Virtual impedance design method and system considering high-precision power output of inverter

Abstract

The application provides a virtual impedance design method and system considering high-precision power output of an inverter, and is suitable for a capacitive coupling inverter. The application firstly selects an equivalent coupling impedance boundary according to a physical impedance calculated active power output limit value; secondly, an inner boundary and an outer boundary meeting instantaneous response requirements are added to reduce the selection range of the virtual impedance; further, a stability margin parameter is introduced to derive a stability boundary of the coupling impedance, further reducing the selection range of the virtual impedance; then, considering possible power loss, a range in which the equivalent impedance approaches zero is taken as a feasible range of the equivalent coupling impedance; finally, a virtual impedance value is obtained by using the difference between the physical impedance and the equivalent coupling impedance. The application can reduce control errors in droop control and reduce capacity waste of CCI.

Description

Technical Field

[0001] This invention belongs to the field of power quality control technology, specifically relating to a virtual impedance design method and system that considers the high-precision power output of inverters. Background Technology

[0002] Microgrids (MGs) have gained increasing attention as an effective means of utilizing renewable and clean energy and reducing carbon emissions from fossil fuels. A microgrid is a small- to medium-sized autonomous power system, typically composed of distributed generation (DG) units, loads, and controllers. It can operate in grid-connected mode or completely isolated mode. In microgrids, inductive inverters are usually used to output active power; however, due to their low reactive power compensation capacity, additional reactive power compensators are typically required to stabilize the bus voltage and ensure normal load operation. With the increasing penetration of renewable energy and load capacity in microgrids, the intermittency of renewable energy generation will exacerbate the deviation between the bus voltage and its rated value. Therefore, strengthening reactive power regulation capabilities is essential to improve the power supply efficiency and voltage stability of microgrids.

[0003] To improve reactive power regulation capabilities, capacitive coupling inverters (CCIs) based on LC series structures have emerged. Traditional droop control is also applied to CCIs. However, existing research has not considered the capacity waste problem caused by control errors in CCIs. This problem will diminish the advantages of CCIs in terms of power output. Summary of the Invention

[0004] In view of this, the present invention aims to solve the problem of capacity waste caused by control errors in capacitively coupled inverters employing droop control.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] In a first aspect, the present invention provides a virtual impedance design method considering the high-precision power output of an inverter, applicable to capacitively coupled capacitors, comprising the following steps:

[0007] The equivalent coupling impedance boundary is selected based on the active power output limit value calculated from the physical impedance, thus obtaining the first feasible range of the equivalent coupling impedance.

[0008] By adding inner and outer boundaries that meet the instantaneous response requirements, a second feasible range of equivalent coupling impedance is obtained, thus narrowing the selection range of virtual impedance;

[0009] By introducing a stability margin parameter, the stability boundary of the coupling impedance is derived and determined, resulting in a third feasible range of the equivalent coupling impedance, which further narrows down the selection range of the virtual impedance.

[0010] Within the third feasible range, the range where the equivalent impedance approaches zero is taken as the final feasible range of the equivalent coupling impedance;

[0011] The virtual impedance value is obtained by using the difference between the physical impedance and the equivalent coupling impedance.

[0012] Furthermore, the equivalent coupling impedance boundary is selected based on the active power output limit calculated from the physical impedance, specifically according to the following formula:

[0013] P max (R 2 +X 2 )-VE(Rcosδ max -Xsinδ max )+RE 2 ≤0

[0014] In the formula, P max The active power output limit is calculated based on the physical impedance, where E and V are the grid connection point voltage and inverter output voltage, respectively; R and X are the resistance and reactance of the equivalent coupling impedance, respectively; δ max This represents the maximum value of the phase angle.

[0015] Furthermore, inner and outer boundaries that satisfy the instantaneous response requirements are added, specifically according to the following formula:

[0016]

[0017] In the formula, K Im-min K Im-max These represent the upper and lower limits of the instantaneous response margin, respectively; Im (poles) Re (poles) These represent the values ​​of the imaginary and real parts of the governing equations in the complex plane, respectively.

[0018] Furthermore, the stability margin parameter is calculated according to the following formula:

[0019] Max(Re (poles) )≤K Re

[0020] In the formula, Re (poles) K represents the real part of the governing equation in the complex plane. Re This represents the stability margin parameter.

