Optical storage and charging three-port single-stage bidirectional DC-AC converter and control method thereof

Abstract

This invention relates to power electronic conversion technology, aiming to provide a three-port single-stage bidirectional DC-AC converter with photovoltaic, energy storage, and charging capabilities, and its control method. It includes a public grid interface unit and two DC port power units connected to different DC sources. The former includes a grid-side full-bridge circuit, a power frequency polarity reversal circuit, and a filter circuit, with the output terminal on the public grid side led out from the power frequency polarity reversal circuit. The latter includes an input filter capacitor, a full-bridge circuit, and a high-frequency transformer. The input filter capacitor is connected in parallel across the DC source and the full-bridge circuit, and the output midpoint of the full-bridge circuit is connected to the primary winding of the high-frequency transformer. The secondary windings of the high-frequency transformers in the two DC port power units are connected in parallel, and their common connection point is connected to the midpoint of the bridge arm of the grid-side full-bridge circuit. This invention completely eliminates the intermediate high-voltage DC bus and large-capacity electrolytic capacitor, structurally improving power density and long-term reliability; it can flexibly support various complex operating modes.

Description

Technical Field

[0001] This invention belongs to the field of power electronic conversion technology and relates to a novel three-port single-stage bidirectional DC-AC converter. Background Technology

[0002] With the increasing penetration of renewable energy and the large-scale application of electric vehicles, integrated systems supporting flexible energy interaction between photovoltaics, energy storage, electric vehicles, and the power grid have become an important development direction. In integrated systems such as photovoltaics, energy storage, and electric vehicle charging, there is an urgent need for efficient and highly integrated power conversion interfaces capable of enabling flexible bidirectional energy flow. Traditional solutions often employ multiple independent converters or a two-stage architecture based on a DC bus. While these can achieve basic functions, they suffer from limited system efficiency, low power density, high cost, strong coupling between port controls, insufficient dynamic response, and complex energy coordination management.

[0003] As a key device connecting various DC sources to the AC power grid, multi-port isolated DC-AC converters must simultaneously meet requirements such as bidirectional power control, high power density, high efficiency, electrical isolation, and low cost. Existing solutions mainly include independent two-stage, DC bus-coupled, transformer-coupled, and independent single-stage types. Among them, the independent two-stage structure relies on a high-voltage DC bus and large-capacity capacitors, which limits reliability and power density and seriously affects service life; although the DC bus-coupled type reduces components, it does not fundamentally solve the bus capacitance problem; the transformer-coupled type has a high degree of integration, but it brings challenges such as design complexity, tight port coupling, and difficult control.

[0004] Single-stage DC-AC conversion technology, by integrating isolated DC-DC and AC conversion functions, eliminates the intermediate DC bus, which is beneficial for improving efficiency and power density. However, existing parallel schemes of multiple independent single-stage converters still use a large number of power devices, and the integration and cost need further optimization. Therefore, how to achieve efficient multi-port integration and control decoupling within a single-stage architecture through innovative topology has become a key technical problem.

[0005] The present invention aims to propose a novel multi-port single-stage bidirectional DC-AC converter topology and its control strategy that is highly integrated, efficient and reliable and has completely independent port control capabilities, in order to address the above challenges. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a three-port single-stage bidirectional DC-AC converter for photovoltaic-energy storage-charging integrated systems and its control method.

[0007] To solve the technical problem, the solution of the present invention is:

[0008] A three-port single-stage bidirectional DC-AC converter for photovoltaic energy storage and charging is provided, including a public grid interface unit and two DC port power units, with the DC ports of each DC port power unit connected to different DC sources.

[0009] The public power grid interface unit includes a power grid-side full-bridge circuit, a power frequency polarity reversal circuit, and a filter circuit, with the output terminal of the public power grid side led out from the power frequency polarity reversal circuit.

