Electric power system optimization scheduling method and system

Abstract

The invention relates to the technical field of power system optimization scheduling, and discloses a power system optimization scheduling method and system, and the method comprises the steps: collecting a power grid parameter, an inverter parameter and an atmosphere parameter, and determining a voltage critical state and an atmosphere parameter upper and lower switching threshold value based on a reactive power balance relation; judging the current operation branch of the system in combination with the historical operation branch state and the current atmospheric condition; and calculating the reactive output of the inverter according to the branch state, determining the photovoltaic active power upper limit in combination with the capacity constraint, and evaluating the stability margin of the system. And finally, by taking the minimum comprehensive operation cost as an optimization target, outputting the optimal unit output, photovoltaic active power and system operation state under the conditions of power balance, photovoltaic output upper limit, stability margin lower limit and unit operation constraint, thereby realizing safe, economic and efficient cooperative scheduling of the power grid.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system optimal scheduling, more particularly, it relates to a power system optimal scheduling method and system. BACKGROUND

[0002] In the photovoltaic and thermal power integrated grid in northwest and north China, the length of the transmission line is often long, and the system short-circuit ratio is low. During the noon high photovoltaic output period, the line is lightly loaded, and the distributed capacitor charging reactive power makes the receiving end voltage rise significantly. According to the experience of power system operation, this receiving end voltage self-rise can be maintained stable by the reactive power compensation device under the conventional load level, but when the high proportion of photovoltaic is connected to the grid, the inverter needs to actively absorb the reactive power according to the voltage-reactive power droop curve to suppress the voltage rise. Although this can keep the voltage qualified, it will occupy the rated apparent power of the inverter, thereby compressing the active power that can be output.

[0003] On the other hand, in the sand-dust season or high aerosol concentration weather, the solar radiation is weakened, and the direct irradiance available for the photovoltaic power station decreases. At this time, the reactive power demand of the photovoltaic inverter is also adjusted with the receiving end voltage change, resulting in that the active power output of the system does not monotonically decrease with the illumination intensity, but presents a nonlinear change in a certain interval. The matching relationship between the photovoltaic power and the thermal power output obtained by the dispatching center according to the conventional prediction model is thus distorted, and the thermal power unit needs to frequently correct the power instruction or even be forced to run out of limit.

[0004] Specifically: when the illumination, aerosol, line reactive power and inverter control act simultaneously, the voltage at the grid-connected point and the photovoltaic active power are no longer one-to-one corresponding. The system can have two stable operating states under the same environmental parameters: one is the photovoltaic apparent power limited state, and the other is the resource limited state under the voltage control. The dispatching system cannot distinguish the current state only by the meteorological and power prediction data, resulting in that the thermal power output optimization algorithm misjudges the upper limit or lower limit of the photovoltaic output. If the thermal power is run according to the wrong boundary, it will cause the system frequency deviation, or even lead to the receiving end voltage out of limit and the inverter off-grid. SUMMARY

[0005] The present application provides a power system optimal scheduling method and system, which solves the technical problem that when the receiving end voltage is affected by the natural condition change and the inverter reactive power control, the output optimization calculation of the thermal power unit cannot accurately identify the actual operating state of the grid-connected point, resulting in that the dispatching plan is invalid in a short time in the grid environment with large-scale photovoltaic grid connection.

[0006] In a first aspect, a power system optimal scheduling method comprises:

[0007] Collecting and obtaining grid parameters, inverter parameters and atmospheric parameters;

[0008] Determine the voltage critical state and the upper and lower switching thresholds of the atmospheric parameter based on the reactive power balance relationship between the grid parameters and the inverter parameters;

[0009] Determine the current operating branch state according to the relationship between the historical operating branch state and the upper and lower switching thresholds of the atmospheric parameter;

[0010] Based on the current operating branch state, calculate the inverter reactive power output, determine the upper limit of photovoltaic active power in combination with the capacity constraint in the atmospheric parameter and the inverter parameter, and calculate the system stability margin;

[0011] With the minimum comprehensive operation cost as the target, output the unit output, photovoltaic active power and current operating branch state under the power balance, upper limit of photovoltaic active power, lower limit of system stability margin, unit operation constraint and branch state consistency constraint.

