RU2093971C1 - Power supply for inductance heater - Google Patents

Abstract

FIELD: temperature-processing using high-frequency currents. SUBSTANCE: power transformer has primary and secondary windings, operates in short-circuit mode. This is achieved by connection of primary winding of feedback transformer to secondary winding of power transformer. Primary winding of power transformer is connected to supply line through serial input circuit. Secondary winding of feedback transformer is connected in parallel to output circuit through isolating capacitor. Inductance heater is connected to coil of circuit through matching winding. EFFECT: increased reliability, increased efficiency, decreased materials consumption. 2 dwg

Description

 The present invention relates to energy and electrical engineering and can be used in technological equipment using heat treatment with high frequency currents.

 Known power sources for induction heaters, including a constant voltage source containing a power transformer, a rectifying unit, filtering devices, a voltage stabilization unit, a high-frequency generator containing a master oscillator, a power amplification unit, an output circuit ("Electrotechnological installations". A. Bolotov. Shepel G. A. M. Higher School, 1988, p. 335). The disadvantages of these sources are: low reliability of the output lamps of the generators, low efficiency, low operational properties, high material consumption per unit of useful power. Power sources for induction heaters are also known, in which tube generators are replaced by thyristor converters (Thyristor converters of increased frequency for electrotechnological installations. E.B. Berkovich and others. Energoatomizdat, 1983, p. 208). Their disadvantages are: sensitivity to current overloads, the need for water cooling with high requirements for the quality of cooling water, increased sensitivity to external environmental conditions (temperature, dust, gas contamination), significant material consumption.

 The proposed power source for induction heaters, which differs from the known one containing a power transformer, rectifying and filtering blocks, frequency converter, output circuit, in that the primary winding of the power transformer is connected at one end to one of the buses of the industrial network, and the second end is connected through the output circuit to the second network bus, in parallel to the circuit is connected a matching device for turning on the induction heater; the secondary winding of the power transformer is connected to the primary winding of the feedback transformer, the secondary winding of which is connected at one end to the input of the output circuit and the other through the feedback capacitor is connected to the output of the circuit.

 The achieved positive effect (increased reliability, material consumption, efficiency) is created by eliminating insufficiently reliable elements of powerful lamps or thyristors, reducing material consumption by eliminating rectifying, stabilizing, filtering and generating units.

 The essence of the invention is illustrated by the drawing shown in FIG. 1, which shows a block diagram of a power source of an induction heater.

The power source of the induction heater contains:
1 power transformer;
2 primary winding of transformer 1;
3 output circuit;
4 industrial network;
5 secondary winding of the power transformer 1;
6 primary winding of the feedback transformer;
7 feedback transformer 7;
8 secondary winding of the feedback transformer 7;
9 feedback capacitor;
10 compensating capacitor 10;
11 matching winding;
12 induction heater.

 The proposed power source for the induction heater consists of a power transformer 1 with primary and secondary windings 2 and 5, respectively, an output circuit 3, a feedback transformer 7 with primary and secondary windings 5 and 6, respectively, a feedback capacitor 9, a compensating capacitor 10, a matching winding 11 ; the primary winding 2 of the transformer 1 through a series-connected output circuit 3 is connected to the industrial network 4, and its secondary winding 5 is connected in parallel with the primary winding 6 of the feedback transformer 7, the secondary winding 8 of which is connected through the feedback capacitor 9 to the output circuit 3, a compensating capacitor 10 is connected parallel to the primary circuit of the transformer 4, an induction heater 12 is connected parallel to the output circuit 3 through the matching winding 11.

The proposed power source induction heater operates as follows. Power transformer 1 operates in the form of a pulse voltage shaper. This mode is created by connecting its primary winding 2 with the output circuit 3 connected in series with it to the industrial network 4 and loading the secondary winding 5 with the low-impedance primary winding 6 of the feedback transformer 7, which determines the operation mode of the transformer 1, which is close to the short circuit mode. In this case, the parameters of the windings 2 and 5 are selected based on the equality of their flux linkages:
l ₁ W ₁ + l ₂ W ₂ ≈0 (1),
where l ₁ W _{1 the} flux linkage of the primary winding 2;
l ₂ W ₂ flux linkage of the secondary winding 5.

Φ_o результирующий магнитный поток в сердечнике трансформатора 1;
R₁ активное сопротивление обмотки 2 трансформатора 1.The operation mode of the primary circuit of the power transformer 1 is described by the equation
U ₁ e ₁ + U _k + l ₁ R ₁ (2),
where U _{1 is the} instantaneous voltage value of the network;
U ₂ current in the primary winding 2;
U _{k the} voltage on the circuit 3;

Φ _{o the} resulting magnetic flux in the core of the transformer 1;
R _{1 the} active resistance of the winding 2 of the transformer 1.

