JPH043597Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a current source inverter device applied to an induction heating power source, etc., and in particular, when the output frequency variable range of the inverter is expanded, the output frequency is changed in response to changes in the output frequency setting value. The present invention relates to a current source inverter device equipped with means for switching and controlling voltage setting values in multiple stages.

The main circuit of this type of current source inverter device is
As shown in the figure. 10A is a forward converter composed of a controlled rectifying element such as a thyristor, and an electromagnetic contactor 10M
A rectified output is obtained by converting the AC input input through the converter. 10L is forward converter 10
DC reactor connected to the output end of A, 10B
is an inverse converter composed of a controlled rectifying element such as a thyristor, and based on the output obtained by inversely converting the rectified output obtained through the DC reactor 10L, the required current is sent to the tank circuit 20 consisting of the matching capacitor 20C and the work coil 20L. is supplied to heat a load such as an object to be heated (not shown).

By the way, the normal frequency variable range of the inverter device shown in Figure 1 is from 100% of the rated frequency to
It is 60%. However, depending on the material of the heated load, the frequency may significantly deviate from the above frequency range. Conventionally, such a case has been dealt with by providing a starting circuit 12 upstream of the inverter 10B as shown in FIG. This starting circuit 12 has starting thyristors 12S ₁ and 12S ₂ and a rush current suppressing resistor 12R connected in series, and is connected between the connection point of starting thyristors 12S ₁ and 12S ₂ and an inverter 10B. It is constructed by connecting a series circuit of a magnetic contactor contact 12MS and an auxiliary capacitor 12CS in parallel to a series capacitor 12C.

By configuring as above, the number at startup
Starting thyristor 1 if the frequency between Hz _{and z} is low
The thyristors 2S ₁ , 12S ₂ and one arm of the inverter are controlled ON and OFF alternately at predetermined timing, and the contact 12MS is turned on to increase the capacitor capacity and give the tank circuit 20 the required power. Establishing voltage. Also tank circuit 2
When the voltage of 0 is established, the output of the starting circuit 12 is cut off, and the other arm of the inverter 10B, which has been in the OFF state, is triggered by the thyristor.
The output frequency of the inverter is switched to a predetermined output frequency to perform predetermined heating control in the normal operating mode.

However, when attempting to operate this inverter device under, for example, constant output voltage control, when the frequency is switched, the output voltage changes, making it impossible to realize constant output voltage control. That is, for example, if the output voltage during high frequency operation is set as the rated voltage, when operating at low frequency, a starting capacitor 12CS is inserted to increase the capacitor capacity and control the predetermined voltage to be constant. In Although,
At the time of such frequency switching, in the conventional device shown in FIG. 1, the output voltage itself decreases. These problems are mainly caused by the following causes. Conventionally, in order to perform the above-described constant output voltage control, a phase control loop has been provided that controls the gate of the forward converter 10A based on the deviation between the output of the output voltage setter and the output voltage detection value of the inverse converter 10B. . Normally, the output voltage is detected using a voltage detection transformer, but when the frequency changes significantly as mentioned above, the frequency characteristics of this voltage detection transformer are matched to the rated frequency of the inverter, so In the frequency domain, the distortion factor of the voltage appearing on the secondary side of the detection transformer becomes extremely large, and the detection voltage itself changes, causing a fluctuation factor (regulation) to the transfer characteristic of the phase control loop assumed under the rated frequency. ). For this reason, especially when using such an inverter device as an induction heating power source, it is difficult to uniformly heat the heated object, and if the material of the heated object is changed, it is difficult to use the same power source. There were some problems, such as difficulty in doing so.

The present invention has been developed in view of the above points, and includes means for equivalently controlling the output voltage setting value in multiple stages in response to changes in the output frequency setting value, and changing the output frequency setting value. Another object of the present invention is to provide a current source inverter device that allows the output voltage to remain constant at all times.

An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 3 is a block diagram showing an embodiment of an inverter device for driving a resonant load according to the present invention, and the same reference numerals as in FIGS. 1 and 2 indicate the same parts.

