Current stress optimization method and system for isolated three-phase bidirectional energy storage converter

Abstract

The invention provides a current stress optimization method and system for an isolated bidirectional three-phase energy storage converter, and relates to the technical field of power conversion. Firstly, Fourier series analysis is carried out on primary and secondary side voltages of a high-frequency transformer, and leakage inductance current and active power are calculated accordingly; carrying out per-unit processing on the active power and the square of the primary side current, and obtaining the active power and the square of the peak current under the fundamental component based on a per-unit processing result; then, with the minimum square of the peak current as an optimization target and the transmission power under the fundamental component as a constraint, constructing and solving a current stress optimization model so as to obtain an optimal matrix converter parameter; and finally, performing current stress optimization control based on the optimal parameters to reduce the current stress. According to the method, the current stress is remarkably reduced while the set transmission power requirement is met, the direct current side dynamic response is improved, and the converter performance is improved.

Description

Technical Field

[0001] This invention relates to the technical field of power conversion, and more specifically, to a current stress optimization method and system for isolated three-phase bidirectional energy storage converters. Background Technology

[0002] With the development of technology, human demand for energy is increasing. To reduce environmental pollution during energy acquisition, a low-carbon development model for power systems, combining new energy technologies such as photovoltaic and wind power generation with energy storage technology, is being gradually promoted. Energy storage systems require bidirectional AC-DC converters to achieve grid-connected interaction and bidirectional power regulation. These devices feature controllable grid-side power factor, bidirectional power transmission, high power density, and electrical isolation.

[0003] Traditional three-phase bidirectional isolated AC-DC matrix converters employ a two-stage topology combining three-phase rectification with isolated DC-DC conversion. Due to the need for decoupling capacitors between the two stages, the large size of the power frequency transformer, and the large number of components, the system efficiency is limited. In contrast, single-stage isolated three-phase bidirectional AC-DC matrix converters directly connect to a high-frequency transformer after three-phase rectification, with the subsequent stage controlled by an H-bridge. Compared to traditional three-phase bidirectional isolated AC-DC matrix converters, this eliminates the need for decoupling capacitors, reduces size, and significantly improves power density.

[0004] Regarding the development of converters in terms of current stress optimization, existing technologies introduce LCL resonant cavities into matrix converters. While this optimizes return power during operation, reduces the impact of current stress, and minimizes component damage, high-frequency hard switching losses still lead to significant power loss. Even with various feedback control methods to compensate for the converter's modulation parameters, although system stability is enhanced, load-switching output voltage is stabilized, and unity power factor operation is achieved, hard switching losses remain unresolved, resulting in substantial power loss and inability to guarantee output active power. Furthermore, the relationship between the modulation coefficient and phase shift angle in the modulation parameters is ignored in optimizing current stress, leading to poor optimization results. In addition, traditional control methods adjust only a single variable, making it difficult to effectively reduce current stress. Summary of the Invention

[0005] To address the issues of high transmission power loss and poor optimization effect in current stress optimization methods for converters, this invention proposes a current stress optimization method and system for isolated three-phase bidirectional energy storage converters. Under the premise of ensuring transmission power, the method utilizes the relationship between modulation coefficient and phase shift angle under minimum current stress to significantly reduce current stress, improve DC-side dynamic response, and enhance converter performance.

[0006] To achieve the above-mentioned technical effects, the technical solution of the present invention is as follows: In a first aspect, this application proposes a current stress optimization method for an isolated bidirectional three-phase energy storage converter, wherein the isolated bidirectional three-phase energy storage converter includes a three-phase AC power supply, a filter circuit, a matrix converter, an LCL filter circuit, a high-frequency transformer, a DC H-bridge circuit, and a DC output circuit connected in sequence, comprising the following steps: S1. Perform Fourier series transformation analysis on the primary and secondary voltages of the high-frequency transformer respectively; S2. Based on the Fourier series transform analysis results, calculate the leakage inductance current, and based on the leakage inductance current, calculate the transmitted active power; S3. Normalize the active power and the square of the primary inductance current of the high-frequency transformer. Based on the normalization result, obtain the active power and the square of the peak current under the fundamental component. S4. Taking the minimum square of peak current as the objective function, considering the transmission power constraint under the fundamental component, construct and solve the current stress optimization model to obtain the matrix converter parameters under the optimal current stress. S5. Based on the matrix converter parameters under optimal current stress, perform current stress optimization control.

