JP2001309664A - Inverter device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To perform equalization of output current balance among devices even when loads such as a coil load and a capacitor load are used in parallel operation. SOLUTION: A microcomputer 61 detects active power, and controls so as to decrease the frequency of the AC output as the active power increases. When two AC power supplies 21 are operated in parallel, for example, the higher power exchange power supply is controlled in the direction of decreasing frequency, and the lower frequency inverter is controlled in the direction of increasing frequency. Will be. Thereby, the output current balance between each AC power supply device is equalized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device suitable for a portable AC power supply and the like.

[0002]

Inverters are widely used in portable AC power supplies, AC motor driving apparatuses, uninterruptible power supplies, and the like. Among them, in the case of a portable AC power supply, a plurality of portable AC power supplies may be connected in parallel to drive a load. In this case, the operation is performed by synchronizing the output frequency of the portable AC power supply. By the way, when the frequency of any one of the portable AC power supplies is slightly changed due to a load change or the like, a current (cross current) flows from one portable AC power supply to the other portable AC power supply, and The circuit components of the AC power supply may be damaged. In this case, a cross current flows from a higher output frequency to a lower output frequency.

Conventionally, as a countermeasure for preventing a cross current between portable AC power supplies, the delay or advance of the phase of the output voltage / current is monitored, the output frequency is adjusted based on this, and thus the cross current is reduced. Some are designed to suppress them. FIG. 14 shows an example of the configuration. The portable AC power supply 1 includes an engine-driven AC generator 2 and an inverter unit 3, and outputs sine-wave AC voltages from output terminals 3 a and 3 b of the inverter unit 3. The inverter unit 3 includes a rectifier circuit 4 for rectifying a three-phase AC voltage output from the AC generator 2, a smoothing capacitor 5, a single-phase full-bridge type inverter circuit 6, a filter circuit 7, a control circuit 8, and a drive circuit. 9 and the like. The control circuit 8 mainly includes a microcomputer 10 (hereinafter, referred to as a microcomputer 10) and a PWM circuit 11 that generates a drive signal.

In this configuration, the control circuit 8 controls the generator 2 so that the engine maintains a predetermined rotation speed, and outputs a predetermined frequency (50 Hz) from the output terminals 3a and 3b.
Alternatively, at a predetermined voltage (for example, 100
PWM control is performed so as to output a sine-wave AC voltage having V).

Further, the control circuit 8 includes an output voltage detection circuit 12 for detecting an output voltage of the inverter circuit 6, an output current detection circuit 13 for similarly detecting an output current, and an output voltage and an output current detected by these. And a phase difference detecting circuit 14 for detecting a phase difference between the output current and the output current. When the output current is delayed from the output voltage, the output frequency is controlled to increase, and when the output current is advanced, the output frequency is decreased. In this way, the output is balanced when two AC power supply units are operated in parallel. In this case, in the case of a 50 Hz power supply,
The frequency is adjusted between 9.90 Hz and 50.10 Hz.

However, when the above-described voltage / current phase detection is performed, for example, a variable output frequency is applied to a coil (L) load or a capacitor (C) load in which the current phase is shifted from the voltage by nearly 90 °. Frequency adjustment is performed in a frequency band near the lower limit or the upper limit within the allowable range. For example, in the case of a coil load, the frequency is adjusted around 50.10 Hz. If the load fluctuates under such a load,
Since the frequency adjustment width cannot be secured, the output current balance of each portable AC power supply deteriorates, the temperature of each component of the inverter circuit rises, or the overcurrent limiter operates to reduce the load for the number of parallel operation units. Can not withdraw,
There is a problem.

[0007] The present invention has been made in view of the above-mentioned circumstances, and has as its object to perform parallel operation.
Even for a load such as a coil load or a capacitor load, the current phase of which is shifted by about 90 ° from the voltage phase,
An object of the present invention is to provide an inverter device in which the output current balance between the devices is equal.

[0008]

According to a first aspect of the present invention, there is provided an inverter device having a DC power supply circuit and a switching element, and switching an output of the DC power supply circuit based on a PWM signal to output a high-frequency voltage. An inverter circuit, a filter circuit for converting the high-frequency voltage into a sine-wave AC voltage and outputting the same, an active power detecting means for detecting active power of the AC output, and an active power detected by the active power detecting means increases. Control means for controlling the frequency of the output voltage to decrease.

For example, when two inverters are connected in parallel to drive a load, and one of the inverters fluctuates in frequency instantaneously, the cross current increases from a higher frequency to a lower frequency. Flows. The inverter device having a higher frequency has a large active power due to the outflow of a cross current, and the active device having a low frequency has a small active power. That is, between the two inverter devices, it was found that the active power increased on the side with the higher frequency and the active power decreased on the side with the lower frequency.

Thus, the inverter device according to the first aspect of the invention is controlled so that the frequency decreases as the active power increases, and conversely, the inverter device is controlled to increase the frequency as the active power decreases. Therefore, when two inverter devices are operated in parallel, for example, the higher frequency inverter device is controlled in the direction of decreasing frequency, and the lower frequency inverter device is controlled in the direction of increasing frequency, As a result, the output frequencies of the inverter devices match, the cross current is reliably suppressed, and the output current balance between the inverter devices can be kept uniform. In this case, when a cross current occurs, a difference in the active power is generated between the two units, and the difference is controlled in a direction approaching. Therefore, the frequency adjustment band is not biased toward the upper limit or the lower limit, and the output is reduced. Unlike the configuration in which the output frequency is controlled in accordance with the phase difference between the voltage and the output current, the output current balance is surely uniform even if the load is a coil load, a capacitor load, or the like.

According to a second aspect of the present invention, the active power detecting means comprises:
It is characterized in that active power is detected during at least a half cycle of the output voltage. According to this, active power detection can be performed in a short time, and subsequent frequency control can be performed quickly.

According to a third aspect of the present invention, the active power detecting means comprises:
It is characterized in that output current detecting means for detecting an output current by an average value is provided. According to this, the output current can be easily detected.

[0013] In a fourth aspect of the present invention, the active power detecting means comprises:
It is characterized in that output current detecting means for detecting an output current as an effective value is provided. According to this, even when the load of the inverter device is a load including the full-wave rectifier, the output current can be detected well.

According to a fifth aspect of the present invention, the active power detecting means comprises:
The present invention is characterized in that output voltage detecting means for converting a high-frequency output voltage of the inverter circuit into a sine-wave AC voltage by a filter and detecting the AC voltage is provided. According to this, it is possible to detect a sine-wave AC voltage despite the fact that the output of the inverter circuit is a rectangular-wave high-frequency output voltage,
In addition, the effect of the reactor voltage drop of the filter circuit can be eliminated.

According to a sixth aspect of the present invention, the PWM signal is generated based on a sine wave reference signal and a carrier signal, and the active power detecting means includes an output current detecting means, wherein the sine wave reference signal and the output current are output. It is characterized in that the active power is detected based on the output current detection signal of the detection means. Since the sine wave reference signal is equivalent to the sine wave AC voltage although having a level difference, the sine wave reference signal can be regarded as an output voltage without providing the output voltage detecting means. There is no need to provide output voltage detection means on the output side of the circuit.

