A single-stage isolated bidirectional ac-dc converter

Abstract

The application relates to the field of power electronic conversion technology and discloses a single-stage isolated bidirectional AC-DC converter. The primary side and the secondary side of the single-stage isolated bidirectional AC-DC converter both adopt full-bridge structures or half-bridge structures, and the primary side is used for PFC rectification and power transmission together with the secondary side; wherein the duty cycle of the switch tube in the full-bridge structure or the half-bridge structure of the primary side changes continuously and regularly with the input AC voltage of the single-stage isolated bidirectional AC-DC converter, so that the average value of the square wave voltage at the bridge arm midpoint of the primary side in a switching cycle is equal to the instantaneous value of the AC voltage, thereby performing PFC rectification on the AC voltage; by controlling the phase shift angle of the switch tube in the secondary side relative to the switch tube in the primary side, a voltage difference is generated at the two ends of the power transmission inductance in the isolation conversion module between the primary side and the secondary side, so as to drive the current of the primary side to the secondary side and perform power transmission. The number of switch tubes is small, and the control strategy is simple.

Description

Technical Field

[0001] This invention relates to the field of power electronic conversion technology, and in particular to a single-stage isolated bidirectional AC / DC converter. Background Technology

[0002] Currently, AC / DC converters that combine AC-side power factor correction (PFC) and DC-side wide-range voltage regulation are facing increasingly stringent requirements in fields such as on-board chargers for new energy vehicles and distributed energy storage microgrids. The performance of such converters not only directly determines the overall efficiency of system energy conversion but also directly affects the power quality on the grid side and the battery lifespan. Traditional two-stage isolated AC / DC converters, due to the independence of the PFC and DC / DC stages, suffer from problems such as a large number of switching components, large size, and reliance on a large DC bus capacitor. To improve power density and extend system lifespan, single-stage AC / DC converters have become a key research direction in recent years.

[0003] In the research of single-stage AC / DC converters, existing schemes employ a single-stage isolated AC / DC converter that reuses the arms of a totem-pole bridgeless power-controlled converter (PFC) and a dual-active bridge (DAB). This scheme multiplexes the high-frequency arm of the totem-pole PFC with the first arm of the DAB primary side in its topology. Its main circuit includes two power-frequency inverting switches and eight high-frequency switches (a total of ten switches). In terms of control strategy, this scheme forces the multiplexed primary-side arms to operate at a constant 0.5 duty cycle. To achieve power factor correction at a 0.5 duty cycle, it relies on real-time modulation of the phase shift angle between the primary and secondary bridges and the phase shift angle within the secondary bridge. Another solution uses a matrix bridge arm topology to realize a single-stage AC / DC. The primary side uses four sets of anti-series switches (a total of 12 switches) to realize the conduction of the positive and negative regions of the sinusoidal voltage. In terms of control strategy, the primary side bridge arm is fixed with a duty cycle of 0.5 to obtain a two-level square wave. The secondary side relies on the variable duty cycle combined with single-sided extended phase-shift modulation to realize PFC and power transmission.

[0004] However, the aforementioned single-stage AC / DC converter topologies contain a large number of switches. Whether it's the totem-pole multiplexed architecture with 10 switches or the matrix switching architecture with 12 switches, a significant number of switches are retained, resulting in high hardware redundancy and cost. Furthermore, the excessive number of switching devices severely restricts further improvements in system power density and reliability. Simultaneously, the control algorithms employing real-time calculation of intra-bridge and inter-bridge phase shift angles are extremely complex, placing a heavy computational burden on the system and leading to control instability issues during load transitions or grid disturbances. Summary of the Invention

[0005] The purpose of this invention is to provide a single-stage isolated bidirectional AC / DC converter that can solve the problems of a large number of switching transistors and complex control strategies in existing single-stage AC / DC converters.

