High altering regularity about three-phase latest-resource converters in addition to their control

Within this design, if the efficiency was saturated, the essential difference between brand new control productivity plus the real output was given returning to this new input of integrator having a gain out of K a so that the brand new built-up worth of the fresh integrator will likely be remaining within a real worth. Brand new acquire of a keen anti-windup controller is commonly chose just like the K good = step one / K p to avoid this new personality of one’s restricted voltage.

Fig. dos.37 reveals new phenomenon out-of integrator windup having a good PI most recent control, which is from a big improvement in the latest reference well worth. Fig. 2.37A suggests the fresh results of a recent controller without a keen anti-windup handle. Due to the saturated yields current, the actual newest showcases a giant overshoot and you can a lengthy mode date. Simultaneously, Fig. dos.37B reveals a recent operator that have an enthusiastic anti-windup control. In the event that productivity was soaked, the collected property value the brand new integrator should be kept from the a beneficial best worthy of, causing a far better results. Increases alternatives means of new proportional–integral latest controller

Discover enlace favorables manage bandwidth ? c c of your most recent operator to-be within this step 1/10–1/20 of your modifying regularity f s w and less than 1/twenty five of the sampling frequency.

The brand new methods 1 and you may dos was compatible with each other, we.elizabeth., the fresh modifying frequency should be determined by the necessary data transfer ? c c to possess current control.

twelve.dos.2 Stable area for unmarried-circle DC-hook up current-control

According to the Nyquist stability criterion, a system can be stabilized by tuning the proportional gain under the condition, i.e., the magnitude is not above 0 dB at the frequency where the phase of the open-loop gain is (-1-2k)? (k = 0, 1, 2.?) [ 19 ]. Four sets of LC-filter parameter values from Table 12.1 , as listed in Table 12.2 , are thus used to investigate the stability of the single-loop DC-link current control. Fig. 12.4 shows the Bode plots of the open-loop gain of the single-loop DC-link current control Go, which can be expressed as

Figure 12.4 . Bode plots of the open-loop gain Go of the single-loop DC-link current control (kpdc = 0.01) corresponding to Table II. (A) Overall view. (B) Zoom-in view, 1000–1900 Hz. (C) Zoom-in view, 2000–3500 Hz.

where Gdel is the time delay, i.e., G d e l = e ? 1.5 T s and Gc is the DC-link current PI controller, i.e., Gc = kpdc + kidc/s. The proportional gain kpdc of the PI controller is set to 0.01 and the integrator is ignored since it will not affect the frequency responses around ?c1 and ?c2. It can be seen that the CSC system is stable in Cases II, III, and IV. However, it turns out to be unstable in Case I, because the phase crosses ?540 and ?900 degrees at ?c1 and ?c2, respectively.

To further verify the relationship between the LC-filter parameters and the stability, root loci in the z-domain with varying kpdc under the four sets of the LC-filter parameters are shown in Fig. 12.5 . It can be seen that the stable region of kpdc becomes narrow from Case IV to Case II. When using the LC-filter parameters as Cases I, i.e., L = 0.5 mH and C = 5 ?F, the root locus is always outside the unity circle, which indicates that the system is always unstable. Thus, the single-loop DC-link current control can be stabilized with low resonance frequency LC filter, while showing instability by using high resonance frequency LC filter. The in-depth reason is that the phase lag coming from the time delay effect becomes larger at the resonances from low frequencies to high frequencies, which affect the stability of the single-loop DC-link current control.

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