JP3423196B2 - Inverter circuit - 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 circuit for converting DC power obtained from a DC power source such as a solar cell into AC power and outputting the AC power to an AC power system, and more particularly to an AC current output from the inverter circuit. The present invention relates to an inverter circuit capable of detecting a direct current component included in a high precision and suppressing the generation of the direct current component.

[0002]

2. Description of the Related Art A solar power generation system, as shown in FIG. 11, outputs the output power of a DC power source (1) composed of solar cells.
The inverter main circuit (2) converts it into AC power and supplies it to a load such as an AC power system (4) and a motor. The operation of the inverter main circuit (2) is an inverter control circuit.
It is controlled by (3).

As shown in FIG. 12, the inverter main circuit (2) outputs the DC output generated between the P-phase and the V-phase of the solar cell to PW.
A filter circuit (6) comprising a switching circuit (5) composed of a plurality of M-modulating switching elements Q1 to Q4, and a filter circuit (6) for shaping a pulsed AC waveform obtained from the switching circuit (5) into a sine waveform. The AC output of the sine waveform obtained from 6) is supplied to the AC power system (4) via the line (7).

By the way, when the switching circuit (5) converts direct current into alternating current, a direct current component may be superimposed on the alternating current output current I1. In this case, transformers connected to the same system, especially pole transformers, The magnetic flux is magnetized and saturated, the transformer does not function normally, and a system failure occurs. When supplying AC power to a load such as a motor, if a DC component is superimposed on the current that should be applied to the motor, the motor will be demagnetized and torque ripple will occur, resulting in troubles such as smooth rotation. To do.

Therefore, conventionally, the DC component of the AC output current I1 is detected, and the switching circuit (5) is switching-controlled so as to suppress the DC component, and when an excessive DC component is generated, the inverter is turned on. It is being stopped.

When detecting the direct current component of the output current, the following two methods have been conventionally adopted as methods for detecting the change in the output current. The first method is as shown in FIG.
A current sensor (8) is installed so as to surround the AC output line (7), and the current is detected based on the magnetic field generated when the current flows through the AC output line (7). The second method is to detect the output current I1 by interposing a shunt resistor (9) on the AC output line (7) and detecting the voltage across the shunt resistor (9) as shown in FIG. To do. Incidentally, in order to suppress the loss due to the current flowing through the shunt resistor (9), a resistor of about several tens mΩ is usually adopted as the shunt resistor (9).

Whichever detecting method is adopted, a current control circuit as shown in FIG. 15 is required. The current detection signal obtained from the current sensor (8) or the shunt resistor (9) is subjected to amplification and low pass filter processing in the signal processing circuit (10) to detect a direct current component. The DC component detection signal is supplied to the PWM control circuit via a signal isolation transmitter (11) such as an isolation amplifier and is used for control for suppressing the DC component. The DC component detection signal obtained from the signal isolation transmitter (11) is supplied to the value determination circuit (12) to determine the magnitude of the DC component. When the DC component exceeds the predetermined reference level,
An OFF command is issued to the PWM control circuit, and the operation of the inverter is stopped. However, when the current sensor (8) is adopted, the signal isolation transmitter (11) is not required.

[0008]

However, according to the method using the current sensor (8), the current can be detected in a non-contact manner while being electrically insulated from the AC output line (7). Therefore, it is possible to easily obtain the control signal for controlling the direct current component, but there is a problem that the zero point of the current sensor (8) is unstable and the current detection accuracy is as low as about 1% at most.

According to the method using the shunt resistor (9),
High detection accuracy of 1% or less can be obtained, but AC output line
Since the detection signal is obtained directly from (7), it is necessary to electrically insulate the signal by some method in order to transmit the detection signal to the control circuit. In general, a signal isolation transmitter such as an isolation amplifier is provided to insulate and transmit an analog value, which causes a problem of increasing the number of parts and cost.

Particularly, in the inverter for photovoltaic power generation, it is necessary to suppress the direct current component to 1% or less of the rated current, and the accuracy of the direct current component detection by the current sensor is insufficient. The DC component detection method using resistors was inevitably adopted, and an increase in the number of parts and an increase in cost could not be avoided.

Therefore, an object of the present invention is to provide an inverter circuit capable of accurately detecting the DC component contained in the output current of the inverter main circuit with a simple structure and controlling the DC component.

[0012]

The present invention focuses on the fact that the detection accuracy of the DC component by the current sensor depends on the accuracy of the zero point of the sensor itself, and by combining it with the DC component detection by the shunt resistance, By adopting a new method of correcting the zero point of the sensor, we have realized an inverter circuit that has a simple structure as a whole and that can detect DC components with high accuracy.

[0013]

[0014]

[0015]

The inverter circuit according to the present invention is a DC power supply.
An inverter main circuit (2) for converting DC power obtained from (1) into AC power and outputting the AC power to an AC output line (7), and an inverter control circuit for controlling the operation of the inverter main circuit (2)
(3), the inverter control circuit (3) has a control function of suppressing the DC component contained in the current flowing through the AC output line (7) to zero. 3) is a shunt resistor (9) interposed in the AC output line (7) and a first DC component included in the output current of the inverter main circuit (2) based on the voltage across the shunt resistor (9). Whether the first DC component detecting means and the DC component detected by the first DC component detecting means exceed one of the at least two reference levels set on the plus side and the minus side. 1 for the level determination means for determining whether or not and the determination result by the level determination means
Alternatively, a signal insulation transmission means for converting into a digital value of a plurality of bits and electrically insulating the digital value and outputting it, a current sensor (8) equipped on the AC output line (7), and a current sensor (8) And a second DC component for detecting a DC component contained in the output current of the inverter main circuit (2) on the basis of the offset adding means for adding the offset amount to the current detection signal The offset adding means comprises a detecting means and a current controlling means for controlling the direct current component to zero based on the direct current component detected by the second direct current component detecting means, and the offset adding means is provided for the signal insulation transmission. The current sensor (8) is executed by executing a predetermined offset amount adjusting operation using the digital value output from the means.
It is characterized in that the zero point of the current detection signal due to is corrected.

In the above-mentioned inverter circuit of the present invention, the offset adding means performs a predetermined offset amount adjusting operation using the digital value output from the signal insulation transmission means, and outputs a current detection signal by the current sensor (8). The offset amount to be added is forcibly changed. As a result, the DC component contained in the output current of the inverter main circuit (2) changes due to the operation of the current control means. In this process, the DC component is set to the plus side and the minus side.
It becomes equal to one reference level, and these states are judged by the level judging means. These judgment results are
As a digital value of 1 or a plurality of bits, it is supplied from the signal insulation transmission means to the offset addition means. If the two offset amounts added by the offset adding means at the time when the DC component becomes equal to the two reference levels have no deviation of the zero point in the current detection signal from the current sensor (8),
There are two values with opposite polarities and equal absolute values, but if there is a zero point deviation in the current detection signal from the current sensor (8),
The two offset amounts are biased toward the plus side or the minus side according to the shift of the zero point. Therefore, by averaging the two offset amounts, the offset amount corresponding to the shift of the zero point can be obtained. Therefore, the offset adding means corrects the zero point of the current detection signal from the current sensor (8) based on the average value of the two offset amounts. The offset amount for the zero point correction is theoretically obtained by averaging the two offset amounts, but the average value is subjected to a predetermined correction as necessary.

[0018]

According to the inverter circuit of the present invention,
Since the zero point of the current detection signal of the current sensor is accurately corrected by the detection result of the direct current component by the shunt resistance,
The current sensor can detect the direct current component with high accuracy, and thus the direct current component can be accurately controlled. Further, since the signal indicating the detection result of the DC component by the shunt resistor (9) is digital data with a small bit width, in order to electrically insulate and transmit the signal, the signal isolation of a simple structure such as a photo coupler is used. A transmitter can be used, and the configuration is simpler than before.

