A microgrid inverter adaptive droop control method and system

Abstract

The application relates to the technical field of inverter operation control, and discloses a microgrid inverter adaptive droop control method and system, which introduces virtual complex impedance to make the output impedance of the microgrid inverter inductive, obtains a droop control equation of the microgrid inverter under rated power, keeps the droop coefficient of a droop characteristic curve unchanged, converts the droop control equation into an adaptive droop control equation corresponding to real-time power, calculates the difference between the adaptive droop control equation and the droop control equation, obtains a power deviation value of the microgrid inverter, inputs the power deviation value into a proportional integral controller, obtains a power regulation value, superimposes the power regulation value on the rated power, obtains the latest output power of the microgrid inverter for output, thereby reducing the voltage amplitude and frequency fluctuation caused by load change, and improving the droop control stability and working efficiency of the inverter.

Description

Technical Field

[0001] This invention relates to the field of inverter operation control technology, and in particular to an adaptive droop control method and system for microgrid inverters. Background Technology

[0002] With the depletion of traditional energy sources, renewable energy sources such as solar and wind power have received increasing attention. Distributed generation is an effective means of utilizing renewable energy, and microgrid systems composed of distributed power sources are an effective supplement to the main power grid, improving the security and reliability of power supply. A microgrid is a single, controllable unit formed by combining distributed power sources (including wind, solar, and fuel cells), loads, energy storage devices, and control devices to supply users with electricity and heat. Microgrids can operate in grid-connected and islanded modes. In the operation of microgrids, the control strategy is extremely important. Among microgrid control strategies, droop control is a crucial one. Droop control simulates the output characteristics of a synchronous generator, minimizing voltage and frequency fluctuations in the micro-sources during load changes.

[0003] In droop control, the output voltage and frequency of a microgrid inverter are related to the droop factor and load changes. An excessively large or small droop factor can cause system instability. Droop control allows the microgrid inverter's output power to automatically adjust to track load power changes; however, this control method sacrifices frequency and voltage accuracy. When the load and the inverter's rated power are not equal, voltage and frequency losses will occur. If load fluctuations are too large, the output voltage and frequency of the microgrid inverter may exceed the grid's power supply standards. If this happens, it will affect grid stability and cause significant losses to users and equipment.

[0004] Existing methods actively adjust the droop coefficient when the load power changes, restoring the system output voltage and frequency to their rated values. However, the output voltage and frequency still fluctuate at their rated values, exhibiting oscillation, resulting in unstable inverter droop control. Furthermore, the complex control structure of existing methods leads to low efficiency in inverter droop control. Summary of the Invention

[0005] This invention provides an adaptive droop control method and system for microgrid inverters, which solves the technical problems of unstable inverter droop control and low operating efficiency.

[0006] In view of this, the first aspect of the present invention provides an adaptive droop control method for a microgrid inverter, comprising the following steps:

[0007] Introducing a virtual complex impedance makes the output impedance of the microgrid inverter inductive;

[0008] Obtain the rated power of the microgrid inverter to derive the corresponding droop control equation;

[0009] Obtain the real-time power of the load, keep the droop coefficient of the droop characteristic curve unchanged, and convert the droop control equation into an adaptive droop control equation corresponding to the real-time power.

[0010] The power deviation value of the microgrid inverter is obtained by calculating the difference between the adaptive droop control equation and the droop control equation.

[0011] The power deviation value is input to the proportional-integral controller, which outputs a power adjustment value. The power adjustment value is then added to the rated power to obtain the latest output power of the microgrid inverter for output.

[0012] Preferably, the droop control equation is:

[0013]

[0014] In Equation 1, P * The rated active power output of the microgrid inverter. ω represents the maximum rated active power of the microgrid inverter, m is the droop coefficient of the active-frequency droop characteristic curve, n is the droop coefficient of the reactive-voltage droop characteristic curve, and ω is the maximum rated active power of the microgrid inverter. * E is the rated angular frequency of the microgrid inverter. * Q is the rated voltage of the microgrid inverter. * This refers to the rated reactive power output of the microgrid inverter.

[0015] Preferably, the adaptive droop control equation is:

[0016]

[0017] In Equation 2, p is the active power of the load, q is the reactive power of the load, and P m Q is the maximum rated active power of the load. m This represents the maximum reactive power of the load.

[0018] Preferably, the rated angular frequency ω of the microgrid inverter * =100π, rated output voltage amplitude E * =311V.

