Active frequency coordination control method and device for network construction type power distribution network

Abstract

The invention discloses an active frequency coordination control method and device for a network construction type power distribution network. The method comprises the following steps: determining a multi-inverter aggregation model based on grid-connected inverters in a network construction type power distribution network; determining an active output range of each grid-connected inverter based on a multi-inverter aggregation model; based on the active output range of each grid-connected inverter, constructing an active power control strategy model by taking the benefit maximization of the grid-connected inverter as a target; and optimizing the active power control strategy model, carrying out iteration until convergence, giving an active power control strategy of the grid-connected inverter, and carrying out active frequency coordination control on the network construction type power distribution network. According to the invention, all grid-connected inverters can be allowed to participate in frequency adjustment of the power distribution network.

Description

Technical Field

[0001] The present invention belongs to the technical field of power grid frequency control, and in particular relates to a method and device for coordinated control of active frequency of a grid-type distribution network. Background Art

[0002] The high proportion of renewable energy connected to the grid is becoming an inevitable trajectory and significant feature of the development of future power systems. In high-renewable energy systems, as renewable energy is connected to the grid through power electronic inverters, the grid structure will change. With the increasing popularity of inverters in power systems, many challenges have been raised to power systems in terms of voltage and frequency regulation. The grid connection mode and control strategy of the inverter not only determine the safe and stable operation of the inverter, but also have an important impact on the overall stability of the power grid. The control methods of the inverter can be divided into two types: grid-forming (GFM) inverter and grid-following (GFL) inverter. The GFM inverter adopts a power synchronization strategy similar to that of a synchronous generator, which can provide frequency and voltage support.

[0003] Research on cooperative control strategies for dual inverters in microgrids is booming. A distributed control scheme for voltage regulation based on range consistency is proposed, which uses power coupling and extended state observers to coordinate the different internal dynamics and control structures of the inverters. By designing the same distributed controller, the voltage of different inverters can be regulated. A distributed secondary control scheme based on the leader-follower consensus framework is also proposed to achieve accurate power sharing between GFM and GFL inverters. In this scheme, GFM acts as a leader to directly control frequency and voltage, and GFL acts as a follower to measure frequency and voltage for power modulation. This coordinated control helps to reasonably allocate power among all inverters and ensure frequency / voltage recovery after system disturbances. Consensus control is also the most widely used cooperative control strategy for GFM and GFL inverters. In view of the problem that droop control under nonlinear loads will cause steady-state voltage / frequency deviation, a unified droop-free distributed secondary control framework for GFM and GFL inverters is proposed. The goal of this scheme is to achieve zero deviation in frequency and voltage, and to achieve proportional sharing of active and reactive power among all inverters, and to design the control link according to the partial derivative of the objective function. However, these methods do not adequately consider the situation where a large number of inverters are connected to the distribution network, and lack the determination of approximate optimal control strategies for a large number of inverters in the distribution network.

[0004] Therefore, how to provide a method for determining control strategies for a large number of inverters in a distribution network is a technical problem that needs to be solved urgently in the art. Summary of the invention

[0005] In view of the defects existing in the above-mentioned prior art, the present invention provides a method and device for coordinated control of active frequency of a grid-type distribution network, which can allow all grid-connected inverters to participate in frequency regulation of the distribution network.

[0006] In a first aspect, the present invention provides a method for coordinated control of active frequency of a grid-type distribution network, comprising:

[0007] Based on the grid-connected inverters in the grid-type distribution network, a multi-inverter aggregation model is determined;

[0008] Based on the multi-inverter aggregation model, determine the active output range of each grid-connected inverter;

[0009] Based on the active output range of each grid-connected inverter, an active power control strategy model is constructed with the goal of maximizing the revenue of the grid-connected inverter;

[0010] The active power control strategy model is optimized and iterated until convergence. The active power control strategy of the grid-connected inverter is given to carry out active frequency coordinated control of the grid-connected distribution network.

[0011] Furthermore, based on the grid-connected inverters in the grid-type distribution network, a multi-inverter aggregation model is determined, including:

[0012] Based on the grid-connected inverter in the grid-type distribution network, a grid-connected inverter model is constructed;

[0013] Based on the voltage characteristics of multiple grid-connected inverters in parallel in a grid-connected distribution network and combined with the grid-connected inverter model, a multi-inverter aggregation model is constructed.

[0014] Furthermore, the grid-connected inverter model satisfies the following relationship:

[0015] ω i =ω i,ref -m p,i (P i -P i,ref )

[0016] V i =V i,ref -m p,i (Q i -Q i,ref )

[0017] In the formula, ω i and V i are the frequency and voltage amplitude of the i-th grid-connected inverter, ω i,ref ,V i,ref They represent the rated frequency and rated voltage of the i-th grid-connected inverter, P i,ref , P iRepresent the active power setting value and actual active power output of the i-th grid-connected inverter, Q i,ref , Q i Represent the reactive power setting value and the actual reactive power output of the i-th grid-connected inverter, m p,i and m q,i They represent the droop coefficients of active power-frequency and reactive power-voltage control of the i-th grid-connected inverter respectively;

[0018] The multi-inverter aggregation model satisfies the following relationship:

[0019]

[0020] Where P a is the actual output of the equivalent total active power of multiple grid-connected inverters in parallel, n is the number of grid-connected inverters in parallel, m is p,a It is the equivalent total droop coefficient of active power-frequency of multiple grid-connected inverters in parallel.

