Single-phase cascaded H-bridge photovoltaic power generation system and control system, method and equipment thereof

Abstract

The invention relates to the technical field of photovoltaic systems, in particular to a single-phase cascaded H-bridge photovoltaic power generation system and a control system, method and equipment thereof, and the power generation system comprises a filter inductor and n photovoltaic power generation subsystems. Each photovoltaic power generation subsystem comprises a photovoltaic module, a boosting unit and an H-bridge unit which are connected in sequence; the output sides of the n H-bridge units are connected in series and then connected to a power grid through a filter inductor. The control system comprises a sampling circuit, a digital controller and a signal conditioning circuit which are connected in sequence. The power generation system provided by the invention realizes expansion of mismatched power capacity under the condition of ensuring maximum power point work of the photovoltaic module. According to the control system provided by the invention, the modulation signal of the H-bridge unit is adjusted by dynamically adjusting the output voltage of each boosting unit, so that the maximum voltage output capability of the H-bridge unit entering over-modulation due to overlarge mismatch power is improved, and then the H-bridge unit exits from the over-modulation state; therefore, the stable working range of the power generation system is expanded, and the mismatched power capacity is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic systems, and in particular to a single-phase cascade H-bridge photovoltaic power generation system and a control system, method and equipment thereof. Background Art

[0002] Among many renewable energy sources, solar energy, with its abundant resources, environmental friendliness, safety, and reliability, is considered one of the cleanest energy sources with the greatest potential for power generation. Traditional power generation architectures are primarily categorized into centralized photovoltaic (PV) systems, string photovoltaic (PV) systems, and microinverter PV systems, each designed to collect photovoltaic energy from PV arrays at varying granularities. However, all of these grid-connected PV systems require several bulky and heavy power-frequency transformers to step up the low-voltage AC output of the PV inverters for connection to the medium-voltage grid. This requires significant construction space and is costly.

[0003] The emergence of cascaded H-bridge converters has made it possible to directly integrate photovoltaic power generation systems into the medium-voltage grid. This modular structure allows for independent input terminals for each submodule, enabling independent MPPT control of its connected photovoltaic array, resulting in high solar energy utilization. Furthermore, there's no need for bulky power-frequency transformers. Each submodule utilizes lower-voltage, less expensive switching devices, enabling direct connection to the medium-voltage grid through cascaded boosting. Furthermore, the output voltage is multi-level, reducing harmonic content. Carrier phase shifting technology can be used to increase the system's equivalent switching frequency, achieving high-quality output waveforms at a lower switching frequency and enabling the use of smaller filter inductors. Therefore, a modular approach can effectively enhance the flexibility of the overall photovoltaic power generation system and significantly reduce its size. However, this modularity also introduces the issue of power balancing between modules.

[0004] Due to certain inconsistencies in the environments and characteristic parameters of each photovoltaic panel, the maximum power points of each photovoltaic module are inconsistent. In the cascaded H-bridge topology, the input terminals of each sub-module are independent of each other, and the output terminals are connected in series. Mismatches in sub-module input power can lead to mismatches in output voltage. Modules with high transmission power are more prone to overmodulation, which increases the harmonic content of the cascade system's output current and, in severe cases, may cause system instability. Therefore, the cascaded H-bridge converter's ability to withstand mismatched power between photovoltaic modules is limited, significantly reducing the cascaded H-bridge converter's photovoltaic energy acquisition efficiency and limiting its inherent advantages.

[0005] Currently, some researchers have addressed the issue of power mismatch between H-bridge units by selecting power factor as a control degree of freedom for the stable operation of cascaded H-bridge systems, maintaining system stability by compensating for reactive power. However, severe power mismatches can result in a low output power factor, limiting their application. Another approach is to employ a hybrid modulation method, where only one module in the cascaded H-bridge system operates under high-frequency sinusoidal pulse-width modulation (SPWM) to generate AC current, while the remaining modules operate under low-frequency square-wave modulation to balance the DC-side capacitor voltages, thereby expanding the system's stable operating range. This modulation method essentially operates the submodules under square-wave modulation, effectively increasing the system's modulation ratio by a factor of 4 / π. Further, based on hybrid modulation, the stable operating range of the cascaded H-bridge system is expanded by superimposing harmonics on the modulated wave. However, this expansion is still very limited; injecting the third harmonic can achieve a 0.27-fold increase. In summary, cascaded H-bridge systems still face challenges with low mismatch power capacity and a narrow stable operating range when faced with power mismatch. Summary of the Invention

[0006] In response to the problems in the prior art, the present invention provides a single-phase cascade H-bridge photovoltaic power generation system and its control system, method and equipment. The specific technical solutions are as follows:

[0007] A single-phase cascade H-bridge photovoltaic power generation system includes a filter inductor and n photovoltaic power generation subsystems; each photovoltaic power generation subsystem includes a photovoltaic module, a boost unit, and an H-bridge unit connected in sequence; the output sides of the n H-bridge units are connected in series and then connected to the power grid through the filter inductor.

[0008] Preferably, the Nth boost unit includes an input capacitor C N1 , switch tube Q N1 , switch tube Q N2 and boost inductor L N ; Wherein the input capacitor C N1 One end of the photovoltaic module and the boost inductor L N One end of the input capacitor C N1 The other end of the photovoltaic module and the switch tube Q N2 The source connection of the boost inductor L N The other end is connected to the switch tube Q N2 The drain of the switch tube Q N1 source connection.

