JP4294346B2 - Photovoltaic power generation system and its maximum power point tracking control method - Google Patents

Description

【００６２】
低照度領域での追従は、山登り法では微分値を得るためにかなり早い段階で制御不能の現象が起きる。
これに対して、本制御方式では、単純な最大値検出のため、スキャン全幅の中に勾配があれば追従可能である。
図１１からわかるように、本制御方式では、日射強度Ｇがピーク時８００Ｗ／ｍ² のとき１００／ｍ² まで照度が低下しても出力利用率ＵＵＦが９０％を維持している。
【００６３】
また、図１２は、本制御方式における低照度時の電力取得特性を示す図である。
図１２において、横軸が時刻を、左側縦軸が太陽電池出力電力ＰPVおよび太陽電池出力利用率ＵＵＦを、右側縦軸がパネル面日射強度Ｇをそれぞれ表している。
なお、太陽電池出力利用率ＵＵＦは、最大電力点検出周期をＴとすると、上記数１で与えられる。
【００６４】
本制御方式では、図１２に示すように、日射強度Ｇが５０Ｗ／ｍ² で太陽電池出力利用率ＵＵＦが８０％以上と高い効率を示す。
また、本制御方式では、日射強度Ｇが５０Ｗ／ｍ² 以下では、太陽電池出力利用率ＵＵＦは低下するが６０％程度エネルギーを回収することがきる。
【００６５】
以上説明したように、本実施形態によれば、ＤＣ−ＤＣコンバータなどの電力変換回路１４に含まれるインダクタＬ１４１に流れる電流の変化によって変化する太陽電池電流ＩPVを零から短絡電流まで変化させ、太陽電池のＩ−Ｖ特性を瞬時にスキャンし、最適太陽電池電流ＩOPに太陽電池電流ＩPVを追従させ、得られた最大電力動作点で動作するように追従制御を行うＤＳＰ１５を設けたので、太陽電池の最大電力点を確実にかつ高い精度で検出することができる。
実測例によれば、本制御方式と独立型の太陽光発電システムで広く利用されているバッテリィ制御装置を搭載した従来方式を発電電力量について比較すると１４．８％程度増加し、太陽電池出力利用率ＵＵＦは約９９％と非常に高い値を得ることができる。また、負荷変動に対する制御特性も良いという利点がある。
【００６６】
なお、以上の説明では、電力変換回路としてのＤＣ−ＤＣコンバータは、昇圧型を例に説明した。この昇圧型ＤＣ−ＤＣコンバータでは、太陽電池電圧より高い負荷電圧を得ることができる。
【００６７】
たとえば、負荷電圧を太陽電池電圧より下げたい場合には、図１３に示すような、電力変換回路１４Ａとして降圧型ＤＣ−ＤＣコンバータを用いた回路構成が適している。
降圧型ＤＣ−ＤＣコンバータにおいては、太陽電池パネル１１の第１端子ＴＯ１および第２端子ＴＯ２に対して並列にキャパシタＣF が接続される。
また、ＭＯＳＦＥＴ１４１のドレインが太陽電池パネル１１の第１端子ＴＯ１に接続され、ソースがダイオードＤ１４１のカソードおよびインダクタＬ１４１の一端に接続される。ダイオードＤ１４１のアノードが太陽電池パネル１１の第２端子ＴＯ２、キャパシタＣ１４１，ＣF の第１電極に接続され、インダクタＬ１４１の他端がキャパシタＣ１４１の第２電極に接続される。
この降圧型ＤＣ−ＤＣコンバータを用いる場合、検出動作時にインダクタＬ１４１を流れる電流ＩL 、太陽電池電流ＩPV、および太陽電池電圧ＰPVを３つのセンサで検出する必要がある。
【００６８】
図１４（Ａ）〜（Ｄ）は、電力変換回路として降圧型ＤＣ−ＤＣコンバータを用いた場合の太陽光発電システム１０Ａの各要部波形を示す図である。
図１４（Ａ）はＤＳＰ１５のＰＷＭ信号出力部１５９のＰＷＭ信号を、図１４（Ｂ）は太陽電池電圧ＶPVおよび太陽電池電流ＩPVを、図１４（Ｃ）は電力変換回路１４ＡのインダクタＬ１４１を流れる電流ＩL を、図１４（Ｄ）は太陽電池電力ＰPVをそれぞれ示している。
また、ＳＣＮは最大電力点Ｐmax 検出のためのスキャン期間、ＴＲＫは追従動作期間をそれぞれ示している。
【００６９】
電力変換回路として降圧型ＤＣ−ＤＣコンバータを用いた場合の太陽光発電システム１０Ａの動作が昇圧型ＤＣ−ＤＣコンバータを用いた場合と異なる点は、ＰＷＭ信号のオン、オフが逆となることである。
【００７０】
また、負荷電圧を太陽電池電圧により下げたり上げたりしたい場合には、図１５に示すような、電力変換回路１４Ｂとして昇降圧型ＤＣ−ＤＣコンバータを用いた回路構成が適している。
昇降圧型ＤＣ−ＤＣコンバータにおいては、太陽電池パネル１１の第１端子ＴＯ１および第２端子ＴＯ２に対して並列にキャパシタＣF が接続される。
また、ＭＯＳＦＥＴ１４１のドレインが太陽電池パネル１１の第１端子ＴＯ１に接続され、ソースがダイオードＤ１４１のカソードおよびインダクタＬ１４１の一端に接続される。インダクタＬ１４１の他端が太陽電池パネル１１の第２端子ＴＯ２、キャパシタＣ１４１，ＣF の第１電極に接続され、ダイオードＤ１４１のアノードがキャパシタＣ１４１の第２電極に接続される。
この昇降圧型ＤＣ−ＤＣコンバータを用いる場合も、検出動作時にインダクタＬ１４１を流れる電流ＩL 、太陽電池電流ＩPV、および太陽電池電圧ＰPVを３つのセンサで検出する必要がある。
【００７１】
図１６（Ａ）〜（Ｄ）は、電力変換回路として昇降圧型ＤＣ−ＤＣコンバータを用いた場合の太陽光発電システム１０Ｂの各要部波形を示す図である。
動作波形としては、図１５（Ａ）〜（Ｄ）とほぼ同じであるが、ＰＷＭ信号のオン、オフが逆となる。
【００７２】
このように、電力変換回路の種類によらずその電力変換回路に挿入されたインダクタに流れる電流の変化を利用して、瞬時に太陽電池のＩ−Ｖ特性をスキャンし、その結果をもとに追従制御を行い、太陽電池の高精度なＭＰＰＴ制御を実現することが可能である。
【００７３】
なお、上述の実施形態では、最大電力点のときの最適太陽電池電流に太陽電池電流を追従させるように追従制御を行う例を説明したが、最大電力点のときの最適太陽電池電圧に太陽電池電圧を追従させるように追従制御を行う構成を採用することも可能である。
この場合も、上述した効果と同様の効果を得ることができる。
【００７４】
【発明の効果】
以上説明したように、本発明によれば、最大電力点を確実に高い精度で検出することが可能となり、発電電力量を増大でき、電力取得の効率を大幅に向上させることができる。
また、負荷変動に対する制御特性も良いという利点がある。
【図面の簡単な説明】
【図１】従来の山登り法を採用した太陽光発電システムの構成例を示す図である。
【図２】図１の太陽光発電システムの動作原理を説明するための図である。
【図３】本発明に係る太陽光発電システムの一実施形態を示す構成図である。
