A control method of a grid-connected inverter

Abstract

This invention relates to a control method for a grid-connected inverter. Based on a basic vector reconstructed virtual small vector and a reconstructed virtual mid-vector, the mid-point voltage of the grid-connected inverter is controlled using these two vectors, enabling control of the mid-point voltage in each region of each sector. The reconstructed virtual mid-vector reduces the impact of voltage equalization control on the grid-connected current, balancing mid-point potential control with grid current power quality. This invention also introduces a voltage equalization factor, resulting in a stronger voltage equalization effect as the mid-point voltage deviation increases. The reconstructed virtual mid-vector improves the voltage equalization effect and speed at the mid-point potential under high modulation depth conditions, while ensuring grid-connected power quality.

Description

Technical Field

[0001] This invention relates to a control method for a grid-connected inverter, belonging to the field of inverter technology. Background Technology

[0002] Traditional two-level inverters exhibit significant voltage and current variations. Due to factors such as switching stress, two-level inverters face certain challenges in high-voltage, high-power applications. Consequently, many researchers have continuously improved the inverter circuit structure, leading to the development of multi-level inverters such as three-level and four-level inverters. Under the same voltage level, the voltage resistance of each power electronic switch is lower than that of a two-level inverter, making it more suitable for high-voltage, high-power applications. With the development of electronic power, research on multi-level inverter technology has penetrated into power plants, variable frequency speed control of high-voltage AC motors, microgrids, metallurgy, steel, and other related fields.

[0003] The NPC (neutral-point clamped) three-level inverter contains two equal-value DC capacitors on its DC side, clamped by diodes. This circuit structure increases the number of output levels, allowing for three different phase voltage output states compared to a two-level inverter, hence the name "three-level inverter." However, in non-ideal conditions, the limited size of the DC-side capacitors and manufacturing limitations can cause a voltage difference between the two capacitors. This results in uneven withstand voltage during switching, increasing stress on the switching devices and introducing low-order harmonics into the load output, leading to high harmonic content and increased harmonic distortion. Severe voltage fluctuations can also affect capacitor lifespan. Furthermore, grid connection requires strict current conditions. Only when the midpoint potential is balanced will the spatial hexagon formed by the basic vectors exhibit a centrally symmetrical distribution. Excessive midpoint potential deviation leads to large deviations in the positive and negative voltage amplitudes of the output, causing a significant discrepancy between the synthesized voltage vector and the target vector. This distortion in the output waveform can, in severe cases, reduce the number of output levels or cause grid connection failure.

[0004] Chinese patent application CN113783452A discloses a modulation method, device, inverter, storage medium and processor for an inverter. This patent uses virtual vectors to synthesize a reference voltage vector, which avoids grid connection failure caused by distortion of the inverter output waveform. However, when modulating the inverter, the voltage equalization effect of the midpoint voltage is poor and the voltage equalization speed is slow. Summary of the Invention

[0005] The purpose of this invention is to provide a control method for grid-connected inverters to solve the problems of poor voltage equalization effect and slow voltage equalization speed in grid-connected inverters.

[0006] To achieve the above objectives, the solutions and technical effects of the present invention include:

[0007] The present invention provides a control method for a grid-connected inverter, comprising the following steps:

[0008] 1) Construct a space voltage vector, which includes multiple basic vectors. The types of basic vectors include zero vector, small vector, medium vector and large vector;

[0009] 2) Construct virtual small vectors using the following formula:

[0010]

[0011] Where V1 is a virtual small vector, T1 is the duration of action of the virtual small vector, V2 and V3 are small vectors corresponding to the virtual small vector V1, σ is the self-adjusting equalization factor, and -1≤σ≤1;

[0012] 3) Construct the virtual vector using the following formula:

[0013]

[0014] Among them, V 11 For virtual vectors, T 11 V4, V5, and V6 are the time of action of the virtual vector V. 11 The corresponding vectors are small or medium vectors, τ and υ are reconstruction factors, and -1≤τ and υ≤1, μ and δ are self-adjusting equalization factors, and -0.5≤μ≤0.5 and -0.5≤δ≤0.5;

[0015] 4) Obtain the reference voltage vector of the grid-connected inverter, determine the sector in which the reference voltage vector is located in the space voltage vector and the region within the sector, and select the composite vector required to synthesize the reference voltage vector. The composite vector includes the zero vector and the large vector, and also includes any one of the following three types: small vector and virtual medium vector, virtual small vector and medium vector, and virtual small vector and virtual medium vector; determine the basic vector according to the composite vector and determine the output order of the basic vector; determine the switching sequence of the switching devices in the inverter according to the output order.

[0016] 5) Determine the basic vector time of the basic vector that constitutes the composite vector using the volt-second balance principle; obtain the vector pulse width modulation wave of the grid-connected inverter based on the output order and basic vector time of the basic vector, and control the grid-connected inverter based on the vector pulse width modulation wave.

[0017] The beneficial effects of the above technical solution are as follows: The control method for grid-connected inverters provided by this invention, based on the reconstruction of virtual small vectors and reconstructed virtual mid-vectors using basic vectors, controls the mid-point voltage of the grid-connected inverter using these virtual small vectors and reconstructed virtual mid-vectors, enabling control of the mid-point voltage in each region of each sector. The reconstructed virtual mid-vector of this invention reduces the impact of voltage equalization control on the grid-connected current, balancing mid-point potential control with the power quality of the grid-connected current. This invention also introduces a voltage equalization factor, resulting in a stronger voltage equalization effect when the mid-point voltage deviation is larger. The reconstructed virtual mid-vector used improves the voltage equalization effect and speed of the mid-point potential under high modulation depth conditions, while ensuring the power quality of the grid connection.

[0018] Further, in step 2), the adaptive equalizing pressure factor is obtained by the following formula:

[0019] σ=λ*(ΔV * *ξ)

[0020] Where, ΔV * The midpoint potential deviation is the normalized value, ξ is the empirical proportionality coefficient, and λ is the sign coefficient, which is determined by the current direction of the basic voltage vector and the midpoint potential deviation; the midpoint potential deviation is the voltage difference between the DC side terminals of the normalized inverter.

[0021] The beneficial effects of the above technical solution are: by using the midpoint potential deviation as a control condition to adjust the adaptive voltage equalization factor, the control effect and voltage equalization speed of voltage equalization are improved.

[0022] Furthermore, the empirical proportionality coefficient is determined based on the control accuracy of the midpoint potential, the DC bus voltage, and the midpoint potential deviation during the dynamic process; wherein, the empirical proportionality coefficient is directly proportional to the control accuracy of the midpoint potential and inversely proportional to the ratio of the midpoint potential deviation to the DC bus voltage.

[0023] Furthermore, the reconstruction factor is determined based on the midpoint potential deviation; when the synthesized vector used in the synthesized reference voltage vector makes the midpoint potential balanced, the corresponding reconstruction factor is greater than 0; when the synthesized vector used in the synthesized reference voltage vector makes the midpoint potential deviation increase, the corresponding reconstruction factor is less than or equal to 0.

