A single-stage isolated bidirectional ac-dc converter

Abstract

This invention discloses a single-stage isolated bidirectional AC / DC converter, which consists of a primary-side inverter bridge, a high-frequency transformer, a transmission inductor, a DC blocking capacitor, a secondary-side inverter bridge, a secondary-side DC capacitor, an LC filter, a DC port, and an AC port. The primary-side inverter bridge can be one of a full-bridge, a half-bridge, or an interleaved parallel Boost multiplexed full-bridge; the secondary-side inverter bridge can be one of a full-bridge or a half-bridge. Depending on the different secondary-side inverter bridge topologies and control methods, the LC filter can be one of a single-ended filter circuit consisting of one inductor and one capacitor, or a double-ended filter circuit consisting of two inductors and one capacitor. This invention utilizes the high-frequency AC component in the output waveform of the secondary-side inverter bridge under SPWM control, isolates the low-frequency AC component through capacitors, and uses dual active bridges for power transmission and control.

Description

Technical Field

[0001] This invention relates to the field of power electronics application technology, specifically a single-stage isolated bidirectional AC / DC converter. Background Technology

[0002] In the face of the global energy crisis, the search for efficient, sustainable, and clean new energy sources has become a key theme of international development. Photovoltaic power generation and energy storage batteries all output direct current (DC), requiring DC-AC conversion for grid connection or to power AC appliances. The AC-DC converter plays a crucial role in voltage conversion and power transmission, making it essential for the effective utilization of new energy sources; its performance is paramount. Small-sized, high-efficiency converters can significantly reduce losses and minimize space requirements.

[0003] Traditional converters typically employ a two-stage topology: a boost converter and an inverter. The first stage converts the DC input voltage to approximately 350V DC, while the second stage uses this boosted DC voltage to convert it to 220V AC. In applications requiring isolation, the boost stage often uses a push-pull circuit with a high-frequency transformer. The inverter stage uses a common full-bridge topology with unipolar or bipolar SPWM modulation. Because this type of scheme usually operates unidirectionally, transferring power only from the DC side to the AC side, it is commonly referred to as an inverter. In traditional schemes, both stages are relatively mature solutions, and the independent operation and control of each stage makes control relatively simple and easy to design. However, in two-stage schemes, each stage needs to handle all the transmitted power, requiring the power to undergo two conversions, which reduces the overall efficiency of the converter and increases the number of components, making it difficult to reduce its size.

[0004] To address the aforementioned issues, numerous studies have been conducted on single-stage converter topologies. Among these, high-frequency converter topologies are particularly popular. These topologies utilize bidirectional series-connected switches to form a two-way switch, directly employing SPWM modulation of the AC voltage output from the high-frequency transformer. This approach eliminates the DC link between the boost stage and the inverter stage, removing the DC filter capacitor and significantly reducing size. However, the bidirectional switch structure requires a large number of switching devices, leading to complex control and drive mechanisms and high application costs. Summary of the Invention

[0005] To address the shortcomings mentioned in the technical background, the present invention aims to provide a single-stage isolated bidirectional AC / DC converter. This invention employs a dual active bridge and inverter bridge arm multiplexing topology. By multiplexing the secondary bridge arm of the dual active bridge and the bridge arm of the inverter circuit, the number of components is reduced, and the rectifier bridge loss of the boost stage is eliminated. This topology retains the DC bus filter capacitor, resulting in more constant and controllable voltage stress on the switching devices compared to high-frequency inverter topologies. The dual active bridge provides better wide voltage input performance, adapting to a wider range of applications. Due to the bidirectional power transfer capability of the dual active bridge, this converter can operate in both directions.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A single-stage isolated bidirectional AC / DC converter, wherein the inverter circuit includes a primary-side inverter bridge. M 1. Transmission inductance L t High-frequency transformers Tr DC blocking capacitor C b Secondary side inverter bridge M 2. Secondary DC capacitor C s_dc It consists of an LC filter, a DC port, and an AC port.

[0008] The primary-side inverter bridge M The DC port of port 1 is the DC input port of the converter, the primary-side inverter bridge. M The high-frequency AC port 1 is connected to a high-frequency transformer. Tr Primary side; high-frequency transformer Tr Secondary series transmission inductor L t DC blocking capacitor C b Rear connected to secondary inverter bridge M 2. High-frequency AC ports. Secondary inverter bridge. M The high-frequency AC port of 2 is connected to the high-frequency port of the LC filter, and the low-frequency port of the LC filter constitutes the AC output port of the converter.

