Photovoltaic heating system and control method thereof

Abstract

The invention provides a photovoltaic heating system and a control method thereof. The invention relates to the field of photovoltaic technology. A photovoltaic heating system comprises a photovoltaic assembly, a resistor unit, a first switch and a controller. The resistor unit and the first switch are connected in series and then are connected between the positive electrode output end and the negative electrode output end of the photovoltaic module. The controller is connected with the control end of the first switch; the controller is used for determining the reference resistance of the resistance unit based on a maximum power point tracking (MPPT) algorithm when the photovoltaic module works at the maximum power point; and determining a control signal for controlling the duty ratio of the first switch based on the reference resistor, and outputting the control signal to the first switch. By controlling the duty ratio of the first switch, the equivalent resistance of the resistor unit connected in series with the first switch is adjusted, so that the photovoltaic module can operate at the maximum power point, the power loss of the photovoltaic module is reduced, and the effect of reducing energy waste is achieved.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic technology, and in particular, to a photovoltaic heating system and a control method thereof. Background Art

[0002] In applications such as a photovoltaic water heater or other photovoltaic heating systems that provide thermal energy through photovoltaics, a photovoltaic module is used as a current source to connect a heating resistor for heating.

[0003] However, since the resistance value of the heating resistor is fixed, and due to factors such as changes in light intensity on the photovoltaic module, the output current of the photovoltaic module will change. Furthermore, according to Ohm's law, the output voltage of the photovoltaic module will deviate from the maximum power point, making it difficult for the photovoltaic module to maintain at the maximum power point and resulting in energy waste. Summary of the Invention

[0004] In view of this, the present application provides a photovoltaic heating system and a control method thereof, aiming to avoid the problem that when the photovoltaic module powers the heating resistor, it is difficult for the photovoltaic module to maintain at the maximum power point and energy is wasted.

[0005] In a first aspect, the present application provides a photovoltaic heating system, including: a photovoltaic module, a resistor unit, a first switch, and a controller;

[0006] After the resistor unit and the first switch are connected in series, they are connected between the positive output terminal and the negative output terminal of the photovoltaic module; the controller is connected to the control terminal of the first switch;

[0007] The controller is configured to determine a reference resistance of the resistor unit when the photovoltaic module operates at the maximum power point based on the maximum power point tracking (MPPT) algorithm; determine a control signal for controlling the duty cycle of the first switch based on the reference resistance, and output the control signal to the first switch.

[0008] Optionally, the controller is configured to sample the output voltage and output current of the photovoltaic module, determine a first voltage and a first current corresponding to when the photovoltaic module operates at the maximum power through the maximum power point tracking (MPPT) algorithm; calculate a ratio of the first voltage to the first current to obtain the reference resistance; calculate a ratio of the actual resistance of the resistor unit to the reference resistance to obtain the duty cycle; generate a PWM drive signal according to the duty cycle, and output the PWM drive signal to the control terminal of the first switch.

[0009] Optionally, it further includes a second switch, and the second switch is connected in parallel with the resistor unit;

[0010] The second switch is used to conduct when the first switch is turned off, so as to provide freewheeling for the resistor unit. The first switch and the second switch are in an interlocked working state.

[0011] Optionally, the second switch is a freewheeling diode. The negative electrode of the freewheeling diode is connected to the first end of the resistor unit, and the positive electrode of the freewheeling diode is connected to the second end of the resistor unit. The first end of the resistor unit is the end connected to the positive output terminal of the photovoltaic module.

[0012] Optionally, the second switch is a fast recovery diode.

[0013] Optionally, the first switch is a MOS transistor or an IGBT.

[0014] Optionally, the resistor unit includes a heating resistor, and the resistance value of the heating resistor is less than or equal to a first resistance value, where the first resistance value is the ratio of the first voltage corresponding to the maximum power point when the photovoltaic module operates under the maximum irradiance to the first current.

[0015] In a second aspect, the present application further provides a control method for a photovoltaic heating system. The photovoltaic heating system includes a photovoltaic module, a resistor unit, a first switch, and a controller. After the resistor unit and the first switch are connected in series, they are connected between the positive output terminal and the negative output terminal of the photovoltaic module. The controller is connected to the control terminal of the first switch. The control method includes:

[0016] Based on the maximum power point tracking (MPPT) algorithm, determine the reference resistance of the resistor unit when the photovoltaic module operates at the maximum power point; determine a control signal for controlling the duty cycle of the first switch based on the reference resistance, and output the control signal to the control terminal of the first switch.

[0017] Optionally, the step of determining the reference resistance of the resistor unit when the photovoltaic module operates at the maximum power point based on the maximum power point tracking includes:

[0018] Sample the output voltage and output current of the photovoltaic module, and determine the first voltage and the first current corresponding to the photovoltaic module operating at the maximum power through the maximum power point tracking (MPPT) algorithm;

[0019] Calculate the ratio of the first voltage to the first current to obtain the reference resistance; and / or,

[0020] The step of determining a control signal for controlling the duty cycle of the first switch based on the reference resistance and outputting the control signal to the control terminal of the first switch includes:

[0021] Calculate the ratio of the actual resistance of the resistor unit to the reference resistance to obtain the duty cycle;

[0022] Generate a PWM driving signal according to the duty cycle and output the PWM driving signal to the control end of the first switch.

[0023] Optionally, before determining the reference resistance of the resistance unit when the photovoltaic module operates at the maximum power point based on the maximum power point tracking (MPPT) algorithm, the following steps are further included:

[0024] In response to the output voltage of the photovoltaic module reaching the startup voltage of the auxiliary power supply of the controller, the controller is powered on and initialized;

[0025] Collect the output voltage and output current of the photovoltaic module, and determine whether the collected output voltage of the photovoltaic module is greater than or equal to the MPPT voltage under the minimum irradiance of the photovoltaic module;

[0026] If the collected output voltage of the photovoltaic module is greater than or equal to the MPPT voltage under the minimum irradiance, then when the duty cycle of the first switch is 1 and the photovoltaic string operates for a first duration, collect the second voltage and second current output by the photovoltaic string;

[0027] Calculate the ratio of the second voltage to the second current as the actual resistance of the resistance unit, and record the actual resistance to the controller;

[0028] Confirm that the controller is fault-free.

[0029] In a third aspect, the present application provides a computer storage medium, in which code is stored. When the code is run, the device running the code implements a photovoltaic heating system control method according to any one of the foregoing first aspects.

[0030] The present application provides a photovoltaic heating system and its control method. The photovoltaic heating system includes a photovoltaic module, a resistance unit, a first switch, and a controller; after the resistance unit and the first switch are connected in series, they are connected between the positive output terminal and the negative output terminal of the photovoltaic module; the controller is connected to the control end of the first switch; the controller is configured to determine the reference resistance of the resistance unit when the photovoltaic module operates at the maximum power point based on the maximum power point tracking (MPPT) algorithm; determine a control signal for controlling the duty cycle of the first switch based on the reference resistance, and output the control signal to the first switch. In this way, by determining the reference resistance of the corresponding resistance unit when the photovoltaic module operates at the maximum power point based on the MPPT algorithm, and then determining the duty cycle of the first switch based on the reference resistance, thus, by controlling the duty cycle of the first switch, the equivalent resistance of the resistance unit connected in series with the first switch is adjusted, so that the photovoltaic module can operate at the maximum power point, reducing the power loss of the photovoltaic module and achieving the effect of reducing energy waste. Description of the Drawings

[0031] To more clearly illustrate the technical solutions in this embodiment or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiment or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0032] Figure 1 Schematic diagram of the circuit structure of a photovoltaic heating system provided by an embodiment of the present application;

[0033] Figure 2 Schematic diagram of an IV / PV curve provided by an embodiment of the present application;

[0034] Figure 3 Schematic diagram of an IV / PV curve corresponding to different irradiances provided by an embodiment of the present application;

[0035] Figure 4 Schematic diagram of the circuit of another photovoltaic heating system provided by an embodiment of the present application;

[0036] Figure 5 Schematic diagram of the flow of a control method for a photovoltaic heating system provided by an embodiment of the present application;

[0037] Figure 6 Schematic diagram of the control strategy of the first switch provided by an embodiment of the present application;

[0038] Figure 7 Schematic diagram of a preprocessing flow provided by an embodiment of the present application. Detailed implementation manners

[0039] In order to be able to understand the features and technical content of the embodiments of the present disclosure in more detail, the following will elaborate on the implementation of the embodiments of the present disclosure in conjunction with the accompanying drawings. The attached drawings are only for reference and explanation, and are not used to limit the embodiments of the present disclosure. In the following technical description, for the sake of explanation, a sufficient understanding of the disclosed embodiments is provided through multiple details. However, one or more embodiments can still be implemented without these details. In other cases, well-known structures and devices can be shown in a simplified manner.

[0040] The terms "first", "second", etc. in the specification, claims and above-mentioned accompanying drawings of the embodiments of the present disclosure are used to distinguish similar objects, and do not necessarily need to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances, so as to implement the embodiments of the present disclosure described here. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusion.

[0041] Unless otherwise specified, the term "a plurality of" means two or more.

[0042] In the embodiments of the present disclosure, the character " / " indicates that the objects before and after are in an "or" relationship. For example, A / B means: A or B.

[0043] The term "and / or" is an associative relationship describing an object, indicating that three relationships can exist. For example, A and / or B means: A or B, or, the three relationships of A and B.

[0044] In order to make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present application.

[0045] See Figure 1 , Figure 1 FIG. is a schematic circuit diagram of a photovoltaic heating system provided by an embodiment of the present application. A photovoltaic heating system includes a photovoltaic module, a resistance unit R1, a first switch Q1, and a controller;

[0046] After the resistance unit R1 and the first switch Q1 are connected in series, they are connected between the positive output terminal and the negative output terminal of the photovoltaic module; the controller is connected to the control terminal of the first switch Q1;

[0047] The controller is configured to determine the reference resistance of the resistance unit R1 when the photovoltaic module operates at the maximum power point based on the maximum power point tracking (MPPT) algorithm; determine a control signal for controlling the duty cycle of the first switch Q1 based on the reference resistance, and output the control signal to the first switch Q1.

[0048] The above-mentioned resistance unit R1 includes a heating resistor. This heating resistor is a resistance element for converting electrical energy into heat energy in the photovoltaic heating system of the present application. Optionally, since when the loop connecting the photovoltaic string to the heating resistor is conducting, the resistance values of other components are relatively small and can be ignored except for the resistance value of the heating resistor, the resistance unit R1 can also be regarded as a heating resistor.

[0049] The above-mentioned first switch Q1 is a semiconductor switch tube. For example, MOS tube, IGBT, etc. The control terminal of the above-mentioned first switch is connected to the controller, and the connection and disconnection of the first switch Q1 are controlled by the controller.

[0050] The positive output terminal and the negative output terminal of the above-mentioned photovoltaic module cooperate to output direct current.

[0051] The above-mentioned controller can be a controller configured to implement the overall functions of the photovoltaic heating system (such as starting the photovoltaic heating system to provide heat energy, temperature measurement control, etc.), or a controller independently set for implementing the first switch control.

[0052] The controller of the above-mentioned photovoltaic heating system determines the reference resistance of the resistance unit R1 corresponding to the photovoltaic module operating at the maximum power point based on the MPPT algorithm. Based on this reference resistance, the controller controls the duty cycle of the first switch Q1, adjusts the equivalent resistance of the resistance unit R1 connected in series with the first switch Q1, so that the photovoltaic module can operate at the maximum power point, reducing the power loss of the photovoltaic module and achieving the effect of reducing energy waste.

[0053] Combined with the above embodiments, the specific processing process of the above-mentioned controller in the present application can be:

[0054] The controller is used to sample the output voltage and output current of the photovoltaic module, and determine the first voltage and the first current corresponding to the photovoltaic module operating at the maximum power through the maximum power point tracking (MPPT) algorithm; calculate the ratio of the first voltage to the first current to obtain the reference resistance; calculate the ratio of the actual resistance of the resistance unit R1 to the reference resistance to obtain the duty cycle; generate a PWM drive signal according to the duty cycle, and output the PWM drive signal to the control terminal of the first switch Q1.

[0055] The above-mentioned maximum power point tracking (MPPT) algorithm can adopt the constant voltage tracking method (CVT for short), the perturbation and observation method (P&O for short), the incremental conductance method (INC for short), the conductance increment method based on gradient variable step size, etc., to calculate the first voltage at the maximum power of the photovoltaic module based on the output voltage and output current of the photovoltaic module sampled by the controller. Exemplarily, refer to Figure 2 the schematic diagram of an IV / PV curve shown. Through MPPT control, find the first voltage at the maximum power of the photovoltaic string in the direction indicated by the arrow in Figure 2 to determine the first current corresponding to the first voltage when the photovoltaic module operates at the maximum power.

[0056] It can be understood that in a conventional photovoltaic heating system, the photovoltaic module is directly connected to the heating resistor for power supply. For the current source of the photovoltaic string loop, since the current of the photovoltaic string changes under different irradiances and other conditions, when the resistance value of the heating resistor is fixed, it is difficult for the photovoltaic module to operate at the first voltage Vmp corresponding to the maximum power point. For example, referring to Figure 3 the schematic diagram of the IV / PV curve corresponding to different irradiances shown in Figure 3 , each color of the IV / PV curve corresponds to the IV / PV curve of an irradiance. At different irradiation intensities, the output current of the photovoltaic module will change. To enable the photovoltaic module to still operate at the maximum power point, the present application introduces the first switch Q1, and the controller determines the electrical parameters (the first voltage and the first current) corresponding to the maximum power point at which the photovoltaic string is currently operating based on the electrical parameter information currently collected from the photovoltaic string, and understands the current operating state of the photovoltaic string (exemplarily, under different irradiances, the electrical parameters corresponding to the maximum power point at which the photovoltaic string operates are different). Furthermore, the on and off of the first switch Q1 can be controlled to change the equivalent value of the resistance unit R1. The specific steps are as follows:

[0057] Calculate the ratio of the above-mentioned first voltage Vmp and the first current Imp to obtain the reference resistance Rref. The specific formula is: Rref = Vmp / Imp. This reference resistance is the target value for adjusting the equivalent value of the resistance unit R1.

[0058] Furthermore, based on the area equivalence principle of PWM modulation, it can be known that by adjusting the duty cycle duty of the PWM signal, the resistance value can be changed. The specific formula is: Rref = Rdc / duty. Therefore, calculate the ratio of the actual resistance Rdc of the resistance unit R1 to the reference resistance Rref to obtain the duty cycle duty.

[0059] Optionally, the value range of duty is 0 - 1. However, considering the characteristics of the switching tube, the value range of duty is limited to be greater than or equal to 0.05 and less than or equal to 0.95.

[0060] Optionally, from the above formula, it can be seen that Rref ≥ Rdc. Therefore, in order to achieve the maximum power output of the photovoltaic module, Rdc should not be greater than the ratio of the photovoltaic first voltage Vmp to the first current Imp corresponding to the maximum power point Pmax under the maximum irradiance of the IV / PV curve shown in Figure 2 .

[0061] The above-mentioned maximum irradiance can be the maximum irradiance in the historical records of the location where the photovoltaic module is located.

[0062] The above-mentioned PWM drive signal is sent by the controller MCU to the first switch Q1. This controller can be a programmable element such as DSP or ARM.

[0063] Thus, based on the duty cycle calculated above, a PWM drive signal is generated by a PWM generator and output to the first switch Q1 to change the equivalent resistance of the resistance unit R1 connected to the photovoltaic module, achieving an adaptive resistance of the photovoltaic heating system, obtaining the maximum conversion of electrical energy of the photovoltaic module into resistive heat energy, achieving the maximum power output of the photovoltaic module, improving the utilization efficiency of the photovoltaic heating system, and reducing energy waste.

[0064] Based on the above embodiments, in Figure 1 the circuit shown, when the above first switch Q1 is turned off, a counter electromotive force will be generated. When the first switch Q1 changes from the on state to the off state, the counter electromotive force generated by the inductor may instantaneously raise the voltage across the two ends of the first switch Q1. Therefore, the rated voltage of the first switch Q1 needs to be higher than the elevated voltage, but this will result in a relatively high cost of the first switch Q1.

[0065] Therefore, the present application also provides a second switch connected in parallel with the above resistance unit R1. The second switch is specifically configured to conduct when the first switch Q1 is turned off, and provide a freewheeling current for the resistance unit R1.

[0066] Specifically, the first switch Q1 and the second switch are in an interlocked operating state to achieve the alternating conduction of the first switch Q1 and the second switch. The current flow direction after the second switch conducts is opposite to the current flow direction after the first switch Q1 conducts. Thus, when the first switch Q1 is turned off, the current in the inductor cannot change suddenly, generating a counter electromotive force. The second switch can provide a freewheeling path for the inductor current, enabling the energy in the inductor to continue to be released in the form of current, avoiding damage to the switching tube or other circuit components due to excessive counter electromotive force, and thus eliminating the need to select a first switch Q1 with a relatively high rated voltage, reducing costs. In addition, during the period when the first switch Q1 is turned off, the energy of the inductor is transferred to the load (resistance unit R1), enabling the load to continuously obtain energy and reducing energy waste.

[0067] In a specific implementation manner, referring to Figure 4 the circuit schematic diagram of another photovoltaic heating system shown, the second switch can be a freewheeling diode. The negative electrode of the freewheeling diode D1 is connected to the first end of the resistance unit R1, and the positive electrode of the freewheeling diode D1 is connected to the second end of the resistance unit R1. The first end of the resistance unit R1 is the end connected to the positive output terminal of the photovoltaic module. In this way, the freewheeling diode D1 provides a freewheeling path for the inductor current to prevent the counter electromotive force. At the same time, through the freewheeling action of the freewheeling diode D1, the energy in the inductor can be fully utilized.

[0068] Optionally, the freewheeling diode described above can be a fast recovery diode. During the freewheeling process, when the first switch is turned off, the current in the inductor needs to form a loop through the freewheeling diode. If the reverse recovery time of the freewheeling diode is too long, a large reverse current will be generated during the reverse recovery period, resulting in current spikes in the circuit, which may damage other components in the circuit and increase the losses of the circuit. Using a fast recovery diode can effectively reduce the reverse recovery time and reduce the adverse effects on the circuit.

[0069] In a possible implementation, referring to Figure 2 , to improve the safety of the circuit during use, based on the above embodiment, the photovoltaic heating system further includes an overheat protector FR; after the resistor unit R1 and the first switch Q1 are connected in series, they are connected to the photovoltaic module through the overheat protector FR.

[0070] In a possible implementation, referring to Figure 2 , to achieve start control and remote control of the heating resistor circuit, based on the above embodiment, the photovoltaic heating system further includes a relay KM, and a relay KM is provided on the circuit where the resistor unit R1 and the first switch Q1 are connected in series.

[0071] Optionally, the above photovoltaic heating system is provided with a third switch K1 at the positive output end of the photovoltaic module and a fourth switch K2 at the negative output end of the photovoltaic module, and the operation of the photovoltaic module is controlled by the third switch K1 and the fourth switch K2.

[0072] The above are some specific implementation manners of a photovoltaic heating system provided by the embodiments of the present application. Based on this, the present application also provides a corresponding control method. The following will be introduced from the perspective of the control method.

[0073] Referring to Figure 5 as shown in the schematic flowchart of the control method of a photovoltaic heating system, a control method of a photovoltaic heating system, the photovoltaic heating system includes a photovoltaic module, a resistor unit R1, a first switch Q1, and a controller; after the resistor unit R1 and the first switch Q1 are connected in series, they are connected between the positive output end and the negative output end of the photovoltaic module; the controller is connected to the control end of the first switch Q1;

[0074] The control method includes:

[0075] S501. Based on the maximum power point tracking MPPT algorithm, determine the reference resistance of the resistor unit R1 when the photovoltaic module operates at the maximum power point.

[0076] S502. Determine a control signal for controlling the duty cycle of the first switch Q1 based on the reference resistance, and output the control signal to the control end of the first switch Q1.

[0077] Based on the above method, due to the influence of environmental factors such as different irradiation intensities, the output current of the photovoltaic module will change. To enable the photovoltaic module to operate at the maximum power point, this application combines the maximum power point tracking (MPPT) algorithm to determine the reference resistance corresponding to the output voltage and output current of the photovoltaic module when operating at the maximum power point. In this way, the target value of the equivalent resistance of the first switch Q1 can be adjusted based on the reference resistance as the equivalent resistance of the resistance unit R1, so as to enable the photovoltaic module to operate at the maximum power point when the resistance value of the resistance unit R1 is fixed.

[0078] See Figure 6 the schematic diagram of the control strategy of the first switch shown. Based on the above method embodiment, the specific implementation manner of the above step S501 can be:

[0079] First, sample the output voltage Vpv and output current Ipv of the photovoltaic module, and determine the first voltage Vmp and the first current Imp corresponding to the photovoltaic module when operating at the maximum power through the maximum power point tracking (MPPT) algorithm.

[0080] Exemplarily, see Figure 2 the schematic diagram of an IV / PV curve shown. Based on the MPPT control, search for the first voltage at the maximum power of the photovoltaic string in the direction indicated by the arrow in Figure 2 and then determine the output current corresponding to the first voltage when the photovoltaic module operates at the maximum power as the first current.

[0081] Secondly, calculate the ratio of the first voltage Vmp to the first current Imp to obtain the reference resistance Rref.

[0082] Combined with the above method embodiment, see Figure 6 and the specific implementation manner of the above step S502 can be:

[0083] First, calculate the ratio of the actual resistance Rdc of the resistance unit R1 to the reference resistance Rref to obtain the duty cycle duty.

[0084] Secondly, generate a PWM drive signal through a PWM generator according to the duty cycle duty and output the PWM drive signal to the control terminal of the first switch Q1.

[0085] Exemplarily, the above second switch can be a MOS transistor. The gate of the MOS transistor is connected to the controller, and the current flow direction between the source and drain when the MOS transistor is turned on is opposite to the current flow direction in the resistance unit when the first switch is turned on. The controller controls the first switch and the second switch to be in an interlocked working state.

[0086] Based on the above method embodiments, refer to Figure 7 the schematic diagram of a preprocessing process shown in FIG. Before the above step S501, the method may further include:

[0087] S701. In response to the output voltage of the photovoltaic module reaching the startup voltage of the controller auxiliary power supply, the controller is powered on and initialized.

[0088] S702. Collect the output voltage and output current of the photovoltaic module, and determine whether the collected output voltage Vpv of the photovoltaic module is greater than or equal to the MPPT voltage at the minimum irradiance of the photovoltaic module.

[0089] The above MPPT voltage at the minimum irradiance refers to the lowest input voltage at which the maximum power point tracking circuit can achieve maximum power point tracking when the photovoltaic module it is connected to is at the minimum irradiance (which can be the minimum irradiance in the historical records of the location of the photovoltaic module).

[0090] S703. If the collected output voltage Vpv of the photovoltaic module is greater than or equal to the MPPT voltage at the minimum irradiance, then when the duty cycle of the first switch Q1 is 1 and the photovoltaic string operates for a first duration, collect the second voltage and second current output by the photovoltaic string.

[0091] Exemplarily, the above first duration can be 0.5 seconds. Without adjusting the duty cycle of the first switch Q1, after the first switch Q1 remains conducting for 0.5 seconds, collect the second voltage and second current output by the photovoltaic module, and actually determine the resistance of the circuit powered by the photovoltaic string as the resistance of the resistance unit R1.

[0092] S704. Calculate the ratio of the second voltage to the second current as the actual resistance of the resistance unit R1, and record it in the controller.

[0093] Record the actual resistance of the resistance unit R1 in the controller for use in the subsequent calculation in step S502.

[0094] S705. Detect whether there is a fault in the controller that controls the first switch. If there is no fault, execute the above S501 and subsequent steps; if there is a fault, re-execute step S701 and subsequent steps, and / or issue an alarm signal.

[0095] The faults include related faults such as abnormal controller communication and abnormal power supply that cannot output correct control signals.

[0096] Based on the above embodiments of a photovoltaic heating system and a control method for a photovoltaic heating system, this application uses 72 pieces of 560 - 580W topcon components, calculates the optimal equivalent resistance corresponding to the power under different irradiance conditions to select the resistance value of the heating resistor, calculates and compares the power loss, with a maximum loss of 82%. By adjusting the duty cycle of the first switch Q1, the power loss can be effectively reduced, as shown in Tables 1 - 5 below. Among them, P1 is the maximum power output by the photovoltaic module using the control scheme of this application, and P2 is the maximum power output by the photovoltaic module of the conventional scheme without duty cycle adjustment.

[0097] Table 1

[0098]

[0099] Table 2

[0100]

[0101] Table 3

[0102]

[0103]

[0104] Table 4

[0105]

[0106] Table 5

[0107]

[0108] Based on the data in the above table, it can be seen that the greater the irradiance, the smaller the reference resistance. Therefore, according to the average irradiance of the area where the photovoltaic modules are arranged, the reference resistance can be tested and calculated, and a heating element with a resistance value smaller than the reference resistance can be selected. Then, combined with the scheme of this application, when the irradiance fluctuates, the equivalent resistance value of the photovoltaic heating system can be adaptively adjusted to reduce the power loss.

[0109] The embodiment of this application also provides a corresponding computer storage medium for implementing the scheme provided by the embodiment of this application.

[0110] The computer storage medium stores code. When the code is run, the device running the code implements the control method of a photovoltaic heating system described in any embodiment of this application.

[0111] In the embodiments of this application, the "first", "second" (if any) in the names such as "first" and "second" are only used as name identifiers and do not represent the first and second in order.

[0112] As can be seen from the description of the above embodiments, those skilled in the art can clearly understand that all or part of the steps in the above method embodiments can be implemented by means of software plus a general hardware platform. Based on such an understanding, the technical solution of the present application can be embodied in the form of a software product, which can be stored in a storage medium, such as read-only memory (ROM) / RAM, magnetic disk, optical disk, etc., and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network communication device such as a router) to execute the methods described in various embodiments or some parts of the embodiments of the present application.

[0113] Each embodiment in this specification is described in a progressive manner. The same or similar parts among the embodiments can be referred to each other, and the differences between each embodiment and other embodiments are emphasized. In particular, for the device embodiments, since they are basically similar to the method embodiments, they are described relatively simply, and the relevant parts can be referred to the partial description of the method embodiments. The purpose of the present embodiment solution can be achieved by selecting some or all of the modules according to actual needs. Those of ordinary skill in the art can understand and implement it without creative efforts.

[0114] The above are only exemplary embodiments of the present application and are not used to limit the protection scope of the present application.

Claims

1. A photovoltaic heating system, characterized in that, Comprising: A photovoltaic module, a resistance unit, a first switch, and a controller; After the resistance unit and the first switch are connected in series, they are connected between the positive output terminal and the negative output terminal of the photovoltaic module; the controller is connected to the control terminal of the first switch; The controller is configured to determine a reference resistance of the resistance unit when the photovoltaic module operates at the maximum power point based on the maximum power point tracking (MPPT) algorithm; Determine a control signal for controlling the duty cycle of the first switch based on the reference resistance, and output the control signal to the first switch.