[0021] Furthermore, the active output range of each grid-connected inverter satisfies the following relationship:

[0022] P i,max =min((P i +ΔP i ), P N,i )

[0023] P i,min =max((P i -ΔP i ),0)

[0024]

[0025] Where P N,i is the rated active power of the i-th grid-connected inverter, P i,min and P i,max are the minimum and maximum active output of the ith grid-connected inverter, ΔP i It represents the maximum value of the active power fluctuation output by the ith grid-connected inverter within the maximum frequency fluctuation range allowed by the grid-connected distribution network, Δf max Indicates the maximum frequency fluctuation allowed in the grid-type distribution network.

[0026] Furthermore, based on the active output range of each grid-connected inverter, an active power control strategy model is constructed with the goal of maximizing the revenue of the grid-connected inverter, including:

[0027] Determine the supply price function of the distribution network and give the power supply revenue of the grid-connected inverter;

[0028] Determine the frequency regulation benefit of the grid-connected inverter according to the active power-frequency droop coefficient of the grid-connected inverter;

[0029] Determine the operating loss cost of the grid-connected inverter based on the actual active power output of the grid-connected inverter;

[0030] Based on the power supply income, frequency regulation income and operation loss cost of the grid-connected inverter, an active power control strategy model is constructed.

[0031] Furthermore, the supply price function of the distribution network is determined, including:

[0032] Determine the demand utility function based on the demand parameters of the grid-connected inverter;

[0033] Derivative the demand utility function and make it equal to zero to determine the relationship between demand price and demand power;

[0034] Based on the relationship between demand price and demand power, the supply price function is determined.

[0035] Furthermore, the active power control strategy model satisfies the following relationship:

[0036] P i * (P -i )=argmaxJ i (P i ,P -i ), P i ∈Y i

[0037]

[0038] Where P * i is the active power control strategy model, J i (P i ,P -i ) is the revenue of the grid-connected inverter, P i is the actual active power output of the i-th grid-connected inverter, P -i The active power supply for the grid-connected inverter, P -i =(P1,P2,...,P N ), Y i is the active output range of the i-th grid-connected inverter, ξ is the demand elasticity, D max represents the maximum required power, N is the total number of grid-connected inverters, χ is the price per unit droop coefficient, m p,i is the active power-frequency droop coefficient of the i-th grid-connected inverter, α i , β i and γ iare the power loss coefficients of the i-th grid-connected inverter.

[0039] Furthermore, the active power control strategy model is optimized and iterated until convergence, and the active power control strategy of the grid-connected inverter is given, including:

[0040] Determine the average field parameters based on the number of grid-connected inverters and the actual active power output;

[0041] Based on the mean field parameters, the active power control strategy model is optimized and adjusted, and the active power optimization control strategy model is given;

[0042] The active power optimization control strategy model is derived and equal to zero to determine the mapping model;

[0043] Constructing a control strategy iteration model for the grid-connected inverter based on the mapping model;

[0044] Initialize the actual active power output and iteration operator of the grid-connected inverter, iterate the control strategy iteration model of the grid-connected inverter until convergence, and give the active power control strategy of the grid-connected inverter.

[0045] Furthermore, the mapping model satisfies the following relationship:

[0046]

[0047] In the formula, is the mapping model, αi and βi are the power loss coefficients of the ith grid-connected inverter, ξ is the demand elasticity, D max represents the maximum required power, N is the total number of grid-connected inverters, z k is the mean field parameter of the kth iteration, P i,k is the actual active power output of the i-th grid-connected inverter in the k-th iteration;

[0048] The control strategy iteration model of the grid-connected inverter satisfies the following relationship:

[0049]

[0050] Where P i,k+1 is the actual active power output of the i-th grid-connected inverter in the k+1th iteration, λ k is the iteration operator of the kth iteration, λ k =λ / k, λ is the initial iteration operator, And k ∈(0,1).

[0051] In a second aspect, the present invention further provides a network-type distribution network active frequency coordination control device, which adopts the above-mentioned network-type distribution network active frequency coordination control method, including:

[0052] An aggregation model building module, which is used to determine a multi-inverter aggregation model based on grid-connected inverters in a grid-type distribution network;

[0053] An active output determination module, which is used to determine the active output range of each grid-connected inverter based on a multi-inverter aggregation model;

[0054] A strategy model building module, which is used to build an active power control strategy model based on the active output range of each grid-connected inverter and with the goal of maximizing the profit of the grid-connected inverter;

[0055] A control strategy determination module is used to optimize the active power control strategy model and iterate until convergence, and provide an active power control strategy for the grid-connected inverter;

[0056] The power grid coordination control module is used to coordinate the active frequency control of the grid-forming distribution network.

