JPH11299251A - Parallel-connected type inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inverter which is able to properly correct an overlapping angle without the loss of the synchronization of respective output currents, even if a plurality of lines of inverter circuits are formed. SOLUTION: When a plurality of current-mode inverter circuits are operated in parallel, the largest output current is selected from the respective output currents of a plurality of current-mode inverter circuits by a comparative selection circuit 67, and the selected output current is inputted into an overlapping angle correction circuit 64 to correct an overlapping angle β, based on the output current. Even if the output currents of the respective current-mode inverter circuits are different from each other, commutation is controlled by the identical overlapping angle β, the respective output currents are synchronized, and the overlapping angle β is corrected by the largest output current, so that the overlapping angle β can be corrected properly without lacking a commutation period, and no delay in the current output is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a parallel type inverter device having a plurality of current type inverter circuits which can be connected in parallel, and these current type inverter circuits can be operated in parallel.

[0002]

2. Description of the Related Art Conventionally, in controlling the output of an induction load such as an induction motor or an induction heating device having an inductance component, an inverter device capable of adjusting the frequency of AC power supplied to the load has been used. . The inverter device converts AC power supplied from a commercial power supply into DC power once by a forward conversion circuit, and further converts the DC power into AC power by an inverse conversion circuit, so that AC power of a desired frequency is obtained. What is obtained is common. The maximum output of such an inverter device is mainly determined by the capacity of a power control switching element employed in the inverter circuit. Therefore, when an output larger than the capacity of the switching element is required, a parallel type inverter device in which a plurality of inverter circuits are connected in parallel is used as shown in Japanese Patent Application Laid-Open No. 9-19149. ing.

FIG. 3 shows an example of such a parallel type inverter device. In the figure, the inverter device
Reference numeral 90 denotes a circuit in which two systems of a main inverter circuit 91 and a slave inverter circuit 92 are connected in parallel. Each of the inverter circuits 91 and 92 is of a current type having a large output impedance, and is connected to a commercial power supply for supplying three-phase AC power via the transformers 1 and 2. Also,
Each of the inverter circuits 91 and 92 includes a matching transformer 13
Is connected to an induction heating device (not shown), which is a load. Each of the inverter circuits 91 and 92 has a forward conversion circuit 14 for converting three-phase AC power into DC power, and an inverse conversion for converting the DC power from the forward conversion circuit 14 into high-frequency AC power that can be regarded as a high frequency. A circuit 15 is provided. In each of the forward conversion circuits 14 of the inverter circuits 91 and 92, a thyristor 16 as an active element is provided as a rectifying element, and the timing for applying a control voltage to the gate is changed. In other words, the control angle is set to 0. By changing the output voltage in the range of π to π, the output voltage can be adjusted.

Each inverse conversion circuit 15 of the inverter circuits 91 and 92
Is a plurality of switching elements 15 as shown in FIG.
A, 15B is a bridge. Each inverse conversion circuit 15
IGBT (Insu) as switching elements 15A and 15B
(latedGate Bipolar Transistor) 17 are provided two by two, and a diode 18 for protecting these IGBTs 17 is provided. By alternately conducting these switching elements 15A and 15B, a forward conversion circuit
The DC power from 14 is converted to AC power. In other words, the current i1 is supplied to the load side by the conduction of one set of switching elements 15A, and the current i2 in the opposite phase to the current i1 is supplied to the load side by the conduction of the other set of switching elements 15B. The current i1 and the current i2 are supplied alternately. In such an inverter device 90, the AC power output from each of the inverter circuits 15 is controlled so that its frequency becomes the resonance frequency of the induction heating device as a load, and the phases are synchronized. Further, since the inverter circuits 91 and 92 are of the current type, the output current waveform of the inverse conversion circuit 15 has a square waveform.

Here, each inverting circuit 15 has a commutation inductance which is the sum of leakage inductances as viewed from the secondary side (load side) of each inverting circuit 15. Due to this commutation inductance, even if the conduction of the switching elements 15A and 15B is switched, the output current does not instantaneously switch from one of the current i1 and the current i2 to the other, and outputs the output current from one phase to another phase. A certain amount of time (commutation period) is required to perform switching commutation. In the current-type inverter device, when the phase of the current is delayed due to an inappropriate commutation period, problems such as generation of a large surge voltage occur. Such a problem also occurs when a required commutation period fluctuates due to a change in the load impedance, and the phase of the current is delayed due to the fluctuation in the commutation period. Therefore, in the current-type inverter circuit, the switching elements 15A and 15B are simultaneously turned on during the commutation period in order to follow the output current without delaying the load fluctuation, and the switching elements 15A and 15B are turned on simultaneously. The overlap angle β representing the commutation period is corrected according to the load, and the commutation is actively controlled. The overlap angle β is expressed by the following equation (1). Here, ω, L, Id, and Ve are angular frequency, commutation inductance, load current (output current), and load voltage (output voltage), respectively.

