CN103997060A - Grid-connected photovoltaic power generation system electromechanical transient model based on power decoupling control - Google Patents

Abstract

The invention discloses a grid-connected photovoltaic power generation system electromechanical transient model based on power decoupling control. The grid-connected photovoltaic power generation system electromechanical transient model based on power decoupling control is characterized by comprising a photovoltaic battery unit, a maximum power tracking unit, a direct current voltage stabilizing unit, a PQ decoupling control unit and a protective configuration unit, wherein the output end of the photovoltaic battery unit is connected with the input end of the direct current voltage stabilizing unit, the output end of the direct current voltage stabilizing unit is connected with the input end of the photovoltaic battery unit and the input end of the PQ decoupling control unit, the output end of the PQ decoupling control unit is connected with the input end and the output link of the direct current voltage stabilizing unit, the output end of the maximum power tracking unit is connected with the input end of the photovoltaic battery unit, the input end of the direct current voltage stabilizing unit and the input end of the PQ decoupling control unit, and the protective configuration unit is connected with the output link. The grid-connected photovoltaic power generation system electromechanical transient model based on power decoupling control is suitable for transient stability calculation in the electromechanical transient simulation process of the power system, can analyze the transient stability of a photovoltaic access system, and can study the reactive voltage problem of part of the power grid.

Description

A kind of grid-connected photovoltaic power generation system electromechanical transient model of controlling based on power decoupled

Technical field

The present invention relates to electric power system power transmission and distribution technical field, relate in particular to a kind of grid-connected photovoltaic power generation system electromechanical transient model of controlling based on power decoupled.

Background technology

For this new forms of energy form of photovoltaic, be incorporated into the power networks more and more, its impact on electric power system also more and more can not be ignored, and especially, in partial electric grid and micro-electrical network, it is by the very important effect of performance.After photovoltaic generating system access electrical network, due to its randomness of exerting oneself and the transient characterisitics that are different from conventional power source, will cause various new impacts to electric power system.Therefore, set up a kind of grid-connected photovoltaic power generation system model that is applicable to electromechanical transient stability analysis and seem particularly important.And the feature of considering large-scale power grid electromechanical transient simulation, requires simulation model will take into account efficiency and precision.

Photovoltaic generation is due to its randomness of exerting oneself and uncertainty, is all generally in MPPT mode or determines power mode and carry out grid-connected.Under this control strategy, existing photovoltaic generating system electromechanical transient model modelling approach mainly adopts a kind of dq decoupling control policy based on outer voltage current inner loop of electro-magnetic transient model being simplified to rear proposition.

Application number is that 201210328721.6 Chinese patent application discloses a kind of general parallel net type photovoltaic generating system electromechanical transient model, and described in it, the shortcoming of model is:

(1) thought that has in fact still continued electromagnetic transient simulation is controlled in the dq decoupling zero that it adopts, and inner and outer ring control system is complicated, and parameter adjustment is difficult for;

(2) this model does not have the various salvos of complete consideration and measure;

(3) simulation step length that this model needs is 1ms, analyzes the requirement of 10ms simulation step length much smaller than electromechanical transient simulation.

Summary of the invention

The object of the invention is to provide a kind of grid-connected photovoltaic power generation system electromechanical transient model of controlling based on power decoupled, the transient stability being applicable in Electrical-Machanical Transient Simulation of Power System calculates, and can analyze transient stability, the research partial electric grid reactive voltage problem of photovoltaic connecting system.The technical problem underlying solving has: set up photovoltaic generating system quasi steady state model, accurately simulated light photovoltaic generating system meritorious idle variation in Steady state and transient state process; Disturbance S and T are set, the impact that simulated disturbance brings to photovoltaic generating system output and partial electric grid.

To achieve these goals, the present invention adopts following technical scheme:

A grid-connected photovoltaic power generation system electromechanical transient model of controlling based on power decoupled, comprises photovoltaic cell unit, maximal power tracing unit, direct-flow voltage regulation unit, PQ decoupling zero control unit and protection dispensing unit;

The output of photovoltaic cell unit connects the input of direct-flow voltage regulation unit, the output of direct-flow voltage regulation unit connects the input of photovoltaic cell unit and the input of PQ decoupling zero control unit, and the output of PQ decoupling zero control unit connects input and the output element of direct-flow voltage regulation unit;

The output of maximal power tracing unit connects photovoltaic cell unit, direct-flow voltage regulation unit and PQ decoupling zero control unit;

Protection dispensing unit connects described output element.

Further, described PQ decoupling zero control unit comprises meritorious ring and idle ring; The input of described meritorious ring connects output, the output of maximal power tracing unit and the output of idle ring of direct-flow voltage regulation unit, and the input of described idle ring connects the output of direct-flow voltage regulation unit.

Further, photovoltaic cell unit meets conventional photovoltaic cell engineering simplified model, with illumination S, temperature T, battery terminal voltage U _pvas variable input, I _pvas single photovoltaic cell output current, expression formula is:

$I_{\mathrm{pv}}=f(U_{\mathrm{pv}},S,T)=I_{\mathrm{scc}}[1-C_1(\exp \frac{U_{\mathrm{pv}}}{C_2{U}_{\mathrm{occ}}}-1)]---\left(1\right)$

In formula:

$C_1=(1-\frac{I_{\mathrm{mm}}}{I_{\mathrm{scc}}})\exp (-\frac{U_{\mathrm{mm}}}{U_{\mathrm{occ}}})---\left(2\right)$

$C_2=(\frac{U_{\mathrm{mm}}}{U_{\mathrm{occ}}}-1){\left[\ln (1-\frac{I_{\mathrm{mm}}}{I_{\mathrm{scc}}})\right]}^{-1}---\left(3\right)$

$\mathrm{\ΔS}=\frac{S}{1000}-1---\left(4\right)$

ΔT＝T-25 (5)

$I_{\mathrm{scc}}=I_{\mathrm{sc}}\×\frac{S}{1000}\×(1+0.0025\mathrm{\ΔT})---\left(6\right)$

$I_{\mathrm{mm}}=I_m\×\frac{S}{1000}\×(1+0.0025\mathrm{\ΔT})---\left(7\right)$

U _occ＝U _oc(1-0.00288ΔT)×ln(e+0.5ΔS) (8)

U _mm＝U _m(1-0.00288ΔT)×ln(e+0.5ΔS) (9)

In formula:

I _m, I _sc, U _m, U _oc---temperature T is that 25 ℃, intensity of sunshine S are 1000W/m ²single photovoltaic cell maximum power point electric current under condition, short circuit current, maximum power point voltage, open circuit voltage; The parameter of single photovoltaic cell is definite value: I _m=13.74A, I _sc=14.98A, U _m=348V, U _oc=444V; And I _mm, I _scc, U _mm, U _occrespectively maximum power point electric current, short circuit current, maximum power point voltage, the open circuit voltage through S and T correction.

Further, maximal power tracing unit makes DC voltage U _dcfollow the tracks of the single group maximum power of photovoltaic cell point voltage U through revising _mm, expression formula is:

U _mm＝U _m(1-0.00288ΔT)×ln(e+0.5ΔS)(10)

Further, direct-flow voltage regulation unit is stage type or single stage type; Stage type is expressed as U _dc=kU _pv; K is DC side booster circuit step-up ratio; Single stage type is expressed as U _dc=U _pv; Direct-flow voltage regulation unit has a DC voltage-stabilizing capacitor C, and the power of its both sides transmits expression formula and is:

$P_{\mathrm{dc}}-S_{\mathrm{pv}}=C\frac{{\mathrm{dU}}_{\mathrm{dc}}}{\mathrm{dt}}{U}_{\mathrm{dc}}---\left(11\right)$

P wherein _dcfor DC link input power; S _pvfor DC link power output.

Further, to the gain merit idle link decoupling zero of PQ decoupling zero control unit is controlled, utilize RL filter circuit both sides phase difference of voltage δ as the control object of meritorious ring, using inverter modulation ratio M as the control object of idle ring, by following formula, complete meritorious idle decoupling zero is controlled to (ignoring filter resistance R):

$\left\{\begin{array}{c}P=\frac{U_i{U}_s\sin \mathrm{\δ}}{\mathrm{\ωL}}\≈\frac{U_i{U}_s\mathrm{\δ}}{\mathrm{\ωL}}\\ Q=\frac{U_s{(U_i\cos \mathrm{\δ}-U_s)}_{}}{\mathrm{\ωL}}\≈\frac{U_s(U_i-U_s)}{\mathrm{\ωL}}\end{array}\right.---\left(12\right)$

In formula:

U _iand U _s---inverter outlet side voltage and voltage on line side, U _i=MU _dc;

L---filter inductance;

ω---electrical network angular frequency;

P and Q---meritorious, idle output;

Further, protection dispensing unit comprises voltage protection module, frequency protection module, overcurrent and short circuit current protection module and Voltage unbalance protection module.

Further, the described grid-connected photovoltaic power generation system electromechanical transient model of controlling based on power decoupled comprises two kinds of working methods: determine photovoltaic cell group quantity and automatically calculate required photovoltaic cell group number, two kinds of modes all suppose that initial steady state working point is maximum power working point; The first working method is: by trend, calculate resulting meritorious initial value P _g0peak power output P divided by single photovoltaic cell _max=U _mm ^*i _mm, calculate required photovoltaic cell group and count Nvp, suppose initialization state S ₀=1000W/m ², T ₀=25 ℃, the second working method is: self-defined required photovoltaic cell group is counted Nvp, Nvp*P _max>=P _g0, by the relation of photovoltaic cell illumination S and power output P, obtain the intensity of illumination of present operating point, initialization state is T ₀=25 ℃, 0≤S≤1000W/m ².

Further, in meritorious ring, between variable, relation is expressed by following formula:

$\left\{\begin{array}{c}\mathrm{\δ}=(K_{\mathrm{pP}}+{\frac{K_{\mathrm{pI}}}{s}}^{})*(U_{\mathrm{dc}}-U_{\mathrm{dcref}})+{\mathrm{\δ}}_0\\ P\≈\frac{U_i*U_s}{\mathrm{\ωL}}\mathrm{\δ}\\ \frac{{\mathrm{dU}}_{\mathrm{dc}}}{\mathrm{dt}}=\frac{I_{\mathrm{dc}}}{C}-\frac{S_{\mathrm{pv}}}{{\mathrm{CU}}_{\mathrm{dc}}}\\ I_{\mathrm{dc}}=f\left(I_{\mathrm{pv}}\right)\end{array}\right.---\left(14\right)$

In formula:

K _pPand K _pI---meritorious ring PI adjustment factor;

U _dcref---the DC voltage reference value calculating by MPPT;

δ ₀---the initial value of δ;

I _dc---DC link input current.

In idle ring, between variable, relation is expressed by following formula:

$\left(\begin{array}{c}M=(K_{\mathrm{pP}}+\frac{K_{\mathrm{pI}}}{s})*(Q_{\mathrm{ref}}-Q)+M_0\\ Q=\frac{U_s}{\mathrm{\ωL}}(M*U_{\mathrm{dc}}-U_s)\end{array}\right.---\left(15\right)$

In formula:

K _qPand K _qI---idle ring PI adjustment factor;

Q _ref---idle reference value;

M ₀---the initial value of M;

The variable relation of output element is expressed by following formula:

$\left(\begin{array}{c}{\mathrm{\θ}}_I={\mathrm{\θ}}_V-\arctan \frac{Q}{P}\\ I^2=\frac{P^2+Q^2}{U_s^2}\\ I_{\mathrm{TR}}=I*\cos {\mathrm{\θ}}_I\\ I_{\mathrm{TI}}=I*\sin {\mathrm{\θ}}_I\end{array}\right.---\left(16\right)$

In formula:

θ _iand θ _v---photovoltaic output current and line voltage phase angle;

I _tRand I _tI---real part and the imaginary part of photovoltaic output current.

The present invention is a kind of grid-connected photovoltaic power generation system electromechanical transient model of controlling based on power decoupled, has 3 hypotheses:

(1) ignore the power loss of inversion link and DC link.Because photovoltaic generating system power loss proportion is in the course of the work very little, and the size of loss can change along with the change of disturbance, is difficult to carry out accurately effectively calculate simulation.

(2) ignore the high-frequency fluctuation of DC link.Because the step-length of large-scale power system electromechanical transient simulation is longer, be approximately 10ms, therefore can think that the high frequency response of DC link is fast more a lot of than this, can ignore.

(3) suppose that all photovoltaic cells in photovoltaic array are operated under identical operational environment.The reasons such as the photovoltaic plant in reality may be because of blocking, indivedual battery failure cause output uneven, but such disturbance is random, cannot accurately simulate, so this model is ignored this class enchancement factor.

The present invention is a kind of grid-connected photovoltaic power generation system electromechanical transient model of controlling based on power decoupled, comprises photovoltaic cell unit, maximal power tracing unit, direct-flow voltage regulation unit, PQ decoupling zero control unit and protection dispensing unit.

(1) photovoltaic cell unit meets conventional photovoltaic cell engineering simplified model, can use illumination S, temperature T, battery terminal voltage U _pvas variable input, I _pvas single photovoltaic cell output current, expression formula is:

$I_{\mathrm{pv}}=f(U_{\mathrm{pv}},S,T)=I_{\mathrm{scc}}[1-C_1(\exp \frac{U_{\mathrm{pv}}}{C_2{U}_{\mathrm{occ}}}-1)]---\left(1\right)$

In formula:

$C_1=(1-\frac{I_{\mathrm{mm}}}{I_{\mathrm{scc}}})\exp (-\frac{U_{\mathrm{mm}}}{U_{\mathrm{occ}}})---\left(2\right)$

$C_2=(\frac{U_{\mathrm{mm}}}{U_{\mathrm{occ}}}-1){\left[\ln (1-\frac{I_{\mathrm{mm}}}{I_{\mathrm{scc}}})\right]}^{-1}---\left(3\right)$

$\mathrm{\ΔS}=\frac{S}{1000}-1---\left(4\right)$

ΔT＝T-25 (5)

$I_{\mathrm{scc}}=I_{\mathrm{sc}}\×\frac{S}{1000}\×(1+0.0025\mathrm{\ΔT})---\left(6\right)$

$I_{\mathrm{mm}}=I_m\×\frac{S}{1000}\×(1+0.0025\mathrm{\ΔT})---\left(7\right)$

U _occ＝U _oc(1-0.00288ΔT)×ln(e+0.5ΔS) (8)

U _mm＝U _m(1-0.00288ΔT)×ln(e+0.5ΔS) (9)

In formula:

I _m, I _sc, U _m, U _oc---temperature T is that 25 ℃, intensity of sunshine S are 1000W/m ²single photovoltaic cell maximum power point electric current under condition, short circuit current, maximum power point voltage, open circuit voltage; The parameter of single photovoltaic cell is definite value: I _m=13.74A, I _sc=14.98A, U _m=348V, U _oc=444V; And I _mm, I _scc, U _mm, U _occrespectively maximum power point electric current, short circuit current, maximum power point voltage, the open circuit voltage through S and T correction.

