SU686138A1 - Three-phase frequency converter control method - Google Patents

Description

(54) METHOD OF MANAGING THREE-PHASE FREQUENCY CONVERTER

The invention relates to the field of converter technology and can be used in three-phase frequency converters with an explicit or implicit DC voltage link intended for a frequency-controlled electric drive. "Methods are known for controlling three-phase frequency converters for an adjustable electric drive by pulse-pulse module output voltage (PWM), over which switching of controlled gates is performed by comparing triangular or sawtooth carrier signals from three hfasny sinusoidal, trapezoidal or triangular modulating signals 1. The disadvantages of these methods of implementing PWM are the increased complexity of their control systems, the increased performance requirements of the power section of these systems, the limitation of the upper limit of output voltage regulation, which leads to the difference between the maximum output voltage at PWM and voltage in the DC circuit of the converter, There is also known a method that is realizable by the converter with a UMM output voltage With in-phase rectangles with modulating and carrier signals, having a ratio of periods, expressed by integers, and coinciding in phase 2. This method of voltage regulation is called pulse-width regulation (WID). 4 The advantages of voltage regulation are "1 SHIR method" that are reduced. as compared to the PII, the switching frequency of the power switches and the absence of subharmonic components, and the disadvantages, the lower order of higher harmonic components in the output voltage than in the PWM, and relate them Flax high content. The closest to the invention to the technical essence and the achieved result is a method of controlling a three-phase frequency converter for an adjustable electric drive by pulse-width modulation by rectangular modulation and carrier signals with the closure of all phases of the load on one of the power poles at intervals of zero pauses between pulses 3. The disadvantages of this method, based on, are a lower order of higher harmonic components in BFJXoiiHOM voltage to their relatively high Content The purpose of the invention is to increase in the order of higher harmonic components in the output voltage to reduce the ripple of one second of the drive torque and simplify the implementation. This goal is achieved due to the fact that, when generating control signals, do not change the duration of the carrier signals that form the first (last) two-thirds of the half-wave voltage pulses in kDa phase, from the front (front) front, the signals that form the last (first a third of the half-wave voltage in each phase. FIG. 1-5 are diagrams of control signals that implement the proposed method of controlling a three-phase frequency converter and the corresponding forms of the phase voltage, with the diagrams in FIG. 1 and 2 correspond to a bipolar control signal system; in fig. 3 and 4 - unipolar, diagrams in FIG. 5, the control of converter valves at different phase current displacements in the case of a unipolar signal system is explained; Fig. 6 is a block diagram of a control oscillator generating signals for implementing the proposed method for controlling a three-phase frequency converter. The figures contain the following designations: M and Md are modulating signals for the cathode and anodic groups of the same phase, H and dH are carrier and truncated carrier signals, respectively, G and Gd are the control signals of the cathode and anode ventilators, Bx, BO and I Signals of valve glueing in rectifying and inverting modes, respectively, for the cathode and anode groups, and - the output phase voltage, and / - the input signal for frequency control, Tsu-input signal for voltage control. FIG. Figure 1a shows the in-phase rectangular modulating signals M and Md for a single phase of a three-phase sistem1T and carrier signals H with a ratio multiplicity of their periods equal to 12, All control signals G, and Gd, shown in FIG. 1-5, are formed on the basis of modulating and carrier signals, Nschoven, E {s in FIG. 1a FIG. Figure 1 shows two-point control signals with shortened 1 and from the side of the front front by signals that form the last third of the half-wave voltage. In addition, in FIG. and one carrier signal is shortened, which forms the last voltage pulse, and in FIG. 16 both signals, FIGS. 2a and b show bipolar control signals I1, Ij, and G, respectively, with one and two carrier signals shortened from the front Fronts. Forming the first third of the half-wave voltage. The phase voltage in FIG. 1 and 2 correspond to 1 of the control signals shown on each of them. FIG. Pros and b show unipolar control signals G and Gd, equivalent to the bipolar signals in FIG. 1a and b, t, e, respectively, with the shortening of one and two carrier signals, forming the last third of the half-wave voltage, the unipolar control signals with the shortening of the carrier signals, forming the first third of the half-wave voltage, equivalent to the signals in FIG. 2a and b are given respectively on Fng. 4a and b. The phase voltages Uq do not depend on whether a single or two polarity control signal is applied, i.e. identical respectively to FIG. 1a and 3a; FIG. 16 and ST, etc. Using the example of the unipolar control signals shown in FIG. Pro, the diagram in FIG. 5 shows the inclusion of single-phase valves in the rectifying and inverting modes, depending on the amount of lagging shift of the signals of the current