Hybrid modulation method for three-phase high-frequency isolated dc-ac matrix converter

Abstract

This invention discloses a hybrid modulation method for a three-phase high-frequency isolated DC-AC matrix converter. The method first divides the power frequency cycle into 12 operating intervals based on the overlap and zero-crossing points of the three-phase AC voltages, and sorts the line voltages within each interval according to their absolute values. The maximum power factor angle is determined based on the amplitudes of the DC-side and AC-side voltages, and the AC-side current reference value and the limited reference power factor angle are obtained through power closed-loop control. In the modulation stage, dual-line voltage modulation is first attempted. Two line voltages are selected based on the instantaneous product of the voltage and current reference values, and the outward phase shift angle and the duty cycle of the second-largest line voltage are calculated. If the results meet the constraints, the drive signal is updated; otherwise, the mode switches to three-line voltage modulation. In this mode, three line voltages are selected, and the optimal ratio of the minimum and second-largest line voltage duty cycles is obtained by looking up a table based on the DC voltage and the reference power factor angle. The control parameters are then recalculated, and the drive signal is updated accordingly.

Description

Technical Field

[0001] This invention relates to the field of power converter control, and more specifically, to a hybrid modulation method for a three-phase high-frequency isolated DC-AC matrix converter. Background Technology

[0002] High efficiency is the core pursuit of next-generation power electronic conversion technology, especially in energy storage and electric vehicles involving high-power charging and discharging, where even a small improvement in efficiency translates into significant economic benefits. Currently, the conventional approach to achieving bidirectional energy flow between the grid and batteries is to use a two-stage isolated DC-AC converter. Although this architecture is technically mature, it involves multiple energy conversion processes, with a large number of stages through which power flows, and some power devices struggle to achieve zero-voltage / zero-current (ZVS / ZCS) soft-switching operation over a wide voltage range or under light load conditions.

[0003] The matrix-type three-phase single-stage isolated DC-AC converter circuit has no intermediate DC energy storage stage, and can achieve soft switching of all power devices through appropriate modulation strategies. Therefore, it is a highly promising high-efficiency, high-power-density isolated energy storage converter topology. However, its complex topology also brings technical challenges to modulation and closed-loop control.

[0004] Patent CN116545296A provides a topology and modulation method for a high-frequency isolated three-phase inverter with bidirectional energy flow. It uses a capacitor to replace the bidirectional switch of the lower bridge arm on the AC side, reducing the use of active devices. However, the patent does not analyze the reactive power output capability.

[0005] Patent CN120855928B discloses a closed-loop control method for a single-stage three-phase high-frequency isolated converter circuit, which generates a drive signal based on the modulation ratio and vector angle. However, its main purpose is to achieve unity power factor correction, and it cannot perform reactive power control on the AC side over a wide voltage range. Existing patents mostly focus on performance optimization of three-phase high-frequency isolated DC-AC matrix converters at unity power factor, and rarely address the reactive power output capability of the converter, making it difficult to meet the power factor range requirements of applications such as energy storage, photovoltaic power generation, and vehicle-to-grid interaction. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a hybrid modulation method for a three-phase high-frequency isolated DC-AC matrix converter.

[0007] According to the present invention, 1. A hybrid modulation method for a three-phase high-frequency isolated DC-AC matrix converter, comprising:

[0008] Step S1: Divide one power frequency cycle into multiple working intervals based on the overlap points and zero-crossing points of the three-phase AC voltages; Step S2: Within each working interval, sort the absolute values ​​of the three-phase line voltages and define the line voltage with the largest absolute value. The second largest absolute value of the line voltage Minimum absolute value of the term line voltage ; Step S3: Calculate the maximum allowable power factor angle of the converter based on the DC side voltage and AC side voltage amplitude; based on the maximum power factor angle and the three-phase voltage and current on the AC output side, obtain the AC side current reference value and reference power factor angle through power closed-loop control; Step S4: Sort the three-phase line voltages according to the instantaneous product of the AC side voltage and the corresponding AC side current reference value and the absolute value of the three-phase line voltage. Select two line voltages to be applied to the secondary side of the high-frequency transformer in sequence, and calculate the external phase shift angle of the AC and DC sides and the duty cycle of the second largest AC side line voltage. Step S5: Determine whether the outward phase angle and the duty cycle meet the preset constraint conditions. If they do, update the drive signals of each power device according to the outward phase angle and the duty cycle. Step S6: If the external phase shift angle and the duty cycle do not meet the preset constraints, then three line voltages are selected and applied sequentially to the secondary side of the high-frequency transformer. Based on the DC side voltage and the reference power factor angle, the optimal ratio between the duty cycle of the minimum AC side line voltage and the second largest AC side line voltage is obtained by looking up a table. Based on the optimal ratio, the external phase shift angle of the AC / DC side and the duty cycle of each line voltage on the AC side are recalculated, and the drive signals of each power device are updated based on the recalculated results.