[0057] Furthermore, the aggregation model building module includes:

[0058] Based on the grid-connected inverter in the grid-type distribution network, a grid-connected inverter model is constructed;

[0059] Based on the voltage characteristics of multiple grid-connected inverters in parallel in a grid-connected distribution network and combined with the grid-connected inverter model, a multi-inverter aggregation model is constructed.

[0060] Furthermore, the strategy model building module includes:

[0061] Determine the supply price function of the distribution network and give the power supply revenue of the grid-connected inverter;

[0062] Determine the frequency regulation benefit of the grid-connected inverter according to the active power-frequency droop coefficient of the grid-connected inverter;

[0063] Determine the operating loss cost of the grid-connected inverter based on the actual active power output of the grid-connected inverter;

[0064] Based on the power supply income, frequency regulation income and operation loss cost of the grid-connected inverter, an active power control strategy model is constructed.

[0065] Furthermore, the strategy model building module also includes:

[0066] Determine the demand utility function based on the demand parameters of the grid-connected inverter;

[0067] Derivative the demand utility function and make it equal to zero to determine the relationship between demand price and demand power;

[0068] Based on the relationship between demand price and demand power, the supply price function is determined.

[0069] Furthermore, the control strategy determination module includes:

[0070] Determine the average field parameters based on the number of grid-connected inverters and the actual active power output;

[0071] Based on the mean field parameters, the active power control strategy model is optimized and adjusted, and the active power optimization control strategy model is given;

[0072] The active power optimization control strategy model is derived and equal to zero to determine the mapping model;

[0073] Constructing a control strategy iteration model for the grid-connected inverter based on the mapping model;

[0074] Initialize the actual active power output and iteration operator of the grid-connected inverter, iterate the control strategy iteration model of the grid-connected inverter until convergence, and give the active power control strategy of the grid-connected inverter.

[0075] The present invention provides a method and device for coordinated control of active frequency of a grid-type distribution network, which at least has the following beneficial effects:

[0076] (1) By constructing a multi-inverter aggregation model, combined with building a shared objective function, and continuously updating it during the iterative solution process, the inverters are finally balanced, which promotes the consistency between inverters. In addition, since there is no information exchange between inverters, the communication burden can be greatly reduced.

[0077] (2) Based on the mean field game theory, a competitive game environment is created for the inverters. The interaction between the inverters is approximated by the influence caused by the average inverter control strategy. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 A flow chart of a method for coordinated control of active frequency of a grid-type distribution network provided by the present invention;

[0079] Figure 2 A flowchart of determining a multi-inverter aggregation model provided by an embodiment of the present invention;

[0080] Figure 3 A flowchart of constructing an active power control strategy model provided by an embodiment of the present invention;

[0081] Figure 4 A flow chart of a function for determining a supply price provided for one embodiment of the present invention;

[0082] Figure 5 A flowchart of an active power control strategy provided in an embodiment of the present invention;

[0083] Figure 6 A schematic diagram of active power transmitted before and after disturbance of each branch provided by an embodiment of the present invention;

[0084] Figure 7 A schematic diagram of a transient output active power change of an inverter bus provided by an embodiment of the present invention;

[0085] Figure 8 A schematic diagram of frequency change provided by an embodiment of the present invention;

[0086] Fig. 9 A schematic diagram of a grid-type distribution network active frequency coordination control device provided by the present invention. DETAILED DESCRIPTION

[0087] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0088] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "said" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings, and "multiple" generally includes at least two.

[0089] It should also be noted that the term "includes", "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, so that a commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprising a ..." do not exclude the existence of other identical elements in the commodity or device including the elements.

[0090] like Figure 1 As shown, the present invention provides a method for coordinated control of active frequency of a grid-type distribution network, which may include:

[0091] Based on the grid-connected inverters in the grid-type distribution network, a multi-inverter aggregation model is determined;

[0092] Based on the multi-inverter aggregation model, determine the active output range of each grid-connected inverter;

[0093] Based on the active output range of each grid-connected inverter, an active power control strategy model is constructed with the goal of maximizing the revenue of the grid-connected inverter;

[0094] The active power control strategy model is optimized and iterated until convergence. The active power control strategy of the grid-connected inverter is given to carry out active frequency coordinated control of the grid-connected distribution network.

[0095] The present invention aggregates the grid-connected inverters in the grid-connected distribution network to form a multi-inverter aggregation model, then constructs an active power control strategy model, and performs optimization iterative solution to give the final active power control strategy of the grid-connected inverter, thereby completing the active power control of all grid-connected inverters in the grid-connected distribution network to achieve control and regulation of the active frequency of the grid-connected distribution network.

[0096] like Figure 2 As shown, based on the grid-connected inverters in the grid-type distribution network, a multi-inverter aggregation model is determined, which may include:

[0097] Based on the grid-connected inverter in the grid-type distribution network, a grid-connected inverter model is constructed;

[0098] Based on the voltage characteristics of multiple grid-connected inverters in parallel in a grid-connected distribution network and combined with the grid-connected inverter model, a multi-inverter aggregation model is constructed.

