Wind and light storage coordination control method based on multi-inflection-point droop control

Abstract

The invention discloses a wind and light storage coordination control method based on multi-inflection-point droop control, and belongs to the field of power grids, and the method comprises the following steps: S1, respectively establishing a photovoltaic output mathematical model, a wind power output mathematical model and an energy storage output mathematical model for a photovoltaic system, a wind power system and an energy storage system; s2, calculating an active droop coefficient and a reactive droop coefficient based on the characteristics of the multi-inflection-point droop control characteristic curve; s3, building a simulation model through MATLAB, and carrying out simulation verification on the active droop coefficient and the reactive droop coefficient; and S4, the charging and discharging output range of the energy storage unit is adjusted in real time through multi-inflection-point droop control. According to the wind and light storage coordination control method based on multi-inflection-point droop control, the charging and discharging output range of the energy storage unit is adjusted in real time through the multi-inflection-point droop control, the stability of combined operation of multiple kinds of energy can be improved, and the control robustness of energy storage of a micro-grid system facing electric quantity and electric power balance multi-scene requirements is effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of power grid technology, and in particular to a wind-solar-storage coordinated control method based on multi-inflection point droop control. Background Art

[0002] With the continuous advancement of electrochemical energy storage technology and the continuous reduction of costs, electrochemical energy storage technology has been vigorously developed. Various regions have also accelerated the application of energy storage technology, which is conducive to energy transformation and development layout.

[0003] At present, in power grid companies, grid-side energy storage is basically all included in the dispatching management scope, but the energy storage control methods are rarely reflected, and the energy storage on the power supply side and the user side is mostly in an "invisible and intangible" state; for the multi-energy complementary control level, power distribution is generally achieved by controlling the power converter, thereby improving the reliability of the power grid, but there is a lack of consideration of the composite control system of new energy and energy storage.

[0004] At present, the common multi-energy complementary control methods are generally divided into master-slave control and droop control. Compared with master-slave control, the biggest advantage of droop control is that power can be shared between parallel power sources without any communication. Although droop control can achieve power sharing without communication between parallel power sources, it cannot guarantee that the microgrid obtains the maximum energy from renewable energy and regulates its power flow.

[0005] At present, there are three common multi-energy control modes for power grids:

[0006] 1. Multi-energy constant power control mode:

[0007] The goal of constant power control is to make the active and reactive power output by the micro power source follow its power reference value. Under this control mode, the fluctuations of load power, voltage and frequency in the microgrid are all borne by the distribution network to which the microgrid is incorporated. Each micro power source does not need to participate in the regulation, and directly collects the voltage and frequency of the distribution network as its reference value, and then uses the power controller to adjust the active frequency droop characteristic curve so that the active power output of the micro power source is always kept near the reference value; adjust the reactive voltage droop characteristic curve so that the reactive power also follows the corresponding reference value.

[0008] It has the following defects:

[0009] After adopting constant power control (PQ control), only the active and reactive power output by the inverter can be guaranteed to be constant, but the voltage and frequency sliding cannot be guaranteed. Therefore, other distributed power modules in the network or the main network are required to support the bus stability.

[0010] 2. Multi-energy constant voltage and constant frequency control mode:

[0011] The basic idea of ​​constant voltage and constant frequency control is to adjust the voltage and frequency of the micro power supply output so that the output active and reactive power meet the load demand, maintain the power balance in the microgrid, and maintain the voltage and frequency stability of the microgrid. When the load power or micro power supply output in the microgrid changes, the inverter detects the power change in the microgrid, changes the output voltage, frequency and power angle by changing the frequency of the control wave, and adjusts the output power.

[0012] It has the following defects:

[0013] Compared with constant power control (PQ) control, the control mode is complex and its application scope has certain limitations. It is only applicable to off-grid operation mode.

[0014] 3. Multi-energy droop control strategy

[0015] The micro-power inverter is controlled in a similar way to the traditional power system, and the voltage and frequency of the micro-power output are adjusted by using the relationship between active and reactive power and voltage and frequency. There are currently two types of droop control used by inverters. One is to simulate the traditional synchronous generator to adjust, using the active frequency and reactive voltage droop control method, and the other is to use the active voltage and reactive frequency adjustment method.

