Single-stage three-phase high-frequency isolation type conversion circuit and closed-loop control method

Abstract

The application discloses a single-stage three-phase high-frequency isolation type conversion circuit and a closed-loop control method. The single-stage three-phase high-frequency isolation type conversion circuit generates a modulation ratio and a vector angle on the basis of synchronous control of a fundamental wave and a harmonic wave of a three-phase current based on three-phase voltage of a three-phase three-wire power grid and the three-phase current of the three-phase three-wire power grid, generates a primary side driving signal and a secondary side driving signal according to the modulation ratio and the vector angle, the primary side driving signal is used for driving a three-phase matrix converter, and the secondary side driving signal is used for driving a full-bridge inverter. The fundamental wave and the low-frequency harmonic wave of the power grid current can be synchronously controlled, low-order harmonics can be eliminated, the sinusoidal degree of the grid-connected current can be improved, and thus the quality of the power grid current and total harmonic distortion can be improved.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, specifically to a single-stage three-phase high-frequency isolated converter circuit and a closed-loop control method. Background Technology

[0002] A single-stage three-phase high-frequency isolated AC / DC converter can achieve all the functions of a traditional two-stage architecture through only one stage of conversion. This solution does not use electrolytic capacitors and features high efficiency, high power density, long lifespan, and wide voltage regulation range, making it extremely promising for applications.

[0003] However, due to the complex circuit structure and numerous control variables of single-stage three-phase high-frequency isolated AC / DC converters, which require both DC voltage control and grid-side unity power factor correction (PFC) functions, the control of single-stage three-phase high-frequency isolated AC / DC converters is very difficult, resulting in large grid current distortion and poor total harmonic distortion (THD). Summary of the Invention

[0004] This application provides a single-stage three-phase high-frequency isolated converter circuit and a closed-loop control method to alleviate at least some of the above-mentioned technical problems.

[0005] In a first aspect, this application provides a single-stage three-phase high-frequency isolated converter circuit. This single-stage three-phase high-frequency isolated converter circuit includes a closed-loop control module, a pulse width modulation module, and a three-phase LC filter, a three-phase matrix converter, a first inductor, a high-frequency transformer, and a full-bridge inverter connected in sequence. The three-phase LC filter is connected between the three-phase three-wire power grid and the three-phase matrix converter. The closed-loop control module is connected to the three-phase three-wire power grid and is used to generate a modulation ratio and a vector angle based on the three-phase voltage and three-phase current of the three-phase three-wire power grid, while synchronously controlling the fundamental and harmonic frequencies of the three-phase current. The pulse width modulation module is connected to the three-phase matrix converter, the full-bridge inverter, and the closed-loop control module, and is used to generate a primary-side drive signal and a secondary-side drive signal according to the modulation ratio and vector angle. The primary-side drive signal is used to drive the three-phase matrix converter, and the secondary-side drive signal is used to drive the full-bridge inverter.

[0006] Secondly, this application provides a closed-loop control method applied to a single-stage three-phase high-frequency isolated converter circuit. The single-stage three-phase high-frequency isolated converter circuit includes a three-phase LC filter, a three-phase matrix converter, a first inductor, a high-frequency transformer, and a full-bridge inverter connected in sequence. The three-phase LC filter is connected between the three-phase three-wire power grid and the three-phase matrix converter. The closed-loop control method includes: generating a modulation ratio and a vector angle based on the three-phase voltage and three-phase current of the three-phase three-wire power grid, and synchronously controlling the fundamental and harmonic frequencies of the three-phase current; generating a primary-side drive signal and a secondary-side drive signal according to the modulation ratio and vector angle. The primary-side drive signal is used to drive the three-phase matrix converter, and the secondary-side drive signal is used to drive the full-bridge inverter.

[0007] The single-stage three-phase high-frequency isolated converter circuit and closed-loop control method provided in this application generate modulation ratio and vector angle based on the three-phase voltage and three-phase current of the three-phase three-wire power grid, and synchronously control the fundamental and harmonic frequencies of the three-phase current. Primary-side drive signal and secondary-side drive signal are generated according to the modulation ratio and vector angle. The primary-side drive signal is used to drive the three-phase matrix converter, and the secondary-side drive signal is used to drive the full-bridge inverter. This can synchronously control the fundamental and low-frequency harmonics of the grid current, which is beneficial to eliminating low-order harmonics and improving the sinusoidal nature of the grid current, thereby improving the quality of the grid current and the total harmonic distortion. Attached Figure Description

[0008] The technical solution and other beneficial effects of this application will become apparent from the following detailed description of specific embodiments in conjunction with the accompanying drawings.

[0009] Figure 1 The circuit diagram of the single-stage three-phase high-frequency isolated converter circuit provided in the embodiments of this application is shown.

[0010] Figure 2 The circuit schematic diagram of the closed-loop control module provided in the embodiments of this application.

[0011] Figure 3 The waveform diagrams of the primary and secondary voltages provided in the embodiments of this application are shown.

[0012] Figure 4 This is a schematic diagram of the regional division of the power grid voltage provided in the embodiments of this application.

[0013] Figure 5 This is a schematic diagram of the vector distribution corresponding to the spatial vector modulation provided in the embodiments of this application. Detailed Implementation

[0014] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0015] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Features thus defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more unless otherwise explicitly specified.

[0016] Three-phase high-frequency isolated bidirectional AC / DC converters are widely used in battery energy storage, electric vehicles, and grid-connected power generation of new energy sources. Most three-phase high-frequency isolated AC / DC converters adopt a two-stage architecture. The grid voltage is first converted into DC by a single-stage AC / DC circuit, and then the voltage is converted again by a single-stage isolated DC / DC circuit. The two stages are decoupled by an electrolytic capacitor in between.

[0017] Due to the presence of electrolytic capacitors, two-stage AC / DC solutions are larger in size and have a shorter lifespan. Furthermore, because energy requires multiple transformations and soft switching of all switching transistors is not possible, overall efficiency is difficult to improve.

[0018] The single-stage three-phase high-frequency isolated AC / DC converter overcomes the aforementioned shortcomings, achieving all the functions of a traditional two-stage architecture through a single-stage conversion. This solution does not use electrolytic capacitors and features high efficiency, high power density, long lifespan, and a wide voltage regulation range, making it extremely promising for applications.

[0019] However, due to the complex circuit structure and numerous control variables of single-stage three-phase high-frequency isolated AC / DC converters, which require both DC voltage control and grid-side unity power factor correction (PFC), controlling these converters is very challenging. Most solutions use open-loop control on the grid side, with only a few allowing closed-loop control. However, existing solutions have one or more shortcomings:

[0020] (1) It can only control the fundamental current of the power grid, resulting in large current distortion and poor total harmonic distortion (THD).

[0021] (2) During the switching cycle, the number of switching device actions increases significantly, resulting in high circuit losses.

[0022] (3) Using a complex controller makes it difficult to set control parameters and the system is prone to instability.

