SU849410A1 - Method of starting thyristorized inverter with dependent excitation - Google Patents

Description

(5) STARTING METHOD FOR THIRISTOR INVERTER WITH INDEPENDENT EXCITATION

I

The invention relates to a converter technique and can be used to start up autonomous thyristor inverters as well as constant voltage converters with an independently excited inverter as an intermediate link.

There is a known method for starting a thyristor inverter by pre-forming the initial voltages on, p the switching capacitor and the current in the input choke. The implementation of this method is carried out by introducing into the inverter circuit auxiliary thyristors and an additional capacitor ,, 5 operating only during the start-up period LlJ,

The disadvantage of this method is the relatively high voltage on the thyristors, the ability to start only in JQ limited load range, as well as the complexity of the control system associated with the necessity of fixing the steady state and turning off

at this point an additional capacitor.

The closest to the proposed technical essence and the achieved result is the method of starting the thyristor inverter with independent excitation, which consists in forming the initial voltage on the switching capacitor and the current in the input choke simultaneously with the supply of control pulses to the inverter thyristors. 2j.

However, this method is associated with large starting losses, and the need to regulate the supply voltage during the start-up period, in order to obtain a stable start for a different number of loads, is associated with the complication of the entire device that implements this method.

The purpose of the invention is to increase the reliability of start-up and reduce start-up losses. This goal is achieved by the fact that, in a known method of starting a thyristor inverter with HeaaBHCHhfjM excitation, the input current of the inverter is interrupted at the end of each half-period when it reaches its amplitude, the installation current is short-circuited, and the input choke is discharged through inverter. FIG. Figure 1 shows a DC voltage thyristor converter circuit with a series resonant inverter; in fig. 2 curves of starting current, input choke current and output voltage. The constant voltage converter consists of an inverter on thyristors 1–4, a serial LC circuit containing an input choke 5 and a switching capacitor 6, and a bridge rectifier on diodes 7–10 connected with one diagonal to the output winding of the transformer 11 the inverter, and the second to the smoothing capacitor 12 fnp'tra, is connected to the power source via a fully controllable key 13. The input buses of the inverter 14 and 15 are shunted by the second key 16. The diagrams denote the input current of the inverter 17; The current of the setpoint is 18, the current of the droplets is 5-curve 19; the voltage across the condenser torus 12 is curve 20; input current amplitude 21. The start-up process in this scheme proceeds in the following way. At the initial moment, control impulses are supplied to the thyristors 1 and 4 and the key 13. and in the oscillating circuit of the LC circuit (choke 5 and capacitor 6): a current impulse equal to the input current of the inverter 17 is formed. At the same time as the thyristors 1 and 4 are turned on, diodes 7 and 10 and capacitors 6 and 12, the voltage on which is zero at the initial moment, will begin to charge. Under the condition that the output filter of the output filter of the capacitor 12 of the output filter reduced to the primary winding of I1 of the capacitor 6 - circuit, is more than an order of magnitude, which is often done in practice, the amplitude and duration of the input current are determined mainly by the supply voltage and the choke inductance 5, the capacitance of the capacitor 6 and the quality factor of the charging circuit. When the amplitude of the input current of the inverter 17 reaches the moment t, the current of the setpoint 18 is switched off by the fully controlled key 13 and the key 16 closes its input buses 14 and 15. The input current of the inverter is also interrupted and the energy stored in the choke 5, is transmitted through the inverter and its shorted busses to the output of the converter. The curve of the current 19 drossel 5 drops to zero. At the moment t of reaching the circuit 1C current of zero value, the voltage of the capacitor 6 is applied to the thyristors in the opposite direction, causing the flow of the reverse current and the locking of these thyristors. In the next half-period, unlocking pulses are applied to thyristors 2 and 3 and again to key 13, and to key 16 - a locking pulse. The supply voltage and the capacitor 6 are applied to the oscillating LG circuit in accordance with and the following current pulse is formed in the circuit (curve 19). Diodes 8 and 9 come off, capacitor 6 will begin to recharge, and capacitor 12 will recharge to a high voltage (curve 20). At the moment when the amplitude of the current of the inverter 17 reaches the current value of the installation 18, the power supply circuit is open again and the choke 5 is again discharged through the inverter and its input busbars shorted to the end of the half-transition. At the moment of equality of the current (curve 19) of the LC circuit to zero, the voltage on the capacitor 6 is applied to the thyristors 2 and 3 in the opposite direction and locks them. As the output voltage reaches a steady state value, the open state interval of the fully controllable key 13 increases. In a steady state setting, the current of the setpoint 18 sets the amplitude of the input current 21 so that the key 13 is constantly in the open state. In this case, the conduction angle of the thyristors becomes maximum and equal to the duration of the half-period of free oscillations of the circuit. When starting such a circuit for a smaller load, it is necessary to reduce the current of the setpoint for the period of the start. This will lead to a greater limitation of the amplitude of the starting current and a more gradual increase of the voltage across the load. The duration of the transition process is slightly increased. However, this method allows to achieve aperiodic nature of the starting process and low loads.

This method of starting allows to limit the starting current in inverters operating in the continuous current mode in the input choke. In such inverters, the throttle current, after interrupting it along the power supply, drops to a certain minimum value and at the beginning of the next half period it will increase from this minimum value to a certain maximum value limited by the value of the current setting.

Thus, the proposed method allows a reliable start-up of the inverter in a wide range of loads, and limiting the starting current, using key elements, makes it possible to reduce the starting losses to a minimum. A reduction in the energy stored in the reactive elements during the start-up period reduces the starting overvoltages on the load and on the circuit elements, and thus, reduces the installed H-o

power of all elements. This gives a slight improvement in the overall device dimensions.

Claims (2)

1. US patent number 3757197, cl. H 02 M 7/52, 1971. 2. USSR author's certificate number 288112, cl. H 02 M 7/52, 1969. FIG.