Micro-grid harmonic power distribution method and device, control device and readable storage medium

Abstract

The invention relates to a micro-grid harmonic power distribution method and device, a control device and a readable storage medium. The method is applied to a control device of a micro-grid system. The control device is respectively connected with the inverters connected in parallel in the micro-grid system; the method comprises the steps of obtaining harmonic apparent power corresponding to each inverter according to a fundamental component of an output voltage of each inverter and each harmonic of an output current of each inverter; based on the harmonic apparent power, determining a harmonic power distribution coefficient corresponding to each inverter; obtaining harmonic compensation current required by each inverter according to the harmonic power distribution coefficient; and based on the harmonic compensation current and the harmonic power distribution coefficient, the equivalent harmonic impedance of the corresponding inverter is adjusted through the voltage and current double-closed-loop control loop corresponding to each inverter, so that the equivalent harmonic impedance is matched with the rated apparent power corresponding to the inverter. According to the invention, the harmonic current is reasonably distributed, and the voltage quality of the grid-connected point is ensured.

Description

Technical Field

[0001] The present application relates to the field of microgrid technology, and in particular to a microgrid harmonic power distribution method, device, control device and readable storage medium. Background Art

[0002] When multiple inverters are dynamically networked in an AC microgrid, they can serve as the microgrid's multi-source inputs. At the same time, the AC microgrid's load side contains numerous nonlinear loads, generating harmonic currents that flow into the microgrid's upstream multi-source inputs. Understandably, the voltage drop caused by these harmonic currents can degrade the power quality of the microgrid's node voltages. Furthermore, when the equivalent harmonic impedance of each inverter mismatches its rated apparent power, this can further lead to harmonic circulating currents in the microgrid system, further degrading power quality and even causing inverter overload.

[0003] Traditional harmonic power distribution methods are difficult to implement and can easily cause a considerable harmonic voltage drop between the inverter and the microgrid's grid connection point, resulting in serious voltage distortion at the grid connection point and affecting the voltage quality of the microgrid system's grid connection point. Summary of the Invention

[0004] Based on this, it is necessary to provide a microgrid harmonic power distribution method, device, control device and readable storage medium to address the above technical problems, which can ensure the voltage quality of the grid connection point while reasonably distributing the harmonic current.

[0005] In a first aspect, in one embodiment, the present application provides a microgrid harmonic power distribution method, which is applied to a control device of a microgrid system; the control device is respectively connected to each parallel inverter in the microgrid system; the method includes:

[0006] According to the fundamental component of the output voltage of each inverter and the harmonics of the output current, the harmonic apparent power corresponding to each inverter is obtained;

[0007] Based on the harmonic apparent power, determine the harmonic power distribution coefficient corresponding to each inverter;

[0008] According to the harmonic power distribution coefficient, the harmonic compensation current required by each inverter is obtained;

[0009] Based on the harmonic compensation current and the harmonic power distribution coefficient, the equivalent harmonic impedance of the inverter corresponding to the voltage and current dual closed-loop control loop is adjusted through the voltage and current dual closed-loop control loop corresponding to each inverter, so that the equivalent harmonic impedance matches the rated apparent power corresponding to the inverter.

[0010] In one embodiment, the harmonic apparent power corresponding to each inverter is obtained based on the fundamental component of the output voltage and each harmonic of the output current of each inverter, including:

[0011] Extracting the harmonics of the output current of each inverter; the harmonic current extractor includes a plurality of multi-resonance controllers for respectively extracting different harmonic orders;

[0012] Based on the fundamental component of the output voltage of each inverter and the harmonics of the output current, the harmonic apparent power corresponding to each inverter is calculated.

[0013] In one embodiment, determining the harmonic power allocation coefficient corresponding to each inverter based on the harmonic apparent power includes:

[0014] Determine the droop coefficient corresponding to each inverter based on the rated apparent power of each inverter;

[0015] According to the apparent power difference, droop coefficient and droop control reference value of each inverter, the harmonic power distribution coefficient corresponding to each inverter is obtained.

[0016] In one embodiment, based on the harmonic compensation current and the harmonic power distribution coefficient, the equivalent harmonic impedance of the inverter corresponding to the voltage and current dual closed-loop control loop is adjusted through the voltage and current dual closed-loop control loop corresponding to each inverter, including:

[0017] Obtaining a reference voltage of each inverter through an inverter control loop corresponding to the inverter; wherein the inverter control loop is used to simulate the operation process of a synchronous generator to obtain the reference voltage;

[0018] Based on the reference voltage and harmonic power distribution coefficient, the equivalent harmonic impedance of the inverter is adjusted through a voltage-current dual closed-loop control loop according to the filter capacitor voltage, filter inductor current and harmonic compensation current of each inverter.

[0019] In one embodiment, obtaining a reference voltage of each inverter through an inverter control loop corresponding to the inverter includes:

[0020] By simulating the motion process of the synchronous generator rotor, the voltage phase angle of the reference voltage is obtained;

[0021] The voltage amplitude of the reference voltage is obtained by simulating the reactive power-voltage droop characteristics of the synchronous generator;

[0022] According to the voltage phase angle and voltage amplitude, the reference voltage of the inverter corresponding to each inverter control loop is obtained.

[0023] In one embodiment, obtaining the harmonic compensation current required by each inverter according to the harmonic power distribution coefficient includes:

[0024] According to the harmonics of the output current of each inverter, the harmonic compensation current corresponding to the harmonics of the output current of each inverter is obtained through the impedance control link; the impedance control link is as follows:

[0025]

[0026] in, is the harmonic power distribution coefficient, is the filter inductor of the inverter, is the filter capacitor of the inverter, is the transfer function of the current regulator of the voltage-current dual closed-loop control loop, is the transfer function of the voltage regulator of the voltage-current dual closed-loop control loop, It is the inherent delay link of PWM modulation. is the modulation coefficient, To obtain the transfer function of the bandpass filter for each harmonic of the output current, is the transfer function corresponding to the impedance control link; the input of the transfer function corresponding to the impedance control link is the harmonics of the output current, and the output is the harmonic compensation current corresponding to the harmonics of the output current of each inverter, and s is the complex variable of Laplace transform.

