Method, system, device and medium for reactive power distribution of multi-parallel grid-connected converter

Abstract

This invention relates to a method, system, device, and medium for reactive power distribution in a multi-parallel grid-connected converter. The method includes the following steps: establishing the control equations for the multi-parallel grid-connected converter; determining the reactive power distribution mechanism and equalization conditions based on the established control equations; constructing a control model for the multi-parallel grid-connected converter based on adaptive virtual impedance based on the determined reactive power distribution mechanism and equalization conditions; and distributing the reactive power of the multi-parallel grid-connected converter based on the control model. This invention can be widely applied in the field of power electronic inverter control technology.

Description

Technical Field

[0001] This invention belongs to the field of power electronic inverter control technology, specifically relating to a reactive power distribution method, system, equipment, and medium for multi-parallel grid-type converters based on adaptive virtual impedance. Background Technology

[0002] The increasing penetration rate of new energy sources and power electronic equipment poses a risk of reduced inertia to the power system, threatening the safe and reliable operation of the power grid. Currently, most converters adopt grid-following control, relying on phase-locked loops (PLLs) to synchronize with the grid, which makes stable operation difficult in weak grids. Grid-Forming Converters (GFCs), employing power synchronization strategies and possessing voltage source characteristics, can provide voltage and frequency support in weak grid connection and islanded operation modes, and have broad application prospects.

[0003] Droop control is one of the most widely used grid-based control strategies. Ideally, parallel converters based on droop control can achieve uniform load power distribution according to their respective capacities without relying on communication. However, due to differences in line impedance and load fluctuations, the actual reactive power distribution accuracy is low. This can lead to overload of some converters and the generation of circulating currents, causing stability problems.

[0004] Common methods for improving reactive power distribution accuracy in islanded microgrids include: improved droop control methods, such as adaptive droop coefficients and adjusting rated voltage; hierarchical control methods; and virtual impedance methods. Existing reactive power distribution strategies mainly suffer from the following problems: they cannot balance the contradiction between power distribution accuracy and output voltage sag; and the power distribution effect relies on additional communication equipment, requiring knowledge of specific line impedances or the use of complex online impedance measurement methods, which are inconvenient in practice. Therefore, studying the rational load distribution problem in islanded microgrids is of great significance for improving their operational capabilities. Summary of the Invention

[0005] To address the aforementioned problems, the purpose of this invention is to provide a reactive power distribution method, system, device, and medium for multi-parallel grid-type converters. Through adaptive virtual impedance design, it can achieve high-precision reactive power distribution and suppress reactive power circulation between converters even when the actual line impedance is unknown and there is no interconnection communication between distributed units.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a reactive power distribution method for a multi-parallel grid-type converter, comprising the following steps:

[0008] Establish the control equations for a multi-parallel grid-type converter;

[0009] Based on the established control equations of the multi-parallel grid-type converter, the reactive power distribution mechanism and equal distribution conditions of the multi-parallel grid-type converter are determined.

[0010] Based on the established reactive power distribution mechanism and equal distribution conditions of the multi-parallel grid converter, a control model for the multi-parallel grid converter based on adaptive virtual impedance is constructed to distribute the reactive power of the multi-parallel grid converter.

[0011] Furthermore, the control equations for the multi-parallel grid-type converter are as follows:

[0012]

[0013]

[0014] In the formula, U i V represents the amplitude of the actual output voltage of the i-th grid-type converter. PCC R represents the amplitude of the common bus voltage. i and X i Let θ represent the resistance and inductance of the output line of the i-th grid-type converter, respectively. i U is the actual output voltage of the i-th grid-type converter. i With common bus voltage V PCC The phase angle difference between them, P i and Q i These represent the active power and reactive power flowing from the i-th grid-type converter to the common bus, respectively.

[0015] Furthermore, based on the established control equations for the multi-parallel grid-type converter, the reactive power distribution mechanism and equal distribution conditions of the multi-parallel grid-type converter are determined, including:

[0016] The control strategy of grid-type converter based on the droop principle is analyzed to determine the reactive power distribution mechanism of multi-parallel grid-type converter;

[0017] Based on the analysis results of the reactive power distribution mechanism of multi-parallel grid-type converters, the reactive power equalization conditions of multi-parallel grid-type converters are determined.

[0018] Furthermore, the reactive power sharing condition for the multi-parallel grid-type converter is as follows:

[0019]

[0020] In the formula, Q i * X is the reactive power that the i-th grid-type converter should bear according to its rated value. i Let k be the inductance of the output line of the i-th grid-type converter; Qi Let be the reactive power droop coefficient of the i-th grid-type converter.

[0021] Furthermore, based on the determined reactive power distribution mechanism and equalization conditions of the multi-parallel grid-type converter, a control model for the multi-parallel grid-type converter based on adaptive virtual impedance is constructed to distribute the reactive power of the multi-parallel grid-type converter, including:

[0022] Based on the control equations of a multi-parallel grid-type converter, droop control is performed on the multi-parallel grid-type converter, and the angular frequency ω of the i-th grid-type converter is calculated. t and rated output voltage u ref ;

[0023] Based on the determined reactive power distribution conditions of the multi-parallel grid converter, the voltage reference value u in the dq coordinate system when adopting the adaptive virtual impedance control strategy is calculated. vd and u vq ;

[0024] Based on the voltage reference value u in the dq coordinate system when adopting an adaptive virtual impedance control strategy vd and u vq The voltage and current dual-loop control is applied to the multi-parallel grid-type converter to achieve precise distribution of reactive power.

[0025] Furthermore, the control equations based on the multi-parallel grid-type converter are used to perform droop control on the multi-parallel grid-type converter, and the angular frequency ω of the i-th grid-type converter is calculated. t and rated output voltage u ref ,include:

[0026] Based on the control equations of a multi-parallel grid-connected converter, the active power P of the i-th grid-connected converter is calculated. i and reactive power Q i ;

[0027] Based on the active power P of the i-th grid-type converter i and reactive power Q i The angular frequency ω of the i-th grid converter is calculated. t and rated output voltage u ref .

[0028] Furthermore, based on the determined reactive power allocation conditions of the multi-parallel grid-connected converters, the virtual inductance L of the i-th grid-connected converter is calculated. vi ,include:

[0029] Based on the active power P of the i-th grid-type converter i Reactive power Q i The reactive power Q to be borne according to the rated value ratio i *and the effective value u of the line voltage orms The virtual inductance L of the i-th grid-type converter is calculated. vi ;

[0030] The angular frequency ω of the i-th grid converter t and rated output voltage u ref Perform an abc / dq transformation to obtain the voltage reference value in the dq coordinate system when the droop control strategy is adopted;

[0031] Based on the calculated virtual inductance L v Voltage reference value u under droop control strategy vd and u vq Adaptive adjustments are made to obtain the voltage reference value u in the dq coordinate system when the adaptive virtual impedance control strategy is adopted. vd and u vq .

[0032] Secondly, the present invention provides a reactive power distribution system for multi-parallel grid-type converters, comprising:

[0033] The control equation establishment module is used to establish the control equations for multi-parallel grid-type converters;

[0034] The equal distribution condition determination module is used to determine the reactive power distribution mechanism and equal distribution conditions of the multi-parallel grid-type converter based on the established control equations of the multi-parallel grid-type converter.

[0035] The control module is used to construct a control model for the multi-parallel grid converter based on adaptive virtual impedance, based on the determined reactive power distribution mechanism and equal distribution conditions of the multi-parallel grid converter, and to distribute the reactive power of the multi-parallel grid converter.

[0036] Thirdly, the present invention provides a computer-readable storage medium for storing one or more programs, the one or more programs including instructions that, when executed by a computing device, cause the computing device to perform any of the methods.

[0037] Fourthly, the present invention provides a computing device, comprising: one or more processors and a memory, wherein the memory stores one or more programs and is configured to be executed by the one or more processors, the one or more programs including instructions for performing any of the methods.

[0038] The present invention has the following advantages due to the adoption of the above technical solutions:

[0039] (1) This invention establishes the control equations of a multi-parallel grid-type converter, studies and analyzes the reactive power distribution mechanism and equal distribution conditions of the multi-parallel grid-type converter, and uses the control model of the multi-parallel grid-type converter to distribute the reactive power of the multi-parallel grid-type converter; by combining the reactive power distribution error of each converter with the output voltage to design an adaptive virtual impedance, the reactive power distribution accuracy of the grid-type converter can be significantly improved, while suppressing the circulating current between converters;

[0040] (2) This invention is applicable to reactive power distribution in different scenarios, and does not require knowing the precise line impedance or conducting interconnection communication between various converters.

[0041] Therefore, this invention can be widely applied in the field of power electronic inverter control technology. Attached Figure Description

[0042] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. In the drawings:

[0043] Figure 1 This is a flowchart of the reactive power distribution method for multi-parallel grid-type converters provided in an embodiment of the present invention;

[0044] Figure 2 This is a schematic diagram of the multi-parallel grid-type converter structure used in this invention;

[0045] Figure 3 This is a control block diagram of a grid-type converter based on virtual impedance;

[0046] Figure 4 It is a block diagram of the transfer function of a grid-type converter with virtual impedance;

[0047] Figure 5a It is the output active power of parallel converters with equal capacity under the traditional droop control strategy;

[0048] Figure 5b It refers to the output reactive power of parallel converters with equal capacity under the traditional droop control strategy;

[0049] Figure 6a It refers to the output active power of parallel converters with equal capacity under the control strategy proposed in this invention;

[0050] Figure 6b The reactive power output of parallel converters with equal capacity under the control strategy proposed in this invention;

[0051] Figure 7aIt is the output current of phase A of parallel converters with equal capacity;

[0052] Figure 7b It is a parallel converter with equal capacity, with phase A circulating current;

[0053] Figure 8a The active power output of a parallel converter with a capacity ratio of 2:1:1 under the control strategy proposed in this invention;

[0054] Figure 8b The reactive power output of a parallel converter with a capacity ratio of 2:1:1 under the control strategy proposed in this invention;

[0055] Figure 9a It is the output current of phase A of a parallel converter with a capacity ratio of 2:1:1;

[0056] Figure 9b It is a parallel converter with a capacity ratio of 2:1:1 and a circulating current in phase A. Detailed Implementation

[0057] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0058] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0059] In some embodiments of the present invention, a reactive power distribution method for a multi-parallel grid-connected converter is provided, comprising: establishing the control equations of the multi-parallel grid-connected converter; determining the reactive power distribution mechanism and equalization conditions of the multi-parallel grid-connected converter based on the established control equations; and constructing a control model of the multi-parallel grid-connected converter based on adaptive virtual impedance based on the determined reactive power distribution mechanism and equalization conditions, and distributing the reactive power of the multi-parallel grid-connected converter. This invention can be widely applied in the field of power electronic inverter control technology.

[0060] Correspondingly, other embodiments of the present invention provide a reactive power distribution system, device, and medium for a multi-parallel grid-type converter.

[0061] Example 1

[0062] like Figure 1 As shown, this embodiment provides a reactive power distribution method for multi-parallel grid-type converters, including the following steps:

[0063] Step 1: Establish the control equations for a multi-parallel grid-type converter;

[0064] Step 2: Based on the established control equations of the multi-parallel grid-type converter, determine the reactive power distribution mechanism and equal distribution conditions of the multi-parallel grid-type converter;

[0065] Step 3: Based on the determined reactive power distribution mechanism and equal distribution conditions of the multi-parallel grid converter, construct a control model of the multi-parallel grid converter based on adaptive virtual impedance, and accurately distribute the reactive power of the multi-parallel grid converter based on the control model.

[0066] Preferably, in step 1 above, such as Figure 2 As shown, in a multi-parallel grid-connected converter topology, distributed power sources are connected to the common bus after passing through the grid-connected converter, filters, and line impedances, jointly supplying power to the loads. When the line inductive reactance is much greater than the resistance (i.e., the inductive reactance Li in the line impedance is much greater than Ri), the active power P flowing from the i-th grid-connected converter to the common bus... i and reactive power Q i The expression is:

[0067]

[0068]

[0069] In the formula, U i V represents the amplitude of the actual output voltage of the i-th grid-type converter. PCC R represents the amplitude of the common bus voltage. i and X i Let θ represent the resistance and inductance of the output line of the i-th grid-type converter, respectively. i U is the actual output voltage of the i-th grid-type converter. i With common bus voltage V PCC The phase angle difference between them.

[0070] When the inductive reactance of a medium-voltage line is much greater than its resistance, the line impedance Z i ≈X i And the phase angle difference θ i It is usually very small, i.e., sinθ i ≈θ i cosθ i ≈1. Therefore, equations (1) and (2) can be simplified to:

[0071]

[0072]

[0073] From equations (3) and (4), it can be seen that when the line is inductive, the active power P i Mainly related to the phase difference θ of the voltage at both ends of the line i Related, reactive power Q i It is mainly related to the voltage amplitude. Since the phase angle and angular frequency satisfy ω=dθ / dt, the active power P flowing to the common bus from the grid-type converter can be controlled by controlling the angular frequency and the voltage amplitude, respectively. i and reactive power Q i .

[0074] Preferably, step 2 above includes the following steps:

[0075] Step 2.1: Analyze the control strategy of grid-type converter based on the droop principle and determine the reactive power distribution mechanism of multi-parallel grid-type converter.

[0076] The traditional grid-type converter control strategy based on the droop principle can be expressed as:

[0077] ω i =ω 0i -k Pi P i (5)

[0078] U i =U 0i -k Qi Q i (6)

[0079] In the formula, ω i and U i ω represents the frequency and amplitude of the actual output voltage of the i-th grid-type converter, respectively. 0i and U 0i Let k be the frequency and amplitude of the no-load output voltage of the i-th grid-type converter, respectively. Pi and k Qi P represents the active power droop factor and reactive power droop factor of the i-th grid-type converter, respectively. i and Q i These represent the active power and reactive power output of the i-th grid-type converter, respectively.

[0080] Assuming that the frequency ω0 and amplitude U0 of the no-load output voltage of each grid-type converter are the same, and since the system frequency is consistent in steady state, when the active power droop factor is inversely proportional to the rated active power, the active power P of each grid-type converter will be... iReactive power can be allocated proportionally to its rated power. However, since the impedance of the output lines of grid-type converters is generally different in practice, the actual output voltage of each grid-type converter is also different, resulting in lower reactive power allocation accuracy.

[0081] Step 2.2: Based on the analysis results of Step 2.1, determine the conditions for accurate equal distribution of reactive power in multi-parallel grid-type converters.

[0082] First, the reactive power distribution error of the i-th grid-type converter is calculated using the following formula:

[0083]

[0084] In the formula, Q i Q is the actual reactive power output of the i-th grid-type converter. i * ΔQ is the reactive power that the i-th grid-type converter should bear according to its rated value. i It is the difference between the actual reactive power output of the i-th grid-type converter and the reactive power it should bear; e i Let be the reactive power distribution error of the i-th grid-type converter.

[0085] The sum of the actual reactive power outputs of each grid-type converter is equal to the sum of its reference values. Therefore:

[0086] ΔQ1+ΔQ2+…+ΔQ i =0 (8)

[0087] From equation (4), we can obtain:

[0088]

[0089] Combining equations (6) and (9), we can obtain:

[0090]

[0091] Taking two grid-connected converters in parallel as an example, assuming that their respective reactive power droop coefficients are inversely proportional to their rated reactive power, then their reactive power satisfies:

[0092]

[0093] From equation (11), the reactive power distribution errors of the two grid-type converters are respectively:

[0094]

[0095]

[0096] As shown in the above equation, to eliminate reactive power distribution errors, the output line impedance of a grid-connected converter must be proportional to its reactive power droop factor. Therefore, the condition for accurate reactive power distribution in a multi-parallel grid-connected converter is:

[0097]

[0098] Preferably, in step 3 above, such as Figure 3 The diagram shown is a block diagram of the control model for a multi-parallel grid converter based on adaptive virtual impedance. Specifically, it includes the following steps:

[0099] Step 3.1: Based on the control equations of the multi-parallel grid-type converter, perform droop control on the multi-parallel grid-type converter and calculate the angular frequency ω of the i-th grid-type converter. t and rated output voltage u ref .

[0100] Step 3.2: Based on the determined reactive power precise allocation conditions of the multi-parallel grid-type converter, calculate the voltage reference value u in the dq coordinate system when adopting the adaptive virtual impedance control strategy. vd and u vq ;

[0101] Step 3.3: Obtain the voltage reference value u in the dq coordinate system when the adaptive virtual impedance control strategy is adopted. vd and u vq The voltage and current dual-loop control is applied to the multi-parallel grid-type converter to achieve precise distribution of reactive power.

[0102] Furthermore, step 3.1 above includes the following steps:

[0103] Step 3.1.1: Based on the control equations (i.e., formulas (3) and (4)) of the multi-parallel grid-type converter, calculate the active power P of the i-th grid-type converter. i and reactive power Q i .

[0104] Step 3.1.2: Based on the active power P of the i-th grid-type converter i and reactive power Q i The angular frequency ω of the i-th grid converter is calculated. t and rated output voltage u ref .

[0105] Furthermore, step 3.2 above includes the following steps:

[0106] Step 3.2.1: Based on the active power P of the i-th grid-type converter i Reactive power Q iThe reactive power Q to be borne according to the rated value ratio i * and the effective value u of the line voltage orms The virtual inductance L of the i-th grid-type converter is calculated. vi .

[0107] Traditional droop control strategies assume that the output impedance of a grid-connected converter is purely inductive. However, in low-voltage power grids, line impedance is predominantly resistive, leading to active and reactive power coupling and poor power distribution. When the virtual inductance L... v0 By selecting a relatively large value, it can be ensured that the total impedance of the system is close to that of pure inductance, thereby achieving a better power decoupling control effect.

[0108] Assuming that the equivalent output impedance of the system can be approximated as purely inductive when the impedance ratio X / R ≥ 7, combining equations (20), (21), and (23), we can obtain the required L v0 ≥2.7mH, taking into account the impact of reactive power distribution accuracy and output voltage drop, this invention selects L v0 =3mH.

[0109] For multiple parallel grid-connected converters with different rated reactive power, according to equation (14), the total system impedance should be proportional to its reactive droop coefficient and inversely proportional to its rated reactive power. Therefore, the virtual inductance of the j-th grid-connected converter with the largest rated reactive power is set to L. v0j =3mH, the virtual inductance of the i-th grid-connected converter is:

[0110]

[0111] This invention proposes a reactive power allocation strategy based on adaptive virtual impedance, where the adaptive virtual inductance ΔL of the i-th grid-connected converter is used. vi The expression is:

[0112]

[0113] Where k is the adaptive virtual impedance coefficient, e i Let U be the reactive power distribution error of the i-th grid-type converter. i Let be the output voltage of the i-th grid-type converter.

[0114] The total virtual inductance of the i-th grid-type converter is the sum of the constant inductance and the adaptive virtual inductance, that is:

[0115] L vi =L v0i +ΔL vi (17)

[0116] Step 3.2.2: For the angular frequency ω of the i-th grid converter...t and rated output voltage u ref Perform an abc / dq transformation to obtain the voltage reference value in the dq coordinate system when the droop control strategy is adopted.

[0117] Step 3.2.3: Based on the calculated virtual inductance L v Voltage reference value u under droop control strategy vd and u vq Adaptive adjustments are made to obtain the voltage reference value u in the dq coordinate system when the adaptive virtual impedance control strategy is adopted. vd and u vq .

[0118] The calculation formula is:

[0119]

[0120] Among them, u refd and u refq The rated output voltage u of the grid-type converter are respectively ref The d-axis components and q-axis components, i od and i oq The line current i oabc The d-axis and q-axis components, where ω is the angular frequency.

[0121] Furthermore, step 3.3 above includes the following steps:

[0122] Step 3.3.1: abc / dq coordinate transformation: Transform the line voltage u in the abc coordinate system oabc Line current i oabc And the inductor current i through the filter inductor Labc Perform an abc / dq coordinate transformation to obtain the line voltage u in the dq coordinate system. odq Line current i odq and inductor current i Ldq .

[0123] Step 3.3.2: Line voltage u based on the dq coordinate system odq Line current i odq and inductor current i Ldq and voltage reference value u vd and u vq The d-axis and q-axis components u of the PWM input three-phase voltage are obtained. d and u q .

[0124] Specifically, u vd u vq u odq and i odqAs the input to the voltage loop, the output i of the voltage loop refd and i refq As the input to the current loop, the d-axis and q-axis components u of the PWM input three-phase voltage are obtained. d and u q ; where u odq and i odq These are the d-axis and q-axis components of the line voltage and line current, respectively; i refd and i refq These are the d-axis and q-axis components of the voltage loop output reference current, respectively.

[0125] Step 3.3.3: Calculate the d-axis and q-axis components u of the PWM input three-phase voltage. d and u q After performing dq / abc coordinate transformation, the result is used as the input to PWM to control the multi-parallel grid-type converter, thereby realizing reactive power distribution of the multi-parallel grid-type converter.

[0126] like Figure 4 As shown, the transfer function block diagram of the grid-type converter can be obtained from its control block diagram. To achieve independent regulation of active and reactive power, the grid-type converter employs dq-axis decoupled control for both voltage and current loops, and both utilize proportional-integral controllers, denoted as G... i (s)=K p1 +K i1 / s, G u (s)=K p2 +K i2 / s. Where K p1 and K i1 These are the proportional and integral coefficients of the inner current loop, respectively, K p2 and K i2 These are the proportional coefficient and integral coefficient of the outer voltage loop, respectively.

[0127] The rated output voltage signal u of the grid-type converter ref and load current disturbance signal i o Under the influence of the virtual impedance (i.e., virtual inductance Lv), the output voltage expression of the grid-type converter before adding the virtual impedance is:

[0128] U o =G u (s)U ref -Z o (s)I o (19)

[0129] In the formula, U o and I o These represent the output voltage and output current of the grid-connected converter, respectively; G u (s) is the closed-loop voltage transfer function, Zo (s) is the equivalent output impedance of the grid-type converter, and its expression is shown in Equation (17) and Equation (18) respectively.

[0130]

[0131]

[0132] In the formula, K PWM This represents the gain coefficient for the PWM control of the grid-connected converter. To ensure the output voltage of the grid-connected converter perfectly tracks the reference voltage, appropriate control parameters should be selected to satisfy |G| at the base frequency. u (s)|≈1,|Z o (s)|≈0.

[0133] After introducing adaptive virtual impedance, the output voltage expression of the grid converter is:

[0134] U o =G u [U ref -sL v I o ]-Z o (s)I o =G u U ref -[Z o (s)+G u ·sL v ]I o (twenty two)

[0135] Therefore, the equivalent output impedance of the grid-type converter is:

[0136] Z o ′(s)=Z o (s)+G u (s)·sL v (twenty three)

[0137] After adding the virtual impedance, the reactive power distribution error of GFC1 changes from equation (12) to:

[0138]

[0139] Let e v1 =e1'+e1", where:

[0140]

[0141]

[0142] Assume that the two grid-connected converters satisfy k Q1 Q1 * =kQ2 Q2 * But X1 / k Q1 >X2 / k Q2 From equations (12), (13), and (24), we know that e1 < 0, e2 > 0, and e1′ < 0, therefore e1″ > 0. Comparing equations (12) and (24), we know that |e1| > |e1'|. Therefore, |e v1 The equation |=|e1'|-|e1”|<|e1| means that the reactive power distribution error of grid-type converter 1 is reduced. The reactive power distribution error analysis of grid-type converter 2 is similar.

[0143] Example 2

[0144] In this embodiment, a simulation model of three parallel grid-type converters is built using Matlab / Simulink. From 0 to 1.2s, the grid-type converters jointly supply power to the 6kW+6kVar load 1, and at 1.2s, the 3kW+3kVar load 2 is put into operation.

[0145] The power distribution of three parallel grid-connected converters with the same rated reactive power under the traditional droop control strategy is as follows: Figure 5a and Figure 5b As shown, the system frequency is consistent in steady state, so active power can always be evenly distributed. However, due to the impedance mismatch of the output lines of each grid-type converter, reactive power cannot be accurately distributed. From 0 to 1.2 s, the reactive power distribution errors of the three grid-type converters are 39.03%, -7.48%, and -31.54%, respectively. From 1.2 to 2 s, the reactive power distribution errors of the three grid-type converters are 39.07%, -7.57%, and -31.5%, respectively.

[0146] When using the method proposed in this invention, the output power of the grid converter is as follows: Figure 6a and Figure 6b As shown, after adding the adaptive virtual impedance at 0.4s, the reactive power distribution errors of each grid-type converter are 2.69%, -0.21%, and -2.48%, respectively. After 1.2s, the reactive power distribution errors of each grid-type converter are 2.65%, -0.21%, and -2.44%, respectively. The reactive power distribution accuracy is significantly improved.

[0147] Figure 7a The images show the A-phase output current waveforms and partial magnified views of various grid-type converters using the method proposed in this invention. It can be seen that before the addition of the virtual impedance, the amplitude and phase of the A-phase output current of each grid-type converter are different, and reactive power circulating current exists between the grid-type converters. Figure 7b As shown, after adding the adaptive virtual impedance proposed in this invention at 0.4s, the amplitude and phase of the A-phase output current of each grid-type converter are basically the same, which can significantly suppress reactive circulating current.

[0148] For three parallel grid-connected converters with a rated power ratio of 2:1:1, the power distribution after adopting the control strategy proposed in this invention is as follows: Figure 8a and Figure 8b As shown. From 0 to 0.4s, the three grid-type converters jointly supply power to load 1. Under the traditional droop control strategy, the reactive power distribution errors of the three grid-type converters are -24.02%, 39.28%, and 8.76%, respectively. After adding the adaptive virtual impedance proposed in this invention at 0.4s, the reactive power distribution errors of the three grid-type converters are -1.3%, 2.21%, and 0.39%, respectively. At 1.2s, load 2 is put into operation, and the reactive power distribution errors of the three converters are -1.26%, 2.2%, and 0.32%, respectively. The active power distribution ratio of the grid-type converters remains at 2:1:1 throughout. It can be seen that the method proposed in this invention is also applicable to reactive power distribution between grid-type converters with different rated power.

[0149] Figure 9a The image shows the A-phase output current waveforms and partial magnifications of grid-type converters with different rated power ratings under the method proposed in this invention. It can be seen that before the virtual impedance is added, reactive circulating current exists between the grid-type converters, such as... Figure 9b As shown, after adding the adaptive virtual impedance proposed in this invention at 0.4s, the phase of the output current of phase A of each grid-type converter is basically the same, and the amplitude ratio is 2:1:1. This method can significantly suppress circulating current.

[0150] Example 3

[0151] The above-described embodiment 1 provides a reactive power distribution method for multi-parallel grid-connected converters. Correspondingly, this embodiment provides a reactive power distribution system for multi-parallel grid-connected converters. The system provided in this embodiment can implement the reactive power distribution method for multi-parallel grid-connected converters of embodiment 1. This system can be implemented through software, hardware, or a combination of both. For example, the system may include integrated or separate functional modules or units to execute the corresponding steps in the methods of embodiment 1. Since the system in this embodiment is basically similar to the method embodiment, the description process in this embodiment is relatively simple. Relevant details can be found in the description of embodiment 1. The system embodiment provided in this embodiment is merely illustrative.

[0152] The reactive power distribution system for multi-parallel grid-type converters provided in this embodiment includes:

[0153] The control equation establishment module is used to establish the control equations for multi-parallel grid-type converters;

[0154] The equal distribution condition determination module is used to determine the reactive power distribution mechanism and equal distribution conditions of the multi-parallel grid-type converter based on the established control equations of the multi-parallel grid-type converter.

[0155] The control module is used to construct a control model for the multi-parallel grid converter based on adaptive virtual impedance, based on the determined reactive power distribution mechanism and equal distribution conditions of the multi-parallel grid converter, and to accurately distribute the reactive power of the multi-parallel grid converter based on the control model.

[0156] Furthermore, the control equations for a multi-parallel grid-type converter are:

[0157]

[0158]

[0159] In the formula, U i V represents the amplitude of the actual output voltage of the i-th grid-type converter. PCC R represents the amplitude of the common bus voltage. i and X i Let θ represent the resistance and inductance of the output line of the i-th grid-type converter, respectively. i U is the actual output voltage of the i-th grid-type converter. i With common bus voltage V PCC The phase angle difference between them, P i and Q i These represent the active power and reactive power flowing from the i-th grid-type converter to the common bus, respectively.

[0160] Furthermore, the module for determining the equal distribution conditions includes:

[0161] The mechanism analysis module is used to analyze the control strategy of grid-type converters based on the droop principle and determine the reactive power distribution mechanism of multi-parallel grid-type converters.

[0162] The reactive power distribution condition analysis module is used to determine the reactive power distribution conditions of multi-parallel grid-type converters based on the analysis results of the reactive power distribution mechanism.

[0163] Furthermore, the reactive power sharing condition for multi-parallel grid-connected converters is as follows:

[0164]

[0165] In the formula, Q i * X is the reactive power that the i-th grid-type converter should bear according to its rated value. i Let k be the inductance of the output line of the i-th grid-type converter; Qi Let be the reactive power droop coefficient of the i-th grid-type converter.

[0166] Furthermore, the control module includes:

[0167] The droop control module is used to perform droop control on multiple parallel grid-type converters based on the control equations of the multiple parallel grid-type converters, and calculates the angular frequency ω of the i-th grid-type converter. t and rated output voltage u ref ;

[0168] The virtual impedance control module is used to calculate the voltage reference value u in the dq coordinate system when an adaptive virtual impedance control strategy is adopted, based on the determined reactive power distribution conditions of the multi-parallel grid converter. vd and u vq ;

[0169] A dual-loop control module is used to control the voltage reference value u in the dq coordinate system when an adaptive virtual impedance control strategy is employed. vd and u vq The voltage and current dual-loop control is applied to the multi-parallel grid-type converter to achieve precise distribution of reactive power.

[0170] Furthermore, the droop control module includes:

[0171] The power calculation module is used to calculate the active power P of the i-th grid-type converter based on the control equations of multiple parallel grid-type converters. i and reactive power Q i ;

[0172] The power control module is used to control the active power P of the i-th grid-type converter. i and reactive power Q i The angular frequency ω of the i-th grid converter is calculated. t and rated output voltage u ref .

[0173] Furthermore, the virtual impedance control module includes:

[0174] The adaptive virtual inductance calculation module is used to calculate the active power P of the i-th grid-type converter. i Reactive power Q i The reactive power Q to be borne according to the rated value ratio i * and the effective value u of the line voltage orms The virtual inductance L of the i-th grid-type converter is calculated. vi ;

[0175] The abc / dq conversion module is used to convert the angular frequency ω of the i-th grid-type converter. t and rated output voltage u ref Perform an abc / dq transformation to obtain the voltage reference value in the dq coordinate system when the droop control strategy is adopted;

[0176] The adaptive virtual impedance module is used to calculate the virtual inductance L. v Voltage reference value u under droop control strategy vd and u vq Adaptive adjustments are made to obtain the voltage reference value u in the dq coordinate system when the adaptive virtual impedance control strategy is adopted. vd and u vq .

[0177] Example 4

[0178] This embodiment provides a processing device corresponding to the reactive power distribution method of multi-parallel grid-type converters provided in Embodiment 1. The processing device can be a processing device for clients, such as mobile phones, laptops, tablets, desktop computers, etc., to execute the method of Embodiment 1.

[0179] The processing device includes a processor, a memory, a communication interface, and a bus. The processor, memory, and communication interface are connected via the bus to enable communication between them. The memory stores a computer program that can run on the processor. When the processor runs the computer program, it executes the reactive power distribution method for multi-parallel grid-type converters provided in Embodiment 1.

[0180] Preferably, the memory may be high-speed random access memory (RAM), and may also include non-volatile memory, such as at least one disk storage device.

[0181] Preferably, the processor can be any type of general-purpose processor such as a central processing unit (CPU) or a digital signal processor (DSP), and there is no limitation herein.

[0182] Example 5

[0183] The reactive power distribution method for multi-parallel grid-type converters in Embodiment 1 can be specifically implemented as a computer program product. The computer program product may include a computer-readable storage medium on which computer-readable program instructions for executing the reactive power distribution method for multi-parallel grid-type converters described in Embodiment 1 are loaded.

[0184] A computer-readable storage medium can be a tangible device that holds and stores instructions for use by an instruction execution device. A computer-readable storage medium can be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any combination thereof.

[0185] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0186] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0187] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0188] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0189] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A reactive power distribution method for multi-parallel grid-type converters, characterized in that, Includes the following steps: Establish the control equations for a multi-parallel grid-type converter; Based on the established control equations of the multi-parallel grid-type converter, the reactive power distribution mechanism and equal distribution conditions of the multi-parallel grid-type converter are determined. Based on the established reactive power distribution mechanism and equal distribution conditions of the multi-parallel grid converter, a control model of the multi-parallel grid converter based on adaptive virtual impedance is constructed, and the reactive power of the multi-parallel grid converter is distributed based on the control model. The process involves determining the reactive power distribution mechanism and equalization conditions of the multi-parallel grid-type converter based on the established control equations. This includes: analyzing the control strategy of the grid-type converter based on the droop principle to determine the reactive power distribution mechanism of the multi-parallel grid-type converter; and determining the reactive power equalization conditions of the multi-parallel grid-type converter based on the analysis results of the reactive power distribution mechanism. The reactive power sharing condition for the multi-parallel grid-type converter is as follows: In the formula, Q i * It is the first i The reactive power that each grid-type converter should bear according to its rated value. X i For the first i Inductance of the output line of a grid-type converter; k Qi For the first i The reactive power droop coefficient of a grid-type converter; Based on the determined reactive power distribution mechanism and equalization conditions of the multi-parallel grid-type converter, a control model for the multi-parallel grid-type converter based on adaptive virtual impedance is constructed. The reactive power distribution of the multi-parallel grid-type converter is then performed based on this control model, including: droop control of the multi-parallel grid-type converter based on its control equations, and calculation of the... i The angular frequency ω of the grid converter t and rated output voltage u ref Based on the determined reactive power distribution conditions of the multi-parallel grid-type converter, the voltage reference value in the dq coordinate system when adopting the adaptive virtual impedance control strategy is calculated. u vd and u vq Based on the voltage reference value in the dq coordinate system when adopting an adaptive virtual impedance control strategy. u vd and u vq The voltage and current dual-loop control is performed on the multi-parallel grid-type converter to achieve precise distribution of reactive power in the multi-parallel grid-type converter; The reactive power allocation conditions of the multi-parallel grid-type converter, based on the determined conditions, are used to calculate the first... i Virtual inductance of a grid-type converter L vi Including: according to the i Active power of individual grid-type converters P i reactive power Q i The reactive power to be undertaken according to the rated value ratio Q i * and the effective value u of the line voltage orms Calculate the first i Virtual inductor of individual grid-type converter L vi ; for the first i The angular frequency ω of the grid converter t and rated output voltage u ref Perform an abc / dq transformation to obtain the voltage reference value in the dq coordinate system when using a droop control strategy; based on the calculated virtual inductance... L v Voltage reference value under droop control strategy u vd and u vq Adaptive adjustments are made to obtain the voltage reference value in the dq coordinate system when the adaptive virtual impedance control strategy is adopted. u vd and u vq ; The first i The total virtual inductance of a grid-type converter is the sum of the constant inductance and the adaptive virtual inductance, expressed as: In the formula, and Δ L vi The first i Constant inductance and adaptive virtual inductance of grid-type converters; In the formula, k For adaptive virtual impedance coefficient, e i For the first i Reactive power distribution error of individual grid-type converters U i For the first i Output voltage of a grid-type converter.

2. The reactive power distribution method for a multi-parallel grid-type converter as described in claim 1, characterized in that: The control equations for the multi-parallel grid-type converter are as follows: In the formula, U i For the first i The amplitude of the actual output voltage of a grid-type converter. V PCC The amplitude of the common bus voltage. R i and X i The first i Resistance and inductance of the output line of a grid-type converter θ i For the first i The actual output voltage of the individual grid converter U i With common bus voltage V PCC The phase angle difference between them P i and Q i The first i The active and reactive power flowing from a grid-type converter to the common bus.

3. The reactive power distribution method for a multi-parallel grid-type converter as described in claim 1, characterized in that: The control equations based on the multi-parallel grid-type converter are used to perform droop control on the multi-parallel grid-type converter, and the result is obtained. i The angular frequency ω of the grid converter t and rated output voltage u ref ,include: Based on the control equations of a multi-parallel grid-connected converter, the first... i Active power of individual grid-type converters P i and reactive power Q i ; According to the i Active power of individual grid-type converters P i and reactive power Q i Calculate the first i The angular frequency ω of the grid converter t and rated output voltage u ref .

4. A reactive power distribution system for multi-parallel grid-type converters, characterized in that... include: The control equation establishment module is used to establish the control equations for multi-parallel grid-type converters; The equal distribution condition determination module is used to determine the reactive power distribution mechanism and equal distribution conditions of the multi-parallel grid-type converter based on the established control equations of the multi-parallel grid-type converter. The control module is used to construct a control model for a multi-parallel grid converter based on adaptive virtual impedance, based on the determined reactive power distribution mechanism and equal distribution conditions of the multi-parallel grid converter, and to distribute the reactive power of the multi-parallel grid converter based on the control model. The process involves determining the reactive power distribution mechanism and equalization conditions of the multi-parallel grid-type converter based on the established control equations. This includes: analyzing the control strategy of the grid-type converter based on the droop principle to determine the reactive power distribution mechanism of the multi-parallel grid-type converter; and determining the reactive power equalization conditions of the multi-parallel grid-type converter based on the analysis results of the reactive power distribution mechanism. The reactive power sharing condition for the multi-parallel grid-type converter is as follows: In the formula, Q i * It is the first i The reactive power that each grid-type converter should bear according to its rated value. X i For the first i Inductance of the output line of a grid-type converter; k Qi For the first i The reactive power droop coefficient of a grid-type converter; Based on the determined reactive power distribution mechanism and equalization conditions of the multi-parallel grid-type converter, a control model for the multi-parallel grid-type converter based on adaptive virtual impedance is constructed. The reactive power distribution of the multi-parallel grid-type converter is then performed based on this control model, including: droop control of the multi-parallel grid-type converter based on its control equations, and calculation of the... i The angular frequency ω of the grid converter t and rated output voltage u ref Based on the determined reactive power distribution conditions of the multi-parallel grid-type converter, the voltage reference value in the dq coordinate system when adopting the adaptive virtual impedance control strategy is calculated. u vd and u vq Based on the voltage reference value in the dq coordinate system when adopting an adaptive virtual impedance control strategy. u vd and u vq The voltage and current dual-loop control is performed on the multi-parallel grid-type converter to achieve precise distribution of reactive power in the multi-parallel grid-type converter; The reactive power allocation conditions of the multi-parallel grid-type converter, based on the determined conditions, are used to calculate the first... i Virtual inductance of a grid-type converter L vi Including: according to the i Active power of individual grid-type converters P i reactive power Q i The reactive power to be undertaken according to the rated value ratio Q i * and the effective value u of the line voltage orms Calculate the first i Virtual inductor of individual grid-type converter L vi ; for the first i The angular frequency ω of the grid converter t and rated output voltage u ref Perform an abc / dq transformation to obtain the voltage reference value in the dq coordinate system when using a droop control strategy; based on the calculated virtual inductance... L v Voltage reference value under droop control strategy u vd and u vq Adaptive adjustments are made to obtain the voltage reference value in the dq coordinate system when the adaptive virtual impedance control strategy is adopted. u vd and u vq ; The first i The total virtual inductance of a grid-type converter is the sum of the constant inductance and the adaptive virtual inductance, expressed as: In the formula, and Δ L vi The first i Constant inductance and adaptive virtual inductance of grid-type converters; In the formula, k For adaptive virtual impedance coefficient, e i For the first i Reactive power distribution error of individual grid-type converters U i For the first i Output voltage of a grid-type converter.

5. A computer-readable storage medium for storing one or more programs, characterized in that, The one or more programs include instructions that, when executed by a computing device, cause the computing device to perform any of the methods described in claims 1 to 3.

6. A computing device, characterized in that, include: One or more processors and a memory, wherein the memory stores one or more programs and is configured to be executed by the one or more processors, the one or more programs including instructions for performing any of the methods described in claims 1 to 3.

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