SU1283916A1 - Method of starting parallel current inverter - Google Patents

Abstract

The invention relates to electrical engineering and can be used when starting a parallel current inverter. The aim of the invention is to improve the stability and reliability of the start-up when the inverter operates on a load with varying parameters. Simultaneously with the process of forming the starting pulses, the instantaneous voltage value at the load 7 is continuously measured and the analog signal proportional to this voltage is compared in the comparator 15 with the setting signal 14. R the moment of their equality at the output of the comparator 15 a pulse of inhibiting the starting pulses is generated. 3 il. (L

Description

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The invention relates to electrical engineering, in particular, to methods and devices for starting a parallel current inverter.

The purpose of the invention is to increase the stability and reliability of the start-up when the inverter operates on a load with varying parameters.

FIG. 1 shows a diagram of a device that implements a method for starting a parallel current inverter; Fig diagram of the start process; on fig.Z dependence Sinin f (n).

The power part of the parallel current inverter (FIG. 1) contains a smoothed throttle 1 connected to the DC circuit, a thyristor

bridge assembled on thyristors 2-5, included in the inverter AC circuit, compensating capacitor 6 and active-inductive load 7.

The start-up device 8 includes a current sensor 9 (shunt) included in the inverter DC circuit, a load current sensor 10 (non-inductive shunt) included in the load circuit 7. Sensors 9 and 10 are connected by outputs to the inputs of comparator 11. Device 8 also contains an amplifier 12 control pulses, an output connected to control electrodes of thyristors 2-5, a load voltage sensor 13 (voltage transformer) connected in parallel with the computing capacitor 6, setpoint 14, additional comparator 15, switch 16 with two pulse inputs and control input

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limited by the class of thyristors used 2-5 and the maximum allowable voltage at the terminals of the compensating capacitor 6. The limiting values of these voltages are calculated from the parameters of the quasi-steady-state mode of the inverter. Before starting, the output of the switch 16 is connected to its first pulse input. When a signal is applied to turn on the inverter, its control system (not shown) generates the first control pulse. This includes, for example, a pair of thyristors 2, 5. A circuit is formed for current flow in load 7 and a compensating capacitor 6. Since the active-inductive load 7 together with the compensating capacitor 6 form an oscillating circuit, the voltage on the compensating capacitor 6 varies along law, close to sinusoidal. The next pair of power thyristors 3,4 of the inverter bridge, previously in the off state, is turned on at time t, corresponding to the maximum instantaneous value of voltage U (. On the compensating capacitor 6 (Fig. 2). At this moment the current compensating the capacitor 6 is equal to zero, and the instantaneous value of the load current 7 in absolute value is equal to the instantaneous value of the current consumed from the power source and the heater.

5 as the angle to lock thyristors 2-5 depends on the magnitude of the voltage. the compensating capacitor 6, then turning on the thyristors at the moment corresponding to the maximum instant

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neither, and the voltage sensor 13 is powered by a nag-40 to the nominal value of this voltage sporizka output connected to the first input of an additional comparator

15, to the second input of which the output of the setting device 14 is connected, and the output of the additional comparator 15 is connected to the control input of the switch

16, to the first pulse input of which the output of the comparator 11 is connected, and the output of the switch 16 is connected to the input of the amplifier 12 of control pulses.

The start of the parallel current inverter is provided by starting pulses generated by the start device 8. Before starting the inverter, using the setting device 14, a reference signal is generated, proportional to the maximum permissible instantaneous value of the voltage on the load 7 Unp (Fig. 3), which

It increases the angle of the lock. To obtain a starting control pulse, the sensor 10 measures the current in the inverter load circuit, and

45 by sensor 9 is the current consumed by the inverter from the power source. Analog signals proportional to the instantaneous values of these currents are fed to the inputs of the comparator 11.

50 At the moment of equality in absolute value, the instantaneous values of these currents at the output of the comparator 11 form a control pulse, which through the switch 16 and the amplifier 12

55 is supplied to the control electrodes of the thyristors 3 and 4. The next starting control pulse is obtained in an alternating manner and fed to the thyristors 2 and 5. Next, the processes are repeated.

