Split-capacitor three-phase LCL-DAB converter and its control method

Abstract

This invention discloses a split-capacitor three-phase LCL-DAB converter and its control method. The converter includes an LCL resonant branch, a primary side, and a secondary side. The primary side is a three-phase bridge circuit connected to a PWM rectifier. The LCL resonant branch consists of a resonant split-capacitor branch, a three-phase resonant inductor, and an output inductor. The secondary side is a full-bridge circuit, and the primary and secondary sides are connected through the LCL resonant branch. The primary and secondary sides are electrically isolated by a single-phase high-frequency transformer. This converter eliminates the need for an external power decoupling circuit. By absorbing second-harmonic frequency fluctuation power through the internal resonant split-capacitor branch, it significantly reduces the required DC-side capacitance while maintaining electrical isolation characteristics, thus greatly improving the converter's power density. This method significantly reduces the converter's capacitor requirements, further improving both its power density and reliability.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology and relates to a split capacitor three-phase LCL-DAB converter and its control method. Background Technology

[0002] Single-phase AC / DC converters are widely used in photovoltaic power generation systems, electric vehicle charging systems, electric multiple electric aircraft power systems, and railway traction systems. As an energy routing unit directly connecting a single-phase AC grid and a DC load, the performance of the single-phase AC / DC converter plays a crucial role in the entire single-phase power system. However, due to the instantaneous power imbalance at its AC and DC ports, the double-frequency ripple power generated by the AC side, as a disturbance in the input power, introduces severe double-frequency voltage fluctuations and disturbance currents on the intermediate DC bus of a two-stage single-phase AC / DC converter. In practical engineering, a large-capacity intermediate DC bus capacitor is often used to absorb and eliminate this. This leads to a significant increase in the size and weight of the converter, as well as a reduction in reliability and lifespan. To solve the above problems, this invention proposes a three-phase LCL-DAB topology based on split capacitors, which serves as the downstream DC link in a two-stage single-phase AC / DC converter. The split capacitor structure within the resonant cavity absorbs the double-frequency AC power transmitted from the upstream PWM rectifier, so that the intermediate DC bus capacitor no longer needs to bear a large amount of ripple power. This significantly reduces the capacitor requirements of the converter, thereby further improving the power density and reliability of the converter. Summary of the Invention

[0003] To address the aforementioned issues, this invention proposes a split-capacitor three-phase LCL-DAB converter and its control method. This method significantly reduces the converter's capacitor requirements, thereby further improving the converter's power density and reliability.

[0004] To achieve the above-mentioned objectives, the present invention employs the following technical solution:

[0005] In a first aspect, the present invention provides a split capacitor type three-phase LCL-DAB converter, including an LCL resonant branch, a primary side and a secondary side;

[0006] The primary side is a three-phase bridge circuit, which is connected to the PWM rectifier.

[0007] The LCL resonant branch is composed of a resonant split capacitor branch, a three-phase resonant inductor, and an output inductor.

[0008] The secondary side is a full-bridge circuit, and the primary and secondary sides are connected through the LCL resonant branch; and the primary and secondary sides are electrically isolated through a single-phase high-frequency transformer.

[0009] As a further improvement of the present invention, the PWM rectifier consists of a switching transistor S ap S an S bp S bn The full-bridge configuration, combined with a single-phase AC power grid u ac Through the grid-side inductor L ac Connected.

[0010] As a further improvement of the present invention, the three-phase bridge circuit includes a primary-side switching transistor T. 11 ,T 12 ,T 13 ,T 14 ,T 15 ,T 16 A three-phase bridge inverter circuit is formed, which adopts three-phase symmetrical control, with the switching signals of each phase arm differing by 120 degrees in phase.

[0011] As a further improvement of the present invention, the resonant split capacitor branch includes a split capacitor C. ab C bc split capacitor C ab C bc The branch circuit is formed through a three-phase resonant inductor L a L b L c Connected to the primary three-phase AC port; output inductor L a Connected to the split capacitor branch and the isolation high-frequency transformer, it transfers the energy stored in the inductor to the secondary side of the converter.

[0012] As a further improvement of the present invention, the three-phase resonant inductor and the output inductor have the same inductance value, then L a =L b =L c =L r If the upper and lower split capacitors have the same capacitance value, then C ab =C bc =C r .

[0013] Secondly, the present invention provides an active power decoupling control method for a split capacitor three-phase LCL-DAB converter, comprising the following steps:

[0014] By introducing a fluctuating duty cycle on the primary side, the input power is mixed with the DC power P. dc Coupled disturbance power p ripple The disturbance power p is decoupled and separated, and then modulated using the primary-side three-phase bridge. ripple The voltage is transferred to the resonant branch of the split capacitor, which requires a wide range of voltage fluctuations, so that the intermediate DC-side capacitor no longer needs to absorb and absorb disturbance power.

[0015] As a further improvement of the present invention, the switching signals of the left and right arms of the secondary full-bridge circuit are 180 degrees out of phase; the phase difference between the A-phase arm of the secondary full-bridge and the A-phase arm of the primary three-phase bridge is an outward phase shift angle D. f It is used to control the power transmission of the converter. The upper and lower switch signals of all bridge arms are complementary, and the duty cycle is always 50%.

[0016] As a further improvement to this invention, the three-phase duty cycle expression that satisfies the active power decoupling of the split capacitor type three-phase LCL-DAB is as follows:

[0017]

[0018]

[0019]

[0020] The above equation is the control variable expression for active power decoupling in a split-capacitor three-phase LCL-DAB.

[0021] As a further improvement to the present invention, it specifically includes:

[0022] In the closed-loop control of active power decoupling, the output voltage V2 of the split capacitor three-phase LCL-DAB is related to the voltage command V. 2ref The difference between the two values ​​is used by PI control to generate an outward phase shift angle D. f D f The output control quantity of the voltage loop controls the output power of the split capacitor three-phase LCL-DAB;

[0023] Acquire the input AC voltage u of the front stage of the AC / DC power converter ac and input AC current i ac For the input AC voltage u ac and input AC current i ac Phase-locked loop (PLL) is performed to obtain the angular frequency ω of the single-phase power grid. g and power factor angle θ;

[0024] Find the input AC voltage u ac and input AC current i ac The effective value of the fluctuation power p is obtained. ripple amplitude P m According to the fluctuation power p ripple amplitude P m Circuit parameters L r C r ω s Given the DC input voltage V1 of the split capacitor three-phase LCL-DAB, the primary-side duty cycle D that satisfies active power decoupling control is calculated. pa Dpb and D pc .

[0025] The present invention, by adopting the above technical solution, has the following beneficial effects:

[0026] This invention addresses the inherent low-frequency oscillation problem on the DC side of existing two-stage single-phase AC / DC power converters by proposing a novel split-capacitor three-phase LCL-DAB topology. This significantly reduces the DC-side capacitor value and suppresses DC-side voltage fluctuations. Eliminating the need for external power decoupling circuits, the converter absorbs second-harmonic frequency fluctuation power through its internal resonant split-capacitor branch. While maintaining electrical isolation characteristics, this significantly reduces the required DC-side capacitor value, substantially increasing the converter's power density. Based on a split-capacitor three-phase LCL-DAB topology, this converter serves as the downstream DC link in a two-stage single-phase AC / DC converter. The split-capacitor structure within the resonant cavity absorbs the double-frequency AC power transmitted from the preceding PWM rectifier, eliminating the need for the intermediate DC bus capacitor to bear significant ripple power. This drastically reduces the converter's capacitor requirements, further improving both power density and reliability.

[0027] The split capacitor three-phase LCL-DAB topology and active power decoupling control method proposed in this invention can decouple the disturbance power p in the input power. ripple The voltage ripple is transferred to the split capacitor branch of the resonant cavity, which requires voltage fluctuation, thus preventing it from negatively impacting the intermediate DC-side voltage. This significantly reduces DC-side voltage fluctuations and drastically reduces the required DC-side capacitor value. Compared to traditional two-stage single-phase AC / DC converters and their conventional control strategies, the two-stage single-phase AC / DC converter based on the split capacitor three-phase LCL-DAB topology employs active power decoupling control. Under the same DC-side voltage ripple requirements, it can reduce the DC-side capacitor value requirement to 1 / 9 of the original value, significantly improving the overall power density of the converter. Attached Figure Description

[0028] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way. Furthermore, the shapes and proportions of the components in the drawings are merely schematic to aid in understanding the invention and do not specifically limit the shapes and proportions of the components. In the drawings:

[0029] Figure 1 A schematic diagram of a two-stage single-phase AC / DC converter topology based on a split capacitor three-phase LCL-DAB proposed in this invention;

[0030] Figure 2 The front-end PWM rectifier of this invention operates according to the traditional control method;

[0031] Figure 3 The diagram shows the active power decoupling control strategy adopted by the split capacitor three-phase LCL-DAB of this invention.

[0032] Figure 4 These are the key waveforms of a traditional two-stage single-phase AC / DC converter, where (a) is the input voltage and current waveform; and (b) is the intermediate DC-side voltage ripple waveform.

[0033] Figure 5 Key waveforms of a two-stage single-phase AC / DC converter based on a split-capacitor three-phase LCL-DAB are shown. (a) represents the input voltage and current waveforms; (b) represents the voltage ripple waveform on the middle DC side; and (c) represents the voltage waveforms of the upper and lower split capacitors.

[0034] Figure 6 These are key waveforms of a traditional two-stage single-phase AC / DC converter. The capacitance value of the intermediate DC-side capacitor differs, where (a) is the input voltage and current waveform; and (b) is the intermediate DC-side voltage ripple waveform. Detailed Implementation

[0035] To make the objectives and technical solutions of this invention clearer and easier to understand, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0036] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. 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 indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more. In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0037] The purpose of this invention is to overcome the inherent low-frequency oscillation problem on the DC side of existing two-stage single-phase AC / DC power converters, and to propose a novel split-capacitor three-phase LCL-DAB that can significantly reduce the DC side capacitor value and suppress DC side voltage fluctuations. For example... Figure 1 As shown, it includes the LCL resonant branch, primary side, and secondary side;

[0038] The primary side is a three-phase bridge circuit, which is connected to the PWM rectifier.

[0039] The LCL resonant branch is composed of a resonant split capacitor branch, a three-phase resonant inductor, and an output inductor.

[0040] The secondary side is a full-bridge circuit, and the primary and secondary sides are connected through the LCL resonant branch; and the primary and secondary sides are electrically isolated through a single-phase high-frequency transformer.

[0041] This converter does not require an external power decoupling circuit. It absorbs the second-harmonic fluctuation power through the resonant split capacitor branch inside the converter. While maintaining electrical isolation characteristics, it significantly reduces the capacitance value required on the DC side and greatly improves the power density of the converter.

[0042] The circuit structure and basic working principle are introduced below:

[0043] A novel split-capacitor three-phase LCL-DAB converter topology suitable for the DC link of a two-stage single-phase AC / DC power converter is proposed. Its primary side is a three-phase bridge circuit, and its secondary side is a full-bridge circuit. The resonant split capacitor branch, the three-phase resonant inductor, and the output inductor constitute the LCL resonant branch. Electrical isolation between the primary and secondary sides is achieved through a single-phase high-frequency transformer. The specific structural diagram of the two-stage single-phase AC / DC power converter topology based on the novel split-capacitor three-phase LCL-DAB converter is shown below. Figure 1 .

[0044] In a specific embodiment, the front-end topology of the two-stage single-phase AC / DC converter adopts a traditional PWM rectifier, which consists of a switching transistor S. ap S an S bp S bn The full-bridge configuration, combined with a single-phase AC power grid u ac Through the grid-side inductor L ac The circuit is connected. It adopts traditional SPWM control, which is responsible for controlling the phase of AC voltage and current and maintaining a constant voltage amplitude of the intermediate DC bus V1. It often has power factor correction function and is often controlled to operate at unity power factor. This part of the control and topology adopts the traditional form and is not the main content of this invention, so it will not be discussed in detail.

[0045] This invention focuses on the topology and control method of a novel split-capacitor three-phase LCL-DAB. The primary-side switch T of the novel split-capacitor three-phase LCL-DAB... 11 ,T 12 ,T 13 ,T 14 ,T 15 ,T 16 This forms a three-phase bridge inverter circuit, employing three-phase symmetrical control, with the switching signals of each phase arm differing by 120 degrees in phase. (Split capacitor C) ab C bc The branch circuit is formed through a three-phase resonant inductor L a L b L c Connected to the primary three-phase AC port. Output inductor L a Connected to the split capacitor branch and the isolation high-frequency transformer, it transfers the energy stored in the inductor to the secondary side of the converter.

[0046] For ease of circuit analysis, the three-phase resonant inductor and the output inductor have the same inductance value, L. a =L b =L c =L r Split capacitors have the same capacitance value, C. ab =C bc =C r This invention defines Figure 1 i in L1a i L1b i L1c For the three-phase primary current, i tr This is the input current of the high-frequency transformer, i.e., the secondary current. The secondary switch transistor T... 21 ,T 12 ,T 13 ,T 24 ,T 25 This constitutes a full-bridge inverter circuit. The switching signals of the left and right arms of the full-bridge circuit are 180 degrees out of phase. The phase difference between the A-phase arm of the secondary full-bridge and the A-phase arm of the primary three-phase bridge is an outward phase shift angle D. f This is used to control the power transmission of the converter. The switching signals of the upper and lower transistors of all bridge arms are complementary, and the duty cycle is always 50%. This invention introduces a split capacitor structure in the resonant cavity to absorb the inherent double power frequency disturbance power in single-phase AC / DC conversion, reduce the DC side capacitor value, and significantly improve the power density of the converter.

[0047] Let the input voltage u of a two-stage single-phase AC / DC power converter topology based on a novel split-capacitor three-phase LCL-DAB be... ac and input current i ac The expression for is shown in equation (1).

[0048]

[0049] In equation (1), V m and I m ω represents the sinusoidal amplitude of the AC input voltage and AC input current. g For single-phase AC power grid voltage and current angular frequencies, in China, ω g It is 100π. The power factor angle is the relationship between the input AC voltage and current. To achieve unity power factor operation. According to equation (1), the input power P of the two-stage single-phase AC / DC power converter topology based on the novel split capacitor three-phase LCL-DAB can be obtained. in The expression for is shown in equation (2).

[0050]

[0051] From equation (2), we can obtain that the input power P in It consists of two parts. The first part is P. dc It is equal to the required DC power output, determined by the load on the output side. Part 2 p ripple The disturbance power is p, which is coupled into the input power at twice the power grid frequency. ripple The voltage is transmitted to the intermediate DC-side bus V1 via the front-stage PWM rectifier. All of this voltage fluctuation is absorbed and absorbed by the DC-side capacitor. Under conditions where the capacitor is small, this can cause severe second-harmonic voltage fluctuations on the DC bus. This significantly affects the steady-state operation of the two-stage single-phase AC / DC converter and degrades its voltage quality.

[0052] To solve the input power P in In-situ coupling disturbance power p ripple To address the impact of DC-side voltage fluctuations, this invention proposes a novel active power decoupling control strategy based on a novel split-capacitor three-phase LCL-DAB topology. This novel control strategy introduces a fluctuating duty cycle on the primary side of the novel split-capacitor three-phase LCL-DAB topology, thereby reducing the DC power P in the input power. dc Coupled disturbance power p ripple The disturbance power p is decoupled and separated, and then modulated using the primary-side three-phase bridge. ripple The voltage fluctuations are shifted to the resonant branch of the split capacitor, which requires a wide range of voltage fluctuations. This eliminates the need for the intermediate DC-side capacitor to absorb and absorb disturbance power, significantly reducing the voltage fluctuations on the DC side and greatly reducing the required capacitance on the DC side. Under the new active power decoupling control strategy, the duty cycle control signal of the primary three-phase bridge arm can be described by the following equation (3).

[0053]

[0054] In equation (3) above, D pa D pb D pc These represent the duty cycles of the primary side bridge arms A, B, and C, respectively. The steady-state duty cycle of the three-phase bridge arms is 0.5. Based on the steady-state duty cycle, the active power decoupling control introduces a three-phase fluctuating duty cycle D. aω *sin(ω g *t), D bω *sin(ω g *t), D cω *sin(ω g *t), where D aω D bω and D cω This represents the amplitude of the duty cycle of the three-phase fluctuation, ω g The angular frequency represents the single-phase AC power grid, indicating that the frequency of the fluctuating duty cycle is consistent with the frequency of the single-phase power grid, which is a low frequency of 50Hz. Substituting the primary-side duty cycle signal into the analysis of the split capacitor three-phase LCL-DAB circuit, the Kirchhoff voltage and current equations are obtained as shown in equation (4) below.

[0055]

[0056] In equation (4), U 1abf_ωg and U 1bcf_ωg These represent the line voltages between primary phases A and B, and between phases B and C, of ​​a split-capacitor three-phase LCL-DAB under active power decoupling control; i 1a_ωg i 1b_ωg and i 1c_ωg These represent the primary-side three-phase currents under active power decoupling control; i tr This represents the secondary phase current under active power decoupling control. cab (t), u cbc (t), i cab (t), i cbc (t) represent the voltage and current of the upper and lower split capacitors under source power decoupling control, respectively. Based on the equation set in (4), we can obtain u cab (t), u cbc (t), i cab (t), i cbc The expression for (t) is shown in equation (5).

[0057]

[0058] In equation (5) ω s This represents the switching frequency of a split-capacitor three-phase LCL-DAB. To ensure the disturbance power p...ripple The power of the split capacitor branch under active power decoupling control needs to be equal to the disturbance power p to be completely absorbed by the split capacitor branch. ripple They are equal. The sum of the mains frequency voltages of the upper and lower split capacitors is 0. As shown in equations (6) and (7).

[0059]

[0060]

[0061] Solving equations (6) and (7) and substituting them into equation (3) yields the three-phase duty cycle expression that satisfies the active power decoupling of the split capacitor three-phase LCL-DAB, as shown in equation (8) below.

[0062]

[0063] Equation (8) above is the core control variable expression for active power decoupling in the split-capacitor three-phase LCL-DAB. Controlling according to equation (8) transfers disturbance power to the split-capacitor branch, eliminating the need for the DC-side capacitor to absorb disturbance power. This significantly reduces the DC-side voltage's double-frequency fluctuation and drastically decreases the required DC-side capacitor value. Compared to traditional control methods and traditional two-stage single-phase AC / DC topologies, under the same DC-side voltage ripple requirements, the capacitance of the intermediate DC-side capacitor in the new split-capacitor three-phase LCL-DAB topology using active power decoupling can be reduced to 1 / 9 of its original value.

[0064] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0065] The two-stage single-phase AC / DC converter topology based on split capacitor three-phase LCL-DAB proposed in this invention is as follows: Figure 1 As shown. The front-end PWM rectifier operates according to the traditional control method, and its control block diagram is as follows. Figure 2 As shown, the DC-side voltage U of the PWM rectifier is obtained through AD sampling. dc Combine it with the DC voltage command U dc After comparison, the difference is fed into a PI regulator to form the voltage loop of the PWM rectifier. The PI output of the voltage loop serves as the active current i. d The instruction * is related to the actual i obtained from AD sampling. d The currents are compared, and the difference is also sent to the PI regulator for control, forming the i... d Inner current loop. In engineering, i is often set... q * = 0, enabling the PWM rectifier to operate at unity power factor, hence i q The command value for the inner current loop is 0, which is different from the i obtained by AD sampling. qAfter comparing the actual current values, the difference is sent to i. q The PI regulator of the current loop constitutes i q Inner current loop. d i q After the current inner loop output is supplemented by dq axis decoupling control and grid voltage feedforward control, the control loop response speed is accelerated. Finally, after 2-3 inverse Park transformation to generate a modulation wave, it is compared with the carrier wave to generate a switching signal, which is transmitted to the switching transistor of the PWM rectifier to control the PWM rectifier to achieve unity power factor operation.

[0066] It is worth noting that the PWWM rectifier in this invention is a single-phase rectifier. The 2-3 inverse Park transformation and 3-2 Park transformation in the control are derived from single-phase virtual three-phase. Therefore, in the PWM rectifier switching signal, only the A-phase switching signal is used for control.

[0067] The downstream split-capacitor three-phase LCL-DAB employs an active power decoupling control strategy. Its control block diagram is shown below. Figure 3 As shown. In the closed-loop control of active power decoupling, the output voltage V2 of the split capacitor three-phase LCL-DAB is related to the voltage command V. 2ref The difference between the two values ​​is used by PI control to generate an outward phase shift angle D. f D f The output control quantity of the voltage loop controls the output power of the split capacitor three-phase LCL-DAB. It acquires the input AC voltage u of the AC / DC power converter's pre-amplifier stage. ac and input AC current i ac For the input AC voltage u ac and input AC current i ac Phase-locked loop (PLL) is performed to obtain the angular frequency ω of the single-phase power grid. g And the power factor angle θ. Simultaneously, calculate the input AC voltage u. ac and input AC current i ac The effective value of the fluctuation power p is obtained. ripple amplitude P m , and circuit parameters (L r C r ω s The DC input voltage V1 of the split capacitor three-phase LCL-DAB is combined with the input quantity and calculated in Equation (8). Based on Equation (8), the primary-side duty cycle D that satisfies the active power decoupling control is obtained. pa D pb and D pc The duty cycle of the secondary-side full-bridge switch is constant at 0.5, and the phase difference between the left and right bridge arms is 180 degrees. The original secondary-side duty cycle variable and the outward phase shift angle D are then adjusted. fThe signal is fed into the drive unit generation module, compared with its respective carrier wave, and used to generate switching signals for all switching transistors. This signals control the split capacitor three-phase LCL-DAB topology to achieve active power decoupling control.

[0068] according to Figure 3 The control block diagram of this invention controls the proposed split-capacitor three-phase LCL-DAB, enabling the transfer and absorption of input disturbance power. This significantly reduces voltage fluctuations on the intermediate DC side and substantially decreases the required DC-side capacitor value. MATLAB / Simulink simulations verified the effectiveness and correctness of the proposed topology and the novel active power decoupling control algorithm.

[0069] Figure 4 and Figure 5 These represent key waveforms of a traditional two-stage single-phase AC / DC converter and a two-stage single-phase AC / DC converter based on a split capacitor three-phase LCL-DAB, respectively, under the same transmission power of 5kW and the same intermediate DC-side capacitor of 800μF. Figure 4 (a) Represents the input voltage and current waveforms of a traditional two-stage single-phase AC / DC converter. Figure 4 (b) Represents the intermediate DC side voltage ripple waveform of a traditional two-stage single-phase AC / DC converter. Figure 5 (a) represents the input and output voltage and current waveforms of a two-stage single-phase AC / DC converter based on a split capacitor three-phase LCL-DAB. Figure 5 (b) Represents the intermediate DC-side voltage ripple waveform of a two-stage single-phase AC / DC converter based on a split-capacitor three-phase LCL-DAB. Figure 5 (c) represents the split capacitor voltage waveform of a two-stage single-phase AC / DC converter based on a split capacitor three-phase LCL-DAB.

[0070] from Figure 4 and Figure 5 Comparison shows that, under the same conditions of 800μF capacitor and 5kW transmission power, the intermediate DC-side voltage ripple of the traditional two-stage single-phase AC / DC converter is 22V, while the intermediate DC-side voltage ripple of the two-stage single-phase AC / DC converter based on the split capacitor three-phase LCL-DAB using active power decoupling is 2.5V. Voltage fluctuations are significantly suppressed. From the voltage waveform of the split capacitor, it can be seen that the disturbance power is almost completely absorbed by the split capacitor branch.

[0071] Figure 5 and Figure 6 The key waveforms represent the two-stage single-phase AC / DC converter based on the split capacitor three-phase LCL-DAB and the traditional two-stage single-phase AC / DC converter, respectively, under the conditions of the same transmission power of 5kW and the same DC-side voltage ripple of 2.5V.

[0072] Figure 4 and Figure 6 These are all key waveforms from a traditional two-stage single-phase AC / DC converter. The capacitance values ​​on the intermediate DC side differ. Figure 4 The capacitance value of the DC-side capacitor in the conventional topology corresponding to the waveform is fixed at 800μF. Figure 6 In order to ensure that the DC voltage ripple is less than or equal to 2.5V, the intermediate DC-side capacitor of the traditional topology corresponding to the waveform is increased to 7200μF. Figure 4 and Figure 6 (a) is the input voltage and current waveform; (b) is the intermediate DC side voltage ripple waveform.

[0073] Figure 6 (a) Represents the input voltage and current waveforms of a traditional two-stage single-phase AC / DC converter. Figure 6 (b) represents the intermediate DC-side voltage ripple waveform of a conventional two-stage single-phase AC / DC converter. In this case, the intermediate DC-side capacitance of the conventional two-stage single-phase AC / DC converter is 7200μF.

[0074] from Figure 5 and Figure 6 Comparison shows that, under the same transmission power of 5kW and a DC-side voltage ripple of 2.5V, a traditional two-stage single-phase AC / DC converter requires an electrolytic capacitor of up to 7200μF to meet the corresponding DC voltage ripple requirements. The two-stage single-phase AC / DC converter based on a split-capacitor three-phase LCL-DAB using an active power decoupling method only requires an 800μF DC-side capacitor to meet the required DC-side voltage ripple conditions. The capacitor value is reduced to 1 / 9 of that of the traditional topology. Therefore, thin-film capacitors can be used, significantly saving costs, extending equipment lifespan, and reducing equipment size. Compared to the traditional topology, the new topology under active power decoupling control significantly reduces the DC capacitor value and significantly improves power density.

