A resonant DC / AC converter based on two-path MPPT and a modulation method thereof

Abstract

The application discloses a resonant DC / AC converter based on two MPPTs and a modulation method thereof, and relates to the technical field of power electronic conversion. The resonant DC / AC converter based on two MPPTs 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; a high-frequency resonant cavity, which is formed by series connection of a resonant inductor and a resonant capacitor and is coupled to a secondary side of a transformer; two independent MPPT input ports, which are connected in parallel to the resonant cavity through the DC side H bridge switch group; and a control module, which is configured to output a driving signal by adopting a three-degree-of-freedom modulation strategy of inner phase shift angle, outer phase shift angle and switching frequency. The converter simultaneously optimizes a soft switching range of double input ports, improves working efficiency and reduces total harmonic distortion.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power electronic conversion, in particular to a resonant DC / AC converter based on two MPPTs and a modulation method thereof. BACKGROUND

[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- alternating current conversion) converter needs to be used.

[0003] However, the traditional two-stage DC / AC converter has the problems of more power switching tubes, larger volume and lower efficiency. In view of these problems, the single-stage isolated DC / AC converter has been widely concerned due to its high efficiency and high power density. However, the single-stage structure in the prior art still has the problem of small soft switching range. SUMMARY

[0004] To solve the above problems, the present application provides a resonant DC / AC converter based on two MPPTs (maximum power point tracking), which realizes the simultaneous optimization of the soft switching range of the double input ports, improves the working efficiency, and reduces the total harmonic distortion. A corresponding modulation method is provided, which can be applied to the resonant DC / AC converter based on two MPPTs in different situations.

[0005] The first technical solution adopted by the present application is to provide a resonant DC / AC converter based on two MPPTs, comprising:

[0006] The single-stage isolated DC / AC converter topology includes an AC side bidirectional matrix switch group and a DC side H bridge switch group;

[0007] The high-frequency resonant cavity is composed of a resonant inductor and a resonant capacitor in series and is coupled to the secondary side of the transformer;

[0008] Two independent MPPT input ports are connected in parallel to the resonant cavity through the DC side H bridge switch group;

[0009] The control module is configured to output a driving signal using a three-degree-of-freedom modulation strategy of internal phase angle shifting, external phase angle shifting and switching frequency.

[0010] In an optional embodiment, the bidirectional matrix switch group includes 8 switching tubes wherein:

[0011] When the AC input voltage is positive, the power frequency is always on, the high frequency is switched;

[0012] When the AC input voltage is negative, line frequency always on, high frequency switching;

[0013] or the bidirectional matrix switch group comprises 4 switch tubes wherein:

[0014] when the AC input voltage is positive, line frequency always on, high frequency switching;

[0015] when the AC input voltage is negative, line frequency always on, high frequency switching.

[0016] In an optional embodiment, the control variables of the three-degree-of-freedom modulation strategy include:

[0017] inner phase-shift angle control of the phase difference between the leading and lagging bridge arms of the DC side H-bridge;

[0018] outer phase-shift angle control of the phase difference between the AC side voltage square wave and the DC side equivalent voltage square wave;

[0019] switching frequency dynamic adjustment to maintain the inductive impedance of the resonant cavity.

[0020] 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;

[0021] The outer phase-shift angle is determined based on the minimum turn-on current required to achieve soft switching and the resonant cavity impedance.

[0022] In an optional embodiment, the control module performs the following procedures:

[0023] real-time sampling of the AC input voltage and the DC side voltage;

[0024] simultaneous solution of the power transmission equation, the soft switching condition equation, and the phase-shift angle relationship;

[0025] output of the inner phase-shift angle, the outer phase-shift angle, and the switching frequency to the drive circuit to generate PWM signals.

[0026] In an optional embodiment, the extended phase-shift modulation achieves full-range soft switching:

[0027] The AC side switch tube achieves zero-voltage turn-on through the resonant current and the body diode in the same direction;

[0028] The DC side switch tube meets the output capacitor charging and discharging requirements within the dead time by adjusting the turn-on current.

[0029] In an alternative 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.

[0030] In an alternative embodiment, the two MPPT inputs share the same AC side matrix switch group.

[0031] The control module is configured to calculate the common switching frequency of the two MPPTs and ensure the cooperative work of the two MPPTs based on the frequency synchronization strategy.

