CN106877344B - Grid-connected photovoltaic power station reactive-voltage control method based on power prediction - Google Patents

Grid-connected photovoltaic power station reactive-voltage control method based on power prediction Download PDF

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CN106877344B
CN106877344B CN201510921217.0A CN201510921217A CN106877344B CN 106877344 B CN106877344 B CN 106877344B CN 201510921217 A CN201510921217 A CN 201510921217A CN 106877344 B CN106877344 B CN 106877344B
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reactive
power
reactive power
photovoltaic
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CN106877344A (en
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郭宁明
汪筱巍
梁晓东
董志猛
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State Grid Corp of China SGCC
North China Electric Power University
Nanjing NARI Group Corp
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State Grid Corp of China SGCC
North China Electric Power University
Nanjing NARI Group Corp
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Abstract

The invention provides a grid-connected photovoltaic power station reactive-voltage control method based on power prediction, which is characterized in that a photovoltaic AVC system coordinates reactive power regulation equipment in a grid-connected photovoltaic power station to complete voltage control of a grid-connected point; the method comprises the following steps: determining reactive loss when grid-connected photovoltaic power station grid-connected point voltage regulation is finished based on power prediction data; determining the total reactive power regulation amount of the grid-connected photovoltaic power station; determining reactive power limits of the photovoltaic inverter and the static reactive power compensation equipment; switching control of the parallel compensation capacitor bank is carried out; and controlling the photovoltaic inverter and the static reactive power compensation equipment. The method accurately calculates the control sensitivity of the photovoltaic power station, and has better reactive-voltage control precision and response speed; the power prediction is combined with the AVC system of the photovoltaic power station, so that the sectional control of the capacitor bank of the photovoltaic power station is realized, and the better balance between the reactive-voltage control and the equipment protection is realized.

Description

Grid-connected photovoltaic power station reactive-voltage control method based on power prediction
Technical Field
The invention relates to a control method, in particular to a grid-connected photovoltaic power station reactive-voltage control method based on power prediction.
Background
The solar photovoltaic power generation has the characteristics of randomness, intermittence, periodicity and volatility, and the influence on the voltage stability of a power grid is increasingly obvious along with the continuous increase of the scale of the photovoltaic power generation. The installation of a reactive-voltage automatic control system (hereinafter referred to as a photovoltaic AVC system) in a grid-connected photovoltaic power station is an important means for ensuring the voltage stability and reactive balance of a power grid, the structure of a typical photovoltaic AVC system is shown in figure 1, and the photovoltaic AVC system coordinates the output of reactive power regulating equipment in the photovoltaic power station to complete the voltage control of grid-connected points.
Compared with thermal power/wind power, due to the fact that the rotational inertia and the damping characteristic of mechanical equipment are lacked, the output change is of a step characteristic, the requirements for the response time (generally required to be about 10-20 seconds and different in regulations of each place) and the control precision of a photovoltaic AVC system are obviously improved, and therefore the requirements of the traditional fixed-step-length adjustment and multi-round feedback control method cannot be met. The following problems are exposed in practical engineering applications:
(1) the reactive power regulation equipment is difficult to control and coordinate, theoretically, the photovoltaic inverter and the static reactive power compensation equipment have millisecond-level response speed, the switching time of a capacitor is less than 1 second, and in actual engineering, the response speed of each reactive power regulation equipment is greatly influenced by a communication mode. Particularly, if the photovoltaic inverter is independently controlled, the inverter with a slow response speed is often more than several seconds if the photovoltaic inverter is communicated in a ring mode instead of an optical fiber direct connection mode, and the problem that the bus voltage is over-regulated or cannot be regulated within a specified regulation time is easily caused by adopting a traditional control method.
(2) The reactive power adjustment total amount is difficult to calculate, and due to the influence of factors such as reactive power of a grid-connected point, small voltage change, asynchronous measured data and the like, the error of system impedance obtained through online calculation according to voltage deviation and reactive power change is often large, so that the problem of calculation of the adjustment total amount exists, and the response time and the control precision of the photovoltaic AVC system are further influenced.
(3) In the prior reactive power optimization algorithm, the switching times of a capacitor are used as a calculation constraint condition and as a final regulation means. Therefore, the capacitor switching operation generally lags behind the voltage change condition of the grid-connected point of the power station, and causes the reactive power output of the photovoltaic inverter and the static reactive power compensation equipment in partial time period to be higher, thereby affecting the power generation efficiency.
(4) The influence of reactive loss in a power station is less considered, when the whole reactive power balance of a power grid is realized, one of important factors influencing the voltage of a grid-connected point of a photovoltaic power station is reactive loss in the power station, therefore, the change condition of the reactive loss in the power station is fully considered in the reactive-voltage regulation process, and the conventional reactive-voltage control algorithm does not take the reactive loss in the power station into account.
(5) Unreasonable application of static var compensation equipment (SVC/SVG/MCR). In order to ensure transient reactive reserve under the power grid fault, a photovoltaic AVC system developed based on a traditional thermal power/wind power AVC system does not generally use a control strategy of static reactive compensation equipment in the adjusting process. This aspect easily leads to frequent switching of the capacitor; on the other hand, the main transformer reactive power requirement is completely provided by a remote photovoltaic inverter, and the line loss is increased to a certain extent. Practical operation experience shows that on the basis of accurate power prediction and reactive margin calculation, capacity is adjusted by reasonably and limitedly applying static reactive compensation equipment, voltage control precision and AVC system response speed can be effectively improved, and switching times of capacitors are reduced.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a grid-connected photovoltaic power station reactive-voltage control method based on power prediction, aiming at the difference of response speeds of different reactive power adjusting devices, the accuracy and the response speed of the photovoltaic power station reactive-voltage control are ensured by using step-by-step control.
In order to achieve the purpose of the invention, the invention adopts the following technical scheme:
the invention provides a grid-connected photovoltaic power station reactive-voltage control method based on power prediction, which is characterized in that a photovoltaic AVC system coordinates reactive power regulation equipment in a grid-connected photovoltaic power station to complete voltage control of a grid-connected point; the reactive power adjusting equipment comprises a photovoltaic inverter, a parallel compensation capacitor bank and static reactive power compensation equipment;
the method comprises the following steps:
step 1: determining reactive loss when grid-connected photovoltaic power station grid-connected point voltage regulation is finished;
step 2: determining the total reactive power regulation amount of the grid-connected photovoltaic power station;
and step 3: determining reactive power limits of the photovoltaic inverter and the static reactive power compensation equipment;
and 4, step 4: switching control of the parallel compensation capacitor bank is carried out;
and 5: and controlling the photovoltaic inverter and the static reactive power compensation equipment.
In the step 1, the grid-connected photovoltaic power station comprises a current collection circuit and a transformer; the method comprises the following steps:
step 1-1: calculating the total reactive loss of the power collection line, comprising:
setting the voltage and current of current collecting line as U, I and XlIs the equivalent reactance, x, of the collector linelIs the reactance per unit length of the current collecting line, l is the length of the current collecting line, and has an Xl＝xl·l；
Thus the reactive loss Q of the collector linelAnd charging power QcRespectively expressed as:
Ql＝3·I2Xl＝3·I2xl·l (1)
QC＝U2ωC/1000＝U2·2πf·c·l/1000 (2)
wherein f is the frequency of the power system and is 50 Hz; omega is the angular speed of the power system; c is the earth capacitance of the collecting line, and C is the earth capacitance of the collecting line per unit length;
the total reactive loss of the collector line is then Ql-QC；
Step 1-2: calculating the total reactive loss of the transformer, comprising:
reactive loss Q 'of single transformer'TExpressed as:
Figure BDA0000875853610000031
wherein S isNIs rated power of the transformer, I0% is transformer no-load current percentage, Uk% is short-circuit voltage percentage of transformer, S is apparent power of transformer, beta is load factor of transformer, and beta is S/SN；
Thus, the total reactive loss Q of the transformer in the grid-connected photovoltaic power stationTExpressed as:
QT＝ΣQ'T(4)
step 1-3: calculating reactive loss Q of grid-connected photovoltaic power station at the beginning of grid-connected point voltage regulationΣ(t0) It is expressed as:
QΣ(t0)＝Ql-QC+QT(5)
the sum autoregressive moving average model is adopted to predict the reactive loss of the grid-connected photovoltaic power station in the grid-connected point voltage regulation process, so that the reactive loss Q of the grid-connected photovoltaic power station is up when the grid-connected point voltage regulation is finishedΣ(t) is expressed as:
QΣ(t)＝QΣ(t0)+▽Q'Σ+▽Q”Σ(6)
wherein, t0Is the grid connection point voltage regulation starting time, t is the grid connection point voltage regulation ending time, ▽ Q'ΣFor the difference of reactive loss of the grid-connected photovoltaic power station caused by the output variation of the grid-connected photovoltaic power station, ▽ Q "ΣThe difference value of the reactive loss of the grid-connected photovoltaic power station caused by the voltage change of the grid-connected point is obtained.
The step 2 comprises the following steps:
grid point voltage UpccAnd grid point reactive power QpccThe following relationship is satisfied:
Figure BDA0000875853610000041
wherein, Q'PVIs the total reactive power currently output by the photovoltaic inverter, and Q'PV＝Qinv-QΣ(t0)，QinvRepresenting the reactive power, Q, of the output of the photovoltaic inverterΣ(t0) The reactive loss of the grid-connected photovoltaic power station at the beginning of the voltage regulation of the grid-connected point is obtained; qcapFor the current output of reactive power, Q, of the parallel compensation capacitor banksvcOutputting reactive power for the static reactive compensation equipment at present; delta UpccFor dot-on-grid voltage increment, Δ QpccIs a grid-connected point reactive power increment, delta Q'PVOutput of reactive power delta Q for photovoltaic inverterscapOutputting a reactive power increment, Δ Q, for a combined compensation capacitor banksvcOutputting reactive power increment for the static reactive power compensation equipment;
grid point voltage UpccAnd infinite bus voltage U∞Respectively expressed as:
Figure BDA0000875853610000042
Figure BDA0000875853610000043
wherein, UPVFor the low-voltage side bus voltage, P, of a grid-connected photovoltaic power stationPVAnd QPVRespectively injecting active power and reactive power into the low-voltage side of the grid-connected photovoltaic power station; intermediate quantity RΣAnd XΣAre respectively represented as RΣ＝R1+R2，XΣ＝X1+X2，R1And X1Respectively, the main transformer equivalent resistance and reactance, R2And X2Respectively representing external equivalent resistance and reactance of the grid-connected point;
obtained from formulae (8) and (9):
Figure BDA0000875853610000051
the voltage control sensitivity and the reactive power control sensitivity of the grid-connected photovoltaic power station are respectively set as
Figure BDA0000875853610000052
And
Figure BDA0000875853610000053
comprises the following steps:
Figure BDA0000875853610000054
from formula (11):
Figure BDA0000875853610000055
grid-connected photovoltaic output reactive power QpccExpressed as:
Figure BDA0000875853610000056
from formulae (11) and (13):
Figure BDA0000875853610000057
reactive power regulation total quantity Q of grid-connected photovoltaic power stationtargetExpressed as:
Qtarget≈Q'PV+Qcap+Qsvc+Qinitial+ΔQpcc+ΔQΣ(t-t0) (12)
wherein, is Δ QΣ(t-t0) For reactive losses of grid-connected photovoltaic power stations in the grid-connected point voltage regulation period, and delta QΣ(t-t0)＝ΔQΣ(t)-ΔQΣ(t0)，QΣ(t0) For reactive losses, delta Q, of grid-connected photovoltaic power stations at the start of the grid-connection point voltage regulationΣAnd (t) is the reactive loss of the grid-connected photovoltaic power station when the grid-connected point voltage regulation is finished.
The step 3 comprises the following steps:
step 3-1: determining a reactive power limit Q of a photovoltaic inverterinvmaxThe method comprises the following steps:
Figure BDA0000875853610000061
wherein, UinvFor photovoltaic inverter output voltage, UpccIs the grid-connected point voltage, omega is the angular velocity of the power system, L is the AC side inductance of the photovoltaic inverter, PinvAnd QinvRepresents the active power and the reactive power output by the photovoltaic inverter, and
Figure BDA0000875853610000062
Pinvand QinvAlso satisfies
Figure BDA0000875853610000063
Theta is UinvAnd UpccA phase difference therebetween;
step 3-2: determining absence of static var compensation equipmentWork power limit QsvcmaxSatisfies the following conditions:
Q'linemin≤Qsvcmax≤Q'linemax(14)
wherein, Q'linemin、Q'linemaxThe lower limit and the upper limit of the reactive power output by the branch in the grid-connected photovoltaic power station are respectively.
In step 4, switching control is performed on the parallel compensation capacitor bank in a segmented control mode, including:
1) in the steady-step rising stage, namely the output steady-step rising stage of the grid-connected photovoltaic power station, the corresponding typical time period is from 6 am to 10 am of the grid-connected photovoltaic power station, and in the typical time period, the parallel compensation capacitor bank adopts advanced control, namely the parallel compensation capacitor bank is put into use before the predicted load rises;
2) an inflection point stage, namely a relatively stable output stage of the grid-connected photovoltaic power station, wherein a corresponding typical time period is from 10 am to 4 pm of the grid-connected photovoltaic power station, and in the typical time period, the parallel compensation capacitor bank adopts hysteresis control, namely the parallel compensation capacitor bank is switched under the condition that the adjustable margin of the photovoltaic inverter is lower than the reactive power adjustment increment of the grid-connected photovoltaic power station, wherein the reactive power adjustment increment of the grid-connected photovoltaic power station is Qinvmax-QPV；
3) And in the steady step-down stage, namely the output steady step-down stage of the grid-connected photovoltaic power station, the corresponding typical time period is in the period of the grid-connected photovoltaic power station from 4 to 8 pm, and in the typical time period, the parallel compensation capacitor bank adopts advanced control, namely the parallel compensation capacitor bank is switched out before the predicted load is reduced.
The step 5 comprises the following steps:
step 5-1: photovoltaic AVC system carries out control to photovoltaic inverter, includes:
1) in the voltage regulation period of the grid-connected point, the reactive power of the photovoltaic inverter is changed to realize the voltage control of the grid-connected point;
2) after the voltage regulation of the grid-connected point is finished, under the condition that the reactive power of the grid-connected point is kept unchanged, the reactive power output by the static reactive power compensation equipment is replaced by the reactive power of the photovoltaic inverter, the reactive power output by the static reactive power compensation equipment is reduced to zero, and meanwhile, the voltage distribution of a current collecting line in the grid-connected photovoltaic power station is optimized;
step 5-2: the photovoltaic AVC system controls the static reactive compensation equipment, and the method comprises the following steps:
1) before the voltage regulation of the grid-connected point is finished, if the voltage of the grid-connected point still does not meet the corresponding set target value, the reactive power output by the static reactive power compensation equipment needs to be regulated;
2) after the voltage regulation of the grid connection point is finished, if the static reactive power compensation equipment outputs reactive power and the photovoltaic inverter has adjustable margin, the reactive power output by the static reactive power compensation equipment is replaced by the reactive power of the photovoltaic inverter, and the reactive power output by the static reactive power compensation equipment is reduced to zero.
Compared with the closest prior art, the technical scheme provided by the invention has the following beneficial effects:
(1) the reactive loss of a current collecting circuit and a transformer in the grid-connected photovoltaic power station is comprehensively considered, the change of the reactive loss in the adjusting process is predicted, and the reactive adjusting total amount of the grid-connected photovoltaic power station can be accurately calculated;
(2) the control sensitivity of the photovoltaic power station is accurately calculated, and better reactive-voltage control precision and response speed are achieved;
(3) the power prediction is combined with the AVC system of the photovoltaic power station, so that the sectional control of the capacitor bank of the photovoltaic power station is realized, and the better balance between the reactive-voltage control and the equipment protection is realized.
Drawings
FIG. 1 is a diagram of a photovoltaic AVC system according to an embodiment of the present invention;
FIG. 2 is an equivalent circuit diagram of a collector line in the grid-connected photovoltaic power station in the embodiment of the invention;
FIG. 3 is a topological structure diagram of a typical grid-connected photovoltaic power plant in an embodiment of the present invention;
FIG. 4 is a graph of an exemplary photovoltaic power prediction in an embodiment of the present invention;
FIG. 5 is a closed-loop control block diagram of an AVC control system of a grid-connected photovoltaic power station in the embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
The invention provides a grid-connected photovoltaic power station reactive-voltage control method based on power prediction, as shown in figure 5, a photovoltaic AVC system coordinates reactive power regulation equipment in a grid-connected photovoltaic power station to complete voltage control of a grid-connected point; the reactive power adjusting equipment comprises a photovoltaic inverter, a parallel compensation capacitor bank and static reactive power compensation equipment;
the method comprises the following steps:
step 1: determining reactive loss when grid-connected photovoltaic power station grid-connected point voltage regulation is finished;
step 2: determining the total reactive power regulation amount of the grid-connected photovoltaic power station;
and step 3: determining reactive power limits of the photovoltaic inverter and the static reactive power compensation equipment;
and 4, step 4: switching control of the parallel compensation capacitor bank is carried out;
and 5: and controlling the photovoltaic inverter and the static reactive power compensation equipment.
In the step 1, the grid-connected photovoltaic power station comprises a current collection circuit and a transformer; the method comprises the following steps:
step 1-1: calculating the total reactive loss of the power collection line, comprising:
the equivalent circuit of the current collecting line in the photovoltaic power station is shown in figure 2, and the voltage and the current of the current collecting line are respectively set as U, I and XlIs the equivalent reactance, x, of the collector linelIs the reactance per unit length of the current collecting line, l is the length of the current collecting line, and has an Xl＝xl·l；
Thus the reactive loss Q of the collector linelAnd charging power QcRespectively expressed as:
Ql＝3·I2Xl＝3·I2xl·l (1)
QC＝U2ωC/1000＝U2·2πf·c·l/1000 (2)
wherein f is the frequency of the power system and is 50 Hz; omega is the angular speed of the power system; c is the earth capacitance of the collecting line, and C is the earth capacitance of the collecting line per unit length;
the total reactive loss of the collector line is then Ql-QC；
Step 1-2: calculating the total reactive loss of the transformer, comprising:
reactive loss Q 'of single transformer'TExpressed as:
Figure BDA0000875853610000091
wherein S isNIs rated power of the transformer, I0% is transformer no-load current percentage, Uk% is short-circuit voltage percentage of transformer, S is apparent power of transformer, beta is load factor of transformer, and beta is S/SN；
Thus, the total reactive loss Q of the transformer in the grid-connected photovoltaic power stationTExpressed as:
QT＝ΣQ'T(4)
step 1-3: calculating reactive loss Q of grid-connected photovoltaic power station at the beginning of grid-connected point voltage regulationΣ(t0) It is expressed as:
QΣ(t0)＝Ql-QC+QT(5)
the sum autoregressive moving average model is adopted to predict the reactive loss of the grid-connected photovoltaic power station in the grid-connected point voltage regulation process, so that the reactive loss Q of the grid-connected photovoltaic power station is up when the grid-connected point voltage regulation is finishedΣ(t) is expressed as:
QΣ(t)＝QΣ(t0)+▽Q'Σ+▽Q”Σ(6)
wherein, t0Is the grid connection point voltage regulation starting time, t is the grid connection point voltage regulation ending time, ▽ Q'ΣFor the difference of reactive loss of the grid-connected photovoltaic power station caused by the output variation of the grid-connected photovoltaic power station, ▽ Q "ΣThe difference value of the reactive loss of the grid-connected photovoltaic power station caused by the voltage change of the grid-connected point is obtained.
The step 2 comprises the following steps:
a typical grid-connected photovoltaic power station structure is shown in FIG. 3, and the grid-connected point voltage UpccAnd grid point reactive power QpccThe following relationship is satisfied:
Figure BDA0000875853610000101
wherein, Q'PVIs the total reactive power currently output by the photovoltaic inverter, and Q'PV＝Qinv-QΣ(t0)，QinvRepresenting the reactive power, Q, of the output of the photovoltaic inverterΣ(t0) The reactive loss of the grid-connected photovoltaic power station at the beginning of the voltage regulation of the grid-connected point is obtained; qcapFor the current output of reactive power, Q, of the parallel compensation capacitor banksvcOutputting reactive power for the static reactive compensation equipment at present; delta UpccFor dot-on-grid voltage increment, Δ QpccIs a grid-connected point reactive power increment, delta Q'PVOutput of reactive power delta Q for photovoltaic inverterscapOutputting a reactive power increment, Δ Q, for a combined compensation capacitor banksvcOutputting reactive power increment for the static reactive power compensation equipment;
grid point voltage UpccAnd infinite bus voltage U∞Respectively expressed as:
Figure BDA0000875853610000102
Figure BDA0000875853610000103
wherein, UPVFor the low-voltage side bus voltage, P, of a grid-connected photovoltaic power stationPVAnd QPVRespectively injecting active power and reactive power into the low-voltage side of the grid-connected photovoltaic power station; intermediate quantity RΣAnd XΣAre respectively represented as RΣ＝R1+R2，XΣ＝X1+X2，R1And X1Respectively, the main transformer equivalent resistance and reactance, R2And X2Respectively representing external equivalent resistance and reactance of the grid-connected point;
obtained from formulae (8) and (9):
Figure BDA0000875853610000104
the voltage control sensitivity and the reactive power control sensitivity of the grid-connected photovoltaic power station are respectively set asAnd
Figure BDA0000875853610000106
comprises the following steps:
from formula (11):
Figure BDA0000875853610000112
grid-connected photovoltaic output reactive power QpccExpressed as:
Figure BDA0000875853610000113
from formulae (11) and (13):
Figure BDA0000875853610000114
the total reactive power regulation of the grid-connected photovoltaic power station is expressed as:
Qtarget≈Q'PV+Qcap+Qsvc+Qinitial+ΔQpcc+ΔQΣ(t-t0) (12)
wherein, is Δ QΣ(t-t0) For reactive losses of grid-connected photovoltaic power stations in the grid-connected point voltage regulation period, and delta QΣ(t-t0)＝ΔQΣ(t)-ΔQΣ(t0)，QΣ(t0) For reactive losses, delta Q, of grid-connected photovoltaic power stations at the start of the grid-connection point voltage regulationΣAnd (t) is the reactive loss of the grid-connected photovoltaic power station when the grid-connected point voltage regulation is finished.
The step 3 comprises the following steps:
step 3-1: determining a reactive power limit Q of a photovoltaic inverterinvmaxThe method comprises the following steps:
wherein, UinvFor photovoltaic inverter output voltage, UpccIs the grid-connected point voltage, omega is the angular velocity of the power system, L is the AC side inductance of the photovoltaic inverter, PinvAnd QinvRepresents the active power and the reactive power output by the photovoltaic inverter, andPinvand QinvAlso satisfies
Figure BDA0000875853610000122
Theta is UinvAnd UpccA phase difference therebetween;
step 3-2: determining a reactive power limit Q of a static reactive power compensation devicesvcmax：
The short-time reactive power limit of the static reactive power compensation equipment is determined based on the following factors:
and the steady-state power output limit of the static reactive power compensation equipment is 50-80% of the rated value under most conditions.
The grid-connected safety of the photovoltaic power station is guaranteed, when a certain electrical element in a power generation system of the photovoltaic power station quits due to faults, standby reactive compensation equipment needs to be put into use in order to keep the voltage of a grid-connected point stable, and the situation that the voltage of the main grid is influenced by the fact that the voltage of the grid-connected point is too low is avoided. The most common fault causing voltage drop in a photovoltaic power station is tripping and exiting of a current collection circuit, so that the photovoltaic power station can support the voltage of a power grid in a reactive mode after an accidentThe AVC system has to be provided with enough transient reactive reserves at any time, so that the power limit of the static reactive power compensation device cannot exceed the current maximum branch output reactive power in the photovoltaic power station. Combining the above two conditions, QsvcmaxSatisfies the following conditions:
Q'linemin≤Qsvcmax≤Q'linemax(14)
wherein, Q'linemin、Q'linemaxThe lower limit and the upper limit of the reactive power output by the branch in the grid-connected photovoltaic power station are respectively.
In step 4, switching control is performed on the parallel compensation capacitor bank in a segmented control mode, including:
1) a steady-step-up stage, namely a steady-step-up stage of output of the grid-connected photovoltaic power station, as shown in fig. 4, wherein a corresponding typical time period is from 6 am to 10 am of the grid-connected photovoltaic power station, and in the typical time period, the parallel compensation capacitor bank adopts advanced control, namely the parallel compensation capacitor bank is put into use before the predicted load is raised;
2) an inflection point stage, namely a relatively stable output stage of the grid-connected photovoltaic power station, wherein a corresponding typical time period is from 10 am to 4 pm of the grid-connected photovoltaic power station, and in the typical time period, the parallel compensation capacitor bank adopts hysteresis control, namely the parallel compensation capacitor bank is switched under the condition that the adjustable margin of the photovoltaic inverter is lower than the reactive power adjustment increment of the grid-connected photovoltaic power station, wherein the reactive power adjustment increment of the grid-connected photovoltaic power station is Qinvmax-QPV；
3) And in the steady step-down stage, namely the output steady step-down stage of the grid-connected photovoltaic power station, the corresponding typical time period is in the period of the grid-connected photovoltaic power station from 4 to 8 pm, and in the typical time period, the parallel compensation capacitor bank adopts advanced control, namely the parallel compensation capacitor bank is switched out before the predicted load is reduced.
The step 5 comprises the following steps:
step 5-1: photovoltaic AVC system carries out control to photovoltaic inverter, includes:
1) in the voltage regulation period of the grid-connected point, the reactive power of the photovoltaic inverter is changed to realize the voltage control of the grid-connected point;
2) after the voltage regulation of the grid-connected point is finished, under the condition that the reactive power of the grid-connected point is kept unchanged, the reactive power output by the static reactive power compensation equipment is replaced by the reactive power of the photovoltaic inverter, the reactive power output by the static reactive power compensation equipment is reduced to zero, and meanwhile, the voltage distribution of a current collecting line in the grid-connected photovoltaic power station is optimized;
step 5-2: the photovoltaic AVC system controls the static reactive power compensation equipment:
the control of the static reactive compensation equipment mainly undertakes the following three tasks: 1) calculating the auxiliary reactive-voltage control sensitivity; 2) when the voltage regulation period is close to the end and the reactive power output of the photovoltaic inverter temporarily difficultly reaches a calculated value, providing rapid reactive power regulation to ensure the success rate of the voltage regulation; 3) the output of the photovoltaic inverter is close to the power limit, and the short-time reactive output is borne when the integral output of the power station is close to an inflection point.
The photovoltaic AVC system for controlling the static reactive compensation equipment comprises the following steps:
1) before the voltage regulation of the grid-connected point is finished, if the voltage of the grid-connected point still does not meet the corresponding set target value, the reactive power output by the static reactive power compensation equipment needs to be regulated;
2) after the voltage regulation of the grid connection point is finished, if the static reactive power compensation equipment outputs reactive power and the photovoltaic inverter has adjustable margin, the reactive power output by the static reactive power compensation equipment is replaced by the reactive power of the photovoltaic inverter, and the reactive power output by the static reactive power compensation equipment is reduced to zero.
Finally, it should be noted that: the above embodiments are only intended to illustrate the technical solution of the present invention and not to limit the same, and a person of ordinary skill in the art can make modifications or equivalents to the specific embodiments of the present invention with reference to the above embodiments, and such modifications or equivalents without departing from the spirit and scope of the present invention are within the scope of the claims of the present invention as set forth in the claims.

Claims (1)

1. A grid-connected photovoltaic power station reactive-voltage control method based on power prediction is characterized by comprising the following steps: coordinating reactive power regulation equipment in a grid-connected photovoltaic power station through a photovoltaic AVC system to complete voltage control of a grid-connected point; the reactive power adjusting equipment comprises a photovoltaic inverter, a parallel compensation capacitor bank and static reactive power compensation equipment;
the method comprises the following steps:
step 1: determining reactive loss when grid-connected photovoltaic power station grid-connected point voltage regulation is finished;
step 2: determining the total reactive power regulation amount of the grid-connected photovoltaic power station;
and step 3: determining reactive power limits of the photovoltaic inverter and the static reactive power compensation equipment;
and 4, step 4: switching control of the parallel compensation capacitor bank is carried out;
and 5: controlling the photovoltaic inverter and the static reactive power compensation equipment;
in the step 1, the grid-connected photovoltaic power station comprises a current collection circuit and a transformer; the method comprises the following steps:
step 1-1: calculating the total reactive loss of the power collection line, comprising:
setting the voltage and current of current collecting line as U, I and XlIs the equivalent reactance, x, of the collector linelIs the reactance per unit length of the current collecting line, l is the length of the current collecting line, and has an Xl＝xl·l；
Thus the reactive loss Q of the collector linelAnd charging power QcRespectively expressed as:
Ql＝3·I2Xl＝3·I2xl·l (1)
QC＝U2ωC/1000＝U2·2πf·c·l/1000 (2)
wherein f is the frequency of the power system and is 50 Hz; omega is the angular speed of the power system; c is the earth capacitance of the collecting line, and C is the earth capacitance of the collecting line per unit length;
the total reactive loss of the collector line is then Ql-QC；
Step 1-2: calculating the total reactive loss of the transformer, comprising:
none of single transformerWork loss Q'TExpressed as:
Figure FDA0002115559870000011
wherein S isNIs rated power of the transformer, I0% is transformer no-load current percentage, Uk% is short-circuit voltage percentage of transformer, S is apparent power of transformer, beta is load factor of transformer, and beta is S/SN；
Thus, the total reactive loss Q of the transformer in the grid-connected photovoltaic power stationTExpressed as:
QT＝∑Q'T(4)
step 1-3: calculating reactive loss Q of grid-connected photovoltaic power station at the beginning of grid-connected point voltage regulationΣ(t0) It is expressed as:
QΣ(t0)＝Ql-QC+QT(5)
the sum autoregressive moving average model is adopted to predict the reactive loss of the grid-connected photovoltaic power station in the grid-connected point voltage regulation process, so that the reactive loss Q of the grid-connected photovoltaic power station is up when the grid-connected point voltage regulation is finishedΣ(t) is expressed as:
Figure FDA0002115559870000021
wherein, t0The point-to-point voltage regulation starting time, t the point-to-point voltage regulation finishing time,
Figure FDA0002115559870000022
for the difference value of the reactive power loss of the grid-connected photovoltaic power station caused by the output change of the grid-connected photovoltaic power station,
Figure FDA0002115559870000023
the difference value of the reactive loss of the grid-connected photovoltaic power station caused by the voltage change of the grid-connected point is obtained;
the step 2 comprises the following steps:
grid point voltage UpccAnd grid point reactive power QpccThe following relationship is satisfied:
Figure FDA0002115559870000024
wherein, Q'PVIs the total reactive power currently output by the photovoltaic inverter, and Q'PV＝Qinv-QΣ(t0)，QinvRepresenting the reactive power, Q, of the output of the photovoltaic inverterΣ(t0) The reactive loss of the grid-connected photovoltaic power station at the beginning of the voltage regulation of the grid-connected point is obtained; qcapFor the current output of reactive power, Q, of the parallel compensation capacitor banksvcOutputting reactive power for the static reactive compensation equipment at present; delta UpccFor dot-on-grid voltage increment, Δ QpccIs a grid-connected point reactive power increment, delta Q'PVOutput of reactive power delta Q for photovoltaic inverterscapOutputting a reactive power increment, Δ Q, for a combined compensation capacitor banksvcOutputting reactive power increment for the static reactive power compensation equipment;
grid point voltage UpccAnd infinite bus voltage U∞Respectively expressed as:
Figure FDA0002115559870000026
wherein, UPVFor the low-voltage side bus voltage, P, of a grid-connected photovoltaic power stationPVAnd QPVRespectively injecting active power and reactive power into the low-voltage side of the grid-connected photovoltaic power station; intermediate quantity RΣAnd XΣAre respectively represented as RΣ＝R1+R2，XΣ＝X1+X2，R1And X1Respectively, the main transformer equivalent resistance and reactance, R2And X2Respectively representing external equivalent resistance and reactance of the grid-connected point;
obtained from formulae (8) and (9):
Figure FDA0002115559870000031
the voltage control sensitivity and the reactive power control sensitivity of the grid-connected photovoltaic power station are respectively set as
Figure FDA0002115559870000032
And
Figure FDA0002115559870000033
comprises the following steps:
Figure FDA0002115559870000034
from formula (11):
Figure FDA0002115559870000035
grid-connected photovoltaic output reactive power QpccExpressed as:
Figure FDA0002115559870000036
from formulae (11) and (13):
the total reactive power regulation of the grid-connected photovoltaic power station is expressed as:
Qtarget≈Q'PV+Qcap+Qsvc+Qinitial+ΔQpcc+ΔQΣ(t-t0) (12)
wherein, is Δ QΣ(t-t0) For reactive losses of grid-connected photovoltaic power stations in the grid-connected point voltage regulation period, and delta QΣ(t-t0)＝ΔQΣ(t)-ΔQΣ(t0)，QΣ(t0) For reactive losses, delta Q, of grid-connected photovoltaic power stations at the start of the grid-connection point voltage regulationΣ(t) is the reactive loss of the grid-connected photovoltaic power station when the grid-connected point voltage regulation is finished;
the step 3 comprises the following steps:
step 3-1: determining a reactive power limit Q of a photovoltaic inverterinvmaxThe method comprises the following steps:
Figure FDA0002115559870000041
wherein, UinvFor photovoltaic inverter output voltage, UpccIs the grid-connected point voltage, omega is the angular velocity of the power system, L is the AC side inductance of the photovoltaic inverter, PinvAnd QinvRepresents the active power and the reactive power output by the photovoltaic inverter, and
Figure FDA0002115559870000042
Pinvand QinvAlso satisfiesTheta is UinvAnd UpccA phase difference therebetween;
step 3-2: determining a reactive power limit Q of a static reactive power compensation devicesvcmaxSatisfies the following conditions:
Q'linemin≤Qsvcmax≤Q'linemax(14)
wherein, Q'linemin、Q'linemaxRespectively obtaining the lower limit and the upper limit of reactive power output by a branch in the grid-connected photovoltaic power station;
in step 4, switching control is performed on the parallel compensation capacitor bank in a segmented control mode, including:
1) in the steady-step rising stage, namely the output steady-step rising stage of the grid-connected photovoltaic power station, the corresponding typical time period is from 6 am to 10 am of the grid-connected photovoltaic power station, and in the typical time period, the parallel compensation capacitor bank adopts advanced control, namely the parallel compensation capacitor bank is put into use before the predicted load rises;
2) an inflection point stage, namely a relatively stable output stage of the grid-connected photovoltaic power station, wherein a corresponding typical time period is from 10 am to 4 pm of the grid-connected photovoltaic power station, and in the typical time period, the parallel compensation capacitor bank adopts hysteresis control, namely the parallel compensation capacitor bank is switched under the condition that the adjustable margin of the photovoltaic inverter is lower than the reactive power adjustment increment of the grid-connected photovoltaic power station, wherein the reactive power adjustment increment of the grid-connected photovoltaic power station is Qinvmax-QPV；
3) In the steady step-down stage, namely the output steady step-down stage of the grid-connected photovoltaic power station, the corresponding typical time period is in the period of the grid-connected photovoltaic power station from 4 to 8 pm, and in the typical time period, the parallel compensation capacitor bank adopts advanced control, namely the parallel compensation capacitor bank is switched out before the predicted load is reduced;
the step 5 comprises the following steps:
step 5-1: photovoltaic AVC system carries out control to photovoltaic inverter, includes:
1) in the voltage regulation period of the grid-connected point, the reactive power of the photovoltaic inverter is changed to realize the voltage control of the grid-connected point;
2) after the voltage regulation of the grid-connected point is finished, under the condition that the reactive power of the grid-connected point is kept unchanged, the reactive power output by the static reactive power compensation equipment is replaced by the reactive power of the photovoltaic inverter, the reactive power output by the static reactive power compensation equipment is reduced to zero, and meanwhile, the voltage distribution of a current collecting line in the grid-connected photovoltaic power station is optimized;
step 5-2: the photovoltaic AVC system controls the static reactive compensation equipment, and the method comprises the following steps:
1) before the voltage regulation of the grid-connected point is finished, if the voltage of the grid-connected point still does not meet the corresponding set target value, the reactive power output by the static reactive power compensation equipment needs to be regulated;
2) after the voltage regulation of the grid connection point is finished, if the static reactive power compensation equipment outputs reactive power and the photovoltaic inverter has adjustable margin, the reactive power output by the static reactive power compensation equipment is replaced by the reactive power of the photovoltaic inverter, and the reactive power output by the static reactive power compensation equipment is reduced to zero.
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