A modulation method of high frequency link structure of power electronic transformer capable of suppressing direct current output voltage ripple

Abstract

The application discloses a modulation method of a high-frequency link structure of a power electronic transformer capable of inhibiting direct-current output voltage ripple. The power electronic transformer topology adopts the structure of a front-stage CHB rectifier and a rear-stage DAB converter. A carrier phase-shift modulation strategy is adopted on the CHB rectification side, so that a direct-current voltage of each sub-module generates a same-phase double-frequency voltage ripple, and the same-phase double-frequency voltage ripple is used as input of each DAB unit. On the DAB isolated transmission side, a suppression ripple strategy based on a DAB secondary side triangular connection method and phase complementary modulation is designed, the secondary side of the DAB unit is restructured into the triangular connection method, a zero sequence loop is constructed for the same-phase double-frequency voltage ripple on a propagation path, and meanwhile, a modulation strategy with a phase difference of 120 degrees between the primary side modulation phases is combined, so that the natural circuit phase complementary characteristics of a three-phase system are utilized, the ripple energy is made to be cancelled after vector superposition in the triangular loop in vector operation, and then the effect of direct-current voltage ripple suppression is realized.

Description

Technical Field

[0001] This invention relates to the field of power electronic transformers, and more particularly to a modulation method for a high-frequency link structure of a power electronic transformer that can suppress DC output voltage ripple. Background Technology

[0002] In power electronic transformer systems, a modular architecture employing a cascaded H-bridge (CHB) in the front stage and a dual active bridge (DAB) in the rear stage is the mainstream solution for high-voltage AC to low-voltage DC conversion. In this modular topology, the front-stage CHB module, acting as a rectifier stage, is physically limited by the single-phase AC power characteristics, inevitably generating inherent power ripple at twice the power frequency on its DC bus. Without intervention, this rippled power directly converts into voltage ripple on the DC bus, which is further transmitted to the DAB converter along the energy propagation path. If the system lacks effective internal mitigation strategies, this rippled energy can only be passively absorbed by increasing the DC support capacitor, or it can directly penetrate the DAB unit, affecting the power quality of the subsequent load. Currently, suppression strategies for this voltage ripple typically employ independent or synchronized modulation methods, leading to phase overlap of the in-phase ripples generated by each module. This further amplifies the rippled energy on the DC side, making it difficult to effectively suppress the output voltage ripple. Summary of the Invention

[0003] This invention provides a modulation method for the high-frequency link structure of a power electronic transformer that can suppress DC output voltage ripple, thereby solving the technical problem of poor suppression effect of existing voltage ripple suppression strategies.

[0004] This invention provides a modulation method for the high-frequency link structure of a power electronic transformer capable of suppressing DC output voltage ripple. The method involves the CHB rectifier side and the DAB isolation transmission side; the method includes:

[0005] On the CHB rectifier side, the AC input terminal of each sub-module of the CHB is connected in series to the same AC power supply, and the DC output side of each sub-module in the CHB rectifier side is connected to the corresponding small-capacity thin film capacitor, so that the CHB rectifier side outputs a double power frequency voltage ripple in phase.

[0006] On the DAB isolation transmission side, the DC bus of each sub-module in the CHB rectification side is connected to the primary side of the corresponding DAB unit through a small-capacity thin film capacitor, and the primary side of each DAB unit is subjected to single-phase shift modulation, so that the modulation phase of the primary side of each DAB unit is 120 degrees different from each other in sequence, thereby outputting multiple primary side voltage ripples with modulation phases 120 degrees different from each other.

[0007] The secondary side of each DAB unit is connected in a delta configuration to form a closed zero-sequence loop. Multiple primary voltage ripples with a phase difference of 120 degrees are transmitted to the secondary side of the corresponding DAB unit through transformer isolation, and the duty cycle of each DAB unit is modulated.

[0008] In the zero-sequence loop, the vector superposition characteristic of the output voltages on the secondary side of each DAB unit is utilized to enable the voltage ripple components with a modulation phase difference of 120 degrees transmitted from the primary side to the secondary side of each DAB unit to undergo vector cancellation in the zero-sequence loop. This results in the output voltage of each DAB unit retaining only the fundamental active component, thereby suppressing voltage ripple.

[0009] Optionally, the step of connecting the DC bus of each sub-module in the CHB rectifier side to the primary side of the corresponding DAB unit via a small-capacity thin-film capacitor, and performing single-phase-shift modulation on the primary side of each DAB unit so that the modulation phases of the primary side of each DAB unit differ by 120 degrees sequentially, thereby outputting multiple primary-side voltage ripples with modulation phases differing by 120 degrees, includes:

[0010] By using small-capacity thin-film capacitors, the DC bus of each sub-module in the CHB rectifier side is connected to the primary side of the corresponding DAB unit, so that the double power frequency voltage ripple of each in phase is used as the input voltage of the primary side of the corresponding DAB unit.

[0011] Single-phase-shift modulation is applied to the primary side of each DAB unit, causing the turn-on time of the diagonal switches on the primary side of each DAB unit to be delayed by 120 degrees in sequence. This results in the modulation phases on the primary side of each DAB unit being 120 degrees apart in sequence, thereby outputting multiple primary-side voltage ripples with modulation phases 120 degrees apart.

[0012] Optionally, the switching drive signals on the primary side of each DAB unit are represented as follows:

[0013] ;

[0014] In the formula: , and These are the primary-side switch drive signals for the first DAB unit, the second DAB unit, and the third DAB unit, respectively. For high-frequency switching frequency, This refers to the runtime.

[0015] Optionally, on the CHB rectifier side, the step of connecting the AC input terminal of each sub-module of the CHB in series to the same AC power supply, and connecting the DC output side of each module of the CHB to a corresponding small-capacity thin-film capacitor, so that the CHB rectifier side outputs a voltage ripple of twice the power frequency in phase, includes:

[0016] On the rectifier side of the CHB, the AC input terminal of each sub-module of the CHB is connected in series to the same AC power supply. A carrier phase-shift modulation strategy is adopted to generate a double power frequency voltage ripple in phase with the DC voltage of each sub-module in the CHB, which is used as the input of each DAB unit.

