Flexible starting device of box-type transformer and grid-connected power generation system of photovoltaic power station

Abstract

The invention discloses a box-type transformer flexible starting device and a photovoltaic power station grid-connected power generation system, which are applied to boosting from zero of a current collection circuit, the current collection circuit comprises a box-type transformer and a circuit breaker, and the device comprises a main controller, a semiconductor controller and an electric isolation disconnecting link. The first end of the semiconductor controller is connected in series with the first end of the electric isolation knife switch, the second end of the electric isolation knife switch is connected in parallel with the first end of the circuit breaker, and the second end of the semiconductor controller is connected in parallel with the second end of the circuit breaker; the main controller is used for sending a first control signal to the electric isolation knife switch, controlling the opening and closing of the electric isolation knife switch, and calculating a conduction angle alpha reached by the semiconductor controller within a control period delta t according to the rated voltage Urated, the boost rate k and the total boost time T of the current collection circuit; converting the conduction angle alpha into a second control signal and sending the second control signal to the semiconductor controller; and the semiconductor controller starts to conduct according to the conduction angle alpha in response to the second control signal, so that the voltage of the current collection circuit is slowly increased.

Description

Technical Field

[0001] This application relates to the field of photovoltaic power generation technology, and in particular to a flexible starting device for a box-type transformer and a grid-connected power generation system for a photovoltaic power station. Background Technology

[0002] In photovoltaic power generation systems, the operation and control of the collection lines are crucial. During the nighttime shutdown of the photovoltaic power station, the box-type transformer (hereinafter referred to as the box transformer) needs to be disconnected to reduce the no-load loss of the box transformer at night. Before the photovoltaic power station generates electricity during the day, the box transformer needs to be connected to the grid without impact, which requires suppressing the inrush current generated when the box transformer is connected.

[0003] Currently, the main methods for suppressing inrush current and their existing problems are as follows: (1) Use special transformer core materials, optimize the transformer design structure, and add current-limiting reactors in the circuit. However, using special core materials will increase the manufacturing cost of the transformer and the effect is limited; optimizing the transformer design structure often requires large-scale modification of the transformer, which is difficult to implement; while adding current-limiting reactors will increase line losses and costs, and while suppressing inrush current, it will also hinder normal current transmission.

[0004] (2) Connecting a small-capacity pre-magnetized transformer in series in the transformer substation line to achieve inrush current suppression can be summarized as follows: before the main transformer is closed, the pre-magnetized transformer is closed first, so that the windings of the main transformer have established a steady-state magnetic flux before the main transformer is closed, thereby reducing the amplitude of the excitation inrush current generated after the main transformer is connected, and achieving the goal of inrush current suppression. However, the overall cost of connecting a small-capacity pre-magnetized transformer in series is relatively high, and the inrush current suppression effect is limited.

[0005] (3) For example, the invention with application number "202310936244X" and title "Flexible Starting Device for Box-Type Transformer Based on Energy Storage" includes: an energy storage battery module, a circuit breaker, a converter, an isolation transformer, a contactor, and a controller. The energy storage battery module is connected to the DC side of the converter module via the circuit breaker, and the AC side of the converter module is connected to the low-voltage bus side of the box-type transformer via the isolation transformer and the contactor. The controller's communication ports are connected to the communication ports of the battery module and the converter module, respectively. The controller's analog and digital ports are connected to the secondary signal side of the box-type transformer. The controller is used to control the switching of the box-type transformer when it switches from off-grid to grid-connected status in the morning, and uses the energy storage battery module as a power input source to control the converter to output AC voltage to the box-type transformer, thereby achieving flexible starting of the box-type transformer. This device reduces the inrush current impact when the box-type transformer is connected to the grid and reduces the no-load power loss at night. However, this approach requires the design of a complex electrical system, which is costly. Voltage fluctuations and overshoot may occur during the voltage boosting process. It cannot guarantee the accuracy and stability of controlling the voltage boosting process of the box-type transformer, and it cannot monitor and suppress the inrush current that may be generated during the voltage boosting process of the box-type transformer in real time. Summary of the Invention

[0006] The main purpose of this application is to provide a flexible starting device for a box-type transformer and a grid-connected power generation system for a photovoltaic power station, so as to solve the problems of poor effect in suppressing inrush current, high cost, inability to accurately control the voltage step-up process of the box-type transformer, and inability to monitor and suppress the inrush current that may be generated during the voltage step-up process of the box-type transformer in real time in the existing technology.

[0007] To achieve the above objectives, this application provides the following technical solution: A flexible starting device for a prefabricated transformer is used for zero-start voltage boosting of a collector line. The collector line includes a prefabricated transformer and a circuit breaker connected in series with the prefabricated transformer. The device includes a main controller, a semiconductor controller, and an electric isolating switch. The first terminal of the semiconductor controller is connected in series with the first terminal of the electric isolating switch, the second terminal of the electric isolating switch is connected in parallel with the first terminal of the circuit breaker, and the second terminal of the semiconductor controller is connected in parallel with the second terminal of the circuit breaker. The main controller is used to send a first control signal to the electrically operated isolating switch to control the opening and closing of the electrically operated isolating switch, and to control the rated voltage U of the collector line. rated Given the boost rate k and the total boost time T, calculate the conduction angle α that the semiconductor controller needs to reach within one control cycle Δt, and convert the conduction angle α into a second control signal and send it to the semiconductor controller; The semiconductor controller is used to respond to the second control signal and start conducting at a conduction angle α, so that the voltage of the collector line begins to rise slowly.

