Zero-common-mode-current single-phase non-isolated photovoltaic boost inverter and its control method

Abstract

The present invention belongs to the technical field of inverters, and discloses a zero-common-mode current single-phase non-isolated photovoltaic boost inverter and its control method. Its input capacitor C pv has its positive electrode connected to one end of the boost inductor L in ; the other end of the boost inductor L in is connected to the anode of the anti-reverse diode D; the cathode of the anti-reverse diode D is connected to the drain of the first switch tube S1, the drain of the third switch tube S3, and the positive electrode of the bus capacitor C dc ; the source of the third switch tube S3 is connected to the drain of the fourth switch tube S4 and one end of the output filter inductor L1; the source of the fourth switch tube S4 is connected to the negative electrode of the bus capacitor C dc and the source of the second switch tube S2; the negative electrode of the input capacitor C pv is connected to the source of the first switch tube S1 and the drain of the second switch tube S2. It realizes input-output common ground, eliminates common-mode current, has fewer power devices, strong boost ability for solar cells, lower cost, and high safety.

Description

Technical Field

[0001] The present invention belongs to the technical field of inverters, and particularly relates to a zero-common-mode-current single-phase non-isolated photovoltaic boost inverter and a control method thereof. Background Art

[0002] Photovoltaic power generation, as a new energy power generation method with great development potential, has always attracted much attention. Isolated and non-isolated inverters, as the core components of photovoltaic power generation, their performance affects the entire system. Most countries and regions require the inverter to contain a high-frequency transformer or place a power-frequency transformer between the inverter and the grid to achieve electrical isolation between the grid and the solar cell, to ensure personal safety, and at the same time can provide voltage matching and suppression of the DC component of the grid-injected current. However, this solution increases the system volume, weight and cost, and reduces the conversion efficiency.

[0003] The front stage of a non-isolated grid-connected inverter usually adopts a non-isolated boost converter, and the rear stage adopts a voltage-source full-bridge inverter. Compared with the isolated type, since there is no transformer (high-frequency and low-frequency) in the main circuit, the non-isolated grid-connected inverter has more performance advantages in terms of conversion efficiency, volume, weight and cost. However, the elimination of the transformer results in an electrical connection between the solar cell and the grid. The switching action of the power devices of the grid-connected inverter may generate a high-frequency time-varying voltage on the parasitic capacitance of the solar cell to the ground, and then form a common-mode current in the loop composed of the parasitic capacitance, the AC filter and the grid impedance. Since the impedance of this loop is small, the common-mode current may exceed the allowable range, which may bring a series of problems such as conduction and radiation interference, increased grid-injected current harmonics and power losses, and endanger the safety of equipment and personnel. Therefore, various grid-connected inverters capable of suppressing common-mode current have been proposed by enterprises and scholars in various countries, such as H5, H6, etc. The number of power devices of these topologies is still relatively large, and the structure and modulation strategy are relatively complex. Therefore, how to balance the elimination of common-mode current and the reduction of the number of power devices has become a key technical problem that must be solved for non-isolated grid-connected inverters. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a zero-common-mode-current single-phase non-isolated photovoltaic boost inverter and a control method thereof, which have fewer power devices and stronger boost ability, and the input and output are grounded together, so that the negative terminal of the solar cell is directly connected to the neutral line of the grid, clamping the common-mode voltage to zero, eliminating the common-mode current, and improving the safety.

[0005] In order to achieve the above purpose, the technical solutions proposed by the present invention are as follows:

[0006] A zero-common-mode-current single-phase non-isolated photovoltaic boost inverter, including an input capacitor C pv , a boost inductor L in , an anti-reverse diode D, a bus capacitor Cdc , the first switching transistor S1, the second switching transistor S2, the third switching transistor S3, the fourth switching transistor S4, and the output filter inductor L1.

[0007] The positive electrode of the input capacitor C pv is connected to one end of the boost inductor L in ;

[0008] The other end of the boost inductor L in is connected to the anode of the anti-reverse diode D;

[0009] The cathode of the anti-reverse diode D is connected to the drain of the first switching transistor S1, the drain of the third switching transistor S3, and the positive electrode of the bus capacitor C dc ;

[0010] The source of the third switching transistor S3 is connected to the drain of the fourth switching transistor S4 and one end of the output filter inductor L1;

[0011] The source of the fourth switching transistor S4 is connected to the negative electrode of the bus capacitor C dc and the source of the second switching transistor S2;

[0012] The negative electrode of the input capacitor C pv is connected to the source of the first switching transistor S1 and the drain of the second switching transistor S2;

[0013] The positive electrode of the input capacitor C pv is connected to the positive terminal of the solar cell;

[0014] The other end of the output filter inductor L1 is connected to one end of the single-phase AC grid u g ;

[0015] The negative electrode of the input capacitor C pv is connected to the negative terminal of the solar cell and the other end of the single-phase AC grid u g ;

[0016] The current of the boost inductor L in is discontinuous, and the design of the boost inductor L in is as follows:

[0017]

[0018] In the formula, f s1,min is the lowest switching frequency of the first switching transistor S1; U dc is the average value of the terminal voltage of the bus capacitor C dc in a power frequency cycle; U pv is the average value of the output voltage of the solar cell in a power frequency cycle; P in,maxis the maximum output power of the solar cell.

[0019] The control method of the single-phase non-isolated photovoltaic boost inverter includes the following steps:

[0020] S1. Feed the sampled value u of the output voltage of the solar cell pv and the sampled value i of the output current of the solar cell pv into the MPPT controller to obtain the reference value u of the output voltage of the solar cell mpp ;

[0021] S2. Compare the reference value u of the output voltage of the solar cell mpp with the sampled value u of the output voltage of the solar cell pv to obtain the first error signal u pv,e ;

[0022] S3. Send the first error signal u pv,e to the output voltage controller G of the solar cell upv (s). Its output passes through the first amplitude limiting link Lim1 and the voltage-frequency conversion module, and then obtains the first triangular carrier wave u with a frequency of f s1 ; c1 ;

[0023] S4. Compare the first triangular carrier wave u c1 with 0 to generate the first drive signal, and the first drive signal is used as the drive signal u of the first switch tube S1 gs,S1 ; Invert the first drive signal to be used as the drive signal u of the second switch tube S2 gs,S2 ;

[0024] S5. Compare the sampled value u of the terminal voltage of the bus capacitor C dc with the reference value u dc to obtain the second error signal u dc,ref ; dc,e ;

[0025] S6. Send the second error signal u dc,e to the terminal voltage controller G of the bus capacitor udc (s). Its output passes through the second amplitude limiting link Lim2 to obtain the reference value I of the grid-connected current amplitude gm,ref ;

[0026] S7. Feed the sampled value u of the grid voltage g into the phase-locked loop PLL to obtain the unit sine signal sinωt, and multiply it by the reference value I of the grid-connected current amplitude gm,ref to obtain the reference value i of the grid-connected current g,ref ;

[0027] S8. Compare the incoming grid current reference i g,ref with the sampled value of the incoming grid current i g to obtain a third error signal i g,e ;

[0028] S9. Send the third error signal i g,e to the incoming grid current controller G ig (s). After its output is processed by the third limiter Lim3, an AC modulation signal u rac is obtained;

[0029] S10. Compare the AC modulation signal u rac with a second triangular carrier wave u s2 with a fixed frequency of f c2 to generate a third drive signal, which is used as the drive signal u gs,S3 for the third switch tube S3; Invert the third drive signal to obtain the drive signal u gs,S4 for the fourth switch tube S4.

[0030] Furthermore, the solar cell output voltage controller G upv (s) in step S3 adopts a PI regulator.

[0031] Furthermore, the bus voltage controller G udc (s) in step S7 adopts a PI regulator.

[0032] Furthermore, the incoming grid current controller G ig (s) in step S10 adopts a PR regulator.

[0033] Furthermore, both the first triangular carrier wave u c1 and the second triangular carrier wave u c2 are bipolar triangular carrier waves.

[0034] Compared with the prior art, the zero - common - mode - current single - phase non - isolated photovoltaic boost inverter and its control method proposed by the present invention achieve input - output common - ground, eliminate the common - mode current, have fewer power devices, strong boost ability, low cost, and high safety. Description of the Drawings

[0035] Figure 1 is the main circuit diagram of the single - phase non - isolated photovoltaic boost inverter provided by this application;

[0036] Figure 2 is Figure 1 the control block diagram of the single - phase non - isolated photovoltaic boost inverter shown;

[0037] Figure 3 (a)-(f) are Figure 1Modal equivalent circuit diagram of the single-phase non-isolated photovoltaic boost inverter shown; among them, Figure 3 (a) shows the equivalent circuit diagram when the first switch tube S1 and the third switch tube S3 are both turned on, and the boost inductor L in is charging; Figure 3 (b) shows the equivalent circuit diagram when the first switch tube S1 is turned on and the third switch tube S3 is turned off, and the boost inductor L in is discharging; Figure 3 (c) shows the equivalent circuit diagram when the first switch tube S1 is turned off and the third switch tube S3 is turned on, and the current i in of the boost inductor L Lin = 0; Figure 3 (d) shows the equivalent circuit diagram when the first switch tube S1 is turned on and the third switch tube S3 is turned off, and the boost inductor L in is charging; Figure 3 (e) shows the equivalent circuit diagram when the first switch tube S1 and the third switch tube S3 are both turned off, and the boost inductor L in is discharging; Figure 3 (f) shows the equivalent circuit diagram when the first switch tube S1 and the third switch tube S3 are both turned off, and the current i in of the boost inductor L Lin = 0;

[0038] Figure 4 is Figure 1 the voltage gain diagram of the single-phase non-isolated photovoltaic boost inverter shown.

[0039] Figure 5 is Figure 1 the simulation waveform diagram of the single-phase non-isolated photovoltaic boost inverter shown. Specific implementation manners

[0040] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0041] The present invention provides a single-phase non-isolated photovoltaic boost inverter with zero common-mode current, and its circuit structure is as Figure 1 shown. This topology includes an input capacitor C pv , a boost inductor L in , an anti-reverse diode D, a bus capacitor C dc , a first switch tube S1, a second switch tube S2, a third switch tube S3, a fourth switch tube S4, and an output filter inductor L1; the positive electrode of the input capacitor C pv is connected to the boost inductor L inis connected to one end; Boost inductor L in The other end is connected to the anode of the anti - reverse diode D; The cathode of the anti - reverse diode D is connected to the drain of the first switch tube S1, the drain of the third switch tube S3, and the bus capacitor C dc The positive electrode; The source of the third switch tube S3 is connected to the drain of the fourth switch tube S4 and one end of the output filter inductor L1; The source of the fourth switch tube S4 is connected to the bus capacitor C dc The negative electrode, the source of the second switch tube S2; The negative electrode of the input capacitor C pv The negative electrode is connected to the source of the first switch tube S1 and the drain of the second switch tube S2; The positive electrode of the input capacitor C pv The positive electrode is connected to the positive - polarity terminal of the solar cell; The other end of the output filter inductor L1 is connected to one end of the single - phase AC grid u g One end; The input capacitor C pv The negative electrode is connected to the negative - polarity terminal of the solar cell and the other end of the single - phase AC grid u g The other end.

[0042] In order to make the single - phase non - isolated photovoltaic boost inverter of the present invention have a boosting ability, the input inductor current i Lin Must be discontinuous. To meet this requirement, the input inductance L in Must be designed according to the following conditions:

[0043]

[0044] In the formula, f s1,min Is the lowest switching frequency of the first switch tube S1; U dc Is the average value of the terminal voltage of the bus capacitor C dc In a power frequency cycle; U pv Is the average value of the output voltage of the solar cell in a power frequency cycle; P in,max Is the maximum output power of the solar cell.

[0045] The present invention provides a control method for a zero - common - mode - current single - phase non - isolated photovoltaic boost inverter, which specifically includes: performing closed - loop regulation on the output voltage u pv Of the solar cell to achieve MPPT control and boost control; performing double - closed - loop control on the bus voltage u dc , the grid - connected current i g To achieve the sinusoidality of the grid - connected current and pure - active power grid connection, and its control block diagram is as shown in Figure 2 Shown.

[0046] The specific steps are as follows:

[0047] S1. Compare the sampled value u pv Of the output voltage of the solar cell with the sampled value ipv It is sent to the MPPT controller to obtain the reference value u of the output voltage of the solar cell mpp ;

[0048] S2. Compare the reference value u of the output voltage of the solar cell mpp with the sampled value u of the output voltage of the solar cell to obtain the first error signal u pv ; pv,e ;

[0049] S3. Send the first error signal u pv,e to the output voltage controller G upv (s) of the solar cell. Its output passes through the first limiter Lim1 and the voltage-frequency conversion module, and then the first triangular carrier wave u with frequency f s1 is obtained c1 ;

[0050] S4. Compare the first triangular carrier wave u c1 with 0 to generate the first driving signal, which is used as the driving signal u of the first switching tube S1 gs,S1 ; Invert the first driving signal to be used as the driving signal u of the second switching tube S2 gs,S2 ;

[0051] S5. Compare the sampled value u of the terminal voltage of the bus capacitor C dc with the reference value u dc to obtain the second error signal u dc,ref ; dc,e ;

[0052] S6. Send the second error signal u dc,e to the terminal voltage controller G udc (s) of the bus capacitor. Its output passes through the second limiter Lim2 to obtain the reference value I of the amplitude of the grid-connected current gm,ref ;

[0053] S7. Send the sampled value u of the grid voltage g into the phase-locked loop PLL to obtain the unit sine signal sinωt, and multiply it by the reference value I of the amplitude of the grid-connected current gm,ref to obtain the reference value i of the grid-connected current g,ref ;

[0054] S8. Compare the reference value i of the grid-connected current g,ref with the sampled value i of the grid-connected current to obtain the third error signal i g ; g,e ;

[0055] S9. Send the third error signal i g,e to the grid-connected current controller G ig(s), whose output is processed by the third limiter Lim3 to obtain the AC modulation signal u rac ;

[0056] S10. Compare the AC modulation signal u rac with the second triangular carrier u s2 with a fixed frequency of f c2 to generate a third driving signal, which is used as the driving signal u gs,S3 of the third switch tube S3; Invert the third driving signal to obtain the driving signal u gs,S4 of the fourth switch tube S4.

[0057] Next, the working process of the zero - common - mode - current single - phase non - isolated photovoltaic boost inverter shown in Figure 1 will be described.

[0058] Due to the discontinuous current of the boost inductor L in , there are six possible equivalent circuits in the single - phase non - isolated photovoltaic boost inverter shown in Figure 1 , as shown in Figure 3 (a) - Figure 3 (f) respectively. It can be seen that when the first switch tube S1 is turned on and the second switch tube S2 is turned off, the solar cell charges the boost inductor L in through the anti - reverse diode D and the first switch tube S1, and the current i in of the boost inductor L Lin linearly rises from zero; when the first switch tube S1 is turned off and the second switch tube S2 is turned on, the current i in of the boost inductor L Lin starts to linearly decrease, and the energy stored in the boost inductor L in is released to the bus capacitor C dc through the anti - reverse diode D and the second switch tube S2. When the boost inductor current i Lin drops to zero, the anti - reverse diode D naturally turns off. i Lin remains in the discontinuous state until the next switching period T s1 arrives. Since the first triangular carrier u Figure 2 in c1 is compared with zero to generate the driving signal u gs,S1 of the first switch tube S1 and the driving signal u gs,S2 of the second switch tube S2, the duty cycles of u gs,S1 and u gs,S2 are fixed at 0.5. However, its switching frequency f s1 is regulated by the output voltage controller G upv (s) of the solar cell to control the output voltage u pvThe third switching transistor S3 and the fourth switching transistor S4 are in sinusoidal pulse width modulation, and the switching frequency is fixed at f s2 , and the modulation ratio is controlled by the bus capacitor terminal voltage controller G udc (s) and the grid-connected current controller G ig (s) to change the magnitude of the grid-connected power and achieve a constant bus voltage.

[0059] If the negative terminal of the bus capacitor C dc is used as the zero potential reference point, then Figure 2 the potential of point a in s1 (=1 / f s1 ) within one switching period T

[0060]

[0061] In the formula, U rm is the amplitude of the AC modulation signal u rac , U cm2 is the amplitude of the second triangular carrier u c2 , ω g =2πf g is the angular frequency of the grid voltage, and f g is the frequency of the grid voltage.

[0062] Since the duty ratio of the first switching transistor S1 is fixed at 0.5, therefore Figure 2 the potential of point b in s2 within one switching period T

[0063] <u b >=0.5U dc (3)

[0064] According to Equation (1) and Equation (2), the average value of the fundamental component of the output voltage of the single-phase non-isolated photovoltaic boost inverter of the present invention in one switching period can be obtained:

[0065]

[0066] In the formula, M is the modulation ratio of the single-phase non-isolated photovoltaic boost inverter; U om is the amplitude of its output voltage. It can be seen that the bus voltage utilization rate of the single-phase non-isolated photovoltaic boost inverter is the same as that of the traditional half-bridge inverter, which is 0.5M.

[0067] The voltage transfer ratio of the DC boost link is:

[0068]

[0069] P in is the output power of the solar cell, f s1is the first triangular carrier wave u c1 frequency.

[0070] Combining Equation (4) and Equation (5), the voltage gain of the single-phase non-isolated photovoltaic boost inverter of the present invention can be obtained as follows:

[0071]

[0072] According to Equation (6), the voltage gain characteristic of the single-phase non-isolated photovoltaic boost inverter shown in Figure 1 can be plotted, as shown in Figure 4 . Among them, Figure 4 (a) is the three-dimensional diagram of the voltage gain G(M, f om = 156V, L in = 160 μH, P in = 500W of the single-phase non-isolated photovoltaic boost inverter; s1 ) Figure 4 (b) is the projection of the intersection line of the surface G(M, f s1 ) and the plane G = 1 in the M, f s1 coordinate system. It can be seen from Figure 4 (b) that when the modulation ratio M and the first switching frequency f s1 are located in the upper left shaded part, the voltage gain G of the single-phase non-isolated photovoltaic boost inverter is greater than 1.

[0073] Next, the stress of the single-phase non-isolated photovoltaic boost inverter shown in Figure 1 will be analyzed.

[0074] Assuming that all components are ideal devices and the bus capacitor voltage ripple is ignored, then from Figure 3 the voltage stresses of the first switching tube S1, the second switching tube S2, the third switching tube S3, and the fourth switching tube S4 can be obtained as follows:

[0075] U S1 = U S2 = U S3 = U S4 = U dc (7)

[0076] The voltage stress of the anti-reverse diode D is:

[0077] U D = U dc - U pv (8)

[0078] The average current stress of the anti-reverse diode D is I D = I pv . I pv is the average value of the output current of the solar cell.

[0079] Next, analyze the mechanism of suppressing the common-mode current of the single-phase non-isolated photovoltaic boost inverter shown below. Figure 1

[0080] It can be clearly seen from Figure 1 that the input and output terminals of the single-phase non-isolated photovoltaic boost inverter of the present invention are grounded, so the capacitance C of the solar cell to the ground cm is short-circuited, and thus its terminal voltage (i.e., the common-mode voltage) u cm = 0. At this time, the common-mode current is:

[0081]

[0082] This indicates that the single-phase non-isolated photovoltaic boost inverter proposed by the present invention can completely eliminate the common-mode current i cm .

[0083] Next, specific embodiments of the present invention are given. Its design indexes are shown in Table 1.

[0084] Table 1 Prototype design indexes

[0085]

[0086] Based on the design indexes shown in Table 1, the present invention designs the boost inductance L in .

[0087] Substituting the parameters shown in Table 1 into Equation (1), we can obtain:

[0088]

[0089] The actual boost inductance L taken is in = 160 μH.

[0090] In order to verify the correctness of the theoretical analysis, according to the above parameter design, the Saber simulation software is used to simulate and verify the boost converter. The specific values are as follows: The solar cell PV is replaced by a DC power supply in series with a resistor, where the DC power supply U s is 200 V, the resistor R s is 20 Ω, the input capacitor C pv is 100 μF, the boost inductance L in is 160 μH, the bus capacitor C dc is 244 μF, the output filter inductance L1 is 10 mH, and the parasitic capacitance C of the solar cell to the ground cm is 100 nF. The output voltage controller G upv (s) adopts a PI regulator, and its specific parameters are: k p1 = 10, k i1 = 3000; the bus voltage controller G​udc (s) The PI regulator is adopted, and its specific parameters are: k p2 = 10, k i2 = 800; The grid-connected current controller G ig (s) The PR regulator is adopted, and its specific parameters are: k p = 4, k r = 20000, ω c = 46rad / s, ω0 = 100πrad / s.

[0091] Figure 5 The simulation waveform diagram of the single-phase non-isolated photovoltaic boost inverter of the present invention is given. Among them, Figure 5 (a) gives the drive signal u gs,S1 of the first switch tube S1, the drive signal u gs,S3 of the third switch tube S3, the current i in of the boost inductor L Lin , the AC modulation signal u rac , the second triangular carrier u c2 , the voltage u a at point a, the voltage u b at point b, and the inverter output voltage u ab in one switching period. It can be seen that the switching frequency f gs,S1 of the drive signal u s1 of the first switch tube S1 is 20.3kHz, the switching frequency f gs,S3 of the drive signal u s2 of the third switch tube S3 is 20kHz, the current i in of the boost inductor L Lin is discontinuous, and the inverter output voltage u ab is a positive and negative alternating signal.

[0092] Figure 5 (b) gives the voltage stress waveforms of the first switch tube S1, the second switch tube S2, the third switch tube S3, and the fourth switch tube S4 in one switching period. It can be seen that U S1 = U S2 = U S3 = U S4 = U dc = 400V, U D = U dc - U pv = 300V, I D = I pv = 5.2A, which is consistent with the theoretical analysis and meets the design requirements.

[0093] Figure 5 (c) shows the solar cell output voltage u pv , the boost inductor Lin The current i Lin and the bus capacitor C dc at the terminal voltage u dc and the incoming current i g and the grid voltage u g as well as the common-mode current i cm within one power frequency cycle. It can be seen that the average value U of the output voltage of the solar cell pv = 100V, and the average value U of the terminal voltage of the bus capacitor C dc = 400V. The incoming current and the grid voltage are of the same frequency and in phase. The effective value I of the incoming current dc = 4.5A, THD = 4.528%, meeting the design requirements; the amplitude U of the grid voltage g,rms = 156V, so the voltage gain G = 1.56 > 1. Therefore, the single-phase non-isolated photovoltaic boost inverter has the boosting ability; the common-mode current i om = 0A. cm = 0A.

[0094] It can be seen from the above simulation results that the zero-common-mode current single-phase non-isolated photovoltaic boost inverter and its control method proposed by the present invention have the following advantages: realizing input-output common ground, eliminating common-mode current, having fewer power devices, strong boosting ability for solar cells, lower cost, and high safety.

[0095] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0096] The description of the above embodiments is only used to help understand the method and its core idea of the present invention, rather than to limit it. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the present invention.

Claims

1. A control method for a single-phase non-isolated photovoltaic boost inverter, characterized in that, The single-phase non-isolated photovoltaic boost inverter is a zero-common-mode-current single-phase non-isolated photovoltaic boost inverter, and the single-phase non-isolated photovoltaic boost inverter includes an input capacitor C pv , a boost inductor L in , an anti-reverse diode D, a bus capacitor C dc , a first switching tube S1, a second switching tube S2, a third switching tube S3, a fourth switching tube S4, and an output filter inductor L1; The positive electrode of the input capacitor C pv is connected to one end of the boost inductor L in ; The boost inductor L in has its other end connected to the anode of the anti - reverse diode D; The cathode of the anti - reverse diode D is connected to the drain of the first switching transistor S1, the drain of the third switching transistor S3, and the positive electrode of the bus capacitor C dc ; The source electrode of the third switching tube S3 is connected to the drain electrode of the fourth switching tube S4 and one end of the output filter inductor L1; The source of the fourth switching transistor S4 is connected to the negative electrode of the bus capacitor C dc and the source of the second switching transistor S2; The negative electrode of the input capacitor C pv is connected to the source electrode of the first switching transistor S1 and the drain electrode of the second switching transistor S2; The input capacitor C pv has its positive electrode connected to the positive terminal of the solar cell; The other end of the output filter inductor L1 is connected to one end of the single-phase AC power grid u g ; The input capacitor C pv has its negative terminal connected to the negative terminal of the solar cell and the other end of the single-phase AC grid u g . The boost inductor L in is designed as follows: where f s1,min is the minimum switching frequency of the first switching transistor S1; U dc is the average value of the terminal voltage of the bus capacitor C dc within one power frequency period; U pv is the average value of the output voltage of the solar cell within one power frequency period; P in,max is the maximum output power of the solar cell; The control method includes the following steps: S1. Feed the sampled value u of the output voltage of the solar cell pv and the sampled value i of the output current of the solar cell pv into the MPPT controller to obtain the reference value u of the output voltage of the solar cell mpp ; S2. Compare the reference value u of the output voltage of the solar cell with the sampled value u of the output voltage of the solar cell to obtain a first error signal u mpp pv pv,e ;​​ S3. Send the first error signal u pv,e to the solar cell output voltage controller G upv (s), whose output passes through a first limiting link Lim1 and a voltage-frequency conversion module, and then a first triangular carrier wave u s1 with a frequency of f c1 is obtained; S4. Compare the first triangular carrier wave u c1 with 0 to generate a first driving signal, and the first driving signal is used as the driving signal u of the first switching tube S1 gs,S1 ; Invert the first driving signal to be used as the driving signal u of the second switching tube S2 gs,S2 ; S5. Sample the terminal voltage u of the bus capacitor C dc and compare it with the reference value u dc to obtain the second error signal u dc,ref ; dc,e ; S6. Send the second error signal u dc,e to the bus capacitor terminal voltage controller G udc (s). After its output passes through the second limiting link Lim2, the reference value I of the grid-connected current amplitude is obtained gm,ref ; S7. Feed the sampled value u of the grid voltage g into the phase-locked loop PLL to obtain a unit sine signal sinωt, and multiply it by the reference amplitude I gm,ref of the incoming grid current to obtain the reference incoming grid current i g,ref ; S8. Compare the incoming network current reference i g,ref with the sampled value i g of the incoming network current to obtain a third error signal i g,e ; S9. Send the third error signal i g,e to the grid-connected current controller G ig (s). After the output is processed by the third limiter Lim3, an AC modulation signal u rac is obtained; S10. Compare the AC modulation signal u rac with a second triangular carrier wave u s2 with a fixed frequency of f c2 to generate a third driving signal, which is used as the driving signal u gs,S3 of the third switching transistor S3; invert the third driving signal to obtain the driving signal u gs,S4 of the fourth switching transistor S4.

2. The control method according to claim 1, wherein The output voltage controller G of the solar cell upv (s) adopts a PI regulator.

3. The control method according to claim 1, wherein, The bus capacitor terminal voltage controller G udc (s) uses a PI regulator.

4. The control method according to claim 1, characterized in that, The incoming line current controller G ig (s) adopts a PR regulator.

5. The control method according to claim 1, wherein The first triangular carrier wave u c1 and the second triangular carrier wave u c2 are both bipolar triangular carrier waves.

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