[0017] The DC output side of each submodule in the CHB rectifier side is connected to a corresponding small-capacity thin-film capacitor, so that the voltage of each small-capacity thin-film capacitor generates a quadratic ripple in phase with the corresponding double power frequency pulsation, thereby causing the CHB rectifier side to output a double power frequency voltage ripple in phase; to analyze this voltage, the primary-side AC voltage of the i-th DAB unit on the DAB isolation transmission side is... Performing Fourier decomposition yields the following:

[0018] ;

[0019] In the formula: It is twice the power frequency voltage ripple component. is the steady-state value of the DC bus voltage, and k is the harmonic order.

[0020] Optionally, for the i-th DAB unit, performing a Fourier expansion on the DC voltage component output from its secondary side while retaining the fundamental component yields:

[0021] ;

[0022] In the formula: This refers to the fundamental component output from the secondary side of the i-th DAB unit; This represents the phase shift angle, and π / 6 represents the voltage gain coefficient resulting from the star-to-delta conversion. It is an inherent phase shift in the spectrum. The phase introduced by Ts / 3, the amplitude of the primary side square wave fundamental is ;

[0023] The three DAB units on the DAB isolation transmission side are algebraically summed in the zero-sequence loop, and their total output port voltage Vout(t) is expressed as follows:

[0024] ;

[0025] As shown in the above equation, the orthogonal components generated by submodule 2 and submodule 3 always cancel each other out, and the sum of the in-phase components precisely smooths out the potential fluctuations of submodule 1. At the physical level, the instantaneous vector sum of ripple energy is reduced to zero, and residual harmonics are only distributed in the 6k±1 high-frequency band, significantly improving the DC output quality. Ripple can cancel each other out in the delta circuit, leaving only the steady-state value, thus ensuring ripple-free voltage transmitted to the load side.

[0026] This invention also provides a modulation device for a high-frequency link structure of a power electronic transformer capable of suppressing DC output voltage ripple, the device comprising:

[0027] The double power frequency voltage ripple input module is used to connect the AC input terminal of each sub-module of CHB in series to the same AC power supply on the rectifier side of CHB, and connect the DC output side of each module of CHB to the corresponding small-capacity thin film capacitor, so that the rectifier side of CHB outputs a double power frequency voltage ripple in phase.

[0028] The primary-side single-phase-shift modulation module is used to connect the DC bus of each sub-module in the CHB rectifier side to the primary side of the corresponding DAB unit through a small-capacity thin-film capacitor on the DAB isolation transmission side, and to perform single-phase-shift modulation on the primary side of each DAB unit so that the modulation phases of the primary side of each DAB unit are sequentially 120 degrees apart, thereby outputting multiple primary-side voltage ripples with modulation phases 120 degrees apart.

[0029] The secondary side is connected to the modulation module, which is used to connect the secondary side of each DAB unit in a delta configuration to form a closed zero-sequence loop; multiple primary side voltage ripples with a modulation phase difference of 120 degrees are transmitted to the secondary side of the corresponding DAB unit through transformer isolation, and the duty cycle of each DAB unit is modulated.

[0030] The voltage ripple suppression output module is used in the zero-sequence circuit to utilize the vector superposition characteristics of the output voltages on the secondary side of each DAB unit, so that the voltage ripple components with a modulation phase difference of 120 degrees transmitted from the primary side to the secondary side of each DAB unit are vector-cancelled in the zero-sequence circuit, thereby so that the output voltage of each DAB unit retains only the fundamental active component, thus achieving voltage ripple suppression.

[0031] Optionally, the primary-side single-phase-shift modulation module is specifically used for,

[0032] By using small-capacity thin-film capacitors, the DC bus of each sub-module in the CHB rectifier side is connected to the primary side of the corresponding DAB unit, so that the double power frequency voltage ripple of each in phase is used as the input voltage of the primary side of the corresponding DAB unit.

[0033] Single-phase-shift modulation is applied to the primary side of each DAB unit, causing the turn-on time of the diagonal switches on the primary side of each DAB unit to be delayed by 120 degrees in sequence. This results in the modulation phases on the primary side of each DAB unit being 120 degrees apart in sequence, thereby outputting multiple primary-side voltage ripples with modulation phases 120 degrees apart.

[0034] This invention also provides a computer device, including a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the modulation method for the high-frequency link structure of the power electronic transformer as described above.

[0035] This invention also provides a computer-readable storage medium storing a computer program or instructions thereon, which, when executed by a processor, implements the steps of the modulation method for the high-frequency link structure of the power electronic transformer as described above.

[0036] This invention also provides a computer program product, including a computer program or instructions, which, when executed by a processor, implement the steps of the modulation method for the high-frequency link structure of the power electronic transformer as described above.

[0037] As can be seen from the above technical solutions, the present invention has the following advantages:

[0038] This invention provides a modulation method for the high-frequency link structure of a power electronic transformer capable of suppressing DC output voltage ripple. The method involves the CHB rectifier side and the DAB isolation transmission side. The method includes: on the CHB rectifier side, connecting the AC input terminals of each sub-module of the CHB in series to the same AC power supply, and connecting the DC output side of each sub-module in the CHB rectifier side to a corresponding small-capacity thin-film capacitor; employing a carrier phase-shift modulation strategy to generate a double-power-frequency voltage ripple in phase with the DC voltage of each sub-module in the CHB; on the DAB isolation transmission side, connecting the DC bus of each sub-module in the CHB rectifier side to the primary side of the corresponding DAB unit through small-capacity thin-film capacitors, and performing single-phase phase-shift modulation on the primary side of each DAB unit, so that... The modulation phases of the primary side of each DAB unit are sequentially 120 degrees apart, resulting in multiple primary-side voltage ripples with 120-degree phase differences. The secondary side of each DAB unit is connected in a delta configuration, forming a closed zero-sequence loop. These multiple primary-side voltage ripples with 120-degree phase differences are transmitted to the secondary side of the corresponding DAB unit via transformer isolation, and the duty cycle of each DAB unit's secondary side is modulated. In the zero-sequence loop, utilizing the vector superposition characteristic of the secondary-side output voltages of each DAB unit, the voltage ripple components with 120-degree phase differences transmitted from the primary side to the secondary side of each DAB unit undergo vector cancellation in the zero-sequence loop. This ensures that the output voltage of each DAB unit retains only the fundamental active component, achieving voltage ripple suppression.

