CN104578167A - Power feedforward control method for single stage type three-phase photovoltaic grid-connected inverter - Google Patents

Abstract

The invention discloses a power feedforward control method for a single stage type three-phase photovoltaic grid-connected inverter. The single stage type three-phase photovoltaic grid-connected inverter consists of a photovoltaic cell panel, a three-phase grid-connected inverter body and a filtering link. According to an inverter grid-connected control strategy, a current inner ring is provided with a PI (proportional integral) adjuster, a new PI computing method is used, an outer ring is controlled in a power feedforward manner, and the frequency and the phase of grid-connected current outputted by the inverter are the same with those of voltage of a power grid. The problem that parameters of the adjuster are not consistent in simulation and test is solved. Blindness of trial and errors of parameters of the PI adjuster in a test process is avoided, a test debugging process is accelerated, the time is saved, and the efficiency is high. The power feedforward control method has a wide application prospect in the field of grid connection of inverters.

Description

The power feedforward control method of single stage type three-phase photovoltaic grid-connected inverting device

Technical field

The present invention relates to photovoltaic combining inverter grid-connected control method, particularly the power feedforward control method of combining inverter, belong to power electronics photovoltaic combining inverter closed loop control method field.

Background technology

Stage photovoltaic single grid-connected system forms primarily of photovoltaic battery array, dc-link capacitance Cpv, DA/AC current transformer, output filter and electrical network.Its operation principle is: the voltage of DC side is raised to guarantee that inverter can normally work by connection in series-parallel by photovoltaic cell component.Realize the grid-connected of MPPT maximum power point tracking and unity power factor by control DC/AC converter simultaneously.Therefore can find out, stage photovoltaic single combining inverter just can complete MPPT maximum power point tracking and these two functions grid-connected by means of only one-level inverter, the efficiency that stage photovoltaic single grid-connected system overcomes the multilevel energy conversion of the photovoltaic synchronization inverter system of traditional two-stage type is low, power consumption high shortcoming, circuit is simple, and required components and parts are few; Without energy storage link, decrease risk capital.

For stage photovoltaic single combining inverter in order to enable grid-connected current and line voltage with frequency homophase, general method adopts Double closed-loop of voltage and current, electric current loop and Voltage loop all adopt pi regulator, in stage photovoltaic single combining inverter, DC bus-bar voltage given is the disturbance voltage of MPPT algorithm, and therefore the given reference value of DC bus-bar voltage is the amount of a change in MPPT perturbation process.Outer shroud controls the given reference value must following the tracks of change fast, and to ensure the correctness of MPPT Perturbed algorithms, current inner loop also must have higher response speed to meet the requirement of outer voltage simultaneously.If outer voltage adopts pi regulator, and when needing to improve outer voltage bandwidth to meet dynamic performance, its stability can be affected.

Summary of the invention

The object of the invention is to solve known stage photovoltaic single combining inverter control in current inner loop and outer voltage when adopting pi regulator, when needs improve outer voltage bandwidth to meet dynamic performance, the affected problem of its stability, proposition simply and reliably can realize the power feedforward control method of single stage type three-phase photovoltaic grid-connected inverting device, and proposes a kind of new PI computational methods.

For solving the problems of the technologies described above, the technical solution used in the present invention is:

In the present invention, the current regulator of three-phase photovoltaic grid-connected inverting device adopts pi regulator, first by three-phase abc coordinate system transformation under two-phase dq synchronous rotating frame, realize the transformation of of ac to DC quantity, then decoupling zero is carried out to d, q axle, remove their coupling terms, realize the independent control to d axle and q axle, and realize the calculating to electric current loop pi regulator parameter.

Calculating for pi regulator have employed a kind of new computational methods, and the computational methods of pi regulator parameter are:

1) can obtain its closed loop transfer function, according to the control block diagram of electric current loop is:

$G_c\left(s\right)=\frac{{\mathrm{kk}}_{p}s+{\mathrm{kk}}_i}{{\mathrm{Ls}}^2+({\mathrm{kk}}_p+r)s+{\mathrm{kk}}_i}$

Omitted by resistance in inductance, namely the r in closed loop transfer function, is dispensed, can obtain a new closed loop transfer function, this system is regarded as an approximate system, and the major premise changing into approximation system is: wherein k _ipfor the proportional gain factor of electric current loop, k _iifor integration gain factor, N is error (N is more little more similar), during process above formula closed-loop system, has negative real root to design pi regulator by it.