[0007] In this technical solution, Fourier series analysis is first performed on the primary and secondary voltages of the high-frequency transformer to calculate the leakage inductance current and active power. Next, the active power and the square of the primary current are normalized. Based on the normalization results, the active power and the square of the peak current under the fundamental component are obtained. Then, with the minimum of the square of the peak current as the optimization objective and the transmission power under the fundamental component as the constraint, a current stress optimization model is constructed and solved to obtain the optimal matrix converter parameters. Finally, current stress optimization control is performed based on these optimal parameters to reduce current stress. This method significantly reduces current stress and improves the dynamic response on the DC side while meeting the given transmission power requirements, thus improving converter performance.

[0008] Preferably, the primary voltage of the high-frequency transformer Perform Fourier series transform analysis, the expression is:

[0009] in, This represents the switching frequency of the transistors within the matrix converter. Indicates the harmonic order. Indicates the primary voltage No. The amplitude of the second harmonic component is expressed as:

[0010] in, This represents the maximum line voltage of the matrix converter within one switching cycle. This represents the second largest line voltage of the matrix converter within one switching cycle. This represents the on-time of the switching transistor that causes the matrix converter to output the maximum line voltage. This represents the on-time of the switch that causes the matrix converter to output the second largest line voltage.

[0011] Preferably, for the secondary voltage of the high-frequency transformer Perform Fourier series transform analysis, the expression is:

[0012] in, This represents the DC bus voltage of the DC H-bridge circuit on the secondary side of the high-frequency transformer. The phase shift angle represents the leakage inductance current. Indicates secondary voltage No. The amplitude of the second harmonic component, .

[0013] Preferably, the primary winding of the high-frequency transformer is connected to an LCL filter circuit, the LCL filter circuit comprising: a filter inductor. Filter inductor and filter capacitors Filter capacitor One end is connected to a filter inductor. one end and filter inductor At one end, the expression for calculating the leakage inductance current is:

[0014] in, The phase shift angle represents the leakage inductance current. These represent the two filter inductors in the LCL filter circuit. This refers to the filter capacitor in the LCL filter circuit. Indicates the sector it belongs to.

[0015] Preferably, the process of calculating the transmitted active power is as follows: Calculate apparent power based on leakage inductance current. The expression is:

[0016] The apparent power is decomposed into: , The active power transmitted is expressed as:

[0017] The expression for the transmitted reactive power is: .

[0018] Preferably, before normalizing the active power and the square of the primary inductance current of the high-frequency transformer, the method further includes calculating the transmitted active power. The reference value of the primary inductance current of the high-frequency transformer, and the transmitted active power. The benchmark value Satisfying the expression:

[0019] in, Indicates secondary voltage The amplitude of the fundamental component; Reference value of primary inductance current of high-frequency transformer Satisfying the expression:

[0020] Transmitted active power Perform per-unit processing to obtain the per-unit processing result. The expression is:

[0021] The square of the primary inductance current of the high-frequency transformer is normalized to obtain the normalized result. The expression is:

[0022] The transmission power under the fundamental frequency component and the square of the peak current The expressions are as follows:

[0023] .

[0024] Preferably, the expression for the current stress optimization model is:

[0025]

[0026] in, This represents the square of the peak current under the fundamental component. This represents the transmission power under the fundamental frequency component. Indicates the active power reference for transmission; The current stress optimization model is solved using the Lagrange multiplier method to obtain the matrix converter parameters under optimal current stress. These matrix converter parameters include: modulation coefficients. and phase shift angle .

[0027] Preferably, the process of optimizing current stress control based on the matrix converter parameters under optimal current stress is as follows: The actual output voltage of the DC output circuit is sampled, compared with the rated output voltage, and then input to the PI controller to obtain the predicted voltage V1. Based on the predicted voltage V1 and known constraint parameters Calculate the phase shift angle under optimal current stress. The calculation expression is:

[0028] The input voltage and input current of the isolated bidirectional three-phase energy storage converter are sampled and processed using a phase-locked loop device to obtain the voltage phase shift angle; The input voltage and input current are synchronized based on the voltage phase shift angle. The synchronized input voltage and input current are then transformed by dq to obtain the components of the input voltage and input current in the dq coordinate system. Based on the predicted voltage V1 and the active power reference value, the expected reference value of the d-axis current is calculated. ,Will With the input current component on the d-axis The difference is input to the PI controller, which decouples the output of the PI controller to obtain the modulation signal under the d-axis. ; Based on the active power reference value, the expected reference value of the q-axis current is calculated. ,Will With the q-axis component of the input current The difference is input to the PI controller, and the output of the PI controller is decoupled to obtain the modulation signal under the q-axis. ; For modulated signals and modulated signal Perform SVM modulation and calculate the modulation coefficients. The expression is:

[0029] in, This is the DC bus voltage.

