PP * ); m = (f max -f min ) / P max ; Where, f represents the actual value of the inverter output voltage frequency; f * Indicates the frequency rating of the inverter output voltage; P indicates the actual value of the active power output of the photovoltaic power generation equipment; P * Indicates the rated value of active power output by photovoltaic power generation equipment; m indicates the active power droop coefficient; f max Indicates the maximum value of the inverter output voltage frequency; f min Indicates the minimum value of the inverter output voltage frequency; P max Indicates the maximum value of the inverter output active power; By changing the output voltage amplitude of the inverter, the reactive power output of the photovoltaic power generation equipment can be adjusted; The adjustment relationship includes: u=u * -n(QQ * ); n = (u max -u min ) / Q max ; Where u represents the actual value of the inverter output voltage amplitude; u * Indicates the rated value of the inverter output voltage; n indicates the reactive power droop coefficient; u max Indicates the maximum value of the inverter output voltage amplitude; u min Indicates the minimum value of the inverter output voltage amplitude; Q max Indicates the maximum value of the reactive power output by the inverter; Q indicates the actual value of the reactive power output by the photovoltaic power generation equipment; Q * Indicates the reactive power rating output by photovoltaic power generation equipment.

[0007] A further optimization scheme is that the second-level control includes centralized control: the microgrid central controller is used to collect electrical information and switch status of each photovoltaic power generation device, and calculate the voltage frequency deviation and voltage amplitude deviation and send them to each photovoltaic power generation device for execution; Voltage frequency deviation of photovoltaic power generation equipment i and voltage amplitude deviation It is expressed as: ; Where, t represents time; g i and h i It represents the frequency pulling coefficient and the amplitude pulling coefficient; Indicates rated voltage frequency, Indicates the rated voltage amplitude; Represents the voltage frequency of photovoltaic power generation equipment i; Represents the voltage amplitude of photovoltaic power generation equipment i.

[0008] A further optimization scheme is that the second level control also includes distributed control: Each photovoltaic power generation device exchanges information with adjacent photovoltaic power generation devices; Taking the voltage and frequency received by at least one photovoltaic power generation device as reference signals, performing secondary recovery control based on a consistency algorithm, and calculating corresponding voltage amplitude deviation and voltage frequency deviation; Voltage frequency deviation of photovoltaic power generation equipment i and voltage amplitude deviation It is expressed as: ; in, represents the set of neighbors of photovoltaic power generation equipment i; t represents time; f j Indicates the frequency value corresponding to photovoltaic power generation equipment j, u j represents the voltage amplitude corresponding to photovoltaic power generation equipment j; g i and h i It represents the frequency pulling coefficient and the amplitude pulling coefficient; Indicates rated voltage frequency, Indicates the rated voltage amplitude; Represents the voltage frequency of photovoltaic power generation equipment i; Represents the voltage amplitude of photovoltaic power generation equipment i; Represents the voltage-frequency weight coefficient; Represents the voltage amplitude weight coefficient.

[0009] A further optimization scheme is that the third level control includes the following method: The state variables of the line transmission power are rewritten to obtain a small signal model, and the coupling mechanism and coupling characteristics of the photovoltaic distribution network are analyzed based on the small signal model; Based on the coupling mechanism and coupling characteristics, the coupling term is accurately estimated through a linear extended state observer; The coupling term is introduced into the photovoltaic power generation power loop to generate a power decoupling control strategy.

[0010] A further optimization scheme is that the coupling term is accurately estimated through a linear extended state observer based on the coupling mechanism and coupling characteristics; including the method: Considering the influence of line resistance and inductance characteristics, small power angle approximation error and the voltage change at the photovoltaic power generation terminal, the photovoltaic power closed-loop control result is obtained: ;

[0011] in, , , , They are the small disturbance components of the photovoltaic power generation output active power, reactive power, voltage and power angle; m 1 , m 2 , m 3 , m 4 They respectively represent the frequency droop coefficient of active power, the droop coefficient of the controlled variable of active power, the frequency droop coefficient of reactive power, and the droop coefficient of the controlled variable of reactive power; The parameters of the linear extended state observer and the linear state error feedback are configured based on the coupling mechanism and coupling characteristics. The coupling term is obtained according to the linear extended state observer and the linear state error feedback: ;

[0012] in, and are the active power and reactive power after coupling respectively; b 1 and b 2 are the first coupling coefficient and the second coupling coefficient respectively; f1 represents the total disturbance of the active power loop; f2 represents the total disturbance of the reactive power loop.

