RU2517300C2 - Method for control of static converter in alternating-current generation system in short-circuit conditions - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention is related to the field of electric engineering and power electronics and can be used for design of alternating-current generation systems or AC uninterrupted power supply systems with a voltage inverter. In the suggested method for control of a static converter in an alternating-current generation system in short-circuit conditions load current is measured and when it reaches the preset value a control signal for the voltage converter is changed providing the maximum value of short-circuit current thus regulating the direct-current value at the inverter input, stabilising short-circuit current in the load during a certain period of time.

EFFECT: providing selectivity of loads shedding where short-circuit conditions occur, improving service life of the system and reducing active losses in the voltage inverter in short-circuit conditions.

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Description

The present invention relates to the field of electrical engineering and power electronics and can be used in the construction of alternating current electric power generation systems or guaranteed alternating current power supply systems, in which a static electric energy converter is used to reduce the mass and dimensions of the generation system, increase the working life. The primary sources with unstable input energy parameters in such systems can be an industrial frequency network, a synchronous generator with a variable shaft speed. The function of ensuring quality indicators of the generated electric energy is assigned to the static converter and the output power low-pass filter.

A known method of controlling a static converter of electrical energy [Device for controlling a three-phase frequency converter with direct connection: 983971 USSR No. 3304894 / 24-07; declared 04/15/81; publ. 08/23/82, bull. 47, 6 pp.], Based on the control valves of a three-phase frequency converter with direct connection, consisting in the fact that in the short-circuit mode in the load, the control signals are generated in the form of trapezoidal bipolar pulses with a duty cycle of two, and the phase of the pulses are shifted relative to each other at 120 email hail. the frequency of the output voltage of the Converter.

However, the disadvantage of this method is that in the frequency converter with direct connection in view of the final value of the ratio between the frequencies of the input and output voltages in the short circuit mode, a constant component occurs in the current, which greatly complicates the output from the short circuit mode. In addition, in the short circuit mode, losses in the valves increase sharply in this converter, because the voltage applied to them increases (in the load the voltage is zero due to a short circuit) and the current, which becomes equal to the short circuit current.

In addition, there is a known method of controlling a static converter in a power supply system [Transistor DC / AC transformer with electronic protection device: patent 2249295 Ros. Federation No. 2003111111/09; declared 04/17/03; publ. 03/27/05, bull. 9, 7 pp.], Which is the prototype of the present invention, namely, that in a system containing a constant voltage source, a voltage inverter and an output low-pass filter with a load, when a short circuit occurs in the load, the load current is measured and when it reaches a predetermined value, reduce the input voltage of the inverter to zero and close the transistors of the inverter.

The disadvantage of this control method is that in the short circuit mode there is no selective disconnection of the loads due to the burning of fusible inserts or the operation of the circuit breakers. When the inverter is turned on again, the short circuit mode will be identified again, many of these modes will reduce the working life of the system.

The objective of the invention is to ensure the selectivity of disconnecting loads in the short circuit mode in the load, which increases the working life of the system, as well as reducing active losses in the voltage inverter in the short circuit mode.

The problem is achieved in that in the known method of controlling a static converter as part of a power supply system, which consists in the fact that in a system containing a constant voltage source, a voltage inverter and an output low-pass filter with a load, the load current is measured in the short circuit mode and when it reaches a predetermined value change the control signal of the voltage inverter, providing the maximum possible value of the short circuit current, adjust the value of the constant voltage to During inverter stabilizing predetermined short-circuit current in the load for a predetermined time interval.

The drawing shows one of the possible structural diagrams that implements the proposed method of controlling a static converter.

It can conditionally be divided into a power circuit and a control system. The power circuit (SS) contains a controlled rectifier (HC) (11), the input of which is connected to a magnetoelectric generator (MEG) (10) (or any other generator), and the output to the input of a voltage inverter (ID) (12), the output of which connected to the input of the low-pass filter (LF) (13), the output of the latter through current sensors (17) is connected to the input of the load (14). The control system (SU) includes an amplifier (6), the input of which is connected to a current sensor (17), the output of the amplifier is connected to the input of a rectangular pulse shaper (5), a comparator (8), and a summing circuit (7). The second input of the summing circuit (7) is connected to the output of the reference signal source by the short circuit current (16), and the output of the summing circuit (7) is connected to the input of the current regulator (9), the output of which is connected to the second input of the switch (4), the first the input of the switch is connected to the output of the block (15), which forms the reference signal for the voltage of the rectifier Ud. The output of the rectangular pulse shaper is connected to the input of the voltage inverter, and the output of the comparator (8) is connected to the control input of the switch (4). The output of the switch is connected to the non-inverting input of the adder (3), the inverting input of which is connected to the output of the rectifier (11). The output of the adder (3) is connected to the input of the controller (2), the output of which is connected to the input of the pulse-phase control system (SIFU) (1), the output of which is connected to the input of the controlled rectifier (11).

