SU748789A1

SU748789A1 - Method of control of thyristorized inverter output power

Info

Publication number: SU748789A1
Application number: SU782621510A
Authority: SU
Inventors: Александр Васильевич Иванов; Петр Семенович Ройзман; Анатолий Михайлович Уржумсков; Рифхат Гадылевич Юнусов
Original assignee: Уфимский авиационный институт им. Орджоникидзе
Priority date: 1978-06-02
Filing date: 1978-06-02
Publication date: 1980-07-15

Description

Изобретение относится к электротехнике и может применяться в источниках питания индукционных электротермических установок.The invention relates to electrical engineering and can be used in power sources of induction electrothermal installations.

Известны, способы регулирования выходной мощности тиристорного инвертора, работающего на колебательный контур, путём изменения выходной частоты инвертора. При этом использу~|0 ют зависимость импеданса нагрузочного колебательного контура От частоты напряжения на нём [1] , [2] и £3]Known methods for regulating the output power of a thyristor inverter operating on an oscillatory circuit by changing the output frequency of the inverter. In this case, ~ | 0 are used, depending on the impedance of the load oscillating circuit on the frequency of voltage on it [1], [2] and £ 3]

Недостатком известных способов регулирования является снижение КПД при регулировании мощности/A disadvantage of the known methods of regulation is the reduction of efficiency in the regulation of power /

Наиболее близким к изобретению по технической сущности является спо соб, при котором регулирование выходной мощности осуществляют путем jn изменения частоты управляющих,сигналов на вентили инвертора [3].Technically closest to the invention is a method in which the output power is controlled by jn changing the frequency of the control signals to the inverter valves [3].

Недостатком указанного способа является низкий КПД, так как при таком способе регулирования выходная J5 (полезная) мощность инвертора снижается, а потери в инверторе остаются, примерно, постоянными. Это объясняется тем, что при регулировании уменьшается выходное напряжение йнверто- ,_п ра, а выходной ток, меняется незначи'тельно. Кроме того, при уменьшении мощности по известному способу уменьшается и cos-p нагрузки, а следовательно, возрастают потери в ней и в подводящих проводах.The disadvantage of this method is the low efficiency, since with this method of regulation, the output J5 (useful) inverter power is reduced, and the losses in the inverter remain approximately constant. This is because when regulating the output voltage decreases ynverto-, _f pa, and the output current varies neznachi'telno. In addition, when the power is reduced by the known method, the cos-p load decreases, and consequently, the losses in it and in the supply wires increase.

Цель изобретения — повышение КПД. Поставленная цель достигается •тем, что в способе регулирования выходной мощности тиристорного инвертора, состоящим в том, что изменяют частоту управляющих импульсов на вентили инвертора, частоту управляющих импульсов изменяют от величины, соответствующей минимальной мощности, до величины, соответствующей максимальной мощности, и поцдорживяют необходимое время на заданном уровне, затем изменяют частоту управляющих импульсов до величины, соответствующей минимальной мощности, и прекращают подачу управляющих импульсов и после необходимой выдержки времени операции Периодически повторяют, причем соотношение между временем работы инвертора на частоте, соответствующей максимальной мощности, и Временем, когда управля;ющие сигналы на вентили инвертора не поступают, устанавливают в соответствии с заданной мощностью. Кроме того, при регулировании с целью повышения надежности измеряют напряжение на вентилях инвертора и скорость изменения частоты устанавливают обратно пропорционально этому напряжению, а также при регулирований 'ё' целью повышёнйя надежности измеряют время, предоставляемое вентилями на восстановление управляемости, и скорость изменения частоты устанавливают прямо пропорционально этому времени.The purpose of the invention is improving efficiency. This goal is achieved • by the fact that in the method of controlling the output power of the thyristor inverter, which consists in changing the frequency of the control pulses to the valves of the inverter, the frequency of the control pulses is changed from the value corresponding to the minimum power to the value corresponding to the maximum power, and the necessary time is delayed at a given level, then change the frequency of the control pulses to a value corresponding to the minimum power, and stop the supply of control pulses and after necessary In winter time delay operation is periodically repeated, the ratio between the time of the inverter at a frequency corresponding to the maximum power and the time when the control, signals from the inverter gates are not available, is set according to a predetermined power. In addition, when regulating, in order to increase reliability, the voltage on the inverter valves is measured and the rate of change of frequency is set inversely to this voltage, as well as when adjusting “ё” to increase reliability, the time provided by the valves to restore control is measured, and the rate of change of frequency is set directly proportional this time.