[0013] A further optimization scheme is that the coupling term is obtained according to the linear extended state observer and the linear state error feedback, including the method: The photovoltaic power closed-loop control results are transformed as follows: ; by , As the control quantity, and configure f n (n=1, 2) is the coupling term obtained after the total disturbance.

[0014] A further optimization scheme is to introduce coupling terms into the photovoltaic power generation power loop to generate a power decoupling control strategy, including the following methods: Based on the first-order power decoupling control method, the active loop and reactive loop are controlled, and the first tracking state ; Second tracking state ; Third tracking state ; Third tracking state ; Then the second-order linear extended state observer is: ; in: Respectively represent the first error gain, the second error gain, the third error gain, and the fourth error gain; z1 represents the state of the first tracking state x1 in the linear extended state observer; z2 represents the state of the tracking expansion state f1 in the linear extended state observer; Z1 is the state of the tracking third tracking state X1 in the linear extended state observer; Z2 is the state of the tracking expansion state f2 in the linear extended state observer; , , , They are the tracking results of the linear extended state observer respectively; Then the linear error feedback control rate is: ; ; Where: K p , K Q are active proportional constant and reactive proportional constant; Indicates the reference active power; Indicates the reference reactive power; and Respectively represent the initial control rate of active and reactive power; and Respectively represent the control rate when active and reactive power are applied; According to the pole placement rule, we get: ;

[0015] in, , are the active power loop observer bandwidth and controller bandwidth respectively; , is the reactive power loop observer bandwidth and controller bandwidth.

[0016] The present invention also provides an operation control system for a photovoltaic distribution network, characterized in that the system is used to implement the above-mentioned operation control method for a photovoltaic distribution network, and comprises: The first-level control module is used to adjust the output power of each inverter based on the reference voltage value calculated by the current inner loop and the voltage outer loop; The second-level control module is used to compensate for the voltage deviation and frequency deviation caused by the first-level control, and is responsible for ensuring the seamless access or seamless exit of the photovoltaic power generation equipment in the microgrid; The third-level control module is used to optimize the power flow distribution between the microgrid and the photovoltaic distribution network.

[0017] The present solution also provides a computer-readable medium on which a computer program is stored. The computer program is executed by a processor to implement the operation control method of a photovoltaic distribution network as described above.

[0018] Compared with the prior art, the present invention has the following advantages and beneficial effects: The present invention provides an operation control method, system and medium for a photovoltaic distribution network; the operation control of the photovoltaic distribution network is divided into first-level control, second-level control and third-level control; the first-level control adjusts the output voltage and frequency of the inverter according to the reference voltage value calculated by the current inner loop and the voltage outer loop to achieve flexible operation of photovoltaic power generation under non-communication conditions; the second-level control is used to compensate for the voltage and frequency deviations caused by the primary control, and is also responsible for ensuring the seamless access or exit of photovoltaic power generation equipment in the microgrid; the third-level control is used to optimize the power flow distribution between the microgrid and the distribution network, and perform overall energy management of the microgrid from the system level; multi-level control cooperates to manage the energy of the microgrid, improves the system energy efficiency and economy, and ensures the effectiveness and rationality of the overall energy scheduling. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings: Figure 1 This is a schematic diagram of the operation control method of the photovoltaic distribution network; Figure 2 It is the equivalent circuit diagram of photovoltaic power generation after being connected to the grid through pre-synchronization control; Figure 3 This is a schematic diagram of the closed loop circuit for active power / frequency control of photovoltaic power generation; Figure 4 Schematic diagram of the closed-loop reactive power / voltage control for photovoltaic power generation. DETAILED DESCRIPTION

[0020] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0021] The intermittency and volatility of photovoltaic power generation is one of the key factors affecting the stable operation of the distribution network. Since photovoltaic power generation relies on solar energy and is affected by natural factors such as weather and day and night changes, the output power of photovoltaic power generation is random and uncertain. This instability causes fluctuations in grid voltage and frequency, resulting in poor power supply quality and stability of the grid. In view of this, this solution provides the following embodiments to solve the above technical problems.

[0022] Embodiment 1: This embodiment provides an operation control method of a photovoltaic distribution network, such as Figure 1 As shown, including: This embodiment takes the AC microgrid as an example, and divides the operation control of the AC microgrid into the first level control, the second level control and the third level control; each level control has its specific control target, and monitors and adjusts the lower level, and the control instructions and reference signals of each level control have an auxiliary effect on the lower level, otherwise the stability and robustness of the system may be destroyed. As the control level increases, the information bandwidth will gradually decrease.

