RU2776027C1 - Arc load ac controller - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to electrical engineering, mainly to powerful semiconductor AC controllers intended for use in power supply systems for electric arc loads, such as, for example, plasma torches. The arc load alternating current controller consists of back-to-back thyristors connected in series, an electric reactor and an active filter in the form of a transistor width-modulated converter connected in parallel with the load and absorbing higher harmonics so that a sinusoidal continuous current enters the load. At the same time, an active filter-compensating device is connected to the AC busbars, consisting of an active filter in the form of a transistorized width-modulated converter and a capacitor bank connected in parallel, and providing compensation for the reactive power consumed by the load and filtering higher voltage harmonics arising from for the distorting action of the non-sinusoidal current of the regulator.

EFFECT: reducing the rate of rise of the plasma torch current to the required value and the corresponding suppression of higher harmonics in the plasma torch current.

2 cl, 4 dwg

Description

The claimed technical solution relates to electrical engineering, mainly to powerful semiconductor AC controllers intended for use in power supply systems for electric arc loads, such as, for example, plasma torches [1, 2, 3]. An AC plasma torch is a non-linear load for a power source, the parameters of which (power, voltage drop, current, current and voltage ripples) depend on many factors (changes in gas flow, arc burning mode, geometric dimensions of the electric arc chamber, etc.). This imposes specific requirements on the power source, for example, it requires the presence of a regulating element that ensures the stability of operation, the required power level of the plasma torch and maintaining stable arcing during the current zero transition. The power supply system of the AC plasma torch must have such characteristics as to ensure a decrease in the rate of rise of the plasma torch current to the required value and the corresponding suppression of higher harmonics in the plasma torch current, so that both static and dynamic stability of the plasma torch arc is ensured. Reducing the level of higher harmonics in the plasma torch current is also necessary to meet the requirements for electromagnetic compatibility of plasma torches with other equipment.

A simple thyristor AC regulator (TP) is known, consisting of anti-parallel thyristors connected in series with the load [4]. It is also known to use such controllers, connected in series with an electric reactor and forming a thyristor-reactor group, to change its inductive response by regulating the current in it in order to compensate for reactive power in high voltage networks [5]. Due to the discontinuous nature of the regulated current, such a simple regulator is not applicable for use in power supply systems for consumers that require a continuous change in current, as in the supply of arc plasma torches. A power supply system for electric arc furnaces is also known, consisting of a regulator based on anti-parallel thyristors, in parallel and in series with which electric reactors are connected [6, 7]. To compensate for the reactive power consumed by the power supply system and filter higher harmonics in such systems, it is necessary to install static thyristor compensators with resonant filters of higher harmonics [7].

The development of high-power Pulse-Width Modulation (PWM) voltage converters (Voltage Sourced Converter, VSC) [8] and the emergence of modular multilevel converters [9, 10] open up new opportunities for building power control systems and maintaining network parameters in systems alternating current and allows you to use a simple controller based on back-to-back thyristors to control the current and stabilize the arc in the plasma torch.

The claimed technical solution solves the problem of creating a continuous current in the arc load (plasma torch) using a thyristor current regulator connected in series with an electric reactor. In accordance with the proposed technical solution, the known AC regulator, consisting of series-connected back-to-back thyristors and a reactor [5], additionally contains a transistor-capacitor pulse-width-modulated converter, which is connected in parallel with the load and is controlled using current feedback.

TP transfers energy from the electrical network to the load, while the regulation of the energy flow is carried out by controlling the turn-on phase of the thyristors. In this case, the controller current is can be decomposed into the main harmonic of the mains frequency isl and the current of higher harmonics ish:

High-frequency PWM converter, which is an active filter, absorbs higher current harmonics

and the differential current is supplied to the load

those. sinusoidal uninterrupted current equal to the fundamental harmonic of the TR current.

Figure 1 shows the inventive circuit of the AC arc load controller. The setting of the voltage u, which forms the current setting of the converter, is carried out by the voltage regulator regu of the control system, the input of which receives a difference signal

according to the feedback signal from the current sensor is of the thyristor controller, minus the first harmonic of this current isl, allocated by the regi block of the control system.

The use of an active filter that shunts a non-linear load provides filtering of harmonics created not only by a thyristor controller, but also arising in the process of arc discharge combustion due to arc column fluctuations [2, 3], providing an additional increase in its combustion stability.

The operation of the proposed AC regulator is illustrated by process graphs (Fig. 2) obtained using the ELTRAN model. ELTRAN [11, 12] is a universal system for modeling valve converters of any configuration and purpose. Together with the power part of the converter, the ELTRAN model also displays the control system, as well as, if necessary, adjacent external circuits. The implemented model, firstly, displays in detail all the power circuits of the thyristor regulator with an active filter, presented in Fig. 1, including:

питающую сеть, отображаемую источником напряжения и индуктивностью сети;

the supply network, displayed by the voltage source and the network inductance;

тиристорный регулятор (TP) с последовательным реактором L;

thyristor regulator (TP) with series reactor L;

ШИМ-конвертор (АФ1);

PWM converter (AF1);

дуговую нагрузку;

arc load;

сетевое фильтро-компенсирующее устройство (АФ2 и КБ). Математическое описание модели дуги было представлено в виде аппроксимации ее вольтамперной характеристики в соответствии с [13].

network filter-compensating device (AF2 and KB). The mathematical description of the arc model was presented as an approximation of its current-voltage characteristic in accordance with [13].

