JPH09117153A - Inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high frequency link system inverter being driven through solar battery in which an insulating transformer is prevented from being saturated by abrupt variation of current command value. SOLUTION: An inverter main circuit 6 is controlled through a main control circuit 7 and a PWM control circuit 8. After generating a voltage command value for bringing the operating voltage of solar battery close to an optimum level, the main control circuit 7 generates a command value Io of operating current for solar battery based on the difference of solar battery operating voltage from a voltage command value. Based on the current command value, the PWM control circuit 8 generates driving signals G1, G2 to be fed to a high frequency push-pull inverter circuit 10. If the voltage difference exceeds a specified threshold level, the main control circuit 7 sustains the set current variation at a specified upper limit when the current command value is generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device for converting a direct current output obtained from a solar cell into an alternating current output for reverse flow to a commercial power system.

[0002]

2. Description of the Related Art In recent years, a solar power generation system as shown in FIG. 6 has been put into practical use. Solar cells in the system
The DC output obtained from (1) is converted to an AC output through the inverter main circuit (2) and the inverter control circuit (4) and then supplied to the domestic load (5), and the surplus power is supplied to the commercial power system. Reverse flow is made to (3).

As the inverter main circuit (2), a low frequency link system is generally used in which the DC output of the solar cell is subjected to pulse width modulation (PWM) by switching the system frequency (50 Hz or 60 Hz). The isolation transformer provided in the latter stage of the inverter main circuit is driven at a low frequency, and therefore has a drawback that it becomes large. On the other hand, the high frequency link type inverter main circuit shown in FIG.
(6) is equipped with a high frequency push-pull inverter circuit (10) that performs pulse width modulation on the DC output of the solar cell by high frequency switching of 20 to 40 kHz, and a high frequency transformer (11) for insulation at the subsequent stage. It is installed, and the output pulse obtained from the secondary side of the high frequency transformer (11) is converted into a sine wave of the system frequency by the rectifier circuit (12), the full bridge folding circuit (13) and the filter circuit (17). After that, it is output to the commercial power system. Since the high frequency transformer (11) is driven at a high frequency, it can be miniaturized.

By the way, the inverter control circuit shown in FIG.
As the control method of (4), the maximum power point tracking control is adopted in which the operating point of the solar cell (1) is gradually changed toward the optimum operating point where the maximum power can be obtained. In the maximum power point tracking control system, the output characteristics (I
-V characteristic), first, the operating voltage V of the solar cell
A voltage command value Vo for making n close to the optimum operating voltage is created. Next, the solar cell operating voltage Vn and the voltage command value V
A command value Io of the operating current of the solar cell is created based on the deviation ΔV from o. In this case, it is possible to obtain the current command value Io corresponding to the voltage command value Vo based on the output characteristic curve shown in FIG. 2, but the output characteristics of the solar cell are constantly changing depending on the amount of solar radiation and the temperature at that time. Therefore, the voltage deviation ΔV and the current change amount ΔI are conventionally changed.
7 is approximated by a fixed correspondence relationship as shown in FIG. 7, and the current change amount ΔI is determined from the voltage deviation ΔV based on the correspondence relationship.

Then, the solar cell operating current In at that time
Is added to the current change amount ΔI determined as described above,
The current command value Io is created. Then, based on the current command value Io, the high frequency push-pull inverter circuit (1
PWM control of 0) is performed.

[0006]

However, in the conventional inverter control circuit (4), as shown in FIG. 7, the current change amount ΔI increases proportionally as the voltage deviation ΔV increases. Therefore, for example, when a large voltage deviation ΔVb is set by abrupt change of the optimum operating point of the solar cell, the current change amount Δ is correspondingly increased.
Ib also increases, and the current command value sharply increases. As a result, as shown in FIG. 8 (a), the on period (pulse width) of the PWM on / off pulse is rapidly expanded from the width W to the width W'in the figure, and due to the expansion of this pulse width, the high frequency transformer (11) Is DC biased, and the high frequency transformer (11) is saturated. As a result, 1 of the high frequency transformer (11)
The current Im (see FIG. 1) flowing into the next winding sharply increases as shown in FIG. 8 (b), and an excessive current Ip exceeding 100 A is exceeded.
Will flow. Therefore, not only the circuit element on the primary side is destroyed by this excessive current, but also the circuit element on the secondary side may be destroyed by the excessive current induced on the secondary side.