[0008] As a further improvement to this application, the step of basing the voltage U of the collector line on the rated voltage U... rated Given the boost rate k and the total boost time T, calculate the conduction angle α that the semiconductor controller needs to achieve within one control cycle Δt, including: The initial conduction angle α of the semiconductor controller is set during the first control cycle Δt. i ; Calculate at the initial conduction angle α i Below, the voltage increment of the collector line during the control period Δt is given by equation (1): ΔU calculated =i(Δt)R+L + + In equation (1): ΔU calculated Let i(Δt) be the voltage increment, i(Δt) be the current of the collector line, R be the equivalent resistance of the collector line, L be the equivalent inductance of the collector line, and C1 and C2 be the equivalent capacitances of the collector line, respectively. Calculate the target voltage increment ΔU1=kU of the collector line within one control cycle Δt. rated Where: ΔU1 is the target voltage increment, k is the preset boost rate, and U rated The voltage is the rated voltage, and T is the total time for the collector circuit to complete the voltage boost. Calculate the voltage increment ΔU calculated The absolute value of the difference between the target voltage increment ΔU1 and |ΔU calculated -ΔU1│, when │ΔU calculated -ΔU1│> ( When the allowable voltage increment deviation is set, if ΔU calculated >ΔU1, then the initial conduction angle α i Decrease by a step size Δα, i.e., α i+1 =α i -Δα, if ΔU calculated If ΔU1 <, then the initial conduction angle α i Increase by a step size Δα, i.e., α i+1 =α i +Δα; With the first conduction angle α i+1 As the initial conduction angle α i Recalculate the corresponding voltage increment ΔU calculated and the voltage increment ΔU calculatedThe absolute value of the difference from the target voltage increment ΔU1 until │ΔU calculated -ΔU1│≤ At this point, the initial conduction angle α i is the required conduction angle α. The conduction angle α that the semiconductor controller needs to reach within the next control period Δt is calculated by analogy.

[0009] As a further improvement of the present application, the box-type transformer flexible starting device further includes a voltage acquisition device and a current acquisition device for continuously acquiring the real-time voltage signal and real-time current signal of the collector line within each control period Δt. The main controller is further configured to analyze the operating parameters of the collector line based on the real-time voltage signal and the real-time current signal, so as to determine whether it is necessary to adjust the working state of the semiconductor controller.

[0010] As a further improvement of the present application, the main controller analyzes the real-time voltage signal and the real-time current signal to calculate the current actual voltage rise rate k of the collector line u = ; Compare the actual voltage rise rate k u with the boost rate k. If k u <k, calculate the conduction angle Δα that the semiconductor controller needs to increase in the next control period Δt up , then the conduction angle α of the semiconductor controller within the next control period Δt n+1 =α n +Δα up ; If k u >k, calculate the conduction angle Δα that the semiconductor controller needs to decrease in the next control period Δt down , then the conduction angle α of the semiconductor controller within the next control period Δt n+1 =α n -Δα down ; where α n is the conduction angle of the semiconductor controller within the current control period Δt.

[0011] As a further improvement of the present application, the main controller performs A / D conversion analysis on the real-time current signal to calculate the amplitude i of the current signal m , and compares the amplitude i m with the set current threshold i threshold . If i m >i threshold , it can be determined that inrush current appears in the collector line; The main controller based on the amplitude I mThe required reduction in current increment Δi = k0 (i) of the collector circuit is calculated. m -i n ), where k0 is a coefficient set according to the transformer characteristics and the degree of inrush current suppression, i n The normal excitation current is determined based on the rated parameters of the transformer; the main controller calculates the conduction angle Δα that the semiconductor controller needs to adjust based on the current increment Δi.

[0012] As a further improvement of this application, the main controller also performs time-frequency analysis on the real-time current signal to calculate the ratio i of the multiple harmonic components to the fundamental component in the current signal. k and the ratio i k With the set percentage threshold i k0 Compare, if i k >i k0 , and combined with i m >i threshold If so, it can be determined that an inrush current has occurred in the collector line.

[0013] As a further improvement to this application, the main controller calculates the conduction angle Δα that the semiconductor controller needs to adjust based on the current increment Δi, including: Calculate the voltage change corresponding to the reduction of the current increment Δi in the collector line within the control period Δt, as shown in equation (2): ΔU switch =Δi(Δt)R+L + + In equation (2): Δi is the current increment that the collector line needs to reduce, R is the equivalent resistance of the collector line, L is the equivalent inductance of the collector line, and C1 and C2 are the equivalent capacitances of the collector line, respectively. Through equation (3): f(α2) f(α1)=ΔU switch Solve equation (4) simultaneously: Δα = α2 - α1 to calculate the value of Δα. In equation (3), f(α) is the function relating the conduction angle of the semiconductor controller to the output voltage, f(α1) is the output voltage of the collector circuit before adjustment, f(α2) is the output voltage of the collector circuit after adjustment, α1 is the conduction angle of the semiconductor controller before adjustment, and α2 is the conduction angle of the semiconductor controller after adjustment. In equation (4), α1 is the conduction angle of the semiconductor controller before adjustment, and α2 is the conduction angle of the semiconductor controller after adjustment.

[0014] As a further improvement of this application, the main controller calculates the current actual current rise rate k of the collector line based on the real-time current signal.i = Compare the actual current rise rate k i With the rate of rise of short-circuit current k d The size of k i >k d If the current collector is short-circuited, the main controller sends a shutdown signal to the semiconductor controller to quickly cut off the current loop.

