Method for suppressing bus voltage fluctuation of single-bus direct-current micro-grid

Abstract

The invention belongs to the related technical field of power electronics and micro-grid control, and particularly relates to a direct current micro-grid voltage fluctuation suppression method, which comprises the following steps of: dynamically adjusting the following output voltage reference value of each power supply unit in a micro-grid: determining an estimated value of small-amplitude load disturbance by adopting an observer; calculating a compensation signal for compensating small-amplitude load disturbance; adding the compensation signal to the secondary control layer output in the droop control-based micro-grid primary and secondary control layers; in the primary control layer, an output voltage reference value is calculated based on the output of the secondary control layer, and small-amplitude load disturbance compensation is realized; calculating a product variable quantity of a steady-state output current and a preset droop coefficient caused by sudden load change and a line impedance partial voltage variable quantity of the power supply unit; and adding a product variable quantity and a partial voltage variable quantity in the primary control output, updating the reference value, and realizing voltage compensation for large-amplitude load abrupt change. According to the invention, the transient fluctuation of the bus voltage can be effectively inhibited.

Description

Technical Field

[0001] The invention belongs to the technical field related to power electronics and microgrid control, and more specifically, relates to a method for suppressing bus voltage fluctuations in a single-bus DC microgrid. Background Art

[0002] At present, with the continuous increase in energy demand, microgrids have become an effective architecture for integrating renewable energy, energy storage systems, and user loads. With the rapid development of DC loads such as renewable energy generation, electric vehicles, and data centers, DC microgrids have received extensive attention due to their advantages of simple structure, high energy conversion efficiency, and easy integration, and are an important form of future energy systems. However, the high proportion of power electronic converters in DC microgrids and the frequent switching of loads in practical applications have led to large transient fluctuations in bus voltage, threatening the stability of the system. Specifically, the voltage stability of DC microgrids faces the following two types of disturbance challenges: one is unknown small-amplitude and continuous disturbances, including model uncertainties and small fluctuations in load demand; the other is predictable large-amplitude and sudden load changes, such as the instantaneous connection or disconnection of loads.

[0003] In the existing DC microgrid voltage control strategies, the methods for suppressing bus voltage fluctuations mainly fall into three categories: one is to uniformly regard the disturbances as unmodeled dynamics and process them through disturbance observers or other single disturbance compensation strategies to reduce the impact on the bus voltage; one is to gradually correct the droop coefficient or voltage reference value to gradually adjust the bus voltage when disturbances occur; the other is to add hardware devices such as supercapacitor energy storage systems to the DC microgrid system to suppress bus voltage fluctuations. In practical application scenarios such as ship microgrids and electric vehicle charging stations, it is required that the control method of the DC microgrid has the ability to highly accurately suppress continuous small disturbances and instantaneously compensate for predictable load mutations. However, the first type of method does not consider the characteristics of large-amplitude load mutations, and the compensation effect is limited; the second type of method has too slow a dynamic response and is difficult to meet the power supply quality requirements of highly sensitive loads; the third type of method requires additional hardware devices, increasing the system cost and complexity.

[0004] Therefore, the suppression of DC microgrid voltage fluctuations still needs to be effectively solved. Summary of the Invention

[0005] Aiming at the above defects or improvement requirements of the prior art, the invention provides a method for suppressing bus voltage fluctuations in a single-bus DC microgrid, aiming to effectively suppress the transient bus voltage fluctuation problems caused by unknown small-amplitude disturbances and predictable large-amplitude load mutations while ensuring the basic requirements of restoring the common bus voltage to the rated value and distributing the output current according to a preset ratio.

[0006] To achieve the above object, according to one aspect of the present invention, a method for suppressing the bus voltage fluctuation of a single-bus DC microgrid is provided, which is realized by dynamically adjusting the output voltage reference value of each power supply unit in the DC microgrid as follows:

[0007] Calculate the difference between the current bus voltage and the preset rated voltage as the current bus voltage regulation error; according to the preset communication topology of the power supply units, collect the output currents of each power supply unit and its neighboring units communicating with it to calculate the sum of the output current distribution deviations between the power supply unit and its neighboring units; use an observer to determine the estimated value of a small load disturbance to calculate a compensation signal for compensating the small load disturbance; take the negative value of the weighted sum of the current bus voltage regulation error, the sum, and the compensation signal as the output of the secondary control layer in the primary and secondary control layers of the single-bus DC microgrid based on droop control; in the primary control layer, calculate the output voltage reference value based on the output of the secondary control layer to achieve compensation for small load disturbances;

[0008] Calculate the difference between the actual steady-state output currents of the power supply unit before and after the predictable large load mutation, and calculate the PI controller conversion coefficient from the output voltage reference value to the actual output voltage value according to the preset control parameters of the local voltage PI controller of the power supply unit; calculate the product of the actual steady-state current difference and the preset droop coefficient of the power supply unit as the change amount of the product of the steady-state output current and the preset droop coefficient caused by the load mutation; use the actual steady-state current difference, combine the conversion coefficient and the known line impedance of the power supply unit to calculate the change amount of the line impedance voltage division of the power supply unit caused by the load mutation; add the change amount of the product and the change amount of the voltage division in the primary control output to update the output voltage reference value to achieve voltage compensation for large load mutations.

[0009] Furthermore, the current bus voltage regulation error is the difference between the estimated value of the current bus voltage and the preset rated voltage; wherein, the estimated value of the current bus voltage is determined by the observer.