An object of the present invention is to prevent breakdown of circuit elements in advance in an inverter device of a high frequency link system using a solar cell as a power source, by preventing saturation of an insulating transformer due to a rapid change of a current command value. It is to be.

[0008]

An inverter device according to the present invention is a primary side inverter circuit for performing pulse width modulation on a DC output of a solar cell by switching a frequency higher than a system frequency, and an output pulse of the primary side inverter circuit. Side inverter circuit that converts the sine wave to the sine wave of the system frequency and outputs it to the commercial power system, an insulation transformer interposed between the primary side inverter circuit and the secondary side inverter circuit, and inverter control that controls both inverter circuits It has a circuit and. Here, the inverter control circuit includes a current command means for creating a current command value for bringing the operating point of the solar cell close to the optimum operating point, and a control means for controlling the primary side inverter circuit based on the current command value. The current command means sets a current change amount that does not exceed a certain upper limit value regardless of the deviation of the operating point of the solar cell from the optimum operating point.

In the above inverter device, when the deviation of the operating point of the solar cell from the optimum operating point is relatively small,
A current change amount that is substantially proportional to the shift amount of the operating point is set, and as a result, the operating point of the solar cell gradually approaches the optimum operating point. On the other hand, when the deviation of the operating point of the solar cell from the optimum operating point becomes large, the current change amount is not increased or decreased and is maintained at a constant upper limit value. here,
Saturation of the insulating transformer can be prevented by setting a current change amount that does not saturate the insulating transformer as a fixed upper limit value. After that, after the operating point of the solar cell approaches the optimum operating point by setting the current changing amount, the current changing amount is set according to the deviation amount between the current operating point of the solar cell and the optimum operating point as described above. Then, the operating point of the solar cell is finally set to the optimum operating point.

In another configuration of the present invention, the inverter control circuit includes voltage command means for creating a voltage command value for bringing the operating voltage of the solar cell close to the optimum operating voltage, and the voltage of the solar cell operating voltage. The current command means for creating a command value of the operating current of the solar cell based on the deviation from the command value, and the control means for controlling the primary side inverter circuit based on the current command value, the current command means, When the voltage deviation exceeds a predetermined threshold value, the amount of current change to be set when creating the current command value is maintained at a fixed upper limit value.

In the above inverter device, when the voltage deviation is smaller than the predetermined threshold value, the amount of change in current is set in proportion to the voltage deviation, and as a result, the operating point of the solar cell gradually becomes the optimum operating point. Will approach. In contrast,
When the voltage deviation exceeds a predetermined threshold value, the amount of change in current is not increased or decreased and is maintained at a constant upper limit value. Here, if a current change amount that does not saturate the insulation transformer is set as the fixed upper limit value, the saturation of the insulation transformer can be prevented. After that, when the operating point of the solar cell approaches the optimum operating point and the voltage deviation becomes smaller than the predetermined threshold value by the setting of the current change amount, the current change amount according to the voltage deviation is set as described above. Finally, the operating point of the solar cell will be set to the optimum operating point.

In a specific configuration, the inverter control circuit has a maximum power point tracking function that gradually changes the operating point of the solar cell toward the optimum operating point at which the maximum power can be obtained. Control the pulse width of the primary side inverter circuit. According to this specific configuration, the maximum electric power can always be obtained regardless of environmental conditions such as the amount of solar radiation and the temperature.

[0013]

According to the inverter device of the present invention,
Since the saturation of the insulation transformer due to the abrupt change of the current command value is prevented, there is no fear that the circuit element will be destroyed.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. The inverter device according to the present invention, as shown in FIG. 1, has a pair of input terminals (15) for inputting a DC input (for example, DC200V) from a solar cell.
(15) and the AC output that should be supplied to the commercial power system (for example, A
A pair of output terminals (16) (16) for taking out C200V)
And a high-frequency push-pull inverter circuit (10), a high-frequency transformer (11), a rectifier circuit (12), a full-bridge folding circuit (13) and a filter circuit (17) are connected in series to form a high-frequency push-pull inverter circuit. (10) primary side inverter circuit, rectifier circuit (12), full bridge folding circuit (13)
The filter circuit (17) is used as a secondary side inverter circuit to form a high frequency link inverter in which both inverter circuits are insulated by the high frequency transformer (11).