[0016] It has the following defects:

[0017] When traditional droop is applied to multiple inverters operating independently in parallel, there is a problem of load power distribution caused by different line impedances. In addition, traditional droop is a differential control. During island operation, the output voltage and frequency will change with the system load. During grid-connected operation, the inverter output power will be affected by the voltage amplitude and frequency fluctuations of the grid. Summary of the invention

[0018] To solve the above problems, the present invention provides a wind-solar-storage coordinated control method based on multi-inflection point droop control, which can achieve a larger compression ratio and a smaller area error, providing a better data basis for subsequent research and is of great significance to time series data work.

[0019] To achieve the above object, the present invention provides a wind-solar-storage coordinated control method based on multi-inflection point droop control, comprising the following steps:

[0020] S1. For the photovoltaic system, wind power system and energy storage system, a photovoltaic output mathematical model, a wind power output mathematical model and an energy storage output mathematical model are established respectively;

[0021] S2. Calculate the active power droop coefficient and reactive power droop coefficient based on the characteristics of the multi-inflection point droop control characteristic curve;

[0022] S3. Use MATLAB to build a simulation model and perform simulation verification on the active power droop coefficient and reactive power droop coefficient;

[0023] S4. Use multi-inflection point droop control to adjust the charging and discharging output range of the energy storage unit in real time.

[0024] Preferably, the photovoltaic system described in step S1 uses a photovoltaic cell, and its IV characteristic curve is expressed as:

[0025]

[0026] In the formula, I sc is the short-circuit current, in A; V oc is the open circuit voltage, in V;

[0027] The coefficients C1 and C2 are solved by the following system of equations:

[0028]

[0029] Where V m is the maximum power point voltage, in V; I m is the maximum power point current, in A; i sc is the short-circuit current, in A;

[0030] The wind power system described in step S1 adopts a direct-drive wind turbine generator, which is mainly composed of a wind turbine and a permanent magnet synchronous generator. According to Betz's law, the characteristics of the direct-drive wind turbine generator are expressed as follows:

[0031] P W =0.5ρπR 2 v 3 C p (3)

[0032] Where P W is the output power, in W; ρ is the air density; R is the rotor radius, in m; v is the tip wind speed, in m / s; C p is the wind energy utilization coefficient;

[0033] The energy storage system described in step S1 uses lithium-ion batteries, and its mathematical model expression is as follows:

[0034] For the discharge process, the low-frequency current dynamics i * >0, there are:

[0035]

[0036] Where, E0 is the constant voltage, in V; K is the polarization resistance, in Ω; Q is the maximum capacity of the lithium-ion battery, in A·h; it is the extraction capacity, in A·h; A is the voltage index; B is the capacity index; i * is the low-frequency current power, unit is A;

[0037] For the charging process, the low-frequency current power i * <0, there are:

[0038]

[0039] Preferably, step S2 specifically includes the following steps:

[0040] S21. In order to ensure the voltage quality of the energy storage inverter during the grid connection and disconnection process, the inverter optimization control based on improved self-recovery droop (SRDC) is adopted:

[0041] Calculate the load active and reactive power Pload and Qload in the inverter control strategy:

[0042] The calculation formula is:

[0043] (P load +Q load )=(P o +Q o )-(P g +Q g ) (6)

[0044] Where P load and Q load are load active power and load reactive power respectively; P o and Q o are the active power and reactive power output by the inverter respectively; P g and Q g They are grid-connected active power and grid-connected reactive power respectively;

[0045] The corresponding droop control equation is:

[0046]

[0047] Where, ω is the inverter angular frequency; is the inverter voltage amplitude change rate; ω ref is the reference angular frequency; is the change in reference voltage amplitude, P res , Q res Respectively restore active and reactive power; k resP , k resQ They are ω, Coefficient of restitution in the recovery mechanism; mp, n Q are active and reactive droop control coefficients respectively; K(S) is the deviation proportional feedforward coefficient;

[0048] Preferably, in step S3, a microgrid model is built using MATLAB. In the microgrid model, the photovoltaic system and the wind power system always operate at the maximum power point. When the power generated by the photovoltaic system and the wind power system is greater than the load demand, the excess power is stored in the energy storage system; when the load power consumption is greater than the power generated by the photovoltaic system and the wind power system, the energy storage system provides additional power, and the photovoltaic system and the wind power system both achieve discharge and maximum power point tracking through a DC / DC converter, and the energy storage system achieves charging and discharging through a bidirectional DC / DC converter.

