Abstract: Studied one kind to control and the redundant control invertor control technology based on Shuanghuan, this plan attached one outside the electric current link and the instantaneous electricity pressure ring repeatedly to control the link. After realizing the output voltage decoupling and the perturbation electric current compensation, enabled the invertor according to the dead beat principle design’s Shuanghuan controller to achieve the very quick dynamic response speed; Increased the stable state precision located at the outer layer redundant controller. This plan invertor obtains the confirmation in a station base in DSPTMS320F240 on control system’s PWM.
Key word: Invertor; Shuanghuan; Dead beat; Redundant control
Introduction
Adjusts the PWM invertor’s in low power situation massive uses along with the closed loop, is also getting higher and higher to its output voltage profile’s request. The high grade output wave shape not only requests the stable state precision to be high moreover requests the dynamic response to be quick.
The traditional single closed-loop system is unable to use system’s status messages fully, therefore, the output feedback will change the state feedback, changes an invertor pair of too close s territory axis of imaginaries’s extreme in the state space through the reasonable choice feedback gain matrix, increases its damping, can achieve good dynamic effect [1]. The single closed loop is similar in the resistance load perturbation aspect and the direct current machine, only then, when load perturbation influence after the out-port displays finally, can present the corresponding error signal drive regulator, additionally builds electric current link limit starting current and the constitution electric current servo system may also speed up the resistance perturbation greatly dynamic process [2]. The spurt value feedback adopts enhances the system dynamic response the method to eliminate the error of tracking, but the static characteristic is not good, but based on the cyclical control is through to error’s periodic compensation, realizes the stable state not static difference effect, it mainly divides into repeatedly controls [3] and overtone reaction control [4].
This article proposed one kind controls and the redundant control invertor control plan based on Shuanghuan, gives dual attention to the invertor to move the static effect, moreover the running condition sight enhances the numerical control system performance.
1 invertor mathematical model
Single-phase half bridge invertor as shown in Figure 1, L is outputs the filter inductance, C is outputs the filter electric capacity, the load is random, r is outputs the inductance equivalent resistance and the dead area and so on each kind of damping factor grand total. U is the PWM voltage which the contravariant bridge outputs.
Choice inductance electric current iL and electric capacity voltage vc takes the state variable, id regards as the disturbance input, obtains half bridge invertor’s continual condition mean space model is
According to type (1), very easy to obtain invertor’s under frequency range block diagram, as shown in Figure 2. The PWM invertor’s dynamic model and the direct current machine are similar, the rotational speed server’s design method is also suitable in here. This article profits from the direct current machine Shuanghuan control technology, and transforms into the multi-link control system, has made the very good progress in the invertor profile control.
2 control program analysis
This control plan and is situated the outer layer including the Shuanghuan control system the redundant control system. In the transient wave form control situation, control algorithm’s execution time and a/D transformation time delay are opposite in the sampling period usually may not neglect, it is necessary to use the condition sight, will use its forecast function the control algorithm a racket to carry on ahead of time. This plan uses the dead beat sight carries on the forecast to the output voltage and the inductance electric current.
2.1 Shuanghuan controls
Shuanghuan control system diagram as shown in Figure 3, Z (s) is the unknown load. Needs to examine the signal which and to feed back to have three, namely inductance electric current iL, output voltage vc, load current id. The inductance electric current examination supposes for the electric current link. Is similar with the direct current machine, the examination output voltage not only uses in the voltage transient wave form control moreover realizing the output voltage decoupling, eliminates the output voltage to the electric current link’s perturbation, lightens the electric current link controller’s burden. Similarly, the load current to the instantaneous electricity pressure ring is also an exterior perturbation, the compensation load current can suppress it effectively to the output wave shape influence, increases the stable state precision. Is precisely because has carried on the compensation to the load current, the electric current link does not need to the load current perturbation to carry on suppresses, therefore, this plan feedback capacity electric current, but will disturb contains in feedback loop’s forward channel. If uses the charging current feedback, must obtain the good perturbation to suppress the effect, will certainly to cause the electric current link’s gain to be oversized. Not only this is disadvantageous to the stability, moreover causes the over modulation to increase, the electric current track’s rapidity is affected.
The analogue control system’s closed-loop pole is farther to the axis of imaginaries the dynamic response to be quicker, but is unable it to dispose negative infinitely to the s plane place, but the s plane negative is mapped infinitely the z plane zero point, if disposes completely numerical control system’s closed-loop pole to the plane zero point, then may achieve the extremely quick dynamic response speed, this is the so-called dead beat technology.
Because this plan has realized the output voltage decoupling and the load current compensation, the electric current link and the electricity pressure ring’s structure big simplification, controller’s design may to use the P link merely simply. Here uses dead beat principle determination electric current link controller KC and instantaneous electricity pressure ring controller KV.
2.1.1 electric current link design
Shown in Figure 4(a) for the electric current link diagram, to realize the output voltage overlapping feedback decoupling, the control algorithm (2) gives by the type.
vcom(k)=KC(iL*(k)-iL(k)) vc(k) (2)
In the formula: iL* is the inductance electric current instruction;
vcom is the control quantity which the electric current link calculates.
After Figure 4(b) is the decoupling, simplifies the electric current link diagram, ZOH is the zeroth order retainer. Will use the zeroth order retainer law the controlled member discretization.
Gc (z) =Z [(1-e - ts) /s) (1/L)/(s a) =1/r (1-e - aT)/(z-e - aT) (3)
In the formula: T is the sampling period;
a=r/L.
Closed-loop system's secular equation is
According to the dead beat principle, disposes completely its characteristic root in the zero point, therefore has
2.1.2 instantaneous electricity pressure ring design
Because the electric current link's cut-off frequency is higher than the instantaneous electricity pressure ring, wants far to the electric current instruction's track speed quickly in the instantaneous electricity pressure ring to the profile track, when design instant electricity pressure ring may think that the inner rim is a constant gain link. Figure 5(a) is the instantaneous electricity pressure ring diagram. Carries on the compensation after the load current, the corresponding control algorithm (6) gives by the type.
icom(k)=KV(vref(k)-vc(k)) id(k) (6)
In the formula: vref is the sine reference voltage;
icom is the electric current ring finger command which the electricity pressure ring figures out.
, and after Figure 5(b) is compensates the load current, neglects the electric current link dynamic process the simplified electricity pressure ring. Similarly determines electricity pressure ring controller KV with the dead beat principle.
Obtains the separate controlled member transfer function with the zeroth order retainer law is
Its closed loop secular equation is
z-[1-(KvT/C)]=0 (8)
Disposes completely the closed loop characteristic root in the zero point, obtains
KV=C/T (9)
Figure 6 is the invertor logarithm frequency response curve, the dashed line for the split-ring frequency characteristic, the solid line after passing through the decoupling and the compensation the Shuanghuan dead beat system’s closed loop frequency characteristic. Very obvious, the invertor split-ring resonance peak has been sliced off, the Underdamping nature originally had the enormous improvement, is also advantageous regarding the stability. The closed loop band width increases 2kHz, the dynamic response speed speeds up greatly.
The instantaneous electricity pressure ring the compensation which carried on to the load current has suppressed the waveform distortion which to a certain extent caused by the load. But this kind of compensation when the electric current link’s transfer function is 1 can carry on completely, otherwise, gives the compensation signal always has the phase error. When design instant electricity pressure ring can only think approximately the electric current link transfer function is 1, therefore, Shuanghuan system, although can achieve the very quick dynamic response speed, but to suppresses the waveform distortion effect which the rectification load creates to be limited. In order to obtain the better stable state profile, will use one kind to be able inevitably to compensate the perturbation completely the plan, the redundant control is one mature effective method. This control plan joins a redundant control link constitution compound control system in the electric current voltage Shuanghuan’s foundation. It located at Shuanghuan’s outer layer, carries on the control to the stable state profile quality.
2.2 redundant controller designs
As shown in Figure 7, PB(z) is designs the good Shuanghuan system, the load and other factor influence measures d by the perturbation equivalent. The redundant controller’s output superimposition above the original reference input, has the correction function.
The redundant controller is composed of the cycle delay regeneration link and compensator KrzkS(z), N is the digital controller the time sampling number of times, Q(z) uses to strengthen system’s stability every week, Chang Quwei 0.95. The cycle delay regeneration link carries on to the invertor outlet error by the fundamental wave cycle accumulation. Compensator’s function is realizes, the low frequency cancellation and the high frequency weaken with the invertor object, like this is redundant the compensation signal which the cast (i.e. cycle delay regeneration link) gives to be able the peak-to-peak value and the phase correctly with the perturbation cancels, realizes the stable state profile no discrepancy. After PB(z) adds Shuanghuan’s equivalent invertor object, might see its resonance peak from Figure 6 already to counter-balance, therefore, compensator’s design big simplification, only need complete the high frequency weaken and the phase compensation function. Kr is the redundant controller increases, S(z) takes is a cut-off frequency and the PB(z) approximate second-order filter realizes the high frequency weaken, link Zk realizes the S(z)PB(z) phase compensation in advance. As a result in advance link’s existence, therefore introduction cycle delay link z-N, otherwise, the redundant controller is unable physics to realize.
Because of the z-N introduction, the redundant controller must retard a fundamental wave cycle to the perturbation correction, but has the extremely quick inhibitory action located at the inner layer Shuanghuan dead beat controller to the perturbation. On the contrary, the Shuanghuan dead beat controller to the perturbation compensation is limited, but is redundant the introduction which controls to be possible to disturb approaching to compensate completely, the stable state effect is extremely good. In addition, as shown in Figure 6, Shuanghuan controls causes the invertor object the cut-off frequency to enlarge 2kHz, the redundant controller’s compensation range can also expand.
3 system designs and experiment
This control plan single-phase half bridge invertor test installation obtained the confirmation in a station base in DSPTMS320F240 in control system’s IGBT. The test installation parameter is: Filter inductance 1.14mH; Filter electric capacity 20μF; Input DC voltage 250V; Output alternating voltage peak-to-peak value 100V.
Figure 9
The switch and the sampling frequency is 10kHz, according to the above analysis, calculates KV=0.2, KC=11.1.
After adding Shuanghuan’s equivalent invertor controlled member is
PB(z)= (10)
According to the above choice second-order filter
S(z)= (11)
The link is z4 in advance, takes Kr=1, N=200.
Figure 10
Figure 8 is time the Shuanghuan system belt misalignment load profile, THD reaches 4.84%, obviously the instantaneous electricity pressure ring is limited to the electric current perturbation’s compensation effect. Figure 9 is the compound control system load impact process, when impact resistive load, restores normally after the 0.5ms wave advantage of terrain, when the worst situation is the impact rectification load, can also restore normally completely after 5 fundamental wave cycle profile. Figure 10 is the compound control system stable state work profile, time band elimination load THD is 1.71%, brings time rectification load THD is 1.54%.
4 conclusions
This article proposed the control project design is simple, the spurt value feedback part only need determine that two gains, favor the programming to realize. The experimental result showed that controls and the redundant control invertor system based on Shuanghuan has the strong robustness to the load perturbation, can output the high grade sinusoidal voltage.
