JP3234908B2 - Inverter device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter for converting DC power of a DC power supply such as a solar cell into AC power, and more particularly, to a control for determining whether or not to start the inverter.

[0002]

2. Description of the Related Art In an inverter device, when determining whether or not to start the inverter device (hereinafter referred to as "start control"), a DC power supply (solar cell) output provides an output sufficient to start the inverter. You need to check if you have one.

[0003] As a method of confirming the output of a DC power supply (solar cell), the voltage of the output of the DC power supply (solar cell) is conventionally known as
There is a method of monitoring whether or not a set value (a voltage value necessary and sufficient for starting the inverter) is exceeded.

However, in this method, there is a possibility that a phenomenon (a chattering phenomenon) in which starting and stopping are repeated may occur. That is, while the output of the DC power supply (solar cell) fluctuates depending on the presence or absence of the connection of the load, in this method, the output voltage (open voltage) of the DC power supply (solar cell) is not connected to the load. Is monitoring. Therefore, when the inverter device is started with the output voltage slightly higher than the set value, the load is connected to the solar cell by starting the inverter, and the solar cell output voltage changes from the open-circuit voltage side to the short-circuit current side. , And falls below the set value. When this is detected, the inverter startup is immediately stopped. Then, when the inverter device is stopped, the DC power supply (solar cell) enters a no-load state, and its output voltage rises again and exceeds the set value. Then, upon detecting this, the inverter device is restarted. The phenomenon of repeated starting and stopping in this way (chattering phenomenon)
Had occurred.

In order to prevent such a phenomenon, conventionally, there has been proposed a method of providing a hysteresis width to the set value or providing a timer to delay the start of the inverter.

However, even with these methods, although the number of chattering phenomena can be reduced, they cannot be completely prevented. Furthermore, even if a sufficient output is output from the DC power supply (solar cell), it takes time until the inverter device starts up, which hinders the effective use of the DC power supply (solar cell). Was.

Therefore, conventionally, Japanese Patent Application Laid-Open No. 60-8311
As shown in No. 5, when the inverter is stopped, at least one set of the bridges of the inverter bridge is short-circuited to form a closed circuit, and the short-circuit current of the inverter output flowing through the closed circuit is detected to detect the sun. A method of monitoring the battery output and performing startup control (hereinafter referred to as a first conventional example) has been considered. Further, Japanese Unexamined Patent Application Publication No.
As shown in Japanese Patent No. 243826, there has been proposed a method of providing startup control by providing an AC switch and an AC load on the AC output side of an inverter (hereinafter, referred to as a second conventional example). These conventional examples will be described below.

As shown in FIG. 9, a first prior art inverter device 50 converts a DC power output from a solar cell 51 into an inverter bridge 53 controlled by a control circuit 52.
The same phase and frequency 50 as the commercial power system 54
/ 60 Hz to the commercial power system 54
To be supplied.

A DC input current detector 55 for measuring the current of the solar cell output input to the inverter device 50 is provided at a stage preceding the inverter bridge 53. Also,
At the subsequent stage of the inverter bridge 53, an inverter output current detector 56 for detecting the current of the inverter output, and a connection relay 5 for connecting and disconnecting from the commercial power system 54 side.
7 are provided.

[0010] The inverter device 50 thus configured
Then, when the inverter stops, the inverter bridge 5
The switching elements (Q1 and Q2, or Q3 and Q4) constituting at least one set of bridges of No. 3 are short-circuited. Then, the DC power is generated by the solar cell 51, the short-circuit current I _in the closed circuit formed by the short circuit of the switching element flows, and detects the short-circuit current I _in the DC input current detector 55, the control It is input to the short-circuit current comparison unit 59 of the circuit 52. In the short-circuit current comparing section 59, the short-circuit current I
_{When in} exceeds a preset threshold, the solar cell 51
Is determined to be large enough to operate the inverter device 50, the short circuit of the inverter bridge 53 is stopped, the inverter bridge 53 is turned on / off, and the inverter operation is started. Further, the interconnection relay 57 is connected to connect the inverter device 50 to the commercial power system 5.
Run to 4

The on / off control of the inverter bridge 53 is performed as follows.

In a PWM modulation control unit 60 in the control circuit 52, an error between the current command signal _Iref and the inverter output current signal _Iout detected by the current detector 56 is amplified to form an error amplified signal. Then, PWM modulation control is performed from the error amplified signal and the carrier signal, and the generated pulse train signal is output to the gate drive signal generation unit 61, and the four switching elements Q1 to Q4 of the inverter bridge 53 are output.
Q4 is normally turned on / off to convert DC power into AC power.

Next, a second conventional inverter device 70 will be described.
Will be described with reference to FIG. The inverter device 70 according to the second conventional example has basically the same configuration as the inverter device 50 according to the first conventional example shown in FIG. 9, and the same parts are denoted by the same reference numerals. are doing. Further, the inverter operation of the inverter device 70 is also the same as the first operation described above.
The description is omitted because it is the same as the conventional example.

In the inverter device 70, a DC capacitor 71 for suppressing a change in input power to the inverter device 70 is connected to a stage preceding the inverter bridge 53.
Further, at the subsequent stage of the inverter bridge 53, an AC switch 72 for starting the inverter and an AC load 73, which are features of this conventional example, are connected.

The inverter device 70 thus configured
Then, the DC input voltage Vin detected at both ends of the DC capacitor 71 is input to the DC voltage comparison unit 75 of the control circuit 74, where the first threshold value J ₁ and the second threshold value J ₁ set in advance are set. ₂ (J ₁ <J ₂ ) is compared with the DC input voltage Vin. Then, the DC input voltage Vin becomes the first threshold value J ₁ or more, when the DC voltage comparator 75 detects,
The AC switch 72 is closed, and in this state, the inverter bridge 53 is turned on / off to operate the inverter.
The AC power converted by the inverter device 70 is supplied to the AC load 73 and consumed there because the AC switch 72 is closed.

[0016] Then, the DC input voltage V _in is the second threshold value J
When ₂ (J _l <J ₂₎ DC voltage comparing unit 75 that is larger than is detected, it is determined that the output of the solar cell 51 has reached a sufficient size to start the inverter 70, AC The switch 72 is opened and the interconnection relay 57 is closed to connect the inverter device 70 to the commercial power system 54.

[0017]

However, the first and second prior art examples thus improved have the following problems.

In the first conventional example, a dedicated circuit component such as a DC input current detector 55 is required to control the start of the inverter, and the number of components is increased accordingly, and the structure is simplified and downsized. This has been an obstacle in reducing weight and further reducing costs.

Further, after the power failure occurs in the commercial power system 54 during the daytime and the inverter device 50 stops, the power failure is restored and the inverter device 50 attempts to restart. A large current may suddenly flow through a closed circuit formed by the short circuit, possibly damaging the switching element and the like.

In the second conventional example, start-up control is performed by measuring a DC input voltage that requires almost no additional circuit components, and the number of components is reduced by that much compared to the first conventional example. Can do it. Further, structurally, by adjusting the load capacity of the AC load 73, it is possible to prevent damage to the components due to the large current described in the problem of the first conventional example.

However, in order to prevent damage to components due to a large current, it is necessary to use an AC load 73 having a large load capacity. However, the AC load 73 is a component that becomes larger, heavier, and more expensive in proportion to the magnitude of the load capacity. Therefore, in order to prevent damage to the component due to a large current, the structure of the inverter device 70 is required. Simplified, smaller, lighter,
There was a problem that cost reduction was sacrificed.

The present invention has been made in order to solve such a problem, and has as its object to enhance the safety at the time of starting without incurring a complicated structure.

[0023]

The invention according to claim 1 of the present invention converts the power of a DC power supply such as a solar cell into AC power by opening and closing a switching circuit, and supplies the AC power to a load or an existing commercial power system. An inverter device for supplying, when an inverter output rises, an inverter short-circuit means for short-circuiting the inverter output, and a current for gradually increasing a current flowing through a closed circuit formed by the short-circuit of the inverter output from the point of the short circuit. Rising means, short-circuit period control means for controlling the short-circuit period of the inverter output, and when the DC input voltage of the closed circuit exceeds a preset threshold value, the short-circuiting operation by the inverter short-circuit means is stopped and the inverter normal operation is stopped. Start-up determining means for permitting driving while continuing the short-circuit operation by the short-circuit means when the DC input voltage does not exceed a threshold value Is characterized by having, therefore, it has the following effects.

That is, according to the present invention, the inverter is started after judging that the output of the DC power supply for operating the inverter device is sufficient, so that the start of the inverter is smooth.

Further, the current flowing through the closed circuit formed by the short circuit gradually increases due to the operation of the current increasing means, and the period during which the closed circuit current is generated is regulated by the operation of the short circuit period control means. Therefore, the maximum value of the closed circuit current is
The control can be performed according to the length of the short circuit period set by the short circuit period control means.

Further, since the voltage of the closed circuit formed by the short circuit is monitored and the current is not detected, the configurations of the detector and the detection circuit can be simplified.

According to a second aspect of the present invention, in the first aspect of the present invention, the short-circuit period control means sets and sets the duty ratio of the switching circuit according to a specified short-circuit period. It is characterized in that the switching circuit is operated at a constant duty ratio with a duty ratio, and therefore has the following operation.

That is, since the short-circuit period control means can be configured by slightly changing the control method of the existing inverter control circuit only at the time of starting the inverter, it is necessary to form a separate circuit as the short-circuit period control means. Disappears.

According to a third aspect of the present invention, in the second aspect of the present invention, the short-circuit period control means determines that the DC input voltage of the closed circuit does not exceed the threshold value by the early-stage determination means. The duty ratio is set again each time the duty ratio is set, and the duty ratio is gradually increased each time the duty ratio setting is reviewed. Therefore, the following operation is provided.

That is, although the current flowing in the closed circuit can be restricted to some extent by the action of the current increasing means and the short-circuit period control means, when the solar cell is used as the DC power supply, the duty ratio is fixed without changing. If this is done, a large short-circuit current may flow from a DC power supply (solar cell) into a closed circuit at the time of restarting after a power failure that occurs when the solar irradiance during the day is high, and may destroy a switching circuit or the like. However, if the duty ratio is gradually increased as in the present invention, the value of the current flowing through the closed circuit can be limited to a small value when the duty ratio is initially small, and the switching circuit and the like are damaged. Does not happen. On the other hand, since the voltage change is small when the duty ratio is kept small, it is difficult to perform the operation of comparing the measured voltage and the threshold value by the activation determination unit. However, since the duty ratio is gradually increased, the operation of comparing the measured voltage and the threshold value by the activation determination unit becomes easy over time, and the activation determination operation can be performed reliably.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the activation determining means varies the threshold value in response to a duty ratio enlarging operation by the short-circuit period control means. Which has the following effects.

That is, since the threshold value is changed in accordance with the duty ratio enlarging operation, the accuracy of determining whether to start the inverter is improved.

According to a fifth aspect of the present invention, in the first aspect of the present invention, the current increasing means is a reactor connected to the closed circuit. Therefore, the following operation is provided. That is, the current increasing means can be simply configured.

According to a sixth aspect of the present invention, there is provided an inverter device which converts the power of a DC power supply such as a solar cell into AC power by opening and closing a switching circuit and supplies the AC power to a load or an existing commercial power system. When the inverter output rises, prior to normal driving of the inverter, the inverter short-circuiting means for short-circuiting the inverter output, and a reactor which is provided at a subsequent stage of the switching circuit and constitutes a filter circuit, comprising: Current increasing means for gradually increasing the current flowing in the closed circuit formed by the short circuit from the time of the short circuit, short circuit period control means for controlling the short circuit period of the inverter output, and the DC input voltage of the closed circuit is preset. If the threshold value is exceeded, the short-circuit operation by the inverter short-circuiting means is stopped and the inverter normal operation is stopped. While allowing the dynamic, the DC input voltage has a start determination means for continuing the short circuit operation by the shorting means and not exceed the threshold value, for which, has the following effects.

That is, since a reactor which is an existing component is used for the inverter device as a component of the filter circuit, the current increasing means can be simply configured.

The invention according to claim 8 of the present invention is characterized in that, in the invention according to claim 1, the inverter short-circuit means short-circuits the switching circuit. It has such an effect.

That is, since the inverter output is short-circuited by using an existing switching circuit as a component of the inverter device, the inverter short-circuit means can be easily configured.

According to a ninth aspect of the present invention, in the first aspect of the present invention, the switching circuit includes a high frequency switching circuit for converting the power of the DC power supply to a high frequency power, and a high frequency switching circuit for converting the high frequency power to a low frequency power. A low-frequency switching circuit for converting power, and a filter circuit including a reactor and a capacitor is provided between the high-frequency switching circuit and the low-frequency switching circuit; and The short-circuit means causes the low-frequency switching circuit to perform a short-circuit operation, the current increasing means includes the reactor, and the short-circuit period control means controls the high-frequency switching in accordance with a prescribed short-circuit period. In addition to setting the duty ratio of the circuit, the high-frequency switch is used with the set duty ratio. It has characterized in that to operate the quenching circuit at a duty ratio constant, because its has the following effects.

That is, in the present invention, the inverter short-circuit means is constituted by a low-frequency switching circuit, the current increasing means is constituted by a reactor of a filter circuit, and the short-circuit period control means adjusts the duty ratio of the high-frequency switching circuit. It is composed of That is, since all components are configured using the components of the existing inverter device, the present invention can be configured without adding any additional components, so that the configuration is simplified accordingly.

According to a tenth aspect of the present invention, in the first aspect of the present invention, a filter circuit comprising a reactor and a capacitor is provided at a stage subsequent to the switching circuit, The ascending means is constituted by the reactor, the inverter short-circuit means is a switch provided on the circuit downstream side of the filter circuit and short-circuiting the inverter output, and the short-circuit period control means includes a predetermined short-circuit period. In addition to setting the duty ratio of the switching circuit according to the above, the switching circuit is operated at a constant duty ratio with the set duty ratio, and has the following effects.

That is, in the present invention, only the switch constituting the inverter short-circuit means needs to be newly provided.
To that extent, the configuration is simplified.

[0042]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an inverter device according to an embodiment of the present invention will be described in detail with reference to the drawings.

[0043] Embodiment FIG l of the first embodiment is a diagram showing the inverter device 1 of the first embodiment of the present invention. The inverter device 1 converts the DC power output from the solar cell 2 into AC power having the same phase as the commercial power system 3 and a frequency of 50/60 HZ, and supplies the AC power to the commercial power system 3.

The inverter device 1 is a high frequency insulation type inverter, and includes a DC capacitor 4, a high frequency inverter bridge 5, a high frequency transformer 6, a diode bridge 7, a filter circuit 10, a low frequency inverter bridge 11, and System relay 12, AC filter 13, inverter output current detector 14, inverter control circuit 1
5 is provided.

The DC capacitor 4 suppresses fluctuation of DC power input from the solar cell 2. The high-frequency inverter bridge 5 is provided downstream of the DC capacitor 4 in the circuit, and converts DC power input to the inverter device 1 into high-frequency AC (several tens to several hundreds of kHz). The high frequency transformer 6 plays a role of insulating the solar cell side (primary side) from the commercial power system side (secondary side). The diode bridge 7 is connected to the secondary side of the high-frequency transformer 6 and rectifies high-frequency alternating current. The filter circuit 10 includes a DC reactor 8 connected in series to the output of the diode bridge 7 and a capacitor 9 connected in parallel to the output of the diode bridge 7, and includes a high-frequency component included in the rectified waveform. The components are removed and smoothed.

The low-frequency inverter bridge 11 is provided on the downstream side of the filter circuit 10 and controls the return of a full-wave rectified DC at a low frequency (50/60 to several hundred HZ). A sine wave alternating current is formed. The interconnecting relay 12 is provided on the downstream side of the circuit of the low-frequency inverter bridge 11 and interconnects with and disconnects from the commercial power system 3. The AC filter 13 is provided downstream of the interconnection relay 12 and absorbs harmonic components.
It is composed of a C reactor and a capacitor. The inverter output current detector 14 is a low-frequency humberter bridge 1
1, and detects the inverter output current I _OUT .

The inverter control circuit 15 controls the high frequency inverter bridge 5, the low frequency inverter bridge 11, and the interconnection relay 10. The inverter control circuit 15 includes a high-frequency gate drive signal generation unit 16
WM modulation controller 17, low-frequency gate drive signal generator 18, loopback controller 19, short-circuit controller 20
, A current limiting unit 21 and a DC voltage comparing unit 22.

High frequency gate drive signal generator 16
Generates pulse train signals P2 and P4 for performing on / off control of the four switching elements Q1 to Q4 constituting the high-frequency inverter bridge 5. PWM modulation control unit 1
Numeral 7 performs PWM modulation control from the error amplified signal and the carrier signal. The error amplification signal is a signal obtained by amplifying an error between the current command signal and the inverter output current I _OUT (detected by the inverter output current detector 14). Low frequency gate drive signal generator 18
Is a pulse train signal P for controlling on / off of the four switching elements S1 to S4 of the low-frequency inverter bridge 11.
1, P3. The return control unit 19
Based on the commercial power system voltage signal _Vout detected from the subsequent stage of the filter 13, the direct current of the full-wave rectified wave shape is turned back at a low frequency (50/60 to several hundred HZ).
The short-circuit control unit 20 gives a command signal R1 for short-circuiting the switching elements S1 to S4 of the low-frequency inverter bridge 11 to the low-frequency gate drive signal generation unit 18.
The current limiting unit 21 outputs a command signal R2 for controlling the switching elements Q1 to Q4 of the high-frequency inverter bridge 5 with a constant duty ratio to the high-frequency gate drive signal generating unit 1.
6 Or the DC voltage comparator 22 compares the threshold V _S that has been predetermined for the detected DC input voltage V _in from both ends of the DC capacitor 4, as a result, or performs control related to activation, or performs steady operation And command signals L1 to L4, which are the result of the determination,
The signals are output to the short-circuit control unit 20, the return control unit 19, and the PWM control unit 17.

The inverter control circuit 15 determines whether the high-frequency inverter bridge 5
And a part for controlling the low-frequency inverter bridge 11. Further, the control on the high frequency side and the control on the low frequency side are respectively divided into a control for starting and a part for performing a steady operation after the starting.

That is, if the DC voltage comparing section 22 determines that the control relating to the starting is to be performed, the short-circuit controlling section 20 and the current limiting section 21 respectively provide the starting control command signals L 1 and L 1.
Send L2. Upon receiving the command signal L1, the short-circuit control unit 20 generates a command signal R1 for short-circuiting the switching elements S1 to S4, and generates the low-frequency gate drive signal generation unit 18
Give to. On the other hand, the current limiter 21 receiving the command signal L2
Now, the switching elements Q1 to Q4 have a duty ratio of-
A command signal R2 for constant on / off control is generated and given to the high-frequency gate drive signal generator 16.

On the other hand, if the DC voltage comparison unit 22 determines that the control regarding the steady operation is performed, the return control unit 1
9. Send command signals L3, L4, L5 for steady operation control to the PWM modulation control unit 17 and the interconnection relay 12, respectively. The return control unit 19 and the PWM modulation control unit 17 that have received the command signals L3 and L4
, Q1 to Q4 to perform normal switching control to generate command signals R3 and R4 to generate a low-frequency gate drive signal generation section 18 and a high-frequency gate drive signal generation section 1
Give to 6. The interconnection relay 12 receiving the command signal L5
The inverter device 1 and the commercial power system 3 are interconnected.

The switching elements Q1 to Q4, S1
S4 can be made of, for example, IGBT or the like.

Next, the operation of the inverter device 1 having the above configuration will be described with reference to FIG. FIG. 2 shows a change in an operating point in a solar cell characteristic curve in the inverter device 1.

[0054] First, the inverter control circuit 15 keep monitoring the DC input voltage V _in to be detected from both ends of the DC capacitor 4 by the DC voltage comparator 22. At night, the solar radiation intensity is zero, so the DC input voltage Vin is also zero. In the solar cell characteristic E1 of the solar radiation intensity immediately after sunrise, the open-circuit voltage V
_oc (E1) is, for example, around 250 to 300 V,
The short-circuit current _Isc (E1) is almost close to zero, so there is almost no solar cell output. At this time, when viewed from the solar cell 2, it can be considered that no load is connected to the output side of the solar cell 2. Therefore, the operating point A of the solar cell 2
Corresponds to the open circuit voltage V _OC (El) on the solar cell characteristic curve E1, as shown in FIG.

On the other hand, the DC voltage comparator 22 compares the threshold value V _S and the DC input voltage V _in that is stored preset (in this case, V _in is equal to the open circuit voltage V _OC (El)) ing. Then, the DC voltage comparator 22, when the DC input voltage V _in is determined to exceeds the threshold V _S, the command signal L1, L against short circuit control unit 20 and the current limiting unit 21
2 is output.

Upon receiving the command signal L1, the short-circuit control unit 20 generates a command signal R1 for commanding to short-circuit the switching elements S1 and S2 or the switching elements S3 and S4 of the low-frequency inverter bridge 11, and The signal is supplied to the frequency gate drive signal generator 18. The low frequency gate drive signal generation unit 18 generates a pulse train signal P1 such that the switching elements S1 and S2 or the switching elements S3 and S4 are short-circuited based on the command signal R1, and converts the pulse train signal P1 to a low frequency. The signal is output to the inverter bridge 11 to perform switching control.

On the other hand, the current limiting unit 2 receiving the command signal L2
In step 1, a command signal R2 for commanding to perform duty ratio-constant switching control is generated and supplied to the high-frequency gate drive signal generator 16. The high-frequency gate drive signal generator 16 receiving the command signal R2 generates a pulse train signal P2 for controlling the switching of the high-frequency inverter bridge 5 with a fixed duty ratio, and outputs the pulse train signal P2 to the high-frequency inverter bridge 5. Perform switching control.

Then, a closed circuit including the solar cell 2, the high-frequency inverter bridge 5, the high-frequency transformer 6, the filter circuit 10, and the low-frequency inverter bridge 11 is formed inside the inverter device 1. As a result, a short-circuit current flows through the DC reactor 8, which is a reliable load. That is, when viewed from the solar cell 2, a load (DC reactor 8) is connected to the output side of the solar cell 2.

When a short-circuit current flows through the closed circuit thus formed, the operating point in FIG. 2 is determined by the duty ratio from the point A on the open voltage V _OC in the solar radiation intensity immediately after sunrise. To the intersection B of the load characteristic curve α1 and the solar cell characteristic curve El.

[0060] Incidentally, the proportional relationship between the duty ratio duty ratio of fixed pulse train signal P2 and the slope of the load characteristic curve [alpha] 1. That is, as the duty ratio of the pulse train signal P2 increases, the slope of the load characteristic curve α1 also increases. On the other hand, if the duty ratio of the pulse train signal P2 decreases, the slope of the load characteristic curve α1 also decreases.

In this way, the inverter device 1 is controlled so that a short-circuit current flows through the inverter device 1 so that the load (DC reactor 8) is connected to the output side of the solar cell. The 'measured in the DC voltage comparator 22, the DC input voltage V _in' DC input voltage V _in this case again is compared with the threshold V _S and. Then, the DC input voltage V _in 'threshold V
If it is smaller than _S (V _in ′ <V _S ), the DC voltage comparison unit 22 determines that the solar cell output is not enough to start the inverter, and continues to issue the command signals L1 and L2.
Is output to the short-circuit controller 20 and the voltage limiter 21 to continue the short-circuit control of the low-frequency inverter bridge 11 and the duty ratio-constant control of the high-frequency inverter bridge 5.

When the solar radiation intensity increases and the solar radiation intensity reaches E2, the operating point is shifted from the point B to the solar cell characteristic curve E2.
2, and the intersection point C F movement of the load characteristic curve [alpha] 1, the DC input voltage V _in 'exceeds the threshold value _{V S (V in'> V} S). When the DC voltage comparison unit 22 detects that such a state has occurred, the DC voltage comparison unit 22 determines that the solar cell output has reached a value sufficient to start and operate the inverter device 1,
The output of the command signals L1 and L2 to the short-circuit control unit 20 and the current limiting unit 21 is stopped, and the start control (closed circuit formation control) is released. Then, the DC voltage comparison unit 22 outputs the command signal L5 to the interconnection relay 12, and causes the interconnection relay 12 to interconnect the inverter device 1 and the commercial power system 3. Further, the DC voltage comparison unit 22 sends command signals L4 and L3 to the PWM modulation control unit 17 and the loopback control unit 19. Upon receiving the command signal L4, the PWM modulation control unit 17
It generates a command signal R4 for turning on / off the switching elements Q1 to Q4 based on the PWM modulation, and outputs the command signal R4 to the high frequency gate drive signal generation unit 16. Command signal R
The high-frequency gate drive signal generator 16 receiving the signal 4 generates a pulse train signal P4 for controlling the switching elements Q1 to Q4 to be turned on / off based on the PWM modulation, and outputs the pulse train signal P4 to the high-frequency inverter bridge 5. Perform switching control.

On the other hand, the return control unit 19 that has received the command signal L3 generates a command signal R3 for controlling the return of the switching elements S1 to S4, and outputs it to the low frequency gate drive signal generation unit 18. Upon receiving the command signal R3, the low frequency gate drive signal generation unit 18 generates a pulse train signal P3 for controlling the switching elements S1 to S4 to fold back at a low frequency (50/60 to several hundred Hz), and generates the pulse train signal P3. The signal is output to the low frequency inverter bridge 11 to perform switching control. Thereby, the inverter device 1
Will be operated in a steady state.

Next, a description will be given of a threshold value V _S set for starting operation of the inverter device 1.

First, how the threshold value V _S is defined will be described. That is, the minimum power required for the inverter device 1 to start and operate (hereinafter referred to as “inverter minimum power”) is the inverter main circuit and the inverter control circuit 1.
5 plus the power consumed during the inverter minimum output operation. The voltage value at the time of outputting the minimum inverter power thus obtained is defined as a threshold value V _S.

Next, a method of setting the threshold value V _S defined as described above will be described with reference to FIG. That is, the load characteristic curve is set to α1 ′ in the figure by the pulse train signal P2 ′ that is controlled to be constant at an arbitrary duty ratio. In this state, the solar radiation intensity immediately after sunrise (the solar cell characteristic curve E
In 1), as a result of performing the above-described startup control (closed circuit formation control), the inverter device 1 moves the solar cell operating point from the point A to the point B, and the DC power output from the solar cell 2 is a square in FIG. (0, B ', B, B''). On the other hand, in the relatively strong sunlight intensity during the day (solar cell characteristic curve E2), the solar cell operating point is point C, and the DC power output from the solar cell 2 is square (0, C ′, C, C ″). Becomes

The output power of the solar cell (square 0, B ', B, B'') at the operating point B is naturally smaller than the minimum power of the inverter. On the other hand, the solar cell output power (square 0, C ′, C, C ″) at the operating point C is equal to or more than the inverter minimum power. Therefore, of the operating points on the load characteristic curve α1 ′, an operating point at which the output power of the solar cell (square formed at each operating point) matches the minimum power of the inverter is obtained in advance by an experiment or the like. The voltage value at the operating point is defined as the threshold value V _S in the load characteristic curve α1 ′ (pulse train signal P2 ′).

[0068] Incidentally, in the inverter device 1, and setting a plurality of threshold values V _S, by selectively using the respective threshold V _S in accordance with a variation in irradiance (solar cell characteristics curve), high frequency inverter bridge 5 and low frequency inverter Bridge 1
The damage of 1st class etc. is prevented beforehand. Hereinafter, this will be described with reference to FIG. FIG. 4 shows a change in the operating point in the solar cell characteristic curve in the inverter device 1 as in FIG.

In the control for switching the high frequency inverter bridge 5 at a constant duty ratio, the duty ratio has a slope of a load characteristic curve α determined by the load impedance. For example, in FIG. 4, a load characteristic curve of a closed circuit which is relatively controlled by a duty ratio-constant pulse train signal P2 ₁ having a relatively large duty ratio is represented by α.
1 ₁ to. Then, in this control state, a case is considered where the solar radiation intensity is low immediately after sunrise or the like, that is, the short-circuit current I _SC is small and the solar cell characteristic E1 in the drawing is obtained.

In this state, when the above-described start-up control is performed to form a closed circuit and a load (DC reactor 8) is connected to the solar cell 2, the operating point is changed from the point D on the open voltage to the solar cell characteristic curve E1. moves to the intersection F between the load characteristic curve [alpha] 1 _1. At this time, since the solar radiation intensity is low, the short-circuit current flowing through the load (DC reactor 8) becomes small (Ie in FIG. 4).
1) The switching elements and the like constituting each of the inverter bridges 5 and 11 are not destroyed.

However, when the inverter device 1 is restarted after being stopped due to a power failure or the like that occurred during the day, the solar radiation intensity is high, and the solar cell characteristic curve becomes E3 in FIG. The current I _SC increases. In this state, a closed circuit is formed by performing the above-described startup control,
When a load (DC reactor 8) is connected to the solar cell 2,
The operating point from point H on the open circuit voltage V _OC, moves the solar cell characteristic curve E3 in load characteristic curve [alpha] 1 ₁ of intersection K. At this time, the load (DC reactor 8)
Current flowing through the inverter bridges 5 and 11 has an excessive value (Ie3 in the figure), and there is a possibility that the switching elements constituting the inverter bridges 5 and 11 may be destroyed.

In order to prevent such breakage of the switching element and the like, it is conceivable to perform start-up control using a load characteristic curve having a small slope (a small duty ratio). Then, as the slope of the load characteristic curve decreases, the current value at the operating point also decreases, and an excessive current does not flow. However, in the startup control using the load characteristic curve with a small slope, the threshold value V _S increases, and the time required for the startup determination becomes longer, and there is an inconvenience that it is not possible to smoothly shift to normal inverter driving. Hereinafter, this will be described.

First, the threshold value V _S corresponding to the duty ratio
Will be further described with reference to FIG. FIG.
, The horizontal axis represents the DC input voltage V _in, shows a load characteristic curve [alpha] 1 ₁ in the case where the output power at that time (w) on the vertical axis the load characteristic curve [alpha] 1 _2. From this figure, in order to obtain the minimum power P _min required to start the inverter device 1, the load characteristic curve α1 ₁ (duty ratio is large) requires a voltage of V _S1 , The characteristic curve α1 ₂ (small duty ratio) requires a voltage of V _S2 , and it can be understood that these voltages have a relationship of V _S1 <V _S2 . The threshold value V _S is the minimum starting power V _S1 , V _S2 thus obtained.

Small inclination (small duty ratio)
In response to the load characteristic curve [alpha] 1 _2, in the case of performing the activation control threshold VS ₂ adapted to have a high value, when the solar radiation intensity is only after the DC input voltage V _in is increased by increasing to some extent, the DC input It can not be the voltage V _in exceeds the threshold value V _S2, which in the, at relatively low solar irradiance conditions such as immediately after the sunrise, becomes impossible to start the inverter device 1 smoothly.

Therefore, in order to prevent the danger of component damage and to enable a smooth start of the inverter, the inverter device 1 performs the following control. That is, the high-frequency gate drive signal generator 16
Performs a plurality of switching controls with different duty ratios on the high-frequency inverter bridge 5, and stores a plurality of pulse train signals _P21-n corresponding to each duty ratio. Then, the DC voltage comparator 22 stores a threshold value V _S1～n corresponding to the set duty ratio, the DC input voltage V _in, is compared with a threshold value V _S1～n corresponding to the duty ratio at that time ing.

[0076] In the following description, for the convenience of simplicity of explanation, the pulse train signal P2 _{1 to n,} the pulse train signal P2 ₁ corresponding to a relatively large duty ratio, the pulse train signal corresponding to a relatively small duty ratio P2 ₂ will be described in a simplified manner. Similarly load characteristic curve [alpha] 1 is also a load characteristic curve [alpha] 1 ₁ which corresponds to a pulse train signal P2 _1, will be described in simplified to two pulse train signals P2 ₂ load characteristic curve [alpha] 1 ₂ corresponding to. Furthermore, the threshold value V _S1～n also, a threshold V _S1 corresponding to the pulse train signal P2 _1, a pulse train signal P2 _2
VS2 corresponding to FIG. However, it is needless to say that the pulse train signal P2, the load characteristic curve α1, and the threshold value V _S are not limited to such a pair, but may be set to a plurality of pairs or more.

Next, the control in the case where a plurality of load characteristic curves (here, as described above, a pair of load characteristic curves α1 ₁ and α1 ₂ for simplicity of explanation) is provided, FIG. 4 and FIG. This will be described with reference to the flowchart of FIG.

[0078] First, in the DC voltage comparator 22 compares constantly the DC input voltage V _in and the threshold V _S2. Here, a threshold value V _S2 according to the load characteristic curve α1 ₂ (corresponding to a relatively small duty ratio) is used.

[0079] Then, the DC input voltage V _in exceeds the threshold value V _S2 that (V _in> V _S2), the DC voltage comparator 22 detects (T1), starts preparation driving of the inverter device 1. That is, the short-circuit controller 20 short-circuits the low-frequency inverter bridge 11 via the low-frequency gate drive signal generator 18 (T2). Further, the current limiting unit 2
1 controls the switching of the high-frequency inverter bridge 5 via the high-frequency gate drive signal generator 16 at a constant duty ratio. At this time, the high-frequency inverter bridge 5 outputs the pulse train signal P having a relatively small duty ratio.
2 ₂ based are switching-controlled (T3). Thus, in the inverter apparatus 1, a closed circuit current / voltage changes along a relatively inclination small load characteristic curve [alpha] 1 ₂ is formed.

Then, immediately after sunrise (the solar cell characteristic curve E
When the closed circuit is formed in the inverter device 1 in the state (1), the operating point is determined from the open voltage D to the solar cell characteristic curve E
1 and to the intersection M of the load characteristic curve α1 ₂ . Load characteristic curve and the DC input voltage V _in at the operating point of the time α
1 ₂ and a setting value V _S2 corresponding to again compare the DC voltage comparator 22 (T4). In this case, the DC input voltage V
_{Since in} is lower than the set value V _S2 , the DC voltage comparison unit 2
2 outputs a command signal L2 _1, L1 ₁ indicating that the current limiting section 21 and the short circuit control unit 20.

[0081] The DC input voltage current limiting unit 21 V _in is informed by the command signal L2 _1, L1 ₁ that is below the set value V _S2 and the short-circuit control unit 20 continues the activation control. However, the current control unit 21 performs the following start control,
The start control having a relatively small duty ratio is switched to the start control having a relatively large duty ratio (T5).

[0082] Then, the load characteristic curve shifts from a relatively slope small [alpha] 1 ₂ relatively to [alpha] 1 ₁ large slope. In the DC voltage comparator 22 with it, the threshold V _S, the threshold value V _S2 corresponding to the load characteristic curve [alpha] 1 _2, switched to the threshold V _S1 corresponding to the load characteristic curve [alpha] 1 _1.

The start control is changed by changing the pulse train signal P output from the high-frequency gate drive signal generator 16 from the pulse train signal P2 ₂ (load characteristic curve α1 ₂ ) having a relatively small duty ratio to the pulse train having a relatively large duty ratio. This is performed by changing to the signal P2 ₁ (load characteristic curve α1 ₁ ). Also, changing the activation control, 6, as indicated by the dotted line, these _{changes, P2 2 → P2 1 → P2} 2
→ P2 ₁ →... May be repeatedly executed.

In the state where the startup control is continued in this way, the solar radiation intensity slightly increases, and the solar cell characteristic curve changes to E1.
To E2 or E3. Then, in order to load characteristic curve is changed from [alpha] 1 ₂ to [alpha] 1 _1, the operating point moves to J (K) is an intersection of the solar cell characteristic curve E2 (E3) and the load characteristic curve [alpha] 1 _1. And a setting value V _S1 corresponding to the load characteristic curve [alpha] 1 ₁ and the DC input voltage V _in at the operating point in this case is compared in the direct-current voltage comparator 22 (T6).

[0085] In this case, the DC input voltage V _in the set value V _S1
(V _in > V _S1 ), the DC voltage comparison unit 2
2 outputs the command signals L2 ₂ and L1 ₂ indicating this to the current limiting section 21 and the short-circuit control section 20, and also issues command signals L4, L3 and L3 for notifying the start of normal inverter control.
L5 is output to the PWM modulation control unit 17, the return control unit 19, and the interconnection relay 12.

[0086] command signal L2 _2, L1 ₂ current limiting section 21 and the short circuit control unit 20 that is input stops the activation control.
That is, the short-circuit control unit 20 stops the short-circuit control of the low-frequency inverter bridge 11 (T7). Further, the current limiter 21 stops the duty ratio constant control of the high frequency inverter bridge 5 (T8).

On the other hand, the PWM modulation control unit 17, the return control unit 19, and the interconnection relay 12, to which the command signals L4, L3, L5 are input, start normal inverter control (T
9, T10).

On the other hand, after a power failure occurred during the day,
The startup control when the inverter device 1 restarts is as follows. That is, first, in the DC voltage comparator 22, the DC input voltage V _in and comparison operations between the threshold V _S2 (T1)
Is performed, and when V _in > V _S2 , the same startup control as described above is performed (T2, T3). Thus, in the inverter apparatus 1, a closed circuit current / voltage changes along the load characteristic curve [alpha] 1 ₂ is formed.

When the solar radiation intensity is high due to the restart after the power failure during the daytime, that is, when the start control is started and the load is connected to the solar cell 2 according to the solar cell characteristic curve E3,
Operating point moves from the open voltage H at the intersection R of the solar cell characteristic curve E3 the load characteristic curve [alpha] 1 _2. A DC input voltage V _in at the operating point of this time, the set value V _S2 corresponding to the load characteristic curve [alpha] 1 ₂ compares the DC voltage comparator 22 (T4).

[0090] In this case, the DC input voltage V _in the set value V _S2
(V _in > V _S2 ), the DC voltage comparison unit 2
2 outputs the command signals L2 ₂ and L1 ₂ indicating this to the current limiting section 21 and the short-circuit control section 20, and also issues command signals L4, L3 and L3 for notifying the start of normal inverter control.
L5 is output to the PWM modulation control unit 17, the return control unit 19, and the interconnection relay 12.

[0091] command signal L2 _2, L1 ₂ current limiting section 21 and the short circuit control unit 20 that is input stops the activation control (T7, T8). On the other hand, the PWM modulation control unit 17, the return control unit 19, and the interconnection relay 12, to which the command signals L4, L3, and L5 have been input, start normal inverter control (T9, T10).