[0032] The second technical solution adopted by the present application is to provide a modulation method applied to the resonant DC / AC converter based on the two MPPTs as claimed in any one of the above, comprising the following steps:

[0033] An equivalent model of the resonant cavity is established based on the fundamental approximation method.

[0034] The internal phase angle, the external phase angle and the switching frequency are synchronously solved based on the voltage and current phasor relationship.

[0035] The output drive signal realizes full-range soft switching and total harmonic distortion optimization.

[0036] In an alternative embodiment, the modulation method realizes 1-to-N matrix technology based on the AC side shared matrix switch, comprising the following steps:

[0037] The converter parameters are loaded, and the input and output side voltages and currents are sampled.

[0038] The N-way internal and external phase angles and the switching frequency are calculated according to the power transmission regulation and the ZVS condition.

[0039] The N-way frequencies are compared and the minimum value is selected; the control variable is changed based on the minimum value, and the two-way internal and external phase angles and the switching frequency are updated.

[0040] Compared with the prior art, the present application has the following at least one beneficial effect:

[0041] 1. The single-stage isolated DC / AC converter topology reduces the number of power conversion times, thereby reducing energy loss; through the optimized three-degree-of-freedom modulation strategy (internal phase angle, external phase angle and switching frequency), full-range soft switching is realized.

[0042] 2. The present application only needs one power conversion, and adopts a high-efficiency resonant cavity design, greatly reducing the number and size of power switches required, which not only improves the power density but also reduces the manufacturing cost.

[0043] 3. By accurately controlling the internal phase angle, the external phase angle and dynamically adjusting the switching frequency, the present application can effectively reduce the harmonic components in the output electric energy and reduce the total harmonic distortion.

[0044] 4. Support "one-drag-N" technology, that is, multiple MPPT input ports share the same AC side matrix switch group. This design makes the system flexible to different photovoltaic input conditions, while ensuring the cooperative work of double or multiple MPPT through the synchronization strategy, improving the adaptability and stability of the system. BRIEF DESCRIPTION OF DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor. Among them:

[0046] Figure 1 The circuit schematic diagram of the resonant DC / AC converter based on two-way MPPT provided by an embodiment of the present application is shown in the figure;

[0047] Figure 2 The circuit schematic diagram of the resonant DC / AC converter based on two-way MPPT provided by another embodiment of the present application is shown in the figure;

[0048] Figure 3 The schematic diagram of the square wave form of the AC side bridge arm midpoint voltage is shown in the figure;

[0049] Figure 4 The schematic diagram of the square wave form of the DC side bridge arm midpoint voltage is shown in the figure;

[0050] Figure 5 The schematic diagram of the resonant cavity equivalent circuit is shown in the figure;

[0051] Figure 6 The schematic diagram of the phase shift angle relationship of the alternating square wave voltage is shown in the figure;

[0052] Figure 7 The schematic diagram of the high-frequency voltage and current phasor under the fundamental wave approximation is shown in the figure;

[0053] Figure 8 The schematic diagram of the time-domain steady-state waveform and corresponding phasor in the resonant cavity is shown in the figure;

[0054] Figure 9 The schematic diagram of the voltage and current signals and part of the drive signal phasor under the extended phase shift modulation is shown in the figure;

[0055] Figure 10 The flowchart of the modulation method provided by an embodiment of the present application is shown in the figure;

[0056] Figure 11 The one-drag-two single-stage DC / AC converter calculation flowchart provided by the present application is shown in the figure. DETAILED DESCRIPTION

[0057] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. It can be understood that the specific embodiments described herein are only used to explain the present application, rather than limit the present application. In addition, it should be noted that, for the convenience of description, only parts related to the present application are shown in the drawings, rather than all structures. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0058] The terms "first", "second", and the like in the present application are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but can optionally include steps or units not listed, or can optionally include other steps or units inherent to the process, method, product, or device.

[0059] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present application. The phrase appears at various places in the specification does not necessarily all refer to the same embodiment, nor is it necessarily mutually exclusive of other embodiments. It is explicitly and implicitly understood by those skilled in the art that embodiments described herein can be combined with other embodiments.

[0060] The conventional two-stage DC / AC converter uses more power switches, resulting in a larger device size and increasing the overall cost and complexity; the single-stage resonant DC / AC converter proposed in the present application only needs one power conversion, reducing the number of power switches and the space required, thereby improving the power density and reducing the cost. Although existing single-stage structures attempt to reduce switching loss, the efficiency improvement is limited due to the small soft switching range; the present application expands the three-degree-of-freedom modulation strategy combining phase shift + frequency modulation, achieving soft switching of all switches in the full voltage range, significantly improving the efficiency of the converter. As shown in Figure 1 , Figure 1 The circuit schematic diagram of the resonant DC / AC converter based on two-way MPPT provided by an embodiment of the present application includes:

[0061] The 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 fundamental approximation method is used to analyze the DC / AC inverter power circuit. Since the AC input voltage of the DC / AC inverter is time-varying, in order to facilitate analysis, the present application limits the following conditions:

[0062] 1. The inverter has been in steady state operation;

[0063] 2. In a switching cycle, the AC input voltage is approximately considered constant.

[0064] In the embodiment, the AC side bidirectional matrix switch group includes four groups of bidirectional tubes, each group of bidirectional tubes consists of two switching tubes, that is, eight switching tubes ; Based on the characteristics of the matrix switch type circuit, four switching tubes work at power frequency, and the other four work at high frequency; Specifically:

[0065] When the AC input voltage is positive, the power frequency is always on, the high frequency is switched; as Figures 3-4 shown, Figure 3 is a schematic diagram of the square wave of the AC side bridge arm midpoint voltage, Figure 4 is a schematic diagram of the square wave of the DC side bridge arm midpoint voltage; The principle of the square wave of the AC side bridge arm midpoint voltage and the square wave of the DC side bridge arm midpoint voltage is described below:

[0066] When the AC input voltage is positive, the power frequency is always on, the high frequency is switched; resulting in a square wave voltage at the AC side bridge arm midpoint, the square wave voltage is based on the on and off state change of the switching tube, and periodically reflects the frequency of the AC power supply; The power frequency is always on to form a part of the bridge arm, and by controlling the high frequency switching of , the desired square wave voltage at the midpoint of the bridge arm can be generated.

[0067] In another embodiment, the bidirectional matrix switch group contains 4 switching tubes ; as Figure 2 shown, Figure 2 is a circuit schematic diagram of a resonant DC / AC converter based on two-way MPPT provided by another embodiment of the application.

[0068] The AC side bidirectional matrix switch group includes two groups of bidirectional tubes, each group of bidirectional tubes consists of two switching tubes, that is, four switching tubes ; Based on the characteristics of the matrix switch type circuit, two switching tubes work at power frequency, and the other two work at high frequency; Specifically:

[0069] When the AC input voltage is positive, the power frequency is always on, the high frequency is switched; as Figures 3-4 shown, Figure 3 is a schematic diagram of the square wave of the AC side bridge arm midpoint voltage,Figure 4 Fig. 1 is a schematic diagram of the square wave of the DC side bridge leg midpoint voltage; the principle of the square wave of the AC side bridge leg midpoint voltage and the square wave of the DC side bridge leg midpoint voltage is described below:

[0070] When the AC input voltage is positive, the power frequency is always on, the high frequency switching; resulting in the AC side bridge leg midpoint generates a square wave voltage , square wave voltage based on the on and off state changes of the switch, the frequency of the AC power is reflected periodically; the power frequency is always on forms a part of the bridge leg, by controlling the high frequency switching, can be generated in the midpoint of the bridge leg desired square wave voltage .

[0071] In the DC side, the switch in the H bridge structure includes DC side bridge leg midpoint voltage ; by adjusting the phase difference of the switch in the H bridge, the amplitude and polarity of can be controlled, thereby affecting the transmission efficiency and direction of energy from the DC side to the AC side.

[0072] Fig. and are the fundamental components obtained by Fourier decomposition of the square wave of the DC side bridge leg midpoint voltage and the square wave of the AC side bridge leg midpoint voltage respectively.

[0073] When the AC input voltage is negative, the power frequency is always on, high frequency switching; based on the same technical means, the square wave of the AC side bridge leg midpoint voltage and the square wave of the DC side bridge leg midpoint voltage can be adjusted, which will not be described here.