[0099] Among them, the grid-connected inverter model satisfies the following relationship:

[0100] ω i =ω i,ref -m p,i (P i -P i,ref )

[0101] V i =V i,ref -m p,i (Q i -Q i,ref )

[0102] In the formula, ω i and V i are the frequency and voltage amplitude of the i-th grid-connected inverter, ω i,ref ,V i,ref They represent the rated frequency and rated voltage of the i-th grid-connected inverter, P i,ref , P i Represent the active power setting value and actual active power output of the i-th grid-connected inverter, Q i,ref , Q i Represent the reactive power setting value and the actual reactive power output of the i-th grid-connected inverter, m p,i and m q,iThey represent the droop coefficients of active power-frequency and reactive power-voltage control of the i-th grid-connected inverter respectively;

[0103] Considering that multiple grid-connected inverters can be connected in parallel to the same common connection point (PCC), it is necessary to derive and construct an aggregation model of multiple inverters. Specifically, the voltage at the PCC of N parallel inverters is constant, and the current is the sum of the outputs of the N inverters. Active frequency control is used as a specific embodiment of the large-scale inverter collaborative control framework. In the collaborative control framework, two parameters of a single inverter are required, namely, the active output value P i and Pf (active power-frequency) droop control parameter m p,i Therefore, in the parameters of the aggregation model, only the changes of these two parameters are considered. In actual application scenarios, the multi-inverter aggregation model can satisfy the following relationship:

[0104]

[0105] Where P a is the actual output of the equivalent total active power of multiple grid-connected inverters in parallel, n is the number of grid-connected inverters in parallel, m is p,a It is the equivalent total droop coefficient of active power-frequency of multiple grid-connected inverters in parallel.

[0106] like Figure 3 As shown, after determining the active output range, an active power control strategy model is constructed based on the active output range of each grid-connected inverter and with the goal of maximizing the benefit of the grid-connected inverter, which may include:

[0107] Determine the supply price function of the distribution network and give the power supply revenue of the grid-connected inverter;

[0108] Determine the frequency regulation benefit of the grid-connected inverter according to the active power-frequency droop coefficient of the grid-connected inverter;

[0109] Determine the operating loss cost of the grid-connected inverter based on the actual active power output of the grid-connected inverter;

[0110] Based on the power supply income, frequency regulation income and operation loss cost of the grid-connected inverter, an active power control strategy model is constructed.

[0111] Among them, Figure 4 As shown, the supply price function of the distribution network can include:

[0112] Determining a demand utility function based on demand parameters of the grid-connected inverter;

[0113] Derivative the demand utility function and make it equal to zero to determine the relationship between demand price and demand power;

[0114] Based on the relationship between demand price and demand power, the supply price function is determined.

[0115] In the actual application scenario, the present invention introduces a group of participants N (N grid-connected inverters), and the control strategy P i , objective function J i , with the goal of achieving optimal control of the inverter active output, the mean field game function G = (N, {Y i} i∈N},{J i} i∈N ).

[0116] The control target of the mean field game control function is the active power P of inverter i i , the active output of the inverter is subject to integral constraints, while taking into account the frequency fluctuation range specified by the standard. i ∈Y i , where Y i =[P i,min ,P i,max ]. That is, the active output range of each grid-connected inverter satisfies the following relationship:

[0117] P i,max =min((P i +ΔP i ), P N,i )

[0118] P i,min =max((P i -ΔP i ),0)

[0119]

[0120] Where P N,i is the rated active power of the i-th grid-connected inverter, P i,min and P i,max are the minimum and maximum active output of the ith grid-connected inverter, ΔP i It represents the maximum value of the active power fluctuation output by the ith grid-connected inverter within the maximum frequency fluctuation range allowed by the grid-connected distribution network, Δf max Indicates the maximum frequency fluctuation allowed in the grid-type distribution network.

[0121] Objective function J i It aims to maximize the benefit of inverter i while meeting the power demand and various operating constraints. Therefore, the optimal active power control strategy of inverter i considering the frequency constraint, that is, the active power control strategy model, satisfies the following relationship:

[0122] P i * (P-i )=argmaxJ i (P i ,P -i ), P i ∈Y i

[0123]

[0124] Where P * i is the active power control strategy model, J i (P i ,P -i ) is the revenue of the grid-connected inverter, P i is the actual active power output of the i-th grid-connected inverter, P -i The active power supply for the grid-connected inverter, P -i =(P1,P2,...,P N ), Y i is the active output range of the i-th grid-connected inverter, ξ is the demand elasticity, D max represents the maximum required power, N is the total number of grid-connected inverters, χ is the price per unit droop coefficient, m p,i is the active power-frequency droop coefficient of the i-th grid-connected inverter, α i , β i and γ i are the power loss coefficients of the i-th grid-connected inverter.

