CN101976850A - Direct-current side control method for midline arm control model of four bridge arm photovoltaic inverter - Google Patents

Abstract

The invention discloses a direct-current side control method for a midline arm control model of a four bridge arm photovoltaic inverter. The midline arm control model comprises a photovoltaic direct-current input, a stabilized voltage capacitor, a direct-current booster circuit, two groups of inverter side storage capacitors, two equivalent bleeder resistors connected in series, a midline inductor and a midline arm. The invention discloses a direct-current side midpoint balance control method and a controller design method suitable for the midline arm control mode., wherein an average value of signals in a switching period of a midline arm switching function is used as a control variable; an H-infinity controller is designed by adopting an H-infinity control method; and the H infinite norm of the input midline current, measurement error, equivalent external disturbance, half of the sum of the output voltages of the two capacitors relative to a neutral point and midline arm midpoint voltage is minimum; and the invention provides implementation of a corresponding generalized controlled object, a controller structure and a corresponding weighting function selection method. The method can ensure that the stability of the direct-current side midpoint of the four bridge arm photovoltaic inverter still can be kept in high midline current.

Description

DC side control method at four brachium pontis photovoltaic DC-to-AC converter center line arm controlling models

Technical field

This DC side control method that relates to a kind of at four brachium pontis photovoltaic DC-to-AC converter center line arm controlling models belongs to photovoltaic parallel in system control technology field.

Background technology

Along with the consumption of non-renewable energy resources, the harshness of environment situation and the lasting rising of energy demand, new energy technology has obtained paying close attention to widely as a kind of practicable energy solution route of human future development.Photovoltaic parallel in system is the active platform that solar energy generation technology is used.Be applicable to the photovoltaic combining inverter of low-voltage network, need obtain zero line usually.Obtain in the mode of center line, use four brachium pontis photovoltaic DC-to-AC converters stronger zero sequence compensation ability to be arranged, and be more suitable in adopting advanced control method, balance DC side midpoint potential than three brachium pontis photovoltaic DC-to-AC converters, thereby effectively suppress its current in middle wire, improve the system works performance.

The balance method of midpoint potential commonly used has: 1) adopt the multipath independent direct current source; 2) adopt balance resistance, the dc capacitor voltage mid point is linked to each other with the neutral line; 3) select Vector Modulation action time and order.Wherein method 1) increased device volume and energy consumption; Method 2) simple in structure but effect is relatively poor; Have certain limitation when method 3) using, for example some special P WM modulation scheme all is only applicable to multi-electrical level inverter and does not connect center line.And by independently center line arm is set, center line arm mid point linked to each other with the DC side mid point control the method for mid point input and output electric current, the center line arm can independently be controlled and most current in middle wire will effectively reduce the dc bus capacitor capacity mainly by the switching device of center line arm.

Utilize classical control theory to control the center line arm, must adopt fully big amplitude gain and phase margin, just can make reponse system when big disturbance, still keep systematic function and effectively suppress disturbing; And it can't directly apply to multi-input multi-output system.H ∞ is a kind of method of design multivariable input and output (MIMO) robust control system in the modern control theory, H ∞ control theory is as the important method of modern robust control theory, have overcome probabilistic influence, simultaneously keep system operation stability, improve advantages such as control precision, system's interference free performance, and multi-input multi-output system use do not have extra demand.The present invention proposes to use H ∞ control method to come the controlling of four brachium pontis photovoltaic DC-to-AC converter center line controlling models DC side neutral balances realized corresponding broad sense controlled device P first, has provided the method for designing of H ∞ controller, the system of selection of weighting function.The invention belongs to understandable technological improvement scope in the development in science and technology process.

Summary of the invention

The objective of the invention is, adopt classical control theory to control the problem that the center line arm exists at four brachium pontis photovoltaic DC-to-AC converters, the present invention adopts a kind of DC side neutral balance control method and controller design method, guarantee when big current in middle wire, still can keep the stable of photovoltaic DC-to-AC converter DC side mid point, improve the performance of photovoltaic DC-to-AC converter.

