Power grid multi-power electronic equipment networking stability online monitoring method, control terminal and system

Abstract

The application discloses a kind of power grid multi power electronic equipment networking stability online monitoring method, control terminal and system, including according to the voltage and current sampling value of measuring point, get net side transient voltage and valve side transient voltage by transient voltage instability model, and analyze and judge whether instability exists in net side and valve side;The system operation stability of the patent can be monitored online after each power electronic equipment networking of power grid, mainly including transient voltage stability and power electronic dynamic control stability, and instability risk can be analyzed, diagnosed and disposed in emergency according to the four-quadrant power operation condition of power electronic equipment and network frame measuring point data, voltage transient fluctuation caused by multiple parallel machines of power grid, power electronic control instability and other problems are solved.

Description

Technical Field

[0001] This invention relates to a power system operation control method, and more particularly to an online monitoring method, control method, and system for the stability of a power grid with multiple power electronic devices. Background Technology

[0002] With the increasing demand for green energy transformation and low-carbon development both domestically and internationally, the proportion of new energy converters and four-quadrant frequency converters connected to the power grid in my country is constantly increasing, forming a power grid network system with a high proportion of power electronics. Its rapid operation and control characteristics differ from the previous power grid architecture, leading to problems such as the risk of transient voltage instability in the power grid.

[0003] While individual power electronic devices do not exhibit operational instability when operating independently, they become unstable when operating in a network of multiple devices. On one hand, fluctuations in the grid-side voltage due to power variations in both directions can easily lead to transient voltage instability. On the other hand, excessive reverse power feeds in, causing a rise in grid-side voltage, coupled with voltage components on the lines connected to the power electronic devices, results in higher control voltages on the valve side of the devices. This leads to frequent voltage limiting loop constraints on the control voltage, ultimately causing converter dynamic control instability. In severe cases, the random and simultaneous operation of multiple power electronic devices can cause abnormally frequent voltage fluctuations at the vertical levels after networking, increasing the risk of grid voltage exceeding limits and instability. However, conventional power grids primarily rely on S-level monitoring and lack transient voltage monitoring mechanisms. They cannot accurately determine transient voltage levels along the vertical grid structure, nor can they provide alarms for operational anomalies or implement corresponding stability control mechanisms. Summary of the Invention

[0004] Purpose of the invention: To address the above problems, this invention proposes an online monitoring method, control method, and system for the stability of a power grid with multiple power electronic devices. This system can dynamically monitor the transient voltages at measurement points and vertical nodes, assess the transient operational stability of the network system and power electronic devices, and perform emergency stabilization control on instability risks based on the adjustable power range of the frequency converter's four quadrants. This solves the problem of varying voltage distribution instability in the power grid caused by the integration of multiple power electronic devices into the network.

[0005] Technical Solution: The technical solution adopted in this invention is an online monitoring method for the stability of a power grid with multiple power electronic devices. It can be used in instability scenarios caused by the networking of multiple converter devices. The method includes: obtaining the grid-side transient voltage and valve-side transient voltage based on the voltage and current sampling values ​​at the measuring points using a transient voltage instability model; calculating the transient volatility and deviation distribution of the grid-side voltage based on the grid-side transient voltage within a period; calculating the dynamic operating stability of the valve-side voltage based on the valve-side transient voltage within a period; determining whether instability exists on the grid side based on the transient volatility and deviation distribution of the grid-side voltage; and determining whether instability exists on the valve side based on the dynamic operating stability of the valve-side voltage.

[0006] The transient voltage instability model includes: based on the d-axis and q-axis components of the voltage at the measuring point, and the d-axis and q-axis components of the upward grid-connected line current at the measuring point, the d-axis voltage drop of the grid-side bus circuit impedance is superimposed on the d-axis voltage component, and the q-axis voltage drop of the grid-side bus circuit impedance is superimposed on the q-axis voltage component, and then the grid-side transient voltage is calculated by vector superposition; the current of the upward grid-connected line is the sum of the currents of each branch between the measuring point and the valve side;

[0007] Based on the d-axis and q-axis components of the voltage at the measuring point and the d-axis and q-axis components of the current at the measuring point, the d-axis voltage drop of the valve-side circuit impedance is superimposed on the d-axis voltage component, and the q-axis voltage drop of the valve-side circuit impedance is superimposed on the q-axis voltage component. Then, the transient voltage on the valve side is calculated by vector superposition.

[0008] Determining whether grid-side instability exists based on the transient volatility and deviation distribution of grid-side voltage includes: if the transient volatility exceeds the allowable value of grid-side voltage transient volatility, or the deviation distribution exceeds the allowable value of grid-side voltage deviation distribution, the two instability criteria are logically ORed, and the determination is made by accumulating the instability determination time. If the conditions are met, it is determined that the grid-side voltage is transiently unstable.

[0009] Determining whether valve-side voltage instability exists based on dynamic operational stability includes: setting a first instability criterion value for judgment; if the number of times the accumulated valve-side transient voltage exceeds the first instability criterion value is greater than a first threshold, it is judged as valve-side voltage instability risk level one; setting a second instability criterion value for judgment; if the number of times the accumulated valve-side transient voltage exceeds the second instability criterion value is greater than a second threshold, it is judged as valve-side voltage instability risk level two; both valve-side voltage instability risk level one and level two are judged as instability type 1; the instability threshold value of the dynamic operational stability of valve-side voltage is adjusted according to the aggregated distribution parameters during normal system operation; if it exceeds the allowable range, it is judged as instability type 2; instability type 2 and instability type 1 are logically ORed to obtain the operational instability diagnostic index of valve-side voltage.

[0010] The formula for calculating grid-side transient voltage is:

[0011]

[0012] In the formula, U grid For grid-side transient voltage, U grid_d U grid_ q represents the dq-axis component of the grid-side transient voltage, and U represents the dq-axis component. gd U gq These are the transient components of the voltage at the measuring point along the dq axis, I. d I q These represent the transient components of the current along the dq axis at each measuring point, R. s L s These are the resistance and inductance parameters of the grid-side bus circuit impedance, respectively, where ω is the frequency and t is the time.

[0013] The formula for calculating the transient voltage on the valve side is:

[0014]

[0015] In the formula, U c U is the valve-side transient voltage. cd U cq These are the dq-axis components of the valve-side transient voltage, R. c L c These are the resistance and inductance parameters of the valve-side circuit impedance, respectively.

[0016] The formula for calculating the transient fluctuation rate of grid-side voltage is:

[0017]

[0018] In the formula, Γ represents the transient fluctuation of the grid-side voltage, and U grid_MAX U grid_MIN These represent the maximum and minimum values ​​of the grid-side transient voltage, respectively.

[0019] The formula for calculating the deviation distribution of grid-side voltage is:

[0020]

[0021] In the formula, Λ represents the deviation distribution degree of the grid-side voltage, and U DB For dead zone, U E U is the rated voltage value. grid For grid-side transient voltage, s N s F These represent the number of times the grid-side transient voltage falls within the dead zone range and the number of times it falls outside the dead zone range, respectively.

[0022] The formula for calculating the dynamic operating stability of the valve-side voltage is:

[0023]

[0024]

[0025] In the formula, Δ M For the dynamic operating stability of the valve-side voltage, U C-MAX U is the maximum available valve-side voltage of the converter. dc M represents the real-time DC-side voltage value of each power electronic device. MAX U is the modulation coefficient. c T is the valve-side transient voltage, δ is the instability criterion setting, and T is the voltage across the valve side. N T F These represent the number of times the transient voltage on the valve side is normal and the number of times it is unstable, respectively.

[0026] This invention proposes a power grid operation control terminal, comprising:

[0027] The acquisition module is used to obtain the voltage and current sample values ​​at the measurement points;

[0028] The synchronous phase-locked loop (PLL) calculation module is used to obtain frequency and phase through the PLL, and to obtain the grid-side transient voltage and valve-side transient voltage based on the voltage and current sampling values ​​at the measurement points through a transient voltage instability model. Based on the grid-side transient voltage within a period, it calculates the transient fluctuation rate and deviation distribution of the grid-side voltage; based on the valve-side transient voltage within a period, it calculates the dynamic operating stability of the valve-side voltage; and based on the dynamic operating stability of the valve-side voltage, it determines whether instability exists on the valve side.

[0029] The control module is used to receive system control commands and dynamically adjust the power electronic equipment according to the valve-side voltage dynamic stabilization control strategy.

[0030] The valve-side voltage dynamic stability control strategy includes: reactive power cluster control mode and virtual negative impedance control mode;

[0031] The aforementioned reactive power cluster control method, based on the degree of over-limit of the power electronic equipment whose valve-side voltage exceeds the limit, and according to the governance target, divides by the access circuit impedance to obtain the reactive current command; on the other hand, through the cluster reactive power regulation effect of several power electronic equipment, the overall voltage level of the measuring point is reduced, and the valve-side voltage of the converter whose valve-side voltage exceeds the limit is further reduced.

[0032] The virtual negative impedance control method reduces the valve-side voltage control value by using virtual complex impedance. A negative inductance component is introduced through the current inner loop of the power electronic device. The target current control value is obtained by dividing the voltage difference between the converter valve-side control voltage and the valve-side transient voltage by the negative inductance component. The output voltage of the PT controller in the current inner loop is changed by the negative inductance current control part, thereby changing the valve-side voltage control value.

[0033] This invention provides an online control method for the stability of a power grid with multiple power electronic devices. According to the online monitoring method for the stability of a power grid with multiple power electronic devices, the transient voltage on the grid side and the transient voltage on the valve side are obtained, and the deviation between the transient voltage on the grid side and the access side is calculated.

[0034] When the transient voltage deviation directions of the grid side and the access side are consistent, the reactive power demand on both sides is calculated based on the transient voltage deviation between the grid side and the access side, and the reactive power adjustable resources on both sides are allocated according to the reactive power demand ratio.

[0035] When the transient voltage deviation directions of the grid side and the access side are inconsistent, the reactive power demand on both sides is calculated according to the transient voltage deviation between the grid side and the access side. The actual reactive power demand on the grid side is calculated as the reactive power demand on the grid side plus the reactive power demand on the access side in the opposite direction. If the actual reactive power demand on the grid side exceeds the upper limit of the adjustable reactive power resources on the grid side, the difference between the voltage limit exceedance value on the valve side and the voltage dead zone, and the difference between the voltage limit exceedance value on the access side and the voltage dead zone are used as the balancing ratio. The reactive power adjustment command on both sides is calculated according to the balancing ratio.

[0036] When the transient voltage deviation directions of the grid side and the access side are consistent, when the average deviation of the voltage distribution increases, the allocation ratio is adjusted to prioritize the side with the larger deviation. When it is impossible to simultaneously address the voltage deviation on both sides, reactive power is allocated according to the ratio of the transient voltage deviation on both sides. This method also employs multi-timescale collaborative control to achieve graded reactive power targets. The multi-timescale includes minute-level, hour-level, and day-level timescales.

[0037] This invention also proposes a grid multi-power electronic device network operation control system, including a grid multi-power electronic device network operation monitoring system and a grid operation control terminal. The grid operation control terminal transmits grid-side and valve-side transient voltage data and analysis conclusions to the grid multi-power electronic device network operation monitoring system via a communication network. The grid multi-power electronic device network operation monitoring system is used to determine whether there is instability on the grid side based on the transient fluctuation rate and deviation distribution of the grid-side voltage. When an over-limit risk occurs, an alarm is issued. Based on the aforementioned grid multi-power electronic device network stability online control method, the system calculates the power command of the power electronic devices and sends it to the grid operation control terminal for execution.

[0038] Beneficial Effects: Compared with existing technologies, this invention has the following advantages: Utilizing the principle of current superposition, the transient active current component and transient reactive current component on the grid side are obtained, and the transient voltage value on the grid side can be calculated by taking their square roots. This method avoids PTCT sampling at the measurement point and multiple voltage levels above and below, avoiding the inconvenience and high cost of installing high-voltage transformers. Simultaneously, this invention can also directly install PTCTs on the grid side for transient voltage sampling. This method mainly solves the deviation between the valve-side voltage control value and the real-time value during the dq feedforward decoupling control of the converter, because in practice, a PI control loop is used to simulate... There is a significant fluctuation in the control value, especially under unstable conditions, the control value is even less able to reflect the real-time value of the valve side voltage. Attached Figure Description

[0039] Figure 1 The instability models of the power grid multi-power electronic equipment networking system described in this invention are (a) the grid side and (b) the valve side.

[0040] Figure 2 This is a diagram of the voltage phase-locked loop strategy for the power grid networking system described in this invention.

[0041] Figure 3 For the power electronic grid operation and control system architecture of the power grid;

[0042] Figure 4 This is a schematic diagram of the power grid network operation control system described in this invention.

[0043] Figure 5 The transient voltage stabilization control strategy of the power grid system (a) grid side and (b) valve side as described in this invention;

[0044] Figure 6 This is a typical architecture for power grid networking systems;

[0045] Figure 7 This is the regulation-valve-side power generation utilization curve of the grid parallel system described in this invention. Detailed Implementation

[0046] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0047] Example 1

[0048] The online monitoring method for the stability of multiple power electronic devices in a power grid, as described in this invention, calculates the grid-side transient voltage and valve-side transient voltage based on the voltage and current sampling values ​​at measurement points using a transient voltage instability model. It then calculates the transient volatility and deviation distribution of the grid-side voltage within a period, and calculates the dynamic operating stability of the valve-side voltage based on the valve-side transient voltage within a period. The measurement point is a PTCT connection point selected in the impedance line between the power electronic device and the power grid. The measurement point is only on the grid side. The grid-side transient voltage is calculated using the measurement point data, and the valve-side transient voltage is obtained by superimposing the measurement point data through the impedance voltage relationship between the grid side and the valve side.

[0049] The following section details the transient voltage instability model and related index calculations.

[0050] Power grids typically employ a tiered substation power supply method, where the grid is transformed from 110kV to 35kV distribution substations, and then stepped down to 10kV at these substations to supply power to various power electronic devices. These devices are often interconnected through grid-connected networks. The grid connection of multiple power electronic devices typically uses a tree-like power supply structure. In this networked system, each power electronic device operates in four quadrants, meaning both active and reactive power flow bidirectionally. Therefore, in multi-device grid-connected systems, the system's transient voltage operation faces instability boundaries and risks.

[0051] Current I of power electronic equipment in the circuit g Assuming the flow of power from the power electronic equipment out of the power grid is the positive direction, the voltage V at the measuring point is... g Effective value of valve-side voltage U of power electronic equipment c and grid-side voltage V s The relationship is as follows:

[0052]

[0053] This invention proposes an online monitoring method for grid-side / valve-side transient voltages based on synchronous dq rotating coordinates. By performing Park transformation on the voltage and current sampling values ​​of the measuring points, transient voltage / current calculations are obtained and vector superposition is performed vertically upward and downward. This allows for the acquisition of real-time transient values ​​and phase differences of the grid-side and valve-side voltages, respectively. Upward dynamic analysis and judgment are performed based on the dead zone interval of the grid-side voltage, while downward dynamic analysis and judgment are performed based on the over-limit conditions of the valve-side voltage.

[0054] After performing Park transformation on the measured point voltages according to the obtained phase and frequency, the active d-axis and reactive q-axis voltage components (transient voltages) of each measured point are obtained. Simultaneously, the active d-axis and reactive q-axis current components (transient currents) of the line current connected to the measured point are obtained based on the Park transformation. Using the calculation formulas in ① and ②, the real-time values ​​of the grid-side transient voltage and the valve-side transient voltages of each power electronic device can be obtained. Based on the real-time and rated values ​​of the grid-side transient voltages, the transient fluctuation rate and deviation distribution of the grid-side voltage can be obtained; based on the real-time transient voltage values ​​of the valve-side voltages and the maximum available valve-side voltage, the operating stability of the valve-side voltage can be obtained. Finally, the above data is transmitted to the power grid operation and control system via a high-speed communication network.

[0055] ①For example Figure 1 As shown in (a), based on the grid-side voltage (feed-in point) in the synchronous rotating coordinate system, and after vector superposition of the d-axis and q-axis, the ∑I after the current collection of each circuit is calculated. d , ∑I q , Then, compare it with the impedance parameter (L) of the bus circuit. s With R s Multiplying the components yields the impedance voltage of the grid-side bus circuit. Adding this to the transient component of the measuring point voltage gives the grid-side voltage transient value, calculated using formula (2). Utilizing the principle of current superposition, the transient active current component and transient reactive current component of the grid side are obtained. The grid-side voltage can be obtained by vector superposition of the dq-axis voltage drop of the upward grid-connected line impedance, based on the dq component of the measuring point voltage. The transient value of the grid-side voltage can be obtained by taking the square root. This method avoids PTCT sampling at the measuring point and the upper and lower multi-layer voltages, avoiding the inconvenience and high cost of installing high-voltage transformers. Furthermore, this invention can also directly install PTCTs on the grid side for transient voltage sampling.

[0056]

[0057] Among them, the measuring point current is the current of the upward grid-connected line, which is the sum of the currents of all branches between the measuring point and the valve side. L s With R s The impedance parameters of the grid-side bus circuit are calculated as follows: the short-circuit impedance and copper loss resistance of the step-up transformer of the grid-side bus circuit are solved, and the distributed inductance and resistance are calculated according to the length of the bus line. The impedance parameters of the grid-side bus circuit can be obtained by summing them.

[0058] The transient fluctuation of the grid-side voltage is shown in the following formula. By dividing the difference between the maximum and minimum transient voltage values ​​within the evaluation period by the maximum transient voltage value, the transient fluctuation of the grid-side voltage can be analyzed.

[0059]

[0060] The deviation distribution rate of the grid-side voltage is shown in the following formula. Using a digital discrete voltage acquisition method, V is set... DB For dead zone, V E By summing the number of transient voltage events within the dead zone and outside the dead zone, the duration of transient voltage compliance and non-compliance within the set evaluation period can be obtained, and the deviation distribution of grid-side voltage can be analyzed.

[0061]

[0062] ② Based on the Park transformation in synchronous rotating coordinates, the real-time transient voltage values ​​of the measuring point (feed-in point) along the d-axis and q-axis are obtained. The valve-side circuit impedance, i.e., the circuit impedance of each power electronic device connected to the circuit (L), is then superimposed on both the d-axis and q-axis. c With R c The transient voltage components on the circuit are used to obtain the real-time values ​​of the d-axis / q-axis transient voltages on the valve side of the power electronic device, as shown in the following formula. Wherein, ωL·I in the circuit... d ,ωL·I d After vector rotation based on the dq-axis current direction, R is calculated according to the real-time value. c I d With R c I q Similarly, Dynamic sliding window solutions are applied based on the changes in the previous and subsequent values ​​at discrete points. The superposition methods for each transient voltage are as follows: Figure 1 As shown in (b) above. This method mainly addresses the deviation between the valve-side voltage control value and the real-time value during the dq feedforward decoupling control of the converter, because in practice, a PI control loop is used to simulate... There is a significant fluctuation in the control value, especially under unstable conditions, the control value is even less able to reflect the real-time value of the valve side voltage.

[0063] Among them, L c With R c The impedance parameters of each device's valve-side circuit can be obtained by mainly calculating the short-circuit impedance and copper loss resistance of the step-down transformer connected to the circuit of each power electronic device, and by calculating the distributed inductance and resistance according to the length of the connected line.

[0064] The real-time value of the valve side voltage of each power electronic device can be calculated according to the following formula (5). The critical instability state can be determined based on the maximum rated operating range of the voltage.

[0065]

[0066] Among them U cd Let Uc (voltage measurement by power electronic equipment method) be the d-axis component.cq Let q be the q-axis component of Uc. The transient values ​​(d and q real-time values) of the valve-side voltage of the power electronic equipment will be obtained. Then, the square root of the dq component of the valve-side voltage will be calculated in real time to obtain the valve-side voltage Uc of each power electronic equipment. c The real-time value, where the critical range of the valve-side voltage is as follows: Figure 1 As shown in the red circle in (b). Based on the formula for calculating the maximum available valve-side voltage of the converter, the dynamic operating stability of the valve-side voltage is obtained, as shown in the following formula.

[0067]

[0068] The transient operating range and stable operating parameters of the transient voltages on the grid side and valve side are adjusted as follows:

[0069] ①Comprehensive diagnosis of grid-side voltage stability

[0070] The grid-side voltage is dynamically calculated in real time by the acquisition terminal. The stability of the grid-side voltage is comprehensively judged based on the distribution of the grid-side voltage within a time period, namely transient fluctuation and deviation distribution. If the transient fluctuation exceeds the allowable value of the grid-side voltage transient fluctuation, or the deviation distribution exceeds the allowable value of the grid-side voltage deviation distribution, the two instability criteria are logically ORed, and the judgment is made by accumulating the instability judgment time. If the conditions are met, the grid-side voltage is judged to be transiently unstable.

[0071] ②Comprehensive Valve Side Voltage Stability

[0072] The valve-side voltage is dynamically calculated in real-time using a data acquisition terminal. Based on the real-time DC-side voltage of each power electronic device, the maximum usable valve-side voltage for each device is calculated. A typical instability criterion of 0.95 pu is used as a benchmark. This benchmark is compared with the real-time valve-side voltage of each device. If the cumulative sum exceeds 5 times, the device is classified as having a level 2 valve-side voltage instability risk. If the cumulative sum exceeds 0.9 pu, it is compared with the real-time valve-side voltage of each device. If the cumulative sum exceeds 3 times, the device is classified as having a level 1 valve-side voltage instability risk. Both are classified as instability type 1. The critical value for dynamic operational stability instability of the valve-side voltage is set according to the aggregated distribution parameters during normal system operation. If it exceeds the allowable range, it is classified as instability type 2. Instability type 2 and instability type 1 are logically ORed to obtain the operational instability diagnostic index of the valve-side voltage.

[0073] Example 2

[0074] The power grid operation control terminal of this invention includes a data acquisition module, a synchronous phase-locked loop (PLL) calculation module, and a control module. The data acquisition module acquires voltage and current sampling values ​​at measurement points. The PLL calculation module, based on the voltage and current collected at the access nodes (measurement points) of each power electronic device, employs a positive and negative sequence mutually exclusive PLL control technique in a dq rotating coordinate system. For positive sequence PLL, the negative sequence component of the reverse Park transformation is subtracted from the two stationary coordinate systems; for negative sequence PLL, the positive sequence component of the reverse Park transformation is subtracted from the two stationary coordinate systems. This yields the precise transient voltage, frequency, and phase of each measurement point in the power grid system. Specifically, as follows... Figure 2 As shown in the figure. Since the dq component is a DC digital quantity, the phase delay caused by the filtering stage after Clark transform affects the accuracy of the integrated phase. Therefore, the phase delay of the digital filter is obtained through the phase-frequency characteristic curve of the filter, and then the phase is corrected by reverse phase compensation, thereby obtaining accurate phase and frequency data.

[0075] Following the calculation method for transient voltages and performance indicators on both sides of the valve network in Example 1, the dynamic real-time values ​​of the valve-side voltage and the transient values ​​of the grid-side voltage for each power electronic device are analyzed and obtained. Based on the grid-side transient voltage within a period, the transient fluctuation rate and deviation distribution of the grid-side voltage are calculated; based on the valve-side transient voltage within a period, the dynamic operating stability of the valve-side voltage is calculated. The control module performs dynamic reactive voltage support control through the three-layer valve grid connection, and sends calculation commands to each power electronic converter, transformer tap changer, fixed capacitor compensation, and other equipment via fast communication to perform multi-time-scale control coordination, achieving optimal vertical voltage distribution. Simultaneously, when multiple layers of the grid voltage continuously exhibit abnormalities or unresolved risks, the stability control commands are updated through cluster closed-loop regulation until the instability risk is eliminated.

[0076] To address the transient voltage instability risk in power grid systems with multiple power electronic interconnects, the following solutions are proposed:

[0077] ① Transient stability control strategy for grid-side voltage

[0078] Based on the adjustment target of the system's longitudinal transient voltage deviation control, the system leverages the long-term adjustment capabilities of discrete reactive power equipment, the short-term adjustment capabilities of continuous reactive power equipment, and their synergistic effect to achieve optimal transient voltage distribution along the longitudinal axis of the grid system. Discrete reactive power equipment includes on-load tap changers of grid-side step-up transformers, as well as reactive power compensation devices such as fixed capacitor compensation, SVC, or SVG. Continuous reactive power equipment mainly consists of power electronic converters, such as four-quadrant frequency converters and wind power converters, which can dynamically and continuously output reactive power.

[0079] The control terminal controls and regulates the reactive power of the converter, transformer, SVG, and fixed compensator, and coordinates the three strategies. For the converter, it uses remote adjustment signals, such as 104 / Modbus / Goose; for the transformer tap changer, it uses remote control signals, mainly changing the contact position of the transformer tap; for the SVG, it uses remote adjustment signals; and for the fixed capacitor, it uses remote control information. These three functions are all located within the control terminal's control software, which dynamically adjusts the three types of equipment according to the system's operating instructions and fixed adjustment strategies. Vertical consistency balancing is achieved through the cooperation of three modules: tap changer adjustment adjusts the reference voltage range of the access node (measuring point); the compensation equipment adjusts the upward voltage to meet the grid-side voltage compensation requirements; and the reactive power compensation of the power electronic equipment mainly plays a differential supplementary role from the downward direction. For example... Figure 5 As shown in (a) in the figure.

[0080] Layered voltage reactive power coordinated control architecture, such as Figure 4 As shown, when grid-side overvoltage or access-side overvoltage occurs, the transformer tap changes down or the compensation value of the fixed compensation equipment decreases, and the converter adopts a clustered reactive power absorption control mode; when grid-side undervoltage or access-side overvoltage occurs, the transformer tap changes up or the compensation value of the fixed compensation equipment increases, and the converter adopts a clustered reactive power absorption control mode; when grid-side overvoltage or access-side undervoltage occurs, the transformer tap changes down or the compensation value of the fixed compensation equipment decreases, and the converter adopts a clustered reactive power absorption control mode; when grid-side undervoltage or access-side undervoltage occurs, the transformer tap changes up or the fixed compensation value increases, and the converter adopts a clustered reactive power emission control mode.

[0081] This invention proposes a longitudinal consistency principle for addressing longitudinal transient voltage deviation. It coordinates longitudinal reactive power regulation based on the center of gravity and deviation of the longitudinal voltage distribution, according to different operating conditions. 1) When the transient voltage deviation directions on the grid side and the access side are consistent (i.e., both the grid side and the access side are undervoltage or overvoltage), a longitudinal consistency coordination method is adopted. This involves calculating reactive power demand based on the transient voltage deviations on both the grid side and the access side, and allocating it proportionally according to the available reactive power resources on both sides. This achieves a pre-set allocation in the longitudinal direction. Simultaneously, it utilizes fast-timescale reactive power deviation regulation to achieve graded reactive power targets, achieving coordinated coordination of regulation methods at different time scales. Grid-side regulation measures can act as a safety net; when the average deviation of the voltage distribution increases, the reactive power compensation portion of the main voltage is adjusted. If it is impossible to completely address the voltage deviations on both sides, reactive power is allocated according to the proportion of transient voltage deviations on both sides.

[0082] 2) When the transient voltage deviation directions of the grid side and the access side are inconsistent, a fast / slow time scale adjustment coordination strategy is used for longitudinal voltage coordination. That is, one side is undervoltage and the other side is overvoltage, and their adjustment directions are opposite. Adjusting one side will cause the transient voltage of the other side to deteriorate. Therefore, this invention proposes a longitudinal consistency balancing method. Reactive power demand is calculated according to the transient voltage deviation between the grid side and the access side. The actual reactive power demand of the grid side needs to be superimposed with the opposite value of the reactive power demand of the access side. If it exceeds the upper limit of the adjustable reactive power resources of the grid side, the reactive power adjustment command of the grid side and the access side can be recalculated using the upper limit value of the grid side reactive power. However, there may be problems with suboptimal distribution. Therefore, this invention proposes to use the difference between the voltage limit exceedance value and the voltage dead zone on the valve side, and the difference between the voltage limit exceedance value and the voltage dead zone on the access side as a ratio. Combined with the voltage-reactive power calculation formula, the reactive power adjustment command of each side is calculated according to the balancing ratio of the grid side and the access side, respectively, to achieve optimal voltage distribution in the longitudinal direction.

[0083] ② Dynamic stability control strategy for valve-side voltage

[0084] When the risk of dynamic instability of the valve-side voltage occurs, the reactive power regulation function of the power electronic equipment cluster and the virtual negative impedance control technology are used to achieve dynamic stability of the control voltage of the power electronic equipment, such as... Figure 5 As shown in (b) of the diagram.

[0085] 1) Reactive power cluster control mode. Based on the degree of over-limit of the power electronic equipment whose valve-side voltage exceeds the limit, and according to the mitigation level (typically 0.8), divided by the impedance of the access circuit, a reactive current command (absorbing reactive power, Iq is negative) is obtained. This causes the combined valve-side control voltage of the converter after vector superposition of circuit voltages to decrease. On the other hand, by utilizing the clustered reactive power regulation effect of multiple power electronic equipment, according to the reactive voltage control quantity calculation formula, the overall level of the measuring point voltage Ug decreases. This further reduces the valve-side voltage of the converter with over-limit valve-side voltage, thereby preventing the regulation from exceeding the limit and restoring the valve-side voltage of the unstable converter to within the usable range. Figure 7 This is the regulation-valve-side power generation utilization curve of the grid parallel system described in this invention.

[0086] 2) Virtual negative impedance control method. Due to the decrease in Iq (I... q -ΔI q ), making jωL c I q The vector components decrease, but bring about Therefore, the valve-side voltage of an over-limit converter may not decrease to the stable operating range. Therefore, this invention proposes to use a virtual complex impedance to effectively reduce Lc, thereby lowering the valve-side voltage control value. Specifically, a negative inductance component is introduced through the inner current loop of the power electronic equipment. The target current control value is obtained by dividing the voltage difference between the converter valve-side control voltage and the actual value by this component. After the initial closed loop of the reactive current outer loop, the output voltage of the PT controller in the inner current loop can be changed through this negative inductance current control section, thereby changing the control value of the valve-side voltage. Figure 5 As shown in (b) in the figure. This method can be achieved by modifying the inverter control algorithm, and can utilize the fast communication of the control terminal to perform local on-loop control of each inverter.

[0087] Example 3

[0088] The grid multi-power electronic equipment network operation control system of the present invention has the following architecture: Figure 3 As shown, it includes a power grid network operation monitoring system and a power grid operation control terminal. By installing the power grid operation control terminal near the connection point of the power electronic equipment in the power grid, the voltage and current at the port machinery connection point are sampled and transiently calculated, and the transient voltage and current at the measurement point based on synchronous rotating coordinates are analyzed in real time. This control system can be used in applications such as... Figure 6 The typical architecture of the power grid networking system shown is as follows.

[0089] The power grid operation control terminal, following the calculation method for transient voltages and performance indicators on both sides of the grid as given in Example 1, analyzes and obtains the dynamic real-time values ​​of the valve-side voltage and the transient values ​​of the grid-side voltage for each power electronic device. Based on the valve-side voltage transient values, the dynamic stability of the power electronic devices is determined; based on the grid-side voltage transient values, the transient volatility and deviation distribution of the grid-side voltage are determined. The control terminal transmits the three-layer longitudinal transient voltage data and analysis conclusions to the power grid network operation control system via the 104 / GOOSE fast communication network. This yields the transient voltage change curves and key indicator monitoring status of the power grid network operation system. When the monitoring curves in the system show risks such as approaching limits, an early warning is issued. Dispatchers can issue stable control values ​​through preset measures and setpoints, and rapidly adjust the power commands of the power electronic devices via fast communication to preemptively or prevent transient instability of the system and equipment.

Claims

1. A method for online monitoring of the stability of a power grid network consisting of multiple power electronic devices, characterized in that, include: Based on the voltage and current sampling values ​​at the measuring points, the transient voltage on the grid side and the transient voltage on the valve side are obtained through a transient voltage instability model. Based on the grid-side transient voltage within a period, the transient volatility and deviation distribution of the grid-side voltage are calculated. Based on the valve-side transient voltage within a period, the dynamic stability of the valve-side voltage is calculated. Based on the transient volatility and deviation distribution of the grid-side voltage, it is determined whether instability exists on the grid side. Based on the dynamic stability of the valve-side voltage, it is determined whether instability exists on the valve side. The transient voltage instability model includes: based on the d-axis and q-axis components of the voltage at the measuring point, and the d-axis and q-axis components of the upward grid-connected line current at the measuring point, the d-axis voltage drop of the grid-side bus circuit impedance is superimposed on the d-axis voltage component, and the q-axis voltage drop of the grid-side bus circuit impedance is superimposed on the q-axis voltage component, and then the grid-side transient voltage is calculated by vector superposition; the current of the upward grid-connected line is the sum of the currents of each branch between the measuring point and the valve side; Based on the d-axis and q-axis components of the voltage at the measuring point and the d-axis and q-axis components of the current at the measuring point, the d-axis voltage drop of the valve-side circuit impedance is superimposed on the d-axis voltage component, and the q-axis voltage drop of the valve-side circuit impedance is superimposed on the q-axis voltage component. Then, the transient voltage on the valve side is calculated by vector superposition.

2. The online monitoring method for the stability of a power grid multi-power electronic equipment network according to claim 1, characterized in that, Determining whether grid-side instability exists based on the transient volatility and deviation distribution of grid-side voltage includes: if the transient volatility exceeds the allowable value of grid-side voltage transient volatility, or the deviation distribution exceeds the allowable value of grid-side voltage deviation distribution, the two instability criteria are logically ORed, and the determination is made by accumulating the instability determination time. If the conditions are met, it is determined that the grid-side voltage is transiently unstable. Determining whether valve-side voltage instability exists based on dynamic operational stability includes: setting a first instability criterion value for judgment; if the number of times the accumulated valve-side transient voltage exceeds the first instability criterion value is greater than a first threshold, it is judged as valve-side voltage instability risk level one; setting a second instability criterion value for judgment; if the number of times the accumulated valve-side transient voltage exceeds the second instability criterion value is greater than a second threshold, it is judged as valve-side voltage instability risk level two; both valve-side voltage instability risk level one and level two are judged as instability type 1; the instability threshold value of the dynamic operational stability of valve-side voltage is adjusted according to the aggregated distribution parameters during normal system operation; if it exceeds the allowable range, it is judged as instability type 2; instability type 2 and instability type 1 are logically ORed to obtain the operational instability diagnostic index of valve-side voltage.

3. The online monitoring method for the stability of a power grid multi-power electronic equipment network according to claim 1, characterized in that: The formula for calculating grid-side transient voltage is: ； In the formula, U grid U is the grid-side transient voltage. grid_d U grid_q These are the dq-axis components of the grid-side transient voltage, respectively. , These are the transient components of the voltage at the measuring point along the dq axis, I. d I q These represent the transient components of the current along the dq axis at each measuring point, R. s L s These are the resistance and inductance parameters of the grid-side bus circuit impedance, respectively, where ω is the frequency and t is the time. The formula for calculating the transient voltage on the valve side is: ； In the formula, U c U is the valve-side transient voltage. cd U cq These are the dq-axis components of the valve-side transient voltage, R. c L c These are the resistance and inductance parameters of the valve-side circuit impedance, respectively.

4. The online monitoring method for the stability of a power grid multi-power electronic equipment network according to claim 1, characterized in that: The formula for calculating the transient fluctuation rate of grid-side voltage is: ； In the formula, U represents the transient fluctuation of the grid-side voltage. grid_MAX U grid_MIN These represent the maximum and minimum values ​​of the grid-side transient voltage, respectively.

5. The online monitoring method for the stability of a power grid multi-power electronic equipment network according to claim 1, characterized in that: The formula for calculating the deviation distribution of grid-side voltage is: ； In the formula, The deviation distribution of grid-side voltage, For dead zone, U is the rated voltage value. grid For grid-side transient voltage, s N s F These represent the number of times the grid-side transient voltage falls within the dead zone range and the number of times it falls outside the dead zone range, respectively. The formula for calculating the dynamic operating stability of the valve-side voltage is: ； In the formula, For the dynamic operating stability of the valve-side voltage, U is the maximum available valve-side voltage of the converter. dc M represents the real-time DC-side voltage value of each power electronic device. MAX U is the modulation coefficient. c T is the valve-side transient voltage, δ is the instability criterion setting, and T is the voltage across the valve side. N T F These represent the number of times the transient voltage on the valve side is normal and the number of times it is unstable, respectively.

6. A power grid operation control terminal, characterized in that, include: The acquisition module is used to obtain the voltage and current sample values ​​at the measurement points; The synchronous phase-locked loop (PLL) calculation module is used to obtain frequency and phase through the PLL, and to obtain the grid-side transient voltage and valve-side transient voltage based on the voltage and current sampling values ​​at the measurement points through a transient voltage instability model. Based on the grid-side transient voltage within a period, it calculates the transient fluctuation rate and deviation distribution of the grid-side voltage; based on the valve-side transient voltage within a period, it calculates the dynamic operating stability of the valve-side voltage; and based on the dynamic operating stability of the valve-side voltage, it determines whether instability exists on the valve side. The control module is used to receive system control commands and dynamically adjust the power electronic equipment according to the valve-side voltage dynamic stabilization control strategy. The transient voltage instability model includes: based on the d-axis and q-axis components of the voltage at the measuring point, and the d-axis and q-axis components of the upward grid-connected line current at the measuring point, the d-axis voltage drop of the grid-side bus circuit impedance is superimposed on the d-axis voltage component, and the q-axis voltage drop of the grid-side bus circuit impedance is superimposed on the q-axis voltage component, and then the grid-side transient voltage is calculated by vector superposition; the current of the upward grid-connected line is the sum of the currents of each branch between the measuring point and the valve side; Based on the d-axis and q-axis components of the voltage at the measuring point and the d-axis and q-axis components of the current at the measuring point, the d-axis voltage drop of the valve-side circuit impedance is superimposed on the d-axis voltage component, and the q-axis voltage drop of the valve-side circuit impedance is superimposed on the q-axis voltage component. Then, the transient voltage on the valve side is calculated by vector superposition.

7. The power grid operation control terminal according to claim 6, characterized in that, The valve-side voltage dynamic stability control strategy includes: reactive power cluster control mode and virtual negative impedance control mode; The aforementioned reactive power cluster control method, based on the degree of over-limit of the power electronic equipment whose valve-side voltage exceeds the limit, and according to the governance target, divides by the access circuit impedance to obtain the reactive current command; on the other hand, through the cluster reactive power regulation effect of several power electronic equipment, the overall voltage level of the measuring point is reduced, and the valve-side voltage of the converter whose valve-side voltage exceeds the limit is further reduced. The virtual negative impedance control method reduces the valve-side voltage control value by using virtual complex impedance. A negative inductance component is introduced through the current inner loop of the power electronic device. The target current control value is obtained by dividing the voltage difference between the converter valve-side control voltage and the valve-side transient voltage by the negative inductance component. The output voltage of the PT controller in the current inner loop is changed by the negative inductance current control part, thereby changing the valve-side voltage control value.

8. A method for online control of the stability of a power grid with multiple power electronic devices, characterized in that: According to the online monitoring method for the stability of a multi-power electronic equipment network in a power grid as described in claim 1, the transient voltage on the grid side and the transient voltage on the valve side are obtained, and the deviation between the transient voltage on the grid side and the access side is calculated. When the transient voltage deviation directions of the grid side and the access side are consistent, the reactive power demand on both sides is calculated based on the transient voltage deviation between the grid side and the access side, and the reactive power adjustable resources on both sides are allocated according to the reactive power demand ratio. When the transient voltage deviation directions of the grid side and the access side are inconsistent, the reactive power demand on both sides is calculated according to the transient voltage deviation between the grid side and the access side. The actual reactive power demand on the grid side is calculated as the reactive power demand on the grid side plus the reactive power demand on the access side in the opposite direction. If the actual reactive power demand on the grid side exceeds the upper limit of the adjustable reactive power resources on the grid side, the difference between the voltage limit exceedance value on the valve side and the voltage dead zone, and the difference between the voltage limit exceedance value on the access side and the voltage dead zone are used as the balancing ratio. The reactive power adjustment command on both sides is calculated according to the balancing ratio.

9. The online control method for the stability of a power grid multi-power electronic equipment network according to claim 8, characterized in that: When the transient voltage deviation directions of the grid side and the access side are consistent, when the average deviation of the voltage distribution increases, the allocation ratio is adjusted to prioritize the side with the larger deviation. When it is impossible to simultaneously address the voltage deviation on both sides, reactive power is allocated according to the ratio of the transient voltage deviation on both sides. This method also employs multi-timescale collaborative control to achieve graded reactive power targets. The multi-timescale includes minute-level, hour-level, and day-level timescales.

10. A grid-connected operation control system for multiple power electronic devices in a power grid, characterized in that: The system includes a power grid multi-power electronic device network operation monitoring system and a power grid operation control terminal. The power grid operation control terminal transmits transient voltage data and analysis conclusions from the grid side and valve side to the power grid multi-power electronic device network operation monitoring system via a communication network. The power grid multi-power electronic device network operation monitoring system is used to determine whether there is instability on the grid side based on the transient fluctuation rate and deviation distribution of the grid side voltage. When an over-limit risk occurs, an alarm is issued. According to the online control method for the stability of the power grid multi-power electronic device network as described in claim 8, the system calculates the power electronic device power command and sends it to the power grid operation control terminal for execution.

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