【図４】本実施形態に係る太陽光発電システムの要部波形を示す図である。
【図５】本制御方式および従来方式における一日の太陽電池出力電力の変化（バッテリィ負荷）を示す図である。
【図６】負荷を純抵抗ＲL とし、その値を１０Ω→２０Ω→１０Ωとステップ状に変化させ、急激な負荷変動を与えたとき応答特性を示す図である。
【図７】本制御方式における日射強度急変時の応答特性の一例を示す図である。
【図８】図７との比較のための図であって、従来の山登り法による日射強度急変時の応答特性の一例を示す図である。
【図９】太陽電池パネルに影が生じない場合と生じた場合の制御方式の追従性を示す図である。
【図１０】図９との比較のための図であって、太陽電池パネルに影が生じない場合と生じた場合の従来の山登り法の追従性を示す図である。
【図１１】本制御方式における低照度時の電力取得性能を示す図である。
【図１２】本制御方式における低照度時の電力取得特性を示す図である。
【図１３】降圧型ＤＣ−ＤＣコンバータの構成を示す回路図である。
【図１４】電力変換回路として降圧型ＤＣ−ＤＣコンバータを用いた場合の太陽光発電システムの各要部波形を示す図である。
【図１５】昇降圧型ＤＣ−ＤＣコンバータの構成を示す回路図である。
【図１６】電力変換回路として昇降圧型ＤＣ−ＤＣコンバータを用いた場合の太陽光発電システムの各要部波形を示す図である。
【符号の説明】
１０，１０Ａ，１０Ｂ…太陽光発電システム、１１…太陽電池パネル（ＰＶ）、１２…電圧検出センサ部、１３…電流検出センサ部、１４，１４Ａ，１４Ｂ…電力変換回路、１４１…ＭＯＳＦＥＴ、Ｌ１４１…インダクタ、Ｄ１４１…ダイオード、Ｃ１４１…キャパシタ、１５…デジタルシグナルプロセッサ（ＤＳＰ）、１５１…アナログ−デジタル変換回路（ＡＤＣ）、１５２…乗算器、１５３…最大電力点検出回路（Ｐmax DET ）、１５４…加算器（減算器）、１５５…ＰＩ制御器、１５６…搬送波生成器、１５７…加算器（減算器）、１５８…コンパレータ、１５９…ＰＷＭ信号出力部、１６…負荷。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solar power generation system that converts output power of a solar cell into desired power by a power conversion circuit and supplies the power to a load side. In particular, a maximum power point tracking (MPPT) control system is used. The present invention relates to a adopted solar power generation system and its maximum power point tracking control method.
[0002]
[Prior art]
Since the maximum power operating point varies greatly depending on solar radiation intensity, temperature, or load conditions, solar cell requires maximum power point tracking (hereinafter referred to as MPPT) control in order to use it with high efficiency.
[0003]
In a grid-connected solar power generation system, MPPT control using a so-called hill-climbing method has been proposed (see, for example, Patent Document 1) and put into practical use.
[0004]
FIG. 1 is a diagram illustrating a configuration example of a photovoltaic power generation system employing a conventional hill-climbing method.
[0005]
As shown in FIG. 1, the solar power generation system 1 includes a solar cell panel (PV) 2, a power conversion circuit 3, and a control circuit 4.
The power conversion circuit 3 includes a voltage detection sensor unit 31, a current detection sensor unit 32, a MOSFET 33 as a switching element, an inductor (choke coil) L1, a diode D1, and capacitors C1 and C2. VB represents the battery voltage. MOSFET33, inductor (choke coil) L1, diode D1, capacitor C2 More buck A type DC-DC converter is configured.
The control circuit 4 includes an interface circuit (I / F) 41, a microprocessor (μPRO) 41, a MOSFET driver (DRV) 43, an EPROM 44, and an SRAM 45.
[0006]
The operation principle of the solar power generation system 1 will be described with reference to FIG. In FIG. 2, the horizontal axis represents the duty cycle (DutyCycle) of the PWM control signal, and the vertical axis represents the output power of the solar cell panel 2.
In FIG. 2, STP1 and STP2 indicate startable points.