[0039] In this invention, the CHB rectifier side adopts a carrier phase-shift modulation strategy to generate a DC voltage ripple of twice the power frequency in phase with the DC voltage of each submodule in the CHB, which is then used as the input of each DAB unit. To solve the problem of larger ripple caused by small-capacity thin-film capacitors, the DAB isolation transmission side is designed with a ripple suppression strategy based on the DAB secondary side delta connection and phase complementary modulation. The secondary side of the DAB unit is reconstructed into a delta connection, and a zero-sequence loop is constructed for the twice-power frequency voltage ripple in phase in the propagation path. At the same time, combined with the modulation strategy of 120-degree phase difference on the primary side, the natural circuit phase complementary characteristics of the three-phase system are utilized to make the ripple energy vector superimposed and canceled in the vector operation inside the delta loop, thereby achieving the effect of DC voltage ripple suppression. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1A flowchart illustrating the steps of a modulation method for a high-frequency link structure of a power electronic transformer capable of suppressing DC output voltage ripple, provided in an embodiment of the present invention.

[0042] Figure 2 A circuit diagram of the high-frequency link structure of a power electronic transformer provided in an embodiment of the present invention;

[0043] Figure 3 A circuit diagram of the DAB isolation transmission side of the high-frequency link structure of a power electronic transformer provided in an embodiment of the present invention;

[0044] Figure 4 The waveform diagram of the drive signal of the switching transistor of the first DAB unit provided in the embodiment of the present invention;

[0045] Figure 5 The waveform diagram of the drive signal of the switching transistor of the second DAB unit provided in the embodiment of the present invention;

[0046] Figure 6 The waveform diagram of the drive signal of the switching transistor of the third DAB unit provided in the embodiment of the present invention;

[0047] Figure 7 The waveforms of the voltage and current signals and the load-side voltage of the first DAB unit provided in this embodiment of the invention;

[0048] Figure 8 The voltage and current signal waveforms of the second DAB unit provided in this embodiment of the invention;

[0049] Figure 9 The voltage and current signal waveforms of the third DAB unit provided in this embodiment of the invention;

[0050] Figure 10 This is a structural block diagram of a modulation device for a high-frequency link structure of a power electronic transformer that can suppress DC output voltage ripple, provided as an embodiment of the present invention. Detailed Implementation

[0051] This invention provides a modulation method for the high-frequency link structure of a power electronic transformer that can suppress DC output voltage ripple, thereby solving the technical problem of poor suppression effect of existing voltage ripple suppression strategies.

[0052] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0053] It should be noted that, in the optional embodiments of the present invention, the data related to object information, etc., requires the permission or consent of the object when the embodiments of the present invention are applied to specific products or technologies. Furthermore, the collection, use, and processing of the relevant data must comply with the relevant laws, regulations, and standards of the relevant countries and regions. In other words, if the embodiments of the present invention involve data related to an object, it needs to be obtained with the object's authorization and consent, the authorization and consent of relevant departments, and in accordance with the relevant laws, regulations, and standards of the country and region. If the embodiments involve personal information, the acquisition of all personal information requires the individual's consent. If sensitive information is involved, the separate consent of the information subject is required. The embodiments also need to be implemented with the object's authorization and consent.

[0054] Please see Figure 1 This invention provides a modulation method for the high-frequency link structure of a power electronic transformer capable of suppressing DC output voltage ripple. The method involves the CHB rectifier side and the DAB isolation transmission side; the method includes:

[0055] Step 101: On the CHB rectifier side, connect the AC input terminal of each sub-module of CHB in series to the same AC power supply, and connect the DC output side of each sub-module on the CHB rectifier side to the corresponding small-capacity thin film capacitor. Use a carrier phase-shift modulation strategy to generate a double power frequency voltage ripple in phase with the DC voltage of each sub-module in CHB.

[0056] Please see Figure 2 The high-frequency stage structure of the power electronic transformer involved in this invention includes a front-stage cascaded H-bridge rectifier module (i.e., CHB module) and a rear-stage DAB converter; on the CHB rectifier side, the AC input terminals of three structurally identical sub-modules are connected to the same AC power supply. A carrier phase-shift modulation strategy is adopted to generate a double power frequency voltage ripple in phase with the DC voltage of each submodule in the CHB. At the same time, small-capacity film capacitors (C1, C2 and C3) are connected in parallel to the DC output side of each submodule in the CHB. Since the energy storage capacity of the small-capacity film capacitors is limited, the double power frequency pulsation power of the CHB module cannot be completely absorbed, thus keeping the in-phase voltage ripple on the DC bus and providing a ripple input source for the phase complementary modulation and circulating current cancellation of the subsequent DAB converter.

[0057] In one specific implementation, step 101 may include the following steps:

[0058] S11. On the CHB rectifier side, the AC input terminals of each sub-module in the CHB rectifier side are connected in series to the same AC power supply. A carrier phase-shifting modulation strategy is adopted to make the CHB module output twice the power frequency pulsating power in phase.

[0059] S12. Connect the DC output side of each submodule in the CHB rectifier side to the corresponding small-capacity thin-film capacitor, so that the voltage of each small-capacity thin-film capacitor generates in-phase secondary ripple with the corresponding double power frequency pulsation, thereby causing the CHB rectifier side to output in-phase double power frequency voltage ripple.

[0060] Understandably, since the AC input terminals of each submodule of the CHB are connected in series to the same AC power supply... Furthermore, by employing a carrier phase-shift modulation strategy, the double power frequency pulsating power output by each submodule of the CHB is completely identical in phase.

[0061] During operating time t, the voltage on the AC side of the CHB module With current and the instantaneous power output of the CHB module It is expressed as follows:

[0062] ;

[0063] In the formula: The amplitude of the AC voltage. It is the power frequency angular frequency; The amplitude of the alternating current; This represents the average active power output by the CHB module.

[0064] From the above formula, we can see that the instantaneous power output by the CHB module is... Including the inherent double power frequency ripple power The DC bus of the CHB module uses small-capacity film capacitors (C1, C2 and C3) for voltage support, directly coupling the double power frequency pulsating power to the DC voltage of the small-capacity film capacitors. However, due to the limited energy buffering capacity of the capacitors, the double power frequency pulsating power cannot be completely absorbed, and the DC voltage of the small-capacity film capacitors generates significant in-phase secondary ripples as the double power frequency pulsating power pulsates.

[0065] Based on the instantaneous energy storage change relationship of the capacitor: ,in, For instantaneous energy storage in small-capacity film capacitors, This refers to the capacitance value of a small-capacity film capacitor. The steady-state value of the DC bus voltage is given. It can be seen that the relationship between capacitor energy storage and ripple is a nonlinear equation, and directly solving for ripple is quite complex.

[0066] Therefore, a Fourier decomposition of the DC bus voltage at this time is performed. It not only contains the steady-state DC component, but also necessarily has an AC ripple component with a frequency of twice the DC frequency. The mathematical expression of the decomposed DC bus voltage can be:

[0067] ;

[0068] in, It is twice the power frequency voltage ripple component. To change the amplitude of the voltage ripple, based on the derivation of power and capacitance, its magnitude can be approximated as follows:

[0069] ;

[0070] The above formula shows that the ripple of the double power frequency voltage... The voltage amplitude is inversely proportional to the capacitance C of the small-capacity film capacitor. The use of small-capacity film capacitors instead of traditional large-volume electrolytic capacitors is precisely to actively retain this pulsating energy, allowing it to fully manifest as voltage ripple on the DC bus. Furthermore, since the three sub-modules of the CHB are connected to the same AC source and employ a carrier phase-shift modulation strategy, the resulting ripple components are completely synchronized in phase and frequency.

[0071] Double power frequency voltage ripple component If all submodules in the CHB operate at the same frequency, then the DC bus output voltage of each submodule in the CHB is... All are expressed as follows:

[0072] ;

[0073] It should be noted that, in order to overcome the disadvantage of large size of traditional capacitors, this embodiment uses a small-capacity thin-film capacitor as the supporting capacitor of the DC bus. This design not only significantly reduces the hardware size and cost, but more importantly, it preserves the physical form of pulsating energy. By utilizing the limited energy storage capacity of the small-capacity capacitor, the twice-power frequency pulsating power cannot be completely absorbed, thus preserving the pulsating energy as voltage ripple on the DC bus. This allows it to propagate smoothly to the subsequent DAB converter, providing a double-power frequency voltage ripple in phase for the cancellation of the subsequent DAB converter.

[0074] Step 102: On the DAB isolation transmission side, each submodule in the CHB rectification side is connected to the primary side of the corresponding DAB unit through a small-capacity thin-film capacitor, and the primary side of each DAB unit is subjected to single-phase shift modulation, so that the modulation phase of the primary side of each DAB unit differs from each other by 120 degrees, thereby outputting multiple primary side voltage ripples with modulation phases differing from each other by 120 degrees.

[0075] It is understandable that each sub-module in the CHB rectifier side is connected to the primary side of the corresponding DAB unit via small-capacity thin-film capacitors, so that the DC bus voltage of each CHB module (including the in-phase double power frequency voltage ripple) serves as the primary side input of the DAB conversion module; please refer to [link to relevant documentation]. Figure 2 and Figure 3 On the DAB isolation transmission side, single-phase shift control is applied to the primary side of each DAB unit in the DAB conversion module, causing the modulation phases of the primary sides of each DAB unit to differ by 120 degrees sequentially. Through this modulation, the high-frequency switching carrier phases on the primary side of each DAB unit form a distribution differing by 120 degrees, while the in-phase low-frequency ripple envelope in the input voltage remains unchanged. This provides a condition for the formation of the zero-sequence circulating current Ic in the subsequent secondary side delta loop (i.e., the delta loop) and the cancellation of the output ripple, with complementary high-frequency excitation and in-phase low-frequency ripple superposition. The DAB conversion module includes three DAB units, an isolation capacitor, and a load.

[0076] It should be noted that each DAB unit includes a primary-side circuit, a transformer, and a secondary-side circuit; the primary-side circuit includes two pairs of diagonal switching transistors and an inductor; the secondary-side circuit includes two switching transistors. Specifically, as shown... Figure 2 and Figure 3As shown, the DAB isolation transmission side includes three DAB units, an isolation capacitor, and a load. The first DAB unit includes switches S1, S2, S3, and S4 on the primary side, an inductor, a transformer A, and switches S5 and S6 on the secondary side. The second DAB unit includes switches Q1, Q2, Q3, and Q4 on the primary side, an inductor, a transformer B, and switches Q5 and Q6 on the secondary side. The third DAB unit includes switches T1, T2, T3, and T4 on the primary side, an inductor, a transformer C, and switches T5 and T6 on the secondary side.

