JP2800383B2 - High frequency inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a high-frequency generator for switching a transistor or an electron tube switch at a high frequency to generate a high-frequency alternating current from a DC power supply, and to use the induction or dielectric heating for induction heating or dielectric heating. Related to inverters.

[Conventional technology]

When high frequency inverters are connected in parallel for the purpose of increasing the output, a slight difference between the ON and OFF times of the switch elements
A cross current flows via the inverter output line. As a result, the output currents of the respective inverters are not balanced, and are likely to be unbalanced.

For this reason, conventionally, as shown in FIG. 5, for example, a configuration is known in which two inverter output lines are penetrated through one iron core (core) 7 in opposite directions.

That is, by passing the output line of the inverter 3 through the current balancing cores 7 of the inverters 1 and 2 in opposite directions, a magnetic flux is generated in the core 7 when an unbalanced current flows, and the unbalanced current is applied to the output line. A counter electromotive force in the direction of suppressing the current is generated so that the unbalanced current does not flow.

Reference numeral 4 in FIG. 5 denotes a control circuit, 5 denotes a load, and 8 denotes a current detection current transformer. By feeding back a load current detected via the current transformer 8 to the control circuit 4, Current control of the load 5 is performed. Reference numerals 12 and 13 denote series resonance capacitors.

[Problems to be solved by the invention]

In the circuit as described above, it is necessary to pass the output conductor of the inverter through one window of the balance core 7 in the opposite direction.
There is a problem that production becomes difficult.

It is therefore an object of the invention to balance the output currents of a plurality of inverters in a simple manner.

[Means for solving the problem]

A plurality of high frequency inverters are connected in parallel, the secondary windings of each current transformer for detecting the output current of each inverter are connected in series with each other, and the output currents are balanced.

[Action]

Since the current transformer operates to maintain a constant current ratio between the primary and secondary windings, connect the secondary windings in series with each other so that the secondary current has only one value. Thus, the current on each primary side can be equalized (balanced).

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which half-bridge high-frequency inverters 1, 2, 3 comprising two switches Q1, Q2 and series resonance capacitors 12, 13 are connected in parallel.
An example in which AC power is supplied to two common loads 5 is shown.

Then, the current transformers 21, 22, 2 are connected to the output lines of the inverters 1, 2, 3.
3 is provided and the secondary sides are connected in series with each other. Further, an auxiliary current transformer 31 is connected to the secondary side circuit, and the output current of the secondary winding is fed back to the control circuit 4 so that the inverter 1
-3 are controlled. Therefore,
The current transformers 21, 22, and 23 function not only for current balance but also for current detection.

FIG. 2 shows an example in which full-bridge connected inverters 1 and 2 composed of four switches Q1 to Q4 are connected in parallel, and power is supplied to a load 5 via a resonance capacitor 6 by these.
Here, since the DC power supplies 11 are insulated from each other, only two current transformers 21 and 22 are needed to balance the output current. Reference numeral 31 denotes an auxiliary current transformer similar to that shown in FIG.

FIG. 3 shows an example in which the DC power supply 11 is shared with FIG. 2. In this case, it is necessary to consider the cross current on the DC side. Therefore, four current transformers 21 to 24 are provided. It is like that.

FIG. 4 is a partial detailed view of FIG. 3, showing the current transformers 21 and 22 specifically divided into a core and a coil.

FIG. 4A is an example in which one of the current transformers, for example, 22 is omitted from FIG. 4, and a balance core 7 is provided instead, and a relationship between currents iU, iV flowing through output conductors U, V is expressed by: The same effect as in the case of FIG. 4 is provided by setting iU = −iV. In this case, the balance core 7
Since the conductor to be passed through is determined from the beginning, the operation is significantly simplified as compared with the case where the conductor is passed through later as shown in FIG. The secondary winding of the current transformer 21 is of course connected in series with the secondary winding of the current transformer of another conductor.

FIG. 4B shows the current transformer 21 and the core 7 of FIG.
The number of cores is reduced by replacing with a tripod core 7A formed in a U-shape. The tripod core 7A can be formed by combining, for example, three rod-shaped ferrites with an appropriate magnetic material into a “sun” shape.

〔The invention's effect〕

According to the present invention, the secondary windings of the plurality of current transformers coupled to the inverter output line are connected in series with each other to balance the output current of each inverter, so that only wiring of thin wires is required. In addition, problems in design and manufacturing can be avoided. As described above, using the secondary side of the current transformer near the open state cannot be considered with the common sense of the conventional electric circuit, but this problem is solved here by providing the auxiliary current transformer. This makes it possible to reduce the current transformer ratio of the current transformer for balance.

Also, if the current transformer ratio (turn ratio) of the current transformer for balance is large, an excessive voltage is generated in the secondary winding of the current transformer in correcting the imbalance of the output current, and the insulation of the winding is reduced. If a current transformer having a large turns ratio (several hundreds or more) is required, the auxiliary current transformer is particularly indispensable because the current transformer may be broken and burnt.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment in which the present invention is applied to a half bridge. FIG. 2 is a circuit diagram showing an embodiment in which the present invention is applied to a full bridge having individual DC power supplies. FIG. 4 is a circuit diagram showing an embodiment in which the present invention is applied to a full bridge sharing a DC power supply, and FIG.
FIG. 4A is a main part circuit diagram showing a modification of FIG. 4; FIG. 4B is a main part circuit diagram showing a modification of FIG. 4A;
FIG. 1 is a circuit diagram showing a conventional example. 1,2,3 ... high frequency inverter, 4 ... control circuit, 5 ...
Load, 6, 12, 13 ... series resonance capacitor, 7 ... balance core, 7A ... tripod core, 8, 21, 22, 23, 24, 31 ... current transformer, 11 ... DC power supply, Q1 , Q2, Q3, Q4 ... Switch element.

Claims (4)

(57) [Claims] 1. A high-frequency inverter in which a plurality of high-frequency inverters are connected in parallel, the secondary windings of each current transformer for detecting the output current of each inverter are connected in series with each other, and the output currents are balanced. . 2. The high-frequency inverter according to claim 1, wherein an auxiliary current transformer is provided in the series circuit of the secondary winding of the current transformer. 3. A plurality of high-frequency inverters sharing a DC power supply are connected in parallel,
A high-frequency inverter comprising a combination of a current transformer for balance and a core provided on the output conductor, and secondary windings of the current transformers connected to each other in series. 4. The high frequency inverter according to claim 3, wherein a current transformer comprising a tripod core and a secondary winding is provided in place of the current transformer and the core for balance.