JP2002108466A - Device and method for controlling power and power generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that the output of a solar battery is slightly lowered in the fluctuation period of an operating point and the utilization ratio of the solar battery falls because the operating point of the solar battery is always made to fluctuate by MPPT control in order to make the operation of the solar battery a maximum output point. SOLUTION: The average value of operating voltages V becomes V1 because a voltage target value VR at t0 is set to V1. The maximum value of the operating voltage V becomes V3 and the minimum value becomes V2 because ripples caused by the operation of a power controller take place in the operating voltage V. A generated power P pulsates in accordance with the pulsation of the operating voltage V, and shows the maximum power P0 at an operating voltage V2 and the minimum power P1 at an operating voltage V3. P0 is detected as a detected maximum power value Pmax and V2 is detected as a voltage detection value VPmax in a period up to t1. Then, the voltage target value VR after t1 is updated to V2, and the voltage target value V2 is held at least up to t2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power control device, a control method therefor, and a power generation device, for example, a power control device for converting DC power supplied from a solar cell or the like into power corresponding to a load, and control thereof. A method and a power plant using such a power converter.

[0002]

2. Description of the Related Art Today, with increasing awareness of the global environment, great expectations are placed on photovoltaic power generators that provide clean energy. Recently, a grid-connected solar power generation system that converts DC power generated by solar cells into AC power using a power conditioner (power control device) and outputs it to a commercial power system (hereinafter referred to as “system”). Widespread.

[0003] The output of a solar cell varies considerably depending on the amount of solar radiation, temperature, operating point voltage and the like. Therefore, it is desired to adjust the load viewed from the solar cell and to always extract the maximum power from the solar cell. Therefore, the power conditioner is a control to extract the maximum power from the solar cell, so-called MP
Performs PT (abbreviation for Maximum Power Point Tracking, maximum output point tracking) control.

In the MPPT control, a voltage or current at an operating point of a solar cell is detected, a voltage target value of the solar cell is set, and an output of the power conditioner is adjusted so that the detected voltage value matches the voltage target value. It is to adjust. That is, the voltage of the solar cell is varied, the current value for each voltage value is detected, and the output power of the solar cell is calculated from the product of the voltage value and the current value. Then, control is performed such that the output power of the solar cell is maximized using the voltage value indicating the maximum power as the voltage target value.

For example, Japanese Patent Application Laid-Open No. 62-85312 discloses that the voltage of a solar cell is changed by changing a voltage target value, and the detected values of power before and after the change are compared. The MPPT control using a so-called hill-climbing method that fluctuates is disclosed. There is also MPPT control in which the voltage target value is varied, power for each voltage target value is detected, and the voltage target value having the maximum detected value is set as the next voltage target value.

[0006]

In the above-described MPPT control, the operating point of the solar cell is constantly changed in order to make the operation of the solar cell the maximum output point. And the utilization rate of the solar cell decreases.

On the other hand, Japanese Patent Publication No. Hei 8-27671 and Japanese Patent Laid-Open Publication No. Hei 7-334260 disclose that the voltage target value is held constant for a predetermined time and the voltage target value is intermittently changed. An MPPT control that suppresses a decrease in output caused by changing an operating point of a solar cell after the battery reaches a maximum output point is disclosed. However, in this method, if the maximum output point of the solar cell changes while maintaining the voltage target value constant,
Since the output of the solar cell is reduced, and the output of the solar cell is reduced during the fluctuation period of the voltage target value, the utilization rate of the solar cell is also reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and has as its object to increase the efficiency of use of a DC power supply when converting input DC power into power corresponding to a load. I do.

[0009]

The present invention has the following configuration as one means for achieving the above object.

[0010] The power control device according to the present invention comprises: power conversion means for converting input DC power into power corresponding to a load; detection means for detecting the voltage and current of the input DC power; Setting means for setting a target value of the voltage or current of the input DC power based on the current and the current, and control means for controlling the power conversion means so that the detected voltage or current becomes the target value. The setting unit detects a characteristic of the supply source of the input DC power from a ripple included in the input DC power, which is generated by an operation of the power conversion unit, and detects a voltage or a voltage of the input DC power based on the detected characteristic. It is characterized in that a current target value is set.