[0049] Preferably, in step S4, the duty cycle of the photovoltaic system and the wind power system converter is adjusted by the MPPT algorithm, and then the DC bus voltage is balanced by absorbing or emitting power through the energy storage system;

[0050] It specifically includes the following steps:

[0051] S41, using the disturbance observation method to track the maximum power point of the photovoltaic system and the wind power system respectively;

[0052] S42. The conductance increment method is applied to photovoltaic systems to verify the universality of the improved droop control.

[0053] S43. The duty cycle of the photovoltaic and wind power system converters is adjusted through the MPPT algorithm to ensure that the photovoltaic and wind power systems operate at the maximum power point.

[0054] Preferably, step S43 specifically includes the following steps:

[0055] S431, monitoring the initial voltage and initial current as well as the current and voltage at subsequent moments;

[0056] S432, using the difference between the current and the voltage before and after to obtain the change of the current and voltage;

[0057] S433, determine whether the maximum change amount △V of the DC bus voltage and the maximum change amount △I of the current are 0:

[0058] When △V=0, △I≠0, and the next voltage monitoring value is greater than the previous voltage monitoring value, the next voltage monitoring value V(K+1)=V(K)+step length is output;

[0059] When △V=0, △I≠0, and the next voltage monitoring value is less than the previous voltage monitoring value, the next voltage monitoring value V(K+1)=V(K)-step length is output;

[0060] When △V≠0, determine whether the ratio of the current and voltage change values ​​is the opposite of the ratio of the initial current and initial voltage:

[0061] When △I / △V≠-I / V, the next voltage monitoring value V(K+1)=V(K)-step length is output;

[0062] When △I / △V=-I / V, the next voltage monitoring value V(K+1)=V(K)+step length is output.

[0063] The present invention has the following beneficial effects:

[0064] In order to improve the utilization rate of renewable energy, from the perspective of power generation units, the maximum power tracking technology is combined with the traditional droop control, and an improved multi-inflection point droop control method is proposed. This method provides an extreme point recognition algorithm with staggered maximum and minimum values ​​and a data compression algorithm for equally spaced time series that retains timing characteristics, which can give priority to ensuring the maximum output of wind and light, and then the energy storage system absorbs or supplements power.

[0065] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 It is an overall flow chart of a wind-solar-storage coordinated control method based on multi-inflection point droop control of the present invention;

[0067] Figure 2 It is a flow chart of the MPPT algorithm of a wind-solar-storage coordinated control method based on multi-inflection point droop control of the present invention;

[0068] Figure 3 A photovoltaic cell droop control block diagram of a wind-solar-storage coordinated control method based on multi-inflection point droop control of the present invention;

[0069] Figure 4 A diagram showing a change in DC bus voltage under conventional droop control according to an embodiment of the present invention;

[0070] Figure 5 A diagram showing a change in DC bus voltage under improved droop control according to an embodiment of the present invention;

[0071] Figure 6 It is a curve diagram of output fluctuation suppression of an embodiment of the present invention under a traditional method;

[0072] Figure 7 This is a curve diagram of output fluctuation suppression under the improved droop control method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0073] In order to make the purpose, technical scheme and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention are further described in detail in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not intended to limit the embodiments of the present invention. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions.

[0074] It should be noted that the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or server that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or inherent to these processes, methods, products or devices.

[0075] Like reference numerals and letters denote similar items in the following drawings, and thus, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0076] like Figure 1 As shown, a wind-solar-storage coordinated control method based on multi-inflection point droop control includes the following steps:

[0077] S1. For the photovoltaic system, wind power system and energy storage system, a photovoltaic output mathematical model, a wind power output mathematical model and an energy storage output mathematical model are established respectively;

[0078] like Figure 3 As shown, the photovoltaic system described in step S1 uses a photovoltaic cell, and its IV characteristic curve is expressed as:

[0079]

[0080] In the formula, I sc is the short-circuit current, in units of A ; V oc is the open circuit voltage, in V;

[0081] The coefficients C1 and C2 are solved by the following system of equations:

[0082]

[0083] Where V m is the maximum power point voltage, in V; I m is the maximum power point current, in A; i sc is the short-circuit current, in A;

[0084] The wind power system described in step S1 adopts a direct-drive wind turbine generator, which is mainly composed of a wind turbine and a permanent magnet synchronous generator. According to Betz's law, the characteristics of the direct-drive wind turbine generator are expressed as follows:

[0085] P W =0.5ρπR 2 v 3 C p (3)

[0086] Where P W is the output power, in W; ρ is the air density; R is the rotor radius, in m; v is the tip wind speed, in m / s; C p is the wind energy utilization coefficient;

[0087] The energy storage system described in step S1 uses lithium-ion batteries, and its mathematical model expression is as follows:

[0088] For the discharge process, the low-frequency current dynamics i * >0, there are:

[0089]

[0090] Where, E0 is the constant voltage, in V; K is the polarization resistance, in Ω; Q is the maximum capacity of the lithium-ion battery, in A·h; it is the extraction capacity, in A·h; A is the voltage index; B is the capacity index; i * is the low-frequency current power, unit is A;

[0091] For the charging process, the low-frequency current power i * <0, there are:

[0092]

[0093] S2. Calculate the active power droop coefficient and reactive power droop coefficient based on the characteristics of the multi-inflection point droop control characteristic curve;

[0094] Step S2 specifically includes the following steps:

[0095] S21. In order to ensure the voltage quality of the energy storage inverter during the grid connection and disconnection process, the inverter optimization control based on improved self-recovery droop (SRDC) is adopted:

[0096] Calculate the load active and reactive power Pload and Qload in the inverter control strategy:

[0097] The calculation formula is:

[0098] (P load +Q load)=(P o +Q o )-(P g +Q g ) (6)

[0099] Where P load and Q load are load active power and load reactive power respectively; P o and Q o are the active power and reactive power output by the inverter respectively; P g and Q g They are grid-connected active power and grid-connected reactive power respectively;

[0100] The corresponding droop control equation is:

[0101]

[0102] Where, ω is the inverter angular frequency; is the inverter voltage amplitude change rate; ω ref is the reference angular frequency; is the change in reference voltage amplitude, P res , Q res Respectively restore active and reactive power; k resP , k resQ They are ω, Coefficient of restitution in the recovery mechanism; mp, n Q are active and reactive droop control coefficients respectively; K(S) is the deviation proportional feedforward coefficient;

[0103] S3. Use MATLAB to build a simulation model and perform simulation verification on the active power droop coefficient and reactive power droop coefficient;

[0104] In step S3, a microgrid model is built using MATLAB. In the microgrid model, the photovoltaic system and the wind power system always operate at the maximum power point. When the power generated by the photovoltaic system and the wind power system is greater than the load demand, the excess power is stored in the energy storage system; when the load power consumption is greater than the power generated by the photovoltaic system and the wind power system, the energy storage system provides additional power, and the photovoltaic system and the wind power system both achieve discharge and maximum power point tracking through DC / DC converters, and the energy storage system achieves charging and discharging through a bidirectional DC / DC converter.

[0105] It specifically includes the following steps:

[0106] First, the conventional droop control method is applied to the converter; then, the droop control described in this embodiment is applied to the converter. According to the simulation results, after the droop control method described in this embodiment is adopted, both photovoltaic and wind power can output the maximum power first.

[0107] like Figure 2 As shown, S4, using multi-inflection point droop control to adjust the charging and discharging output range of the energy storage unit in real time.

[0108] In step S4, the duty cycle of the photovoltaic system and the wind power system converter is adjusted by the MPPT algorithm, and the DC bus voltage is balanced by absorbing or emitting power through the energy storage system;

[0109] Since the output power of photovoltaic cells is jointly affected by light intensity, temperature and working voltage; the output power of wind turbines is jointly affected by wind speed and pitch angle, the universality of the improved droop control is verified. In step S4, the duty cycle of the photovoltaic system and wind power system converter is adjusted by the MPPT algorithm, thereby giving priority to the maximum output of wind energy and photovoltaics, and then balancing the DC bus voltage by absorbing or emitting power through the energy storage system;

[0110] Among them, the converter (inverter) can convert the direct current from the wind, light, and storage side into the alternating current required by the power grid through droop control. Its role is equivalent to that of a load and can draw a specific amount of power. The droop control of a three-phase converter is slightly different from that of a DC / DC converter. Its principle is to detect the output power of the inverter, decouple the active power and reactive power independently, and obtain the reference value of the output frequency and voltage amplitude through the droop characteristics, thereby reasonably allocating the active power and reactive power of the system.

