JPH02213912A - Power converter for solar battery - Google Patents

Abstract

PURPOSE:To obtain the maximum power out of a solar battery in accordance with the incident light quantity by setting a control current so as to increase the chopping frequency in response to the rise of the DC output voltage of the solar battery. CONSTITUTION:A solar battery 1 supplies the power to an inverter 2 in accordance with the incident light quantity, and a voltage/current controlled oscillator 3 oscillates at a frequency (f) in response to the output voltage Ei of the battery 1 and a control current Ic. The inverter 2 is chopped at the frequency (f) and converts the output direct current Ii received from the battery 1 into an alternating current of a frequency (f). The oscillation frequency (f) increases as the voltage Ei and the current Ic increase as long as the current Ic of a control power supply 31 is set at a proper level. Thus it is possible to obtain the maximum power out of the battery 1 in accordance with the solar radiation value.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a power conversion device for solar cells, and in particular, it is capable of extracting maximum power from a solar cell according to the amount of input light, and moreover, The present invention relates to a power conversion device for solar cells that can also connect a battery to a commercial power source.

(Prior Art) As is well known, solar cells absorb sunlight and generate current, so the generated current or power fluctuates with changes in the amount of solar radiation, and during the night cannot extract power.

For this reason, in solar cell power supply devices currently in practical use, a backup storage battery is usually used in combination to form a so-called floating charging circuit.

With this configuration, charging can be performed during the daytime when there is a lot of solar radiation, so the necessary power can be extracted even at night or when there is little solar radiation due to rain or cloudy weather.

However, in conventional equipment, even when a commonly used lead-acid battery is used as a storage battery, hydrogen gas and oxygen gas are generated, which is not only dangerous, but also requires maintenance such as replenishing the electrolyte. Therefore, it has the disadvantage that it cannot be used in general households or small-scale places.

In addition, other types of storage batteries are not only expensive, but also have problems in that they do not have sufficient capacity.

Furthermore, commercial power (100/200
50/60 cycles), it is desirable to be able to connect such solar cells to a commercial power source.

In order to meet such demands, the present inventor first controlled the oscillation frequency of the voltage controlled oscillator using the output voltage of the solar cell, and used an inverter that was chopping-controlled with this oscillation output to adjust the output DC of the solar cell. A solar cell power conversion device configured to convert current into alternating current at the commercial power frequency was proposed (Japanese Patent Application Laid-Open No. 60-79417). With this device, the output frequency of the inverter is automatically synchronized with the commercial power frequency, so the commercial power source can be used as a backup instead of a storage battery without the need for a special control device, and it has a simple configuration. It is possible to connect a solar cell to a commercial power source, and moreover, it is possible to extract maximum power from the solar cell according to the amount of solar radiation.

(Problem to be Solved by the Invention) However, the proposed device does not have a function to adjust the power generated from the solar cells, as in the case of conventional storage battery backup, and always outputs the maximum power according to the amount of solar radiation. Therefore, in the case of a light load, the surplus power generated by the solar cells will be regenerated to the commercial power source. However, in current commercial power systems, this type of power regeneration is prohibited by law. Furthermore, even when extracting the maximum power from a solar cell according to the amount of solar radiation, the maximum voltage output condition will vary due to temperature changes, aging, etc., but in the proposed device, the output voltage of the solar cell Since it was not possible to move the operating point with respect to the output voltage, there was a problem in that when the above-mentioned change occurred, the maximum output condition could not be adjusted in response to the change.

Therefore, an object of the present invention is not only to enable a solar cell to be connected to a commercial power source under optimal operating conditions such that the maximum power according to the amount of solar radiation can be extracted from the solar cell, but also to
A solar cell that can extract power corresponding to the required load below the maximum output from the solar cell without changing the frequency of the output AC, thus preventing surplus power from being regenerated into the commercial power system. An object of the present invention is to provide a power conversion device.

(Means for Solving the Problems) In order to achieve the above-mentioned object, in the present invention, even if the input power supply voltage fluctuates, the oscillation frequency can be kept constant by adjusting the control current. Equipped with a voltage/current controlled oscillator, this voltage/current controlled oscillator is driven by the output DC of the solar cell, and the AC output of the voltage/current controlled oscillator converts the output DC of the solar cell into AC (commercial frequency). The inverter is chopped and driven, and the control current is adjusted so that the power extracted from the solar cells can be controlled to any value below the maximum output. In addition, the current between the backup commercial power source and the load is monitored, and when regeneration of power from the load to the commercial power source is detected, the control current is adjusted to reduce the power extracted from the solar cells. By controlling
It becomes possible to prevent power regeneration to the commercial power source side. By monitoring the temperature of the solar cell 5 and adjusting the control current according to the rise in temperature, the solar cell can always be operated at maximum output conditions. It is clear that the maximum output condition can be set by similarly performing correction control for aging of the solar cell.

For example, the voltage/current controlled oscillator mentioned above is a pan/current controlled oscillator.
A modified Pan-Allen type oscillator can be used in which a compensation winding is added to the Van-Alien type oscillator to supply a current according to the output voltage of the solar cell.

(Function) In the present invention, since the modified Pan-Allen oscillator as described above is used as an inverter drive signal generator, the oscillation frequency of the modified Pan-Allen oscillator, that is, the output of the inverter, can be adjusted by adjusting the control current. It becomes possible to control the amount of power extracted from the solar cell to a value that corresponds to the required load by moving the operating point regarding the output voltage of the solar cell while making the frequency match the commercial frequency. In addition, even if the operating voltage conditions for extracting the maximum output power from the solar cells fluctuate due to temperature changes or aging, the operating point related to the output voltage of the solar cells can be moved and adjusted to satisfy the maximum output conditions. You will be able to do this.

(Example) The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the basic configuration of the present invention.

Solar cell 1 supplies power to inverter 2 according to the amount of incident light. A voltage/current controlled oscillator 3 (for example, a modified Pan-Allen oscillator to be described later) oscillates at a frequency r depending on the output voltage E1 of the solar cell 1 and the control current 1c. The inverter 2 is chopped at the frequency f and converts the output DC current II from the solar cell 1 into an AC current at the frequency r. As will be described in detail later, if the control current Ic from the control power supply 31 is set to an appropriate value, the oscillation frequency becomes higher as the output voltage El becomes higher and the control current becomes larger.

The output (alternating current) current of the inverter 2 is connected to a commercial power source 5 via an inductor 4. The load 6 is connected to the output side of the inverter 2 or to the commercial power supply 5.

During operation, the terminal voltage of the solar cell 1 is El, and the current 11 generated from the solar cell 1 at this time is
and is supplied to the voltage/current controlled oscillator 3. The voltage/current controlled oscillator 3 has the terminal voltage E1 and the control current I.
The inverter 2 oscillates at a frequency r according to c, and thereby the inverter 2 generates an alternating current voltage Einv (however, the effective value of the fundamental frequency component) having the frequency f.

Therefore, the effective voltage value of the commercial power supply 5 is EBe.

Also, if the inductance of the inductor 4 is L, then from the inverter 2 to the commercial power supply 5 through the inductor 4,
Or, conversely, the voltage P supplied is expressed by the following equation (1), as is well known.

P-(Elnv-Eac/2 rrr L)
sin θ---(1) In the above formula (1),
θ is a phase difference between the AC voltage Einv of the inverter 2 and the AC waveform Eac of the commercial power supply 5.

As can be seen from this equation, the AC voltage Eln of inverter 2
If the phase of v is ahead of that of the AC waveform Eac of the commercial power source 5, power will flow from the inverter 2 side to the commercial power source 5 side, and the load 6 will be supplied with power by the solar cell 1. .

In the present invention, the output frequency of the inverter 2 is
automatically synchronizes to the frequency of The principle will be explained below.

It is now assumed that the voltage/current controlled oscillator 3 oscillates at a frequency r due to the output voltage El and the control current 1e of the solar cell 1, and that the inverter 2 outputs an alternating current voltage Einv with a fundamental frequency f. Furthermore, the phase of the output AC voltage Elnv of the inverter 2 is ahead of that of the commercial power supply 5, and therefore, power flows from the solar cell 1 side to the load 6 or the commercial power supply 5 side via the inductor 4. Assume that there is.

In the second state, when the incident light to the solar cell 1 increases, its output voltage El increases, and accordingly, the oscillation frequency r of the voltage controlled oscillator 3 also tends to increase. As a result, the frequency of the output AC of the inverter 2 also tends to increase, and its phase advances; that is, the phase advance angle of the output AC voltage Einv of the inverter 2 with respect to the voltage Eac of the commercial power supply 5 tends to increase.

Then, as is clear from equation (1) above, the power supplied from the solar cell 1 to the commercial power source 5 through the inductor 4 increases.

Along with this, the current flowing from the solar cell 1 to the inverter 2 increases, so the voltage drop due to the internal resistance of the solar cell 1 increases, which acts to reduce the output voltage El of the solar cell 1. As a result, an increase in the output voltage Ei of the solar cell 1--therefore, an increase in the AC frequency of the inverter 2 is suppressed.

Moreover, contrary to the above, when the incident light to the solar cell 1 decreases, the output voltage El decreases, and accordingly, the oscillation frequency of the voltage controlled oscillator 3 also tends to decrease.

Then, the frequency of the output AC of the inverter 2 also tends to become low, and its phase is delayed.

As a result, the power supplied from the solar cell 1 to the commercial power supply 5 through the inductor 4 decreases.

Along with this, the current flowing from the solar cell 1 to the inverter 2 decreases.

Therefore, the voltage drop due to the internal resistance of the solar cell 1 becomes smaller, which acts to increase the output voltage El of the solar cell 1, and as a result, the output voltage Ei of the solar cell 1 decreases - therefore, the AC frequency of the inverter 2 The decrease in

As described above, even if the amount of light incident on the solar cell 1 changes, the frequency of the output AC voltage Einv of the inverter 2 is
It is automatically held constant and synchronized with the frequency of the commercial power supply 5.

This also means that the output voltage of the solar cell 1 is kept approximately constant, which further brings about the favorable characteristics described below.

The solid line curve in FIG. 2 represents the terminal voltage El of the solar cell 1.
(horizontal axis) and output power P11 (vertical axis) is shown using incident light amount (or incident light energy) as a parameter. As can be seen from this figure, the power that can be extracted from the solar cell 1 not only increases as the incident light energy increases, but also changes depending on the terminal voltage.

Note that at this time, the temperature of the solar cell 1 is a constant value (298'
K).

In other words, even if the incident light energy is constant, the output power will increase as the terminal voltage increases, and if the terminal voltage exceeds a certain value, the output power will actually decrease.In other words, if the output power is There is an optimal terminal voltage such that Furthermore, the optimum terminal voltage is approximately constant (near 16 volts) as seen from FIG.

Therefore, in the embodiment shown in FIG. 1, if the circuit constants of each part are selected so that the output voltage of the solar cell 1 is equal to the optimum terminal voltage, the maximum power corresponding to the amount of incident light at that time is always achieved. You will be able to take it out.

FIG. 3 is a diagram showing a specific example of a circuit according to an embodiment of the present invention. In the figure, the same reference numerals as in FIG. 1 represent the same or equivalent parts.

The first saturable core 7 has a primary winding 8. Feedback winding 9, current control winding 14. Compensation winding 15. and output winding 21.2
4 is wrapped. Further, the second saturable iron core 7a has a primary winding 8a and a feedback winding 9a.

A current control winding 114a, a compensation winding 15a, and output windings 22 and 23 are wound.

Each end of the primary winding 8.8a is commonly connected, and the solar cell 1
Connected to one terminal of The other ends are connected to the collectors of the corresponding transistors 12 and 12a, respectively. The emitters of each of the transistors 12 and 12a are commonly connected and connected to the other terminal of the solar cell 1.

The base of each of the transistors 12.12a is connected to one end of the feedback winding 9, 9a, respectively.
The other end of a is commonly connected through a resistor, and further connected to one terminal of the solar cell 1 through another resistor.

Current control windings 14.14a are connected in series and connected to control power source 31 via resistor 17. Compensation winding 15, L5
a is also connected in series and connected between both terminals of the solar cell 1 via a resistor 18 . Furthermore, between both terminals of the solar cell 1,
Four switch elements 81 to S4 forming inverter 2
is connected as a full bridge. The switch elements 81-S
4, the output windings 21-24 in a known manner and timing.
On/off control is performed by the output of The output AC of the inverter 2 is supplied to a load 6 via an inductor 4. The load 6 is also connected to a commercial AC power supply 5 on the one hand. If necessary, a current detector 33 for detecting the current supplied from the commercial AC power supply 5 to the load 6 and/or a temperature detector 32 for measuring the temperature of the solar cell are provided.