[0019]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below with reference to FIGS.
Regarding the embodiment implemented in the inverter for photovoltaic power generation shown in
A detailed description will be given with reference to the drawings.

First Embodiment In the inverter according to the present invention, as shown in FIG. 1, a current sensor is provided for the AC output line (7) shown in FIG.
(8) is equipped (see FIG. 13) to configure the current control circuit (13) together with the current sensor (8), while the AC output line (7)
A shunt resistor (9) is interposed between the shunt resistor (9) (see FIG. 14) to form a high precision detection circuit (14) including the shunt resistor (9).

As shown in FIG. 1, in the detection section of the current control circuit (13), the current value detection signal from the current sensor (8) is used for current control and is supplied to the signal processing circuit (15) for amplification and Low-pass filter is applied to detect DC component. Further, an offset signal obtained from a microcomputer (16) having a D / A converter is added to the current value detection signal from the current sensor (8).

On the other hand, in the high-accuracy detection circuit (14), the minute detection voltage obtained from the shunt resistor (9) is supplied to the signal processing circuit (17) for amplification and low-pass filtering, and the AC output line ( The DC component contained in the AC current flowing through 7) is detected. The detected DC component is added to the positive side judgment circuit (1
8) and the negative side determination circuit (19), it is determined whether or not the DC component exceeds a predetermined positive side determination value or a predetermined negative side determination value, both determination circuits (18) (19) The determination result as the binarized data obtained from is further ORed, and the result is passed through the signal isolation transmitter (20) composed of a photocoupler, and the microcomputer of the current control circuit (13) ( It is output to the input port of 16).

In response to this, the microcomputer (16) of the current control circuit (13) creates an offset adjustment signal for shifting the DC offset value of the current sensor (8) to both the plus side and the minus side. Output from the D / A converter and added to the current value detection signal from the current sensor (8). The offset adjustment signal can be easily created by using a voltage dividing resistor or the like.

Since the high precision detection circuit (14) shown in FIG. 1 employs the shunt resistor (9), the output voltage of the inverter main circuit is directly applied to the high precision detection circuit (14). Only digital data insulated by the signal isolation transmitter (20) composed of a photocoupler is transmitted to the current control circuit (13).

In the high precision detection circuit (14) shown in FIG.
As shown in, the signal isolation transmitter (20) is turned on when the main circuit DC component is larger on the plus side than the plus side judgment value or on the minus side than the minus side judgment value, and the result is It is output as 1-bit digital data to the microcomputer (16) of the current control circuit (13).

Since the data input to the microcomputer (16) here is only 1 bit, it is unknown whether the DC component is generated on the plus side or the minus side. Therefore, the following correction method is adopted. That is,
The DC component was generated during the operation of the inverter, and the judgment value by the positive side judgment circuit (18) or the negative side judgment circuit (19) was exceeded at point A in Fig. 3, so the signal isolation transmitter (20) was turned on. Then, the fact is notified to the microcomputer (16).
In response to this, the microcomputer 16 starts the adjustment operation of points B to F in FIG.

First, the microcomputer (16) is a D / A
Set the output of the converter to the positive side maximum controlled variable. As a result, the DC component contained in the current detection signal input to the signal processing circuit (15) increases, so that the control works to cancel the DC component, and as a result, the DC component flowing through the AC output line (7). Will increase to point C in FIG. 3, and the input port of the microcomputer (16) will show the state of detection. Next, the D / A output value is gradually lowered, and the D / A output value at the time D when the detection is first released is stored. Further, the D / A output value is gradually lowered, and the D / A output value at point E where the DC component is detected next is stored. Finally, the average value of the D / A output value at point D and the D / A output value at point E
(Point F) is calculated, the calculation result is output as an offset amount for zero point correction, and the adjustment sequence ends. As a result, the zero point of the current sensor (8) is corrected with high accuracy.

According to the above-described embodiment, the plus side determination circuit (1
8) and the judgment result of the minus side judgment circuit (19) are supplied from the signal isolation transmitter (20) as 1-bit digital data to the current control circuit (13), and the zero point of the current sensor (8) is accurately measured. Since it is corrected, the signal isolation transmitter (20) can adopt a simple structure consisting of one photocoupler in comparison with the conventional zero point correction by the shunt resistor (9) only. Only one signal line (1 bit) is required to connect the transmitter (20) to the microcomputer (16).

Although some adjustment sequences are conceivable in addition to the above adjustment sequence, in any case, in the case of a 1-bit input port, the microcomputer (16) has a DC component in either the positive or negative direction. Since it is not possible to know whether or not occurs, in Fig. 3, although the direct current component first exceeded the judgment value on the minus side, the adjustment sequence once temporarily changed the polarity to the plus side maximum control amount in the opposite direction. Is giving. This may cause a certain amount of direct current to flow out. Therefore, the present embodiment can be applied only when the DC component generated in the offset adjustment process is acceptable, for example, when the DC component is allowed to flow for a short time.

Second Embodiment In the high-accuracy detection circuit (21) shown in FIG. 4, the determination results of the positive side determination circuit (18) and the negative side determination circuit (19) are converted into two signals each consisting of a photocoupler. Isolation transmitter (2
2) It is supplied to the microcomputer (16) via (23).

In the high precision detection circuit (21), as shown in FIG.
When exceeding the (minus side determination value), a predetermined adjustment sequence operates from the point B where the microcomputer (16) confirms this state. That is, at point B, the DC component exceeds the negative judgment value, so the current D / A output value is gradually increased in the positive direction and the negative judgment value is cleared. The value and the D / A output value at point D that exceeds the positive side determination value are stored. And D / of C point and D point
The average value of A output values (point E) is calculated, the calculation result is output as an offset amount for adjusting the zero point, and the adjustment sequence ends. As a result, the zero point of the current sensor (8) is corrected with high accuracy.

According to this embodiment, no DC component exceeding the initial DC component (a value slightly larger than the positive or negative determination value) is not generated during the adjustment sequence. or,
The judgment results of the positive side judgment circuit (18) and the negative side judgment circuit (19) are supplied from the two signal isolation transmitters (22) and (23) as 2-bit digital data to the current control circuit (13) to obtain the current. Since the zero point of the sensor (8) is corrected with high accuracy, 2
Both signal isolation transmitters (22) and (23) can be configured by using one photocoupler, and only two signal lines (2 bits) with the microcomputer (16) are enough. In the case where a DC component flows out to the plus side, which is the opposite of FIG. 5, the same zero point correction can be performed by executing the sequence completely opposite to the above.

By the way, in the inverter for photovoltaic power generation, it is required to stop the operation of the inverter when the DC component exceeds a certain judgment level. In the first and second embodiments, since the adjustment sequence works from the time when the DC component exceeds the determination level, the inverter is temporarily stopped when the DC component reaches the determination level, and then the inverter is restarted. Procedure is required. As an example for avoiding this, the following third example will be given.

Third Embodiment As shown in FIG. 6, the high precision detection circuit (24) is a signal processing circuit.
The positive side determination circuit (25) and the negative side determination circuit (26) for determining the direct current component obtained from (17) by two high and low reference levels are provided. Then, by taking the logical sum of the judgment results by both judgment circuits, when the DC component exceeds the high level of either one, two signal isolation transmitters (27) (28)
Are turned on at the same time, and when the direct current component exceeds only the low level on either the plus side or the minus side, one of the corresponding signal isolation transmitters is turned on. The on / off state of both signal isolation transmitters (27) and (28) is output to the microcomputer (16) of the current control circuit (13) as 2-bit digital data.

Accordingly, the microcomputer (16)
As shown in FIG. 7, when the DC component is somewhat large on the plus side or the minus side and either one of the signal isolation transmitters (photocouplers) is turned on, the same adjustment sequence as in the second embodiment is used. to start. On the other hand, the DC component becomes excessive on the plus side or minus side, and both signal isolation transmitters (27)
If (28) is turned on at the same time, stop the operation of the inverter.

According to the above embodiment, the zero point of the current sensor (8) is adjusted without stopping the inverter within the range where the DC component does not become excessive on the plus side or the minus side, and the DC component with high accuracy is obtained. You can control.
In the above embodiment, when the DC component of the stop level of the inverter flows out, the information on whether the DC component is excessive on the plus side or on the minus side is lost, so the offset readjustment is performed. For this, it is possible to adopt a method in which an adjustment sequence similar to that of the first embodiment is first executed, and after the plus / minus is found, an adjustment sequence similar to that of the second embodiment is executed.

Fourth Embodiment In this embodiment, as shown in FIG. 8, a high precision detection circuit (29) is equipped with a plus side judgment circuit (25) and a minus side judgment circuit (26) as in the third embodiment. Together with the first to third 3
It is equipped with two signal isolation transmitters (30), (31) and (32), and when both judgment circuits (25) and (26) judge that the DC component exceeds the high level, Taking the logical sum of the judgment results, the third signal isolation transmitter (32) is turned on, and it is judged by both judgment circuits (25) and (26) that the DC component has exceeded the low level of either one. If so, one of the corresponding one of the first and second signal isolation transmitters (30) and (31) is turned on. And these three signal isolation transmitters (30) (31) (3
The output of 2) is supplied to the microcomputer (16) of the current control circuit (13) via three (3 bit) signal lines.

Accordingly, the microcomputer (16)
Performs the same adjustment sequence as in the second embodiment when either one of the first and second signal isolation transmitters (30) and (31) is turned on. On the other hand, the third signal isolation transmitter (3
When 2) is turned on, stop the operation of the inverter.

According to the above-mentioned inverter circuit, the judgment results of the plus side judgment circuit (25) and the minus side judgment circuit (26) are determined by 3
Since it is supplied to the current control circuit (13) as bit digital data to correct the zero point of the current sensor (8) with high accuracy, compared with the conventional DC component control using only the shunt resistor (9), The configuration is simple.

Fifth Embodiment The embodiment shown in the drawing employs a control for constantly reducing the DC component to a value near zero by using two photocouplers. The detection signal of the DC component obtained from the signal processing circuit (17) of the high-accuracy level detection circuit (33) is the positive side determination circuit (3
4), and input to the minus side determination circuit (35) and the polarity determination circuit (36).

The polarity judgment circuit (36) judges whether the DC component is positive or negative and inputs the result to the signal isolation transmitter (38) as 1-bit digital data. . Here, as shown in FIG. 10, when the direct current component is positive, it is turned on, and when it is negative, the digital data is turned off. The creation of the digital data is
It can be easily configured by a comparator or the like that detects the zero cross of the direct current component. On the other hand, the positive side judgment circuit (3
4) and the minus side decision circuit (35) decides whether or not the DC component exceeds a predetermined plus and minus side decision value, and inputs the logical sum of the results to the signal isolation transmitter (37). To do.

The 1-bit digital data representing the polarity judgment result output from the signal isolation transmitter (38) is input to the microcomputer (16) of the current control circuit (13) and used for feedback control of the direct current component. To be done. Specifically,
As indicated by 0, when the polarity determination result is ON, the microcomputer 16 reduces the D / A output value by a constant value in order to reduce the direct current component. On the contrary, when the polarity determination result is OFF, the microcomputer 16 increases the D / A output value by a constant value in order to reduce the DC component.

By repeating the above control operation at an appropriate cycle, the DC component output from the inverter is adjusted so as to always approach zero. When a change in the direct current component that the control does not follow occurs and the direct current component exceeds a predetermined upper limit value or lower limit value as shown in FIG. 10, this state is indicated by the plus side determination circuit (34 ) Or by the minus side determination circuit (35), and the detection result is supplied from the signal isolation transmitter (37) to the current control circuit (13) as 1-bit digital data to forcibly stop the operation of the inverter.

Further, the adjustment sequence shown in each embodiment is an example, and various other sequences can be adopted. For example, in FIG. 5, when the point C is detected, the adjustment amount up to ± 0 (D / A corresponding to the negative determination value)
When the output value) is known from the circuit design, it is possible to roughly specify the necessary offset amount from the point C and specify it.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of an inverter circuit according to the present invention.

FIG. 2 is a diagram illustrating a method of determining a DC component according to the first embodiment.

FIG. 3 is a diagram illustrating an adjustment sequence in the first embodiment.

FIG. 4 is a block diagram showing a second embodiment of the inverter circuit according to the present invention.

FIG. 5 is a diagram illustrating an adjustment sequence in the second embodiment.

FIG. 6 is a block diagram showing a third embodiment of the inverter circuit according to the present invention.

FIG. 7 is a diagram illustrating a method of determining a DC component according to the third embodiment.

FIG. 8 is a block diagram showing a fourth embodiment of the inverter circuit according to the present invention.

FIG. 9 is a block diagram showing a fifth embodiment of the inverter circuit according to the present invention.

FIG. 10 is a diagram illustrating a control operation in the fifth embodiment.

FIG. 11 is a block diagram showing a configuration of a solar power generation system.

FIG. 12 is a circuit diagram showing a configuration of an inverter main circuit.

FIG. 13 is a perspective view of a current sensor.

FIG. 14 is a diagram showing a shunt resistance.

FIG. 15 is a block diagram showing a conventional control method based on a detected current value.

[Explanation of symbols]

(1) DC power supply (2) Inverter main circuit (3) Inverter control circuit (4) AC power system (7) AC output line (8) Current sensor (9) Shunt resistance (13) Current control circuit (14) High-precision detection circuit (16) Microcomputer (18) Positive side judgment circuit (19) Negative side judgment circuit (20) Signal isolation transmitter

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI H02M 7/5387 H02M 7/5387 Z

Claims (6)