[0009] Preferably, the Nth H-bridge unit includes an input capacitor C N2 , switch tube S N1 , switch tube S N2 , switch tube S N3 And switch tube SN4 ;

[0010] Input capacitor C N2 One end of the switch tube Q N1 The drain of the switch tube S N1 The drain of the switch tube S N2 The drain connection, input capacitor C N2 The other end is connected to the switch tube Q N2 The source of the switch tube S N3 The source of the switch tube S N4 The source connection of the switch tube S N4 The drain and switch tube S N3 The drain of the Nth H-bridge unit is connected, and the switch tube S N3 The drain and switch tube S N1 The drain of the H-bridge unit is connected and serves as the second output end of the N-th H-bridge unit; the first output end of the N-th H-bridge unit is used to be connected in series with the second output end of another H-bridge unit or to be connected to the power grid through a filter inductor;

[0011] The second output end of the Nth H-bridge unit is used to be connected in series with the first output end of another H-bridge unit or to the power grid.

[0012] A control system for a single-phase cascade H-bridge photovoltaic power generation system is used to control the single-phase cascade H-bridge photovoltaic power generation system, comprising a sampling circuit, a digital controller, and a signal conditioning circuit connected in sequence; the digital controller comprises a maximum power tracking control unit, a grid-connected current control unit, a mismatched power capacity expansion control unit, and a boost unit output capacitor voltage control unit; the sampling circuit is respectively connected to the single-phase cascade H-bridge photovoltaic power generation system, the maximum power tracking control unit, the grid-connected current control unit, and the boost unit output capacitor voltage control unit; the grid-connected current control unit is respectively connected to the maximum power tracking control unit, the mismatched power capacity expansion control unit, and the signal conditioning circuit; the boost unit output capacitor voltage control unit is respectively connected to the mismatched power capacity expansion control unit and the signal conditioning circuit; and the signal conditioning circuit is connected to the single-phase cascade H-bridge photovoltaic power generation system;

[0013] The maximum power tracking control unit is used to obtain a grid-connected current amplitude reference value based on the voltage and current of the Nth photovoltaic module collected by the sampling circuit;

[0014] The grid current control unit is used to obtain the switch tube S of the Nth H-bridge unit according to the voltage, current and grid current amplitude reference value of the grid collected by the sampling circuit. N1 , switch tube S N2 , switch tube S N3 And switch tube S N4The first control signal is input into the signal conditioning circuit for conditioning and then output to the photovoltaic power generation system, thereby controlling the switch tube S of the Nth H-bridge unit. N1 , switch tube S N2 , switch tube S N3 And switch tube S N4 Working status;

[0015] The mismatched power capacity expansion control unit is used to obtain an output voltage reference value of the Nth boost unit according to the modulation signal of the Nth H-bridge unit;

[0016] The boost unit output capacitor voltage control unit is used to obtain the switch tube Q of the Nth boost unit according to the input capacitor voltage of the Nth H-bridge unit and the output voltage reference value of the Nth boost unit collected by the sampling circuit. N1 , switch tube Q N2 The second control signal is input into the signal conditioning circuit for conditioning and then output to the photovoltaic power generation system, thereby controlling the switch tube Q of the Nth boost unit. N1 , switch tube Q N2 working status.

[0017] Preferably, the working process of the maximum power tracking control unit includes the following steps:

[0018] Step 1.1: The voltage v of the Nth photovoltaic module collected by the sampling circuit is pvN_s , current i pvN_s Multiply to get the output power p of the Nth photovoltaic module pvN ;

[0019] Step 1.2: Obtain the power reference value p of the Nth photovoltaic module by the conductance increment method. refN ;

[0020] Step 1.3: The output power p of the Nth photovoltaic module pvN and the power reference value p of the Nth photovoltaic module refN The power error Δp of the Nth photovoltaic module is obtained by subtraction pvN ;

[0021] Step 1.4: The power error Δp of the Nth photovoltaic module is pvN Input the first proportional-integral controller PI pv (s) Get the grid current amplitude reference value I gm .

[0022] Preferably, the working process of the grid-connected current control unit includes the following steps:

[0023] Step 2.1: The grid voltage v collected by the sampling circuit isg_s The grid voltage phase ω is obtained through the phase-locked loop PLL;

[0024] Step 2.2: The grid voltage phase ω and the grid current amplitude reference value I gm Multiply to get the grid current reference value I*g;

[0025] Step 2.3: Compare the grid current reference value I*g with the grid current i collected by the sampling circuit. g_s The grid current error value Δi is obtained by subtracting g ; Step 2.4, the grid current error value Δi g Through the second proportional-integral controller PI g (s) Generate the modulation signal m of the Nth H-bridge unit N .

