Nonlinear droop control method and system suitable for DC micro-grid

Abstract

The invention provides a nonlinear droop control method suitable for a DC micro-grid, and the method comprises the steps: obtaining system parameters of the DC micro-grid based on sectional droop control, and calculating a droop coefficient ki of each section in sectional linear droop control; according to the droop coefficient ki, determining the boundary range of the junction area of each segment, and calculating the control point of the Bezier curve; and according to the control points, generating a Bezier curve, applying the Bezier curve to a junction of two sections of the sectional droop, and performing smooth conversion between different sections of the sectional droop. By introducing the Bezier curve, the sectional type linear droop control is optimized and upgraded, the problem of insufficient stability of the traditional sectional type linear droop control at the junction point is effectively solved, and stable operation of the system in all load ranges is ensured.

Description

Technical Field

[0001] The present application relates to the field of microgrid operation control technology, and in particular, to a nonlinear droop control method and system applicable to a DC microgrid. Background Art

[0002] As an innovative form of small-scale power system networking, DC microgrids are becoming an important means of efficiently utilizing distributed power sources. Their simple control structure, excellent reliability, and high integration rate of renewable energy resources have broad application potential in various fields, including electric vehicles, electric ships, and buildings.

[0003] In the actual operation of DC microgrids, the parallel operation of multiple power sources is particularly common. This characteristic highlights the importance of ensuring accurate power distribution between different power sources. Traditional linear droop control can ensure good current distribution accuracy if a large droop coefficient is selected, but the voltage drop under heavy loads will be large, and the overall efficiency will be low. On the other hand, a small droop coefficient cannot guarantee accurate current distribution. Although exchanging converter output information through a communication network can achieve accurate current distribution and bus voltage compensation, this method relies on the communication network and may increase system complexity and cost.

[0004] Patent publication number CN112531763A discloses a nonlinear droop control method for DC distribution network converter stations. The method involves: constructing a multi-terminal ring DC distribution network structure consisting of a master and slave converter stations, with the master converter station employing a constant voltage control method and the slave converter stations employing a nonlinear droop control method; constructing a modified nonlinear function; determining the maximum value of the nonlinear droop coefficient based on the converter station active capacity and the maximum allowable DC voltage deviation during steady-state operation of the DC distribution system; and determining the nonlinear droop coefficient. By adjusting the droop coefficient, the method achieves precise current distribution, simplifies the system structure, reduces costs, and improves system flexibility and adaptability. However, piecewise linear droop control faces stability challenges at segment boundaries. Sudden changes in slope can cause oscillations or slow response. While introducing hysteresis at these transition points can alleviate these issues, a smoother droop curve is still required to achieve optimal performance. Summary of the Invention

[0005] In response to the defects in the existing technology, the purpose of this application is to provide a nonlinear droop control method suitable for DC microgrids. On the basis of the traditional piecewise linear droop control, a Bezier curve is added to smooth the intersection of the piecewise droop curves, which not only solves the stability problem of the piecewise linear droop at the intersection, but also further improves the dynamic performance of the system.

[0006] In one aspect of the present application, a nonlinear droop control method applicable to a DC microgrid is provided, comprising:

[0007] Obtain the system parameters of the DC microgrid based on segmented droop control and calculate the droop coefficient k of each segment in the segmented linear droop control i ;

[0008] According to the droop coefficient k i , determine the boundary range of each segment intersection area and calculate the control points of the Bezier curve;

[0009] A Bezier curve is generated according to the control points, and the Bezier curve is used for the intersection of two sections of the segmented droop to perform smooth conversion between different sections of the segmented droop.