[0077] Among them, Figure 2 middle, Vpi (i=1, 2, 3) is the AC input current on the rectifier side of CHB; Ii (i=1, 2, 3) is the output voltage on the primary side of the DAB unit; Vload (i=1, 2, 3) is the leakage inductance current on the primary side of the DAB unit; and Vload is the load voltage.

[0078] In one specific implementation, step 102 may include the following steps:

[0079] S21. Connect the DC bus of each sub-module in the CHB rectifier side to the primary side of the corresponding DAB unit through a small-capacity thin-film capacitor, so that the double power frequency voltage ripple of each phase is used as the input voltage of the primary side of the corresponding DAB unit.

[0080] To clearly see the voltage composition, we need to analyze the primary AC voltage of the i-th module. Performing Fourier decomposition yields the following: ;in, ;So, In the formula: It is a standard symmetrical square wave with an amplitude of ±1, and k is the harmonic order.

[0081] S22. Perform single-phase-shift modulation on the primary side of each DAB unit, so that the conduction time of the diagonal switch on the primary side of each DAB unit is delayed by 120 degrees in sequence, so that the modulation phase on the primary side of each DAB unit is 120 degrees different from each other in sequence, thereby outputting multiple primary side voltage ripples with modulation phases 120 degrees different from each other.

[0082] In practical control, please refer to Figures 4-6The drive signals on the primary side of the three DAB units are strictly controlled to have a phase relationship of 120 degrees. That is, the switches S1 and S4 on the primary side of the first DAB unit, the switches Q1 and Q4 on the primary side of the second DAB unit, and the switches T1 and T4 on the primary side of the third DAB unit are sequentially lagging by 120 degrees. When the diagonal switches on the primary side, namely S1S4, Q1Q4, and T1T4, are fully turned on, the voltage flowing out of the switches is positive, that is, Vpi = +Vin, i = 1, 2, 3; where Vin is the input voltage on the primary side of the DAB unit, that is, the voltage flowing into the DAB unit (i.e., Vdc1, Vdc2, and Vdc3).

[0083] At this time, the leakage inductance currents (I1, I2 and I3) of each DAB unit rise linearly to store and transfer energy. When the switching transistor of the DAB unit receives the turn-off signal, the circuit does not immediately turn off and enters the dead time. At this time, in order to maintain the circuit, the leakage inductance currents (I1, I2 and I3) will be forced to flow through the other pair of diagonal switching transistors, namely diagonal switching transistors S2S3, Q2Q3 and T2T3, to freewheel. This freewheeling will clamp the terminal voltage of the diagonal switching transistors (i.e. S2S3, Q2Q3 and T2T3) to zero, thereby ensuring that the other pair of diagonal switching transistors (i.e. S1S4, Q1Q4 and T1T4) achieve zero-voltage turn-on.

[0084] The switching drive signal on the primary side of the first DAB unit is defined as follows: To construct a three-phase balanced system, the driving signals of subsequent modules are sequentially delayed by a fundamental phase of Ts / 3 in the time domain, as shown below:

[0085] ;

[0086] In the formula: High-frequency switching frequency, For runtime, the primary-side switch drive signal of the second DAB unit is... The primary-side switch drive signal of the third DAB unit is The aforementioned time-domain delay is equivalent to introducing initial phase deviations of 0°, 120°, and 240° into each DAB submodule. Furthermore, considering the phase shift angle Φ between the primary and secondary sides of the DAB, the secondary side switching signal... There is an inherent time-domain propagation delay relative to the original edge. Where ws is the switching angular frequency, i.e., satisfying .

[0087] Step 103: Connect the secondary side of each DAB unit using a delta connection to form a closed zero-sequence loop; transmit multiple primary-side voltage ripples with a phase difference of 120 degrees through a transformer isolation to the secondary side of the corresponding DAB unit, and perform duty cycle modulation on the secondary side of each DAB unit. For the i-th module, the secondary side output voltage.

[0088] Please see Figure 2 and Figure 3 In this embodiment, a delta connection is used to connect the secondary side of each DAB unit. Therefore, the primary voltage ripple, after isolation and transformation by the DAB transformer, forms a closed zero-sequence loop on the secondary side (e.g., ...). Figure 3 The triangular circulation path marked in red is superimposed in series, meaning the zero-sequence loop provides an internal circulation channel for ripple energy.

[0089] Since these three primary-side voltage ripples are in phase, according to Kirchhoff's Voltage Law (KVL), their superposition forms a non-zero zero-sequence electromotive force with an amplitude three times that of a single-phase ripple. ,Right now:

[0090] ;

[0091] In the formula: This represents the turns ratio of the transformer on the primary and secondary sides; since the ripple components of the CHB modules are completely synchronized, then... , and Equal. A delta connection is used to connect the secondary sides of each DAB unit, creating a closed cancellation path for voltage ripple. The energy flow containing twice the power frequency voltage ripple in phase is isolated and transmitted through a transformer. Combined with a single-phase-shift modulation strategy with a 120-degree phase difference on the primary side, the three voltage ripple components referred to the secondary side have a 120-degree spatial vector difference in phase. According to Kirchhoff's Voltage Law (KVL), these three staggered voltage ripples are vector-summed within the delta closed loop. Utilizing the complementary characteristics of sinusoidal quantities, the instantaneous vector sum of the three-phase ripple voltages is always equal to zero, thus locking the ripple energy within the internal channels of the delta for physical cancellation, ensuring a stable output DC voltage.

[0092] Please see Figures 4-6In the DAB unit, the H-bridge switches on the secondary side do not operate synchronously with the primary side but instead combine with the single-phase-shift control strategy of the primary side, switching on and off with a 50% duty cycle. When the switches on the secondary side are turned on, the primary-side voltage and the calculated secondary-side voltage work together on the leakage inductance. Simultaneously, the delta connection on the secondary side of the DAB unit forms a closed zero-sequence loop. Because the modulation phases on the primary side differ by 120 degrees, the three ripple voltages transmitted to the secondary side are also staggered in modulation phase. Utilizing the complementary characteristics of the modulation phases, the in-phase ripple from the previous stage is transmitted to the circulating current, and the phase difference effectively cancels out the ripples in the circulating current. Figures 4-6 The horizontal axis of the waveform graph represents the sampling point (s), and the vertical axis represents the amplitude of the drive signal voltage of the switching transistor (V).