[0006] To solve the above technical problems, the present invention provides a single-stage isolated bidirectional AC / DC converter. The primary and secondary sides of the single-stage isolated bidirectional AC / DC converter both adopt a full-bridge structure or a half-bridge structure, and the primary side is used for PFC rectification and power transmission together with the secondary side. In the primary side, the duty cycle of the switching transistor in the full-bridge or half-bridge structure changes continuously with the AC voltage of the input single-stage isolated bidirectional AC-DC converter, so that a square wave voltage with an average value equal to the instantaneous value of the AC voltage is obtained at the midpoint of the primary side bridge arm, so as to perform PFC rectification on the AC voltage. By controlling the phase shift angle of the switching transistor in the secondary side relative to the switching transistor in the primary side, a voltage difference is generated across the power transfer inductor in the isolation converter module between the primary and secondary sides, thereby driving the current from the primary side to the secondary side for power transfer.

[0007] Furthermore, the isolation conversion module includes a DC blocking capacitor, which is used to perform volt-second self-balancing of the square wave voltage at the midpoint of the primary side bridge arm using its own charging characteristics.

[0008] Furthermore, the DC blocking capacitor performs volt-second self-balancing on the square wave carrying DC bias output from the primary side using the following formula: ; In the formula, This is the voltage across the DC blocking capacitor. This is the DC input voltage on the primary side. This is the DC output voltage on the secondary side. Duty cycle, This refers to the transformer turns ratio.

[0009] Furthermore, the selection of power transfer inductors and switching transistors in a single-stage isolated bidirectional AC / DC converter is carried out in the following manner: A switching cycle is segmented in the time domain, and within each time domain segment, the voltage on the power transfer inductor is obtained based on the voltage of the DC blocking capacitor and the absolute values ​​of the voltage amplitudes at the primary and secondary bridge ports. Based on Faraday's law of electromagnetic induction, the current increment of the power transmission inductor is calculated according to the voltage across the power transmission inductor. Based on the ampere-second balance law of inductor current under steady state, the transient current of each section node is solved according to the current increment of the power transmission inductor, and the average active power is calculated by integrating the product of instantaneous voltage and instantaneous current over time. The design boundaries of the power transfer inductor and the switching transistor are determined based on the transient current and average active power for selection.

[0010] Furthermore, the duty cycle of the switching transistor in the primary side varies continuously with the AC voltage according to the following formula: ; In the formula, for t The duty cycle of the switching transistor at any given time. V ac This is the effective value of the input AC voltage. V Cbus This is the intermediate DC bus voltage. ω is the angular frequency.

[0011] Furthermore, the control method for the single-stage isolated bidirectional AC / DC converter is as follows: S1. Set the reference values ​​for the DC bus voltage and output voltage of the single-stage isolated bidirectional AC / DC converter; S2. Collect the bus voltage, input voltage, output voltage, and input current of the current single-stage isolated bidirectional AC / DC converter; S3. The difference between the DC bus voltage reference value and the currently acquired bus voltage is passed through a PI regulator as the output of the voltage outer loop. The currently acquired input voltage is then passed through a phase-locked loop and multiplied with the output of the voltage outer loop. The multiplication result is then passed through a PI regulator as the output of the current inner loop. The duty cycle signal is obtained through the input voltage feedforward circuit. S4. The difference between the output voltage reference value and the currently acquired output voltage is used to obtain a phase-shifted modulation signal through a PI regulator. S5. Drive the switching transistors in the secondary side using the obtained duty cycle signal and phase shift modulation signal, and drive the switching transistors in the primary side using the duty cycle signal and the phase shift modulation signal with a fixed phase shift angle of 0, so as to control the single-stage isolated bidirectional AC / DC converter.

[0012] Furthermore, the isolation transformation module adopts a DAB structure, a CLLC structure, or an LLC structure.

