JP6236625B2 - Power converter - Google Patents

Description

The present invention relates to a power conversion device that converts power generated by a solar cell into AC power.

Conventionally, the system voltage is detected, and the AC power is controlled so that the difference between the voltage and the peak value of the AC power voltage superimposed on the system is constant. (Patent Document 1)

Some inverters generate AC power to be superimposed on the system, detecting the gate pulse width of the gate pulse signal sent to the inverter, and stopping the inverter when an overvoltage occurs due to the change in the gate pulse width. It was. (Patent Document 2)

Japanese Patent No. 3862320 Japanese Patent No. 3111745

In the one described in Patent Document 1, the voltage of the AC power superimposed on the system also fluctuates in accordance with the fluctuation of the system voltage, so that the voltage of the AC power becomes too high and may be unfavorable for the system.

Moreover, in the thing of patent document 2, since the gate pulse width is made into the reference | standard, when fluctuation | variation arises in the generated electric power of a solar cell, the voltage of the alternating current power superimposed on a system | strain will also fluctuate, and sufficient follow-up of control is possible. In some cases, the device could not be obtained and the device stopped unnecessarily.

The present invention provides an apparatus that considers the stability of the system and the continuity of the operation of the apparatus with respect to such a conventional apparatus.

The present invention increases the generated voltage as the output voltage increases and exceeds the point of maximum generated power.
In the power conversion device that inputs the generated power of the solar cell having the characteristic that the generated power changes to decrease, converts it into alternating current power and superimposes it on the system, when the voltage of the wiring connected to the system exceeds a predetermined value, The control unit that performs control to reduce the generated power by changing the output voltage of the battery includes means for changing the variable range of the output voltage.

In the power conversion device of the present invention, it is possible to continue the power generation by changing the control range when the generated power of the solar cell is controlled.

It is explanatory drawing of the electric circuit which shows the Example of this invention. It is explanatory drawing which shows an example of the characteristic of the solar cell shown in FIG.

In the power conversion device of the present invention, the generated voltage of the solar cell is controlled so that the voltage of the wiring corresponding to the voltage of the system or the voltage of the system does not exceed a predetermined value, and the variable range can be changed. Is.

FIG. 1 is an explanatory diagram of an electric circuit showing the utility of the present invention. Reference numeral 1 denotes a solar cell. As shown in FIG. 2, the generated power increases as the output voltage increases at a predetermined temperature and exceeds the point P of the maximum generated power (corresponding to the rated generated power at the predetermined temperature). It has a characteristic that power is reduced. When the generated voltage is V1, the generated power is at the point P1, and when the generated voltage is V2, the generated power is at the point P2. This solar cell is configured to have a predetermined rated output by connecting a plurality of solar cells in series and in parallel.

Reference numerals 2 and 3 are contact pieces of a DC relay that are opened and closed in conjunction with each other, and the generated power (output) of the solar cell is taken into the power converter through the contact pieces 2 and 3. The contact pieces 2 and 3 are closed when the generated power of the solar cell 1 is a predetermined value or more. That is, it is closed while the power converter is outputting AC power. In addition, the contact pieces 2 and 3 are opened at the time of abnormality.

Reference numeral 4 denotes a direct current detector, which detects the current value from the generated power of the solar cell 1 taken in through the contact pieces 2 and 3, and the detected value is taken into the control unit 6. Reference numeral 5 denotes a DC voltage detector, which similarly detects the voltage value from the generated power of the solar cell 1, and the detected value is taken into the control unit 6. The controller 6 calculates and stores the generated power of the solar cell from the product of the current value and the voltage value detected by these detectors.

Reference numeral 7 denotes a DC booster circuit, which boosts the generated power (DC power) from the solar cell 1 obtained through the contact pieces 2 and 3, and includes a reactor 8, a switching element 9 such as an FET or a transistor, and a diode 10. And a smoothing capacitor 11 for switching the switching element 9 with PWM (
A general-purpose three-terminal type booster circuit that performs boosting by controlling the pulse width modulation is configured.