[0021] Furthermore, the virtual impedance value is calculated using the following formula:

[0022]

[0023] In the formula, and These are the physical coupling impedance of the capacitively coupled inverter and the equivalent coupling impedance after applying virtual impedance, respectively. This is the virtual impedance value that needs to be applied to capacitively coupled inverters.

[0024] Secondly, this invention provides a virtual impedance design system considering the high-precision power output of inverters, applicable to capacitively coupled capacitors, comprising:

[0025] The first range selection unit is used to select the equivalent coupling impedance boundary based on the active power output limit value calculated from the physical impedance, so as to obtain the first feasible range of the equivalent coupling impedance.

[0026] The second range selection unit is used to add inner and outer boundaries that meet the instantaneous response requirements to obtain a second feasible range of equivalent coupling impedance, thereby narrowing the selection range of virtual impedance.

[0027] The third range selection unit is used to introduce the stability margin parameter, derive and determine the stability boundary of the coupling impedance, obtain the third feasible range of the equivalent coupling impedance, and further narrow the selection range of the virtual impedance.

[0028] The fourth range selection unit is used to select the range in the third feasible range where the equivalent impedance approaches zero as the final feasible range of the equivalent coupling impedance.

[0029] The calculation unit is used to obtain the virtual impedance value by using the difference between the physical impedance and the equivalent coupling impedance.

[0030] Furthermore, in the first range selection unit, the equivalent coupling impedance boundary is selected based on the active power output limit value calculated from the physical impedance, specifically according to the following formula:

[0031] P max (R 2 +X 2 )-VE(Rcosδ max -Xsinδ max )+RE 2 ≤0

[0032] In the formula, P max The active power output limit is calculated based on the physical impedance, where E and V are the grid connection point voltage and inverter output voltage, respectively; R and X are the resistance and reactance of the equivalent coupling impedance, respectively; δ max This represents the maximum value of the phase angle.

[0033] Furthermore, in the second range selection unit, inner and outer boundaries that meet the instantaneous response requirements are added, specifically according to the following formula:

[0034]

[0035] In the formula, K Im-min K Im-max These represent the upper and lower limits of the instantaneous response margin, respectively; Im (poles) Re (poles) These represent the values ​​of the imaginary and real parts of the governing equations in the complex plane, respectively.

[0036] Furthermore, in the third range selection unit, the stability margin parameter is calculated according to the following formula:

[0037] Max(Re (poles) )≤K Re

[0038] In the formula, Re (poles) K represents the real part of the governing equation in the complex plane. Re This represents the stability margin parameter.

[0039] Furthermore, in the calculation unit, the virtual impedance value is calculated according to the following formula:

[0040]

[0041] In the formula, and These are the physical coupling impedance of the capacitively coupled inverter and the equivalent coupling impedance after applying virtual impedance, respectively. This is the virtual impedance value that needs to be applied to capacitively coupled inverters.

[0042] In summary, this invention provides a virtual impedance design method and system considering the high-precision power output of inverters, applicable to capacitively coupled inverters. First, this invention selects the equivalent coupling impedance boundary based on the active power output limit calculated from the physical impedance. Second, it adds inner and outer boundaries that meet instantaneous response requirements, narrowing the selection range of the virtual impedance. Then, it introduces a stability margin parameter to derive the stability boundary of the coupling impedance, further narrowing the selection range of the virtual impedance. Next, considering possible power losses, it takes the range where the equivalent impedance approaches zero as the feasible range of the equivalent coupling impedance. Finally, it uses the difference between the physical impedance and the equivalent coupling impedance to obtain the virtual impedance value. This invention can reduce control errors in droop control and reduce capacity waste in capacitive coupling control (CCI). Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 A flowchart illustrating a virtual impedance design method considering high-precision power output of an inverter, provided as an embodiment of the present invention;

[0045] Figure 2 This is an example diagram of equivalent impedance design provided in an embodiment of the present invention. Detailed Implementation

[0046] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0047] Microgrids (MGs) have gained increasing attention as an effective means of utilizing renewable and clean energy and reducing carbon emissions from fossil fuels. Strengthening reactive power regulation capabilities is essential to improving the power supply efficiency and voltage stability of microgrids.

