A control method, device and readable medium for interleaved parallel flyback microinverter

Abstract

The present invention discloses a control method, device and readable medium for an interleaved parallel flyback micro-inverter, comprising: obtaining the DC voltage and DC current of a photovoltaic module at the input end of the micro-inverter and calculating a reference output power using maximum power point tracking; obtaining the instantaneous value of the grid voltage and performing effective value calculation to obtain the effective value of the grid voltage; calculating the effective value of the grid-connected reference current based on the reference output power and the effective value of the grid voltage; and calculating and adjusting the switching frequency and duty cycle by setting a secondary current overlap factor to minimize the secondary current overlap area and the secondary current peak value, 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.

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 for 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 use the peak current of the primary side of the flyback converter transformer as the control object. By sampling the input voltage and the grid voltage, the reference peak value of the primary current is calculated. Then, the on and off time of the main switch tube is calculated based on 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 flyback output is lower than the input voltage u g / N dc When using DCM interleaved parallel flyback converters, the secondary currents of the transformers will overlap when the output power is large; while in BCM, the secondary currents will overlap regardless of the output power. The overlap of the secondary currents will excite a large number of high-order harmonics and increase the current stress of the subsequent stage. The overlap of the primary and secondary currents is shown in the figure below. Figure 2 shown. ​

[0005] The invention patent with publication number CN102594180A, "Control method for switching tubes of photovoltaic grid-connected interleaved flyback inverters," proposes a method of dividing the reference current curve of the switching tube within half a power frequency cycle into three intervals and using different breaking times for each interval. 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, thereby improving 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 "Research on Control Strategies for Interleaved Flyback Photovoltaic Grid-Connected Inverters" uses an interleaved modulation scheme in which the switching phases of the two main switches of the interleaved flyback circuits are shifted by half a carrier cycle. This scheme reduces current stress and current ripple. This is the most basic implementation of interleaved control. When the grid power is high, the two secondary currents overlap, and no specific optimization of the interleaved control technology has been performed. 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 to address 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 microinverter 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 effective value of the grid voltage; 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 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; the preferred duty cycle is calculated based on the DC voltage of the photovoltaic module at the input end of the microinverter, 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] Determine whether the preferred switching frequency exceeds the upper limit. If so, adjust the preferred switching frequency to the upper limit to obtain an adjusted switching frequency. Calculate an adjusted secondary current overlap factor based on 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 and primary sides of the flyback transformer. Calculate an adjusted duty cycle based on the DC voltage of the photovoltaic module at the input end of the microinverter, the instantaneous value of the grid voltage, the adjusted secondary current overlap factor, and the turns ratio between the secondary and primary sides 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 the two flyback switches. Otherwise, input the preferred switching frequency and the preferred duty cycle into the PWM generator, output two control pulse signals staggered by 180°, and respectively drive the two flyback switches. The calculation formula for 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 Indicates the effective value of the grid voltage, N indicates the turns ratio between the secondary side and the primary side 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 represents 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 microinverter, 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 performing effective value calculation on the instantaneous value of the grid voltage.

[0022] Preferably, the grid-connected reference current effective value is calculated based on 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 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 configured to obtain a DC voltage and a DC current of the photovoltaic module at the input end of the micro-inverter and calculate a reference output power;

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

[0027] The switching frequency and duty cycle calculation module is configured to calculate a grid-connected reference current effective value based on a reference output power and an effective value of a 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 a preferred switching frequency based on 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; and calculate a preferred duty cycle based on the DC voltage of the photovoltaic module at the input end of the microinverter, 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 an upper limit value. If so, the preferred switching frequency is adjusted to the upper limit value to obtain an adjusted switching frequency. The adjusted secondary current overlap factor is calculated based on 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 and primary sides of the flyback transformer. The adjusted duty cycle is calculated based on the DC voltage of the photovoltaic module at the input end of the microinverter, the instantaneous value of the grid voltage, the adjusted secondary current overlap factor, and the turns ratio between the secondary and primary sides of the flyback transformer. The adjusted switching frequency and the adjusted duty cycle are input into the PWM generator, which outputs two control pulse signals staggered by 180 degrees and drives the two flyback switches. Otherwise, the preferred switching frequency and the preferred duty cycle are input into the PWM generator, which outputs two control pulse signals staggered by 180 degrees and drives the two flyback switches respectively. The calculation formula for 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 Indicates the effective value of the grid voltage, N indicates the turns ratio between the secondary side and the primary side 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 represents 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 microinverter, 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 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 implements the method described in any implementation manner in the first aspect when the computer program is executed by a processor.

[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 the appropriate D off , minimizing the overlapping area of ​​the secondary current and minimizing 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 grid-connected current quality.

[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 following briefly introduces the drawings required for use in the description of the embodiments. 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 any creative work.

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

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

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

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

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

[0046] Figure 6 A logic flow chart of a control method for interleaved parallel flyback micro-inverters 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 the total secondary current in parallel when the secondary current is 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] Figure 9 The interleaved parallel flyback micro-inverter control method of the embodiment of the present application is in P o = Schematic diagram of the total secondary current in parallel when the secondary current is 160W;

[0050] Figure 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] Figure 11 Schematic diagram of a control device for an interleaved parallel flyback micro-inverter according to an embodiment of the present application;

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

[0053] To make the objectives, technical solutions, and advantages of the present invention more apparent, the present invention will be further described in detail below with reference to the accompanying drawings. It is apparent that the embodiments described are only some, not all, of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are intended to fall within the scope of protection of the present invention.

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

[0055] S1, 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.

[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 point tracking control.

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

[0058] Among them, the flyback converter 1# includes: high-frequency switch 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: power frequency switch tube S1, power frequency switch tube S2, power frequency switch tube S3 and 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 inversion circuit. The power frequency inversion circuit inverts the current modulated by the flyback converter into a sinusoidal AC quantity, and the output end of the power frequency inversion 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 photovoltaic module at the input end of the microinverter, 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 1# transformer of the flyback converter; i s1 is the secondary current of the #1 transformer of the flyback converter; 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 the instantaneous value of the grid-connected current reference The relationship is:

[0064]

[0065] Among them, T sw is the switching period 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 of the secondary side to the primary side 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 peak current of the secondary side 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 the 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 input to the microinverter input terminal;

[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 the above two formulas, we have:

[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, is the effective value of the 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 the secondary currents of two flyback transformers are connected in parallel, the embodiment of the present application adopts the value of the secondary current overlap factor to calculate the switching frequency and 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 grid current reference instantaneous value remains unchanged, the secondary current peak value 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 current is large, D off =0.5 to reduce the peak current of the secondary side of the flyback transformer and avoid the overlapping area of ​​the secondary side 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, calculates the effective value of the grid-connected reference current based on the reference output power and the effective value of the grid voltage; sets a preset secondary current overlap factor and obtains the primary excitation inductance of the flyback transformer and the turns ratio between the secondary and primary sides of the flyback transformer, and calculates the preferred switching frequency based on 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 between the secondary and primary sides of the flyback transformer; calculates the preferred duty cycle 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.

[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 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, determining whether the preferred switching frequency exceeds the upper limit; if so, adjusting the preferred switching frequency to the upper limit to obtain an adjusted switching frequency; calculating an adjusted secondary current overlap factor based on 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 and primary sides of the flyback transformer; calculating an adjusted duty cycle based on the DC voltage of the photovoltaic module at the input end of the microinverter, the instantaneous value of the grid voltage, the adjusted secondary current overlap factor, and the turns ratio between the secondary and primary sides of the flyback transformer; inputting the adjusted switching frequency and the adjusted duty cycle into a PWM generator, outputting two control pulse signals staggered by 180°, and driving the two flyback switching 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 respectively driving the two flyback switching tubes; wherein, the calculation formula for 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 Indicates the effective value of the grid voltage, N indicates the turns ratio between the secondary side and the primary side 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 represents 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 microinverter, u g (t) represents the instantaneous value of the grid voltage.