[0030] Secondly, this application also proposes a current stress optimization system for isolated bidirectional three-phase energy storage converters, the system comprising: The primary and secondary voltage extraction module is used to perform Fourier series transformation analysis on the primary and secondary voltages of a high-frequency transformer, respectively. The transmission power calculation module is used to calculate the leakage inductance current based on the Fourier series transform analysis results, and to calculate the transmitted active power based on the leakage inductance current. The per-unit processing module is used to standardize the active power and the square of the primary inductance current of the high-frequency transformer. Based on the per-unit processing result, the active power and the square of the peak current under the fundamental component are obtained. The current stress optimization model construction and solution module is used to construct and solve the current stress optimization model with the objective function of minimizing the square of the peak current, considering the transmission power constraint under the fundamental component, and obtain the matrix converter parameters under the optimal current stress. The matrix converter parameter application module is used to perform current stress optimization control based on the matrix converter parameters under optimal current stress.

[0031] Thirdly, this application also proposes a current stress optimization device for isolated bidirectional three-phase energy storage converters. The device includes a memory, a processor, and a computer program stored in the memory that can be run by the processor. The processor executes the computer program to implement the current stress optimization method for isolated bidirectional three-phase energy storage converters.

[0032] Compared with the prior art, the beneficial effects of the present invention are: This invention proposes a current stress optimization method and system for isolated three-phase bidirectional energy storage converters. Fourier series analysis is performed on the primary and secondary voltages of the high-frequency transformer to calculate the leakage inductance current and active power. Then, the active power and the square of the primary current are normalized. Based on the normalization results, the active power and the square of the peak current under the fundamental component are obtained. Next, with the minimum of the square of the peak current as the optimization objective and the transmission power under the fundamental component as the constraint, a current stress optimization model is constructed and solved to obtain the optimal matrix converter parameters. Finally, current stress optimization control is performed based on these optimal parameters to reduce current stress. This method significantly reduces current stress and improves the dynamic response on the DC side while meeting the given transmission power requirements, thus improving converter performance. Attached Figure Description

[0033] Figure 1 This is a flowchart illustrating a current stress optimization method for an isolated three-phase bidirectional energy storage converter proposed in Embodiment 1 of the present invention. Figure 2 This is a schematic diagram of the structure of the isolated three-phase bidirectional energy storage converter proposed in Embodiment 1 of the present invention; Figure 3This diagram illustrates the sector division of the current vector proposed in Embodiment 2 of the present invention. Figure 4 This diagram illustrates the specific output voltage waveform of the matrix converter proposed in Embodiment 2 of the present invention. Figure 5 This diagram illustrates the current stress optimization control strategy proposed in Embodiment 2 of the present invention. Figure 6 This diagram illustrates the primary-side current waveform after utilizing the conventional control method as proposed in Embodiment 2 of the present invention. Figure 7 This diagram illustrates the primary-side current waveform after utilizing the control strategy proposed in this application, as shown in Embodiment 2 of the present invention. Figure 8 This diagram illustrates the voltage and current waveforms of the DC output circuit after utilizing the conventional control method as proposed in Embodiment 2 of the present invention. Figure 9 This diagram illustrates the voltage and current waveforms of the DC output circuit after utilizing the control strategy proposed in this application, as shown in Embodiment 2 of the present invention. Figure 10 This is a schematic diagram of the current stress optimization system for an isolated three-phase bidirectional energy storage converter proposed in Embodiment 3 of the present invention. Figure 11 This is a schematic diagram of the current stress optimization device for an isolated bidirectional three-phase energy storage converter proposed in Embodiment 4 of the present invention. Detailed Implementation

[0034] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the scope of this patent. To better illustrate this embodiment, some parts of the accompanying drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions; It is understandable to those skilled in the art that some well-known details may be omitted from the accompanying drawings.

[0035] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0036] The positional relationships depicted in the accompanying drawings are for illustrative purposes only and should not be construed as limiting this patent. Example 1 This embodiment proposes a current stress optimization method for isolated bidirectional three-phase energy storage converters. A flowchart illustrating this method can be found here. Figure 1 This includes the following steps: S1. Perform Fourier series transformation analysis on the primary and secondary voltages of the high-frequency transformer respectively; S2. Based on the Fourier series transform analysis results, calculate the leakage inductance current, and based on the leakage inductance current, calculate the transmitted active power; S3. Normalize the active power and the square of the primary inductance current of the high-frequency transformer. Based on the normalization result, obtain the active power and the square of the peak current under the fundamental component. S4. Taking the minimum square of peak current as the objective function, considering the transmission power constraint under the fundamental component, construct and solve the current stress optimization model to obtain the matrix converter parameters under the optimal current stress. S5. Based on the matrix converter parameters under optimal current stress, perform current stress optimization control.