[0024] Furthermore, the self-adjusting equalizing pressure factor is obtained by the following formula:

[0025]

[0026] Where, ΔV *The midpoint potential deviation is the normalized value, where ξ1 and ξ2 are empirical proportionality coefficients, and λ1 and λ2 are both sign coefficients, determined by the current direction of the reference voltage vector and the midpoint potential deviation; the midpoint potential deviation is the voltage difference between the two equalizing capacitors set on the DC side of the normalized grid-connected inverter.

[0027] The beneficial effects of the above technical solution are: by using the midpoint potential deviation as a control condition to adjust the self-adjusting voltage equalization factor, the control effect and speed of voltage equalization are improved.

[0028] Furthermore, the empirical proportionality coefficient is determined based on the control accuracy of the midpoint potential, the DC bus voltage, and the midpoint potential deviation; wherein, the empirical proportionality coefficient is directly proportional to the control accuracy of the midpoint potential, and inversely proportional to the ratio of the midpoint potential deviation to the DC bus voltage.

[0029] Furthermore, the reference voltage vector is obtained by the following method: obtaining the reference current, the current value of the filter output, the capacitor current, and the grid voltage; inputting the difference obtained by subtracting the reference current value and the current value of the filter output to the regulator; performing transformation and adjustment to obtain the output value; adding the grid voltage to the output value and subtracting the capacitor current by a set multiple to obtain the reference voltage vector.

[0030] Furthermore, the space voltage vector comprises six sectors, each containing five regions. When the reference voltage vector is located in the first region of the first sector of the space voltage vector, the output order of the basic vector is: PPO, POO, OOO, OON, ONN, OON, OOO, POO, PPO; when the reference voltage vector is located in the second region of the first sector of the space voltage vector, the output order of the basic vector is: PPO, POO, PON, OON, ONN, OON, PON, POO, PPO; when the reference voltage vector is located in the third region of the first sector of the space voltage vector, the output order of the basic vector is: PPO, POO, PON, PNN, ONN, PNN, PON, POO, PPO; When the reference voltage vector is in the fourth region of the first sector of the space voltage vector, the output order of the basic vector is: PPO, PPN, PON, OON, ONN, OON, PON, PPN, PPO; When the reference voltage vector is in the fifth region of the first sector of the space voltage vector, the output order of the basic vector is: PPO, PPN, PON, PNN, ONN, PNN, PON, PPN, PPO; When the reference voltage vector is in the first region of the second sector of the space voltage vector, the output order of the basic vector is: PPO, OPO, OOO, OON, NON, OON, OOO, OPO, PPO; When the reference voltage vector is in the fourth region of the second sector of the space voltage vector, the output order of the basic vector is: PPO, OPO, OOO, OON, NON, OON, OOO, OPO, PPO; When the reference voltage vector is in the fifth ...ON, PPO, PPO; When the reference voltage vector is in the fifth region of the second sector of the space voltage vector, the output order of the basic vector is: PPO, OPO, OOO, OON, OON, PON, PON, PPO, P In the two-region scenario, the output order of the basic vector is: PP0, OPO, OPN, OON, NON, OON, OPN, OPO, PPO; when the reference voltage vector is in the third region of the second sector of the space voltage vector, the output order of the basic vector is: PPO, PPN, OPN, OON, NON, OON, OPN, PPN, PPO; when the reference voltage vector is in the fourth region of the second sector of the space voltage vector, the output order of the basic vector is: PPO, OPO, OPN, NPN, NON, NPN, OPN, OPO, PPO; when the reference voltage vector is in the fifth region of the second sector of the space voltage vector, the output order of the basic vector is: PPO, PPN, OPN, OPN, OPN, OPN, OPN, PPO. N, NPN, NON, NPN, OPN, PPN, PPO; When the reference voltage vector is in the first region of the third sector in the space voltage vector, the output order of the basic vector is: OPP, OPO, OOO, NOO, NON, NOO, OOO, OPO, OPP; When the reference voltage vector is in the second region of the third sector in the space voltage vector, the output order of the basic vector is: OPP, OPO, NPO, NOO, NON, NOO, NPO, OPP, OPP; When the reference voltage vector is in the third region of the third sector in the space voltage vector, the output order of the basic vector is: OPP, OPO, NPO, NPN, NON, NPN, NPO, OPP, OPP;When the reference voltage vector is in the fourth region of the third sector of the space voltage vector, the output order of the basic vector is: OPP, NPP, NPO, NOO, NON, NOO, NPO, NPP, OPP; when the reference voltage vector is in the fifth region of the third sector of the space voltage vector, the output order of the basic vector is: OPP, NPP, NPO, NPN, NON, NPN, NPO, NPP, OPP; when the reference voltage vector is in the first region of the fourth sector of the space voltage vector, the output order of the basic vector is: OPP, OOP, OOO, NOO, NNO, NOO, OOO, OOP, OPP; when the reference voltage vector is in the fourth region of the fourth sector of the space voltage vector, the output order of the basic vector is: OPP, OOO, NOO, NNO, NOO, OOO, OOP, OPP; when the reference voltage vector is in the fifth region of the third sector of the space voltage vector, the output order of the basic vector is: OPP, OOO, NOO, NNO, NOO, OOO, OOP, OPP; when the reference voltage vector is in the fifth region of the third sector of the space voltage vector, the output order of the basic vector is: OPP, OOO, NOO, NNO, NOO, OOO, OOP, OPP; when the reference voltage vector is in the fifth region of the third sector of the space voltage vector, the output order of the basic vector is: OPP, OOO, NOO, NPO, NPO, NPO, NPO, OPP, OPP; when the reference voltage vector is in the fifth region of the third sector of the space voltage vector, the output order of the basic vector is: OOP ... When the reference voltage vector is in the second region of the sector, the output order of the basic vector is: OPP, OOP, NOP, NOO, NNO, NOO, NOP, OOP, OPP; when the reference voltage vector is in the third region of the fourth sector of the space voltage vector, the output order of the basic vector is: OPP, NPP, NOP, NOO, NNO, NOO, NOP, NPP, OPP; when the reference voltage vector is in the fourth region of the fourth sector of the space voltage vector, the output order of the basic vector is: OPP, OOP, NOP, NNP, NNO, NNP, NOP, OOP, OPP; when the reference voltage vector is in the fifth region of the fourth sector of the space voltage vector, the output order of the basic vector is: The output order of the basic vectors is: POP, OOP, NOP, NNP, NNO, NNP, NOP, NPP, OPP; when the reference voltage vector is in the first region of the fifth sector of the space voltage vector, the output order of the basic vectors is: POP, OOP, OOO, ONO, NNO, ONO, OOO, OOP, POP; when the reference voltage vector is in the second region of the fifth sector of the space voltage vector, the output order of the basic vectors is: POP, OOP, ONP, ONO, NNO, ONO, ONP, OOP, POP; when the reference voltage vector is in the third region of the fifth sector of the space voltage vector, the output order of the basic vectors is: POP, OOP, ONP, NNP, N... NO, NNP, ONP, OOP, POP; When the reference voltage vector is in the fourth region of the fifth sector of the space voltage vector, the output order of the basic vector is: POP, PNP, ONP, ONO, NNO, ONO, ONP, PNP, POP; When the reference voltage vector is in the fifth region of the fifth sector of the space voltage vector, the output order of the basic vector is: POP, PNP, ONP, NNP, NNO, NNP, ONP, POP, POP; When the reference voltage vector is in the first region of the sixth sector of the space voltage vector, the output order of the basic vector is: POP, POO, OOO, ONO, ONN, ONO, OOO, POO, POP;When the reference voltage vector is in the second region of the sixth sector of the space voltage vector, the output order of the basic vector is: POP, POO, PNO, ONO, ONN, ONO, PNO, POO, POP; when the reference voltage vector is in the third region of the sixth sector of the space voltage vector, the output order of the basic vector is: POP, PNP, PNO, ONO, ONN, ONO, PNO, PNP, POP; when the reference voltage vector is in the fourth region of the sixth sector of the space voltage vector, the output order of the basic vector is: POP, POO, PNO, PNN, ONN, PNN, PNO, POO, POP; when the reference voltage vector is in the fifth region of the sixth sector of the space voltage vector, the output order of the basic vector is: POP, PNP, PNO, PNN, ONN, PNN, PNO, PNP, POP.