On the other hand, even after restarting after a power failure during the daytime, when the solar radiation intensity is relatively low, that is, when the solar cell characteristic curve E
2, activation control is started, if the load on the solar cells 2 are connected, the operating point moves from the open voltage G at the intersection Q of the solar cell characteristic curve E2 the load characteristic curve [alpha] 1 _2. And a setting value V _S2 corresponding to the load characteristic curve [alpha] 1 ₂ and the DC input voltage V _in at the operating point in this case DC voltage comparator 22
Are compared (T4). In this case, the DC input voltage V
_{Since in} is smaller than the set value V _S2 (V _in <V _S2 ), the DC voltage comparison unit 22 outputs the command signals L2 ₁ and L2 indicating this.
Outputs 1 ₁ to the current limiting unit 21 and the short circuit control unit 20.

[0093] The DC input voltage current limiting unit 21 V _in is informed by the command signal L2 _1, L1 ₁ that is below the set value V _S2 and the short-circuit control unit 20 continues the activation control. However, the current control unit 21 performs the following start control,
The start control having a relatively small duty ratio is switched to the start control having a relatively large duty ratio (T5).

[0094] Then, the load characteristic curve shifts from a relatively slope small [alpha] 1 ₂ relatively to [alpha] 1 ₁ large slope. Along with this, the threshold V _S which is set by the DC voltage comparator 22, the threshold value V _S2 corresponding to the load characteristic curve [alpha] 1 _2, is switched to the threshold V _S1 corresponding to the load characteristic curve [alpha] 1 _1.

[0095] Then, move the operating point is an intersection of the solar cell characteristic curve E2 and load characteristic curve [alpha] 1 ₁ J. And a setting value V _S1 corresponding to the load characteristic curve [alpha] 1 ₁ and the DC input voltage V _in at the operating point in this case is compared in the direct-current voltage comparator 22 (T6).

[0096] In this case, the DC input voltage V _in the set value V _S1
(V _in > V _S2 ), the DC voltage comparison unit 2
Reference numeral ₂ denotes command signals L4, L3, L for stopping the output of the command signals L2 ₂ and L1 _{2 to} the current limiting section 21 and the short-circuit control section 20 and for notifying the start of normal inverter control.
5 is output to the PWM modulation control unit 17, the return control unit 19, and the interconnection relay 12.

[0097] command signal L2 _2, L1 ₂ input is stopped current limiting unit 21 and the short circuit control unit 20 stops the activation control (T7, T8). On the other hand, command signals L4, L3, L5
Modulation control unit 17 and aliasing control unit 1 to which
9 and the interconnection relay 12 start normal inverter control (T9, T10).

By controlling the start-up as described above, the switching element and the like are not destroyed even when the driving is performed again during the daytime when the solar radiation intensity is large. Further, even immediately after the sunrise, it is possible to smoothly shift from the start control to the normal inverter control.

Next, a configuration for limiting the current in the inverter device 1 will be described. The combination of the short-circuit control of the low-frequency inverter bridge 9 and the duty ratio-constant switching control of the high-frequency inverter bridge 5 cannot limit the short-circuit current flowing in the inverter circuit. This is because an infinite current flows in the closed circuit formed by the short-circuit control of the low-frequency inverter bridge 11 at the moment when the circuit is formed.

Therefore, in the inverter device 1, the high-frequency inverter bridge 5 and the low-frequency inverter bridge 1
1, a DC reactor 8 for limiting current is provided. The short-circuit current rectified by the action of the diode bridge 7 and turned into a direct current flows into the DC reactor 8. For this reason, as shown in FIG. 7A, the current does not flow through the DC reactor 8 at the moment when the current flows, and the current gradually increases with time. Note that the current increase characteristic (the gradient in FIG. 7A) is determined by the unique electric characteristic of the DC reactor 8.

The DC reactor 8 having such characteristics
7 by a high-frequency inverter bridge 5.
When the current supply control with a constant pulse train as shown in (b) is performed, a current having a waveform as shown in FIG. 7 (c) flows through the transformer 6, and further rectified by the diode bridge 7, resulting in DC In the reactor 8, the current increasing characteristics are as shown in FIG. In other words, the current outflow period of the short-circuit current flowing through the closed circuit is controlled by performing switching control of the high-frequency inverter bridge 5 with a constant duty ratio. Specifically, the current outflow period of the short-circuit current is an on-period (indicated by O in the figure) at a duty ratio controlled to be constant, and therefore, the short-circuit current has a current value during the outflow period. At the end of the ON period O, and reaches the maximum current.

As described above, the high-frequency inverter bridge 5
Switching control with a constant duty ratio,
By combining with the DC reactor 8, the maximum current value flowing through the closed circuit can be determined by changing the duty ratio and the D value.
It can be controlled by the electric characteristics of the C reactor.

The inverter device 1 is a high-frequency insulated inverter device having a high-frequency inverter bridge 5 and a low-frequency inverter bridge 11. A DC-DC converter is provided between the high-frequency inverter bridge 5 and the low-frequency inverter bridge 11. The configuration is such that a filter circuit 10 including a reactor 8 and a capacitor 9 is provided. Therefore, since the DC reactor 8 of the filter circuit 10 can be used as a current limiting reactor, it is not necessary to newly provide a DC reactor for current limiting, and an increase in the number of components can be prevented.

The current limiting section 21 and the short-circuit limiting section 20 can be configured by software, similarly to the PWM modulation control section 17 and the return control section 19.

In the operation of the short-circuit control unit 20, the control for short-circuiting the low-frequency inverter bridge 11 is described in the description of the above-described embodiment. The switching element (S1, S2) is turned on, and the switching element (S3, S4) is turned off. The switching element (S3, S4) is turned on, and the switching element (S1, S2) is turned off. [ON operation of switching elements (S1, S2) + OFF operation of switching elements (S3, S4)]
And [the turning-on of the switching elements (S3, S4) + the turning-off of the switching elements (S1, S2)] are alternately and periodically repeated, so that the low-frequency inverter bridge 1
1 may be short-circuit controlled. This has the following advantages. That is, the switching elements S1 to S
The switching transistor constituting 4 has a characteristic that, as one conduction time becomes longer, the load on the element becomes as large as possible, which may adversely affect the life and the like. Therefore, if the control of periodically repeating the switching operation is performed, the load on each of the switching elements S1 to S4 is correspondingly reduced, and the adverse effect on the life and the like can be reduced correspondingly.

Further, in the inverter device 1, during the start-up control (closed circuit formation control), the DC input voltage V
When _in falls below the set value V _s, sufficient photovoltaic output to make the inverter start is determined that has not yet been output, it is configured to continue the activation control (closed circuit forming control) Was. However, if it is determined that the solar cell output sufficient to start the inverter has not been output yet, the above-described start control is temporarily stopped, and the solar cell 2 and the inverter device 1 are separated from each other. May be configured to perform the same activation control again after elapse of.

Second Embodiment FIG. 8 is a diagram showing an inverter device 30 according to a second embodiment of the present invention. The inverter device 30 converts the DC power output from the solar cell 2 into the commercial power system 3.
, And the AC power having a frequency of 50/60 Hz is supplied to the commercial power system 3.

The inverter device 30 includes the DC capacitor 3
1, an inverter bridge 32, and a filter circuit 33
, A switching element 34, an interconnection relay 35, an inverter output current detector 36, and an inverter control circuit 37.

