A Method and System for Suppressing Inrush Current of Transformer under a Power Grid Simulator

Abstract

The present invention provides a method and system for suppressing inrush current of a transformer under a power grid simulator, belonging to the technical field of power grid simulators. Specifically, it includes: using a voltage measuring device to measure the voltage output by the inverter to obtain a measured voltage, using a magnetic field measuring device to measure the real-time magnetic flux of the transformer to obtain a real-time magnetic flux, and using a current measuring device to measure the current output by the inverter in real time to obtain a measured current; when the voltage drop amount of the measured voltage is greater than a first threshold, record the real-time magnetic flux at this time. When the drop is completed, determine the compensation voltage at this time according to the real-time magnetic flux at the end of the drop, the maximum saturation magnetic flux of the transformer, and the voltage angular velocity and voltage effective value of the inverter command voltage, and compensate the command voltage of the inverter until the output voltage of the inverter is greater than a second threshold or the time for the output voltage to rise is greater than a third threshold, and then stop the compensation, so as to effectively suppress the inrush current of the transformer of the power grid simulator.

Description

Technical Field

[0001] The present invention belongs to the technical field of grid simulators, and particularly relates to a method and a system for suppressing transformer inrush current under a grid simulator. Background Technique

[0002] When studying a distributed generation system, its adaptability under grid fault conditions and its supporting ability for the grid are particularly important. However, the occurrence of a grid fault is a random event, and it is difficult to predict the occurrence time and type of the fault, and it is extremely easy to cause more equipment damage. Therefore, there is an urgent need for a special device to accurately simulate various states of the grid (normal state and abnormal state), such as voltage variation, frequency deviation, and waveform distortion, etc., to carry out necessary working condition tests before the new energy power electronic equipment is connected to the grid, so as to ensure that the distributed generation system meets relevant standards and requirements. This special test device is called a grid state simulation device in the engineering, that is, a grid simulator. In a grid simulator with a relatively large capacity, the inverter is directly connected to the transformer. When the grid simulator simulates a grid fault, due to the fluctuation of the inverter output voltage, the magnetic field inside the transformer will not change immediately with the voltage fluctuation, and a part of the residual magnetism will remain. Therefore, when the fluctuation of the inverter output voltage is relatively severe, at this time, the magnetic flux of the output voltage and the residual magnetism of the transformer may be superimposed together, resulting in the saturation of the transformer core and generating a serious inrush current, which may damage both the switching tube of the inverter and the transformer itself.

[0003] The most commonly used method for suppressing the grid inverter is to improve it by adding a current limiting circuit and a series transformer design. Increasing the rated magnetic flux of the transformer so that it is much higher than the original magnetic flux can not only efficiently suppress the inrush current, but also reasonably control its cost and volume. However, it is difficult to transform the existing transformer. Installing a current limiting circuit requires controlling the peak value of the current on the primary side of the series transformer between the inverter and the transformer in series to control the inrush current, resulting in unnecessary energy loss. In the master's thesis "Research on the Magnetic Saturation and Inrush Current Suppression Strategy of the Series Transformer between the Microgrid and the Distribution Grid", the author Sun Zhi proposed an inrush current control method in the stationary coordinate system. By subtracting the reference voltage from the actual voltage feedback signal of the transformer, the obtained value is input into the voltage regulator, and the output signal obtained is the reference value of the filter capacitor current. The obtained reference value is subtracted from the filter capacitor current, and the obtained value is input into the current regulator. The output signal of the current regulator is input into the PWM generator to obtain a PWM signal to control the inverter. However, in the field of grid simulators, the reference signal of the voltage changes in real time according to the control requirements. Using the above control method cannot suppress the inrush current of the grid inverter.

[0004] Thoughts on existing technical problems: It is difficult to transform the inside of the transformer, there is energy loss in current limiting, and traditional voltage compensation is not applicable to the suppression of inrush current under a grid simulator.

[0005] Based on the above technical problems, it is necessary to design a method and system for suppressing inrush current of a transformer under a grid simulator. Summary of the Invention

[0006] The purpose of the present invention is to provide a method and system for suppressing inrush current of a transformer under a grid simulator.

[0007] To solve the above technical problems, the first aspect of the present invention provides a method for suppressing inrush current of a transformer under a grid simulator, which is characterized in that it specifically includes:

[0008] Step S1: Use a voltage measuring device to measure the voltage output by the inverter to obtain a measured voltage, use a magnetic field measuring device to measure the real-time magnetic flux of the transformer to obtain a real-time magnetic flux, and use a current measuring device to measure the current output by the inverter in real time to obtain a measured current;

[0009] Step S2: When the drop amount of the measured voltage is greater than a first threshold, record the real-time magnetic flux at this time. When the drop is completed, determine the compensation voltage at this time according to the real-time magnetic flux at the end of the drop, the maximum saturation magnetic flux of the transformer, and the voltage angular velocity and voltage effective value of the inverter command voltage, and compensate the command voltage of the inverter until the output voltage of the inverter is greater than a second threshold or the time for the output voltage to rise is greater than a third threshold, then stop the compensation.

[0010] Measure the voltage and current of the inverter through a voltage measuring device and a current measuring device, and measure the real-time magnetic flux of the transformer through a magnetic field measuring device. When the voltage drop of the voltage measured by the voltage measuring device is greater than the first threshold, the output voltage of the inverter has a serious drop at this time. If the command voltage is not compensated, there will still be a serious residual magnetism inside the transformer at this time. When the voltage of the inverter suddenly increases next time, a serious inrush current will occur in the transformer at this time. Therefore, by using the maximum saturation magnetic flux and real-time magnetic flux at the moment of voltage drop of the transformer, and by constructing a form of compensation voltage to change the output angle of the command voltage at this time, thereby changing the output voltage angle of the inverter at this time, so that the real-time magnetic flux of the transformer at this time changes, compensating for the residual magnetism of the transformer, so that the transformer does not generate a serious inrush current when boosting. After avoiding the technical problems of difficult internal structure transformation of the transformer, energy loss in current limiting, and inapplicability of existing voltage compensation to inrush current suppression under the grid simulator, by starting from the magnetic field, compensating the command voltage of the inverter, changing the magnetic flux of the transformer, and then changing the magnetic field of the internal magnetic flux of the transformer, compensating the internal magnetic flux of the transformer, so that the transformer no longer generates a serious inrush current.

[0011] By measuring the voltage, when the drop amount of the measured voltage is greater than the first threshold, the compensation is started by confirming the voltage drop magnitude, preventing the voltage from having a weak fluctuation and causing incorrect activation of the compensation measure. Only when the voltage of the inverter drops to a certain extent, the compensation measure is activated. Based on the saturation magnetic flux of the transformer, the real-time magnetic flux of the transformer, the voltage angular velocity and the voltage effective value of the inverter command voltage, the compensation voltage of the inverter is determined, thereby compensating the original command voltage of the inverter, thus realizing the change of the magnetic flux of the transformer, realizing the compensation of the residual magnetism, making the total magnetic flux of the transformer no longer saturated, and then suppressing the inrush current, preventing the inrush current from damaging the transformer and the switching tube. By setting the second threshold or the third threshold, the compensation is stopped when the output voltage of the inverter is greater than the second threshold or the time when the output voltage rises is greater than the third threshold, preventing the compensation from stopping before the inverter has completed boosting due to a slight fluctuation of the output voltage of the inverter, so that the transformer may still generate a relatively serious inrush current, thus greatly improving the reliability of the entire system.

[0012] A further technical solution is that the magnetic field measuring device adopts a Hall effect solenoid magnetic field measuring instrument.

[0013] By using a Hall effect solenoid magnetic field measuring instrument to realize the measurement of the real-time magnetic field, it lays a foundation for compensating the output voltage of the inverter according to the real-time magnetic field.

[0014] A further technical solution is that the first threshold and the second threshold are determined according to the capacity of the transformer, the rated voltage, the internal winding form, and the core material of the transformer.

