System and method of measuring maximum power point tracking efficiency

Disclosed is a system for tracking a maximum power point. The system includes an energy harvesting device, a power management integrated circuit including a switching circuit that adjusts an input voltage that is transmitted from the energy harvesting device and a conversion circuit that converts the input voltage adjusted by the switching circuit to output an output voltage, and a measuring device that calculates a ratio of a second power based on the input voltage to a first power based on an open circuit voltage of the energy harvesting device, using an internal impedance of the energy harvesting device and an input impedance of the power management integrated circuit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 to Korean Patent Application Nos. 10-2019-0128471 filed on Oct. 16, 2019, and 10-2020-0001999 filed on Jan. 7, 2020, respectively, in the Korean Intellectual Property Office, the disclosures of which are incorporated by reference herein in their entireties.

BACKGROUND

Embodiments of the inventive concept described herein relate to a measuring device for tracking a maximum power point, a system for tracking the maximum power point, and a method of tracking the maximum power point by using the measuring device.

As an energy harvesting device that harvests energy wasted in a surrounding environment, there are a thermoelectric energy harvesting device (thermoelectric generator), a piezoelectric energy harvesting device (piezoelectric generator), an RF energy harvesting device (radio frequency generator), a photoelectric energy harvesting device (photovoltaic generator), etc. For example, the thermoelectric energy harvesting device generates electromotive force by using electrons that move from a high temperature to a low temperature when a uniform temperature difference occurs between an upper part and a lower part of the thermoelectric energy harvesting device.

Electrical energy generated by the energy harvesting device is transferred to a power management integrated circuit (PMIC). The power management integrated circuit may convert the electrical energy and may supply the converted electrical energy to a battery or a load.

A maximum power point tracking (MPPT) technology is a technology for satisfying a condition of transferring a maximum power from the energy harvesting device to the load. To determine a loss between the electromotive force generated by the energy harvesting device and a power transferred from the energy harvesting device to the power management integrated circuit, a method for measuring an efficiency of the maximum power point tracking technology is needed.

SUMMARY

Embodiments of the inventive concept provide a measuring device for tracking a maximum power point by using an internal impedance of an energy harvesting device and an input impedance of a power management integrated circuit, a system for tracking the maximum power point, and a method of tracking the maximum power point by using the measuring device.

According to an exemplary embodiment of the inventive concept, a system for tracking a maximum power point includes an energy harvesting device, a power management integrated circuit including a switching circuit that adjusts an input voltage that is transmitted from the energy harvesting device and a conversion circuit that converts the input voltage adjusted by the switching circuit to output an output voltage, and a measuring device that calculates a ratio of a second power based on the input voltage to a first power based on an open circuit voltage of the energy harvesting device, using an internal impedance of the energy harvesting device and an input impedance of the power management integrated circuit.

According to an exemplary embodiment of the inventive concept, a method of tracking a maximum power point of an energy harvesting device connected to a power management integrated circuit, using a measuring device including a processor and an interface circuit, includes receiving, by the interface circuit, an internal impedance of an energy harvesting device and an input impedance of the power management integrated circuit, calculating, by the processor, a ratio of a second power based on the input voltage to a first power based on an open circuit voltage of the energy harvesting device, using the internal impedance of the energy harvesting device and the input impedance of the power management integrated circuit; and outputting the calculated ratio by the interface circuit.

DETAILED DESCRIPTION

Hereinafter, embodiments of the inventive concept will be described clearly and in detail such that those skilled in the art may easily carry out the inventive concept.

Hereinafter, with reference to the accompanying drawings, a preferred embodiment of the inventive concept will be described in more detail. To facilitate the overall understanding in describing the inventive concept, the similar reference numerals will be used for the similar components in the drawings, and additional descriptions for the similar components will be omitted to avoid redundancy.

FIG. 1is a block diagram illustrating a system for tracking a maximum power point according to an embodiment of the inventive concept. Referring toFIG. 1, a system10for tracking a maximum power point may include an energy harvesting device11, a power management integrated circuit12, and a measuring device100.