[0125] The objective function J is represented by the power supply benefit, frequency regulation benefit and operation loss cost of the inverter. i Specifically,

[0126] Power supply income:

[0127] First, from the perspective of supply and demand equilibrium, the demand utility function is constructed, which can be expressed as:

[0128]

[0129] Where ξ is the demand elasticity. max Indicates the maximum demand. price represents the demand price in [$ / kW]. d is a constant.

[0130] The demand price is a continuous, convex, and differentiable function of demand. The optimal demand is the maximum value of the utility function U(D), which is obtained when the first-order derivative is equal to zero. The first-order derivative is made equal to 0 by taking the derivative of the demand utility function. Therefore, the relationship between the demand price and demand can be expressed as:

[0131] r price=ξD max -ξD

[0132] Assumptions: (1) There is no energy storage equipment, which means that the supply and demand of the electricity market must match. (2) The supply and demand prices of the electricity market are equal. Then the supply price function can be expressed as:

[0133]

[0134] Where P -i =(P1,P2,…,P i …,P N ).

[0135] From the supply price function, we can see that the market price reflects the control strategy of each inverter. Therefore, the gain of active power provided by the inverter (power supply benefit) can be expressed as:

[0136] H(P i ,P -i )=r price (P i ,P -i )×P i

[0137] In the formula, H(P i ,P -i ) is the power supply income of the i-th grid-connected inverter.

[0138] Frequency Regulation Gains

[0139] As traditional synchronous generators are gradually replaced by renewable energy generators, the problem of insufficient frequency response will become more serious in future power systems. To solve this problem, a market mechanism should be designed to alleviate the shortage of frequency regulation resources. Therefore, it is expected that each inverter will join the ancillary service market and provide frequency regulation services, and the revenue generated can be expressed as:

[0140]

[0141] Where χ is the droop coefficient per unit and the quoted unit is [$ / (Hz / kW)].

[0142] Operation loss

[0143] In addition, the inverter will generate power loss during operation. The operating loss cost of the inverter is:

[0144] L(P i )=α i P i 2 +β i P i +γ i

[0145] Where α, β and γ represent power loss coefficients, all of which are positive.

[0146] In summary, the inverter competition game objective function is defined as:

[0147] J(P i ,P -i )=H(P i ,P -i )+B(P i )-L(P i )

[0148] like Figure 5 As shown, the present invention optimizes the active power control strategy model and iterates until convergence to provide an active power control strategy for the grid-connected inverter, which may include:

[0149] Determine the mean field parameters based on the number of grid-connected inverters and the actual active power output;

[0150] Based on the mean field parameters, the active power control strategy model is optimized and adjusted, and the active power optimization control strategy model is given;

[0151] The active power optimization control strategy model is derived and equal to zero to determine the mapping model;

[0152] Constructing a control strategy iteration model for the grid-connected inverter based on the mapping model;

[0153] Initialize the actual active power output and iteration operator of the grid-connected inverter, iterate the control strategy iteration model of the grid-connected inverter until convergence, and give the active power control strategy of the grid-connected inverter.

[0154] The present invention will i (P i ,P -i ) function is called an N-person game. The mean field game has the ability to control the number of inverters to N→∞. In order to apply the grid-connected inverter scenario modeling of the present invention to the mean field game, it is necessary that the individuals are indistinguishable, which means that all grid-connected inverters in the same population have similar power control capabilities and are mathematically identical.

[0155] The mean field can be expressed as:

[0156]

[0157] By substituting the mean field z, we get J i (P i ,P -i ) can be expressed as:

[0158]

[0159] In the formula, ξ'=Nξ, dmax=Dmax / N.

[0160] Therefore, the optimal active power control strategy of inverter i considering frequency constraints is adjusted to:

[0161] P i * (z) = argmaxJ i (P i ,z) P i ∈Y i

[0162] The inverter of the present invention independently establishes a control strategy based on the senior control output and the MF information in the broadcast. The decision-making process is decentralized, and the shared MF information is integrated into the objective function and continuously updated during the iterative solution process, which ultimately makes the inverter reach equilibrium and promotes consistency between inverters. In addition, since there is no information exchange between inverters, the communication burden can be greatly reduced.

[0163] In practical application scenarios, the objective function of the inverter (J i (P i ,z) function) is coupled through the power supply price affected by the control strategies of all inverters. Therefore, based on the mean field game theory, each inverter can determine its optimal response strategy to the strategies of other inverters. Then, the NE point of the game is obtained by calculating the optimal control strategies of all inverters. The NE point is the Nash equilibrium point, which is a strategy combination in which the strategy of each participant is the best response to the strategies of other participants. Under the Nash equilibrium, no participant can improve his own benefits by unilaterally changing the strategy.