(57) [Claims] 1. An inverter main circuit (2) for converting DC power obtained from a DC power supply (1) into AC power and outputting the AC power to an AC output line (7), and controlling the operations of the inverter main circuit (2). It is composed of an inverter control circuit (3), and the inverter control circuit (3) is included in the current flowing through the AC output line (7).
Inverter with a control function that suppresses the direct current component to zero.
In the inverter circuit, the inverter control circuit (3) uses the shunt resistor (9) interposed in the AC output line (7) and the voltage across the shunt resistor (9) to determine the inverter main circuit.
The first to detect the DC component contained in the output current of the circuit (2)
The direct current component detecting means and the direct current component detected by the first direct current component detecting means are
At least two groups set on the lath side and the minus side
Whether one of the sub-levels exceeds the reference level
And a determination result by the level determination means of 1 or a plurality of bits.
Convert to a digital value and electrically insulate the digital value
An offset amount is added to the signal isolation transmission means for outputting , the current sensor (8) equipped on the AC output line (7), and the current detection signal by the current sensor (8).
Based on the offset adding means to be added and the current detection signal to which the offset amount is added,
DC component included in output current of inverter main circuit (2) is detected
Based on the direct current component detected by the second direct current component detecting means and the second direct current component detecting means.
The current for controlling the DC component to zero.
Control means, and the offset adding means outputs from the signal insulation transmission means.
Predetermined offset amount adjustment operation using digital value
Is executed to correct the zero point of the current detection signal from the current sensor (8). 2. The level determination means is a plus side determination circuit (1
8) and the minus side judgment circuit (19), either one
Judgment circuit determines that the DC component exceeds the reference level
Signal isolation transmission means, the result of the determination is
Is supplied to the offset adding means as a digital value
However, the offset adding means uses the DC component as a reference for either one.
When the level is exceeded, current detection by current sensor (8)
The maximum offset amount of plus or minus side signal
After the addition, the DC component has a polarity opposite to that of the offset amount.
Change the offset amount until it returns to the quasi level,
When the direct current component reaches two reference levels,
Offset amount for zero point correction based on the amount of fuzz
The inverter circuit according to claim 1, wherein: 3. The level judging means is a plus side judging circuit (1
8) and the negative side judgment circuit (19), each judgment circuit
It was determined that the DC component exceeded the reference level by
Then, the signal isolation transmission means outputs the judgment results of both judgment circuits by 2 bits.
Is supplied to the offset adding means as a digital value
However, the offset adding means uses the DC component as a reference for either one.
When the level is exceeded, the DC component has a polarity opposite to that of the reference level.
Change the offset until it reaches the reference level of
Offset when the flow reaches two reference levels
Offset amount for zero correction is calculated based on
The inverter circuit according to claim 1 . 4. The level determining means determines whether the level is high or low.
Positive side judgment circuit (25) with level and negative side judgment
It consists of the circuit (26), and the DC component is
When it is judged that one of the high judgment levels is exceeded,
The signal isolation transmission means uses the determination result as a 2-bit digital signal.
Is supplied to the offset addition means as a
By the constant circuit, the low judgment level of the DC component
When it is determined that the signal is exceeded, the signal insulation transmission means
Offset is added with the fixed result as a 2-bit digital value
The DC component exceeds the high judgment level of either one.
In this case, the inverter control circuit (3) is the main inverter circuit.
While the operation of (2) is stopped, the DC component
When the low judgment level is exceeded, the offset adding means
Until the flow reaches the reference level with the opposite polarity to the reference level.
The offset amount is changed with, and the DC component has two low judgment levels.
Based on the offset amount at the time
The inverter circuit according to claim 1 , wherein an offset amount for correction is calculated . 5. The level determining means determines whether the level is high or low, respectively.
Positive side judgment circuit (25) with level and negative side judgment
It consists of the circuit (26), and the DC component is
When it is judged that one of the high judgment levels is exceeded,
The signal isolation transmission means uses the judgment result as a 1-bit digital signal.
As Le value, while subjected sheet to the offset adding means, both determine
By the constant circuit, the low judgment level of the DC component
When it is determined that the signal is exceeded, the signal insulation transmission means
The set result is a 2-bit digital value different from the 1-bit
Is supplied to the offset adding means as a
When one of the high judgment levels is exceeded, the inverter control circuit
(3) After stopping the operation of the inverter main circuit (2),
In the offset adding means, the DC component is opposite to the reference level.
Change the offset amount until it becomes the reference level of polarity,
When the DC component becomes two low determination levels in the change process
Based on the offset amount at
While calculating the fuzz amount, the DC component is low
When the level exceeds a certain level, the DC component is
Change the offset amount until it becomes the reference level of polarity,
Off when the DC component becomes two low judgment levels
Set the offset amount for zero correction based on the set amount.
The inverter circuit according to claim 1, which is calculated . 6. A positive side determination circuit (3
4) and the negative side judgment circuit (35) and the polarity judgment circuit (36)
The DC component is determined by one of the judgment circuits.
When it is determined that the reference level is exceeded, the signal isolation transfer
The stage sets the decision result as a 1-bit digital value, and
To the polarity determination circuit (36) while supplying the
The polarity judgment result of the DC component by
Supply to offset adding means as bit digital value
However, the offset adding means is based on the polarity determination circuit (36).
Constant to reduce the DC component according to the determined polarity
Repeats the control operation to add the amount offset at a constant cycle
However, the positive side judgment circuit (34) or the negative side judgment circuit (3
It was determined by 5) that the DC component exceeded the reference level.
The inverter control circuit (3) is the same as the inverter main circuit (2).
The inverter circuit according to claim 1 , which stops operation .