Photovoltaic inverter control method and control circuit based on near virtual vector pulse width modulation

Abstract

A photovoltaic inverter control method based on near virtual vector pulse width modulation comprises the following steps: collecting a grid-side current, a grid-side voltage and a power grid phase of a photovoltaic inverter, and processing the grid-side current, the grid-side voltage and the power grid phase to obtain a reference voltage; the reference voltage is mapped to a vector space constructed in advance, the vector space comprises six large sectors, and each large sector is divided into five small sectors through two long vectors, two virtual small vectors and one virtual medium vector; adjusting a midpoint potential control factor based on the relationship between the midpoint potential deviation and the midpoint current, and adjusting a switching sequence of the photovoltaic inverter; and outputting a PWM control signal based on the adjusted switching sequence of the photovoltaic inverter. According to the invention, the problems of difficulty in common-mode voltage suppression and difficulty in neutral-point voltage balance of an existing NPC type photovoltaic inverter can be effectively solved.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic inverters, and in particular to a photovoltaic inverter control method and a control circuit based on adjacent virtual vector pulse width modulation. Background Art

[0002] After years of development, global electricity consumption has continued to increase, fossil energy resources are becoming increasingly depleted, and environmental issues are becoming increasingly prominent. Traditional coal-fired power generation, due to its high pollution and other drawbacks, is no longer able to meet the demands of today. There is an urgent need for environmentally friendly, sustainable, and clean energy sources for power generation. A number of renewable energy sources, such as wind, solar, geothermal, and tidal energy, have become a hot topic. Solar energy is utilized by converting solar energy into electricity using photovoltaic cells. This form of energy utilization is considered clean and has minimal environmental impact, as waste is only generated during the manufacturing and disposal of the photovoltaic cells. For this reason, photovoltaic power generation is considered a highly promising new energy source among the many forms of renewable energy generation.

[0003] Grid-connected inverters are a crucial interface for connecting photovoltaic power generation to the grid, and their performance directly determines the quality of the incoming power. In low-power photovoltaic power generation applications, two-level inverters are widely used due to their low manufacturing cost and ease of design. However, due to the voltage and overcurrent limitations of individual semiconductor devices, high-power photovoltaic power generation often utilizes a multi-level inverter system in series and parallel configurations. However, this system structure is complex and difficult to control. To address these issues, high-power multi-level inverters have emerged. Compared to two-level inverters, three-level inverters offer the advantages of higher output power and higher voltage ratings. NPC three-level inverters are the fastest-growing and most widely used type of multi-level inverter.

[0004] While NPC three-level inverters offer many advantages, they face two key technical challenges in practical operation: common-mode voltage suppression and neutral-point potential balancing. Common-mode voltage refers to the voltage fluctuation at the inverter output relative to the neutral point. Excessively high common-mode voltage can cause problems such as electrocorrosion in motor bearings and electromagnetic interference in cables, potentially impacting overall system stability. Therefore, measures must be taken to limit the amplitude of the common-mode voltage when designing the inverter. In NPC three-level topologies, the presence of DC bus capacitance makes the system more susceptible to neutral-point potential shifts, especially under dynamic load changes or unbalanced conditions. This shift can lead to uneven voltage stress on switching devices, impacting system reliability and lifespan. Summary of the Invention

[0005] In order to address the deficiencies in the prior art, the present invention provides a photovoltaic inverter control method and control circuit based on adjacent virtual vector pulse width modulation, which can effectively solve the problems of common-mode voltage suppression and mid-point voltage balancing difficulties in existing NPC type photovoltaic inverters.

[0006] In order to achieve the above object, the specific solution adopted by the present invention is: a photovoltaic inverter control method based on adjacent virtual vector pulse width modulation, comprising the following steps: Collect the grid-side current, grid-side voltage and grid phase of the photovoltaic inverter and obtain the reference voltage after processing; The reference voltage is mapped to a pre-built vector space. The vector space includes six large sectors. Each large sector is divided into five small sectors by two long vectors, two virtual small vectors, and a virtual middle vector. The virtual small vector is synthesized based on the zero vector and the two long vectors. The virtual middle vector is synthesized based on the three middle vectors and the midpoint potential control factor. The three middle vectors are the middle vectors of the large sector and the two other adjacent large sectors. Each small sector contains a virtual middle vector. Adjusting the midpoint potential control factor based on the relationship between the midpoint potential deviation and the midpoint current, and adjusting the switching sequence of the photovoltaic inverter; A PWM control signal is output based on the adjusted switching sequence of the photovoltaic inverter.