According to a seventh aspect of the present invention, the PWM signal is generated based on a sine wave reference signal and a carrier signal, and the active power detection means detects a high frequency output voltage of the inverter circuit and outputs an output voltage detection signal. Output voltage detecting means, and an output current detecting means for detecting a zero cross of each of the sine wave reference signal and the output voltage detection signal, detecting a phase difference of each zero cross, and correcting the phase difference to obtain an active power. Is characterized in that it is detected. The sine wave AC voltage has a time lag with respect to the sine wave reference signal. This appears as a phase difference between the two zero crossings.
However, according to the seventh aspect of the invention, since the active power is detected by correcting the phase difference (time delay) of the sine wave reference signal with respect to the output voltage, it is possible to accurately detect the active power.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment in which the inverter device of the present invention is applied to a portable AC power supply device will be described below with reference to FIGS. First, FIG. 1 shows an electrical configuration of a portable AC power supply 21 that generates an AC power of, for example, 100 V, 50 Hz or 60 Hz. The portable AC power supply 21 includes a three-phase AC generator 22 driven by an engine (not shown).
And a single-phase inverter unit 2 connected to the subsequent stage
And 3.

The alternator 22 includes fuel (gasoline) for the engine in addition to the rotor and the armature (both not shown).
A stepping motor 24 is provided for controlling the rotation speed of the engine by controlling the supply amount. Armature has Y
Connected main windings 25u, 25v, 25w and auxiliary winding 2
6 are wound, and the main winding terminals 27u, 27v, 2
7w and the auxiliary winding terminals 28a, 28b are connected to input terminals 29u, 29v, 29w and input terminals 30a, 30b of the inverter unit 23, respectively.

On the other hand, the inverter unit 23 is configured as follows. That is, the input terminals 29u,
A rectifier circuit 33 is connected between 9v, 29w and the DC power supply lines 31, 32. A smoothing capacitor 34 is connected between the DC power lines 31 and 32,
An inverter circuit 37 and a filter circuit 38 are cascaded between the output terminals 1 and 32 and the output terminals 35 and 36. Note that the rectifier circuit 33 corresponds to a DC power supply circuit in the present invention.

The rectifier circuit 33 has a configuration in which thyristors 39 to 41 and diodes 42 to 44 are connected in the form of a so-called three-phase mixed bridge.
7 has a configuration in which transistors 45 to 48 (corresponding to switching elements) and free-wheel diodes 49 to 52 are connected in a so-called full bridge form.

The filter circuit 38 includes an inverter circuit 37
Output terminal 53 and output terminal 3 of inverter unit 23
5 and a capacitor 56 connected between the output terminals 35 and 36 of the inverter unit 23. Inverter circuit 37
Is directly connected to the output terminal 36 of the inverter unit 23, and a current transformer 57 for detecting an output current is provided in a current path from the output terminal 54 to the filter circuit 38. .

Further, the inverter unit 23 includes a control power supply circuit 58, a control circuit 59, and a drive circuit 60. The control power supply circuit 58 includes the input terminal 30
a, an AC voltage induced in the auxiliary winding 26 is input through the terminals 30 and 30b, the DC voltage is rectified and smoothed, and a control DC voltage (for example, 5 V, ± 15 V) for operating the control circuit 59 is generated. Has become. The AC voltage induced in the auxiliary winding 26 is also input to the control circuit 59 to detect the engine speed.

The control circuit 59 includes the microcomputer 6
1 (hereinafter, referred to as microcomputer 61), DC voltage detection circuit 6
2. It comprises an output voltage detection circuit 63, an output current detection circuit 64, and a PWM circuit 65. Microcomputer 61
Although not specifically shown, CPU, RAM, ROM,
The input / output port, the A / D converter, the timer circuit, the oscillation circuit, and the D / A converter are configured as one-chip ICs.

The DC voltage detection circuit 62 is connected to the DC power supply line 31.
And a DC voltage Vdc between the DC voltage V.sub.32 and the detected DC voltage V.sub.dc, and outputs the detected DC voltage to the microcomputer 61 as a DC voltage detection signal. In this case, the microcomputer 61 controls the thyristors 39 to 41 based on the DC voltage detection signal so that the DC voltage Vdc becomes a predetermined voltage, for example, 180V.

The output voltage detecting circuit 63 includes a voltage dividing circuit for dividing the voltage between the output terminals 53 and 54 of the inverter circuit 37, and a filter for removing a carrier component from the divided rectangular wave voltage. , And outputs the detected output voltage Vs to the microcomputer 61 and the PWM circuit 65 as an output voltage detection signal.

