RU2370872C1 - Method for limitation of overstrain in high-voltage converter installations (versions) - Google Patents

Abstract

FIELD: electric engineering.

SUBSTANCE: in suggested method parametres of RC circuit are defined for a specific converter installation with account of mutual effect of separate elements in this installation. In order to define parametres of RC circuit, they excide internal oscillations in converter installation by any method and define either period T₀, or frequency of oscillations F₀ with maximum amplitude, and then capacity C₁ is connected to converter installation, and they repeatedly define either t₁, or frequency F₁ of internal oscillations in converter installation with connected capacity C₁. Then using suggested formulas, they define values C and R to form RC circuit, and thus generated RC circuit is connected to converter installation.

EFFECT: increased reliability and efficiency of protection against overstrain.

12 cl, 4 dwg

Description

Technical field

The invention relates to electrical engineering, in particular to systems for converting electric current, and is intended to limit overvoltages in converting installations, for example in high-voltage rectifier installations, in high-voltage converting installations for microwave generators, etc.

State of the art

Converting installations are complex electrical systems that have spurious inductances and capacitors that form oscillatory circuits, which are usually called spurious circuits. Overvoltages arising in converting installations are usually caused by shock and, as a rule, are associated with the operation of switching equipment, in particular, with an abrupt change in voltage, for example, when thyristors are triggered.

The most common way to limit overvoltages in converter plants is to introduce various protective devices into the converter plant.

A known method of limiting overvoltages in a conversion installation using a device for limiting overvoltages, which is used as a non-linear resistor. When the maximum permissible voltage is reached on the converter unit, the non-linear resistor goes into a conducting state, providing protection for the unit (see RF patent for utility model No. 14694, H01F 27/00, 2000.08.10).

A known method of limiting overvoltages in a converter installation using a device for limiting overvoltages, which is used as a series-connected resistor R and capacitance C - RC circuit (see. "Semiconductor rectifiers." / Edited by F.I. Kovalev and G.P. Mostikova M.: Energy, 1978, pp. 366-375). In the known method, the parameters of the resistor R and capacitance C for a particular installation are determined by calculation using an equivalent installation circuit. When performing calculations to determine the inductance of the circuit summarize the inductance of the individual elements of the installation. Then, using this calculated inductance, the values of R and C for the RC circuit are determined.

However, when calculating the inductance of the installation circuit, the mutual influence and not ideal nature of the elements of the converter installation are taken into account, which leads to the formation of so-called stray circuits, which can significantly change its real frequency characteristics from the calculated ones. As a result, the effectiveness of this method drops significantly and, as a rule, it is not possible to minimize overvoltages in the installation, which leads to failure of not only the semiconductor elements of the installation, but even power transformers and loads.

Disclosure of invention

An object of the present invention is to provide a method for limiting overvoltages in a converter installation using a protective device comprising a resistor R and a capacitance C connected in series to minimize overvoltages. This is achieved by isolating the parasitic circuit that has the highest Q factor and therefore gives the maximum oscillation amplitude upon excitation, and calculating the R and C values in the RC circuit to minimize overvoltage in this converter unit, taking into account the features of this particular converter unit.

To solve this problem and achieve other advantages, a method for limiting overvoltages in a converter plant is proposed, which consists in the fact that

the parasitic oscillatory circuit of the converter unit is transferred to the aperiodic mode by connecting the corresponding RC circuit to the converter unit, for which

excite natural vibrations in the converter unit, isolate the oscillations with maximum amplitude from them, and determine the period of these isolated oscillations T _{0 of the} converter unit;

a capacitance C _{1 is} connected to the converter unit, natural vibrations are repeatedly excited in the converter unit, vibrations with a maximum amplitude are extracted from them, and an oscillation period T ₁ with a maximum oscillation amplitude is determined for the converter installation with a connected capacitance C ₁ ;

using the measured oscillation periods T ₀ and T ₁ , determine the value of C for the capacitance for transferring the detected parasitic contour of the Converter installation in aperiodic mode in accordance with the ratio

C = (6 ÷ 10) C ₁ T ² ₀ / (T ² ₁ -T ² ₀ )

determine the resistance R for the resistor to translate the selected parasitic circuit of the Converter installation in aperiodic mode in accordance with the ratio

R = (0.08 ÷ 0.12) (T ² ₁ -T ₀ ² ) / C ₁ T ₀

sequentially connect the indicated resistor R and capacitance C to an RC circuit and connect the indicated RC circuit to the converter unit to transfer the selected stray circuit into aperiodic mode.

