JPS5850104B2 - frequency converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency conversion device, and particularly to a method for starting a frequency conversion circuit.

Conventionally, there have been many methods for starting frequency conversion circuits, that is, inverter circuits that convert direct current to alternating current, or high-frequency cycloconverter circuits that directly convert alternating current to high-frequency alternating current. The activation method for the control gate trigger circuit has not yet been established.

The present invention provides a startup method that enables reliable and stable startup in a frequency conversion circuit that performs commutation margin time control.

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

In FIG. 1, a DC voltage is applied to a frequency conversion circuit 2 from a DC power supply 1.

The frequency conversion circuit 2 converts direct current into high-frequency current, and connects a current-limiting inductor 21a from the + terminal of the DC power supply 1, a current-limiting inductor 21b from one terminal of the DC power supply 1, and connects the thyristors 22a and 22b connected in series. Connect the anode and cathode in series.

Diodes 23 a t 23 b are connected in anti-parallel relationship with each of the cyrisks 22 a and 22 b.

Connection point N of series-connected cyrisks 22a and 22b
Thus, a series resonant circuit consisting of a resonant capacitor 24, a resonant inductor 25, and a load resistor 26 is connected to one side of the DC power supply 1.

Thyristor 22a. 22b are alternately triggered by the control circuit 3, and the trigger timing is controlled by the commutation margin time by detecting the zero point by the current transformer 31.

That is, in FIG. 2, A shows the current waveform of the thyristor 22a and the diode 23a, B shows the current waveform of the gate trigger current, A' shows the current waveform of the thyristor 22b1 diode 23b, and B' shows the current waveform of the gate trigger current. .

As shown in FIG. 2, the time tD from when the thyrisk current reaches zero until the next thyrisk is triggered is controlled so that it is longer than the turn-off time of the thyrisk.

The current transformer 31 shown in Fig. 1 is for detecting the zero point of the output resonance current, which is the same as the silisk current, and after detecting the zero point,
It is intended to trigger a system risk with a certain delay time.

The cyrisk trigger control method shown in FIGS. 1 and 2 is generally called commutation margin time control.

The delay time tp shown in FIG. 2 becomes the commutation margin time.

The selection of the commutation margin time is normally feedback-controlled to a value that corresponds to the load, but at startup, it is necessary to set the commutation margin time to a predetermined value.

Figures 3 and 4 show the current i as I/E/J "7",
Voltage V is V/E, a=R/2 J[As time T is t/
Calculated by making it dimensionless using πv/LC1. If the inductance of the resonant inductor 25 is 0, and the values of the current limiting inductors 21a and 21b are equal L2, then L-L, +L.
2, and the value of the load resistance 26 is defined as R.

FIG. 3C shows the si-risk and diode current waveforms when the non-dimensional commutation margin time at α-0,1 is set to 0,9, and D is the output resonant circuit current waveform at that time.

Furthermore, when E is α=0.005 and the dimensionless commutation margin time is set to 0.3, it can be seen that the output resonant circuit current increases abnormally.

In other words, when the load resistance is small, if the commutation margin time is shortened, the load current becomes large, and the SI risk current also increases, which may lead to the failure of the SI risk.

On the other hand, if the commutation margin time is made longer, that is, 0.9 or more, the zero point will be crossed again, causing malfunction of the control circuit.

In FIG. 4, D shows the C1 output resonant current waveform and the diode current waveform when α-0.1 and the commutation margin time is 0.9.

In addition, when α-=0.005 and the commutation margin time is 0.9, the C1 output resonant circuit current is shown as C1, and the diode current waveform is shown as D'.

In this way, if the commutation margin time is 0.9, both the output current and the sirisk current can be started with small values.

FIG. 5 shows another embodiment of the present invention, in which an AC power source 1' is connected to an input capacitor 27, the AC is directly converted into a high frequency current, and a resonant inductor 25' which also serves as an induction heating coil is used to This is a frequency conversion circuit that inductively heats metal pots, etc.

This circuit also performs commutation margin time control in the same way, and the commutation margin time t at startup is half the period of the output resonant circuit, that is, πV
Stable startup is possible by starting with 0.9 times I.

In the case of an induction heating cooker, in an aluminum pot, the inductance of the resonance inductor that also serves as an induction heating coil is small, so when calculating the commutation margin time at startup, L is determined taking the aluminum pot into account.

As described above, the present invention provides a method for controlling the commutation margin time in an inverter circuit including a series resonant circuit consisting of a plurality of syrisks, a diode, and a resonant inductor, or in a high-frequency cycloconvert circuit. It starts with a commutation margin time of half a cycle, that is, 0.9 times πVI.

Therefore, the starting current is small and soft start is possible, and stable oscillation starting is possible.

Further, since there is sufficient commutation margin time, commutation failure does not occur, and the same is true when the induction heating coil also serves as a resonance inductor.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a frequency converter according to the present invention, FIG. 2 is a diagram showing waveforms of various parts of the frequency converter shown in FIG. 1, and FIGS. 3 and 4 are explanations of the present invention. FIG. 5 is a circuit diagram showing an embodiment in which the present invention is applied to an induction heating device. 1... DC power supply, 2... Frequency conversion circuit, 3... Control circuit, 22a, 22b...
...Sirisk.

Claims (1)

[Claims] 1 Consists of a frequency conversion circuit for converting alternating current or direct current into high-frequency current, and its control circuit, the frequency conversion circuit consisting of at least a plurality of cyrisks, a series resonant circuit including a resonant capacitor and a resonant inductor, The control circuit detects the zero point of one thyrisk current in order to control the commutation margin time of the thyrisk, and controls the time to trigger the other thyrisk, and when the frequency conversion circuit is activated, The frequency conversion device is characterized in that the commutation margin time is activated from a time that is 0.9 times or less of a series resonance frequency formed by a resonance inductor and a resonance capacitor.