CN115242231A - Auxiliary branch circuit turn-off method for overcurrent IGCT - Google Patents

Abstract

The invention relates to a method for turning off an auxiliary branch of an overcurrent IGCT, which assists in turning off the IGCT when the IGCT device operates in a working condition that exceeds its maximum turn-off current. The auxiliary branch is formed by inductance, capacitor and auxiliary switching element in series, and is connected in parallel at both ends of the IGCT device. When the IGCT device needs to be turned off, the auxiliary switching element is put into operation. The auxiliary switching element is closed, the branch capacitor is discharged, and a reverse current opposite to the current flowing through the IGCT device is generated, which offsets the main circuit current flowing through the IGCT and reduces it to the maximum turn-off current of the IGCT device. The IGCT is turned off reliably. The invention effectively solves the problem of controllable turn-off of the IGCT device in the straight-through state, and the turn-off strategy logic is simple, efficient and reliable.

Description

A kind of auxiliary branch shutdown method for overcurrent IGCT

technical field

The invention belongs to the research field of solid-state switches in high-current and high-power circuits, and in particular relates to an auxiliary branch shutdown method for an overcurrent IGCT.

Background technique

Semiconductor power devices are widely used in power electronic circuits due to their advantages of arc-free fast breaking and long life. Among them, IGCT devices have the advantages of high current, high voltage, high switching frequency, compact structure, good reliability, low loss, etc., and their breaking performance in high-power circuits is more prominent, which is the current research focus and trend in power conversion circuits . Power electronic switches based on IGCT devices in high-power circuits may often require or be forced to withstand large currents, but the maximum turn-off current parameters of IGCT devices limit their maximum current-carrying capability under controlled turn-off conditions. The solution to this problem is generally to improve its overall current-carrying capacity by connecting multiple IGCT devices in parallel, and limit the current of a single device to be below its maximum turn-off current level, thereby avoiding the phenomenon of “pass-through” of the device under high current. Controlled shutdown is not possible. However, this solution increases circuit complexity, cost, volume, and needs to consider the problem of current sharing control of multiple branches in parallel. Therefore, the reliable turn-off of the overcurrent IGCT is an unavoidable problem in semiconductor switching power electronic circuits. Secondly, the shutdown strategy also needs to have the advantages of simple logic, high efficiency and reliability, and avoid introducing other influencing factors.

SUMMARY OF THE INVENTION

The present invention aims to propose a method for turning off an auxiliary branch of an overcurrent IGCT, so as to solve the problem that the IGCT is difficult to turn off due to the "shoot-through" phenomenon when a large current flows. In the invention, auxiliary branches are connected in parallel at both ends of the IGCT, and the current of the main loop is reduced to below the maximum turn-off current of the IGCT through the reverse current of the branch, thereby reliably turning off the IGCT device.

To achieve the above object, the technical scheme adopted in the present invention is:

A method for turning off an auxiliary branch of an overcurrent IGCT, when an IGCT device is in an overcurrent state, the auxiliary branch is used to turn off the auxiliary branch, wherein the auxiliary branch is formed of an inductor, a capacitor, and an auxiliary switching element in series, and the auxiliary branch is connected in parallel. At both ends of the IGCT device; when the IGCT device in the overcurrent state needs to be turned off, the auxiliary switching element in the auxiliary branch is closed, the auxiliary branch capacitor is discharged, and a reverse current opposite to the current flowing through the IGCT device is generated, The main loop current flowing through the IGCT device is offset so that it falls below the maximum turn-off current of the IGCT device, and then the IGCT is controlled to be turned off.

Further, the overcurrent state refers to the working condition of the IGCT device exceeding its maximum turn-off current.

Further, the capacitor has a charging loop and charging control logic to pre-charge it to a specified voltage level, and when the auxiliary branch is not working, the capacitor is in a ready state.

Further, by designing the electrical parameters of the inductance and capacitance in the auxiliary branch, the off-time of the IGCT device and the rate of decrease of the IGCT current can be adjusted.

Compared with the prior art, the beneficial effects of the present invention include:

The present invention proposes a method for turning off an auxiliary branch of an overcurrent IGCT, which solves the problem that the IGCT cannot be turned off in a "straight-through" condition under a high current by paralleling an inductor and a capacitor in series, and the turn-off strategy is simple, efficient and reliable. The problems such as increased cost, increased volume, and complicated circuit and control logic caused by the method of using multiple IGCT devices in parallel and shunting are avoided.

Description of drawings

1 is a schematic diagram of a circuit structure of the present invention;

FIG. 2 is a schematic diagram of the circuit structure of the auxiliary branch in the present invention.

Detailed ways

Embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood, however, that these descriptions are exemplary only, and are not intended to limit the scope of the present invention.

A method for turning off an auxiliary branch of an overcurrent IGCT in the present invention is a method for turning off an IGCT device in an overcurrent state. The overcurrent state refers to the working condition of the IGCT device exceeding its maximum turn-off current. The auxiliary branch is formed of an inductor, a capacitor and an auxiliary switching element in series, and is connected in parallel to both ends of the IGCT device. The capacitor in the auxiliary branch needs to be designed with a charging circuit and a charging control logic to be pre-charged to a specified voltage level, and the capacitor is in a ready state when the auxiliary branch is not working. The auxiliary branch is put into operation by means of an auxiliary switch when the IGCT device needs to be turned off.

When the IGCT device in the overcurrent state needs to be turned off, the auxiliary switch in the auxiliary branch is closed, the branch capacitor is discharged, and a reverse current opposite to the current flowing through the IGCT device is generated to offset the main circuit flowing through the IGCT device. The current can be reduced below the maximum turn-off current of the IGCT device, so that the IGCT device can be controlled to turn off reliably. The auxiliary branch can realize the adjustment of index values such as the turn-off time of the IGCT and the rate of decline of the IGCT current by designing the electrical parameters of the inductance and the capacitor. The pulse current generated by the auxiliary branch when it is initially put into operation needs to be opposite to the direction of the current flowing through the IGCT device, so as to prepare for the current reduction for turning off the IGCT device.

A circuit structure of a method for turning off an auxiliary branch of an overcurrent IGCT according to the present invention is shown in FIG. 1 . Among them, the IGCT branch is the main current loop, which is set to work in a current flow environment that exceeds its maximum turn-off current, and i1 is its current value. The auxiliary branch is connected in parallel at both ends of the IGCT device, and the auxiliary circuit is used to turn off the overcurrent IGCT, and i2 is the current value during operation. When the IGCT device in the overcurrent state needs to be turned off, the auxiliary branch is put into operation, and the generated reverse current i2 offsets the main circuit current i1 below its maximum turn-off current. At this time, the IGCT responds to the turn-off command of the control circuit, Finally, the controllable shutdown under the overcurrent state is realized.

The circuit structure of the auxiliary branch is shown in FIG. 2 , which is formed by an inductor L, a capacitor C, and an auxiliary switching element S connected in series, and then connected in parallel to both ends of the IGCT device. When the IGCT turn-off process is not started, the precharging device in FIG. 2 is used to precharge the capacitor C in the auxiliary branch to a specified voltage level, so as to prepare for the auxiliary branch to be put into operation. When the IGCT device needs to be turned off, the auxiliary branch is put into operation by means of the auxiliary switching element S, that is, the auxiliary switching element S is closed, and the auxiliary branch begins to provide reverse current. In addition, the auxiliary branch can also adjust the IGCT turn-off time, IGCT current drop rate and other index values by designing the electrical parameters of the inductance L and capacitor C, that is, the auxiliary branch current and the inductance L and capacitance are calculated based on the LC series circuit. C, select different values of inductance L and capacitance C to obtain different auxiliary branch current changes, such as current rise rate. Combined with the IGCT device parameters and the actual operating state of the circuit, the corresponding circuit index values that meet the system requirements are determined.

The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto, and these embodiments are only for the purpose of illustration, not for limiting the scope of the present invention. The scope of the invention is defined by the appended claims and their equivalents. Without departing from the scope of the present invention, those skilled in the art can make various substitutions and modifications, and these substitutions and modifications should all fall within the scope of the present invention.

Claims (4)

1. a method for turning off an auxiliary branch of an overcurrent IGCT is characterized in that: when the IGCT device is in an overcurrent state, the auxiliary branch is used to turn it off, and the auxiliary branch consists of an inductance, a capacitor, an auxiliary switch The components are connected in series and connected in parallel at both ends of the IGCT device; when the IGCT device in the overcurrent state needs to be turned off, the auxiliary switching element in the auxiliary branch is closed, and the auxiliary branch generates a reverse reaction to the current flowing through the IGCT device. To offset the main loop current flowing through the IGCT device to make it drop below the maximum turn-off current of the IGCT device, and then realize the controllable turn-off of the IGCT. 2 . The method for turning off an auxiliary branch of an overcurrent IGCT according to claim 1 , wherein the overcurrent state means that the IGCT device operates under a working condition that exceeds its maximum turn-off current. 3 . 3. The method for turning off an auxiliary branch of an overcurrent IGCT according to claim 1, wherein the capacitor is designed with a charging loop and a charging control logic to pre-charge to a specified voltage level, and the auxiliary circuit is designed with a charging circuit and a charging control logic. When the branch is not working, the capacitor is in a ready state. 4. A kind of auxiliary branch shut-off method for overcurrent IGCT according to claim 1, is characterized in that: realize the turn-off time to IGCT device, by designing the electrical parameters of inductance and capacitance in the auxiliary branch. Regulation of IGCT current drop rate.

Images