阅读说明：本技术 一种无需外接传感器的光伏组件积雪自动检测电路、方法 (Photovoltaic module accumulated snow automatic detection circuit and method without external sensor ) 是由 郑佳楠 刘�文 陈方才 凡流露 陈宇轩 张昕昱 于 2021-08-26 设计创作，主要内容包括：本发明涉及光伏运维技术领域,公开了一种无需外接传感器的光伏组件积雪自动检测电路、方法,用于检测光伏组件上是否存在积雪；本发明在改进型的Buck-Boost电路和继电器矩阵网络的电路设计基础上,通过基于MPPT思想的控制算法检测各光伏组串在当前辐照强度下的最大输出功率或通过调整PWM信号的占空比测量各光伏组串的短路电流,并通过参考光照传感器测量当前阳光辐照状态的参考值判断此时待检测光伏组串是否被积雪覆盖以及被积雪覆盖的程度,无需在光伏系统上外接传感器即可实现精准的积雪自动检测,改造成本低廉。(The invention relates to the technical field of photovoltaic operation and maintenance, and discloses a photovoltaic module accumulated snow automatic detection circuit and method without an external sensor, which are used for detecting whether accumulated snow exists on a photovoltaic module; on the basis of the circuit design of an improved Buck-Boost circuit and a relay matrix network, the maximum output power of each photovoltaic string under the current irradiation intensity is detected through a control algorithm based on the MPPT idea or the short-circuit current of each photovoltaic string is measured by adjusting the duty ratio of a PWM signal, and whether the photovoltaic string to be detected is covered by snow and the degree of the coverage of the snow is judged by measuring the reference value of the current sunlight irradiation state through a reference illumination sensor.)

1. The utility model provides a need not external sensor's photovoltaic module snow automated inspection circuit for whether there is snow on the detection photovoltaic module, its characterized in that includes:

at least one photovoltaic module which is connected in series in sequence;

the Buck-Boost circuit comprises a controllable switch controlled by a PWM signal, an input end connected with the photovoltaic module and an output end;

the current and voltage detection module is used for measuring the voltage and the current of the input end and the output end of the Buck-Boost circuit;

a reference light irradiation sensor for measuring the current solar light irradiation intensity I_RefAnd deducing kSI the maximum output power of the uncovered photovoltaic module through a coefficient related to the placing inclination angle and the number of the photovoltaic modules_RefWherein k is a proportionality coefficient, and S is a coefficient related to the total light receiving area of the reference illumination sensor and the current photovoltaic module to be detected;

the relay matrix network is used for respectively connecting different photovoltaic modules to the input end of the Buck-Boost circuit through relays;

the control chip is connected with the controllable switch, and the output voltage of the photovoltaic module connected to the input end of the Buck-Boost circuit is globally scanned from small to large in a voltage domain by changing the duty ratio of the PWM signal to obtain the maximum output power P of the photovoltaic module in the current load state and the irradiation state_x(ii) a By comparing P_xAnd kSI_RefThe snow cover degree on the photovoltaic module is judged according to the size of the snow cover.

2. The photovoltaic module snow cover automatic detection circuit without an external sensor according to claim 1, characterized in that: the Buck-Boost circuit comprises an IN + end, a COM end and an OUT-end, wherein the IN + end and the COM end form an input end of the Buck-Boost circuit, and the COM end and the OUT-end form an output end of the Buck-Boost circuit; the voltage at the input end has the opposite polarity with the voltage at the output end.

3. The photovoltaic module snow cover automatic detection circuit without an external sensor according to claim 2, characterized in that: the IN + end is connected with the anode of each photovoltaic assembly through a relay, and the COM end is connected with the cathode of each photovoltaic assembly through a relay; the relay matrix network formed by the relays can connect different photovoltaic modules to the input end of the Buck-Boost circuit; the COM terminal and the OUT-terminal are connected with a load.

4. The photovoltaic module snow cover automatic detection circuit without an external sensor according to claim 2, characterized in that: the N photovoltaic modules are sequentially connected IN series, N is more than or equal to 2, the IN + end is connected with the anode of each photovoltaic module through a relay, the COM end is connected with the cathode of each photovoltaic module through a relay, and the OUT-end is connected with the cathode of each photovoltaic module from the second through a relay; the relay matrix network formed by the relays can connect different photovoltaic modules to the input end or the output end of the Buck-Boost circuit.

5. The photovoltaic module snow cover automatic detection circuit without an external sensor according to claim 2, characterized in that: the photovoltaic module heating system comprises heating loads arranged on the back of each photovoltaic module, wherein the heating loads are connected to the output end of a Buck-Boost circuit or connected with commercial power.

6. The photovoltaic module snow cover automatic detection circuit without an external sensor according to claim 1, characterized in that: all the photovoltaic modules jointly form a photovoltaic system; the accumulated snow automatic detection circuit comprises a photovoltaic inverter connected with a mains supply and a relay used for controlling the on-off of the photovoltaic inverter and a photovoltaic system.

7. The photovoltaic module snow cover automatic detection circuit without an external sensor according to claim 1, characterized in that: the reference illumination sensor comprises any one of a miniature silicon photocell, a photoelectric detector, an illuminometer, a small photovoltaic module and a photovoltaic module with a conventional size.

8. The utility model provides a need not external sensor's photovoltaic module snow automated inspection circuit for whether there is snow on the detection photovoltaic module, its characterized in that: replacing the photovoltaic module in the automatic snow detection circuit of any one of claims 1-7 with a string of photovoltaic modules; each photovoltaic group string comprises at least one photovoltaic assembly; when the photovoltaic group string comprises a plurality of photovoltaic components, the photovoltaic components are sequentially connected in series, the anode of the first photovoltaic component is the anode of the photovoltaic group string, and the cathode of the last photovoltaic component is the cathode of the photovoltaic group string.

9. The method for detecting the automatic detection circuit of the snow cover of the photovoltaic module without the external sensor according to claim 8, when the current input to the photovoltaic inverter is smaller than a set threshold and the irradiation intensity of the sunlight obtained by the reference illumination sensor is greater than the threshold, the photovoltaic string N is connected to the input end of the Buck-Boost circuit through the relay matrix network, and the following steps are performed on the photovoltaic string N:

the duty ratio of the PWM signal is gradually increased from 0 by a set large step;

recording the output power of the input end of the Buck-Boost circuit, namely the output power of the photovoltaic string N after the duty ratio of the PWM signal is changed every time; comparing the current power with the power obtained under the previous duty ratio, and if the current power is higher, recording and refreshing the duty ratio, the power and the voltage corresponding to the current power; if the power is lower, no processing is carried out;

when the duty ratio is increased to 1 or increased to X, finishing global optimization to obtain the duty ratio, power and voltage corresponding to the maximum power region in the global range; wherein X is more than 0.8 and less than 1;

increasing the perturbation by taking the duty ratio of the PWM signal of the maximum power area obtained in the global range as the center, and recording the power after the perturbation is increased;

if the power is larger than that before the perturbation is increased, the maximum power point is in the direction of increasing the perturbation, and the perturbation is continuously increased in the direction;

if the power is reduced compared with that before the perturbation is increased, the maximum power point is in the opposite direction of the increase of the perturbation, and the perturbation is increased again after the sign of the perturbation is changed;

when the direction of the perturbation changes twice, the maximum power point under the current load and the irradiation state is found in the local range, and the maximum output power P of the photovoltaic string corresponding to the maximum power point is returned_xThe duty ratio of the PWM signal and the voltage of the input end of the Buck-Boost circuit;

current sun measured with reference illumination sensorCalculating the maximum output power kSI of the uncovered photovoltaic string under the current sunlight irradiation intensity on the basis of the light irradiation intensity value_Ref；