(2) maximal power tracing unit adopts the improved voltage control method of determining, and makes DC voltage U _dcfollow the tracks of the single photovoltaic cell maximum power point voltage U through revising _mm, expression formula is:

U _mm＝U _m(1-0.00288ΔT)×ln(e+0.5ΔS) (10)

(3) direct-flow voltage regulation unit comprises stage type and single stage type; Stage type is expressed as U _dc=kU _pv, k is DC side booster circuit step-up ratio; Middle employing single stage type embodiment illustrated in fig. 1, single stage type is expressed as U _dc=U _pv; Direct-flow voltage regulation unit has a DC voltage-stabilizing capacitor C, and the power of its both sides transmits expression formula and is:

$P_{\mathrm{dc}}-S_{\mathrm{pv}}=C\frac{{\mathrm{dU}}_{\mathrm{dc}}}{\mathrm{dt}}{U}_{\mathrm{dc}}---\left(11\right)$

(4) PQ decoupling zero control unit.Based on Vector Theory, ignore the resistance R of filter inductance, set up a kind of quasi steady state model, the idle link decoupling zero of gaining merit is controlled.Due to filter circuit both sides, phase difference of voltage δ is generally very little, sin δ ≈ δ, cos δ ≈ 1, can utilize this phase difference of voltage δ as the control object of meritorious ring in model, using inverter modulation ratio M as the control object of idle ring, by following formula, complete meritorious idle decoupling zero is controlled.

$\left\{\begin{array}{c}P=\frac{U_i{U}_s\sin \mathrm{\δ}}{\mathrm{\ωL}}\≈\frac{U_i{U}_s\mathrm{\δ}}{\mathrm{\ωL}}\\ Q=\frac{U_s{(U_i\cos \mathrm{\δ}-U_s)}_{}}{\mathrm{\ωL}}\≈\frac{U_s(U_i-U_s)}{\mathrm{\ωL}}\end{array}\right.---\left(12\right)$

In formula:

U _iand U _s---inverter outlet side voltage and voltage on line side, U _i=MU _dc;

L---filter inductance;

ω---electrical network angular frequency;

P and Q---meritorious, idle output.

(5) protection dispensing unit comprises at present general voltage protection, frequency protection, overcurrent and short circuit current protection and Voltage unbalance protection.

A. overvoltage/under voltage protection model

Cross/under voltage protection is that photovoltaic generating system should stop to grid transmission when electrical network interface voltage exceeds the voltage range of regulation.System should be able to detect abnormal voltage and make a response, and the root mean square value of voltage is measured at electrical network interface, requires small-sized photovoltaic power station to meet requirement shown in table 1 in regulation.

The grid-connected voltage request of table 1 low profile photovoltaic

Large-scale and medium-sized photovoltaic plant should possess the ability that certain withstand voltage is abnormal, and for avoiding when line voltage is abnormal departing from, so its action protection adjusts again, meets the low voltage crossing characteristic of national grid regulation.

B. cross/underfrequency protection model

Cross/underfrequency protection is when electrical network interface frequency exceeds the frequency range of regulation, should at the appointed time photovoltaic generating system and electrical network be disconnected.When in standard, regulation surpasses 49.5-50.2Hz scope for the grid-connected dot frequency of small-sized photovoltaic power station, should in 0.25s, stop to power network line power transmission; Large-scale and medium-sized photovoltaic plant should possess the ability of certain tolerance system frequency abnormality, meets requirement shown in table 2.

The running time requirement of the large-scale and medium-sized photovoltaic plant of table 2 when mains frequency is abnormal

C. overcurrent and short-circuit protection model

Photovoltaic plant need possess certain overcurrent capability, and below 120% rated current, the continuous reliably working time of photovoltaic plant is not less than 1 minute; In 120%-150% rated current, the continuous reliably working time of photovoltaic plant should be not less than 10 seconds.When grid side being detected and be short-circuited, photovoltaic plant should be not more than 150% of rated current to the short circuit current of electrical network output, and 0.15 with interior by photovoltaic generating system and electrical network disconnection.

D. Voltage unbalance protection model

When photovoltaic generating system is incorporated into the power networks (only to three-phase output), the negative sequence voltage degree of unbalance of electrical network interface should be no more than 2%, must not surpass 4% in short-term.The computing formula of negative sequence voltage degree of unbalance is the ratio of negative sequence voltage and positive sequence voltage.

Simulation requirements input basic parameter according to required, comprising: temperature T, control system parameter and variable, identification capacity, initialization mode, perturbation scheme and DC side structure;

(1) this model can be simulated the photovoltaic generating system of random capacity, and the dilatation way of employing is single photovoltaic cell in parallel, does not change outlet voltage, and only the mode of simple employing parallel connection is carried out dilatation; Inverter outlet system voltage reference value U _b=0.4kV, therefore need to connect a step-up transformer and be connected to the grid.

(2) different working methods comprises two kinds: determine photovoltaic cell group quantity and automatically calculate required photovoltaic cell group number, two kinds of modes all suppose that initial steady state working point is maximum power working point.The first working method is: by trend, calculate resulting meritorious initial value P _g0peak power output (P divided by single group photovoltaic cell _max=U _mm ^*i _mm), calculate required photovoltaic cell group and count Nvp, suppose initialization state S ₀=1000W/m ², T ₀=25 ℃, the second working method is: self-defined required photovoltaic cell group is counted Nvp (Nvp*P _max>=P _g0), by the relation (adopting piecewise linear mode to portray) of photovoltaic cell illumination S and power output P, obtain the intensity of illumination of present operating point, initialization state is T ₀=25%,

$S_0=f\left(\frac{P_{G0}}{\mathrm{Nvp}*P_{\max }}\right)$ (0≤S≤1000W/m ²)。

The first working method is the acquiescence working method of this model, adopts and becomes photovoltaic cell group number, is relatively applicable to general simulation calculation and studies interior external characteristic; The second working method has considered that in actual use, photovoltaic cell group number is constant, and intensity of illumination is situation about changing, and is more applicable for the emulation of real system.

(3) different perturbation schemes comprises the disturbance of illumination temporal evolution and the disturbance of temperature temporal evolution: effectively illumination simulation and the thermal perturbation impact on grid-connected photovoltaic power generation system characteristic.

According to the parameter of input, the change curve of each variable initial value under calculative determination working method and disturbance variable (S and T), and be written into steady-state load flow result of calculation and jointly complete initialization, and the inner perunit value that all adopts of this model calculates, numerical stability is better, and model parameter fiducial value can self-defining according to different systems.Power in this model ac and dc systems, voltage, current reference value are calculated as follows:

$\begin{array}{c}{S}_{\tilde{B}}\sqrt{3}{U}_B^{~}{I}_B^{~}=U_B^{-}{I}_B^{-}=S_{\stackrel{\‾}{B}}\\ Z_{\stackrel{\‾}{B}}=\frac{U_B^{-}}{I_{\stackrel{\‾}{B}}}\\ Z_{\tilde{B}}=\frac{U_B^{~}}{\sqrt{3}{I}_{\tilde{B}}}\end{array}---\left(13\right)$

Generally, S _b=100MVA, U _b=0.4kV, acquiescence illumination S=1000W/m ², T=25 ℃.

According to the requirement of emulation, establish the boundary number between photovoltaic generating system model and electrical network, there is different interface data in different simulation softwares in transient stability calculates, and can select suitable interface data to replace the meritorious idle control variables in PQ decoupling control policy.This model is at Based on Power System Analysis Software Package (Power System Analysis Software Package, PSASP) User Defined (User Determined, UD) (but be not limited only to PSASP UD module modeling) set up under module, therefore the interaction data as photovoltaic generating system and electrical network is: and site busbar voltage amplitude U _sand phase angle theta _v, photovoltaic generating system output current real part I _tRwith imaginary part I _tI.

Set transient stability account form and refer to determine that carrying out the transient stability that illumination S, temperature T disturbance calculating or network failure, network voltage fall calculates.

Utilize numerical computation method, between photovoltaic generating system internal model and electrical network, replace iteration, calculate electric current and built-in variable that photovoltaic generating system injects electrical network, comprise the front electric current I of electric capacity of voltage regulation _dc, electric capacity of voltage regulation voltage U _dc, inverter modulation ratio M, filter circuit both sides phase difference of voltage δ.Expression formula is:

$\left\{\begin{array}{c}\mathrm{\δ}=(K_{\mathrm{pP}}+{\frac{K_{\mathrm{pI}}}{s}}^{})*(U_{\mathrm{dc}}-U_{\mathrm{dcref}})+{\mathrm{\δ}}_0\\ P\≈\frac{U_i*U_s}{\mathrm{\ωL}}\mathrm{\δ}\\ \frac{{\mathrm{dU}}_{\mathrm{dc}}}{\mathrm{dt}}=\frac{I_{\mathrm{dc}}}{C}-\frac{S_{\mathrm{pv}}}{{\mathrm{CU}}_{\mathrm{dc}}}\\ I_{\mathrm{dc}}=f\left(I_{\mathrm{pv}}\right)\end{array}\right.---\left(14\right)$

$\left(\begin{array}{c}M=(K_{\mathrm{pP}}+\frac{K_{\mathrm{pI}}}{s})*(Q_{\mathrm{ref}}-Q)+M_0\\ Q=\frac{U_s}{\mathrm{\ωL}}(M*U_{\mathrm{dc}}-U_s)\end{array}\right.---\left(15\right)$

At active-power P and the output current after reactive power Q of considering photovoltaic generating system output, comprise real part I _tRwith imaginary part I _tI, expression formula is:

$\left(\begin{array}{c}{\mathrm{\θ}}_I={\mathrm{\θ}}_V-\arctan \frac{Q}{P}\\ I^2=\frac{P^2+Q^2}{U_s^2}\\ I_{\mathrm{TR}}=I*\cos {\mathrm{\θ}}_I\\ I_{\mathrm{TI}}=I*\sin {\mathrm{\θ}}_I\end{array}\right.---\left(16\right)$

Internal and external parameter by photovoltaic generating system under given transient stability account form changes, and judges himself stability and the impact on local Power Network Transient Stability, and the while is also for the research of reactive voltage relation provides foundation.

(1), according to the stability of transient stability result of calculation judgement photovoltaic generating system self, observe inner parameter and comprise the front electric current I of electric capacity of voltage regulation _dc, electric capacity of voltage regulation voltage U _dc, inverter modulation ratio M, filter circuit both sides phase difference of voltage δ, whether active power of output P and reactive power Q shake is determined that whether it is stable;

(2) impact of judgement on partial electric grid angle stability, voltage stabilization, whether all the other generator's power and angles of observing partial electric grid are stable with respect to the merit angle of balancing machine, and whether voltage and the phase angle of observing all generator access buses be stable;

(3) the idle configuration that the variation of the reactive power Q sending according to photovoltaic generating system is this bus place provides feasible proposal.

The present invention has following outstanding benefit:

(1) the present invention only needs to utilize meritorious, idle, voltage magnitude and four amounts of phase angle at photovoltaic generating system and external system interface place, and just good simulated light photovoltaic generating system inside and outside electromechanical transient characteristic, has good encapsulation characteristic, practical.

(2) the present invention has set up photovoltaic generation quasi steady state model, the inner PQ decoupling control policy that adopts, and simpler compared to the control structure of traditional outer loop voltag, interior circular current, parameter is easy to adjust.

(3) the inner perunit value that all adopts of model of the present invention calculates, and numerical stability is strong.

(4) the present invention meets the requirement of Electrical-Machanical Transient Simulation of Power System to simulation step length 10ms, and simulation velocity is fast, is applicable to stability analysis.

Accompanying drawing explanation

Below in conjunction with accompanying drawing, the present invention is further described.

Fig. 1 illustrates the entire block diagram of model;

Fig. 2 illustrates electric capacity of voltage regulation, three-phase inverter, ac filter circuit to the grid-connected schematic diagram of electrical network;

Fig. 3 illustrates DC link and meritorious ring control block diagram;

Fig. 4 illustrates idle ring control block diagram;

Fig. 5 illustrates output element block diagram;

Fig. 6 illustrates 7 node example figure;

Fig. 7 a to Fig. 7 f illustrates the simulation result figure of photovoltaic generating system 0.1s excision fault after fault;

Fig. 8 a to Fig. 8 c illustrates the simulation result figure of photovoltaic generating system after being subject to illumination S disturbance.

Embodiment

Please refer to shown in Fig. 1, Fig. 1 illustrates the overall structure of this model, comprises photovoltaic cell unit, maximal power tracing unit, direct-flow voltage regulation unit, meritorious ring, idle ring, output element.Photovoltaic cell be input as temperature T, maximum power point electric current I _m, short circuit current I _sc, maximum power point voltage U _m, open circuit voltage U _oc, initial power P _g0with battery outlet port voltage U _pv, the variable that outputs to DC voltage-stabilizing link is photovoltaic cell electric current I _pv, photovoltaic cell power P _pv; DC voltage-stabilizing link be input as I _pv, P _pv, U _mm, active-power P and reactive power Q, the variable that outputs to photovoltaic cell is U _pv, the variable that outputs to meritorious ring and idle ring is U _dc; The U that is input as that gains merit and encircle _dc, the DC side reference voltage U that calculates of MPPT _dcrefwith inverter outlet side voltage U _i, the variable that outputs to DC voltage-stabilizing link and output element is P; Idle ring be input as U _dcwith idle reference value Q _ref, the variable that outputs to output element is Q, the variable that outputs to meritorious ring is U _i; Output element be input as P, Q, line voltage phase angle theta _vwith amplitude U _s, the variable that outputs to electrical network is grid-connected current real part I _tRwith imaginary part I _tI; The grid-connected current of output element output is through circuit breaker P ₁grid-connected, P ₁state by the output of voltage protection, frequency protection, overcurrent and short circuit current protection and Voltage unbalance protection, determined.

Fig. 2 comprises photovoltaic generating system DC side electric capacity of voltage regulation, three-phase inverter, AC filter circuit to the grid-connected schematic diagram of electrical network.I in figure _dcfor the electric current of DC side input, the I being produced by photovoltaic cell _pvthrough conversion, obtain, if stage type I _dc=f (I _pv), if single stage type I _dc=I _pv; P _dcfor DC link input power; S _pvthe power of inputting for inverter is also the power output of DC link, under the hypothesis starting most, ignores the power loss of inverter at this model, thinks that inverter outputs to the power of electrical network just equal S _pv, complex power for inverter output; R and L represent resistance and the inductance of filter circuit, in the calculating of this model, ignore R, if because R crosses conference and consumes a lot of meritoriously in reality, so R is generally less, can ignore, for being input to the electric current of electrical network; VD ₁～VD ₆formed three-phase inverter.

Fig. 3 shows DC link and meritorious ring control block diagram.K in figure _pPand K _pIfor meritorious ring PI adjustment factor, δ ₀for the initial value of filter circuit both sides phase difference of voltage δ, U _iand U _sbe respectively inverter outlet voltage and grid-connected point voltage amplitude, between its variable, relation is expressed by following formula:

$\left\{\begin{array}{c}\mathrm{\δ}=(K_{\mathrm{pP}}+{\frac{K_{\mathrm{pI}}}{s}}^{})*(U_{\mathrm{dc}}-U_{\mathrm{dcref}})+{\mathrm{\δ}}_0\\ P\≈\frac{U_i*U_s}{\mathrm{\ωL}}\mathrm{\δ}\\ \frac{{\mathrm{dU}}_{\mathrm{dc}}}{\mathrm{dt}}=\frac{I_{\mathrm{dc}}}{C}-\frac{S_{\mathrm{pv}}}{{\mathrm{CU}}_{\mathrm{dc}}}\\ I_{\mathrm{dc}}=f\left(I_{\mathrm{pv}}\right)\end{array}\right.---\left(14\right)$

Fig. 4 illustrates the control block diagram of idle ring.Between its variable, relation is expressed by following formula:

$\left(\begin{array}{c}M=(K_{\mathrm{pP}}+\frac{K_{\mathrm{pI}}}{s})*(Q_{\mathrm{ref}}-Q)+M_0\\ Q=\frac{U_s}{\mathrm{\ωL}}(M*U_{\mathrm{dc}}-U_s)\end{array}\right.---\left(15\right)$

Fig. 5 illustrates the link that photovoltage model outputs to electrical network.In figure, I is for passing through P, Q, U _sthe photovoltaic output current amplitude calculating, remaining variables is expressed by following formula:

$\left(\begin{array}{c}{\mathrm{\θ}}_I={\mathrm{\θ}}_V-\arctan \frac{Q}{P}\\ I^2=\frac{P^2+Q^2}{U_s^2}\\ I_{\mathrm{TR}}=I*\cos {\mathrm{\θ}}_I\\ I_{\mathrm{TI}}=I*\sin {\mathrm{\θ}}_I\end{array}\right.---\left(16\right)$

Fig. 6 is the example of 7 nodes.This model is (but be not limited only to PSASP, can realize identical model equally in other simulation softwares) set up in the UD of PSASP module, has certain general applicability.In this example, choose acquiescence working method, adopt to become the form of photovoltaic cell group number, think initial illumination S=1000W/m ², T=25 ℃, photovoltaic generating system initialization is at maximum functional point.DC side for simplicity adopts single-stage type, i.e. U _pv=U _dc, I _pv=I _dc.The parameter of single group photovoltaic cell is definite value: I _m=13.74A, I _sc=14.98A, U _m=348V, U _oc=444V; System side reference voltage U _b=0.4kV, S _b=100MVA.

Emulation is carried out in 7 node systems shown in Fig. 6, and in figure, G1 bus connects photovoltaic generating system, is PQ node, P=20MW, Q=0,0.4kV; G2 bus connects common synchronous generator, is PV node P=2500MW, 18kV; S1 is balance node, 35kV; In figure, all the other buses are all 220kV bus.In this system, photovoltaic generation proportion is smaller, the situation in more realistic electrical network.

Three-phase metallic short circuit during emulation 1:B1-220 bus 1s, 1.1s excises fault, simulation time 10s, as shown in Figure 7, the parameter value in figure except phase angle is all perunit value to simulation result, rear same, no longer explanation.0.1s excision fault after fault, whole system transient stability, the phase angle of all generator bus and voltage magnitude are all stablized after earthquake; Photovoltaic generating system exit voltage U _swhen fault, decline obviously, fault current amplification when fault is obvious, but due to the effect of current limliting link, I is only the rated current of 2 times, realistic; After the P of photovoltaic generating system output and Q earthquake, also get back to stable; The inner DC bus-bar voltage U of photovoltaic generating system _dcat the fault initial stage because power cannot be exported and obviously rise, I _pvdue to U _dcrising and decline to some extent, cause the meritorious P of output obviously to decline, effectively alleviate the harm that short trouble brings, realistic.After obtaining simulation curve, can formulate as required protection allocation plan.

Emulation 2: consider the output characteristic under illumination disturbance, initial illumination S=1000W/m ², 1s～4s illumination decline 500W/m ², 4s～6s illumination is stabilized in 500W/m ², 6s～9s illumination rising 500W/m ², 9s～10s illumination is stabilized in S=1000W/m ², simulation result as shown in Figure 8.After illumination disturbance occurs, the active power of photovoltaic generating system output is followed illumination variation and changes, and variation tendency is consistent, and power output amplitude of variation conforms to illumination variation amplitude.

By above two simulation examples, can find out, this model is the interior external characteristic of simulated light photovoltaic generating system under fault transient and illumination disturbance well, and characteristic conforms is actual.The present invention only needs to utilize meritorious, idle, voltage magnitude and four amounts of phase angle at photovoltaic generating system and external system interface place; with regard to the good simulated light photovoltaic generating system of energy inside and outside characteristic; there is good encapsulation characteristic, practical, and comprise at present general protection configuration.The inner PQ decoupling control policy that adopts of model, control structure compared to traditional outer loop voltag, interior circular current is simpler, parameter is easy to adjust, adopt perunit value to calculate, numerical stability is strong, and meet the requirement of Electrical-Machanical Transient Simulation of Power System to simulation step length 10ms, simulation velocity is fast, is applicable to stability analysis.

According to specific illustrative examples, invention has been described herein.It will be apparent under not departing from the scope of the present invention, suitably replacing to one skilled in the art or revise.Illustrative examples is only illustrative, rather than the restriction to scope of the present invention, and scope of the present invention is defined by appended claim.

Claims (9)

1. a grid-connected photovoltaic power generation system electromechanical transient model of controlling based on power decoupled, is characterized in that, comprises photovoltaic cell unit, maximal power tracing unit, direct-flow voltage regulation unit, PQ decoupling zero control unit and protection dispensing unit;

The output of photovoltaic cell unit connects the input of direct-flow voltage regulation unit, the output of direct-flow voltage regulation unit connects the input of photovoltaic cell unit and the input of PQ decoupling zero control unit, and the output of PQ decoupling zero control unit connects input and the output element of direct-flow voltage regulation unit;

The output of maximal power tracing unit connects photovoltaic cell unit, direct-flow voltage regulation unit and PQ decoupling zero control unit;

Protection dispensing unit connects described output element.