The control method according to the present invention comprises: power conversion means for converting input DC power into power corresponding to a load; detection means for detecting the voltage and current of the input DC power;
And a control means for controlling the power conversion means so that a detected voltage or current becomes a target value, wherein the input DC power generated by the operation of the power conversion means is provided. The characteristic of the input DC power supply source is detected from the ripple included in the above, and the target value is set based on the detected characteristic.

[0012] The power generating apparatus according to the present invention comprises: a power conversion means for converting input DC power into power corresponding to a load;
Detecting means for detecting the voltage and current of the input DC power, and setting means for setting a target value of the voltage or current of the input DC power based on the detected voltage and current,
Control means for controlling the power conversion means so that the detected voltage or current becomes the target value, wherein the setting means includes a ripple included in the input DC power, which is generated by an operation of the power conversion means. And a power control device that detects a characteristic of the supply source of the input DC power from the power supply and sets a target value of the voltage or current of the input DC power based on the detected characteristic.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a power control device according to an embodiment of the present invention will be described in detail with reference to the drawings.

[Ripple] Ripple (pulsation) occurs in the output of the solar cell due to the power conversion operation of the power conditioner, input voltage control, and the like. If the ripple is too large, the operation of the solar cell moves away from the maximum output point, causing a decrease in output.
Therefore, usually, a capacitor or a reactor for smoothing the ripple is installed, and the ripple is suppressed to a level without a problem by optimizing a control system. However, it is difficult to reduce the ripple to zero due to the size, weight, cost, etc. of the electronic components, and a slight ripple remains in the output of the solar cell.

This ripple can cause a malfunction of the MPPT control. Therefore, in the normal MPPT control, the configuration is such that the detected value of the voltage or current is averaged by hardware or software, or the fluctuation of the voltage target value is increased to remove the influence of ripple.

[0016]

First Embodiment [Configuration] FIG. 1 is a block diagram showing a configuration example of a photovoltaic power generator using a power control device 2 according to a first embodiment.

The DC power output from the solar cell 1 is power-converted by the power control device 2 and supplied to the load 3. As the solar cell 1, a solar cell using amorphous silicon, microcrystalline silicon, polycrystalline silicon, single crystal silicon, or a compound semiconductor is used. Normally, the solar cell 1 is configured by combining a plurality of solar cell modules in series and parallel to form an array so that a desired voltage and current can be obtained.

The power converter 4 of the power control device 2 comprises a DC / DC converter, a DC / AC inverter, or a DC / DC converter and a DC / AC inverter connected in series. The switching elements of DC / DC converters and DC / AC inverters include power transistors, power MOSFETs,
A self-extinguishing type element such as IGBT is used. By changing the on / off ratio (duty ratio) of the pulse for driving the power conversion unit 4, the power flow, the input / output voltage of the power conversion device 2, the output frequency, and the like are controlled.

The voltage detector 5 and the current detector 6 detect a voltage and a current output from the solar cell 1 and output a voltage detection signal and a current detection signal. The voltage detector 5 and the current detector 6 only need to have a response speed and an accuracy that can detect a DC voltage and a DC current, respectively, and can also detect a ripple used in the power control of the first embodiment.

The voltage detector 5 and the current detector 6 perform A / D conversion in order to supply a digital signal when the control unit described later is a digital circuit. The resolution of this A / D conversion must be set according to the size of the ripple.
8-bit resolution is required. However, considering the applicable range and control accuracy, A / D with resolution of 10 bits or more
Conversion is desired. The sample and hold time for A / D conversion must also be sufficiently short with respect to the ripple frequency. However, since the ripple frequency is 50/60 Hz or a frequency several times higher, A / D conversion should be performed without any problem. Can be.

