Virtual impedance angle adaptive control method and system for parallel operation of converters

Abstract

Disclosed in the present invention are a virtual impedance angle adaptive control method and system for parallel operation of converters, relating to the technical field of converter system control, and comprising: by means of a consistency control algorithm, observing an active average value and a reactive average value; by means of the active average value and the reactive average value, obtaining a trigonometric function value corresponding to the virtual impedance angle; obtaining a virtual resistance and a virtual negative reactance corresponding to each converter; using a dynamically changing virtual impedance angle to perform power coordinate transformation on the active power and reactive power of the converter in order to obtain generalised active power and generalised reactive power; and controlling the generalised active power and generalised reactive power. The present invention is applicable to a scenario of parallel operation of converters, such as a microgrid; by dynamically adjusting the virtual impedance angle in real time, the problem of voltage deviation after the introduction of virtual impedance can be significantly improved, and the voltage quality can be improved.

Description

Virtual Impedance Angle Adaptive Control Method and System for Parallel Operation of Converters Technical Field

[0001] This invention relates to the field of converter system control technology, specifically to a virtual impedance angle adaptive control method and system for parallel operation of converters. Background Technology

[0002] The goal of parallel converter operation control is to achieve proportional sharing of active and reactive power, reducing frequency and voltage deviations. Virtual impedance technology is widely used in parallel converter operation, including but not limited to microgrids. It can reshape the converter's output impedance characteristics as needed, achieving decoupling of active and reactive power control under complex line impedance characteristics (such as resistive, or neither resistive nor inductive), resulting in better control performance. However, adding virtual impedance can lead to significant voltage deviations and degrade power quality. Currently, a secondary voltage regulation method based on consistency control is generally used to restore the average voltage (i.e., the average voltage of all controlled converters) to its rated value. However, the large voltage dips caused by virtual impedance cannot be avoided, and secondary voltage recovery takes time. Summary of the Invention

[0003] In view of the above-mentioned problems, the present invention is proposed.

[0004] Therefore, the technical problem solved by this invention is: how to effectively control the sharing of active and reactive power under complex line impedance characteristics, while reducing voltage deviation and sag caused by virtual impedance, so as to improve power quality and shorten voltage recovery time.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a virtual impedance angle adaptive control method for parallel operation of converters, which includes the following steps:

[0006] The average active and reactive power values ​​are observed through a consistency control algorithm; the trigonometric function values ​​corresponding to the virtual impedance angle are obtained from the average active and reactive power values; the virtual resistance and virtual negative reactance of each converter are obtained; the power coordinate transformation of the active and reactive power of the converter is performed using the dynamically changing virtual impedance angle to obtain the generalized active and generalized reactive power; and the generalized active and generalized reactive power are controlled.

[0007] As a preferred embodiment of the virtual impedance angle adaptive control method for parallel operation of converters described in this invention, wherein: the average active power is expressed as:

[0008] As a preferred embodiment of the virtual impedance angle adaptive control method for parallel operation of converters described in this invention, wherein the average reactive power is expressed as:

[0009] The ratio of the average active power to the average reactive power is

[0010] The P ∑ Q represents the sum of the active power of N converters. ∑ P represents the sum of reactive power from N converters. i and Q i These represent the real-time active and reactive power of converter i, respectively. These are the elements in the i-th row and j-th column of the adjacency matrix of the active and reactive power mean observation communication network, respectively, C Pi and C Qi These are the active power observation coupling coefficient and the reactive power observation coupling coefficient, respectively. and These are the average active and average reactive power values ​​obtained from the active and reactive power observers of converters i and j, respectively.

[0011] As a preferred embodiment of the virtual impedance angle adaptive control method for parallel operation of converters described in this invention, wherein: through Calculate the virtual impedance angle of converter i The corresponding trigonometric function values ​​are expressed as follows:

[0012] in, and These represent the sine, cosine, tangent, and cotangent values ​​corresponding to the virtual impedance angle, respectively.

[0013] As a preferred embodiment of the virtual impedance angle adaptive control method for parallel operation of converters described in this invention, the virtual resistance and virtual negative reactance of each converter are obtained by means of the fixed amplitude method, the fixed resistance method, and the fixed reactance method after obtaining the trigonometric function values.

[0014] As a preferred embodiment of the virtual impedance angle adaptive control method for parallel operation of converters described in this invention, wherein: in the fixed amplitude method, the amplitude of the virtual impedance of converter i is fixed, and the virtual resistance and virtual negative reactance are determined by the virtual impedance trigonometric function, expressed as follows:

[0015] Among them, Z vi The magnitude of the virtual impedance of the fixed converter i, ωL vi This represents virtual negative reactance.

[0016] In the fixed resistance method, the virtual negative reactance is obtained by fixing the virtual resistance of the converter, and is expressed as follows:

[0017] Among them, R vi This represents the virtual resistance value of the fixed converter i;

[0018] In the fixed reactance method, the virtual resistance is obtained by using the virtual negative reactance of the fixed converter, and is expressed as follows:

[0019] Where, ωL vi This represents the virtual reactance value of the fixed converter i.

[0020] As a preferred embodiment of the virtual impedance angle adaptive control method for parallel operation of converters described in this invention, wherein: the control of generalized active power and generalized reactive power includes controlling P gi and Q gi The converter is controlled using traditional droop control and consistency control algorithms.

[0021] Another objective of this invention is to provide a virtual impedance angle adaptive control system for parallel operation of converters, which can solve the problems of excessive voltage sag and slow voltage recovery caused by fixed virtual impedance in the prior art by dynamically adjusting the virtual impedance angle in real time.

[0022] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a virtual impedance angle adaptive control system for parallel operation of converters, including an observation module, a calculation and conversion module, an impedance adjustment module, and a power control module.

[0023] The observation module observes the average active and reactive power of each converter through a consistency control algorithm.

[0024] The calculation and conversion module calculates the trigonometric function value of the virtual impedance angle by observing the average active and reactive power values, calculates the virtual resistance and virtual negative reactance of each converter, and uses the dynamically changing virtual impedance angle to perform power coordinate transformation, converting it into generalized active and generalized reactive power.

[0025] The impedance adjustment module adjusts the virtual impedance according to the fixed amplitude method, the fixed resistance method, and the fixed reactance method.

[0026] The power control module controls the generalized active and generalized reactive power obtained through coordinate transformation.

[0027] A computer device includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the steps of the virtual impedance angle adaptive control method for parallel operation of converters as described above.

[0028] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the virtual impedance angle adaptive control method for parallel operation of converters as described above.

[0029] The beneficial effects of this invention are as follows: This invention is applicable to applications where multiple converters operate in parallel, such as microgrids. By dynamically adjusting the virtual impedance angle in real time, it can significantly improve voltage deviation issues introduced by virtual impedance and enhance voltage quality. Furthermore, this invention enhances system flexibility and stability, optimizes energy utilization efficiency, supports better integration of renewable energy, and strengthens the grid's anti-interference capabilities. Similarly, this invention not only improves the adaptability and response speed of grid operation but also contributes to improving the efficiency and reliability of the entire system, which is particularly important in environments with large load fluctuations or unstable energy sources. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 is an overall flowchart of the virtual impedance angle adaptive control method for parallel operation of converters provided in the first embodiment of the present invention.

[0032] Figure 2 is a schematic diagram of the voltage drop caused by virtual impedance in the virtual impedance angle adaptive control method for parallel operation of converters provided in the first embodiment of the present invention.

[0033] Figure 3 is a schematic diagram of the converter grid connection in the virtual impedance angle adaptive control method for parallel operation of converters provided in the first embodiment of the present invention.

[0034] Figure 4 is an overall framework diagram of the virtual impedance angle adaptive control system for parallel operation of converters provided in the second embodiment of the present invention.

[0035] Figure 5 is a schematic diagram of the converter system in the virtual impedance angle adaptive control method for parallel operation of converters provided in the third embodiment of the present invention.

[0036] Figure 6(a) is a simulation result of the active power generated by the traditional method in the conventional virtual impedance control method for parallel operation of converters provided in the third embodiment of the present invention.

[0037] Figure 6(b) shows the reactive power simulation results generated by the traditional method in the conventional virtual impedance control method for parallel operation of converters provided in the third embodiment of the present invention.

[0038] Figure 6(c) shows the voltage simulation results generated by the traditional method in the conventional virtual impedance control method for parallel operation of converters provided in the third embodiment of the present invention.

[0039] Figure 7(a) shows the active power simulation results generated by the fixed amplitude method in the virtual impedance angle adaptive control method for parallel operation of converters provided in the third embodiment of the present invention.

[0040] Figure 7(b) shows the reactive power simulation results generated by the fixed amplitude method in the virtual impedance angle adaptive control method for parallel operation of converters provided in the third embodiment of the present invention.

[0041] Figure 7(c) shows the voltage simulation results generated by the fixed amplitude method in the virtual impedance angle adaptive control method for parallel operation of converters provided in the third embodiment of the present invention.

[0042] Figure 7(d) shows the converter (P) generated by the fixed amplitude method in the virtual impedance angle adaptive control method for parallel operation of converters provided in the third embodiment of the present invention. ∑ / Q ∑ ) i Observation results diagram.

[0043] Figure 8(a) shows the active power simulation results generated by the fixed resistance method in the virtual impedance angle adaptive control method for parallel operation of converters provided in the third embodiment of the present invention.

[0044] Figure 8(b) shows the reactive power simulation results generated by the fixed resistance method in the virtual impedance angle adaptive control method for parallel operation of converters provided in the third embodiment of the present invention.

[0045] Figure 8(c) shows the voltage simulation results generated by the fixed resistance method in the virtual impedance angle adaptive control method for parallel operation of converters provided in the third embodiment of the present invention.

[0046] Figure 8(d) shows the converter (P) generated by the fixed resistance method in the virtual impedance angle adaptive control method for parallel operation of converters provided in the third embodiment of the present invention. ∑ / Q ∑ ) i Observation results diagram.

[0047] Figure 9(a) shows the active power simulation results generated by the fixed reactance method in the virtual impedance angle adaptive control method for parallel operation of converters provided in the third embodiment of the present invention.

[0048] Figure 9(b) shows the reactive power simulation results generated by the fixed reactance method in the virtual impedance angle adaptive control method for parallel operation of converters provided in the third embodiment of the present invention.

[0049] Figure 9(c) shows the voltage simulation results generated by the fixed reactance method in the virtual impedance angle adaptive control method for parallel operation of converters provided in the third embodiment of the present invention.

[0050] Figure 9(d) shows the converter (P) generated by the fixed reactance method in the virtual impedance angle adaptive control method for parallel operation of converters provided in the third embodiment of the present invention. ∑ / Q ∑ ) i Observation results diagram. Detailed Implementation

[0051] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0052] Example 1, referring to Figures 1-3, is an embodiment of the present invention, providing a method for controlling parallel operation of converters, characterized in that:

[0053] The technical solutions to supplement existing technologies are as follows.

[0054] When multiple converters operate in parallel, the control of each converter typically includes a power loop and a voltage tracking loop. The goal of the power loop is to utilize the active and reactive power of the converters through an algorithm (a common technique is a combination of droop control and consistency control algorithms) to generate voltage amplitude and frequency (phase angle), thereby generating a command voltage (which may introduce virtual impedance). The goal of the voltage tracking loop is to control the converter's output voltage to track this command voltage, typically using a dual closed-loop control method of voltage and current. This invention focuses on the power loop; therefore, it only introduces droop control, virtual impedance, and consistency control algorithms, which are closely related to the power loop.

[0055] (1) Drooping control

[0056] Pf,QV droop control is widely used in the parallel operation control of converters. When the line is inductive (i.e., the line reactance X is much greater than the line resistance R), the active power P of the converter mainly depends on the frequency, and the reactive power Q of the converter mainly depends on the voltage V. Therefore, the frequency and voltage of converter i can be calculated using equations (1) and (2). i =f N -m i P i (1) V i =V N -n i Q i (2)

[0057] Active power control can also employ a drooping power angle, with the power angle of converter i calculated using equation (3). θ i =θ N -mi P i (3)

[0058] In equations (1) to (3), f i V i θ i f N V N and θ N These represent the frequency, voltage, and power angle of converter i and their rated values, respectively, and P. i and Q i These represent the active and reactive power of converter i, respectively, and m i and n i The normalization coefficients for active and reactive power are generally selected inversely to the rated capacity.

[0059] Get f i (or θ) i and voltage V i The original command voltage of converter i can then be synthesized and written in phasor form V without loss of generality. * ∠δ i .

[0060] (2) Virtual impedance.

[0061] In microgrids and similar applications, the line is neither resistive nor inductive (i.e., the line reactance X and line resistance R are not significantly different). In this case, P and Q are strongly coupled, and the droop control effect of Pf and QV is greatly affected, even making it difficult to maintain stability. Virtual impedance is an effective means to solve this problem. It involves subtracting the converter output current at the virtual impedance R from the original converter command voltage. V +jωL V The voltage drop across the virtual impedance is used to simulate the impedance. Taking a three-phase three-wire dq rotating coordinate system as an example, the voltage drop of the converter i output current across the virtual impedance is shown in equation (4).

[0062] In equation (4), I oi-d I oi-q V vi-d and V vi-d R represents the d-axis and q-axis components of the output current of converter i and its voltage drop across the virtual impedance. vi and L vi Let ω = 2πf be the virtual resistance and reactance introduced by converter i, respectively. i For simplicity, the rated frequency f can be directly used when calculating the angular frequency of an electrical quantity. N .

[0063] The command voltage of converter i is calculated according to equation (5):

[0064] In formula (5) The original command voltage V of converter i are respectively * ∠δ i The d-axis and q-axis components, V di-ref V qi-ref These are the d-axis and q-axis components of the actual command voltage of converter i after considering the effect of virtual impedance.

[0065] (3) Consistency control algorithm

[0066] Consensus algorithms are decentralized control algorithms. Each agent (corresponding to the various converters in this invention) forms a consensus protocol by interacting with neighboring agents. Based on this protocol, they control themselves to achieve consensus. In a consensus algorithm, the communication network between N agents can be represented by an adjacency matrix A. G =[a ij ]∈R N×N It means that element a ii =0, a ij Let a represent the communication weight between agents i and j. If agent i can obtain information from agent j, then a ij >0. All agents that can provide information to agent i constitute its neighbors, denoted by N. i Indicates. If a ij =a ji If the expression is true, the communication network is called an undirected graph; otherwise, it is called a directed graph. The Laplace matrix of a communication network is an N-order matrix L. G =[l ij ]∈R N×N Its diagonal element is l ii =∑a ij The off-diagonal element is l ij =-a ij .

[0067] In the consensus algorithm, each agent follows A G It communicates with neighboring intelligent agents to obtain their state information X, generates a consensus protocol, and updates its own state. Taking the linear consensus algorithm as an example, each intelligent agent updates its own state according to equation (6).

[0068] When graph G is a connected undirected graph or a strongly connected directed graph, 0 is L. G The simple eigenvalues ​​are all positive real parts. Therefore, equation (6) ensures that the states of all agents converge asymptotically to the same value in an exponential manner.

[0069] In the parallel operation control of converters, the consensus control algorithm is mainly used to realize the proportional sharing of active and reactive power and restore the average voltage of the converter to the rated value. In order to realize the proportional sharing of reactive power, the consensus protocol shown in equation (7) can be used.

[0070] In equation (7), g Q n is the reactive power control coupling coefficient. i and n j is the reactive power normalization coefficient. In order to restore the average voltage of the converter, the average voltage of all converters needs to be observed according to equation (8).

[0071] in, and V i These are the average observed voltage value and the measured voltage value obtained by converter i, respectively; C represents the average voltage observation value of converter j. V For voltage observation coupling coefficient, Let N be the elements in the i-th row and j-th column of the adjacency matrix of the voltage observation communication network. i Let be the set of neighboring converters of converter i, and s be the Laplace operator. When the algorithm converges, the average voltage observations obtained by all converters are equal. Consider the original command voltage magnitude V based on proportional reactive power sharing and average voltage recovery. * As shown in equation (9).

[0072] To achieve proportional distribution of active power, the power angle δ of converter i can be adjusted according to equation (10). i Adjustments were made.

[0073] In equation (10), g P This is the active power control coupling coefficient.

[0074] Get V * and δ i Then the original command voltage can be synthesized, and the actual command voltage of converter i can be obtained by subtracting the voltage drop across the virtual impedance of the output current of converter i.

[0075] The shortcomings of existing technologies.

[0076] The main drawbacks of existing technologies are: adding virtual impedance leads to large voltage deviations and degrades power quality; although the secondary voltage regulation method based on consistency control can restore the average voltage to the rated value, the secondary voltage recovery takes a certain amount of time, and the large temporary low voltage caused by virtual impedance cannot be avoided.

[0077] To solve the above-mentioned technical problems, the principle of the method of the present invention is shown in Figure 2.

[0078] According to circuit principles, for converter i, a virtual reactance ωL is introduced. vi After that, the resulting voltage will mainly include the longitudinal component ΔV and the transverse component δV. The voltage drop caused by the virtual impedance is mainly due to the longitudinal component ΔV, as shown in equation (11).

[0079] As can be seen from equation (11), if virtual resistance and virtual negative reactance are selected to satisfy equation (12), the longitudinal component of voltage drop can be eliminated.

[0080] As can be seen from equation (12), in order to eliminate the longitudinal component of the voltage drop caused by the virtual impedance, it is necessary to determine the reactive power Q of converter i. i and merit P i The ratio of virtual resistance to virtual negative reactance is used to adjust the virtual resistance and virtual negative reactance. To ensure control stability, all converters should use the same ratio of virtual resistance to virtual negative reactance. Let N be the number of converters operating in parallel, and P be the active power. ∑ And total no achievement Q ∑ These represent the sum of active and reactive power from N converters, respectively, because P ∑ and Q ∑ As the situation continues to change, a consistent approach should be adopted when calculating the virtual resistance and virtual negative reactance ratios of all converters. To obtain For any converter i, the average active power is obtained using reactive and active power observers. and reactive power mean The ratio of the two is pass Achieve The estimate.

[0081] S1: Observe the average active power and average reactive power through the consistency control algorithm.

[0082] For any converter i, the reactive power observer and the active power observer can be obtained through equations (13) and (14), respectively. and

[0083] In equations (13) and (14), These are the elements in the i-th row and j-th column of the adjacency matrix of the active and reactive power mean observation communication network, respectively, C Pi and C Qi These are the active power observation coupling coefficient and the reactive power observation coupling coefficient, respectively, P i and Q i These represent the real-time active and reactive power of converter i, respectively. and These are the average active and average reactive power values ​​obtained from the active and reactive power observers of converters i and j, respectively.

[0084] S2: Obtain the trigonometric function value corresponding to the virtual impedance angle through the average active power and average reactive power.

[0085] Obtained through active power observers and reactive power observers After the ratio, the virtual impedance angle of converter i is calculated using equation (15). The corresponding trigonometric function values.

[0086] in, and These represent the sine, cosine, tangent, and cotangent values ​​corresponding to the virtual impedance angle, respectively.

[0087] S3: Obtain the virtual resistance and virtual negative reactance corresponding to each converter.

[0088] After obtaining the trigonometric function values, the virtual resistance and virtual negative reactance can be obtained through one of the following three methods.

[0089] The methods include the fixed amplitude method, the fixed resistance method, and the fixed reactance method.

[0090] Method 1: Fixed Amplitude Method: Fix the amplitude Z of the virtual impedance of converter i. vi The virtual resistance and virtual negative reactance are determined by the virtual impedance trigonometric function, that is, the virtual resistance R is calculated according to equations (16) and (17). vi and virtual negative reactance ωL vi (where ω represents the angular frequency of the electrical quantity)

[0091] Method 2: Fixed Resistance Method: Fix the virtual resistance R of converter i. vi The virtual negative reactance ωL is obtained through equation (18). vi :

[0092] Method 3: Fixed Reactor Method: Fix the virtual negative reactance ωL of converter i vi Find the virtual resistance R. vi As shown in equation (19):

[0093] S4: Use the dynamically changing virtual impedance angle to perform power coordinate transformation on the active and reactive power of the converter to obtain generalized active and generalized reactive power.

[0094] After obtaining the virtual impedance, the active power P of converter i i and no Q iPerform a power coordinate transformation to obtain the generalized active power and generalized reactive power, as shown in equation (20).

[0095] In equation (20), P gi and Q gi Let P represent the generalized active power and generalized reactive power of converter i, respectively; referring to Figure 3, for any converter i, its active power P i and no Q i The expression is shown in (21):

[0096] In equation (21), R vi X is a virtual resistance. vi =ωL vi For virtual reactance, V i ∠δ i V is the voltage phasor before the virtual reactance of converter i. bi ∠δ0 is the grid connection point voltage phasor of converter i (please refer to Figure 3).

[0097] After power coordinate transformation, P gi and Q gi The expression is shown in (22):

[0098] In equations (21) and (22), V i ∠δ i and V bi ∠0 represents the voltage phasor before the virtual impedance of converter i and the voltage at the grid connection point, V i and V bi For the effective value, if voltage tracking error is not considered, Vi is equal to the effective value of the original command voltage of converter i; δ i X is the phase angle difference, i.e., the power angle of converter i. vi =-ωL vi This is the introduced virtual negative reactance.

[0099] S5: Control generalized active power and generalized reactive power.

[0100] For P gi and Q gi The converter is controlled by traditional droop control (frequency droop or phase droop) and consistency control algorithms, thereby achieving proportional sharing of active and reactive power and restoration of frequency and voltage.

[0101] Example 2, referring to Figure 4, is an embodiment of the present invention, providing a system for a virtual impedance angle adaptive control method for parallel operation of converters, characterized in that it includes an observation module 100, a calculation and conversion module 200, an impedance adjustment module 300, and a power control module 400.

[0102] The observation module 100 observes the average active and reactive power of each converter through a consistency control algorithm.

[0103] The calculation and conversion module 200 calculates the trigonometric function value of the virtual impedance angle by observing the average active and reactive power values, calculates the virtual resistance and virtual negative reactance of each converter, and uses the dynamically changing virtual impedance angle to perform power coordinate transformation, converting it into generalized active and generalized reactive power.

[0104] The impedance adjustment module 300 adjusts the virtual impedance according to the fixed amplitude method, the fixed resistance method, and the fixed reactance method.

[0105] The power control module 400 controls the generalized active and generalized reactive power obtained through coordinate transformation.

[0106] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, essentially, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0107] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device.

[0108] More specific examples (a non-exhaustive list) of computer-readable media include: electrical connections (electronic devices) having one or more wires, portable computer disk drives (magnetic devices), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Furthermore, computer-readable media can even be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in computer memory.

[0109] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0110] Example 3, referring to Figures 5-9, in this example, to verify the beneficial effects of the present invention, scientific demonstration is carried out through economic benefit calculations and simulation experiments. This example presents experiments comparing both existing conventional methods and the method of this example.

[0111] To verify the effectiveness of this invention, simulations were performed. The system used is shown in Figure 5, comprising four three-phase three-wire parallel voltage source converters (VSCs) with LC filtering, a rated line voltage of 380V (phase voltage of 220V), and a rated frequency of 50Hz, connected to each other via RL lines; loads 1, 2, 3, and 4 are Y-connected series RL constant impedance loads, and their electrical parameters are shown in Table 1. The method in this paper requires the communication topology to be an undirected graph, as shown by the gray dashed line network in Figure 5.

[0112] The same communication network is used for active and reactive power consistency control, active and reactive power observation and voltage observation, and the adjacency matrix is ​​shown in (22).

[0113] Table 1 System Electrical Parameters

[0114] The rated capacity ratio of the four converters, VSC1:VSC2:VSC3:VSC4, is 2:1:2:1. A comparison was made between the traditional method and this invention. The traditional method directly introduces virtual reactance and uses a linear consistency algorithm to regulate the voltage, achieving proportional reactive power sharing and voltage mean recovery (as shown in equations (7) and (9)). The linear consistency algorithm is used to adjust the converter phase angle, thereby achieving proportional active power sharing, as shown in equation (10). The power loop control parameters are set as shown in Table 2, and voltage tracking is performed using a dual closed-loop voltage and current system.

[0115] Table 2 Control Parameters

[0116] Load 1 is connected at 0.5s and disconnected at 1s. Since the rated capacity ratio of the four converters is VSC1:VSC2:VSC3:VSC4 = 2:1:2:1, we want the active and reactive power ratios to be 2:1:2:1 respectively. To facilitate analysis of whether the power sharing is achieved proportionally, the active power P and reactive power Q of each converter are multiplied by a certain coefficient. In all the simulation diagrams below, k1 = k3 = 1; k2 = k4 = 2; r1 = r3 = 1; r2 = r4 = 2. The results are shown in Figures 6 to 9. In Figures 6 to 9, P1, P2, P3, and P4 represent the active power of converters 1, 2, 3, and 4 respectively; Q1, Q2, Q3, and Q4 are the reactive power of the four converters; and V1, V2, V3, V4, and V... avg These represent the phase voltage and the average phase voltage of the four converters, respectively.

[0117] Simulation results of traditional methods

[0118] The simulation results of the traditional method are shown in Figure 6, where Figures 6(a), (b), and (c) show the simulation results of active power, reactive power, and voltage for the four converters, respectively. Figures 6(a) and (b) show that the converters can achieve the required proportional sharing of active and reactive power; Figure 6(c) shows that the average voltage of the four converters can be restored to the rated value, but due to the effect of virtual reactance, there is a large voltage sag in each converter, and the recovery process takes a relatively long time.

[0119] Simulation results of this invention

[0120] Figures 7-9 show the simulation results of this invention, where Figure 7 shows the simulation results of the fixed amplitude method, Figure 8 shows the simulation results of the fixed resistance method, and Figure 9 shows the simulation results of the fixed reactance method. As can be seen from Figures 7-9, this invention can achieve proportional sharing of active and reactive power. Comparing the voltage simulation results of Figures 7(c), 8(c), and 9(c) with the traditional method's Figure 6(c), it can be seen that using this invention can significantly reduce the voltage sag caused by virtual impedance: the lowest converter phase voltage is above 205V, while the lowest converter phase voltage using the traditional method is less than 195V. Furthermore, compared to the traditional method, this invention can significantly shorten the voltage recovery time. Figures 7(d), 8(d), and 9(d) show the simulation results of four converters (P) using the three methods. ∑ / Q ∑ ) i As shown in the figure, the observation results of the four converters are highly consistent. This invention can achieve accurate observation of the ratio of active power to reactive power of the total load.