Comparison P_xAnd kSI_RefIf P is_x≤x·kSI_RefIf x is a proportionality coefficient, the photovoltaic string N is covered by the accumulated snow;

n is N +1, namely, the next group of photovoltaic groups are connected to the input end of the Buck-Boost circuit in series through a relay matrix network;

and repeating the steps until the accumulated snow detection of all the photovoltaic group strings is completed.

10. The method for detecting the automatic detection circuit of the snow cover of the photovoltaic module without an external sensor according to claim 9, is characterized in that: setting an increasing series a_n}; if a is_n·kSI_Ref＜P_x≤a_n+1·kSI_RefAnd if n is larger than or equal to 1, the snow cover grade of the photovoltaic string to be detected is n, and the snow cover thickness corresponding to the grade n is larger than that corresponding to the grade n + 1.

11. The method for detecting the automatic detection circuit of the snow cover of the photovoltaic module without the external sensor according to claim 8, when the current input to the photovoltaic inverter is smaller than a set threshold and the irradiation intensity of the sunlight obtained by the reference illumination sensor is greater than the threshold, the photovoltaic string N is connected to the input end of the Buck-Boost circuit through the relay matrix network, and the following steps are performed on the photovoltaic string N:

controlling the duty ratio of the PWM signal to be 1, and measuring the short-circuit current I of the photovoltaic string N_SC；

Calibrating to obtain a current threshold I for judging the accumulated snow degree of the photovoltaic string N based on the current sunlight irradiation intensity value measured by the reference illumination sensor₀；

If I_SC≤y·I₀If y is a proportionality coefficient, the photovoltaic string N is covered by the accumulated snow;

n is N +1, namely, the next group of photovoltaic groups are connected to the input end of the Buck-Boost circuit in series through a relay matrix network;

and repeating the steps until the accumulated snow detection of all the photovoltaic group strings is completed.

12. The method for detecting the automatic detection circuit of the snow cover of the photovoltaic module without an external sensor according to claim 11, is characterized in that: setting an increasing number series b_n}; if b is_n·I₀＜I_SC≤b_n+1·I₀And if n is larger than or equal to 1, the snow cover grade of the photovoltaic string to be detected is n, and the snow cover thickness corresponding to the grade n is larger than that corresponding to the grade n + 1.

Technical Field

The invention relates to the technical field of photovoltaic operation and maintenance, in particular to a photovoltaic module accumulated snow automatic detection circuit and method without an external sensor.

Background

The global economic center of gravity is located in high latitude areas in the northern hemisphere, such as the united states, china, japan, germany, uk, france, canada, etc., where the enormous energy consumption and carbon emissions pressures from energy conversion also create a huge photovoltaic market. According to statistics of the international energy agency IEA, by the end of 2019, the global photovoltaic accumulated loading amount reaches 623GW, which is equivalent to the total loading power of 28 three gorges dams, and the market scale is 9 billion yuan, wherein the photovoltaic loading amount of China, America, Japan and Germany accounts for 63.1% of the whole world. However, in the middle and high latitude areas, the photovoltaic system can be influenced by the accumulated snow in winter, so that the photovoltaic system cannot generate electricity efficiently, 90% -100% of expected generated energy is lost, which accounts for about 25% of annual generated energy, and the risk of building collapse is increased due to the excessive accumulated snow on the roof.

The existing automatic detection mode of the accumulated snow of the photovoltaic module mainly comprises the following steps: the snow detection method comprises the steps of detecting the snow accumulation condition on the surface of a photovoltaic panel by using a pressure sensor, judging the snow accumulation condition by using an ultrasonic/laser/infrared light sensor and a receiver in a pairing mode and judging whether a signal can be successfully received by the receiver, and identifying an image or a color by using a vision sensor to detect the snow accumulation and the thickness of the snow accumulation.

The automatic detection method for the accumulated snow of the photovoltaic module depends on an additional sensor, in order to accurately judge the accumulated snow condition of the photovoltaic module, for example, a pressure sensor is required to be arranged on each photovoltaic module according to the scheme of the pressure sensor, and the reconstruction cost is huge for an installed roof photovoltaic system or a large-scale ground photovoltaic power station; the scheme of matching the ultrasonic/laser/infrared light sensor and the receiver needs accurate matching of the transmitter and the receiver, misjudgment is easy to occur, the precise sensing structure has high cost and frequent operation and maintenance requirements, and the defect of high modification cost of the existing photovoltaic system also exists; the snow detection scheme based on the visual method requires a relatively more expensive visual/color sensor, and simultaneously requires a high-performance processor capable of processing variable image information in a shorter time, or relies on massive data/calibrated picture sets to complete machine learning training to improve the judgment accuracy.

Generally, the automatic snow detection scheme disclosed at present has the defects of high reconstruction cost, high maintenance cost and high initial investment cost. In view of the above, the invention provides a photovoltaic module accumulated snow automatic detection circuit and method without an external sensor, which can realize accurate photovoltaic module accumulated snow automatic detection on the premise of meeting the requirements of low reconstruction cost, low maintenance cost and low initial investment.

Disclosure of Invention

In order to solve the technical problems, the invention provides a photovoltaic module accumulated snow automatic detection circuit and method without an external sensor.

In order to solve the technical problems, the invention adopts the following technical scheme:

the photovoltaic module, i.e. the photovoltaic panel, is usually a sandwich structure, and mainly comprises eight main materials, i.e. photovoltaic glass, a solar cell, a back plate, a frame, an EVA (ethylene vinyl acetate) adhesive film, a welding strip, a junction box and the like, wherein the core is the solar cell. The solar cell is essentially a large area PN junction diode with the same properties as a silicon photovoltaic cell. In dark environment, the solar cell is equivalent to a common diode, and the volt-ampere characteristic is as follows:

in the formula I_dFor the current flowing through the PN junction, also known as dark current, I₀Is reverse saturation current, q is electron charge, k_BIs the boltzmann constant, T is the absolute temperature, and U is the voltage across the PN junction. For an applied forward voltage, I increases exponentially with U and is called forward current; when the applied voltage is reverse, the reverse saturation current is substantially constant within the reverse breakdown voltage.