In PWM control, an output obtained by modulating a carrier wave (for example, a triangular wave) with a modulated wave (constant voltage level) is supplied to the switching element 9 as a signal, and the duty that becomes an ON signal within the period of the carrier wave is modulated wave. Control by changing the constant voltage level. For example, the on-duty can be increased if the constant voltage level of the modulation wave is lowered, and the on-duty can be shortened if the constant voltage level is increased. If this on-duty is increased, the step-up ratio is increased and a high voltage can be obtained. The output voltage of the DC booster circuit 7 (hereinafter referred to as intermediate voltage) is detected by the intermediate voltage detector 12 and stored in the control unit 6. Note that the control unit 6 may be configured to directly calculate the on-duty periodically and supply the on-signal to the switching element 9.

The constant voltage level of the modulated wave, that is, the boost ratio of the DC boost circuit 7 is the product of the current value detected by the DC current detector 4 and the DC voltage value detected by the DC voltage detector 5, that is, the generated power of the solar cell 1. Is controlled to increase and decrease so as to reach a maximum value (point P shown in FIG. 2). The DC booster circuit 7 changes the output voltage of the solar cell 1 because the impedance viewed from the solar cell 1 side is changed by changing the on-duty. Therefore, the output voltage of the solar cell 1 changes on the characteristics shown in FIG. 2 by changing the step-up ratio.

If the DC voltage VP detected by the DC voltage detector 5 is increased to the DC voltage V1 when the solar cell 1 is generating the maximum generated power, the generated power of the solar cell 1 is reduced to the point P1, and similarly the DC voltage is detected. If the voltage VP is lowered to the DC voltage V2, the generated power of the solar cell 1 is reduced to the point P2.

Reference numeral 13 denotes an inverter circuit, in which four switching elements are configured in a single-phase bridge shape, and each switching element is turned on / off by a switching signal obtained by modulating a carrier wave (for example, a triangular wave) and a modulation wave (for example, a sine wave). It operates to convert DC power to AC power (pseudo sine wave). This AC power (pseudo sine wave) is superposed on the system 19 as single-phase AC power by removing or attenuating the high frequency component and direct component by the filter circuit 14 composed of a reactor and a capacitor.

15 is an AC current detector (for example, CT (current transformer)), 16 is an AC voltage detector, and 17 and 18 are contact pieces of a relay that is closed when the power converter performs system interconnection.
The AC current detector 15 and the AC voltage detector 16 are for detecting the current and voltage on the wiring connected from the filter circuit 14 to the system 19, and since this current is the current supplied to the system by the power converter, this current and The product with this voltage corresponds to the power generated by the solar cell 1 (when there is no conversion loss). The inverter circuit 13 changes the modulation rate (amplitude ratio between the carrier wave and the modulated wave) so that the detection current of the AC current detector 15 becomes a current corresponding to the generated power of the solar cell 1 and is output from the inverter circuit 13. The amplitude (voltage) of the pseudo sine wave is controlled.

The control unit 6 protects the current supplied to the system 19, that is, the current value detected by the AC current detector 15, so that the voltage detected by the AC voltage detector 16 does not become higher than a predetermined voltage (predetermined value). The operation can be performed by changing the on-duty of the switching element 9 of the DC booster circuit 7, that is, the boost ratio. Therefore, if the generated power of the solar cell 1 is, for example, the point P, the output voltage of the solar cell 1 is set to VP so that it moves to the point P1 or P2.
To V1 or V2. If the generated power of the solar cell 1 decreases, the current supplied to the grid 19 also decreases and the voltage detected by the AC voltage detector 16 also decreases.

The voltages V1 and V2 are gradually increased or decreased according to the difference between the voltage detected by the AC voltage detector 16 and the predetermined voltage, and are varied until the detected voltage does not exceed the predetermined voltage. The variable width may be a constant voltage fluctuation width or a different voltage fluctuation width. An upper limit value is set for the voltage V1, and a lower limit value is set for the voltage V2. When the power generation voltage of the solar cell 1 reaches the voltages V1 and V2, the voltage V1 and the voltage V2 are maintained. Therefore, the output voltage of the solar cell 1 is controlled to fluctuate within the variable range of the voltage V1 to the voltage V2.

