A power control method for microgrid inverter under complex network topology

Abstract

The present invention relates to a power control method for a microgrid inverter under a complex network topology, and the control method comprises the following steps: Step 1: Perform power distribution error analysis based on coupled droop control for the complex network topology to determine whether the resistive-inductive droop control needs to be improved; Step 2: When it is determined that improvement is needed, set a complex network topology improvement control strategy; Step 3: Control the power of the microgrid inverter based on the complex network topology improvement control strategy. Compared with the prior art, in an actual microgrid system, the line impedance corresponding to the inverter unit changes due to the switching of the load and the inverter unit, which makes the traditional droop control unable to be used, and the power distribution of the load also becomes a problem. The present invention adopts an improved coupled droop control, and it has been verified through theory and simulation that it can be applied under a complex network topology, and the power distribution effect is good.

Description

Technical Field

[0001] The present invention relates to the technical field of microgrid inverter unit control, and in particular to a microgrid inverter power control method under complex network topology. Background Art

[0002] The mainstream control of microgrid inverters adopts non-communication droop control technology, which mainly imitates the operating characteristics of synchronous generators in large power systems. Under the premise that the line impedance is inductive, the inverter output active power is adjusted by the system frequency, and the inverter output reactive power is adjusted by the inverter output voltage. For droop control under inductive conditions, since the system frequency is a global variable, the active power output of each inverter can be reasonably distributed, while the inverter output voltage is a local variable, that is, the output voltage of each inverter is different due to the different line impedance, and thus the reactive power output of each inverter cannot be reasonably distributed.

[0003] The technologies for realizing reasonable distribution of inverter output power in the prior art are as follows: 1. Through virtual impedance, the line impedance corresponding to each inverter unit is made the same, and then the output voltage of each inverter unit tends to be the same, so that the inverter output power is reasonably distributed. 2. By constructing an adaptive virtual impedance, its essence is to construct an integral term of the inverter output reactive power and the given reactive power, so that the inverter output power is reasonably distributed. 3. By improving the droop curve and using the thinking of replacing the straight with the curved one, the power distribution error can be reduced as much as possible. 4. By introducing the coupling term of power, the active and reactive power output of the inverter is connected, so as to solve the power distribution problem, etc.

[0004] In these existing technologies, the influence of impedance characteristics in the network on the droop control strategy is ignored. In actual microgrids, the switching of inverters and loads will cause the resistance-inductance characteristics of the line impedance corresponding to each inverter unit to change. At this time, the line impedance may present the following conditions: resistance, inductance, and resistance-inductance. Therefore, the conventional virtual impedance method is no longer applicable to complex network topologies (virtual impedance is used to improve the resistance-inductance characteristics of line impedance). At this time, the application of traditional droop control will reduce the stability of the system due to system power coupling, so it cannot be used in complex network topologies. How to select appropriate droop control and how to achieve reasonable distribution of inverter output power in complex network topologies has become a problem to be solved. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a power control method for a microgrid inverter under a complex network topology. The method is based on wP&Q and UP&Q coupled droop control, and on this basis, the proportional integral term of P, Q and the difference between the inverter no-load voltage and the system node voltage is used to reasonably distribute the active and reactive power output by the inverter. The improved coupled droop control does not require understanding of the structural information of the network topology, and can be used not only in resistive-inductive environments, but also in resistive and inductive environments.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A power control method for a microgrid inverter under a complex network topology, the control method comprising the following steps:

[0008] Step 1: Perform power distribution error analysis based on coupled droop control for complex network topologies to determine whether the resistive-inductive droop control needs to be improved;

[0009] Step 2: When it is determined that improvement is needed, a complex network topology improvement control strategy is set;

[0010] Step 3: Improve the control strategy based on complex network topology to control the power of microgrid inverter.