[0074] For the circuit provided by Figure 2 when the AC input voltage is negative, the power frequency is always on, high frequency switching; based on the same technical means, the square wave of the AC side bridge leg midpoint voltage and the square wave of the DC side bridge leg midpoint voltage can be adjusted, which will not be described here.

[0075] By making different switch groups work in power frequency or high frequency mode in the positive and negative half cycle of the AC input voltage respectively, the switching loss can be effectively reduced. The switch in high frequency switching is responsible for fast response and adjustment, while the switch in power frequency always on reduces unnecessary frequent operation, thereby improving the overall efficiency; the configuration allows the converter to more accurately control the energy conversion process from the DC side to the AC side, especially under different load conditions, which can maintain a high energy transmission efficiency.

[0076] The high-frequency resonant cavity is composed of a resonant inductor and a resonant capacitor in series; in the embodiment, the resonant inductor and the resonant capacitor are connected in series to form a resonant cavity, and the first resonant cavity is composed of a resonant inductor and a resonant capacitor in series, and the second resonant cavity is composed of a resonant inductor and a resonant capacitor in series; the resonant frequency of the first resonant cavity is adjusted based on the inductance value and the capacitance value, and the resonant frequency of the second resonant cavity is adjusted based on the inductance value and the capacitance value, and .

[0077] The transformer secondary side is coupled to the resonant cavity, which is directly connected to the transformer secondary side, and serves as a key medium for energy transmission. It not only helps to smooth voltage fluctuations, but also optimizes output characteristics by adjusting circuit parameters. In the embodiment, the transformer turns ratio is n, as shown in Figure 5 , Figure 5 is the equivalent circuit diagram of the resonant cavity.

[0078] Fourier decomposition is performed on and , respectively, and the fundamental component expressions of the two are as follows:

[0079]

[0080] In the formula, the instantaneous value of the alternating current side power supply voltage is ; the direct current side power supply voltage is ; the transformer turns ratio is ; the switching angle frequency is ( is the switching frequency); the internal phase shift angle of the direct current side leading leg drive and the lagging leg drive is ; wherein and are in the leading leg, and are in the lagging leg; the external phase shift angle of the leading is .

[0081] It should be noted that, in the embodiment, the resonant inductor and the resonant capacitor are connected in series to form a resonant cavity, and in other embodiments, the resonant inductor and the resonant capacitor can be connected in parallel or in series-parallel to form a resonant cavity, which is not limited.

[0082] Two independent MPPT input ports are connected in parallel to the resonant cavity through the direct current side H-bridge switch group; each MPPT input is responsible for obtaining electrical energy from a photovoltaic array or module, and finds the optimal operating point of the array through its own control logic to maximize energy extraction.

[0083] Each of the two MPPT inputs is 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 power the resonant cavity simultaneously, thereby optimizing the overall system's energy utilization efficiency.

[0084] The two MPPT inputs share the same AC-side matrix switch group, which can work together and flexibly adjust the output under different load conditions to ensure system stability and efficiency.

[0085] The control module is configured to calculate the common switching frequency of the dual MPPTs, ensuring coordinated operation of the two MPPTs based on a frequency synchronization strategy. By calculating and using a common switching frequency, the energy conversion process of the two MPPT inputs can be more coordinated and consistent. This helps reduce energy loss and unnecessary losses caused by frequency mismatch. The frequency synchronization strategy enables more efficient and smooth energy conversion from the DC side to the AC side, thereby improving the overall energy utilization efficiency of the system.

[0086] In this embodiment, the first MPPT input port is... 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.

[0087] For ease of analysis, this application defines some parameters and variables of the converter:

[0088] AC / DC voltage gain ratio: ;

[0089] Resonant frequency: ;

[0090] Resonant cavity impedance: .

[0091] Inward phase angle and outward phase angle The specific situation when working in both directions is as follows: Figure 6 As shown, Figure 6 This is a schematic diagram showing the phase shift angle relationship of an 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, such as... Figure 7 As shown, Figure 7 This is a schematic diagram of high-frequency voltage and current phasors under the fundamental frequency approximation.