[0007] As a further optimization of the photovoltaic inverter control method based on adjacent virtual vector pulse width modulation, a method for synthesizing a small virtual vector is to add a zero vector and a half value of a long vector to obtain a small virtual vector. The synthesis method of the virtual mid-vector is: V′ m =kV m1 +(1-2k)V m2 +kV m3 , where V m1 、V m2 and V m3 are the three midpoint vectors involved in the synthesis, and k is the midpoint potential control factor.

[0008] As a further optimization of the photovoltaic inverter control method based on adjacent virtual vector pulse width modulation: after constructing the vector space, a value table of the midpoint potential control factor is set; When the midpoint potential control factor is adjusted based on the relationship between the midpoint potential deviation and the midpoint current, the value of the midpoint potential control factor is determined according to a pre-set value table.

[0009] As a further optimization of the above-mentioned photovoltaic inverter control method based on adjacent virtual vector pulse width modulation: after the vector space is constructed, multiple switch sequence tables corresponding to large sectors are constructed, and each switch sequence table includes multiple switch sequence entries corresponding to small sectors.

[0010] A photovoltaic inverter control circuit based on adjacent virtual vector pulse width modulation includes: The first acquisition module is used to collect the grid-side current, grid-side voltage and grid phase of the photovoltaic inverter, and obtain the reference voltage after processing; A PWM output module is used to map the reference voltage into a pre-built vector space, adjust the midpoint potential control factor based on the relationship between the midpoint potential deviation and the midpoint current, adjust the switching sequence of the photovoltaic inverter, and output a PWM control signal based on the adjusted switching sequence of the photovoltaic inverter; The driving circuit is used to drive the photovoltaic inverter based on the PWM control signal.

[0011] As a further optimization of the above-mentioned photovoltaic inverter control circuit based on adjacent virtual vector pulse width modulation: the first acquisition module includes a phase-locked loop PLL and a voltage and current measurement module, wherein the phase-locked loop PLL is used to acquire the grid phase and transmit it to the PWM output module, and the voltage and current measurement module is used to acquire the grid-side current and grid-side voltage and transmit them to the PWM output module.

[0012] As a further optimization of the photovoltaic inverter control circuit based on adjacent virtual vector pulse width modulation, a Clark transformation module, a Park transformation module, a PI controller and an inverse Park transformation module are sequentially arranged between the voltage and current measurement module and the PWM output module.

[0013] As a further optimization of the above-mentioned photovoltaic inverter control circuit based on adjacent virtual vector pulse width modulation: the circuit includes a second acquisition module, which is used to collect first voltage values and second voltage values of two equalizing capacitors of the photovoltaic inverter, and calculate the midpoint potential based on the first voltage value and the second voltage value.

[0014] As a further optimization of the above photovoltaic inverter control circuit based on adjacent virtual vector pulse width modulation: the control circuit is suitable for a neutral point clamped three-level photovoltaic inverter.

[0015] Beneficial effects: The control method of the present invention discards all small vectors in the vector space and the zero vector that generates a high common-mode voltage amplitude, thereby suppressing the common-mode voltage problem; then, a virtual small vector is synthesized using the zero vector that does not generate a common-mode voltage and the long vector, and then a virtual middle vector is synthesized using three adjacent middle vectors, and a midpoint potential control factor k is introduced into the virtual middle vector. By adjusting the control factor k, the inflow and outflow of the midpoint current are controlled to balance the midpoint potential; based on the redesigned small sector arrangement, the virtual middle vector participates in the control when the reference voltage vector falls into any sector, thereby ensuring that the virtual middle vector always plays a role; and the output order of the voltage vectors is rearranged to avoid direct P→N jumps in the switching tube. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a flow chart of the method of the present invention; Figure 2 Schematic diagram of a method for dividing small sectors in a large sector 1 in an embodiment; Figure 3 It is a schematic diagram of the control circuit of the present invention; Figure 4 This is the simulation result diagram of common mode voltage, DC side capacitor voltage and grid current when the modulation index is 0.8; Figure 5 This is the simulation result diagram of common mode voltage, DC side capacitor voltage and grid current when the modulation index is 0.5; Figure 6 This is the simulation result diagram of common mode voltage, DC side capacitor voltage and grid current when the modulation index is 0.2; Figure 7 This is the simulation result diagram of grid current power quality when the modulation index is 0.8; Figure 8 This is the simulation result of grid current power quality when the modulation index is 0.5 Figure 9 This is the simulation result diagram of grid current power quality when the modulation index is 0.2. DETAILED DESCRIPTION