[0013] The single-stage isolated bidirectional AC / DC converter provided by this invention has at least the following advantages: The improved AC / DC converter of this invention adopts a full-bridge or half-bridge configuration for both the primary and secondary sides. The primary side participates in rectification and power factor correction (PFC rectification) and works with the secondary side to achieve power transmission. By reusing the primary side bridge arms, the independent power frequency inversion bridge arm or rectifier bridge arm is completely eliminated from the physical topology. Single-stage isolated bidirectional conversion is achieved with the minimum number of switches (4 primary side + 4 / 2 secondary side). Compared with the existing 10 / 12-switch scheme, more than 2 switches are saved, thereby reducing switching losses, reducing converter size and hardware cost, and improving power density.

[0014] The specific control strategy for PFC rectification and power transfer is as follows: By making the duty cycle of the primary-side switch change continuously and sinusoidally with the input AC voltage, a square wave voltage with an average value equal to the instantaneous value of the input AC voltage is obtained at the midpoint of the primary-side bridge arm over one switching cycle, thereby achieving PFC rectification and simultaneously maintaining voltage regulation on the input side. Under the aforementioned variable duty cycle, by controlling the phase shift angle of the secondary-side switch relative to the primary-side switch, a voltage difference is generated across the power transfer inductor in the isolation converter module, thereby driving a high-frequency current to transfer power to the secondary side, achieving power transfer. This variable duty cycle and phase shift control method achieves PFC rectification and power transfer without complex phase shift calculations, reducing algorithm complexity and chip computing power burden, and significantly improving control stability under load jumps and grid disturbances. Attached Figure Description

[0015] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0016] Figure 1 The present invention provides an overall circuit topology diagram of a single-stage isolated bidirectional AC / DC converter; Figure 2 A circuit topology diagram using DAB as an example is provided for this invention; Figure 3 A circuit control block diagram provided by the present invention; Figure 4 This invention provides a waveform diagram of bridge port voltage duty cycle variation within a power frequency cycle; Figure 5 This invention provides a waveform diagram of inductor current operation with different switching cycles at power frequency. Figure 6 This invention provides a "variable duty cycle + phase shift" control block diagram using DAB as an example. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0018] The technical solutions provided by the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0019] One embodiment of the present invention relates to a single-stage isolated bidirectional AC / DC converter, wherein both the primary and secondary sides of the single-stage isolated bidirectional AC / DC converter adopt a full-bridge structure or a half-bridge structure, and the primary side is used for PFC rectification and power transmission together with the secondary side; In the primary side, the duty cycle of the switching transistor in the full-bridge or half-bridge structure changes continuously with the AC voltage of the input single-stage isolated bidirectional AC-DC converter, so that a square wave voltage with an average value equal to the instantaneous value of the AC voltage is obtained at the midpoint of the primary side bridge arm, so as to perform PFC rectification on the AC voltage. By controlling the phase shift angle of the switching transistor in the secondary side relative to the switching transistor in the primary side, a voltage difference is generated across the power transfer inductor in the isolation converter module between the primary and secondary sides, thereby driving the current from the primary side to the secondary side for power transfer.

[0020] The implementation details of the single-stage isolated bidirectional AC / DC converter in this embodiment are described below. The following content is only for the convenience of understanding and is not necessary for implementing this solution.

[0021] The specific topology of the single-stage isolated bidirectional AC / DC converter in this embodiment can be as follows: Figure 1 As shown, the main circuit consists of four parts: an AC input interface and filtering module, a primary-side high-frequency multiplexed full-bridge, a high-frequency isolation converter stage (isolation converter module), a secondary-side high-frequency full-bridge, and an output side. The AC input interface and filtering module includes an input-side filter inductor. L in The primary-side high-frequency multiplexed full-bridge includes a primary-side supporting capacitor. C bus Primary-side full-bridge switch tube S 1~ S 4 and its anti-parallel diodes; secondary-side high-frequency full-bridge and output side including secondary-side full-bridge switching transistors. S 5~ S 8 and its anti-parallel diode, output-side support capacitor C oThe intermediate isolation transform stage can adopt structures such as DAB, CLLC, and LLC. For distinction, C b It is a DC blocking capacitor. C r It is a resonant capacitor. L 1 For power transfer inductors, L m For transformer magnetizing inductance, L r For resonant inductance ( L 1r , L 2r (This is a primary-secondary resonant inductor of a CLLC structure).

[0022] For ease of explanation, this embodiment uses the DAB isolation converter stage structure as an example for analysis. The overall circuit topology is as follows: Figure 2 As shown, the isolation converter stage circuit includes a DC blocking capacitor. C b High-frequency transformer T, power transmission inductor L 1. The transformer turns ratio is set to minimize the return power. V Cbus : U o , V Cbus for C bus Voltage at both ends.

[0023] In the specific implementation, the control block diagram of the AC / DC core solution in this embodiment is as follows: Figure 3 As shown, a dual-loop control is used to obtain the duty cycle signal, thereby achieving variable duty cycle, while a single-loop control obtains the phase-shift modulation signal. Based on the aforementioned isolation converter stage structure of DAB, the circuit topology employs "variable duty cycle + phase shift" modulation, multiplexing the PFC full-bridge switches with the DAB primary-side switches. The circuit contains four bridge arms, with the upper and lower switches of each arm conducting complementaryly. The primary and secondary sides of the full bridge simultaneously exhibit bipolar variable duty cycle modulation, as shown... Figure 4 As shown, the duty cycle of the primary and secondary full-bridge circuits within one power frequency cycle is... To achieve AC-side PFC by varying the input voltage sinusoidally. V Cbus Stable, phase-shift modulation between the primary and secondary bridges is used to achieve stable output voltage. (Settings are missing from the original text.) This is the phase shift angle.

[0024] To implement the aforementioned PFC function at the mathematical control level, a mapping logic between the duty cycle and the grid input voltage must be established. This is achieved by utilizing the input AC voltage under bipolar modulation and the average voltage at the primary bridge port. Solving duty cycle for time-domain relationships The expression, due to the switching frequency Much greater than the power frequency Within a single switching cycle Can be seen as Instantaneous value, i.e., within a single switching cycle It can be assumed to be a constant value. This is the voltage at the primary bridge port. This is the voltage at the secondary bridge port. for Average voltage over a single switching cycle:

[0025] (1); For AC input voltage, since Solving for the duty cycle yields the expression: (2); Therefore, the duty cycle of the switching transistor in the primary side changes continuously and sinusoidally with the AC voltage according to the above formula.

[0026] Because the duty cycle varies with the sine wave and is asymmetrical when deviating from the zero-crossing point of the input voltage, the square wave output by the primary side bridge arm has a DC bias within a single cycle, leading to magnetic saturation of the high-frequency transformer. This invention addresses this by using a series DC blocking capacitor. C b The volt-second balance is achieved, and the specific derivation is as follows: (3); Solving for the results That is, the DC blocking capacitor performs volt-second self-balancing on the square wave with DC bias output from the primary side based on this formula.

[0027] in, For the switching cycle, This is the primary-side DC input voltage. The secondary side DC output voltage is provided by this mechanism, which ensures that the high-frequency transformer will not experience magnetic saturation even under asymmetrical duty cycle conditions.

[0028] After clarifying the DC bias principle, it is necessary to further analyze the power transfer capability of this structure at various transient points in the power grid cycle to provide calculation criteria for actual system hardware design. Since the intermediate isolation converter stage is a DAB, the derivation methods for its power transfer and inductor current expressions are also based on the DAB structure. For example... Figure 5 The figures show the inductor current waveforms near the zero-crossing point and near the positive peak value within one power frequency cycle. (a) shows the inductor current waveform near the zero-crossing point during the switching cycle, and (b) shows the inductor current waveform near the positive peak value during the switching cycle. The magnitude of the voltage superimposed on the primary and secondary sides of the auxiliary inductor in DAB is due to the asymmetrical duty cycle. After the zero-crossing point, the superimposed waveform of the inductor voltage shifts, and the inductor current loses its symmetrical characteristics. The same applies near the negative peak.

[0029] Specifically, the single switching cycle is segmented in the time domain. Within each time domain segment, the voltage across the power transfer inductor is obtained based on the voltage of the DC blocking capacitor and the absolute values ​​of the voltage amplitudes at the primary and secondary bridge ports. Based on Faraday's law of electromagnetic induction, the current increment of the power transfer inductor is calculated based on the voltage across it. Based on the ampere-second balance law of inductor current under steady state, the transient current at each node is calculated based on the current increment of the power transfer inductor. The average active power is calculated by integrating the product of the instantaneous voltage and the instantaneous current over time. The design boundaries of the power transfer inductor and the switching transistor are determined based on the transient current and the average active power for selection.

[0030] In practical implementation, to accurately solve the true current stress under this asymmetric duty cycle configuration, it is necessary to perform time-domain segmented calculations for a single switching cycle. Let... and ( The transmission power inductor voltage is calculated using formula (3) and the inductor voltage formula. The expression:

[0031] (4); in, , Given the absolute value of the voltage amplitude at the primary and secondary bridge ports, Faraday's law of electromagnetic induction is used to calculate the current increment in each segment during the switching cycle. : (5); To achieve stress control of the switching transistor, according to the ampere-second balance law... That is, the current at the start and end of the cycle is equal in steady state. The current node expression is obtained for a single switching cycle: (6); After obtaining the precise transient current, the average active power is calculated by integrating the product of the instantaneous voltage and current over time. The integral equation for transmission power is as follows: The expression for the transmitted power is obtained by integrating the integral equation piecewise over the switching period:

[0032] (7); The power of the converter is set according to the derived power expression. At the same time, the current stress expression of the switching tube is combined to provide an accurate analytical boundary for the high-frequency inductor design and switching device selection under bias conditions, preventing blind over-design and core saturation risks.

[0033] Furthermore, the control method for the single-stage isolated bidirectional AC / DC converter in this embodiment is as follows: Step 1: As Figure 6 The control block diagram sets the converter output voltage reference value and the DC bus voltage reference value respectively. and .

[0034] Step 2: Obtain the current converter bus voltage through sampling. Input voltage Output voltage Input current .

[0035] Step 3: Use the reference values ​​obtained in Step 1 With step two, sample the transmission bus voltage. The difference is calculated, and the voltage is used as an outer loop through a PI regulator before sampling the input voltage. After passing through a phase-locked loop, the voltage output is multiplied by the outer voltage loop output. The multiplication result is then multiplied by the sampled input current. The difference is calculated, and the current is passed through a PI regulator as the inner current loop, then through the input voltage. The feedforward circuit obtains the duty cycle signal.

[0036] Step 4: Use the reference values ​​obtained in Step 1 With sampling output voltage The difference is calculated, and the signal is converted into a phase-shifted modulation signal by a PI regulator.

[0037] Step 5: Input the duty cycle signal and phase-shift modulation signal obtained in Step 3 and Step 4 into the phase-shift PWM module to generate S5~S8 switch drive signals. Input the duty cycle signal and the fixed value 0 into the phase-shift PWM module to generate S1~S4 switch drive signals, thereby realizing PFC and output voltage stabilization.

[0038] In summary, addressing the shortcomings of existing solutions, this invention proposes a novel single-stage isolated bidirectional AC / DC converter structure based on bridge arm multiplexing. Unlike existing technologies that retain independent rectifier bridge arms (cascading PFC with DC / DC converters or incomplete switch multiplexing) and matrix bridge arm solutions, this solution abandons independent power frequency inverting bridge arms or rectifier bridge arms and complex matrix structures. It aims to achieve both isolated bidirectional performance while significantly reducing the number of switches and utilizing variable duty cycle modulation to achieve AC / DC conversion at low cost and high efficiency. Physically, the primary side employs a full-bridge four-switch configuration, while the secondary side uses either a full-bridge or half-bridge configuration depending on requirements. The four switches on the AC input side participate in rectification and power factor correction, and also form a phase-shifting control mechanism with the secondary full-bridge to achieve power transfer, minimizing the number of switches. The intermediate isolation conversion stage can adopt structures such as LLC, CLLC, or DAB to form a single-stage isolated AC / DC converter. Furthermore, through "variable duty cycle + phase shifting" control, AC-side power factor correction and DC-side voltage regulation functions are achieved, reducing control complexity. Finally, to verify the safe operation capability of this new structure under complex working conditions and to provide a basis for design selection, the principle analysis and derivation of the high-frequency quasi-steady-state method were carried out.

[0039] This invention achieves a continuous sinusoidal variation of the duty cycle of the primary-side full-bridge under dual closed-loop voltage and current control, resulting in a square wave voltage at the midpoint of the primary-side bridge arm where the average value of the switching cycle is equal to the instantaneous value of the AC voltage. This low-frequency average voltage, together with the grid voltage, acts on the input filter inductor Lin, achieving sinusoidal input current and grid-side power factor correction (PFC) from a physical mechanism, while maintaining Cbus voltage regulation. Furthermore, by maintaining the aforementioned variable duty cycle, the high-frequency switch output of the primary-side bridge arm carries a DC-biased square wave. This is self-balancing in volt-seconds by introducing a DC blocking capacitor Cb, and by utilizing the phase shift angle between the primary and secondary full-bridge sides, a high-frequency voltage difference is generated across the transformer auxiliary inductor, thereby driving a high-frequency current to transfer power to the secondary side. The synchronous combination of phase-shift modulation and PWM variable duty cycle modulation enables full-bridge four-switch multiplexing on the AC input side. The primary side participates in rectification and power factor correction, and also forms a phase-shift control mode with the secondary full-bridge. From a physical topology perspective, it completely eliminates independent power frequency inverting bridge arms or rectifier bridge arms, eliminating two switching transistors to minimize the number of switches, significantly reducing converter losses, size, and cost, and improving converter efficiency. Furthermore, it establishes expressions for transmission power and current stress as the basis for converter design and component selection, ensuring safe and stable operation of the multiplexed full-bridge under high load conditions with a simple control algorithm.

[0040] In other words, this invention provides a novel AC / DC converter architecture, such as Figure 1As shown: The AC input side adopts a four-quadrant switch bridge arm multiplexing form, which participates in rectification and power factor correction, and also achieves power transmission together with the secondary full bridge. The intermediate isolation converter stage can adopt LLC, CLLC, DAB and other structures. The secondary side adopts full bridge or half bridge switches as needed to achieve power transmission together with the primary side.

[0041] A novel single-stage AC / DC converter architecture is provided, employing a "variable duty cycle + phase shift" control strategy, such as... Figure 3 As shown: A dual closed-loop control of voltage and current is used to generate the duty cycle signal of the AC-side switching transistor, thereby realizing variable duty cycle control. The outer voltage loop controls the primary side DC bus voltage to stabilize, while the inner current loop controls the primary side PFC. At the same time, a single closed-loop control generates a phase-shift modulation signal to achieve constant current or constant voltage control of the output according to actual needs.

[0042] Those skilled in the art will understand that the above embodiments are specific embodiments for implementing the present invention, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of the embodiments of the present invention. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the embodiments of the present invention; therefore, the scope of protection of the embodiments of the present invention should be determined by the scope defined in the claims.

Claims

1. A single-stage isolated bidirectional AC / DC converter, characterized in that, The primary and secondary sides of the single-stage isolated bidirectional AC / DC converter both adopt a full-bridge or half-bridge structure, and the primary side is used for PFC rectification and power transmission together with the secondary side. In the primary side, the duty cycle of the switching transistor in the full-bridge or half-bridge structure changes continuously with the AC voltage of the input single-stage isolated bidirectional AC-DC converter, so that a square wave voltage with an average value equal to the instantaneous value of the AC voltage is obtained at the midpoint of the primary side bridge arm, so as to perform PFC rectification on the AC voltage. By controlling the phase shift angle of the switching transistor in the secondary side relative to the switching transistor in the primary side, a voltage difference is generated across the power transfer inductor in the isolation converter module between the primary and secondary sides, thereby driving the current from the primary side to the secondary side for power transfer.

2. The single-stage isolated bidirectional AC / DC converter according to claim 1, characterized in that, The isolation conversion module includes a DC blocking capacitor, which is used to perform volt-second self-balancing of the square wave voltage at the midpoint of the primary side bridge arm using its own charging characteristics.

3. The single-stage isolated bidirectional AC / DC converter according to claim 2, characterized in that, The DC blocking capacitor performs volt-second self-balancing on the square wave with DC bias output from the primary side using the following formula: ； In the formula, This is the voltage across the DC blocking capacitor. This is the DC input voltage on the primary side. This is the DC output voltage on the secondary side. Duty cycle, This refers to the transformer turns ratio.

4. The single-stage isolated bidirectional AC / DC converter according to claim 3, characterized in that, The following methods can be used to select the power transfer inductor and switching transistor in a single-stage isolated bidirectional AC / DC converter: A switching cycle is segmented in the time domain, and within each time domain segment, the voltage on the power transfer inductor is obtained based on the voltage of the DC blocking capacitor and the absolute values ​​of the voltage amplitudes at the primary and secondary bridge ports. Based on Faraday's law of electromagnetic induction, the current increment of the power transmission inductor is calculated according to the voltage across the power transmission inductor. Based on the ampere-second balance law of inductor current under steady state, the transient current of each section node is solved according to the current increment of the power transmission inductor, and the average active power is calculated by integrating the product of instantaneous voltage and instantaneous current over time. The design boundaries of the power transfer inductor and the switching transistor are determined based on the transient current and average active power for selection.

5. The single-stage isolated bidirectional AC / DC converter according to claim 1, characterized in that, The duty cycle of the switching transistor in the primary side varies with the AC voltage in a continuous sinusoidal manner according to the following formula: ； In the formula, for t The duty cycle of the switching transistor at any given time. V ac This is the effective value of the input AC voltage. V Cbus This is the intermediate DC bus voltage. ω is the angular frequency.

6. The single-stage isolated bidirectional AC / DC converter according to claim 1, characterized in that, The control method for the single-stage isolated bidirectional AC / DC converter is as follows: S1. Set the reference values ​​for the DC bus voltage and output voltage of the single-stage isolated bidirectional AC / DC converter; S2. Collect the bus voltage, input voltage, output voltage, and input current of the current single-stage isolated bidirectional AC / DC converter; S3. The difference between the DC bus voltage reference value and the currently acquired bus voltage is passed through a PI regulator as the output of the voltage outer loop. The currently acquired input voltage is then passed through a phase-locked loop and multiplied with the output of the voltage outer loop. The multiplication result is then passed through a PI regulator as the output of the current inner loop. The duty cycle signal is obtained through the input voltage feedforward circuit. S4. The difference between the output voltage reference value and the currently acquired output voltage is used to obtain a phase-shifted modulation signal through a PI regulator. S5. Drive the switching transistors in the secondary side using the obtained duty cycle signal and phase shift modulation signal, and drive the switching transistors in the primary side using the duty cycle signal and the phase shift modulation signal with a fixed phase shift angle of 0, so as to control the single-stage isolated bidirectional AC / DC converter.

7. The single-stage isolated bidirectional AC / DC converter according to claim 1, characterized in that, The isolation transformation module adopts a DAB structure, CLLC structure, or LLC structure.

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