[0012] In the second aspect, a power system optimal dispatching system is applied to any one of the power system optimal dispatching methods, and comprises:

[0013] A data acquisition module acquires and obtains the grid parameters, inverter parameters and atmospheric parameters;

[0014] A threshold calculation module determines the voltage critical state and the upper and lower switching thresholds of the atmospheric parameter based on the reactive power balance relationship between the grid parameters and the inverter parameters;

[0015] A state determination module determines the current operating branch state according to the relationship between the historical operating branch state and the upper and lower switching thresholds of the atmospheric parameter;

[0016] A margin identification module calculates the inverter reactive power output based on the current operating branch state, determines the upper limit of photovoltaic active power in combination with the capacity constraint in the atmospheric parameter and the inverter parameter, and calculates the system stability margin;

[0017] A planning control module takes the minimum comprehensive operation cost as the target, and outputs the unit output, photovoltaic active power and current operating branch state under the power balance, upper limit of photovoltaic active power, lower limit of system stability margin, unit operation constraint and branch state consistency constraint.

[0018] The beneficial effects of the present application are that: by introducing the multi-dimensional coupling modeling of the grid parameters, the inverter parameters and the atmospheric parameters, the dynamic corresponding relationship of voltage reactive power balance and photovoltaic output is established, the running branch state of the photovoltaic grid-connected system under different meteorological conditions can be accurately identified, and the accurate calculation of the photovoltaic active upper limit and the system stability margin is realized. The present application breaks through the limitation that the traditional scheduling model cannot distinguish the state of photovoltaic resource limitation and apparent power limitation, significantly improves the real-time performance and reliability of the joint optimization scheduling of thermal power and photovoltaic, and avoids the risks of voltage out-of-limit, frequency deviation and inverter off-grid caused by state misjudgment. At the same time, the optimization control strategy with the minimum comprehensive operation cost as the target considers the system safety and economy, improves the new energy consumption capacity and the overall operation efficiency of the power system. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a flow chart of a power system optimization scheduling method of the present application;

[0020] Figure 2 is a module diagram of a power system optimization scheduling system of the present application. DETAILED DESCRIPTION

[0021] The subject matter described herein will now be discussed with reference to example implementations. It should be understood that the discussion of these implementations is merely meant to provide a better understanding of the subject matter described herein and can include changes, modifications, or additions of elements to the functions and arrangements of the elements discussed without departing from the scope of the present description. Various examples can omit, substitute, or add various procedures or components as appropriate, or in appropriate combination. Also, features described with respect to some examples can be combined in other examples.

[0022] As shown in Figure 1 , a power system optimization scheduling method comprises:

[0023] Collecting and acquiring grid parameters, inverter parameters and atmospheric parameters;

[0024] Determining the voltage critical state and the upper and lower switching threshold of the atmospheric parameters based on the reactive power balance relationship of the grid parameters and the inverter parameters;

[0025] Determining the current running branch state according to the relationship between the historical running branch state and the current atmospheric parameters and the upper and lower switching threshold;

[0026] Based on the current running branch state, the inverter reactive output is calculated, the photovoltaic active upper limit is determined in combination with the capacity constraint in the atmospheric parameters and the inverter parameters, and the system stability margin is calculated;

[0027] With the minimum comprehensive operation cost as the target, under the power balance, photovoltaic active upper limit, system stability lower limit, unit operation constraint and branch state consistency constraint, the unit output, photovoltaic active and current running branch state are output.

[0028] In an embodiment of the application, based on the reactive power balance relationship between the grid parameters and the inverter parameters, the voltage critical state and the upper and lower switching thresholds of the atmospheric parameters are determined, including:

[0029] Establishing a reactive power balance function :

[0030] ;

[0031] Wherein, is the grid point voltage, is the line equivalent parallel susceptance parameter, is the receiving end equivalent voltage reactive slope parameter, is the inverter reactive output function;

[0032] When , then ;

[0033] When , then ;

[0034] When , then ;

[0035] Wherein, is the inverter voltage reactive droop slope parameter, is the inverter reactive saturation value parameter;

[0036] Solving the voltage value satisfying and as the voltage critical state;

[0037] Wherein, , When , it is equal to , and when , it is equal to 0; wherein, represents the effective slope;

[0038] Let the photovoltaic available active function be ;

[0039] Wherein, represents the aerosol optical depth, and the aerosol optical depth is an atmospheric parameter, is the photovoltaic rated available active calibration value parameter, is the available active first-order coefficient parameter;

[0040] Let the active power upper limit function under apparent power constraint be ;

[0041] wherein, is the inverter rated apparent power parameter;

[0042] In the interval of , solve and to get the downlink switching threshold aerosol optical thickness ;

[0043] In the interval of , solve and to get the uplink switching threshold aerosol optical thickness .

