A power optimization control method for distributed photovoltaic battery energy storage system based on inductor current

Abstract

The present invention discloses a power optimization control method for a distributed photovoltaic battery energy storage system based on inductor current. In an improved distributed photovoltaic system, only one power converter and one inductor current sensor are used to achieve time-sharing input boost control for multiple photovoltaic channels, resulting in a simple overall system structure. Each photovoltaic channel has independent outputs and does not affect each other. Even if each photovoltaic channel receives different amounts of illumination, each photovoltaic channel can still output its maximum power under shaded conditions through MPPT. Furthermore, the proposed inductor current MPPT method utilizes traditional P&O principles, detecting only the inductor current and adjusting the duty cycle of the converter in the photovoltaic system through two operating modes (I-II) of the algorithm, achieving maximum power output for multiple photovoltaic channels while reducing the overall system device cost and algorithm complexity.

Description

Technical Field

[0001] The present invention belongs to the field of photovoltaic power optimization control, and more specifically, relates to a power optimization control method for a distributed photovoltaic battery energy storage system based on inductive current. Background Art

[0002] Currently, implementing Maximum Power Point Tracking (MPPT) is crucial in photovoltaic systems. The maximum power point (MPP) refers to the state at which a photovoltaic cell can output maximum power under specific conditions. This maximum power point fluctuates with changing environmental conditions. MPPT technology can help photovoltaic systems adjust their operating point in real time, maintaining optimal conditions. This maximizes energy conversion efficiency and minimizes energy loss. This improves the stability, reliability, and cost-effectiveness of photovoltaic power generation systems under varying weather and seasonal conditions.

[0003] Photovoltaic power generation systems typically consist of two parts: photovoltaic modules and power electronic converters. Centralized photovoltaic power generation systems are the most common and widely used structure. This structure only requires a single centralized power converter with MPPT control. However, when a large number of photovoltaic modules are connected in series or parallel, especially in partial shading scenarios, when operating conditions vary between modules, it is impossible to ensure that each module can output its maximum power. The distributed photovoltaic power generation system structure that has emerged in recent years can effectively solve the problem of power differences caused by shading of photovoltaic modules in photovoltaic power generation systems. In the distributed photovoltaic power generation system structure, each photovoltaic module is attached with a DC / DC converter, and accurate MPPT is achieved by controlling each DC / DC converter. However, compared to the centralized structure, the system requires more power converters and controllers, which increases system costs.

[0004] Figure 1 This is a schematic diagram of the structure of a centralized photovoltaic power generation system. Figure 2 This is a schematic diagram of the distributed photovoltaic power generation system structure. Figure 1 and Figure 2 It can be seen that for a PV system with the same number of PV panels, a distributed structure requires more power converters and corresponding MPPT controllers than a centralized structure. This means that the number of electronic components, such as electronic switches and energy storage elements (inductors and capacitors), must be increased to ensure that the PV panels can accurately track their maximum output power under partial shading conditions, which will increase the size and cost of the system.

[0005] If it is necessary to reduce the number of converters and controllers in a distributed photovoltaic power generation system, designing a multi-input power converter is an effective solution, such as Figure 3In addition, it is worth considering how to design a photovoltaic power generation system specifically for this structure, reduce the complexity of the control algorithm in its MPPT controller, and improve the maximum power generation efficiency, which can enable the photovoltaic system to simply implement accurate MPPT control.

[0006] like Figure 1-3 As shown, the main shortcomings of using the existing methods to achieve the maximum power output of distributed photovoltaic power generation systems are:

[0007] 1. To enable individual PV panels to track their own power under partial shading conditions, more power converter circuits are required, increasing the number of components and costs. Using a traditional MPPT controller requires numerous sensors to collect voltage and current signals from the PV panels. This sensor-intensive design requires installation, connection, and maintenance, resulting in high maintenance and hardware costs.

[0008] 2. In addition, when using a multi-input power converter for MPPT control, considering that the duty cycle signal of the MISO multi-input single-output converter generated by the MPPT controller is different when each photovoltaic module is input under different environmental conditions, if the input switch is switched at the next moment to switch the next photovoltaic module, the saved values ​​of the inductor current and duty cycle signal at the current moment will no longer be applicable to the next moment, which will result in the system's power generation being insufficient. Therefore, it is impossible to truly achieve maximum power point tracking of all photovoltaic modules and achieve maximum power generation in one MPPT controller.

[0009] Therefore, there is an urgent need to design a power optimization control method for a distributed photovoltaic battery energy storage system based on inductor current. Power optimization control can be achieved through a multi-input power converter, thereby reducing the overall design cost while still being able to effectively guarantee the maximum power generation power through hardware improvements to the system. Summary of the Invention

[0010] (1) Technical issues to be resolved

[0011] Based on the defects mentioned in the above background technology, the present invention discloses a power optimization control method for a distributed photovoltaic battery energy storage system based on inductive current, which can achieve power optimization control of boosting through a multi-input power converter, thereby reducing the overall design cost while still being able to effectively ensure the maximum power generation power by improving the system hardware.