[0007]
In this solar power generation system 1, the voltage and current of the solar cell are detected by the voltage detection sensor unit 31 and the current detection sensor unit 32 and supplied to the microprocessor 42 via the interface circuit 41 of the control circuit 4.
The microprocessor 42 converts the input voltage value and current value into digital values, and obtains the power P from the product of both. As shown in FIG. 2, the microprocessor 42 changes the drive pulse width of the MOSFET 33 of the DC-DC converter 3 by a certain minute width, and gradually increases the power P. Then, if the change in the power P starts to decrease, the pulse width is changed in the opposite direction.
Therefore, in the steady state, the power P constantly vibrates in the vicinity of the maximum power Pmax.
[0008]
[Patent Document 1]
JP-A-7-234733
[0009]
[Problems to be solved by the invention]
In the MPPT control employing the above-described hill-climbing method, as apparent from the operating principle, in order to approach the true maximum power point Pmax of the power P, the change width of the pulse width of the DC-DC converter may be reduced. .
[0010]
However, this is limited by the switching frequency of the DC-DC converter and the processing capability of the microprocessor. Even if the change width of the pulse width of the DC-DC converter can be reduced to some extent, the maximum power with respect to the change in the solar radiation intensity. It takes time to reach the point, and as a result, the efficiency of power acquisition decreases.
Conversely, if the change width of the pulse width is increased in order to improve the responsiveness, the power P vibrates greatly in the steady state, resulting in a disadvantage that the efficiency of power acquisition is greatly reduced.
[0011]
In the control system already put into practical use in the grid interconnection, there has been reported a case where a loss of up to 25% is caused in the actual operation due to the above-described MPPT mismatch.
[0012]
An object of the present invention is to provide a solar power generation system and its maximum power point tracking control method capable of easily and accurately performing MPPT control of a solar cell and improving the efficiency of power acquisition. is there.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, a photovoltaic power generation system according to the first aspect of the present invention includes: Output required power from 2 terminals A solar cell, a voltage detector that detects the voltage of the solar cell, a current detector that detects at least the current of the solar cell, and an inductor; A switching element whose conduction is controlled by a control signal; A power conversion circuit that converts the output power value of the solar cell into a power value; A control circuit, wherein the inductor of the power conversion circuit and the switching element are connected in series, and a circuit is formed in which both ends are connected to the two terminals of the solar cell, and the circuit is formed on the circuit. A voltage detector and the current detector are arranged, and the control circuit is the above Voltage detector The solar cell voltage detected in the above and Current detector In response to the solar cell current detected in When obtaining the maximum power point of the solar cell, the switching element of the power conversion circuit is held in an off state by a control signal, and the solar cell current that changes due to a change in the current flowing through the inductor of the power conversion circuit is zero. The switching element is held in the on state, Flowing through inductor Varies with changes in current The solar cell current is changed from zero to the short-circuit current, the current-voltage characteristic is scanned to detect the maximum power point, and the solar cell current or the optimum solar cell current at the maximum power point obtained by the scan is detected. Make the solar cell voltage follow the solar cell voltage and operate at the maximum power operating point obtained. ON / OFF of the switching element Take control.
[0014]
Preferably, the control circuit operates only during the scan period, receives the solar cell voltage detected by the voltage detection unit and the solar cell current detected by the current detection unit, and during the scan period, The switching element of the power conversion circuit is held in an off state by a control signal, and when the solar cell current that changes due to a change in the current flowing through the inductor of the power conversion circuit becomes zero, the switching element is turned on. The solar cell current that changes due to the change in the current flowing through the inductor is changed from zero to a short-circuit current, the current-voltage characteristic is scanned to detect the maximum power point, and the maximum power obtained by the scan A maximum power point detection circuit for obtaining an optimum solar cell current or an optimum solar cell voltage at a point, and the control circuit includes a scan period There ended, the maximum power point detection circuit is held in a non-operating state, the power control is transferred from the scan period following the operation period .
[0015]
Preferably, the control circuit repeatedly performs the maximum power point detection operation and the tracking operation alternately.
[0016]
Preferably, the power conversion circuit the above An inductor current detection sensor unit that detects a current flowing through the inductor, and the control circuit includes a solar cell voltage detected by the voltage detection sensor unit, a solar cell current detected by the current detection sensor unit, and the above Based on the inductor current detected by the inductor current detection sensor, the maximum Power point detection Controls motion and follow-up motion.
[0017]
Of the present invention Second The perspective is Output required power from 2 terminals Output power value of solar cell, inductor And a switching element connected in series to the inductor, both ends of which are respectively connected to two terminals of the solar cell. A maximum power point tracking control method for a photovoltaic power generation system that converts a power value into a desired power value by a power conversion circuit and supplies the load to a load. of Voltage and at least solar cell of Based on the detected solar cell voltage and solar cell current, The switching element of the power conversion circuit is held in an off state so that the solar cell current that changes due to the change of the current flowing through the inductor of the power conversion circuit becomes zero, and the change of the current flowing through the inductor of the power conversion circuit When the solar cell current that changes due to becomes zero, the switching element is held in the on state, Flowing through inductor Varies with changes in current The solar cell current is changed from zero to the short-circuit current, the current-voltage characteristic is scanned to detect the maximum power point, and the solar cell current or the optimum solar cell current at the maximum power point obtained by the above scan is detected. Make the solar cell voltage follow the solar cell voltage and operate at the maximum power operating point obtained. Performs on / off control of the switching element. .
[0018]
According to the present invention, the current flows through an inductor included in a power conversion circuit such as a DC-DC converter. Varies with changes in current The solar cell current is changed from zero to a short-circuit current, and the IV characteristics of the solar cell are instantaneously scanned.
Then, the solar cell current is caused to follow the optimum solar cell current, and the follow-up control is performed so as to operate at the obtained maximum power operating point.
Thereby, the maximum power point of the current solar cell can be reliably detected with high accuracy.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0020]
FIG. 3 is a configuration diagram showing an embodiment of the photovoltaic power generation system according to the present invention.
