SU752748A1 - Three-phase frequency converter control method - Google Patents

Description

one

The invention relates to a converter technique and the molset should be used in three phase frequency converters with a clearly or implicitly expressed constant voltage link intended for a variable frequency drive.

Known methods for controlling the three-phase converters frequency to link the DC voltage to the controlled electric drives with shnrotno-pulse control (br) voltage INS load soednnenii in are realized star or by switching the thyristors in the two output phases nodklyucheniyh narallelno one conclusion pitayugtsey network, or by switching the thyristors of the third phase of the load, in series, to two parallel and connected to the phase of the network of opposite polarity 1.

The control signals that implement these WIDs are generated by summing the unregulated and adjustable parts. The unregulated part of the signal in the first of the above methods of WID is in the range of 60-120 °, and in the second, the sum of the O-60 ° and 120-180 ° intervals of the output voltage half-wave.

There is a known method of controlling transducers, in which the control signals

they are formed only in the presence of a modulating signal related to a given voltage wavelength 2. In this method using current direction sensors

5 switching on the rectifying mode of the cathode Ba (anodic V.x) valves of the phase A group, for example, was made not only in the presence of a control signal of the cathode Ha (anodic Gh) group and the absence of a signal

10 current sensor of the opposite group Tj (Ta), but also in the interval of the lagging current shift by the opposite half-wave in the presence of a modulating signal of the anode Ala; (cathodic Ma) group and absence

15 control sigial T (Ha), i.e.

in „gd, -f / and / d and B, g, m / d.

With such a control algorithm, if the lagging shift of the signal of the current direction sensor by the opposite half of the waveform does not exceed the duration of the first part of the sigpal control, then the switching is performed at the time of the end of the voltage pulses.

25 If the lagging current shift exceeds the specified limit value, i.e., to the momeit of the first part of the control section, the phase valves are switched on in the imperator mode, then the rectifier

30 mode is on at the moment of pause between

control signals. In this case, the moment of artificial switching coincides with the end, and with the start of the n-pulse that forms the voltage wave of this phase. However, in this way, in the event of significant phase shifts in the load current, the number of art commutations increases, and the limiting signals in the extreme limits of the control of the width of the voltage pulses and the intervals between them appear and continuously form control signals.

Closest to the described method of controlling a three-phase frequency converter for controlling an electric drive with pulse-width modulation of output voltage, which consists in closing all phases of the load on one of the supply poles at intervals of zero pauses between voltage pulses by generating signals of unregulated duration adjustable carrier and shortened signaling 3.

This control method allows to increase the order of higher harmonic components in the output voltage compared to WID and thereby reduce the ripple torque of the drive motor, as well as to simplify the implementation of pulse width modulation (PWM) converter inverting. The disadvantage of this control method, with the known implementation method of which the sigpal of unregulated duration as well as with the first of the listed WID methods, is formed in the 60-120 ° section, is limited to the extreme limits of the control of the width of the voltage pulses and zero pauses, as well as dependence of the frequency of artificial commutation on the phase shift of the load current under the described control algorithm.

The purpose of the described control method is to extend the functionality by increasing the limits of the regulated voltage. The goal is achieved by the fact that the signals forming the voltage half-wave are filled with unregulated signals at intervals O-30 ° and 90-150 °, the interval between them is filled with carrier signals, and the interval 150-180 ° - with carrier signals shortened with sides of the rear fronts.

FIG. 1 shows a diagram of an apparatus for generating signals implementing the described control method; in fig. 2 is a diagram of signals according to the described control method; in fig. 3 is a diagram illustrating the generation of control signals for the method described.

In the drawings, the following notation is accepted: 1-4 - AND logical elements; 5 - logical element OR (Fig. 1); G - control signals; M - modulating signals; a, x, o, y, c, z are auxiliary sigals that destroy the modulating phase in the DZ; T - sigals of current direction sensors.

