A bidirectional single-stage resonant AC-DC converter and its modulation method

Abstract

This invention relates to the field of power electronics and AC-DC converter technology, specifically to a bidirectional single-stage resonant AC-DC converter and its modulation method. The modulation method includes: S1: constructing a corresponding operating mode based on the power transmission direction between the AC and DC sides of the bidirectional single-stage resonant AC-DC converter; S2: generating an optimized modulation scheme for the operating mode based on the equivalent circuit of the bidirectional single-stage resonant AC-DC converter; S3: modulating the bidirectional single-stage resonant AC-DC converter based on the optimized modulation scheme to bring it into the corresponding operating mode, while simultaneously utilizing the excitation current flowing through the magnetizing inductor to achieve soft switching of the device. In this invention, the converter design fully considers the changes in the AC side's power frequency voltage, enabling bidirectional energy flow; simultaneously, it utilizes the transformer's excitation current to achieve soft switching of the device, expands the soft switching range through the optimized modulation scheme, reduces converter operating losses, and improves overall operating efficiency.

Description

Technical Field

[0001] This invention relates to the field of power electronics and AC-DC converter technology, specifically to a bidirectional single-stage resonant AC-DC converter and its modulation method. Background Technology

[0002] In recent years, bidirectional isolated AC-DC converters have developed rapidly and are widely used in electric vehicles, DC power supplies, new energy grid connection, and energy storage systems. Currently, mainstream bidirectional isolated AC-DC converters include bidirectional two-stage AC-DC converters and bidirectional single-stage AC-DC converters. Because bidirectional two-stage AC-DC converters employ two stages of power conversion, their efficiency, reliability, and power density are limited. Furthermore, the converter uses a large number of components, and the complex control loop increases the system cost.

[0003] A bidirectional single-stage AC-DC converter is a power conversion device capable of bidirectional energy transfer between AC and DC power sources. It typically consists of a high-frequency transformer, passive components, and switching transistors. Due to its single-stage structure and the use of component multiplexing, it offers advantages such as compact design, high efficiency, and flexible control. However, it requires connection to the AC power grid, and issues related to grid-connected current quality, power control, and power factor correction (PFC) limit its application scope.

[0004] Bidirectional single-stage AC-DC converters can be further divided into two categories: DAB type and resonant type. Single-stage DAB type AC-DC converters suffer from problems such as inability to decouple input current, inability to achieve complete soft switching, and power recirculation; their operating efficiency and current control accuracy still need improvement. Resonant type converters generally have higher operating efficiency than their DAB counterparts. Applying resonant type converters to single-stage AC-DC converters is one solution, but resonant type converters also suffer from problems such as the resonant current not being zero at the initial moment of the switching cycle and the difficulty in obtaining an analytical solution for the resonant current.

[0005] Therefore, how to design a bidirectional single-stage resonant AC-DC converter and modulation method that can achieve bidirectional energy flow and high operating efficiency is an urgent technical problem to be solved. Summary of the Invention

[0006] To address the shortcomings of the existing technologies, the technical problem to be solved by this invention is: how to provide a bidirectional single-stage resonant AC-DC converter and its modulation method. The converter design fully considers the changes in the AC power frequency voltage, enabling bidirectional energy flow. At the same time, the excitation current of the transformer is used to realize soft switching of the device. By optimizing the modulation scheme, the soft switching range is expanded, the converter operating loss is reduced, thereby improving the overall operating efficiency of the converter.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A bidirectional single-stage resonant AC-DC converter, comprising:

[0009] AC side circuit, set at AC side power supply U g The AC side includes a half-bridge and an H-bridge connected in parallel with the half-bridge; the half-bridge is composed of a totem pole upper switch Q5 and a totem pole lower switch Q6 connected in series; the H-bridge is composed of a first AC side upper switch Q1 and a first AC side lower switch Q2 connected in series, and a second AC side upper switch Q3 and a second AC side lower switch Q4 connected in series in parallel.

[0010] DC-side circuit, located at DC-side power supply U s The DC side includes a half-bridge consisting of a DC-side upper switch S1 and a DC-side lower switch S2 connected in series.

[0011] A transformer is connected between the AC side circuit and the DC side circuit; the magnetizing inductance of the transformer is L. m ;

[0012] A resonant circuit, connected between the DC-side circuit and the transformer, includes a resonant inductor L connected in series with the transformer. r And the resonant capacitor C connected in parallel with the half-bridge of the DC-side circuit. r Resonant capacitor C r Including the resonant capacitor C in series r1 and C r2 .

[0013] Preferably, the AC side circuit also includes a grid-side inductor L. g1 L g2 and grid-side capacitor C p ;

[0014] Grid-side inductor L g1 and L g2 One end of each is connected to the AC power supply U g One end is connected to the other end, which is connected to the two terminals on the low-voltage side of the transformer; grid-side capacitor C p It is positioned between the half-bridge and the H-bridge in the AC side circuit and is connected in parallel with both the half-bridge and the H-bridge.

[0015] A modulation method for a bidirectional single-stage resonant AC-DC converter, implemented based on the bidirectional single-stage resonant AC-DC converter of the present invention, includes:

[0016] S1: Construct the corresponding operating mode based on the power transmission direction between the AC side circuit and the DC side circuit of the bidirectional single-stage resonant AC-DC converter;

[0017] S2: Based on the equivalent circuit of the bidirectional single-stage resonant AC-DC converter, an optimized modulation scheme is generated for the working mode;

[0018] S3: Based on the optimized modulation scheme, the bidirectional single-stage resonant AC-DC converter is modulated to enter the corresponding working mode, and the excitation current flowing through the excitation inductor is used to realize the soft switching of the device.

[0019] Preferably, in step S1, the operating mode includes operating mode one, which involves the forward transmission of power from the AC side circuit to the DC side circuit.

[0020] Preferably, in step S2, the optimized modulation scheme corresponding to operating mode one is:

[0021] The upper switch Q5 and the lower switch Q6 of the totem pole are connected to the AC power supply U. g Switched at 50Hz power frequency;

[0022] The first AC side upper switch Q1 and the first AC side lower switch Q2 connected in series, and the second AC side upper switch Q3 and the second AC side lower switch Q4 connected in series, are mutually complementary and conduct with a 50% duty cycle.

[0023] By using phase shifting, the rising edge of the PWM drive signal of the second AC side upper switch Q3 is aligned with the rising edge of the PWM drive signal of the DC side upper switch S1, and the rising edge of the PWM drive signal of the second AC side lower switch Q4 is aligned with the rising edge of the PWM drive signal of the DC side lower switch S2.

[0024] The duty cycles of the PWM drive signals of the DC-side upper switch S1 and the DC-side lower switch S2 are equal and less than 0.5;

[0025] The DC-side upper switch S1 and the DC-side lower switch S2 adopt variable pulse width modulation, and the pulse width varies with the input AC power and the power frequency AC voltage.

[0026] Preferably, in the optimized modulation scheme of operating mode one, the formula for calculating the transmission power of the resonant circuit is:

[0027]

[0028] U p =2U g ;

[0029] In the formula: T s For switching cycles; D is the resonant angular frequency; b This refers to the duty cycle of the DC-side switching transistor.

[0030]

[0031] P S =P PFC ,

[0032] U gm This refers to the amplitude of the power frequency AC voltage.

[0033] The falling edge of the PWM drive signal of the first AC side lower switch Q2 lags behind the rising edge of the PWM drive signal of the DC side upper switch S1, and the lag time is the duration of the resonant current.

[0034] The falling edge of the PWM drive signal of the first AC side upper switch Q1 lags behind the rising edge of the PWM drive signal of the DC side lower switch S2, and the lag time is the duration of the resonant current.

[0035] When one switch in the same bridge arm of the AC side circuit is turned off, the resonant current flows through the magnetizing inductor, and the anti-parallel diode of the other switch turns on in advance, achieving zero-voltage turn-on.

[0036] Preferably, in step S1, the operating mode includes operating mode two, in which power is transmitted in reverse from the DC side circuit to the AC side circuit.

[0037] Preferably, in step S2, the optimized modulation scheme corresponding to operating mode two is:

[0038] The upper switch Q5 and the lower switch Q6 of the totem pole are connected to the AC power supply U. g Switched at 50Hz power frequency;

[0039] The first AC side upper switch Q1 and the first AC side lower switch Q2 connected in series, and the second AC side upper switch Q3 and the second AC side lower switch Q4 connected in series, are mutually complementary and conduct with a 50% duty cycle.

[0040] By using phase shifting, the rising edge of the PWM drive signal of the second AC side lower switch Q4 is aligned with the rising edge of the PWM drive signal of the DC side upper switch S1, and the rising edge of the PWM drive signal of the second AC side upper switch Q3 is aligned with the rising edge of the PWM drive signal of the DC side lower switch S2.

[0041] The duty cycles of the PWM drive signals of the DC-side upper switch S1 and the DC-side lower switch S2 are equal and less than 0.5;

[0042] The DC-side upper switch S1 and the DC-side lower switch S2 adopt variable pulse width modulation, and the pulse width varies with the output AC power and the power frequency AC voltage.

[0043] Preferably, in the optimized modulation scheme of operating mode two, the formula for calculating the transmission power of the resonant circuit is:

[0044]

[0045] U p =2U g ;

[0046] In the formula: T s For switching cycles; D is the resonant angular frequency; f This refers to the duty cycle of the DC-side switching transistor.

[0047]

[0048] P S =-P PFC ,

[0049] U gm This refers to the amplitude of the power frequency AC voltage.

[0050] The falling edge of the PWM drive signal of the first AC side upper switch Q1 lags behind the rising edge of the PWM drive signal of the DC side upper switch S1, and the lag time is the duration of the resonant current.

[0051] The falling edge of the PWM drive signal of the first AC side lower switch Q2 lags behind the rising edge of the PWM drive signal of the DC side lower switch S2, and the lag time is the duration of the resonant current.

[0052] When one switch in the same bridge arm of the AC side circuit is turned off, the resonant current flows through the magnetizing inductor, and the anti-parallel diode of the other switch turns on in advance, achieving zero-voltage turn-on.

[0053] Compared with existing technologies, the bidirectional single-stage resonant AC-DC converter and modulation method of this invention have the following advantages:

[0054] First, the bidirectional single-stage resonant AC-DC converter and its modulation method of this invention fully consider the changes in the AC side's power frequency voltage, enabling bidirectional energy flow. Simultaneously, the transformer's excitation current is used to achieve soft switching of the devices. By optimizing the modulation scheme, the soft-switching range is expanded, reducing converter operating losses and improving the overall operating efficiency of the converter. Second, all switches in the bidirectional single-stage resonant AC-DC converter can achieve zero-voltage turn-on, and only two switches experience losses during turn-off, while the others achieve zero-current turn-off, resulting in low overall converter losses. Third, the resonant current is zero at the initial moment of each switching cycle in the converter, and the analytical solution of the resonant current can be calculated, improving the accuracy of power control. Finally, by phase shifting the AC-side switches and changing the pulse width of the DC-side switches, power factor correction, flexible bidirectional energy flow, and no backflow power are achieved in the bidirectional single-stage resonant AC-DC converter. Attached Figure Description

[0055] To make the objectives, technical solutions, and advantages of the invention clearer, the invention will now be described in further detail with reference to the accompanying drawings, wherein:

[0056] Figure 1 This is a circuit diagram of a bidirectional single-stage resonant AC-DC converter.

[0057] Figure 2 This is a timing diagram of the drive state waveform under forward power transfer.

[0058] Figure 3 This is a timing diagram of the drive state waveform under reverse power transfer. Detailed Implementation

[0059] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but only to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0060] It should be noted that similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the figures, or the orientation or positional relationship commonly used when the product is in use. They 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. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance. In addition, the terms "horizontal," "vertical," etc., do not indicate that the component is required to be absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted. In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" 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.

[0061] The following detailed explanation illustrates the specific implementation methods:

[0062] Example 1:

[0063] This embodiment discloses a bidirectional single-stage resonant AC-DC converter.

[0064] like Figure 1 As shown, a bidirectional single-stage resonant AC-DC converter includes:

[0065] AC side circuit, set at AC side power supply U g On the AC side, it includes a half-bridge and an H-bridge connected in parallel with the half-bridge, as well as a grid-side inductor L. g1 L g2 and grid-side capacitor C p The half-bridge consists of a series-connected totem pole switch Q5 and a series-connected totem pole switch Q6; the full-bridge consists of a series-connected first AC side upper switch Q1 and a series-connected first AC side lower switch Q2, connected in parallel with a series-connected second AC side upper switch Q3 and a series-connected second AC side lower switch Q4; the grid-side inductor L... g1 and Lg2 One end of each is connected to the AC power supply U g One end is connected to the other end, which is connected to the two terminals on the low-voltage side of the transformer; grid-side capacitor C p It is positioned between the half-bridge and the H-bridge in the AC side circuit and is connected in parallel with both the half-bridge and the H-bridge.

[0066] DC-side circuit, located at DC-side power supply U s The DC side includes a half-bridge consisting of a DC-side upper switch S1 and a DC-side lower switch S2 connected in series.

[0067] A transformer is connected between the AC side circuit and the DC side circuit; the magnetizing inductance of the transformer is L. m ;

[0068] A resonant circuit, connected between the DC-side circuit and the transformer, includes a resonant inductor L connected in series with the transformer. r And the resonant capacitor C connected in parallel with the half-bridge of the DC-side circuit. r Resonant capacitor C r Including the resonant capacitor C in series r1 and C r2 .

[0069] The transformer has two terminals on both the low-voltage and high-voltage sides; the two terminals on the low-voltage side are connected to the AC power supply U. g The connection is as follows: one terminal on the high-voltage side is connected between the upper DC-side switch S1 and the lower DC-side switch S2; the other terminal is connected to the resonant capacitor C. r1 and C r2 between.

[0070] AC power supply U g The AC side is equipped with an output capacitor C. p Used to filter out high-frequency components in the rectified voltage; power supply U s A voltage regulator capacitor C is installed on the DC side. S .

[0071] The totem pole upper switch Q5, totem pole lower switch Q6, first AC side upper switch Q1, first AC side lower switch Q2, second AC side upper switch Q3, second AC side lower switch Q4, DC side upper switch S1, and DC side lower switch S2 are respectively equipped with corresponding anti-parallel diodes and parasitic capacitances: D Q5 and C Q5 D Q6 and C Q6 D Q1 and C Q1 D Q2 and C Q2 D Q3 and C Q3D Q4 and C Q4 D S1 and C S2 D S2 and C S2 .

[0072] In this embodiment, the AC power supply U g DC power supply U s The transmission is forward transmission, DC side power supply U s AC power supply U g The transmission is a reverse transmission.

[0073] Example 2:

[0074] This embodiment discloses a modulation method for a bidirectional single-stage resonant AC-DC converter, which is implemented based on the bidirectional single-stage resonant AC-DC converter in Embodiment 1.

[0075] A modulation method for a bidirectional single-stage resonant AC-DC converter includes:

[0076] S1: Construct the corresponding operating mode based on the power transmission direction between the AC side circuit and the DC side circuit of the bidirectional single-stage resonant AC-DC converter;

[0077] S2: Based on the equivalent circuit of the bidirectional single-stage resonant AC-DC converter, an optimized modulation scheme is generated for the working mode;

[0078] S3: Based on the optimized modulation scheme, the bidirectional single-stage resonant AC-DC converter is modulated to enter the corresponding working mode, and the excitation current flowing through the excitation inductor is used to realize the soft switching of the device.

[0079] First, the bidirectional single-stage resonant AC-DC converter and its modulation method of this invention fully consider the changes in the AC side's power frequency voltage, enabling bidirectional energy flow. Simultaneously, the transformer's excitation current is used to achieve soft switching of the devices. By optimizing the modulation scheme, the soft-switching range is expanded, reducing converter operating losses and improving the overall operating efficiency of the converter. Second, all switches in the bidirectional single-stage resonant AC-DC converter can achieve zero-voltage turn-on, and only two switches experience losses during turn-off, while the others achieve zero-current turn-off, resulting in low overall converter losses. Third, the resonant current is zero at the initial moment of each switching cycle in the converter, and the analytical solution of the resonant current can be calculated, improving the accuracy of power control. Finally, by phase shifting the AC-side switches and changing the pulse width of the DC-side switches, power factor correction, flexible bidirectional energy flow, and no backflow power are achieved in the bidirectional single-stage resonant AC-DC converter.

[0080] To better illustrate the technical solution of the present invention, this embodiment is described in the following parts.

[0081] I. Working Mode 1

[0082] In this embodiment, the operating mode includes operating mode one, which involves the forward transmission of power from the AC side circuit to the DC side circuit.

[0083] In working mode one, U s ≥2*nU p =4*nU g .

[0084] The optimized modulation scheme corresponding to operating mode one is:

[0085] The upper switch Q5 and the lower switch Q6 of the totem pole are connected to the AC power supply U. g Switched at 50Hz power frequency;

[0086] The first AC side upper switch Q1 and the first AC side lower switch Q2 connected in series, and the second AC side upper switch Q3 and the second AC side lower switch Q4 connected in series, are mutually complementary and conduct with a 50% duty cycle.

[0087] By using phase shifting, the rising edge of the PWM drive signal of the second AC side upper switch Q3 is aligned with the rising edge of the PWM drive signal of the DC side upper switch S1, and the rising edge of the PWM drive signal of the second AC side lower switch Q4 is aligned with the rising edge of the PWM drive signal of the DC side lower switch S2.

[0088] The duty cycles of the PWM drive signals of the DC-side upper switch S1 and the DC-side lower switch S2 are equal and less than 0.5;

[0089] The DC-side upper switch S1 and the DC-side lower switch S2 adopt variable pulse width modulation, and the pulse width varies with the input AC power and the power frequency AC voltage.

[0090] Specifically, in the optimized modulation scheme of working mode one:

[0091] The formula for calculating the transmission power of a resonant circuit is:

[0092]

[0093] U p =2U g ;

[0094] In the formula: T s For switching cycles; D is the resonant angular frequency; b This refers to the duty cycle of the DC-side switching transistor.

[0095] To ensure open-loop PFC is achieved, the power frequency AC voltage and input current must be in phase. The formula for calculating the input AC power is as follows:

[0096]

[0097] By precisely controlling the resonant circuit in each switching cycle using a variable pulse width modulation strategy, the transmitted power is equal to the input AC power.

[0098] P S =P PFC ;

[0099] The expression for the pulse width as a function of input AC power and power frequency AC voltage is:

[0100]

[0101] To ensure the stability of the bidirectional single-stage resonant AC-DC converter during operation, the range of resonant capacitor voltage variation is set as follows:

[0102] The range of input AC power is determined. U gm This refers to the amplitude of the power frequency AC voltage.

[0103] The falling edge of the PWM drive signal of the first AC side lower switch Q2 lags behind the rising edge of the PWM drive signal of the DC side upper switch S1, and the lag time is the duration of the resonant current.

[0104] The falling edge of the PWM drive signal of the first AC side upper switch Q1 lags behind the rising edge of the PWM drive signal of the DC side lower switch S2, and the lag time is the duration of the resonant current.

[0105] When one switch in the same bridge arm of the AC side circuit is turned off, the resonant current flows through the magnetizing inductor, and the anti-parallel diode of the other switch turns on in advance, achieving zero-voltage turn-on.

[0106] Figure 2 The PWM drive waveform in the forward power transfer mode from the AC side circuit to the DC side circuit, and the current i flowing through the input inductor. g and resonant inductor L r The resonant current i Lr .

