JPS6027271B2 - Inverter device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a forced commutation type thyristor inverter, and more particularly to protection of elements when a reverse conduction thyristor is used as the main thyristor through which a load current flows.

Forced commutation type thyristor inverters are classified into voltage control type, current control type inverters, etc., or constant voltage constant frequency (CVCF) and variable voltage variable frequency (VV) depending on the control method.
VF) There is a distinction between isoverters, etc., but below, voltage control type C
This will be explained by taking a VCF inverter as an example.

FIG. 1 shows a conventional circuit, and FIG. 2 is a diagram for explaining the operation of the conventional example shown in FIG. In FIG. 1, for example, to explain the configuration of the R-phase AC output, DC power is supplied from a constant voltage power supply 11 through an actuator 12 for dv/dt suppression and current suppression at the time of a short circuit, through a series circuit of reverse conducting resistors. It is converted into AC power by turning on and off 20 and 21. The reverse conduction thyristor 20, 2
A series circuit of commutation assisting thyristors 26 and 27 is connected in parallel with 1, and a series circuit of a commutation capacitor 24 and a commutation reactor 25 is connected between the intermediate connection points of the series. Saturable reactors 22 and 23 are connected in series with reverse conduction thyristors 20 and 21, respectively, and dv/dt and d
The saturable reactors 28 and 29 are connected in series with commutation assisting thyristors 26 and 27, respectively, and serve to suppress dv/dt. Further, in FIG. 1, 300 and 40 rivers show an S phase and a T phase, which have exactly the same configuration as the R phase 200. The operation of the circuit is based on the Tokuko Sho 4.
2-15061 etc., so it is omitted here. As the technology trend is that inverters become higher in voltage and capacity,
Improvements have been made in large-capacity reverse-blocking thyristors, but as the capacity increases, the turn-off time of reverse-blocking thyristors becomes longer, and conventional circuit design methods no longer provide sufficient margin.

In contrast, reverse conduction thyristors have recently been developed, making it possible to increase the capacity without increasing the turn-off time, but on the other hand, their semiconductor structure means that the current flowing through the reverse conduction part
It became necessary to suppress di/dt. However, against this phenomenon, the circuit shown in FIG. 1 is used because if a saturable reactor is connected in series with the reverse conduction thyristor, desirable protection for the element can be provided due to the nature of the saturable reactor. The shortcomings of FIG. 1 will be explained in conjunction with FIG. 2 as follows. In FIG. 2, a and b are a current ia flowing through the reverse conduction thyristor 201 and an anode-cathode voltage va, respectively, and c and d are a current ib flowing through the reverse conduction thyristor 21 and an anode-cathode voltage ve, respectively. Taking as an example the commutation period from time t to time t, just before time t, the load current is R terminal - reverse conduction thyristor 21 - saturable reactor 23 - DC power supply 11
), and the commutating capacitor 24 is charged as shown. When the commutation assisting thyristor 27 is turned on at a certain time, commutation capacitor 24 - commutation assisting thyristor 27 - saturable reactor 29 - saturable reactor 23 - reverse conduction thyristor 21 - commutation reactor 25
A discharge current flows along the path of the commutating capacitor 24, but at the beginning of the flow, the saturable reactor 29 bears almost the voltage of the commutating capacitor 24 due to the nature of the saturable reactor. When the saturable reactor 29 is saturated, the current increases at a slope determined by the commutating capacitor and the commutating reactor, but when the discharge current reaches the same level as the load current, the saturable reactor 23 changes from the saturated region to the unsaturated region. Since the saturable reactor 23 enters the region, the commutating capacitor 24 at that time
bears the voltage of Since this voltage is in the forward voltage direction for the reverse conduction thyristor, which is non-conducting, the forward voltage element capability at this time is required to be (supply voltage) + (capacitor voltage), and when selecting a thyristor, it is necessary to It is necessary to select a voltage higher than that required by the power supply voltage, which is extremely uneconomical. After this, the saturable reactor 23 is saturated,
When the discharge current exceeds the peak value and decreases, it enters the non-saturation region again, but at this time the reverse conduction thyristor 21 -
It plays a role in suppressing di/dt. The purpose of this invention was to eliminate the above-mentioned drawbacks, and by inserting a saturable reactor between the series intermediate connection point of the reverse conduction thyristor and the commutation circuit, the overvoltage applied to the reverse conduction thyristor can be reduced. An object of the present invention is to provide an inverter device that eliminates the problem.

