Modulation method and device of photovoltaic grid-connected inverter, inverter and storage medium

Abstract

The application relates to a modulation method and device of a photovoltaic grid-connected inverter, an inverter and a storage medium, the modulation method comprising the following steps: under a preset carrier ratio condition, determining a first voltage vector based on collected direct-current bus voltage and three-phase voltage of the inverter; generating a virtual vector based on a basic voltage vector of a preset two-level inverter space vector diagram to obtain a first virtual vector and a second virtual vector; selecting a target vector from the basic voltage vector and the calculated virtual vector, synthesizing a second voltage vector equivalent to the first voltage vector by using the target vector, determining a target switching sequence corresponding to the second voltage vector; determining the duty cycle corresponding to each kind of vector in the corresponding target vector according to the target switching sequence, and modulating the inverter by using the pulse modulation PWM pulse determined by the corresponding duty cycle. Through the application, the problems of high low-order harmonic content and poor inverter output waveform quality of a two-level inverter synchronous modulation method are solved.

Description

Technical Field

[0001] This application relates to the field of inverter control technology, and in particular to a modulation method, device, inverter and storage medium for a photovoltaic grid-connected inverter. Background Technology

[0002] In related technologies, photovoltaic grid-connected inverters, as power conversion mechanisms, play an important role in photovoltaic systems. However, the modulation method of two-level photovoltaic grid-connected inverters suffers from large output harmonics, which can easily lead to increased equipment noise and losses. As the inverter switching frequency decreases, the aforementioned problems will gradually worsen. When the carrier ratio drops to a low level, severe distortion of the inverter output waveform may occur, and even damage to the equipment may result.

[0003] In related technologies, at low switching frequencies, synchronous modulation is used for the modulation of two-level photovoltaic grid-connected inverters to ensure that the inverter output phase voltage meets the requirements of synchronization, three-phase symmetry and half-wave symmetry, thereby suppressing low-order harmonics caused by low switching frequencies. However, because two-level inverters have fewer switching transistors and limited switching states, the inverter's harmonic suppression capability is insufficient, resulting in high low-order harmonic content and poor output waveform quality.

[0004] There is still no effective solution to the problems of high low-order harmonic content and poor inverter output waveform quality in the synchronous modulation method of two-level inverters in related technologies. Summary of the Invention

[0005] This application provides a modulation method, device, inverter, and storage medium for a photovoltaic grid-connected inverter, which at least solves the problems of high low-order harmonic content and poor inverter output waveform quality in the synchronous modulation method of two-level inverters in related technologies.

[0006] In a first aspect, this application provides a modulation method for a photovoltaic grid-connected inverter, used for modulation of a two-level photovoltaic grid-connected inverter. The modulation method includes: under a preset carrier ratio condition, determining a first voltage vector based on the collected DC bus voltage and three-phase voltage of the inverter, wherein the first voltage vector represents a reference voltage vector corresponding to the inverter; generating a virtual vector based on the basic voltage vector of a preset two-level inverter space vector diagram to obtain a first virtual vector and a second virtual vector, wherein the first virtual vector is generated from one of the basic voltage vectors with the same phase, and the second virtual vector is generated based on two adjacent basic voltage vectors, and the phase of the second virtual vector is the average phase of the corresponding two basic voltage vectors. The voltage amplitudes of the first virtual vector and the second virtual vector are M times the voltage amplitude of the basic voltage vector, where M is a preset trigonometric function value. A preset number of target vectors are selected from the basic voltage vector and the operational virtual vectors. A second voltage vector equivalent to the first voltage vector is synthesized using the target vectors, and a target switching sequence corresponding to the second voltage vector is determined. The operational virtual vectors include at least one of the first virtual vector and the second virtual vector, and the target vectors include at least two operational virtual vectors. Based on the target switching sequence, the duty cycle corresponding to each vector in the target vectors is determined, and the inverter is modulated according to the pulse modulation (PWM) pulse determined by the corresponding duty cycle.

[0007] Secondly, this application provides a modulation device for a photovoltaic grid-connected inverter, used for modulation of a two-level photovoltaic grid-connected inverter, comprising:

[0008] The determination module is used to determine a first voltage vector based on the collected DC bus voltage and three-phase voltage of the inverter under a preset carrier ratio condition, wherein the first voltage vector represents the reference voltage vector corresponding to the inverter;

[0009] The generation module is used to generate virtual vectors based on the basic voltage vectors of a preset two-level inverter space vector diagram, to obtain a first virtual vector and a second virtual vector. The first virtual vector is generated from one of the basic voltage vectors with the same phase, and the second virtual vector is generated based on two adjacent basic voltage vectors. The phase of the second virtual vector is the average of the phases of the corresponding two basic voltage vectors. The voltage amplitudes of the first virtual vector and the second virtual vector are M times the voltage amplitude of the basic voltage vector, where M is a preset trigonometric function value.

[0010] A synthesis module is configured to select a preset number of target vectors from the basic voltage vector and the operational virtual vector, synthesize a second voltage vector equivalent to the first voltage vector using the target vectors, and determine the target switching sequence corresponding to the second voltage vector, wherein the operational virtual vector includes at least one of the first virtual vector and the second virtual vector, and the target vector includes at least two of the operational virtual vectors;

[0011] The processing module is configured to determine the duty cycle corresponding to each vector in the target vector according to the target switching sequence, and modulate the inverter according to the pulse modulation (PWM) pulse determined by the corresponding duty cycle.

