SU1415385A1 - Method of controlling inverter with several resonance loads - Google Patents

Abstract

The invention relates to electrical engineering and can be used in inverter control systems. The purpose of the invention is to simplify and increase reliability. In the inverter control method, the frequency of the output current of the inverter is changed during each cycle at a rate limited by lower and upper limits. When the opposite limit of the frequency range is reached, the sign of the speed is reversed. With negative deviations of the electrical parameters of the loads from their tasks, the rate of change of the frequency is set to an upper limit, and with positive ones, the indicated speed is changed as a function of the deviation of the technological parameter from its task. 2 hp f-ly, 2 ill. with f cl

Description

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The invention relates to a conversion technique and can be used to create nitromatizing control systems for induction installations powered by an increased frequency current with simultaneous and independent pei elimination of the modes of several resonant loads and the corresponding technological zones,

The purpose of the invention is to simplify and improve reliability.

Fig. 1 shows a control circuit CHcreNfoi, with which it can be implemented in a case where power is distributed between three loads; FIG. 2 are diagrams illustrating the implementation of the method;

The control system (Fig. 1) of the inverter 1 with resonant loads 2-4 consists of a master oscillator 5, sensors 6-8 and setters 9-11 of electrical parameters of loads,

sensors 12-14 and setters 15-17 of technological parameters, elements T8-23 of comparison, relay elements 24-29, elements AND 30-32, elements OR-NOT 33 and SHSh 34, unit 35 of the lower limit of the rate of change in frequency, adder 36, the multiplication unit 37, the integrator 38, the trigger element 39, the sensor 40 and the voltage setting unit 41 J on the inverter power element (thyristor or choke), the sensor. 42 and master 43 of restoration time t, comparison elements 44 and 45, nonlinear elements 46 and 47, and cvMMaTopa 48,

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The electrical parameter U of the load can be the voltage or current of the inductor, and the technological parameter T is the temperature of the object being heated.

The method of controlling inverter 1 with resonant loads 2-4 tuned to different frequencies fpo, fp, fp (diagrams, fig 2) consists in cyclically changing the frequency of the inverter output current in the range f ,, jn-f. the minimum (fp;) and maximum% then fp4) resonant frequencies of the loads, while using sensors 6-8 and 12-14 control the electrical (U, Uj, U) and technological (T, T, T) parameters of the loads 2-4, compare them with the set points (setpoint signals; s 9-11 1 o 3 - Uo, 1 n4 sig

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setting points 15-17 -1, T, T and, as a function of the deviation signals received at the output of comparison elements 18-23, change the frequency of the output current f, equal to or a multiple of the frequency of the master oscillator 5, the frequency f is changed during each cycle starting from the lower mchi upper limit of the frequency range is continuous and monotonous with a speed limited by lower and upper limits, and at times t,, t, 4, t, (, L jg, t ,, t, 3,

tj4 reaching opposite limits of the frequency range, the sign of the speed is reversed, and with negative deviations of the electrical parameters of all loads 2-4 from their tasks (Uj UQJ, Uj ,, U; Ug), the rate of frequency change is set to an upper limit (intervals,, tg

t 1i IS H

. a, in the presence of a positive deviation of the electrical parameter, the rate of change of frequency is changed as a function of the deviation of the corresponding technological parameter from its reference TOJ,

The law of regulation of the rate of change of frequency as a function of the deviation of the technological parameter can be both continuous (for example, proportional) and relay. , 27 and 29, controlling the rate of change of frequency.

The frequency change cycle (FIG. 2) starts at time t ,,, starting with the lower limit of the frequency range. Output signal of the integrator 38

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the output signal of the element triggers, taking values + 1 and; 1 and -1 at the moments of reaching the lower and upper iipi: MU. u-n frequency range;

K. - coeff (}); 1is1p- transfer integral; ;, .-,

Jj - the output signal of the adder 36.

In the interval parameters U2, From, U

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j of all loads less than the specified threshold levels 02 0 04, the output signals of the elements 24, 26 and 28 of the comparison are negative, the output signals of the AND elements 30-32 are low, and the output signal of the OR-HE-33 element has a high level, which is 34 and the adder 36 is fed to the input of the multiplication unit 37, at the second input of which a signal +1 is present. Due to this, in the interval tj-t, the rate of change of frequency is positive and corresponds to its upper limit.

