SU474095A1 - Control method for autonomous inverter - Google Patents

Description

one

The invention relates to the field of converter technology and can be used in valve frequency converters with a pulse width and pulse output voltage (current) (PWM) shaping.

A known PWM frequency converter control method is used to form the output voltage (current) from a series of square pulses that follow at a certain frequency (carrier frequency), the duration of which is nromodulated according to the law of modulating voltage.

The disadvantage of this method is the appearance of subharmonic components in the output voltage (current) due to the multiplicity of the carrier frequency and the frequency of the modulating voltage, especially noticeable at multiples below eight (carrier frequency to the frequency of the modulating signal).

In the case of the biennial modulation, in addition to the indicated deficiency, the asymmetry of the radiation along the half-waves can also occur. In the control of a three-phase inverter, voltage asymmetry in phases can also occur.

The described method is free from the indicated disadvantages due to the fact that the reference voltage generator forcibly returns to the initial state twice during the period at the moments of transitions of the modulating voltage.

voltage through zero value. In addition, the on-voltage voltage phase is inverted at the moments of the transition of the modulating voltage through zero. In a three-phase inverter, the reference voltage generator, the common

for all three phases, return to the original

state at zero time

modulating voltage of all three phases.

FIG. 1 shows a single-phase inverter; in fig. Figures 2 and 3 show diagrams, as shown in Figure 1.

For convenience of consideration, an illustration of this method is given with reference to a unipolar, one-way (trailing edge) sinusoidal pulse-width modulation.

The power part of the inverter is assembled according to a bridge circuit consisting of four fully controlled valves 1–4, four reverse diodes 5–8, and a load 9.

At the time of the formation of the positive half-wave output output U, (interval / 2- / 4, fig. 2, o), valve 4 is turned on, and valves 1 and 2 are switched in accordance with the law of sinusoidal width-pulse-controlled regulation: valve 1 at the beginning t / roii reference sawtooth voltage (steep negative decay, fig. 2, a and b), gate 2 in. comparing the positive front and positive half-waves of the modulating voltage U,. „|, (fig. 2, but not) .

Similarly, a negative half-wave of the output voltage L ,, (interval, fig. 2 a) is formed: valve 2 is lit continuously for the entire hf / G interval (fig. 2 a, and c), the trilogram turns on by a clock pulse (php 2, a and d), valve 4 is turned on at the moments of comparison of Y ™ and the positive front u, on (Fig. 2, a and e).

To eliminate the appearance of subharmonic components, their synchronization of the reference voltage f / gon is introduced in the output voltage (current) of the inverter, i.e., at the moments of the zero value of the modulating voltage UGM, the reference voltage returns to its original state therefore, each half-wave of the output voltage begins with a new cycle (time 2, U, te, Fig. 2, a), similar to all previous half-waves.

The incremental increments in the output voltage of the inverter due to the change in the duration of synchronized cycles (intervals, tz-t,, Fig. 2, a) are symmetrically distributed over the half-waves of the output voltage (current), which eliminates the appearance of a constant component in output voltage (current) of the inverter.

When using two-pole pulse-width modulation at the moments of synchronization of the reference voltage at the same time with returning to the initial state of the reference voltage f / roii, its phase should be reversed (Fig. Z.a), since the modulating voltage here, unlike modulation is also bipolar. In order to obtain the same wavelength of output, the polarity of the modulating and reference voltages in each half-wave must be the same (positive with a positive half-wave and negative with a negative half-wave).

In a three-phase inverter to obtain

voltage symmetry in phases; the reference voltage generator is common to all phases and therefore it should be synchronized six times during the period of modulating voltage with respect to the moments of voltage transition through zero value in all three phases.

Subject invention

Claims (3)

1. Control method for autonomous pnvertorO: M with pulse-width modulation, characterized in that, in order to eliminate subharmonics and asymmetry in the output voltage, the on-voltage voltage generator is forcibly returned to its original state twice in the non-period at the moments of the modulating voltage transitions through zero. 2. A method according to claim 1, characterized in that, in the case of bipolar modulation, in the transition point of the modulating voltage through zero invert the phase of the reference voltage. 3. A method according to claim 1, characterized in that, on a three-phase inverter, the on-line generator common to all phases returns to its original state at non-transitional moments through the zero modulating voltage of the other two phases. and