CN115989610A - System and method for charging solar panels - Google Patents

Abstract

The present subject matter includes a solar panel charging system (100) that includes a solar panel (105) that is a current source, a converter module (110), a feed-forward loop (125), and a battery (115). Accordingly, the feed forward loop (125) comprises a signal inversion circuit (120). According to an embodiment, the solar panel (105) sends an input voltage Vin to the converter module (110) and the signal inversion circuit (120). The signal inverting circuit (120) inverts the input voltage Vin to an inverted voltage Vin' signal and sends it to the converter module (110). Furthermore, the converter module (1 l 0) then modulates and transmits the output voltage Vo to the battery (115). Thus, the output voltage (Vo) is caused to be equal to the desired voltage (Vd), ensuring that the maximum power is extracted from the solar panel (105) with a simple and inexpensive circuit.

Description

System and method for charging solar panels

Technical Field

The present subject matter relates generally to vehicles. More particularly, the present invention relates to systems and methods for charging solar panels.

Background

Solar powered automobiles, i.e., vehicles that operate in whole or in part by on-board solar collectors, are an implementable solution to address the energy crisis that the world may face in the future. Due to the high efficiency, low cost and availability of silicon-based solar panels, conventional solar panels, such as silicon-based solar panels, may be used for products or devices with mobility, e.g. automotive applications.

A solar charging controller, also known as a solar regulator, is essentially a solar cell charger connected between a solar panel and a battery. Which regulates the battery charging process to ensure that the battery is properly charged, or more importantly, not overcharged. Direct Current (DC) coupled solar charging controllers have existed for decades and are used in almost all small off-grid solar power generation systems. Simple PWM, or pulse width modulated, solar charging controllers have a direct connection from the solar array to the battery and use basic fast switches to modulate or control the battery charging. The switch (transistor) opens until the battery reaches the absorption charge voltage. The switch then begins to open and close rapidly (hundreds of times per second) to reduce the current and maintain a constant battery voltage. The problem with this technique is that the voltage of the solar panel is pulled down to match the cell voltage. This in turn causes the panel voltage to deviate from its optimal operating voltage (Vmp) at which the solar panel generates maximum power output and reduces the efficiency of the solar panel.

Drawings

The detailed description is made with reference to the accompanying drawings. The same reference numbers will be used throughout the drawings to refer to similar features and components.

FIG. 1 illustrates an exemplary side view of a vehicle for implementing the present subject matter.

Fig. 2 shows a block diagram of an integrated driver circuit with LED lights in a vehicle.

Fig. 3 shows a circuit level diagram depicting the present subject matter of an integrated driver circuit.

Fig. 4 shows a circuit configuration for setting the operating mode of the position light.

Fig. 5 shows a circuit configuration for setting the operation mode of the position light.

Detailed Description

Solar panels are basically series connections of solar cells (PV photovoltaic cells), which are combinations of P-N type materials. Each solar cell has independent voltage and current ratings. In general, all solar cells should have the same rating for series connection. The solar cells in series contribute to achieving the same current rating of the voltage. The solar panel is a current source. The voltage-current V-I characteristic of the known solar cell is shown in the graph in fig. 3. In general, solar cells are rated for open circuit voltage and short circuit current. Open circuit voltage refers to the voltage of the solar panel under no-load conditions. Short circuit current is the current drawn from the solar panel when the load is short circuited. The transferable power depends on the operating point, i.e. the output voltage and the output current of the solar panel, which are the inputs of the DC-DC converter.

Typically, a (direct current) DC-DC converter takes a voltage from a DC source and converts the supply voltage to another DC voltage level. They are used to increase or decrease the voltage level. Some devices require a certain amount of voltage to operate the device. Additionally, too much power may damage the device, or less power may not be able to start the device or operate the device efficiently. The converter draws power from the battery and reduces the voltage level, and similarly, the converter may increase the voltage level. The DC-DC converter is intended to increase or decrease the DC voltage without changing the power. Generally, DC-DC converters in electronic circuits use switching technology. A switch mode DC-DC converter converts DC voltage levels by temporarily storing input energy and then discharging that energy at a different voltage output.

There are various types of DC-DC converters, i.e., a Buck (Buck) converter, a Boost (Boost) converter, a Buck-Boost converter, etc. The buck converter is used to generate a voltage lower than the input. Buck converters are also referred to as step-down converters. In a buck converter, the polarity is the same as the input. Further, in the step-down converter, the relationship between the voltage and the current is (output voltage) Vo = D (constant) × Vin (input voltage); ii (input current) = D (constant) × Io (output current).

The boost converter is used to generate a voltage higher than the input voltage. The boost converter is called a booster and its polarity is the same as the input polarity. In a boost converter, the relationship between voltage and current is Vo (output voltage) = [ 1/(1-D) ] + Vin (input voltage); ii (input current) = [ 1/(1-D) ] × Io (output current). Here, D is a constant.

Furthermore, in a buck-boost converter, the output voltage may be increased or decreased compared to the input voltage. A common use of buck-boost converters is to reverse polarity. The relationship between voltage and current in the buck-boost converter is Vo (output voltage) = [ D/(1-D) ] + Vin (input voltage); ii (input current) = [ D/(1-D) ] + Io (output current). Here, D is a constant.

Typically, maximum Power Point Tracking (MPPT) charges the controller, ensuring that the load receives the maximum current to be used (by charging the battery quickly). The maximum power point is the ideal voltage at which maximum power is transferred to the load with minimum losses. The maximum power point is also commonly referred to as the peak power voltage. Generally, a Maximum Power Point Tracking (MPPT) solar charger operates with a microcontroller, supporting the use of different control algorithms to achieve maximum power transfer. This technique uses a switch to control charging. The switch (transistor) opens until the battery reaches the absorption charge voltage. Once the battery reaches the absorption charge voltage, the switch begins to open and close rapidly to reduce current and maintain a constant battery voltage for maximum power transfer.

Generally, maximum Power Point Tracking (MPPT) uses a microcontroller unit (MCU). When solar input is available and the battery is available for charging, the MCU has a predefined algorithm to operate in the maximum power point region. The inputs received by the MCU are solar panel voltage, solar panel current, output voltage and stable power supply value. Furthermore, the MCU should have at least three ADC channels, at least one PWM channel, at least one 16-bit/32-bit processor, RAM for data storage. The MCU will then generate an output as a gate signal to the gate drive circuit.

The MCU will sense the solar voltage and current at a specified sampling rate and multiply the voltage and current by the power, storing the power value for reference. During the next sampling it will again sense the voltage and current and multiply the power and compare the present power with the previous power, compare the present voltage with the previous voltage if the power increases and reduce the duty cycle if the voltage increases. Otherwise, the duty cycle is increased. If the present power is less than the previous power and the present voltage is less than the previous voltage, the duty cycle is decreased, otherwise the duty cycle is increased. However, the MCU requires a stable and regulated power supply on the order of 3.3V or 5V, which requires the use of another buck circuit to provide these bias supplies. This in turn increases the number of components and complexity. In addition, there are other disadvantages, such as more programming effort, increased complexity, additional circuitry required for the MCU to operate, etc. Furthermore, as discussed, the MCU requires a stable power supply, which needs to be derived from the solar panel through an additional voltage reduction circuit.

The problem with this technique is that the voltage of the solar panel is pulled down to match the cell voltage. This in turn causes the voltage of the solar panel to deviate from its optimum operating voltage (Vo) at which the solar panel generates maximum power output and thus reduces the efficiency of the solar panel. Accordingly, there is a need for an improved solar charging system that overcomes all of the above-referenced problems as well as other problems of the known art. In order to overcome the problem of the panel voltage not reaching its optimum operating voltage and thereby causing a reduction in the efficiency of the solar panel, according to one aspect of the present subject matter, the solar panel charger is configured with adjustable operating points, i.e. the input voltage and the input current of the DC-DC converter. Accordingly, the present invention discloses a solar panel charger capable of adjusting an input voltage of a DC-DC converter, which can be set at an operating point and can always maintain the operating point. According to an embodiment of the invention, the operating point is predetermined and is selected to be close to the maximum power point throughout the day.

In one embodiment of the invention, the solar panel charger comprises a combination of a DC-DC converter and an analog PWM controller. According to one embodiment, the DC-DC converter and the analog PWM controller control an input voltage of the DC-DC converter from the current source. Solar panels are current sources whose current values depend on the irradiance of the sun.