[0019] Preferably, the step of calculating the difference between the adaptive droop control equation and the droop control equation to obtain the power deviation value of the microgrid inverter is as follows:

[0020] The power deviation value of the microgrid inverter is obtained by calculating the difference between the adaptive droop control equation and the droop control equation:

[0021] Δp=ΔP m Formula 3

[0022] Δq=ΔQ m Formula 4

[0023] In equations 3 and 4, Δp represents the active power deviation, Δq represents the reactive power deviation, and ΔP m ΔQ represents the difference between the maximum rated active power and the maximum rated active power. m This represents the difference in maximum rated reactive power.

[0024] Secondly, the present invention also provides an adaptive droop control system for a microgrid inverter, comprising:

[0025] The inductive module is used to introduce a virtual complex impedance to make the output impedance of the microgrid inverter inductive.

[0026] The first equation module is used to obtain the rated power of the microgrid inverter and obtain the corresponding droop control equation;

[0027] The second equation module is used to obtain the real-time power of the load, keep the droop coefficient of the droop characteristic curve unchanged, and convert the droop control equation into an adaptive droop control equation corresponding to the real-time power.

[0028] The difference calculation module is used to calculate the difference between the adaptive droop control equation and the droop control equation to obtain the power deviation value of the microgrid inverter.

[0029] The control module is used to input the power deviation value to the proportional-integral controller, output the power adjustment value, and add the power adjustment value to the rated power to obtain the latest output power of the microgrid inverter for output.

[0030] As can be seen from the above technical solutions, the present invention has the following advantages:

[0031] This invention introduces a virtual complex impedance to make the output impedance of the microgrid inverter inductive, thereby obtaining the droop control equation of the microgrid inverter at rated power. Keeping the droop coefficient of the droop characteristic curve constant, the droop control equation is converted into an adaptive droop control equation corresponding to the real-time power. The difference between the adaptive droop control equation and the droop control equation is calculated to obtain the power deviation value of the microgrid inverter. This power deviation value is input into a proportional-integral controller to obtain a power adjustment value. The power adjustment value is then superimposed on the rated power to obtain the latest output power of the microgrid inverter, which is then output. This reduces voltage amplitude and frequency fluctuations caused by load changes, improving the stability and efficiency of the inverter's droop control. Attached Figure Description

[0032] Figure 1A flowchart of an adaptive droop control method for a microgrid inverter provided in an embodiment of the present invention;

[0033] Figure 2 The active power-frequency droop characteristic curve of the microgrid inverter provided in the embodiment of the present invention;

[0034] Figure 3 The reactive power-voltage droop characteristic curve of the microgrid inverter provided in the embodiment of the present invention;

[0035] Figure 4 This is a schematic diagram of the output frequency variation of a microgrid inverter provided in an embodiment of the present invention;

[0036] Figure 5 This is a schematic diagram of the output voltage variation of a microgrid inverter provided in an embodiment of the present invention;

[0037] Figure 6 This is a schematic diagram of the structure of an adaptive droop control system for a microgrid inverter provided in an embodiment of the present invention. Detailed Implementation

[0038] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] For easier understanding, please refer to Figure 1 The present invention provides an adaptive droop control method for a microgrid inverter, comprising the following steps:

[0040] S1. Introducing a virtual complex impedance makes the output impedance of the microgrid inverter inductive.

[0041] Here, the output impedance of the microgrid inverter is taken as R+jX, and the output impedance of the microgrid inverter is inductive, i.e., X >> R. Here, R is the output resistance of the microgrid inverter, X is the output reactance of the microgrid inverter, and j is an imaginary number.

[0042] S2. Obtain the rated power of the microgrid inverter and derive the corresponding droop control equation.

[0043] The droop control equation is:

[0044]

[0045] In Equation 1, P * The rated active power output of the microgrid inverter. ω represents the maximum rated active power of the microgrid inverter, m is the droop coefficient of the active-frequency droop characteristic curve, n is the droop coefficient of the reactive-voltage droop characteristic curve, and ω is the maximum rated active power of the microgrid inverter. * E is the rated angular frequency of the microgrid inverter. * Q is the rated voltage of the microgrid inverter. * This refers to the rated reactive power output of the microgrid inverter.

[0046] S3. Obtain the real-time power of the load, keep the droop coefficient of the droop characteristic curve unchanged, and convert the droop control equation into the adaptive droop control equation corresponding to the real-time power.

[0047] The adaptive droop control equation is as follows:

[0048]

[0049] In Equation 2, p is the active power of the load, q is the reactive power of the load, and P m Q is the maximum rated active power of the load. m This represents the maximum reactive power of the load.

[0050] In one example, the rated angular frequency ω of the microgrid inverter * =100π, rated output voltage amplitude E * =311V.

[0051] S4. Calculate the difference between the adaptive droop control equation and the droop control equation to obtain the power deviation value of the microgrid inverter.