An output current detection circuit 64 (corresponding to an output current detection means) converts the output current detected by the current transformer 57 to a predetermined voltage level, and outputs the detected output current Is.
Is output to the microcomputer 61 and the PWM circuit 65 as an output current detection signal.

The PWM circuit 65 executes PWM control to generate drive signals G1 to G4 for the transistors 45 to 48. The drive signals G1 to G4 are applied to the bases of the transistors 45 to 48 via the drive circuit 60, respectively.

The microcomputer 61 has an output frequency of 50 Hz by a switch input from a switch input unit (not shown).
It can be set to any of 60 Hz. For example, when an AC power supply of 50 Hz and 100 V is to be generated, a sine wave reference signal Vsin having the same frequency as the set output frequency is supplied to the PWM circuit 65. I have.
However, the sine wave reference signal Vsin is adjusted so that the detection output voltage Vs of the output voltage detection circuit 63 becomes equivalent to 100 V output, that is, output voltage feedback control is performed. . Further, as will be described later, the sine wave reference signal Vsin is also for adjusting the output frequency based on the output active power.

As shown in FIG. 2A, the PWM circuit 65 uses the sine wave reference signal Vsin and a carrier wave Sc composed of, for example, a triangular wave of 16 kHz (for the sake of convenience, the frequency is extremely reduced in the drawing). The high-frequency voltage Vo having a rectangular wave shape shown in FIG.
Hz or 60 Hz).
4 is generated. The high frequency voltage V thus generated
The high frequency component o is removed by a filter circuit 38, for example, as shown in FIG.
An AC output Voac of z or 60 Hz is formed.

The microcomputer 61 functions as active power detection means and control means, and these functions will be described below together with their functions. When the operation is started, the microcomputer 61 controls the output frequency according to the control flowchart shown in FIG. That is, in step Q1, the first zero cross of one cycle of the output voltage Vo (see FIG. 3, timing t0) is detected. In this case, since the effective zero crossing between the sine wave reference signal Vsin and the output voltage Vo ideally coincides with each other, the microcomputer 61 determines the first (the timing to change to the plus side) of one cycle of the sine wave reference signal Vsin. The timing t0 of the zero cross is determined. After this, 6 times for 1/2 cycle
The detected output current I is output four times (equally spaced in time).
The instantaneous values Is (n) (n is 1 to 64) are detected from s, and are sequentially summed (step Q2, step Q3, step Q4). Then, when the total of 64 times is completed (“YES” in step Q4), the process proceeds to step Q5 to calculate (detect) the active power. In this case, the output voltage is uniquely treated as 100 V, and the product of the total value and the output voltage 100 V is obtained. At this time, when the load W (see FIG. 5) is a resistive load, the voltage / current phase does not change,
In the case of a coil load and a capacitor load, the voltage / current phase changes. In the case of a coil load and a capacitor load, a minus portion also appears in the instantaneous value Is (n) of the output current, and reactive power is generated. . In addition,
The total value of step Q5 can be regarded as an average current if the number of detection timings 64 is not taken into account (even if the total value is not divided by 64).

In the next step Q6, a frequency difference for frequency correction is set. In this case, the frequency difference is obtained by an equation obtained by multiplying the active power by a constant (0.2 Hz / 2.8 kW). Then, in step Q7, a sine wave reference frequency Vsin to be changed is obtained. In this case, the frequency fluctuation range is 50.10 Hz at the upper limit and 49.90 Hz at the lower limit, and the upper limit frequency is 50.10 Hz as the reference frequency. The sine wave reference frequency Vsin to be changed is obtained by subtracting the frequency difference from the reference frequency. FIG. 6A shows the relationship between the active power and the sine wave reference frequency Vsin to be changed.