[0021]
As shown in FIG. 3, the photovoltaic power generation system 10 includes a solar battery panel (PV) 11, a voltage detection sensor unit 12, a current detection sensor unit 13, a power conversion circuit 14, and a digital signal processor (DSP: control circuit). A digital signal processor 15 and a load 16 such as a battery. The load 16 is adjusted such that, for example, two 12V batteries are connected in series, and a 100 W light bulb is connected in parallel thereto, so that the load voltage is constant at approximately 25V.
[0022]
The solar cell panel 11 is configured by arranging a plurality of solar cells having a predetermined electromotive force in an array, and outputs required power (voltage) from the terminals TO1 and TO2.
A plurality of solar cells are connected in parallel, but the number is selected according to the required power.
[0023]
The voltage detection sensor unit 12 detects the solar cell voltage VPV in real time from the output power of the solar cell panel 11 and supplies it to the DSP 15.
[0024]
The current detection sensor unit 13 detects the solar cell current IPV from the output power of the solar cell panel 11 in real time and supplies it to the DSP 15.
[0025]
The power conversion circuit 14 is configured by a so-called step-up DC-DC converter, boosts the output voltage of the solar panel 11, and applies the boost voltage VL to the load 16.
[0026]
As shown in FIG. 3, the step-up DC-DC converter constituting the power conversion circuit 14 includes an insulated gate field effect transistor (MOSFET) 141, an inductor (choke coil) L141, a diode D141, and a smoothing element as switching elements. Capacitor C141.
The MOSFET 141 is formed of, for example, an n-channel MOS transistor.
[0027]
The source of the MOSFET 141 is connected to the power output terminal TO2 of the solar cell panel 11, and the connection point is connected to the first electrode of the capacitor C141. In addition, the current detection sensor of the current detection sensor unit 13 is disposed on a connection line between the source of the MOSFET 141 and the power output terminal TO2.
The drain of the MOSFET 141 is connected to one end of the inductor L141, and the connection point is connected to the anode of the diode D141. The cathode of the diode D141 is connected to the second electrode of the capacitor C141.
A connection point between the first electrode of the capacitor C141 and the source of the MOSFET 141 and a connection point between the second electrode and the cathode of the diode D141 are connected to the load 16.
The MOSFET 141 has a control signal from the DSP 15 at its gate terminal. CTL Is supplied and its conduction state is controlled.
[0028]
When the DSP 15 receives the solar cell voltage VPV detected by the voltage detection sensor unit 12 and the solar cell current IPV detected by the current detection sensor unit 13, and obtains the maximum power Pmax of the solar cell panel 11, the DSP 15 controls the control signal CTL. Thus, the MOSFET 141 of the power conversion circuit 14 is held in an off state (if the MOSFET has n channels, the control signal CTL is held at a low level) and flows through the inductor L141 built in the power conversion circuit 14 Varies with changes in current When the solar cell current IPV becomes zero, the MOSFET 141 is held in the ON state and flows through the inductor L141 built in the power conversion circuit 14. Varies with changes in current The solar cell current IPV is changed from zero to a short-circuit current, the current-voltage (IV) characteristic is scanned, the off-state of the MOSFET 141 is released so as to follow the maximum power point obtained thereby, and the MOSFET 141 High-precision MPPT control is performed by performing PWM control and alternately repeating this maximum power point detection operation (IV scan) and follow-up operation.
[0029]
That is, the DSP 15 incorporates an operation for instantaneously scanning the IV characteristic into the MPPT control by using a change in the current flowing through the inductor L141 incorporated in the power conversion circuit 14 to follow the operation for detecting the maximum power point. By repeatedly operating the operation as one cycle (detection cycle T: for example, 1 second), control is performed so that the maximum power point is determined accurately and accurately.
[0030]
Specifically, as shown in FIG. 3, the DSP 15 includes an analog-digital conversion circuit (ADC) 151, a multiplier 152, a maximum power point detection circuit (Pmax DET) 153, an adder (subtractor) 154, PI control. And an adder (subtracter) 157, a comparator 158, and a PWM signal output unit 159.
Below, the function of each component of the DSP 15 will be described with reference to FIGS.
[0031]
4 (A) to 4 (E) are diagrams showing waveforms of respective main parts of the solar power generation system 10.
4A shows the short-circuit current ISC of the inductor L141 of the power conversion circuit 14, FIG. 4B shows the reference signal wave Vref by the PI controller 155 of the DSP 15 and the carrier wave Vc by the carrier generator 156, and FIG. ) Shows the PWM signal of the PWM signal output unit 159 of the DSP 15, FIG. 4D shows the solar cell voltage VPV and the solar cell current IPV, and FIG. 4E shows the solar cell power PPV.
SCN represents a scan period for detecting the maximum power point Pmax, and TRK represents a follow-up operation period.
[0032]
The ADC 151 converts the solar cell voltage VPV detected by the voltage detection sensor unit 12 from an analog value to a digital value and supplies the converted value to the first terminal of the multiplier 152.
Further, the ADC 151 converts the solar cell current IPV detected by the current detection sensor unit 13 from an analog value to a digital value, and supplies the converted value to the second terminal of the multiplier 152 and the adder 154.
[0033]
The multiplier 152 multiplies the digital solar cell voltage VPV by the ADC 151 by the solar cell current IPV, and outputs the result VI (= PPV) to the maximum power point detection circuit 153.
The multiplier 152 is controlled so as to operate only in the detection period (only the scan period) of the maximum power point Pmax.