[0164] Since the mean field game function J i is piecewise smooth and concave, so candidates for the optimal policy can be derived from the first-order derivative. To do this, derive J i (P i ,z) function for P i The first-order partial derivative of , and set the first-order derivative equal to zero. It can be represented by the following mapping function:

[0165]

[0166] The mapping model can also take the following relationships:

[0167]

[0168] In the formula, is the mapping model, α i and β iare the power loss coefficients of the ith grid-connected inverter, ξ is the demand elasticity, D max represents the maximum required power, N is the total number of grid-connected inverters, z k is the mean field parameter of the kth iteration, P i,k is the actual active power output of the i-th grid-connected inverter in the k-th iteration;

[0169] Based on the above mapping function, a decentralized strategy iteration algorithm based on Mann iteration is used to solve the problem, where the control strategy iteration equation of inverter i is:

[0170]

[0171] Where P i,k+1 is the actual active power output of the i-th grid-connected inverter in the k+1th iteration, k represents the number of iterations, k≥1. k is the iteration operator of the kth iteration, equal to λ / k, λ is the initial iteration operator, satisfying And k ∈(0,1). In addition, P i,k and z k is the kth iteration i and z. In each iteration, the inverter responds optimally to the broadcasted intermediate frequency signal and updates the control strategy. The broadcast center then updates the mean field z entry according to the inverter's updated control strategy and broadcasts the updated mean field z. This information must continue to interact and iterate until convergence is achieved to obtain a set of network element solutions.

[0172] In the decentralized strategy iteration algorithm adopted by the present invention, ε is the threshold of the control strategy iteration convergence error, that is, |P i,k+1 -P i,k |<ε. In addition, P i,MF is an intermediate variable. It can be understood in two ways. During the iteration process, it means that the control strategy of each inverter will be updated as the mean field z is updated. After the iteration is completed, it means that each inverter has an optimal control strategy under the control of the mean field balance. For the distributed strategy iteration algorithm, the initial value of the inverter output active power is calculated by the optimal power flow, and ... i,MF Satisfy the convergence condition, that is, P i,MF =P i,k+1 And |P i,k+1 -P i,k |<ε, we also need to check P i,MF Whether it exceeds the limit Y i If the limit is exceeded, set it to a constant equal to the limit, i.e. P i,MF ≡P i,max ∥P i,MF ≡Pi,min , and iterate the solution again until it converges.

[0173] The present invention is based on the mean field equilibrium theory and creates a competitive gaming environment for inverters. The interaction between inverters is approximated by the influence caused by the average inverter control strategy. The inverter independently establishes the control strategy based on its own control output and the broadcast intermediate frequency information. The decision-making process is decentralized, and the shared information MF (mean field z) project promotes consistency between inverters. In addition, since there is no information exchange between inverters, the communication burden can be greatly reduced. The coordinated control method of the present invention is suitable for large-scale inverters and allows all grid-connected inverters to participate in frequency regulation. In addition, the coordinated control method can achieve frequency regulation and active power distribution at the same time.

[0174] The present invention is demonstrated based on the case of the improved IEEE33 system to verify the effectiveness of the proposed MFG (mean field gain) control framework.

[0175] Busbars 7, 14, 20 and 30 are connected to grid-connected inverter groups. Each group consists of 100 inverters, and the active rated power of each inverter is 10 kW. The remaining parameters of the MFG control framework are shown in Table 1. It is assumed that all GFM inverters (grid-connected inverters) have the same structure and parameters.

[0176] Table 1 MPG parameters

[0177]

[0178] The case is simulated using MATLAB / Simulink 2020a. The effect of active frequency control is illustrated by introducing a 0.15MW disturbance at bus 20. First, the new steady-state operating point of the inverter after the disturbance is checked. After 174 iterations, the algorithm converges to an accuracy of 10 -3 In the inverter population distributed on four different buses, the NE point of each inverter is 8.147kW, 6.533kW, 5.057kW and 7.716kW respectively, and the MF value is 6.863kW.

[0179] Figure 6 The active power delivered to each branch before and after the disturbance. The power flow changes near bus 20 and 30 are highlighted. After the disturbance, under the MFG control of the present invention, the active power of the 20 bus inverter increases, but this is not enough to meet the needs of the additional load. Therefore, the active power delivered from bus 19 to bus 20 increases. On the contrary, under MFG control, the active power generated by the inverter at bus 30 decreases, resulting in a decrease in the active power it provides to bus 29 in the opposite direction.

[0180] The transient output active power changes of inverter 20 bus before and after MFG control are as follows: Figure 7 After the disturbance occurs, the active power first surges to cope with the load change, and then gradually decreases according to the active power control strategy until a new steady-state operating point is reached.

[0181] Importantly, with the addition of MFG control, the inverter output is significantly amplified. That is, within the MFG control framework, the inverters of bus 20 meet more load demands than without supplemental control.

[0182] Frequency changes such as Figure 8 As shown. The disturbance occurred at 45 seconds. The change in frequency is mainly determined by the imbalance between supply and demand. Frequent control updates can minimize the immediate supply and demand difference. Faced with a sudden increase in load, the frequency should drop. However, due to the fast and timely MFG control, the active power of the inverter rises rapidly, causing the frequency to increase instead. Under MFG control, the maximum frequency deviation |f-50|max is 0.059Hz, and the frequency recovery time +t is 4.345s. Without any auxiliary control, |f-50|max=0.078Hz,+t=14.852s. After adding MFG control, the frequency deviation is reduced by 0.019Hz and the frequency recovery time is accelerated by 10.511s. It emphasizes that the additional MFG control is effective in quickly recovering the frequency and minimizing the frequency deviation after the disturbance.