[0048] To improve reactive power regulation capabilities, capacitive coupling inverters (CCIs) based on LC series structures have emerged. Traditional droop control is also applied to CCIs. However, existing research has not considered the capacity waste problem caused by control errors in CCIs. This problem will diminish the advantages of CCIs in terms of power output.

[0049] Based on this, the present invention provides a virtual impedance design method and system that takes into account the high-precision power output of the inverter.

[0050] The following is a detailed description of an embodiment of the virtual impedance design method of the present invention that takes into account the high-precision power output of the inverter.

[0051] Please see Figure 1 This embodiment provides a virtual impedance design method considering the high-precision power output of the inverter, mainly applied to capacitively coupled inverters, including the following steps:

[0052] S100: Select the equivalent coupling impedance boundary based on the active power output limit value calculated from the physical impedance to obtain the first feasible range of the equivalent coupling impedance.

[0053] It should be noted that the active power output limit is calculated based on the physical impedance, and then the selection boundary of the equivalent coupling impedance is derived according to Equation 1.

[0054] P max (R 2 +X 2 )-VE(Rcosδ max -Xsinδ max )+RE 2 ≤0 (1)

[0055] In the formula, P max The active power output limit is calculated based on the physical impedance, where E and V are the grid connection point voltage and inverter output voltage, respectively; R and X are the resistance and reactance of the equivalent coupling impedance, respectively; δ max This represents the maximum value of the phase angle.

[0056] To minimize active power loss, the real part of the coupling impedance should be kept as low as possible, i.e., the equivalent resistance should be limited to around R = 0. In one example, as described in this step, in Figure 2 Within the boundary shown in Figure 1, only the coupling impedance of the shaded area should be selected.

[0057] S200: Add inner and outer boundaries that meet the instantaneous response requirements to obtain a second feasible range of equivalent coupling impedance, thus narrowing the selection range of virtual impedance.

[0058] It should be noted that, since the system damping is mainly affected by the conjugate poles of the imaginary part of the equivalent coupling impedance, the damping ratio needs to satisfy the following constraints:

[0059]

[0060] In the formula, K Im-min K Im-max These represent the upper and lower limits of the instantaneous response margin, respectively; Im (poles) Re (poles) These represent the values ​​of the imaginary and real parts of the governing equations in the complex plane, respectively.

[0061] The inner and outer boundaries that satisfy the instantaneous response requirement are determined based on the above formula. Figure 2 In the design example shown, the inner boundary is a circle centered at (0,0) with a radius of 1.6. The outer boundary is also a circle centered at (0,0) with a radius of 40. To better study the selection of the virtual impedance value, only the inner boundary was selected in this example. Therefore, the coupling impedance selection region is narrowed down to... Figure 2The shaded area in Figure 2.

[0062] S300: By introducing a stability margin parameter, the stability boundary of the coupling impedance is derived and determined, and the third feasible range of the equivalent coupling impedance is obtained, further narrowing the selection range of the virtual impedance.

[0063] The real part of all poles should be less than a specific stability parameter K. Re To ensure sufficient stability margin:

[0064] Max(Re (poles) )≤K Re (3)

[0065] In the formula, Re (poles) K represents the real part of the governing equation in the complex plane. Re This represents the stability margin parameter.

[0066] The stability margin parameter is calculated using the above formula, thus obtaining the stability boundary of the coupling impedance. Figure 2 In the design example shown, the stability boundary of the coupling impedance is derived as a circle with center (0,0) and radius 2.5. The intersection of this circle and the range in step 200 is taken as the feasible range of the equivalent coupling impedance. Thus, the selection region for the coupling impedance is narrowed down to... Figure 2 The shaded area in Figure 3.

[0067] S400: In the third feasible range, the range where the equivalent impedance approaches zero is taken as the final feasible range of the equivalent coupling impedance.

[0068] It should be noted that, in Figure 2 In the design example shown, the range where the equivalent impedance approaches zero is taken as the final feasible range of the equivalent coupling impedance. Figure 2 The black part in Figure 4.

[0069] S500: The virtual impedance value is obtained by using the difference between the physical impedance and the equivalent coupling impedance.

