Light load variable frequency phase-shift modulation method and system of three-phase single-stage isolated DC / AC matrix converter

Abstract

This invention provides a light-load frequency conversion phase-shift modulation method and system for a three-phase single-stage isolated DC / AC matrix converter, comprising: acquiring the current output power information of the converter and obtaining the per-unit value of the output power based on the rated power; determining the current target power range based on the per-unit value of the output power, and reading the corresponding recommended switching frequency from a preset power-frequency lookup table using the current target power range number as an index; substituting the recommended switching frequency as a known frequency parameter into a two-line voltage phase-shift modulation time-domain model to solve for the outward shift ratio between the DC-side full-bridge output voltage and the AC-side equivalent voltage, as well as the proportion of the selected line voltage on the AC side, and generating PWM drive signals for the DC-side full-bridge module and the AC-side three-phase matrix converter module accordingly.

Description

Technical Field

[0001] This invention relates to the field of power electronic power converter control technology, specifically to a light-load frequency conversion phase shift modulation method and system for a three-phase single-stage isolated DC / AC matrix converter. Background Technology

[0002] Three-phase single-stage isolated DC / AC matrix converters are a type of isolated power conversion device without an intermediate DC bus. These converters achieve electrical isolation through a high-frequency transformer and directly convert high-frequency AC quantities to three-phase AC quantities via a three-phase matrix converter module on the AC side. They feature compact structure, high power density, and bidirectional energy transmission capabilities, and can be applied to isolated energy storage converters, grid-connected energy storage, and flexible power conversion applications.

[0003] In the control of this type of converter, power transmission control is typically achieved by adjusting the phase relationship between the equivalent voltages on both sides of the high-frequency transformer. Existing dual-line voltage phase-shift modulation methods can select two AC-side line voltages to participate in the synthesis based on the grid voltage phase. The transmitted power is adjusted by utilizing the outward shift ratio between the DC-side full-bridge output voltage and the AC-side equivalent voltage, and the AC-side voltage duration and grid-side current synthesis are adjusted by utilizing the selected line voltage's active proportion. This type of method can achieve power transmission, current synthesis, and partial soft switching within a certain load range.

[0004] However, under light load conditions, the reduced transmission power leads to a decrease in the shift ratio and the amplitude of the high-frequency inductor current. The direction or amplitude of the inductor current at some commutation moments may not meet the zero-voltage switching requirements of the power devices, resulting in some commutation actions losing soft switching capability. For three-phase single-stage isolated DC / AC matrix converters, the line voltage synthesized on the AC side varies with the grid phase, and the zero-voltage switching conditions required for AC side commutation also change accordingly. Therefore, the limitation of soft switching under light load conditions is not only related to the output power but also to the grid phase and the line voltage amplitude.

[0005] Existing fixed-frequency phase-shift modulation methods typically solve for the external phase shift ratio and the proportion of the AC side line voltage at a given switching frequency. This limits their adjustable degrees of freedom and makes it difficult to simultaneously achieve light-load power transmission, AC side current synthesis, and soft-switching coverage across the entire power frequency phase range. Therefore, it is necessary to provide a light-load modulation method suitable for three-phase single-stage isolated DC / AC matrix converters. This method maintains the basic structure of dual-line voltage phase-shift modulation, selects a suitable switching frequency based on the light-load power range, and re-solves for the modulation degrees of freedom at the selected switching frequency to improve the soft-switching coverage under light-load conditions. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a light-load frequency conversion phase-shift modulation method and system for a three-phase single-stage isolated DC / AC matrix converter.

[0007] A light-load frequency conversion phase-shift modulation method for a three-phase single-stage isolated DC / AC matrix converter, provided by the present invention, includes: Step S1: Obtain the current output power information of the three-phase single-stage isolated DC / AC matrix converter, and preprocess the obtained current output power information to obtain the preprocessed current output power information; obtain the per-unit value of the output power based on the preprocessed current output power information and the rated power. Step S2: Determine the current target power range based on the per-unit output power value; Step S3: Using the current target power range number as an index, read the corresponding recommended switching frequency from the preset power-frequency lookup table. f s The recommended switching frequency f s The soft-switching coverage evaluation is pre-determined based on the maximum power transmission capacity constraint and multiple power test points and multiple grid phase sampling points within the target power range; Step S4: Set the recommended switching frequency f s Substituting the known frequency parameters into the two-wire voltage phase-shift modulation time-domain model, we can solve for the outward shift ratio between the DC-side full-bridge output voltage and the AC-side equivalent voltage. d f and the proportion of the selected line voltage effect on the AC side d 1; Step S5: Based on the outward shift comparison d f and the proportion of the selected line voltage on the AC side d 1. Generate PWM drive signals for the DC-side full-bridge module and the AC-side three-phase matrix converter in the three-phase single-stage isolated DC / AC matrix converter, so as to improve the soft switching margin at the commutation moment in the current target power range while meeting the requirements of power transmission and AC-side current synthesis.

[0008] Preferably, step S1 includes: Step S1.1: Obtain the current output power through upper-level power commands, power closed-loop controller output, power estimation module output, or voltage and current sampling calculation; wherein, the voltage and current sampling calculation includes: sampling the three-phase voltage and three-phase current on the AC side and calculating the active power on the AC side, or sampling the voltage and current on the DC side and calculating the power on the DC side. Step S1.2: Perform preprocessing on the acquired current output power information, including low-pass filtering, moving average, delay compensation or rate of change limiting, to obtain the preprocessed current output power information; Step S1.3: Obtain the per-unit value of output power based on the preprocessed current output power information and rated power.