2. The photovoltaic heating system according to claim 1, wherein: The controller is configured to sample the output voltage and output current of the photovoltaic module, and determine a first voltage and a first current corresponding to the photovoltaic module operating at the maximum power through the maximum power point tracking (MPPT) algorithm; calculate a ratio of the first voltage to the first current to obtain a reference resistance; Calculate a ratio of the actual resistance of the resistance unit to the reference resistance to obtain a duty cycle; generate a PWM drive signal according to the duty cycle, and output the PWM drive signal to the control terminal of the first switch.

3. The photovoltaic heating system according to claim 1 or 2, wherein: It further includes a second switch, and the second switch is connected in parallel with the resistance unit; The second switch is configured to conduct when the first switch is turned off to provide freewheeling for the resistance unit, and the first switch and the second switch are in an interlocked operating state.

4. The photovoltaic heating system according to claim 3, wherein The second switch is a freewheeling diode, the negative electrode of the freewheeling diode is connected to the first end of the resistance unit, the positive electrode of the freewheeling diode is connected to the second end of the resistance unit, and the first end of the resistance unit is the end connected to the positive output terminal of the photovoltaic module.

5. The photovoltaic heating system according to claim 4, wherein, The second switch is a fast recovery diode.

6. The photovoltaic heating system according to claim 1, 2, 4 or 5, characterized in that The first switch is a MOS transistor or an IGBT.

7. The photovoltaic heating system according to claim 1, 2, 4, or 5, wherein: The resistance unit includes a heating resistor, and the resistance value of the heating resistor is less than or equal to a first resistance value, and the first resistance value is the ratio of the first voltage to the first current corresponding to the maximum power point under the maximum irradiance operation of the photovoltaic module.

8. A control method for a photovoltaic heating system, characterized in that, The photovoltaic heating system includes a photovoltaic module, a resistance unit, a first switch, and a controller; after the resistance unit and the first switch are connected in series, they are connected between the positive output terminal and the negative output terminal of the photovoltaic module; The controller is connected to the control terminal of the first switch; The control method includes: Determine a reference resistance of the resistance unit when the photovoltaic module operates at the maximum power point based on the maximum power point tracking (MPPT) algorithm; Determine a control signal for controlling the duty cycle of the first switch based on the reference resistance, and output the control signal to the control terminal of the first switch.

9. The method according to claim 8, characterized in that, The determining a reference resistance of the resistance unit when the photovoltaic module operates at the maximum power point based on the maximum power point tracking includes: Sample the output voltage and output current of the photovoltaic module, and determine a first voltage and a first current corresponding to the photovoltaic module operating at the maximum power through the maximum power point tracking (MPPT) algorithm; Calculate the ratio of the first voltage to the first current to obtain a reference resistance; and / or, Determining a control signal for controlling the duty cycle of the first switch based on the reference resistance and outputting the control signal to the control terminal of the first switch includes: Calculating the ratio of the actual resistance of the resistance unit to the reference resistance to obtain a duty cycle; Generating a PWM drive signal according to the duty cycle and outputting the PWM drive signal to the control terminal of the first switch.

10. The method according to claim 8 or 9, characterized in that, Before determining the reference resistance of the resistance unit when the photovoltaic module operates at the maximum power point based on the maximum power point tracking (MPPT) algorithm, it further includes: In response to the output voltage of the photovoltaic module reaching the startup voltage of the controller's auxiliary power supply, the controller is powered on and initialized; Collecting the output voltage and output current of the photovoltaic module and determining whether the collected output voltage of the photovoltaic module is greater than or equal to the MPPT voltage under the minimum irradiance of the photovoltaic module; If the collected output voltage of the photovoltaic module is greater than or equal to the MPPT voltage under the minimum irradiance, then after the duty cycle of the first switch is 1 and the photovoltaic string operates for a first duration, collect the second voltage and second current output by the photovoltaic string; Calculate the ratio of the second voltage to the second current as the actual resistance of the resistance unit and record the actual resistance in the controller; Confirm that the controller is free of faults.

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