[0023] This embodiment provides a single-stage three-phase high-frequency isolated converter circuit, such as... Figure 1 As shown, the single-stage three-phase high-frequency isolated converter circuit includes a three-phase LC filter 10, a three-phase matrix converter 20, a first inductor L, a high-frequency transformer T1, and a full-bridge inverter 30 connected in sequence.

[0024] The three-phase LC filter 10 is connected between the three-phase three-wire power grid 110 and the three-phase matrix converter 20. The full-bridge inverter 30 is connected between the high-frequency transformer T1 and the DC source 120. The primary-side drive signal PWM1 drives the three-phase matrix converter 20, and the secondary-side drive signal PWM2 drives the full-bridge inverter 30. The turns ratio n of the high-frequency transformer T1 is equal to np:ns.

[0025] The three terminals of the three-phase three-wire power grid 110 are connected to the first node O. The voltage at the first terminal of the three-phase three-wire power grid 110 is va, and the output current is ia; the voltage at the second terminal is vb, and the output current is ib; the voltage at the third terminal is vc, and the output current is ic. That is, the three-phase voltages of the three-phase three-wire power grid 110 are va, vb, and vc, and the three-phase currents are ia, ib, and ic.

[0026] In some embodiments, the three-phase LC filter 10 includes a first-phase inductor La, a second-phase inductor Lb, a third-phase inductor Lc, a first capacitor ca, a second capacitor cb, and a third capacitor cc. The first terminal of the first-phase inductor La is connected to the first second terminal of the three-phase three-wire power grid 110, and the second terminal of the first-phase inductor La is connected to the first terminal of the first capacitor ca. The first terminal of the second-phase inductor Lb is connected to the second second terminal of the three-phase three-wire power grid 110, and the second terminal of the second-phase inductor Lb is connected to the first terminal of the second capacitor cb. The first terminal of the third-phase inductor Lc is connected to the third second terminal of the three-phase three-wire power grid 110, and the second terminal of the third-phase inductor Lc is connected to the first terminal of the third capacitor cc. The second terminal of the first capacitor ca is connected to the second terminals of the second capacitor cb and the second terminals of the third capacitor cc.

[0027] The current at the second terminal of the first-phase inductor La is denoted as iha, the current at the second terminal of the second-phase inductor Lb is denoted as ihb, and the current at the second terminal of the third-phase inductor Lc is denoted as ihc.

[0028] The inductor voltages of the three-phase LC filter 10 include the voltage of the first-phase inductor La (vLa), the voltage of the second-phase inductor Lb (vLb), and the voltage of the third-phase inductor Lc (vLc). The capacitor currents of the three-phase LC filter 10 include the current flowing to the first capacitor ca (ica), the current flowing to the second capacitor cb (icb), and the current flowing to the third capacitor cc (icc).

[0029] In some embodiments, the three-phase matrix converter 20 includes parallel A-phase bridge arms, B-phase bridge arms, and C-phase bridge arms. Each bridge arm consists of upper and lower sets of switches, and each set of switches consists of two switches connected in reverse series. Specifically: the upper set of switches for the A-phase bridge arm is Sa11 and Sa12, and the lower set of switches for the A-phase bridge arm is Sa21 and Sa22; the upper set of switches for the B-phase bridge arm is Sb11 and Sb12, and the lower set of switches for the B-phase bridge arm is Sb21 and Sb22; the upper set of switches for the C-phase bridge arm is Sc11 and Sc12, and the lower set of switches for the C-phase bridge arm is Sc21 and Sc22.

[0030] The voltage between the two output terminals (P, N) of the three-phase matrix converter 20 is denoted as the primary voltage vp of the high-frequency transformer T1. The current flowing through the first inductor L is denoted as ip.

[0031] In some embodiments, the full-bridge inverter 30 includes parallel D-phase bridge arms and E-phase bridge arms, each bridge arm consisting of upper and lower switches. Specifically, the upper switch of the D-phase bridge arm is Sd1, and the lower switch of the D-phase bridge arm is Sd2; the upper switch of the E-phase bridge arm is Se1, and the lower switch of the E-phase bridge arm is Se2.

[0032] The voltage between the two input terminals of the full-bridge inverter 30 is the secondary voltage vs of the high-frequency transformer T1, i.e., vs. The current flowing from the full-bridge inverter 30 to the DC source 120 is denoted as idc.

[0033] It should be noted that the above-mentioned single-stage three-phase high-frequency isolated converter circuit can reduce the size and increase the power density by eliminating the electrolytic capacitors in the two-stage scheme, avoid the aging and failure of electrolytic capacitors and extend the service life, and the transformer turns ratio can be flexibly adapted to a wide voltage input to achieve a wide voltage regulation range.

[0034] In some embodiments, such as Figure 1As shown, the single-stage three-phase high-frequency isolated converter circuit also includes a closed-loop control module 40 and a pulse width modulation module 50. The closed-loop control module 40 is connected to the three-phase three-wire power grid 110 and is used to generate the modulation ratio m and the vector angle θ based on the three-phase voltage and three-phase current of the three-phase three-wire power grid 110, and on the basis of synchronously controlling the fundamental and harmonic waves of the three-phase current. The pulse width modulation module 50 is connected to the three-phase matrix converter 20, the full-bridge inverter 30 and the closed-loop control module 40, and is used to generate the primary-side drive signal PWM1 and the secondary-side drive signal PWM2 according to the modulation ratio m and the vector angle θ.

[0035] It is understood that the single-stage three-phase high-frequency isolated converter circuit provided in this embodiment generates a modulation ratio m and a vector angle θ based on the three-phase voltage and three-phase current of the three-phase three-wire power grid 110, and synchronously controls the fundamental and harmonic waves of the three-phase current. Based on the modulation ratio m and the vector angle θ, it generates a primary-side drive signal PWM1 and a secondary-side drive signal PWM2. The primary-side drive signal PWM1 is used to drive the three-phase matrix converter 20, and the secondary-side drive signal PWM2 is used to drive the full-bridge inverter 30. It can synchronously control the fundamental and low-frequency harmonic waves of the grid current, which is beneficial to eliminate low-order harmonics and improve the sinusoidal nature of the grid current, thereby improving the quality of the grid current and the total harmonic distortion.