When a silicon photocell receives illumination, incident photons excite bound electrons in a valence band to a conduction band according to a photovoltaic effect, excited electron-hole pairs float to an N-type region and a P-type region respectively under the action of an internal electric field, and when loads are applied to two ends of a PN junction, namely two ends of a solar cell piece, photoproduction current flows through the loads, wherein the flowing current is as follows:

in the formula I_phIs the photo-generated current which is proportional to the intensity of the incident light, and the proportionality coefficient of the photo-generated current is related to the size of the load resistance and the structural characteristics of the silicon photocell.

When the silicon photocell is in a short circuit state (U ═ 0), the short circuit current is: i is_SC＝I_ph(ii) a When the silicon photocell is in an open circuit state (I ═ 0), the open circuit voltage is:

as shown in fig. 2, the voltammetry curves of a solar cell, i.e., a silicon photovoltaic cell, under different illumination intensities are shown, the short-circuit current of the silicon photovoltaic cell is linearly related to the illumination intensity, and the open-circuit voltage is logarithmically related to the illumination intensity.

When we examine the output power of the silicon photocell (i.e. the rectangular area enclosed by any working point and two coordinate axes on the volt-ampere characteristic curve), it is found that the loads applied to the two ends of the silicon photocell are different, the output power is different, and a maximum output power point exists. As shown in fig. 3, when the load of the solar cell is constant, the output power of the cell will change correspondingly with the change of the voltage across the solar cell, and there is a maximum output power point, which can represent the illumination intensity of the current solar cell. Based on the experimental conclusion, the maximum output power of the silicon photocell is in a linear relationship with the illumination intensity, as shown in fig. 4. Therefore, starting from the physical principle, two schemes can accurately detect the irradiance received by the photovoltaic module, and then accurately deduces the snow coverage degree of the photovoltaic module: firstly, detecting the accumulated snow degree by using the short-circuit current of the photovoltaic module; and secondly, detecting the accumulated snow degree by using the maximum output power of the photovoltaic module.

Based on the physical principle and experimental conclusion, the invention provides the photovoltaic assembly accumulated snow automatic detection circuit and method without an external sensor by combining an improved Buck-Boost circuit, a control algorithm based on the MPPT idea and a relay matrix network, so as to solve the problem of accurate accumulated snow detection of the photovoltaic assembly.

The utility model provides a need not external sensor's photovoltaic module snow automated inspection circuit for whether there is snow on the detection photovoltaic module, include:

at least one photovoltaic module which is connected in series in sequence;

the Buck-Boost circuit comprises a controllable switch controlled by a PWM signal, an input end connected with the photovoltaic module and an output end;

the current and voltage detection module is used for measuring the voltage and the current of the input end and the output end of the Buck-Boost circuit;

a reference light irradiation sensor for measuring the current solar light irradiation intensity I_RefAnd deducing kSI the maximum output power of the uncovered photovoltaic module through a coefficient related to the placing inclination angle and the number of the photovoltaic modules_RefWherein k is a proportionality coefficient, and S is a coefficient related to the total light receiving area of the reference illumination sensor and the current photovoltaic module to be detected;

the relay matrix network is communicated with each photovoltaic string to control the serial numbers of the photovoltaic strings connected to the input end and the output end of the Buck-Boost circuit; and controlling whether the photovoltaic string is connected with the photovoltaic inverter or not. The relay matrix network is a mesh circuit structure consisting of relays, and can realize that each photovoltaic group string is freely connected to the input end or the output end of the Buck-Boost circuit along with the promotion of an automatic snow accumulation detection method and a snow removal process;

the control chip is connected with the controllable switch, and the output voltage of the photovoltaic module connected to the input end of the Buck-Boost circuit is globally scanned from small to large in a voltage domain by changing the duty ratio of the PWM signal to obtain the maximum output power P of the photovoltaic module in the current load state and the irradiation state_x(ii) a By passingComparison P_xAnd kSI_RefThe snow cover condition and the coverage degree on the photovoltaic module are judged. The control chip receives signals from the current and voltage detection module to judge the accumulated snow condition and degree, controls the circuit state of the relay matrix network, outputs PWM signals to the controllable switch in the Buck-Boost circuit, and controls the start and stop of the photovoltaic snow removal device; in the invention, a control algorithm based on MPPT idea runs in a control chip so as to control the detection of the snow accumulation state.

The Buck-Boost circuit is a DC/DC conversion circuit and is characterized in that the polarity of output voltage is opposite to that of input voltage, the output voltage can be lower than the input voltage or higher than the input voltage, a photovoltaic component and a photovoltaic group string to be detected are used as the input of the Buck-Boost circuit, the output voltage can be changed in a large range, and the maximum output power point of the photovoltaic component to be detected can be found.

The schematic diagram of the Buck-Boost circuit is shown in FIG. 5-1, and the schematic circuit comprises a power supply, a controllable switch, a diode, an inductor, a capacitor and a load. The controllable switch is modulated by the PWM signal output by the control chip, the whole circuit is divided into two states, and when the controllable switch is closed, the equivalent circuit is as shown in figure 5-2: in a short time after the switch is closed, the left side of the circuit is equivalent to a short-circuit state, and the current I of the power supply_sThrough the inductor back to the power supply. In this process, the diode is equivalent to a circuit breaking process, and the inductor stores part of the electric energy. When the controllable switch is open, the equivalent circuit is as shown in fig. 5-3: after the circuit is disconnected, the inductor releases electric energy stored in the inductor for realizing follow current, the direction of current is unchanged, the inductor can be equivalent to a power supply at the stage, the diode is equivalent to a conducting wire for processing, the current returns to the inductor through a load, and meanwhile, the capacitor is charged.

Suppose a switching cycle is T, where the switch closure time is T_ONThe switch off time is T_OFF，T＝T_ON+T_OFFControllable switching frequency of the switchDuty cycleThe following equations can be listed by KVL during switch closure:

V_S＝V_L；

when the switch is open, the following equations can be listed according to KVL:

V_L＝V_O；

where Δ T ═ T_OFF＝T-T_ON＝T-DT＝(1-D)T；

The change in inductor current should be 0 during one complete cycle, so:

(Δi_L)_{switch closure}+(Δi_L)_{Switch off}＝0；

Therefore, the voltage output by the Buck-Boost circuit is opposite to the input voltage, and when the duty ratio D of the PWM signal is larger than 0.5, the output voltage is larger than the input voltage; when D is less than 0.5, the output voltage is less than the input voltage; when D is 0.5, the output voltage is equal to the input voltage. In the above equation, the input voltage is V_SAn output voltage of V_OAn inductance of L and an inductance voltage of V_LThe instantaneous current of the inductor is i_L。

Furthermore, the Buck-Boost circuit comprises an IN + end, a COM end and an OUT-end, wherein the IN + end and the COM end form an input end of the Buck-Boost circuit, and the COM end and the OUT-end form an output end of the Buck-Boost circuit; the voltage at the input end has the opposite polarity with the voltage at the output end.

The Buck-Boost circuit is the core of the whole accumulated snow automatic detection method, is combined with a control chip, can control the output voltage of the photovoltaic string accessed to the input end of the Buck-Boost circuit, changes the duty ratio of a PWM (pulse width modulation) signal according to a control algorithm, enables the output voltage of the photovoltaic string accessed to the input end of the Buck-Boost circuit to realize global scanning from small to large in a voltage domain, and obtains the maximum output power P under the current load state and the irradiation state_x(ii) a If the duty ratio of the PWM signal is 1, the short-circuit current I of the photovoltaic string connected to the input end of the Buck-Boost circuit in the current irradiation state can be obtained_SC。

The reference illumination sensor is characterized in that the reference illumination sensor can never be covered by accumulated snow, and the reference illumination sensor plays a role in comparing with the maximum output power or short-circuit current of the photovoltaic string obtained by an accumulated snow automatic detection method. The reference illumination sensor can be a miniature silicon photocell, a photoelectric detector, an illuminometer, a small photovoltaic module, a photovoltaic module with a conventional size and the like, is vertically placed towards the south, and can be prevented from being covered by snow or dust even in snowy weather; a protective cover can also be arranged to protect the reference illumination sensor when the reference illumination sensor is not usedIs free from being covered; or any other easily imaginable way of ensuring that it is not covered by snow. The sunlight irradiation intensity I of the current environment can be obtained by directly detecting the current or the voltage of the reference illumination sensor or indirectly obtaining the current and voltage parameters of the reference illumination sensor through a relay matrix network and a Buck-Boost circuit_Ref. If the reference illumination sensor is vertically placed towards the south, the included angle between the reference illumination sensor and the direct solar ray is different from the included angle between the photovoltaic string to be detected and the direct solar ray, so that the maximum output power kSI of the uncovered photovoltaic string under the current solar radiation intensity can be obtained by multiplying the reference value by a calibratable coefficient k and a coefficient S related to the total light receiving area of the current photovoltaic string to be detected_Ref. Intensity of solar radiation I through the current environment_RefThe short-circuit current I of the uncovered photovoltaic string under the current sunlight irradiation intensity can be obtained by combining the characteristics and parameters of the reference illumination sensor₀。

By comparing the two results P obtained in the above process_xAnd kSI_RefAnd the snow cover degree of the photovoltaic string to be detected can be obtained. If P_xAnd kSI_RefIf the difference is not large, the photovoltaic string to be detected is not covered by the accumulated snow; if P_x≤x·kSI_RefAnd x is a proportionality coefficient which can be set to be 20% or other values, and the photovoltaic string to be detected is covered by the accumulated snow. Further scaling factor intervals, e.g. z kSI, may be provided_Ref＜P_x≤x·kSI_RefIndicating that the photovoltaic string to be detected is covered by the thin snow; p_x≤z·kSI_RefIndicating that the photovoltaic string to be detected is covered by thick snow; it is of course also possible to obtain a more refined scaling factor defining the degree of snow accumulation by experiment, setting the increasing series { a }_nIf a_n·kSI_Ref＜P_x≤a_n+1·kSI_RefAnd if n is larger than or equal to 1, the snow cover grade of the photovoltaic string to be detected is n, and the snow cover thickness corresponding to the grade n is larger than that corresponding to the grade n + 1.

Two results I obtained by comparing the above procedures_SCAnd I₀And the snow cover degree of the photovoltaic string to be detected can be obtained. If I_SCAnd I₀If the difference is not large, the photovoltaic string to be detected is not covered by the accumulated snow; if I_SC≤y·I₀And y is a proportionality coefficient which can be set to be 50% or other values, and the photovoltaic string to be detected is covered by the accumulated snow. Further scale factor intervals, e.g. m.I, may be provided₀＜I_SC≤y·I₀Indicating that the photovoltaic string to be detected is covered by the thin snow; i is_SC≤m·I₀Indicating that the photovoltaic string to be detected is covered by thick snow; it is of course also possible to obtain a more refined scaling factor defining the degree of snow accumulation by experiment, setting the increasing series b_nIs provided with b_n·I₀＜I_SC≤b_n+1·I₀And if n is larger than or equal to 1, the snow cover grade of the photovoltaic string to be detected is n, and the snow cover thickness corresponding to the grade n is larger than that corresponding to the grade n + 1.

Furthermore, the IN + end is connected with the anode of each photovoltaic assembly through a relay, and the COM end is connected with the cathode of each photovoltaic assembly through a relay; the relays form the relay matrix network; the COM terminal and the OUT-terminal are connected with a load.

Further, all the photovoltaic modules jointly form a photovoltaic system; the accumulated snow automatic detection circuit comprises a photovoltaic inverter connected with a mains supply and a relay used for controlling the on-off of the photovoltaic inverter and a photovoltaic system.

Furthermore, N photovoltaic modules are sequentially connected IN series, N is more than or equal to 2, the IN + end is connected with the anode of each photovoltaic module through a relay, the COM end is connected with the cathode of each photovoltaic module through a relay, and the OUT-end is connected with the cathode of each photovoltaic module from the second through a relay; the relay matrix network formed by the relays can connect different photovoltaic modules to the input end or the output end of the Buck-Boost circuit.

Further, the photovoltaic module comprises heating loads arranged on the back of each photovoltaic module, and the heating loads are connected to the output end of the Buck-Boost circuit or connected with commercial power.

When snow is removed, the photovoltaic module and a heating load can be connected to the output end of the Buck-Boost circuit through a relay matrix network, and the photovoltaic module at the input end is electrified to heat and remove snow; the photovoltaic module and the heating load can also be connected into the commercial power, and the photovoltaic module and the heating load are electrified to heat and remove snow; the commercial power and the photovoltaic self-generating power can be combined to remove snow; the detailed description is presented in terms of specific embodiments.

An automatic photovoltaic module snow accumulation detection circuit without an external sensor is used for detecting whether snow exists on a photovoltaic module or not, and replacing the photovoltaic module in the automatic snow accumulation detection circuit with a photovoltaic group string; each photovoltaic group string comprises at least one photovoltaic assembly; when the photovoltaic group string comprises a plurality of photovoltaic components, the photovoltaic components are sequentially connected in series, the positive pole of the first photovoltaic component is defined as the positive pole of the photovoltaic group string, and the negative pole of the last photovoltaic component is defined as the negative pole of the photovoltaic group string.

