JP2003032897A - Solar generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform the control of operating a solar cell at its maximum point of output power simply and safely by limited detection systems. SOLUTION: The DC power of the solar cell 1 is converted into AC by an inverter 3 after boosting with a chopper 2, and it is linked with a commercial power system 5. At this time, a chopper circuit 6 generates a control voltage command value by detecting the current Is of the solar cell 1 and the voltage Es of a capacitor C1 parallel with the solar cell 1, and also superposes offset voltage on the control command value only at start. Consequently, even if it does not detect a reactor current Ii, it can generate a chopper control signal, equivalent to having detected the current of the capacitor C1. Therefore, this generator can control the voltage of the solar cell at its maximum point of output power of itself 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic power generator for connecting the power of a DC power source such as a solar cell to a commercial power system.

[0002]

2. Description of the Related Art In recent years, a solar power generation system in which DC power generated by a solar cell is connected to a commercial power system has begun to spread. As a solar power generation device used in such a system, a boost chopper (hereinafter referred to as a chopper)
And a single-phase PWM inverter (hereinafter referred to as an inverter) are generally used. In other words, due to safety issues based on electrical equipment standards, the generated voltage of the solar cell should be kept low, boosted to a desired DC voltage by a chopper, then converted to an AC voltage by an inverter, and connected to a commercial power grid. ing. Such a solar power generation system
For example, Japanese Unexamined Patent Publication No. 10-97330 and the Institute of Electrical Engineers of Japan, D11
Vol.8, No.12 (Maximum power control method for photovoltaic power generation system based on voltage differential of electric power: Published in 1998).

According to the techniques described in the above publications, in the chopper control, the maximum power follow-up control for always supplying the maximum power from the solar cell is performed regardless of changes in the solar radiation amount and temperature of the solar cell. ing. In the inverter control, AC output current control and inverter DC input voltage control are performed. Among these, the maximum power follow-up control performed by the chopper control is performed by paying attention to the fact that the voltage differential value of the output power of the solar cell becomes zero at the maximum power point. That is, a control system is formed in which the voltage differential value of the output power of the solar cell is feedback-controlled to make it zero. As a result, the voltage control of the solar cell that always tracks the maximum output power of the solar cell can be performed regardless of the amount of solar radiation and the temperature change of the solar cell.

FIG. 4 is a main circuit configuration diagram of a conventional solar power generation device. In the figure, a solar cell 1 which is a DC power source.
The DC power from is supplied to the chopper 2, boosted to a desired voltage, converted to AC by PWM control by the inverter 3, and then supplied to the commercial power system 5 via the output filter 4. At this time, the chopper controller 6 controls the solar cell current (hereinafter referred to as battery current) Is and the capacitor C1 connected in parallel with the solar cell in order to perform the control of operating the solar cell 1 at the maximum output power point at high speed and stably. (Hereinafter, battery voltage) Es and the current of reactor L (hereinafter, reactor current) Ii are detected, and the transistor T is switching-controlled to control the voltage of the solar cell that tracks the maximum output power of the solar cell 1. Is going.

That is, the battery current Is and the battery voltage Es are detected, and the solar battery power (hereinafter, output power) Ps (= Is) is detected.
XEs) differentiated by the battery voltage Es (dPs / dE)
Maximum power tracking control is performed from s). At this time, as the characteristics of the solar cell, the battery voltage Es decreases when the battery current Is increases. Therefore, the reactor current Ii is detected and the switching duty ratio of the transistor T is controlled to control the battery voltage Es. There is. That is, the output voltage Ps of the solar cell is controlled by controlling the battery voltage Es.
To control the capacitor C1 at the input of the chopper 2
It is necessary to control the current (Is-Ii) flowing into the device.
Therefore, three systems of the battery current Is, the battery voltage Es, and the reactor current Ii are detected. In the inverter 3, the inverter controller 7 controls the inverter input voltage Ed, the inverter output voltage Vo, and the inverter output current Io.
Is detected to perform AC output current control and DC input voltage control.