[0006]

(Equation 1)

In a general inverter device having only one inverter circuit, the output voltage is controlled to be constant when the overlap angle is corrected in accordance with the load. If the output current is corrected based on the output current, the output current can follow the load impedance fluctuation without delay.

[0008]

However, in the parallel inverter device 90, the two inverter circuits 91 and 92 are provided.
There is a variation in the DC resistance of each circuit element provided in the inversion circuit 15, and the voltage drops V1 and V2 of both inversion circuits 15
(See FIG. 3) do not match, and the magnitudes of the output currents of the inverter circuits 91 and 92 differ. Therefore, the overlapping angle β
Is corrected according to the load, the inverter circuit 91,
If the overlap angle β is corrected based on the magnitude of the output current of each of the 92, the magnitudes of the output currents of the inverter circuits 91 and 92 are different from each other. Controlled, there is a problem that output currents are not synchronized. In order to synchronize the output current, the output current of one of the inverter circuits 91 and 92 is detected,
It is conceivable to correct the overlap angle β based on the detected magnitude of the output current. However, since the other output currents of the inverter circuits 91 and 92 are ignored without being involved in the correction of the overlap angle β, the output current that is not detected may be larger than the detected output current. As described above, if the output current that is not detected is larger than the detected output current, the commutation period of one of the inverter circuits 91 and 92 is insufficient, and the output current cannot follow the impedance fluctuation of the load and is delayed. However, the above-described problem may occur.

An object of the present invention is to provide a multi-system inverter circuit without losing synchronization of each output current.
An object of the present invention is to provide a parallel inverter device that can appropriately correct the overlapping angle β.

[0010]

According to the present invention, there is provided a forward conversion circuit for converting AC power supplied from an AC power supply into DC power, and a plurality of switching elements, and these switching elements are turned on alternately. Thus, a plurality of current-type inverter circuits including a reverse conversion circuit that converts DC power from the forward conversion circuit into AC power are provided,
A parallel-type inverter device capable of driving the current-type inverter circuit in parallel when supplying AC power to a load, wherein the plurality of alternately conductive switching elements are simultaneously conductive in the reverse conversion circuit. Overlap angle correction means for correcting an overlap angle representing a commutation period, which is a period in which the current type inverter circuit provided in the plurality of systems, is provided. The overlapping angle is corrected based on a large one.

According to the present invention, the overlapping angle is corrected based on the largest output current of the current type inverter circuits provided in a plurality of systems, so that the output current of each current type inverter circuit is Even if they are different, the commutation is controlled at the same overlapping angle, so that the synchronization of the output current is not lost. In addition, since the overlap angle is corrected with the largest output current among the current inverter circuits of a plurality of systems, the commutation period does not run short, and even if the output current advances with respect to the load impedance fluctuation, There is no delay and no problems such as generation of a large surge voltage occur.

In the above, the current-type inverter circuit is provided with two systems, a master and a slave. Of these, the overlap angle correction means of the current-type inverter circuit serving as the master includes each of the current-type inverter circuits. A comparison and selection circuit that compares the output currents and selects the larger one of these currents, and an overlap angle correction circuit that corrects the overlap angle based on the current selected by the comparison and selection circuit are provided. Preferably, the overlap angle correction means of the current type inverter circuit includes an overlap angle correction circuit for correcting the overlap angle based on the current selected by the master-side comparison and selection circuit. As described above, the comparison and selection circuit provided in the current type inverter circuit serving as the master selects the maximum output current and outputs a signal corresponding to the maximum output current value to the current type inverter circuit serving as the slave. This eliminates the need for the comparison / selection circuit in the current-side inverter circuit on the slave side, thereby simplifying the configuration of the parallel-type inverter device.