The voltage setting unit 7 receives a voltage and a current detection signal from the voltage detector 5 and the current detector 6 and, based on a power detection value calculated from a result of multiplication of the signals, performs a predetermined algorithm on the solar cell. Set and output the voltage target value indicating the operating voltage of 1.

The voltage control unit 8 receives an operating voltage target value from the voltage setting unit 7 and a voltage detection signal from the voltage detector 5,
In order for the difference between the voltage target value and the voltage detection signal to be zero,
Adjust the output command value and output.

The control section 9 receives the output command value from the voltage control section 8 and generates and outputs a drive pulse corresponding to the output command value by a triangular wave comparison method, a hysteresis comparator method, or the like. This drive pulse is supplied to the switching element of the power conversion unit 4.

With the above configuration, feedback control is performed, and the output voltage of the solar cell 1 is controlled to a voltage target value.

The voltage setting section 7, the voltage control section 8 and the control section 9 are constituted by an analog circuit or a digital circuit, or a combination thereof. If a CPU or a DSP (Digital Signal Processor) is used for these configurations, there is an advantage that the configuration is simplified.

The load 3 is not limited to DC and AC, and various loads can be connected. If the load is an AC load with a relatively low frequency, such as an electric heater or a motor or a system, the ripple frequency will be the load frequency or a frequency that is an integral multiple of the load frequency,
The first embodiment is easily adapted. When load 3 is a grid,
Since there is no limit on the power supplied to the grid, it is very preferable to use the power control device 2 of the first embodiment that extracts more power from the solar cell 1 and supplies it to the load 3.

[MPPT Control] FIG. 2 shows an MPPT control performed by the voltage setting unit 7.
It is a flowchart which shows an example of control. First, in step S1, an initial value of the voltage target value VR is set, and the voltage target value VR is set.
Upper limit of the number of times voltage and current are detected while
Set Cmax.

Next, in step S2, variables used in the following iterative loop are initialized. Zero is substituted for Pmax for storing the maximum value of the detected power at the current voltage target value VR, VPmax for storing the voltage value at the time of Pmax, and C for storing the number of times of detection.

Next, in step S3, it is determined whether or not the timing to detect the voltage and the current has been reached. If it is the detection timing, the process proceeds to step S4, and if not, the process returns to step S3. The detection timing is set to, for example, eight times the ripple frequency. However, if the detection is performed at a higher frequency, it is needless to say that the ripple can be traced more finely and precise detection can be performed. Note that the detection timing is not limited to an integer multiple of the ripple frequency.
For example, a frequency such as 1.1 times the ripple frequency may be used as the detection timing.

In step S4, the output voltage and current of the solar cell 1 are obtained as a detected voltage value V and a detected current value I. Then, in step S5, a power detection value P is calculated from the voltage detection value V and the current detection value I.

Next, in step S6, the detected power value P is compared with the stored detected power maximum value Pmax. If P> Pmax, the detected power maximum values Pmax and VPmax are compared in step S7 with the detected power value Pmax. And the voltage detected value V, that is, the storage of the operating point at which the maximum power is detected is updated.

Next, in step S8, the number of detections C is incremented, and in step S9, the number of detections C and the upper limit C of the number of detections are set.
Compare with max. If C <Cmax, the process returns to step S3 to continue detection. If C ≧ Cmax, the process proceeds to step S10. That is, steps S3 to S9 are repeated until the number of detections C reaches the upper limit Cmax of the number of detections.

Next, in step S10, the voltage detection value VPmax when the detected maximum power value Pmax is finally detected is determined to be the maximum output point of the solar cell 1 at that time, and it should be set next. Set the voltage target value VR to VPmax. Then, the process returns to step S2, and the above operation is repeated.

FIG. 3 shows the target voltage VR and the operating voltage of the solar cell 1.
FIG. 6 is a diagram showing a time change of V and generated power P. Also figure
4 is a diagram illustrating a relationship between the operating voltage V of the solar cell 1 and the generated power P, that is, an example of operating characteristics of the solar cell 1. FIG.

Since the voltage target value VR is set to V1 at the timing t0, the average value of the operating voltage V becomes V1 under the control of the voltage controller 8. Power control device 2 for operating voltage V
3, the maximum value of the operating voltage V is V3, and the minimum value is V2, as shown in FIG. In addition, the generated power P indicates the operating characteristics of the solar cell 1 at that time.
If the characteristic is shown in FIG. 4, it pulsates according to the pulsation of the operating voltage V, indicates the maximum power P0 at the operating voltage V2, and indicates the operating voltage V3.
Indicates the minimum power P1.

During the period up to the timing t1, the voltage setting unit 7
As a result, P0 is detected as the maximum detection power value Pmax, and the voltage detection value VPma
V2 is detected as x. Therefore, the voltage target value VR after the timing t1 is updated to V2, and the voltage target value V2 is held at least until the timing t2.

After the timing t2, the average value of the operating voltage V becomes V2 under the control of the voltage controller 8, and its maximum value becomes V1,
The minimum value is V4. The generated power P indicates the maximum power P0 when the operating voltage is V2, and indicates the minimum power P2 when the operating voltages V1 and V4.

During the period from the timing t1 to the timing t2, the detected maximum power Pmax is P0 and the detected voltage value VPmax is V2, so that the voltage target value VR after the timing t2 continues to be V2.

As described above, the MPPT control of the first embodiment is as follows.
The maximum output point can be found using the ripple generated in the output voltage of the solar cell 1. Therefore, unlike the MPPT control by the hill-climbing method, for example, since the maximum output point is not searched by changing the voltage set value VR, the voltage target value VR is changed after the voltage target value VR reaches the maximum power operating point. I won't let you. In other words, since the voltage target value VR is not actively changed, the maximum output point can be maintained continuously.

Further, as shown in FIG.
The pulsation of the generated power P up to 1 is P0-P1 (corresponding to the range indicated by arrow A in FIG. 4), and the pulsation after timing t1 is P0-P2 (corresponding to the range indicated by arrow B in FIG. 4). Here, since P1 <P2, the power generation loss (so-called mismatch loss) is suppressed to be lower after the timing t2 than before the timing t1. For example, in the MPPT control by the hill-climbing method, a state in which the pulsation is large and a state in which the pulsation is small are constantly repeated alternately.
1, the power generation efficiency will be reduced. On the other hand, in the first embodiment, the pulsation (power generation loss) is constantly kept small, so that the power generation efficiency of the solar cell 1 is improved.

Further, when the fluctuation of the voltage target value VR is temporarily stopped to obtain a constant voltage target value VR, if the maximum output point fluctuates during the pause, power generation loss increases.
Of course, after the suspension is released, the power generation loss increases because the voltage target value VR is actively changed. On the other hand, in the first embodiment,
Even if the voltage target value VR is constant, since the maximum output point is always detected using ripples, even if the maximum output point fluctuates, the voltage target value VR is immediately followed to increase power generation loss. Can be suppressed.

As described above, according to the present invention, a plurality of voltages and currents on a ripple are detected and calculated in a power control device in which an operating point ripples during a period in which an operating voltage target value is constant. By setting the operating voltage target value based on the power value, it is possible to reach the maximum output operating voltage, continue operating at the maximum output operating voltage without changing the operating voltage target value, A large amount of power can be extracted, and the utilization rate of the solar cell is improved. In addition, when the maximum output operating voltage fluctuates, the operating voltage target value immediately follows, and the mismatch loss can be effectively suppressed.

In the above description, the example in which the number of detections is fixed to Cmax has been described. However, the number of detections and the detection timing may be made variable in accordance with the magnitude of the ripple. For example, when the ripple is small, the number of detections is increased, and the detection values of the operating voltage V and the generated power P of the solar cell 1 are statistically processed, so that the influence of noise can be suppressed. And the maximum output point can be tracked with high accuracy.

[0044]

Second Embodiment Hereinafter, a power control device according to a second embodiment of the present invention will be described. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

In many cases, the magnitude of the ripple has a characteristic proportional to the power as shown in FIG. Therefore, when the power is large, the ripple is large, and highly accurate MPPT control can be performed using the ripple. However, when the power is small, the ripple is small, and the accuracy using the ripple is high.
MPPT control becomes difficult. Hereinafter, the MPPT control of the second embodiment in consideration of this point will be described.

FIG. 6 is a flowchart showing an example of the MPPT control performed by the voltage setting section 7.

In step S11, the MP characteristic of the second embodiment
Set a power reference value Px that is a reference for switching the PT mode.
The criteria for switching the MPPT mode may be determined based on the magnitude of the ripple that provides sufficient control accuracy with respect to the voltage and current detection accuracy. In the second embodiment, a power value corresponding to the magnitude of the ripple as shown in FIG. 5 is used.

Next, in step S12, the detected voltage value V and the detected current value I are obtained, and in step S13, the detected power value P is calculated from the detected voltage value V and the detected current value I. Then, in step S14, the power detection value P is compared with the power reference value Px,
If P> Px, it is determined that the size of the ripple is sufficient to obtain sufficient detection accuracy, and “MPPT mode 1” is set in step S15. In the case of P ≦ Px, it is determined that the ripple is too small to obtain sufficient detection accuracy by the ripple alone, and “MPPT mode 2” is set in step S16.

In the MPPT mode 1, similar to the first embodiment,
A plurality of operating points on the ripple are detected during the period controlled by the constant voltage target value VR, and the voltage target value VR is set so as to become the maximum output point based on the detection results. Also MP
In the PT mode 2, the voltage target value VR is positively fluctuated like the hill-climbing method, and the voltage target value VR is set so as to be the maximum output point based on the operating points detected by the plurality of voltage target values VR. . When the setting of the voltage target value VR ends, the process returns to step S12.

By repeating the above processing, two MPPT modes are switched according to the power generated by the solar cell 1,
Control can be performed so that the power generated by the solar cell 1 is maximized. If the generated power is large, that is, if the ripple is large, the voltage target value VR is set to be the maximum output point based on the result of detecting the operating point at a constant voltage target value VR using the ripple, as described above. Thus, the utilization rate of the solar cell 1 is improved.

When the generated power is small, that is, when the ripple is small, the voltage target value VR is set so as to become the maximum output point based on the result of detecting the operating point with the different voltage target value VR, so that malfunction is suppressed. As a result, the utilization rate of the solar cell 1 comparable to that of the hill-climbing method can be secured.

As described above, according to the second embodiment, when the power generated by the solar cell 1 is large, the utilization factor of the solar cell 1 can be effectively improved, which is extremely effective.

Note that the MPPT mode 1 is not limited to the method described in the first embodiment, but is applied to a constant voltage target value.
Any method may be used as long as it detects a plurality of operating points on the ripple during the period controlled by VR and sets the voltage target value VR so that the maximum output point is obtained based on the detection results.

Also, the MPPT mode 2 is not limited to the hill-climbing method, and the voltage target value VR is positively fluctuated to reach the maximum output point based on the operating points detected by the plurality of voltage target values VR. What is necessary is just to set the voltage target value VR so as to be as follows. For example, the voltage target value VR may be positively changed, the generated power at each voltage target value VR may be detected, and the voltage target value VR at which the maximum power is obtained may be set as the next voltage target value VR. Alternatively, the method described in Japanese Patent No. 2771096 may be used.

In the above description, based on the power generated by the solar cell 1, M
Although the example in which the PPT mode is switched has been described, the present invention is not limited to this, and the ripple amplitude (peak to peak value) detected by detecting a voltage or a current a plurality of times and the output power of the power control device 2 Alternatively, the MPPT mode may be switched based on the output current or the output command value.

[0056]

Third Embodiment Hereinafter, a power control device according to a third embodiment of the present invention will be described. In the third embodiment,
The same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

In many cases, the ripple has a predetermined period,
In particular, the ripple generated at the input of the power control device 2 that outputs the AC power has a predetermined relationship with the output power waveform. In other words, it is easy to grasp the timing of a predetermined point on the ripple, for example, the maximum point, the minimum point, the center point, etc. of the ripple voltage.

Assume that the voltage target value VR is set to V1, the maximum output point as shown in FIG. In this case, the operating voltage V of the solar cell 1 has a ripple whose minimum value is V2 and whose maximum value is V3.

The voltage setting unit 7 controls the operation voltage V and the current of the solar cell 1 at a timing determined by the operation of the power control device 2.
By detecting I, the maximum value, the minimum value, and the center value of the ripple voltage are detected. In other words, the center value of the ripple voltage at the timing t1 shown in FIG. 7, the minimum value of the ripple voltage at the timing t2, the center value of the ripple voltage at the timing t3,
At t4, the maximum value of the ripple voltage is detected, the current I at those timings is detected, and the power value is calculated.

Then, the influence of solar radiation fluctuation is estimated from the difference between the detected power values P at the same operating voltage V1. This includes
If the operating voltage V is the same, the generated power P of the solar cell 1 is substantially proportional to the solar radiation fluctuation, and the characteristic that the power detection value P is proportional to the solar radiation fluctuation if the detection timings of the two detection values are close. Use That is, the difference between the detected power values P at the same operating voltage V is information indicating the amount of change in solar radiation during that period, and the difference ΔP between the detected power values described below indicates the amount of change in solar radiation between timings t1 and t3. The data is corrected using the information ΔP indicating the amount of change in solar radiation. ΔP = P3-P1

Normally, since the time from timing t1 to t4 is short, the change in solar radiation from timing t1 to t4 can be regarded as linear. In addition, the operating voltage V1 near the maximum output point
The difference between the power detection value P and the power detection value P2 is small, and the change in the power detection value P due to the short-term fluctuation of the solar radiation can be regarded as the same regardless of the operating voltage V1 or V2. The same applies to operating voltages V1 and V3. Accordingly, the power detection value P2 of the operating voltage V2 at the timing t2 is changed to the power value P2 of the operating voltage V2 at the timing t3.
Correct to a. The following relationship exists between the time from timing t2 to t3 and the time from timing t1 to t3. (t3-t2) / (t3-t1) = 1/2

Accordingly, the influence of the solar radiation fluctuation from the timing t2 to t3 is considered to be 1/2 of ΔP corresponding to the solar radiation fluctuation from the timing t1 to t3, and the power value P2a is expressed by the following equation. P2a = P2 + ΔP / 2

Similarly, power detection value P4 is corrected to power value P4a at timing t3. P4a = P4-ΔP / 2

As a result, information indicating the generated power P at the three operating voltages V1, V2 and V3 from which the influence of the solar radiation fluctuation has been removed is obtained. Based on these information, the output characteristics are approximated by a quadratic function, the operating voltage V at which the generated power P is maximized is calculated, and set to the next voltage target value VR. Since V1 is the center value of the ripple, V3−V1 = V1−V2 = ΔV, and the voltage target value V
R can be easily calculated by the following equation. VR = V1 + ΔV / 2 × {(P2a-P4a) / (2 × P1-P2a-P4a)}

By repeating the above operation, the solar cell 1
Can follow the maximum output point.

In the example shown in FIG. 7, since there is no variation in the solar radiation, the power detection value P1 at the timing t1 and the power detection value P3 at the timing t3
Are the same value and ΔP is zero. In this case, the correction amount ΔP / 2
Also becomes zero. Therefore, the power value P2a of the operating voltage V2 = P2 and the power value P4a of the operating voltage V3 = P4. Furthermore, P2 = P4
Therefore, P2a = P4a. In this case, the voltage at which the generated power P becomes maximum on the approximated quadratic function is V1, and V1
Is set to the next voltage target value VR.

