Active non-disturbance closing method for interconnecting substations using flexible power electronic switches

Abstract

The invention discloses an active non-disturbance closing method for a transformer substation interconnected by a flexible power electronic switch. A circuit breaker is installed between a main transformer 1 and a busbar I, and between a main transformer 2 and a busbar II, respectively. The main transformer 1 and the main transformer 2 are interconnected by a flexible interconnection device to form a closed-loop operation. When any main transformer is overhauled and decommissioned, the power at the decommissioned main transformer end is gradually transferred to another main transformer by the active regulation capability of the flexible interconnection device. When the current on the decommissioned main transformer side approaches zero, the circuit breaker is disconnected to decommission the main transformer. When the main transformer changes from decommissioning to commissioning, the voltage amplitude, frequency and phase at both ends of the circuit breaker of the main transformer on the commissioning side are collected. When the voltage amplitude, frequency and phase values ​​remain consistent, the circuit breaker is closed to successfully commission. Then, the active power flow regulation capability of the flexible interconnection device is used to gradually increase the load power of the commissioned main transformer from zero load, thereby realizing active non-disturbance closing of the flexible interconnection transformer substation. The service life of the circuit breaker and the stability of the system are improved.

Description

Technical Field

[0001] The invention belongs to the field of power system control, and in particular relates to an active non-disturbance closing method for interconnecting substations using flexible power electronic switches. Background Art

[0002] With the continuous expansion of the scale of power systems and the gradual improvement of power quality requirements on the demand side, the disadvantages of traditional substations have gradually emerged. For example, they have strong coupling and local faults occur from time to time. In addition, the operation mode and control mode of traditional substations are relatively simple and passive, and cannot meet the flexible operation requirements. The penetration rate of flexible loads and DG in the power grid is gradually increasing, and their positions in the power grid are relatively concentrated and dense. These problems seriously affect the stability and economy of substations. To solve these problems, advanced power electronic devices are invested in traditional power systems to flexibly interconnect multiple feeders and realize closed-loop operation in a true sense. The flexible interconnection device consists of two back-to-back hybrid submodules MMC. Embedding flexible interconnection devices in substations can make substations have the characteristics of active control, and can more actively coordinate flexible interconnection devices in the power grid. This can provide convenient conditions for the access of DG and meet the high-demand load power supply needs. It can adjust active power and reactive power, improve power flow, and respond quickly and controllably. It can meet users' high demands for power quality and largely make up for the shortcomings of traditional substations. The integration of large-scale power electronic equipment makes the power system exhibit the characteristics of low damping and low inertia, which has an adverse impact on the safe and stable operation of the power system, resulting in increasingly serious stability problems in the power system. Summary of the invention

[0003] The technical problem to be solved by the present invention is: to provide an active undisturbed closing method for interconnecting substations using flexible power electronic switches, so as to solve the technical problem that the integration of large-scale power electronic equipment in the prior art makes the power system present the characteristics of low damping and low inertia, which has an adverse effect on the safe and stable operation of the power system, resulting in increasingly serious stability problems of the power system.

[0004] The technical solution of the present invention is:

[0005] An active non-disturbance closing method for interconnecting substations using flexible power electronic switches, wherein a circuit breaker is installed between a main transformer 1 and a busbar I, and between a main transformer 2 and a busbar II, and a contact switch is connected between the main transformer 1 and the main transformer 2; the main transformer 1 and the main transformer 2 are interconnected through a flexible interconnection device to form a closed-loop operation; when any main transformer is overhauled and decommissioned, the power at the decommissioned main transformer end is gradually transferred to another main transformer through the active regulation capability of the flexible interconnection device, until the current on the decommissioned main transformer side approaches zero, and the circuit breaker is disconnected to decommission the main transformer; when the main transformer changes from decommissioning to commissioning, the voltage amplitude, frequency and phase at both ends of the circuit breaker of the main transformer on the commissioning side are collected; when the voltage amplitude, frequency and phase values ​​at both ends of the circuit breaker are consistent, the circuit breaker is closed to successfully commission, and then the active power flow regulation capability of the flexible interconnection device is used to gradually increase the load power of the commissioned main transformer from zero load, thereby realizing active non-disturbance closing of the flexible interconnected substation.

[0006] When the main transformer is out of service for maintenance, the current on one side of the main transformer is first transformed into the dq coordinate to obtain the current command i d * and i q * And send it to the outer loop of the dual-loop control as input; then make the current reference value of the outer loop and The output of the outer loop is obtained and sent to the current inner loop; finally, the modulation signal is synthesized to control the output of the converter so that the load power at one end of the main transformer is gradually transferred to the other end of the main transformer, until the current on one side of the main transformer is close to zero and the circuit breaker disconnects the main transformer and it is decommissioned.