In addition, the reverse conversion circuit is provided with phase control means for controlling the conduction cycle of these switching elements to be the resonance frequency of the load when alternately conducting the plurality of switching elements. Is preferred. With this configuration, the load is supplied with AC power having the resonance frequency, so that the load can be operated with high efficiency and the parallel inverter device can operate even when the impedance of the load changes. , The overlapping angle β is appropriately corrected according to the fluctuation,
Even if the impedance of the load fluctuates, it is possible to maintain high-efficiency operation of the load in a stable state.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. In the following description, the same elements and circuits as those already described are denoted by the same reference numerals, and description thereof will be omitted or simplified. FIG. 1 shows an inverter device 10 according to the present embodiment. The inverter device 10 is a current-type inverter device that converts AC power supplied from a three-phase AC power supply into high-frequency power required for driving an induction heating device. The inverter device 10 includes:
Two current-type inverter circuits 11, 12 connected in parallel are provided. The inverter circuit 11 is a main inverter circuit, and is connected to three-phase AC power via a △ -Y connection type transformer 1. The inverter circuit 12 is a slave inverter circuit, and is connected to three-phase AC power via a △-△ connection type transformer 2. Each of these inverter circuits 11, 12 is connected to a load via a matching transformer 13 that steps down its output voltage.

Each of the inverter circuits 11 and 12 includes a forward conversion circuit 14 for converting three-phase AC power into DC power and an inverse conversion circuit 15 for converting DC power from the forward conversion circuit 14 into AC power. Is provided. The forward conversion circuit 14 is provided with a thyristor 16 that is an active rectifying element having a gate that is a control electrode, and a reactor 19 that is a smoothing element that smoothes pulsating DC power rectified by the thyristor 16. I have. Here, the reactor 19 has a relatively large inductance. By providing such a reactor 19 in the forward conversion circuit 14, the inverter device 10 is a current-type inverter device having a large output impedance. Here, inverter circuit 1
During operation, each of the thyristors 1 and 12 is controlled such that its output voltage becomes a predetermined voltage and both control angles become the same.

As described above, the inversion circuit 15 is an IG that is a switching element that opens and closes electrical connections at both ends.
A BT17 and a diode 18 for protecting these IGBTs 17 form a full bridge, and two IGBTs 17 and one diode 18 are provided on each of four sides of the bridge. (See FIG. 4). The diode 18 is connected to the collector of one of the IGBTs 17, so that the withstand voltage of the switching element portion of the inversion circuit 15 is improved. Also, two IG
The BT17 has one emitter connected to the other collector. A control voltage signal transmitted by a control circuit described later is simultaneously input to each gate of the IGBT 17. Each of the inverter circuits 11 and 12 has, in addition to the above-described forward conversion circuit 14 and inverse conversion circuit 15,
Breaker 22 and main switch connected sequentially from the power supply side
23 and a fuse 24 are provided. A matching transformer 13 connected to each of the inverter circuits 11 and 12
In the subsequent stage, a switching circuit 25 for switching connection between the inverter circuits 11 and 12 and a load is provided. The switching circuit 25 enables the inverter device 10 to selectively perform both independent driving of one of the inverter circuits 11 and 12 and simultaneous and parallel driving of the inverter circuits 11 and 12.

The inverter circuit 11 has a DC voltage detection terminal 26 and a DC current detection terminal 27 for detecting the DC voltage and the DC current output from the forward conversion circuit 14.
Are provided, and an AC voltage detection terminal 28 and an AC current detection terminal 29 are provided to detect the AC voltage and the AC current output from the inverter circuits 11 and 12. The DC voltage detection terminal 26 is directly connected to the output stage of the forward conversion circuit 14, and the DC current detection terminal 27 is connected to a current detector 30 provided in the forward conversion circuit 14. Here, the current detector 30 is connected to the reactor 19 provided in the forward conversion circuit 14.
The DC current output of the forward conversion circuit 14 is detected based on the voltage drop of the current. The AC voltage detection terminal 28 is connected to an inverse conversion circuit.
The 15 output stages are connected via a transformer 31, and the AC current detection terminal 29 is connected to the output stage of the inverse conversion circuit 15 via a current transformer 32.

