Self-adjusting power ripple buffering method based on switch multiplexing type AC-DC converter

Abstract

The invention discloses a self-regulation power ripple buffering method based on a switch multiplexing type AC-DC converter, which comprises the following steps of: decomposing the switch multiplexing type AC-DC converter into an AC-DC conversion unit and a power ripple buffering unit by using an equivalent modeling method, and then regulating a reference voltage vector of each unit according to a proportional parameter of a reference voltage vector, alternating current side power is distributed to different units according to frequency characteristics, and self-adjusting power ripple buffering is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronic conversion, and more particularly relates to a self-regulating power ripple buffering method based on a switch multiplexing type AC-DC converter. Background Art

[0002] With the continued expansion of renewable energy integration and the increasing prevalence of nonlinear loads, three-phase grid-connected systems are facing an increasingly prominent problem: grid voltage imbalance. Under voltage imbalance, power ripple at twice the grid frequency is generated on the AC side of the system. This ripple is transmitted to the DC side of the converter, causing severe fluctuations in the DC bus voltage. These dramatic DC bus voltage fluctuations not only reduce the efficiency of system power transmission but also pose a serious threat to the stability and reliability of the entire grid-connected system. Therefore, developing effective power ripple buffering technology—dynamically absorbing or smoothing this power ripple through energy storage elements—is a key technology for maintaining DC bus voltage stability and ensuring safe and stable system operation.

[0003] Early solutions mainly relied on increasing the capacity of electrolytic capacitors on the DC side and passively absorbing power ripple through the capacitor charging and discharging process. However, electrolytic capacitors have many inherent defects: high equivalent series resistance, short life (usually only 5-10 years), and strong temperature sensitivity. More importantly, its buffering capacity is determined by a fixed capacity and cannot be actively adjusted and optimized according to the actual grid operating status or power fluctuations. Especially under extreme operating conditions such as grid voltage drops (such as voltage drops exceeding 30%), a large amount of secondary power ripple may cause the voltage fluctuations across the capacitor to exceed the acceptable range or control margin of the system, thereby causing severe overshoot or undervoltage of the DC bus voltage, and there is a risk of buffer failure causing converter protection shutdown or even system collapse.

[0004] To overcome the inherent limitations of passive buffering technology, active power ripple buffering technology has emerged. This type of technology typically decouples the secondary power ripple from the main power transmission path by introducing an additional power conversion link, such as an independent bidirectional DC-DC converter or a carefully designed resonant circuit, and dynamically absorbs it using auxiliary energy storage elements. Although this solution can improve the power ripple suppression accuracy and buffering margin to a certain extent, it significantly increases the system's hardware cost and overall system complexity. In addition, issues such as control coordination, power distribution, and system stability brought about by the cascade of multiple converters have become challenges that need to be urgently addressed in practical engineering applications.

[0005] In order to further optimize the cost and volume of active buffering solutions, in recent years, research has focused on achieving lightweight design of power buffering architectures by reusing the inherent power devices of the main circuit. A typical solution is to reuse the existing active switches and filter inductors of the grid-connected converter, and to divert the power ripple to the energy storage capacitor through modulation strategy optimization, thus avoiding the addition of additional hardware. However, since the power components need to serve both the main power transmission and ripple buffering tasks, the independent control freedom of the power ripple buffer is subject to certain restrictions. At the control level, this type of solution relies on frequency selective controllers such as PR and quasi-PR to control the power ripple, which requires cumbersome controller parameter tuning and is difficult to meet the needs of modern power grids for flexible power scheduling of converters. Summary of the Invention

[0006] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a self-regulating power ripple buffering method based on a switch-multiplexed AC-DC converter. The method realizes self-regulating power ripple buffering without introducing additional circuits, thereby solving the problems of complex structure and cumbersome power ripple control caused by external buffer circuits in unbalanced power grid applications.