[0107] In operating mode one, the bidirectional single-stage resonant AC-DC converter exhibits the following mode patterns during half a PWM control cycle (t0~t5): Figure 2 As shown.

[0108] like Figure 2Description, Mode 1 [t0, t1]: At time t0, switches S2, Q1, and Q4 are turned on, and inductor L... r The resonant current i Lr The following expression exists:

[0109]

[0110]

[0111] Resonant impedance

[0112] Within half a switching cycle, the DC-side switch conduction time t1-t0=T s D b .

[0113] like Figure 2 Description, Mode 2 [t1, t2]: At time t1, switch S1 is off, switches Q1 and Q4 remain on, and inductor L... r The resonant current i Lr The following expression exists:

[0114]

[0115] Duration of resonant current:

[0116] like Figure 2 Description, Mode 3 [t2, t3]: At time t2, switch Q1 is turned off, where Q1 is turned off with near-zero current.

[0117] like Figure 2 Description, Mode 4 [t3, t4]: At time t3, switches Q2 and Q4 are turned on, with Q2 turning on at zero voltage. The current flowing through Q2 and Q4 is the magnetizing current i. Lm .

[0118] like Figure 2 Description, Mode 5 [t4, t5]: At time t4, switch Q4 is turned off, where Q4 is turned off with near-zero current.

[0119] II. Working Mode Two

[0120] In this embodiment, the operating mode includes operating mode two, which involves the reverse transmission of power from the DC-side circuit to the AC-side circuit.

[0121] In working mode two, U s ≥2*nU p =4*nU g .

[0122] The optimized modulation scheme corresponding to working mode two is as follows:

[0123] The upper switch Q5 and the lower switch Q6 of the totem pole are connected to the AC power supply U. g Switched at 50Hz power frequency;

[0124] The first AC side upper switch Q1 and the first AC side lower switch Q2 connected in series, and the second AC side upper switch Q3 and the second AC side lower switch Q4 connected in series, are mutually complementary and conduct with a 50% duty cycle.

[0125] By using phase shifting, the rising edge of the PWM drive signal of the second AC side lower switch Q4 is aligned with the rising edge of the PWM drive signal of the DC side upper switch S1, and the rising edge of the PWM drive signal of the second AC side upper switch Q3 is aligned with the rising edge of the PWM drive signal of the DC side lower switch S2.

[0126] The duty cycles of the PWM drive signals of the DC-side upper switch S1 and the DC-side lower switch S2 are equal and less than 0.5;

[0127] The DC-side upper switch S1 and the DC-side lower switch S2 adopt variable pulse width modulation, and the pulse width varies with the output AC power and the power frequency AC voltage.

[0128] Specifically, in work mode two:

[0129] The formula for calculating the transmission power of a resonant circuit is:

[0130]

[0131] U p =2U g ;

[0132] In the formula: T s For the switching cycle, D is the resonant angular frequency. f This refers to the duty cycle of the DC-side switching transistor.

[0133] To ensure open-loop PFC is achieved, the power frequency AC voltage is out of phase with the input current, and the expression for the output AC power is:

[0134]

[0135] By precisely controlling the resonant circuit in each switching cycle using a variable pulse width modulation strategy, the transmitted power equals the output AC power.

[0136] P S =-P PFC ;

[0137] The expression for the pulse width as a function of output AC power and power frequency AC voltage:

[0138]

[0139] To ensure the stability of the bidirectional single-stage resonant AC-DC converter during operation, the range of resonant capacitor voltage variation is set as follows:

[0140] The range of output AC power variation is determined as follows: U gm This refers to the amplitude of the power frequency AC voltage.

[0141] The falling edge of the PWM drive signal of the first AC side upper switch Q1 lags behind the rising edge of the PWM drive signal of the DC side upper switch S1, and the lag time is the duration of the resonant current.

[0142] The falling edge of the PWM drive signal of the first AC side lower switch Q2 lags behind the rising edge of the PWM drive signal of the DC side lower switch S2, and the lag time is the duration of the resonant current.