The solar panel V-I (voltage-current), V-W (voltage-power) characteristics are as shown in fig. 3, represented by curves a and W, respectively. As shown in fig. 3, vo is the ideal operating voltage, since there it will deliver maximum power to the DC-DC converter. In accordance with embodiments of the present subject matter, a solar panel charger system has a feed-forward loop and a feedback loop to control the input voltage and the output voltage, respectively. In one embodiment of the present subject matter, an input voltage is sensed using a resistive divider bridge and compared to a reference value. According to an embodiment of the present invention, an error value is generated when comparing an input voltage with a reference value and then provided as an input to a PWM controller. In one embodiment, upon receiving the error value as an input, the PWM controller generates pulses having a particular duty cycle corresponding to the error value. According to an embodiment, the MOSFET is triggered by a pulse generated by the PWM controller. According to embodiments of the present subject matter, the relationship between input voltage and duty cycle should be directly proportional, i.e. if Vin (input voltage) increases beyond a predetermined value, i.e. the desired value of the optimal voltage required for the solar panel to generate, the duty cycle is increased and if Vin decreases beyond a predetermined value, i.e. the desired value, the duty cycle is decreased to maintain the desired voltage value.

The detailed control flow is as follows, if Vin (input voltage) increases, since the battery load Vo (output voltage) is constant, the duty ratio D will increase. As the duty cycle D increases, the input current Ii will increase (because Ii = D × Io), and as Ii increases, vin will decrease. When the input voltage decreases, it will also remain unchanged. Thus, the input voltage will be maintained at the desired value. When the output voltage exceeds a certain value, the switching off of the output voltage will be achieved by disabling the PWM comparator.

The invention and all of the attendant embodiments and other advantages thereof will be described in more detail in connection with the accompanying drawings in the following paragraphs. The subject matter is further described with reference to the accompanying drawings. It should be noted that the description and drawings merely illustrate the principles of the present subject matter. Various arrangements may be devised which, although not explicitly described or shown herein, embody the principles of the present subject matter. Moreover, all statements herein reciting principles, aspects, and examples of the subject matter, as well as specific examples thereof, are intended to encompass equivalents thereof.

Fig. 1 shows a block diagram of a solar panel charging system in accordance with the present subject matter, depicting the interaction of each component for input and output voltage control. According to embodiments of the present subject matter, a solar panel charging system (100) includes a solar panel (105), a converter module (110), a feed-forward loop (125), and a battery (115). In one embodiment of the invention, the feed forward loop (125) includes a signal inversion circuit. In one embodiment of the invention, the converter module (110) is a DC-DC converter. In one embodiment of the present subject matter, the solar panel (105) is used as a current source for an electrical circuit. According to an embodiment of the present subject matter, the solar panel (105) sends an input voltage Vin to the converter module (110) and the signal inversion circuit (120). In one embodiment of the present subject matter, the converter module (110) includes a buck converter (not shown) and an analog controller (not shown). According to an embodiment of the present subject matter, the signal inverting circuit (120) inverts the input voltage Vin to an inverted voltage Vin' and sends it to the converter module (110). According to an embodiment of the present subject matter, the converter module (110) is then modulated and sends an output voltage Vo to the battery (115). Furthermore, according to an embodiment of the present invention, a portion of the output voltage Vo is sent back to the converter module (110) again as an input to generate an error value E (as shown in fig. 2).

Fig. 2 shows a block diagram of the present subject matter describing the interaction of each component of the converter module (110). Therefore, according to an embodiment of the invention, the solar panel charging system (100) comprises a feed-forward loop (125) and a feedback loop (not shown) to control the input voltage Vin and the output voltage, respectively. In one embodiment of the invention, the input voltage Vin is sensed using a resistive voltage dividing bridge (not shown). According to an embodiment of the invention, the converter module (110) comprises a comparator module (210) and a pulse modulation (PWM) controller (215). According to an embodiment of the invention, the comparator module (210) compares the input voltage Vin with a predetermined reference voltage Vref. According to an embodiment of the present invention, the comparator module (210) generates the error value E when comparing the input voltage Vin and the reference voltage Vref. In one embodiment of the invention, the error value E will be sent as an input to the PWM controller (215). According to an embodiment of the present invention, the PWM controller (215) compares the error value E with a reference value R and generates a plurality of modulation signal voltages P having a specific duty ratio D corresponding to the error value E. In one embodiment of the invention, the plurality of modulated signal voltages P trigger MOSFETs (metal-oxide-semiconductor field effect transistors). Furthermore, according to an embodiment of the present invention, the relationship between the input voltage Vin and the duty cycle D is directly proportional, i.e. when Vin increases beyond a predetermined value, the duty cycle D increases, and when Vin decreases beyond a predetermined value, the duty cycle decreases to maintain a desired value of the voltage (Vd) corresponding to the generation of the maximum power Pmax (as shown in fig. 3). In one embodiment of the invention, the desired voltage value (Vd) is in the range of 48V to 60V.

According to an embodiment of the present invention, the duty ratio D increases when the input voltage Vin increases and since the battery load Vo is constant. In one embodiment of the invention, when said duty cycle D increases, the input current Ii increases [ due to (input current) Ii = (duty cycle) D = (output current) ] i.e. the input current Ii is equal to the duty cycle D times the output current Io. Further, according to an embodiment of the present invention, when the input current Ii increases, the input voltage Vin decreases. Similarly, according to an embodiment of the present invention, when the input voltage Vin decreases, the relationship as described above will increase the input voltage Vin to a desired value, thereby generating the maximum power Pmax. Therefore, according to an embodiment of the present application, the input voltage Vin is always maintained at the desired value in order to generate the maximum power Pmax. Further, according to embodiments of the present subject matter, the output voltage cutoff as described above is accomplished by disabling the PWM comparator (215) when the PWM comparator (215) crosses a predetermined value. Fig. 3 shows a graphical representation of voltage-current and voltage-power of the solar panel (105), wherein the output voltage Vo is equal to the desired voltage Vd for achieving the maximum power Pmax, and the power line is denoted by W and the current line is denoted by a.

Fig. 4 shows a flow chart for the main circuit according to an embodiment of the invention. According to an embodiment of the invention, when the solar panel charging system (100) is turned on or enabled, if the battery (115) is connected, a first step (405) checks if the battery (115) is connected. The solar panel charging system (100) is shut down or stopped if the battery is not connected. A next step (410) includes checking the output voltage Vo against the desired voltage Vd. At step (415), the input voltage Vin from the solar panel (105) is sensed if the output voltage Vo is greater than the desired voltage Vd. However, at step (410), when Vd is not greater than Vo, the solar panel charging system (100) is turned off or stopped. Further, the next step is to compare the input voltage Vin with the reference voltage Vref (420). The signal inverting circuit (120) inverts the input voltage Vin to an inverted voltage Vin' (425) if the input voltage Vin is greater than the reference voltage Vref. However, at step (420), if the input voltage Vin is not greater than the reference voltage Vref, the solar panel charging system (100) is turned off or stopped. In one embodiment of the present invention, vin is compared with the reference voltage Vref to generate an error value E. The error value E is then sent as an input to the PWM comparator (215) and compared to the reference value R to generate the plurality of modulated signal voltages P. The duty cycle D is increased (430) based on steps within the signal inversion circuit (120) as will be explained in detail in fig. 5. As a result of the increase in the duty cycle D, the input voltage Vin decreases (435) based on the relationship explained via fig. 2. The next step (440) is to check if the output voltage Vo is equal to the desired voltage Vd. Further, the process stops (440) when the output voltage Vo is equal to the desired voltage Vd. However, if Vo is not equal to the desired voltage Vd at step (440), the solar panel charging system (100) is turned off or stopped.

Fig. 5 shows a flow diagram for the signal inversion circuit (120) according to an embodiment of the invention. According to an embodiment of the invention, a first step (505) is for the signal inverting circuit (120) to check whether the input voltage Vin from step (420) is available (420) (fig. 4). However, if at step (505) the input voltage Vin is not available, the system stops. Further, if the input voltage Vin is available, a next step includes scaling the input voltage down to a signal level (510). The next step is to send the scaled down input voltage Vin to an inverting amplifier (not shown) to amplify the input voltage Vin (515). Next, step (520) includes sending an amplified version of the input voltage Vin signal to the PWM controller (215), after which the flow diagram of the signal inverting circuit (120) is stopped.

According to an embodiment of the invention, the pulse width modulation unit (215) generates the plurality of modulated signal voltages P which are sent to the converter module (110). In one embodiment of the invention, the plurality of modulation signal voltages P is then added to the input voltage (Vin) so that the output voltage (Vo) is equal to the desired voltage (Vd), ensuring that maximum power is extracted from the solar panel (105) with simple and inexpensive circuitry.

Many modifications and variations of the present subject matter are possible in light of the above disclosure. Therefore, within the scope of the claims of the present subject matter, the disclosure may be practiced other than as specifically described.

List of reference numerals

100. Solar panel charging system

105. Solar panel

110. Converter module

115. Battery with a battery cell

120. Signal inverting circuit

125. Feedforward loop

210. Comparator module

215. Pulse Width Modulation (PWM) controller

Vo output voltage

Vd desired voltage

Vin input voltage

Vin' inverting input voltage

P multiple modulated signal voltages

E error value

Reference voltage of R

Duty ratio of D

Maximum power generated by Pmax

Claims (7)

1. A solar panel charging system (100), comprising:

solar panel (105):

a converter module (110) communicatively connected to the solar panel (105);

a feed-forward loop (125) comprising a signal inversion circuit (120) communicatively connected to the solar panel (105) and the converter module (110);

wherein the converter module (110) comprises a comparator module (210) and a Pulse Width Modulation (PWM) controller (215);

a battery (115) receiving power from the solar panel (105) through the converter module (110);

wherein the output voltage (Vo) is extracted from the converter module (110);

wherein a feedback input of the output voltage (Vo) is received by the converter module (110);

wherein if the output voltage (Vo) is less than a desired voltage (Vd), the output voltage (Vo) is compared to the desired voltage (Vd); an input voltage (Vin) generated by the solar panel (105) is received by the converter module (110) and the signal inversion circuit (120);

wherein the signal inverting circuit (120) receives the input voltage (Vin) to generate an inverted signal (Vin'), which is sent back to the converter module (110);

wherein the comparator module (210) of the converter module (110) compares the input voltage (Vin) with a reference voltage (Vref) signal to generate an error value (E);

-the error value (E) is sent to the pulse width modulation unit (215);

wherein the pulse width modulation unit (215) compares the error value with a reference value (R) and generates a modulated voltage signal (P) which is sent to the converter module (110) and then added to the input voltage (Vin) so as to make the output voltage (Vo) equal to the desired voltage (Vd), ensuring that the maximum power is extracted from the solar panel (105).

2. The invention of claim 1, wherein the converter module (110) compares the output voltage (Vo) to a desired voltage (Vd); the desired voltage (Vd) is a standard output voltage (i.e., a maximum voltage) of the solar panel at any point in time, and the desired voltage (Vd) is in a range of 48V to 60V.

3. The invention of claim 1, wherein the PWM controller (215) generates the plurality of pulses (P) having a duty cycle (D) corresponding to the error value (E).

4. The invention of claim 1, wherein the input voltage (Vin) is sensed using a resistive voltage dividing bridge.

5. The invention of claim 1, wherein the relationship between the input voltage (Vin) and the duty cycle (D) is directly proportional, i.e. when the input voltage (Vin) decreases beyond a predetermined value, the duty cycle (D) decreases to maintain the desired voltage (Vd) corresponding to a maximum power (Pmax).

6. The invention of claim 1, wherein the reference voltage (R) is a voltage provided by the solar panel (105) to produce a desired voltage (Vd) corresponding to a maximum power (Pmax).

7. A method of charging a solar panel, the method comprising:

checking whether a battery (115) is connected to the solar panel charging system (100);

checking the output voltage (Vo) with respect to the desired voltage (Vd) via a converter module (110):

sensing an input voltage (Vin) from the solar panel (105) if the output voltage (Vo) is greater than the desired voltage (Vd);

sending the input voltage (Vin) to a signal inverting circuit (120), and the signal inverting circuit generating an inverted voltage (Vin');

comparing, via the comparator module (210), the input voltage (Vin) with a reference voltage (Vref) to generate an error value (E);

sending the error value (E) to a pulse width modulation unit (215) and the pulse width modulation unit (215) comparing the error value (E) with a reference voltage (R);

generating a plurality of modulated signal voltages P via the pulse width modulation unit (215);

adding the plurality of modulation signal voltages P to the input voltage (Vin) within the converter module (110) such that the output voltage (Vo) is equal to the desired voltage (Vd).

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