The use of a thyristor-reactor controller to power an arc load is also associated with a negative effect on the supply network due to the consumption of large reactive power and distortion of the supply network voltage waveform due to the corresponding voltage distortion on the network inductance when a distorted load current flows. These distortions are especially pronounced when superpowered plasma torches are powered from a public network or the arc load is powered from a limited power network, in particular, from autonomous power generation systems [2, 3]. To stabilize and bring the voltage shape on the network buses to the standard values, it is proposed to use an active shunt-type filter-compensating device [14], consisting of an active filter AF2 and a capacitor bank KB, as shown in Fig. 1. The operation of the network active filter-compensating device (AFKU) of the shunt type is illustrated by process graphs (Fig. 3, Fig. 4) obtained using the ELTRAN model. In FIG. 3 shows the usb voltage on the buses of the supply substation in the absence of a network AFC. It can be seen how the voltage is distorted by higher harmonics.

In FIG. 4 shows the currents and voltages in the regulator circuit with a network active filter-compensating device; the usb voltage on the buses after connecting the network AFC becomes almost sinusoidal, and the network load power factor increases from 0.75 to 0.94.

Sources of information

1. Plasma torches: designs, characteristics, calculation / A.S. Koroteev, V.M. Mironov, Yu.S. Sverchuk. - M.: Mashinostroenie, 1993 - 296 p.

2. Rutberg F.G., Goncharenko R.B., Kumkova I.I., Safronov A.A. Peculiarities of AC plasma torches and the choice of their autonomous power supply sources in relation to installations for producing synthesis gas. Proceedings of the Academy of Sciences, Energy, No. 4, 2015, pp. 104-115.

3. Goncharenko R.B., Kiselev A.A., Rutberg A.F. and other Features of power supply systems of three-phase AC plasmatrons. Proceedings of the Academy of Sciences, Energy, No. 3, 2012, pp. 122-127.

4. Thyristor voltage converters for asynchronous drive / L.P. Petrov, O.A. Andryushchenko, V.I. Kapinos and others - M., Energoatomizdat, 1986. - 200 p.

5. Static reactive power compensators for electrical networks: Sat. articles / ed. IN AND. Kochkin. - M.: ELEKS-KM, 2010. - 206 p.

6. Patent USA US 2002/0136260 Al. Power Control System For AC Arc Furnace/ T.L. Wai Ma, M. Sedighy, B.K. Perkins, TA. Gerrtsen, J. Rajda, 26.09.2002.

7. Getopanov A.Yu., Tabkarov B.D., Klimash B.C. Investigation of the regulating properties and influence on the network of a reactor-thyristor device on the high side of a furnace transformer. Industrial electronics, automation and control systems, No. 2 (39), 2018, pp. 49-55.

8. Rozanov Yu.K. Power electronics: account. for universities / Yu.K. Rozanov, M.V. Ryabchitsky, A.A. Kvasnyuk. - M.: Ed. House MPEI, 2007. - 632 p.

9. Marquardt Rainer (DE) - Current rectification circuit for voltage source inverters with separate energy stores replaces phase blocks with energy storing capacitors. Publication number DE10103031, 2002-07-25

10. A. Lesnicar, and R. Marquardt, "An Innovative Modular Multilevel Converter Topology Suitable for a Wide Power Range", IEEE PowerTech Conference, Bologna, Italy, June 23-26, 2003.

11. Mustafa G.M. - Matrices for describing the topology of transformers. "Electricity", No. 10, 1977, pp. 34-39.

12. Mustafa G.M., Sharanov I.M. - Mathematical modeling of thyristor converters, "Electricity", No. 1, 1978, pp. 40-45.

13. A.N. Chernenko. Generalized model of the furnace and welding arc / Vector of Science TSU, No. 3 (17), 2011, p. 68-70.

14. Mustafa G.M., Gusev S.I. Active filter-compensating devices of shunt and serial type in electrical networks. Energetik, No. 8, 2019, pp. 3-10.

Claims (2)

1. An arc load alternating current controller, consisting of series-connected anti-parallel thyristors and an electrical reactor, characterized in that it contains a transistor-capacitor pulse-width modulated converter acting as an active filter controlled by current feedback, which is turned on parallel to the load and absorbs the higher harmonics of the thyristor controller current, as a result of which a differential sinusoidal continuous current equal to the fundamental harmonic of the thyristor controller current enters the load. 2. The AC regulator according to claim 1, characterized in that an active filter-compensating device is connected to the power supply buses, consisting of an active filter and a capacitor bank connected in parallel, and providing compensation for the reactive power consumed by the load and filtering the higher harmonics of the mains voltages arising from the distorting action of the non-sinusoidal current of the regulator.

Images