A large-scale distributed photovoltaic voltage-frequency coordinated support control method

Abstract

The present invention discloses a large-scale distributed photovoltaic voltage-frequency coordinated support control method, which establishes a distributed photovoltaic local droop control parameter optimization model to optimize local active power / frequency and reactive power / voltage droop control parameters. In the real-time control stage, the distributed photovoltaic combines local measurement and optimized droop control curves to quickly adjust the output power in response to system voltage and frequency deviations. The method of the present invention can make full use of the flexible power regulation capability of distributed photovoltaics, ensure the voltage safety of the distribution network and improve the frequency response characteristics of the system. In view of the coupling interference between the local active power / frequency and reactive power / voltage droop control loops of distributed photovoltaics, a critical voltage boundary is proposed to characterize the voltage regulation capability limit of distributed photovoltaics, and the critical voltage boundary is used to reconstruct the voltage constraint of the droop control parameter optimization model, which can effectively prevent the local voltage of the distribution network from exceeding the limit due to the participation of distributed photovoltaics in frequency regulation.

Description

Technical Field

[0001] The invention relates to a large-scale distributed photovoltaic voltage-frequency coordinated support control method, belonging to the field of power system operation control. Background Art

[0002] With the massive access of distributed photovoltaics in the distribution network, the safe and stable operation of the power system faces huge challenges. Among them, the most prominent impacts of large-scale access of distributed photovoltaics are: first, the large-scale access of distributed photovoltaics in the distribution network, its output timing characteristics and load characteristics are mismatched, which can easily cause the reverse flow of the distribution network and local voltage over-limit, threatening the voltage safety of the distribution network; second, distributed photovoltaics are connected to the grid through inverters and cannot provide inertia support. Its large-scale access greatly reduces the proportion of rotating equipment such as synchronous generators in the system, resulting in a decrease in system inertia and a greater risk of system frequency stability. Through the coordinated control of large-scale distributed photovoltaics, fully exploring and utilizing its flexible active and reactive power regulation capabilities to simultaneously adjust the distribution network voltage and participate in system frequency control has far-reaching significance for improving the safety and efficiency of power system operation.

[0003] Distributed photovoltaics participate in distribution network voltage regulation and system frequency control. The most mature solution at present is to use active / frequency and reactive / voltage droop control with fixed parameters, but it is difficult to adapt to complex and changeable system operating conditions and cannot guarantee the effect of voltage and frequency control. Although the control scheme of updating the active and reactive reference values ​​of distributed photovoltaics regularly (15 minutes, 1 hour, etc.) can simultaneously support voltage and frequency, this control method cannot achieve continuous power regulation. The response speed of distributed photovoltaics is limited by the update frequency of power reference values, and this method does not consider the objective coupling relationship between voltage regulation and frequency control, resulting in poor control effect. Summary of the invention

[0004] In view of the limitations of the relevant background technology, the present invention provides a large-scale distributed photovoltaic voltage-frequency coordinated support control method, which optimizes the design of distributed photovoltaic local active / frequency and reactive / voltage droop control curves, and considers the coupling relationship between the two tasks of voltage and frequency control. It can minimize the distributed photovoltaic active standby and reactive output, regularly update and set the local droop control parameters of distributed photovoltaics, and comprehensively balance the optimality and rapidity of large-scale distributed photovoltaic voltage and frequency support control. The present invention overcomes the problems of slow response speed, inability to provide continuous power regulation, and mutual interference between voltage and frequency control tasks in traditional control methods.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A large-scale distributed photovoltaic voltage-frequency coordinated support control method comprises the following steps:

[0007] 1) By analyzing the coupling relationship between the active power / frequency and reactive power / voltage droop control loops, the critical voltage boundary that characterizes the maximum voltage regulation capability of distributed photovoltaics is derived;

[0008] 2) Based on the model predictive control theory, considering the distributed photovoltaic reactive power / voltage and active power / frequency droop control functions, with the goal of minimizing the distributed photovoltaic active reserve and reactive power output, a distributed photovoltaic local droop control parameter optimization model is constructed;

[0009] 3) By linearizing the distributed photovoltaic local droop control parameter optimization model, a distributed photovoltaic local droop control parameter mixed integer linear optimization model is obtained, wherein the distributed photovoltaic local droop control parameter mixed integer linear optimization model specifically includes a linearized distribution network power flow model, a linearized distributed photovoltaic reactive power / voltage droop control function, a linearized inverter capacity constraint, and a linearized objective function;

[0010] 4) Reconstruct the voltage constraint of the distributed photovoltaic local droop control parameter mixed integer linear optimization model based on the critical voltage boundary, use the solver to solve the distributed photovoltaic local droop control parameter mixed integer linear optimization model and configure the distributed photovoltaic local droop control parameters based on the solution results. The distributed photovoltaic quickly changes its output power according to local measurement and droop control to achieve voltage and frequency coordinated support.