[0007] To achieve the above-mentioned object of the invention, the present invention provides a self-regulating power ripple buffering method based on a switch-multiplexed AC-DC converter, characterized by comprising the following steps:

[0008] (1) Obtain the reference voltage vector v of the switch multiplexing AC-DC converter ref ;

[0009] (1.1) Collect the three-phase voltage e on the AC side of the switch-multiplexed AC-DC converter x , three-phase current i x , x represents the phase, x = a, b, c;

[0010] (1.2) The collected three-phase voltage e x and three-phase current i x Input them into the abc-αβ coordinate conversion unit respectively to obtain the grid voltage e in the αβ coordinate system αβ and grid current i αβ ;

[0011] (1.3) Based on the biquad generalized integrator phase-locked loop, the grid voltage synchronization phase angle θ is obtained. + ;

[0012] (1.4), the reference voltage vector V of the AC-DC conversion unit 1ref The error between the DC load port voltage V1 is input to the proportional-integral controller for regulation to generate the d-axis reference current

[0013] (1.5) The d-axis reference current q-axis reference current and the phase angle θ + Input to the dq-αβ coordinate conversion unit to obtain the reference grid current in the αβ coordinate system

[0014] (1.6) with i αβ The error is input to the proportional resonant controller for regulation to generate the reference voltage vector v ref ;

[0015] (2) Using the equivalent modeling method, the switch multiplexing AC-DC converter is decomposed into an AC-DC conversion unit and a power ripple buffer unit;

[0016] The DC bus voltage of the AC-DC conversion unit is equal to the DC load port voltage V1, which is used to transfer the DC component of the AC input port power to the DC load R1; the DC bus voltage of the power ripple buffer unit is equal to the ripple buffer port voltage V2, which is used to transfer the AC component of the AC input port power to the decoupling capacitor C2;

[0017] (3) The reference voltage vector v of the switch multiplexing AC-DC converter ref break down;

[0018] Based on the decomposition model of step (2), the reference voltage vector v ref Breaks down to:

[0019] v ref =v ref1 +v ref2

[0020] Among them, v ref1 is the reference voltage vector of the AC-DC conversion unit; v ref2 is the reference voltage vector of the power ripple buffer unit;

[0021] Set the decomposition ratio parameter k and convert the above reference voltage vector v ref The decomposition is rewritten as:

[0022] v ref1 =kv ref and v ref2 =(1-k)v ref ,

[0023] (4) Calculate the active power P1 output by the AC-DC conversion unit:

[0024]

[0025] Among them, Pout is the total output active power of the switch-multiplexed AC-DC converter;

[0026] (5) Adjust the reference voltage vector of each unit and achieve constant power control by controlling the active power P1;

[0027] (5.1) and use the positive sequence component extractor to obtain the grid voltage e αβ The positive sequence component and Then and Input to the αβ-dq coordinate conversion unit to obtain the positive sequence component of the grid voltage on the d axis

[0028] (5.2), the positive sequence component and d-axis reference current Input to the reference power calculation module to obtain the reference active power

[0029] (5.3) Considering that the input and output of the switch-multiplexed AC-DC converter meet power balance, that is, the active power P at the input port in Equal to the total output active power P out In order to achieve self-regulating power ripple buffering, it is necessary to ensure that the active power P1 at the DC load port accurately tracks the active power reference P ref , further, determine the scale parameter k:

[0030]

[0031] Among them, P0 is the active power P in The DC component, P r is the active power P in The communication component;

[0032] (5.4), use a low-pass filter to obtain the average value of the ripple buffer port voltage V2, and then use the reference voltage V 2ref The error with the average value of V2 is input to the PI controller for adjustment, generating the feedback control quantity Δk for adjusting the average voltage of the ripple port;

[0033] (5.5), add the feedback control quantity Δk to the proportional parameter k, and then decompose the reference voltage vector: v ref1 =(k+Δk)v ref and v ref2 =(1-k-Δk)v ref ;

[0034] (5.6), according to the obtained reference voltage vector v ref1 and v ref2Solve for the duty cycle d of the active switch x1 and d x2 ;

[0035] (5.7) The driving signals of the active switches are generated according to the duty cycles of the active switches, thereby controlling the on and off timing of each active switch and completing the power conversion control of the switch-multiplexing AC-DC converter.

[0036] The object of the invention of the present invention is achieved like this:

[0037] The present invention is based on a self-regulating power ripple buffering method for a switch-multiplexed AC-DC converter. The switch-multiplexed AC-DC converter is decomposed into an AC-DC conversion unit and a power ripple buffering unit using an equivalent modeling method. The reference voltage vector of each unit is then adjusted according to a proportional parameter of the reference voltage vector, and the AC-side power is distributed to different units according to frequency characteristics, thereby achieving self-regulating power ripple buffering.

