Hybrid modulation method for realizing direct power distribution of single-stage multi-port inverter

Abstract

The invention discloses a hybrid modulation method for realizing direct power distribution of a single-stage multi-port inverter, and the method comprises the steps: firstly obtaining an AC side reference voltage of the single-stage multi-port inverter in a static coordinate system and an output reference power of a photovoltaic unit; then synthesizing a reference voltage through a virtual two-level model under a space vector framework to realize voltage construction, and generating a three-phase duty ratio; establishing a quantitative relation model of photovoltaic port power and a zero-sequence component under a carrier framework, determining the injected zero-sequence component, injecting the zero-sequence component to a three-phase duty ratio, and directly splitting at a voltage ratio to obtain a three-phase duty ratio of a split switch tube; and finally, comparing the split three-phase duty ratio with a carrier wave to generate a driving signal of a switching tube of the single-stage multi-port inverter, controlling an active device to perform switching operation, and outputting voltage and power.

Description

Technical Field

[0001] The present invention belongs to the technical field of power distribution modulation of single-stage multi-port inverters, and more particularly, relates to a hybrid modulation method for realizing direct power distribution of single-stage multi-port inverters. Background Art

[0002] For remote areas such as plateaus, border areas, and isolated islands, where public power grids are inaccessible, multi-source integrated island microgrids have become a key technology for electrifying these regions. Among the numerous multi-source integrated solutions, the combination of photovoltaics and energy storage has attracted widespread attention due to its advantages in cost and power generation efficiency. To leverage these advantages, a large number of topologies have been proposed to interconnect photovoltaics, energy storage, and AC loads in microgrids. Among them, the two-stage topology is widely used, but it requires multi-stage energy transmission and bulky filters, resulting in low efficiency and high cost. In contrast, the single-stage multi-port inverter eliminates the DC conversion stage, enabling single-stage energy transmission from the source to the load, offering advantages such as high efficiency and low cost.

[0003] The design of modulation schemes for single-stage, multi-port inverters faces two major challenges. First, the inherent imbalance of port voltages complicates reference voltage synthesis. Second, the need to simultaneously achieve reference voltage synthesis and DC port power distribution within limited degrees of freedom. Existing schemes often synthesize reference voltage vectors within a space vector framework to construct AC voltages and indirectly adjust redundant vectors to achieve port power distribution. This results in heavy computational burden, low efficiency, and high power ripple. Therefore, a modulation method with low computational burden, high efficiency, and direct power distribution is urgently needed. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a hybrid modulation method for realizing direct power distribution of a single-stage multi-port inverter. By combining the advantages of the space vector framework and the carrier framework, the present invention solves the technical problems of the existing technology in realizing AC voltage construction and port power distribution under a single space vector framework, such as heavy computational burden, low efficiency, and large power ripple.

[0005] To achieve the above-mentioned object of the invention, the present invention provides a hybrid modulation method for implementing direct power distribution of a single-stage multi-port inverter, characterized by comprising the following steps:

[0006] (1) Obtain the AC side reference voltage of the single-stage multi-port inverter in the stationary coordinate system Obtain the output reference power of the photovoltaic unit through the power management module

[0007] (2) Under the space vector framework, the voltage is constructed by synthesizing the reference voltage through the virtual two-level model and generating the three-phase duty cycle dx , x=a, b, c represents the three phases of the power grid;

[0008] (3) Establishing the photovoltaic port power P under the carrier framework H A quantitative relationship model with the zero-sequence component d0 is used to determine the injected zero-sequence component d0;

[0009] (4) Inject the determined zero sequence component d0 into the three-phase duty cycle d x , and then directly split at the voltage ratio ζ to obtain the three-phase duty ratio d′ of the first switch tube and the second switch tube after splitting x1 , d′ x2 ;

[0010] (5) The three-phase duty ratio d′ x1 , d′ x2 The signal is compared with the carrier wave to generate the driving signal of the switch tube of the single-stage multi-port inverter, control the active device to perform switching operation, and output voltage and power to realize the establishment of the island microgrid.

[0011] The object of the invention of the present invention is achieved like this:

[0012] The present invention discloses a hybrid modulation method for realizing direct power distribution of a single-stage multi-port inverter. The method comprises the following steps: first, obtaining an AC side reference voltage of the single-stage multi-port inverter and an output reference power of a photovoltaic unit in a stationary coordinate system; then, synthesizing the reference voltage through a virtual two-level model in a space vector framework to realize voltage construction and generate a three-phase duty cycle; then, establishing a quantitative relationship model between photovoltaic port power and a zero-sequence component in a carrier framework, determining the injected zero-sequence component, and injecting it into the three-phase duty cycle; and obtaining the three-phase duty cycle of a switch tube after the splitting by directly splitting the zero-sequence component at the voltage ratio; finally, comparing the split three-phase duty cycle with the carrier to generate a drive signal for the switch tube of the single-stage multi-port inverter, controlling the active device to perform switching operations, and outputting voltage and power.

[0013] At the same time, the hybrid modulation method for realizing direct power distribution of a single-stage multi-port inverter of the present invention also has the following beneficial effects:

[0014] (1) The present invention uses a virtual two-level model in the space vector framework to realize AC voltage construction, while ensuring high voltage utilization on the DC side, simplifying the reference voltage vector synthesis;

[0015] (2) The present invention uses the three-phase duty ratio d′ after splitting under the carrier frame. x1 , d′ x2 Direct power allocation avoids the heavy computational burden and slow dynamic response caused by indirect adjustment of redundant vectors in the space vector framework, improving power allocation performance and enhancing system efficiency by leveraging the discontinuous nature of the duty cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a flow chart of a hybrid modulation method for achieving direct power distribution of a single-stage multi-port inverter according to the present invention;

[0017] Figure 2 This is a block diagram of the overall control and hybrid modulation scheme for achieving direct power distribution of a single-stage multi-port inverter according to the present invention;

[0018] Figure 3 is a schematic diagram of a virtual two-level model;

[0019] Figure 4 It is a schematic diagram of duty cycle waveform splitting;

[0020] Figure 5 is a schematic diagram of duty cycle distribution of the first switching tube and the second switching tube;

[0021] Figure 6 This is the experimental diagram of the steady-state performance of a single-stage multi-port inverter at different port voltages;

[0022] Figure 7 It is a dynamic performance diagram of a single-stage multi-port inverter at given values ​​of output power at different ports;

[0023] Figure 8 This is a comparison chart of the power control performance of the present invention and the traditional solution;

[0024] Figure 9 This is a comparison chart of the computational burden of the present invention and the traditional solution;

[0025] Figure 10 This is a comparison chart of the conversion efficiency of the present invention and the traditional solution. DETAILED DESCRIPTION

[0026] 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 noted that in the following description, when detailed descriptions of known functions and designs may dilute the main content of the present invention, such descriptions will be omitted here.

[0027] Example

[0028] In this embodiment, Figure 2 This is a block diagram of the overall control and hybrid modulation scheme for achieving direct power distribution of a single-stage multi-port inverter. Figure 2 The present invention provides a hybrid modulation method for realizing direct power distribution of a single-stage multi-port inverter in detail. Figure 1 As shown, the specific steps include:

[0029] S1. Obtain the AC side reference voltage of the single-stage multi-port inverter in the stationary coordinate system Obtain the output reference power of the photovoltaic unit through the power management module

[0030] In this embodiment, the AC side reference voltage The specific method to obtain is:

[0031] S1.1. Collect the grid-side voltage V of the single-stage multi-port inverter gx and current I gx , then calculate the active power P and reactive power Q on the grid side of the single-stage multi-port inverter through the power calculation module;

[0032] S1.2. Input the active power P and reactive power Q into the droop control loop to generate a voltage signal and obtain the phase angle θ of the voltage signal; then pass the voltage signal through the cascaded voltage and current PI control loop to obtain the AC side reference voltage in the rotating dq coordinate system.