FIG. 3 shows an embodiment of the present invention, and FIG. 4 is a diagram for explaining the operation of this embodiment.

In FIG. 3, elements with the same symbols as in FIG.
It has the same function as shown in the figure, and the difference from Fig. 1 is that a saturable reactor 201 is connected between the series intermediate connection point of the reverse conduction thyristors 20 and 21 and the commutation reactor 25 in the commutation circuit. , an AC output terminal R is taken from the connection point between the commutation reactor 25 and the saturable reactor 201. S
The configurations of phase 310 and T phase 410 are exactly the same as R phase 310. In addition, in FIG. 4, a and b are the current ic and voltage vc flowing through the saturable 1' factor 201, and c and d are the second
They are va and vb as in the figure. To explain the circuit operation in FIG. 3 using times t and - as an example, just before time t, the load current flows in the direction of R terminal - saturable reactor 201 - reverse conduction thyristor 21 - DC power supply 11 (1) side. Also, the commutation capacitor is charged as shown.

When the commutation assisting thyristor 27 is turned on at a certain time, a discharge occurs in the path of commutation capacitor 24 - commutation assisting thyristor 27 - saturable reactor 29 - reverse conduction thyristor 21 - saturable reactor 201 - commutation reactor 25 - commutation capacitor 24. Current flows, but the voltage that occurs at the point causing the aforementioned drawbacks is not applied to the reverse conducting thyristors 20 and 21, so that only the DC supply voltage has to be taken into account when selecting the reverse conducting thyristors. After this, when the saturable IJ vector 201 is saturated and enters the non-saturation region again, the commutation is started by -di/d of the reverse conduction thyristor 21.
Suppress t. If the load is inductive after commutation, the load current flows in the direction of R terminal - saturable reactor 201 - reverse conduction thyristor 20 - reactor 12 - DC power supply 11 (10), but the direction of the current will eventually reverse. Since the saturable reactor 201 is sometimes reset, the same operation as the above-mentioned commutation is repeated in the next commutation. Although FIG. 3 has been explained using a three-phase example, it is needless to say that it is not limited to three phases, and the important points in this invention are the reverse conduction thyristors 20 and 21, the saturable reactor 201, and Since this is related to the AC output terminal R, the configuration of the other commutation circuits is not limited to this embodiment. that's all,
According to this invention, the saturable reactor is connected between the series intermediate connection point of the reverse conduction thyristor and the commutation circuit, and the load terminal is taken from the connection point between the saturable reactor and the commutation circuit, so that the main circuit Since overvoltage is not applied to the reverse conduction thyristor, only the main circuit DC power supply voltage needs to be considered when selecting the reverse conduction thyristor, making it economical and reliable even in high voltage and large capacity inverter devices. Therefore, it is possible to provide an inverter device with higher performance.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a conventional device, Fig. 2 is an explanatory diagram of the operation of the conventional example shown in Fig. 1, Fig. 3 is a circuit diagram showing an embodiment of the present invention, and Fig. 4 is shown in Fig. 3. It is an explanatory diagram of operation of an example. 11... Constant voltage DC power supply, 12... Reactor, 2, 21...
Reverse conducting thyristor, 22, 23, 28, 29, 201・
... Saturable reactor, 24 ... Commutation capacitor, 2
5... Commutation reactor, 26, 27... Commutation auxiliary thyristor. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. In an inverter device comprising a series circuit of reverse conduction thyristors through which a load current flows, and a commutation circuit connected to a series connection point of the reverse conduction thyristors to cause the load current to flow in reverse, the series connection of the reverse conduction thyristors A saturable reactor for suppressing di/dt of the reverse conduction thyristor is inserted between the point and the commutation circuit, and a load is connected to the connection point of the commutation circuit and the saturable reactor. An inverter device characterized by: