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

Abstract

The invention discloses a single-stage three-phase high-frequency isolation type conversion circuit and a closed-loop control method, and the single-stage three-phase high-frequency isolation type conversion circuit is based on the three-phase voltage of a three-phase three-wire system power grid and the three-phase current of the three-phase three-wire system power grid. A modulation ratio and a vector angle are generated on the basis of synchronously controlling fundamental waves and harmonic waves of three-phase current, a primary side driving signal and a secondary side driving signal are generated 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, the elimination of the low-order harmonic wave is facilitated, and the sine degree of the grid-connected current can be improved, so that the quality of the power grid current and the total harmonic distortion are 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: (1) It can only control the fundamental current of the power grid, resulting in large current distortion and poor total harmonic distortion (THD).

[0020] (2) During the switching cycle, the number of switching device actions increases significantly, resulting in high circuit losses.

[0021] (3) Using a complex controller makes it difficult to set control parameters and the system is prone to instability.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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).

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] It should be noted that the ninth level can be the DC voltage applied to the DC source 120 by the full-bridge inverter 30. 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.

[0053] 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.

[0054] 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.

[0055] The phase of the secondary voltage vs has a delay of one-quarter of a switching cycle Ts 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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 converter circuit, characterized in that, include: A three-phase LC filter, a three-phase matrix converter, a first inductor, a high-frequency transformer, and a full-bridge inverter are connected in sequence, wherein the three-phase LC filter is connected between a three-phase three-wire power grid and the three-phase matrix converter; A closed-loop control module, connected to the three-phase three-wire power grid, is used to generate a modulation ratio and 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 waves of the three-phase current. The pulse width modulation module, connected to the three-phase matrix converter, the full-bridge inverter, and the closed-loop control module, is used to generate a primary-side drive signal and a secondary-side drive signal according to the modulation ratio and the 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.

2. The single-stage three-phase high-frequency isolated converter circuit according to claim 1, characterized in that, The closed-loop control module includes: A sampling unit is used to sample the three-phase voltage and the three-phase current; A phase-locked loop, connected to the sampling unit, is used to obtain the grid phase of the three-phase three-wire power grid based on the three-phase voltage; A fundamental frequency loop, connected to the sampling unit and the phase-locked loop, is used to generate α-axis fundamental frequency components and β-axis fundamental frequency components based on the three-phase current and the power grid phase. A harmonic suppression loop, connected to the sampling unit and the phase-locked loop, is used to generate α-axis harmonic components and β-axis harmonic components based on the three-phase current and the grid phase. An accumulation and conversion unit, connected to the fundamental frequency ring, the harmonic suppression ring, and the pulse width modulation module, is used to accumulate the α-axis fundamental frequency component and the α-axis harmonic component to obtain the α-axis current component, and to accumulate the β-axis fundamental frequency component and the β-axis harmonic component to obtain the β-axis current component, and to obtain the modulation ratio and the vector angle based on the α-axis current component and the β-axis current component.

3. The single-stage three-phase high-frequency isolated converter circuit according to claim 2, characterized in that, The harmonic suppression loop includes: A positive-sequence harmonic suppression sub-loop, connected to the sampling unit, the phase-locked loop, and the accumulation conversion unit, is used to suppress the 6K+1th positive-sequence harmonics according to the three-phase current and the grid phase, so as to generate α-axis positive-sequence harmonic components and β-axis positive-sequence harmonic components, where K is a positive integer; The negative sequence harmonic suppression sub-loop is connected to the sampling unit, the phase-locked loop and the accumulation conversion unit, and is used to suppress the 6K-1th positive sequence harmonics according to the three-phase current and the grid phase to generate α-axis negative sequence harmonic components and β-axis negative sequence harmonic components. The accumulation conversion unit is further configured 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 and the vector angle based on the α-axis current component and the β-axis current component.

4. The single-stage three-phase high-frequency isolated converter circuit according to claim 3, characterized in that, The positive-sequence harmonic suppression sub-ring includes: The first conversion unit is used to convert the three-phase current into a d-axis positive sequence DC component and a q-axis positive sequence DC component in a rotating coordinate system based on the grid phase of 6K+1 times. A first low-pass filter, connected to the first conversion unit, is used to perform low-pass filtering on the positive sequence DC component of the d-axis. The first subtractor, connected to the first low-pass filter, 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. A first PI controller, connected to the first subtractor, is used to perform proportional-integral calculations on the d-axis positive sequence error signal to generate a d-axis positive sequence compensation current. The second low-pass filter is connected to the first conversion unit and is used to perform low-pass filtering on the positive sequence DC component of the q-axis. The second subtractor, connected to the second low-pass filter, 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, connected to the second subtractor, is used to perform proportional-integral calculation on the q-axis positive sequence error signal to generate the q-axis positive sequence compensation current. The second conversion unit is connected to the first PI controller, the second PI controller, and the accumulation conversion unit, and is used 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 respectively according to the grid phase of 6K+1 times.

5. The single-stage three-phase high-frequency isolated converter circuit according to claim 3, characterized in that, The negative-order harmonic suppression sub-ring includes: The third conversion unit is used to convert 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 according to -(6K-1) times the grid phase. The third low-pass filter, connected to the third conversion unit, is used to perform low-pass filtering on the d-axis negative sequence DC component. The third subtractor, connected to the third low-pass filter, 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, connected to the third subtractor, is used to perform proportional-integral calculations on the d-axis negative sequence error signal to generate the d-axis negative sequence compensation current. The fourth low-pass filter, connected to the third conversion unit, is used to perform low-pass filtering on the q-axis negative sequence DC component; The fourth subtractor, connected to the fourth low-pass filter, 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, connected to the fourth subtractor, is used to perform proportional-integral calculation on the q-axis negative sequence error signal to generate a q-axis negative sequence compensation current. The fourth conversion unit, connected to the third PI controller, the fourth PI controller and the accumulation conversion unit, is used 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 respectively according to -(6K-1) times the grid phase.

6. The single-stage three-phase high-frequency isolated converter circuit according to claim 2, characterized in that, The sampling unit is also used to sample the inductor voltage and the capacitor current of the three-phase LC filter; The closed-loop control module also includes an LC oscillation active damping ring, which is connected to the sampling unit and the accumulation conversion unit, and is used to suppress the inherent oscillation of the three-phase LC filter through the negative feedback of the inductor voltage and the capacitor current.

7. The single-stage three-phase high-frequency isolated converter circuit according to claim 6, characterized in that, The LC oscillation active damping ring includes: The fifth conversion unit, connected to the sampling unit and the phase-locked loop, is used to convert the inductor voltage into the α-axis initial voltage component and the β-axis initial voltage component in the stationary coordinate system according to the grid phase. The first gain amplifier, connected to the fifth conversion unit and the accumulator conversion unit, is used to obtain the α-axis voltage component based on the product of the initial α-axis voltage component and the voltage gain coefficient. The second gain amplifier, connected to the fifth conversion unit and the accumulation conversion unit, is used to obtain the β-axis voltage component based on the product of the initial β-axis voltage component and the voltage gain coefficient. The sixth conversion unit, connected to the sampling unit and the phase-locked loop, is used to convert the capacitor current into the α-axis initial current component and the β-axis initial current component in the stationary coordinate system according to the grid phase. The third gain amplifier, connected to the sixth conversion unit and the accumulator conversion unit, is used to obtain the target current component of the α-axis based on the product of the initial current component of the α-axis and the current gain coefficient. The fourth gain amplifier, connected to the sixth conversion unit and the accumulator conversion unit, is used to obtain the target current component of the β-axis based on the 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 the α-axis current component, and to 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 the β-axis current component, and to obtain the modulation ratio and the vector angle based on the α-axis current component and the β-axis current component.

8. The single-stage three-phase high-frequency isolated converter circuit according to any one of claims 1-7, characterized in that, The primary-side drive signal controls the primary-side voltage of the high-frequency transformer through the three-phase matrix converter. The primary-side voltage decreases in a stepwise manner within one switching cycle, and the primary-side voltage is symmetrical in the first half of the switching cycle and the second half of the switching cycle. The secondary drive signal controls the secondary voltage of the high-frequency transformer through the full-bridge inverter, and the secondary voltage exhibits a symmetrical square wave distribution within one switching cycle.

9. The single-stage three-phase high-frequency isolated converter circuit according to claim 8, characterized in that, The primary voltage has 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 during one switching cycle. 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. The third level is the line voltage with the second largest absolute value. The fifth level is the reverse voltage of the third level. The sixth level is the reverse voltage of the second level. The secondary voltage has an eighth level, a ninth level, and a tenth level sequentially from front to back within one switching cycle. The eighth level is equal to the tenth level, the ninth level is a positive level, and both the eighth level and the tenth level are reverse voltages of the ninth level.

10. The single-stage three-phase high-frequency isolated converter circuit according to claim 9, characterized in that, 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. The duration of the eighth level and the duration of the tenth level are both one-quarter of the switching cycle, and the duration of the ninth level is one-half of the switching cycle.

11. A closed-loop control method, characterized in that, The closed-loop control method is applied to a single-stage three-phase high-frequency isolation converter circuit. The single-stage three-phase high-frequency isolation 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: Based on the three-phase voltage and three-phase current of the three-phase three-wire power grid, a modulation ratio and vector angle are generated by synchronously controlling the fundamental and harmonic frequencies of the three-phase current. The primary-side drive signal and the secondary-side drive signal are generated according to the modulation ratio and the 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.

12. The closed-loop control method according to claim 11, characterized in that, The closed-loop control method further includes: The three-phase voltages and three-phase currents are sampled; The grid phase of the three-phase three-wire power grid is obtained based on the three-phase voltage; The α-axis fundamental wave component and the β-axis fundamental wave component are generated based on the three-phase current and the power grid phase. The α-axis harmonic components and β-axis harmonic components are generated based on the three-phase current and the power grid phase. The α-axis fundamental component and the α-axis harmonic component are summed to obtain the α-axis current component, and the β-axis fundamental component and the β-axis harmonic component are summed to obtain the β-axis current component. The modulation ratio and the vector angle are obtained based on the α-axis current component and the β-axis current component.

13. The closed-loop control method according to claim 12, characterized in that, The closed-loop control method further includes: Based on the three-phase current and the power grid phase, 6K+1 positive sequence harmonics are suppressed to generate α-axis positive sequence harmonic components and β-axis positive sequence harmonic components, where K is a positive integer; Based on the three-phase current and the power grid phase, the 6K-1th positive sequence harmonic is suppressed to generate the α-axis negative sequence harmonic component and the β-axis negative sequence harmonic component. The α-axis fundamental component, the α-axis positive-sequence harmonic component, and the α-axis negative-sequence harmonic component are accumulated to obtain the α-axis current component, and the β-axis fundamental component, the β-axis positive-sequence harmonic component, and the β-axis negative-sequence harmonic component are accumulated to obtain the β-axis current component, and the modulation ratio and the vector angle are obtained based on the α-axis current component and the β-axis current component.

14. The closed-loop control method according to claim 13, characterized in that, The closed-loop control method further includes: According to the grid phase conversion of 6K+1 times, the three-phase current is the d-axis positive sequence DC component and the q-axis positive sequence DC component in the rotating coordinate system. The positive sequence DC component of the d-axis is low-pass filtered; The d-axis positive sequence error signal is obtained based on the difference between the zero reference and the low-pass filtered d-axis positive sequence DC component. Perform proportional-integral calculation on the d-axis positive sequence error signal to generate the d-axis positive sequence compensation current; The positive-sequence DC component of the q-axis is low-pass filtered; The q-axis positive sequence error signal is obtained based on the difference between the zero reference and the low-pass filtered q-axis positive sequence DC component. Perform proportional-integral operation on the q-axis positive sequence error signal to generate a q-axis positive sequence compensation current; Based on the grid phase of 6K+1 times, the d-axis positive sequence compensation current and the q-axis positive sequence compensation current are respectively converted into the α-axis positive sequence harmonic component and the β-axis positive sequence harmonic component.

15. The closed-loop control method according to claim 13, characterized in that, The closed-loop control method further includes: According to the power grid phase conversion of -(6K-1) times, the three-phase current is the d-axis negative sequence DC component and the q-axis negative sequence DC component in the rotating coordinate system; The negative sequence DC component along the d-axis is low-pass filtered. The d-axis negative sequence error signal is obtained based on the difference from the zero reference and the low-pass filtered d-axis negative sequence DC component. Perform proportional-integral operation on the d-axis negative sequence error signal to generate d-axis negative sequence compensation current; The negative sequence DC component of the q-axis is low-pass filtered; The q-axis negative sequence error signal is obtained based on the difference between the zero reference and the low-pass filtered q-axis negative sequence DC component. Perform proportional-integral operation on the q-axis negative sequence error signal to generate a q-axis negative sequence compensation current; Based on -(6K-1) times the grid phase, the d-axis negative sequence compensation current and the q-axis negative sequence compensation current are respectively converted into the α-axis negative sequence harmonic component and the β-axis negative sequence harmonic component.

16. The closed-loop control method according to claim 12, characterized in that, The closed-loop control method further includes: The inductor voltage and capacitor current of the three-phase LC filter are sampled. The inherent oscillation of the three-phase LC filter is suppressed through the negative feedback of the inductor voltage and the capacitor current.

17. The closed-loop control method according to claim 16, characterized in that, The closed-loop control method further includes: Based on the power grid phase conversion, the inductor voltage is converted into the α-axis initial voltage component and the β-axis initial voltage component in the stationary coordinate system; The α-axis voltage component is obtained by multiplying the initial α-axis voltage component with the voltage gain coefficient. The β-axis voltage component is obtained by multiplying the initial β-axis voltage component by the voltage gain coefficient. According to the power grid phase transformation, the capacitor current is the initial current component along the α-axis and the initial current component along the β-axis in the stationary coordinate system. The target current component of the α-axis is obtained by multiplying the initial current component of the α-axis with the current gain coefficient. The target current component of the β-axis is obtained by multiplying the initial current component of the β-axis with the voltage gain coefficient. 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 the α-axis current component. 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 the β-axis current component. The modulation ratio and the vector angle are obtained based on the α-axis current component and the β-axis current component.

18. The closed-loop control method according to claim 11, characterized in that, The closed-loop control method further includes: The primary-side drive signal is configured to control the primary-side voltage of the high-frequency transformer through the three-phase matrix converter. The primary-side voltage decreases in a stepwise manner within one switching cycle, and the primary-side voltage is symmetrical in the first half of the switching cycle and the second half of the switching cycle. The secondary drive signal is configured to control the secondary voltage of the high-frequency transformer through the full-bridge inverter, and the secondary voltage exhibits a symmetrical square wave distribution within one switching cycle.

19. The closed-loop control method according to claim 18, characterized in that, The closed-loop control method further includes: 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 sequentially from front to back within one switching cycle. 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. The third level is the line voltage with the second largest absolute value. The fifth level is the reverse voltage of the third level. The sixth level is the reverse voltage of the second level. The secondary voltage is configured to have an eighth level, a ninth level, and a tenth level sequentially from front to back within 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 both the reverse voltages of the ninth level.

20. The closed-loop control method according to claim 19, characterized in that, The closed-loop control method further includes: The duration of the first level is configured 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. The sum of Tx, Ty, and Tz is the switching period. The duration of the eighth level and the tenth level are both configured to be one-quarter of the switching cycle, and the duration of the ninth level is one-half of the switching cycle.

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