JPS6225879A - High-frequency inverter - Google Patents

Abstract

PURPOSE:To reduce the ripple currents of a capacitor fitted to a DC intermediate circuit by equally dividing a capacitor for resonance connected to an output from an inverter into two and connecting the capacitors divided to the inverter in predetermined relationship. CONSTITUTION:A power supply having commercial frequency is rectified by a rectifying circuit 1, smoothed by a capacitor 2, and fed to an inverter 3. A capacitor for resonance connected on the output side of the inverter 3 is divided equally into two, and a series circuit of the capacitors C1, C2 is connected between a positive pole and a negative pole at DC voltage. A heating coil 5 as load is connected between the middle point of the capacitors C1, C2 and the middle point of transistors Q1, Q2.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to a high-frequency inverter for supplying high-frequency current to a heating coil in an electromagnetic induction heating device, and in particular, to a high-frequency inverter for supplying high-frequency current to a heating coil in an electromagnetic induction heating device. This is what I did.

[Conventional technology and problems]

In general, an induction heating device uses the amount of heat generated by the wax current product generated in a heated object by an alternating magnetic field generated by a heating coil. Since this heating coil has a poor power factor, a power factor adjusting capacitor is connected thereto and an LC resonant circuit is formed.

As this type of high-frequency inverter, a single-end push-pull type shown in FIG. 5 is conventionally known. In the figure, 1 is a rectifier for converting the commercial frequency M[ into a DC voltage, 2 is a capacitor connected between the positive and negative output terminals of the rectifier 1 and has a smoothing effect, and 8 is a power transistor with Ql and Q'' alternately connected. 4 is a power transistor Q1.
It is directly at the midpoint of Ql.

FIG. 6 shows the waveforms of the output voltage vo and output current io of the inverter 8 shown in FIG. It is a figure showing the relationship with on-off operation. In the figure, an example is shown in which the output voltage vo is operated in phase leading by the output current α angle.

In such a device, the current ia flowing through the part connecting the capacitor 2 and the inverter 8 of the DC intermediate circuit is as follows: as shown in FIG. 6, the power transistor QI turns off, then the power transistor Qt turns on, and then During the period until it is turned off, no current flows, and a direct current containing a large alternating current component matching the output current io flows. That is, ia
The DC component includes a large ripple current (harmonic) that is a fundamental harmonic of the frequency of the output current io. This ripple current flows to capacitor 2 of the DC intermediate circuit, so capacitor 2 must be selected to withstand this ripple current.
There was a problem in that the number of capacitors had to be increased more than necessary to increase the capacitance [UF] required by the C resonant circuit.

[Purpose of the invention]

The present invention has focused on this point, and an object of the present invention is to provide an inverter that can reduce the ripple current of a capacitor provided in a DC intermediate circuit.

[Key points of the invention]

This invention reduces the ripple current of the capacitor connected to the DC intermediate circuit by dividing the resonance capacitor connected to the output of the inverter into two equal parts and improving the connection with the inverter. This is an attempt to reduce the capacity.

[Embodiments of the invention]

FIG. 1 shows an embodiment of the present invention, and the same reference numerals as shown in FIG. 5 are the same members. The resonance capacitor 4 is equally divided into two to form capacitors Cs and C! Connect the series circuit between the positive and negative poles of the DC voltage. And the midpoint between capacitors C1 and 02 and transistors Ql, Q!
A heating coil 5, which is a load, is connected between the midpoints of .

In such a configuration, now the power transistor Q1
is turned on and the power transistor Q! is turned off, the current io flowing through the heating coil 5 flows from the positive electrode side of the DC intermediate circuit to the power transistor Ql
The sum of the current 11 flowing through the heating coil 5 to the negative electrode side of the DC intermediate circuit and the current is flowing in the path of the power transistor Q1% heating coil 5 and the capacitor C1 for discharging the energy stored in the resonance capacitor 0. becomes. At this time, if the capacitance of the capacitor 0"IC' is made exactly the same, the current value will be it=ig, and the current io flowing through the heating coil 5 will be io=2Xit.

Then, when the power transistor Q is on and iQt is off, the heating coil current io flows from the positive voltage side of the DC intermediate circuit to the capacitor C+, the heating coil 5, and the power transistor Q!, as shown in FIG. The current iz flowing to the negative voltage side of the DC intermediate circuit through the resonance capacitor C2
Due to the energy stored in the capacitor C! , heating coil 5, power transistor Q”% capacitor Q
It is determined by the sum of the current it flowing along the path 't. If the capacitance of the capacitor is Qs = C*, the current value will be 11=i-th, so similarly the current io flowing through the heating coil will be io=2 it.

Therefore, in FIG. 1, the current ia flowing through the portion connecting the capacitor 2 connected to the DC intermediate circuit and the inverter 3 has a waveform as shown in FIG. This current waveform is significantly different from ia shown in FIG. 6, and does not include an AC component generated as a fundamental harmonic of the frequency of the current io flowing through the heating coil 5, but is a ripple current whose main component is twice the frequency. It can be seen that Moreover, the current ia in Fig. 1 is 5th
The amplitude of the AC component is significantly smaller than the current in the figure, and as a result, the ripple current is also smaller.

Also, by using two capacitors, the resistance of the capacitor decreases and the current flowing through the heating coil increases.

〔Effect of the invention〕

According to this invention, the resonance capacitor connected in series to the heating coil is divided into two parts, two capacitors are connected in series to both ends of the series circuit of the semiconductor switch 2a, and the midpoint of each circuit is Since a heating coil serving as a load is inserted in between, the ripple current flowing from the DC intermediate circuit to the inverter can be significantly reduced, and as a result, the capacitor provided in the DC intermediate circuit can be significantly downsized.

Furthermore, the current flowing through the heating coil can be increased.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Figs. 2.8 and 4 are circuit diagrams and waveform diagrams for explaining the invention in detail, and Fig. 5 is a circuit diagram showing a conventional device. , FIG. 6 is a waveform diagram for explaining the operation of the conventional device. 2... Capacitor, 3... Inverter, 5... Heating coil, Ql, Ql... Semiconductor switch, Qt,
Ct...Resonance capacitor. Figure '1 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1) In a high frequency inverter in which a series circuit of two semiconductor switches is connected between the positive and negative poles of a DC power source, two capacitors are connected in series at both ends of the series circuit,
A high frequency inverter characterized in that a load is connected between the midpoint of these two capacitors and the midpoint of the two semiconductor switches.