The DC capacitor 31 suppresses fluctuations in DC power input from the solar cell 2. The inverter bridge 32 is provided downstream of the DC capacitor 31 and converts DC power input to the inverter device 30 into AC (50/60 to several hundred HZ). The filter circuit 33 includes a DC reactor 38 connected in series with the output of the inverter bridge 32 and a capacitor 39 connected in parallel with the output of the inverter bridge 32, and removes and smoothes high-frequency components included in the rectified waveform. It is carried out. The switching element 34 is a filter circuit 3
3 is provided at the subsequent stage of the circuit, and the inverter bridge 32
Short circuit operation. The interconnection relay 35 is provided downstream of the inverter bridge 32 and is connected to the commercial power system 3.
Connection with the side and disconnection. The inverter control circuit 37 controls the inverter bridge 32 and the interconnection relay 35. The inverter control circuit 37 includes a gate drive signal generation unit 40 and a PWM modulation control unit 41
, A short-circuit control unit 42, a current limiting unit 43, and a DC voltage comparing unit 44.

The gate drive signal generation section 40 includes four switching elements Q constituting the inverter bridge 32.
A pulse train signal P for performing on / off control of 1 to Q4 is generated. The PWM modulation control unit 41 performs PWM modulation control from the error amplified signal and the carrier signal. The short-circuit control unit 42 gives the switching element 34 a command signal R5 for short-circuiting the switching element 34. The current limiter 43 supplies the gate drive signal generator 40 with a command signal R6 for controlling the switching elements Q1 to Q4 of the inverter bridge 32 at a constant duty ratio. DC voltage comparing unit 44, a threshold V _s that has been predetermined DC input voltage V _in detected from both ends of the DC capacitor 31
As a result, it is determined whether to perform the start-up control or to perform the inverter steady-state operation, and the command signals L6 to L9 indicating this are sent to the short-circuit control unit 42, the current limiting unit 43, P
The signal is output to the WM modulation control unit 41 and the interconnection relay 35.

The inverter control circuit 37 is divided into a part for performing control relating to start-up and a part for performing control relating to steady-state operation after the start-up, based on the determination result of the DC voltage comparison part 44.

That is, if the DC voltage comparing section 44 determines that the control relating to the start is to be performed, the short-circuit control section 42 and the current limiting section 43 respectively provide the start control command signals L6 and L6.
Send L7. Upon receiving the command signal L <b> 6, the short-circuit control unit 42 generates a command signal R <b> 5 for instructing the switching element 34 to perform a short-circuit, and supplies the command signal R <b> 5 to the switching element 34. On the other hand, the current limiter 43 receiving the command signal L7 generates a command signal R6 for turning on / off the switching elements Q1 to Q4 at a fixed duty ratio and supplies the command signal R6 to the gate drive signal generator 40.

On the other hand, if the DC voltage comparing section 44 determines that the control relating to the steady operation is to be performed, the PWM voltage controlling section 4
1 sends a command signal L8 for steady operation control and a command signal L9 to the interconnection relay 35. In the PWM modulation control unit 41 receiving the command signal L8, the switching elements Q1 to Q
4 to generate a command signal R7 for performing normal switching control, and supply the command signal R7 to the gate drive signal generation unit 40. The interconnection relay 35 receiving the command signal L9 interconnects the inverter device 30 and the commercial power system 3.

Next, the operation of the inverter device 30 will be described with reference to FIG. First, the inverter control circuit 3
7 keep monitoring the DC input voltage V _in to be detected from both ends of the DC capacitor 4 by the DC voltage comparator 44. At night, the solar radiation intensity is zero, so the DC input voltage Vin is also zero. In the solar cell characteristics E1 insolation intensity immediately after sunrise, open circuit voltage V _oc (E1) is, for example, a near 250～300V, short-circuit current I _sc (E1) is almost close to zero,
Therefore, there is almost no solar cell output. At this time, when viewed from the solar cell 2, it can be considered that no load is connected to the output side of the solar cell 2. Therefore, the operating point A of the solar cell 2 matches the open circuit voltage V _OC (El) on the solar cell characteristic curve E1, as shown in FIG.

[0115] On the other hand, the DC voltage comparator 44, which compares the threshold value V _S which stores preset a DC input voltage V _in. Then, the DC voltage comparison unit 44, when the DC input voltage V _in is determined to exceeds the threshold V _S, short circuit control unit 42 and the current limiting unit 43 instruction signal L6 respect,
L7 is output.

Upon receiving the command signal L6, the short-circuit control unit 42 outputs a command signal R5 for commanding a short circuit to the switching element 3.
Give to 4. Switching element 3 receiving command signal R5
4 is short-circuited (conductive).

On the other hand, current limiter 4 receiving command signal L7
In step 3, a command signal R6 for commanding to perform a duty ratio-constant on / off control is generated and given to the gate drive signal generation unit 40. Upon receiving the command signal R6, the gate drive signal generator 40 generates a pulse train signal P5 for controlling the inverter bridge 32 to be turned on / off at a fixed duty ratio, and outputs the pulse train signal P5 to the inverter bridge 32 to perform switching control. .

Then, a closed circuit including the solar cell 2, the inverter bridge 32, the filter circuit 33, and the switching element 34 is formed inside the inverter device 30. As a result, a short-circuit current flows through the DC reactor 38, which is a reliable load.

In this way, the inverter device 30 is preparatoryly driven, thereby forming a closed circuit. When a short-circuit current flows through this closed circuit, the operating point in FIG. The shift from the point A on the voltage V _OC to the intersection B of the load characteristic curve α1 determined by the load impedance of the load (DC reactor 38) and the solar cell characteristic curve El.

In this way, the inverter device 30 is controlled to cause a short-circuit current to flow therein so that the load (DC reactor 38) is connected to the output side of the solar cell.
Then, the DC input voltage V _in ′ at this time is measured, and the DC input voltage V _in ′ and the threshold V
Compare with _S again. When the DC input voltage V _in 'is smaller than the threshold value V _S (V _in '<V _S ), the DC voltage comparison unit 44 determines that the solar cell output is not sufficient to start the inverter. , The command signal L6
L7 is output to the short-circuit controller 42 and the voltage limiter 43,
The short-circuit control of the switching element 34 and the duty ratio-constant control of the inverter bridge 32 are continued.

When the solar radiation intensity increases and the solar radiation intensity reaches E2, the operating point changes from the point B to the solar cell characteristic curve E2.
2, and the intersection point C F movement of the load characteristic curve [alpha] 1, the DC input voltage V _in 'exceeds the set value _{V S (V in'> V} S). When the DC voltage comparison unit 44 detects that such a state has occurred, the DC voltage comparison unit 44 determines that the solar cell output has reached a value sufficient to start and operate the inverter device 1,
The output of the command signals L6 and L7 to the short-circuit control unit 42 and the current limit unit 43 is stopped, and the closed-circuit formation control is released. Then, DC voltage comparing section 44 outputs command signal L9 to interconnection relay 35, and interconnects inverter device 1 and commercial power system 3 by interconnection relay 35. further,
The DC voltage comparison unit 44 sends a command signal L8 to the PWM modulation control unit 41. Upon receiving the command signal L8, the PWM modulation control unit 41 generates a command signal R7 for turning on / off the switching elements Q1 to Q4 based on the PWM modulation,
Output to the gate drive signal generation unit 40. Command signal R
7, the gate drive signal generator 40 generates a pulse train signal P6 for controlling ON / OFF of the switching elements Q1 to Q4 based on the PWM modulation, and outputs the pulse train signal P6 to the inverter bridge 32 to perform switching control. I do. This PWM modulation is performed based on the inverter output current I _OUT detected by the inverter output current detector 36. As a result, the inverter device 30 is operated in a steady state.

In the inverter device 30, it has been described that short-circuit control is performed by the switching element 34, while switching control with a constant duty ratio is performed by the inverter bridge 32.
3, the short-circuit control of the inverter bridge 32 can be performed, and the short-circuit control unit 42 can perform the switching control of the switching element 34 at a constant duty ratio. In this case, to form a closed circuit, the switching elements Q1 and Q4 may be short-circuited or the switching elements Q3 and Q2 may be short-circuited.

