JP2012181608A - Energy conversion device and maximum power conversion circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve efficiency by making it unnecessary to perform current measurement for power detection necessary for the detection of the maximum power point in an energy conversion device for converting natural energy into a power in desired configurations.SOLUTION: This energy conversion device is configured to perform an arithmetic operation to a power to be converted from the input/output voltage of power conversion means and the converting operation of the power conversion means.

Description

  The present invention relates to an energy conversion device and an energy conversion method for generating electric energy and converting it into a predetermined form by performing step-down, step-up, conversion to alternating current, and the like. In particular, when power is generated by a solar cell, the form of power is efficiently converted.

  Natural energy has unpredictable fluctuations. For example, changes in the illuminance of sunlight or changes in wind power. When converting the generated power generated from such natural energy into predetermined electrical energy by stepping down, boosting, or converting to alternating current, optimal power conversion according to the supply power is required to improve the conversion efficiency. It is desirable to do. As described above, a method of performing power conversion at the maximum power point at which the power is maximized is widely known as a maximum power point tracking method (see, for example, Patent Document 1).

An example of the prior art for this purpose is shown in FIG.
In FIG. 16, the power generation means 111 generates electrical energy from other energy. Specifically, a solar cell or the like is an example of the power generation unit 111.

  The power conversion means 120 converts the generated power generated by the power generation means 111 into a predetermined form of electrical energy by performing step-down, step-up, conversion to alternating current, and the like.

  The power calculation means 1621 calculates the generated power output from the power generation means 111 in order to maximize the power converted by the power conversion means 120. For this reason, the voltage and current of the generated power are measured, and the generated power is obtained from the product of the measured voltage and current. Here, in order to measure the current of the generated power, the resistor 1612 is inserted and the voltage drop of the resistor 1612 is measured.

  The MPPT control unit 1631 detects a maximum power point for performing optimal power conversion according to the supply power of the power generation unit 111 by the power conversion unit 120, and uses the detected maximum power point as an operating point of the power conversion unit 120. Set. Therefore, the MPPT control unit 1631 detects the operating point at which the power calculated by the power calculating unit 1621 is maximized while moving the operating point of the power conversion unit 120, and follows the detected maximum power point. . As a method of detecting the maximum power point, a hill-climbing method has been disclosed in the past, and many improvements of the configuration method for efficiently reaching the maximum power point have been disclosed.

JP 2001-67134 A

  However, in the conventional energy conversion device, since a resistor is inserted to measure the current, a loss corresponding to the power consumed by the resistor occurs. In particular, when the voltage is low, such as a single-cell solar cell, the ratio of the voltage drop due to resistance to the power supply voltage is large, and power loss due to resistance cannot be ignored.

  Therefore, the present invention solves this problem and provides an energy conversion device and a maximum power conversion circuit capable of detecting power without measuring current and eliminating power loss for current measurement.

  The maximum power conversion circuit according to the present invention includes a power conversion unit that converts the form of input power and outputs converted power, and converts the power converted by the power conversion unit into the input voltage of the power conversion unit and the conversion of the power conversion unit. It comprises power calculating means for calculating from the operation and MPPT control means for controlling the power converted by the power converting means to become maximum.

  The energy conversion device according to the present invention includes a power generation unit that generates electrical energy and the maximum power conversion circuit that receives and converts the generated power from the power generation unit.

  According to the present invention, power can be measured without a voltage drop, so that the power form can be converted efficiently following the maximum power point. In particular, the drop is significant when the voltage of the power generation means is low.

  When the load impedance is commensurate with the supply power of the power generation means, the power drawn from the power generation means is maximized. The MPPT method performs power conversion while following this maximum power point. In the MPPT method, it is necessary to detect power in order to follow the maximum power point.

Regarding the features of the present invention, differences from the conventional example will be described.
It differs from the conventional energy conversion device in how to calculate the power converted by the power conversion means. In the conventional power calculation means, since the power is obtained by measuring the current and voltage of the generated power generated by the power generation means and input by the power conversion means and calculating the product thereof, the resistance for measuring the current Caused power loss. Therefore, in the present invention, power is calculated from the input voltage of the power conversion means and the conversion operation of the power conversion means.

  By configuring and operating in this manner, it is possible to realize an energy conversion device and a maximum power conversion circuit that can efficiently convert while suppressing loss for power detection. In particular, the drop is significant when the voltage of the power generation means is low.

1 is a block diagram illustrating a preferred embodiment of an energy conversion device according to the present invention. It is a characteristic view of the electric power generation means which concerns on this invention. It is a characteristic view of the electric power generation means which concerns on this invention. It is a block diagram of the power conversion means which concerns on this invention. It is a timing diagram which shows operation | movement of the electric power detection means which concerns on this invention. It is a block diagram which shows the structure of the electric power calculating means which concerns on this invention. It is a process flow figure showing operation of a maximum power conversion method concerning the present invention. It is a process flow figure showing operation of an MPP detection process concerning the present invention. It is a conceptual diagram which shows operation | movement of the MPP detection process based on this invention. It is a conceptual diagram which shows operation | movement of the MPP detection process based on this invention. It is a conceptual diagram which shows operation | movement of the MPP detection process based on this invention. It is a conceptual diagram which shows operation | movement of the MPP detection process based on this invention. It is a conceptual diagram which shows operation | movement of the MPP detection process based on this invention. It is a conceptual diagram which shows operation | movement of the maximum power conversion method which concerns on this invention. It is a process flow figure showing operation of a maximum power conversion method concerning the present invention. It is a block diagram which shows the structure of the conventional energy converter.

  Embodiments for carrying out the present invention will be described with reference to the drawings.

  Preferred embodiments of the energy conversion device 101, the maximum power conversion circuit 112, and the maximum power conversion method 701 according to the present invention will be described with reference to the drawings. In the following description, <> represents a large heading and [] represents a small heading.

<Energy conversion device 101>
FIG. 1 is a block diagram of an energy conversion device 101 according to the present invention.
[Energy conversion device 101]
The energy conversion device 101 according to the present invention includes a power generation unit 111 that generates electric energy and outputs generated power, and a maximum power conversion circuit 112 that converts the form of generated power while extracting the maximum power from the power generation unit 111. .

[Maximum power conversion circuit 112]
The maximum power conversion circuit 112 includes a power conversion unit 120 that converts the form of the generated power output from the power generation unit, a power calculation unit 121 that calculates and detects the power converted by the power conversion unit 120, and the power MPPT control means 131 that detects and follows the maximum power point so that the power converted by the power conversion means 120 is maximized by moving the operating point of the conversion means 120, and the maximum power point detected by the MPPT control means 131 Is constituted by an MPP characteristic storage means 124 that stores the information in association with the supply power of the power generation means 111.

[Maximum power conversion method 701]
In the maximum power conversion method 701, as shown in FIG. 7, the power generation unit 111 generates electric energy (not shown), and the power conversion unit 120 converts the form of the generated power to output the converted power. A power conversion step (not shown), an operating point update determination step 711 for determining the operating point update, a supply force detection step 712 for detecting the supply force of the power generation means, and a change for determining the amount of power generation change from the change in the supply force A detection step 713, a cumulative filter step 714 for accumulating the power generation change amount to obtain a cumulative change amount, a learning determination step 715 for determining whether to perform learning, a learning step 716 for detecting and storing the maximum power point, The operation is performed by a reference step of updating the operating point of the power conversion means with reference to the characteristic of the maximum power point stored by the supply power.

[Constant voltage output control function]
In addition, since there is almost no relation with the feature of the present invention, detailed description is omitted. For example, when the output voltage is higher than the target voltage, the output voltage is a constant voltage instead of the maximum power point tracking. Control may be performed so that The same applies to the overvoltage prevention function and the constant current output control function.
Each component will now be described in detail.

<Power generation means 111>
The power generation means 111 supplies generated power to the maximum power conversion circuit 112. As the power generation means 111, any power supply means having a maximum power point such as a solar battery, a generator, or a battery may be used.

  FIG. 2 shows the characteristics of the solar cell in the case of a certain supply power as an example of the characteristics of the power generation means 111. Here, although the solar cell used what connected two power generation cells in series, there is no restriction | limiting in particular in the number of cells. Further, the supply power is the ability to supply power from the power generation means 111. For example, in the case of a solar cell, the supply power changes when the amount of light to the solar cell changes. The generated power actually output by the power generation means 111 is the power input by the power conversion means 120, and the generated power and the supply power are essentially different.

  In FIG. 2, the horizontal axis indicates the voltage value of the solar cell, the left vertical axis indicates the current value, and the right vertical axis indicates the value of the generated power. Here, the solid line indicates the voltage-current characteristic, and the dotted line indicates the voltage-power characteristic. The alternate long and short dash line indicates the voltage at which the power of the dotted line is maximized, and the black circle is at the position where the alternate long and short dash line and the solid line indicating the voltage-current characteristics intersect, and represents the voltage and current at the maximum power point. That is, the power from the power generation means 111 cannot be extracted most efficiently unless power conversion is performed at the maximum power point that is the optimum operating point.

  As shown by the solid-line voltage-current characteristics, since there is a one-to-one relationship between current and voltage, in order to extract the maximum power point from the power generation means 111, the voltage should be the maximum power point voltage. Or the current may be controlled to be the maximum power point current, or the impedance represented by the ratio of the voltage and the current may be controlled to be the maximum power point impedance. good. In the present invention, the voltage, current, and impedance values controlled in this way are referred to as operating points.

  The supply power can be obtained by an illuminance sensor provided in the vicinity of the solar cell, but the cost of the sensor, the location, the wiring, and the mounting for detection is relatively large. There is also a problem that even in the vicinity, the way the light strikes may differ between the sensor and the solar cell.

  FIG. 3 shows the relationship between the short-circuit current and the maximum power point when a solar cell is used. Here, the short-circuit current is a current that flows when both ends of the output of the solar cell are short-circuited, and is approximately proportional to the supply power. For this reason, a short circuit current can be used as supply power.

  As can be seen from FIG. 3, since the maximum power point varies depending on the supply power, in order to maintain the maximum power point, either continuously detecting the maximum power point or detecting the supply power and It is necessary to refer to the characteristics with the maximum power point. In other words, the power from the power generation means 111 cannot be extracted most efficiently unless the power is converted at the maximum power point that is the operating point corresponding to the supply power.

  As can be seen from FIG. 2, it is known that the voltage at the maximum power point in the solar cell is about 80% of the open-circuit voltage that is the voltage when the current is zero. Therefore, this open-circuit voltage changes corresponding to the supply power. For this reason, in this embodiment, an open circuit voltage is used instead of the supply force.

<Power conversion means 120>
An example of the circuit configuration of the power conversion means 120 will be described with reference to FIG.
The power conversion means 120 converts the form of generated power and outputs converted power. As the power conversion means 120, a DC-DC converter for converting to direct current, a DC-AC inverter for converting to alternating current, or the like is used. The power conversion means 120 may be a step-up type or a step-down type. The example shown in FIG. 4A is a circuit configuration of a step-up DC-DC converter, and the example shown in FIG. 4B is a circuit configuration of a step-down DC-DC converter.

  The generated power from the power generation means 111 is transmitted by two conductors. The positive potential side conductor was applied to the circuit of the conversion means, and the negative potential side conductor was connected to the ground of 0 V which is the reference potential.

[First smoothing means 401]
Both ends of the first smoothing means 401 were connected to two conductors of generated power. The first smoothing means 401 has two roles. One is to reduce the fluctuation of the operating point of the power generation means 111 by keeping the output voltage of the power generation means 111 constant. In other words, even if the current flowing into the power conversion means 120 changes due to switching or the like, it does not greatly deviate from the maximum power point. The other is to reduce the AC impedance supplied into the power conversion means 120 to enable stable energy conversion and measurement of converted power. The first smoothing means 401 is realized by a capacitor. However, there are cases where the change in the generated power current is small, such as when the plurality of power conversion means 120 are operated while shifting the phase. Therefore, the first smoothing means 401 may be provided as necessary.

[Inductor 402]
The inductor 402 converts voltage by storing and discharging current. The inductor 402 is realized by a coil.

[First switching means 403]
When the first switching means 403 is turned on, the current flowing through the inductor 402 increases. The first switching means 403 repeats on and off alternately. The first switching means 403 is realized by a field effect transistor that is turned on by a pulse from the PWM means 407, but other switching means may be used.

[Second switching means 404]
The second switching means 404 is turned on almost simultaneously with the first switching means 403 being turned off. While the second switching means 404 is on, the current flowing through the inductor 402 decreases while flowing to the converted power side. The second switching means 404 is turned off when the current flowing through the inductor 402 becomes approximately zero. The second switching means 404 is realized by a diode, but may be realized by switching means such as a field effect transistor.

[Second smoothing means 405]
The second smoothing unit 405 is for stabilizing the voltage on the output side of the power conversion unit 120 and may be provided as necessary. For this reason, the second smoothing means 405 is realized by a capacitor.

[Loop filter means 406]
4 is controlled by a negative feedback control loop so that the voltage of the generated power output from the power generation means 111 approaches the operating point. That is, when the voltage of the generated power becomes higher than the voltage at the operating point, the time for turning on the first switching means 403 is lengthened, and the current accumulated in the inductor 402 is increased so as to lower the generated voltage. Conversely, when the voltage of the generated power becomes lower than the voltage at the operating point, the time for turning on the first switching means 403 is shortened, and the current accumulated in the inductor 402 is decreased to increase the generated voltage.

The loop filter means 406 ensures the response and stability of the feedback loop. For this reason, the loop filter means 406 performs PID control, but this is not restrictive.
The loop filter unit 406 is realized by an analog circuit, but may be realized by a digital circuit.

[PWM means 407]
The PWM unit 407 generates a pulse signal having a pulse width corresponding to the output of the loop filter unit 406. The pulse signal generated by the PWM means 407 is generated periodically in order to continuously perform power conversion. Increasing the frequency of the pulse signal can reduce the capacitance of the inductor 402, the transistor of the switching means 403, and the capacitors of the first and second smoothing means 401, 405, but the switching loss increases. When the frequency of the pulse signal is lowered, the switching loss can be kept small. In this embodiment, a 100 kHz pulse signal is output.

  The PWM means 407 generates a triangular wave or a sawtooth wave by comparing it with the output of the loop filter means 406, but it may be generated by a digital circuit such as a timer.

[Conversion power of power conversion means 120]
The conversion power of the power conversion means 120 will be described with reference to the case of the step-up DC-DC converter shown in FIG.

  Since the converted power of the power conversion means 120 can be considered as power supplied to the inductor 402 from the power generation means 111 side, the relationship between the current and voltage of the inductor 402 will be described with reference to FIG. The vertical axis at the top of FIG. 5 represents the voltage applied to the inductor 402, and the vertical axis at the bottom of FIG. The horizontal axis is a time axis common to the upper part and the lower part of FIG. 5, and FIG. 5 shows the relationship between current and voltage with the passage of time.

  Here, definitions of characters used in the following description will be described in advance. L is the inductance of the inductor 402. Vi is an input voltage to which the power conversion unit 120 inputs the generated power from the power generation unit 111. Vo is the output voltage of the power conversion means 120 that outputs the converted power. Ip is the maximum value of the current flowing through the inductor 402.

  The increase in current to the inductor 402 starts by turning on the first switching means 403 at time 0, and ends by turning off the first switching means 403 at time t1. Therefore, t1 is also the time during which the first switching means 403 is turned on and current is accumulated in the inductor 402. During this time, current is accumulated in the inductor 402 by the input voltage Vi.

The discharge of current from the inductor 402 starts at time t1 and ends when the current becomes 0 at time t2. This is because the current from the output side does not flow into the inductor 402 by the second switching means 404. During this time, a voltage difference (Vi−Vo) between the input and output of the power conversion means 120 is applied to the inductor 402. Since this potential difference is a negative value, the current of the inductor 402 decreases.
The increase / decrease of the current to the inductor 402 is repeated at the period T.

  Furthermore, preconditions for convenience in the following description will be described. First, it is assumed that fluctuations in one cycle of the input voltage Vi and the output voltage Vo are smoothed by the first and second smoothing means 401 and 405, respectively, and can be ignored. The on-resistances of the inductor 402, the first switching unit 403, and the second switching unit 404 are sufficiently small.

Here, due to the accumulation of current from time 0 to time t1 in the inductor 402, the current flowing through the inductor 402 at time t1 is maximized. The maximum current Ip at that time satisfies Expression 1. This is because the voltage applied to the inductor 402 having the inductance L during this period is a constant input voltage Vi.
(Formula 1) Vi = L · Ip / t1
Similarly, between time t1 and time t2, the voltage difference (Vi−Vo) between the input and output of the power conversion means 120 is applied to the inductor 402, and the current of the inductor 402 is released. Since the power conversion means 120 is a step-up type, a voltage is applied to the inductor 402 so as to reduce the current, and the current flowing through the inductor 402 becomes zero at time t2. The voltage (Vi−Vo) and the current decrease Ip applied during this time satisfy Expression 2.
(Formula 2) Vi-Vo = -L * Ip / (t2-t1)
When the inductance L and the maximum current Ip are eliminated from Equation 1 and Equation 2 and solved for the time t2 when the current of the inductor 402 becomes zero, Equation 3 is obtained.
(Formula 3) t2 = t1 · Vo / (Vo−Vi)
The average value of the current flowing from time 0 to time t2 is half of the maximum current Ip, as is apparent from the current waveform of the inductor 402 at the bottom of FIG. Therefore, the average value Ia of the current flowing during the period T is expressed by Equation 4.
(Formula 4) Ia = (Ip / 2) · t2 / T
Therefore, the average power P in the period T supplied from the power generation means 111 to the power conversion means 120 is substantially the same as the average power flowing into the inductor 402, and thus is obtained by the product of the input voltage Vi and the average current Ia obtained by Expression 4. Is satisfied.
(Formula 5) P = Vin · Ia = Vin · (Ip / 2) · t2 / T
By substituting a value obtained by solving Equation 1 for Ip in Equation 5 and substituting Equation 3 for t2 in Equation 5, Equation 6 is obtained as conversion power P.
(Formula 6) P = (Vi · t1) ² · {Vo / (Vo−Vi)} / (2 · T · L)
Here, if the inductance L and the period T of the inductor 402 are constant, the converted power P satisfies the proportional relationship of Equation 7.
(Formula 7) P∝ (Vi · t1) ² · {Vo / (Vo−Vi)}
Further, when the variation of the input voltage Vi is sufficiently small with respect to the output voltage Vo, such as when an element having a constant voltage, such as a secondary battery, is connected to the output of the energy conversion device 101, the converted power P is expressed by the formula As shown in FIG. 8, it is proportional to the square of the product of the input voltage Vi and the time t1.
(Formula 8) P∝ (Vi · t1) ²
[Conversion power of step-down power conversion means 120]
Also in the example of the step-down DC-DC converter shown in FIG. 4B, a mathematical expression can be easily derived based on the same concept as that of the step-up type. As a result, it is possible to replace the curly braces {} in Equations 6 and 7 with ones minus 1 by replacing the denominator and numerator.

That is, the conversion power P in the step-down power conversion means 120 corresponding to Equation 6 is expressed by Equation 9.
(Formula 9) P = (Vi · t1) ² · {(Vi−Vo) / Vo} / (2 · T · L)
Similarly to the step-up type, when the inductance L and the period T of the inductor 402 are constant, the converted power P satisfies the proportional relationship of Expression 10 corresponding to Expression 7.
(Expression 10) P∝ (Vi · t1) ² · {(Vi−Vo) / Vo}
<Power calculation means 121>
The power calculation unit 121 detects the power converted by the power conversion unit 120. For example, since the power converted by the power conversion unit 120 by the step-up DC-DC converter shown in FIG. 4A satisfies Expression 7, the input voltage Vi, the output voltage Vo of the power conversion unit 120, and the power conversion unit From the time t1 when the first switching means 403 is turned on as the 120 conversion operation, the power converted by the power calculating means 121 is obtained by the calculation shown in Equation 7. That is, in order to detect the maximum power point, it is only necessary to know the magnitude relation of the power, so that the proportional relation with the power P from which the constant is removed is used as the output of the power calculation means 121 as shown in Equation 7. did.