[0121] 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 it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A virtual impedance angle adaptive control method for parallel operation of converters, characterized in that, include: The average active power and average reactive power are observed using a consistency control algorithm. The trigonometric function value corresponding to the virtual impedance angle is obtained by using the average active power and average reactive power. Obtain the virtual resistance and virtual negative reactance corresponding to each converter; By utilizing the dynamically changing virtual impedance angle, the active and reactive power of the converter are transformed by power coordinates to obtain generalized active and generalized reactive power. Control over generalized positive and negative contributions.

2. The virtual impedance angle adaptive control method for parallel operation of converters as described in claim 1, characterized in that: The average active power is expressed as follows:

3. The virtual impedance angle adaptive control method for parallel operation of converters as described in claim 2, characterized in that: The average reactive power is expressed as: The ratio of the average active power to the average reactive power is The P ∑ Q represents the sum of the active power of N converters. ∑ P represents the sum of reactive power from N converters. i and Q i These represent the real-time active and reactive power of converter i, respectively. These are the elements in the i-th row and j-th column of the adjacency matrix of the active and reactive power mean observation communication network, respectively, C Pi and C Qi These are the active power observation coupling coefficient and the reactive power observation coupling coefficient, respectively. and These are the average active and average reactive power values ​​obtained from the active and reactive power observers of converters i and j, respectively.

4. The virtual impedance angle adaptive control method for parallel operation of converters as described in claim 3, characterized in that: pass Calculate the virtual impedance angle of converter i The corresponding trigonometric function values ​​are expressed as follows: in, and These represent the sine, cosine, tangent, and cotangent values ​​corresponding to the virtual impedance angle, respectively.

5. The virtual impedance angle adaptive control method for parallel operation of converters as described in claim 4, characterized in that: After obtaining the trigonometric function values, the virtual resistance and virtual negative reactance of each converter are obtained through the fixed amplitude method, fixed resistance method, and fixed reactance method.

6. The virtual impedance angle adaptive control method for parallel operation of converters as described in claim 5, characterized in that: In the fixed amplitude method, the amplitude of the virtual impedance of converter i is fixed, and the virtual resistance and virtual negative reactance are determined by the virtual impedance trigonometric function, expressed as follows: Among them, Z vi The magnitude of the virtual impedance of the fixed converter i, ωL vi Indicates virtual negative reactance; In the fixed resistance method, the virtual negative reactance is obtained by fixing the virtual resistance of the converter, and is expressed as follows: Among them, R vi This represents the virtual resistance value of the fixed converter i; In the fixed reactance method, the virtual resistance is obtained by using the virtual negative reactance of the fixed converter, and is expressed as follows: Where, ωL vi This represents the virtual reactance value of the fixed converter i.

7. The virtual impedance angle adaptive control method for parallel operation of converters as described in claim 6, characterized in that: The control of generalized active power and generalized reactive power includes controlling P gi and Q gi The converter is controlled using traditional droop control and consistency control algorithms.

8. A system employing the virtual impedance angle adaptive control method for parallel operation of converters as described in any one of claims 1 to 7, characterized in that: It includes an observation module (100), a calculation and conversion module (200), an impedance adjustment module (300), and a power control module (400); The observation module (100) observes the average active and reactive power of each converter through a consistency control algorithm; The calculation and conversion module (200) calculates the trigonometric function value of the virtual impedance angle by observing the average active power and average reactive power, calculates the virtual resistance and virtual negative reactance of each converter, and uses the dynamically changing virtual impedance angle to perform power coordinate transformation, converting it into generalized active power and generalized reactive power. The impedance adjustment module (300) adjusts the virtual impedance according to the fixed amplitude method, the fixed resistance method, and the fixed reactance method; The power control module (400) controls the generalized active and generalized reactive power obtained through coordinate transformation.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the virtual impedance angle adaptive control method for parallel operation of converters as described in any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the virtual impedance angle adaptive control method for parallel operation of converters as described in any one of claims 1 to 7.

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