The MPPT idea-based control algorithm realizes the detection of the maximum output power of the photovoltaic string by adjusting the duty ratio of the PWM signal on the basis of the circuit design. The control flow is shown in fig. 6: the control algorithm divides the judgment of the maximum output power of a photovoltaic assembly or a photovoltaic string to be detected into a global optimization part and a local optimization part, so that the maximum power point can be rapidly positioned in a global range and accurately positioned in a local area, namely the maximum power area.

Firstly, the duty ratio of a PWM signal is gradually increased from 0 by a larger step length, the output power of the input end of the Buck-Boost circuit is recorded after the duty ratio is changed every time, the output power is compared with the output power obtained under the last duty ratio, and if the power is higher, the duty ratio, the power and the voltage corresponding to the current power are recorded and refreshed; if the power is smaller, no processing is done. When the duty ratio is increased to 1 (or approaches to 1), the global optimization is completed, the duty ratio, the power and the voltage corresponding to the maximum power area in the global range are obtained, and then the local optimization process is started. Taking the PWM duty ratio of the maximum output power area obtained by global optimization as a center, adding micro-disturbance on the PWM duty ratio, and recording the power after the micro-disturbance is added, wherein if the power is larger than that before the micro-disturbance is added, the maximum power point is in the positive direction of the micro-disturbance, and the micro-disturbance is continuously added in the direction; if the power is reduced compared with that before the perturbation is increased, the maximum power point is in the opposite direction of the increased perturbation, and the perturbation is increased again after the sign of the perturbation is changed. And when the direction of the perturbation changes for 2 times, finding out the maximum power point under the current load and irradiation state in the local area, and returning the maximum output power, the PWM duty ratio and the input end voltage corresponding to the maximum power point.

The perturbation is micro perturbation, the large step length is relative to the perturbation, the duty ratio value corresponding to the large step length is larger than that corresponding to the perturbation, and the values of the two are manually set according to requirements.

The invention also includes a photovoltaic inverter; the photovoltaic inverter is a common commercial photovoltaic inverter and is connected to the rear end of the photovoltaic module snow accumulation automatic detection circuit, when snow accumulation detection is carried out on a photovoltaic group string, connection with the photovoltaic inverter is disconnected, a photovoltaic system is enabled to be off-grid, and impact or other accidental dangers to a power grid caused by circuit state change in the detection process are prevented.

The invention also comprises a photovoltaic snow removal device, which is described in the detailed description.

The automatic detection method of the accumulated snow of the photovoltaic module is carried out according to the working flow shown in figure 7: the method comprises the following steps that in an initial state, a photovoltaic system works in a normal power generation state, and when the fact that the current input into a photovoltaic inverter is smaller than a set threshold value is detected, the normal power generation of the photovoltaic system is considered to be influenced; the current sunlight irradiation state is obtained by referring to the illumination sensor, and when the sunlight irradiation intensity is larger than a set threshold value, the current input into the photovoltaic inverter is reduced because the photovoltaic system is covered by snow, so that the influence of weak irradiation intensity factors caused by non-snow such as night, cloudy day and the like is eliminated. In addition, if the photovoltaic module is used as a snow removal energy source, the operation can judge whether the current sunlight irradiation state is enough to support the power requirement of the photovoltaic module for completing the snow removal task; if the sunlight irradiation intensity is proper, converting the sunlight irradiation value obtained by the reference illumination sensor into a power threshold value or a short-circuit current threshold value which is beneficial to snow detection of each photovoltaic string by a control method; starting from a first photovoltaic group string, judging whether the photovoltaic group string with the current number is covered by snow and the coverage degree of the snow through a control algorithm based on the MPPT thought, if not, switching to the next photovoltaic group string to detect the photovoltaic group string through a relay matrix network, if the photovoltaic group string with the current number is covered by the snow, performing snow removal operation on the photovoltaic group string with the current number through a photovoltaic snow removal device, switching to the next photovoltaic group string to detect the photovoltaic group string through the relay matrix network after snow removal is completed, and completing the snow removal until all the photovoltaic group strings are detected and completed.

In the above process, for the automatic detection of the accumulated snow of the photovoltaic string, a method for detecting the maximum output power or a method for detecting the short-circuit current may be used, or the method for detecting the maximum output power and the method for detecting the short-circuit current may be combined; when the photovoltaic system comprises N photovoltaic string, the snow accumulation detection is carried out on the front N-1 photovoltaic string by using a method for detecting the maximum output power, and the snow accumulation detection is carried out on the Nth photovoltaic string by using a method for detecting the short-circuit current.

The detection method disclosed by the invention can be suitable for detecting the accumulated snow of the photovoltaic assembly and can also be suitable for detecting the accumulated snow of the photovoltaic assembly string.

Compared with the prior art, the invention has the beneficial technical effects that:

1. on the basis of the circuit design of an improved Buck-Boost circuit and a relay matrix network, the maximum output power of each photovoltaic string under the current irradiation intensity is detected through a control algorithm based on the MPPT idea or the short-circuit current of each photovoltaic string is measured by adjusting the duty ratio of a PWM signal, and whether the photovoltaic string to be detected is covered by snow and the degree of the coverage of the snow is judged by measuring the reference value of the current sunlight irradiation state through a reference illumination sensor.

2. The reference illumination sensor can adopt a conventional photovoltaic module besides a miniature silicon photocell, a photoelectric detector, an illuminometer and a small photovoltaic module, and can realize automatic detection of accumulated snow of off-grid photovoltaic modules which use the conventional photovoltaic modules as all energy supplies.

Drawings

FIG. 1 is an overall structure diagram of an automatic snow detection circuit of a photovoltaic module according to the present invention;

FIG. 2 is a plot of the current-voltage characteristics of solar cells under different illumination intensities;

FIG. 3 is a plot of current-voltage characteristics and output power versus voltage for a solar cell;

FIG. 4 is a graph showing the relationship between the output power of a solar cell and the irradiation intensity of sunlight at different temperatures;

FIG. 5-1 is a Buck-Boost circuit schematic diagram;

FIG. 5-2 is a Buck-Boost equivalent circuit when the switch is closed;

FIG. 5-3 is a Buck-Boost equivalent circuit when the switch is turned off;

FIG. 6 is a flow chart of a MPPT concept based control algorithm of the present invention;

FIG. 7 is a flowchart of the automatic snow detection method for photovoltaic modules according to the present invention;

FIG. 8 is a diagram of a Buck-Boost circuit and photovoltaic string (different in the number of components) connection mode according to the invention;

FIG. 9 is a modified Buck-Boost circuit;

fig. 10 is a diagram of a photovoltaic module snow accumulation automatic detection circuit structure in which a load is fixed at the output end of the Buck-Boost circuit, and the number of photovoltaic modules in each photovoltaic module string is different without an external sensor;

fig. 11 is a structural diagram of an automatic detection circuit for accumulated snow of photovoltaic modules without external sensors, wherein photovoltaic module strings are used as loads of an output end of a Buck-Boost circuit, and the number of the photovoltaic modules in each photovoltaic module string is different;

fig. 12 is a diagram of a photovoltaic module snow accumulation automatic detection circuit structure without an external sensor, in which a load is fixed at the output end of the Buck-Boost circuit, and the number of photovoltaic modules in each photovoltaic module string is the same;

fig. 13 is a structural diagram of an automatic detection circuit for accumulated snow of photovoltaic modules without external sensors, in which photovoltaic module strings are used as loads at the output end of a Buck-Boost circuit, and the number of photovoltaic modules in each photovoltaic module string is the same;

fig. 14 is a diagram of a commercial power and photovoltaic self-generating hybrid snow removal circuit (the number of the series components in each group is different);

fig. 15 is a structural diagram of a commercial power and photovoltaic self-generating hybrid snow removal circuit (the number of the series components in each group is the same).

Detailed Description

A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

The photovoltaic modules are basic units used for power generation in a photovoltaic system and are sequentially connected in series; the photovoltaic group string is a group which is artificially divided and contains a certain number of photovoltaic modules, and is convenient for rapidly detecting and removing accumulated snow of the whole photovoltaic system. The photovoltaic group strings are sequentially arranged according to numbers, each photovoltaic group string contains a certain number of photovoltaic modules, and the number of the photovoltaic modules in the photovoltaic group strings with different numbers can be the same or different.

As shown IN fig. 8, the Buck-Boost circuit is abstracted into a three-port circuit, three ports are respectively an IN + terminal, a COM terminal and an OUT-terminal, wherein the COM terminal exists as IN-and OUT +, that is, the IN + terminal and the COM terminal form an input terminal of the Buck-Boost circuit, and the COM terminal and the OUT-terminal form an output terminal of the Buck-Boost circuit, and the change is performed by the on-off of the controllable switch. On the basis of a schematic diagram, a design of an improved Buck-Boost circuit is shown in FIG. 9, the basic principle of the improved Buck-Boost circuit is the same as that of the conventional Buck-Boost circuit, and the improved Buck-Boost circuit comprises a current detection module with an input end and an output end.

Example 1:

taking a photovoltaic system including 20 photovoltaic modules as an example, in order to realize the snow accumulation detection function of the present invention, a circuit structure as shown in fig. 10 may be adopted, the number of photovoltaic modules in each photovoltaic group string connected by a relay matrix network is different, and the number of photovoltaic modules increases with the increase of the serial number of the photovoltaic group string, for example, the photovoltaic group string 0 includes 2 photovoltaic modules, the photovoltaic group string 1 and the photovoltaic group string 2 each include 1 photovoltaic module, the photovoltaic group string 3 includes 2 photovoltaic modules, the photovoltaic group string 4 includes 3 photovoltaic modules, the photovoltaic group string 5 includes 4 photovoltaic modules, the photovoltaic group string 6 includes 7 photovoltaic modules, and the Buck-Boost circuit output end is fixedly connected to a load.

When the current sensor A1 detects that the current input into the photovoltaic inverter is reduced, the reference illumination sensor eliminates the reduction of the power generation power caused by non-accumulated snow such as dark night or cloudy day, the control chip carries out accumulated snow detection on the photovoltaic strings one by one, and the strings covered by the accumulated snow are accurately positioned. When the accumulated snow degree of the photovoltaic string 0 is detected, the relays k01 and k02 are closed, the photovoltaic string 0 is connected to the Buck-Boost circuit input end, at the moment, the maximum output power of the photovoltaic string 0 is detected through a control chip running a control algorithm based on the MPPT idea, and is compared with a power threshold value which is obtained through calibration of a reference illumination sensor and used for judging the accumulated snow degree of the photovoltaic string 0, so that whether the accumulated snow degree is accumulated or not and the accumulated snow degree is determined. If the snow is accumulated, snow removal operation is carried out on the snow; if no snow is accumulated, the photovoltaic group string 1 is detected, k01 and k02 are disconnected, and relays k11 and k12 are closed; whether or not the photovoltaic array 1 is snow-covered and the degree of snow-covered are detected by the same procedure as described above. And analogizing until the accumulated snow detection of all the photovoltaic group strings is completed.

Example 2:

taking a photovoltaic system comprising 20 photovoltaic modules as an example, in order to realize the snow accumulation detection function, a circuit structure shown in fig. 11 can be adopted, and the snow accumulation detection function is characterized in that the number of the photovoltaic modules in each photovoltaic group string connected with a relay matrix network is different, and the number of the modules is increased along with the serial number of the group string, for example, a photovoltaic group string 0 comprises 2 photovoltaic modules, a photovoltaic group string 1 and a photovoltaic group string 2 both comprise 1 photovoltaic module, a photovoltaic group string 3 comprises 2 photovoltaic modules, a photovoltaic group string 4 comprises 3 photovoltaic modules, a photovoltaic group string 5 comprises 4 photovoltaic modules, a photovoltaic group string 6 comprises 7 photovoltaic modules, the output end of a Buck-Boost circuit is connected with different photovoltaic group strings through a series of relays, and the scheme utilizes the next group string of the group strings to be detected as the output end load of the Buck-Boost circuit.

When the current sensor A1 detects that the current input into the photovoltaic inverter is reduced, the reference illumination sensor eliminates the reduction of the power generation power caused by non-accumulated snow such as dark night or cloudy day, the control chip carries out accumulated snow detection on the photovoltaic strings one by one, and the strings covered by the accumulated snow are accurately positioned. When the photovoltaic group string 0 is detected, the relays k01, k02 and k03 are closed, the photovoltaic group string 0 is connected to the input end of the Buck-Boost circuit, the photovoltaic group string 1 is connected to the output end of the Buck-Boost circuit, and due to the fact that the Buck-Boost circuit reverses the output voltage, the output voltage of the photovoltaic group string 0 is equivalent to the fact that the positive electrode of the photovoltaic group string 1 is connected with the positive electrode of the photovoltaic group string 1 after being modulated by the Buck-Boost circuit, and the negative electrode of the photovoltaic group string 1 is connected with the negative electrode of the photovoltaic group string 1, at the moment, the photovoltaic group string 1 is equivalent to a load, and in the later embodiment 5, the photovoltaic group string 0 can be used for providing energy to reversely electrify the photovoltaic group string 1 and remove snow. The control chip runs a control algorithm based on the MPPT idea, the maximum output power of the photovoltaic string 0 is detected, and the maximum output power is compared with a power threshold value which is obtained by calibrating the reference illumination sensor and is used for judging the snow accumulation degree of the photovoltaic string 0, so that whether snow is accumulated or not and the snow accumulation degree are determined. If the snow is accumulated, snow removal operation is carried out on the snow; and if the accumulated snow is not available, starting to detect the photovoltaic string 1. The degree of snow accumulation in photovoltaic array 1 is detected by opening k01, k02, and k03 and closing relays k11, k12, and k13 in the same manner as described above. By analogy, when the last group string, namely the photovoltaic group string 6, is carried out, other photovoltaic group strings do not exist subsequently, and the snow accumulation degree is detected by using the short-circuit current of the photovoltaic group string. The relays k61 and k62 are closed, the photovoltaic string 6 is connected to the input end of the Buck-Boost circuit, the PWM signal with the duty ratio of 1 is output through the control chip, at the moment, the state of the Buck-Boost circuit is as shown in the figure 5-2, after the current state in the circuit is stable, the inductor can be approximately processed by a wire, and the short-circuit operation of the photovoltaic string 6 is realized. The short-circuit current of the photovoltaic string 6 is measured through the current sensor A2, and compared with a current threshold value which is obtained through calibration of the reference illumination sensor and used for judging the snow accumulation degree of the photovoltaic string 6, whether snow is accumulated or not and the snow accumulation degree are determined. If the snow is accumulated, snow removal operation is carried out on the snow; if there is no snow, the snow detection and snow removal operation of the whole photovoltaic system is completed.

