Single-stage interconnection converter port power distribution method based on multilayer space vector modulation strategy

Abstract

The invention discloses a single-stage interconnection converter port power distribution method based on a multilayer space vector modulation strategy. The method comprises the following steps: firstly, obtaining a single-stage interconnection converter alternating current side reference voltage vector through an energy management strategy, a power control loop and a current and voltage double closed loop of a hybrid alternating current and direct current micro-grid; then, the single-stage interconnection converter is subjected to equivalent decoupling modeling to form four virtual two-level converters, a four-layer space vector diagram is obtained, scaling factors for decomposing reference voltage vectors are calculated according to given reference power, and therefore the two reference voltage vectors on the alternating current side are decomposed into four independent voltage vectors; and synthesizing the four voltage vectors in a four-layer space vector diagram to obtain the duty ratio of each phase of the four two-level converters so as to obtain the switching sequence of the single-stage interconnection converter.

Description

Technical Field

[0001] The present invention belongs to the technical field of AC-DC hybrid microgrid control. More specifically, it relates to a method for power distribution at the ports of a single-stage interconnected converter based on a multi-layer space vector modulation strategy. Background Art

[0002] In order to give full play to the advantages of the microgrid in connecting distributed renewable energy, selecting a suitable single-stage interconnected converter topology to connect multiple AC-DC microgrids simultaneously and giving corresponding modulation strategies can reduce the energy loss during transmission and achieve high-efficiency energy transfer. Currently, interconnected converters mostly adopt a bus-type structure to connect multiple AC subnets and DC subnets. Inevitably, separate DC-DC or DC-AC converters need to be installed to match different bus voltage levels. Such a structure not only increases the weight and volume of the system but also reduces the power density of the system. The single-stage interconnected converter, while removing the extra DC-DC and DC-AC converters, provides multiple AC-DC power ports for direct connection of AC-DC subnets with different voltage levels, having the advantages of single energy conversion between subnets, high system power density, and low initial investment cost.

[0003] However, since the AC-DC subnets are directly connected to the power ports of the interconnected converter, it causes the port voltages on the DC side of the interconnected converter to be unbalanced, which brings difficulties to the synthesis of the reference voltage vector at the AC side ports of the system and cannot guarantee the power quality of the AC subnets. In addition, the complex power flow path and coupled port powers in the single-stage interconnected converter topology make it difficult to simultaneously achieve flexible power distribution between the connected subnets during the synthesis of the reference voltage vector, thus unable to adapt to the complex power demands of the subnets, which greatly limits the application of the AC-DC hybrid microgrid system.

[0004] Existing methods for synthesizing the reference voltage vector under unbalanced port voltages usually achieve port power control based on virtual vectors. However, this method requires complex trigonometric function calculations, bringing difficulties to the design of the system controller. In order to simplify the design of the system controller and achieve flexible power distribution between multiple ports, an improved space vector modulation strategy realizes ideal power distribution by specifying the operation of the single-stage multi-port inverter in the two-level mode. However, the system always operates in the two-level mode, reducing the system efficiency. The unbalance of the port voltages and the coupling of the port powers of the single-stage interconnected converter bring difficulties to the modulation and control strategies of the system. Currently, there is no simple and effective power distribution method to achieve flexible power distribution between multiple ports of the single-stage interconnected converter. Summary of the Invention

[0005] The object of the present invention is to overcome the deficiencies of the prior art and provide a single-stage interconnected converter port power distribution method based on a multi-layer space vector modulation strategy, which can not only synthesize an ideal reference voltage vector on the AC side under the condition of unbalanced DC side port voltages, but also flexibly distribute power among multiple subnets simultaneously, enabling the AC-DC hybrid microgrid system to operate stably in multiple working modes and achieve good self-adaptability to complex working conditions.

[0006] To achieve the above object of the invention, a single-stage interconnected converter port power distribution method based on a multi-layer space vector modulation strategy is characterized by the following steps:

[0007] (1) Calculate the reference voltage vectors v ac1-ref and v ac2-ref of the two AC ports on the AC side of the single-stage interconnected converter;

[0008] (2) Perform equivalent decoupling modeling on the single-stage interconnected converter to obtain four virtual two-level converter models and a four-layer space vector distribution diagram; among them, each two-level converter is composed of two complementary switching tubes; the four virtual two-level converters are respectively denoted as two-level converter one, two-level converter two, two-level converter three, and two-level converter four, and the output powers of the four two-level converters are denoted as P1, P2, P3, and P4, and the output voltage vectors are denoted as v 1-ref 、v 2-ref 、v 3-ref and v 4-ref ;

[0009] (3) Calculate the actual active powers on the DC side and AC side of the single-stage interconnected converter, namely the active power P HV of the high-voltage DC port, the active power P LV output by the low-voltage DC port, the required active power P AC1 of the first AC port, and the required active power P AC2 of the second AC port:

[0010] (4) Calculate the proportional factor k for decomposing the reference voltage vector according to the reference active powers P HV-ref and P LV-ref given by the energy management strategy module of the AC-DC hybrid microgrid;

[0011] (5) Calculate the voltage vectors v 1-ref 、v 2-ref 、v 3-ref and v 4-ref output by the four two-level converters according to the proportional factor k;

[0012] (6) According to the voltage vectors v 1-ref 、v2-ref , v 3-ref and v 4-ref Calculate the duty ratio of each phase of each two-level converter;

[0013] (7) Generate a modulation waveform through the duty ratio of each phase of the four two-level converters, and then compare the amplitude of the modulation wave with that of the triangular carrier within a switching period to generate eight switching signals for driving the single-stage interconnected converter, thereby controlling the switching actions of the three arms of the single-stage interconnected converter.

[0014] The invention object of the present invention is achieved as follows:

[0015] The method for power distribution among ports of a single-stage interconnected converter based on a multi-layer space vector modulation strategy of the present invention first obtains the reference voltage vector on the AC side of the single-stage interconnected converter through the energy management strategy, power control loop, and current-voltage double closed-loop loop of the hybrid AC-DC microgrid. Subsequently, by equivalently decoupling and modeling the single-stage interconnected converter as four virtual two-level converters, a multi-layer space vector diagram and the decomposed DC port power and reference voltage vector are obtained. Calculate the scaling factors from the reference power given by the energy management strategy to the decomposed reference voltage vector and DC port power. The scaling factors decompose the two reference voltage vectors on the AC side into four independent voltage vectors. By synthesizing these four voltage vectors in the multi-layer space vector diagram, the duty ratio of each phase of the four virtual converters is obtained, and then the switching sequence of the single-stage interconnected converter is obtained. In this process, flexible power distribution among the ports of the single-stage interconnected converter can be achieved by adjusting the scaling factors without affecting the synthesis of the reference voltage vector on the AC side.

[0016] Meanwhile, the method for power distribution among ports of a single-stage interconnected converter based on a multi-layer space vector modulation strategy of the present invention also has the following beneficial effects

[0017] (1) The single-stage interconnected converter connecting multiple AC-DC microgrids of the present invention can simultaneously provide two DC ports and two AC ports to connect AC-DC microgrids with different voltage levels. In addition, only a single power conversion stage is required for power transmission between the DC side and the AC side of the system, effectively reducing the system energy loss and power switching devices, meeting the current requirements for high power transmission efficiency and high reliability of hybrid microgrids.

[0018] (2) The present invention proposes a simple and effective port power allocation method based on a multi-layer space vector modulation strategy to address the inherent port coupling characteristics of single-stage interconnected converters connected to an AC / DC hybrid microgrid system. By decoupling and modeling the port power of the topology, a multi-layer space vector distribution diagram and a decomposed reference voltage vector are obtained, wherein each layer of the space vector diagram adjusts the output of a virtual two-level converter. This not only realizes the formation of AC voltage under unbalanced DC port voltage, but also realizes flexible active power distribution between multiple subgrids.