[0023] The first level of control is used to adjust the output power of each inverter based on the reference voltage value calculated by the current inner loop and the voltage outer loop; to achieve flexible operation of photovoltaic power generation without communication conditions, and to ensure that the system has high adaptability. The first level of control is the fastest response control level. When the microgrid encounters a major disturbance (for example, switching from grid-connected mode to island mode), the first level of control is the key to maintaining the stability of the system voltage and frequency. In the case of both linear and nonlinear loads, the first level of control avoids the occurrence of circulating current problems through allocation strategies. The first level of control adjusts the output voltage and frequency of the inverter according to the reference voltage value calculated by the current inner loop and the voltage outer loop to achieve flexible operation of photovoltaic power generation without communication conditions.

[0024] In the first level of control, when several inverters are connected in parallel to the microgrid, the active power output by the photovoltaic power generation equipment is adjusted by changing the frequency of the inverter output voltage, thereby improving the reliability of system operation.

[0025] The adjustment relationship includes: f=f * -m(PP * ); m = (f max -f min ) / P max ; Where, f represents the actual value of the inverter output voltage frequency; f *Indicates the frequency rating of the inverter output voltage; P indicates the actual value of the active power output of the photovoltaic power generation equipment; P * Indicates the rated value of active power output by photovoltaic power generation equipment; m indicates the active power droop coefficient; f max Indicates the maximum value of the inverter output voltage frequency; f min Indicates the minimum value of the inverter output voltage frequency; P max Indicates the maximum value of the inverter output active power; By changing the output voltage amplitude of the inverter, the reactive power output of the photovoltaic power generation equipment can be adjusted; The adjustment relationship includes: u=u * -n(QQ * ); n = (u max -u min ) / Q max ; Where u represents the actual value of the inverter output voltage amplitude; u * Indicates the rated value of the inverter output voltage; n indicates the reactive power droop coefficient; u max Indicates the maximum value of the inverter output voltage amplitude; f min Indicates the minimum value of the inverter output voltage amplitude; P max Indicates the maximum value of the inverter output reactive power.

[0026] The first level of control, i.e., primary control, can reasonably distribute the active power and reactive power output by each photovoltaic power generation device. Specifically, when the active power output by the photovoltaic power generation device is too large / too small, the output of active power can be reduced / increased by reducing / increasing the frequency of the inverter output voltage. Similarly, when the reactive power output by the photovoltaic power generation device is too large / too small, the output of reactive power can also be adjusted by adjusting the amplitude of the inverter output voltage.

[0027] The first-level control obtains the reference voltage signal and decomposes it, and makes a difference with the actual dq axis voltage value output by the inverter as the input reference signal of the voltage outer loop. The reference signal of the current dq axis is obtained through the voltage outer loop, and the reference signal of the current dq axis is subtracted from the dq axis current value output by the inverter as the input reference value of the current inner loop; where the dq axis represents the reactive component and the active component; after calculation by the current inner loop, the voltage reference signal is obtained as the modulation signal of the pulse width modulation, which drives the inverter to work and controls the actual stable operation of the microgrid. Among them, the expression of the voltage outer loop controller is as follows: ; in, i dref , i qrefRespectively represent the current reference values ​​under active power and reactive power; K pv 、 K iV Indicates the proportional adjustment coefficient and integral adjustment coefficient of the voltage outer loop; u ddtoop 、u qdroop They represent the reference voltage value of the primary control output under active power and the reference voltage value of the primary control output under reactive power respectively. , They represent the voltage coupling term under active power and the voltage coupling term under reactive power respectively; u d 、u q 、i d 、i q Respectively represent the output voltage value under the active power of the inverter, the output voltage value under the reactive power of the inverter, the output current value under the active power of the inverter, and the output current value under the reactive power of the inverter; u qref Indicates the reference voltage output value under the inverter reactive power; Voltage outer loop controller when representing active power; Indicates the control reference value under active power. Indicates the control reference value under reactive power; The first-level control has a fast response speed, but cannot achieve zero-error control. Therefore, the second-level control is needed to restore the voltage and frequency of the microgrid. The second-level control is used to compensate for the voltage and frequency deviations caused by the first-level control, and is responsible for ensuring the seamless access or exit of photovoltaic power generation equipment in the microgrid; From the perspective of information interaction mode, the second-level control can be divided into two types: centralized control and distributed control, as follows: Centralized control: In this mode, the control structure adopts a master-slave architecture, that is, the microgrid central controller is the leader and each photovoltaic power generation device is a slave. The microgrid central controller is used to collect the electrical information and switch status of each photovoltaic power generation device, and calculate the voltage frequency deviation and voltage amplitude deviation and send them to each photovoltaic power generation device for execution; Voltage frequency deviation of photovoltaic power generation equipment i and voltage amplitude deviation It is expressed as: ;

