CN201937327U - Photovoltaic power generation control system - Google Patents

Abstract

The utility model relates to a string type photovoltaic power generation control system, comprising: a main controller of the system and at least two photovoltaic DC components; each photovoltaic DC component includes a solar cell module, a photovoltaic slave controller and a storage battery module, and the photovoltaic slave In order to track the maximum power point of the solar cell module and make the DC voltage output by the solar cell module charge and discharge the battery module, at least two battery modules are connected in series to output high-voltage DC voltage; the main controller of the system includes a control unit and an inverter unit, the control unit is used to control the inverter unit to invert the high-voltage DC voltage, and monitor each photovoltaic DC module in real time, and switch the abnormal solar cell module and/or battery module in real time. Implementing the technical solution of the utility model, a plurality of photovoltaic DC modules are connected in series to form a high-voltage DC power supply, which directly performs DC/AC inversion, saves the traditional step-up transformer, and improves the energy conversion efficiency of the photovoltaic power generation system.

Description

A photovoltaic power generation control system

technical field

The utility model relates to the technical field of solar energy, in particular to a photovoltaic power generation control system.

Background technique

Solar energy is inexhaustible and inexhaustible, and it is an ideal energy source for human beings. As early as more than 100 years ago, Einstein discovered the photoelectric effect, which provided a theoretical basis for human beings to use solar energy. In 1954, Bell Laboratories of the United States developed a monocrystalline silicon solar cell with a photoelectric conversion efficiency of 4.5%, making the human dream of directly using solar energy to generate electricity a reality. Since entering the 21st century, the United States, Japan, Germany, etc. have formulated support policies and development plans, and the photovoltaic industry has shown a booming situation. The rapid development of the photovoltaic industry is rare in modern industries, even surpassing the semiconductor industry, which is known for its rapid development. In the near future, it will be the main energy consumption component in the world, which is enough to change the current consumption structure with oil and coal as the main energy.

However, the existing photovoltaic power generation control system has low efficiency and complex structure.

Utility model content

The technical problem to be solved by the utility model is to provide a photovoltaic power generation control system with high efficiency and simple structure for the defects of low efficiency and complex structure of the photovoltaic power generation control system in the prior art.

The technical solution adopted by the utility model to solve the technical problem is: to construct a photovoltaic power generation control system, including: the main controller of the system and at least two photovoltaic DC components; wherein,

Each photovoltaic DC assembly includes a solar cell module, a storage battery module, and is connected to the solar cell module and the storage battery module, and is used to track the maximum power point of the solar cell module and make the output DC voltage of the solar cell module equal to the A photovoltaic slave controller for charging and discharging the battery module, and the battery modules in the at least two photovoltaic DC components are connected in series;

The main controller of the system includes an inverter unit and is connected to the inverter unit and the photovoltaic slave controller, and is used to control the inverter unit to invert the high-voltage DC voltage, and monitor each photovoltaic DC module in real time and detect abnormalities in real-time switching control unit for solar cell modules and/or battery modules.

In the photovoltaic power generation control system of the present invention, the control unit is connected to the photovoltaic slave controller in one of the following ways: RS485 bus, RS232 bus, RS422 bus.

In the photovoltaic power generation control system described in the utility model, the battery module includes at least two batteries, and the at least two battery groups are connected in series.

In the photovoltaic power generation control system described in the present invention, the photovoltaic DC assembly further includes a switch matrix connected to the photovoltaic slave controller and the battery module and used to switch the abnormal battery module.

In the photovoltaic power generation control system described in the present invention, the photovoltaic power generation control system also includes an AC load, an AC power supply and a switching device, the first input end of the switching device is connected to the AC power supply, and the second input terminal of the switching device The input end is connected to the output end of the inverter unit, the output end of the switching device is connected to an AC load, and the control end of the switching device is connected to the control unit.

In the photovoltaic power generation control system described in the utility model, the photovoltaic power generation control system further includes a DC load connected to the storage battery module.

Implementing the technical solution of the utility model has the following beneficial effects:

1. Multiple photovoltaic DC modules are connected in series to form a high-voltage DC power supply, which directly performs DC/AC inversion, eliminating the traditional step-up transformer and improving the energy conversion efficiency of the photovoltaic power generation system;

2. The main controller of the system performs full-duplex communication with the photovoltaic DC components to realize distributed control;

3. Photovoltaic power generation and mains power can be switched automatically, and the real-time working status of the system can be monitored online;

4. The abnormal solar cell components and storage battery components can be switched in real time by the switch matrix.

Description of drawings

The utility model will be further described below in conjunction with accompanying drawing and embodiment, in the accompanying drawing:

Fig. 1 is a structural schematic diagram of the first embodiment of the photovoltaic power generation control system of the present invention;

Fig. 2 is a partial structural schematic diagram of the first embodiment of the photovoltaic power generation control system of the present invention;

Fig. 3 is the graph of voltage and current and time of storage battery of the present utility model;

Fig. 4 is a photovoltaic curve diagram of Embodiment 1 of tracking the maximum power point of the solar cell module of the present invention;

Fig. 5 is a photovoltaic curve diagram of the second embodiment of tracking the maximum power point of the solar cell module of the present invention.

Fig. 6 is a flow chart of the third embodiment of tracking the maximum power point of the solar cell module of the present invention.

Detailed ways

As shown in Figure 1, in the first embodiment of the photovoltaic power generation control system of the present invention, the system mainly includes two photovoltaic DC components 110, a system main controller 120, an RS485 bus 130, a switching device 140, an AC power supply 150, AC load 160 and DC load 170 . Wherein, each photovoltaic DC assembly includes a solar cell module 111, a photovoltaic slave controller 112, and a battery module 113, and the photovoltaic slave controller 112 is used to track the maximum power point of the solar cell module 111 and make the output DC voltage of the solar cell module 111 To charge and discharge the battery module 113 , the battery modules 113 in the two photovoltaic DC assemblies 110 are connected in series (not shown) to output a high-voltage DC voltage. The main controller 120 of the system includes a control unit 122 and an inverter unit 121, wherein the control unit 122 is used to control the inverter unit 121 to invert the high-voltage DC voltage outputted by the series connection of multiple battery modules 113, and transmit the voltage through the RS485 The bus 130 is connected with the photovoltaic slave controller 112 for real-time monitoring of each photovoltaic DC module 110 and real-time switching of abnormal solar cell modules 111 and/or battery modules 113 .

In addition, the control unit 122 enables the inverter voltage output by the inverter unit 121 or the AC power source 150 to supply power to the AC load 160 by controlling the switching state of the switching device 140 . The DC voltage output by the battery module 113 supplies power to the DC load 170 .

First of all, it should be noted that the term "series connection" mentioned in this application refers to a series-parallel connection, where the voltage is increased in series and the current is increased in parallel.

In addition, it should be noted that although FIG. 1 only shows two photovoltaic direct current modules 110 , the present invention is not limited to two, and may be other numbers of more than two. In addition, the present invention is not limited to the RS485 bus connecting the control unit 122 and the photovoltaic slave controller 112, and may also be an RS485 bus, an RS232 bus, or an RS422 bus.

Fig. 2 is a partial structural diagram of the first embodiment of the photovoltaic power generation control system of the present invention. Compared with the first embodiment, the photovoltaic DC module 110 in this embodiment also includes a battery charging and discharging module 115 and a switch matrix 114, and the photovoltaic slave controller 112 switches the abnormal battery module 113 by controlling the switch state of the switch matrix 114 . When the storage battery module 113 is normal, the photovoltaic slave controller 112 makes the DC voltage output by the solar battery module (not shown) charge and discharge the storage battery module 113 by controlling the storage battery charging and discharging module 115. The battery module 113 includes at least two batteries connected in series.

In this embodiment, when the photovoltaic slave controller 112 detects an abnormality of a battery component online, it switches the corresponding battery pack 113 in time by controlling the switch matrix 114 to meet the DC load requirements of the system, and informs the system master through the RS485 bus 130 The controller 120 adjusts the inverter unit 121 in real time to meet the requirements of the AC load of the system.

Traditional battery charging adopts simple strategies such as constant voltage or constant current charging, which takes a long time and has low efficiency. Due to the different sunshine intensity and temperature changes in different seasons, the battery is prone to undercharging. In order to prevent the battery from being undercharged, the battery group is divided into several groups with smaller capacity, and the photovoltaic slave controller 120 controls the switch matrix 114 to charge different battery modules 113 in a cycle, so that each group reaches a fully charged state. The current provided by the solar battery module 111 does not exceed the maximum allowable charging current of each group of batteries and the discharge current of each group of batteries to the load is controlled individually at the discharge rate of the capacity recommended by the battery manufacturer. In order to avoid oscillation during the charging process, the transmission characteristic of the charging control circuit is in the form of hysteresis, and the discharge control wire is used to control the discharge depth of the battery to prolong its service life.

The system includes four charging stages: trickle current, constant current, overvoltage, and float charge, as shown in Figure 3, in which, when the voltage of the battery is lower than the set threshold voltage V _ch , trickle charge is performed with the current I _ir (T0~T1); when the battery voltage gradually rises to V _ch , the current I _bulk is used for constant current charging (T1~T2); the battery capacity increases rapidly until the battery voltage rises to a constant voltage slightly higher than the rated voltage of the battery V _oc enters the overvoltage charging stage (T2~T3), and the charging current gradually decreases; when the charging current gradually decreases to I _oct , the battery is fully charged and enters the float charging stage (T3~). At this stage, the system provides a constant temperature-compensated voltage V _f to the battery to maintain the capacity of the battery, and at the same time provides a small floating charge current to compensate for the capacity loss caused by the self-discharge of the battery. When the storage battery drops to 90% of V _oc due to the usage voltage, the system automatically enters the state of trickle charging or constant current charging.

Fig. 4 and Fig. 5 are respectively the photovoltaic graphs of embodiments 1 and 2 of the utility model tracking the maximum power point of the solar cell module. Perform maximum power point tracking (MPPT) on solar cells. The purpose of solar cell MPPT is to find the maximum value of the curve on the P-V characteristic curve shown in Figure 4 and Figure 5. Commonly used MPPT methods are: constant voltage tracking (CVT), perturbation and observation (P&O), incremental conductance (IncCond), etc.

The constant voltage method regards the maximum power output point of the photovoltaic cell as a constant voltage output, which greatly simplifies the realization of MPPT, but this method ignores the influence of temperature on the open circuit voltage of the photovoltaic cell, and its accuracy and adaptability are relatively low. Poor, especially not conducive to use in areas with drastic temperature changes in the morning and evening and four seasons; the disturbance observation method constantly disturbs the operating point of the solar photovoltaic power generation system to find the direction of the maximum power point, the tracking method is simple, the sensor accuracy is not high, and the disturbance There are few parameters, but its output power is easy to oscillate near the maximum power point of the photovoltaic array, and it has the disadvantage that it is difficult to set the tracking step size to take into account the tracking accuracy and response speed; Good tracking performance, when the irradiance and temperature change, the output voltage of the solar cell array can smoothly follow the change of the environment, and the output voltage swing is small. However, this algorithm also has the situation that the setting of the step size is difficult to balance the tracking accuracy and response speed. Optimal Gradient is a numerical calculation method for gradient-based multidimensional unconstrained optimization problems.

Fig. 6 is a flow chart of the third embodiment of tracking the maximum power point of the solar cell module of the present invention. Since the terminal voltage of the solar cell is bounded, the maximum power point searched must be global when the gradient method is applied to MPPT. For this reason, the utility model also proposes the conductance incremental method based on the optimal gradient, dynamically changes the step size of the MPPT through the optimal gradient, and takes into account the tracking accuracy and response speed of the MPPT, so as to solve the problem caused by the improper setting of the fixed step size. Low work efficiency and other issues, the method specifically includes the following steps:

A. Sampling the current voltage and current output by the solar cell module;

B. Calculate the current voltage change, current current change, current conductance, current conductance change, and current power change based on the current voltage, current current, previous voltage, and previous current, and calculate the current power change based on the current power change Calculate the current gradient with the current voltage variation;

C. multiplying the gradient with a preset proportional coefficient to obtain a voltage change value;

H. Judging whether the absolute value of the current voltage variation is zero, if so, then perform step D; if not, then perform step I;

D. Judging whether the absolute value of the current current variation is zero, if so, then return; if not, then perform step E;

E. Determine whether the current current variation is greater than zero, if so, execute step F; if not, execute step G;

F. Add the current voltage to the voltage change value, and then return;

G. Subtract the voltage change value from the current voltage, and then return;

I. judge whether the absolute value of current power variation is zero, if so, then return; If not, then execute step J;

J. Determine whether the current conductance variation is equal to the current conductance, if so, return; if not, perform step K;

K. Determine whether the current conductance variation is greater than the current conductance, if yes, execute step F; if not, execute step G.

It should be noted that, in FIG. 6 , |dP _k |<ε ₁ , |dU _k |<ε ₂ , |dI _k |<ε ₃ are regarded as the case where dP _k , dU _k , and dI _k are approximately equal to zero.

In this method, assuming that the positive gradient is g _k , the iterative algorithm of the gradient method can be defined as:

X _k+1 ＝X _k +a _k g _k (1)

Among them, a _k is a non-negative constant, and the maximum point of the search function is always searched along the direction of g _k .

According to the electrical characteristics of the solar cell, ignoring the effect of its series resistance, the relationship between the output power P and the output voltage U of the solar cell can be obtained from formula (1):

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; sc</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{\frac{\mathrm{<span\; class="notranslate">\; wxya</span>}}{\mathrm{<span\; class="notranslate">\; AKT</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

P _PV is a first-order continuous differentiable nonlinear function, and U _PV is used as the only variable, and its gradient with respect to U _PV is calculated:

${\mathrm{<span\; class="notranslate">\; g</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; g</span>}}_{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; dP</span>}}_{\mathrm{<span\; class="notranslate">\; PV</span>}}}{{\mathrm{<span\; class="notranslate">\; U</span>}}_{\mathrm{<span\; class="notranslate">\; PV</span>}}}{<span\; class="notranslate">\; |</span>}_{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; PV</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; sc</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{\frac{\mathrm{<span\; class="notranslate">\; wxya</span>}}{\mathrm{<span\; class="notranslate">\; AKT</span>}}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\frac{\mathrm{<span\; class="notranslate">\; wxya</span>}}{\mathrm{<span\; class="notranslate">\; AKT</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{\frac{\mathrm{<span\; class="notranslate">\; wxya</span>}}{\mathrm{<span\; class="notranslate">\; AKT</span>}}}<span\; class="notranslate">\; )</span>{<span\; class="notranslate">\; |</span>}_{\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

The voltage iterative formula based on the optimal gradient is obtained from formulas (1) and (3):

U _k+1 =U _k +a _k g _k (4)

On this basis, assuming the maximum power point voltage of the solar cell is U _m , from P=UI:

$\frac{\mathrm{<span\; class="notranslate">\; dP</span>}}{\mathrm{<span\; class="notranslate">\; U</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; u</span>}\frac{\mathrm{<span\; class="notranslate">\; dI</span>}}{\mathrm{<span\; class="notranslate">\; U</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

Therefore, when dP/dU>0, U<U _m , dI/dU>-I/U; when dP/dU<0, U>U _m , dI/dU<-I/U; when dP/dU =0, U=U _m , dI/dU=-I/U.

If dU=0, dI=0, the maximum power point is found, and the operating point of the photovoltaic power generation system does not need to be adjusted. If dU=0, dI≠0, the system reference voltage U _r is adjusted according to the positive or negative of dI. If dU≠0, adjust the operating point voltage according to the relationship between dI/dU and -I/U to achieve maximum power point tracking.

When the operating point is far away from the maximum power point, the operating point voltage will change in a large range; when the operating point is close to the maximum power point, the operating point voltage will change in a small range; when the operating point is at the maximum power When you click to the left, the system will increase the operating point voltage, and vice versa, it will decrease the operating point voltage. When the operating point is very close to the maximum power point, because the slope is very small, the operating point is stabilized within this very small range and considered as the maximum power point.

The output voltage at the maximum power point of the solar cell is about 75% of the open circuit voltage U _oc . If the output voltage of the solar cell is directly set to 75% of U _oc when the system is started, the operating point will be near the maximum power point from the very beginning. , that is, the CVT startup mode is adopted, and the system automatically switches to the conductance incremental method based on the optimal gradient for MPPT control after entering the vicinity of the maximum power point, which can effectively increase the speed of entering the steady state. Wherein, |dP _k |<ε ₁ , |dU _k |<ε ₂ , |dI _k |<ε ₃ are regarded as the case where dP _k , dU _k , and dI _k are approximately equal to zero. If dP _k =0, dU _k =dI _k =0, or ΔG=G, the solar cell output is at the maximum power point; otherwise, according to the relationship between ΔG and G, it is judged that the operating point is on the left side of the maximum operating point or is the right side to adjust the operating point voltage. When dU _k is equal to zero and dI _k is not equal to zero, then according to whether dI _k is greater than zero, the operating point voltage is increased or decreased to find and reach the maximum power point.

The above descriptions are only preferred embodiments of the utility model, and are not intended to limit the utility model. For those skilled in the art, the utility model can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present utility model shall be included within the scope of the claims of the present utility model.

Claims (6)

1. A photovoltaic power generation control system, characterized in that it includes: a system main controller and at least two photovoltaic DC components; wherein, Each photovoltaic DC assembly includes a solar cell module, a storage battery module, and is connected to the solar cell module and the storage battery module, and is used to track the maximum power point of the solar cell module and make the output DC voltage of the solar cell module equal to the A photovoltaic slave controller for charging and discharging the battery module, and the battery modules in the at least two photovoltaic DC components are connected in series; The main controller of the system includes an inverter unit and is connected to the inverter unit and the photovoltaic slave controller, and is used to control the inverter unit to invert the high-voltage DC voltage, and monitor each photovoltaic DC module in real time and detect abnormalities in real-time switching control unit for solar cell modules and/or battery modules. 2. The photovoltaic power generation control system according to claim 1, wherein the control unit is connected to the photovoltaic slave controller in one of the following ways: RS485 bus, RS232 bus, RS422 bus. 3. The photovoltaic power generation control system according to claim 1, wherein the battery module includes at least two batteries, and the at least two battery groups are connected in series. 4 . The photovoltaic power generation control system according to claim 3 , wherein the photovoltaic DC assembly further includes a switch matrix connected to the photovoltaic slave controller and the battery module and used to switch the abnormal battery module. 5. The photovoltaic power generation control system according to any one of claims 1 to 4, characterized in that, the photovoltaic power generation control system also includes an AC load, an AC power supply, and a switching device, and the first input end of the switching device is connected to AC power supply, the second input terminal of the switching device is connected to the output terminal of the inverter unit, the output terminal of the switching device is connected to an AC load, and the control terminal of the switching device is connected to the control unit. 6. The photovoltaic power generation control system according to claim 5, characterized in that, the photovoltaic power generation control system further comprises a DC load connected to the storage battery module.

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