[0017] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0018] like Figure 1 As shown, the photovoltaic inverter control method based on adjacent virtual vector pulse width modulation includes S1 to S4.

[0019] S1. Collect the grid-side current, grid-side voltage, and grid phase of the photovoltaic inverter and process them to obtain a reference voltage. Specifically, the reference voltage is generated based on the grid-side current and voltage. In the subsequent process of generating a PWM control signal for controlling the photovoltaic inverter, the reference voltage can control the waveform of the PWM control signal, and the grid phase can control the phase of the PWM control signal.

[0020] S2. Map the reference voltage to a pre-constructed vector space. The vector space includes six large sectors. Each large sector is divided into five small sectors by two long vectors, two virtual small vectors, and one virtual middle vector. The virtual small vectors are synthesized based on the zero vector and the two long vectors. The virtual middle vector is synthesized based on the three middle vectors and the midpoint potential control factor. The three middle vectors are the middle vectors of the large sector and the other two adjacent large sectors. When the reference voltage vector is located in any small sector, the virtual middle vector participates in the synthesis.

[0021] When constructing the vector space, the present invention first constructs six large sectors based on the existing VSVPWM (Virtual Space Vector Pulse Width Modulation) strategy, designated Large Sector I, Large Sector II, Large Sector III, Large Sector IV, Large Sector V, and Large Sector VI. Furthermore, five small sectors are partitioned from each large sector. Taking Large Sector I as an example, to reduce the common-mode voltage amplitude, the zero vectors PPP and NNN with high common-mode voltage amplitudes, as well as all small vectors, are discarded. The long vectors PNN and PPN are retained, and only the zero vector V′0, OOO, is used.

[0022] More specifically, the virtual small vector is synthesized by adding the zero vector to half the value of the long vector. There are two virtual small vectors: small vector V1', which is a virtual synthesis of half the zero vector OOO and half the long vector PNN to compensate for the small vector discarded due to common-mode voltage suppression. Small vector V2', which is a synthesis of half the zero vector OOO and half the long vector PPN.

[0023] The synthesis method of the virtual mid-vector is: V′ m =kV m1 +(1-2k)V m2 +kV m3 , where V m1 、V m2 and V m3are the three midpoint vectors involved in the synthesis, and k is the midpoint potential control factor. Because the long vector does not affect the midpoint potential and the resulting common-mode voltage amplitude is small, it is not used for virtual vector synthesis. On the other hand, to control midpoint potential fluctuations, three adjacent midpoint vectors PNO, PON, and OPN are selected to synthesize a virtual midpoint vector V′3. A midpoint potential control factor k is designed within the virtual midpoint vector V′3 to control its magnitude and maintain midpoint potential equilibrium. The midpoint potential control factor k has a value range of k∈(0,1).

[0024] Based on the above virtual vector synthesis process, there are six vectors in large sector I, which are as follows: Zero vector: V′0=V OOO ; Virtual small vector: Virtual mean vector: V′3=kV PNO +(1-2k)V PON +kV OPN Long vector:

[0025] The common-mode voltage data of each vector are shown in Table 1.

[0026] Table 1 Common mode voltage data of space vector

[0027] The midpoint current data of each vector are shown in Table 2.

[0028] Table 2 Midpoint current data of space vector

[0029] After improving the VSVPWM strategy, the improved strategy of the present invention can be called NVSVPWM (Near Virtual Space Vector Pulse Width Modulation). As can be seen from Table 2, V OOO 、V PNO 、V PNO 、V OPN No common mode voltage is generated, V PNN 、V PPN Can generate an amplitude of 1 / 6V dc Common mode voltage, so the NVSVPWM strategy can reduce the common mode voltage to 1 / 6V dc the following.