On the other hand, similarly to the inverter circuit 11, the inverter circuit 12 has a DC voltage detection terminal 33 for detecting the DC voltage and DC current output from the forward conversion circuit 14.
In addition, a DC current detection terminal 34 is provided, and an AC voltage detection terminal 35 and an AC current detection terminal 36 are provided to detect the AC voltage and the AC current output from the inverter circuits 11 and 12. DC voltage detection terminal 33
Is directly connected to the output stage of the forward conversion circuit 14, the DC current detection terminal 34 is connected to the current detector 30 provided in the forward conversion circuit 14, and the AC voltage detection terminal 35 is connected to the output of the inverse conversion circuit 15. The stage is connected via a transformer 31 and an AC current detection terminal 36
Is connected to the output stage of the inverse conversion circuit 15 via the current transformer 32.

FIG. 2 shows control circuits 41 and 42 for controlling the inverter circuits 11 and 12, respectively. The control circuit 41 controls the master inverter circuit 11, and the control circuit 42 controls the slave inverter circuit 12. The control circuit 41 includes a forward conversion control circuit 43 for controlling the forward conversion circuit 14 of the inverter circuit 11 and an inverse conversion control circuit 44 for controlling the inverse conversion circuit 15 of the inverter circuit 11.
In order to receive various signals transmitted from the inverter circuit 11, a DC voltage input terminal 45, a DC current input terminal 46,
An AC voltage input terminal 47 and an AC current input terminal 48, and a parallel operation signal input terminal 49 for receiving a parallel operation signal transmitted by manual operation or the like are provided. Here, DC voltage input terminal 45, DC current input terminal 46, AC voltage input terminal 47
And the AC current input terminal 48 is connected to the inverter circuit 11
, A DC voltage detection terminal 26, a DC current detection terminal 27, an AC voltage detection terminal 28, and an AC current detection terminal 29.

The forward conversion control circuit 43 has a function of controlling the output voltage of the forward conversion circuit 14 to have a predetermined voltage value, and an excessive current from the forward conversion circuit 14 in order to protect the reverse conversion circuit 15. It has a function of preventing output. To control the output voltage of the forward conversion circuit 14, the forward conversion control circuit 43 includes a variable resistor 51 for setting the output voltage,
An amplifier that amplifies the difference between the set voltage value set by the variable resistor 51 and the output voltage value output from the forward conversion circuit 14.
52, a phase controller 53 for adjusting the control delay angle of the thyristor 16 of the forward conversion circuit 14 based on the difference between the set voltage value and the output voltage value, and driving the thyristor 16 by amplifying the output signal of the phase controller 53 Drive amplifier 54
Are provided. In addition to the above, the forward conversion control circuit 43 receives the start command signal from the push button switch 55, and the start / stop circuit 56 for starting / stopping the inverter circuit 11 and the output current of the forward conversion circuit 14 A trip circuit 57 that outputs a cutoff signal when the current value deviates from a predetermined range,
And a cut-off drive amplifier 58 for turning off the thyristor 16 with the output signal of.

Here, in the transient state at the time of starting the inverter circuit 11, the output current output from the forward conversion circuit 14 is smaller than a predetermined range, or the output current temporarily becomes a rush current and falls within a predetermined range. And so on.
In these periods, when the thyristor 16 is turned off, the inverter circuit 11 does not reach the steady state forever, so the start / stop circuit 56 operates only for the time necessary to reach the steady state from the transient state at the time of starting. A pause signal is sent to the trip circuit 57 to temporarily suspend the operation of the trip circuit 57. Also, start / stop circuit
To 56, not only the start command signal from the push button switch 55 but also the parallel operation signal received at the parallel operation signal input terminal 49 is input. Start / stop circuit 56
When at least one of the start command signal and the parallel operation signal is input, an operation permission signal is transmitted to the phase controller 53 and the inverse conversion control circuit 44 of the forward conversion control circuit 43.