[0031] Furthermore, the sector in which the reference voltage vector lies within the space voltage vector is obtained using the following formula:

[0032]

[0033] Where N is the sector position of the space voltage vector, V REFα V REFβ V REF In the αβ coordinate system, the α and β components are calculated using the remainder method;

[0034] The region where the reference voltage vector is located within the sector of the space voltage vector is determined by the following method: when When, the reference voltage vector is located in the first region of the sector in the space voltage vector; when and and When, the reference voltage vector is located in the second region of the sector in the space voltage vector; when and When, the reference voltage vector is located in the third region of the sector in the space voltage vector; when and When, the reference voltage vector is located in the fourth region of the sector in the space voltage vector; when and At that time, the reference voltage vector is located in the fifth region of the sector within the space voltage vector; where, and These are the per-unit components of the reference voltage vector within a 60° sector in the gh coordinate system, representing the g-axis and h-axis components, respectively.

[0035] Furthermore, the space voltage vector is a space voltage vector in the α-β coordinate system, and the space voltage vector is transformed to the gh 60° coordinate system using the following formula:

[0036]

[0037] Among them, V α V β These are the reference voltage components along the α-axis and β-axis in the α-β coordinate system, respectively; V g V h These are the reference voltage components along the g-axis and h-axis in the gh 60° coordinate system, respectively.

[0038] Based on rotational symmetry, the remaining sectors are rotated to the first sector using the following formula for corresponding calculations:

[0039]

[0040] in, These represent the g-axis reference voltage component and the h-axis reference voltage component of the first largest sector in the g-h60° coordinate system, respectively, where N is the Nth largest sector. V h N These are the g-axis reference voltage and h-axis reference voltage components of the Nth sector in the gh coordinate system, respectively.

[0041] The beneficial effects of the above technical solution are as follows: It transforms the spatial vector coordinate system from the α-β coordinate system to the gh 60° coordinate system, avoiding trigonometric function calculations and greatly improving calculation speed. Utilizing rotational symmetry to rotate the remaining sectors to the first sector for calculation makes the calculation faster and more convenient. Attached Figure Description

[0042] Figure 1 This is a control system diagram for an NPC-type three-level inverter;

[0043] Figure 2 This is a block diagram of the grid-connected current control of the present invention;

[0044] Figure 3 This is the overall flowchart of the invention for obtaining VSVPWM;

[0045] Figure 4 It is the SVPWM space vector diagram in a 60° coordinate system after standardization;

[0046] Figure 5 This is the VSVPWM space vector diagram in the 60° coordinate system after per-unit scaling according to the present invention;

[0047] Figure 6 This is the spatial vector diagram of VSVPWM in a sector under the normalized 60° coordinate system of this invention;

[0048] Figure 7This is a schematic diagram of the simulation results of the midpoint potential control speed of the existing VSVPWM technology;

[0049] Figure 8 This is a schematic diagram of the simulation results of the midpoint potential control speed of VSVPWM containing virtual small vector voltage equalization control;

[0050] Figure 9 This is a schematic diagram of the simulation results of the midpoint potential control speed of the present invention;

[0051] Figure 10 This is a schematic diagram of the simulation results of the midpoint potential control deviation of VSVPWM with virtual indicator voltage equalization control;

[0052] Figure 11 This is a schematic diagram of the simulation results of the midpoint potential control deviation of the present invention;

[0053] Figure 12 This is a schematic diagram of the grid-connected current simulation results of the present invention. Detailed Implementation

[0054] The present invention will now be described in further detail with reference to the accompanying drawings.

[0055] Example:

[0056] This invention provides a control method for grid-connected inverters, specifically a full-range fast voltage equalization virtual space vector pulse width modulation (VSVPMN) algorithm applied to neutral-point clamped (NPC) three-level grid-connected AC inverters. This method is based on... Figure 1 The proposed NPC-type three-level inverter control system uses an NPC-type three-level inverter, with its AC side connected to the public grid via an LCL filter. During the LCL filtering process, the system acquires the reference current value of the grid-connected inverter, the current value of the public grid current, and the current value of the public grid voltage. It then adjusts and controls these acquired reference values ​​to output a reference voltage vector. The proposed grid-connected inverter control method is then used to obtain the vector pulse width modulation (PWM) wave for the grid-connected inverter. After modulation, a PWM wave is output to the drive circuit, which in turn drives the power electronic switching devices in the inverter based on the obtained PWM wave.

[0057] The main concept of the modulation method proposed in this invention is as follows: First, the input signal is per-unitized. The reference voltage vector, midpoint potential voltage deviation, and DC side voltage output by the alignment PR controller are per-unitized, which reduces the difficulty of subsequent calculations. Then, large sector determination is performed. In the αβ axis, the position of the large sector where the reference voltage vector is located can be obtained using the per-unitized reference voltage vector. Next, the per-unitized signal is subjected to coordinate transformation, that is, transformed from the αβ axis to the gh axis. In a 60° coordinate system, this avoids a large amount of subsequent trigonometric function calculations. Based on rotational symmetry, the per-unit reference voltage vector is transformed by coordinate rotation. After calculating the relevant parameters of the first large sector, the parameters of the remaining five sectors can be obtained. Then, virtual zero vector, virtual small vector, virtual medium vector, and virtual large vector are constructed based on the zero vector, small vector, medium vector, and large vector. At the same time, small sector division and determination of the small sector position of the reference voltage vector are performed. Due to the topology of the three-level inverter, it is not possible to accurately select the basic vector to synthesize the reference voltage vector using only six large sectors. Therefore, small sector division is required. The premise of division is to determine the virtual small vector, virtual medium vector, and virtual large vector. The constructed virtual vector has no effect on the midpoint potential during steady-state operation.