[0033] In this embodiment, the voltage signal is first sent to the voltage PI control loop, and the current loop reference I is generated through PI control. ref_dq , and then send this reference signal into the current PI control loop to perform negative feedback PI control similar to the voltage loop to obtain the reference voltage signal V ref_dq ;

[0034] S1.3, through T1 coordinate transformation, the AC side reference voltage in the rotation dq coordinate system is becomes the reference voltage in the stationary αβ coordinate system

[0035] Among them, the transformation formula of the T1 coordinate transformation unit is:

[0036]

[0037] S1.4. Monitor the status of the photovoltaic and energy storage units through the power management module to generate the output reference power of the photovoltaic unit

[0038] S2, in the space vector framework, the reference voltage is synthesized by the virtual two-level model to realize voltage construction and generate the three-phase duty cycle d x , x=a, b, c represents the three phases of the power grid, which simplifies the reference vector synthesis under unbalanced power grid voltage and reduces the amount of calculation;

[0039] S2.1. Equivalently convert the single-stage multi-port inverter into a virtual two-level inverter, such as Figure 3As shown, the virtual basic voltage vector of the virtual two-level inverter is then divided into 6 sectors F1 to F6, as follows:

[0040]

[0041] S2.2. Determine the reference voltage vector based on the phase angle θ In the corresponding sector, two adjacent basic voltage vectors and zero vector are selected to synthesize the reference voltage vector V ref_αβ , then solve for the reference voltage vector V ref_αβ The corresponding volt-second balance equation gives the three-phase duty cycle d x ;

[0042] Among them, the reference voltage vector The volt-second balance equation corresponding to the sector is:

[0043] First sector:

[0044]

[0045] Second sector:

[0046]

[0047] The third sector:

[0048]

[0049] The fourth sector:

[0050]

[0051] Fifth sector:

[0052]

[0053] Sector 6:

[0054]

[0055] Among them, T s is the sampling period, T0 is the duration of the zero vector, T1 and T2 are the durations of two adjacent basic voltage vectors respectively.

[0056] S3. Establishing photovoltaic port power P under the carrier framework H The quantitative relationship model with the zero-sequence component d0 is used to determine the injected zero-sequence component d0;

[0057] S3.1, under the carrier frame, according to the three-phase duty cycle d a d b d cThe size relationship is divided into 6 areas A1-A6;

[0058] Among them, if d a >d b >d c , it is divided into area A1;

[0059] If d b >d a >d c , then it is divided into area A2;

[0060] If d b >d c >d a , then it is divided into area A3;

[0061] If d c >d b >d a , then it is divided into area A4;

[0062] If d c >d a >d b , then it is divided into area A5;

[0063] If d a >d c >d b , then it is divided into area A6;

[0064] S3.2. Add the zero-sequence component d0 to the three-phase duty cycle to generate the three-phase duty cycle d′ after the zero-sequence component is injected. a , d′ b , d′ c ;

[0065]

[0066] S3.3. Calculate the voltage ratio ζ;

[0067] ζ=V L / V H

[0068] Among them, V L is the energy storage port voltage, V H is the PV port voltage;

[0069] S3.4. In each region, according to the three-phase duty cycle waveform d′ a , d′ b , d′ c and voltage ratio ζ=V L / V H The relationship between the size of the photovoltaic port power P H Quantitative relationship model with zero sequence component d0;

[0070] The quantitative relationship model established in the first area A1 is:

[0071] When d′ a ≥d′ b ≥d′ c When ≥ζ, P H =V H (i ga d a +i gb d b +i gc d c );

[0072] When d′ a ≥d′ b ≥ζ≥d′ c hour,

[0073] When d′ a ≥ζ≥d′ b ≥d′ c hour,

[0074] When ζ>d′ a ≥d′ b ≥d′ c When P H =0;

[0075] The quantitative relationship model established in the second area A2 is:

[0076] When d′ b ≥d′ a ≥d′ c When ≥ζ, P H =V H (i ga d a +i gb d b +i gc d c );

[0077] When d′ b ≥d′ a ≥ζ≥d′ c hour,

[0078] When d′ b ≥ζ≥d′ a ≥d′ c hour,

[0079] When ζ>d′ b ≥d′ a≥d′ c When P H =0;

[0080] The quantitative relationship model established in the third area A3 is:

[0081] When d′ b ≥d′ c ≥d′ a When ≥ζ, P H =V H (i ga d a +i gb d b +i gc d c );

[0082] When d′ b ≥d′ c ≥ζ≥d′ a hour,

[0083] When d′ b ≥ζ≥d′ c ≥d′ a hour,

[0084] When ζ>d′ b ≥d′ c ≥d′ a When P H =0;