[0010] Furthermore, the observer is a finite-time observer, and its expression is:

[0011]

[0012] In the formula, V b represents the current bus voltage; sgn(·) is the sign function; v0, v1, and p are intermediate variables, is the derivative of p; η n (n = 0, 1, 2) represents the convergence gain coefficient of the nth-order dynamics of the observer; M is the hierarchical gain adjustment coefficient of the observer; and respectively represent the estimated values of the current bus voltage and the actual small - scale load disturbance; denotes the derivative of; denotes the derivative of; R * (t) represents the known part of the resistive load in the equivalent total load of the micro - grid, which can be considered a normal constant, m i represents the droop coefficient of the i - th power supply unit, R i represents the line impedance between the i - th power supply unit and the bus, ν S ={1,2,...,N} represents the set of power supply unit converters, and N represents the total number of power supply units in the single - bus DC micro - grid; u i (t) represents the output of the secondary control layer of the i - th power supply unit.

[0013] Furthermore, the compensation signal

[0014] In the formula, represents the estimated value of the small - scale load disturbance; is an N×N matrix, H = γα1 N +γβLΞ -1 K1 N is an N×1 column vector; R * (t) represents the known part of the resistive load in the equivalent total load of the micro - grid, which can be considered a normal constant, m i represents the droop coefficient of the i - th power supply unit, R i represents the line impedance between the i - th power supply unit and the bus, ν S ={1,2,...,N} represents the set of power supply unit converters, and N represents the total number of power supply units in the single - bus DC micro - grid; α represents the positive voltage regulation gain; 1 N represents an N×1 column vector with all elements being 1; is the transpose of 1 N ; β represents the positive current regulation gain; L represents the Laplacian matrix of the undirected connected graph corresponding to the communication topology of the power supply units; K = diag{k1,k2,...,k N} and Ξ = diag{ξ1,ξ2,...,ξ N} are both N×N diagonal matrices, and their physical meanings are respectively based on the model coefficients of the actual system and the preset current distribution ratio; Ξ -1 represents the inverse of Ξ; is an N×N matrix.

[0015] Furthermore, the conversion coefficient ρ of the PI controller of the i-th power supply unit i is:

[0016]

[0017] In the formula, a i = k pv,i represents the proportional coefficient of the local voltage PI controller of the i-th power supply unit; b i = k iv,i represents the integral coefficient of the local voltage PI controller of the i-th power supply unit; c i = C i represents the converter capacitor of the i-th power supply unit.

[0018] Furthermore, the product change amount of the i-th power supply unit is expressed as m i ΔI i , and the voltage division change amount is expressed as ρ i R i ΔI i ; in the formula, ΔI i represents the actual steady-state current difference; m i represents the preset droop coefficient of the i-th power supply unit; ρ i represents the key coefficient of the i-th power supply unit; R i represents the line impedance between the i-th power supply unit and the common bus;

[0019] Then the final output of the primary control layer is expressed as:

[0020] V i ref (t) = V * - m i I i (t) + z i (t) + ΔV i cps μ(t - t c )

[0021] In the formula, V i ref (t) represents the output voltage reference value at the current moment t output by the primary control layer; V * represents the preset rated voltage; I i (t) represents the steady-state output current at the current moment t; is the derivative of z i (t), u i (t) represents the output at the current moment t of the secondary control layer; ΔV i cpsrepresents the sum of the change in the product and the change in the partial pressure; μ(t - t c ) represents the unit step function with a step time of t c , where t c is the occurrence time of a predictable large-scale load mutation.

[0022] According to another aspect of the present invention, there is provided an electronic device, including a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, the steps of the method described above are implemented.

[0023] According to another aspect of the present invention, there is provided a computer-readable storage medium, which includes a stored computer program. When the computer program is run by a processor, the device where the storage medium is located is controlled to execute the steps of the method described above.

[0024] According to another aspect of the present invention, there is provided a computer program product, including a computer program or instruction. When the computer program or instruction is executed by a processor, the steps of the method described above are implemented.

[0025] Generally speaking, compared with the prior art through the above technical solutions conceived by the present invention, the technical solutions provided by the present invention mainly have the following beneficial effects:

[0026] 1. The present invention proposes a method for suppressing voltage fluctuations in a DC microgrid. For each power supply unit, under the primary and secondary control layer paradigm of a single-bus DC microgrid based on droop control, in the secondary control layer, based on the estimated value of a small load disturbance, a compensation signal for compensating the small load disturbance is calculated; the compensation signal is added to the conventional output of the secondary control layer. In the primary control layer, on the basis of obtaining the output voltage reference value using the actual output of the secondary control layer, it is proposed to calculate the product of the actual steady-state current difference and the preset droop coefficient of this power supply unit, which is used to compensate for the change in the product of the output current and the preset droop coefficient caused by a large load mutation, and suppress the disturbance brought by the large load mutation to the output voltage reference value output by the primary control layer; considering the indirect control of the actual output voltage by adjusting the change in the output voltage reference value, the method also calculates the PI controller conversion coefficient from the output voltage reference value to the actual output voltage according to the preset control parameters of the local voltage PI controller of this power supply unit, and uses the actual steady-state current difference, combined with the product of the conversion coefficient and the known line impedance of this power supply unit, to calculate the line impedance voltage division change compensation amount, and convert the voltage division change compensation amount into the actual output voltage, so that it generates a voltage change equal to the line impedance voltage division change of this power supply unit caused by the load mutation, and reduces the change in the bus voltage generated to offset the line impedance voltage division change of this power supply unit, thereby suppressing the voltage fluctuation brought by the large load mutation to the bus voltage. Further, the above product and the above line impedance voltage division change compensation amount are added to the primary control output, and the output voltage reference value of the primary control output is updated to achieve voltage compensation for the large load mutation. Generally speaking, the method of the present invention can effectively suppress the bus voltage transient fluctuation problem brought by unknown small disturbances and predictable large load mutations while ensuring that the common bus voltage is restored to the rated value and the output current is distributed according to the preset ratio.