[0010] The DC port power unit includes an input filter capacitor, a full-bridge circuit, and a high-frequency transformer. The input filter capacitor is connected in parallel across the DC source and the two ends of the full-bridge circuit. The output midpoint of the full-bridge circuit is connected to the primary winding of the high-frequency transformer. The secondary windings of the high-frequency transformers in the two DC port power units are connected in parallel, and their common connection point is connected to the midpoint of the bridge arm of the full-bridge circuit on the grid side.

[0011] As a preferred embodiment of the present invention, the full-bridge circuit in the DC port power unit includes four switching transistors connected in series in pairs to form two bridge arms, and the midpoint of the series connection of the two bridge arms serves as the output midpoint connected to the primary winding of the high-frequency transformer inside the unit.

[0012] As a preferred embodiment of the present invention, the grid-side full-bridge circuit includes four switching transistors connected in series in pairs to form two bridge arms. The midpoint of the series connection of the two bridge arms serves as the input midpoint connected to the common connection point of the secondary windings of the high-frequency transformers in the two DC port power units.

[0013] As a preferred embodiment of the present invention, the power frequency polarity reversal circuit is an H-bridge decoupling circuit composed of four switching transistors, with the midpoint of its two bridge arms serving as the output terminal on the public power grid side.

[0014] As a preferred embodiment of the present invention, the filtering circuit includes a filtering capacitor and a filtering inductor; the former is connected in parallel across the two ends of the full-bridge circuit on the power grid side and the power frequency polarity reversal circuit, and the latter is connected to the output end of the power frequency polarity reversal circuit.

[0015] This invention further provides a control method for the aforementioned three-port single-stage bidirectional DC-AC converter for optical storage and charging. Based on the extended phase-shift principle, two sets of phase-shift angles are introduced, including an internal phase-shift angle that controls the pulse width of the full-bridge output voltage in each DC port power unit, and an external phase-shift angle that adjusts the relative phase between the full-bridge output voltage and the grid-side voltage reference. By independently adjusting the two sets of phase-shift angles, complete decoupling and precise control of the amplitude and direction of the transmitted power at each port are achieved.

[0016] As a preferred embodiment of the present invention, the method specifically includes:

[0017] (1) Generate and adjust three sets of pulse width modulation signals to achieve independent and controllable power transmission; the three sets of pulse width modulation signals include: a first set of signals and a second set of signals used to control the full-bridge circuit in the two DC port power units, and a third set of signals used to control the full-bridge circuit on the grid side.

[0018] (2) By adjusting the width of the corresponding bridge arm drive pulses in the first group of signals and the second group of signals, the first internal phase shift angle α1 and the second internal phase shift angle α2 are generated respectively; by adjusting the relative phase between the first group of signals as a whole and the third group of signals, the first external phase shift angle β1 is generated; by adjusting the relative phase between the second group of signals as a whole and the third group of signals, the second external phase shift angle β2 is generated; by independently adjusting the values ​​of α1, α2, β1, and β2, the amplitude and direction of the power transmitted between the two independent DC sources and the AC grid are independently and precisely controlled.

[0019] In a preferred embodiment of the present invention, when power flows from a DC source to an AC grid, the first external phase shift angle β1 and the second external phase shift angle β2 are positive values, and the first internal phase shift angle α1 and the second internal phase shift angle α2, according to their respective port target output power, follow a sinusoidal law with the grid voltage phase angle θ. g Changes; when power flows from the AC grid to the DC port, the first external phase shift angle β1 and / or the second external phase shift angle β2 are negative, and the first internal phase shift angle α1 and / or the second internal phase shift angle α2 change sinusoidally with the grid voltage phase angle θ according to their respective port target input power. g The change; wherein, the first external phase shift angle β1 and the second external phase shift angle β2 are controlled to constant values ​​during operation.

[0020] The present invention also provides a computing device, comprising: at least one processor, and a memory communicatively connected to the at least one processor, wherein the memory stores instructions that are executed by the at least one processor, the instructions being executed by the at least one processor to cause the at least one processor to perform a control method for the optical storage-charging three-port single-stage bidirectional DC-AC converter.