One or both of the outputs of these detectors can be used to control the control current Ic, as described below.

In FIG. 3, each transistor, the saturable core, the -order winding, and the feedback winding constitute a pair of parallel inverters, each of which is connected to the base-emitter circuit of the transistor by the corresponding feedback winding. Self-oscillation is caused by the feedback signal. The oscillation frequency in this case is the control current 1c supplied to the current control winding and compensation winding, and the compensation current I
This can be controlled by controlling the magnitude of s. If the output voltage Ei of the solar cell is constant, the oscillation frequency f is proportional to the control current Ic.

Compensation winding 15.1 from voltage/current controlled oscillator 3 in FIG.
As is clear, the circuit other than 5a corresponds to a known Pan-Allen oscillation circuit. The Pan-Allen oscillation circuit has a characteristic that as the power supply voltage increases, the oscillation frequency decreases in inverse proportion to this. In the invention, the compensation winding 15.1
By adding 5a, the control current 1c can be maintained within a certain limited range, and as the power supply voltage increases,
The voltage/current controlled oscillator 3 has a characteristic that its oscillation frequency also increases. That is, the compensation winding 15.15a is added to the Pan-Allen oscillation circuit to form a so-called modified Pan-Allen oscillation circuit, and the value of the control current Ic is determined by F c /N (where N is the winding 8.14 The number of turns is .15, and Fc is the magnetomotive force applied to the supersaturated magnetic core 7)
A feature of the present invention lies in that the range is set to a range that is not larger than that.

An example of main circuit constants suitable for the embodiment of FIG. 3 is shown in Table 1.

In operation, the voltage-current controlled oscillator or modified Pan-Allen oscillator 3 oscillates at a frequency approximately equal to the mains frequency. The oscillation frequency is the output voltage Ei of the solar cell 1
If is constant, it increases monotonically as the control current Ic increases. In addition, when the control current 1c is constant, the value of the control current 1c is Fc/N (however, N is the winding 8.14.1
5, and Fc is the magnetomotive force applied to the supersaturated magnetic core 7), the power supply voltage Ei
As the oscillation frequency increases, its oscillation frequency also increases monotonically.

1st Part name Number of series solar cells (1) Optimal output voltage saturable iron core (7) (50%NlFe: Excitation current saturation inductance control resistor (17) Transistor current amplification base resistor (2728) Compensation resistor (18) Commercial Power supply frequency inductor (sign) 38 table values te, yv cell delta) Pc/N 4.82mA 1.5a+H 38Ω β 30 560Ω 3Ω Eac 15V fac 60Hz L 94.7m) I Voltage/current controlled oscillator The oscillation output of 3 is output from the output windings 21 to 2.
4, which turns on/off switch elements 81 to S4 of inverter 2 in a predetermined order and timing.
Control off. The AC output of inverter 2 is
), it is supplied to the load 6 via the inductor 4.

When the amount of light that the solar cell 1 receives increases, surplus power that is not consumed by the load tends to be regenerated to the commercial power source.

As mentioned above, such power regeneration is prohibited by law, so when the current flowing from the load to the commercial power source is detected by the current detection means 33 and power regeneration is detected,
The control power source 31 is adjusted to control the control current 1c, and the operating voltage point of the solar cell is moved in a direction that reduces the power extracted from the solar cell.

As can be seen from the Et-Pm characteristic curve shown by the solid line in FIG. It increases as the value increases from 0, but after reaching the maximum value, it decreases again. Therefore, there are generally two operating voltage points suitable for extracting a certain scheduled power: a high voltage point and a low voltage point. From the viewpoint of simply moving the operating voltage point to control the power extracted from the solar cell, it is the same no matter which operating voltage point is adopted.

However, when controlling the control current 1c to shift the operating point voltage, it is better to adopt the lower operating voltage point, as seen from the El-Ic characteristic curve shown by the dotted line in Figure 2. This is advantageous in that sensitivity can be obtained. That is,
A slight change in the control current Ic can greatly shift the operating voltage point and greatly change the extracted power.

When such a lower operating voltage point is adopted, as described above, when power regeneration from the load 6 side to the commercial power supply 5 is detected, the control current 1c is increased to lower the operating voltage point. and reduce the power extracted from the solar cells.

