SU1339821A1 - Method of combined control of thyristor frequency converter - Google Patents

Description

The invention relates to electrical engineering and can be used to control thyristor frequency converters operating on the principle of phase-sensitive rectification of a voltage beat.

The purpose of the invention is to improve the power characteristics of the converter by reducing output distortion.

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FIG. 1 shows time diagrams of voltages and currents at the input and output of the converter, as well as control signals; in fig. 2 - diagram of a three-phase-single-phase frequency converter.

The graphs (fig. 1) change, or the beatings of the voltages UQ, U-b, and Uc at the input of the converter, the source of the bijII of the voltage (fig. 2) are given

on the envelope of the beats and forming a three-phase system on the carrier frequency (phase shift 120 e. hail). When generating the thyristor control signals of the semiconductor switch 2, the carrier frequency is separated from the voltage beats, the control signals are synchronized with it, and shifted in the direction of advance by the value of the control angle. In this case, the leading edge of thyristor control signals 2.1 and 2.2 UN, is combined with zero voltage Ug, thyristors 2.3 and 2.4 - U, 2.5 and 2.6 - U {,. The duration of the control signals is taken equal to 120 e. hail When the current at the output of the converter exceeds the setting of current sensor 3, control device 4 removes the permission to turn on the opposing group of thyristors (and, 0). Switching of valves occurs in the moments of equality of potentials at the inputs of the thyristors of the switched phases (since the control signal is already present). Thus, a part of the output voltage curve is formed in the rectifying mode. In the invert mode of operation (from the moment of time corresponding to the beat unit to the moment of changing the sign of the load current) as a result of the overturning phase of the beat filling voltage (Ug, and ,, U (.), The adjustment angle is equal to / i 180 - lai ,, t. E. The rectifier is automatically transferred to the inverter mode. At the same time, in the zone of small currents (| 1ts1 N, -, where H; is the current sensor setting), the prohibition of switching on counter thyristors is removed.

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The control signal on them is given in phase ;, according to the same control law. This allows a smooth transition to the group of counter thyristors after changing the sign of the load current.

If in the rectifying mode the separate control method is not applied, the graph of the output voltage variation is shown respectively in FIG. 1g. The failures in the output voltage in this case are due to the early switching of the counter-parallel valves,

The implementation of the proposed control method is possible if the frequency converter contains a carrier frequency sensor, a load current level sensor and a control system consisting of a control pulse generator, a phase shifter and a logic device,

Depending on the purpose of the converter, the carrier frequency sensor can be made according to the balancing frequency converter scheme.

In a contactless excitation system of an asynchronized turbo-generator, a control machine, made in the form of an inverted synchronous generator, can be used as a carrier frequency sensor 7. The frequency at the output of sensor 7 is proportional to the speed of rotation of the rotor, and the carrier frequency of the beats is also proportional to the speed of rotation of the rotor. By appropriate selection of the numbers of pairs of poles, it is possible to achieve the equality of the frequency at the control byh of the driving machine and the carrier frequency of the voltage beating.

The control pulse shaper for the control machine may consist of a series-connected Zener diode 8, a diode 9 and a resistor 10 connected to the main windings of the control machine,

The logic device may consist of a comparison node (comparators 5 and 6) and a switching node. The current level sensor 3 can be made on the basis of known current sensors with less rigid AND, requirements to the sensor setting.

When such a device is in operation, a carrier frequency sensor 7 extracts a carrier frequency of voltage beats, control signals are generated in a pulse shaper, phase control signals are shifted by phase in a phase shifter, and distribution of received control signals by channel in a logical device based on information from a current level sensor management

The proposed control method allows one to improve the energy performance of multi-phase-to-input frequency converters by eliminating the faults in the output voltage curve at a preemptive control angle. At the same time, the positive properties of the basic control method are preserved: reliability of the converter operation at the load with variable cos tf, absence of discontinuous current zones (breaks of the load circuit in the low current zone), continuity of control.

Claims (1)

Invention Formula A method for combined control of a thyristor frequency converter with two groups of anti-parallel 25 thyristors powered by a three-phase networks with voltage beating, consisting in that the voltage of the carrier frequency of the beating voltage from the power supply network, form a phase-carrier frequency of the network synchronization pulses, set the angle of control of the thyristors of the frequency converter, form and serve to the groups of counter-parallel thyristors, control pulses with an angle ahead of the synchronization pulses by a given angle, characterized in that, in order to improve the energy characteristics of the converter by reducing the output voltage distortions, load current, set the current setting, compare the current setting with the load current, if the load current exceeds the current setting, then control pulses are applied to one thyristor group in accordance with the desired polarity of the output voltage, if the load current is less than the set value, then control pulses serve both groups of thyristors at the same time. but , i,. (a and, 4, Lll, Lll Lllii, Lllll, W H. Editor N. Tupitsa Order 4241/52 Circulation 659Under VNIIPI USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35; Raushska nab ,, d. 4/5 Production and printing company, GoUgorod. ; l "Project, 4 Compiled by S. Lueanov Tehred M, .STC Proofreader C, Shekmar;