[0027] In a second aspect, in one embodiment, the present application provides a microgrid harmonic power distribution device, which is applied to a control device of a microgrid system; the control device is respectively connected to each parallel inverter in the microgrid system; the microgrid harmonic power distribution device includes:

[0028] The harmonic power acquisition module is used to obtain the harmonic apparent power corresponding to each inverter based on the fundamental component of the output voltage and the harmonics of the output current of each inverter;

[0029] A power distribution coefficient acquisition module is used to determine the harmonic power distribution coefficient corresponding to each inverter based on the harmonic apparent power;

[0030] The harmonic compensation current calculation module is used to obtain the harmonic compensation current required by each inverter according to the harmonic power distribution coefficient;

[0031] The equivalent harmonic impedance adjustment module is used to adjust the equivalent harmonic impedance of the inverter corresponding to the voltage and current dual closed-loop control loop based on the harmonic compensation current and the harmonic power distribution coefficient, so that the equivalent harmonic impedance matches the rated apparent power corresponding to the inverter through the voltage and current dual closed-loop control loop corresponding to each inverter.

[0032] In a third aspect, in one embodiment, the present application provides a control device including a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the steps in the above-mentioned method embodiments of the first aspect are implemented.

[0033] In a fourth aspect, in one embodiment, the present application provides a microgrid system, comprising a control device as in the embodiment of the third aspect.

[0034] In a fifth aspect, in one embodiment, the present application provides a computer-readable storage medium having a computer program stored thereon, which implements the steps in the various method embodiments of the above-mentioned first aspect when the computer program is executed by a processor.

[0035] The aforementioned microgrid harmonic power distribution method, device, control device, and readable storage medium obtain the harmonic apparent power corresponding to each inverter based on the fundamental component of the output voltage and the harmonics of the output current of each inverter. Based on the harmonic apparent power, the corresponding harmonic power distribution coefficient is further determined. The harmonic compensation current required for each inverter is obtained using the harmonic power distribution coefficient. Finally, based on the harmonic compensation current, the equivalent harmonic impedance of the corresponding inverter is adjusted using the corresponding voltage-current dual closed-loop control loop, thereby matching the equivalent harmonic impedance to the rated apparent power of the inverter. This approach ensures that the voltage quality at the grid connection point is maintained while ensuring the rational distribution of harmonic currents. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the following briefly introduces the drawings required for use in the embodiments of the present application or related technical descriptions. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying any creative work.

[0037] Figure 1 This is a diagram of an application environment of a microgrid harmonic power distribution method in one embodiment;

[0038] Figure 2 1 is a flow chart of a microgrid harmonic power distribution method according to an embodiment;

[0039] Figure 3 1 is a schematic diagram of the topological structure of the inverter main circuit in one embodiment;

[0040] Figure 4 1 is an equivalent block diagram of a voltage and current dual closed-loop control loop in one embodiment;

[0041] Figure 51 is a flow chart of calculating the apparent power of harmonics in one embodiment;

[0042] Figure 6 is a schematic diagram of the operation of a harmonic current extractor in one embodiment;

[0043] Figure 7 A schematic diagram of a process for obtaining a harmonic power distribution coefficient in one embodiment;

[0044] Figure 8 Schematic diagram of an equivalent circuit of parallel inverters in an AC microgrid in one embodiment;

[0045] Figure 9 1 is a schematic diagram of a process for adjusting the equivalent harmonic impedance of an inverter in one embodiment;

[0046] Figure 10 A schematic diagram of a process for obtaining a reference voltage of an inverter in one embodiment;

[0047] Figure 11 An equivalent block diagram for obtaining harmonic compensation current in one embodiment;

[0048] Figure 12 Schematic diagram of a flow chart of a microgrid harmonic power distribution method according to another embodiment;

[0049] Figure 13 is a structural block diagram of a microgrid harmonic power distribution device in one embodiment;

[0050] Figure 14 FIG. 4 is a diagram showing the internal structure of a control device in one embodiment. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0052] With the development of green energy technologies, the proportion of distributed generation, primarily based on clean energy, continues to increase. Currently, clean energy is primarily generated through photovoltaic and wind power generation. Unlike traditional thermal power plants, photovoltaic and wind power stations are more dispersed, necessitating the use of distributed generation equipment. To accommodate the flexible location of clean energy distributed generation and address the issue of reliable grid access for distributed generation, the concept of microgrids has been proposed. Microgrids can effectively manage loads and support energy storage devices through the complementary synergy of multiple energy sources, ultimately suppressing power fluctuations within the microgrid system, effectively addressing the impact of distributed generation and random load fluctuations on the grid.

[0053] The microgrid harmonic power distribution method provided in the embodiment of the present application can be applied to Figure 1 In the application environment shown. The microgrid system 100 includes a plurality of power supply devices 104, and each power supply device 104 is connected in parallel to the common grid connection point of the microgrid system 100 through the inverter 102 connected thereto to form an AC microgrid. Furthermore, the load side of the microgrid system 100 also includes a common nonlinear load 106 and a common linear load 108. The microgrid system 100 also includes a control device 110 ( Figure 1 (not shown). Optionally, the power supply device 104 may include photovoltaic power generation equipment, wind power generation equipment, and energy storage batteries.

