CN113765384A - Continuous maximum power point tracking method - Google Patents

Continuous maximum power point tracking method Download PDF

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CN113765384A
CN113765384A CN202111134395.0A CN202111134395A CN113765384A CN 113765384 A CN113765384 A CN 113765384A CN 202111134395 A CN202111134395 A CN 202111134395A CN 113765384 A CN113765384 A CN 113765384A
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buck
energy
voltage
boost converter
maximum power
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CN113765384B (en
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周泽坤
李世磊
王佳文
王卓
张波
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University of Electronic Science and Technology of China
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • H02M3/1582—Buck-boost converters
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
    • G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
    • G05F1/66—Regulating electric power
    • G05F1/67—Regulating electric power to the maximum power available from a generator, e.g. from solar cell
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02N—ELECTRIC MACHINES NOT OTHERWISE PROVIDED FOR
    • H02N2/00—Electric machines in general using piezoelectric effect, electrostriction or magnetostriction
    • H02N2/18—Electric machines in general using piezoelectric effect, electrostriction or magnetostriction producing electrical output from mechanical input, e.g. generators
    • H02N2/181—Circuits; Control arrangements or methods
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02N—ELECTRIC MACHINES NOT OTHERWISE PROVIDED FOR
    • H02N2/00—Electric machines in general using piezoelectric effect, electrostriction or magnetostriction
    • H02N2/18—Electric machines in general using piezoelectric effect, electrostriction or magnetostriction producing electrical output from mechanical input, e.g. generators
    • H02N2/186—Vibration harvesters

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Sustainable Development (AREA)
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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Automation & Control Theory (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention belongs to the technical field of power management, and particularly relates to a continuous maximum power point tracking method. The invention provides an MPPT method suitable for a simplified ripple association method of a closed-loop MPPT system aiming at a BUCK-BOOST power level converter specific to a vibration energy collecting system on the basis of the MPPT method of the closed-loop MPPT system and the ripple association method.

Description

Continuous maximum power point tracking method
Technical Field
The invention belongs to the technical field of power management, and particularly relates to a continuous maximum power point tracking method.
Background
Many electronic devices, such as wireless sensor network nodes or implanted devices that are inconvenient to disassemble, require constant power from a battery. However, the use of batteries not only increases the area and weight of these small devices, but also requires periodic replacement due to limited working time, which wastes a lot of money and resources, and more importantly, in many cases, the device structure and system do not support the replacement of batteries or are desired to be avoided, such as monitoring on tunnels, bridges and roads or biological tissue network devices implanted into human bodies. Therefore, the replacement of chemical batteries is one of the development bottlenecks in the technology of the current internet of things devices, and the adoption of self-powered technology is one of the directions for solving the problems.
Self-powering technology essentially uses energy harvesting technology to allow devices to draw energy from the environment and supply itself to form a virtuous cycle, which not only can be used as a backup supplement for some batteries, but also can directly replace some power supply schemes with large area size, poor environmental protection or high cost, and the ultimate achievement goal of energy harvesting technology is the infinite life of the devices. Therefore, this technique has received much attention from researchers and research institutions. The energy collection system can collect the widely existing energy such as photoelectric energy, heat energy, radio frequency energy, vibration energy, biological energy and the like in the environment.
Because the energy collected from the environment is usually small, the design optimization goal of the power management circuit is to achieve low power consumption as much as possible to improve the energy collection efficiency, for example, a low-voltage low-power circuit structure or an intermittent working mode can be adopted to achieve the goal. Meanwhile, the control circuit module needs to adopt a Maximum Power Point Tracking (MPPT) module, and the MPPT method can enable the Power management system to work at a Maximum Power transmission Point so as to improve the energy collection efficiency. In consideration of the characteristics of unpredictability and insufficient stability of external environment energy, the MPPT module has the advantages of high tracking speed, strong adaptability and real-time capability, and the MPPT module can be started only when the energy source changes so as to reduce the working time of a circuit. On the basis of ensuring the performances, the low-cost and small-volume IoT can be realized to meet the requirement of laying IoT in a large area.
In order to operate the energy collection circuit system at the optimal efficiency point, a maximum power point tracking technology is introduced, which can be divided into open-loop MPPT and closed-loop MPPT according to the loop characteristics of the system. The open-loop MPPT method is mainly adjusted according to a relationship between an open-circuit voltage of an energy harvester and a maximum power point voltage, for example, the maximum power point voltage of a solar energy collection system is about 0.7 times of the open-circuit voltage of the solar energy harvester, and the maximum power point voltage of a thermal energy and vibration energy collection system is 1/2 times of the open-circuit voltage of the harvester. The traditional open circuit voltage method belongs to open loop MPPT. The open-loop MPPT has the advantages that the structure is simple and easy to implement, but the switch connection between the primary energy collector and the subsequent power stage circuit is disconnected within a fixed time to obtain a constantly-changing open-circuit voltage, the collection efficiency is low due to energy loss, and the tracking error is large. The closed-loop MPPT technology is based on a closed-loop control method, real-time adjustment is carried out by utilizing output voltage and current to achieve a maximum power point, and compared with the open-loop MPPT, the adjustment precision and complexity are higher. Closed loop MPPT includes a perturbation and observation method and a conductance increment method. The hill climbing algorithm is a common disturbance observation method, and is simple, high in applicability, wide in application and gradually developed to multiple dimensions. A Ripple Correlation Control (RCC) also belongs to a closed-loop MPPT technique, which utilizes the rule that the power of an energy source becomes a single peak point under the coordinate of the input voltage of a system, and compares the relationship between the output power of the energy source and the derivative of the input voltage of a power stage to determine whether the system is operated at the maximum power point. The implementation of the RCC method requires a circuit with large power consumption, such as a differentiator and a multiplier, which violates the low power consumption goal of the energy collection system. In addition, other MPPT methods include a short-circuit current method, a sliding mode control method, and the like, which are comparatively less used.
Disclosure of Invention
In order to solve the above problems, the present invention provides a continuous maximum power point tracking technique.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a continuous maximum power point tracking method is used for a BUCK-BOOST converter, energy is input into the BUCK-BOOST converter through an AC-DC rectifying circuit by a piezoelectric sensor, specifically, a capacitor is connected between the output of the AC-DC rectifying circuit and the input of the BUCK-BOOST converter, energy is provided for the BUCK-BOOST converter through discharge of the capacitor, and the voltage of the capacitor is defined as VINThen at VINIn the voltage drop stage, the capacitor is discharged to BUCK-BOOST converter inductance providing energy by switching at VINDuring voltage drop period TONThe method for tracking the maximum power point is characterized in that the input voltage is detected in stages, and comprises the following steps:
s1, setting TONSetting the initial working frequency f of the BUCK-BOOST converter;
s2, at TONSampling in time VINInformation;
s3, judgment
Figure BDA0003281500110000021
Is established, wherein
Figure BDA0003281500110000022
Is VINSpeed varying with time, i.e. VINIf the derivative of time is positive, go to step S4, otherwise go to step S5;
s4 delaying preset time taThen sampling V againINInformation, where taThe system fixes the delay time and judges the sampling again
Figure BDA0003281500110000023
If yes, locking and outputting the current working frequency f, otherwise, entering the step S5;
s5, judgment
Figure BDA0003281500110000024
If so, the operating frequency f is increased and the process returns to step S3, otherwise the operating frequency f is decreased and the process returns to step S3.
The MPPT method has the beneficial effects that on the basis of a closed-loop MPPT system and an MPPT method based on a ripple association method, the MPPT method suitable for the ripple association method is simplified for a BUCK-BOOST power level converter specific to a vibration energy collecting system.
Drawings
Fig. 1 is a schematic diagram of a vibration energy collection system with MPPT functionality.
Figure 2MPP area schematic.
Figure 3MPPT schematic diagram.
Fig. 4 shows a MPP tracking flow chart of the RCC method according to the present invention, i.e., a frequency adjustment method.
Detailed Description
The technical scheme of the invention is described in detail below with reference to the accompanying drawings:
in the case of a vibration energy harvesting system, as shown in fig. 1, the output port of the energy source is connected to the input port of the BUCK-BOOST converter via an AC-DC rectifier, the voltage at the connection being defined as VIN. From the above, the maximum power point tracking technique is actually to adjust the input resistance R of the BUCK-BOOST converterINInternal resistance R of piezoelectric collectorPMatched to achieve maximum energy transfer efficiency, when the system reaches the maximum power point, VINThe voltage will be at VMPPNear the point. Due to the instantaneity and fluctuation of the piezoelectric energy source, VINThe voltage inevitably has some ripples, so the MPPT precision can not reach 100 percent, namely VINNot hundreds of equal to VMPPVoltage, only adjusting V as much as possibleINVoltage to make it approach VMPPAnd (4) point. Generally, a tuning accuracy of more than 90% is considered to be at the maximum optimization point. Schematically shown in fig. 2, the area S is referred to as an MPP region.
The specific operating principle of MPPT is shown in fig. 3. The energy collected by the piezoelectric collector passes through an AC-DC rectifying circuit and then is stored in an input capacitor CINWhen the capacitance C isINThe BUCK-BOOST converter is connected to the capacitor C after the voltage on the BUCK-BOOST converter is charged to the maximum power point voltageINAnd starting the working cycle of the device, namely opening the upper pipe and the lower pipe in sequence to transmit energy to the output capacitor. Slave capacitor CINIn view of the above, it is equivalent to a reservoir, and the input energy source firstly gives the capacitor CINCharging, when the water level reaches a certain value VINTo reach VMPPAfter voltage, the outlet brake pipe is opened and the converter is driven from CINThe capacitor draws charge when the capacitor CINWhen the upper voltage falls outside the maximum power point voltage region, namely exceeds the S area shown in FIG. 2, the converterIs disabled, capacitor CINThe voltage on is recharged to the maximum power point and the process continues to repeat. When V isINWhen the voltage reaches the maximum power point and the system is in a steady state, the capacitor CINThe upper charge flows in and out to reach an equilibrium state, VINV of voltage not exceeding MPP areaMPPThe vicinity of the point fluctuates.
The traditional RCC method can calculate the actual MPP value, and only needs the current converter input voltage and current. It does not require any stored values. To calculate MPP, two differentiators and three multipliers are required. Usually, the multiplier can use a four-quadrant analog multiplier or an analog multiplier with some amplifiers, but these structural components are complex and consume much power, which reduces the chip area efficiency and the input voltage range. In order to avoid using a multiplier in an analog low-power system, the invention provides a novel continuous maximum power point tracking technology.
The energy collecting system applicable to the invention uses the BUCK-BOOST converter in the DCM working mode as the power stage, the control mode adopts the COT mode for control, and the power stage converter of the vibration energy collecting system is only controlled at TONThe stage is connected with the piezoelectric collector, and the input capacitor C is connected with the piezoelectric collectorINDischarge provides energy to the inductor, VINVoltage drop; and at TOFFAnd TIDLEThe (upper and lower power tubes are turned off simultaneously) stage is disconnected with the piezoelectric collector, and the energy source is the input capacitor CINCharging, VINThe voltage rises. In this case at VINDuring the rise period, I cannot be performedINDetection of voltage, therefore, is selected at VINDuring voltage drop period TONThe detection of the input voltage and current is performed in stages, then it can be deduced that:
Figure BDA0003281500110000041
wherein
Figure BDA0003281500110000042
Is an inputThe time derivative of the current, known from the input current characteristic of the BUCK-BOOST converter, the TON phase, the input current IINI.e. the inductor current and IINThere is a correlation between the derivatives of (c). So that there are:
Figure BDA0003281500110000043
therefore, a very ingenious conclusion is obtained, and in the DCM BUCK-BOOST converter, under the condition that the control method selects the COT mode, only the COT mode is needed to be set at TONThe phase detection input voltage information is passed through a differentiator and multiplied by a fixed value TONThe obtained information is compared with the input voltage, so that whether the input voltage is at the maximum power point voltage or not can be accurately judged. Compared with an open-circuit voltage method, the RCC method special for the BUCK-BOOST converter in the DCM working mode has great advantages, because the RCC method not only inherits the advantages of the open-circuit voltage method, but also completely avoids energy loss caused by frequent switching of the open-circuit voltage method, and has the advantages of high tracking precision, high speed and real-time tracking of the closed-loop MPPT method.
Considering the RCC method used in the DCM BUCK-BOOST converter, it can be known from the simplified relationship between the input voltage and the maximum power point voltage that the converter needs to have the on-time TONFixed, i.e. using COT control, by adjusting the frequency f of the converter to the input voltage VINThe maximum power point voltage is reached. In order to increase the MPPT tracking accuracy and avoid misjudgment of the maximum power point caused by some unstable factors, continuous twice judgment is designed to meet the requirement of VIN＝VMPPThe locking of the operating frequency is only performed under the condition. The specific work flow diagram is shown in fig. 4.