The energy harvesting device11may output electrical energy by harvesting energy wasted in a surrounding environment. For example, the energy harvesting device11may transmit power based on the electrical energy to the power management integrated circuit12as a voltage or a current. The energy harvesting device11may transmit power to the power management integrated circuit12instead of a uniform power source such as a battery. The energy harvesting device11may harvest energy from energy sources such as heat, sunlight, and vibration in the surrounding environment, and may convert the harvested energy into electrical energy to transmit power to the power management integrated circuit12. In one embodiment, the energy harvesting device11may be one of a thermoelectric energy harvesting device, a piezoelectric energy harvesting device, a radio frequency (RF) energy harvesting device, and a photoelectric energy harvesting device, but is not limited thereto.

The power management integrated circuit (PMIC)12may adjust the level of the voltage and current received from the energy harvesting device11, and may transmit the adjusted voltage and current to an external device. For example, the external device may be the battery or a load, but is not limited thereto.

The power management integrated circuit12may include a switching circuit13and a conversion circuit14.

The switching circuit13may adjust an input voltage transmitted from the energy harvesting device11. The conversion circuit14may convert the input voltage adjusted by the switching circuit13, and may output the converted voltage to the external device as an output voltage.

The measuring device100may calculate a ratio of a power based on the input voltage of the power management integrated circuit12and a power based on an open circuit voltage of the energy harvesting device11, using an internal impedance ZSof the energy harvesting device11and an input impedance ZINof the power management integrated circuit12. For example, the measuring device100may calculate the ratio of the power based on the input voltage of the power management integrated circuit12to the power based on the open circuit voltage of the energy harvesting device11. In one embodiment, the power based on the input voltage of the power management integrated circuit12may be determined based on the internal impedance ZSof the energy harvesting device11and the input voltage of the power management integrated circuit12. The detail operation of the measuring device100will be described later.

FIG. 2is a circuit diagram illustrating a system ofFIG. 1. Referring toFIG. 2, for convenience of illustration, only the energy harvesting device11, and the switching circuit13and the conversion circuit14of the power management integrated circuit12are illustrated in the system10, and the measuring device100is omitted from the illustration. Also referring toFIG. 2, a load RLof the external device is exemplarily illustrated as being connected to the conversion circuit14.

The energy harvesting device11may include an internal voltage source and an internal resistor RSfor outputting an open circuit voltage VOCby harvesting energy from the surrounding environment. The energy harvesting device11may transmit an input voltage V1of the switching circuit13to the switching circuit13. In this case, the open circuit voltage VOCmay represent the voltage of the energy harvesting device11when the energy harvesting device11is in an open circuit state (e.g., when there is no device connected to the energy harvesting device11or the input impedance ZINof the power management integrated circuit12is infinite). In contrast, the input voltage V1that is transmitted to the switching circuit13may represent the voltage of the energy harvesting device11when the energy harvesting device11is not in the open circuit state and is connected to the power management integrated circuit12. The open circuit voltage VOCand the input voltage V1may be different from each other due to the internal resistor RSof the energy harvesting device11.

The switching circuit13may include first to fourth switching transistors131to134, first to third switching capacitors135,136, and Ctem, and a comparator137. The switching circuit13may transmit an adjustment voltage Vtemgenerated by adjusting the input voltage V1to the conversion circuit14. For example, the switching circuit13may control a level of the adjustment voltage Vtemby controlling an operation (e.g., turn on or turn off) of the switching transistors131to134. The switching capacitors135,136, and Ctemmay store capacitive energy. The switching capacitors135,136, and Ctemmay discharge the stored capacitive energy.

The switching circuit13may transmit the adjustment voltage Vtemthat satisfies a maximum power transfer condition to the conversion circuit14by controlling the level of the adjustment voltage Vtem. In one embodiment, the level of the adjustment voltage Vtemmay be determined by characteristics of the energy harvesting device11. For example, the switching circuit13may be directly connected to the energy harvesting device11, and the input impedance ZINof the power management integrated circuit12may be determined by the operation of the switching circuit13.