[0011] Furthermore, the step 1 specifically includes:

[0012] Step 101: deriving active and reactive power output by each inverter based on coupled droop control;

[0013] Step 102: converting the corresponding formula form of active and reactive power output by each inverter based on coupled droop control into the expression form of virtual active and reactive power output by each inverter through simplified analysis;

[0014] Step 103: simplify and analyze the complex network topology based on the expression of virtual active and reactive power output by each inverter, and obtain an error expression of virtual reactive power output by the inverter;

[0015] Step 104: determining whether the corresponding satisfying condition expression obtained when the inverter output virtual reactive power error expression is 0 is established to determine whether the resistive-inductive droop control needs to be improved. If not, the resistive-inductive droop control needs to be improved.

[0016] Furthermore, each inverter in step 101 outputs active power and reactive power, and its mathematical description formula is:

[0017] U i =U * -K pvi P i -Kqvi Q i

[0018] w i =w * -K pwi P i +K qwi Q i

[0019] Where U i and w i are the inverter output voltage and angular velocity, U * and w * are the rated output voltage and rated angular frequency of the inverter, P i and Q i are the active and reactive power output of the corresponding inverter, K pvi , K pwi With K qvi , K qwi are the droop coefficients of active and reactive power respectively.

[0020] Furthermore, the expression form of the virtual active and reactive power output by each inverter in step 102 is mathematically described as follows:

[0021] U i =U * -K(P i +Q i )=U * -KQ i *

[0022] w i =w * -K(P i -Q i )=w * -KP i *

[0023] Where U i and w i are the inverter output voltage and angular velocity, U * and w * are the rated output voltage and rated angular frequency of the inverter, P i and Q i are the active and reactive power output of the corresponding inverter, K is the droop coefficient of virtual active and reactive power, P i * and Q i * They are the virtual active and reactive powers output by the corresponding inverters respectively.

[0024] Furthermore, the inverter output virtual reactive power error expression in step 103 is mathematically described as follows:

[0025]

[0026] in,

[0027] E=Q loc1 +Q pub1 -P loc1 -P pub1

[0028] F=P pub2 +P loc2 -Q pub2 -Q loc2

[0029] G=-(P loc1 +P pub1 +Q loc1 +Q pub1 )

[0030] H=P pub2 +P loc2 +Q pub2 +Q loc2

[0031] I=P loc2 R2+Q loc2 X2-P loc1 R1-Q loc1 X1

[0032] Where ΔQ * is the inverter output virtual reactive power error, Q1 * and Q2 * are the output virtual reactive power of the first and second inverters respectively, i=1, 2, 3, R i and X i They are the resistive and inductive parts of the corresponding line impedance, P * The virtual active power output of the inverter, P pub1 , Q pub1 With P pub2 , Q loc2 The active and reactive power of the bus load and the local load of the first and second inverters respectively.

[0033] Furthermore, the conditional expression in step 104 is mathematically described as follows:

[0034]

[0035] in,

[0036] E=Q loc1 +Q pub1 -P loc1 -P pub1

[0037] F=P pub2 +P loc2 -Q pub2 -Q loc2

[0038] G=-(P loc1 +P pub1 +Q loc1 +Q pub1 )

[0039] H=P pub2 +P loc2 +Q pub2 +Q loc2

[0040] I=P loc2 R2+Q loc2 X2-P loc1 R1-Q loc1 X1

[0041] In the formula, i=1, 2, 3, R i and X i They are the resistive and inductive parts of the corresponding line impedance, P * Output virtual active power for the inverter.

[0042] Furthermore, the complex network topology improvement control strategy in step 2 includes a control strategy corresponding to the case where the resistance-inductance type is inductive and a control strategy corresponding to the case where the resistance-inductance type is resistive.