At the interval t, -t, j (near the resonance of the load 2) a positive signal of the comparison element 18 becomes and at the output of the relay element 29 a high level signal appears. The output signal of the OR-HE 33 element takes a low level of logic zero, and The code of the OR 34 element appears as a low level signal, since the output of the relay element 25 is a zero signal (T2 - cTj) and the output of the AND 25 element is a low level signal. Thus, in the interval, the rate of change of frequency is determined by the output

signal setting unit 35 of the lower limit of the rate of change of frequency. During this interval, the inverter operates at a frequency close to the resonant frequency of the load 2 | And a large part of the inverter output power is released (a small part of the power is used in other loads connected in series with each other and with the load 2). The duration of the interval t, -tj depends on the magnitude of the setting UQ in the case of the continuous law of adjustment of technological parameters, the duration of the interval of power allocation in the load 2 depends on the magnitude of the deviation of the technological parameter and decreases with negative deviations and decreases with positive deviations.

In the deviation interval, the electrical parameters of all loads are again negative (the power level in the loads is below the threshold), at all inputs of the element OR-NOT 33

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zero signals, and at its output a high level signal, which through elements 34, 36 and 37 acts on integrator 38, sets an upper limit for the rate of change of frequency of the master oscillator 5.

When approaching the resonant frequency of the load 3 f p during the interval, the lower limit of the rate of change of frequency is again set, while the inverter power is mainly in the load 3.

In the interval when the level of the parameter U falls below the threshold value U, the frequency changes with the maximum speed.

On the interval t, reestablish

The lower limit of the growth rate of the frequency is cast, the power is mainly in the load 4.

After the parameter CD decreases below the threshold level and 0 at time tj, the frequency with the maximum speed reaches the upper limit of the frequency range f, o (Kc time tj the trigger element 39 switches, thus the sign of the speed change changes to negative - the frequency starts to decrease. The second half of the cycle of frequency change (Fig. 2) is symmetrical to the first half of t (-t-, and differs from it only by the sign of the rate of change of frequency.

A variant of the method is possible, in which at the moment when one of the limits of the frequency range is reached, for example, at time t-, simultaneously with

the sign of the rate of change of frequency by changing the sign of the output signal of the trigger element 39 sets the value of this speed to an upper limit until reaching the opposite limit of the range frequency f d, in this variant of the system when the output signal of the trigger element 39 is negative to another input of the multiplication unit 37 regardless of the signal of the adder 36, a high level signal is sent, which corresponds to the upper limit of the rate of change in frequency and a rapid return to the level occurs (strokes and the line on the frequency diagram f, Fig. 2). If in the first embodiment of the method the power pulses are delivered to different loads

through different inhalations for loading: tk tuned to the upper and ti lower resonant frequencies, the period of these pulses practically coincides with the cycle time, in the second variant the period of following power pulses for each load is constant and close to the half cycle duration for the first variant. Due to the pulse frequency of power P, which is more than 1 high and equal for all loads, the amplitude of pulsations of the technological parameters in the second variant is almost 2 times smaller.

The disadvantage of this variant is a slightly lower power compared to the first variant given to loads, which is due to the loss of time to return the frequency to the lower limit of the frequency range during which the amplitude of oscillations of currents and loads of loads is small due to the inertia of the latter.

After the technological parameter (temperature of the heated object) of one or several loads exceeds the reference, the mode of operation of the system (Fig. 1) becomes different. In particular, with T. 7 T Q 2 5 T; (FIG. 2) a decrease in the rate of change in frequency occurs only at intervals t, −tj. and, corresponding to the passage of the frequency range adjacent to fp4. In this case, power is mainly allocated in load 4, and in other loads, because of the high rate of change of frequency near their resonant frequencies, the increase in oscillations is either short-term or slightly and its amplitudes

After all the technological parameters of their tasks have been reached, one of the resonant frequencies is not slowed down.