As described above, by estimating the solar radiation fluctuation from the power detection value P of the same operating voltage V and correcting the data,
Operating voltage-generated power characteristics at the same timing can be obtained. By determining the voltage target value VR based on the obtained characteristics, no malfunction of the search control algorithm due to solar radiation fluctuation occurs, the solar cell 1 is controlled to the maximum output point, and the maximum power is extracted from the solar cell 1 In addition, unstable operation of the power control device 2 can be suppressed. Furthermore, since the unnecessary voltage fluctuation does not occur when the maximum output point is reached, the utilization rate of the solar cell 1 is further improved. Also, since the operating voltage V at which the maximum generated power P is estimated from the approximation curve of the operating voltage-generated power characteristic, the voltage target value is finer than the above ΔV.
VR can be set, and the maximum output point can be tracked with high accuracy. In addition, when the operating voltage V is far from the maximum output point, a value outside the range of the detected voltage value can be set as the voltage target value VR, so that the maximum output point can be quickly followed.

In the third embodiment, the detection value is corrected by ΔP indicating the amount of solar radiation fluctuation. However, when ΔP is larger than a predetermined value, the next voltage target value VR is unconditionally held at the same value as the current value. Then, the voltage target value VR may not be changed until the solar radiation fluctuation stops. In this case, it is possible to suppress a malfunction due to a rapid change in solar radiation.

As described above, according to each of the above-described embodiments, the power supplied from the solar cell 1 undergoes a predetermined period of ripple due to the power conversion operation of the power control device 2. Utilizing this ripple, currents at a plurality of operating voltages V of the solar cell 1 are detected, and based on a power value P calculated therefrom, the next target is set so that the generated power P of the solar cell 1 is maximized. Set the voltage value V. Thereby, the following effects can be obtained. (1) After the voltage target value VR reaches the maximum output point, it follows the maximum output point without changing the voltage target value VR, thereby preventing power generation loss caused by actively changing the voltage target value VR. And the utilization rate of the solar cell 1 is improved. (2) According to the ripple of the solar cell 1, the voltage target value V
By switching between the MPPT mode in which R does not fluctuate actively and the MPPT mode in which the voltage target value VR fluctuates,
When the ripple is large, the utilization rate of the solar cell 1 can be improved, and when the ripple is small, malfunction of the MPPT control can be prevented. The switching of the MPPT mode is reliable and easy because the switching is performed not by the magnitude of the ripple itself but by the input or output power or current, or the variation of the input voltage or input current detection value. (3) By correcting the fluctuation of the generated power corresponding to the solar radiation fluctuation, the maximum output point can be accurately searched without being affected by the solar radiation fluctuation. (4) When the fluctuation of the generated power corresponding to the solar radiation fluctuation exceeds a predetermined value, by temporarily stopping the search for the maximum output point, it is possible to prevent the malfunction of the MPPT control due to the influence of the solar radiation fluctuation.

As described above, the power control device 2 of the present embodiment
Is very useful, and is particularly effective when used in a grid-connected photovoltaic power generator that is connected to grid 3.

In the above description, the example in which the voltage target value VR is set has been described. However, the current target value IR can be set. Furthermore, the supply source of the DC power is not limited to the solar cell 1, but any supply source having an operating voltage (or current) -power characteristic, such as a solar cell, in which ripple occurs due to the power conversion operation of the power control device 2. Good.

[0072]

As described above, according to the present invention,
When converting the input DC power into power corresponding to the load, it is possible to increase the utilization efficiency of the DC power supply source.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of a solar power generation device using a power control device according to a first embodiment;

2 is a flowchart illustrating an example of MPPT control performed by a voltage setting unit illustrated in FIG. 1,

FIG. 3 is a diagram showing a time change of a voltage target value, an operating voltage of a solar cell, and generated power;

FIG. 4 is a diagram showing an example of operating characteristics of a solar cell;

FIG. 5 is a diagram showing an example of the relationship between the magnitude of ripple and power.