[0007] The control methods adopted by the two MMC converters in the flexible interconnection device when the substation is put into operation are as follows: MMC1 adopts current inner loop control and VSG control, and MMC2 adopts PV droop control and constant reactive power control; the current on the main transformer side is converted into dq to obtain the current command i d * and i q * And send it to the outer loop of the dual-loop control as input; then make the current reference value of the outer loop and The output of the outer loop is obtained and sent to the current inner loop; the inner loop control realizes fast tracking of the dq axis voltage and current according to the current reference instruction, and uses a phase-locked loop to track the input signal frequency through the output signal frequency to provide a phase signal, and then through dq coordinate transformation, the NLM modulation method is adopted to control the number of sub-modules put into the upper and lower bridge arms to make the converter output voltage change with the change of the sinusoidal modulation wave to approach the modulation wave; finally, the on and off of the switch in the MMC is controlled to control the output of the converter.

[0008] VSG control methods include:

[0009] The main circuit of the MMC converter is equivalent to the electrical part of the synchronous generator. The VSG control is applied to the MMC converter based on the regulation principle of the synchronous generator to simulate the damping characteristics and primary frequency and voltage regulation characteristics of the synchronous generator. The conventional inverter is controlled as a virtual synchronous generator by adding the VSG control strategy. The VSG controller includes a virtual speed regulator controller and a virtual exciter controller. The VSG virtual inertia link is used to simulate the inherent rotational inertia of the synchronous generator rotor to suppress frequency fluctuations.

[0010] The modeling of the mechanical part of VSG reflects the virtual inertia and damping characteristics of VSG, which is realized through the rotor motion equation. The expression is as follows:

[0011]

[0012] Where: J is the rotor moment of inertia; D is the damping coefficient; ω, ω ref are the actual angular velocity and rated angular velocity of VSG respectively; T m and T e are mechanical torque and electromagnetic torque respectively;

[0013] The primary voltage regulation characteristics of the VSG excitation regulator have the following relationship:

[0014]

[0015] Where: Q set and Q e Respectively represent the reactive power set value and actual measured value of VSG; K u Represents the reactive power-voltage droop coefficient.

[0016] When the main transformer changes from decommissioning to operation, pre-synchronization control is added to the VSG control.

[0017] Pre-synchronization control specifically includes: collecting the voltage amplitude E on the main transformer side g The difference between the current output voltage U0 controlled by VSG is sent to the PI controller; then the output E controlled by PI is syn As a correction value, the output voltage amplitude of VSG is corrected; when the main transformer voltage E g When it is greater than the output voltage U0 of the virtual synchronous generator, the input of the PI controller is positive, and the output voltage of the VSG increases until the deviation between the two is 0, and the PI controller enters a steady-state operation state; similarly, when E g When it is less than U0, the input of the PI controller is negative, and the output voltage amplitude of VSG decreases until E syn =0.

[0018] The beneficial effects of the present invention are:

[0019] The substation of the present invention uses a flexible interconnection device to flexibly interconnect the main transformer 1 and the main transformer 2. When the main transformer 1 is overhauled and decommissioned, the power at one end of the main transformer is gradually transferred to the second end of the main transformer through the active allocation capability of the flexible interconnection device, until the current on one side of the main transformer is close to zero, and the circuit breaker K101 is disconnected to decommission the main transformer 1. When the main transformer 1 changes from decommissioning to commissioning, it is necessary to collect the voltage amplitude, frequency and phase at both ends of the circuit breaker of the main transformer 1. When the voltage amplitude, frequency and phase values ​​at both ends of the circuit breaker are basically consistent, the circuit breaker is closed and the commissioning is successful, and then the active flow control capability of the flexible interconnection device is used to gradually increase the load power of the main transformer 1 from zero load, thereby realizing the active worry-free closing of the flexible interconnection substation. The active non-disturbance closing technology reduces the damage to the circuit breaker and the impact on the stability of the system caused by the circuit breaker opening and closing, and improves the service life of the circuit breaker and the stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The flexible interconnected substation topology structure of the present invention;

[0021] Figure 2 This is a control block diagram of the active worry-free loop closing technology of the flexible interconnected substation of the present invention;

[0022] Figure 3 This is a double-loop control block diagram of the present invention;