[0092] definition The phasor is , The phasor is At this time, the voltage excitation applied across the resonant cavity is... , under the premise that the switching frequency is higher than the resonant frequency, a resonant current is generated which lags behind the voltage excitation by 90° phase . For the convenience of analysis, the resonant current corresponding phasor is divided into active current phasor and reactive current phasor by phase, and the expression of the length of the two current phasors is as follows:

[0093]

[0094] At this time , the time domain expression is as follows:

[0095] .

[0096] The power transmission characteristics of the DC / AC converter are particularly critical, that is, whether the instantaneous transmitted current size can follow the alternating voltage to ensure a small current total harmonic distortion (THD) to meet the grid connection requirements, so it is necessary to control the average value of the resonant current transmitted to the output end of the alternating side in each switching period in the high-frequency resonant cavity.

[0097] In addition, the realization of soft switching of the switching tube is also important for improving the efficiency and reducing the loss of the DC / AC converter; to realize soft switching, it is necessary to ensure that the current direction is the same as that of the body diode in the dead time before the switching tube is turned on, and the charging and discharging of the output junction capacitor on both sides of the drain and source of the switching tube is completed in the dead time between the bridge arm switching tubes.

[0098] For the alternating side switching tube, the waveform diagrams of the voltage and current phasors and the driving signal under the fundamental approximation method are as shown in Figure 8 , Figure 8 is the time domain steady-state waveform and corresponding phasor diagram in the resonant cavity. At this time, the waveform diagrams of the voltage and current phasors and the driving signal under the fundamental approximation method are as shown in Figure 8 , Figure 8 is the time domain steady-state waveform and corresponding phasor diagram in the resonant cavity. At this time, the waveform diagrams of the voltage and current phasors and the driving signal under the fundamental approximation method are as shown in , is the time domain steady-state waveform and corresponding phasor diagram in the resonant cavity. At this time, the waveform diagrams of the voltage and current phasors and the driving signal under the fundamental approximation method are as shown in Figure 9 , Figure 9 is the time domain steady-state waveform and corresponding phasor diagram in the resonant cavity. At this time, the waveform diagrams of the voltage and current phasors and the driving signal under the fundamental approximation method are as shown in

[0099] In summary, in order to improve the performance of the DC / AC converter, the soft switching operation needs to be realized while optimizing the power transmission characteristics, to ensure efficient operation under various working conditions and reduce the total harmonic distortion (THD).

[0100] The application adopts a three-degree-of-freedom modulation strategy of extended phase shift + frequency modulation, and the control quantity is the inner phase shift angle , the outer phase shift angle and the switching frequency ; specifically, the control module is configured to output a driving signal using a three-degree-of-freedom modulation strategy of the inner phase shift angle , the outer phase shift angle and the switching frequency ; the following describes the role of the control variables of the three-degree-of-freedom modulation strategy:

[0101] The inner phase shift angle controls the phase difference between the leading bridge arm and the lagging bridge arm of the DC side H-bridge; by adjusting the inner phase shift angle , the energy level and timing transmitted from the DC side to the resonant cavity can be adjusted. Specifically, when the leading bridge arm is turned on earlier than 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.

[0102] The outer phase shift angle controls the phase difference between the AC side voltage square wave and the DC side equivalent voltage square wave; the outer phase shift angle is used to ensure 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 appropriately setting the outer phase shift angle, the AC side switch tube can be switched under zero voltage or zero current conditions, reducing switching loss.

[0103] The switching frequency is dynamically adjusted to maintain the inductive impedance of the resonant cavity; based on the system load condition and the input and output voltage level, the switching frequency is adjusted in real time. This not only helps to maintain the inductive characteristics of the resonant cavity, but also optimizes the effective value of the resonant current, reduces switching loss, and improves the efficiency of the entire system.

[0104] The control module performs the following procedures:

[0105] 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 the actual working conditions, ensuring efficient energy transmission under different loads.

[0106] Simultaneous solution of power transmission equation, soft switching condition equation and phase shift angle relationship; based on the fundamental wave approximation method to analyze the circuit model, determine the energy transmission efficiency from the DC side to the AC side, ensure that the switching elements can be switched under zero voltage or zero current conditions, reduce switching loss, and solve the optimal inner phase shift angle, outer phase shift angle and switching frequency by solving the power transmission equation and soft switching condition equation.