All the above signals related to the cathode grooves of the valves, in accordance with their belonging to the phases, are marked with the indices a, b, c, and to the iodimes x, y, z; IS / C, (... - moments of artificial

switching the converter valves, corresponding to the signals of the sensors and the direction of the current IT, 2T, and so on; Ua is the output voltage of phase A; N and DN - respectively carrying and shortened by

trailing edge carrier signals.

In the diagrams of FIG. 2, a, b, and c are the control signals Ha, G ;, Gs and Gh, Gu, Gg, formed by the described method (for modulation ratio K. 1,

/ (2 and K,. For all modulation multiplicities, an output of Na is given, and for K, 1, / (2 (Fig. 2, a and 2, b) is a signal from the sensors of the direction of current of phase A and the moments of artificial commutation. Corresponding to two and three different lags from the scientific research institute of the current phase from the voltage.

FIG. Fig. 3 shows the modulating signals of the cathode Ma, Mi, MS and the anode groups of the M, My, Mz valves, as well as the auxiliary signals, a, b, C, X, Y, Z, which are ahead of them in phase by 30 °. and auxiliary signals that form unregulated parts of the control signals, and produce modulating, auxiliary and carrier signals, as well as modulating, auxiliary and shortened from the rear edges of the carrier signals, which form adjustable parts of the control signals. The diagram also shows the signals Ha, Hb, Gsn YX, Hy, Gg, which are formed by summing the corresponding regulated and unregulated signals.

The control method of the three-phase frequency converter is implemented as follows.

Areas of control signals of unregulated duration are formed on

intervals 0–30 ° and 90–150 °, the interval 30–90 ° is filled with carrier signals, and the interval 150–180 ° with carrier signals with shortened trailing edges (Fig. 3, a, b, c). In the control signals generated in this way, zero voltages between the impulses are formed by switching the valves of the same phase, in series with the other two, connected in parallel to each other.

friend to the conclusion of the source iitani other polarity. With the described control algorithm, an increase in the phase shift between current and voltage leads to a reversal of the switching moment from the moment of

the end of the output voltage pulse at the time of its beginning (12 / C and 21, K in Fig. 2, a, ISK and 2S / C, 2I.K and WE / C in Fig. 2, b). Since with this method of generating control signals a single phase is switched at each moment, the transfer of switching times does not affect their number, therefore, the switching frequency does not depend on the phase shift between current and voltage.

Control signals for this control method are generated as follows (FIG. 3).

By producing the corresponding modulating and auxiliary signals shifted in relation to them by 30 °, the necessary intervals of the unregulated duration of the control signals are selected. The product of the modulating and auxiliary signals related to the generated half-wave and the carrier signal fills the adjustable part of the control signal at an interval of 30-90 °, and the product of the modulating signal and the auxiliary signal related to the opposite half-wave of the same phase is a shortened carrier signal at the interval 150- 180 °. Logical expressions for generating control signals, e.g., Phase A, are defined by the following expressions:

Ga Md-c-f Md-a-H-f a - & - f + M.; c-H +; c.y + M -a-AH.

The generation of control signals for the present control method is performed by the output generator of the control generator containing six identical AND-OR gates. A diagram of one such element, the inputs of which are connected to form the signal Go, is shown in FIG. 3. The specified element contains four elements of type And, each of which forms a signal, respectively, at intervals of 0-30 °, 30-90 °, 90-150 ° and 150-180 °. Summation of these signals

element OR forms the control signal of the valves (gates) of the cathode or anode group of the same phase.

A variable frequency drive for an adjustable drive using the present control method has improved functionality due to an increase in voltage control limits and a decrease in the frequency of commutation.

Claims (3)

1.Labuntsov V.A., Zabrodin Yu.S., Sytin A.P. Pulseless width control method for autonomous inverters with a form independent of load parameters output voltage curve. M., “Proceedings of MEI, vol. 275, 1975, p. 27-35. 2. USSR author's certificate L 547029, cl. H 02 P 13/30, 1977. 3. USSR author's certificate for application No. 2325725/07, cl. H 02 P 13/18, 1976.