[0043] Furthermore, the control strategy corresponding to the resistive-sensing type is inductive, and its corresponding mathematical description formula is:

[0044]

[0045] In the formula, U and w are the inverter output voltage and angular frequency under the improved control strategy of complex network topology, k p and k q are the proportional and integral coefficients, k e is the voltage difference coefficient, P and Q are the active and reactive power output by the inverter respectively, w * is the rated angular frequency of the corresponding inverter output, m and n are active power droop coefficient and reactive power droop coefficient respectively, U *The rated voltage of the corresponding inverter output.

[0046] Furthermore, the control strategy corresponding to the resistive type is a resistive control strategy, and its corresponding mathematical description formula is:

[0047]

[0048] In the formula, U and w are the inverter output voltage and angular frequency under the improved control strategy of complex network topology, k p and k q are the proportional and integral coefficients, k e is the voltage difference coefficient, P and Q are the active and reactive power output by the inverter respectively, w * is the rated angular frequency of the corresponding inverter output, m and n are active power droop coefficient and reactive power droop coefficient respectively, U * The rated voltage of the corresponding inverter output.

[0049] Furthermore, the expression of the inverter output voltage when the microgrid inverter power is controlled based on the improved control strategy of complex network topology in step 3 is:

[0050]

[0051] in,

[0052]

[0053] Where U i1 is the inverter output voltage when the power of the microgrid inverter is controlled based on the improved control strategy of complex network topology, Z is the impedance of each inverter, θ and are the line impedance angle and the phase of the inverter output voltage, P locali and Q locali is the active and reactive power of the corresponding local load, U * is the rated output voltage of the corresponding inverter, U j Indicates the voltage at a certain point on the bus, k p and k q are the proportional and integral coefficients respectively.

[0054] Compared with the prior art, the present invention has the following advantages:

[0055] (1) The present invention aims at the problem that the line impedance corresponding to the inverter unit changes due to the switching of the load and the inverter unit in the actual microgrid system, which makes the traditional droop control unable to be used and the power distribution of the load also becomes a problem. The improved coupled droop control is used, and it is verified through theory and simulation that it can be applied in complex network topology and has a good power distribution effect.

[0056] (2) The present invention takes into account that the impedance characteristics of the line impedance may change due to the switching of the inverter unit and the load under complex network topology, and improves the power control strategy under the complex network topology to achieve reasonable distribution of the inverter output power.

[0057] (3) In the prior art, the main focus is on power control strategies, ignoring the actual operating conditions of the microgrid. This solution takes into account the actual operating conditions of the microgrid, explains the impact of line impedance characteristics on the control itself, and improves the coupled droop control to achieve power allocation in complex situations.

[0058] (4) The present invention can be applied in various complex network topologies. Through simulation and theory, it can be known that the present invention can be applied in various impedance characteristics and has high power distribution accuracy in various impedance characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0060] Figure 1 A schematic diagram of a complex network topology in an embodiment of the present invention;

[0061] Figure 2 Schematic diagram of a two-inverter parallel system in an embodiment of the present invention;

[0062] Figure 3 is a system control block diagram in an embodiment of the present invention;

[0063] Figure 4 It is a schematic diagram of the change of active power and reactive power output by a conventional resistance-inductance droop inverter in an embodiment of the present invention;

[0064] Figure 5 It is a schematic diagram of the change of output active power and reactive power of the improved resistance-inductance droop inverter in the embodiment of the present invention;

[0065] Figure 6It is a schematic diagram of the change of active power and reactive power output by the improved inductive droop inverter in the embodiment of the present invention;

[0066] Figure 7 It is a schematic diagram of the change of output active power and reactive power of the improved resistive-inductive droop inverter in the embodiment of the present invention;

[0067] Figure 8 It is a schematic diagram of the change of active power and reactive power output by the improved resistive droop inverter in the embodiment of the present invention;

[0068] Fig. 9 It is a schematic diagram of the change of output active power and reactive power of the improved resistive-inductive droop inverter in the embodiment of the present invention;

[0069] Fig.10 The figure is a schematic diagram of the changes in active power and reactive power output by the inverter in the embodiment of the present invention. DETAILED DESCRIPTION

[0070] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0071] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0072] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0073] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the product of the invention is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0074] In addition, the terms "horizontal", "vertical" and the like do not mean that the components are required to be absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0075] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0076] I. First, analyze the power allocation error under complex network topology

[0077] Complex network topology such as Figure 1 As shown, taking three distributed generation units as an example, DG1, DG2, and DG3 are three distributed generation units, and the inverter unit and the load are connected to each node in the network. When the distributed generation unit and the load are switched arbitrarily, the line impedance will change, such as Figure 1 For load 4, when load 4 is connected and removed, the line impedance corresponding to distributed generation unit 1 will change, and it is difficult to identify the line impedance at this time.

[0078] The coupled droop control takes into account the problem of inverter output active and reactive power coupling caused by the equivalent resistance-inductance ratio in the system impedance, and decouples the active and reactive power output of each inverter to a certain extent. Its expression is shown in formula (1).

[0079]

[0080] Where U i and w i are the inverter output voltage and angular velocity, U * and w * are the rated output voltage and rated angular frequency of the inverter, P i and Q i are the active and reactive power output of the corresponding inverter, K pvi , K pwi With K qvi , K qwi are the droop coefficients of active and reactive power respectively.

[0081] As with conventional droop control, the system angular frequency is a global variable and the inverter output voltage is a local variable. Therefore, the output power of each inverter has the following relationship, as shown in equations (2) and (3).

[0082] K pw1 P1-K qw1 Q1=K pw2 P2-K qw2 Q2=...=K pwn P n -K qwn Q n (2)

[0083] K pv1 P1+K qv1 Q1≠K pv2 P2+K qv2 Q2≠...≠K pvn P n +K qvn Q n (3)

[0084] At the same time, in the resistive-inductive droop control, the product of the droop coefficient of each inverter and the rated capacity satisfies equation (4).

[0085]

[0086] From (2) and (3), it can be seen that once the values ​​of the elements in formula (3) are the same, the reasonable distribution of the active and reactive power output of the inverter can be achieved. This section will derive the expression that affects the inverter output power distribution error. To simplify the analysis, it is assumed that the droop coefficient of each inverter satisfies formula (5). At this time, the capacity of each inverter is the same. The output power distribution error analysis process of inverters with different capacities is similar to the following derivation process.

[0087] K pwi =K qwi =K pvi =K qvi =K (5)

[0088] Then equation (1) can be transformed into equation (6).

[0089]

[0090] Where U i and w i are the inverter output voltage and angular velocity, U * and w * are the rated output voltage and rated angular frequency of the inverter, P i and Q iare the active and reactive power output of the corresponding inverter, K is the droop coefficient of virtual active and reactive power, P i * and Q i * They are the virtual active and reactive powers output by the corresponding inverters respectively.

[0091] Since the angular frequency is a global variable, the virtual active power in equation (6) can be reasonably distributed, but the virtual reactive power cannot be reasonably distributed because the inverter output voltage is a local variable, and thus the actual output active and reactive power of the inverter cannot be reasonably distributed. When the virtual reactive power is reasonably distributed, the actual output active and reactive power distribution error of the inverter is 0. Corresponding to equation (6), we have:

[0092]

[0093] From the above analysis, it can be seen that whether the virtual reactive power is reasonably distributed directly affects whether the actual active and reactive power output of the inverter is reasonably distributed. Therefore, the factors affecting the power distribution error can be studied by deriving the expression of the virtual reactive power output of the inverter. At the same time, in order to simplify the analysis, take the two-inverter system as an example, the schematic diagram is as follows Figure 2 shown.

[0094] The inverter output voltage expression is shown below.

[0095]

[0096] Among them, U j is the voltage at a certain point on the bus, P loci , Q loci are respectively the active and reactive power of the local load, R i , X i are the resistive and inductive components of the line impedance respectively. Combined with the virtual power expression, equation (8) can be transformed into:

[0097]

[0098] in,

[0099]

[0100] From the above content, it can be seen that the virtual active power output by the inverter can be reasonably distributed, that is, it satisfies formula (10).

[0101]

[0102] Among them, P pubi , Q pubi They are the active and reactive power of the bus load respectively.

[0103] For the power flow at the common load node,

[0104]

[0105] Then the virtual active and reactive power at the public load node is as shown in formula (12).

[0106]

[0107] Combining equations (6) to (12), the inverter output virtual reactive power error expression can be obtained, as shown in equation (13).

[0108]

[0109] in,

[0110] E=Q loc1 +Q pub1 -P loc1 -P pub1

[0111] F=P pub2 +P loc2 -Q pub2 -Q loc2

[0112] G=-(P loc1 +P pub1 +Q loc1 +Q pub1 )

[0113] H=P pub2 +P loc2 +Q pub2 +Q loc2

[0114] I=P loc2 R2+Q loc2 X2-P loc1 R1-Q loc1 X1

[0115] Where ΔQ * is the inverter output virtual reactive power error, Q1 * and Q2 * are the output virtual reactive power of the first and second inverters respectively, i=1, 2, 3, R i and X i They are the resistive and inductive parts of the corresponding line impedance, P * The virtual active power output of the inverter, P pub1 , Q pub1 With P pub2, Q loc2 The active and reactive power of the bus load and the local load of the first and second inverters respectively.

[0116] From formula (13), it can be seen that the rated active and reactive power of the load and the line impedance will affect the virtual reactive power distribution error of the inverter output. To make the virtual reactive power distribution error zero, formula (14) must be satisfied.

[0117]

[0118] in,

[0119] E=Q loc1 +Q pub1 -P loc1 -P pub1

[0120] F=P pub2 +P loc2 -Q pub2 -Q loc2

[0121] G=-(P loc1 +P pub1 +Q loc1 +Q pub1 )

[0122] H=P pub2 +P loc2 +Q pub2 +Q loc2

[0123] I=P loc2 R2+Q loc2 X2-P loc1 R1-Q loc1 X1

[0124] In the formula, i=1, 2, 3, R i and X i They are the resistive and inductive parts of the corresponding line impedance, P * Output virtual active power for the inverter.

[0125] However, in the actual network topology, factors such as load switching and line impedance changes will cause equation (14) to be invalid. It is difficult to reasonably distribute power through parameter configuration. Therefore, it is necessary to improve the resistive-inductive droop control.

[0126] II. Inverter Improvement Control Strategy

[0127] In a complex network topology, assuming that the total number of inverters is n, the total rated capacity of the inverters in the system is as shown in formula (15).

[0128] S 总 * =S1 * +S2 * +...+S n * (15)

[0129] Combining (4) and (15), we can get:

[0130]

[0131] From formula (16), we can get:

[0132]

[0133] where k i It is the ratio of the rated capacity of each inverter to the total rated capacity of the system. When the actual output power of each inverter is distributed according to the above rated capacity ratio, the reasonable distribution of the system load is achieved.

[0134] As mentioned above, since the inverter output voltage is a local variable and the system angular velocity is a global variable, the inverter output power cannot be reasonably distributed, so the power control link needs to be improved.

[0135] The improved power control strategy for complex network topology is shown in equation (18).

[0136]

[0137] where k p and k q are proportional and integral coefficients respectively, U j Indicates the voltage at a certain point on the bus, P i , Q i The expression of can be shown as formula (19).

[0138]

[0139] Among them U Ti is the neighboring node of the inverter output node, θ, are the line impedance angle and the phase of the inverter output voltage respectively. The power control block diagram of the control strategy proposed in this paper is as follows: Figure 3 shown.

[0140] in

[0141]

[0142] Then there is

[0143]

[0144] According to the final value theorem,

[0145]

[0146] Therefore, there is

[0147] K pv1 P1+K qv1 Q1=K pv2 P2+K qv2 Q2=...=K pvn P n +K qvn Q n

[0148] K pw1 P1-K qw1 Q1=K pw2 P2-K qw2 Q2=...=K pwn P n -K qwn Q n (twenty two)

[0149] Combining equations (17) and (22), we can obtain:

[0150] P1:P2:...:P n =k1:k2:...:k n

[0151] Q1:Q2:...:Q n =k1:k2:...:k n (twenty three)

[0152] It can be seen from formula (23) that the inverter output power can be reasonably distributed according to the ratio of the rated capacity of each inverter to the total capacity of the system, so that the power distribution error is zero.

[0153] In order to verify that the proposed resistance-sensing improved droop control can be applied in resistive and inductive environments and the power distribution accuracy of the proposed resistance-sensing improved droop control in resistive and inductive environments, comparative experiments of resistance-sensing improved droop control and resistive improved droop control, resistance-sensing improved droop control and inductive improved droop control are carried out under resistive and inductive conditions to illustrate the power distribution performance of the proposed control strategy. The improved inductive and resistive control strategies are shown in Table 1.

[0154] Table 1 Resistive and inductive control strategies

[0155]

[0156] For the inverter output voltage, combined with equation (19), let

[0157]

[0158] in

[0159]

[0160] Combining (18) and (24), we can get the expression of the inverter output voltage, as shown in formula (25).

[0161]

[0162] in,

[0163]

[0164] Where U i1 is the inverter output voltage when the power of the microgrid inverter is controlled based on the improved control strategy of complex network topology, Z is the impedance of each inverter, θ and are the line impedance angle and the phase of the inverter output voltage, P locali and Q locali is the active and reactive power of the corresponding local load, U * is the rated output voltage of the corresponding inverter, U j Indicates the voltage at a certain point on the bus, k p and k q are the proportional and integral coefficients respectively.

[0165] It can be seen from formula (25) that the inverter output voltage of the improved resistance-inductive droop control strategy consists of two parts. The first part is the steady-state part, which ensures the reasonable distribution of the output power of each inverter. The second part is the transient part. From its expression, it can be seen that the only physical quantities that can be artificially changed are the proportion and integral coefficient. Therefore, the rate at which the inverter output voltage reaches the steady state can be adjusted by adjusting the proportion and integral coefficient, thereby indirectly adjusting the rate at which the inverter output power reaches the steady state.

[0166] III. Simulation Verification

[0167] The above theoretical explanation shows that the improved resistive-inductive droop control strategy can be applied in complex network topologies. The feasibility of the proposed control strategy will be verified through multiple sets of comparative simulation experiments. The parameter settings are shown in Table 2.

[0168] Table 2 Simulation parameter settings

[0169]

[0170] Simulation 1: Comparison between traditional coupled droop control and improved coupled droop control (line impedance is resistive and inductive)

[0171] In the traditional resistance-inductance droop control, the inverter outputs active power and reactive power as Figure 4 As shown, since the inverter output voltage is a local variable, the first sub-formula in equation (22) is different, and the load cannot be distributed according to the inverter capacity ratio.

[0172] The improved control strategy can satisfy equation (22), so the inverter output active and reactive power can be distributed according to the capacity ratio. In this example, the rated capacity of each inverter is equal, and the improved power distribution diagram is as follows: Figure 5 shown.

[0173] Simulation 2: The line impedance in the complex network is inductive, and the comparison between the resistance-inductive improved droop control and the inductive improved droop control

[0174] As mentioned above, the inverter unit and the load position can be changed at will in the system, resulting in the line impedance corresponding to the inverter unit being diversified, and inductive, resistive, and resistive-inductive situations are all possible. Simulation 2 assumes that the system impedance is inductive at this time, and compares the improved resistive-inductive droop control with the inductive improved droop control in terms of power distribution.

[0175] Improved inductive droop control inverter output active and reactive power such as Figure 6 As shown in the figure, the inverter output active and reactive power in the improved resistance-inductance droop control is as follows Figure 7 shown.

[0176] The inverter capacity ratio is 3:4:3. As shown in the figure above, in the improved inductive droop control, the active power ratio of each inverter output is 1:1.333:1, and the reactive power ratio is 1:1.334:1. In the improved coupling droop control, the active power ratio of each inverter output is 1:1.333:1, and the reactive power ratio is 1:1.335:1. Therefore, it is proved that the resistive-inductive improved droop control can be applied to the inductive line, and the power distribution accuracy is almost the same as the inductive improved droop control.

[0177] Simulation 3: The line impedance in the complex network is resistive, and the improved impedance-inductive droop control is compared with the improved resistive droop control

[0178] Similar to Example 2, the output power of the resistive improved droop control is as follows: Figure 8 As shown, under resistive conditions, the output power of the resistive-inductive droop control is as follows: Fig. 9 shown.

[0179] In this simulation, the capacity ratio of each inverter is still set to 3:4:3, and the analogy process is similar to that of Simulation Example 2. In the improved resistive droop control, the active power ratio of each inverter output is 1:1.336:1, and the reactive power ratio is 1:1.332:1. In the improved coupled droop control, the active power ratio of each inverter output is 1:1.334:1, and the reactive power ratio is 1:1.333:1. Therefore, the resistive-inductive droop control can be applied in a resistive environment, and its power distribution accuracy is almost the same as that of the resistive improved droop control.

[0180] Simulation 4: Plug-and-play feature verification (same capacity for each inverter)

[0181] In actual systems, distributed generation units and loads may be connected to the system or removed at any time. In this simulation, there are initially two distributed generation units supplying power to the load. At the 1st second, distributed generation unit 3 is connected to the system and removed at the 3rd second. At the 4th second, a new load is connected and removed at the 5th second.

[0182] In this simulation, the capacity of each inverter is the same. Fig.10 It can be seen that in the whole process, the active and reactive power output by the inverter can be reasonably distributed according to the capacity ratio of the inverter, and the power distribution performance is good.