[0107] The output inner phase angle, outer phase angle, and switching frequency are output to the drive circuit to generate PWM signals. The inner phase angle, outer phase angle, and switching frequency are accurately calculated and applied, so that all switching elements can be switched under optimal conditions, significantly reducing switching loss and improving overall system efficiency. The principle of how the control module obtains the inner phase angle, outer phase angle, and switching frequency is described in detail below:

[0108] Optimizing power transmission characteristics can be achieved by adjusting to ensure the quality of the AC current waveform. The specific relationship can be obtained by substituting equation (2) into equation (3):

[0109]

[0110] The inner phase angle is based on the AC / DC voltage gain ratio and the active component of the resonant current By calculating the inner phase 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.

[0111] Expanding the phase modulation to achieve full-range soft switching:

[0112] The AC side switch tube realizes zero-voltage turn-on by ensuring that the resonant current and the body diode of the switch tube are in the same direction. Since the AC side H-bridge is a high-frequency rectification link, the direction of the high-frequency current is naturally consistent with the direction of the body diode of the switch tube. By ensuring and the same phase and appropriately increasing the dead time of the AC side switch tube, zero-voltage turn-on of all AC side switch tubes can be achieved. According to equation (4), at this time:

[0113]

[0114] Similarly, soft switching operation is also required on the DC side. The turn-on current is adjusted to meet the charging and discharging requirements of the output capacitor within the dead time. The turn-on current reference value is determined by the output capacitor 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 the switch tube must be turned on before the resonant current is positive and its size meets the sufficient charging and discharging requirements of its output capacitor within the dead time. Accordingly, the required turn-on current of the switch tube is:

[0115]

[0116] where the phase angle is defined as Figure 8 shown. This value can be obtained using the inner phase angle and the phase angle of the external shift denotes:

[0117]

[0118] To ensure that the switch tube Realize soft switch, can obtain the opening current reference value at this time ; The phase angle of the external shift is determined based on the minimum turn-on current required to achieve soft switching and the resonant cavity impedance. By precisely controlling the phase angle of the external shift, 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 stable, and reducing unnecessary energy loss. Soft switching operation reduces electromagnetic interference (EMI) during switching, while reducing total harmonic distortion (THD) and providing higher quality sine wave output.

[0119] As shown in the following formula (10), wherein 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, from which the phase angle of the external shift The size can be obtained.

[0120]

[0121] By combining formulas (6), (7), (9), (10), the phase angle of the internal shift θ and the phase angle of the external shift are:

[0122]

[0123]

[0124] Based on this, formulas (11), (12) are substituted into formula (6), and the resonant cavity impedance is:

[0125]

[0126] The switching frequency can be represented as:

[0127]

[0128] The entire control quantity of the extended phase shift + frequency modulation can be obtained. Based on these control quantities, the drive signals of each switch tube can be obtained by peripherals in the digital processor to modulate the power of the inverter and achieve optimization of power transmission characteristics, full-range soft switching, and total harmonic distortion optimization.

[0129] The application further provides a modulation method applied to the two-path MPPT-based resonant DC / AC converter of the above embodiment, as shown in Figure 10 Figure 10 A flowchart of the modulation method provided by an embodiment of the application comprises the following steps:

[0130] S1: establishing an equivalent model of the resonant cavity based on the fundamental approximation method;

[0131] S2: synchronously solving the inner phase shift angle, the outer phase shift angle and the switching frequency based on the voltage-current phasor relationship;

[0132] S3: outputting the driving signal to realize full-range soft switching and total harmonic distortion optimization.

[0133] As shown in Figure 11 Figure 11 A calculation flowchart of the one-to-two single-stage DC / AC converter provided by the application comprises the following steps:

[0134] Loading the converter parameters, sampling the input and output side voltages and currents;

[0135] Calculating the two-path inner and outer phase shift angles and the switching frequency according to the power transmission regulation and the ZVS (zero voltage switching) condition;

[0136] Comparing the two-path frequencies and selecting the minimum value; changing the control variable based on the minimum value, and updating the two-path inner and outer phase shift angles and the switching frequency.

[0137] In addition, the modulation method can also realize the one-to-N matrix technology based on the AC side shared matrix switch, comprising the following steps:

[0138] Loading the converter parameters, sampling the input and output side voltages and currents;

[0139] Calculating the N-path inner and outer phase shift angles and the switching frequency according to the power transmission regulation and the ZVS condition;

[0140] Comparing the N-path frequencies and selecting the minimum value; changing the control variable based on the minimum value, and updating the two-path inner and outer phase shift angles and the switching frequency.

[0141] In the several embodiments of the application, it should be understood that the disclosed method and device can be implemented in other ways. For example, the device embodiments described above are only schematic. The division of the modules or units is only a logical function division. There can be another division manner in actual implementation. For example, a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not executed.

[0142] ​​The units described as separate components may or may not be physically separate, and the components displayed as units may or may not be physical units, that is, may be located in one place, or may be distributed to multiple network units. Part or all of the units can be selected according to actual needs to achieve the purpose of the present embodiment scheme.

[0143] In addition, each functional unit in each embodiment of the present application can be integrated into one processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The integrated unit can be realized in the form of hardware or in the form of a software functional unit.

[0144] The above is only an embodiment of the present application, and does not limit the patent scope of the present application, and any equivalent structure or equivalent flow transformation using the content of the present application specification and drawings, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A two-path MPPT-based resonant DC / AC converter, characterized in that, The single-stage isolated DC / AC converter topology comprises a bidirectional matrix switch group on the AC side and an H-bridge switch group on the DC side. A high-frequency resonant cavity is coupled to the secondary side of the transformer and is formed by a series connection of a resonant inductor and a resonant capacitor. Two independent MPPT input ports are connected in parallel to the resonant cavity through the DC side H-bridge switch group. A control module is configured to output a driving signal by using a three-degree-of-freedom modulation strategy of inner phase shift angle, outer phase shift angle and switching frequency. The control variables of the three-degree-of-freedom modulation strategy include: The inner phase shift angle controls the phase difference between the leading arm and the lagging arm of the DC side H-bridge; The outer 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 cavity. 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 the minimum turn-on current required to achieve soft switching and the impedance of the resonant cavity. The control module performs the following processes:

2. The two-path MPPT-based resonant DC / AC converter according to claim 1, characterized in that, The bidirectional matrix switch group comprises 8 switch tubes wherein: When the AC input voltage is positive, Power frequency always on, High frequency switching; when the ac input voltage is negative, line frequency always on, high frequency switching; or the bidirectional matrix switch group comprises 4 switch tubes wherein: when the ac input voltage is positive, line frequency always on, high frequency switching; When the AC input voltage is negative, Power frequency always on, High frequency switching. 3.The two-path MPPT-based resonant DC / AC converter of claim 1, wherein Real-time sampling of AC input voltage and DC side voltage; Simultaneous solution of power transmission equation, soft switching condition equation and phase shift angle relationship; Output of inner phase shift angle, outer phase shift angle and switching frequency to the driving circuit to generate PWM signal. Expanding phase shift modulation to achieve full-range soft switching:

4. The two-path MPPT-based resonant DC / AC converter of claim 1, wherein The AC side switch tube realizes zero-voltage turn-on by the same direction of the resonant current and the body diode; The DC side switch tube meets the output capacitor charging and discharging requirement in the dead time by adjusting the turn-on current. The turn-on current reference value is determined by the output capacitor value of the DC side switch tube, the DC voltage and the preset dead time.

5. The two-path MPPT-based resonant DC / AC converter according to claim 4, characterized by Two MPPT inputs share the same AC side matrix switch group.

6. The two-path MPPT-based resonant DC / AC converter of claim 1, wherein, The control module is configured to calculate the common switching frequency of the two MPPTs and ensure the cooperative work of the two MPPTs based on the frequency synchronization strategy. The modulation method is based on the 1-to-N matrix technology of the AC side shared matrix switch and includes the following steps:

7. A modulation method applied to the two-path MPPT-based resonant DC / AC converter of any one of claims 1-6, characterized in that, Load the converter parameters, sample the input and output side voltages and currents; Calculate the N-way inner and outer phase shift angles and switching frequency according to the power transmission regulation and ZVS condition; Compare the N-way frequencies and select the minimum frequency; Based on the minimum frequency, change the control variables and update the two-way inner and outer phase shift angles and switching frequency.

8. The modulation method of claim 7, wherein, ​ ​ ​ ​ ​

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