[0054] It can be understood that the microgrid system 100 is dynamically networked through multiple inverters 102 connected to power supply devices 104, serving as the microgrid's multi-source input. Furthermore, in practical applications, the load side of the microgrid system 100 contains numerous common nonlinear loads 106 (only one of which is shown in the figure). These loads can be approximated as harmonic current sources, generating harmonic currents that flow into the upstream multi-source inputs of the microgrid system 100 (i.e., the grid branches corresponding to the various power supply devices). On the one hand, the voltage drop generated by the harmonic currents of these common nonlinear loads in the microgrid system 100 will degrade the power quality of the node voltages within the microgrid. On the other hand, if the equivalent harmonic impedance of each inverter participating in the microgrid does not match its rated apparent power, inverters with smaller capacity and lower harmonic impedance will bear more harmonic power, while inverters with larger capacity and higher harmonic impedance will bear less harmonic power. In this case, harmonic circulating currents will occur in the microgrid system 100, leading to more severe power quality degradation and even inverter overload.

[0055] Traditional harmonic power distribution methods for microgrid systems mainly achieve reasonable distribution of harmonics by introducing virtual inductors in the control loop of the inverters, and by introducing virtual inductors based on the capacity ratio of each inverter. However, due to the large inductance of the virtual inductors, a considerable harmonic voltage drop will be generated between the inverter and the grid connection point, resulting in serious voltage distortion at the grid connection point. Other traditional harmonic power distribution methods propose to introduce negative virtual inductors or virtual capacitors to compensate for the harmonic voltages at both ends of the inductors and reduce the voltage distortion at the public grid connection point. However, the design of negative virtual inductors in the above traditional methods requires measuring the accurate value of the grid-side impedance of the microgrid system, and this measurement process is quite difficult to implement.

[0056] In one embodiment, Figure 2As shown, the present application provides a microgrid harmonic power distribution method, which is applied to the control device 110 of the microgrid system; the method includes the following steps S202 to S208. Among them:

[0057] Step S202 : Obtaining the harmonic apparent power corresponding to each inverter according to the fundamental component of the output voltage and each harmonic of the output current of each inverter.

[0058] Among them, the main circuit topology of the inverter can be as follows Figure 3 As shown, the inverter main circuit includes filter capacitors , filter inductor , switching devices and energy storage capacitors In some examples, the DC power output by power supply equipment such as photovoltaic power generation, wind power generation, and energy storage batteries can be stored in energy storage capacitors. The AC power is then converted to AC power by the inverter's switching devices. After passing through the LC filter, the AC power is filtered by the local nonlinear load and the line impedance (including the line resistance). and line inductance ) and incorporated into the public grid connection point.

[0059] Exemplarily, the output voltage and output current of the inverter both correspond to the output voltage and output current output by the LC filter link of the main circuit of the inverter.

[0060] In some possible implementations, based on the output current of the inverter, a multi-resonant controller that extracts harmonics of preset orders can be used to obtain harmonics corresponding to the output current of the inverter.

[0061] Specifically, the control device can calculate the harmonic apparent power corresponding to each inverter based on the fundamental component of the output voltage and each harmonic of the output current of each inverter.

[0062] Step S204: determining the harmonic power distribution coefficient corresponding to each inverter based on the harmonic apparent power.

[0063] The harmonic power distribution coefficient can be used to adjust the equivalent harmonic impedance of each inverter to control the compensated harmonic power corresponding to the inverter.

[0064] In some possible implementations, the harmonic power can be distributed based on the rated power capacity of each inverter. For example, define To reflect the parameters of different inverter rated power capacities, the following relationship will exist in the microgrid system:

[0065] (Formula 1)

[0066] in, Indicates the rated apparent power of the nth inverter.

[0067] Specifically, the control device can determine the harmonic power distribution coefficient corresponding to each inverter in the microgrid system based on the harmonic apparent power. The harmonic power distribution coefficient can be used to further calculate the harmonic compensation current of each inverter.

[0068] Step S206: Obtain the harmonic compensation current required by each inverter according to the harmonic power distribution coefficient.

[0069] Exemplarily, the harmonic compensation current can be used as a harmonic reference current input to a current regulator of a voltage-current dual closed-loop control loop to achieve regulation of the harmonic impedance of the inverter.

[0070] Specifically, the control device may further obtain the harmonic compensation current required by each inverter based on the harmonic power distribution coefficient corresponding to each inverter obtained above.

[0071] Step S208 , based on the harmonic compensation current, the equivalent harmonic impedance of the inverter corresponding to each inverter is adjusted through the voltage-current dual closed-loop control loop corresponding to each inverter, so that the equivalent harmonic impedance matches the rated apparent power corresponding to the inverter.

[0072] For example, Figure 4 As shown, the present application provides an equivalent control block diagram corresponding to the voltage and current double closed-loop control loop of an inverter. Figure 4 In the voltage and current dual closed-loop control loop shown, is the equivalent impedance of the inverter connected to the grid (i.e., the public grid connection point), is the equivalent inductance of the grid to which the inverter is connected, is the filter capacitor of the inverter, is the filter inductor of the inverter, is the equivalent transfer function corresponding to the inherent delay link of the microgrid system, is the transfer function of the current regulator (i.e., the system current loop controller), is the transfer function of the voltage regulator (i.e., the system voltage loop controller), is the sampling delay; s is the complex variable of Laplace transform (i.e. frequency domain), is the output voltage (i.e. the filter capacitor voltage), is the grid-side voltage, is the grid-connected current, is the inverter filter inductor current, is the reference current of the current loop, is the reference voltage of the voltage loop, is the harmonic compensation current of the hth harmonic.