[0034]
The maximum power point detection circuit 153 operates only during the detection period (only the scan period) of the maximum power point Pmax, and during this scan period, the MOSFET 141 of the power conversion circuit 14 is held in the OFF state by the control signal CTL. As shown to (D) and (E), it flows through the inductor L141 built in the power converter circuit 14. Varies with changes in current When the solar cell current IPV becomes zero, the MOSFET 141 is held in the ON state to change the solar cell current IPV from zero to a short-circuit current, and the current-voltage (IV) based on the solar cell power PPV by the multiplier 152. ) The characteristic is scanned to detect the maximum power point Pmax, the optimum solar cell current IOP at that time is obtained and output to the adder 154.
When the maximum power point detection circuit 153 detects the maximum power point Pmax and obtains the optimum solar cell current IOP at that time, the on / off control of the MOSFET 141 in the power conversion circuit 14 is canceled.
[0035]
The adder 154 adds the optimum solar cell current IOP by the maximum power point detection circuit 153 and the solar cell current IPV by the ADC 151 (takes a difference), and outputs the result to the PI controller 155 as a signal S154.
[0036]
The PI controller 155 receives the output signal of the adder 154, generates a reference signal wave Vref as shown in FIG. 4B, and outputs it to the adder 157.
[0037]
The carrier wave generator 156 generates a carrier wave Vc that is a so-called sawtooth wave (triangular wave) as shown in FIG. 4B and outputs it to the adder 157.
[0038]
The adder 157 combines the reference signal wave Vref from the PI controller 155 and the carrier wave Vc from the carrier wave generator 156 and outputs the combined signal as a signal S157 to the comparator 158.
[0039]
Comparator 158 receives output signal S157 from adder 157, compares reference signal wave Vref and carrier wave Vc, and outputs the result to PWM signal generation section 159.
The PWM signal generation unit 159 receives the comparison result of the comparator 158, and as shown in FIGS. 4B and 4C, the PWM signal generation unit 159 increases the time from the rising timing of the carrier wave Vc to the time point when the carrier wave Vc and the reference signal wave Vref intersect. A pulse having a level “1” period and a low level “0” period from this intersection to the rising timing of the next carrier wave Vc is continuously generated. During the follow-up operation period TRK, the power conversion circuit 14 serves as a PWM signal. Is supplied to the gate of the MOSFET 141.
[0040]
The output of the PWM signal by the PWM signal generation unit 159 is performed in the follow-up operation period TRK in which the solar cell current IPV follows the optimum solar cell current IOP detected in the scan period.
At this time, the DSP 15 performs switching control of the MOSFET 141 at a frequency fc as high as several tens of kHz (for example, 10 kHz) in order to increase the power acquisition capability.
[0041]
Next, the operation according to the above configuration will be described.
[0042]
Depending on the amount of light irradiated from the solar cell panel 11, required power is output from the terminals TO1 and TO2 to the power conversion circuit.
At this time, in the voltage detection sensor unit 12, the solar cell voltage VPV is detected in real time from the output power of the solar cell panel 11 and supplied to the ADC 151 of the DSP 15.
Similarly, in the current detection sensor unit 13, the solar cell current IPV is detected in real time from the output power of the solar cell panel 11 and supplied to the ADC 151 of the DSP 15.
In the power conversion circuit 14, the output voltage of the solar cell panel 11 is boosted and applied to the load 16 as the boosted voltage VL.
[0043]
The solar cell voltage VPV and the solar cell current IPV detected in real time are converted from analog values to digital values in the ADC 151 and supplied to the multiplier 152, and the solar cell current IPV is supplied to the adder 154.
[0044]
Here, when the maximum power point Pmax is detected, that is, when the scan operation is performed, the multiplier 152 and the maximum power point detection circuit 153 are put into an operation state in the DSP 15.
In the maximum power point detection circuit 153, the MOSFET 141 of the power conversion circuit 14 is held in the OFF state by the control signal CTL.
The multiplier 152 multiplies the digital solar cell voltage VPV by the ADC 151 and the solar cell current IPV, and the result VI (= PPV) is input to the maximum power point detection circuit 153.
In the maximum power point detection circuit 153, the current flows through the inductor L141 built in the power conversion circuit 14. Varies with changes in current When it is confirmed that the solar cell current IPV has become zero, the control is performed so that the MOSFET 141 is turned on by the control signal CTL.
Thereby, it flows through the inductor L141 built in the power conversion circuit 14. Varies with changes in current The solar cell current IPV is changed from zero to a short-circuit current, and the current-voltage (IV) characteristic is scanned based on the solar cell power PPV by the multiplier 152 to detect the maximum power point Pmax. The maximum power point detection circuit 153 obtains the optimum solar cell current IOP at that time and outputs it to the adder 154.
[0045]
When the maximum power point detection circuit 153 detects the maximum power point Pmax and obtains the optimum solar cell current IOP at that time, the on / off control of the MOSFET 141 in the power conversion circuit 14 is canceled, and the multiplier 152 and the maximum power detection The circuit 153 is held in a non-operating state.
In the DSP 15, the power control shifts from the scan period SCN to the follow-up operation period TRK.
[0046]
In the follow-up operation period TRK, the adder 154 adds the optimum solar cell current IOP by the maximum power point detection circuit 153 and the solar cell current IPV by the ADC 151 and outputs the result to the PI controller 155 as S154.
The PI controller 155 receives the output signal of the adder 154, generates a reference signal wave Vref, and outputs it to the adder 157.
In the adder 157, the reference signal wave Vref by the PI controller 155 and the carrier wave Vc by the carrier wave generator 156 are combined and output to the comparator 158 as a signal S157.
The comparator 158 receives the output signal S157 of the adder 157, compares the reference signal wave Vref and the carrier wave Vc, and supplies the result to the PWM signal generator 159.
Then, the PWM signal generation unit 159 receives the comparison result of the comparator 158, generates a predetermined PWM signal, and supplies it to the gate of the MOSFET 141 of the power conversion circuit 14. Thereby, the MOSFET 141 is switching-controlled at a high frequency fc of several tens of kHz, and is controlled so that the current solar cell current IPV follows the optimum solar cell current IOP obtained in the scan period SCN.