[0006]

That is, in the conventional photovoltaic power generation apparatus, as is apparent from FIG. 4, in order to perform maximum power tracking control by the chopper 2, the chopper controller 6 sets the battery current Is. It is necessary to detect and control the three systems of information including the battery voltage Es and the reactor current Ii. That is, the battery current Is and the battery voltage Es are detected, the battery power Ps is calculated from the product Es · Is, and the differential value (dPs / dE) of the output power Ps with respect to the battery voltage Es.
s) is controlled to be zero and maximum power tracking control is performed, while the reactor current Ii is detected and the battery current Ii is detected.
The output voltage of the chopper is controlled so that a predetermined battery voltage Es can be obtained at the maximum power point from the difference (Is-Ii) between s and the reactor current Ii.

That is, the maximum output follow-up control on the chopper side in the conventional photovoltaic power generation device necessarily includes three detectors because the number of detection systems is three. For this reason,
As the detection system and the control system become complicated, it becomes a factor that deteriorates the stability of the control system, and the number of detectors and the number of parts of the control circuit increase. There was a problem of becoming. Further, there is a problem that when a high DC bus voltage is applied to the inverter even though the voltage of the commercial power system is low, the loss of the switching element forming the inverter becomes large.

The present invention has been made in view of such circumstances, and an object thereof is to make it possible to easily and stably perform control for operating at the maximum output power point of a solar cell with a small number of detection systems. It is in. Another object is to reduce the switching loss of the switching element that constitutes the inverter by changing the DC bus voltage, that is, the inverter input voltage, along with the voltage change of the commercial power system.

[0009]

In order to solve the above problems, the photovoltaic power generation device of the present invention takes the following means. The solar power generation device according to claim 1 is a solar power generation device in which the voltage of a solar battery power source is boosted by a boosting means and then converted into an AC voltage by a DC-AC conversion means to be connected to a commercial power system. The boosting means detects the output current of the solar cell power supply and the input voltage of the boosting means, and superimposes the offset voltage on the voltage level of the control signal generated by the detected output current and input voltage at startup. Thus, the maximum output tracking control for tracking the maximum output power value of the solar cell power source is performed.

With this means, the boosting means for boosting the DC voltage of the solar cell power supply and supplying it to the DC-AC converting means does not perform the two-system current detection and the one-system voltage detection as in the conventional case. Instead, the maximum output tracking control can be performed by only one system current detection and one system voltage detection. In other words, in order to detect the current of one system,
In the present invention, by superposing the changing offset voltage on the control signal, the output voltage control of the solar cell is performed so as to track the maximum output power value of the solar cell power source as in the case of the conventional three-system detection. You can As described above, even if the number of current detectors is reduced by one compared with the conventional method, the maximum output power tracking control can be performed at high speed and stably, so the control system is simplified and Cost reduction can be achieved.

The invention described in claim 2 is the same as claim 1.
In the solar power generation device described in, the boosting means is a chopper circuit, and the chopper circuit includes a chopper control means for performing output voltage control at the maximum output power value of the solar cell power source. Then, the chopper control means detects the output current Is of the solar cell power source and the input voltage Es of the capacitor formed at the input of the chopper circuit, and the control generated by the detected output current Is and input voltage Es. The maximum output follow-up control is performed by superimposing an offset voltage on the voltage level of the signal at the time of startup.

By this means, the maximum output of the solar battery power source can be obtained by the current detection of one system and the battery voltage detection of one system without the conventional two system current detection and one system battery voltage detection in the chopper circuit. Follow-up control can be performed. However, at start-up, for the control signal,
The maximum output tracking control can be performed by superimposing the offset voltage. With such a control system, relatively accurate control can be performed, and since the number of detectors is reduced by one, the control system is simplified, so that the control stability is improved and the control is performed. The entire circuit can be simplified, and the cost of the entire photovoltaic power generation device can be reduced.

The invention described in claim 3 is the same as that of claim 2
In the solar power generation device described in (1), in the maximum output tracking control, the chopper control means calculates the output power Ps of the solar cell power source based on the detected output current Is and the input voltage Es, and further, the output power Ps. Is differentiated by the input voltage Es to calculate a differential value (dPs / dEs), and this differential value (dPs
It is realized by setting the target value of / dEs) to zero.

By this means, the solar cell has the maximum output power Ps at the point of dPs / dEs = 0, which is the voltage differential value of the output power. Therefore, if the control is performed so that dPs / dEs becomes zero. The maximum power follow-up control can always be performed regardless of changes in solar radiation amount and temperature of the solar cell.

The invention according to claim 4 or 5 is characterized in that the offset voltage is variable. Furthermore, the offset voltage is characterized in that a limit value is set so that the control signal of the chopper control means performs control in the vicinity of the maximum output power of the solar cell power supply. Therefore, even if the number of current detectors is reduced by one, the maximum power tracking control can be performed as in the conventional technique.

The invention according to claim 6 or 7 is the photovoltaic power generator according to any one of claims 1 to 5, wherein the chopper control means controls the voltage of the commercial power system. A voltage detection unit for detecting and a voltage command table defining a DC bus voltage command value corresponding to the voltage detected by the voltage detection unit are provided, and the DC bus voltage is changed in accordance with the voltage change at the interconnection point. In the voltage command table, the voltage at the interconnection point and the DC bus voltage command value are first-order increasing functions within a predetermined range.

By this means, when the voltage of the commercial power system is low, the switching loss of the switching element forming the inverter can be reduced by controlling the DC bus voltage.

The invention described in claim 8 is the same as claim 1.
Therefore, in the solar power generation device according to claim 7, the DC-AC conversion means is a PWM control inverter.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a photovoltaic power generator according to the present invention will be described in detail below with reference to the drawings. FIG. 1 is a main circuit configuration diagram of a solar power generation device according to an embodiment of the present invention. In the figure, the DC power from the solar cell 1, which is a DC power supply, is supplied to the chopper 2, boosted to a desired voltage, and further converted into AC by the PWM control by the inverter 3, and then the output filter 4
Is supplied to the commercial power system 5 via. At this time, in order to perform the control for operating at the maximum output power point of the solar cell 1 at high speed and stably, the chopper controller 6 controls the cell current Is, which is the output current of the solar cell, and the capacitor C1 connected in parallel with the solar cell. Of the battery voltage Es, which is the voltage of, and the voltage command value for controlling the battery voltage,
The offset voltage is superimposed only at startup
Is switching controlled. As a result, the voltage of the battery voltage is controlled according to the magnitude of the battery current Is (that is, the detected current) while tracking the maximum output power of the solar cell 1 from the start-up to the steady state.

Further, in the inverter 3, the inverter controller 7 detects the inverter input voltage Ed, the inverter output voltage Vo and the inverter output current Io, and performs the AC output current control and the inverter input voltage control. . That is, since the output side of the inverter 3 is interconnected to the commercial power source side without passing through the insulation transformer, the AC output current control is performed so that the AC output current does not include the DC component. Since the operation on the inverter side is not directly related to the present invention, it will be omitted in the following description.

That is, the feature of the present invention is that the chopper controller 6 controls the switching of the transistor T without detecting the reactor current Ii as in the prior art shown in FIG. That is, maximum power tracking control is performed. That is, when the photovoltaic power generator is activated, the battery current Is is charged in the capacitor C1 and the reactor current Ii is zero.

However, in the present invention, the reactor current Ii
Is not detected, the capacitor current cannot be detected. Therefore, at the time of startup, the output power Ps based on the battery voltage Es and the voltage differential value dPs / dEs of the output power cannot be calculated, so that the voltage command value necessary for control cannot be generated. Therefore, in the present invention, the maximum output tracking control can be performed by superimposing the offset voltage on the command value of the battery voltage at startup. Hereinafter, this will be described in detail.

FIG. 2 shows an example of the output characteristics of the solar cell. That is, at a certain amount of solar radiation, the battery voltage Es-battery current Is characteristic of the solar cell, the battery voltage Es-output power Ps characteristic, and the battery voltage Es-voltage differential value dPs / d of the output power.
The Es characteristic is shown. That is, as is apparent from FIG. 2, the relationship between the voltage differential value dPs / dEs of the output power and the cell voltage Es of the solar cell is monotonous, and the solar cell has dPs / d
At the point of Es = 0, the output power Ps has the maximum value (Psmax). In other words, dPs / dEs = 0 at the maximum power point Psmax of the output power Ps, regardless of fluctuations in solar radiation or temperature of the solar cell.
Is established. Therefore, it is understood that the maximum power follow-up control may be controlled so that dPs / dEs of the solar cell is set to zero.