2) the system closed loop transfer function, after approximate processing is:

$G_c\left(s\right)=\frac{\frac{s}{\frac{k_{\mathrm{ii}}}{k_{\mathrm{ip}}}}+1}{\frac{L}{{\mathrm{Kk}}_{\mathrm{ii}}}{s}^2+\frac{k_{\mathrm{ip}}}{k_{\mathrm{ii}}}s+1}=\frac{\frac{s}{a_1}+1}{(\frac{s}{a_2}+1)(\frac{s}{a_3}+1)}$

Wherein, if a ₁with a ₂approximately equal, then can offset, and carries out abbreviation to its closed loop transfer function, wherein, and a ₃for closed-loop system bandwidth, a ₁with a ₂can only approximately equal, therefore in order to characterize a ₁with a ₂equality, if n, more close to 1, offsets degree better, and the approximation system finally obtained is more close with real system, according to a ₂, a ₃relation and a ₂expression formula, can obtain:

$k_{\mathrm{ip}}=\frac{{\mathrm{Lna}}_3}{K}$

As N=10%, $\frac{{k_{\mathrm{ip}}}^2}{k_{\mathrm{ii}}}>\frac{4L}{\mathrm{KN}}\⇒\frac{{k_{\mathrm{ip}}}^2}{k_{\mathrm{ii}}}\≥\frac{40L}{K}\⇒\frac{k_{\mathrm{ip}}}{d}\≥\frac{40L}{K}\⇒d\≤\frac{K{k}_{\mathrm{ip}}}{40L}\⇒d\≤\frac{a_{3}n}{40},$ Wherein, d=k _ii/ k _ip, meet engineering precision time equal in above formula, in order to accurate further, if

$d=\frac{a_{3}n}{40}m,0<m<1$

The less approximate condition satisfaction degree of m is better, and approximation system differs less with real system, according to expression formula and the k of d _ipexpression formula obtain:

$k_{\mathrm{ii}}=\frac{{\mathrm{Ln}}^2{a}_3^{2}m}{40K}$

3) calculating proportional gain factor k is obtained above _ipwith integration gain factor k _iiformula, determine n and m relation below, according to 2) in closed loop transfer function, after approximate processing, two closed-loop pole can be obtained, according to calculating proportional gain factor k _ipwith integration gain factor k _iiformula also have approximate processing after two closed-loop poles of the closed loop transfer function, expression formula that can obtain m and n be:

$m=\frac{40n-40}{n^2}$

Wherein, n>1, gets n=1.005, m=0.19801.

The outer shroud of three-phase grid-connected inverter adopts power feedforward to control, and directly the information of input power can be passed to the given of grid-connected current like this, system be played to the effect of quick adjustment, and power feedforward controls sampling inverter input side voltage U _dcand electric current I _dc, calculate the power P of inverter input side, ignore inverter switching device loss and line loss, equal with grid-connected power by inverter input side power, can i be calculated _pdf.

$i_{\mathrm{pdf}}=\frac{2P}{3e_d}$

Wherein e _dfor voltage on line side, by i _pdfas the output variable i of feedforward amount and outer voltage adjuster _rbe added given as d shaft current, such as formula

i _d ^*＝i _pdf+i _r

Wherein i _d ^*for d shaft current is given, the switching loss of inverter and line loss can be regulated by the proportional component of outer voltage adjuster, because the given of d shaft current comprises input power in power feedforward algorithm.When input power changes, directly information can be passed to grid-connected current controlling unit, the response speed of system can be improved like this, realize the dynamic adjustments of MPPT.

Beneficial effect of the present invention is:

Because the given of d shaft current comprises input power in power feedforward algorithm.When input power changes, directly information can be passed to grid-connected current controlling unit, the response speed of system can be improved like this, make outer shroud control to follow the tracks of fast the given reference value of change, ensure that the correctness of MPPT Perturbed algorithms.The regulator parameter adopting new PI computational methods to calculate, solves the problem that in emulation and experiment, regulator parameter is inconsistent.To it also avoid in experimentation because pi regulator parameter tries the blindness of gathering simultaneously, experimental debugging process can be accelerated, time-saving and efficiency.

Accompanying drawing explanation

Below in conjunction with the drawings and specific embodiments, the present invention is further detailed explanation.

Fig. 1 is three-phase photovoltaic grid-connected inverting device system construction drawing of the present invention.

Fig. 2 is d shaft current ring structure block diagram of the present invention.

Fig. 3 is system schematic of the present invention.

Fig. 4 is power feedforward control block diagram.

Embodiment

The power feedforward control method of single stage type three-phase photovoltaic grid-connected inverting device, comprises the following steps:

The power feedforward control method of step 1 single stage type three-phase photovoltaic grid-connected inverting device adopts Double closed-loop of voltage and current;

Step 2 single stage type three-phase photovoltaic grid-connected inverting device current inner loop adopts traditional PI to control, wherein the parameter of pi regulator adopts a kind of closed loop transfer function, directly to calculate the computational algorithm of the parameter of adjuster, series resistance in inductance is ignored, regarded as an approximation system, be there is negative real root to design pi regulator, in current inner loop by it, d, q axle achieves decoupling zero, system can carry out independent control respectively to d axle and q axle, for d axle, and given current i ^* _d, with grid-connected current i _ddo difference, produce the work of drive waveforms control inverter through pi regulator;

Step 3 outer voltage adopts power feedforward to control, and directly the information of input power is passed to the given of grid-connected current, system is played to the effect of quick adjustment.

The voltage of sampling inverter input side and Current calculation obtain the power of inverter input side, ignore inverter switching device loss and line loss, equal with grid-connected power by inverter input side power, can obtain current i _pdf,

$i_{\mathrm{pdf}}=\frac{2P}{3e_d}$

By i _pdfto be added as d shaft current with the output variable of line voltage outer shroud adjuster as feedforward amount given, because the given of d shaft current comprises input power in such power feedforward algorithm, when input power changes, directly information can be passed to grid-connected current controlling unit.

In described step 2, the computational methods of pi regulator parameter are:

21) can obtain its closed loop transfer function, according to the control block diagram of electric current loop is:

$G_c\left(s\right)=\frac{{\mathrm{kk}}_{p}s+{\mathrm{kk}}_i}{{\mathrm{Ls}}^2+({\mathrm{kk}}_p+r)s+{\mathrm{kk}}_i}$

Omitted by resistance in inductance, namely the r in closed loop transfer function, is dispensed, can obtain a new closed loop transfer function, this system is regarded as an approximate system, and the major premise changing into approximation system is: wherein k _ipfor the proportional gain factor of electric current loop, k _iifor integration gain factor, N is error (N is more little more similar), during process above formula closed-loop system, has negative real root to design pi regulator by it;

22) the system closed loop transfer function, after approximate processing is:

$G_c\left(s\right)=\frac{\frac{s}{\frac{k_{\mathrm{ii}}}{k_{\mathrm{ip}}}}+1}{\frac{L}{{\mathrm{Kk}}_{\mathrm{ii}}}{s}^2+\frac{k_{\mathrm{ip}}}{k_{\mathrm{ii}}}s+1}=\frac{\frac{s}{a_1}+1}{(\frac{s}{a_2}+1)(\frac{s}{a_3}+1)}$

Wherein, a ₁with a ₂approximately equal, can offset, and carries out abbreviation to closed loop transfer function, wherein, and a ₃for closed-loop system bandwidth, a ₁with a ₂can only approximately equal, in order to characterize a ₁with a ₂equality, if n, more close to 1, offsets degree better, and the approximation system finally obtained is more close with real system, according to a ₂, a ₃relation and a ₂expression formula, try to achieve k _ipexpression formula be:

$k_{\mathrm{ip}}=\frac{{\mathrm{Lna}}_3}{K}$

23) in order to accurate further, adopt:

$d=\frac{a_{3}n}{40}m,0<m<1$

Wherein, d=k _ii/ k _ip, the less approximate condition satisfaction degree of m is better, and approximation system differs less with real system, according to expression formula and the k of d _ipexpression formula obtain k _iiexpression formula be:

$k_{\mathrm{ii}}=\frac{{\mathrm{Ln}}^2{a}_3^{2}m}{40K}$

24) according to the closed loop transfer function, after approximate processing in step 21, two closed-loop pole can be obtained, according to calculating proportional gain factor k _ipwith integration gain factor k _iiformula also have approximate processing after two closed-loop poles of closed loop transfer function, can obtain the expression formula of m and n, its expression formula adopts:

$m=\frac{40n-40}{n^2}$

Wherein, n>1, gets n=1.005, m=0.19801.

Fig. 1 is three-phase photovoltaic grid-connected inverting device system construction drawing of the present invention.This system visible is made up of photovoltaic cell component, three-phase inverter, filtering link and electrical network, wherein C _pvfor dc-link capacitance, L is three-phase filter inductance, and r is the equivalent series resistance of inductance, and C is output filter capacitor, e _a, e _b, e _cbe respectively three-phase symmetrical line voltage, u _a, u _b, u _cfor inverter ac side output voltage, the mid point of line voltage and the mid point of output filter capacitor are equipotentiality points, are O point.Photovoltaic cell component carries out connection in series-parallel and makes its output reach requirement, through dc-link capacitance, converting through inverter, be connected to the grid after eventually passing filter, through the Closed-loop Control Strategy of MPPT and inverter, make the efficiency of inverter reach the highest, grid-connected current and line voltage are with frequency homophase.

Fig. 2 is d shaft current ring structure block diagram of the present invention.By three-phase abc coordinate system transformation under two-phase dq synchronous rotating frame, realize the transformation of of ac to DC quantity, then decoupling zero is carried out to d, q axle, remove their coupling terms, realize the independent control to d axle and q axle, given value of current i _d ^*=i _pdf+ i _r, electric current loop adopts pi regulator, and in order to eliminate the impact of grid disturbances on system, feedover in the controlling to it, the coefficient of voltage feed-forward control link is G _fs ()=1/K, electric current eventually passes filtering link and is connected to the grid.

Fig. 3 is system schematic of the present invention.I in figure _pvfor photovoltaic cell output current (A), I _cfor dc-link capacitance charging current (A), i _dfor grid-connected current (A), U _dfor grid-connected voltage (V), if ignore switching tube loss and line loss, photovoltaic system power output equals the grid-connected power of inverter, i.e. (3/2) e _di _d=u _dci _dcbe I according to the current relationship of node current method dc-link capacitance _c=I _pv-I _dc, therefore can in the hope of U _dc=I _c/ SC.

Fig. 4 is power feedforward control block diagram.Power feedforward controls sampling inverter input side voltage U _dcand electric current I _dc, calculate the power P of inverter input side, ignore inverter switching device loss and line loss, equal with grid-connected power by inverter input side power, can calculate wherein e _dfor voltage on line side, by i _pdfas the output variable i of feedforward amount and outer voltage adjuster _rbe added given as d shaft current, such as formula i _d ^*=i _pdf+ i _r, wherein i _d ^*for d shaft current is given, because the given of d shaft current comprises input power in power feedforward algorithm.When input power changes, directly information can be passed to grid-connected current controlling unit, the response speed of system can be improved like this, realize the dynamic adjustments of MPPT.

Be only the specific embodiment of this patent above, but this patent is not limited thereto, for the person of ordinary skill of the art, under the premise without departing from the principles of the invention, the distortion made should be considered as belonging to scope.

Claims (3)

1. the power feedforward control method of single stage type three-phase photovoltaic grid-connected inverting device, is characterized in that comprising the following steps:

The power feedforward control method of step 1 single stage type three-phase photovoltaic grid-connected inverting device adopts Double closed-loop of voltage and current;

Step 2 single stage type three-phase photovoltaic grid-connected inverting device current inner loop adopts traditional PI to control, wherein the parameter of pi regulator adopts a kind of closed loop transfer function, directly to calculate the computational algorithm of the parameter of adjuster, series resistance in inductance is ignored, regarded as an approximation system, be there is negative real root to design pi regulator, in current inner loop by it, d, q axle achieves decoupling zero, system can carry out independent control respectively to d axle and q axle, for d axle, and given current i ^* _d, with grid-connected current i _ddo difference, produce the work of drive waveforms control inverter through pi regulator;

Step 3 outer voltage adopts power feedforward to control, and directly the information of input power is passed to the given of grid-connected current, system is played to the effect of quick adjustment.

2. the power feedforward control method of single stage type three-phase photovoltaic grid-connected inverting device according to claim 1, it is characterized in that: the voltage of sampling inverter input side and Current calculation obtain the power of inverter input side, ignore inverter switching device loss and line loss, equal with grid-connected power by inverter input side power, can current i be obtained _pdf,

$i_{\mathrm{pdf}}=\frac{2P}{{3e}_d}$

By i _pdfto be added as d shaft current with the output variable of line voltage outer shroud adjuster as feedforward amount given, because the given of d shaft current comprises input power in such power feedforward algorithm, when input power changes, directly information can be passed to grid-connected current controlling unit.

3. the power feedforward control method of single stage type three-phase photovoltaic grid-connected inverting device according to claim 1, is characterized in that, in described step 2, the computational methods of pi regulator parameter are:

21) can obtain its closed loop transfer function, according to the control block diagram of electric current loop is:

$G_C\left(s\right)=\frac{{\mathrm{kk}}_{p}s+{\mathrm{kk}}_i}{{\mathrm{Ls}}^2+({\mathrm{kk}}_p+r)s+{\mathrm{kk}}_i}$

Omitted by resistance in inductance, namely the r in closed loop transfer function, is dispensed, can obtain a new closed loop transfer function, this system is regarded as an approximate system, and the major premise changing into approximation system is: wherein k _ipfor the proportional gain factor of electric current loop, k _iifor integration gain factor, N is error (N is more little more similar), during process above formula closed-loop system, has negative real root to design pi regulator by it;

22) the system closed loop transfer function, after approximate processing is:

$G_c\left(s\right)=\frac{\frac{s}{\frac{k_{\mathrm{ii}}}{k_{\mathrm{ip}}}}+1}{\frac{L}{{\mathrm{Kk}}_{\mathrm{ii}}}{s}^2+\frac{k_{\mathrm{ip}}}{k_{\mathrm{ii}}}s+1}=\frac{\frac{s}{a_1}+1}{(\frac{s}{a_2}+1)(\frac{s}{a_3}+1)}$

Wherein, a ₁with a ₂approximately equal, can offset, and carries out abbreviation to closed loop transfer function, wherein, and a ₃for closed-loop system bandwidth, a ₁with a ₂can only approximately equal, in order to characterize a ₁with a ₂equality, if n, more close to 1, offsets degree better, and the approximation system finally obtained is more close with real system, according to a ₂, a ₃relation and a ₂expression formula, try to achieve k _ipexpression formula be:

$k_{\mathrm{ip}}=\frac{{\mathrm{Lna}}_3}{K}$

23) in order to accurate further, adopt:

$d=\frac{a_{3}n}{40}m,0<m<1$

Wherein, d=k _ii/ k _ip, the less approximate condition satisfaction degree of m is better, and approximation system differs less with real system, according to expression formula and the k of d _ipexpression formula obtain k _iiexpression formula be:

$k_{\mathrm{ii}}=\frac{{\mathrm{Ln}}^2{a}_3^{2}m}{40K}$ 2 -->

24) according to the closed loop transfer function, after approximate processing in step 21, two closed-loop pole can be obtained, according to calculating proportional gain factor k _ipwith integration gain factor k _iiformula also have approximate processing after two closed-loop poles of closed loop transfer function, can obtain the expression formula of m and n, its expression formula adopts:

$m=\frac{40n-40}{n^2}$

Wherein, n>1, gets n=1.005, m=0.19801.3 -->