The reverse conversion control circuit 44 controls the reverse conversion circuit so that the output voltage and the output current of the reverse conversion circuit 15 have the same phase.
This is for adjusting the period of sending the control voltage signal to the 15 IGBTs 17. By the control operation of the reverse conversion control circuit 44, the output frequency of the reverse conversion circuit 15 matches the resonance frequency of the load. The inversion control circuit 44 detects a phase difference between the output voltage and the output current of the inversion circuit 15 and outputs a voltage signal corresponding to the phase difference. A voltage controlled oscillator 62 that oscillates a signal having a frequency corresponding to the output voltage signal
According to the frequency of the signal output from the voltage controlled oscillator 62, a flip-flop 63 that alternately sends a drive signal from two output ports, and a drive signal output from two output ports of the flip-flop 63 An overlap angle β corresponding to a required commutation period, an overlap angle correction circuit 64 for correcting the overlap angle β according to the output current of the inverse conversion circuit 15, and an output of the overlap angle correction circuit 64. Drive amplifiers 65 and 66 for amplifying signals and driving IGBT 17
And an output current of both inverter circuits 11 and 12, and a comparison / selection circuit 67 for comparing these output voltages and selecting a larger one of these currents is provided. Note that the output of the drive amplifier 65 is
IGBT forming the switching element 15A provided in the IGBT
The output of the drive amplifier 66 is output to the IG which forms the switching element 15B provided in the inverse conversion circuit 15.
The data is transmitted to the BT 17 (see FIG. 4).

Here, the phase difference detection circuit 61, the voltage controlled oscillator 62, and the flip-flop 63 generate a drive signal for alternately turning on the switching elements 15A, 15B of the inverse conversion circuit 15, and generate the driving signal of the switching elements 15A, 15B. In the alternate driving, a phase control means for controlling the conduction cycle of these switching elements 15A and 15B to become the resonance frequency of the load. A large output current selected by the comparison and selection circuit 67 among the output currents of the inverter circuits 11 and 12 is input to the overlap angle correction circuit 64. Thereby, the overlap angle correction circuit 64 and the comparison selection circuit 67
The overlap angle correction means corrects the overlap angle β representing the commutation period of the inverse conversion circuit 15 based on the largest output current of the inverter circuits 11 and 12.

As with the control circuit 41, the control circuit 42 includes a forward conversion control circuit 43 for controlling the forward conversion circuit 14 of the inverter circuit 12, and an inverse conversion control circuit for controlling the inverse conversion circuit 15 of the inverter circuit 11. 70, a DC voltage input terminal 71, a DC current input terminal 72, an AC voltage input terminal 73, and an AC current input terminal 74 to receive various signals transmitted from the inverter circuit 12, and are transmitted by manual operation or the like. A parallel operation signal input terminal 75 for receiving the parallel operation signal is provided.
Here, each of the DC voltage input terminal 71, the DC current input terminal 72, the AC voltage input terminal 73, and the AC current input terminal 74 is
DC voltage detection terminal 33, DC current detection terminal 34, AC voltage detection terminal 35, and AC current detection terminal 36 of inverter circuit 12
Are electrically connected to each other. Forward conversion control circuit 43
Has the same configuration as that provided in the control circuit 41, and a description thereof will be omitted. The inverse conversion control circuit 70 includes a comparison selection circuit 67 from the inverse conversion control circuit 44 provided in the control circuit 41.
Except for omitting, the configuration is the same as that of the inverse conversion control circuit 44. Here, the overlap angle correction circuit of the inverse conversion control circuit 70
64 receives the current selected by the comparison selection circuit 67 on the master inverter circuit 11 side, and based on this current, the overlap angle β of the inverse conversion circuit 15 provided in the slave inverter circuit 12
Is corrected.

According to the above-described embodiment, the following effects can be obtained. That is, a parallel inverter device 10 in which two current-type inverter circuits 11 and 12 can be driven in parallel.
Control circuits 41 and 42 as overlap angle correction means for correcting the overlap angle β of the inverse conversion circuit 15 according to the load, based on the largest one of the output currents of the current type inverter circuits 11 and 12, Is provided, the commutation is controlled at the same overlapping angle β even if the magnitudes of the output currents of the current type inverter circuits 11 and 12 are different. Synchronization is not lost. In addition, since the overlapping angle β is corrected with the maximum output current among the output currents of the current-type inverter circuits 11 and 12 of a plurality of systems, the commutation period does not run short in both the current-type inverter circuits 11 and 12. Although the output current may advance with respect to the load impedance fluctuation, it does not delay, and it is possible to prevent a problem such as a large surge voltage from occurring.

The output currents of the master and slave inverter circuits 11 and 12 are compared with an inversion control circuit 44 for controlling the inversion circuit 15 of one master inverter circuit 11 of the parallel inverter device 10. A comparison selection circuit 67 for selecting the larger one of these currents and an overlap angle correction circuit 64 for correcting the overlap angle β based on the current selected by the comparison selection circuit 67 are provided. Inverse conversion control circuit 70 for controlling circuit 15
Since the overlap angle correction circuit 64 for correcting the overlap angle β based on the current selected by the comparison and selection circuit 67 provided in the master-side inverse conversion control circuit 44 is provided, the slave inverter circuit 12 includes a comparison and selection circuit. Since the configuration of the parallel inverter device 10 can be simplified, the reliability can be improved.