When the voltage detected by the AC voltage detector 16 exceeds the predetermined voltage in a short time, the output voltage of the solar cell 1 is varied to the voltage V1 side to quickly reduce the generated power of the solar cell 1 and the AC voltage. When the voltage detected by the voltage detector 16 slowly exceeds the predetermined voltage, the generated power of the solar cell 1 is slowly decreased by changing the voltage to the voltage V2 side. In this case, the variable range of the output voltage of the solar cell 1 can be set to the variable range of the voltage VP to the voltage V1 or the voltage VP to the voltage V2.

A switch 20 changes the variable range of the voltage V1 and the voltage V2. For example, the output voltage corresponding to half of the generated power at the point P at which the values of the voltage V1 and the voltage V2 become the rated output on the characteristic shown in FIG. 2 and the generated power is substantially zero (converted to AC power) The output voltage is equivalent to a value lower than the minimum generated electric power required for the output. The voltage V1,
The variable range of the voltage V2 is not limited to this value and the number of switching, and can be arbitrarily changed. For example, the output voltage corresponding to 2/3 of the generated power at the point P when the voltage detected by the AC voltage detector 16 exceeds a predetermined voltage or the output voltage corresponding to the generated power of 4/5 is switched. It may be added to the 20 types of switching selection.

Further, the switch 20 may be a manual operation switch as shown in FIG. 1, or the control unit 6 can be configured to automatically switch according to control. In the former case, when the voltage detected by the AC voltage detector 16 frequently exceeds a predetermined voltage, switching is made so that the variable range of the output voltage becomes narrow so that the generated power of the solar cell 1 does not decrease too much. In the latter case, when the voltage detected by the AC voltage detector 16 frequently exceeds a predetermined voltage, the output voltage is automatically changed when the number of times exceeds a certain value for a predetermined period. Switching is performed so that the range is narrowed, and control is performed so that the generated power of the solar cell 1 does not decrease too much. That is, the power generation of the solar cell 1 can be stabilized and continued while suppressing the voltage increase of the system 19.

In the above embodiment, the DC booster circuit 7 is not limited to the non-insulated type as shown in FIG. 1, but can also be constituted by an insulated type using a booster transformer, and the inverter circuit 13 has a neutral point. Any circuit configuration that can convert DC power into AC power, such as a clamp method, may be used.

In the power conversion device configured as described above, when the system voltage increases, the generated power of the solar cell is decreased to suppress the increase in the system voltage, and the reduction range is changed to reduce the power generation of the solar cell. It can ensure continuity.

As mentioned above, although one Embodiment of this invention was described, the above description is for making an understanding of this invention easy, and does not limit this invention. It goes without saying that the present invention can be changed and improved without departing from the gist thereof, and that the present invention includes equivalents thereof.

DESCRIPTION OF SYMBOLS 1 Solar cell 4 DC current detector 5 DC voltage detector 6 Control part 7 DC booster circuit 13 Inverter circuit 15 AC current detector 16 AC voltage detector 20 Switch

Claims (2)

A power conversion device that inputs the generated power of a solar cell having a characteristic that the generated power increases as the output voltage increases and exceeds the point of maximum generated power, and then the generated power changes to decrease, and converts it into AC power and superimposes it on the system In
The output voltage of the solar cell is set to the output voltage so that the generated power of the solar cell is maximized.
It has a control unit that changes within a variable range,
Wherein, when the voltage of the wiring connected to the system exceeds a predetermined value, the power conversion device according to claim Rukoto reduce the generated power by changing the variable range. The solar cell has a characteristic that a change in the generated power with respect to the increase in the output voltage after the point is larger than a change in the generated power with respect to the increase in the output voltage before the point of the maximum generated power. The power converter according to claim 1, wherein when the power is decreased, the output voltage of the solar cell is increased.

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