Although not shown in this flowchart, the microcomputer 61 supplies the PWM circuit 65 with the sine wave reference frequency Vsin in the next half cycle so that the output frequency becomes the sine wave reference frequency Vsin. In this way, the output frequency is adjusted according to the active power.

The case where power is supplied to the load F by connecting such portable AC generators 21 in parallel will be described. In FIG. 5A, for example, one of the two portable AC generators is a portable AC generator 21A, and the other is a portable AC generator 21B. Now, load F is 100
Assume that 35A is consumed by V. And each device 21
Assuming that A and 21B are operating in a well-balanced manner, for example, both output 50 Hz, 100 V, and 17.5 A of power. In this case, no cross current occurs between the devices 21A and 21B.

Here, as shown in FIG. 5 (b), one of the AC generators 21A
, Instantaneously becomes, for example, 49.96 Hz, a cross current flows from the other AC generator 21B to one AC generator 21A. Then, the active power of the AC generator 21B on the side where the cross current flows out increases, and the active power of the AC generator 21A on the side where the cross current flows enters decreases.

Then, in one AC generator 21A, the active power in step Q5 of the flowchart of FIG. 4 is reduced, so that the frequency difference in step Q6 is reduced. Thereby, the sine wave reference frequency Vsi of step Q7
n increases. That is, the output frequency is increased (FIG. 6
(B)).

In the other AC power generator 21B, the active power in step Q5 of the flowchart of FIG. 4 increases, so that the frequency difference in step Q6 increases. Thereby, the sine wave reference frequency Vsin of step Q7 decreases. That is, the output frequency is reduced.

The above-described control is performed separately in each of the devices 21A and 21B. On the one hand, the output frequency is controlled in the increasing direction and on the other hand the output frequency is controlled in the decreasing direction. The output frequencies of 21A and 21B match (see FIG. 6C), and the cross current is suppressed.

As described above, according to the present embodiment, the frequency is controlled to decrease as the active power increases.
Conversely, since the frequency is controlled to increase as the active power decreases, the two AC power generators 21A and 21B
Are operated in parallel, even if the output frequencies do not match, the output frequencies of the two AC power generators 21A and 21B immediately match, so that the cross current can be reliably suppressed.

In particular, according to the present embodiment, the active power is detected during a half cycle of the AC voltage, so that the active power can be detected in a short time, and Frequency control can be performed quickly. However, the active power may be detected in one cycle of the AC voltage.

Further, according to the present embodiment, the output current is detected by the average value, so that the output current can be easily calculated, that is, the output current can be easily detected. In the above embodiment, in detecting the active power, the output voltage is set to 100 V without detecting the output voltage.
V and the average value of the detected current (step Q5 in the flowchart)
The active power is detected by the product of the output voltage and the output voltage. The output voltage is equal to the detection voltage Vs of the output voltage detection circuit 63 as shown in FIG. 7 shown as the second embodiment of the present invention.
May be used to detect the active power (in step R3 of the flowchart, the instantaneous value V
s (n) is detected). In this case, the output voltage detection circuit 63 corresponds to output voltage detection means. Since the output voltage detection circuit 63 is provided with a filter (not shown), a high-frequency carrier component of the output voltage Vo can be removed, and the AC output voltage Voac can be reliably detected. The influence of the reactor voltage drop of the filter circuit 38 is removed from Vs. Note that the zero crossing in step R1 is equal to the detection voltage V as shown in FIG.
This is the zero cross of s (timing t0 '). And
In steps R2 to R7, the instantaneous active power is calculated based on the instantaneous value Vs (n) and the instantaneous value Is (n) of the output current detection signal Is, and the active power is detected by summing the active powers. .

FIG. 9 shows a third embodiment of the present invention. In this embodiment, active power is detected based on a sine wave reference signal Vsin and an output current detection signal Is (see FIG. 3). (Computation). That is, in step S3, the instantaneous value Vsin (n) of the sine wave reference signal Vsin
Is determined, and the instantaneous active power is calculated based on the instantaneous value Vsin (n) and the instantaneous value Is (n) of the output current detection signal Is, and the active power is calculated by summing the results.

The third embodiment has the following advantages. That is, since the sine wave reference signal Vsin is equivalent to the output voltage Vo although the voltage level is different, the sine wave reference signal Vsin can be regarded as the output voltage Vo without the need for bothersome output voltage detection means. Thus, there is no need to provide an output voltage detecting means on the output side of the inverter circuit, and the configuration can be simplified.

FIG. 10 shows a fourth embodiment of the present invention. This embodiment differs from the third embodiment in the following points. That is, as shown in FIG. 11, the output voltage detection signal Vs is delayed with respect to the sine wave reference signal Vsin. In consideration of this, the sine wave reference signal Vsi
n, a zero-cross of the output voltage detection signal Vs is detected to detect a phase difference θ of each zero-cross, and the instantaneous value Vsin (n) of the sine wave reference signal Vsin is detected based on the phase difference θ.
Is corrected to detect the active power.

In step T1, the zero cross (timing t)
0) is a zero crossing of the sine wave reference signal Vsin, the instantaneous value Vsin (n) in step T3 is an instantaneous value earlier than the actual output voltage Vo by the phase difference θ, and in step T4, The value Vsin (n) is corrected so as to be an instantaneous value advanced by the phase difference θ. Thus, accurate active power can be detected.

FIG. 12 shows a fifth embodiment of the present invention. This embodiment is characterized in that the output current is detected by an effective value. That is, the instantaneous value Is (n) is squared and summed as shown in step U3 in FIG. 12, and the sum is squared as shown in step U5.
Thus, the output current is detected as an effective value.

According to this embodiment, the output current can be detected satisfactorily even when the load of the AC power generator 21 includes the full-wave rectifier. Incidentally, when the load includes the full-wave rectifier, an output current flows as shown in FIG. In this case, the output current of the output active power of the AC power generator 21 is not a sine wave AC, so that the effective value is better, so that even if the load is a load including a full-wave rectifier, the output current is reduced. It can be detected well. In this case, the load may be a resistive load, a coil load, or a capacitor load, and may be applied to any load. When the output current is detected as an average value, the load is preferably a resistance load, a coil load, or a capacitor load.

[0047]

As apparent from the above description, the present invention has the following effects. According to the invention of claim 1, since the active power of the AC output is detected and the frequency is controlled so as to decrease as the active power increases, even when a plurality of inverter devices of the present invention are operated in parallel, The output current balance among the inverter devices can be kept uniform, and the output current balance can be surely equalized even if the load is a coil load, a capacitor load, or the like.

According to the second aspect of the present invention, since the active power detecting means detects the active power in at least a half cycle of the output voltage, the active power can be detected in a short time. The subsequent frequency control can be performed quickly. According to the third aspect of the present invention, since the active power detecting means includes the output current detecting means for detecting the output current with the average value, the output current can be easily detected. According to the fourth aspect of the present invention, since the active power detection means includes the output current detection means for detecting the output current as an effective value, even if the load of the inverter device is a load including the full-wave rectification means, As a result, active power can be detected well.

According to the fifth aspect of the present invention, the active power detecting means includes the output voltage detecting means for converting the high frequency output voltage of the inverter circuit into a sine-wave AC voltage by a filter and detecting the sine wave AC voltage. Although the output is a rectangular high frequency output voltage, a sine wave AC voltage can be detected, and the effect of the reactor voltage drop of the filter circuit can be eliminated.

According to the sixth aspect of the present invention, there is no need to provide output voltage detecting means on the output side of the inverter circuit. According to the invention of claim 7, since the active power is detected by correcting the time delay of the sine wave reference signal with respect to the output voltage, it is possible to accurately detect the active power, and the time delay is determined by the output voltage and the sine wave reference signal. Since the detection is performed based on the phase difference of each zero cross, the detection is simplified.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a waveform diagram of each part.