[0085] The quantitative relationship model established in the fourth area A4 is:

[0086] When d′ c ≥d′ b ≥d′ a When ≥ζ, P H =V H (i ga d a +i gb d b +i gc d c );

[0087] When d′ c ≥d′ b ≥ζ≥d′ a hour,

[0088] When d′ c ≥ζ≥d′ b ≥d′ a hour,

[0089] When ζ>d′ c ≥d′ b ≥d′ a When P H =0;

[0090] The quantitative relationship model established in the fifth area A5 is:

[0091] When d′ c ≥d′ a ≥d′ b When ≥ζ, P H =V H (i ga d a +i gb d b +i gc d c );

[0092] When d′ c ≥d′ a ≥ζ≥d′ b hour,

[0093] When d′ c ≥ζ≥d′ a ≥d′ b hour,

[0094] When ζ>d′ c ≥d′ a ≥d′ b When P H =0;

[0095] The quantitative relationship model established in the sixth area A6 is:

[0096] When d′ a ≥d′ c ≥d′ b When ≥ζ, P H =V H (i ga d a +i gb d b +i gc d c );

[0097] When d′ a ≥d′ c ≥ζ≥d′ b hour,

[0098] When d′ a ≥ζ≥d′ c ≥d′ b hour,

[0099] When ζ>d′ a ≥d′ c ≥d′ b When P H =0.

[0100] S3.5, according to the above three-phase duty cycle d x The output reference power of the photovoltaic unit is divided into areas of different sizes. , three-phase duty cycle d x , three-phase grid-side current i gx , three-phase duty cycle d x , PV port voltage V H , energy storage port voltage V L Input into the quantitative relationship model under the corresponding area, and obtain the required injected zero-sequence component d0 by solving the quantitative relationship model.

[0101] S4, inject the determined zero sequence component d0 into the three-phase duty cycle d x , and then directly split at the voltage ratio ζ to obtain the three-phase duty ratio d′ of the first switch tube and the second switch tube after splitting x1 , d′ x2 ;

[0102] In this embodiment, the duty cycle of the first switch tube is d′ x1 , the second switch duty cycle d′ x2 Satisfy respectively:

[0103]

[0104] In this embodiment, the duty cycle waveform splitting mechanism is as follows Figure 4 As shown, it is not difficult to see that either the duty cycle of the upper switch tube is clamped at 0 or the duty cycle of the lower switch tube is clamped at 1, which means that the duty cycle waveform has a discontinuous characteristic. Therefore, each phase switch tube only operates once in each switching cycle, as shown in Figure 5 As shown, the switching loss is reduced and the system efficiency is improved. x1 , d′ x2 By directly implementing power distribution, the system avoids the heavy computational burden and slow dynamic response caused by indirectly adjusting redundant vectors in the space vector framework. The discontinuous nature of the duty cycle waveform improves system conversion efficiency.

[0105] S5, the three-phase duty cycle d' x1 , d′ x2 Compare with the carrier to generate the driving signal of the single-stage multi-port inverter switch tube, control the active device to perform switching operation, and output voltage and power;

[0106] In this embodiment, the duty cycle d′ of the first switch tube is set to x1 and the duty cycle of the second switch d′ x2 Compare the amplitude with the carrier respectively to obtain the switching signal G x1 , G x2 To drive the first and second switch tubes, wherein the switch signal G x1 Control switch tube S x1 , switching signal G x1 The complementary signal G x3 Control switch tube S x3 , switching signal G x2 Control switch tube S x2 , switching signal G x2 The complementary signal G x4 Control switch tube S x4 ; Among them, S x1 、S x2 、S x3 、S x4 The first switch tube, the second switch tube, the third switch tube and the fourth switch tube correspond to each bridge arm respectively.