[0028] Where, t represents time; g i and h iIt represents the frequency pulling coefficient and the amplitude pulling coefficient; Indicates rated voltage frequency, Indicates the rated voltage amplitude; Represents the voltage frequency of photovoltaic power generation equipment i; Represents the voltage amplitude of photovoltaic power generation equipment i.

[0029] In the centralized control mode, the microgrid central controller aggregates the information of each photovoltaic power generation device, can quickly calculate the optimal strategy and send it to the photovoltaic power generation device for operation, and the system responds quickly and converges quickly. However, this mode also brings some challenges, such as the large amount of data in the information link leading to the microgrid central controller, which places extremely high requirements on the reliability and security of the microgrid central controller. Once the microgrid central controller is attacked or fails, the consequences will be very serious.

[0030] Distributed control: Setting up photovoltaic power generation equipment The neighbor of photovoltaic power generation device i needs to transmit information to photovoltaic power generation device i. is the neighbor set of photovoltaic power generation equipment i. The second-level control mainly receives the voltage and frequency values ​​of adjacent photovoltaic power generation equipment and the system reference value through information exchange, calculates the corresponding adjustment amount, and feeds it back to the first-level control for compensation.

[0031] Each photovoltaic power generation device exchanges information with adjacent photovoltaic power generation devices; Taking the voltage and frequency received by at least one photovoltaic power generation device as reference signals, secondary recovery control is performed based on a consistency algorithm, thereby calculating corresponding voltage frequency deviation and voltage amplitude deviation; Voltage frequency deviation of photovoltaic power generation equipment i and voltage amplitude deviation It is expressed as: ;

[0032] in, represents the set of neighbors of photovoltaic power generation equipment i; t represents time; f j Indicates the frequency value corresponding to photovoltaic power generation equipment j, u j represents the voltage amplitude corresponding to photovoltaic power generation equipment j; g i and h i It represents the frequency pulling coefficient and the amplitude pulling coefficient; Indicates rated voltage frequency, Indicates the rated voltage amplitude; Represents the voltage frequency of photovoltaic power generation equipment i; Represents the voltage amplitude of photovoltaic power generation equipment i; Represents the voltage-frequency weight coefficient; Represents the voltage amplitude weight coefficient.

[0033] The distributed control structure is more flexible. Each photovoltaic power generation device does not need to upload all data to the microgrid central controller, but exchanges information with adjacent photovoltaic power generation devices. In this interactive mode, the system only needs at least one photovoltaic power generation device to receive the reference signal of voltage and frequency, and then perform secondary recovery control based on the consistency algorithm to calculate the corresponding voltage and frequency compensation values.

[0034] In the distributed control structure, each photovoltaic power generation device narrows the voltage and frequency gap between each other, and finally achieves the goal of all photovoltaic power generation devices approaching the reference value. This interactive mode reduces the dependence on the core information link and also improves the convenience of controlling a single photovoltaic power generation device.

[0035] The third level of control is used to optimize the power flow distribution between the microgrid and the photovoltaic distribution network, manage the energy of the microgrid as a whole, improve the energy efficiency and economy of the system, and ensure the effectiveness and rationality of the overall energy dispatch. The third level of control includes the following methods: S31, firstly, analyze the coupling mechanism of photovoltaic power output power, mainly rewriting the state variables of line transmission power to obtain a small signal model, and analyze the coupling mechanism and coupling characteristics of photovoltaic distribution network based on the small signal model; After pre-synchronization control, photovoltaic power generation is connected to the grid for power output. Its equivalent circuit is as follows: Figure 2 As shown in the figure; Assuming that the grid voltage phase is the reference phase, the difference between the photovoltaic power generation output voltage and the grid voltage reference phase is the power angle ; The power transmitted in the line can be expressed as: ;

[0036] in, P e It is the active output power transmitted in the photovoltaic power generation line; E o is the voltage reference value, V g is the effective value of the grid voltage, R g is the value of the series resistor, X g is the inductive reactance value, Q e It is the reactive output power transmitted in the photovoltaic power generation line; By rewriting the above equation with state variables, we can get the small signal model as follows: ; in, , , , They are the small disturbance components of the photovoltaic power generation output active power, reactive power, voltage and power angle; E n , They are the steady-state values ​​of photovoltaic power generation output voltage and power angle respectively.