[0030] Furthermore, based on the new virtual small vectors V1'V'2, the virtual middle vector V'3 and the two retained long vectors PNN and PPN, the large sector I is divided into five small sectors, which are respectively recorded as small sector 1, small sector 2, small sector 3, small sector 4 and small sector 5.

[0031] Based on the distribution of the above small sectors, V PNO The output midpoint current in the corresponding switching state is i c , V PON The output midpoint current in the corresponding switching state is positive i b , V OPN The output midpoint current in the corresponding switching state is i a The zero vector and the large vector have no effect on the midpoint potential. Combined with the calculation formula of the virtual midpoint vector, the midpoint current generated by the virtual midpoint vector is as follows:

[0032] From the above formula, we can know that the midpoint current generated by the virtual mid vector is (1-3k)i b When the reference voltage is located in small sector 2, small sector 3, small sector 4 and small sector 5, under the action of the virtual voltage vector, the midpoint current generated is (1-3k)i b Combined with the range of k value, the controllable range of midpoint current is [-2i b ,i b ], at this time, you only need to adjust k to control the midpoint current i o The inflow and outflow of the circuit can be controlled in real time to achieve real-time control of the midpoint potential.

[0033] However, under the traditional VSVPWM sector division, when the reference voltage vector is in small sector 1, the reference voltage is synthesized by the virtual zero vector V′0 and the virtual small vectors V1' and V′2 respectively. Therefore, when there is a deviation in the midpoint potential, the midpoint potential cannot be controlled to a balanced state by adjusting the midpoint potential control factor k. Moreover, when the reference voltage is in small sector 1 after the virtual vector is redefined, only the zero vector and the large vector participate in the synthesis, and the photovoltaic inverter switch tube will have a direct jump from P to N, and the small sector arrangement needs to be re-divided. The 1 and 2 small sectors are divided by the virtual mid vector, and new 1 and 2 small sectors are re-divided to ensure that the reference voltage vector has a virtual mid vector in each sector. Finally, in the large sector I, the distribution of the five small sectors is as follows: Figure 2 shown.

[0034] In summary, the main principles of the NVSVPWM strategy provided by the present invention are as follows.

[0035] Set midpoint current i oThe outflow midpoint is positive. According to the formula for generating midpoint current under the action of the virtual midpoint vector, according to i o The influence of the flow direction on the voltage of the clamping capacitor of the photovoltaic inverter requires a reasonable design of the inference rule to adjust the k value so that the midpoint potential is stable at the equilibrium position. When the voltage difference ΔU between the upper and lower equalizing capacitors on the DC side of the grid-connected photovoltaic inverter is zero, it indicates that the current midpoint potential has no deviation. At this time, according to the midpoint potential change trend (i.e., i o direction), reasonably determine the control factor. If the midpoint current is zero at this time, it means that the midpoint potential has no fluctuation and can be kept in equilibrium. No additional control is required, and the midpoint current is kept at zero. If the midpoint potential change trend is positive (i o <0), indicating that the midpoint potential will shift upward at the next moment, the midpoint current needs to be reversed to reduce the midpoint potential and compensate for the fluctuation caused by the upward shift of the midpoint potential in the current control cycle, and vice versa. When the voltage difference between the upper and lower equalizing capacitors on the DC side is greater than zero, it indicates that the current midpoint potential is too low. To increase the midpoint potential, it is necessary to control the midpoint current to flow into the midpoint. If the trend of the midpoint potential change is positive at this time, it indicates that the midpoint current is flowing into the midpoint, then it is necessary to maintain the direction of the midpoint current and raise the midpoint potential; otherwise, the midpoint current should be controlled in the reverse direction. When the voltage difference between the upper and lower capacitors on the DC side is less than zero, it indicates that the current midpoint potential is too high, and the midpoint current needs to be controlled to flow out of the midpoint. If the trend of the midpoint potential change is positive at this time, the midpoint current needs to be reversed to make the current flow out of the midpoint; if the midpoint potential is still decreasing at this time, the direction of the midpoint current remains unchanged.

[0036] To efficiently control the midpoint current, after constructing the vector space, a table of midpoint potential control factors is set. When adjusting the midpoint potential control factor based on the relationship between the midpoint potential deviation and the midpoint current, the value of the midpoint potential control factor is determined according to the pre-set table. Taking large sector I as an example, the table of midpoint potential control factors is shown in Table 3.