Technical scheme of the present invention is, the present invention adopts a kind of DC side neutral balance control method that is applicable to four brachium pontis photovoltaic DC-to-AC converter center line arm controlling models, wherein center line arm controlling models comprises photovoltaic DC input, electric capacity of voltage regulation, DC voltage booster circuit, DC side is flat to involve the equivalent bleeder resistance of the equivalence of two groups of electric capacity of energy storage, two series connection, a center line inductance that connects center line arm mid point and capacitance group mid point, and the center line arm.Described method comprises DC side neutral point voltage balance H ∞ control modeling and H ∞ design of Controller, the realization of broad sense controlled device P, the realization of closed loop transfer function, and the selection of weighting function.

Described method adopts H ∞ control method design H ∞ controller,, makes from input current in middle wire i as control variables with the mean value p of signal in switch periods of center line arm switch function _N, measure error n, equivalent external disturbance V ₀To two electric capacity of output half V with respect to the neutral point voltage sum _Ave, center line arm mid-point voltage u _NThe infinite norm minimum of H.

The present invention proposes a kind of DC side neutral point voltage balance control method that is applicable to above-mentioned model.The target of its control is to ensure measure error n, equivalent external disturbance V ₀And bigger current in middle wire i _NAll to two electric capacity half V with respect to the neutral point voltage sum _AveInfluence very little because capacitance group mid-point voltage V _C=V _Ave-V ₀, also just guaranteed the balance of DC side mid-point voltage.

The present invention be overcome probabilistic influence in the center line arm control procedure, simultaneously keep system operation stability, improve control precision, system's interference free performance etc., adopt H ∞ control method center line arm to control.With i _N, V _cBe the initial condition variable; The mean value p of signal is control variables u in switch periods of center line arm switch function; i _N, and with n, V ₀Linear respectively I _n, I ₀As input w, obtain state equation; With V _Ave, u _NRespectively with weighting function W _v, W _uProduct as output z; With the capacitive branch current i that obtains by the detection link _C, through low-pass filtering link F (s), and the V that obtains of stack n _i, and V _AveBe output y.Definition broad sense controlled device P satisfies

So just can realize controlled target in the hope of from being input to the H ∞ minimum norm of output.

The present invention is with V _Ave, V _iBe the controller input, u is output.Obtain from w '=[i by H ∞ control algolithm _NV ₀N] ^TTo z '=[V _Aveu _N] ^TClosed loop transfer function,, adopt MATLAB to calculate optimum H ∞ controller K=[K _vK _i], and its any zero limit greater than the 10000rad/s corner frequency replaced by a proportionality coefficient, obtain reduced order controller K _rIts weighting function is selected W _vIn that effectively forcing frequency scope place value is big, little in the high frequency treatment value; W _uLittle in the low frequency duration, the high frequency treatment value is big.And to set its lower frequency limit be w _l=1rad/s, upper limiting frequency is w _h=10000rad/s.

The present invention's beneficial effect compared with the prior art is, adopt the optimum H ∞ controller of H ∞ control algolithm design, and reduced order controller can guarantee that systematic measurement error, equivalent external disturbance are very little to the stabilizing influence of DC side mid-point voltage, even occur bigger current in middle wire simultaneously, mid-point voltage also can be stablized.This service behaviour to four brachium pontis photovoltaic DC-to-AC converters has greatly improved, thereby the power quality controlling work of being incorporated into the power networks contributes to new forms of energy indirectly.

The four brachium pontis photovoltaic DC-to-AC converter center line arm mid points that the present invention is applicable to power distribution network or microgrid when center line arm control model that the center line inductance links to each other with DC side, the Balance Control of its DC side mid-point voltage.

Description of drawings

Fig. 1 is described four brachium pontis photovoltaic DC-to-AC converter center line arm controlling models structural representations;

Fig. 2 is for being fit to the center line arm control block diagram of the described controlling models of Fig. 1;

Fig. 3 is for being fit to the described center line arm of Fig. 2 H ∞ controlling models;

Picture in picture number expression: the 1st, the photovoltaic input; The 2nd, DC voltage booster circuit; The 3rd, the center line arm; The 4th, photovoltaic inversion three-phase bridge.