[0026] Preferably, the working process of the mismatch power capacity expansion control unit includes the following steps:

[0027] Step 3.1, according to the grid current error value Δi g Get the Nth boost unit bus capacitor voltage increment Δv CmN ;

[0028] Step 3.2, according to the upper limit of the output voltage of the Nth H-bridge unit, the modulation coefficient limit value m of the Nth H-bridge unit is given. max ; Step 3.3, determine the modulation signal m of the Nth H-bridge unit N The modulation coefficient limit value m of the Nth H-bridge unit max If the modulation signal m of the Nth H-bridge unit is N Greater than the modulation coefficient limit value m of the Nth H-bridge unit max , then enable mismatch power capacity expansion control; if the modulation signal m of the Nth H-bridge unit N Less than the modulation coefficient limit value m of the Nth H-bridge unit max , then the mismatch power capacity expansion control is locked; then the Nth boost unit bus capacitor voltage reference value increment Δv CrN Expressed as:

[0029]

[0030] Preferably, the working process of the boost unit output capacitor voltage control unit includes the following steps:

[0031] Step 4.1: The input capacitor voltage v of the Nth H-bridge unit collected by the sampling circuit is cN Perform average low-pass filtering to extract the input capacitor voltage v of the Nth H-bridge unit cN The DC component v CdcN ;

[0032] Step 4.2, the DC component v CdcN The increment of the Nth boost unit bus capacitor voltage reference value Δv CrN The output voltage given value v of the Nth boost unit can be obtained by adding CrefN ;

[0033] Step 4.3: The input capacitor voltage sampling value v of the Nth H-bridge unit collected by the sampling circuit is CN_s The output voltage of the boost unit is given by v CrefN The difference is used to obtain the capacitance voltage error Δv of the Nth H-bridge unit. cN ;

[0034] Step 4.4: Set the voltage error of the capacitor of the Nth H-bridge unit Δv cN Through the third proportional-integral controller PI c (s) Generate a duty cycle signal reference value d for the Nth boost unit.

[0035] A control method for a single-phase cascade H-bridge photovoltaic power generation system, applied to the control system, comprises the following steps: step S1, collecting the voltage and current of the Nth photovoltaic module, the voltage and current of the power grid, and the input capacitor voltage of the Nth H-bridge unit;

[0036] Step S2, obtaining a grid-connected current amplitude reference value based on the voltage and current of the Nth photovoltaic module collected by the sampling circuit;

[0037] Step S3, the switch tube S of the Nth H-bridge unit is obtained according to the voltage, current and grid-connected current amplitude reference value collected by the sampling circuit. N1 , switch tube S N2 , switch tube S N3 And switch tube S N4 a first control signal;

[0038] Step S4, obtaining an output voltage reference value of the Nth boost unit according to the modulation signal of the Nth H-bridge unit;

[0039] Step S5: The switch tube Q of the Nth boost unit is obtained according to the input capacitor voltage of the Nth H-bridge unit and the output voltage reference value of the Nth boost unit collected by the sampling circuit. N1 , switch tube Q N2 a second control signal;

[0040] Step S6: controlling the working state of the single-phase cascade H-bridge photovoltaic power generation system according to the first control signal and the second control signal.

[0041] A computer device includes a memory and a processor, wherein the memory is used to store a computer program, and the processor runs the computer program to enable the computer device to execute the control method of the single-phase cascade H-bridge photovoltaic power generation system.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] The present invention provides a single-phase cascade H-bridge photovoltaic power generation system, which realizes the expansion of mismatch power capacity under the condition of ensuring the maximum power point operation of the photovoltaic module.

[0044] The control system and control method provided by the present invention adjust the modulation signal of the H-bridge unit by dynamically adjusting the output voltage of each boost unit, so that the maximum voltage output capacity of the H-bridge unit that originally entered overmodulation due to excessive mismatch power is improved and then exits the overmodulation state, thereby achieving the expansion of the stable operating range of the power generation system and the increase of the mismatch power capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly describes the drawings required for the specific embodiments or the description of the prior art. Similar elements or parts are generally identified by similar reference numerals throughout the drawings. Elements or parts in the drawings are not necessarily drawn to scale.

[0046] Figure 1 This is a topological diagram of the single-phase cascade H-bridge photovoltaic power generation system of the present invention.

[0047] Figure 2 Schematic diagram of the control system of the single-phase cascade H-bridge photovoltaic power generation system of the present invention.

[0048] Figure 3 This is a control block diagram of the control system of the single-phase cascade H-bridge photovoltaic power generation system of the present invention.

[0049] Figure 4 This is a diagram of the simulation results of the output power of three photovoltaic modules under different light intensities in a specific example of the implementation of the present invention.

[0050] Figure 5 This is a diagram of simulation results of the output voltages of three photovoltaic modules under different light intensities, a specific example of the implementation of the present invention.

[0051] Figure 6 This is a diagram of the output voltage simulation results of three boost units under different working conditions in a specific example of the implementation of the present invention.

[0052] Figure 7 This is a simulation result diagram of the grid-connected current of the cascaded H-bridge system under different working conditions, a specific example of the implementation of the present invention.

[0053] Figure 8 This is a diagram showing the simulation results of the modulation waves of three H-bridge units under different working conditions in a specific example of the implementation of the present invention.

[0054] Figure 9 Flowchart of the control method of the present invention. DETAILED DESCRIPTION

[0055] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0056] It will be understood that when used in this specification and the appended claims, the terms “comprises” and “comprising” indicate the presence of described features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0057] It should also be understood that the terms used in the present specification are only for the purpose of describing particular embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms unless the context clearly indicates otherwise.

[0058] It should be further understood that the term "and / or" used in the present description and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0059] Example 1:

[0060] like Figure 1 As shown, this embodiment provides a single-phase cascade H-bridge photovoltaic power generation system, including a filter inductor L f and n photovoltaic power generation subsystems; each photovoltaic power generation subsystem includes a photovoltaic module, a boost unit, and an H-bridge unit connected in sequence; the output sides of the n H-bridge units are connected in series and then connected to the power grid through a filter inductor.

[0061] The Nth boost unit includes an input capacitor C N1 , switch tube Q N1 , switch tube Q N2 and boost inductor L N ;

[0062] The input capacitor C N1One end of the photovoltaic module and the boost inductor L N One end of the input capacitor C N1 The other end of the photovoltaic module and the switch tube Q N2 The source connection of the boost inductor L N The other end is connected to the switch tube Q N2 The drain of the switch tube Q N1 The source connection of . Where N = 1, 2, 3…, n.

[0063] The Nth H-bridge unit includes an input capacitor C N2 , switch tube S N1 , switch tube S N2 , switch tube S N3 And switch tube S N4 ; Input capacitor C N2 One end of the switch tube Q N1 The drain of the switch tube S N1 The drain of the switch tube S N2 The drain connection, input capacitor C N2 The other end is connected to the switch tube Q N2 The source of the switch tube S N3 The source of the switch tube S N4 The source connection of the switch tube S N4 The drain and switch tube S N3 The drain of the Nth H-bridge unit is connected, and the switch tube S N3 The drain and switch tube S N1 The drain of the Nth H-bridge unit is connected to the drain of the H-bridge unit and serves as the second output terminal of the Nth H-bridge unit; the first output terminal of the Nth H-bridge unit is connected in series with the second output terminal of another H-bridge unit or connected to the power grid through a filter inductor; the second output terminal of the Nth H-bridge unit is connected in series with the first output terminal of another H-bridge unit or connected to the power grid. The output sides of the N H-bridge units are connected in series to achieve output voltage boosting.

[0064] Specifically, the first output terminal of the first photovoltaic module is connected to the filter inductor L f One end of the filter inductor L f The other end of the photovoltaic module is connected to the positive busbar of the power grid, the second output end of the first photovoltaic module is connected to the first output end of the second photovoltaic module, and so on, the first output end of the Nth photovoltaic module is connected to the second output end of the N-1th photovoltaic module, and the second output end of the Nth photovoltaic module is connected to the negative busbar of the power grid.

[0065] Example 2:

[0066] like Figure 2As shown, this embodiment provides a control system for a single-phase cascade H-bridge photovoltaic power generation system, which is used to control the single-phase cascade H-bridge photovoltaic power generation system, including a sampling circuit, a digital controller, and a signal conditioning circuit connected in sequence; the digital controller includes a maximum power tracking control unit, a grid-connected current control unit, a mismatched power capacity expansion control unit, and a boost unit output capacitor voltage control unit; the sampling circuit is respectively connected to the single-phase cascade H-bridge photovoltaic power generation system, the maximum power tracking control unit, the grid-connected current control unit, and the boost unit output capacitor voltage control unit; the grid-connected current control unit is respectively connected to the maximum power tracking control unit, the mismatched power capacity expansion control unit, and the signal conditioning circuit; the boost unit output capacitor voltage control unit is respectively connected to the mismatched power capacity expansion control unit and the signal conditioning circuit; the signal conditioning circuit is connected to the single-phase cascade H-bridge photovoltaic power generation system;

[0067] The maximum power tracking control unit is used to obtain a grid-connected current amplitude reference value based on the voltage and current of the Nth photovoltaic module collected by the sampling circuit;

[0068] The grid current control unit is used to obtain the switch tube S of the Nth H-bridge unit according to the voltage, current and grid current amplitude reference value of the grid collected by the sampling circuit. N1 , switch tube S N2 , switch tube S N3 And switch tube S N4 The first control signal is input into the signal conditioning circuit for conditioning and then output to the photovoltaic power generation system, thereby controlling the switch tube S of the Nth H-bridge unit. N1 , switch tube S N2 , switch tube S N3 And switch tube S N4 Working status;

[0069] The mismatched power capacity expansion control unit is used to obtain an output voltage reference value of the Nth boost unit according to the modulation signal of the Nth H-bridge unit;

[0070] The boost unit output capacitor voltage control unit is used to obtain the switch tube Q of the Nth boost unit according to the input capacitor voltage of the Nth H-bridge unit and the output voltage reference value of the Nth boost unit collected by the sampling circuit. N1 , switch tube Q N2 The second control signal is input into the signal conditioning circuit for conditioning and then output to the photovoltaic power generation system, thereby controlling the switch tube Q of the Nth boost unit. N1 , switch tube Q N2 working status.

[0071] like Figure 3As shown, as a preferred embodiment, the working process of the maximum power tracking control unit includes the following steps:

[0072] Step 1.1: The voltage v of the Nth photovoltaic module collected by the sampling circuit is pvN_s , current i pvN_s Multiply to get the output power p of the Nth photovoltaic module pvN ; The details are as follows:

[0073] v pvN_s =H vpv *v pvN ;

[0074] i pvN_s =H ipv *i pvN ;

[0075] p pvN =i pvN_s *v pvN_s ;

[0076] Among them, v pvN 、i pvN are the original voltage signal and original current signal of the Nth photovoltaic module respectively; H vpv 、H ipv They are the original voltage signal v of the Nth photovoltaic module for the sampling circuit respectively pvN , original current signal i pvN The voltage conversion ratio coefficient and current conversion ratio coefficient for sampling.

[0077] Step 1.2: Obtain the power reference value p of the Nth photovoltaic module by the conductance increment method. refN ;

[0078] Step 1.3: The output power p of the Nth photovoltaic module pvN and the power reference value p of the Nth photovoltaic module refN The power error Δp of the Nth photovoltaic module is obtained by subtraction pvN ;Δp pvN =p refN —p pvN ;

[0079] Step 1.4: The power error Δp of the Nth photovoltaic module is pvN Input the first proportional-integral controller PI pv (s) Get the grid current amplitude reference value I gm Grid-connected current amplitude reference value I gm is calculated as follows:

[0080]

[0081] where k pvp is the proportional coefficient of the first proportional-integral controller, k pvi is the integral coefficient of the first proportional-integral controller. In this embodiment, k pvp =0.01245, k pvi =2.553.

[0082] like Figure 3 As shown in the figure, as a preferred embodiment, the working process of the grid current control unit includes the following steps: Step 2.1, the grid voltage v collected by the sampling circuit is g_s The grid voltage phase ω is obtained through the phase-locked loop PLL;

[0083] v g_s =v g *H vg ;

[0084] Among them, v g is the original voltage signal of the power grid, H vg The sampling circuit is the original voltage signal v of the power grid g The voltage conversion scaling factor for sampling.

[0085] Step 2.2: The grid voltage phase ω and the grid current amplitude reference value I gm Multiply the grid current reference value I*g by the grid current reference value I*g and the grid current i g_s The grid current error value Δi is obtained by subtracting g ;i g_s =i g *H ig ;

[0086] Among them, i g is the original current signal of the power grid, H ig The sampling circuit is the original current signal i of the power grid g The current conversion scale factor for sampling.

[0087]

[0088] Step 2.4: Set the grid current error value Δi g Through the second proportional-integral controller PI g (s) Generate the modulation signal m of the Nth H-bridge unit N .

[0089]

[0090] where k ip is the proportional coefficient of the second proportional-integral controller, k iiis the integral coefficient of the second proportional-integral controller. In this embodiment, k ip =0.4452, k ii =10.53.

[0091] like Figure 3 As shown, as a preferred embodiment, the signal conditioning circuit is based on the modulation signal m of the Nth H-bridge unit. N Generate the control square wave signal G of the Nth H-bridge unit Sn1 , G Sn2 , G Sn3 and G Sn4 And sent to the Nth H-bridge unit to control the switch tube S of the Nth H-bridge unit respectively. N1 , switch tube S N2 , switch tube S N3 And switch tube S N4 Working state. Control square wave signal G Sn1 , G Sn2 , G Sn3 and G Sn4 is calculated as follows:

[0092]

[0093] Among them, k pwm is the pulse width modulation equivalent gain.

[0094] like Figure 3 As shown, as a preferred embodiment, the working process of the mismatch power capacity expansion control unit includes the following steps:

[0095] Step 3.1, according to the grid current error value Δi g Get the Nth boost unit bus capacitor voltage increment Δv CmN ; Its expression is:

[0096] Δv C =k pm Δi g ; where k pm is the proportional coefficient, in this embodiment k pm =0.2.

[0097] Step 3.2, according to the upper limit of the output voltage of the Nth H-bridge unit, the modulation coefficient limit value m of the Nth H-bridge unit is given. max ; Step 3.3, determine the modulation signal m of the Nth H-bridge unit N The modulation coefficient limit value m of the Nth H-bridge unit max If the modulation signal m of the Nth H-bridge unit is N Greater than the modulation coefficient limit value m of the Nth H-bridge unit max, then enable mismatch power capacity expansion control; if the modulation signal m of the Nth H-bridge unit N Less than the modulation coefficient limit value m of the Nth H-bridge unit max , then the mismatch power capacity expansion control is locked; then the Nth boost unit bus capacitor voltage reference value increment Δv CrN Expressed as:

[0098]

[0099] like Figure 3 As shown, as a preferred embodiment, the working process of the boost unit output capacitor voltage control unit includes the following steps:

[0100] Step 4.1: The input capacitor voltage v of the Nth H-bridge unit collected by the sampling circuit is cN Perform average low-pass filtering to extract the input capacitor voltage v of the Nth H-bridge unit cN The DC component v CdcN ;

[0101] Step 4.2, the DC component v CdcN The increment of the Nth boost unit bus capacitor voltage reference value Δv CrN The output voltage given value v of the Nth boost unit can be obtained by adding CrefN ; That is v CrefN =Δv CrN +v CdcN ; The details are as follows:

[0102]

[0103] Among them, ω g is the cut-off frequency of the low-pass filter, and ξ is the damping coefficient of the low-pass filter. In this embodiment, ω g is 100Hz and ξ is 0.707.

[0104] Step 4.3: The input capacitor voltage sampling value v of the Nth H-bridge unit collected by the sampling circuit is CN_s The output voltage of the boost unit is given by v CrefN The difference is used to obtain the capacitance voltage error Δv of the Nth H-bridge unit. cN ;Δv cN =v CrefN -v CN_s ;

[0105] v cN_s =v cN *H vc ;

[0106] Among them, H vcis the input capacitor voltage v of the sampling circuit to the Nth H-bridge unit cN The voltage conversion ratio coefficient of the sampling is used. Step 4.4, the voltage error of the capacitor of the Nth H-bridge unit Δv cN Through the third proportional-integral controller PI c (s) Generate a duty cycle signal reference value d for the Nth boost unit.

[0107]

[0108] where k Cp is the proportional coefficient of the third proportional-integral controller, k Ci is the integral coefficient of the third proportional-integral controller. In this embodiment, k Cp =0.0018, k Ci =0.23.

[0109] like Figure 3 As shown, as a preferred embodiment, the signal conditioning circuit generates the control square wave signal G of the Nth boost unit according to the duty cycle signal reference value d of the Nth boost unit. Qn1 and G Qn2 And sent to the Nth boost unit, thereby controlling the switch tube Q of the Nth boost unit N1 , switch tube Q N2 Working state. Control square wave signal G Qn1 and G Qn2 The calculation formula is:

[0110]

[0111] Among them, k pwm is the pulse width modulation equivalent gain.

[0112] In the present invention, Simulink simulation software is used to build the single-phase cascade H-bridge photovoltaic power generation system and the mismatched power capacity expansion control method proposed in the present invention, and simulation verification is carried out. The parameters are shown in Table 1.

[0113] Table 1 Simulation parameters of single-phase cascade H-bridge photovoltaic power generation system and mismatched power capacity expansion control method

[0114] Cascade H-bridge photovoltaic power generation system rated power 900W Total number of photovoltaic modules in the cascaded H-bridge photovoltaic power generation system 3 Rated transmission power of photovoltaic modules 300W PV module voltage 40V Boost unit output capacitor voltage 40V Power factor angle 0 Output voltage, current frequency 50Hz Boost unit input capacitor 10μF H-bridge unit input side capacitance (x=a,b,c) 10μF H-bridge inverter switching frequency 50kHz filter inductors 20μH Grid voltage amplitude 100V

[0115] Figure 4 This is a diagram showing the output power simulation results of three photovoltaic modules under different light intensities according to a specific example of the present invention; Figure 5 This is a diagram showing simulation results of the output voltages of three photovoltaic modules under different light intensities in a specific example of the present invention; Figure 6 This is a diagram showing simulation results of output voltages of three boost units under different working conditions in a specific example of the present invention; Figure 7 This is a simulation result diagram of the grid-connected current of a cascaded H-bridge system under different working conditions, which is a specific example of the present invention; Figure 8 This is a diagram showing the simulation results of the modulation waves of three H-bridge units under different working conditions in a specific example of the implementation of the present invention.

[0116] like Figure 4-6 As shown, in the initial state, the three PV modules operate stably at their respective maximum power points. At the first switching point, the output power of the second PV module switches to 220W, and the output power of the third PV module switches to 260W. The cascaded H-bridge photovoltaic power generation system still operates stably at the maximum power points of each PV module. Because the modulation ratio of the H-bridge unit does not reach the limit, the output voltage of the boost unit remains consistent. At the second switching point, the output power of the second PV module switches to 100W, and the output power of the third PV module switches to 120W. The modulation ratio of the H-bridge unit connected to the first PV module reaches the limit, so mismatch power capacity expansion control is implemented. The output voltage of the boost unit connected to the first PV module increases, causing the connected H-bridge unit to exit the overmodulation state, ensuring stable system operation. At the third switching point, the output power of the second PV module switches to 20W, and the output power of the third PV module switches to 40W. This further increases the modulation ratio of the H-bridge unit connected to the first PV module, and the output voltage of the boost unit connected to the first PV module further increases, causing the connected H-bridge unit to exit the overmodulation state. At the fourth switching point, the output powers of the three photovoltaic modules return to consistency, and the system returns to its initial operating state.

[0117] like Figure 7 As shown in the figure, during the whole process, the system output current can maintain a good sinusoidal shape, and there is no waveform distortion caused by overmodulation. Figure 8 As shown in the figure, when the output power of the first photovoltaic module is too large compared to the other two photovoltaic modules, the boost unit promptly controls the bus capacitor voltage to increase, so the modulation ratio of the first photovoltaic module remains less than 1, avoiding overmodulation. Therefore, it is verified that the proposed mismatch power capacity expansion method can quickly and effectively suppress the occurrence of overmodulation when power mismatch occurs in the H-bridge unit, and can ensure stable and reliable operation of the system under all operating conditions. It also expands the maximum power tracking capability range of the photovoltaic module in the case of power mismatch and improves the solar energy utilization rate of the photovoltaic power generation system.

[0118] In summary, the control system for the single-phase cascaded H-bridge photovoltaic power generation system proposed in the present invention enables independent maximum power tracking of each photovoltaic module, maximizing photovoltaic energy acquisition efficiency. By dynamically adjusting the output voltage of the boost unit to eliminate the overmodulation of the H-bridge unit due to power imbalance, the present invention expands the steady-state operating range of the cascaded H-bridge photovoltaic power generation system. This also provides the cascaded H-bridge photovoltaic power generation system with a greater mismatch power capacity and a wider operating range, further improving the photovoltaic energy collection rate of the cascaded H-bridge photovoltaic power generation system.

[0119] Example 3:

[0120] like Figure 9 As shown, this embodiment provides a control method for a single-phase cascade H-bridge photovoltaic power generation system, which is applied to the control system, including the following steps:

[0121] Step S1, collecting the voltage and current of the Nth photovoltaic module, the voltage and current of the grid, and the input capacitor voltage of the Nth H-bridge unit;

[0122] Step S2, obtaining a grid-connected current amplitude reference value based on the voltage and current of the Nth photovoltaic module collected by the sampling circuit;

[0123] Step S3, the switch tube S of the Nth H-bridge unit is obtained according to the voltage, current and grid-connected current amplitude reference value collected by the sampling circuit. N1 , switch tube S N2 , switch tube S N3 And switch tube S N4 a first control signal;

[0124] Step S4, obtaining an output voltage reference value of the Nth boost unit according to the modulation signal of the Nth H-bridge unit;

[0125] Step S5: The switch tube Q of the Nth boost unit is obtained according to the input capacitor voltage of the Nth H-bridge unit and the output voltage reference value of the Nth boost unit collected by the sampling circuit. N1 , switch tube Q N2 a second control signal;

[0126] Step S6: controlling the working state of the single-phase cascade H-bridge photovoltaic power generation system according to the first control signal and the second control signal.

[0127] Example 4:

[0128] This embodiment provides a computer device, including a memory and a processor, wherein the memory is used to store a computer program, and the processor runs the computer program to enable the computer device to execute the control method of the single-phase cascade H-bridge photovoltaic power generation system.

[0129] Those skilled in the art will appreciate that the modules of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition of each example has been generally described in terms of function in the above description. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0130] In the embodiments provided by the present invention, it should be understood that the division of modules is merely a logical function division, and there may be other division methods in actual implementation, for example, multiple modules can be combined into one module, one module can be split into multiple modules, or some features can be ignored, etc.

[0131] In addition, the functional modules in various embodiments of the present invention may be integrated into a single processing module, or each module may exist physically separately, or two or more modules may be integrated into a single module. The aforementioned integrated modules may be implemented in the form of hardware or software functional modules.

[0132] If the integrated module is implemented in the form of a software functional module and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, server or network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, read-only memory (ROM, Read-0nly Memory), random access memory (RAM, Random Access Memory), mobile hard disk, magnetic disk or optical disk, etc., various media that can store program code.

[0133] 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 make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and description of the present invention.

Claims

1. A single-phase cascade H-bridge photovoltaic power generation system, characterized in that: It includes a filter inductor and n photovoltaic power generation subsystems; each photovoltaic power generation subsystem includes a photovoltaic module, a boost unit, and an H-bridge unit connected in sequence; the output sides of the n H-bridge units are connected in series and then connected to the power grid through the filter inductor.

2. A single-phase cascade H-bridge photovoltaic power generation system according to claim 1, characterized in that: The Nth boost unit includes an input capacitor C N1 , switch tube Q N1 , switch tube Q N2 and boost inductor L N ; The input capacitor C N1 One end of the photovoltaic module and the boost inductor L N One end of the input capacitor C N1 The other end of the photovoltaic module and the switch tube Q N2 The source connection of the boost inductor L N The other end is connected to the switch tube Q N2 The drain of the switch tube Q N1 source connection.

3. The single-phase cascade H-bridge photovoltaic power generation system according to claim 1, characterized in that: The Nth H-bridge unit includes an input capacitor C N2 , switch tube S N1 , switch tube S N2 , switch tube S N3 And switch tube S N4 ; Input capacitor C N2 One end of the switch tube Q N1 The drain of the switch tube S N1 The drain of the switch tube S N2 The drain connection, input capacitor C N2 The other end is connected to the switch tube Q N2 The source of the switch tube S N3 The source of the switch tube S N4 The source connection of the switch tube S N4 The drain and switch tube S N3 The drain of the Nth H-bridge unit is connected, and the switch tube S N3 The drain and switch tube S N1 The drain of the H-bridge unit is connected and serves as the second output end of the N-th H-bridge unit; the first output end of the N-th H-bridge unit is used to be connected in series with the second output end of another H-bridge unit or to be connected to the power grid through a filter inductor; The second output end of the Nth H-bridge unit is used to be connected in series with the first output end of another H-bridge unit or to the power grid.

4. A control system for a single-phase cascade H-bridge photovoltaic power generation system, characterized in that: Used to control the single-phase cascade H-bridge photovoltaic power generation system described in any one of claims 1-3, comprising a sampling circuit, a digital controller, and a signal conditioning circuit connected in sequence; the digital controller comprises a maximum power tracking control unit, a grid-connected current control unit, a mismatched power capacity expansion control unit, and a boost unit output capacitor voltage control unit; the sampling circuit is respectively connected to the single-phase cascade H-bridge photovoltaic power generation system, the maximum power tracking control unit, the grid-connected current control unit, and the boost unit output capacitor voltage control unit; the grid-connected current control unit is respectively connected to the maximum power tracking control unit, the mismatched power capacity expansion control unit, and the signal conditioning circuit; the boost unit output capacitor voltage control unit is respectively connected to the mismatched power capacity expansion control unit and the signal conditioning circuit; the signal conditioning circuit is connected to the single-phase cascade H-bridge photovoltaic power generation system; The maximum power tracking control unit is used to obtain a grid-connected current amplitude reference value based on the voltage and current of the Nth photovoltaic module collected by the sampling circuit; The grid current control unit is used to obtain the switch tube S of the Nth H-bridge unit according to the voltage, current and grid current amplitude reference value of the grid collected by the sampling circuit. N1 , switch tube S N2 , switch tube S N3 And switch tube S N4 The first control signal is input into the signal conditioning circuit for conditioning and then output to the photovoltaic power generation system, thereby controlling the switch tube S of the Nth H-bridge unit. N1 , switch tube S N2 , switch tube S N3 And switch tube S N4 Working status; The mismatched power capacity expansion control unit is used to obtain an output voltage reference value of the Nth boost unit according to the modulation signal of the Nth H-bridge unit; The boost unit output capacitor voltage control unit is used to obtain the switch tube Q of the Nth boost unit according to the input capacitor voltage of the Nth H-bridge unit and the output voltage reference value of the Nth boost unit collected by the sampling circuit. N1 , switch tube Q N2 The second control signal is input into the signal conditioning circuit for conditioning and then output to the photovoltaic power generation system, thereby controlling the switch tube Q of the Nth boost unit. N1 , switch tube Q N2 working status.

5. The control system of a single-phase cascade H-bridge photovoltaic power generation system according to claim 4, characterized in that: The working process of the maximum power tracking control unit includes the following steps: Step 1.1: The voltage v of the Nth photovoltaic module collected by the sampling circuit is pvN_s , current i pvN_s Multiply to get the output power p of the Nth photovoltaic module pvN ; Step 1.2: Obtain the power reference value p of the Nth photovoltaic module by the conductance increment method. refN ; Step 1.3: The output power p of the Nth photovoltaic module pvN and the power reference value p of the Nth photovoltaic module refN The power error Δp of the Nth photovoltaic module is obtained by subtraction pvN ; Step 1.4: The power error Δp of the Nth photovoltaic module is pvN Input the first proportional-integral controller PI pv (s) Get the grid current amplitude reference value I gm .

6. The control system of a single-phase cascade H-bridge photovoltaic power generation system according to claim 5, characterized in that: The working process of the grid-connected current control unit includes the following steps: Step 2.1: The grid voltage v collected by the sampling circuit is g_s The grid voltage phase ω is obtained through the phase-locked loop PLL; Step 2.2: The grid voltage phase ω and the grid current amplitude reference value I gm Multiply to get the grid current reference value I*g; Step 2.3: Compare the grid current reference value I*g with the grid current i collected by the sampling circuit. g_s The grid current error value Δi is obtained by subtracting g ; Step 2.4: Set the grid current error value Δi g Through the second proportional-integral controller PI g (s) Generate the modulation signal m of the Nth H-bridge unit N .

7. The control system of a single-phase cascade H-bridge photovoltaic power generation system according to claim 6, characterized in that: The working process of the mismatch power capacity expansion control unit includes the following steps: Step 3.1, according to the grid current error value Δi g Get the Nth boost unit bus capacitor voltage increment Δv CmN ; Step 3.2, according to the upper limit of the output voltage of the Nth H-bridge unit, the modulation coefficient limit value m of the Nth H-bridge unit is given. max ; Step 3.3, determine the modulation signal m of the Nth H-bridge unit N The modulation coefficient limit value m of the Nth H-bridge unit max If the modulation signal m of the Nth H-bridge unit is N Greater than the modulation coefficient limit value m of the Nth H-bridge unit max , then enable mismatch power capacity expansion control; if the modulation signal m of the Nth H-bridge unit N Less than the modulation coefficient limit value m of the Nth H-bridge unit max , then the mismatch power capacity expansion control is locked; then the Nth boost unit bus capacitor voltage reference value increment Δv CrN Expressed as:

8. The control system of a single-phase cascade H-bridge photovoltaic power generation system according to claim 7, characterized in that: The working process of the boost unit output capacitor voltage control unit includes the following steps: Step 4.1: The input capacitor voltage v of the Nth H-bridge unit collected by the sampling circuit is cN Perform average low-pass filtering to extract the input capacitor voltage v of the Nth H-bridge unit cN The DC component v CdcN ; Step 4.2, the DC component v CdcN The increment of the Nth boost unit bus capacitor voltage reference value Δv CrN The output voltage given value v of the Nth boost unit can be obtained by adding CrefN ; Step 4.3: The input capacitor voltage sampling value v of the Nth H-bridge unit collected by the sampling circuit is CN_s The output voltage of the boost unit is given by v CrefN The difference is used to obtain the capacitance voltage error Δv of the Nth H-bridge unit. cN ; Step 4.4: Set the voltage error of the capacitor of the Nth H-bridge unit Δv cN Through the third proportional-integral controller PI c (s) Generate a duty cycle signal reference value d for the Nth boost unit.

9. A control method for a single-phase cascade H-bridge photovoltaic power generation system, characterized in that: The control system according to any one of claims 4 to 8 comprises the following steps: Step S1, collecting the voltage and current of the Nth photovoltaic module, the voltage and current of the grid, and the input capacitor voltage of the Nth H-bridge unit; Step S2, obtaining a grid-connected current amplitude reference value based on the voltage and current of the Nth photovoltaic module collected by the sampling circuit; Step S3, the switch tube S of the Nth H-bridge unit is obtained according to the voltage, current and grid-connected current amplitude reference value collected by the sampling circuit. N1 , switch tube S N2 , switch tube S N3 And switch tube S N4 a first control signal; Step S4, obtaining an output voltage reference value of the Nth boost unit according to the modulation signal of the Nth H-bridge unit; Step S5: The switch tube Q of the Nth boost unit is obtained according to the input capacitor voltage of the Nth H-bridge unit and the output voltage reference value of the Nth boost unit collected by the sampling circuit. N1 , switch tube Q N2 a second control signal; Step S6: controlling the working state of the single-phase cascade H-bridge photovoltaic power generation system according to the first control signal and the second control signal.

10. A computer device, characterized in that: It includes a memory and a processor, the memory is used to store a computer program, and the processor runs the computer program to enable the computer device to execute the control method of the single-phase cascade H-bridge photovoltaic power generation system.

Images