JPH07298625A - System interconnection inverter - Google Patents

Abstract

PURPOSE:To automatically stop the interconnection operation when there is a fear of a fault due to a waveform distortion of an output current. CONSTITUTION:Power to be output from an inverter main circuit 2 is detected by a current controller 6, and a continuing time of the state in which the detected power is lower than a set value is measured by an operation controller 13. When the measured continued time exceeds a predetermined time, a system interconnection of the inverter is stopped by a fault discriminator 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grid-connected inverter for connecting a DC power source such as a solar cell to a commercial power system, and more particularly, to a system that automatically and automatically operates when the waveform distortion of an output current increases. The present invention relates to a grid-connected inverter that protects equipment connected to (hereinafter referred to as grid protection).

[0002]

2. Description of the Related Art In recent years, the development of new energy sources represented by solar cells has been earnestly pursued, and such new energy sources have been installed in homes, factories, or areas and connected to commercial power grids of electric power companies. Therefore, it is considered that the surplus power of the new energy source flows backward to the commercial power system.

FIG. 7 shows a configuration example of an inverter for connecting a DC power source to a commercial power system. The inverter main circuit (120) is composed of a plurality of switching elements and the switching of the inverter main circuit (120). PWM to control
It has a control circuit (121) and an output filter (122).

The PWM control circuit (121) includes a differential amplifier (12
4), multiplier (125), operational amplifier (error amplifier) (126), P
A feedback control system is composed of a WM pulse generation circuit (127) and a bandpass filter (123) for extracting the reference frequency component of the output voltage.
The WM pulse is output as a gate control signal to each switching element of the inverter main circuit (120).

In the PWM control circuit (121), for example, an input voltage Vi from a solar cell and a predetermined voltage command value Vre
An input error signal Sa indicating a difference from f is generated by the differential amplifier (124), and the input error signal Sa is multiplied by the signal Sb corresponding to the fundamental frequency component of the commercial AC voltage in the multiplier (125). Thus, the current command value signal Si indicating the control target value is generated.

Then, the operational amplifier (126) generates a signal Sd indicating the difference between the current command value signal Si and the output current value Sc, and the signal Sd is supplied to the PWM pulse generation circuit (127). Thus, a PWM pulse having a pulse width corresponding to the magnitude of the signal Sd is generated. The PWM pulse controls conduction of the switching element of the inverter main circuit (120).

As a result, the inverter main circuit (120) outputs a sinusoidal current and voltage as shown in FIG. 6 (a).

[0008]

However, in the conventional grid-connected inverter, when the output of the DC power supply decreases and the power output from the inverter main circuit (120) decreases, the error amplifier (126) Since both the current command value signal Si and the output current value Sc input to the control signal are reduced, the accuracy of the signal Sd, which is the deviation between the two, decreases, and the feedback system based on the deviation decreases the control resolution. As a result, a large waveform distortion occurs in the output current as shown in FIG. 6 (b). Also, when the circuit forming the inverter is deteriorated or a failure occurs, waveform distortion occurs in the output current. When the waveform distortion of the output current increases, there is a problem that various kinds of obstacles are caused in the operation of the electric device connected to the commercial power system.

An object of the present invention is to provide a grid interconnection inverter that automatically stops grid interconnection operation when there is a risk of a failure due to waveform distortion of an output current.

[0010]

A first grid interconnection inverter according to the present invention is a detection means for detecting electric power output from an inverter main circuit and a state in which the detected electric power is below a set value. It comprises a time measuring means for measuring the time and a protection means for stopping the interconnection operation of the inverter when the measured duration exceeds a predetermined time.

The second grid-connected inverter according to the present invention measures the duration of the state in which the detected distortion exceeds the set value and the detection means for detecting the waveform distortion of the current output from the inverter main circuit. And a protection means for stopping the interconnection operation of the inverter when the measured duration exceeds a predetermined time.

The third system interconnection inverter according to the present invention comprises a storage means for storing in advance the relationship between the power output from the inverter main circuit and the waveform distortion of the current output from the inverter main circuit, and the inverter. Based on the first detection means for detecting the power output from the main circuit, the second detection means for detecting the waveform distortion of the current output from the inverter main circuit, and the detected value of the power obtained from the first detection means. A reference value of the waveform distortion corresponding to the detected value is derived from the storage means, and the detected value of the waveform distortion obtained from the second detection means exceeds a predetermined allowable range with respect to the reference value of the waveform distortion. Detecting means for detecting the increased abnormal condition, time measuring means for measuring the duration of the detected abnormal condition, and keeping the interconnected operation of the inverter stopped when the measured duration exceeds a predetermined time. It is and means.

[0013]

The above-mentioned first system interconnection inverter focuses on the fact that the waveform distortion of the output current increases when the output is low, as described above. That is, when the detected value of the power output from the inverter main circuit falls below a predetermined set value, the duration of this state is measured, and when the measured duration exceeds a predetermined time, the output current waveform It is judged that the strain is increasing, and the interconnection operation is stopped. In addition, when the duration of the lowered state of the power detection value is shorter than the predetermined time, the disturbance due to the waveform distortion is minor and can be ignored, so that the importance is attached to the stability and the interconnection operation is continued.

Here, the interconnection operation can be stopped by a method of stopping the operation of the inverter itself, or a method of opening a relay or breaker provided on the output side of the inverter main circuit at the same time.

The second grid interconnection inverter is intended to protect the grid by a direct method of detecting the waveform distortion itself of the output current. Here, the cause of the waveform distortion is considered to be due to a decrease in output power and deterioration or failure of the circuit. To detect the waveform distortion, for example, a method of performing Fourier analysis on the output current of the inverter main circuit can be adopted.

The third system interconnection inverter is intended for system protection and circuit protection, paying attention to the deterioration or failure of the circuit included in the cause of waveform distortion. That is,
Between the power output from the inverter main circuit and the waveform distortion of the current output from the inverter main circuit, there is a certain relationship determined by the characteristics of the inverter control circuit, and this relationship is obtained experimentally in advance, This is made into a function or a table and stored in a storage means such as a memory.

During the protection operation, the reference value of the corresponding waveform distortion is read from the storage means based on the detected value of the output power of the inverter main circuit, and the detected value of the waveform distortion is read with respect to the reference value of the waveform distortion. Is detected to have increased beyond a predetermined allowable range, and it is determined that the circuit has deteriorated or has failed. Here, if the duration of the detected state is shorter than the predetermined time, it is determined that it is due to a temporary disturbance, and only when the duration exceeds the predetermined time,
Stop the interconnection operation of the inverter. If the detected value of the waveform distortion is within the predetermined allowable range, it is determined that the waveform distortion is due to a measurement error or the like, and the interconnection operation of the inverter is stopped only when the detected value exceeds the allowable range.

[0018]

According to the grid interconnection inverter of the present invention, the waveform distortion of the output current is detected directly or indirectly, and the grid interconnection operation is automatically stopped based on the detection. Therefore, there is no possibility that a failure will occur in the electric device connected to the system.

[0019]

First Embodiment As shown in FIG. 1, a solar cell (1) as a DC power source is connected to a commercial power system (3) through an inverter main circuit (2), and the inverter main circuit (2) ) Is driven by the drive circuit (21). Further, between the inverter main circuit (2) and the commercial power system (3), a relay (23) opened and closed by a relay drive circuit (22) and a breaker (25) cut off by a breaker trip circuit (24). Is intervening.

Drive circuit (21) for the inverter main circuit (2)
Receives a PWM pulse from the current control circuit (6) and sends a drive signal to a plurality of switching elements (not shown) constituting the inverter main circuit (2).

The output voltage and output current of the inverter main circuit (2) are converted into digital signals through the A / D converters (4) and (5), respectively, and then supplied to the current control circuit (6). On the other hand, the input voltage and the input current of the inverter main circuit (2) are converted into digital signals through the A / D converters (16) and (17) and then supplied to the operation control circuit (13).

The current control circuit (6) is composed of a digital signal processor and executes high-speed arithmetic processing. The current control circuit (6) is an inverter main circuit
BPF (11) and PWM for PWM control of (2)
The AC voltage data from the A / D converter (4) including the pulse generation circuit (12) is subjected to the BPF (11) to extract the reference frequency component. The reference frequency component is a PWM pulse generation circuit (12)
Sent to. The PWM pulse generation circuit (12) is basically composed of the same feedback control system as the conventional circuit shown in FIG. 7, and has a reference frequency component from the BPF (11) and an A / D converter ( A PWM pulse is generated based on the AC current data from 5) and is supplied to the drive circuit (21) of the inverter main circuit (2).

Further, the current control circuit (6) includes an A / D converter.
A first frequency analysis circuit (7) that performs FFT on the AC voltage data obtained from (4) and a second frequency analysis circuit (7) that performs FFT on the AC current data obtained from the A / D converter (5). It is equipped with each frequency analysis circuit (7) (8),
Each frequency component in the alternating current is calculated. The calculation result is output to the operation control circuit (13).