A first current sensor (9) is attached to the line from one DC input terminal (15) to the high frequency push-pull inverter circuit (10), and one AC output from the full bridge folding circuit (13). Second on the line leading to terminal (16)
The current sensor (14) is installed. A solar cell operating voltage Vn obtained from a pair of DC input terminals (15) (15),
Solar cell operating current I obtained from the first current sensor (9)
n, the inverter output voltage Sa obtained from the pair of AC output terminals (16) (16), and the inverter output current Sb obtained from the second current sensor (14) are the main control circuit (7 ), And the current command value Io is created. The current command value Io is supplied to the PWM control circuit (8) composed of a digital signal processor, whereby signals G1 and G2 for driving the high frequency push-pull inverter circuit (10) are created.

FIGS. 5 (a) to 5 (e) show the manner of signal processing in the process in which the DC input from the solar cell is converted into the AC output by the inverter main circuit (6). That is, the DC input shown in FIG. 5 (a) is switched by the high frequency push-pull inverter circuit (10) to a switching frequency of 20 to 40 kHz.
By receiving the PWM control of z, the modulated pulse shown in FIG. 5B is created. The modulated pulse is rectified by the rectifier circuit (12).
After being rectified as shown in FIG. 5 (c) by the full bridge folding circuit (13) as shown in FIG. 5 (d), the system frequency (5
The switching frequency is returned to 0 Hz or 60 Hz, and further converted through the filter circuit (17) into the AC output of the system frequency shown in FIG. 5 (e).

The main control circuit (7) shown in FIG. 1 has a maximum power point tracking function for gradually changing the operating point of the solar cell toward the optimum operating point where the maximum power can be obtained. That is, the output power is calculated from the output voltage Sa and the output current Sb of the inverter main circuit (6), and the voltage command value for defining the operating voltage is increased or decreased by a very small amount to determine whether the output power is increased or decreased. By changing the voltage command value in the direction in which the output power increases, the operating point of the solar cell is gradually approached to the optimum operating point.

In the maximum power point tracking operation, the main control circuit
In (7), first, the voltage command value Vo for making the operating voltage of the solar cell close to the optimum operating voltage is created, and the deviation ΔV of the solar cell operating voltage Vn from the voltage command value Vo is calculated. Next, the main control circuit (7) uses the relationship between the voltage deviation ΔV and the current change amount ΔI shown in FIG. 3 to calculate the calculated voltage deviation ΔV.
The current change amount ΔI is derived from
The current command value Io is created by adding the current change amount ΔI to. The voltage command value Vo is 500
The current command value Io is created in a cycle of 50 ms.

The voltage deviation ΔV and the current change amount ΔI shown in FIG.
In the range where the voltage deviation ΔV is smaller than a predetermined threshold value ΔVa, the proportional relation: ΔI = f (Δ
However, when the voltage deviation ΔV exceeds the threshold value ΔVa, the current change amount ΔI is maintained at a constant limit value ΔIa. Therefore, when the voltage deviation ΔV is smaller than the predetermined threshold value ΔVa, the current variation ΔI corresponding to the magnitude of the voltage deviation ΔV is obtained, but when the voltage deviation ΔV exceeds the threshold value ΔVa, the voltage deviation ΔV becomes large or small. Regardless of current variation Δ
I will be set to a constant limit value ΔIa.

Here, the upper limit value ΔIa of the current change amount is the current change amount ΔI at which the high frequency transformer (11) is saturated.
It is set to a value smaller than s (see FIG. 3). For example, when the voltage deviation ΔVa is 17 V or more, the current change amount ΔIa is maintained at 1000 hexa (3.7 A). As a result, the DC bias magnetism of the high frequency transformer (11) is suppressed, and the full bridge folding circuit (13) and full bridge folding circuit (1
The destruction of the circuit element of 3) is prevented in advance.

FIG. 4 shows a specific procedure for creating a current command value for the main control circuit (7). First, in step S1,
The absolute value of the difference between the operating voltage Vn and the voltage command value Vo is calculated to obtain the voltage deviation ΔV. Next, in step S2, it is determined whether or not the voltage deviation ΔV is smaller than a predetermined threshold value ΔVa, and if YES, the process proceeds to step S3 to change the current according to a predetermined functional expression ΔI = f (ΔV). Calculate the quantity ΔI. On the other hand, when the voltage deviation ΔV is equal to or larger than the predetermined threshold value ΔVa, the process proceeds to step S4 and the current change amount ΔI is set to the constant limit value ΔIa.