[0183] The present invention also provides a network-type distribution network active frequency coordination control device, which adopts the above-mentioned network-type distribution network active frequency coordination control method, including:

[0184] An aggregation model building module, which is used to determine a multi-inverter aggregation model based on grid-connected inverters in a grid-type distribution network;

[0185] An active output determination module, which is used to determine the active output range of each grid-connected inverter based on a multi-inverter aggregation model;

[0186] A strategy model building module, which is used to build an active power control strategy model based on the active output range of each grid-connected inverter and with the goal of maximizing the profit of the grid-connected inverter;

[0187] A control strategy determination module is used to optimize the active power control strategy model and iterate until convergence, and provide an active power control strategy for the grid-connected inverter;

[0188] The power grid coordination control module is used to coordinate the active frequency control of the grid-forming distribution network.

[0189] Furthermore, the aggregation model building module includes:

[0190] Based on the grid-connected inverter in the grid-type distribution network, a grid-connected inverter model is constructed;

[0191] Based on the voltage characteristics of multiple grid-connected inverters in parallel in a grid-connected distribution network and combined with the grid-connected inverter model, a multi-inverter aggregation model is constructed.

[0192] Furthermore, the strategy model building module includes:

[0193] Determine the supply price function of the distribution network and give the power supply revenue of the grid-connected inverter;

[0194] Determine the frequency regulation benefit of the grid-connected inverter according to the active power-frequency droop coefficient of the grid-connected inverter;

[0195] Determine the operating loss cost of the grid-connected inverter based on the actual active power output of the grid-connected inverter;

[0196] Based on the power supply income, frequency regulation income and operation loss cost of the grid-connected inverter, an active power control strategy model is constructed.

[0197] Furthermore, the strategy model building module also includes:

[0198] Determining a demand utility function based on demand parameters of the grid-connected inverter;

[0199] Derivative the demand utility function and make it equal to zero to determine the relationship between demand price and demand power;

[0200] Based on the relationship between demand price and demand power, the supply price function is determined.

[0201] Furthermore, the control strategy determination module includes:

[0202] Determine the average field parameters based on the number of grid-connected inverters and the actual active power output;

[0203] Based on the mean field parameters, the active power control strategy model is optimized and adjusted, and the active power optimization control strategy model is given;

[0204] The active power optimization control strategy model is derived and equal to zero to determine the mapping model;

[0205] Constructing a control strategy iteration model for the grid-connected inverter based on the mapping model;

[0206] Initialize the actual active power output and iteration operator of the grid-connected inverter, iterate the control strategy iteration model of the grid-connected inverter until convergence, and give the active power control strategy of the grid-connected inverter.

[0207] Although preferred embodiments of the present invention have been described, additional changes and modifications may be made to these embodiments by those skilled in the art once the basic inventive concepts are known. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention. Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for coordinated control of active frequency of a grid-type distribution network, characterized in that: include: Based on the grid-connected inverters in the grid-type distribution network, a multi-inverter aggregation model is determined; Based on the multi-inverter aggregation model, determine the active output range of each grid-connected inverter; Based on the active output range of each grid-connected inverter, an active power control strategy model is constructed with the goal of maximizing the revenue of the grid-connected inverter; The active power control strategy model is optimized and iterated until convergence. The active power control strategy of the grid-connected inverter is given to carry out active frequency coordinated control of the grid-connected distribution network.

2. The method for coordinated control of active frequency of a grid-type distribution network according to claim 1, characterized in that: Based on the grid-connected inverters in the grid-type distribution network, a multi-inverter aggregation model is determined, including: Based on the grid-connected inverter in the grid-type distribution network, a grid-connected inverter model is constructed; Based on the voltage characteristics of multiple grid-connected inverters in parallel in a grid-connected distribution network and combined with the grid-connected inverter model, a multi-inverter aggregation model is constructed.

3. The method for coordinated control of active frequency of a grid-type distribution network according to claim 2, characterized in that: The grid-connected inverter model satisfies the following relationship: oh i =ω i,ref -m p,i (P i -P i,ref ) V i =V i,ref -m p,i (Q i -Q i,ref ) In the formula, ω i and V i are the frequency and voltage amplitude of the i-th grid-connected inverter, ω i,ref ,V i,ref Respectively represent the rated frequency and rated voltage of the i-th grid-connected inverter, P i,ref , P i Represent the active power setting value and actual active power output of the i-th grid-connected inverter, Q i,ref , Q i Represent the reactive power setting value and the actual reactive power output of the i-th grid-connected inverter, m p,i and m q,i They represent the droop coefficients of active power-frequency and reactive power-voltage control of the i-th grid-connected inverter respectively; The multi-inverter aggregation model satisfies the following relationship: Where P a is the actual output of the equivalent total active power of multiple grid-connected inverters in parallel, n is the number of grid-connected inverters in parallel, m is p,a It is the equivalent total droop coefficient of active power-frequency of multiple grid-connected inverters in parallel.