На фиг. 1 приведена блок-схема устройства, реализующая способ, на фиг. 2 — зависимость мощности, выделяемой в колебательном контуре нагрузки, от частоты напряжения на нем, на фиг. 3 — кривые, поясняющие принцип регулирования по данному способу. ,In FIG. 1 shows a block diagram of a device that implements the method, FIG. 2 - dependence of the power allocated in the oscillatory circuit of the load, on the frequency of the voltage across it, in FIG. 3 - curves explaining the principle of regulation for this method. ,

Устройство (см.фиг.1) содержит последовательно соединенную цепь из' частотно-задающей цепи 1, ключа 2, управляемого инерционного звена 3, задающего генератора 4, инвертора 5 и нагрузки 6. Вход управления ключа • 2 соединен.через модулятор 7 скважности со вторым генератором 8 и задатчиком 9 мощности. Инерционное звено 3 через устройство управления 10 соединено с инвертором 5.The device (see Fig. 1) contains a series-connected circuit of the 'frequency-setting circuit 1, key 2, controlled inertial link 3, master oscillator 4, inverter 5 and load 6. Key control input • 2 is connected through the duty cycle modulator 7 with the second generator 8 and the setter 9 power. The inertial link 3 through the control device 10 is connected to the inverter 5.

Выходная частота инвертора 5, а следовательно, мгновенная мощность, выделяемая в нагрузке 6, определяется частотой задающего генератора 4.The output frequency of the inverter 5, and therefore, the instantaneous power allocated to the load 6, is determined by the frequency of the master oscillator 4.

Напряжение на выходе генератора 8 показано на фиг.За. Частота U_e выбирается на несколько порядков (3—10) ниже частоты задающего генератора 4. Модулятор 7 скважности преобразует импульсы U_e в прямоугольные (фиг.36), скважность которых зависит От величины сигнала Ug' с задатчика 9 мощности. Изменяя скважность импульсов U₇, поступающих на вход управления ключа 2, изменяют время пребывания ключа 2 в закрытом и .открытом состояниях, а тем самым, время, в течение которого частота, задающая цепь 1, через инерционное звено 3 подключена к задающему генератору 4. Частотно-задающая цепь 1 представляет собой регулируемый источник постоянного напряжения (фиг.Зв), выходное напряжение И, которого определяет амплитуды выход.ных напряжений ключа 2 и инерционного звена 3 (фиг.Зг ид).The voltage at the output of the generator 8 is shown in FIG. The frequency U _e is selected several orders of magnitude (3-10) below the frequency of the master oscillator 4. The duty cycle modulator 7 converts the pulses U _e into rectangular ones (Fig. 36), the duty cycle of which depends on the value of the signal Ug 'from the power generator 9. Changing the duty cycle of the pulses U ₇ received at the control input of the key 2, the residence time of the key 2 in the closed and open states is changed, and thereby, the time during which the frequency that sets the circuit 1 through the inertial link 3 is connected to the master oscillator 4. The frequency-setting circuit 1 is an adjustable source of constant voltage (Fig. Sv), the output voltage And, which determines the amplitudes of the output voltages of the key 2 and the inertial link 3 (Fig. Zg id).

Задающий генератор 4 выполнен так, что его частота Ό пропорциональна, в определенном диапазоне, величине напряжения инерционного звена . 3. При уменьшении частоты до ве- >’ личины (фиг.Зе) задающий генератор 4 прекращает генерирование коле-/ баний, а следовательно, инвертор 5 выключается.The master oscillator 4 is designed so that its frequency Ό is proportional, in a certain range, to the magnitude of the inertial link voltage. 3. When the frequency decreases to a magnitude> ’value (Fig. Ze), the master oscillator 4 stops generating oscillations / vibrations, and therefore, the inverter 5 turns off.

Управляемое инерционное звено 3 введено в устройство для повышения надежности работы инвертора. При отсутствии инерционного звена 3 частота задающего генератора 4, а следовательно, и частота выходного напряжения и₅ инвертора 5 изменялись бы скачком. Это приводило бы к скачкообразному изменению мощности, выделяемой в нагрузке 6. При скачкообразном уменьшении мощности в нагрузке б энергия, запасенная во входном дросселе инвертора 5, переходит в конденсаторы, установленные в его схеме, что вызывает рост напряжения на них, а следовательно, рост напряжения на вентилях инвертора и сокращение времени, предоставляемого вентилем на восстановление управляемости, что резко снижает надежность инвертора.A controlled inertial link 3 is introduced into the device to increase the reliability of the inverter. In the absence of an inertial link 3, the frequency of the master oscillator 4, and hence the frequency of the output voltage and _{5 of the} inverter 5, would change abruptly. This would lead to an abrupt change in the power released in the load 6. With an abrupt decrease in the power in the load, the energy stored in the input inductor of the inverter 5 goes to the capacitors installed in its circuit, which causes an increase in voltage on them, and therefore, an increase in voltage on the inverter valves and reducing the time provided by the valve to restore control, which dramatically reduces the reliability of the inverter.

Для надежной работы инвертора снижение мощности необходимо производить с низкой скоростью. Но это ведет к увеличению времени переходного процесса и снижению эффективности регулирования. Поэтому для уменьшения времени переходного процесса при сохранении надежности инвертора целесообразно при снижении мощности контролировать параметр инвертора, определяющий его надежность, и скорость изменения частоты задающего генератора 4 устанавливать в соответствии с этим параметром.For reliable operation of the inverter, a decrease in power must be performed at a low speed. But this leads to an increase in the transition process and a decrease in regulatory efficiency. Therefore, to reduce the time of the transition process while maintaining the reliability of the inverter, it is advisable to control the inverter parameter, which determines its reliability, and to set the rate of change of the frequency of the master oscillator 4, in accordance with this parameter, while reducing power.

В случае, если параметром, определяющим надежность инвертора, является напряжение на его вентилях, то с помощью устройства 10 управления измеряют указанное напряжение, и скорость изменения напряжения на выходе инерционного звена 3, а следовательно, и частоты задающего генератора устанавливают обратно пропорционально напряжению на вентилях. Это ведет к стабилизации напряжения на вентилях инвертора и повышению надежности преобразователя.If the parameter determining the reliability of the inverter is the voltage at its valves, then the indicated voltage is measured using the control device 10, and the rate of change of voltage at the output of the inertial link 3, and therefore the frequencies of the master oscillator, is set inversely to the voltage at the valves. This leads to voltage stabilization on the inverter valves and to increase the reliability of the converter.

В случае, если параметром, определяющим надежность инвертора, являфФся время, предоставляемое на восстановление управляемости, то с помощью устройства 10 управления измеряют указанное время,и скорость изменения напряжения на выходе инерционного звена 3, а следовательно, и частоты задающего генератора устанавливают прямо пропорционально времени предоставляемого вентиля на восстановление управляемости.If the parameter determining the reliability of the inverter is the time allowed to restore controllability, then the indicated time is measured using the control device 10, and the rate of change of voltage at the output of the inertial link 3, and therefore the frequency of the master oscillator, is set directly proportional to the time provided valve to restore control.

При увеличении мощности возрастания напряжения на элементах инвертора не происходит, поэтому для снижения времени переходного процесса целесообразно скорость изменения частоты выбирать более высокой, чем при Уменьшении мощности.With an increase in power, an increase in voltage at the inverter elements does not occur, therefore, to reduce the transition process, it is advisable to choose a rate of change of frequency higher than with a decrease in power.

В момент t, (фиг.З) происходит замыкание ключа 2 и напряжение на его выходе становится равным и_£ . За время Δί^ частота задающего генерато'ра устанавливается равной* f, , соответствующей максимальной мощности ин- 5 вертора. В момент t₂ происходит размыкание ключа 2 и напряжение на его выходе становится равным 0. Это приводит к тому, что частота задающего^ генератора 4 за время at уменьшает- Ю ся до величины f/; генератор 4 прекращает генерирование колебаний и инвертор 5 выключается. Причем скорость изменения частоты в течение времени t_z< t < t_z + at₂ пропорциональна времени, предоставляемому венти лям на восстановление управляемости, или обратно пропорциональна напряжению на вентилях. В момент t = t_b ключ 2 опять включается и указанные процессы повторяются.At time t, (FIG. 3), the key 2 closes and the voltage at its output becomes equal to _£ . During the time Δί ^ the frequency of the master oscillator is set equal to * f, corresponding to the maximum power of the inverter 5. At time t ₂ , the key 2 opens and the voltage at its output becomes equal to 0. This leads to the fact that the frequency of the master oscillator 4 decreases during time at to the value f /; the generator 4 stops generating oscillations and the inverter 5 is turned off. Moreover, the rate of frequency change over time t _z <t <t _z + at _{2 is} proportional to the time provided to the valves for regaining control, or is inversely proportional to the voltage at the valves. At time t = t _b, key 2 is turned on again and the indicated processes are repeated.

