JP3402388B2 - How to determine the maximum power operating point of a solar cell - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic power generation system using a solar cell, and more particularly to a method for determining an operating point at which the output of the solar cell is maximized. 2. Description of the Related Art Conventionally, a solar power generation system using a solar cell is used for charging a storage battery once with energy generated by the solar cell and reusing the storage battery, and for using a motor via a chopper or an inverter. It is used for driving, for use after being converted to a commercial frequency power supply by an inverter, or for use alone or in conjunction with a distribution network as a power supply. In that case, the solar cell is relatively expensive and the conversion efficiency is not high, so it is important to utilize the generated energy as effectively as possible. By the way, as for the characteristics of the solar cell, the output power with respect to the operating voltage or the operating current changes according to the change in the illuminance and the temperature. In other words, the operating point of the voltage or current at which the maximum power is output changes due to changes in illuminance or temperature, so that the solar cell automatically tracks its maximum power operating point under any conditions and uses solar energy efficiently. A system for performing is disclosed. As an example, the operating voltage is changed by applying a disturbance to the load, and a mode in which the reference value of the power is increased and a mode in which the reference value of the power is reduced are obtained according to the change in the power at that time. A device for selecting a mode so as to approach an operating point is disclosed. As a specific example, as shown in FIG. 3, for example, the power generated by the solar cell 1 is transferred to a load such as a storage battery, an electric motor, and a power distribution network via a smoothing capacitor 2 and a power controller 3 such as a chopper or an inverter. In a system including a main circuit 10 for supplying power to the device 4,
The power controller 3 is feedback-controlled so that the output voltage of the solar cell 1 detected by the voltage detector 5 becomes the value set by the voltage setting device 6, and a small signal is added to the voltage setting value by the signal superposition device 7. Or subtraction, and at this time, based on signals from the voltage detector 5 and the current detector 8 for detecting the output current of the solar cell, whether the power calculated by the power calculation comparator 9 has increased or decreased, The voltage set value of the voltage setter 6 is corrected in a direction to increase the output of the solar cell 1 (for example, see Japanese Patent Application Laid-Open No. 61-97721).
issue). To explain the principle of correcting the voltage setting value of the voltage setting unit 6, for example, when increasing the voltage set value by the signal superposition unit 7, as shown in FIG. 4, during operation in the output voltage V _0, the superposed voltage Variation Δ of power P when ΔV is added
If P is positive, the output voltage V ₀ is the maximum power operating point voltage V
Judgment is made smaller than _max , and V ₀ + ΔV is set as a new operating point. If the variation ΔP is negative, the output voltage V ₀
It is determined as greater than the maximum power operating point voltage V _max, the V ₀ - [Delta] V as a new operating point. Determine the maximum power operating point voltage V _max by repeating this operation, the output of the solar cell 1 can be brought close briefly to the maximum power P _max. Also, when correcting the voltage set value, the output voltage is sequentially changed from the no-load state to the current operating point at predetermined sampling intervals, and the output voltage and output current are detected at predetermined time intervals to calculate the power. From the stored past output voltage and power values and the current operating point output voltage and power values, the increasing and decreasing trends of both the current operating point output voltage and power are determined, and the set voltage is determined by the tendency. In this case, two modes, i.e., increasing and decreasing, are selected, and a voltage set value at which the maximum power of the solar cell is obtained. In the prior art, however, a new operating point is obtained by sequentially changing the output voltage and comparing the power at that time with the power before the output voltage is changed. This operation has to be repeated until the maximum power operating point is reached, which takes a long time. Further, since the output value in the previous sampling period is compared with the current output value and the mode for increasing or decreasing the set voltage is selected, the voltage cannot be set by detecting the voltage or power at one time. Therefore, it is necessary to detect the voltage and the power at a plurality of time points, and there is a problem that it takes much time to track the maximum power. The present invention
It is an object of the present invention to provide a method for determining a maximum power operating point of a solar cell, which obtains a maximum power operating point by a simple approximation calculation and can reduce a tracking time of the maximum power. [0004] In order to solve the above problems, the present invention provides a main circuit for supplying power generated by a solar cell to a load device through a smoothing capacitor and a power controller. In a maximum power operating point determination method for a system that includes a voltage detector for detecting an output voltage of a solar cell or a current detector for detecting an output current and controls an output of the solar cell, a maximum power P is determined in advance from an operating characteristic of the solar cell. exit _max
Voltage V _max or the current I _max of the maximum power operating point for the force
Obtains an outline range, relatively close to the maximum power operating point V _max
Is the first operating point V ₁ , and the power P ₁ at that time is
Measured load disturbance or voltage superimposed on the first operating point V ₁
Then, the deviation voltage ΔV is added, and the operating voltage is changed to the next second operation.
Move to the point V ₂ = V ₁ + ΔV and measure the power P ₂ at that time.
And then subtract the operating voltage ΔV from the first operating point V ₁
3 Move to operating point V ₃ , measure power P ₃ at that time ,
Next, the power characteristic near the maximum power operating point is expressed by the following equation (2).
Approximated by the following ^{equation, P = aV 2 + bV +} c ... ( b) the destination of the voltage value and the power value of each operating point determined (V _1, P _1),
Substituting (V ₂ , P ₂ ) and (V ₃ , P ₃ ) into equation (a)
And solve the simultaneous equations to obtain constants a, b, and c.
The maximum power _Pmax and the operating voltage at that time
Operation point V _max, determined by the following (b) and (c) ^{_{below, P max = - (b 2}} -4ac) / 4a ... ( _{b) V max = -b / 2a ...} ( iii) The maximum power operating point a solar cell the V _max as a voltage command
It is characterized by control . By the above means, the power at three or more operating points of the voltage or current near the maximum power operating point is measured, and the voltage or current of the voltage or current is calculated from the measured value by a second or higher order approximation equation. Find the maximum power operating point. If the operating voltage or current is continuously changed in a short time within the range including the maximum power operating point, and multiple voltages and currents are detected by high-speed sampling during this time, the multiple power values obtained during the sampling period The maximum value is selected by mutual comparison to determine the maximum power operating point. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram showing the relationship between the operating voltage V or the operating current I and the output power P of the solar cell according to the embodiment of the present invention. The control device for controlling the solar cell is the same as the device described above with reference to FIG. In the figure, previously obtained a schematic range of the voltage V _max or the current I _max of the maximum power operating point for outputting the maximum power P _max from the operating characteristics of the pre-solar cell. To describe the case of obtaining the maximum power by the voltage of the maximum voltage operating point, the maximum power operating point V _max
Is set as the first operating point V ₁ , and the power P ₁ at that time is measured. The first operating point V ₁ load disturbance or deviation voltage [Delta] V by the voltage superimposing etc. In addition, by moving the operating voltage for the next second operating point V ₂ = V ₁ + [Delta] V, measures the power P ₂ at that time. Next, it is moved to a third operating point V _{3 obtained} by subtracting the operating voltage ΔV from the first operating point V _1, and the power P ₃ at that time is measured. Note that V ₁ , V ₂ , and V ₃ are selected so as to fall within the approximate range of V _max obtained from the characteristics of the solar cell. Next, the power characteristic near the maximum power operating point is next approximated by a quadratic expression shown in Expression (1). P = aV ² + bV + c (1) The voltage value and power value (V ₁ , P ₁ ) of each operating point obtained earlier,
By substituting (V ₂ , P ₂ ) and (V ₃ , P ₃ ) into equation (1) and solving the simultaneous equations, constants a, b, and c are obtained.
Now the maximum power P _max and a maximum power operating point V _max the operating voltage at that time is determined by the following (2) and (3) below. P _max = − (b ² −4ac) / 4a (2) V _max = −b / 2a (3) If the maximum power operating point V _max is used as a voltage command to control the solar cell, operation is performed at the maximum power. be able to. In addition,
In the above description of FIG. 1, the deviation voltage Δ is set so that the maximum power operating point V _max comes between the first operating point V ₁ and the second operating point V _2.
V was selected, but the maximum power operating point V _max is the first operating point V ₁
If it may be on the outside of the second operating point V _2.
