CN106877344A - A kind of grid-connected photovoltaic power station based on power prediction is idle-voltage control method - Google Patents

Abstract

A kind of grid-connected photovoltaic power station based on power prediction of present invention offer is idle-voltage control method, by the Reactive-power control equipment in photovoltaic AVC system coordination grid-connected photovoltaic power stations, complete the control of grid entry point voltage；Method includes：Determine reactive loss of the grid-connected photovoltaic power station again at the end of grid entry point voltage-regulation based on power prediction data；Determine the Reactive-power control total amount of grid-connected photovoltaic power station；Determine the reactive power auxiliary service of photovoltaic DC-to-AC converter and static reactive power compensation equipment；Carry out the switching control of parallel capacitor group；Carry out the control of photovoltaic DC-to-AC converter and static reactive power compensation equipment.The accurate photovoltaic plant that calculates of the invention controls sensitivity, possesses more preferable idle-voltage control accuracy and response speed；Power prediction is combined with photovoltaic plant AVC systems, so as to realize photovoltaic plant capacitor bank Discrete control, realizes idle-voltage and controls preferably to be balanced and between equipment protection.

Description

A kind of grid-connected photovoltaic power station based on power prediction is idle-voltage control method

Technical field

The present invention relates to a kind of control method, and in particular to a kind of grid-connected photovoltaic power station based on power prediction is idle-voltage control method.

Background technology

The characteristics of solar energy power generating has randomness, intermittence, periodicity and fluctuation, as photovoltaic generation scale constantly increases, the influence to Network Voltage Stability is increasingly apparent.The important means that idle-Voltage Automatic Control System (hereinafter referred to as photovoltaic AVC systems) is guarantee Network Voltage Stability, reactive balance is installed in grid-connected photovoltaic power station, typical photovoltaic AVC system architectures are as shown in figure 1, photovoltaic AVC systems are controlled by coordinating the completion grid entry point voltage of exerting oneself of Reactive-power control equipment in photovoltaic plant.

Photovoltaic generation is compared with thermoelectricity/wind-powered electricity generation, due to lacking the rotary inertia and damping characteristic of plant equipment, change exert oneself in step response, to photovoltaic AVC system response times, (various regions regulation is different, typically require at 10~20 seconds or so), the requirement of control accuracy significantly improve, this causes that the regulation of traditional fixed step size, many wheel feedbacks are difficult to meet system requirements.Problems with is exposed in practical engineering application：

(1) Reactive-power control equipment control difficult coordination, photovoltaic DC-to-AC converter and static reactive power compensation equipment have Millisecond response speed in theory, the capacitor switching time, each Reactive-power control equipment response speed was influenceed larger by communication modes again smaller than 1 second, but in Practical Project.The particularly photovoltaic DC-to-AC converter of independent control, according to annular rather than the communication of optical fiber associated mode, the slower inverter of response speed often more than the several seconds, busbar voltage overshoot or regulation problem not in place in regulation regulating time is easily occurred in using traditional control method.

(2) Reactive-power control total amount dyscalculia, due to the influence of the factor such as grid entry point is idle, voltage change is smaller and measurement data is asynchronous, often error is larger to be calculated system impedance online according to voltage deviation and idle change, cause regulation total amount to calculate and there is problem, and then have influence on response time and the control accuracy of photovoltaic AVC systems.

(3) continuously adjust the Harmonic Control of equipment and discrete adjustment equipment, in existing Reactive Power Optimization Algorithm for Tower, capacitor switching number of times as calculating restrictive condition, and as last regulating measure.Therefore, capacitor switching operation is general lags behind electric station grid connection point voltage change situation, and causes photovoltaic DC-to-AC converter and static reactive power compensation environment division period idle higher, influence generating efficiency of exerting oneself.

(4) in less consideration power station reactive loss influence, when power network entirety reactive balance, it is reactive loss in station to influence one of key factor of photovoltaic electric station grid connection point voltage, therefore, reactive loss situation of change in station should be taken into full account during idle-voltage-regulation, existing idle-voltage control algolithm is usually to take no account of reactive loss in station.

(5) irrational use of static reactive power compensation equipment (SVC/SVG/MCR).It is to ensure the transient state reactive reserve under electric network fault, the photovoltaic AVC systems come based on traditional thermoelectricity/wind-powered electricity generation AVC System Developments do not use the control strategy of static reactive power compensation equipment typically during regulation.This aspect is easily caused the frequent switching of capacitor；On the other hand also cause that main transformer reactive requirement is provided by the photovoltaic DC-to-AC converter in a distant place completely, line loss is increased to a certain extent.Practical operating experiences show, on the basis of exact power prediction and Reactive Power Margin are calculated, by reasonable, conditional application static reactive power compensation equipment pondage, can effectively improve voltage control accuracy and AVC system response times, the switching frequency of reduction capacitor.

The content of the invention

In order to overcome the above-mentioned deficiencies of the prior art, a kind of grid-connected photovoltaic power station based on power prediction of present invention offer is idle-voltage control method, for different Reactive-power control equipment response speed differences, then used substep control ensure photovoltaic plant it is idle-voltage-controlled precision and response speed.

In order to realize foregoing invention purpose, the present invention is adopted the following technical scheme that：

A kind of grid-connected photovoltaic power station based on power prediction of present invention offer is idle-voltage control method, by the Reactive-power control equipment in photovoltaic AVC system coordination grid-connected photovoltaic power stations, complete the control of grid entry point voltage；The Reactive-power control equipment includes photovoltaic DC-to-AC converter, parallel capacitor group and static reactive power compensation equipment；

Methods described includes：

Step 1：Determine reactive loss of the grid-connected photovoltaic power station again at the end of grid entry point voltage-regulation；

Step 2：Determine the Reactive-power control total amount of grid-connected photovoltaic power station；

Step 3：Determine the reactive power auxiliary service of photovoltaic DC-to-AC converter and static reactive power compensation equipment；

Step 4：Carry out the switching control of parallel capacitor group；

Step 5：Carry out the control of photovoltaic DC-to-AC converter and static reactive power compensation equipment.

In the step 1, grid-connected photovoltaic power station includes collection electric line and transformer；Including：

Step 1-1：Total reactive loss of collection electric line is calculated, including：

If current collection line voltage distribution and electric current are respectively U and I, X_lTo collect the equivalent reactance of electric line, x_lIt is collection electric line unit length reactance, l is current collection line length, there is X_l=x_l·l；

Then the reactive loss Q of electric line is collected_lWith charge power Q_cIt is expressed as：

Q_l=3I²X_l=3I²x_l·l (1)

Q_C=U²ω C/1000=U²·2πf·c·l/1000 (2)

Wherein, f is power system frequency, takes 50Hz；ω is power system angular speed；C is current collection line mutual-ground capacitor, and c is collection electric line unit length direct-to-ground capacitance；

Then, the total reactive loss for integrating electric line is Q_l-Q_C；

Step 1-2：Total reactive loss of calculating transformer, including：

The reactive loss Q' of single transformer_TIt is expressed as：

Wherein, S_NIt is the rated power of transformer, I₀% is no-load transformer percentage of current, U_k% is transformer short-circuit voltage percentage, and S is transformer apparent energy, and β is transformer load rate, and β=S/S_N；

Then, in grid-connected photovoltaic power station transformer total reactive loss Q_TIt is expressed as：

Q_T=Σ Q'_T (4)

Step 1-3：Calculate reactive loss Q of the grid-connected photovoltaic power station when grid entry point voltage-regulation starts_Σ(t₀), it is expressed as：

Q_Σ(t₀)=Q_l-Q_C+Q_T (5)

The reactive loss of grid-connected photovoltaic power station during grid entry point voltage-regulation is predicted using Auto regressive integrated moving average model, then reactive loss Q of the grid-connected photovoltaic power station at the end of grid entry point voltage-regulation_ΣT () is expressed as：

Q_Σ(t)=Q_Σ(t₀)+▽Q'_Σ+▽Q”_Σ (6)

Wherein, t₀It it is grid entry point voltage-regulation start time, t is grid entry point voltage-regulation finish time, ▽ Q'_ΣExerted oneself for grid-connected photovoltaic power station and change the reactive loss difference of caused grid-connected photovoltaic power station, ▽ Q "_ΣIt is the reactive loss difference of grid-connected photovoltaic power station caused by grid entry point voltage change.

The step 2 includes：

Grid entry point voltage U_pccWith grid entry point reactive power Q_pccMeet following relation：

Wherein, Q'_PVIt is total reactive power that photovoltaic DC-to-AC converter is currently exported, and Q'_PV=Q_inv-Q_Σ(t₀), Q_invRepresent the reactive power of photovoltaic DC-to-AC converter output, Q_Σ(t₀) it is reactive loss of the grid-connected photovoltaic power station when grid entry point voltage-regulation starts；Q_capIt is the current output reactive power of parallel capacitor group, Q_svcIt is the current output reactive power of static reactive power compensation equipment；ΔU_pccIt is grid entry point voltage increment, Δ Q_pccIt is grid entry point reactive power increment, Δ Q'_PVIt is photovoltaic DC-to-AC converter output reactive power increment, Δ Q_capIt is connection compensation capacitor group output reactive power increment, Δ Q_svcIt is static reactive power compensation equipment output reactive power increment；

Grid entry point voltage U_pccWith infinite busbar voltage U_∞It is expressed as：

Wherein, U_PVIt is grid-connected photovoltaic power station low-pressure side bus voltage, P_PVAnd Q_PVRespectively grid-connected photovoltaic power station low-pressure side injects active power and reactive power；Intermediate quantity R_ΣAnd X_ΣIt is expressed as R_Σ=R₁+R₂, X_Σ=X₁+X₂, R₁And X₁Respectively main transformer substitutional resistance and reactance, R₂And X₂Respectively grid entry point outside substitutional resistance and reactance；

Obtained by formula (8) and (9)：

If the voltage control sensitivity of grid-connected photovoltaic power station and idle control sensitivity are respectivelyWithHave：

Can be obtained by formula (11)：

Grid-connected photovoltaic output reactive power Q_pccIt is expressed as：

Can be obtained by formula (11) and (13)：

The Reactive-power control total amount Q of grid-connected photovoltaic power station_targetIt is expressed as：

Q_target≈Q'_PV+Q_cap+Q_svc+Q_initial+ΔQ_pcc+ΔQ_Σ(t-t₀) (12)

Wherein, Δ Q_Σ(t-t₀) it is reactive loss of the grid-connected photovoltaic power station within the grid entry point voltage-regulation cycle, and Δ Q_Σ(t-t₀)=Δ Q_Σ(t)-ΔQ_Σ(t₀), Q_Σ(t₀) it is reactive loss of the grid-connected photovoltaic power station when grid entry point voltage-regulation starts, Δ Q_ΣT () is reactive loss of the grid-connected photovoltaic power station at the end of grid entry point voltage-regulation.

The step 3 includes：

Step 3-1：Determine the reactive power auxiliary service Q of photovoltaic DC-to-AC converter_invmax, have：

Wherein, U_invIt is photovoltaic DC-to-AC converter output voltage, U_pccIt is grid entry point voltage, ω is power system angular speed, and L is photovoltaic DC-to-AC converter Inductor, P_invAnd Q_invPhotovoltaic DC-to-AC converter active power of output and reactive power are represented, andP_invAnd Q_invBetween also meetθ is U_invAnd U_pccBetween phase difference；

Step 3-2：Determine the reactive power auxiliary service Q of static reactive power compensation equipment_svcmaxMeet：

Q'_linemin≤Q_svcmax≤Q'_linemax (14)

Wherein, Q'_linemin、Q'_linemaxThe reactive power lower and upper limit of branch road output respectively in grid-connected photovoltaic power station.

In the step 4, switching control is carried out to parallel capacitor group using Discrete control mode, including：

1) grow steadily the stage, i.e. grid-connected photovoltaic power station is exerted oneself the stage that grows steadily, corresponding typical time period is during grid-connected photovoltaic power station is in 6 points to 10 points of the morning, in this typical time period, parallel capacitor group uses controls in advance, i.e. parallel capacitor group to be put into before forecast demand rising；

2) the flex point stage, i.e. grid-connected photovoltaic power station is exerted oneself with respect to plateau, corresponding typical time period is in grid-connected photovoltaic power station during at 10 points in the morning at 4 points in afternoon, in this typical time period, parallel capacitor group uses Delay control, i.e. less than switching is carried out in the case of the Reactive-power control increment of grid-connected photovoltaic power station to parallel capacitor group, the wherein Reactive-power control increment of grid-connected photovoltaic power station is Q to the adjustable nargin of photovoltaic DC-to-AC converter_invmax-Q_PV；

3) the steady decline stage, i.e. grid-connected photovoltaic power station is exerted oneself the steady decline stage, corresponding typical time period is during grid-connected photovoltaic power station in the afternoon 4 points to 8 points, in this typical time period, parallel capacitor group uses controls in advance, i.e. parallel capacitor group to be cut out before forecast demand decline.

The step 5 includes：

Step 5-1：Photovoltaic AVC systems are controlled to photovoltaic DC-to-AC converter, including：

1) in the grid entry point voltage-regulation cycle, change the reactive power of photovoltaic DC-to-AC converter and controlled with realizing grid entry point voltage；

2) after grid entry point voltage-regulation finish time, in the case of keeping grid entry point reactive power constant, the reactive power exported using the reactive power displacement static reactive power compensation equipment of photovoltaic DC-to-AC converter, and the reactive power that static reactive power compensation equipment is exported is reduced to zero, while optimizing current collection line voltage distribution distribution in grid-connected photovoltaic power station；

Step 5-2：Photovoltaic AVC systems are controlled to static reactive power compensation equipment, including：

1) before grid entry point voltage-regulation finish time, if grid entry point voltage does not meet corresponding sets target value yet, need to adjust the reactive power of static reactive power compensation equipment output；

2) after grid entry point voltage-regulation finish time, if static reactive power compensation equipment output reactive power, and photovoltaic DC-to-AC converter possesses adjustable nargin simultaneously, the reactive power for then being exported using the reactive power displacement static reactive power compensation equipment of photovoltaic DC-to-AC converter, and the reactive power that static reactive power compensation equipment is exported is reduced to zero.

Compared with immediate prior art, the technical scheme that the present invention is provided has the advantages that：

(1) collection electric line, the reactive loss of transformer in grid-connected photovoltaic power station have been considered, and change to reactive loss during regulation is predicted, more can accurately calculate the Reactive-power control total amount of grid-connected photovoltaic power station；

(2) it is accurate to calculate photovoltaic plant control sensitivity, possess more preferable idle-voltage control accuracy and response speed；

(3) power prediction is combined with photovoltaic plant AVC systems, so as to realize photovoltaic plant capacitor bank Discrete control, realizes idle-voltage and controls preferably to be balanced and between equipment protection.

Brief description of the drawings

Fig. 1 is photovoltaic AVC system construction drawings in the embodiment of the present invention；

Fig. 2 is current collection equivalent line circuit diagram in grid-connected photovoltaic power station in the embodiment of the present invention；

Fig. 3 is typical parallel networking type photovoltaic power station topology diagram in the embodiment of the present invention；

Fig. 4 is typical photovoltaic power prediction curve figure in the embodiment of the present invention；

Fig. 5 is grid-connected photovoltaic power station AVC control system closed-loop control block diagrams in the embodiment of the present invention.

Specific embodiment

The present invention is described in further detail below in conjunction with the accompanying drawings.

A kind of grid-connected photovoltaic power station based on power prediction of present invention offer is idle-voltage control method, such as Fig. 5, by the Reactive-power control equipment in photovoltaic AVC system coordination grid-connected photovoltaic power stations, complete the control of grid entry point voltage；The Reactive-power control equipment includes photovoltaic DC-to-AC converter, parallel capacitor group and static reactive power compensation equipment；

Methods described includes：

Step 1：Determine reactive loss of the grid-connected photovoltaic power station again at the end of grid entry point voltage-regulation；

Step 2：Determine the Reactive-power control total amount of grid-connected photovoltaic power station；

Step 3：Determine the reactive power auxiliary service of photovoltaic DC-to-AC converter and static reactive power compensation equipment；

Step 4：Carry out the switching control of parallel capacitor group；

Step 5：Carry out the control of photovoltaic DC-to-AC converter and static reactive power compensation equipment.

In the step 1, grid-connected photovoltaic power station includes collection electric line and transformer；Including：

Step 1-1：Total reactive loss of collection electric line is calculated, including：

Current collection equivalent line circuit in photovoltaic plant is as shown in Fig. 2 set current collection line voltage distribution and electric current respectively U and I, X_lTo collect the equivalent reactance of electric line, x_lIt is collection electric line unit length reactance, l is current collection line length, there is X_l=x_l·l；

Then the reactive loss Q of electric line is collected_lWith charge power Q_cIt is expressed as：

Q_l=3I²X_l=3I²x_l·l (1)

Q_C=U²ω C/1000=U²·2πf·c·l/1000 (2)

Wherein, f is power system frequency, takes 50Hz；ω is power system angular speed；C is current collection line mutual-ground capacitor, and c is collection electric line unit length direct-to-ground capacitance；

Then, the total reactive loss for integrating electric line is Q_l-Q_C；

Step 1-2：Total reactive loss of calculating transformer, including：

The reactive loss Q' of single transformer_TIt is expressed as：

Wherein, S_NIt is the rated power of transformer, I₀% is no-load transformer percentage of current, U_k% is transformer short-circuit voltage percentage, and S is transformer apparent energy, and β is transformer load rate, and β=S/S_N；

Then, in grid-connected photovoltaic power station transformer total reactive loss Q_TIt is expressed as：

Q_T=Σ Q'_T (4)

Step 1-3：Calculate reactive loss Q of the grid-connected photovoltaic power station when grid entry point voltage-regulation starts_Σ(t₀), it is expressed as：

Q_Σ(t₀)=Q_l-Q_C+Q_T (5)

The reactive loss of grid-connected photovoltaic power station during grid entry point voltage-regulation is predicted using Auto regressive integrated moving average model, then reactive loss Q of the grid-connected photovoltaic power station at the end of grid entry point voltage-regulation_ΣT () is expressed as：

Q_Σ(t)=Q_Σ(t₀)+▽Q'_Σ+▽Q”_Σ (6)

Wherein, t₀It it is grid entry point voltage-regulation start time, t is grid entry point voltage-regulation finish time, ▽ Q'_ΣExerted oneself for grid-connected photovoltaic power station and change the reactive loss difference of caused grid-connected photovoltaic power station, ▽ Q "_ΣIt is the reactive loss difference of grid-connected photovoltaic power station caused by grid entry point voltage change.

The step 2 includes：

Typical grid-connected photovoltaic power station structure is as shown in figure 3, grid entry point voltage U_pccWith grid entry point reactive power Q_pccMeet following relation：

Wherein, Q'_PVIt is total reactive power that photovoltaic DC-to-AC converter is currently exported, and Q'_PV=Q_inv-Q_Σ(t₀), Q_invRepresent the reactive power of photovoltaic DC-to-AC converter output, Q_Σ(t₀) it is reactive loss of the grid-connected photovoltaic power station when grid entry point voltage-regulation starts；Q_capIt is the current output reactive power of parallel capacitor group, Q_svcIt is the current output reactive power of static reactive power compensation equipment；ΔU_pccIt is grid entry point voltage increment, Δ Q_pccIt is grid entry point reactive power increment, Δ Q'_PVIt is photovoltaic DC-to-AC converter output reactive power increment, Δ Q_capIt is connection compensation capacitor group output reactive power increment, Δ Q_svcIt is static reactive power compensation equipment output reactive power increment；

Grid entry point voltage U_pccWith infinite busbar voltage U_∞It is expressed as：

Wherein, U_PVIt is grid-connected photovoltaic power station low-pressure side bus voltage, P_PVAnd Q_PVRespectively grid-connected photovoltaic power station low-pressure side injects active power and reactive power；Intermediate quantity R_ΣAnd X_ΣIt is expressed as R_Σ=R₁+R₂, X_Σ=X₁+X₂, R₁And X₁Respectively main transformer substitutional resistance and reactance, R₂And X₂Respectively grid entry point outside substitutional resistance and reactance；

Obtained by formula (8) and (9)：

If the voltage control sensitivity of grid-connected photovoltaic power station and idle control sensitivity are respectivelyWithHave：

Can be obtained by formula (11)：

Grid-connected photovoltaic output reactive power Q_pccIt is expressed as：

Can be obtained by formula (11) and (13)：

The Reactive-power control total amount of grid-connected photovoltaic power station is expressed as：

Q_target≈Q'_PV+Q_cap+Q_svc+Q_initial+ΔQ_pcc+ΔQ_Σ(t-t₀) (12)

Wherein, Δ Q_Σ(t-t₀) it is reactive loss of the grid-connected photovoltaic power station within the grid entry point voltage-regulation cycle, and Δ Q_Σ(t-t₀)=Δ Q_Σ(t)-ΔQ_Σ(t₀), Q_Σ(t₀) it is reactive loss of the grid-connected photovoltaic power station when grid entry point voltage-regulation starts, Δ Q_ΣT () is reactive loss of the grid-connected photovoltaic power station at the end of grid entry point voltage-regulation.

The step 3 includes：

Step 3-1：Determine the reactive power auxiliary service Q of photovoltaic DC-to-AC converter_invmax, have：

Wherein, U_invIt is photovoltaic DC-to-AC converter output voltage, U_pccIt is grid entry point voltage, ω is power system angular speed, and L is photovoltaic DC-to-AC converter Inductor, P_invAnd Q_invPhotovoltaic DC-to-AC converter active power of output and reactive power are represented, andP_invAnd Q_invBetween also meetθ is U_invAnd U_pccBetween phase difference；

Step 3-2：Determine the reactive power auxiliary service Q of static reactive power compensation equipment_svcmax：

Static reactive power compensation equipment reactive power auxiliary service in short-term is determined based on following factor in the present invention：

The steady state power output limit of static reactive power compensation equipment, in most cases the stable state output limit of static reactive power compensation equipment for rated value 50~80% between.

Ensure photovoltaic electric station grid connection safety, when in photovoltaic power station power generation system certain electrical equipment due to failure is exited when, in order to keep grid entry point voltage stabilization, it is necessary to put into standby reactive-load compensation equipment, it is to avoid due to grid entry point brownout influence major network voltage stabilization.What is most generally occurred in photovoltaic plant causes voltage die failure to be that the tripping operation for collecting electric line is exited, requirement of the photovoltaic plant to line voltage reactive power support from after meeting accident, enough transient state reactive reserves must be at any time had in AVC system fading margins, therefore, static passive compensation device power limit is idle no more than current maximum branch road output in photovoltaic plant.In summary two conditions, Q_svcmaxMeet：

Q'_linemin≤Q_svcmax≤Q'_linemax (14)

Wherein, Q'_linemin、Q'_linemaxThe reactive power lower and upper limit of branch road output respectively in grid-connected photovoltaic power station.

In the step 4, switching control is carried out to parallel capacitor group using Discrete control mode, including：

1) grow steadily the stage, i.e. grid-connected photovoltaic power station is exerted oneself the stage that grows steadily, as shown in Figure 4, corresponding typical time period is during grid-connected photovoltaic power station is in 6 points to 10 points of the morning, in this typical time period, parallel capacitor group uses controls in advance, i.e. parallel capacitor group to be put into before forecast demand rising；

2) the flex point stage, i.e. grid-connected photovoltaic power station is exerted oneself with respect to plateau, corresponding typical time period is in grid-connected photovoltaic power station during at 10 points in the morning at 4 points in afternoon, in this typical time period, parallel capacitor group uses Delay control, i.e. less than switching is carried out in the case of the Reactive-power control increment of grid-connected photovoltaic power station to parallel capacitor group, the wherein Reactive-power control increment of grid-connected photovoltaic power station is Q to the adjustable nargin of photovoltaic DC-to-AC converter_invmax-Q_PV；

3) the steady decline stage, i.e. grid-connected photovoltaic power station is exerted oneself the steady decline stage, corresponding typical time period is during grid-connected photovoltaic power station in the afternoon 4 points to 8 points, in this typical time period, parallel capacitor group uses controls in advance, i.e. parallel capacitor group to be cut out before forecast demand decline.

The step 5 includes：

Step 5-1：Photovoltaic AVC systems are controlled to photovoltaic DC-to-AC converter, including：

1) in the grid entry point voltage-regulation cycle, change the reactive power of photovoltaic DC-to-AC converter and controlled with realizing grid entry point voltage；

2) after grid entry point voltage-regulation finish time, in the case of keeping grid entry point reactive power constant, the reactive power exported using the reactive power displacement static reactive power compensation equipment of photovoltaic DC-to-AC converter, and the reactive power that static reactive power compensation equipment is exported is reduced to zero, while optimizing current collection line voltage distribution distribution in grid-connected photovoltaic power station；

Step 5-2：Photovoltaic AVC systems are controlled to static reactive power compensation equipment：

The control of static reactive power compensation equipment mainly undertakes three below task：1) calculating of idle-voltage control sensitivity is aided in；2) when the voltage-regulation cycle is close to terminating, and photovoltaic DC-to-AC converter is idle exerts oneself temporarily when being difficult to reach calculated value, there is provided fast reactive is adjusted to ensure that voltage-regulation success rate；3) photovoltaic DC-to-AC converter is exerted oneself close to power limit, and power station is integrally exerted oneself during close to flex point, undertakes idle in short-term exerting oneself.

Photovoltaic AVC systems static reactive power compensation equipment is controlled including：

1) before grid entry point voltage-regulation finish time, if grid entry point voltage does not meet corresponding sets target value yet, need to adjust the reactive power of static reactive power compensation equipment output；

2) after grid entry point voltage-regulation finish time, if static reactive power compensation equipment output reactive power, and photovoltaic DC-to-AC converter possesses adjustable nargin simultaneously, the reactive power for then being exported using the reactive power displacement static reactive power compensation equipment of photovoltaic DC-to-AC converter, and the reactive power that static reactive power compensation equipment is exported is reduced to zero.

Finally it should be noted that：The above embodiments are merely illustrative of the technical solutions of the present invention rather than its limitations; those of ordinary skill in the art can still modify or equivalent with reference to above-described embodiment to specific embodiment of the invention; these are applying within pending claims of the invention without departing from any modification of spirit and scope of the invention or equivalent.

Claims (6)

1. a kind of grid-connected photovoltaic power station based on power prediction it is idle-voltage control method, it is characterised in that：By photovoltaic AVC Reactive-power control equipment in system coordination grid-connected photovoltaic power station, completes the control of grid entry point voltage；The Reactive-power control equipment includes light Volt inverter, parallel capacitor group and static reactive power compensation equipment；

Methods described includes：

Step 1：Determine reactive loss of the grid-connected photovoltaic power station again at the end of grid entry point voltage-regulation；

Step 2：Determine the Reactive-power control total amount of grid-connected photovoltaic power station；

Step 3：Determine the reactive power auxiliary service of photovoltaic DC-to-AC converter and static reactive power compensation equipment；

Step 4：Carry out the switching control of parallel capacitor group；

Step 5：Carry out the control of photovoltaic DC-to-AC converter and static reactive power compensation equipment.

2. the grid-connected photovoltaic power station based on power prediction according to claim 1 it is idle-voltage control method, its feature exists In：In the step 1, grid-connected photovoltaic power station includes collection electric line and transformer；Including：

Step 1-1：Total reactive loss of collection electric line is calculated, including：

If current collection line voltage distribution and electric current are respectively U and I, X_lTo collect the equivalent reactance of electric line, x_lFor collection electric line unit is long Degree reactance, l is current collection line length, there is X_l=x_l·l；

Then the reactive loss Q of electric line is collected_lWith charge power Q_cIt is expressed as：

Q_l=3I²X_l=3I²x_l·l (1)

Q_C=U²ω C/1000=U²·2πf·c·l/1000 (2)

Wherein, f is power system frequency, takes 50Hz；ω is power system angular speed；C is current collection line mutual-ground capacitor, c It is collection electric line unit length direct-to-ground capacitance；

Then, the total reactive loss for integrating electric line is Q_l-Q_C；

Step 1-2：Total reactive loss of calculating transformer, including：

The reactive loss Q' of single transformer_TIt is expressed as：

${Q^{\′}}_T=S_N\·(\frac{I_0\%}{100}+\frac{U_k\%}{100}{\mathrm{\β}}^2)=S_N\·(\frac{I_0\%}{100}+\frac{U_k\%}{100}\frac{S^2}{{S_N}^2})---\left(3\right)$

Wherein, S_NIt is the rated power of transformer, I₀% is no-load transformer percentage of current, U_k% is transformer short-circuit voltage Percentage, S is transformer apparent energy, and β is transformer load rate, and β=S/S_N；

Then, in grid-connected photovoltaic power station transformer total reactive loss Q_TIt is expressed as：

Q_T=∑ Q'_T (4)

Step 1-3：Calculate reactive loss Q of the grid-connected photovoltaic power station when grid entry point voltage-regulation starts_Σ(t₀), it is expressed as：

Q_Σ(t₀)=Q_l-Q_C+Q_T (5)

The reactive loss of grid-connected photovoltaic power station during grid entry point voltage-regulation is carried out using Auto regressive integrated moving average model pre- Survey, then reactive loss Q of the grid-connected photovoltaic power station at the end of grid entry point voltage-regulation_ΣT () is expressed as：

Q_Σ(t)=Q_Σ(t₀)+▽Q'_Σ+▽Q”_Σ (6)

Wherein, t₀It it is grid entry point voltage-regulation start time, t is grid entry point voltage-regulation finish time, ▽ Q'_ΣIt is grid-connected photovoltaic The reactive loss difference of grid-connected photovoltaic power station, ▽ Q caused by output of power station change "_ΣIt is grid-connected photovoltaic caused by grid entry point voltage change The reactive loss difference in power station.

3. the grid-connected photovoltaic power station based on power prediction according to claim 1 it is idle-voltage control method, its feature exists In：The step 2 includes：

Grid entry point voltage U_pccWith grid entry point reactive power Q_pccMeet following relation：

$\left\{\begin{array}{c}\frac{\∂U_{pcc}}{\∂Q_{PV}^{\′}}{\mathrm{\ΔQ}}_{PV}^{\′}+\frac{\∂U_{pcc}}{\∂Q_{cap}}{\mathrm{\ΔQ}}_{cap}+\frac{\∂U_{pcc}}{\∂Q_{svc}}{\mathrm{\ΔQ}}_{svc}={\mathrm{\ΔU}}_{pcc}\\ \frac{\∂Q_{pcc}}{\∂Q_{PV}^{\′}}{\mathrm{\ΔQ}}_{PV}^{\′}+\frac{\∂Q_{pcc}}{\∂Q_{cap}}{\mathrm{\ΔQ}}_{cap}+\frac{\∂Q_{pcc}}{\∂Q_{svc}}{\mathrm{\ΔQ}}_{svc}={\mathrm{\ΔQ}}_{pcc}\end{array}\right.---\left(7\right)$

Wherein, Q'_PVIt is total reactive power that photovoltaic DC-to-AC converter is currently exported, and Q'_PV=Q_inv-Q_Σ(t₀), Q_invRepresent that photovoltaic is inverse Become the reactive power of device output, Q_Σ(t₀) it is reactive loss of the grid-connected photovoltaic power station when grid entry point voltage-regulation starts；Q_capFor simultaneously The connection current output reactive power of compensation capacitor group, Q_svcIt is the current output reactive power of static reactive power compensation equipment；ΔU_pccFor simultaneously Site voltage increment, Δ Q_pccIt is grid entry point reactive power increment, Δ Q'_PVIt is photovoltaic DC-to-AC converter output reactive power increment, Δ Q_cap It is connection compensation capacitor group output reactive power increment, Δ Q_svcIt is static reactive power compensation equipment output reactive power increment；

Grid entry point voltage U_pccWith infinite busbar voltage U_∞It is expressed as：

$U_{\mathrm{\∞}}=U_{PV}-\frac{P_{PV}{R}_{\mathrm{\Σ}}+Q_{PV}{X}_{\mathrm{\Σ}}}{U_{PV}}---\left(8\right)$

$U_{pcc}=U_{PV}-\frac{P_{PV}{R}_1+Q_{PV}{X}_1}{U_{PV}}---\left(9\right)$

Wherein, U_PVIt is grid-connected photovoltaic power station low-pressure side bus voltage, P_PVAnd Q_PVRespectively grid-connected photovoltaic power station low-pressure side injection Active power and reactive power；Intermediate quantity R_ΣAnd X_ΣIt is expressed as R_Σ=R₁+R₂, X_Σ=X₁+X₂, R₁And X₁Respectively It is main transformer substitutional resistance and reactance, R₂And X₂Respectively grid entry point outside substitutional resistance and reactance；

Obtained by formula (8) and (9)：

$\begin{array}{c}{U}_{PCC}=U_{\mathrm{\∞}}+\frac{P_{PV}{R}_2+Q_{PV}{X}_2}{U_{PV}}=U_{\mathrm{\∞}}+\frac{P_{PV}{R}_2+(Q_{inv}-Q_{\mathrm{\Σ}}(t_0)+Q_{cap}+Q_{svc})X_2}{U_{PV}}\\ =U_{\mathrm{\∞}}+\frac{P_{PV}{R}_2+(Q_{PV}^{\′}+Q_{cap}+Q_{svc})X_2}{U_{PV}}\end{array}---\left(10\right)$

If the voltage control sensitivity of grid-connected photovoltaic power station and idle control sensitivity are respectivelyWithHave：

$\left\{\begin{array}{c}{\mathrm{\λ}}_{u_{pcc}}=\frac{\∂U_{pcc}}{\∂Q_{PV}^{\′}}\≈\frac{\∂U_{pcc}}{\∂Q_{cap}}\≈\frac{\∂U_{pcc}}{\∂Q_{svc}}\\ {\mathrm{\λ}}_{Q_{pcc}}=\frac{\∂Q_{pcc}}{\∂Q_{PV}^{\′}}\≈\frac{\∂Q_{pcc}}{\∂Q_{cap}}\≈\frac{\∂Q_{pcc}}{\∂Q_{svc}}\end{array}\right.---\left(11\right)$

Can be obtained by formula (11)：

${\mathrm{\λ}}_{u_{pcc}}=\frac{\∂U_{pcc}}{\∂Q_{PV}^{\′}}\≈\frac{X_2}{U_{PV}}---\left(12\right)$

Grid-connected photovoltaic output reactive power Q_pccIt is expressed as：

$Q_{pcc}=Q_{PV}-\frac{P_{PV}^2+Q_{PV}^2}{U_{PV}^2}{X}_1=Q_{PV}^{\′}+Q_{cap}+Q_{svc}-\frac{P_{PV}^2+{(Q_{PV}^{\′}+Q_{cap}+Q_{svc})}^2}{U_{PV}^2}{X}_1---\left(13\right)$

Can be obtained by formula (11) and (13)：

${\mathrm{\λ}}_{Q_{pcc}}=\frac{\∂Q_{pcc}}{\∂Q_{PV}^{\′}}\≈1-\frac{2(Q_{PV}^{\′}+Q_{cap}+Q_{svc})}{U_{PV}^2}{X}_1---\left(14\right)$

The Reactive-power control total amount of grid-connected photovoltaic power station is expressed as：

Q_target≈Q'_PV+Q_cap+Q_svc+Q_initial+ΔQ_pcc+ΔQ_Σ(t-t₀) (12)

Wherein, Δ Q_Σ(t-t₀) it is reactive loss of the grid-connected photovoltaic power station within the grid entry point voltage-regulation cycle, and ΔQ_Σ(t-t₀)=Δ Q_Σ(t)-ΔQ_Σ(t₀), Q_Σ(t₀) it is reactive loss of the grid-connected photovoltaic power station when grid entry point voltage-regulation starts, ΔQ_ΣT () is reactive loss of the grid-connected photovoltaic power station at the end of grid entry point voltage-regulation.

4. the grid-connected photovoltaic power station based on power prediction according to claim 1 it is idle-voltage control method, its feature exists In：The step 3 includes：

Step 3-1：Determine the reactive power auxiliary service Q of photovoltaic DC-to-AC converter_invmax, have：

$-\sqrt{{\left(\frac{U_{inv}{U}_{pcc}}{\mathrm{\ω}L}\right)}^2-{P_{inv}}^2}-\frac{U_{pcc}^2}{\mathrm{\ω}L}\≤Q_{inv\max }\≤\sqrt{{\left(\frac{U_{inv}{U}_{pcc}}{\mathrm{\ω}L}\right)}^2-{P_{inv}}^2}-\frac{U_{pcc}^2}{\mathrm{\ω}L}---\left(13\right)$

Wherein, U_invIt is photovoltaic DC-to-AC converter output voltage, U_pccIt is grid entry point voltage, ω is power system angular speed, and L is photovoltaic Inverter ac side inductance, P_invAnd Q_invPhotovoltaic DC-to-AC converter active power of output and reactive power are represented, and $\begin{array}{cc}{P}_{inv}=\frac{U_{inv}{U}_{pcc}}{\mathrm{\ω}L}sin\mathrm{\θ},& Q_{inv}=\frac{U_{inv}{U}_{pcc}}{\mathrm{\ω}L}cos\mathrm{\θ}-\frac{U_{pcc}^2}{\mathrm{\ω}L}\end{array},$ P_invAnd Q_invBetween also meet ${P_{inv}}^2+{(Q_{inv}+\frac{U_{pcc}^2}{\mathrm{\ω}L})}^2={\left(\frac{U_{inv}{U}_{pcc}}{\mathrm{\ω}L}\right)}^2,$ θ is U_invAnd U_pccBetween phase difference；

Step 3-2：Determine the reactive power auxiliary service Q of static reactive power compensation equipment_svcmaxMeet：

Q'_linemin≤Q_svcmax≤Q'_linemax (14)

Wherein, Q'_linemin、Q'_linemaxThe reactive power lower and upper limit of branch road output respectively in grid-connected photovoltaic power station.

5. the grid-connected photovoltaic power station based on power prediction according to claim 1 it is idle-voltage control method, its feature exists In：In the step 4, switching control is carried out to parallel capacitor group using Discrete control mode, including：

1) grow steadily the stage, i.e., grid-connected photovoltaic power station is exerted oneself the stage that grows steadily, corresponding typical time period is in grid-connected photovoltaic electricity Stand during 6 points to 10 points of morning, in this typical time period, parallel capacitor group uses controls in advance, i.e. shunt compensation Capacitor bank puts into before forecast demand rising；

2) flex point stage, i.e. grid-connected photovoltaic power station exert oneself with respect to plateau, and corresponding typical time period exists in grid-connected photovoltaic power station During at 10 points in the morning at 4 points in afternoon, in this typical time period, parallel capacitor group uses Delay control, i.e. photovoltaic inversion Nargin that device is adjustable carries out switching in the case of being less than the Reactive-power control increment of grid-connected photovoltaic power station to parallel capacitor group, wherein simultaneously The Reactive-power control increment of net photovoltaic plant is Q_invmax-Q_PV；

3) decline stage, i.e. grid-connected photovoltaic power station are exerted oneself the steady decline stage steadily, and corresponding typical time period is in grid-connected photovoltaic electricity Stand in the afternoon during 4 points to 8 points, in this typical time period, parallel capacitor group uses controls in advance, i.e. shunt compensation Capacitor bank cuts out before forecast demand decline.

6. the grid-connected photovoltaic power station based on power prediction according to claim 1 it is idle-voltage control method, its feature exists In：The step 5 includes：

Step 5-1：Photovoltaic AVC systems are controlled to photovoltaic DC-to-AC converter, including：

1) in the grid entry point voltage-regulation cycle, change the reactive power of photovoltaic DC-to-AC converter and controlled with realizing grid entry point voltage；

2) after grid entry point voltage-regulation finish time, in the case of keeping grid entry point reactive power constant, using photovoltaic DC-to-AC converter Reactive power displacement static reactive power compensation equipment output reactive power, and make the reactive power that static reactive power compensation equipment exports Zero is reduced to, while optimizing current collection line voltage distribution distribution in grid-connected photovoltaic power station；

Step 5-2：Photovoltaic AVC systems are controlled to static reactive power compensation equipment, including：

1) before grid entry point voltage-regulation finish time, if grid entry point voltage does not meet corresponding sets target value yet, regulation is needed The reactive power of static reactive power compensation equipment output；

2) after grid entry point voltage-regulation finish time, if static reactive power compensation equipment output reactive power, and photovoltaic inversion simultaneously Device possesses adjustable nargin, then the reactive power for being exported using the reactive power displacement static reactive power compensation equipment of photovoltaic DC-to-AC converter, and The reactive power for exporting static reactive power compensation equipment is reduced to zero.