The conversion circuit14may include first and second conversion inductors L1and L2, first and second conversion transistors141and142, and first and second conversion diodes D1and D2, and first and second conversion capacitors Cmpand Cout. The conversion circuit14may convert the adjustment voltage Vtemto an output voltage Voutof the conversion circuit14by controlling the operation of the conversion transistors141and142. In one embodiment, the conversion circuit14may include one of a boost converter, a buck converter, and a buck-boost converter.

The load RLmay consume power transferred from the conversion circuit14. In one embodiment, the load RLmay include a light-emitting diode (LED). In one embodiment, the load RLmay include household appliances such as a TV, a refrigerator, an air conditioner, etc.

FIG. 3is a diagram illustrating a circuit diagram of a system ofFIG. 2more briefly. Referring toFIGS. 1 and 3, the system10for tracking the maximum power point may include the energy harvesting device11, the power management integrated circuit12, and a load ZL.

The energy harvesting device11may include an internal voltage source and the internal impedance ZSfor outputting the open circuit voltage VOCand a short circuit current ISCby harvesting energy from the surrounding environment. The internal voltage source of the energy harvesting device11may output power PMPPbased on the open circuit voltage VOC. For example, the power PMPPmay be ½×VOC×ISC. The short circuit current ISCmay represent a current flowing through the energy harvesting device11when both ends of the energy harvesting device11are shorted.

The power management integrated circuit12may include the input impedance ZIN. The power management integrated circuit12may receive an input voltage YINand an input current IINfrom the energy harvesting device11. The power management integrated circuit12may receive power P2based on the internal impedance ZSand the input voltage VINfrom the energy harvesting device11. The power management integrated circuit12may adjust the level of the input voltage VIN, based on power required by the load ZL. The power management integrated circuit may transmit the output voltage VOUTto the load ZL.

The load ZLmay receive the output voltage VOUTfrom the power management integrated circuit12. The load ZLmay receive the power based on the output voltage VOUTfrom the power management integrated circuit12.

FIG. 4is a graph illustrating characteristics of a short circuit current-to-an open circuit voltage of a thermoelectric energy harvesting device, based on a temperature of the thermoelectric energy harvesting device.FIG. 5is a graph illustrating characteristics of an open circuit voltage of a thermoelectric energy harvesting device-to-an output power of the thermoelectric energy harvesting device, based on a temperature of the thermoelectric energy harvesting device. Referring toFIGS. 1, and 3 to 5, in one embodiment, the energy harvesting device11may include a thermoelectric energy harvesting device (thermoelectric generator; TEG).FIGS. 4 and 5illustrated a graph when the energy harvesting device11is the thermoelectric energy harvesting device TEG, but the inventive concept is not limited to the case where the energy harvesting device11is the thermoelectric energy harvesting device TEG.

Short circuit current-to-open circuit voltage characteristics and open circuit voltage-to-output power characteristics of the energy harvesting device11may be determined based on a type of the energy harvesting device11. Conditions for supplying a maximum power to the load ZLmay be determined based on the type of the energy harvesting device11.

Referring to a graph ofFIG. 4, the short circuit current ISCof the thermoelectric energy harvesting device TEG may be inversely proportional to the open circuit voltage VOCof the thermoelectric energy harvesting device TEG. The open circuit voltage VOCof the thermoelectric energy harvesting device TEG may increase as a temperature of the thermoelectric energy harvesting device TEG increases.

Referring to Equation 1 to Equation 3 below, when the internal impedance ZSof the thermoelectric energy harvesting device TEG is the same as the input impedance ZINof the power management integrated circuit12, the maximum power may be obtained from the thermoelectric energy harvesting device TEG. That is, the thermoelectric energy harvesting device TEG may output the maximum power when the internal impedance ZSis matched to the input impedance ZIN. A loss may occur between power P1based on the open circuit voltage VOCof the thermoelectric energy harvesting device TEG and power P2based on the input voltage VINof the power management integrated circuit12by a difference between the internal impedance ZSof the thermoelectric energy harvesting device TEG and the input impedance ZINof the power management integrated circuit12.

In Equation 1, the power P2may be expressed as a product of the input voltage VINand the input current IINof the power management integrated circuit12. The power P2may be expressed by a relational equation between the input voltage VINand the open circuit voltage VOC.

In Equation 2 and Equation 3, the condition of the input voltage VINfor obtaining the maximum power ‘Pmax’ in the thermoelectric energy harvesting device TEG may be expressed. When a magnitude of the input voltage VINcorresponds to a half of the magnitude of the open circuit voltage VOC, the maximum power ‘Pmax’ may be transmitted from the thermoelectric energy harvesting device TEG to the power management integrated circuit12. Referring to a graph ofFIG. 5, when the magnitude of the input voltage VINcorresponds to a half of the magnitude of the open circuit voltage VOC, it may be confirmed that the maximum power is transferred by matching between the internal impedance ZSand the input impedance ZIN.

In one embodiment, to accomplish the matching between the internal impedance ZSand the input impedance ZIN, the switching circuit13of the power management integrated circuit12may control the operation of the switching transistors131to134to adjust the level of the input voltage VIN.

To obtain the maximum power from the energy harvesting device11, maximum power point tracking (MPPT) technology may be applied. Equation for measuring a maximum power point tracking efficiency is shown in Equation 4 below.

In Equation 4, ‘ηm’ represents the maximum power point tracking efficiency. ‘PMPP’ represents the maximum power that can be obtained from the energy harvesting device11. The efficiency ‘ηm’ may be expressed as a ratio of the power P2based on the input voltage VINof the power management integrated circuit12to the maximum power ‘PMPP’.

In one embodiment, a device that measures the efficiency ‘ηm’ may measure the maximum power ‘PMPP’ that can be obtained from the energy harvesting device11, may connect the power management integrated circuit12and the energy harvesting device11, and may measure the power P2based on the input voltage VINof the power management integrated circuit12. That is, the device that measures the efficiency ‘ηm’ may measure the open circuit voltage VOCand the short circuit current ISCof the energy harvesting device11and the input voltage VINand the input current IINof the power management integrated circuit12. Accordingly, since the device for measuring the efficiency ‘ηm’ needs to measure a plurality of voltages and currents, it requires a high cost and a lot of time to measure.

FIG. 6is a block diagram illustrating a measuring device ofFIG. 1according to an embodiment of the inventive concept. Referring toFIGS. 1, 3, and 6, the measuring device100may include a processor110, a memory120, an interface circuit130, a bus140, and storage150.

The processor110may perform a function as a central processing unit of the measuring device100. For example, the processor110may execute application, software, firmware, or program code to calculate the efficiency ‘ηm’ using the internal impedance ZSof the energy harvesting device11received through the interface circuit130and the input impedance ZINof the power management integrated circuit12. The processor110may control the memory120, the interface circuit130, and the storage150. The number of the processor110may be one or more. The processor110may operate by utilizing storage areas of the memory120, and may load the above-described application, software, firmware, or program code from the storage150into the memory120. The processor110may further execute operating system and various applications loaded in the memory120, as well as the above-described application, software, firmware, or program code. The detailed operation method of the measuring device100controlled by the processor110will be described later.

The memory120may store data and program codes processed or to be processed by the processor110. The memory120may be used as a main memory of the measuring device100. The memory120may include a Dynamic Random Access Memory (DRAM), a Static Random Access Memory (SRAM), a Phase-change Random Access Memory (PRAM), a Magnetic Random Access Memory (MRAM), a Ferroelectronic Random Access Memory (FeRAM), and a Resistive Random Access Memory (RRAM), and may also be referred to as a buffer memory or a cache memory. The number of the memories120may be one or more. The memory120may also be implemented as an external device that can communicate with the measuring device100.

The interface circuit130may communicate with the energy harvesting device11and the power management integrated circuit12, based on various wired or wireless protocols under a control of the processor110. For example, the interface circuit130may receive a value of the internal impedance ZSof the energy harvesting device11from the energy harvesting device11in response to a request of the processor110. The interface circuit130may receive a value of the input impedance ZINof the power management integrated circuit12from the power management integrated circuit12in response to the request of the processor110. The interface circuit130may output the efficiency ‘ηm’ calculated by the processor110.