[0047]
The maximum power point Pmax can be obtained reliably and strictly by repeatedly operating the detection operation and the follow-up operation of the maximum power point as one cycle (detection cycle T: for example, 1 second).
[0048]
In order to confirm the effect of the control method according to this embodiment described above, a comparison was made with a conventional method equipped with a battery control device widely used in independent solar power generation.
[0049]
FIG. 5 is a diagram showing a change (battery load) of solar cell output power in one day in the present control method and the conventional method.
[0050]
The characteristic of FIG. 5 is that the solar cell panel 11 is configured by connecting two panels in parallel in the present control method, and connecting two panels in series in the conventional method, and a DC-DC converter (power conversion circuit 14). The inductance L of the inductor 141 is 7.5 mH, the capacitance C of the smoothing capacitor C 141 is 200 μF, two 12 V batteries are connected in series as the load 16, and a 100 W bulb is connected in parallel to this, and the load voltage is The switching frequency fc was adjusted to 10 kHz, and the detection cycle T was set to 1 second. Also, the conversion of solar cell output power PPV from 7:30 am to 4 pm during the day is compared.
[0051]
In FIG. 5, the horizontal axis represents time, the left vertical axis represents solar cell output power and panel surface temperature, and the right vertical axis represents solar radiation temperature.
In FIG. 5, the curve indicated by A indicates the solar radiation intensity, the curve indicated by B indicates the characteristics of this control method, the curve indicated by C indicates the characteristics of the conventional method, and the curve indicated by D indicates the panel surface temperature. Yes.
[0052]
As can be seen from FIG. 5, in this control method, the output power PPV of the solar cell is greatly increased as compared with the conventional method.
Compared with the generated power, the conventional method was 462.6 Wh, but this control method increased by about 14.8% to 531.2 Wh.
The ratio of the actually obtained power to the maximum power Pmax at this time was very high at about 99%.
[0053]
FIG. 6 is a diagram showing response characteristics when the load is a pure resistance RL and the value is changed stepwise from 10Ω → 20Ω → 10Ω to give a sudden load fluctuation.
In FIG. 6, the horizontal axis represents time, the left vertical axis represents solar cell output power, and the right vertical axis represents solar radiation temperature.
In FIG. 6, the curve indicated by A indicates the solar radiation intensity, the curve indicated by B indicates the characteristics of this control method, and the curve indicated by C indicates the characteristics of the conventional method.
[0054]
As can be seen from FIG. 6, the present control method can stably extract power proportional to the solar radiation intensity without being affected by load fluctuations, as compared with the conventional method.
[0055]
Next, the response characteristics when the solar radiation intensity changes suddenly, such as at sunset, will be considered in association with FIGS.
[0056]
FIG. 7 is a diagram showing an example of response characteristics when the solar radiation intensity changes suddenly in this control method.
In FIG. 7, the horizontal axis represents time, the left vertical axis represents solar cell output power, and the right vertical axis represents solar radiation temperature.
FIGS. 8A and 8B are diagrams for comparison with FIG. 7, and are diagrams illustrating an example of response characteristics at the time of a sudden change in solar radiation intensity by the conventional hill-climbing method (reference: plateau, Yamanouchi, Matsuda, D. D, 119, 12, quoted from 1999).
[0057]
FIGS. 9A and 9B are diagrams showing the followability of the present control method when a shadow does not occur on the solar cell panel and when it occurs.
FIGS. 10 (A) and 10 (B) are diagrams for comparison with FIGS. 9 (A) and 9 (B), and the conventional hill climbing in the case where the shadow does not occur in the solar cell panel and in the case where it occurs. It is a figure which shows the tracking property of a method.
[0058]
The current technical problem of solar cells is how much power can be captured and supplied when the follow-up to a sudden change in sunlight illuminance and the absolute value of illuminance decrease (such as sunset).
The present control method is superior in any problem to the hill-climbing method that is currently in practical use in MPPT control.
[0059]
As shown in FIGS. 7 and 8 (A) and 8 (B), the tracking capability for sudden changes in illuminance allows the maximum power point after change to be detected by a single scan in this control method. In the hill-climbing method, the peak value is searched by repeating scanning near the maximum point before the change.
In this case, as shown in FIGS. 10A and 10B, in the hill-climbing method, when the influence of the shadow on the solar cell panel occurs unevenly, the peak value may greatly change. The follow-up control will drop.
On the other hand, according to this control method, as shown in FIGS. 9A and 9B, when the influence of the shadow on the solar cell panel occurs non-uniformly, it has good followability. Indicates.
[0060]
FIG. 11 is a diagram showing the power acquisition performance at low illuminance in this control method.
In FIG. 11, the horizontal axis represents time, the left vertical axis represents solar cell output utilization rate UUF representing power acquisition efficiency, and the right vertical axis represents panel surface solar radiation intensity G.
The solar cell output utilization rate UUF is given by the following equation, where T is the maximum power point detection period.
[0061]
[Expression 1]

[0062]
The tracking in the low illuminance region causes an uncontrollable phenomenon at a very early stage in order to obtain a differential value in the hill climbing method.
On the other hand, in this control method, for simple maximum value detection, if there is a gradient in the entire scan width, it can be followed.
As can be seen from FIG. 11, in this control method, the solar radiation intensity G is 800 W / m at the peak time. ² At 100 / m ² Even if the illuminance decreases to 90%, the output utilization factor UUF maintains 90%.
[0063]
FIG. 12 is a diagram showing power acquisition characteristics at low illuminance in this control method.
In FIG. 12, the horizontal axis represents time, the left vertical axis represents the solar cell output power PPV and the solar cell output utilization factor UUF, and the right vertical axis represents the panel surface solar radiation intensity G.
The solar cell output utilization rate UUF is given by the above formula 1, where T is the maximum power point detection period.
