Resonant DC / AC converter based on two paths of MPPT and modulation method thereof

Abstract

The invention discloses a resonant DC / AC converter based on two paths of MPPT and a modulation method thereof, and relates to the technical field of power electronic conversion. The resonant DC / AC converter based on two paths of MPPT comprises a single-stage isolated DC / AC converter topology which comprises an AC-side bidirectional matrix switch group and a DC-side H-bridge switch group; the high-frequency resonant cavity is formed by connecting a resonant inductor and a resonant capacitor in series and is coupled to the secondary side of the transformer; the two paths of independent MPPT input ports are connected in parallel with the resonant cavity through the direct current side H-bridge switch group; and the control module is configured to output a driving signal by adopting a three-degree-of-freedom modulation strategy of an inner phase shifting angle, an outer phase shifting angle and switching frequency. According to the converter, the soft switching range is optimized while double input ports are realized, the working efficiency is improved, and the total harmonic distortion degree is reduced.

Description

Technical Field

[0001] The present application relates to the field of power electronic conversion technology, and in particular to a resonant DC / AC converter based on two-way MPPT and a modulation method thereof. Background Art

[0002] With the development of green energy, solar energy has been widely used as a clean energy. In order to convert solar energy into usable electrical energy, a DC / AC (direct current to alternating current) converter is required.

[0003] However, traditional two-stage DC / AC converters suffer from numerous power switches, large size, and low efficiency. To address these issues, single-stage isolated DC / AC converters have attracted widespread attention due to their high efficiency and high power density. However, existing single-stage structures still suffer from a limited soft switching range. Summary of the Invention

[0004] To solve the above problems, the present application provides a resonant DC / AC converter based on two-way MPPT (maximum power point tracking), which realizes dual input ports while optimizing its soft switching range, improving working efficiency, and reducing total harmonic distortion; correspondingly, a modulation method is provided, which can be applied to resonant DC / AC converters based on two-way MPPT in different situations.

[0005] The first technical solution adopted in this application is to provide a resonant DC / AC converter based on two MPPT paths, including: Single-stage isolated DC / AC converter topology, including an AC-side bidirectional matrix switch group and a DC-side H-bridge switch group; A high-frequency resonant cavity, composed of a resonant inductor and a resonant capacitor in series, is coupled to the secondary side of the transformer; Two independent MPPT input ports are connected in parallel to the resonant cavity through the DC side H-bridge switch group; The control module is configured to output a driving signal using a three-degree-of-freedom modulation strategy of an inner phase shift angle, an outer phase shift angle, and a switching frequency.

[0006] In an optional embodiment, the bidirectional matrix switch group includes 8 switch tubes ,in: When the AC input voltage is positive, The power frequency is always on. High frequency switching; When the AC input voltage is negative, The power frequency is always on. High frequency switching; Or the bidirectional matrix switch group includes 4 switch tubes ,in: When the AC input voltage is positive, The power frequency is always on. High frequency switching; When the AC input voltage is negative, The power frequency is always on. High frequency switching.

[0007] In an optional embodiment, the control variables of the three-degree-of-freedom modulation strategy include: The internal phase shift angle controls the phase difference between the leading and lagging arms of the H-bridge on the DC side; The external phase shift angle controls the phase difference between the AC side voltage square wave and the DC side equivalent voltage square wave; The switching frequency is dynamically adjusted to maintain the inductive impedance of the resonant tank.

[0008] In an optional embodiment, the inner phase shift angle is calculated based on the AC / DC voltage gain ratio and the active component of the resonant current; The outer phase shift angle is determined based on a minimum turn-on current and a resonant cavity impedance required to achieve soft switching.

[0009] In an optional embodiment, the control module performs the following process: Real-time sampling of AC input voltage and DC side voltage; Simultaneously solve the power transfer equation, soft switching condition equation and phase shift angle relationship; Output the inner phase shift angle, outer phase shift angle, and switching frequency to the drive circuit to generate a PWM signal.

[0010] In an optional embodiment, extended phase shift modulation is used to achieve full range soft switching: The AC side switch tube achieves zero voltage turn-on through the resonant current and the direction of the body diode; The DC side switch tube meets the output capacitor charging and discharging requirements during the dead time by adjusting the turn-on current.

[0011] In an optional embodiment, the turn-on current reference value is determined by the output capacitance value of the DC side switch tube, the DC voltage and the preset dead time.