[0038] At the same time, the self-regulating power ripple buffering method based on the switch multiplexing AC-DC converter of the present invention also has the following beneficial effects:

[0039] (1) The present invention reuses the existing filter inductor and active switch of the converter to build a power ripple buffer path together with the decoupling capacitor, thus achieving the power buffering function without the need for an external power buffer circuit;

[0040] (2) The present invention utilizes an equivalent modeling method to decompose the switch-multiplexed AC-DC converter into an AC-DC conversion unit and a power ripple buffer unit, thereby separating the constant power transmission path and the power ripple transmission path, simplifying the power flow analysis, and enabling the design of the power control loop to be performed on the voltage vector plane;

[0041] (3) The present invention relies on the power conservation characteristics between the three ports of the converter. By adjusting the reference voltage vector of each unit, the power ripple buffer function is dynamically adapted to the grid operating conditions, thereby realizing self-adjustable power ripple buffering without the need to design complex control algorithms and perform tedious parameter settings. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a switch multiplexing AC-DC converter topology;

[0043] Figure 2 It is an optional active switch group in the switch multiplexing AC-DC converter topology;

[0044] Figure 3 This is a control block diagram of a self-regulating power ripple buffering method based on a switch-multiplexed AC-DC converter;

[0045] Figure 4is a schematic diagram of the equivalent modeling approach;

[0046] Figure 5 This is a power control diagram of a switch-multiplexed AC-DC converter;

[0047] Figure 6 These are three operating condition diagrams of switch multiplexing AC-DC converters;

[0048] Figure 7 This is the operating condition diagram of the switch multiplexing AC-DC converter when the single-phase grid voltage drops by 50%;

[0049] Figure 8 The steady-state waveforms of the switch-multiplexed AC-DC converter are shown in Figure 1 when the single-phase grid voltage drops by 50% and when the power ripple buffer is applied to the converter.

[0050] Figure 9 It is a dynamic waveform diagram of the switch multiplexing AC-DC converter when the single-phase grid voltage suddenly drops by 50%. DETAILED DESCRIPTION

[0051] The following describes the specific embodiments of the present invention in conjunction with the accompanying drawings so that those skilled in the art can better understand the present invention. It should be noted that in the following description, when detailed descriptions of known functions and designs may dilute the main content of the present invention, such descriptions will be omitted here.

[0052] Example

[0053] In this embodiment, a switch multiplexing AC-DC converter with self-regulating power ripple buffering capability is provided, and its typical topology is as follows: Figure 1 As shown, it includes: AC input port, DC load port, ripple buffer port, filter unit and active switch group; the filter unit of the converter, active switch group S x Shared by the DC load port and the ripple buffer port, where the active switch group S x It can be used to control the power flow between the DC load port and the ripple buffer port, thereby avoiding the introduction of additional power ripple buffer circuits; the three ports satisfy the power conservation relationship: P in =P0+P r =P ref +P r =P1+P2, where P in P0 and P are the AC input port power. r P in The DC and AC components, P refis the power reference of P0, P1 is the output power of the DC load port, and P2 is the output power of the ripple buffer port. According to the power conservation relationship, when P0 is assigned to the DC load port, self-regulating power ripple buffering will be achieved. The detailed implementation method is as follows:

[0054] like Figure 1 As shown, the AC input port is connected to a three-phase AC source e a 、e b 、e c The DC load port is connected to the DC load R1 and the DC bus capacitor C1; R1 and C1 are connected in parallel, and their voltage is V1; the ripple buffer port is connected to the decoupling capacitor C2, and its voltage is V2; the decoupling capacitor C2 is a film capacitor with long life and high reliability, and its voltage is based on the power ripple amplitude P m , grid angular frequency ω, capacitor voltage maximum value V 2m And the capacitance value of the decoupling capacitor C2 is determined, assuming that the power ripple flowing through the capacitor is described as: P r =P m sin(2ωt), then the capacitor voltage V2 should satisfy: Further solving, the capacitor voltage is calculated by the following formula:

[0055]

[0056] in, And k≥1; the filter unit only contains the inductor L for suppressing high-frequency harmonics ac .

[0057] like Figure 2 As shown, the active switch group S x Active switches of multi-level converters can be selected. Multi-level converters include but are not limited to ANPC type, NPC type, T type, etc. In view of the significant advantages of NPC type multi-level converters such as mature topology, relatively simple circuit structure, and highly perfect engineering application, active switches of NPC type multi-level converters are selected to construct switch group S. x .

[0058] Next we combine Figure 3 The present invention provides a self-regulating power ripple buffering method based on a switch multiplexing AC-DC converter, comprising the following steps:

[0059] (1) Obtain the reference voltage vector v of the switch multiplexing AC-DC converter ref ;

[0060] (1.1) Collect the three-phase voltage e on the AC side of the switch-multiplexed AC-DC converter x , three-phase current i x , x represents the phase, x = a, b, c;

[0061] (1.2) The collected three-phase voltage e x and three-phase current i x Input them into the abc-αβ coordinate conversion unit respectively to obtain the grid voltage e in the αβ coordinate system αβ and grid current i αβ ;

[0062] (1.3) Based on the biquad generalized integrator phase-locked loop, the grid voltage synchronization phase angle θ is obtained. + ;

[0063] (1.4), the reference voltage vector V of the AC-DC conversion unit 1ref The error between the DC load port voltage V1 is input to the proportional-integral controller for regulation to generate the d-axis reference current

[0064] (1.5) The d-axis reference current q-axis reference current and the phase angle θ + Input to the dq-αβ coordinate conversion unit to obtain the reference grid current in the αβ coordinate system

[0065] (1.6) with i αβ The error is input to the proportional resonant controller for regulation to generate the reference voltage vector v ref ;

[0066] (2) If Figure 4 As shown in the figure, the switch-multiplexed AC-DC converter is decomposed into an AC-DC conversion unit and a power ripple buffer unit using an equivalent modeling method. In this way, the operating state and output characteristics of the entire converter can be mapped to the AC-DC conversion unit and the power ripple buffer unit respectively, thereby simplifying the power ripple control.

[0067] The DC bus voltage of the AC-DC conversion unit is equal to the DC load port voltage V1, which is used to transfer the DC component of the AC input port power to the DC load R1; the DC bus voltage of the power ripple buffer unit is equal to the ripple buffer port voltage V2, which is used to transfer the AC component of the AC input port power to the decoupling capacitor C2;

[0068] (3) The reference voltage vector v of the switch multiplexing AC-DC converter ref break down;

[0069] Based on the decomposition model of step (2), the reference voltage vector v ref Breaks down to:

[0070] vref =v ref1 +v ref2

[0071] Among them, v ref1 is the reference voltage vector of the AC-DC conversion unit; v ref2 is the reference voltage vector of the power ripple buffer unit;

[0072] Set the decomposition ratio parameter k and convert the above reference voltage vector v ref The decomposition is rewritten as:

[0073] v ref1 =kv ref and v ref2 =(1-k)v ref ,

[0074] (4) Calculate the active power P1 output by the AC-DC conversion unit:

[0075]

[0076] Among them, P out is the total output active power of the switch-multiplexed AC-DC converter;

[0077] (5) Adjust the reference voltage vector of each unit and achieve constant power control by controlling the active power P1;

[0078] (5.1) and use the positive sequence component extractor to obtain the grid voltage e αβ The positive sequence component and Then and Input to the αβ-dq coordinate conversion unit to obtain the positive sequence component of the grid voltage on the d axis

[0079] (5.2), the positive sequence component and d-axis reference current Input to the reference power calculation module to obtain the reference active power

[0080] (5.3) Considering that the input and output of the switch-multiplexed AC-DC converter meet power balance, that is, the active power P at the input port in Equal to the total output active power P out ,like Figure 5 As shown, in order to achieve self-regulating power ripple buffering, it is necessary to ensure that the active power P1 of the DC load port accurately tracks the active power reference P ref , further, determine the scale parameter k:

[0081]

[0082] Among them, P0 is the active power P in The DC component, P r is the active power P in The communication component;

[0083] (5.4), use a low-pass filter to obtain the average value of the ripple buffer port voltage V2, and then use the reference voltage V 2ref The error with the average value of V2 is input to the PI controller for adjustment, generating the feedback control quantity Δk for adjusting the average voltage of the ripple port;

[0084] (5.5), add the feedback control quantity Δk to the proportional parameter k, and then decompose the reference voltage vector: v ref1 =(k+Δk)v ref and v ref2 =(1-k-Δk)v ref ;

[0085] (5.6), according to the obtained reference voltage vector v ref1 and v ref2 Solve for the duty cycle d of the active switch x1 and d x2 ;

[0086] (5.7) The driving signals of the active switches are generated according to the duty cycles of the active switches, thereby controlling the on and off timing of each active switch and completing the power conversion control of the switch-multiplexing AC-DC converter.