A configuration example of the power calculation unit 121 will be described with reference to FIG.
In FIG. 6, the first ADC means converts the voltage of the generated power into a digital value. The output of the first ADC means is used for obtaining a digital value of the open-circuit voltage as the supply power of the power generation means 111 in addition to the power calculation. The second ADC means converts the converted power voltage into a digital value. Although not shown, the third ADC means converts the output level of the loop filter means 406 into a digital value as one cycle time t1 for turning on the first switching means 403. In order to obtain the time t1 of one cycle for turning on the first switching means 403, a signal for actually driving the first switching means 403 is counted by a digital circuit, or the loop filter means 406 and the PWM means 407 are digitally set. In the case of realizing with a circuit or a processor, the third ADC means can be omitted.

  The first multiplication unit 621 multiplies the output of the first ADC unit 611 and the output of the third ADC unit 613. The second multiplication unit 622 squares the calculation result of the first multiplication unit 621. The subtracting means 623 subtracts the output of the first ADC means 611 from the output of the second ADC means 612. The dividing unit 624 divides the output of the second ADC unit 612 by the calculation result of the subtracting unit 623. The third multiplication unit 625 multiplies the calculation result of the second multiplication unit 622 and the calculation result of the division unit 624 and outputs the converted power P.

  In the configuration shown in FIG. 6, the voltage drop of the second switching means 404 can be ignored. However, if necessary, the value obtained by adding the voltage drop of the second switching means 404 to the output voltage Vo is the output voltage. The power may be calculated by using it as Vo.

  Moreover, what is necessary is just to change a structure as needed, when using Numerical formula 6 and Numerical formula 8 thru | or 10. Further, the configuration of the power calculation means 121 described above is merely an example, and the calculation order is changed, the table or the like is referred to, the calculation is performed using a processor, or the calculation is performed by an analog calculation circuit. Needless to say.

  In this embodiment, in order to eliminate the resistance for current measurement and eliminate the power loss at the resistor, the converted power is obtained from the input / output voltage of the power conversion means 120 and the conversion operation of the power conversion means 120. Configured. However, the converted power P can be obtained by calculating the product of the input current and the input voltage of the power conversion means 120 or calculating the output current and the output voltage of the power conversion means 120.

  The converted power P detected by the power calculation means 121 is used by the MPPT control means 131 to obtain the maximum power point.

<MPP characteristic storage means 124>
The MPP characteristic storage means 124 stores the characteristic of the maximum power point with respect to the supply power in order to easily reach the maximum power point even if the supply power changes.

  In the first embodiment, an open circuit voltage is used as the supply power, but the supply power may be illuminance near the solar cell, short-circuit current, or power at the maximum power point. In addition, the maximum power point stores the voltage characteristics as the operating point set in the power conversion means 120 that achieves the maximum power, but the power at a certain supply power, such as the ratio of the current, the input impedance, and the switch-on time. Any characteristic that can control the operation of the conversion means 120 may be stored.

[Relationship with temperature]
In the first embodiment, the MPP characteristic storage unit 124 stores the maximum power point in association with the temperature and the supply force. For this reason, a temperature sensor is provided in the vicinity of the power generation means. The main items affecting the maximum power point are supply power, temperature, and aging. Therefore, if the maximum power point is stored in association with the temperature and the supply force, it is only necessary to cope with the change with time, so that the frequency of the learning step 716 to be performed later can be greatly reduced. However, if the change in temperature is relatively gradual and the characteristics of the maximum power point with respect to the supply power at the new temperature are updated sufficiently quickly, the storage in the MPP characteristic storage means 124 does not necessarily have to be associated with the temperature.

[Reduction of storage capacity]
When storing the maximum power point corresponding to the supply power, the storage capacity can be reduced by dividing the supply power into regions and storing the maximum power points for each region. In this case, a representative value of the supply power is defined for each region, and when referring to the supply power between the representative values, the value of the maximum power point is interpolated as necessary, or newly obtained when updating. The maximum power point obtained may be updated by dividing the weight if necessary. The same applies to the temperature.

[Non-linear supply capacity]
FIG. 3 shows the relationship between the short-circuit current and the maximum power point when a solar cell is used. As shown in FIG. 3, when the supply power is expressed in logarithm, the characteristic of the maximum power point with respect to the supply force is relatively close to a straight line. Therefore, it is preferable to perform nonlinear conversion such as logarithm of the supply force.

[Handling of unlearned areas]
The maximum power point with respect to the supply force stored in the MPP characteristic storage unit 124 is stored by dividing the supply force into regions as described above, but can be referred to even if all regions are not updated. . The areas that have not been learned are rarely referenced because they have little or no supply power. If the reference is still made, the learning step 716 may be newly executed or may be obtained by interpolation from the maximum power point stored in the surrounding area. Alternatively, since 0.8 times the open circuit voltage is approximately equal to the voltage at the maximum power point, 0.8 times the open circuit voltage may be set as the initial value of the maximum power point.

[Updating maximum power point]
In the first embodiment, when the stored maximum power point is updated, the new maximum power point is stored as it is every time the MPPT control means 131 detects the maximum power point.

  In addition to this, in order to eliminate the influence of noise, the maximum power point stored so far is multiplied by 0.8, the newly detected maximum power point is multiplied by 0.2, and the sum of them is newly set. The filtered value such as updating as the maximum power point may be stored. However, this ratio is an example, and differs depending on the number of updates for each supply force, the noise environment, and the like. Therefore, a value indicating the reliability of the stored maximum power point, such as the number of updates for each supply force, may be stored together. Furthermore, information related to the elapsed time since the update may be stored together. If the elapsed time from learning is long, the information becomes old, and the reliability of the learning content decreases.

  Further, the stored maximum power point value may be corrected according to the difference between the maximum power point stored at the time of updating and the newly obtained maximum power point.

[Storing numerical values indicating characteristics]
The MPP characteristic storage means 124 stores the maximum power point corresponding to the supply power, but further obtains a formula that approximates the characteristic of the maximum power point with respect to the supply power by the least square method or the like. You may make it memorize | store numerical values, such as a coefficient to show. However, in that case, an operation for deriving the characteristics and an operation for returning to the maximum power point at the time of reference are required.

[Retention of memory]
The maximum power point stored in the MPP characteristic storage unit 124 is stored in a non-volatile memory so that the stored value is maintained even if power generation is lost at night. Although it is not always necessary to store in the nonvolatile memory, the frequency of the learning step 716 can be reduced by storing in the nonvolatile memory.

<MPPT control means 131>
The MPPT control unit 131 controls the operating point of the power conversion unit so that the power converted by the power conversion unit 120 is maximized. The MPPT control means 131 intermittently detects the maximum power point, learns the relationship between the supply power and the maximum power point by storing the detected maximum power point in association with the supply power, and when the supply power changes Control so as to efficiently follow the maximum power point. For this purpose, a preferred embodiment of the maximum power conversion method 701 by the MPPT control means 131 will be described based on the process flow shown in FIG.

  The maximum power conversion method 701 operates by an operating point update determination step 711, a supply force detection step 712, a learning determination step 715, a learning step 716, and a reference step 717.

  However, while this process flow shown in FIG. 7A is being executed, although not shown, the power generation process for generating electrical energy by the power generation means 111 and the form of power generated by the power conversion means 120 are shown. The power conversion process of converting and outputting the converted power is operating, and energy conversion is performed unless otherwise specified.

  Hereafter, each process of the maximum power conversion method 701 is demonstrated in detail.

[Operation point update determination step 711]
When light starts to hit the solar cell and the energy conversion device 101 starts to move, the process proceeds to the operating point determination step. In the operating point update determination step 711, it is determined whether or not to update the operating point. When the frequency of the operating point update increases, it becomes possible to follow the change in the amount of light to the solar cell at high speed, but the power required for detecting the supply power for the update increases. Therefore, there is a desirable update frequency that matches the speed of light quantity change.

  The update may be determined based on a fixed time, for example, when the elapsed time from the previous update is 10 seconds or more. However, in order to reduce power consumption for updating the operating point, it is desirable to automatically change the frequency at which the operating point is updated according to the speed of change in the supply power.

  For example, when the amount of light hitting the solar cell of the power generation means 111 changes in a short time, such as when a large number of small clouds are flowing in the wind or in the case of a running car, the change in supply power is fast. Increase the frequency of operating point updates. On the contrary, when the solar battery of the power generation means 111 is in clear weather, there is almost no change in the supply power, so the frequency of the operating point update is lowered. For this reason, what is necessary is just to determine so that an operating point may be updated, when the accumulated change amount which accumulated the change of supply force with the filter etc. becomes a predetermined value.

  However, an upper limit may be provided for the time interval for updating the operating point so that the operating point is updated periodically even when there is no change in the supply power. In addition, when the supply power changes very quickly, the power consumption for following the maximum power point is large, so that the overall efficiency is not lowered and the operating point is updated at the time interval. A lower limit may be provided.

  Alternatively, the operating point update may be determined using both the accumulated change amount and the elapsed time from the previous operating point update. That is, the larger the cumulative change amount, the shorter the operation point update time interval. For example, in this embodiment, when the value obtained by multiplying the cumulative change amount and the elapsed time by a coefficient is less than a predetermined value, the operating point update determination step 711 is repeated, and when the value is equal to or larger than the predetermined value, the operating point To update the supply force detection step 712. Therefore, the supply force is detected in the supply force detection step 712, the change in supply force is detected in the change detection step 713 as a power generation change amount, and the cumulative change amount obtained by accumulating the power generation change amount by the filter is obtained in the cumulative filter step 714. I did it.

  The supply force detection step 712, the change detection step 713, and the cumulative filter step 714 may be at other positions on the process flow diagram. For example, as shown in FIG. 7B, these can be executed each time before the operating point update determination step 711 is executed.

  Note that when the operating point is regularly updated, the change detection step 713 and the cumulative filter step 714 are not necessary.

[Supply force detection step 712]
In the supply force detection step 712, the supply force of the power generation means 111 is detected. For this reason, in the supply force detection step 712, the open circuit voltage is measured.

  However, the measurement of the open circuit voltage of the power generation unit 111 is performed after the first switching unit 403 of the power conversion unit 120 is continuously turned off and the voltage of the first smoothing unit 401 rises to the open voltage and stabilizes. Therefore, power conversion is not performed during the waiting time, resulting in power loss. This time becomes longer when the supply force is small. Alternatively, although not shown, when the power conversion means 120 is separated by the third switching means and the open circuit voltage is measured, not only the on-resistance of the third switching means causes power loss but also the cost of the third switching means. Is also big.

Similarly, when measuring the short-circuit current as the supply force, it is necessary to wait until the power conversion unit 120 is disconnected or the voltage of the first capacitor becomes zero.
Further, in the supply force detection step 712, the temperature of the power generation means 111 may be detected as necessary, for example, when the temperature change is large.
When the supply force detection step 712 is executed, the process proceeds to the change detection step 713.

[Change detection step 713]
In the change detection step 713, the change in the supply force detected in the supply force detection step 712 is extracted to obtain the power generation change amount. For this reason, in the change detection step 713, the power generation change amount is obtained from the absolute value of the value obtained by subtracting the supply force detected one time before from the latest supply force detected in the supply force detection step 712. Furthermore, the change rate obtained by dividing the subtracted absolute value by the supply power may be used as the power generation change amount. In addition to this, the power generation change amount is any method or means for obtaining the power generation change amount by extracting the change in supply power, such as obtaining the ratio of the latest supply power and the previous supply power. A thing may be used.

[Cumulative filter step 714]
In the cumulative filter step 714, the power generation change amount obtained in the change detection step 713 is accumulated by a filter or the like to obtain a cumulative change amount.

  For this reason, in the cumulative filter step 714, the cumulative change amount thus far is multiplied by 7/8, and the power generation change amount is multiplied by 1/8 to be added as a new cumulative change amount. However, these numerical values are examples, and it goes without saying that the present invention is not limited. The accumulated change amount obtained in this way is also a moving average of the power generation change amount.

  The cumulative filter step 714 is for searching for a tendency of the power generation change amount by detecting the supply force a plurality of times. However, for example, a single power generation change amount itself can be used as the cumulative change amount. Therefore, the cumulative filter step 714 may be provided as necessary.

  Further, in the example shown in FIG. 7B, the power generation change amount may be simply accumulated in the accumulation filter step 714. However, in this case, it is necessary to initialize the power generation change amount when the operating point is updated.

[Learning determination step 715]
In the learning determination step 715, it is determined whether the process proceeds to the learning step 716 or the reference step 717. The frequency of learning in the learning step 716 is lower than that in the reference step 717. Therefore, power consumption required for maximum power point detection is reduced.

  For example, in the learning determination step 715, if the combination of supply force and temperature is the first region on the day, the process proceeds to the learning step 716, and if the combination is learned on that day, the process proceeds to the reference step 717. However, this is only an example, and the frequency of the learning step 716 is not particularly limited. Increasing the frequency of the learning step 716 increases the power consumption for learning.

[Learning step 716]
In the learning step 716, after executing the MPP detection step 721 for detecting the maximum power point, the characteristic of the maximum power point stored in the MPP characteristic storage unit 124 is updated in association with the supply power and the temperature by the detected maximum power point. Then, the storing step 722 is executed.

The characteristic of the maximum power point stored in the storing step 722 is the characteristic of impedance, voltage, or current that is the operating point of the power conversion means 120 associated with the supply power. In addition, the supply power for associating the memory in the memory step 722 is logarithmic. Furthermore, when the characteristic of the maximum power point is updated in the storage process 722, the maximum power point detected in the MPP detection process may be filtered.
The detection method in the MPP detection step 721 will be described in detail later.
When the learning process 716 is executed, the process proceeds to the reference process 717.

[Reference Step 717]
In the reference step 717, the operating point of the power conversion means 120 is set by referring to the characteristic of the maximum power point stored in the MPP characteristic storage means 124 by the supply force and temperature. When the reference process 717 is executed, the process returns to the operating point update determination process 711.

[Another Example of Maximum Power Conversion Method 701]
The example in which the learning step 716 is performed as necessary before the reference step 717 has been described above, but the maximum power conversion method 701 is not limited to this. The learning step 716 is executed at a timing as necessary for reasons such as a change over time, such as the reference step 717 and the learning step 716 being executed independently, and the reference step 717 is executed at intervals corresponding to the change in the supply force. If so, there are no other restrictions.

<MPP detection step 721>
A method for detecting the maximum power point in the MPP detection step 721 will be described in detail with reference to FIG.

The MPP detecting step 721 includes an initial value setting step 811 for setting an operating point before approaching that is an operating point before approaching the maximum power point, and power conversion at two different operating points having a fixed relationship with the operating point before approaching. The two-point detection step 812 for detecting the power to be converted by the means 120, the comparison value calculation step 813 for comparing the power detected in the two-point detection step 812 to obtain a comparison value, and the comparison value calculation step 813 The operation is performed by a conversion step 815 in which the operation point before approach is corrected so that the comparison value approaches the target value and the operation point after approach is obtained.
Hereafter, each process is demonstrated in detail.

[Initial value setting step 811]
In an initial value setting step 811, an initial value of the pre-approach operating point that is an operating point before approaching the maximum power point is set. The initial value may be the value of the operating point set in the power conversion means 120 before the update, or may be set to a voltage obtained by multiplying the open circuit voltage obtained in the supply force detection step 712 by a factor, You may set using the operating point obtained with reference to the MPP characteristic memory | storage means 124 with the supply force detected by the supply force detection process 712. FIG.

[Two-point detection step 812]
In the two-point detection step 812, the power obtained by the power calculation unit 121 at the voltages at two different operating points set in the power conversion unit 120 is detected. That is, the first power obtained by temporarily setting the power conversion means 120 as the first operating point and the second power obtained by temporarily setting the second operating point are detected.

  Here, the first operating point was set to a voltage higher than the pre-approach operating point, and the second operating point was set to a voltage lower than the pre-approach operating point. Further, the value obtained by subtracting the pre-approach operating point from the first operating point is set to be smaller than the value obtained by subtracting the second operating point from the pre-approaching operating point. In this embodiment, the value obtained by subtracting the voltage at the pre-approach operating point from the voltage at the first operating point is set to 0.6 times the value obtained by subtracting the voltage at the second operating point from the voltage at the pre-approaching operating point. Specifically, the first operating point is set to a voltage 0.06V higher than the operating point before the update, and the second operating point is set to a voltage 0.1V lower than the operating point before the update. It goes without saying that the voltage at this operating point varies depending on the difference in voltage-power characteristics such as the number of cells in series of the solar battery. In addition, when the supply power is large, the change in power also increases. For example, the first operating point is 0.03 V higher than the operating point before updating, and the second operating point is higher than the operating point before updating. The difference between the first operating point and the second operating point may be changed according to the supply power, such as a voltage lower by 0.05V.

A desirable voltage at the first operating point and the second operating point will be described with reference to FIG.
In FIG. 9, the horizontal axis represents the voltage at the operating point set in the power conversion means 120, and the vertical axis represents the converted power. The solid curve represents the voltage-power characteristic, and the alternate long and short dash line represents the maximum power point. Here, the dotted line curve is obtained by making the distance between the solid line voltage-power characteristic and the alternate long and short dash line close to 0.6 times in a region lower than the maximum power point. This is because, in the vicinity of the maximum power point, the solid line in the region larger than the dotted line and the maximum power point is almost a line object with the one-dot chain line of the maximum power point as an axis. That is, the absolute value of the change in power is larger in the region larger than the maximum power point than in the region smaller than the maximum power point. For this reason, the value obtained by subtracting the pre-approach operating point from the first operating point is set to be smaller than the value obtained by subtracting the second operating point from the pre-approaching operating point.

  Moreover, in FIG. 9, the 1st area | region 911 has shown that it is the range of 1.02 times to 1.12 times the maximum power point. Further, the second region 912 indicates a range from 0.75 times to 0.97 times the maximum power point. The first operating point and the second operating point are set in these areas, respectively. This is because the change of power is small in the range of 0.97 times to 1.02 times the maximum power point and is not suitable for power detection. Also, in the region of 1.12 times or more or 0.75 times or less from the maximum power point, the power is small, so that the power loss at the time of power detection is large and is not suitable for power detection.

[Comparison value calculation step 813]
In the comparison value calculation step 813, the first power and the second power are compared to obtain a comparison value.
The first power and the second power compared in the comparison value calculation step 813 will be described with reference to FIG.

  In FIG. 10, the horizontal axis represents the voltage at the operating point set in the power conversion means 120, the vertical axis represents the power converted by the power conversion means 120, and the curve represents the voltage-power characteristics. For the three vertical lines, the solid line indicates the pre-approach operating point, the dotted line indicates the first operating point, and the broken line indicates the voltage at the second operating point.

  FIG. 10A shows an example in which the pre-approach operating point is slightly deviated from the maximum power point. The power change at the first and second operating points is much larger than the power change at the maximum power point, so even if the pre-approach operating point is slightly lower than the maximum power point, P1 is sufficiently larger than the second power P2. Therefore, deviation from the maximum power point can be detected with high sensitivity.

  FIG. 10B shows a case where the operating point before approaching coincides with the maximum power point. In this embodiment, the value obtained by dividing the value obtained by subtracting the operating point before approach from the first operating point by the value obtained by subtracting the second operating point from the operating point before approach is set to 0.6. In terms of the point, the first power and the second power substantially coincide.

For this reason, the comparison value is obtained by normalizing the difference between the first power and the second power by the sum of the first power and the second power according to Formula 11.
(Formula 11) Comparison value = (first power−second power) ÷ (first power + second power)
That is, the comparison value is obtained by dividing the difference between the first power and the second power by the sum. Here, what is divided by the sum of the first power and the second power is normalization so that the comparison value is less affected even if the amount of light to the solar cell changes. Divide accordingly. Instead of dividing by the sum of the first power and the second power, divide by the average value of the first power and the second power, the first power, the second power, the power at the operating point before the update, etc. Any method may be used as long as it eliminates the influence of supply power.