[0012] In an optional embodiment, the two MPPT inputs share the same AC-side matrix switch group; The control module is configured to calculate the common switching frequency of the dual MPPTs and ensure the coordinated operation of the dual MPPTs based on a frequency synchronization strategy.

[0013] The second technical solution adopted in the present application is to provide a modulation method, which is applied to the resonant DC / AC converter based on two MPPT paths as described in any of the above items, comprising the following steps: Establish a resonant cavity equivalent model based on the fundamental wave approximation method; Synchronously calculate the inner phase shift angle, outer phase shift angle and switching frequency based on the voltage and current phasor relationship; The output drive signal achieves full range soft switching and total harmonic distortion optimization.

[0014] In an optional embodiment, the modulation method implements a 1-to-N matrix technology based on an AC-side common matrix switch, comprising the following steps: Load converter parameters and sample input and output voltages and currents; Calculate the internal and external phase shift angles and switching frequencies of N circuits based on power transmission regulation and ZVS conditions; Compare N frequencies and select a minimum frequency; change the control variable based on the minimum frequency, and update the inner and outer phase shift angles and switching frequencies of the two channels.

[0015] Due to the adoption of the above technical solution, the present application has at least one of the following beneficial effects compared with the prior art:

[0016] 1. The single-stage isolated DC / AC converter topology reduces the number of power conversions, thereby reducing energy loss; through the optimized three-degree-of-freedom modulation strategy (inner phase shift angle, outer phase shift angle and switching frequency), full-range soft switching is achieved.

[0017] 2. This application only requires one stage of power conversion and adopts an efficient resonant cavity design, which greatly reduces the number of power switching tubes required and their volume, which not only improves the power density but also reduces the manufacturing cost.

[0018] 3. By precisely controlling the inner phase shift angle, the outer phase shift angle and dynamically adjusting the switching frequency, the present invention can effectively reduce the harmonic components in the output power and reduce the total harmonic distortion.

[0019] 4. Supports "one-to-N" technology, meaning multiple MPPT input ports share the same AC-side matrix switch group. This design enables the system to flexibly respond to different photovoltaic input conditions. At the same time, a synchronization strategy ensures the coordinated operation of dual or multiple MPPTs, improving the system's adaptability and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without inventive efforts. Among them: Figure 1 A circuit diagram of a resonant DC / AC converter based on two MPPT paths according to an embodiment of the present application; Figure 2 A circuit diagram of a resonant DC / AC converter based on two MPPT paths according to another embodiment of the present application; Figure 3 Schematic diagram of the square wave waveform of the midpoint voltage of the AC side bridge arm; Figure 4 Schematic diagram of the square wave waveform of the DC side bridge arm midpoint voltage; Figure 5 is the schematic diagram of the resonant cavity equivalent circuit; Figure 6 Schematic diagram of the phase shift angle relationship of the alternating square wave voltage; Figure 7 This is a schematic diagram of high-frequency voltage and current phasors under fundamental wave approximation; Figure 8 It is a schematic diagram of the time domain steady-state waveform and corresponding phasor in the resonant cavity; Figure 9 To expand the schematic diagram of the phase quantities of each voltage and current signal and some driving signals under phase shift modulation; Figure 10 A schematic diagram of a flow chart of a modulation method provided in one embodiment of the present application; Figure 11 This is a calculation flow chart of the one-to-two single-stage DC / AC converter provided in this application. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. It will be understood that the specific embodiments described herein are only used to explain the present application, rather than to limit the present application. It should also be noted that, for ease of description, only some, rather than all, structures related to the present application are shown in the drawings. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0022] The terms "first," "second," and the like in this application are used to distinguish between different objects, not to describe a particular order. Furthermore, the terms "including," "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements, but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

[0023] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0024] Traditional two-stage DC / AC converters use a large number of power switching tubes, resulting in a larger device size and increasing overall cost and complexity. The single-stage resonant DC / AC converter proposed in this application only requires one stage of power conversion, reducing the number of power switching tubes and the space required, thereby increasing power density and reducing costs. Although single-stage structures have been used to try to reduce switching losses, their efficiency improvements are limited due to their small soft switching range. This application achieves soft switching of all switching tubes within the full voltage range by expanding the three-degree-of-freedom modulation strategy that combines phase shifting and frequency modulation, significantly improving the working efficiency of the converter. Figure 1 As shown, Figure 1 A circuit diagram of a resonant DC / AC converter based on two MPPT paths provided in one embodiment of the present application includes: A single-stage isolated DC / AC converter topology includes an AC-side bidirectional matrix switch group and a DC-side H-bridge switch group. First, the DC / AC inverter power circuit is analyzed using the fundamental wave approximation method. Since the DC / AC inverter AC input voltage is time-varying, for ease of analysis, this application defines the following conditions: 1. The inverter is in steady-state operation; 2. During one switching cycle, it is approximately assumed that the AC input voltage remains unchanged.

[0025] In this embodiment, the AC side bidirectional matrix switch group includes four groups of bidirectional tubes, each group of bidirectional tubes consists of two switch tubes, that is, eight switch tubes. Based on the characteristics of the matrix switching circuit, it can be seen that four switching tubes work at the power frequency while the other four work at high frequency; specifically: When the AC input voltage is positive, The power frequency is always on. High frequency switching; e.g. Figure 3-Figure 4 As shown, Figure 3 This is a schematic diagram of the square wave waveform of the AC side bridge arm midpoint voltage. Figure 4 The diagram below shows the waveform of the DC side bridge arm midpoint voltage square wave. The following describes the principles of the AC side bridge arm midpoint voltage square wave and the DC side bridge arm midpoint voltage square wave: When the AC input voltage is positive, The power frequency is always on. High-frequency switching; resulting in a square wave voltage at the midpoint of the AC bridge arm ,The square wave voltage changes based on the on and off states of the switch tube, and periodically reflects the frequency of the AC power supply; The power frequency is always on and forms part of the bridge arm. High-frequency switching can generate the desired square wave voltage at the midpoint of the bridge arm. .

[0026] In another embodiment, the bidirectional matrix switch group includes 4 switch tubes. ;like Figure 2 As shown, Figure 2 A circuit diagram of a resonant DC / AC converter based on two MPPT paths is provided in another embodiment of the present application.

[0027] The AC side bidirectional matrix switch group includes two groups of bidirectional tubes, each group of bidirectional tubes consists of two switch tubes, that is, four switch tubes. Based on the characteristics of the matrix switching circuit, it can be seen that two switching tubes work at the power frequency while the other two work at high frequency; specifically: When the AC input voltage is positive, The power frequency is always on. High frequency switching; e.g. Figure 3-Figure 4 As shown, Figure 3 This is a schematic diagram of the square wave waveform of the AC side bridge arm midpoint voltage. Figure 4 The diagram below shows the waveform of the DC side bridge arm midpoint voltage square wave. The following describes the principles of the AC side bridge arm midpoint voltage square wave and the DC side bridge arm midpoint voltage square wave: When the AC input voltage is positive, The power frequency is always on. High-frequency switching; resulting in a square wave voltage at the midpoint of the AC bridge arm ,The square wave voltage changes based on the on and off states of the switch tube, and periodically reflects the frequency of the AC power supply; The power frequency is always on and forms part of the bridge arm. High-frequency switching can generate the desired square wave voltage at the midpoint of the bridge arm. .

[0028] On the DC side, the switching tubes in the H-bridge structure include DC side bridge arm midpoint voltage By adjusting the phase difference of the switch tube in the H bridge, the The amplitude and polarity of the DC side affect the efficiency and direction of energy transmission from the DC side to the AC side.

[0029] In the picture and They are the fundamental components obtained by Fourier decomposition of the DC side bridge arm midpoint voltage square wave and the AC side bridge arm midpoint voltage square wave.

[0030] When the AC input voltage is negative, The power frequency is always on. High-frequency switching; based on the same technical means, the AC side bridge arm midpoint voltage square wave and the DC side bridge arm midpoint voltage square wave can be adjusted, which will not be repeated here.

[0031] for Figure 2 The circuit provided is: When the AC input voltage is negative, The power frequency is always on. High-frequency switching; based on the same technical means, the AC side bridge arm midpoint voltage square wave and the DC side bridge arm midpoint voltage square wave can be adjusted, which will not be repeated here.

[0032] By operating different groups of switches in either power-frequency or high-frequency mode during the positive and negative half-cycles of the AC input voltage, switching losses are effectively reduced. The high-frequency switching switches ensure rapid response and regulation, while the switches operating at constant power frequency reduce unnecessary frequent operation, thereby improving overall efficiency. This configuration allows the converter to more precisely control the energy conversion process from DC to AC, maintaining high energy transfer efficiency under varying load conditions.