[0064]
In this control method, as shown in FIG. 12, the solar radiation intensity G is 50 W / m. ² The solar cell output utilization factor UUF is as high as 80% or higher.
In this control method, the solar radiation intensity G is 50 W / m. ² Below, the solar cell output utilization factor UUF decreases, but it is possible to recover energy by about 60%.
[0065]
As described above, according to the present embodiment, the current flows through the inductor L141 included in the power conversion circuit 14 such as a DC-DC converter. Varies with changes in current The solar cell current IPV is changed from zero to a short-circuit current, the IV characteristics of the solar cell are instantaneously scanned, the solar cell current IPV is made to follow the optimum solar cell current IOP, and the operation is performed at the maximum power operating point obtained. Since the DSP 15 that performs the follow-up control is provided as described above, the maximum power point of the solar cell can be reliably detected with high accuracy.
According to an actual measurement example, when this method and a conventional method equipped with a battery control device widely used in an independent solar power generation system are compared with each other in terms of the amount of generated electric power, the use of solar cell output is increased. The rate UUF can be as high as about 99%. In addition, there is an advantage that the control characteristic against the load fluctuation is also good.
[0066]
In the above description, the DC-DC converter as the power conversion circuit is described as a boost type. In this step-up DC-DC converter, a load voltage higher than the solar cell voltage can be obtained.
[0067]
For example, when the load voltage is desired to be lower than the solar cell voltage, a circuit configuration using a step-down DC-DC converter as the power conversion circuit 14A as shown in FIG. 13 is suitable.
In the step-down DC-DC converter, a capacitor CF is connected in parallel to the first terminal TO1 and the second terminal TO2 of the solar cell panel 11.
The drain of the MOSFET 141 is connected to the first terminal TO1 of the solar cell panel 11, and the source is connected to the cathode of the diode D141 and one end of the inductor L141. The anode of the diode D141 is connected to the second terminal TO2 of the solar cell panel 11, the first electrodes of the capacitors C141 and CF, and the other end of the inductor L141 is connected to the second electrode of the capacitor C141.
When this step-down DC-DC converter is used, it is necessary to detect the current IL flowing through the inductor L141, the solar cell current IPV, and the solar cell voltage PPV with three sensors during the detection operation.
[0068]
FIGS. 14A to 14D are diagrams illustrating waveforms of respective main parts of the solar power generation system 10A when a step-down DC-DC converter is used as a power conversion circuit.
14A shows the PWM signal of the PWM signal output unit 159 of the DSP 15, FIG. 14B shows the solar cell voltage VPV and the solar cell current IPV, and FIG. 14C shows the inductor L141 of the power conversion circuit 14A. FIG. 14D shows the current IL, and FIG. 14D shows the solar cell power PPV.
SCN represents a scan period for detecting the maximum power point Pmax, and TRK represents a follow-up operation period.
[0069]
The difference between the operation of the photovoltaic power generation system 10A when the step-down DC-DC converter is used as the power conversion circuit and the case where the step-up DC-DC converter is used is that the PWM signal is turned on and off in reverse. is there.
[0070]
Further, when it is desired to lower or increase the load voltage by the solar cell voltage, a circuit configuration using a step-up / step-down DC-DC converter as the power conversion circuit 14B as shown in FIG. 15 is suitable.
In the step-up / step-down DC-DC converter, a capacitor CF is connected in parallel to the first terminal TO1 and the second terminal TO2 of the solar cell panel 11.
The drain of the MOSFET 141 is connected to the first terminal TO1 of the solar cell panel 11, and the source is connected to the cathode of the diode D141 and one end of the inductor L141. The other end of the inductor L141 is connected to the second terminal TO2 of the solar cell panel 11, the first electrodes of the capacitors C141 and CF, and the anode of the diode D141 is connected to the second electrode of the capacitor C141.
Even when this step-up / step-down DC-DC converter is used, it is necessary to detect the current IL flowing through the inductor L141, the solar cell current IPV, and the solar cell voltage PPV with three sensors during the detection operation.
[0071]
FIGS. 16A to 16D are diagrams illustrating waveforms of respective main parts of the photovoltaic power generation system 10B when a step-up / step-down DC-DC converter is used as a power conversion circuit.
The operation waveforms are substantially the same as those shown in FIGS. 15A to 15D, but the PWM signal is turned on and off in the opposite direction.
[0072]
In this way, regardless of the type of power conversion circuit, the change in current flowing through the inductor inserted in the power conversion circuit is used to instantaneously scan the IV characteristics of the solar cell, and based on the results. It is possible to perform high-precision MPPT control of the solar cell by performing follow-up control.
[0073]
In the above-described embodiment, the example in which the follow-up control is performed so that the solar cell current follows the optimum solar cell current at the maximum power point is described. However, the solar cell is applied to the optimum solar cell voltage at the maximum power point. It is also possible to employ a configuration in which tracking control is performed so that the voltage follows.
In this case, the same effect as described above can be obtained.
[0074]
【The invention's effect】
As described above, according to the present invention, the maximum power point can be reliably detected with high accuracy, the amount of generated power can be increased, and the efficiency of power acquisition can be greatly improved.
In addition, there is an advantage that the control characteristic against the load fluctuation is also good.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration example of a photovoltaic power generation system employing a conventional hill-climbing method.
FIG. 2 is a diagram for explaining the operation principle of the photovoltaic power generation system of FIG. 1;
FIG. 3 is a configuration diagram showing an embodiment of a photovoltaic power generation system according to the present invention.
FIG. 4 is a diagram showing a main waveform of the photovoltaic power generation system according to the present embodiment.
FIG. 5 is a diagram showing a change (battery load) of solar cell output power in one day in the present control method and the conventional method.
FIG. 6 is a diagram showing response characteristics when the load is a pure resistance RL and the value is changed stepwise from 10Ω → 20Ω → 10Ω to give a sudden load change.