The characteristics of the comparison value obtained in this way will be described with reference to FIG.
In FIG. 11, the horizontal axis represents the voltage at the operating point of the power conversion means 120, the first vertical axis on the left represents the power, and the second vertical axis on the right represents the comparison value. The three solid curves are the voltage-power characteristics with different supply forces. The three dotted lines are the operating point before approaching of the supply force corresponding to the three solid lines-comparison value characteristics. As indicated by the three arrows, even if the supply force changes, the maximum power is reached at the operating point voltage at which the comparison value is almost zero.

In order to more simply normalize with electric power, a comparison value may be obtained from the ratio of the first electric power and the second electric power as shown in Expression 12.
(Formula 12) Comparison value = first power ÷ second power [conversion step 815]
In the conversion step 815, the pre-approach operating point is corrected with the comparison value, and the post-approach operating point closer to the maximum power point is obtained.

  The post-approach operating point can be brought closer to the maximum power point by increasing or decreasing a predetermined value to the pre-approach operating point. That is, when the comparison value is larger than the target value, a predetermined value is added to the pre-approach operation point, and when the comparison value is smaller than the target value, the predetermined value is subtracted from the pre-approach operation point. Here, if the predetermined value is large, the operating point cannot be adjusted to the maximum power point with high accuracy. If the predetermined value is small, the time and power consumption required to reach the maximum power point are increased.

Thus, in this embodiment, the relationship between the pre-approach operating point and the comparison value indicated by the dotted line in FIG. 11 is used to correct the comparison value with an optimum correction amount according to the deviation from the target value. .
The conversion characteristics in the conversion step 815 will be described with reference to FIG. In FIG. 12, the horizontal axis represents the comparison value obtained in the comparison value calculation step 813, and the vertical axis represents the correction amount for the pre-approach operating point.

  The comparison value-correction amount characteristic shown in FIG. 12 is obtained from the pre-approach operating point-comparison value characteristic indicated by the dotted line in FIG. That is, the amount of correction is obtained by subtracting the voltage at the operating point corresponding to each comparison value from the voltage at the maximum power point. Here, the three dotted lines in FIG. 11 have substantially the same characteristics, and the deviation from the maximum power point is almost the same even if the supply power changes, so the same conversion characteristics are used. However, the conversion characteristics differ depending on the supply power. Also good. In addition, although the pre-approach operating point-comparison value characteristic indicated by the dotted line in FIG. 11 is a curve, in order to simplify the calculation, the correction amount characteristic is approximated by four straight lines as shown in FIG. Using. Here, when the comparison value increases, the correction amount increases, and an error in the correction amount cannot be ignored due to a change in the supply force. Therefore, an upper limit is set for the correction amount.

The conversion shown in FIG. 12 may be realized by calculation or may be realized by referring to a table.
In the conversion step 815, the operating point before approach is corrected by adding the correction amount of the operating point obtained by the function shown in FIG.

[Other examples of the first voltage and the second voltage]
An example in which the first voltage is 0.06 V higher than the voltage before update, the second voltage is 0.1 V lower than the voltage before update, and the comparison value becomes approximately 0 at the maximum power point. However, this is not the case. An example in which the first voltage and the second voltage are set to other values will be described with reference to FIG.

  In FIG. 13, as in FIG. 11, the horizontal axis represents the voltage at the operating point of the power conversion means 120, the first vertical axis on the left represents power, and the second vertical axis on the right represents the comparison value. Represents. The three solid curves are the voltage-power characteristics with different supply forces. The three dotted lines are the operating point before approaching of the supply force corresponding to the three solid lines-comparison value characteristics.

  FIG. 13A shows a comparison of the maximum power point by setting the first voltage to a value 0.08V higher than the operating point before the update and setting the second voltage to a value 0.08V lower than the first voltage. This is an example when the value is about -0.07.

  Similarly, in FIG. 13B, the first voltage is set to a value 0.02V lower than the operating point before the update, and the second voltage is set to a value 0.2V lower than the operating point before the update. This is an example in which the power point comparison value is about 0.12.

  As can be seen from the examples shown in FIGS. 13A and 13B, the first voltage and the second voltage are not particularly limited, and the above-described maximum power point comparison value is zero. As in the example, a correction amount obtained by subtracting a voltage corresponding to each comparison value from the voltage at the maximum power point is obtained in advance, and the operating point before approach is corrected in the conversion step 815 to obtain the operating point after approach. The maximum power point can be approached in a short time.

  However, in the example shown in FIG. 13B, the ratio of the voltage change to the change in the comparison value is large, and in FIG. 13B, the slopes of the three dotted lines at the maximum power point are greatly different. This is not desirable. Therefore, the maximum power point can be detected with higher accuracy when the maximum power point exists between the first voltage and the second voltage.

[Repeat maximum power point approach]
In the MPP detection step 721 shown in FIG. 8A, the two-point detection step 812, the comparison value calculation step 813, and the conversion step 815 are executed once, so that the maximum power point is significantly approached from the pre-approach operating point. The operating point after approach can be obtained. However, since the conversion characteristic shown in FIG. 12 is approximated by a straight line, common conversion is performed for different supply forces, and an upper limit is set for the correction amount, an accurate maximum power point cannot always be obtained. Nevertheless, an accurate maximum power point can be obtained by operating the MPP detection step 721 shown in FIG.

  In the example shown in FIG. 8B, it is determined whether or not the comparison value obtained in the comparison value calculation step 813 by the MPP determination step 814 is sufficiently close to the comparison value at the predetermined maximum power point. When not approaching, after the conversion step 815 is executed, the two-point detection step 812 is repeated. Alternatively, the MPP determination step 814 may determine whether or not the correction amount of the operating point as a result of performing the conversion step 815 is sufficiently small. Thus, by repeating a series of steps a plurality of times, the error from the maximum power point can be reduced exponentially.

  In addition, the detection method of the maximum power point by the MPP detection step 721 in this embodiment can be used also in the energy conversion device 101 or the energy conversion circuit that does not have the MPP characteristic storage unit 124. It can be used regardless of the configuration of the power calculation means 121 and the power detection method.

<Supplementary explanation>
The example in the case where the power calculation unit 121 and the MPPT control unit 131 are configured by digital circuits and the loop filter unit 406 and the PWM unit 407 are configured by analog circuits has been described above. It can be realized with a circuit or a digital circuit. There is no particular limitation on the boundary between the portion realized by the analog circuit and the portion realized by the digital circuit. Although not particularly illustrated, the energy conversion device 101 according to the present invention operates satisfactorily if analog-digital conversion, digital-analog conversion, or the like is provided at the boundary between the analog circuit and the digital circuit.
Needless to say, the calculation by each means may be performed with reference to a table.

<Summary>
In the energy conversion device 101, the maximum power conversion circuit 112, and the maximum power conversion method 701 described above in the first embodiment, the maximum power point corresponding to variations and changes with time can be suppressed while suppressing the loss for detecting the maximum power point. Therefore, the power efficiency can be greatly improved.

