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Large modifying frequency three-phase current-supply converters as well as their manage
Within this program, when the output is actually soaked, the difference between new operator production while the real returns was fed back to the enter in of your own integrator with a gain of K a to let the newest gathered property value the latest integrator are leftover from the an actual worth. The obtain regarding a keen anti-windup operator is normally chosen since the K an effective = step one / K p to end the fresh personality of your own restricted voltage.
Fig. dos.37 reveals the fresh experience off integrator windup for an effective PI current control, that’s produced by a big improvement in the fresh reference value. Fig. dos.37A shows the brand new show out of a recent controller as opposed to an enthusiastic anti-windup control. Simply because of its over loaded returns current, the genuine newest shows a big overshoot and you may an extended mode go out. In addition, Fig. 2.37B suggests a recently available control having an enthusiastic anti-windup manage. In the event the output is saturated, the brand new built-up worth of new integrator will be left within a good proper worth, causing a better show.
2.6.dos.step 1 Progress choice process of the fresh proportional–integral current control
Discover manage data transfer ? c c of one’s current controller to be within 1/10–1/20 of your own switching volume f s w and less than step one/25 of your own testing volume.
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The fresh actions step 1 and you can 2 try interchangeable together, we.elizabeth., brand new modifying regularity will be dependent on the required data transfer ? c c for current-control.
a dozen.dos.dos Steady region of single-loop DC-link 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.