[0037] From the above formula, we can see that The presence of enables power coupling, and P e 、Q e At the same time, it is controlled by the photovoltaic power generation output voltage and power angle; if the control loop parameters are changed by introducing virtual inductance, virtual negative impedance, etc., the equivalent impedance between the photovoltaic power generation output voltage and the grid voltage is close to pure inductance. , then the above formula can be rewritten as: ;

[0038] Among them, X is the equivalent inductive reactance value. From the above formula, it can be seen that even if the resistance-inductance characteristics of the line are changed by introducing virtual inductance, virtual negative impedance and other methods, the output power of photovoltaic power generation is still controlled by voltage and power angle at the same time. Therefore, the reasons for the strong coupling characteristics of photovoltaic power generation output power include: 1. The resistance-inductance characteristics of the transmission line, especially the impedance of the low-voltage line; 2. The active power reference value fluctuates greatly or the grid frequency changes, causing large errors in the small power angle approximation; 3. The voltage change at the photovoltaic power generation end caused by the change of reactive power reference value. These three factors can enter the power loop through the coupling channel to further amplify the degree of power coupling.

[0039] S2, considering the influence of line resistance and inductance characteristics, small power angle approximation error and photovoltaic power generation terminal voltage change, the double closed loop can be ignored when designing the control system. It is assumed that the photovoltaic power generation output voltage can quickly track the given reference voltage, and the photovoltaic power generation power closed-loop control block diagram is obtained, as shown in Figure 3 and Figure 4 As shown in the figure m 1 , m 2 , m 3 , m 4 They represent the frequency droop coefficient of active power, the droop coefficient of the controlled variable of active power, the frequency droop coefficient of reactive power, and the droop coefficient of the controlled variable of reactive power respectively; the corresponding expressions are: ;

[0040] By using the estimation and compensation capabilities of the power decoupling control method, the parameters of the linear extended state observer and the linear state error feedback are reasonably designed. The coupling term is accurately estimated by the linear extended state observer and introduced into the power loop of photovoltaic power generation to eliminate it, thereby simultaneously solving the power coupling problem caused by line impedance characteristics, small power angle approximation errors, and photovoltaic power generation terminal voltage changes; the photovoltaic power closed-loop control result is obtained: ;

[0041] Based on the coupling mechanism and coupling characteristics, the parameters of the linear extended state observer and the linear state error feedback are configured, and the photovoltaic power closed-loop control results are transformed as follows: ;

[0042] Pick , △E is the control quantity, and configure After the total disturbance, the coupling term is obtained: ;

[0043] in, and are the active power and reactive power after coupling respectively; b 1 and b 2 are the first coupling coefficient and the second coupling coefficient respectively; f 1 represents the total disturbance of the active power loop; f 2 Represents the total disturbance of the reactive power loop.

[0044] S3, introducing the coupling term into the photovoltaic power generation power loop to generate a power decoupling control strategy, thereby effectively solving the power coupling problem. This step includes the following methods: Based on the first-order power decoupling control method, the active loop and reactive loop are controlled, and the first tracking state ; Second tracking state ; Third tracking state ; Third tracking state ; Then the second-order linear extended state observer is: ; in: They represent the first error gain, the second error gain, the third error gain, and the fourth error gain respectively; z1 represents the state of the first tracking state x1 in the linear extended state observer; z2 represents the state of the tracking expansion state f1 in the linear extended state observer; Z 1 is the state of tracking the third tracking state X1 in the linear extended state observer;Z 2 is the state of tracking the expansion state f2 in the linear expansion state observer; , , , They are the tracking results of the linear extended state observer respectively; Then the linear error feedback control rate is: ; ;

[0045] in: are active proportional constant and reactive proportional constant; Indicates the reference active power; Indicates the reference reactive power; and Respectively represent the initial control rate of active and reactive power; and Respectively represent the control rate when active and reactive power are applied; According to the pole placement rule, we get: ;

[0046] in, , are the active power loop observer bandwidth and controller bandwidth respectively; , is the reactive power loop observer bandwidth and controller bandwidth.