[0011] In the above technical solution, further, in step 1), by analyzing the coupling relationship between the active power / frequency and reactive power / voltage droop control loops, the critical voltage boundary for maintaining the voltage safety of the distribution network when distributed photovoltaics participate in frequency control is derived. The specific derivation process is:

[0012] The reactive power / voltage droop control function is a typical piecewise function, which can be expressed as:

[0013]

[0014]

[0015] Where: i represents the i-th distributed photovoltaic; , , as well as They are the saturation threshold lower limit, dead zone lower limit, dead zone upper limit, and saturation threshold upper limit of the reactive power / voltage droop control function respectively; Represents the voltage on the node connected to distributed photovoltaic i; and Respectively represent upward and downward reactive power / voltage droop control gains; and are the reactive power reference value and the maximum available reactive power corresponding to the voltage dead zone respectively; Represents the reactive control instruction of reactive voltage droop control output.

[0016] To prevent voltage oscillation, the upward and downward reactive power / voltage droop control gains are set and Set to:

[0017]

[0018] Where: is a scaling factor; Represents the reactive power-voltage sensitivity matrix of the distribution network The i-th diagonal element in .

[0019] Assume that the reactive power / voltage droop control parameters of all distributed photovoltaics are and All meet ( and Represent the maximum and minimum allowable voltage limits respectively), then for any initial voltage When all the distributed photovoltaic power generation reserves are used for frequency regulation, the steady-state voltage of the system It can be obtained by solving the following equation:

[0020]

[0021] Where: Represents the reactive power / voltage droop control function tuple vector of all distributed photovoltaics; Represents the vector of all distributed photovoltaic upward reserves; is the active power-voltage sensitivity matrix of the distribution network.

[0022] The above equations are difficult to solve directly. Without loss of generality, the reactive power / voltage droop controllers of all distributed photovoltaics can be forced to operate in the linear segment in steady state to achieve effective voltage regulation. In this way, the above equations can be simplified to:

[0023]

[0024] Where: is the auxiliary matrix of the upper bound of the critical voltage; The diagonal element is The diagonal matrix of ; represents the identity matrix; The droop gain Vector composed of.

[0025] According to the Gale disk theorem, as long as the scaling factor satisfy , then the matrix Reversible. Represents the voltage-reactive sensitivity matrix of the distribution network The i-th row and j-th column element of Represents the reactive power-voltage sensitivity matrix of the distribution network The jth diagonal element in . Thus, the steady-state voltage It can be expressed analytically as:

[0026]

[0027] To ensure that the voltage of the distribution network does not exceed the limit after the distributed photovoltaic participates in the frequency regulation, the steady-state voltage must meet ( Indicates that all elements are at the maximum allowable voltage limit The column vector of the critical voltage is obtained from this :

[0028]

[0029] Similarly, when all the distributed photovoltaic power is used for frequency regulation, the critical voltage lower limit to maintain the distribution network voltage is It can be expressed as:

[0030]

[0031] Where: is the auxiliary matrix of the lower bound of the critical voltage; The diagonal element is The diagonal matrix of ; The droop gain The vector composed of Indicates that all elements are at the minimum allowable voltage Column vector of .

[0032] Based on the above derivation, the initial voltage of the distribution network is calculated by Adjust to the range formed by the upper and lower limits of the critical voltage, that is, , which can ensure that the voltage will not exceed the limit when distributed photovoltaics participate in system frequency modulation.

[0033] Furthermore, in step 2), the distributed photovoltaic local droop control parameter optimization model can be expressed as:

[0034]

[0035]

[0036]

[0037]

[0038]

[0039]

[0040]

[0041]

[0042]

[0043]

[0044]

[0045]

[0046] Where: For the The objective function of the optimization time period; express norm; , , as well as are vectors, representing the distributed photovoltaic Upward reserve, downward reserve, output of active power and reactive power output; and Respectively expressed in Predicted at any time Active and reactive loads at all times; , and Respectively The apparent power, active power and reactive power injected into the distribution network nodes at all times; express The measured value of node voltage at the moment; Indicated in Predicted at any time Node voltage at time instant; The diagonal element is The diagonal matrix of ; represents the matrix remaining after removing the rows and columns related to the reference node from the admittance matrix; represents the vector consisting of the columns of the admittance matrix corresponding to the reference node and excluding the first element; express The reference voltage at the moment; represents the conjugate operation; and They are the upper and lower voltage limits respectively; and Respectively Active and reactive power adjustment of distributed photovoltaic i at time; and They represent the local active power / frequency and reactive power / voltage droop control functions of distributed photovoltaic i respectively; express The voltage on the node connected to the i-th distributed photovoltaic measured at the moment; and They represent the upward and downward frequency droop control gains of distributed photovoltaic i respectively; , , as well as They are the saturation threshold lower limit, dead zone lower limit, dead zone upper limit, and saturation threshold upper limit of the active power / frequency droop control function respectively; and They represent the upward and downward reserve powers of distributed photovoltaic i respectively; , , as well as They are the saturation threshold lower limit, dead zone lower limit, dead zone upper limit, and saturation threshold upper limit of the reactive power / voltage droop control function respectively; and are the reactive power reference value and the maximum available reactive power corresponding to the voltage dead zone respectively; for The local frequency at the moment; Indicates that distributed photovoltaic The active power output at the moment is The i-th element of ; Indicates that distributed photovoltaic The maximum available active power forecast value at the moment; and They respectively represent the maximum upward and downward active reserve coefficients allowed by distributed photovoltaics; and They are respectively the upward and downward aggregated active power / frequency droop control gains specified by the transmission system operator; , , and They respectively represent the saturation threshold lower limit, dead zone lower limit, dead zone upper limit, and saturation threshold upper limit of the active power / frequency droop control function given by the transmission system operator; represents the installed capacity of distributed photovoltaic i; Indicates the actual output reactive power of distributed photovoltaics, The i-th element of ; is the linearization coefficient, which is used to express the relationship between the power injection change of each node in the distribution network and the power adjustment of the substation outlet; Indicates the number of distributed photovoltaics; A collection of node indexes representing distributed photovoltaics; Represents the control time domain.

[0047] Furthermore, in step 3), the linearized distribution network power flow model is obtained by linearizing the distribution network power flow model, and the specific process is as follows:

[0048] The nonlinear distribution network power flow model is expressed as:

[0049]

[0050] Where: Indicates the power injected into each node of the distribution network; and denote the active and reactive power injection of the node respectively; Indicates that the diagonal element is the voltage of the distribution network node The diagonal matrix of ; Represents the reference voltage, which is 1.0 pu.

[0051] Assume that the voltage corresponding to the steady-state operating point of the system is , and there is a small voltage disturbance , then Substituting into the above formula, expanding the formula and ignoring the second-order terms, and rearranging the real and imaginary parts, the linearized power flow model can be obtained, which is specifically expressed as:

[0052]

[0053] Where: and Respectively represent The real and imaginary parts of , , , , and are all constant coefficient matrices or vectors, defined as:

[0054]

[0055] Where: Denotes constructing a diagonal matrix.

[0056] In addition, since the phase angle of node voltage in the distribution network does not change much, the voltage longitudinal component Much smaller than the transverse component Therefore, the voltage longitudinal component can be further ignored and the distribution network voltage change can be calculated using the following formula:

[0057]

[0058] Where: and They represent the changes in active power and reactive power injected into the distribution network nodes respectively; and express The active and reactive power injected into the distribution network node at every moment.

[0059] On this basis, the distribution network node injects active power variation The power change at the substation outlet It can be approximately expressed as the following linear relationship:

[0060]

[0061]

[0062] Where: is a constant coefficient matrix; Indicates the reference voltage amplitude; Indicates the reference voltage phase angle; and are the conductance and susceptance of the line connected to the substation, respectively; and The matrices are and The first line in .

[0063] Furthermore, in step 3), the linearized distributed photovoltaic reactive power / voltage droop control function is obtained by linearizing the distributed photovoltaic reactive power / voltage droop control function. The linearized distributed photovoltaic reactive power / voltage droop control function is:

[0064]

[0065]

[0066]

[0067]

[0068]

[0069]

[0070]

[0071]

[0072] Where: i represents the i-th distributed photovoltaic; , , as well as They are the saturation threshold lower limit, dead zone lower limit, dead zone upper limit, and saturation threshold upper limit of the reactive power / voltage droop control function respectively; is a 0-1 variable indicating whether the nth area of ​​reactive power / voltage droop control is activated. When it is 1, it means that the nth area of ​​reactive power / voltage droop control is activated; represents the measured voltage on the node connected to the i-th distributed photovoltaic; is a large constant ( ); is a very small constant ( ), to prevent numerical problems; is an auxiliary vector, indicating the corresponding reactive power reference command when different areas of reactive power / voltage droop control are activated; and are the reactive power reference value and the maximum available reactive power corresponding to the voltage dead zone respectively; Defined as , represents the reactive power reference command actually output by the reactive power / voltage droop controller, represents the Hadamard product; Represents a vector of 0-1 variables related to the five linear regions of reactive power / voltage droop control; and Represents vectors and The nth element in ; and Indicates the upper and lower limits of the voltage saturation threshold parameter. As mentioned above, in order to prevent voltage oscillation, the reactive power / voltage droop control gain and All are set to , so and All are linear terms.

[0073] Furthermore, in step 3), the linearized inverter capacity constraint is specifically obtained by linearizing the secondary capacity constraint of the distributed photovoltaic inverter, and the specific method is:

[0074] Introducing auxiliary angles , the inverter capacity constraint is expressed as , and linearize the inverter capacity constraint:

[0075]

[0076]

[0077]

[0078] Where: Indicates the number of linearization segments; 0-1 variable Used to indicate the activated area; express ,in for .

[0079] Furthermore, in step 3), the linearized objective function is specifically obtained by linearizing the objective function, and the linearized objective function is:

[0080]

[0081]

[0082] Where: Represents a unit vector; vector ; Represents the auxiliary vector used for objective function transformation; is the objective function after transformation.

[0083] Furthermore, in step 4), based on the derived critical voltage boundary, the voltage constraint of the mixed integer linear optimization model of the distributed photovoltaic local droop control parameters is reconstructed, specifically:

[0084]

[0085] Where: Indicated in Predicted at any time The node voltage at the moment, and express Moment based on The upper and lower critical voltage boundaries are calculated from the moment prediction values.

[0086] In the droop control parameter optimization phase, the distribution network voltage is adjusted to the range To prevent the distribution network voltage from exceeding the limit due to the control of distributed photovoltaic participation in frequency.

[0087] Furthermore, in step 4), the distributed photovoltaic local droop control parameter optimization model is solved by using a solver, and the distributed photovoltaic local droop control parameters are configured based on the solution results. The distributed photovoltaic quickly changes its output power according to local measurement and droop control to achieve voltage and frequency coordination support for distributed photovoltaics, specifically:

[0088] The mixed integer linear programming model with tight voltage constraints is solved by using solvers such as Gurobi, and the optimized distributed photovoltaic active / frequency and reactive / voltage droop control parameters are obtained and sent to each distributed photovoltaic. Based on the local voltage and frequency measurement values, each distributed photovoltaic adjusts its active and reactive power output in real time according to the configured active / frequency and reactive / voltage droop control parameters, so as to participate in the local voltage regulation of the distribution network and the global frequency control of the system at the same time.

[0089] The beneficial results of the present invention are as follows: in view of the problem that large-scale distributed photovoltaics participate in distribution network voltage regulation and system frequency control at the same time, a distributed photovoltaic active / frequency and reactive / voltage droop control parameter optimization model based on model predictive control is proposed. The model takes into account the distributed photovoltaic local droop control logic and operation constraints, and optimizes the distributed photovoltaic local voltage and frequency droop control parameters with the goal of minimizing the distributed photovoltaic active reserve and reactive output; by linearizing the distribution network flow constraints, the reactive / voltage droop control function is modeled using the large M method, the inverter secondary capacity constraints are linearized in combination with the piecewise linearization technology, and the absolute value type objective function is converted into a linear objective function, which greatly improves the model solution efficiency. It can be applied online. By analyzing the coupling relationship between the active / frequency and reactive / voltage droop control loops, the critical voltage boundary is derived to accurately characterize the maximum voltage regulation capability of distributed photovoltaics when participating in frequency control. Based on the derived critical voltage boundary, the voltage constraint of the droop control parameter optimization model is reconstructed to adjust the distribution network voltage to a reasonable range, effectively avoiding the distribution network voltage over-limit problem caused by the participation of distributed photovoltaics in frequency control. By solving the droop control parameter optimization model and configuring the distributed photovoltaic droop control parameters, the distributed photovoltaics respond to the system voltage and frequency deviations in real time, improving the system frequency response characteristics while ensuring the voltage safety of the distribution network, and comprehensively balancing the optimality and response speed of the distributed photovoltaic voltage and frequency support control. BRIEF DESCRIPTION OF THE DRAWINGS

[0090] Figure 1 A large-scale distributed photovoltaic voltage-frequency coordination support control process according to an embodiment of the present invention;

[0091] Figure 2 The control effect comparison between the method of the present invention and the existing control scheme on the IEEE 33-node test system, where (a) is the frequency control effect comparison and (b) is the voltage control effect comparison. DETAILED DESCRIPTION

[0092] The present invention is further described below in conjunction with the accompanying drawings and embodiments. The embodiment of the present invention provides a large-scale distributed photovoltaic voltage-frequency coordination support control method process as shown in FIG. Figure 1 shown.

[0093] (1) First, the basic parameters such as network topology, line impedance and distributed photovoltaic capacity are initialized, the voltage sensitivity coefficient and power flow linearization coefficient of the distribution network are calculated, the coupling relationship between the active / frequency and reactive / voltage droop control loops is analyzed, and the critical voltage boundary is derived.

[0094] The critical voltage boundary is specifically:

[0095]

[0096]

[0097]

[0098]

[0099] Where: and Indicates the upper and lower limits of critical voltage; and Respectively represent the maximum and minimum voltage allowed; represents the voltage-active power sensitivity matrix of the distribution network; and They represent the vectors composed of the upward and downward voltage droop control gains of distributed photovoltaics, and their elements are and ; The diagonal element is The diagonal matrix of ; represents the identity matrix; and are the auxiliary matrices of the upper and lower bounds of the critical voltage respectively; the parameters Must meet ; and Represent the voltage-reactive sensitivity matrix of the distribution network The i-th and j-th diagonal elements of ; Represents the voltage-reactive sensitivity matrix of the distribution network The element in the i-th row and j-th column of .

[0100] (2) Based on model predictive control theory, distributed photovoltaics quickly change their output power according to local measurement and droop control, with the goal of minimizing the active reserve and reactive output of distributed photovoltaics, and constructing a distributed photovoltaic local droop control parameter optimization model.

[0101] (3) By linearizing the distribution network flow model, distributed photovoltaic reactive power / voltage droop control function, inverter capacity constraint and objective function, the distributed photovoltaic local droop control parameter optimization model is transformed into a mixed integer linear optimization model.

[0102] The linearized distribution network power flow model is:

[0103]

[0104]

[0105] Where: Indicates the voltage change caused by the change of node injection power; and They represent the changes in active power and reactive power injected into the distribution network nodes respectively; and denote the active and reactive power injection of the node respectively; and Represents the active and reactive power injected into the distribution network node in steady state; Indicates the output power change of the substation connected to the distribution network; , and Are all constant coefficient matrices, defined as:

[0106]

[0107]

[0108] Where: Indicates the construction of a diagonal matrix; and Respectively represent the real part and imaginary part; represents the matrix remaining after removing the rows and columns related to the reference node from the admittance matrix; represents the vector consisting of the columns of the admittance matrix corresponding to the reference node and excluding the first element; Indicates the reference voltage; represents the conjugate operation; Indicates the voltage corresponding to the steady-state operating point of the system; Indicates the reference voltage amplitude; Indicates the reference voltage phase angle; and are the conductance and susceptance of the line connected to the substation, respectively; and The matrices are and The first row in is a constant coefficient matrix and can be calculated by the following formula:

[0109]

[0110] The linearized distributed photovoltaic reactive power / voltage droop control function is:

[0111]

[0112]

[0113]

[0114]

[0115]

[0116]

[0117]

[0118]

[0119] Where: i represents the i-th distributed photovoltaic; , , as well as They are the saturation threshold lower limit, dead zone lower limit, dead zone upper limit, and saturation threshold upper limit of the reactive power / voltage droop control function respectively; and They represent the upward and downward voltage droop control gains of the i-th distributed photovoltaic respectively; is a 0-1 variable indicating whether the nth area of ​​reactive power / voltage droop control is activated; represents the measured voltage on the node connected to the i-th distributed photovoltaic; and is a constant; is an auxiliary vector, which indicates the corresponding reactive power reference command when different areas of reactive power / voltage droop control are activated; and are the reactive power reference value and the maximum available reactive power corresponding to the voltage dead zone respectively; Defined as , represents the reactive power reference command actually output by the reactive power / voltage droop controller, represents the Hadamard product; Represents a vector of 0-1 variables related to the five linear regions of reactive power / voltage droop control; and Represents vectors and The nth element in ; and Indicates the upper and lower limits corresponding to the voltage saturation threshold parameter.

[0120] The method for obtaining the inverter capacity constraint after linearization is:

[0121] Introducing auxiliary angles , the inverter capacity constraint is expressed as ; and linearize the inverter capacity constraint:

[0122]

[0123]

[0124]

[0125] Where: Indicates the number of linearization segments; 0-1 variable Used to indicate the activated area; = ,in, , for .

[0126] The linearized objective function is:

[0127]

[0128]

[0129] Where: Represents a unit vector; vector ; Represents the auxiliary vector used for objective function transformation; is the objective function after transformation.

[0130] (4) The voltage constraint of the mixed integer linear optimization model of the local droop control parameters of distributed photovoltaics is reconstructed based on the critical voltage boundary. The mixed integer linear optimization model of the local droop control parameters of distributed photovoltaics is solved by a solver and the local droop control parameters of distributed photovoltaics are configured based on the solution results. Distributed photovoltaics can quickly change their output power according to local measurement and droop control to achieve voltage and frequency coordinated support.

[0131] The voltage constraint of the mixed integer linear optimization model of the distributed photovoltaic local droop control parameters is reconstructed based on the critical voltage boundary, specifically:

[0132]

[0133] Where: Indicated in Predicted at any time The node voltage at the moment, and express Moment based on The upper and lower critical voltage boundaries are calculated from the moment prediction values.

[0134] Three methods, namely fixed parameter droop control, uncoordinated droop control and coordinated active and reactive control, are selected for comparison. The voltage safety range is set to [0.95, 1.05] pu, and the active tracking error is defined as the difference between the regulated power at the substation connected to the distribution network and the main grid and the active reference value given by the transmission system operator to reflect the control effect of different methods.

[0135] Table 1 compares the voltage and frequency control effects of the method of the present invention and three control methods: fixed parameter droop control, uncoordinated droop control, and coordinated active and reactive power control.

[0136] It can be seen from the table that compared with other methods, the method of the present invention can completely track the given active reference value, the tracking error is 0, and the voltage can be adjusted to a safe range. Although the uncoordinated droop control can also adjust the voltage to a safe range, the reactive power compensation amount is 0.5806 MVar more than the method of the present invention. The coordinated active and reactive control scheme cannot accurately track the given active reference value, and the tracking error is as high as 0.3254 MW. The fixed parameter droop control scheme causes the voltage to exceed the limit due to insufficient reactive compensation. In summary, the method of the present invention performs well in both voltage regulation and frequency control tasks, and the control effect is better than that of the traditional method.

[0137] Table 1 Comparison of voltage and frequency control effects of different control methods

[0138] method Maximum voltage (pu) Maximum reactive power compensation (MVar) Maximum active tracking error (MW) Fixed parameter droop control 1.0612 0.2964 0.0264 Coordinated active and reactive power control 1.0501 1.1809 0.3254 Uncoordinated droop control 1.0316 1.1610 0.0242 Method of the present invention 1.0460 0.6524 0

[0139] Figure 2 The dynamic performance of different control methods is demonstrated. The frequency ( Figure 2 (a)) and voltage control results ( Figure 2Compared with (b) in Figure 2, the proposed method has better dynamic response characteristics. Especially in terms of frequency support, compared with the coordinated active and reactive power control scheme, the proposed method increases the lowest frequency point by 0.0469 Hz and reduces the steady-state frequency deviation by 0.0123 Hz on average.

[0140] The above describes the specific implementation methods of the present invention in conjunction with the accompanying drawings, which is not intended to limit the scope of protection of the present invention. All equivalent models or equivalent algorithm processes made using the contents of the present invention specification and drawings, directly or indirectly applied to other related technical fields, are within the scope of patent protection of the present invention.

Claims

1. A large-scale distributed photovoltaic voltage-frequency coordinated support control method, characterized in that: The following steps are involved: 1) By analyzing the coupling relationship between the active power / frequency and reactive power / voltage droop control loops, the critical voltage boundary that characterizes the maximum voltage regulation capability of distributed photovoltaics is derived; 2) Based on model predictive control theory, the distributed photovoltaic reactive power / voltage and active power / frequency droop control functions are considered. With the goal of minimizing the active reserve and reactive output of distributed photovoltaics, a distributed photovoltaic local droop control parameter optimization model is constructed; 3) By linearizing the distributed photovoltaic local droop control parameter optimization model, a distributed photovoltaic local droop control parameter mixed integer linear optimization model is obtained, wherein the distributed photovoltaic local droop control parameter mixed integer linear optimization model specifically includes a linearized distribution network power flow model, a linearized distributed photovoltaic reactive power / voltage droop control function, a linearized inverter capacity constraint, and a linearized objective function; 4) reconstructing the voltage constraint of the distributed photovoltaic local droop control parameter mixed integer linear optimization model based on the critical voltage boundary, solving the distributed photovoltaic local droop control parameter mixed integer linear optimization model by using a solver, configuring the distributed photovoltaic local droop control parameters based on the solution results, and the distributed photovoltaic quickly changes its output power according to local measurement and droop control to achieve voltage and frequency coordination support; In step 1), the critical voltage boundary is: Where: and Indicates the upper and lower limits of the critical voltage; V max and V min Respectively represent the maximum and minimum voltage allowed; represents the voltage-active power sensitivity matrix of the distribution network; k vu and k vl They represent the vectors composed of the upward and downward voltage droop control gains of distributed photovoltaics, and their elements are and Λ(k vu ) indicates that the diagonal element is k vu The diagonal matrix of ; represents the identity matrix; Γ u and Γ l are the auxiliary matrices for the upper and lower bounds of the critical voltage respectively; the parameter γ must satisfy and Represent the voltage-reactive sensitivity matrix of the distribution network The i-th and j-th diagonal elements of ; Represents the voltage-reactive sensitivity matrix of the distribution network The element in the i-th row and j-th column of ; To prevent voltage oscillation, the upward and downward reactive power / voltage droop control gains are set and Set to: Where: γ is a scaling factor; Represents the reactive power-voltage sensitivity matrix of the distribution network The i-th diagonal element in ; The distributed photovoltaic local droop control parameter optimization model is specifically: s(t+h|t)=p(t+h|t)+jq(t+h|t), p(t+h|t)=P pv (t+h|t)-P L (t+h|t),q(t+h|t)=Q pv (t+h|t)-Q L (t+h|t), V min ≤V(t+h|t)≤V max , Where: is the objective function of the hth optimization period; ||·||1 represents the l-1 norm; P pv,ru (t+h|t), P pv,rd (t+h|t), P pv (t+h|t) and Q pv (t+h|t) are all vectors, representing the upward reserve, downward reserve, output active power and reactive power output of distributed photovoltaic at time t+h respectively; P L (t+h|t) and Q L (t+h|t) respectively represent the active and reactive loads at time t+h predicted at time t; s(t+h|t), p(t+h|t) and q(t+h|t) respectively represent the apparent power, active power and reactive power injected into the distribution network node at time t+h; V(t|t) represents the measured value of the node voltage at time t; V(t+h|t) represents the node voltage at time t+h predicted at time t; Λ(V(t+h|t)) represents the diagonal matrix with diagonal elements V(t+h|t); Y represents the matrix remaining after removing the rows and columns related to the reference node from the admittance matrix; y0 represents the vector consisting of the columns in the admittance matrix corresponding to the reference node and not containing the first element; represents the reference voltage at time t; V represents the conjugate operation; max and V min are the maximum and minimum allowable voltages respectively; and They represent the active and reactive power adjustment of distributed photovoltaic i at time t respectively; and Respectively represent the local active power / frequency and reactive power / voltage droop control functions of distributed photovoltaic i; V i,t represents the voltage on the node connected to the i-th distributed photovoltaic measured at time t; and They represent the upward and downward frequency droop control gains of distributed photovoltaic i respectively; as well as They are the saturation threshold lower limit, dead zone lower limit, dead zone upper limit, and saturation threshold upper limit of the active power / frequency droop control function respectively; and The vector P pv,ru (t+h|t) and P pv,rd The i-th element in (t+h|t); as well as They are the saturation threshold lower limit, dead zone lower limit, dead zone upper limit, and saturation threshold upper limit of the reactive power / voltage droop control function respectively; and are the reactive power reference value and the maximum available reactive power corresponding to the voltage dead zone respectively; f t is the local frequency at time t; represents the active power output of distributed photovoltaic i at time t, which is P pv The i-th element of (t+h|t); represents the predicted value of the maximum available active power of distributed photovoltaic i at time t; and They respectively represent the maximum upward and downward active reserve coefficients allowed by distributed photovoltaics; and They are respectively the upward and downward aggregated active power / frequency droop control gains specified by the transmission system operator; and They respectively represent the saturation threshold lower limit, dead zone lower limit, dead zone upper limit, and saturation threshold upper limit of the active power / frequency droop control function given by the transmission system operator; represents the installed capacity of distributed photovoltaic i; Indicates the actual output reactive power of distributed photovoltaics, which is Q pv The i-th element of (t+h|t); ψ i is the linearization coefficient, which is used to express the linear relationship between the power injection change of each node in the distribution network and the power adjustment of the substation outlet; N pv represents the number of distributed photovoltaics, Represents the set of node indexes where distributed photovoltaics are located; represents the control time domain; In step 3), the linearized distribution network power flow model is: ΔV≈H 11 Δp+H 12 Δq,Δp=p-p ss ,Δq=q-q ss , Δp d =ΨΔp, Where: ΔV represents the voltage change caused by the change of node injection power; Δp and Δq represent the changes of active and reactive power injected into the distribution network node respectively; p and q represent the active and reactive power injection of the node respectively; p ss and q ss Indicates the active and reactive power injected into the distribution network node in steady state; Δp d Indicates the change in power at the substation outlet; H 11 , H 12 and Ψ are both constant coefficient matrices, defined as: Where: Λ(·) represents the construction of a diagonal matrix; and represents the real part and the imaginary part respectively; Y represents the matrix remaining after removing the rows and columns related to the reference node in the admittance matrix; y0 represents the vector consisting of the columns corresponding to the reference node and excluding the first element in the admittance matrix; V0 represents the reference voltage; V represents the conjugate operation; ss Indicates the voltage corresponding to the steady-state operating point of the system; |V0| indicates the reference voltage amplitude; θ0 represents the reference voltage phase angle; g 01 and b 01 are the conductance and susceptance of the line connected to the substation, respectively; and The matrix H 11 and H 21 The first row in 21 is a constant coefficient matrix, calculated using the following formula: In step 4), the voltage constraint of the mixed integer linear optimization model of the distributed photovoltaic local droop control parameters is reconstructed based on the critical voltage boundary, specifically: Where: V(t+h|t) represents the node voltage at time t+h predicted at time t, and Represents the upper and lower critical voltage boundaries calculated at time t based on the predicted value at time t+h.

2. A large-scale distributed photovoltaic voltage-frequency coordinated support control method according to claim 1, characterized in that: In step 3), the linearized distributed photovoltaic reactive power / voltage droop control function is: Where: i represents the i-th distributed photovoltaic; as well as They are the saturation threshold lower limit, dead zone lower limit, dead zone upper limit, and saturation threshold upper limit of the reactive power / voltage droop control function respectively; and They represent the upward and downward voltage droop control gains of the i-th distributed photovoltaic respectively; V is a 0-1 variable indicating whether the nth area of ​​reactive power / voltage droop control is activated; i,t represents the measured voltage on the node connected to the i-th distributed photovoltaic; M and ε are constants; is an auxiliary vector, which indicates the corresponding reactive power reference command when different areas of reactive power / voltage droop control are activated; and are the reactive power reference value and the maximum available reactive power corresponding to the voltage dead zone respectively; Defined as It represents the reactive power reference command actually output by the reactive power / voltage droop controller, ⊙ represents the Hadamard product; Represents a vector of 0-1 variables related to the five linear regions of reactive power / voltage droop control; and Represents vectors and The nth element in ; and Indicates the upper and lower limits corresponding to the voltage saturation threshold parameter.

3. A large-scale distributed photovoltaic voltage-frequency coordinated support control method according to claim 1, characterized in that: In step 3), the method for obtaining the linearized inverter capacity constraint is: Introduce auxiliary angle θ t , the inverter capacity constraint is expressed as (θ t ∈[0,π / 2]); and linearize the inverter capacity constraint: β i,j,t ≤θ i,j+1,t z i,j,t ,β i,j,t ≥θ i,j,t z i,j,t , β i,j,t ≥0, Where: N seg Indicates the number of linearization segments; 0-1 variable z i,j,t Used to indicate the activated area; θ i,j,t = jΔθ, where j = 0, …, N seg -1, and Δθ is π / (2N seg ).

4. A large-scale distributed photovoltaic voltage-frequency coordinated support control method according to claim 1, characterized in that: In step 3), the linearized objective function is specifically: u(t+h|t)≤U(t+h|t), -u(t+h|t)≤U(t+h|t), Where: I represents the unit vector; vector u(t+h|t)=[(P pv,ru ) T ,(P pv,rd ) T ,(Q pv ) T ] T ; U(t+h|t) represents the auxiliary vector used for objective function transformation; is the objective function after transformation.

5. A large-scale distributed photovoltaic voltage-frequency coordinated support control method according to claim 1, characterized in that: In step 4), the distributed photovoltaic local droop control parameters are configured based on the solution results to achieve voltage and frequency support for distributed photovoltaics, specifically: based on the solution results, the active / frequency and reactive / voltage droop control parameters of each distributed photovoltaic are configured; each distributed photovoltaic is based on the local voltage and frequency measurement values, according to the configured active / frequency and reactive / voltage droop control parameters, and adjusts its active and reactive power output in real time to participate in the local voltage regulation of the distribution network and the global frequency control of the system at the same time.

6. A computer-readable storage medium having computer instructions stored thereon, characterized in that: The computer instructions are used to enable a computer to execute the steps of the method according to any one of claims 1 to 5.

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