[0009] Preferably, in step S3, the formula for calculating the maximum power factor angle includes:

[0010] in, The angle representing the maximum power factor. DC voltage This refers to the phase voltage amplitude on the AC side. This refers to the turns ratio of a high-frequency transformer.

[0011] Preferably, the method for calculating the reference power factor angle in step S3 includes: Step S3.1: Obtain the three-phase voltage and current on the AC output side; Step S3.2: Transform the three-phase voltage and current in the stationary coordinate system to the rotating coordinate system through coordinate transformation. Coordinate system; Step S3.3: Calculate the actual output active power and reactive power; Step S3.4: Perform closed-loop control on the active and reactive power on the AC side to obtain... Shaft current reference value and Shaft current reference value ; Step S3.5: Based on Shaft current reference value and Shaft current reference value Calculate the AC side current reference value and reference power factor angle; Step S3.6: Limit the reference power factor angle to ensure it does not exceed the maximum power factor angle allowed by the converter.

[0012] Preferably, in step S4, the three-phase line voltages are sorted according to the instantaneous product of the AC side voltage and the corresponding AC side current reference value and the absolute value of the three-phase line voltage, and two line voltages are selected to be applied sequentially to the secondary side of the high-frequency transformer, including: Calculate the phase voltage at the intermediate value. Phase voltage The corresponding current reference value product ; when At that time, the selected AC side line voltage is the line voltage with the largest absolute value. The second largest absolute value of the line voltage ; when At that time, the selected AC side line voltage is the line voltage with the largest absolute value. Minimum absolute value of the term line voltage .

[0013] Preferably, in step S4, calculating the outward phase shift angle on the AC / DC side and the duty cycle of the second largest line voltage on the AC side includes: According to phase voltage The corresponding AC side current reference value From the expression for the active power transmitted by the converter and the analytical formula for the line voltage, the line voltage duty cycle of the smaller absolute value term in the selected line voltage is calculated. Outward phase angle between AC and DC sides .

[0014] Preferably, the analytical expression for the active power transmitted by the converter is as follows:

[0015] In the formula, For switching frequency, The duty cycle of the line voltage with the smaller absolute value among the selected line voltages. The outward phase shift angle between the AC and DC sides. DC voltage This indicates a power transfer inductance.

[0016] The phase voltage The corresponding AC side current reference value The expression is as follows:

[0017] In the formula, For switching frequency, The duty cycle of the line voltage with the smaller absolute value among the selected line voltages. The outward phase shift angle between the AC and DC sides. DC voltage This indicates a power transfer inductance.

[0018] Preferably, in step S5, the preset constraints include: the range of values ​​for the outward phase angle, the range of values ​​for the duty cycle of the second largest AC line voltage, and the range of values ​​for the sum of the outward phase angle and the duty cycle of the second largest line voltage; if the constraints are not met, the three line voltages selected in step S6 are: the negative minimum term line voltage, the positive second largest term line voltage, and the positive maximum term line voltage.

[0019] Preferably, in step S6, the table in the lookup method is obtained in the following way: The converter is tested across different combinations of DC-side voltage and power factor angles throughout its full operating range. Calculate the peak inductor current for each set of operating conditions under different duty cycle ratios, where the duty cycle ratio is the ratio of the absolute value of the minimum term line voltage to the absolute value of the second largest term line voltage. The duty cycle ratio that minimizes the peak inductor current is selected as the optimal ratio under this operating condition. A lookup table is formed by establishing a mapping relationship between the DC side voltage, power factor angle, and the corresponding optimal duty cycle ratio.

[0020] Preferably, in step S6, recalculating the outward phase shift angle on the AC / DC side and the duty cycle of each line voltage on the AC side based on the optimal ratio includes: After obtaining the duty cycle ratio of the minimum absolute value term line voltage and the second largest absolute value term line voltage on the AC side by looking up the table, the intermediate value phase voltage is... The corresponding AC side current and the active power transmitted by the converter are uniformly represented as functions of the duty cycle of the second largest line voltage and the outward phase shift angle of the AC and DC sides; Using the AC / DC outward phase shift angle and the duty cycle of the second largest term line voltage as unknowns, based on the transmission power reference value and the intermediate phase voltage... The corresponding AC side current reference value The external phase shift angle and the duty cycle of the AC side second largest line voltage that satisfy the constraints are calculated. The duty cycle of the AC side minimum absolute term line voltage is calculated based on the ratio of the duty cycles of the AC side minimum absolute term line voltage and the AC side second largest absolute term line voltage obtained from the table, and the duty cycle of the AC side second largest absolute term line voltage.