[0012] Thirdly, this application provides an inverter, including a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other through the communication bus;

[0013] Memory, used to store computer programs;

[0014] When a processor executes a program stored in a memory, it implements the steps of the modulation method described in any embodiment of the first aspect.

[0015] Fourthly, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, implements the steps of the modulation method as described in any embodiment of the first aspect.

[0016] Compared with related technologies, this embodiment provides a modulation method, device, inverter, and storage medium for a photovoltaic grid-connected inverter. Under a preset carrier ratio, based on the collected DC bus voltage and three-phase voltage of the inverter, a first voltage vector is determined. This first voltage vector represents the reference voltage vector corresponding to the inverter. Based on the basic voltage vector of a preset two-level inverter space vector diagram, virtual vectors are generated to obtain a first virtual vector and a second virtual vector. The first virtual vector is generated from a basic voltage vector with the same phase, and the second virtual vector is generated based on two adjacent basic voltage vectors. The phase of the second virtual vector is the average phase of the corresponding two basic voltage vectors. The voltage amplitudes of the first and second virtual vectors are M times the voltage amplitude of the basic voltage vector, where M is a preset trigonometric function value. From the basic voltage vector and the calculated virtual vector... A preset number of target vectors are selected, and a second voltage vector equivalent to the first voltage vector is synthesized using the target vectors. A target switching sequence corresponding to the second voltage vector is determined. The operational virtual vector includes at least one of the first virtual vector and the second virtual vector, and the target vector includes at least two operational virtual vectors. According to the target switching sequence, the duty cycle corresponding to each vector in the target vector is determined, and the inverter is modulated according to the pulse modulation (PWM) pulse determined by the corresponding duty cycle. This solves the problems of high low-order harmonic content and poor inverter output waveform quality in the synchronous modulation method of two-level inverters in related technologies. It realizes the expansion of the space vector of the two-level inverter to the space vector of a three-level inverter. By increasing the vector of the inverter, the nearest three-vector synthesis method is made more accurate, thereby improving the inverter output waveform quality and reducing the beneficial effect of low-order harmonics.

[0017] Details of one or more embodiments of this application are set forth in the following drawings and description to make other features, objects and advantages of this application more readily apparent. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart of the modulation method for a photovoltaic grid-connected inverter provided in the embodiments of this application;

[0021] Figure 2 This is a topology diagram of a two-level photovoltaic grid-connected inverter according to an embodiment of this application;

[0022] Figure 3 This is a spatial vector diagram of a two-level inverter according to an embodiment of this application;

[0023] Figure 4 This is a schematic diagram of a three-level space vector in an embodiment of this application;

[0024] Figure 5 This is a schematic diagram of the equivalent synthesized reference voltage vector in an embodiment of this application;

[0025] Figure 6 This is a control block diagram of the virtual vector modulation method of this application;

[0026] Figure 7 This is a structural block diagram of the modulation device of the photovoltaic grid-connected inverter according to an embodiment of this application;

[0027] Figure 8 This is a schematic diagram of the inverter structure of this application. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] The technical solutions in the embodiments of this application will now be described with reference to the accompanying drawings.

[0030] Figure 1 This is a flowchart illustrating a modulation method for a photovoltaic grid-connected inverter provided in an embodiment of this application. Figure 1 As shown in the figure, this application provides a modulation method for a photovoltaic grid-connected inverter, which includes the following steps:

[0031] Step S101: Under the preset carrier ratio condition, based on the collected DC bus voltage and three-phase voltage of the inverter, determine the first voltage vector, wherein the first voltage vector represents the reference voltage vector corresponding to the inverter.

[0032] Step S102: Based on the basic voltage vector of the preset two-level inverter space vector diagram, virtual vectors are generated to obtain a first virtual vector and a second virtual vector. The first virtual vector is generated by a basic voltage vector with the same phase, and the second virtual vector is generated based on two adjacent basic voltage vectors. The phase of the second virtual vector is the average of the phases of the corresponding two basic voltage vectors. The voltage amplitude of the first virtual vector and the second virtual vector is M times the voltage amplitude of the basic voltage vector, where M is a preset trigonometric function value.

[0033] Step S103: Select a preset number of target vectors from the basic voltage vector and the operational virtual vector, synthesize a second voltage vector equivalent to the first voltage vector using the target vectors, and determine the target switching sequence corresponding to the second voltage vector. The operational virtual vector includes at least one of the first virtual vector and the second virtual vector, and the target vector includes at least two operational virtual vectors.

[0034] Step S104: Based on the target switching sequence, determine the duty cycle corresponding to each vector in the target vector, and modulate the inverter according to the pulse modulation PWM pulse determined by the corresponding duty cycle.

[0035] Through steps S101 to S104 above, under a preset carrier ratio, a first voltage vector is determined based on the acquired DC bus voltage and three-phase voltage of the inverter. The first voltage vector represents the reference voltage vector corresponding to the inverter. Based on the basic voltage vector of the preset two-level inverter space vector diagram, virtual vectors are generated to obtain a first virtual vector and a second virtual vector. The first virtual vector is generated from a basic voltage vector with the same phase, and the second virtual vector is generated based on two adjacent basic voltage vectors. The phase of the second virtual vector is the average phase of the corresponding two basic voltage vectors. The voltage amplitudes of the first and second virtual vectors are M times the voltage amplitude of the basic voltage vectors, where M is a preset trigonometric function value. A preset number of target vectors are selected from the basic voltage vectors and the calculated virtual vectors. A second voltage vector equivalent to the first voltage vector is synthesized using the target vector, and the target switching sequence corresponding to the second voltage vector is determined. The computational virtual vector includes at least one of the first virtual vector and the second virtual vector, and the target vector includes at least two computational virtual vectors. Based on the target switching sequence, the duty cycle corresponding to each vector in the target vector is determined, and the inverter is modulated according to the pulse modulation PWM pulse determined by the corresponding duty cycle. This solves the problems of high low-order harmonic content and poor inverter output waveform quality in the synchronous modulation method of two-level inverters in related technologies. It realizes the expansion of the space vector of two-level inverters to the space vector of three-level inverters. By increasing the vector of the inverter, the nearest three-vector synthesis method is made more accurate, thereby improving the inverter output waveform quality and reducing the beneficial effect of low-order harmonics.