[0073] Specifically, the control device adjusts the equivalent harmonic impedance of the corresponding inverter based on the harmonic compensation current required by each inverter through the voltage and current dual closed-loop control loop corresponding to each inverter, so that the equivalent harmonic impedance matches the rated apparent power corresponding to the inverter.

[0074] In one embodiment, Figure 5 As shown, according to the fundamental component of the output voltage of each inverter and the harmonics of the output current, the harmonic apparent power corresponding to each inverter is obtained, including the following steps S302 to S304.

[0075] Step S302: extracting the harmonics of the output current of each inverter.

[0076] In some examples, a harmonic current extractor may be used to extract the harmonics of the output current of each inverter. For example, Figure 6 As shown, the harmonic current extractor includes multiple multi-resonance controllers that extract different harmonic orders respectively. Figure 6 The harmonic current extractor shown in The output current of the inverter obtained by sampling (corresponding to the grid-connected current in the voltage-current dual closed-loop control loop) ), is the obtained hth harmonic component, To extract the transfer function corresponding to the multi-resonant controller of the hth harmonic, its expression is shown as follows:

[0077] (Formula 2)

[0078] in, is the gain coefficient, is the bandwidth of the multi-resonant controller, h is the harmonic order of the inverter output current, s is the complex variable of Laplace transform (frequency domain), is the fundamental angular frequency equal to 2*pi*50 (the fundamental frequency is 50 Hz). In some instances, the harmonic order can be an odd-order harmonic such as the 5th, 7th, or 11th. It is understandable that since the grid fundamental frequency is 50 Hz, the frequency of the nth harmonic is n*50. For a three-phase system, due to symmetry, even harmonics (such as the 2nd, 4th, and 6th) are suppressed due to the asymmetry between the positive and negative half-waves, while odd harmonics (such as the 3rd, 5th, and 7th) are more likely to exist. Furthermore, since the 3rd harmonic is a zero-sequence component, it may flow through the neutral point in a star-grounded system, but it is suppressed in an ungrounded system or when passing through delta-connected equipment (such as a transformer). As a result, odd harmonics such as the 5th and 7th become the main remaining components.

[0079] Specifically, the control device may extract the harmonics of the output currents of the respective inverters using a harmonic current extractor provided with a plurality of multi-resonance controllers.

[0080] Step S304 : Based on the fundamental component of the output voltage of each inverter and the harmonics of the output current, the harmonic apparent power corresponding to each inverter is calculated.

[0081] For example, the harmonic apparent power corresponding to each inverter can be calculated according to Formula 3 shown below:

[0082] (Formula 3)

[0083] in, is the effective value of the fundamental voltage of the inverter (effective value of the fundamental voltage of the inverter The fundamental component of the inverter output voltage It's the same concept. is a valid value, is the amplitude, the difference between the two times); is the effective value of the inverter harmonic current, which can be calculated by the harmonic current extractor; h is the harmonic order of the inverter output current; is the apparent harmonic power of the i-th inverter. The above formula 3 can be used to calculate the harmonic power.

[0084] In one embodiment, Figure 7 As shown, based on the harmonic apparent power, determining the harmonic power distribution coefficient corresponding to each inverter includes the following steps S402 to S404.

[0085] Step S402: determining the droop coefficient corresponding to each inverter based on the rated apparent power of each inverter.

[0086] For example, the relationship between the droop coefficients corresponding to the inverters is shown in the following formula:

[0087] (Formula 4)

[0088] in, is the droop coefficient corresponding to the nth inverter (its design is inversely proportional to the rated power of the inverter), is the rated apparent power of the i-th inverter. It can be understood that the above droop coefficient actually corresponds to the parameter of the inverter rated power capacity shown in Formula 1.

[0089] Specifically, the control device may determine the droop coefficient corresponding to each inverter according to the rated apparent power of each inverter.

[0090] Step S404 : obtaining the harmonic power distribution coefficient corresponding to each inverter according to the apparent power difference, the droop coefficient, and the droop control reference value of each inverter.

[0091] In some examples, the equivalent circuit of parallel inverters in an AC microgrid at harmonic frequencies is as follows: Figure 8 As shown. Figure 8 The equivalent circuit shown is analyzed to Figure 8 Taking the grid-type inverter-1 in the example, the equivalent output current of the inverter can be approximately calculated as shown in the following formula:

[0092] (Formula 5)

[0093] in, is the harmonic current of grid-type inverter-1; is the line resistance of the branch corresponding to the grid-connected inverter-1; is the line inductance of the branch corresponding to the grid-connected inverter-1; is the harmonic angular frequency; is the harmonic impedance of the grid; is the harmonic current of the local nonlinear load; j is the imaginary unit; h is the harmonic frequency (such as h=5, which means the 5th harmonic); is the equivalent harmonic impedance of the grid-type inverter-1. In the microgrid system, the harmonic impedance of the grid is The expression can be shown as follows.

[0094] (Formula 6)

[0095] Furthermore, the harmonic power distribution coefficient corresponding to each inverter can be calculated according to the following formula 6:

[0096] (Formula 7)

[0097] in, is the harmonic power distribution coefficient of the nth inverter; It is the reference value for droop control of harmonic power distribution coefficient; is the droop coefficient; is the harmonic apparent power of the nth inverter; is the rated apparent power of the i-th inverter; is the apparent power difference.

[0098] Specifically, the control device can calculate the harmonic power distribution coefficient corresponding to each inverter according to the apparent power difference, droop coefficient and droop control reference value of each inverter.

[0099] In one embodiment, Figure 9 As shown, based on the harmonic compensation current and the harmonic power distribution coefficient, the equivalent harmonic impedance of the inverter corresponding to the voltage and current double closed-loop control loop is adjusted through the voltage and current double closed-loop control loop corresponding to each inverter, including the following steps S502 to S504.