[0033] The high-frequency resonant cavity is composed of a resonant inductor and a resonant capacitor connected in series; in this embodiment, and The first resonant cavity is formed in series. and The second resonant cavity is formed in series; based on the adjustment The inductance value and The capacitance value adjusts the resonant frequency of the first resonant cavity; based on the adjustment The inductance value and The capacitance value adjusts the resonant frequency of the second resonant cavity.

[0034] The resonant cavity is coupled to the secondary side of the transformer, that is, it is directly connected to the secondary side of the transformer. As a key medium for energy transfer, it not only helps to smooth voltage fluctuations, but also optimizes output characteristics by adjusting circuit parameters. In this embodiment, the transformer turns ratio is n, such as Figure 5 As shown, Figure 5 Schematic diagram of the resonant cavity equivalent circuit.

[0035] respectively and Performing Fourier decomposition, the expressions of the fundamental components of the two can be obtained as follows:

[0036] Where, the instantaneous value of the AC side power supply voltage is: ;DC side power supply voltage: ; Transformer ratio: ;Switching angular frequency: ( is the switching frequency); the internal phase shift angle of the leading bridge arm driving the leading and lagging bridge arm driving on the DC side is: ;in and The bridge arm where it is located is the leading bridge arm. and The bridge arm where it is located is the lagging bridge arm; Ahead The outward shift angle: .

[0037] It should be noted that, in this embodiment, the resonant inductor and the resonant capacitor are connected in series to form a resonant cavity. In other embodiments, the resonant inductor and the resonant capacitor may be connected in parallel or in series and parallel to form a resonant cavity, and there is no limitation on this.

[0038] Two independent MPPT input ports are connected in parallel to the resonant cavity through the DC side H-bridge switch group; each MPPT input is responsible for obtaining power from a photovoltaic array or module and finding the optimal operating point of the array through its own control logic to maximize energy extraction.

[0039] The two MPPT inputs are each connected to a DC-side H-bridge switch group, and then the two H-bridges are connected in parallel to the high-frequency resonant cavity through appropriate circuit design; this configuration allows two independent energy sources to supply energy to the resonant cavity simultaneously, thereby optimizing the energy utilization efficiency of the overall system.

[0040] The two MPPT inputs share the same AC-side matrix switch group and can work together to flexibly adjust the output under different load conditions to ensure system stability and efficiency.

[0041] The control module is configured to calculate the common switching frequency for the two MPPTs, ensuring their coordinated operation based on a frequency synchronization strategy. By calculating and using a common switching frequency, the energy conversion process for the two MPPT inputs is more coordinated and consistent. This helps reduce energy loss and unnecessary losses caused by frequency mismatch. The frequency synchronization strategy enables more efficient and smoother energy conversion from the DC side to the AC side, thereby improving the energy utilization efficiency of the entire system.

[0042] In this embodiment, the first MPPT input port is connected to The DC side H-bridge switch group is connected; the second MPPT input port is connected to The DC side H-bridge switch group is connected.

[0043] To facilitate analysis, this application defines some parameters and variables of the converter: AC / DC voltage gain ratio: ; Resonant frequency: ; Resonant cavity impedance: .

[0044] Internal phase shift angle and outward phase angle The specific situation when working in both directions is as follows Figure 6 As shown, Figure 6 The diagram is a diagram of the phase shift angle relationship of the alternating square wave voltage. Based on the results obtained from the fundamental wave approximation, the fundamental waves of each voltage and current can be represented in the form of a phasor diagram, as shown in Figure 7 As shown, Figure 7 Schematic diagram of high-frequency voltage and current phasors under fundamental wave approximation.

[0045] definition The phasor is , The phasor is At this time, the voltage excitation applied to both ends of the resonant cavity is When the switching frequency is higher than the resonant frequency, a resonant current will be generated that lags behind the voltage excitation by 90°. For the convenience of analysis, this application will correspond the resonant current to the phase Divided into active current phasors according to phase and reactive current phasor , the expression of the modulus length of the two current phasors is as follows:

[0046] at this time The time domain expression of is as follows: .

[0047] The power transmission characteristics of the DC / AC converter are particularly critical. That is, whether the instantaneous current transmitted can keep pace with the AC voltage to ensure a small total harmonic distortion (THD) to meet grid connection requirements. Therefore, it is necessary to control the average value of the resonant current transmitted to the AC output terminal in each switching cycle in the high-frequency resonant cavity.

[0048] In addition, the implementation of soft switching of the switch tube is equally important for improving the efficiency and reducing losses of the DC / AC converter. To achieve soft switching, it is necessary to ensure that the current direction is the same as the direction of its body diode during the dead time before the switch tube is turned on, and to complete the charging and discharging of the output junction capacitance on both sides of the drain and source of the switch tube during the dead time between the bridge arm switches.

[0049] For the AC side switch tube, the waveforms of the voltage and current phasors and the drive signal under the fundamental wave approximation method are as follows: Figure 8 As shown, Figure 8 The diagram of the steady-state waveform and corresponding phasor in the time domain of the resonant cavity is shown below. At this time, the waveform of each voltage and current phasor and the driving signal under the fundamental wave approximation method for the AC side switch is defined as follows: Figure 8 As shown, Figure 8 It is the time domain steady-state waveform and corresponding phasor diagram in the resonant cavity. The phasor corresponding to the fundamental wave of the driving square wave is , the phasor diagram can be drawn as Figure 9 As shown, Figure 9 To expand the schematic diagram of the phase quantities of each voltage and current signal and some driving signals under phase-shift modulation.

[0050] In summary, in order to improve the performance of DC / AC converters, soft switching operation must be implemented while optimizing power transfer characteristics to ensure efficient operation under various operating conditions and reduce total harmonic distortion (THD).

[0051] This application adopts the three-degree-of-freedom modulation strategy of extended phase shift + frequency modulation, and the control quantity is the inner phase shift angle , outward shift phase angle and switching frequency ; Specifically, the control module is configured to use an internal phase shift angle , outward shift phase angle and switching frequency The three-degree-of-freedom modulation strategy outputs a driving signal; the following describes the role of the control variables of the three-degree-of-freedom modulation strategy:

[0052] The internal phase shift angle controls the phase difference between the leading bridge arm and the lagging bridge arm of the H-bridge on the DC side; by adjusting the internal phase shift angle , the amount and timing of energy transferred from the DC side to the resonant cavity can be adjusted. Specifically, when the leading bridge arm turns on before the lagging bridge arm, energy can be injected into the resonant cavity at different times, thereby affecting the waveform and effective value of the resonant current.

[0053] The external phase shift angle controls the phase difference between the AC side voltage square wave and the DC side equivalent voltage square wave; the external phase shift angle This ensures synchronization between the AC side voltage square wave and the DC side voltage waveform to achieve optimal energy conversion efficiency and soft switching conditions. By properly setting the external phase shift angle, the AC side switch can switch at zero voltage or zero current, reducing switching losses.

[0054] The switching frequency is dynamically adjusted to maintain the inductive impedance of the resonant cavity; based on the system load and input and output voltage levels, the switching frequency is adjusted in real time. This not only helps maintain the inductive characteristics of the resonant cavity, but also optimizes the effective value of the resonant current, reduces switching losses, and improves overall system efficiency.

[0055] The control module performs the following process:

[0056] Real-time sampling of AC input voltage and DC side voltage; through real-time sampling and dynamic adjustment, the control system can optimize the energy conversion process according to actual working conditions, ensuring efficient energy transmission under different loads.

[0057] The power transmission equation, soft switching condition equation and phase shift angle relationship are solved simultaneously; the circuit model is analyzed based on the fundamental wave approximation method to determine the energy transmission efficiency from the DC side to the AC side, ensure that the switching elements can switch under zero voltage or zero current conditions, reduce switching losses, and solve the optimal inner phase shift angle, outer phase shift angle and switching frequency through the simultaneous equations combined with the power transmission equation and soft switching condition equation.

[0058] The internal phase-shift angle, external phase-shift angle, and switching frequency are output to the drive circuit to generate a PWM signal. Accurately calculating and applying these angles and switching frequency allows all switching elements to switch under optimal conditions, significantly reducing switching losses and improving overall system efficiency. The following details how the control module obtains these angles and switching frequency:

[0059] Optimizing the power transfer characteristics can be achieved by adjusting Ensure the quality of AC current waveform; the specific relationship can be obtained by substituting formula (2) into expression (3):

[0060] The internal phase shift angle is based on the AC / DC voltage gain ratio and the active component of the resonant current. By calculating the internal phase shift angle based on the AC / DC voltage gain ratio and the active component of the resonant current, the energy level transferred from the DC side to the resonant cavity can be more accurately controlled, ensuring that the system can achieve efficient energy conversion under different load conditions.

[0061] Extended phase-shift modulation to achieve full-range soft switching:

[0062] The AC side switch tube realizes zero voltage turn-on by aligning the direction of the resonant current with the body diode. Since the AC side H bridge is a high-frequency rectifier link, the direction of the high-frequency current is naturally consistent with the direction of the body diode of its switch tube. and By keeping the phases the same and appropriately increasing the dead time of the AC side switches, the zero voltage turn-on of all the AC side switches can be achieved. According to formula (4), we have:

[0063] Similarly, the DC side also needs to implement soft switching operation, by adjusting the turn-on current to meet the output capacitor charging and discharging requirements within the dead time; the turn-on current reference value is determined by the output capacitance value of the DC side switch tube, the DC voltage and the preset dead time; the DC side H bridge is a high-frequency inverter link, and it is necessary to ensure that the switch tube Before turning on, the resonant current The direction is positive and the size is sufficient to meet the output capacitance within the dead time. The switch tube is fully charged and discharged. The required turn-on current is:

[0064] The phase shift angle Definition as Figure 8 As shown, this value can be used to shift the phase angle and outward phase angle express:

[0065] To ensure that the switch To achieve soft switching, the reference value of the turn-on current can be obtained The external phase shift angle is determined based on the minimum turn-on current and resonant cavity impedance required to achieve soft switching. By precisely controlling the external phase shift angle, the phase difference between the AC side voltage square wave and the DC side equivalent voltage square wave can be optimized, making energy transmission more efficient and smooth, and reducing unnecessary energy loss. Soft switching operation reduces electromagnetic interference (EMI) during the switching process, while reducing total harmonic distortion (THD), providing higher quality sinusoidal wave output.

[0066] As shown in the following formula (10), is the equivalent value of the output junction capacitance of the DC side switch tube, is the dead time set for the DC side switch tube, based on which the phase shift angle can be obtained size.

[0067]

[0068] Combining equations (6), (7), (9), and (10), we can obtain the internal phase shift angle at this time: θ and outward phase angle for:

[0069]

[0070] Based on this, by substituting equations (11) and (12) into equation (6), the resonant cavity impedance at this time can be obtained: for:

[0071] Therefore, the switching frequency Can be expressed as:

[0072] All control quantities of extended phase shift + variable frequency modulation can be obtained. Based on these control quantities, the driving signals of each switching tube can be obtained from the peripherals in the digital processor to perform power modulation on the inverter to achieve optimization of power transmission characteristics, full-range soft switching and total harmonic distortion optimization.

[0073] The present application also provides a modulation method, which is applied to the resonant DC / AC converter based on two MPPT paths as in the above embodiment. Figure 10 As shown, Figure 10 A schematic flow chart of a modulation method provided in an embodiment of the present application includes the following steps: S1: Establish the equivalent model of the resonant cavity based on the fundamental wave approximation method; S2: Synchronously calculate the inner phase shift angle, outer phase shift angle and switching frequency based on the voltage and current phasor relationship; S3: The output drive signal achieves full-range soft switching and total harmonic distortion optimization.

[0074] like Figure 11 As shown, Figure 11 The calculation flow chart of the one-to-two single-stage DC / AC converter provided in this application includes the following steps: Load converter parameters and sample input and output voltages and currents; Calculate the inner and outer phase shift angles and switching frequencies of the two paths based on power transfer regulation and ZVS (zero voltage switching) conditions; Compare the two frequencies and select the minimum frequency; change the control variable based on the minimum frequency, and update the inner and outer phase shift angles and switching frequencies of the two channels.

[0075] In addition, the modulation method can also implement a 1-to-N matrix technology based on a common matrix switch on the AC side, including the following steps: Load converter parameters and sample input and output voltages and currents; Calculate the internal and external phase shift angles and switching frequencies of N circuits based on power transmission regulation and ZVS conditions; Compare N frequencies and select the minimum frequency; change the control variable based on the minimum frequency, and update the inner and outer phase shift angles and switching frequencies of the two channels.

[0076] In the several embodiments provided in this application, it should be understood that the disclosed methods and devices can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of the modules or units is merely a logical functional division. In actual implementation, other division methods may be used, such as combining or integrating multiple units or components into another system, or ignoring or not implementing certain features.