[0109] Specifically, refer to Figure 6First, set the preset secondary current overlap factor to 0.5, and calculate the preferred duty cycle and preferred switching frequency. Determine whether the preferred switching frequency exceeds an upper limit. If so, adjust the preferred switching frequency to the upper limit, i.e., set the switching frequency to the upper limit to obtain an adjusted switching frequency. Given the adjusted switching frequency, the adjusted secondary current overlap factor can be calculated. The adjusted secondary current overlap factor can be a value less than 0.5. Given the adjusted secondary current overlap factor, the adjusted duty cycle can be calculated. The adjusted duty cycle and the adjusted switching frequency are input into a PWM generator, which outputs two control pulse signals offset by 180° and drives two flyback switches. If the preferred switching frequency does not exceed the upper limit, the preferred duty cycle and the preferred switching frequency are directly input into the PWM generator, which outputs two control pulse signals offset by 180° and drives two flyback switches.

[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 , minimizing the secondary current overlap area and the secondary current peak of the flyback transformer, thereby reducing the current stress on the flyback diode and the power frequency flip-flop circuit switch, and improving the grid current quality. In the embodiment of the present application, the switching frequency is fixed in steady state, and there is no mode switching control. Moreover, near the grid voltage peak with high instantaneous power, the current density is close to that of the BCM control mode.

[0114] The following further explains this control technology in combination with specific trial methods.

[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 of the inverter P o =600W, grid-connected reference current effective value Take D off =0.5, according to There is f s =92.59kHz, according to D=0.486sin(ωt). The total current after the secondary current is connected in parallel is as follows Figure 7 As shown in Figure 1, it can be seen that full interleaving control has been achieved in the left half of the sine half wave, and there is still overlap in the right half, but the degree of overlap is very small. Figure 8 As shown, the grid current THD is 0.74%.

[0119] When the reference output power of the inverter P 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, calculate D off =0.425, D = 0.413sin(ωt). The total current after the secondary current is connected in parallel is as follows Figure 9 As shown in Figure 2, it can be seen that full-cycle full-interleaved control is basically achieved. The grid-connected voltage and grid-connected current are shown in Figure 2. Figure 10 As shown, the grid current THD is 1.13%.

[0120] Further references Figure 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. 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 based on 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 based on 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; and calculate the preferred duty cycle based on the DC voltage of the photovoltaic module at the input end of the microinverter, 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] Adjustment module 4 is configured to determine whether the preferred switching frequency exceeds an upper limit value. If so, the preferred switching frequency is adjusted to the upper limit value to obtain an adjusted switching frequency. An adjusted secondary current overlap factor is calculated based on 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 and primary sides of the flyback transformer. An adjusted duty cycle is calculated based on the DC voltage of the photovoltaic module at the input end of the microinverter, the instantaneous value of the grid voltage, the adjusted secondary current overlap factor, and the turns ratio between the secondary and primary sides of the flyback transformer. The adjusted switching frequency and the adjusted duty cycle are input into a PWM generator, which outputs two control pulse signals staggered by 180° and drives the two flyback switches. Otherwise, the preferred switching frequency and the preferred duty cycle are input into the PWM generator, which outputs two control pulse signals staggered by 180° and drives the two flyback switches respectively. The calculation formula for 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 Indicates the effective value of the grid voltage, N indicates the turns ratio between the secondary side and the primary side 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 represents 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 microinverter, u g (t) represents the instantaneous value of the grid voltage.

[0130] Figure 12 Schematic diagram of the hardware structure of the electronic device provided by the embodiment of the present invention. Figure 12 As shown, the electronic device of this embodiment includes: a processor 1201 and a memory 1202; wherein the memory 1202 is configured to store computer-executable instructions; and the processor 1201 is configured to execute the computer-executable instructions stored in the memory to implement the various steps performed by the electronic device in the above-described embodiment. For details, please refer to the relevant description of the aforementioned 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] An 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] An 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 herein, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the module division is merely a logical functional division. In actual implementation, other division methods may be used. For example, multiple modules may be combined or integrated into another system, or some features may be ignored or not implemented. In addition, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection through some interface, device or module, which may be electrical, mechanical or other forms.

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

[0137] In addition, the functional modules in various embodiments of the present invention may be integrated into a single processing unit, each module may exist physically separately, or two or more modules may be integrated into a single unit. The units formed by the above modules may be implemented in the form of hardware or 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 and includes a number of instructions for causing a computer device (which can be a personal computer, server, or network device, etc.) or 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), or application-specific integrated circuits (ASIC). A general-purpose processor may be a microprocessor, or the processor 1201 may be any conventional processor 1201. The steps of the method disclosed in the present invention may be directly implemented by the hardware processor 1201, or implemented 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] Bus 1203 can be an Industry Standard Architecture (ISA), a Peripheral Component Interconnect (PCI) bus, or an Extended Industry Standard Architecture (EISA) bus. Bus 1203 can be classified as an address bus, a data bus, a control bus, etc. For ease of illustration, the bus 1203 in the drawings of this application is not limited to a single bus 1203 or a single type of bus 1203.

[0142] The storage medium may be implemented by any type of volatile or non-volatile memory 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 storage, flash memory, magnetic disk, or optical disk. The storage medium may be any available medium that can be accessed by a general-purpose 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 an integral part 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 will appreciate that all or part of the steps in the above-described method embodiments can be implemented using hardware associated with program instructions. The aforementioned program can be stored in a computer-readable storage medium. When executed, the program performs the steps of the above-described method embodiments. The aforementioned storage medium includes various media capable of storing program code, such as ROM, RAM, magnetic disks, or optical disks.

[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 above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above 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 microinverter and calculate the reference output power; Obtain the instantaneous value of the grid voltage and the effective value of the grid voltage; Calculate the effective value of the grid-connected reference current according to the reference output power and the effective value of the grid voltage; 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; a preferred switching frequency is calculated based on 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 based on the DC voltage of the photovoltaic module at the input end of the microinverter, 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; determining whether the preferred switching frequency exceeds an upper limit; if so, adjusting the preferred switching frequency to the upper limit to obtain an adjusted switching frequency; calculating an adjusted secondary current overlap factor based on 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 and primary sides of the flyback transformer; calculating an adjusted duty cycle based on the DC voltage of the photovoltaic module at the input end of the microinverter, the instantaneous value of the grid voltage, the adjusted secondary current overlap factor, and the turns ratio between the secondary and primary sides of the flyback transformer; inputting the adjusted switching frequency and the adjusted duty cycle into a PWM generator, outputting two control pulse signals staggered by 180°, and driving two flyback switches; Otherwise, the preferred switching frequency and the preferred duty cycle are input into the PWM generator, which outputs two control pulse signals staggered by 180° and drives two flyback switching tubes respectively. The preferred switching frequency or the adjusted switching frequency is calculated as follows: Among them, f s Indicates the preferred switching frequency or the adjusted switching frequency, U g Indicates the effective value of the grid voltage, N indicates the turns ratio between the secondary side and the primary side 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 represents 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 microinverter, 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 grid-connected reference current effective value is calculated based on the reference output power and the grid voltage effective value, specifically including: The reference output power P o Divide by the effective value of the grid voltage U g , get the grid reference current effective value I g * .

6. A staggered parallel flyback micro-inverter control device, characterized in that: include: a power calculation module configured to obtain a DC voltage and a DC current of the photovoltaic module at the input end of the micro-inverter and calculate a reference output power; A grid voltage data acquisition module is configured to acquire an instantaneous value of the grid voltage and an effective value of the grid voltage; A switching frequency and duty cycle calculation module is configured to calculate a grid-connected reference current effective value 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; a preferred switching frequency is calculated based on 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 based on the DC voltage of the photovoltaic module at the input end of the microinverter, 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 configured to determine whether the preferred switching frequency exceeds an upper limit, and if so, adjust the preferred switching frequency to the upper limit to obtain an adjusted switching frequency; calculate an adjusted secondary current overlap factor based on 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 and primary sides of the flyback transformer; calculate an adjusted duty cycle based on the DC voltage of the photovoltaic module at the input end of the microinverter, the instantaneous value of the grid voltage, the adjusted secondary current overlap factor, and the turns ratio between the secondary and primary sides 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 degrees, and drive two flyback switching tubes; Otherwise, the preferred switching frequency and the preferred duty cycle are input into the PWM generator, which outputs two control pulse signals staggered by 180° and drives two flyback switching tubes respectively. The preferred switching frequency or the adjusted switching frequency is calculated as follows: Among them, f s Indicates the preferred switching frequency or the adjusted switching frequency, U g Indicates the effective value of the grid voltage, N indicates the turns ratio between the secondary side and the primary side 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 represents 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 microinverter, 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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