FIG. 3 is a block diagram of a chopper control system in the solar power generator of the present invention. That is, this figure shows a maximum power follow-up control unit including a power differential calculator 11 and a maximum power compensator 12, a startup offset voltage superimposing unit including an integrator 13 and a limiter 14, and a proportional-plus-integral control unit 1.
5 and a chopper control unit.
In the figure, Es is the battery voltage, Es * is the battery voltage command value, Ps is the output power of the battery, dPs / dEs is the voltage differential value of the output power, and (dPs / dEs) * is the command value of dPs / dEs. , ΔEs are deviations of the battery voltage Es from the battery voltage command value Es *. Further, S1 is a transistor T of the chopper 2.
Is a chopper control signal input to
It is represented by the addition value of the proportional control signal having the above and the integral control signal having the integral gain KI. That is, S1 is expressed by the following equation (1), the former term is the proportional control signal and the latter term is the integral control signal. S1 = KpΔEs + KI∫ΔEs dt (1)

First, the operation in the steady state will be described for easy understanding. In FIG. 3, when the detection signals of the battery current Is and the battery voltage Es are input to the power differentiation calculator 11, the output power Ps = Is × Es is obtained, and the output power Ps is further differentiated by the battery voltage Es to obtain dPs / dEs
Is obtained. And this dPs / dEs is (dPs / dE
s) The deviation is calculated by comparing with the command value of * = 0, and the power compensator 1
When input to 2, a voltage command signal for performing maximum power tracking control is generated.

Here, the function of the maximum power tracking control in the solar cell will be considered. Now, when the ON ratio D of the duty cycle in the transistor T is increased, the battery current Is simply increases and the battery voltage Es simply drops. At this time, the voltage differential value dPs / dEs of the output power simply increases. Therefore, the target value of dPs / dEs (d
Ps / dEs) * is set to 0 and dPs / dEs is fed back, and the deviation between them is amplified to the battery voltage command value Es *,
If the ON ratio D of the transistor T is controlled by controlling the battery voltage Es, the maximum power follow-up control can be performed.

According to such a detection method, the gain of the control system is slightly reduced in the steady state as compared with the case where the reactor current Ii of the prior art is detected and the control is performed, but there is a problem in the normal use state. With no level of gain,
Maximum power tracking control can be performed. That is, in a steady state, the gain of the proportional-plus-integral controller 15 for performing the maximum power follow-up control can be held at a predetermined level without detecting the reactor current Ii. Therefore, another solution of the present invention is that the maximum power follow-up control can be normally performed without detecting the reactor current Ii at the time of startup.

Now, returning to FIG. 3, the operation at the time of starting will be described. First, the power differentiation calculator 11 determines that the battery current Is
And the detection signal of the battery voltage Es are input to output power Ps = Is
X Es is obtained, the output power Ps is differentiated by the battery voltage Es, and d
Generate Ps / dEs. Then, this dPs / dEs is (d
Ps / dEs) * is compared with a command value of 0 to obtain a deviation, which is input to the power compensator 12 to generate a voltage command signal for performing maximum power tracking control. In order to follow the maximum power of the solar cell, the above dPs / dEs
Must be negative. However, the battery current at start-up is almost zero, and there are errors in the battery voltage and battery current detection values due to the effects of detector noise such as quantization error and detection delay, so the value of dPs / dEs Is greatly affected by the error. On the other hand, dPs
Once the value of / dEs becomes a positive value, the voltage command signal increases, but the battery voltage cannot be higher than the open circuit voltage.
dPs / dEs will maintain a positive value. In other words, the present invention cannot follow the maximum output power at the time of startup due to the influence of detector noise and the like. Therefore, at the time of startup, an offset voltage is generated when a certain constant value is input to the integrator 13, and the battery voltage command value E * can be generated by superimposing this offset voltage on the voltage command signal.

That is, when a constant negative value a is input to the integrator 13, an initial value b preset in the integrator 13 is input.
Then, the integrated value c obtained by time-integrating the input constant value a is subtracted. Then, bc (that is, the value obtained by subtracting the integral value c from the initial value b) is subtracted until the limit value d set by the limiter 14 is reached. Such b-c
The value of is attenuated so that it finally reaches the limit value d. As a result, dPs / dE is activated at startup.
By superimposing the offset voltage on the voltage command signal generated by the deviation of s from the target value, the battery voltage command value E * at the time of startup can be set to a value equivalent to that when the reactor current Ii is detected.