FIG. 7 is a diagram showing an example of response characteristics at the time of sudden change in solar radiation intensity in the present control method.
FIG. 8 is a diagram for comparison with FIG. 7, and is a diagram showing an example of a response characteristic at the time of a sudden change in solar radiation intensity by a conventional hill-climbing method.
FIG. 9 is a diagram showing the followability of a control method when a shadow does not occur on a solar cell panel and when it occurs.
FIG. 10 is a diagram for comparison with FIG. 9 and shows the followability of a conventional hill-climbing method when a shadow does not occur on a solar cell panel.
FIG. 11 is a diagram showing power acquisition performance at low illuminance in this control method.
FIG. 12 is a diagram showing power acquisition characteristics at low illuminance in this control method.
FIG. 13 is a circuit diagram showing a configuration of a step-down DC-DC converter.
FIG. 14 is a diagram showing waveforms of main parts of a photovoltaic power generation system when a step-down DC-DC converter is used as a power conversion circuit.
FIG. 15 is a circuit diagram showing a configuration of a step-up / step-down DC-DC converter.
FIG. 16 is a diagram showing waveforms of main parts of a photovoltaic power generation system when a buck-boost DC-DC converter is used as a power conversion circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10, 10A, 10B ... Solar power generation system, 11 ... Solar cell panel (PV), 12 ... Voltage detection sensor part, 13 ... Current detection sensor part, 14, 14A, 14B ... Power conversion circuit, 141 ... MOSFET, L141 ... Inductor, D141 ... Diode, C141 ... Capacitor, 15 ... Digital signal processor (DSP), 151 ... Analog-digital conversion circuit (ADC), 152 ... Multiplier, 153 ... Maximum power point detection circuit (Pmax DET), 154 ... Addition 155 ... PI controller, 156 ... carrier wave generator, 157 ... adder (subtractor), 158 ... comparator, 159 ... PWM signal output unit, 16 ... load.

Claims (6)

A solar cell that outputs the required power from two terminals ;
A voltage detector for detecting the voltage of the solar cell;
A current detector for detecting at least the current of the solar cell;
A power conversion circuit that includes an inductor and a switching element that is conductively controlled by a control signal, and that converts an output power value of the solar cell into a power value;
A control circuit,
The inductor and the switching element of the power conversion circuit are connected in series, and a circuit is formed in which both ends are respectively connected to the two terminals of the solar cell, and the voltage detection unit and the current detection unit are formed on the circuit. Is placed,
The control circuit is
Receiving solar battery current detected by the solar cell voltage detected by the voltage detecting unit and said current detecting unit, when determining the maximum power point of the solar cell, the control signal the switching elements of the power converter circuit and is held in the oFF state, when the solar cell current that varies with changes in the current flowing through the inductor of the power conversion circuit becomes zero, thereby holding the switching element into the on state, the change in current flowing through the inductor The changing solar cell current is changed from zero to the short-circuit current, the current-voltage characteristic is scanned to detect the maximum power point, and the solar cell current is obtained as the optimum solar cell current at the maximum power point obtained by the scan. Or, the solar cell voltage is made to follow the optimum solar cell voltage, and the switching element is operated so as to operate at the obtained maximum power operating point. Off control solar power system to perform. The control circuit is
It operates only during the scan period, receives the solar cell voltage detected by the voltage detector and the solar cell current detected by the current detector, and during the scan period, the control signal causes the power conversion circuit to When the switching element is held in the OFF state, and the solar cell current that changes due to the change in the current flowing through the inductor of the power conversion circuit becomes zero, the switching element is held in the ON state, and the current flowing through the inductor By changing the solar cell current that changes due to the change from zero to the short-circuit current, the current-voltage characteristic is scanned to detect the maximum power point, and the optimum solar cell current at the maximum power point obtained by the scan or Including a maximum power point detection circuit to find the optimum solar cell voltage,
The control circuit is
The photovoltaic power generation system according to claim 1 , wherein the scanning period ends, the maximum power point detection circuit is held in a non-operating state, and power control shifts from the scanning period to the follow-up operation period . The photovoltaic power generation system according to claim 1, wherein the control circuit repeatedly performs the maximum power point detection operation and the tracking operation alternately. Further comprising an inductor current detecting sensor unit for detecting a current flowing through the inductor of the power conversion circuit,
The control circuit, based on the voltage detected solar battery voltage detecting sensor unit, the current detected by the detection sensor unit solar cell current and the inductor current sensed inductor current detection sensor unit, the maximum The photovoltaic power generation system according to claim 1, 2, or 3, wherein power point detection operation and tracking operation are controlled. A power conversion circuit including an output power value of a solar cell that outputs required power from two terminals , an inductor and a switching element connected in series to the inductor, and both ends of which are respectively connected to the two terminals of the solar cell A maximum power point tracking control method for a photovoltaic power generation system that converts a desired power value and supplies the load to a load,
Detecting a current of at least solar cell to the voltage of the solar cell,
Based on the detected solar cell voltage and solar cell current, the switching element of the power conversion circuit is turned off so that the solar cell current that changes due to the change of the current flowing through the inductor of the power conversion circuit becomes zero. Hold
When the solar cell current that changes due to a change in the current flowing through the inductor of the power conversion circuit becomes zero, the switching element is held in an on state, and the solar cell current that changes due to the change in the current flowing through the inductor is reduced to zero. To the short circuit current, scan the current-voltage characteristics and detect the maximum power point,
The switching element is turned on to operate at the maximum power operating point obtained by causing the solar cell voltage to follow the optimal solar cell current or the optimal solar cell voltage at the maximum power point obtained by the scan. A maximum power point tracking control method for a photovoltaic power generation system that performs off control . The maximum power point tracking control method for a photovoltaic power generation system according to claim 5, wherein the maximum power point detection operation and the tracking operation are alternately repeated.

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