direction indicators. According to the proposed three-phase frequency converter control method, the width-modulated voltage is generated as follows. In converters with a direct link voltage - autonomous voltage inverters, control is performed, as a rule, by bipolar control signals. The activation of the controlled valves of the cathode and anode groups of the power circuit is carried out according to the control signals without tracking the phase of the current. During the moments of pauses between voltage pulses, all the gates of one group are turned on, and the closure of the load current of all phases is carried out along circuits containing reverse gates of the gates of this group. Control signals, formed from the in-phase system of modulating and carrier signals of the same width for all three phases, form a voltage regulated by the WIDER method, i.e. a non-modulated pulse voltage sequence in a three-phase system. The narrowing of one carrier signal, which forms the last rj r: c5v5v5. Without a voltage pulse (fig. 1a), leads to modulation, i.e. reversing the sign or changing the amplitude of the second pulse, if the period of the output frequency voltage is formed from the pulses, all voltage pulses are modulated if all carrier signals on the last third half-wave at a given multiplicity and modulating signals are narrowed - two signals (Fig. 16). The narrowing of the pulses, which form the first third of the half-wave voltage (Fig. 2c and b), leads to similar forms of voltage, but having a phase shift in the opposite direction to the original, controlled by the RR method. Uni-polar iMoryT control signals are used only with current direction indicators, which are fundamentally necessary in frequency converters without an explicit DC link of direct frequency converters with artificial switching; 1, and where the inverter current is passed through controlled gates . In this case, the controlled valves are turned on either in the rectifier or in the inverter mode. In the presence of a modulating signal of the cathode (anode) group M (M), the cathode direct mode (the anode group of valves C (A)) turns on with the presence of a control signal D (D) if there is no signal from the indicator of the current of the anode (cathode) group Td (T) , and at the opposite voltage half-wave, i.e. under the action of the signal Mp (M, the rectification mode is activated at intervals between the control signals Gd (G) in the presence of a signal of the indicator of the current direction of the cathode (anode) group T (TD). Inverter cathode (anode) mode valve trials AND (HQ) under the action of the signal M (M) is switched on at intervals between control signals (Gy), if there are no signals from the current direction indicator of the anodic (cathodic) group TO (T), and in the interval of the current lagging under the action of the signal Md (M) - in the presence of control signals Gd (H) The control of the transformer valves according to the described algorithm with different values of the lagging shift k is illustrated by the diagrams in Fig. 5b, c, the guide, and the phase voltage generated in this block in fig. 5e, For forming control signals that implement the proposed control method of a three-phase frequency converter by pulse-width modulation, a slightly modified control generator can be used (Fig. B), used for converters with the UNR. The input signal to the frequency control Uj .. is fed to the master oscillator 1. Its output signal is fed to the ring scaling circuit 2 and the clock input of the generator 3 carrier signals. To the other input of the generator 3 receives an input signal for regulating the voltage of the converter and ,,. Signals from the output of the cxe; vfci 2 recalculate trigger six to the anal shapers 4 modul1 p 1.c; cycle M and 5 auxiliary m (shifted in phase by 30 relative to the modulating) signals. The fop 1 driver 6 controls the logical processing of incoming signals M, Mj H and DN at its inputs generates control signals r. The proposed control method increases the order of higher hapmonic components in the output voltage, which reduces the ripple and torque of the drive motor and simplifies control system, T-formula of invention. Three-phase control method. frequency converter to regulate the drive by pulse-width modulation of the output voltage by rectangular modulating and carrier signals with the closure of all phases of the load to one of the supply poles at intervals of zero pauses between voltage pulses, in order to increase the order of higher harmonics components in the output voltage to reduce the ripple torque of the drive motor and simplify the implementation, when generating control signals, do not change the duration The carrier signals that form the first (last) two thirds of the voltage half-wave pulses in each phase shorten the carrier signals from the rear (front) front, which form the last (first) third voltage half-wave in each phase. Sources of information taken into account in the examination 1. AS. Gustsky Yu.M. Thyristor Inverters with Pulse Width Modulation, M., Energie, 1968, p. 20-23. 2.Trenikhin V.V. The advantages of the synchronous method of frequency control in the inverter with pulse-width NELM regulation of the output voltage. Sb.trudov LIIZHT, vol. 336, L., 1972 3. Doroshin E.R. Principles of pulse-width voltage control of frequency converters. E.P., Converting Technique, Inform-Scientific and Technical Collection, Vol.6 (65), 1975, p. 17-20 - the prototype.

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