JPH0654448A - Power converter for solar cell - Google Patents

Abstract

PURPOSE:To follow up a maximum power of an output of a solar cell and to reduce a loss of a maximum power follow-up converter by so controlling an output of a DC/DC converter that a current value of current detecting means becomes maximum as a special circuit configuration. CONSTITUTION:In order to output maximum power from a solar cell 1, a series circuit of the cell 1, a reverse blocking diode 2 and an input circuit of a DC/DC converter 3 is connected to an output of the converter 3. The output of the converter 3 is connected to a load 4 through current detecting means 7, and an output of a rectifier 6 which inputs a commercial power source 5 is supplied to the load 4. The output of the converter 3 is so controlled that the current value of the means 7 becomes maximum. Thus, an output capacity of the converter 3 becomes smaller than a load output and further its loss is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell power conversion device for efficiently supplying a solar cell output to a load such as a home or office air conditioner (hereinafter referred to as an air conditioner).

[0002]

2. Description of the Related Art The output of a solar cell varies depending on the amount of solar radiation and is unstable, and it is necessary to use a commercial power source as an auxiliary in order to supply a stable power to a load. In this case, the maximum electric power of the solar cell is taken out from the solar cell, and the electric power that is insufficient for the load is supplied from the commercial power source.

The operation of the solar cell will be described below by taking the case where it is directly connected to an air conditioner as a load. FIG. 3 is an explanatory view of the sharing of the air conditioner current consumption, where S1, S2 and S3 represent the output IV characteristics of the solar cell, and C1, C2 and C3 represent the DC voltage characteristics of the air conditioner. Air conditioner D
The C voltage characteristics are shown with the direction of the current reversed from that of the solar cell characteristics. In the figure, S1 is the amount of solar radiation,
S3 is small, S2 is intermediate,
C1 indicates a high commercial voltage, C3 indicates a low commercial voltage, and C2 indicates an intermediate voltage. The intersection of the S curve and the C curve becomes the operating point, and the air conditioner consumption current is shared by the solar cell supply current and the commercial supply current. Is is the solar cell shared supply current, Ic is the commercial power shared supply current, and IL is the air-conditioner consumption current as a load.
= Is + Ic.

FIG. 5 shows the characteristics of the solar cell output power (curve of P) obtained from the IV characteristics of the solar cell (curve of S).
Indicates. As is clear from this, there is a solar cell output voltage that maximizes the output power Ps of the solar cell. The voltage depends on the amount of solar radiation and the temperature of the solar cell.

FIG. 4 is an explanatory diagram of current sharing when the current consumption of the air conditioner is reduced. From FIGS. 3 to 5, there is only one voltage at which the maximum power of the solar cell is constant when the amount of solar radiation and the temperature of the solar cell are constant, but the operating voltage of the solar cell changes due to changes in the air conditioner consumption current and changes in commercial voltage. Deviations from the maximum power point easily occur.

In order to always operate near the maximum power point, a DC / DC converter that fixes the input voltage at the maximum power point while matching the output voltage with the characteristic curve of the commercial power supply is required.
The conventional DC / DC converter is a system that converts all the electric power of the solar cell as shown in FIG. 6, and is capable of following the maximum electric power of the solar cell except for the micro output area of the solar cell. However, if the loss of the DC / DC converter for converting the full output of the solar cell is large, the direct connection method of the solar cell is superior.

FIG. 6 is a circuit configuration diagram of a conventional solar cell power conversion device, in which the output of the solar cell 1 is applied to the input of a DC / DC converter 3 via a reverse current blocking diode 2. The output of the DC / DC converter is connected to the DC circuit of VVVF4, which is the load. The load VVVF4 has a circuit configuration in which the rectified output is supplied from the commercial power source 5 through the rectifier 6. 7 is a current detector. Taking a numerical value that is close to the actual value as an example, assuming that the efficiency of the DC / DC converter is 90% and the output deviation from the maximum power point of the above-mentioned solar cell direct connection method is 10%, the utilization of the solar cell is the same. Becomes If the usage is the same, the cost of the DC / DC converter is less than the direct connection method.

[0008]

If a DC / DC converter for converting the solar cell full output is provided in order to extract the maximum electric power from the solar cell, the same degree as when the solar cell is directly connected due to the loss of the DC / DC converter or There is a problem that only the power less than that can be taken out.

[0009]

[Solution for solving the problems] In order to extract maximum power from a solar cell,
A series circuit with the input circuit of the DC converter is connected to the output of the DC / DC converter, the output of the DC / DC converter is connected to the load via the current detection means, and the output of the rectifier using the commercial power supply as the input is connected to the load. To control the output of the DC / DC converter so that the current value of the current detection means is maximized, thereby maximizing the power following of the solar cell and reducing the loss of the DC / DC converter. be able to.

[0010]

[Function] The input voltage of the DC / DC converter becomes the difference between the solar cell voltage and the load DC voltage, and the power burden on the DC / DC converter can be reduced to 1/10 to 1/4. as a result,
The loss of the DC / DC converter is also reduced to 1/10 to 1/4, and 95% or more of the maximum power of the solar cell can be effectively used.

[0011]

1 is a circuit configuration diagram showing an embodiment of a power conversion device for a solar cell according to the present invention, in which an air conditioner DC circuit in which the voltage of the solar cell 1 is a load and an input circuit of a DC / DC converter 3 are connected. It is applied to the series circuit and supplies a part of the electric power of the solar cell 1 directly to the air conditioner DC circuit of the load, and the remaining electric power is DC.
The DC / DC converter converts the voltage and supplies it to the air conditioner DC circuit. The DC / DC converter may be of any type as long as it can insulate the input from the output and control the output voltage. Reference numeral 2 is a reverse current element diode, 4 is a VVVF load, 5 is a commercial power source, 6 is a rectifier, and 7 is a current detector.

The voltage difference between the solar cell voltage and the load air conditioner DC circuit is applied to the input of the DC / DC converter,
When the converter starts flowing the output current by the pulse width control, the input current of the DC / DC converter also starts to flow, and the solar cell output voltage decreases according to the IV characteristic curve of FIG. Specifically, the DC / DC converter output current control controls the DC / DC
It controls the input current of the DC converter, that is, the output current of the solar cell. The maximum power point can be approximated by the point where the sum of the input current and output current of the DC / DC converter becomes maximum. The reason is that it can be considered that the voltage of the DC circuit of the air conditioner hardly changes even if the current on the solar cell side changes.

FIG. 2 is an explanatory view of the sharing of the load current consumption of the device of the present invention. The voltage applied to the input of the DC / DC converter is the voltage at the maximum power point X and the operating point of the IV characteristic curve S of FIG. This is the difference from the voltage of Y, and at the operating point Y, the areas of the two shaded areas A and B are equal and the characteristic curve C2 of the DC voltage of the air conditioner.
Required as the upper point. However, the DC / DC converter loss is ignored. If not neglected, the operating point will move slightly to the left and the voltage will drop slightly.

The sharing of the load current consumption in this case is as shown in FIG. 2, and Is1 is the solar cell direct sharing supply current, Is2.
Is an indirect solar cell shared supply current through the DC / DC converter, Ic is a commercial power supply shared supply current, and IL is an air conditioner consumption current as a load, and IL = Is1 + I
The relationship is s2 + Ic.

This system is not limited to a solar cell air conditioner, and since the solar cell power and the commercial power are coupled by a DC voltage, it has the feature that it does not generate reverse power flow, and is used as a DC power source by a solar cell. it can.

[0016]

The output capacity of the DC / DC converter is smaller than the load output, and the loss is smaller, so this method has more advantages than the solar cell direct connection method. That is, when the price of the solar cell panel corresponding to the output increase when the DC / DC converter follows the maximum power and the price of the DC / DC converter are compared, the DC / DC converter method is cheaper.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an output conversion device for a solar cell of the present invention.

FIG. 2 is an explanatory diagram of sharing of load current consumption in the case of the present invention.

FIG. 3 is an explanatory diagram of sharing of air conditioner current consumption.

FIG. 4 is an explanatory diagram of current sharing when the current consumption of an air conditioner decreases.

FIG. 5: Output power characteristic diagram of solar cell

FIG. 6 is a circuit configuration diagram of a conventional device.

[Explanation of symbols]

 1 Solar cell 2 Reverse current blocking diode 3 DC / DC converter 4 Load (VVVF) 5 Commercial power supply 6 Rectifier 7 Current detector

Claims (1)

[Claims] 1. A solar cell, a reverse current blocking diode, and DC / DC.
A series circuit with the converter input circuit is connected to the output of the DC / DC converter, the output of the DC / DC converter is connected to the load via the current detection means, and the output of the rectifier with the commercial power supply as the input is connected to the load. A power conversion device for a solar cell, which has a circuit configuration for supplying and controls the output of the DC / DC converter so that the current value of the current detection means is maximized.