[0077] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of this embodiment.

[0078] In addition, each functional unit in each embodiment of the present application may be integrated into a processing unit, each unit may exist physically separately, or two or more units may be integrated into a single unit. The above-mentioned integrated units may be implemented in the form of hardware or software functional units.

[0079] The above description is only an implementation method of the present application and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the description and drawings of this application, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A resonant DC / AC converter based on two MPPT paths, characterized in that: include: Single-stage isolated DC / AC converter topology, including an AC-side bidirectional matrix switch group and a DC-side H-bridge switch group; A high-frequency resonant cavity, composed of a resonant inductor and a resonant capacitor in series, is coupled to the secondary side of the transformer; Two independent MPPT input ports are connected in parallel to the resonant cavity through the DC side H-bridge switch group; The control module is configured to output a driving signal using a three-degree-of-freedom modulation strategy of an inner phase shift angle, an outer phase shift angle, and a switching frequency.

2. The resonant DC / AC converter based on two-way MPPT according to claim 1, characterized in that: The bidirectional matrix switch group includes 8 switch tubes ,in: When the AC input voltage is positive, The power frequency is always on. High frequency switching; When the AC input voltage is negative, The power frequency is always on. High frequency switching; Or the bidirectional matrix switch group includes 4 switch tubes ,in: When the AC input voltage is positive, The power frequency is always on. High frequency switching; When the AC input voltage is negative, The power frequency is always on. High frequency switching.

3. The resonant DC / AC converter based on two-way MPPT according to claim 1, characterized in that: The control variables of the three-degree-of-freedom modulation strategy include: The internal phase shift angle controls the phase difference between the leading and lagging arms of the H-bridge on the DC side; The external phase shift angle controls the phase difference between the AC side voltage square wave and the DC side equivalent voltage square wave; The switching frequency is dynamically adjusted to maintain the inductive impedance of the resonant tank.

4. The resonant DC / AC converter based on two-way MPPT according to claim 3, characterized in that: The inner phase shift angle is calculated based on the AC / DC voltage gain ratio and the active component of the resonant current; The outer phase shift angle is determined based on a minimum turn-on current and a resonant cavity impedance required to achieve soft switching.

5. The resonant DC / AC converter based on two-way MPPT according to claim 1, characterized in that: The control module performs the following process: Real-time sampling of AC input voltage and DC side voltage; Simultaneously solve the power transfer equation, soft switching condition equation and phase shift angle relationship; Output the inner phase shift angle, outer phase shift angle, and switching frequency to the drive circuit to generate a PWM signal.

6. The resonant DC / AC converter based on two-way MPPT according to claim 1, characterized in that: Extended phase-shift modulation to achieve full-range soft switching: The AC side switch tube achieves zero voltage turn-on through the resonant current and the direction of the body diode; The DC side switch tube meets the output capacitor charging and discharging requirements during the dead time by adjusting the turn-on current.

7. The resonant DC / AC converter based on two-way MPPT according to claim 6, characterized in that: The turn-on current reference value is determined by the output capacitance value of the DC side switch tube, the DC voltage and the preset dead time.

8. The resonant DC / AC converter based on two-way MPPT according to claim 1, characterized in that: Two MPPT inputs share the same AC side matrix switch group; The control module is configured to calculate the common switching frequency of the dual MPPTs and ensure the coordinated operation of the dual MPPTs based on a frequency synchronization strategy.

9. A modulation method, applied to the resonant DC / AC converter based on two-way MPPT according to any one of claims 1 to 8, characterized in that: The steps include: Establish a resonant cavity equivalent model based on the fundamental wave approximation method; Synchronously calculate the inner phase shift angle, outer phase shift angle and switching frequency based on the voltage and current phasor relationship; The output drive signal achieves full range soft switching and total harmonic distortion optimization.

10. The modulation method according to claim 9, characterized in that: The modulation method implements a 1-to-N matrix technology based on a common matrix switch on the AC side, and includes the following steps: Load converter parameters and sample input and output voltages and currents; Calculate the internal and external phase shift angles and switching frequencies of N circuits based on power transmission regulation and ZVS conditions; Compare N frequencies and select the minimum frequency; The control variable is changed based on the minimum frequency value, and the two-way inner and outer phase shift angles and the switching frequency are updated.

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