[0058] Combination Figure 4 , Figure 5 As shown, the virtual small vector V ZS1 By V POO and V ONN The structure consists of a basic vector whose length each accounts for 50%, and a virtual vector V. ZM By V PON V ONN and V PPO Composition, in which V ONN and V PPO The proportion is affected by the reconstruction factor. The reconstructed virtual mid-vector can perform potential equalization control when the mid-point potential is unbalanced. Since the base zero vector and the base large vector have no effect on the mid-point voltage, the base large vector is selected as the virtual large vector. At the same time, in order to reduce the common-mode voltage, the base zero vector V is selected. OOO This is the virtual zero vector. After determining the virtual vector, small sectors can be divided. Because in the gh coordinate system, the region containing the reference vector can be determined using a few simple relationships, and then a set of composite virtual vectors can be selected for synthesis. Then, the reference voltage vector is decomposed in the gh coordinate system, and using the volt-second balance principle, the value can be obtained within one control cycle T. SThe duration of the internal virtual voltage vector is calculated, and then the duration of each virtual vector is allocated to the base voltage vector. At this point, a self-adjusting voltage equalization factor (including adaptive and self-adjusting voltage equalization factors) is used to modify the time allocation scheme of the base voltage vector, achieving control of the midpoint voltage. Finally, the duration of the base vectors is standardized to ensure that the sum of their durations equals one control cycle T. S To ensure the timing of space vector modulation, the standardized base vector time is mapped to the nine-segment output voltage vector sequence. The base voltage vector output in the nine-segment sequence is then converted into the switching state of the actual power electronic switch tube, and a PWM signal containing full-range midpoint potential control is output to achieve fast midpoint potential equalization control under high modulation depth.

[0059] The overall control block diagram of the modulation method for the inverter provided by this invention is as follows: Figure 2 As shown, the overall flowchart is as follows: Figure 3 As shown, the method specifically includes the following steps:

[0060] 1) Input reference voltage standardization and coordinate transformation.

[0061] like Figure 1 The diagram shows the control system of an NPC-type three-level inverter. The grid-connected control method of this invention adopts a quasi-PR controller and selects an LCL filter to reduce the design cost of the circuit. However, the transfer function Bode plot of the LCL filter has resonance spikes, which may cause the control system to diverge. Therefore, an active damping resonance suppression method is introduced to suppress the LCL resonance peak. The active damping method used is capacitor current proportional feedback control based on state variable feedback.

[0062] First, the controller output V REF The signals input to the VSVPWM module are standardized to simplify subsequent calculations. Then, the V output from the controller is... REF Transforming from the ABC coordinate system to the αβ coordinate system, that is:

[0063]

[0064] Among them, V REFA V REFB V REFC For V REF At the three-phase reference voltage ABC, V REFα V REFβ V REF From the α and β components, the reference voltage vector is obtained as: V REF =V REFα +jV REFβ The reference vector V can be obtained. REFRadians in the αβ coordinate system: Virtual space vector graphics use 60° as a sector, so divide this radius by... Performing the up modulo operation yields the sector location of the reference voltage vector, i.e.:

[0065]

[0066] Ceil is used for the up modulo operation.

[0067] 2) Coordinate transformation from αβ coordinate system to g-h60° coordinate system.

[0068] The basic voltage vector and the per-unitized Transforming to a 60° coordinate system reduces the amount of trigonometric function calculations, thus accelerating the system's control speed. The transformation formula used is:

[0069]

[0070] Among them, V g V h Let V be the reference voltage along the g-axis and the reference voltage along the h-axis in the gh coordinate system. α V β These are the reference voltages along the α-axis and β-axis in the α-β coordinate system, respectively.

[0071] The composite virtual vector used for the basic voltage vector differs in different sectors. The composite virtual vector is decomposed along the gh coordinate axis, and the gh component of each composite virtual vector is different. This means that the determined composite virtual vector will change every time the sector changes, so it needs to be recalculated every time the sector changes, which is quite complicated.

[0072] Therefore, since gh is a 60° coordinate system, and each sector is also 60°, by utilizing rotational symmetry, the reference vectors in other large sectors can be rotated and transformed to the first large sector. Thus, once the parameters and logic of the first large sector are obtained, the logic and parameters of the remaining five sectors can be calculated based on the parameters within sector one. This further reduces the computational load of VSVPWM and improves control speed. The rotational coordinate formula is as follows:

[0073]

[0074] in, These represent the g-axis reference voltage component and h-axis reference voltage component under the gh coordinate system, respectively, after coordinate rotation to the first major sector. N represents the Nth major sector. V h NThese are the g-axis reference voltage component and the h-axis reference voltage component of the Nth sector under the gh coordinate system, respectively.

[0075] For example: when in the second sector, the g-axis is established on V. ZL2 Above, at this time, V ZL2 It's equivalent to the V of a sector. ZL1 Its per-unit coordinates are (2.0). ; When in the third sector, the g-axis is established at V. ZL3 On, at this time, V ZL3 It's equivalent to the V of a sector. ZL1 Its per-unit coordinates are also (2.0). The same applies to the subsequent sectors. After rotation, the coordinates of the synthesized virtual vector can all correspond to the virtual vector in the first sector. Therefore, in solving the volt-second balance formula, it is not necessary to perform vector decomposition of the virtual vector gh axis according to different sectors. It is only necessary to solve it using the one-sector decomposition method, which can greatly reduce the amount of calculation.

[0076] Small region judgment is also calculated using the reference voltage vector. After rotation transformation, the judgment method for small regions in other sectors can also use the judgment method for one sector. In other words, after rotation transformation, the calculation logic of other sectors can refer to the calculation logic of one sector, which greatly simplifies the entire VSVPWM algorithm.

[0077] 3) Construct virtual vectors.

[0078] The design incorporates virtual zero vector, virtual small vector, reconstructed virtual medium vector, and virtual large vector, and divides the sector into regions to select the composite virtual vector of the reference voltage vector.

[0079] First, taking phase A bridge arm as an example, the output level corresponds to the output state of the switch as shown in Table 1:

[0080] Table 1

[0081]

[0082]

[0083] For the other phase bridge arms of the present invention, the output level corresponds to the output state of the switch as shown in Table 1.

[0084] like Figure 4 As shown, in VSVPWM in the 60° coordinate system, because V PPP V NNN The common-mode voltage is V IN V OOOWith zero common-mode voltage, the high-frequency common-mode voltage generated by the inverter will produce a high-amplitude current in the grid connection, forming current harmonics, which "pollute" the grid and affect grid connection quality and efficiency. Therefore, V is selected. OOO It is a virtual zero vector.

[0085] Combination Figure 5 As shown in Table 2, the basic composite vectors of the virtual small vectors are set.

[0086] Table 2

[0087] Virtual small vector Basic composite vector 1 Basic composite vector 2 <![CDATA[V ZS1 ]]> <![CDATA[V ONN ]]> <![CDATA[V POO ]]> <![CDATA[V ZS2 ]]> <![CDATA[V PPO ]]> <![CDATA[V ONN ]]> <![CDATA[V ZS3 ]]> <![CDATA[V NON ]]> <![CDATA[V OPO ]]> <![CDATA[V ZS4 ]]> <![CDATA[V OPP ]]> <![CDATA[V NOO ]]> <![CDATA[V ZS5 ]]> <![CDATA[V NNO ]]> <![CDATA[V OOP ]]> <![CDATA[V ZS6 ]]> <![CDATA[V POP ]]> <![CDATA[V ONO ]]>

[0088] Among them, both basic composite vector 1 and basic composite vector 2 are small vectors.

