SU1700720A1 - Device to control the three-phase bridge inverter - Google Patents

Abstract

The invention relates to electrical engineering and can be used in a variable frequency asynchronous electric drive. The aim of the invention is to improve the harmonic composition of the inverter output voltage. The device contains a master oscillator 1, a modulo-six counter 2, three elements OR 4-6, a code converter 3. A code converter 8 is inserted into the device and three flip-flops 9-11. The introduction of these elements makes it possible to control the bridge inverter in such a way that when the three-phase load is disconnected from the power source of the bridge inverter, it is short-circuited. Due to this, the required constant ratio of the amplitude of the main harmonic of the output voltage of the bridge inverter to the frequency is achieved. 2 Il. 2 tab. S i / -

Description

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The invention relates to electrical engineering and can be used in a variable frequency asynchronous electric drive.

The aim of the invention is to improve the harmonic composition of the output voltage of the bridge inverter.

FIG. 1 is a diagram of a device for controlling a three-phase bridge inverter; in fig. 2 - time diagrams that show his work.

A device for controlling a three-phase bridge inverter contains a master oscillator 1, a modulo-six counter 2 connected by an input to the first output of a master oscillator 1, a converter of 3 codes programmed in accordance with the table. 1, connected by the first three inputs to the corresponding outputs of the counter 2, s by the fourth input to the second output of the master oscillator 1, three OR 4-6 circuits connected by the inputs to the outputs of the decoder 3, and the outputs to the control inputs of the power elements of the anode group of the bridge inverter 1 respectively.

In the device entered the converter 8 codes, programmed in accordance with the table. 2, and jpn RS-flip-flop 9-11. At the same time, the converter of 8 codes is connected with the three three inputs to the corresponding outputs of counter 2, and the fourth input to the first output of the master oscillator 1. Triggers 9-11 are connected by unit installation inputs to the outputs of the converter of three codes, and the zero inputs to the outputs of the converters 8 codes, and the outputs - to the control inputs of the power elements of the cathode group of the bridge inverter 7, respectively. Three-phase load 12 is connected to the diagonal of the bridge inverter 7.

The device works as follows.

The master oscillator 1 generates two pulse sequences of constant duration, following with an adjustable period t. At the first output of the generator 1, short pulses are formed with a duration that is determined by the time required for complete locking of the previously opened power element of the bridge inverter 7. At the second output, pulses with duration fa are formed. which sets the required amplitude ratio of the main harmonic of the output voltage of the bridge inverter 7 to the frequency.

Each formed pulse train is distributed over

six channels using counter 2 and converters 3 and 8 codes,

At the outputs of the OR 4-6 circuits, a three-phase sequence of groups of pulses arises, following with a period of 6m. Each group consists of three successive pulses of the second sequence. At the outputs of flip-flops 9-11, a second three-phase sequence is generated,

but already single pulses with duration (3T - TI), following with a period of 6m. This three-phase sequence of pulses is shifted relative to the first three-phase sequence in phase by

angle to

The time is necessary to eliminate the through currents that can occur at the moments of switching the power elements in the arms of the bridge inverter 7.

When the elements of the bridge inverter 7 are closed for a time equal to the duration of the pulses arriving at their control inputs, voltages with a period of 6 tons are generated at the three-phase load 12.

In this case, each half-wave is linear with 5

It consists of two voltage pulses with a duration of T2, shifted in phase by an angle l / 3.

FIG. 2 shows phased

0 diagrams of signals at the outputs of the blocks, illustrating the operation of the proposed device, where Ui-j is the signal at the jth output of the 1st

block; 1.26; i 1.211; UAB, Ivsiksa

-line output voltages of a bridge inverter 7.

When the power elements of the anode group are opened, the three-phase load, disconnected from the inverter power supply, is short-circuited, thus, no parasitic pulses are generated at the output of the bridge inverter.

Thus, the introduction of a second decoder and three flip-flops with the indicated links into the device for controlling the bridge inverter allows shorting. three-phase load when disconnecting it from the power source of the bridge inverter. Due to this, the constant amplitude ratio of the main harmonic is maintained.

0 of the output voltage of the bridge inverter to the frequency, thereby achieving a constant maximum torque of the induction motor with its frequency control,

Claims (1)

5 claims A device for controlling a three-phase bridge inverter, comprising a master oscillator with two outputs, respectively, short and long pulses, h a modulo-six meter, connected by an input to the output of short pulses of the master oscillator; a six-output code converter, programmed according to the table. 1, connected by inputs to the outputs of the counter modulo six and to the output of long pulses of the master oscillator, the first, second and third outputs to the first OR element, intended to be connected to the control input of the first power element of the anode group of the bridge inverter, third, fourth and the fifth outputs - to the second element OR, intended for connection to the control input of the second power element of the anode group of the bridge inverter, the fifth, sixth and first outputs - to the third element OR, intended to connect to the control input of the third power element of the anode group of the bridge inverter, characterized in that, in order to improve the harmonic composition of the output voltage of the bridge inverter, it is equipped with a second code converter for three outputs programmed in accordance with the table. 2, and three triggers, while the second code converter is connected by inputs to the counter outputs modulo six and k1 to the output of short pulses of the master oscillator, the first output to the input of the zero setting of the first trigger, the second output to the input of the zero setting of the second trigger, the third output - to the installation input zero of the third trigger, the first trigger is connected to the installation input of the unit to the fourth output of the first code converter, and the output is intended to be connected to the control input of the first power element cathode the bridge inverter, the second trigger is connected to the unit installation input to the sixth output of the first code converter, and the output is intended to be connected to the control input of the second power element of the cathode group of the bridge inverter, the third trigger is connected to the unit installation input to the second output of the first code converter, and the output is intended for connection to the control input of the third power element of the cathode group of the bridge inverter. Table 1 Table 2