  In the first embodiment, the MPP characteristic storage unit 124 stores the characteristic of the maximum power point with respect to the supply force. For this reason, the supply force is detected by an open circuit voltage or a short circuit current. However, with this method, power conversion cannot be performed while measuring a short-circuit current or an open-circuit voltage, which causes a reduction in efficiency. Moreover, a short-circuit means, an open means for detecting the supply force, a means for detecting illuminance, and the like are necessary.

<Maximum power conversion method 1501>
In order to improve this problem, the power converted by the power conversion means 120 is used instead of the supply power in the second embodiment.

  In the following description of the second embodiment, the difference from the first embodiment will be mainly described in order to avoid duplication of description. For this reason, the contents not described in the second embodiment are the same as those in the first embodiment.

[Detection of power supply by power and voltage]
The operation when electric power is used instead of the supply power will be described with reference to FIG. In FIG. 14, the first solid line 1401 indicates the relationship between voltage and power in the first supply force, and the second solid line 1402 indicates the relationship between voltage and power in the second supply force. Is. The black circles on the first solid line 1401 and the second solid line 1402 indicate the maximum power point in each supply power. A dotted line characteristic 1403 represents the locus of the maximum power point when the supply force changes.

  Originally, the maximum power point changes according to the supply power. It is not possible to know the supply power just by knowing the power. For example, the electric power P1 in FIG. 14 exists on the first solid line and the second solid line having different supply powers. However, if both power and voltage are known, the supply power is determined. For example, in FIG. 14, the intersection of the power P1 and the voltage V1 can occur only in the second supply force. Therefore, both power and voltage are detected by the power calculation means 121, the maximum power point is detected by the learning step 1516, and the maximum power point detected in association with the power and voltage before learning is detected by the MPP characteristic storage means 124. If stored, the maximum power point can be obtained by referring to the MPP characteristic storage means 124 by the power and voltage in the reference step 1517 even if the supply power changes, and is set in the power conversion means 120 as the operating point. be able to.

  However, in order to store the maximum power point in association with voltage and power in the MPP characteristic storage means 124, the problem is that not only the storage capacity increases due to the increase in dimensions, but also the time required for learning also increases. Remains.

[Associate with power]
A method for solving this problem will be described based on the example shown in FIG. A maximum power conversion method 1501 shown in FIG. 15 is obtained by replacing the supply power detection step 712 of the maximum power conversion method 701 shown in FIG. Accordingly, the characteristic of the operating point of the maximum power point is stored in association with the power of the maximum power point obtained in the MPP detection process 1521 as the characteristic stored in the MPP characteristic storage unit 124 in the storage process 1522 of the learning process 1516. I made it. Further, the maximum power point is referred to from the MPP characteristic storage unit 124 in the reference step 1517 based on the power detected in the power detection step 1512.

  Here, an operating point obtained by referring to the MPP characteristic storage unit 124 using the power detected in the power detection step 1512 as an initial value for obtaining the maximum power point in the MPP detection step 1521 may be used.

  Further, when storing in the learning step 1516, the power at the maximum power point is used as the supply power, and the power at that time is used in the reference step 1517. Therefore, the operating point obtained in the reference step 1517 has an error from the maximum power point. Although it occurs, this error is relatively practical because it is relatively small.

  This will be described based on the example shown in FIG. For example, when the supply power changes and the power conversion at the maximum power point of the first supply power changes to the second supply power, the power detected at that time is the voltage at the maximum power point of the first solid line 1401. This is the electric power P1 at the intersection of the second solid line 1402 corresponding to V1 and the second supply force. This is because the power conversion means 120 operates so that the voltage becomes constant. By referring to the relationship between the power and voltage at the maximum power point stored in the MPP characteristic storage means 124 by this power P1, the voltage V2 at which the dotted line becomes the power P1 is obtained. The power obtained by converting the power with the voltage V2 at the time of the second supply force is the power P2 at which the second solid line 1402 becomes the voltage V2. The power P2 is sufficiently larger than the power P1, and is sufficiently close to the power at the maximum power point.

  This is because if it is assumed that the electric power P1 is larger than the electric power P2, the solid line and the dotted line must be in contact with each other at the maximum power point. Will have. However, this assumption is incorrect because the voltage and power do not match at different supply forces. This also means that the solid line voltage range is wider than the dotted line voltage range, so that at the same power, the intersection with the dotted line is closer to the maximum power point at that time than the intersection with the solid line. be able to.

  When this reference process 1517 is executed a plurality of times, the deviation from the maximum power point becomes exponentially small.

<Summary>
As described above, in the energy conversion device 101, the maximum power conversion circuit 112, and the maximum power conversion method 1501 according to the second embodiment, the loss for supplying power detection can be reduced with a simpler operation than the first embodiment. Therefore, the efficiency of power conversion as a whole can be further improved.

  As described above, the energy conversion method and the maximum power conversion circuit according to the present invention can measure the power to be converted without a voltage drop due to resistance, and thus are suitable for following the maximum power point efficiently.

DESCRIPTION OF SYMBOLS 101 Energy converter 111 Power generation means 112 Maximum power conversion circuit 120 Power conversion means 121 Power calculation means 124 MPP characteristic storage means 131 MPPT control means 401 First smoothing means 402 Inductor 403 First switching means 404 Second switching means 405 Second smoothing Means 406 Loop filter means 407 PWM means 621, 622, 625 Multiplication means 623 Subtraction means 624 Division means 701 Maximum power conversion method 711 Operating point update determination step 712 Supply force detection step 713 Change detection step 714 Cumulative filter step 715 Learning determination step 716 , 1516 Learning step 717, 1517 Reference step 721, 1521 MPP detection step 722, 1522 Storage step 811 Initial value setting step 812 Two-point detection step 813 Comparison value calculation step 814 MPP determination process Step 815 Conversion step 911 First region 912 Second region 1512 Power detection step

Claims (4)

In the maximum power conversion circuit that converts input power,
Power conversion means for converting the form of the input power;
Power calculating means for calculating the power converted by the power converting means from the input voltage of the power converting means and the converting operation of the power converting means;
MPPT control means for controlling so that the power converted by the power conversion means is maximized, and a maximum power conversion circuit. The power conversion means includes inductor means for storing current, first switching means that is turned on to store current in the inductor means, and second switching means that is turned on to discharge the current of the inductor. And
2. The maximum power conversion according to claim 1, wherein the power calculation unit calculates a power to be converted by the power conversion unit from an input voltage of the power conversion unit and an ON time of the first switching unit. circuit.   The maximum power conversion circuit according to claim 2, wherein the power calculation by the power calculation means is a calculation for obtaining a product of a square of an input voltage and a square of an on-time of the first switching means. Power generation means for generating electrical energy;
An energy conversion device comprising the maximum power conversion circuit according to any one of claims 1 to 3.

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