[0089] The basic composite vectors of the virtual vectors are set as shown in Table 3:

[0090] Table 3

[0091] Virtual vector Basic composite vector 3 Basic Composite Vector 4 Basic composite vector 5 <![CDATA[V ZM1 ]]> <![CDATA[V PON ]]> <![CDATA[V ONN ]]> <![CDATA[V PPO <!-- 8 -->]]> <![CDATA[V ZM2 ]]> <![CDATA[V OPN ]]> <![CDATA[V NON ]]> <![CDATA[V PPO ]]> <![CDATA[V ZM3 ]]> <![CDATA[V NPO ]]> <![CDATA[V NON ]]> <![CDATA[V OPP ]]> <![CDATA[V ZM4 ]]> <![CDATA[V NOP ]]> <![CDATA[V NNO ]]> <![CDATA[V OPP ]]> <![CDATA[V ZM5 ]]> <![CDATA[V ONP ]]> <![CDATA[V NNO ]]> <![CDATA[V POP ]]> <![CDATA[V ZM6 ]]> <![CDATA[V PNO ]]> <![CDATA[V ONN ]]> <![CDATA[V POP ]]>

[0092] Among them, the basic composite vector 3, basic composite vector 4 and basic composite vector 5 are small or medium vectors.

[0093] The two composite fundamental vectors, 1 and 2, are both redundant vectors. They have the same amplitude and direction, but opposite effects on the midpoint potential. When the midpoint potential is balanced, according to the volt-second balance principle, the duration of action of the two composite fundamental vectors should be equal, thus having no effect on the midpoint potential.

[0094]

[0095] Among them, T ZS1 For V ZS1 The vector action time.

[0096] Assuming the current flows out from the midpoint potential at this moment, and setting this direction as the positive reference direction, and combining it with the following formula:

[0097]

[0098] It can be known that when V ONN When in operation, the current flowing out is the A-phase grid current I. A The direction is positive, which increases the voltage across the upper capacitor and decreases the voltage across the lower capacitor; while V POO When in operation, assuming the current flows out from the critical current, the current flowing out at this time is the grid-connected current I of phase A. A The direction is negative, causing the voltage of the upper capacitor to decrease and the voltage of the lower capacitor to increase. Introducing the adaptive voltage equalization factor σ allows the virtual small vector to control the midpoint potential. Therefore:

[0099]

[0100] Where σ=λ*(ΔV) * *ξ)(-1≤σ≤1), ΔV * Let ξ be the normalized midpoint potential deviation, and ξ be an empirical proportionality coefficient. When the DC bus voltage is 700V, and the control accuracy of the critical potential is set to within 1V, there is still a strong voltage equalization capability even with a midpoint deviation of 10. Therefore, the empirical proportionality coefficient ξ can be taken as: When the midpoint potential deviation is 10V, the equalization factor remains at its upper limit of 1 or -1, giving the virtual small vector strong equalization control capability. This is related to the sector N where the reference voltage vector is located, the region position n within the sector, and the midpoint potential deviation ΔV. * It is related to the actual direction of the neutral point current flow. Considering that the power factor cannot be exactly 1, the direction of the neutral point current flow cannot be determined solely by the switching state. Therefore, sampling the three-phase current can yield the direction of the current flowing into the neutral point at this time.

[0101] Taking region one in sector one as an example, let the virtual small vector be V. ZS1 V ZS2 Assuming the midpoint potential deviation is less than zero, that is If the grid current I at this time A If it is positive, then use vector V. ONN The amplitude can be I A The current flows into the midpoint of the capacitor to increase the midpoint voltage and improve the midpoint potential deviation. Meanwhile, the redundant vector V... POO Since they have the opposite effect, the sign of σ should be positive, and more time should be allocated to V. ONN To balance the midpoint potential, λ is taken as -1. Since V POO V ONN These are a pair of redundant vectors with equal amplitude and direction, so the influence of the final synthesized reference vector is minimal. Selecting an appropriate adaptive voltage equalization factor can achieve control over key potentials. The above explanation uses only the first virtual small vector within a sector as an example; the same principle applies to the remaining small vectors. It is important to note that when using V... POO V ONN When synthesizing virtual small vectors, if any one of them is 0, the synthesized vector is V. POO or V ONN If the vector is not a virtual small vector, then it is still a small vector.

[0102] Taking the virtual center vector within a sector as an example, the expression for the virtual center vector is:

[0103]

[0104] Where τ and υ are reconstruction factors, μ and δ are self-adjusting equalization factors, and T ZM1 For V ZM1 The base vector time.

[0105] The selection principles for reconstruction factors τ and υ are as follows: based on the current midpoint potential deviation and midpoint current direction, if the basic synthesized voltage vector can balance the voltage, the reconstruction factor is greater than 0; if the basic synthesized voltage vector further increases the midpoint potential deviation, the reconstruction factor is less than 0. Simultaneously considering the magnitude of the reconstructed virtual midpoint vector and the range of space vector pulse width modulation, it should be ensured that -1≤τ, υ≤1. The selection of reconstruction factors is completed when constructing the virtual midpoint vector, and will not affect the accuracy of the volt-second balance equation of the reference voltage vector, while also allowing for control of the midpoint voltage.

[0106] When the midpoint potential is balanced, the self-adjusting equalization factors μ and δ and the reconstruction factors τ and υ are zero, then the base voltage synthesis vector V ONN V PPO V PON The three forces act for equal durations, and when the three fundamental composite vectors act, the midpoint currents flowing out are respectively I... A I B I C Since the three-phase operation is symmetrical during grid connection, and the duration of a PWM control cycle is very short, it can be assumed that the virtual mid-vector's basic function is to make the average current flowing into or out of the mid-point zero, i.e.:

[0107] I A +I B +I C =0

[0108] Similarly, it should be noted that the three basic composite vectors in the reconstructed virtual vector are not redundant vectors; their directions and magnitudes are different. This means that if the self-adjusting voltage equalization factor is not chosen appropriately, it will increase the harmonic components in the grid-connected current. Therefore, a voltage equalization factor with self-adjusting capability should be used, namely:

[0109]

[0110] The methods for determining the values ​​of the empirical coefficients λ1, λ2, and ξ are similar to those for the virtual small vector. The empirical coefficient ξ, which controls the self-adjusting voltage equalization factor of the reconstructed virtual mid-vector, is set to a smaller value. This ensures that when the mid-point potential deviation is large, both the reconstructed virtual mid-vector and the virtual small vector work simultaneously to equalize the mid-point voltage; when the mid-point potential deviation is small, the virtual small vector is used more for voltage equalization without affecting the distortion factor of the grid-connected current. This balances the accuracy of the reference voltage vector synthesis with mid-point potential control. Since the basic large vector has no effect on the mid-point potential, the basic voltage large vector is used as the virtual large vector.

[0111] 4) Divide into smaller areas.

[0112] The sector is further divided into smaller regions to facilitate the selection of the synthesized vector. The regions within the sector are divided using the virtual zero vector, virtual small vector, virtual medium vector, and virtual large vector reconstructed in step 3). For example... Figure 6 As shown in the figure, to avoid complexity, only the area within sector one is labeled; the other sectors are labeled similarly. The figure shows that each sector is divided into 5 regions. In the traditional αβ axis, region identification requires extensive trigonometric function calculations. However, this invention uses a 60° coordinate system for region discrimination calculations, which significantly reduces the system's computational load. Under the 60° coordinate system, based on geometric relationships, the discrimination methods shown in Tables 4 and 5 are obtained. The division rule of dividing each sector into 5 regions in this invention is consistent with the existing technology's division rule of dividing each sector into 5 regions.

[0113] Table 4

[0114]

[0115] Table 5

[0116]

[0117] V in the table * g V * h The reference voltage vector after rotation can be determined by referring to Tables 4 and 5. Furthermore, the calculation process does not involve trigonometric function operations, which greatly reduces the design difficulty and computational load.

[0118] 5) Calculate the duration of action of each basic vector.

[0119] Using the volt-second balance principle, the duration of each basic vector is calculated. Based on the position of the reference voltage vector within its sector, a specific set of composite virtual vectors is obtained. For example... Figure 6 As shown, assuming the current reference vector is in region 3 of sector 1, the selected composite virtual vector is V. *ZS1 V * ZL1 V * ZM1 According to the volt-second balance principle, we have:

[0120] V * REF T S =V * ZS1 T ZS1 +V * ZL1 T ZL1 +V * ZM1 T ZM1

[0121] Among them, V * REF T S V * ZS1 V * ZL1 V * ZM1 These are the standardized voltage reference vector, a single control cycle, the standardized virtual small vector, the virtual large vector, and the virtual medium vector, all of which are known. There are three unknowns: T. ZS1 T ZL1 T ZM1 These represent the normalized virtual small vector action time, virtual large vector action time, and virtual medium vector action time, respectively. Decomposing the normalized voltage reference vector along the coordinate direction and considering the timing of vector control, we obtain:

[0122]

[0123] Among them, V * REFg V * REFh V * REF Reference voltages along the g-axis and h-axis in the gh coordinate system, V * ZS1g V * ZS1h V * ZS1 Reference voltages along the g-axis and h-axis in the gh coordinate system, V * ZL1g V * ZL1h V * ZL1 Reference voltages along the g-axis and h-axis in the gh coordinate system, V* ZM1g V * ZM1h V * ZM1 Reference voltages along the g-axis and h-axis in the gh coordinate system.

[0124] The action time of each virtual composite vector can be obtained from the above formula. Due to symmetry, and after calculating the parameters within sector one using the rotation coordinate formula, the parameters of the remaining sectors can be obtained. Then, the action time of the basic voltage vector is calculated using the following formula from step 3):

[0125]

[0126]

[0127] In addition to region 3 of sector 1 where the current reference vector is located, this invention also lists the duration of action of virtual vectors in all regions of sector 1, as shown in Table 6. The same applies to the other sectors as to sector 1.

[0128] Table 6

[0129]

[0130] When the reference voltage vector is within the first region of sector 1, TX, TY, and TZ in Table 6 correspond to... Figure 6 The duration of action of the virtual vector is: T ZS1 T ZS2 T Z0 When the reference voltage vector is in the second region of sector 1, the corresponding Figure 6 The duration of action of the virtual vector is: T ZS1 T ZS2 T ZM1 When the reference voltage vector is in the third region of sector 1, the corresponding Figure 6 The duration of action of the virtual vector is: T ZS1 T ZM1 T ZL1 When the reference voltage vector is in the fourth region of sector 1, the corresponding Figure 6 The duration of action of the virtual vector is: T ZS2 T ZM1 T ZL2 When the reference voltage vector is in the fifth region of sector 1, the corresponding Figure 6 The duration of action of the virtual vector is: T ZL1 T ZL2 T ZM1 .

[0131] Then standardization is performed to ensure that the sum of the basic vector action times equals one control period T.S Finally, in order to reduce the harmonic content and common-mode voltage of the grid-connected current, and to follow the vector output sequence rules, a nine-segment symmetrical sequence output with the small vector as the first vector is adopted. This invention lists all the sequences in the first sector, as shown in Table 7.

[0132] Table 7

[0133] n＝1 PPO POO OOO OON ONN OON OOO POO PPO n＝2 PPO POO PON OON ONN OON PON POO PPO n＝3 PPO POO PON PNN ONN PNN PON POO PPO n＝4 PPO PPN PON OON ONN OON PON PPN PPO n＝5 PPO PPN PON PNN ONN PNN PON PPN PPO

[0134] The order of all items within the second sector is shown in Table 8.

[0135] Table 8

[0136] n＝1 PPO OPO OOO OON NON OON OOO OPO PPO n＝2 PPO OPO OPN OON NON OON OPN OPO PPO n＝3 PPO PPN OPN OON NON OON OPN PPN PPO n＝4 PPO OPO OPN NPN NON NPN OPN OPO PPO n＝5 PPO PPN OPN NPN NON NPN OPN PPN PPO

[0137] The order of all items within the third sector is shown in Table 9.

[0138] Table 9

[0139] n＝1 OPP OPO OOO NOO NON NOO OOO OPO OPP n＝2 OPP OPO NPO NOO NON NOO NPO OPO OPP n＝3 OPP OPO NPO NPN NON NPN NPO OPO OPP n＝4 OPP NPP NPO NOO NON NOO NPO NPP OPP n＝5 OPP NPP NPO NPN NON NPN NPO NPP OPP

[0140] The order of all items in the fourth sector is shown in Table 10.

[0141] Table 10

[0142] n＝1 OPP OOP OOO NOO NNO NOO OOO OOP OPP n＝2 OPP OOP NOP NOO NNO NOO NOP OON OPP n＝3 OPP NPP NOP NOO NNO NOO NOP NPP OPP n＝4 OPP OOP NOP NNP NNO NNP NOP OOP OPP n＝5 OPP NPP NOP NNP NNO NNP NOP NPP OPP

[0143] The order of all items within the fifth sector is shown in Table 11.

[0144] Table 11

[0145]

[0146]

[0147] The order of all items in the sixth sector is shown in Table 12.

[0148] Table 12

[0149] n＝1 POP POO OOO ONO ONN ONO OOO POO POP n＝2 POP POO PNO ONO ONN ONO PNO POO POP n＝3 POP PNP PNO ONO ONN ONO PNO PNP POP n＝4 POP POO PNO PNN ONN PNN PNO POO POP n＝5 POP PNP PNO PNN ONN PNN PNO PNP POP

[0150] Then, the basic voltage vector time of the nine-segment sequential voltage vector output in the table is mapped to the actual switch to output the PWM waveform, thus completing the space vector pulse width modulation.

[0151] In this embodiment, both the virtual small vector and the virtual medium vector are reconstructed. Alternatively, a preset virtual small vector (i.e., the virtual small vector in the prior art) can be combined with the virtual medium vector of this embodiment to determine the basic voltage vector time, which is then mapped to the actual switch to output a PWM waveform, thus completing space vector pulse width modulation. Furthermore, the virtual small vector in this embodiment can be combined with a preset virtual medium vector (i.e., the virtual medium vector in the prior art) to determine the basic voltage vector time.