[0009] Preferably, in step S2, the current target power range is a power sub-range within a preset light load optimization range; The preset light-load optimization range is determined based on the soft-switching coverage distribution corresponding to different output powers under fixed-frequency phase-shift modulation, and according to the per-unit value of output power. P / P N The system is divided into multiple power sub-intervals, and the per-unit width of adjacent power sub-intervals is a preset step size.

[0010] Preferably, step S3 includes: Step S3.1: Generate a preset power-frequency lookup table offline; the preset power-frequency lookup table is a one-dimensional configuration table indexed by the current target power range number, and the recommended switching frequency... f s It is a scalar value independent of the instantaneous phase of the power grid; Step S3.2: Using the current target power range number as an index, read the corresponding recommended switching frequency from the preset power-frequency lookup table. f s .

[0011] Preferably, step S3.1 includes: Step S3.1.1: For each target power range, set up multiple power test points, multiple grid phase sampling points covering at least one power frequency cycle, and multiple candidate switching frequencies; Step S3.1.2: For each candidate switching frequency, first perform maximum power transmission capability screening. If the maximum transmission power at the candidate frequency is less than the upper limit of the target power range, then the candidate frequency is eliminated. For the candidate frequencies that pass the screening, then solve the outward shift ratio at each power test point and each grid phase sampling point. d f The proportion of the selected line voltage effect on the AC side d 1. The high-frequency inductor current at each commutation moment is obtained from the time-domain model; Step S3.1.3: Determine whether each commutation operation meets the zero-voltage switching condition based on the direction and amplitude of the inductor current, and calculate the soft-switching coverage rate; calculate the soft-switching coverage rate based on the number of commutation operations that do not meet the zero-voltage switching condition and the total number of commutation operations included in the statistics; use the lowest soft-switching coverage rate as the evaluation index for the candidate switching frequency, and select the candidate switching frequency with the highest evaluation index as the recommended switching frequency. f s If the evaluation indicators of multiple candidate frequencies are similar and meet the preset requirements, the lower frequency is selected first, and the target power range number - recommended switching frequency is written into the lookup table.

[0012] Preferably, the zero-voltage switching conditions include: the inductor current direction and amplitude conditions for the DC-side commutation operation, and the inductor current direction and amplitude conditions for the AC-side three-phase matrix converter module commutation operation. The amplitude condition is determined based on the equivalent output capacitance of the commutation device, the dead time, and the voltage amplitude of the corresponding commutation stage, so that the current flowing through the high-frequency inductor can charge or discharge the equivalent output capacitance of the commutation device during the dead time.

[0013] Preferably, the time-domain model of the dual-line voltage phase-shift modulation in step S4 includes:

[0014] The transmission power constraint is expressed as:

[0015] The AC-side current synthesis constraint is expressed as:

[0016] in, , , Let be the inductor currents at times t0, t1, and t2, respectively. For the selected line voltage v mid Duty cycle; Compared to the outward shift between the DC side and the AC side; The transformer turns ratio The absolute maximum line voltage, The second largest absolute value line voltage, It is a DC voltage; For power transfer inductors, The switching frequency; Select recommended switching frequency f s Then, a numerical method was used to solve for the outward shift ratio between the DC-side full-bridge output voltage and the AC-side equivalent voltage. df The proportion of the selected line voltage effect on the AC side d 1; The numerical methods include: table lookup interpolation, binary search, Newton iteration, or damped Newton iteration.

[0017] Preferably, step S5 includes: Step S5.1: The control system performs sector determination based on the currently sampled or estimated three-phase AC voltage; Step S5.2: Determine the AC side line voltages participating in the synthesis during the current switching cycle based on the sector, and assign the proportion of the selected AC side line voltages to the total voltages. d 1 is converted into the conduction time of the corresponding AC side bidirectional switch; Step S5.3: Compare the outward movement d f This is converted into a phase-shifting time base that leads or lags the DC-side full-bridge output voltage relative to the AC-side equivalent voltage range. Step S5.4: The PWM generator generates PWM drive signals for the DC-side full-bridge module and the AC-side three-phase matrix converter module based on the conduction time and phase-shifting time base.

[0018] Preferably, when the output power per unit value P / P N When the target power range is near the boundary of an adjacent target power range, the current target power range is updated using a hysteresis switching method. When the recommended switching frequency needs to be updated f s At the end of the current switching cycle, at the PWM carrier synchronization time, or at a preset synchronization time, the frequency is switched to a new recommended switching frequency. f s And recalculate the outward shift ratio during the switching cycle after the switch. d f The proportion of the selected line voltage effect on the AC side d 1.