Preferably, at least one voltage step with a steep edge is generated in the converter unit to excite natural oscillations in the converter unit.

At the same time, said at least one voltage step with a steep edge is formed at a supply voltage less than the operating voltage of the converter unit.

Moreover, the specified at least one power surge with a steep front is formed at a supply voltage equal to 0.05 ÷ 0.15 of the operating voltage of the converter unit.

In addition, the specified at least one voltage step with a steep front is formed in the downward or upward section of the sinusoidal oscillations of the voltage of the electric current.

To solve this problem and achieve other advantages, a method for limiting overvoltage in a converter installation is also proposed, which consists in the fact that

the parasitic oscillatory circuit of the converter unit is transferred to the aperiodic mode by connecting the corresponding RC circuit to the converter unit, for which

excite natural vibrations in the converter unit, isolate the oscillations with the maximum amplitude from them, and determine the frequency of these distinguished oscillations F _{0 of the} converter unit;

connected to a converter installation ₁ C capacity to re-excite the natural vibration of the converter installation, isolated from their oscillation with the maximum amplitude and to determine the converter installation is connected capacitance C ₁ natural frequency F ₁ of the converter plant with a capacity C ₁ is connected;

using the measured frequencies of natural vibrations F ₀ and F ₁ , determine the value of C for the capacitance to translate the selected parasitic circuit of the Converter installation in aperiodic mode in accordance with the ratio

determine the value of R for the resistor for the RC circuit to translate the selected parasitic circuit of the Converter installation in aperiodic mode in accordance with the ratio

sequentially connect the indicated resistor R and capacitance C to an RC circuit and connect the indicated RC circuit to the converter unit to transfer the selected stray circuit into aperiodic mode.

Preferably, at least one voltage step with a steep edge is created in the circuit of the converter unit to excite natural oscillations in the circuit of the converter unit.

Moreover, the specified at least one power surge with a steep front is formed from an input alternating electric current coming from the network or from another power supply unit.

At the same time, said at least one voltage step with a steep edge is formed at a supply voltage less than the operating voltage of the converter unit.

Moreover, the specified at least one power surge with a steep front is formed at a supply voltage equal to 0.05 ÷ 0.15 of the operating voltage of the converter unit.

In addition, the specified at least one voltage step with a steep front is formed in the downward or upward section of the sinusoidal oscillations of the voltage of the electric current.

The use of the claimed invention provides a minimum voltage increase in the converter unit when the switching equipment is triggered and the thyristors work, since when connected, for example, to the transformer of the converter unit, an RC circuit in which the values of R and C are set in accordance with the present invention taking into account the real frequency characteristics of the converter installation, we obtain a significant reduction in overvoltage in the converter installation compared with the known technical p sheniyami.

The invention is illustrated by the example of its implementation for a conversion installation, in particular for a conversion installation for supplying magnetrons with a power of 5 kW and above. The description is provided only to illustrate the invention and in no way limits the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Drawings of the application are presented in the form of a general scheme sufficient to understand the principles of the invention by specialists in this field of technology.

In figure 1. one of the possible circuits of a converter installation for supplying a magnetron is shown.

Figure 2 shows a preferred circuit for the formation of a voltage surge with a steep front for excitation of natural oscillations in the Converter installation in accordance with the present invention.

Figure 3 presents a General diagram of a conversion installation with a connected capacitance C ₁ for determining the frequency or period of natural oscillations in accordance with the present invention.

Figure 4 presents a General diagram of a conversion installation in a connected RC circuit in accordance with the present invention.

MODES FOR CARRYING OUT THE INVENTION

To illustrate the implementation of the invention, a conversion installation is selected, for example, to power a magnetron, for example, with a power of 5 kW, but the present invention can be applied to any similar installations. To simplify, it is assumed that a converter unit operating on a single-phase network is used, but the invention can be used in installations operating on a three-phase network, using well-known schemes for connecting a power transformer to the network and to the bridge rectifier.

In the General case, the conversion installation includes a high-voltage power transformer 1, the primary winding 2 of which is connected to the AC input network, for example, through a thyristor switch 3, controlled by the command unit 4. To the terminals of the secondary high-voltage winding 5 of the transformer using buses 6 and 7 connected bridge rectifier 8. The bridge rectifier may have means for smoothing the ripples of the rectified high voltage: capacitors, chokes, etc. (not shown). The positive terminal of the rectifier 8 is connected to the anode of the magnetron 9. The negative terminal of the rectifier 8 is connected to the cathode of the magnetron 9.