Embodiment

The specific embodiment of the present invention comprises: set up four brachium pontis photovoltaic DC-to-AC converter center line arm controlling models; DC side neutral point voltage balance H ∞ control modeling and H ∞ design of Controller; The realization of broad sense controlled device P; The realization of closed loop transfer function; The selection of weighting function.

(1) sets up four brachium pontis photovoltaic DC-to-AC converter center line arm controlling models

With neutral point N is benchmark, and defining two electric capacity is V with respect to half of the voltage sum of neutral point _Ave, the difference of voltage is the dc voltage value, then has:

$\left[\begin{array}{c}{V}_{+}\\ V_{-}\end{array}\right]=\left[\begin{array}{cc}0.5& 1\\ -0.5& 1\end{array}\right]\left[\begin{array}{c}{V}_{\mathrm{dc}}\\ V_{\mathrm{ave}}\end{array}\right]---\left(1\right)$

Definition DC side electrochemical capacitor foozle is an external disturbance:

$V_0=-\frac{C_{N+}-C_{N-}}{C_{N+}+C_{N-}}\·\frac{V_{\mathrm{dc}}}{2}---\left(2\right)$

Capacitive branch current i then _CTo satisfy:

$i_C=(C_{N+}+C_{N-})\frac{d(V_{\mathrm{ave}}-V_0)}{\mathrm{dt}}---\left(3\right)$

Because center line arm mid-point voltage u _NQ has identical waveform with center line arm switch function, and definition is a control variables with the mean value p of q in a switch periods, u _NMean value can be:

$u_N=d{V}_{+}+(1-d)V_{-}=\frac{p}{2}{V}_{\mathrm{dc}}+V_{\mathrm{ave}}---\left(4\right)$

In conjunction with Fig. 1 by Kirchhoff's theorem, the circuit characteristic equation that obtains:

$\left\{\begin{array}{c}{u}_N=L_N\frac{{\mathrm{di}}_L}{\mathrm{dt}}+R_N{i}_L\\ i_N=i_L+i_C\end{array}\right.---\left(5\right)$

Can obtain as shown in Figure 2 corresponding center line arm controlling models by formula (3) (4) (5), wherein dc voltage can be stable by DC voltage booster circuit from net the time, and being incorporated into the power networks constantly can be by the closed-loop control of three-phase inverter direct voltage, so disturbance is less.This controlling models can dynamically be controlled the dc voltage mid point when big current in middle wire disturbance and external condition interference.

(2) DC side neutral point voltage balance H ∞ control modeling and H ∞ design of Controller

For overcoming control system itself uncertain (comprising the uncertainty of Mathematical Modeling itself and the uncertainty of external interference), adopt H ∞ control theory that the DC side neutral point voltage balance is controlled.By H ∞ control theory standard control block diagram and center line arm controlling models shown in Figure 2, can set up H ∞ controlling models shown in Figure 3.Wherein disturbance is current in middle wire i _N, V ₀Be equivalent external interference.One low pass filter F (s) filtering i is set simultaneously _CNear the switching frequency that contains ripple.The definition filter not ripple of filtering is measure error n.Represent Laplace transformation with ^, then have: For avoiding u _NToo big (V-＜u in the reality _N＜V ₊), by weighting function W is set _vWith V _AveMultiply each other W _uWith u _nMultiply each other, can design feasible system on the engineering.Introduce two new variables I simultaneously ₀And I _n, they respectively with V ₀, n is proportional.Its corresponding proportionality coefficient is ρ, ζ.Then H control problem can be summed up as minimize from the input w=[i _NI ₀I _n] ^TTo output z=[V _vV _u] ^TPass the H ∞ norm of letter, it is defined as: T _Zw=ξ _l(P, K).Closed-loop system can be described as with Laplace transformation:

$\left[\begin{array}{c}\hat{z}\\ \hat{y}\end{array}\right]=P\left[\begin{array}{c}\hat{w}\\ \hat{u}\end{array}\right],\hat{u}=K\hat{y}$