[0107] Example verification

[0108] The following describes this embodiment with reference to a specific example. Assume that the voltage of the unidirectional DC source simulating photovoltaic power generation is V H =400V, the voltage of the bidirectional DC source simulating energy storage is v L =160V~240V, the output power of the unidirectional DC source simulating photovoltaic is given as The effective value of the given voltage on the AC side is 110V. Figure 5 The steady-state performance of a single-stage multi-port inverter at different port voltages is demonstrated. The AC side simulates the load through a resistor box, where Figure 6 (a) V L =160V, Figure 6 (b) v L =200V, Figure 6 (c) v L =240V. By observing the line voltage v ab , a phase voltage v an and AC side voltage v ga Current i ga It can be seen that under the power allocation scheme proposed in this embodiment, the single-stage multi-port inverter can stably build an island microgrid, and the voltage of the island microgrid is not affected by the port voltage change.

[0109] like Figure 7As shown in the figure, when the AC side power of the single-stage multi-port inverter is constant at 1000W, the output power given value of the photovoltaic port is changed. When jumping from 800W to 1200W and then back to 800W, it can be seen that the PV port can quickly and accurately track the changes in the power set value, and the grid voltage remains unaffected, which verifies the dynamic performance of the solution. Figure 8 A comparison of the power control performance of the traditional scheme and the proposed scheme is given, and it can be seen that the proposed scheme has a higher quality port power control effect. Figure 9 The computational burden comparison between the proposed scheme and the previous scheme is given, and it can be seen that the proposed scheme significantly reduces the computational burden. Figure 10 The efficiency comparison shown verifies the efficiency improvement brought by the proposed scheme due to the discontinuous duty cycle characteristic.

[0110] Although the above describes the illustrative specific embodiments of the present invention to facilitate 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, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concepts of the present invention are protected.

Claims

1. A hybrid modulation method for achieving direct power distribution of a single-stage multi-port inverter, characterized in that: The following steps are involved: (1) Obtain the AC side reference voltage of the single-stage multi-port inverter in the stationary coordinate system Obtain the output reference power of the photovoltaic unit through the power management module (2) Under the space vector framework, the reference voltage is synthesized by the virtual two-level model to realize voltage construction and generate the three-phase duty cycle d x , x=a, b, c represents the three phases of the power grid; (3) Establishing the photovoltaic port power P under the carrier framework H A quantitative relationship model with the zero-sequence component d0 is used to determine the injected zero-sequence component d0; (4) Inject the determined zero sequence component d0 into the three-phase duty cycle d x , and then directly split at the voltage ratio ζ to obtain the three-phase duty ratio d of the first switch tube and the second switch tube after splitting x ′1, d x '2; (5) Set the three-phase duty cycle d x ′1, d x ′2 is compared with the carrier to generate the driving signal of the single-stage multi-port inverter switch tube, control the active device to perform switching operation, and output voltage and power.

2. A hybrid modulation method for implementing direct power distribution of a single-stage multi-port inverter according to claim 1, characterized in that: The AC side reference voltage The specific method to obtain is: (2.1) Collect the grid-side voltage V of the single-stage multi-port inverter gx and current I gx , then calculate the active power P and reactive power Q on the grid side of the single-stage multi-port inverter through the power calculation module; (2.2) Input the active power P and reactive power Q into the droop control loop to generate a voltage signal and obtain the phase angle θ of the voltage signal; then pass the voltage signal through the cascaded voltage and current PI control loop to obtain the AC side reference voltage in the rotating dq coordinate system (2.3) The AC side reference voltage in the rotated dq coordinate system is transformed by T1 coordinate transformation becomes the reference voltage in the stationary αβ coordinate system (2.4) Monitor the status of the photovoltaic and energy storage units through the power management module to generate the output reference power of the photovoltaic unit 3. The hybrid modulation method for realizing direct power distribution of a single-stage multi-port inverter according to claim 1, characterized in that: The three-phase duty cycle d x The specific generation method is: (3.1) The single-stage multi-port inverter is equivalent to a virtual two-level inverter, and then divided into 6 sectors according to the virtual basic voltage vector of the virtual two-level inverter; (3.2) Determine the reference voltage vector according to the phase angle θ In the corresponding sector, two adjacent basic voltage vectors and zero vector are selected to synthesize the reference voltage vector V ref_αβ , then solve for the reference voltage vector V ref_αβ The corresponding volt-second balance equation gives the three-phase duty cycle d x ; Among them, the reference voltage vector The volt-second balance equation corresponding to the sector is: First sector: Second sector: The third sector: The fourth sector: Fifth sector: Sector 6: Among them, T s is the sampling period, T0 is the duration of the zero vector, T1 and T2 are the durations of two adjacent basic voltage vectors respectively.