Example 3:

as shown in fig. 12, embodiment 3 differs from embodiment 1 in that: the number of photovoltaic modules in each photovoltaic group string connected with the relay matrix network is the same, and the photovoltaic group strings are numbered from 1.

When the current sensor A1 detects that the current input into the photovoltaic inverter is reduced, the power generation power reduction caused by non-accumulated snow such as dark night or cloudy day is eliminated by referring to the illumination sensor, the control chip carries out accumulated snow detection one by one on the photovoltaic strings, and the strings covered by the accumulated snow are accurately positioned. When the accumulated snow degree of the photovoltaic string 1 is detected, the relays k11 and k12 are closed, the photovoltaic string 1 is connected to the Buck-Boost circuit input end, at the moment, the maximum output power of the photovoltaic string 1 is detected through a control chip running a control algorithm based on the MPPT idea, and is compared with a power threshold value which is obtained through calibration of a reference illumination sensor and used for judging the accumulated snow degree of the photovoltaic string 1, and whether the accumulated snow degree is accumulated snow or not is determined. If the snow is accumulated, snow removal operation is carried out on the snow; if there is no accumulated snow, the detection of the photovoltaic string 2 is started. The relays k21 and k22 are closed while k11 and k12 are opened, and the snow accumulation degree of the photovoltaic array 2 is detected by the same procedure as described above. And analogizing until the accumulated snow detection of all the photovoltaic group strings is completed.

Example 4:

as shown in fig. 13, embodiment 4 differs from embodiment 2 in that: the number of photovoltaic modules in each photovoltaic group string connected with the relay matrix network is the same, and the photovoltaic group strings are numbered from 1.

When the current sensor A1 detects that the current input into the photovoltaic inverter is reduced, the reference illumination sensor eliminates the reduction of the power generation power caused by non-accumulated snow such as dark night or cloudy day, the control chip carries out accumulated snow detection on the photovoltaic strings one by one, and the strings covered by the accumulated snow are accurately positioned. When the accumulated snow degree of the photovoltaic string 1 is detected, the relays k11, k12 and k13 are closed, the photovoltaic string 1 is connected to the input end of the Buck-Boost circuit, the photovoltaic string 2 is connected to the output end of the Buck-Boost circuit, the output voltage of the Buck-Boost circuit is reversed, namely the output voltage of the photovoltaic string 1 is modulated by the Buck-Boost circuit, the positive electrode of the photovoltaic string 2 is connected with the positive electrode of the photovoltaic string 2, the negative electrode of the photovoltaic string 2 is connected with the negative electrode of the photovoltaic string 2, and the photovoltaic string 2 is equivalent to a load. The control chip runs a control algorithm based on the MPPT idea, the maximum output power of the photovoltaic string 1 is detected, and the maximum output power is compared with a power threshold value which is obtained by calibrating the reference illumination sensor and used for judging the snow accumulation degree of the photovoltaic string 1, so that whether snow is accumulated or not and the snow accumulation degree are determined. If the snow is accumulated, snow removal operation is carried out on the snow; if there is no accumulated snow, the detection of the photovoltaic string 2 is started. The degree of snow accumulation in the photovoltaic array 2 is detected by opening k11, k12, and k13 and closing the relays k21, k22, and k23 in the same procedure as described above. By analogy, when the last group string, namely the photovoltaic group string 5, is carried out, other photovoltaic group strings do not exist subsequently, and the snow accumulation degree is detected by using the short-circuit current of the photovoltaic group string. The relays k51 and k52 are closed, the photovoltaic string 5 is connected to the input end of the Buck-Boost circuit, the PWM signal with the duty ratio of 1 is output through the control chip, at the moment, the state of the Buck-Boost circuit is as shown in the figure 5-2, after the current state in the circuit is stable, the inductor can be approximately processed by a wire, and the short-circuit operation of the photovoltaic string 5 is realized. The short-circuit current of the photovoltaic string 5 is measured through the current sensor A2, and compared with a current threshold value which is obtained through calibration of the reference illumination sensor and used for judging the snow accumulation degree of the photovoltaic string 5, whether snow is accumulated or not and the snow accumulation degree are determined. If the snow is accumulated, snow removal operation is carried out on the snow; if there is no snow, the snow detection and snow removal operation of the whole photovoltaic system is completed.

Example 5:

the invention can also realize snow removal through the photovoltaic snow removal device.

Photovoltaic snow removing device can realize through following mode:

(1) attaching devices with an electric heating function, such as a carbon film heating sheet, an electric heating wire and the like, to the photovoltaic module backboard;

(2) a mechanical scraping device such as a rail-mounted robot and a mechanical device similar to an automobile windscreen wiper is arranged on the photovoltaic module;

(3) the photovoltaic module is electrified reversely to perform self-heating snow removal;

the snow removal method in which reverse energization of the photovoltaic module is used has an advantage in terms of economy and modification cost, namely, mode (3).

The invention provides five preferable embodiments which can be adapted to the automatic snow detection circuit and the detection method.

Example 5-1:

reverse electrification of the photovoltaic module: the photovoltaic module is used as an energy source. As shown in fig. 11, when the embodiment 2 determines that snow is accumulated in a certain photovoltaic string, taking the photovoltaic string 1 as an example, the photovoltaic string 0 is connected to the input end of the Buck-Boost circuit as an energy source for removing snow, the relays k01 and k02 are closed, the photovoltaic string 1 is connected to the output end of the Buck-Boost circuit as a load, and the relay k03 is closed. The control algorithm based on the MPPT idea can accurately position the maximum power output point of the photovoltaic string 0 and ensure that the photovoltaic string 1 covered by accumulated snow is efficiently supplied with energy and removed with snow. Treat that the photovoltaic group cluster of snow removing is by the snow removing of its preorder all photovoltaic group clusters common energy supply, and it is worth noting through rationally dividing photovoltaic group cluster in photovoltaic system, can make energy supply photovoltaic module quantity: the number of photovoltaic modules to be snow-removed is approximately equal to 2: 1, realizing efficient snow removal. For clearer explanation, firstly, snow removal of the photovoltaic group string 1 is taken as an example, the photovoltaic group string 0 is connected to the input end of the Buck-Boost circuit as energy for snow removal, the relays k01 and k02 are closed, the photovoltaic group string 1 is connected to the output end of the Buck-Boost circuit as a load, and the relay k03 is closed, so that 2 photovoltaic modules supply energy to 1 photovoltaic module for snow removal. Along with the promotion of snow removing process, the group cluster quantity of joining the energy supply end becomes more, and the efficiency of snow removing can improve. With the snow removing example of photovoltaic group cluster 6, photovoltaic group cluster 0 ~ 5 inserts at Buck-Boost circuit input as the energy of snow removing, and relay k01, k52 are closed, and photovoltaic group cluster 6 inserts at Buck-Boost circuit output as the load, and relay k53 is closed, makes 13 photovoltaic module to 7 photovoltaic module energy supply snow removals. Snow removing efficiency improves step by step.

As shown in fig. 13, in embodiment 4, when each photovoltaic string includes the same number of photovoltaic modules, after the photovoltaic string 1 completes reverse energization snow removal on the photovoltaic string 2, the ratio of the number of energy-supplying photovoltaic modules to the number of photovoltaic modules to be removed is still approximately equal to 2: 1, for example, the photovoltaic string 1 and the photovoltaic string 2 remove snow from the photovoltaic string 3, the photovoltaic string 2 and the photovoltaic string 3 remove snow from the photovoltaic string 4, and so on; the proportion of 2: 1 is only used for rapidly removing snow, and 1: 1 can also realize corresponding functions in principle, but the time consumption is longer; the snow removal speed can be increased by 3: 1. The ratio of the number of the photovoltaic modules at the energy supply end to the number of the photovoltaic modules at the load end in the embodiment is only an exemplary description, and should not be considered as a limitation, and a person skilled in the art can set the ratio according to the actual snow removal requirement.

The photovoltaic snow removing device in this embodiment is the photovoltaic group cluster itself.

Example 5-2:

reverse electrification of the photovoltaic module: the commercial power is used as energy. As shown in fig. 12 and 13, the number of photovoltaic modules in each of the photovoltaic strings in embodiments 3 and 4 is the same, and when it is determined that a certain photovoltaic string is covered by snow through the MPPT concept-based control algorithm of the present invention, the photovoltaic string may be reversely electrified and snow removed by using commercial power as an energy source. Commercial power is converted into direct current through the filter rectification circuit, and the direct current is reversely connected with two ends of the string to be snow-removed after boosting, so that the components are uniformly heated and snow-removed (the filter rectification circuit and the boosting circuit are not shown in the figure).

The photovoltaic snow removing device in this embodiment is commercial power and the relay of control commercial power break-make promptly.

Examples 5 to 3:

an electric heating method: the photovoltaic module is used as an energy source. As shown in fig. 10 and 12, in embodiments 1 and 3, carbon film heating sheets, resistance wires and the like required by an electrical heating method are mounted on a photovoltaic module back plate and connected to the output end of a Buck-Boost circuit as a load; after the control algorithm based on the MPPT concept of the present invention determines that a certain photovoltaic string is covered with snow, taking the example that the photovoltaic string 6 is covered with snow in embodiment 1, the control relays k01 and k52 are closed, and all strings in the preamble of the string covered with snow supply the load to heat it, so as to clear away the snow on the surface of the photovoltaic module. With the progress of snow removal, the number of the groups of the energy supply end is increased, the heating power of the load is increased, and the snow removal efficiency is improved.

The photovoltaic snow removal device in this embodiment is photovoltaic group cluster itself and heating load promptly.

Examples 5 to 4:

an electric heating method: the commercial power is used as energy. As shown in fig. 10, 11, 12, 13 (wherein fig. 11, 13 do not show the load of carbon film heating sheet, etc. required for electric heating), in examples 1, 2, 3, 4, carbon film heating sheet, resistance wire, etc. required for electric heating method are mounted on the photovoltaic module back sheet and connected to the commercial power; the same or different numbers of photovoltaic modules in each photovoltaic group string can be used. After the control algorithm based on the MPPT idea judges that a certain photovoltaic string is covered by accumulated snow, the commercial power is used as an energy source to supply energy to devices such as a carbon film heating sheet, a resistance wire and the like in the string, so that the device can generate heat to remove snow.

The photovoltaic snow removing device in this embodiment is commercial power and heating load.

Examples 5 to 5:

commercial power and photovoltaic self-generating mixed snow removal. In the snow removal embodiment in which the photovoltaic modules themselves are used as energy sources, the problem that the accumulated snow of the first photovoltaic string cannot be automatically removed exists, and a feasible scheme is to specially mount the photovoltaic modules of the first string, such as vertically placing the photovoltaic modules, so that the photovoltaic modules cannot be covered by the accumulated snow; as in example 5-1, fig. 11, 2 photovoltaic modules of photovoltaic string 0 were mounted vertically; or the variable-inclination-angle bracket is used, and snow can slide off by changing the inclination angle of the photovoltaic bracket; or the first string of pv strings is cleared of snow by human means, in which case string 0 may act as a reference light sensor, while this way a completely off-grid automatic detection and clearing of snow is achieved.

In order to realize the automation of the whole accumulated snow detection and snow removal process, the transformation cost increased by the specially placed photovoltaic module is avoided, the accumulated snow detection and the snow removal task can be automatically completed while the electric energy is saved by a mode of combining the commercial power and the photovoltaic self-generation.

After the photovoltaic system is detected to be covered by the accumulated snow, snow removal of the first photovoltaic string is completed through the commercial power, namely the initial energy for removing snow for other photovoltaic strings is obtained, and then the accumulated snow detection and snow removal process is completed according to the mode of the embodiment. As shown in fig. 14 and 15, when the commercial power is used for removing snow from the first photovoltaic string, the relays ks1 and ks2 are controlled to be closed, the first photovoltaic string is connected to the output end of the Buck-Boost circuit, meanwhile, the commercial power after being filtered and rectified is connected to the input end of the Buck-Boost circuit, the commercial power after being rectified into direct current is boosted, and the commercial power is supplied to the first photovoltaic string at a certain power for removing snow.

The automatic snow cover detection method and circuit and the embodiment provided for more clearly explaining the invention content are not only suitable for small-scale photovoltaic systems, but also can enlarge the number of photovoltaic components of each group string, inherit or comprise the solution of the idea of the invention and can be used for large-scale photovoltaic systems, such as centralized photovoltaic ground power stations, industrial and commercial photovoltaic roofs and the like.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein, and any reference signs in the claims are not intended to be construed as limiting the claim concerned.

Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.