[0021] The present invention also provides a computer-readable storage medium storing computer instructions for causing the computer to execute a control method for the optical storage and charging three-port single-stage bidirectional DC-AC converter.

[0022] Description of the invention principle:

[0023] 1. In response to the needs of photovoltaic-energy storage-charging systems, existing multi-port DC-AC converters can be mainly classified into the following four types: independently configured two-stage type, DC bus coupled two-stage type, transformer coupled two-stage type, and independently configured single-stage type.

[0024] like Figure 1 The independent two-stage scheme shown equips each DC source with a complete isolated DC-DC converter and a non-isolated DC-AC converter. Although its structure facilitates modular design, its overall efficiency and power density are limited, and it is heavily dependent on the high-voltage DC bus and large-capacity electrolytic capacitors. The latter, as a weak link in the system's reliability, limits the overall service life.

[0025] To simplify the structure, existing technologies have seen the emergence of technologies such as... Figure 2 The DC bus coupling scheme shown retains multiple isolated DC-DC converters on the DC side, while the subsequent stages share a common DC-AC converter. Although this scheme reduces the number of DC-AC stages, it does not eliminate the dependence on the DC bus and its supporting capacitors.

[0026] Another improvement approach is to use a multi-winding transformer to achieve port coupling, such as... Figure 3 As shown. This topology reduces the number of magnetic components by sharing a magnetic core, thus increasing integration, but it also brings problems such as complex transformer design and manufacturing, tight electromagnetic coupling between ports, and increased control difficulty. Figure 4 The single-stage isolated DC-AC converter on display integrates isolated DC-DC conversion and DC-AC inverter functions into a single stage, effectively avoiding the intermediate DC bus stage, thus offering advantages in efficiency and power density. However, if multiple such single-stage converters are directly connected in parallel, the total number of switching devices remains relatively large, and there is still room for improvement in system integration and cost-effectiveness.

[0027] 2. The core circuit topology of the multi-port single-stage DC-AC converter proposed in this invention is as follows: Figure 5 As shown, this topology isolates and transforms the two DC ports through independent high-frequency transformers. After being connected in parallel on the secondary side, they are jointly connected to a reused grid-side power bridge arm and subsequent filtering and grid-connected circuits. This innovative structure achieves single-stage power conversion, fundamentally eliminating the high-voltage DC bus and its large-capacity supporting capacitor in traditional schemes, thereby significantly improving the system's power density and reliability. Simultaneously, by employing an independent control strategy based on extended phase shifting, this topology can achieve complete decoupling and precise control of the power flow at each port while ensuring high efficiency (e.g., achieving zero-voltage switching of the main switching transistors) and high power quality (e.g., achieving unity power factor grid connection), effectively meeting the core requirements of multi-energy systems for flexible energy management.

[0028] 3. The key innovations of this invention are mainly reflected in three aspects:

[0029] Firstly, in terms of topology, by reusing the grid-side bridge arm and coupling the two DC ports to the transformer secondary side via independent transformers, true single-stage power conversion is achieved, significantly reducing the total number of high-frequency power switching devices, magnetic components, and passive components, thus greatly simplifying the system structure. Secondly, in terms of control strategy, a modulation method based on the extended phase-shift principle is proposed and applied. This method achieves complete decoupling and precise control of the amplitude and direction of the transmitted power at each port by introducing two independently adjustable sets of phase-shift angles—internal phase-shift angles (α1, α2) controlling the pulse width of the full-bridge output voltage at each DC port, and external phase-shift angles (β1, β2) adjusting the relative phase between the above voltages and the grid-side voltage reference. Thirdly, in terms of performance optimization, the modulation strategy makes full use of the transformer leakage inductance energy to ensure that all high-frequency main power switching transistors achieve zero-voltage switching over a wide load range, which greatly reduces switching losses. At the same time, by setting the external phase shift angle to a constant value and modulating the internal phase shift angle according to a sine law, a sinusoidal grid-connected current that is strictly in phase with the grid voltage can be automatically generated, achieving unity power factor operation and high power quality.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] 1. This invention proposes an innovative circuit topology and modulation strategy. The converter employs a single-stage power conversion structure, mainly comprising two independent DC ports and one public grid interface. Each DC port is formed by a full-bridge circuit connected in series with the primary winding of an independent high-frequency transformer. The secondary windings of the transformer are connected in parallel and then connected to the full-bridge circuit on the public grid side, before being connected to the AC grid via a power frequency polarity reversal circuit and an LC filter circuit. This topology, through circuit multiplexing, completely eliminates the intermediate high-voltage DC bus and large-capacity electrolytic capacitors, structurally improving power density and long-term reliability.

[0032] 2. Through the synergistic effect of the aforementioned topology and modulation strategy, the converter of this invention can flexibly support a variety of complex operating modes, including but not limited to: simultaneous power supply (discharge) from the grid by two DC ports, simultaneous energy absorption (charging) from the grid, and a hybrid energy dispatch mode where one port is charging while the other port is discharging. Simulation and experimental results show that the converter can achieve precise power control, efficient energy transfer, and high-quality energy conversion in all modes.

[0033] 3. This invention, through its unique single-stage multi-port integrated topology and extended phase-shift modulation strategy, achieves multiple objectives—simplified system structure, increased power density, optimized conversion efficiency, increased control freedom, and reduced overall cost—while ensuring electrical isolation safety and bidirectional power flow capability. This solution provides a core power electronics solution for building next-generation, highly reliable, flexible, and economical photovoltaic-energy storage-charging systems and vehicle-to-grid (V2G) interaction platforms, possessing significant practical value and promising prospects for widespread adoption. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the topology of a three-port DC-AC converter based on an existing independent two-stage scheme.

[0035] Figure 2 This is a schematic diagram of the topology of a three-port DC-AC converter using an existing DC bus coupling scheme.

[0036] Figure 3 This is a schematic diagram of the topology of a three-port DC-AC converter based on an existing multi-winding transformer scheme.

[0037] Figure 4 This is a schematic diagram of the topology of a three-port DC-AC converter with an existing single-stage isolation scheme.

[0038] Figure 5 This is a circuit diagram of a three-port single-stage DC-AC converter in this invention.

[0039] Figure 6 It is the equivalent circuit diagram of the topology proposed in the invention.

[0040] Figure 7 This is the theoretical current waveform of the first DC port power unit in DC-to-AC operating mode.

[0041] Figure 8 This is a schematic diagram of the transient operating phase 1 of the converter circuit.

[0042] Figure 9 This is a schematic diagram of the transient operating stage 2 of the converter circuit.

[0043] Figure 10 This is a schematic diagram of the transient operating stage 3 of the converter circuit.

[0044] Figure 11 This is a schematic diagram of the transient operating stage 4 of the converter circuit.

[0045] Figure 12 This is a schematic diagram of the transient operating stage 5 of the converter circuit.

[0046] Figure 13This is a schematic diagram of the transient operating stage 6 of the converter circuit.

[0047] Figure 14 This is a schematic diagram of the transient operating stage 7 of the converter circuit.

[0048] Figure 15 This is a schematic diagram of the transient operating stage 8 of the converter circuit.

[0049] Figure 16 This is a schematic diagram of the transient operating stage 9 of the converter circuit.

[0050] Figure 17 This is a schematic diagram of the transient operating phase 10 of the converter circuit.

[0051] Figure 18 This is the theoretical current waveform of the first DC port power unit in AC-to-DC operating mode. Detailed Implementation

[0052] To enable those skilled in the art to better understand the technical solutions of the present invention, a description is provided below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the descriptions of orientations in the present invention, such as up, down, front, back, left, and right, are based on the orientations or positional relationships shown in the accompanying drawings and are only for the purpose of facilitating and simplifying the description of the present invention. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the present invention.