[0019] A light-load frequency conversion phase-shift modulation system for a three-phase single-stage isolated DC / AC matrix converter, according to the present invention, comprises: Module M1: Acquires the current output power information of the three-phase single-stage isolated DC / AC matrix converter, preprocesses the acquired current output power information to obtain preprocessed current output power information, and obtains the per-unit value of output power based on the preprocessed current output power information and the rated power. Module M2: Determines the current target power range based on the per-unit output power value; Module M3: Using the current target power range number as an index, reads the corresponding recommended switching frequency from the preset power-frequency lookup table. f s The recommended switching frequency f s The soft-switching coverage evaluation is pre-determined based on the maximum power transmission capacity constraint and multiple power test points and multiple grid phase sampling points within the target power range; Module M4: The recommended switching frequency f s Substituting the known frequency parameters into the two-wire voltage phase-shift modulation time-domain model, we can solve for the outward shift ratio between the DC-side full-bridge output voltage and the AC-side equivalent voltage. d f and the proportion of the selected line voltage effect on the AC side d 1; Module M5: Based on the outward shift comparison d f and the proportion of the selected line voltage on the AC side d 1. Generate PWM drive signals for the DC-side full-bridge module and the AC-side three-phase matrix converter in the three-phase single-stage isolated DC / AC matrix converter, so as to improve the soft switching margin at the commutation moment in the current target power range while meeting the requirements of power transmission and AC-side current synthesis.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention selects a recommended switching frequency based on the target power range, which can improve the inductor current distribution during commutation under light load conditions and increase the range of zero-voltage switching of power devices on both the DC and AC sides. 2. When generating the power-frequency lookup table offline, this invention simultaneously considers the maximum power transmission capacity constraint and the soft-switching coverage under multiple power test points and multiple power grid phase sampling points, which can avoid the problem that a single fixed switching frequency cannot take into account the soft-switching performance of the entire power frequency phase. 3. When the present invention is running online, it only needs to acquire power information, determine power range, select frequency by looking up table and solve modulation degree of freedom. It does not need to traverse candidate switching frequencies and grid phase sampling points in real time, which can reduce the amount of online calculation and facilitate its implementation in digital controllers. 4. This invention can suppress frequent frequency jumps near the power range boundary by preprocessing power information, switching power range hysteresis, and synchronously switching recommended switching frequencies; at the same time, when multiple candidate switching frequencies have the same or similar soft switching coverage, the lower frequency is preferentially selected to avoid unnecessary increases in the switching frequency. Attached Figure Description

[0021] 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 schematic diagram of the topology of a three-phase single-stage isolated DC / AC matrix converter.

[0022] Figure 2 This is a schematic diagram of two-line voltage phase-shift modulation.

[0023] Figure 3 This is a flowchart of online light-load frequency conversion phase-shift modulation.

[0024] Figure 4 Flowchart for offline generation of power-frequency lookup table.

[0025] Figure 5 This is a schematic diagram of a light-load frequency conversion phase-shift modulation control system. 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 scope of protection of the present invention.

[0027] Example 1 The present invention provides a light-load frequency conversion phase-shift modulation method for a three-phase single-stage isolated DC / AC matrix converter, applicable to a three-phase single-stage isolated DC / AC matrix converter including a DC-side full-bridge module, a high-frequency transformer, an AC-side three-phase matrix converter module, and an AC-side filter stage, comprising the following steps: Step 1: Obtain the current output power information of the three-phase single-stage isolated DC / AC matrix converter, and based on the current output power information... P and rated power P N Obtain the per-unit value of output power P / P N ; Specifically, the current output power information is obtained from upper-level power commands, power closed-loop controller output, power estimation module output, or voltage and current sampling calculation; wherein, the voltage and current sampling calculation includes sampling the three-phase voltage and three-phase current on the AC side and calculating the active power on the AC side, or sampling the voltage and current on the DC side and calculating the power on the DC side.

[0028] Step 2: Based on the output power per unit value P / P NDetermine the current target power range; Specifically, the target power range is a sub-range of power within a preset light-load optimization range; the preset light-load optimization range is determined based on the soft-switching coverage distribution corresponding to different output powers under fixed-frequency phase-shift modulation, and according to the per-unit value of output power. P / P N The system is divided into multiple power sub-intervals, and the per-unit width of adjacent power sub-intervals is a preset step size, preferably 0.05.

[0029] Step 3: Using the current target power range number as an index, read the corresponding recommended switching frequency from the preset power-frequency lookup table. f s The recommended switching frequency f s The soft-switching coverage evaluation is pre-determined based on the maximum power transmission capacity constraint and multiple power test points and multiple grid phase sampling points within the target power range; Specifically, the preset power-frequency lookup table is a one-dimensional configuration table indexed by the current target power range number, and the recommended switching frequency... f s It is a scalar value independent of the instantaneous phase of the power grid.

[0030] The preset power-frequency lookup table is generated offline, and the generation process includes: For each target power range, multiple power test points, multiple grid phase sampling points covering at least one power frequency cycle, and multiple candidate switching frequencies are set up; Solving the outward shift ratio at each candidate switching frequency, each power test point, and each grid phase sampling point d f The proportion of the selected line voltage effect on the AC side d 1; The inductor current at each commutation moment is obtained from the solution results; Based on the direction and magnitude of the inductor current at each commutation moment, determine whether the corresponding commutation action meets the zero-voltage switching condition; Based on the assessment results, a target power range and a recommended switching frequency are determined. f s The correspondence between them.

[0031] The zero-voltage switching conditions include the inductor current direction and amplitude conditions for DC-side commutation operation, and the inductor current direction and amplitude conditions for AC-side three-phase matrix converter module commutation operation. The amplitude condition is determined based on the equivalent output capacitance of the device to be commutated, the dead time, and the voltage amplitude of the corresponding commutation stage, so that the current flowing through the high-frequency inductor can charge or discharge the equivalent output capacitance of the device to be commutated during the dead time.

[0032] The offline method first filters candidate switching frequencies based on maximum power transmission capability. If the maximum transmission power of a candidate switching frequency is less than the upper limit of the corresponding target power range, the candidate switching frequency is eliminated. From the remaining candidate switching frequencies, a recommended switching frequency is then determined based on soft-switching coverage. f s .

[0033] For each candidate switching frequency, the commutation operation is assessed at each power test point and each grid phase sampling point within the same target power range to determine whether it meets the zero-voltage switching condition. The soft-switching coverage rate is calculated based on the number of commutation operations that do not meet the zero-voltage switching condition and the total number of commutation operations included in the statistics. The lowest soft-switching coverage rate is used as the evaluation index for that candidate switching frequency, and the candidate switching frequency with the highest evaluation index is selected as the recommended switching frequency. f s When the difference in evaluation metrics among multiple candidate switching frequencies is no greater than a preset threshold, the lower candidate switching frequency is selected as the recommended switching frequency. f s .