[0111] It specifically includes the following steps:

[0112] S41, using the disturbance observation method to track the maximum power point of the photovoltaic system and the wind power system respectively;

[0113] S42. The conductance increment method is applied to photovoltaic systems to verify the universality of the improved droop control.

[0114] S43. The duty cycle of the photovoltaic and wind power system converters is adjusted through the MPPT algorithm to ensure that the photovoltaic and wind power systems operate at the maximum power point.

[0115] Step S43 specifically includes the following steps:

[0116] S431, monitoring the initial voltage and initial current as well as the current and voltage at subsequent moments;

[0117] S432, using the difference between the current and the voltage before and after to obtain the change of the current and voltage;

[0118] S433, determine whether the maximum change amount △V of the DC bus voltage and the maximum change amount △I of the current are 0:

[0119] When △V=0, △I≠0, and the next voltage monitoring value is greater than the previous voltage monitoring value, the next voltage monitoring value V(K+1)=V(K)+step length is output;

[0120] When △V=0, △I≠0, and the next voltage monitoring value is less than the previous voltage monitoring value, the next voltage monitoring value V(K+1)=V(K)-step length is output;

[0121] When △V≠0, determine whether the ratio of the current and voltage change values ​​is the opposite of the ratio of the initial current and initial voltage:

[0122] When △I / △V≠-I / V, the next voltage monitoring value V(K+1)=V(K)-step length is output;

[0123] When △I / △V=-I / V, the next voltage monitoring value V(K+1)=V(K)+step length is output.

[0124] Example

[0125] The droop control based on the P&O algorithm is applied to the converters of the photovoltaic system and the wind power system. Since the microgrid is to be connected to the large power grid with a phase voltage of 220V and a frequency of 50Hz, the DC bus voltage needs to be controlled at 700V. Using traditional droop control, the DC bus voltage changes as follows Figure 4 As shown; the target curve for smoothing is as follows Figure 6 According to the analysis of the results of the embodiment, under the traditional droop control method, there is no obvious energy supply priority between renewable energy and energy storage.

[0126] When the droop control described in this embodiment (microgrid combined with P&O and IC algorithm improvement) is adopted, the DC bus voltage changes as follows: Figure 5 As shown in Figure 7 shown.

[0127] It can be seen that after adopting the droop control method described in this embodiment, both photovoltaic and wind power can output the maximum power first, and the energy storage system absorbs or outputs power according to the profit or loss of energy. The calculation results are shown in Table 1.

[0128] Table 1 Comparison of calculation results

[0129]

[0130]

[0131] As can be seen from Table 1, in terms of capacity planning, the method described in this embodiment effectively optimizes the energy storage capacity; in terms of smoothing power offset, the method described in this embodiment has an increase compared with the conventional method; in terms of over-limit operation, the method described in this embodiment greatly reduces the number of over-limit times, with a reduction of 96.2%, and the effect is obvious.

[0132] Therefore, the present invention adopts the above-mentioned wind-solar-storage coordinated control method based on multi-inflection point droop control, which can achieve a larger compression ratio and a smaller area error, providing a better data basis for subsequent research.

[0133] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A wind-solar-storage coordinated control method based on multi-inflection point droop control, characterized in that: The following steps are involved: S1. For the photovoltaic system, wind power system and energy storage system, a photovoltaic output mathematical model, a wind power output mathematical model and an energy storage output mathematical model are established respectively; S2. Calculate the active power droop coefficient and reactive power droop coefficient based on the characteristics of the multi-inflection point droop control characteristic curve; S3. Use MATLAB to build a simulation model and perform simulation verification on the active power droop coefficient and reactive power droop coefficient; S4. Use multi-inflection point droop control to adjust the charging and discharging output range of the energy storage unit in real time.

2. The wind-solar-storage coordinated control method based on multi-inflection point droop control according to claim 1, characterized in that: The photovoltaic system described in step S1 uses a photovoltaic cell, and its IV characteristic curve is expressed as: In the formula, I sc is the short-circuit current, in A; V oc is the open circuit voltage, in V; The coefficients C1 and C2 are solved by the following system of equations: Where V m is the maximum power point voltage, in V; I m is the maximum power point current, in A; i sc is the short-circuit current, in A; The wind power system described in step S1 adopts a direct-drive wind turbine generator, which is mainly composed of a wind turbine and a permanent magnet synchronous generator. According to Betz's law, the characteristics of the direct-drive wind turbine generator are expressed as follows: P W =0.5ρπR 2 v 3 C p (3) Where P W is the output power, in W; ρ is the air density; R is the rotor radius, in m; v is the tip wind speed, in m / s; C p is the wind energy utilization coefficient; The energy storage system described in step S1 uses lithium-ion batteries, and its mathematical model expression is as follows: For the discharge process, the low-frequency current dynamics i * >0, there are: Where, E0 is the constant voltage, in V; K is the polarization resistance, in Ω; Q is the maximum capacity of the lithium-ion battery, in A·h; it is the extraction capacity, in A·h; A is the voltage index; B is the capacity index; i * is the low-frequency current power, unit is A; For the charging process, the low-frequency current power i * <0, there are:

3. The wind-solar-storage coordinated control method based on multi-inflection point droop control according to claim 1, characterized in that: Step S2 specifically includes the following steps: S21. In order to ensure the voltage quality of the energy storage inverter during the grid connection and disconnection process, the inverter optimization control based on improved self-recovery droop (SRDC) is adopted: Calculate the load active and reactive power Pload and Qload in the inverter control strategy: The calculation formula is: (P load +Q load )=(P o +Q o )-(P g +Q g ) (6) Where P load and Q load are load active power and load reactive power respectively; P o and Q o are the active power and reactive power output by the inverter respectively; P g and Q g They are grid-connected active power and grid-connected reactive power respectively; The corresponding droop control equation is: Where, ω is the inverter angular frequency; is the inverter voltage amplitude change rate; ω ref is the reference angular frequency; is the reference voltage amplitude change, P res , Q res Respectively restore active and reactive power; k resP , k resQ They are ω, Coefficient of restitution in the recovery mechanism; mp, n Q are the active and reactive droop control coefficients respectively; K(S) is the deviation proportional feedforward coefficient.

4. The wind-solar-storage coordinated control method based on multi-inflection point droop control according to claim 1, characterized in that: In step S3, a microgrid model is built using MATLAB. In the microgrid model, the photovoltaic system and the wind power system always operate at the maximum power point. When the power generated by the photovoltaic system and the wind power system is greater than the load demand, the excess power is stored in the energy storage system; when the load power consumption is greater than the power generated by the photovoltaic system and the wind power system, the energy storage system provides additional power, and the photovoltaic system and the wind power system both achieve discharge and maximum power point tracking through DC / DC converters, and the energy storage system achieves charging and discharging through a bidirectional DC / DC converter.

5. The wind-solar-storage coordinated control method based on multi-inflection-point droop control according to claim 1, characterized in that: In step S4, the duty cycle of the photovoltaic system and the wind power system converter is adjusted by the MPPT algorithm, and the DC bus voltage is balanced by absorbing or emitting power through the energy storage system; It specifically includes the following steps: S41, using the disturbance observation method to track the maximum power point of the photovoltaic system and the wind power system respectively; S42. The conductance increment method is applied to photovoltaic systems to verify the universality of the improved droop control. S43. The duty cycle of the photovoltaic and wind power system converters is adjusted through the MPPT algorithm to ensure that the photovoltaic and wind power systems operate at the maximum power point.

6. The wind-solar-storage coordinated control method based on multi-inflection point droop control according to claim 5, characterized in that: Step S43 specifically includes the following steps: S431, monitoring the initial voltage and initial current as well as the current and voltage at subsequent moments; S432, using the difference between the current and the voltage before and after to obtain the change of the current and voltage; S433, determine whether the maximum change amount △V of the DC bus voltage and the maximum change amount △I of the current are 0: When △V=0, △I≠0, and the next voltage monitoring value is greater than the previous voltage monitoring value, the next voltage monitoring value V(K+1)=V(K)+step length is output; When △V=0, △I≠0, and the next voltage monitoring value is less than the previous voltage monitoring value, the next voltage monitoring value V(K+1)=V(K)-step length is output; When △V≠0, determine whether the ratio of the current and voltage change values ​​is the opposite of the ratio of the initial current and initial voltage: When △I / △V≠-I / V, the next voltage monitoring value V(K+1)=V(K)-step length is output; When △I / △V=-I / V, the next voltage monitoring value V(K+1)=V(K)+step length is output.

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