Имея зависимость выходной частоты инвертора от времени (фиг.Зе) и зависимости мощности, выделяемой в нагрузке, от частоты напряжений на ней (фиг.2), построить зависимость мгновенной мощности инвертора от времени (фиг.Зж).Having the dependence of the output frequency of the inverter on time (Fig. Ze) and the dependence of the power released in the load on the frequency of the voltages on it (Fig. 2), build the dependence of the instantaneous power of the inverter on time (Fig. Zzh).

Среднее значение мощности за период изменения частоты, считая At« и At^t^-t^ , равно где t_u=t₂-t·, ,The average value of power over a period of changing the frequency, considering At «and At ^ t ^ -t ^, is equal to where t _u = t ₂ -t ·,,

T=tj-t, — период изменения частоты инвертора. “T = tj-t, is the period of the inverter frequency change. “

Изменяя задатчиком 9 мощности соотношение и Т, регулируют среднее значение выходной мощности инвертора.By changing the ratio and T by the power setter 9, the average value of the inverter output power is adjusted.

Период изменения выходной частоты инвертора выбирают много меньше 40 тепловой постоянной времени нагрузки. Например, тепловая постоянная времени индукционной печи ИСТ-0,16 составляет.несколько часов, а период изменения частоты F, выбирается 45 порядка нескольких десятков секунд. Поэтому колебания мгновенной мощности инвертора относительно среднего значения никак не сказываются на тепловых процессах в нагрузке. 5QThe change period of the inverter output frequency is chosen much less than 40 thermal load time constant. For example, the thermal time constant of the IST-0.16 induction furnace is several hours, and the period of the frequency change F is 45, of the order of several tens of seconds. Therefore, fluctuations in the instantaneous power of the inverter relative to the average value do not affect thermal processes in the load. 5Q

Если на максимальное значение мощности не накладывается ограничений со стороны нагрузки и инверто- ^!ра, то значение Р, и соответственно f, выбирают равным Рр , fp (фиг. 2). Если по каким-либо причинам, например технологическим, недопустимо значительное превышение Р₁ над Р_ср, то выбирают f, / fp . При этом то же самое значение Р_ср будет получено при меньших значениях.отношений /Т и колебания мгновенной мощности над средним ее значением будут уменьшены.If the maximum power value does not impose restrictions on the load side and invert- ^! pa, then the value of P, and accordingly f, is chosen equal to Pp, fp (Fig. 2). If for some reason, for example, technological, a significant excess of P ₁ over P _{cf is} unacceptable, then f, / fp is chosen. In this case, the same value of P _cf will be obtained at lower values. The ratio / T and the fluctuations of the instantaneous power over its average value will be reduced.

КПД инвертора при данном способе регулирования практически не зависит 65The efficiency of the inverter with this method of regulation is practically independent 65

От глубины регулирования. Действительно, в интервале времени t_f<t< мощность потерь Р_п< в инверторе примерно равна где Т, — КПД инвертора при мощности ¹ .·From the depth of regulation. Indeed, in the time interval t _f <t <the power of losses R _{p <} in the inverter is approximately equal to where T, is the efficiency of the inverter at a power of ¹ .

В интервале времени t₂<t< t_?инвертор не работает и мощность потерь в нем равна 0. Поэтому средняя мощность потерь за период изменения частоты равна р -р-¹?..*¹;. ll-η ср < 1, Т срIn the time interval t ₂ <t <t _? the inverter does not work and the power of losses in it is 0. Therefore, the average power of losses during the period of frequency change is p-p- ¹ ? .. * ¹ ;. ll-η cf <1, T cf

КПД инвертора при регулировании мощности /ц, равенThe efficiency of the inverter when regulating power / c is

М'т?M't?

Vp лер ’Т.е. КПД инвертора при предлагаемом способе регулирования не зависит от глубины регулирования и равен КПД при номинальной мощности.Vp ler ’i.e. The efficiency of the inverter with the proposed method of regulation does not depend on the depth of regulation and is equal to the efficiency at rated power.

Таким образом, данный способ регулирования выходной мощности тиристорного инвертора обеспечивает плавное регулирование средней мощности с высоким значением КПД.Thus, this method of controlling the output power of the thyristor inverter provides smooth control of the average power with a high value of efficiency.