[0021] Preferably, the function relating the duty cycle of the second-largest line voltage to the outward phase shift angle of the AC / DC side is as follows:

[0022]

[0023] In the formula, Indicates power transfer inductance ， For switching frequency, The duty cycle of the line voltage with the smallest absolute value among the selected line voltages. The duty cycle of the line voltage with the smaller absolute value among the selected line voltages. This is the outward phase shift angle between the AC and DC sides.

[0024] Compared with the prior art, the present invention has the following beneficial effects: By flexibly switching modulation modes within different operating ranges, the converter can maintain strong reactive power regulation capabilities under a wide range of DC voltage conditions. This method not only effectively increases the upper limit of reactive power output of the system under high DC voltage, but also significantly reduces the peak value of inductor current and stress level during reactive power output, thereby improving the thermal performance and reliability of the devices, enhancing system operational stability, and further broadening the application scope of the converter in scenarios such as new energy grid connection and flexible power conversion. Attached Figure Description

[0025] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a topology diagram of a three-phase high-frequency isolated DC-AC matrix converter in one embodiment; Figure 2 This is a flowchart illustrating the control method for the three-phase high-frequency isolated DC-AC matrix converter of the present invention. Figure 3 This is a preferred embodiment of the AC side voltage range division diagram; Figure 4 This is a typical waveform of the interval 2 two-line voltage modulation method in a preferred embodiment; Figure 5 This is a typical waveform of the three-wire voltage modulation method in a preferred embodiment of the interval 2; Figure 6 This is the result of the modulation degree of freedom calculation in a preferred embodiment; Figure 7 This is a simulation diagram of the AC side voltage and current in a preferred embodiment; Figure 8 This is a simulation diagram of the switching cycle voltage and current in a preferred embodiment. Detailed Implementation

[0026] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0027] Example 1: This invention provides a hybrid modulation method for a three-phase high-frequency isolated DC-AC matrix converter, comprising: Step S1: Based on the overlap points and zero-crossing points of the three-phase AC voltages, divide one power frequency cycle into 12 working intervals; Step S2: Within each working interval, sort the absolute values ​​of the three-phase line voltages and define the line voltage with the largest absolute value. The second largest absolute value of the line voltage Minimum absolute value of the term line voltage ; Step S3: Calculate the maximum allowable power factor angle of the converter based on the DC-side voltage and AC-side voltage amplitudes; Step S4: Based on the maximum power factor angle and the three-phase voltage and current on the AC output side, obtain the AC side current reference value and reference power factor angle through power closed-loop control; Step S5: Sort the three-phase line voltages according to the instantaneous product of the AC side voltage and the corresponding AC side current reference value and the absolute value of the three-phase line voltage. Select two line voltages to be applied to the secondary side of the high-frequency transformer in sequence, and calculate the external phase shift angle of the AC and DC sides and the duty cycle of the second largest AC side line voltage. Step S6: Determine whether the outward phase angle and the duty cycle meet the preset constraint conditions. If they do, update the drive signals of each power device according to the outward phase angle and the duty cycle. If the external phase shift angle and the duty cycle do not meet the preset constraints, three line voltages are selected to be applied sequentially to the secondary side of the high-frequency transformer. Based on the DC side voltage and the reference power factor angle, the optimal ratio between the duty cycle of the minimum AC side line voltage and the second largest AC side line voltage is obtained by looking up a table. Based on the optimal ratio, the external phase shift angle of the AC / DC side and the duty cycle of each line voltage on the AC side are recalculated, and the drive signals of each power device are updated based on the recalculated results.

[0028] In this embodiment, the formula for calculating the maximum power factor angle in step S3 includes:

[0029] in, The angle representing the maximum power factor. DC voltage This refers to the phase voltage amplitude on the AC side. This refers to the turns ratio of a high-frequency transformer.

[0030] In this embodiment, step S4 includes: Step S4.1: Obtain the three-phase voltage and current on the AC output side; Step S4.2: Transform the three-phase voltage and current in the stationary coordinate system to the rotating coordinate system through coordinate transformation. Coordinate system; Step S4.3: Calculate the actual output active power and reactive power; Step S4.4: Perform closed-loop control on the active and reactive power on the AC side to obtain... Shaft current reference value and Shaft current reference value ; Step S4.5: Based on Shaft current reference value and Shaft current reference value Calculate the AC side current reference value and reference power factor angle; Step S4.6: Limit the reference power factor angle to ensure it does not exceed the maximum power factor angle allowed by the converter.

[0031] In this embodiment, the calculation formulas for the AC side current reference value and the reference power factor angle in step S4.5 are as follows:

[0032] In the formula, Indicates the reference value of the AC side current. This represents the reference power factor angle.

[0033] In this embodiment, in step S5, the three-phase line voltages are sorted according to the instantaneous product of the AC side voltage and the corresponding AC side current reference value and the absolute value of the three-phase line voltage, and two line voltages are selected to be applied sequentially to the secondary side of the high-frequency transformer, including: Calculate the phase voltage at the intermediate value. Phase voltage The corresponding current reference value product ; when At that time, the selected AC side line voltage is the line voltage with the largest absolute value. The second largest absolute value of the line voltage ; when At that time, the selected AC side line voltage is the line voltage with the largest absolute value. Minimum absolute value of the term line voltage .

[0034] In this embodiment, step S5, calculating the outward phase shift angle on the AC / DC side and the duty cycle of the second largest line voltage on the AC side, includes: According to phase voltage The corresponding AC side current reference value From the expression for the active power transmitted by the converter and the analytical formula for the line voltage, the line voltage duty cycle of the smaller absolute value term in the selected line voltage is calculated. Outward phase angle between AC and DC sides .

[0035] In this embodiment, the analytical expression for the active power transmitted by the converter is obtained as follows: One switching cycle is divided into 6 stages, and the inductor current is obtained based on the voltage across the inductor. Expressions within each stage; During one switching cycle, the DC side voltage and inductor current are compared... The average of the products of the two powers is used to obtain the analytical expression for the transmitted active power.

[0036] In this embodiment, the analytical expression for the active power transmitted by the converter is as follows:

[0037] In the formula, For switching frequency, The duty cycle of the line voltage with the smaller absolute value among the selected line voltages. The outward phase shift angle between the AC and DC sides. DC voltage Indicates power transfer inductance The phase voltage The corresponding AC side current reference value The expression is as follows:

[0038] In the formula, For switching frequency, The duty cycle of the line voltage with the smaller absolute value among the selected line voltages. The outward phase shift angle between the AC and DC sides. DC voltage Indicates power transfer inductance In this embodiment, in step S6, the preset constraints include: the range of values ​​for the outward phase angle, the range of values ​​for the duty cycle of the second largest AC line voltage, and the range of values ​​for the sum of the outward phase angle and the duty cycle of the second largest line voltage.

[0039] In this embodiment, the three line voltages selected in step S6 are: the negative minimum term line voltage, the positive second largest term line voltage, and the positive maximum term line voltage.

[0040] In this embodiment, in step S6, the table in the lookup method is obtained in the following way: The converter is tested across different combinations of DC-side voltage and power factor angles throughout its full operating range. Calculate the peak inductor current for each set of operating conditions under different duty cycle ratios, where the duty cycle ratio is the ratio of the absolute value of the minimum term line voltage to the absolute value of the second largest term line voltage. The duty cycle ratio that minimizes the peak inductor current is selected as the optimal ratio under this operating condition. A lookup table is formed by establishing a mapping relationship between the DC side voltage, power factor angle, and the corresponding optimal duty cycle ratio.

[0041] In this embodiment, step S6, recalculating the outward phase shift angle of the AC / DC side and the duty cycle of each line voltage on the AC side based on the optimal ratio, includes: After obtaining the duty cycle ratio of the minimum absolute value term line voltage and the second largest absolute value term line voltage on the AC side by looking up the table, the intermediate value phase voltage is... The corresponding AC side current and the active power transmitted by the converter are uniformly represented as functions of the duty cycle of the second largest line voltage and the outward phase shift angle of the AC and DC sides; Using the AC / DC outward phase shift angle and the duty cycle of the second largest term line voltage as unknowns, based on the transmission power reference value and the intermediate phase voltage... The corresponding AC side current reference value The external phase shift angle and the duty cycle of the AC side second largest line voltage that satisfy the constraints are calculated. The duty cycle of the AC side minimum absolute term line voltage is calculated based on the ratio of the duty cycles of the AC side minimum absolute term line voltage and the AC side second largest absolute term line voltage obtained from the table, and the duty cycle of the AC side second largest absolute term line voltage.

[0042] In this embodiment, the function relating the duty cycle of the second-largest line voltage to the outward phase shift angle of the AC / DC side is as follows:

[0043]

[0044] In the formula, Indicates power transfer inductance ， For switching frequency, The duty cycle of the line voltage with the smaller absolute value among the selected line voltages. This is the outward phase shift angle between the AC and DC sides.

[0045] Example 2: Typically, the DC side of a three-phase single-stage isolated DC-AC converter is configured with one or more full-bridge circuits, while the AC side consists of a three-phase matrix circuit with bidirectional switches. The DC and AC sides are interconnected via a high-frequency transformer, and power is transferred between the DC and AC sides through an inductor, which can also be integrated into the leakage inductance of the high-frequency transformer. Furthermore, a DC blocking capacitor can be connected in series in either the primary or secondary circuit.

[0046] like Figure 1 The diagram illustrates a specific three-phase high-frequency isolated DC-AC matrix converter topology, including a DC-side full-bridge module, a high-frequency transformer, a power transfer inductor, and an AC-side three-phase matrix converter module. For a three-phase single-stage isolated DC-AC converter with the same or similar topology, a preferred embodiment of the present invention provides a control method flowchart, as shown below. Figure 2 As shown, the method includes steps 1 to 6: Step 1: Based on the overlap points and zero-crossing points of the three-phase AC voltages, divide one power frequency cycle into 12 working intervals, and sort the absolute values ​​of the three-phase line voltages within each working interval. Step 2: Determine the maximum allowable power factor angle of the converter based on the DC-side voltage and AC-side voltage amplitude, and obtain the AC-side current reference value and reference power factor angle through power closed-loop control; Step 3: Based on the instantaneous product of AC side voltage and AC side current, two line voltages are selected and applied sequentially to the secondary side of the high-frequency transformer. The external phase shift angle of the AC and DC sides and the duty cycle of the second largest line voltage on the AC side are obtained through numerical calculation. Step 4: Determine whether the external phase shift angle and the duty cycle of the AC side secondary line voltage meet the preset constraint conditions. If they do, update the drive signals of each power device according to the calculation results. Step 5: If the external phase shift angle and the duty cycle of the second largest AC line voltage do not meet the preset constraints, then three line voltages are selected and applied sequentially to the secondary side of the high-frequency transformer, and the optimal ratio of the duty cycle of the minimum AC line voltage to the second largest AC line voltage is obtained by looking up a table based on the DC side voltage and power factor angle. Step 6: Recalculate the external phase shift angle on the AC / DC side and the duty cycle of each line voltage on the AC side based on the optimal ratio, and update the drive signals of each power device based on the recalculation results.

[0047] The above embodiments can flexibly switch modulation modes in different operating ranges, enabling the converter to maintain strong reactive power regulation capability under a wide range of DC voltage conditions, and reducing the peak value and stress level of inductor current during reactive power output.

[0048] In a preferred embodiment, such as Figure 3 As shown, the power frequency cycle is divided into 12 intervals based on the overlap points and zero-crossing points of the three-phase phase voltages, including interval 1, interval 2, interval 3, interval 4, interval 5, interval 6, interval 7, interval 8, interval 9, interval 10, interval 11, and interval 12. The three line voltages within each interval are sorted according to their absolute values, as follows: v max , v mid and v min Taking interval 2 as an example, the line voltage with the largest absolute value is v. ac The second largest absolute value of the line voltage is v. bc The line voltage with the smallest absolute value is v. ab .

[0049] Measure the amplitudes of the DC-side voltage and AC-side voltage. Calculate the theoretical maximum power factor angle under the current DC voltage based on the theoretically derived relationship between the maximum power factor angle and the DC voltage. The calculation formula is as follows:

[0050] in, max The angle of maximum power factor, v dc It is a DC voltage, V m V is the amplitude of the AC phase voltage, and n is the turns ratio of the high-frequency transformer. In this example, v dc 200V, V m If the voltage is 155.5V and n is 0.8, then... max It is 47.1°.

[0051] The three-phase voltage and current at the sampled AC output side are transformed from the stationary coordinate system to the rotating coordinate system through coordinate transformation. dq A coordinate system is established, and the actual output active and reactive power are calculated. Closed-loop control is then performed on the active and reactive power on the AC side to obtain... d shaft current reference value i dref and q shaft current reference value i qrefThe amplitude of the output current reference value and the power factor angle are calculated according to the following formula.

[0052] The power factor angle reference value is limited to ensure that it does not exceed the theoretical maximum power factor angle under the current DC voltage.

[0053] Calculate the phase voltage at the intermediate value. v gmid Reference value of current corresponding to intermediate phase voltage i gmidref product q th .when q th When the value is greater than 0, the selected AC side line voltage is the line voltage with the largest absolute value. v max The second largest absolute value of the line voltage v mid .when q th When <0, the selected AC side line voltage is the line voltage with the largest absolute value. v max Minimum absolute value of the term line voltage v min .

[0054] In this implementation, taking a voltage in interval 2, a current leading the voltage by 37.5°, and a closed-loop output current reference amplitude of 4.29A as an example, the phase voltage in interval 2, where the voltage is at its midpoint, is v. b The corresponding phase current reference value is i bref

[0055] Therefore, the line voltage selected for interval 2 is the line voltage v with the largest absolute value. ac The second largest absolute value of the line voltage v bc .

[0056] like Figure 4 As shown, each switching moment divides one switching cycle into 6 stages. The inductor current can be obtained from the voltage across the inductor. i L Expressions within each stage. DC-side voltage and inductor current within one switching cycle. i L Averaging the products of these factors, we can obtain the analytical expression for the transmitted active power as follows:

[0057] In the formula, f s The switching frequency is 50kHz in this example.d 1 represents the line voltage duty cycle of the smaller absolute value term among the selected line voltages. d f This is the outward phase shift angle between the AC and DC sides.

[0058] Inductor current i L Three-phase current i x ( x The positive direction of (a, b, c) is as follows: Figure 1 As indicated by the label, the expression for the phase b current in interval 2 is:

[0059] Calculate based on the AC side current reference value corresponding to the intermediate phase voltage and the converter transmission power. d 1 and d f ,in, d The value of 1 ranges from [0, 0.5]. d f The value range is [0, 0.25]. d 1 and d f The sum can take values ​​in the range [0, 0.5]. d 1 and d f When the corresponding value range constraints are satisfied at the same time, according to d 1 and d f Update the drive signals for each power device on both the DC and AC sides. The order of action of the transformer secondary voltage within one switching cycle is v. bc v ac -v bc -v ac .

[0060] In this embodiment, when the calculated AC / DC side outward phase shift angle and AC side second-largest line voltage duty cycle do not meet the preset constraints, the AC side switches from two-line voltage modulation to three-line voltage modulation, such as... Figure 5 As shown, in interval 2, the three line voltages on the AC side are successively the line voltage v, which is the smallest term with the smallest negative absolute value. ba The second largest positive absolute value of the line voltage v bc The maximum absolute value of the positive term line voltage v ac .

[0061] Each switching moment divides a switching cycle into 8 stages. The expression for the active power transmitted within a switching cycle is as follows:

[0062] The expression for the phase b current in interval 2 is:

[0063] d 0 represents the duty cycle of the line voltage with the smallest absolute value among the selected line voltages. When using a three-line voltage modulation method to control the converter, it is necessary to redetermine the duty cycle of each line voltage on the AC side and the outward phase shift angle on the AC and DC sides to meet the requirements of power transmission and current control.

[0064] First, regarding the duty cycle allocation problem of the minimum and second-largest line voltages on the AC side in the three-wire voltage modulation method, a lookup table method is adopted to determine the optimal ratio, with the goal of minimizing the peak inductor current during the switching cycle. Specifically, during the control parameter design phase, numerical calculations are performed across the entire operating range of the converter, traversing different combinations of DC-side voltage and power factor angles. For each set of operating conditions, the peak inductor current under different duty cycle ratios is calculated. The duty cycle ratio that minimizes the peak inductor current is selected as the optimal ratio for that operating condition. A mapping relationship is established between the DC-side voltage, power factor angle, and the corresponding optimal duty cycle ratio, forming a lookup table.

[0065] During converter operation, the duty cycle ratio of the minimum and second-largest AC line voltages is obtained by looking up a table based on the current DC-side voltage and power factor angle. In this embodiment, v dc 200V ref The angle is 37.5°, and the optimal ratio k = d0 / d1 = 2.3 obtained by looking up the table. Based on this, the control parameters under three-wire voltage modulation are recalculated. Specifically, the AC side current corresponding to the intermediate phase voltage on the AC side and the transmission power of the converter are uniformly expressed as functions of the external phase shift angle on the AC / DC side and the duty cycle of the second largest line voltage on the AC side.

[0066] Subsequently, using the AC / DC side outward phase shift angle and the duty cycle of the second largest line voltage on the AC side as the variables to be solved, and the target transmission power of the converter and the AC side current reference value corresponding to the intermediate phase voltage as the control targets, the outward phase shift angle and the duty cycle of the second largest line voltage on the AC side that satisfy the constraints are calculated through numerical solution. After obtaining the duty cycle of the second largest line voltage on the AC side, the duty cycle of the minimum line voltage on the AC side is further calculated by combining the ratio of the duty cycle of the minimum line voltage to the duty cycle of the second largest line voltage obtained from the table lookup, thereby completing the update of the duty cycle of each line voltage on the AC side and the outward phase shift angle on the AC / DC side, and updating the drive signals of each power device accordingly. When k=2.3, the calculation results of each control variable are as follows. Figure 6 As shown.

[0067] The drive signals of each power device cause the AC side line voltages to act in the following order during the switching cycle: the negative absolute minimum term line voltage, the positive absolute second largest term line voltage, the positive absolute maximum term line voltage, the positive absolute minimum term line voltage, the negative absolute second largest term line voltage, and the negative absolute maximum term line voltage. Corresponding to interval 2, the line voltages are v... ba v bc v ac -v ba -v bc -v ac .

[0068] In a preferred embodiment, after implementing steps 1 to 6 above, the simulated AC side voltage and current waveforms of the three-phase high-frequency isolated DC-AC matrix converter are as follows: Figure 7 As shown, the simulated waveforms of voltage and current across the inductor during the switching cycle are as follows: Figure 8 As shown.

[0069] The present invention also provides a hybrid modulation system for a three-phase high-frequency isolated DC-AC matrix converter. The hybrid modulation system for the three-phase high-frequency isolated DC-AC matrix converter can be implemented by executing the process steps of the hybrid modulation method for the three-phase high-frequency isolated DC-AC matrix converter. That is, those skilled in the art can understand the hybrid modulation method for the three-phase high-frequency isolated DC-AC matrix converter as a preferred embodiment of the hybrid modulation system for the three-phase high-frequency isolated DC-AC matrix converter.

[0070] Those skilled in the art will understand that, besides implementing the system and its various devices, modules, and units provided by this invention in the form of purely computer-readable program code, the same functions can be achieved entirely through logical programming of the method steps, making the system and its various devices, modules, and units of this invention function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system and its various devices, modules, and units provided by this invention can be considered as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; alternatively, the devices, modules, and units for implementing various functions can be considered as both software modules implementing the method and structures within the hardware component.

[0071] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A hybrid modulation method for a three-phase high-frequency isolated DC-AC matrix converter, characterized in that, include: Step S1: Divide one power frequency cycle into multiple working intervals based on the overlap points and zero-crossing points of the three-phase AC voltages; Step S2: Within each working interval, sort the absolute values ​​of the three-phase line voltages and define the line voltage with the largest absolute value. The second largest absolute value of the line voltage Minimum absolute value of the term line voltage ; Step S3: Calculate the maximum allowable power factor angle of the converter based on the DC side voltage and AC side voltage amplitude; based on the maximum power factor angle and the three-phase voltage and current on the AC output side, obtain the AC side current reference value and reference power factor angle through power closed-loop control; Step S4: Sort the three-phase line voltages according to the instantaneous product of the AC side voltage and the corresponding AC side current reference value and the absolute value of the three-phase line voltage. Select two line voltages to be applied to the secondary side of the high-frequency transformer in sequence, and calculate the external phase shift angle of the AC and DC sides and the duty cycle of the second largest AC side line voltage. Step S5: Determine whether the outward phase angle and the duty cycle meet the preset constraint conditions. If they do, update the drive signals of each power device according to the outward phase angle and the duty cycle. Step S6: If the external phase shift angle and the duty cycle do not meet the preset constraints, then three line voltages are selected and applied sequentially to the secondary side of the high-frequency transformer. Based on the DC side voltage and the reference power factor angle, the optimal ratio between the duty cycle of the minimum AC side line voltage and the second largest AC side line voltage is obtained by looking up a table. Based on the optimal ratio, the external phase shift angle of the AC / DC side and the duty cycle of each line voltage on the AC side are recalculated, and the drive signals of each power device are updated based on the recalculated results.

2. The method according to claim 1, characterized in that, In step S3, the formula for calculating the maximum power factor angle includes: in, The angle representing the maximum power factor. DC voltage This refers to the phase voltage amplitude on the AC side. This refers to the turns ratio of a high-frequency transformer.

