JPS6352630A - Overload dete tion system for power converter - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an overload detection method for a power conversion device using a thyristor as a switching element.

[Conventional technology and its problems]

Thyristors are used as switching elements in various devices that control electric power, such as non-aligned motor drive devices as shown in Fig. One important protection function of equipment
It is listed as one of the In the figure, 1 is a power supply side converter, 2 is a motor side converter, and 3 is a synchronous motor. Conventionally, this protective function and overload detection have been performed using overcurrent relays with inverse time-limiting characteristics, but there have been problems with detection accuracy and the like.

On the other hand, the method shown in FIG. 5 is conventionally used as an overload detection method for the electric motor 3. In this method, the detected current Id is squared by a multiplier 4, passed through a first-order lag filter 5, and this output is compared with a set value by a comparator 6, and the output of the first-order lag filter 5 is equal to this set value. When the limit is exceeded, it is detected as an overload. This means that the square value of the detected current Id is the loss generated within the motor 3,
The motor's thermal system is expressed as a first-order lag and the temperature rise is calculated.

However, when this method is applied to the converters 1 and 2, a large error occurs when the loss caused by the flowing current is expressed as the square value of the current.

This is because the pressure on the thyristor element cannot be ignored.

An object of the present invention is to provide an accurate overload detection method suitable for a power converter device, taking into consideration the heat system and generated losses specific to thyristor elements.

[Means for solving problems]

In order to achieve the above object, the present invention, in a power conversion device using a thyristor as a switching element, adds the square value of the current flowing through the thyristor element and the value multiplied by the gain of the power conversion device of this current flowing. , this added value is input to a first-order lag filter, and the output of the first-order lag filter is compared with a set value using a comparator, and when the output of the first-order lag filter exceeds the set value, it is determined that an overload has occurred. That is.

[Effect]

According to the present invention, the sum of the square value of the current flowing through the thyristor element and the double value of the current is defined as the loss generated within the thyristor element, and the thermal time constant is represented by the time constant of the cooling body. The temperature rise of the thyristor is calculated by approximating it using a first-order lag system that has the same time constant.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the overload detection method for a power converter according to the present invention, in which 4 represents a multiplier, 7 represents a gain whose coefficient k is determined by the converter, and 8 represents an addition point. Also, in the figure, 5 is a first-order lag filter, and 6 is a comparator.
These time constant tc and comparison level Qc are values that depend on the thyristor element, cooling method, etc.

Thermal model of the thyristor element is the square value of the passing current id 12
The value obtained by adding this current id to the value ki multiplied by the gain determined by the converter is considered to be the loss generated in the thyristor element, and the thyristor element is Calculate the temperature rise θ.

When a constant loss P is given to the thyristor, the temperature rise becomes a function of time due to the heat capacity of each component. However, when considering the overload of the converter, the temperature between the thyristor junction and the case is negligibly small compared to the temperature time constant of the case and the cooling body.
Case←It may be assumed that it depends on the temperature time constant of the cooling body.

Figure 3 shows the characteristics of the transient thermal resistance Ra (t) between the case and the cooling body. Although the actual Ra (t) is a function as shown by the solid line, there is no problem in practice even if it is assumed to be a first-order lag as shown by the dotted line so as to be on the safe side for the thyristor element. Therefore, the transient thermal resistance Rja(t) between the junction ← cooling body is expressed by the following formula % Formula % (1) Rca: Steady thermal abrasive resistance between case ← cooling body tC: Time constant of the cooling body The loss generated from the thyristor element is Po Then, the temperature rise θj at the junction can be found by the following equation.

θj=Po Rja (t) = Po Rca (1-
(2) On the other hand, the relationship between the voltage drop of the thyristor element and the average forward current (2) can generally be approximated as shown in FIG.

VD-Vi+r, I, Vi: Enlayer voltage rp
: Differential resistance Therefore, forward loss Po is Po = V i I, +r, (f i IF )
``--------(3) fi: Waveform factor Substituting equation (3) into equation (2), θj-(V i IF + rp f 12-I," )
・Rca・ (1-e part) Therefore θj': L (+ Ip to 1, 2+) (1-e flower)・
−・・−(4) However, =V i/(rGl f i”) For example, 3
In a thyristor converter with phase-pure bridge configuration, r i
= If the DC current is Id, then Id = 3'L, and rearranging equation (4), θJ 2 (Iy ” +kl
IF ) (1e-”) However, kz −Vi/rI
.

The above formula is Id. . When unitized by (rated DC current), θ j; (id” + 3 id) (1-e--
ac) --------・ (5) However, k 3 ” V i / r p ・I d +
o.

Therefore, by comparing θ obtained by equation (5) with the comparison level θC determined by the overload rate and overload time using the comparator 6, it is possible to detect an overload of the converter.

〔Effect of the invention〕

As described above, the overload detection method for a power conversion device of the present invention accurately detects overload in a power conversion device using a thyristor as a switching element, taking into consideration the heat system and generated loss specific to the thyristor element. It is something that can be done.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the overload detection method of the power conversion device of the present invention, Fig. 2 is a diagram showing the forward voltage characteristics of the thyristor element, and Fig. 3 is a diagram showing the transient thermal resistance characteristics of the cooling body. 4 is a circuit diagram showing an example of application of a thyristor converter,
FIG. 5 is a block diagram showing a conventional overload detection method.

Claims (1)

[Claims] In a power converter using a thyristor as a switching element, the square value of the current flowing through the thyristor element and the value multiplied by the gain of the power converter for this current are added, and this added value is applied to the first-order lag filter. An overload detection method for a power conversion device, characterized in that the output of the first-order lag filter is compared with a set value by a comparator, and an overload is determined when the output of the first-order lag filter exceeds the set value. .