[0143] When one switch in the same bridge arm of the AC side circuit is turned off, the resonant current flows through the magnetizing inductor, and the anti-parallel diode of the other switch turns on in advance, achieving zero-voltage turn-on.

[0144] Figure 3 The PWM drive waveform and the current i flowing through the input inductor in the reverse power transmission mode from the DC side circuit to the AC side circuit. g and resonant inductor L r The resonant current i Lr .

[0145] In operating mode two, the bidirectional single-stage resonant AC-DC converter exhibits the following mode patterns during half a PWM control cycle (t0~t5): Figure 3 As shown.

[0146] like Figure 3 Description, Mode 1 [t0, t1]: At time t0, switches S1, Q1, and Q4 are turned on, and inductor L... r The resonant current i Lr The following expression exists:

[0147]

[0148] Resonant impedance

[0149] Within half a switching cycle, the DC-side switch conduction time t1-t0=T s D f .

[0150] like Figure 3Description, Mode 2 [t1, t2]: At time t1, switches Q1 and Q4 remain on, switch S1 is off, and inductor L... r The resonant current i Lr The following expression exists:

[0151]

[0152] Duration of resonant current:

[0153] like Figure 3 Description, Mode 3 [t2, t3]: At time t2, switch Q1 is turned off, where Q1 is turned off with near-zero current.

[0154] like Figure 3 Description, Mode 4 [t3, t4]: At time t3, switches Q2 and Q4 are turned on, with Q2 turning on at zero voltage. The current flowing through Q2 and Q4 is the magnetizing current i. Lm .

[0155] like Figure 3 Description, Mode 5 [t4, t5]: At time t4, switch Q4 is turned off, where Q4 is turned off with near-zero current.

[0156] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A modulation method for a bidirectional single-stage resonant AC-DC converter, characterized in that: Implementation based on a bidirectional single-stage resonant AC-DC converter, including: S1: Construct the corresponding operating mode based on the power transmission direction between the AC side circuit and the DC side circuit of the bidirectional single-stage resonant AC-DC converter; S2: Based on the equivalent circuit of the bidirectional single-stage resonant AC-DC converter, an optimized modulation scheme is generated for the working mode; S3: Modulate the bidirectional single-stage resonant AC-DC converter based on the optimized modulation scheme to enable it to enter the corresponding working mode, and at the same time use the excitation current flowing through the excitation inductor to realize the soft switching of the device. A bidirectional single-stage resonant AC-DC converter includes: an AC side circuit, located at the AC side power supply U. g The AC side includes a half-bridge and an H-bridge connected in parallel with the half-bridge; the half-bridge consists of a series-connected totem-pole upper switch Q5 and a series-connected totem-pole lower switch Q6; the H-bridge consists of a series-connected first AC-side upper switch Q1 and a first AC-side lower switch Q2, connected in parallel with a series-connected second AC-side upper switch Q3 and a second AC-side lower switch Q4; the DC-side circuit is located at the DC-side power supply U. s The DC side includes a half-bridge consisting of a DC-side upper switch S1 and a DC-side lower switch S2 connected in series; a transformer is connected between the AC-side circuit and the DC-side circuit; the transformer's magnetizing inductance is L. m A resonant circuit, connected between the DC-side circuit and the transformer, includes a resonant inductor L connected in series with the transformer. r And the resonant capacitor C connected in parallel with the half-bridge of the DC-side circuit. r Resonant capacitor C r Including the resonant capacitor C in series r1 and C r2 ; The operating modes include operating mode one, which involves the forward transfer of power from the AC side circuit to the DC side circuit; The optimized modulation scheme corresponding to operating mode one is: The upper switch Q5 and the lower switch Q6 of the totem pole are connected to the AC power supply U. g Switched at 50Hz power frequency; The first AC side upper switch Q1 and the first AC side lower switch Q2 connected in series, and the second AC side upper switch Q3 and the second AC side lower switch Q4 connected in series, are mutually complementary and conduct with a 50% duty cycle. By using phase shifting, the rising edge of the PWM drive signal of the second AC side upper switch Q3 is aligned with the rising edge of the PWM drive signal of the DC side upper switch S1, and the rising edge of the PWM drive signal of the second AC side lower switch Q4 is aligned with the rising edge of the PWM drive signal of the DC side lower switch S2. The duty cycles of the PWM drive signals of the DC-side upper switch S1 and the DC-side lower switch S2 are equal and less than 0.5; The DC-side upper switch S1 and the DC-side lower switch S2 adopt variable pulse width modulation, and the pulse width varies with the input AC power and the power frequency AC voltage.