3. The method according to claim 1, characterized in that, The method for calculating the reference power factor angle in step S3 includes: Step S3.1: Obtain the three-phase voltage and current on the AC output side; Step S3.2: Transform the three-phase voltage and current in the stationary coordinate system to the rotating coordinate system through coordinate transformation. Coordinate system; Step S3.3: Calculate the actual output active power and reactive power; Step S3.4: Perform closed-loop control on the active and reactive power on the AC side to obtain... Shaft current reference value and Shaft current reference value ; Step S3.5: Based on Shaft current reference value and Shaft current reference value Calculate the AC side current reference value and reference power factor angle; Step S3.6: Limit the reference power factor angle to ensure it does not exceed the maximum power factor angle allowed by the converter.

4. The method according to claim 1, characterized in that, In step S4, the three-phase line voltages are sorted according to the instantaneous product of the AC side voltage and the corresponding AC side current reference value and the absolute value of the three-phase line voltage. Two line voltages are then applied sequentially to the secondary side of the high-frequency transformer, including: Calculate the phase voltage at the intermediate value. Phase voltage The corresponding current reference value product ; when At that time, the selected AC side line voltage is the line voltage with the largest absolute value. The second largest absolute value of the line voltage ; when At that time, the selected AC side line voltage is the line voltage with the largest absolute value. Minimum absolute value of the term line voltage .

5. The method according to claim 1, characterized in that, In step S4, calculating the outward phase shift angle on the AC / DC side and the duty cycle of the second largest line voltage on the AC side includes: According to phase voltage The corresponding AC side current reference value From the expression for the active power transmitted by the converter and the analytical formula for the line voltage, the line voltage duty cycle of the smaller absolute value term in the selected line voltage is calculated. Outward phase angle between AC and DC sides .

6. The method according to claim 5, characterized in that, The analytical expression for the active power transmitted by the converter is as follows: In the formula, For switching frequency, The duty cycle of the line voltage term with the smaller absolute value among the selected line voltages. The outward phase shift angle between the AC and DC sides. DC voltage Indicates power transfer inductance; The phase voltage The corresponding AC side current reference value The expression is as follows: In the formula, For switching frequency, The duty cycle of the line voltage term with the smaller absolute value among the selected line voltages. The outward phase shift angle between the AC and DC sides. DC voltage This represents the power transfer inductance.

7. The method according to claim 1, characterized in that, In step S5, the preset constraints include: the range of values ​​for the outward phase angle, the range of values ​​for the duty cycle of the second largest AC line voltage, and the range of values ​​for the sum of the outward phase angle and the duty cycle of the second largest line voltage. If the constraints are not met, the three line voltages selected in step S6 are: the negative minimum term line voltage, the positive second largest term line voltage, and the positive maximum term line voltage.

8. The method according to claim 1, characterized in that, In step S6, the table obtained through the lookup method is obtained in the following way: The converter is tested across different combinations of DC-side voltage and power factor angles throughout its full operating range. Calculate the peak inductor current for each set of operating conditions under different duty cycle ratios, where the duty cycle ratio is the ratio of the absolute value of the minimum term line voltage to the absolute value of the second largest term line voltage. The duty cycle ratio that minimizes the peak inductor current is selected as the optimal ratio under this operating condition. A lookup table is formed by establishing a mapping relationship between the DC side voltage, power factor angle, and the corresponding optimal duty cycle ratio.

9. The method according to claim 1, characterized in that, In step S6, recalculating the outward phase shift angle on the AC / DC side and the duty cycle of each line voltage on the AC side based on the optimal ratio includes: After obtaining the duty cycle ratio of the minimum absolute value term line voltage and the second largest absolute value term line voltage on the AC side by looking up the table, the intermediate value phase voltage is... The corresponding AC side current and the active power transmitted by the converter are uniformly represented as functions of the duty cycle of the second largest line voltage and the outward phase shift angle of the AC and DC sides; Using the AC / DC outward phase shift angle and the duty cycle of the second largest term line voltage as unknowns, based on the transmission power reference value and the intermediate phase voltage... The corresponding AC side current reference value The external phase shift angle and the duty cycle of the AC side second largest line voltage that satisfy the constraints are calculated. The duty cycle of the AC side minimum absolute term line voltage is calculated based on the ratio of the duty cycles of the AC side minimum absolute term line voltage and the AC side second largest absolute term line voltage obtained from the table, and the duty cycle of the AC side second largest absolute term line voltage.

10. The method according to claim 9, characterized in that, The function relating the duty cycle of the second-largest line voltage to the outward phase shift angle of the AC / DC side is as follows: In the formula, Indicates power transfer inductance ， For switching frequency, The duty cycle of the line voltage with the smallest absolute value among the selected line voltages. The duty cycle of the line voltage term with the smaller absolute value among the selected line voltages. This is the outward phase shift angle between the AC and DC sides.

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