[0009] Furthermore, the primary-side inverter bridge M 1 can be one of the following: full-bridge, half-bridge, or staggered parallel Boost multiplexed full-bridge. If... M 1 represents a full-bridge or half-bridge bridge, with its upper and lower arms connected to the positive and negative terminals of the DC input port, respectively, and the high-frequency AC port connected to a high-frequency transformer. Tr The primary winding.

[0010] Furthermore, the interleaved parallel Boost multiplexed full bridge is composed of inductors L boost_1 ,L boost_2 Switching transistor Q 1~ Q 4. Boost output DC filter capacitor C boost Composition. Inductor L boost_1 , L boost_2 One end is connected to the positive input terminal, and the other end is connected to the midpoint of the half-bridge formed by Q1, Q2 or Q3, Q4. The DC port of the half-bridge formed by Q1, Q2 or Q3, Q4 is connected to... C boost The positive and negative poles. Q 1~ Q The high-frequency AC output port of the 4-unit full-bridge is connected to a high-frequency transformer. Tr The primary winding.

[0011] Furthermore, the secondary-side inverter bridge M 2 can be either a full bridge or a half bridge.

[0012] If the secondary inverter bridge M 2. Using a full-bridge topology, the drive signal can be either a unipolar or bipolar SPWM modulation signal; if the secondary-side inverter bridge... M 2. A half-bridge topology is used, and its drive signal adopts bipolar SPWM modulation.

[0013] If the secondary inverter bridge M 2. Using a full-bridge topology with unipolar modulation or a half-bridge topology with bipolar modulation, the corresponding LC filter employs a... L f_1 , C f The single-ended filter is constructed using an inductor. L f_1 Connect the high-frequency bridge arm output of the full bridge or the high-frequency output of the half bridge; if the secondary inverter bridge M 2. Using a full-bridge topology and bipolar modulation, the corresponding LC filter is composed of... L f_1 , L f_2 , C f A two-ended filter is constructed.

[0014] The converter has a secondary inverter bridge M 2. During SPWM modulation, the output waveform contains low-frequency AC and high-frequency pulse components. After passing through an LC filter, the low-frequency AC component is retained as the AC output. Simultaneously, the converter utilizes the high-frequency pulse wave contained in the SPWM modulation waveform for power transfer from the primary side to the secondary side. Due to the secondary-side inverter bridge... M2. The generated waveform contains low-frequency AC components. If a high-frequency transformer is directly connected... Tr The secondary winding will cause the core to saturate, therefore a capacitor is required. C b Isolate low-frequency AC components.

[0015] The secondary-side inverter bridge of the present invention M 2. Traditional SPWM control is adopted, and the low-frequency AC component is retained as the AC output through an LC filter. The output waveform of the secondary inverter bridge under SPWM control contains a large number of high-frequency AC components. The low-frequency AC components are separated by DC blocking capacitors, and the high-frequency pulses are retained for power transmission of the dual active bridge.

[0016] The beneficial effects of this invention are:

[0017] 1. This invention reuses the secondary arm of the dual active bridge and the arm of the inverter circuit, shortening the power transfer link and reducing the number of components.

[0018] 2. This invention employs a design that retains the DC bus capacitor, resulting in more stable voltage and power control. The DC bus capacitor can withstand a certain amount of current ripple, thereby reducing input power fluctuations.

[0019] 3. The secondary-side inverter bridge control employed in this invention can utilize mature SPWM inverter control strategies or PWM rectifier control strategies, reducing design complexity. The control of the secondary-side inverter bridge and the power transmission control of the dual active bridge operate independently, allowing for more effective and precise power and voltage control, which helps reduce the complexity of DC bus voltage control, grid connection control, and other related controls.

[0020] 4. The bridge arm reuse design adopted in this invention retains the voltage and power regulation capabilities of the dual active bridge, and has a stronger wide voltage operating capability compared with the existing single-stage topology.

[0021] 5. The interleaved parallel Boost multiplexed full bridge included in this invention has a boost function, which can effectively reduce the current stress on the primary winding of the transformer in low input voltage applications. In addition, the input current ripple of the interleaved parallel Boost can offset the primary winding current to a certain extent, reducing the current stress on the primary inverter bridge switching devices.

[0022] 6. This invention leverages the characteristics of a dual active bridge, enabling bidirectional power transfer from the primary side to the secondary side or from the secondary side to the primary side, thus meeting the application requirements of AC-DC. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 : A circuit diagram of a single-stage isolated bidirectional AC / DC converter;

[0025] Figure 2 : Secondary side structure diagram using full-bridge topology;

[0026] Figure 3 : Secondary side structure diagram using half-bridge topology;

[0027] Figure 4 A diagram of an interleaved parallel Boost multiplexing full-bridge topology;

[0028] Figure 5 : The main waveform of the secondary side using a full-bridge topology and unipolar modulation;

[0029] Figure 6 : Equivalent duty cycle diagram;

[0030] Figure 7 : Equivalent duty cycle change curve within one cycle;

[0031] Figure 8 The main waveforms of an interleaved parallel Boost multiplexed full bridge;

[0032] Figure 9 : Relationship between equivalent volt-second product and duty cycle of interleaved parallel Boost multiplexed full-bridge single pulse;

[0033] Figure 10 Simulation prototype structure diagram;

[0034] Figure 11 Main waveforms of the prototype with 15V input and 200W output;

[0035] Figure 12 Main waveforms of the prototype with 30V input and 400W output;

[0036] Figure 13 Main waveforms of the prototype with 60V input and 400W output; Detailed Implementation

[0037] 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 embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] In a specific embodiment, such as Figure 1 As shown, a single-stage isolated bidirectional AC / DC converter is described. The converter circuit consists of a primary-side inverter bridge. M 1. Transmission inductance L t High-frequency transformers Tr DC blocking capacitor C b Secondary side inverter bridge M 2. Secondary DC capacitor C s_dc It consists of an LC filter, a DC port, and an AC port.

[0039] The primary-side inverter bridge M 1 can be one of the following: full-bridge, half-bridge, or staggered parallel Boost multiplexed full-bridge. M When 1 is a full-bridge or half-bridge converter, the topology of the secondary side of the converter is as follows: Figure 2 , Figure 3 As shown, the upper and lower ends of its bridge arm are connected to the positive and negative terminals of the DC input port, respectively, and the high-frequency AC port is connected to the high-frequency transformer. Tr The primary winding and LC filter.

[0040] The interleaved parallel Boost multiplexing full-bridge topology is as follows: Figure 4 As shown, by inductor L boost_1 , L boost_2 Switching transistor Q 1~ Q 4. Boost output DC filter capacitor C boost Composition. Inductor L boost_1 , L boost_2 One end is connected to the positive input terminal, and the other end is connected to the midpoint of the half-bridge formed by Q1, Q2 or Q3, Q4. The DC port of the half-bridge formed by Q1, Q2 or Q3, Q4 is connected to... C boost The positive and negative poles. Q 1~ Q The high-frequency AC output port of the 4-unit full-bridge is connected to a high-frequency transformer. Tr The primary winding.

[0041] If the secondary inverter bridge M 2. Using a full-bridge topology, the drive signal can be either a unipolar or bipolar SPWM modulation signal; if the secondary-side inverter bridge... M 2. A half-bridge topology is used, and its drive signal adopts bipolar SPWM modulation.

[0042] If the secondary inverter bridge M 2. Using a full-bridge topology with unipolar modulation or a half-bridge topology with bipolar modulation, the corresponding LC filter employs a... L f_1 , C f The single-ended filter is constructed using an inductor. L f_1 Connect the high-frequency bridge arm output of the full bridge or the high-frequency output of the half bridge; if the secondary inverter bridge M 2. Using a full-bridge topology and bipolar modulation, the corresponding LC filter is composed of... L f_1 , L f_2 , C f A two-ended filter is constructed.

[0043] The output waveform of the secondary inverter bridge under SPWM control contains a large number of high-frequency AC components. (The second part of the text appears to be a fragment and requires further context for accurate translation.) M 2. Taking a full-bridge topology and unipolar modulation as an example, the main waveform on the secondary side during normal operation is as follows: Figure 5 As shown. Among them, v CD The output of the secondary inverter bridge is a unipolar SPWM modulated wave, which, after LC filtering, produces a 50Hz sine wave output voltage. v s for v CD The waveform after passing through the DC blocking capacitor is specifically a pulse wave with a duty cycle that varies periodically with the SPWM control signal, but its average value is 0. Let... V s_dc This is the voltage across the secondary-side full-bridge filter capacitor. v CD , v s The peak voltage within a single cycle is V s_dc .

[0044] For dual active bridge circuits, the volt-second product of the positive and negative pulses of the waveform can be used as one of the criteria for power transfer control. Based on the calculation method for equal volt-second products, such as... Figure 6 As shown, it can be v s The waveform is converted to peak-to-peak value asV s_dc Symmetrical positive and negative pulse voltage waveforms v e . v e The waveform is consistent with the output waveform of the secondary full-bridge when the dual active bridge uses phase shifting within the secondary side. This can be... v e The duty cycle of the waveform is considered as the equivalent duty cycle of the secondary inverter bridge used for dual active bridge power transmission.

[0045] Because the SPWM waveform output by the secondary-side full-bridge directly affects the AC port output voltage, the duty cycle of the secondary-side full-bridge cannot be used to control the power transfer of the dual active bridge. Furthermore, calculated using the single-pulse equivalent volt-second product, the equivalent duty cycle of the secondary-side full-bridge waveform fluctuates significantly within one cycle. When the secondary-side inverter bridge uses a full-bridge topology and unipolar control, the equivalent duty cycle within one cycle... Figure 7 As shown.

[0046] In addition to the internal phase shift on the secondary side, the dual active bridge topology also has two control degrees of freedom for power regulation: internal phase shift on the primary side and external phase shift on both the primary and secondary sides. Although the equivalent duty cycle of the secondary-side inverter bridge fluctuates significantly within a single cycle, the average equivalent duty cycle remains the same across all cycles. If a standard full-bridge topology is used on the primary side, the transmitted power can be adjusted by controlling the duty cycle of the full-bridge drive signal, the internal phase shift of the full-bridge, and the external phase shift of the secondary side relative to the primary side. This closed-loop control maintains the voltage across the secondary-side DC filter capacitor at a set value. Figure 7 As shown, the transmission power of the converter can be controlled by adjusting the outward phase shift angle of the primary and secondary sides.

[0047] When the interleaved parallel Boost multiplexed full-bridge is working normally, the main operating waveforms are as follows: Figure 8 As shown. Let Q 1( Q 3) The duty cycle is D p ,but C boost Voltage at both ends V boost It can be represented as V boost = V in / D p . v AB The high-frequency output port voltage of the interleaved parallel Boost multiplexed full bridge is a positive and negative pulse wave with a peak value of V boost The duty cycle expression is as follows:

[0048] (1)

[0049] Interleaved parallel Boost multiplexed full-bridge bridges can alter their power transfer characteristics by changing the duty cycle, and their voltage adaptability is wider than that of conventional half-bridges and full-bridges. For dual active bridges, the volt-second product of a single pulse of the high-frequency AC voltage output by each bridge arm can be used as a measure of its power transfer capability. D p When varying between 20% and 100%, the normalized value is... v AB The volt-second product of a single pulse of the waveform follows D p The changing curve is as follows Figure 9 As shown.

[0050] Conventional two-stage topologies often employ unidirectional converter topologies in their boost stages, limiting the bidirectional application of AC / DC converters. Dual active bridge topologies, however, possess bidirectional power transfer capabilities. Generally, when the secondary-side drive signal lags behind the primary-side drive signal, power is transferred in the forward direction; when the secondary-side drive signal leads the primary-side drive signal, power is transferred in the reverse direction. If the secondary-side inverter bridge... M By changing the control method of 2 to a PWM rectifier, reverse power transmission can be achieved, meeting the application requirements of AC-DC.

[0051] To verify the feasibility of this converter, a simulator was used for verification. The simulation prototype uses an interleaved parallel Boost multiplexed full-bridge as the primary-side inverter bridge and a half-bridge as the secondary-side inverter bridge, employing bipolar modulation. The circuit is as follows: Figure 10 As shown. The simulated prototype parameters are as follows: rated input voltage 30V, supporting input from 15V to 60V; output voltage 220V 50Hz; rated power 400W; switching frequency 100kHz. The transformer turns ratio is 1:5, the transmission inductance is 200μH, and the DC blocking capacitor is 300nF. In the simulation, the prototype can output 400W at rated input voltages of 30V and 60V, and 200W at an input voltage of 15V. Under different input voltage conditions, the key voltage and current waveforms during stable operation of the converter are as follows. Figure 10 , Figure 11 , Figure 12 As shown, where v AC Indicates the AC output voltage. i s Indicates the secondary current of the transformer. v s Indicates the secondary voltage of the transformer. v CD This represents the voltage after passing through the transmission inductor and before the DC blocking capacitor.

[0052] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0053] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A single-stage isolated bidirectional AC / DC converter, characterized in that, Including primary-side inverter bridge M 1. The primary-side inverter bridge M The DC port of 1 is connected to the input DC port of the converter, and the primary-side inverter bridge M 1. High-frequency AC output connected to high-frequency transformer Tr The primary winding of the high-frequency transformer Tr One end of the secondary winding is connected to the transmission inductor L t DC blocking capacitor C b After being connected in series, the secondary inverter bridge is also connected. M One end of the AC port and one end of the LC filter, and the other end of the secondary winding of the high-frequency transformer Tr are simultaneously connected to the secondary inverter bridge. M The other end of the AC port and the other end of the LC filter, the secondary-side inverter bridge M The DC port of 2 is connected to the secondary DC capacitor. C s_dc The output of the LC filter is connected to an AC port; The secondary inverter bridge M 2. SPWM modulation is used, and its output waveform contains low-frequency AC and high-frequency pulse components. The low-frequency AC component is retained as the AC output through an LC filter; a DC blocking capacitor is used. C b Low-frequency AC components are separated, while high-frequency pulses are retained for power transmission in dual active bridges; this is achieved by modifying the primary-side inverter bridge. M 1 and secondary inverter bridge M The external phase angle between 2 and 3 adjusts the inverter's transmission power.

2. The single-stage isolated bidirectional AC / DC converter according to claim 1, characterized in that, Primary-side inverter bridge M 1 is one of the following: full-bridge, half-bridge, or staggered parallel Boost multiplexed full-bridge; like M 1 represents a full-bridge or half-bridge converter, with its upper and lower arms connected to the DC input ports of the converter, and its high-frequency AC ports connected to the high-frequency transformer. Tr The primary winding; like M 1 is an interleaved parallel Boost multiplexed full-bridge converter, where the Boost input port is connected to the DC input port of the converter, and the high-frequency AC port is connected to the high-frequency transformer. Tr The primary winding.

3. A single-stage isolated bidirectional AC / DC converter according to claim 2, characterized in that, The interleaved parallel Boost multiplexed full bridge is composed of Boost inductors. L boost_1 , L boost_2 Switching transistor Q 1~ Q 4. Boost output DC filter capacitor C boost Composition; Inductance L boost_1 , L boost_2 One end is connected to the positive input terminal, and the other end is connected to the midpoint of the half-bridge formed by Q1, Q2 or Q3, Q4. The DC port of the half-bridge formed by Q1, Q2 or Q3, Q4 is connected to... C boost The positive and negative poles; Q 1~ Q The high-frequency AC output port of the 4-unit full-bridge is connected to a high-frequency transformer. Tr The primary winding.

4. A single-stage isolated bidirectional AC / DC converter according to claim 1, characterized in that, Including secondary side inverter bridge M 2. Secondary-side inverter bridge M 2 is one of the two types: full bridge or half bridge; M 2. When using a full-bridge topology, use either unipolar modulation or bipolar modulation. M 2. When using a half-bridge topology, bipolar modulation is employed.

5. A single-stage isolated bidirectional AC / DC converter according to claim 1, characterized in that, According to the secondary side inverter bridge M The different topologies used in 2, and the corresponding unipolar and bipolar control methods, all indicate that the LC filter consists of an inductor. L f_1 and a capacitor C f A single-ended filter circuit composed of two inductors or L f_1 , L f_1 and a capacitor C f One type of dual-ended filter circuit.

6. A single-stage isolated bidirectional AC / DC converter according to claim 1, characterized in that, Primary-side inverter bridge M 1 and secondary inverter bridge M 2 have the same operating frequency.

7. A single-stage isolated bidirectional AC / DC converter according to claim 1, characterized in that, If the original side inverter bridge M 1. A full-bridge topology is adopted, by changing... M The transmission power of the full-bridge internal phase-shift adjustable converter is 1; if the primary-side inverter bridge M 1. An interleaved parallel Boost multiplexed full bridge is adopted, and the transmission power of the converter is adjusted by changing the duty cycle of the Boost in the bridge arm.

8. A single-stage isolated bidirectional AC / DC converter according to claim 1, characterized in that, The converter is capable of bidirectional power transmission.

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