SU752688A1 - Frequency converter control method - Google Patents

Description

one

The invention relates to methods for controlling a valve-mounted frequency converter for controlling the operating modes of an asynchronous, including a traction motor, connected via a converter to a power source. The proposed method can be used primarily in two-link converters, in particular, consisting of an autonomous inverter (AI) and a direct frequency converter (NFC).

In the general case, a rectifier and a stand-alone inverter can be included in the input link of the converter, or a direct frequency converter with artificial switching, or any alternating current source with a smoothly controlled frequency.

The known methods of controlling the converters of this structure and the devices that implement them 1 consist in that the supply of control pulses to the valves of the AI and FFC power circuits is carried out in such a way that the output frequency is controlled in the output link.

Disadvantages of the known methods are discreteness of adjustment of the output frequency, which is determined by the frequency of the alternating voltage at the inverter output (intermediate frequency of the converter) and the number of phases at the NFC input, and the upper limit of the output frequency depends on the intermediate frequency of the converter and the number of phases in the intermediate link and at the exit of the second link.

The introduction of a half-cycle variable output voltage of the LPS control angle allows to increase the smoothness of the controlled output frequency of the converter, but complicates the NFC control system and makes it difficult to compensate the reactive power at its input, which increases the installed electrical equipment power.

15 AI and converter as a whole. Therefore, the NFC with a constant adjustment angle, varying in a sinusoidal or triangular law, did not find practical application in electric drives with ns20 alternating current motors.

It is possible to increase the smoothness of adjusting the output frequency of the converter by choosing the number of half-waves of the intermediate frequency voltage that form the half-periods of the LPS output voltage curve.

In this case, the output voltage will contain subharmonic and constant components, which is unacceptable

The work of the generator on the asynchronous motor.

The proposed method aims to eliminate these disadvantages. This goal is achieved by dividing the entire output frequency control into noddnanazonny, inside each of which the output frequency control is carried out by changing the frequency of the NPCH source and maintaining the frequency ratio of the input to the output frequency of the NFC, but not from one range to another. by changing the indicated multiplicity of the voltage of a constant initial output frequency on the probes under investigation and the final output frequency on the usual subdiasenes.

The method is described by the example of a converter, in the input link of which a stand-alone inverter (AI) of current or voltage is established, and in the output link - a direct frequency converter (NFC). The block diagram of the converter is shown in FIG. 1, where 1 -AP, 2- NPC. In this case, the AI can be performed with both single-phase and three-phase output. Accordingly, the NFC should have single-phase or three-phase input.

FIG. Figure 2 shows diagrams of a jannip in intermediate link U n at the output Vz of a two-link converter, the power circuits of which contain an autonomous naryl inverter (AIN) with a single-phase output and a NFC with a three-phase output. The output frequency control range is 1.5-150 Hz, which, for example, is generally accepted at the frequency control of asynchronous motors for traction electric drives.

In this case, for intermediate frequencies, it is possible to limit by intermediate values, for example / 450 Hz, and the range of variation of the intermediate frequency (or AIN frequency) in each range will be 225-450 Hz. Then the value of the ratio of the frequency of the FPA to the output frequency of the NFC but as the output frequency fz decreases

 3-2J, where, 1, 2, 3 ...

/ 2;

It is strictly possible to use another law of change / Skr, for example

, 2, 3 ...

/ 2;

But In this case, the frequency control range (i) in each range of the changed output frequency will not be constant, which in a certain degree makes it difficult to implement it in the control system and the inverter.

The range of output frequency, 5-150 Hz, can be divided by the proposed method of control, for example, into 7 subnapasons, within each of which the output frequency fz and the frequency of Qc vary in accordance with the table

FIG. 2 illustrates the transition from 5 to 6 and from 6 to 7 subbands of variation of the output frequency of the converter.

As can be seen from the table and FIG. 2, in the whole range of variation of the output frequency of the converter, its smooth regulation takes place, which cannot be achieved with the known control methods.

The proposed converter control method allows for smooth control of the output frequency over a wide frequency range with high quality output voltage waveforms (symmetry, the absence of subharmonics, and a constant component). In addition, due to the small frequency control range

At the output of the autonomous inverter, the installed power of the power circuit elements of the inverter and, consequently, of the converter as a whole, is reduced. The application of the method is particularly advisable in converters designed for frequency control of electric drives with asynchronous motors and, in particular, traction drives.

Claims (1)

Invention Formula A method of controlling a frequency converter containing a power supply with an up-level controlled frequency with the output connected to its output. mon. rm frequency and designed primarily for a frequency-controlled electric drive by changing the output frequency of the direct frequency converter, characterized in that, in order to increase the control of the output frequency and reduce the installed power of the converter, the entire range of change of the output frequency of the converter is divided into subranges, within each of which the output frequency is controlled by changing the frequency of said source while maintaining the same the ratios of the input and output frequencies of the direct converter, and when switching from one subband to another - by changing the specified multiplicity while maintaining the initial starting frequency on the subsequent subband and the final output frequency on the previous subband. Sources of information taken into account in the examination 1. USSR Author's Certificate No. 179829, H 02M 7/515, 16.01.63. P If „con. f .e h5ogts