[0027] 2. The present invention also proposes that the current bus voltage regulation error is the difference between the estimated value of the current bus voltage and the preset rated voltage; among them, the estimated value of the current bus voltage is determined by an observer. The finite-time observer hides discontinuous signals in higher-order dynamics through the differential operation of the high-order sliding mode technique. Therefore, the estimated value of the current bus voltage output by the finite-time observer is a continuous signal, and the current bus voltage regulation error calculated from it is smoother than using the actual value of the current bus voltage. Therefore, the secondary control effect using the estimated value of the current bus voltage is better, and the bus voltage oscillation of the DC microgrid is smaller.

[0028] 3. The present invention also proposes a new finite-time observer. The finite-time observer adopts a term with a fractional power (such as ) The non-smooth feedback law can accelerate the convergence process when the observation error between the estimated value and the actual value approaches zero, enabling the estimated value to accurately converge to the actual value within a finite time. This overcomes the defect that the linear feedback law adopted by traditional observers has a decreasing convergence rate when the observation error approaches zero. Additionally, the current bus voltage, the output of the secondary control layer, and the disturbance caused by small-scale load changes are respectively used as the state variable, input variable, and disturbance variable of the finite-time observer. The estimated value of the disturbance variable is differentiated multiple times to construct a nested multi-order sliding mode surface based on the dynamic equation of the bus voltage, causing the estimated value of the state variable to converge to the actual value of the state variable along the high-order derivative of the sliding mode surface within a finite time.

[0029] 4. The present invention also specifically proposes a compensation signal expression for compensating small-scale load disturbances. The estimated value of the disturbance caused by small-scale load changes is distributed according to the steady-state output of the power supply unit characterized by the matrix K containing the droop coefficient and line impedance and the matrix Ξ containing the output current distribution ratio. The compensation signal as the distribution result is added to the output of the secondary control layer to compensate for small-scale load disturbances in the bus voltage dynamics, achieving the collaborative suppression of the bus voltage fluctuations caused by small-scale load changes by the power supply units. Meanwhile, it does not affect the output of the power supply units, ensuring that the bus voltage recovers to the rated value and the output current is distributed according to the expected ratio when reaching the stable state. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a flowchart of a method for suppressing bus voltage fluctuations in a single-bus DC microgrid provided by an embodiment of the present invention;

[0031] Figure 2 It is a hierarchical control architecture diagram of a DC microgrid system provided by an embodiment of the present invention;

[0032] Figure 3 It is a bus voltage evolution diagram when an unknown slow resistive load change occurs under the control method of this embodiment provided by an embodiment of the present invention;

[0033] Figure 4 It is an output current evolution diagram of each power supply unit when an unknown slow resistive load change occurs under the control method of this embodiment provided by an embodiment of the present invention;

[0034] Figure 5 It is a bus voltage evolution diagram when a known step current load change occurs under the control method of this embodiment provided by an embodiment of the present invention;

[0035] Figure 6 It is an output current evolution diagram of each power supply unit when a known step current load change occurs under the control method of this embodiment provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] Embodiment 1

[0038] A method for suppressing the bus voltage fluctuation of a single-bus DC microgrid, as Figure 1 shown, is achieved by dynamically adjusting the output voltage reference value of each power supply unit in the DC microgrid as follows:

[0039] Calculate the difference between the current bus voltage and the preset rated voltage as the current bus voltage regulation error; according to the preset communication topology of the power supply unit, collect the output currents of each power supply unit and its neighboring units that communicate with it to calculate the sum of the output current distribution deviations between the power supply unit and its neighboring units; use an observer to determine the estimated value of small-scale load disturbances to calculate the compensation signal for compensating small-scale load disturbances; take the negative value of the weighted sum of the current bus voltage regulation error, the sum, and the compensation signal as the output of the secondary control layer in the primary and secondary control layers of the single-bus DC microgrid based on droop control; in the primary control layer, calculate the output voltage reference value based on the output of the secondary control layer to achieve the compensation for small-scale load disturbances;

[0040] Calculate the difference between the actual steady-state output currents of the power supply unit before and after the predictable large-scale load mutation, and calculate the PI controller conversion coefficient from the output voltage reference value to the actual output voltage value according to the preset control parameters of the local voltage PI controller of the power supply unit; calculate the product of the actual steady-state current difference and the preset droop coefficient of the power supply unit as the change amount of the product of the steady-state output current and the preset droop coefficient caused by the load mutation; use the actual steady-state current difference, combine the key coefficient and the known line impedance of the power supply unit to calculate the change amount of the line impedance voltage division of the power supply unit caused by the load mutation; add the change amount of the product and the change amount of the voltage division in the primary control output to update the output voltage reference value to achieve the voltage compensation for large-scale load mutations.

