WO2023243770A1 - Maximum power point tracking algorithm with separate double loops, and dc-dc converter for executing same - Google Patents

Abstract

A DC-DC converter of an energy-harvesting system according to an embodiment of the present invention is connected to a plurality of energy-generating modules that collect and convert external energy to electric energy, and controls the level of voltage supplied from the energy-generating modules, the DC-DC converter comprising: a buck converter; a main loop circuit for controlling the duty ratio of the buck converter so that the input voltage applied thereto can be maintained at a set level; and an auxiliary loop circuit for guiding the input voltage of the main loop circuit to reach the maximum power voltage, wherein the maximum power voltage is the voltage value at which the energy-harvesting system can generate energy at the maximum power.

Description

Maximum power tracking algorithm operating as a separated double loop and a direct current converter that performs it

The present invention relates to a maximum power point tracking (MPPT) algorithm that operates in an isolated double loop, and discloses a DC-DC converter for an energy harvesting system that performs this.

Energy harvesting is a technology that harvests natural energy generated around us and converts it into electrical energy.

A representative example is a solar power generation facility that converts collected sunlight into electrical energy and supplies it.

One of the most key issues in solar power generation is to continuously generate and supply the maximum possible power from an array of solar cells.

In other words, it is essential to find the maximum power point of the solar panel according to changes in conditions such as sunlight, temperature, and load, and this is implemented by the maximum power tracking (MPPT) algorithm.

One of the conventional MPPT algorithms is the P&O (Perturbation & Observation) algorithm set in solar inverters.

The P&O algorithm is a method of tracking the maximum point of the P-V curve (power-voltage curve) by gradually reducing or increasing the output voltage of the solar array and comparing the before and after power values.

Meanwhile, in solar power plants, deviations between individual panels occur due to various reasons, such as a shadow appearing on a specific panel, contamination of the panel by dust, snow, etc., or physical or electrical damage. It is a common reality that a P-V curve with multiple maximum points is formed depending on the variation between panels.

In relation to this, the existing P&O algorithm has a problem in that, as the number of maximum points increases, the speed and accuracy of MPPT are significantly reduced while the phenomenon of vibration increases. In other words, it is efficient in the P-V curve with one maximum point, but when it has multiple maximum points, it is difficult to determine which maximum point is the maximum power point, so the performance and results of MPPT cannot be guaranteed.

Additionally, VOLTAGE NOISE occurs in the process of changing current or voltage, and as a result, there is a risk that duty may be controlled in the wrong direction if an error occurs in voltage measurement.

Additionally, because existing inverters are generally directly connected to the grid, there are restrictions on the frequencies at which they can operate. Therefore, if the frequency is changed quickly, there is a high possibility that the system will not be able to respond, reaching a limit where it is impossible to perform MPPT above a certain speed.

The present invention is intended to solve the problems of the prior art described above, and provides energy harvesting that generates maximum power at all times by achieving fast and accurate MPPT through a DC-DC converter of a double loop circuit with different operating bandwidth. The purpose is to do so.

However, the technical challenges that this embodiment aims to achieve are not limited to the technical challenges described above, and other technical challenges may exist.

In the DC-DC converter of an energy harvesting system according to an embodiment of the present invention, the DC-DC converter is each connected to a plurality of energy generation modules that collect external energy and convert it into electrical energy, It adjusts the voltage level of direct current power provided from the energy generation module, and the DC-DC converter includes: a buck converter; a main loop circuit that controls the duty ratio of the buck converter so that the input voltage applied to the buck converter is maintained constant; and an auxiliary loop circuit that guides the input voltage of the main loop circuit to become the maximum power voltage, where the maximum power voltage is a voltage value that allows the energy harvesting system to generate energy at maximum power.

According to one embodiment of the present invention, the auxiliary loop circuit calculates the power of the output stage of the buck converter by calculating based on at least one of the input voltage, input current pair, output voltage, and output current pair of the buck converter. power calculation unit; When a current change occurs through load adjustment of the output stage of the buck converter, the N-1th output stage power before the current change occurs (N is a natural number greater than 1) and the Nth output stage power after the current change occurs. A power difference calculation unit that calculates the power difference between the two; and a reference voltage correction unit that generates a first correction value based on the power difference and reflects the first correction value in the reference voltage applied to the main loop circuit.

According to one embodiment of the present invention, the reference voltage correction unit adds or subtracts the first correction value to the reference voltage so that the power of the output terminal reaches the maximum power.

According to an embodiment of the present invention, when the Nth output stage power is greater than the N-1th output stage power and the N+1th output stage power is greater than the Nth output stage power, the first correction value applied to the Nth plus or The minus operator sign is maintained as is in the N+1th output stage, and the Nth output stage power is greater than the N-1th output stage power, but if the N+1th output stage power is less than the Nth output stage power, the 1st output stage applied to the Nth The operation sign opposite to the plus or minus operation sign of the correction value is applied to the N+1th operation.

According to one embodiment of the present invention, the auxiliary loop circuit determines the Nth reference voltage by plus or minus the first correction value to the N-1th reference voltage, and provides the Nth reference voltage to the main loop circuit. .

According to one embodiment of the present invention, the main loop circuit includes: an arithmetic unit that calculates a difference between the reference voltage and the input voltage of the buck converter; and a duty ratio control unit that calculates a second correction value based on the difference between the reference voltage and the input voltage and controls the duty ratio of the buck converter based on the second correction value.

According to one embodiment of the present invention, the calculation of the second correction value is performed so that when the input voltage is lower than the previous input voltage, the duty ratio is lower than the previous input voltage, so that the input voltage is greater than the previous input voltage. In this case, the duty ratio is performed so that it is greater than the previous duty ratio, so that the input voltage is maintained constant.

According to one embodiment of the present invention, the DC-DC converter calculates the Nth reference voltage by reflecting the second correction value for the N-1th reference voltage through a feedback loop, thereby reducing the input voltage. This is to prevent separation between and the reference voltage.

According to one embodiment of the present invention, it is assumed that the main loop cycle is a one-time process in which the main loop circuit calculates the difference between the reference voltage and the input voltage of the buck converter and controls the duty ratio of the buck converter. , when the auxiliary loop circuit calculates a power difference value according to the power change of the output terminal of the buck converter and corrects the reference voltage based on the power difference value, when the auxiliary loop cycle is a one-time process, the main When the loop cycle is executed multiple times, the auxiliary loop cycle is executed once.

According to one embodiment of the present invention, the MPPT direction is determined only according to whether the power increases or decreases, not the direction of the increase or decrease of the voltage.

Therefore, in situations where there are multiple maximum points, the maximum power point can be found more quickly and accurately, and it is easy to deal with the occurrence of vibration or noise.

According to one embodiment of the present invention, the input voltage of the DC-DC converter is fixed and the output power is maintained, so the voltage does not drop sharply no matter what current is required within the limit capacity.

According to one embodiment of the present invention, the MPPT algorithm is designed as a double loop operation, and the cycle of the loop to maintain the input voltage is set faster than the cycle of the loop to find the maximum power point.

Therefore, even if the current flowing through the output terminal increases rapidly due to load adjustment or the input power suddenly decreases due to external factors, response is possible, and the input voltage is maintained constant.

In addition, since it is implemented as a double loop, there is no risk of MPPT proceeding in the wrong direction, and stability is guaranteed while operating at high speed.

That is, according to an embodiment of the present invention, energy at maximum power is stably provided at all times through energy harvesting.

1 is a schematic structural diagram of an energy harvesting system according to an embodiment of the present invention.

Figure 2 is a schematic structural diagram of a DC-DC converter according to an embodiment of the present invention.

Figure 3 is a schematic structural diagram of an auxiliary loop circuit according to an embodiment of the present invention.

Figure 4 is a schematic structural diagram of the main loop circuit according to an embodiment of the present invention.

Figure 5 is an example diagram schematically showing the operation process of the MPPT algorithm according to an embodiment of the present invention.

Figure 6 is an operation flowchart of the MPPT algorithm according to an embodiment of the present invention.

Below, with reference to the attached drawings, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. In order to clearly explain the present invention in the drawings, parts that are not related to the description are omitted, and similar parts are given similar reference numerals throughout the specification.

Throughout the specification, when a part is said to be "connected" to another part, this includes not only the case where it is "directly connected," but also the case where it is "electrically connected" with another element in between. . Additionally, when a part "includes" a certain component, this means that it may further include other components rather than excluding other components, unless specifically stated to the contrary.

In this specification, 'part' includes a unit realized by hardware, a unit realized by software, and a unit realized using both. Additionally, one unit may be realized using two or more pieces of hardware, and two or more units may be realized using one piece of hardware. Meanwhile, '~ part' is not limited to software or hardware, and '~ part' may be configured to reside in an addressable storage medium or may be configured to reproduce one or more processors. Therefore, as an example, '~ part' refers to components such as software components, object-oriented software components, class components, and task components, processes, functions, properties, and procedures. , subroutines, segments of program code, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and variables. The functions provided within the components and 'parts' may be combined into a smaller number of components and 'parts' or may be further separated into additional components and 'parts'. Additionally, components and 'parts' may be implemented to regenerate one or more CPUs within a device or a secure multimedia card.

In this specification, “energy harvesting system” refers to equipment that harvests natural energy collected from the surroundings by converting it into electric energy, and may include both industrial and household equipment. For example, in the case of a solar power generation system, it can include both stand-alone and grid-connected systems.

Natural energy used as renewable energy in the present invention is not limited in type, such as body energy, light energy, vibration energy, heat energy, electromagnetic wave energy, gravitational energy, and potential energy, but for explanation purposes, a representative example is the solar power generation system. The description should focus on .

In this specification, the “P-V curve (current-voltage curve)” is a piece of information representing the operating characteristics of an electronic device, and is defined as a set of graphic curves that visually show the relationship between power and voltage that occurs within a circuit. Typically, in the present invention, it is used as one of the elements that defines the electrical characteristics at the output stage of a DC-DC converter.

In this specification, “MPPT” refers to a series of processes from tracking the maximum generated power to providing it within the energy harvesting system. Typically, the present invention includes the process of finding the maximum point corresponding to the maximum power within the P-V curve of the DC-DC converter and maintaining the output of maximum power through this process.

In this specification, “maximum power voltage” refers to a voltage value that allows energy to be generated at maximum power through energy harvesting, and is the voltage corresponding to the maximum power point (MP) tracked by MPPT. This applies to this.

Hereinafter, an embodiment of the present invention will be described in detail using the attached drawings.

1 is a structural diagram of an energy harvesting system according to an embodiment of the present invention.

Referring to FIG. 1, an energy harvesting system according to an embodiment of the present invention may include an energy generation module 10 and a DC-DC converter 100.

The energy generation module 10 according to one embodiment is a device that collects surrounding external energy and converts it into electrical energy. For example, in the case of a solar power generation system, it may be a cell-level “solar cell” that produces electricity through the photoelectric effect. Preferably, the module may be a “solar panel” in which a plurality of solar cells are connected vertically and horizontally and assembled.

At least one or more energy generation modules 10 according to an embodiment may be connected to each other. For example, in the case of a solar power generation system, a plurality of energy generation modules 10 may be connected in series to form an array.

The DC-DC converter 100 according to one embodiment is connected to each energy generation module 10 and adjusts the voltage level of direct current power provided from them. For example, in the case of a solar power generation system, the DC-DC converter 100 can be modularized according to unit capacity and connected to each solar panel 10 installed in the system.

The DC-DC converter 100 according to one embodiment converts an input voltage (V _in ) into a predetermined output voltage (V _out ) according to a device that transmits the generated electrical energy. For example, in the case of an independent solar power generation system, it is boosted or stepped down to a DC voltage suitable for the connected battery, or in the case of a grid-connected system, the generated power is converted into stabilized DC power to suit the power system.

Meanwhile, in MPPT in the existing energy harvesting system, the maximum power point is tracked by the inverter, and the process of adjusting the output voltage of the DC-DC converter to the maximum power voltage determined through this is carried out in one cycle. Therefore, there was a restriction that the inverter had to operate within a preset frequency (e.g., 60 Hz) depending on the system connected to it. In other words, due to problems such as power factor, if the frequency is changed faster than the set frequency, there is a high possibility that the connection with the grid will be broken, making it impossible to perform MPPT with a bandwidth above a certain level.

In order to improve such conventional problems, an embodiment of the present invention discloses a feature of a DC-DC converter 100 that performs MPPT through a separated double loop operation.

Figure 2 is a schematic structural diagram of a DC-DC converter according to an embodiment of the present invention.

Referring to FIG. 2, the DC-DC converter 100 according to one embodiment may include an auxiliary loop circuit 110, a main loop circuit 120, and a buck converter 130.

First, in the DC-DC converter 100, the direct current converter may be composed of a buck converter 130. The buck converter 130 is a step-down converter used when a voltage lower than the input voltage is required, and is stable because it exhibits I-V characteristics without voltage divergence. Therefore, compatibility with various inverters is possible. In addition, it has the advantage of being a relatively less complex structure that can be implemented simply and manufactured at a low cost.

The main loop circuit 120 may be configured as a feedback loop connected to the buck converter 130 to receive input voltage (V _in ) of the buck converter 130 as feedback.

The main loop circuit 120 calculates the difference between the voltage (V _in ) applied to the input terminal of the buck converter 130 and the reference voltage (V _ref ) and adjusts the duty ratio of the PWM (Pulse Width Modulation) signal to offset the difference. Adjust. That is, the main loop circuit 120 controls the duty ratio of the buck converter 130 so that the input voltage (V _in ) applied to the buck converter 130 is maintained constant.

Here, the cycle in which the above process is performed once is defined as the main loop cycle.

According to one embodiment, the reference voltage (V _ref ) may be preset in the DC-DC converter 100, but the maximum power voltage (V _MP ) corresponding to the maximum power point is preferable.

The auxiliary loop circuit 110 receives the input voltage (V _in ), input current (I _in ), output voltage (V _out ), and output current (V _in ) of the buck converter 130 as feedback. It can be composed of a feedback loop connected to the input and output terminals.

The auxiliary loop circuit 110 calculates a power difference value according to the power change at the output stage of the buck converter 130 using the current and voltage of the input and output terminals that are fed back. Afterwards, the reference voltage (V _ref ) is corrected so that the reference voltage (V _ref ) becomes the maximum power voltage (V _MP ) based on the calculated value. That is, the auxiliary loop circuit 110 serves to guide the input voltage (V _in ) of the main loop circuit 120 to become the maximum power voltage (V _MP ).

Here, a cycle in which the above process is performed once is defined as an auxiliary loop cycle.

According to one embodiment, in the auxiliary loop cycle, when the duty ratio is changed in the main loop circuit 120, a voltage (V _out ) or a current (I _out ) according to the duty ratio change is applied to the output terminal of the buck converter 130. ) can be determined based on the time it takes for the flow to flow.

According to one embodiment, the main loop cycle and the auxiliary loop cycle are designed to have different execution speeds. Preferably, when the main loop cycle is executed multiple times (k times), the auxiliary loop cycle is executed once, and the main loop can be designed to operate relatively quickly at a ratio of k:1 (k>1).

In this way, since the MPPT of the present invention operates as a separate double loop, errors in the MPPT progress direction are prevented. In addition, each loop operates at a different bandwidth, ensuring loop stability and implementing fast MPPT with relaxed frequency constraints. As a result, it is possible to respond to unexpected situations such as sudden changes in the amount of sunlight incident, contributing to the construction of a stable system.

Hereinafter, an embodiment of the double loop of the present invention will be described using FIGS. 3 and 4.

Figure 3 is a schematic structural diagram of an auxiliary loop circuit according to an embodiment of the present invention.

Referring to FIG. 3, the auxiliary loop circuit 110 according to one embodiment may include a power calculation unit 111, a power difference calculation unit 112, and a reference voltage correction unit 113.

Roughly speaking, the power calculation unit 111 calculates the power of the output stage of the buck converter 130 and transfers it to the power difference calculation unit 112, and the power difference calculation unit 112 calculates the received output stage power and the previous output stage power. The difference is calculated and transmitted to the reference voltage correction unit 113, and the reference voltage correction section 113 corrects the reference voltage applied to the main loop circuit 120 to the current maximum power voltage based on the received power difference. do.

The power calculation unit 111 according to an embodiment is configured to calculate at least one of the input voltage (V _in ), input current (I _in ), output voltage (V _out ), and output current (V _in ) fed back from the buck converter 130. It may be a type of power calculator that calculates the power of the output stage of the buck converter 130 by using two or more measured values.

According to one embodiment, the power calculation unit 111 generates output power based on at least one of the input voltage (V _in ) and input current (I _in ) pairs and the output voltage (V _out ) and output current (V _in ) pairs. can be calculated. That is, the power calculated by the power calculation unit 111 may be the product of the input voltage (V _in ) and the input current (I _in ) or the product of the output voltage (V _out ) and the output current (V _in ). Of course, it is assumed that the law of energy conservation is satisfied, and even if there is some power loss during the direct current conversion process, it can be excluded as it is within the error range.

According to one embodiment, the power calculation unit 111 may calculate the output power of the buck converter 130 at least once during the auxiliary loop cycle. In other words, high reliability of MPPT can be secured by deriving the output power using the current and voltage of the input and output terminals measured several times.

According to one embodiment, the power calculation unit 111 may calculate the average value of the output power calculated during the auxiliary loop cycle. In this case, the influence of noise that may occur when current and voltage values are measured or when the measured values are converted to analog-to-digital can be minimized.

The power difference calculation unit 112 according to one embodiment calculates the power difference between the previously stored N-1th output stage power and the Nth output stage power received from the power calculation unit 111. Here, N is a natural number greater than 1.

For example, in the power difference calculation unit 112, when a current change occurs through load adjustment connected to the output terminal of the buck converter 130, the N-1th output terminal power and current change occur before the current change occurs. Calculate the power difference between the power of the Nth output stage.

This applies not only to cases where the current flowing in the circuit suddenly changes, but also to cases where the input power changes suddenly, such as when a shadow suddenly falls on a solar panel. In other words, conditions may change rapidly due to various causes in energy harvesting, and if a change in power occurs, it should be interpreted as being included in the scope of this embodiment.

The reference voltage correction unit 113 according to one embodiment generates a first correction value based on the power difference received from the power difference calculation unit 112 and applies the reference voltage (V) to the main loop circuit 120. _ref ) reflects the first correction value. The first correction value is a value that corrects the reference voltage (V _ref ) so that the reference voltage (V _ref ) approaches the maximum power voltage.

According to one embodiment, the first correction value is plus or minus the N-1th reference voltage through the auxiliary loop circuit 110 to determine the Nth reference voltage, which is provided to the main loop circuit 120.

According to one embodiment, the reference voltage correction unit 113 calculates the reference voltage by adding or subtracting the first correction value to the previous reference voltage so that the output power of the buck converter 130 reaches the currently tracked maximum power. The voltage (V _ref ) is stored as the currently tracked maximum power voltage and transmitted to the main loop circuit 120.

That is, the reference voltage (V _ref ) is continuously maintained close to the maximum power voltage due to tracking of the maximum power point on the auxiliary loop circuit 110, which means that the input voltage (V _in ) in the main loop circuit 120 is the maximum power. It guides you to follow the voltage, and related details will be described later using FIG. 4.

According to one embodiment, the sign of the first correction value during calculation is based on the power difference received from the power difference calculation unit 112, and determines whether the output stage power increases or decreases, or whether there is a change in the increase or decrease flow of the output stage power. Depending on this, it is determined as a plus sign (+) or minus sign (-).

Specifically, when the power is continuously increasing, such as when the power of the Nth output stage is greater than the power of the N-1th output stage and the power of the N+1th output stage is greater than the power of the Nth output stage, the control applied to the Nth The plus or minus operation sign of the 1 correction value is maintained as is for the N+1th time. Of course, even when the power continues to decrease, the operation code remains the same.

On the other hand, when the power increases and then decreases, such as when the power of the Nth output stage is greater than the power of the N-1th output stage, but the power of the N+1th output stage is less than the power of the Nth output stage, the control applied to the Nth output stage is 1The operation sign opposite to the plus or minus operation sign of the correction value is applied to the N+1th. Of course, the same applies when the power decreases and then increases. That is, when the power flow changes, the operation sign of the first correction value is reversely changed.

In this way, in maximum power tracking according to an embodiment of the present invention, the tracking direction is determined solely based on the change in power, not the increase or decrease in voltage. Therefore, even if there are multiple maximum points in the P-V curve, the phenomenon of progressing in the wrong direction does not occur, and the maximum power point can be accurately found without being affected by vibration or noise.

Figure 4 is a schematic structural diagram of the main loop circuit according to an embodiment of the present invention.

Referring to FIG. 4, the main loop circuit 120 according to one embodiment may include an operation unit 121 and a duty ratio control unit 122.

Roughly, the calculation unit 121 calculates the difference between the reference voltage received from the auxiliary loop circuit 110 and the input voltage of the buck converter 130, and the duty ratio control unit 122 adjusts the duty ratio of the PWM to offset this difference. By controlling, the input voltage is maintained at the reference voltage.

The calculation unit 121 according to one embodiment calculates the difference between the currently measured input voltage (V _in ) and the currently set reference voltage (V _ref ). That is, how far the current input voltage (V _in ) is from the maximum power voltage, which is the reference voltage (V _ref ), is determined and transmitted to the duty ratio control unit 122 .