[0036] In step S101 of this embodiment, the preset carrier ratio condition is low switching frequency and low carrier ratio.

[0037] In step S102 of this embodiment, synthesizing a reference voltage vector from the DC bus voltage and three-phase voltage means converting the corresponding inverter control parameters into a given reference value. Simultaneously, since the reference voltage vector cannot directly control the inverter's switching action, it is necessary to use a basic voltage vector and a virtual vector that can characterize the inverter's switching to equivalently control the inverter's switching, thereby controlling the inverter's switching and achieving the purpose of controlling the inverter system's output waveform. This process is called modulation. Because the basic voltage vector (reference) of the two-level inverter space vector diagram... Figure 3 The number of basic voltage vectors (V0 to V7) is relatively small, and these few basic voltage vectors cannot participate in the synthesis of all first voltage vectors (reference voltage vectors) in the space vector diagram. That is, when the first voltage vector is located in a specific sector of the two-level inverter space vector diagram (including sectors I to VI), such as the high-modulation region (the area near the outer edge of each sector), the designable switching sequences are limited, making it impossible to control all switching combinations of the inverter or to accurately approximate the first voltage vector. Based on this, by subdividing the two-level inverter space vector diagram into sectors, a quasi-three-level space vector diagram (reference voltage vector) is formed. Figure 4 The number of sectors has been increased from 6 to 24. Virtual vectors (corresponding to the first and second virtual vectors) are set at the sector boundaries after subdivision. This allows for an equivalent replacement of the first voltage vector based on the basic voltage vector and the newly added virtual vectors. It also enables more accurate synthesis when synthesizing the reference voltage vector, improving the synthesis accuracy of the first voltage vector. Simultaneously, the newly added first virtual vector (reference...) Figure 4 V8-V 13 ) and the second virtual vector (reference) Figure 4 V in 14 -V 19 ) and the fundamental voltage vector (reference) Figure 4 The values ​​of V0-V7 in the vector are directly related. For example, the magnitude of the basic voltage vector has a typical numerical multiple relationship with the magnitude and phase of the first and second virtual vectors (such as typical trigonometric function values), which facilitates the calculation of trigonometric functions. In this embodiment, the first virtual vector is generated from a basic voltage vector with the same phase (see reference). Figure 4 V1 and V8, V2 and V9, V3 and V 10 V4 and V 11 V5 and V 12 V6 and V 13The voltage amplitude of the first virtual vector is M times that of the corresponding basic voltage vector, where M is a preset trigonometric function value, preferably M = 1 / 2; the second virtual vector is generated based on two adjacent basic voltage vectors (see reference). Figure 4 In the context of V1 and V2, V2 and V3, V3 and V4, V4 and V5, V5 and V6, and V6 and V1, the phase of the second virtual vector is the average phase of the corresponding two basic voltage vectors, and the voltage amplitude of the second virtual vector is M times the voltage amplitude of the basic voltage vectors, preferably...

[0038] In step S102 of this embodiment, the space vector diagram of the two-level inverter (e.g.) Figure 3 As shown, its corresponding spatial vector diagram is divided into six sectors: sector I to sector VI. The basic voltage vectors are V0-V7, where V0 and V7 are zero vectors, and V1-V6 are valid vectors. Each vector also has a corresponding switching state, with each switching state having two states: "1" and "0". This is mapped to... Figure 2 In the middle, they correspond to respectively Figure 2 Three-phase switching devices (switching transistor S) A S B S C The first switching transistor S) x1 The opening or closing of (x = A, B, C), that is, when S x1 When activated, the switch state is "1". When S x1 When switched off, the switch state is "0". Taking the effective vector V1 as an example, when the switch state is 100, it represents... Figure 1 S in the middle A phase A1 Activation, S A2 Turn off, S phase B B1 Off, S B2 Activation, C-phase S C1 Off, S C2 Once activated, the status of other vector switches follows the same principle.

[0039] In step S102 of this embodiment, in the three-level space vector diagram (e.g.) Figure 4 As shown, its corresponding spatial vector diagram is divided into 24 sectors, where V0-V7 are all basic voltage vectors, and V8-V... 13 V is the first virtual vector corresponding to the newly added virtual vector. 14 -V 19 This is the second virtual vector corresponding to the newly added virtual vector; for example... Figure 4 As shown in the diagram, taking sector I as an example, after adding a virtual vector, the original sector can be divided into 4 smaller sectors; when the reference vector is in a certain smaller sector, it can be determined by the virtual voltage vector (reference... Figure 5 Vref θ is V ref The angle between the horizontal axis and the fundamental voltage vector acts together with the reference voltage vector V. ref Approximate equivalent synthesis is performed to improve synthesis accuracy and output waveform quality, and reduce low-order harmonics.

[0040] In this embodiment, reference Figure 4 and Figure 5 and based on Figure 3 As can be seen from the switching state of the basic voltage vector in the two-level inverter space vector diagram, the newly added first and second virtual vectors can be represented by the following formula:

[0041]

[0042] Wherein, virtual vector V 14 The switching action is a combination of the actions of the two basic voltage vectors, which is synthesized from the two basic voltage vectors. Correspondingly, in the inverter, the switching state is: 100→110, as shown below. Figure 2 As shown, "100" refers to phase S of the inverter A. A1 Activate, S A2 Turn off, phase B S B1 Shutdown, S B2 Activation, C-phase S C1 Shutdown, S C2 After activation and a corresponding time has elapsed, switch to "110", which is the inverter's A phase S. A1 Activate, S A2 Turn off, phase B S B1 Activate, S B2 Turn off, C phase S C1 Shutdown, S C2 The activation process corresponds to the second virtual vector V. 14 The complete switching action, with its respective turn-on and turn-off times, is calculated using the subsequent volt-second balance formula. In this embodiment, compared to the first and second virtual vectors, the effective basic voltage vector is the original vector in the two-level inverter space vector diagram, such as V1, whose state is represented as 100. The inverter A phase S... A1 Activate, S A2 Turn off, phase B S B1 Shutdown, S B2 Activation, C-phase S C1 Shutdown, S C2The activation process requires only this one action, and the switching time is also calculated using the volt-second balance equation. For V8 and V9, they are not formed by combining two basic voltage vectors, but rather by proportional coefficients of a single basic voltage vector, such as V1 and V8. For the first virtual vector V8, its switching action is the same as the basic voltage vector V1, such as 100, but when calculating the volt-second balance equation, its first phase is the same as V1, and its voltage amplitude is reduced by 1 / 2. It should be noted that for other sectors (e.g., sectors II to VI), the generated first and second virtual vectors can be generated in the same way, but the corresponding basic voltage vectors used will be different.

[0043] In step S103 of this embodiment, selecting a target vector from the basic voltage vector and the operational virtual vector including at least one of the first virtual vector and the second virtual vector is to obtain the three vectors closest to the first voltage vector, so as to achieve the minimum comprehensive error voltage and the higher waveform quality when the reference voltage vector is synthesized from the three closest vectors; in this embodiment, the corresponding first virtual vector and second virtual vector are generated, and as shown in the figure... Figure 4 Following the three-level space vector diagram shown, each sub-sector (e.g.: Figure 4 Sector ④ in the diagram will correspond to a set of target vectors (the target vectors corresponding to sector ④ are: basic voltage vector V2, first virtual vector V9, and second virtual vector V). 14 The target vectors selected from the basic voltage vectors and operational virtual vectors are determined by determining the sub-sector in which the first voltage vector is located. Of course, in other optional embodiments, the target vectors in this embodiment can also be determined by other methods of determining the three nearest vectors. In this embodiment, the corresponding target vectors include at least two operational virtual vectors; specifically, they can be three operational virtual vectors. For example, the target vectors corresponding to sector ② are: V8, V9, and V... 14 It can also be a basic voltage vector and two operational virtual vectors. For example, the target vectors corresponding to sector ③ are: V1, V8, and V. 14 After selecting the target vector, the first voltage vector is equivalently synthesized using the three target vectors, which is represented by a second voltage vector containing the three target vectors. For example, when the first voltage vector is in sector ①, it can be referenced... Figure 5 The f shown is equivalently synthesized;

[0044] In this embodiment, after the equivalent second voltage vector is obtained, it is necessary to determine the target switching sequence corresponding to the second voltage vector. The following states that the number of first voltage vectors N = 4, and the first voltage vector is in... Figure 4 and Figure 5 Taking sector ① (where the first voltage vector is in low-level mode) as an example, the set second voltage vector Vref The corresponding switching sequences are described below, with reference to the table below (where the on state in the switching sequence is represented by the corresponding virtual vector and / or basic voltage vector):

[0045]

[0046] In this embodiment, synchronous modulation under low switching frequency conditions is considered. This requires the inverter output phase voltage to satisfy synchronization, three-phase symmetry, and half-wave symmetry. Taking sector ① in sector I as an example, the designed switching sequence is shown in the table below (where the corresponding switching state represents the corresponding vector):

[0047]

[0048] After determining the gaze switch sequence corresponding to each second voltage vector, the duty cycle confirmation step S104 of this embodiment can be performed.

[0049] In step S104 of this embodiment, the action time of the corresponding virtual vector and the basic voltage vector in the second voltage vector is determined by the volt-second balance equation based on the target switching sequence. That is, the action time of the switching state corresponding to each vector is determined, thereby determining the PWM waveform for inverter control, so as to accurately control the inverter.

[0050] In some embodiments, the virtual vector generation in step S102, based on the basic voltage vector of a preset two-level inverter space vector diagram, yields a first virtual vector and a second virtual vector, which is achieved through the following steps:

[0051] Step 21: Obtain all basic voltage vectors located on the sector boundaries of the two-level inverter space vector diagram.

[0052] Step 22: On each sector boundary line, generate the first virtual vector based on the corresponding basic voltage vector.

[0053] Step 23: Obtain the two basic voltage vectors corresponding to each sector of the two-level inverter space vector diagram, and synthesize the second virtual vector based on the two basic voltage vectors on the first high line corresponding to each sector. The first high line is the high line that passes through the center of the two-level inverter space vector diagram among the high lines corresponding to the sector.

[0054] The above steps involve obtaining all basic voltage vectors located on the sector boundaries of the two-level inverter space vector diagram; generating a first virtual vector based on the corresponding basic voltage vector on each sector boundary line; obtaining two basic voltage vectors corresponding to each sector of the two-level inverter space vector diagram; and synthesizing a second virtual vector based on the corresponding two basic voltage vectors on the first high line corresponding to each sector. The first high line is the high line that passes through the center of the two-level inverter space vector diagram among the high lines corresponding to the sector. This achieves the generation of the first and second virtual vectors based on voltage vectors, thereby satisfying the requirement to add new virtual vectors. This expands the two-level inverter space vector diagram to a three-level-like space vector diagram, improves the modulation accuracy of the two-level inverter, and broadens the set of switching states and switching sequences.

[0055] In some embodiments, step S101, under a preset carrier ratio condition, determines the first voltage vector based on the collected DC bus voltage and three-phase voltage of the inverter, which is achieved through the following steps:

[0056] Step 31: Acquire the DC bus voltage and three-phase voltage, and convert the DC bus voltage and three-phase voltage into the first voltage signal and the second voltage signal in the preset static coordinate system, respectively;

[0057] Step 32: Based on the first voltage signal and the second voltage signal, generate a first voltage vector, wherein,

[0058] Calculate the first voltage amplitude corresponding to the first voltage vector using the following formula:

[0059]

[0060] Where V ref Let |V be the first voltage vector. ref | represents the first voltage amplitude, V α The first voltage signal, V β This is the second voltage signal;

[0061] Calculate the first phase θ corresponding to the first voltage vector using the following formula. n :

[0062]

[0063] By acquiring the DC bus voltage and three-phase voltage in the above steps, and converting the DC bus voltage and three-phase voltage into a first voltage signal and a second voltage signal in a preset static coordinate system, respectively; and generating a first voltage vector based on the first voltage signal and the second voltage signal, the conversion of the three-phase voltage of the inverter's three-phase switching devices into the corresponding reference voltage vector is realized, thereby realizing the equivalent synthesis of the corresponding reference voltage vector and further realizing the synchronous modulation control of the inverter.

[0064] In this embodiment, based on the judgment V ref The first voltage amplitude and the first phase θ n This determines its sector I-sector VI; after further subdividing sector I-sector VI, it is necessary to determine its sector V. ref The modulation index determines the sub-sector in which it is located. Therefore, after calculating the first voltage amplitude and the first phase, it is also necessary to calculate the corresponding modulation index based on the first voltage amplitude and the DC bus voltage.

[0065] In some optional implementations, the first modulation index corresponding to the first voltage vector is calculated based on the first voltage amplitude corresponding to the first voltage vector, and this is achieved through the following steps:

[0066] Calculate the first modulation index m corresponding to the first voltage vector using the following formula:

[0067]

[0068] Among them, V dc The DC bus voltage is |V ref | represents the first voltage amplitude.

[0069] In some embodiments, the synthesis of a second voltage vector equivalent to the first voltage vector using the basic voltage vector and two operational virtual vectors in step S103 is achieved through the following steps:

[0070] Step 41: Based on the basic voltage vector, the first virtual vector, and the second virtual vector, convert the two-level inverter space vector diagram into a three-level analog space vector diagram, and determine the large sector corresponding to the three-level analog space vector diagram and the sub-sector corresponding to each large sector. Each sub-sector corresponds to a set of target vectors.

[0071] In this embodiment, based on the basic voltage vector, the first virtual vector, and the second virtual vector, the conversion from a two-level inverter space vector diagram to a three-level-like space vector diagram is realized. When the two-level inverter space vector diagram corresponds to only six sectors, the sectors are subdivided into at least 24 sub-sectors. When the first voltage vector is in any sector, the newly added first virtual vector and the second virtual vector are combined with the original basic voltage vector to perform equivalent synthesis, which can further improve the inverter output waveform quality.

[0072] In this embodiment, after generating the three-level spatial vector diagram, each sub-sector is configured with a target vector for equivalent synthesis of the first voltage vector. Thus, as long as the sub-sector corresponding to the first voltage vector is determined, the corresponding target vector can be obtained quickly. Based on the equivalent synthesis of the first voltage vector from the nearest three vectors, the inverter's overall error voltage is minimized, resulting in higher waveform quality.

[0073] Step 42: Calculate the first modulation degree corresponding to the first voltage vector based on the first voltage amplitude corresponding to the first voltage vector, and determine the first sub-sector corresponding to the sub-sector in the three-level analog space vector diagram based on the first modulation degree and the first phase.

[0074] Step 43: Based on the determined first sub-sector, select the corresponding target vector from the three-level space vector diagram to synthesize the second voltage vector based on the target vector.

[0075] Through the steps described above, based on the basic voltage vector, the first virtual vector, and the second virtual vector, the two-level inverter space vector diagram is converted into a three-level analog space vector diagram. The large sectors corresponding to the three-level analog space vector diagram and the sub-sectors corresponding to each large sector are determined, with each sub-sector corresponding to a set of target vectors. Based on the first voltage amplitude corresponding to the first voltage vector, the first modulation index corresponding to the first voltage vector is calculated. Based on the first modulation index and the first phase, the first sub-sector corresponding to the sub-sector where the first voltage vector is located in the three-level analog space vector diagram is determined. Based on the determined first sub-sector, the corresponding target vector is selected from the three-level analog space vector diagram to synthesize the second voltage vector. This achieves the selection of the target vectors, i.e., the basic voltage vector and virtual vector used for equivalent synthesis. Furthermore, by subdividing the sectors, when the first voltage vector is in any sector, the newly added first and second virtual vectors, together with the original basic voltage vector, perform accurate equivalent synthesis, improving the inverter output waveform quality.

[0076] In some embodiments, step S104, which involves determining the duty cycle corresponding to each vector in the target vector based on the target switching sequence, and modulating the inverter according to the pulse modulation (PWM) pulse determined by the corresponding duty cycle, is achieved through the following steps:

[0077] Step 51: Calculate the duty cycle of each vector in the target vector using the following volt-second balance equation;

[0078]

[0079] Among them, V ref Let T be the first voltage vector. s V is the unit sampling time. x V y V z Each of these corresponds to one of the target vectors, with T0, T1, and T2 representing V respectively. x V y V z The duty cycle of the corresponding vector;

[0080] Step 52: Generate corresponding PWM pulses based on T0, T1, and T2, and modulate the inverter with PWM pulses.

[0081] It should be noted that those skilled in the art should understand that after equivalently synthesizing the first voltage vector and determining the corresponding switching sequence, calculating the duty cycle of each vector in the target vector based on the volt-second balance equation and modulating the inverter based on the duty cycle are techniques well known to those skilled in the art. Based on the above, those skilled in the art can realize the control of the inverter, and the relevant control process will not be described in detail here.

[0082] Figure 6 This is a control block diagram of the virtual vector modulation method of this application. In some alternative embodiments, it is also based on... Figure 6 The control block diagram shown modulates and controls a two-level photovoltaic grid-connected inverter, where V A V B V C For the sampled three-phase voltage, V dc T0 represents the DC bus voltage, and T1, T2 represent the duration of action of each vector participating in the approximate synthesis of the second voltage vector, i.e., the corresponding duty cycle.

[0083] This embodiment also provides a modulation device for a photovoltaic grid-connected inverter, which is used to implement the above embodiments and preferred embodiments; details already described will not be repeated. The terms "module," "unit," "subunit," etc., used below refer to combinations of software and / or hardware that achieve a predetermined function. Although the device described in the following embodiments is preferably implemented in software, hardware implementation, or a combination of software and hardware, is also possible and contemplated.

[0084] Figure 7This is a structural block diagram of the modulation device of the photovoltaic grid-connected inverter according to an embodiment of this application, as shown below. Figure 7 As shown, the device includes:

[0085] The determination module 71 is used to determine a first voltage vector based on the collected DC bus voltage and three-phase voltage of the inverter under a preset carrier ratio condition, wherein the first voltage vector represents the reference voltage vector corresponding to the inverter;

[0086] The generation module 72, coupled to the determination module 71, is used to generate virtual vectors based on the basic voltage vectors of the preset two-level inverter space vector diagram, to obtain a first virtual vector and a second virtual vector. The first virtual vector is generated from a basic voltage vector with the same phase, and the second virtual vector is generated based on two adjacent basic voltage vectors. The phase of the second virtual vector is the average of the phases of the corresponding two basic voltage vectors. The voltage amplitudes of the first virtual vector and the second virtual vector are M times the voltage amplitudes of the basic voltage vectors, where M is a preset trigonometric function value.

[0087] The synthesis module 73, coupled to the generation module 72, is used to select a preset number of target vectors from the basic voltage vector and the operational virtual vector, synthesize a second voltage vector equivalent to the first voltage vector using the target vectors, and determine the target switching sequence corresponding to the second voltage vector. The operational virtual vector includes at least one of the first virtual vector and the second virtual vector, and the target vector includes at least two operational virtual vectors.

[0088] The processing module 74, coupled to the synthesis module 73, is used to determine the duty cycle of each vector in the target vector according to the target switching sequence, and to modulate the inverter according to the pulse modulation PWM pulse determined by the corresponding duty cycle.

[0089] The modulation device of the photovoltaic grid-connected inverter in this application embodiment, under a preset carrier ratio condition, determines a first voltage vector based on the collected DC bus voltage and three-phase voltage of the inverter. The first voltage vector represents the reference voltage vector corresponding to the inverter. Based on the basic voltage vector of the preset two-level inverter space vector diagram, virtual vectors are generated to obtain a first virtual vector and a second virtual vector. The first virtual vector is generated from a basic voltage vector with the same phase, and the second virtual vector is generated based on two adjacent basic voltage vectors. The phase of the second virtual vector is the average phase of the corresponding two basic voltage vectors. The voltage amplitude of the first virtual vector and the second virtual vector is M times the voltage amplitude of the basic voltage vector, where M is a preset trigonometric function value. A preset number of target vectors are selected from the basic voltage vector and the calculated virtual vector. The method involves synthesizing a second voltage vector equivalent to the first voltage vector using the target vector, and determining the target switching sequence corresponding to the second voltage vector. The computational virtual vector includes at least one of the first and second virtual vectors, and the target vector includes at least two computational virtual vectors. Based on the target switching sequence, the duty cycle corresponding to each vector in the target vector is determined, and the inverter is modulated using a pulse modulation (PWM) pulse determined by the corresponding duty cycle. This addresses the issues of high low-order harmonic content and poor inverter output waveform quality in the synchronous modulation method for two-level inverters in related technologies. It extends the space vector of a two-level inverter to a space vector similar to a three-level inverter. By increasing the inverter's vectors, the closest three-vector synthesis method becomes more accurate, thereby improving the inverter output waveform quality and reducing the beneficial effects of low-order harmonics.

[0090] In some embodiments, the generation module 73 further includes:

[0091] The first acquisition unit is used to acquire all basic voltage vectors located on the sector boundary lines of the two-level inverter space vector diagram.