Then, the battery voltage command value E * of the battery voltage Es
By inputting the deviation ΔEs to the proportional-plus-integral controller 15, a chopper control signal composed of the proportional control signal and the integral control signal as shown in the above equation (1) can be generated to perform maximum power tracking control. it can. In addition, limiter 1
The setting value of 4 is that the output power of the solar cell is the maximum power point Psmax.
If the value is set so as to come close to, the maximum power follow-up control can be immediately started at the time of transition from the start-up to the steady state. Further, according to the experiment, since it takes less than 10 seconds to reach the maximum power point from startup, it is necessary to secure a sufficiently practical level of gain without detecting the reactor current Ii as in the conventional case. You can

The DC bus voltage Ed of FIG.
If the AC voltage inversely converted by the method is lower than the interconnection point voltage Vo of the commercial AC power system 5, electric power cannot be sent out, so that it is customary to set it as the voltage defined by the following equation (2). . Ed = α · √2 · Vo (2) where α is the switching elements T1 to T of the inverter 3
4 is a margin ratio including loss due to the saturation voltage of 4 and others.

When the maximum value of the interconnection point Vo is 220 [V] and the margin ratio α is 1.12 and is substituted into the equation (2), the DC bus voltage Ed is approximately 350 [V], and normally the DC bus has this voltage. Chopper control is performed so as to maintain. However,
The voltage Vo at the interconnection point may drop below 200 [V], and in this case, the DC bus voltage and Ed as 350
The voltage can be lower than [V], and the loss of the chopper 2 and the inverter 3 can be reduced.

I which is a switching element of the inverter 3
The switching loss Psw of the GBT is given by the equation (3). Psw ＝ (1 / 6π) (Ed + 2Vce) (Ton + Toff) ・ Ic ・ fsw (3) Where, Vce: Collector-emitter saturation voltage, Ton, Tof
f: turn-on time and turn-off time of switching element, Ic: collector current, fsw: switching frequency. The turn-on time Ton and turn-off time Toff of the switching element are determined by the element, and the collector current Ic and switching frequency fsw are determined by the operating conditions.
It can be thought of as a constant. Since the collector-emitter saturation voltage Vce is sufficiently smaller than the DC bus voltage Ed, the switching loss Psw is proportional to the DC bus voltage Ed when approximated to Vce = 0.

Therefore, if the DC bus voltage Ed is controlled to the minimum required voltage level, the switching loss of the inverter 3 can be reduced and the efficiency can be improved. Therefore, by incorporating the voltage command table having the characteristics shown in FIG. 6 in the chopper control unit 6 and driving the switching element T of the chopper 2 so as to control the DC bus voltage in accordance with the change in the interconnection point voltage, Inverter 3
It is possible to reduce the switching loss.

In the table of FIG. 6, the interconnection point voltage Vo is 20.
The DC bus voltage Ed is 300 [V] at 0 [V], the DC bus voltage Ed is 350 [V] at the interconnection point voltage Vo of 220 [V], and the interconnection point voltage Vo is 200.
In the range of [V] to 220 [V], it has a linear increasing function characteristic. In the range where Vo exceeds 220 [V],
Since the interconnection operation is not performed, Ed is kept at a constant voltage 350 [V] as shown in the figure. Vo is 200
In the range of [V] or less, interconnection must be possible up to 170 [V], but Ed is set to a constant voltage of 300 [V] in order to simplify control.

The embodiment described above is an example for explaining the present invention, and the present invention is not limited to the above-mentioned embodiment, and various modifications can be made within the scope of the gist of the invention. is there. For example, another embodiment of the present invention will be described. FIG. 5 is a main circuit configuration diagram of a photovoltaic power generator according to another embodiment of the present invention. This diagram is different from FIG. 1 of the above-described embodiment only in that the chopper control unit 6 detects the voltage Vo of the commercial power system, and is otherwise the same as FIG. Further, in the above embodiment, the case where the chopper circuit is used as the means for boosting the solar cell voltage has been described as an example, but the invention is not limited to this, and for example, a ringing choke type converter (so-called RCC) is used. Or any other circuit. That is, the present invention can be realized in any circuit as long as the control system is configured to generate an offset voltage and add the offset voltage to the control voltage command value at the time of startup. Needless to say.

[0037]

As described above, according to the photovoltaic power generator of the present invention, even if the number of current detectors is reduced by one compared with the conventional method, the maximum output power tracking control and the chopper can be performed at high speed and stably. Output voltage control can be performed. In this way, since the control system can be simplified by reducing the number of detectors, the stability of control is improved, and the entire control circuit is simplified to reduce the cost of the entire photovoltaic power generation device. Can be planned.

Further, by controlling the DC bus voltage in accordance with the change in the interconnection point voltage, the loss of the switching element of the inverter can be reduced and the efficiency of the device can be improved.

[Brief description of drawings]

FIG. 1 is a main circuit configuration diagram of a photovoltaic power generator according to an embodiment of the present invention.

FIG. 2 is an example of output characteristics of a solar cell.

FIG. 3 is a block diagram of a chopper control system in the solar power generation device of the present invention.

FIG. 4 is a main circuit configuration diagram of a conventional solar power generation device.

FIG. 5 is a main circuit configuration diagram of a solar power generation device according to another embodiment of the present invention.

FIG. 6 is a characteristic diagram of a voltage command table of a photovoltaic power generator according to another embodiment of the present invention.

[Explanation of symbols]

1 solar cell 2 chopper 3 inverter 4 output filters 5 Commercial power system 6 Chopper controller 7 Inverter controller 11 Power differentiation calculator 12 Maximum power compensator 13 Start signal integrator 14 limiter 15 Proportional Integral Controller

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shinichi Kobayashi             1 Takamichi, Iwatsuka-cho, Nakamura-ku, Nagoya-shi, Aichi               Mitsubishi Heavy Industries Nagoya Research Center (72) Inventor Hidehiko Sugimoto             16 from 3-4 Iwanaridai, Kasugai City, Aichi Prefecture F-term (reference) 5G066 HB06                 5H420 BB03 BB12 BB14 CC03 CC09                       DD03 DD09 EA11 EB01 EB04                       FF03 FF04 FF05 FF24 FF25                 5H730 AA14 AS04 BB14 DD03 FD11                       FD41 FG05

Claims (8)

[Claims] 1. A solar power generation device for boosting the voltage of a solar cell power source by a boosting means, converting the voltage to an AC voltage by a DC-AC converting means, and linking it to a commercial power system, wherein the boosting means is the solar power source. By detecting the output current of the battery power source and the input voltage of the boosting means, and superimposing the offset voltage at the time of startup on the voltage level of the control signal generated by the detected output current and input voltage, A solar power generation device characterized by performing maximum output tracking control for tracking the maximum output power of a solar battery power source. 2. The step-up means is a chopper circuit, and the chopper circuit comprises chopper control means for controlling the voltage of the solar cell at the maximum output power value of the solar cell power source, wherein the chopper control means is the solar cell. The output current Is of the battery power source and the input voltage Es of the capacitor formed at the input of the chopper circuit are detected, and the detected output current Is and the voltage level of the control signal generated by the input voltage Es are detected. The solar power generation device according to claim 1, wherein the maximum output tracking control is performed by superimposing the offset voltage at startup. 3. The maximum output tracking control is performed by the chopper control means by detecting the output current Is.
And based on the input voltage Es, the output power Ps of the solar battery power source is calculated, and the output power Ps is differentiated by the input voltage Es to calculate a differential value (dPs / dEs),
The solar power generation device according to claim 2, which is realized by controlling an output current of the chopper circuit with a target value of the differential value (dPs / dEs) set to zero. 4. The solar power generation device according to claim 2, wherein the offset voltage is variable. 5. The limit value of the offset voltage is set so that the control signal of the chopper control means performs control in the vicinity of the maximum output power value of the solar cell power supply. 4. The solar power generation device according to 4. 6. The chopper control means defines a voltage detection unit that detects a connection point voltage of the commercial power system, and a voltage command table that defines a DC bus voltage command value corresponding to the voltage detected by the voltage detection unit. The solar power generation device according to any one of claims 1 to 5, further comprising: and changing the DC bus voltage in accordance with a change in voltage at the interconnection point. 7. The voltage command table is characterized in that the voltage at the interconnection point and the DC bus voltage command value are first-order increasing functions within a predetermined range.
The solar power generation device described in. 8. The solar power generation device according to claim 1, wherein the DC-AC conversion unit is a PWM control inverter.