[0053] Part 1: Topology of the Converter in this Invention

[0054] Figure 5 The circuit topology of the three-port single-stage bidirectional DC / AC converter proposed in this invention is shown. This converter has two DC ports and one grid connection interface, enabling the integration of various DC sources such as photovoltaics, energy storage, and electric vehicles, and achieving single-stage power conversion and multi-mode interaction with the grid. The specific structure is described below:

[0055] The converter includes a first DC port power unit, a second DC port power unit, a public grid interface unit, and a control unit (not shown in the figure).

[0056] The first DC-DC power unit includes a first full-bridge circuit and a first high-frequency transformer T1. The output midpoint of the first full-bridge circuit is connected to the primary winding of the first high-frequency transformer T1. The first full-bridge circuit consists of a first switch S1, a second switch S2, a third switch S3, and a fourth switch S4, where S1 and S2 are connected in series to form the first bridge arm, and S3 and S4 are connected in series to form the second bridge arm. The second DC-DC power unit includes a second full-bridge circuit and a second high-frequency transformer T2. The output midpoint of the second full-bridge circuit is connected to the primary winding of the second high-frequency transformer T2. The second full-bridge circuit consists of a fifth switch S5, a sixth switch S6, a seventh switch S7, and an eighth switch S8, where S5 and S6 are connected in series to form the third bridge arm, and S7 and S8 are connected in series to form the fourth bridge arm. The midpoint voltages of the first and second full-bridge circuits are denoted as v0 and v1, respectively. p1 or v p2 They are connected to a high-frequency transformer to form an independent port. The turns ratios of high-frequency transformers T1 and T2 are denoted as n1 and n2, respectively, and their leakage inductance is concentrated equivalently to the secondary side, denoted as L. k1 and L k2 Secondary midpoint voltage v s It is clamped by the grid voltage.

[0057] The public power grid interface unit includes a grid-side full-bridge circuit, a power frequency polarity reversal circuit, and a filter circuit. The secondary windings of the first high-frequency transformer T1 and the second high-frequency transformer T2 are connected in parallel, and their common connection point is connected to the midpoint of the bridge arm of the grid-side full-bridge circuit. The output terminal of the grid-side full-bridge circuit is sequentially connected to the power frequency polarity reversal circuit and the filter circuit. Specifically, the grid-side full-bridge circuit consists of a ninth switch S9 and a tenth switch S... 10 Eleventh switch S 11 12th switch S 12 Composition, in which S9 and S 10 The fifth bridge arm is formed by series connection, S 11 With S 12 The fifth and sixth bridge arms are connected in series, and the connection point between them forms the midpoint of the bridge arm. The power frequency polarity reversal circuit uses a decoupling bridge circuit to reverse the grid voltage V. g With current i g The polarity of the circuit is determined by an H-bridge circuit consisting of the thirteenth switch Q1, the fourteenth switch Q2, the fifteenth switch Q3, and the sixteenth switch Q4. Its input is connected to the output of the full-bridge circuit on the power grid side, and the midpoint of its two bridge arms is connected to the input of the filter circuit as the output.

[0058] During the positive half-cycle of the grid voltage, Q1 and Q4 are turned on, while Q2 and Q3 are turned off; during the negative half-cycle of the grid voltage, Q2 and Q3 are turned on, while Q1 and Q4 are turned off. The filter circuit includes a filter capacitor C.f and filter inductor L f The high-frequency component of the bypass current is is used to generate the grid current i. g Filter capacitor C f The filter inductor L is connected in parallel across the full-bridge circuit on the mains side and the power frequency polarity reversal circuit. f Connect it to the output terminal of the power frequency polarity reversal circuit (midpoint between the thirteenth switch Q1 and the fifteenth switch Q3).

[0059] The high-frequency transformer described in this invention refers to an isolation transformer operating at kHz or higher, used for electrical isolation, voltage matching, and bidirectional energy transfer. It is a core electromagnetic component for miniaturizing and increasing the efficiency of converters. High-frequency transformers in bidirectional DC-AC converters typically operate at frequencies ≥10kHz (mostly between 20kHz and 500kHz). This frequency band is much higher than the power frequency and intermediate frequency, which can significantly reduce the core size and increase power density. It also requires the use of low-loss core materials such as ferrite, amorphous, or nanocrystalline materials to control high-frequency losses; therefore, it is defined as the high-frequency transformer described in this invention.

[0060] Part Two: Control Method of the Converter in this Invention

[0061] 1. In this invention, the control unit of the three-port single-stage bidirectional DC / AC converter is configured to execute a bidirectional control strategy based on extended phase shift, generating and adjusting three sets of pulse width modulation signals to achieve independent and precise control of power transmission. Among them: (1) generating a first set of signals for controlling the first full-bridge circuit, a second set of signals for controlling the second full-bridge circuit, and a third set of signals for controlling the grid-side full-bridge circuit; (2) generating a first internal phase shift angle α1 by adjusting the width of the corresponding bridge arm drive pulse in the first set of signals; generating a second internal phase shift angle α2 by adjusting the width of the corresponding bridge arm drive pulse in the second set of signals; generating a first external phase shift angle β1 by adjusting the relative phase between the first set of signals as a whole and the third set of signals; generating a second external phase shift angle β2 by adjusting the relative phase between the second set of signals as a whole and the third set of signals; and achieving independent and precise control of the amplitude and direction of power transmission between the first DC port, the second DC port and the AC grid by independently adjusting the values ​​of α1, α2, β1 and β2.

[0062] When power flows from the DC port to the AC grid, the first external phase shift angle β1 and the second external phase shift angle β2 are positive. The first internal phase shift angle α1 and the second internal phase shift angle α2, based on their respective port target output power, follow a sinusoidal law with the grid voltage phase angle θ. gChanges; when power flows from the AC grid to the DC port, the first external phase shift angle β1 and / or the second external phase shift angle β2 are negative, and the first internal phase shift angle α1 and / or the second internal phase shift angle α2 change sinusoidally with the grid voltage phase angle θ according to their respective port target input power. g The change; wherein, the first external phase shift angle β1 and the second external phase shift angle β2 are controlled to constant values ​​during operation.

[0063] 2. Based on the understanding of those skilled in the art, in order to achieve the above control method, the present invention further proposes:

[0064] A computing device (i.e., a control unit) includes: at least one processor and a memory communicatively connected to the at least one processor, wherein the memory stores instructions that are executed by the at least one processor to cause the at least one processor to perform a control method for the optical storage and charging three-port single-stage bidirectional DC-AC converter.

[0065] A computer-readable storage medium storing computer instructions for causing the computer to execute a control method for a three-port single-stage bidirectional DC-AC converter for optical storage and charging.

[0066] 3. Specific examples of the control method of the present invention

[0067] The following is based on Figure 5 The process of implementing specific control of the three-port single-stage bidirectional DC-AC converter for optical storage and charging shown is described in detail.

[0068] To simplify the analysis, we assume that all components are ideal in steady state and that the converter is lossless, i.e., satisfying V in ×I in =v g ×i g Due to the switching frequency f s Much higher than the power grid frequency f g Assuming the grid voltage v g It is a pure sine wave, and its expression is shown in equation (1).

[0069]

[0070] Among them, V g With θ g These represent the peak value and phase angle of the grid voltage, respectively.

[0071] Figure 6 The equivalent circuit of the proposed three-port converter is shown. It is worth noting that the voltage v... p1 v p2 and v sThe waveform can be controlled independently. Therefore, by adjusting v... p1 and v p2 The internal phase shift angles α1, α2, and v p1 v p2 With v s The external phase shift angles β1 and β2 between them can independently control the current i s1 i s2 and i s .

[0072] To achieve precise control, this invention introduces a modulation strategy based on extended phase shift (EPS). Since each DC port power unit is independent, the following explanation uses the operation of the first DC port power unit as an example.

[0073] Figure 7 This shows the voltage n1×v at the midpoint of the primary side. p1 Secondary midpoint voltage v s and secondary current i s1 The theoretical waveform. Three-level voltage v p1 In V in1 0 and -V in1 Switching between them, with a pulse width of α1T s Two-level voltage v s In |v g |to-|v g The pulses between | have a pulse width of 0.5T. s The phase shift angle β1 is defined as v p1 Pulse center relative to v s The pulse center lead time ratio. In this operating mode, the primary side voltage v p1 The range of variation is located at the secondary voltage v s The range of values ​​for the phase shift angle β1 is within the range of variation. Therefore, the range of values ​​for the phase shift angle β1 is given by the following formula:

[0074]

[0075] Transformer current i s1 The slopes for each time interval can be derived as follows:

[0076]

[0077] Furthermore, the current waveform within half a switching cycle is symmetrical along the t-axis, which means that i s1 (t0) equals -i s1 (t3). i can be obtained. s1 (t0) is:

[0078]

[0079] The average output current i generated by the first DC port power unit g1 is:

[0080]

[0081] where, represents the time constant;

[0082] This equation shows that there is a linear relationship between the control variables α1, β1 and the average output current i g1 Therefore, precise control of the output power can be achieved by adjusting their amplitudes. To simplify the controller structure and obtain a sinusoidal grid-connected current, β1 is designed as a constant value, and the phase-shift angle α1 can be expressed as:

[0083]

[0084] where α 1m represents the peak value of α1.

[0085] The switching frequency f in the equation s is designed as a fixed switching frequency of 50 kHz. By adopting the control law, the power flow of the first DC port power unit and the second DC port power unit can be precisely controlled. Figure 8-17 shows the dynamic process of the converter circuit from t0 to t3, including ten working stages. Among them, Figure 8 is stage 1: at the moment t = t0; Figure 9 is stage 2: in the interval t0 < t < t1 and i s1 > 0; Figure 10 is stage 3: in the interval t0 < t < t1 and i s1 < 0; Figure 11 is stage 4: at the moment t = t1; Figure 12 is stage 5: in the interval t1 < t < t2 and i s1 < 0; Figure 13 is stage 6: in the interval t1 < t < t2 and i s1 > 0; Figure 14 is stage 7: at the moment t = t2; Figure 15 is stage 8: in the interval t2 < t < t3 and i s1 > 0; Figure 16 is stage 9: in the interval t2 < t < t3 and i s1 < 0; Figure 17 is stage 10: at the moment t = t3. In the first stage, the fourth stage, and the seventh stage, all switches S1 - S4 and S9 - S12 achieve zero-voltage switching, thus ensuring the efficient operation of the proposed topology.

[0086] The power transmission working principle of AC - DC is similar to the DC - AC mode, but its voltage vp1 The geometric center will lag behind v s ,like Figure 18 As shown. The negative sign of β1 indicates the lag angle. Therefore, the average input current i of the first DC port power unit. g1 This can be deduced as:

[0087]

[0088] In the formula, i g1 The negative sign to the right of the equals sign in the calculation formula indicates that the power flows from the AC power grid to the first DC port power unit.

[0089] Therefore, bidirectional power control is achieved, and the proposed control strategy enables independent bidirectional power regulation for all ports.

[0090] Finally, it should be noted that the above examples are merely some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A three-port single-stage bidirectional DC-AC converter for optical storage and charging, characterized in that, It includes a public grid interface unit and two DC port power units, with each DC port power unit's DC port connected to a different DC source; The public power grid interface unit includes a power grid-side full-bridge circuit, a power frequency polarity reversal circuit, and a filter circuit, with the output terminal of the public power grid side led out from the power frequency polarity reversal circuit. The DC port power unit includes an input filter capacitor, a full-bridge circuit, and a high-frequency transformer. The input filter capacitor is connected in parallel across the DC source and the two ends of the full-bridge circuit. The output midpoint of the full-bridge circuit is connected to the primary winding of the high-frequency transformer. The secondary windings of the high-frequency transformers in the two DC port power units are connected in parallel, and their common connection point is connected to the midpoint of the bridge arm of the full-bridge circuit on the grid side.