где ω_п промышленная частота

.Since the current in the secondary winding 5 has a time delay Φ with respect to the current in the primary winding 2 and is directed counterclockwise to the latter, condition (1) will be fulfilled outside the delay angle. Within the time delay, the flux linkages will add up, since they have the same direction. As a result, in the indicated interval the EMF e ₁ will be significant, and outside it it is approximately equal to zero. Therefore, equation (2) can be represented as:

where ω _p industrial frequency

.

Иной интерпретацией выражений (3) и (3а) является увеличение реактивного сопротивления первичной обмотки 2 трансформатора 1 на интервале θ и резкое падение его (≈ до 0) на интервале

. В результате на интервале

выходной контур 3 подвергается воздействию ступенчатого напряжения, что приводит к возникновению в нем собственных колебаний с резонансной частотой контура. Для увеличения амплитуды и длительности этих колебаний с помощью трансформатора обратной связи 7 формируется положительная обратная связь по напряжению U_k. С этой целью первичная обмотка 6 трансформатора 7 включается в сеть вторичной обмотки 5 трансформатора 1. Так как направление тока в обмотках 5 и 6 противоположно направлению тока в обмотке 2 трансформатора 1, то ЭДС е₂, формируемая магнитным потоком сердечника трансформатора 7, будет противоположна ЭДС е₁. Поэтому напряжение на выходе обмотки 8 трансформатора 7, равное е₂, будет иметь составляющую, согласно направленную с напряжением U_k на выходном контуре 3. Осциллограммы напряжений на первичной обмотке 2 и на выходном контуре 3 приведены на фиг. 2. Напряжение с выхода обмотки 8 через конденсатор 9 подается на выход контура 3. С целью повышения cosΦ установки в первичную цепь трансформатора 1 включен конденсатор 10. Напряжение питания индукционного нагревателя снимается с контурной катушки выходного контура 3 через согласующую обмотку 11. При этом для повышения добротности контура его катушка намотана на ферритовом сердечнике. Преимущества предлагаемого изобретения перед известными состоят: в увеличении надежности источника питания индукционного нагревателя за счет устранения ненадежных элементов ламп, тиристоров; существенном сокращении материалоемкости за счет исключения выпрямительных, стабилизирующих, фильтрующих блоков, задающего генератора и "обвязки" нелинейного элемента.Solving (3) with respect to U _k , we obtain:

Another interpretation of expressions (3) and (3a) is an increase in the reactance of the primary winding 2 of transformer 1 in the interval θ and its sharp drop (≈ to 0) in the interval

. As a result, on the interval

the output circuit 3 is subjected to a step voltage, which leads to the occurrence of natural oscillations in it with the resonant frequency of the circuit. To increase the amplitude and duration of these oscillations using a feedback transformer 7, a positive voltage feedback U _{k is formed} . To this end, the primary winding 6 of the transformer 7 is included in the network of the secondary winding 5 of the transformer 1. Since the current direction in the windings 5 and 6 is opposite to the current direction in the winding 2 of the transformer 1, the EMF e ₂ formed by the magnetic flux of the core of the transformer 7 will be opposite to the EMF e ₁ . Therefore, the voltage at the output of the winding 8 of the transformer 7, equal to e ₂ , will have a component, in accordance with the direction with the voltage U _k on the output circuit 3. The voltage waveforms on the primary winding 2 and on the output circuit 3 are shown in FIG. 2. The voltage from the output of the winding 8 through the capacitor 9 is fed to the output of the circuit 3. In order to increase the cosΦ of the installation, the capacitor 10 is connected to the primary circuit of the transformer 1. The supply voltage of the induction heater is removed from the contour coil of the output circuit 3 through the matching winding 11. Moreover, to increase of the quality factor of the circuit, its coil is wound on a ferrite core. The advantages of the invention over the known ones are: to increase the reliability of the power source of the induction heater by eliminating unreliable elements of lamps, thyristors; a significant reduction in material consumption due to the elimination of rectifying, stabilizing, filtering blocks, a master oscillator and the "strapping" of a nonlinear element.

Claims (1)

 An induction heater power supply comprising a power transformer and an output circuit, characterized in that the output winding is connected in series to the primary winding of the power transformer and connected through the matching winding to the induction heater, and the secondary winding of the power transformer is connected to the primary winding of the feedback transformer, the secondary winding of which connected via an isolation capacitor in parallel to the output circuit.

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