[0044] The reactive power balance function is established to quantify the reactive power supply and demand balance relationship of the grid-connected point, that is, the sum of the line charging reactive power, the reactive power provided by the upper-level power grid and the reactive power output by the inverter is zero, to ensure that the system can operate stably at the voltage.

[0045] The grid-connected point voltage refers to the voltage at the connection point of the photovoltaic inverter and the power grid, which is an electrical quantity reflecting the reactive power state of the system. The line equivalent parallel susceptance parameter reflects the size of the distributed capacitance of the long-distance transmission line, and the capacitance will generate charging reactive power. The larger the parameter, the more the line charging reactive power. The receiving end equivalent voltage reactive power slope reflects the support capacity of the upper-level power grid to the grid-connected point voltage. The larger the value, the stronger the ability of the power grid to stabilize the voltage through reactive power adjustment. The inverter reactive power output function describes the law of the inverter outputting (or absorbing) reactive power according to the change of the grid-connected point voltage.

[0046] The inverter reactive power output function is divided into three sections, and the specific rules are as follows by combining linear droop regulation and reactive power saturation limitation (the inverter reactive power output capacity has an upper limit):

[0047] When the theoretical reactive power output calculated according to the voltage does not exceed the saturation value: the inverter linearly regulates the reactive power according to the voltage reactive power droop slope, that is, absorbs reactive power when the voltage is higher than the rated value (suppresses the voltage rise), and emits reactive power when the voltage is lower than the rated value (lifts the voltage), and the droop slope determines the amplitude of the inverter reactive power regulation per unit change of the voltage;

[0048] When the theoretical absorbed reactive power calculated according to the voltage exceeds the saturation value: the inverter cannot continue to increase the absorbed reactive power, and the maximum absorbed reactive power (i.e. the negative value of the reactive power saturation value) is fixed;

[0049] When the theoretical emitted reactive power calculated according to the voltage exceeds the saturation value: the inverter cannot continue to increase the emitted reactive power, and the maximum emitted reactive power (i.e. the positive value of the reactive power saturation value) is fixed.

[0050] Voltage critical state is the dividing point of system voltage from stable to unstable, which needs to meet two conditions at the same time, which are explained as follows:

[0051] Satisfy the reactive power balance function: it means that the supply and demand of reactive power at the grid-connected point are equal, and the system is in stable operation;

[0052] The derivative of the reactive power balance function to voltage is zero: the derivative reflects the degree of influence of voltage change on reactive power balance. When the derivative is zero, a small change in voltage will break the reactive power balance and the system will lose stability. In the derivative calculation, the value of the effective slope is as follows: when the inverter is not saturated, the actual droop slope is used (which reflects the adjustment ability of the inverter to voltage change); when the inverter is saturated, the slope is 0 (at this time, the inverter output is fixed and no longer adjusts with voltage change, and the adjustment ability to voltage disappears).

[0053] The available active power function of photovoltaic is used to quantify the influence of atmospheric parameters (aerosol optical depth) on the available active power of photovoltaic. The larger the aerosol optical depth, the more serious the solar radiation is weakened, and the less the available active power of photovoltaic is. In the parameter, the rated available active power of photovoltaic is the maximum available active power of photovoltaic without dust, and the first-order coefficient of available active power is the proportional coefficient of active power attenuation caused by aerosol (the larger the coefficient, the more obvious the weakening of active power by aerosol);

[0054] Active power upper limit function under apparent power constraint: the apparent power of the inverter has a rated limit (the output of active power and reactive power needs to meet the capacity constraint), and when the inverter outputs a certain reactive power, the available active power will be squeezed. This function is used to calculate the maximum active power that the inverter can output under the current reactive power output, wherein the rated apparent power parameter of the inverter is the total capacity upper limit of the inverter.