The duty ratio control unit 122 according to one embodiment calculates the second correction value based on the difference received from the calculation unit 121. The second correction value may mean a duty ratio control value for correcting the input voltage (V _in ) so that the input voltage (V _in ) reaches the reference voltage (V _ref ). Afterwards, the duty ratio control unit 122 controls the duty ratio for the PWM signal of the buck converter 130 based on the second correction value.

The calculation for the second correction value according to one embodiment is such that when the current input voltage (V _in ) is lower than the previous input voltage, the current input voltage (V _in ) is lower than the previous input voltage so that the current duty ratio is smaller than the previous duty ratio. If it is greater than the voltage, it can be performed so that the current duty ratio is greater than the previous duty ratio.

That is, the duty ratio control unit 122 increases the duty ratio to decrease the input voltage (V _in ) when it increases, and performs control to reduce the duty ratio to increase it when the input voltage (V _in ) decreases. Accordingly, the input voltage can be kept constant by being fixed to the reference voltage (V _ref ), which is the currently tracked maximum power voltage.

According to one embodiment, when the voltage (V _in ) applied to the input terminal of the buck converter 130 is fixed to the reference voltage (V _ref ), the current flowing to the input terminal is also fixed. Accordingly, the power generated at the input terminal of the buck converter 130 is also fixed to a constant level.

According to energy conservation, the power at the input terminal and the power at the output terminal in the buck converter 130 are the same, so the power at the output terminal is also fixed to a constant. Since power is the product of current and voltage, when power is fixed, an inverse relationship is established with the output current (I _out ) for the output voltage (V _out ) below the reference voltage (V _ref ). In other words, instead of the conventional non-linear IV characteristic, it is converted to a linear IV characteristic in which the voltage applied to the output stage decreases when the current flowing through the output stage increases.

Therefore, even if the output terminal current (I _out ) increases above a certain level due to adjusting the load connected to the output terminal or other causes, the output terminal voltage (V _out ) does not change drastically. In other words, the DC-DC converter 100 according to an embodiment of the present invention can be stably driven no matter how much current flows as long as it is within the limit capacity of the circuit.

According to one embodiment, the current and voltage at the output terminal of the buck converter 130 have an inverse relationship below the reference voltage (V _ref ), so the PV curve below the reference voltage (V _ref ) has a gentle slope. For example, in an array unit where a plurality of energy generation modules 10 are connected in series, even if a deviation occurs between each module 10, one maximum point may be formed in the PV curve instead of a plurality of maximum points.

According to one embodiment, the reference voltage (V _ref ) is the maximum power voltage (V _MP ) provided from the auxiliary loop circuit 110, and the slope of the PV curve below the reference voltage (V _ref ) is used to maintain maximum power. is preferably designed to be “0”.

According to one embodiment, according to the voltage drop characteristics of the buck converter 130, the voltage (V _out ) applied to the output terminal of the buck converter 130 is a voltage lower than the reference voltage (V _ref ). Therefore, according to the above-described embodiment, since the PV curve is saturated below the reference voltage (V _ref ), the maximum power output can be maintained at all times to achieve maximum efficiency of energy harvesting.

As described above, the main loop cycle can be designed faster than the auxiliary loop cycle at a ratio of k:1. In other words, the main loop operates with a faster bandwidth than the auxiliary loop. For example, if the ratio is 5:1, the loop that keeps the input voltage (V _in ) constant at the maximum power voltage during the auxiliary loop cycle operates 5 times faster. Therefore, even if the current is suddenly pulled at the output terminal or the power at the input terminal is suddenly reduced, the maximum power voltage is maintained constant, so a sudden deviation from the maximum power does not occur.

In addition, while the main loop operates quickly, it tracks the current maximum power point through a relatively slow auxiliary loop, thereby averaging the power and getting closer to the maximum power point with more accurate values. As such, MPPT according to an embodiment of the present invention can be performed at a significantly faster speed than before, and at the same time can maintain accurate maximum power output.

Meanwhile, according to an embodiment of the present invention, the DC-DC converter 100 may further include a feedback loop that prevents separation between the input voltage (V _in ) and the reference voltage (V _ref ). For example, the main loop circuit 120 may transmit the second correction value calculated based on the N-1th reference voltage to the auxiliary loop circuit 120. When calculating the N-th reference voltage, the auxiliary loop circuit 120 performs correction to reflect the received second correction value to the N-th reference voltage by adding or subtracting the second correction value. can do. In this way, even in an unexpected situation where the input power suddenly changes due to internal or external causes, the input voltage (V _in ) is not too far from the reference voltage (V _ref ), preventing an error in which the MPPT proceeds in the wrong direction. there is.

Hereinafter, with reference to FIGS. 5 and 6, an embodiment of the MPPT algorithm of the present invention will be described. Here, it is assumed that the current and voltage of the input and output terminals of the DC-DC converter 100 are measured as digital signals through an analog-to-digital converter (ADC). Of course, the above-described information is the same algorithm based on an analog circuit, and any overlapping content will be replaced by this.

FIG. 5 is an example diagram schematically showing the operation process of the MPPT algorithm according to an embodiment of the present invention, and FIG. 6 is an operation flowchart of the MPPT algorithm according to an embodiment of the present invention.

First, steps S61 to S65 are a process of finding the maximum power point and are performed every auxiliary loop cycle, and step S66 is a process of fixing the voltage applied to the input terminal of the buck converter to the maximum power voltage derived in step S65 and are performed every main loop cycle. do. Here, when the auxiliary loop cycle operates once, the main loop cycle can operate multiple times (k, k is a number greater than 1). In other words, the main loop cycle can be designed with a faster bandwidth than the auxiliary loop cycle.

Therefore, assuming that the maximum power voltage determined in step S65 is the N-1th maximum power voltage, while the loop that fixes the input voltage to the N-1th maximum power voltage through step S66 operates k times, the Nth maximum power voltage is simultaneously maintained. The tracking loop operates once.

In step S61, at least two of the input voltage (adc_V _in ), output voltage (adc_V _out ), input current (adc_I _in ), and output current (adc_I _out ) of the buck converter are measured. For example, at least one of a pair of voltage (adc_V _in ) and current (adc_I _in ) at the input terminal and a pair of voltage (adc_V _out ) and current (adc_I _out ) at the output terminal is measured.

In step S62, the power of the buck converter output stage is calculated. An operation is performed to multiply the voltage (adc_V _in ) and current (adc_I _in ) of the input terminal or the voltage (adc_V _out ) and current (adc_I _out ) of the output terminal. At this time, a plurality of powers can be calculated through various measurement values collected during the auxiliary loop cycle, and ultimately step S63 can be performed using the average value of these values.

In step S63, a first correction value (err_s) is calculated based on the calculated power (power). Preferably, the first correction value (err_s) is calculated based on the change rate of power (power). For example, when there is an adjustment of the load, the rate of change between the power before adjustment and the power after adjustment is calculated, and the voltage value required to reach the power after adjustment is calculated based on the P-V curve.

In step S64, the operation sign (sign) of the first correction value (err_s) is determined. In other words, it is determined whether the first correction value should be plus or minus in order to reach the maximum power point on the P-V curve. At this time, when the rising or falling flow of power is maintained, the sign of the first correction value is determined as calculated. On the other hand, when the flow of power changes, the sign of the first correction value changes to the opposite of the calculated state.

In step S65, the reference voltage (adc_V _ref ) corresponding to the current maximum power voltage is determined by reflecting the first correction value (err_s). At this time, the first correction value (err_s) can be integrated into the previous reference voltage based on the operation sign (sign), and a preset integration constant (K _I ) can be applied.

In step S66, the difference between the reference voltage (adc_V _ref ) determined in step S66 and the voltage (adc_V _in ) measured at the input terminal of the buck converter is calculated. In addition, based on the calculated power difference, a second correction value (err_p) is calculated for the input voltage (adc_V _in ) to reach the reference voltage (adc_V _ref ). At this time, the second correction value (err_p) can be integrated into the input voltage (adc_V _in ), and a preset integration constant (K _I ) or proportional constant (K _P ) can be applied. Afterwards, duty ratio control is performed based on the second correction value (err_p), and accordingly, the input voltage (adc_V _in ) is fixed to the reference voltage (adc_V _ref ) to maintain output of maximum power.

Meanwhile, in step S66, in order to prevent a large gap between the input voltage (adc_V _in ) and the reference voltage (adc_V _ref ), the second correction value (err_p) for the N-1th reference voltage is reflected and the Nth A reference voltage can be calculated.

The description of the present invention described above is for illustrative purposes, and those skilled in the art will understand that the present invention can be easily modified into other specific forms without changing the technical idea or essential features of the present invention. will be.

For example, an embodiment related to the above-described maximum power tracking has been described assuming that the P-V curve is always fixed over time, but when a predetermined change occurs in the P-V curve (e.g., solar power generation The same can be applied to cases where the illuminance changes slowly over time due to changes in the illuminance incident on the system.

Therefore, the embodiments described above should be understood in all respects as illustrative and not restrictive. For example, each component described as single may be implemented in a distributed manner, and similarly, components described as distributed may also be implemented in a combined form.

The scope of the present invention is indicated by the claims described below rather than the detailed description above, and all changes or modified forms derived from the meaning and scope of the claims and their equivalent concepts should be construed as being included in the scope of the present invention. do.

Claims (9)

1. In the DC-DC converter of an energy harvesting system,

   The DC-DC converter is each connected to a plurality of energy generation modules that collect external energy and convert it into electrical energy, and adjusts the voltage level of direct current power provided from the energy generation modules,

   The DC-DC converter is,

   buck converter;

   a main loop circuit that controls the duty ratio of the buck converter so that the input voltage applied to the buck converter is maintained constant; and

   Including an auxiliary loop circuit that guides the input voltage of the main loop circuit to become the maximum power voltage,

   The maximum power voltage is a voltage value that allows the energy harvesting system to generate energy at maximum power, a DC-DC converter.
2. According to clause 1,

   The auxiliary loop circuit is,

   a power calculation unit that calculates the power of the output stage of the buck converter by calculating based on at least one of the input voltage, input current pair, and output voltage and output current pair of the buck converter;

   When a current change occurs through load adjustment of the output stage of the buck converter, the N-1th output stage power before the current change occurs (N is a natural number greater than 1) and the Nth output stage power after the current change occurs. A power difference calculation unit that calculates the power difference between the two; and

   a reference voltage correction unit that generates a first correction value based on the power difference and reflects the first correction value in the reference voltage applied to the main loop circuit;

   DC-DC converter, including.
3. According to clause 2,

   The reference voltage correction unit,

   A DC-DC converter that adds or subtracts the first correction value to the reference voltage so that the power of the output stage reaches the maximum power.
4. According to claim 3,

   If the Nth output stage power is greater than the N-1th output stage power, and the N+1th output stage power is greater than the Nth output stage power, the plus or minus operation sign of the first correction value applied to the Nth is also applied to the N+1th output stage. keep it the same,

   If the power of the Nth output stage is greater than the power of the N-1th output stage, but the power of the N+1th output stage is less than the power of the Nth output stage, the operation sign opposite to the plus or minus operation sign of the first correction value applied to the Nth A DC-DC converter that applies to the N+1th.
5. According to clause 4,

   The auxiliary loop circuit is,

   A DC-DC converter wherein the N-th reference voltage is determined by plus or minus the first correction value to the N-1th reference voltage, and the N-th reference voltage is provided to the main loop circuit.
6. According to clause 2,

   The main loop circuit is,

   a calculation unit that calculates a difference between the reference voltage and the input voltage of the buck converter; and

   a duty ratio control unit that calculates a second correction value based on the difference between the reference voltage and the input voltage and controls the duty ratio of the buck converter based on the second correction value;

   DC-DC converter, including.
7. According to clause 6,

   The calculation for the second correction value is,

   When the input voltage is lower than the previous input voltage, the duty ratio is smaller than the previous duty ratio,

   When the input voltage is greater than the previous input voltage, the duty ratio is performed so that it is greater than the previous duty ratio,

   A DC-DC converter that ensures that the input voltage is kept constant.
8. According to claim 6,

   The DC-DC converter is,

   A DC-DC converter that prevents separation between the input voltage and the reference voltage by calculating the Nth reference voltage by reflecting the second correction value for the N-1th reference voltage through a feedback loop. .
9. According to clause 6,

   Assuming that one process in which the main loop circuit calculates the difference between the reference voltage and the input voltage of the buck converter and controls the duty ratio of the buck converter is a main loop cycle,

   When the auxiliary loop circuit calculates a power difference value according to the power change of the output stage of the buck converter and corrects the reference voltage based on the power difference value, a single process is called an auxiliary loop cycle,

   A DC-DC converter in which the auxiliary loop cycle is executed once when the main loop cycle is executed multiple times.

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