Frequencies, while the power allocated in all loads, is minimal. In this mode, frequency modulation can also be terminated in one of the extreme To4tMc frequency ranges. It may be Hz eaus motrei prohibiting the supply of impulses of a secondary power supply to inverter 1 (stop -i / i / uiiouitTi generator 3), at which iiiaii. (- Tiiii about and 1 stops noTiH 0, h ;; n load.

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loads below the reference when the frequency of the master oscillator approaches the resonant frequency of the given load at the output of the corresponding element AND a low level signal appears, while from the outputs of the remaining AND elements and the output of the OR-NOT 33 element the low level signals enter the inputs of the OR 34 element. Therefore, the output

element 34, a low level signal appears and the rate of change of frequency is set to its lower limit, which is determined by setting unit 35. Thanks to this, a power pulse arrives at the corresponding load.

Thus, the temperature in all loads is maintained with a certain accuracy, which is determined by the hysteresis zone of the relay elements 25, 27 and 29 and the duration of the frequency change cycle.

It should be noted that the upper limit of the rate of change of frequency or g of inverters with an input choke is limited by the conditions of permissible overvoltages on the thyristors and the permissible reduction in the recovery time. With a rapid change in frequency, abrupt changes in the power delivered to the load occur. When the power is reduced, the electromagnetic energy stored by the input choke goes into the switching capacitor of the inverter, which causes the rise of the voltage on the thyristors. At the same time, the voltage amplitude on the choke itself increases. With an increase in power consumption, the slowly varying current of the input drossel does not have time to carry out the increasing consumption of energy stored by the switching capacitor, the voltage decreases at the latter, and together with nkm the switching energy of the thyristors decreases and the recovery time decreases. Therefore, it is advisable to use a variant in which, using sensors 40 and 42, control the voltage amplitude on the thyristor or inverter input choke and the time represented by the thyristors

for restoring t., compare these parameters with ongils of knobs 41 and 43, and in the case of reaching the target value: 1yub1 1m of these parameters has received a iii note this limitN frequencies .bi, i0

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the division of the deviations of an unacceptable sign and the formation of control actions is provided by nonlinear elements 46 and 47, the output signals of which, through the adders 48 and 36, affect the rate of change of the frequency in the direction of decrease.

The proposed method does not require the use of an inverter self-tuning system for the resonant frequencies of loads that are critical to the parameters of the elements from the point of view of stability. This greatly simplifies and increases the reliability of the equipment used and the method itself. In addition, the method makes it possible to improve the accuracy of adjusting the process parameters by increasing the frequency of supplying power pulses to resonant loads. The method allows the use of both relay temperature controllers and high-precision continuous-current controller.

Claims (3)

1. A method of controlling an inverter with several resonant loads tuned to different frequencies, which consist in cyclically changing the frequencies of the output current of the inverter in the range covering the minimum and maximum resonant frequencies of the loads, controlling the electrical and technological parameters of each of the loads, comparing them with predetermined values and as a function of deviation signals change the frequency of the output current, characterized in that, in order to simplify and increase reliability, the frequency change during dogo 0 cycles are made, starting from the lower or upper limit of the frequency range, continuously and monotonously with a speed limited by lower and upper limits, and when the opposite limit of the frequency range is reached, the sign of the speed is reversed, and with negative deviations of the electrical parameters of all loads from of their assignments, the frequency change rate is set to an upper limit, and if there is a positive deviation of the electrical parameter, the rate of the frequency change changes as a function of the deviation Corresponding technological parameter from the task. 2. A method according to claim 1, characterized in that, in order to improve the accuracy of adjusting the technological parameters, at the time the frequency of the inverter reaches one 5 of the limits of the frequency range, simultaneously with the change of the sign of the rate of change in frequency, the value of this speed is set to an upper limit until the opposite limit of the frequency range is reached. 3. Method according to paragraphs. 1 and 2, characterized in that they additionally control the voltage amplitude on the power elements of the inverter and the time represented by the thyristors 5 for restoring the locking properties, compare these parameters with the specified limit values and, if any of these parameters reach the limit value, maintain this limit value by lowering the upper limit of the rate of change of frequency. 0 0 (rig.1 5 LH r - f V7Ji / Z it „: IL-X and L-. F l  / tzW, t, ts t, TZ 01; j o: s: T TC O f II . "F K / AH K" / J F l u .. /. ,, f