[0047] In this scheme, △E is used as the control quantity in active power control and By designing a decoupling controller for the control quantity, active power / voltage and reactive power / frequency control can be obtained, and the corresponding control strategy can be selected according to the actual engineering needs. Control system stability analysis The stability analysis of the power decoupling control system based on the power decoupling control method includes two parts. One part is the stability analysis of the power loop based on the power decoupling control method. The other part is the stability analysis of the photovoltaic power loop after the introduction of the observation term. From the above analysis, it can be seen that the active power loop of the photovoltaic power closed-loop control after decoupling is a second-order model, and the reactive power loop is Q / V first-level control, and its stability is good.

[0048] This scheme fully considers the random output problem of new energy, and also proposes a random arrangement point method based on simple dimension and sparse grid. This method uses the idea of ​​black box, regards the optimal operation mode problem containing random variables as a black box, and then uses tensor product to approximate the internal structure of the black box to simulate the input and output of the black box. Among them, the tensor product process is deeply simplified by the sparse grid of simple dimension, which compresses the content of the simulation process.

[0049] Based on the maximum power tracking of renewable energy, that is, the active power output of photovoltaic power generation is directly specified as its corresponding predicted value, while the reactive power output slides within a certain power factor range. The photovoltaic power generation model of this application takes into account factors such as weather, geography, and prediction accuracy. Its allowable output power is no longer specified as a predicted value, but a random value with the predicted value as the mean and a normal distribution; in addition, photovoltaic power generation adds an active scheduling link, allowing appropriate wind and solar power abandonment, and the output can be freely adjusted within the maximum allowable output range. Therefore, the model of photovoltaic power generation is: ;

[0050] in, is the active power output of photovoltaic power generation; and are the dispatched / actual active and reactive power outputs of PV generation at node i, respectively; represents the power factor angle; and are the maximum upward and minimum downward ramp rates of reactive power output, respectively; The normal distribution represents the error in the prediction.

[0051] Objective function: This application synthesizes the objective function from three parts: network loss cost, power generation cost and clean energy abandonment penalty, referred to as operating cost. The network loss cost is represented by the difference between power generation and power consumption, C1: ; in t 0 and t f They represent the start time and end time considered for the optimal operation mode respectively; P Si ( t )and C S (t) Respectively indicate at time t The active power and the corresponding unit price; N B Indicates the total number of nodes; and Respectively represent nodes i The charging power and discharging power of P Li ( t ) is a node i Active load; Electricity provided by fossil energy photovoltaic power generation and high voltage requires power generation costs C 2 : ;

[0052] Clean energy requires almost no power generation cost and has less environmental pollution. Generally, clean energy photovoltaic power generation should be kept at full capacity. However, from the perspective of distribution network operation and line congestion, it is sometimes necessary to dispatch the active and reactive output of clean energy photovoltaic power generation, and the resulting clean energy abandonment penalty C3 is: ; in, represents the predicted active power output; Objective Function J It is a combination of three parts of expenses:

[0053] The random point method transforms the model into a black box of input and output through tensor product. Before the transformation, it is necessary to analyze what the input and output specifically refer to.

[0054] For optimization problems, to obtain the optimal solution, the input of the random point method is various decision variables. The decision variables for the optimal operation mode of this application are: and , and Except for photovoltaic power generation, other devices / variables do not involve random problems. In order to arrange the random arrangement point method, since the decision variables can take any value within the value range, the variables not involving randomness can be converted into uniform distribution within the upper and lower limits.

[0055]

[0056] Indicates the minimum charging power; Indicates the maximum charging power; represents the predicted charging error;

[0057] The output of the random point method is analyzed from the perspective of the objective function, which contains variables as well as ,in as well as Because the decision variables have been specified as input variables. Therefore, in order to obtain the minimum objective function, the output setting of the random permutation method is .

[0058] To generalize the following random arrangement point method, this application defines is a column vector of output variables, where For special problems with one dimension (i.e., only one input variable), the output variable can be approximated by Lagrange interpolation (linear superposition):

[0059] in, M is the input variable The number of interpolation points; Representative output The approximate value of Represents the kth interpolation point of the input variable, which is a certain constant: and Represents the interpolation points Department, Specific numerical values ​​and Lagrange polynomials; Lag() represents the Lagrange function.

[0060] However, practical problems often correspond to multiple input variables, such as the optimal operation mode problem of this application. For this multi-dimensional (i.e., multiple input variables) universal problem, one-dimensional linear superposition needs to be upgraded to tensor product:

[0061] Among them, i1, i2, …, i n and k1, k2, …, k n Corresponding to the interpolation levels and interpolation points of 1, 2, ..., n-dimensional input variables: This application adopts as well as The form of tensor product is simplified; is the input variable, is the intermediate parameter of the corresponding dimension; represents the Kronecker product.

[0062] From the above formula, we can see that the input variables of the 1st, 2nd, ..., nth dimensions correspond to interpolation points; therefore, for the optimization problem with n-dimensional input, the total number of interpolation points is ; The optimal solution for the optimal operating mode is obtained.

[0063] Embodiment 2: This embodiment provides an operation control system of a photovoltaic distribution network, which is used to implement an operation control method of a photovoltaic distribution network described in Embodiment 1. The system includes: The first-level control module is used to adjust the output power of each inverter based on the reference voltage value calculated by the current inner loop and the voltage outer loop; The second-level control module is used to compensate for the voltage deviation and frequency deviation caused by the first-level control, and is responsible for ensuring the seamless access or exit of photovoltaic power generation equipment in the microgrid; The third-level control module is used to optimize the power flow distribution between the microgrid and the photovoltaic distribution network.

[0064] Embodiment 3: This embodiment provides a computer-readable medium on which a computer program is stored. The computer program is executed by a processor to implement an operation control method of a photovoltaic distribution network as described in Embodiment 1.

[0065] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A photovoltaic distribution network operation control method, characterized in that: include: The operation control of the photovoltaic distribution network is divided into first-level control, second-level control and third-level control; The first level control is used to adjust the output power of each inverter based on the reference voltage value calculated by the current inner loop and the voltage outer loop; The second level control is used to compensate for the voltage deviation and frequency deviation caused by the first level control, and is responsible for ensuring the seamless access or exit of the photovoltaic power generation equipment in the microgrid; The third level control is used to optimize the power flow distribution between the microgrid and the photovoltaic distribution network.

2. The operation control method of a photovoltaic distribution network according to claim 1, characterized in that: In the first level of control, when several inverters are connected in parallel to the microgrid, the active power output by the photovoltaic power generation equipment is adjusted by changing the frequency of the inverter output voltage; The adjustment relationship includes: f=f * -m(PP * ); m = (f max -f min ) / P max ; Where, f represents the actual value of the inverter output voltage frequency; f * Indicates the frequency rating of the inverter output voltage; P indicates the actual value of the active power output of the photovoltaic power generation equipment; P * Indicates the rated value of active power output by photovoltaic power generation equipment; m indicates the active power droop coefficient; f max Indicates the maximum value of the inverter output voltage frequency; f min Indicates the minimum value of the inverter output voltage frequency; P max Indicates the maximum value of the inverter output active power; By changing the output voltage amplitude of the inverter, the reactive power output of the photovoltaic power generation equipment can be adjusted; The adjustment relationship includes: u=u * -n(QQ * ); n = (u max -u min ) / Q max ; Where u represents the actual value of the inverter output voltage amplitude; u * Indicates the rated value of the inverter output voltage; n indicates the reactive power droop coefficient; u max Indicates the maximum value of the inverter output voltage amplitude; f min Indicates the minimum value of the inverter output voltage amplitude; P max Indicates the maximum value of the inverter output reactive power.

3. The operation control method of a photovoltaic distribution network according to claim 2, characterized in that: The second level control includes centralized control: the microgrid central controller is used to collect electrical information and switch status of each photovoltaic power generation device, and calculate the voltage frequency deviation and voltage amplitude deviation and send them to each photovoltaic power generation device for execution; Voltage frequency deviation of photovoltaic power generation equipment i and voltage amplitude deviation It is expressed as: ； Among them, t represents time; g i and h i It represents the frequency pulling coefficient and the amplitude pulling coefficient; Indicates rated voltage frequency, Indicates the rated voltage amplitude; Represents the voltage frequency of photovoltaic power generation equipment i; Represents the voltage amplitude of photovoltaic power generation equipment i.

4. The operation control method of a photovoltaic distribution network according to claim 2, characterized in that: The second level of control also includes distributed control: Each photovoltaic power generation device exchanges information with adjacent photovoltaic power generation devices; Taking the voltage and frequency received by at least one photovoltaic power generation device as reference signals, performing secondary recovery control based on a consistency algorithm, and calculating corresponding voltage amplitude deviation and voltage frequency deviation; Voltage frequency deviation of photovoltaic power generation equipment i and voltage amplitude deviation It is expressed as: ； in, represents the set of neighbors of photovoltaic power generation equipment i; t represents time; f j Indicates the frequency value corresponding to photovoltaic power generation equipment j, u j represents the voltage amplitude corresponding to photovoltaic power generation equipment j; g i and h i It represents the frequency pulling coefficient and the amplitude pulling coefficient; Indicates rated voltage frequency, Indicates the rated voltage amplitude; Represents the voltage frequency of photovoltaic power generation equipment i; Represents the voltage amplitude of photovoltaic power generation equipment i; Represents the voltage-frequency weight coefficient; Represents the voltage amplitude weight coefficient.