4. The hybrid modulation method for realizing direct power distribution of a single-stage multi-port inverter according to claim 1, characterized in that: The photovoltaic port power P is established under the carrier framework H The method of the quantitative relationship model with the zero-sequence component d0 is: (4.1), under the carrier frame, according to the three-phase duty cycle d a d b d c The size relationship is divided into 6 areas A1-A6; Among them, if d a >d b >d c , it is divided into area A1; If d b >d a >d c , then it is divided into area A2; If d b >d c >d a , then it is divided into area A3; If d c >d b >d a , then it is divided into area A4; If d c >d a >d b , then it is divided into area A5; If d a >d c >d b , then it is divided into area A6; (4.2) Add the zero-sequence component d0 to the three-phase duty cycle to generate the three-phase duty cycle d after the zero-sequence component is injected. a ′、d b ′、d c '; (4.3), calculate the voltage ratio ζ; ζ=V L / V H Among them, V L is the energy storage port voltage, V H is the PV port voltage; (4.4), in each region, according to the three-phase duty cycle waveform d a ′、d b ′、d c ′ and voltage ratio ζ=V L / V H The relationship between the size of the photovoltaic port power P H Quantitative relationship model with zero sequence component d0; The quantitative relationship model established in the first area A1 is: When d a ′≥d b ′≥d c When ′≥ζ, P H =V H (i ga d a +i gb d b +i gc d c ); When d a ′≥d b ′≥ζ≥d c 'hour, When d a ′≥ζ≥d b ′≥d c 'hour, When ζ>d a ′≥d b ′≥d c ′, P H =0; The quantitative relationship model established in the second area A2 is: When d b ′≥d a ′≥d c When ′≥ζ, P H =V H (i ga d a +i gb d b +i gc d c ); When d b ′≥d a ′≥ζ≥d c 'hour, When d b ′≥ζ≥d a ′≥d c 'hour, When ζ>d b ′≥d a ′≥d c ′, P H =0; The quantitative relationship model established in the third area A3 is: When d b ′≥d c ′≥d a When ′≥ζ, P H =V H (i ga d a +i gb d b +i gc d c ); When d b ′≥d c ′≥ζ≥d a 'hour, When d b ′≥ζ≥d c ′≥d a 'hour, When ζ>d b ′≥d c ′≥d a ′, P H =0; The quantitative relationship model established in the fourth area A4 is: When d c ′≥d b ′≥d a When ′≥ζ, P H =V H (i ga d a +i gb d b +i gc d c ); When d c ′≥d b ′≥ζ≥d a 'hour, When d c ′≥ζ≥d b ′≥d a 'hour, When ζ>d c ′≥d b ′≥d a ′, P H =0; The quantitative relationship model established in the fifth area A5 is: When d c ′≥d a ′≥d b When ′≥ζ, P H =V H (i ga d a +i gb d b +i gc d c ); When d c ′≥d a ′≥ζ≥d b 'hour, When d c ′≥ζ≥d a ′≥d b 'hour, When ζ>d c ′≥d a ′≥d b ′, P H =0; The quantitative relationship model established in the sixth area A6 is: When d a ′≥d c ′≥d b When ′≥ζ, P H =V H (i ga d a +i gb d b +i gc d c ); When d a ′≥d c ′≥ζ≥d b 'hour, When d a ′≥ζ≥d c ′≥d b 'hour, When ζ>d a ′≥d c ′≥d b ′, P H =0.

5. The hybrid modulation method for realizing direct power distribution of a single-stage multi-port inverter according to claim 1, characterized in that: The specific method for determining the zero-sequence component d0 is: According to the three-phase duty cycle d x The output reference power of the photovoltaic unit is divided into areas of different sizes. Three-phase duty cycle d x , three-phase grid-side current i gx , three-phase duty cycle d x , PV port voltage V H , energy storage port voltage V L Input into the quantitative relationship model under the corresponding area, and obtain the required injected zero-sequence component d0 by solving the quantitative relationship model.

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