Blocks of the circuit perform the following functions. The current sensor (17) measures the instantaneous value of the load current and generates a signal proportional to the amplitude value of the measured current. The source of the reference signal (16) generates the necessary setting for a given value of the short circuit current I _ass. Source (15) generates a reference signal for the value of the output voltage (U _d ) of the controlled rectifier in normal operation. The blocks of the power circuit 10-14 convert the mechanical energy of a synchronous generator rotating at a variable speed shaft into alternating current electrical energy with specified parameters. Blocks (3, 7) perform the function of algebraic summation, regulators (9, 2) perform the function of regulation according to a certain law of current and voltage, respectively, as an example, proportional-integral or proportional control laws can be implemented. The comparator (8) implements the sign (x) function, where x is the input signal of the block, in emergency mode, the logical unit value appears on its output, and with this signal in the switch block (4) the key is transferred from position “I” to position “2” thereby closing the short-circuit current control circuit. Amplifier (6) implements the functional dependence represented by the relation (1)

$$i_{\mathrm{at}sx}=\{\begin{array}{l}k{i}_{\mathrm{at}x},i_{\mathrm{at}x}>I_{s\mathrm{but}d};\\ 0i_{\mathrm{at}x}\le I_{s\mathrm{but}d},\end{array}$$

where k is a constant gear ratio;

i _in, i _out - input and output signals of the amplifier.

Block (5) generates rectangular bipolar pulses with a duration of each half-wave of 180 el. hail. according to the output frequency of the voltage inverter. SIFU (1) generates control pulses of HC thyristors, the moments of output of which depend on the value of the signal of the controller (2).

The proposed method is as follows. In normal mode, when the load current is less than the specified value of the short circuit current I _ass , voltage U _et is supplied from block 15 through the switch (4) connected to position “1” to the adder (3), where the operation of subtracting the real voltage from the output of the shock wave ( 11), from the reference voltage (15). The signal from the output of the adder is fed to the input of the controller (2), the output signal of which is fed to the input of the SIFU (1), and from there to the power switches of the HC rectifier (11). This closes the negative feedback on the output voltage of the controlled rectifier, which stabilizes the voltage U _d . The voltage inverter generates an AC output voltage of a given frequency and magnitude in accordance with the control method incorporated in it in normal operation (as a rule, this control method assumes the presence of high-frequency pulse-width modulation - PWM). The system functions as in the known methods, forming an AC voltage with the necessary parameters in the load.

In the event of a short circuit in the load (14), the signal received from the current sensor (17) exceeds the setting I _ass in value, resulting in a non-zero signal at the output of the amplifier (6). The consequence of the appearance of this signal is that rectangular bipolar pulses with a duration of each half-wave of 180 e. Are applied to the input of the voltage inverter. hail. according to the output frequency of the voltage inverter, this allows the voltage inverter to form the maximum possible current in the load. In addition, the comparator (8) is triggered, under the action of its output signal, the switch (3) puts the internal key in position “2”. In this case, the negative feedback closes according to the amplitude value of the load current. The feedback loop includes: a current sensor (17), an amplifier (6), adders (7 and 3), regulators (9, 2), a switch (3), SIFU (1), a controlled rectifier (11), a voltage inverter ( 12), a low-pass filter (13). As a result of this feedback, the current in the load becomes proportional to the value of the setpoint I _ass . This mode in the system saves a predetermined period of time (usually 7 ÷ 10 sec.), During which the part of the load in which a short circuit occurs selectively is switched off. After holding this period of time, the system is returned to normal operation.

In the short circuit mode, the load resistance is almost zero, the inverter transistors operate in 180-degree conductivity (do not limit the load current), therefore, the current in the load is limited by the longitudinal impedance of the low-pass filter (13), the value of which at the inverter output frequency is also small, t .to. The filter is designed to suppress harmonics of high frequency PWM. Therefore, a closed feedback loop on the load current will automatically reduce the output voltage of the controlled rectifier to the required value to create a given short circuit current in the load. Reducing the voltage at the inverter input and putting it into operation with a 180-degree conductivity in the output frequency will lead to a significant reduction in active power losses in the inverter transistors and HC filter capacitors, which will increase the life of the system.

Thus, the proposed method for controlling a static converter in an alternating current electric power generation system in a short circuit mode allows to selectively disconnect loads in which a short circuit mode occurs, which leads to an increase in the operating life of the system, as well as to a decrease in active losses in the voltage inverter short circuit mode.

Claims (1)

A method of controlling a static converter in a short-circuit mode of generating alternating current electric energy, comprising a constant voltage source, a voltage inverter and an output low-pass filter with a load, which comprises monitoring the achievement of a load current during a short circuit of a predetermined value, characterized in that at the time when the load current reaches the set value, the voltage inverter control signal is changed, providing the maximum possible value of the short-circuit current Addi ctive regulate the DC voltage to the inverter input, stabilizing the predetermined short-circuit current in the load for a predetermined time interval.