JPS5931310B2 - current type inverter - Google Patents

Description

[Detailed description of the invention] The present invention relates to a current type inverter.

Conventionally, only small-capacity self-extinguishing switching elements were available, so large-capacity current-type inverters were constructed with thyristors. When starting a current-type inverter, various starting methods have been proposed because the current cannot be commutated by itself during the initial starting when no induced voltage is generated on the load side. For example, the circuit was complicated because it used a thyristor for starting and a series capacitor for starting. The present invention was made in view of these points, namely, a forward converter to which an AC input is supplied, and a reverse bridge configuration that converts the DC output of this forward converter into an AC output and supplies it to an inductive load. In the current type inverter, the inverter has a plurality of thyristors connected in series in the forward direction, and each arm is formed by connecting a self-extinguishing switching element in parallel with one of the thyristors. At the time of starting, the self-arc-extinguishing switching element in each arm is used for operation, and during steady operation, the thyristor connected in parallel with the self-arc-extinguishing switching element in each arm is used for operation. The purpose of this invention is to provide a current type inverter which is characterized in that it can be started in a simple manner and can produce a high-voltage output, and will be described below using examples.

FIG. 1 shows an embodiment of the current type inverter according to the present invention, in which Rf is a forward converter that converts AC input into DC, Ld is a DC reactor, and IV is a bridge-configured inverse converter, This inverter V has thyristors SCR1 and SCR3 connected in series in the forward direction, and a self-extinguishing switching element G1 such as a gate turn-off thyristor (hereinafter referred to as GTO) or a transistor in parallel with the thyristor SCR3. an arm formed by connecting thyristors SCR2 and SCR4 in series in the forward direction, and a self-extinguishing switching element G2 such as a GTO or a transistor connected in parallel with thyristor SCR4; SCR5
and SCR7 are connected in series in the forward direction, and a self-extinguishing switching element G3 such as a GTO or a transistor is connected in parallel with the thyristor SCR5, and thyristors SCR6 and SCR8 are connected in series in the forward direction. , and an arm in which a self-extinguishing switching element G4, such as a GTO (GTO) transistor, is connected in parallel with the thyristor SCR6.

Here, as self-extinguishing switching elements G1 to G4, G
TO is used. LC is a load circuit connected to the output side of the inverter 1, and this load circuit LC is a circuit formed by connecting a power factor adjustment capacitor C and a work coil L in parallel. A material M is inserted into the work coil L and heated by induction. In order to obtain a high voltage output, a plurality of thyristors (in this case two thyristors) are connected in series in each arm of the inverter V.

Furthermore, the voltage tolerance of each of the thyristors SCR3 to SCR6 connected in parallel with each of the self-arc-extinguishing switching elements G1 to G4 is the same as that of the self-arc-extinguishing switching elements G1 to G4.
Same value as G4, current capacity is used only for starting 7
Keep it small.

The operation of the current type inverter configured in this way will be explained using FIGS. 2 and 3. First, at the time of starting from the initial time T to time Tn, as shown in the time chart of FIG.
R2, SCR. ts self-extinguishing switching element G2,
A signal is given alternately to G3. At this time, even if there is no back power on the load side, the self-arc switching element Gl,
G4, G2, and G3 can self-commutate, so they start stably. Here, the waveforms of the output voltage and output current during the starting operation are constant in a low state as shown in section T in FIG. 3.
Next, when the transient phenomenon during starting ends at time Tnl and the load circuit LC becomes stable, thyristors SCR4 and SCR5 are fired instead of self-extinguishing switching elements Gl and G4, and self-extinguishing switching is started. Thyristors SCR3 and SCR6 are fired instead of elements G2 and G3, and a steady mode is established.

At this time, the output voltage of the inverter is controlled to a value with voltage and current withstand voltage by one of the self-extinguishing switching elements G, ~G4, and the output voltage of the inverter is controlled by one of the self-extinguishing switching elements G1~G4.
After the thyristors SCR to SCR8 are in operation, the output voltage is increased as shown in FIG. During steady operation, only the divided voltage of the thyristor is applied to the self-arc-extinguishing switching elements G1 to G4, so that the self-arc-extinguishing switching elements G1 to G4 are not destroyed by voltage. As described above, if the current type inverter according to the present invention is used, the following various effects can be achieved.

(1) The starting circuit is simple, making it economical and improving reliability. (2) Even in the case of an inverter that produces high voltage output, it can be started with four small self-extinguishing switching elements.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the current type inverter according to the present invention, and FIGS. 2 and 3 are diagrams explaining the operation of FIG. 1, in which Rf is a forward conversion device and V is an inverse conversion device. equipment, SC
R, ~SCR. 8, thyristors G1 to G4 are self-extinguishing switching elements, LC is a load circuit, L is a work circuit,
C indicates a power factor adjustment capacitor, and Ld indicates a DC reactor.

Claims (1)

[Claims] 1. A current type inverter comprising a forward converter to which an AC input is supplied, and a bridge-configured inverter that converts the DC output of the forward converter into an AC output and supplies it to an inductive load, wherein the inverter consists of each arm made up of a plurality of thyristors connected in series in the forward direction and a self-arc-extinguishing switching element connected in parallel with one of the thyristors, and when starting, the self-arc-extinguishing switching element in each arm 1. A current type inverter, characterized in that the current type inverter is operated using a type switching element, and in steady operation, it is operated using the thyristor connected in parallel with the self-extinguishing type switching element in each arm.