In the following formula, P is the broad sense controlled device, and K is a The controller.Utilize the MATLAB instrument, K=[K _vK _i] optimal value can draw by H ∞ control algolithm (as 2-Riccati equation algorithm), for the engineering practical application may, its any zero limit greater than the 10000rad/s corner frequency is replaced by a proportionality coefficient, obtain reduced order controller K _r

$K_v\left(s\right)=\frac{-0.0025(s-9.134\×{10}^{10})(s+8.041\×{10}^4)(s+1.002\×{10}^4)(s+80.12)(s+73.21)}{(s+3.126\×{10}^8)(s+1.032\×{10}^5)(s+6061)(s+76.03)(s+1)}$

$K_i\left(s\right)=\frac{5.9668\×{10}^8(s+{10}^4)(s+1000)(s+80)}{(s+3.126\×{10}^8)(s+1.032\×{10}^5)(s+6061)(s+76.03)}$

$K_r\left(s\right)=\left[\begin{array}{cc}0.5692\frac{(s+1.002\×{10}^4)(s+80.12)(s+73.21)}{(s+6061)(s+76.03)(s+1)}& 1.9088\frac{(s+{10}^4)(s+1000)(s+80)}{(s+1.032\×{10}^5)(s+6061)(s+76.03)}\end{array}\right]$

(3) realization of broad sense controlled device P

Select inductive current i _LAnd V _C=V _Ave-V ₀As the initial condition variable, that is:

Simultaneously, control input variable u=p then can obtain following state equation by Fig. 3:

$\stackrel{\·}{x}=\mathrm{Ax}+B_{1}w+B_{2}u---\left(7\right)$

$A=\left[\begin{array}{cc}-\frac{R_N}{L_N}& \frac{1}{L_N}\\ -\frac{1}{C_{N+}+C_{N-}}& 0\end{array}\right]{\mathrm{<figure-callout\; id="1"\; label="B"\; filenames="HSA00000297469500012.png,HSA00000297469500021.png"\; state="\{\{state\}\}">B</figure-callout>}}_1=\left[\begin{array}{ccc}0& \frac{\mathrm{\&rho;}}{L_N}& 0\\ \frac{1}{C_{N+}+C_{N-}}& 0& 0\end{array}\right]{\mathrm{<figure-callout\; id="2"\; label="B"\; filenames="HSA00000297469500011.png,HSA00000297469500021.png"\; state="\{\{state\}\}">B</figure-callout>}}_2=\left[\begin{array}{c}\frac{V_{\mathrm{dc}}}{2L_N}\\ 0\end{array}\right]$

Output equation is as follows:

V _Ave=C _aX+D _1aW+D _2aU i _C=C _2bX+D ₂₁Bw+D ₂₂Bu u _N=C _1bX+D _11bW+D _12bUC _a=[0 1] D _1a=[0 ρ 0] D _2a=[0] C _1b=[0 1] D _11b=[0 ρ 0] D _12b=[V _Dc/ 2] C _2b=[1 0] D _21b=[1 0 0] D _22bWeighting function W is supposed in=[0] _v, W _u, and the F structure as follows:

This symbology W _v(s)=D _v+ C _v(sI-A _v) ^-1B _v, have so:

In conjunction with above-mentioned three formulas, can be at known input w, being achieved as follows of broad sense controlled device P under u and output z and the y:

(4) realization of closed loop transfer function,

Definition

P ₊For from

Arrive Transfer function, so:

Suppose that controller architecture to be designed is as follows:

Usually use H ∞ control algolithm to obtain the K value, D is then arranged _k=0.According to classical formulas, can try to achieve the transfer function of w, wherein to z '

Further, from W is as follows to the closed loop transfer function, of z ':

$T_{z^{\&prime;}{w}^{\&prime;}}=T_{z^{\&prime;}w}\left[\begin{array}{ccc}1& 0& 0\\ 0& 1/\mathrm{\&rho;}& 0\\ 0& 0& 1/\mathrm{\&zeta;}\end{array}\right]$

(5) selection of weighting function

Specific H ∞ control problem, suitable weighting function must be able to reflect the relative weighting of unlike signal and frequency characteristic separately, makes corresponding equation separate simultaneously.The selection principle of weighting function is as follows among the present invention:

1) because switching frequency has limited attainable control bandwidth, weighting function Wu must satisfy:

Value is bigger at effective forcing frequency scope place (50Hz and integral multiple thereof are inferior); But it is little in the high frequency treatment value.Therefore, can select weighting function following (wherein g is a regulated variable) in the reality:

2) signal u _NAlmost linear with u=p.

