SU1676043A1 - Device for automatic tuning of operating frequency of self-exciting inverters - Google Patents

Abstract

The invention relates to electrical engineering and allows self-tuning of the frequency of an autonomous inverter 1 loaded on both parallel and serial oscillatory circuits. The purpose of the invention is to improve accuracy. When the inverter 1 is turned on, the frequency increment of the master gene is set

Description

The invention relates to electrical engineering, in particular to frequency controlled frequency converters for induction heating.

The aim of the invention is to expand the field of application of the device, increase accuracy and reduce the cost of auto-tuning, increase the efficiency of the inverter.

The drawing shows a device diagram.

The device contains an inverter 1, an inverter control unit 2, an inductor 3 connected to the output of inverter 1, a compensating capacitor 4, an inductive current sensor 5, a rectifier 6, a derivative voltage measuring unit 7, switch 8 and elements 9 and 10, element OR 11, RS-trigger 12, keys 13 and 14, trigger 15, connected in series, control bus Start 16. Block 7 contains memory element 17, keys 18 and 19, memory element 20, keys 21 and 22, element 23 comparison, the generator 24 switching pulses, half-wave rectifiers 25 and 26, transform spruce layer 27.

The device works as follows

With the passage of alternating current through a controlled busbar, an alternating magnetic field is created around this bus, the magnetic lines of which cross the plane of the turns of the inductive current sensor 5. In the winding of the sensor 5, an emf of mutual induction is induced, the magnitude of which is directly proportional to the current flowing through the controlled bus. After the full-wave ripple 6 is straightened and smoothed by the pulse 6, the positive polarity is applied to the input of the block 7. The input voltage goes directly to the non-inverting input of the reference element 23, and through the keys 18 and 21 to the memory elements 17 and 20, which through the keys 19 and 22 are connected to the inverting input of the reference element 23. The keys 18 and 22 are closed during the pulse from the direct output of the generator 24

pulse, resulting in the memory element 17 during the action of the pulse from the direct output of the generator 24 monitors the input voltage change, and during the pulse from the inverted output of the generator 24 is connected to the inverting input of the comparison element 23. The memory element 20, on the contrary, during the operation of the pulse from the direct output of the generator 24 is connected to the inverting input of the comparison element 23, and during the operation of the pulse from the inverse output of the generator 24 monitors the change in the input voltage. Thus, on the comparison element 23, at the 1st instant of time, the input signal of positive polarity is compared with the voltage stored on the memory elements 17 mlm 20. If the input voltage rises, then at any time the condition UH ii and the output voltage of the reference element 23 has a positive sign, where UH is the non-inverting voltage; UH is the voltage of the inverting inputs of the reference element 23. If there is no increase (decrease) in the input voltage, then the output signal of the comparison element 23 is zero. In the case of a drop in input voltage, i.e. UH UH, this signal has a negative sign. The output signal of the positive sign comparison element 23 via the half-wave rectifier 26 is supplied to the disconnecting contact of switch 8, and the output signal of the negative sign comparison element 23 via the full-wave rectifier 25 is fed to the level converter 27, from which the positive polarity signal goes to and. . switch 8 contact. Since the common contact of switch 8 is connected to the first inputs of And 9 and 10 elements, the output signal of the derivative voltage sign unit 7 is fed to the first inputs of And 9 and 10 elements. To consider the operation of the rest of the device and the device as a whole assume that inverter 1 is loaded on a parallel oscillating circuit /

