CN104810859A - Self-adaption quasi-PRD control method for photovoltaic grid-connected inverter - Google Patents

Abstract

The invention relates to a self-adaption quasi-PRD control method for a photovoltaic grid-connected inverter. The self-adaption quasi-PRD control method for the photovoltaic grid-connected inverter relates to the technical field of photovoltaic grid-connected inverter control, and aims to solve the problems that the existing photovoltaic grid-connected inverter has poor adaptability on power grid impedance change, and the stability of a photovoltaic grid-connected system is poor in a weak current grid. The method comprises the following steps of injecting disturbance current with specific frequency into a power grid through a disturbance current injection method; then obtaining a relational expression of current controller parameters and power grid impedance based on the principle of closed loop pole parameter configuration; when the power grid impedance Rg and power grid inductance Lg are changed, realizing self-adapting adjustment on controller parameters Kp, Kr and Kd so as to adapt to the ever-changing power grid impedance, so that the adaptability and the stability of the photovoltaic grid-connected inverter control system are improved. The self-adaption quasi-PRD control method for the photovoltaic grid-connected inverter can be used for controlling the photovoltaic grid-connected inverter.

Description

The accurate PRD control method of photovoltaic combining inverter self adaptation

Technical field

The present invention relates to the accurate PRD control method of photovoltaic combining inverter self adaptation.Belong to photovoltaic combining inverter control technology field.

Background technology

Along with the consumption of traditional energy and the increasingly mature of photovoltaic power generation technology, its range of application is also in continuous expansion, in order to solve the electrical problem of the dispersion user such as remote districts, island, and making full use of local abundant regenerative resource, photovoltaic generation has started to be promoted and application in these areas.But the electrical network in above-mentioned area is generally the end of electrical network, because of will through longer transmission line and stage variable pressure link between itself and Generation Side, contact dies down, and the line impedance of equivalence increases, and electrical network now presents the characteristic of light current net.And photovoltaic combining inverter is as the key equipment connecting photovoltaic power generation apparatus and electrical network, usually the actual conditions of electrical network are not considered in its design process, to such an extent as in actual applications, due to the impact by electric network impedance, systematic function can not reach desirable control effects.

By analysis, the electric network impedance of change can produce considerable influence to combining inverter control performance, even easily causes system unstable.When electric network impedance increases, the bandwidth of open-loop control system can reduce, this reduces causing the dynamic response performance of system, meanwhile, along with the increase of sensitive ingredients in electric network impedance, electrical network equivalent inductance very easily produces resonance with inverter output filter, and inductance is larger, resonance frequency is less, and resonance peak is larger, therefore can the stability of influential system, and cause the power quality problems such as the harmonic content increase in grid-connected current.

Summary of the invention

The present invention changes bad adaptability in order to solve existing photovoltaic combining inverter to electric network impedance, and the problem of the poor stability of light current photovoltaic parallel in system off the net.Now provide photovoltaic combining inverter self adaptation accurate PRD control method.

The accurate PRD control method of photovoltaic combining inverter self adaptation, it comprises the following steps:

Step one, in electrical network, injected the current perturbation of setpoint frequency with current perturbation injection method by inverter, then detecting element is utilized to detect and the response of the voltage and current at site place, incorporating signal processing techniques again, isolate the modulus value of injected specific order harmonic components, obtain the electrical network resistance R of equivalence according to this modulus value _gwith electrical network inductance L _g,

Step 2, by inverter leg export sinusoidal pulse width modulation voltage be equivalent to a voltage source, and according in step one obtain electrical network resistance R _gwith electrical network inductance L _g, set up the transfer function G of the controlled object of LC type single-phase photovoltaic grid-connected inverter grid-connected current control loop _os (), to this transfer function G _os () carries out discretization, obtain corresponding discretization expression formula G _o(z ^-1),

Step 3, adopt accurate PRD controller as the controller of current inner loop, the transfer function expression formula of accurate PRD controller is $G_c\left(s\right)=K_p+\frac{2K_r{\mathrm{\ω}}_{c}s}{s^2+2{\mathrm{\ω}}_{c}s+{\mathrm{\ω}}_0^2}+\frac{K_{d}s}{1+\mathrm{\τs}},$

Wherein, K _pbe as the criterion PRD controller proportionality coefficient, K _rbe as the criterion PRD controller resonance coefficient, K _dbe as the criterion PRD controller differential coefficient, ω ₀for the angular frequency that dfundamental-harmonic pair is answered, ω _cfor cut-off angular frequency, for low-pass filtering link, τ is the time of delay in filtering link,

Aim at the transfer function G of PRD controller _cs () carries out discretization, obtain its discretization expression formula G _c(z ^-1), to discretization expression formula G _c(z ^-1) carry out conversion and obtain difference equation:

u(k)＝b ₀e(k)+b ₁e(k-1)+b ₂e(k-2)+b ₃e(k-3)-a ₁u(k-1)-a ₂u(k-2)-a ₃u(k-3)，

Wherein, k is sampling step number, and u (k) is in the kth sampling period, and the output variable of accurate PRD digitial controller, the input variable that e (k) is controller is also the difference of given electric current and actual current, a _iand b _jfor system parameters, i=1,2,3; J=1,2,3;

$a_1=\frac{(3T+2\mathrm{\τ})T^2{\mathrm{\ω}}_0^2+(T-2\mathrm{\τ})4T{\mathrm{\ω}}_c-4(T+6\mathrm{\τ})}{(T+2\mathrm{\τ})(4+4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2)},$

$a_2=\frac{(3T-2\mathrm{\τ})T^2{\mathrm{\ω}}_0^2-4T{\mathrm{\ω}}_c(T+2\mathrm{\τ})-4(T-6\mathrm{\τ})}{(T+2\mathrm{\τ})(4+4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2)},$

$a_3=\frac{(T-2\mathrm{\τ})(T^2{\mathrm{\ω}}_0^2-4T{\mathrm{\ω}}_c+4)}{(T+2\mathrm{\τ})(4+4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2)},$

$b_0=K_p+\frac{4K_{r}T{\mathrm{\ω}}_c}{4+4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2}+\frac{2K_d}{T+2\mathrm{\τ}},$