So should avoid the u value to become big, particularly high frequency treatment.Therefore, should select can be little and at the big weighting function W of high frequency duration in the low frequency duration _uH ∞ control conventional algorithm requires matrix

Be necessary for the row non-singular matrix.And D _2a=0 o'clock, D _uThen can not be zero.So, when we design, W _uMust use approximation to replace, can select as follows:

$W_u\left(s\right)=k\frac{s+w_l}{s+w_h}=\left[\begin{array}{cc}-w_h& k\\ w_l-w_h& k\end{array}\right]$

In the following formula, the k value can be adjusted W _uBaud curve offset amount.Wherein fundamental frequency is 50Hz, and HFS can be to 31 subharmonic.Set w _hBe 10000rad/s, k=0.1, g=10.

Claims (4)

1. DC side control method at four brachium pontis photovoltaic DC-to-AC converter center line arm controlling models, wherein center line arm controlling models comprises the flat equivalent bleeder resistance of the equivalence of two groups of electric capacity of energy storage, two series connection, the center line inductance center line arm that connects center line arm mid point and capacitance group mid point of involving of DC side, it is characterized in that

Described method comprises DC side neutral point voltage balance H ∞ control modeling and H ∞ design of Controller, the realization of broad sense controlled device P, the realization of closed loop transfer function, and the selection of weighting function;

Described method adopts H ∞ control method design H ∞ controller,, makes from input current in middle wire i as control variables with the mean value p of signal in switch periods of center line arm switch function _N, measure error n, equivalent external disturbance V ₀To two electric capacity of output half V with respect to the neutral point voltage sum _Ave, center line arm mid-point voltage u _NThe infinite norm minimum of H.

2. the DC side control method at four brachium pontis photovoltaic DC-to-AC converter center line arm controlling models according to claim 1 is characterized in that the implementation method of described broad sense controlled device P is that described H ∞ controller is with i _N, capacitance group mid-point voltage V _cBe the initial condition variable; P is control variables u; i _N, and with n, V ₀Linear respectively I _n, I ₀As input w, obtain state equation; With V _Ave, u _NRespectively with weighting function W _v, W _uProduct as output z; With the capacitive branch current i that obtains by the detection link _C, through low-pass filtering link F (s), and the V that obtains of stack n _i, and V _AveBe output y, broad sense controlled device P satisfies

${\left[\begin{array}{cc}\hat{z}& \hat{y}\end{array}\right]}^T=P{\left[\begin{array}{cc}\hat{w}& \hat{u}\end{array}\right]}^T.$

3. the DC side control method at four brachium pontis photovoltaic DC-to-AC converter center line arm controlling models according to claim 1 is characterized in that, described closed loop transfer function, for by H ∞ control algolithm try to achieve from w '=[i _NV ₀N] ^TTo z '=[V _Aveu _N] ^TClosed loop transfer function,, calculate optimal controller K=[K by MATLAB _vK _i], its any zero limit greater than the 10000rad/s corner frequency is replaced by a proportionality coefficient, obtain reduced order controller K _r

4. the DC side control method at four brachium pontis photovoltaic DC-to-AC converter center line arm controlling models according to claim 1 is characterized in that described weighting function W _v, W _uBe chosen as W _vIn that effectively forcing frequency scope place value is big, little in the high frequency treatment value; W _uLittle in the low frequency duration, the high frequency treatment value is big; Setting its lower frequency limit is w _l=1rad/s, upper limiting frequency is w _h=10000rad/s.

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