[0036] In some embodiments, such as Figure 2 As shown, the closed-loop control module 40 includes a sampling unit 41, a phase-locked loop 42, a fundamental frequency loop 43, a harmonic suppression loop 44, and an accumulation and conversion unit 45. The sampling unit 41 is used to sample the three-phase voltage and three-phase current; the phase-locked loop 42 is connected to the sampling unit 41 and is used to obtain the grid phase θg of the three-phase three-wire power grid 110 based on the three-phase voltage; the fundamental frequency loop 43 is connected to the sampling unit 41 and the phase-locked loop 42 and is used to generate the α-axis fundamental frequency component and the β-axis fundamental frequency component based on the three-phase current and the grid phase θg; the harmonic suppression... Ring 44 is connected to sampling unit 41 and phase-locked loop 42, and is used to generate α-axis harmonic components and β-axis harmonic components based on three-phase current and grid phase θg; accumulation and conversion unit 45 is connected to fundamental ring 43, harmonic suppression ring 44 and pulse width modulation module 50, and is used to accumulate α-axis fundamental component and α-axis harmonic component to obtain α-axis current component, accumulate β-axis fundamental component and β-axis harmonic component to obtain β-axis current component, and obtain modulation ratio m and vector angle θ based on α-axis current component and β-axis current component.

[0037] It should be noted that this embodiment improves the sinusoidal nature of the grid-connected current by simultaneously controlling the fundamental frequency and low-frequency harmonics of the grid current. Furthermore, the use of a traditional PI controller with mature theoretical parameter design facilitates implementation. Additionally, the adoption of multiple parallel processing loops, such as the fundamental frequency loop 43 and the harmonic suppression loop 44, reduces harmonic suppression delay and provides a fast dynamic response.

[0038] In some embodiments, such as Figure 2 As shown, the harmonic suppression ring 44 includes a positive-sequence harmonic suppression sub-ring 441 and a negative-sequence harmonic suppression sub-ring 442. The positive-sequence harmonic suppression sub-ring 441 is connected to the sampling unit 41, the phase-locked loop 42, and the accumulation conversion unit 45. It is used to suppress the 6K+1th positive-sequence harmonics according to the three-phase current and the grid phase θg to generate the α-axis positive-sequence harmonic component and the β-axis positive-sequence harmonic component, where K is a positive integer. The negative-sequence harmonic suppression sub-ring 442 is connected to the sampling unit 41, the phase-locked loop 42, and the accumulation conversion unit 45. It is used to suppress the 6K-1th positive-sequence harmonics according to the three-phase current and the grid phase θg to generate the α-axis negative-sequence harmonic component and the β-axis negative-sequence harmonic component. The accumulation conversion unit 45 is also used to accumulate the α-axis fundamental component, the α-axis positive sequence harmonic component, and the α-axis negative sequence harmonic component to obtain the α-axis current component, and to accumulate the β-axis fundamental component, the β-axis positive sequence harmonic component, and the β-axis negative sequence harmonic component to obtain the β-axis current component, and to obtain the modulation ratio m and the vector angle θ based on the α-axis current component and the β-axis current component.

[0039] It should be noted that in this embodiment, the positive-sequence harmonic suppression sub-ring 441 and the negative-sequence harmonic suppression sub-ring 442 control the positive-sequence harmonics and negative-sequence harmonics simultaneously, which helps to eliminate more low-order harmonics, improves the sinusoidal nature of the grid-connected current, and thus improves the quality of the grid current and the total harmonic distortion.

[0040] In some embodiments, such as Figure 2As shown, the positive sequence harmonic suppression sub-ring 441 includes a first conversion unit abc / dq1, a first low-pass filter LPF1, a first subtractor CF1, a first PI controller PI1, a second low-pass filter LPF2, a second subtractor CF2, a second PI controller PI2, and a second conversion unit dq / αβ1. The first conversion unit abc / dq1 is connected to the grid phase θg (6K+1 times) and the three-phase current. The first low-pass filter LPF1 is connected to the first conversion unit abc / dq1, the first subtractor CF1 is connected to the first low-pass filter LPF1, the first PI controller PI1 is connected to the first subtractor CF1, the second low-pass filter LPF2 is connected to the first conversion unit abc / dq1, the second subtractor CF2 is connected to the second low-pass filter LPF2, the second PI controller PI2 is connected to the second subtractor CF2, and the second conversion unit dq / αβ1 is connected to the first PI controller PI1, the second PI controller PI2, and the accumulation conversion unit 45.

[0041] It should be noted that the first conversion unit abc / dq1 is used to convert the three-phase current into d-axis positive-sequence DC components and q-axis positive-sequence DC components in a rotating coordinate system based on the grid phase θg, which is 6K+1 times the grid phase. The first low-pass filter LPF1 is used to perform low-pass filtering on the d-axis positive-sequence DC component. The first subtractor CF1 is used to obtain the d-axis positive-sequence error signal based on the difference between the zero reference and the low-pass filtered d-axis positive-sequence DC component. The first PI controller PI1 is used to perform proportional-integral calculations on the d-axis positive-sequence error signal to generate the d-axis positive-sequence compensation current. The second low-pass filter LPF2 is used to perform low-pass filtering on the q-axis positive-sequence DC component. The second subtractor CF2 is used to obtain the q-axis positive-sequence error signal based on the difference between the zero reference and the low-pass filtered q-axis positive-sequence DC component. The second PI controller PI2 is used to perform proportional-integral calculations on the q-axis positive-sequence error signal to generate the q-axis positive-sequence compensation current. The second conversion unit dq / αβ1 is used to convert the d-axis positive sequence compensation current and the q-axis positive sequence compensation current into α-axis positive sequence harmonic components and β-axis positive sequence harmonic components respectively, based on the grid phase θg of 6K+1 times.

[0042] In some embodiments, such as Figure 2As shown, the negative sequence harmonic suppression sub-ring 442 includes a third conversion unit abc / dq2, a third low-pass filter LPF3, a third subtractor CF3, a third PI controller PI3, a fourth low-pass filter LPF4, a fourth subtractor CF4, a fourth PI controller PI4, and a fourth conversion unit dq / αβ2. The third conversion unit abc / dq2 is connected to -(6K-1) times the grid phase θg and the three-phase current. The third low-pass filter LPF3 is connected to the third conversion unit abc / dq2, the third subtractor CF3 is connected to the third low-pass filter LPF3, the third PI controller PI3 is connected to the third subtractor CF3, the fourth low-pass filter LPF4 is connected to the third conversion unit abc / dq2, the fourth subtractor CF4 is connected to the fourth low-pass filter LPF4, the fourth PI controller PI4 is connected to the fourth subtractor CF4, and the fourth conversion unit dq / αβ2 is connected to the third PI controller PI3, the fourth PI controller PI4, and the accumulation conversion unit 45.

[0043] It should be noted that the third conversion unit abc / dq2 is used to convert the three-phase current into d-axis negative-sequence DC components and q-axis negative-sequence DC components in a rotating coordinate system based on -(6K-1) times the grid phase θg. The third low-pass filter LPF3 is used to perform low-pass filtering on the d-axis negative-sequence DC component. The third subtractor CF3 is used to obtain the d-axis negative-sequence error signal based on the difference between the zero reference and the low-pass filtered d-axis negative-sequence DC component. The third PI controller PI3 is used to perform proportional-integral operation on the d-axis negative-sequence error signal to generate the d-axis negative-sequence compensation current. The fourth low-pass filter LPF4 is used to perform low-pass filtering on the q-axis negative-sequence DC component. The fourth subtractor CF4 is used to obtain the q-axis negative-sequence error signal based on the difference between the zero reference and the low-pass filtered q-axis negative-sequence DC component. The fourth PI controller PI4 is used to perform proportional-integral operation on the q-axis negative-sequence error signal to generate the q-axis negative-sequence compensation current. The fourth conversion unit dq / αβ2 is used to convert the d-axis negative sequence compensation current and the q-axis negative sequence compensation current into α-axis negative sequence harmonic components and β-axis negative sequence harmonic components respectively, based on -(6K-1) times the grid phase θg.

