Staggered parallel flyback micro inverter control method and device and readable medium

Abstract

The invention discloses an interleaved parallel flyback micro inverter control method and device, and a readable medium. The method comprises the steps of obtaining a direct current voltage and a direct current of a photovoltaic module at an input end of a micro inverter, and performing maximum power point tracking calculation to obtain a reference output power; obtaining a power grid voltage instantaneous value and carrying out effective value calculation to obtain a power grid voltage effective value; calculating a grid-connected reference current effective value according to the reference output power and the grid voltage effective value; by setting a secondary side current overlapping factor and calculating and adjusting the switching frequency and the duty ratio, a secondary side current overlapping area is reduced to the greatest extent, and the peak value of the secondary side current can be reduced as far as possible, so that the current stress of a flyback diode and a power frequency flip circuit switching tube is reduced, and the grid-connected current quality is improved.

Description

Technical Field

[0001] The present invention relates to the field of inverter control, and in particular to a control method, device and readable medium of an interleaved parallel flyback micro inverter. Background Art

[0002] Photovoltaic power generation is one of the main ways to utilize solar energy, among which grid-connected photovoltaic power generation systems are the most commonly used form. However, traditional grid-connected photovoltaic power generation systems have disadvantages such as power loss and hot spots caused by local shadow coverage. In order to solve these problems, micro photovoltaic inverters came into being. The micro photovoltaic inverter adopts a modular design, and each module has its own maximum power point tracking (MPPT) function, which can track the maximum power to the maximum extent, reduce power loss and eliminate the impact of local shadows. In addition, the micro photovoltaic inverter also has the advantages of plug-and-play, flexible installation, and easy maintenance. It is widely used in various small and medium power photovoltaic power generation fields. In the design of micro photovoltaic inverters, the staggered parallel flyback micro inverter has the advantages of simple structure, low cost, and easy implementation. It is widely used in medium and small power distributed photovoltaic power generation occasions. Its circuit topology is as follows: Figure 1 shown.

[0003] Interleaved parallel flyback microinverters are usually open-loop controlled, and are mainly based on discontinuous conduction mode (DCM), boundary conduction mode (BCM) and a hybrid control of the two.

[0004] At present, most of the existing control methods take the peak value of the primary current of the flyback converter as the control object. By sampling the input voltage and the grid voltage, the reference peak value of the primary current is calculated, and then the on and off time of the main switch tube is calculated according to the peak current or controlled by hardware triggering. Most of the existing control technologies are DCM or DCM / BCM hybrid control. When two flyback converters work at the same time, the control method for the primary current cannot avoid the overlap of the secondary current under some working conditions, which increases the current stress of the switch tube of the subsequent power frequency flip circuit and affects the quality of the grid-connected current. The reflected voltage at the output end of the flyback is lower than the input voltage u g / N dc When using DCM interleaved parallel flyback converter transformer secondary currents will overlap when the output power is large; while in BCM, there will be overlap regardless of the output power. The overlap of secondary currents will excite a large number of high-order harmonics and increase the current stress of the subsequent stage. The overlap of the original secondary current is shown in the figure below: Figure 2 shown. ​

[0005] The invention patent "Control method for the switch tube of photovoltaic grid-connected interleaved flyback inverter" with publication number CN102594180A proposes a method of dividing the reference current curve of the switch tube within half a power frequency cycle into three intervals and using different breaking times respectively. By deriving the formula of the switching cycle and the energy relationship, the parameters are optimized, and the switching point of each interval is accurately calculated to meet the working conditions of the quasi-resonant switch to improve the output current quality.

[0006] The invention patent with publication number CN104269877A, "Hybrid modulation system and method for interleaved reverse PV grid-connected inverter", adopts a control strategy of two-phase DCM and one-phase DCM hybrid modulation within half of the power frequency cycle to optimize the converter loss according to the load conditions and improve the efficiency of the converter within the full load range.

[0007] The above two patents do not specifically optimize and describe the interleaving control technology.

[0008] The paper "Study on Control Strategy of Interleaved Flyback Photovoltaic Grid-connected Inverter" adopts an interleaved modulation method with a half carrier cycle difference between the two main switch tubes of the interleaved parallel flyback, which can reduce current stress and current ripple. This method is the most basic implementation form of interleaved control. When the grid-connected power is large, there is an overlapping area between the two secondary currents, and the interleaved control technology has not been specifically optimized. Summary of the invention

[0009] The purpose of this application is to propose a control method, device and readable medium for an interleaved parallel flyback micro-inverter in response to the above-mentioned technical problems.