[0023] Figure 4 Make a block diagram for VSG of the present invention;

[0024] Figure 5 This is a control block diagram of the pre-synchronization process based on VSG of the present invention;

[0025] Figure 6 This is a control flow chart of the main transformer 1 of the present invention when it changes from commissioning to decommissioning;

[0026] Figure 7 This is a control flow chart of the active loop closing technology when the main transformer 2 of the present invention changes from decommissioning to operation. DETAILED DESCRIPTION

[0027] An active worry-free loop closing method for interconnecting substations using flexible power electronic switches, the method comprising:

[0028] A circuit breaker K101 is installed between the main transformer 1 and the 10KV busbar I, and a circuit breaker K102 is installed between the main transformer 2 and the 10KV busbar II. A flexible interconnection device is embedded between the main transformer 1 and the main transformer 2 to flexibly interconnect the main transformer 1 and the main transformer 2. A contact switch is connected between the main transformer 1 and the main transformer 2, and the contact switch is disconnected most of the time. The corresponding loads and distributed energy (DG) are connected to the 10KV busbar I and the 10KV busbar II respectively, and the VSG control and dual-loop control are designed to act on the two operating modes of the substation decommissioning and commissioning respectively, completing the active non-disturbance closing technology of the flexible interconnected substation. The wiring method is as follows Figure 1 As shown. The MMCs in the flexible interconnection device are named MMC1 and MMC2, MMC1 is the rectifier station converter, and MMC2 is the inverter station converter. VSG control technology can be applied to both the rectifier station control and the inverter station control. In both cases, the MMC converter can simulate the external characteristics of SG. Main transformer 1 and main transformer 2 are interconnected through a back-to-back flexible interconnection device to form a closed-loop operation. The MMC converter can actively cooperate with the external AC system to maintain the stability of the entire system. When any main transformer is overhauled and decommissioned, the active regulation capability of the flexible interconnection device is used to gradually transfer the power of the decommissioned main transformer to another main transformer until the current on the decommissioned main transformer side is close to zero, and the circuit breaker is disconnected to decommission the main transformer. When the main transformer is decommissioned to operation, it is necessary to collect the voltage amplitude, frequency and phase at both ends of the circuit breaker of the main transformer on the operation side. When the voltage amplitude, frequency and phase values ​​at both ends of the circuit breaker are basically consistent, the circuit breaker is closed and put into operation successfully. Then, the active power flow control capability of the flexible interconnection equipment is used to gradually increase the load power of the main transformer from zero load, realizing the active and worry-free closing of the flexible interconnection substation.

[0029] When the main transformer is out of service for maintenance, the current on one side of the main transformer is first transformed into the dq coordinate to obtain the current command i d * and i q * And send it to the outer loop of the dual-loop control as input; then make the current reference value of the outer loop and The output of the outer loop is obtained and sent to the current inner loop. Finally, the modulation signal is synthesized to control the output of the converter so that the load power at one end of the main transformer is gradually transferred to the other end of the main transformer until the current on one side of the main transformer is close to zero, and the circuit breaker disconnects the main transformer and retires. The two MMC converters in the flexible interconnection device adopt different control strategies when the substation is put into operation. MMC1 adopts current inner loop control and VSG control, and MMC2 adopts PV droop control and constant reactive power control. The current on one side of the main transformer is transformed into dq to obtain the current command i d * and i q *And send it to the outer loop of the dual-loop control as input; then make the current reference value of the outer loop and The output of the outer loop is obtained and sent to the current inner loop. The inner loop control realizes fast tracking of dq axis voltage and current according to the current reference instruction. The phase-locked loop can provide a phase signal by tracking the input signal frequency through the output signal frequency, and then through the dq coordinate transformation, the NLM modulation method is adopted, which controls the number of sub-modules put into the upper and lower bridge arms to make the output voltage of the converter follow the change of the sinusoidal modulation wave to approach the modulation wave. Finally, the on and off of the switch in the MMC is controlled to control the output of the converter. The control block diagram is shown as follows Figure 3 As shown. Main transformer 1 is decommissioned for maintenance. In order to maintain the normal operation of the load on the main transformer side, the MMC increases or decreases its output active power and reactive power accordingly according to the droop curve. The increased or decreased power is absorbed by main transformer 2 according to the control strategy. Although there may be a large power jump when the circuit breaker is disconnected, the VSG has a virtual inertia link that can simulate the inherent rotational inertia of the synchronous generator rotor to suppress frequency fluctuations, thereby ensuring a smooth transition of the switching process. The control block diagram of the VSG is shown in Figure 4 shown.

[0030] When the main transformer 1 can be put into operation after the overhaul is completed, the main transformer 1 must be put into operation from the decommissioning mode. It is necessary to collect the voltage amplitude, frequency and phase at both ends of the circuit breaker K101 on the main transformer side. When the flexible interconnection device MMC switches from the decommissioning operation mode to the commissioning operation mode, the voltage and frequency at both ends of the circuit breaker are different. Directly closing the switch will cause a large impact current. To achieve a smooth switch from decommissioning to commissioning mode, it is necessary to add a pre-synchronization control strategy to the VSG control to achieve tracking of the grid voltage and frequency. When the voltage amplitude, frequency and phase values ​​at both ends of the circuit breaker K101 are synchronized, the circuit breaker is closed and the operation is successful. The pre-synchronization control block diagram is as follows Figure 5 shown.

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] The purpose of the present invention is to provide an active worry-free loop closing technology for interconnecting substations using flexible power electronic switches, reducing the impact of flexible interconnected substations on circuit breaker damage and system stability during commissioning and decommissioning switching. The flexible interconnection equipment can realize flexible interconnection of two substations. Applying VSG control and dual-loop control to MMC converters can realize smooth switching of substation commissioning and decommissioning, reducing the impact on circuit breakers and systems.

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] Figure 1 It is a flexible interconnected substation topology structure. The main transformer 1 and the 10KV bus I are connected by a circuit breaker K101, which is used for the commissioning and decommissioning of the main transformer 1. The main transformer 2 and the 10KV bus II are connected by a circuit breaker K102, which is used for the commissioning and decommissioning of the main transformer 2. The main transformer 1 and the main transformer 2 carry different types of loads and distributed power sources (DG), respectively, and are interconnected by flexible interconnection equipment. MMC1 is a rectifier station converter, and MMC2 is an inverter station converter. The present invention is a new function and new technology expanded beyond the commonly used functions. It uses the flexible interconnection (i.e., SNOP) formed by advanced power electronics technology to improve the controllability of the power grid system, and improve the overall power transfer capacity and power supply reliability. Flexible interconnection has the outstanding advantage of power mutual assistance, can realize the active distribution of loads by substations, has a relatively complete observable and controllable level, and a flexibly adjustable network topology.

[0035] Figure 2 This is a control block diagram of the active worry-free closing technology of the flexible interconnected substation of the present invention. The control based on the VSG flexible interconnected substation mainly includes VSG control, voltage synthesis and nearest level approach (NLM) modulation. The voltage, current and other information on the main transformer side are collected and the active power and reactive power are calculated. The power calculation value is brought into the VSG control and dual-loop control to obtain the output voltage reference amplitude and phase of the system. The two are synthesized into an output voltage, and then the switch trigger signal of the MMC converter is obtained through NLM modulation, and finally the output of the MMC converter is controlled.

[0036] Figure 3 The dual-loop control block diagram of the present invention, the MMC controller is mainly divided into a power outer loop controller and a voltage and current inner loop controller. The outer loop controller collects the current on one side of the main transformer, first performs a dq coordinate transformation to obtain the current command i d * and i q * , and then let the current reference value of the outer loop and The output of the outer loop is obtained and sent to the current inner loop. After adjustment by the PI link, the current reference instruction i is obtained. dref and i qref The inner loop tracks the voltage and current based on the current reference value provided by the outer loop, and finally synthesizes the modulation signal to control the output of the converter. Through this vector control method, active control and reactive control can be decoupled from each other to achieve their independent control, and different controls can be formed according to the different input and reference quantities of the outer loop.

[0037] Figure 4 This is the VSG control block diagram of the present invention. The main circuit of the MMC converter can be equivalent to the electrical part of the synchronous generator. Drawing on the regulation principle of the synchronous generator, the VSG control can be applied to the MMC converter to realize the simulation of the damping characteristics and primary frequency and voltage regulation characteristics of the synchronous generator. By adding the VSG control strategy, the conventional inverter is controlled as a virtual synchronous generator. Its VSG controller mainly includes a virtual speed regulator controller and a virtual exciter controller. VSG technology can overcome the shortcomings of low inertia and no damping of power electronic equipment. When the main transformer is overhauled and decommissioned, the active power may jump greatly at the moment the circuit breaker is disconnected. However, VSG has a virtual inertia link, which can simulate the inherent rotational inertia of the synchronous generator rotor to suppress frequency fluctuations, thereby ensuring a smooth transition of the switching process.

[0038] The modeling of the mechanical part of VSG should reflect the virtual inertia and damping characteristics of VSG. This can be achieved by using the rotor motion equation, which is expressed as follows:

[0039]

[0040] Where: J is the rotor moment of inertia; D is the damping coefficient; ω, ω ref are the actual angular velocity and rated angular velocity of VSG respectively; T m and T e They are mechanical torque and electromagnetic torque respectively.

[0041] The primary voltage regulation characteristics of the VSG excitation regulator have the following relationship:

[0042]

[0043] Where: Q set and Q e Respectively represent the reactive power set value and actual measured value of VSG; K u Represents the reactive power-voltage droop coefficient.

[0044] Figure 5This is the pre-synchronization processing control block diagram based on VSG of the present invention. When the main transformer needs to be switched from the decommissioning operation mode to the commissioning operation mode after the maintenance is completed, the voltage and frequency at both ends of the circuit breaker are different. Direct closing will cause a large impact current. Pre-synchronization control is added to the VSG control to achieve tracking of the grid voltage and frequency. When the voltage amplitude, frequency and phase values ​​at both ends of the circuit breaker are synchronized, the circuit breaker is closed and put into operation successfully.

[0045] Figure 6 This is a control flow chart of the main transformer 1 of the present invention when it changes from commissioning to decommissioning, including the following steps:

[0046] Step 601: When the main transformer 1 switches from operation to de-operation;

[0047] Step 602: Collect the current i on the main transformer side abc ;

[0048] Step 603: i abc Perform dq coordinate changes to obtain the input signal of the outer loop and

[0049] Step 604: Set the current reference value of the outer loop and

[0050] Step 605: The output of the outer loop is brought into the current inner loop, and the NLM modulates and controls the switch opening and closing in the MMC to control the output of the converter;

[0051] Step 606: gradually transfer the load power of the main transformer 1 to the main transformer 2;

[0052] Step 607: When it is detected that the current on the main transformer side is close to zero;

[0053] Step 608: Open the circuit breaker K101;

[0054] Step 609: The return of the main transformer 1 is completed;

[0055] Figure 7 This is a control flow chart of the active loop closing technology when the main transformer 1 is switched from decommissioning to commissioning, including the following steps:

[0056] Step 701: When the main transformer 1 switches from decommissioning to commissioning;

[0057] Step 702: collecting the voltage amplitude, phase, and frequency on both sides of the circuit breaker K101;

[0058] Step 703: pre-synchronization unit control;

[0059] Step 704: superimposing the deviation signal on the active loop and reactive loop controlled by the VSG respectively;

[0060] Step 705: quickly tracking the voltage, phase, and frequency of the main transformer 1;

[0061] Step 706: When the voltage amplitude, phase and frequency on both sides of the circuit breaker K101 are substantially consistent;

[0062] Step 707: closing the circuit breaker K101;

[0063] Step 708: The main transformer 1 is put into operation;

[0064] Step 709: The flexible interconnection device actively performs power flow control;

[0065] Step 710: gradually increasing the load of the main transformer 1 until the current on one side of the main transformer returns to normal;

[0066] The logic of the pre-synchronization control process described in step 703 is as follows:

[0067] (1) After receiving the main transformer 1 commissioning command, the main transformer 1 voltage is used as the reference value of the controller to continuously adjust the output so that the voltage amplitude, phase and frequency on both sides of the circuit breaker K101 are synchronized.

[0068] (2) After the commissioning conditions are met, the circuit breaker K101 is closed and the controller performs a rapid mode switch.

[0069] The voltage tracking operation process of pre-synchronization control is as follows:

[0070] like Figure 5 As shown, the voltage amplitude E on the main transformer side is collected g The difference between the current output voltage U0 controlled by VSG is sent to the PI controller; then the output E controlled by PI is syn As a correction value, the output voltage amplitude of the VSG is corrected. g When it is greater than the output voltage U0 of the virtual synchronous generator, the input of the PI controller is positive, and the output voltage of the VSG increases until the deviation between the two is 0, and the PI controller enters a steady-state operation state. g When it is less than U0, the input of the PI controller is negative, and the output voltage amplitude of VSG decreases until E syn = 0. Phase and frequency are similar to voltage.