[0055] The upper and lower switching thresholds of atmospheric parameters (aerosol optical depth) are the critical values of the system switching between photovoltaic resource limited (active power limited by light) and apparent power limited (active power limited by inverter capacity). There are two scenarios for solving:

[0056] Downlink switching threshold (critical value of smaller aerosol optical depth): in the interval of unsaturated reactive power output of the inverter (linear adjustment according to the droop slope), the reactive power balance function (determining the relationship between voltage and reactive power) and the available active power of photovoltaic equal to the active power upper limit under apparent power constraint (at this time, photovoltaic changes from resource limited to apparent power limited) are solved to obtain the corresponding aerosol optical depth, which is the downlink switching threshold;

[0057] The up-switch threshold (critical value of aerosol optical depth): in the interval where the inverter reactive power output has been saturated (reactive power output is fixed), the corresponding aerosol optical depth is solved by simultaneously solving the reactive power balance function and the active power upper limit under the constraint of available active power of photovoltaic (at this time, photovoltaic is switched from apparent power limited to resource limited), which is the up-switch threshold.

[0058] In an embodiment of the present application, the current operating branch state is determined according to the relationship between the historical operating branch state and the current atmospheric parameters and the up-down switching threshold, comprising:

[0059] Let the historical operating branch state variable be , wherein, represents the resource limited state, represents the apparent power limited state.

[0060] The current aerosol optical depth is determined as .

[0061] Let the unit step function be , wherein, is 1 when , and is 0 when .

[0062] The current operating branch state variable is calculated, and the calculation formula is:

[0063] ; wherein, represents the resource limited state, represents the apparent power limited state.

[0064] The historical operating branch state variable is used to record the operating state of the system at the last time, and its value corresponds to two operating branches:

[0065] When the variable is 0, it represents that the system was in a resource limited state at the last time, that is, the photovoltaic active power output was limited by atmospheric conditions (such as aerosol weakening irradiation) at this time, and the inverter did not occupy the apparent power due to reactive power output.

[0066] When the variable is 1, it represents that the system was in an apparent power limited state at the last time, that is, the photovoltaic active power output was limited by the apparent power constraint of the inverter at this time, and the inverter occupied part of the capacity due to adjusting reactive power (suppressing voltage), resulting in the output active power being occupied.

[0067] Current aerosol optical depth is a parameter reflecting the current atmospheric turbidity (such as dust concentration), and the current aerosol optical depth affects the photovoltaic available active (the higher the concentration, the weaker the irradiation, and the less the photovoltaic available active), and is also a basis for judging whether the system needs to switch between the two branches. It needs to be compared with the up-down switching threshold (the critical value calculated based on the reactive power balance before) to determine whether the current atmospheric condition triggers the branch switching.

[0068] The unit step function is a mathematical tool for judging whether the condition is established, and its value is as follows:

[0069] When the input judgment condition (such as the difference between the current aerosol optical depth and the switching threshold) is greater than or equal to 0, the function takes 1, which means that the condition is established;

[0070] When the input judgment condition is less than 0, the function takes 0, which means that the condition is not established. The function is used to convert the relationship between the current atmospheric parameter and the threshold into a calculable value.

[0071] The calculation formula of the current running branch state variable determines the current branch state through the logic of historical state guidance and current condition verification, and is specifically disassembled as follows:

[0072] If the historical state variable is 0 (the last time is resource limited), the unit step function is used to judge whether the current aerosol optical depth is greater than or equal to the uplink switching threshold. If it is true (the function takes 1), it means that the current atmospheric condition has caused the photovoltaic to change from resource limited to apparent power limited, and the current state variable takes 1; if it is not true (the function takes 0), the current is still resource limited, and the state variable takes 0.

[0073] If the historical state variable is 1 (the last time is apparent power limited), the unit step function is used to judge whether the current aerosol optical depth is less than the downlink switching threshold. If it is true (the function takes 1, and 1 minus the function value is 0), it means that the current atmospheric condition has caused the photovoltaic to change from apparent power limited to resource limited, and the current state variable takes 0; if it is not true (the function takes 0, and 1 minus the function value is 1), the current is still apparent power limited, and the state variable takes 1.

[0074] Through the logical superposition of the above two parts, the current running branch state variable (0 for resource limited, 1 for apparent power limited) is finally obtained, which ensures that the state judgment not only meets the current atmospheric condition, but also inherits the historical running trend, avoiding the system fluctuation caused by frequent branch switching.