[0100] Step S502 : obtaining a reference voltage of each inverter through an inverter control loop corresponding to the inverter.

[0101] Among them, the inverter control loop is used to simulate the operation process of the synchronous generator to obtain a reference voltage; illustratively, the inverter control loop corresponding to the inverter can generate a fundamental reference voltage with inertia, thereby realizing the networking function.

[0102] In some possible implementations, when the power supply equipment is a photovoltaic power generation equipment, wind power generation equipment or other power generation equipment, the inverter control loop can simulate the movement process of the rotor of the synchronous generator by simulating the second-order model of the synchronous generator, so as to use the second-order model to determine the reference voltage corresponding to the inverter.

[0103] Specifically, the control device may obtain the reference voltage of each inverter through the inverter control loop corresponding to the inverter.

[0104] Step S504 , based on the reference voltage and the harmonic power distribution coefficient, the equivalent harmonic impedance of the inverter is adjusted through a voltage-current dual closed-loop control loop according to the filter capacitor voltage, filter inductor current and harmonic compensation current of each inverter.

[0105] For example, the harmonic power allocation coefficient can be used by the following formula 8: Adjust the inverter equivalent harmonic impedance:

[0106] (Formula 8)

[0107] in, It is understood that when the harmonic power distribution of the nth inverter does not match the rated harmonic apparent power of each inverter, that is, When the control device can adjust the harmonic power distribution coefficient through the droop coefficient , the process is as follows:

[0108] when When , according to the above expression of droop control, will decrease, and the equivalent harmonic impedance of the nth inverter will increase, resulting in a decrease in the harmonic power it compensates for, and ultimately matching its rated capacity; similarly, when When the inverter is in operation, the harmonic power required to be compensated can be matched with its rated capacity through a process similar to the above.

[0109] Furthermore, through the combined effect of the calculated harmonic compensation current and the above harmonic power distribution coefficient adjustment mechanism, the following Figure 4 The voltage and current dual closed-loop control loop shown can adjust the equivalent harmonic impedance of each inverter in the microgrid system.

[0110] Specifically, the control device can adjust the equivalent harmonic impedance of the inverter using a voltage-current dual closed-loop control loop based on the obtained reference voltage and harmonic power distribution coefficient, combined with the filter capacitor voltage, filter inductor current and harmonic compensation current of each inverter, so that the equivalent harmonic impedance matches the rated apparent power corresponding to the inverter.

[0111] In one embodiment, Figure 10 As shown, the reference voltage of each inverter is obtained through the inverter control loop corresponding to the inverter, including the following steps S602 to S606.

[0112] Step S602 , obtaining a voltage phase angle of a reference voltage by simulating the motion process of a synchronous generator rotor.

[0113] For example, the inverter control loop may simulate the motion process of the rotor of the synchronous generator by simulating the second-order model of the synchronous generator, as shown in the following formula:

[0114] (Formula 9)

[0115] (Formula 10)

[0116] in, is the phase of the simulated electromotive force of the synchronous generator, through which the phase of the reference voltage can be further determined; t is the motion time of the synchronous generator; is the moment of inertia simulated by the inverter control loop, given by This allows the inverter control loop to exhibit the same active power-frequency characteristics as a synchronous generator; is the damping coefficient of the inverter control loop simulation; and They are the virtual angular frequency and rated angular frequency simulated by the inverter control loop, where the rated angular frequency is based on the grid power frequency, and the virtual angular frequency is the angular frequency of the inverter output voltage generated with inertia; and are the mechanical torque and electromagnetic torque simulated by the inverter control loop. In some examples, the mechanical torque and electromagnetic torque It can be obtained by the following expression:

[0117] (Formula 11)

[0118] (Formula 12)

[0119] in, and They are the virtual mechanical power and virtual battery power of the synchronous generator simulated by the inverter control loop.

[0120] Specifically, the inverter control loop can simulate the second-order model of the synchronous generator of the power supply equipment. The control device can use the second-order model of the synchronous generator to simulate the movement process of the synchronous generator rotor to obtain the voltage phase angle corresponding to the reference voltage of each inverter.

[0121] Step S604 , obtaining the voltage amplitude of the reference voltage by simulating the reactive power-voltage droop characteristic of the synchronous generator.

[0122] For example, the virtual mechanical power It can be obtained by the following expression:

[0123] (Formula 13)

[0124] in, is the active power setting value of the inverter control loop, Is the regulation coefficient. The reactive power instruction for power control by the inverter control loop As shown in the following formula 14, the inverter control loop can simulate the reactive power-voltage droop characteristics of the synchronous generator through the following formula:

[0125] (Formula 14)

[0126] in, is the reactive power setpoint of the inverter control loop; is the effective value of the rated phase voltage, is the effective value of the capacitor phase voltage; Is the voltage regulation coefficient. In order to make the reactive power output by the inverter control loop (i.e. the output reactive power of the inverter) according to the reactive power command value By performing deviation integration on the reactive power, the amplitude of the reference voltage output by the inverter control loop can be obtained. The process is shown in the following formula 15:

[0127] (Formula 15)

[0128] Specifically, the inverter control loop can obtain the voltage amplitude of the reference voltage by simulating the reactive power-voltage droop characteristics of the synchronous generator.

[0129] Step S606 : Obtaining the reference voltage of the inverter corresponding to each inverter control loop according to the voltage phase angle and the voltage amplitude.

[0130] For example, according to the following formula 16, the reference voltages of the three phases of the inverter corresponding to each inverter control loop can be calculated based on the obtained voltage phase angle and voltage amplitude:

[0131] (Formula 16)

[0132] in, 、 and is the three-phase reference voltage corresponding to the inverter, is the amplitude of the reference voltage, is the phase of the simulated electromotive force.