[0183] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A power control method for a microgrid inverter under a complex network topology, characterized in that: The control method comprises the following steps: Step 1: Perform power distribution error analysis based on coupled droop control for complex network topologies to determine whether the resistive-inductive droop control needs to be improved; Step 2: When it is determined that improvement is needed, a complex network topology improvement control strategy is set; Step 3: Improve the control strategy based on complex network topology to control the power of microgrid inverter; The step 1 specifically includes: Step 101: deriving active and reactive power output by each inverter based on coupled droop control; Step 102: converting the corresponding formula form of active and reactive power output by each inverter based on coupled droop control into the expression form of virtual active and reactive power output by each inverter through simplified analysis; Step 103: simplify and analyze the complex network topology based on the expression of virtual active and reactive power output by each inverter, and obtain an error expression of virtual reactive power output by the inverter; Step 104: determining whether the corresponding satisfying condition expression obtained when the inverter output virtual reactive power error expression is 0 is established, so as to determine whether the resistive-inductive droop control needs to be improved. If it is not established, the resistive-inductive droop control needs to be improved. Each inverter in step 101 outputs active and reactive power, and its mathematical description formula is: U i =U * -K pvi P i -K qvi Q i w i =w * -K pwi P i +K qwi Q i Where U i and w i are the inverter output voltage and angular velocity, U * and w * are the rated output voltage and rated angular frequency of the inverter, P i and Q i are the active and reactive power output of the corresponding inverter, K pvi , K pwi With K qvi , K qwi are the droop coefficients of active and reactive power respectively; The expression form of the virtual active and reactive power output by each inverter in step 102 is mathematically described as follows: U i =U * -K(P i +Q i )=U * -KQ i * w i =w * -K(P i -Q i )=w * -KP i * Where U i and w i are the inverter output voltage and angular velocity, U * and w * are the rated output voltage and rated angular frequency of the inverter, P i and Q i are the active and reactive power output of the corresponding inverter, K is the droop coefficient of virtual active and reactive power, P i * and Q i * They are the virtual active and reactive power outputs of the corresponding inverters respectively; The inverter output virtual reactive power error expression in step 103 is mathematically described as follows: in, E=Q loc1 +Q pub1 -P loc1 -P pub1 F=P pub2 +P loc2 -Q pub2 -Q loc2 G=-(P loc1 +P pub1 +Q loc1 +Q pub1 ) H=P pub2 +P loc2 +Q pub2 +Q loc2 I=P loc2 R2+Q loc2 X2-P loc1 R1-Q loc1 X1 Where ΔQ * is the inverter output virtual reactive power error, Q1 * and Q2 * are the output virtual reactive power of the first and second inverters respectively, R i and X i They are the resistive and inductive parts of the corresponding line impedance, P * The virtual active power output of the inverter, P pub1 , Q pub1 With P pub2 , Q loc2 The active and reactive powers of the bus loads and local loads of the first and second inverters respectively; The conditional expression in step 104 is mathematically described as follows: in, E=Q loc1 +Q pub1 -P loc1 -P pub1 F=P pub2 +P loc2 -Q pub2 -Q loc2 G=-(P loc1 +P pub1 +Q loc1 +Q pub1 ) H=P pub2 +P loc2 +Q pub2 +Q loc2 I=P loc2 R2+Q loc2 X2-P loc1 R1-Q loc1 X1 In the formula, R i and X i They are the resistive and inductive parts of the corresponding line impedance, P * Output virtual active power for the inverter; The complex network topology improvement control strategy in step 2 includes a control strategy corresponding to the case where the resistance-sensing type is inductive and a control strategy corresponding to the case where the resistance-sensing type is resistive; The resistance-sensitivity type is the corresponding control strategy under the inductive case, and its corresponding mathematical description formula is: in=in * -mP Where U and w are the inverter output voltage and angular frequency under the improved control strategy of complex network topology, respectively, and k is p and k q are the proportional and integral coefficients, k e is the voltage difference coefficient, P and Q are the active and reactive power output by the inverter respectively, w * is the rated angular frequency of the corresponding inverter output, m and n are the active power droop coefficient and reactive power droop coefficient respectively, and U* is the rated voltage of the corresponding inverter output; The resistance-sensing type is the corresponding control strategy in the case of resistance, and its corresponding mathematical description formula is: <h2 style=";text-align:left;direction:ltr">w=w<h2 style=";text-align:left;direction:ltr"> * <h2 style=";text-align:left;direction:ltr"> +nQ Where U and w are the inverter output voltage and angular frequency under the improved control strategy of complex network topology, respectively, and k is p and k q are the proportional and integral coefficients, k e is the voltage difference coefficient, P and Q are the active and reactive power output by the inverter respectively, w * is the rated angular frequency of the corresponding inverter output, m and n are the active power droop coefficient and reactive power droop coefficient respectively, and U* is the rated voltage of the corresponding inverter output.

2. The method for controlling power of a microgrid inverter under a complex network topology according to claim 1, characterized in that: The expression of the inverter output voltage when the microgrid inverter power is controlled based on the improved control strategy of complex network topology in step 3 is: in, Where U i1 is the inverter output voltage when the microgrid inverter power is controlled based on the improved control strategy of complex network topology, Z is the impedance of each inverter, U j represents the voltage at a certain point on the bus, θ and are the line impedance angle and the phase of the inverter output voltage, P locali and Q locali is the active and reactive power of the corresponding local load, U * is the rated output voltage of the corresponding inverter, k p and k q are the proportional and integral coefficients respectively.

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