It should be understood that this description of the installation is only to illustrate the implementation of the invention and there are many circuits of converter installations in which this invention can be implemented, for example, to power any other microwave generators or other high-voltage devices.

According to the first embodiment of the invention, the proposed method is implemented as follows.

The conversion installation in the original layout is connected to the input network and, in idle mode, excites its own vibrations in it. By any known measuring means (not shown), these natural vibrations are recorded, vibrations having a maximum amplitude are isolated from them, and a period T _{0 of} these vibrations of the converter unit is determined. If there are several frequencies of natural oscillations, a period T _{0 of} natural oscillations with a maximum amplitude of oscillations is recorded. In order to excite their own vibrations in the conversion installation, create at least one voltage step with a steep front. When natural oscillations are excited using a voltage jump with a steep front, the natural oscillations with a wide range of vibration frequencies are excited in the converter unit, from which natural oscillations with a maximum oscillation amplitude are isolated by any known method. The indicated voltage step can be formed from an input alternating electric current coming from the network, as shown in Fig., Or another power unit using a thyristor switch 3, but it is possible to form a voltage step with a steep edge using other methods. The formation of a voltage surge can be performed, for example, as shown in the graph in figure 2.

2, the dotted line shows the change in voltage U at the input to the converter unit. Thyristor switch 3 is off. At time t ₁ , the thyristor switch 3 is turned on, through which power is supplied to the transformer 1. Given that the thyristors have an extremely short response time, at the time of switching on we obtain an abrupt increase in the voltage at the input of transformer 1 from 0 to the current voltage in the network - voltage jump ΔU . To excite natural oscillations, you can use one voltage spike or several consecutive voltage spikes, as shown in figure 2. For a converter installation with a high-voltage transformer, when exciting natural oscillations, unacceptably high values of overvoltage can be observed, therefore, it is advisable to lower the input voltage and conduct excitation of natural oscillations in the converter installation, for example, at a voltage of 0.05-0.15 from the operating voltage of the converter installation. Similarly form a power surge when using any other device.

Next, a capacitance C _{1 is} connected between the buses 6 and 7 to the converter installation, the natural oscillations are repeatedly excited in the converter circuit by the method described above, and for oscillations with a maximum amplitude, the oscillation period T _{1 of the} converter installation with the connected capacitor C _{1 is} determined. Although the connection of capacitance C ₁ between buses 6 and 7 can be performed anywhere in the converter unit, it is advisable to connect capacitance C ₁ directly at the output of power transformer 1, for example, connect capacitance C ₁ to the output terminals of transformer 1.

Knowing the oscillation periods T ₀ and T ₁ and the value C _{1 of the} connected capacitance, you can determine the values for the resistor R and capacitance C for the RC circuit, which must be connected between the buses 6 and 7 of the converter unit in order to limit overvoltage when switching the converter unit on / off.

The value for capacity C is determined from the relation

C = (6 ÷ 10) C ₁ T ₀ ² / (T ₁ ² -T ₀ ² ).

The value for the resistor R is determined from the ratio

R = (0.08 ÷ 0.12) (T ₁ ² -T ₀ ² ) / C ₁ T ₀ .

In series, connect the indicated resistor R and capacitance C to an RC circuit and connect the assembled RC circuit between the buses 6 and 7 of the converter unit. It is most advisable to connect the RC chain where the capacitance C _{1 was} connected.

The implementation of the second variant of the method in a sequence of operations and technological methods repeats the above-described embodiment of the invention and differs from it in that upon excitation of natural oscillations of the original converter and the converter with connected capacitance C ₁ , the natural frequency F _{0 of the} original converter and the natural frequency are determined fluctuations F ₁ Converter installation with connected capacity C ₁ .

Accordingly, the value of capacitance C for the RC chain is determined from the relation

C = (6 ÷ 10) C ₁ F ₁ ² / (F ₀ ² -F ₁ ² )

and the resistance value of the resistor R for the RC chain is determined from the relation

R = (0.08 ÷ 0.12) (F ₀ ² -F ₁ ² ) / С ₁ F ₀ F ₁ ² .

INDUSTRIAL APPLICABILITY

The proposed method was tested on a 10 kW converter for powering a 5 kW magnetron. With an input operating voltage of 220 V and an operating voltage at a 5000 V high voltage winding in a converter unit with an RC circuit connected, the parameters of which are determined in accordance with the described method, the overvoltage during its switching on / off is significantly less than with known protection methods and does not exceed 5% of operating voltage on a high voltage winding.