[0044] In some embodiments, such as Figure 2 As shown, the sampling unit 41 is also used to sample the inductor voltage and capacitor current of the three-phase LC filter 10. The closed-loop control module 40 also includes an LC oscillation active damping ring 46, which is connected to the sampling unit 41 and the accumulation conversion unit 45.

[0045] It should be noted that the LC oscillation active damping ring 46 is used to suppress the inherent oscillation of the three-phase LC filter 10 through the negative feedback of inductor voltage and capacitor current, which is beneficial to further improve the grid-connected current quality.

[0046] In some embodiments, such as Figure 2 As shown, the LC oscillation active damping ring 46 includes a fifth conversion unit abc / αβ1, a first gain amplifier Kvl1, a second gain amplifier Kvl2, a sixth conversion unit abc / αβ2, a third gain amplifier Kic1, and a fourth gain amplifier Kic2. The fifth conversion unit abc / αβ1 is connected to the sampling unit 41 and the phase-locked loop 42. The first gain amplifier Kvl1 is connected to the fifth conversion unit abc / αβ1 and the accumulation conversion unit 45. The second gain amplifier Kvl2 is connected to the fifth conversion unit abc / αβ1 and the accumulation conversion unit 45. The sixth conversion unit abc / αβ2 is connected to the sampling unit 41 and the phase-locked loop 42. The third gain amplifier Kic1 is connected to the sixth conversion unit abc / αβ2 and the accumulation conversion unit 45. The fourth gain amplifier Kic2 is connected to the sixth conversion unit abc / αβ2 and the accumulation conversion unit 45.

[0047] It should be noted that the fifth conversion unit abc / αβ1 is used to convert the inductor voltage into initial α-axis and β-axis voltage components in the stationary coordinate system based on the grid phase θg. The first gain amplifier Kvl1 is used to obtain the α-axis voltage component by multiplying the initial α-axis voltage component by the voltage gain coefficient. The second gain amplifier Kvl2 is used to obtain the β-axis voltage component by multiplying the initial β-axis voltage component by the voltage gain coefficient. The sixth conversion unit abc / αβ2 is used to convert the capacitor current into initial α-axis and β-axis current components in the stationary coordinate system based on the grid phase θg. The third gain amplifier Kic1 is used to obtain the target α-axis current component by multiplying the initial α-axis current component by the current gain coefficient. The fourth gain amplifier Kic2 is used to obtain the target β-axis current component by multiplying the initial β-axis current component by the voltage gain coefficient. The accumulation conversion unit 45 is also used to accumulate the α-axis fundamental component, α-axis harmonic component, α-axis voltage component and α-axis target current component to obtain the α-axis current component, and to accumulate the β-axis fundamental component, β-axis harmonic component, β-axis voltage component and β-axis target current component to obtain the β-axis current component, and to obtain the modulation ratio m and vector angle θ based on the α-axis current component and the β-axis current component.

[0048] In some embodiments, such as Figure 2As shown, the fundamental frequency ring 43 includes a seventh conversion unit abc / dq3, a fifth low-pass filter LPF5, a fifth subtractor CF5, a fifth PI controller PI5, a sixth low-pass filter LPF6, a sixth subtractor CF6, a sixth PI controller PI6, and an eighth conversion unit dq / αβ3. The seventh conversion unit abc / dq3 is connected to the grid phase θg and the three-phase current. The fifth low-pass filter LPF5 is connected to the seventh conversion unit abc / dq3, the fifth subtractor CF5 is connected to the fifth low-pass filter LPF5, the fifth PI controller PI5 is connected to the fifth subtractor CF5, the sixth low-pass filter LPF6 is connected to the seventh conversion unit abc / dq3, the sixth subtractor CF6 is connected to the sixth low-pass filter LPF6, the sixth PI controller PI6 is connected to the sixth subtractor CF6, and the eighth conversion unit dq / αβ3 is connected to the fifth PI controller PI5, the sixth PI controller PI6, and the accumulation conversion unit 45.

[0049] It should be noted that the seventh conversion unit abc / dq3 is used to convert the three-phase current into the d-axis fundamental DC component and the q-axis fundamental DC component in a rotating coordinate system based on the grid phase θg. The fifth low-pass filter LPF5 is used to perform low-pass filtering on the d-axis fundamental DC component. The fifth subtractor CF5 is used to obtain the d-axis fundamental error signal based on the difference between the first reference current (idr) and the low-pass filtered d-axis fundamental DC component. The fifth PI controller PI5 is used to perform proportional-integral operation on the d-axis fundamental error signal to generate the d-axis fundamental compensation current. The sixth low-pass filter LPF6 is used to perform low-pass filtering on the q-axis fundamental DC component. The sixth subtractor CF6 is used to obtain the q-axis fundamental error signal based on the difference between the second reference current (iqr) and the low-pass filtered q-axis fundamental DC component. The sixth PI controller PI6 is used to perform proportional-integral operation on the q-axis fundamental error signal to generate the q-axis fundamental compensation current. The eighth conversion unit dq / αβ3 is used to convert the d-axis fundamental compensation current and q-axis fundamental compensation current into α-axis fundamental components and β-axis fundamental components respectively according to the grid phase θg.

[0050] In some embodiments, such as Figure 3 As shown, the primary-side drive signal PWM1 controls the primary-side voltage vp of the high-frequency transformer T1 through the three-phase matrix converter 20. The primary-side voltage vp decreases in a stepwise manner within one switching cycle Ts, and the primary-side voltage vp is symmetrical in the first half of the switching cycle Ts and the second half of the switching cycle Ts. The secondary-side drive signal PWM2 controls the secondary-side voltage vs of the high-frequency transformer T1 through the full-bridge inverter 30. The secondary-side voltage vs exhibits a symmetrical square wave distribution within one switching cycle Ts.

[0051] It should be noted that this embodiment can make the primary side voltage vp form a symmetrical stepped wave within one switching cycle Ts, which helps to reduce the number of switching cycles of each switching transistor in the three-phase matrix converter 20 and the full-bridge inverter 30, and can reduce switching losses.