[0010] In a first aspect, the present invention provides a control method for an interleaved parallel flyback micro-inverter, comprising the following steps:

[0011] Obtain the DC voltage and DC current of the photovoltaic module at the input end of the micro inverter and calculate the reference output power;

[0012] Obtain the instantaneous value of the grid voltage and the effective value of the grid voltage;

[0013] The grid-connected reference current effective value is calculated based on the reference output power and the grid voltage effective value; a preset secondary current overlap factor is set and the primary magnetizing inductance of the flyback transformer and the turns ratio between the secondary and primary sides of the flyback transformer are obtained, and the preferred switching frequency is calculated based on the grid-connected reference current effective value, the grid voltage effective value, the preset secondary current overlap factor, the primary magnetizing inductance of the flyback transformer and the turns ratio between the secondary and primary sides of the flyback transformer; the preferred duty cycle is calculated based on the DC voltage of the photovoltaic module at the input end of the micro-inverter, the instantaneous value of the grid voltage, the preset secondary current overlap factor and the turns ratio between the secondary and primary sides of the flyback transformer;

[0014] It is determined whether the preferred switching frequency exceeds the upper limit value. If so, the preferred switching frequency is adjusted to the upper limit value to obtain the adjusted switching frequency. The adjusted secondary current overlap factor is calculated according to the adjusted switching frequency, the effective value of the grid-connected reference current, the effective value of the grid voltage, the primary magnetizing inductance of the flyback transformer, and the turns ratio between the secondary side and the primary side of the flyback transformer. The adjusted duty cycle is calculated according to the DC voltage of the photovoltaic module at the input end of the micro-inverter, the instantaneous value of the grid voltage, the adjusted secondary current overlap factor, and the turns ratio between the secondary side and the primary side of the flyback transformer. The adjusted switching frequency and the adjusted duty cycle are input into the PWM generator, and two control pulse signals staggered by 180° are output to drive the two flyback switch tubes; otherwise, the preferred switching frequency and the preferred duty cycle are input into the PWM generator, and two control pulse signals staggered by 180° are output to drive the two flyback switch tubes respectively; wherein, the calculation formula of the preferred switching frequency or the adjusted switching frequency is as follows:

[0015]

[0016] Among them, f s Indicates the preferred switching frequency or the adjusted switching frequency, U g represents the effective value of the grid voltage, N represents the turns ratio between the secondary and primary sides of the flyback transformer, L m represents the primary magnetizing inductance of the flyback transformer, Indicates the effective value of the grid-connected reference current, D off Indicates the preset secondary current overlap factor or the adjusted secondary current overlap factor; the preferred duty cycle or the adjusted duty cycle is calculated as follows:

[0017]

[0018] Where D is the preferred duty cycle or the adjusted duty cycle, U dc Indicates the DC voltage of the photovoltaic module at the input end of the micro-inverter, u g (t) represents the instantaneous value of the grid voltage.

[0019] Preferably, the preset secondary current overlap factor is 0.5, and the adjusted secondary current overlap factor is less than 0.5.

[0020] Preferably, the reference output power is obtained by sampling the DC voltage and DC current of the photovoltaic module at the input end of the inverter and performing maximum power tracking control.

[0021] Preferably, the effective value of the grid voltage is obtained by calculating the effective value of the instantaneous value of the grid voltage.

[0022] Preferably, the grid-connected reference current effective value is calculated according to the reference output power and the grid voltage effective value, specifically including:

[0023] The reference output power P o Divide by the effective value of the grid voltage U g , get the grid-connected reference current effective value

[0024] In a third aspect, the present invention provides a staggered parallel flyback micro-inverter control device, comprising:

[0025] A power calculation module is configured to obtain a DC voltage and a DC current of a photovoltaic module at an input end of the micro-inverter and calculate a reference output power;

[0026] A grid voltage data acquisition module is configured to acquire a grid voltage instantaneous value and a grid voltage effective value;

[0027] The switching frequency and duty cycle calculation module is configured to calculate the effective value of the grid-connected reference current according to the reference output power and the effective value of the grid voltage; set a preset secondary current overlap factor and obtain the primary magnetizing inductance of the flyback transformer and the turns ratio between the secondary and primary sides of the flyback transformer, and calculate the preferred switching frequency according to the effective value of the grid-connected reference current, the effective value of the grid voltage, the preset secondary current overlap factor, the primary magnetizing inductance of the flyback transformer and the turns ratio between the secondary and primary sides of the flyback transformer; calculate the preferred duty cycle according to the DC voltage of the photovoltaic module at the input end of the micro-inverter, the instantaneous value of the grid voltage, the preset secondary current overlap factor and the turns ratio between the secondary and primary sides of the flyback transformer;

[0028] The adjustment module is configured to determine whether the preferred switching frequency exceeds the upper limit value. If so, the preferred switching frequency is adjusted to the upper limit value to obtain the adjusted switching frequency. The adjusted secondary current overlap factor is calculated according to the adjusted switching frequency, the effective value of the grid-connected reference current, the effective value of the grid voltage, the primary excitation inductance of the flyback transformer, and the turns ratio between the secondary side and the primary side of the flyback transformer. The adjusted duty cycle is calculated according to the DC voltage of the photovoltaic module at the input end of the micro-inverter, the instantaneous value of the grid voltage, the adjusted secondary current overlap factor, and the turns ratio between the secondary side and the primary side of the flyback transformer. The adjusted switching frequency and the adjusted duty cycle are input into the PWM generator, and two control pulse signals staggered by 180° are output to drive the two flyback switch tubes; otherwise, the preferred switching frequency and the preferred duty cycle are input into the PWM generator, and two control pulse signals staggered by 180° are output to drive the two flyback switch tubes respectively; wherein, the calculation formula of the preferred switching frequency or the adjusted switching frequency is as follows:

[0029]

[0030] Among them, f s Indicates the preferred switching frequency or the adjusted switching frequency, U g represents the effective value of the grid voltage, N represents the turns ratio between the secondary and primary sides of the flyback transformer, Lm represents the primary magnetizing inductance of the flyback transformer, Indicates the effective value of the grid-connected reference current, D off Indicates the preset secondary current overlap factor or the adjusted secondary current overlap factor; the preferred duty cycle or the adjusted duty cycle is calculated as follows:

[0031]

[0032] Where D is the preferred duty cycle or the adjusted duty cycle, U dc Indicates the DC voltage of the photovoltaic module at the input end of the micro-inverter, u g (t) represents the instantaneous value of the grid voltage.

[0033] In a third aspect, the present invention provides an electronic device comprising one or more processors; a storage device for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors implement the method described in any implementation manner in the first aspect.

[0034] In a fourth aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method described in any implementation manner in the first aspect.

[0035] In a fifth aspect, the present invention provides a computer program product, comprising a computer program, which, when executed by a processor, implements the method described in any implementation manner in the first aspect.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) The interleaved parallel flyback micro-inverter control method proposed in the present invention calculates the switching frequency and duty cycle of the main switch tube through the secondary current overlap factor and outputs a PWM control signal, which can avoid the overlap area when the secondary currents of two flyback transformers are connected in parallel.

[0038] (2) The interleaved parallel flyback micro-inverter control method proposed in the present invention limits the upper limit of the switching frequency to select a suitable D off , minimize the overlapping area of ​​the secondary current, and minimize the peak value of the secondary current, thereby reducing the current stress of the flyback diode and the power frequency flip circuit switch tube, and improving the quality of the grid-connected current.

[0039] (3) The interleaved parallel flyback micro-inverter control method proposed in the present invention has a fixed switching frequency in steady state, and there is no mode switching control. Moreover, near the grid voltage peak with large instantaneous power, the current density is close to the BCM control mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0041] Figure 1 A circuit topology diagram of an interleaved parallel flyback micro-inverter of the prior art;

[0042] Figure 2 A schematic diagram of the overlap of primary and secondary currents in the prior art;

[0043] Figure 3 A schematic flow chart of a control method for an interleaved parallel flyback micro-inverter according to an embodiment of the present application;

[0044] Figure 4 The interleaved parallel flyback micro-inverter control method of the embodiment of the present application is in D off Schematic diagram of primary and secondary current when ≤0.5;

[0045] Figure 5 A control block diagram of a staggered parallel flyback micro-inverter control method according to an embodiment of the present application;

[0046] Figure 6 A logic flow chart of a control method for an interleaved parallel flyback micro-inverter according to an embodiment of the present application;

[0047] Figure 7 The interleaved parallel flyback micro-inverter control method of the embodiment of the present application is in P o = Schematic diagram of total secondary current in parallel when 600W;

[0048] Figure 8 The interleaved parallel flyback micro-inverter control method of the embodiment of the present application is in P o =Result diagram of grid-connected voltage and grid-connected current when 600W;

[0049] Fig. 9 The interleaved parallel flyback micro-inverter control method of the embodiment of the present application is in P o = Schematic diagram of total secondary current in parallel when 160W;

[0050] Fig.10 The interleaved parallel flyback micro-inverter control method of the embodiment of the present application is in P o =Result diagram of grid-connected voltage and grid-connected current when 160W;

[0051] Fig.11 A schematic diagram of a staggered parallel flyback micro-inverter control device according to an embodiment of the present application;

[0052] Fig.12 A schematic diagram of the hardware structure of an electronic device provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0054] Figure 3 A staggered parallel flyback micro-inverter control method provided in an embodiment of the present application is shown, comprising the following steps:

[0055] S1, obtaining the DC voltage and DC current of the photovoltaic module at the input end of the micro inverter and calculating the reference output power.

[0056] In a specific embodiment, the reference output power is obtained by sampling the DC voltage and DC current of the photovoltaic module at the input end of the inverter and performing maximum power tracking control.

[0057] Specifically, refer to Figure 1 The circuit topology mentioned in the embodiment of the present application includes the following parts: an input decoupling capacitor C in , flyback converter 1#, flyback converter 2#, industrial frequency flipping circuit and LC filtering circuit.

[0058] Among them, the flyback converter 1# includes: high-frequency switch tube Q1, primary excitation inductor L m , ideal transformer T1 and secondary diode D1;

[0059] Flyback converter 2# includes: high-frequency switch Q2, primary excitation inductor L m , ideal transformer T2 and secondary diode D2;

[0060] The power frequency flip circuit includes: a power frequency switch tube S1, a power frequency switch tube S2, a power frequency switch tube S3 and a power frequency switch tube S4;

[0061] The LC filter circuit includes: filter inductor L f And filter capacitor C f .