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Simultaneously with the process of forming the starting pulses, the instantaneous voltage value at the load 7 is continuously measured. An analog signal proportional to this voltage is obtained at the output of the sensor .13 the load voltage. In the comparator 15, the signal from the sensor 13 is compared with the analog signal of the setting device 14. At the moment they are equal, a inhibit impulse is generated at the output of the comparator 15, which is fed to the control input of the switch 16. At the same time, the output of the switch is connected to its second impulse input and feed the starting pulses to the inverter thyristors cease. Further, the second pulse input of the switch 16 receives the control pulses Uyn (Fig. 1), which are generated by the inverter control system in accordance with the adopted control method that implements the self-excitation process. The inverter operates in quasi-installed mode.

Investigation of the inverter start-up process according to the proposed method for a common converter operation mode, when H n -45 ° (load angle), performed on a mathematical model, showed that the frequency of following control pulses exceeds the frequency of control pulses in quasi-fixed . It also follows from the analysis that the minimum value of the thyristor locking angle in the inverter start-up interval substantially depends on the number of starting control pulses n formed according to the proposed method. As an example, neither FIG. Figure 3 shows the dependence 6 (| f (n), obtained by calculating the Q value of the oscillatory circuit formed by the load 7 and the compensating capacitor 6, and equal to O 20. It can be seen that the premature removal of the triggering control pulses leads to a decrease in the angle shut off thyristors, decreasing the stability of the start-up. During the start-up of the inverter, the voltage at load 7 increases, and when the starting control pulses are applied after the process leaves the quasi-set mode, the voltage exceeds the allowable limits and The user is shut off by the appropriate device.

zapshty. A significant voltage rise across the load 7 in a quasi-established mode is explained by the fact that the switching on of the thyristors in accordance with the considered method is performed with the leading angle f) OT / 2 relative to the output voltage curve. Indeed, in the quasi-established mode, the ratio of the voltage across the load (compensating capacitor 6) to the voltage of the inverter's power source is

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Ui oh, 9 COS &

In the p - / 2 mode, the voltage on the compensating capacitor 6, and subsequently, on the thyristors of the inverter is large and exceeds the allowable limits.

The supply of start-up control pulses is stopped at the moment when the start-up process reaches the quasi-set mode, when the instantaneous value of the voltage on the load 7 (11 of Fig. 3) reaches the maximum permissible level (Unp). This ensures a sufficiently large angle to lock up the thyristors and exclude overdamping. In the quasi-stationary mode, the inverter operates with a leading angle of ps ir / 2.

The duration of the starting process depends on the load parameters of the inverter (inductance, resistance), which in most cases change. Correspondingly, the start-up exhaust torque changes to a quasi-set-up mode. In the known method and starting device (see the prototype), it was not possible to control the termination time (supply of control pulses. Therefore, when the inverter starts to load with varying parameters, the inverter may interrupt if the thyristor locking angle decreases or the protection devices turn off The proposed method and device for its implementation allow stopping the supply of starting control pulses at the time of starting the process on the KB In this case, the stability and reliability of the start-up increases, the number of failed starts is reduced,

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The starting method of the parallel current inverter, which, since the start-up signal arrives, generates and alternately falls on the thyristors of the parallel current inverter starting pulses generated at the moments of equality of the input current of the parallel current inverter O load, remove the starting pulses

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and serves the main control pulses. NIN, characterized in that, in order to increase the reliability of the start when the load changes, the voltage on the load is measured, the signal corresponding to the maximum allowable voltage on the load is set, the signals are compared and, at the time of their equality, the starting pulses are removed and .

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Claims (1)

Claim The method of starting a parallel current inverter, which consists in the fact that, from the moment the start signal arrives, start pulses are generated and alternately fall on the thyristors of the parallel current inverter, which are formed when the input current of the parallel current inverter and the load current are equal, remove the start pulses and supply the main pulses control, characterized in that, in order to increase the reliability of starting when the load changes, measure the voltage at the load, set the signal corresponding to the maximum allowable voltage at Loading the, comparing said signals and when they are equal removed starting 10 pulses and start pulses supplied workers. FIG. 3