CN104319818A - Grid connection and independence dual mode switching method based on grid voltage positive sequence extractor - Google Patents

Abstract

The invention discloses a grid connection and independence dual mode switching method based on a grid voltage positive sequence extractor. The switching method can be used in a photovoltaic three-phase distributed power generation system, a fan three-phase distributed power generation system, a fuel cell three-phase distributed power generation system and other three-phase distributed power generation systems. The grid voltage positive sequence extractor, the switching process from grid connection to independence, grid connection current control, the switching process from independence to grid connection and load voltage control are involved in the switching method. The grid voltage positive sequence extractor can extract the positive-sequence component of a three-phase grid in a grid connection mode without amplitude attenuation or phase deviation, provide a phase position for load voltage control in an independence mode and trace grid voltage when the grid voltage is recovered. Based on the extractor, by the adoption of a proportional double-resonance controller, current control in the grid connection mode and load voltage control in the independence mode have good performance and ensure seamless switching between the grid connection mode and the independence mode.

Description

A kind of based on the grid-connected of line voltage positive sequence extractor and independent double mode changing method

Technical field

The invention belongs to distributed power generation field, can be applicable in the three-phase distributed generation systems such as photovoltaic, blower fan, fuel cell.

Background technology

The new forms of energy distributed grid-connected generatings such as solar energy, wind energy, fuel cell are at the current most attention being subject to countries in the world.These new forms of energy access electrical network by combining inverter, in the normal situation of line voltage, can according to the phase place of line voltage, and stably to electrical network transmission power.But, when grid cut-off, the ac output end of inverter and electrical network parallel off.Now, the output voltage of inverter can change, and generally, common grid-connected inverting system can because overvoltage or under-voltage and out of service.This distributed generation system depending on electrical network no longer can meet the demand of people for uninterrupted power supply.The power-off of the key equipments such as such as Medical Devices, medium equipment, communication equipment can bring very large loss or safety problem.If the control of combining inverter can be improved, make its after cutting off electrical network with independent operation mode be near critical load uninterrupted power supply, and when power system restoration can also auto-parallel run, then can play the effect of distributed power source better.

The seamless switching realized between grid-connect mode and stand-alone mode in the key that all can generate electricity with or without distributed power source under electrical network.Although seamless switching technique has become the hot issue in current distributed power generation and micro-capacitance sensor field, due to its technical difficult problem, in the field of businessly thoroughly to solve not yet so far.Its difficult point is mainly reflected in: one, under grid-connect mode, and control objectives is networking power or electric current, and in the independent mode, control objectives is load voltage, the difference of two kinds of control objectives, makes processor need comprise two kinds of control flows; Two, under grid-connect mode, during the unexpected power-off of electrical network, if when DC input power does not mate with critical load power, overvoltage or under-voltage will be there is in inverter output end, force inverter to be shut down time serious or damage load, this requires that cutting-in control has the ability of anti-overvoltage/undervoltage and can be switched to stand-alone mode as quickly as possible; Three, during independent operating, when power system restoration being detected, need load voltage be regulated, making impulse current when itself and electric network voltage phase and amplitude are completely the same just can be avoided again grid-connected.The present invention designs for solving above technological difficulties exactly.

Summary of the invention

For solving above technical problem, the invention provides a kind of based on the grid-connected of line voltage positive sequence extractor and independent double mode changing method of a kind of smooth transition again between grid-connect mode and stand-alone mode.

Technical solution of the present invention is as follows: a kind of based on the grid-connected of line voltage positive sequence extractor and independent double mode changing method, the line voltage positive sequence extractor comprised extracts the positive sequence component of line voltage by following formula:

$\left[\begin{array}{c}{u}_{\mathrm{g\α}}^{+}\left(n\right)\\ u_{\mathrm{g\β}}^{+}\left(n\right)\end{array}\right]=a\left[\begin{array}{cc}\cos \left({\mathrm{\ω}}_{1}T\right)& -\sin \left({\mathrm{\ω}}_{1}T\right)\\ \sin \left({\mathrm{\ω}}_{1}T\right)& \cos \left({\mathrm{\ω}}_{1}T\right)\end{array}\right]\left[\begin{array}{c}{u}_{\mathrm{g\α}}^{+}(n-1)\\ u_{\mathrm{g\β}}^{+}(n-1)\end{array}\right]+(1-a)\left[\begin{array}{c}{u}_{\mathrm{g\α}}\left(n\right)\\ u_{\mathrm{g\β}}\left(n\right)\end{array}\right]$

In formula: it was the n-th moment that sequence number n represents current, u _{g α}(n), u _{g β}line voltage value under n two-phase rest frame that () is current time, namely $\left[\begin{array}{c}{u}_{\mathrm{g\α}}\\ u_{\mathrm{g\β}}\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right]\left[\begin{array}{c}{u}_{\mathrm{ga}}\\ u_{\mathrm{gb}}\\ u_{\mathrm{gc}}\end{array}\right],$ Wherein, u _ga, u _gb, u _gcfor line voltage sampled value; with be respectively the line voltage fundamental positive sequence in current time and a upper moment, their initial value is taken as zero; ω ₁for fundamental frequency, T is the controlling of sampling cycle; A ∈ [0,1] is filter factor, and when grid-connect mode, filter factor a is less than 1, and during stand-alone mode, filter factor a is 1.

Improve as one, grid-connected current controls adoption rate double resonance controller, and governing equation is:

$\left\{\begin{array}{c}{v}_{\mathrm{\α}}=k_p(i_{\mathrm{\α}}^{*}-i_{\mathrm{\α}})+c_{\mathrm{\α}}-{\mathrm{\ω}}_1{L}_1{i}_{\mathrm{\β}}+u_{\mathrm{g\α}}\\ v_{\mathrm{\β}}=k_p(i_{\mathrm{\β}}^{*}-i_{\mathrm{\β}})+c_{\mathrm{\β}}+{\mathrm{\ω}}_1{L}_1{i}_{\mathrm{\α}}+u_{\mathrm{g\β}}\end{array}\right.$

In formula: v _α, v _βfor the modulation voltage value under two-phase rest frame; for the given value of current under two-phase rest frame, computing formula is: $\left[\begin{array}{c}{i}_{\mathrm{\α}}^{*}\\ i_{\mathrm{\β}}^{*}\end{array}\right]=\frac{1}{{\left(u_{\mathrm{g\α}}^{+}\right)}^2+{\left(u_{\mathrm{g\β}}^{+}\right)}^2}\left[\begin{array}{cc}{u}_{\mathrm{g\α}}^{+}& {-u}_{\mathrm{g\β}}^{+}\\ u_{\mathrm{g\β}}^{+}& u_{\mathrm{g\α}}^{+}\end{array}\right]\left[\begin{array}{c}{P}^{*}\\ Q^{*}\end{array}\right],$ Wherein $u_{\mathrm{g\α}}^{+},u_{\mathrm{g\β}}^{+}$ For the Output rusults of line voltage positive sequence extractor, and P ^*and Q ^*be inverter need as electrical network send active power and reactive power, depending on the size of DC input power and the requirement of electrical network; Proportionality coefficient value is wherein L ₁for inverter net side inductance, L ₂for inverter side inductance;-ω ₁l ₁i _βwith ω ₁l ₁i _αfor decoupling zero item; Line voltage value u _{g α}with u _{g β}be used as the impact that feedforward term offsets electrical network; Resonance item c _α, c _βbe used for realizing the DAZ gene of alternating current, specific implementation formula is:

$\left[\begin{array}{c}{c}_{\mathrm{\α}}\left(n\right)\\ c_{\mathrm{\α}1}\left(n\right)\end{array}\right]=\left[\begin{array}{cc}\cos \left({\mathrm{\ω}}_{1}T\right)& -\sin \left({\mathrm{\ω}}_{1}T\right)\\ \sin \left({\mathrm{\ω}}_{1}T\right)& \cos \left({\mathrm{\ω}}_{1}T\right)\end{array}\right]\left[\begin{array}{c}{c}_{\mathrm{\α}}(n-1)\\ c_{\mathrm{\α}1}(n-1)\end{array}\right]+k_{r}T\left[\begin{array}{c}{i}_{\mathrm{\α}}^{*}-i_{\mathrm{\α}}\\ 0\end{array}\right]$

$\left[\begin{array}{c}{c}_{\mathrm{\β}}\left(n\right)\\ c_{\mathrm{\β}1}\left(n\right)\end{array}\right]=\left[\begin{array}{cc}\cos \left({\mathrm{\ω}}_{1}T\right)& -\sin \left({\mathrm{\ω}}_{1}T\right)\\ \sin \left({\mathrm{\ω}}_{1}T\right)& \cos \left({\mathrm{\ω}}_{1}T\right)\end{array}\right]\left[\begin{array}{c}{c}_{\mathrm{\β}}(n-1)\\ c_{\mathrm{\β}1}(n-1)\end{array}\right]+k_{r}T\left[\begin{array}{c}{i}_{\mathrm{\β}}^{*}-i_{\mathrm{\β}}\\ 0\end{array}\right]$

In formula, resonance control coefrficient value is the intermediate variable c of structure _{α 1}, c _{β 1}and the initial value of resonance item is zero.For preventing overvoltage, amplitude limiting processing is done to resonance item and intermediate variable.Namely when time, to c _β, c _{β 1}also similar amplitude limiting processing is done, amplitude limit value C _limvalue is 0.1 times of specified grid voltage amplitude.Adopt after technique scheme, cutting-in control and changing method make system from grid-connected be switched to stand-alone mode time, load voltage can maintain and seamlessly transit, and can not make load voltage exception because of the power-off of electrical network.

Improve as one, load voltage controls to have employed ratio double resonance controller, and governing equation is:

$\left\{\begin{array}{c}{v}_{\mathrm{\α}}=k_{\mathrm{pu}}(u_{\mathrm{Z\α}}^{*}-u_{\mathrm{Z\α}})+d_{\mathrm{\α}}\\ v_{\mathrm{\β}}=k_{\mathrm{pu}}(u_{\mathrm{Z\β}}^{*}-u_{\mathrm{z\β}})+d_{\mathrm{\β}}\end{array}\right.$

Wherein the value of Voltage loop proportionality coefficient is k _pu=0.5, AC load voltage given is calculated as follows:

$\left[\begin{array}{c}{u}_{\mathrm{Z\α}}^{*}\\ u_{\mathrm{Z\β}}^{*}\end{array}\right]=\frac{1}{\sqrt{{\left(u_{\mathrm{g\α}}^{+}\right)}^2+{\left(u_{\mathrm{g\β}}^{+}\right)}^2}}\left[\begin{array}{c}{u}_{\mathrm{g\α}}^{+}\\ u_{\mathrm{g\β}}^{+}\end{array}\right]U^{*}$

In formula: U ^*for load rated voltage amplitude, for the AC network of single-phase 220V, its value is 311;

D _αwith d _βfor in order to realize floating voltage-controlled voltage error resonance item.Concrete discretization expression formula is:

$\left[\begin{array}{c}{d}_{\mathrm{\α}}\left(n\right)\\ d_{\mathrm{\α}1}\left(n\right)\end{array}\right]=\left[\begin{array}{cc}\cos \left({\mathrm{\ω}}_{1}T\right)& -\sin \left({\mathrm{\ω}}_{1}T\right)\\ \sin \left({\mathrm{\ω}}_{1}T\right)& \cos \left({\mathrm{\ω}}_{1}T\right)\end{array}\right]\left[\begin{array}{c}{d}_{\mathrm{\α}}(n-1)\\ d_{\mathrm{\α}1}(n-1)\end{array}\right]+k_{\mathrm{ru}}T\left[\begin{array}{c}{u}_{\mathrm{Z\α}}^{*}-u_{\mathrm{Z\α}}\\ 0\end{array}\right]$

$\left[\begin{array}{c}{d}_{\mathrm{\β}}\left(n\right)\\ d_{\mathrm{\β}1}\left(n\right)\end{array}\right]=\left[\begin{array}{cc}\cos \left({\mathrm{\ω}}_{1}T\right)& -\sin \left({\mathrm{\ω}}_{1}T\right)\\ \sin \left({\mathrm{\ω}}_{1}T\right)& \cos \left({\mathrm{\ω}}_{1}T\right)\end{array}\right]\left[\begin{array}{c}{d}_{\mathrm{\β}}(n-1)\\ d_{\mathrm{\β}1}(n-1)\end{array}\right]+k_{\mathrm{ru}}T\left[\begin{array}{c}{u}_{\mathrm{Z\β}}^{*}-u_{\mathrm{Z\β}}\\ 0\end{array}\right]$

In formula, the value of resonance control coefrficient is k _ru=0.005, d _{α 1}, d _{β 1}for the intermediate variable of structure, the initialization value of resonance item is taken as the modulation voltage value that also net state is last, d _α(0)=v _α, d _{α 1}(0)=v _β, d _β(0)=v _β, d _{β 1}(0)=-v _α.After adopting technique scheme, independent control is with when independently making system detect that line voltage recovers in the independent mode to grid-connected changing method, line voltage can be traced into by quick and smooth, load voltage and line voltage are reached unanimity, then realizes the grid-connected of no current impact when controller detects consistent.

The positive sequence extractor of the present invention's design has the effect of filtering, and it does not extract the positive sequence component of first-harmonic and all inhibited to other harmonics and negative sequence component with can having amplitude attenuation and phase deviation.And because positive sequence extractor is that iteration performs, the change of coefficient can't cause the sudden change of output, but seamlessly transit.Theoretical and the asymmetrical component method according to Fourier analysis, the line voltage of three-phase three wire system can be analyzed to positive sequence and the negative sequence component sum of different frequency.Might as well set the component of wherein angular frequency as: wherein, ω is greater than 0 expression positive sequence component, is less than 0 expression negative sequence component.Positive sequence extractor is an iterative equation, and the mould of transfer matrix characteristic root is a, because it is less than 1, so be stable, and more close to 0, restrains faster.The stable state that can solve exports: wherein: amplitude amplification coefficient, namely amplitude-frequency characteristic is phase deviation, namely phase-frequency characteristic is get ω ₁=314rad/s, T=100 μ s.

From amplitude-frequency and phase-frequency characteristic, if ω=ω ₁, then the input and output of positive sequence extractor are completely equal in amplitude and phase place.For fundamental frequency without phase deviation with without amplitude attenuation characteristic, this is better than other extracting method.If or and a is more close to 1, larger to the decay of harmonic wave.Although work as (k is natural number) is also undamped output, but due to T be the sampling period, its value is very little, above frequency component itself is very little, and be sampling less than, therefore positive sequence extractor is only, without the extraction of amplitude attenuation, negative phase-sequence and other harmonic component have been carried out filtering to fundamental positive sequence.

Accompanying drawing explanation

Fig. 1 is containing the distributed generation system figure of critical load.

The double mode switching flow figure of Fig. 2.

Fig. 3 grid-connect mode control block diagram.

Fig. 4 stand-alone mode control block diagram.

The amplitude-frequency of Fig. 5 positive sequence extractor and phase-frequency characteristic figure.

Fig. 6 is grid-connected to independently switching design sketch.

Fig. 7 independently arrives grid-connected switching design sketch.

Embodiment

Below in conjunction with accompanying drawing, specific embodiments of the invention are elaborated.

1. circuit system wiring

Containing critical load distributed generation system as shown in Figure 1.C in Fig. 1 _dfor DC filter capacitor, AC inductance L ₁, L ₂form LCL filter with electric capacity C, Z is the critical load needing uninterrupted power supply; i _1a, i _1b, i _1cfor inverter side inductive current, i _ga, i _gb, i _gcfor networking electric current; u _ga, u _gb, u _gcfor line voltage, u _za, u _zb, u _zcfor load voltage, v _a, v _b, v _cfor modulation voltage.In figure, distributed DC power can be the various DC power supply such as photovoltaic battery panel, fuel cell, storage battery, wind power generation rectification unit.Direct current is modulated to three-phase alternating current through inversion unit.LCL filter need be installed with the harmonic wave of filtering modulation generation at AC.Grid-connected switch and circuit breaker is equiped with between inverter and electrical network.Described grid-connected switch can be the alternating-current switch such as IGBT of contactor, relay, bidirectional thyristor, anti-series.The critical load of uninterrupted power supply is needed to be connected between filter and grid-connected switch.When circuit breaker disconnects, distributed generation system and electrical network parallel off.Grid-connected switch in figure is controlled, when controller detects grid cut-off, grid-connected switch must be disconnected, load voltage and the line voltage inconsistent and rush of current come during to prevent circuit breaker reclosing.After power system restoration being detected, load voltage must be first regulated to make it consistent with electric network voltage phase and amplitude, just can by closed for grid-connected switch to be incorporated into the power networks.

2. sampled signal preliminary treatment

The sampled point of line voltage is between grid-connected switch and circuit breaker.The sampled point of load voltage meets place at critical load.Inverter inductance current sampled point is at inversion inductor branch road.By line voltage, load voltage, inverter side inductive current through analog-to-digital conversion, be input to digital signal processor.Consider that gained three-phase sampled signal sum is zero, only have two-phase independently signal, to simplify the process, in digital signal processor, carry out the conversion of three-phase to two-phase rest frame:

$\left[\begin{array}{c}{u}_{\mathrm{g\α}}\\ u_{\mathrm{g\β}}\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right]\left[\begin{array}{c}{u}_{\mathrm{ga}}\\ u_{\mathrm{gb}}\\ u_{\mathrm{gc}}\end{array}\right],\left[\begin{array}{c}{u}_{\mathrm{z\α}}\\ u_{\mathrm{z\β}}\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right]\left[\begin{array}{c}{u}_{\mathrm{za}}\\ u_{\mathrm{zb}}\\ u_{\mathrm{zc}}\end{array}\right],\left[\begin{array}{c}{i}_{1\mathrm{\α}}\\ i_{1\mathrm{\β}}\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right]\left[\begin{array}{c}{i}_{1a}\\ i_{1b}\\ i_{1c}\end{array}\right]---\left(1\right)$

3. the realization of positive sequence extractor

The discretization equation of line voltage fundamental positive sequence extraction module is as follows:

$\left[\begin{array}{c}{u}_{\mathrm{g\α}}^{+}\left(n\right)\\ u_{\mathrm{g\β}}^{+}\left(n\right)\end{array}\right]=a\left[\begin{array}{cc}\cos \left({\mathrm{\ω}}_{1}T\right)& -\sin \left({\mathrm{\ω}}_{1}T\right)\\ \sin \left({\mathrm{\ω}}_{1}T\right)& \cos \left({\mathrm{\ω}}_{1}T\right)\end{array}\right]\left[\begin{array}{c}{u}_{\mathrm{g\α}}^{+}(n-1)\\ u_{\mathrm{g\β}}^{+}(n-1)\end{array}\right]+(1-a)\left[\begin{array}{c}{u}_{\mathrm{g\α}}\left(n\right)\\ u_{\mathrm{g\β}}\left(n\right)\end{array}\right]---\left(2\right)$

In formula: u _{g α}(n), u _{g β}line voltage value under n two-phase static coordinate that () is current time, this value derives from formula (1); with be respectively the line voltage fundamental positive sequence in current time and a upper moment, its initial value is taken as zero; ω ₁for fundamental frequency, for the electrical network of 50Hz, its value is 314.16rad/s, T is the controlling of sampling cycle, and this cycle is taken as consistent with the carrier cycle of inverter, and when inverter switching frequency is 10kHz, this value is taken as 100 microseconds; A ∈ (0,1) is filter factor, different in the value of grid-connect mode, stand-alone mode.

4. grid-connected and independent double mode switching flow

DC input power is sent to load and electrical network by system under grid-connect mode, performs Current Control.Under independent operation mode, perform voltage control, for load provides stable voltage.Except the control itself completing two kinds of patterns, also must realize the switching between two kinds of patterns.

The grid-connected switching flow to independent operating is as shown in Fig. 2 (a).Under the pattern of being incorporated into the power networks, need regularly to judge that whether electrical network is normal.Criterion of the present invention be voltage effective value between 0.9 times and 1.1 times of rated values and frequency between 47Hz and 50.5Hz.If electrical network is normal, perform Current Control; If electrical network is abnormal, control chip sends the instruction of grid-connected switch separating brake, continues to perform Current Control program before gate-dividing state feedback does not receive, and after receiving gate-dividing state feedback, is switched to independent operation mode.

Independent of being incorporated into the power networks switching flow as shown in Fig. 2 (b).Under independent operation mode, for realizing running by auto-parallel after power system restoration, electrical network need be made regular check on and whether recover normal.If electrical network is not yet normal, perform voltage control; If power system restoration, then perform Synchronization Control, namely regulate load voltage, until it is consistent with electric network voltage phase and amplitude.If synchronously, then send grid-connected contactor reclosing command, before "on" position feedback does not receive, continue to keep Synchronization Control, if receive "on" position feedback, then switch to the pattern of being incorporated into the power networks.

5. grid-connect mode controls

The control block diagram of grid-connect mode as shown in Figure 3.In Fig. 3, system is in grid-connect mode, and grid-connected switch and circuit breaker are all "on" positions.Inverter, according to the electric network voltage phase sampled, sends meritorious and reactive power to electrical network.I in figure _{1a, b, c}the abbreviation of three-phase inversion electric current, u _{ga, b, c}it is the abbreviation of three-phase power grid voltage.Filter factor in positive sequence extraction module is 0.98.In figure, PDR is ratio double resonance control module, and SVPWM is space vector pulse width modulation, and its effect is the duty ratio determining each phase switching tube according to modulation voltage.

The given P of active power in figure ^*known conditions is given as with reactive power.According to the result of positive sequence extractor, be calculated as follows the given value of current under two-phase rest frame:

$\left[\begin{array}{c}{i}_{\mathrm{\α}}^{*}\\ i_{\mathrm{\β}}^{*}\end{array}\right]=\frac{1}{{\left(u_{\mathrm{g\α}}^{+}\right)}^2+{\left(u_{\mathrm{g\β}}^{+}\right)}^2}\left[\begin{array}{cc}{u}_{\mathrm{g\α}}^{+}& {-u}_{\mathrm{g\β}}^{+}\\ u_{\mathrm{g\β}}^{+}& u_{\mathrm{g\α}}^{+}\end{array}\right]\left[\begin{array}{c}{P}^{*}\\ Q^{*}\end{array}\right]---\left(5\right)$

In formula for the Output rusults of the positive sequence extractor of gained under the condition of filter factor a=0.95.

Current Control adoption rate double resonance controller, governing equation is:

$\left\{\begin{array}{c}{v}_{\mathrm{\α}}=k_p(i_{\mathrm{\α}}^{*}-i_{\mathrm{\α}})+c_{\mathrm{\α}}-{\mathrm{\ω}}_1{L}_1{i}_{\mathrm{\β}}+u_{\mathrm{g\α}}\\ v_{\mathrm{\β}}=k_p(i_{\mathrm{\β}}^{*}-i_{\mathrm{\β}})+c_{\mathrm{\β}}+{\mathrm{\ω}}_1{L}_1{i}_{\mathrm{\α}}+u_{\mathrm{g\β}}\end{array}\right.---\left(6\right)$

Wherein proportionality coefficient value is resonance item c _α, c _βconcrete discretization expression formula be:

$\left[\begin{array}{c}{c}_{\mathrm{\β}}\left(n\right)\\ c_{\mathrm{\β}1}\left(n\right)\end{array}\right]=\left[\begin{array}{cc}\cos \left({\mathrm{\ω}}_{1}T\right)& -\sin \left({\mathrm{\ω}}_{1}T\right)\\ \sin \left({\mathrm{\ω}}_{1}T\right)& \cos \left({\mathrm{\ω}}_{1}T\right)\end{array}\right]\left[\begin{array}{c}{c}_{\mathrm{\β}}(n-1)\\ c_{\mathrm{\β}1}(n-1)\end{array}\right]+k_{r}T\left[\begin{array}{c}{i}_{\mathrm{\β}}^{*}-i_{\mathrm{\β}}\\ 0\end{array}\right]---\left(8\right)$

In formula, resonance control coefrficient value is the intermediate variable c of structure _{α 1}, c _{β 1}and the initial value of resonance item is zero.For preventing overvoltage, amplitude limiting processing is done to resonance item and intermediate variable.Namely when time, to c _β, c _{β 1}also similar amplitude limiting processing is done, C _limvalue is 0.1 times of specified grid voltage amplitude.

6. the control strategy of stand-alone mode

The control block diagram of stand-alone mode as shown in Figure 4.In Fig. 4, system is in stand-alone mode, and grid-connected switch is in off-state.If circuit breaker is also in off-state, the line voltage that inverter detects is abnormal, and the phase place that the constant frequency that the positive sequence extractor that inverter is 1 by rated voltage and filter factor provides exports carries out load voltage control.If breaker closing, when detecting that line voltage recovers normal, the filter factor of positive sequence extractor reverts to 0.98, makes load voltage follow the tracks of line voltage gradually.U in figure _{ga, b, c}the abbreviation of three-phase power grid voltage, u _{za, b, c}it is the abbreviation of three-phase load voltage.Before electrical network is abnormal, the coefficient a of positive sequence extractor is taken as 1, and now, positive sequence extractor extracts the permanent amplitude of the sine wave basis of result keeping rated frequency for the last time in grid-connected positive sequence component and exports.AC load voltage given is calculated as follows:

$\left[\begin{array}{c}{u}_{\mathrm{Z\α}}^{*}\\ u_{\mathrm{Z\β}}^{*}\end{array}\right]=\frac{1}{\sqrt{{\left(u_{\mathrm{g\α}}^{+}\right)}^2+{\left(u_{\mathrm{g\β}}^{+}\right)}^2}}\left[\begin{array}{c}{u}_{\mathrm{g\α}}^{+}\\ u_{\mathrm{g\β}}^{+}\end{array}\right]U^{*}---\left(9\right)$

U in formula ^*for load rated voltage amplitude, for the AC network of single-phase 220V, its value is 311.

Load voltage controls also adoption rate double resonance controller, and governing equation is:

$\left\{\begin{array}{c}{v}_{\mathrm{\α}}=k_{\mathrm{pu}}(u_{\mathrm{Z\α}}^{*}-u_{\mathrm{Z\α}})+d_{\mathrm{\α}}\\ v_{\mathrm{\β}}=k_{\mathrm{pu}}(u_{\mathrm{Z\β}}^{*}-u_{\mathrm{z\β}})+d_{\mathrm{\β}}\end{array}\right.---\left(10\right)$

Wherein the value of Voltage loop proportionality coefficient is k _pu=0.5, d _αwith d _βfor voltage error resonance exports.Concrete discretization expression formula is:

$\left[\begin{array}{c}{d}_{\mathrm{\α}}\left(n\right)\\ d_{\mathrm{\α}1}\left(n\right)\end{array}\right]=\left[\begin{array}{cc}\cos \left({\mathrm{\ω}}_{1}T\right)& -\sin \left({\mathrm{\ω}}_{1}T\right)\\ \sin \left({\mathrm{\ω}}_{1}T\right)& \cos \left({\mathrm{\ω}}_{1}T\right)\end{array}\right]\left[\begin{array}{c}{d}_{\mathrm{\α}}(n-1)\\ d_{\mathrm{\α}1}(n-1)\end{array}\right]+k_{\mathrm{ru}}T\left[\begin{array}{c}{u}_{\mathrm{Z\α}}^{*}-u_{\mathrm{Z\α}}\\ 0\end{array}\right]---\left(11\right)$

$\left[\begin{array}{c}{d}_{\mathrm{\β}}\left(n\right)\\ d_{\mathrm{\β}1}\left(n\right)\end{array}\right]=\left[\begin{array}{cc}\cos \left({\mathrm{\ω}}_{1}T\right)& -\sin \left({\mathrm{\ω}}_{1}T\right)\\ \sin \left({\mathrm{\ω}}_{1}T\right)& \cos \left({\mathrm{\ω}}_{1}T\right)\end{array}\right]\left[\begin{array}{c}{d}_{\mathrm{\β}}(n-1)\\ d_{\mathrm{\β}1}(n-1)\end{array}\right]+k_{\mathrm{ru}}T\left[\begin{array}{c}{u}_{\mathrm{Z\β}}^{*}-u_{\mathrm{Z\β}}\\ 0\end{array}\right]---\left(12\right)$

In formula, the value of resonance control coefrficient is k _ru=0.005, d _{α 1}, d _{β 1}for the intermediate variable of structure.Due to adding of resonance item, achieve interchange DAZ gene.The initialization value of resonance item is taken as the modulation voltage value that also net state is last, d _α(0)=v _α, d _{α 1}(0)=v _β, d _β(0)=v _β, d _{β 1}(0)=-v _α, which ensure that from grid-connected seamlessly transitting to independent operation mode voltage waveform.

If electrical network recovers, then start Synchronization Control, Synchronization Control itself is also voltage control, and just reference voltage is no longer that controller produces automatically, and needs to determine according to line voltage.The coefficient a of positive sequence extractor is diminished by 1, is taken as 0.98 here, then the phase place of reference voltage can be made consistent with electric network voltage phase gradually.Again by U ^*be adjusted to grid voltage amplitude, the Complete Synchronization of load voltage and line voltage can be realized.

After adopting technical scheme of the present invention, there is good technique effect.As shown in Figure 5, be 314rad/s in fundamental frequency, the amplitude-frequency characteristic of the positive sequence extractor under control cycle 100 microsecond and phase-frequency characteristic, filter factor is taken as 0.98 and 0.95 respectively and contrasts.

Fig. 6 is grid-connected to independently switching effect, and in figure, four road waveforms are from top to bottom respectively line voltage, networking electric current, load voltage, load current.

Fig. 7 independently arrives grid-connected switching effect, and the waveform above in figure is load voltage and line voltage, be wherein sinusoidal wave is load voltage always, and what after the first lattice, just have waveform is line voltage.Waveform below in figure is networking electric current, and only in the end lattice are grid-connected just has afterwards.

Claims (3)

1., based on the grid-connected of line voltage positive sequence extractor and an independent double mode changing method, it is characterized in that the line voltage positive sequence extractor comprised extracts the positive sequence component of line voltage by following formula:

$\left[\begin{array}{c}{u}_{\mathrm{g\α}}^{+}\left(n\right)\\ u_{\mathrm{g\β}}^{+}\left(n\right)\end{array}\right]=a\left[\begin{array}{cc}\cos \left({\mathrm{\ω}}_{1}T\right)& -\sin \left({\mathrm{\ω}}_{1}T\right)\\ \sin \left({\mathrm{\ω}}_{1}T\right)& \cos \left({\mathrm{\ω}}_{1}T\right)\end{array}\right]\left[\begin{array}{c}{u}_{\mathrm{g\α}}^{+}(n-1)\\ u_{\mathrm{g\β}}^{+}(n-1)\end{array}\right]+(1-a)\left[\begin{array}{c}{u}_{\mathrm{g\α}}\left(n\right)\\ u_{\mathrm{g\β}}\left(n\right)\end{array}\right]$

In formula: it was the n-th moment that sequence number n represents current, u _{g α}(n), u _{g β}line voltage value under n two-phase rest frame that () is current time, namely $\left[\begin{array}{c}{u}_{\mathrm{g\α}}\\ u_{\mathrm{g\β}}\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right]\left[\begin{array}{c}{u}_{\mathrm{ga}}\\ u_{\mathrm{gb}}\\ u_{\mathrm{gc}}\end{array}\right],$ Wherein, u _ga, u _gb, u _gcfor line voltage sampled value; with be respectively the line voltage fundamental positive sequence in current time and a upper moment, their initial value is taken as zero; ω ₁for fundamental frequency, T is the controlling of sampling cycle; A ∈ [0,1] is filter factor, and when grid-connect mode, filter factor a is less than 1, and during stand-alone mode, filter factor a is 1.

2. according to claim 1 a kind of based on the grid-connected of line voltage positive sequence extractor and independent double mode changing method, it is characterized in that grid-connected current controls adoption rate double resonance controller, governing equation is:

$\left\{\begin{array}{c}{v}_{\mathrm{\α}}=k_p(i_{\mathrm{\α}}^{*}-i_{\mathrm{\α}})+c_{\mathrm{\α}}-{\mathrm{\ω}}_1{L}_1{i}_{\mathrm{\β}}+u_{\mathrm{g\α}}\\ v_{\mathrm{\β}}=k_p(i_{\mathrm{\β}}^{*}-i_{\mathrm{\β}})+c_{\mathrm{\β}}+{\mathrm{\ω}}_1{L}_1{i}_{\mathrm{\α}}+u_{\mathrm{g\β}}\end{array}\right.$

In formula: v _α, v _βfor the modulation voltage value under two-phase rest frame; for the given value of current under two-phase rest frame, computing formula is: $\left[\begin{array}{c}{i}_{\mathrm{\α}}^{*}\\ i_{\mathrm{\β}}^{*}\end{array}\right]=\frac{1}{{\left(u_{\mathrm{g\α}}^{+}\right)}^2+{\left(u_{\mathrm{g\β}}^{+}\right)}^2}\left[\begin{array}{cc}{u}_{\mathrm{g\α}}^{+}& -u_{\mathrm{g\β}}^{+}\\ u_{\mathrm{g\β}}^{+}& u_{\mathrm{g\α}}^{+}\end{array}\right]\left[\begin{array}{c}{P}^{*}\\ Q^{*}\end{array}\right],$ Wherein for the Output rusults of line voltage positive sequence extractor, and P ^*and Q ^*be inverter need as electrical network send active power and reactive power, depending on the size of DC input power and the requirement of electrical network; Proportionality coefficient value is wherein L ₁for inverter net side inductance, L ₂for inverter side inductance;-ω ₁l ₁i _βwith ω ₁l ₁i _αfor decoupling zero item; Line voltage value u _{g α}with u _{g β}be used as the impact that feedforward term offsets electrical network; Resonance item c _α, c _βbe used for realizing the DAZ gene of alternating current, specific implementation formula is:

$\left[\begin{array}{c}{c}_{\mathrm{\α}}\left(n\right)\\ c_{\mathrm{\α}1}\left(n\right)\end{array}\right]=\left[\begin{array}{cc}\cos \left({\mathrm{\ω}}_{1}T\right)& -\sin \left({\mathrm{\ω}}_{1}T\right)\\ \sin \left({\mathrm{\ω}}_{1}T\right)& \cos \left({\mathrm{\ω}}_{1}T\right)\end{array}\right]\left[\begin{array}{c}{c}_{\mathrm{\α}}(n-1)\\ c_{\mathrm{\α}1}(n-1)\end{array}\right]+k_{r}T\left[\begin{array}{c}{i}_{\mathrm{\α}}^{*}-i_{\mathrm{\α}}\\ 0\end{array}\right]$

$\left[\begin{array}{c}{c}_{\mathrm{\β}}\left(n\right)\\ c_{\mathrm{\β}1}\left(n\right)\end{array}\right]=\left[\begin{array}{cc}\cos \left({\mathrm{\ω}}_{1}T\right)& -\sin \left({\mathrm{\ω}}_{1}T\right)\\ \sin \left({\mathrm{\ω}}_{1}T\right)& \cos \left({\mathrm{\ω}}_{1}T\right)\end{array}\right]\left[\begin{array}{c}{c}_{\mathrm{\β}}(n-1)\\ c_{\mathrm{\β}1}(n-1)\end{array}\right]+k_{r}T\left[\begin{array}{c}{i}_{\mathrm{\β}}^{*}-i_{\mathrm{\β}}\\ 0\end{array}\right]$

In formula, resonance control coefrficient value is the intermediate variable c of structure _{α 1}, c _{β 1}and the initial value of resonance item is zero.For preventing overvoltage, amplitude limiting processing is done to resonance item and intermediate variable.Namely when time, to c _β, c _{β 1}also similar amplitude limiting processing is done, amplitude limit value C _limvalue is 0.1 times of specified grid voltage amplitude.

3. according to claim 1 a kind of based on the grid-connected of line voltage positive sequence extractor and independent double mode changing method, it is characterized in that load voltage controls to have employed ratio double resonance controller, governing equation is:

$\left\{\begin{array}{c}{v}_{\mathrm{\α}}=k_{\mathrm{pu}}(u_{\mathrm{Z\α}}^{*}-u_{\mathrm{Z\α}})+d_{\mathrm{\α}}\\ v_{\mathrm{\β}}=k_{\mathrm{pu}}(u_{\mathrm{Z\β}}^{*}-u_{\mathrm{z\β}})+d_{\mathrm{\β}}\end{array}\right.$

Wherein the value of Voltage loop proportionality coefficient is k _pu=0.5, AC load voltage given is calculated as follows:

$\left[\begin{array}{c}{u}_{\mathrm{Z\α}}^{*}\\ u_{\mathrm{Z\β}}^{*}\end{array}\right]=\frac{1}{\sqrt{{\left(u_{\mathrm{g\α}}^{+}\right)}^2+{\left(u_{\mathrm{g\β}}^{+}\right)}^2}}\left[\begin{array}{c}{u}_{\mathrm{g\α}}^{+}\\ u_{\mathrm{g\β}}^{+}\end{array}\right]U^{*}$

In formula: U ^*for load rated voltage amplitude, for the AC network of single-phase 220V, its value is 311;

D _αwith d _βfor in order to realize floating voltage-controlled voltage error resonance item.Concrete discretization expression formula is:

$\left[\begin{array}{c}{d}_{\mathrm{\α}}\left(n\right)\\ d_{\mathrm{\α}1}\left(n\right)\end{array}\right]=\left[\begin{array}{cc}\cos \left({\mathrm{\ω}}_{1}T\right)& -\sin \left({\mathrm{\ω}}_{1}T\right)\\ \sin \left({\mathrm{\ω}}_{1}T\right)& \cos \left({\mathrm{\ω}}_{1}T\right)\end{array}\right]\left[\begin{array}{c}{d}_{\mathrm{\α}}(n-1)\\ d_{\mathrm{\α}1}(n-1)\end{array}\right]+k_{\mathrm{ru}}T\left[\begin{array}{c}{u}_{\mathrm{Z\α}}^{*}-u_{\mathrm{Z\α}}\\ 0\end{array}\right]$

$\left[\begin{array}{c}{d}_{\mathrm{\β}}\left(n\right)\\ d_{\mathrm{\β}1}\left(n\right)\end{array}\right]=\left[\begin{array}{cc}\cos \left({\mathrm{\ω}}_{1}T\right)& -\sin \left({\mathrm{\ω}}_{1}T\right)\\ \sin \left({\mathrm{\ω}}_{1}T\right)& \cos \left({\mathrm{\ω}}_{1}T\right)\end{array}\right]\left[\begin{array}{c}{d}_{\mathrm{\β}}(n-1)\\ d_{\mathrm{\β}1}(n-1)\end{array}\right]+k_{\mathrm{ru}}T\left[\begin{array}{c}{u}_{\mathrm{Z\β}}^{*}-u_{\mathrm{Z\β}}\\ 0\end{array}\right]$

In formula, the value of resonance control coefrficient is k _ru=0.005, d _{α 1}, d _{β 1}for the intermediate variable of structure, the initialization value of resonance item is taken as the modulation voltage value that also net state is last, d _α(0)=v _α, d _{α 1}(0)=v _β, d _β(0)=v _β, d _{β 1}(0)=-v _α.