[0062] Figure 1In the figure, the decoupling capacitor and the two flyback converters are connected in parallel and connected to the photovoltaic module for power decoupling; the two flyback converters are used to modulate the sinusoidal half-wave current, and their output ends are connected in parallel and connected to the power frequency reversal circuit; the power frequency reversal circuit reverses the current modulated by the flyback converter into a sinusoidal alternating current, and the output end of the power frequency reversal circuit is connected to the LC filter circuit; the LC filter circuit is used to filter out the harmonic components of the grid-connected current and retain the power frequency fundamental current. dc is the DC current of the PV module at the input end of the micro-inverter, U dc is the DC voltage of the photovoltaic module at the input end of the micro-inverter; i p1 is the primary current of the flyback converter 1# transformer; i s1 is the secondary current of the flyback converter 1# transformer; i p2 is the primary current of the 2# transformer of the flyback converter; i s2 is the secondary current of the 2# transformer of the flyback converter; i sum is the current of the industrial frequency flip bridge.

[0063] A single-channel flyback converter includes a flyback transformer, a switch tube, and a secondary diode. In half a power frequency cycle, the primary current of the flyback transformer is referenced to the peak value i ref (t) and grid-connected current reference instantaneous value The relationship is:

[0064]

[0065] Among them, T sw is the switch cycle of the flyback converter switch, t off is the time required for the secondary current of the flyback transformer to drop to 0, N is the turns ratio between the secondary and primary sides of the flyback transformer,

[0066] According to the characteristics of the flyback converter, the primary and secondary currents of the flyback transformer have the following relationship:

[0067]

[0068] Among them, i p is the peak current of the primary side of the flyback transformer, i s is the secondary current peak value of the flyback transformer, t on is the conduction time of the switch tube, u g (t) is the instantaneous value of the grid voltage, U g Represents the effective value of the grid voltage, and sin(ωt) represents a unit sinusoidal signal with the same phase as the grid voltage.

[0069] From the above formula we can get:

[0070]

[0071] Among them, U dc Indicates the DC voltage of the PV module at the input end of the micro-inverter;

[0072] Because in a single switching cycle, i p =i ref , switching frequency f s =1 / T sw , substituting into the above two formulas, we have:

[0073]

[0074] Among them, L m Represents the primary magnetizing inductance of the flyback transformer;

[0075] Order: t on =DT sw , t off =D off T sw , where D is the duty cycle, D off is the secondary current overlap factor, which indicates the ratio of the time required for the secondary current of the flyback transformer to drop to zero to the entire switching cycle. off When >0.5, the secondary current will overlap. Substituting into the above two formulas, we get:

[0076]

[0077] Considering the unity power factor grid connection, with u g In phase, Further simplified to:

[0078]

[0079] Among them, U g is the effective value of the grid voltage, It is the effective value of grid-connected reference current.

[0080] In continuous conduction mode (DCM), f s unchanged, when When D is greater than a certain value, off It will be greater than 0.5, and the secondary currents of the two flyback transformers connected in parallel will overlap.

[0081] The main parameter relationships in critical conduction mode (BCM) are as follows:

[0082]

[0083] When NU dc >u g (t)off >0.5, there is an overlapping area in the secondary currents of the two flyback transformers connected in parallel.

[0084] In order to avoid overlapping areas when two secondary currents of the flyback transformers are connected in parallel, the embodiment of the present application uses the value of the secondary current overlap factor to calculate the switching frequency and the duty cycle.

[0085] f s =1 / T sw and t off =D off T sw Substitution And the two reference output powers each account for 1 / 2 of the grid-connected power, so the derived single-channel grid-connected reference current is 1 / 2 of the grid-connected reference current, and we can get:

[0086]

[0087] t on =DT sw and t off =D off T sw Substitution We can get:

[0088]

[0089] Considering the unity power factor grid connection, with u g In phase, Further simplified to:

[0090]

[0091] according to t off =D off T sw and f s =1 / T sw Substitution The peak current of the secondary side of the flyback transformer is obtained as:

[0092]

[0093] It shows that when the instantaneous value of the grid-connected current reference remains unchanged, the switching frequency and the overlap factor D off Proportional, D off The larger the value, the higher the switching frequency.

[0094] It shows that when the instantaneous value of the grid-connected current reference remains unchanged, the peak value of the secondary current of the flyback transformer is proportional to D off Inversely proportional, that is, Doff The larger it is, the smaller the current stress of the flyback diode and the switch tube of the subsequent flip circuit. off The upper limit of the value is limited by the upper limit of the switching frequency, and in order to ensure that the secondary currents of the two flyback transformers are staggered as much as possible, D off The value should not be greater than 0.5. Figure 4 As shown, when D off When ≤0.5, there will be no overlapping area in the secondary current of the flyback transformer.

[0095] When the grid-connected power is small, the secondary current peak of the flyback transformer is small, and a smaller D off To reduce the switching frequency; when the grid-connected current is large, D off =0.5 to reduce the secondary current peak of the flyback transformer and avoid the overlap of the secondary current of the flyback transformer.

[0096] refer to Figure 5 First, the DC voltage and DC voltage of the photovoltaic module at the input end of the inverter are sampled to perform maximum power point tracking to obtain the reference output power P of the inverter. o .

[0097] S2, obtain the instantaneous value of the grid voltage and the effective value of the grid voltage.

[0098] In a specific embodiment, the effective value of the grid voltage is obtained by performing effective value calculation on the instantaneous value of the grid voltage.

[0099] Specifically, the instantaneous value of the grid voltage is sampled, and the RMS effective value of the instantaneous value of the grid voltage is calculated to obtain the effective value of the grid voltage U g .

[0100] S3, calculate the effective value of the grid-connected reference current according to the reference output power and the effective value of the grid voltage; set a preset secondary current overlap factor and obtain the primary excitation inductance of the flyback transformer and the turns ratio of the secondary side to the primary side of the flyback transformer, and calculate the preferred switching frequency according to the effective value of the grid-connected reference current, the effective value of the grid voltage, the preset secondary current overlap factor, the primary excitation inductance of the flyback transformer and the turns ratio of the secondary side to the primary side of the flyback transformer; calculate the preferred duty cycle according to the DC voltage of the photovoltaic module at the input end of the micro-inverter, the instantaneous value of the grid voltage, the preset secondary current overlap factor and the turns ratio of the secondary side to the primary side of the flyback transformer.

[0101] In a specific embodiment, the grid-connected reference current effective value is calculated based on the reference output power and the grid voltage effective value, specifically including:

[0102] The reference output power P o Divide by the effective value of the grid voltage U g , get the grid-connected reference current effective value

[0103] In a specific embodiment, the preset secondary current overlap factor is 0.5, and the adjusted secondary current overlap factor is less than 0.5.

[0104] S4, judging whether the preferred switching frequency exceeds the upper limit value, if so, adjusting the preferred switching frequency to the upper limit value to obtain the adjusted switching frequency, calculating the adjusted secondary current overlap factor according to the adjusted switching frequency, the effective value of the grid-connected reference current, the effective value of the grid voltage, the primary magnetizing inductance of the flyback transformer and the turns ratio between the secondary side and the primary side of the flyback transformer, calculating the adjusted duty cycle according to the DC voltage of the photovoltaic module at the input end of the micro-inverter, the instantaneous value of the grid voltage, the adjusted secondary current overlap factor and the turns ratio between the secondary side and the primary side of the flyback transformer, inputting the adjusted switching frequency and the adjusted duty cycle into the PWM generator, outputting two control pulse signals staggered by 180° and driving the two flyback switch tubes; otherwise, inputting the preferred switching frequency and the preferred duty cycle into the PWM generator, outputting two control pulse signals staggered by 180° and driving the two flyback switch tubes respectively; wherein, the calculation formula of the preferred switching frequency or the adjusted switching frequency is as follows:

[0105]

[0106] Among them, f s Indicates the preferred switching frequency or the adjusted switching frequency, U g represents the effective value of the grid voltage, N represents the turns ratio between the secondary and primary sides of the flyback transformer, L m represents the primary magnetizing inductance of the flyback transformer, Indicates the effective value of the grid-connected reference current, D off Indicates the preset secondary current overlap factor or the adjusted secondary current overlap factor; the preferred duty cycle or the adjusted duty cycle is calculated as follows:

[0107]

[0108] Where D is the preferred duty cycle or the adjusted duty cycle, U dc Indicates the DC voltage of the photovoltaic module at the input end of the micro-inverter, u g (t) represents the instantaneous value of the grid voltage.

[0109] Specifically, refer to Figure 6, first set the preset secondary current overlap factor to 0.5, and calculate the preferred duty cycle and the preferred switching frequency. Determine whether the preferred switching frequency exceeds the upper limit value. If the preferred switching frequency exceeds the upper limit value, adjust the preferred switching frequency to the upper limit value, that is, the switching frequency takes the upper limit value to obtain the adjusted switching frequency; when the adjusted switching frequency is known, the adjusted secondary current overlap factor can be calculated, and the adjusted secondary current overlap factor can be a value less than 0.5. When the adjusted secondary current overlap factor is known, the adjusted duty cycle can be calculated, and the adjusted duty cycle and the adjusted switching frequency are input into the PWM generator, and two control pulse signals staggered by 180° are output and two flyback switching tubes are driven. If the preferred switching frequency does not exceed the upper limit value, the preferred duty cycle and the preferred switching frequency are directly input into the PWM generator, and two control pulse signals staggered by 180° are output and two flyback switching tubes are driven.

[0110] After the above derivation process, the peak current of the secondary side of the flyback transformer is:

[0111]

[0112] Among them, i s Indicates the peak current of the secondary side of the flyback transformer, D off Indicates the preset secondary current overlap factor or the adjusted secondary current overlap factor, Indicates the instantaneous value of the grid-connected current reference.

[0113] According to the instantaneous value of the grid-connected current reference and the upper limit of the switching frequency, select the appropriate D off , minimize the secondary current overlap area, and minimize the secondary current peak of the flyback transformer, thereby reducing the current stress of the flyback diode and the power frequency flip circuit switch tube, and improving the grid current quality. In the embodiment of the present application, the switching frequency is fixed in steady state, there is no mode switching control, and near the grid voltage peak with large instantaneous power, the current density is close to the BCM control mode.

[0114] The following is a further explanation of this control technology in conjunction with a specific trial method.

[0115] Some parameters of the interleaved parallel flyback micro-inverter in this embodiment are shown in Table 1.

[0116] Table 1

[0117]

[0118] When the reference output power P of the inverter o =600W, grid-connected reference current effective value Take D off =0.5, according to There is s =92.59kHz, according to D=0.486sin(ωt). After the secondary current is connected in parallel, the total current is as follows Figure 7 As shown in the figure, it can be seen that the left half of the sine half wave has been completely staggered, and there is still overlap in the right half, but the overlap is very small. Figure 8 As shown, the grid current THD is 0.74%.

[0119] When the reference output power P of the inverter o =160W, grid-connected reference current effective value If D off =0.5, according to f s =346.24kHz exceeds the upper limit of the switching frequency. In this case, D should be reduced. off Make the switching frequency meet the limit requirements. Take f s =250kHz, calculated D off =0.425, D = 0.413sin(ωt). The total current after the secondary current is connected in parallel is as follows Fig. 9 As shown in Figure 1, it can be seen that full-cycle full interleaving control is basically achieved. The grid-connected voltage and grid-connected current are shown in Figure 1. Fig.10 As shown, the grid current THD is 1.13%.

[0120] Further references Fig.11 As an implementation of the methods shown in the above figures, the present application provides an embodiment of a staggered parallel flyback micro-inverter control device, and the device embodiment is similar to Figure 3 Corresponding to the method embodiment shown, the device can be specifically applied to various electronic devices.

[0121] The embodiment of the present application provides a staggered parallel flyback micro-inverter control device, comprising:

[0122] The power calculation module 1 is configured to obtain the DC voltage and DC current of the photovoltaic module at the input end of the micro inverter and calculate the reference output power;

[0123] The grid voltage data acquisition module 2 is configured to acquire the instantaneous value of the grid voltage and the effective value of the grid voltage;

[0124] The switching frequency and duty cycle calculation module 3 is configured to calculate the effective value of the grid-connected reference current according to the reference output power and the effective value of the grid voltage; set a preset secondary current overlap factor and obtain the primary magnetizing inductance of the flyback transformer and the turns ratio between the secondary and primary sides of the flyback transformer, and calculate the preferred switching frequency according to the effective value of the grid-connected reference current, the effective value of the grid voltage, the preset secondary current overlap factor, the primary magnetizing inductance of the flyback transformer and the turns ratio between the secondary and primary sides of the flyback transformer; calculate the preferred duty cycle according to the DC voltage of the photovoltaic module at the input end of the micro-inverter, the instantaneous value of the grid voltage, the preset secondary current overlap factor and the turns ratio between the secondary and primary sides of the flyback transformer;

[0125] The adjustment module 4 is configured to determine whether the preferred switching frequency exceeds the upper limit value. If so, the preferred switching frequency is adjusted to the upper limit value to obtain the adjusted switching frequency. The adjusted secondary current overlap factor is calculated according to the adjusted switching frequency, the effective value of the grid-connected reference current, the effective value of the grid voltage, the primary excitation inductance of the flyback transformer, and the turns ratio between the secondary side and the primary side of the flyback transformer. The adjusted duty cycle is calculated according to the DC voltage of the photovoltaic module at the input end of the micro-inverter, the instantaneous value of the grid voltage, the adjusted secondary current overlap factor, and the turns ratio between the secondary side and the primary side of the flyback transformer. The adjusted switching frequency and the adjusted duty cycle are input into the PWM generator, and two control pulse signals staggered by 180° are output to drive the two flyback switch tubes; otherwise, the preferred switching frequency and the preferred duty cycle are input into the PWM generator, and two control pulse signals staggered by 180° are output to drive the two flyback switch tubes respectively; wherein, the calculation formula of the preferred switching frequency or the adjusted switching frequency is as follows:

[0126]

[0127] Among them, f s Indicates the preferred switching frequency or the adjusted switching frequency, U g represents the effective value of the grid voltage, N represents the turns ratio between the secondary and primary sides of the flyback transformer, L m represents the primary magnetizing inductance of the flyback transformer, Indicates the effective value of the grid-connected reference current, D off Indicates the preset secondary current overlap factor or the adjusted secondary current overlap factor; the preferred duty cycle or the adjusted duty cycle is calculated as follows:

[0128]

[0129] Where D is the preferred duty cycle or the adjusted duty cycle, U dc Indicates the DC voltage of the photovoltaic module at the input end of the micro-inverter, u g (t) represents the instantaneous value of the grid voltage.

[0130] Fig.12 Schematic diagram of the hardware structure of the electronic device provided by the embodiment of the present invention. Fig.12 As shown, the electronic device of this embodiment includes: a processor 1201 and a memory 1202; wherein the memory 1202 is used to store computer-executable instructions; the processor 1201 is used to execute the computer-executable instructions stored in the memory to implement the various steps performed by the electronic device in the above embodiment. For details, please refer to the relevant description in the above method embodiment.

[0131] Optionally, the memory 1202 may be independent or integrated with the processor 1201 .

[0132] When the memory 1202 is independently provided, the electronic device further includes a bus 1203 for connecting the memory 1202 and the processor 1201 .

[0133] The embodiment of the present invention further provides a computer storage medium, in which computer execution instructions are stored. When the processor 1201 executes the computer execution instructions, the above method is implemented.

[0134] The embodiment of the present invention further provides a computer program product, including a computer program. When the computer program is executed by the processor 1201, the above method is implemented.

[0135] In the embodiments provided by the present invention, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic, for example, the division of modules is only a logical function division, and there may be other division methods in actual implementation, such as multiple modules can be combined or integrated into another system, or some features can be ignored or not executed. Another point, the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or modules, which can be electrical, mechanical or other forms.

[0136] The modules described as separate components may or may not be physically separated, and the components shown as modules may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the modules may be selected according to actual needs to implement the solution of this embodiment.

[0137] In addition, each functional module in each embodiment of the present invention may be integrated into one processing unit, each module may exist physically separately, or two or more modules may be integrated into one unit. The unit formed by the above modules may be implemented in the form of hardware or in the form of hardware plus software functional units.

[0138] The above-mentioned integrated module implemented in the form of a software function module can be stored in a computer-readable storage medium. The above-mentioned software function module is stored in a storage medium, including a number of instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) or a processor 1201 to perform some steps of the methods of various embodiments of the present application.

[0139] It should be understood that the processor 1201 may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), etc. A general-purpose processor may be a microprocessor or the processor 1201 may be any conventional processor 1201, etc. The steps of the method disclosed in the invention may be directly embodied in the hardware processor 1201 for execution, or may be executed by a combination of hardware and software modules in the processor 1201.

[0140] The memory 1202 may include a high-speed RAM memory, and may also include a non-volatile storage NVM, such as at least one disk memory, and may also be a USB flash drive, a mobile hard disk, a read-only memory, a magnetic disk, or an optical disk.

[0141] The bus 1203 may be an Industry Standard Architecture (ISA), a Peripheral Component Interconnect (PCI) bus, or an Extended Industry Standard Architecture (EISA) bus, etc. The bus 1203 may be divided into an address bus, a data bus, a control bus, etc. For ease of representation, the bus 1203 in the drawings of the present application is not limited to only one bus 1203 or one type of bus 1203.

[0142] The above storage medium can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic memory, flash memory, magnetic disk or optical disk. The storage medium can be any available medium that can be accessed by a general or special purpose computer.

[0143] An exemplary storage medium is coupled to the processor 1201, so that the processor 1201 can read information from the storage medium and write information to the storage medium. Of course, the storage medium can also be a component of the processor 1201. The processor 1201 and the storage medium can be located in an application specific integrated circuit (ASIC). Of course, the processor 1201 and the storage medium can also exist as discrete components in an electronic device or a main control device.

[0144] Those skilled in the art can understand that all or part of the steps of implementing the above-mentioned method embodiments can be completed by hardware related to program instructions. The aforementioned program can be stored in a computer-readable storage medium. When the program is executed, the steps of the above-mentioned method embodiments are executed; and the aforementioned storage medium includes: ROM, RAM, disk or optical disk and other media that can store program codes.

[0145] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A control method for interleaved parallel flyback micro-inverters, characterized in that: The following steps are involved: Obtain the DC voltage and DC current of the photovoltaic module at the input end of the micro inverter and calculate the reference output power; Obtain the instantaneous value of the grid voltage and the effective value of the grid voltage; Calculate the grid-connected reference current effective value according to the reference output power and the grid voltage effective value; A preset secondary current overlap factor is set and the primary magnetizing inductance of the flyback transformer and the turns ratio between the secondary and primary sides of the flyback transformer are obtained, and a preferred switching frequency is calculated according to the effective value of the grid-connected reference current, the effective value of the grid voltage, the preset secondary current overlap factor, the primary magnetizing inductance of the flyback transformer and the turns ratio between the secondary and primary sides of the flyback transformer; a preferred duty cycle is calculated according to the DC voltage of the photovoltaic module at the input end of the micro-inverter, the instantaneous value of the grid voltage, the preset secondary current overlap factor and the turns ratio between the secondary and primary sides of the flyback transformer; Determine whether the preferred switching frequency exceeds the upper limit value, if so, adjust the preferred switching frequency to the upper limit value to obtain an adjusted switching frequency, calculate an adjusted secondary current overlap factor according to the adjusted switching frequency, the effective value of the grid-connected reference current, the effective value of the grid voltage, the primary magnetizing inductance of the flyback transformer, and the turns ratio between the secondary side and the primary side of the flyback transformer, calculate an adjusted duty cycle according to the DC voltage of the photovoltaic module at the input end of the micro-inverter, the instantaneous value of the grid voltage, the adjusted secondary current overlap factor, and the turns ratio between the secondary side and the primary side of the flyback transformer, input the adjusted switching frequency and the adjusted duty cycle into a PWM generator, output two control pulse signals staggered by 180°, and drive two flyback switch tubes; Otherwise, the preferred switching frequency and the preferred duty cycle are input into the PWM generator, and two control pulse signals staggered by 180° are output to drive two flyback switch tubes respectively; wherein the calculation formula of the preferred switching frequency or the adjusted switching frequency is as follows: Among them, f s Indicates the preferred switching frequency or the adjusted switching frequency, U g represents the effective value of the grid voltage, N represents the turns ratio between the secondary and primary sides of the flyback transformer, L m represents the primary magnetizing inductance of the flyback transformer, Indicates the effective value of the grid-connected reference current, D off Indicates the preset secondary current overlap factor or the adjusted secondary current overlap factor; the preferred duty cycle or the adjusted duty cycle is calculated as follows: Where D is the preferred duty cycle or the adjusted duty cycle, U dc Indicates the DC voltage of the photovoltaic module at the input end of the micro-inverter, u g (t) represents the instantaneous value of the grid voltage.

2. The interleaved parallel flyback micro-inverter control method according to claim 1, characterized in that: The preset secondary current overlap factor is 0.5, and the adjusted secondary current overlap factor is less than 0.

5.

3. The interleaved parallel flyback micro-inverter control method according to claim 1, characterized in that: The reference output power is obtained by sampling the DC voltage and DC current of the photovoltaic module at the input end of the inverter and performing maximum power tracking control.

4. The interleaved parallel flyback micro-inverter control method according to claim 1, characterized in that: The effective value of the grid voltage is obtained by performing effective value calculation on the instantaneous value of the grid voltage.

5. The interleaved parallel flyback micro-inverter control method according to claim 1, characterized in that: The effective value of the grid-connected reference current is calculated according to the reference output power and the effective value of the grid voltage, specifically including: The reference output power P o Divide by the effective value of the grid voltage U g , get the grid-connected reference current effective value I g * .

6. A staggered parallel flyback micro-inverter control device, characterized in that: include: A power calculation module is configured to obtain a DC voltage and a DC current of a photovoltaic module at an input end of the micro-inverter and calculate a reference output power; A grid voltage data acquisition module is configured to acquire a grid voltage instantaneous value and a grid voltage effective value; A switching frequency and duty cycle calculation module is configured to calculate a grid-connected reference current effective value according to the reference output power and the grid voltage effective value; A preset secondary current overlap factor is set and the primary magnetizing inductance of the flyback transformer and the turns ratio between the secondary and primary sides of the flyback transformer are obtained, and a preferred switching frequency is calculated according to the effective value of the grid-connected reference current, the effective value of the grid voltage, the preset secondary current overlap factor, the primary magnetizing inductance of the flyback transformer and the turns ratio between the secondary and primary sides of the flyback transformer; a preferred duty cycle is calculated according to the DC voltage of the photovoltaic module at the input end of the micro-inverter, the instantaneous value of the grid voltage, the preset secondary current overlap factor and the turns ratio between the secondary and primary sides of the flyback transformer; An adjustment module is configured to determine whether the preferred switching frequency exceeds an upper limit value, and if so, adjust the preferred switching frequency to the upper limit value to obtain an adjusted switching frequency, calculate an adjusted secondary current overlap factor according to the adjusted switching frequency, the effective value of the grid-connected reference current, the effective value of the grid voltage, the primary magnetizing inductance of the flyback transformer, and the turns ratio between the secondary side and the primary side of the flyback transformer, calculate an adjusted duty cycle according to the DC voltage of the photovoltaic module at the input end of the micro-inverter, the instantaneous value of the grid voltage, the adjusted secondary current overlap factor, and the turns ratio between the secondary side and the primary side of the flyback transformer, input the adjusted switching frequency and the adjusted duty cycle into a PWM generator, output two control pulse signals staggered by 180°, and drive two flyback switch tubes; Otherwise, the preferred switching frequency and the preferred duty cycle are input into the PWM generator, and two control pulse signals staggered by 180° are output to drive two flyback switch tubes respectively; wherein the calculation formula of the preferred switching frequency or the adjusted switching frequency is as follows: Among them, f s Indicates the preferred switching frequency or the adjusted switching frequency, U g represents the effective value of the grid voltage, N represents the turns ratio between the secondary and primary sides of the flyback transformer, L m represents the primary magnetizing inductance of the flyback transformer, Indicates the effective value of the grid-connected reference current, D off Indicates the preset secondary current overlap factor or the adjusted secondary current overlap factor; the preferred duty cycle or the adjusted duty cycle is calculated as follows: Where D is the preferred duty cycle or the adjusted duty cycle, U dc Indicates the DC voltage of the photovoltaic module at the input end of the micro-inverter, u g (t) represents the instantaneous value of the grid voltage.

7. An electronic device comprising: one or more processors; a storage device for storing one or more programs, When the one or more programs are executed by the one or more processors, the one or more processors implement the method according to any one of claims 1 to 5.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the method according to any one of claims 1 to 5 is implemented.

9. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the method according to any one of claims 1 to 5 is implemented.

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