[0075] In an embodiment of the present application, based on the current running branch state, the inverter reactive output is calculated, including:

[0076] Establishing a reactive power balance function :

[0077]

[0078] When

[0079] Calculate the discriminant

[0080]

[0081] Calculate the first root of the grid-connected point voltage

[0082] Calculate the second root of the grid-connected point voltage

[0083] Select the root that satisfies as

[0084] Get the inverter reactive power output as

[0085] When

[0086] Calculate the discriminant of the absorption reactive power case , and calculate the corresponding grid-connected point voltage

[0087] Calculate the discriminant of the emission reactive power case , and calculate the corresponding grid-connected point voltage

[0088] If , the inverter reactive power output is

[0089] Otherwise, select the case that satisfies , and the inverter reactive power output is .

[0090] Since the inverter reactive power is not saturated at this time, the reactive power balance function can be converted into a quadratic equation, and the discriminant is used to determine whether the quadratic equation has real solutions (i.e., whether there is an actual feasible grid-connected point voltage).

[0091] The quadratic equation has two possible real roots, corresponding to the two possible voltage operating points of the system.

[0092] From the two voltage roots, select the root that allows the inverter to calculate the reactive power output according to the droop slope without exceeding the saturation value as the actual operating voltage, because the inverter does not enter the reactive power saturation state under resource-limited conditions, and needs to meet this condition.

[0093] ​​​​​​​​​​​​According to the screened actual voltage, combining the voltage reactive power droop slope of the inverter, the reactive power output of the inverter is calculated by the difference between the voltage and the rated value multiplied by the slope, and at this time, the output is a linear regulation value (unsaturated).

[0094] The discriminant and corresponding voltage of two reactive power conditions are calculated: at this time, the inverter has entered the reactive power saturation, and needs to distinguish the two saturation conditions of absorbing reactive power and emitting reactive power. Equations are established for the two conditions, the discriminant (whether there is a feasible voltage) is calculated, and then the corresponding grid point voltage of each condition is obtained through the discriminant.

[0095] The reactive power output of the inverter is determined: first, it is judged whether the voltage of the absorbing reactive power condition satisfies the theoretical absorbing reactive power calculated according to the droop slope exceeding the saturation value. If it is satisfied, it means that the inverter is in the absorbing reactive power saturation state, and outputs the maximum absorbing reactive power; if it is not satisfied, it means that it is in the emitting reactive power saturation state, and outputs the maximum emitting reactive power, so as to ensure that the final reactive power output is the saturation value (in line with the constraint in the apparent power limited state).

[0096] In an embodiment of the present application, the photovoltaic active power upper limit is determined in combination with the atmospheric parameters and the capacity constraint in the inverter parameters, and the system stability margin is calculated, including:

[0097] The available photovoltaic active power is calculated as ;

[0098] The working value of the grid point voltage is determined as ; wherein, is , or ;

[0099] The reactive power output of the inverter is determined as ; wherein, is , or ;

[0100] The active power upper limit under the apparent power constraint is calculated as ;

[0101] The photovoltaic active power upper limit is determined as ;

[0102] The voltage stability margin is calculated as ;

[0103] The capacity stability margin is calculated as .

[0104] The calculation of the photovoltaic available active is to obtain the maximum active power that the photovoltaic power station can theoretically output under the current atmospheric conditions (such as aerosol optical thickness), and the atmospheric parameters directly affect the solar irradiance, and then determine the photovoltaic power generation potential.

[0105] The grid-connected point voltage working value is calculated according to the current running branch state (resource limited or apparent power limited), and the effective voltage (i.e. the feasible voltage value selected under different branches) that meets the reactive power balance. Only based on the actual running voltage, the reactive power output of the inverter can be calculated.

[0106] The reactive power output of the inverter is associated with the grid-connected point voltage, so the voltage working value needs to be selected, and the previously calculated reactive power output value matched with the voltage is selected, so that the reactive power output meets the control logic under the current voltage.

[0107] The apparent power of the inverter has a rated limit (the active and reactive power outputs need to meet the capacity constraint), and when the inverter has output a certain reactive power, the quota available for outputting active power will be squeezed. The calculation of the active upper limit is to obtain the maximum active output allowed by the inverter capacity level, so as to avoid the photovoltaic active power exceeding the inverter capacity and causing equipment overload.

[0108] The photovoltaic active upper limit needs to meet the resource level and capacity level restrictions simultaneously: taking the smaller value of the photovoltaic available active (determined by atmospheric conditions) and the active upper limit under the apparent power constraint (determined by inverter capacity). This is because the actual output of the photovoltaic cannot exceed the power generation potential provided by the atmosphere, nor can it exceed the output upper limit allowed by the inverter capacity. The value is the maximum available active when the photovoltaic is actually running.

[0109] The value of the effective slope is determined by whether the inverter is in reactive saturation:

[0110] If the reactive power output of the inverter does not exceed the saturation value (linearly regulated according to voltage), the effective slope takes the actual voltage reactive droop slope, which reflects the adjustment ability of the inverter to voltage changes;

[0111] If the reactive power of the inverter has been saturated (output fixed), the effective slope takes 0, which reflects that the inverter cannot adjust the reactive power with voltage changes at this time, and the adjustment ability disappears.

[0112] The voltage stability margin is a measure of the distance of the system voltage from the unstable critical state: by quantifying the influence of voltage changes on reactive power balance (based on the correlation of effective slope, voltage and grid parameters), the larger the margin value, the easier the system is to maintain reactive power balance when the voltage changes slightly, and the stronger the voltage stability; otherwise, it is close to the unstable critical state and needs to be avoided.

[0113] Capacity stability margin is a measure of the distance of the inverter from the apparent power saturation state: by quantifying the difference between the sum of the current active and reactive output and the rated apparent power of the inverter, the larger the margin value, the more remaining capacity of the inverter, and the less likely to cause active or reactive output to be limited due to insufficient capacity; otherwise, the capacity is insufficient, and the output needs to be adjusted to avoid equipment over-limit operation.

[0114] In an embodiment of the present application, the minimum comprehensive operation cost is taken as the target, and the unit output, photovoltaic active power and current running branch state are output under the constraints of power balance, photovoltaic active upper limit, system stability margin lower limit, unit operation constraint and branch state consistency constraint, including:

[0115] The target function is constructed as a comprehensive operation cost ; wherein, is the unit output, is the photovoltaic active power, is the fuel consumption cost function, is the unit light rejection cost;

[0116] The target function is minimized under the following constraints:

[0117] The first constraint is: ;

[0118] The second constraint is: ;

[0119] The third constraint is: , and ;

[0120] The fourth constraint is: , and ;

[0121] The fifth constraint is: ;

[0122] Wherein, is the system load, is the system active loss, is the lower limit of voltage stability margin, is the lower limit of capacity stability margin, is the maximum active power output limit, is the historical unit output, is the upper limit of unit variation rate;

[0123] Solving the target function, the unit output , the photovoltaic active power and the current running branch state are obtained.

[0124] The comprehensive operation cost is the optimization target and needs to be minimized, which consists of two parts:

[0125] Fuel consumption cost function: corresponding to the generation cost of thermal power units, the cost is directly related to the unit output (the larger the output, the more fuel consumption and the higher the cost), which reflects the economic demand of scheduling;

[0126] Unit abandoned light cost related term: corresponding to the loss of unused photovoltaic active power (part of photovoltaic available but not grid-connected), which reflects the scheduling demand for new energy consumption. The superposition of the two achieves the dual goals of reducing photovoltaic waste and achieving economic and efficient consumption while controlling thermal power cost.

[0127] The first constraint (power balance constraint) is to ensure real-time supply and demand balance of the power grid: the sum of thermal power unit output and photovoltaic active power is equal to the sum of system load and system active power loss. System load is the user's electricity demand, and active power loss is the power loss in the power grid transmission. This constraint is the basis for safe operation of the power grid to avoid frequency fluctuations or power outages due to supply and demand imbalance.

[0128] The second constraint (photovoltaic active power range constraint): photovoltaic active power must be greater than or equal to 0 and less than or equal to the previously calculated photovoltaic active power upper limit. The lower limit of 0 is a restriction (photovoltaic cannot emit negative power), and the upper limit is a resource + capacity double restriction (neither can it exceed the available active power allowed by the atmospheric conditions, nor can it exceed the active power allowed by the inverter capacity), ensuring that the photovoltaic output is within a feasible range.

[0129] The third constraint (stability margin lower limit constraint): voltage stability margin and capacity stability margin must be greater than or equal to their respective lower limits. The voltage stability margin lower limit is the critical value to avoid voltage instability, ensuring that the system voltage will not collapse due to small disturbances; the capacity stability margin lower limit is the critical value to avoid inverter apparent power exceeding the limit, ensuring device safety, both of which ensure the safety of system operation.