The maximum power operating point of the above embodiment, the operating point I ₁ of the three points of the current I in place of the voltage V, I _2, I _3, may be determined as the maximum power operating point I _max by. Furthermore, by setting four or more operating points and approximating the information of four or more sets of voltage or current and power based on a third or higher order equation, a high-precision maximum power operating point is calculated. Can be. Further, in explaining FIG. 2 showing another embodiment, varied briefly continuously operating voltage within a range including the maximum power operating point V _max, by a high-speed sampling during which a plurality of output voltage and current The power is detected and stored by a high-speed CPU or the like, and the power is calculated from the output voltage and the current. Performs mutual comparison of a plurality of power values obtained during the sampling period, the maximum power operating point V _max. If the maximum power operating point V _max is not reached within the change range of the set voltage at time t ₁ , the operating point fluctuation range is further moved to the larger one of the power at both ends of the sampling time, and the time t ₂ , t _{2 The} same operation can be repeated in step ₃ . The calculation and comparison of the power value can be sufficiently performed in about 1 to 10 ms by using a high-speed CPU.
Although it may be performed simultaneously with high-speed sampling, arithmetic processing may be performed after high-speed sampling in order to level the load on the CPU. In this method, since there is no restriction on the voltage range for the second-order approximation as in the method shown in the previous embodiment, the voltage is changed over a wide range to find the maximum power operating point once and accurately. be able to. In addition, it is possible to cope with a case where the characteristics of each element of the solar cell connected in series / parallel have two peaks due to a variation in characteristics. Further, if this method is combined with a method of superimposing a voltage or a current on the solar cell side from the smoothing capacitor, the effect on the load is small even if the operating point is varied over a wide range, so that it is more effective. As described above, according to the present invention, the power at three or more operating points of the voltage or current near the maximum power operating point can be calculated from the measured values by a simple approximation equation. Can be calculated, so that the tracking time of the maximum power can be greatly reduced. When the maximum power operating point V _max is obtained from the power detected by the high-speed sampling, 2
Since there is no restriction on the voltage range for the next approximation, the voltage can be changed over a wide range, and the maximum power operating point can be found exactly once and accurately.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an operation explanatory diagram showing an embodiment of the present invention. FIG. 2 is an operation explanatory view showing another embodiment of the present invention. FIG. 3 is a block diagram of a control device for a solar cell. FIG. 4 is an operation explanatory view showing a conventional example. P _max maximum power value V ₁ [Description of symbols], I ₁ first operating point V _2, I ₂ second operating point V _3, I ₃ third operating point

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Sadao Ishii 2-1 Kurosaki Castle Stone, Yawatanishi-ku, Kitakyushu-shi, Fukuoka Inside Yaskawa Electric Co., Ltd. (56) References JP-A-62-93719 (JP, A) JP-A Sho 63-36317 (JP, A) JP-A-2-228715 (JP, A) JP-A-4-40633 (JP, A) JP-A-4-115376 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G05F 1/67

Claims (1)

(57) [Claim 1] A main circuit for supplying power generated by a solar cell to a load device via a smoothing capacitor and a power controller, and a voltage for detecting an output voltage of the solar cell. In the maximum power operating point determination method for a system that controls the output of a solar cell including a detector or a current detector that detects an output current, the maximum power _Pmax is determined in advance from the operating characteristics of the solar cell
Voltage of maximum power operating point for outputting V _max or the current I _max
Seek generally range, relatively close to the maximum power operating point V _max
The operating point of the value is defined as the first operating point V ₁ , and the power P ₁ at that time is
Is measured, and a load disturbance or a voltage load is applied to the first operating point V _1.
The deviation voltage ΔV is added by tatami or the like, and the operating voltage is changed to the next second operation voltage.
The point P ₂ is moved to V ₂ = V ₁ + ΔV, and the power P ₂ at that time is
Measured, and then the operating voltage ΔV was subtracted from the first operating point V ₁
Is moved to the third operating point V _3, measures the power P ₃ at that time
Next, the power characteristics near the maximum power operating point are shown in equation (a).
Approximated by to a quadratic ^{equation, P = aV 2 + bV +} c ... ( b) a voltage value for each operating point determined previously and the power value (V _1, P _1),
Substituting (V ₂ , P ₂ ) and (V ₃ , P ₃ ) into equation (a)
And solve the simultaneous equations to obtain constants a, b, and c.
The maximum power _Pmax and the operating voltage at that time
Operation point V _max, determined by the following (b) and (c) ^{_{below, P max = - (b 2}} -4ac) / 4a ... ( _{b) V max = -b / 2a ...} ( iii) The maximum power operating point a solar cell the V _max as a voltage command
A method for determining a maximum power operating point of a solar cell, wherein the method is controlled.