[0010] Furthermore, the system parameters of the DC microgrid based on the segmented droop control are obtained, and the droop coefficient k of each segment in the segmented linear droop control is calculated. i ,include:

[0011] Obtain the segmented linear droop control curve, determine the upper and lower limits of bus voltage fluctuation, the maximum load current that each power supply can withstand, and the number of segmented control segments N, and calculate the maximum voltage deviation ΔV max , Maximum load current I max ;

[0012] Obtain the control constants α and β of the piecewise linear droop control curve, and calculate the maximum voltage deviation ΔV max and the maximum load current I max , calculate the voltage change value ΔV1 of the first segment and the current change value ΔI of the Nth segment N ;

[0013] According to the calculation of the first voltage change value ΔV1 and the Nth current change value ΔI N And the control constant, calculate the voltage variation range ΔV of each section i , Current variation range ΔI i and the droop coefficient k of each segment of the piecewise linear droop control i .

[0014] Furthermore, the maximum voltage deviation ΔV is calculated max , Maximum load current I max The formula is:

[0015]

[0016] Where, ΔV i and ΔI i It is the voltage and current variation range in different intervals of droop control.

[0017] Furthermore, the first voltage change ΔV1 and the Nth current change ΔI N The expression is:

[0018]

[0019] Furthermore, the voltage variation range ΔV i , Current variation range ΔI i and droop coefficient k i The expression is:

[0020] ΔV i =α(i)ΔV1;

[0021] ΔI i =β(N+1-i)ΔI N ;

[0022]

[0023] Where α and β are control constants, k i is the droop coefficient corresponding to the i-th straight line.

[0024] Furthermore, the step of determining the boundary range of each segment boundary region according to the droop coefficient and calculating the control points of the Bezier curve includes:

[0025] Get the droop coefficient k i , calculate the straight line expression of each segment of the piecewise linear droop control and determine the boundary range of the intersection area of ​​each segment;

[0026] A piecewise linear droop control line is determined according to the boundary range of each segment intersection area;

[0027] According to the piecewise linear droop control line, each section of the control line is evenly divided into four equal parts, and the 75% position point P0 of each section and the 25% position point P2 of the next section, as well as the intersection point P1 of these two sections are selected as control points of the Bezier curve.

[0028] Furthermore, each straight line expression of the piecewise linear droop control includes: a rated voltage expression at the start and a starting rated voltage expression of the next segment;

[0029] The rated voltage expression at the starting point is:

[0030] V ref =V * -k i I i ;

[0031] Where Vref is the reference voltage, V * is the rated voltage at the beginning of each segment, k i is the droop coefficient corresponding to the i-th straight line, I i is the output current;

[0032] The starting rated voltage expression of the next section is:

[0033]

[0034] Where, is the rated voltage of the next control line, k i is the droop coefficient of this straight line, ΔI i is the maximum current variation range corresponding to this straight line;

[0035] The expression of P0 is: P0(I1-ΔI i / 4,V1+ΔV i / 4);

[0036] The expression of P2 is: P2(I1+ΔI i+1 / 4,V1-ΔV i+1 / 4);

[0037] Where P0 is the starting point of the last quarter of this straight line, ΔI i is the maximum current variation range corresponding to this straight line, ΔV i This section of the straight line corresponds to the maximum voltage change range, ΔI i+1 is the maximum current variation range corresponding to the next straight line, ΔV i+1 is the maximum voltage variation range corresponding to the next straight line;

[0038] The coordinates of the control points are:

[0039]

[0040] Furthermore, generating a Bezier curve based on the control point, and applying the Bezier curve to the junction of two sections of the segmented droop to smoothly convert between different sections of the segmented droop includes:

[0041] Obtaining the control point, determining that the Bezier curve is a second-order Bezier curve, and substituting the control point into the second-order Bezier curve to obtain a Bezier curve;

[0042] The Bezier curve is used to replace the intersection of two sections of the segmented droop to obtain the corresponding relationship between the voltage and the current, thereby achieving smooth conversion between different sections of the segmented droop.