[0152] 6) Simulation modeling.

[0153] Simulation modeling was performed using the SIMULINK simulation platform. Quasi-PR control was employed, simulating a situation where the capacitor value deviates. Traditional VSVPWM, VSVPWM with only small vector voltage equalization, and the VSVPWM of this invention were used as space vector pulse width modulations, keeping other conditions constant. The simulation results for the midpoint potential equalization speed are as follows: Figure 7 , Figure 8 , Figure 9 As shown, the voltage equalization effect of VSVPWM with small vector voltage equalization and the VSVPWM of the present invention are compared. Figure 10 , Figure 11 As shown, the grid-connected current of the present invention is finally observed as follows. Figure 12 As shown.

[0154] The grid-connected inverter control method provided by this invention utilizes coordinate transformation to convert the spatial vector to a 60° coordinate system, and then uses coordinate transformation to convert the remaining sectors into the first sector, greatly reducing the computational load of the entire system. Simultaneously, this invention reconstructs virtual small vectors and virtual medium vectors, using them to control the midpoint voltage. This allows for control of the midpoint voltage in every region within each sector. The virtual medium vector reduces the impact of voltage equalization control on the grid-connected current, balancing midpoint potential control with grid-connected current power quality. This invention also introduces a voltage equalization factor, adjusting it based on the midpoint potential deviation as a control condition. This ensures a stronger voltage equalization effect as the midpoint voltage deviation increases. Furthermore, the reconstructed virtual medium vector improves the voltage equalization effect and speed at high modulation depths, while simultaneously guaranteeing grid-connected power quality.

Claims

1. A control method of a grid-connected inverter, characterized by, Includes the following steps: 1) Construct a space voltage vector, which includes multiple basic vectors. The types of basic vectors include zero vector, small vector, medium vector and large vector; 2) Construct virtual small vectors using the following formula: Where V1 is a virtual small vector, T1 is the duration of action of the virtual small vector, V2 and V3 are small vectors corresponding to the virtual small vector V1, σ is the self-adjusting equalization factor, and -1≤σ≤1; 3) Construct the virtual vector using the following formula: Among them, V 11 For virtual vectors, T 11 V4, V5, and V6 are the time of action of the virtual vector V. 11 The corresponding vectors are small or medium vectors, τ and υ are reconstruction factors, and -1≤τ and υ≤1, μ and δ are self-adjusting equalization factors, and -0.5≤μ≤0.5 and -0.5≤δ≤0.5; 4) Obtain the reference voltage vector of the grid-connected inverter, determine the sector in which the reference voltage vector is located in the space voltage vector and the region within the sector, and select the composite vector required to synthesize the reference voltage vector. The composite vector includes the zero vector and the large vector, and also includes any one of the following three types: small vector and virtual medium vector, virtual small vector and medium vector, and virtual small vector and virtual medium vector; determine the basic vector according to the corresponding composite vector and determine the output order of the basic vector; determine the switching sequence of the switching devices in the grid-connected inverter according to the output order. 5) Determine the basic vector time of the basic vector that constitutes the composite vector using the volt-second balance principle; obtain the vector pulse width modulation wave of the grid-connected inverter based on the output order and basic vector time of the basic vector, and control the grid-connected inverter based on the vector pulse width modulation wave.

2. The control method of the grid-connected inverter according to claim 1, characterized by, In step 2), the adaptive equalization factor is obtained using the following formula: σ = λ * (ΔV * *ξ) Wherein, ΔV * is the normalized midpoint potential deviation, ξ is an empirical proportionality coefficient, λ is a sign factor determined by the current direction of the reference voltage vector and the midpoint potential deviation; the midpoint potential deviation is the voltage difference of the two voltage-sharing capacitors set on the DC side of the grid-connected inverter after normalization processing.

3. The control method of the grid-connected inverter according to claim 2, characterized by, The empirical proportionality coefficient is determined based on the control accuracy of the midpoint potential, the DC bus voltage, and the midpoint potential deviation during the dynamic process. The empirical proportionality coefficient is directly proportional to the control accuracy of the midpoint potential and inversely proportional to the ratio of the midpoint potential deviation to the DC bus voltage.

4. The control method of the grid-connected inverter according to claim 1, characterized by, The reconstruction factor is determined based on the midpoint potential deviation; when the synthesized vector used in the synthesized reference voltage vector makes the midpoint potential balanced, the corresponding reconstruction factor is greater than 0; when the synthesized vector used in the synthesized reference voltage vector makes the midpoint potential deviation increase, the corresponding reconstruction factor is less than or equal to 0.

5. The control method of the grid-connected inverter according to claim 1, characterized by, The self-adjusting equal pressure factor is obtained by the following formula: Wherein, ΔV * is the normalized midpoint potential deviation, ξ1 and ξ2 are both empirical proportionality coefficients, λ1 and λ2 are both sign coefficients, determined by the current direction of the reference voltage vector and the midpoint potential deviation; the midpoint potential deviation is the voltage difference of the two voltage-sharing capacitors set on the DC side of the grid-connected inverter after normalization processing.

6. The control method of the grid-connected inverter according to claim 5, characterized by, The empirical proportionality coefficient is determined based on the control accuracy of the midpoint potential, the DC bus voltage, and the midpoint potential deviation. The empirical proportionality coefficient is directly proportional to the control accuracy of the midpoint potential and inversely proportional to the ratio of the midpoint potential deviation to the DC bus voltage.

7. The control method of the grid-connected inverter according to claim 1, characterized by, The reference voltage vector is obtained by the following method: obtaining the current reference value, the current value of the grid current, the current value of the capacitor current, and the current value of the grid voltage. The capacitor current is the capacitor current of the LCL filter set on the AC side of the grid-connected inverter. The difference between the current reference value and the current grid current is used to adjust and control the output value. The current grid voltage is added to the output value and the current capacitor current value, which is then subtracted by a set multiple, to obtain the reference voltage vector.