[0130] The fourth constraint (unit operation constraint) contains two sub-constraints, both of which are derived from the limitations of thermal power units:

[0131] Output range constraint: unit output must be between minimum active output and maximum active output to avoid unit output being too low to cause flameout or too high to exceed device carrying capacity;

[0132] Variable rate constraint: the difference between the current unit output and the historical unit output must not exceed the upper limit of the unit variable rate to avoid sudden changes in unit output (such as sudden changes in boiler pressure and turbine speed), which can cause equipment damage or unstable operation.

[0133] Ensure that the current running branch state (resource limited / power available limited) is consistent with the historical state, current conditions (such as the relationship between atmospheric parameters and switching thresholds). Avoid frequent switching of branch states (such as repeatedly jumping between the two states in a short period of time), which can cause frequent adjustments of photovoltaic active power and unit output, leading to power and voltage fluctuations in the power grid, and ensuring the stability of scheduling.

[0134] By minimizing the comprehensive operation cost and meeting all the above constraints, the final result is:

[0135] Unit output: the optimal power generation of thermal power units, taking into account cost and supply and demand balance;

[0136] Photovoltaic active power: the optimal grid-connected power of photovoltaic power stations, taking into account consumption and safety constraints;

[0137] Current running branch state: clearly defines the current operating mode of the system, providing historical basis for scheduling calculations for the next time.

[0138] Embodiment two

[0139] As shown in Figure 2 A power system optimization scheduling system, applied to any of the power system optimization scheduling methods described, includes:

[0140] A data acquisition module acquires and obtains grid parameters, inverter parameters and atmospheric parameters;

[0141] A threshold calculation module determines the voltage critical state and the upper and lower switching thresholds of atmospheric parameters based on the reactive power balance relationship between grid parameters and inverter parameters;

[0142] A state determination module determines the current running branch state according to the relationship between the historical running branch state and the current atmospheric parameters and the upper and lower switching thresholds;

[0143] A margin identification module calculates the inverter reactive power output based on the current running branch state, determines the upper limit of photovoltaic active power in combination with the capacity constraints in atmospheric parameters and inverter parameters, and calculates the system stability margin;

[0144] A planning control module outputs the unit output, photovoltaic active power and current running branch state under the constraints of power balance, photovoltaic active power upper limit, system stability margin lower limit, unit operation constraints and branch state consistency constraints, with the goal of minimizing the comprehensive operation cost.

[0145] The above describes the embodiments of the present embodiment, but the present embodiment is not limited to the specific embodiments described above, which are only illustrative and not limiting. Those skilled in the art can make many forms under the inspiration of the present embodiment, which are all within the protection scope of the present embodiment.

Claims

1. A power system optimal dispatching method, characterized in that, The method comprises the following steps: collecting and obtaining power grid parameters, inverter parameters and atmospheric parameters; determining voltage critical state and upper and lower switching thresholds of atmospheric parameters based on reactive power balance relationship between the power grid parameters and the inverter parameters; determining current running branch state according to relationship between historical running branch state and current atmospheric parameters and the upper and lower switching thresholds; calculating inverter reactive power output based on the current running branch state, determining photovoltaic active power upper limit in combination with capacity constraints in the atmospheric parameters and the inverter parameters, and calculating system stability margin; outputting unit output, photovoltaic active power and current running branch state under power balance, photovoltaic active power upper limit, system stability margin lower limit, unit operation constraint and branch state consistency constraint with the minimum comprehensive operation cost as the target.

2. The power system optimal dispatching method according to claim 1, wherein, The method for determining voltage critical state and upper and lower switching thresholds of atmospheric parameters based on reactive power balance relationship between the power grid parameters and the inverter parameters comprises the following steps: Establishing a reactive power balancing function : ； wherein, is a point of common coupling voltage, is a line equivalent parallel susceptance parameter, is a receiving end equivalent voltage reactive slope parameter, is an inverter reactive output function; When then ; When then ; When then ; wherein, is an inverter voltage reactive droop slope parameter, is an inverter reactive saturation value parameter; solving for the voltage value that satisfies and as the voltage critical state; wherein , At is equal to 0; wherein , at is equal to 0; wherein denotes the effective slope; Let the photovoltaic available active function be ; wherein, represents the aerosol optical thickness, the aerosol optical thickness being an atmospheric parameter, is a photovoltaic rated available active calibration value parameter, is an available active first order coefficient parameter; Let the active power upper limit function under the apparent power constraint be ; wherein, is the inverter rated apparent power parameter.

3. The power system optimal dispatching method of claim 2, wherein, The method for determining voltage critical state and upper and lower switching thresholds of atmospheric parameters based on reactive power balance relationship between the power grid parameters and the inverter parameters comprises the following steps: In the interval, the simultaneous and , the downlink switching threshold aerosol optical depth ; In the interval, the simultaneous and , the uplink switching threshold aerosol optical depth is obtained.

4. The power system optimal dispatching method of claim 3, wherein, The method for determining current running branch state according to relationship between historical running branch state and current atmospheric parameters and the upper and lower switching thresholds comprises the following steps: Let the historical run branch state variable be wherein, denotes a resource limited state, denotes an apparent power limited state; determining a current aerosol optical depth as ; Let the unit step function be where 1 if 0 if 0. calculating the current running branch state variable the calculation formula is: ; wherein, denotes a resource limited state, denotes an apparent power limited state.

5. The power system optimal dispatching method of claim 4, wherein, The method for calculating inverter reactive power output based on the current running branch state comprises the following steps: Establishing a reactive power balancing function : ； When time: Computing the discriminant : ； First root of grid point voltage calculation ; Second root of grid point voltage calculation ; selecting a root from the first and second roots that satisfies as the root ; The inverter reactive output is obtained as ; When Time: Computing a discriminant for the absorption reactive case and computing the corresponding grid point voltage ; Computing a discriminant of a reactive situation and computing a corresponding grid point voltage .

6. The power system optimal dispatching method according to claim 5, wherein, The method for calculating inverter reactive power output based on the current running branch state further comprises the following steps: If the following condition is satisfied , the inverter reactive power output is ; Otherwise, select the case satisfying , the reactive output of the inverter is .

7. The power system optimal dispatching method according to claim 6, wherein, The method for determining photovoltaic active power upper limit in combination with capacity constraints in the atmospheric parameters and the inverter parameters and calculating system stability margin comprises the following steps: Computing the photovoltaic available active power as ; determining the operating value of the grid point voltage as ; wherein is , or ; determining the inverter reactive output as ; wherein, is , or .

8. The power system optimal dispatching method according to claim 7, characterized in that, The method for determining photovoltaic active power upper limit in combination with capacity constraints in the atmospheric parameters and the inverter parameters and calculating system stability margin further comprises the following steps: The active power upper limit under the calculated apparent power constraint is ; determining a photovoltaic active upper limit as ; The voltage stability margin is calculated as ; The computing capacity stability margin is .

9. The power system optimal dispatching method of claim 8, wherein, The method for outputting unit output, photovoltaic active power and current running branch state under power balance, photovoltaic active power upper limit, system stability margin lower limit, unit operation constraint and branch state consistency constraint with the minimum comprehensive operation cost as the target comprises the following steps: The objective function is constructed as a comprehensive operation cost ; wherein, is the unit generation cost, is the photovoltaic active power, is the fuel consumption cost function, is the unit cost of abandoned light; The objective function is minimized under the following constraint conditions: First constraint: ; Second constraint: ; Third constraint: , and ; Fourth constraint: , and ; Fifth constraint: ; wherein, is the system load, is the system active power loss, is the lower limit of the voltage stability margin, is the lower limit of the capacity stability margin, is the maximum active power output limit, is the historical unit output, is the upper limit of the unit ramp rate; Solving the objective function, obtaining the unit output , photovoltaic active power and current operating branch state .

10. A power system optimal dispatch system applied to the power system optimal dispatch method of any one of claims 1-9, characterized in that, The method comprises the following steps: a data collection module for collecting and obtaining power grid parameters, inverter parameters and atmospheric parameters; a threshold calculation module for determining voltage critical state and upper and lower switching thresholds of atmospheric parameters based on reactive power balance relationship between the power grid parameters and the inverter parameters; a state determination module for determining current running branch state according to relationship between historical running branch state and current atmospheric parameters and the upper and lower switching thresholds; a margin identification module for calculating inverter reactive power output based on the current running branch state, determining photovoltaic active power upper limit in combination with capacity constraints in the atmospheric parameters and the inverter parameters, and calculating system stability margin; a planning control module for outputting unit output, photovoltaic active power and current running branch state under power balance, photovoltaic active power upper limit, system stability margin lower limit, unit operation constraint and branch state consistency constraint with the minimum comprehensive operation cost as the target.

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