[0015] Since the capacity, rated voltage, form of the internal winding, and core material of the transformer are different, the output voltages of the inverters that cause the core to enter the saturation state are also different. Therefore, according to the actual situation of the transformer, when the drop amplitude of the output voltage of the inverter is not enough to cause the inrush current of the transformer, no compensation will be carried out. Only when the drop amplitude of the output voltage of the inverter is enough to cause the inrush current of the transformer, it will lead to the generation of the inrush current of the transformer. A further technical solution is that the calculation formula of the compensation voltage is:

[0016] ΔU = U m cos(ωt + β) - U *

[0017] where ΔU is the compensation voltage, U m is the effective value of the command voltage, ω is the angular velocity of the command voltage, t is the time, β = arcsin(Φ / Φ m ), Φ is the real-time magnetic flux, Φ m is the maximum saturation magnetic flux, and U * is the original command voltage.

[0018] By setting the compensation voltage, on the basis of not changing the output voltage of the inverter of the grid simulator and meeting the simulation of the voltage fluctuation of the original grid simulator, it can also prevent the magnetic core of the transformer from saturating, avoid distortion of the output voltage and current of the grid simulator, and prevent damage to the switching tubes and transformers of the inverter.

[0019] A further technical solution is that the optimal phase angle can also be predicted by a prediction model based on a combined prediction algorithm.

[0020] Due to the differences in transformer types and winding methods, as well as the differences in the internal temperature and operating mode of the transformer during operation, the monitoring of its magnetic field intensity often cannot be accurately measured. Therefore, by adopting a combined prediction algorithm and combining the advantages of different algorithms, the optimal phase angle at this time can be better predicted, avoiding the problem of low accuracy caused by the measurement accuracy problem before.

[0021] A further technical solution is that the combined prediction algorithm adopts a method combining PSO - BP and Boosting algorithms. The specific steps of using the prediction model to predict the optimal phase angle are as follows:

[0022] S11 When the transformer is in a state of failure or other voltage mutations, record the output voltage angle of the inverter, the output current of the inverter, and the inrush current situation at this time;

[0023] S12 Estimate and calculate the optimal phase angle in the transformer magnetic circuit at this voltage angle based on the detected inrush current, and construct a training set based on the output voltage angle, the output current, and the optimal phase angle, where the input is the output voltage angle and the output current, and the output is the optimal phase angle;

[0024] S13 Input the training set into the prediction model based on PSO-BP and the prediction model based on the Boosting algorithm for training;

[0025] S14 Obtain the trained prediction model based on PSO-BP and the trained prediction model based on the Boosting algorithm, assign weights to the prediction model based on PSO-BP and the prediction model based on the Boosting algorithm respectively, and combine them to obtain a comprehensive prediction model;

[0026] S15 Input the output voltage angle and the output current of the inverter at this time into the comprehensive prediction model to obtain the final optimal phase angle.

[0027] A further technical solution lies in that the calculation formula of the comprehensive prediction model is:

[0028] β = a1β1 + a2β2

[0029] Where β is the optimal phase angle, β1 and β2 are the prediction results of the prediction model based on PSO-BP and the prediction model based on the Boosting algorithm respectively, and a1 and a2 are the weights of different prediction results, with values between 0 and 1.

[0030] A further technical solution lies in that an optimization algorithm based on the bat algorithm is used to determine the weights.

[0031] A further technical solution lies in that the instruction voltage controls the inverter using a control method in the rotating coordinate system. First, construct a virtual β coordinate, use the instruction voltage as the α coordinate, and delay the α coordinate by 90° to obtain the β coordinate, and then perform dq transformation to obtain the d-axis instruction voltage and the q-axis instruction voltage respectively.

[0032] By using the control method in the rotating coordinate system, the situation of static error existing in the original static coordinate system is solved, making the overall control accuracy higher.

[0033] On the other hand, the present invention provides a transformer inrush current suppression system under a power grid simulator, which adopts the above-mentioned method for suppressing transformer inrush current under a power grid simulator, and is characterized in that it specifically includes:

[0034] A voltage measurement device, a magnetic field measurement device, a current measurement device, and a control module;

[0035] The voltage measurement device is responsible for measuring the voltage output by the inverter to obtain the measured voltage, and transmitting the measured voltage to the control module;

[0036] The magnetic field measurement device is responsible for measuring the real-time magnetic flux of the transformer to obtain the real-time magnetic flux, and transmitting the real-time magnetic flux to the control module;

[0037] The current measurement device is responsible for measuring the current output by the inverter in real time to obtain the measured current, and transmitting the measured current to the control module;

[0038] When the drop amount of the measured voltage is greater than the first threshold, the control module stores the real-time magnetic flux of the transformer at this time. When the drop is completed, according to the real-time magnetic flux at the end of the drop, the maximum saturation magnetic flux of the transformer, and the voltage angular velocity and voltage effective value of the inverter command voltage, the compensation voltage at this time is determined, and the command voltage of the inverter is compensated until the output voltage of the inverter is greater than the second threshold or the time for the output voltage to rise is greater than the third threshold, then the compensation stops.

[0039] Other features and advantages will be described in the following specification, and, in part, will be obvious from the specification, or will be understood by implementing the present invention. The objectives and other advantages of the present invention are achieved and obtained by the structures specifically pointed out in the specification and the drawings.

[0040] To make the above objectives, features, and advantages of the present invention more obvious and understandable, the following specific preferred embodiments are given, and in conjunction with the accompanying drawings, the detailed description is as follows. Description of the Drawings

[0041] By referring to the drawings and describing its exemplary embodiments in detail, the above and other features and advantages of the present invention will become more obvious.

[0042] Figure 1 It is a flowchart of a method for suppressing transformer inrush current under a power grid simulator of the present invention;

[0043] Figure 2 It is a waveform diagram of inrush current without adding a suppression strategy;

[0044] Figure 3 It is a current waveform diagram after adding a suppression strategy;

[0045] Figure 4 It is a specific step flowchart for predicting the optimal phase angle by the prediction model based on the combined prediction algorithm of the present invention;

[0046] Figure 5 It is a double closed-loop control block diagram in the rotating coordinate system;

[0047] Figure 6 It is a schematic structural diagram of a transformer inrush current suppression system under a power grid simulator of the present invention;

[0048] Figure 7 It is the main circuit topology of the single-phase power grid simulator of the present invention. Specific embodiments

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0050] When studying a distributed generation system, its adaptability under power grid fault conditions and its supporting ability for the power grid are particularly important. However, the occurrence of a power grid fault is a random event, and it is difficult to predict the occurrence time and type of the fault, and it is extremely easy to cause more equipment damage. Therefore, there is an urgent need for a special device to accurately simulate various states of the power grid (normal state and abnormal state), such as voltage fluctuations, frequency offsets, and waveform distortions, etc., to conduct necessary working condition tests before the new energy power electronic equipment is connected to the grid, and to ensure that the distributed generation system meets relevant standards and requirements. This special test device is called a power grid state simulation device, that is, a power grid simulator in the engineering. In a power grid simulator with a relatively large capacity, the inverter is directly connected to the transformer. When the power grid simulator simulates a power grid fault, due to the voltage fluctuation of the inverter output, the magnetic field inside the transformer will not change immediately with the voltage fluctuation, and a part of the residual magnetism will remain. Therefore, when the voltage fluctuation of the inverter output is relatively severe, at this time, the magnetic flux of the output voltage and the residual magnetism of the transformer may be superimposed together, resulting in the saturation of the transformer core and generating a serious inrush current, which may damage both the switching tube of the inverter and the transformer itself.

[0051] When suppressing a grid inverter, the most commonly used methods are to add a current-limiting circuit and improve the design of the series transformer. By increasing the rated magnetic flux of the transformer to be much higher than the original magnetic flux, not only can the inrush current be effectively suppressed, but also the cost and volume can be reasonably controlled. However, it is difficult to transform the existing transformer. Installing a current-limiting circuit requires controlling the peak value of the primary-side current of the series transformer between the series-link inverter and the transformer to control the inrush current, resulting in unnecessary energy losses. In the master's thesis "Research on the Magnetic Saturation and Inrush Current Suppression Strategy of the Series Transformer between the Microgrid and the Distribution Grid", the author Sun Zhi proposed a method for controlling the inrush current in the stationary coordinate system. By subtracting the actual voltage feedback signal of the transformer from the reference voltage, the obtained value is input into the voltage regulator, and the output signal is the reference value of the filter capacitor current. The obtained reference value is subtracted from the filter capacitor current, and the obtained value is input into the current regulator. The output signal of the current regulator is input into the PWM generator to obtain a PWM signal for controlling the inverter. However, in the field of grid simulators, the reference signal of the voltage changes in real time according to the control requirements. Using the above control method cannot suppress the inrush current of the grid inverter.

[0052] Thoughts on the existing technical problems: It is difficult to transform the inside of the transformer, there is energy loss in current limiting, and the traditional voltage compensation is not applicable to the inrush current suppression under the grid simulator.

[0053] Embodiment 1

[0054] To solve the above technical problems, as Figure 1 shown, the first aspect of the present invention provides a method for suppressing the inrush current of a transformer under a grid simulator, which is characterized in that it specifically includes:

[0055] Step S1: Use a voltage measuring device to measure the voltage output by the inverter to obtain a measured voltage, use a magnetic field measuring device to measure the real-time magnetic flux of the transformer to obtain a real-time magnetic flux, and use a current measuring device to measure the current output by the inverter in real time to obtain a measured current;

[0056] Step S2: When the drop amount of the measured voltage is greater than the first threshold, record the real-time magnetic flux at this time. When the drop is completed, determine the compensation voltage at this time according to the real-time magnetic flux at the end of the drop, the maximum saturation magnetic flux of the transformer, and the voltage angular velocity and voltage effective value of the inverter command voltage, and compensate the command voltage of the inverter until the output voltage of the inverter is greater than the second threshold or the time for the output voltage to rise is greater than the third threshold, then stop the compensation.

[0057] The voltage and current of the inverter are measured by a voltage measuring device and a current measuring device, and the real-time magnetic flux of the transformer is measured by a magnetic field measuring device. When the voltage drop measured by the voltage measuring device is greater than the first threshold, the output voltage of the inverter has a serious drop at this time. If the command voltage is not compensated, there will still be a serious residual magnetism inside the transformer at this time. When the voltage of the inverter suddenly increases next time, a serious inrush current will occur in the transformer at this time. Therefore, by calculating the maximum saturation magnetic flux and the real-time magnetic flux at the moment of voltage drop of the transformer, and by constructing a form of compensating voltage to change the output angle of the command voltage at this time, thereby changing the output voltage angle of the inverter at this time, so that the real-time magnetic flux of the transformer at this time changes, compensating the residual magnetism of the transformer, so that the transformer will not generate a serious inrush current when boosting. After avoiding the technical problems of difficult internal structure transformation of the transformer, energy loss in current limiting, and inapplicability of existing voltage compensation to inrush current suppression under a grid simulator, by starting from the magnetic field, compensating the command voltage of the inverter, changing the magnetic flux of the transformer, and further changing the magnetic field of the internal magnetic flux of the transformer, compensating the internal magnetic flux of the transformer, so that the transformer will no longer generate a serious inrush current.

[0058] By measuring the voltage, when the drop of the measured voltage is greater than the first threshold, the compensation is started by confirming the voltage drop magnitude, preventing weak voltage fluctuations from causing incorrect activation of the compensation measures. Only when the voltage of the inverter drops to a certain extent, the compensation measures are activated. Based on the saturation magnetic flux of the transformer, the real-time magnetic flux of the transformer, the voltage angular velocity and the voltage effective value of the inverter command voltage, the compensation voltage of the inverter is determined, thereby compensating the original command voltage of the inverter, thus realizing the change of the magnetic flux of the transformer, realizing the compensation of the residual magnetism, making the total magnetic flux of the transformer no longer saturated, and further suppressing the inrush current, preventing the inrush current from damaging the transformer and the switching tube. By setting the second threshold or the third threshold, the compensation is stopped when the output voltage of the inverter is greater than the second threshold or the time when the output voltage rises is greater than the third threshold, preventing the compensation from stopping before the inverter has completed boosting due to slight fluctuations in the output voltage of the inverter, so that the transformer may still generate a relatively serious inrush current, thus greatly improving the reliability of the entire system.

[0059] For example

[0060] Table 1 Parameters used to establish the model

[0061]

[0062] Figure 2The waveform diagram of inrush current without adding suppression strategy is shown. When the voltage drops to 0.5 KV and the voltage drop time is 4.01 s, when the PI parameters of the current loop are optimal, since the magnetic flux of the transformer at this time contains a large amount of transient components, after half a cycle of voltage boost, the magnetic flux reaches the maximum inrush current amplitude. At this time, the magnetic circuit is over-saturated and the inrush current peak reaches 4 KA.