[0133] Specifically, the control device can further obtain the reference voltage of the inverter corresponding to each inverter control loop according to the voltage phase angle and the voltage amplitude.

[0134] In one embodiment, obtaining the harmonic compensation current required by each inverter according to the harmonic power distribution coefficient includes:

[0135] According to the harmonics of the output current of each inverter and the harmonic power distribution coefficient, the harmonic compensation current corresponding to the harmonics of the output current of each inverter is obtained through the impedance control link; the impedance control link is as follows:

[0136] (Formula 17)

[0137] in, is the harmonic power distribution coefficient, is the filter inductor of the inverter, is the filter capacitor of the inverter, is the transfer function of the current regulator of the voltage-current dual closed-loop control loop, is the transfer function of the voltage regulator of the voltage-current dual closed-loop control loop, It is the inherent delay link of PWM modulation. is the modulation coefficient, To obtain the transfer function of the bandpass filter for each harmonic of the output current, It is the transfer function corresponding to the impedance control link; the input of the transfer function corresponding to the impedance control link is the harmonics of the output current, and the output is the harmonic compensation current corresponding to the harmonics of the output current of each inverter.

[0138] Specifically, the equivalent block diagram for obtaining harmonic compensation current is as follows: Figure 11 As shown, represents the transfer function corresponding to the impedance control link, The transfer function of the bandpass filter that obtains the harmonics of the output current is shown in Figure 2. Taking the impedance control link into consideration, the equivalent impedance of the inverter is The expression is as follows:

[0139] (Formula 18)

[0140] in, is the filter inductor of the inverter; It is the filter capacitor of the inverter; is the transfer function of the current regulator of the voltage-current dual closed-loop control loop; is the transfer function of the voltage regulator of the voltage-current dual closed-loop control loop; It is the inherent delay link of PWM modulation. The inherent delay link mainly refers to the unavoidable time delay caused by hardware device characteristics or system control logic; is the modulation coefficient; The transfer function of the bandpass filter for obtaining each harmonic of the output current also corresponds to the multi-resonance controller of the above-mentioned harmonic current extractor.

[0141] It can be understood that based on the above formula 18, when the equation of the following formula 19 is satisfied at the harmonic frequency, the equivalent harmonic impedance of the inverter is theoretically equal to 0:

[0142] (Formula 19)

[0143] The calculated harmonic power distribution coefficient Introducing the above formula 19, we can get the transfer function corresponding to the impedance control link shown in formula 17 .

[0144] In one embodiment, Figure 12 As shown in the figure, the harmonic power distribution method of the microgrid can be composed of a harmonic power calculation module, a harmonic power distribution module, a harmonic compensation module, an inverter control loop, a voltage and current double closed-loop control loop, and PWM (Pulse Width Modulation) modulation. Figure 12 In the harmonic power distribution method shown in FIG, are the harmonics of the inverter output current, is the fundamental component of the inverter’s output voltage, is the harmonic apparent power output by the inverter, is the harmonic power distribution coefficient, is the harmonic compensation current, is the inverter filter inductor current, is the filter capacitor voltage of the inverter; It is the reference voltage output by the inverter control loop.

[0145] Among them, the harmonic power calculation module can be used to extract the harmonics of the inverter output current through the harmonic current extractor, and output the corresponding harmonic apparent power of the inverter; the harmonic power distribution module can be set at the command output of the inverter control (that is, the reference voltage input of the double closed loop), and is used to distribute the harmonic power of each inverter based on its own capacity, so as to calculate the harmonic compensation current command of each inverter, and realize the distribution ratio adjustment of the harmonic compensation current between multiple inverters in the same microgrid through the harmonic impedance adjustment module; the harmonic impedance adjustment module is used to adjust the inverter output through the bandpass filter and impedance control link. The harmonic components of the current are added to the command side of the current inner loop, and work together with the harmonic power distribution module to adjust the harmonic impedance of the inverter, thereby realizing the harmonic current distribution of the multi-node dynamic networking of the microgrid; the inverter control loop can be used to simulate the synchronous generator by simulating the second-order model of the synchronous generator to output the reference voltage of the inverter to the voltage-current dual closed-loop control loop; the voltage-current dual closed-loop control loop can be used to realize signal sampling and control of the inverter physical system, so that the equivalent harmonic impedance of each inverter can match the rated apparent power, thereby achieving reasonable distribution of harmonic current while ensuring the voltage quality of the grid connection point.

[0146] It can be understood that the microgrid harmonic power distribution method of the present application can solve the harmonic power distribution problem of multiple inverters running in parallel in an AC microgrid without affecting the voltage distortion rate at the grid connection point. Furthermore, the microgrid harmonic power distribution method of the present application includes at least the following technical effects:

[0147] ① Compared with traditional technologies, this application can solve the trade-off between harmonic distribution accuracy and voltage quality without measuring the PCC (Point of Common Coupling) voltage and grid-side impedance.

[0148] ② The present application can automatically adjust the control loop of each inverter based on the capacity of the inverter and avoid introducing additional virtual impedance. In this way, the performance of the harmonic power distribution method of the present application is independent of the closed-loop gain of the inverter, thereby achieving accurate harmonic distribution and improving the power quality of the microgrid system without the need to obtain the line and grid-side circuit parameters in advance.

[0149] It should be understood that, although the various steps in the flowcharts involved in the various embodiments described above are displayed in sequence according to the instructions of the arrows, these steps are not necessarily executed in sequence in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order restriction on the execution of these steps, and these steps can be executed in other orders. Moreover, at least a portion of the steps in the flowcharts involved in the various embodiments described above can include multiple steps or multiple stages, and these steps or stages are not necessarily executed and completed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a portion of steps or stages in other steps.