2. a kind of grid-connected photovoltaic power generation system electromechanical transient model of controlling based on power decoupled according to claim 1, is characterized in that, described PQ decoupling zero control unit comprises meritorious ring and idle ring; The input of described meritorious ring connects output, the output of maximal power tracing unit and the output of idle ring of direct-flow voltage regulation unit, and the input of described idle ring connects the output of direct-flow voltage regulation unit.

3. a kind of grid-connected photovoltaic power generation system electromechanical transient model of controlling based on power decoupled according to claim 1, is characterized in that, photovoltaic cell unit meets conventional photovoltaic cell engineering simplified model, with illumination S, temperature T, battery terminal voltage U _pvas variable input, I _pvas single photovoltaic cell output current, expression formula is:

In formula:

ΔT＝T-25 (5)

U _occ＝U _oc(1-0.00288ΔT)×ln(e+0.5ΔS) (8)

U _mm＝U _m(1-0.00288ΔT)×ln(e+0.5ΔS) (9)

In formula:

I _m, I _sc, U _m, U _ocrespectively that temperature T is that 25 ℃, intensity of sunshine S are 1000W/m ²single photovoltaic cell maximum power point electric current under condition, short circuit current, maximum power point voltage, open circuit voltage; The parameter of single photovoltaic cell is definite value: I _m=13.74A, I _sc=14.98A, U _m=348V, U _oc=444V; And I _mm, I _scc, U _mm, U _occrespectively maximum power point electric current, short circuit current, maximum power point voltage, the open circuit voltage through S and T correction.

4. a kind of grid-connected photovoltaic power generation system electromechanical transient model of controlling based on power decoupled according to claim 1, is characterized in that, maximal power tracing unit makes DC voltage Udc follow the tracks of the single photovoltaic cell maximum power point voltage U through revising _mm, expression formula is:

U _mm＝U _m(1-0.00288ΔT)×ln(e+0.5ΔS) (10)。

5. a kind of grid-connected photovoltaic power generation system electromechanical transient model of controlling based on power decoupled according to claim 1, is characterized in that, direct-flow voltage regulation unit is stage type or single stage type; Stage type is expressed as U _dc=kU _pv; K is DC side booster circuit step-up ratio; Single stage type is expressed as U _dc=U _pv; Direct-flow voltage regulation unit has a DC voltage-stabilizing capacitor C, and the power of its both sides transmits expression formula and is:

P wherein _dcfor DC link input power; S _pvfor DC link power output.

6. a kind of grid-connected photovoltaic power generation system electromechanical transient model of controlling based on power decoupled according to claim 1, it is characterized in that, to the gain merit idle link decoupling zero of PQ decoupling zero control unit is controlled, utilize RL filter circuit both sides phase difference of voltage δ as the control object of meritorious ring, using inverter modulation ratio M as the control object of idle ring, by following formula, complete meritorious idle decoupling zero is controlled:

In formula:

U _iand U _s---inverter outlet side voltage and voltage on line side, U _i=MU _dc;

L---filter inductance;

ω---electrical network angular frequency;

P and Q---meritorious, idle output.

7. a kind of grid-connected photovoltaic power generation system electromechanical transient model of controlling based on power decoupled according to claim 1; it is characterized in that, protection dispensing unit comprises voltage protection module, frequency protection module, overcurrent and short circuit current protection module and Voltage unbalance protection module.

8. a kind of grid-connected photovoltaic power generation system electromechanical transient model of controlling based on power decoupled according to claim 1, it is characterized in that, the described grid-connected photovoltaic power generation system electromechanical transient model of controlling based on power decoupled comprises two kinds of working methods: determine photovoltaic cell group quantity and automatically calculate required photovoltaic cell group number, two kinds of modes all suppose that initial steady state working point is maximum power working point; The first working method is: by trend, calculate resulting meritorious initial value P _g0peak power output P divided by single photovoltaic cell _max=U _mm ^*i _mm, calculate required photovoltaic cell group and count Nvp, suppose initialization state S ₀=1000W/m ², T ₀=25 ℃, the second working method is: self-defined required photovoltaic cell group is counted Nvp, Nvp*P _max>=P _g0, by the relation of photovoltaic cell illumination S and power output P, obtain the intensity of illumination of present operating point, initialization state is T ₀=25 ℃, 0≤S≤1000W/m ².

9. a kind of grid-connected photovoltaic power generation system electromechanical transient model of controlling based on power decoupled according to claim 2, is characterized in that, in meritorious ring, between variable, relation is expressed by following formula:

In formula:

K _pPand K _pI---meritorious ring PI adjustment factor;

U _dcref---the DC voltage reference value calculating by MPPT;

δ ₀---the initial value of δ;

I _dc---DC link input current;

In idle ring, between variable, relation is expressed by following formula:

In formula:

K _qPand K _qI---idle ring PI adjustment factor;

Q _ref---idle reference value;

M ₀---the initial value of M;

The variable relation of output element is expressed by following formula:

In formula:

θ _iand θ _v---photovoltaic output current and line voltage phase angle;

I _tRand I _tI---real part and the imaginary part of photovoltaic output current.