JPH08163873A - Inverter - Google Patents

Abstract

PURPOSE: To apply a required voltage to a load without requiring any matching transformer by matching the impedance at the time of resonance without varying the rated voltage and current of an inverter. CONSTITUTION: A work W is connected in series with a capacitor Ca and in parallel with a capacitor Cb. The capacitors are selected such that the total capacitance thereof will be equal to the capacitance required for resonance of an inverter 5. In other words, when the load work and a work coil are determined, inductance and resistance of the inverter 5 are determined and when the frequency of AC power being fed to the load is determined, the capacitance required for resonance of the inverter is determined. The capacitors Ca, Cb are selected such that the total capacitance thereof will be equal to the capacitance thus determined.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device having a voltage type inverter.

[0002]

2. Description of the Related Art An inverter converts a direct current into an alternating current, and can be divided into the following two types of inverters depending on the provided direct current power source. One is a voltage-type inverter equipped with a DC voltage source that attempts to supply a constant voltage even if the resistance value of the load changes by connecting a capacitor with an extremely large capacitance value to the output section. Is a current type inverter equipped with a DC voltage source that attempts to supply a constant current even if the resistance value of the load changes by connecting a choke coil to the output section.

FIG. 1 shows the configuration of an inverter device for supplying alternating current from the former voltage type inverter to a load. In the figure, 1 is a DC power supply, 2 is a capacitor, 3A, 3B,
3C and 3D are switching elements forming the main part of the inverter, and are composed of, for example, transistors. Reference numeral 4 denotes a load, which is composed of a work body W composed of a work and a work coil, and a matching capacitor C having a capacitance value necessary for the inverter to resonate. In the figure, the inductance of the workpiece W is represented by L and the resistance is represented by R. In such a configuration, when the switching elements 3A and 3B are in the ON state, 3
When C and 3D are in the off state and switching elements 3A and 3B are in the off state, 3C and 3D are in the on state, and this on / off switching is performed by an external gate signal generator (not shown). ) Is controlled by a gate signal of a predetermined frequency. Therefore, the direct current from the direct current power source 1 is converted into an alternating current having a predetermined frequency by the inverter, and the alternating current is supplied to the load.

It is extremely advantageous in operation that such an inverter device is operated without changing the rated voltage and rated current of the inverter, that is, the output voltage and output current of the inverter, regardless of the load. . Therefore, a matching transformer is usually used in the inverter device. That is, the impedance of the load is uniquely determined when the work and the work coil are determined. Therefore, without changing the rated voltage and rated current of the inverter, the secondary side of the matching transformer,
That is, by adjusting the voltage applied to the load side and adjusting the impedance on the load side to the impedance on the inverter side, the voltage at both ends of the work body is changed so that the necessary voltage is applied to the work body. There is. 2 is the same as FIG.
Is an equivalent circuit in which the circuit diagram of the inverter device is represented only by the inverter and the load. In the figure, 5 is the inverter, and e is the output voltage of the so-called inverter applied from the inverter to the load. FIG. 3 is a circuit diagram in which the matching transformer 6 is added to the circuit of FIG. 2, and e'in the figure is the output side voltage of the matching transformer 6, that is, the voltage applied to the load side when the matching transformer is used. is there. In FIG. 2, the work body W
Let e _W be the voltage across both ends of, then this is expressed by the following equation.
The current flowing through the circuit is i, and the impedance of the entire circuit is (1 / jωC) + jωL + R.

E_W= (JωL + R) · i = (jωL + R) · e / {(1 / jωC) + jωL + R} (1) Here, when ωL / R is Q in the equation (1), e
_WIs e_W= {-Ω²LC + j (ω²LC / Q)} ・ e / {1-ω²LC + j (ω^{2 LC / Q)} (2) Becomes Now, when the inverter is operated at the resonance point, jω
Since L + (1 / jωC) becomes 0, from here, ω 2} =
1 / LC is derived, and ω in equation (2) above²1 / LC
Is replaced by e_WIs e_W= (1 + jQ) · e (3) Therefore, the matching transformer 6 in FIG.
Voltage e across work W_WIs e_W= (1 + jQ) · e '(4) Therefore, as can be seen from this equation, it can be adjusted according to the load.
Change e'by the combined transformer 6 and change the rated voltage of the inverter.
By matching at resonance without changing the pressure and rated current,
Voltage e across work W_WCan be changed arbitrarily
It That is, the required voltage can be applied to the workpiece.
It

[0006]

However, when such a matching transformer is used, since the loss due to Joule heat due to the windings of the matching transformer is large, the heating efficiency of the work and the like are reduced. Further, since such a matching transformer is extremely expensive, it is costly.

The present invention has been made to solve such a problem, and an object thereof is to provide a novel inverter device.

[0008]

[Means for Solving the Problems] In order to achieve such an object, an inverter device of the present invention provides an inverter device configured to supply an output of an inverter to a work body having an inductance and a resistance. Two capacitors, each having a capacitance whose sum is equal to the capacitance value for the inverter to resonate, were connected in series to the work body and the other was connected in parallel.

[0009]

[Action] Two capacitors having a capacitance whose total capacitance value is equal to the capacitance value for the inverter to resonate,
One is connected in series to the work body and the other is connected in parallel. Therefore, if the capacitance value of each capacitor is changed according to the load, matching at resonance can be achieved without changing the rated voltage and rated current of the inverter. A required voltage can be applied to both ends of the body W.

[0010]

Embodiment FIG. 4 is a schematic diagram of an inverter device shown as an embodiment of the present invention. In the figure, the same parts as those in FIGS. 2 and 3 are designated by the same reference numerals and symbols. In the figure, i is the rated current of Invar, that is, the output current of the inverter.
In the figure, Ca is a capacitor connected in series to the workpiece W,
Cb is a capacitor connected in parallel to the workpiece W. As these capacitors, capacitors having a capacitance such that the sum of the respective capacitance values is equal to the capacitance value for causing the inverter to resonate are selected. That is, when the work and work coil of the load are determined, the inductance and resistance of the inverter device are determined, and when the frequency of the alternating current supplied to the load is determined, the capacitance value of the capacitor for resonating the inverter is determined. Capacitors Ca and Cb having such capacitance values that the sum of the capacitance values of the two capacitors are equal to this capacitance value are selected. In the inverter device configured as described above, when the voltage e _W across the workpiece W is obtained (note that the symbols Ca and Cb representing the capacitors are used as the capacitance values of the capacitors as they are), e _W = {− ω ² LCa + j (Ω ² LCa / Q)} e / {1-ω ² L (Ca + Cb) + j (ω ² L (Ca + Cb) / Q)} (5) Now, when the inverter is operated at the resonance point, Since the resistance can be seen to be almost 0, it can be seen that the capacitor Ca is substantially connected in parallel with the capacitor Cb, and jωL + {1 / jω
(Ca + Cb)} can be set to 0. from here,
ω ² = 1 / L (Ca + Cb) is derived, and the above (5)
Substituting into the equation, e _W becomes e _W = {Ca / (Ca + Cb)} · (1 + jQ) · e (6). In this equation, (1 + jQ) is constant if the load is determined, and e is the output voltage of the inverter, which is constant, so C
By changing a / (Ca + Cb), the voltage e _W across the workpiece W can be changed. That is, if the capacitance values of the capacitors Ca and Cb are changed according to the load, matching at resonance can be achieved without changing the rated voltage and rated current of the inverter, and the voltage e _W required at both ends of the workpiece _{W can be obtained.} Can be applied. The values of Ca and Cb must be selected so that Ca + Cb becomes equal to the capacitance value of the capacitor for resonating this inverter.

[0011]

According to the present invention, two capacitors having a capacitance whose total capacitance value is equal to the capacitance value for causing the inverter to resonate are connected in series to the work body and the other is connected in parallel. Therefore, if the capacitance value of each capacitor is changed according to the load, matching at resonance can be achieved without changing the rated voltage and rated current of the inverter, and the required voltage is applied to both ends of the work body W. Can be done. Therefore, the matching transformer is not required, the heating efficiency of the work is not deteriorated, and the two capacitors are extremely low in price, which is extremely advantageous in terms of cost.

[Brief description of drawings]

FIG. 1 illustrates a configuration of an inverter device that supplies alternating current from a voltage type inverter to a load.

FIG. 2 is an equivalent circuit in which the circuit diagram of the inverter device of FIG. 1 is represented only by an inverter and a load.

FIG. 3 is a circuit diagram in which a matching transformer is inserted in the circuit of FIG.

FIG. 4 is a schematic diagram of an inverter device shown as an embodiment of the present invention.

[Explanation of symbols]

 1 DC power supply 2 Extraction electrodes 3A, 3B, 3C, 3D Switching element 4 Load W Work body 5 Inverter 6 Matching transformer Ca, Cb Capacitor

Claims (1)

[Claims] 1. An inverter device configured to supply the output of an inverter to a work body having an inductance and a resistance, and two capacitors having a capacitance such that the total capacitance value is equal to the capacitance value for the inverter to resonate. , One is connected in series to the work body, and the other is connected in parallel.