[0015] To achieve the above objectives, this application also provides the following technical solutions: A photovoltaic power plant grid-connected power generation system includes a busbar and several collector lines connected in parallel with the busbar. Each collector line includes a prefabricated transformer and a circuit breaker connected in series with the prefabricated transformer. A flexible starting device for the prefabricated transformer, according to any of the above-mentioned schemes, is connected in parallel to the circuit breaker of the collector line. The first terminal of the circuit breaker is connected in parallel with the busbar, and the second terminal of the circuit breaker is connected in series with the prefabricated transformer. The first terminal of the semiconductor controller is connected in series with the first terminal of the electrically operated isolating switch, and the second terminal of the electrically operated isolating switch is connected in parallel with the first terminal of the circuit breaker of the collector line. The second terminal of the semiconductor controller is connected in parallel with the second terminal of the circuit breaker.

[0016] As a further improvement of this application, a step-up transformer is also included, which is connected in series with the flexible starting device and is used to raise the voltage of the collector line to a predetermined value before the flexible starting device operates.

[0017] This application involves connecting a flexible starting device in parallel with the circuit breaker of the collector line. The device includes a main controller, a semiconductor controller, and a motorized isolating switch. Before the circuit breaker closes, the main controller sends a first control signal to the motorized isolating switch to close it, thus connecting the flexible starting device to the collector line. The main controller then adjusts the signal according to the rated voltage U of the collector line. rated Given the boost rate k and the total boost time T, calculate the conduction angle α that the semiconductor controller needs to reach within one control cycle Δt, so that the semiconductor controller can start conducting at the conduction angle α, causing the voltage of the collector line to rise slowly, effectively suppressing the inrush current generated during the boosting process of the transformer substation.

[0018] The flexible starting device of this application mainly includes a main controller, a semiconductor controller, and an electric isolating switch. While achieving zero-start voltage boost in the collector line and effectively suppressing inrush current generated during the voltage boosting process, it can significantly simplify the electrical structure of the collector line and reduce the technical cost of solving the inrush current problem. Furthermore, this application uses the main controller to adjust the starting voltage based on the rated voltage U of the collector line. ratedThe boost rate k and the total boost time T are used to precisely control the conduction angle α of the semiconductor controller to achieve zero-start boost of the collector circuit. The zero-start boost process can be completed automatically by simply setting the boost parameters through the main controller, avoiding voltage fluctuations and overshoot that may occur during the boost process, and improving the accuracy and reliability of the boost. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the system structure of the flexible starting device for the prefabricated transformer of this application; Figure 2 This is a simplified connection diagram of the flexible starting device and collector line of the transformer box of this application; Figure 3 This is a simplified structural diagram of a photovoltaic power plant grid-connected power generation system according to an embodiment of this application; Figure 4 This is a simplified structural diagram of a photovoltaic power plant grid-connected power generation system according to another embodiment of this application; Figure 5 This is a simplified structural diagram of a photovoltaic power plant grid-connected power generation system according to another embodiment of this application. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0021] like Figure 1 As shown, this embodiment provides an example of a flexible starting device for a prefabricated transformer. In this embodiment, the flexible starting device for a prefabricated transformer is mainly used for zero-start voltage boosting of the collector line to effectively suppress the inrush current generated in the windings of the prefabricated transformer when the circuit breaker of the collector line is closed. The collector line can be the electrical line in a photovoltaic power station grid-connected power generation system, or it can be the electrical line in other similar grid-connected power generation systems, such as wind power grid-connected power generation systems, tidal power grid-connected power generation systems, and hydropower unit grid-connected power generation systems.

[0022] Such as combination Figure 1 and Figure 2As shown, the power collection line includes a transformer substation 10 and a circuit breaker 20 connected in series with the transformer substation 10. The flexible starting device 1 includes a main controller 11, a semiconductor controller 12, and an electrically operated isolating switch 13. The first terminal of the semiconductor controller 12 is connected in series with the first terminal of the electrically operated isolating switch 13, the second terminal of the electrically operated isolating switch 13 is connected in parallel with the first terminal of the circuit breaker 20, and the second terminal of the semiconductor controller 12 is connected in parallel with the second terminal of the circuit breaker 20. The descriptions of the first and second terminals in this embodiment are mainly used to distinguish the different connection terminals of each device, facilitating an accurate description of the connection relationships of each device, and do not have a specific limiting function.

[0023] For ease of understanding, in this embodiment, the main controller 11 can be a PLC controller (programmable controller), a microcontroller, a PID controller (proportional-integral-derivative controller), an ARM controller, etc. The semiconductor controller 12 mainly includes a trigger board and a power unit with multiple thyristors connected in series or parallel. The trigger board receives control signals and controls the conduction angle of the thyristors. The power unit with multiple thyristors connected in series or parallel can meet the output requirements of high voltage and high current. The electrically operated isolating switch 13 mainly includes a switch, a stationary contact, a drive motor, and a mechanical linkage mechanism. The drive motor is connected to the mechanical linkage, and the mechanical linkage is connected to the switch. The drive motor connects and disconnects the switch and the stationary contact through the mechanical linkage mechanism, realizing the closing and opening of the electrically operated isolating switch 13. The electrically operated isolating switch 13 can be considered a mechanical switch, capable of providing safe isolation and carrying steady-state current.

[0024] like Figure 1 As shown, the main controller 11 is used to send a first control signal to the electric isolating switch 13 to control the opening and closing of the electric isolating switch 13, and to control the opening and closing of the electric isolating switch 13 according to the rated voltage U of the collector line. rated Given the boost rate k and the total boost time T, calculate the conduction angle α that the semiconductor controller 12 needs to achieve within one control cycle Δt, and convert the parameter of the conduction angle α into a second control signal and send it to the semiconductor controller 12.

[0025] After receiving the second control signal sent by the main controller 11, the semiconductor controller 12 starts to conduct according to the conduction angle α, causing the voltage of the collector line to slowly rise.

[0026] Rated voltage U of the collector line rated It is mainly determined by the power generation capacity of the power grid, for example, the rated voltage U of the collector line. ratedThe voltage can be 10KV or 35KV, etc. To achieve smooth voltage boosting and effectively suppress the inrush current generated during the voltage boosting process of the transformer substation, the operator can pre-set key parameters such as the boosting rate k (e.g., boosting k% of the rated voltage per second) and the total boosting time T (the time to reach the rated voltage is T seconds) in the main controller 11. The main controller 11 can then automatically calculate the conduction angle α that the semiconductor controller 12 needs to reach within one control cycle Δt, automatically completing the zero-start boosting process, avoiding voltage fluctuations and overshoot that may occur during the boosting process, and improving the accuracy and reliability of the boosting.

[0027] Specifically, the steps by which the main controller 11 calculates the conduction angle α that the semiconductor controller 12 needs to achieve within one control cycle Δt include: Set the initial conduction angle α of semiconductor controller 12 within the first control cycle Δt. i The conduction angle range of semiconductor controller 12 is 0°-180°. The conduction degree of semiconductor controller 12 gradually increases with the increase of the conduction angle. In order to achieve the purpose of zero-start voltage boost in the collector circuit, the initial conduction angle α can be increased. i Set a small conduction angle close to 0° to allow the voltage of the collector line to rise smoothly and linearly from near 0V. For example, set the initial conduction angle α... i The setting is to start conducting at 0.5°.

[0028] Calculate at the initial conduction angle α i Below, the voltage increment of the collector line within the control period Δt is given by equation (1): ΔU calculated =i(Δt)R+L + + In equation (1): ΔU calculated The voltage increment, i(Δt), represents the current in the collector line, which can be obtained by installing a current acquisition device in the collector line. R is the equivalent resistance of the collector line, L is the equivalent inductance of the collector line, and C1 and C2 are the equivalent capacitances of the collector line, respectively. In this step, the initial conduction angle α is calculated using the equivalent circuit model of the collector line. i The voltage increment under the current can be equivalent to a circuit containing a resistor R, an inductor L, and a capacitor C. Taking the commonly used π-type equivalent circuit as an example (the line resistor R and inductor L are connected in series, and capacitors C1 and C2 are connected in parallel at both ends respectively).

[0029] The derivation of equation (1) is as follows: Based on Kirchhoff's laws (KCL and KVL), the circuit equation is established: U=iR+L + + This is a first-order linear differential-integral equation concerning the current i. For this equation, under the condition of zero-start voltage boost, the initial current i(0) can be assumed to be 0, and the time can be discretized into t using the Euler method. n =nΔt1, where n=0,1,2,3…, then the recursive formula for the current is: i n+1 =i n + Ui n R- - By iteratively calculating step by step, the current i at different times can be obtained. n .

[0030] Therefore, in equation (1), when solving for the voltage increment within a control cycle Δt, i(0) = 0. This can be achieved by analyzing the discrete current value i n Approximate calculation of summation: = Here, Δt = nΔt1, and the voltage increment ΔU within one control cycle Δt can be calculated. calculated The specific value.

[0031] Calculate the target voltage increment ΔU1=kU within one control cycle Δt of the collector line. rated Where: k is the preset boost rate, U rated The rated voltage of the collector line is given by T, which is the total time for the collector line to complete the voltage boost. Thus, the specific value of the target voltage increment ΔU1 within a control cycle Δt can be calculated.

[0032] Calculate the voltage increment ΔU calculated The absolute value of the difference between the target voltage increment ΔU1 and the target voltage increment ΔU1 | ΔU calculated -ΔU1│, when │ΔU calculated -ΔU1│> ( When the allowable voltage increment deviation is set, if ΔU calculated >ΔU1, then the initial conduction angle α i Decrease by a step size Δα, i.e., α i+1 =α i -Δα, if ΔU calculated If ΔU1 <, then the initial conduction angle α i Increase by a step size Δα, i.e., α i+1 =α i +Δα; Allowable voltage increment deviation in this step The specific value of the step size Δα of the conduction angle can be set according to the actual application environment conditions.

[0033] With the first conduction angle αi+1 As the initial conduction angle α i Recalculate the corresponding voltage increment ΔU calculated and voltage increment ΔU calculated The absolute value of the difference between the target voltage increment ΔU1 and the target voltage increment ΔU1, up to |ΔU calculated -ΔU1│≤ This indicates the voltage increment ΔU at this point. calculated The requirements are met; the initial conduction angle α at this point is... i This is the conduction angle α required by the semiconductor controller 12 within the first control cycle Δt. The conduction angle α required by the semiconductor controller 12 within the next control cycle Δt can be calculated by repeating the above steps.

[0034] The flexible starting device for the box-type transformer in this embodiment starts according to the rated voltage U of the collector line via the main controller. rated By precisely calculating the boost rate k and the total boost time T, the conduction angle α of the semiconductor controller 12 within each control cycle Δt is determined. This allows for precise and continuous control of the semiconductor controller 12's conduction, achieving precise and continuous adjustment of the collector circuit from zero start-up voltage. This improves the accuracy and reliability of the boost process and effectively suppresses inrush current generated during the boost process. Furthermore, the semiconductor controller 12's response to control signals and its own conduction angle adjustment are at the millisecond or even microsecond level, enabling rapid handling of unexpected situations. The zero-start-up voltage boost process can be automatically completed simply by setting the boost parameters through the main controller, avoiding voltage fluctuations and overshoot that may occur during the boost process.

[0035] like Figure 1As shown, in some embodiments, the box-type flexible starting device further includes a voltage acquisition device 14 and a current acquisition device 15, which are used to continuously acquire the real-time voltage signal and real-time current signal of the collector line in each control period Δt. Specifically, the voltage acquisition device 14 is a voltage sensor, which works based on the principle of electromagnetic induction or capacitive voltage division. It can convert the high voltage of the collector line into a low voltage signal suitable for measurement, and preliminarily condition the voltage signal, such as filtering, amplification, etc. Then, it converts the analog voltage signal into a digital signal through an A / D converter and transmits it to the main controller 11. The current acquisition device 15 is a current sensor, which is based on the Hall effect or Rogowski coil principle and can accurately measure the current in the collector line. Similarly, after conditioning and digitizing the acquired current signal, the current sensor sends it to the main controller 11. The main controller 11 is used to analyze the current operating parameters of the collector line based on the acquired real-time voltage signal and real-time current signal, so as to determine whether it is necessary to adjust the operating state of the semiconductor controller 12. In this embodiment, by using the voltage acquisition device 14 and the current acquisition device 15 to monitor the operating state of the collector line during the zero-start voltage rise process in real time, it can diagnose whether the zero-start voltage rise process of the collector line is operating normally, and can give early warnings of some sudden situations. The main controller 11 analyzes the current operating parameters of the collector line based on the acquired real-time voltage signal and real-time current signal, and quickly responds to sudden situations, improving the stability and safety of the zero-start voltage rise process of the collector line.

[0036] For example, the main controller 11 analyzes the acquired real-time voltage signal and real-time current signal to calculate the current actual voltage rise rate k of the collector line u = ; the main controller 11 compares the size of the actual voltage rise rate k u with the preset voltage rise rate k. If k u < k, then calculate the conduction angle Δα that the semiconductor controller 12 needs to increase in the next control period Δt up , then the conduction angle α of the semiconductor controller 12 in the next control period Δt n+1 =α n + Δα up ; if k u > k, then calculate the conduction angle Δα that the semiconductor controller 12 needs to decrease in the next control period Δt down , then the conduction angle α of the semiconductor controller 12 in the next control period Δt n+1 =α n - Δα down ; where, α nis the conduction angle of the semiconductor controller 12 within the current control period Δt. By analyzing the collected real-time voltage signal and real-time current signal, the boost rate of the collector line is tracked in real time, facilitating real-time adjustment and correction of the actual boost rate of the collector line, enabling closed-loop control of the boost process of the collector line to obtain the best control effect, allowing the zero-start boost process of the collector line to accurately rise smoothly according to the preset boost rate, and improving the accuracy of the zero-start boost process of the collector line.

[0037] Specifically, the error between the set value (the voltage change value corresponding to the preset boost rate) and the actual measured value (the current actual voltage rise rate of the collector line) can be subjected to proportional (P), integral (I), and derivative (D) operations through the PID control algorithm to generate the adjustment control quantity Δα(k) = P(k) + I(k) + D(k) of the semiconductor controller 12. If k u < k, the conduction angle Δα that needs to be increased for the next control period Δt of the semiconductor controller 12 is calculated up , at this time, Δα up = Δα(k), then the conduction angle α of the semiconductor controller 12 within the next control period Δt n+1 = α n + Δα(k); if k u > k, the conduction angle Δα that needs to be decreased for the next control period Δt of the semiconductor controller 12 is calculated down , at this time, Δα down = Δα(k), then the conduction angle α of the semiconductor controller 12 within the next control period Δt n+1 = α n - Δα(k).

[0038] For another example, the main controller 11 calculates the amplitude i of the current signal through A / D conversion analysis of the real-time current signal m , and compares the amplitude i m with the set current threshold i threshold . If i m > i threshold , it can be intuitively determined that inrush current appears in the collector line. The digital signal obtained after A / D conversion of the real-time current signal is a series of discrete sampling values i(n). The amplitude i of the current signal can be calculated through the root mean square (RMS) algorithm m . For N sampling values x(n) within a control period Δt, n = 0, 1, 2, 3…, N - 1, the root mean square value I of the current RMS is: I RMS = , and the relationship between the amplitude i of the collector line current m and the root mean square value I of the current RMS is: For example, N=1000 current sample values ​​within one control cycle Δt are obtained through A / D conversion, and the root mean square value I is obtained through the above calculation. RMS =5A, then the current amplitude A≈7.07A.

[0039] The main controller determines the amplitude i m The required reduction in current increment Δi = k0 (i) of the collector line is calculated. m -i n ), where k0 is a constant coefficient set according to the transformer characteristics and the degree of inrush current suppression, i n The normal excitation current is determined based on the rated parameters of the transformer substation; the main controller 11 calculates the conduction angle Δα that the semiconductor controller needs to adjust based on the current increment Δi.

[0040] Furthermore, the main controller 11 performs time-frequency analysis on the real-time current signal to calculate the ratio i of the multiple harmonic components to the fundamental component in the current signal. k and the ratio i k With the set percentage threshold i k0 Compare, if i k >i k0 , and combined with i m >i threshold If this is the case, it can be determined that an inrush current has occurred in the collector line. For example, the time-domain signal in the real-time current signal can be converted into a frequency-domain signal using Fourier transform, and the amplitude and phase information of different frequency components in the frequency-domain signal can be extracted. For a discrete current signal i(n), its discrete Fourier transform is defined as... Where N is the signal length, c = 0, 1, 2, 3…, N-1, and I(c) is the frequency domain coefficient. The frequency domain coefficient I(c) is a complex number, and its amplitude |I(c)| represents the magnitude of the frequency component. For the fundamental component and each harmonic component, its amplitude is calculated as follows: │I(c h For example, suppose we acquire a current signal i(n) of length N=1024, with a sampling frequency f. s =1000Hz, fundamental frequency f1=50Hz, then the frequency index c1 corresponding to the fundamental frequency is= The fundamental amplitude A1 = │I(51)│;Second harmonic frequency c2= Hz, corresponding frequency index c2= The amplitude of the second harmonic is A2= │I(102)│.