FIG. 6 is a flowchart illustrating an example of MPPT control performed by a voltage setting unit according to the second embodiment;

FIG. 7 is a diagram showing a time change of a voltage target value, an operating voltage of a solar cell, and generated power,

FIG. 8 is a diagram showing an example of operating characteristics of a solar cell.

Claims (18)

[Claims] 1. A power conversion means for converting input DC power into a power corresponding to a load, a detection means for detecting a voltage and a current of the input DC power, and the input based on the detected voltage and current. Setting means for setting a target value of the voltage or current of the DC power; andcontrol means for controlling the power conversion means so that the detected voltage or current becomes the target value. A characteristic of a source of the input DC power is detected from a ripple included in the input DC power generated by an operation of the power conversion unit, and a target value of the voltage or current of the input DC power is set based on the detected characteristic. A power control device characterized by the above-mentioned. 2. The method according to claim 1, wherein the setting unit sets a plurality of target values when the amplitude of the ripple does not exceed a predetermined value, and sets the target values based on detection results of voltage and current for each target value. The power control device according to claim 1, wherein: 3. The power control device according to claim 2, wherein the setting unit determines the amplitude of the ripple from a product of the detected voltage and current. 4. The apparatus according to claim 1, further comprising power detection means for detecting power output from said power conversion means, wherein said setting means determines the amplitude of said ripple from the detected power. 2. The power control device described in 2. 5. The power control device according to claim 2, wherein the setting unit determines the amplitude of the ripple from a variation in the detected voltage or current. 6. The method according to claim 1, wherein the setting unit sets the target value based on the detected characteristic of the supply source so that the output power of the supply source is maximized. The power control device according to any one of the above. 7. The setting means detects input power at a plurality of different voltages or currents using the ripple, and approximates the characteristics of the supply source from the detected voltage or current and the power. 7. The power control device according to claim 6, wherein: 8. The method according to claim 7, wherein the setting unit detects power at at least three different voltages or currents, and approximates a characteristic of the supply source by a quadratic function based on a result of the detection. The described power control device. 9. The method according to claim 1, wherein the setting unit detects input power at a plurality of different voltages or currents by using the ripple, and sets a voltage or a current showing a maximum power to a target value. 6. The power control device according to claim 1, wherein: 10. The method according to claim 1, wherein the difference between currents or powers detected at different timings and at the same voltage or a difference between voltages or powers detected at different timings and at the same current exceeds a predetermined value. 6. The power control device according to claim 1, wherein a target value is held regardless of a detection result. 11. The power supply apparatus according to claim 1, wherein the setting unit adjusts a difference between currents or powers detected at different timings and at the same voltage, or a power corrected according to a difference between voltage or power detected at different timings and at the same current. 6. The power control device according to claim 1, wherein the target value is set based on the target value. 12. The power control device according to claim 10, wherein the setting unit detects a voltage and a current at a predetermined timing synchronized with the ripple. 13. The power control according to claim 12, wherein the setting unit detects the voltage and the current at timings synchronized with two or three points of the double peak and the intermediate point of the ripple. apparatus. 14. The apparatus according to claim 1, wherein the setting unit sets the number of times of detecting the voltage and the current for setting the target value in accordance with the magnitude of the ripple. Or a power control device. 15. A power generator comprising the power control device according to claim 1. Description: 16. The power generator according to claim 15, wherein the power controller can be connected to a commercial power system. 17. The power generating apparatus according to claim 15, wherein the supply source of the input DC power is a solar cell. 18. Power conversion means for converting input DC power into power corresponding to a load, detection means for detecting the voltage and current of the input DC power, and the detected voltage or current becomes a target value. And a control means for controlling the power conversion means as described above, wherein the supply of the input DC power from a ripple included in the input DC power, which is generated by the operation of the power conversion means. A control method comprising: detecting a characteristic; and setting the target value based on the detected characteristic.