[0063] Figure 3 The current waveform diagram after adding the phase angle detection voltage compensation strategy is shown. When the voltage drop time is 4.01 s, since the phase angle detection voltage compensation strategy is added at this time, the transient components in the magnetic flux of the transformer are significantly suppressed. The current waveform is slightly distorted in the initial stage and enters the steady-state current after several cycles of adjustment, and the suppression effect is remarkable.

[0064] In another possible embodiment, the magnetic field measuring device adopts a Hall effect solenoid magnetic field measuring instrument.

[0065] By using a Hall effect solenoid magnetic field measuring instrument to measure the real-time magnetic field, it lays a foundation for compensating the output voltage of the inverter according to the real-time magnetic field.

[0066] In another possible embodiment, the first threshold and the second threshold are determined according to the capacity, rated voltage, internal winding form, and core material of the transformer.

[0067] Since the capacity, rated voltage, internal winding form, and core material of the transformer are different, the output voltage of the inverter that causes the core to enter the saturation state is also different. Therefore, according to the actual situation of the transformer, when the drop amplitude of the output voltage of the inverter is not enough to cause the inrush current of the transformer, no compensation will be carried out. Only when the drop amplitude of the output voltage of the inverter is enough to cause the inrush current of the transformer, it will cause serious inrush current of the transformer. In another possible embodiment, the calculation formula of the compensation voltage is:

[0068] ΔU=U m cos(ωt+β)-U *

[0069] where ΔU is the compensation voltage, U m is the effective value of the command voltage, ω is the voltage angular velocity, t is the time, β=arcsin(Φ / Φ m ), Φ is the real-time magnetic flux, Φ m is the maximum saturation magnetic flux, U * is the original command voltage.

[0070] By setting the compensation voltage, without changing the output voltage of the inverter of the grid simulator, on the basis of meeting the simulation of voltage fluctuations by the original grid simulator, it is also possible to prevent the magnetic core of the transformer from saturation, avoid distortion of the output voltage and current of the grid simulator, and prevent damage to the switching tubes and transformers of the inverter.

[0071] In another possible embodiment, the optimal phase angle can also be predicted by a prediction model based on a combined prediction algorithm.

[0072] Due to differences in transformer types and winding methods, as well as differences in internal temperature and operating modes during transformer operation, the monitoring of its magnetic field intensity often cannot be accurately measured. Therefore, by adopting a combined prediction algorithm and combining the advantages of different algorithms, the optimal phase angle at this time can be better predicted, avoiding the problem of low accuracy caused by the original measurement accuracy problem.

[0073] In another possible embodiment, as Figure 4 shown, the combined prediction algorithm adopts a combination of PSO-BP and Boosting algorithms. The specific steps for predicting the optimal phase angle using the prediction model are as follows:

[0074] S11 When the transformer is in a state of failure or other voltage mutations, record the output voltage angle of the inverter, the output current of the inverter, and the inrush current situation at this time;

[0075] S12 Based on the monitored inrush current, estimate and calculate the optimal phase angle in the transformer magnetic circuit at this voltage angle. Based on the output voltage angle, the output current, and the optimal phase angle, construct a training set, where the input is the output voltage angle and the output current, and the output is the optimal phase angle;

[0076] S13 Input the training set into the prediction model based on PSO-BP and the prediction model based on the Boosting algorithm for training;

[0077] S14 Obtain the trained prediction model based on PSO-BP and the trained prediction model based on the Boosting algorithm, assign weights to the prediction model based on PSO-BP and the prediction model based on the Boosting algorithm respectively, and combine them to obtain a comprehensive prediction model;

[0078] S15 Input the output voltage angle and the output current of the inverter at this time into the comprehensive prediction model to obtain the final optimal phase angle.

[0079] In another possible embodiment, the calculation formula of the comprehensive prediction model is as follows:

[0080] β = a1β1 + a2β2

[0081] Where β is the optimal phase angle, β1 and β2 are the prediction results of the prediction model based on PSO-BP and the prediction model based on the Boosting algorithm respectively, and a1 and a2 are the weights of different prediction results, with values between 0 and 1.