When inverter 1 is turned on, bus 16 starts the signal of logical 1, which through the OR 11 element sets RS-flip-flop 12 to one state. The logical 1 signal from the direct output of the RS flip-flop is fed to the control input of the key 13, which is triggered, and a negative sign is sent to the input of the integrator 15. The voltage at the output of the integrator 15 begins to grow smoothly with a constant integration of Ti -. So

to with

As the output signal of the integrator 15 is fed to the input of the inverter control unit that is controlled by the voltage of the master oscillator, its frequency begins to increase from the initial f0. If, as the frequency of the master oscillator increases, the current in the common circuit of the parallel circuit begins to decrease, then, firstly, this indicates that the frequency of the master oscillator approaches the resonant frequency of the oscillating circuit, and, secondly, the negative signal from the output of element 23 comparison does not pass through a half-wave rectifier 26 and does not change the states of the RS flip-flop 12. If, however, after turning on the inverter into operation and with increasing frequency of the master oscillator, the currents of the common oscillating circuit increases, Firstly, it indicates that the frequency of the master oscillator moves away from the resonant one, and, secondly, the positive sign from the output of the block 7 for determining the direction of current change through the element 10, at the second input of which the signal is logical 1 from the direct output The RS flip-flop 12, flips the trigger to the zero state. The logical 1 signal from the inverse output of the RS flip-flop is fed to the control input of the key 14. The key 14 is triggered and the reference voltage E0p2 of the positive sign is fed to the input of the integrator 15. The integrator begins to smoothly decrease its output voltage, as a result and approach the resonance. After the resonant frequency passes by the master oscillator, the current in the common circuit of the oscillating circuit increases, the output signal at the output of the comparison element 23 changes sign from negative to positive, which causes the RS flip-flop 12 to be moved to another position, as a result of which the integrator input signal changes sign to the opposite . The frequency of the master oscillator again approaches the resonant one, passes it, and returns back. It follows from the above that the proposed device ensures the operation of the master oscillator of the inverter control unit 2 at the resonant frequency of the oscillatory circuit by maintaining the minimum current value in the common circuit circuit. Voltage fluctuations of a triangular shape at the output of the integrator 15 are conducted to oscillations of the frequency of the master oscillator of the inverter control unit 2 ± Af from the initial

f0 level. The magnitude of the frequency oscillations is set when designing the device. The magnitude of the oscillations ± Af is determined by the sensitivity of the inductive current sensor 5, the sensitivity of the comparison element 23 and the frequency of the generator 24 switching pulses. The higher the sensitivity of the elements 5 and 23 and the higher the frequency of the generator 24, the smaller the value of At.

When the opening contact of the switch 8 is closed, the device maintains the maximum current value in the controlled circuit, which is necessary when the inverter operates on a series oscillating circuit. The device works in the same way, only in this case the signal of the negative sign from the output of the comparison element 23 is used, which through a half-wave rectifier 25

It is formed in the level converter 27 into a positive sign signal and through the disconnecting NO, the contact of the switch 8 is fed to the first inputs of the elements AND 9 and 10.

The device allows you to increase the accuracy of the automatic frequency control, eliminate the parasitic effects of the elements of the device on the oscillating circuit, and increase the efficiency of the inverter.

Claims (1)

Invention Formula A device for auto-tuning the frequency of an autonomous inverter containing a control unit with an input of the frequency setting of the inverter and loaded on an oscillating circuit, containing a series-connected current sensor and a rectifier, the current sensor input is intended to be included in the oscillating circuit, increase accuracy, it is equipped with a block for determining the sign of the derivative of the voltage with antiphase outputs, the first and second elements are AND, a switch, an OR element, an RS trigger, two keys and an integrator, the input of the derivative sign determining unit is connected to the output of the rectifier, its antiphase outputs are connected to the first combined inputs of the first and second elements AND, the second input The first and second elements And are connected to the inverse and direct output of the RS flip-flop, respectively, the output of the second element And is connected to the R-input of the RS-flip-flop, the output of the first element And through the first input of the element OR is connected to the S-input RS-trigger, RS-flip-flop outputs are connected to control inputs with corresponding keys, whose inputs are intended to be connected to different polarity sources of the reference voltage, and the outputs are combined, are connected to the integrator input, the integrator output is intended to be connected to the inverter input frequency control input of the control unit, the second input of the OR element is intended to be connected to signal source start.