[0012] (2) Technical solution

[0013] The present invention discloses a power optimization control method for a distributed photovoltaic battery energy storage system based on inductive current. The distributed photovoltaic battery energy storage system based on inductive current includes n photovoltaic modules, a multi-input single-output Boost power converter circuit, an MPPT controller and n input switches S pv1 ,S pv2 ,...,S pvn Based on the original Boost power converter circuit, the positive electrode of each photovoltaic module is connected to the filter inductor L in the Boost power converter circuit through an input switch. pv Connection: filter inductor L pv The inductor current I L As the only input signal of the MPPT controller, the duty cycle signal D pv1 ~D pvn Can control n input switches S separately pv1 ~S pvn The alternating on / off makes the pvi Only the i-th photovoltaic module is connected to the Boost power converter circuit, i ranges from 1 to n, when the i-th photovoltaic module is connected to the Boost power converter circuit through the input switch S pvi When connected to the Boost power converter circuit, the MPPT controller controls the power by controlling the duty cycle D corresponding to the output;

[0014] The power optimization control method includes: setting I L is the filter inductor L pv The inductor current value is I L / (1-D)-dI L / dD is defined as Flag; when the photovoltaic output power is at the maximum power point, dI is satisfied L / dD=I L / (1-D), Flag=0; if Flag>0, then dP in / dV in >0, then it is necessary to increase the duty cycle D to approach the maximum power point; if Flag<0, then the dP in / dV in <0, then the duty cycle D needs to be reduced to approach the maximum power point, dP in and dV in are the changes in input power and input voltage of the converter respectively.

[0015] Furthermore, n input switches S are set pv1 ~S pvn The conduction time is the same, that is, T pv =T pv1 =T pv2 =…=Tpvn , add a dead time T between each two driving signals d , for a system with n photovoltaic channels, the input switching period is n(T pv +T d ); For two adjacent input switches, the delayed turn-on time is (T pv +T d ). The set duty cycle D i for:

[0016]

[0017] i represents the input switch S pvi To achieve the access of the ith photovoltaic channel, such as V pvi is the output voltage of the photovoltaic module when the i-th photovoltaic channel is connected, V outi Represents the output voltage at this time, I outi Represents the output current at this time, D i This is the duty cycle signal of the MOS switch tube in the Boost power converter circuit at this time;

[0018] Since the input switching frequency is high, it is considered that the photovoltaic channels are connected to the system at the same time. For the inductor current I L Expressed as:

[0019]

[0020] Therefore, the distributed photovoltaic battery energy storage system based on inductive current allows each photovoltaic module to independently reach its own maximum power point without affecting each other.

[0021] Furthermore, the power optimization control method includes mode I and mode II. First, mode I is used to apply a uniform direction of disturbance to the duty cycle signals of the photovoltaic channels of all photovoltaic modules, and then mode II is used to adjust the corresponding converter duty cycle signals when each photovoltaic channel is connected, and finally independent power control of each channel is achieved.

[0022] Furthermore, the mode I includes the following steps 1.1-1.6:

[0023] Step 1.1: Initialize and set the counter variable a, counter variable b, threshold R, disturbance direction memory variable X, duty cycle disturbance step ΔD, and duty cycle minimum value D. min , the maximum value of the duty cycle D max The value of a, b, and X are initialized to 0;

[0024] Step 1.2: Collect the inductor current value I at the current moment k L (k), calculate the differential of the inductor current dI L =IL (k)-I L (k-1) and the differential of the duty cycle dD=D1(k)-D1(k-1); and according to Flag=I L / (1-D)-dI L / dD Calculate the value of the flag bit Flag;

[0025] Step 1.3: Determine dI L =0 is established, if so, then the duty cycle assignment D1(k-1)=D1(k), ..., D n (k-1)=D n (k) and determine whether X=1. If so, execute step 1.4; if not, execute step 1.5; if not, execute the inductor current and duty cycle assignment I L (k-1)=I L (k), D1(k-1)=D1(k),...,D n (k-1)=D n (k) Determine whether Flag>0 is true. If so, execute step 1.4. If not, execute step 1.5.

[0026] Step 1.4: Increase the duty cycle of n photovoltaic channels and execute D1(k)=D1(k-1)+△D,……,D n( k)=D n (k-1)+△D, and execute a=a+1; then judge D i (k)>D max Is it true? If so, execute D i (k) = D max Post-set X=1, if not, execute X=1; after step 1.4 is completed, execute step 1.6;

[0027] Step 1.5: Reduce the duty cycle of n photovoltaic channels by executing D1(k)=D1(k-1)-△D, ..., D n( k)=D n (k-1)-△D, and execute b=b+1; then judge D i (k)<D min Is it true? If so, execute D i (k) = D min Post-set X=0, if not, execute X=0; after step 1.5 is completed, execute step 1.6;

[0028] Step 1.6: Determine whether a>R or b>R is established. If so, end mode I and jump to mode II. If not, delay the jump and execute step 1.2 of mode I.

[0029] Furthermore, the mode II includes the following steps 2.1-2.7:

[0030] Step 2.1: Initialization: Set the values ​​of counter variable c, counter variable d, threshold Q, and disturbance direction memory variable Y. Set the PV channel number i to 1 and initialize the values ​​of c, d, and Y to 0.

[0031] Step 2.2: Collect the inductor current value I at the current moment k L (k), calculate the differential of the inductor current dI L =I L (k)-I L (k-1) and the differential of the duty cycle dD = D i (k)-D i (k-1); and according to Flag=I L / (1-D)-dI L / dD Calculate the value of the flag bit Flag;

[0032] Step 2.3: Determine dI L =0 is true, if so, then the duty cycle assignment D is executed i (k-1)=D i (k) and determine whether Y=1 is true. If so, execute step 2.4. If not, execute step 2.5. If not, execute the inductor current and duty cycle assignment I L (k-1)=I L (k), D i (k-1)=D i (k) and determine whether Flag>0 is true. If so, execute step 2.4; if not, execute step 2.5;

[0033] Step 2.4: Increase the duty cycle of the ith photovoltaic channel and execute D i (k) = D i (k-1)+△D, and execute c=c+1; then judge D i (k)>D max Is it true? If so, execute D i (k) = D max Post-set Y=1, if not, execute Y=1; after step 2.4 is completed, execute step 2.6;

[0034] Step 2.5: Reduce the duty cycle of the ith photovoltaic channel and execute D i (k) = D i (k-1)-△D, and execute d=d+1; then judge D i (k)<D min Is it true? If so, execute D i(k) = D min Post-set Y=0, if not, execute Y=0; after step 2.5 is completed, execute step 2.6;

[0035] Step 2.6: Determine whether c>Q or d>Q. If so, initialize c=d=0 and i=i+1, and then execute step 2.7. If not, delay jump to step 2.2 of mode II.

[0036] Step 2.7: Determine whether i≤n is true. If so, jump to step 2.2 of mode II after a delay. If not, jump to mode I after a delay.

[0037] On the other hand, the present invention also discloses a power optimization control system for a distributed photovoltaic battery energy storage system based on inductive current, comprising:

[0038] at least one processor; and at least one memory communicatively coupled to the processor, wherein:

[0039] The memory stores program instructions that can be executed by the processor, and the processor calls the program instructions to execute any of the above-mentioned methods for optimizing the power of a distributed photovoltaic battery energy storage system based on inductive current.

[0040] (3) Beneficial effects

[0041] 1. The present invention proposes a power optimization control method for a distributed photovoltaic battery energy storage system based on inductor current, which includes improvements in both hardware and software. By alternately opening / closing the corresponding n input power switches S pv1 、S pv2 ,..., S pvn Connecting each photovoltaic module to the same MISO power converter allows for optimized power control of multiple photovoltaic channels in a distributed photovoltaic system, all boosted simultaneously under partial shading conditions. This ensures that the outputs of each photovoltaic channel do not affect each other, effectively reducing hardware design costs. Furthermore, the power optimization method used to control the power converter circuit of this photovoltaic system only collects the inductor current signal, eliminating the need for additional current and voltage sensors on the photovoltaic panel side, significantly reducing costs.

[0042] 2. In addition, based on the above-mentioned hardware improvements of the present invention, considering that the stored values ​​of the inductor current and duty cycle signals at the current moment in the power tracking controller may not be applicable at the next moment, in order to further truly and accurately achieve maximum power point tracking after boosting, the present invention also designs an MPPT method for controlling the power converter circuit of the above-mentioned photovoltaic system. By only collecting the inductor current signal and controlling and switching between the two operating modes I and II in the MPPT control algorithm, the duty cycle of the converter connected to each photovoltaic channel is adjusted, and ultimately the maximum power output of the photovoltaic panel is controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions of the present invention or the prior art, the following briefly introduces the drawings required for the embodiments:

[0044] Figure 1 This is a schematic diagram of the structure of a centralized photovoltaic power generation system;

[0045] Figure 2 This is a schematic diagram of the distributed photovoltaic power generation system structure;

[0046] Figure 3 This is a schematic diagram of the distributed photovoltaic power generation system based on multiple input power converters;

[0047] Figure 4 This is a schematic diagram of the structure of the distributed photovoltaic power generation system proposed in the present invention;

[0048] Figure 5 It is a traditional single photovoltaic channel photovoltaic system circuit;

[0049] Figure 6 This is the circuit diagram of a traditional photovoltaic system with n photovoltaic channels distributed structure;

[0050] Figure 7 This is a circuit diagram of the distributed photovoltaic energy storage system of the present invention;

[0051] Figure 8 Schematic diagram of the main switch drive signals and inductor waveforms of the SI-MISO power converter of the present invention;

[0052] Figure 9 Schematic diagram of the flow of the inductor current MPPT control algorithm mode I in the present invention;

[0053] Figure 10 It is a flow chart of the MPPT control algorithm mode II based on the inductor current in the present invention. DETAILED DESCRIPTION

[0054] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0055] The present invention aims to provide a single-inductor current MPPT method for distributed photovoltaic systems. This method first requires hardware improvements. In this distributed photovoltaic system, a single-inductor multiple-input single-output (MISO) power converter is used to implement MPPT based on the inductor current. This method requires only a single current sensor, thus reducing the number of system components and overall cost.

[0056] By setting the input switch (S pv1 ,S pv2 ,...,S pvn ) of the control signal (PWM signal) duty cycle D pvi , switching frequency f1, each photovoltaic channel can be connected to the system in turn. Using the MPPT algorithm of the inductor current, the duty cycle D of the control signal of the adjustable power converter switch S is output. When photovoltaic modules under different shadow conditions are connected to the system, the corresponding duty cycles are different. Each photovoltaic module can independently output the maximum power without affecting each other. The structural diagram of the distributed photovoltaic battery energy storage system based on inductor current of the present invention is shown as follows Figure 4 shown.

[0057] The photovoltaic power generation system described in this invention primarily comprises photovoltaic modules, a MISO (Multi-Input Single-Output) converter, an MPPT controller, and connected loads. In photovoltaic power generation systems, a stable voltage output is often required before being connected to the power grid or other devices to ensure stable operation. Therefore, the following description of the present invention assumes that the photovoltaic power generation system is connected to a DC load and that the voltage at the load terminal remains stable. Figure 5 The photovoltaic system circuit diagram for a single photovoltaic channel includes a boost circuit and an MPPT controller. For n photovoltaic channels, Figure 6 The distributed photovoltaic system circuit diagram shown includes n boost circuits. The traditional MPPT method requires detecting the output voltage and current of all photovoltaic modules. Figure 7 The distributed photovoltaic system circuit diagram of n photovoltaic channels of the present invention only includes 1 MISO power converter circuit, 1 MPPT controller and n input switches (S pv1 ,S pv2 ,...,Spvn ), only the current flowing through the converter's inductor needs to be detected. Based on the change in inductor current, the MPPT controller outputs a duty cycle signal, which, through a PWM signal generator, drives the converter's switches, thereby tracking the PV module's maximum output power point.

[0058] Specifically, such as Figure 7 As shown, the distributed photovoltaic battery energy storage system based on inductive current of the present invention includes n photovoltaic modules, a multi-input single-output Boost power converter circuit, an MPPT controller and n input switches S pv1 ,S pv2 ,...,S pvn Based on the original Boost power converter circuit structure, the positive electrode of each photovoltaic module is connected to the filter inductor L in the Boost power converter circuit through an input switch. pv Connection, that is, n photovoltaic modules are connected in parallel, and the positive poles of the n photovoltaic modules connected in parallel are connected through n input switches S pv1 ,S pv2 ,...,S pvn Connected to the same filter inductor L pv Upper: Filter inductor L pv The inductor current I L As the only input signal of the MPPT controller, the duty cycle signal D pv1 ~D pvn Can control n input switches S separately pv1 ~S pvn The alternating on / off makes the pvi There is only one PV module i connected to the Boost power converter circuit, and the input switch S pv1 ~S pvn Specifically, the corresponding duty cycle signal D pv1 ~D pvn Alternately open / close, when the i-th photovoltaic module is turned on / off through the input switch S pvi When connected to the Boost power converter circuit (i is 1 to n), the MPPT controller outputs the corresponding duty cycle signal D by controlling i Perform power control.

[0059] Based on the present invention Figure 7 The circuit diagram introduces the setting of input switch signal and the overall controllability analysis of the circuit. Figure 8 Based on single inductor multiple input single output (ie SI-MISO, single inductor refers to the shared filter inductor L pv ) of the Boost power converter, and the schematic diagram of the main driving signal and inductor waveform of the switch, in which the photovoltaic module is connected to the corresponding input power switch (Spv1 、S pv2 ,..., S pvn ) are connected to the Boost power converter, and these switches are alternately turned on / off according to the driving signal.

[0060] To simplify the setup, input switch S pv1 ~S pvn The conduction time is the same, that is (T pv =T pv1 =T pv2 =…=T pvn ) Add a dead time T between each two driving signals d To avoid simultaneous conduction of the switches. Therefore, for a system with n photovoltaic channels, the input switch period is n(T pv +T d ); For two adjacent input switches, the delayed turn-on time is (T pv +T d ). The set duty cycle D i for:

[0061]

[0062] For this SI-MISO Boost power converter, when each photovoltaic module is connected to the system through the corresponding photovoltaic channel, it has an intrinsic boost function, and its output voltage equation satisfies:

[0063]

[0064] Under steady-state conditions, the relationship between the input voltage of the Boost power converter circuit (which is also the output voltage of the photovoltaic module) and the output voltage (which is also the load voltage) is:

[0065]

[0066] Among them, the mark i represents the input switch S pvi To achieve the access of the ith photovoltaic channel, such as V pvi is the output voltage of the photovoltaic module when the i-th photovoltaic channel is connected, V outi Represents the output voltage at this time, D i This is the duty cycle signal of the switching tube in the converter at this time.

[0067] Similarly, the relationship between output current and input current is:

[0068]

[0069] Due to the high frequency of input switching, the photovoltaic channels can be connected to the system at the same time. For the average current I L It can be expressed as:

[0070]

[0071] therefore:

[0072] V pv I L =V out1 I out1 +V out2 I out2 +...+V outn I outn (6)

[0073] This demonstrates that the system structure allows each PV module to independently reach its maximum power point without interfering with each other. When a PV channel is connected to the system, the system structure is equivalent to a traditional single-channel PV system. The proposed inductive current MPPT method can then be analyzed using this traditional single-channel PV system structure.

[0074] For a traditional photovoltaic system with a single photovoltaic channel, in the traditional perturbation-observation method for tracking the maximum power point, based on the PV output characteristic curve of the photovoltaic module, the basis for determining whether the power reaches the maximum value is:

[0075]

[0076] Among them, P in and V in are the input power and voltage of the converter (also the output power and voltage of the PV module).

[0077] For the boost conversion circuit in a traditional single-photovoltaic channel photovoltaic system, the following requirements are met:

[0078] P in =V in I in (8)

[0079] V in =V out (1-D) (9)

[0080] Among them I in is the input current of the converter (also the output current of the photovoltaic module), and D is the duty cycle of the Boost power converter.

[0081] For the Boost power converter circuit, the average current of the filter capacitor is zero in steady state, and the input current can be regarded as the average inductor current I L , so combined with formula (8), formula (7) can be transformed into:

[0082]

[0083] Combined with the relationship between the input voltage and output voltage of the Boost converter expressed in equation (9), equation (10) can be transformed into:

[0084]

[0085] Arranging formula (11), the criterion for the PV module output power to reach the maximum power point MPP can be expressed as:

[0086]

[0087] I L / (1-D)-dI L / dD is defined as Flag. When the photovoltaic output power is at the maximum power point MPP, dI is satisfied. L / dD=I L / (1-D), Flag=0; if Flag>0, then dP in / dV in >0, then the duty cycle D (ie D i ) to approach the maximum power point; if Flag<0, the dP in / dV in <0, then the duty cycle D needs to be reduced to approach the maximum power point.

[0088] Based on the above principle analysis of the MPPT algorithm for single inductor current disturbance, if the algorithm is used in the conversion circuit of the designed distributed photovoltaic system, only one current sensor is needed to collect the inductor current as the input of the controller to achieve MPPT control. The application of this algorithm in multi-input photovoltaic systems is slightly different from that in single-input systems. In the proposed multi-input photovoltaic system structure, when each photovoltaic module is input under different environmental conditions, the MPPT controller generates a duty cycle signal D of the MISO type Boost power converter. i Different, if the next moment happens to be the input switch S pv1 ~S pvn When switching occurs, the next photovoltaic module is switched. The saved values ​​of the inductor current and duty cycle signal at the current moment will no longer be applicable to the next moment, which may make the power control effect at this moment not optimal.

[0089] Based on the above analysis of the inventors, it can be seen that in order to Figure 7The improved circuit and its time-sharing control method with the same conduction time can truly achieve the control effect of maximum power point output. The present invention further proposes an MPPT control algorithm for inductor current, that is, the MPPT algorithm for single inductor current variable step disturbance in the SI-MISO type photovoltaic system structure is designed into two modes. First, a uniform direction of disturbance is applied to the duty cycle signals of all photovoltaic component input channels, and then the corresponding converter duty cycle signals when each input channel is connected are adjusted, and finally independent MPPT of each channel is achieved.

[0090] Based on the above theoretical analysis, combined with Figure 7 The proposed photovoltaic system structure and Figure 8 The MPPT control algorithm of the inductor current proposed by the present invention mainly includes two operation modes. The flowchart of the algorithm operation mode I is as follows: Figure 9 As shown, the flowchart of the algorithm operation mode II is as follows Figure 10 shown.

[0091] All input switches work in sequence at a fixed frequency. When the i-th input switch S pvi When the i-th photovoltaic channel is connected to the system, the duty cycle of the converter switch S is D i The main control strategy of this algorithm is to continuously adjust the duty cycle D by observing the change of inductor current. i , so that each photovoltaic module reaches its maximum power point (MPP). This control algorithm is based on the principle of the P&O algorithm and includes two operating modes I and II. The control principles and specific steps for the execution of modes I and II are as follows:

[0092] Mode I and Mode II control principles:

[0093] In Mode I, the algorithm perturbs the duty cycle of all channels of the power converter in the same direction to track the MPP of all PV channels. The inductor current value is compared with the inductor current value of the previous algorithm iteration to obtain the inductor current value (dI L ) changes. Similarly, the change in duty cycle (dD) is determined. Since the duty cycle is perturbed in the same direction in this mode, the duty cycle change corresponding to each PV channel connected is the same. Here, dD is represented by the duty cycle change corresponding to the first PV channel connected. Then, based on the theoretical analysis above, Flag is calculated.

[0094] Before judging the sign of the Flag, first determine whether the inductor current has changed. When the ADC is sampling, the resolution may not be enough to record the inductor current change caused by the last duty cycle disturbance. Therefore, the variable "X" is used to memorize the duty cycle D. i The disturbance direction, where the duty cycle D iThe variable is set to "1", the duty cycle D i The variable decrease is set to "0". If the inductor current change is 0, the variable "X" is determined to be 1, corresponding to the step size of increasing or decreasing the duty cycle, so that the duty cycle has the same perturbation direction as the last iteration, and the inductor current value does not need to be updated. If the inductor current change is not 0, the flag sign is determined.

[0095] Based on the theoretical analysis above, if Flag is greater than 0, the duty cycle D i Then increase △D; if Flag is less than 0, the duty cycle D i ΔD is reduced. Variables "a" and "b" record the number of duty cycle increases or decreases, respectively. In Mode I, each duty cycle is tracked uniformly to ensure that the output power of each PV channel reaches a certain point, preventing the duty cycle from increasing or decreasing indefinitely. Therefore, variables "a" and "b" have a threshold R. When the threshold is exceeded, the condition for entering Mode II is met, and each duty cycle is independently perturbed. Without variables "a" and "b" as the criteria for entering Mode II, independent MPPT cannot be achieved if the light intensity received by each PV input channel is different. This threshold can be determined through repeated testing and adjustment.

[0096] In Mode II, the algorithm tracks the MPP of each PV channel and adjusts the duty cycle of the converter (D1, D2, ...., D n ) gap to achieve power optimization of each photovoltaic channel. The perturbation principle of mode II is the same as that of mode I, but mode II perturbs the duty cycle D of the converter corresponding to the input of a single photovoltaic channel in turn. i During Mode II operation, the duty cycles of the converters corresponding to the other PV channels remain unchanged. Variables "c" and "d" function similarly to variables "a" and "b" in Mode I. A threshold Q is required to switch the duty cycle to a perturbation. If this threshold is exceeded, the next duty cycle perturbation is performed, and variables "c" and "d" are reset to zero, re-recording the number of perturbations. This process continues until all duty cycles are perturbed. When i > n, Mode II is exited and Mode I is re-entered, repeating the above process. Variable Y functions similarly to X in Mode I, recording duty cycle changes.

[0097] In addition, during the entire algorithm operation, the duty cycle D output by the MPPT controller is always limited to the minimum value D min and the maximum value D maxModes I and II use four counters (a, b, c, and d) to switch between these two modes. If "a" and "b" exceed the set values, Mode I switches to Mode II. Counters "c" and "d" are used in Mode II to control the PV input channels. Mode II returns to Mode I when all connected PV input channels are able to operate at their respective MPPs.

[0098] Specifically, Mode I includes the following steps 1.1-1.6:

[0099] Step 1.1: Initialize and set the counter variable a, counter variable b, threshold R, disturbance direction memory variable X, duty cycle disturbance step ΔD, and duty cycle minimum value D. min , the maximum value of the duty cycle D max The value of a, b, and X are initialized to 0;

[0100] Step 1.2: Collect the inductor current value I at the current moment k L (k), calculate the differential of the inductor current dI L =I L (k)-I L (k-1) and the differential of the duty cycle dD=D1(k)-D1(k-1); and according to Flag=I L / (1-D)-dI L / dD Calculate the value of the flag bit Flag;

[0101] Step 1.3: Determine dI L =0 is established, if so, then the duty cycle assignment D1(k-1)=D1(k), ..., D n (k-1)=D n (k) and determine whether X=1. If so, execute step 1.4; if not, execute step 1.5; if not, execute the inductor current and duty cycle assignment I L (k-1)=I L (k), D1(k-1)=D1(k),...,D n (k-1)=D n (k) Determine whether Flag>0 is true. If so, execute step 1.4. If not, execute step 1.5.

[0102] Step 1.4: Increase the duty cycle of n photovoltaic channels and execute D1(k)=D1(k-1)+△D,……,D n( k)=D n (k-1)+△D, and execute a=a+1; then judge D i (k)>D max Is it true? If so, execute Di (k) = D max Post-set X=1, if not, execute X=1; after step 1.4 is completed, execute step 1.6;

[0103] Step 1.5: Reduce the duty cycle of n photovoltaic channels by executing D1(k)=D1(k-1)-△D, ..., D n( k)=D n (k-1)-△D, and execute b=b+1; then judge D i (k)<D min Is it true? If so, execute D i (k) = D min Post-set X=0, if not, execute X=0; after step 1.5 is completed, execute step 1.6;

[0104] Step 1.6: Determine whether a>R or b>R is established. If so, end mode I and jump to mode II. If not, delay the jump and execute step 1.2 of mode I.

[0105] Specifically, Mode II includes the following steps 2.1-2.7:

[0106] Step 2.1: Initialization: Set the values ​​of counter variable c, counter variable d, threshold Q, and disturbance direction memory variable Y. Set the PV channel number i to 1 and initialize the values ​​of c, d, and Y to 0.

[0107] Step 2.2: Collect the inductor current value I at the current moment k L (k), calculate the differential of the inductor current dI L =I L (k)-I L (k-1) and the differential of the duty cycle dD = D i (k)-D i (k-1); and according to Flag=I L / (1-D)-dI L / dD Calculate the value of the flag bit Flag;

[0108] Step 2.3: Determine dI L =0 is true, if so, then the duty cycle assignment D is executed i (k-1)=D i (k) and determine whether Y=1 is true. If so, execute step 2.4. If not, execute step 2.5. If not, execute the inductor current and duty cycle assignment I L (k-1)=I L (k), D i (k-1)=D i(k) and determine whether Flag>0 is true. If so, execute step 2.4; if not, execute step 2.5;

[0109] Step 2.4: Increase the duty cycle of the ith photovoltaic channel and execute D i (k) = D i (k-1)+△D, and execute c=c+1; then judge D i (k)>D max Is it true? If so, execute D i (k) = D max Post-set Y=1, if not, execute Y=1; after step 2.4 is completed, execute step 2.6;

[0110] Step 2.5: Reduce the duty cycle of the ith photovoltaic channel and execute D i (k) = D i (k-1)-△D, and execute d=d+1; then judge D i (k)<D min Is it true? If so, execute D i (k) = D min Post-set Y=0, if not, execute Y=0; after step 2.5 is completed, execute step 2.6;

[0111] Step 2.6: Determine whether c>Q or d>Q. If so, initialize c=d=0 and i=i+1, and then execute step 2.7. If not, delay jump to step 2.2 of mode II.

[0112] Step 2.7: Determine whether i≤n is true. If so, jump to step 2.2 of mode II after a delay. If not, jump to mode I after a delay.

[0113] From the above process of mode I-II, it can be seen that because the present invention sets the disturbance direction memory variable XY, Flag flag, counter abcd and corresponding judgment logic to perform the assignment operation of the inductor current and duty cycle, and first applies a disturbance in a unified direction to the duty cycle signals of all photovoltaic module input channels, and then adjusts and controls the corresponding converter duty cycle signals when each input channel is connected, so even if the next moment happens to be the input switch S pv1 ~S pvn When switching occurs, the next photovoltaic module is switched, and the saved values ​​of the inductor current and duty cycle signal at the current moment can still be applied to the next moment, so that Figure 7 The system can truly obtain the optimal power tracking control of MPPT.

[0114] Compared with the existing technology, the advantages of the present invention are:

[0115] 1. The proposed distributed photovoltaic system utilizes a single boost power converter to time-share power control for n photovoltaic panels, enabling multiple photovoltaic channel inputs. Only a single inductive current sensor is required, resulting in a simple overall system structure and low hardware cost. Each photovoltaic channel provides independent output without interfering with each other. Even when exposed to varying amounts of sunlight, each channel can still output its maximum power under shaded conditions through MPPT.

[0116] 2. The proposed inductor current MPPT method utilizes the traditional P&O concept, only detecting the inductor current and adjusting the duty cycle of the converter in the photovoltaic system through the two operating modes I and II of the algorithm, effectively achieving maximum power output of multiple photovoltaic channels, while reducing the device cost and algorithm complexity of the entire system.

[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A power optimization control method for a distributed photovoltaic battery energy storage system based on inductor current, characterized in that: The distributed photovoltaic battery energy storage system based on inductive current includes n photovoltaic panels, a multi-input single-output Boost power converter circuit, an MPPT controller and n input switches S pv1 ,S pv2 ,...,S pvn Based on the original Boost power converter circuit, the positive electrode of each photovoltaic module is connected to the filter inductor L in the Boost power converter circuit through an input switch. pv Connection: filter inductor L pv The inductor current I L As the only input signal of the MPPT controller, the duty cycle signal D pv1 ~D pvn Can control n input switches S separately pv1 ~S pvn The alternating on / off makes the pvi Only the i-th photovoltaic module is connected to the Boost power converter circuit, i ranges from 1 to n, when the i-th photovoltaic module is connected to the Boost power converter circuit through the input switch S pvi When connected to the Boost power converter circuit, the MPPT controller controls the power by controlling the duty cycle D corresponding to the output; The power optimization control method includes: setting I L is the filter inductor L pv The inductor current value is I L / (1-D)-dI L / dD is defined as Flag; when the photovoltaic output power is at the maximum power point, dI is satisfied L / dD=I L / (1-D), Flag=0; if Flag>0, then dP in / dV in >0, then it is necessary to increase the duty cycle D to approach the maximum power point; if Flag<0, then the dP in / dV in <0, then the duty cycle D needs to be reduced to approach the maximum power point, dP in and dV in are the changes in input power and input voltage of the converter respectively.

2. The power optimization control method for a distributed photovoltaic battery energy storage system based on inductive current according to claim 1 is characterized in that: Set n input switches S pv1 ~S pvn The conduction time is the same, that is, T pv =T pv1 =T pv2 =…=T pvn , add a dead time T between each two driving signals d , for a system with n photovoltaic channels, the input switching period is n(T pv +T d ); For two adjacent input switches, the delayed turn-on time is (T pv +T d );The set duty cycle D i for: i represents the input switch S pvi To achieve the access of the ith photovoltaic channel, V pvi is the output voltage of the photovoltaic module when the i-th photovoltaic channel is connected, V outi Represents the output voltage at this time, I outi Represents the output current at this time, D i This is the duty cycle signal of the MOS switch tube in the Boost power converter circuit at this time; Since the input switching frequency is high, it is considered that the photovoltaic channels are connected to the system at the same time. For the inductor current I L Expressed as: Therefore, the distributed photovoltaic battery energy storage system based on inductive current allows each photovoltaic module to independently reach its own maximum power point without affecting each other.

3. The power optimization control method for a distributed photovoltaic battery energy storage system based on inductive current according to claim 2 is characterized in that: The power optimization control method includes Mode I and Mode II. First, Mode I applies a uniformly directed disturbance to the duty cycle signals of the photovoltaic channels of all photovoltaic modules. Then, Mode II adjusts the corresponding converter duty cycle signals when each photovoltaic channel is connected, ultimately achieving independent power control of each channel.

4. The power optimization control method for a distributed photovoltaic battery energy storage system based on inductive current according to claim 3 is characterized in that: Mode I includes the following steps 1.1-1.6: Step 1.1: Initialize and set the counter variable a, counter variable b, threshold R, disturbance direction memory variable X, duty cycle disturbance step ΔD, and duty cycle minimum value D. min , the maximum value of the duty cycle D max The value of a, b, and X are initialized to 0; Step 1.2: Collect the inductor current value I at the current moment k L (k), calculate the differential of the inductor current dI L =I L (k)-I L (k-1) and the differential of the duty cycle dD=D1(k)-D1(k-1); and according to Flag=I L / (1-D)-dI L / dD Calculate the value of the flag bit Flag; Step 1.3: Determine dI L =0 is established, if so, then the duty cycle assignment D1(k-1)=D1(k), ..., D n (k-1)=D n (k) and determine whether X=1. If so, execute step 1.4; if not, execute step 1.5; if not, execute the inductor current and duty cycle assignment I L (k-1)=I L (k), D1(k-1)=D1(k),...,D n (k-1)=D n (k) Determine whether Flag>0 is true. If so, execute step 1.

4. If not, execute step 1.

5. Step 1.4: Increase the duty cycle of n photovoltaic channels and execute D1(k)=D1(k-1)+△D,……,D n( k)=D n (k-1)+△D, and execute a=a+1; then judge D i (k)>D max Is it true? If so, execute D i (k) = D max Post-set X=1, if not, execute X=1; After step 1.4 is completed, proceed to step 1.6; Step 1.5: Reduce the duty cycle of n photovoltaic channels by executing D1(k)=D1(k-1)-△D, ..., D n( k)=D n (k-1)-△D, and execute b=b+1; then judge D i (k)<D min Is it true? If so, execute D i (k) = D min Post-set X=0, if not, execute X=0; after step 1.5 is completed, execute step 1.6; Step 1.6: Determine whether a>R or b>R is established. If so, end mode I and jump to mode II. If not, delay the jump and execute step 1.2 of mode I.

5. The power optimization control method for a distributed photovoltaic battery energy storage system based on inductive current according to claim 4 is characterized in that: The mode II includes the following steps 2.1-2.7: Step 2.1: Initialization: Set the values ​​of counter variable c, counter variable d, threshold Q, and disturbance direction memory variable Y. Set the PV channel number i to 1 and initialize the values ​​of c, d, and Y to 0. Step 2.2: Collect the inductor current value I at the current moment k L (k), calculate the differential of the inductor current dI L =I L (k)-I L (k-1) and the differential of the duty cycle dD = D i (k)-D i (k-1); and according to Flag=I L / (1-D)-dI L / dD Calculate the value of the flag bit Flag; Step 2.3: Determine dI L =0 is true, if so, then the duty cycle assignment D is executed i (k-1)=D i (k) and determine whether Y=1 is true. If so, execute step 2.

4. If not, execute step 2.

5. If not, execute the inductor current and duty cycle assignment I L (k-1)=I L (k), D i (k-1)=D i (k) and determine whether Flag>0 is true. If so, execute step 2.4; if not, execute step 2.5; Step 2.4: Increase the duty cycle of the ith photovoltaic channel and execute D i (k) = D i (k-1)+△D, and execute c=c+1; then judge D i (k)>D max Is it true? If so, execute D i (k) = D max Post-set Y=1, if not, execute Y=1; after step 2.4 is completed, execute step 2.6; Step 2.5: Reduce the duty cycle of the ith photovoltaic channel and execute D i (k) = D i (k-1)-△D, and execute d=d+1; then judge D i (k)<D min Is it true? If so, execute D i (k) = D min Post-set Y=0, if not, execute Y=0; after step 2.5 is completed, execute step 2.6; Step 2.6: Determine whether c>Q or d>Q. If so, initialize c=d=0 and i=i+1, and then execute step 2.

7. If not, delay jump to step 2.2 of mode II. Step 2.7: Determine whether i≤n is true. If so, jump to step 2.2 of mode II after a delay. If not, jump to mode I after a delay.

6. A power optimization control system for a distributed photovoltaic battery energy storage system based on inductive current, characterized in that: include: at least one processor; and at least one memory communicatively connected to the processor, wherein: The memory stores program instructions that can be executed by the processor, and the processor calls the program instructions to execute the power optimization control method of the distributed photovoltaic battery energy storage system based on inductive current as described in any one of claims 1 to 5.

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