[0070] It should be noted that the virtual impedance value is calculated using the following formula:

[0071]

[0072] In the formula, and These are the physical coupling impedance of the capacitively coupled inverter and the equivalent coupling impedance after applying virtual impedance, respectively. This is the virtual impedance value that needs to be applied to capacitively coupled inverters.

[0073] This embodiment provides a virtual impedance design method considering the high-precision power output of inverters, applicable to capacitively coupled inverters. The invention first selects the equivalent coupling impedance boundary based on the active power output limit calculated from the physical impedance; secondly, it adds inner and outer boundaries that meet instantaneous response requirements, narrowing the selection range of the virtual impedance; furthermore, it introduces a stability margin parameter to derive the stability boundary of the coupling impedance, further narrowing the selection range of the virtual impedance; then, considering possible power losses, it takes the range where the equivalent impedance approaches zero as the feasible range of the equivalent coupling impedance; finally, it uses the difference between the physical impedance and the equivalent coupling impedance to obtain the virtual impedance value. This invention can reduce control errors in droop control and reduce capacity waste in capacitive coupling control (CCI).

[0074] The above is a detailed description of an embodiment of the virtual impedance design method of the present invention that considers the high-precision power output of the inverter. The following will provide a detailed description of an embodiment of the virtual impedance design system of the present invention that considers the high-precision power output of the inverter.

[0075] This embodiment provides a virtual impedance design system considering the high-precision power output of the inverter, applicable to capacitively coupled capacitors, including:

[0076] The first range selection unit is used to select the equivalent coupling impedance boundary based on the active power output limit value calculated from the physical impedance, thereby obtaining the first feasible range of the equivalent coupling impedance.

[0077] In the first range selection unit, the equivalent coupling impedance boundary is selected based on the active power output limit value calculated from the physical impedance, specifically according to the following formula:

[0078] P max (R 2 +X 2 )-VE(Rcosδ max -Xsinδ max )+RE 2 ≤0

[0079] In the formula, P max The active power output limit is calculated based on the physical impedance, where E and V are the grid connection point voltage and inverter output voltage, respectively; R and X are the resistance and reactance of the equivalent coupling impedance, respectively; δ max This represents the maximum value of the phase angle.

[0080] The second range selection unit is used to add inner and outer boundaries that meet the instantaneous response requirements to obtain a second feasible range of equivalent coupling impedance, thereby narrowing the selection range of virtual impedance.

[0081] In the second range selection unit, inner and outer boundaries that meet the instantaneous response requirements are added, specifically according to the following formula:

[0082]

[0083] In the formula, K Im-min K Im-max These represent the upper and lower limits of the instantaneous response margin, respectively; Im (poles) Re (poles) These represent the values ​​of the imaginary and real parts of the governing equations in the complex plane, respectively.

[0084] The third range selection unit is used to introduce a stability margin parameter, derive and determine the stability boundary of the coupling impedance, obtain the third feasible range of the equivalent coupling impedance, and further narrow the selection range of the virtual impedance.

[0085] In the third range selection cell, the stability margin parameter is calculated according to the following formula:

[0086] Max(Re (poles) )≤K Re

[0087] In the formula, Re (poles) K represents the real part of the governing equation in the complex plane. Re This represents the stability margin parameter.

[0088] The fourth range selection unit is used to select the range in the third feasible range where the equivalent impedance approaches zero as the final feasible range of the equivalent coupling impedance.

[0089] The calculation unit is used to obtain the virtual impedance value by using the difference between the physical impedance and the equivalent coupling impedance.

[0090] In the calculation unit, the virtual impedance value is calculated according to the following formula:

[0091]

[0092] In the formula, and These are the physical coupling impedance of the capacitively coupled inverter and the equivalent coupling impedance after applying virtual impedance, respectively. This is the virtual impedance value that needs to be applied to capacitively coupled inverters.

[0093] 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 virtual impedance design method considering high-precision power output of inverters, characterized in that, For capacitively coupled capacitors, the following steps are included: The equivalent coupling impedance boundary is selected based on the active power output limit value calculated from the physical impedance, thus obtaining the first feasible range of the equivalent coupling impedance. By adding inner and outer boundaries that meet the instantaneous response requirements, a second feasible range of the equivalent coupling impedance is obtained, thus narrowing the selection range of the virtual impedance; By introducing a stability margin parameter, the stability boundary of the coupling impedance is derived and determined, and the third feasible range of the equivalent coupling impedance is obtained, further narrowing the selection range of the virtual impedance. Within the third feasible range, the range where the equivalent impedance approaches zero is taken as the final feasible range of the equivalent coupling impedance; The virtual impedance value is obtained by using the difference between the physical impedance and the equivalent coupling impedance; The equivalent coupling impedance boundary is selected based on the active power output limit calculated from the physical impedance, specifically according to the following formula: In the formula, P max The active power output limit is calculated based on the physical impedance, where E and V are the grid connection point voltage and inverter output voltage, respectively; R and X are the resistance and reactance of the equivalent coupling impedance, respectively. This represents the maximum value of the phase angle.

2. The virtual impedance design method considering high-precision power output of the inverter according to claim 1, characterized in that, Add inner and outer boundaries that meet the instantaneous response requirements, specifically according to the following formula: In the formula, These represent the upper and lower limits of the instantaneous response margin, respectively. These represent the values ​​of the imaginary and real parts of the governing equations in the complex plane, respectively.

3. The virtual impedance design method considering high-precision power output of the inverter according to claim 1, characterized in that, The stability margin parameter is calculated according to the following formula: In the formula, This represents the value of the real part of the governing equation in the complex plane. This represents the stability margin parameter.

4. The virtual impedance design method considering high-precision power output of the inverter according to claim 1, characterized in that, The virtual impedance value is calculated according to the following formula: In the formula, and These are the physical coupling impedance of the capacitively coupled inverter and the equivalent coupling impedance after applying virtual impedance, respectively. This is the virtual impedance value that needs to be applied to capacitively coupled inverters.

5. A virtual impedance design system considering the high-precision power output of an inverter, characterized in that, Suitable for capacitively coupled capacitors, including: The first range selection unit is used to select the equivalent coupling impedance boundary based on the active power output limit value calculated from the physical impedance, so as to obtain the first feasible range of the equivalent coupling impedance. The second range selection unit is used to add inner and outer boundaries that meet the instantaneous response requirements to obtain a second feasible range of the equivalent coupling impedance and narrow the selection range of the virtual impedance. The third range selection unit is used to introduce a stability margin parameter, derive and determine the stability boundary of the coupling impedance, obtain the third feasible range of the equivalent coupling impedance, and further narrow the selection range of the virtual impedance. The fourth range selection unit is used to select the range in the third feasible range where the equivalent impedance approaches zero as the final feasible range of the equivalent coupling impedance. The calculation unit is used to obtain the virtual impedance value by using the difference between the physical impedance and the equivalent coupling impedance; In the first range selection unit, the equivalent coupling impedance boundary is selected based on the active power output limit value calculated from the physical impedance, specifically according to the following formula: In the formula, P max The active power output limit is calculated based on the physical impedance, where E and V are the grid connection point voltage and inverter output voltage, respectively; R and X are the resistance and reactance of the equivalent coupling impedance, respectively. This represents the maximum value of the phase angle.

6. The virtual impedance design system considering high-precision power output of the inverter according to claim 5, characterized in that, In the second range selection unit, inner and outer boundaries that meet the instantaneous response requirements are added, specifically according to the following formula: In the formula, These represent the upper and lower limits of the instantaneous response margin, respectively. These represent the values ​​of the imaginary and real parts of the governing equations in the complex plane, respectively.

7. The virtual impedance design system considering high-precision power output of the inverter according to claim 5, characterized in that, In the third range selection unit, the stability margin parameter is calculated according to the following formula: In the formula, This represents the value of the real part of the governing equation in the complex plane. This represents the stability margin parameter.

8. The virtual impedance design system considering high-precision power output of the inverter according to claim 5, characterized in that, In the calculation unit, the virtual impedance value is specifically calculated according to the following formula: In the formula, and These are the physical coupling impedance of the capacitively coupled inverter and the equivalent coupling impedance after applying virtual impedance, respectively. This is the virtual impedance value that needs to be applied to capacitively coupled inverters.

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