[0093] Step 104: In the zero-sequence loop, by utilizing the vector superposition characteristic of the output voltages on the secondary side of each DAB unit, the voltage ripple components with a modulation phase difference of 120 degrees transmitted from the primary side to the secondary side of each DAB unit are vector-cancelled in the zero-sequence loop, so that the output voltage of each DAB unit retains only the fundamental active component, thereby achieving voltage ripple suppression.

[0094] Specifically, to prevent the transmission of double-frequency voltage ripple to the load side at its physical source, this embodiment utilizes the spatial superposition characteristic of voltage vectors in a delta connection. By applying a 120-degree phase modulation to each DAB unit, the originally in-phase voltage ripples, after being transmitted to the secondary delta loop, exhibit a spatially complementary 120-degree phase distribution. According to Kirchhoff's Voltage Law (KVL), these three staggered voltage ripple vectors instantaneously superimpose at the nodes of the delta closed loop, and their vector sum is mathematically always equal to zero. Thus, the voltage ripple energy is locked within the internal channels of the delta, achieving physical cancellation. This ensures that the DC voltage output to the load side retains only a stable fundamental component, significantly improving the output power quality.

[0095] For the i-th module of DAB, performing a Fourier expansion on the DC voltage component output from its secondary side while retaining the fundamental component yields:

[0096] ;

[0097] In the formula: This refers to the fundamental component output from the secondary side of the i-th DAB unit; This represents the phase shift angle, and π / 6 represents the voltage gain coefficient resulting from the star-to-delta conversion. It is an inherent phase shift in the spectrum. The phase introduced by Ts / 3, the amplitude of the primary side square wave fundamental is ;

[0098] The three DAB units on the DAB isolation transmission side are algebraically summed in the zero-sequence loop, and their total output port voltage Vout(t) is expressed as follows:

[0099] ;

[0100] As shown in the above equation, the orthogonal components generated by unit 2 and unit 3 always cancel each other out, and the sum of the in-phase components precisely smooths out the potential fluctuations of submodule 1. At the physical level, the instantaneous vector sum of ripple energy is reduced to zero, and residual harmonics are only distributed in the 6k±1 high-frequency band, significantly improving the DC output quality. Ripple can cancel each other out in the delta circuit, leaving only the steady-state value, thus ensuring ripple-free voltage transmitted to the load side.

[0101] This embodiment, without requiring large-capacity electrolytic capacitors, not only completely absorbs the power ripple caused by single-phase rectification through internal circulating current, but also ensures that the voltage output to the load is a DC voltage with suppressed ripple.

[0102] In this embodiment, three in-phase double-frequency voltage ripples are used as input sources. By applying phase complementary modulation with a 120-degree phase difference to each DAB unit, the originally in-phase voltage ripples are given spatial complementary properties. In the zero-sequence channel formed by the secondary delta connection, the three equivalent voltage ripple vectors with a 120-degree phase difference are instantaneously superimposed. Based on the vector synthesis characteristics of the three-phase balanced system, the synthesis result is always equal to zero at each node, thereby locking the ripple voltage in the internal loop of the system to achieve physical cancellation. Thus, the output end physically blocks the transmission path of the double-frequency ripple energy, retaining only the stable DC fundamental component, thereby achieving efficient suppression of DC output voltage ripple without the need for a large-capacity capacitor. , and Each DAB unit corresponds to a DAB secondary triangle network node that outputs current to the external load. , and These are the branch currents between each DAB unit in the zero-sequence loop.

[0103] This invention provides a modulation method for the high-frequency link structure of a power electronic transformer that can suppress DC output voltage ripple. It has the following effects: a ripple suppression strategy based on the DAB secondary delta connection and phase complementary modulation is designed. By reconstructing the DAB secondary side into a delta connection, a zero-sequence circulating current channel is constructed for in-phase ripple in the propagation path. At the same time, with the 120-degree phase difference modulation strategy, the natural phase complementary characteristics of the three-phase system are utilized to make the ripple energy vector superimposed and canceled inside the delta loop, thereby achieving the effect of ripple suppression.

[0104] To verify the effectiveness of this solution, please refer to [link / reference]. Figures 7-9 .by Figure 7 For example, the output voltage Vp1 on the primary side of the DAB unit is a high-frequency square wave. The primary-side switch operates normally under single-phase-shift modulation. The phase-shifted voltage distribution synthesizes a zero-sequence electromotive force in the secondary-side delta circulating current. This electromotive force utilizes the channel established when the secondary-side switch is turned on to drive ripple energy to circulate internally in the form of a circulating current, achieving instantaneous power balance. This allows the load voltage Vload to remain stable even when there are large fluctuations on the input side. Combined with... Figures 7-9 It can be observed that the conduction times of the output voltages Vp1, Vp2, and Vp3 on the primary side of the DAB unit are delayed by 120 degrees sequentially, while the leakage inductance currents I1, I2, and I3 on ​​the primary side provide freewheeling current for the diagonal switching transistors during the dead time, resulting in a continuous waveform without sharp peaks; and Figure 7 The output of the load voltage Vload is a straight line, which has a good ripple suppression effect.

[0105] The modulation device for the high-frequency link structure of a power electronic transformer capable of suppressing DC output voltage ripple provided in the embodiments of this application will be described below. The modulation device for the high-frequency link structure of a power electronic transformer capable of suppressing DC output voltage ripple described below can be referred to in correspondence with the modulation method for the high-frequency link structure of a power electronic transformer capable of suppressing DC output voltage ripple described above.