Then, in step S5, it is determined whether or not the operating voltage Vn of the solar cell is smaller than the voltage command value Vo. If YES, the process proceeds to step S6, and the current change amount ΔI is subtracted from the current command value Io. Then, a new current command value Io is created. On the other hand, when the operating voltage Vn is the voltage command value Vo
In the above case, the process proceeds to step S7, and the current change amount ΔI is added from the current command value Io to create a new current command value Io.

The current command value Io created in this way
Is supplied to the PWM control circuit (8) shown in FIG. In response to this, the PWM control circuit (8) creates drive signals G1 and G2 to be sent to the high frequency push-pull inverter circuit (10). As a result, the high frequency push-pull inverter circuit (10) is driven. As a result, the DC input terminals (15) (1
The DC power input to 5) is converted into AC by the signal processing shown in Fig. 5 (a) to (e), and AC power of the system frequency is obtained from the AC output terminals (16) (16). Will be done.

The description of the above embodiments is for the purpose of explaining the present invention, and should not be construed as limiting the invention described in the claims or reducing the scope thereof.
In addition, the configuration of each part of the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made within the technical scope described in the claims.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an inverter device according to the present invention.

FIG. 2 is a graph showing output characteristics of a solar cell.

FIG. 3 is a graph showing a relationship between a voltage deviation and a current change amount set in the inverter device of the present invention.

FIG. 4 is a flowchart showing a procedure for creating a current command value.

FIG. 5 is a series of waveform diagrams illustrating a signal processing process by the inverter device.

FIG. 6 is a block diagram showing a configuration of a solar power generation system.

FIG. 7 is a graph showing a relationship between a voltage deviation and a current change amount set in a conventional inverter device.

FIG. 8 is a graph showing measured waveforms of a PWM on / off pulse and a current flowing into a high frequency transformer in a conventional device.

[Explanation of symbols]

 (1) Solar cell (6) Inverter main circuit (7) Main control circuit (8) PWM control circuit (10) High frequency push-pull inverter circuit (11) High frequency transformer (12) Rectifier circuit (13) Full bridge folding circuit (17) ) Filter circuit

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Nio Togashi 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Electric Co., Ltd. (72) Inventor Masahiro Maekawa 2-5 Keihan Hondori, Moriguchi City, Osaka Prefecture No. 5 Sanyo Electric Co., Ltd.

Claims (4)

[Claims] 1. A primary side inverter circuit that performs pulse width modulation on the DC output of a solar cell by switching at a frequency higher than the system frequency, and commercial power by converting the output pulse of the primary side inverter circuit into a sine wave of the system frequency. An inverter device comprising a secondary-side inverter circuit for outputting to a grid, an insulating transformer interposed between a primary-side inverter circuit and a secondary-side inverter circuit, and an inverter control circuit for controlling both inverter circuits. The control circuit comprises a current command means for creating a current command value for bringing the operating point of the solar cell close to the optimum operating point, and a control means for controlling the primary side inverter circuit based on the current command value. The means sets a current change amount that does not exceed a certain upper limit value regardless of the deviation of the operating point of the solar cell from the optimum operating point. An inverter device characterized in that 2. A primary side inverter circuit that performs pulse width modulation on the DC output of a solar cell by switching at a frequency higher than the system frequency, and commercial power by converting the output pulse of the primary side inverter circuit into a sine wave of the system frequency. An inverter device comprising a secondary-side inverter circuit for outputting to a grid, an insulating transformer interposed between a primary-side inverter circuit and a secondary-side inverter circuit, and an inverter control circuit for controlling both inverter circuits. The control circuit is a voltage command means for creating a voltage command value for bringing the operating voltage of the solar cell close to the optimum operating voltage, and a command value of the operating current of the solar cell based on the deviation from the voltage command value of the solar cell operating voltage. And a control means for controlling the primary side inverter circuit based on the current command value. An inverter device, characterized in that, when the voltage deviation exceeds a predetermined threshold value, the current change amount to be set when creating the current command is maintained at a constant upper limit value. 3. The inverter device according to claim 1, wherein the upper limit value of the current change amount is set to a value such that the insulation transformer is not saturated even when the upper limit value is set. 4. The inverter control circuit has a maximum power point tracking function that gradually changes the operating point of the solar cell toward the optimum operating point at which maximum power can be obtained, and based on the function, the primary side inverter circuit is provided. 4. The inverter device according to claim 1, wherein the pulse width is controlled.