[0041] In a current collector circuit, the current during normal operation is mainly the fundamental frequency component, while the inrush current contains a large number of higher harmonic components, especially the second and third harmonics. For example, the amplitude of the second harmonic A2 and the amplitude of the fundamental frequency A1 are calculated, and the ratio i of the second harmonic content A2 / A1 is determined. k Assume the ratio of the second harmonic content to the fundamental frequency exceeds the percentage threshold i. k0 (For example, 10%), which serves as an important criterion for judging inrush current. At the same time, observe the amplitude of other higher harmonics (such as the third harmonic, fifth harmonic, etc.). If the amplitude of multiple higher harmonics is significantly higher than the level during normal operation, the possibility of inrush current is further increased.

[0042] By analyzing the real-time current signal collected and fed back, including A / D conversion analysis and time-frequency analysis, it is beneficial to accurately identify abnormal current changes in advance during the zero-start voltage boosting process of the collector line. This allows for early warning of potential inrush current phenomena and the calculation of the conduction angle Δα that the semiconductor controller 12 may need to adjust based on the current increment Δi. This timely avoidance of potential inrush current phenomena during the zero-start voltage boosting process reduces grid voltage disturbances and overvoltage phenomena caused by the combined effect of inrush current and line inductance, maintains grid voltage stability, ensures the normal operation of other equipment in the grid, and improves the stability and power supply quality of the entire power system.

[0043] Preferably, the main controller 11 calculates the conduction angle Δα that the semiconductor controller 12 needs to adjust based on the current increment Δi. The specific calculation process is as follows: Calculate the voltage change ΔU corresponding to the decrease in current increment Δi within the control period Δt of the collector line. switch Similarly, based on Kirchhoff's laws (KCL and KVL), the circuit equation is derived, and equation (2) is obtained: ΔU switch =Δi(Δt)R+L + + Where: Δi(Δt) is the current increment that the collector circuit needs to reduce, R is the equivalent resistance of the collector circuit, L is the equivalent inductance of the collector circuit, C1 and C2 are the equivalent capacitances of the collector circuit, and ΔU is the equivalent capacitance of the collector circuit. switch The specific derivation and calculation process is similar to that of equation (1), and will not be repeated here.

[0044] Through equation (3): f(α2) f(α1)=ΔU switch And equation (4): Δα=α2 Solve the equations simultaneously to calculate the value of Δα. In equation (3), f(α) is the function relating the conduction angle of semiconductor controller 12 to the output voltage, f(α1) is the output voltage of the collector circuit before adjustment, f(α2) is the output voltage of the collector circuit after adjustment, α1 is the conduction angle of semiconductor controller 12 before adjustment, and α2 is the conduction angle of semiconductor controller 12 after adjustment. In equation (4), α1 is the conduction angle of semiconductor controller (12) before adjustment, and α2 is the conduction angle of semiconductor controller (12) after adjustment.

[0045] It should be noted that the function f(α) relating the conduction angle of the semiconductor controller 12 to the output voltage can be derived from the operating characteristics of the semiconductor controller 12, as shown in equation (5) f(α) = In equation (5), A, B, and C are constants related to the semiconductor controller 12 and circuit parameters, which can be obtained from the semiconductor controller 12 manual. max The maximum value of the conduction angle of the conductor controller (12) is usually the firing angle corresponding to the full conduction of the semiconductor controller 12. For example, in a 50Hz power frequency circuit, if one period is considered to be 2π, then α max =π=180°.

[0046] In some extreme cases, the main controller 11 calculates the current actual current rise rate k of the collector line based on the real-time current signal. i = Compare the actual current rise rate k i With the rate of rise of short-circuit current k d The size of k i >k d If a short circuit is detected in the collector line, the main controller 11 sends a shutdown signal to the semiconductor controller 12, quickly cutting off the current loop. This improves the safety of the collector line's zero-start voltage boost process, ensures the normal operation of other equipment in the power grid, and enhances the stability and power supply quality of the entire power system.

[0047] To achieve the above objectives, this application also provides the following technical solutions: like Figure 3 As shown in the comparative embodiment, in the existing photovoltaic power station grid-connected power generation system, a pre-magnetizing transformer 16 is connected in parallel across the two ends of the circuit breaker 20. The pre-magnetizing transformer 16 pre-magnetizes the transformer 10, so that the winding of the transformer 10 has established a steady-state magnetic flux before the circuit breaker 20 is closed. This is used to offset the inrush current amplitude generated by the transformer 10 after the circuit breaker 20 is closed and connected to the collector line 200, thereby achieving the inrush current suppression target.

[0048] like Figure 4As shown, this embodiment provides a photovoltaic power station grid-connected power generation system, including a bus 100 and several collector lines 200 connected in parallel with the bus 100. Each collector line 200 includes a prefabricated transformer 10 and a circuit breaker 20 connected in series with the prefabricated transformer 10. A flexible starter device 30 for the prefabricated transformer, as described above, is connected in parallel to the circuit breaker 20 of the collector line 200. The first end of the circuit breaker 20 is connected in parallel with the bus 100, and the first end of the circuit breaker 20 is connected in series with the prefabricated transformer 10. The first end of the semiconductor controller 12 is connected in series with the first end of the electrically operated isolating switch 13, the second end of the electrically operated isolating switch 13 is connected in parallel with the first end of the circuit breaker 20 of the collector line, and the second end of the semiconductor controller 12 is connected in parallel with the second end of the circuit breaker 20.