Reference numeral 30 denotes a circuit that equivalently sets an output voltage setting value in response to changes in n output frequency setting values, and a setter ₃₀ is provided for each output frequency setting value f ₁ , f ₂ , . . . (1), 30(2), . . . 30n are provided. 32 is a contact circuit that switches and selects the output of a desired setter in accordance with a predetermined output frequency change command, and each setter 30(1), ...30i, ...30
Contacts 32(1), 32(2), . . . correspond to n, respectively.
...32n is provided. 34 is the inverse converter 10
In the output voltage detection circuit of B, voltage detection transformer 3
4T, a rectifier 34R that rectifies the secondary output of the transformer 34T, and a variable resistor 34VR that detects the output of the rectifier 34R.

Reference numeral 36 indicates the output of the desired setter selected by switching by the contact circuit 32 mentioned above and the output voltage detection circuit 34.
This is a matching circuit that matches the output of 38
40 is a voltage amplifier that amplifies the voltage obtained as the deviation amount of the matching circuit 36, and 40 is a phase control circuit that controls the gate of the forward converter 10A in accordance with the output of the voltage amplifier 38.

One embodiment of the present invention is as described above, and its operation will now be described.

When the output frequency is 100 to 60% of the rated frequency, for example as described above, the inverter 10B
The oscillation frequency may be adjusted by a gate control circuit (not shown). Furthermore, when the output frequency is 60% or less of the rated frequency, it is not possible to secure the margin angle r (reverse voltage period) of the thyristor group of the inverter by simply adjusting the oscillation frequency of the inverter 10B. As in the prior art shown in FIG. 2, a series capacitor for starting is introduced and the capacitance of the capacitor is changed.

In such a case, the present invention realizes constant output voltage control even when the output frequency is changed beyond the above-mentioned range of 100 to 60% of the rated frequency. Now, the contact 32 (1) is closed by a predetermined output frequency change command, and the output of the setting device 30 (1) and the output of the output voltage detection circuit 34 are matched in the matching circuit 36, and the amplified value of the deviation is is input to the phase control circuit 40, and the gate of the thyristor constituting the forward converter 10A is controlled by its output. The forward converter 10A forward converts the AC input according to the conductivity of the thyristor. The rectified output thus obtained is inversely converted by the inverse converter 10B, and the output thereof is supplied to the tank circuit 20 to heat the object to be heated. Assume that in such a state, a predetermined output frequency change command is given to the contact circuit 32 in order to change the output frequency setting beyond the above-mentioned range, and for example, the contact 32i is turned on. With this, the control input to the matching circuit 32 is from the output of the setting device 30(1) to the setting device 3.
Switched to 0i output. In this case, the output voltage setting value that corresponds to the change in the output frequency setting value is set equivalently in each setting device in advance, so the output voltage setting value is automatically changed in accordance with the change in the output frequency setting value. , so the matching circuit 36
An appropriate amount of deviation is output from , and the output voltage level of forward converter 10A is controlled by that value. Therefore, the output voltage of the inverter 10B remains constant even if the output frequency setting is changed.

FIG. 4 is a block diagram showing another embodiment of the present invention, and the same reference numerals as in FIG. 3 indicate the same parts. In this embodiment, the setting circuit 30 includes a voltage setter 30V corresponding to a predetermined output frequency setting value.
There are several. Further, as variable resistors of the output voltage detection circuit 34, n pieces of 34VRl, . . . 34VRi, . Further, a circuit 32' is connected to the output end of each variable resistor to switch and select the output of a desired variable resistor in accordance with a predetermined output frequency change command. and the contacts 32'(1),...32'i,...32'n, respectively.
is provided.