It should be understood by those skilled in the art that although the present invention has been described with reference to a converter installation for supplying a magnetron from a single-phase network, it is not limited to this particular case and can be used to supply magnetrons from a three-phase network, as well as for supplying any power and technological installations where, when turned on On / off and during power control of the installation, overvoltages can be observed and where it is necessary to limit these overvoltages.

Claims (12)

1. A method of limiting overvoltage in a converter installation, namely, that the parasitic oscillatory circuit of the converter installation is switched to an aperiodic mode by connecting the corresponding RC circuit to the converter installation, for which own oscillations are excited in the converter installation, the oscillations with maximum amplitude are extracted from them and determined the period of these distinguished oscillations T _{0 of the} converter unit; a capacitance C _{1 is} connected to the converter unit, natural vibrations are repeatedly excited in the converter unit, vibrations with a maximum amplitude are extracted from them, and an oscillation period T ₁ with a maximum oscillation amplitude is determined for the converter installation with a connected capacitance C ₁ ; using the measured oscillation periods T ₀ and T ₁ , determine the value of C for the capacitance for transferring the detected parasitic contour of the Converter installation in aperiodic mode in accordance with the ratio
C = (6 ÷ 10) C ₁ T ² ₀ / (T ² ₁ -T ² ₀ );
determine the resistance R for the resistor to translate the selected parasitic circuit of the Converter installation in aperiodic mode in accordance with the ratio
R = (0.08 ÷ 0.12) (T ² ₁ -T ₀ ² ) / C ₁ T ₀ ;
sequentially connect the indicated resistor R and capacitance C to an RC circuit and connect the indicated RC circuit to the converter unit to transfer the selected stray circuit into aperiodic mode. 2. The method according to claim 1, in which at least one voltage step with a steep front is created in the circuit of the converter unit to excite natural oscillations in the circuit of the converter unit. 3. The method according to claim 2, wherein said at least one voltage step with a steep edge is formed from an input alternating electric current coming from a network or from another power supply unit. 4. The method according to claim 2, wherein said at least one voltage step with a steep edge is formed at a supply voltage less than the operating voltage of the converter unit. 5. The method according to claim 4, in which said at least one voltage step with a steep edge is formed at a supply voltage of 0.05 ÷ 0.15 of the operating voltage of the converter unit. 6. The method according to claim 3, in which said at least one voltage step with a steep front is formed in the downward or upward section of the sinusoidal oscillations of the voltage of the electric current at the input to the installation. 7. A method of limiting overvoltage in a converter installation, which consists in transferring the parasitic oscillatory circuit of the converter installation to aperiodic mode by connecting the corresponding RC circuit to the converter installation, for which they excite their own oscillations, isolate the oscillations with the maximum amplitude from them, and determine the frequency of these distinguished oscillations F _{0 of the} converter unit; connected to a converter installation ₁ C capacity to re-excite the natural vibration of the converter installation, isolated from their oscillation with the maximum amplitude and to determine the converter installation is connected capacitance C ₁ natural frequency F ₁ of the converter plant with a capacity C ₁ is connected; using the measured frequencies of natural vibrations F ₀ and F ₁ , determine the value of C for the capacitance to translate the selected parasitic circuit of the Converter installation in aperiodic mode in accordance with the ratio
C = (6 ÷ 10) C ₁ F ₁ ² / (F ₀ ² -F ₁ ² );
determine the value of F ₁ for the resistor for the RC circuit to translate the selected parasitic circuit of the Converter installation in aperiodic mode in accordance with the ratio
R = (0.08 ÷ 0.12) (F ₀ ² -F ₁ ² ) / C ₁ F ₀ F ₁ ²
sequentially connect the indicated resistor R and capacitance C to an RC circuit and connect the indicated RC circuit to the converter unit to transfer the selected stray circuit into aperiodic mode. 8. The method according to claim 7, in which at least one voltage step with a steep front is created in the circuit of the converter unit to excite natural oscillations in the circuit of the converter unit. 9. The method according to claim 7, in which said at least one voltage step with a steep edge is formed from an input alternating electric current coming from a network or from another power supply unit. 10. The method according to claim 8, in which said at least one voltage step with a steep edge is formed at a supply voltage less than the operating voltage of the converter unit. 11. The method of claim 10, wherein said at least one voltage step with a steep edge is formed at a supply voltage of 0.05 ÷ 0.15 of the operating voltage of the converter unit. 12. The method according to claim 9, in which the specified at least one power surge with a steep front is formed in the downward or upward section of the sinusoidal oscillations of the voltage of the electric current at the entrance to the installation.

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