CN106099918A - A kind of method of simulation calculation multi-infeed DC mains frequency emergency control policy - Google Patents

Abstract

The invention discloses a kind of simulation calculation multi-infeed DC mains frequency emergency control policy computational methods, belong to power system automation technology field and dispatching of power netwoks runs and controls technical field.Frequency urgent control after fault is divided into two-stage by the present invention；Based on a time-domain-simulation, carry out frequency-response analysis, estimate the whole network LOAD FREQUENCY factor；Meter and LOAD FREQUENCY control characteristic, consider that emergent control pumped storage cuts the priority of the three controlled measures of class such as pump load, the control of emergency lifting dc power and urgent cutting load control, by algebraic manipulation, respectively obtain the whole network two-stage, the control total quantity of three class emergent control measures；When calculating II level emergent control measure, the effect after meter and I level emergent control measure enforcement and generating set primary frequency regulation effect.The present invention works in coordination with emergent control frequency offer technical support for realizing multi-infeed DC all kinds of controllable resources of receiving end electrical network, facilitates and reaches frequency security control target comprehensively, improves frequency security and stablize emergent control benefit.

Description

Method for simulating and calculating frequency emergency control strategy of multi-direct-current feed-in power grid

Technical Field

The invention belongs to the technical field of power system operation control, and particularly relates to a method for simulating and calculating a multi-direct-current feed-in power grid frequency emergency control strategy.

Background

The frequency characteristics of the power system directly have important influence on the safety stability and the power quality of the system. After a fault of high-power loss occurs, the frequency fluctuation amplitude is reduced, the frequency is ensured to be in an allowable range, and the method is one of important tasks of safe and stable operation control of a power grid. Therefore, on one hand, the related technical management standard has clear requirements on the minimum value of the frequency in the dynamic process after the fault and the steady-state frequency after the recovery; on the other hand, a great deal of theoretical research has been carried out, and in the long-term grid operation control practice, a great deal of effective technical measures are formed, mainly for controlling the load, for example, low-frequency load reduction plays an effective role in frequency safety and stability control of conventional grid operation.

With the gradual operation of high-capacity ultrahigh-voltage direct current, a plurality of high-capacity multi-direct current feed-in receiving-end power grids are presented in a global range, and the proportion of receiving external incoming calls is continuously improved. The high-capacity direct current fault is an important factor causing the high-power shortage of the power grid, so that the probability of the occurrence of the full-network frequency problem is increased, the severity of the full-network frequency problem can be increased, and the full-network resources need to be coordinated to realize effective control of the frequency.

The direct current transmission has the capability of rapidly and emergently increasing the power, and after a plurality of direct currents are fed into a receiving end power grid and high power is lost due to certain direct current faults, the adverse effect of the direct current faults on the frequency safety stability can be reduced to a certain extent by emergently increasing the power of other direct currents. In addition, in order to enhance the frequency modulation and peak shaving capability of the multi-dc feed receiving-end power grid, pumped storage power stations are generally configured. Therefore, compared with a common power grid, the frequency control means for dealing with the sudden loss of high power is richer when a plurality of direct current feed-in receiving-end power grids are adopted, and measures for emergently increasing direct current power and emergently controlling the load of the pump of the pumping and storage cut pump are added on the basis of generally controlling the load. Therefore, the problem of frequency safety and stability of a multi-direct-current feed-in receiving-end power grid after high power is lost due to partial direct-current faults is efficiently solved, and three types of emergency control measures, namely emergency direct-current power boosting, emergency control of pumping and storage switching pump load and emergency switching load, must be coordinated to form a unified frequency emergency control strategy.

The calculation of the frequency safety and stability control strategy is a very complex work, the frequency regulation characteristics of the generator set and the load are considered, the cost performance of different control strategies is compared, a proper control measure is selected from a large number of candidate measures, and at present, the simulation calculation is usually carried out repeatedly for each expected fault, so that the time and the labor are consumed.

Therefore, the method for researching the frequency emergency control strategy through simulation calculation aiming at the characteristics of a large-capacity multi-direct-current feed-in receiving-end power grid and combining with the frequency safety and stability control requirement provides technical support for realizing the cooperation of various controllable resources and emergency control frequency of the whole grid, achieves the frequency safety control target comprehensively, improves the frequency safety and stability emergency control benefit, and has very important significance for improving the safety and stability economic operation level of the power grid.

Disclosure of Invention

The invention aims to: aiming at the characteristic of the safety and stability of the frequency of a high-capacity multi-direct-current feed-in receiving-end power grid, a method for simulating and calculating the emergency control strategy of the power grid frequency is provided. The method provides technical support for realizing the cooperative emergency control frequency of various controllable resources of the multi-direct-current feed-in receiving-end power grid, has important value for comprehensively achieving the frequency safety control target and improving the frequency safety and stability emergency control benefit, and can also improve the frequency emergency control strategy calculation work efficiency.

Specifically, the invention is realized by adopting the following technical scheme, which comprises the following steps:

1) and preparing basic data. The basic data is divided into 3 types such as data used for safety and stability simulation calculation, power grid frequency safety control target data, control measure constraint and the like.

The data for the safety and stability simulation calculation comprises load flow data, stability data and frequency emergency control expected faults, wherein the load flow data and the stability data can be derived from off-line typical mode calculation data and can also be acquired from an intelligent power grid dispatching technology support system; frequency emergency control the fault envisioned is primarily a consideration of dc blocking, including single dc bipolar blocking and different dc combined blocking faults.

The power grid frequency safety control target data comprises frequency drop maximum allowable offset delta f in the dynamic process after high power and fault shortage_LmitmaxAnd a post-fault steady-state frequency droop allowable offset Δ f_∞max. Wherein, Δ f_LmitmaxFrequency f of the whole network before the moment of occurrence of a fault₀Minimum value f of frequency allowed after occurrence of fault_Lmitmin，Δf_∞maxFrequency f of the whole network before the moment of occurrence of a fault₀Allowed steady-state frequency minimum f after fault occurrence_∞min。

The control measure constraint comprises the total load P of the pumping and storage unit in a pumping state_Pump0And maximum emergency power boost control quantity delta PDC allowed by each direct current_imax. Wherein,NP is the number of pumped storage units in the pumped state, P_umpi0The ith pumping and storage unit load in a pumping state; what is needed isThe maximum emergency power boost control quantity delta PDC allowed by each direct current_imaxAnd simultaneously, considering the safety and stability constraints of the direct current system and the power grid.

2) Time domain simulation, frequency characteristic analysis of the whole network and information statistics. The method comprises the following two steps:

the first step is time domain simulation, aiming at the expected faults covered by the frequency emergency control, the method is mainly used for carrying out time domain simulation analysis and calculation on the expected faults of high-power shortage of a multi-direct-current feed-in receiving-end power grid caused by direct-current blocking and the like under the condition of not considering safety control measures (including low-frequency low-voltage load shedding).

The second step is the frequency characteristic analysis and information statistics of the whole network, according to the time domain simulation process information, the analysis statistics: frequency f of the whole network before the moment of occurrence of a fault₀Load of whole network P_L0And the power generation output P of the whole network_G0(ii) a Moment T when the frequency of the whole network falls to the lowest point in the dynamic process after the fault_fminFrequency f of the whole network_minLoad of whole network P_LfminAnd the power generation output P of the whole network_Gfmin(ii) a Full network frequency f of power grid in steady state operation after fault_∞Load of whole network P_L∞And the power generation output P of the whole network_G∞(ii) a Moment T when full-network power generation output begins to increase after fault_Gup(ii) a The full-network frequency and the full-network load at the typical moment in the frequency reduction process after the fault, and the full-network frequency and the full-network load at the typical moment in the frequency recovery process form a full-network load series data set (f) corresponding to the full-network frequency_i,P_Li) Should include the time T_fminAnd T_GupThe data in the frequency reduction process is not less than 3 groups, and the data in the frequency recovery process is not less than 5 groups.

3) And estimating a load frequency factor of the whole network. The method comprises the following two steps:

the first step is that each point (f) in the full network load series data corresponding to the full network frequency obtained in the step 2)_i,P_Li) Estimating the corresponding network-wide load frequency factor K according to the following formula_Li：

$P_{Li}=P_0{\left(\frac{f_i}{f_0}\right)}^{K_{Li}}$

Secondly, estimating the whole network load frequency factor K by using a least square method according to the following formula_Lav：

$min\underset{i=1}{\overset{NK}{\Σ}}{(K_{LAv}-K_{Li})}^2$

Where NK is the number of typical frequency load data sets in the dynamic process after failure.

4) And calculating the I-level emergency control quantity. The basic idea is that the total load of a full-network I-level emergency control pumping and storage switching pump, the total control amount of the full-network I-level emergency boost direct-current power and the total control amount of the full-network I-level emergency switching load are calculated according to a frequency drop maximum allowable offset control target in a dynamic process after a fault and by combining control measure constraints. The priority order of the 3 types of measures is: and (3) emergency control of pumping and storage switching pump load, emergency lifting direct current power control and emergency load switching control is performed, and the control quantity required by the measure with the lower priority is calculated only when the total control quantity of the measure with the higher priority is used up and the control target cannot be realized.

The specific implementation is divided into the following three stages:

the first stage is to calculate the total load CP of I-class emergency control pumping and storage switching pump of the whole network_IThe method comprises the following two steps:

(1) calculating the total quantity P of the pumping storage cut pump for implementing the control measure_Pump0(i.e., the load of the pumped storage unit in the pumped state is completely removed) and then the maximum frequency drop offset delta f_IminPumpCalculated as follows:

${\mathrm{\Δf}}_{\mathrm{Im}inPump}=\frac{(P_{m0}+P_{Pump0})-P_{L0}}{(P_{m0}+P_{Pump0})+(K_{LAv}-1)P_{L0}}(1-e^{-{\mathrm{AT}}_{f\min }})f_0$

$A=\frac{(P_{m0}+P_{Pump0})+(K_{LAv}-1)P_{L0}}{\mathrm{\ω}M}$

wherein ω is 2 π f₀And M is the system inertia constant. P_m0＝P_G0+P_HVDC0，P_HVDC0The total power of the power grid input through direct current after the fault occurs.

If | Δ f_IminPump|≤Δf_LmitmaxTurning to (2); otherwise, the total load CP of the pump is cut off by I-level emergency control of the whole network_I＝P_Pump0And finishing the calculation work of the first stage and turning to the second stage.

(2) Calculating the total load CP of the I-grade emergency control pumping storage cut pump of the whole network according to the following formula_I：

${\mathrm{CP}}_I=min\underset{i=1}{\overset{N_{Pump}}{\Σ}}{p}_{icpI}*P_{iPump}$

Constraint conditions are as follows:

$A=\frac{(P_{m0}+{\mathrm{CP}}_I)+(K_{LAv}-1)P_{L0}}{\mathrm{\ω}M}$

wherein N is_PumpThe number of pumping units in the pumping state, P_iPumpLoad of pumping and storage unit for ith station in pumping state, p_icpIThe I-level emergency control coefficient of the pumping and storage unit in the pumping state of the ith unit, if the unit is controlled, p is_icpI1, otherwise p_icpI＝0。

Setting the total amount of the full-network direct current I-level emergency power boost control to 0 (namely CH)_I0), the total network level I emergency load shedding control amount is set to 0 (i.e., CL)_I0), end step 4), go to step 5).

The second stage is to take account of the total load CP of the I-grade emergency control pumping storage and cutting pump of the whole network_IThe total control quantity CH of I-level emergency boost DC power control of the whole network is calculated_IThe method comprises the following two steps:

(1) calculating the total quantity CH of emergency boost DC power for implementing control measures_max(namely the control quantity is the maximum control quantity of the emergency boost direct current power allowed by the whole network after the fault) and then the maximum frequency drop offset delta f_IminHVDCCalculated as follows:

${\mathrm{\Δf}}_{\mathrm{Imin}HVDC}=\frac{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max})-P_{L0}}{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max})+(K_{LAv}-1)P_{L0}}(1-e^{-{\mathrm{AT}}_{fmin}})f_0$

$A=\frac{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max})+(K_{LAv}-1)P_{L0}}{\mathrm{\ω}M}$

wherein,NDC is the number of dc systems with emergency power boost capability after a fault.

If | Δ f_IminHVDC|≤Δf_LmitmaxTurning to (2); otherwise, I-level emergency boost DC power control quantity CH of the whole network_I＝CH_maxAnd finishing the calculation work of the second stage and turning to the third stage.

(2) Calculating the I-level emergency power boost control quantity CH of the whole network direct current according to the following formula_I：

${\mathrm{\Δf}}_{Lmitmax}=\frac{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_I)-P_{L0}}{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_I)+(K_{LAv}-1)P_{L0}}(1-e^{-{\mathrm{AT}}_{fmin}})f_0$

$A=\frac{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_I)+(K_{LAv}-1)P_{L0}}{\mathrm{\ω}M}$

The total network I-level emergency load shedding control amount is set to 0 (namely CL)_I0), end step 4), go to step 5).

The third stage is to take account of the total load CP of the I-grade emergency control pumping storage and cutting pump of the whole network_IControl effect and total control quantity CH of I-level emergency boost DC power of whole network_IThe total I-level emergency load shedding control quantity CL of the whole network is calculated_ICL is calculated as follows_I：

${\mathrm{\Δf}}_{Lmitmax}=\frac{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max})-(P_{L0}-{\mathrm{CL}}_I)}{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max})+(K_{LAv}-1)(P_{L0}-{\mathrm{CL}}_I)}(1-e^{-{\mathrm{AT}}_{fmin}})f_0$

$A=\frac{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max})+(K_{LAv}-1)(P_{L0}-{\mathrm{CL}}_I)}{\mathrm{\ω}M}$

5) And calculating the II-level emergency control quantity. The basic idea is that according to a steady-state frequency drop allowable offset control target after a fault, combining control measure constraint, considering I-level emergency control quantity requirement and control effect, considering the influence of primary frequency modulation action of a generator set, calculating the total load of a whole-network II-level emergency control pumping and storage switching pump, the total control quantity of whole-network II-level emergency boost direct-current power and the total control quantity of whole-network II-level emergency switching load. The priority order of the 3 types of measures is: and emergency control of pumping and storage switching pump load, emergency lifting direct current power control and emergency switching load control is performed, and control of measures with lower priorities is performed only when the total control amount of measures with higher priorities is used up and the control target cannot be realized.

The concrete implementation is subdivided into the following 3 steps:

(1) calculating the total CL of the II-level emergency load shedding control_IICalculated as follows:

${\mathrm{\Δf}}_{\mathrm{\∞}max}=\frac{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max}+P_{mI})-(P_{L0}-{\mathrm{CL}}_I-{\mathrm{CL}}_{II})}{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max}+P_{mI})+(K_{LAv}-1)(P_{L0}-{\mathrm{CL}}_I-{\mathrm{CL}}_{II})}{f}_0$

wherein P is_mI＝P_G∞-P_G0The generated output is newly increased under the action of primary frequency modulation of the whole network generator set after the fault.

(2) If CL is present_IIIf the total load control quantity is more than 0, the total load control quantity CP of the pumping storage cut pump is controlled in II-level emergency control of the whole network_II＝P_Pump0-CP_ITotal amount of total network II level emergency boost DC power control CH_II＝CH_max-CH_IAnd ending; otherwise, go to (3).

(3) If CL is present_II<0, the total control quantity CL of the II-level emergency load shedding of the whole network_II＝0。

First, CP is calculated as follows_IIAnd CH_IISum CT_II：

${\mathrm{\&Delta;f}}_{\mathrm{\&infin;}\max }=\frac{(P_{m0}+{\mathrm{CP}}_I+{\mathrm{CH}}_I+P_{mI}+{\mathrm{CT}}_{II})-(P_{L0}-{\mathrm{CL}}_I)}{(P_{m0}+{\mathrm{CP}}_I+{\mathrm{CH}}_I+P_{mI}+{\mathrm{CT}}_{II})+(K_{LAv}-1)(P_{L0}-{\mathrm{CL}}_I)}{f}_0$

Recalculating CP_IIAnd CH_IIThe calculation method is as follows:

if CT_II-P_Pump0-CP_IIf the total load control quantity is more than 0, the total load control quantity CP of the pumping storage cut pump is controlled in II-level emergency control of the whole network_II＝P_pump0-CP_ITotal amount of total network II level emergency boost DC power control CH_II＝CT_II-CP_II(ii) a Otherwise, the total load control quantity CP of the pumping storage cut pump is controlled in the II-level emergency control of the whole network_II＝CT_IITotal amount of total network II level emergency boost DC power control CH_II＝0。

The invention has the following beneficial effects: the invention provides a method for calculating an emergency control strategy of power grid frequency based on one-time domain simulation, aiming at the characteristics of safety and stability of the frequency of a high-capacity multi-direct-current feed-in receiving-end power grid and combining frequency control targets of each stage after a fault. The invention divides the frequency emergency control after the fault into two stages, corresponds to the maximum deviation control of the frequency drop in the dynamic process after the fault and the steady-state frequency control after the fault, and meets the requirement of the safe and stable control of the operation frequency of the power grid. The invention mainly considers the problem of safe and stable frequency of the multi-direct-current feed-in receiving-end power grid caused by direct-current blocking faults and is consistent with the actual scene of the multi-direct-current feed-in receiving-end power grid in operation. The control measures related to the invention comprise emergency control of pumping and storage switching pump load, emergency boost direct current power control and emergency load switching control, and are consistent with the actual situation of safe and stable emergency control of controllable resources of a multi-direct current feed-in receiving-end power grid. When the frequency emergency control strategy is calculated, the load frequency regulation characteristic and the primary frequency modulation function of the generator are considered, and the frequency change characteristic of the power grid can be reflected more truly. The method is based on one-time simulation calculation, frequency characteristic analysis is carried out, the whole network frequency emergency control strategy is obtained, repeated simulation calculation of an expected fault is avoided, and the working efficiency of control strategy calculation is improved. The method provided by the invention provides technical support for realizing the cooperative emergency control frequency of various controllable resources of a multi-direct-current feed-in receiving-end power grid, and has important value for comprehensively achieving the frequency safety control target and improving the frequency safety and stability emergency control benefit, thereby improving the safe and economic operation level of the power grid.

Drawings

FIG. 1 is a block flow diagram of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the following examples and the accompanying drawings.

Example 1:

one embodiment of the present invention includes the steps shown in FIG. 1:

step 1 depicted in fig. 1 is the basic data preparation: the basic data is divided into 3 types such as data used for safety and stability simulation calculation, power grid frequency safety control target data, control measure constraint and the like.

The data for the safety and stability simulation calculation comprises load flow data, stability data and frequency emergency control expected faults, wherein the load flow data and the stability data can be derived from off-line typical mode calculation data and can also be acquired from an intelligent power grid dispatching technology support system; frequency emergency control the fault envisioned is primarily a consideration of dc blocking, including single dc bipolar blocking and different dc combined blocking faults.

The power grid frequency safety control target data comprises frequency drop maximum allowable offset delta f in the dynamic process after high power and fault shortage_LmitmaxAnd a post-fault steady-state frequency droop allowable offset Δ f_∞max. Wherein, Δ f_LmitmaxFrequency f of the whole network before the moment of occurrence of a fault₀Minimum value f of frequency allowed after occurrence of fault_Lmitmin，Δf_∞maxFrequency f of the whole network before the moment of occurrence of a fault₀Allowed steady-state frequency minimum f after fault occurrence_∞min。

The control measure constraint comprises the total load P of the pumping and storage unit in a pumping state_Pump0And maximum emergency power boost control quantity delta PDC allowed by each direct current_imax. Wherein,NP is the number of pumped storage units in the pumped state, P_umpi0The ith pumping and storage unit load in a pumping state; each DC allowed maximum emergency power boost control quantity delta PDC_imaxAnd simultaneously, considering the safe and stable operation constraints of the direct current system and the power grid.

Step 2 depicted in fig. 1 is time domain simulation and frequency characteristic analysis and information statistics of the whole network.

The method comprises the following two steps:

the first step is time domain simulation, and adopts commercialized power system safety and stability analysis software to carry out electromechanical transient time domain simulation analysis calculation on the expected faults covered by frequency emergency control, especially the expected faults of high-power shortage of a multi-direct-current feed-in receiving-end power grid caused by direct-current blocking and the like, under the condition of not considering safety control measures (including low-frequency low-voltage load shedding).

The second step is the frequency characteristic analysis and information statistics of the whole network, according to the time domain simulation process information, the analysis statistics: frequency f of the whole network before the moment of occurrence of a fault₀Load of whole network P_L0And the power generation output P of the whole network_G0(ii) a Moment T when the frequency of the whole network falls to the lowest point in the dynamic process after the fault_fminFrequency f of the whole network_minLoad of whole network P_LfminAnd the power generation output P of the whole network_Gfmin(ii) a Full network frequency f of power grid in steady state operation after fault_∞Load of whole network P_L∞And the power generation output P of the whole network_G∞(ii) a Moment T when full-network power generation output begins to increase after fault_Gup(ii) a The full-network frequency and the full-network load at the typical moment in the frequency reduction process after the fault, and the full-network frequency and the full-network load at the typical moment in the frequency recovery process form a full-network load series data set (f) corresponding to the full-network frequency_i,P_Li) Should include the time T_fminAnd T_GupThe data in the frequency reduction process is not less than 3 groups, and the data in the frequency recovery process is not less than 5 groups.

Step 3 depicted in fig. 1 is to estimate the network wide load frequency factor. Two steps, corresponding to step 3-1) and step 3-2 in fig. 1):

step 3-1) in fig. 1 illustrates each point (f) in the whole network load series data corresponding to the whole network frequency obtained in step 2_i,P_Li) Estimating the corresponding network-wide load frequency factor K according to the following formula_Li：

$P_{Li}=P_0{\left(\frac{f_i}{f_0}\right)}^{K_{Li}}$

Step 3-2) of FIG. 1 illustrates estimating the network wide load frequency factor K by least squares using the following equation_Lav：

$min\underset{i=1}{\overset{NK}{\&Sigma;}}{(K_{LAv}-K_{Li})}^2$

Where NK is the number of typical frequency load data sets in the dynamic process after failure.

Step 4 depicted in fig. 1 is to calculate I-level emergency control quantities, including a total network I-level emergency control pumping and switching pump load quantity, a total network I-level emergency boost dc power control quantity, and a total network I-level emergency switching load control quantity.

The basic idea is that the total load of a full-network I-level emergency control pumping and storage switching pump, the total control amount of the full-network I-level emergency boost direct-current power and the total control amount of the full-network I-level emergency switching load are calculated according to a frequency drop maximum allowable offset control target in a dynamic process after a fault and by combining control measure constraints. The priority order of the 3 types of measures is: and (3) emergency control of pumping and storage switching pump load, emergency lifting direct current power control and emergency load switching control is performed, and the control quantity required by the measure with the lower priority is calculated only when the total control quantity of the measure with the higher priority is used up and the control target cannot be realized.

The specific implementation is divided into three stages, corresponding to step 4-1), step 4-2) and step 4-3) in fig. 1. In the implementation process, the three complete stages are not necessarily executed in sequence according to the intermediate calculation result, which will be described in detail below.

Step 4-1) depicted in fig. 1 is a first stage of calculating a total network I-level emergency control dump pump load CP_IThe method can be subdivided into the following two steps. It should be noted that, in the execution process, according to the intermediate calculation result, not both steps are necessarily executed, which will be described in detail below.

(1) Calculating the total load P of the emergency control pumping and storage switching pump for implementing the control measure_Pump0(i.e., the load of the pumped storage unit in the pumped state is completely removed) and then the maximum frequency drop offset delta f_IminPumpCalculated as follows:

${\mathrm{\&Delta;f}}_{\mathrm{Imin}Pump}=\frac{(P_{m0}+P_{Pump0})-P_{L0}}{(P_{m0}+P_{Pump0})+(K_{LAv}-1)P_{L0}}(1-e^{-{\mathrm{AT}}_{fmin}})f_0$

$A=\frac{(P_{m0}+P_{Pump0})+(K_{LAv}-1)P_{L0}}{\mathrm{\&omega;}M}$

wherein ω is 2 π f₀And M is the system inertia constant. P_m0＝P_G0+P_HVDC0，P_HVDC0The total power of the power grid input through direct current after the fault occurs.

According to Δ f_IminPumpAnd determining the subsequent flow according to the calculation result.

If | Δ f_IminPump|≤Δf_LmitmaxThen, the step (2) of the current stage is carried out; otherwise, the total load CP of the pump is cut off by I-level emergency control of the whole network_I＝P_Pump0And finishing the calculation work of the first stage and turning to the second stage.

(2) Calculating the total load CP of the I-grade emergency control pumping storage cut pump of the whole network according to the following formula_I：

${\mathrm{CP}}_I=min\underset{i=1}{\overset{N_{Pump}}{\&Sigma;}}{p}_{icpI}*P_{iPump}$

Constraint conditions are as follows:

$A=\frac{(P_{m0}+{\mathrm{CP}}_I)+(K_{LAv}-1)P_{L0}}{\mathrm{\&omega;}M}$

wherein N is_PumpThe number of pumping units in the pumping state, P_iPumpLoad of pumping and storage unit for ith station in pumping state, p_icpIThe I-level emergency control coefficient of the pumping and storage unit in the pumping state of the ith unit, if the unit is controlled, p is_icpI1, otherwise p_icpI＝0。

Setting the total I-level emergency boost DC power control of the whole network to 0 (namely CH)_I0), the total network level I emergency load shedding control amount is set to 0 (i.e., CL)_I0), end step 4, go to step 5.

Step 4-2) depicted in fig. 1 is a second phase, accounting for total network I-level emergency control dump pump load CP_IThe total control quantity CH of I-level emergency boost DC power control of the whole network is calculated_IThe division is subdivided into the following two steps. It should be noted that, in the execution process, according to the intermediate calculation result, not both steps are necessarily executed, which will be described in detail below.

(1) Calculating the total quantity CH of emergency DC power control_max(namely the control quantity is the maximum control quantity of the emergency boost direct current power allowed by the whole network after the fault) and then the maximum frequency drop offset delta f_IminHVDCCalculated as follows:

${\mathrm{\&Delta;f}}_{\mathrm{Imin}HVDC}=\frac{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max})-P_{L0}}{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_I)+(K_{LAv}-1)P_{L0}}(1-e^{-{\mathrm{AT}}_{f\min }})f_0$

$A=\frac{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max})+(K_{LAv}-1)P_{L0}}{\mathrm{\&omega;}M}$

wherein,NDC is the number of dc systems with emergency power boost capability after a fault.

According to Δ f_IminHVDCAnd determining the subsequent flow according to the calculation result.

If | Δ f_IminHVDC|≤Δf_LmitmaxThen, the step (2) of the current stage is carried out; otherwise, I-level emergency boost DC power control quantity CH of the whole network_I＝CH_maxAnd finishing the calculation work of the second stage and turning to the third stage.

(2) Calculating total control quantity CH of I-level emergency boost direct current power of the whole network according to the following formula_I：

${\mathrm{\&Delta;f}}_{Lmitmax}=\frac{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_I)-P_{L0}}{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_I)+(K_{LAv}-1)P_{L0}}(1-e^{-{\mathrm{AT}}_{fmin}})f_0$

$A=\frac{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_I)+(K_{LAv}-1)P_{L0}}{\mathrm{\&omega;}M}$

The total network I-level emergency load shedding control amount is set to 0 (namely CL)_I0), end step 4, go to step 5.

Step 4-3) depicted in fig. 1 is a third phase, accounting for total network I-level emergency control dump pump load CP_IControl effect and total control quantity CH of I-level emergency boost DC power of whole network_IThe control effect of (1) calculating the I-level emergency load shedding control quantity CL of the whole network_ICL is calculated as follows_I：

${\mathrm{\&Delta;f}}_{Lmitmax}=\frac{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max})-(P_{L0}-{\mathrm{CL}}_I)}{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max})+(K_{LAv}-1)(P_{L0}-{\mathrm{CL}}_I)}(1-e^{-{\mathrm{AT}}_{fmin}})f_0$

$A=\frac{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max})+(K_{LAv}-1)(P_{L0}-{\mathrm{CL}}_I)}{\mathrm{\&omega;}M}$

Step 5 depicted in fig. 1 is to calculate a level II emergency control amount, which includes a total network level II emergency control pumping and storage switching pump load amount, a total network level II emergency boost dc power control amount, and a total network level II emergency switching load control amount.

The basic idea is that according to a steady-state frequency drop allowable offset control target after a fault, combining control measure constraint, considering I-level emergency control quantity requirement and control effect, considering the influence of primary frequency modulation action of a generator set, calculating the total load of a whole-network II-level emergency control pumping and storage switching pump, the total control quantity of whole-network II-level emergency boost direct-current power and the total control quantity of whole-network II-level emergency switching load. The priority order of the 3 types of measures is: and emergency control of pumping and storage switching pump load, emergency lifting direct current power control and emergency switching load control is performed, and control of measures with lower priorities is performed only when the total control amount of measures with higher priorities is used up and the control target cannot be realized.

The specific implementation is subdivided into the following three steps. It should be noted that, during the execution, according to the intermediate calculation result, it is not necessary to execute all three steps, which will be described in detail below.

(1) Calculating the total CL of the II-level emergency load shedding control_IICalculated as follows:

${\mathrm{\&Delta;f}}_{\mathrm{\&infin;}max}=\frac{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max}+P_{mI})-(P_{L0}-{\mathrm{CL}}_I-{\mathrm{CL}}_{II})}{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max}+P_{mI})+(K_{LAv}-1)(P_{L0}-{\mathrm{CL}}_I-{\mathrm{CL}}_{II})}{f}_0$

wherein P is_mI＝P_G∞-P_G0The generated output is newly increased under the action of primary frequency modulation of the whole network generator set after the fault.

(2) If CL is present_IIIf the total load control quantity is more than 0, the total load control quantity CP of the pumping storage cut pump is controlled in II-level emergency control of the whole network_II＝P_Pump0-CP_III-level emergency boost DC power control quantity CH of whole network_II＝CH_max-CH_IAnd ending; otherwise, go to (3).

(3) If CL is present_II<0, the total control quantity CL of the II-level emergency load shedding of the whole network_II＝0。

First, CP is calculated as follows_IIAnd CH_IISum CT_II：

${\mathrm{\&Delta;f}}_{\mathrm{\&infin;}max}=\frac{(P_{m0}+{\mathrm{CP}}_I+{\mathrm{CH}}_I+P_{mI}+{\mathrm{CT}}_{II})-(P_{L0}-{\mathrm{CL}}_I)}{(P_{m0}+{\mathrm{CP}}_I+{\mathrm{CH}}_I+P_{mI}+{\mathrm{CT}}_{II})+(K_{LAv}-1)(P_{L0}-{\mathrm{CL}}_I)}{f}_0$

Recalculating CP_IIAnd CH_IIThe calculation method is as follows:

if CT_II-P_Pump0-CP_IIf the total load control quantity is more than 0, the total load control quantity CP of the pumping storage cut pump is controlled in II-level emergency control of the whole network_II＝P_Pump0-CP_ITotal amount of total network II level emergency boost DC power control CH_II＝CT_II-CP_II(ii) a Otherwise, the total load control quantity CP of the pumping storage cut pump is controlled in the II-level emergency control of the whole network_II＝CT_IITotal amount of total network II level emergency boost DC power control CH_II＝0。

In summary, the method provides a method for calculating the power grid frequency emergency control strategy based on one-time domain simulation by combining the actual conditions of the frequency control target and the frequency emergency control controllable resource at each stage after the power grid operation fault aiming at the characteristic of the frequency safety and stability of the large-capacity multi-direct-current feed-in receiving-end power grid. The method divides the frequency emergency control after the fault into two stages, corresponds to the maximum deviation control of frequency drop in the dynamic process after the fault and the steady-state frequency control after the fault, and meets the requirement of safe and stable control of the operation frequency of the power grid. The method mainly considers the problem of safety and stability of the frequency of the multi-direct-current feed-in receiving-end power grid caused by direct-current blocking faults, and is identical with the actual scene of the multi-direct-current feed-in receiving-end power grid in operation. The control measures related to the method comprise emergency control of pumping and storage switching pump load, emergency lifting direct current power control and emergency load switching control, and are consistent with the actual situation of safe and stable emergency control of controllable resources of a multi-direct current feed-in receiving-end power grid. When the method is used for calculating the frequency emergency control strategy, the load frequency regulation characteristic and the primary frequency modulation function of the generator are taken into account, and the frequency change characteristic of the power grid can be reflected more truly. The method is based on one-time simulation calculation, frequency characteristic analysis is carried out, the whole network frequency emergency control strategy is obtained, repeated simulation calculation of an expected fault is avoided, and the working efficiency of control strategy calculation is improved. The method provided by the method provides technical support for realizing the cooperative emergency control frequency of various controllable resources of the multi-direct-current feed-in receiving-end power grid, achieves the aim of frequency safety control comprehensively, and improves the frequency safety and stability emergency control benefit, so that the safe and economic operation level of the power grid is improved, and the method has important value.

Although the present invention has been described in terms of the preferred embodiment, it is not intended that the invention be limited to the embodiment. Any equivalent changes or modifications made without departing from the spirit and scope of the present invention also belong to the protection scope of the present invention. The scope of the invention should therefore be determined with reference to the appended claims.

Claims (6)

1. A method for simulating and calculating a frequency emergency control strategy of a multi-direct-current feed-in power grid is characterized by comprising the following steps:

1) preparing basic data preparation:

the basic data is divided into 3 types of data used for safety and stability simulation calculation, power grid frequency safety control target data and control measure constraint;

the data used for the safety and stability simulation calculation comprise load flow data, stability data and frequency emergency control expected faults;

power grid frequency safety control target dataIncluding a frequency dip after failure by a maximum allowable offset deltaf_LmitmaxAnd a post-fault steady-state frequency droop allowable offset Δ f_∞maxWherein:

Δf_Lmitmax＝f₀-f_Lmitmin

Δf_∞max＝f₀-f_∞min

f₀the frequency of the whole network before the fault occurrence moment f_LmitminIs the minimum value of the frequency allowed after the fault occurs, f_∞minIs the minimum value of the allowed steady-state frequency after the fault occurs;

the control measure constraint comprises the total load P of the pumping unit in a pumping state_Pump0And each DC allowed maximum emergency power boost control quantity;

2) time domain simulation, frequency characteristic analysis and information statistics of the whole network:

performing time domain simulation analysis calculation on an expected fault of high-power shortage of a multi-direct-current feed-in receiving-end power grid caused by direct-current blocking and the like under the condition of not considering safety control measures including low-frequency low-voltage load shedding; analyzing and counting according to the time domain simulation process information: frequency f of the whole network before the moment of occurrence of a fault₀Load of whole network P_L0And the power generation output P of the whole network_G0(ii) a Time T for full network frequency to fall to lowest point after fault_fminFrequency f of the whole network_minLoad of whole network P_LfminAnd the power generation output P of the whole network_Gfmin(ii) a Full network frequency f of power grid in steady state operation after fault_∞Load of whole network P_L∞And the power generation output P of the whole network_G∞(ii) a Time T for starting to increase power generation output of whole network after fault_Gup(ii) a The full-network frequency and the full-network load at the typical moment in the frequency reduction process after the fault, and the full-network frequency and the full-network load at the typical moment in the frequency recovery process form full-network load series data (f) corresponding to the full-network frequency_i,P_Li)；

3) Estimating a load frequency factor of the whole network:

for each point in the whole network load series data corresponding to the whole network frequency, estimating a corresponding whole network load frequency factor K according to the following formula_Li：

$P_{Li}=P_0{\left(\frac{f_i}{f_0}\right)}^{K_{Li}}$

Estimating the load frequency factor K of the whole network by using a least square method according to the following formula_Lav：

$\min \underset{i=1}{\overset{N}{\&Sigma;}}{(K_{LAv}-K_{Li})}^2$

4) Calculating I-level emergency control quantity:

according to the frequency drop maximum allowable offset control target and in combination with control measure constraints, calculating the total load of a full-network I-level emergency control pumping and storage switching pump, the total control amount of full-network I-level emergency boost direct-current power and the total control amount of full-network I-level emergency switching load;

the priority order of the 3 types of measures is: emergency control of pumping storage cut pump load, emergency boost direct current power control and emergency cut load control, wherein only when the total control quantity of measures with higher priority is used up and the control target cannot be realized, the control quantity required by the measures with lower priority is calculated;

5) calculating a II-level emergency control quantity:

according to a steady-state frequency drop allowable offset control target, combining control measure constraint, considering I-level emergency control quantity requirement and control effect, considering the influence of the primary frequency modulation action of a generator set, and calculating the total load of a full-network II-level emergency control pumping and storage switching pump, the total control quantity of full-network II-level emergency lifting direct-current power and the total control quantity of full-network II-level emergency switching load;

the priority order of the 3 types of measures is: and (3) emergency control of pumping and storage switching pump load, emergency lifting direct current power control and emergency load switching control is performed, and the control quantity required by the measure with the lower priority is calculated only when the total control quantity of the measure with the higher priority is used up and the control target cannot be realized.

2. The method for simulation calculation of frequency emergency control strategy of multi-fed dc power grid according to claim 1, wherein the frequency emergency control is divided into two stages according to the frequency control requirement, the I stage emergency control is corresponding to the frequency drop deviation maximum amplitude control target and is implemented before the frequency drop reaches the lowest value; the stage II emergency control corresponds to the steady-state frequency offset control target, and the frequency recovery phase is implemented.

3. The method for simulating and calculating the frequency emergency control strategy of the multi-fed direct current power grid according to claim 1, wherein the method for calculating the total load of the pumping and cutting pump of the whole grid I-class emergency control in the step 4) comprises the following steps:

first, calculating the maximum frequency drop offset delta f after implementing all controllable emergency control pumping and storage switching pump load measures_IminPumpCalculated as follows:

${\mathrm{\&Delta;f}}_{\mathrm{Imin}Pump}=\frac{(P_{m0}+P_{Pump0})-P_{L0}}{(P_{m0}+P_{Pump0})+(K_{LAv}-1)P_{L0}}(1-e^{-{\mathrm{AT}}_{fmin}})f_0$

$A=\frac{(P_{m0}+P_{Pump0})+(K_{LAv}-1)P_{L0}}{\mathrm{\&omega;}M}$

wherein ω is 2 π f₀M is the system inertia constant; p_m0＝P_G0+P_HVDC0，P_HVDC0The total power of the power grid input through direct current after the fault occurrence moment;

if | Δ f_IminPump|≤Δf_LmitmaxThen, the second step is carried out; otherwise, the total load control amount CP of the I-grade emergency control pumping storage switching pump of the whole network_I＝P_Pump0The second step is not executed any more;

secondly, calculating the total load control quantity CP of the I-grade emergency control pumping and storage switching pump of the whole network according to the following formula_I：

${\mathrm{CP}}_I=min\underset{i=1}{\overset{N_{Pump}}{\&Sigma;}}{p}_{icpI}*P_{iPump}$

Constraint conditions are as follows:

$A_1=\frac{(P_{m0}+{\mathrm{CP}}_I)+(K_{LAv}-1)P_{L0}}{\mathrm{\&omega;}M}$

wherein N is_PumpThe number of pumping units in the pumping state, P_iPumpLoad of pumping and storage unit for ith station in pumping state, p_icpIThe I-level emergency control coefficient of the pumping and storage unit in the pumping state of the ith unit, if the unit is controlled, p is_icpI1, otherwise p_icpI＝0。

4. The method for simulating and calculating frequency emergency control strategy of multi-fed DC power grid according to claim 3, wherein the method for calculating I-class total emergency boost DC power control amount in step 4) is to calculate I-class total emergency control total load control amount CP of pumped storage and cut pump in I-class total emergency control_IControl effect of (1), only | Δ f_IminPump|>Δf_LmitmaxThen, the total I-level emergency boost DC power control CH of the whole network needs to be calculated_IThe calculation method is as follows:

firstly, calculating the maximum frequency drop offset delta f after implementing the maximum emergency boost direct current power control measure allowed by the whole network_IminHVDCCalculated as follows:

${\mathrm{\&Delta;f}}_{\mathrm{Imin}HVDC}=\frac{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max})-P_{L0}}{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max})+(K_{LAv}-1)P_{L0}}(1-e^{-A_2{T}_{fmin}})f_0$

$A_2=\frac{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max})+(K_{LAv}-1)P_{L0}}{\mathrm{\&omega;}M}$

wherein, CH_maxThe maximum emergency boost direct current power control quantity allowed by the whole network is obtained;

if | Δ f_IminHVDC|≤Δf_LmitmaxThen, the second step is carried out; otherwise, I-grade emergency boost DC power control total CH of the whole network_I＝CH_maxThe second step is not executed any more;

secondly, calculating the total I-level emergency boost DC power control CH of the whole network according to the following formula_I：

${\mathrm{\&Delta;f}}_{Lmitmax}=\frac{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_I)-P_{L0}}{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_I)+(K_{LAv}-1)P_{L0}}(1-e^{-A_3{T}_{fmin}})f_0$

$A_3=\frac{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_I)+(K_{LAv}-1)P_{L0}}{\mathrm{\&omega;}M}.$

5. The method for simulating and calculating the frequency emergency control strategy of the multi-fed DC power grid according to claim 4, wherein the method for calculating the total I-class emergency load shedding control amount of the whole grid in the step 4) is to calculate the total I-class emergency control pumping and pumping pump load control amount CP of the whole grid_IControl effect and total I-level emergency boost DC power CH of the whole network_IControl effect of (1), only | Δ f_IminHVDC|>Δf_LmitmaxThen, the total I-level emergency load shedding control quantity CL of the whole network needs to be calculated_ICL is calculated as follows_I：

${\mathrm{\&Delta;f}}_{Lmitmax}=\frac{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max})-(P_{L0}-{\mathrm{CL}}_I)}{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max})+(K_{LAv}-1)(P_{L0}-{\mathrm{CL}}_I)}(1-e^{-A_4{T}_{fmin}})f_0$

$A_4=\frac{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max})+(K_{LAv}-1)(P_{L0}-{\mathrm{CL}}_I)}{\mathrm{\&omega;}M}.$

6. The method for simulating and calculating the frequency emergency control strategy of the multiple direct current feed-in power grid according to claim 5, wherein in the step 5), the method for calculating the class II emergency control quantity is to take into account the influence of the primary frequency modulation action characteristic of the generator set and the influence of the class I emergency control action effect according to the steady-state frequency drop allowable offset control target after the fault, and the specific method is as follows:

first, calculating the total CL of the II-level emergency load shedding control_IICalculated as follows:

${\mathrm{\&Delta;f}}_{\mathrm{\&infin;}max}=\frac{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max}+P_{mI})-(P_{L0}-{\mathrm{CL}}_I-{\mathrm{CL}}_{II})}{(P_{m0}+P_{Pump0}+{\mathrm{CH}}_{max}+P_{mI})+(K_{LAv}-1)(P_{L0}-{\mathrm{CL}}_I-{\mathrm{CL}}_{II})}{f}_0$

wherein P is_mI＝P_G∞-P_G0The power generation output is newly increased under the action of primary frequency modulation of the whole network generator set after the fault occurs;

step two, if: CL_II>0, the total load control quantity CP of the pumping storage cut pump is controlled in the II-level emergency control of the whole network_II＝P_Pump0-CP_ITotal amount of total network II level emergency boost DC power control CH_II＝CH_max-CH_IAnd ending; otherwise, turning to the third step;

thirdly, if: CL_II<0, then CL_II＝0；

Calculating CP_IIAnd CH_IISum CT_IICalculated as follows:

${\mathrm{\&Delta;f}}_{\mathrm{\&infin;}max}=\frac{(P_{m0}+{\mathrm{CP}}_I+{\mathrm{CH}}_I+P_{mI}+{\mathrm{CT}}_{II})-(P_{L0}-{\mathrm{CL}}_I)}{(P_{m0}+{\mathrm{CP}}_I+{\mathrm{CH}}_I+P_{mI}+{\mathrm{CT}}_{II})+(K_{LAv}-1)(P_{L0}-{\mathrm{CL}}_I)}{f}_0$

recalculating CP_IIAnd CH_IIThe calculation method is as follows:

if CT_II-P_Pump0-CP_I>0, the total load control quantity CP of the pumping storage cut pump is controlled in the II-level emergency control of the whole network_II＝P_Pump0-CP_ITotal amount of total network II level emergency boost DC power control CH_II＝CT_II-CP_II(ii) a Otherwise, the total load control quantity CP of the pumping storage cut pump is controlled in the II-level emergency control of the whole network_II＝CT_IITotal amount of total network II level emergency boost DC power control CH_II＝0。