Further, the inverse conversion control circuit 43 is provided with a phase difference detection circuit 61, a voltage controlled oscillator 62 and a flip-flop 63, and a plurality of switching elements 15A,
In alternately conducting the 15B, the conduction cycle of these switching elements 15A and 15B is controlled so as to be the resonance frequency of the load, so that the load is supplied with AC power having the resonance frequency. As a result, high-efficiency operation of the load
Means that the overlap angle β is appropriately corrected according to the fluctuation even if the impedance of the load fluctuates. Therefore, even if the impedance of the load fluctuates, the high-efficiency operation of the load is maintained in a stable state. can do.

Inverting circuit for inverter circuits 11 and 12
By providing two IGBTs 17 in 15, the IGBT 17
And the output voltage of the inverse conversion circuit 15 can be increased, and a matching transformer 13 for step-down is provided in the output stage. Since the output current of the transformer 13 is increased, it is possible to output a current that is significantly larger than the limit current value of the IGBT 17.

Although the present invention has been described with reference to the preferred embodiment, the present invention is not limited to this embodiment, and various improvements and design changes may be made without departing from the gist of the present invention. It is possible. That is, the forward conversion circuit is not limited to a rectifier that performs rectification using a thyristor, and may be a chopper-type forward conversion circuit that performs rectification using a chopper. The switching element of the inversion circuit is not limited to the IGBT, but may be a general bipolar power transistor or MOSFET. However, when a high-frequency current output is obtained, a high-speed switching operation is possible, and It is desirable to use an IGBT having a large value. Further, the number of inverter circuits provided in the parallel inverter device is not limited to two, and may be three or more.

[0030]

As described above, according to the present invention, even when a plurality of inverter circuits are provided, the overlap angle β can be appropriately corrected while synchronizing the respective output currents.

[Brief description of the drawings]

FIG. 1 is a single connection diagram illustrating a parallel inverter device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a control circuit of the embodiment.

FIG. 3 is a single connection diagram showing a conventional example.

FIG. 4 is a circuit diagram showing a conventional inverse conversion circuit.

[Explanation of symbols]

10 Parallel inverter device 11 Master inverter circuit which is a current type inverter circuit 12 Slave inverter circuit which is a current type inverter circuit 14 Forward conversion circuit 15 Reverse conversion circuit 15A, 15B Switching element 17 IGBT 61 as switching element Constructs phase control means Phase difference detection circuit 62 voltage-controlled oscillator that forms phase control means 63 flip-flop that forms phase control means 64 overlap angle correction circuit that forms overlap angle correction means 67 comparison and selection circuit that forms overlap angle correction means

Claims (3)

[Claims] 1. A forward conversion circuit for converting AC power supplied from an AC power supply into DC power, and a plurality of switching elements are provided. A parallel inverter in which a plurality of current-type inverter circuits each including a reverse conversion circuit that converts DC power into AC power are provided, and in supplying AC power to a load, the current-type inverter circuits can be driven in parallel. In the apparatus, the inverse conversion circuit is provided with overlap angle correction means for correcting an overlap angle representing a commutation period, which is a period during which the plurality of alternately conductive switching elements are simultaneously conductive, according to the load. The overlap angle correcting means calculates the overlap angle based on the largest output current of the current type inverter circuits provided in the plurality of systems. A parallel-type inverter device for correcting. 2. The parallel type inverter device according to claim 1, wherein said current type inverter circuit is provided with two systems of a master type and a slave type. The means includes comparing each output current of the current-type inverter circuit, selecting a larger one of the currents, and correcting the overlap angle based on the current selected by the comparison / selection circuit. An overlap angle correction circuit is provided, and the overlap angle correction means of the current type inverter circuit serving as a slave includes an overlap angle correction circuit for correcting the overlap angle based on the current selected by the comparison selection circuit on the master side. A parallel-type inverter device, which is provided. 3. The parallel inverter device according to claim 1, wherein, when the plurality of switching elements are alternately turned on, the conduction cycle of the switching elements is equal to or less than one. A parallel type inverter device provided with phase control means for controlling a resonance frequency of a load.