[0150] Based on the same inventive concept, embodiments of the present application also provide a microgrid harmonic power distribution device for implementing the aforementioned microgrid harmonic power distribution method. The solution provided by this device is similar to the solution described in the aforementioned method. Therefore, the specific limitations of one or more microgrid harmonic power distribution device embodiments provided below can be found in the above-described limitations of the microgrid harmonic power distribution method and will not be further elaborated here.

[0151] In one embodiment, Figure 13 As shown, the present application provides a microgrid harmonic power distribution device 130, which is applied to a control device of a microgrid system; the control device is respectively connected to each parallel inverter in the microgrid system; the microgrid harmonic power distribution device 130 includes:

[0152] The harmonic power acquisition module 132 is used to obtain the harmonic apparent power corresponding to each inverter based on the fundamental component of the output voltage and each harmonic of the output current of each inverter;

[0153] A power allocation coefficient acquisition module 134 is configured to determine the harmonic power allocation coefficient corresponding to each inverter based on the harmonic apparent power;

[0154] The harmonic compensation current calculation module 136 is used to obtain the harmonic compensation current required by each inverter according to the harmonic power distribution coefficient;

[0155] The equivalent harmonic impedance adjustment module 138 is used to adjust the equivalent harmonic impedance of the inverter corresponding to the voltage-current dual closed-loop control loop based on the harmonic compensation current and the harmonic power distribution coefficient, so that the equivalent harmonic impedance matches the rated apparent power corresponding to the inverter through the voltage-current dual closed-loop control loop corresponding to each inverter.

[0156] In one embodiment, the harmonic power acquisition module 132 is further configured to:

[0157] Extracting the harmonics of the output current of each inverter; the harmonic current extractor includes a plurality of multi-resonance controllers for respectively extracting different harmonic orders;

[0158] Based on the fundamental component of the output voltage of each inverter and the harmonics of the output current, the harmonic apparent power corresponding to each inverter is calculated.

[0159] In one embodiment, the power allocation coefficient acquisition module 134 is further configured to:

[0160] Determine the droop coefficient corresponding to each inverter based on the rated apparent power of each inverter;

[0161] According to the apparent power difference, droop coefficient and droop control reference value of each inverter, the harmonic power distribution coefficient corresponding to each inverter is obtained.

[0162] In one embodiment, the equivalent harmonic impedance adjustment module 138 is further configured to:

[0163] Obtaining a reference voltage for each inverter through an inverter control loop corresponding to the inverter; wherein the inverter control loop is used to simulate the operation process of a synchronous generator to obtain the reference voltage;

[0164] Based on the reference voltage and harmonic power distribution coefficient, the equivalent harmonic impedance of the inverter is adjusted through a voltage-current dual closed-loop control loop according to the filter capacitor voltage, filter inductor current and harmonic compensation current of each inverter.

[0165] In one embodiment, the equivalent harmonic impedance adjustment module 138 is further configured to:

[0166] By simulating the motion process of the synchronous generator rotor, the voltage phase angle of the reference voltage is obtained;

[0167] The voltage amplitude of the reference voltage is obtained by simulating the reactive power-voltage droop characteristics of the synchronous generator;

[0168] According to the voltage phase angle and voltage amplitude, the reference voltage of the inverter corresponding to each inverter control loop is obtained.

[0169] In one embodiment, the harmonic compensation current calculation module 136 is further configured to:

[0170] According to the harmonics of the output current of each inverter, the harmonic compensation current corresponding to the harmonics of the output current of each inverter is obtained through the impedance control link; the impedance control link is as follows:

[0171]

[0172] in, is the harmonic power distribution coefficient, is the filter inductor of the inverter, is the filter capacitor of the inverter, is the transfer function of the current regulator of the voltage-current dual closed-loop control loop, is the transfer function of the voltage regulator of the voltage-current dual closed-loop control loop, It is the inherent delay link of PWM modulation. is the modulation coefficient, To obtain the transfer function of the bandpass filter for each harmonic of the output current, is the transfer function corresponding to the impedance control link; the input of the transfer function corresponding to the impedance control link is the harmonics of the output current, and the output is the harmonic compensation current corresponding to the harmonics of the output current of each inverter, and s is the complex variable of Laplace transform.

[0173] Each module in the aforementioned microgrid harmonic power distribution device can be implemented in whole or in part through software, hardware, or a combination thereof. Each module can be embedded in or independent of a processor in a computer device in hardware form, or can be stored in a computer device memory in software form, so that the processor can call and execute the corresponding operations of each module.

[0174] In an exemplary embodiment, a control device is provided. The control device may be a server, and its internal structure diagram may be as follows: Figure 14As shown. The control device includes a processor, a memory, an input / output interface (Input / Output, abbreviated as I / O) and a communication interface. The processor, memory and input / output interface are connected through a system bus, and the communication interface is connected to the system bus through the input / output interface. The processor of the control device is used to provide computing and control capabilities. The memory of the control device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and computer program in the non-volatile storage medium. The database of the control device is used to store output voltage data, output current data, etc. of each inverter. The input / output interface of the control device is used to exchange information between the processor and external devices. The communication interface of the control device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, a microgrid harmonic power distribution method is implemented.

[0175] Those skilled in the art will understand that Figure 14 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than shown in the figure, or combine certain components, or have a different component arrangement.

[0176] In one embodiment, the present application provides a control device including a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps in the above-mentioned method embodiments when executing the computer program.

[0177] In one embodiment, the present application provides a microgrid system, including the control device as described in the above embodiments.

[0178] In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the steps in the above-mentioned method embodiments are implemented.