Further, the current control circuit (6) includes an effective value calculating circuit (9) (1) for calculating the effective values of the output current and the output voltage.
0) is provided, and these calculation results are also supplied to the operation control circuit (13). Since the current control circuit (4) is composed of a digital signal processor as described above, the frequency analysis and the calculation of the effective value are performed at high speed, and the operation result is sent to the operation control circuit (13) in real time.

On the other hand, the operation control circuit (13) is composed of a microcomputer including a CPU and the like. The operation control circuit (13) includes a frequency analysis circuit (7) for the current control circuit (6).
A failure determination circuit (18) is provided for receiving a frequency analysis result from (8) and making a failure determination. Failure determination circuit (18)
First, when the inverter is started, whether the system frequency is 50 Hz or 60 H based on the result of the frequency analysis of the output current.
The mode is determined whether it is z.

Further, the operation control circuit (13) is provided with a frequency-specific data output circuit (20), and in the circuit, the power factor for the system frequencies of 50 Hz and 60 Hz, respectively. The protection data such as the abnormality determination value, the over frequency and the under frequency are stored.

The operation control circuit (13) reads the protection data according to the system frequency from the frequency-specific data output circuit (20) based on the mode discrimination result when the inverter is started.

Further, the operation control circuit (13) includes a current control circuit.
A power point tracking circuit (14) for setting the optimum operating voltage to be output by the solar cell (1) is provided based on the effective values of the voltage and current sent from (6). The set optimum operating voltage is sent to the AC current amplitude command (15). The AC current amplitude command (15) creates a command for the AC current amplitude based on the difference between the optimum operating voltage and the input voltage of the inverter main circuit (2).
It is sent to the PWM pulse generation circuit (12) of (6).

As a result, the PWM pulse generation circuit (9)
The operation characteristic is switched and set according to the system frequency, and an appropriate PWM pulse is generated by receiving a command about the amplitude of the alternating current from the operation control circuit (10), and the PWM pulse is generated by the inverter main circuit (2). It is supplied to the drive circuit (21).

The failure determination circuit (18) includes an inverter main circuit.
The input current and input voltage of (2), the effective value of the output current and output voltage sent from the current control circuit (6), and the above-mentioned protection data read from the frequency-specific data output circuit (20) are supplied. To be done.

In response to this, the failure determination circuit (18) calculates the output power of the inverter main circuit (2) in step S1 shown in FIG. 2, and the output power is set to a set value (for example, 50 W) in step S2. It is determined whether or not If YES, then in step S3, the state below the set value is 10
Determine if it continues for more than a second. If YES, the operation of the inverter is set to the standby mode and the circuit operation is stopped in step S4. Then, when the output power increases continuously, the inverter is restarted.

Further, the failure judging circuit (18) compares the actually measured values of the power factor and the frequency as protection data to judge the occurrence of a failure, and when the failure occurs, the protection operation circuit (19) functions. Let As a result, the relay drive circuit (22)
3) is opened. Further, when a serious failure occurs, the breaker trip circuit (24) forcibly trips the breaker (25) to cut off the interconnection to the commercial power system (3).

According to the grid-connected inverter of this embodiment,
By detecting the decrease in output power, which is the fundamental cause of the waveform distortion of the output current, system protection is realized with a simple circuit configuration.

Second Embodiment FIG. 3 shows another system protection operation of the operation control circuit (13). First, in step S11, the waveform distortion of the output current of the inverter is measured. In measuring the waveform distortion, the fundamental frequency component I ₁ contained in the output current and the higher-order harmonics of the second or higher order are based on the FFT analysis result for the output current obtained from the frequency analysis circuit (8) shown in FIG. Component Ii (i =
2, 3, ..., N) are detected, and the total current distortion rate E is calculated from the following equation 1.

[0035]

[Equation 1]

Then, in step S12 of FIG. 3, the measured waveform distortion (total current distortion rate E) is a set value (for example, 10).
%) Is exceeded, and if the result is YES, then in step S13, the state of being equal to or greater than the set value is 1
Judge whether it continues for 0 seconds or more. If YES, the inverter is set to the standby mode and the circuit operation is stopped in step S14. After that, when 10 minutes have passed in the inverter standby mode, the inverter is restarted.

According to the grid-connected inverter of this embodiment, the waveform distortion of the output current is directly measured, and the measured value serves as a criterion for judging the grid-interruption. Therefore, more accurate grid protection is realized. To be done.