[0041] The present invention proposes a method for suppressing voltage fluctuations in a DC microgrid. For each power supply unit, under the primary and secondary control layer paradigm of a single-bus DC microgrid based on droop control, in the secondary control layer, based on the estimated value of a small load disturbance, a compensation signal for compensating the small load disturbance is calculated; the compensation signal is added to the conventional output of the secondary control layer. In the primary control layer, on the basis of obtaining the output voltage reference value by using the actual output of the secondary control layer, it is proposed to calculate the product of the actual steady-state current difference and the preset droop coefficient of this power supply unit, which is used to compensate for the change in the product of the output current and the preset droop coefficient caused by a large load mutation, and suppress the disturbance brought by the large load mutation to the output voltage reference value output by the primary control layer; considering the indirect control of the actual output voltage by adjusting the change in the output voltage reference value, the method also calculates the PI controller conversion coefficient from the output voltage reference value to the actual output voltage according to the preset control parameters of the local voltage PI controller of this power supply unit, and uses the actual steady-state current difference, combined with the product of the conversion coefficient and the known line impedance of this power supply unit, to calculate the line impedance voltage division change compensation amount, and convert the voltage division change compensation amount into the actual output voltage, so that it generates a voltage change equal to the change in the line impedance voltage division of this power supply unit caused by the load mutation, and reduces the change in the bus voltage generated to offset the change in the line impedance voltage division of this power supply unit, thereby suppressing the voltage fluctuation brought by the large load mutation to the bus voltage. Further, the above product and the above voltage division change compensation amount are added to the primary control output to update the output voltage reference value of the primary control output, and realize the voltage compensation for the large load mutation. Therefore, the method of this embodiment can effectively suppress the bus voltage transient fluctuation problem caused by unknown small disturbances and predictable large load mutations while ensuring that the common bus voltage is restored to the rated value and the output current is distributed according to the preset ratio.

[0042] The use of a control strategy with instantaneous compensation capability to deal with large load mutations helps to reduce the bus voltage fluctuation amplitude of the DC microgrid, thereby speeding up the adjustment process of the controller and improving the dynamic response; in addition, the control method only involves the design of the software algorithm level without the use of hardware equipment. Therefore, it is a technical problem to be solved urgently to design an effective control strategy to suppress the transient fluctuation of the bus voltage caused by unknown small disturbances and predictable large load mutations, while ensuring voltage regulation and current distribution. The secondary control strategy containing the observer in the method of this embodiment can estimate and compensate for small unknown disturbances, improve the steady-state accuracy and dynamic response of the DC microgrid, and realize the bus voltage recovery and proportional distribution of the output current; the jump compensation mechanism pre-calculates the voltage adjustment amount (i.e., the sum of the product change amount and the voltage division change amount) and applies it to the output voltage reference value in real time, effectively suppressing the transient fluctuation of the bus voltage caused by the predictable large load mutation. In addition, the method does not require additional hardware complexity, so it is suitable for a variety of load changes and has a wide range of application prospects.

[0043] As a preferred implementation, the current bus voltage regulation error is the difference between the estimated value of the current bus voltage and the preset rated voltage; wherein the estimated value of the current bus voltage is determined by an observer.

[0044] In the method of this embodiment, the finite-time observer hides the discontinuous signal in the higher-order dynamics through the differential operation of the high-order sliding mode technology. Therefore, the current bus voltage estimate output by the finite-time observer is a continuous signal, and the current bus voltage regulation error calculated by it is smoother than using the current bus voltage actual value. Therefore, the secondary control effect using the current bus voltage estimate is better, and the bus voltage oscillation of the DC microgrid is smaller.

[0045] As a preferred implementation, the observer is a finite time observer, and the expression is:

[0046]

[0047] Where V b represents the current bus voltage; sgn(·) is the sign function; v0, v1 and p are intermediate variables, is the derivative of p; η n (n=0,1,2) represents the convergence gain coefficient of the nth-order dynamics of the observer; M is the hierarchical gain adjustment coefficient of the observer; and Represent the estimated values of the current bus voltage and actual small-amplitude load disturbance respectively; express of the guide; express of the guide; R * (t) represents the known part of the resistive load in the equivalent total load of the microgrid, which can be considered as a normal constant. m i represents the droop coefficient of the i-th power supply unit, R i represents the line impedance between the i-th power supply unit and the bus, ν S = {1, 2,..., N} represents the set of power supply unit converters, and N represents the total number of power supply units in the single-bus DC microgrid; u i (t) represents the output of the secondary control layer of the i-th power supply unit.

[0048] The derivation process of this observer expression is explained as follows:

[0049] First, establish a hierarchical control model for the single-bus DC microgrid, including the physical layer, primary control layer, secondary control layer, and communication layer;

[0050] Establish the physical layer model of the single-bus DC microgrid system. According to Kirchhoff's law, the power flow relationship can be obtained as shown in formulas (1) and (2):

[0051]

[0052] V i (t) = R i I i (t) + V b (t), i ∈ ν S (2)

[0053] In the above formula, ν S = {1, 2,..., N} and ν L = {1, 2,..., M} represent the set of power supply unit converters and the system load set respectively; i ∈ ν S and j ∈ ν L represent the i-th power supply unit converter and the j-th load respectively; V b (t) represents the bus voltage; I i (t) and V i (t) represent the output current and output voltage of the i-th power supply unit respectively; R i represents the line impedance between the i-th power supply unit and the common bus; and represent the inductive load and resistive load of the j-th load respectively.

[0054] Establish the primary and secondary control layer models of the single-bus DC microgrid system based on droop control, as shown in formula (3):

[0055]

[0056] In the above formula, V i ref (t) represents the output voltage reference value of the i-th power supply unit; V * is the rated bus voltage; m i represents the droop coefficient of the i-th power supply unit; z i (t) and u i (t) represent the output of the secondary control layer to be determined.

[0057] Establish the communication layer model of the single-bus DC microgrid system, and realize the information interaction between power supply units through the communication network. This communication network can be modeled as an undirected connected graph G c =(ν S , Ε, Α), where Ε = ν S ×ν S represents the set of edges; Α = [a ij N×N is an N×N matrix, representing the adjacency matrix of graph G c , a ij >0 indicates that the i-th power supply unit can receive information from the j-th power supply unit, otherwise a ij =0; define the Laplacian matrix of graph G c as L = [l ij N×N , if i = j, then otherwise l ij =-a ij ; in the Figure 2 shown DC microgrid system, the communication topology diagram among the four power supply units satisfies:

[0058]

[0059] In the DC microgrid system, each power generation unit needs to achieve the steady-state control objectives of restoring the common bus voltage to the rated value and distributing the output current according to the preset ratio. The mathematical expression is:

[0060]

[0061] In the above formula, ξ i and ξ j are positive constants, representing the output current distribution ratio. For example, for four power supply units, the distribution ratio of the i-th power supply unit to its neighbor units is 1:2:4:3, then ξ i takes the value of 1.

[0062] ​​Secondly, a secondary control strategy with a finite-time observer is designed to achieve the steady-state bus voltage regulation and output current distribution of the DC microgrid system while estimating and compensating for the disturbances caused by unknown small-amplitude load variations.

[0063] First, the system load with unknown small variations is expressed as:

[0064]

[0065] In the above formula, and represent the equivalent total load values of all resistive loads and current loads respectively; R * (t) and I * (t) represent the known parts of the total load, which can be considered as constant values in practice; ΔR L (t) and ΔI L (t) represent unknown small load fluctuations.

[0066] On the time scale of the secondary control layer, it can be considered that the output voltage of the power supply unit follows well, that is, V i (t) = V i ref (t). Then, combining formula (2) and formula (3), the output current dynamics of the power supply unit are obtained as shown in formula (6):

[0067]

[0068] In the above formula, is a positive constant related to the system parameters m i and R i .

[0069] Combining formula (1), formula (5) and formula (6), the dynamics of the bus voltage are obtained as shown in formula (7):

[0070]

[0071] In the above formula, represents the disturbance caused by small-amplitude load variations.

[0072] According to the nonlinear model in formula (7), a finite-time observer is designed to estimate and compensate for the disturbances caused by unknown small-amplitude load variations, and the specific expression is shown in formula (8):

[0073]

[0074] In the above formula, represents the input of the nonlinear system; sgn(x) is the sign function; v0, v1 and p are intermediate variables; η n(n = 0, 1, 2) and M are observer coefficients; and represent the estimated values of the actual bus voltage and the actual small - amplitude load disturbance respectively.

[0075] This finite - time observer adopts a non - smooth feedback law with fractional - power terms (such as ). When the observation error between the estimated value and the actual value approaches zero, it can accelerate the convergence process, enabling the estimated value to accurately converge to the actual value within a finite time, overcoming the defect that the linear feedback law adopted by traditional observers has a decreasing convergence rate when the observation error approaches zero. Additionally, the current bus voltage, the output of the secondary control layer, and the disturbance caused by small - amplitude load changes are respectively used as the state variable, input variable, and disturbance variable of the finite - time observer. The estimated value of the disturbance variable is differentiated multiple times to construct a nested multi - order sliding mode surface based on the dynamic equation of the bus voltage, enabling the estimated value of the state variable to converge to the actual value of the state variable along the high - order derivative of the sliding mode surface within a finite time.

[0076] On this basis, a secondary control strategy containing a finite - time observer is designed, that is, the negative value of the weighted sum of the current bus voltage regulation error, the sum of the output current distribution deviations between the i - th power supply unit and its neighbor units, and the compensation signal for compensating small - amplitude load disturbances is used as the output of the secondary control layer in the primary and secondary control layers of a single - bus DC microgrid based on droop control, as shown in formula (9):

[0077]

[0078] where, Ν i ={j ∈ ν S |(i, j) ∈ Ε} represents the set of all neighbors of the converter of the i - th power supply unit; α and β are two positive gains; ζ i (t) is the compensation signal of the i - th power supply unit for compensating small - amplitude load disturbances. For the convenience of stability analysis, an N×1 column vector ζ = col(ζ1, ζ2,..., ζ N ) is introduced, and the compensation signal vector is designed as In formula (9), the secondary control signal u i (t) is composed of the difference between the estimated value and the rated value of the bus voltage, the difference in output current distribution between each unit and its neighbor units, and the compensation signal ζ i (t). The effects of the first two are to achieve bus voltage restoration and output current distribution respectively, and ζ i (t) is responsible for compensating the disturbance caused by small - amplitude load changes.

[0079] As a preferred implementation, the compensation signal

[0080] In the formula, Represents the estimated value of a small - amplitude load disturbance; is an N×N matrix, H = γα1 N +γβLΞ -1 K1 N is an N×1 column vector; R * (t) represents the known part of the resistive load in the equivalent total load of the micro - grid, which can be considered a normal constant, m i represents the droop coefficient of the i - th power supply unit, R i represents the line impedance between the i - th power supply unit and the bus, ν S ={1, 2,..., N} represents the set of power supply unit converters, N represents the total number of power supply units in the single - bus DC micro - grid; α represents the positive voltage regulation gain; 1 N represents an N×1 column vector with all elements being 1; is the transpose of 1 N ; β represents the positive current regulation gain; L represents the Laplacian matrix of the undirected connected graph corresponding to the communication topology of the power supply unit; K = diag{k1, k2,..., k N} and Ξ = diag{ξ1, ξ2,..., ξ N} are both N×N diagonal matrices, and their physical meanings are the model coefficients of the actual system and the preset current distribution ratio respectively; Ξ -1 represents the inverse of Ξ; is an N×N matrix.

[0081] In the method of this embodiment, the estimated value of the disturbance caused by small - amplitude load changes is distributed according to the steady - state output situation of the power supply unit characterized by the matrix K containing the droop coefficient and line impedance and the matrix Ξ containing the output current distribution ratio. The compensation signal as the distribution result is added to the output of the secondary control layer to compensate for the small - amplitude load disturbance in the bus voltage dynamics, realizing the collaborative suppression of the bus voltage fluctuation caused by small - amplitude load changes by the power supply units, and at the same time not affecting the output situation of the power supply units, ensuring that the bus voltage returns to the rated value and the output current is distributed according to the expected ratio when reaching the stable state.

[0082] Next, the effectiveness of the above - mentioned DC micro - grid voltage fluctuation suppression method of adding a compensation signal in the secondary control is described, and its effectiveness is characterized by the stability of the bus voltage and output current:

[0083] Define the output current distribution error, bus voltage - related error, and combined error, as shown in formula (10):

[0084]

[0085] In the above formula, e I,i (t) represents the output current distribution error; e V (t) represents the bus voltage regulation error; e OB (t) represents the bus voltage observation error; ψ i (t) represents the combined error, and the effectiveness of the designed control algorithm will be verified by analyzing ψ i (t) later.

[0086] Substitute the output current dynamics and bus voltage dynamics shown in formulas (6) and (7) into the error system shown in formula (10), and convert it into matrix form as shown in formula (11):

[0087]

[0088] In the above formula, e I = col(e I,1 , e I,2 ,..., e I,N ) and u = col(u1, u2,..., u N ) are both N×1 column vectors, and their physical meanings are current distribution error and secondary control input respectively; K = diag{k1, k2,..., k N} and Ξ = diag{ξ1, ξ2,..., ξ N} are both N×N diagonal matrices, and their physical meanings are the model coefficients of the actual system and the preset current distribution ratio respectively; is an N×N matrix.

[0089] Substitute formula (11) into the expression of the combined error ψ i (t) in formula (10) to obtain the combined error dynamics shown in formula (12) to form a closed-loop system:

[0090]

[0091] In the above formula, ψ = col(ψ1, ψ2,..., ψ N ) is an N×1 column vector, and its physical meaning is the combined error of each unit; is an N×N matrix; H = γα1 N + γβLΞ -1 K1 N is an N×1 column vector.

[0092] For the finite-time observer, construct a V function, that is, a Lyapunov function, as shown in formula (13):

[0093]

[0094] In the above formula, and represent the errors between the respective actual values and the observed values, and their dynamics are shown in Equation (14):

[0095]

[0096] In the above formula, L0 is the known upper bound of the disturbance that satisfies . By designing the finite observer coefficients that satisfy the conditions η1M 1 / 2 ≥|ε2 / |ε1| 1 / 2 | and η2M ≥ L0, the positive definiteness of the V function and the negative definiteness of the first derivative of the V function are obtained, which proves that the finite-time observer can reach stability within a finite time, that is, the observed values and can both converge to the actual values V b and d.

[0097] For the above constructed closed-loop system, substituting the designed compensation signal into Equation (12), we can obtain:

[0098]

[0099] Based on the design of appropriate observer coefficients, according to the results of the observer stability analysis, it can be known that there are and existing. Then, on the long time scale, Equation (15) is transformed into:

[0100]

[0101] In the above formula, the eigenvalues of the matrix S all have positive real parts. Therefore, the state matrix of the closed-loop system described by Equation (15) is a Hurwitz matrix, which proves that the system is asymptotically stable, that is Furthermore, it is deduced that and This shows that the DC microgrid system can achieve the steady-state control objectives of bus voltage recovery and output current proportional distribution as described in Equation (4).

[0102] The simulation parameters are set as shown in Table 1. Under the designed secondary control strategy with a finite-time observer, the evolution results of the bus voltage and the output currents of each power supply unit are as shown in Figure 3 and Figure 4 . The simulation results show that when an unknown slow load change occurs, the bus voltage can be restored to the rated value, the output currents of each power supply unit meet the set distribution ratio, and compared with the traditional secondary control strategy, the proposed method can better suppress the voltage fluctuations of the bus and improve the dynamic performance of the system.

[0103] Table 1 Simulation Parameter Table

[0104]

[0105]

[0106] As a preferred embodiment, the conversion coefficient ρ of the PI controller of the i-th power supply unit i is:

[0107]

[0108] In the formula, a i = k pv,i represents the proportional coefficient of the local voltage PI controller of the i-th power supply unit; b i = k iv,i represents the integral coefficient of the local voltage PI controller of the i-th power supply unit; c i = C i represents the converter capacitor of the i-th power supply unit.

[0109] As a preferred embodiment, the product change amount of the i-th power supply unit is expressed as m i ΔI i , and the voltage division change amount is expressed as ρ i R i ΔI i ; in the formula, ΔI i represents the actual steady-state current difference; m i represents the preset droop coefficient of the i-th power supply unit; ρ i represents the key coefficient of the i-th power supply unit; R i represents the line impedance between the i-th power supply unit and the common bus;

[0110] Then the final output of the primary control layer is expressed as:

[0111] V i ref (t) = V * - m i I i (t) + z i (t) + ΔV i cps μ(t - t c )

[0112] In the formula, V i ref (t) represents the output voltage reference value at the current moment t output by the primary control layer; V * represents the preset rated voltage; I i(t) represents the steady-state output current at the current time t; is the derivative of z i (t), u i (t) represents the output at the current time t of the secondary control layer; ΔV i cps represents the sum of the product change amount and the partial voltage change amount; μ(t - t c ) represents the unit step function with a step time of t c , and t c is the occurrence time of a predictable large-scale load mutation.

[0113] The large-scale load mutation voltage compensation scheme in the method of this embodiment is analyzed and described as follows:

[0114] For a predictable large-scale load mutation, the method of this embodiment proposes a jump compensation mechanism to achieve the suppression of transient bus voltage fluctuations.

[0115] Specifically, the corresponding changed load values R p and I p , and the connection or disconnection time t c are obtained through the load connection or disconnection request information. According to the power relationship described by formula (1) and the steady-state control target described by formula (4), the steady-state current difference of the DC microgrid system before and after the load change needs to satisfy:

[0116]

[0117] In the above formula, represents the steady-state output current difference of the i-th power supply unit before and after the load change; represents the steady-state output current before the load change (i.e., t < t c ); represents the steady-state output current after the load change (i.e., t > t c ).

[0118] Based on the consensus algorithm, the steady-state current difference ΔI i is pre-iteratively solved, and the iterative process is as follows:

[0119]

[0120] In the above formula, ΔI i (k) represents the magnitude of the steady-state current difference ΔI i of the i-th power supply unit at the k-th iteration, where the initial value is set to and ΔI i (0) = 0 (i = 2, 3,..., N).

[0121] Design the key coefficient in the jump compensation mechanism (i.e., the conversion coefficient of the PI controller), and the specific expression is shown in formula (19):

[0122]

[0123] In the above formula, and where a i = k pv,i represents the proportional coefficient of the voltage PI controller of the i-th power supply unit; b i = k iv,i represents the integral coefficient of the voltage PI controller of the i-th power supply unit; c i = C i represents the converter capacitor of the i-th power supply unit.

[0124] According to the steady-state current difference ΔI i and the key coefficient ρ i , calculate the voltage adjustment amount required by the jump compensation mechanism, and the specific expression is shown in formula (20):

[0125] ΔV i cps = m i ΔI i + ρ i R i ΔI i (20)

[0126] In the above formula, ΔV i cps represents the voltage adjustment amount. According to the power relationship described in formula (1), a large load mutation will directly cause a change in the sum of the output currents I i of all power supply units. Then, according to the power relationship described in formula (2), the influence caused by the change in the output current I i can be offset by adjusting the output voltage V i of each unit, thereby reducing the transient fluctuation magnitude of the bus voltage V b . Using the steady-state current difference ΔI i to approximately represent the change in the output current of each power supply unit caused by a large load mutation, the first term m i ΔI i on the right side of formula (20) is responsible for offsetting the change in the m i I i (t) term in the droop control, and the second term is responsible for offsetting the change in the R i I i (t) term in formula (2), thereby reducing the change in the bus voltage, that is, suppressing the bus voltage fluctuation.

[0127] Combined with the established primary control layer, the jump compensation mechanism needs to adjust the output voltage reference value at the moment when the known load mutation occurs, specifically as follows:

[0128] V i ref (t) = V * -m i I i (t) + z i (t) + ΔV i cps μ(t - t c ), (21)

[0129] In the above formula, μ(t) is the unit step function, μ(t) = 0 if t < 0; μ(t) = 1 if t ≥ 0.

[0130] In the embodiment of the present invention, it is known that the load will be connected at the set time, and the remaining simulation parameters are still shown in Table 1. Under the designed jump compensation mechanism and the secondary control strategy with a finite-time observer, the evolution results of the bus voltage and the output current of each power supply unit are as Figure 5 and Figure 6 shown. The simulation results show that when a known step load change occurs, the maximum transient fluctuation of the bus voltage is significantly suppressed, the dynamic response of the system is improved, and after the DC microgrid reaches stability, the bus voltage can recover to the rated value, and the output current of each power supply unit conforms to the set distribution ratio.

[0131] In one implementation, the secondary control strategy with a finite-time observer can estimate and compensate for small unknown disturbances, improve the steady-state accuracy and dynamic response of the DC microgrid, and achieve bus voltage recovery and proportional distribution of output current; the jump compensation mechanism effectively suppresses the transient fluctuation of the bus voltage caused by predictable large load mutations by pre-calculating the voltage adjustment amount and applying it to the output voltage reference value in real time. In addition, this method does not require additional hardware complexity, so it is applicable to various load change situations and has broad application prospects.

[0132] Embodiment 2

[0133] This application also relates to an electronic device, including a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, the steps of the above method are implemented.

[0134] The electronic device can be a computing device such as a desktop computer, notebook, handheld computer, and cloud server. The so-called processor can be a Central Processing Unit (CPU), or can also be other general-purpose processors, Digital Signal Processors (DSPs), Application-Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The memory can be used to store computer programs and / or modules. The processor realizes various functions of the electronic device by running or executing the computer programs and / or modules stored in the memory, and by calling the data stored in the memory.

[0135] The related technical solutions are the same as above and will not be elaborated here.

[0136] Embodiment III

[0137] This application also relates to a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the above method are realized.

[0138] Specifically, the memory can include high-speed random access memory, and can also include non-volatile memory, such as hard disks, memory, plug-in hard disks, Smart Media Cards (SMCs), Secure Digital (SD) cards, Flash Cards, at least one magnetic disk storage device, flash device, or other volatile solid-state storage devices.

[0139] The related technical solutions are the same as above and will not be elaborated here.

[0140] Embodiment IV

[0141] The embodiments of this application provide a computer program product or a computer program. The computer program product or the computer program includes computer instructions, and the computer instructions are stored in a computer-readable storage medium. The processor of the computer device reads the computer instructions from the computer-readable storage medium, and the processor executes the computer instructions, so that the computer device executes the steps of the method in the above embodiments of this application.

[0142] The related technical solutions are the same as above and will not be elaborated here.

[0143] Those skilled in the art can easily understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for suppressing the voltage fluctuation of the bus in a single-bus DC microgrid, characterized in that, It is achieved by dynamically adjusting the output voltage reference value of each power supply unit in the DC microgrid as follows: Calculate the difference between the current bus voltage and the preset rated voltage as the current bus voltage regulation error; according to the preset communication topology of the power supply unit, collect the output currents of each power supply unit and its neighboring units that communicate with it to calculate the sum of the output current distribution deviations between the power supply unit and its neighboring units; use an observer to determine the estimated value of small-scale load disturbances to calculate the compensation signal for compensating small-scale load disturbances; take the negative value of the weighted sum of the current bus voltage regulation error, the sum, and the compensation signal as the output of the secondary control layer in the primary and secondary control layers of the single-bus DC microgrid based on droop control; in the primary control layer, calculate the output voltage reference value based on the output of the secondary control layer to achieve compensation for small-scale load disturbances; Calculate the difference in the actual steady-state output current of the power supply unit before and after the predictable large-scale load mutation, and calculate the PI controller conversion coefficient from the output voltage reference value to the actual output voltage value according to the preset control parameters of the local voltage PI controller of the power supply unit; Calculate the product of the actual steady-state current difference and the preset droop coefficient of the power supply unit as the change in the product of the steady-state output current and the preset droop coefficient caused by the load mutation; use the actual steady-state current difference, combined with the conversion coefficient and the known line impedance of the power supply unit, to calculate the change in the line impedance voltage division of the power supply unit caused by the load mutation; add the product change and the voltage division change to the primary control output to update the output voltage reference value to achieve voltage compensation for large-scale load mutations.

2. The inhibition method according to claim 1, wherein The current bus voltage regulation error is the difference between the estimated value of the current bus voltage and the preset rated voltage; among them, the estimated value of the current bus voltage is determined by the observer.

3. The suppression method according to claim 2, wherein The observer is a finite-time observer, and the expression is: where V b represents the current bus voltage; sgn(·) is the sign function; v0, v1, and p are intermediate variables, is the derivative of p; η n (n = 0, 1, 2) represents the convergence gain coefficient of the nth - order dynamics of the observer; M is the hierarchical gain adjustment coefficient of the observer; and represent the estimated values of the current bus voltage and the actual small - amplitude load disturbance respectively; denotes the derivative of; denotes the derivative of; R * (t) represents the known part of the resistive load in the equivalent total load of the micro - grid, and takes a positive constant value, m i represents the droop coefficient of the ith power supply unit, R i represents the line impedance between the ith power supply unit and the bus, ν S ={1, 2,..., N} represents the set of power supply unit converters, and N represents the total number of power supply units in the single - bus DC micro - grid; u i (t) represents the output of the secondary control layer of the ith power supply unit.

4. The inhibition method according to claim 1, characterized in that The compensation signal In the formula, represents the estimated value of a small - amplitude load disturbance; is an N×N matrix, H = γα1 N +γβLΞ -1 K1 N is an N×1 column vector; R * (t) represents the known part of the resistive load in the equivalent total load of the micro - grid, and its value is a positive constant. m i represents the droop coefficient of the i - th power supply unit, R i represents the line impedance between the i - th power supply unit and the bus, ν S ={1,2,...,N} represents the set of power supply unit converters, and N represents the total number of power supply units in the single - bus DC micro - grid; α represents a preset positive voltage regulation gain; 1 N represents an N×1 column vector with all elements being 1; is the transpose of 1 N ; β represents a preset positive current regulation gain; L represents the Laplacian matrix of the undirected connected graph corresponding to the communication topology of the power supply units; K = diag{k1,k2,...,k N} and Ξ = diag{ξ1,ξ2,...,ξ N} are both N×N diagonal matrices. m i represents the droop coefficient of the i - th power supply unit, R i represents the line impedance between the i - th power supply unit and the bus; ξ i represents the current distribution ratio of the pre-set i-th power supply unit; Ξ -1 represents the inverse of Ξ; is an N×N matrix.

5. The suppression method according to claim 1, characterized in that, The conversion coefficient ρ of the PI controller of the i-th power supply unit i is as follows: In the formula, a i = k pv,i represents the proportional coefficient of the local voltage PI controller of the i-th power supply unit; b i = k iv,i represents the integral coefficient of the local voltage PI controller of the i-th power supply unit; c i = C i represents the converter capacitor of the i-th power supply unit.

6. The inhibition method according to claim 1, wherein The product change amount of the i-th power supply unit is expressed as m i ΔI i , and the partial pressure change amount is expressed as ρ i R i ΔI i ; where ΔI i represents the actual steady-state current difference; m i represents the preset droop coefficient of the i-th power supply unit; ρ i represents the conversion factor of the i-th power supply unit; R i represents the line impedance between the i-th power supply unit and the common busbar; Then the final output of the primary control layer is expressed as: Wherein, represents the output voltage reference value at the current moment t output by the primary control layer; V * represents the preset rated voltage; I i (t) represents the steady-state output current at the current moment t; is the derivative of z i (t), u i (t) represents the output at the current moment t of the secondary control layer; ΔV i cps represents the sum of the product change amount and the partial pressure change amount; μ(t - t c ) represents the unit step function with the step time of t c , and t c is the occurrence time of a predictable large-amplitude load mutation.

7. An electronic device, comprising a memory and a processor, the memory storing a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 6.

8. A computer-readable storage medium, characterized in that, The computer-readable storage medium includes a stored computer program, wherein when the computer program is run by a processor, it controls the device where the storage medium is located to execute the steps of the method according to any one of claims 1 to 6.

9. A computer program product comprising a computer program or instructions, characterized in that, When the computer program or instruction is executed by a processor, it implements the steps of the method according to any one of claims 1 to 6.

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