The bus140may provide a communication path among components of the measuring device100. The processor110, the memory120, the interface circuit130, and the storage150may exchange data with one another through the bus140. The bus140may be configured to support various types of communication formats used in the measuring device100.

The storage150may store data generated for long-term storage by the operating system or applications, a file for driving the operating system, or executable files of applications. For example, the storage150may store files for execution of the memory120. The storage150may be used as an auxiliary memory device of the measuring device100. The storage150may include a flash memory, the PRAM, the MRAM, the FeRAM, the RRAM, etc.

FIG. 7is a block diagram illustrating a measuring device ofFIG. 1according to another embodiment of the inventive concept. Referring toFIGS. 1, 3, and7, a measuring device200according to another embodiment of the inventive concept may include a calculator210, a register220, an interface circuit230, and a bus240. The measuring device200may be an example of the measuring device100ofFIG. 1.

The calculator210may perform a function as a central processing unit of the measuring device200. For example, the calculator210may calculate the efficiency ‘ηm’ using the internal impedance ZSof the energy harvesting device11received by the interface circuit230and the input impedance ZINof the power management integrated circuit12. The detailed operation of the calculator210will be described later.

The register220may store values calculated by the calculator210and values received by the interface circuit230. For example, the register220may store the efficiency ‘ηm’ calculated by the calculator210. The register220may store the internal impedance ZSand the input impedance ZINreceived by the interface circuit230.

The measuring device200may receive and transmit information from the energy harvesting device11and the power management integrated circuit12through the interface circuit230. The interface circuit230may communicate with the energy harvesting device11and the power management integrated circuit12, based on various wired or wireless protocols. For example, the interface circuit230may receive information on the value of the internal impedance ZSfrom the energy harvesting device11. The interface circuit230may receive information on the value of the input impedance ZINfrom the power management integrated circuit12. The interface circuit230may output information associated with the efficiency ‘ηm’ calculated by the calculator210.

The bus240may provide a communication path among components of the measuring device200. The calculator210, the register220, and the interface circuit230may exchange data with one another through the bus240. The bus240may be configured to support various types of communication formats used in the measuring device200.

FIG. 8is a block diagram specifically describing an operation of a calculator ofFIG. 7. Referring toFIGS. 1, 3, and 6 to 8, the calculator210of the measuring device200may include an adder211, a multiplier212, and a divider213.

Referring to Equations 5 to 7 below, the efficiency ‘ηm’ is expressed as the internal impedance ZSof the energy harvesting device11and the input impedance ZINof the power management integrated circuit12.

The efficiency ‘ηm’ expressed associated with the power ‘P2’ and the maximum power ‘PMPP’ in Equation 4 may be expressed in relation to the input voltage VIN, the input current IIN, the open circuit voltage VOC, and the short circuit current ISCin Equation 5.

The efficiency ‘ηm’ expressed in relation to the input voltage VIN, the input current IIN, the open circuit voltage VOC, and the short circuit current ISCin Equation 5 may be expressed associated with the input voltage VIN, the open circuit voltage VOC, the internal impedance ZS, and the input impedance ZIN. Equation 7 summarizes Equation 6.

Through Equation 7, the efficiency ‘ηm’ may be expressed associated with the internal impedance ZSand the input impedance ZIN. In one embodiment, the calculator210of the measuring device200may calculate the efficiency ‘ηm’ based on Equation 7. In one embodiment, the calculator210may calculate the efficiency ‘ηm’ using only the internal impedance ZSand the input impedance ZIN.

For example, the adder211of the calculator210may receive the internal impedance ZSand the input impedance ZINfrom the interface circuit230through the bus240. The adder211may calculate a first value C1that is a sum of the internal impedance ZSand the input impedance ZIN. The adder211may transmit the first value C1to the multiplier212.