[0037] Table 3 Midpoint potential control factor value table

[0038] Because the value of the midpoint potential control factor depends on the reference voltage, and the coordinate system used in the VSVPWM strategy is a rectangular coordinate system, the reference voltage vector needs to be calculated using complex trigonometric functions. To avoid the problems of increased load and increased delay caused by complex trigonometric function calculations in a rectangular coordinate system, the present invention adopts a 60° coordinate system. To calculate in a 60° coordinate system, the rectangular coordinate system must be converted to a 60° coordinate system. The relationship between the reference voltage vector in the gh coordinate system and in the rectangular coordinate system can be seen in Figure 2 As shown, the specific formula is as follows:

[0039] From the above formula, we can derive the matrix required to transform from the 60° coordinate system to the rectangular coordinate system:

[0040] According to Clark transformation, the matrix formula of the three-phase coordinate system to the two-phase rectangular coordinate system is:

[0041] Therefore, the matrix form from the three-phase coordinate system ABC to the two-phase stationary coordinate system gh, i.e. the 60° coordinate system, is:

[0042] After that, the remaining large sectors can be normalized to large sector I after rotation. The relationship matrix between the two is as follows, where the value of N is 1, 2, 3, 4, 5, or 6.

[0043] Furthermore, for NPC three-level grid-connected inverters, switching losses and temperature requirements need to be further improved. This requires adjusting the switching sequence to minimize the on- and off-frequency of the switches. Greater losses increase the heat generated by the switches, which can compromise normal inverter operation and shorten the inverter's service life. Therefore, optimizing the order of each basic voltage vector can significantly reduce losses, minimize heat dissipation, and extend the inverter's service life. To achieve this, after constructing the vector space, multiple switching sequence tables corresponding to large sectors are constructed. Each switching sequence table includes multiple switching sequence entries corresponding to small sectors. Specifically, the present invention employs a five-segment SVPWM modulation method for ordering, avoiding direct state transitions from P to N for the switches. Table 4 shows the switching sequence table.

[0044] Table 4 Switching sequence table

[0045] S3. Adjust the midpoint potential control factor based on the relationship between the midpoint potential deviation and the midpoint current, and adjust the switching sequence of the photovoltaic inverter. The adjustment is based on the above-mentioned midpoint potential control factor value table and switching sequence table, which will not be repeated here.

[0046] S4 outputs a PWM control signal based on the adjusted switching sequence of the photovoltaic inverter.

[0047] The present invention further provides a photovoltaic inverter control circuit based on adjacent virtual vector pulse width modulation, which is used to implement the above method. The control circuit includes a first acquisition module, a PWM output module, a drive circuit and a second acquisition module.

[0048] The first acquisition module is configured to acquire the grid-side current, grid-side voltage, and grid phase of the photovoltaic inverter and process these data to obtain a reference voltage. The first acquisition module includes a phase-locked loop (PLL) and a voltage and current measurement module. The PLL acquires the grid phase and transmits it to the PWM output module, while the voltage and current measurement module acquires the grid-side current and voltage and transmits them to the PWM output module. A Clark transform module, a Park transform module, a PI controller, and an inverse Park transform module are sequentially arranged between the voltage and current measurement module and the PWM output module.

[0049] The PWM output module is used to map the reference voltage into a pre-built vector space, adjust the midpoint potential control factor based on the relationship between the midpoint potential deviation and the midpoint current, adjust the switching sequence of the photovoltaic inverter, and output a PWM control signal based on the adjusted switching sequence of the photovoltaic inverter.

[0050] The driving circuit is used to drive the photovoltaic inverter based on the PWM control signal.

[0051] The circuit includes a second acquisition module, which is used to acquire a first voltage value and a second voltage value of two equalizing capacitors of the photovoltaic inverter, and calculate a midpoint potential based on the first voltage value and the second voltage value.

[0052] Furthermore, the control circuit is applicable to a midpoint clamped three-level photovoltaic inverter, and the specific structure is as follows: Figure 3 shown.