[0043] Furthermore, the expression of the Bezier curve is:

[0044] B(t)=(1-t) 2 P0+2(1-t)tP1+t 2 P2,0≤t≤1;

[0045] The expressions of the voltage and the current are:

[0046]

[0047] Where t is the interpolation factor that controls the Bezier curve. When t changes from 0 to 1, the Bezier curve smoothly transitions from the starting point P0 to the end point P2 and is controlled by the intersection P1. V0, V1, and V2 are the voltages corresponding to P0, P1, and P2. I0, I1, and I2 are the currents corresponding to P0, P1, and P2.

[0048] In a second aspect of the present application, a nonlinear droop control system suitable for a DC microgrid is provided, comprising:

[0049] The first calculation module is used to obtain the system parameters of the DC microgrid based on the segmented droop control and calculate the droop coefficient k of each segment in the segmented linear droop control. i ;

[0050] The second calculation module is used to calculate the droop coefficient k i , determine the boundary range of each segment intersection area and calculate the control points of the Bezier curve;

[0051] The output module is used to generate a Bezier curve according to the control points, and use the Bezier curve for the intersection of two sections of the segmented droop to perform smooth conversion between different intervals of the segmented droop.

[0052] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0053] This application is based on a nonlinear droop control method of a Bezier curve. Compared with the existing piecewise linear droop control scheme, the present invention smoothes the intersection points of the piecewise linear droop. The present invention not only solves the stability problem of the piecewise linear droop at the intersection section, but also further improves the dynamic performance of the system. Compared with the control method that relies on the communication network, the present invention does not require complex communication network support and simplifies the system structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Other features, objects and advantages of the present application will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0055] Figure 1This is a flow chart of a nonlinear droop control method applicable to a DC microgrid in one embodiment of the present application.

[0056] Figure 2 Schematic diagram of a DC microgrid in one embodiment of the present application.

[0057] Figure 3 This is a flowchart of microgrid control in one embodiment of the present application.

[0058] Figure 4 Schematic diagram of a nonlinear droop curve smoothed by a Bezier curve in one embodiment of the present application.

[0059] Figure 5 The figure is a dynamic response diagram of nonlinear droop, piecewise droop, and linear droop simulation based on Bezier curve in one embodiment of the present application. DETAILED DESCRIPTION

[0060] The present application is described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present application, but are not intended to limit the present application in any form. It should be noted that those skilled in the art may make several variations and improvements without departing from the scope of the present application. These all fall within the scope of protection of the present application.

[0061] Reference Figure 1 As shown, a nonlinear droop control method applicable to a DC microgrid provided in one embodiment of the present application includes:

[0062] S1. Obtain the system parameters of the DC microgrid based on segmented droop control and calculate the droop coefficient k of each segment in the segmented linear droop control. i .

[0063] S2, according to the droop coefficient k i , determine the boundary range of the intersection area of ​​each segment and calculate the control points of the Bezier curve.

[0064] S3. Generate a Bezier curve based on the control points, and use the Bezier curve for the junction of two sections of the segmented droop to perform smooth conversion between different sections of the segmented droop.

[0065] By combining segmented droop control and Bezier curves, this application achieves smooth conversion of segmented droop control intervals in a DC microgrid, avoids the sudden change problem that may occur at the junction of traditional linear droop control, improves the stability and response speed of the system, and compared with the control method that relies on the communication network, does not require complex communication network support and simplifies the system structure.

[0066] Specifically, the droop coefficients for each segment in the piecewise linear droop control are first calculated based on the system parameters of the DC microgrid. Next, the boundary ranges of the intersection regions of each segment are determined based on the droop coefficients, and the control points used to generate the Bezier curves are calculated. Finally, a Bezier curve is generated using these control points and applied to the intersection of two segments in the piecewise droop control to achieve smooth transitions between different intervals.