2. The modulation method for a bidirectional single-stage resonant AC-DC converter as described in claim 1, characterized in that: In the optimized modulation scheme of operating mode one, the formula for calculating the transmission power of the resonant circuit is: And p =2U g ; In the formula: T s For switching cycles; D is the resonant angular frequency; b This refers to the duty cycle of the DC-side switching transistor. U gm This refers to the amplitude of the power frequency AC voltage; The falling edge of the PWM drive signal of the first AC side lower switch Q2 lags behind the rising edge of the PWM drive signal of the DC side upper switch S1, and the lag time is the duration of the resonant current. The falling edge of the PWM drive signal of the first AC side upper switch Q1 lags behind the rising edge of the PWM drive signal of the DC side lower switch S2, and the lag time is the duration of the resonant current. When one switch in the same bridge arm of the AC side circuit is turned off, the resonant current flows through the magnetizing inductor, and the anti-parallel diode of the other switch turns on in advance, achieving zero-voltage turn-on.

3. The modulation method for a bidirectional single-stage resonant AC-DC converter as described in claim 1, characterized in that: In step S1, the operating mode includes operating mode two, which involves the reverse transmission of power from the DC side circuit to the AC side circuit.

4. The modulation method for a bidirectional single-stage resonant AC-DC converter as described in claim 3, characterized in that: In step S2, the optimized modulation scheme corresponding to working mode two is as follows: The upper switch Q5 and the lower switch Q6 of the totem pole are connected to the AC power supply U. g Switched at 50Hz power frequency; The first AC side upper switch Q1 and the first AC side lower switch Q2 connected in series, and the second AC side upper switch Q3 and the second AC side lower switch Q4 connected in series, are mutually complementary and conduct with a 50% duty cycle. By using phase shifting, the rising edge of the PWM drive signal of the second AC side lower switch Q4 is aligned with the rising edge of the PWM drive signal of the DC side upper switch S1, and the rising edge of the PWM drive signal of the second AC side upper switch Q3 is aligned with the rising edge of the PWM drive signal of the DC side lower switch S2. The duty cycles of the PWM drive signals of the DC-side upper switch S1 and the DC-side lower switch S2 are equal and less than 0.5; The DC-side upper switch S1 and the DC-side lower switch S2 adopt variable pulse width modulation, and the pulse width varies with the output AC power and the power frequency AC voltage.

5. The modulation method for a bidirectional single-stage resonant AC-DC converter as described in claim 4, characterized in that: In the optimized modulation scheme of operating mode two, the formula for calculating the transmission power of the resonant circuit is: And p =2U g ; In the formula: T s For switching cycles; D is the resonant angular frequency; f This refers to the duty cycle of the DC-side switching transistor. U gm This refers to the amplitude of the power frequency AC voltage; The falling edge of the PWM drive signal of the first AC side upper switch Q1 lags behind the rising edge of the PWM drive signal of the DC side upper switch S1, and the lag time is the duration of the resonant current. The falling edge of the PWM drive signal of the first AC side lower switch Q2 lags behind the rising edge of the PWM drive signal of the DC side lower switch S2, and the lag time is the duration of the resonant current. When one switch in the same bridge arm of the AC side circuit is turned off, the resonant current flows through the magnetizing inductor, and the anti-parallel diode of the other switch turns on in advance, achieving zero-voltage turn-on.

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