The present embodiment is configured as described above, and for example, when the contact 32' (1) is closed, the output of the output voltage detection circuit 34 and the output of the voltage setting device 30V are brought together by the matching circuit 36. will be combined. This amount of deviation is transmitted to the phase control circuit 4 via the voltage amplifier 38.
0, the output voltage level of the forward converter 10A is controlled, and the output voltage level of the forward converter 10A is controlled.
A predetermined output voltage is output from 0B and the tank circuit 2
0 to heat the object to be heated. Next, when the variable resistor is switched and selected by an output frequency change command, the output voltage detection value changes in accordance with this frequency setting change. Therefore, the amount of deviation of the matching circuit 36 changes accordingly, and the output level of the forward converter 10A changes in the same manner as described above.
Thereby, the output voltage of the inverter 10B is kept constant even if the frequency setting is changed.

As described above, the present invention provides a means for equivalently controlling the output voltage setting value in response to a change in the output frequency setting value based on the output voltage detection value of the inverter, and this switching control means. The gate of the forward converter is controlled by the output, and the gate of the inverse converter is also controlled according to changes in the output frequency setting, so even if the output frequency setting is changed, the inverter's output voltage remains constant. Can be controlled at a constant level. Therefore, when this inverter device is applied to an induction heating power source, even if the output frequency setting value is changed significantly beyond the allowable range for the rated frequency during predetermined heating control, the output voltage setting value will also be changed at the same time. Constant output voltage control can be achieved, and no problems occur during heating work. Furthermore, even if the output frequency setting value needs to be changed due to a change in the material of the heated object, the variable setting range of the output voltage is wide, so it is possible to control the output voltage at a constant level with the same heating power source.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the circuit configuration of a conventional current source inverter device, Figure 2 is a block diagram showing the circuit configuration when a starting circuit is added to the device in Figure 1, and Figure 3 is a block diagram showing the circuit configuration of a conventional current source inverter device. FIG. 4 is a block diagram showing the circuit structure of one embodiment of the current source inverter device. FIG. 4 is a block diagram showing the circuit structure of another embodiment of the current source inverter device according to the present invention. 10A...Forward converter, 10B...Inverse converter, 3
0...Setting circuit, 30(1), 30i, 30n,
30V...setting device, 32, 32'...contact circuit,
32(1), 32i, 32n, 32'(1), 3
2'i, 32'n...Contact, 34...Output voltage detection circuit, 34T...Output voltage detection transformer, 34
VR, 34VRl, 34VRi, 34VRn...output voltage detection resistor, 36...matching circuit.

Claims (1)

[Claims for Utility Model Registration] (1) An AC input is forward-converted by a forward converter consisting of a controlled rectifying element, etc., the converted rectified output is inversely converted by an inverse converter consisting of a controlled rectifying element, etc., and its output is The frequency is set by the output frequency setting value, and the inversely converted output is supplied to the resonant circuit, and this inversely converted output voltage is detected by a voltage detection transformer, and the deviation signal between the detection signal and the setting value is used. In a current source inverter device that controls the gate of a forward converter, the output voltage setting value is equivalently controlled to be switched in multiple stages in response to a change in the output frequency setting value based on the output voltage detection value of the inverse converter. A current source inverter device characterized in that the switching control means is provided with a switching control means for changing the output voltage setting value of the forward converter in response to a change in the output frequency setting value of the inverse converter. . (2) The switching control means includes n setting devices for setting an output voltage setting value corresponding to the output frequency setting value, and means for switching and selecting the output of a desired setting device based on a predetermined output frequency change command; It is characterized by comprising a matching circuit that matches the output of the setting device selected by the switching selection means and the output voltage detection value of the inverse converter and outputs the deviation amount to the gate of the forward converter. A current source inverter device according to claim (1) of the utility model registration claim. (3) The switching control means includes a voltage setting device corresponding to a predetermined output frequency setting value, means for switching and selecting the output voltage detection value of the inverter in accordance with a predetermined output frequency change command, and the switching selection means. A matching circuit that matches the detected output voltage value selected by the above and the output of the voltage setting device and outputs the deviation amount to the gate of the forward converter. The current source inverter device described in (1).