[0067] In some possible embodiments, the system parameters of the DC microgrid based on the segmented droop control are obtained, and the droop coefficient k of each segment in the segmented linear droop control is calculated. i , including: obtaining the segmented linear droop control curve, determining the upper and lower limits of bus voltage fluctuation, the maximum load current that each power supply can withstand and the number of segmented control segments N, and calculating the maximum voltage deviation ΔV max , Maximum load current I max .

[0068] Specifically, calculate the maximum voltage deviation ΔV max , Maximum load current I max The formula is:

[0069]

[0070] Where ΔV i and ΔI i It is the voltage and current variation range in different intervals of droop control.

[0071] Obtain the control constants α and β of the piecewise linear droop control curve, and calculate the maximum voltage deviation ΔV max and maximum load current I max , calculate the voltage change value ΔV1 of the first segment and the current change value ΔI of the Nth segment N .

[0072] Specifically, the first voltage change ΔV1 and the Nth current change ΔI N The expression is:

[0073]

[0074] According to the calculation of the first section voltage change value ΔV1 and the N section current change value ΔI N And the control constant, calculate the voltage variation range ΔV of each section i , Current variation range ΔI i and the droop coefficient k of each segment of the piecewise linear droop control i .

[0075] Specifically, the voltage variation range ΔV i , Current variation range ΔI iand droop coefficient k i The expression is:

[0076] ΔV i =α(i)ΔV1;

[0077] ΔI i =β(N+1-i)ΔI N ;

[0078]

[0079] Where α and β are control constants, k i is the droop coefficient corresponding to the i-th straight line.

[0080] By accurately obtaining the system parameters of the DC microgrid based on segmented droop control, the droop coefficient k of each segment of linear droop control is calculated based on this. i This method ensures stable microgrid operation under varying load conditions while maximizing the output capacity of each power source. The segmented control strategy effectively limits bus voltage fluctuations, preventing damage to equipment caused by excessively high or low voltages. It also ensures that load currents are within the acceptable range of the power sources, improving the reliability and safety of the entire microgrid.

[0081] Specifically, first, it is necessary to collect the key system parameters of the DC microgrid based on segmented linear droop control, including the upper and lower limits of bus voltage fluctuation, the maximum load current bearing capacity of each power source, and the number of segmented control segments N. Then, the maximum voltage deviation ΔV is calculated. max , Maximum load current I max Next, the control constants α and β of the piecewise linear droop control curve are obtained, where the control constants reflect the changing relationship between voltage and current. Then, using the parameters and the control constants, the voltage change value ΔV1 of the first segment and the current change value ΔI of the Nth segment are calculated. N Finally, the voltage variation range ΔV of each segment is calculated based on the voltage variation value of the first segment, the current variation value of the Nth segment, and the control constant. i , Current variation range ΔI i and the droop coefficient k of each segment of the piecewise linear droop control i , which is used to control the stable operation of the microgrid under different load conditions.

[0082] In some possible embodiments, determining the boundary range of each segment intersection area according to the droop coefficient and calculating the control points of the Bezier curve include:

[0083] Get the droop coefficient k iCalculate the expression of each segment of the piecewise linear droop control and determine the boundary range of each segment's intersection area. Based on the boundary range of each segment's intersection area, determine the piecewise linear droop control line. Based on the piecewise linear droop control line, divide each control line into four equal parts. Select the 75% position point P0 of each segment and the 25% position point P2 of the next segment, as well as the intersection point P1 of these two segments as the control points of the Bezier curve.

[0084] By precisely calculating the expression for each segment of the piecewise linear droop control line and determining the boundaries of the intersections between the segments, a precise piecewise linear droop control line can be generated, ensuring stable operation of the microgrid under varying load conditions. Next, by evenly dividing each control line into four equal parts and selecting specific locations as control points for the Bezier curve, a smooth transition between the piecewise linear droop control curves is achieved, avoiding the sudden changes that can occur at the intersections of traditional linear droop control, thereby improving system stability and response speed.

[0085] Among them, by obtaining the droop coefficient corresponding to each control line of the piecewise linear droop control, the expression of each control line can be derived:

[0086] The expression of each straight line of the piecewise linear droop control is:

[0087] V ref =V * -k i I i ;

[0088] Where V ref is the reference voltage, V * is the rated voltage at the beginning of each segment, k i is the droop coefficient corresponding to the i-th straight line, I i is the output current.

[0089] The control line is continuous, which means that the end voltage of the previous segment is equal to the starting rated voltage of the next segment. Specifically, the starting voltage of the next segment of control is expressed as follows:

[0090]

[0091] Where, is the rated voltage of the next control line, k i is the droop coefficient of this straight line, ΔI i It is the maximum current variation range corresponding to this straight line.

[0092] In this application, the DC microgrid considered is as follows Figure 2As shown in the figure, each constant voltage source represents a distributed power supply. Each distributed power supply is connected to the DC bus through an LC filter. The bus is connected to the CPL load after being stepped down by the BUCK. The CPL load includes the resistive load of the BUCK converter.

[0093] Specifically, the distributed power supply G1 is connected to the output of the AC / DC converter 1 to the LC filter composed of capacitor C1, resistor R1 and inductor L1, and is connected to the CPL load after being stepped down by the BUCK; the distributed power supply G2 is connected to the output of the AC / DC converter 2 to the LC filter composed of capacitor C2, resistor R2 and inductor L2, and is connected to the CPL load after being stepped down by the BUCK.

[0094] like Figure 3 As shown, in order to maintain the power balance of the microgrid, keep the system stable, and realize the coordinated work of each distributed power source, a smoothed segmented linear droop control is introduced to control the output voltage and current of each converter and preliminarily realize the current distribution between converters. This application mainly includes three parts: droop control characteristics, voltage PI controller and current PI controller. After the rated voltage V* is drooped, the DC voltage v DC And voltage PI controller, which is used to realize power distribution, voltage stability control and current stability control respectively through current PI controller.

[0095] In this application, the droop control is shown as follows:

[0096] V ref =V * -k i I i ;

[0097] Where V ref is the reference voltage of the droop control output, V* is the rated voltage, k i is the droop coefficient of this straight line, ΔI i It is the maximum current variation range corresponding to this straight line.

[0098] Both the DC voltage outer loop and the AC current inner loop use PI controllers to enable the output voltage and current to reach the reference values:

[0099]

[0100] Where i ref is the voltage PI controller output, v DC is the DC voltage of the converter, d is the duty cycle signal, V in is the input voltage of the distributed power supply; s is the Laplace operator, K pv and K ivThey are the proportional coefficient and integral coefficient of the voltage PI controller, K pc and K ic are the coefficients of the current PI controller of one layer respectively.

[0101] Specifically, in piecewise linear droop control, each linear segment is evenly divided into four equal parts. The last quarter of the current segment and the first quarter of the next segment are selected, and the intersection of these two parts is determined. Let the coordinates of the intersection of the two segments be P1(I1, V1). The expressions for the 75% point of the current segment and the 25% point of the next segment are as follows:

[0102] P0(I1-ΔI i / 4,V1+ΔV i / 4)

[0103] P2(I1+ΔI i+1 / 4,V1-ΔV i+1 / 4)

[0104] Where P0 is the starting point of the last quarter of this straight line, ΔI i is the maximum current variation range corresponding to this straight line, ΔV i This section of the straight line corresponds to the maximum voltage change range, ΔI i+1 is the maximum current variation range corresponding to the next straight line, ΔV i+1 The maximum voltage variation range corresponding to the next straight line is P0(I0,V0) and P2(I2,V2).

[0105] Based on the determined piecewise linear droop control line, divide each straight line into four equal parts. Select the 75% position point P0 of each segment and the 25% position point P2 of the next segment, as well as the intersection point P1 of these two straight lines as the control points of the Bezier curve. The coordinates of the three control points are marked as follows:

[0106]

[0107] In some possible embodiments, a Bezier curve is generated based on the control points, and the Bezier curve is used for the intersection of two segments of the segmented droop to smoothly transition between different intervals of the segmented droop, including:

[0108] The control points are obtained, and the Bezier curve is determined to be a second-order Bezier curve. The control points are substituted into the second-order Bezier curve to obtain the Bezier curve. The Bezier curve is used to replace the two intersections of the segmented droop to obtain the corresponding relationship between the voltage and the current, thereby achieving smooth conversion between different intervals of the segmented droop.

[0109] Specifically, the Bezier curve is determined to be a second-order Bezier curve based on three control points. The expression of the second-order Bezier curve is as follows:

[0110]

[0111] Then, the selected control points P0, P1 and P2 are used to define the Bezier curve and then the expression of the second-order Bezier curve is obtained: B(t) = (1-t) 2 P0+2(1-t)tP1+t 2 P2,0≤t≤1; Finally, use the Bezier curve to replace the intersection of the two end straight lines, and the expressions of voltage and current can be obtained respectively:

[0112]

[0113] Where t is the interpolation factor controlling the Bezier curve. When t changes from 0 to 1, the Bezier curve smoothly transitions from the starting point P0 to the end point P2, controlled by the intersection point P1. V0, V1, and V2 are the voltages corresponding to P0, P1, and P2, respectively; and I0, I1, and I2 are the currents corresponding to P0, P1, and P2. By replacing the intersection of the piecewise linear droop characteristic with this curve, a smooth transition of the overall droop characteristic is achieved.

[0114] In the mathematical expression of a Bezier curve, the parameter t is used to calculate the weight of each control point. These weights determine the degree of influence each control point has on the shape of the curve. When t is 0, it means the curve is at the starting point, and when t=1, it means the curve is at the end point.

[0115] This application obtains each segment of the segmented droop control and calculates the corresponding Bezier curve control point at the intersection of each segment. After calculating the Bezier curve, the Bezier curve is used to replace the intersection part. Finally, the control curve after smoothing is obtained as follows: Figure 4 shown.

[0116] This application introduces a specific embodiment in detail. The rated voltage of the DC microgrid in the embodiment is 540V; the system parameters of the segmented droop control are set as: v0 = 540V, ΔV max =19V,I max =10A, α = 2, β = 1, N = 4; initially, the system load is 4500W. Then, at 1.0 seconds, the system load is increased from 4500W to 4763W. This sudden increase to 4763W ensures that the curve falls within the intersection of the two control lines, allowing comparison between the smoothed curve and the unsmoothed segmented droop curve.

[0117] The simulation results of the traditional piecewise linear droop control embodiment are shown in Figure 5 (a); The simulation results of the traditional linear droop control embodiment are shown in Figure 5(b); The droop control embodiment after Bezier curve smoothing is shown in FIG. Figure 5 (c). From Figure 5 It can be seen that for the same sudden load change, the segmented droop control curve has the worst dynamic response performance, with a response time of 134ms; the linear droop control has a better response time than the segmented droop, with a response time of 106ms; and the droop control after Bezier curve smoothing has the shortest dynamic response time, only 84ms.

[0118] Referring to Table 1 below, it can be seen from this embodiment that the nonlinear droop control scheme based on the Bezier curve proposed in this application can effectively solve the problem of poor dynamic performance of the traditional segmented droop control at the intersection point, and the bus voltage is basically the same as the segmented droop control, and still performs well when the load changes.

[0119] Table 1: Current distribution accuracy results of three strategies

[0120]

[0121]

[0122] Based on the same technical concept, in another embodiment of the present application, a nonlinear droop control system suitable for a DC microgrid is provided, comprising: a first calculation module for obtaining system parameters of a DC microgrid based on segmented droop control, and calculating the droop coefficient k of each segment in the segmented linear droop control. i ; The second calculation module is used to calculate the droop coefficient k i , determine the boundary range of each segmented intersection area and calculate the control points of the Bezier curve; the output module is used to generate a Bezier curve based on the control points, and use the Bezier curve for the intersection of the two segments of the segmented droop to smoothly transition between different intervals of the segmented droop.

[0123] This application first obtains system parameters through the first calculation module and calculates the droop coefficient k i Then, the second calculation module uses the droop coefficient to determine the segmented boundary area and calculates the control points of the Bezier curve. Finally, the output module generates the Bezier curve according to the control points to achieve smooth transition between the segmented droop control intervals, thereby improving the stability and response speed of the DC microgrid and avoiding the sudden change problem that may occur at the boundary of traditional linear droop control.

[0124] It should be noted that the modules in the nonlinear droop control system applicable to the DC microgrid provided in the above embodiments of the present application correspond to the steps of the nonlinear droop control method applicable to the DC microgrid in any of the above embodiments. Those skilled in the art can refer to the step characteristics of the nonlinear droop control method applicable to the DC microgrid to implement the corresponding modules in the nonlinear droop control system applicable to the DC microgrid, which will not be repeated here.

[0125] Those skilled in the art will appreciate that, in addition to implementing the system and its various modules provided by the embodiments of the present invention in purely computer-readable program code, it is entirely possible to implement the same functions of the system and its various modules provided by the embodiments of the present invention in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, embedded microcontrollers, etc. by logically programming the method steps. Therefore, the system and its various modules provided by the embodiments of the present invention can be considered a hardware component, and the devices included therein for implementing various functions can also be considered as structures within the hardware component; the modules for implementing various functions can also be considered as both software modules for implementing the method and structures within the hardware component.

[0126] The above describes the specific embodiments of the present application. It should be understood that the present application is not limited to the specific embodiments described above, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the substantive content of the present application. The above preferred features may be used in any combination as long as they do not conflict with each other.

Claims

1. A nonlinear droop control method suitable for a DC microgrid, characterized in that: include: Obtain the system parameters of the DC microgrid based on segmented droop control and calculate the droop coefficient k of each segment in the segmented linear droop control i ; According to the droop coefficient k i , determine the boundary range of each segment intersection area and calculate the control points of the Bezier curve; A Bezier curve is generated according to the control points, and the Bezier curve is used for the junction of two sections of the segmented droop to perform smooth conversion between different sections of the segmented droop.

2. A nonlinear droop control method suitable for a DC microgrid according to claim 1, characterized in that: The system parameters of the DC microgrid based on the segmented droop control are obtained, and the droop coefficient k of each segment in the segmented linear droop control is calculated. i ,include: Obtain the segmented linear droop control curve, determine the upper and lower limits of bus voltage fluctuation, the maximum load current that each power supply can withstand, and the number of segmented control segments N, and calculate the maximum voltage deviation ΔV max , Maximum load current I max ; Obtain the control constants α and β of the piecewise linear droop control curve, and calculate the maximum voltage deviation ΔV max and the maximum load current I max , calculate the voltage change value ΔV1 of the first segment and the current change value ΔI of the Nth segment N ; According to the calculation of the first voltage change value ΔV1 and the Nth current change value ΔI N And the control constant, calculate the voltage variation range ΔV of each section i , Current variation range ΔI i and the droop coefficient k of each segment of the piecewise linear droop control i .

3. The nonlinear droop control method for a DC microgrid according to claim 2, characterized in that: The calculated maximum voltage deviation ΔV max , Maximum load current I max The formula is: Where, ΔV i and ΔI i It is the voltage and current variation range in different intervals of droop control.