[0037] In this embodiment, the schematic diagram of the isolated bidirectional three-phase energy storage converter is as follows: Figure 2 As shown, the isolated bidirectional three-phase energy storage converter includes a three-phase AC power supply 1, a filter circuit 2, a matrix converter 3, an LCL filter circuit 4, a high-frequency transformer 5, a DC H-bridge circuit 6, and a DC output circuit 7 connected in sequence.

[0038] See Figure 2 The three-phase AC power supply 1 includes three sub-branch terminals, and each sub-branch terminal includes three phase voltage sources. 、 、 In this configuration, one end of each phase voltage source is grounded, and the other end is connected to the resistor at the corresponding sub-branch. and inductor One end, resistor and inductor The other end is connected to the midpoint of one arm of the matrix converter 3 and the capacitor at the end of the corresponding sub-branch. One end, capacitors at the three sub-branch ends The other end is connected to each other; the and The upper bidirectional switch of the bridge arm connected to the sub-branch is The lower bidirectional switching transistor is The above and The upper bidirectional switch of the bridge arm connected to the sub-branch is The lower bidirectional switching transistor is The above and The upper bidirectional switch of the bridge arm connected to the sub-branch is The lower bidirectional switching transistor is The sources of the bidirectional switching transistors on the upper side of the three bridge arms of matrix converter 3 are connected to the filter inductors of LCL filter circuit 4. One end, filter inductor The other end is connected to a filter capacitor. one end and the filter inductor One end, filter capacitor The other end is connected to the source of the bidirectional switching transistor on the lower side of the three bridge arms of the matrix converter 3 and the negative terminal of the primary voltage of the high-frequency transformer 5, respectively, and the filter inductor. The other end is connected to the positive terminal of the primary voltage of the high-frequency transformer 5; one end of the secondary voltage of the high-frequency transformer 5 is connected to the midpoint of one arm of the DC H-bridge circuit 6, and the upper switch of this arm is... The lower switch transistor is The other end of the secondary voltage of the high-frequency transformer 5 is connected to the midpoint of another bridge arm of the DC H-bridge circuit 6, and the upper switch of this bridge arm is... The lower switch transistor is The DC output circuit 7 includes a capacitor. and output voltage ,capacitance and output voltage The two ends are respectively connected to the two ends of the bridge arm of the DC H-bridge circuit 6.

[0039] In this embodiment, Fourier series analysis is performed on the primary and secondary voltages of the high-frequency transformer to calculate the leakage inductance current and active power. Then, the active power and the square of the primary current are normalized. Based on the normalization result, the active power and the square of the peak current under the fundamental component are obtained. Next, with the minimum of the square of the peak current as the optimization objective and the transmission power under the fundamental component as the constraint, a current stress optimization model is constructed and solved to obtain the optimal matrix converter parameters. Finally, current stress optimization control is performed based on these optimal parameters to reduce current stress. This method significantly reduces current stress and improves the DC-side dynamic response while meeting the given transmission power requirements, thus improving converter performance.

[0040] Example 2 In this embodiment, the primary voltage of the high-frequency transformer... Perform Fourier series transform analysis, the expression is:

[0041] in, This represents the switching frequency of the transistors within the matrix converter. Indicates the harmonic order. Indicates the primary voltage No. The amplitude of the second harmonic component is expressed as:

[0042] in, This represents the maximum line voltage of the matrix converter within one switching cycle. This represents the second largest line voltage of the matrix converter within one switching cycle. This represents the on-time of the switching transistor that causes the matrix converter to output the maximum line voltage. This represents the on-time of the switch that causes the matrix converter to output the second largest line voltage.

[0043] Specifically, regarding the primary voltage of the high-frequency transformer Before performing Fourier series transform analysis, it is also necessary to determine the primary voltage of the high-frequency transformer. The process is as follows: S11. The current vectors of each phase current I in the matrix converter are vector synthesized using the current vectors. The expression is:

[0044] in, , These represent the maximum line voltage and the second maximum line voltage path of the matrix converter, respectively, and the on-time of the switch transistors in the matrix converter during one switching cycle. Represents angular frequency. Indicates one switching cycle. This indicates the output voltage of the DC output circuit. This represents the resonant inductance value of the LCL filter circuit. This indicates the duty cycle of the switching transistor in the DC-side H-bridge circuit. The current vector is formed as follows: if the switching state combination in the matrix converter of the isolated bidirectional three-phase energy storage converter causes the current to form a loop between two different phases, the current will flow between the corresponding phases, generating a non-zero line voltage output to the high-frequency transformer; if the switching state combination causes the current to form a loop only in a single phase or cannot form an effective path, then the output current vector is the in-phase current and the output voltage is zero. The switching state combinations of the matrix converter in the isolated bidirectional three-phase energy storage converter are shown in Table 1. In Table 1, "1" represents the switch being on and "0" represents the switch being off. , , , , , There are 6 valid vectors. , , There are 3 zero vectors.