[0087] In this embodiment, Figure 6 Three operating conditions of the switch multiplexing AC-DC converter are given. When k < 1, the active power injected into the DC load will be less than the input power, and v ref1 and v ref2 In phase; when k = 1, all active power is injected into the DC load, and v ref1 With v ref When k>1, the active power injected into the DC load will be greater than the input power, and v ref1 With v ref2 Reverse.

[0088] Example verification

[0089] Below we illustrate the embodiment with reference to examples. Figure 7-9As shown. The experimental setting is that the grid voltage is 55V effective value and the grid frequency is set to 50Hz. In terms of load configuration, the DC load R1 is a linear load with a resistance of 80Ω. In terms of circuit component parameter selection, the capacitance of the decoupling capacitor C2 is determined to be 120μF, the capacitance of the DC load port capacitor C1 is determined to be 150μF, and the filter inductor L is determined to be 150μF. ac The inductance is 5mH. In addition, the control frequency is set to 10kHz. In order to simplify the experimental analysis, the ripple buffer port voltage reference V 2ref Set as DC load port voltage reference V 1ref half.

[0090] Figure 7 The operating condition diagram of the switch-multiplexed AC-DC converter with power ripple buffering when the single-phase grid voltage drops by 50% is shown. From top to bottom, they are: DC load port voltage V1, ripple buffer port voltage V2, AC input port active power P in , the ripple buffer port active power P2, and the proportional parameter k. The waveform clearly shows that when the pulsating power component is injected into the grid, the active power at the AC input port fluctuates. By adjusting the proportional parameter in each control cycle, the ripple buffer port can track the pulsating power component. As a result, the power imbalance between the AC input and the DC load is automatically buffered by the decoupling capacitor C2, and the voltage across the DC load R1 is maintained constant.

[0091] Figure 8 The steady-state waveforms of the switch-multiplexed AC-DC converter with and without power ripple buffering are shown when the single-phase grid voltage drops by 50%. From top to bottom, they are: DC load port voltage V1, ripple buffer port voltage V2, ripple buffer port active power P2, and power ripple P r . Figure 8 (a) shows the case where no power ripple buffer is applied. It can be found that in this case, the ripple buffer port cannot track the power ripple, resulting in voltage fluctuations at the DC load port, and the peak-to-peak value of the fluctuation reaches 15.5V. Figure 8 (b) shows the application of a power ripple buffer. It can be seen that in this case, the ripple buffer port can track the power ripple, thereby transferring the power pulsation at the DC load port to the ripple buffer port. In this case, the DC load voltage can be maintained stable, with a peak-to-peak voltage fluctuation of only 4.6V.

[0092] Figure 9 The dynamic waveforms of the switch-multiplexed AC-DC converter are shown when the single-phase grid voltage suddenly drops by 50%. From top to bottom, they are: DC load port voltage V1, ripple buffer port voltage V2, three-phase grid current i abc, ripple buffer port active power P2, and power ripple P r It can be seen that under the action of balanced current control, the grid current can remain sinusoidal and balanced throughout the process. Before the unbalanced grid condition occurs, both V1 and V2 show low voltage fluctuations. However, after the grid condition occurs, V2 pulsates at twice the grid frequency, which means that the power buffer unit successfully performs the power buffering function. During the entire dynamic process, P2 can always track the upper P r , which means that power imbalance can still be automatically buffered by the decoupling capacitor C2 in the event of a sudden power outage.

[0093] Although the above describes the illustrative specific embodiments of the present invention to facilitate understanding of the present invention by those skilled in the art, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concepts of the present invention are protected.

Claims

1. A self-regulating power ripple buffering method based on a switch-multiplexed AC-DC converter, characterized in that: The following steps are involved: (1) Obtain the reference voltage vector v of the switch multiplexing AC-DC converter ref ; (1.1) Collect the three-phase voltage e on the AC side of the switch-multiplexed AC-DC converter x , three-phase current i x , x represents the phase, x = a, b, c; (1.2) The collected three-phase voltage e x and three-phase current i x Input them into the abc-αβ coordinate conversion unit respectively to obtain the grid voltage e in the αβ coordinate system αβ and grid current i αβ ; ( 1.3) Based on the biquad generalized integrator phase-locked loop, the grid voltage synchronization phase angle θ is obtained + ; (1.4), the reference voltage vector V of the AC-DC conversion unit 1ref The error between the DC load port voltage V1 is input to the proportional-integral controller for regulation to generate the d-axis reference current (1.5) The d-axis reference current q-axis reference current and the phase angle θ + Input to the dq-αβ coordinate conversion unit to obtain the reference grid current in the αβ coordinate system (1.6) with i αβ The error is input to the proportional resonant controller for regulation to generate the reference voltage vector v ref ; (2) Using the equivalent modeling method, the switch multiplexing AC-DC converter is decomposed into an AC-DC conversion unit and a power ripple buffer unit; The DC bus voltage of the AC-DC conversion unit is equal to the DC load port voltage V1, which is used to transfer the DC component of the AC input port power to the DC load R1; the DC bus voltage of the power ripple buffer unit is equal to the ripple buffer port voltage V2, which is used to transfer the AC component of the AC input port power to the decoupling capacitor C2; (3) The reference voltage vector v of the switch multiplexing AC-DC converter ref break down; Based on the decomposition model of step (2), the reference voltage vector v ref Breaks down to: v ref =v ref1 +v ref2 Among them, v ref1 is the reference voltage vector of the AC-DC conversion unit; v ref2 is the reference voltage vector of the power ripple buffer unit; Set the decomposition ratio parameter k and convert the above reference voltage vector v ref The decomposition is rewritten as: v ref1 = kv ref and v ref2 = (1 - k)v ref , (4) Calculate the active power P1 output by the AC-DC conversion unit: Among them, P out is the total output active power of the switch-multiplexed AC-DC converter; (5) Adjust the reference voltage vector of each unit and achieve constant power control by controlling the active power P1; (5.1) and use the positive sequence component extractor to obtain the grid voltage e αβ The positive sequence component and Then and Input to the αβ-dq coordinate conversion unit to obtain the positive sequence component of the grid voltage on the d axis (5.2), the positive sequence component and d-axis reference current Input to the reference power calculation module to obtain the reference active power (5.3) Considering that the input and output of the switch-multiplexed AC-DC converter meet power balance, that is, the active power P at the input port in Equal to the total output active power P out In order to achieve self-regulating power ripple buffering, it is necessary to ensure that the active power P1 at the DC load port accurately tracks the active power reference P ref , further, determine the scale parameter k: Among them, P0 is the active power P in The DC component, P r is the active power P in The communication component; (5.4), use a low-pass filter to obtain the average value of the ripple buffer port voltage V2, and then use the reference voltage V 2ref The error with the average value of V2 is input to the PI controller for adjustment, generating the feedback control quantity Δk for adjusting the average voltage of the ripple port; (5.5), add the feedback control quantity Δk to the proportional parameter k, and then decompose the reference voltage vector: v ref1 =(k+Δk)v ref and v ref2 =(1-k-Δk)v ref ; (5.6), according to the obtained reference voltage vector v ref1 and v ref2 Solve for the duty cycle d of the active switch x1 and d x2 ; (5.7) The driving signals of the active switches are generated according to the duty cycles of the active switches, thereby controlling the on and off timing of each active switch and completing the power conversion control of the switch-multiplexing AC-DC converter.

2. The self-regulating power ripple buffering method according to claim 1, characterized in that: The duty cycle is calculated as follows: (1) Select the active switches of the three-level NPC converter as the active switch group of the switch multiplexing AC-DC converter; (2) Define the volt-second balance equation satisfied by the switch multiplexing AC-DC converter, AC-DC conversion unit, and power ripple buffer unit: v xn =V1d x1 +V2(d x2 -d x1 )=v xn1 +v xn2 =V1d' x +V2d” x Among them, v xn is the phase voltage output by the switch multiplexing AC-DC converter, d x1 d x2 They are the duty cycles of the two switches on the upper arm of the active switch group, v xn1 is the phase voltage output by the AC-DC conversion unit, v xn2 is the phase voltage output by the power ripple buffer unit, d' x is the active switch S' of the AC-DC conversion unit x Duty cycle, d” x It is the power ripple buffer unit active switch S" x Duty cycle; (3) According to the SVPWM principle of the two-level converter, the reference voltage vector v ref1 Calculate the active switch S' of the AC-DC conversion unit x The duty cycle is calculated as d' x =d x1 ; Similarly, through the reference voltage vector v ref2 Calculate the active switch S" of the power ripple buffer unit x The duty cycle is calculated as d" x =d x2 -d x1 ; According to the calculation results of the duty cycle of the two conversion units, the duty cycle of the active switch of the switch multiplexing AC-DC converter is calculated, which are: x1 =d' x , d x2 =d' x +d” x .

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