2. The converter according to claim 1, characterized in that, The full-bridge circuit in the DC port power unit includes four switching transistors connected in series in pairs to form two bridge arms. The midpoint of the series connection between the two bridge arms serves as the output midpoint connected to the primary winding of the high-frequency transformer inside the unit.

3. The converter according to claim 1, characterized in that, The grid-side full-bridge circuit includes four switching transistors connected in series in pairs to form two bridge arms. The midpoint of the series connection of the two bridge arms serves as the input midpoint connected to the common connection point of the secondary windings of the high-frequency transformers in the two DC port power units.

4. The converter according to claim 1, characterized in that, The power frequency polarity reversal circuit is an H-bridge decoupling circuit composed of four switching transistors, with the midpoint of its two bridge arms serving as the output terminal on the public power grid side.

5. The converter according to claim 1, characterized in that, The filtering circuit includes a filter capacitor and a filter inductor; the former is connected in parallel across the two ends of the full-bridge circuit on the power grid side and the power frequency polarity reversal circuit, while the latter is connected to the output end of the power frequency polarity reversal circuit.

6. The control method for the three-port single-stage bidirectional DC-AC converter for optical storage and charging according to any one of claims 1 to 5, characterized in that, Based on the extended phase shift principle, two sets of phase shift angles are introduced, including an internal phase shift angle that controls the pulse width of the full-bridge output voltage in each DC port power unit, and an external phase shift angle that adjusts the relative phase between the full-bridge output voltage and the grid-side voltage reference. By independently adjusting the two sets of phase shift angles, complete decoupling and precise control of the amplitude and direction of the power transmitted at each port can be achieved.

7. The method according to claim 6, characterized in that, The method specifically includes: (1) Generate and adjust three sets of pulse width modulation signals to achieve independent and controllable power transmission; the three sets of pulse width modulation signals include: a first set of signals and a second set of signals used to control the full-bridge circuit in the two DC port power units, and a third set of signals used to control the full-bridge circuit on the grid side. (2) By adjusting the width of the corresponding bridge arm drive pulses in the first group of signals and the second group of signals, the first internal phase shift angle α1 and the second internal phase shift angle α2 are generated respectively; by adjusting the relative phase between the first group of signals as a whole and the third group of signals, the first external phase shift angle β1 is generated; by adjusting the relative phase between the second group of signals as a whole and the third group of signals, the second external phase shift angle β2 is generated; by independently adjusting the values ​​of α1, α2, β1, and β2, the amplitude and direction of the power transmitted between the two independent DC sources and the AC grid are independently and precisely controlled.

8. The method according to claim 7, characterized in that, When power flows from a DC source to an AC grid, the first external phase shift angle β1 and the second external phase shift angle β2 are positive. The first internal phase shift angle α1 and the second internal phase shift angle α2, based on their respective port target output power, follow a sinusoidal law with the grid voltage phase angle θ. g Changes; when power flows from the AC grid to the DC port, the first external phase shift angle β1 and / or the second external phase shift angle β2 are negative, and the first internal phase shift angle α1 and / or the second internal phase shift angle α2 change sinusoidally with the grid voltage phase angle θ according to their respective port target input power. g The change; wherein, the first external phase shift angle β1 and the second external phase shift angle β2 are controlled to constant values ​​during operation.

9. A computing device, characterized in that, include: At least one processor and a memory communicatively connected to the at least one processor, wherein the memory stores instructions that are executed by the at least one processor to cause the at least one processor to perform the control method of the optical storage and charging three-port single-stage bidirectional DC-AC converter of claim 6.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions, which are used to cause the computer to execute the control method of the three-port single-stage bidirectional DC-AC converter for optical storage and charging as described in claim 6.

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