[0049] like Figure 4 As shown, before the circuit breaker 20 of the transformer substation 10 is closed, the main controller 11 controls the electric isolating switch 13 to close. The main controller 11 calculates the conduction angle α that the semiconductor controller 12 needs to reach in each control cycle Δt, and converts the parameter of conduction angle α into a second control signal and sends it to the semiconductor controller 12. The semiconductor controller 12 starts to conduct at conduction angle α, and the collector line 200 starts to rise from zero voltage until the voltage of the collector line 200 slowly rises to the rated voltage. The circuit breaker 20 closes, and the main controller 11 controls the electric isolating switch 13 to open, so that the transformer substation 10 enters steady-state operation after a short transition.

[0050] This embodiment of a photovoltaic power station grid-connected power generation system includes a flexible start-up device for a transformer substation, one of the aforementioned schemes, connected in parallel to the circuit breakers of a portion of the collector lines. This achieves zero-start voltage boost in the collector lines, effectively suppresses inrush current generated during the voltage boosting process, and significantly simplifies the electrical structure of the collector lines, reducing the technical cost of solving the inrush current problem. Furthermore, this application uses a main controller to adjust the voltage U of the collector lines based on the rated voltage U... rated The boost rate k and the total boost time T are used to precisely control the conduction angle α of the semiconductor controller to achieve zero-start boost of the collector circuit. The zero-start boost process can be completed automatically by simply setting the boost parameters through the main controller, avoiding voltage fluctuations and overshoot that may occur during the boost process, and improving the accuracy and reliability of the boost.

[0051] like Figure 5As shown, as a further improvement to the above embodiment, the photovoltaic power station grid-connected power generation system of this embodiment also includes a step-up transformer 17, which is connected in series with a flexible start-up device 30 on the collector line 200. The flexible start-up device 30 is powered by a low-voltage substation, enabling the step-up transformer 17 to start stepping up from zero voltage, while simultaneously pre-magnetizing the box-type transformer 10. This helps to reduce the time for the collector line 200 to start up from zero voltage while achieving the inrush current suppression target, and can significantly reduce the energy consumption during the zero-start voltage rise process of the collector line 200, reduce the economic losses from energy consumption, and achieve the goals of cost reduction, efficiency improvement, energy saving, and emission reduction.

[0052] For example, in this embodiment, the step-up transformer 17 is a small-capacity transformer. The flexible start-up device 30 is powered by a 400V low-voltage substation, which enables the step-up transformer 17 to start stepping up from zero voltage. At the same time, the transformer 10 is pre-magnetized, and the voltage of the collector line 200 is slowly increased to the rated voltage of 35KV. Then the circuit breaker 20 is closed, and the main controller 11 controls the electric isolating switch 13 to open, so that the transformer 10 enters steady-state operation after a short transition.

[0053] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces, or indirect coupling or communication connection between apparatuses or units, and may be electrical, mechanical, or other forms.

[0054] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated units described above can be implemented in hardware or as software functional units. The above are merely embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made based on the description and drawings of this application, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

[0055] The specific embodiments of the invention have been described in detail above, but they are only examples, and this application is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications or substitutions to the invention are also within the scope of this application. Therefore, all equivalent changes, modifications, and improvements made without departing from the spirit and principles of this application should be covered within the scope of this application.

Claims

1. A flexible starting device for a prefabricated transformer, used for zero-start voltage boosting of a collector line, wherein the collector line includes a prefabricated transformer and a circuit breaker connected in series with the prefabricated transformer, characterized in that, The device includes a main controller, a semiconductor controller, and an electric isolating switch. The first terminal of the semiconductor controller is connected in series with the first terminal of the electric isolating switch, the second terminal of the electric isolating switch is connected in parallel with the first terminal of the circuit breaker, and the second terminal of the semiconductor controller is connected in parallel with the second terminal of the circuit breaker. The main controller is used to send a first control signal to the electrically operated isolating switch to control the opening and closing of the electrically operated isolating switch, and to control the rated voltage U of the collector line. rated Given the boost rate k and the total boost time T, calculate the conduction angle α that the semiconductor controller needs to reach within one control cycle Δt, and convert the conduction angle α into a second control signal and send it to the semiconductor controller; The semiconductor controller is used to respond to the second control signal and start conducting at a conduction angle α, so that the voltage of the collector line begins to rise slowly.

2. The flexible starting device for a box-type transformer according to claim 1, characterized in that, The voltage U based on the rated voltage U of the collector line rated Given the boost rate k and the total boost time T, calculate the conduction angle α that the semiconductor controller needs to achieve within one control cycle Δt, including: The initial conduction angle α of the semiconductor controller is set during the first control cycle Δt. i ; Calculate at the initial conduction angle α i Below, the voltage increment of the collector line during the control period Δt is given by equation (1): ΔU calculated =i(Δt)R+L + + In equation (1): ΔU calculated Let i(Δt) be the voltage increment, i(Δt) be the current of the collector line, R be the equivalent resistance of the collector line, L be the equivalent inductance of the collector line, and C1 and C2 be the equivalent capacitances of the collector line, respectively. Calculate the target voltage increment ΔU1=kU of the collector line within one control cycle Δt. rated Where: ΔU1 is the target voltage increment, k is the preset boost rate, and U rated The voltage is the rated voltage, and T is the total time for the collector circuit to complete the voltage boost. Calculate the voltage increment ΔU calculated The absolute value of the difference between the target voltage increment ΔU1 and |ΔU calculated -ΔU1│, when │ΔU calculated -ΔU1│> ( When the allowable voltage increment deviation is set, if ΔU calculated >ΔU1, then the initial conduction angle α i Decrease by a step size Δα, i.e., α i+1 =α i -Δα, if ΔU calculated If ΔU1 <, then the initial conduction angle α i Increase by a step size Δα, i.e., α i+1 =α i +Δα; With the first conduction angle α i+1 As the initial conduction angle α i Recalculate the corresponding voltage increment ΔU calculated and the voltage increment ΔU calculated The absolute value of the difference between the target voltage increment ΔU1 and the target voltage increment ΔU1, up to |ΔU1|U1. calculated -ΔU1│≤ Up to this point, the initial conduction angle α i This is the desired conduction angle α, which is the conduction angle α that the semiconductor controller needs to achieve in the next control cycle Δt, and so on.

3. The flexible starting device for a prefabricated transformer according to claim 1 or 2, characterized in that, The flexible starting device for the transformer substation also includes a voltage acquisition device and a current acquisition device, used to continuously acquire the real-time voltage signal and real-time current signal of the collector line within each control cycle Δt. The main controller is also used to analyze the operating parameters of the collector line based on the real-time voltage signal and the real-time current signal, thereby determining whether it is necessary to adjust the working state of the semiconductor controller.

4. The flexible starting device for a box-type transformer according to claim 3, characterized in that, The main controller analyzes the real-time voltage signal and the real-time current signal to calculate the current actual voltage rise rate k of the collector line. u = ; Compare the actual voltage rise rate k u with the magnitude of the boost rate k. If k u < k, calculate the conduction angle Δα that needs to be increased in the next control period Δt of the semiconductor controller up . Then, within the next control period Δt, the conduction angle α of the semiconductor controller n+1 = α n + Δα up ; if k u > k, calculate the conduction angle Δα that needs to be decreased in the next control period Δt of the semiconductor controller down . Then, within the next control period Δt, the conduction angle α of the semiconductor controller n+1 = α n - Δα down ; where α n is the conduction angle of the semiconductor controller within the current control period Δt.

5. The flexible starting device for a prefabricated transformer according to claim 3, characterized in that, The main controller calculates the amplitude i of the real-time current signal by performing A / D conversion analysis on the signal. m and the amplitude i m With the set current threshold i threshold Compare, if i m >i threshold If so, it can be determined that an inrush current has occurred in the collector line; The main controller is based on the amplitude I m The required reduction in current increment Δi = k0 (i) of the collector circuit is calculated. m -i n ), where k0 is a coefficient set according to the transformer characteristics and the degree of inrush current suppression, i n The normal excitation current is determined based on the rated parameters of the transformer; the main controller calculates the conduction angle Δα that the semiconductor controller needs to adjust based on the current increment Δi.

6. The flexible starting device for a prefabricated transformer according to claim 5, characterized in that, The main controller also performs time-frequency analysis on the real-time current signal to calculate the ratio i of the multiple harmonic components to the fundamental component in the current signal. k and the ratio i k With the set percentage threshold i k0 Compare, if i k >i k0 , and combined with i m >i threshold If so, it can be determined that an inrush current has occurred in the collector line.

7. The flexible starting device for a prefabricated transformer according to claim 5, characterized in that, The main controller calculates the required adjustment of the conduction angle Δα of the semiconductor controller based on the current increment Δi, including: Calculate the voltage change corresponding to the reduction of the current increment Δi in the collector line within the control period Δt, as shown in equation (2): ΔU switch =Δi(Δt)R+L + + In equation (2): ΔU switch Let Δi be the voltage change, Δi be the current increment that the collector circuit needs to reduce, R be the equivalent resistance of the collector circuit, L be the equivalent inductance of the collector circuit, and C1 and C2 be the equivalent capacitances of the collector circuit, respectively. Through equation (3): f(α2) f(α1)=ΔU switch Solve equation (4) simultaneously: Δα = α2 - α1 to calculate the value of Δα. In equation (3), f(α) is the function relating the conduction angle of the semiconductor controller to the output voltage, f(α1) is the output voltage of the collector circuit before adjustment, f(α2) is the output voltage of the collector circuit after adjustment, α1 is the conduction angle of the semiconductor controller before adjustment, and α2 is the conduction angle of the semiconductor controller after adjustment. In equation (4), α1 is the conduction angle of the semiconductor controller before adjustment, and α2 is the conduction angle of the semiconductor controller after adjustment.

8. The flexible starting device for a prefabricated transformer according to claim 3, characterized in that, The main controller calculates the current actual current rise rate k of the collector line based on the real-time current signal. i = Compare the actual current rise rate k i With the rate of rise of short-circuit current k d The size of k i >k d If the current collector is short-circuited, the main controller sends a shutdown signal to the semiconductor controller to quickly cut off the current loop.

9. A photovoltaic power station grid-connected power generation system, characterized in that, The device includes a busbar and several collector lines connected in parallel with the busbar. Each collector line includes a prefabricated transformer and a circuit breaker connected in series with the prefabricated transformer. A flexible starting device for the prefabricated transformer as described in any one of claims 1-8 is connected in parallel to the circuit breaker of the collector line. The first end of the circuit breaker is connected in parallel with the busbar, and the second end of the circuit breaker is connected in series with the prefabricated transformer. The first end of the semiconductor controller is connected in series with the first end of the electrically operated isolating switch, and the second end of the electrically operated isolating switch is connected in parallel with the first end of the circuit breaker of the collector line. The second end of the semiconductor controller is connected in parallel with the second end of the circuit breaker.

10. The photovoltaic power station grid-connected power generation system according to claim 9, characterized in that, It also includes a step-up transformer, which is connected in series with the flexible starting device, and is used to raise the voltage of the collector line to a predetermined value before the flexible starting device is operated.

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