[0123] Also in the inverter device 30, similarly to the inverter device of the first embodiment described above, the threshold V _S set multiple, the variation of the respective threshold V _S irradiance (solar cell characteristics curve) By properly using them, it is possible to prevent damage to the high-frequency inverter bridge 5 and the low-frequency inverter bridge 11 beforehand.

[0124]

As described above, according to the present invention,
The following effects can be obtained.

[0125] Since the output of the DC power supply for operating the effect inverter apparatus according to claim 1 is able to start the inverter after determining that there is sufficient, Invar evening start of becomes smooth, inconvenience chatter No longer occurs.

The current flowing in the closed circuit formed by the short circuit gradually increases due to the operation of the current increasing means, and the period during which the closed circuit current is generated is regulated by the operation of the short circuit period control means. Therefore, the maximum value of the closed circuit current is
Control can be performed according to the length of the short-circuit period set by the short-circuit period control means, and there is no inconvenience that an excessive current flows in the inverter device and destroys electronic components constituting the inverter device.

Furthermore, since the voltage of the closed circuit formed by the short circuit is monitored and the current is not detected, the configurations of the detector and the detection circuit can be simplified, and the cost can be reduced accordingly. Was achieved.

[0128] so that it is possible to construct a short period control unit simply by slightly changing the method of controlling the effects existing to have an inverter control circuit according to claim 2 only when the inverter starts, as a short-circuit period control unit, separate circuits Need not be formed, and the cost can be further reduced.

By gradually increasing the effect duty ratio according to the third aspect, the start-up determination operation is facilitated without inconvenience such as breaking of the switching circuit. That is, it was possible to achieve both prevention of element damage and improvement in the reliability of the startup determination operation.

By changing the threshold value in accordance with the effect duty ratio enlarging operation of the fourth aspect, the accuracy of determining whether to start the inverter is improved.

The effect current increasing means according to claim 5 can be simply configured, and the cost can be reduced accordingly.

Since the reactor, which is an existing component, is used for the inverter device as a component of the effect filter circuit according to the sixth and seventh aspects, the current increasing means can be simply configured, and the cost can be reduced accordingly. Was.

[0133] As component effects the inverter apparatus according to claim 8, since the short-circuiting the inverter output with a switching circuit that existing and,
Inverter short-circuit means can be easily configured, and the cost can be reduced accordingly.

Since all of the effects of the ninth aspect are configured by applying the components of the existing inverter device, the present invention can be configured without adding new components, and the configuration can be simplified accordingly. And cost reduction.

[0135] may be provided newly only switch constituting the effect inverter short-circuit device of claim 10, otherwise, since this structure is constructed by applying the parts of the existing inverter, correspondingly, construction It became simple and cost was reduced.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a change in an operating point on a solar cell characteristic curve in the inverter device of the present invention.

FIG. 3 is a diagram showing an area of a solar cell output in the inverter device of the present invention.

FIG. 4 is a diagram showing a change in operating point between a load characteristic curve and a solar cell characteristic curve in the inverter device of the present invention.

FIG. 5 is a diagram for explaining setting of a threshold value V _S of the inverter device of the present invention.

FIG. 6 is a flowchart showing a procedure of a control operation of the inverter device of the present invention.

FIG. 7 is a diagram for explaining a current limiting operation performed by the inverter device of the present invention.

FIG. 8 is a block diagram illustrating a configuration of an inverter device according to a second embodiment of the present invention.

FIG. 9 is a block diagram showing a configuration of a first conventional example.

FIG. 10 is a block diagram showing a configuration of a second conventional example.

[Explanation of symbols]

2 Solar Battery 3 Commercial Power System 5 High Frequency Inverter Bridge 8 DC Reactor 11 Low Frequency Inverter Bridge 15 Inverter Control Circuit 20 Short Circuit Limiter 21 Current Limiter 22 DC Voltage Comparison Unit 22 AC Switch

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI H02J 3/38 H02J 3/38 Q (72) Inventor Tsukasa Takebayashi 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp Corporation ( 56) References JP-A 7-28538 (JP, A) JP-A 62-293936 (JP, A) JP-A 8-171430 (JP, A) JP-A 4-284516 (JP, A) Hei 4-35631 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02M 7/48 G05F 1/67 H02H 7/122 H02J 3/38

Claims (10)

(57) [Claims] An inverter device for converting the power of a DC power supply such as a solar cell into AC power by opening and closing a switching circuit and supplying the AC power to a load or an existing commercial power system. Prior to driving, inverter short-circuit means for short-circuiting the inverter output, current increasing means for gradually increasing the current flowing through the closed circuit formed by the short-circuit of the inverter output from the point of short-circuit, and short-circuit for controlling the short-circuit period of the inverter output When the DC input voltage of the closed-circuit exceeds a preset threshold, the short-circuiting operation by the inverter short-circuiting unit is stopped to allow normal driving of the inverter, and the DC input voltage is set to the threshold. Starting determination means for continuing the short-circuiting operation by the short-circuiting means if not exceeding The inverter apparatus according to symptoms. 2. The inverter device according to claim 1, wherein the short-circuit period control means sets a duty ratio of the switching circuit according to a specified short-circuit period, and the switching circuit uses the set duty ratio. Wherein the inverter is operated at a constant duty ratio. 3. The inverter device according to claim 2, wherein the short-circuit period control means controls the duty ratio every time the startup determination means determines that the DC input voltage of the closed circuit does not exceed the threshold value. And the duty ratio is gradually increased each time the duty ratio setting is reviewed. 4. The inverter device according to claim 3, wherein said activation judging means changes said threshold value in response to an operation of increasing a duty ratio by said short-circuit period control means. Inverter device. 5. The inverter device according to claim 1, wherein said current increasing means is a reactor connected to said closed circuit. 6. A switch for switching the power of a DC power supply such as a solar cell.
Convert More AC power to the opening and closing operation of the ring circuit is load
Or an inverter device that supplies the existing commercial power system.
When the inverter output rises,
Inverter short circuit that shorts the inverter output prior to
Means, and a filter provided at a stage subsequent to the switching circuit.
The reactor is composed of reactors
Current flowing in the closed circuit formed by the
Current increasing means for gradually increasing from the time of the short circuit, and short-circuit period controlling means for controlling the short-circuit period of the inverter output
And the DC input voltage of the closed circuit is a predetermined threshold
If it exceeds, the short-circuit operation by the inverter short-circuit means is stopped.
While allowing the inverter to operate normally,
If the input voltage does not exceed the threshold value,
It has a startup determining means for continuing the short-circuit operation.
Inverter device. 7. The inverter device according to claim 6, wherein said inverter short-circuit means is provided at a stage subsequent to said filter circuit. 8. The inverter device according to claim 1, wherein said inverter short-circuit means short-circuits said switching circuit. 9. The inverter device according to claim 1, wherein the switching circuit is a high-frequency switching circuit that converts power of the DC power supply to high-frequency power, and a low-frequency switching circuit that converts high-frequency power to low-frequency power. A switching circuit, and a filter circuit including a reactor and a capacitor is provided between the high-frequency switching circuit and the low-frequency switching circuit. The short-circuit period control means sets the duty ratio of the high-frequency switching circuit according to a specified short-circuit period. At the same time, the high-frequency switching circuit is operated at the duty ratio according to the set duty ratio. Inverter apparatus characterized in that to operate in a constant. 10. The inverter device according to claim 1, wherein a filter circuit including a reactor and a capacitor is provided at a stage subsequent to the switching circuit, and the current increasing unit is configured to detect a current from the reactor. Wherein the inverter short-circuiting means is a switch provided on the circuit downstream side of the filter circuit to short-circuit the inverter output, and wherein the short-circuiting period control means controls the switching circuit according to a specified short-circuiting period. An inverter device, wherein a duty ratio is set and the switching circuit is operated at a constant duty ratio with the set duty ratio.