5. The operation control method of a photovoltaic distribution network according to claim 1, characterized in that: The third level of control includes methods: The state variables of the line transmission power are rewritten to obtain a small signal model, and the coupling mechanism and coupling characteristics of the photovoltaic distribution network are analyzed based on the small signal model; Based on the coupling mechanism and coupling characteristics, the coupling term is accurately estimated through a linear extended state observer; The coupling term is introduced into the photovoltaic power generation power loop to generate a power decoupling control strategy.

6. The operation control method of a photovoltaic distribution network according to claim 5, characterized in that: Based on the coupling mechanism and coupling characteristics, the coupling term is accurately estimated through a linear extended state observer; including the method: Considering the influence of line resistance and inductance characteristics, small power angle approximation error and the voltage change at the photovoltaic power generation terminal, the photovoltaic power closed-loop control result is obtained: ； in, , , , They are the small disturbance components of the photovoltaic power generation output active power, reactive power, voltage and power angle; m 1 , m 2 , m 3 , m 4 They respectively represent the frequency droop coefficient of active power, the droop coefficient of the controlled variable of active power, the frequency droop coefficient of reactive power, and the droop coefficient of the controlled variable of reactive power; The parameters of the linear extended state observer and the linear state error feedback are configured based on the coupling mechanism and coupling characteristics. The coupling term is obtained according to the linear extended state observer and the linear state error feedback: ； in, and are the active power and reactive power after coupling respectively; b1 and b2 are the first coupling coefficient and the second coupling coefficient respectively; f1 represents the total disturbance of the active power loop; f2 represents the total disturbance of the reactive power loop.

7. A photovoltaic distribution network operation control method according to claim 6, characterized in that: The coupling term is obtained according to the linear extended state observer and the linear state error feedback, including the method: The photovoltaic power closed-loop control results are transformed as follows: ； by , is the control quantity, and configure f n (n=1, 2) is the coupling term obtained after the total disturbance.

8. The operation control method of a photovoltaic distribution network according to claim 6, characterized in that: The coupling term is introduced into the photovoltaic power generation power loop to generate a power decoupling control strategy, including the following methods: Based on the first-order power decoupling control method, the active loop and reactive loop are controlled, and the first tracking state is ; Second tracking state ; Third tracking state ; Third tracking state ; Then the second-order linear extended state observer is: ； in: They represent the first error gain, the second error gain, the third error gain, and the fourth error gain respectively; z1 represents the state of the first tracking state x1 in the linear extended state observer; z2 represents the state of the tracking expansion state f1 in the linear extended state observer; Z 1 is the state of tracking the third tracking state X1 in the linear extended state observer; Z 2 is the state of tracking the expansion state f2 in the linear expansion state observer; , , , They are the tracking results of the linear extended state observer respectively; Then the linear error feedback control rate is: ； ； Where: K p , K Q are active proportional constant and reactive proportional constant; Indicates the reference active power; Indicates the reference reactive power; and Respectively represent the initial control rate of active and reactive power; and Respectively represent the control rate when active and reactive power are applied; According to the pole placement rule, we get: ； in, , are the active power loop observer bandwidth and controller bandwidth respectively; , is the reactive power loop observer bandwidth and controller bandwidth.

9. An operation control system for a photovoltaic distribution network, characterized in that: A method for controlling the operation of a photovoltaic distribution network according to any one of claims 1 to 8, the system comprising: The first-level control module is used to adjust the output power of each inverter based on the reference voltage value calculated by the current inner loop and the voltage outer loop; The second-level control module is used to compensate for the voltage deviation and frequency deviation caused by the first-level control, and is responsible for ensuring the seamless access or exit of photovoltaic power generation equipment in the microgrid; The third-level control module is used to optimize the power flow distribution between the microgrid and the photovoltaic distribution network.

10. A computer readable medium having a computer program stored thereon, characterized in that: The computer program is executed by a processor to implement an operation control method for a photovoltaic distribution network as described in any one of claims 1 to 8.

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