[0045] Table 1

[0046] Wherein, current vector , , , , , The space is evenly divided into six sectors. A schematic diagram of the sector division for the current vector is shown below. Figure 3 As shown, Figure 3 Roman numerals This indicates the sector number. In sector I, the current I can be represented by the current vector. and based on To synthesize, voltage V can be derived from voltage. and based on Synthesis is performed, and the phase difference between voltage V and current I is... .

[0047] S12. Calculate the maximum line voltage and the second largest line voltage path of the matrix converter during one switching cycle. Calculate the on-time of the matrix converter's switching transistors. , , , The expression is:

[0048] in, , , Indicates the sector number, Indicates the initial phase angle of the current. Indicates zero vector conduction time. This represents the modulation coefficient.

[0049] S13. Based on the maximum line voltage and the second largest line voltage of the matrix converter, obtain the output voltage waveform of the matrix converter; Specifically, the schematic diagram of the specific output voltage waveform of the matrix converter is as follows: Figure 4 As shown, in Figure 4 middle, For one During the period, the maximum line voltage of the matrix converter corresponds to the current vector as follows: The corresponding on-time of the switching transistor is , The second largest line voltage of the matrix converter within one Ts cycle corresponds to the current vector as follows: The corresponding on-time of the switching transistor is Similarly, and For one The maximum and second largest reverse voltages within the cycle.

[0050] In this embodiment, the secondary voltage of the high-frequency transformer... Perform Fourier series transform analysis, the expression is:

[0051] in, This represents the DC bus voltage of the DC H-bridge circuit on the secondary side of the high-frequency transformer. The phase shift angle represents the leakage inductance current. Indicates secondary voltage No. The amplitude of the second harmonic component.

[0052] In this embodiment, the primary winding of the high-frequency transformer is connected to an LCL filter circuit, which includes a filter inductor. Filter inductor and filter capacitors Filter capacitor One end is connected to a filter inductor. one end and filter inductor At one end, the expression for calculating the leakage inductance current is:

[0053] in, The phase shift angle represents the leakage inductance current. These represent the two filter inductors in the LCL filter circuit. This refers to the filter capacitor in the LCL filter circuit. Indicates the sector it belongs to.

[0054] In this embodiment, the process of calculating the transmitted active power is as follows: Calculate apparent power based on leakage inductance current. The expression is:

[0055] The apparent power is decomposed into: , The active power transmitted is expressed as:

[0056] The expression for the transmitted reactive power is: .

[0057] In this embodiment, before normalizing the active power and the square of the primary inductance current of the high-frequency transformer, the method further includes calculating the transmitted active power. The reference value of the primary inductance current of the high-frequency transformer, and the transmitted active power. The benchmark value Satisfying the expression:

[0058] in, Indicates secondary voltage The amplitude of the fundamental component; Reference value of primary inductance current of high-frequency transformer Satisfying the expression:

[0059] Transmitted active power Perform per-unit processing to obtain the per-unit processing result. The expression is:

[0060] The square of the primary inductance current of the high-frequency transformer is normalized to obtain the normalized result. The expression is:

[0061] The transmission power under the fundamental frequency component and the square of the peak current The expressions are as follows:

[0062] .

[0063] Specifically, the squared per-unit peak current under different harmonic components and different phase shift angle dimensions. The schematic diagram is as follows Figure 5 As shown, in Figure 5 In the figure, the square of the per-unit peak current varies with the phase shift angle. As the fundamental frequency increases, the peak current increases, and the fundamental component is the main component of the peak current. The square of the per-unit peak current under the fundamental component... The values ​​at each phase shift angle are significantly different from those of other components; Specifically, the per-unit active power under different harmonic components and different phase shift angle dimensions. The schematic diagram is as follows Figure 6 As shown, Figure 6 The fundamental frequency component is the main component of the total transmitted power, and the transmitted power is in The fundamental component is at its maximum. Therefore, the fundamental component can be used as the main basis for characterizing peak current and transmission power, and its error is negligible.

[0064] In this embodiment, the expression for the current stress optimization model is:

[0065]

[0066] in, This represents the square of the peak current under the fundamental component. This represents the transmission power under the fundamental frequency component. Indicates the active power reference for transmission; The current stress optimization model is solved using the Lagrange multiplier method to obtain the matrix converter parameters under optimal current stress. These matrix converter parameters include: modulation coefficients. and phase shift angle .

[0067] In this embodiment, the process of optimizing current stress control based on the matrix converter parameters under optimal current stress is as follows: The actual output voltage of the DC output circuit is sampled, compared with the rated output voltage, and then input to the PI controller to obtain the predicted voltage V1. Based on the predicted voltage V1 and known constraint parameters Calculate the phase shift angle under optimal current stress. The calculation expression is:

[0068] The input voltage and input current of the isolated bidirectional three-phase energy storage converter are sampled and processed using a phase-locked loop device to obtain the voltage phase shift angle; The input voltage and input current are synchronized based on the voltage phase shift angle. The synchronized input voltage and input current are then transformed by dq to obtain the components of the input voltage and input current in the dq coordinate system. Based on the predicted voltage V1 and the active power reference value, the expected reference value of the d-axis current is calculated. ,Will With the input current component on the d-axis The difference is input to the PI controller, which decouples the output of the PI controller to obtain the modulation signal under the d-axis. ; Based on the active power reference value, the expected reference value of the q-axis current is calculated. ,Will With the q-axis component of the input current The difference is input to the PI controller, and the output of the PI controller is decoupled to obtain the modulation signal under the q-axis. ; For modulated signals and modulated signal Perform SVM modulation and calculate the modulation coefficients. The expression is:

[0069] in, This is the DC bus voltage.

[0070] Specifically, the schematic diagram of the current stress optimization control strategy is as follows: Figure 5 As shown, in Figure 5 First, the actual output voltage of the DC output circuit is sampled, compared with the rated output voltage, and then input to the PI controller to obtain the predicted voltage V1; based on the predicted voltage V1 and known constraint parameters... Calculate the phase shift angle under optimal current stress. The input voltage and current of the isolated bidirectional three-phase energy storage converter are sampled and processed using a phase-locked loop (PLL) device to obtain the voltage phase shift angle. Based on the voltage phase shift angle, the input voltage and current are synchronized. The synchronized input voltage and current are then subjected to a dq transformation to obtain the components of the input voltage and current in the dq coordinate system. Based on the predicted voltage V1 and the active power reference value, the expected reference value of the d-axis current is calculated. ,Will With the input current component on the d-axis The difference is input to the PI controller, which decouples the output of the PI controller to obtain the modulation signal under the d-axis. Based on the active power reference value, the expected reference value of the q-axis current is calculated. ,Will With the q-axis component of the input current The difference is input to the PI controller, and the output of the PI controller is decoupled to obtain the modulation signal under the q-axis. ; for modulated signals and modulated signal Perform SVM modulation and calculate the modulation coefficients. .

[0071] A comparative model using traditional control methods was built on the Simulink platform of Matlab to verify the effect of the proposed control strategy on optimizing grid-side current stress. Specific parameters were: input three-phase voltage of 50Hz and 220V, high-frequency transformer N maintained at 1, switching frequency of 25kHz, and three different loads (208, 104, and 52) were used. The value of k was kept at 2. The experiment was conducted at 208... The operation is performed under load. The primary current waveform diagram after using the traditional control method is shown below. Figure 6 As shown, the ordinate The x-axis represents the primary current, and the x-axis represents the time period. We can see... Figure 6 Central Plains Current Although it generally follows a sinusoidal trend, it exhibits very noticeable high-frequency ripple. This ripple, caused by PWM switching, has a large amplitude, indicating poor current quality and high harmonic content. The peak current is approximately 10A. This could lead to higher losses, electromagnetic interference (EMI), and negative impacts on the power grid or other loads.

[0072] The control strategy for the isolated bidirectional three-phase energy storage converter proposed in this application was established under the same conditions. A schematic diagram of the primary-side current waveform using the proposed control strategy is shown below. Figure 7 As shown, Figure 7 In the middle, the vertical axis The x-axis represents the primary current, and the y-axis represents the time period. You can see the primary current... The waveform is extremely smooth, and the high-frequency switching ripple is significantly suppressed, making the waveform very close to an ideal sine wave.

[0073] Specifically, a comparative model using the traditional control method was built on the Matlab Simulink platform. The voltage and current waveforms of the DC output circuit after using the traditional control method are shown in the diagram below. Figure 8 As shown, Figure 8 In the experiment, the converter starts at full load, switches to half load at 0.3 seconds, and switches to light load at 0.6 seconds. It can be seen that at the load switching points of 0.3 seconds and 0.6 seconds, the output voltage fluctuates significantly and takes some time to recover to the rated voltage (250V).

[0074] To verify the effect of the proposed control strategy on improving the dynamic response performance of the DC side, the control strategy of the proposed isolated bidirectional three-phase energy storage converter was built under the same conditions. The voltage and current waveforms of the DC output circuit under the proposed control strategy are shown in the figure below. Figure 9 As shown, Figure 9 In the experiment, the converter started from full load, switched to half load at 0.3 seconds, and switched to light load at 0.6 seconds. It can be seen that the output voltage remained stable at 250V with almost no fluctuation during load switching. By comparing the waveforms at the switching moments, it is clear that the voltage waveform under the control strategy proposed in this application is smoother, which significantly improves the dynamic response speed of the DC side.

[0075] Example 3 This embodiment proposes a current stress optimization system for isolated bidirectional three-phase energy storage converters. In this embodiment, the system is used to implement the current stress optimization method for isolated bidirectional three-phase energy storage converters described in any of Embodiments 1-2. The structural schematic diagram is shown below. Figure 10 As shown, it includes: The primary and secondary voltage extraction module is used to perform Fourier series transformation analysis on the primary and secondary voltages of a high-frequency transformer, respectively. The transmission power calculation module is used to calculate the leakage inductance current based on the Fourier series transform analysis results, and to calculate the transmitted active power based on the leakage inductance current. The per-unit processing module is used to standardize the active power and the square of the primary inductance current of the high-frequency transformer. Based on the per-unit processing result, the active power and the square of the peak current under the fundamental component are obtained. The current stress optimization model construction and solution module is used to construct and solve the current stress optimization model with the objective function of minimizing the square of the peak current, considering the transmission power constraint under the fundamental component, and obtain the matrix converter parameters under the optimal current stress. The matrix converter parameter application module is used to perform current stress optimization control based on the matrix converter parameters under optimal current stress.

[0076] Example 4 In this embodiment, a current stress optimization device for isolated bidirectional three-phase energy storage converters is proposed. The structural schematic diagram of the device is shown below. Figure 11 As shown, the dynamic detection device includes a memory 101, a processor 102, and a computer program stored in the memory 101 that can be run by the processor. The processor 102 executes the computer program to implement a current stress optimization method for isolated bidirectional three-phase energy storage converters.

[0077] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A current stress optimization method for an isolated bidirectional three-phase energy storage converter, wherein the isolated bidirectional three-phase energy storage converter comprises a three-phase AC power supply, a filter circuit, a matrix converter, an LCL filter circuit, a high-frequency transformer, a DC H-bridge circuit, and a DC output circuit connected in sequence, characterized in that, Includes the following steps: Fourier series transform analysis was performed on the primary and secondary voltages of the high-frequency transformer. Based on the Fourier series transform analysis results, the leakage inductance current is calculated, and based on the leakage inductance current, the transmitted active power is calculated. The active power and the square of the primary inductance current of the high-frequency transformer are normalized. Based on the normalization result, the active power and the square of the peak current under the fundamental component are obtained. With the objective function of minimizing the square of the peak current, and considering the transmission power constraint under the fundamental component, a current stress optimization model is constructed and solved to obtain the matrix converter parameters under the optimal current stress. Current stress optimization control is performed based on the matrix converter parameters under optimal current stress.

2. The current stress optimization method for isolated bidirectional three-phase energy storage converters according to claim 1, characterized in that, For the primary voltage of a high-frequency transformer Perform Fourier series transform analysis, the expression is: in, This represents the switching frequency of the transistors within the matrix converter. Indicates the harmonic order. Indicates the primary voltage No. The amplitude of the second harmonic component is expressed as: in, This represents the maximum line voltage of the matrix converter within one switching cycle. This represents the second largest line voltage of the matrix converter within one switching cycle. This represents the on-time of the switching transistor that causes the matrix converter to output the maximum line voltage. This represents the on-time of the switch that causes the matrix converter to output the second largest line voltage.

3. The current stress optimization method for isolated bidirectional three-phase energy storage converters according to claim 1, characterized in that, For the secondary voltage of a high-frequency transformer Perform Fourier series transform analysis, the expression is: in, This represents the DC bus voltage of the DC H-bridge circuit on the secondary side of the high-frequency transformer. The phase shift angle represents the leakage inductance current. Indicates secondary voltage No. The amplitude of the second harmonic component, .

4. The current stress optimization method for isolated bidirectional three-phase energy storage converters according to claim 3, characterized in that, The primary winding of the high-frequency transformer is connected to an LCL filter circuit, which includes a filter inductor. Filter inductor and filter capacitors Filter capacitor One end is connected to a filter inductor. one end and filter inductor At one end, the expression for calculating the leakage inductance current is: in, The phase shift angle represents the leakage inductance current. These represent the two filter inductors in the LCL filter circuit. This refers to the filter capacitor in the LCL filter circuit. Indicates the sector it belongs to.

5. The current stress optimization method for isolated bidirectional three-phase energy storage converters according to claim 4, characterized in that, The process of calculating the transmitted active power is as follows: Calculate apparent power based on leakage inductance current. The expression is: The apparent power is decomposed into: , The active power transmitted is expressed as: The expression for the transmitted reactive power is: 。 6. The current stress optimization method for isolated bidirectional three-phase energy storage converters according to claim 5, characterized in that, Before normalizing the active power and the square of the primary inductance current of the high-frequency transformer, the process also includes calculating the transmitted active power. The reference value of the primary inductance current of the high-frequency transformer, and the transmitted active power. The benchmark value Satisfying the expression: in, Indicates secondary voltage The amplitude of the fundamental component; Reference value of primary inductance current of high-frequency transformer Satisfying the expression: Transmitted active power Perform per-unit processing to obtain the per-unit processing result. The expression is: The square of the primary inductance current of the high-frequency transformer is normalized to obtain the normalized result. The expression is: Transmission power under the fundamental frequency component and the square of the peak current The expressions are as follows: 。 7. The current stress optimization method for isolated bidirectional three-phase energy storage converters according to claim 6, characterized in that, The expression for the current stress optimization model is: in, This represents the square of the peak current under the fundamental component. This represents the transmission power under the fundamental frequency component. Indicates the active power reference for transmission; The current stress optimization model is solved using the Lagrange multiplier method to obtain the matrix converter parameters under optimal current stress. These matrix converter parameters include: modulation coefficients. and phase shift angle .

8. The current stress optimization method for isolated bidirectional three-phase energy storage converters according to claim 6, characterized in that, The process of optimizing current stress control based on the matrix converter parameters under optimal current stress is as follows: The actual output voltage of the DC output circuit is sampled, compared with the rated output voltage, and then input to the PI controller to obtain the predicted voltage V1. Based on the predicted voltage V1 and known constraint parameters Calculate the phase shift angle under optimal current stress. The calculation expression is: The input voltage and input current of the isolated bidirectional three-phase energy storage converter are sampled and processed using a phase-locked loop device to obtain the voltage phase shift angle; The input voltage and input current are synchronized based on the voltage phase shift angle. The synchronized input voltage and input current are then transformed by dq to obtain the components of the input voltage and input current in the dq coordinate system. Based on the predicted voltage V1 and the active power reference value, the expected reference value of the d-axis current is calculated. ,Will With the input current component on the d-axis The difference is input to the PI controller, which decouples the output of the PI controller to obtain the modulation signal under the d-axis. ; Based on the active power reference value, the expected reference value of the q-axis current is calculated. ,Will With the q-axis component of the input current The difference is input to the PI controller, and the output of the PI controller is decoupled to obtain the modulation signal under the q-axis. ; For modulated signals and modulated signal Perform SVM modulation and calculate the modulation coefficients. The expression is: in, This is the DC bus voltage.

9. A current stress optimization system for isolated bidirectional three-phase energy storage converters, characterized in that, The system is used to implement the method according to any one of claims 1 to 7, comprising: The primary and secondary voltage extraction module is used to perform Fourier series transformation analysis on the primary and secondary voltages of a high-frequency transformer, respectively. The transmission power calculation module is used to calculate the leakage inductance current based on the Fourier series transform analysis results, and to calculate the transmitted active power based on the leakage inductance current. The per-unit processing module is used to standardize the active power and the square of the primary inductance current of the high-frequency transformer. Based on the per-unit processing result, the active power and the square of the peak current under the fundamental component are obtained. The current stress optimization model construction and solution module is used to construct and solve the current stress optimization model with the objective function of minimizing the square of the peak current, considering the transmission power constraint under the fundamental component, and obtain the matrix converter parameters under the optimal current stress. The matrix converter parameter application module is used to perform current stress optimization control based on the matrix converter parameters under optimal current stress.

10. A current stress optimization device for isolated bidirectional three-phase energy storage converters, characterized in that, The current stress optimization device for isolated bidirectional three-phase energy storage converter includes a memory, a processor, and a computer program stored in the memory that can be run on the processor. The processor executes the computer program to implement the method described in any one of claims 1 to 8.

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