As is well known, the power extracted from a solar cell changes depending on the temperature of the solar cell, and the lower the temperature, the more the generated power increases. Therefore, the temperature of the solar cell 1 is monitored by the temperature detector 32, and when a decrease in temperature is detected, the control current 1c is similarly increased to lower the operating voltage point, and the power extracted from the solar cell is It is desirable to reduce the

Naturally, when a higher operating voltage point is adopted, contrary to the above, the control current Ic is controlled in the direction of decreasing to raise the operating voltage point and reduce the power extracted from the solar cell. .

It goes without saying that the control current 1c may be controlled not only by directly controlling the power supply 31 as described above, but also by controlling the value of the series resistor 17. As the resistor 17, a semiconductor variable resistor or the like is suitable. In addition to the full bridge type exemplified above, the inverter of the present invention may be a half bridge type or a PW inverter.
An appropriate type such as an M (pulse width modulation) type can be used.

Further, as the switch elements constituting the inverter bridge, voltage effect transistors (FETs), gate control thyristors, and the like are suitable.

(Effects of the Invention) As is clear from the above description, according to the present invention, the following effects are achieved.

(1) Maximum electric power can be extracted from the solar cell according to the amount of incident light, and the electric power extracted from the solar cell can be controlled according to the required load amount.

(2 solar cells can be connected to a commercial power source.

If solar cells can be connected to a commercial power source, there will be no need for storage batteries, and when the power from the solar cells runs out, it can be replenished from the commercial power source, which is convenient, and there is almost no need for maintenance. Furthermore, when the power from the solar cells exceeds the required load amount, it is possible to limit the power taken out from the solar cells to prevent surplus power from being regenerated to the commercial power source. Therefore, it can be put to practical use by general electric power consultants.

(a) Maintenance is easy because no storage batteries are used,
It will be widely available to the general public.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the basic configuration of the present invention, and Fig. 2 shows the terminal voltage E1 (horizontal axis) of the solar cell and the output power P.
Fig. 3 is a graph showing the relationship between g and control current Ic (vertical axis) using the amount of incident light (or incident light energy) as a parameter. be. DESCRIPTION OF SYMBOLS 1...Solar cell, 2...Inverter, 3...Voltage/current control oscillator, 4...Inductor, 5...Commercial power supply, 6...Load, 7, 7a...Saturable iron core, 14
゜14a...Current control winding, 15,15a river compensation winding

Claims (6)

[Claims] (1) A solar cell having a pair of output terminals, and a voltage/current controlled oscillator connected to the output terminal and oscillating at a frequency that is a function of the DC output voltage of the solar cell and the control current supplied thereto. an inverter that has a chopping frequency controlled based on the output frequency of the voltage/current controlled oscillator and is supplied with the DC output current of the solar cell and converts it into AC; an AC output of the inverter; an inductor connected to a commercial power source, the control current being set such that the chopping frequency increases as the DC output voltage of the solar cell increases. . (2) The power conversion device for a solar cell according to claim 1, wherein the AC output fundamental frequency of the voltage/current controlled oscillator is substantially equal to the frequency of a commercial power source. (3) The AC output fundamental frequency of the voltage/current controlled oscillator is substantially equal to an integral multiple of the frequency of the commercial power source, and the inverter is of a multiple pulse width modulation type. The power conversion device for solar cells described above. (4) The voltage/current controlled oscillator is a modified Pan-Allen oscillator in which a current control winding is added to the saturable core of a Pan-Allen oscillator whose operating power source is the output of a solar cell. A power conversion device for a solar cell according to claim 1 or 2. (5) a load connected to a connection node between a commercial power source and an inductor, a means for detecting a current between the load and the commercial power source, and a current supplied with the detection output of the current detecting means and flowing through the current control winding. and means for controlling the voltage in response to the detected output of the current detecting means, and moving the operating point regarding the voltage of the solar cell to prevent regeneration of power from the load side to the commercial power source. A power conversion device for a solar cell according to any one of claims 1 to 4. (6) A load connected to a connection node between a commercial power source and an inductor, a means for detecting the temperature of the solar cell, and a detection output of the temperature detecting means is supplied, and the current flowing through the current control winding is controlled at the temperature of the solar cell. Claims 1 to 4 further include means for controlling in response to the detection output of the detection means, and setting an operating point regarding the voltage of the solar cell to a point at which maximum power is obtained. 2. The power conversion device for solar cells according to any one of the items.