Claims

The invention relates to electrical engineering and can be applied in power supplies of induction electrothermal installations. There are known methods for adjusting the output power of a thyristor inverter operating on an oscillating circuit by varying the output frequency of the inverter. In this case, the dependence of the impedance of the load oscillating circuit on the frequency of the voltage 1, 2 and 3 is used. A disadvantage of the known methods is control. is a decrease in efficiency at power regulation D The closest to the invention in technical essence is a method in which the adjustment of output power is carried out by changing the frequency of control signals at the inverter 3 valves. The disadvantage of this method is low efficiency, since In this method of controlling the output (useful) power of the inverter is reduced, and the losses in the inverter remain approximately constant. This explains: the fact that during regulation the output voltage of the inverter decreases, and the output current changes slightly. In addition, when the power is reduced by a known method, the cs-f load also decreases, and consequently, the losses in it and in the supply wires increase. The purpose of the invention is to increase efficiency. This goal is achieved by the fact that in the method of controlling the output power of the thyristor investor E, consisting in that the frequency of the control pulses on the inverter valves is changed, the frequency of the control pulses is changed from the value corresponding to the minimum power to the value corresponding to maximum power, and maintain the required time at a given level, then change the frequency of the control pulses to a value corresponding to the minimum power, and stop the supply of control pulses after not Circumferencing time delays. Periodically, the ratio between the time of operation of the inverter at the frequency corresponding to the maximum power and the burden when the control signals to the inverter valves are not received is set in accordance with the specified power. In addition, when adjusting to increase reliability, the voltage at the inverter valves is measured and the rate of change of frequency is set inversely proportional to this voltage, as well as when the control target is elevated to Reliable, and the time provided by the vents for control recovery is measured. capacity, and the rate of change of frequency is set in direct proportion to this time. FIG. 1 shows a block diagram of the device implementing the method, FIG. 2 shows the dependence of the power emitted in the oscillatory circuit of the load on the frequency of the voltage in FIG. 3 - curves explaining the regulation principle for this method. The device (see Fig.1) contains a series-connected circuit of the frequency-setting circuit 1, key 2, controlled inertial link 3, master oscillator 4, inverter 5 and load 6. The control input of the key 2 is connected through the modulator 7 duty cycle with the second generator 8 and unit 9 power. The inertial link 3 is connected via control unit 10 to inverter 5. The output frequency of inverter 5, and therefore, the instantaneous power released in load b, is determined by the frequency of the master oscillator 4. The voltage Ug at the output of generator 8 is shown in Fig. 3a. The frequency Ug is selected several orders of magnitude (3-10) below the frequency of the master oscillator 4. The duty cycle modulator 7 converts the UQ pulses into squares (Fig. 36), the duty cycle of which depends on the magnitude of the Ug signal from the power setpoint 9. Changing the duty cycle of the pulses Uy entering the control key input 2, exchanging the interrupt key 2 in the closed and open state, and thus the time during which the frequency specifying the circuit 1 is connected to the master oscillator through the inertial link 3 4. The frequency reference circuit 1 is an adjustable source of constant voltage (Fig. 3), the output voltage U-, which determines the amplitude of the output. key voltages} of the key 2 and U of the inertia element 3 (Fig. 3d id). . . The master oscillator 4 is designed so that its frequency P is proportional to, in a certain range, the magnitude of the voltage of the inertial link 3. When the frequency H decreases to the value (Fig. Ze), the master oscillator 4 stops oscillation generation and, therefore, inverter 5 turns off. A controlled inertia link 3 is inserted into the device to increase the reliability of the inverter. In the absence of the inertial link 3, the frequency of the master oscillator 4, and hence the frequency of the output voltage Ug of the inverter 5, would change abruptly. This would lead to an abrupt change in the power released in the load 6. With an abrupt decrease in power in the load b, the energy stored in the input choke of the inverter 5 transfers to the capacitors installed in its circuit, which causes an increase in the voltage on them, and therefore the increase in voltage on the inverter valves and the reduction in the time provided by the valve for control recovery, which drastically reduces the inverter reliability. For reliable operation of the inverter, power down needs to be performed at low speed. But this leads to an increase in the transient time and a decrease in the efficiency of regulation. Therefore, in order to reduce the transient time while maintaining the inverter reliability, it is advisable to control the inverter parameter, which determines its reliability, and the rate of change of the frequency of the master oscillator 4, in accordance with this parameter, when the power decreases. If the parameter determining the reliability of