8. The control method of the grid-connected inverter according to claim 1, characterized by The space voltage vector comprises six sectors, each containing five regions. When the reference voltage vector is located in the first region of the first sector of the space voltage vector, the output order of the basic vector is: PPO, POO, OOO, OON, ONN, OON, OOO, POO, PPO. When the reference voltage vector is located in the second region of the first sector of the space voltage vector, the output order of the basic vector is: PPO, POO, PON, OON, ONN, OON, PON, POO, PPO. When the reference voltage vector is located in the third region of the first sector of the space voltage vector, the output order of the basic vector is: PPO, POO, PON, PNN, ONN, PNN, PON, POO, PPO. When the reference voltage vector is in the fourth region of the first sector of the space voltage vector, the output order of the basic vector is: PPO, PPN, PON, OON, ONN, OON, PON, PPN, PPO; when the reference voltage vector is in the fifth region of the first sector of the space voltage vector, the output order of the basic vector is: PPO, PPN, PON, PNN, ONN, PNN, PON, PPN, PPO; when the reference voltage vector is in the first region of the second sector of the space voltage vector, the output order of the basic vector is: PPO, OPO, OOO, OON, NON, OON, OOO, OPO, PPO; when the reference voltage vector is in the second region of the second sector of the space voltage vector, the output order of the basic vector is: PPO, OPO, OPN, OON, NON, OON, OPN, OPO, PPO. When the reference voltage vector is in the third region of the second sector of the space voltage vector, the output order of the basic vector is: PPO, PPN, OPN, OON, NON, OON, OPN, PPN, PPO; when the reference voltage vector is in the fourth region of the second sector of the space voltage vector, the output order of the basic vector is: PPO, OPO, OPN, NPN, NON, NPN, OPN, OPO, PPO. When the reference voltage vector is in the fifth region of the second sector in the space voltage vector, the output order of the basic vector is: PPO, PPN, OPN, NPN, NON, NPN, OPN, PPN, PPO; When the reference voltage vector is in the first region of the third sector of the space voltage vector, the output order of the basic vector is: OPP, OPO, OOO, NOO, NON, NOO, OOO, OPO, OPP; when the reference voltage vector is in the second region of the third sector of the space voltage vector, the output order of the basic vector is: OPP, OPO, NPO, NOO, NON, NOO, NPO, OPP, OPP; when the reference voltage vector is in the third region of the third sector of the space voltage vector, the output order of the basic vector is: OPP, OPO, NPO, NPN, NON, NPN, NPO, OPP, OPP. When the reference voltage vector is in the fourth region of the third sector of the space voltage vector, the output order of the basic vector is: OPP, NPP, NPO, NOO, NON, NOO, NPO, NPP, OPP; when the reference voltage vector is in the fifth region of the third sector of the space voltage vector, the output order of the basic vector is: OPP, NPP, NPO, NPN, NON, NPN, NPO, NPP, OPP; when the reference voltage vector is in the first region of the fourth sector of the space voltage vector, the output order of the basic vector is: OPP, OOP, OOO, NOO, NNO, NOO, OOO, OOP, OPP. When the reference voltage vector is in the second region of the fourth sector in the space voltage vector, the output order of the basic vector is: OPP, OOP, NOP, NOO, NNO, NOO, NOP, OOP, OPP; When the reference voltage vector is in the third region of the fourth sector in the space voltage vector, the output order of the basic vector is: OPP, NPP, NOP, NOO, NNO, NOO, NOP, NPP, OPP; When the reference voltage vector is in the fourth region of the fourth sector in the space voltage vector, the output order of the basic vector is: OPP, OOP, NOP, NNP, NNO, NNP, NOP, OOP, OPP; When the reference voltage vector is in the fifth region of the fourth sector of the space voltage vector, the output order of the basic vector is: OPP, NPP, NOP, NNP, NNO, NNP, NOP, NPP, OPP; when the reference voltage vector is in the first region of the fifth sector of the space voltage vector, the output order of the basic vector is: POP, OOP, OOO, ONO, NNO, ONO, OOO, OOP, POP; when the reference voltage vector is in the second region of the fifth sector of the space voltage vector, the output order of the basic vector is: POP, OOP, ONP, NNP, N... NO, NNP, ONP, OOP, POP; When the reference voltage vector is in the third region of the fifth sector of the space voltage vector, the output order of the basic vector is: POP, OOP, ONP, ONO, NNO, ONO, ONP, PNP, POP; When the reference voltage vector is in the fourth region of the fifth sector of the space voltage vector, the output order of the basic vector is: POP, PNP, ONP, ONO, NNO, ONO, ONP, PNP, POP; When the reference voltage vector is in the fifth region of the fifth sector of the space voltage vector, the output order of the basic vector is: The output order of the basic vectors is: POP, PNP, ONP, NNP, NNO, NNP, ONP, PNP, POP; when the reference voltage vector is in the first region of the sixth sector of the space voltage vector, the output order of the basic vectors is: POP, POO, OOO, ONO, ONN, ONO, OOO, POO, POP; when the reference voltage vector is in the second region of the sixth sector of the space voltage vector, the output order of the basic vectors is: POP, POO, PNO, ONO, ONN, ONO, P ... second region of the sixth sector of the space voltage vector, the output order of the basic vectors is: POP, POO, PNO, ONO, ONN, ONO, PNO, POO, POP; when the reference voltage vector is in the second region of the sixth sector of the space voltage vector, the output order of the basic vectors is: POP, POO, PNO, ONO, ONO, PNO, PNO, POP; when the reference voltage vector is in the second region of the sixth sector of the space voltage vector, the output order of the basic vectors is: POP, POO, PNO, ONO, ONO, PNO, PNO, POP; when the reference voltage vector is in the second region of the sixth sector of the space voltage vector, the output order of the basic vectors When the reference voltage vector is in the third region of the sector, the output order of the basic vector is: POP, PNP, PNO, ONO, ONN, ONO, PNO, PNP, POP; when the reference voltage vector is in the fourth region of the sixth sector of the space voltage vector, the output order of the basic vector is: POP, POO, PNO, PNN, ONN, PNN, PNO, POO, POP; when the reference voltage vector is in the fifth region of the sixth sector of the space voltage vector, the output order of the basic vector is: POP, PNP, PNO, PNN, ONN, PNN, PNO, PNP, POP.

9. The control method of the grid-connected inverter according to any one of claims 1 to 8, characterized by, The sector in which the reference voltage vector lies within the space voltage vector is obtained using the following formula: Where N is the sector position of the space voltage vector, V REFα V REFβ V REF In the αβ coordinate system, the α and β components, V REF For the reference voltage vector, Ceil is used for the up modulo operation. The region where the reference voltage vector is located within the sector of the space voltage vector is determined by the following method: when When the reference voltage vector is located in the first region of the sector in the space voltage vector; when and and When, the reference voltage vector is located in the second region of the sector in the space voltage vector; when and When, the reference voltage vector is located in the third region of the sector in the space voltage vector; when and When, the reference voltage vector is located in the fourth region of the sector in the space voltage vector; when and At that time, the reference voltage vector is located in the fifth region of the sector within the space voltage vector; where, and These are the per-unit components of the reference voltage vector within a 60° sector in the gh coordinate system, representing the g-axis and h-axis components, respectively.

10. The control method of the grid-connected inverter according to claim 1, characterized by, The space voltage vector is a space voltage vector in the α-β coordinate system. The space voltage vector is transformed to the gh 60° coordinate system using the following formula: wherein V α , V β are the reference voltage components of the a-axis and the b-axis, respectively, in the a-b coordinate system; V g , V h are the reference voltage components of the g-axis and the h-axis, respectively, in the g-h 60° coordinate system; Based on rotational symmetry, the remaining sectors are rotated to the first sector using the following formula for corresponding calculations: wherein, Vg(N) and Vh(N) are the g-axis and h-axis reference voltage components of the first major sector in g-h 60° coordinates, respectively, and N is the Nth major sector, V h N Vg(N) and Vh(N) are the g-axis and h-axis reference voltage components of the Nth sector in g-h coordinates, respectively.

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