[0082] For example, if the result obtained from the prediction model based on PSO-BP is 31 degrees at this time, and the prediction result of the prediction model based on the Boosting algorithm is 32 degrees, where a1 and a2 are 0.3 and 0.7 respectively, then the final comprehensive prediction result is 31.7 degrees.

[0083] In another possible embodiment, an optimization algorithm based on the bat algorithm is used to determine the weights.

[0084] In another possible embodiment, as Figure 5 shown, the instruction voltage controls the inverter using a control method in the rotating coordinate system. First, a virtual β coordinate is constructed, the instruction voltage is used as the α coordinate, and the α coordinate is delayed by 90° to obtain the β coordinate, and then dq transformation is performed to obtain the d-axis instruction voltage and the q-axis instruction voltage respectively.

[0085] By using the control method in the rotating coordinate system, the situation of static error existing in the original static coordinate system is solved, making the overall control accuracy higher.

[0086] Embodiment 2

[0087] As Figure 5 shown, on the other hand, the present invention provides a transformer inrush current suppression system under a power grid simulator, which adopts the above-mentioned transformer inrush current suppression method under a power grid simulator, and is characterized in that it specifically includes:

[0088] A voltage measurement device, a magnetic field measurement device, a current measurement device, and a control module;

[0089] The voltage measurement device is responsible for measuring the voltage output by the inverter to obtain the measured voltage and transmitting the measured voltage to the control module;

[0090] The magnetic field measurement device is responsible for measuring the real-time magnetic flux of the transformer to obtain the real-time magnetic flux and transmitting the real-time magnetic flux to the control module;

[0091] The current measurement device is responsible for measuring the current output by the inverter in real time to obtain the measured current, and transmitting the measured current to the control module;

[0092] When the drop amount of the measured voltage is greater than the first threshold, the control module is responsible for storing the real-time magnetic flux of the transformer at this time. When the drop is completed, according to the real-time magnetic flux at the end of the drop, the maximum saturation magnetic flux of the transformer, and the voltage angular velocity and voltage effective value of the inverter command voltage, the compensation voltage at this time is determined, and the command voltage of the inverter is compensated until the output voltage of the inverter is greater than the second threshold or the time when the output voltage rises is greater than the third threshold, then the compensation stops.

[0093] In several embodiments provided in the present application, it should be understood that the disclosed systems and methods can also be implemented in other ways. The system embodiments described above are merely illustrative. For example, the flowcharts and block diagrams in the accompanying drawings show the possible architectures, functions, and operations of systems, methods, and computer program products according to multiple embodiments of the present invention. In this regard, each block in the flowchart or block diagram may represent a module, a program segment, or a part of code, and the module, program segment, or part of code contains one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order than marked in the accompanying drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in the reverse order, depending on the functions involved. It should also be noted that each block in the block diagram and / or flowchart, and the combination of blocks in the block diagram and / or flowchart, can be implemented by a dedicated hardware-based system for performing the specified functions or actions, or can be implemented by a combination of dedicated hardware and computer instructions.

[0094] In addition, the functional modules in each embodiment of the present invention may be integrated together to form an independent part, or each module may exist alone, or two or more modules may be integrated to form an independent part.

[0095] If the functions are implemented in the form of software function modules and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art or a part of this technical solution can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods of various embodiments of the present invention. The aforementioned storage medium includes: various media that can store program codes, such as USB flash drives, mobile hard disks, read-only memories (ROM, Read-Only Memory), random access memories (RAM, Random Access Memory), magnetic disks, or optical discs.

[0096] Taking the ideal embodiments of the present invention described above as an inspiration, through the above description, relevant staff can, without departing from the technical idea of this invention, make various changes and modifications. The technical scope of this invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for suppressing transformer inrush current under a power grid simulator, characterized in that, Specifically, it includes: Step S1: Use a voltage measuring device to measure the voltage output by the inverter to obtain a measured voltage, use a magnetic field measuring device to measure the real-time magnetic flux of the transformer to obtain a real-time magnetic flux, and use a current measuring device to measure the current output by the inverter in real time to obtain a measured current; Step S2: When the drop amount of the measured voltage is greater than the first threshold, record the real-time magnetic flux at this time. When the drop is completed, determine the compensation voltage at this time according to the real-time magnetic flux at the end of the drop, the maximum saturation magnetic flux of the transformer, and the voltage angular velocity and voltage effective value of the inverter command voltage, and compensate the command voltage of the inverter until the output voltage of the inverter is greater than the second threshold or the time when the output voltage rises is greater than the third threshold to stop the compensation; The calculation formula of the compensation voltage is: △U = U m cos(ωt + β0) - U * where △U is the compensation voltage, U m is the effective value of the command voltage, ω is the angular velocity of the command voltage, t is the time, β0 = arcsin(Φ / Φ m ), Φ is the real-time magnetic flux, Φ m is the maximum saturation magnetic flux, U * is the original command voltage; The optimal phase angle β0 can also be predicted by a prediction model based on a combined prediction algorithm. The combined prediction algorithm uses a method combining PSO-BP and Boosting algorithm. The specific steps of using the prediction model to predict the optimal phase angle are as follows: S11 When the transformer is in a state of failure or other voltage mutations, record the output voltage angle of the inverter, the output current of the inverter, and the inrush current situation at this time; S12 Estimate and calculate the optimal phase angle in the transformer magnetic circuit at this voltage angle through the monitored inrush current. Based on the output voltage angle, the output current, and the optimal phase angle, construct a training set, where the input is the output voltage angle and the output current, and the output is the optimal phase angle; S13 Input the training set into the prediction model based on PSO-BP and the prediction model based on Boosting algorithm for training; S14 Obtain the trained prediction model based on PSO-BP and the trained prediction model based on Boosting algorithm, assign weights to the prediction model based on PSO-BP and the prediction model based on Boosting algorithm respectively, and combine them to obtain a comprehensive prediction model; S15 Input the output voltage angle and the output current of the inverter at this time into the comprehensive prediction model to obtain the final optimal phase angle.

2. The transformer inrush current suppression method according to claim 1, wherein The magnetic field measuring device uses a Hall effect solenoid magnetic field measuring instrument.

3. The transformer inrush current suppression method according to claim 1, characterized in that, The first threshold and the second threshold are determined according to the capacity, rated voltage, internal winding form, and core material of the transformer.

4. The transformer inrush current suppression method according to claim 1, characterized in that, The calculation formula of the comprehensive prediction model is: β0 = a1β1 + a2β2 Where β0 is the optimal phase angle, β1 and β2 are the prediction results of the prediction model based on PSO-BP and the prediction model based on Boosting algorithm respectively, and a1 and a2 are the weights of different prediction results, with values between 0 and 1.

5. The transformer inrush current suppression method according to claim 4, characterized in that, Use an optimization algorithm based on the bat algorithm to determine the weights.

6. The transformer inrush current suppression method according to claim 1, characterized in that, The instruction voltage controls the inverter using a control method in the rotating coordinate system. First, a virtual β coordinate is constructed, the instruction voltage is used as the α coordinate, and the α coordinate is delayed by 90° to obtain the β coordinate. Then, a dq transformation is performed to obtain the d-axis instruction voltage and the q-axis instruction voltage respectively.

7. A transformer inrush current suppression system under a power grid simulator, adopting the transformer inrush current suppression method described in any one of claims 1-6, characterized in that, Specifically, it includes: a voltage measurement device, a magnetic field measurement device, a current measurement device, and a control module; The voltage measurement device is responsible for measuring the voltage output by the inverter to obtain the measured voltage and transmitting the measured voltage to the control module; The magnetic field measurement device is responsible for measuring the real-time magnetic flux of the transformer to obtain the real-time magnetic flux and transmitting the real-time magnetic flux to the control module; The current measurement device is responsible for measuring the current output by the inverter in real time to obtain the measured current and transmitting the measured current to the control module; When the drop amount of the measured voltage is greater than the first threshold, the control module stores the real-time magnetic flux of the transformer at this time. When the drop is completed, according to the real-time magnetic flux at the time of completion of the drop, the maximum saturation magnetic flux of the transformer, and the voltage angular velocity and voltage effective value of the inverter instruction voltage, the compensation voltage at this time is determined to compensate the instruction voltage of the inverter until the output voltage of the inverter is greater than the second threshold or the time for the output voltage to rise is greater than the third threshold, then the compensation stops.

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