[0052] Specifically, by calculating the difference between the adaptive droop control equation and the droop control equation, the power deviation value of the microgrid inverter is obtained as follows:

[0053] Δp=ΔP m Formula 3

[0054] Δq=ΔQ m Formula 4

[0055] In equations 3 and 4, Δp represents the active power deviation, Δq represents the reactive power deviation, and ΔP m ΔQ represents the difference between the maximum rated active power and the maximum rated active power. m This represents the difference in maximum rated reactive power.

[0056] S5. Input the power deviation value to the proportional-integral controller, output the power adjustment value, and add the power adjustment value to the rated power to obtain the latest output power of the microgrid inverter for output.

[0057] Since the droop coefficient of the droop characteristic curve remains constant, the active power p and reactive power q of the load are monitored in real time. Within the range of the maximum output power of the microgrid inverter, power negative feedback is introduced, and Δp and Δq are introduced into the rated active power P of the microgrid inverter. * Side and rated reactive power Q * On the other hand, after adjustment by the proportional-integral controller, the output power of the microgrid inverter can track the power of the load. Adding a saturator to the feedback loop can ensure that the output power of the microgrid inverter is within its maximum power range.

[0058] It should be noted that the working principle of this embodiment is as follows:

[0059] Combination Figure 2 , Figure 2 The diagram illustrates the active power-frequency droop characteristic curve of a microgrid inverter. When the microgrid inverter operates at its rated power, i.e., at point A of droop characteristic curve 1, it satisfies droop characteristic equation 1. At a certain moment, the load power suddenly increases. Assuming that the rated frequency and rated voltage of the microgrid inverter remain unchanged, the microgrid inverter operates at point B of droop characteristic curve 3, satisfying droop characteristic equation 2. Subtracting equations 1 and 2, we obtain equations 3 and 4.

[0060] Figure 3 The diagram illustrates the reactive power-voltage droop characteristic curve of a microgrid inverter. A proportional-integral (PI) controller with a saturator in the feedback loop can ensure the inverter's output power remains within its maximum power range. Introducing a power feedback loop based on the inverter's rated power allows for adjustments to the output power, tracking load power changes. While a proportional controller can alter the inverter's output power, it cannot match the load power; in this case, the inverter operates at point C on characteristic curve 2. Compared to the traditional droop characteristic curve 1, without the power feedback loop, the inverter operates at point D on curve 1. This demonstrates that this method significantly reduces fluctuations in the inverter's output frequency and voltage during load changes. Using a PPI controller in the feedback loop allows the inverter to operate at point B on curve 3, achieving error-free regulation of the output frequency and voltage.

[0061] The following examples are provided in conjunction with this method:

[0062] Based on this method, a single microgrid inverter was built for simulation. The simulation results using the traditional droop control method and this method are as follows: Figure 4 and 5 As shown. The parameter settings in the simulation model are as follows: active power-frequency droop coefficient is 5×10. -7 The reactive power-voltage droop factor is 1×10. -4The proportional-integral controller parameters are: proportional gain K = 2, time constant T = 0.0001, and rated active power P. * = 4.77kW, rated reactive power Q * =0Var. At the initial moment, the active and reactive power of the load are 4.77kW and 0Var, respectively. At t=0.9s, the active and reactive power of the load become 9.54kW and 1300Var, respectively. At t=1.3s, the load returns to 4.77kW and 0Var. The simulation time is 2s.

[0063] The simulation results show that, compared with the traditional droop control method, the method of this invention, using a proportional-integral controller, can maintain the constant voltage amplitude and frequency of the microgrid inverter output when the load changes, thus verifying the correctness of the method.

[0064] This invention provides an adaptive droop control method for microgrid inverters. By introducing a virtual complex impedance to make the output impedance of the microgrid inverter inductive, a droop control equation for the microgrid inverter under rated power is obtained. The droop coefficient of the droop characteristic curve remains constant. The droop control equation is then converted into an adaptive droop control equation corresponding to the real-time power. The difference between the adaptive droop control equation and the actual droop control equation is calculated to obtain the power deviation value of the microgrid inverter. This power deviation value is input into a proportional-integral controller to obtain a power adjustment value. The power adjustment value is then superimposed on the rated power to obtain the latest output power of the microgrid inverter, which is then output. This reduces voltage amplitude and frequency fluctuations caused by load changes, improving the stability and efficiency of inverter droop control.

[0065] The above is a detailed description of an embodiment of an adaptive droop control method for a microgrid inverter provided by the present invention. The following is a detailed description of an embodiment of an adaptive droop control system for a microgrid inverter provided by the present invention.

[0066] For easier understanding, please refer to Figure 6 The present invention provides an adaptive droop control system for a microgrid inverter, comprising:

[0067] Inductive module 100 is used to introduce a virtual complex impedance to make the output impedance of the microgrid inverter inductive.

[0068] The first equation module 200 is used to obtain the rated power of the microgrid inverter and obtain the corresponding droop control equation;

[0069] The second equation module 300 is used to obtain the real-time power of the load, keep the droop coefficient of the droop characteristic curve unchanged, and convert the droop control equation into an adaptive droop control equation corresponding to the real-time power.

[0070] The difference calculation module 400 is used to calculate the difference between the adaptive droop control equation and the droop control equation to obtain the power deviation value of the microgrid inverter.

[0071] The control module 500 is used to input the power deviation value to the proportional-integral controller, output the power adjustment value, and add the power adjustment value to the rated power to obtain the latest output power of the microgrid inverter for output.

[0072] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0073] In the several embodiments provided by this invention, it should be understood that the disclosed apparatus and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0074] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0075] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0076] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for adaptive droop control of a microgrid inverter, characterized in that, Includes the following steps: Introducing a virtual complex impedance makes the output impedance of the microgrid inverter inductive; By obtaining the rated power of the microgrid inverter, the corresponding droop control equation is derived; the droop control equation is: Formula 1 In Equation 1, The rated active power output of the microgrid inverter. denoted as , where is the maximum rated active power of the microgrid inverter, m is the droop coefficient of the active-frequency droop characteristic curve, and n is the droop coefficient of the reactive-voltage droop characteristic curve. This is the rated angular frequency of the microgrid inverter. This is the rated voltage of the microgrid inverter. The rated reactive power output of the microgrid inverter; Obtain the real-time power of the load, keep the droop coefficient of the droop characteristic curve constant, and transform the droop control equation into an adaptive droop control equation corresponding to the real-time power; the adaptive droop control equation is: Formula 2 In Equation 2, p is the active power of the load, q is the reactive power of the load, and P m Q is the maximum rated active power of the load. m This represents the maximum reactive power of the load. The power deviation value of the microgrid inverter is obtained by calculating the difference between the adaptive droop control equation and the droop control equation, including: The power deviation value of the microgrid inverter is obtained by calculating the difference between the adaptive droop control equation and the droop control equation: Formula 3 Formula 4 In equations 3 and 4, This indicates the active power deviation value. This indicates the reactive power deviation value. This represents the difference between the maximum rated active power. This represents the difference between the maximum rated reactive power; The power deviation value is input to the proportional-integral controller, which outputs a power adjustment value. The power adjustment value is then added to the rated power to obtain the latest output power of the microgrid inverter for output.

2. The microgrid inverter adaptive droop control method according to claim 1, characterized in that, The rated angular frequency of the microgrid inverter Rated output voltage amplitude .

3. A microgrid inverter adaptive droop control system, characterized in that, include: The inductive module is used to introduce a virtual complex impedance to make the output impedance of the microgrid inverter inductive. The first equation module is used to obtain the rated power of the microgrid inverter and derive the corresponding droop control equation; the droop control equation is: Formula 1 In Equation 1, The rated active power output of the microgrid inverter. denoted as , where is the maximum rated active power of the microgrid inverter, m is the droop coefficient of the active-frequency droop characteristic curve, and n is the droop coefficient of the reactive-voltage droop characteristic curve. This is the rated angular frequency of the microgrid inverter. This is the rated voltage of the microgrid inverter. The rated reactive power output of the microgrid inverter; The second equation module is used to obtain the real-time power of the load, keep the droop coefficient of the droop characteristic curve unchanged, and convert the droop control equation into an adaptive droop control equation corresponding to the real-time power; the adaptive droop control equation is: Formula 2 In Equation 2, p is the active power of the load, q is the reactive power of the load, and P m Q is the maximum rated active power of the load. m This represents the maximum reactive power of the load. The difference calculation module is used to calculate the difference between the adaptive droop control equation and the droop control equation to obtain the power deviation value of the microgrid inverter. The power deviation value of the microgrid inverter is obtained by calculating the difference between the adaptive droop control equation and the droop control equation, including: The power deviation value of the microgrid inverter is obtained by calculating the difference between the adaptive droop control equation and the droop control equation: Formula 3 Formula 4 In equations 3 and 4, This indicates the active power deviation value. This indicates the reactive power deviation value. This represents the difference between the maximum rated active power. This represents the difference between the maximum rated reactive power; The control module is used to input the power deviation value to the proportional-integral controller, output the power adjustment value, and add the power adjustment value to the rated power to obtain the latest output power of the microgrid inverter for output.

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