FIG. 3 is a waveform chart showing a sine wave reference signal and a detection output current.

FIG. 4 is a flowchart for explaining control contents.

5A is a diagram showing an operation example of two portable AC generators, and FIG. 5B is a diagram showing the portable AC generator 2 in a cross current generation state.
Figure showing an operation example of a table

FIG. 6 is a diagram illustrating a relationship between active power and frequency for explaining frequency control;

FIG. 7 is a flowchart for explaining control contents according to a second embodiment of the present invention;

FIG. 8 is a diagram corresponding to FIG. 3;

FIG. 9 is a flowchart for explaining control contents according to a third embodiment of the present invention;

FIG. 10 is a flowchart for explaining control contents according to a fourth embodiment of the present invention;

FIG. 11 is a diagram corresponding to FIG. 3;

FIG. 12 is a flowchart for explaining control contents according to a fifth embodiment of the present invention;

FIG. 13 is a diagram corresponding to FIG. 3;

FIG. 14 is a diagram corresponding to FIG. 1 showing a conventional example.

[Explanation of symbols]

21 is a portable AC power supply (inverter), 22
Is an AC generator, 23 is an inverter unit, 33 is a rectifier circuit (DC power supply circuit), 37 is an inverter circuit, 38 is a filter circuit, 59 is a control circuit, 61 is a microcomputer (active power detecting means and control means), 63 is An output voltage detection circuit (output voltage detection means), 64 denotes an output current detection circuit (output current detection means).

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor, etc.Takimoto, etc. 991, Anata-cho, Seto City, Aichi Prefecture Inside the Aichi Factory, Toshiba (72) Inventor Teruya Tanaka 991, Anata-cho, Seto City, Aichi Prefecture, Aichi Higashishiba Corporation Inside the factory (72) Inventor Takatomo Izume 2--24, Harumi-cho, Fuchu-shi, Tokyo Toshiba FA System Engineering Co., Ltd. Shiba FA System Engineering Co., Ltd. (72) Inventor Tohru Yoshioka 3F Hayakawa, Nitta-machi, Nitta-gun, Gunma F-term (reference) 5H007 CA01 CA03 CB05 CC05 CC12 DA03 DA05 DA06 DB01 DB12 DC02 DC03 DC04 DC05 EA04 EA13

Claims (7)

[Claims] An inverter circuit having a DC power supply circuit, a switching element, and switching an output of the DC power supply circuit based on a PWM signal to output a high-frequency voltage; and converting the high-frequency voltage into a sinusoidal AC voltage. Filter circuit for detecting the active power of the AC output, and control means for controlling the frequency of the output voltage to decrease as the active power detected by the active power detection means increases. And an inverter device comprising: 2. The inverter device according to claim 1, wherein the active power detection means detects active power during at least a half cycle of the AC output voltage. 3. The inverter device according to claim 1, wherein said active power detection means includes output current detection means for detecting an output current as an average value. 4. The inverter device according to claim 1, wherein said active power detection means includes output current detection means for detecting an output current as an effective value. 5. The inverter device according to claim 1, wherein the active power detecting means includes an output voltage detecting means for converting a high frequency output voltage of the inverter circuit into a sine-wave AC voltage by a filter and detecting the sine wave AC voltage. 6. A PWM signal is generated based on a sine wave reference signal and a carrier signal. The active power detection means includes an output current detection means, and the sine wave reference signal and an output current of the output current detection means are provided. The inverter device according to claim 1, wherein active power is detected based on the detection signal. 7. A PWM signal is generated based on a sine wave reference signal and a carrier signal, and an active power detection means detects a high frequency output voltage of the inverter circuit and outputs an output voltage detection signal. And an output current detecting means for detecting a zero cross of the sine wave reference signal and the output voltage detection signal to detect a phase difference of each zero cross, and correcting the phase difference to detect active power. The inverter device according to claim 1, wherein: