An inverter control method and system

Abstract

The present invention belongs to the field of electric power, and particularly relates to an inverter control method and system. The method includes calculating active power and reactive power, and respectively setting corresponding droop control loop processes; adjusting parameters according to preset variables and implementing a virtual impedance current limiting control strategy; performing dq coordinate transformation on the collected original inductor current and original capacitor voltage, and calculating the capacitor voltage amplitude; adjusting the reference active power according to the capacitor voltage amplitude, ensuring the safety of the inverter without overcurrent while achieving transient synchronous stability, and improving the reliable grid-connected operation ability of the inverter.

Description

Technical Field

[0001] The present invention belongs to the field of electric power, and particularly relates to an inverter control method and system. Background Art

[0002] With the intensification of the energy crisis, more and more inverter equipment is connected to the grid. An inverter is an important device that can convert DC electrical energy into AC electrical energy and has been widely used in the field of new energy power generation.

[0003] The grid structure is complex, vulnerable to extreme weather, and faces tests such as large-scale unit tripping and short-circuit faults, resulting in large fluctuations in grid voltage and frequency. When a transient fault occurs in the grid, the grid voltage drops rapidly, and the output current of the grid-connected inverter rises rapidly. Due to the weak overcurrent capacity of the inverter, when the fault depth is relatively deep, the fault current may burn out the inverter. Therefore, the emergency current limiting control of the inverter is crucial for the safety of the inverter itself. Existing technologies have studied various current limiting methods, and the main idea is to adjust the amplitude and phase of the equivalent internal potential of the inverter according to the magnitude of the real-time output current of the inverter. However, adjusting the internal potential of the inverter changes the transient operating characteristics of the inverter, which may reduce the stability of the inverter and cause transient instability of the inverter. Although existing research has considered the instability problem of the inverter, it mostly optimizes the influence of disturbances on the stability of the inverter from the small-signal level, without considering the transient stable operating characteristics of the inverter under deep fault conditions, or ignoring the influence of current limiting control. Summary of the Invention

[0004] In order to solve or improve the above problems, the present invention provides an inverter control method and system, and the specific technical solutions are as follows:

[0005] The present invention provides an inverter control method, including: calculating active power and reactive power, and respectively setting corresponding droop control loop processes; adjusting parameters according to preset variables, and implementing a virtual impedance current limiting control strategy; performing dq coordinate transformation on the collected original inductor current and original capacitor voltage, and calculating the capacitor voltage amplitude; adjusting the reference active power according to the capacitor voltage amplitude.

[0006] Preferably, the method further includes: calculating the internal potential and angular frequency output by the control loop; correspondingly, the performing dq coordinate transformation on the collected original inductor current and original capacitor voltage includes: performing dq coordinate transformation on the collected original inductor current and original capacitor voltage based on the internal potential and the angular frequency.

[0007] Preferably, the capacitor voltage amplitude wherein, the v d and v q are the capacitor voltages in the dq coordinate system;

[0008] Among them, v a , v b and v v are the original capacitor voltages.

[0009] Preferably, adjusting the reference active power according to the capacitor voltage amplitude includes:

[0010] The reference active power to be adjusted Among them, P n is the rated reference power value of the inverter, v n is the rated output voltage amplitude of the inverter, h is the power adjustment proportionality coefficient, and R v1 is the low-frequency equivalent impedance.

[0011] Preferably, the preset variable adjustment parameters include: the limit value of the inverter limiter, with a value of 120 A; the virtual impedance ratio value, with a value of 1; the impedance ratio value, with a value of 0.3; the power adjustment proportionality coefficient, with a value of 1; the low-pass filter value, with a value of 0.01 s; the rated reference active power, with a value of 34 kw; the reference angular frequency, with a value of 314.15926 rad / s; the amplitude of the internal potential reference for reactive droop control, with a value of 320 V; the rated capacitor voltage amplitude, with a value of 311 V.

[0012] The present invention provides an inverter control system, including: a first unit for calculating the active power and reactive power and respectively setting corresponding droop control loop processes; a second unit for executing a virtual impedance current limiting control strategy according to the preset variable adjustment parameters; a third unit for performing dq coordinate transformation on the collected original inductor current and original capacitor voltage and calculating the capacitor voltage amplitude; a fourth unit for adjusting the reference active power according to the capacitor voltage amplitude.

[0013] Preferably, the first unit is further used for calculating the internal potential and angular frequency output by the control loop; correspondingly, the third unit is used for performing dq coordinate transformation on the collected original inductor current and original capacitor voltage based on the internal potential and the angular frequency.

[0014] Preferably, the capacitor voltage amplitude Among them, the v d and v q are the capacitor voltages in the dq coordinate system;

[0015] Among them, v a , v b and v v are the original capacitor voltages.

[0016] Preferably, adjusting the reference active power according to the capacitor voltage amplitude includes:

[0017] The reference active power to be adjusted where P n is the rated reference power value of the inverter, v n is the rated output voltage amplitude of the inverter, h is the power adjustment ratio coefficient, R v1 is the low-frequency equivalent impedance.

[0018] Preferably, the preset variable adjustment parameters include: the limit value of the inverter limiter, with a value of 120 A; the virtual impedance ratio value, with a value of 1; the impedance ratio value, with a value of 0.3; the power adjustment ratio coefficient, with a value of 1; the low-pass filter value, with a value of 0.01 s; the rated reference active power, with a value of 34 kw; the reference angular frequency, with a value of 314.15926 rad / s; the reference internal potential amplitude of the reactive power droop control, with a value of 320 V; the rated capacitor voltage amplitude, with a value of 311 V.

[0019] The beneficial effects of the present invention are as follows: calculating the active power and reactive power, and respectively setting the corresponding droop control loop processes; implementing the virtual impedance current limiting control strategy according to the preset variable adjustment parameters; performing dq coordinate transformation on the collected original inductor current and original capacitor voltage, and calculating the capacitor voltage amplitude; adjusting the reference active power according to the capacitor voltage amplitude, ensuring the safety of the inverter without overcurrent while achieving transient synchronous stability, and improving the reliable grid-connected operation ability of the inverter. Description of the Drawings

[0020] Figure 1 is a schematic diagram of the inverter control method according to the present invention;

[0021] Figure 2 is a structural block diagram of the inverter according to the present invention;

[0022] Figure 3 is a structural diagram of the virtual impedance current limiting control according to the present invention;

[0023] Figure 4 is a power curve diagram of the inverter under different control states according to the present invention;

[0024] Figure 5 is a power angle change curve diagram of the inverter using power regulation control according to the present invention;

[0025] Figure 6 is a schematic diagram of the power angle and output power of the inverter in the traditional current limiting control scheme;

[0026] Figure 7 is the A-phase capacitor voltage and A-phase output current of the inverter;

[0027] Figure 8 It is a schematic diagram of the power angle and output power of the inverter according to the present invention;

[0028] Figure 9 It is the capacitor voltage of phase A and the output current of phase A of the inverter according to the present invention;

[0029] Figure 10 It is a schematic diagram of the implementation method according to the present invention. Detailed implementation manners

[0030] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0031] It should be understood that when used in this specification and the appended claims, the terms "comprises" and "comprising" indicate the presence of the described features, wholes, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or their combinations.

[0032] It should also be understood that the terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" are intended to include the plural forms.

[0033] It should be further understood that the term " / and / " used in the specification of the present invention and the appended claims refers to any combination and all possible combinations of one or more of the related listed items, and includes these combinations.

[0034] To solve or improve the problems raised in the background, the present invention provides an inverter control method as shown in Figure 1 : S1, calculating the active power and reactive power, and respectively setting the corresponding droop control loop processes; S2, adjusting the parameters according to the preset variables and implementing the virtual impedance current limiting control strategy; S3, performing dq coordinate transformation on the collected original inductor current and original capacitor voltage, and calculating the capacitor voltage amplitude; S4, adjusting the reference active power according to the capacitor voltage amplitude.

[0035] Solution ideas for inverter control:

[0036] Step 1: Perform dq coordinate transformation on the inductor current and capacitor voltage of the inverter according to the output angular frequency of the inverter.

[0037] Select the droop inverter as the main research object. The structural block diagram of the inverter is as Figure 2 shown. P set and Q set are the reference active / reactive power of the inverter respectively. E0 is the amplitude of the reference internal potential of the reactive droop loop, and ω0 is the reference angular frequency of the active droop control loop. E and ω out are the output internal potential and angular frequency of the active / reactive control loop of the inverter respectively. L f and R f are the inductance value and resistance value of the filter inductor. L g and R g are the inductance value and resistance value of the line inductor. C f is the filter capacitor. i abc and v abc are the filter inductor current and capacitor voltage respectively. U dc is the DC bus voltage.

[0038] The phase of the PWM modulation angle of the inverter can be expressed as: δ = ∫ω out dt, (1), where t is time. The inductor current and capacitor voltage in the dq coordinate system of the inverter are expressed as follows:

[0039]

[0040] where, i dq and v dq are the inductor current and capacitor voltage of the inverter in the dq coordinate system respectively. i0 and v0 are the zero-sequence inductor current and zero-sequence capacitor voltage of the inverter respectively.

[0041] Step 2: Design the virtual impedance current limiting control strategy of the inverter

[0042] When it is detected that the output current of the inverter is greater than the allowable current value of the inverter, in order to suppress the fault current of the inverter, a virtual impedance current limiting control method for the inverter is designed. The structure of the virtual impedance current limiting control is as Figure 3 shown. I max is the limit value of the output current of the inverter, k vr is the proportional coefficient of the virtual resistor, and k xr is the impedance ratio of the virtual impedance. The dq-axis modulation voltage signals input to the switching tubes for PWM modulation are e ind and e inq , which can be expressed as:

[0043] where, u dv and u qvThey are the equivalent voltage drops of the virtual impedance on the dq axes respectively.

[0044] The expression of the power transfer curve of the inverter is as follows: Among them, Einv is the equivalent internal potential of the inverter, U g is the grid voltage, X Σ is the equivalent line inductance between the midpoint of the inverter bridge arm and the grid, and θ is the power angle of the inverter.

[0045] It can be seen from Equation (5) that when a grid-side fault of the inverter occurs, the capacitor voltage of the inverter decreases and the fault current increases, reducing the maximum transmission power allowed by the inverter. When the inverter reaches the current limit condition, the virtual impedance increases and the transmission power of the inverter further decreases. The power curves of the inverter under different control states can be as Figure 4 shown. Figure 4 In it, L1 is the power angle transmission curve of the inverter under fault-free conditions, L2 is the power angle transmission curve of the inverter under fault non-current-limiting conditions, and L3 is the power angle transmission curve when the virtual impedance current-limiting control strategy of the inverter operates under fault conditions. It should be noted that when the inverter operates on curve L2, due to the shallow fault depth, the output current of the inverter does not exceed the limit value of the inverter, and at this time the virtual impedance current-limiting control does not act. When the inverter operates on curve L3, the fault depth is deeper, the output current of the inverter exceeds the limit value of the inverter, and at this time the virtual impedance current-limiting control acts.

[0046] From Figure 4 it can be seen that when a mild fault occurs in the grid, the maximum transmission power of the inverter decreases. During the process of the operating point of the inverter transferring from L1 to L2, the power angle increases and there is a stable equilibrium point for the inverter. When a severe fault occurs, the current-limiting controller acts, and there is no intersection between the power angle transmission curve of the inverter and the reference power line, that is, there is no stable equilibrium point in the system at this time, and the output power angle of the inverter continues to increase. According to the power angle stability theory of the power system, when the power angle of the inverter is greater than 180°, the inverter will experience continuous instability.

[0047] Step 3: Detect the capacitor voltage of the inverter

[0048] It can be seen from the above analysis that under different fault depth conditions, the degree of grid voltage drop is different, the power angle transmission characteristics of the inverter are different, and it causes different changes in the output power and power angle of the inverter. When the grid voltage drops significantly, it will cause a significant decrease in the capacitor voltage of the inverter. Therefore, detecting the capacitor voltage of the inverter is one of the important indicators for adjusting the transient stability of the inverter. The calculation expression of the amplitude of the capacitor voltage of the inverter is as follows: Among them, v ampis the amplitude of the inverter capacitor voltage. The controller of the inverter collects the capacitor voltages of the abc three phases of the inverter in real time through a voltage sensor, and calculates the amplitude of the inverter capacitor voltage according to Equations (3) and (6).

[0049] Step 4: Adjust the reference active power of the inverter

[0050] As can be seen from the above analysis, under deep fault conditions, there is no stable equilibrium point for the inverter, and the power angle will continue to increase during the fault. Therefore, in order to improve the transient stability of the inverter, it is necessary to reduce the output power of the inverter. The adjustment expression of the inverter output power is as follows: where Pn is the rated reference power value of the inverter, vn is the rated output voltage amplitude of the inverter, and h is the power adjustment proportionality coefficient. Rv1 is the low-frequency equivalent impedance, and the expression is: where T f is the time constant of the low-pass filter. The reason for choosing the low-pass filter is that there are high-frequency disturbances in the output of the current limiter. Therefore, the low-pass filter is used to filter out the high-frequency interference to obtain the low-frequency equivalent virtual impedance R v1 . This method adjusts the reference active power according to the amplitude range of v amp . When the fault depth is shallow (v amp ≥0.8v n , where v n is the rated capacitor voltage amplitude), there is a stable equilibrium point in the power angle curve of the inverter, and at this time, there is no need to adjust the reference active power of the inverter. When the fault depth is deep (v amp <0.8v n ), it is difficult for the power angle curve of the inverter to have a stable equilibrium point. Therefore, it is necessary to reduce the reference active power of the inverter. According to Equation (7), when R v1 is 0, P set =P n . When R v1 >0 and v amp <0.8v n , P set <P n . Therefore, this method effectively realizes the adaptive adjustment of the inverter reference power. According to Expression (7), the power angle change curve of the inverter using power regulation control can be drawn, as shown in Figure 5 . Among them, P set and P set1 are the reference powers before and after adjustment respectively, and θ0 is the power angle of the stable equilibrium point of the inverter before the fault occurs. Using this control strategy ensures that there is a stable equilibrium point for the inverter using current limiting control during the fault. At the same time, according to the equal area criterion, the acceleration and deceleration areas of the inverter can be obtained. Since the operating curve of the inverter after the fault transfers to curve L3 and the reference power is reduced to P set1, as can be seen from the figure, there is no accelerating area at this time, only the maximum decelerating area. According to the equal-area criterion, the inverter will maintain stability during the fault.

[0051] The specific verification principle includes:

[0052] Actual tests and verifications are carried out on a grid-connected inverter to obtain various information such as the power angle, output active power, output reactive power, phase-A capacitor voltage, and phase-A output current of the inverter. The grid voltage drops at 4 s and recovers at 4.3 s. When using the traditional current-limiting control scheme, the power angle and output power of the inverter are as Figure 6 shown. It can be seen from the figure that the output power of the inverter before the fault is 34 kW, and the power angle is maintained within a small range. When the fault occurs, the power angle increases rapidly and continues to increase after the fault is cleared, eventually exceeding 360°. At the same time, the output active and reactive power of the inverter still oscillates continuously after the fault is cleared. The phase-A capacitor voltage and phase-A output current of the inverter are as Figure 7 shown. The amplitude of the capacitor voltage of the inverter drops to 100 V during the fault, and the inverter maintains the output at the current limit value after the fault occurs. However, after the fault is cleared, the capacitor voltage recovers, but the output current of the inverter continues to oscillate and the system becomes unstable.

[0053] When using the control scheme proposed by the present invention, the power angle and output power of the inverter are as Figure 8 shown. The phase-A capacitor voltage and phase-A output current of the inverter when using the control scheme proposed by the present invention are as Figure 9 shown. From Figure 8 it can be seen that the power angle of the inverter before the fault is 14°, and the power angle of the inverter increases to 16° after the fault is cleared and finally returns to stability. At the same time, the output active and reactive power of the inverter also returns to stability after the fault is cleared. The amplitude of the capacitor voltage of the inverter drops to 100 V during the fault, and the inverter maintains the output at the current limit value after the fault occurs. However, after the fault is cleared, the capacitor voltage and output current of the inverter recover quickly and the system returns to stability.

[0054] The implementation process of the present invention:

[0055] First, the real-time capacitor voltage and inductor current are obtained through a voltage transformer and a current transformer respectively, and the output active / reactive power of the inverter is calculated.

[0056] Then, the programs of the active and reactive power droop control loops are written into the controller of the inverter to obtain the internal electromotive force and angular frequency output by the active / reactive control loops of the inverter respectively.

[0057] Subsequently, the current-limiting control strategy of the inverter is executed, and the specific execution method is as Figure 10 shown, Figure 10The variable names are as described above. Then, the dq transformation of the capacitor voltage is performed to obtain v d and v q , and the amplitude of the inverter capacitor voltage v amp is calculated.

[0058] Finally, the reference active power of the inverter is adjusted according to the amplitude of the capacitor voltage. If v amp ≥0.8v n , the reference active power of the inverter remains unchanged. If v amp <0.8v n , the reference active power of the inverter is adjusted, and the adjustment expression refers to Equation (7). Figure 10 The parameters of the main variables in

[0059]

[0060]

[0061] The method further includes: calculating the internal electromotive force and angular frequency output by the control loop; correspondingly, the dq coordinate transformation of the collected original inductor current and original capacitor voltage includes: performing the dq coordinate transformation of the collected original inductor current and original capacitor voltage based on the internal electromotive force and the angular frequency.

[0062] The amplitude of the capacitor voltage where the v d and v q are the capacitor voltages in the dq coordinate system;

[0063] where v a , v b and v v are the original capacitor voltages.

[0064] The adjustment of the reference active power according to the amplitude of the capacitor voltage includes:

[0065] The reference active power to be adjusted where P n is the rated reference power value of the inverter, v n is the rated output voltage amplitude of the inverter, h is the power adjustment ratio coefficient, and R v1 is the low-frequency equivalent impedance.

[0066] The preset variable adjustment parameters include: the limit value of the inverter limiter, with a value of 120 A; the virtual impedance ratio value, with a value of 1; the impedance ratio, with a value of 0.3; the power adjustment ratio coefficient, with a value of 1; the low-pass filter value, with a value of 0.01 s; the rated reference active power, with a value of 34 kw; the reference angular frequency, with a value of 314.15926 rad / s; the amplitude of the internal potential of the reactive droop control reference, with a value of 320 V; and the amplitude of the rated capacitor voltage, with a value of 311 V.

[0067] The present invention provides an inverter control system, including: a first unit for calculating the active power and the reactive power and respectively setting corresponding droop control loop processes; a second unit for implementing a virtual impedance current limiting control strategy according to the preset variable adjustment parameters; a third unit for performing dq coordinate transformation on the collected original inductor current and original capacitor voltage and calculating the amplitude of the capacitor voltage; and a fourth unit for adjusting the reference active power according to the amplitude of the capacitor voltage.

[0068] The first unit is further configured to calculate the internal potential and the angular frequency output by the control loop; correspondingly, the third unit is configured to perform dq coordinate transformation on the collected original inductor current and original capacitor voltage based on the internal potential and the angular frequency.

[0069] The amplitude of the capacitor voltage wherein, the v d and v q are the capacitor voltages in the dq coordinate system;

[0070] wherein, v a 、v b and v v are the original capacitor voltages.

[0071] The adjusting the reference active power according to the amplitude of the capacitor voltage includes:

[0072] The reference active power to be adjusted wherein, P n is the inverter rated reference power value, v n is the amplitude of the inverter rated output voltage, h is the power adjustment ratio coefficient, R v1 is the low-frequency equivalent impedance.

[0073] The preset variable adjustment parameters include: the limit value of the inverter limiter, with a value of 120 A; the virtual impedance ratio value, with a value of 1; the impedance ratio value, with a value of 0.3; the power adjustment proportional coefficient, with a value of 1; the low-pass filter value, with a value of 0.01 s; the rated reference active power, with a value of 34 kw; the reference angular frequency, with a value of 314.15926 rad / s; the reactive droop control reference internal potential amplitude, with a value of 320 V; and the rated capacitor voltage amplitude, with a value of 311 V.

[0074] Those of ordinary skill in the art can realize that the units of each example described in combination with the embodiments disclosed in this embodiment can be implemented by electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components of each example have been generally described according to their functions in the above description. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Professional technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

[0075] In the embodiments provided in this application, it should be understood that the division of units is only a logical function division, and there may be other division methods in actual implementation. For example, multiple units can be combined into one unit, one unit can be split into multiple units, or some features can be ignored, etc.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered by the scope of the claims and the description of the present invention.

Claims

1. An inverter control method, characterized in that, Including: Calculating the active power and reactive power, and respectively setting the corresponding droop control loop processes; Adjusting parameters according to preset variables and implementing the virtual impedance current limiting control strategy; Performing dq coordinate transformation on the collected original inductor current and original capacitor voltage, and calculating the capacitor voltage amplitude; Adjusting the reference active power according to the capacitor voltage amplitude; Also including: calculating the internal electromotive force and angular frequency output by the control loop; Correspondingly, the performing dq coordinate transformation on the collected original inductor current and original capacitor voltage includes: Performing dq coordinate transformation on the collected original inductor current and original capacitor voltage based on the internal electromotive force and the angular frequency; The amplitude of the capacitor voltage , where the v d and v q are the capacitor voltages in the dq coordinate system; , where v a , v b and v v are the original capacitor voltages; ； ω out is the output angular frequency of the active / reactive power control loop of the inverter; The adjusting the reference active power according to the capacitor voltage amplitude includes: The reference active power to be adjusted , where P n is the rated reference power value of the inverter, v n is the rated output voltage amplitude of the inverter, h is the power adjustment proportionality coefficient, R v1 is the low-frequency equivalent impedance.

2. The inverter control method according to claim 1, characterized in that, The preset variable adjusting parameters include: The limit value of the inverter limiter, with a value of 120 A; The virtual impedance ratio value, with a value of 1; The impedance ratio value, with a value of 0.3; The power adjustment proportional coefficient, with a value of 1; The low-pass filter value, with a value of 0.01 s; The rated reference active power, with a value of 34 kw; The reference angular frequency, with a value of 314.15926 rad / s; The reference internal electromotive force amplitude for reactive power droop control, with a value of 320 V; The rated capacitor voltage amplitude, with a value of 311 V.

3. An inverter control system, characterized in that, Including: The first unit is used for calculating the active power and reactive power, and respectively setting the corresponding droop control loop processes; The second unit is used for adjusting parameters according to preset variables and implementing the virtual impedance current limiting control strategy; The third unit is used for performing dq coordinate transformation on the collected original inductor current and original capacitor voltage, and calculating the capacitor voltage amplitude; The fourth unit is used for adjusting the reference active power according to the capacitor voltage amplitude; The first unit is also used for calculating the internal electromotive force and angular frequency output by the control loop; Correspondingly, the third unit is used for performing dq coordinate transformation on the collected original inductor current and original capacitor voltage based on the internal electromotive force and the angular frequency; The amplitude of the capacitor voltage , where the v d and v q are the capacitor voltages in the dq coordinate system; , where v a , v b and v v are the original capacitor voltages; ； ω out is the output angular frequency of the active / reactive control loop of the inverter; The adjusting the reference active power according to the capacitor voltage amplitude includes: The reference active power to be adjusted , where P n is the rated reference power value of the inverter, v n is the rated output voltage amplitude of the inverter, h is the power adjustment ratio coefficient, R v1 is the low-frequency equivalent impedance.

4. The inverter control system according to claim 3, wherein, The preset variable adjusting parameters include: The limit value of the inverter limiter, with a value of 120 A; The virtual impedance ratio value, with a value of 1; The impedance ratio value, with a value of 0.3; The power adjustment proportional coefficient, with a value of 1; The low-pass filter value, with a value of 0.01 s; The rated reference active power, with a value of 34 kw; The reference angular frequency, with a value of 314.15926 rad / s; The reference internal electromotive force amplitude for reactive power droop control, with a value of 320 V; The rated capacitor voltage amplitude, with a value of 311 V.

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