the inverter is the voltage on its valves, then using the control device 10, the indicated voltage is measured, and the rate of voltage change at the output of the inertia link 3, and hence the frequency of the master oscillator set inversely with the voltage on the valves. This leads to a stabilization of the voltage on the inverter valves and an increase in the reliability of the converter. , In case the parameter determining the reliability of the inverter was 1c time provided for recovery of controllability, then the indicated time and speed of voltage variation at the output of inertial link 3, and, consequently, frequency the master oscillator is set directly in proportion to the time of the valve provided for restoring controllability. As the power increases, the voltage on the inverter elements does not occur; therefore, to reduce the transient time, it is advisable to choose a rate of frequency change that is higher than when the power is reduced. At time t, (Fig. 3), the key 2 closes and the voltage at its output becomes equal to C. For time At, the frequency of the driver reHepaTota is set to f, corresponding to the maximum power of the inverter. At time tj, the key 2 is disconnected and the voltage at its output becomes equal to O. This leads to the fact that the frequency of the master (/ generator 4 during time at decreases c to the value of f, generator 4 stops generating oscillations and inverter 5 turns off Moreover, the rate of change of frequency during the time ttt + Atj is proportional to the time allowed for the control recovery valves or inversely proportional to the voltage on the valves. At the time key 2 is turned on again and the specified processes are repeated. one frequency of the inverter versus time (Fig. Ze) and the dependence of the power released in the load on the frequency of the voltages on it (Fig. 2), plot the dependence of the instantaneous power of the inverter on time (Fig. Зж). The average power over the period of change frequency, considered as D2 and At2,, is, where,, -t is the period of inverter frequency change. By changing the ratio of t and T by the power setting knob 9, the average value of the inverter's advantageous power is adjusted. this time load. For example, the thermal constant of an ICT-0.16 induction furnace is a few hours, and the period of change of frequency f is chosen in the order of several tens of seconds. Therefore, fluctuations in the instantaneous power of the inverter with respect to the average value have no effect on the thermal processes in the load. If the maximum power value is not imposed by restrictions on the load side and the inverter, then the value of P, and accordingly f, is chosen to be equal to Рр, fp (Fig. 2) If for some reason, for example technological, a significant excess over f is unacceptable , then choose f,; fp. At the same time, the same value of P (.p will be obtained at lower values of ratios / T and the fluctuation of the instantaneous power over its average value will be reduced. The efficiency of the inverter with this method of regulation is practically independent of the depth regulation. Thus, in the time interval t, t tj, the power loss P ,,, in the inverter is approximately equal to where T, is the inverter efficiency at power. In the time interval (, t the inverter does not work and the power loss in it is equal to 0. Therefore, the average power loss over a period of change, the frequency loss period is equal to p li ncp t t, t vip g, the efficiency of the inverter when adjusting the power / c is equal to P p + p av cfl. Ie Inverter efficiency with the proposed control method does not depend on the depth of regulation Efficiency at nominal power. Thus, this method of adjusting the output power of the thyristor inverter provides a smooth control of the average power with a high efficiency value. Claim 1. The method of controlling the output MC8NOST of a thyristor inverter operating on an oscillating circuit, which consists in changing the frequency of the control pulses of the inverter valves, characterized in that, in order to increase efficiency,. the frequency of the control pulses is changed from the value corresponding to the minimum power to the value corresponding to the maximum power, and the required time is maintained at a predetermined level, then the frequency of the control pulses is changed to the value corresponding to the minimum power I and the control pulses are removed the required time lag of the operation is periodically repeated, and the ratio between the operating time of the inverter is: the frequency corresponding to the maximum power and the time when 2. The POP method 1, characterized in that, in order to increase reliability, the voltage at the inverter valves is measured and the rate of change of frequency is set inversely proportional to this voltage. to life. 3. Method POP1, differing from and by the fact that, in order to increase reliability, the time allowed for the control recoupment valves and the frequency change gates are set directly proportional to time. Sources of information should be taken into account in the examination -1. Berkovich E.I. et al. High Frequency Thyristor Converters L., Energie, 1973, p. 168. 8

2. Gitgari D.I. and Ioffe Yu.S. New sources of power and automation of induction systems for heating and melting. M., Energie, 1972, p. 82-33.

3. Ki mrv R.N., et al. Comparison of methods for regulating the power of an inverter with the load between input chokes. Sat Thyristor frequency converters for induction heating of metals, No. 5, Proc. UDI, vol. 91, Ufa, 197-6, p. 48-51.

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