[0053] The output end of the DC source is connected to the input end of the midpoint clamped three-phase three-level inverter circuit. The midpoint clamped three-phase three-level inverter circuit is composed of a voltage-sharing capacitor C1, a voltage-sharing capacitor C2, and an inverter bridge arm. The inverter bridge arm includes 12 power switches and 6 clamping diodes. Each phase bridge arm has 4 power switches, namely S x1 、S x2 、S x3 、S x4 (x=a, b, c), the six clamping diodes are clamping diode D1, clamping diode D2, clamping diode D3, clamping diode D4, clamping diode D5, and clamping diode D6. The cathode terminals of clamping diodes D1, D3, and D5 are connected to the fully controlled switching device S a1 、S b1 、S c1The emitter of the clamping diodes D1, D3, and D5 is connected to the neutral line, the cathode ends of the clamping diodes D2, D4, and D6 are connected to the neutral line, and the anode ends of the clamping diodes D2, D4, and D6 are connected to the fully controlled switching device S a3 、S b3 、S c3 The output of the neutral point clamped three-phase three-level inverter circuit is connected to the input of the LCL filter circuit. The LCL filter circuit consists of a filter inductor L C , filter inductor L g and filter capacitor C. The output of the LCL filter circuit is connected to the public AC grid. The input of the phase-locked loop (PLL) is connected to the public grid, and the output of the phase-locked loop is connected to the input of the controller. The grid-side current and voltage measured by the sensor are converted into a reference voltage U through a series of transformations. ref The grid phase cosθ is fed into the improved VSVPWM modulation strategy to output a PWM wave. The sensor module includes multiple voltage and current sensors for detecting the grid-side voltage, grid-side current, filter capacitor voltage, and inverter output current. It also detects the midpoint potential, midpoint current, and inverter DC voltage. The sensor module's output is connected to the controller's input to transmit the collected data, which the controller then uses for logical analysis and processing. The controller's output is connected to the driver circuit's input to control the clamping diodes and fully controlled switching devices in the diode-clamped three-phase, three-level inverter circuit.

[0054] Inverter bridge when S x1 、S x2 When it is turned on, it is in P state. x2 、S x3 When conducting, it is in the O state. x3 、S x4 When conducting, it is in N state. The three states correspond to three different AC measurement voltages V dc / 2,0,-V dc / 2. After permutation and combination, there are 27 switching states for the three phases A, B, and C, corresponding to 27 voltage vectors. Among them, the zero vector OOO will neither generate common mode voltage nor affect the midpoint potential. The zero vectors PPP and NNN have no effect on the midpoint potential but will generate voltages with amplitudes of V dc / 2 and -V dc / 2 common mode voltage; six pairs of positive and negative redundant small vectors can affect the midpoint potential fluctuation, but the positive small vector can produce an amplitude of ±V dc / 3 of the common mode voltage, and the negative small vector only produces an amplitude of ±V dc / 6 common mode voltage; the six neutral vectors can affect the midpoint potential fluctuation, but will not generate common mode voltage; the six large vectors have no effect on the midpoint potential and only generate an amplitude of ±Vdc The common-mode voltage of / 6, the common-mode voltage corresponding to each space voltage vector and the midpoint current are shown in Table 1 and Table 2. The space voltage vector diagram is constructed by the basic voltage vector.

[0055] The present invention is verified by simulation test. The simulation parameters are shown in Table 5. Figures 4 to 6 This is the grid-connected current simulation result diagram.

[0056] Table 5 Simulation parameters

[0057] A simulation model was built using MATLAB. The DC side capacitors were set to 880μF and 680μF, respectively. This was used to simulate the DC side voltage imbalance caused by capacitor process problems and reduced capacitor life over time. This was also used to verify the algorithm's midpoint potential control capability. Simulations were performed at modulation indexes of 0.8, 0.5, and 0.2, respectively. The simulation results are shown below. Figures 5 to 9 .

[0058] Depend on Figures 4 to 6 It can be seen that under the three modulation indices, the common-mode voltage suppression and mid-point potential control strategy based on NVSVPWM has a maximum common-mode voltage amplitude of only 50V after steady state. Under the full modulation indices, the present invention can control the mid-point potential in a balanced state within one fundamental wave cycle, and has good mid-point potential control capability. The grid-connected current waveform presents a relatively good sinusoidal shape and has good dynamic characteristics. Figures 7 to 9 It can be seen that under modulation intensities of 0.8, 0.5, and 0.2, the total harmonic content of the grid-connected current is 0.95%, 1.02%, and 1.51%, respectively, which meets the grid-connected requirements.

[0059] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present 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 present invention. Therefore, the present invention is not limited to the embodiments shown herein, but is intended to be embodied in the widest possible manner consistent with the principles and novel features disclosed herein.

Claims

1. A photovoltaic inverter control method based on adjacent virtual vector pulse width modulation, characterized in that: The steps include: Collect the grid-side current, grid-side voltage and grid phase of the photovoltaic inverter and obtain the reference voltage after processing; The reference voltage is mapped to a pre-built vector space. The vector space includes six large sectors. Each large sector is divided into five small sectors by two long vectors, two virtual small vectors, and a virtual middle vector. The virtual small vector is synthesized based on the zero vector and the two long vectors. The virtual middle vector is synthesized based on the three middle vectors and the midpoint potential control factor. The three middle vectors are the middle vectors of the large sector and the two other adjacent large sectors. Each small sector contains a virtual middle vector. Adjusting the midpoint potential control factor based on the relationship between the midpoint potential deviation and the midpoint current, and adjusting the switching sequence of the photovoltaic inverter; A PWM control signal is output based on the adjusted switching sequence of the photovoltaic inverter.

2. The photovoltaic inverter control method based on adjacent virtual vector pulse width modulation according to claim 1, characterized in that: The method for synthesizing the virtual small vector is to add the zero vector and the half value of the long vector to obtain the virtual small vector.

3. The photovoltaic inverter control method based on adjacent virtual vector pulse width modulation according to claim 1, characterized in that: The synthesis method of the virtual mid-vector is: V m '=kV m1 +(1-2k)V m2 +kV m3 , where V m1 、V m2 and V m3 are the three midpoint vectors involved in the synthesis, and k is the midpoint potential control factor.

4. The photovoltaic inverter control method based on adjacent virtual vector pulse width modulation according to claim 1, characterized in that: After constructing the vector space, set the value table of the midpoint potential control factor; When the midpoint potential control factor is adjusted based on the relationship between the midpoint potential deviation and the midpoint current, the value of the midpoint potential control factor is determined according to a pre-set value table.

5. The photovoltaic inverter control method based on adjacent virtual vector pulse width modulation according to claim 1, characterized in that: After the vector space is constructed, a plurality of switch sequence tables corresponding to the large sectors are constructed, and each switch sequence table includes a plurality of switch sequence entries corresponding to the small sectors.

6. The photovoltaic inverter control circuit based on adjacent virtual vector pulse width modulation according to claim 1, characterized in that: include: The first acquisition module is used to collect the grid-side current, grid-side voltage and grid phase of the photovoltaic inverter, and obtain the reference voltage after processing; A PWM output module is used to map the reference voltage into a pre-built vector space, adjust the midpoint potential control factor based on the relationship between the midpoint potential deviation and the midpoint current, adjust the switching sequence of the photovoltaic inverter, and output a PWM control signal based on the adjusted switching sequence of the photovoltaic inverter; The driving circuit is used to drive the photovoltaic inverter based on the PWM control signal.

7. The photovoltaic inverter control circuit based on adjacent virtual vector pulse width modulation according to claim 6, characterized in that: The first acquisition module includes a phase-locked loop (PLL) and a voltage and current measurement module, wherein the phase-locked loop (PLL) is used to acquire the grid phase and transmit it to the PWM output module, and the voltage and current measurement module is used to acquire the grid-side current and grid-side voltage and transmit them to the PWM output module.

8. The photovoltaic inverter control circuit based on adjacent virtual vector pulse width modulation according to claim 7, characterized in that: A Clark transformation module, a Park transformation module, a PI controller and an inverse Park transformation module are sequentially arranged between the voltage and current measurement module and the PWM output module.

9. The photovoltaic inverter control circuit based on adjacent virtual vector pulse width modulation according to claim 6, characterized in that: The circuit includes a second acquisition module, which is used to acquire a first voltage value and a second voltage value of two equalizing capacitors of the photovoltaic inverter, and calculate a midpoint potential based on the first voltage value and the second voltage value.

10. The photovoltaic inverter control circuit based on adjacent virtual vector pulse width modulation according to claim 6, characterized in that: The control circuit is suitable for a mid-point clamped three-level photovoltaic inverter.

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