Third Embodiment FIG. 4 shows still another system protection operation of the operation control circuit (13). In this case, as shown in FIG. 5, the relationship between the inverter output and the waveform distortion (distortion characteristic) is measured in advance and is converted into a function by an approximate expression, and the approximate expression is converted into the failure determination circuit (18) of FIG.
It is stored in. In the protection operation, first, the output power of the inverter is measured in step S21 of FIG. 4, and then the waveform distortion Et (see FIG. 5) corresponding to the measured power Pm is calculated based on the approximate expression of the distortion characteristic. .

Next, in step S23, the waveform distortion of the output current of the inverter is measured. The waveform distortion is measured in the same manner as in the second embodiment. Then, step S24
At step S2, the measured waveform distortion value Em (see FIG. 5) is displayed.
It is determined whether or not the calculated value Et of the waveform distortion in 1 is far away. For example, it is determined whether the value F calculated by the following equation 2 is 5% or more.

[0040]

[Equation 2]

Then, in step S25, it is determined whether or not the measured value Em of the waveform distortion is largely separated from the calculated value Et for 10 seconds or more. If YES, the operation of the inverter is set to the standby mode and the circuit operation is stopped in step S26. After that, when 10 minutes have passed in the inverter standby mode, the inverter is restarted.

According to the grid-connected inverter of this embodiment,
Since the system distortion is protected by detecting the waveform distortion due to the deterioration or failure of the inverter circuit, it is particularly effective for the maintenance of the inverter circuit.

The above description of the embodiments is for explaining the present invention, and should not be construed as limiting the invention described in the claims or limiting the scope. The configuration of each part of the present invention is not limited to the above-mentioned embodiment, and it goes without saying that various modifications can be made within the technical scope described in the claims. For example, it is possible to protect the system by combining the method of the first embodiment and the method of the second or third embodiment. Further, in each of the above-mentioned embodiments, the inverter is set to the standby mode at the time of system protection, but the relay (23) shown in FIG. 1 may be opened or the breaker (25) may be tripped depending on the seriousness of the failure. Can be adopted.

[Brief description of drawings]

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

FIG. 2 is a flowchart showing a system protection procedure in the first embodiment.

FIG. 3 is a flowchart showing a system protection procedure in a second embodiment.

FIG. 4 is a flowchart showing a system protection procedure in a third embodiment.

FIG. 5 is a graph showing the relationship between the inverter output and the waveform distortion in the output current.

6A and 6B are graphs showing waveforms of voltage and current output from the inverter, where FIG. 6A shows a high output and FIG. 6B shows a low output.

FIG. 7 is a block diagram of a conventional general grid interconnection inverter.

[Explanation of symbols]

 (1) Solar cell (2) Inverter main circuit (3) Commercial power system (6) Current control circuit (8) Frequency analysis circuit (13) Operation control circuit (18) Failure judgment circuit (19) Protection operation circuit

Front page continuation (72) Inventor Masahiro Makino 2-5-5 Keihan Hondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Kuniho Tanaka 2-5-5 Keihan-hondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd.

Claims (3)

[Claims] 1. A system interconnection inverter comprising an inverter main circuit interposed between a DC power supply and a commercial power system, and an inverter control circuit for driving and controlling the inverter main circuit, wherein the power output from the inverter main circuit is Detecting means for detecting, time measuring means for measuring the duration of time when the detected power is below the set value, and protection means for stopping the interconnection operation of the inverter when the measured duration exceeds the predetermined time A grid-connected inverter characterized by having and. 2. A grid interconnection inverter comprising an inverter main circuit interposed between a DC power source and a commercial power system, and an inverter control circuit for driving and controlling the inverter main circuit, wherein a current output from the inverter main circuit Detecting means to detect waveform distortion, time measuring means to measure the duration of time when the detected distortion exceeds the set value, and stop the interconnection operation of the inverter when the measured duration exceeds a specified time A grid-connected inverter, which is provided with a protection means. 3. A system interconnection inverter comprising an inverter main circuit interposed between a DC power source and a commercial power system, and an inverter control circuit for driving and controlling the inverter main circuit, wherein the power output from the inverter main circuit The storage means in which the relationship between the waveform distortion of the current output from the inverter main circuit is stored in advance, the first detection means for detecting the power output from the inverter main circuit, and the current output from the inverter main circuit. Based on the detected value of the power obtained from the second detecting means for detecting the waveform distortion and the first detecting means, a reference value of the waveform distortion corresponding to the detected value is derived from the storage means, and the reference of the waveform distortion is obtained. A detection unit for detecting an abnormal state in which the detected value of the waveform distortion obtained from the second detection unit exceeds a predetermined permissible range with respect to the detected value; Timing means for measuring the connection time, when the measured duration exceeds a predetermined time, the system interconnection inverter, characterized in that it comprises a protection means for stopping the interconnected operation of the inverter.