$b_1=\frac{K_p[(3T+2\mathrm{\τ})T^2{\mathrm{\ω}}_0^2+4T{\mathrm{\ω}}_c(T-2\mathrm{\τ})-4(T+6\mathrm{\τ})]+K_r\·4T{\mathrm{\ω}}_c(T-2\mathrm{\τ})+2K_d(T^2{\mathrm{\ω}}_0^2-4T{\mathrm{\ω}}_c-12)}{(T+2\mathrm{\τ})(4+4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2)},$

$b_2=\frac{K_p[(3T+2\mathrm{\τ})T^2{\mathrm{\ω}}_0^2-4T{\mathrm{\ω}}_c(T+2\mathrm{\τ})-4(T-6\mathrm{\τ})]-K_r\·4T{\mathrm{\ω}}_c(T+2\mathrm{\τ})+2K_d(12-4T{\mathrm{\ω}}_c-T^2{\mathrm{\ω}}_0^2)}{(T+2\mathrm{\τ})(4+4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2)},$

$b_3=\frac{K_p[(T+2\mathrm{\τ})T^2{\mathrm{\ω}}_0^2-4T{\mathrm{\ω}}_c(T-2\mathrm{\τ})+4(T-2\mathrm{\τ})]-K_r\·4T{\mathrm{\ω}}_c(T-2\mathrm{\τ})-2K_d(4-4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2)}{(T+2\mathrm{\τ})(4+4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2)},$

Step 4, position according to accurate PRD controller ideal close-loop limit, obtain desirable closed loop transform function A _m(z ^-1), according to the controlled object transfer function G that step 2 obtains _o(z ^-1) and the accurate PRD controller transfer function G that obtains of step 3 _c(z ^-1), obtain the closed loop transform function A of system reality _c(z ^-1), make A _c(z ^-1)=A _m(z ^-1), obtain the controling parameters K of accurate PRD controller _p, K _r, K _dwith electrical network resistance R _gwith electrical network inductance L _grelational expression, as electrical network resistance R _gwith electrical network inductance L _gwhen changing, inverter realizes the output of accurate PRD controller according to the difference equation in step 3, to realize the accurate PRD controller of self adaptation to the control of photovoltaic combining inverter.

Beneficial effect of the present invention is: first accurate PRD control method proposed by the invention injects the current perturbation of characteristic frequency in electrical network by current perturbation injection method, realize the on-line checkingi of electric network impedance, then the zero steady-state error by adopting accurate PRD control method to achieve the given electric current of offset of sinusoidal is followed the tracks of and good dynamic response performance, the last principle based on closed-loop pole parameter configuration obtains the relational expression of accurate PRD current controller parameter and electric network impedance, as electrical network resistance R _gwith electrical network inductance L _gwhen changing, realize controller parameter K _p, K _r, K _dautomatic adjusument, to adapt to the electric network impedance of constantly change, further increase the adaptability of combining inverter control system to electrical network and the stability of grid-connected system.

Figure 21 and Figure 22 is depicted as before and after adaptive control, the simulation result of grid-connected electric current and voltage, as can be seen from the figure, when electric network impedance has greatly changed, the grid-connected voltage current waveform distortion not adding adaptive control is serious, and concussion is obvious, after adaptive control, grid-connected voltage current waveform obviously improves, and harmonic wave and reforming phenomena are eliminated.

Accompanying drawing explanation

Fig. 1 is the self adaptation accurate PRD control structure block diagram of LC type single-phase photovoltaic grid-connected inverter;

Fig. 2 is electrical network inductance L _gduring change, the amplitude of combining inverter current control loop is with the changing trend diagram of open loop angular frequency, and in figure, curve 1 represents L _gduring=0.01mH, the amplitude of combining inverter current control loop is with the change oscillogram of open loop angular frequency, and curve 2 represents L _gduring=0.1mH, the amplitude of combining inverter current control loop is with the change oscillogram of open loop angular frequency; Curve 3 represents L _gduring=1mH, the amplitude of combining inverter current control loop is with the change oscillogram of open loop angular frequency, and curve 4 represents L _gduring=3mH, the amplitude of combining inverter current control loop is with the change oscillogram of open loop angular frequency, and curve 5 represents L _gduring=5mH, the amplitude of combining inverter current control loop is with the change oscillogram of open loop angular frequency, and curve 6 represents L _gduring=10mH, the amplitude of combining inverter current control loop is with the change oscillogram of open loop angular frequency;

Fig. 3 electrical network inductance L _gduring change, the phase place of combining inverter current control loop is with the changing trend diagram of open loop angular frequency, and in figure, curve 21 represents L _gduring=0.01mH, the phase place of combining inverter current control loop is with the oscillogram of the change of open loop angular frequency, and curve 22 represents L _gduring=0.1mH, the phase place of combining inverter current control loop is with the oscillogram of the change of open loop angular frequency; Curve 23 represents L _gduring=1mH, the phase place of combining inverter current control loop is with the oscillogram of the change of open loop angular frequency, and curve 24 represents L _gduring=3mH, the phase place of combining inverter current control loop is with the oscillogram of the change of open loop angular frequency, and curve 25 represents L _gduring=5mH, the phase place of combining inverter current control loop is with the oscillogram of the change of open loop angular frequency, and curve 26 represents L _gduring=10mH, the phase place of combining inverter current control loop is with the oscillogram of the change of open loop angular frequency;

Fig. 4 is electrical network resistance R _gduring change, the amplitude of combining inverter current control loop is with the changing trend diagram of open loop angular frequency, and in figure, curve 7 represents R _gduring=1ohm, the amplitude of combining inverter current control loop is with the change oscillogram of open loop angular frequency, and curve 8 represents R _gduring=5ohm, the amplitude of combining inverter current control loop is with the change oscillogram of open loop angular frequency, and curve 9 represents R _gduring=10ohm, the amplitude of combining inverter current control loop is with the change oscillogram of open loop angular frequency, and curve 10 represents R _gduring=15hm, the amplitude of combining inverter current control loop is with the change oscillogram of open loop angular frequency;

Fig. 5 is electrical network resistance R _gduring change, the phase place of combining inverter current control loop is with the changing trend diagram of open loop angular frequency, and in figure, curve 27 represents R _gduring=1ohm, the phase place of combining inverter current control loop is with the oscillogram of the change of open loop angular frequency, and curve 28 represents R _gduring=5ohm, the phase place of combining inverter current control loop is with the oscillogram of the change of open loop angular frequency, and curve 29 represents R _gduring=10ohm, the phase place of combining inverter current control loop is with the oscillogram of the change of open loop angular frequency, and curve 30 represents R _gduring=15hm, the phase place of combining inverter current control loop is with the oscillogram of the change of open loop angular frequency;

Fig. 6 is under the control mode of PI, accurate PR and accurate PRD, the amplitude of control system is with the change curve of open loop frequency, in figure, under curve 11 represents PI control mode, the open loop frequency of control system is with amplitude variation diagram, and under curve 12 represents accurate PRD control mode, the amplitude of control system is with the variation diagram of open loop frequency, under curve 13 represents accurate PR control mode, the amplitude of control system is with the change variation diagram of open loop frequency;

Fig. 7 is under the control mode of PI, accurate PR and accurate PRD, the phase place of control system is with the curve chart of the change of open loop frequency, in figure, under curve 31 represents PI control mode, the phase place of control system is with the variation diagram of open loop frequency, and under curve 32 represents accurate PRD control mode, the phase place of control system is with the variation diagram of open loop frequency, under curve 33 represents accurate PR control mode, the phase place of control system is with the variation diagram of open loop frequency;

Fig. 8 is under the control mode of PI, accurate PR and accurate PRD, the closed loop amplitude of control system is with a kind of curve chart of frequency change of interval, in figure, under curve 14 represents PI control mode, the amplitude of control system is with the variation diagram of open loop frequency, and under curve 15 represents accurate PR control mode, the amplitude of control system is with the variation diagram of open loop frequency, under curve 16 represents accurate PRD control mode, the amplitude of control system is with the variation diagram of open loop frequency;

Fig. 9 is under the control mode of PI, accurate PR and accurate PRD, the closed loop phase of control system is with a kind of curve chart of frequency change of interval, in figure, under curve 34 represents PI control mode, the phase place of control system is with the variation diagram of open loop frequency, and under curve 35 represents accurate PR control mode, the phase place of control system is with the variation diagram of open loop frequency, under curve 36 represents accurate PRD control mode, the phase place of control system is with the variation diagram of open loop frequency;

Figure 10 is under the control mode of PI, accurate PR and accurate PRD, the closed loop amplitude of control system is with the curve chart of another kind of interval frequency change, in figure, under curve 14 represents PI control mode, the amplitude of control system is with the variation diagram of open loop frequency, and under curve 15 represents accurate PR control mode, the amplitude of control system is with the variation diagram of open loop frequency, under curve 16 represents accurate PRD control mode, the amplitude of control system is with the variation diagram of open loop frequency;

Figure 11 is under the control mode of PI, accurate PR and accurate PRD, the closed loop phase of control system is with the curve chart of another kind of interval frequency change, in figure, under curve 34 represents PI control mode, the phase place of control system is with the variation diagram of open loop frequency, and under curve 35 represents accurate PR control mode, the phase place of control system is with the variation diagram of open loop frequency, under curve 36 represents accurate PRD control mode, the phase place of control system is with the variation diagram of open loop frequency; Figure 12 is grid-connected current simulation waveform figure when carrying out electric network impedance on-line checkingi based on biharmonic current injection method;

Figure 13 is current perturbation simulation waveform figure when carrying out electric network impedance on-line checkingi based on biharmonic current injection method;

Figure 14 is electrical network resistance based on the electric network impedance on-line checkingi of biharmonic current injection method and actual resistance simulation result figure,

Figure 15 is the simulation result figure of electrical network inductance based on the electric network impedance on-line checkingi of biharmonic current injection method and actual inductance,

Figure 16 is the A place enlarged drawing in Figure 14, and in figure, curve 37 represents the oscillogram of actual resistance, and in figure, curve 38 represents the oscillogram estimating resistance;

Figure 17 is the B place enlarged drawing in Figure 15, and in figure, curve 37 represents the oscillogram of actual inductance, and in figure, curve 38 represents the oscillogram estimating inductance;

Figure 18 is the flow chart of the accurate PRD control method of photovoltaic combining inverter self adaptation of the present invention;

Figure 19 is as the criterion the changing trend diagram of PRD controller proportionality coefficient with electric network impedance;

Figure 20 is as the criterion the changing trend diagram of PRD controller resonance coefficient with electric network impedance;

Figure 21 is before adaptive control, grid-connected electric current and voltage simulation waveform figure, and in figure, curve 19 represents the waveform of grid-connected voltage, and curve 20 represents the waveform of grid-connected current,

Figure 22 is after adaptive control, grid-connected electric current and voltage simulation waveform figure.

Embodiment

Embodiment one: illustrate present embodiment referring to figs. 1 through Figure 11, Figure 18 to Figure 21, the accurate PRD control method of the photovoltaic combining inverter self adaptation described in present embodiment, it comprises the following steps:

Step one, in electrical network, injected the current perturbation of setpoint frequency with current perturbation injection method by inverter, then detecting element is utilized to detect and the response of the voltage and current at site place, incorporating signal processing techniques again, isolate the modulus value of injected specific order harmonic components, obtain the electrical network resistance R of equivalence according to this modulus value _gwith electrical network inductance L _g,

Step 2, by inverter leg export sinusoidal pulse width modulation voltage be equivalent to a voltage source, and according in step one obtain electrical network resistance R _gwith electrical network inductance L _g, set up the transfer function G of the controlled object of LC type single-phase photovoltaic grid-connected inverter grid-connected current control loop _os (), to this transfer function G _os () carries out discretization, obtain corresponding discretization expression formula G _o(z ^-1),

Step 3, adopt accurate PRD controller as the controller of current inner loop, the transfer function expression formula of accurate PRD controller is $G_c\left(s\right)=K_p+\frac{2K_r{\mathrm{\ω}}_{c}s}{s^2+2{\mathrm{\ω}}_{c}s+{\mathrm{\ω}}_0^2}+\frac{K_{d}s}{1+\mathrm{\τs}},$

Wherein, K _pbe as the criterion PRD controller proportionality coefficient, K _rbe as the criterion PRD controller resonance coefficient, K _dbe as the criterion PRD controller differential coefficient, ω ₀for the angular frequency that dfundamental-harmonic pair is answered, ω _cfor cut-off angular frequency, for low-pass filtering link, τ is the time of delay in filtering link,

Aim at the transfer function G of PRD controller _cs () carries out discretization, obtain its discretization expression formula G _c(z ^-1), to discretization expression formula G _c(z ^-1) carry out conversion and obtain difference equation:

u(k)＝b ₀e(k)+b ₁e(k-1)+b ₂e(k-2)+b ₃e(k-3)-a ₁u(k-1)-a ₂u(k-2)-a ₃u(k-3)，

Wherein, k is sampling step number, and u (k) is in the kth sampling period, and the output variable of accurate PRD digitial controller, the input variable that e (k) is controller is also the difference of given electric current and actual current, a _iand b _jfor system parameters, i=1,2,3; J=1,2,3

$a_1=\frac{(3T+2\mathrm{\τ})T^2{\mathrm{\ω}}_0^2+(T-2\mathrm{\τ})4T{\mathrm{\ω}}_c-4(T+6\mathrm{\τ})}{(T+2\mathrm{\τ})(4+4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2)},$

$a_2=\frac{(3T-2\mathrm{\τ})T^2{\mathrm{\ω}}_0^2-4T{\mathrm{\ω}}_c(T+2\mathrm{\τ})-4(T-6\mathrm{\τ})}{(T+2\mathrm{\τ})(4+4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2)},$

$a_3=\frac{(T-2\mathrm{\τ})(T^2{\mathrm{\ω}}_0^2-4T{\mathrm{\ω}}_c+4)}{(T+2\mathrm{\τ})(4+4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2)},$

$b_0=K_p+\frac{4K_{r}T{\mathrm{\ω}}_c}{4+4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2}+\frac{2K_d}{T+2\mathrm{\τ}},$

$b_1=\frac{K_p[(3T+2\mathrm{\τ})T^2{\mathrm{\ω}}_0^2+4T{\mathrm{\ω}}_c(T-2\mathrm{\τ})-4(T+6\mathrm{\τ})]+K_r\·4T{\mathrm{\ω}}_c(T-2\mathrm{\τ})+2K_d(T^2{\mathrm{\ω}}_0^2-4T{\mathrm{\ω}}_c-12)}{(T+2\mathrm{\τ})(4+4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2)},$

$b_2=\frac{K_p[(3T+2\mathrm{\τ})T^2{\mathrm{\ω}}_0^2-4T{\mathrm{\ω}}_c(T+2\mathrm{\τ})-4(T-6\mathrm{\τ})]-K_r\·4T{\mathrm{\ω}}_c(T+2\mathrm{\τ})+2K_d(12-4T{\mathrm{\ω}}_c-T^2{\mathrm{\ω}}_0^2)}{(T+2\mathrm{\τ})(4+4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2)},$

$b_3=\frac{K_p[(T+2\mathrm{\τ})T^2{\mathrm{\ω}}_0^2-4T{\mathrm{\ω}}_c(T-2\mathrm{\τ})+4(T-2\mathrm{\τ})]-K_r\·4T{\mathrm{\ω}}_c(T-2\mathrm{\τ})-2K_d(4-4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2)}{(T+2\mathrm{\τ})(4+4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2)},$

Step 4, position according to accurate PRD controller ideal close-loop limit, obtain desirable closed loop transform function A _m(z ^-1), according to the controlled object transfer function G that step 2 obtains _o(z ^-1) and the accurate PRD controller transfer function G that obtains of step 3 _c(z ^-1), obtain the closed loop transform function A of system reality _c(z ^-1), make A _c(z ^-1)=A _m(z ^-1), obtain the controling parameters K of accurate PRD controller _p, K _r, K _dwith electrical network resistance R _gwith electrical network inductance L _grelational expression, as electrical network resistance R _gwith electrical network inductance L _gwhen changing, inverter realizes the output of accurate PRD controller according to the difference equation in step 3, to realize the accurate PRD controller of self adaptation to the control of photovoltaic combining inverter.

In present embodiment, when electric network impedance changes, system can according to real-time electrical network resistance R _gwith electrical network inductance L _gthe parameter K of the accurate PRD controller of testing result on-line tuning _p, K _r, K _d, to ensure that system has good control performance all the time.

In present embodiment, Figure 1 shows that the self adaptation accurate PRD control structure block diagram of LC type single-phase photovoltaic grid-connected inverter, what combining inverter adopted is typical double-loop control structure, outer shroud is direct current pressure ring, for stable DC busbar voltage, inner ring is electric current loop, and export grid-connected current and the same homophase frequently of line voltage for controlling, guarantor unit's power factor is grid-connected.

Fig. 2 is with when Figure 3 shows that electrical network inductance changes, and the open-Loop characteristic of Current Control inner ring, as seen from the figure, works as L _gduring increase, the bandwidth of open cycle system reduces, and meanwhile, resonance frequency reduces, and resonance peak increases, and this means that the dynamic responding speed of system is slack-off, and resonance phenomena is obvious, and the unsteadiness of system increases.Fig. 4 is with when Figure 5 shows that electrical network resistance variations, and the open-Loop characteristic of Current Control inner ring, as seen from the figure, when electrical network resistance increases, the gain of open cycle system reduces, and this will cause the dynamic responding speed of system slack-off, and steady-state error increases.

Fig. 6 is with when Figure 7 shows that current inner loop adopts PI, accurate PR and accurate PRD to control respectively, the open loop frequency Character Comparison figure of control system, as seen from the figure, control compared to PI, accurate PR controls and accurate PRD controls all have larger gain at 50Hz frequency place, therefore can realize following the tracks of the zero steady-state error of the given electric current of the sine under fundamental frequency, high band has and controls identical damping capacity with PI, can suppress high-frequency noise; Under accurate PRD controls, the bandwidth of system increases to some extent, and phase margin increases, this is because the phase place adding the system of compensate for of differentiation element, thus improves the dynamic response performance of system.Fig. 8 to Figure 11 shows that adopt PI, accurate PR and accurate PRD to control respectively time, the closed loop frequency characteristics comparison diagram of control system, as seen from the figure, accurate PR and accurate PRD controls amplitude at fundamental frequency place and phase error is 0, and PI controls to there is obvious error.

Although replace PI controller with accurate PRD controller can reach the object improving grid-connected current quality, when electric network impedance has greatly changed, the control performance based on the control system designed by small-signal model will be deteriorated, and even produces instability.For this problem, adaptive control controls to combine with accurate PRD by the present invention, proposes the accurate PRD control method of self adaptation of photovoltaic combining inverter.First the on-line checkingi of electric network impedance is realized by current perturbation injection method, then the relational expression of current controller parameter and electric network impedance is obtained based on the principle of closed-loop pole parameter configuration, according to the accurate PRD controller parameter of the relational expression on-line control obtained, realize adaptive control.

Embodiment two: illustrate present embodiment with reference to Figure 12 to Figure 17, present embodiment is described further the accurate PRD control method of the photovoltaic combining inverter self adaptation described in embodiment one, in present embodiment, in step, what current perturbation injection method adopted is biharmonic current disturbing injection method, namely the current perturbation injected comprises the harmonic wave of two kinds of frequencies, frequency is respectively the harmonic current of 400Hz and 600Hz, the position that disturbance is injected is the given place of grid-connected current, and the mode that disturbance is injected is intermittently be injected into electrical network.

Embodiment three: present embodiment is described further the accurate PRD control method of the photovoltaic combining inverter self adaptation described in embodiment one or two, in present embodiment, obtains the electrical network resistance R of equivalence according to this modulus value _gwith electrical network inductance L _gprocess be:

Following relation is there is between electric network impedance due to different frequency:

$\left\{\begin{array}{c}{Z}_1^2=R_g^2+{\mathrm{\ω}}_1^2\·L_g^2\\ Z_2^2=R_g^2+{\mathrm{\ω}}_2^2\·L_g^2\end{array}\right.,$

Wherein, Z ₁represent the modulus value of the electric network impedance under 400Hz frequency, Z ₂represent the modulus value of the electric network impedance under 600Hz, ω ₁represent the angular frequency value that the first frequency is corresponding, ω ₂represent the angular frequency value that the second frequency is corresponding, ω ₁=2 π f ₁, ω ₂=2 π f ₂,

Ignore resistance R under different frequency _gand inductance L _gminute differences, then electrical network inductance L _gwith electrical network resistance R _gcomputing formula as follows:

$L_g=\sqrt{\frac{Z_1^2-Z_2^2}{{\mathrm{\ω}}_1^2-{\mathrm{\ω}}_2^2}},$

$R_g=\sqrt{\frac{{\mathrm{\ω}}_1^2{Z}_2^2-{\mathrm{\ω}}_2^2{Z}_1^2}{{\mathrm{\ω}}_1^2-{\mathrm{\ω}}_2^2}}.$

In present embodiment, the electric network impedance of different frequency is by the harmonic current injection of 400Hz and 600Hz in electrical network, the modulus value of the electric network impedance under the modulus value of the electric network impedance under isolated 400Hz frequency and 600Hz.

Embodiment four: present embodiment is described further the accurate PRD control method of the photovoltaic combining inverter self adaptation described in embodiment one, in present embodiment, in step 2, set up the transfer function G of the controlled object of LC type single-phase photovoltaic grid-connected inverter grid-connected current control loop _os (), to transfer function G _os () carries out discretization, obtain corresponding discretization expression formula G _o(z ^-1) process be:

Set up the dynamical equation about L and C, after Laplace transform, obtain the expression formula on complex frequency domain:

$\left[\begin{array}{c}{v}_g\\ v_{\mathrm{inv}}\end{array}\right]=\left[\begin{array}{cc}\frac{1}{\mathrm{sC}}& -R-s{L}_g-\frac{1}{\mathrm{sC}}\\ \mathrm{sL}+\frac{1}{\mathrm{sC}}& -\frac{1}{\mathrm{sC}}\end{array}\right]\left[\begin{array}{c}{i}_L\\ i_g\end{array}\right],$

In formula, v _gfor line voltage, v _invfor the sinusoidal pulse width modulation voltage that inverter leg exports, L is filter inductance, and C is filter capacitor, i _gfor grid-connected current, i _lfor inductive current, s is the complex variable introduced in complex frequency domain,

LC filter is equivalent to single L structure, and therefore obtaining filter inductance electric current to the transfer function of inverter output voltage is:

$\frac{i_L\left(s\right)}{v_{\mathrm{inv}}\left(s\right)}=\frac{1}{(L+L_g)s+R_g},$

Inverter is equivalent to a gain link K _pWM, the transfer function setting up the controlled object of LC type single-phase photovoltaic grid-connected inverter grid-connected current control loop is:

$G_o\left(s\right)=\frac{K_{\mathrm{PWM}}}{(L+L_g)s+R_g},$

Carry out discretization to above formula, the discretization model obtaining the controlled object of LC type single-phase photovoltaic grid-connected inverter grid-connected current control loop is as follows:

$G_o\left(z^{-1}\right)=\frac{y\left(k\right)}{u\left(k\right)}=\frac{l_0}{1+g_1{z}^{-1}},$

Wherein, z ^-1for delay component, refer to sampled signal be postponed 1 sampling period, $l_0=\frac{K_{\mathrm{PWM}}T}{L+L_g+R_{g}T},$ T is the sampling time.

Embodiment five: present embodiment is described further the accurate PRD control method of the photovoltaic combining inverter self adaptation described in embodiment one, in present embodiment, in step 4, according to the position of accurate PRD controller ideal close-loop limit, obtain desirable closed loop transform function A _m(z ^-1) process be:

If two ideal close-loop dominant poles of accurate PRD controller are: another ideal close-loop non-dominant limit is: s ₃=-m ξ ω _n, m>5,

Wherein, ξ represents the damping coefficient of control system, ω _nthe resonance angular frequency of expression system, j is the unit of the imaginary axis,

The closed loop transform function on S territory is obtained according to the position of closed-loop pole:

A _m(s)＝(s-s ₁)(s-s ₂)(s-s ₃)，

Again by the closed loop transform function on S territory through discretization, be transformed into Z territory, obtain the ideal close-loop characteristic equation on Z territory:

A _m(z ^-1)＝1+a _m1z ^-1+a _m2z ^-2+a _m3z ^-3，

Wherein, z ^-2for delay component, refer to sampled signal be postponed 2 sampling periods, z ^-3for delay component, refer to sampled signal be postponed 3 sampling periods.

Embodiment six: present embodiment is described further the accurate PRD control method of the photovoltaic combining inverter self adaptation described in embodiment one, in present embodiment, in step 4, according to the controlled object transfer function G that step 2 obtains _o(z ^-1) and the accurate PRD controller transfer function G that obtains of step 3 _c(z ^-1), obtain the closed loop transform function A of system reality _c(z ^-1) process be:

By the discretization expression formula G of the transfer function of the controlled object of control loop _o(z ^-1) be expressed as:

l ₀·u(k)＝(1+g ₁z ^-1)y(k)，

Again by the discretization transfer function G of accurate PRD controller _c(z ^-1) be expressed as:

F(z ^-1)u(k)＝G(z ^-1)[y _r(k)-y(k)]，

In conjunction with G _o(z ^-1) and G _c(z ^-1) these two relational expressions, the closed loop transfer function, obtaining real system is:

$\frac{y\left(k\right)}{y_r\left(k\right)}=\frac{z^{-1}{l}_0\left(z^{-1}\right)}{(1+g_1{z}^{-1})F\left(z^{-1}\right)+z^{-1}{l}_{0}G\left(z^{-1}\right)},$

Therefore, the closed loop transform function of real system is:

A _c(z ^-1)＝(1+g ₁z ^-1)F(z ^-1)+z ^-1l ₀G(z ^-1)，

Wherein, F (z ^-1)=1+a ₁z ^-1+ a ₂z ^-2, G (z ^-1)=b ₀+ b ₁z ^-1+ b ₂z ^-2, a ₁, a ₂, b ₀, b ₁, b ₂for coefficient.

Embodiment seven: present embodiment is described further the accurate PRD control method of photovoltaic combining inverter self adaptation described in embodiment one, five or six, in present embodiment, in step 4, makes A _c(z ^-1)=A _m(z ^-1), obtain the controling parameters K of accurate PRD controller _p, K _r, K _dwith electric network impedance R _g, L _grelational expression be:

K _p′＝f ₁(R _g,L _g)≈K _p+△K _p

K _r′＝f ₂(R _g,L _g)≈K _r+△K _r，

When electric network impedance increases, for ensureing the stability of system, K _dusually reduction that should be suitable, so the controling parameters K of accurate PRD controller _dfor:

K _d′＝K _d+△K _d，

Wherein, △ K _dvariation tendency and electric network impedance R _g, L _gvariation tendency contrary, K _p' be the proportionality coefficient of PRD controller accurate after adaptive control, f ₁(R _g, L _g) Proportional coefficient K of the PRD controller that is as the criterion _p' functional relation represented by electrical network resistance and inductance, △ K _pafter electric network impedance changes, the variable quantity of the new proportionality coefficient obtained on former proportionality coefficient basis, K _r' be the resonance coefficient of PRD controller accurate after adaptive control, f ₂(R _g, L _g) the resonance coefficient K of the PRD controller that is as the criterion _r' functional relation represented by electrical network resistance and inductance, △ K _rafter electric network impedance changes, the variable quantity of the new resonance coefficient obtained on former resonance coefficient basis, K _d' be the differential coefficient of PRD controller accurate after adaptive control, △ K _dafter electric network impedance changes, the variable quantity of the new differential coefficient obtained on former differential coefficient basis.

Claims (7)

1. the accurate PRD control method of photovoltaic combining inverter self adaptation, it is characterized in that, it comprises the following steps:

Step one, in electrical network, injected the current perturbation of setpoint frequency with current perturbation injection method by inverter, then detecting element is utilized to detect and the response of the voltage and current at site place, incorporating signal processing techniques again, isolate the modulus value of injected specific order harmonic components, obtain the electrical network resistance R of equivalence according to this modulus value _gwith electrical network inductance L _g,

Step 2, by inverter leg export sinusoidal pulse width modulation voltage be equivalent to a voltage source, and according in step one obtain electrical network resistance R _gwith electrical network inductance L _g, set up the transfer function G of the controlled object of LC type single-phase photovoltaic grid-connected inverter grid-connected current control loop _os (), to this transfer function G _os () carries out discretization, obtain corresponding discretization expression formula G _o(z ^-1),

Step 3, adopt accurate PRD controller as the controller of current inner loop, the transfer function expression formula of accurate PRD controller is $G_c\left(s\right)=K_p+\frac{2K_r{\mathrm{\ω}}_{c}s}{s^2+2{\mathrm{\ω}}_{c}s+{\mathrm{\ω}}_0^2}+\frac{K_{d}s}{1+\mathrm{\τs}},$

Wherein, K _pbe as the criterion PRD controller proportionality coefficient, K _rbe as the criterion PRD controller resonance coefficient, K _dbe as the criterion PRD controller differential coefficient, ω ₀for the angular frequency that dfundamental-harmonic pair is answered, ω _cfor cut-off angular frequency, for low-pass filtering link, τ is the time of delay in filtering link;

Aim at the transfer function G of PRD controller _cs () carries out discretization, obtain its discretization expression formula G _c(z ^-1), to discretization expression formula G _c(z ^-1) carry out conversion and obtain difference equation:

u(k)＝b ₀e(k)+b ₁e(k-1)+b ₂e(k-2)+b ₃e(k-3)-a ₁u(k-1)-a ₂u(k-2)-a ₃u(k-3)，

Wherein, k is sampling step number, and u (k) is in the kth sampling period, and the output variable of accurate PRD digitial controller, the input variable that e (k) is controller is also the difference of given electric current and actual current, a _iand b _jfor system parameters, i=1,2,3; J=1,2,3;

$a_1=\frac{(3T+2\mathrm{\τ})T^2{\mathrm{\ω}}_0^2+(T-2\mathrm{\τ})4T{\mathrm{\ω}}_c-4(T+6\mathrm{\τ})}{(T+2\mathrm{\τ})(4+4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2)},$

$a_2=\frac{(3T-2\mathrm{\τ})T^2{\mathrm{\ω}}_0^2-4T{\mathrm{\ω}}_c(T+2\mathrm{\τ})-4(T-6\mathrm{\τ})}{(T+2\mathrm{\τ})(4+4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2)},$

$a_3=\frac{(T-2\mathrm{\τ})(T^2{\mathrm{\ω}}_0^2-4T{\mathrm{\ω}}_c+4)}{(T+2\mathrm{\τ})(4+4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2)},$

$b_0=K_p+\frac{4K_{r}T{\mathrm{\ω}}_c}{4+4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2}+\frac{2K_d}{T+2\mathrm{\τ}},$

$b_1=\frac{K_p[(3T+2\mathrm{\τ})T^2{\mathrm{\ω}}_0^2+4T{\mathrm{\ω}}_c(T-2\mathrm{\τ})-4(T+6\mathrm{\τ})]+K_r\·4T{\mathrm{\ω}}_c(T-2\mathrm{\τ})+2K_d(T^2{\mathrm{\ω}}_0^2-4T{\mathrm{\ω}}_c-12)}{(T+2\mathrm{\τ})(4+4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2)},$

$b_2=\frac{K_p[(3T-2\mathrm{\τ})T^2{\mathrm{\ω}}_0^2-4T{\mathrm{\ω}}_c(T+2\mathrm{\τ})-4(T-6\mathrm{\τ})]-K_r\·4T{\mathrm{\ω}}_c(T+2\mathrm{\τ})+2K_d(12-4T{\mathrm{\ω}}_c-T^2{\mathrm{\ω}}_0^2)}{(T+2\mathrm{\τ})(4+4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2)},$

$b_3=\frac{K_p[(T-2\mathrm{\τ})T^2{\mathrm{\ω}}_0^2-4T{\mathrm{\ω}}_c(T-2\mathrm{\τ})+4(T-2\mathrm{\τ})]-K_r\·4T{\mathrm{\ω}}_c(T-2\mathrm{\τ})-2K_d(4-4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2)}{(T+2\mathrm{\τ})(4+4T{\mathrm{\ω}}_c+T^2{\mathrm{\ω}}_0^2)},$

Step 4, position according to accurate PRD controller ideal close-loop limit, obtain desirable closed loop transform function A _m(z ^-1), according to the controlled object transfer function G that step 2 obtains _o(z ^-1) and the accurate PRD controller transfer function G that obtains of step 3 _c(z ^-1), obtain the closed loop transform function A of system reality _c(z ^-1), make A _c(z ^-1)=A _m(z ^-1), obtain the controling parameters K of accurate PRD controller _p, K _r, K _dwith electrical network resistance R _gwith electrical network inductance L _grelational expression, as electrical network resistance R _gwith electrical network inductance L _gwhen changing, inverter realizes the output of accurate PRD controller according to the difference equation in step 3, to realize the accurate PRD controller of self adaptation to the control of photovoltaic combining inverter.

2. the accurate PRD control method of photovoltaic combining inverter self adaptation according to claim 1, it is characterized in that, in step, what current perturbation injection method adopted is biharmonic current disturbing injection method, namely the current perturbation injected comprises the harmonic wave of two kinds of frequencies, frequency is respectively the harmonic current of 400Hz and 600Hz, and the position that disturbance is injected is the given place of grid-connected current, and the mode that disturbance is injected is intermittently be injected into electrical network.

3. the accurate PRD control method of photovoltaic combining inverter self adaptation according to claim 1 and 2, is characterized in that, in step one, obtains the electrical network resistance R of equivalence according to this modulus value _gwith electrical network inductance L _gprocess be:

Following relation is there is between electric network impedance due to different frequency:

$\left\{\begin{array}{c}{Z}_1^2=R_g^2+{\mathrm{\ω}}_1^2\·L_g^2\\ Z_2^2=R_g^2+{\mathrm{\ω}}_2^2\·L_g^2\end{array}\right.,$

Wherein, Z ₁represent the modulus value of the electric network impedance under 400Hz, Z ₂represent the modulus value of the electric network impedance under 600Hz, ω ₁represent the angular frequency value that the first frequency is corresponding, ω ₂represent the angular frequency value that the second frequency is corresponding, ω ₁=2 π f ₁, ω ₂=2 π f ₂,

Ignore resistance R under different frequency _gand inductance L _gminute differences, then electrical network inductance L _gwith electrical network resistance R _gcomputing formula as follows:

$L_g=\sqrt{\frac{Z_1^2-Z_2^2}{{\mathrm{\ω}}_1^2-{\mathrm{\ω}}_2^2}},$

$R_g=\sqrt{\frac{{\mathrm{\ω}}_1^2{Z}_2^2-{\mathrm{\ω}}_2^2{Z}_1^2}{{\mathrm{\ω}}_1^2-{\mathrm{\ω}}_2^2}}.$

4. the accurate PRD control method of photovoltaic combining inverter self adaptation according to claim 1, is characterized in that, in step 2, sets up the transfer function G of the controlled object of LC type single-phase photovoltaic grid-connected inverter grid-connected current control loop _os (), to transfer function G _os () carries out discretization, obtain corresponding discretization expression formula G _o(z ^-1) process be:

Set up the dynamical equation about L and C, after Laplace transform, obtain the expression formula on complex frequency domain:

$\left[\begin{array}{c}{v}_g\\ v_{\mathrm{inv}}\end{array}\right]=\left[\begin{array}{cc}\frac{1}{\mathrm{sC}}& -R_g-s{L}_g-\frac{1}{\mathrm{sC}}\\ \mathrm{sL}+\frac{1}{\mathrm{sC}}& -\frac{1}{\mathrm{sC}}\end{array}\right]\left[\begin{array}{c}{i}_L\\ i_g\end{array}\right],$

In formula, v _gfor line voltage, v _invfor the sinusoidal pulse width modulation voltage that inverter leg exports, L is filter inductance, and C is filter capacitor, i _gfor grid-connected current, i _lfor inductive current, s is the complex variable introduced in complex frequency domain,

LC filter is equivalent to single L structure, and therefore obtaining filter inductance electric current to the transfer function of inverter output voltage is:

$\frac{i_L\left(s\right)}{v_{\mathrm{inv}}\left(s\right)}=\frac{1}{(L+L_g)s+R_g},$

Inverter is equivalent to a gain link K _pWM, the transfer function setting up the controlled object of LC type single-phase photovoltaic grid-connected inverter grid-connected current control loop is:

$G_o\left(s\right)=\frac{K_{\mathrm{PWM}}}{(L+L_g)s+R_g},$

Carry out discretization to above formula, the discretization model obtaining the controlled object of LC type single-phase photovoltaic grid-connected inverter grid-connected current control loop is as follows:

$G_o\left(z^{-1}\right)=\frac{y\left(k\right)}{u\left(k\right)}=\frac{l_0}{1+g_1{z}^{-1}},$

Wherein, z ^-1for delay component, refer to sampled signal be postponed 1 sampling period, $l_0=\frac{K_{\mathrm{PWM}}T}{L+L_g+R_{g}T},$ T is the sampling time.

5. the accurate PRD control method of photovoltaic combining inverter self adaptation according to claim 1, is characterized in that, in step 4, according to the position of accurate PRD controller ideal close-loop limit, obtains desirable closed loop transform function A _m(z ^-1) process be:

If two ideal close-loop dominant poles of accurate PRD controller are: another ideal close-loop non-dominant limit is: s ₃=-m ξ ω _n, m>5,

Wherein, ξ represents the damping coefficient of control system, ω _nthe resonance angular frequency of expression system, j is the unit of the imaginary axis,

The closed loop transform function on S territory is obtained according to the position of closed-loop pole:

A _m(s)＝(s-s ₁)(s-s ₂)(s-s ₃)，

Again by the closed loop transform function on S territory through discretization, be transformed into Z territory, obtain the ideal close-loop characteristic equation on Z territory:

A _m(z ^-1)＝1+a _m1z ^-1+a _m2z ^-2+a _m3z ^-3，

Wherein, a _m3=e ^{-(m+2) σ}, σ=ω _nξ T, z ^-2for delay component, refer to sampled signal be postponed 2 sampling periods, z ^-3for delay component, refer to sampled signal be postponed 3 sampling periods.

6. the accurate PRD control method of photovoltaic combining inverter self adaptation according to claim 1, is characterized in that, in step 4, according to the controlled object transfer function G that step 2 obtains _o(z ^-1) and the accurate PRD controller transfer function G that obtains of step 3 _c(z ^-1), obtain the closed loop transform function A of system reality _c(z ^-1) process be:

By the discretization expression formula G of the transfer function of the controlled object of control loop _o(z ^-1) be expressed as:

l ₀·u(k)＝(1+g ₁z ^-1)y(k)，

Again by the discretization transfer function G of accurate PRD controller _c(z ^-1) be expressed as:

F(z ^-1)u(k)＝G(z ^-1)[y _r(k)-y(k)]，

In conjunction with G _o(z ^-1) and G _c(z ^-1) these two relational expressions, the closed loop transfer function, obtaining real system is:

$\frac{y\left(k\right)}{y_r\left(k\right)}=\frac{z^{-1}{l}_{0}G\left(z^{-1}\right)}{(1+g_1{z}^{-1})F\left(z^{-1}\right)+z^{-1}{l}_{0}G\left(z^{-1}\right)},$

Therefore, the closed loop transform function of real system is:

A _c(z ^-1)＝(1+g ₁z ^-1)F(z ^-1)+z ^-1l ₀G(z ^-1)，

Wherein, F (z ^-1)=1+a ₁z ^-1+ a ₂z ^-2, G (z ^-1)=b ₀+ b ₁z ^-1+ b ₂z ^-2, a ₁, a ₂, b ₀, b ₁, b ₂for coefficient.

7. the accurate PRD control method of the photovoltaic combining inverter self adaptation according to claim 1,5 or 6, is characterized in that, in step 4, make A _c(z ^-1)=A _m(z ^-1), obtain the controling parameters K of accurate PRD controller _p, K _r, K _dwith electric network impedance R _g, L _grelational expression be:

K _p′＝f ₁(R _g,L _g)≈K _p+△K _p

K _r′＝f ₂(R _g,L _g)≈K _r+△K _r，

When electric network impedance increases, for ensureing the stability of system, K _dusually reduction that should be suitable, so the controling parameters K of accurate PRD controller _dfor:

K _d′＝K _d+△K _d，

Wherein, △ K _dvariation tendency and electric network impedance R _g, L _gvariation tendency contrary, K _p' be the proportionality coefficient of PRD controller accurate after adaptive control, f ₁(R _g, L _g) Proportional coefficient K of the PRD controller that is as the criterion _p' functional relation represented by electrical network resistance and inductance, △ K _pafter electric network impedance changes, the variable quantity of the new proportionality coefficient obtained on former proportionality coefficient basis, K _r' be the resonance coefficient of PRD controller accurate after adaptive control, f ₂(R _g, L _g) the resonance coefficient K of the PRD controller that is as the criterion _r' functional relation represented by electrical network resistance and inductance, △ K _rafter electric network impedance changes, the variable quantity of the new resonance coefficient obtained on former resonance coefficient basis, K _d' be the differential coefficient of PRD controller accurate after adaptive control, △ K _dafter electric network impedance changes, the variable quantity of the new differential coefficient obtained on former differential coefficient basis.