Claims

1. An active non-disruptive closing method for interconnecting substations using flexible power electronic switches, characterized in that: A circuit breaker is installed between the main transformer 1 and busbar I, and between the main transformer 2 and busbar II, and a contact switch is connected between the main transformer 1 and the main transformer 2; the main transformer 1 and the main transformer 2 are interconnected through a flexible interconnection device to form a closed-loop operation. When any main transformer is overhauled and decommissioned, the power at the decommissioned main transformer end is gradually transferred to another main transformer through the active regulation capability of the flexible interconnection device, until the current on the decommissioned main transformer side is close to zero, and the circuit breaker is disconnected to decommission the main transformer; when the main transformer changes from decommissioning to commissioning, the voltage amplitude, frequency and phase at both ends of the circuit breaker of the main transformer on the commissioning side are collected; when the voltage amplitude, frequency and phase values ​​at both ends of the circuit breaker are consistent, the circuit breaker is closed to successfully commission, and then the active power flow regulation capability of the flexible interconnection device is used to gradually increase the load power of the commissioned main transformer from zero load, so as to realize the active worry-free closing of the flexible interconnection substation; When the main transformer is out of service for maintenance, the current on one side of the main transformer is first transformed into the dq coordinate to obtain the current command i d * and i q * And send it to the outer loop of the dual-loop control as input; then make the current reference value of the outer loop and The output of the outer loop is obtained and sent to the current inner loop; finally, the modulation signal is synthesized to control the output of the converter so that the load power at one end of the main transformer is gradually transferred to the other end of the main transformer until the current on one side of the main transformer is close to zero, and the circuit breaker disconnects the main transformer and the transformer is decommissioned; the control method adopted by the two MMC converters in the flexible interconnection device when the substation is put into operation is: MMC1 adopts current inner loop control and VSG control, and MMC2 adopts PV droop control and fixed reactive power control; the current on one side of the main transformer is converted into dq to obtain the current instruction i d * and i q * And send it to the outer loop of the dual-loop control as input; then make the current reference value of the outer loop and The output of the outer loop is obtained and sent to the current inner loop; the inner loop control realizes fast tracking of the dq axis voltage and current according to the current reference instruction, and uses a phase-locked loop to track the input signal frequency through the output signal frequency to provide a phase signal, and then through dq coordinate transformation, the NLM modulation method is adopted to control the number of sub-modules put into the upper and lower bridge arms to make the converter output voltage change with the change of the sinusoidal modulation wave to approach the modulation wave; finally, the on and off of the switch in the MMC is controlled to control the output of the converter.

2. According to claim 1, an active non-disturbance closing method for interconnecting substations using flexible power electronic switches is characterized by: VSG control methods include: The main circuit of the MMC converter is equivalent to the electrical part of the synchronous generator. The VSG control is applied to the MMC converter based on the regulation principle of the synchronous generator to simulate the damping characteristics and primary frequency and voltage regulation characteristics of the synchronous generator. The conventional inverter is controlled as a virtual synchronous generator by adding the VSG control strategy. The VSG controller includes a virtual speed regulator controller and a virtual exciter controller. The VSG virtual inertia link is used to simulate the inherent rotational inertia of the synchronous generator rotor to suppress frequency fluctuations. The modeling of the mechanical part of VSG reflects the virtual inertia and damping characteristics of VSG, which is realized through the rotor motion equation. The expression is as follows: Where: J is the rotor moment of inertia; D is the damping coefficient; ω, ω ref are the actual angular velocity and rated angular velocity of VSG respectively; T m and T e are mechanical torque and electromagnetic torque respectively; The primary voltage regulation characteristics of the VSG excitation regulator have the following relationship: Where: Q set and Q e Respectively represent the reactive power set value and actual measured value of VSG; K u Represents the reactive power-voltage droop coefficient.

3. The active non-disturbance closing method for interconnecting substations using flexible power electronic switches according to claim 1 is characterized in that: When the main transformer changes from decommissioning to operation, pre-synchronization control is added to the VSG control.

4. The active non-disturbance closing method for interconnecting substations using flexible power electronic switches according to claim 3 is characterized in that: Pre-synchronization control specifically includes: collecting the voltage amplitude E on the main transformer side g The difference between the current output voltage U0 controlled by VSG is sent to the PI controller; then the output E controlled by PI is syn As a correction value, the output voltage amplitude of VSG is corrected; when the main transformer voltage E g When it is greater than the output voltage U0 of the virtual synchronous generator, the input of the PI controller is positive, and the output voltage of the VSG increases until the deviation between the two is 0, and the PI controller enters a steady-state operation state; similarly, when E g When it is less than U0, the input of the PI controller is negative, and the output voltage amplitude of VSG decreases until E syn =0.

Images