Claims (1)

1. A continuous maximum power point tracking method is used for a BUCK-BOOST converter, energy is input into the BUCK-BOOST converter through an AC-DC rectifying circuit by a piezoelectric sensor, specifically, a capacitor is connected between the output of the AC-DC rectifying circuit and the input of the BUCK-BOOST converter, and the energy is amplified by the capacitorThe electricity supplies energy to the BUCK-BOOST converter, and the voltage of the capacitor is defined as VINThen at VINIn the voltage drop stage, the capacitor discharges to provide energy for the inductance of the BUCK-BOOST converterINDuring voltage drop period TONThe method for tracking the maximum power point is characterized in that the input voltage is detected in stages, and comprises the following steps:
s1, setting TONSetting the initial working frequency f of the BUCK-BOOST converter;
s2, at TONSampling in time VINInformation;
s3, judgment
Figure FDA0003281500100000011
Is established, wherein
Figure FDA0003281500100000012
Is VINSpeed varying with time, i.e. VINIf the derivative of time is positive, go to step S4, otherwise go to step S5;
s4 delaying preset time taThen sampling V againINInformation, and judging after sampling again
Figure FDA0003281500100000013
If yes, locking and outputting the current working frequency f, otherwise, entering the step S5;
s5, judgment
Figure FDA0003281500100000014
If so, the operating frequency f is increased and the process returns to step S3, otherwise the operating frequency f is decreased and the process returns to step S3.
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CN104035476A (en) * 2014-05-13 2014-09-10 西安理工大学 Maximum power point tracing method based on output voltage stepped frequency disturbance
DE102015108822A1 (en) * 2014-06-03 2015-12-03 Infineon Technologies Ag System and method for current sensing in a switched mode power supply
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KR102161812B1 (en) * 2019-06-18 2020-10-05 연세대학교 산학협력단 System and Method for Controlling MPPT of Photovoltaic System Using Active Power Control
CN111208862A (en) * 2020-01-14 2020-05-29 电子科技大学 Three-dimensional maximum power point tracking method
CN113013896A (en) * 2021-03-08 2021-06-22 河海大学 Coordination control method for jointly participating in primary frequency modulation of power grid by light storage

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