[0034] Step 4: Set the recommended switching frequency f s Substituting the known frequency parameters into the two-wire voltage phase-shift modulation time-domain model, we can solve for the outward shift ratio between the DC-side full-bridge output voltage and the AC-side equivalent voltage. d f and the proportion of the selected line voltage effect on the AC side d 1; Step 5: Based on the outward shift comparison d f and the proportion of the selected line voltage on the AC side d 1. Generate PWM drive signals for the DC-side full-bridge module and the AC-side three-phase matrix converter in the three-phase single-stage isolated DC / AC matrix converter, so as to improve the soft switching margin at the commutation moment in the current target power range while meeting the requirements of power transmission and AC-side current synthesis.

[0035] The present invention also provides a light-load frequency conversion phase-shift modulation system for a three-phase single-stage isolated DC / AC matrix converter. The light-load frequency conversion phase-shift modulation system for the three-phase single-stage isolated DC / AC matrix converter can be implemented by executing the process steps of the light-load frequency conversion phase-shift modulation method for the three-phase single-stage isolated DC / AC matrix converter. That is, those skilled in the art can understand the light-load frequency conversion phase-shift modulation method for the three-phase single-stage isolated DC / AC matrix converter as a preferred embodiment of the light-load frequency conversion phase-shift modulation system for the three-phase single-stage isolated DC / AC matrix converter.

[0036] Example 2 Example 2 is a preferred example of Example 1. To address the problems of insufficient commutation current direction or amplitude under light load conditions in existing fixed-frequency phase-shift modulation and the difficulty of some power devices meeting zero-voltage switching conditions, this invention provides a light-load frequency conversion phase-shift modulation method and system for a three-phase single-stage isolated DC / AC matrix converter.

[0037] The light-load frequency conversion phase-shift modulation method for the three-phase single-stage isolated DC / AC matrix converter includes: Obtain the current output power information of the converter, and based on the current output power information and the rated power... P N Obtain the per-unit value of output power P / P N According to the per-unit value of output power P / P N Determine the current target power range; using the current target power range number as an index, read the corresponding recommended switching frequency from a preset power-frequency lookup table. f s Recommended switching frequency f s Substituting known frequency parameters into the two-wire voltage phase-shift modulation time-domain model allows us to calculate the integral time of the switching frequency change on the high-frequency inductor current through the switching period change, the duration of each voltage application phase, and the power transfer process. The external phase shift ratio is then solved within the two-wire voltage phase-shift modulation time-domain model. d f The proportion of the selected line voltage effect on the AC side d 1; According to d f and d 1. Generate PWM drive signals for the DC-side full-bridge module and the AC-side three-phase matrix converter module.

[0038] The current output power information can be obtained from upper-level power commands, power closed-loop controller output, power estimation module output, or voltage and current sampling calculation. Specifically, voltage and current sampling calculation includes sampling the three-phase AC voltage and current and calculating the AC active power, or sampling the DC voltage and current and calculating the DC power. All of these different power acquisition methods are used to characterize the current energy transfer level of the converter and do not change the core process of this invention: power partition lookup table frequency selection and re-solution of modulation degrees of freedom.

[0039] The power-frequency lookup table is generated through offline search. For each target power range, multiple power test points, multiple grid phase sampling points covering at least one power frequency cycle, and multiple candidate switching frequencies are set. First, candidate switching frequencies that cannot cover the upper limit power of the target power range are eliminated based on the maximum power transmission capacity. Then, for the candidate switching frequencies that meet the power transmission constraints, the outward shift ratio is solved at each power test point and each grid phase sampling point. d f The proportion of the selected line voltage effect on the AC side d 1. Obtain the inductor current at each commutation moment; then, determine whether the corresponding commutation action meets the zero-voltage switching condition based on the direction and amplitude of the inductor current; calculate the soft-switching coverage rate based on the number of commutation actions that do not meet the zero-voltage switching condition and the total number of commutation actions included in the statistics; use the lowest soft-switching coverage rate at each power test point and each grid phase sampling point within the same target power range as the evaluation index for the candidate switching frequency; finally, select the candidate switching frequency with the highest evaluation index as the recommended switching frequency for the target power range. f s When the difference in evaluation metrics among multiple candidate switching frequencies is no greater than a preset threshold, the lower candidate switching frequency is selected first.

[0040] In the aforementioned offline search, the maximum power transfer capability constraint and soft-switching coverage evaluation are related by a series filtering relationship. Due to the switching frequency... f s Increasing this will shorten the effective energy transfer time within a single switching cycle, thus limiting the maximum transfer power. P max ( f s The power transmission rate decreases, so it is necessary to first ensure that the selected switching frequency can meet the power transmission requirements of the target power range, and then evaluate the soft switching coverage among the candidate frequencies that meet the power transmission capability. The recommended switching frequency obtained in this way is not a fixed rule that is simply linearly set according to the output power, but a discretized frequency sequence obtained by comprehensively considering the target power range, power frequency phase change, maximum power transmission capability, and zero-voltage switching coverage.