[0092] The first generation unit, coupled to the first acquisition unit, is used to generate a first virtual vector based on the corresponding basic voltage vector on each sector boundary line;

[0093] The second generation unit, coupled to the first acquisition unit, is used to acquire two basic voltage vectors corresponding to each sector of the two-level inverter space vector diagram, and synthesize a second virtual vector based on the two basic voltage vectors on the first high line corresponding to each sector. The first high line is the high line that passes through the center of the two-level inverter space vector diagram among the high lines corresponding to the sector.

[0094] In some embodiments, the acquisition module 71 further includes:

[0095] The first acquisition unit is used to acquire the DC bus voltage and the three-phase voltage, and convert the DC bus voltage and the three-phase voltage into a first voltage signal and a second voltage signal in a preset static coordinate system, respectively.

[0096] The third generation unit, coupled to the first acquisition unit, is used to generate a first voltage vector based on the first voltage signal and the second voltage signal, wherein...

[0097] Calculate the first voltage amplitude corresponding to the first voltage vector using the following formula:

[0098]

[0099] Among them, V ref Let |V be the first voltage vector. ref | represents the first voltage amplitude, V α The first voltage signal, V β This is the second voltage signal;

[0100] Calculate the first phase θ corresponding to the first voltage vector using the following formula. n :

[0101]

[0102] In some embodiments, the synthesis module 73 is further configured to convert a two-level inverter space vector diagram into a three-level analog space vector diagram based on a basic voltage vector, a first virtual vector, and a second virtual vector; determine the large sector corresponding to the three-level analog space vector diagram and the sub-sector corresponding to each large sector, wherein each sub-sector corresponds to a set of target vectors; calculate the first modulation degree corresponding to the first voltage vector based on the first voltage amplitude corresponding to the first voltage vector; and determine the first sub-sector corresponding to the sub-sector where the first voltage vector is located in the three-level analog space vector diagram based on the first modulation degree and the first phase; and filter the corresponding target vectors from the three-level analog space vector diagram based on the determined first sub-sectors to synthesize a second voltage vector based on the target vectors.

[0103] In some embodiments, the synthesis module 73 is further configured to calculate the first modulation index m corresponding to the first voltage vector according to the following formula:

[0104] V dc This is the DC bus voltage.

[0105] In some embodiments, the processing module 71 is further configured to calculate the duty cycle corresponding to each vector in the target vector using the following volt-second balance equation;

[0106]

[0107] Among them, Vref Let T be the first voltage vector. s V is the unit sampling time. x V y V z Each of these corresponds to one of the target vectors, with T0, T1, and T2 representing V respectively. x V y V z The duty cycle of the corresponding vector;

[0108] Based on T0, T1, and T2, corresponding PWM pulses are generated, and the inverter is modulated using PWM pulses.

[0109] Figure 8 This is a schematic diagram of the inverter structure according to an embodiment of this application, as shown below. Figure 8 As shown in the figure, this application provides an inverter, including a processor 81, a communication interface 82, a memory 83, and a communication bus 84, wherein the processor 81, the communication interface 82, and the memory 83 communicate with each other through the communication bus 84.

[0110] Memory 83 is used to store computer programs;

[0111] When processor 81 executes the program stored in memory 83, it implements... Figure 1 The methods and steps in the text.

[0112] The processing implementation in this electronic device Figure 1 The method steps described above, and the resulting technical effects, are the same as those achieved in the embodiments described above. Figure 1 The technical effect of the volume control method is the same as that in the previous example, so it will not be elaborated here.

[0113] The communication bus mentioned in the above electronic devices can be a Peripheral Component Interconnect (PCI) bus or an Extended Industry Standard Architecture (EISA) bus, etc. This communication bus can be divided into address bus, data bus, control bus, etc. For ease of representation, Figure 8 The bus is represented by a single thick line, but this does not mean that there is only one bus or one type of bus.

[0114] The communication interface is used for communication between the aforementioned electronic devices and other devices.

[0115] The memory may include random access memory (RAM) or non-volatile memory, such as at least one disk storage device. Optionally, the memory may also be at least one storage device located remotely from the aforementioned processor.

[0116] The processors mentioned above can be general-purpose processors, including central processing units (CPUs), network processors (NPs), etc.; they can also be digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0117] This application also provides a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the steps of the volume control method provided in any of the foregoing method embodiments.

[0118] In another embodiment provided in this application, a computer program product containing instructions is also provided, which, when run on a computer, causes the computer to perform the steps of any of the volume control methods described in the above embodiments.

[0119] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive elements that are not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0120] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A modulation method for an inverter, used for modulation of a two-level photovoltaic grid-connected inverter, characterized in that, The modulation method includes: Under a preset carrier ratio, a first voltage vector is determined based on the collected DC bus voltage and three-phase voltage of the inverter, wherein the first voltage vector represents the reference voltage vector corresponding to the inverter; Based on the basic voltage vector of the preset two-level inverter space vector diagram, virtual vectors are generated to obtain a first virtual vector and a second virtual vector. The first virtual vector is generated by a basic voltage vector with the same phase, and the second virtual vector is generated based on two adjacent basic voltage vectors. The phase of the second virtual vector is the average of the phases of the corresponding two basic voltage vectors. The voltage amplitude of the first virtual vector and the second virtual vector is M times the voltage amplitude of the basic voltage vector, where M is a preset trigonometric function value. A preset number of target vectors are selected from the basic voltage vector and the operational virtual vector. A second voltage vector equivalent to the first voltage vector is synthesized using the target vectors, and a target switching sequence corresponding to the second voltage vector is determined. The operational virtual vector includes at least one of the first virtual vector and the second virtual vector, and the target vector includes at least two of the operational virtual vectors. Based on the target switching sequence, the duty cycle corresponding to each vector in the target vector is determined, and the inverter is modulated according to the pulse modulation (PWM) pulse determined by the corresponding duty cycle.

2. The modulation method according to claim 1, characterized in that, Based on the basic voltage vector of the preset two-level inverter space vector diagram, virtual vectors are generated to obtain a first virtual vector and a second virtual vector, including: Obtain all the basic voltage vectors located on the sector boundaries of the space vector diagram of the two-level inverter; On each of the sector boundaries, the first virtual vector is generated based on the corresponding basic voltage vector; Obtain the two basic voltage vectors corresponding to each sector of the two-level inverter space vector diagram, and synthesize the second virtual vector based on the two basic voltage vectors on the first high line corresponding to each sector, wherein the first high line is the high line that passes through the center of the two-level inverter space vector diagram among the high lines corresponding to the sector.

3. The modulation method according to claim 2, characterized in that, The M value corresponding to the first virtual vector is 1 / 2, and the M value corresponding to the second virtual vector is...

4. The modulation method according to claim 1, characterized in that, Under a preset carrier ratio, based on the collected DC bus voltage and three-phase voltage of the inverter, a first voltage vector is determined, including: The DC bus voltage and the three-phase voltage are acquired, and the DC bus voltage and the three-phase voltage are converted into a first voltage signal and a second voltage signal in a preset stationary coordinate system, respectively. Based on the first voltage signal and the second voltage signal, the first voltage vector is generated, wherein... The first voltage amplitude corresponding to the first voltage vector is calculated using the following formula: Among them, V ref Let |V be the first voltage vector. ref | represents the first voltage amplitude, V α The first voltage signal, V β This is the second voltage signal; The first phase θ corresponding to the first voltage vector is calculated using the following formula. n :

5. The modulation method according to claim 4, characterized in that, Synthesizing a second voltage vector equivalent to the first voltage vector using the target vector includes: Based on the basic voltage vector, the first virtual vector, and the second virtual vector, the two-level inverter space vector diagram is converted into a three-level-like space vector diagram, and the large sector corresponding to the three-level-like space vector diagram and the sub-sector corresponding to each large sector are determined, wherein each sub-sector corresponds to a set of target vectors; Based on the first voltage amplitude corresponding to the first voltage vector, calculate the first modulation degree corresponding to the first voltage vector, and based on the first modulation degree and the first phase, determine the first sub-sector corresponding to the sub-sector in the three-level space vector diagram where the first voltage vector is located; Based on the determined first sub-sector, the corresponding target vector is selected from the three-level space vector diagram to synthesize the second voltage vector based on the target vector.

6. The modulation method according to claim 5, characterized in that, Based on the first voltage amplitude corresponding to the first voltage vector, calculate the first modulation index corresponding to the first voltage vector, including: The first modulation index m corresponding to the first voltage vector is calculated using the following formula: V dc The DC bus voltage is [value missing].

7. The modulation method according to claim 1, characterized in that, Based on the target switching sequence, determine the duty cycle corresponding to each vector in the target vector, and modulate the inverter according to the pulse modulation (PWM) pulse determined by the corresponding duty cycle, including: The duty cycle corresponding to each of the target vectors is calculated using the following volt-second balance equation; Among them, V ref Let T be the first voltage vector. s V is the unit sampling time. x V y V z Each of these corresponds to one of the target vectors, with T0, T1, and T2 representing V respectively. x V y V z The duty cycle of the corresponding vector; Based on T0, T1, and T2, corresponding PWM pulses are generated, and the inverter is modulated using the PWM pulses.

8. A modulation device for a photovoltaic grid-connected inverter, used for modulation of a two-level photovoltaic grid-connected inverter, characterized in that, include: The determination module is used to determine a first voltage vector based on the collected DC bus voltage and three-phase voltage of the inverter under a preset carrier ratio condition, wherein the first voltage vector represents the reference voltage vector corresponding to the inverter; The generation module is used to generate virtual vectors based on the basic voltage vectors of a preset two-level inverter space vector diagram, to obtain a first virtual vector and a second virtual vector. The first virtual vector is generated from one of the basic voltage vectors with the same phase, and the second virtual vector is generated based on two adjacent basic voltage vectors. The phase of the second virtual vector is the average of the phases of the corresponding two basic voltage vectors. The voltage amplitudes of the first virtual vector and the second virtual vector are M times the voltage amplitude of the basic voltage vector, where M is a preset trigonometric function value. A synthesis module is configured to select a preset number of target vectors from the basic voltage vector and the operational virtual vector, synthesize a second voltage vector equivalent to the first voltage vector using the target vectors, and determine the target switching sequence corresponding to the second voltage vector, wherein the operational virtual vector includes at least one of the first virtual vector and the second virtual vector, and the target vector includes at least two of the operational virtual vectors; The processing module is configured to determine the duty cycle corresponding to each vector in the target vector according to the target switching sequence, and modulate the inverter according to the pulse modulation (PWM) pulse determined by the corresponding duty cycle.

9. An inverter, characterized in that, It includes a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other through the communication bus; Memory, used to store computer programs; When a processor executes a program stored in a memory, it implements the steps of the modulation method for a photovoltaic grid-connected inverter as described in any one of claims 1-7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the modulation method for a photovoltaic grid-connected inverter as described in any one of claims 1-7.

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