[0106] Please see Figure 10 This invention also provides a modulation device for a high-frequency link structure of a power electronic transformer capable of suppressing DC output voltage ripple. The device relates to the CHB rectifier side and the DAB isolation transmission side; the device includes:

[0107] The double power frequency voltage ripple input module 201 is used to connect the AC input terminal of each sub-module of CHB in series to the same AC power supply on the CHB rectifier side, and connect the DC output side of each sub-module in the CHB rectifier side to the corresponding small-capacity thin film capacitor. Carrier phase shift modulation is used to make the CHB rectifier side output double power frequency voltage ripple in phase.

[0108] The primary-side single-phase-shift modulation module 202 is used to connect each sub-module in the CHB rectifier side to the primary side of the corresponding DAB unit through a small-capacity thin-film capacitor on the DAB isolation transmission side, and to perform single-phase-shift modulation on the primary side of each DAB unit so that the modulation phases of the primary side of each DAB unit are sequentially 120 degrees apart, thereby outputting multiple primary-side voltage ripples with modulation phases 120 degrees apart.

[0109] The secondary side is connected to the modulation module 203, which is used to connect the secondary side of each DAB unit in a delta connection to form a closed zero-sequence loop; multiple primary side voltage ripples with a phase difference of 120 degrees are transmitted to the secondary side of the corresponding DAB unit through transformer isolation, and the duty cycle of each DAB unit is modulated.

[0110] The voltage ripple suppression output module 204 is used to utilize the vector superposition characteristics of the output voltages on the secondary side of each DAB unit in the zero-sequence loop, so that the voltage ripple components with a modulation phase difference of 120 degrees transmitted from the primary side to the secondary side of each DAB unit are vector-cancelled in the zero-sequence loop, thereby so that the output voltage of each DAB unit retains only the fundamental active component, thus achieving voltage ripple suppression.

[0111] Optionally, the double power frequency voltage ripple input module 201 is specifically used for,

[0112] The AC input terminals of each submodule of CHB are connected in series to the same AC power supply. A carrier phase-shift modulation strategy is adopted to generate a double power frequency voltage ripple in phase with the DC voltage of each submodule in CHB, which is then used as the input of each DAB unit.

[0113] Optionally, the primary-side single-phase-shift modulation module 202 is specifically used for,

[0114] Each sub-module in the CHB rectifier side is connected to the primary side of the corresponding DAB unit by using a small-capacity thin-film capacitor, so that the double power frequency voltage ripple of each in phase is used as the input voltage of the primary side of the corresponding DAB unit.

[0115] Single-phase-shift modulation is applied to the primary side of each DAB unit, causing the turn-on time of the diagonal switches on the primary side of each DAB unit to be delayed by 120 degrees in sequence. This results in the modulation phases on the primary side of each DAB unit being 120 degrees apart in sequence, thereby outputting multiple primary-side voltage ripples with modulation phases 120 degrees apart.

[0116] This invention also provides a computer device, including a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the modulation method for the high-frequency link structure of any of the power electronic transformers described above.

[0117] This invention also provides a computer-readable storage medium storing a computer program or instructions thereon, wherein the computer program or instructions, when executed by a processor, implement the steps of the modulation method for the high-frequency link structure of any of the above power electronic transformers.

[0118] This invention also provides a computer program product, including a computer program or instructions, wherein when the computer program or instructions are executed by a processor, the steps of the modulation method for the high-frequency link structure of any of the above power electronic transformers are implemented.

[0119] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0120] The terms "first," "second," "third," etc., used in this application's specification and the foregoing drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented, for example, in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0121] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between apparatuses or units through some interfaces, and may be electrical, mechanical, or other forms.

[0122] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0123] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0124] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0125] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A modulation method for the high-frequency link structure of a power electronic transformer capable of suppressing DC output voltage ripple, characterized in that, The method involves the CHB rectifier side and the DAB isolated transmission side; the method includes: On the CHB rectifier side, the AC input terminal of each sub-module in the CHB rectifier side is connected in series to the same AC power supply, and the DC output side of each sub-module in the CHB rectifier side is connected to the corresponding small-capacity thin film capacitor. A carrier phase-shift modulation strategy is adopted to make the DC voltage of each sub-module in the CHB generate a double power frequency voltage ripple in phase, which is used as the input of each DAB unit. On the DAB isolation transmission side, the DC bus of each sub-module in the CHB rectifier side is connected to the primary side of the corresponding DAB unit through a small-capacity thin-film capacitor, and the primary side of the DAB unit is subjected to single-phase-shift modulation, so that the modulation phase of the primary side of the DAB unit is 120 degrees different from each other in sequence, thereby outputting multiple primary side voltage ripples with modulation phases 120 degrees different from each other. The secondary side of each DAB unit is connected in a delta configuration to form a closed zero-sequence loop. Multiple primary-side voltage ripples with a phase difference of 120 degrees are transmitted to the secondary side of the corresponding DAB unit through transformer isolation, and the duty cycle of the secondary side of the DAB unit is modulated. In the zero-sequence loop, the vector superposition characteristic of the output voltages on the secondary side of each DAB unit is utilized to enable the voltage ripple components with a modulation phase difference of 120 degrees transmitted from the primary side to the secondary side of each DAB unit to undergo vector cancellation in the zero-sequence loop. This results in the output voltage of each DAB unit retaining only the fundamental active component, thereby suppressing voltage ripple.

2. The modulation method for the high-frequency link structure of the power electronic transformer according to claim 1, characterized in that, The step of connecting the DC bus of each submodule in the CHB rectifier side to the primary side of the corresponding DAB unit via a small-capacity thin-film capacitor, and performing single-phase-shift modulation on the primary side of each DAB unit so that the modulation phases of the primary side of each DAB unit differ by 120 degrees sequentially, thereby outputting multiple primary-side voltage ripples with modulation phases differing by 120 degrees, includes: By using small-capacity thin-film capacitors, the DC bus of each sub-module in each CHB rectifier side is connected to the primary side of the corresponding DAB unit, so that the double power frequency voltage ripple of each in phase is used as the input voltage of the primary side of the corresponding DAB unit. Single-phase-shift modulation is applied to the primary side of each DAB unit, causing the turn-on time of the diagonal switches on the primary side of each DAB unit to be delayed by 120 degrees in sequence. This results in the modulation phases on the primary side of each DAB unit being 120 degrees apart in sequence, thereby outputting multiple primary-side voltage ripples with modulation phases 120 degrees apart.

3. The modulation method for the high-frequency link structure of the power electronic transformer according to claim 2, characterized in that, The switching drive signals on the primary side of each DAB unit are represented as follows: ； In the formula: , and These are the primary-side switch drive signals for the first DAB unit, the second DAB unit, and the third DAB unit, respectively. For high-frequency switching frequency, This refers to the runtime.

4. The modulation method for the high-frequency link structure of the power electronic transformer according to claim 1, characterized in that, The step of connecting the AC input terminals of each sub-module of the CHB in series to the same AC power supply on the rectifier side of the CHB, and connecting the DC bus of each CHB module to the corresponding small-capacity thin-film capacitor, and using a carrier phase-shift modulation strategy to generate a DC voltage ripple of twice the power frequency in phase for each sub-module in the CHB, includes: On the CHB rectifier side, the AC input terminal of each CHB submodule is connected in series to the same AC power supply, and a carrier phase shift modulation strategy is adopted to make each CHB module output twice the power frequency pulsating power in phase. The DC output side of each submodule in the CHB rectifier side is connected to the corresponding small-capacity thin-film capacitor, so that the voltage of each small-capacity thin-film capacitor generates in-phase secondary ripple with the corresponding double power frequency pulsation, so that the CHB rectifier side outputs in-phase double power frequency voltage ripple.

5. The modulation method for the high-frequency link structure of the power electronic transformer according to claim 3, for the i-th DAB unit, performing Fourier expansion on the DC voltage component output from its secondary side and retaining the fundamental component during expansion yields: ； In the formula: This is the fundamental component output from the secondary side of the i-th DAB unit; This represents the phase shift angle, and π / 6 represents the voltage gain coefficient resulting from the star-to-delta conversion. It is an inherent phase shift in the spectrum. The phase introduced by Ts / 3, the amplitude of the primary side square wave fundamental is ; The three DAB units on the DAB isolation transmission side are algebraically summed in the zero-sequence loop, and their total output port voltage Vout(t) is expressed as follows: 。 6. A modulation device for a high-frequency link structure of a power electronic transformer capable of suppressing DC output voltage ripple, characterized in that, The device relates to the CHB rectifier side and the DAB isolated transmission side; the device includes: The double power frequency voltage ripple input module is used to connect the AC input terminals of three cascaded CHB modules in series to the same AC power supply on the CHB rectifier side, and connect the DC output side of each sub-module in the CHB rectifier side to the corresponding small-capacity thin film capacitor. The carrier phase-shift modulation strategy is used to generate a double power frequency voltage ripple in phase with the DC voltage of each sub-module in the CHB, which is then used as the input of each DAB unit. The primary-side single-phase-shift modulation module is used to connect the DC bus of each sub-module in the CHB rectifier side to the primary side of the corresponding DAB unit through a small-capacity thin-film capacitor on the DAB isolation transmission side, and to perform single-phase-shift modulation on the primary side of each DAB unit so that the modulation phases of the primary side of each DAB unit are sequentially 120 degrees apart, thereby outputting multiple primary-side voltage ripples with modulation phases 120 degrees apart. The secondary side is connected to the modulation module, which is used to connect the secondary side of each DAB unit in a delta configuration to form a closed zero-sequence loop; multiple primary side voltage ripples with a modulation phase difference of 120 degrees are transmitted to the secondary side of the corresponding DAB unit through transformer isolation, and the duty cycle of each DAB unit is modulated. The voltage ripple suppression output module is used in the zero-sequence circuit to utilize the vector superposition characteristics of the output voltages on the secondary side of each DAB unit, so that the voltage ripple components with a modulation phase difference of 120 degrees transmitted from the primary side to the secondary side of each DAB unit are vector-cancelled in the zero-sequence circuit, thereby so that the output voltage of each DAB unit retains only the fundamental active component, thus achieving voltage ripple suppression.

7. The modulation device for the high-frequency link structure of the power electronic transformer according to claim 6, characterized in that, The primary-side single-phase-shift modulation module is specifically used for... By using small-capacity thin-film capacitors, the DC bus of each sub-module in the CHB rectifier side is connected to the primary side of the corresponding DAB unit, so that the double power frequency voltage ripple of each in phase is used as the input voltage of the primary side of the corresponding DAB unit. Single-phase-shift modulation is applied to the primary side of each DAB unit, causing the turn-on time of the diagonal switches on the primary side of each DAB unit to be delayed by 120 degrees in sequence. This results in the modulation phases on the primary side of each DAB unit being 120 degrees apart in sequence, thereby outputting multiple primary-side voltage ripples with modulation phases 120 degrees apart.

8. A computer device, comprising a memory, a processor, and a computer program stored in the memory, characterized in that, The processor executes the computer program to implement the steps of the modulation method for the high-frequency link structure of the power electronic transformer as described in any one of claims 1-5.

9. A computer-readable storage medium having a computer program or instructions stored thereon, characterized in that, When the computer program or instructions are executed by the processor, they implement the steps of the modulation method for the high-frequency link structure of the power electronic transformer as described in any one of claims 1-5.

10. A computer program product, comprising a computer program or instructions, characterized in that, When the computer program or instructions are executed by the processor, they implement the steps of the modulation method for the high-frequency link structure of the power electronic transformer as described in any one of claims 1-5.

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