Cooperative multi-resource power grid stability control system and method

Abstract

The invention provides a cooperative multi-resource power grid stability control system and a cooperative multi-resource power grid stability control method. The system comprises a frequency control module, a power angle control module and a voltage control module. The frequency module is responsible for power deviation control of the water-fire and wind-light unit. The power angle module deals with power angle swing in stages, including water and fire unit forced excitation, wind and light unit low penetration, and unit state adjustment along with voltage recovery. And the voltage module evaluates the reactive power demand after the power grid partition is short-circuited, and guides the wind-solar unit to increase or decrease the reactive current and the water-fire unit to adjust the forced excitation reference value according to the reactive power source adequacy. The system adopts control measures for the actual state of the power grid, stabilizes the frequency, the power angle and the voltage in all directions, and remarkably improves the stability and the safety of the power grid.

Description

Technical Field

[0001] This application belongs to the field of multi-resource power grid control, and particularly relates to a power grid stability control system and method for coordinating multiple resources. Background Art

[0002] With the development of modern power systems, the stability and security of power grids have become crucial issues in the power industry. Traditional power grid stability control systems mainly rely on the control of single resources, such as only controlling thermal-hydraulic units or only controlling wind-solar units. However, with the large-scale access of new energy and the increasing complexity of power grid structures, the control method of single resources has been difficult to meet the stability control requirements of modern power grids. Summary of the Invention

[0003] The purpose of this application is to overcome the defects in the above-mentioned prior art and provide a power grid stability control system and method for coordinating multiple resources.

[0004] This application provides a power grid stability control system for coordinating multiple resources, including: a frequency control module, a power angle control module, and a voltage control module;

[0005] The frequency control module is used to perform primary and secondary control of power deviation for thermal-hydraulic units and primary and secondary control of power deviation for wind-solar units;

[0006] The power angle control module divides the power angle swing process into a voltage drop non-recovery period, a voltage recovery but power angle difference not pulled back period, and a power angle difference pulled back period; during the voltage drop non-recovery period, the thermal-hydraulic units enter the field forced excitation mode, and the wind-solar units adopt the low voltage ride-through strategy; during the voltage recovery but power angle difference not pulled back period, the thermal-hydraulic units reduce the field forced excitation reference value, and the wind-solar units reduce the reactive current and recover the active power; during the power angle difference pulled back period, the thermal-hydraulic units exit the field forced excitation mode, and the wind-solar units recover the active power and the reactive power returns to the initial value;

[0007] The voltage control module evaluates the maximum demand of reactive power load after a short-circuit fault according to the power grid partition, and judges whether the dynamic reactive power sources arranged in the power grid partition can meet the maximum demand of the reactive power load; for the power grid partition with insufficient reactive power sources, the wind-solar units increase the reactive current during the low voltage ride-through period and maintain the reactive current until the power grid voltage recovers, and the thermal-hydraulic units maintain the field forced excitation until the power grid voltage recovers; for the power grid partition with sufficient reactive power sources, the wind-solar units increase the reactive current during the low voltage ride-through period and reduce the output reactive current after the low voltage ride-through, and the thermal-hydraulic units reduce the field forced excitation reference value.

[0008] Optionally, when the thermal-hydraulic units enter the field forced excitation mode, it includes: reaching the excitation ceiling value according to a preset time.

[0009] Optionally, it further includes: a monitoring module for real-time monitoring of the grid frequency, power angle, and voltage status, as well as the operating parameters of each unit.

[0010] Optionally, the frequency control module is used to perform primary and secondary control of power deviation for thermal-hydropower units, and when performing primary and secondary control of power deviation for wind-solar units, the thermal-hydropower units and the wind-solar units are equivalent to a single-machine system.

[0011] Optionally, it further includes: a human-machine interaction interface for displaying the real-time operating status of the grid, the execution status of stability control measures, and fault alarm information.

[0012] This application also provides a grid stability control method for coordinating multiple resources, including:

[0013] Frequency control step: performing primary and secondary control of power deviation for thermal-hydropower units, and performing primary and secondary control of power deviation for wind-solar units;

[0014] Power angle control step: dividing the power angle swing process of the grid into a voltage dip non-recovery period, a voltage recovery but power angle difference not pulled back period, and a power angle difference pulled back period: during the voltage dip non-recovery period, making the thermal-hydropower units enter the forced excitation mode until reaching the excitation ceiling value according to a preset time, and at the same time making the wind-solar units adopt the low voltage ride-through strategy; during the voltage recovery but power angle difference not pulled back period, reducing the forced excitation reference value of the thermal-hydropower units, and making the wind-solar units reduce the reactive current and recover the active power; during the power angle difference pulled back period, making the thermal-hydropower units exit the forced excitation mode, and at the same time making the wind-solar units recover the active power and return the reactive power to the initial value;

[0015] Voltage control step: evaluating the maximum reactive power load demand after a short-circuit fault according to the grid partition, and judging whether the dynamic reactive power sources arranged in each grid partition meet the maximum demand of the reactive power load; for grid partitions with insufficient reactive power sources, increasing the reactive current during the low voltage ride-through period of the wind-solar units and maintaining the reactive current until the grid voltage recovers after the low voltage ride-through, and at the same time making the thermal-hydropower units maintain the forced excitation state until the grid voltage recovers; for grid partitions with sufficient reactive power sources, increasing the reactive current during the low voltage ride-through period of the wind-solar units and reducing the output reactive current after the low voltage ride-through, and at the same time making the thermal-hydropower units reduce the forced excitation reference value;

[0016] Optionally, the thermal-hydropower units entering the forced excitation mode includes: reaching the excitation ceiling value according to a preset time.

[0017] Optionally, it further includes: real-time monitoring of the grid frequency, power angle, and voltage status, as well as the operating parameters of each unit.

[0018] Optionally, the frequency control module is used for primary control and secondary control of power deviation of the thermal-hydro power unit. When performing primary control and secondary control of power deviation of the wind-solar power unit, the thermal-hydro power unit and the wind-solar power unit are equivalent to a single-machine system.

[0019] Optionally, it further includes: displaying the real-time operation status of the power grid, the execution status of the stability control measures, and the fault alarm information through a human-machine interaction interface.

[0020] The beneficial effects of this application are:

[0021] This application provides a power grid stability control system for coordinating multiple resources, including: a frequency control module, a power angle control module, and a voltage control module; the frequency control module is used for primary control and secondary control of power deviation of the thermal-hydro power unit, and primary control and secondary control of power deviation of the wind-solar power unit; the power angle control module divides the power angle swing process into a voltage drop non-recovery period, a voltage recovery but power angle difference not pulled back period, and a power angle difference pulled back period; during the voltage drop non-recovery period, the thermal-hydro power unit enters the field forcing mode, and the wind-solar power unit adopts the low voltage ride-through strategy; during the voltage recovery but power angle difference not pulled back period, the thermal-hydro power unit reduces the field forcing reference value, and the wind-solar power unit reduces the reactive current and restores the active power; during the power angle difference pulled back period, the thermal-hydro power unit exits the field forcing mode, and the wind-solar power unit restores the active power and the reactive power returns to the initial value; the voltage control module evaluates the maximum demand of the reactive load after a short-circuit fault according to the power grid partition, and judges whether the dynamic reactive power sources arranged in the power grid partition can meet the maximum demand of the reactive load; for the power grid partition with insufficient reactive power sources, the wind-solar power unit increases the reactive current during the low voltage ride-through period and maintains the reactive current until the power grid voltage recovers, and the thermal-hydro power unit maintains the field forcing until the power grid voltage recovers; for the power grid partition with sufficient reactive power sources, the wind-solar power unit increases the reactive current during the low voltage ride-through period and reduces the output reactive current after the low voltage ride-through period, and the thermal-hydro power unit reduces the field forcing reference value. This application realizes the all-round stability control of the power grid frequency, power angle and voltage by taking corresponding control measures for the actual operation status of the multi-resource power grid, and improves the stability and safety of the power grid. Description of the Drawings

[0022] Figure 1 is a schematic diagram of the power grid stability control system for coordinating multiple resources in this application;

[0023] Figure 2 is a schematic diagram of the power grid frequency stability control circuit for multiple resources in this application;

[0024] Figure 3 is a schematic diagram of the equal area criterion principle in this application;

[0025] Figure 4It is a schematic diagram of power angle stability control of the power grid in this application;

[0026] Figure 5 It is a schematic diagram of the PV curve of the new energy unit in this application;

[0027] Figure 6 It is a schematic diagram of power grid voltage stability control in this application. Specific embodiments

[0028] Hereinafter, exemplary embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the drawings, it can be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, the described embodiments are provided so that the present disclosure can be more thoroughly understood and the scope of the present disclosure can be fully conveyed to those skilled in the art.

[0029] Please refer to Figure 1 As shown, a power grid stability control system that coordinates multiple resources includes: a frequency control module, a power angle control module, and a voltage control module.

[0030] The frequency control module is used to perform primary control and secondary control of power deviation for thermal-hydro units and primary control and secondary control of power deviation for wind-solar units.

[0031] When studying the frequency stability problem, the time scale is relatively large, the governor action needs to be considered, and the electromechanical oscillation process between units has ended, and the units in the system oscillate in synchronization. Therefore, when studying the frequency stability problem, the power exchange between units is ignored, and the system is regarded as a single-machine system for research.

[0032] This application uses the center of inertia (COI) model to equivalent the system i as a single-machine system, which is expressed by the following formula:

[0033]

[0034] where, Δδ i is the equivalent power angle deviation of the center of inertia, Δω i is the equivalent rotational speed deviation of the center of inertia, H i is the equivalent inertia of the center of inertia, ΔP m,i is the equivalent mechanical power deviation of the center of inertia, ΔP e,i is the equivalent electromagnetic power deviation of the center of inertia, D i is the equivalent damping coefficient of the center of inertia.

[0035] Please refer to Figure 2 As shown, the power grid frequency stability control includes the primary and secondary control of thermal-hydro units and the primary and secondary control of wind-solar units.

[0036] The function of primary hydro - thermal control can be expressed as:

[0037]

[0038] Among them, ΔP 水火 is the power deviation, Δω i is the speed deviation, M ki (s) is the transfer function of the prime mover and speed control system of the k - th hydro - thermal unit, and R ki is the corresponding feedback coefficient.

[0039] The secondary hydro - thermal control is realized by the frequency regulator.

[0040] As Figure 2 shown, B i is the frequency deviation coefficient, K i (s) is the transfer function of the frequency regulator, and α ki is the regulation coefficient of the k - th hydro - thermal unit.

[0041] The functions of primary wind - solar control are summarized into two types: inertia support and damping support, and are expressed as:

[0042]

[0043] Among them, ΔP 风光 is the power deviation, Δω i is the speed deviation, is the support inertia provided by the wind - solar unit, is the support damping provided by the wind - solar unit, is the time constant for the wind - solar unit to act.

[0044] The secondary wind - solar control is determined by comprehensively considering the system characteristics.

[0045] As Figure 2 shown, γ i is the regulation coefficient of the wind - solar unit.

[0046] Furthermore, this application also considers the influence of other systems.

[0047] Suppose system i and system j are connected by a tie line, and the power increment on the tie line can be expressed as:

[0048]

[0049] Among them, T ij is the coefficient corresponding to the tie line i - j, Δf i is the frequency of system i, and Δf j is the frequency of system j.

[0050] For hydro - thermal units, their mechanical power is regulated by the speed control system to achieve the purpose of primary frequency modulation.

[0051] Due to the inherent characteristics of prime movers, it is difficult to significantly change the primary regulation characteristics of hydrothermal units by altering their control strategies and parameters. Under electromagnetic power disturbances, their behavioral characteristics are relatively fixed. The secondary control of hydrothermal units is accomplished by frequency regulators, which proportionally distribute the unbalanced power among different units to achieve the purpose of constant frequency control.

[0052] For wind-solar units, their behavioral characteristics are adjusted according to the needs of operators.

[0053] Specifically, wind-solar units quickly release their reserve capacity to achieve an effect similar to emergency power support. However, due to the difficulty of real-time information collection and considering the issue of unbalanced power distribution among different types of units, the primary frequency regulation strategy of wind-solar units is virtual synchronous control or droop control.

[0054] Droop control is regarded as a special case with zero inertia in the virtual synchronous control strategy.

[0055] The unbalanced power borne by wind-solar units in secondary regulation is determined by optimizing the operation characteristics and regulation capabilities of multiple types of units including hydrothermal, wind, and solar.

[0056] It should be noted that parameters such as the inertia, damping, and prime movers of hydrothermal units belong to their physical inherent characteristics and cannot be changed, while the inertia and damping parameters of wind-solar units can be modified artificially. Therefore, various control parameters of wind-solar units are not fixed during the process of frequency stability control and are modified according to the system operation conditions and actual needs, and even adaptively adjusted during the dynamic process.

[0057] The power angle control module divides the power angle swing process into a voltage dip non-recovery period, a voltage recovery but power angle difference not pulled back period, and a power angle difference pulled back period; during the voltage dip non-recovery period, the hydrothermal units enter the forced excitation mode, and the wind-solar units adopt the low voltage ride-through strategy; during the voltage recovery but power angle difference not pulled back period, the hydrothermal units reduce the forced excitation reference value, and the wind-solar units reduce the reactive current and restore the active power; during the power angle difference pulled back period, the hydrothermal units exit the forced excitation mode, and the wind-solar units restore the active power and the reactive power returns to the initial value;

[0058] The low voltage ride-through strategy means that when the power grid fails and causes a short-term large voltage drop, wind-solar or thermal power units actively adjust the inverter control mode to maintain grid connection and provide dynamic reactive power support, rather than passive disconnection from the grid. Its purpose is to prevent the large-scale disconnection of new energy units from exacerbating the risk of grid collapse and to assist in system voltage recovery and power angle stability.

[0059] The power angle control is analyzed using the equal area criterion.

[0060] A specific example is that the fault type under investigation is a three-phase short circuit on bus sys, that is, the voltage on bus sys is zero during the fault, from which the output power P of the generator during the fault is deduced gen = 0; and the mechanical power of the generator is equal to the original output power P of the generator gen0 .

[0061] During the fault, the output power P of the generator gen = 0, and the accelerating power of the generator is its own input mechanical power P gen0 .

[0062] Therefore, according to the motion equation of the generator:

[0063]

[0064] where M is the inertia time constant of the generator set; t is time; P m is the input mechanical power of the generator, P m = P gen0 ; P e is the electromagnetic power output by the generator, which is zero during the fault; P D is the damping power of the generator. This application does not consider this parameter, so it is set to zero.

[0065] Based on the boundary conditions of the generator motion equation at the time of fault occurrence, the power angle δ of the generator at the fault clearing time t clear is deduced, and the expression is: clear As

[0066]

[0067] shown, under the above conditions, the abscissa is the power angle δ of the generator Figure 3 , and the ordinate is P gen / P gen / P gen0 ; the fault clearing angle corresponding to the fault clearing time t clear is δ clear , and δ h (δ h1 , δ h2 ) is the intersection point of the output power P of the generator after the fault is cleared and the mechanical power P of the generator gen = P m = gen0 .

[0068] According to the equal area rule, the condition satisfied by the fault critical clearing angle δ clear = t cr corresponding to the fault critical clearing time t clear = δ cr is that "accelerating area" = "decelerating area", that is:

[0069]

[0070] As the penetration rate of the asynchronous machine power supply increases, the critical clearing angle and the critical clearing time will be affected, and the power angle stability of the system will also be affected.

[0071] According to the dynamic process after the disturbance occurs, the power angle swing process is divided into three stages, namely, the period when the voltage dip has not recovered, the period when the voltage has recovered but the power angle difference has not been pulled back, and the period when the power angle difference is pulled back.

[0072] Please refer to Figure 4 as shown, in different stages, the measures that can be taken by different types of units such as thermal, hydro, wind, and photovoltaic units also vary.

[0073] In the stage of voltage dip and non - recovery, the excitation system of thermal and hydro units will enter the forced excitation mode and reach the excitation ceiling value within the specified time as required, so as to quickly increase the output reactive power and attempt to restore the terminal voltage of the unit. The effect of forced excitation effectively improves the terminal voltage of thermal and hydro units, thus relieving the electromagnetic power of thermal and hydro units and reducing the pulling - apart speed of the power angle difference between units. When the voltage dips, wind and photovoltaic units will trigger the low - voltage ride - through control strategy. During the low - voltage ride - through period, the behavior mode of wind and photovoltaic units is not fixed but set artificially. Therefore, the operating personnel set the low - voltage ride - through strategy of wind and photovoltaic units to improve the power angle stability of the system.

[0074] Generally speaking, there are two control routes for wind and photovoltaic units during the low - voltage ride - through period. One is to prioritize active current, and the other is to prioritize reactive current. Since the power angle stability is caused by long lines and heavy loads, reducing the active current of wind and photovoltaic units during the low - voltage ride - through period effectively reduces the active load pressure of the section, while increasing the reactive current of wind and photovoltaic units during the low - voltage ride - through period effectively improves the system voltage level and helps the power angle of thermal and hydro units to recover and stabilize.

[0075] During the period when the voltage has recovered but the power angle difference has not been pulled back, if the thermal and hydro units continue to operate in the forced excitation mode, it will lead to over - voltage at the terminal.

[0076] Therefore, even if the power angle difference of thermal and hydro units has not been pulled back, the forced excitation reference value is still adjusted to avoid over - voltage at the terminal. For wind and photovoltaic units, after the voltage has recovered, their active power resumes, but the rapid recovery of active power will increase the section power flow burden, which is not conducive to the power angle stability of the system. If the active power of wind and photovoltaic units does not recover for a long time, it will also endanger the frequency stability of the system. Therefore, in the stage when the voltage has recovered but the power angle difference will be pulled back, wind and photovoltaic units slow down the active power recovery and reduce the target value of active power. The reactive current of wind and photovoltaic units also decreases, and by adjusting the reactive current output, the occurrence of over - voltage at the terminal is avoided.

[0077] In the stage after the power angle difference is pulled back, the hydro-thermal unit exits the forced excitation mode and resumes normal terminal voltage control. At this time, the power angle stability of the system is abundant and is no longer the main factor restricting the transmission power of the section. The wind-solar units resume their own active power. And in order to avoid adverse effects on the system frequency stability, in this stage, the wind-solar units resume their own active power, while the reactive power returns to the initial value.

[0078] The voltage control module evaluates the maximum demand of reactive power load after a short-circuit fault according to the power grid partition, and judges whether the dynamic reactive power sources arranged in the power grid partition can meet the maximum demand of the reactive power load; for the power grid partition with insufficient reactive power sources, the wind-solar units increase the reactive current during the low-voltage ride-through period and maintain the reactive current until the grid voltage recovers after the low-voltage ride-through period, and the hydro-thermal units maintain forced excitation until the grid voltage recovers; for the power grid partition with sufficient reactive power sources, the wind-solar units increase the reactive current during the low-voltage ride-through period and reduce the output reactive current after the low-voltage ride-through period, and the hydro-thermal units reduce the forced excitation reference value.

[0079] The voltage instability mechanism of the traditional power system dominated by generators is explained by the classical PV curve.

[0080] In the analysis process of the PV curve, the synchronous machine is regarded as a constant voltage source, and the operation mode of the new energy unit will switch with the decrease of the port bus voltage. Therefore, the analysis results of the existing PV curve are not applicable to the new energy unit.

[0081] In this application, when the new energy unit keeps the voltage at the outlet constant, the magnitude of the load power is written as a function of the system parameters and the node voltage:

[0082]

[0083] where, P D and Q D respectively represent the magnitudes of the load active power and reactive power, represents the voltage vector of the load node, represents the conjugate of the RES output current.

[0084] In the above formula, ignoring the resistance in the line, we get:

[0085]

[0086] Eliminating the variable θ in this formula r we get:

[0087]

[0088] Solving this formula gives two solutions for the load node voltage:

[0089]

[0090] Among them, the amplitude of the load bus voltage in the above formula is obtained on the premise that it is assumed that the new energy unit maintains a constant terminal voltage.

[0091] If the new energy unit switches to the constant current control mode, the amplitude of the output current of the new energy unit will remain constant, and the load bus voltage is:

[0092]

[0093] Among them, I lim is the maximum current limit of the new energy unit.

[0094] As Figure 5 shown, assuming that the power factor of the load is determined, then the voltage amplitude at the load is proportional to the apparent power of the load, which is a straight line passing through the origin in the PV diagram.

[0095] In a power grid with multiple resources of wind, light, water, and fire, due to the complex reactive power response characteristics and coupling mechanisms between different types of units, the phenomena of coexistence of low voltage and overvoltage are very likely to occur in the power grid. Therefore, before performing voltage stability control, first judge whether there is a low voltage or overvoltage problem in the target bus or area.

[0096] The power grid voltage stability control in this application includes reactive power adequacy assessment and discrimination, low voltage control architecture, and overvoltage control architecture respectively.

[0097] Through the reactive power adequacy assessment and discrimination part, judge whether the reactive power sources in each area are sufficient in the face of power grid faults and dynamic reactive power loads.

[0098] If the reactive power source in a certain area is sufficient, overvoltage problems are likely to occur during the recovery process when the area faces a power grid fault. On the contrary, if the reactive power source in a certain area is insufficient, there will be low voltage problems when the area faces a power grid fault.

[0099] As Figure 6 shown, different control strategies for multiple resources of wind, light, water, and fire are adopted for low voltage and overvoltage problems respectively.

[0100] For sub-area assessment and discrimination, evaluate the maximum demand of reactive power load after a short-circuit fault according to the power grid partition.

[0101] For the assessment of the maximum reactive power load demand, it is approximately considered that the reactive power demand of the dynamic load during the power grid fault increases at the maximum speed, so as to calculate the maximum reactive power increment of all loads when a severe power grid fault occurs in this area. Based on this, it is judged whether the dynamic reactive power sources arranged in this area can meet the dynamic reactive power load demand under severe faults. If the dynamic reactive power sources are sufficient, overvoltage problems are likely to occur in the initial stage of the recovery after the fault is cleared in this area. If the dynamic reactive power sources are insufficient, low voltage or even voltage collapse problems are likely to occur after the fault is cleared.

[0102] If a certain area faces low voltage problems, start the low voltage control system architecture.

[0103] During the fault, the grid voltage level is low, and the wind-solar units will start the low voltage ride-through strategy. To accelerate the recovery of the grid voltage, during the low voltage ride-through period, the wind-solar units increase the reactive current as much as possible and continue to maintain the reactive current until the grid voltage level in the area where they are located is restored. Under the action of the excitation system, the hydro-thermal units will enter the forced excitation mode during the power grid fault, and after the fault is cleared, they also maintain the forced excitation until the voltage in the area where they are located is restored.

[0104] If a certain area faces overvoltage problems, start the overvoltage control system architecture.

[0105] During the fault, the grid voltage level is still low, and the wind-solar units start the low voltage ride-through strategy. Similarly, to accelerate the recovery of the grid voltage, the wind-solar units increase the reactive current as much as possible during the low voltage ride-through period. However, as the voltage in the area where the wind-solar units are located increases, they reduce the output reactive current to avoid overvoltage after the fault. The hydro-thermal units will still enter the forced excitation mode during the fault, but gradually reduce the forced excitation reference value as the voltage level in the area where they are located increases to avoid overvoltage after the fault.

[0106] This application also provides a power grid stability control method for coordinating multiple resources, which is characterized by including:

[0107] Frequency control step: perform primary control and secondary control on the power deviation of the hydro-thermal units, and perform primary control and secondary control on the power deviation of the wind-solar units;

[0108] Power angle control step: divide the power angle swing process of the power grid into a voltage drop non-recovery period, a voltage recovery but power angle difference non-pulling-back period, and a power angle difference pulling-back period: during the voltage drop non-recovery period, make the hydro-thermal units enter the forced excitation mode until reaching the excitation ceiling value according to the preset time, and at the same time make the wind-solar units adopt the low voltage ride-through strategy; during the voltage recovery but power angle difference non-pulling-back period, reduce the forced excitation reference value of the hydro-thermal units and make the wind-solar units reduce the reactive current and recover the active power; during the power angle difference pulling-back period, make the hydro-thermal units exit the forced excitation mode, and at the same time make the wind-solar units recover the active power and return the reactive power to the initial value;

[0109] Voltage control step: Evaluate the maximum reactive power load demand after a short-circuit fault according to the power grid partition, and determine whether the dynamic reactive power sources arranged in each power grid partition can meet the maximum demand of the reactive power load; for the power grid partitions with insufficient reactive power sources, increase the reactive current during the low voltage ride-through period of the wind-solar units, and maintain this reactive current until the grid voltage recovers after the low voltage ride-through, and at the same time make the hydro-thermal units maintain the forced excitation state until the grid voltage recovers; for the power grid partitions with sufficient reactive power sources, increase the reactive current during the low voltage ride-through period of the wind-solar units, and reduce the output reactive current after the low voltage ride-through, and at the same time make the hydro-thermal units reduce the forced excitation reference value;

[0110] Among them, the hydro-thermal unit enters the forced excitation mode, including: reaching the excitation ceiling value according to the preset time.

[0111] Furthermore, the grid frequency, power angle and voltage status are monitored in real time, as well as the operating parameters of each unit.

[0112] Furthermore, the frequency control module is used to perform primary control and secondary control on the power deviation of the hydro-thermal units. When performing primary control and secondary control on the power deviation of the wind-solar units, the hydro-thermal units and the wind-solar units are equivalent to a single-machine system.

[0113] Furthermore, it also includes: displaying the real-time operating status of the grid, the execution status of the stability control measures, and the fault alarm information through the human-machine interface.

[0114] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and apply the present invention. It is obvious that those skilled in the art can easily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A power grid stability control system that coordinates multiple resources, characterized in that, include: Frequency control module, power angle control module and voltage control module; The frequency control module is used to perform primary and secondary control of power deviation on the hydro-thermal unit, and to perform primary and secondary control of power deviation on the wind-solar unit; The power angle control module divides the power angle swing process into a voltage drop unrecovered period, a voltage recovery but power angle difference unrecovered period, and a power angle difference recovery period; during the voltage drop unrecovered period, the hydro-fired unit enters a forced excitation mode, and the wind-solar unit adopts a low-breakdown strategy; during the voltage recovery but power angle difference unrecovered period, the hydro-fired unit reduces a forced excitation reference value, and the wind-solar unit reduces reactive current to restore active power; during the power angle difference recovery period, the hydro-fired unit exits the forced excitation mode, and the wind-solar unit restores active power and the reactive power returns to the initial value; The voltage control module evaluates the maximum demand of reactive load after a short-circuit fault according to the grid partition, and determines whether the dynamic reactive source arranged in the grid partition can meet the maximum demand of the reactive load; for the grid partition where the reactive source is not sufficient, the wind and solar power units increase the reactive current during the low-voltage run-through period, maintain the reactive current after the low-voltage run-through until the grid voltage recovers, and the hydro-thermal units maintain strong excitation until the grid voltage recovers; for the grid partition where the reactive source is sufficient, the wind and solar power units increase the reactive current during the low-voltage run-through period, reduce the output reactive current after the low-voltage run-through, and the hydro-thermal units reduce the strong excitation reference value.

2. The grid stability control system for collaborative multi-resources according to claim 1, characterized in that The hydro-fired unit enters the strong excitation mode, including: reaching the excitation peak value according to a preset time.

3. The grid stability control system for collaborative multi-resources according to claim 1, wherein Also includes: The monitoring module is used to monitor the grid frequency, power angle and voltage status in real time, as well as the operating parameters of each unit.

4. The grid stability control system for collaborative multi-resources according to claim 1, characterized in that, The frequency control module is used to perform primary and secondary control of power deviation on the water-fired unit. When performing primary and secondary control of power deviation on the wind-solar unit, the water-fired unit and the wind-solar unit are equivalent to a single-machine system.

5. The grid stability control system for collaborative multi-resources according to claim 1, characterized in that, Also includes: The human-computer interaction interface is used to display the real-time operating status of the power grid, the execution of stability control measures, and fault alarm information.

6. A grid stability control method for coordinating multiple resources, characterized in that, include: Frequency control steps: perform primary and secondary control of power deviation for hydro-thermal units, and perform primary and secondary control of power deviation for wind and solar units; Power angle control steps: The power angle swing process of the power grid is divided into a voltage drop unrecovered period, a voltage recovery but power angle difference unrecovered period, and a power angle difference recovery period: During the voltage drop unrecovered period, the hydro-thermal units are put into a forced excitation mode until the excitation peak value is reached according to the preset time, and the wind-solar units are simultaneously made to adopt a low-power wear-through strategy; During the voltage recovery but power angle difference unrecovered period, the forced excitation reference value of the hydro-thermal units is reduced, and the wind-solar units are made to reduce reactive current and restore active power; During the power angle difference pull-back period, the hydro-thermal unit is exited from the strong excitation mode, while the wind and solar units are restored to active power and the reactive power is returned to the initial value; Voltage control step: Evaluate the maximum reactive power load demand after a short-circuit fault according to the power grid partition, and determine whether the dynamic reactive power sources arranged in each power grid partition meet the maximum demand of the reactive power load; for the power grid partitions with insufficient reactive power sources, increase the reactive current during the low voltage ride-through period of the wind-solar units, and maintain this reactive current until the grid voltage recovers after the low voltage ride-through, and at the same time make the hydro-thermal units maintain the forced excitation state until the grid voltage recovers; for the power grid partitions with sufficient reactive power sources, increase the reactive current during the low voltage ride-through period of the wind-solar units, and reduce the output reactive current after the low voltage ride-through, and at the same time make the hydro-thermal units reduce the forced excitation reference value.

7. The grid stability control method for collaborative multi-resources according to claim 6, characterized in that, The hydro-thermal unit enters the forced excitation mode, including: reaching the excitation ceiling value according to a preset time.

8. The grid stability control method for coordinating multiple resources according to claim 6, characterized in that It also includes: The real-time monitored grid frequency, power angle and voltage status, as well as the operating parameters of each unit.

9. The grid stability control method for collaborative multi-resources according to claim 6, wherein, The frequency control module is used to perform primary control and secondary control of power deviation for the hydro-thermal units. When performing primary control and secondary control of power deviation for the wind-solar units, the hydro-thermal units and the wind-solar units are equivalent to a single-machine system.

10. The grid stability control method for coordinating multiple resources according to claim 6, characterized in that, It also includes: Display the real-time operating status of the power grid, the execution status of the stability control measures, and the fault alarm information through the human-machine interface.

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