The multiplier212of the calculator210may receive information associated with the value of the internal impedance ZSand information associated with the value of the input impedance ZINfrom the interface circuit230through the bus240. The multiplier212may calculate a product of the internal impedance ZSand the input impedance ZIN. The multiplier212may calculate a second value C2that is k (k is an integer of 1 or more) times of the calculated product.

The multiplier212may receive the first value C1from the adder211. The multiplier212may calculate a third value C3that is ‘m’-th (‘m’ is an integer of 2 or more) power (or ‘m’ square) of the first value C1. The multiplier212may transmit the second value C2and the third value C3to the divider213.

The divider213may receive the second value C2and the third value C3from the multiplier212. The divider213may calculate the ratio of the second value C2and the third value C3. For example, the divider213may calculate the efficiency ‘ηm’ by calculating the ratio of the second value C2to the third value C3.

For example, ‘k’ may be 4, and ‘m’ may be 2. For another example, ‘k’ may be 400 and ‘m’ may be 2. However, the scope of the inventive concept is not limited to the above-described values. The unit of efficiency ‘ηm’ may be [%].

FIG. 9is a flowchart describing an operating method of a measuring device ofFIG. 1according to an embodiment of the inventive concept. Referring toFIGS. 1, 3, 6, and 9, the measuring device100may perform operations S100to S300under the control of the processor110.

In operation S100, the interface circuit130of the measuring device100may receive the internal impedance ZSof the energy harvesting device11under the control of the processor110from the energy harvesting device11. The interface circuit130may receive the input impedance ZINof the power management integrated circuit12from the power management integrated circuit12under the control of the processor110. The interface circuit130may transmit the internal impedance ZSand the input impedance ZINto the processor110and the memory120through the bus140.

In operation S200, the measuring device100may calculate the maximum power point tracking efficiency ‘ηm’ using the internal impedance ZSand the input impedance ZINunder the control of the processor110. The maximum power point tracking efficiency ‘ηm’ may be the efficiency ‘ηm’ of Equations 4 to 7 described above. The processor110of the measuring device100may transmit the maximum power point tracking efficiency ‘ηm’ to the memory120and the interface circuit130through the bus140. Operation S200will be described later in detail.

In operation S300, the interface circuit130of the measuring device100may output the maximum power point tracking efficiency ‘ηm’ under the control of the processor110. For example, the interface circuit130may output the maximum power point tracking efficiency ‘ηm’ to the power management integrated circuit12or a user terminal. In this case, the switching circuit13of the power management integrated circuit12may control the operation of the switching transistors131to134, based on the maximum power point tracking efficiency ‘ηm’.

In operation S201, the measuring device100may calculate the first value C1that is the sum of the internal impedance ZSand the input impedance ZIN. In operation S202, the measuring device100may calculate the product of the internal impedance ZSand the input impedance ZIN. The measuring device100may calculate the second value C2that is k times of the calculated product. In operation S203, the measuring device100may calculate the third value C3that is ‘m’ square (or ‘m’-th power) of the first value C1. In operation S204, the measuring device100may calculate the ratio of the second value C2and the third value C3. For example, the measuring device100may calculate the maximum power point tracking efficiency ‘ηm’ by calculating the ratio of the second value C2to the third value C3.

In one embodiment, the measuring device100may calculate the maximum power point tracking efficiency ‘ηm’, based on Equation 7 described above. In one embodiment, the measuring device100may calculate the maximum power point tracking efficiency ‘ηm’ using only the internal impedance ZSand the input impedance ZIN.

According to an embodiment of the inventive concept, a measuring device for tracking a maximum power point may economically calculate an efficiency of the maximum power point tracking technology in a short time, by using an internal impedance of an energy harvesting device and an input impedance of a power management integrated circuit.

The contents described above are specific embodiments for implementing the inventive concept. The inventive concept will include not only the embodiments described above but also embodiments in which a design is simply or easily capable of being changed. In addition, the inventive concept may also include technologies easily changed to be implemented using embodiments. Therefore, the scope of the inventive concept is not limited to the described embodiments but should be defined by the claims and their equivalents.