4. The method for coordinated control of active frequency of a grid-type distribution network according to any one of claims 1 to 3, characterized in that: The active output range of each grid-connected inverter satisfies the following relationship: P i,max =min((P i +ΔP i ),P N,i ) P i,min =max((P i -ΔP i ),0) Where P N,i is the rated active power of the i-th grid-connected inverter, P i,min and P i,max are the minimum and maximum active output of the ith grid-connected inverter, ΔP i It represents the maximum value of the active power fluctuation output by the ith grid-connected inverter within the maximum frequency fluctuation range allowed by the grid-connected distribution network, Δf max Indicates the maximum frequency fluctuation allowed in the grid-type distribution network.

5. The method for coordinated control of active frequency of a grid-type distribution network according to claim 1, characterized in that: Based on the active output range of each grid-connected inverter, an active power control strategy model is constructed with the goal of maximizing the revenue of the grid-connected inverter, including: Determine the supply price function of the distribution network and give the power supply revenue of the grid-connected inverter; Determine the frequency regulation benefit of the grid-connected inverter according to the active power-frequency droop coefficient of the grid-connected inverter; Determine the operating loss cost of the grid-connected inverter based on the actual active power output of the grid-connected inverter; Based on the power supply income, frequency regulation income and operation loss cost of the grid-connected inverter, an active power control strategy model is constructed.

6. The method for coordinated control of active frequency of a grid-type distribution network according to claim 5, characterized in that: Determine the supply price function of the distribution network, including: Determine the demand utility function based on the demand parameters of the grid-connected inverter; Derivative the demand utility function and make it equal to zero to determine the relationship between demand price and demand power; Based on the relationship between demand price and demand power, the supply price function is determined.

7. The method for coordinated control of active frequency of a grid-type distribution network according to claim 5 or 6, characterized in that: The active power control strategy model satisfies the following relationship: P i * (P -i )=argmaxJ i (P i ,P -i ),P i ∈Y i Where P * i is the active power control strategy model, J i (P i ,P -i ) is the revenue of the grid-connected inverter, P i is the actual active power output of the i-th grid-connected inverter, P -i The active power supply for the grid-connected inverter, P -i =(P1,P2,...,P N ), Y i is the active output range of the i-th grid-connected inverter, ξ is the demand elasticity, D max represents the maximum required power, N is the total number of grid-connected inverters, χ is the price per unit droop coefficient, m p,i is the active power-frequency droop coefficient of the i-th grid-connected inverter, α i , β i and γ i are the power loss coefficients of the i-th grid-connected inverter.

8. The method for coordinated control of active frequency of a grid-type distribution network according to claim 1 or 7, characterized in that: The active power control strategy model is optimized and iterated until convergence, and the active power control strategy of the grid-connected inverter is given, including: Determine the mean field parameters based on the number of grid-connected inverters and the actual active power output; Based on the mean field parameters, the active power control strategy model is optimized and adjusted, and the active power optimization control strategy model is given; The active power optimization control strategy model is derived and equal to zero to determine the mapping model; Constructing a control strategy iteration model for the grid-connected inverter based on the mapping model; Initialize the actual active power output and iteration operator of the grid-connected inverter, iterate the control strategy iteration model of the grid-connected inverter until convergence, and give the active power control strategy of the grid-connected inverter.

9. The method for coordinated control of active frequency of a grid-type distribution network according to claim 8, characterized in that: The mapping model satisfies the following relationship: In the formula, is the mapping model, α i and β i are the power loss coefficients of the ith grid-connected inverter, ξ is the demand elasticity, D max represents the maximum required power, N is the total number of grid-connected inverters, z k is the mean field parameter of the kth iteration, P i,k is the actual active power output of the i-th grid-connected inverter in the k-th iteration; The control strategy iteration model of the grid-connected inverter satisfies the following relationship: Where P i,k+1 is the actual active power output of the i-th grid-connected inverter in the k+1th iteration, λ k is the iteration operator of the kth iteration, λ k =λ / k, λ is the initial iteration operator, And k ∈(0,1).

10. A grid-type distribution network active frequency coordination control device, characterized in that: The method for coordinated control of active frequency of a grid-type distribution network as claimed in any one of claims 1 to 9 comprises: An aggregation model building module, which is used to determine a multi-inverter aggregation model based on grid-connected inverters in a grid-type distribution network; An active output determination module, which is used to determine the active output range of each grid-connected inverter based on a multi-inverter aggregation model; A strategy model building module, which is used to build an active power control strategy model based on the active output range of each grid-connected inverter and with the goal of maximizing the profit of the grid-connected inverter; A control strategy determination module is used to optimize the active power control strategy model and iterate until convergence, and provide an active power control strategy for the grid-connected inverter; The power grid coordination control module is used to coordinate the active frequency control of the grid-forming distribution network.

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