[0019] (3) The power allocation method based on the multi-layer space vector modulation strategy of the present invention can effectively avoid the complex trigonometric function calculation process, which not only ensures the power quality of the AC subnet, but also solves the problem of voltage imbalance at the converter port. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural topology diagram of a specific implementation of a single-stage interconnected converter connected to an AC / DC hybrid microgrid;

[0021] Figure 2 It is a topological diagram of the structure of a single-stage interconnected converter;

[0022] Figure 3 It is the corresponding output voltage and power path under the partial switching state of the single-stage interconnected converter;

[0023] Figure 4 It is the power transmission direction diagram of the single-stage interconnected converter in five working modes;

[0024] Figure 5 It is a control block diagram of a single-stage interconnected converter port power allocation method based on a multi-layer space vector modulation strategy of the present invention;

[0025] Figure 6 The power decoupling modeling of the single-stage interconnected converter ports is used to obtain the schematic diagram of four virtual converters;

[0026] Figure 7 It is a schematic diagram of multi-layer space vector diagram obtained by modeling the power decoupling of the ports of a single-stage interconnected converter;

[0027] Figure 8 It is a diagram showing the steady-state performance of a single-stage interconnected converter in different operating modes;

[0028] Figure 9 It is a diagram showing the dynamic performance of a single-stage interconnected converter when switching between different working modes. DETAILED DESCRIPTION

[0029] The following describes the specific embodiments of the present invention in conjunction with the accompanying drawings so that those skilled in the art can better understand the present invention. It should be particularly noted that in the following description, when the detailed descriptions of known functions and designs may dilute the main content of the present invention, these descriptions will be omitted here.

[0030] Embodiment

[0031] Figure 1 It is the structural topology diagram of the specific embodiment of the single-stage interconnection converter connecting the AC-DC hybrid microgrid.

[0032] In this embodiment, as Figure 1 shown, the AC-DC hybrid microgrid system is characterized by including: a high-voltage DC subnet 1, a low-voltage DC subnet 2, an AC subnet 5, an AC subnet 6, an LC filter 4, and a single-stage interconnection converter 3;

[0033] In this embodiment, as Figure 2 shown, the topology structure of the single-stage interconnection converter is improved by paralleling two diode-clamped (NPC type) three-level converter topologies. On the DC side, while the positive and negative poles of the two paralleled NPC converters are connected to a high-voltage DC port, a low-voltage DC port is connected between the neutral line and the ground wire; on the AC side, due to the structure of the paralleled converters, the AC side has two independent three-phase AC ports. The topology improved by paralleling still retains the original three bridge arms of the NPC converter.

[0034] From Figure 2 it can be seen that the power flow paths from the two DC subnets to the two AC subnets have reduced multiple DC-DC and DC-AC units compared with traditional similar interconnection converters. This not only reduces the energy level conversion but also improves the energy transmission efficiency of the system;

[0035] In this embodiment, as Figure 3 shown, the switching states of the switching tubes of the single-stage interconnection converter not only determine the output voltage of the AC port but also determine the power paths between the subnets. From Figure 4 it can be seen that there are a total of five working modes of the single-stage interconnection converter system. Mode 1: Both DC subnets simultaneously provide the required active power for the AC side. Mode 2: Only the high-voltage DC subnet provides the required active power for the AC side. Mode 3: The high-voltage DC subnet not only provides the required active power for the AC side but also provides power for the low-voltage DC subnet. Mode 4: The low-voltage DC subnet provides the required active power for the AC side, while the high-voltage DC subnet maintains the balance between supply and demand; Mode 5: The low-voltage DC subnet not only provides the required active power for the AC side but also provides power for the high-voltage DC subnet;

[0036] Next, we will combine Figure 5, describe the control block diagram of the port power distribution method of the single-stage interconnected converter based on the multi-level space vector modulation strategy, which specifically includes the following steps:

[0037] S1. Calculate the reference voltage vectors v ac1-ref and v ac2-ref ;

[0038] S1.1. Collect the capacitor voltages u c1 , u c2 , the inductor currents i lx1 , i lx2 and the grid-side currents i 1x , i 2x of the two AC ports on the AC side of the single-stage interconnected converter, where x = a, b, c represents three phases;

[0039] S1.2. Obtain the required reference active powers P AC1-ref , P AC2-ref and the reference reactive powers Q AC1-ref , Q AC2-ref of the two AC subnets through the energy management strategy module of the AC-DC hybrid microgrid;

[0040] S1.3. As shown in Figure 5 , pass the required reference active powers P AC1-ref , P AC2-ref and the reference reactive powers Q AC1-ref , Q AC2-ref of the two AC subnets through the power control loop of the AC-DC hybrid microgrid to obtain the phase angle θ ref and the reference voltage E ref of the AC subnet system;

[0041] S1.4. Pass the phase angle θ ref , the reference voltage E ref as well as the capacitor voltages u c1 , u c2 , the inductor currents i lx1 , i lx2 and the grid-side currents i 1x , i 2x of the AC subnet through the double PI current-voltage control loop to obtain the reference voltage vectors v ac1-ref and v ac2-ref of the two AC ports on the AC side.

[0042] S2. Conduct equivalent decoupling modeling on the single-stage interconnected converter to obtain four virtual two-level converter models and a four-layer space vector distribution diagram;

[0043] Among them, each two-level converter is composed of two complementary switching tubes; the four virtual two-level converters are respectively denoted as two-level converter one, two-level converter two, two-level converter three, and two-level converter four, and the output powers of the four two-level converters are denoted as P1, P2, P3, and P4, and the output voltage vectors are denoted as v 1-ref 、v 2-ref 、v 3-ref and v 4-ref ;

[0044] In this embodiment, as Figure 6 shown, the single-stage interconnected converter is equivalently modeled as four virtual two-level converters. Each two-level converter is composed of two complementary switching tubes. For example, virtual converter one is composed of S x1 and ; virtual converter two is composed of switching tubes S x2 and ; virtual converter three is composed of switching tubes S x3 and ; virtual converter four is composed of switching tubes S x4 and . Among them, the DC link voltages of virtual converters one and three are V H , and the DC link voltages of virtual converters two and four are V L . S x1 , S x2 , S x3 , S x4 , respectively represent the first switching tube, the second switching tube, the third switching tube, the fourth switching tube, the fifth switching tube, the sixth switching tube, the seventh switching tube, and the eighth switching tube in the x-phase bridge arm of the single-stage interconnected converter;

[0045] In addition, as Figure 7 shown, the space vector distribution diagram of the original single-stage interconnected converter is decomposed into a four-layer space vector diagram. It can be seen from the left figure of Figure 7 that on the AC side, the reference voltage vectors v ac1-ref and v ac2-ref of the AC port of the single-stage interconnected converter are respectively decomposed into two independent voltage vectors v 1-ref and v 2-ref , v 3-ref and v 4-ref , and these decomposed independent voltage vectors can be independently synthesized in the four-layer space vector diagram;

[0046] S3. Calculate the actual active power on the DC side and AC side of the single-stage interconnected converter, i.e., the active power P of the high-voltage DC port HV , the active power P LV output from the low-voltage DC port, AC1 the required active power P AC2 of AC port 1,

[0047]

[0048] where and are the conjugates of the AC sub-network currents i ac1 and i ac2 .

[0049] S4. According to the DC port reference active power P HV-ref and P LV-ref given by the energy management strategy module of the AC-DC hybrid microgrid, calculate the scaling factor k for decomposing the reference voltage vector;

[0050] S4.1. By introducing the scaling factor k for decomposing the reference voltage vector, represent the voltage vectors of the four two-level converters as:

[0051]

[0052] S4.2. Represent the active power P HV of the high-voltage DC port of the single-stage interconnected converter and the active power P LV output from the low-voltage port as:

[0053]

[0054] S4.3. Through the energy management strategy module of the AC-DC hybrid microgrid, given the reference active power P HV-ref of the high-voltage DC port and the reference active power P LV-ref of the low-voltage DC port, substitute the reference active power P HV-ref of the high-voltage DC port as the active power P HV into step S4.2 to obtain the scaling factor k;

[0055]

[0056] S5. According to the expression of the scaling factor k, calculate the voltage vectors v 1-ref , v 2-ref , v 3-ref and v 4-ref ;

[0057] where, v 1-ref and v 3-refIt can be calculated that:

[0058]

[0059] Therefore, v 2-ref and v 4-ref can be calculated from v ac1-ref -v 1-ref and v ac2-ref -v 3-ref ;

[0060] S6. Calculate the duty ratio of each phase of each two-level converter according to the voltage vectors v 1-ref , v 2-ref , v 3-ref and v 4-ref ;

[0061] S6.1 Calculate the duty ratio d x1 of each phase of the first two-level converter;

[0062] Denote the six basic voltage vectors of the synthesized voltage vector v 1-ref as: V H0 , V H1 , V H2 , V H3 , V H4 , V H5 and V H6 ;

[0063] Divide the first layer of the four-layer space vector distribution diagram into six sectors, then determine the sector where the reference voltage vector v 1-ref is located, then select two adjacent basic voltage vectors and the zero vector in the corresponding sector to synthesize the reference voltage vector v 1-ref , and finally solve the volt-second balance equation corresponding to the reference voltage vector v 1-ref to obtain the three-phase duty ratio d x1 ;

[0064] Among them, the volt-second balance equation corresponding to the voltage vector v 1-ref in each sector is:

[0065] First sector:

[0066]

[0067] Second sector:

[0068]

[0069] Third sector:

[0070]

[0071] Fourth sector:

[0072]

[0073] Fifth sector:

[0074]

[0075] Sixth sector:

[0076]

[0077] where, T s is the switching period, and t H0 , t H1 , t H2 , t H3 , t H4 , t H5 , t H6 are the dwell times of the basic voltage vectors V H0 , V H1 , V H2 , V H3 , V H4 , V H5 , and V H6 , and d a1 , d b1 , and d c1 are the duty cycles of each phase of the two-level converter one;

[0078] S6.2. Calculate the duty cycles d x2 of each phase of the two-level converter two;

[0079] Denote the six basic voltage vectors of the synthesized voltage vector v 2-ref as: V L0 , V L1 , V L2 , V L3 , V L4 , V L5 , and V L6 ;

[0080] Divide the second layer of the four-layer space vector distribution diagram into 6 sectors, then determine the sector where the voltage vector v 2-ref is located, and then select two adjacent basic voltage vectors and the zero vector in the corresponding sector to synthesize the reference voltage vector v 2-ref , and finally solve the volt-second balance equation corresponding to the voltage vector v 2-ref to obtain the three-phase duty cycle d x2 ;

[0081] where, the volt-second balance equations corresponding to the voltage vector v 2-ref in each sector are:

[0082] The first sector:

[0083]

[0084] The second sector:

[0085]

[0086] The third sector:

[0087]

[0088] The fourth sector:

[0089]

[0090] The fifth sector:

[0091]

[0092] The sixth sector:

[0093]

[0094] where t L0 、t L1 、t L2 、t L3 、t L4 、t L5 、t L6 are the dwell times of the basic voltage vectors V L0 、V L1 、V L2 、V L3 、V L4 、V L5 and V L6 ; d a2 、d b2 and d c2 are the duty cycles of each phase of the two-level converter II;

[0095] S6.3. Calculate the duty cycle d x3 of each phase of the two-level converter III;

[0096] Denote the six basic voltage vectors of the synthesized voltage vector v 3-ref as: V′ H0 、V' H1 、V′ H2 、V' H3 、V′ H4 、V′ H5 and V′ H6 ;

[0097] Divide the third layer of the four-layer space vector distribution diagram into 6 sectors, and then judge the voltage vector v3-ref In the sector where it is located, select two adjacent basic voltage vectors and the zero vector in the corresponding sector to synthesize the voltage vector v 3-ref , and finally solve the voltage vector v 3-ref The corresponding volt-second balance equation to obtain the three-phase duty cycle d x3 ;

[0098] Among them, the reference voltage vector v 3-ref The volt-second balance equations corresponding to each sector are:

[0099] The first sector:

[0100]

[0101] The second sector:

[0102]

[0103] The third sector:

[0104]

[0105] The fourth sector:

[0106]

[0107] The fifth sector:

[0108]

[0109] The sixth sector:

[0110]

[0111] Among them, T s is the switching period, t' H0 , t' H1 , t' H2 , t' H3 , t' H4 , t' H5 , t' H6 are the dwell times of the basic voltage vectors V′ H0 , V' H1 , V′ H2 , V' H3 , V′ H4 , V′ H5 and V′ H6 The duty cycles d a3 , d b3 and d c3 are the phase duty cycles of the two-level converter three;

[0112] S6.4. Calculate the phase duty cycles d x4;

[0113] Denote the synthetic voltage vector as v 4-ref The six basic voltage vectors are: V′ L0 , V′ L1 , V′ L2 , V′ L3 , V′ L4 , V′ L5 and V′ L6 ;

[0114] Divide the fourth layer of the four-layer space vector distribution diagram into six sectors, then determine the sector where the voltage vector v 4-ref is located, and then select two adjacent basic voltage vectors and the zero vector in the corresponding sector to synthesize the voltage vector v 4-ref , and finally solve the volt-second balance equation corresponding to the reference voltage vector v 4-ref to obtain the three-phase duty cycle d x4 ;

[0115] Among them, the volt-second balance equations corresponding to the reference voltage vector v 4-ref in each sector are:

[0116] First sector:

[0117]

[0118] Second sector:

[0119]

[0120] Third sector:

[0121]

[0122] Fourth sector:

[0123]

[0124] Fifth sector:

[0125]

[0126] Sixth sector:

[0127]

[0128] Among them, T s is the switching period, t' L0 , t' L1 , t' L2 , t' L3 , t' L4 , t' L5 and t' L6is the basic voltage vector V′ L0 、V′ L1 、V′ L2 、V′ L3 、V′ L4 、V′ L5 and V′ L6 and the dwell time, d a4 、d b4 and d c4 are the duty cycles of each phase of the two - level converter four.

[0129] S7. Generate a modulation waveform through the duty cycles of each phase of the four two - level converters, and then compare the amplitude of the modulation wave with that of the triangular carrier within a switching period to generate eight switching signals for driving the single - stage interconnected converter, thereby controlling the switching actions of the three arms of the single - stage interconnected converter.

[0130] As Figure 8 shown, in this embodiment, a method for power distribution at the ports of a single - stage interconnected converter based on a multi - layer space vector modulation strategy is carried out. The results show that: by adopting the power distribution method based on the multi - layer space vector modulation strategy, the single - stage interconnected converter can operate stably in multiple working modes. In addition, the typical sinusoidal current and voltage waveforms on the AC side prove that the power distribution method based on the multi - layer space vector modulation strategy has good steady - state performance.

[0131] As Figure 9 shown, when the power of the DC subnet changes in the single - stage interconnected converter, accurate power distribution can still be achieved at the DC ports without affecting the power demand on the AC side. In addition, the fast output power tracking proves that the power distribution method based on the multi - layer space vector modulation strategy has good dynamic performance. In addition, by adopting the AC - DC hybrid micro - grid system of the present invention, not only high - efficiency power transmission efficiency is achieved between subnets, but also high power quality and flexible power distribution between subnets can be realized under the condition of unbalanced DC - side port voltages.

[0132] Although the above - described illustrative specific embodiments of the present invention have been described to facilitate the understanding of the present invention by those skilled in the art, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art of this technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions created using the concept of the present invention are within the scope of protection.

Claims

1. A single-stage interconnected converter port power distribution method based on a multi-layer space vector modulation strategy, characterized in that Including the following steps: (1) Calculate the reference voltage vectors v ac1-ref and v ac2-ref ; (2) Equivalent decoupling modeling is performed on the single-stage interconnected converter to obtain four virtual two-level converter models and a multi-layer space vector distribution diagram; each two-level converter is composed of two complementary switch tubes; the four virtual two-level converters are respectively recorded as two-level converter one, two-level converter two, two-level converter three and two-level converter four, the output powers of the four two-level converters are recorded as P1, P2, P3 and P4, and the output voltage vector is recorded as v 1-ref 、v 2-ref 、v 3-ref and v 4-ref ; (3) Calculate the actual active power on the DC side and AC side of the single-stage interconnected converter, i.e., the active power P of the high-voltage DC port HV , the active power P LV output from the low-voltage DC port, the required active power P AC1 of AC port 1, and the required active power P AC2 of AC port 2: (4) Calculate the proportionality factor k for decomposing the reference voltage vector according to the reference active power P HV-ref and P LV-ref given by the energy management strategy module of the AC-DC hybrid microgrid; (5) Calculate the voltage vectors v 1-ref , v 2-ref , v 3-ref and v 4-ref ; (6) Calculate the duty cycle of each phase of each two-level converter according to the voltage vectors v 1-ref 、v 2-ref 、v 3-ref and v 4-ref ; (7) Generate a modulation waveform through the duty ratios of each phase of four two-level converters, and then compare the modulation wave with the amplitude of the triangular carrier within a switching period to generate eight switching signals for driving the single-stage interconnected converter, thereby controlling the switching actions of the three arms of the single-stage interconnected converter.

2. The method for port power distribution of the single-stage interconnected converter based on the multi-layer space vector modulation strategy according to claim 1, wherein The reference voltage vectors v ac1-ref and v ac2-ref are calculated as follows: (2.1) Collect the capacitor voltages u c1 and u c2 of the two AC ports on the AC side of the single-stage interconnected converter, the inductor currents i lx1 and i lx2 , and the grid-side currents i 1x and i 2x , where x = a, b, c represents three phases; (2.2) Obtain the required reference active power P AC1-ref and P AC2-ref and reference reactive power Q AC1-ref and Q AC2-ref for the two AC subnets through the energy management strategy module of the AC / DC hybrid microgrid; ( 2.3), obtain the reference active power P AC1-ref and P AC2-ref and the reference reactive power Q AC1-ref and Q AC2-ref through the power control loop of the AC-DC hybrid microgrid to obtain the phase angle θ ref and the reference voltage E ref ; ( 2.4), the phase angle θ of the AC subnet ref , the reference voltage E ref and the capacitor voltage u c1 , u c2 , the inductor current i lx1 , i lx2 and the grid-side current i 1x , i 2x pass through the dual-PI current-voltage control loop to obtain the reference voltage vectors v ac1-ref and v ac2-ref .

3. The method for port power allocation of the single-stage interconnected converter based on the multi-layer space vector modulation strategy according to claim 1, wherein The calculation method for the actual active power on the DC side and AC side of the single-stage interconnected converter is as follows: Among them, and are the conjugates of the AC sub-network currents i ac1 and i ac2 .

4. The method for port power allocation of a single-stage interconnected converter based on a multi-layer space vector modulation strategy according to claim 1, characterized in that The calculation method for the proportionality factor k is as follows: (4.1) By introducing the proportionality factor k for decomposing the reference voltage vector, the voltage vectors of the four two-level converters are expressed as: (4.2) Express the active power P of the high-voltage DC port of the single-stage interconnected converter HV and the active power P output from the low-voltage port LV as follows: (4.3) The reference active power P of the high-voltage DC port is given by the energy management strategy module of the AC-DC hybrid microgrid HV-ref and the reference active power P of the low-voltage DC port LV-ref . The reference active power P of the high-voltage DC port HV-ref is used as the active power P of the high-voltage DC port HV and substituted into step (4.2) to obtain the scaling factor k; 5. The method for power distribution at the ports of a single-stage interconnected converter based on a multi-layer space vector modulation strategy according to claim 1, characterized in that The reference voltage vectors v 1-ref , v 2-ref , v 3-ref and v 4-ref are calculated as follows:

6. The method for port power distribution of the single-stage interconnected converter based on the multi-layer space vector modulation strategy according to claim 1, characterized in that The calculation method for the duty ratio of each phase of the four two-level converters is as follows: (6.1), calculate the duty cycle d of each phase of the two-level converter 1 x1 ; Denote the synthetic voltage vector as v 1-ref The six basic voltage vectors are respectively: V H0 , V H1 , V H2 , V H3 , V H4 , V H5 , and V H6 ; Divide the first layer of the multi-layer space vector distribution diagram into 6 sectors, and then judge the sector where the reference voltage vector v 1-ref is located. Then select two adjacent basic voltage vectors and the zero vector in the corresponding sector to synthesize the reference voltage vector v 1-ref . Finally, solve the volt-second balance equation corresponding to the reference voltage vector v 1-ref to obtain the three-phase duty cycle d x1 ; Among them, the voltage vector v 1-ref The volt-second balance equations corresponding to each sector are: The first sector: The second sector: The third sector: The fourth sector: The fifth sector: The sixth sector: Among them, T s is the switching period, and t H0 , t H1 , t H2 , t H3 , t H4 , t H5 , t H6 are the dwell times of the basic voltage vectors V H0 , V H1 , V H2 , V H3 , V H4 , V H5 and V H6 . d a1 , d b1 and d c1 are the duty cycles of each phase of the first two-level converter; (6.2), calculate the duty cycle d of each phase of the two-level converter II x2 ; Denote the synthetic voltage vector as v 2-ref The six basic voltage vectors are respectively: V L0 , V L1 , V L2 , V L3 , V L4 , V L5 and V L6 ; Divide the second layer of the multi-layer spatial vector distribution diagram into 6 sectors, then judge the sector where the voltage vector v 2-ref is located, and then select two adjacent basic voltage vectors and zero vectors in the corresponding sector to synthesize the reference voltage vector v 2-ref , and finally solve the volt-second balance equation corresponding to the voltage vector v 2-ref to obtain the three-phase duty cycle d x2 ; Among them, the voltage vector v 2-ref The volt-second balance equations corresponding to each sector are: The first sector: The second sector: The third sector: The fourth sector: The fifth sector: The sixth sector: Among them, t L0 、t L1 、t L2 、t L3 、t L4 、t L5 、t L6 are the dwell times of the basic voltage vectors V L0 、V L1 、V L2 、V L3 、V L4 、V L5 and V L6 , and d a2 、d b2 and d c2 are the duty ratios of each phase of the two-level converter two; (6.3), Calculate the duty cycle d of each phase of the two-level converter three x3 ; Denote the synthesized voltage vector as v 3-ref The six basic voltage vectors are respectively: V H '0, V' H1 , V H '2, V' H3 , V H '4, V H '5 and V H '6; Divide the third layer of the multi-layer space vector distribution diagram into 6 sectors, then judge the sector where the voltage vector v 3-ref is located, and then select two adjacent basic voltage vectors and zero vectors in the corresponding sector to synthesize the voltage vector v 3-ref . Finally, solve the volt-second balance equation corresponding to the voltage vector v 3-ref to obtain the three-phase duty cycle d x3 ; Among them, the reference voltage vector v 3-ref The volt-second balance equations corresponding to each sector are: The first sector: The second sector: The third sector: The fourth sector: The fifth sector: The sixth sector: Among them, T s is the switching period, t' H0 , t' H1 , t' H2 , t' H3 , t' H4 , t' H5 , t' H6 are the dwell times of the basic voltage vectors V H '0, V' H1 , V H '2, V' H3 , V H '4, V H '5 and V H '6, and d a3 , d b3 and d c3 are the duty ratios of each phase of the two-level converter three; (6.4), Calculate the duty cycle d of each phase of the two-level converter four x4 ; Denote the synthetic voltage vector as v 4-ref The six basic voltage vectors are respectively: V L '0, V L '1, V L '2, V L '3, V L '4, V L '5, and V L '6; Divide the fourth layer of the multi-layer space vector distribution diagram into 6 sectors, then determine the sector where the voltage vector v 4-ref is located, and then select two adjacent basic voltage vectors and the zero vector in the corresponding sector to synthesize the voltage vector v 4-ref , and finally solve the volt-second balance equation corresponding to the reference voltage vector v 4-ref to obtain the three-phase duty cycle d x4 ; Among them, the reference voltage vector v 4-ref The volt-second balance equations corresponding to each sector are: The first sector: The second sector: The third sector: The fourth sector: The fifth sector: The sixth sector: Among them, T s is the switching period, and t' L0 , t' L1 , t' L2 , t' L3 , t' L4 , t' L5 and t' L6 are the dwelling times of the basic voltage vectors V L '0, V L '1, V L '2, V L '3, V L '4, V L '5 and V L '6, and d a4 , d b4 and d c4 are the duty ratios of each phase of the two-level converter four.

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