4. The nonlinear droop control method for a DC microgrid according to claim 2, characterized in that: The first voltage change ΔV1 and the Nth current change ΔI N The expression is:

5. The nonlinear droop control method applicable to a DC microgrid according to claim 2, characterized in that: The voltage variation range ΔV i , Current variation range ΔI i and droop coefficient k i The expression is: ΔV i =α(i)ΔV1; ΔI i =β(N+1-i)ΔI N ; Where α and β are control constants, k i is the droop coefficient corresponding to the i-th straight line.

6. The nonlinear droop control method for a DC microgrid according to claim 1, characterized in that: Determining the boundary range of each segment intersection area according to the droop coefficient and calculating the control points of the Bezier curve includes: Get the droop coefficient k i , calculate the straight line expression of each segment of the piecewise linear droop control and determine the boundary range of the intersection area of ​​each segment; Determining a piecewise linear droop control line according to the boundary range of each segment intersection area; According to the piecewise linear droop control line, each section of the control line is evenly divided into four equal parts, and the 75% position point P0 of each section and the 25% position point P2 of the next section, as well as the intersection point P1 of the two sections are selected as control points of the Bezier curve.

7. The nonlinear droop control method for a DC microgrid according to claim 6, characterized in that: Each straight line expression of the segmented linear droop control includes: a rated voltage expression at the start and a starting rated voltage expression of the next segment; The rated voltage expression at the starting point is: V ref =V * -k i I i ; Where V ref is the reference voltage, V * is the rated voltage at the beginning of each segment, k i is the droop coefficient corresponding to the i-th straight line, I i is the output current; The starting rated voltage expression of the next section is: Where, is the rated voltage of the next control line, k i is the droop coefficient of this straight line, ΔI i is the maximum current variation range corresponding to this straight line; The expression of P0 is: P0(I1-ΔI i / 4,V1+ΔV i / 4); The expression of P2 is: P2(I1+ΔI i+1 / 4,V1-ΔV i+1 / 4); Where P0 is the starting point of the last quarter of this straight line, ΔI i is the maximum current variation range corresponding to this straight line, ΔV i This section of the straight line corresponds to the maximum voltage change range, ΔI i+1 is the maximum current variation range corresponding to the next straight line, ΔV i+1 is the maximum voltage variation range corresponding to the next straight line; The coordinates of the control points are:

8. The nonlinear droop control method applicable to a DC microgrid according to claim 1, characterized in that: The step of generating a Bezier curve according to the control point and applying the Bezier curve to the intersection of two sections of the segmented droop to smoothly convert between different sections of the segmented droop includes: Obtaining the control point, determining that the Bezier curve is a second-order Bezier curve, and substituting the control point into the second-order Bezier curve to obtain a Bezier curve; The Bezier curve is used to replace the intersection of two sections of the segmented droop to obtain the corresponding relationship between the voltage and the current, thereby achieving smooth conversion between different sections of the segmented droop.

9. The nonlinear droop control method applicable to a DC microgrid according to claim 8, characterized in that: The expression of the Bezier curve is: B(t)=(1-t) 2 P0+2(1-t)tP1+t 2 P2,0≤t≤1; The expressions of the voltage and the current are: Where t is the interpolation factor that controls the Bezier curve. When t changes from 0 to 1, the Bezier curve smoothly transitions from the starting point P0 to the end point P2 and is controlled by the intersection P1. V0, V1, and V2 are the voltages corresponding to P0, P1, and P2. I0, I1, and I2 are the currents corresponding to P0, P1, and P2.

10. A nonlinear droop control system suitable for a DC microgrid, characterized in that: include: The first calculation module is used to obtain the system parameters of the DC microgrid based on the segmented droop control and calculate the droop coefficient k of each segment in the segmented linear droop control. i ; The second calculation module is used to calculate the droop coefficient k i , determine the boundary range of each segment intersection area and calculate the control points of the Bezier curve; The output module is used to generate a Bezier curve according to the control points, and use the Bezier curve for the intersection of two sections of the segmented droop to perform smooth conversion between different intervals of the segmented droop.

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