[0041] Example 3 Example 3 is a preferred example of Example 1. like Figure 1 As shown, the three-phase single-stage isolated DC / AC matrix converter includes: a DC-side full-bridge module, a high-frequency transformer, an AC-side three-phase matrix converter module, and an AC-side filter. The DC-side full-bridge module modulates the DC-side voltage into a high-frequency square wave voltage. The high-frequency transformer connects the DC-side full-bridge module and the AC-side three-phase matrix converter module, enabling high-frequency energy transmission and electrical isolation. The AC-side three-phase matrix converter module selects the appropriate line voltage for synthesis based on the AC-side three-phase voltage state. The AC-side filter removes high-frequency components near the switching frequency. The AC-side three-phase matrix converter module can be composed of multiple four-quadrant bidirectional switches, each of which can consist of two power switching devices connected with common drain or common source. These power switching devices include, but are not limited to, MOSFETs, SiC MOSFETs, GaN, or IGBTs.

[0042] like Figure 2 As shown, the DC-side full-bridge module output voltage during one switching cycle is... v p For high-frequency square wave voltage, the AC side three-phase matrix transformation module selects two AC side line voltages to participate in the synthesis based on the current grid voltage phase, so that the AC side equivalent voltage is... v s It exhibits a segmented multi-level waveform. For any grid phase, the AC line voltage can be divided into terms with the largest absolute value. v max The second largest absolute value term v mid The term with the smallest absolute value v min The main control degrees of freedom of two-wire voltage phase-shift modulation include the DC-side full-bridge output voltage. v p Equivalent voltage of AC side v s Compared to the outward shift d f And the proportion of the selected line voltage effect on the AC side. d 1. Among them, outward relocation compared to d f Used to regulate transmission power, the AC side selects the line voltage's active percentage. d 1. Used to adjust the duration of AC side line voltage and the synthesis of grid side current.

[0043] like Figure 3 As shown, a light-load frequency conversion phase-shift modulation method for a three-phase single-stage isolated DC / AC matrix converter according to the present invention includes: Step S1: Obtain the current output power information of the three-phase single-stage isolated DC / AC matrix converter.

[0044] The current output power information can be obtained from upper-level power commands, power closed-loop controller output, power estimation module output, or voltage and current sampling calculation.

[0045] The power closed-loop controller and power estimation module are functional modules in the three-phase single-stage isolated DC / AC matrix converter control system, which can typically be implemented by a processor, controller or digital control program. The voltage and current sampling calculation includes sampling the three-phase voltage and current on the AC side and calculating the active power on the AC side, or sampling the voltage and current on the DC side and calculating the power on the DC side. All of these different power acquisition methods are used to characterize the current energy transfer level of the converter and do not change the control process of this invention, which is based on power range lookup table frequency selection and re-solving the modulation degrees of freedom.

[0046] Step S2: Based on the current output power information and rated power P N Calculate the per-unit value of output power P / P N In calculating the per-unit value of output power. P / P N Previously, low-pass filtering, moving average, delay compensation, or rate of change limiting could be applied to the current output power information to suppress the impact of power detection noise, command mutations, or load disturbances on the selection of switching frequency.

[0047] Step S3: Based on the per-unit value of output power P / P N Determine the current target power range.

[0048] The target power range is a sub-range of power within a preset light-load optimization range; the preset light-load optimization range is determined based on the soft-switching coverage distribution corresponding to different output powers under fixed-frequency phase-shift modulation, and according to the per-unit value of output power. P / P N The power is divided into multiple power sub-intervals. In a preferred embodiment, the per-unit width between adjacent power sub-intervals is 0.05; in other embodiments, other preset step sizes can be selected based on controller storage space, power change rate, soft-switching coverage variation, or engineering debugging requirements. When the output power per-unit value... P / P N When the target power range is located near the boundary of an adjacent target power range, the current target power range can be updated using a hysteresis switching method.

[0049] Step S4: Using the current target power range number as an index, read the preset power-frequency lookup table to obtain the corresponding recommended switching frequency. f s The power-frequency lookup table is a one-dimensional configuration table, with its index being the current target power range number and the table entry being the corresponding recommended switching frequency. f s The recommended switching frequency f s It is a scalar value independent of the instantaneous phase of the power grid, which is predetermined through offline search.

[0050] Step S5: Recommend the switching frequency f s Substituting the known frequency parameters into the time-domain model of the two-wire voltage phase-shift modulation, and constrained by the target transmission power and AC side current synthesis requirements, the outer phase shift ratio is solved. d f The proportion of the selected line voltage effect on the AC side d 1. The dual-line voltage phase-shift modulation time-domain model can be established based on the piecewise linear variation of the high-frequency inductor current during different voltage application stages within a switching cycle. Switching frequency f s After the change, the duration of each voltage application phase within a switching cycle changes accordingly. Therefore, the integration time of the high-frequency inductor current in each phase, the inductor current at the commutation moment, and the transmitted power all change accordingly. f s Change.

[0051] The time-domain model of the dual-line voltage phase-shift modulation can be expressed as:

[0052] The transmission power constraint can be expressed as:

[0053] The AC-side current synthesis constraint can be expressed as:

[0054] in, , , Let be the inductor currents at times t0, t1, and t2, respectively. For the selected line voltage v mid Duty cycle; Compared to the outward shift between the DC side and the AC side; The transformer turns ratio The absolute maximum line voltage, The second largest absolute value line voltage, It is a DC voltage; For power transfer inductors, The switching frequency; Select recommended switching frequency f s Then, numerical methods can be used to solve it. d f and d 1. The numerical methods include, but are not limited to, table lookup interpolation, binary search, Newton iteration, damped Newton iteration, or other methods applicable to solving nonlinear equation systems.

[0055] Step S6: According to d f and d 1. Generate PWM drive signals for the DC-side full-bridge module and the AC-side three-phase matrix converter module.

[0056] Specifically, the control system combines the currently sampled or estimated three-phase AC voltage to determine the sector, identifies the AC line voltage to be synthesized within the current switching cycle based on the sector it is in, and assigns the selected AC line voltage a certain percentage of its effect. d 1 is converted into the conduction time of the corresponding AC side bidirectional switch; simultaneously, the external shift is compared to d f This is converted into a phase-shifting time base that leads or lags the DC-side full-bridge output voltage relative to the AC-side equivalent voltage's effective range. The PWM generator generates gate drive signals for the DC-side full-bridge module and the AC-side three-phase matrix converter module based on the stated conduction time and phase-shifting time base.

[0057] Step S7: Drive each power device using the PWM drive signal. When it is detected that the recommended switching frequency needs to be updated based on the current output power information... f s At the same time, the frequency can be switched to a new recommended switching frequency at the end of the current switching cycle, at the PWM carrier synchronization time, or at a preset synchronization time. f s And resolve within the switching cycle after the switch. d f and d 1. To maintain continuous PWM timing and suppress current surges caused by frequency switching.

[0058] like Figure 4 As shown, the power-frequency lookup table in this embodiment is obtained through offline search. First, a preset light-load optimization range is determined based on the soft-switching coverage distribution corresponding to different output powers under fixed-frequency phase-shift modulation, and this preset light-load optimization range is then categorized according to the per-unit value of the output power. P / P N It is divided into multiple power sub-intervals. For the first... kThere are several target power ranges, with their lower and upper power limits denoted as follows: P k,min and P k,max Then, a set of candidate switching frequencies is set up, and multiple power test points and multiple grid phase sampling points covering at least one power frequency cycle are set up within each target power range. This avoids insufficient adaptability caused by determining the recommended switching frequency based on a single power point or a single grid phase.

[0059] For each candidate switching frequency, selection is first based on maximum power transfer capability. The maximum transfer power at a given candidate switching frequency is then considered. P max ( f s () less than the upper limit of the corresponding target power range P k,max When this occurs, the candidate switching frequency is discarded. The maximum transmission power... P max ( f s It can be calculated using a two-wire voltage phase-shift modulation time-domain model, and its expression can be given as:

[0060] in, The amplitude of the phase voltage on the AC side; This step is used to ensure that the selected recommended switching frequency can cover the power requirements of the corresponding target power range, and to avoid insufficient power capacity caused by the shortening of the effective energy transfer time in a single switching cycle due to the increase in switching frequency.

[0061] For the candidate switching frequencies selected based on maximum power transmission capability, the outward shift ratio is solved at each power test point and each grid phase sampling point. d f The proportion of the selected line voltage effect on the AC side d 1. The high-frequency inductor current at each commutation moment on both the DC and AC sides is obtained using a time-domain model. Whether the commutation operation satisfies the zero-voltage switching condition is determined by the direction and amplitude of the high-frequency inductor current at the commutation moment. For the DC-side full-bridge commutation operation, the inductor current should satisfy the corresponding direction and amplitude conditions; for the AC-side three-phase matrix converter module commutation operation, the inductor current should also satisfy the corresponding direction and amplitude conditions. The required commutation current threshold can be determined based on the equivalent output capacitance, dead time, and voltage amplitude of the device to be commutated during the corresponding commutation stage, and its expression can be given as:

[0062]

[0063]

[0064] in, This is the minimum soft-switching current threshold required for DC-side commutation operation at time t0. The output capacitor of the DC-side switch. This is the DC-side dead time. This represents the minimum soft-switching current threshold required for AC-side commutation operation at time t1. For the output capacitor of the AC side switch, To facilitate the exchange of dead time, This is the minimum soft-switching current threshold required for AC-side commutation operation at time t2. It is the minimum absolute value of the line voltage; The physical meaning of the threshold is to enable the current flowing through the high-frequency inductor to charge or discharge the equivalent output capacitance of the commutation device during the dead time, thereby reducing the voltage of the device to be turned on to meet the range of zero-voltage turn-on.

[0065] To quantitatively evaluate the soft-switching range at different power and switching frequencies, a soft-switching coverage rate can be defined. η ZVS =(1- N nonZVS / N total )×100%, of which, N nonZVS The number of commutation operations that do not meet the zero-voltage switching condition. N total This represents the total number of converter operations included in the statistics. Depending on the statistical object, the DC-side soft-switching coverage rate, AC-side soft-switching coverage rate, and total soft-switching coverage rate can be obtained separately. For each candidate switching frequency, the soft-switching coverage rate is calculated at each power test point and each grid phase sampling point within the same target power range. The lowest soft-switching coverage rate is used as the evaluation index for that candidate switching frequency. The candidate switching frequency with the highest evaluation index is selected as the recommended switching frequency for that target power range. f s When the difference in evaluation metrics among multiple candidate switching frequencies is no greater than a preset threshold, the lower candidate switching frequency is selected first to avoid unnecessary increases in the switching frequency.

[0066] Through the above offline search, each target power range is matched with the corresponding recommended switching frequency. f s Store the power-frequency lookup table. During online operation, the controller only needs to refer to the per-unit output power value. P / P NDetermine the current target power range and use the current target power range number as an index to read the recommended switching frequency. f s This eliminates the need for real-time traversal of candidate switching frequencies, power test points, grid phase sampling points, and soft-switching coverage. Therefore, the proposed method can improve light-load soft-switching coverage while reducing online computation.

[0067] like Figure 5 As shown, in one embodiment, the light-load frequency conversion phase-shift modulation control system includes a sampling interface, a processor, a memory, and a PWM generator. The sampling interface receives AC-side voltage and current, DC-side voltage and current, or external power commands; the memory stores a power-frequency lookup table and program instructions; the processor executes the program instructions to acquire power information, determine power ranges, select frequencies from the lookup table, and solve for modulation degrees of freedom; the PWM generator calculates the modulation degree of freedom based on the external phase-shift modulation output by the processor. d f The proportion of the selected line voltage effect on the AC side d 1. Generate PWM drive signals for the DC-side full-bridge module and the AC-side three-phase matrix converter module.

[0068] In one embodiment, the converter's rated power P N The power rating is 1200W, the DC side voltage is 180V, the AC side voltage amplitude is 155.5V, the transformer turns ratio is 0.8, and the candidate switching frequency is set in the range of 50kHz to 100kHz. Based on the soft-switching coverage distribution corresponding to different output powers under fixed-frequency phase-shift modulation, the light-load optimization range is divided into multiple power sub-intervals, and the recommended switching frequency corresponding to each target power interval is obtained through offline search.

[0069] Under 30% load conditions, the fixed switching frequency phase-shift modulation results in insufficient inductor current direction or amplitude during some commutation moments, making it difficult to meet the zero-voltage switching condition for some commutation operations. Using the light-load variable-frequency phase-shift modulation method described in this invention, the controller determines the target power range based on the current output power per unit value and reads the corresponding recommended switching frequency from the power-frequency lookup table; subsequently, it recalculates the external phase shift ratio at this recommended switching frequency. d f The proportion of the selected line voltage effect on the AC side d 1. Generate PWM drive signals for the DC-side full-bridge module and the AC-side three-phase matrix converter module.

[0070] After adopting the above method, the direction and amplitude distribution of the high-frequency inductor current during commutation are improved, and some commutation actions that originally did not meet the zero-voltage switching condition are improved. At the same time, the distortion of the AC side output current waveform is suppressed. This embodiment illustrates that the present invention can improve the commutation current distribution, increase the soft-switching coverage, and reduce the online calculation load under light load conditions. However, the present invention is not limited to the specific parameters, power acquisition methods, preset step sizes, candidate frequency ranges, or load conditions mentioned above.

[0071] Those skilled in the art will understand that, in addition to implementing the system, apparatus, and their modules provided by this invention in purely computer-readable program code, the same program can be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system, apparatus, and their modules provided by this invention can be considered a hardware component, and the modules included therein for implementing various programs can also be considered structures within the hardware component; alternatively, modules for implementing various functions can be considered both software programs implementing the method and structures within the hardware component.

[0072] 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 light-load frequency conversion phase-shift modulation method for a three-phase single-stage isolated DC / AC matrix converter, characterized in that, include: Step S1: Obtain the current output power information of the three-phase single-stage isolated DC / AC matrix converter, and preprocess the obtained current output power information to obtain the preprocessed current output power information; obtain the per-unit value of the output power based on the preprocessed current output power information and the rated power. Step S2: Determine the current target power range based on the per-unit output power value; Step S3: Using the current target power range number as an index, read the corresponding recommended switching frequency from the preset power-frequency lookup table. f s The recommended switching frequency f s The soft-switching coverage evaluation is pre-determined based on the maximum power transmission capacity constraint and multiple power test points and multiple grid phase sampling points within the target power range; Step S4: Set the recommended switching frequency f s Substituting the known frequency parameters into the two-wire voltage phase-shift modulation time-domain model, we can solve for the outward shift ratio between the DC-side full-bridge output voltage and the AC-side equivalent voltage. d f and the proportion of the selected line voltage effect on the AC side d 1; Step S5: Based on the outward shift comparison d f and the proportion of the selected line voltage on the AC side d 1. Generate PWM drive signals for the DC-side full-bridge module and the AC-side three-phase matrix converter in the three-phase single-stage isolated DC / AC matrix converter, so as to improve the soft switching margin at the commutation moment in the current target power range while meeting the requirements of power transmission and AC-side current synthesis.

2. The light-load frequency conversion phase-shift modulation method for a three-phase single-stage isolated DC / AC matrix converter according to claim 1, characterized in that, Step S1 includes: Step S1.1: Obtain the current output power through upper-level power commands, power closed-loop controller output, power estimation module output, or voltage and current sampling calculation; wherein, the voltage and current sampling calculation includes: sampling the three-phase voltage and three-phase current on the AC side and calculating the active power on the AC side, or sampling the voltage and current on the DC side and calculating the power on the DC side. Step S1.2: Perform preprocessing on the acquired current output power information, including low-pass filtering, moving average, delay compensation or rate of change limiting, to obtain the preprocessed current output power information; Step S1.3: Obtain the per-unit value of output power based on the preprocessed current output power information and rated power.

3. The light-load frequency conversion phase-shift modulation method for a three-phase single-stage isolated DC / AC matrix converter according to claim 1, characterized in that, In step S2, the current target power range is a sub-range of power within the preset light load optimization range; The preset light-load optimization range is determined based on the soft-switching coverage distribution corresponding to different output powers under fixed-frequency phase-shift modulation, and according to the per-unit value of output power. P / P N The system is divided into multiple power sub-intervals, and the per-unit width of adjacent power sub-intervals is a preset step size.

4. The light-load frequency conversion phase-shift modulation method for a three-phase single-stage isolated DC / AC matrix converter according to claim 1, characterized in that, Step S3 includes: Step S3.1: Generate a preset power-frequency lookup table offline; the preset power-frequency lookup table is a one-dimensional configuration table indexed by the current target power range number, and the recommended switching frequency... f s It is a scalar value independent of the instantaneous phase of the power grid; Step S3.2: Using the current target power range number as an index, read the corresponding recommended switching frequency from the preset power-frequency lookup table. f s .

5. The light-load frequency conversion phase-shift modulation method for a three-phase single-stage isolated DC / AC matrix converter according to claim 4, characterized in that, Step S3.1 includes: Step S3.1.1: For each target power range, set up multiple power test points, multiple grid phase sampling points covering at least one power frequency cycle, and multiple candidate switching frequencies; Step S3.1.2: For each candidate switching frequency, first perform maximum power transmission capability screening. If the maximum transmission power at the candidate frequency is less than the upper limit of the target power range, then the candidate frequency is eliminated. For the candidate frequencies that pass the screening, then solve the outward shift ratio at each power test point and each grid phase sampling point. d f The proportion of the selected line voltage effect on the AC side d 1. The high-frequency inductor current at each commutation moment is obtained from the time-domain model; Step S3.1.3: Determine whether each commutation operation meets the zero-voltage switching condition based on the direction and amplitude of the inductor current, and calculate the soft-switching coverage rate; calculate the soft-switching coverage rate based on the number of commutation operations that do not meet the zero-voltage switching condition and the total number of commutation operations included in the statistics; use the lowest soft-switching coverage rate as the evaluation index for the candidate switching frequency, and select the candidate switching frequency with the highest evaluation index as the recommended switching frequency. f s If the evaluation indicators of multiple candidate frequencies are similar and meet the preset requirements, the lower frequency is selected first, and the target power range number - recommended switching frequency is written into the lookup table.

6. The light-load frequency conversion phase-shift modulation method for a three-phase single-stage isolated DC / AC matrix converter according to claim 5, characterized in that, The zero-voltage switching conditions include: the inductor current direction and amplitude conditions for DC-side commutation operation, and the inductor current direction and amplitude conditions for AC-side three-phase matrix converter module commutation operation. The amplitude condition is determined based on the equivalent output capacitance of the commutation device, the dead time, and the voltage amplitude of the corresponding commutation stage, so that the current flowing through the high-frequency inductor can charge or discharge the equivalent output capacitance of the commutation device during the dead time.

7. The light-load frequency conversion phase-shift modulation method for a three-phase single-stage isolated DC / AC matrix converter according to claim 1, characterized in that, The dual-line voltage phase-shift modulation time-domain model in step S4 includes: The transmission power constraint is expressed as: The AC-side current synthesis constraint is expressed as: in, , , Let be the inductor currents at times t0, t1, and t2, respectively. For the selected line voltage v mid Duty cycle; Compared to the outward shift between the DC side and the AC side; The transformer turns ratio The absolute maximum line voltage, The second largest absolute value line voltage, It is a DC voltage; For power transfer inductors, The switching frequency; Select recommended switching frequency f s Then, a numerical method was used to solve for the outward shift ratio between the DC-side full-bridge output voltage and the AC-side equivalent voltage. d f The proportion of the selected line voltage effect on the AC side d 1; The numerical methods include: table lookup interpolation, binary search, Newton iteration, or damped Newton iteration.

8. The light-load frequency conversion phase-shift modulation method for a three-phase single-stage isolated DC / AC matrix converter according to claim 1, characterized in that, Step S5 includes: Step S5.1: The control system performs sector determination based on the currently sampled or estimated three-phase AC voltage; Step S5.2: Determine the AC side line voltages participating in the synthesis during the current switching cycle based on the sector, and assign the proportion of the selected AC side line voltages to the total voltages. d 1 is converted into the conduction time of the corresponding AC side bidirectional switch; Step S5.3: Compare the outward movement d f This is converted into a phase-shifting time base that leads or lags the DC-side full-bridge output voltage relative to the AC-side equivalent voltage range. Step S5.4: The PWM generator generates PWM drive signals for the DC-side full-bridge module and the AC-side three-phase matrix converter module based on the conduction time and phase-shifting time base.

9. The light-load frequency conversion phase-shift modulation method for a three-phase single-stage isolated DC / AC matrix converter according to claim 1, characterized in that, When the output power per unit value P / P N When the target power range is near the boundary of an adjacent target power range, the current target power range is updated using a hysteresis switching method. When the recommended switching frequency needs to be updated f s At the end of the current switching cycle, at the PWM carrier synchronization time, or at a preset synchronization time, the frequency is switched to a new recommended switching frequency. f s And recalculate the outward shift ratio during the switching cycle after the switch. d f The proportion of the selected line voltage effect on the AC side d 1.

10. A light-load frequency conversion phase-shift modulation system for a three-phase single-stage isolated DC / AC matrix converter, characterized in that, include: Module M1: Acquires the current output power information of the three-phase single-stage isolated DC / AC matrix converter, preprocesses the acquired current output power information to obtain preprocessed current output power information, and obtains the per-unit value of output power based on the preprocessed current output power information and the rated power. Module M2: Determines the current target power range based on the per-unit output power value; Module M3: Using the current target power range number as an index, reads the corresponding recommended switching frequency from the preset power-frequency lookup table. f s The recommended switching frequency f s The soft-switching coverage evaluation is pre-determined based on the maximum power transmission capacity constraint and multiple power test points and multiple grid phase sampling points within the target power range; Module M4: The recommended switching frequency f s Substituting the known frequency parameters into the two-wire voltage phase-shift modulation time-domain model, we can solve for the outward shift ratio between the DC-side full-bridge output voltage and the AC-side equivalent voltage. d f and the proportion of the selected line voltage effect on the AC side d 1; Module M5: Based on the outward shift comparison d f and the proportion of the selected line voltage on the AC side d 1. Generate PWM drive signals for the DC-side full-bridge module and the AC-side three-phase matrix converter in the three-phase single-stage isolated DC / AC matrix converter, so as to improve the soft switching margin at the commutation moment in the current target power range while meeting the requirements of power transmission and AC-side current synthesis.

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