[0052] In some embodiments, such as Figure 3 As shown, the primary-side voltage vp has, from front to back, a first level, a second level, a third level, a fourth level, a fifth level, a sixth level, and a seventh level within one switching cycle Ts. The first, fourth, and seventh levels are all zero. The second level is the line voltage with the largest absolute value, Vmax; the third level is the line voltage with the second largest absolute value, Vmid; the fifth level is the reverse voltage of the third level, -Vmid; and the sixth level is the reverse voltage of the second level, -Vmax. The secondary-side voltage vs has, from front to back, a eighth level, a ninth level, and a tenth level within one switching cycle Ts. The eighth level is equal to the tenth level. The ninth level is a positive level, Vdc; and the eighth and tenth levels are both the reverse voltage of the ninth level, -Vdc.

[0053] It should be noted that the ninth level can be the DC voltage applied by the full-bridge inverter 30 to the DC source 120. The phase of the secondary voltage vs has a certain delay relative to the phase of the primary voltage vp, which helps to improve the sinusoidal wave of the grid-connected current and increase the conversion power.

[0054] In some embodiments, such as Figure 3 As shown, the duration of the first level is Tz / 4, the duration of the second level is Tx / 2, the duration of the third level is Ty / 2, the duration of the fourth level is Tz / 2, the duration of the fifth level is Ty / 2, the duration of the sixth level is Tx / 2, and the duration of the seventh level is Tz / 4. The sum of Tx, Ty, and Tz is the switching period Ts. The durations of the eighth and tenth levels are both one-quarter of the switching period Ts, and the duration of the ninth level is half of the switching period Ts.

[0055] It should be noted that in this embodiment, the positive sequence voltage and the negative sequence voltage each account for 50%, which allows the secondary-side switching transistor to be controlled in an open-loop manner, without being limited by Tx, Ty, and Tz, which is beneficial for the secondary side to adopt single-phase shift control.

[0056] The phase of the secondary voltage vs has a one-quarter switching cycle Ts delay relative to the phase of the primary voltage vp, which maximizes the improvement of the sinusoidal waveform of the grid-connected current and maximizes the conversion power.

[0057] In some embodiments, such as Figure 4As shown, the pulse width modulation module 50 divides the fundamental frequency period into twelve alternating odd-numbered and even-numbered regions based on the variation of the absolute value of the line voltage. Examples of odd-numbered regions include the first region R1, the third region R3, the fifth region R5, the seventh region R7, the ninth region R9, and the eleventh region R11. Examples of even-numbered regions include the second region R2, the fourth region R4, the sixth region R6, the eighth region R8, the tenth region R10, and the twelfth region R12.

[0058] It should be noted that in the odd-numbered region, Tx = m × Ts × sin(π / 6 + θ), Ty = m × Ts × sin(π / 6 - θ), and Tz = 1 - m × Ts × cos(θ). In the even-numbered region, Tx = m × Ts × sin(π / 6 - θ), Ty = m × Ts × sin(π / 6 + θ), and Tz = 1 - m × Ts × cos(θ). Here, m is the modulation ratio, Ts is the switching period, and θ is the vector angle.

[0059] Except for phase-locked loop 42, the outputs of the other four loops all contain α-axis and β-axis components. The α-axis and β-axis components of each loop are accumulated to obtain the α-axis component *iref_α* and the β-axis component *iref_β* of the reference current *iref*. Normalizing the amplitude of the reference current *iref* yields the modulation ratio *m*, satisfying 0 ≤ *m* ≤ 1. Using the ratio of *iref_α* and *iref_β*, the value of the vector angle θ can be determined, and its meaning is related to... Figure 5 The space vector modulation of the current source inverter shown is similar. In each region from the first region R1 to the twelfth region R12, the following condition is satisfied: -π / 6 ≤ θ ≤ π / 6.

[0060] This embodiment also provides a closed-loop control method applied to the aforementioned single-stage three-phase high-frequency isolated converter circuit. The closed-loop control method includes: generating a modulation ratio m and a vector angle θ based on the three-phase voltage and three-phase current of the three-phase three-wire power grid 110, while synchronously controlling the fundamental and harmonic frequencies of the three-phase current; generating a primary-side drive signal PWM1 and a secondary-side drive signal PWM2 based on the modulation ratio m and vector angle θ. The primary-side drive signal PWM1 is used to drive the three-phase matrix converter 20, and the secondary-side drive signal PWM2 is used to drive the full-bridge inverter 30.

[0061] It is understood that the closed-loop control method provided in this embodiment can also generate a modulation ratio m and a vector angle θ based on the three-phase voltage and three-phase current of the three-phase three-wire power grid 110, and synchronously control the fundamental and harmonic waves of the three-phase current. Based on the modulation ratio m and the vector angle θ, a primary-side drive signal PWM1 and a secondary-side drive signal PWM2 are generated. The primary-side drive signal PWM1 is used to drive the three-phase matrix converter 20, and the secondary-side drive signal PWM2 is used to drive the full-bridge inverter 30. This can synchronously control the fundamental and low-frequency harmonic waves of the grid current, which is beneficial for eliminating low-order harmonics and improving the sinusoidal nature of the grid current, thereby improving the quality of the grid current and the total harmonic distortion.

[0062] In some embodiments, the closed-loop control method further includes: sampling the three-phase voltage and three-phase current; obtaining the grid phase θg of the three-phase three-wire power grid 110 based on the three-phase voltage; generating the α-axis fundamental component and the β-axis fundamental component based on the three-phase current and the grid phase θg; generating the α-axis harmonic component and the β-axis harmonic component based on the three-phase current and the grid phase θg; accumulating the α-axis fundamental component and the α-axis harmonic component to obtain the α-axis current component, and accumulating the β-axis fundamental component and the β-axis harmonic component to obtain the β-axis current component; and obtaining the modulation ratio m and the vector angle θ based on the α-axis current component and the β-axis current component.

[0063] In some embodiments, the closed-loop control method further includes: suppressing the 6K+1th positive sequence harmonics based on the three-phase current and the grid phase θg to generate α-axis positive sequence harmonic components and β-axis positive sequence harmonic components, where K is a positive integer; suppressing the 6K-1th positive sequence harmonics based on the three-phase current and the grid phase θg to generate α-axis negative sequence harmonic components and β-axis negative sequence harmonic components; accumulating the α-axis fundamental component, α-axis positive sequence harmonic components, and α-axis negative sequence harmonic components to obtain the α-axis current component; accumulating the β-axis fundamental component, β-axis positive sequence harmonic components, and β-axis negative sequence harmonic components to obtain the β-axis current component; and obtaining the modulation ratio m and vector angle θ based on the α-axis current component and the β-axis current component.

[0064] In some embodiments, the closed-loop control method further includes: converting the three-phase current into d-axis positive-sequence DC components and q-axis positive-sequence DC components in a rotating coordinate system based on a grid phase θg of 6K+1 times; performing low-pass filtering on the d-axis positive-sequence DC components; obtaining a d-axis positive-sequence error signal based on the difference between the zero reference and the low-pass filtered d-axis positive-sequence DC components; generating a d-axis positive-sequence compensation current by performing proportional-integral operation on the d-axis positive-sequence error signal; performing low-pass filtering on the q-axis positive-sequence DC components; obtaining a q-axis positive-sequence error signal based on the difference between the zero reference and the low-pass filtered q-axis positive-sequence DC components; generating a q-axis positive-sequence compensation current by performing proportional-integral operation on the q-axis positive-sequence error signal; and converting the d-axis positive-sequence compensation current and q-axis positive-sequence compensation current into α-axis positive-sequence harmonic components and β-axis positive-sequence harmonic components, respectively, based on a grid phase θg of 6K+1 times.

[0065] In some embodiments, the closed-loop control method further includes: converting the three-phase current into a d-axis negative-sequence DC component and a q-axis negative-sequence DC component in a rotating coordinate system based on -(6K-1) times the grid phase θg; performing low-pass filtering on the d-axis negative-sequence DC component; obtaining a d-axis negative-sequence error signal based on the difference between the zero reference and the low-pass filtered d-axis negative-sequence DC component; performing proportional-integral operation on the d-axis negative-sequence error signal to generate a d-axis negative-sequence compensation current; performing low-pass filtering on the q-axis negative-sequence DC component; obtaining a q-axis negative-sequence error signal based on the difference between the zero reference and the low-pass filtered q-axis negative-sequence DC component; performing proportional-integral operation on the q-axis negative-sequence error signal to generate a q-axis negative-sequence compensation current; and converting the d-axis negative-sequence compensation current and the q-axis negative-sequence compensation current into an α-axis negative-sequence harmonic component and a β-axis negative-sequence harmonic component respectively based on -(6K-1) times the grid phase θg.

[0066] In some embodiments, the closed-loop control method further includes: sampling the inductor voltage and capacitor current of the three-phase LC filter 10; and suppressing the inherent oscillation of the three-phase LC filter 10 through negative feedback of the inductor voltage and capacitor current.

[0067] In some embodiments, the closed-loop control method further includes: converting the inductor voltage into initial α-axis voltage components and initial β-axis voltage components in a stationary coordinate system based on the grid phase θg; obtaining the α-axis voltage component by multiplying the initial α-axis voltage component with the voltage gain coefficient; obtaining the β-axis voltage component by multiplying the initial β-axis voltage component with the voltage gain coefficient; converting the capacitor current into initial α-axis current components and initial β-axis current components in a stationary coordinate system based on the grid phase θg; obtaining the α-axis target current component by multiplying the initial α-axis current component with the current gain coefficient; obtaining the β-axis target current component by multiplying the initial β-axis current component with the voltage gain coefficient; accumulating the α-axis fundamental component, α-axis harmonic component, α-axis voltage component, and α-axis target current component to obtain the α-axis current component; accumulating the β-axis fundamental component, β-axis harmonic component, β-axis voltage component, and β-axis target current component to obtain the β-axis current component; and obtaining the modulation ratio m and vector angle θ based on the α-axis current component and the β-axis current component.

[0068] In some embodiments, the closed-loop control method further includes: configuring the primary-side drive signal PWM1 to control the primary-side voltage vp of the high-frequency transformer T1 through the three-phase matrix converter 20, wherein the primary-side voltage vp decreases in a stepwise manner within one switching cycle Ts, and the primary-side voltage vp is symmetrical in the first half of the switching cycle Ts and the second half of the switching cycle Ts; configuring the secondary-side drive signal PWM2 to control the secondary-side voltage vs of the high-frequency transformer T1 through the full-bridge inverter 30, wherein the secondary-side voltage vs exhibits a symmetrical square wave distribution within one switching cycle Ts.

[0069] In some embodiments, the closed-loop control method further includes: configuring the primary-side voltage vp to have a first level, a second level, a third level, a fourth level, a fifth level, a sixth level, and a seventh level sequentially from front to back within a switching cycle Ts. The first level, the fourth level, and the seventh level are all zero levels. The second level is the line voltage with the largest absolute value, i.e., Vmax. The third level is the line voltage with the second largest absolute value, i.e., Vmid. The fifth level is the reverse voltage of the third level, i.e., -Vmid. The sixth level is the reverse voltage of the second level, i.e., -Vmax. The secondary-side voltage vs has an eighth level, a ninth level, and a tenth level sequentially from front to back within a switching cycle Ts. The eighth level is equal to the tenth level. The ninth level is a positive level, i.e., Vdc. The eighth level and the tenth level are both the reverse voltage of the ninth level, i.e., -Vdc.

[0070] In some embodiments, the closed-loop control method further includes: configuring the duration of the first level to be Tz / 4, the duration of the second level to be Tx / 2, the duration of the third level to be Ty / 2, the duration of the fourth level to be Tz / 2, the duration of the fifth level to be Ty / 2, the duration of the sixth level to be Tx / 2, and the duration of the seventh level to be Tz / 4, wherein the sum of Tx, Ty, and Tz is the switching period Ts; configuring the duration of the eighth level and the duration of the tenth level to be one-quarter of the switching period Ts, and the duration of the ninth level to be half of the switching period Ts.

[0071] In some embodiments, the closed-loop control method further includes: dividing the fundamental frequency period into twelve alternating odd-numbered regions and even-numbered regions based on the change in the absolute value of the line voltage; in the odd-numbered regions, configuring Tx=m×Ts×sin(π / 6+θ), Ty=m×Ts×sin(π / 6-θ), Tz=1-m×Ts×cos(θ); in the even-numbered regions, configuring Tx=m×Ts×sin(π / 6-θ), Ty=m×Ts×sin(π / 6+θ), Tz=1-m×Ts×cos(θ); where m is the modulation ratio, Ts is the switching period, and θ is the vector angle.

[0072] In summary, related technologies employ repetitive control, making parameter design difficult and leading to system instability; using only the fundamental current loop results in abundant harmonics in the grid-connected current, leading to poor performance. The single-stage three-phase high-frequency isolated bidirectional AC / DC converter provided in this application, referencing the space vector modulation method of current-source inverters, performs pulse time distribution on its primary-side three-phase matrix converter 20; and employs single-phase-shift control on its secondary-side full-bridge inverter 30. To address the harmonic problem caused by this modulation scheme, a harmonic control loop is introduced to eliminate low-order harmonics. To further improve grid-connected current quality, an active damping loop is introduced. The closed-loop control scheme significantly improves the grid-connected current quality.

[0073] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0074] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. These modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A single-stage three-phase high-frequency isolated conversion circuit, characterized by comprising: The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method.

2. The single-stage three-phase high-frequency isolated conversion circuit according to claim 1, characterized by The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method.

3. The single-stage three-phase high-frequency isolated converter circuit according to claim 2, wherein, The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a three-phase three-wire power grid and a high-frequency transformer, and relates to a high-frequency transformer control method. The application relates to a first subtractor connected with the first low-pass filter, configured to obtain a d-axis positive sequence error signal according to a difference between a zero reference and the d-axis positive sequence direct current component after low-pass filtering; a first PI controller connected with the first subtractor, configured to perform proportional integral operation on the d-axis positive sequence error signal to generate a d-axis positive sequence compensation current; a second low-pass filter connected with the first conversion unit, configured to perform low-pass filtering on the q-axis positive sequence direct current component; a second subtractor connected with the second low-pass filter, configured to obtain a q-axis positive sequence error signal according to a difference between a zero reference and the q-axis positive sequence direct current component after low-pass filtering; a second PI controller connected with the second subtractor, configured to perform proportional integral operation on the q-axis positive sequence error signal to generate a q-axis positive sequence compensation current; a second conversion unit connected with the first PI controller, the second PI controller and the accumulation conversion unit, configured to convert the d-axis positive sequence compensation current and the q-axis positive sequence compensation current into the α-axis positive sequence harmonic component and the β-axis positive sequence harmonic component according to 6K+1 times of the grid phase respectively.

4. The single-stage three-phase high-frequency isolated converter circuit according to claim 2, wherein, The negative sequence harmonic suppression sub-loop comprises: a third conversion unit configured to convert the three-phase current into a d-axis negative sequence direct current component and a q-axis negative sequence direct current component in a rotating coordinate system according to - (6K-1) times of the grid phase; a third low-pass filter connected with the third conversion unit, configured to perform low-pass filtering on the d-axis negative sequence direct current component; a third subtractor connected with the third low-pass filter, configured to obtain a d-axis negative sequence error signal according to a difference between a zero reference and the d-axis negative sequence direct current component after low-pass filtering; a third PI controller connected with the third subtractor, configured to perform proportional integral operation on the d-axis negative sequence error signal to generate a d-axis negative sequence compensation current; a fourth low-pass filter connected with the third conversion unit, configured to perform low-pass filtering on the q-axis negative sequence direct current component; a fourth subtractor connected with the fourth low-pass filter, configured to obtain a q-axis negative sequence error signal according to a difference between a zero reference and the q-axis negative sequence direct current component after low-pass filtering; a fourth PI controller connected with the fourth subtractor, configured to perform proportional integral operation on the q-axis negative sequence error signal to generate a q-axis negative sequence compensation current; a fourth conversion unit connected with the third PI controller, the fourth PI controller and the accumulation conversion unit, configured to convert the d-axis negative sequence compensation current and the q-axis negative sequence compensation current into the α-axis negative sequence harmonic component and the β-axis negative sequence harmonic component according to - (6K-1) times of the grid phase respectively.

5. The single-stage three-phase high-frequency isolated converter circuit according to claim 1, wherein, The sampling unit is further configured to sample an inductance voltage of the three-phase LC filter and a capacitance current of the three-phase LC filter; The closed-loop control module further comprises an LC oscillation active damping loop connected with the sampling unit and the accumulation conversion unit, configured to suppress an inherent oscillation of the three-phase LC filter through negative feedback of the inductance voltage and the capacitance current.

6. The single-stage three-phase high-frequency isolated converter circuit according to claim 5, wherein, The LC oscillation active damping loop comprises: A fifth conversion unit is connected with the sampling unit and the phase-locked loop, and is configured to convert the inductive voltage into an initial voltage component of an α axis and an initial voltage component of a β axis in a stationary coordinate system according to the grid phase; A first gain amplifier is connected with the fifth conversion unit and the accumulation conversion unit, and is configured to obtain an α axis voltage component according to a product of the initial voltage component of the α axis and a voltage gain coefficient; A second gain amplifier is connected with the fifth conversion unit and the accumulation conversion unit, and is configured to obtain a β axis voltage component according to a product of the initial voltage component of the β axis and the voltage gain coefficient; A sixth conversion unit is connected with the sampling unit and the phase-locked loop, and is configured to convert the capacitive current into an initial current component of an α axis and an initial current component of a β axis in a stationary coordinate system according to the grid phase; A third gain amplifier is connected with the sixth conversion unit and the accumulation conversion unit, and is configured to obtain an α axis target current component according to a product of the initial current component of the α axis and a current gain coefficient; A fourth gain amplifier is connected with the sixth conversion unit and the accumulation conversion unit, and is configured to obtain a β axis target current component according to a product of the initial current component of the β axis and the voltage gain coefficient; The accumulation conversion unit is further configured to accumulate the α axis fundamental component, the α axis harmonic component, the α axis voltage component and the α axis target current component to obtain an α axis current component, and accumulate the β axis fundamental component, the β axis harmonic component, the β axis voltage component and the β axis target current component to obtain a β axis current component, and obtain the modulation ratio and the vector angle according to the α axis current component and the β axis current component.

7. The single-stage three-phase high-frequency isolated converter circuit according to any one of claims 1 to 6, characterized in that, The primary side driving signal controls the primary side voltage of the high-frequency transformer through the three-phase matrix converter, the primary side voltage is stepped down in a switching period, and the primary side voltage is symmetrical in the first half of the switching period and the second half of the switching period. The secondary side driving signal controls the secondary side voltage of the high-frequency transformer through the full-bridge inverter, and the secondary side voltage is distributed in a symmetrical square wave in a switching period.

8. The single-stage three-phase high-frequency isolated converter circuit according to claim 7, wherein, The primary side voltage has a first level, a second level, a third level, a fourth level, a fifth level, a sixth level and a seventh level from front to back in a switching period, the first level, the fourth level and the seventh level are zero levels, the second level is a linear voltage with the largest absolute value, the third level is a linear voltage with the second largest absolute value, the fifth level is a reverse voltage of the third level, and the sixth level is a reverse voltage of the second level. The secondary side voltage has an eighth level, a ninth level and a tenth level from front to back in a switching period, the eighth level is equal to the tenth level, the ninth level is a positive level, and the eighth level and the tenth level are reverse voltages of the ninth level.

9. The single-stage three-phase high-frequency isolated converter circuit according to claim 8, wherein, The first level lasts for Tz / 4, the second level lasts for Tx / 2, the third level lasts for Ty / 2, the fourth level lasts for Tz / 2, the fifth level lasts for Ty / 2, the sixth level lasts for Tx / 2, the seventh level lasts for Tz / 4, and the sum of Tx, Ty and Tz is the switching period; The eighth level and the tenth level each last for one fourth of the switching period, and the ninth level lasts for one half of the switching period.

10. A closed loop control method, characterized by, The closed-loop control method is applied to a single-stage three-phase high-frequency isolation type conversion circuit, and the single-stage three-phase high-frequency isolation type conversion circuit comprises, in sequence, a three-phase LC filter, a three-phase matrix converter, a first inductor, a high-frequency transformer and a full-bridge inverter, wherein the three-phase LC filter is connected between a three-phase three-wire power grid and the three-phase matrix converter, The closed-loop control method comprises: sampling three-phase voltage and three-phase current; obtaining a power grid phase of the three-phase three-wire power grid according to the three-phase voltage; generating an α-axis fundamental component and a β-axis fundamental component according to the three-phase current and the power grid phase; generating an α-axis harmonic component and a β-axis harmonic component according to the three-phase current and the power grid phase; accumulating the α-axis fundamental component and the α-axis harmonic component to obtain an α-axis current component, accumulating the β-axis fundamental component and the β-axis harmonic component to obtain a β-axis current component, and obtaining a modulation ratio and a vector angle according to the α-axis current component and the β-axis current component; generating a primary side driving signal and a secondary side driving signal according to the modulation ratio and the vector angle, wherein the primary side driving signal is used to drive the three-phase matrix converter, and the secondary side driving signal is used to drive the full-bridge inverter.

11. The closed loop control method of claim 10, wherein, The closed-loop control method further comprises: suppressing 6K+1 order positive sequence harmonics according to the three-phase current and the power grid phase to generate an α-axis positive sequence harmonic component and a β-axis positive sequence harmonic component, wherein K is a positive integer; suppressing 6K-1 order positive sequence harmonics according to the three-phase current and the power grid phase to generate an α-axis negative sequence harmonic component and a β-axis negative sequence harmonic component; accumulating the α-axis fundamental component, the α-axis positive sequence harmonic component and the α-axis negative sequence harmonic component to obtain an α-axis current component, accumulating the β-axis fundamental component, the β-axis positive sequence harmonic component and the β-axis negative sequence harmonic component to obtain a β-axis current component, and obtaining the modulation ratio and the vector angle according to the α-axis current component and the β-axis current component.

12. The closed loop control method of claim 11, wherein, The closed-loop control method further comprises: converting the three-phase current into a d-axis positive sequence direct current component and a q-axis positive sequence direct current component in a rotating coordinate system according to 6K+1 times the power grid phase; low-pass filtering the d-axis positive sequence direct current component; obtaining a d-axis positive sequence error signal according to a difference between a zero reference and the low-pass filtered d-axis positive sequence direct current component; generating a d-axis positive sequence compensation current by proportional-integral operation on the d-axis positive sequence error signal; low-pass filtering the q-axis positive sequence direct current component; According to the difference between the zero reference and the low-pass filtered q-axis positive sequence direct current component, a q-axis positive sequence error signal is obtained; A proportional integral operation is performed on the q-axis positive sequence error signal to generate a q-axis positive sequence compensation current; According to the 6K+1 times of the grid phase, the d-axis positive sequence compensation current and the q-axis positive sequence compensation current are converted into the α-axis positive sequence harmonic component and the β-axis positive sequence harmonic component.

13. The closed loop control method of claim 11, wherein, The closed-loop control method further comprises: According to the - (6K-1) times of the grid phase, the three-phase current is converted into a d-axis negative sequence direct current component and a q-axis negative sequence direct current component in the rotating coordinate system; The d-axis negative sequence direct current component is low-pass filtered; According to the difference between the zero reference and the low-pass filtered d-axis negative sequence direct current component, a d-axis negative sequence error signal is obtained; A proportional integral operation is performed on the d-axis negative sequence error signal to generate a d-axis negative sequence compensation current; The q-axis negative sequence direct current component is low-pass filtered; According to the difference between the zero reference and the low-pass filtered q-axis negative sequence direct current component, a q-axis negative sequence error signal is obtained; A proportional integral operation is performed on the q-axis negative sequence error signal to generate a q-axis negative sequence compensation current; According to the - (6K-1) times of the grid phase, the d-axis negative sequence compensation current and the q-axis negative sequence compensation current are converted into the α-axis negative sequence harmonic component and the β-axis negative sequence harmonic component.

14. The closed loop control method of claim 10, wherein, The closed-loop control method further comprises: The inductance voltage of the three-phase LC filter and the capacitance current of the three-phase LC filter are sampled; Through negative feedback of the inductance voltage and the capacitance current, the inherent oscillation of the three-phase LC filter is suppressed.

15. The closed loop control method of claim 14, wherein, The closed-loop control method further comprises: According to the grid phase, the inductance voltage is converted into an α-axis initial voltage component and a β-axis initial voltage component in the stationary coordinate system; According to the product of the α-axis initial voltage component and a voltage gain coefficient, an α-axis voltage component is obtained; According to the product of the β-axis initial voltage component and the voltage gain coefficient, a β-axis voltage component is obtained; According to the grid phase, the capacitance current is converted into an α-axis initial current component and a β-axis initial current component in the stationary coordinate system; According to the product of the α-axis initial current component and a current gain coefficient, an α-axis target current component is obtained; According to the product of the β-axis initial current component and the voltage gain coefficient, a β-axis target current component is obtained; The α-axis fundamental component, the α-axis harmonic component, the α-axis voltage component, and the α-axis target current component are accumulated to obtain an α-axis current component, and the β-axis fundamental component, the β-axis harmonic component, the β-axis voltage component, and the β-axis target current component are accumulated to obtain a β-axis current component, and the modulation ratio and the vector angle are obtained according to the α-axis current component and the β-axis current component.

16. The closed loop control method of claim 10, wherein, The closed-loop control method further comprises: The primary side driving signal is configured to control the primary side voltage of the high-frequency transformer through the three-phase matrix converter, the primary side voltage is stepped down in a switching period, and the primary side voltage is symmetrical in the first half of the switching period and the second half of the switching period; The secondary side driving signal is configured to control the secondary side voltage of the high-frequency transformer through the full-bridge inverter, and the secondary side voltage is in the form of a symmetrical square wave in one switching cycle.

17. The closed loop control method of claim 16, wherein, The closed-loop control method further comprises: The primary side voltage is configured to have a first level, a second level, a third level, a fourth level, a fifth level, a sixth level and a seventh level in sequence from front to back in one switching cycle, the first level, the fourth level and the seventh level are zero levels, the second level is a line voltage with the largest absolute value, the third level is a line voltage with the second largest absolute value, the fifth level is a reverse voltage of the third level, and the sixth level is a reverse voltage of the second level. The secondary side voltage is configured to have an eighth level, a ninth level and a tenth level in sequence from front to back in one switching cycle, the eighth level is equal to the tenth level, the ninth level is a positive level, and the eighth level and the tenth level are reverse voltages of the ninth level.

18. The closed loop control method of claim 17, wherein, The closed-loop control method further comprises: The first level has a duration of Tz / 4, the second level has a duration of Tx / 2, the third level has a duration of Ty / 2, the fourth level has a duration of Tz / 2, the fifth level has a duration of Ty / 2, the sixth level has a duration of Tx / 2, the seventh level has a duration of Tz / 4, and the sum of Tx, Ty and Tz is the switching cycle. The eighth level has a duration of one fourth of the switching cycle, the tenth level has a duration of one fourth of the switching cycle, and the ninth level has a duration of one half of the switching cycle.

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