阅读说明：本技术 基于di-mpc算法的光伏dmppt控制方法及其系统 (Photovoltaic DMPPT control method and system based on DI-MPC algorithm ) 是由 李星硕 梁鹏 丁树业 于 2021-06-21 设计创作，主要内容包括：本发明公开了一种基于DI-MPC算法的光伏DMPPT控制方法及其系统,该系统包括至少两个功率调节单元,所述功率调节单元输出串联,汇于直流母线,为并网逆变器提供输入电压,所述功率调节单元包括相连接的光伏组件和功率调节器,所述功率调节器用于获取功率-电压关系以及最优开关状态。本发明能够实现分布式光伏发电系统在局部遮挡条件下稳定工作在最大功率点附近,有效避免失配现象发生,大大提高光伏组件发电效率,此外,依靠所提出的DI-MPC算法,预测效果更加准确,省去了PWM调制模块的使用,降低整体成本,并且该方法具有快速响应的特性,在光照变化情况下,直流母线电压可快速达到稳态,为逆变器提供稳定的输入条件,具有较大的推广价值与经济效益。(The invention discloses a photovoltaic DMPPT control method based on a DI-MPC algorithm and a system thereof, wherein the system comprises at least two power regulating units, the outputs of the power regulating units are connected in series and converged at a direct current bus to provide input voltage for a grid-connected inverter, the power regulating units comprise photovoltaic assemblies and power regulators which are connected, and the power regulators are used for obtaining a power-voltage relation and an optimal switch state. The method can realize that the distributed photovoltaic power generation system stably works near the maximum power point under the condition of local shielding, effectively avoids the occurrence of mismatch phenomenon, greatly improves the power generation efficiency of the photovoltaic component, has more accurate prediction effect by relying on the proposed DI-MPC algorithm, saves the use of a PWM (pulse-width modulation) module, reduces the overall cost, has the characteristic of quick response, can quickly reach the stable state of the direct-current bus voltage under the condition of illumination change, provides stable input conditions for the inverter, and has great popularization value and economic benefit.)

1. A photovoltaic DMPPT control method based on a DI-MPC algorithm is characterized by comprising the following steps:

s1: calculating the optimal coefficient at the next moment by acquiring data points and deducing a relation between power and voltage by using an interpolation method according to the P-U characteristic of the photovoltaic module when the photovoltaic module runs near the MPP;

s2: calculating a photovoltaic output power reference value under two conditions by using the relational expression of the power and the voltage obtained in the step S1, wherein the two conditions are that the photovoltaic voltage at the next moment makes positive micro-fluctuation on the basis of the voltage at the current moment and the photovoltaic voltage at the next moment makes negative micro-fluctuation on the basis of the voltage at the current moment;

s3: constructing a first cost function by using the power reference value obtained in the step S2 and the actual power value at the current moment, and selecting a photovoltaic voltage reference value at the next moment by comparing the size of the cost function;

s4: establishing a circuit model of the power regulator in two states of on and off, deducing output voltage of the power regulator, and calculating the duty ratio of the power regulator according to a voltage transformation ratio relation;

s5: deducing a predicted value of the power regulator at the next moment of the photovoltaic voltage under two states by utilizing an Euler forward difference formula;

s6: and (4) constructing a second cost function by using the photovoltaic voltage reference value selected in the step (S3) and the voltage predicted value obtained in the step (S5), and determining the switching state of the power regulator by comparing the size of the cost function.

2. The method as claimed in claim 1, wherein the relationship between power and voltage in step S1 is as follows:

P_pv(k)＝aV_pv(k)²+bV_pv(k)+c

wherein, a, b and c are the optimal coefficients of the next moment.

3. The method as claimed in claim 2, wherein the optimal coefficients a, b, and c at the next moment in step S1 are calculated by:

where k represents the current time and k-1 represents the previous time.

4. The method as claimed in claim 1, wherein the first cost function in step S3 includes J₁And J₂：

J_{1,2}＝(P_ref1,2(k+1)-P(k))²

Wherein, P_ref1,2(k +1) is the power reference value, and P (k) is the current output power;

if J₁＞J₂Then the reference voltage at the next time is V_ref1On the contrary, it is V_ref2。

5. The method as claimed in claim 1, wherein the circuit model in the two states of on and off in step S4 is specifically:

wherein, V_oIs the output voltage of the power regulator, T_sD represents the switching duty ratio of the power regulator, R is a load resistor, and C is an output filter capacitor.

6. The method as claimed in claim 1, wherein the step S5 is specifically as follows: deriving the ratio of the output voltage of the power regulator to the time according to the KCL law, and deriving the predicted value V of the output voltage of the power regulator at the next moment by an Euler forward difference formula_o,s＝1,0(k +1), and simultaneously, deducing a predicted value V of the photovoltaic voltage at the next moment according to the voltage conversion ratio relation of the power regulator_pv,s＝1,0(k+1)。

7. The method as claimed in claim 1, wherein the second cost function in step S6 includes g₁And g₀：

g_{1,0}＝|V_pv,s＝1,0(k+1)-V_ref(k+1)|

If g is₁＜g₀If s is equal to 1, the switch is turned on, otherwise, if s is equal to 0, the switch is turned off.

8. The photovoltaic DMPPT control system based on the DI-MPC algorithm is characterized by comprising at least two power regulating units, wherein the outputs of the power regulating units are connected in series and are converged on a direct current bus to provide input voltage for a grid-connected inverter, the power regulating units comprise photovoltaic assemblies and power regulators which are connected, and the power regulators are used for acquiring a power-voltage relation and an optimal switching state.

9. The DI-MPC algorithm based photovoltaic DMPPT control system of claim 8, wherein the power regulator topology type is a DC-DC converter.

10. The DI-MPC algorithm-based photovoltaic DMPPT control system of claim 9, wherein the DC-DC converter is a Boost converter.

Technical Field

The invention belongs to the field of photovoltaic power generation, relates to a DMPPT control strategy of a photovoltaic power generation system, and particularly relates to a photovoltaic DMPPT control method and system based on a DI-MPC algorithm.

Background

Under the background of 'carbon peak reaching and carbon neutralization' required by the current country, the photovoltaic power generation has wide development prospect and research significance. However, the normal operation of the conventional centralized photovoltaic power generation system has a severe requirement on the external environmental conditions, but in practical application, the conditions of battery aging, dust coverage, building shielding and the like are unavoidable, and when the photovoltaic module is under the local shielding condition, the output power of the array is greatly reduced, which is called as a mismatch phenomenon. The mismatched photovoltaic modules not only affect the operating efficiency of the whole array, but also can cause hot spot effect, and bring irreversible influence to the photovoltaic modules. In order to solve the problem, bypass diodes are connected in parallel in a photovoltaic module, although the hot spot effect is effectively limited, a plurality of Maximum Power points are brought to the output characteristic of an array, so that the conventional Maximum Power Point Tracking (MPPT) method is misjudged, and the global Maximum Power Point is difficult to track. In addition, the MPPT function of the traditional centralized photovoltaic power generation system is realized by disturbing the output voltage of the photovoltaic array in the grid-connected inverter, that is, the input voltage of the inverter changes violently, which brings a certain burden to the normal operation of the inverter.

In order to overcome the adverse effect of the traditional photovoltaic Power generation system under the condition of local shielding, scholars at home and abroad put forward the concept of a Distributed Maximum Power Point Tracking (DMPPT) photovoltaic Power generation system. The DMPPT photovoltaic power generation system is characterized in that photovoltaic modules are connected with a power regulator, and the photovoltaic modules are matched with a proper MPPT algorithm to realize independent operation of the photovoltaic modules, so that the mismatch phenomenon is effectively avoided. However, the DMPPT strategy proposed by most researchers is only improved on the topology, the MPPT is still realized by the traditional disturbance control, the system efficiency is not effectively improved, and the cost is also increased. In addition, the traditional tracking method mainly applies disturbance to the voltage, so that the voltage on the direct-current bus side changes along with the disturbance, and the stable operation of the grid-connected inverter is influenced. Therefore, how to still realize the maximum power output of the photovoltaic module under the condition of local shielding, ensure that the direct current bus quickly recovers the stable state when the illumination changes, provide stable input for the grid-connected inverter, realize a distributed photovoltaic power generation operation scheme with low cost and high efficiency, and is worthy of deep research.

Disclosure of Invention

The purpose of the invention is as follows: in order to overcome the defects in the prior art, a photovoltaic DMPPT control method and a photovoltaic DMPPT control system based on a DI-MPC algorithm are provided, a DMPPT control strategy of a photovoltaic power generation system under a local shielding condition is formed by a method of combining data interpolation and model predictive control, the problem of photovoltaic power generation system mismatch under local shielding is solved, each photovoltaic assembly keeps maximum power output, the direct-current bus voltage is quickly recovered to a stable state through the provided method, and a stable input condition is provided for a grid-connected inverter.

The technical scheme is as follows: in order to achieve the purpose, the invention provides a photovoltaic DMPPT control method based on a DI-MPC algorithm, which comprises the following steps:

s1: calculating the optimal coefficient of the next moment by acquiring a large number of data points and deducing a relation between power and voltage by using an interpolation method according to the P-U characteristic of the photovoltaic module when the photovoltaic module runs near the MPP;

s2: calculating the photovoltaic output power reference values under two conditions by using the relational expression of the power and the voltage acquired in the step S1, wherein for a photovoltaic module, the output characteristics of the photovoltaic output power reference values are influenced by the external environment, so that the photovoltaic voltage at the next moment makes positive micro-fluctuation on the basis of the voltage at the current moment and the photovoltaic voltage at the next moment makes negative micro-fluctuation on the basis of the voltage at the current moment;

s3: constructing a first cost function by using the power reference value obtained in the step S2 and the actual power value at the current moment, and selecting a photovoltaic voltage reference value at the next moment by comparing the size of the cost function;

s4: establishing a circuit model of the power regulator in two states of on and off, deducing output voltage of the power regulator, and calculating the duty ratio of the power regulator according to a voltage transformation ratio relation;

s5: deducing a predicted value of the power regulator at the next moment of the photovoltaic voltage under two states by utilizing an Euler forward difference formula;

s6: and (4) constructing a second cost function by using the photovoltaic voltage reference value selected in the step (S3) and the voltage predicted value obtained in the step (S5), and determining the switching state of the power regulator by comparing the size of the cost function.

Further, the relation between the power and the voltage in step S1 is specifically as follows:

P_pv(k)＝aV_pv(k)²+bV_pv(k)+c

wherein, a, b and c are the optimal coefficients of the next moment.

Further, the method for calculating the optimal coefficients a, b, and c at the next time in step S1 includes:

further, the first cost function in step S3 includes J₁And J₂：

J_{1,2}＝(P_ref1,2(k+1)-P(k))²

Wherein, P_ref1,2(k +1) is the power reference value, and P (k) is the current output power;

if J₁＞J₂Then the reference voltage at the next time is V_ref1On the contrary, it is V_ref2。

Further, the circuit model in the two states of on and off in step S4 is specifically:

wherein, V_oIs the output voltage of the power regulator, T_sD represents the switching duty ratio of the power regulator, R is a load resistor, and C is an output filter capacitor.

Further, the step S5 is specifically: deriving the ratio of the output voltage of the power regulator to the time according to the KCL law, and deriving the predicted value V of the output voltage of the power regulator at the next moment by an Euler forward difference formula_o,s＝1,0(k +1) at the same timeAnd deducing a predicted value V of the photovoltaic voltage at the next moment according to the voltage conversion ratio relation of the power regulator_pv,s＝1,0(k+1)。

Further, the second cost function in step S6 includes g₁And g₀：

g_{1,0}＝|V_pv,s＝1,0(k+1)-V_ref(k+1)|

If g is₁＜g₀If s is equal to 1, the switch is turned on, otherwise, if s is equal to 0, the switch is turned off.

A photovoltaic DMPPT control system based on a DI-MPC algorithm comprises at least two power regulating units, wherein the outputs of the power regulating units are connected in series and converged on a direct current bus to provide input voltage for a grid-connected inverter, the power regulating units comprise photovoltaic assemblies and power regulators which are connected, and the power regulators are used for obtaining a power-voltage relation and an optimal switching state.

Furthermore, the topological type of the power regulator is a DC-DC converter, the topological structure of the power regulator can be a Boost converter, a Buck-Boost converter and the like, and a flyback converter can also be selected.

The technical strategy based on the DI-MPC mainly comprises two steps: firstly, the relationship between power and voltage is deduced, and secondly, the switch state of the converter is determined. Unlike other MPC techniques, the present invention uses two cost functions, the first of which J is used to select the reference voltage V_refAnd the second cost function g selects the switching state of the converter, so that the prediction effect is more accurate and a PWM (pulse-width modulation) module is not needed.

In the photovoltaic Power generation system, a plurality of photovoltaic components are connected with matched Power regulators in series, and the Power regulators are controlled by a Distributed Maximum Power Point Tracking (DMPPT) algorithm. The DMPPT Control method adopts an algorithm combining Data Interpolation and Model Predictive Control (DI-MPC), obtains a power-voltage relation by an Interpolation method, and generates an optimal switching state of the power regulator by adopting two cost functions in the Model Predictive Control. The invention can realize that the distributed photovoltaic power generation system stably works near the maximum power point under the condition of local shielding, effectively avoids the occurrence of mismatch phenomenon and greatly improves the power generation efficiency of the photovoltaic module. In addition, by means of the DI-MPC algorithm, the prediction effect is more accurate, the use of a PWM (pulse-width modulation) module is omitted, the overall cost is reduced, the method has the characteristic of quick response, the direct-current bus voltage can quickly reach a stable state under the condition of illumination change, a stable input condition is provided for the inverter, and the method has great popularization value and economic benefit.

Has the advantages that: compared with the prior art, the invention has the following advantages:

(1) by adopting the DI-MPC method, the photovoltaic module under the local shielding condition works at the maximum power point, and the mismatch phenomenon is effectively avoided. Meanwhile, the method directly obtains the pulse sequence by comparing the two cost functions, the prediction result is more accurate, a PWM (pulse width modulation) module is omitted, and the cost is reduced.

(2) The power adjusting units are connected in series, the MPPT function directly acts on the DC-DC converter, the burden of the rear-stage inverter is effectively relieved, and the direct-current bus voltage can quickly reach a stable state when the illumination changes by means of the quick dynamic response characteristic of the DI-MPC algorithm.

Drawings

FIG. 1 is a schematic structural diagram of a photovoltaic DMPPT control method and system based on a DI-MPC algorithm according to the present invention;

FIG. 2 is a schematic control diagram of a photovoltaic DMPPT control method and system based on a DI-MPC algorithm according to the present invention;

FIG. 3 is a topology structure diagram of the Boost converter in two switch states;

FIG. 4 is a flow chart of an algorithm of a DI-MPC algorithm based photovoltaic DMPPT control strategy of the present invention;

FIG. 5 is a graph of the output power of the photovoltaic module 1 under sudden illumination based on disturbance control and DI-MPC algorithm control;

FIG. 6 is a graph of the output power of the photovoltaic module 2 under sudden changes in illumination based on disturbance control and DI-MPC algorithm control;

FIG. 7 is a graph of photovoltaic DMPPT DC bus voltage under sudden illumination change based on disturbance control and DI-MPC algorithm control;

FIG. 8 is a graph of the output power of the photovoltaic module 1 under the control of gradual illumination based on disturbance control and DI-MPC algorithm;

FIG. 9 is a graph of the output power of the photovoltaic module 2 under the control of gradual illumination based on disturbance control and DI-MPC algorithm;

FIG. 10 is a diagram of photovoltaic DMPPT DC bus voltage under the condition of controlling gradual illumination change based on disturbance control and a DI-MPC algorithm.

Detailed Description

The present invention is further illustrated by the following figures and specific examples, which are to be understood as illustrative only and not as limiting the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalent modifications thereof which may occur to those skilled in the art upon reading the present specification.

As shown in fig. 1, the present invention provides a photovoltaic DMPPT control system based on a DI-MPC algorithm, that is, a distributed photovoltaic power generation system, in this embodiment, the system includes two power conditioning units, outputs of the power conditioning units are connected in series and are collected on a dc bus to provide an input voltage for a grid-connected inverter, and the power conditioning units include a photovoltaic module and a Boost converter connected to each other.

The present embodiment also provides a computer storage medium storing a computer program that when executed by a processor can implement the method described above. The computer-readable medium may be considered tangible and non-transitory. Non-limiting examples of a non-transitory tangible computer-readable medium include a non-volatile memory circuit (e.g., a flash memory circuit, an erasable programmable read-only memory circuit, or a mask read-only memory circuit), a volatile memory circuit (e.g., a static random access memory circuit or a dynamic random access memory circuit), a magnetic storage medium (e.g., an analog or digital tape or hard drive), and an optical storage medium (e.g., a CD, DVD, or blu-ray disc), among others. The computer program includes processor-executable instructions stored on at least one non-transitory tangible computer-readable medium. The computer program may also comprise or rely on stored data. The computer programs may include a basic input/output system (BIOS) that interacts with the hardware of the special purpose computer, a device driver that interacts with specific devices of the special purpose computer, one or more operating systems, user applications, background services, background applications, and the like.

As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.

The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

Based on the above scheme, in this embodiment, the photovoltaic DMPPT control is performed on the distributed photovoltaic power generation system, and with reference to fig. 4, a specific control method includes the following steps:

the method comprises the following steps: building a distributed photovoltaic power generation system; firstly, different levels of illumination intensity are provided for each photovoltaic module to simulate the local shielding condition in practical application.

Step two: as shown in fig. 2, the photovoltaic voltage V at the current time and the photovoltaic voltage V at the previous two times are collected according to a specified step length_pvCurrent I_pvAnd the converter output voltage V_oK, k-1 and k-2 are respectively used for representing the current time and the previous two times, the P-U relation near the maximum power point is deduced by using the collected data points, and the obtained equation is as follows:

P_pv(k)＝aV_pv(k)²+bV_pv(k)+c

the optimal coefficients a, b, c are calculated by the following method:

step three: it will be appreciated that the reference value for the photovoltaic voltage at the next instant should be such that there is a fluctuation of av, i.e. V, based on the current instant_ref1＝V_pv(k)+ΔV,V_ref2＝V_pv(k) Two conditions of-delta V, and the two conditions of the reference voltage are substituted into the relation P-U to obtain the output power P at the next moment_ref1(k+1),P_ref2(k +1) reference value.

Step four: by P_ref1,2(k +1) and the current output power P (k) to construct a first cost function J₁And J₂，

J_{1,2}＝(P_ref1,2(k+1)-P(k))²

If J₁＞J₂Then the reference voltage at the next time is V_ref1On the contrary, it is V_ref2。

Step five: respectively establishing models for the DC-DC converter in the states of switch conduction and switch off:

wherein, V_oIs the output voltage of the power regulator, T_sD represents the switching duty ratio of the power regulator, R is a load resistor, and C is an output filter capacitor.

The topology of the Boost converter in two switching states is shown in fig. 3. Deducing the ratio of the output voltage of the converter to the time according to the KCL law, and deducing the predicted value V of the output voltage of the converter at the next moment through an Euler forward difference formula_o,s＝1,0(k + 1). Meanwhile, according to the voltage conversion ratio relation of the Boost converter, a predicted value V of the photovoltaic voltage at the next moment is deduced_pv,s＝1,0(k+1)。

Step six: predicting value V according to photovoltaic voltage at next moment_pv,s＝1,0(k +1) and a reference value V_refConstructing a second cost function g₁And g₀：

g_{1,0}＝|V_pv,s＝1,0(k+1)-V_ref(k+1)|

If g is₁＜g₀If s is equal to 1, the switch is turned on, otherwise, if s is equal to 0, the switch is turned off.

Based on the above scheme, in order to verify the effectiveness of the present invention, the present embodiment compares the disturbance control method with the DI-MPC method in the two modes of light mutation and gradual change.

Fig. 5 is the output power of the photovoltaic module 1 under the sudden change of illumination, and fig. 6 is the output power of the photovoltaic module 2, and it can be seen from the two graphs that when the output power reaches the steady state by adopting the disturbance control method, the power has obvious waveform oscillation, and the output power can stably converge to the MPP by adopting the DI-MPC method. Furthermore, it can be seen from the DC bus voltage waveform of FIG. 7 that the bus voltage has a significantly faster dynamic response speed under DI-MPC control than under disturbance control. Fig. 8 and 9 show the output powers of the photovoltaic module 1 and the module 2 under gradual illumination change, which shows that the output power still rapidly converges to the MPP under the control of the DI-MPC; FIG. 10 shows the DC bus voltage, which changes more smoothly under the control of the DI-MPC and has waveform oscillation under the control of disturbance when the illumination is gradually changed.