[0075] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Any simple modifications, alterations, or equivalent structural changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

[0076] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still make modifications or equivalent substitutions to the specific implementation schemes of the present invention, and these modifications or equivalent substitutions do not depart from the spirit and scope of the present invention, and are all within the protection scope of the claims of the present invention.

[0077] The above content provides a further detailed description of the present invention. It should not be construed that the specific embodiments of the present invention are limited to this. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the scope of protection of the present invention as defined by the submitted claims.

Claims

1. A control method for a split-capacitor three-phase LCL-DAB converter, characterized in that, The converter includes an LCL resonant branch, a primary side, and a secondary side; The primary side is a three-phase bridge circuit, which is connected to the PWM rectifier. The LCL resonant branch is composed of a resonant split capacitor branch, a three-phase resonant inductor, and an output inductor. The secondary side is a full-bridge circuit, and the primary side and the secondary side are connected through the LCL resonant branch; and the primary and secondary sides are electrically isolated by a single-phase high-frequency transformer. The resonant split capacitor branch includes a split capacitor C. ab C bc split capacitor C ab C bc The branch circuit is formed through a three-phase resonant inductor L a L b L c Connected to the primary three-phase AC port; output inductor L a Connected to the split capacitor branch and the isolation high-frequency transformer, it transfers the energy stored in the inductor to the secondary side of the converter; The control method for a split-capacitor three-phase LCL-DAB converter includes the following steps: By introducing a fluctuating duty cycle on the primary side, the input power is mixed with the DC power. P dc Coupled disturbance power p ripple By decoupling and separating the disturbance power through modulation of the primary-side three-phase bridge, this disturbance power is effectively neutralized. p ripple The power is transferred to the resonant branch of the split capacitor that requires a wide range of voltage fluctuations, so that the intermediate DC-side capacitor no longer needs to absorb and absorb disturbance power. The three-phase duty cycle expression that satisfies the split capacitor three-phase LCL-DAB active power decoupling is: The above equation is the control variable expression for active power decoupling in a split-capacitor three-phase LCL-DAB.

2. The control method for a split-capacitor three-phase LCL-DAB converter according to claim 1, characterized in that, The PWM rectifier consists of a switching transistor S. ap S an S bp S bn The full-bridge configuration, combined with a single-phase AC power grid u ac Through the grid-side inductor L ac Connected.

3. The control method for a split-capacitor three-phase LCL-DAB converter according to claim 1, characterized in that, The three-phase bridge circuit includes a primary-side switching transistor T. 11 ,T 12 ,T 13 ,T 14 ,T 15 ,T 16 A three-phase bridge inverter circuit is formed, which adopts three-phase symmetrical control, with the switching signals of each phase arm differing by 120 degrees in phase.

4. The control method for a split-capacitor three-phase LCL-DAB converter according to claim 1, characterized in that, The three-phase resonant inductor and the output inductor have the same inductance value, then L a =L b =L c =L r If the upper and lower split capacitors have the same capacitance value, then C ab =C bc =C r .

5. The control method according to claim 1, characterized in that, The switching signals of the left and right arms of the secondary full-bridge circuit differ by a phase angle of 180 degrees; the phase difference between the A-phase arm of the secondary full-bridge and the A-phase arm of the primary three-phase bridge is an outward phase shift angle. D f It is used to control the power transmission of the converter. The upper and lower switch signals of all bridge arms are complementary, and the duty cycle is always 50%.

6. The control method according to claim 1, characterized in that, Specifically, it includes: In the closed-loop control of active power decoupling, the output voltage V2 of the split capacitor three-phase LCL-DAB is related to the voltage command V. 2ref The difference between the two values ​​is used by PI control to generate an outward phase shift angle D. f D f The output control quantity of the voltage loop controls the output power of the split capacitor three-phase LCL-DAB; Acquire the input AC voltage u of the front stage of the AC / DC power converter ac and input AC current i ac For the input AC voltage u ac and input AC current i ac Phase-locked loop (PLL) is performed to obtain the angular frequency ω of the single-phase power grid. g and power factor angle θ; Find the input AC voltage u ac and input AC current i ac The effective value of the fluctuation power p is obtained. ripple amplitude P m According to the fluctuation power p ripple amplitude P m Circuit parameters L r C r ω s Given the DC input voltage V1 of the split capacitor three-phase LCL-DAB, the primary-side duty cycle D that satisfies active power decoupling control is calculated. pa D pb and D pc .

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