[0179] In one embodiment, a computer program product is provided, including a computer program, which implements the steps in the above method embodiments when executed by a processor.

[0180] Those skilled in the art will understand that all or part of the processes in the above-mentioned embodiments can be implemented by instructing the relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. In particular, any reference to memory, database, or other media used in the embodiments provided in this application can include at least one of non-volatile memory and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The databases involved in the various embodiments provided herein may include at least one of a relational database and a non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the various embodiments provided herein may be, but are not limited to, general-purpose processors, central processing units (CPUs), graphics processing units (GPUs), digital signal processors (DSPs), programmable logic devices (PLDs), quantum computing-based data processing logic devices, artificial intelligence (AI) processors, and the like.

[0181] The technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this application.

[0182] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

Claims

1. A microgrid harmonic power distribution method, characterized in that: Control devices used in microgrid systems; The control device is respectively connected to each parallel inverter in the microgrid system; the method includes: Obtaining harmonic apparent power corresponding to each of the inverters according to the fundamental component of the output voltage and each harmonic of the output current of each of the inverters; Determining a harmonic power distribution coefficient corresponding to each of the inverters based on the harmonic apparent power; Obtaining the harmonic compensation current required by each of the inverters according to the harmonic power distribution coefficient; Based on the harmonic compensation current and the harmonic power distribution coefficient, the equivalent harmonic impedance of the inverter corresponding to the voltage and current dual closed-loop control loop is adjusted through the voltage and current dual closed-loop control loop corresponding to each inverter, so that the equivalent harmonic impedance matches the rated apparent power corresponding to the inverter.

2. The method according to claim 1, characterized in that Obtaining the harmonic apparent power corresponding to each inverter according to the fundamental component of the output voltage and each harmonic of the output current of each inverter includes: Extracting each harmonic of the output current of each inverter; the harmonic current extractor includes a plurality of multi-resonance controllers for respectively extracting different harmonic orders; Based on the fundamental component of the output voltage of each inverter and each harmonic of the output current, the harmonic apparent power corresponding to each inverter is calculated.

3. The method according to claim 1, characterized in that The determining, based on the harmonic apparent power, a harmonic power allocation coefficient corresponding to each of the inverters includes: determining a droop coefficient corresponding to each of the inverters based on the rated apparent power of each of the inverters; The harmonic power distribution coefficient corresponding to each inverter is obtained according to the apparent power difference of each inverter, the droop coefficient and the droop control reference value.

4. The method according to claim 1, wherein The method of adjusting the equivalent harmonic impedance of the inverter corresponding to each of the voltage and current double closed-loop control loops based on the harmonic compensation current and the harmonic power distribution coefficient includes: Obtaining a reference voltage of each inverter through an inverter control loop corresponding to the inverter; wherein the inverter control loop is used to simulate the operation process of a synchronous generator to obtain the reference voltage; Based on the reference voltage and the harmonic power distribution coefficient, and according to the filter capacitor voltage, filter inductor current and harmonic compensation current of each inverter, the equivalent harmonic impedance of the inverter is adjusted through the voltage-current dual closed-loop control loop.

5. The method according to claim 4, characterized in that The obtaining of the reference voltage of each inverter through the inverter control loop corresponding to the inverter includes: By simulating the motion process of the synchronous generator rotor, a voltage phase angle of the reference voltage is obtained; By simulating the reactive power-voltage droop characteristics of the synchronous generator, the voltage amplitude of the reference voltage is obtained; The reference voltage of the inverter corresponding to each inverter control loop is obtained according to the voltage phase angle and the voltage amplitude.

6. The method according to any one of claims 1 to 5, characterized in that Obtaining the harmonic compensation current required by each inverter according to the harmonic power distribution coefficient includes: According to the harmonics of the output current of each inverter and the harmonic power distribution coefficient, the harmonic compensation current corresponding to the harmonics of the output current of each inverter is obtained through an impedance control link; the impedance control link is as follows: in, is the harmonic power allocation coefficient, is the filter inductance of the inverter, is the filter capacitor of the inverter, is the transfer function of the current regulator of the voltage-current dual closed-loop control loop, is the transfer function of the voltage-current dual closed-loop control loop of the voltage regulator, It is the inherent delay link of PWM modulation. is the modulation coefficient, To obtain the transfer function of the bandpass filter for each harmonic of the output current, is the transfer function corresponding to the impedance control link; the input of the transfer function corresponding to the impedance control link is the harmonics of the output current, and the output is the harmonic compensation current corresponding to the harmonics of the output current of each inverter, and s is the complex variable of Laplace transform.

7. A microgrid harmonic power distribution device, characterized in that: Control devices used in microgrid systems; The control device is respectively connected to each parallel inverter in the microgrid system; the microgrid harmonic power distribution device includes: a harmonic power acquisition module, configured to obtain the harmonic apparent power corresponding to each of the inverters based on the fundamental component of the output voltage and the harmonics of the output current of each of the inverters; A power allocation coefficient acquisition module, configured to determine a harmonic power allocation coefficient corresponding to each of the inverters based on the harmonic apparent power; A harmonic compensation current calculation module, configured to obtain the harmonic compensation current required by each of the inverters according to the harmonic power distribution coefficient; An equivalent harmonic impedance adjustment module is configured to adjust, based on the harmonic compensation current and the harmonic power distribution coefficient, the equivalent harmonic impedance of the inverter corresponding to each of the inverters through the voltage-current dual closed-loop control loops corresponding to the voltage-current dual closed-loop control loops, so that the equivalent harmonic impedance matches the rated apparent power corresponding to the inverter.

8. A control device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 6 are implemented.

9. A microgrid system, characterized in that: Comprising the control device as claimed in claim 8.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 6 are implemented.

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